errnal EfIiciencv of C J -
Hydrogenation L. C. SKINNER, R. G. DRESSLER, C. C. CHAFFEE, S. G. MILLER, AND L. L. HIRST Coal to Oil D e m o n s t r a t i o n Branch, O f i c e of S y n t h e t i c L i q u i d Fuels, Bureau of M i n e s , Louisiana, Mo.
T h e t h e r m a l efficiency of an improved coal-hydrogenation p l a n t is discussed in d e t a i l and the efficiencies are c o m p a r e d to a typical G e r m a n hydrogenation plant. The new ideas and processes discussed are incorporated into a p l a n t designed f o r improved t h e r m a l efficiency. The overall heat efficiency of this p l a n t is calculated to be 55.0% a s c o m p a r e d to 28.9a/, for a typical G e r m a n p l a n t . T h e calculations a r e divided into t h r e e sections, hydrogenation proper, hydrogen m a n u f a c t u r e , and power plant. Detailed data are presented to verify the results f o r each section. A comparison is m a d e w i t h t h e G e r m a n efficiency for the individual sections. Flow s h e e t s f o r each section show complete h e a t a n d m a t e r i a l balances. The favorable increase in heat efficiencies shown, accompanied by a considerable decrease in p l a n t costs, i n d i c a t e s the necessity for an aggressive coal-hydrogenation development s t u d y as a p a r t of our national economic and security program.
experimental work a t low and moderate pressures was initiated by the Bureau of Mines in Pittsburgh ( 2 6 ) . The growing realization that oil from coal could be important as a factor in national defense led to authorization for development work on a large scale by the United States Government in 1944 (10). As a first step in fulfilling this assignment, many of the European plants were studied for first-hand information and many technical reports covering the German development were obtained for translation and use in design. Over two years of design work has been done on a coal-hydrogenation demonstration unit, which is nearing completion a t Louisiana, Mo. During the course of designing this plant, many ideas occurred to investigators, or were found in or alluded to, in the German literature, which would simplify and improve the process. For this paper the thermal efficiency of an improved hydrogenati,on plant has been calculated, in which these ideas are incorporated, and for comparison results of a similar calculation of thermal efficiency for a typical German plant have been included (15). This paper does not describe a plant which has actually been built or may be built. The process design is based on information obtained either from German experimental data or by calculations based on sound technical reasoning. Some of the more important improvements that have been incorporated in the improved plant are discussed.
NY discussion of the possibility of producing gasoline or other petroleum oil directly from coal in the United States would have been of purely academic interest in 1936, when the demand for gasoline was down, and crude oil produotion and reserves were above demand. Export was the order of the day. By 1946, high postwar demand, higher crude prices, proration of production, large demand during the war, absence of any recent outstanding domestic oil discoveries, and the fact that Germany was producing most of her wartime liquid fuels from coal, caused the subject to be given serious consideration in this country. An economic study of the European synthetic fuel industry did not warrant undue optimism (18). However, after the calculations for this paper were completed, and it was found that the heat efficiency of a plant incorporating improvements which appear to be possible was almost double that of most of the existing German plants, the authors were led t o wonder what the status of coal hydrogenation will be in 1956. The economic aspects of the process would be of considerable interest; however, data are not yet assembled for this study. For this reason the scope of this paper is limited to thermal efficiency of coal hydrogenation. This also is a rather broad field, and therefore the calculations are limited t o the use of coal as the only source of outside energy and the process design covers only maximum gasoline production. The basic process was discovered by Bergius in Germany about 1911. Construction of the first industrial scale plant was started by I. G. Farbenindustrie a t Leuna, Germany, about 1926. In 1933, when Germany started rapidly t o prepare for war, an enormous amount of effort was expended in experimental development, which led t o the construction of some ten large hydrogenation plants capable of producing 85y0of Germany's gasoline supply for wartime aviation. An active development program was carried on throughout the war, but essential design was irozen in 1938 for practical reasons. As a result, many desirable improvements never reached full scale application. During this period, a few hydrogenation plants were constructed in England, France, Italy, and Japan, and a program of laboratory scale
EUROPEAN PRACTICE
Because the European practices are the basis of design, they should be understood before the improved plant is discussed. I n the conventional coal-hydrogenation process, coal was hydrogenated to high-octane gasoline in either two or three stages, as it was impossible to treat coal in one stage with active catalysts without subsequent loss of catalyst activity, owing to coking of the catalyst surfaces. During the first or liquid stage the coal was converted largely by thermal decomposition and addition of hydrogen t o a heavy liquid used for subsequent coal pasting and to middle oil, which was fed with additional hydrogen to the vapor-phase processes, for conversion to high-octane gasoline. The raw coal was dried, crushed, and ground with the catalyst and recycle oil into a paste containing about 45% coal. The viscous paste was then raised t o 300 or 700 atmospheres pressure by hydraulically operated ram pumps. The paste was mixed with a small amount of hydrogen and heated to the swellin range (about 615" F.) by exchange or more usually by heat suppked in the first section of the vertical, finned tube, convection preheater. At this stage, additional hot hydrogen and hot recycle oil were added before the paste was heated to the outlet temperature of 800' F. in the following two sections of the preheater. The paste next entered the first of a series of three or four unpacked converters. These converters were large steel forgings about 39 inches in inside diameter and 60 feet long, internally insulated to maintain a relatively cool pressure shell. As the reaction is highly exothermic, the temperature normally rose quickly to the reaction temperature of 880' t o 910 F., where it was maintained by injecting cold hydrogen at several points in each converter. The average residence time in the reaction zone was 1 to 2 hours for about 95% carbon conversion to gaseous and liquid products suitable for use or subsequent rocessing. The product then passed to a fifth vessel cated a hot catchpot to achieve a rough separation of heavy oil letdown (H.O.L.D.) 87
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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
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Vol. 41, No. 1
January 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
