11 Catalysis of Coal Gasification at Elevated Pressure W. P. HAYNES, S. J. GASIOR, and A. J. FORNEY Bureau of Mines, U . S. Department of the Interior, Pittsburgh, Pa. 15213
Various additives were evaluated for their catalytic effect on coal gasification. Steam—coal gasification tests were done in bench-scale units at 850°C and 300 psig with coal containing 5 wt % additive. Alkali metal compounds increased carbon gasification the most, by 31 to 66%. Twenty different metal oxides increased carbon gasification by 2030%. Inserts coated with Raney nickel were active but lost activity rapidly. Pilot-plant tests were conducted in a Synthane gasifier at 907°-945°C and 40 atm. A 5% addition to the coal of either dolomite or hydrated lime resulted in significant increases in the amount of carbon gasified and in the amount of CH , CO, and H produced. 4
2
'Tphe gasification of coal with steam and oxygen under elevated pressure is an essential step in the Bureau of Mines Synthane process for con verting coal to synthetic pipeline gas. A suitable catalyst or additive i n the gasification step could conceivably improve the gasification of coal. Earlier investigators have catalyzed the gasification of coke and carbon with various additives and have demonstrated that some benefits would result from the catalysis of gasification at atmospheric pressure. Vignon ( J ) , for example, showed that the per cent of methane i n water gas made from coke increases significantly if lime is added to the coke. Neumann et al. (2) demonstrated the feasibility of improving the gasifi cation of graphite at 450° to 1000°C b y adding K 0 , C u O , and other salts. Continuation of the studies b y Kroger and Melhorn (3) indicated that addition of either 8% L i 0 or ( 8 % K 0 + 3 % C o 0 ) to lowtemperature coke increased steam decomposition at 500° to 700°C. More recently, Kislykh and Shishakov (4) studied the effect of Fe(CO) >, ( F e 0 + C u C l ) , K C 0 , and N a C l on the fluid-bed gasification of wood A
2
2
2
3
4
r
2
3
2
2
3
179
180
COAL GASIFICATION
charcoal at 750°C and atmospheric pressure. They found that sodium chloride was the most effective additive, accelerating gasification by 62% and increasing steam decomposition 2.5-fold. Multiple
thermocouple
connector
Ceramic catalyst support and space filler
Screen Catalyst sprayed insert
Coal
bed
Screen Ceramic catalyst support and s p a c e filler Process gas flow indicator
I TC=thermocouple
Ice
Back pressure regulator 9 TC
bath
Condenser" trap
Figure 1.
r J
J
Gasometer
Apparatus for catalytic gasification of coal
The work on catalysis reviewed thus far does not include either gasification at elevated pressures or the use of volatile coals. The benchscale work now reported compares the catalytic activity of various addi tives in the gasification of volatile coals with steam under pressure and studies other process parameters of interest such as gasification tempera ture, type of contact with the catalyst, degree of gasification, and repeated use of catalyst. Results of pilot plant gasification tests using additives are also reported.
11.
HAYNES E T A L .
Catalysis at Elevated Pressure
181
Bench-Scale Studies The gasification tests were conducted i n two bench-scale reactor units, units A and B . T h e units were essentially the same; each unit con tained an electrically heated reactor constructed of a 21-inch long section of 3/4-inch schedule 160 pipe of type 321 stainless steel. The coal-additive charge was contained i n the middle 6 inches of the reactor to minimize the spread of bed temperatures. Alumina cylinders filled the void at each end of the reactor. Three thermocouples were located i n the 6-inch reactor zone, 1/2 inch, 3 inches, and 5 1/2 inches from the top of the zone. The maximum temperature occurred at the middle thermocouple and was considered the nominal temperature of the reaction. The top and bottom bed temperatures were generally within 35 °C of the maxi mum temperature. During a gasification test the coal charge was gasified by steam which was introduced by saturation of the nitrogen carrier gas. Figure 1 shows a flow sheet of a reactor unit and its auxiliary equip ment: high-pressure gas supply, silica gel and charcoal purifiers, cali brated capillary meter as feed gas flow indicator, gas saturator to humidify the feed gas, condenser and trap for liquid product collection, and gasometer for metering and collecting total product gas. Reactor pressure was controlled by a back-pressure regulator. Temperature of the gas saturation was controlled within ± 0 . 6 ° C by a chromel-alumel thermo couple control system. Analyses of dry product gases were done by mass spectrometer and gas chromatography. The liquid product, about 95% water, was drained and weighed. Coal Used. The coal charged i n all the tests discussed here was a single batch of high-volatile bituminous coal (Bruceton, Pa.) that had been pretreated at 450 °C with a steam-air mixture to destroy its caking quality. The pretreated coal was crushed and sieved to a particle size of 20 to 60 mesh. Proximate and ultimate analyses of the pretreated coal are shown in Table I, i n weight percent. Table I.
