SYNTHETIC FUELS A N D CHEMICALS
Purification of Synthesis Gas Removal of Dust, Carbon Dioxide, and Sulfur Compounds H. W. WAINWRIGHT, L. J. KANE, M. W. WILSON, C.
C. SHALE, AND J.
RATWAY
Branch of Coal Gasification, Bureau of Mines, Morgantown, W . Vu.
T
HE Bureau of Mines, a t its Appalachian Experiment Station in Morgantown, W. Va., in cooperation with West Virginia
University, is carrying out research and development work on the purification of synthesis gas produced by reacting pulverized coal with steam and oxygen. An ideal synthesis gas for producing liquid fuels would be composed solely of a mixture of hydrogen and carbon monoxide in the desired proportions. Any other constituents in the gas may be considered to be impurities and classified as either inert or injurious. Depending on the gasification process, impurities that may exist in the gas are tar, gum-formers, dust, methane, nitrogen, carbon dioxide, oxygen, and sulfur compounds. Analyses of raw synthesis gas resulting from gasification processes under investigation a t Morgantown (16, 17) have revealed the presence of the following injurious impurities in concentrations that will vary with the composition of the coal gasified and with gasifier operating conditions: Dust: 3000 and more grains per 100 std. cu. ft. Carbon dioxide: 7 to 267% .Oxygen: 0.27, and less Organic sulfur compounds: 4 to 40 grains per 100 std. cu. ft Hydrogen sulfide: 80 to 400 grains per 100 std. cu. ft. The Bureau has not, as yet, determined precise purity specifications for synthesis gas for the Fischer-Tropsch synthesis. These are, of course, a matter of economics and will vary with relative costs and with the type of gasification process used. Experience, however, has shown that bhe following approximate specifications are satisfactory: Carbon dioxide, 2 to 3% Dust, not to exceed 0.1 grain per 100 std. cu. ft. Oxygen, less than 0.2% Total sulfur, not to exceed 0.1 grain per 100 std. cu. ft.
Development of Analytical Methods Determination of Sulfur Compounds. Precise, accurate, and rapid analytical procedures are needed for evaluating various removal processes and determining whether purified synthesis gas meets specifications. Significant advancements have been made in developing analytical techniques to meet the requirements. The modified platinum-spiral method (IS) has been adopted for total organic sulfur determination of either raw or purified synthesis gas because of its speed and accuracy. This method employs a hot platinum spiral (Figure I) as a catalyst and utilizes the hydrogen content of the gas to convert organic sulfur *Lf,(PIXL" IUBI"G1
1/16.
Figure 1.
u p p n a i i i a sa0 1i.m l*I"L*IIO",SfUIO
mfw0u)um
A, l l D S OR
Dll. I I U Y , X " *
Platinum-spiral apparatus organic sulfur in gas
for
determining
Spiral made from 36-inch length of 28-gage platinum wire with Electrodes are machined aluminum welding rods
loops of %- to %-inch diameter.
July 1956
compounds to hydrogen sulfide. The hydrogen sulfide is then determined colorimetrically by the methylene blue method (11). As little as 0.00001 grain of sulfide sulfur per 50 ml. of solution can be detected by the methylene blue method. Results obtained with the Institute of Gas Technology combustion method (6) and the modified platinum-spiral method are a2 follows: Sulfur (as Thiophene), Grains/100 Cu. Ft. Platinum Spiral I.G.T. Burnere 4.99 4.99 3.31 3.38 2.56 2.58 0.971 0.992 0.214 0.232 a Sulfate determined turbidimetrically with a spectrophotometer. Except for thiophene and carbonyl sulfide, no attempt has been made to develop methods for determining individual organic suifur compounds. The colorimetric method for determining thiophene sulfur ($0)is based on the reaction between thiophene and isatin, resulting in the characteristic deep blue indophenine color. A procedure was developed, and its applicability to synthesis gas containing low concentrations (less than 2%) of olefins was proved valid. As little as 0,0001 grain of thiophene sulfur per 54.5 ml. of test solution can be detected by this method. One of the more difficult analytical problems is that of determining carbonyl sulfide in the presence of other sulfur compounds, especially carbon disulfide. A satisfactory method has been developed, based on the hydrolysis of carbonyl sulfide in dilute potassium hydroxide, with subsequent determination of the sulfide ion by the methylene blue procedure (8). Thiophene, carbon disulfide, and mercaptan sulfur do not interfere with the test. No special analytical techniques were required for determining carbon dioxide, as this appears in relatively large quantities in the purified gas. Standard absorption in caustic was used. Determination of Dust Concentration. Numerous methods for determining dust concentration have been published. Particle counts are most commonly employed in industrial hygiene work, but weight concentrations are a much better criterion of dust concentration for synthesis gas work. Another method used by some investigators employs the darkening produced on a filter paper, through which the gas is passed, as a measure of dust concentration. The method is simpler but subject to great errors if the particle-size distribution and color are not constant. The decision was made that actually weighing the dust filtered from a known quantity of gas, although difficult, was the most accurate procedure. The use of standard Brady (Soxhlet-extraction) thimbles was satisfactory a t most points in the purification train, and hundreds of determinations were made with this device. These thimbles were unsatisfactory, however, for the crude, hot synthesis gas coming from the top of the gasifier because of the high concentration of dust that plugged the thimblein a very short time and the high concentration of moisture that wet the thimbles unless the gas was preheated and the temperature closely controlled. A practical method was devised, however, that involved collecting and condensing most of the dust and moisture in flasks and then removing the remaining dust with a large-area filter paper
INDUSTRIAL A N D ENGINEERING CHEMISTRY
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and the remaining moisture v i t h a drying agent. This met,hod has the advantage of determining t,he concentrat,ion of moisture as well as dust. The accuracy of the method vas determined on a laboratory scale for moisture coiicentrations from 1.01 to 45.8%. Results were very good ( 7 ) . The Brady method was also unsatisfactory for extremely pure gases, because extremely long sampling times were required to accumulate enough dust to weigh accurately. .4n improved drying procedure for decreasing Tveighing errors was developed ( 7 ) . Later a larye-a,rea filter-paper holder was devised to decrease the sampling time ( 7 ) . With these methods it was possible to determine dust and moisture under a wide variety of conditions. Concentrations of dust varied from thousands of grains to less than 0.01 per 100 cubic feet. T o protect the synthesis catalyst, compressors, fixed beds, and other equipment, a synthetic liquid fuels plant will require an instrument to determine continuoudy t,he concentration of dust in the gas at critical points and immediately give warning whenever it becomes too high. A photoelectric smoke meter, altewd by the manufacturer for the purpo~e,T ~ not S sensitive enough for extremely pure gases (16). This investigat'ion v a s not continued because highly sensitive apparatus is now on the market for use in air pollution work. Determination of Particle Size of Dust. The size of particles over 43 microns is determined most readily by analytical screens. Belox this, many met,hods are used, such as elulriat,ion, sedimentation, and permeabilit>yto air flow. Although more diffic~ultand tedious, a method better suited t>oinitia,l research work is actual measurement of part,icle size under a microscope after suitable dispersion of the dust in a,liquid. h method was devised for obtaining a uniform dispersion in a dry state, so that the particle-size distribution could he calculated from a count over any psrt of the area ( 7 ) . A photograph of such a dispersion is shown in Figure 2 and at, higher magnification in Figure 3. Particles are concentrated near the edge owing to the effect of the menixus,
Figure
I124
2. Typical dust dispersion showing meniscus effect
Figure 3.