and the overhead oil products plus excess hydrogen. The overhead gas and vapors were partly cooled by exchange with the incoming paste or paste injection hydrogen and then finally cooled with water. The condensed liquid was collected in a cold separator, while the gas was purified in an oil scrubber and recycled to the process. The condensed oil was let down (depressured) in steps to effect further recovery of hydrogen and hydrocarbon gases before the liquid was fractionated into gasoline, middle oil, and light recycle pasting oil. The heavy oil letdown from the hot separator contained the solids left from the hydrogenation reaction: catalyst, ash, and unconverted coal amounting to about 20 to 25 weight % of the oil slurry. The material was cooled to about 400" F. before expansion t o atmospheric pressure through special valves constructed to withstand the excessive abrasion to a considerable degree. A portion of the slurry was adjusted in viscosity and solids content by addition of a lighter oil before it was centrifuged to remove sufficient solids to keep the system in equilibrium. The A middle oil, the chief product from distillation of the liquid-phase overhead, contained too much oxygen, nitrogen, and sulfur compounds and had too high a molecular weight to be used directly for gasoline; hence, it was necessary to reduce these compounds in a vapor-phase process known as the saturation step before redistillation of the product and final high-pressure splitting and hydrogenation in the splitting step. The gasoline from the splitting phase had only a nominal octane number and required a third or lowrpressure 50-atmosphere dehydrogenation or aromatizing step to produce SO-octane (unleaded) fuel. The three vapor-phase steps discussed had been successfully carried out in one stage of vapor-phase hydrogenation at Welheim at 700 atmospheres (8). The hydrogen required in the above process was initially manufactured in conventional blue water-gas generators. The Germans recognized the relative inefficiency of this process and had developed and sometimes used more efficient methods (9). Among these processes were the Winkler, utilizing oxygen and a fluidized bed of noncoking coal or coke; Koppers, utilizing oxygen and powdered fuel; Schmalfeld, utilizing high-steam recycle and powdered fuel; Lurgi, utilizing oxygen and a fixed bed under pressure ; and Thyssen-Galocay and Leuna employing oxygen with a stationary bed under slagging conditions. The Koppers process was chosen for hydrogen production in this study of an improved plant because of its adaptability for caking coals and its high thermal efficiency. Flow diagrams on most of the processes mentioned above are available (1, 3, 9). PROPOSED IMPROVED HYDROGENATION PROCESS
The improved plant has been divided into three sections for purposes of calculation: 1. Coal hydrogenation, including treatment of products 2 . Hydrogen manufacture and purification 3. Power plant Flow sheets (Figures 1 and 2) show the results of the calculations. A brief description of the process and a summary of results for each section are given below. HYDROGENATION
h heat and materials balance was calculated for the complete hydrogenation unit, not including hydrogen manufacture or power plant. Figure 1 shows the main features of the plant. The process is essentially as follows: Raw coal as received is crushed to 0.375-inch size for heavy-media ash separation. The low-ash coal then passes to a dryer, where the moisture is reduced to approximately 1%. Following the dryer the coal goes directly to a combined pulverizing-pasting operation. Pulverized catalyst and oil are fed to the pulverizer simultaneously, to provide a paste of approximately 42% coal. This material is kept in agitation and pumped .by reciprocating pumps to the suction of hydraulically operated injection rams
89
which raise the pressure to 700 atmospheres. The paste then gains approximately 120" F. from the heavy oil letdown in exchanger E-1. Further exchange at E-2 with the hot vapor-phase product raises the paste to approximately 635" F. Hydrogen is introduced into the paste prior to E-1 to prevent jelling, which would occur a t about 300" F. in the absence of hydrogen. The balance of the hydrogen (40 tons per hour) is heated as required to secure optimum temperatures of the paste-gas mixture to the preheat converter, a unique feature described below. The material from the preheat converter then flows to the other converters in series where the reaction is completed (a plant consuming 100 tons per hour would require three stalls consisting of one preheat converter and three normal converters each, approximately 4 feet in inside diameter and 60 feet long). The last converter in the series is to have a special bottom construction to permit removal of unconverted coal and ash, plus a minimum of oil. This material will be fed directly td a special flash-distillation column. Overhead from this column, after cooling and condensing the steam, will be used for paste oil. Bottom material, consisting of approximately 35% unconverted coal and coke, 35% ash and catalyst, and 30% oil (mostly asphalt) will amount to 11 tons per hour and have a normal heating value of 10,000 B.t.u. per pound. However, the oil content and other properties of the material can be varied to suit market requirements if desired. The overhead from the last converter goes to a special hot catchpot, which is refluxed with recycle middle oil. The bottom is cooled and stripped with hydrogen. This combination is anticipated to provide a sufficiently clean feed to the vapor-phase converter, as well as a relatively solids-free pasting oil, which is heatexchanged with fresh paste and then depressured through powerrecovery units. The overhead from the hot catchpot passes through E-3, where it approaches reaction temperature and thence goes into a newly conceived, constant temperature, tubular vapor-phase converter. The entrance of the tubes is packed with quartz beads, so that they function as a preheater in raising the reactants to the final heat level. The products from the vapor-phase converter plus the recycle hydrogen pass to the cold catchpot through a series of exchangers consisting of: E-3, feed to vapor phase E-2, coal-paste exchanger E-4, feed to distillation column
3 - 5 , paste-gas exchanger
E-9, low-pressure steam generator E-10,water cooler
At the cold catchpot the fixed gases (mostly hydrogen) are separated from the liquid hydrocarbon products, scrubbed, and returned for recycle hydrogen. The liquid products are then let down to 50 atmospheres through power-recovery units for fixed-gas release before further fractionation. The Hygas (oh-gas from hydrogenation) from the 50-atmosphere receiver is combined with other off-gases and processed in the sulfur-removal plant before going to the hydrogenmanufacturing plant. Liquor containing ammonia, hydrogen sulfide, etc., is drawn off for disposal, or recovery of by-products. The 50-atmosphere liquid products are sent t o the absorberstripper tower for further degasification and propane recovery before distillation, stabilization, and final purification of the products. The above distillation utilizes excess heat from the hydrogenation operation, in addition to the normal interchange of feed and product streams from the individual towers. SUMMARY OF CALCULATIONS. Calculations of the thermal efficiency for the hydrogenation section were prepared on the basis of charging 100 tons per hour of moisture- and ash-free (maf.) coal to the hydrogenation unit. A coal similar in analysis to Illinois No. 6 was chosen as the raw material. Because no actual experimental data meeting the conditions are available for a particular coal, the yield figures have been chosen from average values for bituminous coals. A definition of the over-all heat efficiency for this paper is "the heating value of useful products including gasoline, liquefied petroleum gases, and salable residue divided by the heating value of the coal or fuel required to produce the products, as well as all requirements for steam, power, and other utilities, times 100." Thus:
yoheat efficiency
=
heating value of products X 100 heating value of coal or fuel
90
Vol. 41, No. 1
Flow Sheet for Hydrogen Manufacture
Figure 2.