Analyses of Pretreated Coal Used f o r Feedstock
Proximate Moisture Volatile Fixed carbon Ash
Ultimate 1.5 22.4 65.5 10.6
Hydrogen Carbon Nitrogen Oxygen Sulfur Ash
3.9 74.3 1.5 8.7 1.0 10.6
Standard Gasification Tests for Screening Additives. Standard gasi fication tests were conducted i n units A and B to determine the effect of various additives on the rate of carbon gasification, on the rate of gas production, and on other gasification parameters. In unit A , the standard gasification tests using various catalysts were made at the selected oper ating conditions of 850°C, 300 psig, and 5.8 grams/hr steam feed carried by 2000 c m N / h r . The coal charge was 10 grams plus 0.5 gram of catalyst. A l l catalysts were either powders or crystals that were admixed 3
2
182
COAL GASIFICATION
Table Ha.
Catalyst N o catalyst Raney nickel, unactivated sprayed mixed Raney nickel, activated mixed NaCl KC1 ZnO NiCl .6H 0 NiS0 .6H 0 K C0 ZnBr Sn0 Fe 2
2
4
2
2
3
2
2
Specific Rate of Gas Production
Experiment No.
No. of Tests
Total Dry Gas Production Rate, Ni-Free Basis, std cc/hr/gram coal charged
166
6
331
203 197
6 3
453 414
200 209 212 215 216 217 218 219 224 225
3 3 3 3 3 3 3 3 3 3
442 471 615 440 442 420 578 418 395 367
° Test conditions, unit A : charge, 10 grams pretreated Bruceton coal, 0.5 gram catalyst;
Table lib.
Catalyst N o catalyst Raney nickel, unactivated sprayed mixed Raney nickel, activated mixed NaCl KC1 ZnO NiCl .6H 0 NiS0 .6H 0 K C0 ZnBr Sn0 Fe 2
2
4
2
2
3
2
2
Specific Rate of Liquid Production, Production Using Product Liquid, gram/hr/ gram coal charged
Carbon Gasification Rates, gram/hr/gram coal charged
167
0.478
89 X 10"
203 197
.472 .501
98 X 10~ 106 X 10-
200 209 212 215 216 217 218 219 224 225
.489 .506 .480 .490 .493 .498 .494 .454 .507 .517
107 117 148 112
Experiment No.
110 108 144 104 98 94
X lO" X 10X lO" X 10~
x X
X X X X
3
3 3
3 3 3 3
ioIO" 10~ IO" 10~ 10-
3 3
3
3
3
3
° Test conditions, unit A: charge, 10 grams pretreated Bruceton coal, 0.5 gram catalyst;
11.
HAYNES
E T
Catalysis at Elevated Pressure
A L .
183
Using Various Catalysts (Series A) ° Specific Production Rates of Constituent Gases, std cc/hr/gram coal charged #2
CO
166
49.7
C0
70.2
CH 43.7
0.06
0.93
0.24
0.12
271 216
53.7 52.1
72.3 95.5
54.2 49.1
.12
.80 1.19
.22 .18
.05
243 254 340 232 237 220 309 224 213 193
47.9 53.0 90.1 52.2 51.7 48.0 95.0 53.9 37.7 39.1
104.5 115.5 137.3 104.4 103.6 102.9 126.4 96.2 98.1 88.3
45.3 47.6 46.7 50.0 48.4 48.0 46.2 42.6 44.0 45.4
.10 .33 .07 .05 .14 .21 .31 .18 .15 .09
0.84 .55 .64 .92 .82 .78 .72 .79 .65 .95
.13
— —
.33 .13 .18 .23 .22 .10 .33 .38
.03 .13 .16 .05 .06 .08 .28 .24
2
4
—
feed, 5.8 grams H 0/hr + 2000 std cc N /hr; approximately 4 hrs duration; 300 psig; 850°C. 2
2
Carbon Gasification, and Gaseous Heating Value Various Catalysts (Series A ) a
Unit Heating Value N -Free Product Gas, Btu/scf
Gaseous Heating Value Produced, Btu/hr/ft coal charged
353
57,700
359 336
80,254 68,712
322 318 307 330 328 328 312 324 326 339
70,258 74,032 93,250 71,718 71,716 68,163 89,011 66,783 63,700 61,500
2
3
feed, 5.8 grams H 0/hr + 2000 std cc N /hr; approximately 4 hrs duration; 300 psig; 850°C. 2
2
184
COAL
Table Ilia.
