INDUSTRIAL AND ENGINEERING CHEMISTRY
April 1948
2. Use of the cheaper grades of coal with the plants located close t o the mine mouth. Even underground gasification of coal, whereby the coal is gasified just as it lies in the seam, has been proposed for production of synthesis gas and this scheme should be studied further, particularly from the standpoint of economics. 3. Erection of very large plants, thereby ensuring the lowest unit investment cost and the greatest operating economies. I n this connection, the potentially enormous size of this synthesisgas production must be emphasized. If the equivalent of all our crude-oil production were replaced by plants operating on the Fischer-Tropsch principle, over 50 trillion cubic feet of synthesis gas would be required annually. This is over 100 times the volume of manufactured gas now distributed in our country. From this it appears that the synthesis-gas plants will just naturally be large anyway and that greater economy will follow as a result. 4. Most important of all in securing lower costs will be the research and development efforts that are even ngw well under way and that will swell t o a crescendo within the next few years.
559
Chemists and engineers with a background of experience in petroleum technology and those with a background in coal and manufactured-gas technology are today tackling this problem. The coal industry and the petroleum industry fmd here, certainly, a common meeting ground, and some of the present programs are being, and surely more of the future research programs on synthesis gas will be, carried out cooperatively by the two groups. The present symposium was arranged as a means of reporting progress that has been made in the search for new methods of making and purifying synthesis gas. These nine papers therefore contribute t o the last-named factor-namely, research and development-in working out more economical methods. Admittedly, these papers do not provide the final answers. It is hoped, however, that the papers and the ensuing discussion will stimulate the thinking of those who are interested in and those who are working on this important and interesting problem. A technology that is so closely knit to our future national economy and security as is this one will surely move forward very rapidly.
Oxygen in the production of hydrogen or synthesis gas L. L. NEWMAN,
Bureau of Mines, Washington, D. C .
PROCESSES for the large-scale production of hydrogen and synthesis gas are basically identical. The ratio of hydrogen to carbon monoxide in the synthesis gas may vary from 1 to 2. A plant producing 25,000 barrels of primary liquid fuel per day requires from 700,000,000 to 800,000,000 cubic feet of synthesis gas per day. Low-cost synthesis gas requires the use of lower priced generator fuels, which can best be gasified in continuous internally heated processes using .oxygen. Part, if not all, of the energy requirements for oxygen production may be obtained from the heat evolved in the synthesis reactors. The principal
processes include: Winkler, gasifying fines in a k e d fluidized bed; Koppers, gasifying pulverized coal in suspension; Lurgi, gasifying fines in a fixed bed under pressure; Thyssen-Galocsy and Leuna, gasifying lump fuel and disposing of the ash as a molten slag. Other processes are briefly discussed in relation to the foregoing. I t is concluded that American requirements may best be satisified by gasification processes using pulverized fuel in suspension. These will permit the use of higher rank caking or noncaking coals, as well as the lower rank subbituminous coals or lignite.
T
American conditions makes the fourth method questionable because the hydrogen produced has only a small portion of the thermal value of the coal used for coking. The fifth, re-forming of hydrocarbons, is of interest because of the quantity of noncondensable hydrocarbons made available by the hydrogenation process itself. The amount of such hydrocarbons obtained in the liquid-phase coal-hydrogenation process is, however, inadequate t o supply the required amount of hydrogen through re-forming. Although the volume of gaseous hydrocarbons from liquid-phase and vapor-phase coal-hydrogenation operations may suffice t o supply the required hydrogen by re-forming methods, they are more valuable for the production of iso-octane by polymerization methods (14). The sixth-catalytic conversion of carbon monoxide in water gas-has been used most widely in the production of hydrogen in the large volumes required for liquid-fuel production and is discussed in another paper in this symposium (66). I n general, any process yielding a low-cost water gas would yield, by catalytic conversion of the carbon monoxide, low-cost hydrogen for hydrogenation purposes and low-cost synthesis gas for the Fischer-Tropsch process.
0 OBTAIN engineering and cost data for synthetic liquidfuel processes, the Bureau of Mines has proposed t o build demonstration plants for the production of oil by the hydrogenation of coal and the carbon monoxide-hydrogen synthesis. The cost of hydrogen for hydrogenation has been estimated to be one third t o one half of the cost of the product, while the cost of synthesis gas consisting of carbon monoxide and hydrogen is the major item of expense in the production of liquid fuel by the Fischer-Tropsch process or some variation of it. There are many methods of producing hydrogen. These include the electrolytic dissociation of water, the reduction of steam by iron a t elevated temperatures, the reaction of water and acids with certain metals, the fractional distillation of liquefied gases containing hydrogen-such as coke-oven gas, the re-forming of natural or other hydrocarbon gases, and the catalytic conversion of carbon monoxide in water gas into carbon dioxide and hydrogen \ through the action of steam. Except in unusually well-favored locations, the first three methods have been found generally unsuitable or costly for large scale operations. The remaining three have been in use, to a considerable extent, in European plants. Close scrutiny of
.
INDUSTRIAL AND ENGINEERING CHEMISTRY
560
TABLE I. AVERAGE VALUEPER NET TONOF BITUMINOUS COAL, LIGNITE,AND ANTHR.4CITE I N 1945 Value Kind per Ton Bituminous coal Alabama $4,19 Colorado 3.69 Illinois 2.34 Kansas 2.57 Ohio 2.79 Pennsylvania 3.29 Utah 3.41 West Virginia 3.20 Wyoming 2.83 Average U. S. 3.068 Lignite North a n d South Dakota 1.56 Texas 0.85 Average U. S. 1.553 .4nthracite S t e a m sizes Buckwheat No. 1 4.79 Buckwheat S o . 2 (rice) Buckwheat KO.3 (barley) Buckwheat N,o. 4 Other (including silt)
3.91 2.65 1.85 1.58
Coking coal Alabama Pennsylvania By-product Beehive West Yirginia By-product Beehive
4.47 4.40 3.51
Remarks I'rom Table 6 (58). Prices are for coal f.0.b. mines a n d may include selling costs ranging from 5 t@7 cents per net ton
From Table 5 (58)
From Table 5 (GS) F r o m Tabie 1, Pennsylvania anthracite (6) Through 9/16 over 6/16 , .. inch round testmesh Through 5/16 over 8/16 inch Through 3/18 over 3/82 inch Through 8 / 3 2 over 3/64 inch Through s/84 Prices are for coal a t breaker, washery, or dredge a n d do n o t include selling expenses F r o m Table 20 ( 7 ) . Values are for coal a t ovens, Charges for transportation are reflected in differences between values a t by-product a n d beehive ovens ~
3.56 3.39
Composition o f Synthesis Gas The synthesis gas required for the Fisclier-Tropsch process will vary in volume and composition according t o the catalyst and the pressure, temperature, and time of contact selected to yield a primary product with the desired proportions of saturated to unsaturated hydrocarbons. Fischer-Tropsch catalysts consist essentially of metals in the iron group. The synthesis gas usually consists of 1CO 2Ha for cobalt and nickel catalysts lHz for iron catalysts. Cobalt is best for normal and 1CO (atmospheric) pressure synthesis, iron having a very short life. Cobalt and iron can be used in the middle-pressure synthesis (up t o 10 atmospheres). Nickel catalysts operating a t pressures higher than 1 atmosphere deteriorate rapidly because of the formation of volatile nickel carbonyl, which is lost to the system (@). The primary product of normal and middle-pressure synthesis is composed largely of straight-chain paraffin and olefin hydrocarbons. The effect of increasing the carbon monoxidehydrogen ratio is to produce more olefins and more carbon dioxide. A large excess of hydrogen produces a saturated product and favors the formation of methane. The percentage of olefins decreases in the order iron, cobalt, nickel (60, 40, and 5%, respectively, of olefins in the product) when these are used as catalysts and increases with very short layers of catalysts (high space velocities). The yield of olefins is inversely proportional t o the hydrogen content of the synthesis gas.
feet of synthesis gas. The heat t o be removed is about 7000 B.t.u. per pound of product, or 20% of the heat of combustion of the synthesis gas (13). I n one application of the FischerTropsch process for producing oil from synthesis gas having natural gas as its source, 32,300 cubic feet of synthesis gas are required to produce 1 barrel of liquid product (37). To produce only 25,000 barrels of primary liquid product by the FischerTropsch reaction-a mere 0.5% of the daily crude petroleum run to stills in the United States (S0)-700,000,000 to 800,000,000 cubic feet of synthesis gas would be required. This is estimated t o equal or exceed the total daily production of blue water gas by the entire manufactured-gas utility industry in the United States in 1946 ( I ) . (Manufactured-gas utility sales in 1946 totaled 414,312,500,000 cubic feet, of which approximately 7570 was carbureted water gas composed of 70 to 80% blue gas.) To produce these staggering volumes of synthesis gas, highcapacity processes must be employed. The modern high-speed intermittent water-gas machine is suitable but requires a good grade of coke for its operation. The supply of such coke is limited by the demands of the existing chemical, metallurgical, and manufactured-gas utility industries, and its cost is relatively high. Table I presents the 1945 prices of bituminous coal, lignite, and anthracite. The price of coke is actually a function of the price of coal, coke yield, operating costs, and by-product credits. I n general, the price of coke per net ton may be estimated by adding $2 to the price of coal per net ton of the lovier-priced coking coals, somewhat more for the higher-priced coking coals. Thus, if coal is $3.50 per net ton, the price of coke may be estimated a t $5.50 per net ton. Using the lowest values, which would be likely t o prevail in large scale year-round mining operations, the costs for 1945 compare as follows:
+
+
Synthesis-Gas Requirements The reaction between carbon monoxide and hydrogen t o form hydrocarbons may be represented empirically by means of t h e following equations: Using cobalt catalyst CO 2Hz -+ (CH,)
+ HzO + heat
Using iron. cat,alyst 2co Hz --+
+ COP + heat
+
+
in which the formula (CH,) represents the hydrocarbons produced. The theoretical yield of primary liquid products from 1000 cubic feet of 1CO 2Hz synthesis gas is 2 gallons. However, as incomplete reaction and gas formation reduce the yield of the products, in practice the yield of hydrocarbons other than methane, ethane, and ethylene is 1.4 to 1.5 gallons per 1000 cubic
+
Vol. 40, No. 4
Bituminous coal Small sizes of anthracite Northern Great Plains lignite Texas lignitea
Per Net Ton $2.34 1.58 1.56 0.86
T h e production of Texas lignite is a small fraction of the total a n d bare13 affects the weighted U. S. average value, which is close t o the h u e of the lignite in the Northern Great Plains Province. Q
I n contrast, the lowest cost of coke would be $5.39 per net ton, roughly twice that of any of the other fuels listed, even after adjustment for the moisture and ash differeatials. Increases in cost since 1945 are assumed t o be in direct relation t o each other. The lower-grade and lower-rank fuels cannot, however, be used effectively in the modern intermittent-type water-gas generator because they are incapable of resisting the high blast rates necessary for supplying the heat for the reactions in the fuel bed. For the complete gasification of these fuels the supply of heat to the fuel bed must therefore be continuous and can be accomplished by external heating along the same general principles employed in coke-oven operation or by recirculating gases transferring heat from regenerators or recuperators, or by the direct partial combustion of the fuel with oxygen t o supply the heat required for water-gas formation. Complete gasification methods employing external heating or gas recirculation are suitable only for the more reactive fuels, such as lignite or subbituminous coal, while methods using oxygen may be used on all fuels, regardless of their degree of reactivity. The lattcr methods, especially as regards the yield of gas, are far superior to those in which the heat required is obtained from the separate gasification of part of the fuel. The cost of oxygen has long been the principal obstacle in its use for gas production in the Gnited States. The newer developments in large scale oxygen production indicate that the costs have been reduced enough to fall within the range of general gas manufacture (IO). I n the case of synthesis-gas manufacture, the heat released from the synthesis reactors may suffice
I N D U S T R I A L A N D E N G I N E E R I N GC H E M I S T R Y
April 1948
56 1
AH, AT 298.16' K. (77"F.) AND 1500" K. (2240"F.) . TABLE 11. VALUESOF HEATOF REACTION, IN
CALORIES PER MOLE AND B.T.u.
PER
POUND-MOLE (54)
298.16O K., Reaction Calories -26,416 l/aOz (gas) = CO (gas) '1 C (solid, graphite) -67,636 2 CO (gas) 1/zOz (gas) = COz (gas) -94,052 Oz (gas) = COz (gas) 3 C (solid, graphite) 31,382 4 C (solid, graphite) HzO (gas) = CO (gas) Hz (gas) 21,544 5 C (solid, graphite) 2H20 (gas) = COz (gas) 4- 2Hz (gas) 57,798 6 HZ(gas) ~ / z O Z(gas) = HzO (gas) 41,220 COa (gas) = 2CO (gas) 7 C (solid, graphite) -9,838 8 CO (gas) HzO (gas) = Cot (gas) HZ(gas) -59,109 9 2CO (gas) 2Hz (gas) = CHI (gad COz (gas) -49,271 3Hz (gas) = CH4 (gas) Ha0 (gas) 10 CO (gas) -39,433 11 COz (gas) 4Hz (gas) = CH4 (gas) 2H20 (gas) 17,889 2Hz.(gas) = CH4 (gas) 12 C (solid, graphite)
+
+ + +++
+ + ++ + +
+
to supply the power required for production of the oxygen consumed in any of the gasification processes that depend on it for high-capacity operation. (Approximately 15 kw.-hr. are required t o produce 1000 cubic feet of oxygen by air separation. If we assume a maximum oxygen consumption of 300 cubic feet in the generation of 1000 cubic feet of synthesis gas the energy required would be 4.5 kw.-hr. or 15,40U B.t.u. The heat release in the synthesis reactors is 20% of the heat of combustion of the synthesis ga's or 320,000 x 0.20 = 64,000 B.t.u. which would be ample t o supply prime movers operating a t 25% efficiency.) This saving in power, depending on power rates, may further cut the cost of oxygen to an appreciable extent.
Chemistry of Gasification
~
Reactions in the system carbon, oxygen, and steam are indicated for two temperatures in Table 11. The values of AH are expressed as negative for exothermic reactions and positive for endothermic reactions. At normal pressures the first eight reactions predominate, while the last four are significant in highpressure operations. The reactions primarily desired for synthesis-gas production are and
C C
+ HzO = CO + Hz; AH = 32,265 cal. (1500' K.) + 2Hz0 = COt + 2H2; AH = 25,066 cal. (1500" K.)
Both are endothermic; and, t o supply the heat of reaction, the exothermic reactions, consisting principally of and
C C
+ +
i/202 0 2
=
-
+ +++
CO; AH = -27,545 cal. (1500" K,)
= COZ; AH = -94,555 cal. (1500" K.)
are employed. The formation of methane in a low temperature zone, also exothermic, furnishes additional heat for the reaction. To the extent that heat from the formation of methane is supplied, there is a reduction in the need for supplying oxygen for this purpose. Thus, as will be seen, in the Lurgi pressure gasification process in which methane is formed the volume of oxygen required is relatively low. I n a study of the reactions of the carbon-oxygen-steam system a t atmospheric and higher pressures for the Gas Production Research Committee of the American Gas Association in the laboratories of the Institute of Gas Technology a t Chicago, Ill., calculations have been made on the equilbrium compositions of the gaseous products formed within the temperature range of gas-producer operation, and the net heat effects (increases in enthalpy) were calculated. It is shown that an increase in pressure leads t o a decrease in the equilibrium concentration of carbon monoxide and hydrogen, an increase in the carbon dioxide and methane concentration, and a diminished conversion of water. In general, the oxygen-steam ratio required to maintain a fixed change in heat contents (enthalpy) increases with rising temperature and decreases with rising pressure. The increases are high a t the lower temperatures and diminish a t the higher temperatures t o the point where they finally become very small, while the decreases are most pronounced a t low pressures. The equilibrium yields of carbon dioxide and methane are
-
1500°,K Calories'' -27,545 67,010 -94,555 32,266 25,066 -59,811 39,464 -7,199 -f1,524 04,326 -47,126 -22,060
-
-
77O F., B.t.u. -47,649 -121,744 169,294 56,488 38,779 104,036 74,196 17,708 106,396 -88,688 -70,979 -32,200
2240°F.,
B.t.u.
