LIQUII FUEL
from COAL
May 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
ducting experimental runs xhich have yielded important data as well as many tank cars of usable oil. The second to be completed will be the coal hydrogenation plant with which this article is particularly concerned. This unit is expected to be in full operation sometime this month. A gas synthesis plant also under construction at Louisiana is scheduled for completion late in 1949. The two plants at Louisiana are being built on the site of the wartime Missouri Ordnance Works. This site was chosen even before the wartime ammonia plant was deactivated because it was one of the most expensive ammonia producers in the war program and i t was scheduled for shutdown as soon'as its nitrogenfixing capacity could be spared. 3fuch of its high operating cost was attributable to the expensive pipe line natural gas which it used as a raw material. The plant offered the additional advantage of having five individual synthesis lines which could be operated completely independently. HISTORY OF COAL HYDROGENATlON
The basic process for coal hydrogenation, from which the procedure used a t the Louisiana demonstration plant is derived, was discovered by Bergius (7, 8) in Germany about 1912. (The original Bergius process operated without catalyst. I n 1924 I. G. Farbenindustrie began constructing pilot and demonstration plants using resistant catalysts, which gave improved throughput, yield, and product quality.) Construction of the first industrial scale plant was started by I. G. Farben at Leuna, Germany, in 1926 and began liquefaction of central German brown coal the following year. By 1933, i t became apparent that Germany could no longer import crude petroleum because of currency exchange difficulties and a large scale development program was undertaken which led to the construction of some ten large hydrogenation plants capable of producing 85% of Germany's gasoline supply for wartime aviation. Although essential design was frozen in 1938 for practical reasons, an active development program was carried on throughout the \Tar. Many improvements outlined in wartime European research have never reached full scale application. European hydrogenation operations were .elaborate, costly, and cumbersome and did not appear promising in the American economy when the Bureau of Mines first undertook experimental work in the field. However, preliminary investigations revealed some striking inefficiencies. It appeared that it might be possible to improve the heat efficiency of a plant as much as 1 0 0 ~ oby incorporating certain modifications. Subsequent experimental work has effected some of this improvement and even more efficient techniques are now under investigation.
871
page 874) , perhaps the first of a future industry. Designed to produce 200 to 300 barrels of gasoline per day it is large enough to provide experience and working data (Tables I and 11, page 875) on which industrial operations may be ultimately based. The hydrogenation will be done a t 10,300 pounds per square inch pressure and 840 O to 900 F. corresponding to conditions in the high pressure German plants because these conditions permit smaller reaction vessels and more complete conversion to control formation of asphalts. However, the Bureau of Mines laboratories at Bruceton, Pa., are investigating a new process at 500 t o 1000 pounds per square inch which would cut compression cost measurably and perhaps improve the thermal efficiency of the process. O
The raw coal comes into the plant in railroad cars and is powerconveyed either to the crusher or a storage pile. A ring and hammer type primary crusher reduces the size of the material to less than 0.75 inch and discharges i t into an 80-ton bin. As needed, the coal is dried and pulverized in a mill containing 20,000 pounds of 3-inch diameter cast iron balls. Drying is effected by passing inert flue gas from a specially designed natural gas burner together with a large volume of circulating flue gas through the mill a t 300' to 400" F. The gas stream also serves to carry the pulverized coal into a classifier to remove oversize pieces and then into a cyclone where the minus 60-mesh coal powder is collected. The pasting powder is transferred on a Redler conveyer t o a 60-ton storage bin in the pasting building. The pulverized coal from the storage bin is mixed with pasting oil and catalyst in a 820-gallon, steam-jacketed tank by means of a double motion mixer. The paste from the mixing tank overflows continuously into a steam-heated, 14,000-gallon, mechanically agitated storage tank. Under design charge conditions the
DEMONSTRATION PLANT
The plant that has been built a t Louisiana, Mo., includes the solutions to many of the problems found in the European installations. During the 2 years that the plant has been under construction, additional modifications have been suggested by pilot plant work done a t the bureau's Bruc&on, Pa., laboratories and further studies of German data. These modifications eventually will be incorporated in the demonstration unit along with changes which will be indicated from actual operating experience* As it stands the plant is most important as an actual working unit (Figure 1,
Converter Which Will Perform the First Step in the Bureau of Mines Liquid Fuel Demonstration Plant
812
INDUSTRIAL A N D ENGINEERING CHEMISTRY
tank will hold a reserve sufficient for 9 hours' operation. Three constant-weight vitmting fccders (ID) are used for proportioning the coal and dry catalyst. Two types of dissolved catalysts feed can be prepared and &[soproportioned into the paste or sprayed on the coal prior to drying in the ball mill. The paste is pumped by thrce positive displacement screw type pumps (E.2) through 4-inch steam-jacketcd pipe to the injection pump house. Here two of the tlircc 24 X 2.75 X 18 inch steam-driven, injection pumps deliver a t a rate of 25 gallons per minute and 10,300 pounds pcr square inch gage into a foursection steam-jacketed radiant prchcntrr. Ahead of the preheater a small amount of hydrogon is iiijcctcd into the pastc to reduce viscosit and increase the velocity of the Row. Thc paste is heated in tze prehcater first section to about 550" F. At this stage, additional hot hytirogcn and recycle heavy oil are added to jump the temperature to G O " F. in order to pass through the swelling-range, around 6CO" F., as quickly as possible (Figure 2, page 876). At about, 600" F. the coal s ~ ~ c l rapidly ls and the paste may become dry and extremely viscous, introtiucing the danger of coking and tube failure. After passing through the remainder of the preheater thc mixture leaves at 815" 17. and passes into the bottom of the first of two identical converters. In German installations the paste often was preheated in exchangers in the catch-pot overhead but the small size of the demonstration plant makes such a procedure impractical. Subsequent industrial installations undoubtedly will incorporate such an exchange system. I n these vessels the coal is converted by thermal decomposition and addition of hydrogen into middle and heavy oil and some gasoline. Since the reaction is highly exothermic the temperature in each converter must be maintained a t 890" F. by the addition of cooling hydrogen at three points in the converter. The flow of cooling hydrogen is controlled by means of independcnt recording temperature controllers in each zone. The average residence time of liquids and solids in the converters should be 1 to 2 hours for about 95% conversion of the carbon t o gaseous and liquid products suitable for use or subsequent processing. The reacted product at about 870" F. leaves the converters and passes t o the hot catch pot which is similar in construction to the converters but has an inverted cone bottom. I n this vessel heavy-oil letdown is separated from the oil vapors and excess hydrogen.
