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The Technology of Low Temperature Carbonization
by
Frank M. Gentry
[ Chapter 8: Economics & Conclusions ]
Table of Contents
Preface & Table of
Contents
Chapter I ~ Fundamentals
Chapter II ~ Low Temperature
Coal Gas
Chapter III ~ Low Temperature
Coal Tar
Chapter IV ~ Low Temperature
Coke
Chapter V ~ Nitrogenous &
Other By-Products
Chapter VI ~ Processes of Low
Temperature Carbonization
Chapter VII ~ Operation, Design,
& Materials of Construction
Chapter VIII ~ Economics & Conclusion
Bibliography
Name Index
Subject Index
[ Note: The quality of the scanned graphics (tables & figures) are "uneven" at best despite repeated efforts to scan and tweak the images. Enough is, so here it is anyway: I've had enough and done enough for the time being. ~ R.N. ]
Economics & Conclusion
Yields
Revenue From Operation
Capital & Operating Costs
Economics
The Coke Market
The Gas & Light Oil Markets
The Tar Market
The Fixed Nitrogen Market
Potential Markets
Central Station By-Product Recovery
Plant Location
Fuel Resources
Conclusion
There are such variations between individual processes and particularly between individual coals that it is difficult to make generalized statements on yields from low temperature carbonization. It is well to remember that no processing can increase the heat yield per ton of coal. Aside from a slightly better heat balance in the low temperature process, it must be remembered that individual processes differ only in the distribution of heat units between gas, tar and coke. Low temperature processes obtain more tar at the expense of less gas than the high temperature processes. Likewise, the lower temperature of the former yields less ammonia, and through the absence of cracking, a higher thermal value gas which naturally yields much light oil upon scrubbing.
To present some general idea of the economics of operating a low temperature carbonization plant, assuming the use of a medium grade high volatile bituminous coal as the raw fuel, some representative yields of various types of plants may be set down as a basis of comparison. For convenience of study, we may classify low temperature carbonization processes into 3 types as follows: Type 1, the average externally heated low temperature retort; Type 2, the average internally heated low temperature retort; and Type 3, the average low temperature process combined with complete gasification of the coke. Type 4, as hereafter given for comparison, represents average high temperature practice. The yields per net ton, given in Table 121, are based upon the various processes that have been proposed.
The data in Table 121, for low temperature processes, have been tabulated from the results reported by about 15 full-scale plants, as collected by the author, and as gathered by Sinnatt (357). The yields from high temperature operation are those reported by Tryon and Bennit (358) as the average results from by-product coke oven operation in the US. The reasonability of the results given in Table 121 have been checked by the heat balance given hereafter in Table 122. The fact that the data for Type 1, externally heated process, as given in table 121, are not the same as those reported in table 12 of Chapter I is not conflicting, for the former is an average result, while the latter is an individual case. This apparent difference illustrates what departures specific processes may take from the average yield. In this classification, it is assumed that the Type 2 plant obtains its heating medium by the introduction of air at the bottom of the retort to partially gasify enough of the fuel to distill the charge by the sensible heat of the producer gas thus generated, so that the 34,000 cubic feet of gas produced consist of a mixture of about 4,200 cu ft of low temperature coal gas and about 29,900 cu ft of producer gas. It is further assumed that in the Type 3 plant the low temperature and producer gas are mixed in the proportion of 4,200 cu ft of the former to 107,800 cu ft of the latter.
On the assumption of a 13,000 BTU/lb raw coal, the average calorific value of the semi-coke, in the case of Type 1, is about 12,850 BTU/lb, while the solid residuum in Type 2 has a higher ash content, due to partial gasification, an hence a lower calorific value of about 12,350 BTU/lb. These figures check with the results of a number of full-scale experiments. The average calorific value of low temperature tar ranges from 15,000 BTU to 16,500 BTU/lb. From these figures it is possible to construct a heat balance of the various types of carbonization processes, as given in Table 122. There is very little doubt that Type 2 has the greatest thermal efficiency, compared with the others. This arises from the fact that the heat is generated where it is used, thus increasing the efficiency of heat transfer and reducing radiation losses. The externally heated low temperature process, or Type 1, is next the most efficient, because in comparison to high temperature processes, the thermal gradient is lower with corresponding reduction in heat losses. Furthermore, less sensible heat is carried away by the solid and volatile products.
From the yields reported in Table 121 and known market prices for the products of Type 4, it is possible to construct a financial account for the other types of processes, which, barring prejudice, will represent a fair financial statement in the average case. But is must be borne in mind always that the average represents only a probable condition and a specific situation bears no relation to the average, whatever, but depends upon local market conditions and upon binding contracts for the delivery of large quantities of certain of the carbonization products. Take, for example, the Type 4 process of Table 121, which represents the average high temperature by-product coke oven. As reported by Tryon and Bennit (358), the average price received in the US during 1926 for by-product coke was $6.95/ton, while the same coke, when sold wholesale for domestic fuel, brought an average of $7.40/ton. The coke breeze, of which the total coke yield amount to about 6.5%, was disposed of at an average price of $3.50 per net ton. The average price in the US of by-product coke tar was $0.051/gal and 93.3% of it was used for fuel in boilers and in open hearth or other metallurgical furnaces. The average price of coke oven gas was $0.163 per thousand cu ft, but this average was composed of a wide variation of sale prices. Of the entire by-product of oven gas yielded in the US during 1926, 25.5% was sold for city gas at $0.335 per thousand cu ft, 8.2% was sold as industrial fuel at $0.162 per thousand cu ft, 62.5% was sold to steel mills at $0.112 per thousand cu ft, and the remaining 6.6% was used as boiler fuel at $0.55 per thousand cu ft. Gentry (359) has also pointed out a specific case of this variation in price for a single by-product coke plant.
On the basis of the average prices quoted above and of the average yields reported in Table 121, the author has estimated in Table 123 the average revenue to be expected in the US for Type 4 process. Type 4a is based upon the average known sale prices, while Type 4b is based upon the assumption that all the coke was sold at the average known price received for domestic coke and that all the surplus gas was sold at the known average price obtained for wholesale city supply. The average cost of raw gas coal at the ovens in the US during 1926 was $43.88 per net ton, according to Tryon and Bennit (358). It is possible to use, in low temperature carbonization processes, classes of high grade, high volatile, but yet cheaper coals, which are not suitable for use in high temperature ovens. It is reasonable, therefore, to value the raw coal for a Type 1 process at $3.25/net ton and that for Type and type 3 processes, which can satisfactorily use a lower grade of fuel, at $3.30/net ton. Figured conservatively, n a straight heat content basis from the average price of $0.335 per thousand cubic feet received for coke oven gas sold for city use, the Type 1 process gas is worth $0.54 per thousand cubic feet. N a straight thermal basis, type 2 gas is worth $0.075 per thousand cubic feet and Type 3 gas should bring $0.055 per thousand cubic feet when calculated from the average price of $0.163 obtained for coke oven gas in the US. This more conservative evaluation of the lower calorific gas is adopted because of the greater difficulty associated with its disposition. The price of $0.065/gal assigned to low temperature tar is half a cent higher than that given by Porter (360), is equal to a contract price reported by Runge (361), and is considerably below the value assigned to it by many other authorities. The light oil has been figured at $0.228, which is the average pric3 obtained for benzol in the US during 1926. In all cases, the average ammonium sulfate sale price of $0.021/lb during the same year has been used. The value of Type 2 coke for domestic fuel is deemed equal to that of type 4b, while, all things being considered, that of Type 1 coke should be sold easily at the slightly enhanced price of $7.75/net ton. This figure is considerably lower than that given by Runge (361) and that known to the present author for individual sales.
Since the market conditions in Europe are different from those in the US, and in particular since the operating costs, due largely to cheaper labor, are lower, one may expect lower gross revenue from a carbonization plant in operation abroad than from one in the US. The data in Table 124 are largely from full-scale plants existing in Great Britain. The figures for the Maclaurin plant are after Tupholme (248), those for Coalite are by Everard-Davies (362), those for the Tozer process were announced by the management (363), Tupholme (251) reported the data on the Nielsen process, Runge (361), those for the K.S.G. retort, and Sinnatt (357) secured the figures for the Pure Coal Briquet or Sutcliffe-Evans process from the management. The average gross revenue for these 6 plants is $3.60/ton, which is somewhat greater than the $2.16/ton computed by Pope (364) using ver6 conservative yields, slightly greater than $3.14 given by Brooks (365), and considerably less than the $4.32 figured by Runge (366).
The capital expenditure required to erect a complete low temperature carbonization plant is difficult to ascertain; first, because there is such a variation between the many processes that have been devised and between the numerous coals treated; second, because there is a wide divergence in the cost of labor and material in various localities; and third, because little has been made public, or few records kept, of those large-scale plants which have been built. Even if such records were available, these plants were more or less experimental in nature and many expensive alterations, which would not have been necessary in another installation, were made. The by-product plant, however, is more or less standard, so that for these items in the capital cost, a fairly accurate estimate can be made. As far as the by-product condensing, the light oil scrubbing, and the ammonium sulfate are concerned, a very careful estimate, on a comparative basis, has been made from standard practice. Including everything except land, power plant, and gas-holders, the cost estimates for the various types of plants previously discussed are given in Table 125 on the basis of the investment required per net ton of daily coal throughput. Type 1a refers to the average externally heated low temperature process which involves a large number of static units, while Type 1b refers to an average externally heated low temperature process which involves a large dynamic unit, such as a rotary retort. It is assumed that the plant capacity will be at least 1000 tons of coal per day.
The only point that can really be questioned in Table 125 is the item representing the cost of the various retorts and settings. In justification of these estimates, it may be said that many have been quoted at a higher and many at a lower figure, and in the absence of a more complete knowledge of costs, those estimated in the table are considered as close an approximation as one may expect. As a matte of fact, the present author has record of 11 independent estimates of the total cost of 6 specific low temperature carbonization plants complete, including by-product equipment, the average of which is $1,495 per ton of daily throughput. This is considered an excellent check on the figures of Table 125, when it is noted that the average of the four types of processes is $1,540/ton of daily throughput. Four independent estimates of two Type 2 processes known to the author averaged $1,265 and compare favorably with $1,290 given in the table. Likewise, 3 independent estimates of two Type 1a processes known to the author averaged $1,635, which is in fair agreement with the figure tabulated. In special cases, it is not doubted that the investment given in Table 125 can be considerably reduced, even to the figure of $800/ton of daily throughput, quoted by Brooks (365) as being conservative, but hardly to $600, as given by some other writers unless, of course, radical omissions or departures are made from standard by-product equipment.
Turning attention now to operating expenses and fixed charges, the essential items of cost, as distributed among various accounts, are estimated in Table 126, on the basis of cost per net ton of coal processed, assuming 90% capacity factor for the plant. The supplies include, among other minor items, the sulfuric acid necessary in the manufacture of ammonium sulfate, the steam includes that admitted to the retort and that used in the by-product plant, while the power includes all the requirement for driving the retort mechanism, coal-handling devices, conveyers, pumps, etc. In justification of these figures, it may be said that the average of 5 independent estimates and the records of total operating expenses for different low temperature plants known to the author was $1.39 per ton of coal treated, with a range extending from $1.58 to $1.20. This is in good agreement with the figures given in Table 126. The average cost of labor and supervision combined, as reported in 13 independent estimates known to the author on 6 specific processes was $0.61 per ton of coal. Eight estimates of maintenance and repairs on 5 specific processes averaged $0.36 per ton of coal, while 5 estimates of power and steam for 3 specific processes gave a mean figure of $0.22 per ton of coal. Consequently, the figures of Table 126 are taken to agree with the concensus of expert opinion, both individually and as a whole, although they are somewhat higher than the $0.94 per ton given by Pope (364) for the total average operating expense in low temperature installations. It should be noted that no charge for heating the retorts or for the raw coal has been made in Table 126, as these expenses have already been charged off of the gross receipts in Table 123, the former, by computing the revenue only on surplus gas. It now remains to write off fixed charges, at the rate of 10% for depreciation, 8% for interest on investment, and 3% for taxes and insurance, to give the total operating and fixed charges per ton of coal treated. Subtraction of the total operating and fixed charges per ton of coal in Table 126 from the gross revenue per ton of coal in Table 123 gives the net revenue available for amortization of the investment, reserve funds, and dividends.
