312
Ind. Eng. Chem. Process Des. Dev. 1980, 19, 312-317
Mnj = transformation matrix from jth input to ith output stream of nth subsystem p = pressure of a stream, kg/cm2 Q,, = waste heat in nth subsystem, kcal/h R, = linear inequality constraints of nth subsystem S = entropy of a stream, kcal/kg K S', Sf0= a state and the dead state of a stream T = absolute temperature of a stream, K To = environment temperature, K V = volume of a stream, m3 W = work generated at nth subsystem, kcal/h X,,, = jth input stream vector of nth subsystem X,,, = flowrate of jth input stream of nth subsystem, ton/h or kcal/h &,jk = kth component of jth input stream of nth subsystem, ton/h X E = amount of energy input, ton/h Z,,, = ith output stream vector of nth subsystem bnlrnL= structure variable implying that a flow enters from ith stream of mth subsystem into jth stream of nth subsystem 61 = basic system structure of steam-power system
6 , = structure variable indicating turbine allocation = chemical potential of a stream, l-cal/kg
Literature Cited Itoh, J., Niida, K., Shiroko, K., Umeda, T., Kagaku Kogaku Ronbunshu, 5(1),
l(1979). Keenan, J. H., Mech. fng., 195 (Mar 1932). Nishio, M., Ph.D. Thesis, the University of Western Ontario, London, Ontario, Canada, 1977. Nishio. M., Johnson, A. I.."Optimal Synthesis oi Steam and Power Plant", Proceedings, p 716,The Second PACHEC, Denver, Colo., 1977. Umeda, T., Itoh, J., Shiroko, K., "Heat Exchange System Synthesis by Thermodynamic Approach", Proceedings, p 1216,The Second PACHEC, Denver, Colo., 1977; Chern. f n g . Prog., 74(7),70 (1977). Umeda, T., Niia, K., Shiroko. K.. "A Thermodynamic Approach to Heat Integration in Distillation Systems", presented at the 85th National Meeting of AIChE, Philadelphia, Pa.. June, 1978.
Received for review June 4, 1979 Accepted December 31, 1979 Work was presented at 14th Intersociety Energy Conversion Engineering Conference, Boston, Mass., Aug 1979.
Wood Gasification in a Fluidized Bed Steven R. Beck' and Maw Jong Wang Department of Chemical Engineering, Texas Tech University, Lubbock, Texas 79409
Gasification of oak sawdust in the Synthesis Gas From Manure (SGFM) pilot plant at Texas Tech University has been evaluated. The SGFM reactor operates as a countercurrent fluidized bed in which a biomass feedstock is fed to the top of the reactor and is fluidized by an air-steam mixture fed to the bottom of the reactor. Using oak sawdust from Missouri as the feedstock, the gas yields were 1.1 to 1.4 L l g daf feed when the average reactor temperature was 600 to 800 OC. The gas contaiped about 4 % CpH4and 11 % CH4. The gross heating value of the gas exceeded 1 1.2 MJ/m3 in all cases. The gasification of wood is compared to previous results obtained for cattle manure. The differences are due to the relative amounts of cellulose, hemicellulose, and lignin in the feedstock.
