Alan WEIMER, et al. -- Solar Gasification : ~30%+ Improved efficiency of biofuel production with solar power -- articles & patents

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Alan WEIMER, et al.
Solar Biomass Gasification

~30%+ Improved efficiency of biofuel production & higher yields with solar power

http://biomassmagazine.com/articles/1674/solar-powered-biomass-gasification

Solar-Powered Biomass Gasification
A collaboration of Colorado-based researchers is taking the next step toward the synthesis of carbon-negative biofuels.

by Jessica Ebert

One of the drawbacks of biomass gasification systems is that the energy to power these reactors is typically drawn from coal-fired power plants. To produce a truly carbon-neutral, or even better, a carbon-negative fuel, the electricity to turn waste biomass feedstocks into a syngas, which can be further processed into fuels, must come from a renewable energy source.

To that end, a team of scientists including engineers and horticulturists from the University of Colorado in Boulder, Colorado State University in Fort Collins and the National Renewable Energy Laboratory in Golden, Colo., have embarked on a project to develop rapid solar-thermal reactor systems for the conversion of biomass to syngas. The project is being funded by a three-year, $1 million USDA and U.S. DOE grant, which was announced in early March as part of an $18.4 million package to fund 21 biomass research and development demonstration projects.

The collaboration is led by Alan Weimer, a professor at CU-Boulder and executive director of the Colorado Center for Biorefining and Biofuels who worked for Dow Chemical Co. for more than 16 years before pursuing a career in academia. At Dow, Weimer worked in the area of ultra high-temperature processing for the synthesis of fine materials like tungsten carbide, which is used in the manufacture of mining instruments and other high-tech tools. The materials were generated by flowing chemical precursors through a graphite reactor tube that is heated indirectly by electricity.

When he joined the university's Department of Chemical and Biological Engineering, his first project was an extension of his earlier research, but rather than using electricity from the grid, his work involved using concentrated sunlight for chemical processing. "The process looks a lot like the technology developed at Dow except instead of heating with electricity, we use sunlight," Weimer explains. "We can achieve the same temperatures without generating any greenhouse gases."

During these early studies, Weimer and colleagues established a relationship with the engineers at NREL who had designed what's called a high-flux solar furnace in the late 1980s.

The furnace facility sits on top of a high, barren mesa and consists of two main components: a flat mirror called a heliostat that tracks the sun as it moves across the sky and a primary concentrator, which consists of a series of 25 curved, hexagonal-shaped mirrors. The large, 32-square meter (38-square yard) heliostat reflects sunlight onto the primary concentrator, which focuses the sun to a single point. "It's basically similar to using a magnifying glass to concentrate sunlight to a point, although we use mirrors instead of lenses," explains Carl Bingham, staff engineer at NREL. This concentrated sunlight, which has been reduced to a beam measuring 10 centimeters (4 inches) in diameter, is reflected a second time at a target area inside the test building where researchers run their experiments.

"The original intent was to see what we could do with highly concentrated solar radiation," Bingham says. By tightening the focus of the sunlight or increasing its concentration, temperatures pushing greater than 2,000 degrees Celsius (3,632 degrees Fahrenheit) can be reached. "The idea is that heating things with concentrated sunlight gets things very hot, very quickly," he says. In addition to scorching temperatures, the furnace allows for the selective heating of the sample surfaces.

Bingham, who has worked on the solar furnace nearly since its inception, explains that the early experimentation involved materials synthesis including the application of films onto various substrates, the formation of silicon crystals, the development of new methods for bonding metal onto ceramics and the manufacture of fullerenes, which are carbon structures used in semiconductors, superconductors, high-performance metals and medical technologies.

A New Research Path

Eventually, the NREL engineers started collaborating with the researchers from Boulder. "We developed an alliance with CU and started doing work in the hydrogen program, which is still going on today," Bingham says. This research involved splitting water into hydrogen and oxygen, which requires very high temperatures and special materials. "It's a difficult and challenging problem," Weimer says. A challenge his team continues to tackle. However, it also led one of Weimer's graduate students to suggest an alternative research path.

"He came in one day and said ?with all this interest in biomass, I bet biomass is a piece of cake compared with splitting water,'" Weimer recalls. He proceeded to collect some Kentucky bluegrass from outside the laboratory, grind it up and process it. "What we discovered was that at temperatures of about 1,200 degrees C (2,192 degrees F) the short, rapid pyrolysis or gasification in the presence of steam of the biomass, produced syngas with usage in excess of 90 percent of the biomass," he says. This is significant, Weimer explains, because conventional gasification processes require a partial oxidation of the feedstock, which leads to yield loss. In addition, the very rapid heating for a very short time prevented the formation of tars. This eliminates the need for cleaning the syngas before it's reformulated to fuel, which is a pricey capital cost for a biomass plant, Weimer says.

At CU-Boulder, Weimer's students and staff work with two electrically-heated transport tube reactors. As biomass flows through the tube, either by itself or with some inert gas or steam, the feedstock is heated to high temperatures for only a few seconds. The kinetics of this reaction are closely monitored for various feedstocks and used to develop mathematical models that predict how the solar reactors at NREL should behave. These models are then used to design the reactors that will be used for on-sun demonstrations.

This includes a secondary concentrator, which is a cone-shaped device that essentially wraps the sunlight around the reaction tube. The biomass is gasified as the tube absorbs the heat. "Our students build these reactors here in the shop in our department. They mount them on skids. They put the skids in the back of a pickup truck and drive up to NREL where they locate the reactors in the corner of the test building," Weimer explains.

"With the biomass we're really in the sweet spot," Weimer explains. "The materials issues associated with the water splitting go away." But there are other challenges. The biggest of these is finding biomass feedstocks independent of the food chain. "At the conditions that we operate, however, we can handle huge variability in feedstocks," he says. Weimer's team has gasified grasses, sorghum and even lignin. "Our feedstock could be lignin, sawdust, forestry waste, spent grains from a brewery, switchgrass, corn stover, sorghum," he says. "It could also be municipal solid waste or paper. It could even be glycerin."

The team is also planning to develop algae for gasification. "We see algae as an ideal feedstock," Weimer says. But rather than extracting oil from the microbes for the production of biodiesel, the algae themselves will serve as a biomass feedstock for the production of syngas. In addition to algae processing, researchers at CSU led by Yaling Qian are working to understand how switchgrass can be grown on marginal lands using brown water. "You could consider our process as a renewable, thermochemical sledgehammer," Weimer says.

Another challenge is interfacing the on-sun gasification with the reforming of the syngas. This represents the other half of Weimer's research: the work to develop catalytic processes to do the seamless downstream reforming of the syngas to biofuel.

These are the obstacles that Weimer aims to iron out in the next three years. However, "we don't envision any showstoppers for the conversion of biomass," he says. For one thing, the process is a small version of the system he worked on at Dow to synthesize materials. This process is now commercial and used in large scale to make advanced materials. "So we feel very comfortable that this design can be scaled up," he says. Weimer has also looked into the economics of building solar-powered biomass gasification and conversion plants and it looks encouraging, he says. For this current USDA/DOE funded project, Weimer and colleagues have teamed with several companies including Xcel Energy, Arizona Public Service, Abengoa Bioenergy and Copernican Energy Inc. Weimer expects interest in this type of research to continue to grow.

"There's been a lot of funding-research emphasis on using concentrated sunlight to make electricity," Weimer says. "There's also been a lot of interest in biomass gasification. We operate at the interface of those technologies. Although there's typically not a lot of money at that interface, it has been recognized that when you operate at the interface, there's a huge opportunity for innovation."

http://www.colorado.edu/che/TeamWeimer/ResearchInterests/BiomassGasification.htm

Solar Thermal Biomass Gasification

Biomass gasification is a potential route to renewable fuel production from a domestically produced source. In theory,
all forms of carbonaceous material could be used including energy crops, agricultural and forestry waste, or municipal waste. When biomass and steam are combined at high temperature they react to form synthesis gas, a mixture of H2, CO, and CO2. This synthesis gas can then be sent to a catalytic reactor where it is converted into a variety of fuels such as methanol, ethanol and gasoline.

Currently, the only industrial scale processes to produce biofuels from biomass are the production of biodiesel from bio-oil, and fermentation of sugar cane and corn to produce ethanol. In both cases a high value feedstock is consumed. If renewable fuels are ever going to displace a significant portion of our fossil fuel consumption they need to be produced from a widely available biomass source. Cellulosic ethanol and other bioprocesses that can utilize cellulose are steps in the right direction, but they still only convert a fraction of the biomass feedstock into a useable fuel. Thermochemical conversion is an attractive route because all of the carbon in the feedstock can be utilized.

In traditional gasification, 20-25% of the energy in the biomass is burned to provide the process heat(1). If air is used for combustion, this also dilutes the product stream with large amounts of nitrogen. Solar thermal gasification offers a solution to both of these problems by supplying process heat with an external, renewable, heat source. Another advantage of solar thermal gasification is the relative ease of obtaining high temperatures. Most of the research done on biomass gasification has been performed in the 500-1000 °C range and production of tar has been a significant issue. Operating at higher temperature (1000-1300 °C) allows for better heat transfer, faster reaction kinetics(2; 3), and the breakdown of unwanted tars(4; 5).

In order for solar thermal gasification to become a commercial scale process, a detailed understanding of the important parameters associated with solar thermal reactor design must be developed. Our lab is working on optimizing the solar thermal receiver/reactor system for biomass gasification. This is a combined effort of detailed CFD modeling coupled with laboratory experiments in a tightly controlled environment and validation in a solar thermal environment. Our solar testing is conducted at NREL’s High Flux Solar Furnace shown in. We hope that these efforts will lead to a process for large scale reactor design that can be applied in a commercial setting.

BIBLIOGRAPHY

1. Energy production from biomass (part 3): gasification technologies. McKendry, Peter. s.l. : Bioresource Technology, 2001, Vol. 83. 55-63.
2. Experimental and numerical study of steam gasification of a single char particle. F. Mermoud, F. Golfier, S. Salvador, L. Van de Steene, J. L. Dirion. s.l. : Combustion and Flame, 2006, Vol. 145. 59-79.
3. Alan W. Weimer, Christopher Perkins, Dragan Mejic, Paul Lichty. US 2008/0086946 A1 United States of America, 2008.
4. The reduction and control technology of tar during biomass gasification/pyrolysis: An overview. Jun Han, Heejoon Kim. s.l. : Renewable and Sustainable Energy Reviews, 2006, Vol. 12. 397-416.
5. Temperature impact on the formation of tar from biomass pyrolysis in a free-fall reactor. Qizhuang Yu, Claes Brage, Guanxing Chen, Krister Sjostrom. s.l. : Journal of Analytical and Applied Pyrolysis, 1997, Vols. 40-41. 481-489.

http://www.sundropfuels.com/

The Sundrop Fuels unique ultrahigh-temperature bioreforming process produces a higher yield of renewable liquid fuel per ton of biomass feedstock than any other production method.

How it works

1. Cellulosic biomass material is delivered by entrained flow into Sundrop Fuels’ proprietary ultra-high temperature pressurized bioreforming system, which converts the material. Natural gas is used to power the radiation-driven bioreforming reactor, generating temperatures of more than 1,400 degrees Celsius (2,552 degrees Fahrenheit).

2. Hydrogen-rich natural gas is added after bioreforming to allow for a two-to-one hydrogen-to-carbon ratio – the chemical make-up necessary for transportation fuels that can be used in today’s internal combustion engines. This combination of converted biomass and additional hydrogen creates a renewable feed that is the key ingredient for Sundrop Fuels drop-in biogasoline.

3. The renewable feed is converted into methanol using a commercially available catalyst process.

4. Using a well-established commercial fuels synthesis process, the methanol that was created from the renewable feed is then made into in ready-to-use “green gasoline” – or more easily referred to as biogasoline.

5. The Sundrop Fuels high-octane, drop-in biogasoline is blended and ultimately delivered to the marketplace through the nation’s existing pipeline and distribution infrastructure.

THE TECHNOLOGY BEHIND SUNDROP FUELS’ ULTRA-EFFICIENT CONVERSION OF BIOMASS TO LIQUID FUEL

At the center of its advanced biofuels production is the Sundrop Fuels proprietary, ultra-high temperature pressurized bioreforming system. Inside a specially-designed thermochemical reactor, biomass is quickly converted, then combined with hydrogen from clean-burning natural gas to create a renewable feed stream – the key ingredient for biogasoline that is 100 percent compatible with today’s combustion engines and transportation fuels infrastructure. Sundrop Fuels first converts this renewable feed into methanol using a syngas-to-methanol process, then creates “green gasoline” using a commercially-established methanol-to-gasoline (MTG) fuels synthesis.

Sundrop Fuels’ innovative bioreforming production method is unique from conventional biomass gasification in that it uses indirect radiation heat transfer to rapidly drive the extremely high temperatures needed to create the renewable gas feed, which is then processed to create liquid advanced cellulosic biofuel. Using natural gas, temperatures inside the Sundrop Fuels radiation-driven bioreformer reach more 1,400 degrees Celsius (2,552 degrees Fahrenheit) – hotter than lava flowing from a volcano.

By steadily maintaining these ultra-high temperatures to drive the endothermic bioreforming reaction, the Sundrop Fuels process operates at an extraordinary high-efficiency, producing more yield of renewable liquid fuel per ton of biomass feedstock than any other production method.

As importantly, the Sundrop Fuels biogasoline production path significantly reduces greenhouse gas emissions as compared to the production of conventional petroleum fuels. Every gallon of Sundrop Fuels drop-in cellulosic advanced biofuel will generate RIN credits under the U.S. Renewable Fuel Standard (RFS).

Sundrop Fuels is currently in engineering design stage for its inaugural production facility located just outside of Alexandria, Louisiana – the first operational milestone in the company’s path toward becoming a mass-scale provider of renewable, drop-in biogasoline. When fully operational, Sundrop Fuels’ first facility will produce 15,000 barrels per day of finished, 87-octane gasoline. It will also represent the world’s largest commercial production of cellulosic advanced biofuel using methanol-to-gasoline (MTG) technology, which was originally demonstrated as a commercially available process in the 1980s.

http://www.technologyreview.com/news/417947/gasifying-biomass-with-sunlight/
March 10, 2010

Gasifying Biomass with Sunlight

A solar-driven process could yield far more fuel than conventional biomass production.

by

Tyler Hamilton

Baking biomass: Sundrop Fuels has built a solar gasification R&D facility in Colorado.

Sundrop Fuels, a startup based in Louisville, CO, says it has developed a cleaner and more efficient way to turn biomass into synthetic fuels by harnessing the intense heat of the sun to vaporize wood and crop waste. Its process can produce twice the amount of gasoline or diesel per ton of biomass compared to conventional biomass gasification systems, the company claims.

Gasification occurs when dry biomass or other carbon-based materials are heated to above 700 ºC in the presence of steam. At those temperatures, most of the biomass is converted to a synthetic gas. This “syngas” is made up of hydrogen and carbon monoxide, which are the chemical building blocks for higher-value fuels such as methanol, ethanol, and gasoline.

But the heat required for this process usually comes from a portion of the biomass being gasified. “You end up burning 30 to 35 percent of the biomass,” says Alan Weimer, a chemical engineering professor at the University of Colorado, Boulder.

A few years ago, Weimer and his research team began looking at ways of using concentrated solar heat to drive the gasification process. It worked so well that Weimer and Chris Perkins, the graduate student who came up with the idea, went on to cofound Copernican Energy to commercialize the approach. Copernican was acquired by Sundrop Fuels in 2008, and its solar-reactor technology is now at the heart of a 1.5-megawatt thermal solar gasification demonstration facility in Colorado.

The gasifier system consists of ceramic tubes that pass through a furnace. The gasifier is mounted atop a tower surrounded by a field of solar concentrating mirrors that reflect sunlight back to the furnace. As the biomass is dropped through the intensely hot ceramic tubes, it is vaporized into syngas.

Weimer, a former Dow Chemical engineer, says the system is “agnostic” to the types of biomass it can process. “It’s like a sledgehammer because of the (1,200 to 1,300 ºC) temperatures it operates at,” he says, explaining that conventional gasification uses lower temperatures to try to minimize the volume of biomass used to fuel the process. But keeping the temperature lower poses another problem. Gasification at temperatures below 1,000 ºC leaves behind tar. “And that tar is expensive to get rid of,” says Weimer. “If you leave it in there, it will end up killing your catalysts downstream when you try to reform your product into (liquid) fuel.”

The higher temperatures also make for a better quality syngas. Conventional gasification typically produces a syngas mixture that’s half hydrogen and half carbon monoxide. Sundrop’s process achieves a hydrogen-to-CO ratio of two to one.

“I can tell you, the economics have been looked at quite extensively, and the idea of being able to produce gasoline at less than $2 a gallon without subsidies, we believe that’s a real number,” Weimer says. The financial upside is even greater if carbon pricing becomes a reality, because the solar-driven process results in a reduction in greenhouse-gas emissions compared to conventional fuel production. “The key now is to design a scalable solar reactor.”

Ajay Dalai, an associate professor of chemical engineering at the University of Saskatchewan, says powering gasification with solar energy has merit but could prove tricky. “When you’re transferring the heat into the pipe, how do you make sure that it is distributed thoroughly through the biomass?” Controlling heat transfer and temperature levels will be key, he says.

Wayne Simmons, chief executive officer of Sundrop Fuels, doesn’t underestimate the challenges to commercializing the technology. He acknowledges, for example, that the greatest biomass resources aren’t located where the greatest solar resources are. Still, some woody biomass does exist in the U.S. Southwest, where Sundrop plans to build its first commercial plant. States such as New Mexico and Arizona, for example, regularly thin their forests to lower the risk of forest fires. But to access more feedstock, Sundrop is also looking at transporting energy crops, such as switchgrass, by rail from as far north as Kansas and as far east as Texas.

Construction on Sundrop’s first commercial facility is expected to begin this year. The company plans to couple its solar gasification plant with a pilot-scale biorefinery that can produce up to eight million gallons of transportation fuel annually. It’s targeting 2015 for a full-scale biorefinery that can produce 100 million gallons a year.

The company has attracted some key investors, including venture-capital firm Kleiner Perkins Caufield & Byers.

US2013341175
THERMAL TREATMENT SYSTEM AND METHOD

A improved solar biochar reactor, system including the reactor, and methods of forming and using the reactors and systems are disclosed. The methods and system as described herein provide sufficient solar energy to a biochar reactor to convert animal waste or other biomass to biochar in a relatively cost-effective manner.

FIELD OF THE INVENTION

[0002] The present disclosure generally relates to thermal treatment systems and methods. More particularly, exemplary embodiments of the disclosure relate to systems and methods that use solar thermal processes to produce biochar from biomass.

BACKGROUND OF THE DISCLOSURE

[0003] Animal waste, such as human waste, can be an agent that carries and/or transmits infectious pathogens. Accordingly, such waste is often treated. Typical sewage treatment requires significant infrastructure and large-scale plants to treat the waste. Unfortunately, such systems may not be suitable in developing areas or where such large-scale, high-infrastructure systems are not practical.

[0004] Biochar reactors can be used to treat animal waste in areas where typical sewage treatment systems are not practical. A typical biochar production reactor relies on combustion of material to provide the necessary heat to convert biomass into one or more desired products. Unfortunately, use of combustion to heat the reactor may generate unwanted greenhouse gases.

[0005] Other bioreactors may rely on sunlight to produce requisite reactor temperatures for conversion of biomass to desired products. To achieve the requisite temperatures for such reactions, the solar reactors use concentrated sunlight. For example, a solar biochar reactor often includes a reactor located at a focus of an imaging optic, such as a parabola. Alternatively, solar furnaces or beam-down towers may be used; however, additional optical elements required for such systems increase the cost of the systems and the systems generally require sophisticated optical devices to achieve the suitably high solar concentrations.

[0006] Accordingly, improved solar biochar reactors and methods of forming and using the reactors are desired.

SUMMARY OF THE DISCLOSURE

[0007] Various embodiments of the present disclosure relate to improved solar biochar reactors, systems including the reactors, and methods of forming and using the reactors and systems. While the ways in which the various drawbacks of the prior art are discussed in greater detail below, in general, a method and system as described herein provide sufficient solar energy to a biochar reactor to convert animal waste or other biomass to biochar in a relatively cost-effective manner.

[0008] In accordance with various embodiments of the disclosure, a thermal treatment system includes a solar concentrator having an area of concentrated solar power, one or more fiber optic cables, the one or more fiber optic cables having a first end proximate*the area of concentrated solar power and a second end, a solar reactor coupled to the second end of the one or more fiber optic cables, the reactor comprising, a container to receive material to be treated, and insulating material surrounding the container. In accordance with various aspects of these embodiments, the system is used to treat animal waste, such as human waste. In accordance with further aspects, the thermal treatment system includes a urine diversion device. In accordance with further embodiments, the reactor is a hydrothermal carbonization reactor or a pyrolysis reactor. In accordance with yet additional aspects of these embodiments, the treatment system includes a rotating mechanism to expose a container to the one or more fiber optic cables. And, in accordance with further embodiments, the fiber optic cables are isolated from the reactor and the fiber optic cables may have fused ends. The system may further include a carousel to transfer containers between a treatment area and a collection area.

[0009] In accordance with further exemplary embodiments of the disclosure, a method to treat biomass includes providing a solar collector to obtain concentrated solar thermal energy, providing a reactor, providing biomass, such as animal waste, to the reactor, providing concentrated solar thermal energy to the reactor using one or more fiber optic cables, and treating the biomass with the concentrated solar thermal energy. In accordance with various aspects of these embodiments, the method further includes a step of rotating a carousel to expose the reactor or container to one or more fiber optic cables. In accordance with further aspects, the fiber optic cables that are used include fused ends. In accordance with further aspects, the step of treating the biomass with the concentrated solar thermal energy comprises using hydrothermal carbonization or pyrolysis. In accordance with yet further aspects, the method includes condensing water vapor. And, in accordance with yet further aspects, the method includes removing condensable tars within pyrolysis gas using a removable tar trap prior to further treatment or use of a gas. The method may also include removing odor causing compounds from the pyrolysis gas using one or more of a biochar and activated carbon packed filter bed.