but uniform distribution is obtained over the rest of the a. A large-area dish is used, so that t'he effect of the meniscws is most, negligible. Xicroscopic examina,tion of part,icles has an ad in that it yields information on them and the cond they have been subjected in the gasifier. For example, in Figui 4 the white, unfused ash is readily distinguished from the blac. particles of ca,rbonaeeous residue; surface texture, incliiding g a bloviholes, is readily distinguished, even at fairly high pomrs. The ring forniations are oft,en seen in residues. Further exaniination by electron diffraction and petrographic techniques might yield additional information on the temperatures, residence times, oxicIat#ion-reductionconditions, etc., to n-hich they have been subjected during gasification. Particle-size distribution, as determined by these methods, can be used as a criterion of the performance of dust-removing equipment only if it, is known that the particles do not exist as agglonierates in the gas stream. This can readily occur because of static electrification, moistsure, or other conditions or to the adhesive properties of the particles themselves. After unsuccessful tests of several methods for determining t'he true agglomerate size in the gas stream, a type of plastic filter with very fine openings, lcnown as a molecular membrane filt'er, was found highly satisfactory. The particles and agglomerates remain where they hit the filter. The pore size of the filter is fine enough to retain the smallest particles, and, more important, the surface is smooth eiiougli so that they can be viewed and measured in the microscope. Although black particles are readily determined, small white particles cannot be Seen on white filters. Blue f i k r s , however, were found to be satisfactory for both black and white particles.
Occurrence
of Impurities in Synthesis Gas
Hydrogen Sulfide and Organic Sulfur Compounds. The r < J E t of purifying raw synthesis gas will depend, of course, on the t y p e s
Typical dust dispersion
Figure 4. Residue from gas leaving atmospheric pressure gasifier
INDUSTRIAL AND ENGINEERING CHEMISTRY
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SYNTHETIC FUELS A N D CHEMICALS
Table 1.
Distribution of Sulfur Compounds in Synthesis Gas
S Content of
Type of Coal Gasified
Process Steam, Coal (Diy Basis), Lb./Lb. Carbon in % Coal
Carbon Gasified,
96
Sulfur in Gas for Each Per Operating Cent Sulfur in Coal, Grains/ pressure, 100 Std. Cu. Ft. Lb./Sq. In. HzS S as Organic S Gage
Atmospheric-Pressure Gasifier 4 Sewickley bituminous, run No. 19A 19B 19c 34N 340 34P
2.7 2.7 2.7 2.6 2.5 1.9 2.7 2.0
1.11 0.83 1.11 0.82 0.96 0.96 1.10 0.68
82.6 90.0 87.9 82.3 83.0 83.0 82.8 81.2
167 181 156 188 174 171 180 175
6.7 8.2 6.6
1.0 1.0 1.0 1.1
0.22 0.21 0.14 0.23
81.1 85.5 88.3 88.3
185 180 180 164
a a 12.1 8.8
1.6 1.4
0.75 0.92
80.0 76.3
200 193
8.5 6.7
Kentucky bituminous, run No. 42A 42B
4.6 4.6
0.30 0.58
77.2 85.7
196 189
8.7 8.3
Washington bituminous, run No. 438 45A
0.6 0.5
0.32 0.32
80.6 83.2
150 170
7.2 6.6
83 81 87 82 91 93 88 91 89
164 157 164 163 192 161 182 169 183
8.7 6.9 a 6.5 11.5 6.4 9.2 8.1 9.8
it: WYO.sub-bituminous, run No. 35A 35B 35c 36A Sewickley bituminous, run No. 37A 37D
7.7 9.1 7.0 7.4 7.3
Pressure Gasifier 3 Sewickley bituminous, run No. 25 26 27 28 32A 32B 34A 34B 34c Not determined
2.1 2.1 2.1 2.6 1.4 1.4 1.1 1.3 1.5
0.41 0.38 0.42 0.37 0.47 0.47 0.42 0.42 0.42
and quantities of impurities that must be removed. With respect to sulfur, it is important to know how much sulfur and what types of sulfur compounds are present in the raw gas when various grades of coal having varying sulfur contents are gasified. Correlation of the data is not complete, but Table I gives some idea of the distribution of hydrogen sulfide and organic sulfur in gas made in the Bureau of Mines atmospheric-pressure and pressure gasifiers at Morgantown. In general, regardless of the rank of coal, the hydrogen sulfide concentration in the gas ranged from 160 to 190 grains per 100 standard cubic feet for each per cent of sulfur in the coal gasified and the organic sulfur, from 6.5 to 9 grains for each per cent of sulfur. Tests have shown that all the organic sulfur is present as carbonyl sulfide. From the limited amount of data available, it appears that pressure, percentage of carbon gasified, and steam-coal ratio have little effect on the sulfur content of the gas. Table I1 gives data showing the percentage of the sulfur in the coal fed to the gasifier that appears in the gas stream; this value lies between 70 and 80%. Table I11 gives data for complete sulfur balances. In runs 36, 43A, 27, and 32B, where the scrubber water was not analyzed for sulfur, these values have been combined with that of the unaccountable sulfur. Carbon Dioxide. The amount of carbon dioxide in the raw gas depends to a considerable extent on the steam-carbon ratio used in the gasification step (16). Figure 5 shows a plot of carbon dioxide in the product gas and the steam-carbon ratio for the atmospheric-pressure gasifier. The increased carbon dioxide July 1956
300 300 300 300 450 450 300 200 100
content with an increase in ateam-carbon ratio is apparent, from 10% with a steam-carbon ratio of 0.5 pound per pound to about 22% for a steam-carbon ratio of 1.6. The range of steam to carbon ratio used in the operation of the pressure gasifier has been quite narrow, from 0.36 to 0.47 pound per pound. The carbon dioxide content within this range lies between 7 and 9%, values not too far removed from those that would be expected for the atmospheric-pressure gasifier for similar steam-carbon ratios. For both gasifiers, heat losses, oxygen-carbon ratio, and residence time may be expected to have some effect on carbon dioxide formation but considerably less than the effect of the steam-carbon ratio. Oxygen. There may be traces of unreacted oxygen in the synthesis gas leaving the gasifier. Continuous regeneration of iron oxide purifiers in situ may be considered another source of oxygen. Although the total oxygen content of the synthesis gas entering the synthesis reactors is generally less than 0.274, removal studies were undertaken a t the request of the bureau's demonstration plant at Louisiana, Mo.
Bench Scale Studies on Removal Processes Sulfur Compounds. Bench scale and pilot plant experimentation on the removal of organic sulfur compounds from gas has consisted of catalytic processes operating a t elevated temperatures and pressures and adsorption on activated carbon both a t atmospheric and elevated pressures. The most promis-
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Table II.