--
increased a t the higher pressures, but they are not simply proportional t o the pressures. Af low pressures, a change in pressure produces a greater change in equilibrium composition and shift in thermal balance than a corresponding change a t higher pressures. Figures 1 t o 4 show the temperature dependence of equilibrium compositions a t pressures of 1, 10,20, and 40 atmospheres, respectively (85). Figure 5 shows the Bureau of Standards plot of the logarithm of the equilibrium constant for eight reactions. Equilibrium conditions, as determined in a laboratory study of the reactions of graphite, oxygen, and steam, are rarely, if ever, attained in practical operations. The reactivity of the fuel and its physical characteristics, as well as the desired composition of the gas, will largely determine the temperatures, pressures, and gas velocities that will result in the most economics1 operation. Extensive research has been conducted on the kinetics of these reactions. Recent experiments have shown that carbon monoxide is the primary product when oxygen reacts with solid carbon at temperatures above 1472" F., but when samples are taken from' the combustion zone they are found t o contain more carbon dioxide than carbon monoxide proving that secondary reactions play a large part in the actual fuel bed. It is clear that, so long as free oxygen remains, the carbon monoxide formed a t the surface of fuel will be oxidized in the voids t o carbon dioxide, which in turn will be reduced later to carbon monoxide in contact with carbon. The question whether the primary reaction between steam and carbon is C HzO = CO Hz or C 2Hz0 = C o n 2Hz has not yet been finally settled (50). There is also considerable discussion regarding the mechanism of the formation of methane. I n the reports on German operations the reactions
+
CO
+
+
+
+ 3Hz = CH4 + HzO and GO2 + 4H2 = CH4 + 2H20
are stressed, while from British experiments the impression is obtained that the interaction of carbon with hydrogen in fuel beds is a t least as important in the formation of methane as the reaction between hydrogen and carbon monoxide or carbon dioxide (8, 52). So far as they influence the design of the equipment and the actual operating conditions, the equilibrium conditions and kinetics of the gas reactions will be cited in the review of the oxygen gas processes that follows.
Gas Processes Using Oxygen The four principal groups of gasification processes using oxygen and their subdivisions are as follows:
A.
Processes in which fine fuel is gasified in a fixed fluidized bed. B. Processes in which fine fuel is gasified in suspension. 1. Gasification in a single stage. 2 . Gasification with gas recirculation. C. Processes in which fine fuel is gasified in a fixed bed. 1. Normal-pressure gasification. 2. High-pressure gasification. D. Processes in which lump fuel is gasified in a fixed bed. 1. Standard grate operation. 2. Slagging-type operation.
INDUSTRIAL AND ENGINEERING CHEMISTRY
562
Figure 1. Temperature dependence of equilibrium composition of carbon-water-oxygensystems Net enthalpy change, 0.
Pressure, 1 atmosphere absolute
Vol. 40, No. 4
Figure 2. Temperature dependence of equilibrium compositions of carbon-water-oxygen systems Net enthalpy change, 0.
Pressure, 10 atmospheres absolute
RATIO OF ADMITTED O X Y G E N TO STEAM
(CU.FT.OZ/LB.H Z O )
TEMPERATURE-DEGREES F:
Figure 3. Temperature dependence of equilibrium compositions of carbon-water-oxygen systems Net enthalpy change, 0.
Pressure, 20 atmospheres absolute
PROCESSES IN WHICH FINE FUEL IS GASIFIED IN A FIXED FLUIDIZED BED
Winkler Process. The Winkler process is the only one known to have been in large scale operation in which fine fuel is gasified in a fixed fluidized bed. The most recent information on the process has been collected and summarized by Morley and was reviewed in Coke and Smokeless-Fuel Age (3, S I ) . Much of the following material on the TTinkler process was drawn from these sources. Development of the process was begun in 1921 by Fritz Winkler at the I. G. Farbenindustrie a t Oppau near Ludwigs-
Figure 4. Temperature dependence of equilibrium compositions of carbon-water-oxygensystems Net enthalpy change, 0.
Pressure, 40 atmospheres abeolute
hafen. It was first used in large scale air-blown gas-producer operation at Leuna in 1926. By 1929, the plant, with four more generators, each with a cross-sectional area double that of the original one, often produced 6,850,000 to 7 860,000 cubic feet per hour, with a maximum of 10,250,000 cudic feet per hour of producer gas using a mixture of air and steam. I n 1929 experiments were begun with the use of oxygen and steam for gasifying brown-coal char. Three of the large Winkler machines were converted to this use by 1933, soon after installation of the LindeFrank1 air separation plants, which were built for the specific purpose of supplying oxygen to these units. Since 1933, as a rule, one of the large units regularly generated 1,365,000 to 2,400,000 cubic feet per hour of producer gas and another up to 2,050,000 cubic feet per hour of nitrogen-free gas.
April 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
563
In 1936, when the large scale program of synthetic oil plants was begun for the German war machine, Winkler generators usin oxygen to gasify brown-coal char were adopted as the standari source of hydrogen at the Brabag Works at Bohlen, Zeitz, and Magdeburg. These began operation in 1938-39. Winkler generators were also installed for hydrogen production at Most (Brux), Czechoslovakia, and began operation in 1942. The five known Winkler installations are at Leuna, Bohlen, Zeitz, Magdeburg, and Most (Briix). At Leuna the small generator has an approxmate output of 900,000 cubic feet of water gas a n hour, and each of the four large ones has an approximate output of 2,000,000 cubic feet per hour. At Bohlen are three units, each with an approximate output of 750,000 cubic feet per hour. Each of the Zeitz and Magdeburg plants has three units similar to those a t Bohlen. At Most (Brux) five or six units of the latest design were reported to be installed. I n addition, there are small units at Oppau and Leuna for testing various coals. Three generators were installed in Japan. OPERATINGPRINCIPLE.The operation of the Winkler process for the production of water gas depends upon the interaction of a fixed, fluidized bed of fine fuel with oxygen and steam. A fixed, fluidized bed behaves very much like a liquid. The agitation of the particles by the flowing gmes gives the bed the appearance of boiling and maintains substagti+lly equal temperatures throughout the gasification zone. At low blast rates the pressure drop increases as a function of the velocity of the gases until a point is reached where the tendency is t o lift the fuel bed bodily and increase the voids t o such an extent that the bed begins to boil. Thereafter, the pressure drop remains constant as the velocity increases; but the voids grow larger, and the depth of the bed increases to such a point that the particles begin to be entrained and carried out with the gas. Singh (39),in his exposition of fluidization behavior, has stated: Actual gas velocity through the bed and the ever-changing flow pattern are rather difficult to determine. Particles for which terminal velocity has been exceeded are, to a large extent, retained in the fluidized bed and particles for which terminal velocity has not been attained are lifted into the churning bed. Such behavior can be regarded as being caused by a free exchange of kinetic energy between particles of various diameters. During fluidization those particles for which the terminal velocity is exceeded by the upward flow of the fluidizing medium are gradually carried away from the bed in motion. If the bed is not continuously replenished with these fractions, fluidization will either stop completely or develop undesirable features such as bumping, slugging, and channeling. I n a recycling system provided with efficient dust-arresting means to prevent material loss from the fluidized bed, equilibrium operational velocity for the prevailing particle size range can be established and effective elutriation avoided. Segregation of finer fractions is prevented to some degree by the mechanical interference of other particles and also through formation of agglomerates. It is also generally known that for satisfactory fluidization close siziqg of the material should be avoided. A fluidized bed containing an excess amount of fines may develo channeling, whereas if the coarser fractions predominate, sggging is likely to result. Fundamentally, the behavior of finely divided coal in a fluidization process should be quite similar to that of most other solids as long as there is no change in the physical state of the coal substance. This is shown to be the case by large scale operations involving fluidized gasification of brown coal in Germany.
.....
Uniform mixtures of oxygen and steam are essential to prevent slagging, which happens very quickly at high temperatures resulting from variations in the composition of the blast mixture. Accordingly, the oxygen and steam are mixed 35 to 50 feet from the generator. Care must also be exercised that the velocities are always high enough to maintain the fuel bed in a fluidized state; otherwise, blowholes would form, and unreacted oxygen would get by and inevitably cause explosions or local damage. Blowholes can be quickly detected by a rapid rise in the volume of carbon dioxide in the gases just before free oxygen appears; a sample of the exit gases is burned continuously in front of a photoelectric cell, and when the rise in carbon dioxide extinguishes the flame an alarm is sounded.
-
-6
CH4* GO2 = 2CO + 2 H 2 I
200
Figure 5.
400
I
I
I
I
600 800 1000 TEMPERATURE, 'K.
I
O
1200
I
I
1400
Plot of logarithm of equilibrium constant for eight reactions
Involving oxygen, hydrogen, water, oarbon (graphite), oarbon monoxide, carbon dioxide, and methane
APPARATUS AND MBTHOD OF OPERATION.Of the earlier five generators at Leuna, the oldest and smallest has a diameter of 12.8 feet, and each of the other four has a diameter of 18 feet. In the original design, the upper portion of these generators was enlarged t o a bulb which provided a longer time of contact for the reactions. In later generators, the bulb was eliminated to save capital cost, and the height of the straight, cylindrical portion was increased t o give the same effect. Another reason given was that turbulence near the periphery of the bulbous portion led to uneven times of contact a t diffekent points of the cross section. Because shutdowns for repairs of these large-diameter generators meant too great a loss of production capacity, the latest generators constructed had smaller diameters. Thus, the generators a t Bohlen, Zeitz, and Magdeburg have diameters of l3.r to 14.8 feet at the cylindrical portion and are 65 feet high, whereas the earlier, larger Leuna generators had diameters of 18 feet and an over-all height of 43 feet. The Zeitz method of operation is described as an example of the latest practice: Referring t o Figure 6, brown-coal char ranging in size from 3l/2 to No. 10 mesh is supplied from a hopper beside each generator. For starting up, a small auxiliary generator is used with a vent to the atmosphere always open. A fire is started with wood blown with air, and the char is slowly run in from the hopper. $he glowing char is then run by gravity into the large generator, which is blown with air, while a safety valve is open to the atmosphere. The bed is gradually built up to a depth of 4 to 5 feet in the fluidized state. The blast is then changed to oxygen and steam and when the gas is of sufficiently good uality, the safety v a h e is closed and gas making proceeds. ?Chis can be accomplished, if necessary, in about 2 hours from starting with a cold generator, but usually more time is taken to avoid damaging the brickwork. Ninety per cent of the oxygen-steam mixture is blown up through the grate, while 10% is introduced about 6 feet above the fuel bed through 12 nozzles pointing to the center of the
No.
564 '
INDUSTRIAL AND ENGINEERING CHEMISTRY
X Figure 6. Diagram of Winkler generator generator. Velocities of the mixture flowing through the nozzles in excess of 25 feet per second cause the flame to strike the far side and may burn out the lining, while much lover velocities cause the flame to lick upward onto the lining above the nozzle. The purpose of the secondary blast is t o burn off some of the finely divided fuel entrained in the gases above the fluidized zone, to raise the temperature of the space above the bed and thereby crack as much of the tar and hydrocarbons as possible, and t o cause the maximum possible reaction of steam and carbon dioxide with the finely divided fuel. The secondary blast varies in percentage of the total with each inst,allation. At Zeitz it is 1070,a t Bohlen 20%, and a t Leuna 337,. It is probably significant that the dust content of the exit gases is highest a t Zeitz and lowest at Leuna. These differences, however, may result from differences in the fuel used, as well as differences in the amounts of secondary blast. The vplume of the generator above the fuel bed governs the time available for completing the reactions of steam and carbon dioxide with carbon and for-completing the cracking of the hydrocarbons and tar. This volume is approximately 15 BROWN times that of the fuel bed itself. It was estimated that, of the carbon supplied to the generator at Zeitz, 557, leaves in gaseous form, 407, leaves as entrained dust, and 5 7 , is discharged Kith the ash removed beneath the grate The Zeitz grate is built of firebrick assembled on edge, with 0.25-inch spacing, provided a t 3-inch intervals, for passage of the oxygen-steam mixture. A water-cooled steel scraper, driven by a vertical shaft rotating a t 1 to 2 r.p.m., directs the ashes on the grate to an opening connecting with the ash pit, from which1 the ashes are
Vol. 40, No. 4
removed by two water-cooled screw conveyers into gas-tight hoppers, which are emptied periodically. The grate could be lowered and wheeled away for overhauling and be replaced by a spare grate without cooling off the whole generator. At Bohlen the ash from the grate is dumped into a water trough and sluiced away to a settling pit. The grates a t Bohlen and at Leuna are composed of wedgeshaped, cast-iron elements assembled in groups of three touching each other at the top but with a spacer between each two groups of three. I n one small and one large generator at Leuna and one at Most (Brux), the grate and the water-cooled rotating arm were eliminated, and tuy, res mere provided at the side of the conical base for the oxygen and steam. The ash and refuse are collected at the base and removed by two screw conveyers run intermittently. I n addition to avoiding all shutdoxns for repairs to the rotating arm, it was claimed that the modification has resulted in a saving of 10% in fuel and oxygen. If this claim is true, the heat loss in the cooling water is disproportionally large in the generators with the standard grates. The fuel is introduced continuously by three water-jacketed screw conveyers, all on one side of the generator, about half way up the bed. The depth of the fuel bed is controlled by hand, the operator using the pressure drop through the bed as a guide. The temperature in the fuel bed is kept about 50" F. below the softening point of the ash. This is readily determined by the operator observing the ash: if it is too dusty, a higher proportion of oxygen is used; if signs of clinkering appear, a higher proportion of steam is used. The percentage of oxygen in the primary blast varies from 20 to 50. The lower figures are used in Bohlen and Zeitz and the higher a t Leuna. The percentage of oxygen in the secondary blast may be varied independently, if necessary, to prevent any deposits of liquid slag on the walls. If the ashsoftening point of the coke is, say, 1800" F., the operating temperatures and pressures would be approximately as shown in the flow diagram (Figure 7). Successful operation of the Winkler generator depends upon correct handling of the dust formed. Over SOY0 of the dust carried in the gas, which at Zeitz is about 13,600 grains per 100 cubic feet, is removed in the multiclone separators, leaving about 2700 grains in the gas. The washer cooler reduces the dust content to about 100 grains, and finally the Theissen disintegrator reduces it to less than 0.2 grain per 100 cubic feet. The dust from the multiclones falls into a hopper, from which it is blown with carbon dioxide to the power plant as fuel. Without this power-plant fuel credit, which tends to offset the high fuel consumption, the Winkler process would not have been satisfactory. Dust also collects in the base of the waste-heat boiler and the economizer but is not removed, except when a long shutdown presents the opportunity. The water from the cooler contains approximately 6 grains of dust per gallon and some hydrogen sulfide. It is pumped to a tower where it is blown with carbon dioxide, then t o a second tower, where it is blown with air. The water then passes through three large settling tanks which reduce the solids to a little over 1 grain per gallon, when it can be discharged into the river. Some trouble is experienced with erosion of the tubes in the waste-heat boilers as a result of an excessive amount of dust in the gas during periods when the generators are overloaded. Because of this, the waste-heat boilers in most plants are the principal limitation on the output. The raw water gas is drawn from the holder by a blower, cooled indirectly, and passed through Alkazid liquid purification and finally through - Lux purifiers. GAS
MULTICLONES
per sq
Figure 7.
in
qwqe
Flow diagram of Winkler process
April 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
As a safety precaution, the oxygen and steam entering the generator flow through water-seal pots to prevent explosions in the mains. The inert gas used for purging when starting u p also flows through the seal pots. When dry brown coal was used, it was not admitted to the generator until after the starting-up period to prevent an explosion of oxygen and distillation gas.