[0010] In accordance with yet additional exemplary embodiments of the disclosure, a method to treat animal waste includes providing a waste treatment system comprising a solar collector and a reactor, wherein the reactor receives concentrated solar energy from the solar collector, exposing solid waste to the concentrated solar energy in the reactor to produce char; and exposing liquid waste to one or more of concentrated and passive solar energy to treat the liquid waste. In accordance with various aspects of these embodiments, the method further includes a step of rotating a carousel to expose the reactor or a container therein to one or more fiber optic cables. In accordance with further aspects, the fiber optic cables that are used include fused ends. In accordance with further aspects, the step of treating the biomass with the concentrated solar thermal energy comprises using hydrothermal carbonization or pyrolysis. In accordance with yet further aspects, the method includes condensing the water vapor. And, in accordance with yet further aspects, the method includes removing condensable tars within pyrolysis gas using a removable tar trap prior to further treatment or use of a gas. The method may also include removing odor causing compounds from the pyrolysis gas using one or more of a biochar and activated carbon packed filter bed.

[0011] The system and method disclosed herein can be used to produce biochar from animal waste, such as human waste, using solar thermal processes, such as ultraviolet/thermal driven disinfection, hydrothermal carbonization, and/or pyrolysis. The system and method can be used for, e.g., solar-driven hydrothermal pyrolysis and treatment of mixed human waste, without need for intensive pre-drying, to produce a char that has advantages in soil applications for agriculture. In addition to treating waste and producing char, other valuable end products may be produced using the system and method described herein.

[0012] Both the foregoing summary and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure or the claimed invention.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0013] The exemplary embodiments of the present invention will be described in connection with the appended drawing figures in which like numerals denote like elements and:

[0014] FIG. 1 illustrates a thermal treatment system in accordance with exemplary embodiments of the invention.

[0015] FIGS. 2A and 2B illustrate another thermal treatment system in accordance with additional embodiments of the invention.

[0016] FIG. 3 illustrates hydrothermal carbonization energy requirements.

[0017] FIG. 4 illustrates energy vs. process temperature for mixed or dry waste.

[0018] FIG. 5 illustrates a method in accordance with further exemplary embodiments of the invention.

[0019] FIG. 6 illustrates another method in accordance with additions embodiments of the invention.

[0020] FIG. 7 illustrates yet another thermal treatment system in accordance with additional embodiments of the invention.



[0021] It will be appreciated that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of illustrated embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0022] As set forth in more detail below, the present disclosure provides improved solar biochar reactors, systems including the reactors, and methods of forming and using the reactors and systems. The reactors, systems, and methods may be used to treat biomass, such as animal waste and convert the biomass to biochar, which may be used for various beneficial applications.

[0023] The systems and method described herein use concentrated sunlight to obtain desired operating temperatures within a reactor. In traditional solar thermal systems, the reactor or receiver is located at the focus of the imaging optic, which is typically a parabola. Several concepts have been proposed, and a few have been built, which utilize additional optical elements to redirect the concentrated beam to a more convenient location, such as on the ground level. These include solar furnaces and beam-down towers. Additional optical elements for this redirection drive up costs and require the use of sophisticated optical devices to achieve high concentrations. Thus, designing solar thermal reactors where their location is driven by process rather than optical requirements has not been a successful development path for large-scale applications. To overcome these issues, in accordance with various exemplary embodiments of the invention, concentrated sunlight is delivered via fiber optic cables from a concentrated source of sunlight to a reactor.

[0024] The concept of solar concentrators using fiber optics for delivery of sunlight was first proposed over thirty years ago (Kato 1976); however, the successful demonstration of this approach was only made possible after the development of improved fiber optic technology for communications. The growth in use of fiber optics for a number of applications outside of solar enabled glass fibers of sufficient purity and low enough cost has spurred their use in solar thermal systems (Peill 1997, Zik 1999, Feuermann 1999). While certainly not a mainstream solar thermal approach, fiber optics-based systems have progressed enough to warrant a recent review article (Kandilli 2009). Small-scale demonstrations have been very encouraging and show the potential for both good performance and achievement of high temperature (Nakamura 2011).

[0025] FIG. 1 illustrates a thermal treatment system 100 in accordance with exemplary embodiments of the disclosure. Thermal treatment system 100 includes a reactor 102, one or more fiber optic cables 104, a solar concentrator 108, having an area of concentrated solar power 106, and a container 110. In the illustrated example, concentrated sunlight is delivered to reactor 102 via one or more fiber optic cables 104 (e.g. a fiber optic bundle) located at or proximate area of concentrated solar power 106 (e.g., the focus of a parabolic concentrator 108) as shown in FIG. 1. Fiber optic cable 104 is fed to reactor 102 of the system 100, where the various individual cables may terminate at, e.g., the outside of the reactor or lid (e.g., between insulating material 114 and container 110). In this case, waste container 110 is illuminated via radiation heat transfer, and container 110 is contained within insulated reactor 102. System 100 may additionally include a mirror 112 to concentrate the solar energy. A mirror size may range from, for example, about 2 m<2 >to about 100 m<2 >or about 2 m<2 >to about 50 m<2>. Compared to typical solar thermal reactors, where heat losses to the ambient environment are driven by radiation and convection, the illustrated reactor can achieve high temperatures with low solar input by limiting heat losses to conduction in the surrounding ground. In accordance with exemplary embodiments of the invention, at least some of the insulation may be movable. For example, a solar lid on reactor 102 may be coupled to fiber optic cables, and the lid can be removed or raised as material is collected in reactor 102 and then closed during treatment of the biomass material. See, e.g. system 700, below.

[0026] A design of the solar concentrator may depend on a variety of factors, based on, for example, physical properties of the biomass or waste stream to be treated. An estimate of the energy input required for a family of 4 is from about 4,000 to about 14,000 kJ, depending on specific reaction process and the temperature of that process. Energy inputs for families of 10 and shared toilets for 50 individuals are shown in Table 1. If 3 hours per day of solar operation are assumed, the power requirement is about 1300 W of net input to the reactor (using energy estimates for hydrothermal carbonization at 180[deg.] C. and accounting for conduction loss to the surrounding ground). For readily achievable values for concentrator reflectivity, secondary reflectivity, intercept factor, fiber bundle fill factor, fiber Fresnel reflections and fiber transmission, the solar efficiency can be estimated to be about 0.46. This efficiency with an average direct irradiance of 800 W/m<2 >over the operation period requires a mirror area of around 3.6 m<2 >(diameter about 2.1 m). This size is certainly small enough for use in a single family, developing community setting. Note that with higher efficiency, longer processing time or lower energy requirements, this size could be significantly reduced. A larger scale system supporting 50 people could use an area of about 46 m<2>. This could be achieved with either multiple smaller units or a decreasing number of larger diameter concentrators. While a smaller family scale system may be desirable in some cases, intermediate and large-scale systems may be scaled for business management applications, where operations and maintenance can be integrated for savings.

[0000] TABLE 1
Estimated Maximum Energy Required and Solar Area

Mixed Dry HTC Pyrolysis Pyrolysis
4 person basis
Max energy (kJ) 13911 13341 4064
Solar Area (m<2>) 3.6 3.6 1.3
10 person basis
Max energy (kJ) 34778 33353 10160
Solar Area (m<2>) 8.9 8.9 3.0
50 person basis
Max energy (kJ) 173889 166764 50802
Solar Area (m<2>) 44.5 43.9 14.7

[0027] The system and method described herein may be particularly suitable for a developing community environment. In this case, local materials can be used. The scale of such a system may depend on the degree to which the local labor force can be trained to build and operate the system, the availability of local materials, the cost for off-site versus local fabrication, and the overall economics of the concept as a business venture. Reactor 102 and solar receiving container 110 can be designed with solar power input scaled accordingly.

[0028] FIGS. 2A and 2B illustrate a system 200 including a first container 202 and a second container 204, fiber optic cable 206, a reactor 208, including insulation 210, a biochar removal door (insulated, sealed, latched shut) (212), a feedstock entrance door with tracks (insulated sealed, latched shut) 214, a safety pressure release valve for pyrolysis gases 216, waste inside the reactor 218, an example squat plate in dashed lines 220, a receiver 222, a vent tube 224 connected to a wind driven ventilator, a urine diverter 228 (included for dry pyrolysis toilet), a foot stepping platform 230, a foot operated lid for the waste input hole 232, a urine collection container 234 (e.g., for a dry pyrolysis reactor system), and a waste receiver position 236, where container 204 is in a collection position and waste receiver 202 in a treatment position. Systems in accordance with the present disclosure may also include a rotating mechanism to expose a reactor or portions thereof (e.g., a container) to one or more fiber optic cables.

[0029] In the illustrated system, first container 202 and a second container 204 can be switched between "collecting" and "treatment" positions, as shown in FIG. 2A. The containers may be switched using, for example a carousel to move the reactors-e.g., from the collection position to the treatment position. Although illustrated with only two containers 202, 204, systems in accordance with the present disclosure may include additional containers, which may be, for example on a carousel or track for easy moving between a treatment position and a collection position. Further, although not illustrated, systems in accordance with the present disclosure may include a trap for collecting condensing water vapor from a pyrolysis treatment rector, a removable tar trap for removing condensable tars within a pyrolysis reactor, and/or biochar and/or activated carbon to remove or filter odor-causing compounds.

[0030] Urine collected in urine collection container 234 may be treated using solar energy from one or more fiber optic cables 206 or natural or otherwise concentrated sunlight-e.g., urine may be heat treated to temperature and time combinations that can render it disinfected. Alternatively, a means for continuously treating human fecal sludge using a solids-conveying system where an outer solar tube heats up an inner sheathed auger to produce char may be used. Alternatively, the urine could be treated using a thin film flow reactor using germicidal UV light (254 nm). Or, heat energy from the condensation of water vapor generated during solid waste treatment can be used to heat the urine to temperature and time combinations that can render it disinfected. In accordance with other aspects, a jacketed recirculation of urine around a pyrolysis reactor can be used to heat treat urine to temperature and time combinations that can render it disinfected.

[0031] When a full collection container (e.g., container 202) is transferred (e.g., via a track and wheel system to a treatment (e.g., pyrolysis) zone, door 214 can be shut and sealed with a handle for the user, e.g., similar to a locking freezer door. The pyrolysis zone includes a gas discharge hole above the waste-filled collection container for product gases, roughly 14.2 m<3 >of steam and 0.66 m<3 >of methane per day per family of four, that can be utilized onsite for heating and/or driving electrical generators for lighting and other minor electrical loads. For hydrothermal carbonization (1-ITC), the pyrolysis zone gas discharge can be fitted with a 20 psig pressure-relief valve to allow the reactor to maintain suitable reaction conditions of 180-220[deg.] C. and 18 psig. Fiber-optic cables carrying concentrated solar light can be fed into the walls of the pyrolysis zone (e.g., though walls 210), or through a lid of a container to heat the container up to reaction temperature ~400[deg.] C. for conventional pyrolysis.

[0032] FIG. 7 illustrates another system 700 in accordance with exemplary embodiments of the invention. Similar to systems 100 and 200, system 700 includes a reactor 702, fiber optic cables 704, an area of concentrated sunlight 706, containers 708, 710, a carousel 712 to switch containers 708, 712 between a collection area and a treatment area, a toilet 714, optionally including separate areas for solid 716 and liquid 718 collection, and a vent 720. All of the components of system 700 may be the same or similar to corresponding components of systems 100 and 200 as described herein.

[0033] An estimated maximum energy requirement for the solar powered pyrolysis reaction is at about 14,000 kJ, assuming the system is used by 4 people per day (one household) operating at 34.7 psia and 180[deg.] C. An estimated maximum energy requirement, for charring one person's daily waste at varying temperatures is shown in FIG. 3 for hydrothermal carbonization and in FIG. 4 for pre-dried and mixed pyrolysis in. Human waste is comprised mostly of water, 65% or more, which is energy intensive to heat and boil due to the high heat capacity of water. Approximately 12,800 kJ accounts for heating up wet feces to the boiling point of water and boiling the water off. The balance of heat accounts for estimated heat loss through the walls of the reaction zone to the surroundings. It is important to note that this energy estimate does not include any energy gained back from the exothermic pyrolysis reaction which would be driven by any air/O2 in the system. Exclusion of this energy return allows one to determine the maximum power requirement to achieve the reaction temperature. Table 2 lists assumed physical properties of an exemplary system, such as system 100 or 200.

[0000] TABLE 2
Summary of physical properties and mass flow rates of incoming waste streams

Property Value Units
Mass flow rate feces per person 400 g/day
Mass flow rate urine per person 1017.5 g/day
Estimated specific heat capacity of wet feces 5 J/g-K
Estimated specific heat capacity of dry feces 1 J/g-K
Specific heat capacity of water 4.1813 J/g-K
Mass fraction of water in feces 0.75
Mass fraction of solids in feces 0.25
Heat of vaporization for water 2.257 kJ/g

[0034] The product gas stream of the system can be monitored in situ using a gas chromatograph mass spectrometer (GC-MS). Gas products of pyrolysis are predominately CO2 and CH4 but other noxious gases will likely be present in dilute concentrations and to ensure that the reactor gases do not pose an environmental hazard to the user, adjustments can be made to the oxygen content of the reaction environment. Thus, a usable product for heating requirements in the single-user facility or at the local community level can be produced. The system may include additional controls to ensure proper temperature, pressure, and solar radiation control for the solar reactor.

[0035] Exemplary materials of construction for the reactor include aluminum and stainless steel, both readily available and affordable. Reaction temperatures are unlikely to reach temperatures above the melting points of such metals or alloys. Additionally or alternatively, corrosion resistant materials such as stainless steel (Inconel, for example) that can also withstand high temperatures may be used. Several options for insulation may be suitable to reduce the energy losses to the environment surrounding the reactor (e.g., soil). Viable options include typical fiberglass insulation, ceramic fiber insulation (alumina or silica), and aerogels.

[0036] Design of the reactor may depend of a variety of factors, such as chemistry, namely hydrothermal carbonization (HTC) and conventional pyrolysis, energy requirements, soil amendment characteristics and optimal use of nutrients as described below. Hydrothermal carbonization requires lower reaction temperatures, 180-220[deg.] C. but pressures approaching 20 psig while conventional biomass pyrolysis takes place at atmospheric pressures but much higher temperatures, 400-800[deg.] C. (Libra, 2011). The design of an HTC reactor addresses pressure and temperature control requirements. At increased pressures and temperatures, failure of the reactor wall could lead to a dangerous release in pressure. In both HTC and pyrolysis reactors, biomass conversion is an exothermic process, which carries increased risk of thermal runaway. Accordingly, reactor design accounts for the thermal properties of the respective system, including heat transfer, fluid flow, and time-dependent temperature profiles. Thermocouples, temperature controllers, and data acquisition software such as LabView or Matlab can be used to aide in the reactor design. Real-time analysis of the gas species generated during pyrolysis is used to optimize reaction conditions and, ultimately, the utility of the biochar. These data are obtained with the use of GC-MS. Evaluations of HTC and conventional pyrolysis can balance energy requirements with nutrient recovery as well as product quality and utility of by-product gases.

[0037] An exemplary system may include a pyrheliometer-a device that accurately measures direct solar irradiance. Solar irradiance measurements may be desired to the optimization of the solar concentrator equipment and sun-tracking algorithms. Solar tracking can be accomplished via two pathways: closed- and open-loop control. Closed-loop control utilizes a sun-sensor, which is made up of several small cells around the base of a rod. Throughout the day, the shadow cast down onto the array changes and indicates the position of the sun in the sky. This system would be more expensive than open-loop but has the advantage of feedback control and less risk of error. The control system also includes a resolver or optical encoder to translate the data from the tracking system into a command for motors to adjust the position of the solar concentrator(s). Open-loop control involves motors that will adjust the solar collectors according to a pre-determined program based on latitude, longitude, date and time. This approach, though more affordable, has a high risk of error and may require extra maintenance and monitoring from a trained technician. If solar tracking is desired, a small PV system may be used to power the tracking motor.

[0038] Biochar, a value added product from the system and method described herein, has been utilized to improve agricultural soil fertility, sequester carbon, control transport of environmental contaminants, and remove pesticides as a water filter media (although the latter is not envisioned as a use for the latrine waste biochar). The processes for generation of biochar also produce gases that can be used as cooking and heating fuel or supplemental energy for the biochar production.

[0039] Biochar applied to soil can improve soil structure, water retention and lower the acidity of the soil (Winsley, 2007). Biochar material has high surface area which is capable of supporting microbiota and encouraging healthy biological activity in the soil. These microbiota act as catalysts in reducing nitrogen loss, making nutrients more available to plants. Biochar is made up of 70-80% carbon, a much more condensed quantity when compared to the biomass it is generated from. When it is placed in the soil, this carbon is permanently sequestered in this highly stable form for a net reduction of greenhouse gas emissions (Roberts, 2010). For this reason it has been proposed as an avenue for carbon sequestration credits and therefore these systems could be proliferated (multiplied to many locales) by revenue generated from selling carbon credits.

[0040] Two major factors that may impact the quality of a biochar include manufacturing conditions and the biomass (feedstock) used. Exemplary manufacturing methods include pyrolysis and hydrothermal carbonization (HTC) as these achieve high mass yield during the process and generate biochar with characteristics good for soil amendment (Funke & Ziegler, 2010; Winsley, 2007; Kumar & Gupta, 2009). Pyrolysis of animal waste and wastewater sludge have shown to generate effective biochar for soil amendments; more effective in agricultural field studies than cellulose/wood based feedstock (Meyer et al., 2011; Libra et al., 2011; Steinbeiss, 2009). A potential for generation of fuel from the gases created during pyrolysis has also been documented (Ro et al., 2010). One study has been conducted which evaluates pyrolysis of fresh human waste (US Army, 1974). This study verified that human waste could be converted into a more compact and sterile material.

[0041] For the reactor design, HTC has the advantage that no energy intensive pre-drying is necessary and because the waste is mixed (the waste includes solids and urine) it is thought that nutrients from the urine (as urine contains at least triple the mass of N, P and K of feces) will be taken up by the biochar, which would produce a nutrient enhanced biochar. Dry pyrolysis does not require a pressure rated reaction vessel and can be designed to use passive solar drying or rapid dewatering as the first phase of the solar pyrolysis process.

[0042] In the case of HTC, biochar can be generated in a pressure-rated metal reaction vessel and heated to the desired temperature under autogeneous pressure. The temperatures may range from about 150-300[deg.] C., with 200[deg.] C. expected to be optimal (Libra et al., 2011). The residence times at these temperatures range from about 10 to 90 minutes. For dry pyrolysis, the wet urine and fecal material can be collected in an open vessel and placed in an oven to be heated to the desired temperature. Dry pyrolysis will require higher temperatures between about 400-800[deg.] C. and the residence time will also be much greater because pyrolysis cannot begin until the liquid is evaporated away. Once the feedstock is dried to constant mass, subsequent pyrolysis times range from about 30 to 90 minutes.

[0043] Ultimate and proximate analysis of the char can be conducted, including C, N, H, S, elemental analysis, fixed carbon, moisture content, volatile matter, and ash content. Macro and micronutrients can be quantified by following ashing-digestion protocol and analyzing the samples with an Axial Spectrometer (P and K can be measured using an inductively coupled plasma (ICP) atomic emissions spectroscopy (AES)). The biochar product can be analyzed by field emission scanning electron microscopy (FESEM) to examine pore structure. Surface area of all resulting biochar can be measured using the method of Brunauer, Emmett and Teller (BET). Thermogravimetric analysis (TGA) can be conducted as well as Fourier Transform Infrared (FTIR) analysis in order to isolate the types of functional groups before and after charring.

[0044] It is expected that the biochar yield will be 45-60% for HTC and 20-35% for dry pyrolysis. The oxygen to carbon (O/C) ratio should decrease in the conversion to biochar and the HTC generated biochar will have a higher O/C ratio compared to that of dry pyrolysis. The abundance of oxygen-rich organic compounds on the surface of the biochar generated by HITC adds cation exchange capacity (Kumar, 2011). In general a successful soil amendment should have an O/C ratio of less than 0.2 (Spokas, 2010), a volatile matter content less than 20% (Deenik, 2010), and a BET SA of at least 15 m<2>/g. (Brewer et al., 2011). Additionally, biochar successful as a soil amendment should exhibit a low intrinsic pH, high aromaticity, and lower ash content (Brewer et al., 2011). It is expected that higher amounts of nitrogen and phosphorus will be found in the HTC biochar as the urine is combined with feces. There is evidence of higher nitrogen content with wastewater sludge processed by HTC, but never with mixed fresh human excreta (Hossain et al. 2010). The option of separation of urine and feces may determine biochar quality, energy requirements and nutrient recovery optimization.

[0045] Pyrolysis of the combined urine and feces may mineralize the nutrients found in human excreta, such as nitrogen, phosphorus, and potassium, making them bioavailable for plants. At a biochar yield of 45%, an ideal 9 g of nitrogen and 1 g of phosphorus could be recovered per person per day through the HTC process (Torondel, 2010). Nitrogen and phosphorus recovery from urine alone has been demonstrated through the use of solar thermal evaporation from exposure to direct sunlight. A pilot-scale study evaporating 50 L of undiluted urine yielded 360 g of fertilizer (2% nitrogen and 2% phosphorus by weight), equaling approximately 0.2 g of nitrogen and 0.2 g of phosphorus per person per day. The urine-derived fertilizer led to biomass yields and nutrient uptakes comparable to those from commercial fertilizers (Antonini 2012).

[0046] Potential benefits of urine separation can be weighed alongside the added cost of separate urine purification. In the event that urine is separated for nutrient recovery, pathogens may desirably be inactivated by heat. This scenario may also consider fecal contaminants due to the potential for fecal cross-contamination during urine collection (WHO, 2006). Enteric viruses are killed rapidly at temperatures of 60[deg.] C. Entamoeba hystolytica cysts and hookworm eggs are killed after five minutes at 50[deg.] C. Schistosome eggs require one hour at 50[deg.] C. and Taenia eggs 10 minutes at 59[deg.] C. Bacteria such as Vibrio cholerae and E. coli are killed rapidly above 55 or 60[deg.] C. respectively and Salmonella requires 15 to 20 min at 60[deg.] C. (Feachem 1980, Gottas 1956). Therefore, in the event that urine is separated for nutrient recovery, a temperature of at least 65[deg.] C. can be used for pathogen inactivation. This temperature is practical to achieve outside of the reactor through a passive solar thermal process. Additionally, flowing source-separated urine through a parabolic reflector could take advantage of natural UVB rays from the sun for pathogen inactivation (Mbonimpa 2012). Exemplary systems include thermal and/or natural UV inactivation of pathogens.

