rexresearch.com
Denis RANDALL
Oil from Recycled Tires
https://www.qut.edu.au/news/news?news-id=112276
Tests on oil recycled from tyres finds a
cleaner diesel blend
29 November 2016
Old tyres can be completely recycled into lower emission diesel
engine oil, instead of being dumped in dangerous, highly flammable
stockpiles that become breeding grounds for malaria and
dengue-carrying mosquitoes.
QUT mechanical engineers tested the oil extracted from old tyres
in a process developed by Australian company Green Distillation
Technologies (GDT).
QUT’s Professor Richard Brown and PhD student Farhad Hossain
tested the oil’s emissions and output at QUT's Biofuel Engine
Research Facility.
Professor Brown said that when the oil was blended with diesel it
was found to produce a fuel with reduced emissions and no loss of
engine performance.
“Globally, 1.5 billion tonnes of tyres are discarded each year.
Australia, alone, will generate 55 million disused tyres a year by
2020," Professor Brown said.
“Getting rid of old tyres in an environment-friendly way is a
universal nightmare.
“Stockpiles of used tyres around the world are a health hazard, as
demonstrated by the recent Broadmeadows fire in Victoria, which
was difficult to put out and generated huge amounts of toxic
smoke.”
Mr Farhad said the QUT engineering team, including process
engineer Dr Tom Rainey and air-quality expert Professor Zoran
Ristovski, performed rigorous tests on the oil.
“We tested the oil which GDT produces from both recycled natural
and synthetic rubber tyres in 10 per cent and 20 per cent diesel
blends,” Mr Farhad said.
“We tested the tyre oil blends in a turbocharged, common rail,
direct injection, six-cylinder engine in the Biofuel Engine
Research Facility at QUT.
“The engine is typical of engine types used in the transport
industry.
“Our experiments were performed with a constant speed and four
different engine loads of 25, 50, 75 and 100 per cent of full
load.
“We found a 30 per cent reduction in nitrogen oxide which
contributes to photochemical smog, and lower particle mass which
means fewer problems for emission treatment systems.”
GDT chief operating officer Trevor Bayley said the oil could
also be used as a heating fuel or further refined into automotive
or aviation jet fuel.
“The process recycles end-of-life tyres into oil, carbon and
steel, leaving nothing wasted and even uses some of the recovered
oil as the heat source,” Mr Bayley said.
“Carbon is the most common recovered ingredient and the steel rim
and framework is the third most common ingredient, while the oil
is the most valuable.
“We are delighted at the findings of the QUT research as it will
help us promote the sustainable use for end-of-life tyres.
“The potential of this source of biofuel feedstock is immense, and
it is more sustainable than other bio-oils from plants such as
corn, or algae.
“A recycled 10kg car tyre yields 4 litres of oil, 1.5kg of steel
and 4 kg of carbon,, and a 70kg truck tyre provides 28 litres of
oil, 11kg of steel and 28kg of carbon.
“GDT plans to have the first fully operational commercial plant
delivering eight million litres of oil a year from mid-2017,
followed by a world-first mining tyre processing plant in either
Qld or WA.”
About Green Distillation Technologies: GDT is an Australian
company which has developed world-first technology to recycle
end-of-life car and truck tyres into carbon, oil and steel. The
company won a bronze medal in the world’s top innovation award,
the Edison Awards, last year.
Denis Randall
https://www.fullyloaded.com.au/media/12971428/green-distillation-technologies-tyre-recycling-adison-award-site-atn.jpg
GDT Adison Site
http://www.gdtc6.com/
Cleanly Recycled Tyres – A World Technology
First
Green Distillation Technologies has achieved an Australian world
technological breakthrough by effectively and profitably recycling
end of life car and truck tyres (ELTs) into saleable commodities
of oil, carbon and steel.
End of life car and truck tyres are a blight on the environment
ever since they were invented over a century ago, because until
now no means had been found to effectively and economically
recycle them.
Grinding up old tyres to make crumbs or flakes is not a means of
recycling tyres as the rubber has not been changed and there is a
limit to how much of this material can be used for kindergarten
playgrounds and soccer fields and using it as a furnace fuel in
Asia creates noxious greenhouse damaging emissions.
As well as the environmental problem caused by dumps of old tyres
or illegally discarding them in bushland and waterways, after rain
they become a breeding ground for mosquitoes and a source of such
dangerous diseases as Dengue and Ross River Fever.
However, using a technique known as destructive distillation,
Green Distillation Technologies is able to convert this wasted
resource and an environmental hazard into high demand valuable raw
materials.
The process is emission free and the recycled oil is used as the
heat source for the production process.
The GDT Tyre Recycling Process – How It Works
Destructive Distillation is the name GDT gives to their tyre
recycling process which is developed from basic chemistry, the
genius of Technical Director Denis Randall and his thirty five
years of study and experimentation into organic waste streams. As
a result GDT has developed the knowledge of getting the chemical
reaction to occur.
The process begins by loading whole end of life tyres into a
process chamber, which is evacuated of air and sealed. In the
initial steps no further processing of the tyres, such as chopping
or crumbing is required.
Heat is applied, which acts as a catalyst for the chemical
reaction, which sees the tyre destructed into different compounds,
one of which is collected and condensed into ‘manufactured’ oil.
At the end of the process and the chemical reaction is over, the
carbon and steel can be extracted cooled and separated.
http://www.gdtc6.com/tyre-recycler-determined-longford-plant-go-ahead/
February 22, 2016
Tyre recycler determined for Longford plant
to go ahead
Green Distillation Technologies, the Australian company that has
proposed building the $8.5 million plant to process end of life
car and truck tyres at Longford, Tasmania is still determined to
proceed despite encountering delays in securing Government
approvals.
GDT’s Australian developed technology is a world first and
recycles end of life car and truck tyres into oil, carbon and the
steel reinforcing with a typical end of life 10 kg car tyre
yielding 4kg of carbon, 1.5kg of steel and 4 litres of oil, while
a 70kg truck tyre provides 28 kg of carbon, 11 kg of steel and 28
litres of oil.
GDT Chief Operating Officer Trevor Bayley who was in Tasmania last
week for meetings with the Government and Northern Midlands
Council said that they had applied for Development Approval for
the plant, but still had to secure an OK from the Environmental
Protection Authority.
“From my discussions, I believe that the Government is aware that
they have a responsibility to fix the problem of tyre recycling in
Tasmania and that the first step should be to put it on a sound
financial footing.
“Clearly the Longford site, where there is an estimated 900,000
tyres waiting for processing is a priority, although of course
this stockpile is being added to by the 480,000 to 500,000 end of
life car and truck tyres that Tasmania generates each year. We
estimate that it will take three years to get rid of the existing
stockpile.
“The obvious place to start with generating funds to pay for tyre
recycling is with the fee paid by each motorist when they dispose
of their old tyres and get a new one fitted. This amount varies
with different retailers across the State, but could be as high as
$8 to $9 and of this a fixed amount of $2.50 is paid for
collection and storage, but not for end of life management” Mr
Bayley said.
GDT had initially planned to start work on the site in Longford on
November last year and estimates that it will take six months for
the plant to become operational from the time they receive
Government approval to proceed.