FUELUSED. I n the current Winkler generator operating practice brown-coal char is used as fuel. The use of dry brown coal a t Leuna has been discontinued. The char" is very small in size, usually between a/g inch and No. 140 mesh, with the bulk between No. 5 and No. 70 mesh. This highly reactive fuel is dried, ground, screened, and transported in an inert atmosphere. At Bohlen this atmosphere consists of carbon dioxide, while a t Zeitz it consists of nitrogen from the Linde-Frank1 plants. When dry brown coal was used, its moisture content was reduced t o about S%, while the char has 2 to 3% moisture. The ash content of the dry brown coal was 14 t o 207& while that of the coke is 22 t o 28%. The calorific value of the dry brown coal was about 9400 B.t.u. per pound, and that of the coke is between 9700 and 10,400. The sulfur content is variable. The highly reactive nature of the fuel permits operation a t low temperatures, which should yield higher hydrogen-carbon monoxide ratios in the gas. The range of fuel utilization per thousand cubic feet of hydrogen plus carbon monoxide was 51.5 to 53.5 pounds of dry brown coal and is 41.4 to 66.1 pounds of brown coal char, with corresponding carbon-utilization percentages of 86 to 80 and 88 to 57, respectively. OXYGEN AND STEAM USED. The oxygen is supplied by LindeFrank1 air-separation plants designed to produce oxygen of 98% purity. The oxygen consumption per thousand cubic feet of hydrogen and carbon monoxide was 315 to 360 cubic feet for dry brown coal and is 305 to 335 cubic feet for brown-coal char. The entire steam supply is provided by the waste-heat boilers. I n all the plants there were elaborate installations of high-pressure boilers, superheaters, and economizers. The steam leaving the boilers a t high pressure (265 pound per square inch gage) may be put through turbines and the exhaust steam used in the process. The steam supplied to the generator per thousand cubic feet of hydrogen plus carbon monoxide was 24 to 26 pounds for dry brown coal and is 22.5 to 62 pounds for brown-coal char, with the corresponding steam decompositions of 27 t o 30 and 30 to 357& respectively. The Winkler generator has one of the GAS PRODUCTION. highest outputs per unit of cross section of any process in which comparable fine fuels can be gasified. These high outputs are due primarily to the active nature of the fuel and the intimate
565
contact of fuel with oxygen and steam as a result of the small size of the fuel and the boiling motion of the bed. The outputs of the later installations, computed on an equivalent cross-sectional area, are about half those of the earlier installations. No explanation has been given for this drop, since for a generator of a given cross section, the output can be altered only within a comparatively limited range. Below a certain output, the bed ceases to boil, although what blast there is will still find its way through the fuel bed. This immediately removes the means whereby heat is evenly distributed throughout the fuel bed. Consequently, the lower layers become overheated, and slagging results. On the other hand, as the blast rate increases, larger and larger particles are entrained to the point where the dust content of the gas becomes so high that erosion problems are created and the gas-cleaning apparatus can no longer function properly. The practical limits of output for generators, such as those a t Bdhlen and Zeitz, appear t o be 300,000 to 850,000 cubic feet per hour of water gas. Overloads up t o 1,000,000 cubic feet per hour may be permitted for short periods, but the efficiency decreases and maintenance costs, particularly of the waste-heat boiler tubes, increase. The hydrogen-carbon monoxide ratio ranges from 0.91 t o 1.65, and the corresponding methane content of the gas is 0.7 to 1.5%. Presumably, the sulfur content of the gas varies with that of the fuel. LABORAND MAINTENANCE.Four men are required to operate one generator. One man is in attendance in the control cabin, which may, however, serve more than' one generator; two men tend the waste-heat boilers, dedusting and cooling equipment, and dust handling; and one man tends the ash-handling and miscellaneous tasks. Additional labor is required for handling fuel and for attending the blowers, pumps, disintegrators, etc. At Leuna a figure of 85,000 cubic feet of synthesis gas per manhour has been given, while at Zeitz a figure of 170,000 cubic feet of synthesis gas per man-hour was estimated. SUMMARY OF WINKLERDATA. I n Table I11 a summary of design of the Winkler generators producing water gas is shown. In Table IV operating information is supplied for water-gas production from brown-coal char and brown coal. Adaptability of Winkler Process to U. S. Requirements. The presence of vast deposits of brown coal in Central Germany led to the development of huge chemical plants operating on a wholly integrated basis from mining t o final chemical products. I n these operations the production of brown-coal char occupies a very prominent position. The large quantities of fines resulting from the handling of this char could be consumed under the boilers in the power stations in competition with raw brown coal but have been more valuable for the production of producer gas,
TABLE 1x1. SUMMARY OF DESIQN OF WINRLERGENERATORS Plant Units
Formerly Now Grate
Gasification chamber Fuel bed I D. ft. Area'sq Et. Dept'h it. Over-all height Et. Waste-heat recbvery D u s t removal Prim a r y Final Use of recovered dust
-___Leuna Small 1
Large 4
1370 1025
2740 2050
D r y brown coal
1 small and 1 large grateless, remainder stationary with wedge-shapAd iron castings 400 X 35 X 125 mm. 1.5-mm. spacing between sets of 3 castings Some with bulbs on top, others straight-sided 12.8 129 3.3 43
Bdlilen
Zeitz
Magdeburg
Most (Brax)
3
3
3
5 or 6
855 685 410
750 615 308
Brow&al char Stationary grates similar t o those a t Leuna, 300 X 50 X 125 mm.
68s
...
...
Stationary grates similar t o those a t Bohlen, b u t made of fire brick 300 X 75 X 125 mm. Straight-sided
Stationary grates
18 255 3.3
14.8 13.1-14.8 172 135-172 4.9 4.9 ... 65 65 Waste-heat boiler, superheater, a n d eoonomiser
Cyclone before waste heat boiler Myltiolones after waste-heat boiler Washer cooler and Theissen disintegrator Boiler fuel Boiler fuel, returned to generator or for dephenolation
,..
I . .
685
...
1 1 grateless, remainder stationary
... 14.8 ? 172 ?
..
65
...
.
.. ... .. .. .. ... ... ... . I .
INDUSTRIAL AND ENGINEERING CHEMISTRY
566
Vol. 40, No. 4
OF WINKLER GEIYERATORS PRODUCING SYNTHESIS GAS TABLE IV. PERFORXANCE
-
Plant Fuel used Units Fuel analysis, d r y basis, C
5%
H 0
Leuna Dry brown coal 1-12 1-12,s i t . i.d. 4-18 it. i.d. 4-18 59.3 4.5 15.2
H
0.7 3.6 16.7 (8.71 9,320
S Ash
..
co H?
CH4
N2
Ills
Gross calorific value. B . t . u . / c u . i t . (saturated) T o t a l Hz CO, % Unit figiires/M cu. it. H:1 co Fuel, lb. Carbon, Ib. Oxygen, cu. ft. S t e a m used, lb. Steam raised, lb. Steam decomposition, % Carbon utilization, % D u s t blown over, lb. D u s t recovered, lb G r a t e ash, lb. Power (excluding power for oxygen production kw.-hr.) Cooling mater, U. S.gal. R a w gao produced per unit/hour,
+
+
71.0 2.6
1.3 26.5 (2.0) 10,400
25 1
...
,..
Average through No. 6, o n No. 7. With lOy0 through S o . 31/2 o n No. 4
40-50
... ...
33 1562-1652 1652-1742
,..
4,970
...
... 29 42
..
392 4,520-9,040
... ...
50-55
,..
Magdebnrg i.d
63.7 2.2
1 1
70.7 2.7 4.0 0 0 0.6
5.5 28 5 ( 2 6) 10,400-10,500 1652-2012 Through 8,'s in. o n S o . 10a
( 2 1)
9,300-9,750 Through' ko. 3111 on S o . 230
22
22 (6.4)
10,300
T h r o u g h ' On No. No. 31'2 7 7 10 10 18 18 35 35 70
io
21 302 12 1652 lG52
1472 1652
...
21.5 320-356 10 1652-1742 1652-1832
392-572
572
392-482
482
9,040-11,300
10,200-11,300 1,810-2,720 0 1-0 2 43.1 54.1
13,00o-ie,300 2,720 0.14-0.18 54-56 30
...
...
... 40 40
21.8 35.3 38.5 1.8 1.1 1.5
20 37 5 39.5 1.5 0.5 1.0
24.4 27.6 45.3
257 73.8
37 5
, . .
...
, . .
...
1.5
0.6 0.6
16.5 42.6 39.0 0.7 0 7 0.5
253 77.0
248 72.9
246 73 2
244 i3.4
267 81.6
53.5 29.2 366
41.3 27.6 320-335
50.5
66 1
38.7 33 86.5 9.5
37.4
49.4 34.4 324 53.5 54.8
40.6 28.9 331 26.1
26.3
...
2.5
22.6 , . .
88 8.4-16.8
... . .
...
r.11 ft 7,160 Syhthelis gas/sq. Et. cross section/ hour, cu. it. 5,290 a 3/s inch is a rough conversion from 10 m m .
...
... ... ... ...
68.6
1 5 .S-1'7 . 4 I .07
,..
1.14 178
..
925,000 e82,ooo
...
...
1.4
...
...
333 61 . 9
1,710,000~2,'050,000
...
685,000-855
Odd '
41 0
320 5.5. s 5n.e 35
,..
...
57
86
32.3-35.5 29.5 3.9
,.. . . ,
... ...
2.04 263
...
...
568:ddO
... ...
i , 315,000-i ,'580,000
500,0061624,000
e,700-8,050
3,980-4,QTO
3,300-4,200
6,160-6,200
2,910-3,630
2,420-3,090
rvater gas, or hydrogen. Since the fine pieces could not be gasified by the orthodox methods employed in producer gas or intermittent water-gas production, t,he JTinlrler process was developed. If similar integrated establishments were developed and provided with an abundant supply of char in t'he regions where similar fuels may be found, as in the Dakotas, Rryoming, and Texas, the process may be of value. I n the Interior and Eastern Provinces, the bulk of the bituminous coal, owing: to its plastic pioperty undergoes a change in its physical state during a temperature range where appreciable devolatilization takes place. Such behavior makes its direct use in a Winkler generator impractical, without pretreatment or mixing with a sufficient quantity of char. Grimm (16) has described short tests a t Oppau on American bituminous coal, which was fairly reactive and not strongly coking. Crushed coal, fed by a screw conveyer over the top of the boiling bed of coal, was quickly distributed into the bed and no coking occurred. No gas analyses are given for these tests, but Ilanisch (16) has reported that Brassert coal containing 38,5y0 volatile matter, which was very similar t o the rlmerican coal referred to by Grimm, yielded producer gas with the following results:
16
20
...
23.1 29.6 43.8 0.8 1.5 1.2
0.7 0.5
%
10 8 26 20
147211742 1742-1832
24.4 28.8 44.4 1.3
c u . ft.
Small unit Large unit Synthesis gas produbed/hour, cu. i t . Small unit Large unit R a w gas/sq. ft. cross sectionihoui,
Bahlen Zeita L o w t e m p e r a t u r e brown-coal coke 3-14.8 ft. i.d. 3--13.1-14.8ft.
68 0 2 0 2 2
40
... . .
covery, F. D u s t content of gas, grains/100 cu. f t . d r y gas Before d u s t removal After wriniarv removal After final re"mova1 Carbon in d u s t % Carbon in a s h , '% G a s analysis, % COZ
8 Et. i d . ft. i.d.
416,'OOO
Size of coal Through S o , 3l/z,on KO. 10 mesh \loistiwe in coal 6% 6050-9300 cubic feet per hour per square foot Throuehput Gas analysis, % 9000 c. 1 0 0 0 ~c. 11 7 CO? co 12 17 12 H Z 10 2 2 C Hd 64 x2 e3
Tests made in 1926 on bituminous coal, for vhich no other data are available, yielded producer gas of the following analyses: Source of coal Gas analysis, To
coa
GO Hz C Ha
h-2
Langenbrahm 1300° C. 2.4 29.4 3.2 1.8 63.2
Zentrum (Upper Silesia) 1300' C. 8.4 23.5 14.8 1.6 51.7
The Brassert coal behaved much like brown coal, since it was very reactive and gave a very light coke. The coal was introduced into the generator ab&e the fuel bed to avoid caking and to permit the sensible heat of the gases to evaporate some of the moisture and distill some of the volatile components. The degassing of the coal in the bed was very complete. The dust
April 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
from the Brassert coal was not as reactive as the dust from brown coal. Accordingly, some of the hydrocarbons were destroyed because the gas burned before the dust was gasified, and careful regulation of the secondary blast was required. The carbon recovered in the form of gas was 60 t o 64%, since the dust had a low ash content, and t o avoid slagging an extraordinarily large proportion of carbon was withdrawn in the residue. The fly ash and the dust were unusually light, and this was partly responsible for the high loss of carbon. The thermal efficiency, as a result, did not approach the values obtained with brown coal in the production of producer gas by the Winkler process. The use of fuels less reactive than brown-coal char would result in a greater amount of blown-over dust, since, because of the lower reactivity, it is more difficult t o gasify any dust in the space above the fuel bed, and the secondary blast tends to react with the gas rather than the dust. Operation at higher temperatures would therefore be required and would result in higher exit-gas temperatures and higher consumption of oxygen. There would also be more trouble with clinker formation, especially with fuel having ash of low melting temperature. Nevertheless, where large quantities of coke breeze or anthracite fines are available a t very low cost, the Winkler process may conceivably be used. However, for the anticipated needs of synthesis gas for synthetic liquid-fuel production, the amounts of surplus coke breeze and anthracite fines will not be adequate to supply more than a small fraction of the requirements. That the coking properties of a coal can be reduced by pretreatment has long been recognized. The principle of fluidization has been applied to the devolatilization of coal by Singh (S9),who has suggested that utilization of the char in processes intended for complete gasification of coal has strong possibilities. A continous process, in which hot char flows from a fluidized carbonizer into a fluidized gasifier, has also been suggested in testimony before the Federal Power Commission ($6). Figure 8 is a reproduction of Exhibit 11, which was presented in support of this testimony. The addition of a carbonizer and its auxiliaries t o the Winkler generator would be that much more equipment tacked on t o a process already heavily loaded with dedusting equipment. Although the volume of gas produced per unit of cross-sectional area of the generator is relatively large and although the absence of distribution difficulties in a fluidized bed enables very large units t o be used, if the large reaction space above the fuel bed and the auxiliary equipment incidental t o the removal of dust were taken into consideration and allocated in terms of equivalent cross-sectional area, the production rate might not be as favorable in comparison with other processes. Moreover, if
COAL
I
f
Figure 8.
COAL GAS
Production of city gas from coal
567
the bulk of the process steam for synthesis-gas production is raised in the waste-heat boilers, and the power for the oxygen production has its source in the gas-synthesis reactors, there would be very little credit for the blown-over dust used for power purposes, which, even under German conditions, made the difference between economical and noneconomical operation. I n that case, a dust-recirculation system would be mandatory. With such a system the fines returned t o the generator would be small and t o remain in the generator long enough t o be completely gasified would require low operating velocities. This would result in lower capacities, unless the operation were carried out under pressure. The consumption of oxygen is higher in the Winkler process than in any of the other oxygen processes and is not offset by any other factor, except possibly that fewer employees are needed per unit of gas output. PROCESSES IN WHICH FINE FUEL I S GASIFIED IN SUSPENSION IN A SINGLE STAGE
Koppers Dust-Gasification Process. The Koppers dust-gasification process falls within the seccfnd group, in which powdered fuel is gasified in suspension in a single stage. The early history of the process was reported in a confidential paper presented on June 12, 1942, before the Committee on Energy (49). The first pilot plant for producer gas, in which brown-coal low-temperature coke and brown-coal dust were used, was built early in 1938 by Braunkohle A. G. at Schwartzheide. To study the possibilities of using powdered bituminous coal the pilot plant was dismantled; and, when re-erected between Moers and Homberg a t Colliery No. 4 of the Rheinpreussen Mines, it included many changes in design t o permit the production of water gas. This plant, with an approximate daily gasification capacity of 5.5 tons of fuel, resumed operation in January 1941. By 1943 the firm had enough background of experience in operating this pilot plant to be in a position t o submit a proposal for the construction of six units (including one spare) for producing 3,800,000 cubic feet of synthesis gas per hour. The plant was t o operate on Upper Silesia bituminous coal and was t o cost 16,200,000 Reichsmarks. So far as is known, however, the plant was never built, perhaps because of the decision made in 1943 by Albert Speer, Reich Minister of Armaments and War Production, not to start any construction work that could not be put in operation before the end of the year. OPERATING PRINCIPLE. It has been pointed out frequently that there is a parallel between combustion and gasification of pulverized fuels. However, in pure combustion the reactions are exothermic, while in gasification exothermic reactions are simultaneously balanced by endothermic reactions. I n combustion there is a progressive temperature rise of each particle of fuel and a rising reaction rate until the particle is completely consumed, while in dust gasification, according to the Koppers system, after the initial phase of combustion, the excess carbon is losing heat in the course of the reduction of water vapor and carbon dioxide. This not only presupposes that there is enough heat to carry out the endothermic reaction, but also that the temperature is high enough to have the reaction move a t a rate that will completely gasify the particle within the confines of the generator. It was found in the earlier Koppers tests (at Schwartzheide) that this temperature must be 575" to 750" F. higher than the equilibrium temperatures mentioned in the literature for the corresponding gas compositions. Only then is the rate of reaction adequate for complete gasification.
568
INDUSTRIAL AND ENGINEERING CHEMISTRY
I
From fuel hopper
where the reaction is completed. Agglomerations of ash particles that are too heavy to remain suspended in the gases fall into the dust legs provided for this purpose. The generator is completely lined with a refractory material. The horizontal cylinder is provided with a double shell, the purpose of which may perhaps be for water cooling. The general plant operation is evident from Figure 10. The steam supply for the generator is obtained from the waste-heat boiler and is superheated in one of two regenerators which are used alternately. The regenerators, which are of the design employed in the Koppers and the Schmalfeldt recirculation processes, are heated b y gas from an outside source. The powdered fuel flows from hoppers to the nozzle, where it is picked up by the oxygen. The gas leaving the generator flows through a waste-heat boiler, a primary washer cooler, a disintegrator, and a secondary cooler into a holder.
I
4 .
‘ ~ a r outlet
’ p m jacket & i d ” ‘ 8 ‘ Figure 9.