Sulfur in Coal Appearing in Product Gas Sulfur Content of Coal (Dry Basis), %
Type of Coal Gasi5ed
Total Sulfur in Product Gas, yo of Sulfur Fed to Ga ifier
Atmospheric-Pressure Gasifier 4 Sewickley bituminous, run No. 2.1 1.1 2.7 2.7 2.7 2.6 2.5 1.9 2.7 2.0
73.9 70.7 72.8 86.0 77.5 81.4 77.0 75.8 82.1 71.9
1.0 1.1
80.2 73.1
Sewickley bituminous, run No. 37A 37D
1.6 1.4
81.3 76.0
Kentucky bituminous, run No. 42A 42B
4.6 4.6
75.5 71.6
Washington bituminous, run No. 43A 45A
0.6 0.5
68.9 69.6
14B 15 19A 19B 19C 34N 340 34P 344 34u Wyo. Sub-bituminous,
run No. 35c 36A
Pressure Gasifier 3 Sewickley bituminous, runNo. 2.1 2.1 2.6 1.4 1.4
25 26 28 32A 32B 34A 34B 34c
73.0 69.0 70.5 91.2 77.7 78.0 78.5 81.3
1.1
1.3 1.5
Table 111. Sulfur Fed to Gasifier, Run No. LbJHr.
Sulfur Balances
Other Sulfur., ?% ," Sulfur In Unacin Gas, % In scrubber counted for HpS Organic S residue water
Atmospheric-Pressure Gasifier 4 7 15 36 43A
11.9 3.6 5.9 3.1
71.0 68.0 69.1 66.0
25 26 27 32B
20.6 23.1 20.8 13.7
69.4 65.9 74.7 74.8
3.0 2.8 4.0 2.9
21.2 13.7 20.2 25.4
4.7 7.8
0.1 7.7
6.7 5.7
Pressure Gasifier 3
1126
3.6 3.1 1.3 3.2
15.7 21.8 16.2 18.7
8.8 7.5
2.5 1.7 7.8 3.3
ing catalytic process is that using a copper-chromium-vanadium catalyst (IS), which not only converts the organic sulfur compounds to hydrogen sulfide but also acts as an absorbent for the hydrogen sulfide formed. Periodically, the catalyst must be regenerated with air and then reduced. The process, although expensive, is an excellent means of producing an extremely clean gas at elevated temperatures. Purified gas containing less than 0.001 grain of total sulfur per 100 standard cubic feet can be obtained. The process is most selecti-ve in that no carbon dioxide is removed from the gas. An economical process for removing organic sulfur from synthesis gas is that of adsorption on activated carbon. A rather extensive program ha3 been conducted on the effect of variables on carbon adsorption. Tests yere made Tith carbonyl sulfide, not only because it is the only organic sulfur compound in the r a x gas produced a t Morgantorvn, but also because with gases containing other organic sulfur compounds, carbonyl sulfide, being a gas under normal conditions, would control the operating cycle. Earlier studies (13) with a GW activated carbon, manufactured by Pittsburgh Coke &: Chemical Co., indicated that the adsorption capacity of this carbon i s a linear function of the inlet sulfur concentration, a t least for concentrations between 10 and 50 grains per 100 standard cubic feet. At inlet concentrations of 10 to 30 grains per 100 standard cubic feet, nearly equal volumes of gas n'ere purified per unit of carbon. This earlier work also revealed that the adsorptive capacity of this carbon for carbonyl sulfide is markedly affected by the carbon dioxide content of the gas. .4s an example, GW carbon Kill effectively treat twice as much gas containing 2% carbon dioxide as gas with 10% carbon dioxide. Bench scale experiments have been conducted to study the effect of pressure on removing carbonyl sulfide from gas containing no carbon dioxide and gas containing varying amounts of carbon dioxide. The test procedure used was very similar to that used in all previous activated carbon experiments. Fifty grams (100 cc.) of GW carbon was added to a l/J-inch Schedule 80 pipe, giving a bed depth of approximately 27 inches. I n the first series of experiments, hydrogen containing lees than 0.5% carbon dioxide and 6.2 grains of sulfur (as carbonyl sulfide) per 100 standard cubic feet was used as the test gas. After each adsorption cycle, the carbon was regenerated by passing nitrogen through the bed for 1 hour a t 500' F. It had been found that drying was an essential step, even if regeneration was effected by saturated steam a t 100 pounds pet square inch gage owing to the high retention of water by the carbon, about 50% by weight. Since suitable regeneration could be obtained using hot inert gas only, the steaming cycle was eliminated from the laboratory tests. Figure 6 shows the effect of pressure on adsorption when a gas low in carbon dioxide is used, Runs A, B, and C were made a t constant space velocities with varying linear velocities. At 200 pounds per square inch gage the carbon treated about seven times niorg gas than it did at atmospheric pressuR. At 400 pounds per square inch gage this value increased to nine times. The linear velocity a t atmospheric pressure u as about 30 times that a t 400 pounds per square inch gage. To make certain that this increase in capacity was not due entirely to the difference in linear velocity, run D was made a t atmospheric pressure with a linear velocity corresponding to that used a t 400 pounds per square inch gage. Although the volume of gas that could be treated a t the lower linear velocity increased somewhat, the increase was quite small compared to that a t the increased pressure. The second series of tests was run at 300 pounds per square inch to study the effect of pressure when gas containing varying amounts of carbon dioxide is treated. The results show that with 0.5% carbon dioxide in the gas, the carbon adsorbs about eight times the carbonyl sulfide at 300 pounds per square inch gage as it does a t atmospheric pressure. ,4s the carbon dioxide content of the gas increased, the effect of pressure decreased until, with 20% carbon dioxide, there was only one and one half times 5s
INDUSTRIAL AND ENGINEERING CHEMISTRY
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SYNTHETIC FUELS A N D CHEMICALS much carbonyl sulfide adsorbed a t 300 pounds per square inch gage. Molecular sieves (6) are new commercial adsorbents and are available in three types-4A and 13A (sodium aluminosilicates) and 5A (calcium aluminosilicate). The water of hydration has been removed from these compounds by heating, and the resulting crystals are highly porous; the pores are of molecular dimensions and uniform size. The diameter of the pores of Type 13A is 13 A.; Type 4A, 4 A.; and Type 5A, 5 A. I n principle, the three types adsorb only those molecules that are small enough t o enter their pore systems. Bench scale experiments were run to study the effectiveness of these adsorbents in removing carbonyl sulfide from gas and to compare their GAS VOLUME. SCF performance with that of activated carbon; l/le-inch pellets were used Figure 6. Effect of pressure on adsorptive capacity of GW activated carbon in the tests. The initial tests were COS content of gas: 6.2 grains S per 100 std. cu. ft. hydrogen made with a bed 6 inches deep. SubCarrier gas: with less than 0.5 mole yo COz 5 0 grams sequent tests showed that a bed 30 Weight of carbon: %ace - - vel.. - -, inches deep adsorbed no more carPressure, std. cu. ft./ linear vel., ft./hr. bony1 sulfide based on weight of Curve lb./sq. inch gage cu. ft./hr. at test pressure adsorbate adsorbed per unit weight A 400 3400 262 B 200 3400 505 of adsorbent, than the 6-inch bed. C 0 3400 7350 The carrier gas was a mixture of 80% D 0 136 295 hydrogen and 20% nitrogen containing 20 grains of sulfur (as carbonyl SUIfide) per 100 standard cubic feet. The tests were conducted at capacity, however, is considerably below that of GW carbon room temperature and 300 pounds per square inch gage with a (0.019 gram of sulfur per gram of carbon). Whenever 5.2% of space velocity of 3000 standard cubic feet per cubic foot per hour. carbon dioxide was added to the carrier gas, all three molecular Of the three types tested, 13A showed the greatest capacity, sieves began passing carbonyl sulfide almost immediately. From adsorbing 0.011 gram of sulfur per gram of adsorbent. This these results i t appears that the molecular sieves are less effective than activated carbon for this particular application under these specific conditions. 24 Oxygen. As i t is extremely important to limit the oxygen content of synthesis gas t o prevent oxidation of the FischerTropsch catalyst, laboratory scale experiments were made t o determine the effectiveness of copper turnings in removing small amounts of oxygen. Twenty cc. (8.4grams) of copper turnings (light) was charged 20 into a small pressure reactor. A gas mixture, consisting of approximately equal volumes of hydrogen and carbon monoxide containing 0.6 to 0.9% of oxygen, was used as feed gas. The rn tests were run at 575' F. and 300 pounds per square inch gage with W space velocities from 5,000 t o 20,000 standard cubic feet per cubic + u foot per hour. The experiment had a total on-stream running 2 I6 time of 25 hours. There was no apparent loss of catalyst activity P at the end of this time. Some of the results are tabulated: LL > - 8
a
r
Space Velocity, Std. Cu. Ft./ Cu. Ft./Hr.