Of all the items making up the cost of processing coal by carbonization at low temperatures, the fixed charges are the greatest, cost of labor is second, and maintenance and repairs are third. This indicates that economical primary carbonization requires, first, that the investment per unit throughput must be reduced to a minimum; second, that labor requirements must be kept as low as possible, by simplicity of operations and by the installation of labor-saving machinery; and third, that rugged construction and continuous operation with mass throughput should be encouraged, to gain the benefit of low repair and maintenance charges. Supervision and supplies are practically irreducible quantities.
So far as the economics of low temperature carbonization are concerned, the production of primary products is the only part of the problem which needs consideration, for upon these alone the industry must justify itself. The fractionation of low temperature tar into its many derivatives is another industry, that of tar refining, and it is not anticipated that the economics of primary oil distillation will be greatly different form those already obtaining in the petroleum and tar refining industries, notwithstanding certain plant changes as will be necessary to facilitate treatment of a different crude oil stock.
The sale of low temperature tar and gas is a wholly new problem from that of the disposition of gas and tar from by-product coke ovens or from gas retorts, for they are distinctly different from the analogous products of high temperature distillation. The same may be said of low temperature coke. Nevertheless, there is bound to be a certain amount of indirect competition between them, to the extent that the price fluctuations of the products of the two different methods of coal processing can never be wholly unrelated.
Table 127, illustrating the products of low temperature carbonization and their uses, as slightly modified by the author, was compiled by Ditto (367) and given later by Blauvelt (368). It shows very strikingly a few of the more important derivatives to be obtained from the primary products of coal and the manner in which they are absorbed by the industry. It will be readily appreciated that this table resembles in part a similar tabulation of the products and uses of high temperature by-product coking, of gas manufacture, and of petroleum distillation. A few of the products which occur in each of these industries are missing, and other products take their place. As a whole, however, the final uses are practically the same, a situation which demonstrates an ultimate relationship in the market fluctuations of high and low temperature carbonization products. The difference in the price levels of the two distinct classes of products must, therefore, be justified by their special values and the price movements of each will reflect, not only the conditions of supply and demand for products of its own class, but also for products of the other class. For this reason, no discussion of the economics of low temperature carbonization can avoid a study of the markets for high temperature products. A very excellent and comprehensive study of the problem of marketing the by-products from coal carbonization has been made by McBride (369).
Practically all of the products of coal carbonization compete industrially with other materials. Thus tar, as a fuel, must compete with both anthracite and bituminous coal, as well as with petroleum, and coke must compete with anthracite both as a domestic fuel and a s a fuel for the generation of water gas. Coal gas and water gas compete for their place as domestic and industrial fuels. Light oil is used mostly as a motor fuel, and as such its price is determined by the market for petroleum and its refined products. Ammonia, used largely as a fertilizer, has its price determined by the availability and supply of other forms of fixed nitrogen.
Aside from the prices for carbonization products determined by competitive markets, the rulings of public regulatory bodies further complicate the sale of by-products, particularly in the case of gas, which finds its most logical market in the city gas supply. In ordinary industrial enterprises, the margin of profit is determined by competition, but under the system of public utility regulation, the profits are limited by a public authority endowed with the power of establishing rates. Under such a system of regulation, the consumer of one or more of the products must bear the loss of income from other products. Consequently, a situation arise by virtue of this close relationship, whereby the price of one product can be almost entirely determined by the market conditions for another.
While there are assuredly markets for coke, gas, and oils, they are not, at the present time, markets in which any special advantages of low temperature products are recognized. There is a difference in the quoted prices of foundry and of furnace coke by virtue of their special properties, but there can be no reflection of special value in the price of low temperature coke over coal as a domestic fuel until this special value is recognized by consumers. In the case of low temperature gas, the recognition is not hard to secure, but appreciation of the desirable nature of primary oils will be somewhat more difficult to obtain. It is an illogical proposition to expect an industry to pay the cost of treatment without being entitled to some financial return over the cost of preparing products which are ore desirable for particular purposes. As long as the fundamentals of such an industry are sound, the special value of the products will ultimately be reflected in their price.
A good deal has been said at one time or another about the calorific value of semi-coke, relative t the raw coal from which it was made. As this is the characteristic of most importance in determining the value of low temperature coke, it is worthwhile to examine this point. Runge (366) has determined the thermal value of many semi-cokes produced from coals of the US and elsewhere, as compared with the calorific value of the raw coal before primary distillation. He found, as a general rule for high volatile low oxygen coals, that the thermal value of the coke was from 700 BTU/lb to 1000 BTU/lb less than that of the coal. With high volatile coals, the thermal values of the coal and coke were about the same, or the latter was slightly higher. This was particularly true of lignite, where, because of the high moisture content it was not unusual to find that the char had an increased calorific value of as much as 2000 BTU/lb over the raw material.
Another point of view, in assessing the value of a fuel, is the consideration of what is known as form value or heat availability. A consumer will obviously pay more for a heat unit in the form of gas or of oil in the form of coal or of coke, by reason of the adaptability of these fuels to special purposes, where the heat of coal would not be available. The object of all coal processing is to increase its form value and all processing is accompanied by losses of material, incidental to handling, and of heat units, incidental to the production of power and heat for processing. Consequently, the output of heat units after processing will be materially les than before, but their form or availability will be increased To be economically sound, the conversion of the heat units from one form to another, must be such as to increase the value of the units sufficiently to make up for the conversion losses, pay the cost of processing, and yield a fair return on the capital investment. Doubtlessly, low temperature carbonization raises the form factor of the fuel and increases the availability of heat.
The value of the carbonization products, other than the solid fuel, as seen from Table 123, represents approximately 40% of the total receipts for Type 1, externally heated processes; about 56% for type 2, internally heated processes; and 100% for Type 3, complete gasification processes. It is quite obvious from this that unless the cost of the raw material be unusually cheap, as in the case of shales and coal refuse, low temperature carbonization can never be commercially successful in externally heated processes for the sake of by-products alone, unless there is a great advance in the market price of these materials, relative to the raw coal. It is absolutely essential to the success of externally heated processes that the semi-coke be disposed of adequately, and almost correspondingly essential, in the case of internally heated processes by partial gasification, that the by-products be well marketed. Low grade slack coal is particularly adapted to low temperature carbonization processes. There are many mines in the US and abroad which are closed now but which are capable of producing large quantities of this material. The reopening of such workings to fulfill the demands of a new industry would not only be of mutual benefit, but of national economic importance.
In considering the economics of carbonization, McBride (370) has pointed out that the counter-effect of fluctuations in the price of one by-product on the value of another by-product, or of a principal product, must not be overlooked. In the gas manufacturing industry, for example, it is well known that the price of gas is roughly the difference between the gross expenditure and the income derived from by-products. Consequently, the lowering of ammonium sulfate by as much as one cent a pound may mean a difference of as much as 5 cents per thousand cubic feet of gas. The gas and coke from any coal carbonization industry have to fluctuate inversely with the price of ammonium sulfate to bear the increased cost of production.
Porter (360) has attempted to summarize the 3 phases of development that will give a great impetus to the progress of low temperature carbonization. Form the viewpoint of producing a smokeless fuel, these possibilities are: (1) to lower the cost of production below $1/ton; (2) to establish a sufficiently enhanced value for the semi-coke to enable it to bring a price equal to the coal from which it was made; and (3) to discover new uses for the primary tar and gases, such as will enhance their value above the by-product tar and gas of present commerce. Noteworthy advance in any of these fields will firmly establish the economics of low temperature carbonization, but all three phases will likely be solved in some measure of success. It is merely a question of raising the form value of the products and of lowering costs of conversion.
The only economic justification for low temperature carbonization, or any other carbonization system for that matter, is its ability to show a satisfactory yield on the capital invested, through recovery and sale of by-products. In the case of low temperature carbonization integrated with another industry, such as the manufacture of city gas or the generation of electricity, the financial return need be only such as will show a reduction in the cost per unit of the final product, but in the case of manufacture of a solid fuel, to be merchandized to domestic and industrial consumers, the financial return must be such as to carry the additional costs of distribution.
Unlike many European countries, low temperature carbonization cannot be justified in the US, at the present time, on the grounds of national defense. From a defense standpoint, the only products of importance are the oils and the fixed nitrogen. For oils, the US is now happily independent of other countries; for explosives, sufficient toluene and picric acid can be recovered in existing gasworks and by-product plants; and for nitrogen products, enough can be recovered from gasworks and coke plants, augmented by synthetic fixed nitrogen, to meet all emergency requirements.
In order to avoid confusion, Gentry (371) has noted that it is necessary to distinguish between the production of 3 types of solid fuel: boiler char, smokeless fuel, and anthracite substitute. These 3 cases are rather clearly defined and the price which the semi-coke can command depends greatly upon which of the 3 forms of fuel is produced. The manufacture of an artificial anthracite by low temperature carbonization certainly requires the application of pressure at some stage during carbonization. In some processes, we have seen that this takes the form of briquetting, before, after, or between stages of distillation; in others, the necessary compression is obtained by the weight of the superincumbent charge or by the intumescence of the coal. A number of attempts have been made to effect the same result by introduction of pistons, or other mechanical devices, within the retort. Although it may be said, that the application of pressure to the semi-coke, either by briquetting or otherwise, increases greatly the cost of processing, the resultant artificial anthracite will command a higher price because of its strength and density. Anthracite substitutes can be sold considerably below the market price for anthracite with a substantial profit, but a smokeless fuel cannot sell much below the raw coal and realize sufficient return on the investment. After all is said and done, in a new industry where the advantages of a new fuel are not tremendously self-evident, the new fuel cannot command a price greater than that of the established competitive fuel.
Of the several varieties of coke on the market, that is, beehive, by-product, gas coke, and semi-coke, the price and availability of anyone has its effect on the price of all the others, even though these classes of coke are not strictly competitive, since they are not always directly interchangeable. The first is used almost wholly for metallurgical purposes, the second is used for the manufacture of water gas and as a domestic fuel, as well as metallurgically, while the third s used almost exclusively for water gas manufacture, domestic fuel, and industrial heating. In no case is gas coke suitable for metallurgical purposes. As may be expected from this state of affairs, metallurgical coke plants often place their surplus coke on the market during slack seasons, thereby bringing about considerable price fluctuations and readjustments in the entire industry by a break in spot prices and a sag in the contract market.
Aside from the manufactured gas industry and the metallurgical coke industry, as sources of coke for domestic fuel, there has come into existence the merchant by-product coke ovens. Since these plants are related to neither of the foregoing industries, their existence is justified by their ability to undertake or arrange for the complicated marketing of their coke and by-products. For them, the favorable support of the local fuel merchants is a very necessary factor for their success.
Practically all by-product coke ovens use the breeze as a fuel, so that approximately 80% of it is used in this way. In both high temperature and low temperature practice, the breeze amounts, on the average, to about 10% of the total coke yield. It makes a fairly satisfactory boiler fuel, generally being combusted on chain-grate stokers, since high temperature breeze is too abrasive to pulverize economically. The friability of semi-coke, however, makes it somewhat more desirable as a pulverized fuel, and while there is great variation from process to process in its abrasiveness, generally it is no more abrasive and requires no more power to grind than bituminous coal, and in fact, some experiments report even less. About the only other outlet for coke breeze is to briquet it for a domestic fuel, but the cost of the additional processing, together with the fact that the breeze is always high in ash, makes this procedure undesirable if the products can be directly consumed.