Mr Bayley said that their plant in Warren New South Wales is going
through the commissioning stage after operating as a test facility
since 2009 and is now producing their first commercial quantities
of oil, carbon and steel from old car and truck tyres.
“We have been operating the pilot plant in Warren western New
South Wales since 2009 and the upgrade to full production will see
it capable of processing 19,000 tonnes, or a mix of 658,000 car
and truck tyres per year. This represents approximately 3% of the
24 million end-of-life tyres that are generated in Australia each
year.
“The reason we have been attracted to Tasmania is entirely due to
the work of Tim Chugg of Tyrecycle Tasmania who has been to our
plant at Warren and seen for himself how it works and came away
enthusiastic to establish a plant in Tasmania.
“By the time Tyrecycle Tasmania’s stockpile has been recycled it
is anticipated that we will have extended the scope of our
operations to include mining and agricultural tyres for which
there is currently no solution.
“Our process is unique as the oil produced from the GDT process
can be used as a heating fuel, direct into some stationary diesel
engines or is capable of further refinement into automotive or
aviation fuels, while the carbon is a high grade product that can
replace those sourced from fossil fuels and the steel is returned
directly to tyre manufacturers for reuse.
“The process is not only emission free but the recycled oil is
used as the heat source for the production process.
“It is the only process available in the world that remanufactures
the rubber from old tyres into a different energy form as the
other recycling methods merely change the shape or appearance of
the rubber into crumbs or chips,” Mr Bayley said.
Tim Chugg of Tyre Recycle Tasmania said that he believed that the
GDT technology is by far the best option to recycle end of life
tyres in Tasmania.
“I have been trying to get a viable recycling plant established at
Longford for sixteen years and I am still committed to work to get
it operating.
“The delays have been frustrating and I only hope some wise heads
will prevail to come up with a solution as the stockpile of old
tyres at Longford just gets larger.
“Tasmanians are very environmentally conscious and I am sure that
everyone in the State will want to see a solution found for the
disposal of end-of-life tyres, which are such a major
environmental problem,” Tim Chugg said.
US6863004
Process and system for recovering energy from
carbon-containing materials
Inventor: RANDALL DENIS A [AU]
The invention provides processes and systems for generating heat
from a carbon-containing material or converting a
carbon-containing material to a combustible gaseous fuel,
comprising (a) pyrolysing the material in a reactor to produce a
carbon-enriched solid and a first gaseous product, (b) burning at
least part of the first gaseous product and/or a second gaseous
product obtained by reacting the carbon-enriched solid with water
vapour to generate heat, and (c) returning combustion products
from the burning step to the reactor and/or removing part of the
first gaseous product and/or the second gaseous product as a
combustible fuel.
TECHNICAL FIELD
The invention relates to processes and systems for converting
carbon-containing materials, in particular waste materials
containing organic substances, into combustible fuels and thereby
recovering energy from the carbon-containing materials.
BACKGROUND OF THE INVENTION
The disposal of ever-increasing quantities of waste materials is a
significant challenge in many parts of the world and is becoming a
more significant problem as the world's population becomes
increasingly urbanised. Furthermore, the increasing human
population and increasing levels of affluence are resulting in
larger quantities of waste materials of various kinds being
generated. Disposal strategies currently utilised for dealing with
wastes include landfill, biological degradation by various means,
combustion, and various chemical treatment processes. However,
each of these methods suffers from one or more disadvantages. For
example, existing disposal methods may cause pollution, may be
energy intensive, or may be wasteful of limited resources such as
land. Additionally, many waste materials constitute a source of
useful energy if efficient means of recovery of that energy can be
devised. For example, waste incineration is an effective way of
decreasing the bulk of waste material for disposal, but typically
the heat generated by the incineration is not recovered, and in
addition the process can lead to the generation of pollutants such
as nitrogen oxides and dioxins, and the generation of large
quantities of greenhouse gases. Hence there is a need for improved
waste treatment or disposal processes which are environmentally
benign and which result in the recovery of useful energy from the
wastes.
It is an object of the present invention to provide an efficient
method for the recovery of useful energy from carbon-containing
materials, and simultaneously to provide an environmentally
acceptable way of disposing of waste materials with minimal
adverse environmental impact.
SUMMARY OF THE INVENTION
In a first embodiment of the invention there is provided a process
for generating heat from a carbon-containing material which
includes the steps of:
(a) pyrolysing said material in a pyrolysis zone of a reactor at
an elevated temperature to produce a carbon-enriched solid and a
combustible gaseous product;
(b) burning a first part of said combustible gaseous product to
produce a first gaseous combustion product and to heat said
pyrolysis zone so as to maintain said elevated temperature;
(c) removing a second part of said combustible gaseous product
from said reactor;
(d) burning said second part of said combustible gaseous product
to generate heat and produce second gaseous combustion products;
and
(c) returning said first and second gaseous combustion products to
said pyrolysis zone.
Thus, the process of the first embodiment provides a process
whereby useful energy may be recovered from a carbon-containing
material, but which produces substantially no gaseous emissions,
since substantially all of the gaseous products produced in tile
process are returned to the process after they have been burned.
In one form of the process of the first embodiment of the
invention, the carbon-enriched solid may be contacted with steam
at a temperature at which the water gas reaction occurs, so as to
produce therefrom a mixture containing hydrogen and carbon
monoxide.
Thus, in a second embodiment of the invention there is provided a
process for generating heat from a carbon-containing material
Which includes the steps of:
(a) pyrolysing said material in a pyrolysis zone at a first
elevated temperature to produce a carbon-enriched solid and a
first combustible gaseous product;
(a') transferring said carbon-enriched solid and said first
combustible gaseous product to a reaction zone;
(b) reacting said carbon-enriched solid with water vapour in said
reaction zone at a second elevated temperature to produce a second
combustible gaseous product containing hydrogen gas and carbon
monoxide;
(c) burning a first part of said second combustible gaseous
product to produce first gaseous combustion products and to heat
at least said reaction zone so as to maintain said second elevated
temperature;
(d) removing a second part of said second combustible gaseous
product from said reaction zone;
(e) burning said second part of said second combustible gaseous
product to generate heat and second gaseous combustion products;
and
(f) returning said first and second gaseous combustion products to
said pyrolysis zone.
In a further form of the process of the invention, a part of
combustible gaseous products produced by pyrolysis of the
carbon-containing material, and/or produced by reaction of water
vapour with the carbon-enriched solid, are removed from the
reactor as a combustible gaseous fuel which may be transported if
desired to a location remote from the reactor and from which
energy may be recovered by any convenient method.
Therefore, a third embodiment the invention provides a process for
converting a carbon-containing material to a combustible gaseous
fuel which includes the steps of:
(a) pyrolysing said material in a pyrolysis zone at a first
elevated temperature to produce a carbon-enriched solid and a
first gaseous product;
(b) reacting said carbon-enriched solid with water vapour in a
second reaction zone at a second elevated temperature to produce a
second gaseous product containing hydrogen gas and carbon
monoxide;
(c) burning a first part of (i) said first gaseous product, (ii)
said second gaseous product or (iii) a mixture thereof so as to
heat at least said reaction zone and maintain said second elevated
temperature; and
(d) removing the remainder of said first and second gaseous
products as said combustible gaseous fuel.