Catalyst N o catalyst Ca(OH) Ni 0 NiO Ni Fe 0 CuO Mn0 BaO Zr0 SrO Bi 0 Sb 0 MgO Pb0 Mo0 Ti0 Cr0 LiC0 2
2
3
3
4
2
2
2
3
2
6
2
3
2
3
v o Cr 0 2
3
5
2
3
Pb 0 B 0 A1 0 CoO Cu 0 3
2
4
3
2
3
2
GASIFICATION
Specific Rate of Gas Production
Expteriment No.
No. of Tests
Total Dry Gas Production Rate, Ni-Free Basis, std cc/hr/gram coal charged
300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325
3 3 3 3 3 3 3 3 3 3 3 2 2 3 3 3 3 3 3 3 3 3 3 3 4 6
297 345 359 373 366 380 385 375 395 377 392 390 391 384 400 380 380 378 439 367 374 400 394 380 383 385
° Test conditions, unit B: charge, 10 grams pretreated Bruceton coal, 0.5 gram catalyst;
850°C.
with the coal except for experiment 203. In experiment 203 a metal tubular insert was flame-spray coated with about 10 grams of unactivated Raney nickel, then inserted i n the coal bed. In experiment 200 the Raney nickel catalyst powder was activated or approximately 65% reduced by treatment with 2 % sodium hydroxide solution. In the reduced activated state, the catalyst was dried, mixed with coal, and charged into the unit under an inert atmosphere of nitrogen. Reaction time, at the desired reaction temperature, was held constant at 4 hrs. A n additional heat-up time of about 40 min was needed to reach the desired reaction temperature. Steam flow was not started until bed temperature exceeded 200°C. Conditions i n unit B were the same as i n unit A except that the steam rate was slightly lower at 5.0 grams/hr. Generally, tests were conducted in triplicate or higher replication. The average deviations i n carbon gasification rate determinations generally ranged from 1 to 5 % .
11.
HAYNES
E T
Catalysis at Elevated Pressure
AL.
185
Using Various Catalysts (Series B) ° Specific Production Rate of Constituent Gases, std cc/hr/gram coal charged #2
CO
147 180 189 194 189 195 201 193 202 192 203 200 201 199 210 202 197 194 228 188 184 205 203 196 201 203
37.7 32.0 43.9 52.0 53.6 60.3 56.3 45.7 48.9 57.8 48.2 63.9 63.6 48.4 52.7 45.0 48.9 52.5 64.9 47.7 58.6 57.2 61.0 54.6 48.6 53.1
C0
2
69.9 86.2 80.9 82.0 76.6 78.0 79.9 90.2 97.1 80.0 91.3 80.4 79.7 87.7 89.1 86.6 85.7 84.4 95.9 83.5 83.0 87.3 79.0 82.2 87.0 84.4
CH
CzH$
4
40.8 45.4 42.8 43.9 46.2 45.6 46.8 44.9 45.5 46.2 47.6 44.4 45.9 47.7 47.7 45.5 47.2 46.1 49.2 45.9 47.4 49.1 47.4 46.7 45.4 44.1
0.18 .09 .07
—
.17 .15 .12 .10 .13 .12 .15 .19 .19 .18 .08 .03 .33 .07 .19 .12 .57 .13 .05 .15 .25 .28
0.72 .63 .74 .94 .46 .49 .52 .79 .73 .88 .76 .72 .45 .72 1.00 1.09 0.68 .79 .57 .71 .57 .72 1.59 0.61 .43 .42
0.20 .12 .73 .22 .29 .27 .17 .10 .15 .05 .15 .15 .15 .30 .18 .30 .13 .07 .27 .20 .10 .15 1.32 0.13 .17 .14
0.24 .19 .50 .29 .27 .22 .07 .15 .13 .12 .15 .04 .15 .23 .23 .13 .23 .15
—
.12 .12 .13 .08 .09 .07 .13
feed, 5.0 grams H 0/hr plus 2000 std cc N /hr; approximately 4 hrs duration; 300 psig; 2
2
The experimental results of the screening tests conducted in unit A are presented in Tables H a and l i b , and for unit B they are given in Tables I l i a and I l l b . The specific gas production rates and gasification rates are based on the approximate 4-hr reaction time at 850°C. The results indicate that methane production rates as well as carbon gasifica tion rates can be increased significantly if certain compounds are ad mixed with the coal feed. The rate of carbon gasification for the uncatalyzed coal was about 10% higher in unit A than i n unit B (experiment 167 vs. 300). The slightly higher steam rate, with its correspondingly higher partial pressure of steam and higher gas phase diffusion rate, is suspected as the cause of the higher reaction rate in unit A . Because of this difference in absolute rates, the percentage increases achieved in gasification rates and gas pro-
186
COAL
Table Illb.