N
0 u
g
12
u
W
: 8
OXYGEN :CARBON
.---OVER
13 S i d . C u . F t . / L B
I
I
STEAM :CARBON
Figure 5.
July 1956
40
RATIO
40 80 80
12 Std Cu. F t / L B S t d . CU. F i . / L B
A.--UNDER *-.*l2-13
I
Linear Velocity, Oxygen Concentration Ft./Hr. a t 300 VOl. y* Lb./Sq. Inch Gage Inlet Outlet
I
80 80 160 160
0.9 0.6 0.9 0.6 0.6 0.6 0.6 0.6
RATIO, Lb./ Lb.
Effect of steam-carbon ratio on carbon dioxide content of product gas
The following analysis gives the composition of the gas mixture entering and leaving the catalyst chamber. Considering the
INDUSTRIAL AND ENGINEERING CHEMISTRY
1127
accuracy of an Orsat analysis, it is reasonable to assume that the copper did not alter the gas composition: Constituent
In 0.3 0.9
coz 0 9
important credits mould result from the sale of by-product sulfur ( 1 2 )and that venting to the atmosphere of any large quantity of sulfur in one form or another would not be tolerated. Information based on German practice also indicated that carbon dioxide in purified synthesis gas acted only as a diluent for the Fischer-Tropsch synthesis and not as a catalyst poison. The first pilot plant runs were therefore made to study the selective properties of aqueous solutions of triethanolaniine (191, tripotassium phosphate, and potassium ,V-dimethyl glycine (alkazid D I K ) ( 1 8 ) . The purification pilot plant and the solution and gas cycle used for removing hydrogen sulfide and carbon dioxide have been described in detail in previous publications (18, 19). It is sufficient to say that the studies on selective absorption were carried out in a Raschig ring-packed absorber a t an operating pressure of 300 pounds per square inch gage and gas flows of about 3000 standard cubic feet per hour, The follox-ing tabulation summarizes some of the data obtained xhen a gas containing 10% of carbon dioxide and 1/2yo of hydrogen sulfide was treated. I n all instances the hydrogen sulfide concentration in the scritbbed gas was reduced to 23 grains per 100 standaid cubic feet:
out 0.7 0.1
At the conclusion of these tests the catalyst was examined and weighed. There u-as no change in the weight, but the catalyst had changed from a typical copper color t o dark gray. An analysis revealed the presence of sulfide sulfur, undoubtedly due to traces of sulfur compounds in the feed gas. If, in any liquid-fuels plant, a n oxygen-removal process employing copper should be used, the copper would be subjected to traces of sulfur compounds leaving the activated-carbon vessels. I n view of this a test was made to study the catalytic activity of heavily sulfided copper turnings. Fresh copper turnings were completely sulfided a t 575" F., using pure hydrogen sulfide. Feed gas containing 0.6% of oxygen was then passed over the sulfided copper under the same operating conditions used in the previous test. The following results were obtained a t a space velocity of 5000 standard cubic feet per cubic foot per hour. Oxygen Concentration, 5701. yo Inlet Outlet 0.029 0.6 0.057 0.6 0.031 0.6
Absoi bent 35770 KIP04 Alkazid DIK (sp. gr. 1.1380) 30% T E 4
Pilot- and Plant-Scale Removal of Impurities Pilot plant investigations a t Morgantown have consisted of selective liquid absorption of hydrogen sulfide from synthesis gas containing high carbon dioxide-hydrogen sulfide ratios and the simultaneous liquid absorption of hydrogen sulfide and carbon dioxide As cost estimates showed i t to be uneconomical to remove substantially all of the hydrogen sulfide by conventional liquid absorption, iron oxide purifiers were used for the removal of residual hydrogen sulfide. Organic sulfur compounds were removed by adsorption on activated carbon. Considerable pilot plant work has been done on the removal of particulate matter (dust) from crude synthesis gas. Selective Absorption of Hydrogen Sulfide. I n 1949, when the purification pilot plant was put into operation, special emphasis was placed on selective removal of hydrogen sulfide and its subsequent conversion to elemental sulfur. It was realized that
Soh
Solution Run No.
Strength,
Wt. %
Rate, Gal./ Min.
3-D 4-D 5-D 9-D 10-D 11-D 14-D 16-D 17-D
40 40 40 30 30 30 30 20 20
1.3 1.2 1.0 .55 1.0 1.0 1.0 1 .o 1.0
Hydrogen Sulfide iri Acid Gas Leaving Reactivator, qC 19.0
0.033 0.030
11.5 12.5
Simultaneous Removai of Hydrogen Sulfide and Carbon Dioxide. On the basis of research in this country, it, is nom- believed that carbon dioxide, if present in rather large amounts, has a deleterious effect on some Fischer-Tropsch synthesis catalysts. Because of this, pilot plant research was directed tc:ward si:iiultar.eoue removal of hydrogen sulfide and carbon dioxide. Such removal does not preclude the recovery of elemental sulfur from the acid gases stripped from the spent absorbent, even though the acid-gas stream is lean in hydrogen sulfide (9). -4s already discussed, removal of most of the carbon dioxide would he beneficial for adsorbing carbonyl sulfide on activated carbon. Of the three ethanolamines available for removing hydrogen sulfide and carbon dioxide, monoethanolamine, because of its high basicity, would be the logical one for investigation. Holyever, as it was know1 that carbonyl sulfide had an adverse effect on monoethanolamine, experimental runs were made using diethanolamine (19). Investigations were conducted a t 300 pounds per square inch gage using 20, 30, and 40% aqueous solut'ions. Table IV gives data from some of the pilot plant runs. The results from t'hese runs indicated that reactions with carbonyl sulfide still occurred, but perhaps to a lesser extent than occurred with monoet,hanolamine. Figure i shows various schemes for purifying synthesis gas (after dust removal), based on experimental work a t Morgantoa-n. The process generally wed as a source of purified q-nthesi?