In a fourth embodiment of the invention there is provided a system
for recovering energy from carbon-containing material, the system
including:
a reactor vessel having an exterior and an interior, said reactor
being equipped with means to admit said carbon-containing material
to said vessel and heating means to heat the vessel;
gas offtake means operatively associated with the reactor vessel
to permit combustible gases generated in the vessel to be removed
therefrom;
a first gas conduit between said gas offtake means and said
heating means to transfer a first part of said gases generated in
said vessel to said heating means;
ignition means adapted to ignite said gases in said heating means;
and
energy recovery means operatively associated with the gas offtake
means for recovery of energy from a second part of said gases
generated in said vessel.
In one form of the system of the fourth embodiment, the first gas
conduit includes gas separation means which is capable of
separating at least part of any hydrogen present in the gases
generated in the vessel from other gases present, thereby
producing a hydrogen-rich stream and a hydrogen depicted stream,
and means to transfer the hydrogen-depleted stream to the heating
means.
The system of the fourth embodiment may further comprise a second
gas conduit between said heating means and said reactor vessel, to
transfer gaseous combustion products from said heating means to
the interior of said vessel. The energy recovery means typically
includes a high pressure boiler wherein the second part of the
gases generated in the reactor vessel is burnt. More typically,
the system further includes a further gas conduit adapted to
transfer gaseous combustion products from the energy recovery
means to the interior of the reactor vessel.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of a system for
recovery of energy from carbon-containing materials utilising a
process in accordance with the third embodiment of the present
invention.
FIG. 2 is a schematic representation of a system for
recovery of energy from carbon-containing materials utilising a
process in accordance with the second embodiment of the present
invention.
FIG. 3 is a diagram of a suitable reactor for carrying out
a process in accordance with the invention.
FIG. 4 is a diagrammatic representation of a reactor used
in laboratory scale trials of a process according to the
invention.
FIG. 5 is a schematic representation of a system used in
laboratory scale trials of a process according to the invention.
FIG. 6 is a schematic representation of an alternative
system for recovery of energy from carbon-containing materials
utilising a process in accordance with the third embodiment of
the present invention.
DETAILED DESCRIPTION OF THE INVENTION
In the processes of the invention, the carbon-containing material
usually contains carbon in chemically bound form, and may contain
other elements. Usually, the material additionally contains the
element hydrogen in chemically bound form. It may also contain
oxygen and/or other elements. The material is typically a waste
material, but it need not be. Thus, materials for use in the
process of the invention may also include conventional solid fuels
such as coal, coke, anthracite, bituminous coal, peat etc, or
other materials such as timber, paper, cardboard, etc. However,
advantageously the carbon-containing material is a waste material,
which may be any organic waste such as sewage; municipal solid
waste, agricultural products and waste of various kinds including
wood waste, bagasse, rice hulls, prunings, abattoir waste and
manure; industrial wastes of various kinds including pulping
liquor from paper pulp mills, solids and sludges from waste water
treatment, plastics, coal washing solids, shale, spent solvents,
oil refinery wastes, contaminated soils, car tyres and so on. The
composition of the waste is not critical to the process of the
present invention, nor is its moisture content. However, typically
the waste will have been processed in a preliminary step to remove
gross quantities of water, where present, by one or more methods
which are generally known in the art for that purpose such as
centrifuging, filtering, skimming, evaporation, etc.
The pyrolysis reaction in the processes of the present invention
typically occurs at a temperature in the range of about 200[deg.]
C. to 600[deg.] C. more typically in the range 200[deg.] C. to
400[deg.] C. Generally, in the processes of the second and third
embodiments the pyrolysis reaction occurs in the same reactor as
reaction step (b) but it can occur in a separate reactor. A
substantially oxygen-free atmosphere is typically generated in the
pyrolysis zone by conducting the pyrolysis in a closed vessel so
that any oxygen which the vessel contained initially is consumed
by reaction with the carbon-containing material, or with elemental
carbon, at the temperature of the pyrolysis zone. Alternatively
the pyrolysis reaction zone may be initially purged with an
oxygen-free gas, such as nitrogen, carbon dioxide, steam or
mixtures thereof. For example, in the processes of the second and
third embodiments a part of the gaseous product generated in
reaction step (b) may be passed from the reaction zone for step
(b) into the pyrolysis reaction zone so as to-sweep out oxygen.
The pyrolysis reaction results in coking or charring of the
carbon-containing material to produce a carbon-enriched solid
material and simultaneously generates low molecular weight organic
substances which typically vaporise at the temperature of the
pyrolysis reaction. Water vapour is also typically liberated as
steam by the pyrolysis process, unless the carbon-containing
material is dry and the carbon-containing substances present are
mainly hydrocarbons (for example used car tyres). In the latter
case, it will be necessary to add steam or water to the reaction
zone in the processes of the second and third embodiments.
The pyrolysis reaction produces a carbon-enriched solid material
and a vapour phase. Optionally, the vapour phase may be cooled to
liquefy any condensable materials which it contains before the
remaining gas, or part of it, is sent either to the reaction zone
for step (b) (in the processes of the second and third
embodiments) or for burning (in the process of the first
embodiment). However usually the vapour phase is directed to its
destination without cooling and condensation. Alternatively, in
the processes of the second and third embodiments the vapour phase
may be taken off from the pyrolysis zone and exploited for its
energy content in any convenient way. In that case, it will be
necessary to provide water or steam to the reaction zone.
In one form of the process of the third embodiment, at least part
of the vapour phase from the pyrolysis zone is removed from the
reactor and a portion of it is burned to generate at least part of
the heat necessary to maintain the first and/or second elevated
temperatures. In this form, part or all of the combustion products
generated by burning the vapour phase removed from the pyrolysis
zone is provided to the reaction zone to provide at least part of
the water vapour required for step (b).
In another form of the process of the third embodiment step (c)
consists of burning a first part of a mixture of the first gaseous
product and the second gaseous product. Typically, in this form of
the process the combustion products of step (c) are returned to
the reactor such that they must pass through the carbon-enriched
solid in the reaction zone before leaving the reactor. Usually in
this form of the process of the third embodiment, the first part
of the mixture of first gaseous product and second gaseous product
is typically obtained from a gas separation step whereby it is
relatively enriched in carbon monoxide and/or carbon dioxide,
compared to the mixture of first and second gaseous products as a
whole. Typically, the gas separation step produces a fraction of
the mixture of the first gaseous product and the second gaseous
product, which fraction contains substantially all of the carbon
monoxide and carbon dioxide present in the mixture of first and
second gaseous products. This fraction which contains
substantially all of the carbon monoxide and carbon dioxide is
then combusted, and the combustion products are returned to the
interior of the reactor in such a way that they must pass through
the reaction zone and contact the carbon-enriched solid in the
reaction zone before leaving the reactor once again.
Typically, in the processes of the invention, the amount of oxygen
provided for burning the part or parts of the of the gases which
are removed from the reactor and combusted, is a stoichiometric or
sub-stoichiometric amount, so that the combustion products which
are returned to the reaction zone typically contain substantially
no oxygen gas.