Introduction Wood is one of the oldest energy sources known to man. It has been used for thousands of years to provide heat and light. When liqliid and gaseous fossil fuels were discovered, the use of wood diminished because of the inconvenience associated with collecting, distributing, and using wood. Due to the d.ecreasing supply and increasing costs of fossil fuels, wood and other biomass feedstocks are once again being utilized as an energy source. For example, the forest products industry obtains nearly half its energy from wood residues (Tillman, 1978). Most of this is from spent liquor in the pulp and paper industry. Del Gobbo (1978) reported that forestry residues represent 4.2 Quads of available energy a t present. One method to minimize the inconvenience associated with wood is to convert it to a combustible gas by pyrolysis. Glesinger (1949) reports that wood pyrolysis was first performed in 1792 by Robert Mudoch. Since then wood has been used to produce a variety of fuels and chemicals. Recent interest in wood conversion processes has been increasing due to the desire to develop renewable energy resources and reduce the dependence on imported fossil fuels. The Synthesis Gas From Manure (SGFM) process was developed at Texas Tech [Jniversity in response to a local 0196-4305/80/1 t 19-0312$01.00/0
problem on the High Plains of Texas. Large amounts of cattle manure from feedlots present a serious disposal problem. The SGFM process was designed to produce ammonia synthesis gas from manure. Ammonia was chosen as the desired product because it is in high demand as a fertilizer in the agricultural region where the feedlots are located. It was also found that significant quantities of ethylene were produced in the SGFM process. The SGFM process has been described by Halligan and Sweazy (1972), Halligan et al. (19751, and Beck et al. (1979). The heart of the process is a countercurrent, fluidized bed reactor. The biomass feedstock is fed to the top of the reactor and falls countercurrently to the steam and product gas in the reactor. This provides some flash drying of the cold feedstock in direct contact with hot product gas. Air and steam are introduced a t the bottom of the reactor to partially combust the solids and fluidize the bed. The advantage of this system is that fresh feed enters the pyrolysis zone of the reactor and does not encounter an oxidizing atmosphere. This results in the formation of significant amounts of olefinic hydrocarbons. These quickly exit the reactor and are quenched before they can decompose to lower molecular weight compounds. As a result, the gas produced in this process has a higher heating 1980 American Chemical Society
Ind. Eng. Chem. Process Des. Dev., Vol. 19, No. 2, 1980 313 Table I. Mass Balance for Dry Sawdust (4% H,O) run no. 38
39
40
7.26 3.63 3.18
8.62 5.72 2.72
8.62 5.35 2.77
11.34 4.22 2.95
13.15 4.22 3.99
10.43 3.45 3.63
13.15 2.40 3.63
total output, kg/h product gas aqueous waste tar cyclone fines char
14.07
17.06
16.74
18.51
21.36
17.51
10.88 2.40 0.14 0 0.05
6.89 8.21 0.54 0 0.05
12.29 2.49 0.18 0 0.23
14.61 3.04 0.14 0.82 0.05
17.24 5.81 0.18 0.09 0
15.20 2.09 0.27 0.05 0.45
total material balance closure, % average reactor temperature, "C
13.47
15.69
15.19
95.7
92.0
90.7
input, kg/h sawdust air steam
41
43
44
45
49 10.43 3.63 4.99
8.16 3.63 3.63
19.18
19.05
15.42
17.46 1.63 0.54 0.05 0.18
14.15 3.58 0.05 0.14 1.32
12.79 0.68 0.09 0.09 0.05
----- ~
699
504
668
value than that produced in other air-blown gasifiers. A disadvantage of this mode of operation is that the product contains some tars. The concept of p:yrolysis a t very high heating rates has been employed to produce liquids from municipal solid waste by Occidental Petroleum Co. (Garrett, 1972) and ethylene for production of synthetic gasoline (Diebold, 1979). The key to producing hydrocarbons is to have very high heating rates and short fluid residence times in the reactor. Nikitin (1966) and Shafizadeh et al. (1973) have also reported on the significance of the fluid residence time in the reactor. The results reported by Beck et al. (1979) for manure gasification indicate that a medium calorific gas can be produced in the air-blown SGFM reactor. The evaluation of wood as a feede,tock was initiated to determine the applicability of this process to other types of cellulosic feedstocks.