[0047] Both the initial human waste and biochar produced can be tested for indicator organisms of known pathogens. The material can be diluted into suspension and inoculated with the appropriate culture for each type of bacteria, including mesophile, thermophile, the organic decomposition bacteria, coliform bacteria, fecal coliform, E. coli salmonella and enterococci. Additional testing can be conducted for regrowth of indicator organisms during storage of biochar and more advanced testing for thermotolerant spores and cysts. Reactor exhaust can be analyzed for major hydrocarbons, sulfur containing gases, carbon monoxide, carbon dioxide and higher heating values. This analysis can be done with a GC-MS. This may provide information regarding whether the gases generated in either method present a health risk to the user or if they can be effectively harnessed as an energy source.

[0048] Various factors that can improve the performance of the system include: the tracking performance, reaction time, and insulation. In accordance with exemplary embodiments, the system exhibits hygienic reliability in terms of disinfecting waste on a consistent manner under a given environmental condition without the need for daily adjustments. An exemplary system also provides safe thermal, pressure and gaseous conditions by monitoring these inside the user compartment of the system.

[0049] Individual components which may be optimized for performance and cost include the solar collectors, any necessary tracking system, the reaction chamber, and the biochar production process. Additionally the biochar may be evaluated for soil amendment capabilities as well as nutrient value.

[0050] In evaluating the cost of a waste treatment system, a life cycle approach may be taken that considers not just construction costs, but also costs related to the sustainable delivery of a sanitation service. The system may be maintained to ensure that the service level remains the same as originally intended. Thus "costs" refer to expenditures incurred by the household or community (in case of the public toilet/system) for construction, operation and maintenance, and rehabilitation. This analysis helps one understand cost drivers so as to enable more cost effective service delivery. The benefits, which include elimination of costs associated with emptying, transporting, treating and disposing of traditional latrine human waste material as well as the value added material can be balanced against the costs of the system.

[0051] Table 3 shows cost estimates for system components, annualized and reported as a cost per person per day (6% discount rate and 20 year life). The scenarios analyzed range from household systems (for 4 and 10 individuals) to shared community systems (50 individuals). An estimate of the cost of small-scale solar concentrator systems using fiber optics is in the range of $200-500/m<2 >with an average of $350/m<2 >used in the calculations. The size and cost associated with the solar concentrator system for each biochar production method are shown in Table 3. Other system costs include the solar reactor, toilet base structure and superstructure. The cost estimate for the reactor associated with each system size depends on the desired temperature of reaction and orientation/automation of the collection area below the toilet. Assuming a reactor design without costly automation and with the use of aluminum or stainless steel; a system that serves 4 people is estimated to cost $230 for aluminum or $545 for stainless steel. A system serving 50 people would require a larger reactor for pyrolysis and is estimated at $700 for aluminum or $1635 for stainless. The construction of the collection area and the platform on which to stand in the bathroom can be designed and built out of local materials, e.g., reinforced concrete and brick/mortar; estimated at $100. The superstructure can be largely up to the users, but could likely be safe and private for less than $50. Table 3 shows that the final cost per person per day for these toilet systems are in the range of $0.03-0.10, indicating that the system has a very feasible economic outlook.

[0000] TABLE 3
Solar Energy and Capital Cost Estimates

Mixed Dry
HTC Pyrolysis Pyrolysis
4 person basis
Max energy (kJ) 13911 13341 4064
Solar Area (m<2>) 3.6 3.6 1.3
Solar Cost @$350/m<2> $1,257 $1,253 $438
Additional Toilet Costs $380 $380 $380
Total Capital Costs $1,637 $1,633 $818
Annualized Cost $143 $142 $71
Cost per person per day $0.10 $0.10 $0.05
10 person basis
Max energy (kJ) $34,778 $33,353 $10,160
Solar Area (m<2>) $9 $9 $3
Solar Cost @$350/m<2> $3,129 $3,101 $1,061
Additional Toilet Costs $380 $380 $470
Total Capital Costs $3,509 $3,481 $1,531
Annualized Cost $306 $303 $133
Cost per person per day $0.08 $0.08 $0.04
50 person basis
Max energy (kJ) $173,889 $166,764 $50,802
Solar Area (m<2>) $45 $44 $15
Solar Cost @$350/m<2> $15,582 $15,351 $5,142
Additional Toilet Costs $850 $850 $850
Total Capital Costs $16,432 $16,201 $5,992
Annualized Cost $1,433 $1,412 $522
Cost per person per day $0.08 $0.08 $0.03

[0052] The value of the products produced can also be factored into the economic picture. Biochar is incorporated at a conservative price of $57 per ton, based on biochar without any nutrient content (McCarl et al., 2008). Assuming 400 g of feces per person and a 50% mass yield during the pyrolysis process, a daily value for biochar was calculated. It was calculated that 0.17 m<3 >of methane is produced per person per day and this added value is incorporated into Table 4 at a cost of $80 per 1,000 m<3 >(IndexMundi, 2012). In the case of urine diversion and purification, the product has a high nutrient value and a current price of $506/ton ammonium nitrate (34% N) and $665/ton of a 45% super phosphate (USDA 2012). Table 4 shows the overall value of the products produced in one day from the system designs described herein.

[0053] The technology can serve individual families but additionally could be more economical in peri-urban communities. Depending on the value of the value added products, shared community toilets could generate a large amount of nutrient infused biochar as well as be a site for additional community services such as a kitchen, served by the flammable gases produced during the pyrolysis process. Additionally, maintenance could be paid for by biochar or nutrient sales to rural areas, carbon credits associated with biochar and toilet system user fees.

[0000] TABLE 4
Value Added Product revenue.

Number of users: 4 10 50
Daily Biochar Value $0.01 $0.03 $0.13
Daily Methane Value $0.05 $0.14 $0.68
Daily Nutrient Value $0.07 $0.16 $0.82

[0054] The alternatives for the system design desirably include ease of use and maintenance, safety, affordability, and cultural appropriateness in regards to sanitation practices. A squat or a pedestal/sitting toilet design can be used depending on the cultural preference of end users. For the dry pyrolysis application, a urine diversion variant toilet can be used. The toilet seat may have a slightly elevated position above the floor to minimize water or other cleaning liquid entering the receiver/reactor through the input holes. Foot operated hole seals may be provided to minimize odor and help keep liquid out. A latrine floor may be made of smooth, polished, and durable materials to minimize odor causing adsorption and facilitate cleaning (Rieck, Muench, 2011). Floor drains may be provided to avoid the possibility of reactor/receiver area flooding as some users may utilize the restroom as a bath/shower space for lack of other space. Wind driven ventilation may be used to keep odor to an acceptable level. If desired, however, wood ash, lime, sawdust, soil, etc. can be used to cover fresh excreta. The user may slide/guide the reactor/receiver to the location of the reactor lid and secure the lid in place. This can be done routinely, e.g., every evening after transferring the pyrolysis end product to storage for later sale/use. The use of guides to move the reactor/receivers reduces accidental spilling of raw excreta. For the safety of the user, a temperature measurement unit may be installed to ensure that the reactor contents are cool enough to open. Periodically the user may be expected to replace the o-ring seals that help maintain a pressure seal for the reactor.

[0055] Turning now to FIG. 5, a method 500, which has been described above, is illustrated. Method 500 includes the steps of providing a solar collector to obtain concentrated solar thermal energy (step 502), providing a reactor (step 504), providing biomass to the reactor (step 506), providing concentrated solar thermal energy to the reactor using one or more fiber optic cables, (step 508) and treating the biomass with the concentrated solar thermal energy (step 508). Step 502 may include providing any suitable solar collector, such as concentrator 108. Step 504 may include providing any suitable reactor, such as reactor 102, 208, or 702. Providing biomass, step 506, may include, for example, providing animal waste, such as human waste, to the reactor. Concentrated solar thermal energy is provided to a solar reactor during step 508 using the techniques described herein-e.g., using fiber optic cables with fused fiber ends, terminating the end of the fibers prior to reaching the container, and the like. Method 500 may additionally include additional steps, as described herein, including rotating a carousel to expose the reactor to one or more fiber optic cables, using hydrothermal carbonization or pyrolysis, removing condensable tars within pyrolysis gas using a removable tar trap prior to further treatment or use of a gas, removing odor causing compounds from the pyrolysis gas using one or more of a biochar and activated carbon packed filter bed, and separately or not treating urine.

[0056] FIG. 6 illustrates another method 600 in accordance with yet additional embodiments of the invention. Method 600 includes providing a waste treatment system comprising a solar collector and a reactor (step 602), wherein the reactor receives concentrated solar energy from the solar collector, exposing solid waste to the concentrated solar energy in the reactor to produce char (step 604); and exposing liquid waste to one or more of concentrated and passive solar energy to treat the liquid waste (step 606). The steps of method 600 may employ any of the corresponding techniques described herein. For example, step 602 may include providing a system as described in connection with FIG. 1 or FIG. 2A or 2B. Step 604 may include exposing solid waste in a container to concentrated sunlight as described in connection with FIGS. 1, 2A and 2B. And step 606 may include any of the urine treatment techniques described herein.

[0057] The present invention has been described above with reference to a number of exemplary embodiments and examples. It should be appreciated that the particular embodiments shown and described herein are illustrative of the exemplary embodiments of the invention and its best mode, and are not intended to limit the scope of the invention. For example, although the invention has been described in connection with a system and method for treating human waste, the system and method may be used to treat other forms of animal waste. It will be recognized that changes and modifications may be made to the embodiments described herein without departing from the scope of the present invention. These and other changes or modifications are intended to be included within the scope of the present invention.

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US8673035
US7033570
SOLAR-THERMAL REACTION PROCESSING

In an embodiment, a method of conducting a high temperature chemical reaction that produces hydrogen or synthesis gas is described. The high temperature chemical reaction is conducted in a reactor having at least two reactor shells, including an inner shell and an outer shell. Heat absorbing particles are included in a gas stream flowing in the inner shell. The reactor is heated at least in part by a source of concentrated sunlight. The inner shell is heated by the concentrated sunlight.; The inner shell re-radiates from the inner wall and heats the heat absorbing particles in the gas stream flowing through the inner shell, and heat transfers from the heat absorbing particles to the first gas stream, thereby heating the reactants in the gas stream to a sufficiently high temperature so that the first gas stream undergoes the desired reaction(s), thereby producing hydrogen or synthesis gas in the gas stream.

FIELD

[0003] In general, the disclosure relates to solar-thermal reactors and processes for carrying out high temperature chemical reactions. More particularly in an embodiment, it relates to a rapid-heating, short residence time solar-thermal process for carrying out highly endothermic dissociation reactions to produce hydrogen or hydrogen containing gases. Most particularly, in an embodiment it relates to those dissociation reactions wherein a solid particulate material is produced by the dissociation of a gaseous precursor.

BACKGROUND

[0004] There is a significant interest to develop benign processes for producing hydrogen that can be used as a fuel to power fuel cell vehicles. Such processes should reduce the amount of greenhouse gases produced, thus, minimizing impact on the environment. However, current methods for producing hydrogen incur a large environmental liability, because fossil fuels are burned to supply the energy to reform natural gas (primarily methane, CH4) to produce hydrogen (H2).

[0005] High temperatures above approximately 1500 K are required for producing hydrogen and carbon black at high rates by the direct thermal dissociation of methane [CH4+heat-->C+2H2] (reaction 1), ethane [C2H6+heat->2C+3H2] (reaction 2), propane [C3H8+heat-->3C+4H2] (reaction 3), or, in general, a mixture of gases such as natural gas generically represented as CxHy [CxHy+heat-->xC+(y/2)H2] (reaction 4).

[0006] Hydrogen can also be produced by the dry reforming of methane with carbon dioxide [CH4+CO2-->2CO+2 H2]. It is also possible to carry out dissociation of methane simultaneously with the dry reforming of methane if excess methane is present relative to that required to react carbon dioxide. Such processes are useful since they can provide for a high hydrogen content synthesis gas by utilizing natural gas from natural gas wells that contain a high concentration of carbon dioxide (typically 10 to 20 volume % CO2) or using landfill biogas (30 to 40 volume % CO2).

[0007] Hydrogen can also be produced by the thermal dissociation of hydrogen sulfide [H2S+heat-->H2+S] (reaction 5).

[0008] For these types of dissociation reactions, a solid (either C or S) is formed as a co-product (with H2) of the reaction. Often, the solid that is formed is in the state of fine particles. These particles have a tendency to deposit along the walls of reaction vessels or cooling chambers where the dissociation is occurring. If deposition occurs along the inside walls of the heated reactor, the particles tend to aggregate and crystallize. For the case of carbon deposition, the normally amorphous ultra-fine particles will grow in size and graphitize. Large graphitic carbon particles are less reactive compared to more amorphous fine sized particles and, hence, are of lower value. Furthermore, deposition on the reactor walls can cause plugging of the reactor and eventual shutdown of the process, thus, preventing continuous operation. In addition, carbon deposition on an outer transparent wall of a solar reactor can lead to overheating of the reactor wall.

[0009] U.S. Pat. No. 4,552,741, to Buck et al., reports carbon dioxide reforming of methane in a system comprising two catalytic reactors. One of the catalytic reactors is heatable with solar energy. In the abstract, the reactors are stated to be "filled with a catalyst".

[0010] U.S. Pat. No. 5,647,877 reports solar energy gasification of solid carbonaceous material in a liquid dispersion. The solid carbonaceous material is heated by solar energy and transfers heat to a surrounding liquid. Hydrogen is produced in the process by the decomposition/gasification of the hydrocarbon (coal) particles.

[0011] EP 0675075A reports the use of solar energy to generate hydrogen from water. In the reported process, water is reduced to hydrogen with a metal, followed by reduction of the metal oxide with a reducing agent.

[0012] Hence, there is a need to develop high temperature environmentally benign processes for the production of H2 by thermal dissociation of hydrocarbon gases, such as natural gas, and to prevent the deposition of the products of dissociation on reactor walls.

SUMMARY

[0013] Various methods and apparatus are described for a high temperature chemical reactor. In an embodiment, a high temperature chemical reactor conducts a reaction process to that produces hydrogen or synthesis gas. The reactor may have at least two reactor shells, including an inner shell and an outer shell. The inner shell has an inlet and an outlet and the outer shell is nonporous and substantially encloses the second inner shell. A particle inlet provides heat absorbing particles in a first gas stream flowing in the inner shell. The reactor is heated at least in part by a source of concentrated sunlight. The inner shell is heated by the concentrated sunlight, and the inner shell re-radiates from the inner wall and heats the heat absorbing particles in the first gas stream flowing through the inner shell, and heat transfers from the heat absorbing particles to the first gas stream. The heat absorbing particles heats the reactants in the first gas stream to a sufficiently high temperature so that the first gas stream undergoes the desired reaction(s), thereby producing hydrogen or synthesis gas in the first gas stream.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The multiple drawings refer to the embodiments of the invention.

[0015] FIG. 1 is a cross-sectional view of the central portion of a solar-thermally heated fluid-wall reactor having three walls. The innermost wall of the reactor is a porous "reactor" wall, the next outermost wall of the reactor is a solid "heating" wall, and the outermost wall of the reactor is a transparent "protection wall".

[0016] FIG. 2 is an overall cross-section of another reactor of the disclosure.

[0017] FIG. 3 is a cross-section of a reactor having a transparent window in the outer shell.

[0018] FIG. 4 is a schematic of a solar-thermal natural gas dissociation system employing a solar thermally heated fluid-wall reactor of the disclosure.

[0019] While the invention is subject to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. The invention should be understood to not be limited to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

DETAILED DISCUSSION

[0020] In an embodiment, a high temperature chemical reactor conducts a reaction process to that produces hydrogen or synthesis gas. The reactor may have at least two reactor shells, including an inner shell and an outer shell. The inner shell has an inlet and an outlet and the outer shell is nonporous and substantially encloses the second inner shell. A particle inlet provides heat absorbing particles in a first gas stream flowing in the inner shell. The reactor is heated at least in part by a source of concentrated sunlight. The inner shell is heated by the concentrated sunlight, and the inner shell re-radiates from the inner wall and heats the heat absorbing particles in the first gas stream flowing through the inner shell, and heat transfers from the heat absorbing particles to the first gas stream. The heat absorbing particles heats the reactants in the first gas stream to a sufficiently high temperature so that the first gas stream undergoes the desired reaction(s), thereby producing hydrogen or synthesis gas in the first gas stream. A solar concentrator designed to optimize an amount of solar thermal heating for the reaction process by using concentrated sunlight to transfer heat at extremely high rates by radiation heat transfer from the inner shell. The length of the inner shell and amount of flux provided by the solar concentrator are designed to carry out high temperature thermal dissociation reactions requiring rapid-heating and short residence times using solar energy

[0021] The disclosure provides a method for carrying out high temperature thermal dissociation reactions requiring rapid-heating and short residence times using solar energy. In particular, the method of the disclosure allows production of hydrogen and hydrogen containing gases through thermal dissociation of a gas comprising hydrocarbon gases or mixtures thereof (such as natural gas) and/or hydrogen sulfide. The methods of the disclosure also allow production of hydrogen through dry reforming of methane with carbon dioxide. The disclosure also provides high temperature solar reactors.

[0022] In particular, the disclosure provides a high temperature solar-thermal reactor comprising

[0023] a. a first inner shell which is at least partially porous, the first inner shell having an inlet and an outlet;

[0024] b. a second inner shell which is nonporous and which substantially encloses the first inner shell;

[0025] c. a first gas plenum located substantially between the first and second inner shell, the first plenum having an inlet and an outlet, wherein the first plenum outlet is formed by the pores of the first inner shell;

[0026] d. an outer shell which is nonporous, at least partially transparent, and which substantially encloses the second inner shell; and

[0027] e. a second gas plenum located substantially between the second inner shell and the outer shell, the second plenum having an inlet and an outlet,

[0028] wherein the reactor is heated at least in part by a source of concentrated sunlight and the first inner shell is prevented from fluid communication with the first and second gas plenums inside the reactor, except for fluid communication between the first inner shell and the first gas plenum through the pores of the first inner shell.

[0029] FIG. 1 is a cross-section of the central portion of a reactor in the present disclosure. In the figures, the same numbers are used to identify like features. In the configuration shown in FIG. 1, the reactor (1) has a first, innermost, inner shell (3) which is at least partially porous, a second inner shell (5) which is non-porous, and an outer shell (7) which is at least partially transparent to solar radiation and is also non-porous. As used herein, "shells" encompass tubes, pipes or chambers which are elongated along a longitudinal axis. As used herein, a "porous" shell region permits gas flow through the walls of the region while a "nonporous" shell region does not. In a reactor with three shell, the first inner shell is substantially enclosed by the second inner shell and the outer shell and the second inner shell is substantially enclosed by the outer shell. As used herein, "substantially encloses" means that one shell is enclosed by another for most of the length of the shell. The ends of a shell that is substantially enclosed by another may extend past the ends of the other shell (e.g. the ends of the first inner shell may extend past the ends of the second inner shell and/or the outer shell). FIG. 1 illustrates an embodiment where the "shells" are concentric tubes of circular cross-section.

[0030] FIG. 1 also illustrates the central portion of the first (41) and second (43) gas plenums. During operation of the reactor, gases are flowed through the first inner shell and the two gas plenums by connecting each of the respective inlets to at least one gas source. The porous region(s) of the first inner shell serve as an outlet to the first gas plenum. FIG. 1 illustrates three gas streams, a first gas stream (21) flowing through the first inner shell, a second gas stream (23) flowing through the first plenum, and a third gas stream (25) flowing through the second plenum. Preferably, the first gas stream is prevented from mixing with the third gas stream within the reactor and mixing between the first and second streams is limited to mixing within the first inner shell due to flow of gas from the second gas stream through the porous region(s) of the first inner shell. In other words, the first inner shell is preferably prevented from fluid communication with the first and second plenum inside the reactor, except for fluid communication between the first inner shell and the first plenum through the porous region(s) of the first inner shell. In addition, during operation of the reactor fluid communication between the first inner shell and the first plenum is primarily in the direction from the first plenum to the first inner shell. The pressure within the first plenum is high enough to overcome the resistance of the porous first inner shell and still have a pressure (at the instant the gas from the second gas stream leaves the pore) greater than the pressure inside the shell. Restricting fluid communication between the first inner shell and the first and second plenum can prevent deposition of particulate reaction products on the other shells and reduce the amount of gas from the second and third gas streams which enters the first inner shell. The overall volumetric flow rate of gases through the first inner shell can affect the residence time and the production throughput of the reactor. If the second and third gas streams are different, it is also preferred to prevent mixing of the second and third gas streams within the reactor.

[0031] In one embodiment, mixing of the gas streams is restricted by seals. If the inner and outer shells are tubes as shown in FIG. 1, the plenums are further defined by these seals, since they serve to define the gas volume. Statement that a plenum is located "substantially between" two shells encompasses an extension of the plenum beyond the two shells into a sealing structure. In addition, a plenum being "substantially located" between two shells encompasses reactor configurations where other reactor elements, for example thermal insulation, are also located between the two shells. FIG. 2 illustrates one sealing configuration which can be used to prevent mixing of the gas streams within the reactor. In FIG. 2, the inlet and outlets for the inner and outer shells are illustrated as part of the sealing structures (31) and (33). The inner shell inlet (11) and outlet (12) are substantially sealed from the first plenum (41) and second plenum (43). FIG. 2 also shows the first plenum inlet (13), with the outlet of the first plenum being the porous region of the inner shell, and second plenum inlet (15) and outlet (16). The sealing structures shown in FIG. 2 are cooled with water (34) to prevent heat damage to the fitting and sealing materials. Other suitable seal configurations are known to those skilled in the art. Furthermore, the seal configuration may be different at the inlet and outlet ends of the reactor.