Condensable products obtainable by cooling the vapour phase
removed from the pyrolysis zone depend on the nature and
composition of the carbon-containing material. For example, the
carbon-containing material may contain essential oils or
relatively volatile natural oils which may be recovered by cooling
the vapour phase removed from the pyrolysis zone to a suitable
temperature. Leaves or other parts of plants containing natural
oils may thus be used as the carbon-containing material, for
instance, from which may be recovered at least part of the natural
oils they contain, such as coconut oil, palm oil, cottonseed oil,
corn oil, soybean oil, rapeseed oil, sunflowerseed oil, linseed
oil, eucalyptus oil, tea tree oil and the like.
In step (b) of the processes of the second and third embodiments
the carbon-enriched solid from the pyrolysis step is contacted
with steam in a reaction zone at a second elevated temperature,
thereby undergoing a water gas reaction to produce a gaseous
mixture containing hydrogen and carbon monoxide. Some carbon
dioxide may be produced in this reaction also. Typically, a
mixture of carbon monoxide and carbon dioxide is generated, but it
will be appreciated that the relative proportions of carbon
monoxide and carbon dioxide depend on the ratio of steam to carbon
in the reaction zone, on the temperature of operation and on the
concentration of oxides of carbon already present. Chemical
reactions occurring in the reaction zone may be represented
schematically as follows:
<img class="EMIRef" id="041327880-00010000" />
Additionally, if any oxygen is present in the reaction zone, the
following reactions can occur:
<img class="EMIRef" id="041327880-00020000" />
Hence, if sufficient steam is available and carbon monoxide is
removed from the reaction zone, carbon in the carbon-enriched
solid tends to be consumed and converted into oxides of carbon.
Further charring/coking of the carbon-enriched solid may also
occur in the reaction zone. Advantageously, however, carbon
monoxide is permitted to accumulate in the reactor by recycling to
the reactor all combustion products after burning the first and
second gaseous products, as in the process of the second
embodiment.
In another form of the processes of the invention, gases produced
in the reactor may be removed from the reactor and at least part
of the carbon dioxide and carbon monoxide may be at least
partially separated from hydrogen by conventional means. In this
form, the separated carbon monoxide and carbon dioxide (which may
also contain some nitrogen) are typically combusted and the
combustion products are returned to the interior of the reactor,
typically the reaction zone.
Typically, the water vapour or steam for the reactions in the
reaction zone is provided by the vapour phase from the pyrolysis
reaction. However, depending on the water content of the
carbon-containing material originally, or for other operational
reasons, it may be necessary or desirable to utilise an external
source of water or steam for use in step (b).
Where the vapour phase from the pyrolysis zone supplies some or
all of the water vapour for reactions in the reaction zone, the
vapour phase from the pyrolysis reaction may be caused to flow
through the pyrolysis zone and reactor zone in the same direction
as the carbon-containing material passes through them, or it may
flow countercurrent to them. Alternatively, as noted above, at
least part of the vapour phase from the pyrolysis zone in the
process of the third embodiment, or a part of a mixture of the
vapour phase from the pyrolysis zone and the gaseous products
produced in the reaction zone, may be removed from the reactor and
burned, and the combustion products may then be supplied to the
reaction zone either co-current or countercurrent to the direction
of movement of the carbon-containing material. More typically, the
combustion products are supplied to the reaction zone so that they
pass through the reaction zone in a direction opposite to the
direction in which the carbon-containing material moves.
The second elevated temperature is typically a temperature in the
range of about 200[deg.] and upwards. The temperature is, however,
usually to the lower end of this range, typically about 315[deg.]
C. to about 480[deg.] C., for reasons of energy conservation and
to lower the strength of the ash produced from the
carbon-containing material by the processes of the invention. High
ash strengths can lead to difficulties with ash removal from the
reactor.
Since at least reaction (1) and forward reaction (3) above are
endothermic, an external source of heating must be provided to the
reaction zone in order to maintain the reaction. Except when the
process of the invention is first started up, the heat necessary
to sustain step (b) in the processes of the second and third
embodiments is provided by burning a part of the water gas
generated in step (b) and/or a part of the gaseous product
generated in the pyrolysis step. More typically, substantially all
of the gaseous product generated in the pyrolysis step is passed
to the reaction zone for step (b), and hence the Gaseous product
containing hydrogen and oxides of carbon generated by step (b) is
mixed with gaseous products obtained during the pyrolysis step. It
will be appreciated, however, that low molecular weight organic
substances generated during the pyrolysis step may undergo further
reactions under the conditions of the water gas reaction in step
(b).
In the process of the first embodiment typically about 30% by
volume of the gaseous materials generated in the pyrolysis zone is
burnt to provide the heat necessary to maintain the elevated
temperature in the pyrolysis zone. Similarly, in the in the
processes of the second and third embodiments typically about 30%
by volume of the gaseous materials generated in steps (a) and (b)
is burnt to provide the heat necessary to sustain the reactions in
step (b). However, it will be appreciated that in all cases the
quantity of gaseous product required to be combusted for these
purposes will depend on the carbon content of the
carbon-containing material used, its water content and other
components present.
From the foregoing it will be seen that typically approximately
70% by volume of the gaseous product generated in the processes of
the invention is available for removal from the reactor and
constitutes a useful fuel. For example, the gaseous products
removed from the reactor may be burnt in a high pressure boiler so
as to raise steam for the generation of electricity, or for any
other conventional purpose.
The portion of the gaseous product which is burnt to maintain the
temperature(s) in the reactor may be combusted in air, and the
resulting heat applied externally to the reactor. More usually,
however, the combustion gases are returned to the interior of the
reactor, though they may also be passed through a heating jacket
external to the reactor before being directed to the interior of
the reactor. In the processes of the second and third embodiments
this may provide a further source of water vapour for reaction
step (b). Where the combustion gases are returned to the reactor,
in order to avoid build up of nitrogen in the process, it is more
typical to utilise pure oxygen, rather than air, for the
combustion step. Advantageously, where the gaseous product removed
from the process of the invention is combusted for the purpose of
generating electricity, some of that electricity may be used for
the electrolysis of water to generate oxygen for use in the
combustion of the gaseous product(s) of the process. In one form
of the process of the third embodiment, a further portion of the
first and/or second gaseous product is combusted to provide the
heat necessary to sustain the first elevated temperature for the
pyrolysis step, step (a).
In one form of the processes of the invention, flue gases may be
supplied to the pyrolysis zone or the reaction zone, or both, for
remediation. The flue gas may derive, for example, from combustion
of a fossil fuel such as coal, coke, fuel oil or natural gas in a
boiler. Especially when the fossil fuel is coal, coke or fuel oil,
the flue gas typically contains carbon-containing particulates,
which can be removed by passage of the flue gas through a process
in accordance with the present invention.
In the process of the first embodiment, the combustible gaseous
product is burnt to generate heat and combustion products.
Similarly, in the process of the second embodiment the part of the
second combustible gaseous product which is not burnt to provide
the heat necessary to maintain the temperature of the pyrolysis
zone and/or the reaction zone is burnt to generate heat and
combustion products. The heat generated from these steps may be
recovered and utilised in any desired manner, but typically it is
utilised to raise steam for electricity generation. The combustion
products are returned to the pyrolysis zone in these embodiments
of the invention. The combustible gaseous products may be burnt in
air, whereupon a bleed of vapour from the system will be necessary
to avoid buildup of nitrogen. However, more typically the gaseous
fuel is burnt using pure oxygen. In that case, no buildup of gases
occurs in the system, and no gaseous effluent is produced.