Catalyst N o catalyst Ca(OH) Ni 0 NiO Ni Fe 0 CuO Mn0 BaO Zr0 SrO Bi 0 Sb 0 MgO Pb0 Mo0 Ti0 Cr0 LiC0 V 0 Cr 0 Pb 0 B 0 A1 0 CoO Cu 0 2
2
3
3
4
2
2
2
3
2
5
2
3
2
3
3
2
5
2
3
3
4
2
3
2
3
2
a
GASIFICATION
Specific Rate of Liquid Production, Production Using
Experiment No.
Product Liquid, gram/hr/ gram coal charged
300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325
0.464 .447 .439 .422 .413 .396 .418 .406 .417 .405 .417 .415 .414 .391 .397 .438 .364 .398 .364 .402 .394 .410 .399 .424 .355 .363
Carbon Gasification Rates, gram/hi gram coal charged 81 88 92 97 96 100 99 98 104 99 101 102 102 100 103 96 99 99 113 96 102 105 104 99 98 98
X X X X X X X X X X X X X X X X X X X X X X X X X X
IO" IO" IO" IO" IO" IO" 10" IO" IO" IO" IO" IO" IO" IO" IO" 1010" 10IO" IO" IO" 10" 10IO" IO" IO"
3 3 3 3 3 3
3 3 3 3 3 3 3 3 3
3 3
3 3 3 3
3
3 3 3 3
Test conditions, unit B: charge, 10 grams pretreated Bruceton coal, 0.5 gram catalyst;
850°C.
duction rates resulting from additives were related only to rates obtained in the gasification of the uncatalyzed coal i n the same unit. Shown i n Table I V are the relative effects of 40 additives on the production of methane and hydrogen; Table V shows their relative effects on the pro duction of carbon monoxide and the gasification of carbon. The additives are listed i n decreasing order of per cent increased production. The corresponding reactor unit used (either A or B ) is also listed. Table I V shows that at standard test conditions all the additives listed except Z n B r increased methane production and that all the tested addi tives increased hydrogen production significantly. T h e sprayed Raney nickel catalyst increased methane production b y 24% and was the most effective material for promoting methane production. The next three 2
11.
HAYNES
E T
Catalysis at Elevated Pressure
A L .