For individual sections of the plant, a sindar definition will apply, except that account mill be taken of an excess or deficiency of steam, power, fuel gas, etc. The following values, based on the heat necessary to generate an equivalent amount of steam or power from coal, were used for the various materials: Electrical energy Steam 50 lb./sq. inch gage, saturated 150 lb./sq. inch gage, a t 600" F. 450 lb./s inch gage, a t 600° F. Fuel gas, actual%eating value
.
-
1 kw.-hr. 12,000 B.t.u. 1 lb. 1,474 B.t.u. 1 lb. = 1.496 B.t.u. 1 lb. 1,505 B.t.u.
-
Table I indicates heating values of the various materials used and Table I1 the values ests.blished as a basis for design.
TABLE I. HEATING \7AI,lJES Gasoline Liquefied petroleum gases Coal as received Coal, high-ash t o boiler house and H2 mfg. Coal, moisture- and ash-free Flash oolumn residue Hydrogen
B.l.u./lb. 20,000 21,000 12,360 11,900 14,500 10,000 51,620
B.t.n./ou.ft.
Hydrogen Hygas from hydrogenation operation Fuel gas from gas holder
324 894
645
HYDROGEN MANUFACTURE
The over-all efficiency of any fuel process utilizing hydrogen or synthesis gas depends greatly on the efficiency of the gasification method employed. Although hydrogen can be produced from natural gas with a higher efficiency, the source of fuel in the work reported is limited exclusively to coal. To facilitate selection of efficient methods for hydrogen manu-
facture from coal and plant off-gas, current American and European practices and developments were studied. This stud> and subsequent calculations resulted in selection of the system shown on the flow sheet (Figure 2), which consists of the following components: An oxygen plant capable of efficiently producing oxygen of 98% purity, similar to recent American installations or the Gwman Linde-Frank1 plants (9) A Koppers (18) powdered-fuel plant to gasify powdered coal directly A Linde plant to recover hydrogen from the Hygas, and to maintain a low nitrogen balance through purging a high-nitrogen gas to fuel A splitting or gas-cracking plant for converting the hydrocarbon in the Hygas t o hydrogen and carbon monoxide , A shift-reaction installation common to the gasification and splitting plants Advantages of the Koppers gasification process are its abilitj to handle a variety of fuels, irrespective of their composition and caking characteristics, and its high yield based on carbon supplied. Pilot plant work indicated a thernial efficiency of 75 to 80y0 (18).corresponding t o 94 to 957, carbon utilization. The Linde low temperature gas-fractionation plant is employed to make a separation of the Hygas. Inasmuch as Hygas k introduced into the plant under pressure, use of porn-er-recovery machinery will more than supply the power requirements Incidentally, a stream of high-purity hydrogen is rccoverd, which increases the over-all efficiency of hydrogen manufacture. Combined requirements per 1000 cubic feet of hydrogen are afollows: 1.
2. 3. 4. 6. 6. 7.
Coal maf., lb. Ilygas, ou. ft. Oxygen cu. f t . Steam (50 Ib./sq. inch gage) Ib. Power kw-hr. Steam' roduced (460 lb./sq. inch gage), lb. power For compression, kw.-hr.
16.8 103.4
227.0
60.5 3.89
6.47
12.8,i
INDUSTRIAL AND ENGINEERING CHEMISTRY
January 1949
TABLE 11. BASISFOR DESIGN Paste composition, 42% mat. coal 2. Total charge of maf. coal, 100 tons per hour 3. Catalyst, ammonium molybdate on carrier, total 1% of maf. coal 4. Coal as fed, 1% moisture 3% ash 5. Hydrogen consumption, i Z % absorbed plus 1 % losses 6. Gland oil (still bottoms) 9 tons per hour 7. Ultimate analysis of Illihois No. 6 coal, maf. basis, % (17). H 5,3, C 80.6, N 1.9, 0 10, 8 2.2 1.
8.
Composition of gases iMake-Up Hydrogen % by Vol: 99 0.9 0.1
H2 N Z
Hydrocarbons and CO
Recycle Hydrogen
% by Vol.' 80 12 8
11. Yields, wt. % of maf. coal Material Output (input) Coal 100 HzS (based on 50% organic sulfur in coal) CO Hz 12 CO, 112 Total N Ha Hz0 Cl
.
cz cs
c 4
Gasoline (C1-free) Unconverted coal Asphalt bottoms from flash column Total 12. 13.