These data shorn that sulfided copper also effects the removal of oxygen. Neither hydrogen sulfide nor sulfur dioxide was detected in the outlet gas. This catalytic activity of copper sulfide is important inasmuch as it eliminates the need of regenerating the copper turnings whenever they become fouled with sulfur.
Table IV.
Hydrogen Sulfide Absorbed/ Gal., Lb. 0 023
Data from Pilot Plant Runs Using Diethanolamine Gas Rate, Std. Cu. Ft./Hr. 1,920 1,920 1,920 900 2,750 2,830 2,470 2,450 1,600
~
~
1 Hydrogen . Sulfide, Grains/100 Std. Std. Cu. Ft. Cu. Ft. of Gas In out 10 550 40.6 15 550 37.5 25 550 31.2 25 220 36.7 350 30 21.8 175 25 21.2 350 25 24.3 40 350 24.5 350 1 to2 37.5
COZ, Mole
In
Out
HB in Acid Gas, Mole %
26.7 26.7 26.6 20.8 14.4 14.3 14.4 16.3 15.7
6.0 7.6 10.4 5.1 5.4 5.8 5.7 8.2 2.0
3.7 4.0 4.4 1.9 5.2 2.7 5.4 5.3 3.9
76
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 48, No. 7
SYNTHETIC FUELS AND CHEMICALS ACID GAS TO SULFUR RECOVERY
M
m
Figure 7. Schematic diagram of several purification trains
gas employed diethanolamine for removing the bulk of the carbon dioxide and hydrogen sulfide, iron oxide for removing residual hydrogen sulfide, and activated carbon for removing organic sulfur compounds (scheme A). This process results in a synthesis gas well within the specifications given earlier. As shown in Figure 7, the copper-chromium-vanadium process could replace the iron oxide and activated carbon for removing residual hydrogen sulfide and organic sulfur compounds (scheme B). This would result in a hot gas having a low sulfur content. If carbon dioxide need not be removed, raw synthesis gas may be sent directly to the catalyst reactor, where all the hydrogen sulfide and organic sulfur would be removed (scheme C). Plant Scale Purification of Synthesis Gas. Scheme A, given above, was successfully used on a larger scale a t the bureau's demonstration plant a t Louisiana, Mo. Details on the operation of the plant have been published (21). Carbon dioxide and sulfur compounds were removed at 350 t o 370 pounds per square inch gage. The usual operating rate was about 2,000,000 cubic feet of gas per day containing 16 t o 20yo of carbon dioxide and 100 grains of sulfur per 100 cubic feet. The purified gas contained 2 to 5 % carbon dioxide and less than 0.01 grain of total sulfur per 100 standard cubic feet. I n the iron oxide step, a sample of the used oxide from the inlet end of the tower showed the exceptionally high loading of 2.33 pounds of sulfur per pound of oxide. Samples from the middle and outlet portion of the tower showed appreciably lower sulfur loadings, but all three samples showed only a small percentage of combined sulfur. The feed gas to the tower showed 0.1% oxygen, and it is believed that under prepsure this concentration was sufficient to effectcontinuous regeneration. Those in charge of the plant operations believe that if the tower had been continued in operation the high loadings shown a t the top probably would have been achieved through most of the bed. One significant difference between the pilot plant results at Morgantown and those of the demonstration plant was noted in the performance of the activated-carbon adsorption step. Pilot plant studies showed that it was possible t o treat about 400 cubic feet of gas per pound of carbon before regeneration of the carbon was necessary. Plant scale results showed that twice this amount of gas could be purified before regeneration and, in one special test, ten times this amount was treated before the effluent gas showed 0.1 grain of sulfur per 100 cubic feet. The plant operations were made with a gas containing 0.3 to 1.0 grain of sulfur (as organic sulfur) per 100 cubic feet-considerably lower than the concentration (5 grains and higher) in the gas treated in the pilot plant. When this difference in service time became known, laboratory scale tests were made, and the results indicated that the improved performance in the plant was due, in part, t o each of the following factors: ( a ) Lower concentrations of
July 1956
organic sulfur, ( b ) operation at lower linear velocities, and (c) greater depth of bed. Most plant runs used synthesis gas produced from coke in a Kerpely producer, but one run of 8 days in which coal gas was used indicated that satisfactory purification could be attained in a plant of this type. Hot Potassium Carbonate for Carbon Dioxide Removal. One interesting and attractive process for removing carbon dioxide from synthesis gas is that of scrubbing with a hot (240" F.) concentrated solution of potassium carbonate (@yo). Pilot plant work on carbon dioxide removal by this process has been carried out by the Bureau of Mines a t Bruceton, Pa., and a description of the plant, operating conditions, and results, has been published ( 2 ) . The adaptability of this process to the removal of hydrogen sulfide is currently being investigated. The authors state that such a process appears to be comniercially useful when impure gas is available (or is t o be used) a t elevated temperature and pressure. I n such a case a reduction in cost, over the conventional amine processes, can be realized in the following ways: Reduction in the amount of steam necessary for regenerating the potassium carbonate solution; equipment savings by elimination of heat exchangers and coolers; reduction of the quantity of cooling water; and elimination of loss of scrubbing agent (potassium carbonate). Rectisol Process. A purification process that has been receiving attention lately is the Rectisol process. Essentially, raw gas is cooled by the purified gas and fed t o the bottom of an absorber, where it is scrubbed with methanol a t elevated pressures and -3OO F. Purified gas leaves the top of the absorber and, after being warmed by the raw gas, is discharged from the plant. Some information ( 1 ) has been received on a plant designed t o operate with gas containing 30% of carbon dioxide, 350 grains of hydrogen sulfide, and 50 grains of carbonyl sulfide per 100 standard cubic feet. The design provides for 90% removal of the carbon dioxide, leaving 4.1% in the gas. The total sulfur content of the final gas is 0.1 grain, and carbonyl sulfide is reduced to 0.01 grain per 100 standard cubic feet; 98y0 of the sulfur is made available in an acid-gas stream containing 6% hydrogen sulfide. Operating costs for such a plant, treating 300,000,000 standard cubic feet of gas per day, are reported to be approximately 2 cents per 1000 standard cubic feet of raw gas. As far as the authors know, no pilot plant investigations of this process have been made in this country. Carbon Dioxide Removal in Agitated Gas-Liquid Contactor. About 60% of the cost of removing hydrogen sulfide and carbon dioxide by liquid scrubbing lies in the cost of steam needed to regenerate the spent solution. Under a cooperative agreement between the Federal Bureau of Mines and the Turbo-Mixer Division, General American Transporation Corp., small pilot scale experiments