187
Carbon Gasification, and Gaseous Heating Value Various Catalysts (Series B ) a
Unit Heating Value N -Free Product Gas, Btu/scf
Gaseous Heating Value Produced. Btu/hr/ft coal charged
350 339 344 340 349 345 344 333 328 344 337 340 343 342 339 339 342 340 334 341 345 342 355 342 336 336
51,300 57,700 60,960 62,700 63,100 64,800 65,500 61,700 64,050 64,200 65,200 65,500 66,200 64,900 67,000 63,800 64,200 63,400 72,400 61,900 63,700 67,600 69,200 64,300 63,800 63,900
2
z
feed, 5.0 grams H 0 / h r plus 2000 std cc N /hr; approximately 4 hrs duration; 2
2
psig;
300
materials ranking highest in promoting methane production were L i C 0 , P b 0 , and F e 0 with respective methane increases of 21, 20, and 18%. A comparison of the methanation activity of zinc oxide with that of zinc bromide indicates that the anion group of a catalyst can exert significant influence on the activity. As shown i n Table I V the alkali metal compounds were among the best promoters of hydrogen production. The per cent increases in hydro gen produced were 105, 83, 55, and 54%, respectively, with the addition of KC1, K 0 , L i C 0 , and N a C l . The sprayed Raney nickel was the third most effective promoter of hydrogen production, yielding a hydrogen increase of 6 3 % . Table V shows that the alkali metal compounds K C 0 , KC1, and L i C 0 gave the greatest increase i n carbon monoxide production as well as i n carbon gasification; the increase ranged from 40 to 9 1 % . 3
3
4
3
2
3
4
3
2
3
3
188
COAL
Table IV.
Increase in the Production of Methane and Hydrogen
Catalyst Raney nickel unactivated spray LiC0 Pb 0 Fe 0 MgO Pb0 SrO Ti0 Cr 0 B 0 CuO ZnO A1 0 Ni Zr0 Sb 0 Cr0 V 0 Raney nickel, unactivated mix BaO Mo0 NiCl -6H 0 Ca(OH) CoO NiS0 -6H 0 Mn0 NaCl Bi 0 NiO Cu 0 KC1 K C0 Ni 0 Raney nickel, activated mix Fe Sn0 ZnBr 3
3
4
3
4
2
2
2
3
2
3
2
3
2
2
5
3
2
6
3
2
2
2
4
2
2
2
3
2
2
3
2
3
2
2
GASIFICATION
Unit
Increase in CH
%
A B B B B B B B B B B A B B B B B B
24 21 20 18 17 17 17 16 16 16 15 14 14 13 13 13 13 13
A B B A B B A B A B B B A A B
12 12 12 11 11 11 10 10 9 9 8 8 7 6 5
A A A A
4 4 1 -3
Catalyst
h
KC1 K C0 Raney nickel, unactivated spray LiCO, NaCl Raney nickel, activated mix NiCl -6H 0 Pb0 ZnO Pb 0 SrO B 0 Cu 0 CuO BaO Sb 0 Mo0 CoO Bi 0 ZnBr MgO Ti0 NiS0 -6H 0 Fe 0 A1 0 NiO Cr0 Mn0 Zr0 Raney nickel, unactivated mix Ni 0 Ni Sn0 V 0 Cr 0 Ca(OH) Fe 2
3
2
2
2
3
2
4
3
2
2
5
3
2
3
2
2
4
3
4
2
3
2
3
2
2
2
3
2
2
5
2
3
2
Unit
Increase in H Produced,
A A
105 83
A B A
63 55 53
A A B A B B B B B B B B B B A B B A B B B B B B
46 43 43 40 39 38 38 38 37 37 37 37 37 36 35 35 34 33 33 33 32 32 31 31
A B B A B B B A
30 29 29 28 28 25 22 16
2
%
11.
HAYNES
E T
Table V .
Catalyst
Catalysis at Elevated Pressure
A L .