When flue gas is supplied to the process of the second embodiment,
similarly, a bleed of gases will be required to prevent buildup of
nitrogen. Typically this will occur by removal of a part of the
combustion product produced in step (e), which, apart from water
vapour and possibly nitrogen, contains carbon dioxide which may be
recovered for commercial use by standard methods.
Buildup of carbon monoxide and carbon dioxide in the system during
continuous operation of the process of the first or second
embodiments, and in continuous operation of the process of the
third embodiment when carbon oxides arc returned to the interior
of the reactor, if there is no bleed of gases from the system,
tends to be inhibited by reaction (3) represented above, which is
driven to the left by a tendency of carbon monoxide to accumulate,
and to the right by a tendency of carbon dioxide to accumulate.
Thus, under steady continuous operation conditions the carbon
monoxide and carbon dioxide concentrations reach steady levels
(given a constant rate of feeding carbon in the carbon-containing
material) and substantially all of the carbon which enters the
reactor leaves it as elemental carbon (soot) which is removed from
the reactor with ash from the carbon-containing material. It will
be appreciated that under these conditions the carbon-containing
material must contain at least hydrogen (in chemically bound form)
in addition to carbon, and the energy recovered from the process
derives substantially from the hydrogen which is present in the
material.
It will be appreciated that once the process of the invention has
been initiated, it may be operated so as to be essentially
self-sustaining by feeding to the reactor continuously or
batch-wise additional carbon-containing material and periodically
removing from the reactor ash or other inert materials. Carbon may
also be removed from the reactor with the ash in some embodiments
of the invention. If necessary, the carbon content of the
carbon-containing material may be adjusted by blending different
materials of different carbon contents so as to maintain a
substantially constant supply of carbon to the reactor. Typically,
the carbon content of the carbon-containing material is at least
about 6% by weight, based on the total weight of the carbon
containing material, and the moisture content is typically not
more than about 94% by weight on the same basis, in order for the
process of the invention to be self-sustaining.
When the combustible gaseous product produced by the process of
the invention is burnt to raise steam (and especially when it is
burnt in oxygen rather than air), the combustion gases may be
recycled to the reactor in the pyrolysis zone and/or the reaction
zone. This results in an essentially closed gas circulation system
from which essentially no gaseous effluent is produced.
At start up, an external source of heat is required in order to
elevate the pyrolysis zone to the elevated temperature of the
pyrolysis reaction, and to elevate the reaction zone, when
present, to the second elevated temperature. Such an external
source of heat may be any convenient source, but is typically a
combustible gas or oil.
A reactor vessel for use with a process of the present invention
may conveniently be a twin-bell reactor of the type typically used
in blast furnaces. This type of reactor includes two chambers, one
above the other, the upper of which is a hopper for holding a
quantity of carbon-containing material, and the other chamber is a
reactor chamber. The hopper is separated from the reactor by a
relatively narrow neck which is capable of being closed by a
bell-shaped valve. Similarly, the hopper is closeable at its upper
end by a similar bell-shaped valve. In operation, the hopper
compartment is charged with the lower bell valve in the closed
position and the upper one in the open position, whereafter the
upper bell is closed and the lower one opened so as to cause the
hopper contents to discharge into the reactor. The lower bell is
then closed while the reactions proceed. In this way, charging of
the reactor may be completed without substantial interruption to
the reactions taking place and without the admission of unlimited
quantities of air. The hopper vessel may be purged of air before
it is discharged into the reactor, if so desired. Typically,
purging of air is achieved using steam or carbon dioxide, more
usually steam. The reactor vessel may conveniently be provided
with a suitable bottom valve for removal of ash periodically.
It will be appreciated, however, that other reactor designs may be
employed in the processes of the present invention. Alternative
reactor designs for carrying out processes in accordance with the
invention will be readily apparent to persons of ordinary skill in
the art, given the teaching herein.
Conveniently, any unconverted organic materials present in the ash
discharged from the reactor may be separated by discharging the
ash into water, whereby organic-containing materials tend to float
and may be skimmed off and returned to the reactor. Typically, at
least a part of the ash removed from the reactor is returned to
the pyrolysis zone for mixing with the carbon-containing material,
to increase the porosity of the solid materials in die pyrolysis
zone and/or the reaction zone.
Best Method and Other Methods for Carrying Out the Invention
FIG. 1 is a schematic representation of a system for recovery of
energy from carbon-containing materials utilising a process in
accordance with the third embodiment of the present invention.
Referring to FIG. 1, the system includes reactor 100 which is
charged with carbon-containing materials 105 in an upper part of
the reactor. Below carbon-containing materials 105 is pyrolysis
zone 110 in which carbon-containing materials 105 are converted to
carbon-enriched materials. Beneath pyrolysis zone 110 is reaction
zone 120 in which the carbon-enriched materials react with water
vapour to produce hydrogen and oxides of carbon. Zone 130 is an
ash zone, from which ash may be removed into ash receiver 135. Gas
offtake 133 is provided to reactor 100, for transferring gases
from reactor 100 to boiler 140 for recovery of heat contained in
the gases, and thence to gas cooler 150 via air/oxygen preheater
145. Gas cooler 150 is connected to gas storage vessel(s) 160,
which is equipped with water off-take 165. The gas outlet of
preheater 145 is also connected to burners 170, 171.
In use, reactor 100 is charged with carbon-containing materials
105 near its top which pass through pyrolysis zone 110 and
reaction zone 120 into ash zone 130 prior to removal from the
reactor 100 into ash receptacle 135. That is, as ash is removed
from reactor 100, successive charges of carbon-containing material
105 move down reactor 100 through zones 110, 120 and 130. Gaseous
products 115 of pyrolysis move downwards through reactor 100 into
reaction zone 120 where carbon present in carbon-enriched material
produced in pyrolysis zone 110 reacts with water vapour generated
in that zone or introduced into it, to produce a gaseous product
125 enriched in hydrogen and oxides of carbon which passes out of
reactor 100 through gas collection port 133. Waste heat present in
gaseous product 125 is recovered in boiler 140 from which the
gaseous stream passes into preheater 145, gas cooler ISO and then
into gas storage vessel 160. In preheater 145, oxygen or air are
preheated before being fed to burners 170, 171. A portion of gas
exiting preheater 145 is passed to burners 170, 171 where the gas
is combusted and the generated heat and combustion products are
directed to pyrolysis zone 110 and reaction zone 120 of reactor
100 so as to sustain the desired temperatures in those zones. In
gas cooler 150, water and other condensables 155 are removed from
the gaseous stream exiting preheater 145. Organic condensables may
be separated from water in stream 155 and returned to reactor 100.
Gas from gas storage vessel 160 typically predominantly contains
carbon monoxide, hydrogen and gaseous organics, and may be removed
from storage vessel(s) 160 for combustion and energy, recovery.
FIG. 2 is a schematic representation of a system for recovery of
energy from carbon-containing materials utilising a process in
accordance with the second embodiment of the present invention.
The system illustrated in FIG. 2 includes all of the components of
the system illustrated in FIG. 1 and additionally includes which
pressure boiler 180 connected to gas storage vessel(s) 160 and
provided with preheated air or oxygen 146 from preheater 145.