Coke has been offered to the domestic market in sizes corresponding roughly to those familiar in the anthracite trade, that is, egg, stove, nut, pea, and breeze. It must, however, be as carefully sized as anthracite, for while stove or nut sizes can be used satisfactorily alone, if mixed indiscriminately with the other sizes, the tendency is for the fuel bed to pack, so that a satisfactory fire cannot be maintained. Since these sizes are smaller than the metallurgical sizes, the metallurgical coke industry stands a s a potential producer of domestic fuel, but they can never hope to compete seriously with a more satisfactory fuel, such as semi-coke, unless they are willing to undercut the latter considerably in price and are prepared to change their merchandizing policy, to the extent of assuring the domestic fuel market of an adequate supply at all times. As McBride (369) points out, there are many who believe the fluctuating demands of the metallurgical industry and the steady market for domestic fuel are too wholly incompatible phenomena and that is it utterly impossible to serve both ends at the same time.
The establishment of coke as a permanent domestic fuel, be it low temperature coke, gas coke, or by-product coke, will require a long educational program to overcome the inertia of the public, which is loath to change from established practice. The principal inducement to its use is a price differential in its favor, but often its introduction must be accompanied by an assurance of instruction in the proper method of using it.
Although coke is the best available substitute for anthracite, an is a potential substitute for bituminous coal, it has incurred great disfavor as a domestic fuel for two reasons; first, because of the uncertainty of the supply, due to the irregularity with which it is placed upon the domestic fuel market by the producers, and second, because of the inferior quality of the product diverted from metallurgical uses. Thus, much of the coke which has been placed in the domestic market, while suitable for metallurgical purposes, is wholly unsatisfactory for household use. Occasionally, coke containing excessive sulfur have been dumped on the domestic market by the manufacturers to the end that, while the ordinary domestic purchaser is little concerned with the chemical composition, the odor and corrosive fumes from such a high sulfur product are very objectionable and have, in consequence, injured the reputation of coke. For these reasons, any attempt to introduce low temperature coke extensively in some localities must be associated with an educational program which will eliminate the bad reputation that such indiscretions have aroused.
Much of the difficulty that has been experienced by domestic consumers with the use of coke has been its incombustibility, a feature which semi-coke does not share with the high temperature by-product or gas coke. The low temperature coke contains 2 or 3 times more volatile matter than the others and, structurally, it is of a far more combustible form. In the past, much coke with a low fusion point ash has been put on the market, with the result that the average householder has been annoyed with clinker formation.
Due to its greater bulk, weight for weight, coke requires more storage space than either anthracite or bituminous coal. Likewise, a greater furnace volume is necessary for the same frequency of firing. Some of the difficulties that have arisen from the use of coke may be attributed to the fact that too large sizes have been used in a furnace accustomed to anthracite, with the result that the fire burns out quickly and can be banked only with difficulty on account of the fuels' greater bulk.
The value of semi-coke, as a domestic fuel, depends entirely upon its physical condition when delivered from the retort. There is no doubt that, for domestic use, the semi-coke will have to be in lumps or in briquets. In this form it possesses all the desirable properties of anthracite, except possibly its density. On the other hand, it will, for the most part, contain less ash than the grades of anthracite now found on the market. Runge (366) feels that, as a competitor of anthracite, semi-coke could be marketed as a household fuel at $1/ton less than the former. Since anthracite sells at $8.50 to $9/ton f.o.b. mines and retails for $13 to $15/ton within a radius of 100 miles of the mines, allowing $2 for delivery charges, the semi-coke should be sold at the plant, located near the center of consumption, at $10 to $12/ton from which must be deducted a further $2/ton for merchandizing costs. It is not generally desirable for the carbonization plant to undertake merchandizing its coke, but it is more logical to arrange with local fuel merchants to take care of its distribution to the consumer. From the standpoint of the dealer, this involves new problems, for coke requires greater storage space in is yards, large delivery trucks, and must be handled with greater care of its distribution to the consumer. These considerations, together with the inherent hesitation of people to enter new fields, makes it necessary to offer the merchant a liberal profit, sometimes as much as $3/ton, to induce him to handle the product. Gas coke is often merchandized directly by the producer, however, first, because of the narrow margin of profit, and second, because the strength of the product is such that it will not stand the extra handling and haulage of the middleman.
Porter (360) has noted, in the matte of smoke abatement, that there is a great deal of human psychology involved. Despite the great economic loss to each individual in the form of expenditures for painting, laundry, etc., the consumer, when confronted with additional outlay to secure a smokeless fuel to reduce this atmospheric pollution, hesitates because the returns are intangible. Among the larger consumers, such as the railroads, utilities, and industrial manufacturing establishments, this hesitancy can be overcome by for of pubic opinion. To those, such as the domestic consumer and small manufacturer, who have to take close account of each outlay, the appeal to use smokeless fuels in place of cheaper competitive fuels is useless. Legislation to force smoke abatement upon the masses is as undesirable, as enforcement would be impracticable, so that the only rational solution is to provide a fuel that is smokeless at a price equal to or only slightly in advance of the raw fuels now available.
Large quantities of coke are used in competition with anthracite for the generation of water gas. Although minor changes in the operation of the water gas plant are necessary to change from one to another of these fuels and although each has certain individual advantages, the chief consideration that determines which is used is solely one of price, as reflected in the cost of manufacture of a unit of gas.
Another outlet for low temperature coke has been under experimentation both in the US and in Japan. It consists of associating low temperature carbonization with high temperature coke ovens to precarbonize part of the high temperature charge in order to furnish a low volatile material for blending with the remainder of the coal, thereby obtaining the strength and porosity required in the final metallurgical high temperature coke.
McBride (369) has pointed out that the low average price for coke oven gas in the US arises partly from the fact that some of the largest producers in the country are affiliated with blast furnace or steel plants and the gas is carried on the books and reported to the government at a purely nominal value, which in no respect portrays its true worth, for it represents for real sale of the product in the open market. For this reason, great care must be exercised in applying average statistical values to specific cases.
The serious problem in the disposition of gas is twofold; in the first place, it is bulky and the storage cost is great, so that it cannot be stored more than a few hours, at best not more than one day, and second, the cost of transportation requires a market within the immediate vicinity of the plant or such as can be reached by pipelines or gas mains. In this manner the gas differs from the other products of carbonization, which can be stored for long periods and shipped indefinite distances. The quantity of gas that can be sold at a reasonable profit often determines the size of carbonization plant to be erected and the location of this market often determines the plant location also.
The sale of gas by a carbonization plant to a public utility becomes a matter of negotiation between the parties concerned. Such contracts, however, must usually be approved by the public authority charged with the regulation of public service corporations, so that, in a measure, the price which is received for the gas is determined by an independent group. As a rule, such a supervision offers little trouble, because the carbonization plant can usually offer the by-product gas profitably at a cost slightly below that at which it can be generates as a principal product, with the result that the regulating body will approve the contract as in the best interests of the public. Sometimes, however, even an attractive price for the gas will not induce a coke operator to enter into a contract to supply a public utility with gas for any extended period, preferring to sell his gas industrially at a much lower rate. The reason for this is quite apparent, for such a contract may require him to run his ovens at full capacity to meet the gas contract at a time when the market for his coke and other by-products is depressed, an eventuality which might cause him a good deal of embarrassment.
The light oil is commonly refined at the coke plant, motor benzol being the chief product. Most of this refined motor fuel, and some of the crude benzol, is sold directly to petroleum refiners for blending with gasoline. The sale is usually by contract, so that the producer will not have to provide storage facilities and so that the petroleum refiner will be assured of a continuous supply of benzol. On the whole, spot benzol is distinctly lower than contract benzol and both follow rather closely the trend in gasoline prices, except that the fluctuations are not as great.
The market can absorb readily all light oil that is obtained from coal carbonization, and even all that could be produced, if the entire annual production of bituminous coal were carbonized. According to McBride (369), even in such a contingency, the production of light oil would hardly exceed one-sixth of the requirements for motor fuel. Practically no light oil is produced by gasworks, as it is used to enrich the gas, but quantities of this product are marketed from by-product coke ovens. As pointed out, however, the potential demand is so unlimited that competition from low temperature light oil is unimportant.
The chemical industries can use only limited quantities of light oil for commercial solvents, consequently by far the major proportion goes into blended motor fuel, which because of its various advantages, can command a slightly higher price than ordinary gasoline. Since one gallon of light oil can be used to enrich several gallons of gasoline, to make a blended motor fuel, it is see that the market price of light oil is determined by the gasoline market at a few cents per gallon above the gasoline price.
Weiss (372) states that there is more variation in quality among low temperature tars than among high temperature tars. Secondary tar is so cracked by the temperatures employed that all tars are more or less reduced to the same grade, but the absence of cracking makes the quality of primary tar more closely related to the coal from which it is extracted. Low temperature tars have been known to vary among processes from a content of 7% tar acids to 50% tar acids, as has already been noted in Chapter III under the discussion of tar acids, and from 40% by volume distilled upon fractionation to a temperature of 300° F to 80% distilled to the same pitch. Consequently, in evaluating any low temperature tar, a careful assay is of the utmost importance. And likewise, because of this vast difference in tars, it is dangerous to make generalizations.
While enormous quantities of raw tar are being burned as fuel, a great deal of creosote oil and other derivatives of tar are being imported into the US. The tar is thus debased solely because the producer receives greater economic benefit from it when so used. This leads to a study of the economics of coal tar distillation. Any attempt to refine tar for the purpose of providing creosote to take the place of importations, involves the simultaneous production of other tar derivatives. Besides creosote, the tar refiner must produce light oil and a carbonaceous residuum, which can take any of three forms: soft pitch, hard pitch, or still coke. Which of the latter is the most desirable to produce depends upon market conditions. The production of creosote is at a maximum when soft pitch is produced. In the past, there was no market whatsoever for still coke, and in recent years it has been somewhat limited. Since both the creosote oil and a good road tar contain some of the same constituents, it is obvious that the two cannot be manufactured at the same time.
The reason so much tar is burned as a fuel at large coke ovens which are affiliated with metallurgical plants, according to McBride (369), is one of business and economics, rather than of technical consideration. The only cause for the existence of such coke ovens is to insure continuity of coke supply to the metallurgical department and the policy of most companies is not to encourage expansion into fields of chemical industry other than the smelting of iron and the manufacture of steel. If the tar were not burned, other fuel would have to be purchased for the open hearths, so that it is considered less of an annoyance to burn the tar in the open hearth furnaces or under boilers than to undertake the uncertainties of tar sales. Only a bookkeeping price need be assigned to the tar, in such instances, as a matter of record only, and this is a contributory cause of the low average value assigned to tar for the US as a whole. The net heating value of 166 gallons of tar is approximately equal to that of a short ton of 12,500 BTU/lb coal, which is to say, that when coal is worth $5 per net ton delivered, on a strictly calorific basis, tar is worth $0.03 per gallon. On the other hand, tar has many practical advantages over coal that tend towards greater economy, so that a safe criterion is that the value of the tar as a fuel in cents per gallon is numerically equal to the price of coal in dollars per ton.
Those plants which do not wish to burn their tar as a fuel endeavor to dispose of it with a minimum of effort on their part, with the result that most of the sales are made through a tar broker on a commission basis, or else are delivered directly to the tar distiller under contract. Practically all of the tar placed on the market is thus sold under long term agreements, so that there is really no such thing as a spot price for this by-product.
Competitive bidding is entirely too inactive to advance the price of tar for refining. The situation is very similar to that of any commodity where the supply very greatly exceeds the demand. The refiners do not have to offer the producers a price very far exceeding its worth as a fuel to get all the good quality tar that they can handle. Furthermore, tar is of such low value that it cannot economically stand transportation for very great differences. In certain districts there are very few tar distillers and the producers in such localities are faced with accepting what is offered or with the consequence of having it left on their hands, as a result of their inability to reach other consumers.