Vol. 40, No. 4
Section through coal-dust gasifier
To ensure that the fuel particles will have the required temFUELOXYGENAXD STEAM USED. I n the course of the experiperatures, the Koppers dust-gasification process operates on the ments all types of fuel were considered and tried, including coking coal, noncoking coal, brown coal, and brown-coal char. I n the principle of burning powdered fuel in a deficiency of oxygen, with subsequent addition of superheated steam to the mixture of case of brown coal the moisture offered a problem if it exceeded hot gases and unconsumed fuel. 15%. Where the quality of the ash did not introduce grinding The initial reaction between the oxygen and the fuel is a t a problems, coal containing 25 t o 40% ash and brown-coal char very high temperature and results in a very high concentration with 45% ash were successfully gasified. of carbon monoxide in the mixture of combustion gases and I n the proposal for construction of the synthesis-gas plant for carbon. The immediate addition of superheated steam to this Upper Silesia coal it was specified that the coal must be readily mixture results in the final gasification of the carbon to produce ground, with about 757” passing through a t 4900-mesh sieve, hydrogen and additional quantities of carbon monoxide and equivalent t o U. S. Standard 170-mesh. Presumably, the fineness of brown coal or coke is of the same order (47). The carbon dioxide. By using superheated steam, additional heat is introduced into the system, thereby lowering the amount of oxygen required so that the ratio of hydrogen OF OPERATING DATA,KOPPERS DUSTGASIFICATION PROCESS TABLE V. SUMMARY to carbon monoxide plus carbon diReport for Committee oxide is higher. Superheated steam H. Koppers ( 4 7 ) on Energy (49) Source of data also prevents the temperature of the Central Brown coal Bituminous coal Fuel used German Bituminous steam reaction from falling as rapidly brown coal coal as it would with saturated steam. Proximate analysis, % Moisture 13.00 1.95 The principle of admitting steam Ash 5.96 8.93 Volatile matter 51.40 22.30 separately has been disclosed in many Ultimate analysis, yo patents for gasifying pulverized fuels Moisture .. .... Ash .. .... using oxygen (40, 51, 68) and using , . .... .. ,... air (17-19) and differs considerably S .. from the processes in which the oxyNS .. .... .... 0 2 gen and steam are premixed. Gross calorific value, B.t.u./lb. ... N e t calorific value, B.t.u./lb. 9220 13,780 APPARATUSAND METHODOF OPERAGas composition, yo TION. Relatively few documents with 14 11 19 15 con 35 54 35 42 co a bearing on the Koppers dust45 42 Hz 50 34 N“ 1 1 1 1 gasification process can be used to Gross calorific value, B.t.u./cu. ft. a t 60° F., 30 in Hg (sat.) give a detailed description of the apRaw coal/M cu f t . gas lb. paratus and the method of operation. Raw coal/M cu: f t . Hz ’+ CO, Ib. Oxygen/lb. of coal cu. ft. The following is deduced from the apOxygen/M cu. it. has cu ft. paratus diagrams and heat-balance Oxygen/M cu. f t . Ht ’+ CO 188 284 Steam produced, lb./M cu. ft. Hz + C O ,.. .... calculations available in the microfilm Steam consumed, lb./M cu. f t . Hz + CO ... .... Exoess steam, lb./M cu. f t . HZ+ CO ... .... reels (46, 49). Temperature of steam entering generator, e F. ... .... Temperature of gas leaving generator, F. ,.. . ... Referring to Figure 9, powdered fuel Heat in excess steam is picked up by a stream of oxyB.t.u./lb. fuel 522 703 .. .... B.t.u./M cu. f t . Hz + CO 20,670 19,700 .. .... gen and admitted through nozzles a t Heat required to superheat steam each end of a horizontal cylindrical B.t.u./lb. fuel 1042 1602 ... .... generator. Superheated steam enters B.t.u./M cu. f t . Hz + CO 41,400 44,900 ... .... % carbon gasified 95 94 . . . .... through an annulus surrounding each Gssificrttion efficiency, % nozzle and is apparently directed into Gross B.t.u. in gas .. 84.3 78.8 the burning mixture of oxygen and fuel. Gross B.t.u. in coal The opposing jets promote considerable T o t a l efficiency, % Gross B.t.u. in gas + excess steam turbulence in the space between them. ... .. 80.8 75.5 Gross B.t.u. in coal + heat t o regenerator The mixture of fuel gases and steam flows upward into a vertical cylinder
2
, I . .
t
.
I
April 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
The corresponding coal consumption per thousand cubic feet of hydrogen plus carbon monoxide . was 35.9 and 39k pounds or an increase of lo%, and the oxygen consumption was 188 and 258 cubic feet, an increase of 37%. No figures are available for comparing the steam consumption. The higher consumption of coal and oxygen may be easily explained if it could be established that the reactivity of the Rheinpreussen brown coal was lower than that of the Central German brown Stei coal, thus requiring higher temperatures of operation, which result in higher exit-gas temperatures and sensible-heat losses. Figure 10. Schematic diagram of Koppers coal-dust gasification The differences in operation between the bituminous coals is not greater than one might expect as a result of the difference in calorific value of oxygen is of 98% purity as normally obtained from Lindethe coal and normal fluctuations in operating conditions. HowFrank1 air separation plants. The steam is supplied to the ever, the difference between the brown-coal operations and the biregenerators from a header operating a t a pressure of 30 pounds tuminous-coal operations definitely reflects the difference in reacper square inch gage, while the steam is generated in the wastetivities. The consumption of oxygen for bituminous coal was 16 heat boiler at pressures ranging from 30 to 235 pounds per square t o 51y0greater than for brown coal because the required higher inch gage. operating temperatures resulted in the gas leaving at correspondDISCUSSION OF DATAON FUEL, OXYGEN, AND STEAM. Table ingly higher temperatures (in one case, 360' F. hotter). V presents comparative data on the gasification of Central The extent .to which the carbon was gasified is shown as 94 German brown coal, Rheinpreussen coking coal, Rheinpreussen to 95% and the total gasification efficiency as 75 t o 80%. bituminous coal (not otherwise identified), and Rheinpreussen GAS QUALITY. The hydrogen-carbon monoxide ratio was brown coal. 1.28 to 1.43 in the gas from brown coal and from 0.63 to 1.0 in The calorific values of the brown coals do not differ from each the gas from bituminous coal. The gas is free of gum-forming other to any appreciable extent. There is, however, a considermaterials and any traces of hydrocarbons. The sulfur in the able difference in the quality of the gas which, in the case of the coal appears in the form of hydrogen sulfide, and the amount Ceqtral German brown coal, had 85% hydrogen plus carbon of organic sulfur is small, of the order of 7.5 grains per 100 cubic monoxide, but in the Rheinpreussen brown coal had only 80%. feet when bituminous coal is used. t
Preheatw
'
Excess steam
569
570
INDUSTRIAL AND ENGINEERING CHEMISTRY
. Gas PRODUCTIOX. N o information is available on the rate of gas production per unit of cross section of the generator. I n the proposal previously mentioned five units (and one spare) were specified for the production of 3,800,000 cubic feet of synthesis gas per hour, or 760,000 cubic feet of gas per unit per hour.
Figure 12.
Vol. 40, No. 4
cost fupls, which are not suitable for those processes using less oxygen and are discussed below and in other papers of this symposium. The Koppers dust-gasification process requires less generator volume than the Winkler process, and no multiclone-type de-
Perspective view of Koppers dust gasification p l a n t
In Figure 11 is shown an elevation and in Figure 12 a p ~ 1 ' spect,ive drawing of a plant for gasifying 400 metric tons oi powdered coal per day. One pair of regenerators is designed t o serve four generators, each of which is designed to gasify 100 t,onof coal per day. Each generator has its own waste-heat boiler and primary washer cooler, but the equipment beyond this c o o l e ~ appears to be common to all four generators. These drawing3 are presented here in the hope that skilled designers of gas-plant, cooling equipment may be abIe to estimate t,hc size of thc cooler shown and scale from it the diniensions of the remaining cquipment'. LABORAND MAINTENANCE.In a 1942 estimate of the cost, of producing synthesis gas from poivdercd coai in five generators, each with an hourly capacit'y of 456,000 cubic feet of synthesis gas per hour, 51 man-day8 were used. Alt,hough the larger generators were estimat,ed to produce 760,000 cubic feet per hour, and the labor T o d d be correspondingly lower, no adjustment is made. On the basis of 466,000 cubic feet per genemt,or per hour, using 17 men to operat'e five generators, a figure of 134,000 cubic feet per man-hour is calculated. From another 1042 estimate a figure of 127,000 cubic feet of synthesis gas pcr manhour was calculated. Adaptability of Koppers Dust-Gasification Process to United States Requirements. The process is independent of the quality of the fuel Tvith respect to its composition and coking charactcristics, provided it has reasonable grinding characteristics. If the moisture content of the coal is high, it should be dried to a point where no more than 15y0remains before charging t o the generator. If the melting point of the ash is low, a slag-tapping device would have to replace t,he dust legs in the generator. The oxygen consumption, though lower than in the Winlilcr system, is st,ill rat,her high but may be offset by rhe use of low-
dusting equipment is shown. Sonic of the ash arid blown-over fuel drops out in the waste-heat boiler and the remainder in the scrubbing syst,em. On the other hand, the regenerators for superheating the steam resemble blast furnace stoves and may be costly enough to offset the saving in the cost of the multiclones. The checker bricks in the regenerators, to superheat, the steam to about 2200" F., must be of quality to withstand temperatures up to 2700' F. Elimination of the regenerators would be highly desirable if a suitable substitute means could be developed for superheating the steam, which must be done to conserve oxygen. Fuel Research Board Vortex Chamber. The Fucl Research Board vortex chamber ($281, when used as a gas producer, was found to be capable of gasifying 400 pounds of pulvcrizcd coal per hour in a deficiency of air (without steam) so as to give a producer gas of the percentage composition carbon dioxide, 3.0; oxygen, 0.1; hydrogen, 16.0: carbon monoxide, 25.7; mcthanc, 0.4; and nitrogen, 54.3. The amount, of heat released roached the high figare of 500,000 B.t.u. per hour per cubic foot of chamber space. The chamber, 3 feet in diameter, had provision for air entering tangentially, and the gases leave through a cFntral orifice after describing a vertical course in the chamber. The coal particles, entering a t a convenient point, are impelled by the vortex to take up circular orbits; and thus there is obtained, in effect, a rotating, highly porous, annular fuel bed, through which the air passes. A balance exists betiveen the outward velocity of the solid particle due to centrifugal force and the inward radial veIocity given to it by the fluid movement. I n a smaller vortex, 8 inches in diameter and 0.75 inch deep, tests were made using steam-air mixtures for gasifying pulverized coal. The steam was preheated to 1000" to 1100" F.. On a nitrogen-free basis, the gas had a percentage composition of carbon dioxide, 45.1; oxvgen, 0.8; carbon monoxide, 20.5;
INDUSTRIAL AND ENGINEERING CHEMISTRY
April 1948
571
hydrogen, 30.3; and methane, 3.3. The expedient of introducing hydrogen along with the steam and air and allowing it to burn in the distribution space was employed to obtain the steam-air mixture at or near the actual reaction temperature. This resulted in the production of a gas of the nitrogen-free composition carbon dioxide, 33.0; oxygen, 5.3; carbon monoxide, 19.4; hydrogen, 37.7; and methane, 4.6% (97'). It was recognized that the expedient of burning hydrogen could not be employed in commercial operation to raise the oxygen-steam mixture to the reaction temperature; but the experiments, which were also to include operation under high pressure, have not advanced far enough to provide a solution to the problem.
Coal dust is admitted at the top and picked up in the stream of down-flowing circulating gases. The gases and any unconsumed dust at the bottom of the chamber reverse direction and flow upyard in an annulus around the chamber, giving up.some of their sensible heat to a coil through which the oxygen and steam are supplied. Part of the gas is then withdrawn and the remainder is drawn upward by means of jets of hot oxygen and steam flowing from nozzles connected to the heating coil. A reaction takes place close to the nozzles, and the hot products flow to the top of the generator where they again reverse their direction and again pick u a hesh supply of coal dust. No industrial use has been ma& of this patent so far as is known.
Another approach may be to disregard the need for superheating the steam to the reaction temperature and to use steam superheated only to the extent that modern boiler practice will permit. Saturated steam mixed with oxygen reacting with pulverized coal in a cyclone-type generator, operated by the author, has yielded gas having a representative composition, of which the following percentage is an example: carbon dioxide, 22.2; carbon monoxide, 32.8; methane, 5.3; hydrogen, 35.8; and nitrogen, 7.2. Superheated steam will yield gas with a lower content of carbon dioxide. The extent of the gasification of the fuel may not be as great as in the Koppers dust-gasification process, but the cost of the higher carbon and oxygen requirements may be less than the extra capital costs for the regenerators. Much additional research work in the laboratory and on a pilot plant scale will be needed to determine the most economical balance.
The subject of pulverized-fuel gasification is further dealt with in this symposium (11, 19).
GASIFICATION PROCESSES USING OXYGEN WITH GAS RECIRCULATION
KO processes, depending entirely on oxygen for the heat of reaction, using gas recirculation are known to have been put into operation on a commercial scale. Schmalfeldt Process. The Schmalfeldt process in the Wmtershall A. G. plant was originally designed for gasifying coarsely ground brown coal by means of circulating gases and steam. Regenerators heated by gas from separate producers were used to supply the heat for the reaction to the circulating gases. D r y brown coal, fed into the stream of hot circulating gases and steam, was gasified while in suspension in the stream flowing through two large generators in series. The coarsely ground raw brown coal was fed into the hot gas stream flowing through a dryer beyond the second generator; the sudden heating of the raw brown coal by the sensible heat of the gases caused decrepitation of the coal with explosive violence. The gases, moisture, and dried coal then flowed through separators, from which part of the coal was sent to join the circulating gases at the inlet to the first generator and the remainder to the gas producers. The gas leaving the separators flowed through a washer, after which it was divided, one part for recirculation, and the remainder to another washer and the purification system. I n practice, however, the installation did not function as expected. Although the designed capacity per unit was 760,000 cubic feet of synthesis gas per hour, the maximum obtainable was 570,000 cubic feet. T o provide additional heat for the reaction that was necessary to bring the plant to capacity, oxygen was admitted a t several points in the first and second generators. This raised the maximum output to 1,140,000 cubic feet, although usually it ranged from 760,000 to 950,000 cubic feet per hour. This was the only commercial process functioning on raw brown coal. Since, however, the process was not specifically designed for, but was rescued by, the use of oxygen, no additional space will be devoted to it here. Critical evaluations of the process have been reported by Hollings (20) and Morley (39). Metallgesellschaft Dust-Gasification Process. A process using oxygen for dust gasification which depends on recirculation has been patented by Metallgesellschaft (Lurgi) (33). I n prinCOZ = 2CO and C HzO = ciple, only the reactions C CO Hz take place in a central chamber in which the heat of reaction is provided by hot circulating gases.