Exhaust line 185 from high pressure boiler is connected to reactor
100 and is equipped with valve 188, and is also connected via line
187 to gas cooler 190. Line 187 is equipped with valve 189. Gas
cooler 190 is connected to carbon dioxide storage 195.
In use, the system illustrated in FIG. 2 is operated in the same
way as the system illustrated in FIG. 1, as described above,
except that gas stored in gas storage vessel(s) is not removed for
combustion but is sent to high pressure boiler 180 for combustion.
Exhaust from boiler 180 typically contains predominantly carbon
dioxide and water vapour and is normally returned via line 185 to
reactor 100. That is, normally valve 188 is open and valve 189 is
closed. If it is desired to remove carbon dioxide from the system,
valve 188 may be closed and valve 189 opened, to direct exhaust
from boiler 180 to as cooler 190 and thence to carbon dioxide
storage 195.
FIG. 3 is a diagram of a suitable reactor for carrying out a
process in accordance with the invention. As seen in FIG. 3,
reactor 200 includes hopper 210 and reaction chamber 220 below
hopper 210. Hopper 210 and reaction chamber 220 are separated by
neck region 215 which is closeable by first bell valve 240. Second
bell valve 230 permits the upper end of hopper 210 to be closed to
the atmosphere. Above second bell valve 230 is charging port 250
for charging solid materials into hopper 210. Hopper 210 is
equipped with steam inlet 212 and steam outlet 216, which are
fitted with isolation valves 213, 217 respectively.
Reaction chamber 220 is surrounded in its upper portion by firebox
285 equipped with vents 288 for admission of combustion gases from
firebox 285 into reaction chamber 220. Reaction chamber 220 is
also equipped with ash removal valve 275, gas offtake manifold 293
and gas supply manifold 290 which is connected via gas return 295
to an upper portion of reaction chamber 220.
During continuous operation of reactor 200, first bell valve 240
is normally in the closed position and second hell valve 230 is
moved to the open position for charging carbon-containing material
245 into hopper 210 through charging port 250. When this charging
step has been completed, second bell valve 230 is moved to the
closed position and steam is passed through hopper 210 from steam
inlet 212 to steam outlet 216 by opening valves 213, 216, for a
time sufficient to purge substantially all of the air from hopper
210. Valves 213, 216 are then closed and first bell valve 240 is
opened to permit carbon-containing material 245 to fall into
reaction chamber 220. Materials in reaction chamber 220 occupy a
pyrolysis zone 250 above reaction zone 260 and ash zone 270. In
pyrolysis zone 250 coking or charring of carbon-containing
material 245 occurs at the elevated temperature maintained in
pyrolysis zone 250 owing to heating of reaction chamber 220 from
firebox 285. As additional carbon-containing material 245 is
charged into reaction chamber 220 and ash is removed from ash zone
270, material is pyrolysis zone 250 progresses through reactor
into reaction zone 260. In reaction zone 260, carbon-enriched
material from carbon-containing material 245 reacts with steam
generated in pyrolysis zone 250 or present in gases introduced
into reaction chamber 220 (for example from firebox 285 via vents
288 or through gas return 295) and produces hydrogen and mixed
oxides of carbon. These gases are removed into gas off take
manifold 293. Some gases in gas off-take manifold 293 are returned
to firebox 285 (connection not shown) or returned to gas supply
manifold 290 and thence via gas return 295 to reaction chamber
220. However, the majority of gases are taken off for combustion
and recovery of useful energy therefrom. With further charges of
carbon-containing material into reaction chamber 220 and
progressive removal of ash 270 via ash removal valve 275, material
in reaction zone 260 eventually reaches ash zone 270 and is
ultimately removed from reactor 200.
FIG. 6 is a schematic representation of an alternative system for
recovery of energy from carbon-containing materials utilising a
process in accordance with the third embodiment of the present
invention. Referring to FIG. 6, the system includes reactor 300
which is charged with carbon-containing materials 305 in an tipper
part of reactor 300. Below carbon-containing materials 305 is
pyrolysis zone 310 in which carbon-containing materials 305 are
converted to carbon-enriched materials. Beneath pyrolysis zone 310
is reaction zone 320 in which the carbon-enriched materials react
with water vapour to produce hydrogen and oxides of carbon. Zone
330 is an ash zone, from which ash may be removed into ash
receiver 335.
Gas offtake 333 is provided to reactor 300, for removing gases
from reactor 300. Pipe 338 connects gas offtake 333 to gas
scrubber system 340 in which reactor gases may be separated from
condensables. Gas scrubber system 340 is equipped with
condensables offtake 345 and pipe 346 which connects gas scrubber
system 340 to gas separation system 350 and conveys gases from gas
scrubber system 340 to gas separation system 350.
Optionally, the heat content of gas removed from reactor 300 by
gas offtake 333 may be utilised before the gases reach gas
scrubber system 340. For example, gases in pipe 338 may be passed
though a heat exchanger (not shown) for recovery of useful heat
energy, or the gases may be used to heat the pyrolysis zone and/or
reactor zone of another reactor similar to reactor 300 (also not
shown) being operated at the same time as reactor 300 for recovery
of energy from other carbon-containing materials.
Gas separation system 350 is typically a gas decant system but may
include any suitable means for separating hydrogen, at least
partially, from other gases present, predominantly oxides of
carbon, and nitrogen. Thus, gas separation system 350 is connected
to two gas storage units 351, 352 to permit gases separated in
separation unit 350 to be passed to, and stored in, storage units
351 and 352 for hydrogen-rich and hydrogen-depleted gases
respectively.
Gas storage unit 352 is connected to furnace 360. A supply of air
and/or oxygen is also connected to furnace 360 (not shown).
Exhaust from furnace 360 is connected via line 365 to heater
jacket 370 which is provided to reactor 300. Line 365 is also
equipped with valve 368, an outlet of which is connected to
exhaust 369, which is open to the atmosphere.
Gases leave heater jacket 370 and are led to the interior of
reactor 300 via pipes 375, 375a. Pipes 375, 375a may be equipped
with an exhaust vent to atmosphere (exhaust vent not shown) which
is normally closed by means of a valve but which may be opened if
necessary to release pressure or divert combustion gases exiting
furnace 360 away from reactor 300 if desired.
Reactor 300 is equipped internally with a plurality (typically 4)
of downcorners 385 (two shown in FIG. 6) which extend from above
pyrolysis zone 310 to below reaction zone 320, and with a
plurality (typically 8) of risers 386 (two shown in FIG. 6) which
extend only part of the depth of reactor 300 and typically end in
or above reaction zone 320. Risers 386 are connected at their
upper end via manifold 380 to gas offtake 333. Alternatively;
pipes similar to 375, 375a may lead from heater jacket 370 into
ash zone 330 of reactor directly, instead of into zone 305 as
shown. In that case (which is not shown in FIG. 6) downcorners 385
are omitted.
Gas storage unit 351 is connected to boiler 390 which is equipped
with exhaust vent 398, and steam line 396 which leads to
electricity generation system 395.
In use, reactor 300 is charged with carbon-containing materials
305 near its top, which pass through pyrolysis zone 310 and
reaction zone 320 into ash zone 330 prior to removal from the
reactor 300 into ash receptacle 335. That is, as ash is removed
from reactor 300, successive charges of carbon-containing material
305 move down reactor 300 through zones 310, 320 and 330.