[0032] The reactor shown in FIG. 1 is operated generally as follows. Concentrated solar-thermal radiation (91) passes through the outer "protection" shell (7) and directly heats the second inner "heating" shell (5). The nonporous heating shell re-radiates from its inner wall and heats the first inner "reaction" shell (3). Hence, the inner "reaction" shell (3) is heated indirectly by concentrated sunlight from the surrounding "heating" shell (5). The inner "reaction" shell (3) re-radiates from the inner wall and heats the radiation absorber particles (27) and first gas stream (21) flowing through it. When heated, the first gas stream undergoes the desired reaction(s). As the first gas stream is heated and the desired reaction(s) occur, one or more product gases are added to the gas stream. A second gas stream (23) of non-oxidizing and non-dissociating "fluid-wall" gas flows in the annular region between the central "heating" shell and the inner "reaction" shell. The "fluid-wall" gas enters the first plenum between the inner and outer shell through an inlet and exits the plenum through an outlet. One outlet of the first plenum is the porous section of the inner shell. An additional outlet for the first plenum may be used, so long as sufficient gas flow is provided through the porous section of the inner shell. The "fluid-wall" gas flows through the pores of the porous section of the "reaction" shell (3), exits radially along the inside of the "reaction" shell and provides for an inner "fluid-wall" gas blanket (29) that prevents deposition of dissociation product particles on the inside wall of the "reaction" shell. After entering the first inner shell, the "fluid-wall" gas exits through the outlet of the first inner shell. A third gas stream (25) of non-oxidizing and non-dissociating "purge" gas flows in the annular region between the outer "protection" shell and the center "heating" shell, thus preventing oxidation of the central "heating" shell and any insulation that may be present between the "protection" and "heating" shell.

[0033] In another embodiment, the reactor comprises

[0034] a) an inner shell which is at least partially porous, the inner shell having an inlet and an outlet;

[0035] b) an outer shell which is nonporous, at least partially transparent, and which substantially encloses the second inner shell; and

[0036] c) a gas plenum located substantially between the inner and outer shell, the plenum having an inlet and an outlet,

[0037] wherein the reactor is heated at least in part by a source of concentrated sunlight and the only fluid communication between the inner shell and the gas plenum inside the reactor occurs through the pores of the inner shell.

[0038] This reactor is operated as follows. Concentrated solar-thermal radiation passes through the outer "protection" shell and directly heats the inner "reaction" shell. The inner "reaction" shell re-radiates from the inner wall and heats the radiation absorber particles and first gas stream flowing through it. When heated, the first gas stream undergoes the desired reaction(s). A second gas stream of non-oxidizing and non-dissociating "fluid-wall" gas flows in the annular region between the outer "protection" shell and the inner "reaction" shell. The "fluid-wall" gas enters the plenum between the inner and outer shell through an inlet and exits the plenum through an outlet. The porous section of the inner shell forms one outlet of the plenum. An additional outlet for the plenum may be used, so long as sufficient gas flow is provided through the porous section of the inner shell. The "fluid wall" gas flows through the pores of the porous section of the "reaction" shell, exits radially along the inside of the "reaction" shell and provides for an inner "fluid-wall" gas blanket that prevents deposition of dissociation product particles on the inside wall of the "reaction" shell.

[0039] In general, the shells comprising the reactors of the disclosure may be positioned vertically or horizontally, or in any other spatial orientation. For the case of a vertical reaction shell process, the apparatus may be arranged to provide upward or downward flow of the gas stream and the cloud of particles. Upward flow guarantees that aggregated particles will not be carried through the reaction shell. Downward flow reduces the potential for plugging in the solids feed line, if present. Preferably, the reactor shell is positioned vertically and flow is downward.

[0040] The disclosure provides a method for carrying out a high temperature chemical reaction process to produce hydrogen or synthesis gas comprising the steps of:

[0041] a) providing a reactor comprising at least two reactor shells, including an innermost and an outer shell, wherein the innermost shell is substantially enclosed by each of the other reactor shells, has an inlet and an outlet and is at least partially porous and the outer shell is nonporous and at least partially transparent;

[0042] b) flowing a first gas stream comprising at least one reactant gas from the inlet to the outlet of the innermost shell;

[0043] c) flowing a second gas stream comprising a non-dissociating gas inwardly through the pores of the first inner shell;

[0044] d) providing heat absorbing particles in the first gas stream;

[0045] e) heating the heat absorbing particles at least in part with a source of concentrated sunlight through indirect solar thermal heating; and

[0046] f) transferring heat from the particles to the first gas stream, thereby heating the reactant gas to a sufficiently high temperature so that a desired amount of conversion of the reactant gas occurs, thereby producing hydrogen or synthesis gas.

[0047] For a reactor having a first inner shell, a second inner shell, and an outer shell, the disclosure provides a method comprising the steps of:

[0048] a) providing a reactor comprising a first inner shell which is at least partially porous and has a first inner shell inlet and outlet, a second inner shell which is nonporous and substantially encloses the first inner shell, an outer shell which is nonporous, at least partially transparent and substantially encloses the second inner shell, a first plenum substantially located between the first inner shell and the second inner shell and having a first plenum inlet and outlet, and a second plenum substantially located between the second inner shell and the outer shell and having a second plenum inlet and outlet wherein the first plenum outlet is formed by the pores of the first inner shell and the first inner shell is prevented from fluid communication with the first and second gas plenums inside the reactor, except for fluid communication between the first inner shell and the first gas plenum through the pores of the first inner shell;

[0049] b) flowing a first gas stream comprising at least one reactant gas from the inlet to the outlet of the first inner shell;

[0050] c) flowing a second gas stream comprising a non-dissociating gas through the inlet of the first plenum, thereby causing part of the second gas stream to flow inwardly through the pores of the first inner shell;

[0051] d) flowing a third gas stream comprising a non-dissociating, non-oxidizing gas from the inlet to the outlet of the second plenum;

[0052] d) providing heat absorbing particles in the first gas stream;

[0053] e) heating the heat absorbing particles at least in part with a source of concentrated sunlight through indirect solar thermal heating; and

[0054] g) transferring heat from the particles to the first gas stream, thereby heating the reactant gas to a sufficiently high temperature so that a desired amount of conversion of the reactant gas occurs, thereby producing hydrogen or synthesis gas.

[0055] The innermost inner shell (the first inner shell in a three-shell reactor) has an inlet and an outlet for the first gas stream. The interior of the innermost shell defines a reaction chamber within which the high temperature reaction takes place. The innermost shell is capable of emitting sufficient radiant energy to raise the temperature of the reactant gas(es) within the reaction chamber to a level required to initiate and sustain the desired chemical reaction. The innermost shell is made of a high temperature refractory material. The refractory material subsequently heats flowing radiation absorber particles flowing through the first inner shell and is substantially chemically unreactive with the particles or the reactant or product gases. A preferred material for the innermost shell is graphite.

[0056] The innermost shell is at least partially porous. The innermost shell may be wholly of porous material or may comprise one or more regions of porous material. For example, the innermost shell may take the form of a graphite tube having a central porous region with nonporous ends. The porous region(s) of the innermost shell are selected so that sufficient uniform flow of non-dissociating gas occurs radially inward through the pores to provide a fluid-wall protective blanket for the radially inward surface of the innermost shell. The fluid-wall can prevent particle deposition on the radially inward surface of the innermost shell. The porosity of the porous region(s) can be varied and is selected on the basis of the required gas flow and allowable pressure drop to provide for a fluid-wall of gas to prevent deposition along the inside wall of the reactor. The length of the porous section(s) of the "reaction" shell can be varied and is determined by the zone where particle deposition is most likely to occur. Likewise, the placement of the porous section along the length of the "reaction" shell is determined by the most likely location of particle deposition. Preferably, the length of the porous section of the "reaction" shell is limited to where it is needed to prevent wall deposition of dissociation product particles. Too large of a porous section will provide for too much fluid-wall gas entering the interior of the innermost "reaction" shell. The entry of fluid-wall gas into the "reaction" shell increases the overall volumetric flow rate of gases through the "reaction" shell, thus reducing residence time and limiting the production throughput of the reactor.

[0057] A second inner shell substantially enclosing the first inner shell may be present, but is not required. If no second inner shell is present the "reaction" shell is heated directly by concentrated sunlight passing through the "protection" shell and "fluid wall" gas is flowed in the plenum substantially located between the "reaction" shell and the "protection" shell.

[0058] The use of a second inner shell offers several advantages. The use of a nonporous second inner shell distances the "fluid wall" gas from the outer "protection" shell, which can increase the safety of the process when the "fluid wall" gas is a flammable gas such as hydrogen. Furthermore, if the second inner shell is a tube made of a material such as graphite, an electrical current can be run from one end of the tube to the other and generate additional heat for the process through resistance heating of the tube. This additional heat can supplement the process at times when the source of concentrated sunlight does not provide the desired amount of energy (e.g. a cloudy day).

[0059] Typically, the second inner shell is composed of nonporous high temperature refractory material. The second inner shell is most preferably made of solid graphite. As previously discussed, the second inner shell can function as a "heating" shell, since it radiates heat to the innermost shell. In addition, the combination of the first and the second inner shell at least partially defines a first plenum or volume for the non-dissociating fluid wall gas.

[0060] Additional inner shells can be used in the process. If used, they are sized and positioned so that the innermost shell is enclosed by each of the other reactor shells (i.e. the reactor shells are substantially "nested" one inside the other). If additional inner shells are used, "purge" gas can be used to prevent oxidation of these shells as well.

[0061] The outer "protection" shell is at least in part transparent or semi-transparent to the concentrated sunlight, thereby allowing concentrated sunlight to flow through and heat the inner shell(s) of the reactor. The "protection" shell is made of a high temperature material that is oxidation resistant. A suitable material for the transparent portion of the outer shell is quartz. The transparent portion of the outer shell may be a transparent section, window or opening to allow the concentrated sunlight into the vessel. The shell wall transparent area, allowing for concentrated sunlight entry and subsequent solar thermal heating, should be selected to provide heating during the desired reaction residence time requirements for the process.

[0062] The outer shell may be made entirely of quartz. In this case, the sections of the internal wall of the outer shell where sunlight is not being concentrated and entering the vessel, may be coated with a reflective material, such as silver, to keep the concentrated sunlight inside the reactor. If such a reflective coating is used, there must be an uncoated transparent section, window or opening to allow the concentrated sunlight into the vessel.

[0063] Alternatively, the outer "protection" shell may be made of a refractory non-transparent material with a section containing a transparent window where concentrated sunlight can enter, as schematically illustrated in FIG. 3. In the configuration shown in FIG. 3, both a first (3) and a second inner shell (5) are substantially enclosed by the outer shell. The "heating" shell (5) is directly exposed to concentrated sunlight in the section of the shell located in the path of the sun through the transparent section (9) of the "protection" shell (7). As shown in FIG. 3, the "heating" shell may be surrounded by refractory insulation (6) in the region where it is not directly exposed to concentrated sunlight via the transparent section. The insulation may be concentrically placed and extends substantially from the "heating" shell to the concentric "protection" shell, although it may not completely fill the space between the heating shell and the protection shell. The refractory insulation can be a combination of graphite insulation near the "heating" shell and an alumina type refractory insulation near the "protection" shell. This design arrangement allows concentrated sunlight to enter through a transparent section and heat the "heating" shell while the surrounding insulation reduces losses of ultraviolet radiation from the "heating" shell, thereby increasing the efficiency of the process. It is also possible to provide cooling of the outer metal refractory "protection" shell, particularly in the region immediately surrounding the transparent window allowing concentrated sunlight to directly heat the "heating" shell. The non-transparent refractory material may be a metal with a sufficiently high melting point, such as steel. In FIG. 3, the inlet (11) to the first inner shell is shown as having a feed gas inlet (18) and optional heat absorbing particle feed inlet (19). The particle feed inlet is not required if the heat absorbing particles are wholly generated by the dissociation process.

[0064] The combination of the outermost inner shell and the outer shell at least partially defines a plenum or volume for gas. If no second inner shell is used in the reactor, non-dissociating fluid wall gas flows in the space between the outer shell and the inner shell. Otherwise, a non-oxidizing and non-dissociating "purge" gas typically flows between a second plenum substantially located between the outer shell and the second inner shell to protect the second inner "heating" shell from oxidation.

[0065] The first gas stream initially comprises at least one reactant selected from CH4, C2H6, C3H8, generally CxHy, H2S, natural gas, or a combination thereof. The first gas stream may contain substantial amounts of carbon dioxide, as may be present in "biogases" such as landfill gas. Landfill gases may contain as much as 40% carbon dioxide. The first gas stream may also initially comprise a non-reactive gaseous component. For example, in lab-scale tests, methane is sometimes diluted with argon for safety reasons. As the gas stream is heated and the reaction or reactions occur, one or more product gases are added to the gas stream. These product gases comprise H2 and, depending on the composition of the reactant gases, may also comprise incomplete dissociation products such as C2H2, C2H4, or other gases. In the case of reactions (1 to 4), additional carbon particles are also produced, and in the case of reaction (5), elemental sulfur is produced. A preferred reactant gas stream is natural gas or one containing natural gas. A most preferable reactant gas stream is natural gas which is free of mercaptans and hydrogen sulfide.

[0066] In the method of the disclosure, the first gas stream is heated to a sufficiently high temperature within the reactor that the desired amount of conversion of the reactant gas(es) is obtained. Hydrogen formation may take place below this temperature. Preferably the first gas stream is heated to at least about 1500 K within the reactor. As used herein, the use of "about" with reference to a temperature implies that the temperature is within 25 K of the stated temperature. In other embodiments, the reactant gas is heated to about 2100 K or heated to a maximum temperature in the range between about 1500 K and about 2700 K or between about 1800 K and about 2400 K. The temperature inside the innermost shell of the reactor can be measured with a thermocouple. Alternatively, temperatures inside the reactor can be measured with an optical pyrometer. For a three-shell reactor, the hot zone temperature measured with an optical pyrometer is typically the temperature of the nonporous "heating" shell, since the "heating" shell encloses the "reaction" shell in the hot zone. The temperature inside the inner "reaction" shell may be less than that of the "heating" shell due to thermal losses due to heating the porous shell and the gases in the first plenum and the reaction shell.

[0067] The reactors and methods of the disclosure allow conversion of at least about 30% of a hydrocarbon or hydrogen sulfide reactant gas. As used herein, the amount of conversion is the ratio of the moles of reactant gas reacted to the moles of reactant gas supplied. In various embodiments, the reactors and methods of the disclosure can produce at least 50% or at least 70% conversion of reactant gas.

[0068] As used herein, the "residence time" is the time that the reactant gas(es) spend in the hot zone of the innermost "reaction" shell The hot zone length may be estimated as the length of the reactor directly irradiated by the source of concentrated sunlight. The residence time depends on the flow rate of the first gas stream containing the reactant gas(es), the flow rate of the fluid wall gas through the pores of the inner shell, the reactant gas temperature and the degree of conversion of the reactant gas(es). The residence time may be calculated through modeling or estimated by averaging the residence times of the components of the gas stream flowing through the innermost tube at reaction temperature and assuming that half of the actual conversion occurs over the entire length of the hot zone and contributes to the formation of additional moles of gas (e.g., 2 moles of hydrogen are formed for every mole of methane converted). In the methods of the disclosure, the residence time is preferably between about 1 and about 50 milliseconds. More preferably, the residence time is between about 5 and about 30 ms. Most preferably, the residence time is between about 10 and about 20 ms.

[0069] In the methods of the disclosure, heat absorbing particles are provided in the first gas stream. The radiation absorbing particles are heated indirectly by solar-thermal heating, and they must be easily separated from the gas after processing. Typically, these radiation-absorbing particles are carbon black. As used herein, "indirect" heating means that the heating is by radiation from a heated wall that is itself heated indirectly or directly by solar-radiation. In one embodiment, the particles are fine carbon black particles. Carbon black is chemically stable at extremely high temperatures and can be easily separated from the flowing process gas using a filter and/or cyclone separator. Because carbon is produced according to hydrocarbon dissociation reactions, it is compatible with the hydrocarbon dissociation type of reactions to be carried out in the process for producing H2. Preferably, the particles comprise recycled carbon black synthesized according to the dissociation reactions of the present disclosure. More preferably, the particles are carbon black particles generated in-situ from the dissociation of a reactant gas. In this manner, the carbon black particles can be produced in situ via dissociation reactions of gaseous hydrocarbons, thereby eliminating the need to feed the particles into the reactor. Sulfur particles produced from dissociation of hydrogen sulfide are also suitable for use as heat absorbing particles.

[0070] The radiation absorbing particles must be dispersed in the reactor apparatus, and the form of dispersion is important. The particles should flow as a dust or particle cloud through the apparatus, dispersed in a dispersing process gas. The radiation absorbing particles should have a fine primary particle size, preferably in the sub-micron size range, and be non-agglomerated, thus providing the highest surface area possible for solar radiation absorption. The heat absorbing particles may be provided as a result of the dissociation reaction. For example, carbon black particles can be produced in situ via dissociation reactions of gaseous hydrocarbons. The particles produced via reactions 1-5 using the methods of the disclosure typically have a primary particle size less than about 50 nm and are essentially amorphous. Carbon black particles produced using the methods of the disclosure are essentially ash-free and may be more amorphous than those produced using other commercially available carbon black producing processes. The particles may also be provided by feeding the particles into the reactor.

[0071] When the particles are provided by feeding preformed particles into the reactor, several different methods can be used to disperse the particles. The particles can be dispersed mechanically, such as by shearing on the surface of a rotating drum or brush. Alternatively, the particles can be dispersed using the shear provided by high velocity gas exiting with the particles from a feed injection tube. Experience has shown that the exiting "tip speed" from the injection tube should be at least 10 m/s to provide the shear necessary for complete dispersion of fine powders. Particles generated in-situ are inherently well dispersed in the process.

[0072] The process gas used for dispersing the particles must be compatible with the reaction process or easily separated after processing. It may be a mixture of recycle gases from the process. Preferred dispersing process gases comprise natural gas, CxHy, CH4, or H2, or a combination thereof.

[0073] In general, the radiation absorbing particles flow co-currently with the flowing gas stream through a reaction shell to maximize heat transfer from the particles to the gas. The shell may be oriented horizontally or vertically. For the case of a vertical reaction shell process, the flow direction may be upward or downward. Upward flow guarantees that aggregated particles will not be carried through the reaction shell, and downward flow reduces the potential for plugging in the solids feed line. A preferred flow direction is downward with particles generated internally and separated downstream.

[0074] The second gas stream used to provide the "fluid-wall" blanket gas flowing inward from the porous "reaction" shell wall is preferably a non-dissociating gas so as not to plug the pores of the porous wall. The fluid-wall gas is also selected to be compatible with the reactants and the products, i.e., so that it will not interfere with the reaction or be difficult to separate from the gas stream exiting the reaction shell. The fluid wall gas is preferentially a product of the reaction being carried out. Hydrogen (H2) is a preferred fluid wall gas when carrying out reactions (1) through (5). The H2 may be recycled from a downstream purification process. Inert gases, such as N2 or argon are also suitable for use as the second gas stream.

[0075] In reactors having a first and second inner shell and an outer shell, a third gas stream comprising a non-oxidizing and non-dissociating "purge" gas flows between the outermost "transparent or semi-transparent protection" shell and the solid "heating" shell. This "purge" gas can be an hydrogen or an inert gas such as N2 or argon.

[0076] In the methods of the disclosure, heat absorbing particles are heated at least in part with a source of concentrated sunlight (91). The reactors may be heated by solar energy alone or by a combination of solar energy and resistance heating of one of the shells of the reactor. The source of concentrated sunlight (91) may be a solar concentrator (50), as shown in FIGS. 2 and 3. These two figures also show unconcentrated sunlight (90) entering the solar concentrator. Preferably, the solar concentrator of the apparatus is designed to optimize the amount of solar thermal heating for the process. Solar fluxes between about 1500 and about 2000 kW/m2 have been shown to be sufficient to heat the particles to temperatures between 1675 and 1875 K. More preferably, solar fluxes between about 2000 and 5000 kW/m2 are desired to achieve even higher temperatures and reactor throughputs. Most preferably, reaction temperatures are approximately 2100 K.

[0077] The sunlight can be provided in the form of a collimated beam (spot) source, a concentric annular source distributed circumferentially around the reactor, or in the form of a linearized slot source providing heating axially along the length of reactor. The light can be redirected and focused or defocused with various optical components to provide the concentration on or in the reactor as required. An example of a suitable solar concentrator for use in the present disclosure is the High-Flux Solar Furnace (HFSF) at the National Renewable Energy Laboratory (NREL) in Golden, Colo. The HFSF uses a series of mirrors that concentrate sunlight to an intensified focused beam at power levels of 10 kW into an approximate diameter of 10 cm. The HFSF is described in Lewandowski, Bingham, O'Gallagher, Winston and Sagie, "Performance characterization of the SERI Hi-Flux Solar Furnace," Solar Energy Materials 24 (1991), 550 563. The furnace design is described starting at page 551, wherein it is stated, The performance objectives set for the HFSF resulted in a unique design. To enable support of varied research objectives, designers made the HFSF capable of achieving extremely high flux concentrations in a two-stage configuration and of generating a wide range of flux concentrations. A stationary focal point was mandatory because of the nature of many anticipated experiments. It was also desirable to move the focal point off axis. An off-axis system would allow for considerable flexibility in size and bulk of experiments and would eliminate blockage and consequent reduction in power. In particular, achieving high flux concentration in a two-stage configuration (an imaging primary in conjunction with a nonimaging secondary concentrator) dictates a longer f/D [ratio of focal length to diameter] for the primary [concentrator] than for typical single-stage furnaces. Typical dish concentrators used in almost all existing solar furnaces are about f/D=0.6. To effectively achieve high flux concentration, a two-stage system must have an f/D=2. Values higher than this will not achieve significantly higher concentration due to increased losses in the secondary concentrator. Values lower than this will result in a reduction of maximum achievable two-stage flux. At low values of f/D, the single stage peak flux can be quite high, but the flux profiles are also very peaked and the average flux is relatively low. With a longer f/D, two-stage system, the average flux can be considerably higher than in any single-stage system. The final design of the HFSF has an effective f/D of 1.85. At this f/D, it was also possible to move the focal point considerably off axis (about 30 degrees) with very little degradation in system performance. This was because of the longer f/D and partly because of the multi-faceted design of the primary concentrator. This off-axis angle allows the focal point and a large area around it to be completely removed from the beam between the heliostat and the primary concentrator.