The complex specifications for tar products that are used in various trades, coupled with the difficult problem of merchandizing, have made it desirable, from the viewpoint of most coke oven and gas retort operators, to confine this business to a separate industry of tar distillation, but there are a few small operators who undertake their own tar refining. However, should consideration be given to the financial possibilities of refining low temperature tar, it would be found that about 60% would be yielded as oil and 40% as pitch, with a 300° F melting point. Runge (366) has discussed the economics of this procedure and concludes that the only assured outlet for the pitch, in large quantities, is that of a fuel, for which purpose it should bring $0.25 per ton of coal carbonized. Assuming a yield of 25 gallons of low temperature tar per ton of coal, three would remain about 15 gallons of low temperature oil which could be used principally in 3 ways: as a wood preservative, as a disinfectant, and as a flotation oil, without any regard for its possibilities as a diesel engine fuel, as crude stock for gasoline cracking, for the manufacture of artificial resins and other condensation products, or for many special uses. With creosote oil for wood preservation selling at about $0.17 per gallon wholesale and flotation oils at about $0.22 per gallon, an average value of $0.16 per gallon would seem to be conservative for the distilled low temperature oil. At this value, it would bring a revenue of $2.40, plus the return from the pitch, or a total return of $2.65 per ton of coal carbonized. This is equivalent to over $0.08 per gallon for the raw tar, after deduction of $0.02 per gallon for distilling cost.
The extent to which tar distillation can be carried out successfully essentially is bawd upon a well balanced demand for all of the products. Tar cannot be refined economically unless all of its derivatives can be sold within a reasonable time after production and at a price which represents a fair margin of profit above their allocated costs of crude stock and refining. The unbalanced condition in the market of tar products is responsible for the fluctuation in prices and it depends more upon the relation between supply and demand of specific products than upon any consideration of value or cost of production. As far as the light oil fraction is concerned, there is no limitation to its market, hence the quality of tar which is distilled depends entirely upon the outlets for the other products. While there are various uses in the chemical industries for tar derivatives, the requirements are small compared to the potential supply, and moreover, many of the desired compounds can be manufactured synthetically, a method which has an economic advantage over tar distillation in that it has only one final product to be sold.
During distillation of the tar, the first volatile constituents to be removed are the light oils up to 170° C to 200° C, which contain a very small proportion of nitrogen bases and phenolic derivatives. When only the light oils and water are distilled from the crude stock, the heavy tar remaining is used in surfacing roads, painting of pipe, and for saturating roof felt and other porous materials. Removal of more of the volatile matter leaves a soft pitch suitable for the impregnation of paving blocks, for a road binder, for the manufacture of built-up roofing, and for other waterproofing requirements. If the distillation is carried to a point where all the volatile is removed, pitch or still coke remains. The pitch coke can be used for certain metallurgical requirements where a fuel of low ash and sulfur is desirable. Its strength, however, is such as to prohibit its use in furnaces where the fuel is required to carry a heavy burden. Most of the still coke is used as a fuel but it does not burn very readily on grates. The two most important characteristics of pitch, which determine its availability for various uses, are its hardness and its brittleness at ordinary temperatures. As a roofing material, it is obvious that a pitch which softens and becomes sticky during summer temperatures is quite as undesirable as one which cracks underfoot during the winter because of its brittleness.
The acids are removed from crude tar through forming a water-soluble compound by treatment with caustic soda, after which the tar acids are recovered with sulfuric acid and are finally washed and redistilled. These tar acids, in the form of either crude or refined phenols and cresols, are used in the preparation of synthetic resins and other condensation products, a well as in the manufacture of insecticides and of disinfectants. Although formaldehyde condensation products of the bakelite type have been prepared from the creosote fractions of low temperature tars, Soule (373) has some doubt regarding the ability of this market to absorb any large quantities of low temperature tar products, but their extreme cheapness may stimulate their use in a variety of related ways.
According to Soule (374), the tar distiller receives his largest financial return from creosote oil, which is used as a wood preservative. Coffin (375) ascribes the superiority of low temperature tars for wood preservation, first upon their high acid content, and second upon the oxygenation f the low temperature oil. This oxygenation converts the hydrocarbons from liquids to solids, in the surface layers of the impregnated material, and forms a permanent filler for the cell walls. Consequently, it is felt that low temperature oils are particularly adapted to what is known as the empty cell method of creosoting, regardless of its superiority from a toxic standpoint. While large amounts of tar are refined to produce creosote oil for the preservation of timbers which are placed in the ground or other damp places, it is by no means without competition in this field. Zinc chloride also is used extensively for impregnating mine timbers, posts, railroad ties, etc. The insolubility of creosote oil is distinctly an advantage in its favor. S far as resistance to decay is concerned, there is no doubt that creosote is superior to zinc chloride, but in many cases the timbers have to be removed because of mechanical wear long before they have decayed. In treating railroad ties for main lines, where the traffic is heavy, this consideration is of particular importance and results in selecting the cheaper preservative.
The specifications for creosoting oils are now based principally upon the physical characteristics of the oil, such as the boiling point, viscosity, and specific gravity, instead of upon an analysis of the creosote content. The name of creosote oil is applied to this fraction of the tar because of the phenolic derivatives that are present which prevent the growth of fungi by their toxic action. According to Weiss (372), with a few exceptions, the primary oils are too low in specific gravity to meet the present standards of wood preservation, but this does not mean that they will not make good preservatives. The situation is somewhat analogous to water gas tar, which was pushed for over 10 years before it became acceptable for this purpose, and low temperature tars must face and overcome the same situation by demonstrating their usefulness and by requiring a change in obsolete standards. A number of railroad ties have been in service 8 years after being treated with low temperature creosote oil, and they are in substantially the same condition as those treated with creosote oil which met the specifications for wood preservation.
There has been a good deal of discussion regarding the manufacture of lubricating oils from low temperature tar. It has been thought likely that the ready oxidation of the phenolic constituents would cause trouble. Practical tests, however, have shown that this difficulty is not great for lubrication in accessible places where the parts can be cleaned. A high grade lubricant can be produced, nevertheless, by removing the phenolic derivatives, but that somewhat increases the cost of production. Soule (373) states that the low temperature hydrocarbons below 326° C apparently have only slight value as lubricants, but the readiness with which these compounds polymerize suggest the possibility of treating them further with aluminum chloride as a polymerizing agent according to the method of Heusler (376), to convert them into lubricating oils. The value of unsaturated hydrocarbons in lubricants has often been brought out and it has been shown that the frictional resistance between rubbing surfaces bears a relationship to the amount of unsaturates present. Consequently, it is anticipated that low temperature oils above 300° C possess considerable lubricating value.
This latter view has been substantiated by Nielsen and Baker (377, 378) in tests by the British National Physical Laboratory on the lubricating properties of a refined low temperature oil from the Nielsen process. As compared with a well known English brand of mineral lubricating oil, both the density and the viscosity of the low temperature oil was greater. There was very little difference in the journal friction between the two samples, but the low temperature specimen apparently had a less abrupt seizing temperature and was a more satisfactory lubricant than the mineral oil at high loads. Nielsen and Baker reconcile the difference of opinion, expressed by many authorities, regarding the suitability of low temperature oil for lubrication, by the fact that these oils depend so much upon the process of production for their quality. Thus, redistillation and cracking of the oils in poorly designed externally or internally heated retorts greatly injures the value of the low temperature oil as a lubricant.
For use as a paint, the thickening of low temperature tar in air, due to the oxidation of the phenols, is of practical value. Used alone, the tar gives a soft brown color, but this of course may be modified by the addition of pigments. In one test of low temperature tar as a coating for woodwork and ironwork, after two years of exposure, both the paint and the coated material are said to have been in good condition.
Despite statements to the contrary, Runge (366) has pointed out that very little work has been done in ascertaining the nature of low temperature tar derivatives as applied to their use in the preparation of dyestuffs and pharmaceuticals and comparatively few of the tar derivatives, as now known, can be used for these purposes.
The special properties of low temperature tars adapt them to certain applications where they should command a good price, provided they are not produced in excessive quantities, in which case they can find immediate consumption only as a fuel oil. Undoubtedly important industrial uses will be developed for the special constituents of low temperature tar, but it is inconceivable that any such markets could be of a scale comparable to a national use of semi-coke as a domestic and power fuel. These special uses may be sufficient to command a premium for low temperature tar as a raw material during the initial stages of development in the industry. But when the manufacture of low temperature coke assumes tremendous scale, the only assured price for primary tar is that of its use as raw stock for the manufacture of motor spirit, lubricants, and fuel oils, a price set largely by the petroleum industry at the present time.
As far as ammonium sulfate is concerned, this by-product can be neglected, in most cases, when studying the economics of low temperature carbonization, because of the relatively small amounts that are recovered in the processes of the externally heated type, and because of the great cost of recovery apparatus of large capacity in processes of the internally heated type. The uncertainties of the nitrogen market and present price levels, with little hope for future betterment, strengthen the argument, so that about the best that can be said, in general, for the nitrogen products of low temperature carbonization is that they constitute a potential supply should the nature of the process and market conditions warrant recovery. However, because of the controversial mature on this point, the author included the revenue from ammonium sulfate in Table 123 and estimated the capital cost of the ammonium sulfate plant in Table 125, together with its operating costs and overhead in Table 126. To better clarify the reasons for this situation, it is necessary to study the fixed nitrogen market.
Although the bulk of the fertilizer demands for nitrogen is met by saltpeter an ammonium sulfate, they must compete in a minor way with other plant foods which contain fixed nitrogen, such as tankage, cotton-seed meal, etc. For most agricultural purposes, the two principal nitrogen fertilizers are interchangeable, but both have special advantages under particular conditions. As a consequence, the trend of ammonium sulfate prices follows very closely that of Chilean nitrate. The price of the latter is fixed annually for each country in the world by the association of Chilean producers after consideration of the available supplies of fixed nitrogen throughout the world and the prospects for competition. This price having been fixed, the price of ammonium sulfate is adjusted accordingly and thereafter, throughout the year, the fluctuations of spot sulfate are determined wholly by the demand and available supply in each locality.
By-product coke plants usually recover the ammonia as ammonium sulfate, while gasworks usually recover it as ammoniacal liquor. There is very little difference in the market price of these two nitrogen products per unit of ammonia. Since the liquor is much easier to make than the sulfate, even a very slight advance in the price of liquor, relative to sulfate, will stimulate the manufacture of the former to such an extent that there will be a recession in price. According to McBride (369), in 1920 only about 25% of the gasworks in the US recovered ammonia form their coal gas retorts, even though ammonia had to be scrubbed from the gas by a surplus of water to purify it, simply because the local market value was insufficient to pay the cost of its concentration. The marketing of ammoniacal liquor from the few very large plants which dispose of it is a very simple task, for long term contracts are usually made with ammonia companies to take the entire liquor output. The ammonia company then customarily arranges for a local concentrating plant so that the liquor can be concentrated to a strength that will make shipping economical. The problem of its ultimate disposition is thus left in the hands of an independent company.
The market for liquid ammonia, including the demand of chemical industries and the refrigeration trade, is decidedly limited and is greatly exceeded by the potential production. In the past, these markets have been controlled by a few ammonia companies, which obtained their ammoniacal liquor from gasworks, but the advent of synthetic ammonia ha brought about serious competition in this field. The same may be said of the explosive industry, where in the past ammoniacal liquor concentrated to 25% ammonia content has been used in the manufacture of gunpowder. This requires the concentration of gasworks ammonia to a strength many times exceeding that at which it is produced, an operation far less convenient that dilution of anhydrous synthetic ammonia. The outcome of the entire situation s that, like all other ammonia products, the liquid ammonia price follows very closely the price of fertilizer.
There is a general concensus of opinion that cheap fixed nitrogen is more likely to come from development of the direct synthetic processes than from any other source. According to Curtis (379), a number of estimates indicate that it can be produced at a price ranging near $0.07/lb of fixed nitrogen, or about $0.05/lb of ammonia, and present indications are that the market for anhydrous and aqua ammonia in the US will be saturated from this source. This is about one-half the price of ammonia in ammoniacal liquor and one-third the price of nitrogen in Chilean nitrate. It does not follow that, given cheap ammonia, there will be cheap fertilizer, for it must be combined with sulfuric acid, phosphoric acid, or otherwise, before it is available for this use.