Experimental Studies SGFM Pilot Plant. The SGFM pilot plant a t Texas Tech was described in detail by Beck et al. (1979). The reactor capacity is 20 kg/ h of solid feed. A schematic of the pilot plant is shown in Figure 1. Organic tars are condensed and separated from the gas prior to condensation of the steam. The electric heaters on the reactor are provided to reduce the heat losses. As will be discussed later, a commercial reactor would have a much lower surface-to-volume ratio and, as a result, no external heat source would be required. Analytical Procedure. The gas samples were analyzed using a Carle Modell AGC-111H gas chromatograph. This chromatograph uses helium as the principal carrier gas and is equipped with dual thermal conductivity detectors (TCD). All gas components except hydrogen are measured in the helium. The hydrogen is transferred to a nitrogen carrier through a silver-palladium diffusion tube and measured in a separate TCD. This hydrogen transfer system allows one io achieve a sensitive, linear response from the TCD for hydrogen with no peak reversals. The system was calibrated with a certified standard mixture prepared by Matheson Gas Products Co. Moisture content of the feed was determined by drying the sample in an air atmosphere a t 104 " C for 24 h. The ash content was obtained by heating the sample in an air atmosphere a t 1000 "C for 24 h. Feed Material. The feedstock used in this study was oak sawdust from a lumber mill in Missouri. The as-received sawdust contained 39% moisture and 0.7% ash on
-18.66
23.32
18.06
50
-
19.06
19.24
100.8
109.2
103.1
103.5
101.0
605
631
707
680
692
-
13.70 88.8 780
SOLID FEED
INERT PURGE GAS
-";. \
Lc?JE
VENT
7
H20 OU,'
TAR IMPlNGERS
CONDENSER
VENT
CYCLONE FINES
TURBINE METER
I POWER
AQUEOUS WASTE
Figure 1. SGFM pilot plant. Table 11. Mass Balance for Wet Sawdust (45% H,O) run no. 54
55
56
57
6.35 4.76 1.41
6.35 5.03 1.22
6.35 5.03 0
8.85 5.26 0
12.52
12.60
11.38
14.11
3.90 8.12 0.59 0.14 0.27
4.58 5.90 0.54 0.09 0.14
7.53 2.27 0.18 0.05 0.18
7.76 4.67 0.54 0.09 0.59
11.25
10.21 89.7
13.65 96.7
N
input, kg/h sawdust air steam total output, kg/h product gas aqueous waste tar cyclone fines char total
13.02
material balance closure, % average reactor temperature, " C
104.0
728
89.3
752
760
727
a wet basis. For runs 38 to 50, the sawdust was air-dried to 4 % moisture. For runs 53 to 57, the dry sawdust was rewetted to 45% moisture. For all runs, the sawdust was screened to -0.32 cm to minimize feeding problems. Discussion of Results Gas Yield and Composition. Tables I and I1 show the material balance data for dry sawdust and wet sawdust, respectively. The material balance closure shows that in all runs the unaccounted for material was less than 11%.
-
314
Ind. Eng. Chem. Process Des. Dev., Vol. 19, No. 2, 1980
Table 111. Proximate Analysis of Manure, Mesquite, and Sawdust
moisturea volatile materiala ash contenta
OAK SAWDUST
a
/A'
/
/
I
/
Weight percent.
manureb
mesquiteb
sawdust
14.8 70.7 14.5
8.9 88.5 2.6
4.0 95.0 1.0
From Lin (1978).
MANURE (Beck, et at., 19791
1.8
56 0
P U
; 1.5 V
57
E 0.3 I
I
I
620
660
I 700
I
I
740
780
Average Reactor Temperature, 'C
... 3
0
1.2
55
V. -
; Y)
Figure 2. Product gas yield from dry sawdust.