1.2 1.2 1.1 2.5 9.2 4.2 7.3 10.0 9.5 68.8 4.0 3.0 112.0
Heat of reaction, liquid phase, 10,000 B.t.u./lb. of Ha absorbed Heat of reaction, vapor phase, 9,000 B.t.u./lb. of Hz absorbed
AND TABLE 111. ITEAT INPUT
Input Coal maf 100 ton/hr. 450, Ib./&. inoh gage steam, 90,000 lb./hr. net 150, lb./sq. inch gage steam, 30,000 lb. net Fuel gas 77 600 cu. ft./hr. Hydrogdn 4 920 000 cu. ft./hr. Electrical 'en'erg;, 69,059 kw.-hr. Total output Hygas 884 200 cu. ft./hr. Gaaolihe 6 h tons/hr. (5% C d Liquefied petroleum gases, 13.3 tons/ hr. Residue 11 tons/hr. Total Efficiency of coal hydrogenation (exclusive of Hn production)
~
B.t.u./Lb. or Cu. Ft. 14,500
TABLE 1V. KOPPERS PROCESS Basis
B.t.u./Hr. 2,900 X 10'
1,505
135 X 108
1,496 645 324 12,000
4 4 . 9 x 10' 50 X 10' 1,590 x i o 0 828 X 10' 5,547.9 x IO'
894 20,000
790 x io0 2,480 X 10'
21,000 10,000
559 x 10' 220 x 108 4,049 X 108
Input lb. COLI, maf. Water (in coal) Steam consumed Oxygen (pure) Total
0.37 0.82 2.19
802,000 cu. ft./hr.
Output, lb. Gas product (heating value, 282.5 B.t.u./cu. ft.) Carbon loss Total
2.14 0.05 2.19
3,550,000 cu. ft./hr. 4,470
Energy figures Excess steam produced (450 Ib.! sq. inch gage), lb. Power for oxygen, kw.-hr. Power for plant kw.-hr. Total power k\;.-hr. Fuel gas useh, B.t.u.
0.38 0.135 0.032 0.167 336.0
Heat efficiency =
1 .o
73,255,
Calculations on basis of Table I1 show the results given in Table -..111. Energy items involved in the thermal efficiency of the Koppers plant, the Hygas splitting plant, and the over-all hydrogenproduction system are given in Tables IV, V, and VI. The hydrogen-production plant, as a whole, has a thermal efficiency of 61.7% (without compression) or 47.7% (including compression), which compares very favorably with the figure of 30% (including compression) for hydrogen production from coal by coking and intermittent gasification of coke in watergas sets (15). The existence of efficient, continuous, oxygengasification prooesses justifies an optimistic view of the whole synthetic fuels picture (6). A summation of the power and steam requirements of the operating units (Table VII) shows the requirements t o be 88,379 kw.-hr. of electrical energy and the following net quantities of steam: 57,800 pounds of 450 lb./sq. inch gage steam at 600' F., 30,000 pounds of 150 lb./sq. inch gage steam at 600" F., and 301,950 pounds of 50 Ib./sq. inch gage saturated steam. It was assumed that sufficient preheat would be available from exhaust
32,100 11,200 2,700 13,900 27 X IO'
+
TABLE v.
74%
SPLITTING PL.4NT
1 cu. ft. Hygas feed, heating value, 1250 B.t.u. Lb. 0,0554 0.0526
Basis
Input Hygaa Oxygen Steam consumed Total
Total, 1,796,000 cu. ft./hr. hydrogen Cu. Ft./Hr. 504,800 316,000
0.0185
,....
0.1265
value
Make-up steam (50 lb./sq. inch gage, satd.) Make-up water a t 174' F.
+
0.1265 ___
1,990,000
Kw.-Hr. 0.0087 Lb.
Kw.-Hr. 4420 Lb./Hr.
0.1265
Energy figures Power for oxygen
TABLE VI.
83,500 7,010
.....
2 . 1 4 X 378 X 282.5 19.01 mol. wt. 14,500 f 336 (0.167 X 12,000) - (0.38 X 1505)
Efficiency = 1250
4049 x 5547.9
Total 2,950,000 cu: ft./hr. hydrogen
1 lb. maf. coal
Output Gas product (heating 292.6 B.t.u./cu. ft.) Total
OUTPUT
91
0.065 0.008
32,750 4,060
0.1265 X 378 X 292.6 12.14 mol. wt. (0.0087 x 12,000) ( o . 0 6 5 4 j a 79.4%
+
COMBINED REQUIREMENTS AXD EFFICIENCY
-
1. Heating value of Ha produced 4,920,000 X 324 1,590 X 100 B.t,u. 2. Power consumed, kw.-hr. 0%for Koppers 11,200, Oz for Hygas splitting 4,420, power for Koppers 2,700, miscellaneous 1,000. Total 19,320 = 234 X 106 B.t.u. 2a. Power for compression 63,280 kw.-hr. = 757 X 108 B.t.u. Total power 82 600 kw.-hr. = 991 X 108 B.t.u. 3. MAke-up steam, 50 lb./sq. inch gage Hygas splitting 32,950, shift reaction 269,000. Total 301,950 = 444 X 10.8 B.t.u. 4. Heatinn value of Hyeas from hydrogenation section. 884,200 X 894 = 790 x 108 B.t:u. 5 . Heatinn VL~ l u e ~ o f _ c o taol Koppers process. 83,500 lb. maf. coal X 14-ioo-=-i~2Io x i o m~. U . 6. Fuel to hydrogenation, 50 X 108 B.t.u. 7. Excess steam produced (450 lb./sq. inch gage) 32,200 = 48 X 108
B.t.u.
Over-all hydrogen-production efficiency 1590 X 100 = 1210 790 444 234
+
+
+
- 48
-50
Over-all efficiency, including compression 1590
Efficiency = 1210
x
100
+ 790 + 444 + 991
- 48 - 50
= 61.7%
-
47.7%
steam, condensate return, and waste-heat recovery units to preheat the feed water to approximately 300' F. No definite operating plan was set up for this unit, as data were available from handbooks (7) and general experience to indicate that electrical energy alone can be produced in a large central plant for as low a5 10,000 B.t.u. per kw.-hr. including all accessories. Steam production done can be carried out with efficiencies as high as 85%. However, as the above figures represent maximum prac-
INDUSTRIAL AND ENGINEERING CHEMISTRY
92
tical limits, somewhat lower values have been chosen. There is a considerable advantage in a back-pressure operation from a heatefficiency standpoint; but because less than 257' of the electrical output would be manufactured by this method, it was felt that the net increase would not much more than offset the line losses due to the extensive piping required in the plant as comparcd to a $entral power station; therefore no credit was assumed for back-pressure operations.