+
+
+
PROCESSES IN WHICH FINE FUEL IS GASIFIED IN A FIXED BED AT NORMAL PRESSURE
The gasification of medium-fine, noncoking, low-volatile fuels in a fixed bed at ordinary pressure has long been practiced in airblown gas producers. Recently tests were conducted on the use of rice and barley sizes of anthracite in this type of producer converted to oxygen-blown operations (67). Detailed information on the use of oxygen for gasifying small anthracite sizes is further supplied by Wright and Mitchell (56). PROCESSES IN WHICH FINE FUEL I S GASIFIED IN A FIXED BED AT HIGH PRESSURE
Lurgi Pressure-Gasification Process. The Lurgi pressuregasification process gasifies fine fuel in a fixed bed. This process has been extensively treated in the literature, and almost every review that appeared before 1945 presented information based principally on the material appearing in two reports prepared by members of the Lurgi organization (6, 94). Information on operation of the Bohlen plant, which includes 10 Lurgi pressuregasification units, was recently made available in a Technical Oil Mission Report (21) and in a paper by Weir (55). All the available information on the process has been assembled in a single report (22) and also reviewed in Coke and SmokelessFuel Age (@. The material that follows is based principally on the foregoing reviews and reports. The first high-pressure gasification plant, rated a t 133,000,000 cubic feet of gas per year, was put in operation for city-gas production at the A. G. Sachsische Werke at Hirshfelde (near Zittau) in. 1936, using two generators of 3.77-foot internal diameter and capable of producing up to 570,000 cubic feet per day. I n 1940 the company put in operation at Bohlen a plant consisting of five generators having a n internal diameter of 8.2 feet. In 1944 five additional generators, with a number of improvements, were put in operation at this plant. The total capacity of the ten units a t Bohlen is rated a t 16,400,000 cubic feet per day. The gas is sold to the Energie A. G., which operates a gas grid of 125 miles of mains from which gas is distributed to individual consumers and other gas distributors operating a n additional 600 miles of mains. I n 1942 the Sudetenlandische Treibstoffwerke installed at Most (Brux) equipment for producing some 3,000,000,000 cubic feet of gas per year, or 8,750 000 cubic feet per day. A pipe line from this plant to Prague has recently been constructed, presumably for the transportation of city gas, which includes the Lurgi product. No plant designed primarily for synthesis gas, using the Lurgi pressure-gasification process, is known to have been in operation. Such a plant, however, was proposed for the Societh Italiana Carburanti Sintetici and was to be erected a t San Giovanni Valdarno (near Florence) Italy. Synthesis gas was to be produced from lignite using eight Lurgi generators of 8.2 feet internal diameter and operating at a pressure of 24.5 atmospheres. The invasion of Italy by allied troops ended this project before any appreriable progress was made. OPERATING PRINCIPLE. I n the Lurgi pressure-gasification process, the fuel is gasified in a stationary bed supported on a rotary
INDUSTRIAL AND ENGINEERING CHEMISTRY
512
grate as in any gas producer operating a t normal pressure. The producer, however, is designed to withstand high operating pressures, and provisions are made to permit charging the fuel and discharging the ash through hoppers without interrupting the gas-making operation and disturbing the pressure. I n normal gas-producer operation, the use of very h e fuel is a serious limiting factor on the rate of gasification because of the resistance to the flow of gases. Channeling frequently occurs and requires arduous labor to correct it. Since the velocity of the gases at high pressure decreases in proportion to the pressure, the resistance through the fuel bed falls off, and difficulties such as channeling and blowing over of material are minimized. The velocity of gasification also improves with increasing pressure. The task of stripping tar and light oil, cooling the gas, and removing carbon dioxide and sulfur is greatly simplified in high-pressure operation. The fuel entering the top of the generator is dried by the hot gases leaving. The dried fuel passes down the generator and is carbonized by contact with the gas, yielding a low-temperature tar. The coal must be noncoking or must have been pretreated to prevent caking during the carbonization. After carbonization, the fuel passes through the gasification zone to the combustion zone at the base of the generator. When steam and oxygen reacts with the fuel, a gas practically free from methane is formed first; but as this gas rises through the fuel bed its temperature falls, and reactions occur leading to the formation of methane in the cooler zones. The temperature in the combustion zone depends on the ' melting point of the ash, below which it is necessary to operate. The temperature is controlled by the relative amounts of steam and oxygen admitted. The most favorable ratio must be determined by experience with the particular fuel. The gas composition is influenced by the temperature and pressure of operation. The methane-forming reactions have considerable significance in pressure operation, as is pointed out above. Increases in pressure result in increases in the proportion of methane in the gas, although the rate of increase falls a t the higher pressures. Increases in temperature, however, inhibit the formation of methane, so that the higher the temperature the less the percentage of methane in the gas, even at the higher pressures (see Figures 1 to 4). The formation of methane, which occurs during gasification at high pressure, may be due to a number of causes: Most, if not all, of the hydrogen contained in the fuel is kvolved in combination with carbon as hydrocarbons; little, if any, is obtained as free hydrogen. Hydrocarbons may be synthesized by hydrogen from the decomposition of steam combining directly with the fuel-for example: C f 2H2 = CH4 Hydrocarbons may also be synthesized by interaction of the hydrogen and carbon monoxide produced during gasification
CO
+ 3H2 = CH, + HzO
Hydrocarbons may be formed as primary products during gasification
or
3C
+ 2H20
2C
+ 2Hz0 = CH4 + COz
CH,
+ 2CO
The amount of methane fornied by the last of these methods is negligible under the conditions existing in the Lurgi generator, while the amount that can be formed by the first three methods is limited. The limitation is due to the fact that the methaneproducing reactions liberate heat which, if not absorbed in some way or other, will raise the temperature of the fuel bed to a point where further synthesis is prevented. The heat is absorbed readily and efficiently when the gasification of the fuel in steam can be maintained at Iow temperature, as is the case with fuel of
Vol. 40, No. 4
high reactivity. With fuels of low reactivity, this is difficult to accomplish, except a t low rates of operation (9). Since the formation of methane is exothermic the heat required for the reaction is reduced, and the volume of oxygen required is, therefore, lowered. On the other hand, the methane in synthesis gas is a diluent and is undesirable except as an enricher for the tail gas from the Fischer-Tropsch process which may some day become a substitute for natural gas. APPARATUS AND METHOD OF OPERATION. The A. G. Sachsische Werke plant a t Bohlen had been in operation for about 5 years before the American forces and groups of British and American technical investigators arrived in the Central German brown-coal region. The plant suffered practically no damage, but was shut down for a brief period as a result of dispersion of the German operating personnel and cessation of work by the Eastern European slave labor. Before the zone was turned over to the Russian authorities, the plant resumed operation under the sanction of the United States Military Government, and opportunity was afforded to a group of investigators, including the author, to observe the operation and study the details of the' equipment. The plant is presumably still operated by German personnel under Russian supervision. The fuel gasified usually consisted of mixtures of dried brown coal and pieces of uncarbonized briquets. The material is transported to the plant by rail in special containers holding about 4 tons each. An automatic valve a t the bottom of the container opens when it is lowered by traveling crane into the bunker. Both the five older and the five newer units are housed in the same building, 102 feet long, 56 feet wide, and 105 feet high. The newer generators differ from the older type in the design of the charging hopper, grate-drive mechanism, and arrangement for scraping the generator dome. Each generator has a rated capacity of 114,000 cubic feet per hour and is normally operated a t 95,000 cubic feet per hour of gas having a calorific value of 440 B.t.u. per cubic foot. The charging hopper on the newer generators consists of a chamber 9 feet high by 6.56 feet in external diameter, with a capacity of 265 cubic feet. The top connects with the overhead bunker, which has a capacity of 50 to 60 tons of fuel, and the bottom with the generator through manually operated valves. The method of charging is as follows: The bottom valve is closed, and the gas in the hopper is blown off t o a small holder. The upper valve is then opened, permitting coal from the bunker to fill the hopper. This takes about 5 minutes. The upper valve is then closed. The free opening of the upper and lower valves is 9.8 inches. When the upper valve is lowered, it permits a cylinder resting upon it to move down to an extent limited by lugs specifically provided for the purpose, leaving the coal from the bunker free to flow through the cylinder and the space between the bottom edge of the cylinder and the valve into the hopper. When the upper valve is closing, it makes contact nith the movable cylinder, shutting off the coal and leaving the surface of the valve clean before it is seated. Gas is then admitted t o the hopper through a special connection provided for the purpose and finally the bottom valve is opened. A suction system is prdvided for removing escaping gases and dust during this operation. Nitrogen from the airseparation plant is blown continuously through the bunker. The total volume of the gas blown off during the charging operation represents from 5 to 77, of the total gas made and is not included in the reported production of gas. The frequency of charging is governed by the volume of the hopper. The generator consists of a double shell, the outer one acting as the pressure cylinder and the inner one performing the function of the gas-producing unit. The outer shell is 9.8 feet in diameter and has walls 1.85 inches thick. The inner shell is 9.2 feet in diameter and 22.3 feet high, with a capacity of 1240 cubic feet. The space between the t n o shells constitutes a water jacket connected to a steam drum in which the pressure is maintained equal to that of the inside of the generator. This is accomplished by leading the small quantity of steam produced directly into the generator-gas offtake pipe. As a result of the equalized pressure, the generator wall, which is exposed to the gases at high temperature, is not stressed with the difference between the gasification pressure and the atmosphere. The generator is brick-lined from the top down to within 3.3 feet from the grate. The inside diameter of the lining is 8.2 feet. The bricks are dry-set in contact with the steel; and no difficulty with expansion has been experienced, according to the operators.
April 1948
573
INDUSTRIAL AND ENGINEERING CHEMISTRY
The lining in the generators built earlier was 4 years old in 1945 and still appeared good. The steam drum is a horizontal cylinder 3.3 inches long by 2.0 feet in diameter. A skirt is provided around the coal inlet to maintain a gas space over the fuel bed. The skirt also supports a system of scrapers for removing &ch and carbon from the dome and brickwork of the generators. These scrapers are driven electrically a t the rate of 10 revolutions per hour through reduction gearing by means of a motor rated a t 0.5 kw. and are operated for 6 minutes every 2 hours. Inside the skirt is suspended a conical ring and beneath it a double cone whose combined purpose is to avoid segregation of the fuel and to equalize the pressure across the fuel bed. Figure 13 is a drawing of the generator. The grate is operated continuously, and its speed of rotation is determined by the quantity and the character of the ash. The ash zone normally extends 12 to 20 inches above the grate. The temperature of the fuel bed and condition of the ash are controlled by the relative amounts of steam and oxygen used for gasification. The temperature of the reaction zone was given as 1900" t o 2100" F. The minimum permissible melting point of the ash was 2000" F., and fuels containing up to 30% ash may be used. The carbon content of the ash is 5 to 6%. The grate is slightly domed and composed of three sections, in each of which is fitted a detachable plough arranged to direct the ash falling over the edge of the grate into a cylindrical space beneath it. Stationary plows above the grate were tried and abandoned. A vane attached to the shaft of the grate scrapes the ash into the opening leading to the ash hopper. The diameter of the grate is 5.25 feet, the center being 5.9 inches above the circumference. The grate sections are preferably cast from 25% chromium steel and have a normal life of 3 years. The drive shaft of the grate is hollow, to provide inlet for the oxygen-steam mixture used to gasify the coal. The opening is covered by a cap 2.6 feet in diameter, supported to provide an opening 0.8 inch between the cap and the grate. The grate is driven by a 4.5-kw. motor through a reduction gearing and ratchet device, which can be adjusted t o change the speed of rotation. The grate, complete with the drive mechanism, is supported from the generator shell. The ash leaving the generator passes into the ash hopper through a valve similar in construction to the lower valve of the charging hopper, except for difference in size. The diameter of the ash hopper valve is 11.8inches, while that of the charging hopper is 9.8 inches. The ash hopper is 8 feet high by 5.2 feet in internal diameter and has a capacity of 124 cubic feet. It is inside a heavy pressure cylinder 5.6 feet in diameter. The annulus between them acts as an insulating gas space. The base of the hopper is closed by means of a disk clamped by four swing bolts. The hopper is surrounded by a steam coil a t the base to prevent condensation of water on the ash. The ash is discharged through a portable sieve into a water trough a t intervals of about 2 hours, the procedure being to close the upper valve and release the oxygen and steam to the atmosphere before opening the lower valve. After the lower valve is closed, steam is turned in to build up the pressure before the upper valve is opened. The gas-making operation is not interrupted by the ash-discharging steps.
No clinker difficulties have been experienced, except during periods of irregular operation, and the ash discharged is normally very fine. Irregularities in operation were caused by air raids. Normally the generator can be operated for 250 consecutive days, including about 30 miscellaneous shutdowns totaling 90 hours. The total time lost for both major and minor repairs is about 2000 hours a year. To maintain a high calorific value of the gas, the volume of steam used is kept as low as possible, the limit being defined by the character of the ash. If sintering occurs, the generator must be cooled by the addition of more steam. Formation of slag in the generator is to be suspected if the jacket temperature iluctmates or the gas make varies with a rise in outlet-gas temperature and an increase in the power consumption of the ash extractor. The rate of ash extraction is adjusted to the generator load. If too much ash is extracted, the ash contains too much combustible material, while if too little ash is extracted, the gasification zone moves upward, as shown by a rise in the outlet-gas temperature.
A generator can be started from cold in 12 to 18 hours, using a layer of about 15 inches of ashes over the grate with a thin layer
of coal on the top ignited with wood and wood shavin s. Air ie substituted for oxygen when starting up, and the gas is &char eds t o a stack a t the top of which it is burned. Steam is then adled and the fuel bed built up. When the generator is hot, gas making roceeds, using oxygen and steam. T i e oxygen is su plied by a Linde-Frankl plant consisting of four units, two rateXat 1000 cubic meters per hour and two rated at 2000 cubic meters per hour-equivalent t o a total of about 210,000 cubic feet of free oxygen per hour. The oxygen is of about 9501, purity and is su plied to the generators by compressors a t 23 atmospheres a n x 100' F. The installed power capacity of the oxygen plant is 4600 kw.
\
/FUEL
HOPPER c NITROGEN
-AIR -SUCTION
RELEASE LINE
STEAM DRUM
Figure 13.
Lurgi pressure generator
The gas leaves the generator a t a temperature of about 575" F., passing through an offtake pipe provided with hand-operated scrapers operated twice per shift. The offtake pipe also contains water sprays. The gas then passes into a spray cooler. It is clear that the design of this spray cooler has given trouble. The apparatus is dealing with water, gas, tar, and dust. It appeared that four or five different designs were in use in the plant, the general design in each case making use of changes in the direction and the action of the water spray to wash out tar and dust. The over-all dimensions were 6.6 feet high by 1.6 feet in diameter, and the whole cooler was water-jacketed for additional cooling. The tar is discharged through a trap, and the water is recirculated t o the sprays through an indirect cooler. A total of about 13,200 U. S. gallons of water per day is discharged from the spray cooler systems. Dust is carried away in the water and in the tar. Troubles have been experienced due t o emulsification of the tar and water. The gas, leaving the spray coolers a t about 300" F. and 20 atmospheres, is collected separately from each half of the house. Each stream passes through two vertical water-tube primary coolers in which the temperature is reduced to 212" F., then through a tar precipitator of the multibaffle type, followed by three vertical, water-tube secondary coolers to condense light oils. Each primary cooler has 48 tubes 23.4 feet long (1.9 inches in internal diameter) with walls 0.18 inch thick and has a heattransfer surface area of 640 square feet. Each secondary cooler has 174 tubes 23.4 feet long (0.91 inch in internal diameter) with walls 0.14 inch thick and has a cooling area of 1100 s uare feet. The gas is then washed with oil in a Raschig ring scr&ber 31 feet high by 3.9 feet in diameter t o recover benzene.
INDUSTRIAL AND ENGINEERING CHEMISTRY
574
TABLE VI.
S l i l I ~ I A R YO F LURGIPRESSURE
Period Equipment in operation
September 1942 5 older gcnerators
Cross-sectional area each generator, six. f t . Production Purified, gas, M cu. ft. T a r , short tons Benzene, short ions Gas liquor, U. S.gal. Maximum daily gas production, 11 cu. it. Mean daily gas production, i\I cu. it. Mean hourly generator output, cu. f t . Mean gasification rate Cu. ft. gas/sq. ft./hour Lb. fuel as charged/sq. ft./hour Consumption Coal, short tons, briquet pieces as received Dry, ash-free Lumps, as delivered Dry, ash-free Espenhain coal as delivered D r y ash-free Total coal as delivered Total coal as delivered/M cu. ft., lb. Total coal, dry, ash-free Total, dry ash-free coal, IbJN cu. it. Pure oxy en used R.1 cu. it. Cu. ft.yR.1 c,u. fi.,purified gas Steam for gasificatiqn, short tons Lb./hf cu. f t . purified gas T o t a l steam used, tons Lb.(hI cu. i t . purified gas Electricity used in oxygen plant kw.-hr. Per hf cu. f i . purified gas, kw:-hr. Total electricity used, kw.-hr. Per M cu. ft. purified gas, kw.-lir. A-ater Plant v a t e r , U. S. gal. Drinking x a t e r U S. gal. Total U. S.g a I . ) k cu. ft. purified gas Recycled cooling water/RI c u . ft., U. S. gal. Recycled cooling water/M cu. it., E.S. gal. Analyses, % COZ HzS CnHm €19
\-0
Sp, gr. (air
=
1)
Ratio H9:CO Hz CO in purified gas, % Calorific value, B.t.u. leu. f t Tar Density a t 60' C. kg./litei D u s t content. 7n Jvater content,'% Settling point Gross calorific value, B.t.u. per lb. Benzene Density a t 15O C., icg./'liter Distillate t o 180' C. Distillate i o 190° C. 9570 distilled a t Gross calorific valuk B.t.u./lb. Liquor, gal. per liter. Carbon dioxide Ammonia Phenol Tar
+
Coal, as delivered, 70 composition Combustible material Water Ash T a r content Carbonization water content D r y ash-free C H S N + O Gross calorific value, B.t.u./lb. Yields Purified gas from coal cu. it. per short ton Purified gas from d r y ' ash-free coal, cu. ft./short ton T a r plus benzene c a l c h a t e d on basis of tar in coal by Fischer method, 70 Proportion of benzene i n t a r plus benzene, 7'0 T a r plus benzene recovery from gas, Ih./M cu. ft. Thermal efficiency calculated on gross calorific value % Gas tar benzene, coal Gas Coal Miscellaneous Oxygen purity, % Steam decomposition (excluding jacket), % Oil consumption, Ib. Grease consumption, lb. T a r loss in liquor, short tons Based on coal content % Quantity of released gas: M 011. it. Calorifio value of released gas, B.t.u./cu. f t .
+ -
+
Gas Droduction/man-hour, cu. it.
January 1945 Older and ne\ver gencsators available 53 7
53 7 3,703,000 12,730 4,940 28,700,000 13,220 10,140 94,440
408.400 1,308 555 4,240,000 16,150 14,100 90,860
18,030 15,130 87,000 -93,000
1,690 162 6
1,760 162.5
1.690 157.7
1,fjP0-1,770 152-1 66
...
4,740 3,550 7,260 4.490 12:Odo 96.5 8,040 64.8 30,920 149 10,300 82.6 10,900 87.8 1,244,340 5.01 1,839,008 7.39 3'3,100,000 272,100 158 1P,120,000
56 5 Puiifiod
Crude
0.9
CO
February 1944 Some of newer generator, arailaple ,,3 7
53 7
gay
CHI
GASIFICATIOS RESULTS A T BOHLEN
Year of 1943 5 older generntors
248,700 722 239 2,170,000 10,140 8,284 90,660
3P.Y 1.3
0 2
Vol. 40, No. 4
0.2 13.2 33.0 1,-> ,4 1.0 0.777
...
pas 6.3 0 0 0 8 0.1 !8 6 rl 1 2 22.0 1. 0 0.437 2.73
69.8 454
. .
0 . '332 0.17 0.46 30.9O C 17,080
0 828 81.6% 85.47"
2180 17,580
Brjcjiiet piece 74.9 13.1 12 . 0 14.8 18.9
68.01 7.81 3.29 20 89 12,680
c.