189
Increase in Production of Carbon Monoxide and Gasification of Carbon Increase Unit
in CO produced,
A A B B B B B B B B B B B B B B B B B B B B B B B B
91 81 72 69 69 62 60 55 53 52 49 45 42 41 40 39 38 30 30 29 28 27 21 19 16 15
A A A
8 8 7
A A A A
5 5 4 -3
A B A A
-4 -15 -21 -24
Unit
KC1 K C0 LiC0 NaCl Pb 0 BaO B 0 Pb0 Bi 0 Cr 0 Sb 0 ZnO SrO NiCl -6H 0 MgO Fe 0 CuO Zr0 Ti0 Cr0 A1 0 NiS0 -6H 0 Mn0 CoO Cu 0 Raney nickel, activated mix NiO Raney nickel, unactivated mix Ni Mo0
A A B A B B B B B B B A B A B B B B B B B A B B B
66 62 40 31 30 28 28 27 26 26 26 26 25 24 23 23 22 22 22 22 22 21 21 21 21
2
3
2
3
2
2
6
3
3
4
2
3
2
3
4
2
3
2
2
3
2
v o Mn0 2
5
2
Mo0 Ni 0 SrO Raney nickel, unactivated spray ZnBr NaCl Raney nickel, unactivated mix ZnO NiCl .6H 0 NiS0 -6H 0 Raney nickel, activated mix Ca(OH) Fe Sn0 3
2
3
2
2
2
4
2
2
2
in Carl Gasifit
A B
20 20
A B B B A B
19 19 19 19 17 14
A A B A
10 10 9 6
%
% K C0 KC1 LiCO, Bi 0 Sb 0 B 0 Fe 0 Cr 0 Zr0 Pb 0 CuO A1 0 Ni Cu 0 Pb0 Cr0 NiO BaO Ti0 CoO MgO
Increase
Catalyst
2
3
3
3
2
4
3
2
2
3
2
3
2
6
2
3
2
4
2
2
3
2
3
4
2
2
2
3
v o ZnBr 2
6
2
Ni 0 Raney nickel, unactivated spray Sn0 Ca(0H) Fe 2
3
2
2
190
COAL
GASIFICATION
N a C l gave a significant increase of 3 1 % i n carbon gasification but was much less effective i n increasing the production of carbon monoxide ( 7 % increase). 90 80 701— < £60
i
1
1—i
i
r
ONo catalyst ASprayed Roney nickel, activated A Sprayed Raney nickel, unactivated • Sprayed Raney nickel, charged wet Water rate: Solid line 5.8g/hr Broken line U6g/hr
10
600 650
_L
_L
J_
700 750 800 850 900 950 1,000 COAL BED TEMPERATURE, °C
Figure 2. Effect of temperature on methane production rate using sprayed Raney nickel. Test conditions: pressure, 300 psig; flow, 2000 std cc/hr N ; water, 5.8 and 1.16 grams/hr. 2
As shown i n Tables l i b and I l l b the unit heating values of the total product gases generally decreased if additives were mixed with the coal, but since the total gas make was increased, the total amount of fuel value produced as product gas increased. T w o methods of adding catalyst— by admixing with the coal or by coating the surface of an insert or carrier —may be compared for unactivated Ranel nickel catalyst (experiments 203 and 197). Admixing the catalyst with the coal provides better contact between coal and catalyst than does the insertion of catalyzed surfaces into the bed of coal. The superior contact achieved b y admixing the catalyst and coal is proved by the higher specific rate of carbon gasifica tion obtained by the admixed Raney nickel (unactivated) i n experiment 197 over that of sprayed Raney nickel (unactivated) i n experiment 203 (Tables H a and l i b ) . This is further confirmed analytically by the larger amount of carbon left i n the residue with the sprayed Raney nickel catalyst. Table H a indicates that the Raney nickel (unactivated) catalyst was more effective i n promoting methane production when sprayed on a
11.
HAYNES
E T
AL.
Catalysis at Elevated Pressure
191
surface than when it was admixed with the coal charge. Apparently the process of methane synthesis from C O and H was more effectively pro moted by the sprayed Rany nickel (unactivated) catalyst. Another pos sible reason for the greater production of methane with the sprayed Raney nickel (unactivated) catalyst is that the poorer contact between coal and catalyst resulted in less reforming of methane and other hydro carbons. Hydrogen production was also greater when the sprayed Raney nickel (unactivated) catalyst was used than when Raney nickel (un activated ) was admixed with coal. 2
600
650
700 750 800 850 900 COAL BED T E M P E R A T U R E , ° C
950
1,000
Figure 3. Effect of temperature on specific production of hydrogen, using sprayed Raney nickel. Test conditions: pressure, 300 psig; flow, 2000 std cc/hr N ; water, 5.8 and 1.16 grams/hr. 2
Effect of Temperature and Steam Rate. Gasification experiments similar to the standard tests were conducted in unit A except that the reaction temperatures were varied from 650° to 950°C and steam rates used were 1.16 and 5.8 grams/hr. The catalyst used was flame-sprayed Raney nickel 65% activated. Also, tests were conducted at 750°C and 1.16 grams/hr steam rate with sprayed Ranel nickel activated and charged wet and at 850°C and 5.8 grams/hr steam rate with sprayed Raney nickel unactivated. Results of these experiments are in Figure 2 3, 4, 5, and 6 where production rates of methane, hydrogen, carbon monoxide, carbon gasifica?