have been initiated with the objective of reducing steam costs as well as investment costs by replacing the conventional packed absorber with a Turbo-Mixer-type gas-liquid contactor. It is believed that since absorption of carbon dioxide and hydrogen sulfide is controlled almost entirely by liquid-film resistance, agitation of the liquid phase, resulting in a spray of fine liquid droplets, would increase the rate of mass transfer and would also result in a greater pickup of carbon dioxide per volume of diethanolamine circulated. Figure 8 shows the design of the contactor. It consists of a 42-inch length of Winch Schedule 80 carbon-steel pipe, four vertical baffles I inch wide and equally spaced, a 9-inch i.d. lift tube, annular ring, and an impeller. A 1-hp. motor (1750 r.p.m.) is used to drive the impeller, and the diameters of the sheaves are chosen to give the shaft a speed of 500 to 900 r.p.m. Experiments to date have been made using inert gas containing varying amounts of carbon dioxide. The gas is fed into the bottom of the contactor to the rjght of the lift impeller, so that the gas passes through the spray of liquid distributed by the impeller. A 4oy0 solution of diethanolamine enters at the top of the absorber
INDUSTRIAL AND ENGINEERING CHEMISTRY
1129
Tr 7
LlOUlD FEED
LLC CONNECTION
ABSORBER IMPELLER
ANNULAR RING
7
9" L I F T
TUBE
ADJUSTABLE T SUPPORTS
LI C
Figure 8,
I10
T
GAS IN
Gas-liquid contactor for acid gas absorption (Turbo-contactor)
and is distributed by a sparger, T h e level of the solution in the contactor is maintained above the annular ring. IVhenever the level is below this point foaming occurs; otherwlse, the amine solution is free of foam. The purified gas leaves the top of the contactor through a separator that separates entrained liquid from the gas. Results, to date, are only preliminaly, but the following data indicate there is a greater pickup of caibon dioxide per volume of solution (about 30 to 50% more) with the contactor than there is with either the pilot plant packed column or the demonstration plant bubble-cap column. Absorber _ . .. Carbon Dioxide Pressure, in Lean Soln., Lb./Sq. Cartion Uloxlde Cu. Ft./Gal. Inch Gage In, % Out, yo
300 340
250
hforgantown Packed Column 0 55 5 1 Bubble-Cap Column 0 52 3 0 18.4 Rforgantos-n Contactor 0 51 3 6 18.2
20 8
Csrhon Dioxide _... Removed/Gal. Soln., Cu. Ft.
5 40 5.29
7 77
These initial experiments were conducted primarily to study t h e absorption characteristics of diethanolamine in an agitator gas-liquid contactor. As these preliminary results indicate an
1130
improvement in absorption efficiency, experimental data ai e to be obtained so that a correlation can be made between the carbon dioxide pickup per gallon and the regeneration efficiency (defined as carbon dioxide removed per pound of regenerating steam). Assuming only chemical reaction, 1 gallon of 40Yo diethanolamine solution will absorb, theoretically, about 6.3 cubic feet of carbon dioxide, if the carbon dioxide is converted completely to the amine carbonate, and about 12.6 cubic feet, if the carbon dioxide is converted to t h e amine bicarbonate. As it is reported that only a small amount of bicarbonate is formed in the amine proceqs (3),it is believed that in runs where the fouled solution contains 7 or more cubic feet of carbon dioxide per gallon, the theoretical pickup was attained. This would indicate the need of investigating higher amine concentrations. The ability to use more concentrated solutions is an important advantage the contactor has over the conventional column as highly concentrated solutions of amine are too viscous to be used in packed columns. Removal of Dust. Dust must be removed from the synthesigas because of its effects on the synthesis catalyst, compressors. fixed beds, etc., in the system. A wide variety of dust-removing equipment is used in industry. These devices rely on screening, impingement, inertia, electrical charges, and other effects or, most often, combinations of these. All dust-removal methods may loosely be divided according to the particle sizes they can handle. The first group is suitable for relatively large sizes within the range of analytical screensover 44 microns. Another group is effective for the medium size, down to approximately 5 or 10 microns, while for fine purification other types are needed. The r a F gas leaving the atmosph eric-pressure gasifier contained several thousand grains of dust per 100 cubic feet, the bulk of it larger than 200-mesh (74 microns)-larger, in fact, than the coal fed, which was usually 70younder 200-mesh. This increase in size was obviously due to fusion of particles, as shown in Figure 5 . This dust concentration was reduced to 2000 or 3000 grains by passing it through an unpacked fogging chamber intended merely to cool the gas. About 50% of the weight of the dust leaving the fogging chamber was over 325-mesh (44 microns). A ring-packed scrubber then reduced the dust concentration t o 10 or 30 grains per 100 cubic feet, a removal efficiency of over 99% This again decreased the particle size, half of the mass now being over 10 or 20 microns. Typical results are given in Table V. Fine Purification. Final dust removal vias sometimes done with the electrostatic precipitator, which usually gave dust concentrations from 0.02 t o 0.3 grain per 100 cubic feet, rising as high as 3 grains when it was not operating properly. Some results are given in Table VI. Particle size apparently was not decreased greatly by the electrostatic precipitator. Moving-Bed Filter. Another device for fine purification was the moving-bed filter ( 6 ) . The gas was passed upward thrpugh a bed of coke, which continuously moved downward. Fouled coke was removed from the bottom, washed free from dust, and returned to the top of the bed without interfering with the filtration. The device has the advantages of a filter and still can be continuously cleaned. It can be used a t high temperatures or with gases containing much water. Any desired puiity can be obtained by controlling the fineness of the filtering material, and it can combine filtration with heat transfer, catalysis, etc. Operations on a large scale (3,900,000 standard cubic feet per hour) a t Oppau, Germany (IO),shomed that it was more efficient than an electrostatic precipitator or Theisen disintegrator on acetylene split gas, reducing the dust concentration from about 5 to 0.03 grain per 100 cubic feet which is 99.4% removal, a t a pressure drop of 12 inches of water. Tests a t hlorgantown on the atmospheric pressure gasification system seenxd to corroborate these results, On one test a t least, the dust concentration was reduced from 35 to 0.2 grain per 100 cubic feet or 99.4% removal. However, with the design used a t hforgantown, coke could not be circulated a t this pressure drop, so most tests weie
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 48, No. 7