Vol. 41, No. 5
catalyst and ash were discarded. Recovery has been reportcd as between 75 and 9 0 ~ from c various units. I n a full commercial scale plant such an operation would be desirable and profitable but the small volume which will be handled at the dcrnonstration plant will not warrant the capital expense of coking ovens. The centrifugate is sent to the pasting-oil blending tank where it is combined ~ i t unseparated h H.O.L.D. and light oil bottoms from the liquid-phase still to make new pasting oil. An alternative system (Figure 3) which has been worked out by Bureau of hIines engineers using some German experimental data has been installed also. This system takes the hot catch-pot bottoms before they have been let down, adds super-heated steam a t 1100" F. and 20 pounds per square inch with a steam to oil ratio of 2 to 1, and flashes the mixture into the top of a 2000gallon flash drum. Steam at 300 ' F. introduced in the center of the tank quenches the spray and causes the solids and heavy oils to fall to the bottom of the drum as pitch containing about 70% solids. The pitch is pumped into a cold water spray where it hardens into tarry nodules about 0.5 inch in diameter. Preliminary tests indicate that these nodules may be used for secondary road surfacing by merely spreading them on and flattening with a steam roller. It bas been suggested also that they could be pressed into a durable house shingle. The overhead from the flash drum comes off a t 750" F. and is introduced into a quench toFer \\-here a spray of heavy oil distillate at an oil to vapor ratio of 2 to 1 condenses the oil over a series of horizontal trays, while the dry steam escapes through an overhead exhaust head. The condensed oil is taken from the bottom of the tower at 500' F. and pumped to paste-oil blending. Pilot plant tests predict that this modification will increase the oil yield from the liquid phase unit to 15Tcover that obtained with centrifuge recovery by decreasing oil loss from 130 to 6 pounds per 1000 pounds of moisture- and ash-free coal. Delayed coking of the tar might increase the yield another 5%. The overhead product from the hot catch pot is cooled in three specially designed double-tube exchangers, first with hydrogen for the preheater second pass, then with Kash oil, and
HEAVY-OIL LETDOWN SOLIDS SEPARATION
The recovery of oils from the solids in the heavy-oil letdown (H.O.L.D.) is a critical step in the economy of the hydrogenation process. It is the point where there may occur substantial product losses which can mean the difference between competitive and unprofitable operation. All commercial plants built in Europe utilize centrifuges for this separation. The Louisiana installation contains such a unit which processes about 5070 of the bottoms from the hot catch pot after they have been cooled and let dorm to atmospheric pressure through one of three throttling valve groups into a pressure receiver. The H.O.L.D. from the catch pot contains 20 to 35% solids. For more efficient separation the H.O.L.D. is diluted with light oil to give a composition of about 20% solids before passing through a heat exchanger where i t is heated by low pressure steam or cooled by water before introduction into one of two centrifuges. One of the centrifuges is the convent,ional high speed type used in the German installations (23). The second unit represents an experimental installation with a low speed solid bowl fitted with a screw conveyer specifically designed for the removal of insoluble solids from a liquid suspension (9). Both units (Figure 3, page 877) are designed to discharge a clear centrifugate and a heavy oil containing about 40Yc solids at a rate of approximately 8 tons of solids per day. The solids removed by the centrifuge units must be equal to the amount of unreacting solids in the coal paste charge. The amount of H.O.L.D. processed in the centrifuge is adjusted to maintain this balance. Solids concentrate from either unit a t Louisiana will be pumped to a disposal pit and discarded. However, in German units this material was coked in low temperature ovens to recover part of the volatiles present before the spent
Over-all View of an Experimental Unit for Flash Distillation of Solids from Heavy Oil Disaharged from First Converter
May 1949
4
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
finally with water, before entering the cold catch pot. About 770 of water is injected ahead of the coolers to dissolve precipitated salts. Raw gasoline (6%) is injected ahead of the cold catch pot to lower the gravity of tthe oil layer from about 1.0 to about 0.96 to ensure that the water will settle out completely in the letdown drums. The overhead gas from the cold catch pot is scrubbed with wash oil (about a 37" A.P.I. naphtha) in a high pressure absorber packed with 1.5-inch stwl Raschig rings for removal of light hydrocarbons and fixed gases to prevent the concentration of these nonreacting gases from building up in the hydrogen recycle system and lowering the hydrogen partial pressure below that necessary for efficient hydrogenation. Wash oil is furnished from the distillation area and is injected a t 10,000 pounds per square inch gage by means of a steam-plunger pump similar to the ones used for coal paste. (On leaving the bottom of the scrubber the saturated wash oil is let down t o 7 aim. pressure in two steps and scrubbed with superheated steam at 400' F. Bottoms from the scrubber are returned to wash oil storage tanks.) The recycle gas (about 80% hydrogen) leaves the top-of the wash oil scrubber, passes through a compressor suction trap, that is identical in size and construction to the cold catch pot, and is compressed in two 150-hp. double-end compressors operating a t an average differential of 700 pounds per square inch; these were especially designed for recycling hydrogen in Claude high pressure ammonia producing units. About 20,000 standard cubic feet per hour may be purged to boiler fuel from this line to reduce further the concentration of nonreactive gases. The compressed gas which is recycled from the scrubber to the converter hydrogen feeds represents about 80% of the total feed. Of 400,000 standard cubic feet per hour of hydrogenation gas charged to the liquid-phase converters only about 90,000 cubic feet is fresh make-up hydrogen. The excess hydrogen is introduced to maintain the required hydrogen partial pressure in the reaction zone and to control temperature. The cold catch-pot liquid is let down to 25 atm. and then to 7 atm. in horizontal pressure vessels equipped with water take-off sumps. The letdown product is charged t o the liquid-phase still, a 28-tray column 3 feet in diameter by 73 feet high, equipped with a three-section side cut stripper for separating naphtha, middle oil, and flushing oil. The tower has nonremovable trays equipped with fourteen 3.5-inch standard bubble caps. The light oil bottoms from the still are returned to make additional pasting oil, and the gasoline overhead product, together with the naphtha and middle oil, are blended to obtain stock with an end point of about 610" F.; this stock is combined with a nearly equal amount of vapor-phase middle oil to form the feed for the vapor-phase hydrogenation. This feed is saturated with hydrogen sulfide in a tower to introduce the sulfur necessary to preserve the activity of the vapor-phase catalyst. The vapor-phase hydrogenation system parallels the liquidphase hydrogenation but uses fixed catalysts in trays. The catalysts must perform the triple duty of saturating, splitting, and dehydrogenating the heavy oil molecules. Feed is injected into the system by means of a steam-driven injection pump, and together with added hydrogen passes through a feed-bottoms exchanger and then through a radiant preheater t o about 900' F. The vaporized feed plus hydrogen passes down through the catalyst through the feed-bottoms exchanger and product cooler to the cold catch pot. Cooling hydrogen is introduced a t each of the six catalyst trays. The shell of the vapor-phase converter is identical to the liquid-phase converters. It contains a basket divided into six fixed catalyst beds; the temperature of each bed is automatically held between 912' and 930 F. cooling hydrogen. The overhead product from the cold catch pot (about 80% hydrogen) passes through a suction trap (identical to liquid phase) and to the recycle compressors. Thepvapor phase recycle hydrogen does not require scrubbing since light ends are in O
Coal Paste Preparation Buildings Are Connected by
a73
a
Hedler Conveyer Coal from hopper cars is dumped at pit in front of stockpile (right) '
the catch pot to absorb most of the inert gases present. I t is hoped that under certain operating conditions such self-washing will eliminate the need for the scrubbing step in the liquidphase cycle also. This recycle gas represents about 90% of the total gas injection, only 10% of which reacts in the converters. A small amount of gas may be purged to the power boilers from this line t o reduce the concentration of impurities. The cold catch-pot bottoms are let down to 25 atm., and then to 7 atm., before charging to the vapor-phase still, a 30-tray fractionating tower, 2.5 feet in diameter by 70 feet high. (The letdown is done stepwise to minimize mechanical wear on the throttle valves and letdown tanks and to remove some very lean gas from the stream before it is introduced into the still. The still bottoms, unconverted middle oil representing about 60% of the initial feed which represents 50% of the vapor-phase feed, are blended with liquid-phase products t o make more vapor-phase hydrogenation feed.) The overhead gasoline from the fractionation is freed of objectionable light ends in a stabilizer (1.5 feet in diameter by 27.5 feet high) packed with 1-inch ceramic Raschig rings. After leaving the stabilizer the gasoline is treated with a 3% caustic solution and then with water in a two-compartment tower, to remove traces of hydrogen sulfide before going to tankage. In addition t o the liquid- and vapor-phase stills, the distillation area includes an absorber-stripper system for light hydrocarbon recovery, a water cooling tower for the entire plant, an ethyl gasoline blending plant, liquor treatment, oil-water separator, loading racks, and the necessary tankage and pumps to handle the products. HYDROGEN GENERATION
The approximately 120,000 to 200,000 cubic feet per hour of hydrogen required in the hydrogenation process is manufactured by cracking natural gas, using much of the equipment of one or two ammonia lines of the former Missouri Ordnance Works. Natural gas, containing about 79% methane, 9 t o 10% nitrogen, and traces of CZ,CS, and CChydrocarbons, is obtained a t 450 pounds per square inch from Panhandle-Eastern's main pipe line. Gas and steam, in 1t o 1.8ratio, are cracked a t about 1700' F. over a nickel catalyst in tubes 8 inches by 40 feet long, four
874
INDUSTRIAL A N D BNGINEBRING CHEMISTRY
.: . .
.
INDUSTRIAL AND ENGINEERING CHEMISTRY
May 1949
TABLE I.
Figure 1. Process Flaw Sheet Coal preparation 1. Raw coal to conveyers 2. Feed t o pulverizer 3. Dry, prepared coal Paste preparation 4. Coal feed 5. FeSO4 catalysts 6. Bayermasse 7. Pasting oil
tubes per bank and eight banks per furnace. The cracked gas, containing about 60.1% hydrogen, 2.3y0 nitrogen, 4.6% carbon dioxide, 23.6% carbon monoxide, and 0.4% methane, is cooled to 800" F. and introduced into an integral shift-reaction converter which reacts the * carbon monoxide present with water to form a mixture containing 7701, hydrogen, 18% carbon dioxide, and 1.5% carbon monoxide. This gas is cooled by direct water contact and stored in a 300,000-cubic foot gas holder. The hydrogen is compressed to 11,000 pounds per square inch by two of the five cornpressors formerly used in the Missouri Ordnance Works (18). The compressors have seven stages with a 48-inch cylinder in the first stage. They are driven by a 2500-hp. synchronous motor and have a maximum capacity of 210,000 cubic feet per hour which in average cracked gas would correspond to approximately 125,000 standard cubic feet per hour of 97% hydrogen. When the plant is operating at the nominal capacity a maximum of 165.000 cubic feet
DESIQN
Flow Rate, Lb./Hr.
