26 Fluidized-Bed Gasification of Solid Wastes and Biomass: the CIL Program Downloaded by UCSF LIB CKM RSCS MGMT on December 3, 2014 | http://pubs.acs.org Publication Date: August 29, 1980 | doi: 10.1021/bk-1980-0130.ch026
J. W. BLACK1, K. G. BIRCHER1, and K. A. CHISHOLM1 Eco-Research Limited, P.O. Box 200, Station A, Willowdale, Ontario, Canada M2N 5S8
Canadian Industries Limited (CIL) is a large Canadian chemical company which manufactures a range of heavy industrial chemicals. A significant volume of these products are based on natural gas feedstock. About six years ago; three circumstances evolved which prompted the Company to examine the potential of municipal refuse as a source of synthesis gas for chemicals manufacture. The events were, 1) Threatened curtailment of natural gas supply, 2) Requirement for additional ammonia capacity, 3) Acquisition of a waste disposal company. An initial economic study of the conversion of municipal waste to synthesis gas provided significant justification to proceed with a demonstration plant. The program was designed to demonstrate two new processes; 1) preparation of a solid fuel (RDF) from mixed municipal refuse 2) conversion of this fuel to a lew calorific value gas. A demonstration plant was constructed in 1976. Evaluation of the first module, RDF preparation, was satisfactorily concluded in 1978. The second step, gasification of the RDF, will be completed this year. In late 1978, the gasification program was expanded to include other feedstocks primarily forest biomass and the use of oxygen. This latter program has received partial government support. Experiments are underway also to examine the gas processing steps subsequent to gasification i.e. high temperature gas cleaning and reforming. Refuse as a Substitute Feedstock Municipal refuse is a highly heterogeneous mixture of materials of which more than half are organic. Refuse contains significant amounts of water and has a caiparatively lew heating value. Garbage has, however, one redeeming feature it is cheap. After separation of metals and glass, the combustible fraction can be thermally decomposed into three components; a high ash content char, a mixed condensible phase comprising water and liquid organics and a gas containing primarily 1 Current address: BBC Engineering, 65 Pringle Avenue, Markham, Ontario, Canada L-P 2P5 0-8412-0565-5/80/47-130-351$05.00/0 © 1980 American Chemical Society In Thermal Conversion of Solid Wastes and Biomass; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
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352
THERMAL CONVERSION OF SOLID WASTES AND BIOMASS
carbon oxides, hydrogen and low molecular weight hydrocarbons. Also produced are small but s i g n i f i c a n t quantities of hydrogen sulphide and hydrogen chloride. By contrast the requirements for a chemical feedstock are continuous supply of unvarying composition, minimal inerts and negligible amounts of particul a t e s , corrosives or catalyst poisons. To produce a feedstock from garbage therefore necessitates the separation of a low inert,organic fraction with consistent characteristics,followed by e f f i c i e n t conversion of t h i s material into a clean gas i n a continuous, rapid response r e actor. I t was recognized that such a system would also produce a good f u e l . In fact t h i s was to be the f i r s t commercial objective. Description of the Prototype Unit. As proof of concept, a f a c i l i t y was constructed i n association with a conventional refuse transfer station. The plant i s comprised of two modules, a 15 TPH RDF system i n conjunction with a 1 TPH f l u i d i z e d bed g a s i f i e r . A flow diagram i s shown i n Figure 1. The f i r s t module, the RDF preparation system, was designed with s u f f i c i e n t capacity to separate a l l of the refuse from the C i t y of Kingston, Ontario where i t i s located. Conceptually the system has been engineered to provide the following processing steps, a) I n i t i a l opening of a l l containers to release the refuse for subsequent processing but without s i g n i f i c a n t size reduction, b) Size separation into two fractions, an oversize stream canprised primarily of paper products and an undersize stream containing bottles, cans and wet refuse, c) A i r c l a s s i f i c a t i o n of the undersize to remove the combust i b l e s from the residue, d) Shredding of the organic f r a c t i o n by a cutting action. The basic system which i s designed around low speed equipment can be upgraded to accanmodate metals and glass recovery. As consequence of the fact that only the organic materials are shredded, both glass bottles and cans remain i n t a c t . Maintenance and power consumption are also s i g n i f i c a n t l y reduced. I n addition, the extremely low glass-content of the RDF ininimizes equipment abrasion and reduces potential slagging problems i n the thermal conversion process. Conversion of the RDF into a low c a l o r i f i c value, f u e l gas i s accomplished i n a f l u i d i z e d bed r e a l t o r . Both a i r and s o l i d f u e l are fed into the reactor under p o s i t i v e pressure. The RDF i s immediately decomposed into gas, char and small amounts of t a r . The char i s subsequently oxidized by a i r to provide the heat necessary t o sustain reaction conditions. Ash from the system i s removed by cyclone collectors f o r subsequent disposal. The cleaned off-gas i s then burned i n a tangential l y f i r e d combustor.