However, Curtis (380) says that the cost of producing a synthetic ammonium sulfate by any process now available is considerably in excess of the cost of producing ammonium sulfate in a by-product coke oven. Furthermore, before the gas can be used for most domestic and industrial uses, it must be purified and the ammonia removed either as the sulfate or otherwise, regardless of the market price of fixed nitrogen. Consequently, by-product ammonia is absorbed in the market before the synthetic stocks are drawn upon. By-product ammonium sulfate has never enjoyed a selling price determined by its cost of production. Before the advent of synthetic nitrogen products, the imports of Chilean nitrate set the market price. But even Chilean nitrate was not sold on a basis of production cost, but enjoyed a suspension of the usual laws of economics, in that it formed practically a world monopoly. Apparently, however, the cost of producing synthetic ammonia is now much below the selling price of Chilean nitrate in the past, so that for the first time that source of supply is facing serious competition. It is unlikely that the Chilean guano fields will ever again hold this dominating position over the world market for fixed nitrogen. Consequently, the outlook for the future is lower prices for fixed nitrogen and hence for by-product ammonium sulfate. Despite this forecast of reduced prices, however, the production of by-product ammonium sulfate will continue to increase for reasons already set forth. But even so, the relative place of coal as a source of nitrogenous fertilizer will become of less and less importance. Curtis (380) notes that a score of years ago a Chilean saltpeter was the principle source of supply for fertilizer, a decade ago by-product nitrogen was foremost, but today synthetic fixed nitrogen supplies more than all the rest combined. The relative importance of these 3 major sources as they now stand will probably never change again.
Synthetic ammonia made by the fixation of atmospheric nitrogen has become an active competitor of gasworks in the ammonia market, with the result that the larger gas plants have found it expedient to curtail their production of ammoniacal liquor and produce ammonium sulfate instead. But even in the fertilizer field, where ammonium sulfate competes with Chilean nitrate, synthetic ammonia plants stand as a potential source of these materials.
Among other ammonium salts, ammonium chloride has a large potential market and present demands are largely met by importation. The price differential, however, is such that, whether or not a producer would undertake its production, depends entirely upon its market price relative to ammonium sulfate. If cheap phosphoric acid were made available, ammonium phosphate could be easily manufactured and would find a receptive fertilizer market. Such a compound would be an ideal fertilizer, as it contains two essential foods for plant life.
Chilean nitrate and synthetic fixed nitrogen products can be sold at a market price fixed only by supply and demand and the cost of production, but ammonium sulfate from gasworks or by-product ovens is only one of several related products and there is no relation between its market price and its cost, such as must prevail in the case of the former materials.
McBride (369) points out that approximately 90% of the ammonium sulfate produced in the US is marketed on a commission basis and practically all of the business is done under contract by a single selling agency, which maintains an elaborate organization in this country and abroad to keep in touch with market conditions. Very little of the exported ammonium sulfate is handled independently. The increased production of this chemical by foreign plants, however, has made serious inroads on this foreign trade, to such an extent that the export price is usually below the domestic price, which in turn is so low as to practically prohibit imports.
Nevertheless, the domestic fertilizer business is the greatest potential field for the permanent disposition of ammonium sulfate, but for any great development in this line an educational campaign will be necessary for the benefit of the companies who manufacture fertilizers, as well as for the farmers who consume them. As a matter of national economics, as well as of national independence, it is desirable that much of the Chilean saltpeter that is annually imported for fertilizer in the US be replaced by domestically produced ammonium sulfate. In nitrogen equivalent, the ammonium sulfate that is exported from the US annually amounts to 35% or 50% of the nitrogen equivalent of imported nitrate from Chile. A further consequence of such a development would be the strengthening of the national defense by rendering the country independent of regular nitrate imports for the munitions of war.
Curtis (379) notes that there has always been a great parity in the US between the prices of Chilean nitrate and those of ammonium sulfate, compared on the basis of nitrogen content. Until 1916, Chilean nitrate was always slightly below the price of ammonium sulfate, but after that date the ammonium sulfate has remained correspondingly cheaper. About 1895, Chile supplied approximately 75% of the world's nitrogen requirements, but today that country supplies somewhat less than 40% of the world's demand, although both consumption and production have greatly increased. It would appear, therefore, that at present, Chilean nitrate would no longer control the nitrogen market, but such is not the case. By its very nature, nitrogen from by-product plants will be sold always at a price which will insure its sale, the balance of the market being taken by the Chilean nitrate.
Bain (381) has estimated that Chilean nitrate can be profitably marketed in the US until the price of $35 per short ton is reached. Below that price, even the most improved methods of production, of transportation, and of marketing cannot maintain the full imports and the imports will fall off in proportion as the price falls below that figure. At approximately $28 per short ton, it is estimated that there would be practically no offerings. These figures for nitrate correspond roughly to $46 per ton and $37 per ton, respectively, for ammonium sulfate, when computed on the nitrogen equivalent, and they may be taken as indication of the minimum prices that ammonium sulfate will attain unless synthetic fixed nitrogen can be produced in quantities more cheaply than this. As long as the above prices are maintained, it is assured that ammonium sulfate will continue to be produced by all by-product coke ovens, except the smaller less economical plants, whose shutdown would not materially affect the supply. The production of ammonium sulfate will depend, therefore, more upon the production of coke and gas than upon the market price of sulfate.
It has been noted heretofore that essential to the economic success of any process for the treatment of high or low temperature medium grade fuels by low temperature carbonization is an adequate disposition of the solid residuum. A study of the consumption of solid fuel by industries will give, therefore, some indication of the markets in which semi-coke can compete and also some idea of the extent to which low temperature carbonization can be carried out when proper outlets develop for the by-products which would arise from future expansion.
The last statistics for the consumption of coal by industries in the US were compiled for 1923 by the Dept. of Commerce (382) but, while there have been changes in the total fuel consumption, there is reason to believe that there was no essential change in the percentage consumption by each industry up to 1927. The figures are tabulated in Table 128. It will be observed from the table that the railroads are by far the largest consumers of coal in the US, accounting for 26.5% of the entire consumption. Next, in order of importance, comes the domestic and general industrial trades, each of which use approximately 19.5% of the entire amount. The various methods of coal carbonization that are already in existence, that is, gasworks, beehive ovens, and by-product ovens, all together account for approximately 14% of the total consumption. Deducting that already carbonized, together with that consumed for miscellaneous purposes, we note that about 80% of the entire coal consumption of the US can be substituted by processed solid fuel.
While it is quite true that the future will see increased use of gas by the domestic and industrial markets, such a substitution merely means a shifting of coal consumption from one industry to another and there is no basic reason why such an increase in the use of gas should not be met by carbonization at low temperatures. There is also a tendency towards electrification of railroads, mines, and other industries, a development which, in the future, will doubtlessly shift the coal consumption to large central electric stations. Such impending changes in coal utilization will increase the efficiency with which the fuel is consumed, thereby conserving the national fuel resources. On the other hand, the centralization of fuel utilization will make its processing an altogether more profitable enterprise.
Of the estimated world's production of 117 million net tons of
coke in 1925, the US produced 44%, according to the statistics
gathered by Tryon and Bennit (383). The production of by-product
coke has increased tremendously from 3,462,000 net tons in 1905
to 43,921,000 net tons in 1927, the production of beehive coke
declining from 28,768,000 net tons in 1925 to 7,004,000 net tons
in 1927. The coke imports to the US amount to less than 0.5%,
while the exports account for approximately 2% of that produced.
During the decade from 1917 to 1926, inclusive, the total value
of the products from by-product ovens in the US ranged from
$8.86 to $13.55 per net ton of coal carbonized, the cost of the
raw coal ranged from $3.88 to $7.73 per net ton, while the
excess value of the carbonization products over the coal ranged
from $2.38 to $5.82 per net ton of coal.
From 77% to 83% of the coke produced in the US is consumed by blast furnaces, which, together with other metallurgical uses, leaves less than 5% for consumption in the domestic market, and we have seen that this supply is very irregular, depending as it does upon depression in the steel industry. As interesting as these statistics may be, they do not have as much bearing upon the marketing of low temperature coke as do statistics gathered from the manufactured gas industry. McBride (369) investigated this subject and reported that in 1918 the manufactured gas industry of the US sold 1,813,000 net tons of coke, representing roughly 60% of that produced, at an average price of $7.70 per net ton. In 1920, the sales amounted to 1,378,000 net tons, or roughly 40% of that produced, and were disposed of at an average price of $8.44 per net ton. The reason for his decrease was attributed to the coal strike, which made it desirable to sue the coke at the plant in water gas manufacture. In general, the price received for coke is governed by local conditions and it usually retails at $1 to $2 per ton less than anthracite. In 1918, the sale price ranged from $2.75 to $19.13 per ton, while in 1920, it ranged from $1.00 to $15.17. These figures are all wholesale prices for domestic fuel, or to other countries for use in manufacturing water gas. According to Tryon and Bennit (383), 1,125,000 net tons of by-product coke, valued at $7.92 per net ton, were produced in the manufacture of city gas during 1925. These authorities report a variation in the average value of the coke produced by the by-product ovens of the manufactured gas industry from $7.32 per net ton to $11.42 per net ton over the period 1918 to 1925, inclusive.
The receptiveness of the trade to a processed fuel is indicated by the fact that the production of fuel briquets in the US increased from 581,000 net tons in 1924 to 971,000 net tons in 1927 and the briquetting industry seems to have held its place after an abundance of anthracite was placed on the market, following the end of the coal stoppage. The possibilities of increase in this industry are recognized, when it is noted that Germany alone produced approximately 5,500,000 net tons of coal briquets and 40,100,000 net tons of brown coal briquets during 1927.
In 1918 there were produced 263,300,000 gallons of coke oven tar in the S, of which 200,200,000 gallons, or 76%, were sold. The production increased to 529,500,000 gallons in 1926, while the sales increased to 277,300,000 gallons, or only 52.3%. This great decrease in the percentage of tar that was sold shows the increasing extent to which coke oven tar has found consumption as fuel. Out of a total of 416.979,000 gallons of tar, of all varieties, that were produced during 1918 in the US, the manufactured gas industry contributed 52,694,000 gallons of coal gas tar and 100,985,000 gallons of water and oil gas tar, the remainder being derived from coke ovens, as above. While the total tar production had increased to 549,775,000 gallons in 1923, the increase occurred mainly in coke oven tar, which accounted for 440,907,000 gallons, coal gas tar from the manufactured gas industry increasing only slightly to 58,877,000 gallons. McBride (369) reported that during 1920 about 51,000,000 gallons of tar were produced by the manufactured gas industry, of which approximately 90% was sold and 6% was burned. The average price received in that year for coal gas tar by 316 plants in the US was $0.043 per gallon, although 72 plants received over $0.06 per gallon and 21 plants obtained $0.10 per gallon, or more.
In 1920, the total amount of crude light oil produced by all sources in the US was 123,333,000 gallons, of which 106,564,000 gallons were refined on the premises and the remainder sold as crude stock. Of this total, 109,710,000 gallons were recovered by coke ovens, 2,906,000 gallons by water gas plants, and 10,717,000 gallons came form manufactured coal gas plants. In 1926, the total production had increased to 164,060,000 gallons, of which 159,590,000 gallons were refined on the premises, yielding benzol as the principal product. The total production of benzol in the US, including both the crude and refined, as well as motor benzol, was 83,371,000 gallons in 1920, of which 72,995,000 gallons were sold at an average price of $0.239 per gallon. The total production increased to 112,489,000 gallons in 1926, of which 111,489,000 gallons were sold at an average price of $0.191 per gallon.
The total production of motor fuel in the US during 1918 amounted to 3,901,000,000 gallons, of which 3,570,000,000 gallons came from refining petroleum, 283,000,000 gallons were extracted from natural gas, 45,000,000 gallons came from coke ovens, and 3,000,000 gallons were distilled at tar refineries. The total production had increased to 12,135,000,000 gallons in 1925, of which 10,903,000,000 gallons came from petroleum, 1,128,000,000 gallons came from natural gas, 104,000,000 gallons came from coke ovens, and only 742,000 gallons came from tar refineries. Regarding the other products of petroleum, gas and fuel oil production amounted to 9,660,000,000 gallons in 1921, increasing to 15,340,000,000 gallons in 1926, while lubricating oils were produced to the extent of 876,000,000 gallons in 1921 and 1,355,000,000 gallons in 1926.