SYNTHETIC FUELS AND CHEMICALS made a t 1.25 t o 2.5 inches of water, which usually gave Table V. Performance of Atmospheric Pressure Scrubber outlet dust concentrations from Fogging Chamber Scrubber 0.2 to 3 grains per 100 cubic Run No. Gas Rate, Dust Concn. Water to Water to Dust concn. and Leaving Gasifier, Std. Cu. feet and removals from 85 to Water, jets, leaving serubber, sprays, Period Gr./100 Std. Cu. Ft. Ft./Hr. Ib./hr. lb./hr. Ib./hr. gr./100 std. cu. ft. 98%. 4420 G4-47A 12,990 1375 3000 16.8 When used after the electro7130 G4-48A 13,850 1300 12.5 3100 static precipitator, the filter 5260 G4-51A 12,990 1410 3000 6,600 14.1 usually removed 86 to 95% of G4-53A 13,180 1380 6,600 40.7 3100 G453B the small amount of remaining 14,080 1575 7,300 33.8 3400 G4-54F 14,360 1360 7.0 6,450 2875 dust, resulting in extremely 13,725 G4-55A 2800 1400 13.1 10,700 low concentrations-0.004 to G4-56C 15,490 515 14.7 10,100 3100 0.1 grain per 100 cubic feet. 15,700 1380 G4-56D 11.5 8,940 2700 14,990 1450 Table VI1 gives some results G4-57A 10.8 3100 with the pilot plant filter. Process design information was obtained on the pilot plant was followed by a ring-packed scrubber, which proved very effecfilter and also on a laboratory scale filter. This showed t h a t wet tive a t high pressure. h4any tests were made on the scrubbed beds of coke rapidly developed a high pressure drop, giving very gas. good dust removal. Dry beds, however, gave better removal for The most important variable was pressure, as shown in Figure the same pressure drop. Probably the water covers the irregulari13, which is an assembly of 100 determinations on 29 different ties in the coke, causing them t o act like smooth pebbles, which gasification runs under widely different conditions over a period had previously been proved less effective. Investigators at of a year. It shows that dust concentration decreases greatly as Oppau also found smooth filtering materials less effective than rough. If pressure drop is permitted to increase as a result of the pressure is increased. The effect of scrubber water is shown dust buildup in the bed, the dust removal increases to a maximum, in the curve in the lower right corner, then actually decreases with increased pressure drop, because the Other Methods for Dust Removal. The results obtained with dust layer reaches the top of the bed. In practical operation, this the usual pilot plant equipment have been described, but several means that the coke-recycle rate should be controlled to operate other dust-removing devices were tested in the laboratory or a t this pressure drop for maximum performance. Curves based used on various pilot plant trains a t different times. Laboratory on 98 tests on the laboratory scale filters are shown in Figures 9, work showed that cyclones 2 inches in diameter, when used a t 10, 11, and 12. These curves shorn the effects on filter perform2 inches of water-pressure drop, were suitable for removing pilot ance, in terms of percentage of dust removed, of bed height, dust plant dust particles over 20 microns in diameter. They were used buildup, gas flow, and water on the coke. for dry removal in the pilot plant for a short time, with satisThe dust train used on the pilot plant high pressure gasificafactory results. tion system was somewhat similar to the low pressure train just For removing the fine particles, the first and smallest gasificadescribed. It started with a n unpacked water-spray chamber for tion system (IC) filtered the dust with two micrometallic porous plates in parallel, one being cleaned by blowing back while the quenching the gases, this time inside the gasifier itself. Dust determinations were impossible a t this point; but from calculaother was in use. This yielded gas containing about 0.2 grain per tions on residue obtained it was estimated that the gas leaving the 100 cubic feet but the method probably would not be practical reaction zone contained roughly 3000 grains per 100 cubic feet of on a larger scale. material fine enough to be called dust, plus, of course, much This dust-removal work has given many data and much demolten slag, presumably in large masses a t this point. This sign information and practical skill. It is obvious t h a t no one was reduced to about 1500 grains per 100 cubic feet by the sprays dust-removal system can be recommended for all conditions. in the gasifier. The next dust-removing device was a cyclonic Proper design depends on the requirements of the other equipment section in the bottom of the scrubbing tower, which reduced the in the system, as well as the properties of the dust used and other dust concentration to about 77 grains per 100 cubic feet. This factors. For removing the bulk of the dust from the hot, raw gas large cyclones or knockout chambers before or after the waste-heat boiler probably are most economical. Many types of scrubbers Table VI. Performance of Electrostatic Precipitator for intermediate purification are on the market. Small-diameter Dust Concentration, cyclones may be satisfactory if wet removal is inadvisable. For Grains/100 Std. Cu. Ft. Run No. fine purification the electrostatic precipitator, Theisen disintegraand Period Inlet Outlet Dust Removal, % tor, or possibly the moving-bed filter would be most suitable. G4-48A 12.5 0.28 97.8 Dust Disposal. The disposal of dust, preferably at a profit, is G4-48A 12.5 0.17 98.7 G4-51A a difficult problem. Attempts were made to separate the ash 14.1 0.36 97.5 G4-5 1A 14.1 0.12 99.2 from the combustible material by screening or elutriation so it G4-52 41.4 0.09 99.8 could be recycled, but no important separation could be obG4-53A 40.7 0.11 99.7 tained. If a large part of the solid material is removed as a slag, G4-54F 7.0 0.18 97.4 G4-55A it may be practical to recycle all the dust recovered in the gas. 13.1 0.23 98.2 G4-56C 0.04 14.7 99.8 As some of the residue resembled carbon black in some ways, its G4-56D 11.5 0.02 99.8 use as a rubber compounding agent was investigated. It showed G4-682 12.1 0.86 92.9 some reinforcing power and could be used as a filler but was no G4-69GR 7.8 0.08 98.9 G4-69XR substitute for carbon black. Its value as a soil conditioner is 9.3 0.03 99.6 G4-72B 21.2 3.0 86.1 being investigated.
... ...
... ... ... ... ... ...
...
(34-72 J G4-73A G4-73B G4-761
July 1956
9.9 11.4 17.8 23.0
0.57 0.26 0.29 0.21
94.3 97.8 98.4 99.1
Summary Problems encountered in purifying synthesis gas to meet approximate specifications established for the Fischer-Tropsch
INDUSTRIAL AND ENGINEERING CHEMISTRY
1131
99.9
99.9
W O W 0
0
W
5
p 99.0
E
a
5
99.0 LL
0
k
c w z
c
L n Y
w 0
e P W
95.0
90.0 90.0 I
80.0
A'
I
/
70.0 60.0 ...
Wet B e d , 0.13' hdight of bed, 1500 c f h l s q . f t . c . s . a . 76 q r a i q 8 / 1 0 0 cu, ft. inlet dust c o x .
80.0 70.0
0
2
4
AVERAGE A P
6
IO
8
12
14
16
0
A C R O S S COKE BED, INCHES OF WATER
Figure 9.
I
2
AVERAGE
Effect of bed height
AP ACROSS
Figure 10.
3 COKE
4
6
5
65
B E D , I N C H E S OF WATER
Effect of gas flow with dry bed
Removal of dust by laboratory coke filter
Table VII.