[0078] When the outer shell is wholly transparent or has a window which extends completely around the shell, the concentrated sunlight is preferably distributed circumferentially around the reactor using at least one secondary concentrator. Depending upon the length of the reaction shell, multiple secondary concentrators may be stacked along the entire length of the reaction shell. For the HFSF described above, a secondary concentrator that is capable of delivering 7.4 kW of the 10 kW available (74% efficiency) circumferentially around a 2.54 cm diameter times 9.4 cm long reaction tube has been designed, constructed, and interfaced to the reactor.

[0079] The disclosure also provides reactor systems which combine the reactor of the disclosure with one or more other system elements. System elements useful for use in the present disclosure include, but are not limited to, particle dispersion and feeding devices, sources of concentrated solar energy, cooling zones, filtering devices, various purification devices, hydrogen storage devices, and thermophotovoltaic devices.

[0080] In one embodiment, a cooling zone is located downstream of the aerosol transport reactor. The cooling zone is preferably expanded and of a larger diameter than the inner "reaction" shell. The cooling zone is preferably a jacketed steel tube with a coolant flowing within the jacket of the tube. The function of the cooling zone is to provide a larger volume where product gases and dissociated product particles can be cooled. The purpose of the expanded tube is twofold. First, it provides for a reduced velocity of product gas and entrained particles flowing through it and, hence, an increased residence time for cooling. Second, the expanded design allows for dissociated product particles to be cooled while flowing in the gaseous space, thus, reducing thermophoretic deposition of fine particles on the cooler wall. This design reduces the tendency for dissociated product particles to deposit along the cooling zone wall.

[0081] Additionally, a system element for removing the solid dissociation products from the gas stream can be provided. Carbon black particles are preferably removed from the gas stream after the gas exits the reaction chamber. The carbon black may be removed from the gas stream by suitable methods as known in the art, such as by filtration, cyclonic separation, or a combination thereof. Some of the carbon black particles may be recycled in the process, preferably providing absorber surfaces for heating the gas. The carbon black may be sold as a product or may be used as a raw material to supply a carbon conversion fuel cell for generating electricity. The carbon black from the solar-thermal dissociation process is fine sized and preferably substantially free of sulfur and ash. Hence, it is a preferred feed stock for supplying a carbon conversion fuel cell.

[0082] The system may also comprise a system element for separating hydrogen from non-dissociated gaseous components or otherwise purifying the hydrogen produced by the process. The product gas that is separated from the heat absorbing particles can be purified using a pressure swing adsorber (PSA), membrane or some other type of gas separation device that will separate hydrogen from non-dissociated gaseous reactants (i.e. CH4, CxHy, natural gas, etc.) or byproducts of reaction (e.g. acetylene, etc). Some of the purified hydrogen can be recycled to the process, preferably as the "fluid-wall" gas and "purge gas". Some of the recycled hydrogen can be fed to an upstream hydrogenator to hydrogenate mercaptans that may have been added to the natural gas. The hydrogenated mercaptans are then removed along with H2S in a molecular sieve such as an adsorption bed of zinc oxide particles. The bulk of the hydrogen will be used in downstream processes, preferably to supply fuel cell batteries for stationary generation of electricity or for on board transportation applications involving fuel cell vehicles. The purified hydrogen exiting the separation device (PSA or membrane) may supply a hydrogen pipeline at lower pressure or may be compressed and stored in a storage tank, such as at a service station for servicing fuel cell vehicles.

[0083] FIG. 4 illustrates one system comprising a hydrogenation and ZnO bed (70), solar-thermal fluid wall reactor (1), a cooling zone (60) immediately following the reactor, a baghouse filter (62), a low pressure compressor (64), a pressure swing adsorber (66), and a high pressure compressor (68). The high pressure compressor can additionally be connected to a hydrogen storage device, not shown in FIG. 4.

[0084] In another embodiment, a reactor with a transparent outer shell such as a quartz tube may be coupled to one or more thermophotovoltaic devices. Thermal radiation from the outermost inner shell of the reactor (e.g. from a graphite heating tube in a three shell reactor) which passes out through the transparent outer shell can be used to power the thermophotovoltaic devices. The thermophotovoltaic devices are placed in locations not shielded by the solar concentrator.

[0085] Those of ordinary skill in the art will appreciate that starting materials, reactor components, reactor system components, and procedures other than those specifically exemplified can be employed in the practice of this disclosure without resort to undue experimentation. The skilled artisan will be further aware of materials, methods and procedures which are functional equivalents of the materials, methods and procedures specifically exemplified herein. All such art-known functional equivalents are intended to be encompassed by this disclosure.

[0086] All references cited herein are incorporated by reference herein to the extent that they are not inconsistent with the teachings herein.

EXAMPLES

Example 1
Operation of a Three-Shell Reactor

[0087] In accordance with the present disclosure, a concentric three-tube aerosol transport reactor was constructed and vertically interfaced to the HFSF at NREL. The aerosol transport reactor consisted of an outer 5.1 cm outside diameter times 4 mm thick times 24 cm long quartz "protection" tube, a central 2.4 cm outside diameter times 4 mm thick times 35.6 cm long graphite "heating" tube, and a 1.8 cm outside diameter times 6 mm thick times 44 cm long graphite "reaction" tube. The "reaction" tube consisted of a 30 cm long porous graphite section with 7 cm of solid graphite tube on both ends of the "reaction" tube. The porosity of the graphite tube was 49% with a permeability of air (at standard temperature and pressure (STP)) of 1 ft3/ft2/min. It was a sunny day. A secondary concentrator delivered 7.4 kW of solar-thermal power over a 9.4 cm length. The concentrator was positioned concentrically around the outer quartz "protection" tube. A 99% methane/1% argon gas was fed at a rate of 4 standard liters per minute (slpm) into the top of the graphite "reaction" tube and flowed downward. Hydrogen "fluid-wall" gas was fed at a rate of 1 slpm to the annular region between the inner "reaction" tube and the central "heating" tube. The hydrogen flowed within the annular region and through the porous section of the "reaction" tube and exited radially inward providing a fluid-wall of hydrogen along the inside "reaction" tube wall. Argon "purge" gas flowed at a rate of 2 slpm in the annular region between the outer quartz "protection" tube and the central solid graphite "heating" tube. The argon prevented oxidation of the graphite "heating" tube. No carbon black absorber particles were fed to the inner "reaction" tube. The temperature of the reactor as measured by a Type B thermocouple inserted in the hot zone was 1873 K. Feed gas was flowed for approximately 1 hour. A downstream gas chromatograph analyzed the steady state composition of the exiting stream, after the 1 slpm "fluid-wall" hydrogen was subtracted out. A downstream flowmeter measured the gas flow rate as 3.2 slpm (after subtracting out the 1 slpm fluid-wall H2). The unreacted methane content was 30 mole % with the remaining gas essentially hydrogen. This corresponded to a conversion of 76% of the feed methane for a residence time of approximately 0.03 seconds. The system was taken off sun and allowed to cool. No dissociated carbon was found to be deposited anywhere along the inside wall of the "reaction" tube. The product carbon black collected downstream was analyzed by x-ray diffraction and found to be essentially amorphous carbon black with a primary particle size between approximately 20 and 40 nanometers. This example illustrates that the fluid-wall reactor tube prevented deposition of reaction products within the reactor and allowed continuous operation.

Example 2
Operation of a Three-Shell Reactor with No "Fluid-Wall" Gas Flow

[0088] The process conditions of Example 1 were repeated except that no "fluid-wall" hydrogen gas was flowed through the porous "reaction" tube. Within 8 minutes, the process was shut down due to difficulties maintaining feed gas flow using mass flow controllers. After cooling, the reactor was dismantled and inspected. It was found that carbon was deposited inside of the "reaction" tube. The carbon was analyzed by x-ray diffraction and found to contain a large graphitic content. This comparative example illustrates that, without the fluid-wall, the reactor plugs and prevents continuous operation.

Example 3
Reactor Operation with Increased Fluid-Wall and Purge Gas Flow Rates

[0089] The apparatus described in Example 1 was used except that the "fluid-wall" gas was changed to argon. It was fed at a rate of 4 slpm through the porous tube wall. In addition, the argon "purge" gas flow was increased to 10 slpm.

Examples 4 to 12
Reactor Operation with Varying Methane Flow Rate and Solar Flux

[0090] The apparatus described in Example 1 was used with the gas flow rates given in Example 3. The nonporous "heating" wall temperature was measured through a hole in the trough section of the secondary concentrator using a pyrometer. For this apparatus, the temperature of the wall of the nonporous carbon tube was typically about 100-200 K higher than the temperature inside the reaction tube. The solar flux was varied in order to achieve heating wall temperatures of 1716, 1773, 1923, 2073, and 2140 K. Although the "fluid-wall" argon flow rate was maintained at 4 slpm, the methane flow rate was varied from 0.8 to 2.2 slpm. All flow rates corresponded to average residence times between approximately 10 and 20 milliseconds. The dissociation (conversion) of methane to hydrogen and carbon black was calculated from the measured concentration of H2 and is reported in Table 1.

[0000] TABLE 1
(Examples 4 to 12) Methane Dissociation

Heating Wall Initial Methane Conversion of
Temperature (K.) Flow Rate (slpm) Methane (%)
1716 0.8   0 +- 5
1716 2.2   0 +- 5
1773 1 15 +- 5
1773 2 18 +- 5
1923 1.5 29 +- 5
2073 1 69 +- 5
2073 2 55 +- 5
2140 0.8 81 +- 5
2140 2.2 83 +- 5

[0091] This set of examples indicates that increasing the solar flux, which in turn increases the heating wall temperature and the temperature inside the reactor tube, results in an increase in the thermal dissociation (conversion) of methane to H2 and carbon black. The product carbon black for all runs was analyzed by x-ray diffraction and transmission electron microscope images to determine that it was amorphous carbon black with a primary particle size of 20 to 40 nanometers.

Examples 13 to 24
Dry Reforming with Varying Total Feed Rate and Solar Flux

[0092] The apparatus described in Example 1 was used. During these experiments, the argon "purge gas" was fed at a rate of 10 slpm. The "fluid-wall" argon was fed at a rate of 4 slpm. The reactant gas was maintained at a two to one CH4 to CO2 feed ratio. Total flow rates of 1 and 2 slpm were used. By changing the solar flux, the heating wall temperature was varied from 1873 to 2123 K, with increments of 50 K. The conversion of methane was calculated from the measured concentration of H2, and the conversion of CO2 was calculated from the measured concentration of CO. Both values are reported in Table 2.

[0000] TABLE 2
Examples 13 to 24 (Dry Reforming and Dissociation)

Total Flow Rate CH4 CO2
Heating Wall of CH4 and CO2 Conversion Conversion
Temperature (K.) (slpm) (%) (%)
1873 1   35 +- 14 17 +- 11
1925 1 47 +- 1 22 +- 2
1977 1 58 +- 1 35 +- 5
2025 1 65 +- 7 51 +- 18
2074 1 71 +- 6 65 +- 7
2108 1 69 +- 5 56 +- 16
1924 2 29 +- 5 19 +- 9
1924 2 20 +- 4 6 +- 3
1974 2 27 +- 2 8 +- 3
2022 2 39 +- 3 15 +- 3
1801 2 51 +- 7 30 +- 13
1831 2 55 +- 9 35 +- 16

[0093] The average residence time of all runs was approximately 10 milliseconds. This set of examples indicates that concentrated sunlight can be used to carry out dry CO2 reforming of CH4 reactions in short residence times. It is also evident that both increased temperature and decreased reactant gas flow rate result in higher conversion of CO2 to CO and CH4 to H2.

Examples 25 to 30
Reactor Operation During Dry Reforming with Varying Total Feed Rate and Methane to Carbon Dioxide Feed Ratio

[0094] The apparatus described in Example 1 was used with the flow rates presented in Example 3. For a given day, the highest available solar flux level was utilized. This resulted in heating wall temperatures ranging from 2063 to 2115 K, as seen in Table 3. Total CH4 and CO2 feed rates of 1 and 2 slpm were used. Three CH4 to CO2 feed ratios were utilized: 1 to 1, 1.5 to 1, and 2 to 1. The conversion of methane was calculated from the measured H2 concentration, and the CO2 conversion was calculated from the measured CO concentration. Both values for each experiment appear in Table 3.

[0000] TABLE 3
Examples 25 to 30 (Simultaneous Dry Reforming and Dissociation)

Total Flow CH4 to CO2 Heating Wall
Rate of CH4 Feed Ratio version CH4 CO2 and CO2 (molar Temperature Conversion Conversion
(slpm) volume) (K) (%) (%)
1 1:1 2063 64 +- 7 33 +- 7
1 1.5:1< > 2114 76 +- 2 64 +- 8
1 2:1 2108 69 +- 5   56 +- 16
2 1:1 2083 50 +- 2 20 +- 2
2 1.5:1< > 2115 58 +- 3 34 +- 6
2 2:1 2104 55 +- 9   35 +- 16

[0095] This set of experiments shows that the fluid-wall aerosol flow reactor can be used to carry out dry CO2 reforming of CH4 reactions with various reactant feed ratios. It also indicates that for a given total flow rate, changing the feed ratio does not significantly change the conversion of CH4 to H2 or the conversion of CO2 to CO. However, both conversion values are increased when the total flow rate of CH4 and CO2 is decreased from 2 slpm to 1 slpm.

[0000] Additional points include

[0096] The present disclosure provides a method for carrying out high temperature thermal dissociation reactions requiring rapid-heating and short residence times using solar energy. In particular, the present disclosure provides a method for carrying out high temperature thermal reactions such as dissociation of hydrocarbon containing gases and hydrogen sulfide to produce hydrogen and dry reforming of hydrocarbon containing gases with carbon dioxide. In the methods of the disclosure where hydrocarbon containing gases are dissociated, fine carbon black particles are also produced. The methods of the disclosure reduce or prevent the produced carbon black from depositing along the inside wall of the reactor or cooling zone. The present disclosure also provides solar-thermal aerosol transport reactors and solar-thermal reactor systems. The present disclosure also provides systems and methods for separating the produced carbon black from the product gases, purifying the hydrogen produced by the dissociation reaction, and using the carbon black and hydrogen to generate electricity.

[0097] There is an enormous environmental benefit for carrying out high temperature dissociation reactions directly without the combustion of carbonaceous fuels. Thus, the present disclosure provides a continuous cost-effective, solar-based method of deriving hydrogen and fine carbon black particles from hydrocarbon gases. The process does not result in increased environmental damage due to burning fossil fuels.

[0098] The process of the present disclosure uses concentrated sunlight to transfer heat at extremely high rates by radiation heat transfer to inert radiation absorbing particles flowing in dilute phase in the process gas. The heating to the particles is generally carried out indirectly from a heated wall or series of walls which are themselves heated indirectly or heated directly by solar-thermal radiative heating. The inside most wall ("reaction") is at least partially fabricated of a porous refractory material with a compatible "fluid-wall" gas flowing inward, thus, providing a blanket of gas and preventing deposition of particles on the inside wall. The particles subsequently become radiators themselves and heat flowing gases by conduction, thereby providing the energy to carry out highly endothermic gas phase dissociation reactions. The radiative coupling to heat flowing radiation absorbing particles is beneficial because the gases to be heated are themselves transparent to radiative heating. Preferably, the gases and the particles flow co-currently to maximize the temperature and heating rate of the gases. It is possible for the absorber particles to either be fed into the process with the reactant gas or to be generated in-situ by the reaction itself.

[0099] In an embodiment, a method for carrying out a high temperature chemical reaction process to produce hydrogen or synthesis gas may include at least the following the steps: a) providing a reactor comprising at least two reactor shells, including an innermost and an outer shell, wherein the innermost shell is substantially enclosed by each of the other reactor shells, has an inlet and an outlet and is at least partially porous and the outer shell is nonporous and at least partially transparent; b) flowing a first gas stream comprising at least one reactant gas from the inlet to the outlet of the innermost shell; c) flowing a second gas stream comprising a non-dissociating gas inwardly through the pores of the innermost shell; d) providing heat absorbing particles in the first gas stream; e) heating the heat absorbing particles at least in part with a source of concentrated sunlight through indirect solar thermal heating; and f) transferring heat from the particles to the first gas stream, thereby heating the reactant gas to a sufficiently high temperature so that a desired amount of conversion of the reactant gas occurs, thereby producing hydrogen or synthesis gas.

[0100] The reactant gas may be a gaseous hydrocarbon, hydrogen sulfide or a mixture thereof. For example, the gaseous hydrocarbon is methane, ethane, propane, butane, or a mixture thereof. Alternatively, the reactant gas maybe at least one gaseous carbon oxide including carbon dioxide, carbon monoxide, or mixtures thereof. The volume concentration of carbon dioxide in the reactant gas can be less than 50 volume percent. The heat absorbing particles can be carbon particles, and the carbon particles are fed into the innermost shell with the first gas stream. The temperature of the reactor is at least about 1500 K. The source of concentrated sunlight can have a flux of between 1500 and 5000 kW/m2.

US8287610
RAPID SOLAR-THERMAL CONVERSION OF BIOMASS TO SYNGAS.

Methods for carrying out high temperature reactions such as biomass pyrolysis or gasification using solar energy. The biomass particles are rapidly heated in a solar thermal entrainment reactor. The residence time of the particles in the reactor can be 5 seconds or less. The biomass particles may be directly or indirectly heated depending on the reactor design. Metal oxide particles can be fed into the reactor concurrently with the biomass particles, allowing carbothermic reduction of the metal oxide particles by biomass pyrolysis products. The reduced metal oxide particles can be reacted with steam to produce hydrogen in a subsequent process step.

FIELD

[0003] In general, the disclosure relates to solar-thermal reactors and processes for carrying out high temperature chemical reactions. More particularly in an embodiment, it relates to a rapid-heating, short residence time solar-thermal process for carrying out highly endothermic dissociation reactions to produce hydrogen or hydrogen containing gases. Most particularly, in an embodiment it relates to those dissociation reactions wherein a solid particulate material is produced by the dissociation of a gaseous precursor.

BACKGROUND

[0004] There is a significant interest to develop benign processes for producing hydrogen that can be used as a fuel to power fuel cell vehicles. Such processes should reduce the amount of greenhouse gases produced, thus, minimizing impact on the environment. However, current methods for producing hydrogen incur a large environmental liability, because fossil fuels are burned to supply the energy to reform natural gas (primarily methane, CH4) to produce hydrogen (H2).

[0005] High temperatures above approximately 1500 K are required for producing hydrogen and carbon black at high rates by the direct thermal dissociation of methane [CH4+heat-->C+2H2] (reaction 1), ethane [C2H6+heat->2C+3H2] (reaction 2), propane [C3H8+heat-->3C+4H2] (reaction 3), or, in general, a mixture of gases such as natural gas generically represented as CxHy [CxHy+heat-->xC+(y/2)H2] (reaction 4).

[0006] Hydrogen can also be produced by the dry reforming of methane with carbon dioxide [CH4+CO2-->2CO+2 H2]. It is also possible to carry out dissociation of methane simultaneously with the dry reforming of methane if excess methane is present relative to that required to react carbon dioxide. Such processes are useful since they can provide for a high hydrogen content synthesis gas by utilizing natural gas from natural gas wells that contain a high concentration of carbon dioxide (typically 10 to 20 volume % CO2) or using landfill biogas (30 to 40 volume % CO2).

[0007] Hydrogen can also be produced by the thermal dissociation of hydrogen sulfide [H2S+heat-->H2+S] (reaction 5).

[0008] For these types of dissociation reactions, a solid (either C or S) is formed as a co-product (with H2) of the reaction. Often, the solid that is formed is in the state of fine particles. These particles have a tendency to deposit along the walls of reaction vessels or cooling chambers where the dissociation is occurring. If deposition occurs along the inside walls of the heated reactor, the particles tend to aggregate and crystallize. For the case of carbon deposition, the normally amorphous ultra-fine particles will grow in size and graphitize. Large graphitic carbon particles are less reactive compared to more amorphous fine sized particles and, hence, are of lower value. Furthermore, deposition on the reactor walls can cause plugging of the reactor and eventual shutdown of the process, thus, preventing continuous operation. In addition, carbon deposition on an outer transparent wall of a solar reactor can lead to overheating of the reactor wall.

[0009] U.S. Pat. No. 4,552,741, to Buck et al., reports carbon dioxide reforming of methane in a system comprising two catalytic reactors. One of the catalytic reactors is heatable with solar energy. In the abstract, the reactors are stated to be "filled with a catalyst".

[0010] U.S. Pat. No. 5,647,877 reports solar energy gasification of solid carbonaceous material in a liquid dispersion. The solid carbonaceous material is heated by solar energy and transfers heat to a surrounding liquid. Hydrogen is produced in the process by the decomposition/gasification of the hydrocarbon (coal) particles.

[0011] EP 0675075A reports the use of solar energy to generate hydrogen from water. In the reported process, water is reduced to hydrogen with a metal, followed by reduction of the metal oxide with a reducing agent.

[0012] Hence, there is a need to develop high temperature environmentally benign processes for the production of H2 by thermal dissociation of hydrocarbon gases, such as natural gas, and to prevent the deposition of the products of dissociation on reactor walls.

SUMMARY

[0013] Various methods and apparatus are described for a high temperature chemical reactor. In an embodiment, a high temperature chemical reactor conducts a reaction process to that produces hydrogen or synthesis gas. The reactor may have at least two reactor shells, including an inner shell and an outer shell. The inner shell has an inlet and an outlet and the outer shell is nonporous and substantially encloses the second inner shell. A particle inlet provides heat absorbing particles in a first gas stream flowing in the inner shell. The reactor is heated at least in part by a source of concentrated sunlight. The inner shell is heated by the concentrated sunlight, and the inner shell re-radiates from the inner wall and heats the heat absorbing particles in the first gas stream flowing through the inner shell, and heat transfers from the heat absorbing particles to the first gas stream. The heat absorbing particles heats the reactants in the first gas stream to a sufficiently high temperature so that the first gas stream undergoes the desired reaction(s), thereby producing hydrogen or synthesis gas in the first gas stream.