The shale oil industry of the US (384), while not large, is making progress. In 1923, approximately 10.300 net tons of shale were carbonized to yield 392,000 gallons of oil and in 1924 about 23,400 net tons of oil shale were distilled to recover 600,000 gallons of oil. Some of this oil was sold for fuel, while a large part was refined for its by-products.
Coffin (375) states that from 6 to 12 pounds of creosote oil per cubic feet of timber are used in wood preservation, depending upon whether the vacuum or the pressure process of treating is employed. In other words, form 2.5 to 5 gallons of oil are consumed in creosoting each railroad tie that is so treated. In addition to the treatment of railroad ties, there is a vast outlet for creosote oil in treating poles, posts, piles, mine props, shingles, and other forms of lumber. The domestic production of creosote oil increased from 59,100,000 gallons in 1919 to 90,300,000 gallons in 1926, while imports to the US, mainly from England and Germany, increased from 6,500,000 gallons to 95,400,000 gallons in the same years. There is no real difficulty, therefore, in disposing of the creosote fractions of either low temperature or high temperature tar, as far as the market is concerned. Incidentally, it might be mentioned that a good deal of low temperature oil from the Maclaurin process has actually been imported to the US, where it has been sold as creosote oil and is said to have been of better quality than that ordinarily found in the local market.
The real difficulty in the tar distilling industry has been the burden of pitch disposal. The use of the residual tar and petroleum distillates has grown tremendously in the past decade, until today the demand for road material constitutes on of the largest single fields for tar products. In 1925, there were consumed in the US about 100,000,000 gallons of road bitumen, of all types, and this figure is increasing at the rate of about 8% per annum. Soule (385) states that, while the market for creosote oil is increasing, the market for pitch is rapidly decreasing, due to competition from petroleum asphalt, as a roofing material, and from petroleum asphalt and concrete as a paving material. The tendency, therefore, is for the tar refiners to distill more and more of the tar to a hard pitch. Consequently, the outlook for the pitch is only its value as a fuel, in which field it can command about $0.03 per gallon. For this reason, the tar, which contains the greatest amount of creosote oil and the least amount of pitch, as does primary tar, is worth the most to the distiller and hence will doubtlessly command a higher price in the future than high temperature tar.
Another outlet for low temperature oil is that of gas oil for carbureting water gas, a use for which tests have demonstrated its suitability. Since 743,000,000 gallons of gas oil were used in 1920, according to McBride (386), it is estimated that upwards of one billion gallons were consumed in the US during 1927.
In the past, disposal of pitch has been a difficult problem, as it has faced a highly competitive market from bitumen from other sources, such as the petroleum industry. At times, it could not even be sold at any price and the accumulated surplus itself became a burden. Ultimately, it was found that this pitch could be coked in abandoned beehive ovens to yield a material useful for special purposes. Beehive pitch coke is very hard, and because of its freedom from ash and sulfur, it has been found to be particularly suitable for certain phases of the metallurgical industry, to the extent that its price is considerably greater than that of by-product coke. The pitch coke market is not yet saturated and Weiss (372) states that some 300,000 net tons have been disposed of in the US from 1921 to 1926.
It is generally conceded that the trend is for lower manufactured gas prices in the future, especially if any great expansion takes place, through increased consumption for domestic heating and increased production through a general adoption of low temperature carbonization, either for the preparation of a domestic fuel or a boiler fuel. On the other hand, depletion of the natural gas supply is likely to increase the price of this fuel to a point more compatible with the value per thermal unit that has been enjoyed by other gaseous fuels. While coke oven gas has been gradually replacing natural gas for a number of years, the general trend is yet too indefinite to determine the extent of this substitution. The replacement of natural gas by coke oven gas for city distribution is the normal outcome of depletion of the natural gas fields. There are also additional factors which affect the situation, among them the relative prices of anthracite and gas oil, both of which are used in the production of manufactured gas.
According to Tryon and Bennit (383), the total gas sales of the US increased form 895 billion cu ft in 1915 to 1.834 trillion cu ft in 1925. Of the total in 1915, surplus coke oven gas represented 9.4%, or 34 billion cu ft; manufactured coal and water gas, 20.3%, or 182 billion cu ft; and natural gas 70.3%, or 629 billion cu ft. Of the total in 1925, surplus coke oven gas represented 19.7%, or 362 billion cu ft; and natural gas, 64.9%, or 1.189 trillion cu ft. The production of natural gas in the US has been irregular in trend (387), increasing from 582 billion cu ft in 1913 to 795 billion cu ft in 1917, after which it decreased, through exhaustion of the known fields, to 662 billion cu ft in 1921, rising again to 1.164 trillion cu ft in 1925 with the discovery of new supplies.
Statistics gathered by Curtis (379) show a regularly increasing trend of sodium nitrate importations from Chile, rising from 656,000 net tons in 1910 to a maximum of 2,199,000 net tons in 1919. Thereafter the importations have had erratic fluctuations, rising to 1,282,000 net tons in 1920, falling to only 121,000 net tons in 1921, and again climbing to 1,266,000 net tons in 1925.
The ammonium sulfate produced in by-product coke ovens of the US, according to Curtis (379), increased from 35,000 net tons in 1915 to 348,000 net tons in 1922 and the total ammonium sulfate equivalent, including what might have been manufactured from the ammoniacal liquor which was recovered, increased from 81,000 net tons to 449,000 net tons over the same period. The amount of nitrogen that was recovered from the manufactured gas industry was far less and the trend of production indicated a decrease of recovery. The total ammonium sulfate equivalent, obtained from coal gas plants in the US, decreased from 54,000 net tons in 1912 to 30,000 tons in 1922.
An analysis of the nitrogen supply of the US, made by McBride (369), shows an increase from 76,000 net tons of nitrogen in 1919 to 117,000 net tons in 1924, exclusive of Chilean nitrate, but including all other nitrogenous forms. Of the 1924 supply, 91.5% was recovered from coke ovens, 4.7% came from gas works, 3% was produced from atmospheric fixation, and 0.8% was imported as ammonium sulfate. The production of synthetic ammonia has increased substantially since these statistics were gathered. Of these supplies, 38,5% was consumed in mixed fertilizer, 23.1% was exported, 15.9% was sold as aqua ammonia, and 11.5% as anhydrous ammonia, the remainder being used in the manufacture of chemicals and explosives or consumed directly as unmixed fertilizer.
Orrok (388) has noted that the entire fixed inorganic nitrogen supply of the US in 1926 amounted to 282,000 net tons of nitrogen content, of which roughly 38% was represented by ammonium sulfate, obtained from the distillation of coal; 56% was imported from Chile as saltpeter; 2% consisted of other nitrogenous imports; while the remaining 4% was furnished by the synthetic fixed nitrogen industry. This supply was consumed to the extent of 36% as domestic fertilizer, 24% for export, 28% was used as ammonia, principally as a refrigerant, and 12% found its way into the chemical and explosive industries.
Central Station By-Product Recovery ~
One of the greatest fields for low temperature carbonization is in the preparation of a boiler fuel with simultaneous by-product recovery. In this instance, the smokeless characteristic of semi-coke loses its significance, where large power stations, equipped with modern high-efficiency combustion equipment, are concerned. The application of low temperature carbonization to such plants, therefore, must be largely justified by the economies which it effects in the cost of power, through the recovery and sale of by-products, rather than upon consideration of the civic interests of the community. Economically, the most favorable situation for the integration of low temperature carbonization with central electric stations is obviously where the electric company is affiliated with a city gas company. In such cases, the natural growth of gas load can be met by gas from the carbonization plants, built to provide a processed fuel for a new steam generating capacity, installed to meet the growth in the electric load. Furthermore, such an affiliation provides an assured and adequate outlet for the most difficult of all by-products of carbonization to market.
Brownlie (389), in discussing the application of low temperature carbonization to by-product recovery in central electric stations, classifies the processes into 3 general methods: first, those in which the coal is carbonized in the slack or crushed condition and is fed to the furnace on stokers; second, those in which the coal is distilled while in the powdered form, in which case the semi-coke is fired to the furnace in a pulverized form; and, third, those in which the solid fuel is completely gasified and the gas is burned under boilers or is used as a fuel for internal combustion engines. He further divides the first class into two types: those in which the solid fuel is completely gasified and the gas is burned under boilers or is used as a fuel for internal combustion engines. He further divides the first class into two types: those which are primarily intended to be used in conjunction with a boiler furnace, and those which are segregated from and may be operated entirely independently of a boiler furnace. In the last category, practically all low temperature processes may be included.
Some full-scale experimental work has been carried on in England (390) on the use of low temperature gas from an internally heated partial gasification process as a fuel for internal combustion engines. The scheme has been quite successful, when using a low grade refuse fuel as the raw material. In the US, however, the use of gas fuel in internal combustion engines has never made great headway and it is unlikely that the advent of low temperature carbonization will materially change the situation in America, except possibly for small local power supplies which are remote from markets for the gas. Notwithstanding the successful development of the gas turbine, any extensive expansion of low temperature carbonization, as applied to power generation, is more likely to develop along the lines of preparing a boiler fuel for use in the generation of steam to supply high efficiency, high capacity turbines.
A number of different low temperature processes have been tried experimentally in the preparation of boiler fuel. Among these the McEwen-Runge process for pulverized coal, installed at the Lakeside station in Milwaukee, and the Piron-Caracristi lead bath process, formerly installed at the River Rouge, Michigan, and at the Walkerville, Ontario, plants of the Ford Motor Company, have already been described fully in Chapter VI and need not be further discussed here. A short description of some of the other installations, not heretofore described, are pertinent at this point, however.
The Pintsch process (391) involves the use of a short vertical retort, located immediately above the front end of the chain-grate stoker of a boiler furnace. The raw coal, being fed to the boiler, is thus carbonized by internal heating with a portion of the hot products of combustion withdrawn from the furnace. The semi-coke is delivered from the bottom of the retort directly upon the chain-grate stoker and fed hot to the combustion chamber. The gases, after removal of the volatile products, are returned to the boiler and burned. Approximately 35,000 cu ft to 45,000 cu ft of the combustion gas at 1200° F is withdrawn from the furnace for carbonization purposes and subsequently leaves the furnace at about 250° F. This process is used in Germany for non-coking and brown coals. The first installation was at the Municipal Electricity Station of Lichtenberg, near Berlin, in 1919, but more than 12 plants are said to have been installed in Germany and Sweden since that date.
Practically all of the processes invented by Merz and McLelan (392) involve the use of internal carbonization by superheated steam. The various systems also employ a vertical retort, but their chief novelty lies in the scheme for steam extraction and return of heat to heat-exchangers. These processes have been used experimentally at the Dunstan station, Newcastle-on-Tyne, England. Steam is bled from the turbine at a pressure of about one psi and is superheated to about 950° F in a separate superheater. This superheated steam is then admitted to the bottom of the retort and, as it rises, it distills the descending charge. The mixture of steam and volatile products then passes to a heat exchanger, wherein the heat is extracted and returned as low pressure steam to the lower stages of the turbine.
The Wisner (393) process, otherwise known as the Carbocite process, is a 2-stage method carried out in rotary retorts. It has been under experimental investigation for the preparation of boiler fuel at the Philo, Ohio, station. The coal is treated in the first or upper retort by partial oxidation to destroy its agglutinating properties. Thereafter, the coal descends at a temperature of about 600° F to the second stage, consisting of two parallel retorts, located immediately below. The carbonizing cylinders are heated externally.
The Hanl process (391), used at the Bismark mine in Upper Silesia, Germany, consists of a vertical cast-iron retort which contains an agitator provided for the purpose of stirring the charge vigorously during its descent. The retort is heated internally by the introduction of a regulated amount of air to effect partial gasification. The heating medium, generated by a small amount of partial gasification, is augmented by the withdrawal of a portion of the combusted gas from the furnace. The hot semi-coke discharges directly upon a mechanical stoker.
The Salerni process (394), otherwise known as the Salerno process, has been established experimentally at the Langerbrugge station at Ghent, Belgium This is an externally heated process provided wit a number of long narrow semi-cylindrical cast-iron troughs, each fitted with a paddle agitator. The crushed charge flows along progressively from one trough to another during carbonization.