COAL
GASIFICATION
Figure 4. Effect of temperature on carbon monoxide production rate using sprayed Raney nickel. Test conditions: pressure, 300 psig; flow, 2000 std cc/hr N ; water, 5.8 and 1.16 grams/hr. 2
oNo
catalyst
COAL
BED TEMPERATURE, °C
Figure 5. Effect of temperature on carbon gasification rate using sprayed Raney nickel. Test conditions: pressure, 300 psig; flow, 2000 std cc/hr N ; water, 5.8 and 1.16 grams/hr. 2
11.
HAYNES
E T
A L .
Catalysis at Elevated Pressure
193
tion, and production of total dry gas, respectively, are shown. A t the temperatures and steam rates shown i n these figures the presence of the sprayed Raney nickel insert has resulted i n a higher production of nearly all the major gases and i n a higher carbon gasification than that achieved without catalysts. One exception is methane production with the activated sprayed Raney nickel at 850° and 950°C for 5.8 grams/hr steam rate (Figure 2) when methane production was greater for the uncatalyzed reaction than for the catalyzed reaction. However, a 6% increase i n methane production was achieved at 850°C and 5.8 grams/hr steam rate when the unactivated sprayed Raney nickel was used as compared with the experiment when no catalyst was used (Figure 2 ) . The other excep tion is the production of carbon monoxide at 950°C and 1.16 grams/hr steam rate (Figure 4 ) . In this case, carbon monoxide production was 5 % lower for the catalyzed reaction than for the uncatalyzed reaction.
LiJ r-
< °-
-D
O ? i s cr o °~ o> 00
-C
O to
600
650
700 750 800 850 900 950 1,000 COAL BED TEMPERATURE , °C
Figure 6. Effect of temperature on total dry gas production rate using sprayed Raney nickel. Test conditions: pressure, 300 psig; flow, 2000 std cc/hr N ; water, 5.8 and 1.16 grams/hr. 2
In general the effectiveness of the catalyst decreases as temperature is increased. F o r example, the increases achieved i n carbon gasification and i n total gas production attributable to the catalyst became smaller as the reaction temperature increased from 750° to 950°C (Figures 5 and 6 ) . In the 5.8 grams/hr steam rate tests, the carbon gasification rate at 750°C was increased by 0.017 gram/hr/gram coal charged for a 33% increase whereas at 950°C the increase i n carbon gasification was negligible at an
194
COAL
GASIFICATION
Figure 7. Effect of catalyst service time on gas production rates. Test conditions: temperature, 750°C; flow, 2000 std cc/hr N and 1.16 grams/hr water. 2
increment of 0.001 g r a m / h r / g r a m coal charged. Similarly, total gas pro duction was increased 43% at 750°C and 10% at 950°C. As shown by the gas production and carbon gasification rates in Figures 2-6, for reaction temperatures of 750°C and higher, the higher steam feed rate of 5.8 grams/hr resulted in significantly higher reaction rates and in larger increases in such rates caused by catalysis as compared with those achieved at the lower steam feed rate of 1.16 grams/hr. In the case of the lower steam feed rate, it is possible that much of the potential increase in reaction rate attributable to catalysis may have been masked because of a low diffusion rate in the gas phase. Repeated Use of Sprayed Raney Nickel Catalyst. T o determine the stability of sprayed Raney nickel catalyst, a single insert flame sprayed
11.
HAYNES
E T
AL.