BACKGROUND OF THE INVENTION

[0003] This invention is in the field of solar biomass gasification and pyrolysis

[0004] As processes, biomass gasification and pyrolysis have been known for a long time. Several different types of reactors have been used to gasify and/or pyrolize biomass including fixed bed reactors, fluidized bed reactors, and entrained flow reactors. A variety of sources of heat for biomass gasification and pyrolysis processes have been used, including fossil fuels (Ni, et al, Fuel Processing Technology, 2006, pp. 461-472) and combustion of biomass or biomass reaction products such as pyrolysis oil (e.g. U.S. Pat. No. 4,497,637 to Purdy et al).

[0005] Solar gasification of carbonaceous particles has also been reported in the patent literature. U.S. Pat. No. 5,647,877 to Epstein reports solar energy gasification of solid carbonaceous material in a liquid dispersion. An aqueous dispersion of carbonaceous material is introduced into the reactor so as to form water droplets enclosing particulates of the carbonaceous material. The solid carbonaceous material is heated by solar energy and transfers heat to a surrounding liquid. Hydrogen is produced in the process by the decomposition/gasification of the hydrocarbon (coal) particles. A variety of carbonaceous materials are mentioned as possible feedstocks including coal and various biomasses.

[0006] U.S. Pat. No. 4,290,779 to Frosch et al. reports a solar heated fluidized bed gasification system for gasifying carbonaceous material. Solar radiation is introduced into a refractory honeycomb shell which surrounds the fluidized bed reactor. Both coal and organic biomass materials are mentioned as possible powdered carbonaceous feedstocks.

[0007] U.S. Pat. No. 4,229,184 to Gregg reports an apparatus for using focused solar radiation to gasify coal and other carbonaceous materials. The solar radiation is directed down through a window onto the surface of a vertically moving bed of the carbonaceous material.

[0008] It has been shown that solar thermal reactors can achieve temperatures up to 2500 K (2227[deg.] C.). Temperatures even higher than this are achievable, but in those regimes materials and reradiation loss issues become major concerns. Solar thermal systems have been applied to the dissociation of methane (Dahl, et al., International Journal of Hydrogen Energy, 29, 2004) or ZnO (Perkins, et al., International Journal of Hydrogen Energy, 29, 2004; Steinfeld, Solar Energy, 78, 2005). Carbon has been used as reducing agents for ZnO (Müller, R, P Haeberling, and R Palumbo, "Further advances toward the development of a direct heating solar thermal chemical reactor for the thermal dissociation of ZnO(s)," Solar Energy, 80, 2005, pp. 500-511).

BRIEF SUMMARY OF THE INVENTION

[0009] The invention provides processes that perform biomass gasification or pyrolysis for production of hydrogen, synthesis gas, liquid fuels, or other hydrocarbon based chemicals. The methods of the invention use solar thermal energy as the energy source for the biomass pyrolysis or gasification. This allows operation at temperatures above 950[deg.] C., speeding up reaction kinetics and shifting thermodynamics to various reaction end products, thus, bypassing the formation of tars and other liquids that have a tendency to cause plugging or increased pressure drop in gas/solid filtration devices downstream of the reactor and which are undesired side products. The increase in reaction rate, the use of a renewable energy resource, the avoidance of tars, and the wider range of available thermodynamic regimes give great advantage to one who would utilize solar thermal energy. Usage of solar thermal energy can reduce the overall amount of biomass required to produce the product chemicals, allows for a greater range of product control, does not rely on fossil fuel usage, and takes advantage of a freely available resource (solar energy).

[0010] In the methods of the invention, an entrainment flow solar-thermal reactor is used to carry out the high temperature thermal dissociation reactions, thereby permitting rapid-heating of the biomass particles and short residence times of the particles in the reactor. Rapid heating is of great advantage for this solar chemistry. Rapidly heating to high temperature (>950[deg.] C.) prevents the biomass particles from spending significant portions of time in temperature regimes (200[deg.] C.-800[deg.] C.) where formation of liquid side products and tars is favorable. The selectivity of the reactor toward desired products is thus increased. Likewise, rapid heating allows the particles to spend the most time possible in the temperature regimes where reaction rates are fastest (950[deg.] C. to 1400[deg.] C.). A rapid reaction allows the thermal energy imparted to the particles to be converted to chemical energy more quickly, reducing the portion of incident energy lost to re-radiation or conduction and increasing reactor efficiency. Additionally, a more rapid reaction leads to shorter effective residence times and higher reactor throughput; essentially, the production rates of fuels can be increased while leaving the area of solar concentrators constant. In different embodiments, the residence time is less than or equal to 5 seconds or less than or equal to 3 seconds. In an embodiment, the heating rate of the particles is greater than 100[deg.] C./s; preferably, this heating rate is greater than 1000[deg.] C./s.

[0011] The present invention also provides a method for carrying out a closed thermochemical/photosynthetic cycle for splitting water to produce hydrogen. A biomass feedstock such as algae can be grown in a controlled atmosphere greenhouse environment with algae receiving direct sunlight and being fed water and carbon dioxide and releasing oxygen to the environment via photosynthesis. The algae can be cultivated and fed as a biomass reactant to the reactor described herein. The algae can be pyrolyzed by high temperature solar thermal heating as described herein. The resulting "syngas" of carbon monoxide and hydrogen can be fed to a conventional "water-gas shift reactor" where water is fed and hydrogen and carbon dioxide are produced via a controlled catalytic process (CO+H2O-H2+CO2). The exiting gas is primarily H2 and CO2 which can be separated by conventional membrane or pressure swing adsorption processing. The H2 can be used as a reactant or a fuel while the CO2 is fed to the algae in the greenhouse. Water is effectively split to H2 and O2 via a combined solar thermochemical/photosynthetic process in two separate steps.

[0012] The present invention also provides processes which involve reduction of metal oxide particles with biomass pyrolysis products in a solar-thermal reactor. The invention also provides "renewable" hydrogen producing processes in which the hydrogen produced from reaction of the reduced metal oxide products with water is combined with hydrogen produced by reaction of gaseous products of the solar thermal reactor in a water-gas shift reactor, both processes being as described in Example 6 and elsewhere in this application. The invention also provides processes in which hydrogen produced by the methods of the invention are combined with conventional fossil feeds. For example, hydrogen can be combined with coal to produce methane as described in Example 7. Such a process represents a transitional bridge to a truly hydrogen economy.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is a schematic horizontal cross-section of a solar reactor having a single nonporous inner reaction shell and an outer protection shell, viewed from the top of the reactor.

[0014] FIGS. 2A and 2B are schematic horizontal cross-sections of solar reactors having multiple nonporous inner reaction shells within an outer protection shell, viewed from the top of the reactor.

[0015] FIG. 3 illustrates the monomer unit of the cellulose particles used in the Examples.

[0016] FIG. 4 is schematic vertical cross-section of an electrically heated reactor system used in Examples 1-3, and 5.

[0017] FIG. 5 is a mass spectrometer trace from cellulose gasification as performed in Example 1.

[0018] FIG. 6 illustrates the monomer unit of the lignin particles used in the Examples.

[0019] FIG. 7 is a mass spectrometer trace from lignin gasification as performed in Example 2.

[0020] FIG. 8 is a schematic of the solar heated reactor system used in Example 4. In this reactor system, an alumina reaction tube is contained within a quartz sheath.

[0021] FIG. 9 is a mass spectrometer trace from solar cellulose gasification as performed in Example 4.

[0022] FIG. 10 is a mass spectrometer trace from gasification of grass clippings as performed in Example 5.

[0023] FIG. 11 is a schematic of a solar process for producing hydrogen. In this process, biomass pyrolysis occurs concurrently with carbothermic reduction of metal oxide particles in a solar thermal reactor. Hydrogen is obtained from the gaseous products of the reactor and from reaction of the reduced metal oxide with steam.

[0024] FIG. 12 is a schematic of a process for producing methane in which hydrogen produced via the process of FIG. 11 is fed into a coal hydrogenator.

[0025] FIG. 13 is a mass spectrometer trace for TGA Fe3O4 reduction.

[0026] FIG. 14 is a mass spectrometer trace for TGA steam oxidation of FeO.

DETAILED DESCRIPTION OF THE INVENTION

[0027] In the processes of the invention, a solid or liquid biomass feed is pyrolyzed or gasified in a solar thermal reactor system at elevated temperatures. In different embodiments of the pyrolyzation processes of the invention, no significant source of oxygen or water is supplied during the process. An oxidizing agent is conventionally present in gasification processes. In the gasification processes of the invention, water (generally in the form of steam) is supplied and contacted with the biomass particles.

[0028] In an embodiment, the biomass feed is in the form of solid particles. The biomass feed particles or droplets are entrained in a gas as they move through the reactor. In an embodiment, metal oxide particles are fed into the reactor concurrently with biomass particles. In another embodiment particles of a fossil fuel such as coal are fed into the reactor concurrently with biomass particles. In an embodiment, no additional catalyst is added to the biomass feed.

[0029] The necessary endothermic heat of reaction and sensible heat is supplied by a solar-thermal energy system. The biomass particles or droplets may be directly heated by solar radiation, in which case the reactor is configured to transmit solar radiation to the particles. In another embodiment, the biomass particles or droplets are indirectly heated. As used herein, "indirect" heating means that the heating is by radiation from a heated wall that is itself heated indirectly or directly by solar radiation.

[0030] In an embodiment, the pyrolysis and gasification processes of the invention produce hydrogen and carbon monoxide (synthesis gas or syngas). Other products such as carbon dioxide, carbon, methane and higher molecular weight hydrocarbons may also be produced in the process. In different embodiments, the conversion of the non-ash components of the biomass is greater 30%, greater than or equal to 40%, greater than 50%, greater than or equal to 60%, greater than or equal to 70%, greater than or equal to 75% greater than 80%, greater than 90% or greater than 95%. This extent of conversion may be achieved in a single pass. In different embodiments, the conversion of carbon to carbon monoxide is greater than 30%, greater than 40%, greater than 50%, greater than 60%, greater than 70%, greater than 80%, greater than 90% or greater than 95%. In different embodiments, the molar ratio of carbon dioxide to carbon monoxide is less than 25% or less than 10%. In different embodiments, the molar ratio of hydrogen (H2) to carbon monoxide is 1:1, greater than 1:1 and less than 2:1; less than 2:1; greater than 2:1 and less than 3:1; or greater than 3:1. The ratio of hydrogen to carbon monoxide may be adjusted by adjusting the amount of water added to the feed.

[0031] The products of the biomass pyrolyzation or gasification process can be combined in a Fischer-Tropsch reactor to produce liquid hydrocarbon products, or can be reacted further with water in a Water-Gas Shift reaction to maximize hydrogen yield. Such a process makes use of renewable, biologically derived feedstocks and is, in a worst case, carbon and greenhouse gas neutral.

[0032] As stated above, the invention provides a chemical process in which carbon containing biomass feedstocks (for example, but not limited to, cellulose, hemi-cellulose, lignin, xylose, other plant sugars, algae, agricultural, industrial, brewery, or forestry residues) are either pyrolized or combined with water at high temperature (>950[deg.] C.). In different embodiments, the biomass feedstock may be a tall prairie grass, such as switchgrass and/or miscanthus, algae, pressed algal residue from a biodiesal processing facility, spent grain from a brewery, wood chips, or sawdust. In an embodiment, feedstocks for use with the invention do not include mixtures of coal and biomass. In another embodiment particles of a fossil fuel such as coal are fed into the reactor concurrently with biomass particles. In one aspect of the invention, the biomass feedstock is selected to have an ash content less than about 15%, less than about 10% or less than about 5%.

[0033] In different embodiments, the maximum particle size of the biomass feedstock is less than 10 mm, less than 5 mm, less than 1 mm, less than 500 microns, less than 200 microns, less than 100 microns, less than 50 microns, or less than 20 microns. In an embodiment, the minimum "average" size of the biomass feedstock is 10 microns, as identified by the volume average equivalent spherical particle diameter or as the volume average of the longest particle dimension (if the particles are long and flat, like blades of grass). There may be smaller particles in the system (e.g. submicron), but on a mass basis these particles will be a very small fraction (in an embodiment <5 vol %) of the total.

[0034] The reactor product composition can be thermodynamically and kinetically controlled by reactor temperature, pressure, residence time, water concentration, feedstock concentration, and inert gas concentration, in addition to reactor design, solar energy concentration, and other factors not mentioned here. In different embodiments, the temperature in the hot zone of the reactor is between 750[deg.] C. and 1500[deg.] C., between 950[deg.] C. and 1400[deg.] C., or between 1100[deg.] C. and 1350[deg.] C., where the temperature is the average temperature of the particles in the reaction hot zone. The necessary energy to attain such temperatures and achieve the reaction is, in all cases, derived from a system which converts solar radiation into thermal energy ("solar-thermal").

[0035] In an embodiment, the reactor operates at atmospheric pressure. In another embodiment, the reactor can be run at pressures above atmospheric pressure, but this will drive the thermodynamics toward the liquid products and the reactants. In this embodiment, the compressors can be removed from the downstream side of the reactor and replaced with water pumps.

[0036] During the biomass gasification processes of the invention, the water concentration provides at least a one to one molar ratio of steam to biomass feed. In an embodiment, the water concentration may be increased slightly to compensate for a relatively high carbon to oxygen atomic ratio in the feedstock.

[0037] In an embodiment, the invention provides a method for at least partially converting biomass particles to hydrogen and carbon monoxide, the method comprising the steps of:

[0038] a) providing a solar-thermal reactor comprising an outer protection shell and an inner reaction shell having an inlet and an outlet, the outer protection shell being at least partially transparent or having an opening to the atmosphere for transmission of solar energy,

[0039] b) flowing a gas stream comprising entrained biomass particles from the inlet to the outlet of the reaction shell; and

[0040] c) heating the biomass particles in the reactor at least in part with a source of concentrated sunlight through solar thermal heating to a temperature at which the biomass particles react to form products comprising hydrogen and carbon monoxide.

[0041] The invention also provides methods for at least partially converting the biomass particles to other products in addition to hydrogen and carbon monoxide. These other products include, but are not limited to, carbon and carbon dioxide. In an embodiment, the biomass particles are at least partially converted to carbon, hydrogen, carbon monoxide, and carbon dioxide. In another embodiment, the biomass particles are at least partially converted to hydrogen, carbon monoxide, and carbon dioxide. In other embodiment the reaction products can include higher molecular weight hydrocarbons (e.g. CH4, C2H6, C2H4, C2H2, C3s, C4s, etc), or hydrocarbons with oxygen bearing functional groups (e.g. alcohols, aldehydes).

[0042] FIG. 1 is a schematic top view of a horizontal cross-section of a solar reactor having an outer "protection shell" and a nonporous inner "reaction" shell. The solar reactor shown in FIG. 1 is operated generally as follows. Concentrated solar-thermal radiation (91) passes through an opening in the outer "protection" shell (7) and directly heats the inner "reaction" shell (3). In FIG. 1, the outer shell (7) is shown as having an opening (8) to the atmosphere, but in an alternative embodiment the outer shell contains a window which transmits solar radiation. In an embodiment, the inner surface of the outer shell may reflect solar radiation (in particular radiation in the visible range) and infrared radiation. In another embodiment, the inner surface is capable of absorbing and re-emitting radiation. The entrainment gas and the feedstock flow through the bore of the reaction shell.

[0043] In an embodiment, the inner "reaction" shell is at least partially transparent to solar radiation, in which case the biomass particles are directly heated by the solar-thermal radiation. In an embodiment, the inner shell is at least partially transparent to solar radiation in the wavelength range 200 nm to 20 microns. When heated, the biomass particles undergo the desired reaction(s).

[0044] In another embodiment, the inner "reaction" shell is nonporous and does not transmit solar radiation. In an embodiment, the inner shell does not transmit solar radiation in the wavelength range 200 nm to 20 microns. In this case, the nonporous reaction shell is directly heated to temperatures above the reaction temperature and re-radiates from its inner wall to heat the biomass particles and entraining gas stream flowing through it. The biomass particles are thus indirectly heated. When heated, the biomass particles undergo the desired reaction(s).

[0045] The reactor may also have a plurality of non-concentric reaction shells substantially enclosed by the outer shell, as illustrated in FIGS. 2a and 2b. FIGS. 2a and 2b are also schematic top views of horizontal cross-sections of the reactor. FIG. 2a illustrates a configuration in which the inner tubes (3) are arranged along an arc within the outer tube (7). FIG. 2b illustrates an embodiment in which the inner tubes (3) are arranged in a staggered configuration within the outer tube (7). The tube arrangement is not limited to these two spatial configurations, as explained in more detail below. The specific arrangement can be selected to maximize efficiency. In one embodiment, the tubes are arranged in a staggered pattern. In another embodiment, the centers of the tubes are aligned along a semicircle. In an embodiment, the number of inner reaction shells is from 3 to 10.

[0046] A non-oxidizing and non-dissociating "purge" gas may be flowed in a second plenum substantially located between the outer shell and the inner shells to protect the inner shells from oxidation, depending on the material(s) of the inner shells. In this case, the protection shell does not have an opening to the atmosphere. The purge gas may be argon, helium, neon, nitrogen, or any other chemically inert gas.

[0047] In another embodiment, the reaction shell is at least partially porous, to allow a "fluid wall" to be formed at the inner surface of the reaction shell. A "fluid wall" gas is flowed radically inward into the reaction shell through the porous section of the shell, thus providing a blanket of gas. The "fluid wall" can prevent deposition of particles on the inside wall and protect the inside wall from the reaction products. As used herein, a "porous" shell region permits gas flow through the walls of the region while a "nonporous" shell region does not. In one embodiment, a gas stream of "fluid-wall" gas flows in the annular region between the outer "protection" shell and the inner "reaction" shell. The "fluid-wall" gas enters the plenum between the inner and outer shell through an inlet and exits the plenum through an outlet. The porous section of the inner shell forms one outlet of the plenum. An additional outlet for the plenum may be used, so long as sufficient gas flow is provided through the porous section of the inner shell.

[0048] In another embodiment, an additional nonporous inner shell which substantially encloses the porous reaction shell can be provided. The "fluid wall" gas is supplied to the porous section of the reaction shell by flowing it through the annular space between the two inner shells; this annular space forms a plenum. The "fluid-wall" gas enters the plenum through an inlet and exits the plenum through an outlet. One outlet of the first plenum is the porous section of the inner shell. As used herein, "substantially encloses" means that one shell is enclosed by another for most of the length of the shell. The ends of a shell that is substantially enclosed by another may extend past the ends of the other shell (e.g. the ends of the first inner shell may extend past the ends of the second inner shell and/or the outer shell). In an embodiment, the solar thermal reactor is a solar-thermal fluid-wall reactor as described in United States Patent Application Publication US 2003/0182861 to Weimer et al., which is hereby incorporated by reference to the extent not inconsistent with the disclosure herein. United States Patent Application Publication 20030208959 and U.S. Pat. No. 6,872,378 to Weimer et al. are also hereby incorporated by reference.

[0049] A reactor having two concentric inner shells (a first innermost "reaction" shell and a second inner "heating shell") is operated generally as follows. Concentrated solar-thermal radiation passes through the outer "protection" shell and directly heats the second inner "heating" shell. The nonporous heating shell re-radiates from its inner wall and heats the first inner "reaction" shell. Hence, the inner "reaction" shell is heated indirectly by concentrated sunlight from the surrounding "heating" shell. The inner "reaction" shell re-radiates from the inner wall and heats the biomass particles and gas stream flowing through it.

[0050] In another embodiment, the invention provides a method for reduction of metal oxide particles comprising the steps of:

a) providing a solar-thermal reactor comprising an outer protection shell and an inner reaction shell having an inlet and an outlet, the outer protection shell being either at least partially transparent or having an opening to the atmosphere for transmission of solar energy;
b) flowing a gas stream comprising entrained biomass and metal oxide particles from the inlet to the outlet of the reaction shell, wherein the biomass and gas stream do not comprise substantial amounts of water;
c) heating the biomass and metal oxide particles in the reactor at least in part with a source of concentrated sunlight through solar thermal heating to a temperature at which the biomass particles paralyze to form reaction products comprising hydrogen, carbon, and carbon monoxide and the metal oxide particles react with at least one of the biomass paralysis reaction products to form a reduced metal oxide product which is a metal, a metal oxide of a lower valence state, or a combination thereof.

[0054] In an embodiment, of the metal oxide reduction process, concentrated solar-thermal radiation passes through the outer "protection" shell and directly heats the inner "reaction" shell. The inner "reaction" shell conducts heat and re-radiates from the inner wall and heats the biomass and metal oxide particles and gas stream flowing through it. Other reactor designs described elsewhere in this application can also be used. When heated, the biomass particles undergo a paralysis reaction. Products of the paralysis reaction include hydrogen, carbon monoxide, carbon dioxide, and carbon. At elevated temperatures, metal oxide particles can react with hydrogen, carbon monoxide or carbon to form a reduced metal oxide product. Depending on the reactor temperature, the metal oxide particles may react with more than one of the biomass paralysis reaction products. For example, at temperatures above about 1475 K, both C and CO are expected to reduce Zone. The primary products exiting the solar thermal reactor are the reduced metal oxide product, H2, CO and CO2. Depending on the temperature distribution within the reactor, the reduced metal oxide product may be present in the reactor in gaseous, liquid, or solid forms, or in combinations thereof. If the reduced metal oxide product is present in gaseous form, a cooling device may be connected to the outlet of the reactor to nucleate reduced metal oxide particles (the reduced metal oxide particles can be metal particles) of the desired size. Cooling devices compatible with solar thermal reactors as described in United States Patent Application No. US 2006-0188433 to Weimer et al., hereby incorporated by reference to the extent not inconsistent with the disclosure herein.