4.48 4 , 1J 4.72 27.91 Lumps 61.9
28.9 9,2 12.3 33.9
468.40il 1,212 324
3,340 4,030 10,360 6,530 3,420 2,275 19.120 93.8 12,835 62 9 63,640 156 16,320 79 6 20,300 99 4
, . .
,..
...
...
172,006 92.8 117,200 63.4 533,500 144 140,000 75.6 170,500 91.9
3,3iO
4,020 8.940
5,930 7.330 4,790 21,020
'32 . %5
14.710 62 8 b8,130 14.5 20,100 8 5 . .5 26,330
112.8
( I t was claimed that power consumption in Linile-Frank1 plant a t Ddhlen v a s excessive. A t Leuna power reciuirenients were about SOY0) 2 5,010,000 2,866,404 3,402,865 6.76 7.0 7 24 540,000,000 14.5 93,600,000 23.3 Crude Purified gas
gas
32.4 1.6 0.9 0 2 13.6 35.1
7.7 0 0 0 Y 0.2 18.7 49.6
15.4
22.1
0.8
0.8 0.486 2 66 68.3
..
..
.. , .
456 ,
~1,600,000 875,000 128 14,760.000 Crude gas
32 1
...
~urifi&~ gas 6.8
0 2 12.9 18 3 35.7 52.2 14.9 20.6 1.6 1.2 0 771 0.463 2.85 70,5 442.5
Crude
1;i;iified
"as
gas
35.1 1.6 0 7 0 2 12,l 37 5
9.1
0.0
0.6 0.2 16 7 32 3
20 0 1 1 0.499 3.12
1 4 .i 1.3
0.733
69.0 424
, . .
0 930 0 06 0.63 33 9" c 17,290
17,im
0.827 82.lY0 86.7Cl, 214" C. 17.950
0 828
. .
...
17',i30
R1ixi.d coal 68.1 21 . 0 10.9 13.6 26 9
lid
i::: 0 1
0 933
4 85 4.54 4.9'3 11.25
03,500.000
Br!quer
... ...
4.78 4.07 4.29 14.74 Zs13-
pieces 75.8 14.0 10.2 15.2 21.0
1,ulnp-i
12.7 35.2
8 3
enhain 66.4 19.3 143 12.8 25.7
70.05 5.28 3.00 21.67 12.240
71.22 5 27 3.39 20.12 12,130
69.78 5.51 4.19 20.52 12,400
63.0 28 7
Brici ne t pieces 74.9 13.5 11.6 15.5 20.1
..
Csg-
Lulllps 66.0 24.8 9.1 13.6 31.3
enhain 65.4 21 5 12.9 13.4 26 2
.. .. .. .. ..
..
..
69.89 7.51 3.04 19.56 12,720
69.49 5.85 3.08 21.57 12.620
20,700 30,900
21,580 31.620
60.2
7Z.S
72.7 29.8 9.14
... ... ...
7i.e
78 0
78 6
...
24.9 7.74
... ...
21,400 31,830
.. ..
., ,,
..
I .
21,700 31,900
35.3
57.2
57.7
...
94.5 45.4 3,892
95.0
95.1
... ...
159
250 15.7 126,800 45,(HzS 3.8% not included)
...
3,068 181
...
5.8 1,511,000 90 (HnS 3 . 9 % included)
..,
...
... I..
259 10.1 170,000 104 (HaS 3 . 8 % not included) 10,900
95
.
I
.
... ... ...
... ...
April 1948
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
The cooling of the gas, removal of condensable products, and oil washing are followed by scrubbing under pressure with water to remove carbon dioxide and hydrogen sulfide. Each of the two gas streams is washed in two towers in parallel, 6.9 feet in diameter and 69 feet high, packed with two layers of 2inch by 2-inch Raschig rings, the total packed volume being 1820 cubic feet per tower. Water drawn from a collecting tank is umped to the top of each tower and led from the base to a turine of the impulse type, where its pressure is reduced from 20 atmospheres to 2. During this expansion, carbon dioxide and hydrogen sulfide and other dissolved gases are evolved, and the work performed is used by coupling the turbine to the highpressure water pump and the electric motor that drives it. The mixture of water and gases leaving the turbine is separated in a vessel whose gas space is connected to the turbine housing, so that the rotors run in a water-free atmosphere. The gas and water are led separately under their own pressure to the top of the aeration towers-two for each gas stream, 52.5 feet high and 13 feet in diameter-packed with wooden grids. The aeration towers are divided in two parts. I n the upper part-which contains two layers of grids 11 feet high with 32,500 square feet of surface-the water, now a t atmospheric pressure, releases gas which, together with gas evolved from the separating vessel, is led to the powerhouse and used under the boilers. The water then passes through a seal to the lower part of the tower containing two layers of grids 10.2 feet high with a total of 30,000 square feet of surface, where it is blown with air; this air, containing hydrogen sulfide, is sent to the base of the powerhouse stacks, where it was claimed that the hydrogen sulfide and sulfur dioxide react to give sulfur, which is discharged to the atmosphere. The aerated water returns to the collecting tank. The washed gas passes to a separator for removing entrained water. The volume of water circulated in the pressure washing system is about 70 U. S. gallons per thousand cubic feet. After water washing, the gas passes to the Lux purifiers. These consist of two parallel sets of four boxes, three of which are in use while one is being recharged with oxide. The working life of a charge is about 4 weeks. The boxes are 4.9 feet in diameter by 24.5 feet high and contain five trays, each with two layers of oxide 16 t o 18 inches deep, the gas flowing in parallel through the 10 layers of a box while three boxes operate in series. The gas enters with 4 to 12 grains of hydrogen sulfide per 100 cubic feet and leaves with 0.7 part per million. About 22 tons of Lux are used per year. Since the gas was used for public utility distribution, the organic sulfur content of the gas was not determined. The total pressure drop in the whole cooling and purifying plant is about 1 atmosphere.
FUEL,OXYGEN,AND STEAMUSED. Adjacent to the A. G. Sachsische Werke a large low-temperature carbonization plant of the Lurgi circulating-gas type is in operation in which browncoal briquets are carbonized. Brown coal from the Bohlea strip mine is delivered with about 52% water. It is dried to reduce the moisture content of the finer material to about 15%, although the larger lumps still retain up to 25% water. The dried fine material is then briquetted without binder into 2.5-inch cubes. These are then delivered to the low-temperature carbonization plant. The fines resulting from the handling of the briquets, together with the larger lumps of the dried brown coal, which are unsuitable for briquetting, are gasified in the Lurgi pressure-gasification plant. Additional pieces of briquets often are brought in from Espenhain. In general, the briquet pieces and dried lumps are gasified in the proportion of 1 to 2, but either one may be gasified alone. The size of the material is generally between about 0.375 inch and No. 7 U. S. Standard screen (3 to 10 mm.), with a maximum of about 0.75 inch (20 mm.), and the amount of material smaller than No. 10 (2 mm.) must not exceed 8 to 10%. The material is highly pyrophoric and must be transported in closed containers. On a dry, ash-free basis, approximately 60 to 65 pounds of fuel are used per thousand cubic feet of purified gas produced. Oxygen is supplied a t a purity of 95%, a pressure of 23 atmospheres, and a temperature of 105" F. About 150 cubic feet of oxygen are required per thousand cubic feet of purified gas. Steam reaches the plant at 716' F. and is superheated to 932 O F. by burning the gas blown off from the charging hopper. The amount of steam required to produce 1000 cubic feet of purified gas is 75 to 85 pounds.
575
TABLEVII. TESTSON WIESCHE LEAN COALAND XARSTENZENTRUMCOALIN HIRSCHFELDE GAS WORKS Coal
Wiesche
Karsten-Zentrum
83.6 10.4 2.4 3.6
99:5 0.5
81.24 7.16 5.04 6.56
Ash
.
Water Gas (by difference) I-Iourly coal consumption, lb. As charged Drv MGisture- and ash-free Unit coal consumption, lb./sq. ft./hour As charged
.
54.1 32.3 6 4
i.5
11,920
I
91.40 0.11 0.38 6.56 1.55
72.4 9.0 5.4 7.2 6.0
560 494
765 710 . 660
50 46.8 44.1
68.4 63.4 58.8
__
52.5 .~~
g & t u r e - a n d ash-free
21 Atmospheres Calcd. from Crude Clean crude
5 Atmospheres Calcd. from Crude clean
Gas analyses, %
coz Ill.
n - ."
co
Ha CHI Ne B.t.u. (calorimeter) B.t.u. (calculated) Clean gas produced cu./fr./hour Crude gas produced, cu./ft./hour Oxygen Purity, % Consumption, cu. ft./hour on 100% purity basis Steam Temperature, F. Consumption, lb./hour Yields, cu. ft. Gas/T coal a s charged G a s / T coal dry Gas/T coal moisture and ashfree Coal per M cu. ft., lb. As charged Dry Moisture- a n d ash-free Oxygen (100 per cent pure basis), CU. ft. nf CU. ft. Steam, lb./iM cu. ft. Influence of pressure on gas composition Crude gas, yo COa Ill. 0 2
co
HZ CH4 Na Gross heating value, B.t.u./ cu. f t . Clean gas (calculated), % COa Ill. 0 2
co
Ha CHI N2 Gross heatinn value. B.t.u./ cu. ft. Ratio, Hz:CO Percentage Hz CO Grate area, sq. f t . Gasification rate, cu. ft./sq. ft./hour
-
+
27.0 0.2 0.0 20.3 38.5 12.3 1.7 3i4
0 7 1.0 0.2 0.3 0.0 0.0 26 5 27.9 54 9 52.9 16 1 16.9 16 1.0 410 424 433 16,300
....
26.4 0.4 0.1 21.6 41.9 6.7 3.0
1.0 0.6 0.1 28.9 56.4 9.8 4.i
..
..
19,300' 27,600
84 7
83.2
3230
3580
914 1325
869 1090
58,100 62,200
50,400 54,300
66,000
58,300
34.4 32.3 30.3
39.7 36.8 34.3
198 81.4
186 56.7
Pressure, Atmospheres 10.1 15.0 21.0 30a
27.4 0.3 0.2 17.6 43.8 9.1 1.6
27.7 0.2 0.1 18.2 40.5 10.8 2.5
27.0 0.2 0.0 20.3 38.5 12.3 1.7
28.5 0.2 0.0 22.2 33.3 13.9 1.9
293
299
314
318
5 Atmospheresb
..
..
.. . 1
.. ..
..
..
1 .o 1.0 1.0 1.0 0.4 0.3 0.3 0.3 0.3 0.1 0.0 0.0 24.3 25.6 27.9 31.2 60.4 56.8 52.9 46.9 12.6 15.2 16.9 19.6 1.0 1.0 1.0 1.0
1.0 0.5 0.1 30.3 60.6 5.5 2.0
405 421 432 449 2.48 2.22 1.89 1.50 84.7 82.4 80.8 78.1 11.2
353 2.0 90.9 11.2
1450
1720
a Extrapolated. 6
Adjusted to 2.25 times rate of operation.
GASPRODUCTION AND QUALITY. The rate of gas production is of the order of 1600 to 1800 cubic feet of gas per square foot of generator cross section per hour. The gas has a gross calorific value of about 450 B.t.u. Accordingly, the rate of gasification on a heating-value basis is 7 to 8 therms per square foot per hour.
576
INDUSTRIAL AND ENGINEERING CHEMISTRY
A blue-gas generator may be rated from 2200 to 2800 cubic feet of 300-B.t.u. gas per square foot per hour, and its rate of gasification on a heating value basis is 6.5 to 8.5 therms. There is, therefore, little choice between them on basis of heating value. On a synthesis-gas production basis, however, the capacity of the Lurgi unit is considerably less than that of a blue-gas generator, because the comparison necessarily is on a volumetric basis, taking principally into account the sum of hydrogen plus carbon monoxide, which is about 70Oj,. The hydrogen-carbon monoxide ratio ranges from 2.66 to 3.12.
50
40
4.
8
E
30
I
1
I
2
4
I
I
I
I
6
S
10
I2
14
I
1
16
18
20 I
22
Gasiflcatlon Pressure Atmospheres ((1bS)
Figure 14.
Composition of crude gas as function of pressure
SUMMARY OF BOHLENDAT.~. Table VI shows operating information on the Lurgi pressure-gasification plant a t BiShlen. All the results shown are for dried lumps of brown coal and for pieces of brown-coal briquets before carbonization. LABOR. The gas production per man-shift during February 1944 was 87,200 cubic feet. I n the Winkler process, the figure given was 11.7 man-hours per million cubic feet of synthesis gas. Assuming a man-shift equal to 8 hours, the gas production is 10,900 cubic feet per man-hour in the Lurgi process and 85,500 cubic feet in the Winkler process. The importance of having large units is made clear by this comparison. For pressure gasification, however, there is a technical limit to the size of the unit because the stresses would require construction of the outer shell with too great a thickness. Furthermore-and this applies to any pressure of operation-stationary fuel beds of too great a diameter are extremely difficult to keep uniform when small sizes of fuel are gasified. Adaptability of Lwgi Pressure-Gasification Process to U. S. Requirements. The Lurgi pressure-gasification process has conclusively proved its value for gasifying brown coal. This fuel is non-caking and highly reactive. T o gasify it under pressure, the volume of oxygen consumd is about half the amount required by the other processes in which coal of the same character could be gasified. The American fuels nearest in behavior to brown coal are the lignites and subbituminous coals. There is every reason to believe that these fuels could be handled without difficulty in the Lurgi pressure process. To determine whether the process is suitable for other American coals, some indication may be obtained from short tests made on high-rank fuels in Germany (48). These fuels ranged from
Vol. 40, No. 4
Wiesche lean coal, with a fixed-carbon content of 81.24% and a volatile-matter content of 7.16% to Karsten-Zentrum coal, with a fixed-carbon content of 54.170 and a volatile-matter content of 32.3%. The first coal resembles Pennsylvania anthracite in analysis, while the second resembles a good grade of bituminous coal. The results of the tests are shown in Table VII. The Wiesche lean coal was gasified smoothly, and no signs of caking were detected. The gas yield was satisfactory. The consumption of oxygen and steam was higher than in browncoal operation. This may be partly because of the lower content of volatile matter and partly because of the lower reactivity of the Wiesche coal. A lower reactivity unfavorably influences the decomposition of steam and methane formation. The Karsten-Zentrum coal, although it showed some evidence of caking, was also gasified smoothly and appeared suitable for synthesiegas production. The gas yield was satisfactory. The oxygen consumption was 6% lower than in the Wiesche coal test, while the steam consumption was 30oJ, lower. Both reductions may be attributed to the greater volatile-matter content of the Karsten-Zentrum coal. The gasification rate of the latter was about 1201,higher, but this may have been governed entirely by the quantity of oxygen available for test purposes and not by the characteristics of the coal. Although both coals were gasified successfully, caution should be used in concluding that other coals resembling them will behave equally well. When selecting a coal it is necessary to make sure that it does not cake under the operating pressure and under the conditions of movement in the generator; this, apparently, can be tested only in actual operation. However, an agglutination test made at the operating pressure is a useful indication of the suitability of the coal for the Lurgi pressure-gasification process. Some coals which do not cake at atmospheric pressure develop marked caking properties a t high pressure. On the other hand, the Karsten-Zentrum coal, which was weakly caking at atmospheric pressure, was gasified satisfactorily because pressure did not increase the caking appreciably, and the movement in the generator prevented the caking from becoming effective. In general, lean, hard coal such as anthracites should be gasified satisfactorily under pressure, while higher-volatile caking coals will require pretreatment to reduce their caking properties. It has been claimed that coals with high ash content-up to 30 or 40Yo--can be gasified satisfactorily. The Lurgi pressure-gasification process, as normally operated, yields a considerable amount of methane, which is very desirable for public utility purposes but, in effect, is a diluent in the synthesis gas. It should, however, not be too injurious in the Fischer-Tropsch operation and may be welcome in those integrated operations mhere the tail gases might be used for enriching water gas or as a substitute for natural gas. If, however, methane is not desired, a steam-methane cracking step may be introduced following the generator to reduce the methane content t o less than 1%. Coals containing high-volatile matter have an advantage in the yield of distillation gases which are desirable for enrichment or for substitution purposes. Tars and benzenes yielded by the higher-volatile coals are desirable by-proddcts The tars, for instance, were hydrogenated to produce motor fuels in the Brabag I plant adjacent to the Bohlen plant. Discounting the methane obtained from the distillation gases, the reactivity of the fuel has a decisive influence on the calorific value of the gas because, within the limits imposed by the ashmelting temperature, it governs the temperature of operation. Lower-reactivity fuels must be gasified a t higher temperatures with lower yields of methane in the gas. This can be somewhat overbalanced by operating a t higher pressures, since it has been found from experience as well as the equilibrium data that the methane content rises approximately as the logarithm of the pressure. Figures 14 and 15 show the compositions of crude and purified gases as a function of pressure.