A P across
Entire Filter, Inches Water
Moving-Bed Filter Performance
A P from Above Star Feeder, Inches Water
Gas Flow, Cu. Ft./Hr./ Sq. Ft. CrossSectional Area 3185
Run G4-17 ... G4-19 1910 G4-19 ... 2550 G4-22 ... 1060 G4-22 ... 1820 G4-22 ... 910 G4-22 910 G4-28 1440 G4-33 12 1.0 2270 G4-34 0.8 12.4 1660 G4-34 5.5 0.5 1660 G4-34 ... 2000 G4-65 ... 2000 G4-66 ... 1000 ... G4-66 1000 G4-67 ... ... 1000 1.25 0.38 G4-68 1000 1.25 0.5 G4-68 1000 1.25 G4-68 0.5 796 G4-69 1000 G4-69 1000 G4-71 1.25 0.5 1000 1.25 G4-71 0.5 1000 G4-71 1.25 0.5 1000 G4-72 1000 G4-72 ... ... 1000 G4-72 0.75 G4-72 500 G4-73 500 G4-73 1000 G4-73 1000 G4-73 2.5 1.75 1000 ... G4-74 1000 G4-74 ... 1000 G4-76 ... 1000 ... ... G4-76 1000 2.5 1.5 G4-76 1000 G4-76 2.5 1.5 a Using gas already purified by the electrostatic precipitator.
...
...
... ... ...
.. .. ... ... ... ...
...
...
...
... I
.
.
...
...
...
...
... ... ...
Dust Concn. Gr.1100 Std. Cu. Ft. Entering Leaving 1.45 3 . .
11.7
...
... 32.0 29.4 40.2 40.0 30.3 8.8 11.5 9.46 27.05 29.43 12.46 12.61 0.128 0.865 12.13 7.82 0.034 9.56 10.67 17.70 2.96 21.21 9.94 0.57 11.41 0.26 17.78 0.29 0.53 16.89 0.05 22.99 22.99 0.21
...
3.12 3.71 1.83 6.34 0.85
0.24 0.14 0.49 1.61 1.29 2.98 2.85 1.32 0.94 0.006 0.118 1.82 1.04 0.004 0.78 0.81 0.97 0.04 0.74 0.76 0.05 0.24
0.03 0.22 0.005
0.06 1.07 0.004 0.91 1.02 0.07
Dust Removal Efficiency, %
...
...
...
94.3 78.4 97.9 99.5 99.5 94.4 86.0 86.4 89.0 90.3 89.4 92.6 95.45 86. 4a 84.9 86.7 88. 91.8 92.4 94.5 98.5 96.5 92.4 91.2" 97.9 88. 3a 98.8 98. Za 87.P 93.7 91.7" 96.1 95.6 66. 7a
process have been discussed. With particular reference to gas made directly from reacting coal with oxygen and steam, experimental data have been given on the types and quantities of impurities present, analytical methods suitable for determining low concentrations of these impurities, and processes for removing dust, oxygen, carbonyl sulfide, and hydrogen sulfide from raw synthesis gas. The selection of any one of several purification schemes described Fill depend on the composition of the gas, the gas pressure, comparative costs of the various steps, and other factors.
Literature Cited (1) Beery, D. W., Alberts, L.
W., Chemical Division, Blaw-Knox Co., Pittsburgh, Pa., private communication, April 1955. (2) Benson, H. E., Field, J. H., Jimeson, R. M., Chem. Eng. P r o p . 50, No. 7 , 356-64 (1954).
(3) Bottoms, R. R.,
IND. EXG.
CHEW23, 501-4 (1931). (4) Clark, E. L., Linde Air Products Co., Tonawanda, N. Y . , private comniunication, 1954. (5) Egleson, G. C., Simons, H. P., Kane, L. J., Sands, A. E., IND.ENG.CHEM. 46,1157-62 (1954). (6) Hakewell, H., Rueck, E. RI., Am. Gas Assoc. Proc. 1946, pp. 529-38.
1132
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. 48, No. 'I
SYNTHETIC FUELS AND CHEMICALS
99.99
I
I
I
EFFECT OF GAS FLOW WITH WET COKE BED
I
I
I
I
I
I
I
99.9
n W
0 5 P W
I-m
99.0
Wet Bed,0.83’ height of bed,
ISOO c f h l r q . ft. c.a.0. 73 g r a i na/lOO cu. f t . i n l e t dual conc.
90.0
60.0
2 AVERAGE
Figure 11.
4
6
8
IO
12
14
16
AP ACROSS C O K E BED, INCHES OF WATER
A P ACROSS COKE B E D , INCHES OF WATER
AVERAOE
Figure 12.
Effect of gas flow with wet coke bed
Effect of water on coke
Removal of dust by laboratory coke filter (7) Kane, L. J., Wainwright, H. W.,
Shale, C. C., Sands, A. E., U. S. Bur. ,Mines, Rept. Invest. 5045,
1954. (8) Pursglove, L. A., Wainwright, H. W., Anal. C h m . 26, 1835-9 (1954). (9) Resin, F. L., 0 2 1 Gus J. 50, No. 4 , 59 (1951). (10) Sachsse, E., Technical Oil Mission, Reel 132, Ammonia Laboratory, Oppau, Germany, 1941 (available from Library of Congress, Washington 25, D. C.). (11) Sands, A. E., Grafius, M. A., Wainwright, H. W., Wilson, M. W., U. S. Bur. Mines, Rept. Invest. 4547, 1949. (12) Sands, A. E., Schmidt, L. D., IND. ENG.CHEM.42, 2277-87 (1950). (13) Sands, A. E., Wainwright, H. W., Egleson, G. C., U. S. Bur. Mines, Rept. Invest 4699,1950. (14) Sebastian, J. J. S., Ibid., 44, 1175-84 (1953). (15) Stone, D. E., ICane, L. J., Corrigan, T. E., Wainwright, H. W., Seibeit, C. B., U. S. Bur. Mines, Rept. Invest. 4782, 1951. (16) Strimbeck, G. R., Cordiner, J. B., Baker, N. L., Holden, J. H., Plants, K. D., Schmidt, L. D., Zbid., 5030, 19.54 _ __-
5
SCRUBBER
H20 PER
WATER RATE 162 TO 194 L B 1000 STD. Cu.Ft.GAS
;r \
SCR U B E E R OPERATING P R E S S U R E . 3 0 0 PSlG
I
0
0
100
I
I 200
300
PRESSURE
Figure 13.
0
400
500
- PSI0
0
100
200
FLOW OF SCRUBBER SPRAY WATER POUNDS S T D CU. Ft G A S .
PER I000
Performance of high pressure scrubber
(17) Strimbeck, G. R., Cordiner, J. B.,
Taylor, H. G.. Plants, K. D., Schmidt, L. D., Ibid., 4971, 1953. (18) WTainmright,H. W., Egleson, G. C., Brock, C . M., Fisher, J., Sands, A. E., IND. Exc. CHEM.45, 1378-84 (1953). (19) Wainwright, H. W., Egleson, G. C., Brock, C. M., Fisher, J., Sands, A. E., U. S. Bur. Mines, Rept. Invest. 4891, 1952.
July 1956
(20) Wainwright, H. W., Lambert, G. I., Zbid., 4753, 1950. (21) Wenzell, L. P., Dressler, R. G., Batchelder, H. R., Ibid., 46, 858-62 (1954).
RECEIVED for review September 18, 1955.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
ACCEPTEDJanuary 17, 1956.
1133