[0055] Metal oxides suitable for use with the invention are compounds consisting essentially of one or more metals and oxygen, the compounds being solid at room temperature. In an embodiment, the impurity level is less than or equal to 1%. In an embodiment, the metal oxide is ZnO. In another embodiment, the metal oxide is SnO2. Metal oxides suitable for use with the invention include mixed metal oxides which include more than one metal, such as mixed metal ferrites. As used herein, mixed metal ferrites are compounds of iron oxide with oxides of other transition metals. For example, included would be iron oxides with Ni (II), Co (II), or Man (II) inclusions, such as MnFexO4, NiFexO4, Ni0.5Mn0.5Fe2O4 and Co0.5Mn0.5Fe2O4. High temperature dissociation of such oxides can produce an activated, oxygen deficient form, such as Ni0.5Mn0.5Fe2O(4-delta). This activated form could be combined with water at relatively low temperatures to yield hydrogen and the original mixed metal oxide. Ferrites useful in the present invention have decomposition temperatures substantially below that of iron oxide. In different embodiments, the particle size of the metal oxide is below 150 microns, or below 100 microns;

[0056] The reduced metal oxide product is selected from the group consisting of a metal, a metal oxide and combinations thereof. These combinations can include combinations of metal oxides. For example, Fe2O3 may reduce partially to Fe3O4, partially to FeO, and partially to Fe.

[0057] In different embodiments, the conversion of the metal oxide to a reduced metal or to a lower oxidation state metal oxide is at least 50%, at least 75%, or at least 90%.

[0058] The present invention also provides processes for the production of hydrogen from the reaction of reduced metal oxide products with water. One step in the processes is the reduction of metal oxide particles with biomass pyrolysis products in a high temperature solar thermal reactor as described above. The products of the metal oxide reduction reaction can then be used to react with water in a succeeding step, generating hydrogen and the original metal oxide. Reaction and separation steps following the metal oxide reduction step may be performed "off-sun", allowing continuous production of hydrogen from stored reduced metal oxide product. The "off-sun" step is typically exothermic and can be driven by energy generated by the reaction itself, allowing the entire process to be run on only solar energy.

[0059] As used herein, "shells" encompass tubes, pipes or chambers which are elongated along a longitudinal axis. The shells may be circular in cross-section (i.e. the shells are cylindrical tubes) or may have other shapes in cross-section, including, but not limited to ellipses, rectangles or squares. As shown in FIG. 1, the outer shell of the reactor may essentially form a cavity which is largely non-transparent to solar radiation but contains an opening or transparent window to admit solar radiation into the interior. In an embodiment, reflection or absorption and re-radiation occurs at the inner surface of the outer shell. In an embodiment, the inner surface of the outer shell may reflect solar and/or infrared radiation. In an embodiment, the inner surface of the outer shell reflects both solar and infrared radiation. In an embodiment, the inner wall of the outer protection shell is reflective or absorbing or re-emitting with respect to radiation in the wavelength range 200 nm to 20 micrometers. General designs for these types of cavities are known to those skilled in the art. In an embodiment, the inner wall of the outer protection shell comprises a reflective coating such as a gold, silver, or aluminum coating. The reflective coating can reflect incident solar energy and infrared (IR) radiation emitted from the inner shells. The reflective coating may be protected from oxidation by coating it with a thin layer of silica.

[0060] In an embodiment, the outer shell may be made of a plurality of layers in close proximity to one another. For example, the outer shell may have three layers. A three-layer outer shell may have an outer layer made of a metal (e.g. steel or an aluminum alloy), a middle layer made of a thermally insulating material (e.g. a refractory material such as alumina), and an inner layer which may be either absorbing or reflective. An absorbing inner layer may be made of a material having relatively low thermal conductivity and capable of withstanding high temperatures (e.g. zirconia, hafnia, alumina). In an embodiment, the absorbing inner layer is constructed of ytrria-stabilized zirconia (YSZ) which heats upon contact with solar energy and re-radiates to the reactor tubes. A reflecting inner layer may be made of a metal such as steel and coated with a gold or silver film; in such case a cooling mechanism may be provided in the middle layer to prevent melting of the reflective material. A reflecting inner layer may also be made of polished aluminum. In an embodiment, the outer shell contains a transparent window. Such a window may be a rectangular vertical quartz window (with the long axis of the rectangle aligned perpendicular to the longitudinal axis of the reactor).

[0061] In an embodiment, the outer shell effectively comprises two layers, an outer layer and an inner reflecting or absorbing layer. In an embodiment, the outer layer is made of quartz and the inner layer is a coating of a reflective material such as silver or gold. The coating is applied to the sections of the internal wall of the shell where sunlight is not being concentrated and entering the vessel in order to keep the concentrated sunlight inside the reactor. If such a reflective coating is used, there must be an uncoated transparent section, window or opening to allow the concentrated sunlight into the vessel. The shell wall transparent area, allowing for concentrated sunlight entry and subsequent solar thermal heating, should be selected to provide heating during the desired reaction residence time requirements for the process. If the temperatures at the outer shell wall exceed the melting temperature of the reflective coating, cooling is provided to prevent melting of the reflective coating.

[0062] In another embodiment, the outer shell may be formed of a single layer of material. In this embodiment, the shell is of a material which is either transparent or contains a hole or window which admits solar radiation to the interior.

[0063] Suitable transparent materials for the outer shell include oxidation resistant materials such as quartz. The "protection" shell may also be made of a metal with a sufficiently high melting point, such as stainless steel. The metal "protection shell" may have a transparent window which allows concentrated sunlight to directly heat the "heating" shell. At least part of the non-transparent part of the "protection" shell can be surrounded by heat transfer fluid contained by a jacket to provide cooling of the outer metal refractory "protection" shell, particularly in the region immediately surrounding the window. The heat transfer fluid can be water or a molten salt such as a mixture of sodium and potassium nitrates. Molten salts are capable of operating at temperatures up to about 500[deg.] C. Use of such a cooling jacket can allow for significantly improved efficiency.

[0064] In an embodiment, the "reaction" or "heating" shell may be surrounded by refractory insulation in the region where it is not directly exposed to concentrated sunlight via the transparent section. The insulation may be concentrically placed and extends substantially from the "reaction" or "heating" shell to the concentric "protection" shell, although it may not completely fill the space between the heating shell and the protection shell. The refractory insulation can be a combination of graphite insulation near the "heating" shell and an alumina type refractory insulation near the "protection" shell. This design arrangement allows concentrated sunlight to enter through a transparent section and heat the "reaction" or "heating" shell while the surrounding insulation reduces conductive and convective losses of energy from the "reaction" or "heating" shell, thereby increasing the efficiency of the process.

[0065] The innermost reaction shell has an inlet and an outlet for the entraining gas stream. The inlet end of the inner shell is the upstream end of the shell, while the outlet end is the downstream end. The interior of the innermost shell defines a reaction chamber within which the high temperature reaction takes place. The innermost shell is capable of emitting sufficient radiant energy to raise the temperature of the reactants within the reaction chamber to a level required to initiate and sustain the desired chemical reaction. The innermost shell is made of a high temperature refractory material. When the particles are indirectly heated, the refractory material subsequently heats flowing biomass particles flowing through the first inner shell.

[0066] In an embodiment, the refractory material is substantially chemically unreactive with the particles or the reactant or product gases. In an embodiment, the innermost shell is graphite. In other embodiments, the innermost shell is silicon carbide or a refractory metal or alloy capable of withstanding the temperature required for a given decomposition reaction. Other suitable high temperature ceramics include ytrria-stabilized zirconia (YSZ), silicon nitride, hafnium boride, hafnium carbide, silicon carbide-silicon carbide composites, boron nitride or alumina (aluminum oxide). Refractory metal alloys suitable for temperatures below about 1200[deg.] C. include, but are not limited to, high temperature superalloys, including nickel-based superalloys such as Inconel(R) or Haynes(R) 214. In another embodiment, the innermost shell may be made of quartz. In an embodiment, the reaction shell is made of silicon carbide, Inconel, quartz, silicon nitride, or alumina.

[0067] The inner reaction shell may be made of a nonporous material. In another embodiment, the innermost shell is at least partially porous. The innermost shell may be wholly of porous material or may comprise one or more regions of porous material. The porous region(s) of the innermost shell are selected so that sufficient uniform flow of gas occurs radially inward through the pores to provide a fluid-wall protective blanket for the radially inward surface of the innermost shell. The porosity of the porous region(s) can be varied and is selected on the basis of the required gas flow and allowable pressure drop to provide for a fluid-wall of gas. The length of the porous section(s) of the "reaction" shell can be varied and is determined by the zone where oxidation of the "reaction" shell or particle deposition is most likely to occur. The placement of the porous section along the length of the "reaction" shell is determined by the same considerations. In an embodiment, the length of the porous section of the "reaction" shell is limited to where it is needed. The entry of fluid-wall gas into the "reaction" shell increases the overall volumetric flow rate of gases through the "reaction" shell, thus reducing residence time and limiting the production throughput of the reactor. In an embodiment, the porosity in a given porous region is substantially uniform. A partially porous reaction tube may be made by joining together a porous tube and a solid tube. Graphite tubes may be joined by high temperature sintering using a carbon-containing paste. Silicon carbide tubes may also be joined by sintering with the appropriate sintering aid. Metal or alloy tubes may be welded or brazed, including porous metal or alloy sections. In different embodiments, the ratio of the length of the reaction shell to the inner diameter of the reaction shell is from 2 to 12, from 2 to 4, from 4 to 6, from 6 to 12, between 5 and 30, between 5 and 10, and between 20 and 25.

[0068] When a plurality of reaction shells are present in the reactor, the reaction shells may have the same inner diameter or may have different inner diameters. In an embodiment, the inner shells have different inner diameters and smallest inner shell has an inner diameter one third the inner diameter of the largest inner shell. In this embodiment, the larger inner shells may be located closer to the center of the outer shell then the smaller inner shells.

[0069] If used, the second inner shell is typically composed of nonporous high temperature refractory material. In an embodiment, the second inner shell is made of solid graphite. As previously discussed, the second inner shell can function as a "heating" shell, since it radiates heat to the innermost shell. In addition, the combination of the first and the second inner shell can at least partially define a plenum or volume for the fluid-wall gas. Depending on the material of the second inner shell, a non-oxidizing and non-dissociating "purge" gas may be flowed in a second plenum substantially located between the outer shell and the second inner shell to protect the second inner "heating" shell from oxidation. The purge gas may be argon, helium, neon, nitrogen, or any other chemically inert gas.

[0070] In general, the shells comprising the reactors of the invention may be positioned vertically or horizontally, or in any other spatial orientation. For the case of a vertical reaction shell process, the apparatus may be arranged to provide upward or downward flow of the gas stream and the cloud of particles. Upward flow guarantees that aggregated particles will not be carried through the reaction shell. Downward flow reduces the potential for plugging in the solids feed line. Preferably, the reactor shell is positioned vertically and flow is downward.

[0071] Each of the shells is characterized by a longitudinal axis (vertical centerline). In the plane created by cross-sectioning the reactor transverse to the longitudinal axis of the outer shell so that the plane passes through the outer shell window or aperture, a first horizontal dividing line (this line can also be termed the horizontal centerline) can be defined which passes through the center of the outer shell and the window or aperture, dividing the outer shell and the window or aperture into two equal or nearly equal halves. This horizontal centerline can be said to establish right and left portions inside the outer shell. A second horizontal dividing line can be established in the same plane which passes through the center of the outer shell, is orthogonal to the horizontal centerline, and establishes front and back portions inside the outer shell, with the front portion being the portion nearest the aperture or window.

[0072] To describe positions of the inner shells within the outer shell in a horizontal cross-section of the outer shell, an x,y coordinate system can be defined whose origin is at the center of the outer shell and in which the y axis of the coordinate system is aligned with the horizontal centerline as defined above and the x axis of the coordinate system is aligned with the second horizontal dividing line as defined above.

[0073] Locations of the inner shells can also be specified by their distance from particular locations with respect to the outer shell. For example, the location of the center of an inner shell can be specified by its distance from the intersection of the horizontal centerline with the inner surface of the outer shell at the "back" portion of this inner surface, opposite the aperture or window. Locations may also be determined with respect to the center of the outer shell.

[0074] Locations of the inner shell can also be specified by their orientation with respect to the average direction of the solar radiation entering the solar reactor. In an embodiment, the average direction of the solar radiation is generally aligned with the horizontal centerline.

[0075] If the center of a first inner shell is "farther back" in the outer shell than the center of a second inner shell, the y component of the distance between the center of the first inner shell and the intersection of the horizontal centerline with the "back portion" of inner surface of the outer shell is smaller than the y component of the distance between the center of the second inner shell and the intersection of the horizontal center line with this back portion of the inner surface of the outer shell.

[0076] In an embodiment, at least three inner shells are located within the outer shell. In another embodiment, the number of inner shells is from 3 to 10. In other embodiments, the number of inner shells is 3 or 5.

[0077] In an embodiment, the outer walls of the inner shells are not in contact with one another. In an embodiment, the spacing between the outer walls of the inner shells is a multiple of the diameter of an inner shell. In different embodiments, this multiple is 0.05 to 1.0, 0.05 to 0.1, 0.1 to 0.2, 0.2 to 0.5 and 0.5 to 1.0.

[0078] The inner shells may be arranged in a variety of configurations. For convenience, the configurations may be described by the relative positions of the centers of the inner shells in a planar cross-section transverse to the longitudinal axis of the outer shell. In an embodiment, the centers of the inner shells do not lie along a single straight line.

[0079] In an embodiment, the centers of the inner shells lie along a circular arc, with the ends of the arc being established (anchored) by the positions of the center of the inner shells closest to the outer shell. The arc is bisected by the horizontal centerline. In an embodiment, the circular arc is a semicircle. In an embodiment the center of the arc is farther back in the shell than the ends of the arc (the arc bows towards the aperture).

[0080] In another embodiment, the inner shells are arranged in a staggered pattern. In an embodiment, the inner shells can be grouped into a plurality of rows, each row being generally perpendicular to the horizontal centerline but having a different depth within the outer shell (different y coordinate). The rows may form a straight line or they may be somewhat curved. In an embodiment, the rows form a straight line parallel to the x axis. The centers of the shells in each row are positioned so that they do not "line up" with (do not have the same x coordinate as) shells in adjacent rows. Each row has at least one shell, and may have a plurality of shells. In an embodiment, the pattern is generally symmetric about the horizontal centerline. The pattern can also be viewed in terms of the geometric properties of lines drawn between the centers of neighboring inner tubes. For example, the angle made between a line drawn between the center point of a first inner tube in a "front" row and the center point of a second neighboring tube in the row behind the "front" row and the line drawn between the center point of the second tube and the center point of a third inner tube located in the "front" row (which is a neighbor to both the first and second tube) can be from 40 degrees to 140 degrees or from 60 degrees to 130 degrees. The specific arrangement is chosen so as to maximize interception of incident radiation.

[0081] In an embodiment, three inner shells are arranged in a triangular configuration, so that the line between the centers of the shells forms a triangle in a horizontal cross-section. One of the shells is located farther back in interior of the outer shell than the other two. This can be viewed as a first row of two shells and a second row of one shell, with the second row being farther back than the first row. In an embodiment, the center of inner shell in the second is located along the horizontal centerline.

[0082] In another embodiment, five inner shells are arranged in a staggered pattern. The five inner shells can be separated into a first group of three inner shells and a second group of two inner shells, the two inner shells in the second group being located farther back in the tube than the three inner shells in the first group. In an embodiment, the width (x component of the distance) spanned by the first group of shells is greater than the width spanned by the second group. If lines are drawn between the center points of neighboring inner tubes, a pattern of triangles may be formed.

[0083] In an embodiment, the invention provides a solar thermal reactor system for heating particles entrained within a gas, the reactor comprising:

[0084] a) an outer shell, the side wall of the outer shell not permitting transmission of solar radiation except at a window or aperture in the side wall, at least a portion of the side wall interior away from the window or aperture comprising a material reflective to solar radiation wherein in a cross-section of the reactor made through the outer shell window or aperture and perpendicular to the longitudinal axis of the outer shell, the outer shell is characterized by a horizontal centerline which extends through the window or aperture;

[0085] b) at least three inner shells at least partially located within the outer shell, each inner shell having a longitudinal axis parallel to the longitudinal axis of the outer shell, wherein the inner shells are not concentric and are arranged so that the outer side walls of the inner shells are not in contact with each other and so that in the reactor cross-section, the centers of the inner shells are not aligned along a single straight line; c) a particle entrainment feeding system in fluid communication with the inner shells; and d) a source of concentrated solar radiation disposed so that the window or aperture of the outer shell is exposed to solar radiation

[0086] In the entrained flow reactors used in the practice of the invention, the biomass particles or droplets are entrained in the carrier gas and are generally transported along the longitudinal axis of the reaction tube (or tubes). The biomass particles or droplets are dispersed in the reactor apparatus, and the form of dispersion is important. Preferably, the particles or droplets flow as a dust or particle cloud through the apparatus, dispersed in a dispersing process gas. Preferably, the particles are non-agglomerated. In an embodiment, the biomass is in the form of solid particles. In an embodiment, the solid biomass particles are not enclosed in water droplets. Several different methods can be used to disperse solid particles. In an embodiment, the particles are entrained by a fluidized bed feeder. The particles can also be dispersed mechanically, such as by shearing on the surface of a rotating drum or brush. Alternatively, the particles can be dispersed using the shear provided by high velocity gas exiting with the particles from a feed injection tube. Experience has shown that the exiting "tip speed" from the injection tube should be at least 10 m/s to provide the shear necessary for complete dispersion of fine powders. In other embodiments, the biomass feedstock may also be a liquid and atomized into the aerosol stream or a solid mixed with liquid to create a slurry which is then introduced into the reactor.

[0087] The initial composition of the gas used to entrain the biomass particles or droplets may be an inert gas, steam, a recycled or compatible reaction product gas such as hydrogen, carbon monoxide, carbon dioxide, or a mixture thereof. In an embodiment, the entraining gas is a mixture of inert gas and steam. Suitable inert gases include, but are not limited to nitrogen, argon, helium, or neon. In an embodiment, the initial composition of the entraining gas does not contain substantial amounts of molecular oxygen or air. The composition of the entraining gas may also vary along the reactor. For example, the entraining gas may be provided as an inert gas at the reactor inlet and become a mixture of inert gas and gaseous reaction products downstream of the reactor inlet. Steam can be introduced after the particles are entrained in a gas mixture, but prior to introduction of the entrained particles into the reactor. Steam can also be fed through a steam micronizer as jets of steam, located at the feed inlet of the reactor. In this case, jets of steam impinge on biomass being fed and provide a means to reduce the particle size of the biomass feed in-situ at the entrance of the reactor. The entraining gas stream is selected so that it is compatible with the biomass particle pyrolysis or gasification process and the "reaction" wall of the solar-thermal fluid-wall reactor. The gas stream can be preheated to reduce the requirements of the solar thermal field and increase efficiency by passing it through a heat exchanger, removing heat from the products of the solar thermal reactor. Additionally, heat could be removed from an exothermic downstream fuel processing unit (Fischer-Tropsch reactor, water gas shift reactor, or combustion turbine).

[0088] In the methods of the invention, biomass particles are heated at least in part with a source of concentrated sunlight. The source of concentrated sunlight may be a solar concentrator. Preferably, the solar concentrator of the apparatus is designed to optimize the amount of solar thermal heating for the process. Solar fluxes between about 1000 and about 3000 kW/m<2 > have been shown to be sufficient to heat solar thermal reactors to temperatures between 1000 and 2500 K. In different embodiments, the solar flux is from 500 to 1500 kW/m<2> , from 1500 to 3500 kW/m<2> , from 3000 to 5000 kW/m<2> , or from 3500 to 7000 kW/m<2> . Fluxes above 3000 kW/m<2 > may be used achieve even higher temperatures, receiver efficiencies, and reactor throughputs, although the cost of using fluxes in this range is expected to be higher. Since the solar radiation is generally focused to approximately match the aperture/window size, the size of the aperture and the flux are correlated.

[0089] The temperature inside the innermost shell of the reactor can be measured with a thermocouple. Alternatively, temperatures inside the reactor can be measured with an optical pyrometer. For a three-shell reactor, the hot zone temperature measured with an optical pyrometer is typically the temperature of the nonporous "heating" shell, since the "heating" shell encloses the "reaction" shell in the hot zone. The temperature inside the inner "reaction" shell may be less than that of the "heating" shell due to thermal losses due to heating the porous shell and the gases in the first plenum and the reaction shell.

[0090] The sunlight can be provided in the form of a collimated beam (spot) source, a concentric annular source distributed circumferentially around the reactor, or in the form of a linearized slot source providing heating axially along the length of reactor. The light can be redirected and focused or defocused with various optical components to provide the concentration on or in the reactor as required. In an embodiment, the concentrated solar radiation is further concentrated by a secondary concentrating reflector before entering the reactor. An example of a suitable solar concentrator for use in the present invention is the High-Flux Solar Furnace (HFSF) at the National Renewable Energy Laboratory (NREL) in Golden, Colo. The HFSF uses a series of mirrors that concentrate sunlight to an intensified focused beam at power levels of 10 kW into an approximate diameter of 10 cm. The HFSF is described in Lewandowski, Bingham, O'Gallagher, Winston and Sagie, "Performance characterization of the SERI Hi-Flux Solar Furnace," Solar Energy Materials 24 (1991), 550-563. The furnace design is described starting at page 551, wherein it is stated,

The performance objectives set for the HFSF resulted in a unique design. To enable support of varied research objectives, designers made the HFSF capable of achieving extremely high flux concentrations in a two-stage configuration and of generating a wide range of flux concentrations. A stationary focal point was mandatory because of the nature of many anticipated experiments. It was also desirable to move the focal point off axis. An off-axis system would allow for considerable flexibility in size and bulk of experiments and would eliminate blockage and consequent reduction in power.
In particular, achieving high flux concentration in a two-stage configuration (an imaging primary in conjunction with a nonimaging secondary concentrator) dictates a longer f/D [ratio of focal length to diameter] for the primary [concentrator] than for typical single-stage furnaces. Typical dish concentrators used in almost all existing solar furnaces are about f/D=0.6. To effectively achieve high flux concentration, a two-stage system must have an f/D=2. Values higher than this will not achieve significantly higher concentration due to increased losses in the secondary concentrator. Values lower than this will result in a reduction of maximum achievable two-stage flux. At low values of f/D, the single stage peak flux can be quite high, but the flux profiles are also very peaked and the average flux is relatively low. With a longer f/D, two-stage system, the average flux can be considerably higher than in any single-stage system. The final design of the HFSF has an effective f/D of 1.85. At this f/D, it was also possible to move the focal point considerably off axis (30[deg.]) with very little degradation in system performance. This was because of the longer f/D and partly because of the multi-faceted design of the primary concentrator. This off-axis angle allows the focal point and a large area around it to be completely removed from the beam between the heliostat and the primary concentrator.

