Bioresource Technology 35 ( 1991 ) 217-222
Conversion of Guayule Residues into Fuel Energy Products James L. Kuester Department of Chemical, Bio and Materials Engineering and Center for Energy Systems Research, Arizona State University,Tempe, Arizona 85287-5806, USA
Abstract
A therrnochemical conversion process has been developed that can convert residues from a guayule processing facility to gaseous and/or liquid fuels. This paper presents characterization data and gasifier conversion data for several guayule samples (whole shrub, bagasse, bagasse plus resin). Gas yields of approximately 0"9 g gas g- 1 of feed were achieved. Gas heating values were approximately 20 000 J liter- i (std). Projected liquid fuel yields (no. 2 diesel) for this gas is approximately 0"25 liter kg- 1 of guayule feedstock (dry, ash-free basis). Key words': Guayule, energy, gasification, liquefaction, thermochemical, pyrolysis, diesel. INTRODUCTION A thermochemical process to convert various organic materials to liquid hydrocarbon fuels has been developed at Arizona State University (ASU) (Kuester, 1987). An indirect liquefaction approach is used, i.e, gasification to synthesis (pyrolysis) gas followed by conversion of the synthesis gas to liquid fuels. The primary virtue of an indirect liquefaction approach for cellulosic type feedstocks, such as guayule bagasse, is that the oxygen contained in the feedstocks is easily separated in the processing sequence. Thus, an oxygen-free liquid hydrocarbon fuel, equivalent to those currently derived from petroleum, is produced. Product candidates include no. 2 diesel, kerosene, and/or high-octane gasoline. Electricity and medium heating value gas products also are possible with the system. Alternative second-stage configurations provide flexibility for production of chemicals other than liquid fuels.
Approximately 100 biomass, polymer, and industrial waste type materials have been processed in the ASU laboratories. Results have been reported elsewhere (Davis et al., 1984; Kuester, 1984, 1985, 1986; Kuester et al., 1985). This paper will concentrate on studies concerned with utilizing guayule materials. CONVERSION SYSTEM DESCRIPTION
A schematic of the integrated ASU process (Fig. 1) shows the continuous laboratory scale system. The unit has a capacity to process approximately l l kg h --~ (25 lb h -~) of feedstock. A detailed engineering design and cost estunate for a 9070 kg day ~ ¢10 ton day -~) facility has been completed (UECI, 1985). Diesel product yields are in the range of 0.21-0-42 liter kg -~ (50-100 gal ton-~) of feedstock. The gasification system is comprised of two fluidized beds with connecting circulating solid transfer loops. One fluidized bed is used as a feedstock pyrolyzer while the second bed (regenerator) operates in a combustion mode to heat the circulating solids media. The fuel source for the combustor can be recycled pyrolysis gas, liquefaction reactor off gas, feedstock, or purchased fuel (e.g. natural gas). The fluidized solid material can be tailored for the application and thus may be inert (e.g. sand) and/or catalytic. The fluidizing gas can be recycled gas from the pyrolyzer or liquefaction reactor, steam, or some other reactive gas. The fluidized-bed approach allows for acceptance of diverse feedstocks, efficient heat transfer, continuous solids recirculation, and elimination of a combustion zone in the pyrolyzer. The solids choice may allow for selective removal of contaminants from the feedstock and product recovery via bleed stream processing.
217 Bioresource Technology 0960-8524/91/S03.50 © 199l Elsevier Science Publishers Ltd, England. Printed in Great Britain
218
James L. Kuester VENT SEPARATORS WATER - -
SE.ARATORS
COOLER
[ FILTER
FILTER TAR
ASH
CHAR.
TAR
~
GAS (RC)
FT
RECTOR
PYROLYZER RIOMASS REGENERATOR WATER
DIESEL FUEL
COMPRESSOR AIR (RC)
(nc) GAS (RC)
GASIFICATION
Fig. 1.
LIQUID FUELS SYNTHESIS
Schematicof thermochemicalsystemto convert biomass to energyproducts.