Carbon-containing materials 305 are pyrolysed predominantly in
pyrolysis zone 310 with the generation of carbon-enriched solids
and gaseous pyrolysis products. Also introduced into reactor 300
are combustion gases produced in furnace 360 and passed into
reactor 300 via heater jacket 370 and pipes 375, 375a. These
combustion gases mix in zone 305 with gaseous pyrolysis products
produced in pyrolysis zone 310 and the mixture passes through
downcorners 386 and up through reaction zone 320 before entering
risers 386 and leaving reactor 300 via manifold 380 and gas
offtake 333. In reaction zone 320, water vapour generated
predominantly in pyrolysis zone 310, and carbon dioxide, react
with carbon-enriched material in reaction zone 320 to produce
gaseous products enriched in hydrogen and carbon monoxide.
From gas offtake 333, the mixed gases pass via pipe 338 to gas
scrubber system 340. Gas scrubber system 340 may comprise any
suitable means for separating gases from condensable substances,
such as oils volatilised from carbon-containing materials 305 in
pyrolysis zone 310. For example, gas scrubber system 340 may
comprise a water scrubber for separating gases from less volatile
substances, equipped with a decanter for separating oils from
water. Reactor gases separated in gas scrubber system 340 are
transferred via pipe 346 to gas separation system 350, in which
hydrogen is at least partially separated from other gaseous
products.
Thus, two gaseous streams exit gas separation system 350. A first
stream which is relatively hydrogen-rich, passes to storage unit
351 and the seemed stream passes to storage unit 352 prior to
being passed to furnace 360 where it is burned in air or oxygen.
The combustion product gases are conducted through line 365 to
heater jacket 370 of reactor 300, for heating pyrolysis zone 310
and/or reaction zone 320 of reactor 300, and hence via pipes 375,
375a to the interior of reactor 300 as described above.
If desired, valve 368 may be partially opened or completely opened
temporarily to divert combustion gases 365 partially or completely
to exhaust.
The gases in gas storage unit 351 are utilised as combustible fuel
for recovery of energy, by generating electricity. Thus, gas from
gas storage unit 351 is burned in boiler 390 to raise steam which
is passed via steam line 396 to electricity generation system 395.
Electricity generation system 395 typically includes a turbine and
generator of conventional design.
At startup of the system, if no or insufficient gas is stored in
gas storage unit 352, an alternative combustion fuel is supplied
to furnace 360. This alternative fuel may be fuel oil, natural gas
or similar, or may conveniently include oils removed from gas
scrubber system 340 via condensable offtake 345 during a previous
operation of the system.
Since the processes of the first and second embodiments of the
invention may be operated as essentially a closed system, or at
least one in which the quantity of gaseous effluent is
substantially decreased compared to processes which rely on total
combustion of organic materials in waste, they are processes with
little or no adverse impact on the environment. Although a process
in accordance with the third embodiment of the invention may
release carbon dioxide to the atmosphere, it provides a process
whereby useful energy can be recovered from waste materials with a
net reduction in the volume and other problems associated with
disposal of the waste. However, as noted above, the process of the
third embodiment may be operated essentially as a closed system
with regard to oxides of carbon, so that any carbon introduced
into the reactor in the waste material or other carbon-containing
material, leaves the system not as carbon dioxide, but as
elemental carbon. Other major byproducts of the process are water
and ash, which may be utilised as a soil substitute or soil
conditioner. The other major by-product of the process, namely
water, is in increasingly short supply in many parts of the world,
and the process of the invention provides a new source of water
which may be used, for instance, for irrigation or in domestic
water supply (after appropriate treatment).
EXAMPLE
The following is a description of laboratory scale trials of a
process in accordance with the invention.
Apparatus
The reactor was constructed as in FIG. 4 with schedule 40 pipe and
8 mm plate. In FIG. 4. FIG. 4A is a vertical cross-sectional view
of die reactor, FIG. 4B is a plan view of the reactor, and FIG. 4C
is a diagrammatic representation of the relative position of gas
offtake points from the reactor. Legs, bracing and footings were
constructed from 3*3*0.25-inch (75*75*6.4 mm) angle section. All
flanges and blanks were ANSI 300 lb (2070 kPa) fittings. The lid
to the reactor, a 24'' (600 mm) flange & blank (ANSI-300 lb
(2070 kPa)) was fitted with pressure relief valve set at 100 psi
(689 kPa) and pressure gauge. It was also fitted with a 2.5'' (64
mm) flanged stub and ball valve to allow access of a steel,
graduated dipstick.
As seen in FIGS. 4 and 5, the reactor consists of a firebox 400
surrounding the upper part of the reactor body 450 which consists
of an annular space 410 defined in part by the firebox 400 and by
central downcorner 420. Firebox 400 opens into the reactor body
450 through openings 405, just above the top of downcorner 420.
The overall height of the reactor, not including its legs, is 3.9
m. Downcorner 420 has a diameter of 0.6 m and annular space 410
has a thickness of 0.3 m. Firebox 400 has a height of 2.0 m and an
outside diameter of 1.2 m, the upper end of firebox 400 being 3.15
m above the lower end of downcorner 420. Downcorner has length 3.0
m and opens at its lower end just above a 0.4 m deep tapered end
of reactor body 450. At a height of 1.5 m above its lower end,
reactor body 450 is equipped with gas outlets 430.
Four gas ring burners were installed at 90-degree rotation
intervals at the 0.25 m elevation from the bottom of the firebox
and with the tip of the flame impinging on the heating surface of
reactor body 450. Four more gas ring burners were placed at 45
degree rotation from the first set and again 90 degrees rotation
between the burners at the 1.25 m elevation. Each burner ring was
individually equipped with an isolation valve. 0.5'' (12 mm)
sockets at 4 locations served as inlets for compressed air.
The complete outside surface of the apparatus was insulated with
asbestos cement fibre and coated with phenolic resin. The internal
surface of the external walls of the firebox was coated with
vermiculite refractory paste.
This design results in a 12'' (300 mm) thick annular space to be
charged with waste and heated by the flame on one side and hot
exhaust and volatile gases on the other.
The combustion gases pass from the firebox 400 into the reaction
chamber through 6'' (150 mm) holes 405 and mix with volatile gases
generated by heating carbon-containing material in annular space
410, and the gases pass down the downcorner 420. These gases then
exit the downcorner 420 and migrate back up through carbonaceous
residue in the lower part of annular space 410, to exit to a
compressor 460 by way of 4*6'' (150 mm) outlets as illustrated
diagramatically in FIG. 4C, and a manifold fitted with a rupture
disc.
From the compressor 460, the gas/vapour passes through a
water-cooled heat exchanger 470 and into one of two parallel piped
storage vessels 1, 2, as illustrated schematically in FIG. 5. The
storage vessel design includes a steam trap, fitted with a "goose
neck" water draw. Further it is fitted with 100-psi (689 kPa)
pressure gauge, pressure relief valve, gas purge and product
effluent valves. The effluent valves are joined together by way of
a manifold and then connected to a second compressor 480 by way of
a pipe section containing a rupture disc. The second compressor
480 is then connected to the burner feed manifold. Air compressor
490 supplies air for combustion to firebox 400.