In recent years, central electric stations have shown a tendency to adopt pulverized fuel, in which certain advantages have been seen. If the present trend continues, consideration must be given to the production of semi-coke suitable for firing as a pulverized fuel. There are 3 possible cases: pulverization of the fuel after low temperature carbonization, pulverization between primary and secondary carbonization, and pulverization before carbonization. Practically all processes can more or less lay claim to the first method.
Soule (385) has suggested that between two powdered materials as a pulverized fuel at the same cost per thermal unit, the cost of generating steam will be the least in that (1) which burns faster, (2) which liberates more of its heat in an available form, and (3) which is adapted the more readily to automatic control. The faster a fuel burns, the smaller the furnace volume required to combust a given amount of fuel and also the higher the furnace temperature and the greater is the steam generating capacity for a given area of heating surface. The heat losses in the combustion of bituminous coal are distributed among several items, of which about 4.2% is in the latent heat of water vapor, formed from the combustion of hydrogen in the raw coal; 4% is lost as sensible heat in the flue gas;1% as radiation; 0.5% as unburned combustible in the ash; and 0.3% is lost the evaporation of free moisture in the coal. The first and last of these offer the greatest promise of reduction. Concerning the third point, it is quite obvious that the fuel which involves the lowest firing cost is the one which can be fed to the furnace with the least difficulty under automatic control.
As compared with pulverized coal, powdered semi-coke has no tendency to fuse and agglomerate upon admittance to the furnace, which together with its greater reactivity makes it considerably more combustible. In the second place, removal of practically all the moisture and nearly all the hydrogen during carbonization increases the fuel efficiency of semi-coke 4% to 5%, as compared with the raw coal. Finally, as compared with pulverized coal, the flowing qualities of semi-coke are said to be vastly superior, thereby resulting in greater ease of transport and permitting more success in automatic control. On the other hand, semi-coke will have a greater ash content than the coal from which it was made, and its calorific value per pound may be more or less than the raw coal, depending upon the type of fuel originally carbonized. Taking all these matters into consideration, but without regard to other advantages, such as smokelessness, high combustion rate, etc., Soule (385) concluded that as a pulverized boiler fuel, semi-coke was worth on the whole, pound for pound, as much as the pulverized coal from which it was made, a conclusion reached independently from similar considerations by the present author, under the discussion of power char in Chapter IV.
Some actual tests of a pulverized fuel boiler of the Woodeson type, using semi-coke form the Nielsen process, have been reported (395). The particular boiler had 5,200 sq ft of heating surface and 2,400 sq ft of economizer surface. It was rated at a capacity of 40,000 to 50,000 pounds of steam evaporated per hour at a pressure of 250 psi. The test was highly successful. The calorific value of the fuel was 10,670 BTU/lb and the combusted gas contained 16.5% carbon dioxide with a flue temperature of 390° F. The feed-water temperature was 112° F and the average steam pressure was 218 psi, superheated to 537° F. The equivalent evaporation was 69,300 lb of steam per hour from and at 212° F, which amounted to an evaporation of 9.2 lb of steam from and at 212° F per lb of semi-coke. Each gross ton of the raw coke yielded, aside from the production of 72.5% of its weight as semi-coke, 23.5 gallons of crude oil, of which 25% was a good lubricant, and 7,000 cu ft of gas with a thermal value of 485 BTU/cu ft.
The direct burning of fuel in the generation of electric power with modern large turbo-generators, efficient boilers, and improved methods of firing, requires the minimum capital expenditure, and consumes less fuel in the production of a kilowatt-hour of electricity than does any other method. It does not follow, however, since that procedure does not recover the by-products of the fuel, that it is the cheapest means of electrical generation. The degree to which this is so is contingent upon the cost, capital and operating, of extracting the by-products and upon the condition of the markets for their disposition. As far as conservation of national resources is concerned, while indeed the burning of raw coal constitutes a waste of by-products, the extraction of by-products involves the consumption of more coal. From that standpoint, it is merely a question of which is the more important nationally, conservation of by-products or conservation of coal.
All by-product recovery schemes in central electric stations, as compared with direct coal firing, require a larger outlay of capital, increased cost of operation, and a larger fuel consumption, to provide for a given power demand and to generate a given quantity of electricity. An essential factor in the financial stability of a by-product recovery scheme, in conjunction with a power plant, is a sustained market for the by-products, fluctuations in the market value of which would be reflected in the cost of power generation. Thus, not only would the cost of a unit of electricity depend upon the cost of coal, but also upon the selling price of the tar, gas, light oil, and ammonium sulfate, if it is recovered. From the standpoint of power plant operation, there are many drawbacks to incorporation of a carbonizing plant, such as the increased transportation charges through handling a greater amount of coal, larger employment of labor, and a generally greater complexity in plant operation and coordination. If the production of a boiler fuel is coupled with the manufacture and sale of a certain amount of the coke as a domestic fuel, then the financial aspects of carbonization, as an adjunct to central stations, changes completely, for a portion of the solid fuel is thereby treated as a by-product. It is anticipated, however, that central power stations would be loathe to complicate their business by expansion into the domestic fuel processing field.
Porter (260) feels that an integration of coal carbonization and power generation does not offer great promise of financial success, at the present time, because he believes that the overall efficiency from raw coal to steam by direct burning is too great in modern furnaces with modern combustion equipment to be counter-balanced by the recovery and sale of by-products, through introduction of a less thermally efficient system from coal to steam. From this argument, he concludes that the possibilities of such an integration rest solely on an increased efficiency of the carbonization process, or on the development of some system, such as low temperature carbonization, wherein the by-products are of a character which will yield sufficient returns to reduce the net cost of available heat in the solid fuel.
Wellington and Cooper (89) studied the economics of low temperature carbonization, as applied to English central electric stations, in a number of different forms, including direct firing of the semi-coke, complete gasification of the residual fuel, and various other combinations. They concluded that the method of complete gasification cannot receive serious consideration, as compared with direct coal firing of boilers, but that the best solution of low temperature carbonization applied to a boiler plant is that in which the semi-coke is directly fired to the furnace, along with the surplus gas. In this case, they concluded that the cost of generating a kilowatt-hour of electricity was below that of direct coal firing, but they pointed out that there were certain fluctuations in the market value of the residuals, which would be reflected as a fluctuation in the cost of generating power. It is obviously non-essential that the gas be combusted in the boiler, if it can be profitably disposed of otherwise.
As a matter of record, in connection with the economics of the preparation of boiler fuel by low temperature carbonization, Savage (296) has called attention to a case in the Western US where 65,000 net tons of raw coal, costing $3.05 per net ton delivered, are annually burned as fuel for a large power station. The peculiar market conditions in the vicinity of the plant were such that it was estimated that the entire fuel requirements of the station could be met by carbonizing 93,000 net tons of coal annually, at a net revenue of $1.47 per net ton of raw coal, over and above the cost of the fuel, when the carbonized fuel was charged to the boilers at a price equivalent to the raw coal, weight for weight.
Soule (385) has studied the economics of pulverized coal carbonization in power plants. According to this authority, the investment in such a carbonization plant is less than $1,000 per net ton of raw coal daily throughput, including cost of the by-product plant. He figured the fixed charges, at 80% capacity factor, to be $0.50 per ton and the operating expense to be $0.70 per ton, giving a total carbonizing cost of $1.20 per net ton of coal. With the sale of tar at $0.055 per gallon, motor fuel at $0.15 per gallon, and gas at $0.30 per thousand cubic feet, he calculated the revenue from by-products at $3.60 per net ton, which cost $4.50 delivered. On a yield of 73.8% semi-coke, this places the net cost of one net ton of power char at $2.85, as compared with $4.50 per net ton of raw coal.
Orrok (388, 397), quoting Junkersfeld (398), has demonstrated rather convincingly how rapidly a new turbine, or central electric station, is superseded by more efficient equipment, which in its turn assumes the burden of carrying the base load of a particular electric supply system and he concluded, with Klingenberg (399), that the economical 100% capacity operation of a coal processing plant is difficult to reconcile with the variable output and 50% or lower capacity of a central electric station. The validity of such an argument, however, loses force when it is recognized as non-essential that the sensible heat of the coke be utilized. In reality, the heat lost on this item amounts to comparatively little and a large part of this can be recovered by rational cooling or dry quenching. Consequently, there is no good reason why the carbonization plant cannot be operated at full load, storing processed fuel for use on the peak demands of the system. And in 5 years, when obsolescence shall have reduced the station load factor from 50% to 35%, the carbonization plant will yet be operating at 70% capacity factor.
It is customary for a carbonization plant, located near the market, to carry from one to two months' coal supply in storage, thus assuring the plant against any coal stoppages of short duration, either because of mine shutdown or because of transportation curtailments. Furthermore, the location of coke plants at large transportation centers permits them to draw upon a number of different sources for their fuel supply or to route their raw material by a number of different transportation lines. For this reason, a carbonization plant located near the point of consumption is more independent of conditions beyond its control than one located at the mines and dependent upon a single source for its raw fuel and a single carrier for its transportation facilities. Location of the carbonization plant adjacent to the mine has the distinct advantage of permitting the use of low grade fuels, which cannot be economically transported very great distances, because of their large proportion of incombustible material. Mine-mouth carbonization plants, however, suffer the disadvantage of necessitating transportation of the distillation products, of which the gas becomes particularly burdensome, unless high pressure transmission can be effected or unless there is a nearby market.
Lander (400) is convinced that the proper location for low temperature carbonization is at the mine pit, as far as the use of waste and other low grade fuels is concerned, and he is equally convinced that, for other materials, the gasworks is the proper place for primary carbonization, for there only can the full value be secured for the gas. The value of the gas at the gasworks is roughly 5 times that of the gas for heating purposes at the mine mouth. Lander (400) has also pointed out that it makes little difference where the coke is made, for the freight rate over a given distance is approximately the same for the coke produced from a ton of coal as it is for the ton of raw coal itself. While the weight of coke that must be transported is roughly 70% of the weight of the coal, the volume of the coke produced is approximately the same as that of the raw coal.
Christie (401) has noted that, while in general the low temperature carbonization plant is best located near the market for its products, there are exceptions to this rule. The impending exhaustion of natural gas from districts where coal deposits exist make low temperature carbonization a possibility in such cases, for then the existing natural gas pipelines can be used for its transportation.
In addition to the question of proper location of the carbonization plant, consideration must be given to the best location for the tar refinery, if the two industries are to be integrated under one organization. While in the past there may have been some justification for shipping tar from the producer to a distant point for distillation, because of insufficient quantities to warrant an individual refinery, this is no longer the case when tar is produced in large quantities. Soule (385) says that, by distilling the tar at the point of production, from $0.02 to $0.03 per gallon can be saved in freight and only the high value oil need be shipped. The still coke can then be mixed with the coal and coked to a solid fuel.
Examination of the freight tariffs on bituminous coal for approximately a hundred different sets of origins and destination shows a great diversity (402, 403). While there is much variation from the mean, the average rate increases from about $1.80 per net ton, for a 100-mile haul, to about $3.80 per net ton for a 500-mile haul. Individual tariffs may vary above or below these figures by as much as 25%.
The freight rates on solid fuels depend quite as much on their volume as upon their weight, so that the specific weights of the different materials give some idea of the relative costs of transportation. The freight tariff, for a given distance and a given weight, varies approximately inversely as the weight of the material per cubic feet. The specific weight of anthracite varies from 53 to 60 lb/cu ft, with an average of about 55 lb/cu ft, depending upon its source and size. The specific weight of bituminous coal varies from 43 to 67 lb/cu ft, with an average of 49 lb/cu ft. The specific weight of by-product coke varies from 29 to 32 lb/cu ft, with an average of 30 lb/cu ft.