The gas generated in the pyrolyzer typically contains mostly paraffins (primarily methane), olefins (primarily ethylene), carbon monoxide, hydrogen, and carbon dioxide. The gas has a heating value of approximately 20 515 J liter-~ (std) [550 Btu per standard cubic foot (SCF)]. With waste materials, a wide variety of other contaminant gases also are possible. The gases pass through a cyclone-scrubber system to a compressor. Guard beds could be added as required to remove contaminants. From the compressor, the gas can be distributed to the pyrolyzer, regenerator, or liquefaction reactor, or it can be utilized in an electrical generation system (gas turbine or generator). The off gas from the regenerator is passed through a cyclone-scrubber system before being vented. Heat recovery from the gasification system would lead to additional steam/electrical generation capacity for the system (UECI, 1985). The liquefaction system consists of a catalytic reactor to produce paraffinic liquid fuel. Both fluidized bed and slurry phase systems have been studied. These reactor types allow for effective temperature control in the presence of the significant exothermic heat of reaction that is evolved. They also offer the possibility of continuous regeneration via external circulation if necessary. The fluidized bed is a simpler system than the slurry phase type. The slurry phase system, however, offers the potential advantages of better temperature control, longer catalyst life, residence time flexibility, and improved gas-solid contacting. In both reactor types, the reactive components in the synthesis gas (olefins, carbon monoxide, hydrogen) are converted to a primary
paraffinic hydrocarbon phase and a secondary alcohol-water phase. The off gas from this reactor accumulates an appreciable amount of normal paraffins plus carbon dioxide and exhibits an enhanced heating value as compared to the synthesis gas (due to hydrogen and carbon monoxide depletion). Typical operating conditions are given in Table 1. Work also has been performed on the system to produce a high-octane gasoline via catalytic reforming of the paraffinic liquid phase in a conventional fixed bed system using commercial catalysts. To achieve a commercial octane range, a liquid yield loss of about 20% occurs in the reforming step. The gas has a high heating value -- 85 790 J liter -~ (std) or (2300 Btu SCF -j) -due to the presence of C~ to C 4 normal paraffins. Thus, some of the yield loss could be recovered via recycling of this gas in the overall process. The process is modular in concept. Thus, if one were interested in producing electricity only, the fluidized bed regenerator equipped with steam coils or a gas turbine and feedstock delivery system would be appropriate. If a burnable gas was a desirable product, the fluidized bed pyrolyzer could be added. If a storable, transportable liquid fuel was a virtue, the liquefaction system could be linked. With the volatile climate in energy prices and availability and environmental regulations, this flexibility is considered to be an attractive feature. In an integrated guayule operation, the products would be utilized to power farm machinery, irrigation pumps, extraction equipment, etc., and thus could have a significant impact on overall processing economics.
Conversion of guayule residues into fuel energy products
GUAYULE STUDIES Techniques for extracting rubber from guayule produce several waste streams. The size and composition of these streams vary depending on the type and degree of extraction processing. These streams comprise up to 90% (by dry weight) of the harvested plant. Thus, it is generally acknowledged that guayule industry economics will be heavily influenced by optimal utilization of these materials. Numerous possibilities have been proposed for the cellulosic-bagasse residue including particle board, specialty chemicals, jiffy pots, and paper products. The ASU work was concerned only with the option of producing gaseous and liquid fuels. Nine different guayule materials were received in the laboratory (Table 2). Results from testing materials received from CIQA and USDA (Kuester, 1982, 1984; Kuester & Wang, 1986) resulted in typical synthesis gas compositions (Kuester & Wang, 1986) (Table 3). This gas has a heating value of approximately 20515 J liter -t (std)(550 Btu SCF-~). Thus, all or part of this stream could be utilized as a fuel gas if desired. Typical liquid fuel characteristics JYable 4) for guayule bagasse (Kuester & Wang, 1986) as compared with commercial materials and product from almond prunings feedstock show the properties of the biomass derived fuels to be similar to petroleum derived products. Results for the Amerind and Bridgestone/Firestone samples are reported (Tables 5 through 9)
(AAL/ASU, 1987). Mature (3-year-old) guayule shrubs o! the AAL Gila and bulk USDA cultivars were prepared locally as a finely chipped, solardried biomass feedstock. The bagasse from the Bridgestone/Firestone pilot plant in Akron, Ohio, was prepared as a dry, granular type feedstock without resin. For the bagasse-plus-resin mixture, a representative amount of resin was hand mixed with the bagasse. Characterization of feedstock and gasification testing were done in parallel. ASU performed the heating value determination. Moisture and ash analyses were done by Laboratory Consultants of Tempe, while Guelph Chemical Laboratories of Canada conducted the elemental analyses. Gasification testing was performed at ASU with the indirect liquefaction process. Experimental procedures have been described elsewhere (Kuester, 1982, 1984; Kuester et aL, 1985). Characterization of moisture, ash, heating value, and elemental analyses showed some variation by feedstock (Table 5). Ash content nearly doubled when rubber and resins were removed.