OPERATING CONDITIONS Density
7,
6,000
.. ..
. ., .
40 lb./cu. f t . 53.4 90 lb./cu. f t . 667 50 l b / c u f t 7,000 (9% solids) 1 17 sp gr '60° F./60° F.) 1:11 sp: gr: [350° F./60° F.) 134 (20% solids) 1.117 sp. gr. (SO0 F./60° F.) 12,000 1.2 SP. gr. (60' F./60° F.) I
1.2 sp. gr. (60' F./6Oo F.)
.. ..
.............. ..............
.....
is5 235 210
....
4750
210 125 200 700 767
10,300 12,000 10,300 10,300 10,300
375
..... ... ....
815 125 930 125
10,300 10,300 10,300 10,300
....
930 125 767 867 767 375 375
10,300 10,300 10,300 10,300 10,300 10,300
120
10,300
.. ii
.............. I?.) ..............
1.24 sp. gr. (60' F./60°
....
1.24 sp. gr. (60° F./6Oo F.) 1.25 SP. gr. (60' F./60° F.) 1.25 sp. gr. (60° F./60° F.)
21 110 42
30 (liquid)
..............
.............. 28. .............. 29. *head .............. 30. 7.5 lb./gal. (60° F.) 31. 32. .............. 33. .............. 34. .............. 35. .............. 36. .............. 37. 38. 39. Gasoline Hydrogenation, vapor phase 7,250 0.886 SP. gr. (60' F./60° F.) 40. Vapor-phase feed 41. Vapor-phase feed injection 12,500 (42 wt. .............. % vapor) 12 500 42. Heated feed (100% vapor) 12,500 (100% 43. Converter feed vapor) 13,500 (100% 44. Converter outlet vapor) .............. 13,500 45. Cooled converter product .............. 9,500 46. Cold catch-pot bottoms .............. 5,900 47. Cald catch-pot overhead .............. 8,350 48. Letdown, l * t step ............... 8,900 49. Letdown, 2pd step .............. 2,660 50. Light gasoline
....
20 1285
2i
..............
.... ....
.. .. ..7.
.... ...
1.25 sp. gr. (60' F./6OY P.)
....
..
....
.............. ..............
..............
Bottoms from cold catch
Pressure, Temp., Lb./Sq. In. O F. Gage
cp.
.... ....
8 in. X 0 (3% ash, 30% H20) 0.25in. X 0 -60 mesh (3% ash 1% HzO)
150,000 21,000 15,000
8. Chemical pasting oil 9. Paste feed Hydrogenation, liquid phase 10. Paste injection 12,300 11. Make-up hydrogen 290 12. Feed t o preheater 12,600 13. Circulated hydrogen 1,660 14. Heavy oil recycle 2,000 (24% solids) 15. Feed t o converter No. 1 16,200 (11 ,xggor) 16, 16a. Circulated hydrogen 17. Feed t o converter No. 2 17,700 18. Hydrogen (cooling gas) 780 19. Converter product 18,450 (81 wt. % vapor) 20. Hydrogen 730 21. Heavy oil 5,821 13,400 22. Overhead from hot caQchpot 3,800 23. Heavy oil to storage 3,800 24. Cooled heavy oil 3,760 25. Letdown heavy oil 13,400 (40 wt. 26. Cooled overhead % vapor) 27.
875
...... .. .. .. 150
100
..
....
.... ....
10,300 370 103
io0
.... 10 .... ... .... ....
....
iio
10,300 370 103 10,300
4i0 120 630 580
....
.... .... .... .... ....
.... .... ....
245
56
..
105
..
10,300
785
10,300
..
36 (liquid)
....
920
....
19.0 27
....
. . I .
10,300 10,050 10 050
120 120 120
1o:ooo
10,000 370 103
.. .. ..
....
~~
TABLE 11. ANTICIPATEDCHEMICAL ANALYSISAT ,--
10
Hn Nn HnS
co coz 8"
Hn0
c1 cz c3
C4 c 6 Gasoline (end point 325" F.) Naphtha (end point 450° F.) Middle oil (end point 617O E".) Light oil bottoms Flushing oil Av. molecular weight Heavy oil Coal Ash Catalyst Solids a Vapors. Wash oil. Wash and absorber oil. Total converter product.
11 15 24.6 3.0 4 ~ . 5 5.5 .. .. 08 .. 49 Trace 1.0 1.5 0.2 0 . 2 Trace 014 0.3 1i:9 1.7 3.5 0.4 1.4 0.2
.. ..
17 3.4 8.8 Trace 1.7 0.3 Trace 2.1 2.7 0.7 0.3
.. .. .. .. .. .. .. .. .. .. .. .. .. .. . . . . . . . . . . . . . . . . . . . .
19 3.6 10.2 0.4 2.3 0.6 0.5 2.1 4.1 2.4 2.2 1.3 0.3 2.2 3.2 9.0 21.7 2.4 20.1' 20.3
CRITICAL POINTS I N
Weight 21 0.1 0.2 Trace Trace Trace Trace
...
0.2 0.1 0.1 0.1
... ... ... ... ... ... . . .
30 31 9.9 0.4 0.2 26.1 1.0 0.4 0.4 0.1 0.1 5.6 0.2 0.7 0.5 0.1 0.8 0.2 Trace 13.035.818.1 0.3 9.9 1.0 0.4 6.0 1.6 0.6 4.3 1.7 0.8 1.9 1.0 0.2 0.5 0.3 13.1 6.1 16.9 40.8 4.5 7i:bb . . 6:2 27
0.1
34 18.2 48.6 0.4 10.4 0.6 0.2
.....
. . . . .
. . . . . . . 1.1 ... . . . . ... 7.0 3:6 2.7 2.5 615 ...... ... 5+:6 ... 27.4 46.5 58.2 64.8 . . . . . . . . . . . . . . . . . . . . . . . . . . 36.2 1.1 .. 0 . 9 .. .. . . . .. .. . . . . . . . . . .. .. .. 1.1 . . . ... 09 .. 58 11.2 1 0 . 8 2i:b :: :: . . . "
PROCESS
% a t Point No. (Figure 1)
15:9 4.1 1.6
7
40
42
... ... 2112..30 1.0 ... 00 .. 96 ..... . . 0.. 1. ::: 5.... 4 ...
1.4 0.6
... .. .. .. .. .. .. .. .. . . 5.7 3.2 8.3 4.8 .. .. 78.4 45.8 6.5C 3.7C . . . ... . . 13.2 8:l
46 0.3 0.8 0.8 Trace 0.2 0.2 21.7 0.8 1.3 2.0 2.7 0.7 21.3
47 27.3 52.0 213
50
.... ..
..
.. .. .. ..
13:5 3.5 1.4
.. ..
..
.. 154..51 .. .. 8 0 . 4 . . . . . . .
42.3
i : b C
12.0d
. . . . ' '
6:O
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
"
::
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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
876
Recycle Compressors Unreactcd hydrogenation gas ia brought up tc 10,300 pounds per square inch before reintroducing it into the reaction cycle
per hour of 97% pure hydrogen will be required; about two thirds of this will be consumed in the liquid-phase cycle. This represents about 18,000 standard cubic feet per 1000 pounds of moisture- and ash-free coal. Water intercoolers are provided between each stage and after the last stage to maintain a n overall temperature of about 250" F. Each cooler is equipped with oil and water traps. Between the third and fourth stages the carbon dioxide present is removed by water scrubbing;. The gas leaving the seventh stage of each compressor passes through a purification bomb which contains a sturdy, iron-type ammonia catalyst which converts 40 to 50% of the nitrogen present to ammonia and removes all residual carbon monoxide by converting i t to methanol. The bomb operates a t between 475 and 500' F. Part of a third ammonia line provides high pressure scrubbed inert gas, until a small compressor can be installed in one of the hydrogen compressor buildings. The low oxygen content inert gas will be produced by complete combustion of natural gas to give carbon dioxide and nitrogen (BO) and be held in a 50,000 cubic foot gas holder before compression to about 12,000 pounds per square inch gage. Low pressure (30 pounds per square inch gage) cracking furnace stack gas (2 to 3% oxygen) also will be piped to the hydrogenation area for low pressure purging and blanketing in the coal preparation-paste buildings. iit the present time about 40% of the entire cost of coal hydrogenation is accounted for in the preparation and compression of hydrogen. Direct pressure gaqification of coal may reduce this cost ultimately. An intense invegtigation of this process is being carried out in the coal gasification plant, a unit of the Fischer-Tropsch installation a t Louisiana.