April 1948
517
INDUSTRIAL AND ENGINEERING CHEMISTRY
The rate of operation influences the amount of methane. At higher throughput rates, the amount should fall because of a lesser degree of approach t o equilibrium conditions. It was on the basis of operation a t 2.25 times the actual rate that the adjusted gas analysis was made for the Karsten-Zentrum coal operation a t 5 atmospheres. I n this adjusted analysis, the methane content was 5.5% as compared to the observed figure of 9.8% a t the actual rate of operation. It cannot be stated with certainty that any justification exists for believing that the rate can be increased t o 2.25 times the rate actually used in the tests. No Lurgi pressure-gasification data have been uncovered with appreciably larger gasification rates. However, in all cases, finesize fuels were used. I n normal gas-producer practice, with noncaking fuels such as anthracite and coke, the throughput can be increased considerably by increasing the size of the fuel. This should hold true for pressure gasification also, but certainly the feed mechanism and possibly the height of the generator may have to bcaltered for fuel of coarser size. More generator height may be required to have the gases leave at the same temperatures; otherwise the sensible heat losses may be greater and the tar distilled off from the upper layers of coal other than anthracite may change in quality from low temperature tar to something resembling a pitch if the temperature were high enough, and may lose much of its value. Furthermore, operation of the condensing and scrubbing system may become much more complicated, as is the case in handling the heavy tars produced in caking bituminous-coal gas producers and blue-gas generators. Although the results reported in the Lurgi pressure-gasification, per unit of cross-sectional area, are about one third of that in the Winkler process, the total volume of the Lurgi apparatus is certainly less than a third of the Winkler apparatus and requires a smaller oxygen plant. T o some extent, the heavier construction of the steel work to withstand the high pressures may overbalance the advantage resulting from smaller size. This general relationship may also exist between the Koppers dust-gasification and Lurgi pressure-gasification processes. The Lurgi pressure-gasification process merits every consideration for public utility purposes, especially in regions where suitable fuel is available a t low cost. For the large-scale operations required in connection with the production of synthetic liquid fuels, the labor requirements of the process will have to be lowered or be offset by the lower oxygen requirements and the value of the by-product tars and light oils obtainable from highvolatile coals. PROCESSES IN WHICH LUMP FUEL IS GASIFIED IN A FIXED FUEL BED
Standard Grate Operation. Lump coal and coke are regularly gasified in air-steam mixtures in the normal gas producer. Except for the higher intensities of combustion and the resulting narrower zone of combustion, with the possibility of running into clinker troubles, oxygen can be substituted for air. I n the paper by Wright and Mitchell (56),the behavior of lump coke is discussed. The behavior of lump coke and bituminous coal having coking tendencies has been studied by the author in a water-gas generator 3 feet 2 inches, inside diameter, converted t o producer operation principally by the addition of an injector which supplied the oxygen-steam mixture in any predetermined ratio and a charging hopper t o permit the addition of fuel without the need for shutting down the generator. There were no provisions for continuous removal of the ash and clinker or for agitating the top of the fuel bed, as usually found in bituminous-coal gas producers (34, 41-46). With respect to the lump coke, the absence of these provisions made no difference, except that it was necessary to shut down a t appropriate intervals to remove the clinker, as in normal water-gas operation where no mechanical grates are used. Had there been such grates and a water-jacketed
steel wall in the clinker zone, the operation need never have been interrupted for clinkering. The use of 100% bituminous coal resulted in caking and blowholes which were impossible to overcome without mechanical agitators normally .found on gas producers designed for caking fuels. It was, however, possible t o operate with mixtures of coke and coal, and some indication was obtained of what might be encountered in bituminous-coal operation in fully equipped mechanical generators.
2
Figure 15.
4
Ib
6 8 I2 14 16 18 Gasification Pressure Airnospheres (abs.)
22
Composition and heating value of purified gas as function of pressure
As mentioned in the Lurgi discussion, unless the. gases leaving the generator are a t a low temperature, the tars will have undergone considerable thermal cracking, and heavy tars and pitch will enter the scrubbing system and make operation arduous. The tars will also be low in value and not as desirable for hydrogenation purposes. The ordinary, mechanically agitated, bituminous-coal producer functions precisely because the fuel bed is kept thin and a trickle of coal is continuously spread by the agitator on the hot surface of the fuel bed. Any tendency t o cake is quickly destroyed'by the agitation and by the rapid heating of the lumps by the hot gases sweeping past them. There is no opportunity for the tars t o condense on cooler fuel above, and the tars are overcracked. Nevertheless, mechanical producers with heavy-duty grates and dry ash and clinker removal may prove feasible for synthesis-gas production in which caking coals would be used without any pretreatment. The volume of gas yielded by bituminous coals will vary with the content of the volatile matter. I n round numbers, the hydrogen-carbon monoxide ratio would be about 1 to 1.75, and the hydrogen plus carbon monoxide would be about 90% of the gas. The oxygen consumption would be 215 cubic feet per thousand cubic feet of gas, or about 240 cubic feet per thousand cubic feet of carbon monoxide. The coal consumption would be about 25 pounds per thousand cubic feet of gas, or 28 pounds per thousand cubic feet of hydrogen and carbon monoxide. The corresponding steam c6nsumptions would be 17 and 19 pounds. By increasing the steam-oxygen ratio the hydrogen-carbon monoxide ratio may be increased; but, in general, conversion apparatus will be needed for reversing the ratio of hydrogen to carbon monoxide and particular care will be required in scrubbing to remove the tar and sulfur before the gas is admitted to the catalytic conversion units.
*
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
578
Vol. 40, No. 4
SLAGGING-TYPE OPERATION
February 3 to 10,1944, and the last from April 29 to hIay 22, 1944.
The use of mechanical producers and even those with fluidized or suspended fuel beds imposes definite limitations on the melting point of the ash in the fuel. With many American fuels, this may not be a serious limitation, particularly because the use of higher steam-oxygen ratios with high production of carbon dioxide is not objectionable in synthesis-gas operation. I n fact, higher percentages of carbon dioxide in the gas mean correspondingly lower percentages of carbon monoxide and therefore better hydrogen-carbon monoxide ratios. The capacity of the units, however, is affected by higher steam-oxygen ratios, since the rates of gasification drop with the gasification temperatures. Slagging units may, therefore, be considered for handling fuels with ash of low melting point and for obtaining high throughput rates. Two types of slagging units were in use in Germany-the Thyssen-Galocsy and the Leuna slagging generators. Thyssen-Galocsy Slagging Generator. The Thyssen-Galocsy slagging process has been frequently described in the literature; but, aside from its general principle of operation, reliable operating figures were not available. It was known that one pilot plant with a capacity of 2 tons per day was in operation for several years a t the Thyssen'sche Gas und Wasserwerlte at Duisburg-Hamborn, and one gasifying 10 tons per day in the synthetic ammonia nlant a t Pecs, Hungary.
It was hoped to demonstrate in this unit that it was feasible to
-
Bell in Chcrqing P o s t i
Cooling Boxes.
b
Primary
Nozzles
Avrangement of Cooling Bcres
Figure 16. Thyssen-Galocsy slagging gas generator
The results reported before the war, though sketchy, indicated that noncolring or weakly coking coals having ash of low fusion temperature were suitable and the gas generated had a higher quality than in other continuous gasification processes using oxygen a t normal pressures. The admission of oxygen a t two levels and the use of recirculating gas to spread the zone of reaction were claimed as important advantages because they lessened the iatensity of combustion and lengthened the life of the refractories. During the war, a unit rated at 40 tons per day was erected in the Fischer-Tropsch plant of the Krupp Treibstoffwerke at Wannc-Eickel, and its first test run was made from October 25 t o Sovember 22, 1943. Two other runs were made-one from
gasify any grade of fuel in any size or combination of sizes from No. 4 mesh to 3 inches, caking or noncaking, and regardlcss of the ash content or the ash-melting temperature (35). The tests were frequently interrupted by bombings. One test, however, lasted 4 weeks and demonstrated that coke 1.5 to 2.5 inches in size could be gasified without any difficulty. Although laboratory determinations on coke containing 8 t o 10% ash showed an ash-melting temperature of 2400' F., it was found that a temperature of 2900" F. had to be maintained t o keep the slag molten when no limestone or iron fluxing material was added. Other tests were attempted, with the use of refuse from Demag-Duisburg producers containing 40 t o 50% ash, and with noncaking coal. Various combinations of fluxing material (20 to 40%) were tried, but the tests were interrupted before any conclusive data could be secured, usually because bombs struck in tl;e vicinity of the pilot plant or shut off the supply of electricity, steam, or water from the Krupp plant, or the supply of oxygen from the neighboring Stickstoffwerke Hibernia. Only 2 days of tests were conducted with coal, and the operation dld not attain anv degree of stability. OPERATINGPRINCIPLE.Essentially, the Thyssen-Galocsy generator gasifies coarse fuel in a fixed fuel bed. Gas is burned in a mixture of oxygen and steam, and the products are admitted into the fuel bed at a temperature high enough for a reaction to take place and for the ash to melt. Secondary oxygen is admitted at a higher level to provide additional heat to balance the loss arising from the reduction of the steam and carbon dioxide and from the melting of the ash. The division of the combustion zone, coupled with the burning of the gas in the mixture of the oxygen and steam, is intended to spread the reaction zone. Fluxing material is added if necessary to maintain the ash in molten condition. Slag is tapped a t a level just below the gas burners; and iron, if any, is tapped a t the bottom of the shaft.
APPARATUS AND METHOD OF OPERSTION. Referring to Figure 16, the generator is blast-furnace shaped, and about 35 feet high by 10 feet in diameter. It has provision for three sets of tuyhres, with five tuykres a t each level. The tuyeres at the lowest level are actually water-cooled burners in which gas from the process or any other source is burned in a mixture of oxygen and steam. The steam inlet to the oxygen line is a considerable distance from the burners to ensure thorough mixing of the two. The tuyBres at the upper levels are not water-cooled and are used for admitting the secondary oxygen required for supplying the additional heat for reducing the steam and carbon dioxide and melting the ash. Only one of the two upper levels of the tuyhres is used a t a time, the choice of level depending upon the conditions of operation. The base of the generator has a carbon refractory lining to resist the action of the slag; the remainder is lined with firebrick. Water jackets are provided for cooling the brick just above the lowest set of tuyhres. Fuel is charged by means of a bell arrangement. A telescoping steel cylinder in the upper zone of the generator is used for maintaining a deeper fuel bed adjacent to the wall, thus increasing the resistance of the fuel bed a t the circumference sufficiently to overcome the wall effect. The slag and iron are tapped at appropriate intervals. FUEL, OXYGEX,AXD STEAM USED. The fuel used in one uninterrupted test was coke 1.5 to 2.5 inches in size. It had an ash melting point of 2372" F. and a calorific value as charged of 12,400 B.t.u. per pound. The amount of coke used per thousand cubic feet of hydrogen plus carbon monoxide was 28.5 pound. The oxygen was supplied from a Linde-Frank1 plant in the neighboring Stickstoffwerke Hibernia. The purity of the oxygen was 81 to 90%. On the basis of 100yo purity, the oxygen consumption per thousand cubic feet of hydrogen plus carbon monoxide was 307 to 334 cubic feet. No information is available regarding the quality of the steam, The amount of steam consumed per thousand cubic feet of hydrogen plus carbon monoxide was 13 to 16.3 pound.
PRODUCTIOX AND QUALITYOF G.4s. Some 4,000,000 cubic feet of gas were produced per day, and it was claimed that the capacity of the unit was not reached because of a lack of oxygcii.
INDUSTRIAL AND ENGINEERING CHEMISTRY
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The internal area at the hearth was about 17 square feet, making the hourly capacity per square foot at the hearth some 10,000 cubic feet. The area at the level of the greatest cross section was about 40 square feet, making the hourly capacity per square foot at this level some 4200 cubic feet. The percentage of hydrogen plus carbon monoxide was about 90 to 94y0 of the gas, but the ratio of hydrogen to carbon monoxide was 0.33 to 0.38. T o increase this ratio, catalytic conversion of a part of the carbon monoxide would be required. OPERATINGRESULTS.Table VI11 gives the results of 3 typical days of operation-April 29 to May 22, 1944.
TABLE VIII.
THYSSEN-GALOCSY OPERATING RESULTS
Day Coke Through 21/z inches on l'/z inahes Proximate analysis, Yo Moisture Ash Volatile matter a n d sulfur $sh, melting temperature, 2372' Calorific value, 12,400B.t .u./lb. Coke charged, lb. Oxygen (basis 100% pure), cu. ft. Oxygen purity, % Steam. lb.
-./
1
5.0
8.5 1.5
F.
2
3
.................. ..................
.................. 103,000 1 ,230,000 81 57.000
86,500 942,000 90 39.400
91,200 Q80,OOO
90 41.700
0 - - 1 1
4,050,000 3,215,000 3,385,000
Gas analysis, %
coz 02
CO Hz
C H4
Nz Calorific value, B.t.u./cu. ft. Ht.CO ratio S t e a m decomposition, Yo Oxygen consumption, cu. ft./M cu. it. gas S t e a m consumption, lb./M cu. ft. gas Coke consumotion. l b . / M cu. f t . eas Oxygen consumption, cu. ft./M- cu. f t . Hz CO S t e a m consumption, l b . / M cu.+ft. Hz CO Coke consumption, l b . / M cu. it. H2 CO
+
+
+
4.6 0.1 65.3 24.6 0.2 5 2 288 0.38 82 1 300 14.5 25.6
2.8 0.1 70.4 23.1 0.2 3.4. 299 0.33 90.1 290 12.2 26.7
2.1 0.1 71.0 23.3 0.2 3.3 301 0.33 90.1 290 12.2 26.7
334
310
307
16.3 28.5
13.1 28.4
13.0 28.3
Adaptability of Thyssen-Galocsy Process to United States Requirements. Although the process was intended for use on any fuel in any size or combination of sizes, caking or noncaking, and regardless of ash content or melting point, the only demonstration has been on a closely sized coke of good quality. It does not appear that the process could function satisfactorily with caking coals or with fine sizes of fuel. It should, however, be useful for disposing>of such fuel as large lumps of reclaimed waste material from culm banks in the anthracite area of Pennsylvania. I n this case, the question is how much fluxing material would be required, and, if the amount of ash in the material is very high, how much more oxygen will be required to balance the heat, required to melt it into slag. Leuna Slagging Generator. Six slagging gas generators were in operation at the Leuna plant of I. G. Farbenindustrie A. G. (33). The original slagging generators at Leuna were three Wurth producers, using coke breeze, refuse from the water-gas generators, or simply coke, blown with air only to make producer gas for ammonia synthesis. The producers were completely brick-lined, and ash was removed as molten slag. Steam or oxygen could be used, as conditions permitted. Owing presumably to brickwork failures, the Wiirth type was replaced by another in which the brick lining was removed from the middle zone and water cooling was substituted. There were six of these producers a t the end of the war, each with a nominal capacity of 500,000cubic feet of nitrogen-free gas per hour. OPERATING PRINCIPLE. The Leuna slagging generator differs from the Thyssen-Galocsy slagging generator in pSinciple of operation in two respects: (1) No combustible gas is admitted with the supply of oxygen and steam at the base of the fuel
1
CONCRETE
Figure 17.