Table 3. Typical synthesis gas composition
Compound
Amount (mol %)
Hydrogen Carbon monoxide Olefins Paraffins Carbon dioxide
30 30 10 15 15
Table 1. Fluid bed/slurry phase operating conditions
Parameter
Pyrolyzer
Temperature (°C) Pressure (Pa) Residence time (s)
600-800 0-6895 2
Liquefaction reactor 250-300 9.65 x 105 18
Reformer 490 2.76 x 1()~' 11
Table 2. Guayule material received by ASU
Material Bulk guayule Guayule cork Guayule bagasse Guayule resin Bulk guayule Bulk guayule (USDA 1229) Bulk guayule (Gila) Guayule bagasse (USDA) Guayule bagasse + resin (USDA)
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Source Centro de Investigation en Quimica Aplicada (CIQA) CIQA CIQA CIQA USDA Water Conservation Laboratory Amerind Laboratory Amerind Laboratory Bridgestone/Firestone, Inc. Bridgestone/Firestone, Inc.
James L. Kuester
220
Table 4. Properties of Fischer-Tropsch product and commercial fuel oils
Fischer- Tropsch product
Commercial fuel oils Kerosene
No. 2
Almond prunings feedstock
JP-4
diesel Specific gravity Gravity (API) Boiling point range (°C) 10% Evaporated at 50% 90%
0"8360 37-8
Calculated cetane Index Heating value (J/g)
0.8108 43.0
0"7586 55"0
Guayule bagasse
0"7902 47-6
0"7950 46"5
187 237 295
169 210 248
64 150 226
113 178 244
114 212 274
45"9 45 085
47'8 50 418
48'3 52 195
45"3 45 017
55'7 48 946
Table 5. Summary of feedstock characterization
Feedstock
Gila shrub U S D A shrub Bagasse Bagasse + resin
Moisture (wt %) 4-61 4"86 9.62 8"51
Ash (wt %)
Higher heating value (J g- i)
5.80 5-58 9"88 8.56
20 21 18 20
850 771 306 492
Table 6. Gasification data for pyrolysis of Gila guayule
Parameter
Unit
Results
Elemental analysis (wt %) C
H
N
S
O
49'97 49"35 47-36 51"84
6'47 6'48 6"39 6"92
1'32 1"82 1-18 1"18
0-42 0"59 0"25 0'27
41"81 41'76 44'82 39'79
Table 7. Gasification data for pyrolysis of USDA guayule shrub
Parameter
Unit
Test No. 1 Test No. 2 Operating conditions Feed rate Steam flow Temperature Pressure
Test No. 1 Test No. 2 Operating conditions
kgh t kg h ~ °C Pa
1"73 1-32 840 4 137
2-71 1.32 827 4 137
24"80 34-97 13-74 18.42 4.92 0-72 0" 11 0" 11 0-06 0"00 0"02 1-47 0"06 0"60
23"65 34-49 13"81 18"55 5-49 0"84 0-21 0" 13 0.10 0"01 0"04 1-95 0.04 0"69
100.00
100.00
Pyrolysis gas composition (mol %) Hydrogen Carbon monoxide Carbon dioxide Methane Ethylene Ethane Propylene Propane 1,3-Butadiene Butene Butane High hydrocarbons Oxygen Nitrogen
Results