d-
54
0.9
0
m
1
The major cause of the error in material balance is that the product tar is difficult to collect and probably precipitates or condenses with other material on pipe walls. Another contributing factor is due to variations in the feed rate. T o determine an average feed rate, the mass of the solid in the feed hopper before and after each run was obtained. This was marginally successful because the feed ceased occasionally due to bridging. Therefore, the feed rate was determined after each run by setting the same feeder speed. Because the variations in the bulk density of the solids were sufficient to cause 5-10% differences in mass feed rate a t a given feeder speed, there were a t least two feed rates determined a t each feeder speed and the average feed rate used. The deviations were less than 10%. The gas produced in the SGFM process can be used as fuel, but is probably of more value if it is used for chemical synthesis. Therefore, the composition of the gas is as important as the total yield. As expected, the product gas was composed of H2, CO, C02, CHI, CzH4,C2H6,and N2. Methane and ethylene are the starting materials for hundreds of different chemical products. The production of ethylene is of significant practical interest because the current sales value is 22-25 cents/kg and one major manufacturer indicates that a 44 cent/kg price may evolve by the early 1980's (Wishart, 1975). Using an ethylene yield of 0.5 L/g daf (dry, ash-free) sawdust and the above current price, the ethylene in the synthesis gas has a sales value of $11-$14 per metric ton daf sawdust. The current data show that up to 80 kg of C2H, per metric ton daf sawdust (-0.067 L/g daf) can be produced. Carbon monoxide and hydrogen are raw materials for many synthesis reactions. Carbon monoxide can be equated to hydrogen because carbon monoxide can be shifted to hydrogen by the water gas reaction as shown below. CO + H2O + H2 + C02 Figure 2 shows the total gas yield from dry sawdust (4% moisture) compared with that of the manure runs reported by Beck et al. (1979). As expected, the total gas yield from sawdust is greater than that from manure. Sawdust contains more volatile material than manure (see Table 111) and contains no protein, no fat, and its fiber is a mixture of cellulose (43%), hemicellulose (35%), and lignin (22%). The fiber, especially cellulose, is decomposed more easily than protein and fat. The manure was from green
+ 0.6
0.3 620
660
700
740
780
Average Reactor Temperature, 'C
Figure 3. Product gas yield from wet sawdust.
roughage feeding cattle, contains protein (16.2%), fat (7.5%), fiber and nitrogen-free extract (76.3%). The fiber and nitrogen-free extract can be taken as a mixture of cellulose, hemicellulose, and lignin (Grub, 1969; Morrison, 1959; Crampton and Harris, 1969), but there were no exact data reported. It is assumed that much of the cellulose and hemicellulose in the cattle feed has been digested by the cow. As a result, cattle manure is high in lignin and low in cellulose when compared to wood. Previous studies by Stamm (1956) show that hemicellulose and cellulose gasify a t a much higher rate than does lignin. Therefore, materials such as wood, which are high in cellulose, will produce more gas than cattle manure which is low in cellulose. Shown in Figure 2 is a regression analysis of gas yield as a function of average reactor temperature. This function has a least-square correlation coefficient of 0.891. If the total gas yield of sawdust is assumed to depend on both the average reactor temperature and the ratio of air to dry, ash-free feed, a multiple regression analysis of the data gives the following equation Y = -0.16636 + 0.0020265X, + 0.27803X2 where Y = total product gas yield, L / g daf feed, X , = average reactor temperature, "C, and X 2 = kg of air/kg daf of feed. The multiple correlation coefficient in this case is 0.945. It is a better correlation (significant a t a = 0.0005 level) than that using temperature as the only variable (significant a t a = 0.005 level). Figure 3 shows the total product gas yield from wet sawdust (45% moisture). Runs 56 and 57 were made with no steam injected into the reactor. This resulted in a higher gas yield than runs 54 and 55 which were made with steam injected. The reason for this is not clear, but might be attributed to bed expansion and solids residence time. Runs 54 and 55 were a t a higher ssuperficial gas velocity than runs 56 and 57. This would create a higher void
Ind. Eng. Chem. Process Des. Dev., Vol. 19, No. 2, 1980 315
p U r
. 6 D
0.4
D
I
i
2- 0 3 a
> VI
d
5
02
m
e D
I
0.1
0.0
0.00
660
620
700
740
780
Average Reactor Temperature, 'C
x v
0.5
4 5 49
k
,,y
a
i
J
2-
04
I
I
700
740
I
780
Table IV. Superficial Gas Velocity in the Bottom of Reactor
06
.
I
660
Figure 6. Hydrocarbon yield from dry sawdust.
A co e co,
;
I
620
Average Reactor Temperature, "C
Figure 4. Hydrogen yield from dry sawdust.