[0093] When the outer shell is wholly transparent or has a window which extends completely around the shell, the concentrated sunlight is preferably distributed circumferentially around the reactor using at least one secondary concentrator. Depending upon the length of the reaction shell, multiple secondary concentrators may be stacked along the entire length of the reaction shell. For the HFSF described above, a secondary concentrator that is capable of delivering 7.4 kW of the 10 kW available (74% efficiency) circumferentially around a 2.54 cm diameter*9.4 cm long reaction tube has been designed, constructed, and interfaced to the reactor.

[0094] The invention also provides reactor systems which combine the reactor of the invention with one or more other system elements. Typically, the outlet of the reactor will be coupled to a device for collecting any solids exiting the reactor. These solids may be unreacted or partially reacted biomass particles, ash, or reaction products. Any suitable solids collection device known to the art may be used, including, but not limited to gravity collection vessels and filters.

[0095] As used herein, the "residence time" is the time that the biomass particles spend in the hot zone of the innermost "reaction" shell. The hot zone length may be estimated as the length of the reactor directly irradiated by the source of concentrated sunlight. The residence time depends on the reactor dimensions, such as the hot zone length and the inner diameter of the "reaction" shell. The residence time also depends on the flow rate of the entraining gas stream containing the biomass particles and the flow rate of any fluid-wall gas through the pores of the inner shell. In addition, the residence time may vary across the diameter of the reaction shell, in which case a mean residence time may be calculated. The residence time may be calculated through modeling or estimated from ideal gas considerations. In different embodiments, the residence time is less than or equal to 10 seconds, less than or equal to 5 seconds, or less than or equal to 3 seconds. The biomass may or may not be completely reacted before it leaves the hot zone.

[0096] If used, the fluid-wall gas is selected to be compatible with the reactants and the products. The fluid-wall gas is compatible if it allows the desired reaction to take place and/or it is inert to the reactants, products, and materials of construction for the reaction and protection shells and/or is not difficult to separate from the gas stream exiting the "reaction" shell and/or the cooling device. The fluid-wall gas used in the solar-thermal reactor is also selected so that it is compatible with the "reaction" shell. The gas stream used to provide the "fluid-wall" blanket gas flowing inward from the porous "reaction" shell wall is also preferably not a dissociating gas whose dissociation products would plug the pores of the porous wall. Inert gases, such as helium, N2 or argon are suitable for use as the fluid-wall gas

[0097] Downstream separation units are used to remove entrainment gas from the reaction products and separate the reaction products based on the end application. Possible separation units include pressure swing adsorbers, vacuum swing absorbers, membrane separators, or a combination thereof. In an embodiment, CO2 in the reaction products is recycled and used as the entrainment gas.

[0098] Products from the process can be used in a number of ways. These ways include, but are not limited to:

[0099] 1) Combination of product hydrogen and carbon monoxide or carbon dioxide in a Fischer-Tropsch (FT) style reactor to produce hydrocarbons. These hydrocarbons could include, but are not limited to, methanol, methane, gasoline (C5-C12), ethanol, propane, butane, diesel fuels, jet fuels, and specialty organic chemical products. Uses for such hydrocarbons would include transportation fuels, heating fuels, and fuels for stationary electric power generation, but the uses are not limited to these.

[0100] 2) Combination of the carbon monoxide product with additional water in a Water-Gas Shift reactor to produce additional hydrogen and carbon dioxide. The product hydrogen could be used in fuel cells for electrical power generation, as a combustion fuel, as a desulfurization agent for gasoline, transportation fuels, or coal, or for specialty chemical synthesis, but its uses are not restricted to this. 3) Direct separation of the product hydrogen for use as specified in #2) 4) Direct combustion of the product stream for power generation, heat generation, or other similar purposes.

[0101] As used herein, "comprising" is synonymous with "including," "containing," or "characterized by," and is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. As used herein, "consisting of" excludes any element, step, or ingredient not specified in the claim element. As used herein, "consisting essentially of" does not exclude materials or steps that do not materially affect the basic and novel characteristics of the claim. Any recitation herein of the term "comprising", particularly in a description of components of a composition or in a description of elements of a device, is understood to encompass those compositions and methods consisting essentially of and consisting of the recited components or elements. The invention illustratively described herein suitably may be practiced in the absence of any element or elements, limitation or limitations which is not specifically disclosed herein.

[0102] When a Markush group or other grouping is used herein, all individual members of the group and all combinations and subcombinations possible of the group are intended to be individually included in the disclosure.

[0103] One skilled in the art would readily appreciate that the present invention is well adapted to carry out the objects and obtain the ends and advantages mentioned, as well as those inherent therein. The devices and methods and accessory methods described herein as presently representative of preferred embodiments are exemplary and are not intended as limitations on the scope of the invention. Changes therein and other uses will occur to those skilled in the art, which are encompassed within the spirit of the invention, are defined by the scope of the claims.

[0104] Although the description herein contains many specificities, these should not be construed as limiting the scope of the invention, but as merely providing illustrations of some of the embodiments of the invention. Thus, additional embodiments are within the scope of the invention and within the following claims.

[0105] All patents and publications mentioned in the specification are indicative of the levels of skill of those skilled in the art to which the invention pertains. All references cited herein are hereby incorporated by reference to the extent that there is no inconsistency with the disclosure of this specification.

EXAMPLE 1

Cellulose Gasification in an Electrically Heated Aerosol Transport Tube Reactor

[0106] Cellulose was combined with water vapor in an electric tube furnace at temperatures between 1200 K and 1450 K. The cellulose was composed of fine particles (Sigma-Aldrich #310697, 20 [mu]m) with a monomer unit shown in FIG. 3. The reactor apparatus is shown in FIG. 4. The reactor consisted of a 99.8% Alumina tube (3) (McDanel Technical Ceramics), 3.635'' in internal diameter by 45'' in length. This tube was heated indirectly using a surrounding electrically heated graphite resistance element (800). The interior of the Al2O3 tube was sealed from the outer graphite element and purged with argon gas to eliminate oxygen. Particles of cellulose were placed in a fluidized bed feeder (500); fluidization gas (21) (argon) entrained the particles, carrying them into the hot reactor, where they were combined with water vapor (23). The water flowrate was controlled by a syringe pump, and the water was introduced into the hot reactor environment through a capillary tube. The molar feed ratio of cellulose to water was approximately 1:1. A pyrometer (700) was used to measure the temperature of the reaction tube.

[0107] After leaving the heated portion of the reactor, the reaction products were passed through a gravity collection vessel (350) and an HEPA (high efficiency particulate air) filter (400) (200 nm pore size). Large particles would be collected in the gravity vessel, with smaller, entrained particles accumulating on the HEPA filter. The gravity collection vessel was contained in an outer containment collection vessel (300). The exhaust gases (26) were analyzed using mass spectrometry and NDIR (nondispersive infrared) CO/CO2 detection.

[0108] Experiments were performed in a 2<2 > full factorial design. The two factors were temperature and total entrainment gas flow. The larger the value of the entrainment gas flow, the shorter the residence time within the reactor. The temperature factor levels were 1200 K and 1450 K, and the total gas flow factor levels were 10 SLPM and 15 SLPM (standard liters per minute).

[0109] At the highest temperature condition and lowest flowrate, the mass spectrometer (MS) trace showed an immediate increase in H2 production at the start of feeding. (FIG. 5) The scales for the different molecules differ, so a relatively larger increase in partial pressure of one species does not necessarily mean a larger increase in molar flowrate of that species. This was better determined by NDIR analysis. An increase in CO concentration followed shortly after the H2 peak, and could be seen on the NDIR detector. At the start of feeding, the water concentration decreased, indicating reaction. This amount recovered with the waning of the hydrogen peak, indicating that at least some of the hydrogen was coming from the water. Integration under the NDIR peak yielded 0.006 mol of CO produced. Based on the amount of material fed, this gives conversion of cellulose to CO at 94%. When including CO2 production, the conversion increased to 98%. This is essentially complete gasification of the feed material. No differential pressure increase was detected, and no mass was collected in the gravity vessel, on the HEPA filter, or on the walls of the reactor.

[0110] Reaction of material at 15 SLPM and 1450 K yielded similar results. Gasification conversion of the feed material was 95%, and no material was collected in the reactor for 0.9 g fed. There was no increase in differential pressure across the HEPA filter, indicating no buildup of material.

[0111] At the lower temperature, 950[deg.] C., both flowrate conditions also showed fairly high conversion (65%). Much of this material was collected in the gravity vessel, and resembled the feed material in composition. Also, differential pressure across the HEPA filter indicated a large deposit of material, likely incomplete products of gasification. This differential pressure increased rapidly, and reached a level high enough to trigger the safety pressure relief devices on the apparatus. From the factorial experiments it was clear that more complete gasification was obtained in short residence times at ultra-high temperatures (>1000[deg.] C.). These are temperatures are achievable in concentrated solar energy systems.

EXAMPLE 2

Lignin Gasification in an Electrically Heated Aerosol Transport Tube Reactor

[0112] Lignin was combined with water vapor in an electric tube furnace at 1450 K. The lignin was composed of fine particles (Sigma-Aldrich #371017, 20 [mu]m) with a monomer unit shown in FIG. 6. The reactor was the same as in Example 1. The interior of the Al2O3 tube was sealed from the outer graphite element and purged with argon gas to eliminate oxygen. Particles of lignin were placed in a fluidized bed feeder; fluidization gas (argon) entrained the particles, carrying them into the hot reactor, where they were combined with water vapor. The water flowrate was controlled by a syringe pump, and the water was introduced into the hot reactor environment through a capillary tube.

[0113] After leaving the heated portion of the reactor, the reaction products were passed through a gravity collection vessel and an HEPA filter (200 nm pore size). Large particles would be collected in the gravity vessel, with smaller, entrained particles accumulating on the HEPA filter. Gas analyses were performed using mass spectrometry and NDIR CO/CO2 detection.

[0114] The demonstration experiment was performed at 1450 K and around a 1:1.5 molar feed ratio of lignin to water.

[0115] Conversion of the material was essentially complete (98%), with products existing as C, CO2, and CO. The C was in the form of fine powder and made up about 30% of the carbon in the exit stream. With higher ratios of water to lignin, thermodynamics allow further gasification of this carbon. The CO2 to CO ratio in the outlet gas was about 1:10, showing conversion to favorable to CO.

EXAMPLE 3

Cellulose and Lignin Pyrolysis in an Electrically Heated Aerosol Transport Tube Reactor

[0116] Cellulose and lignin were pyrolyzed in an electric tube furnace at temperatures between 1200 K and 1450 K. Each material was fed in separate experiments. The cellulose was composed of fine particles (Sigma-Aldrich #310697, 20 [mu]m) and the lignin was also composed of fine particles (Sigma-Aldrich #371017) The reactor apparatus is similar to that in Example 1. The interior of the Al2O3 tube was sealed from the outer graphite element and purged with argon gas to eliminate oxygen. Particles of cellulose or lignin were placed in a fluidized bed feeder; fluidization gas (argon) entrained the particles, carrying them into the hot reactor, where they joined by sweep argon gas to control residence time.

[0117] After leaving the heated portion of the reactor, the reaction products were passed through a gravity collection vessel and an HEPA filter (200 nm pore size). Large particles would be collected in the gravity vessel, with smaller, entrained particles accumulating on the HEPA filter. Gas analyses were performed using mass spectrometry and NDIR CO/CO2 detection.

[0118] Experiments were performed in a 2<2 > full factorial design for each feed material. The two factors were temperature and total entrainment gas flow. The larger the value of the entrainment gas flow, the shorter the residence time within the reactor. The temperature factor levels were 1200 K and 1450 K, and the total gas flow factor levels were 10 SLPM and 15 SLPM.

[0119] The mass spectrometry trace for the high temperature, low flowrate cellulose pyrolysis experiment is shown in FIG. 7. As can be seen, both hydrogen and carbon monoxide increase rapidly upon introduction of the feed material. These are the thermodynamically expected products, and this trace is representative of all of experiments as a whole.

[0120] For cellulose pyrolysis, conversion was high at high temperatures. For the short residence time point at 1450 K, the conversion to CO and CO2 was 80%, with CO:CO2 ratios around 12:1. This was similar for the long residence time point, with 85% conversion and CO:CO2 ratios near 10:1. The conversion was lower in the low temperature points, with a significant amount of solid material collected in the reactor (over [1/3] of the mass fed). LECO TC600 and C200 (Leco Corp.) analysis showed carbon and oxygen levels similar to the feed composition, but structural rearrangements would be possible. In any case, at the low temperatures, the conversions to carbon oxides in the gas were 60% and 61%, with similar CO:CO2 ratios as in the high temperature experiments. It is clear that high temperatures (>1300 K) produced more effective pyrolysis of this material.

[0121] Lignin pyrolysis products included a significant amount of fine black powder. LECO C200 analysis of this powder showed it to be >96% carbon for each of the high temperature points, and a lower >75% carbon for the low temperature experiments. This is likely due to unreacted lignin in products. Conversion to CO was higher at higher temperatures, being between 40% and 45%. These are right around the theoretical maximum, although some adsorbed water on the feed material could push the theoretical conversion higher due to gasification. The conversion was lower at 1200 K, at 16% and 18% for the low and high residence time points, respectively. In all of the experiments, the ratio of CO to CO2 in the exit stream was between 8:1 and 10:1.

EXAMPLE 4

Cellulose Gasification in Solar Heated Aerosol Transport Tube Reactor

[0122] Cellulose was combined with water vapor, at a temperature of 1423 K, in a solar heated tube furnace. The solar reactor apparatus is shown in FIG. 8. The reactor consisted of a 99.8% alumina tube (3) (CoorsTek ceramics) having an inner diameter of 0.75'' and a total length of 14''. The heated length of the tube was 8''. The tube was surrounded by a quartz sheath, sealed to the outside air and purged with argon gas. The cellulose was composed of fine particles (Sigma-Aldrich #310697, 20 [mu]m). The cellulose particles (28) were introduced into the system from the top using a fluidized bed feeder (500). Argon was used as the fluidization gas (21) to entrain the particles and carry them into the hot zone of the reactor, where they combined with water vapor. The water was introduced into the reactor with a syringe pump. The molar feed ratio of cellulose to water was approximately 1:1.

[0123] The tube was heated with concentrated solar energy at the High Flux Solar Furnace facility at the National Renewable Energy Laboratory. The solar concentration of the system at the front of the secondary concentrator (50) was approximately 1000 suns (approximately 1000 kW/m<2> ), and at the exit of the concentrator was approximately 2000 suns (approximately 2000 kW/m<2> ).

[0124] After leaving the heated portion of the reactor, the reaction products were passed through a gravity collection vessel and a HEPA filter (200 nm pore size). Large, heavy particles were collected in the gravity vessel (350), while smaller, entrained particles collected on the HEPA filter (400). The product gas (26) was analyzed using a mass spectrometer (MS).

[0125] The entrainment gas flow rate correlated to the residence time of particles within the reactor. For this experiment, the entrainment flow rate was set to 1.25 SLPM. The MS trace showed an immediate increase in H2 and CO production at the onset of particle feeding, accompanied by a decrease in the water trace, indicating reaction of the water and cellulose (FIG. 9). The correlation between partial pressure and concentration for each species differ, so a relatively larger increase in the partial pressure of one species does not necessarily mean a larger increase in the molar flow rate of that species. Calibration of the MS device allowed to convert the partial pressure measurements to moles produced. After integrating the carbon monoxide and comparing it to the cellulose mass feed, the conversion of cellulose to CO was determined to be 92%. No carbon dioxide was detected in the outlet stream.

EXAMPLE 5

Gasification of Clippings of the Grass Poa pratensis

[0126] To demonstrate the gasification of biologically derived cellulose and lignin, grass clippings of the species Poa pratensis were gasified in an electrically heated aerosol transport tube reactor at a temperature of 1450 K. Sample preparation was as follows. 4 grams of clippings of the species Poa pratensis were rinsed in ethanol, and the rinsed clippings vacuum filtered. The residual clippings were dried for 24 hours in a vacuum furnace at 200[deg.] C. The dried material was ground with a mortar and pestle until there were no longer fibers longer than 1 mm in the sample. These clippings were loaded into a fluidized bed feeder.

[0127] The reactor apparatus the same as that in Example 1. The interior of the Al2O3 tube was sealed from the outer graphite element and purged with argon gas to eliminate oxygen. Particles of grass were placed in a fluidized bed feeder; fluidization gas (argon) entrained the particles, carrying them into the hot reactor, where they were combined with water vapor. The water flowrate was controlled by a syringe pump, and the water was introduced into the hot reactor environment through a capillary tube. The molar feed ratio of grass to water was approximately 1:1.

[0128] After leaving the heated portion of the reactor, the reaction products were passed through a gravity collection vessel and an HEPA filter (200 nm pore size). Large particles would be collected in the gravity vessel, with smaller, entrained particles accumulating on the HEPA filter. Gas analyses were performed using mass spectrometry and NDIR CO/CO2 detection.

[0129] 3.2 g of powder was fed into the reactor during the experiment. After the experiment, 0.28 g were collected in the gravity collection vessel, and 0.15 g were collected on the HEPA filter. This material was a fine black powder, and LECO C200 analysis confirmed it to consist of greater than 95% carbon. The mass spectrometer trace for the experiment is shown in FIG. 10. Less than 10% of the evolved gaseous carbon was as CO2. Conversion to CO of the feed carbon was 64%, nearly all of the unconverted carbon existing as the fine black powder collected.

EXAMPLE 6

Hydrogen Production Using Zn as an Energy Storage Medium

[0130] Biomass particles are reacted with zinc oxide (ZnO) particles, using the solar thermal process described herein. Sunlight is used to drive the endothermic biomass pyrolysis (biomass to CO/H2/C) and carbothermal reduction of ZnO (C, CO+ZnO-Zn+CO/CO2) reactions. The reactor temperature can be between approximately 1400 and 2200 K. The reaction is extremely fast at the high temperatures achieved via solar-thermal heating. The primary pyrolysis/carbothermal reduction products are Zn metal, H2, CO, and CO2.

[0131] After cooling, the Zn metal is a solid and can be easily separated from the gaseous products and stored. The gaseous H2, CO, CO2 mixture can be fed to a conventional catalytic water gas shift reactor with water feed to carry out water gas shift (CO+H2O-CO2+H2) reaction producing H2 and CO2. The H2 can be used as a fuel or chemical feedstock for another process. The CO2 can be released to the atmosphere or fed to a greenhouse to grow biomass. The solar-thermal reactor process provides Zn metal to a Zn metal storage system and a water gas shift reactor feed at high rates on-sun. The Zn is effectively an energy storage medium. A secondary step in which the Zn is reacted at approximately 700 K with steam to produce H2 and ZnO is an exothermic process, and can be operated autothermally. Hence, the Zn/steam reactor can be designed to operate at a rate consistent with the production of Zn on-sun ([1/3] to [1/4] of the time) from the solar-thermal step (hence, the Zn/steam reactor will operate to react Zn at a rate of about [1/3] to [1/4] of the rate at which Zn is being produced on-sun, since on-sun time is [1/3] to [1/4] of the typical day). The Zn storage will increase during the daytime when the solar-thermal process is operating and will decrease during the evening when Zn is not being produced on-sun. The ZnO produced via the Zn/steam reaction step is recycled back to the solar-thermal reactor for on-sun reduction to produce Zn. The Zn/ZnO is a closed loop cycle. A schematic of this process is given in FIG. 11.

EXAMPLE 7

Combined Solar-Thermal Biomass/Zn Process with Coal Hydrogenation Process

[0132] A solar-thermal biomass/Zn process, producing renewable H2, can be integrated with a conventional fossil feed process. Such a process represents a transitional bridge to a truly hydrogen economy. FIG. 12 illustrates a process to produce methane by reacting coal with renewable hydrogen. In this process, H2 is supplied continuously via the Zn/steam reactor while the H2/CO/CO2 from the on-sun solar-thermal reactor is supplied to a continuous water gas shift reactor, downstream of the coal hydrogenation reactor. The resulting product is CH4 out of a methanator. The renewable H2 to the process is supplied via pyrolyzed biomass from solar-thermal pyrolysis and water from the Zn/steam reactor. The carbon to the process is supplied by the coal and the biomass. The coal hydrogenator should be operated at high pressure of 1,000 psig or greater. The hydrogen from the Zn/steam reactor can be supplied at the required delivery pressure in the reactor or may require compression.

EXAMPLE 8

Reduction of Fe3O4 by CO and H2 and Generation of H2 by Reaction of Water with the Reduced Products

[0133] To demonstrate the feasibility of Fe3O4 reduction by the products of biomass gasification, Fe3O4 was loaded in a platinum crucible in a thermogravimetric analyzer (TGA). The system was heated to 1000[deg.] C. under 200 sccm of argon gas flow. At 1000[deg.] C., the temperature was held constant while 22.5 sccm of H2 and 22.5 sccm of CO were introduced into the system. The mass of the sample decreased, indicating a reduction reaction; the change in mass was commensurate with that for complete reduction to FeO. The gas products were analyzed using mass spectrometry, and the trace for this analysis is shown in FIG. 13. As can be seen, both CO2 and H2O were produced by reaction, indicating reduction by both CO and H2. In a second experiment, the iron oxide reduced in the first experiment remained in the Pt crucible while water was introduced at 400[deg.] C. The mass of the sample increased, with a total level commensurate with re-oxidation of the FeO to Fe3O4. Gases were analyzed using mass spectrometry. As can be seen in FIG. 14, hydrogen was produced during a corresponding dip in the water concentration. These experiments demonstrate the viability of cycling iron oxide through reduction and oxidation steps for energy storage and hydrogen generation.