H2 CO CO 2 CH 4 C2H4 CzH 6 C3H 6 C3Hs C4H6 C4H 8 C4H 10 C5 + O2 N2
Total Gas molecular weight g g - ~ mol Gas heating value J liter ~(std) Gas yield g gas g - 1 feed
Feed rate Steam flow Temperature Pressure
kg h - ~ kg h - l °C Pa
1-50 0'89 840 4 137
2"48 1.04 838 4 137
23-34 34.96 12.60 20.32 5.04 0.68 0.12 0.16 0.07 0-02 0"01 1.46 0"08 1-14
22"87 34.18 12.97 20.05 5.84 0"86 0.17 0.13 0"09 0.04 0"01 1.95 0"05 0'79
100"00
100'00
Pyrolysis gas composition (mol %)
22"26 22"80 19 568 20 705 0"8893
Hydrogen Carbon monoxide Carbon dioxide Methane Ethylene Ethane Propylene Propane 1,3-Butadiene Butene Butane High hydrocarbons Oxygen Nitrogen
H2 CO CO 2 CH 4 C2H 4 C2H 6 C3H6 C3Hs Call 6 C4H 8 C 4 H 10 C5 + 02 N2
Total Gas molecular weight g g - ~ mol Gas heating value J liter- ~(std) Gas yield g gas g - l feed
22-24 22'68 20 205 21 290 0"8819
Conversion of guayule residues into fuel energy products Table 8. Gasification data for pyrolysis of bagasse
Parameter
Unit
221
Table 9. Gasification data for pyrolysis of bagasse plus resin
Parameter
Results
Unit
Test No. 1 Test No. 2
Test No. 1 Test No. 2 Operating conditions Feed rate Steam flow Temperature Pressure
kg h - ~ kg h - i °C Pa
Pyrolysis gas composition (mol %) Hydrogen H2 Carbon monoxide CO Carbon dioxide CO 2 Methane CH 4 Ethylene C2H 4 Ethane C2H 6 Propylene C3H 6 Propane C3Hs 1,3-Butadiene C4H 6 Butene Calls Butane C4HII I High hydrocarbons C5 + Oxygen 02 Nitrogen N~ Total Gas molccular weight gg ~mol Gas heating value J liter ~(std)
2'43 1"02 799 4 137
2'36 1"02 788 4 137
31'59 24"00 18"94 13'68 4"32 0"80 0"13 0.09 0"00 0"05 0'00 1'08 0" 11 5"21
32'07 26'75 18"81 14"42 4.76 1.03 0.23 0.09 0"00 0-09 0"01 1-41 0.02 0"31
100"00
100"00
21.72 16 106
21.66 17 773
Results
Operating conditions Feed rate Steam flow Temperature Pressure
kg h J kg h - ~ °C Pa
Pyrolysis gas composition (mol %) Hydrogen H2 Carbon monoxide CO Carbon dioxide CO2 Methane CH 4 Ethylene C2H4 Ethane C~H6 Propylene C3H 6 Propane C~H~ 1,3-Butadiene
Butene Butane High hydrocarbons Oxygen Nitrogen
C4H,, C4H~ C4H,~ C5 + O~ N2
Total Gas molecular weight g g ~tool Gas heating value J liter L(std) Gas yield g gas g ~feed
0-98 1.02 782 4 137
0-68 1.{)2 773 4 137
31-52 24-14 18"22 16.88 5.49 1.53 0-18 0"08 0.00 0.08 0-00 1.35 0'03 0.50
31.40 22.91 18.44 17-88 5.10 1.59 0.18 0.07 0.00 0.04 0.00 1.8{) 0.01 {)'58
100.00
100.00
21.38 21.51 18 873 19 522 0.81{)6
Gas yield results were not available.