TABLE VII.
DISTRIBUTION OF POTTER AKD STEAM REQTTREMEKTS
Hz Mfg. Electrical energy kw.-hr. 450 lh./sq. inch i a g e steam, lh./hr. 150 lb./sq. inch gage steam, Ib./hr. 50 Ib./sq. inch gage steam, lh./hr. Coal as recd. tons/hr. Coal, maf., t&/hr. a Excess produced. b Basis of design.
19,320
Hydrogenation 69,059
Power Plant
..
Totals 88,379
(32,200)"
90,000
..
57,800
....
30,000
..
30,000
65: 4 56.2
301,950 231 .O 198.0
301,950 48.8 41.8
....
116.8 lOOb
The following energy requirements were established able to expect under normal full load conditions:
ap
reason-
B.t.u. Coal Input 1 kw.-hr. 1 lb. 450 lb. sq. inch gage, 600° F. steam 1 Ih. 150 lh. sq. inch gage, 600" F.steam 1 lb. 50 Ib. sq. inch gage, saturated steam
12,000
1,505 1,496 1,474
Using these above equivalents 1636.9 X l o 6 B.t.u. of coal input is required, or based on 11,900 B.t.u. per pound as fired, the coal requirement is 68.6 tons per hour. The net energy produced from the power plant is 651.3 x 106 B.t.u. This results in an over-all power-plant efficiency of
Vol. 41, No. 1
MAJOR IMPROVEMENTS OVER PREVIOUS PRACTICES
The following improvements, although technically sound, have not yet been fully developed and tested. Thcy must be subjected t o further laboratory and pilot plant study before being considered suitable for commercial use. Simplified and more efficient coal grinding and past,ing are proposed by combining pulverizing and paste mixing in one operation. It is believed this can be accomplished by use of a vertical hammer mill of the type widely used in similar applications in the food-processing industries, and for ore reduction. The power requirements are estimated to be less than half those for the Concentra rod mill, which performed a similar operation in thc German plants. Other advantages of the verbal, attrition-type hammer mill are lower investment cost aiid reduced operating and maintenance cost, due to fewer parte subject to wear. Elimination of the paste preheater represent's a major improvement, as in the European plants the paste preheater was one of the most costly, inefficient, and troublesome features of the process. The actual final heating of the paste was accomplished in heavy-wglled, alloy, finned hairpin tubes which were installed vertically in three-pass convection-type heaters. The erosion in the heater tubes was often severe, especially at the bottoiii bends, the pressure drop usually was excessive even ai. low velocities, and heat-transfer condit,ions were poor on both sides of the tube. For these reasons, it was extremely difficult to heat the paste to 800' E'. while cont,rolling the tubc wall at a safe temperature of approximately 940" F'. The Germans realized the shortcomings of such equipment arid had already taken steps to improve paste heating by measures such as thick and thin paste streams, heavy oil letdown recycle from the hot catchpot t,o the second pass, injection of hot hydrogen into the second pass, and utilizing more of the heat of reaction for securing high temperature level heat (8, 11, I S , 14). The I. C . Polit,z plant was designed to secure heating of the paste from 740" t o 900" l?. through the heat of reaction in a preheater-converter of large diameter (11).
The calculated efficiency is close to that achieved in German practice. Cheap hydroelectric power mould be a contributing factor in locating a plant with polver requirements of this magnitude.
TABLE VIII. POWER-PLAST OPERATION % Noisture
68.6 tons/hr. coal
11,900 B.t.u./lb.\ =
G
I
I I
Maf. coal
8 10 82
I
POWER PWST I
-+ 88,379 kw.-hr. a t 12,000 B.t.u. = 1060 X 106 B.t.u. -+ 57,800 Ih./hr. 480 lb./sq. inch gage steam a t 1505 B.t.u.
= 87 X 106 B.t.u. 30,000 Ib./hr. 150 lb./sq. inch gage steam a t 1496 B.t.u. = 4 4 . 9 X 108 B.t.u. -+301,950 lb./hr. 60 Ib./sq. inch gage fiteam a t 1474 B.t.u. = 445 X 108 B.t.u. energy produced Efficiency = heating value of fuel loo -c
Energy Produced B.t.u. Electrical energy 88,379 kw-hr. X 3415 B.t.u. 302 X 108 450 lh./sq. inch gage, 600° F. steam 57,800 Ib. X (1302-300)a 5 7 . 8 X 108 150 lh./sq. inch gage, 600° F. steam 30,000 Ib. X (1217-3OO)a 2 7 . 5 X 108 50 lb./sq. inoh gage, satd. steam 301,950 lb. X (1174-300)a 264 X 108 Total 651.3 X 106 Effioiency = 651.3 x 100 = 39,995 1636.9 a It is assumed t h a t sufficient waste heat, condensate, exhaust steam, etc., are available t o provide a feed-water temperature of 300' F.