Catalysis at Elevated Pressure
195
with Raney nickel catalyst was subjected sequentially to four gasification tests at 750°C, 300 psig, and a steam rate of 1.16 grams/hr. A fresh charge of coal was used in each run. Duration of each run was 4 to 5 hours. The resulting gas production rates are shown in Figure 7; also shown is the base case with no catalyst inserted in the bed. Gas production rates in Figure 7 indicate that the activity of the sprayed Raney nickel catalyst insert decreased rapidly with use. The gas production of the fourth test (17.8-hr service) was only about 10% greater than that obtained when no catalyst was used. Extrapolation of the total gas production rate as a function of accumulated service time on one catalyst insert indicates that the catalyst insert would be com pletely ineffective after about 20 hours of operation. Considerable flakingoff of the catalyst is apparent; thus the need is indicated for an effective bonding agent or alloying substance that w i l l increase the physical dura bility of the catalyst. Sulfur compounds gasified from the coal are also suspected of poisoning the nickel catalyst and resulting in the decline in activity with time. Effect of Extent of Gasification Time. Tests were conducted to determine whether catalysts remain effective as the extent of gasification increases. Sprayed Raney nickel inserts and C a O powder were sub jected to the standard test conditions of 850°C, 300 psig, 5.8 grams/hr steam rate but with gasification times varying from 2 to 8 hrs. The abridged results in Table V I show that although the overall rate of gasifi cation decreases with extent of gasification or with gasification time, the catalysts tested still generally increased the rate of carbon gasification and the rate of gas production, as indicated by C H production, over that achieved with no catalyst. 4
Effect of Residues from Catalytic Gasification. The catalytic effec tiveness of ash residues (some contain either residual K C 1 or K C 0 ) from total gasification operations were tested and compared with the effectiveness of the fresh additive, K C 0 and KC1. The gasification residues were prepared by nominally complete steam-gasification of coal in a 1-inch diameter electrically heated, vertically mounted stainless steel reactor. The coal charge consisted of 70 grams of pretreated Rruceton coal plus 3.5 grams of admixed catalyst; the charge was gasified at 950° to 970°C and atmospheric pressure using a steam feed rate of 45 grams/ hr. The preparatory gasification step was stopped whenever the flow of dry product gas appeared to cease. Carbon and ash content of the pre treated coal and of residues after total gasification and residue analyses are presented in Table V I I . The ash analyses show that ash from the catalyzed coals contained significantly larger amounts of potassium than did the ash of uncatalyzed coal. 2
2
3
3
196
COAL
Table VI.
Effect of Extent of Gasification CH± Production
Gasification Time, hr
2 53.3 cc/hr/gram 28.6 cc/hr/gram 56.9 cc/hr/gram 30.7 cc/hr/gram 7% 7%
Rates with no catalyst Rates with C a O Increase caused by C a O Rates with sprayed Raney nickel catalyst Increase caused by Raney nickel 1
GASIFICATION
70.9 cc/hr/gram 38.3 cc/hr/gram 34% 33%
Unit A: temperature, 850° C; N flow, 2000 std cc/hr; steam rate, 5.8 grams/hr. 2
Table VII.
Carbon, Ash Content, and Ash Analysis of Experiment No.
Charge coal Residues no catalyst K C0 KC1 2
3
Carbon and Ash Content, % Carbon
C-l
74.3
D-l D-2 D-3
1.67 0.47 4.7
Ash 10.6 98.9 99.9 95.1
AW
CaO
3
25.9
1.7
25.1 19.7 22.2
1.6 1.1 1.3
° Gasification conditions: charge, 70 grams pretreated Bruceton coal, 3.5 grams of
Table VIII.
Specific Production and Gasification Rates Resulting from Total Dry Gas Production Rate, Residue N -Free Basis, Charged std cc/hr/gram No. grams Coal Charged 2
Experiment No. of No. Tests N o catalyst Catalyst-free residue K C0 K C 0 residue KC1 K C 1 residue 2
3
2
3
167 220 218 221 212 222
Experiment No. N o catalyst Catalyst-free residue K2CO3
K 2 C O 3 residue
KC1 K C 1 residue
167 220
218
221
212 222
6 3 3 3 3 3
D-l
1.12
D-2
1.41
D-3
1.26
Product Liquid, gram/hr/gram Coal Charged 0.478 .449 .494 .487 .480 .469
331 344 578 398 615 370
Carbon Gasification Rates, gram/hr/gram Coal Charged 89 88 144 104 148 104
X X X X X X
10~ 10IO101010-
3 3 3 3 3 3
Standard test conditions, unit A: 10 grams pretreated Bruceton coal, 0.5 gram catalyst 4 hrs duration; 300 psig; 850°C. 0
11.
HAYNES
Catalysis at Elevated Pressure
E T A L .
Time on Overall Effectiveness of Catalyst
197
0
Carbon Gasification 0.087 gram/hr/gram .090 gram/hr/gram 3%
0.062 gram/hr/gram .062 gram/hr/gram 0%
.093 gram/hr/gram 7%
.063 gram/hr/gram 2%
Pretreated Bruceton Coal and of Residues from Total Gasification
0
Mineral Analysis of Ash, % MgO
P 0
10.8
0.9