VOl. 41, No. 5
oxides, produced in the beneficiation of bauxite, was used extensively by the Germans for this purpose and a similar material will be used at Louisiana. Low grade iron ore available in large deposits in Alabama is being considered. The English plants favored a tin salt in the presence of ammonium chloride as a liquid-phase catalyst. This material had the advantage of being more efficient than the iron type. One per cent was usually sufficient for satisfactory conversion whereas as much as 4% of red mud was used. However, tin is expensive and still in short supply, and the chloride which must be used with i t introduces a serious corrosion problem. Some promising work has been done recently on the substitution o€ zinc for a large part of the tin requirement ( $ 7 ) . If this substitution can be accomplished successfully the economic disadvantages of this catalyst will be largely eliminated, although the corrosion problem r i l l still exist. One of the most promising liquid-phase catalysts is molybdic acid deposited on granular charcoal from a water solution. Although the charcoal is not converted in the hydrogenation reaction, i t is very light and the total catalyst contributes litt,le to the volume of solids which must be removed from the oil product. This technique will be investigated a t Louisiana soon after normal operation is attained. However, the initial runs will be made with tin oxalate catalyst equal to 0.05% of the moisture- and ash-free coal feed. Ammonium chloride probably will be added for some runs. Very early in the program runs will be made with 1 to 2% low grade iron oxide catalyst, similar to the German Bayermasse.
O
CATALYSTS
The heart of the coal hydrogenation process is the catalysts which must stimulate the addition of hydrogen t o the coal, form the proper organic compounds, split the oversize molecules, and take out the oxygen, nitrogen, and sulfur present in the coal. Two different types of catalysts are used for the two reaction phases. The liquid-phase catalyst mixed in with the paste charge is lost in the solids separation after one pass. It, therefore, must be inexpensive and yet effect as nearly as possible complete hydrogenation of the carbon. It also must be reasonably efficient and not represent too great a percentage of the total charge because, when i t is removed from the product oil with the other solids by the conventional centrifuge method, it will carry n-ith it about 60% of its weight of absorbed oil which will be lost to the process. Bayermasse, the red mud, containing iron and titanium
IO0
1 ,
50 500
Figure 2.
1,000
2,000
a.000
1
l0,OOO
Viscosity of Coal Paste Feed
Only one type of catalyst has so far been discovered that will convert hydrogenation middle oil into suitable gasoline in a single step. This is the Ruhrol type catalyst which will be used in the Louisiana vapor-phase converter in essentially the same form that i t was used in Germany. About 3900 pounds \vi11 be required for a complete charge which is expect,ed, from German data, to last for about 99,000 barrels of oil. This charge will occupy about 60 cubic feet and provide a contact path of 25 feet. The purchase specification states that the materia,l must contain 7.5 pounds of hydrofluoric acid, 5 pounds zinc oxide, 2 pounds of chromium, as chromic anhydride, 10 pounds of flowers of sulfur, and 0.7 pound of molybdenum, as ammonium molybdate as a 10% solution in aqueous ammonia solution, mixed with 60 pounds of raw fuller's earth and 40 pounds of activated fuller's earth. The paste is extruded into 10-mm. diameter pellct,s, 10 nun. long, and dried at 160" F. for 3 to 4 days. Before use the material must be activated by heating with hydrogen. The heating schedule calls for beginning a t room temperature and increasing the temperature at a rate of 7.5' per hour to a maximum of 665 F. The maximum temperature is maintained for 4 hours and
INDUSTRIAL AND ENGINEERING CHEMISTRY
May 1949
then the mass is &allowed to cool back to room temperature a t a rate of 60" F. per hour. Chromium and molybdenum are the active principals of this catalyst and by varying their proportions the chemical nature of the vapor-phase product can be altered. Increasing the chromium content increases the cracking activity of the converter while a higher degree of saturation can be obtained by increasing the relative amount of molybdenum.
8'17
TABLE 111. DESIGN CHARACTERISTICS OF HIGHPRESSURE VESSELS
Converters (2 liquid phase, 1 vapor phase)
1.
Dimensions Diameter, Height in. 39 ft. 1.5 in. 32 (i.d.)
., ., , .. .
Wall Thickness, In. 8.75
la. Converter heads (also hot catalyst heads) l b . Liquid phase catalyst baskets IC. Gas phase catalyst basket Id. Pyrometer wells
35 it.
2 8 . 5 (i.d.)
0.26
36 ft. 4.75 in.
24 (id.)
0.375
35 ft.
0.875 (i.d.1
0.8625
2 . Hot catch pot 3.5 Cold catch pots ( 2 )
25 ft 5.5 in. 16 f t . 11.375 in.
32 (i.d.) 24 (1.d.)
8.75 6.875
3b.Q Cold catch-pot heads
. .. . . . . .
57 (0.d.)
45 (0.d.)
21.5
18.875
Material, yo
a . n cr -.
0.65 Ni 0 . 3 0 Mo 0.25 C
Fabrication Forged; tensile = 100,000 lb./sq. in. elastic limits = 55,000 lb./sq. in. Forged Welded Welded
Type
16 stainless (16 Cr, 13 Ni, 3 110) (Same as converters) i 2.50-3.25 S
0 . 7 5 Cr
0.3-0.40 &Io Carbon steel
Seamless tubing Forged Forged Forged
T h e compressor suction traps are identical in design, material, and dimensions with the cold catch pots. wash oil scrubber is also identical except t h a t i t is 41 f t . 7.25 in. long.
MATERIALS OF CONSTRUCTION (IO)
Q
The extreme pressures and moderately high temperatures encountered a t Louisiana introduce some serious material problems. Although pressures up t o 15,000 pounds per square inch have been used in commercial ammonia synthesis and at the Cactus and Missouri Ordnance Works and certain equipment has been developed for the production of plastics a t 30,000 pounds per square inch a t moderately elevated temperatures, such pressures are unusual in American industry, and equipment de- ' signed for these conditions is not commonly available. An additional problem is introduced by the diverse nature of the
The
fluids to be handled, ranging from gases t o viscous liquids containing high percentages of abrasive solid particles. Hydrogen, hydrogen sulfide, and other severe corrosive agents are encountered. High Pressure Vessels. All of the pressure vessels a t the new plant have been forged from a relatively low alloy steel (Table 111). In the converters this has been made possible by introducing a 3-inch layer of asbestos cement between the shell and the reaction basket which holds the shell temperature to less than 500' F. to take advantage of the greater strength of the steel a t the lower temperature, to reduce temperature stresses, and to minimize hydrogen FLASH DISTILLATION attack. TO ATMOSPHERE The wall thickness required for a 32-inch inside diameter converter was calculated according FROM HOT CATCH POT to the A.P.1.-A.S.M.E. code (2)using the maxi1110°~-20LB./Sq.ln. Ga. mum principal stress theory. There are no openings in the walls of the converters. The thickness of the heads was determined by the A.P.1.-A.S.M.E. formula with an additional 20% safety factor to allow for the necesTO PASTING OIL sary openings and because of the possibility of higher temperatures at this point. Bolts were TO PITCH DISPOSAL sized in the conventional manner. Temperature measurements within the converters are taken in pyrometer tubes (Figure 4, page 879) which extend down the center of the DILUENT OIL vessel supported by steel spiders. The tube has n a closed end and is designed to withstand 10,300 pounds per square inch a t 1000" F. Inside the WATERCOR STEAM) FROM H.O.L.D. tube there is a 0.125-inch stainless steel pipe to STORAGE TANKS which thermocouple elements are attached a t 6CENTRIFUGE FEED foot intervals. I n the vapor-phase converter this STORAGE tube is replaced by a 0.375-inch rod. The pyrometer tubes are enclosed by a light shielding pipe FILTRATE CENTRIFUGES which permits removal of the tube without disRECEIVER U turbing the catalyst beds. 1 LTJ During the initial planning of the Louisiana installation the relative merits of the layer type pressure vessels and the German Wickelofen ( I S ) SOLIDS BLENDING CONCENTRATE TANKS were considered in addition to the forged vessels. RECEIVER The layer vessels proved to be too expensive and too heavy and the spiral-wound type was not TO BURNING PIT available from American manufacturers. However, continued investigations of the wound Figure 3. Recovery of Oils from Heavy Oil Letdown
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INDUSTRIAL AND ENGINEERING CHEMI