However, ash presented no removal problems in the separators. Heating values for Gila and USDA whole shrub were not significantly different. The removal of rubber and resin from the USDA material lowered the heating value significantly to 18 306 J g-1 (7870 Btu lb-1). However, the addition of resin to bagasse increased the value to almost that of the Gila shrub. Together, rubber and resin account for 3466 J g - 1 (1490 Btu lb -1) of the whole shrub. Therefore, resin accounted for more energy than did the rubber. Part of the reason for this is that there is twice as much resin as rubber in guayule tissues. The pyrolysis gas contains primarily hydrogen, carbon monoxide, carbon dioxide, methane, and ethylene (Tables 6-9). Compared to the whole shrub, the bagasse sample produced a gas with higher H2, lower CO, higher CO2, lower CH4, and unchanged CzH 4. The gas heating value was lower for the bagasse sample, reflecting a lower hydrocarbon content. The Amerind and Bridgestone/Firestone materials were not processed beyond gasification. However, prior experience (Kuester, 1982, 1984; Kuester & Wang, 1986) suggests that product characteristics similar to that reported in Table 4
would be expected at a yield of approximately 0"25 liter kg-~ (60 gal of liquid fuel per ton) of guayule feedstock (dry, ash-free basis).
CONCLUSIONS Results reported in this paper indicate that guayule materials can be readily processed to medium energy content gaseous fuel and/or transportation grade liquid hydrocarbon fuels (e.g. no. 2 diesel) with a thermochemical conversion process. Implementation of this technology will depend on the economic viability of this energy module versus other possible uses for the residues. Enhanced economy of scale for the approach presented in this paper could be achieved by processing additional cellulosic feedstocks that may be available in the vicinity of a guayule processing facility (e.g. cotton wastes, municipal solid wastes).
ACKNOWLEDGMENTS The work cited in this paper has been supported by the US Department of Energy (DOE), US
222
James L. Kuester
Department of Agriculture (USDA), and A m e r i n d Agriculture L a b o r a t o r y (via a contract from the Western A r e a Power Administration, DOE). In addition, guayule materials were supplied by C e n t r o de Investigation en Quimica Aplicada ( C I Q A ) in Saltillo, Mexico, Bridges t o n e / F i r e s t o n e , Inc., and the U S D A Water Conservation L a b o r a t o r y (Tempe, Arizona).
REFERENCES AAL/ASU (1987). Amerind Agrotech Laboratory and Arizona State University, Economic Analysis for Converting Rubber Processing Plant Guayule Biomass to Energy. Final Report Submitted to Western Area Power Administration. Davis, E., Kuester, J. L. & Bagby, M. (1984). Biomass conversion to liquid fuels: potential of some Arizona chaparral brush and tree species, Nature, 307, 726-8. Kuester, J. L. (1982). Conversion of Cellulosic Wastes to Liquid Fuels. Interim Report Submitted to the Waste Products Utilization Branch, Office of Industrial Programs, US Department of Energy, Washington, DC.
Kuester, J. L. (1984). Conversion of Cellulosic Wastes to Liquid Hydrocarbon Fuels. Interim Report Submitted to the Waste Products Utilization Branch, Office of Industrial Programs, US Department of Energy, Washington, DC. Kuester, J. L. (1985). Diesel fuel from biomass via indirect liquefaction. In Bioenergy 84. Volume III: Biomass Conversion, ed. H. Egneus & A. Ellegard. Elsevier Applied Science Publishers, Ltd, London, pp. 48-55. Kuester, J. L. (1987). Process of Producing Liquid Hydrocarbon Fuel from Biomass, Arizona Board of Regents, US Patent 4 678 860. Kuester, J. L. & Wang, T. C. (1986). Conversion of guayule residues to diesel fuel. In Guayule -- A Natural Rubber Source, ed. C. Fangmeier & S. M. Alcorn. Guayule Rubber Society, Dept. of Bot. and Plant Sci., Uni. of California, Riverside, CA, pp. 383-92. Kuester, J. L., Fernandez, C., Wang, T. C. & Heath, G. (1985). Liquid hydrocarbon fuel potential of agricultural materials. In Fundamentals of Thermochemical Biomass Conversion, ed. R. P. Overend, T. A. Milne & L. K. Mudge. Elsevier Applied Science Publishers, Ltd, London, pp. 875-95. VECI, (1985). Ultrasystems Engineers and Constructors Inc., Experimental Test Facility. Final Report Submitted to Arizona State University (4 volumes).