Experience has shown that the paste normally heats up quickly from 800 O to 880' F. in the first converter. This operating characteristic, along with information taken from the German technical reports cited above, had led to t,he conclusion that a preheater-converter can be designed to operate Jvith paste and gas introduced a t 633" F., using the incoming coal paste as cooling medium for the reaction mixture aiid thus raising it to reaction temperature, as a result of natural or induced convection currents. In this converter, 70y0of the heat of reaction is act'ually used for supplying the sensible heat required to bring the paste temperature level up from 633" to 880" F. Cooling gas is introduced for temperature control a t various points in the filial convcrlcrs and hot catchpot. This additioiial gas is alp0 required in the vapor-phase process, which immediately follows. A small, highpressure preheater is required to heat z,limited stream of pastc and gas during start-ups. As the gas preheater operates 011 clean feed a t reduced temperatures, the improved heat transfer d l o w s the choice of a radiant-type heater, if desired, alt,hough the conventional convection heater would be equally suitable. The radiant type is generally considered more efficient than a convection heater. The gas preheater also serves closcly to control the heat input to the preheater-converter. When a number of converters are operated in series, it is possible to remove selectively a material of low oil and high ash and solids content from the final converter or from the hot catchpot. This is accomplished by providing means for deflecting the solids downward while adjusting the agitation hydrogen for satisfactory gravity sett,ling. Rapid and efficient settling is also facilitated by the favorable viscosity of the medium at the elevated temperature (880" to 900" F.). The removal of solids necessary to maintain equilibrium is accomplished in the final
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
January 1949
93
b
U PLAN
VIEW
:*
4
A"oR
3LT
SCHEMATIC PIPING DIAGRAM
v
....
-
.
1
ELEVATION
PLOW OIAGRAM OF TUBULAR
VIEW
Figure 3. A.
B.
C.
D.
Inlet for oil and liquidphase vapors Distribution manifold Four-hole terminal fittings Six-hole terminal fittings
CONVERTER EQUIPMENT
DETAIL OF TUBE CONNECTION8
Vapor-Phase Tubular Converter
E G Reducers F: kairpin tubes H. Outlet manifold I. Outlet J . Quartz beads
K. L.
Catalyst Coolant tank
M. Packing gland
N. Level of coolant 0. Outlet for coolant vapor P.
Q.
Coolant inlet from furnace Coolant inlet from heat exchanger
R. S.
Coolant drain Supporting clamp
T. Supporting I-beam U . Supporting ring
Dimensions of tubing, flanges and fittings taken from existing Bureau of Mines and I. G. Farbenindustrie data on 700atmosphere equipment. All ;ubing and fittings in contact with hydrogen of moderate chrome steel, heat-treated, and normalized. Back pressure may be controlled by orifice plates at reaction tube outlets, if necessary. size to be determined by experiment. Coolant to be melted by steam coils (not ehown) during shutdown. App:oximate weight, 71 tons. Approximate oatalyst space, 63 CU. ft.
converter of the improved plant and is the key to simplification of a number of operations. It is now possible to reflux the hot catchpot with the vapor-phase recycle oil and thereby conserve heat and improve control in the vapor-phase step. It is also possible to practice paste, heavy oil letdown heat exchange and adopt steam flash distillation for oil recovery from the oil-solids slurry (4,6).
A flash-distillation method has been adopted for recovery of oil from residue of high ash and solids. I n European plants it was customary to separate solids from a portion of the heavy oil letdown by centrifuging. This was a very troublesome and inefficient operation. The centrifuge residue required a kiln operation to effect a partial oil recovery. No really satisfactory equipment had been developed for these operations, and the
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
94 TABLE
Ix.
OVER-ALL EFFICIEXCY
input Coal, 231 tons/hr. (as-received basis) 231 X 2000 X 12,350 = Assume losses at 3% = Total coal Products
B.t.u. ,5750 x 100 l i 2 X 10: s922 x 1oe
-___
Vol. 41, No. 1
well with the available heat sources for distillation. Other distillation plans with equal heat efficiency could be used, depending on the separation rcquired; ho\\ever, in the particular plant under consideration, ultimate propane-butane recovery was not of paramount impofiance, as these niaterials are considered of equal value for hydrogen manufacture. SUMMARY O F HEAT EFFICIENCIES
B.t.u. 2480 X 100
Gasoline 62 tons/hr. X 2000 X 20,000 B.t.u./lb. = Liquefied petroleum gases 13.3 tons/hr. X 2000 X 21,000 B.t.u./lb. = 559 X 100 Residue 11tonsjhr. X 2000 X 10,000 B.t.u./lb. = 220 x 100 Total 3239 x 10' Thermal efficiency = 3259 loo = 5 5 . 0 % 5922
Gernians were considering much simpler methods for separating solids and oil, such as steam distillation, vacuum distillat,ion, filtration, and steam flashing. The latter method (4)is adopted in the simplified plant. I t is considered possible to eliminate letdown between the liquid and vapor phases by a combination of well planned opera,;ions. This would be accomplished by removing a small quantity of high-solids-content heavy oil letdown from the final converter, refluxing the hot cat'chpot, and using a sturdy catalyst not adversely affected by some heavy-oil entrainment or by moisture, sulfur, ammonia, tar acids, or other materials which pass overhead from the hot catchpot directly to the vaporphase converter. Such a catalyst had been developed for 700atmosphere vapor-phase operat'ion a t Welheim ( 2 ) . To facilitate this operation further, the vapor-phase converter has been especially designed for positive and easy