Although the coke weighs approximately 70% less than the coal from which it was made, weight for weight, it is bulkier. Consequently, the coke produced form a ton of coal occupies approximately the same volume as the original coal. This means that approximately as many freight cars are required to haul the coke as to transport the raw coal. For this reason, added to the greater value of the coke per ton, freight rtes on coke are distinctly higher than on coal. McBride (369) states that formerly freight rates were based on beehive coke, which was manufactured near the mines and had to be transported to the markets, but with the present tendency to locate by-product ovens at the point of consumption, together with the impending competition of coke with anthracite as a domestic fuel, there are indications of freight readjustments, but for the present, the freight tariff on coke is very complicated. There is also a complicated relationship between coke tariffs and those on bituminous coal. If the rate on coke is relatively the higher, the situation favors location of the plant at the point of consumption, and if it is relatively low, the tendency is to locate near the mines. Finally, the establishment of railroad tariffs is in the hands of a public authority, which may have many consequences to consider in rate fixation.
The freight rate on coke varies form about $2.50 per net ton, for a distance of 100 miles, to about $4.50 per net ton for a 400-mile haul. Chatfield (404) reported the tariff, established by the Interstate Commerce Commission on fuel oil and gas oil in tank cars, as increasing from about $0.19 per 100 lb for a 200-mile haul to about $0.36 per 100 lb for a 700-mile haul. The tariff for gasoline was fixed at about 25% higher than the rate for fuel oil and gas oil. Individual tariffs may vary form these figures by as much as 15%. Coke oven tar takes essentially the same freight rate as fuel oil. The tariff on ammonium sulfate increases from about $0.20 per 100 lb for a distance of 100 miles to about $0.30 per 100 lb for a distance of 400 miles.
According to Wagner (405), natural gas gasoline has been successfully transmitted through a 3-inch pipe for a distance of approximately 15 miles at the rate of 50,000 gal/day. In this case, however, the terrain was almost flat with a gentle downgrade slope, so that this success sets no precedent for transmission over an irregular topography, where gas accumulation at the apex of high points in the pipeline may be a serious difficulty.
If low temperature tar could be transported by pipeline and if the quantities were sufficient to warrant laying the pipe, quite a saving could be effected over the cost of its transportation by rail in tank cars. While the viscosity of most low temperature tars is high, there is no reason why they could not be treated in much the same way as the heavy crude petroleums of the Western US are handled, that is, by warming the fluid between pumping stations to increase its fluidity and by the use of rifled pipe.
The main petroleum trunk lines of the US are 8-inch pipe, but a few 6-inch and 10-inch pipes are in existence, Diesel engines are usually employed to drive the pressure pumps, which are used for forcing the oil through the pipes. These pumping stations are located at intervals of from 10 to 35 miles, depending upon the topography of the country, the viscosity of the oil, and the prevailing temperatures in the region. When a very viscous oil is transported, it is often necessary to heat it at the pumping stations to increase its fluidity. Up to 1920, the longest petroleum pipeline was 1,610 miles. According to Rathburn (406, 407), roughly 95% of the crude petroleum in the US is moved by pipeline at a cost estimated to be approximately 65% of the cost of transportation by rail.
The feasibility of transmitting large quantities of gas by pipeline to the consumption centers depends primarily upon the utilization of this gas for the base load, the peaks of the distribution system being taken by gas which is generated locally. Experience with the transmission of natural gas and coke oven gas by pipeline indicates that the technical aspects of the problem is wholly one of economics.
There are two pipelines over 300 miles long for the transmission of natural gas from West Virginia to Ohio. These lines are composed of 20-inch and 16-inch welded steel pipe. A similar line 450 miles long, operating at 450 psi initial pressure, maintained at intervals by 7 compressor stations. Driven by gas engines supplied with fuel from the line, has been contemplated. In the Ruhr district of Germany, coke oven gas is transmitted 63 miles by pipeline and consideration has been given to the high pressure distribution of coke oven gas from this district over a maximum distance of 450 miles. In the US coke oven gas is transmitted by pipeline from South Bethlehem, PA to the Philadelphia district, and similar projects involving transmission of coke oven gas over distances up to 40 miles have been under consideration.
A low temperature plant, treating 1000 tons of coal per day and selling all the high calorific value low temperature gas, using producer gas for heating the retorts, would generate about 200,000 cu ft of gas per hour by the externally heated method. According to a study made by Crowell (408), a 12-inch pipeline, operating at an initial pressure of 90 psi, would deliver this gas at a terminal pressure of 20 psi at a distance of 100 miles. He figures the total cost of delivery, including all carrying and operating charges at $0.28 per 100 cu ft of gas, when gas engine compressors are used. The present author, however, believes that by raising the initial pressure to 400 psi and using a correspondingly smaller welded pipe, the cost of delivering the gas 100 miles could be reduced to $0.12 per 1000 cu ft, or less. In any event, these figures illustrate how essential it is to transmit the gas at as high a pressure and for as short a distance as is feasible to reach the market.
Redmayne (409) has estimated the coal reserves of the world in 1924 at approximately8.3 trillion tons, of which the US had about half. A tabulation of the reserves by countries is given in Table 129. The reserve given by Redmayne for the US is somewhat larger than the 3,419,300,000,000 tons reported by Cambell (410), at of the end of 1925, but in this latter the resources of Alaska and certain deep deposits are apparently not included. Only about two-thirds of this is recoverable, however, for the mining losses amount to about 35% by the present methods of mining.
The sub-bituminous coals and lignites of the Western US constitute about half of this country's supply and a large proportion of these reserves are of low heating value and contain a large amount of moisture. As the Eastern fuel reserves become exhausted and the cost of power for manufacturing becomes correspondingly greater, the migration of the center of industry westward will draw upon the fuel reserves nearest the market and there will arise a need for processing these low grade fuels to appreciate their market vale and to increase the efficiency of their utilization. Even now, if the Dakota lignites could be treated by low temperature carbonization, or otherwise, to raise their form value sufficiently to meet the local fuel needs, an enormous expenditure for freight on hauling bituminous coal from the Eastern fields would be saved annually.
Statistics gathered by the US Bureau of Mines and shown in table 130 give the world's production of coal by countries for various years. The US is by far the greatest producer, having supplied from 38 to 46% of the entire world's supply for the 15 years preceding 1926. Next in order of importance comes Germany, great Britain, and France. The figures given in Table 130 include anthracite, semi-anthracite, bituminous, semi-bituminous, lignite, and brown coals. About half of the German production and about 13% of the entire world output consists of sub-bituminous coals.
White (411) estimated the proved world's petroleum resources, as of 1928, at 43,100,000,000 barrels, which are recoverable by present methods. This estimated was increased to 60 billion barrels as the world's total resources, proved and prospective, Outside of the US, the most important petroleum deposits are believed to be in Mexico, Venezuala, Columbia, Bolivia, Argentina, Russia, Mesopotamia, Persia, East Indies, China, Siberia, Japan, India, and probably Northern Africa.
A careful examination of the oil reserves of the US, both developed and prospective, was made in 1922 by a joint committee of the US Geological Survey and the American Association of Petroleum Geologists in collaboration with many consulting geologists who were familiar with the stratigraphy and geologic structure of given localities. According to White (411), they concluded that the oil reserve of the US at that time wa 9,150,000,000 barrels recoverable by present methods, about half of which belongs to the heavy grade of fuel oil petroleum. As approximately 55 billion barrels of oil had been produced in the US at the end of 1922, the original oil reserve must have been about 15 billion barrels, of which roughly half had been removed from the ground at the end of 1926. The reserve thus left is less than 15 years supply for the US at the present rate of consumption and by present means of recovery. However, all the oil deposits cannot be located in that period of time, so that in all probability the wells will keep producing a constantly decreasing amount of petroleum for perhaps 75 years to come.
The world's production of crude petroleum by countries, according to statistics by the US Bureau of Mines (382), is given in Table 131. It will be observed that the US is by far the world's largest producer, accounting for 65% of the entire amount in 1922 and 71% in 1926, and even then, it was necessary to import large quantities of petroleum to meet the national requirements.
Oil shales are found in Scotland, England, Wales, Ireland, Canada, Australia, new Zealand, Africa, France, Jugoslavia, Sweden, Bulgaria, Germany, Italy, Switzerland, Estonia, Brazil, Argentina, Chile, Uruguay, China, Arabia, Syria, and Russia. Vast deposits of oil shale are found in the US, notably in Colorado, Nevada, Utah, Wyoming, Illinois, Missouri, Indiana, New York, Kentucky, Ohio, Pennsylvania, Tennessee, California, and West Virginia. There has been practically no increase in the world's production of oil shale from 3,435,000 net tons in 1920 to 3,540,000 net tons in 1924 and about 93% of the entire output came from Scotland alone. The only country which has shown any appreciable growth is Estonia, which increased from 1.5% of the world's production to 7.4% in 1924. Even though the present development of oil shale distillation throughout the world appears to be practically at a standstill the vastness of the world's deposits remains as a potential source of motor fuel and of lubricants.
As the products of carbonization pass from crude to more highly refined and specialized materials, they pass form industry to industry, each step adding an increment t their economic worth. Unfortunately, the demand for the highly refined products is at present limited, and consequently much of the by-product material is used to an inferior economic advantage. Thus, McBride (369) notes that about half of the total tar produced in the US, at the present time, is burned as a fuel instead of being separated into its more valuable constituents. The industrial absorption of all the possible tar derivatives will require many years of study to ascertain their full possibilities, but the time will doubtlessly arrive when no coal will be burned in its raw condition. Such an enlightened epoch may yet remain distantly in the future, but reasonable advances may be expected year by year. However, the practical attainment of this larger vision must rely upon the joint efforts of the various branches of the carbonization industry, of which primary distillation is one, and must rest for its realization upon such sound technical, economic, and business principles, as the present author has endeavored to outline.
In regard to the national problem of coal carbonization, be it either by high or low temperature methods, Porter (260) concludes that it should and will be carbonized only to the extent that the economic demand for the special products thus derived creates a price which will justify their extraction. Furthermore, there is neither economy not conservation in the transformation of energy from the form of coal to those of coke, tar, and gas if in those forms it is generally less useful, as indicated by the market values of these products relative to the raw coal.
There is a certain rivalry between high temperature and low temperature carbonization systems, inasmuch as the former is based upon years of experimentation and practice and has behind it a wealth of data and experience. The high temperature carbonization advocates are apt to judge low temperature carbonization in the light of this specialized experience, with its criteria and dogma and without a true appreciation of the methods underlying the art, its raison d'etre, or the characteristics of its products. Each system fills a distinct field in regard to the markets for its principal products. Runge (412) points out that there is really no ground for fear of serious competition between high temperature and low temperature carbonization, because the solid residuums do not fall in the same sphere of usefulness, due to their difference in physical and chemical properties; the tars are entirely distinct in composition and should find different markets; the low temperature gas should be supplemental to, rather than competitive with, high temperature gas; and finally, the only really common field for the two is sound in the use of light oil as motor fuel.
According to the same authority, low temperature carbonization has suffered because of adverse criticism, arising from 3 sources: failure of a number of full-scale processes, exploitation of untried processes that have been based on ridiculous assertions, and the unfortunate prolific writing of those not familiar with the art. This unfavorable atmosphere, while discouraging, has not prevented progress by those who recognize its possibilities.
Coming now to a conclusion of this presentation of the technology of low temperature carbonization the author has endeavored to fulfill the task which he undertook at the outset, namely to coordinate the experimental researches of many workers and the expert opinion of many authorities in such a way as to establish to art upon firm technical foundations and thereby overcome the empiricism which heretofore has hindered its progress. An earnest effort has been made to present all phases of the subject in an unbiased manner, giving the pros and cons of all controversial subjects. Finally, in denouement, the author can do no better than to quote Slosson (413) in the words with which he addressed the representatives of 13 nations assembled in convention to discuss the world's problems of fuel and fuel processing:
"There is no world organization that can exercise the right of eminent domain over natural resources and compel a country to stop wasting it coal and oil, or to employ its unused land and water power. But all the same, and all the more, we should rejoice when anyone discovers how to make a profit out of a waste product or how to make a process more efficient. When a way is found to convert a low grade lignite into a high class motor fuel, or to clean the air of our industrial towns, or to raise the efficiency of a fuel by low temperature carbonization, he has thereby benefited the human race, living and to come."