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design indicate that this technique has excellent possibilities in future full scale installations especially since i t can be accomplished virtually at the plant site. All high pressure vessels in the unit are contained in B series of three-sided opentopped stalls having malls of 14inch reinforced concrete. The two end stalls contain the proheaters next to which arc the hot stalls for the two phases containing the converters and hot catch pots, In the center are two cold stalls in which are located the cold catch pots, coolers, and the compressor suction traps. Pumps. The major p u m p ing problem of the hydrogenation plant is moving t,he highly viscous coal paste. This material averages 4670 solids consisting of fine pulverized ash, coal, and catalyst and has a viscosity of 1285 cp. a t atmospheric pressure and 210" F. pumping temperature. The most effective pump for transfer of this material has proved to be a two-stage helical screw type (9%). The injection pumps which must introduce the paste into the high pressure converters must operate under even more severe conditionssince at the 10,300 pounds per square inch gage discharge pressure the viscosity is 4750 cp. The pumps used for this purpose are speciallv designed, double acting, duplex plunger type. They employ a loose-fitting plunger which forces the fluid out of the cylinder by displacement, rather than by a lateral push as in conventional piston pumps. Other injection pumps handling recycled hot oil letdown, oil, naphtha, and water injection arc essentially the same as the paste injector. The H.O.L.D. pump has an interesting variation, however, that permits i t to operate without aotually passing the hot oil through the pump body. The pump i s connected to a valve block by two 2-inch pipe lines connected to the inlet and outlet j oil at a moderate temperature in the pipe lines surges back and forth to open and close the hot oil valves in thc valve bloclr and force the hot oil back into the converter. All pumps are steam-driven
INDUSTRIAL A N D ENGINEERING CHEMISTRY
May 1949
6 % ' that alle pipe and fittings should have the same dimensiom to simplify interconnwtionandrephment* inventory. These baaic dimensiom were determined
Of L
CMODUOT OUT
Fkpm 4. V a p a h p a u e Cum-
with the exception of the standby injection pump for lbe flushinp oil line. It is an electricaUy-driven vertical triplex type with an u n d edjustable stroke. By adjusting the stroke from 0 to 4 inches by an air operated control valve the pump capacity can be hanged from 0 to maximum. Other pumw in the plant (over 80 Werent t-) are of WEsntional,low pressure, reciprocatingor centrifugaldesign. Valves, Pip, and pi-. Many msjor problema were encounted in the deaign of piping to witbstand 10,oOO pounds per quare incb i n t e d presure at the various operating temperatures. Hydrogen attack, corrosion, creep at higb temperaturea and d o n due to solid-liquid mixtures bad to be taken into consideration. Of the several diverse theories for determining the strength of thick-walled cylindem under i n t e n d pressure it WBB decided that the maximum principal+tmX theory based on tgnsential strees alone wan the most reliable. It wa8 decided
fromthepropertiesofA.P.1. Type 5L Grade C carbon
steel wbicb has a maximum allowable streas of 22,900 F k u n 5. Mta Type per quare at 375' F. and wan chosen for Gasket ( b e d on R a a s u w Veaeels) low temperature installatiom. It was later disoovered that S.A.E. 4130, a low molybdenum, low cbmmium carbon steel, could be substituted in theae inst9llatious and aEorded better w d d a b i l i ~ . For medium temperature service, between 375" and 85O'F.. Croloy 9M was found to have the proper strength in the staodsrd dimensions. At still bigber tempemtures wbere creep strem is a particular problem, A.I.S.I. Type 316 steel wae used AU pipe ia sesmlags and threaded with American National 8 m w threads. Continuousand intermittent oil samples are taken from various points in the process through 0.1876-inch inside diameter, 0.532&inch outside diameter, Type 304 stainless st@ tubing. Hydrogen samples for the hydrogen analyzers and specificgravity meters, are taken through O.O6%inch inside diameter, 0.2E-iich outaide diameter high chromium-molybdgnum s u e m steel t u b q to obtain a greater pressure drop between the plines and the instruments. All valves and fitting8 on these lines are stainlem steel, cinch-joint type, shigbtway needle stop valves and angle check valves (8. Fittings for the plant are limited to tees, 90 ells. and reducars, and are sll forged. Flanged joints rated a t 10.300 pounds per square inch were not available from American manufacturers and it wan neewary to deaian a joint eswciallv for this installation. After some study wae- decided to &opt the German lens ring type of gaeket (Figure 6, page 879) with the lawring beQring directly on the pipe end ratber than on the b g e a8 is customary in low pres sureinstallatiom. Except for some check valves, all of the valves in the plant are angle type. The straight-tbrough type check valves are of an unusual design similar to a bsl-check valve but having a tear drop shaped disk guided by three vertical vanes. All contact surfaces are faced with SteUite. The most severe seMce demands are made on the throb t l i i valves wbicb are used to let down preeaure from the l0,W pounds per square inch of the converters to low or moder ate distilling or storage premuwa Their design (Figure 7, page 882) is taken from the German P&&I (8) or cartridge valve which has an interchangeable Kennametal disk which may be removed and replaced somewhat like a rifle cartridge. % cause of the critical positiou of thee throttling valves in the pro* em, three parallel lines are available for the flow of the hot oil and solids from the converter to the leMown tank. In normal operation two of the linea are used, leaving the center linefor emergencypurposes. Emh of the three throb tling valves is supplementea bv three sbutoff valvea UP stream and one downFigure 6. Lens Ring Type
.
Gasket
880
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
Vol. 41, No. S
Continuous chemical analysis for hydrogen and oxygen content is made on the make-up hydrogen stream to the converters.
A Specially Designed Duplex Plunger Pump for Injecting Fluids into the 1000-Atmosphere Reaction Units [3STRUMEXTATION
Because the particular function of this plant is to gather operating data, its instrumentation is unusually comprehensive and complex. A complete discussion of the instrument installations is beyond the scope of this article. However, a few special installations are worthy of mention. X special flowmeter has been designed for use in small lines (0.1875 to 0.3125 inch) wit,h a flow of t,he magnitude of 1 cubic foot per minute where fixed orifice type flommeters do not operate accurately. The meter consists of a centerless screw which rotates in the stream. Surrounding the screw is a fixed coil so that tmherot,ation produces a minute electric current as in an electric generator. The current is led to a millivoltineter which is calibrated directly in flow units. The particular virtue of the device lies in the fact that jamming the rotor will not obstruct the flow of fluid. The entire unit is assembled in a disk-shaped, 15,000 pound-test housing which can be handily slipped into a line between flanges. Rates in other lines carrying heavy pastes are determined by area meters in which a metal gate, hinged at, the top, swings free in the flow. The angle to which it is carried up by the stream can be related to the rate of flow of the fluid. .4n unusual level indicator is used in the hot catch pot where the problem of determining the liquid l e d in a vessel having a Y-inch steel shell held at high temperatures and pressure demands a special solution. In the initial installation the device to fulfill this function will be a Gagetron (14)which employs a needle containing 5 mg. of radium attached t o the inside of the vessel at the maximum normal level. Radiation from the needle is picked up by a Geiger tube receiver attached to the exterior of the vessel opposite the minimum level point. 9 s the liquid level rises and falls the proportion of liquid t o gas in the path which the radiation must follow from the emitter to the receiver changes and effects the intensity of radiation transnlitted and the impinging radiation can be related directly to the liquid fuel. h control interlock system operates in the coal preparation area. The system ensures that in starting up, the motors xhich drive the coal-handling equipment are started in reverse sequence so that the conveyer which picks up the coal from atorage cannot be activated until all other units are operating properly. In the event of the failure of any of the driving motors all of the units preceding the casualt'y are automatically stopped while the rest of the system continues t o operate and clear coal t,hrough the rest of the system.
Hydrogen content is determined by thermal conductivity of the gas and recorded continuously in the control house (4). h y g e n analysis is based on the magnetic susceptability of the stream (6). Oxygen is slightlv paramagnetic and is the only common gas which displays this property. This peculiarity affords an extremely simple means of detecting oxygen. Bt the dcmoristration plant the oxygen is recorded continuously and an alarm bell is rung if the reading goes above 0.02% In keeping with standard American practice, all controliing instruments and remotely operated valves are operated by air rather than the hydraulic or electrical systems used in European high pressure units. Lines which carry solid-liquid mixtures in the liquid-phase system require an elaborate flushing oil system to prevent the accumulation of solid deposita 'in sample and instrunient lines and behind closed valves. A 450' to 650" fraction of highly aromatic heavy gas oil, free of crystalline solids and having a low pour point is taken from the liquid-phase still for this purpose. The sytem is maintained at about 10,500 pounds per square inch gage by injection pumps and use3 a German converter, brought to Louisiana for design study, as a reservoir. Flushing oil is injected a t instruments, valves, and sampling points and generally bleeds back to the converters or other large vessels. Bbout 60 gallons of make-up oil per hour must be supplied to this syateni.