control of rea,ction conditions. -4 study of the flow sheet and heat balance will reveal ihe advantages of such an operation. Apparently the Germans appreciated the desirability of eliminating letdovn between phases but had not arrived at a series of operations that could make it feasible. However, they did hope eventually to accomplish this when the two steps could be synchronized to allow 2ontrol of the vapor-phase operation. The conyentional method was to carry out vapor-phase hydrogenation in 2.5- to $-foot,inside diameter reactors containing B number of fixed catalyst beds. Heat generated by the exothermic react'ions vias removed by large amounts of cooling hydrogen introduced betv-een t'he beds. -4lthough this method was entirely successful with plank using carefully fractionated vapor-phase feed stock, and could be utilized in the plant for improved thermal efficiency with little loss in efficiency, it is considered that the alternate type of converter mill prove safer and easier t,o control. Based on successful vapor-phase hydrogenation experiments, carried out in 3-inch tubes without hydrogen cooling and on a thermodynamic study, a vapor-pha,se tubular converter has been proposed (Figure 3) to secure improved heat economy, improved safety, improved gasoline yields and quality, simplified construction and control of converters, simplified series operation, increased flexibility of equipment, and elimination of vapor-phase preheater. KOrecord was found in the German documents which indicated that they had considered the use of a reactor consist,ing of a number of hairpin pressure cubes, suspended in a constant temperature bath, for vaporphase hydrogenation. The distillation operations have been simplified as compared to the German methods. One still is required instead of three, owing to the continuity between liquid- and vapor-phase opcrations. The practice frequently followed in America of letting down directly into an absorber-stripper t o m r for fixed-gas removal and gas reco.r.ery in a single step has been adopted. The letdown material is fractionated into gasoline and recycle middle oil. The gasoline is then stabilized and treated in a single operating step. The equipment indicated for these operations balances
The hydrogenation plant shown in Figure 1 is designed t o produce 62 tons per hour of gasoline, 13.3 tons per hour of lique- , fied petroleum gases, and 11 tons per hour of residue from 100 tons of moisture- and ash-free coal. The plant will require 69,059 kw.-hr. of electrical energy, 90,000 pounds of 450 lb./sq. inch gage 600 O F. steam, 30,000 pounds of 150 lb./sq inch gage 600 O F. steam, 4,920,000 cubic feet per hour of hydrogen, and 77,600 cubic feet per hour of fuel gas. Also produced and credited to the operation are 8%,200 cubic feet per hour of Ilygas. The thermal efficiency of this operation is calculated as 73.2%. The hydrogen-manufacturing plant p1 oduces 4,920,000 cubic feet per hour of hydrogen and 77,600 cubic feet per hour of fuel gas. Requirements are 19,320 kw.-hr. of electrical energy, 301,950 pounds of 50 lb./sq. inch gage saturated steam, 881,200 rubic feet per hour of Hygas, and 41.8 tons per hour of moistureand ash-free coal. Also produced and credited are 32,200 pounds of 450 Ib./sq. inch gage steam. The thermal efficiency of this operation is 61.7%. The pover plant, t o produce the steam and electrical energy for hydrogen production and hydrogenation, will require 56.2 tons per hour of moisture- and ash-free coal and will operate with a thermal efficiency of 39.970. A summation shovs a total requirement of 198.0 tons per hour of moisture- and ash-free coal or 231 tons per hour of coal as received, for a balanced operation when producing the final products. It is assumed that a figure of 3y0 additional coal will cover heat and material losses from miscellaneous small units which have not been previously included. An alternative to the above would involve burning the residue. I n this case, the coal requirement would be decreased by an amount equal to the heat value of the rwidue, and the over-all thermal efficiency would become: 100 X (3259 - 220) -- - 803,900 = 53.2% Thermal efficiency = 5922 220 5702
--
-
The thermal efficiency of a typical German plant (6) using the conventional mater-gas method of hydrogen manufacture and the usual three steps (liquid-phase, saturation-phase, and splittingphase) but not including hydroforming (D.1I.D.) of the hydrogenation process was calculated to be 28.97,. A combination of some of the late German developments, not holly incorpoi*ated in any individual plant, might have given an efficiency as high as 36.8Y0 (16). A comparison has been made with the German heat efficiency for enoh section with lhc folloning results:
1. 2. 3.
4.
Hydrogenation proper
Hydrogen mfg. Power plant Over-all efficiency
Improved Plant,
Plant ( 16)
%
%
73.2 61.7
27.0
39.9 55.0
German
~
31.1
42.0
28.9
The coal usage on such a plant would compare with the proposed plant as shown in Table X. This comparison shom very clearly the relative importance of each phase of the operation and especially the necessity of an efficient method of hydrogen production. A comparison of the German yields to those in the paper is also of interest (Table XI). The bituminous coal selected for this paper differs in some respects from the German bituminous coal cited above; however
January 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY TABLE X. COALUSAW
(Basis, 62 tons per hour of motor gasoline) Improved Plant doal t o hydrogenation (mctf.) tons/hr. 100 Coal t o Hz production (maf.),’tons/hr. 41.8 Gas t o H t production (net), B.t.u. 740 X 106 Coal t o power plant (maf.), tons/hr. 56.2 Gas t o power plant (net), B.t.u. . Total coal charged (maf.), tons/hr. 198
.. . .
German Plant (16) 120 190
....