L
L
/
--
50
A
run
U , cm/s
run
U , cm/s
38 39 40
14 24 26 21 25 23 20
49 50 54 55 56 57
27 21 22 22 16 16
41 43 44 45
$4
/
> 0" 0 U
0.3
m 0 0
0.2
0.1
I 620
I I I 660 700 740 Average Reactor Temperature, "C
I
780
Figure 5. CO and CO1yield from dry sawdust
fraction and possibly a lower solids residence time, although these parameters were not measured. The lower residence time would result in lower conversion to product gas. These results also indicate that the steam-char reaction did not occur. Rensfelt et al. (1978) and Garrett (1977) report that the reaction temperature must exceed 860 "C in order for the steam-char reaction to be significant. In this study, the reaction temperatures were less than 800 "C and consequently the steam-char reaction does not occur. The yields of individual gas components from dry sawdust are plotted against average reactor temperature in Figures 4 to 6. From these figures it can be seen that the compositions for each component follow a clear trend. Carbon dioxide and ethane decrease slightly as the average reactor temperature rises while the other components, hydrogen, carbon monoxide, methane, and ethylene, increase as average reactor temperature rises. The rapid increase in CO yield with reactor temperature is probably due to an increase in carbon conversion and steam reforming of higher hydrocarbons. Carbon dioxide is produced by the initial fragmentation of cellulose and is not strongly affected by temperature in a kinetically controlled
system such as this. The slight decrease of the ethane curve and the sharp increase of the methane curve suggest that high temperature cracking of ethane and higher hydrocarbons (C,+) might have been taking place in the reactor. From Figure 5 it can be seen that the trend of the gas yields of CO and C 0 2of run 38 was in reverse to the other runs, which indicates that combustion was the dominant reaction which occurred. This is due to the high air-towood ratio and low gas velocity in the bed. Table IV shows the superficial gas velocity at the distributor. These were calculated from the inlet air and steam rates and the temperature a t the distributor. Energy Balances. Energy balances required additional studies beyond mass balance results because the reactor system heat losses had to be determined independently. The reactor was insulated with 7.6 cm of Cerapak, manufactured by Johns-Manville, and 2.5 cm of fiberglass manufactured by Owens Corning. To determine the heat losses from the reactor, a mixture of steam and air was fed to the reactor without any solids flow. The heaters were on full power during these tests. The average reactor temperature, the surface temperature of the insulation, and the ambient temperature were measured along with the inlet and outlet enthalpy of the stem-air mixture. A correlation of heat loss as a function of the temperature difference between the reactor and ambient air was determined as shown in Figure 7. During the gasification tests, the temperature and pressure of the inlet air-steam mixture, sawdust, and the outlet product gases were measured. The temperature difference between the average reactor temperature and the ambient temperature was also measured to determine the heat losses. Using the data shown in Figure 7, a convective heat transfer coefficient corrected for radiant losses was cal-
316
Ind. Eng. Chem. Process Des. Dev., Vol. 19, No. 2, 1980
B
2600
200
LL
1
I
I
I
2400
-fm 2
2200
5
c
2
$
/
2000
iz
3U
I 4I
1800 Y = 75.27 + 3.979X BY LEAST SQUARE REGRESSION
50 O0.0
02
04
06
KG A i r / K G daf Feed 400
500
600
700
i A v g Reactor Temp - Room Temp
'C
Figure 7. Experimental heat loss data for SGFM reactor.