Since there are few people with process experience in the plant locality, it xas necessary to make early plans for training
an Operating staff. The first step for the training of plant supervisors and operators was the preparation of written operating manuals, ryhich included the Standard Operating Procedures and Operational Safety bulletins. The Standard Operating Procedures contain a brief description of the equipment and the operation, follo\l-ed by more detailed instructions giving the start-up and normal operat'ing conditions, the correct procedure for normal start-up and shutdowns, emergency shutdonm, how to put in service and take out of service pieces of equipment such as pumps, compressors, etc., and the duties and special precautions for operators and helpers. After careful analysis of the various jobs, particularly as indicated by the length and complexity of the Standard Procedures, the Hydrogenation Operating Section was set up to include: Chief of section (chemical engineer) Assistant chief (chemical engineer) Technical assistants Clerk stenographer General shift superrisors (chemical engineers) Kydrogenation shift supervips (chemical engineers) Gas manufacturing and distillation area supervisors Operatore
Total in section
I
1
2
1
5 5 10
-_103
128
During the year preceding the first actual operations, a cadr of engineers, subprofessional supervisors, and head operatoi was built up. The engineers were obtained through normal chai
nels. The other personnel were secured locally, largely k careful selection of former Missouri Ordnance Works personn with good service records. Since the Civil Service standards f an engineering aid job category had not been approved, the positions were filled on temporary appointments. This nuclc organization WRS grouped in the area office and furnace cont rooms for study and instruction. The group was given a ' hour classroom course using training inanuals written in nl technical language and the Standard Oper$ting Procedui Further intensive instruction was given at the units in the ev ings after construction had stopped. The training program
May 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
881
lizes many training aids, devices, and simplified, colored, composite drawings to illustrate clearly processes and plant equipment normally represented on many complicated engineering drawings. When actual operations began the assembly of general shift personnel was undertaken, using the same general recruiting and training plan used with the initial nucleus. However, the training moved more and more out into the plant since the second group did not need to be quite as familiar with general operations and policies as the more responsible personnel who were then available to explain the equipment and operations on the grounds. INITIAL START-UP
I
3 1
h
The first unit of the Louisiana plant to be completed mas thy distillation area which was turned over to the Bureau of RlineP by the contractor early in November 1918. During a 9-week break-in and test run, completed in February, 110,030 gallons of 37' A.P.I. Oklahoma City crude were fractionzted and blended and refractionated; the oil proved to have boiling characteristics similar to those expected in the hydrogenation product. The high pressure pumps and gas compressors, after a test run-in without load to seat the bearings and expand the packing, were broken in under full pressure load by circulating through break-in lines built espmially for this purpose. Various difficulties with the chevrontype packing in the injection pumps and the ring packing in the recycle compressors were experienced during the break-in and as yet have not been completely circumvented. Preliminary tests of the coal preparation unit during February and March showed that the natural draft gas burner installed in the furnace which was to supply blanketing flue gas to the grinder and classifiers would have to be replaced by a forced draft unit in which the ratio of gas to air is automatically controlled to predetermined amounts. Also, the grinding arrangement produced an excessive percentage of fines; a by-pass, installed around the first cyclone separator t o reduce the resistance to gas flow in the system, should result in more uniform coal powder particle size. The hydrogenation unit was turned over to the bureau on January 28. However, it soon became apparent that because of limited personnel i t would be impossible to prepare the entire unit for operation before its dedication on May 9, and it was decided to concentrate all of the crew on the vapor-phase unit which could be operated separately on middle oil from outside sources. After successful static pressure testing of the vapor-phase unit, pressure was reduced to 1600 pounds and circulation of the nitrogen was begun. The density of nitrogen at thjs pressure is equal to that of the hydrogenation gases a t full operating pressure (10,300 pounds) so that operating flow conditions were duplicated for the calibration of meters and controls. The preheater furnace was lit-off and temperature of the phase brought up to 900' F. to dry out the units and study the effect of temperature on line expansion and vibration. The density of the circulating gas a t operating pressure is such that the compressor surges are carried very strongly through the lines, and result in a serious vibration problem. When the location and magnitude of the vibration had been ascertained, the pressure and temperature of the system were dropped and additional heavy-line bracing was installed. Although stable in its delivered form, the catalyst becomes sensitive to oxygen after activation by hydrogen at operating temperatures and pressure, and must be kept in an oxygen-free atmosphere. Activation was accomplished by repressuring the phase with cold nitrogen to 10,300pounds and then replacing the nitrogen with hydrogen. The hydrogen was circulated through the preheater to bring the temperature to 936" F. and the unit was held a t this temperature, with the gas circulating, for 24 hours. The temperature then was reduced to 720' F. and middle oil (a 300' to 650" F. cut from the distillation unit break-in) was introduced into the preheater at a rate of about 6 gallons per minute, about a fifth of the full operational rate. The con-
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Vol. 41, No. 5
INDUSTRIAL AND ENGINEERING CHEMISTRY
approximately equal G t h e volume of oil feed. After-the completion of this run the vapor phase unit w&8 shut down and flusbed out in preparation for the dedication ceremonies. The ultimate break-in of the liquid-phsse system will follow asimilq pattern. Iron oxide catalyst (2 to 3% German Bayermaaee) will be used for the initial runs. The catalyst will be the only solid introduced into the system and will he allowed to build up the solids concentration hy recirculation of the entire H.O.L.D. until the preheater feed a c q h the consistency of coal paate. A t this point the solids separation unite will be cut in and an increasing amount of Rock Springa, Wyo., coal will be introduced into the feed. It is anticipates that the tar oil will give a product distribution similar to that predicted from actual coal hydrogenation. DESIGN IMPROVEMENTS
One important contribution the hydrogenation demonst&ion plant has offered to the field of coal hydrogenation hae bean the deaigu of new and improved plant equipment and pmoessas for hydrogemtion. These features are generally outgmwtbn of the comparatively large d e Qm of the plant which una American-made equipment and attempt4 to remove reported difficulties or bottlenecks that were in the German plante. Several of these features, though technically sound, may be expected to give serious trouble ~epeciauyduring the initial opem
tion. Unlike German operations where broken coal waa dried and then ground into the pasting oil, the Iauisisns procaaa dries and pulverizes in a single operation 8 n d . h mixes the pulverised 4and the paetine, oil dong with the cutaly8t in a 8imple mix tank. If thia p d u r e provea effective it will repreSent an important simplilication of the paste preparation step. A new and different radiant type preheater replaces the bulky fin-tube convection type p k t e preheaters used in Germany. The modified deign idtmducea a number of structural, operating, and maintenance features not experienced in former plants and is expected to p y n t many problems. Howe~er, if the expected heat economy ia realized such unite will be recommended for full d e installations. .-. ......,
.
Figure 7. Cartridge Type (l'atmrrenventil) Letdown Valve
was held to a 725" F. inlet temperature with a maximum bed temperature of 750" F. The first product sample from the unit, taken some 4 hours after beginning petroleum feed, wan a water-white, sweetmnelling, gaaoline fraction; i t had a 86.8' A.P.I. spec&? gravity (feed middle oil = 44' A.P.I.), an initial boiling point of 92' F., with 50% over at 218O F., and 90% over at 396' F. Under these conditions the
I / KG. HYOROGEN ~
I
verter
converter had apparently removed the nitrogen and sulfur from the middle oil, and cracked and saturated the resultant hydrccarbons. After 25,000 gallons of the middle oil had been p r m eased, the feed was changed to a lignite oil obtained from the Lurgi low tempamture lignite carbonization plant of the Dakota Briquet and Tar Company, Dickinson, N. D. This oil is a creosote type oil with a strong sulfur odor, ahout 50% ammatic, and containing some wax and asphalt. The oil wan distilled to remove a 10% bottom cut giving a feed oil h o i i between 450" and 750" F. About 17,000gallons of this materid were ~n at the enme low feed rate (approximately 7 gsuonS per minute) and reduced temperature (750"F.) to eliminate the aromatie, sulfur, and nitrogen content of the oil and to
I
LOOKO.ORY,bSH-FREE COAL 6 KG. PHENOLICS (1.5 KG.PHENOL. 3.5KG.CRESCL BXYLENOLI 1.5 KG. PIRENES.CORONENE.CAR0ALOLS. CHRYSENE
LIQUID PHbSE HYDROGENATION
I
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PHASE HYDROGENATION
\+
KO METHANE
I7 KG?H'lDRbRSOC' TURPENTlNE SUBSTITUTE I160*-205* C1 42 KO. G b S O L I N E l 4 2 ~ - 1 6 0 * 0 l LCONTAINING 3KG.TOLUOLI I ~ P R O C E S LOSS S I KG.TOTAL
Figure 8.
Possihle R)-l'rodurt Yield front Typical Coal
A greater d e s s e of automatic contml of the H.O.L.D. s y 6 tem is rdorded by the bureau deeign than wa4 arsilable in former unite. The H.O.L.D.from the hot catch pot is letdown through Rir-operated evere throttling valves a u t o m a t i d y
.