A bottled LPG manifold 3 set up as the initial heat source is also
connected to the burner feed manifold.
Charge Volume Calculation
Volume of waste zone
Outer diameter 0.6 m
Inner diameter 0.3 m
Length 2 m
Volume annular space 0.424 m<3>
Volume of carbon zone
Outer diameter 0.6 m
Inner diameter 0.3 m
Length 1 m
Volume annular space 0.212 m<3>
Volume of ash zone
Cone volume 0.038 m<3>
Height 0.4 m
Diameter 0.6 m
INITIAL CHARGE VOLUME 0.674 m<3>
DESIGN CHARGE/HR 0.4 m<3>
Destruction-Principles Involved.
On filling the reactor the waste feeds into the annular space
between the firebox and the central down comer. On entrance to
this space the waste is in the coking (pyrolysis) stage.
Stage I-The Coking Stage
The coking stage of the process takes place in the top 2 m of the
reactor where complex organic compounds are broken down by heating
them to temperatures above 400[deg.] F. (205[deg.] C.) to produce
carbon or char, low molecular weight organics (which volatilise),
water (which is converted to steam) and silica and inorganic ash.
All except the carbon, silica and inorganic ash exit the reaction
in the gas phase. The residual solid is coke or char.
The gas and vapours pass down through the centre co-axial pipe
(the path of least resistance) to exit and migrate back up through
the coke residue where they take part in the Stage II reactions in
which water vapour is converted to water gas.
Stage II-Water Gas Production
WATER GAS (or Blue gas) is produced when steam is blown through an
incandescent bed of Carbon.
The gas production reactions are primarily:
C+H2O=CO+H2
C+2H2O=CO2+2H2
These reactions occur when the water from the waste (steam) is
passed back through the residual coke or char in the bottom 1-m of
the reactor. Both of these reactions are endothermic. Therefore,
the temperature of the bed of carbon through which the steam is
blown would he lowered quickly to a point where no reaction would
occur, if no heat were added to the system.
Operation
Initial Charge
1. The system was constructed and assembled as in FIGS. 4 and 5.
2. The gas extraction and feed lines to the system were
hydraulically tested.
3. The reactor was filled with coconut shells (0.6 m<3> )
and the reactor was sealed.
4. The system was purged with steam.
5. The cooling water system was started and valves in the gas
extraction line to tank 1 were opened.
6. The LPG gas flow and air compressors were started and the gas
was ignited.
7. When the reactor pressure had risen to 60-psi the exhaust
compressor was started with feed to storage tank 1.
8. When the reactor pressure fell away gas to the burners was
stopped.
9. The dipstick ball valve was opened and the system shut down.
10. The reactor was dipped. Steps 3 and 5-9 (but not step 4) were
repeated if the bed depth was below 2 m from the top close valve.
11. If the bed depth was above 2-m, ash was removed to this level
by opening the bottom hatch.
Methods-Testing Procedures
1. Three consecutive charges of 0.4-m<3 > of each of the
following were sequentially added to the reactor.
Municipal Garbage
Rubber tyres
Wet Bagasse
Saw Dust
Oil Sludge
2. The reactor was filled with the respective charge (0.4
m<3> ) and the reactor was scaled.
3. The cooling water system was started and the valves in the gas
extraction line to tank 1 were opened.
4. The gas flow was started from the previous gas storage tank and
the air compressors and the gas was ignited. If no as was
available the LPG gas valve was opened.
5. When the reactor pressure reached 60 psi (about 415 kPa), the
exhaust compressor was opened with feed to the current storage
tank.
6. When the reactor pressure fell away the gas to the burners was
stopped, the dipstick ball valve was opened and the system shut
down.
7. The reactor was dipped.
8. Steps 1-7 were repeated for the next charge.
Results
Fired by
1 Charge 1-Garbage LPG
depth at end of previous 220 cm
charge
depth at end of current 230 cm
charge
residual from this charge 0.1 m
volume 0.021214 m<3>
2 Charge 2-Garbage Produced
gas
depth at end of previous 230 cm
charge
depth at end of current 240 cm
charge
residual from this charge 0.1 m
Volume 0.021214 m<3>
3 Charge 3-Garbage Produced
gas
depth at end of previous 240 cm
charge
depth at end of current 255 cm
charge
residual from this charge 0.15 m
volume 0.031821 m<3>
4 Charge 4-Tires Produced gas
depth at end of previous 255 cm
charge
depth at end of current 300 cm
charge
residual from this charge 0.45 m
volume 0.095464 m<3>
5 Charge 5-Tires LPG
depth at end of previous 300 cm
charge
depth at end of current 350 cm
charge
residual from this charge 0.5 m
volume 0.106071 m<3> ash
removed 200 Liters
94.27609 cm
6 Charge 6-Tires LPG
initial dip 205 cm
depth at end of current 260 cm
charge
residual from this charge 0.55 m
volume 0.116679 m<3>
7 Charge 7-wet bagasse LPG
initial dip 260 cm
depth at end of current 275 cm
charge
residual from this charge 0.5 m
volume 0.031821 m<3>
8 Charge 8-wet bagasse
Produced gas
initial dip 275 cm
depth at end of current 280 cm
charge
residual from this charge 0.05 m
volume 0.010607 m<3>
9 Charge 9-wet bagasse
Produced gas
initial dip 280 cm
depth at end of current 295 cm
charge
residual from this charge 0.15 m
volume 0.031821 m<3>
10 Charge 10-saw dust Produced
gas
initial dip 295 cm
depth at end of current 310 cm
charge
residual from this charge 0.15 m
Volume 0.031821 m<3>
11 Charge 11-saw dust Produced
gas
initial dip 310 cm
depth at end of current 320 cm
charge
residual from this charge 0.1
volume 0.021214 m<3>
12 Charge 12-saw dust Produced
gas
initial dip 310 cm
depth at end of current 320 cm
charge
residual from this charge 0.1 m
volume 0.021214 m<3>
13 Charge 13-oil sludge
Produced gas
initial dip 320 cm
depth at end of current 325 cm
charge
residual from this charge 0.05 m
volume 0.010607 m<3>
14 Charge 14-oil sludge
Produced gas
initial dip 325 cm
depth at end of current 340 cm
charge
residual from this charge 0.15 m
volume 0.031821 m<3>
15 Charge 15-oil sludge
Produced gas
initial dip 340 cm
depth at end of current 355 cm
charge
residual from this charge 0.15 m
Volume 0.031821 m<3>
residual at end of test 355 cm
0.75 m<3>
total through put 6.6 m<3>
% ash 11.41
waste converted to gas 5.8 m<3>
The above results indicate that the destruction of rubber tyres
does not sustain gas production. This is to be expected given the
carbon content and lack of water. It could be expected that if it
were mixed with a high water waste it would effect a very good
yield of water gas.
Given the results of the tyre destruction it was decided to
continue tyre destruction to assess the gas production. It was
found that a further 5 charges of tyres was possible before the
produced gas was exhausted and the system required the supplement
of LPG.
The above results indicate that there is excess gas production
from the destruction of most wastes, compared to the quantity of
gas which is required for the destruction of the waste. In
particular municipal garbage could be effectively disposed in this
manner.