culated. The average, convective heat transfer coefficient was 6.8 W/m2 "C f 15% which is within acceptable engineering limits, considering the nonuniformity of insulation, estimated radiation losses, and conduction losses through connecting piping and superstructure. Using the correlation presented by McAdams (1954) for natural convection to air, the convective heat transfer coefficient was estimated to be 5.8 W/m2 "C f 15%. A general energy balance was performed for each run in order to determine the net heat of reaction a t 25 " C . The time, voltage, and current to the heaters were measured in each material balance period to calculate the heat supplied by the heaters. The enthalpy changes for the product gases were measured by the temperature differences between the temperature at the top of the reactor and the temperature in the sample loop section. The heat capacities of the organic liquids were estimated by the additive contribution method of Johnson and Huang (1955). A complete analysis of the tar and aqueous waste was not available. For the cattle manure runs, Beck et al. (1979) reported that the tar contained mostly long-chain fatty acids and some polyaromatic hydrocarbons. The aqueous waste contained water, long-chain fatty acids (which had not been removed by the impingers), shortchain (C,-C,) carboxylic acids, and aromatic hydrocarbons. Based on the assumption that the long-chain fatty acid is CH3(CH2)&OOH, the additive-contribution method by Johnson and Huang (1955) gives a heat capacity of 0.8 cal/g "C for tar and aqueous waste. For char and cyclone fines, the heat capacities are calculated by the relation presented by Clendenin (1949) C, = 0.20 + 0.00088t + 0.0015V where C is expressed as Btu/b OF (ash-contained basis), t is in and V is weight percent volatile matter. The net heat of reaction as a function of air feed rate is shown in Figures 8 and 9 for dry and wet sawdust, respectively. Using a least-squares correlation, these values were extrapolated to find the net heat of reaction at a zero air-to-wood ratio. This is assumed to be the net heat of pyrolysis in the absence of oxygen. These results indicate that the overall pyrolysis reaction with dry sawdust is mildly exothermic with a heat of reaction of about -120 cal/g daf material converted. The heat of pyrolysis for the wet sawdust is endothermic with a heat of reaction of about 180 cal/g daf material converted. This is consistent with the results reported by Coffman (1978).
"6.
Figure 8. Net heat of reaction of dry sawdust as a function of air-to-wood ratio.
I
I
10
125
5 150 c U
1
I
I
1
1e a -. 1 0
% I
1.5
1.75
2.0
KG AiriKG daf Feed
Figure 9. Net heat of reaction of wet sawdust as a function of air-to-wood ratio.
If one examines the overall net heat of pyrolysis between wet sawdust (45% moisture) and dry sawdust (4% moisture), the difference is 300 cal/g daf feed. It is found that this is the energy required to vaporize the water contained in sawdust with 35% moisture. For run 54 to run 57 the star feeder did not function properly, which allowed hot air to enter the feed hopper during reactor heatup. As a result, one would expect that when the wet sawdust (45% moisture originally) was fed to the reactor, the moisture content of the wood would be less than 45%. Unfortunately, a sample of this feed could not be collected, but it is felt that it is possible to dry the wet sawdust from 45% moisture content to 35% moisture content in the feed hopper. The heat balance results do show, in general, that the SGFM partial oxidation can be considered to be autothermal if proper and efficient heat exchange can be accomplished between the inlet and exit streams with minimum heat losses. If one assumes that the permanent heat losses are 10% of the total heat out of the reactor and that 80% of the remaining sensible heat in the product gases can be recovered in a usable form, one can project the energy required to operate a commercial reactor. The results of such a calculation are shown in Table V. This remaining sensible heat can be recovered by using two heat exchangers and a fluidized bed dryer to preheat the steam and air and to dry the sawdust feed. These calculations show that a net increase in enthalpy is achieved during the reaction and thus the commercial reactor could be operated autothermally. This excess heat would be available to vaporize additional moisture in the feed so that a feed containing a much higher moisture content (up to 18%) could be reacted autothermally. Huffman et al. (1977)
Ind. Eng. Chem. Process Des. Dev., Vol. 19, No. 2, 1980
Table V. Calculatioins Showing Autothermal Character of SGFM Reactor run no. input, kcal /h sawdust (4% H,O) air steam total o u t p u t , kcallh steam gases char + fines tar + liquids total 10% heat losses o f o u t p u t 80% recovery of remaining heat new output-input AHv, water, kcal,lkg potential added water, kg/h potential moistu.re content, %a
43
44
0 560 2890
0 560 2770 3330
3450 3220 1860 20
1580 -6680
- 668 4810 1360 540 2.5 19.4
2870 1950 90 690
5600
- 560 4030 700 540 1.3 14.7
a (potential added ,water t original water)/(sawdust t potential added water) x 100.
reported that for cattle manure using the same SGFM reactor the moisture content of the feed could be as high as 50% even with the assumed losses. The major discrepancy between those studes was caused by the heat balance calculation. In this study the enthalpv change instead of the heat of combustion was used for product gases, organic water, tar, char, and cyclone fines. These estimates do not mean that external heat would not be necessary. Instead the results suggest that external heat duty could be kept to a minimum. Conclusions Based on the results of this study, it was concluded that gas yields from oak sawdust in the SGFM pilot plant are significantly higher than for cattle manure. The heating value of the raw gas is greater than 11.2 MJ/m3 in all cases. This study confirmis that the pyrolysis of dry sawdust is an exothermic reaction. As was observed with cattle manure, the SGFM process produces significant quantities of ethylene from oak sawdust.