May 1949
INDUSTRIAL AND E N G INEERING CHEMISTRY
controlled by the level in the catch pot. A restricting orifice has been placed in the line ahead of the letdown vessels to absorb some of the throttling load and decrease the velocity of the letdown products through the lines. The entire system has been simplified greatly by the use of only one stage of letdown to 100 pounds per square inch gage and the use of this residual pressure for automatic transfer t o storage. The simplified system imposed severe operating conditions a t this vital point but no serious trouble is anticipated. A simplification of high pressure heat exchange design has been attempted by the use of all double-pipe type exchangers (Table V). This type has not been used before a t such high pressures. If they prove mechanically sound for this service and stay clean and are efficient, they will be recommended for subsequent installations. One of the most important advances that has been incorporated in the Louisiana design is the reduction of the catalytic hydrogenation to two steps. German processes required as many as four separate high pressure steps t o produce a high octane motor fuel from coal. Only one plant, a t Wilheim (II), achieved the operation by a two-step process, and it used tar rather than coal as a starting material. Unlike the c d d catch pots in Germany the ones a t Louisiana are vertical and contain a D u Pont separator in the top to aid the separation. The cold catch-pot product in German plants was letdown to atmospheric pressure and allowed to settle for a long time, b u t the system at Louisiana lets the middle oil down to 100 pounds per square inch gage in two stages and utilizes this pressure to charge the oil to the still. Although the vessels used give a settling time of 8 hours, many emulsion problems may be experienced which may require changes in design, heating, or even the use of special emulsion-breaker compounds. A countercurrent system of water washing is used a t the demonstration plant for removing the salts formed in the system. The partly saturated wash water that is injected between the 25- and 7-atm. letdown drums is removed from the 7-atm. drum and injected ahead of the cold catch pot. This saturated liquor is then removed in the 27-atm. letdown drum and sent to liquor treatment This arrangement appears efficient but it must be proved that the equipment will remain clean and that emulsion difficulties will not be aggravated. For the first time in coal hydrogenation a t 10,000 pounds per square inch gage, a split parallel-flow radiant type preheater will be used in the vapor phase. This preheater is automatically gas fired, contains 16-13-3 horizontal tubes, and has a design capacity of 1,890,000B.t.u. per hour. Important advantages in heat efficiency are anticipated, but it remains to be seen whether the service is not too severe for safety and that the heater maintenance will be reasonably low. I n addition to these major modifications many minor changes have been included which may prove t o represent real advances in hydrogenation technique. FUTURE DEVELOPMENTS
The designation of the Louisiana installation as a demonstration plant indicates that it is not intended to be the most efficient, most economic form of hydrogenation unit. It is rather intended to have unusual flexibility and control to enable it to best fulfill its purpose: to furnish industry the necessary cost and engineering data for the development of the best possible commercial units ($5). The installation had already begun to fulfill this function before it was completed or in operation. Combining experience and theory gained from the construction of the Louisiana plant with data gained from pilot plant experiments a t the Bruceton laboratories and data from German and British operations, Bureau of Mines research men and industrial investigators have already postulated many technical and economic improvements in the process.
883
Cold Stalls of Reaction Area Photographed during Construction Tall vessel ( l e f t ) is wash oil scrubber; short vessels are cold catoh pots and a suction trap
BY-PRODUCTS
One of the obvious ways to improve the economics of any process is by the recovery and sale of valuable by-products (Figure 8). I n the coal hydrogenation process such refinements often have the added virtue of increasing the engineering efficiency of the process. Pyrenes, coronene (hexabenzobenzene), carbazol, and similar higher organic compounds important in the production of sulfur dyes and of luminescent and phosphorescent substances, are present in the upper boiling fraction of the liquid-phase catch pot and t o some extent in the letdown. Their recovery from the letdown i s difficult and questionable. However, by inserting a second catch pot behind the hot catch pot, a small part of the catch-pot product containing a concentration of these products may be precipitated free of asphalt, by cooling or by the addition of wash oil. The complete precipitation would have to be done by the addition of low boiling products. Recovery then could be effected by centrifuging. To separate the individual products, subsequent vacuum distillation, fractional crystallization, or other measures, would be required. Inadvertent precipitation of these crystalline products during the process often clogged the catch-pot cooler or the, distillation lines in European plants. Therefore, it may be desirable or even necessary to remove them to maintain the efficiency of the main process. The amount of phenols recoverable from hydrogenation depends upon the oxygen content of the feed coal; this varies from 7 to 20% in American coals (11). They must be recovered from the 180" t o 220' C. boiling fraction in the liquid-phase catch pot. Phenols carried over into subsequent operations are decomposed by the vapor-phase catalyst. About 30% of these phenols consist of carbolic acid, the rest are cresols and xylenols.
884
INDUSTRIAL AND ENGINEERING CHEMISTRY
The mixture of cresol and xylenol, after the removal of the carbolic acid, has been found to be an excellent stabilizer for leaded gasolines. During the late years of the war almost all German aviation gasolines were stabilized with 0.01 % of this inhibitor, If the catalyst is correctly chosen, the entire fraction of the vapor-phase product boiling between 160" and 205" C. may be recovered as a product clear as water and similar in its chemical characteristics to oil of turpentine. Experiments in Germany in recent years have indicated that this hydrogenation product, aromatic solvent), is called Hydrarsol (hydrogenation superior to oil of turpentine for many applications especially in the manufacture of lacquers (16). Toluene may be recovered from the gasoline, depending on whether the cresols are removed before 01 carried over to the vapor phase for reduction. Butane, propane, ethane, and methane are obtained in off-gases. Iso-octane can be made from the butane by alkylation, thus increasing the proportion of gasoline. Valuable lubricating oils can be made from the ethane by way of ethylene and subsequent condensation. About 1%' sulfur (3.5% sulfuric acid) and 1.57' ammonia (6% ammonium-sulfate) can be recovered from the sulfur and nitrogen constituents of the coal. If ilmerica's entire gasoline requirement were derived from coal, these by-products would amount to 3,000,000tons of sulfur and 4,500,000 tons of ammonia.
+
PRODUCTION O F HEAVY OIL
+
Vol. 41. No. 5
PROPOSED COiVIMERCTAL P L A N T
Combining all available information on coal hydrogenation including some still theoretical process techniques, a group of Bureau of Mines engineers recently outlined the design of what they believe to be the best possible commercial coal hgdrogenretion plants at the present stage of the technology ($4).The unit was designed to produce 62 tons per hour of 82 to 85 octane gasoline as well as 13.3 tons of liquefied petroleum gases and 11 tons of residue from 238 tons per hour of Illinois No. 6 type coal as received. This estimate includes the requirements of the hydrogen producing unit, the power plant, and a 3% factor for heat and material losses not otherwise provided for. The plant would have a calculated thermal efficiency of 557, as contrasted with the 28.9% efficiency obtained in the typical German plant or the 36.8 efficiency obtainable if all of the best German developments had been incorporated into a single installation. The major variations from the procedure followed in the 1,ouisiana installation and suggested for the proposed commercial plant is the elimination of the interphase letdown. Such a short cut would save the cost of recompression and injection and simplify the heat balance. It could be accomplished by removing a portion of high solids content heavy oil from the final liquid-phase converter, and then refluxing the hot catch pot, introducing the net overhead from the catch pot directly into the vapor-phase converter. Such a procedure necessitates a sturdy catalyst which would not be adversely affected by any heavy oil, moisture, sulfur, ammonia, tar acids, or other material which might be carried over from the catch pot. However, the German type catalyst to be used in the vapor-phase converters at Louisiana is believed to be adequate for such service. Elimination of the letdown also requires close control of reaction conditions in the vapor-phase converter. Such control, it i s
It has been suggested that perhaps the first commercial application of the production of liquid fuels from coal will be in the synthesis of heavy fuel oil to replace petroleuni residual oils. Such a product could be obtained from the liquid phase alone of the present plant with a few minor alterations. If heavy fuel oils continue to increase in price, because of the tendency to make as much light fuel and gasoline as possible from crude in the petroleurn refining process, it is quite possible that heavy oil from coal will ;";et Xet H2, H2, become economically competiProduct. Lb. C. Lb. Lb. Feed. Lh. C., Lh Lh. tive with petroleum residues LIQUXD-PHASE~ in the near future. Plants to Unconverted coal 40 1.5 797 36.5 l I a f b coal 1000 32 produce such a product could Oillossc from 1I.O.L.D. 134 10.8 Ash 40 120 Water 10 be built from technology now Hydrocarbon gas formed 1 100.7 23.8 Catalyst (0.06%) (Ci.eHs.8) 1.30.5 available without e x t e n s i v e Carbon oxides formed . . Solids in pasting oil 189 9.3 additional study and research. (85% C O , 15% Con) 23.5 Sew-formed gas and 57.8 Oil in pasting oil 1530 535 A recently submitted cost 622 middle oil Light oil bot,toms (to 57 4 3Iake-up liydrogenaestimate (16) of such a plant pasting oil) 567 tion gas (recirculated designed to produce 10,000 gas not included) 233 Oil in H.O.L.D. 422 barrels a, day indicated that Oil in filtrate from centrifuges ( t o pasting an oil having about 16,500 oil) 541 B.t.u. per pound heating value Solids in H.O.L.D. 230 NH3 253 HzO, HzS, could be produced for be3008 93.9 3003 797 Total 797 93.9 tween $3.07 and $4.16 per VAPOR-PIIASE barrel at the plant, depending Hydrocarbon gases 18.3 Liquid phase RIO 477.6 on the source of hydrogen and ,535 j i 8 95.9 formed (14.6% of C) gasoline 622 the process modification used. Cd ( 5 % of carbon i n 4.8 Make-up hydrogena22.9 20 1 total gasoline) 29.7 tion gas 118.3 These figures were based on Gasoline 1 0 s (1% of .7 4.6 coal at $300 per ton and a total) 5.3 capital investment between Gasoline produced (Ca63.1 429.9 free) (12% 9s) 493 $5800 and $7600 per daily HaO, NHa, Hzs 118.4 barrel, amortized over a period Toral j 3 j 86, 940.3 86.9 740.3 535.0 of 15 years. By-product gasoa The txvo liquid-phase converters in the demonstration plant have a combined rcactipn volume of 220 cubio line, liquid pebroleum gas, and feet,. K i t h a calculated space time yield of 20.6 lb./cu. ft./hr., for new-formed middle 011 and gasoline, the production becomes 4332 Ib. ( h I . 0 . + gasoline)/hr. Since 622 lb. of M.0. $. gasoline are produced from 1000 ab. of phenol were credited at July 4532 'Oo0 = 7286 Ib. maf coal/hr. Actual quantities for the demonstration plant may be obtained 1948 prices in Chicago. No maf coal 622 by miiltiplj-ing t h e figures on the 1000 lb. maf coal basis bg 7.286. provision for profit was made. b Moisture- and ash-free coal. Assuming centrifugal separation of solids i n I-I.0,L.D.; by flash distillation this loss may be reduced t o about. The current price of heavy 40 lh. and experimental cvidenoe indicates t h s t delayed coking techniques would recover all but about 17 lb. of fuel oil is about, $2.50 per the H.O.L.D. oil. barrel. -. -.