In Thermal Conversion of Solid Wastes and Biomass; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
In Thermal Conversion of Solid Wastes and Biomass; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
Figure 1. Resource recovery pilot plant—Kingston, Ontario
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LO
L/t
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THERMAL CONVERSION OF SOLID WASTES AND BIOMASS
354
Results. The experimental program for the RDF module was designed to examine both separation e f f i c i e n c i e s and t o t a l power requirements. Evaluation of t h i s module i s now complete and the data are summarized i n Table I . TABLE I Summary of RDF Production Tests CIL (Kingston)
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Plant Location
Ames, : 30 45 1790 26 84 16
Average load Mg/h 20 Peak load Mg/h 40 Installed power kW 140 Power consumption kW.h/Mg 2.7 RDF production % by wt of input MSW 77 Residue production % by wt of imput MSW 23 (glass, metals, etc)
Also included i n the Table are data from a more convent i o n a l garbage processing f a c i l i t y a t Ames, Iowa (1). The power consumption results f o r Ames only include priinary and secondary shredding and a i r c l a s s i f i c a t i o n . The Table shows that the Kingston Plant operates with s i g n i f i c a n t l y less power than conventionally designed RDF plants, i . e . systems i n which size reduction precedes material separation. Actual maintenance costs are d i f f i c u l t to predict because of the intermittent nature of the P i l o t Plant Program. To t h i s point, 3 years after i n s t a l l a t i o n , the only component which has been repaired i s the shredder. The teeth were resharpened after the second year of operation. The second phase of the refuse program, f l u i d i z e d bed g a s i f i c a t i o n , incorporates heat and energy balances, gas analyses and environmental monitoring. Because of i n i t i a l d i f f i c u l t i e s with feeding systems, the evaluation i s not yet complete. Typical gas analysis are shown i n Table I I . TABLE I I Analysis of Fuel Gas (Dry Basis) Fuel
Gas Analysis H
Refuse Rubber Wood
2
12.5 14.0 17.9
CO 11.6 14.4 16.0
CH
co N 15.4 45.1 2.5 3.2 7.9 52.0 5.5 2.9 0.3 5.8 0.1 1.4 0.3 16.7 40.8 4
C H C H C H 2
2
2
4
2
6
2
2
°2 0.8 0.6 0.8
Commercial A c t i v i t i e s . Proposals f o r two plants have been submitted. The f i r s t , a plant t o provide 150 TPD of RDF for use as a f u e l i n a cement plant was guaranteed a t an i n s t a l l e d cost of $1 m i l l i o n including building and s i t e preparat i o n . A submission for conversion of refuse to steam has also been made. This plant i s designed f o r 200 TPD of mixed municipal refuse a t a steam capacity of 20 Mg steam/h.
In Thermal Conversion of Solid Wastes and Biomass; Jones, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
26.
BLACK ET
AL.
Fluidized-Bed Gasification (CIL
Program)
355
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Wood Gasification Program Because of strong government interest and a more immediate market potential, CIL redirected the g a s i f i c a t i o n program to incorporate forest biomass. I t became apparent that there were three areas of interest. In order of increasing complexity these are, 1) An a i r f i r e d , atmospheric pressure system suitable f o r small and medium scale energy producers such as i n d u s t r i a l steam plants or hot gas generators, 2) An a i r f i r e d , high pressure g a s i f i e r more appropriate to large power plants f o r high e f f i c i e n c y , combined cycle e l e c t r i c a l generation, 3) An oxygen f i r e d , high pressure g a s i f i e r necessary f o r chemicals and l i q u i d f u e l production. A program was established to incorporate these three phases of development. We have completed Phase I and are planning f o r Phases 2 and 3. Part of the work has been supported by the Ontario Ministry of Energy and by the ENFOR program of
the Environment Department of the F e d e r a l Government.
Program f o r the Production of a Fuel Gas From Wood. The refuse g a s i f i c a t i o n unit was modified to f a c i l i t a t e wood handl i n g and to incorporate a t e s t u n i t f o r hot gas cleanup, reforming and condensation. The essential system components are shown i n Figure 2. Various forms of forest biomass including wood chips, bark, sawdust and shavings have been evaluated i n the g a s i f i e r . The testing program was i n i t i a l l y designed to evaluate the e f f e c t of parameters such as moisture content, bed temperature and the physical nature of the feed. Subsequently, experiments were conducted to examine long term effects, by simulating commercial operation under a variable load/demand situation for extended periods of time (2 periods of 670 hours continuous operation). Also included i n the program were stack sampling tests, and t a r production measurements. Typical operating characteristics are presented i n Table III. TABLE I I I Operating Characteristics During Wood Gasification Tests Moisture i n Wood Residue Production Combustible Fraction of Residue Turndown Ratio Dust Loading i n Stack (after cyclone) Tar Loading i n Gas Organic Loading of Condensate
12-55% 0.017 kg/kg wood 0.4 kg/kg residue 5:1 1.2g/Nm^