60 1,410 X 10‘
370
TABLE XI. YIELDS (Basis, 1 ton of coal (as received) t o hydrogenation) Yield, Product Improved Plant German Plant (26) Gasoline, ton 0.53 0.515 L.P.G., ton 0.11 0.1 Hygas, B.t.u. 6.76 X 108 8.6 X 10’ Hz consumption and loss, ton 0.111 0.138
the yields, as would be expected, are not appreciably different. This comparison indicates that the increased heat efficiency is due to the application of more efficient methods and processes rather than to any remarkable increase in yield. GENERAL DISCUSSION
The final gasoline is expected to have an octane number of 82 to 85 motor method, and with the addition of 3 ml. of tetraethyllead per gallon this may be increased to 92 to 95. The gasoline will contain a high percentage of aromatics, and, for this reason, the actual full scale engine performance may be considerably better than would be indicated by the usual octane test met hods. Credit has been taken in the heat-efficiency study for C1 and Ca hydrocarbons, with the intent that they would be distributed as liquefied petroleum gas. As an alternative plan, these gases could be isomerized, polymerized, or alkylated to give an additional yield of high-octane gasoline. The asphaltic residue might also be used as a roofing ingredient or road-building material. The recovery of commercially valuable chemical by-products, such as phenols, pyridines, and coronene, has not been given consideration, although their simple recovery would considerably enhance the economic status of the plant. The catalyst proposed for the liquid phase is the well established ammonium molybdate (2%) on 98% terrana (fuller’s earth). The Germans used this catalyst extensively before and occasionally during World War 11. The catalyst, as a powder, is introduced directly with the powdered coal and oil vehicle and used in the proportion of 1% of the moisture- and ash-free coal. This is not only an economical and efficient liquid-phase catalyst, but greatly reduces the solids problem and hence gives improved oil yields. A number of other catalysts have been used commercially in Europe with satisfactory results. Catalysts suited for the vapor-phase operation are those of the K535 series @), used in a k e d bed and in pelleted form. The K535 catalyst, for example, has a composition of 0.7% molybMoS4, 2% chromium as CraOa, 5% zinc denum sulfide as (“32 as ZnO, and 10% sulfur, on terrana. For the proposed plant, a catalyst is required that is capable of contacting a feed not precisely fractionated for removal of heavy ends, without loss of efficiency. For this purpose K535 is suitable. This catalyst is inexpensive and insensitive to oxygen during shut-down for repairs, and does not require the addition of hydrogen sulfide for continuous activation. K535 is a proved catalyst and was used at Welheim (2) under 700 atmospheres for production of high-octane gasoline. Although present catalysts are commercially satisfactory, further study and development may bring about a n improved catalyst with higher selectivity toward gasoline formation with resultant lesser gas production. An improved catalyst may also allow operation at lower hydrogenation pressures and thereby effect a saving in compression costs, as well as give an increased
95
throughput. Such studies are currently being carried on a t the Bureau of Mines Pittsburgh laboratories. No credit is taken in this paper for potentialities of the nature of those cited above, although they are recognized as having a considerable bearing on the efficiencies and economics of future plants. The proposed process has been assembled from the best features of British and German practice, and the innovations proposed are technically sound. The quality of product or the economics of any part of the system have not been sacrificed to achieve a high thermal efficiency. The process as outlined greatly reduces the equipment required and simplifies the operation. Certain features, such as the preheater-converter and the tubular converter, are predicted to give more uniform temperature pontrol and to result in individual contributions toward higher yields and quality of the gasoline. No attempt has been made in this paper to discuss or predict the economics of the process outlined or the economics of coal hydrogenation in general. Many factors must/ be considered in designing a coal-hydrogenation plant representing maximum economy. Studies must be made of markets, location of raw material and services, yields and production ratio of usable products from American coals of different sources, etc. Each item of equipment installed must be justified economically and not merely represent high efficiency. Thus a coal-hydrogenation plant designed for maximum economy may differ in some respects but is expected to follow the general form of a plant representing highest thermal efficiency. LITERATURE ‘CITED
(1) Chaffee, C. C., Thomspon, 0. F., Icing, J. G., Atwell, H. V., and Jones, I. H., Metallgesellschaft-Lurgi, CIOS Rept. X X X 1-23, (Sept. 11, 1945). (2) Cochram, C., and Hirst, L. L., Bottrop-Welheim Hydrogenation Plant, Ibid., XXX 104 (Aug. 8, 1945). (3) Howell, J. H., and Crawford, R. W., U. S. Naval Technical Mission in Europe, Tech. Rept. 217-45 (August 1945). (4) Hupfer, H., “Heavy-Oil-Letdown Distillation,” Technical Oil Mission Reel 145,Frames 35-50,Item No. 7, from the filee of I. G. Farbenindustrie, Ludwigshafen (May 22,1944). (5) Kahl, L. ( t o Rutgerswerke A. G.), Ger. Patent 735,469(April 8, 1943). (6) Keith, P. C., C h m . Eng., 53,No. 12, 101 (1946). (7) Kent, R.T., “Mechanical Engineers Handbook,” 11th ed., Vol. 11,Sec. 8, p. 85,New York, John Wiley & Sons, 1937. (8) Kleber, I. G.Farbenindustrie, Ludwigshafen, Tech. Oil Mission Reel 76, Frames 36-46 (May 25, 1943). (9) Newman, L. L., “Oxygen Production and Utilization in Gas Making Processes,” presented at Am. Gas Assoc. Tech. Sec-
tion, Joint Production and Chemical Committee Conference, New York, June 3 to 5, 1948. (10) Public Law 290,78th Congress (April 5,1944). (11) Rank, V., and Gttnther, “Liquid and Vapor Phase Operations Discussions at Politz,” Tech. Oil Mission Reel 170, Framea 534-547 (March 27 to 29,1944). (12) Russell, R. P., testimony in hearings before subcommittee on Public Lands and Surveys, U. 6 . Senate, 78th Congress,,firat session, on S1243,P-33-59,1943. (13) Schappert, H., Tech. Oil Mission Reel 167,Frames 23-43 (Marah 24, 1944). (14) Schappert, H.,“Reducing the Load on the Liquid Phase Preheaters,” Tech. Oil Mission Reel 164,FTames 794-806 (March 22,1943). (15) Schappert, H., and Wilde, H., “Calorific Efficiency of Bituminous Coal Hydrogenation,” Tech. Oil Mission Reel 57, Frames 183-202 (Feb. 20,1942). (16) Storoh, H.H., Fieldner, A. C., and Hirst, L. L., U. 8 . Bur. Mines, Tech. Paper 666 (1944). (17) Storch, H.H., Hirst, L. L., Fisher, C. H., and Sprunk, G. C. Ibid., 622 (1941). (18) Totzek, F., “Heat Balance of Heinrich Koppers Powdered Coal Gasification,” Tech. Oil Mission &el 188, Frames 20,951-60 (June 17, 1943). RECEIVEDJune 30, 1947. Presented before the Division of Gas and Fuel Chemistry a t the 111th Meeting of the AMERICAN CHEMICAL SOCIETY, Atlantic City, N. J. Published by permission of the director, Bureau of Mines, U. 8. Department of t h e Interior. Technical Oil Mission reels and C.I.O.6. reports may be secured from the Library of Congress, Washington, D. C.