May 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
believed, could be afforded by a heavy-oil cooled, tubular converter having fixed catalyst beds in a bank of 3-inch hairpin tubes, the first sectio; of which would act as a feed preheater. By eliminating the interphase letdown only one still would be required in the proposed unit instead of the three used in all present units. Furthermore by letting down directly into an absorber-stripper column, as is frequently done in American petroleum refineries, fixed gas removal and gas recovery could be effected in a single step, and by a further suggested modification the product gasoline could be stabilized and treated in one operation. Heat balances which have been calculated for these improved techniques indicate that the requirements balance well with the heat available from the over-all operation.
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an appreciable quantity of material product, i t still gives promise of making valuable contributions to the American economy in the form of data and experience. At the present time, the United States Army Engineers are conducting a survey of all suitable areas for installation of commercial hydrogenation plants which will have covered all principal mineral areas by the end of the year. Once regular operation is achieved at Louisiana, the bureau hopes to test all types of American coals for hydrogenation. Preliminary investigations indicate that high volatiles, low ash, low fusain content types will be most suitable. Lignite will b e processed aIso. It is hoped that the high pressure operation will produce better yields than have been obtained by other processes. Shale oil also is a potential raw material for the process. Some investigators predict that the Louisiana process will offer the most practical technique for recovering the oil in this material. Commercial plants based on the bureau prototype could be scaled up a maximum of seven times. The adverse effect of large size on capital cost beyond this size would make larger units uneconomic. A unit of maximum size would use five liquidphase converters in series instead of two, each with a reaction volume of 700 cubic feet. BIBLIOGRAPHY
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(1) Aldrich Pump Co., Allentown, Pa., Bull. 65; Supp. 65; Draw-
ings A-32355, A-33820, A-33779, A-25-A. (2) American Standard Association, New York, N. Y.
Burning Pit a t Far End of Working Area Manually operated and automaiic letdowu valves are in the foreground
a
No attempt was made to analyze the economics of this proposed plant. Although the design is thought to be technically sound, such an analysis would require consideration of markets, location of raw materials and services, yields and production ratios of usable products from American coals from different sources, and other external factors which might make it economically desirable to design a plant which would differ in some respects from that aimed at highest efficiency. However, a plant designed for maximum economy could not differ essentially from that already outlined. A less radically modified process which represents essentially a scaling u p of the Louisiana plant to 30,000 barrels per day production is described in another recent publication ( I ? ) . With by-product credit for only liquefied petroleum gas and phenols, this plant is postulated to produce gasoline at 9.3 cents per gallon without provision for profit or sales expenses but including amortization, taxes, and overhead. Still incomplete experiments indicate that direct hydrogenation of coal a t moderate pressures and higher temperatures may be possible. Such a process would convert part of the coal to coke which would be burned for heat and power. Bnother promising investigation is aimed at replacing the hydrogen used as a hydrogenation gas a t Louisiana with relatively cheap water gas. Suggested commercial design characteristics and theoretical theses are the true product of the Louisiana installation. Prohibited, by the terms of its enabling legislation, from prsducing
“Code for Pressure Piping,” par. 1226, 1942. (3) Autoclave Engineers, Inc., Chicago, Ilt., Bull. 95, p. 8, Catalog 100, p. 19. (4) Bailey iMeter Co., Cleveland, Ohio, Gen. Spec. CE623 (August 1948). (5) Beckman, A. O., Inc., Pasadena, Calif., Gen. Inform. Bull. 101-2-49, Model G2. (6) Benke &Burman, Patronenventil, T.O.M. 78, Frame 1378-86. (7) Berpius, I?., J. Gasbeleucht, 54, 748-9 (1912). (8) Bergius, F., and Billwiller, J., German Patent 301,231 (Aug. 1, 1913), Brit. Application 18,232 (Aug. 1, 1914) granted (Dec. 23, 1915). (9) Bird Machine Co., So. Walpole, Mass., Bird Centrifugal Filter. (10) Braun, K. C., Donovan, J. T., Markovits, J. A., U. 8. Bur. Mines, Rept. Invest., to be published. (11) Coohran, C., and Hirst, L. L., Canadian Intell. Objectives Subcommittee Rept. XXX-104 (Aug. 8, 1945). (12) Donath, E. E., U . S.Bur. Mines, L-71 (Jan. 30, 1948). (13) Ellis, J. F.,“Engineering in Hydrogenation Plants in Germany,” London, Brit. Intell. Objectives, Subcommittee. (14) Engineering Laboratories, Inc., Tulsa, Okla. Bull. 154 ( 15) Frese, Erich, U . S. Bur. Mines, T-219 (Jan. 24, 1947). (16) Hirst, L. L., Skinner, L. C., Clarke, E. A., Dougherty, R. W., ’ and Levene, H. D., presented before the Division of Gas and Fuel Chemistry at the 114th Meeting of the AMERICAN CHEMICAL SOCIETY, St. Louis, Mo. (17) Hirst. L. L., Skinner, L. C., Donath, E. E., U . S . Bur. Mines, Inform. Circ. 7486 (December 1948). (18) Ingersoll-Rand Co., New York, N. Y . ,Form 3262-B, p. 27. (19) Jeffrey .Manufacturing Co., Columbus, Ohio, Catalog 750, pp. 74-5. (20) Kemp, C. M., Manufacturing Co., Baltimore, Md., Bull. 1-10, (21) Levene, H. D., and Donath, E. E., unpublished (Aug. 11, 1948). (22) Robbins & Meyers, Inc., Springfield, Ohio, Frame B-6-6, Type CDC, Book 22, p. 5. (23) Sharples Corporation, Philadelphia, Pa., No. 1236, IM-647 (1947). (24) Skinner, L. C., Dressler, R. G., Chaffee, C. C., Miller, S. G., and Hirst, L. L., IND. ENG.CHEX.,41,87-95 (1949). (25) U S Congress, 78th Session, Public Law 290 (April 1944). (26) U. S. Congress, 80th Session, Public Law 443 (March 15, 1948). (27) Weller, S., Rept. of Conference on Coal Hydrogenation, Bruceton, Pa., p. 5 (Nov. 26, 1948). RECEIVED March 10, 1949.