I
Leuna slagging gas generator
bed; and (2) there is no secondary supply of oxygen to the fuel bed. Evidently, spreading of the combustion zone according to von Galocsy'e principle was not considered necessary. I n operation with oxygen and steam mixtures at temperatures sufficiently high to melt the ash, the reactions occur at such a rapid rate as to be completed in a relatively thin zone. This has been the author's obserhtion during his experience with gasification of coke or coke and coal mixtures or anthracite using oxygen and steam and operating at somewhat lower temperatures, but high enough to produce clinkers of the kind which are normally obtained in intermittent water-gas operations (34, 6 7 ) . As in the Thyssen-Galocsy process, fluxing material is added if necessary to maintain the ash in molten condition, and slag and iron are tapped at appropriate levels. APPARATUSAND METHOD OF OPERATION. As finally developed, the generators have outside diameters of 8 feet 3 inches a t the tuyiires and 12 feet 6 inches higher up, with the corresponding inside diameters of the brick lining 5 feet 6' inches and 10 feet 10 inche The total height is 23 feet above the tuybres and the fuel bed depth is 13 feet above the tuybres. Only the top part, above the fuel bed, and the base of the generator below the tuykres are brick-lined; the remainder is bare metal, -In five generators the producer is water-jacketed, but in the last one built the jacket has been omitted and the metal is cooled merely by trickling water down over the outside, as shown in Figure 17. This modification was carried out after a serious accident a t one of the older generators; as a result of a hole in the steel, the producer became flooded and quenched, and, before this was noticed, unconsumed oxygen reached the gas mains and coolers and caused a serious explosion. This cannot happen with the latest design. I n o eration, a mixture of oxygen and steam is introduced througl! 8 tuyGres and a temperature of 3100" F. is obtained, although the exit gas temperature is 750" F. Limestone is added, if needed, to act as a flux for the liquid slag, which is tapped at intervals of 3 t o 4 hours, depending on the ash content of the fuel. One method of slagging is to run the slag first into troughs, where any iron sinks (and is dug out at intervals), and then into cold water; another method is to t a p off molten iron from the extreme bottom of the generator and molten slag from a t a p somewhat higher.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
FUEL,OXYGEN,AKD STEAMUSED. A wide variety of noncaking fuels can be used, but refuse, containing 50% carbon, from the Brassert generators is normally used. [In the United St.ates, Brassert-type generators are better known as ABC grate generators (Andrews, Brassert, and Chapman) .] The lower limit, on size is 1 inch, but none is placed on the upper sizes, and often clinkers are large as 2 feet are charged. When using nietallurgical coke, it is common practice to add 370 of limestone and 20% of solid slag previously tapped. About 28 pounds are used per thousand cubic feet of hydrogen plus carbon monoxide. When coke is used, the blast mixture is 35% oxygen and 65y0 steam, but the amount of oxygen is increased to between 50 and 58Y0when Brassert, water-gas generator refuse is used. The oxygen required is from 260 to 275 cubic feet per thousand cubic feet of synthesis gas when using metallurgical coke and char, respectively. The corresponding steam requirement,s are 20 and 15 pounds per thousand cubic feet of synthesis gas. Gas PRODUCTION AND QUALITY. The capacit'y of each generator is between 460,000 and 570,000 cubic feet of gas per hour when metallurgical coke is used. The amount falls to 312,000 cubic feet per hour when Brassert generator refuse is used. On the basis of the cross-sectional area of 23.75 square feet a t the tuyeres the hourly capacity per square foot is from 19,300 to 24,000 cubic feet, for metallurgical coke and 13,200 cubic feet for Brassert generator refuse; on t,he basis of the cross-sectional area of 92.5 square feet at the top, the corresponding hourly capacities per square foot are 4980 to 6160 cubic feet for metallurgical coke and 3380 cubic feet for t'he refuse. The percentage of hydrogen plus carbon monoxide in the gas is about 93 for coke and char and close to 90 for refuse, and the hydrogen-carbon monoxide ratio is approximat'ely 0.5 for coke and char and 0.36 for refuse. The hydrogen sulfide coiit'ent of the gas is variable, depending on the sulfur in the coal. Information on organic sulfur is not specifically available for the slagging operation, but, the over-all figure for all the Leuna gas-producing operations was given as approximately 10 grains per 100 cubic feet (250 mg. per cubic meter). OPERATISGRESULTS. I n Table I X are given typical operating results report,ed for the Leuna slagging generators,
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total number of men per day would therefore be 63 for a production of, say, 48,000,000 cubic feet of gas per day, assuming 500,000 cubic feet of gas per generator per hour. This is equivalent to 95,000 cubic feet per man-hour and again illustrates the advantage, from the standpoint of labor requirements, of using large generating units. Adaptability of Leuna Slagging Generator to United States Requirements. The Leuna slagging generator requires a noncaking coal, coke, or refuse. It does not appear t o be adaptable to caking or fine-size fuels. T o the extent that recirculation of gases is eliminated, the generator capacity should be (and is reported) greater than that of the Thyssen-Galocsy type. Like the Thyssen-Galocsy unit it should be useful in disposing of large pieces of reclaimed waste material such as may be obtained from the culm banks of the Pennsylvania anthracite region with results not too far from those obtained in the operation mith the Brassert generator refuse.
Summary and Conclusions
The preceding review and comments on the complete gasification processes using oxygen were made on the broad basis that, although the modern intermittent water-gas process has reached a high state of development, its use is limited to the more expensive fuels, such as the larger sizes of coke and anthracite. The review was further made on the basis that methods employing external heating or gas recirculation are limited to the more reactive fuels and that oxygen gasification methods, especially as regards the yield of gas, are far superior to those in which the heat required is obtained from the separate gasification of part of the fuel. The oxygen processes fully reviewed and discussed are the Winkler, Koppers, Lurgi pressure, Thyssen-Galocsy, and Leuna slagging-gasification processes. I n the course of the discussion of these processes, comparisons were made wherever possible. I n general, comparisons between different processes can be made only when they can be used to gasify the same fuels. It would be pointless, for example, to compare an intermittent water-gas process which can use only scarce noncaking, nondecrepitating lump fuel against the Koppers dust-gasification process, which can use any fuel having suitable grinding characOPERATIKG RESULTS IN LEUNASLAGGING teristics. TABLE IX. TYPICAL Before selecting any gasification process one must therefore GENERATORS Metallurhave a definite knowledge of the fuel- available and, in addiChar hIetallurgical tion, the major objective of the operatio s to be conducted. Brassert from gical Coke Refuse Deuben Coke with COa If the major objective is principally to produce motor fuels Between in the vicinity of the lignite and subbituminous coal deposits 460,000 in the Northern Great Plains Province it is conceivable that, and Gas, CU. ft./hour 312,000 570,000 instead of complete gasification, it might be desirable first to Analysis, 92 recover the tar and oils from the coal, and, secondly, to gasify 5.4 6.8 9.7 3.0 coz 92.5 62.4 61.4 CO 66.5 the char. This may be accomplished in separate carbonization 22.9 3.0 31.2 31.0 Hz and gasification stages, or in a process which in combination * 0.0 0.0 0.0 0.0 CH4 1.5 0.9 1.o 0.8 yields by-products and gas, such as the Lurgi pressure-gasifica570 190 100 120 310 276 262 347 tion process. If two stages are used the second stage may be Nil 12.1 15.5 20.1 selected from among the Lurgi, Winkler, or IZoppers types of Nil h-il Nil 258 30.8 .. 46.5 28.6 processes. 24.6 26.7 28.0 .. Fuel analysis, % If, on the other hand, the objective is to produce motor fuels 45-50 54 86.8 87.2 C and gas for public utility distribution in an integrated operation, 55-40 16.9 9.1 11.8 Ash 22 1.8 1.0 .. Ha0 say, in the anthracite region of Pennsylvania, only a single-stage process would be applicable for gasification purposes. To produce a richer gas and to take advantage of the low-cost anthracite fines, the process chosen may be of the Lurgi pressure-gasification LABOR. At Leuna four generators were normally in operation type. If, on examination, the low reactivity of the anthracite and two were out of service for repairs. I n addition to the superwould appear to inhibit the production of an appreciable amount visory staff who also had charge of ten Pintsch generators, the of methane in the gas, a low-pressure oxygen-blown gas producer operating staff consisted of the following men per each of three may be chosen. I n making the choice a balance would have to shifts: one foreman; one attendant for the pumps, blowers, etc.; be struck between the differences in the amounts of the methane eight slag tappers (abstecher) ; two fuel attendants; six slag in the gas, the oxygen fuel and steam consumptions, the capital removers (after tapping) ; one slag loader; one analyst for oxygen, equipment costs, the labor requirements, etc. If the coal could coal, gas; and one operator, totaling 21 men per shift. The ~~
April 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
be pulverized a t low cost a suspension-gasification type process might also be considered if it should promise to operate at higher rates of throughput than the fixed bed processes. I n regions where caking coals predominate the choice is limited to a suspension process, unless some inexpensive means could be developed for destroying or reducing the caking characteristics of the coal. I n that case a fluidized-bed process may also be considered. I n choosing between a fluidized-bed and a suspension-gasification process consideration would again have to be given to the quality of the gas produced, the oxygen, fuel, and steam consumptions, the equipment and labor requirements, etc. Many combinations of available fuel and product objectives are possible but it would be far beyond the scope of this review to consider them all. Instead, a possibility of immediate importance must be assumed in order to determine the trend of the development work which must be followed to obtain a suitable synthesis gas process. I n the case of the synthetic liquid-fuels program of the Bureau of Mines, the need is to develop or adapt the gasification process that appears to be most universally suited to the utilization of most of our American coals. The Interior Province ' coals have coking characteristics but fall between those of the entirely noncaking and the strongly coking varieties. For the immediate, as distinguished from the long range, program, coals of the Interior Province are being considered. The Interior Province coals can be obtained a t low cost by strip-mining methods. Their caking characteristics make their use difficult in fixed-bed and possibly fluidized-bed operations. Unless some inexpensive method of overcoming these caking characteristics can be found immediately, the trend of the development work to be followed must be in the direction of suspension gasification processes. Accordingly, the bureau is now doing its major gasification development work with pulverized fuel in suspension. One phase of this work is described by Edeburn, Schmidt, McGee, and Bonar (11). A workable suspension-gasification process using pulverized fuel and oxygen can be adapted to any fuel having suitable grinding characteristics and is independent of its caking qualities and ash quantity and melting point. If tKe ash melts a t a low temperature, slag-tapping methods similar to those used in power-plant practice may be employed. To conserve oxygen, means for superheating the steam to a degree which approaches the gasification temperature must be found. The gas produced in a suspension process is relatively free from hydrocarbons and from gum-forming and organic sulfur compounds, making the task of purification that much simpler. If means could be developed for operating the system under pressure, the size of the generator and the auxiliary equipment could be materially reduced, and the problem of condensing, scrubbing, and purification would be further simplified. Although in a fixed-bed process, such as the Lurgi pressure-gasification process, the formation of methane and carbon dioxide-because they are exothermic-results in a considerable reduction in oxygen consumption, no such reduction may be expected in the suspensiongasification operation because the entire gasification is completed in the generator at a substantially uniform high temperature. The oxygen consumption in a suspension operation should be lower than in a fluidized-bed operation because the gasification in suspension is substantially completed in one pass, while considerable recycling of the fuel would be necessary in fluidized operation, with inevitably higher heat losses. The operation in suspension would be less complicated than in a fluidized bed, with its system of multiclones for separating and recycling the blown-over fuel. A distinction was made between the immediate and the longrange purposes of the bureau in its gasification program. Although the trend of suspension-gasification processes is the major one followed for immediate needs, considerable attention is
. 581
devoted to fixed-bed pressure-gasification research, .which includes development work on means for destroying the caking characteristics of coals to permit their use in a Lurgi-type pressure process. For the low-rank, high-reactivity coals, work is in progress on the development of an externally heated gasification process. A report on this work is given by Parry, Wagner, Koth, and Goodman (36). It would, of course, be desirable to supply production-cost comparisons for the various processes. Reliable estimates can be made only after careful engineering and operating plans are completed for any given location. Much information has been obtained on German costs, and it might have been desirable to summarize them in this paper. They have, however, been omitted because it is impossible t o devise a reliable working formula for converting German costs to .American conditions, owing to the abnormal economy under which Germany operated in recent years. I n the fist place, the real value of the Reichsmark in terms of the United States dollar is difficult to determine, regardless of any arbitrary exchange rate quoted. I n the second place, the relations between capital investment and labor, even with a known value of the Reichsmark, would not be the same under American conditions. Many of the most recent German figures for labor are distorted because of the factor of slave labor, which was overabundant and not employed with any economy whatever. Capital investment figures by themselves also may not be accepted without critical analysis. A capital investment figure does not necessarily represent the elements of cost entering into the construction of a plant alone; it may include indirectly a heavy process patent royalty. The latter usually is based on what the traffic will bear. If, for example, in a new process there are important savings in oxygen, fuels, and steam, these economies are taken into consideration; and the amount bid for the construction of the plant embodying this new process may be much higher than for an older competing process, even though the new process may actually use much less or much simpler equipment. This last point must be borne in mind when examining some comparative costs. Schultes (St?), for example, in 1936 gave capital investment and operating costs for a number of different synthesis-gas production methods. Since these figures were prepaSed long before the beginning of hostilities, one would expect no distortion in the unit labor costs by such factors as the use of slave labor. However, in his estimates Schultes lumped the wage costs with costs of catalysts, purification materials, oils, grease, etc., and arbitrarily charged them at 6% of the capital investment. Obviously, this is not a sound method of comparing wage costs in processes differing widely in their labor requirements, some of which, in fact, may have been capitalized at a high figure precisely because of their lower labor costs. Accordingly, Schultes' calculations of cost, in spite of the fact that they have found their way into a t least one good German handbook on gas production (4),are considered of dubious value for anyone seeking a short cut for estimating comparative production costs. It will still be necessary to build and operate suitable demonslration plants before reliable engineering and cost data can be obtained. '
Acknowledgments The author wishes to express his appreciation of the assistance received in the course of the preparation of this paper to: Miss Z. Gruber, Librarian, Foreign Synthetic Liquid Fuels Division, for bibliographic work; R. T. Seltmann, Division of Geography, for the preparation of most of the drawings; the Institute of Gas Technology, for supplying the curves showing the temperature dependence of the equilibrium compositions of carbonwater-oxygen systems; H. H. Storch and Martin A. Elliott, for critically reviewing the first draft of the manuscript and
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INDUSTRIAL AND ENGINEERING CHEMISTRY
for supplying additional drawings; and J. D. Doherty, P. AI. Ambrose, W. C. Schroeder, L. C. McCabe, and A. C. Fieldner for their assistance in reviewing individual portions of thP manuscript. Much of t h e basic material in this paper TYas drawn from reports prepared by members of the Technical Oil Mission and the Solid Fuels Mission and fiom material appearing on t h e microfilm reels prepared by the Combined Intelligence Objectives Subcommittee, the N a v y Department, and t h e Field Intelligence Agency (Technical) of t h e Office of Technical Services. Every effort vias made t o give proper credit in the text to the various sources, and i t is hoped that no inadvertent omissions have been made.
Literature Cited (1) Am. Gas Assoc., “Report of Utility Gas Sales,” 4th quarter, 1946. (2) Anon., Coke Smokeless-Fuel A g e , 8, 49, 50, 54 (March 1946). (3) Ibid., 8, 155-8 (July 1946). (4) Bruckner, H., “Handbuch der Gasindustrie,” Vol. 11, Part 2, “Synthesis, Brown Coal and Peat Gases,” Munich and Leipeig, R. Oldenbourg, 1940. (5) Corgan, J. A., and Cooke, M . I., MineralsYearbook, Bur. Mines, Table 1, Pennsylvania Anthracite, 1946. (6) Danulat, F., Metallges. Periodic Rev., 13, 14-22 (1938). (7) DeCarlo, J . A., Corgan, J. A., and Otero, M. M., MineralsYearbook, Bur. Mines, Table 20, Coke and By-products, 1945. (8) Dent, F. J., Blackburn, W. H., and Millett, H. C., “Synthesis of Hydrocarbons at High Pressure,” Parts I1 and 111, 4% and 43rd Reports of Joint Research Committee, Institution of Gas Engineers and Leeds University, I n s t . Gas Engrs. Pubs. 167/56 (1937) and 190/73 (1938). (9) Dent, F. J., Blackburn, W. H., Millett, H. C., and Moignard, L. A , Ibid., Part IV, 50th Report of Joint Research Committee of Gas Research Board and University of Leeds; Gas Research Board P u b . G R B 26 (1946). (10) Downs, C. R., and Rushton, J. H., Chem. Eng. Progress, 1, 12-20 (1947). (11) Edeburn, P. W., Schmidt, L. D., McGee, J., and Bqnar, F., t o be published. ENG.CHEM.,40, 586 (1948). (12) Foster, J. F., IND. (13) Golumbic, N. R., Bur. Mines, Information Circ. 7366 (1946). (14) Gordon, K., J . I n s t . Fuel., 20, No. 111, 42-58 (December 1946). (15) Grimm, H. G., Proc. I n t e m . Conf. Bituminous Coal, 3rd Conf., 1931, Vol. 1, 874-81. (16) Hanisch, “Experiments on Gasification of Bituminous Coal and Coke by the Winkler Process,” Technical Oil M i s s i o n Reel 188, Item 18, Library of Congress, Washington, D. C. (June 29, 1932). (17) Hirt, J. H., U. S. Patent 1,039,398 (Sept. 24, 1912). (18) Ibid., 1,083,683 (Jan. 6 , 1914). (19) Ibid., 1,110,782 (Sept. 15, 1914). (20) Hollings, H., Wintershall, A. G. Lotekendorf, C.I.O.S. Rept. XXXII-90, P B 2233; Tech. Oil M i s s i o n Reel 197, Library of Congress; Bur. Mines, Information Circ. 7369 (1946). (21) Hollings, H., Hopton, G. E., Newman, L. L., Horne, SV. A., and Spivey, E., A. G. Sachsische Werke Bohlen, Germany; C.I.O.S. Rept. XXX-13, Item 30, Combined Intelligence Objectives Sub-committee (1945) ; Office of Tech. Services, Dept. Commerce, P B 977; Tech. Oil M i s s i o n Reel 197, Library of Congress, Washington, D. C. (22) Hollings, H., Hopton, G. U., and Spivey, E., “Lurgi EIigh Pressure Gasification,” B.I.O.S. Final Rept. 521, Item 30, British Intelligence objectives Sub-committee, London, H.M. Stationery Office, 1946. (23) Holroyd, R., I. G. Farbenindustrie, C.I.O.S. Rept. XXXII-107, Item 30, Combined Intelligence Objectives Sub-committee; Bur. Mines, Information Circ. 7370 (1946); Office of Tech. Services, Dept. Commerce, P B 6650. (24) Hubmann, O., Metallges. Periodic Rev., 8, 9-15 (1934). (25) Kanner, L., Kate, S., and Parent, J . D., “Study of Reactions of
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