317
Acknowledgment The authors wish to thank the U S . Department of Energy (Contract No. EY-76-S-04-3779) for supporting this work. We also wish to thank the Texas Cattle Feeders Association, Pioneer Corporation, and the Enviroiimental Protection Agency for fuiiding the early phases of this work which permitted us to develop the process to the point where it is now. Literature Cited Beck, S.R., Huffman, W. J., Landeene, B. C., Halligan, J. E., Ind. Eng. Chern. Process D e s . D e v . , 18, 328 (J979). Crampton. E. W., Harris, L. E., Applied Animal Nutrition", 2nd ed, W. H. Freeman and Co., San Francisco, CA, 1969. Del Gobbo, N., "Fuels From Biomass Systems Program Overview", Proceedings of the Second Annual Symposium on Fuels From Biomass, W. W. Schuster, Ed., Troy, NY, June 20-22, 1978. Diebold, J. P., Smith, G. D., "Thermochemical Conversion of Biomass to Gasoline", 3rd Annual Biomass Energy Systems Conference, Golden, CO, June 5-7, 1979. Garrett, D. E., "Factors in the Energy Efficiency of Biomass Processing and Disposal", 70th Annual AIChE Meeting, New York, NY, Nov 16, 1977. Garrett Research and Development Co., Inc., "Technical Report On The Garrett Pyrolysis Process for Recycling Municipal Solid Waste", GRBD Report 720228, Dec 29, 1972. Glesinger, E., "The Coming Age of Wood", Simon & Schuster, New York, 1949. Grub, W., "Animal Waste Management", conference at Cornell University, Ithaca, NY. 1969. Halligan, J. E., Herzog, K. L., Parker, H. W., Ind. Eng. Cbern., Process Des. D e v .,. I.d,. 64-69 ~. . .. (1975). > - -, Halligan, J. E., Sweazy, R. M., "Thermochemical Evaluation of Animal Waste Conversion Processes. Texas Tech University, Lubbock, TX", 72nd National Meeting, AIChE, St. Louis, May 21-24, 1972. Huffman, W. J., Peterson, R. L., Halligan, J. E., "Ammonia Synthesis Gas Generation From Cattle Feedlot Manure", Texas Tech University, Lubbock, TX, Centennial ACS Meeting, Div. Fertil. Soil Chem., April 6-7, 1976. Johnson, Huang, Can. J . Techno/., 33, 421 (1955). Lin, C. S.,M. S.Thesis, Texas Tech University, 1978. McAdams, W. H., "Heat Transmission", 3rd ed, pp 172-180, McGaw-Hill, New York, 1954. Morrison, F. B., "Feeds and Feeding", 22nd ed, Morrison Pub. Co., Clinton, Iowa, 1959. Nikitin, N. I., pp 585-594 in "Chemistry of Cellulose and Wood", N. I. Nikitin, Ed. (Transl. by J. Schmorak), Israel Program for Scientific Translations, Jerusalem, Israel, 1966. Rensfelt, E.. Blomkuist, G., Ekstrom, C., Engstrom, S.,Espenas, B. G., Liinanki, L., "Basic Gasification Studies for Development of Biomass Medium BTU Gasification Process", IGT Conference on Energy from Biomass and Wastes, Washington, DC, 1978. Shafizadeh, F., Fu, Y. L., Carbobyd. Res., 29, 113-122 (1973). Stamm, A. J., Ind. Eng. Cbem., 48(3), 413-417 (1956). Tillman, D. A., "Wood as an Energy Resource", pp 34-37, Academic Press, New York. 1978. Wishart, R. S.,Oil Gas J . , 48-50 (May 19, 1975).
Receiued for review July 26, 1979 Accepted January 17, 1980
