A NOVEL CONCEPT FOR EFFICIENT PRODUCTION OF LIQUID FUELS FROM COAL USING FLASH PYROLYSIS IN VIBRATED FLUIDIZED BEDS

IN SPITE OF MAJOR EFFORTS TO DEVELOP PROCESSES FOR CONVERTING COAL INTO LIQUID HYDROCARBONS FOR MOTOR FUEL, NONE HAS ATTAINED COMMERCIAL VIABILITY BECAUSE OF DIFFICULTIES WITH POOR CONVERSION EFFICIENCIES AND HIGH CAPITAL COSTS. THIS PROJECT IS BASED ON THE COUPLING OF FLASH PYROLSIS WITH NEW ADVANCES IN VIBRATED FLUIDIZED BEDS AND PROMISES TO REDUCE COAL-PARTICLE DWELL TIME AND THE TIME TO QUENCH THE PRODUCTS BY AT LEAST AN ORDER OF MAGNITUDE, THUS DRASTICALLY REDUCING POLYMERIZATION OF THE PRODUCTS. THE NOVEL DESIGN FOR THE SKIMMING FLASH PYROLYZERIS AN ADD-ON SYSTEM TO PREHEAT THE COAL EN ROUTE TO THE FURNACE OF THE POWER PLANT. IN THIS WAY, THE COAL UTILIZATION IS UP TO 90% (AS COMPARED TO ABOUT 50% FOR CURRENT COAL LIQUEFACTION PROCESSES), THE SYSTEM CAPITAL COST IS GREATLY REDUCED, AND ENVIRONMENTAL IMPACTS OF THE OVERALL COAL UTILIZATION ARE MINIMIZED. A SIDE STREAM OF 900 DEGREES CENTIGRADE LIME-ASH-CHAR MIXTURE FROM THE TOP OF A FLUIDIZED-BED COAL FURNACE WILL BE DIVERTED TO A NON-OXIDIZING VIBRATORY PYROLYZER INTO WHICH A STREAM OF CRUSHED COAL IS FED. THE FEED RATES FOR THE TWO STREAMS WILL BE ADJUSTED TO GIVE A MIXTURE TEMPERATURE OF ABOUT 550 DEGREES CENTIGRADE. THE BED THICKNESS (ABOUT 2 TO 3 CM)AND THE VIBRATION FREQUENCIES (ABOUT 25 TO 100 HZ) WILL BE ADJUSTED SO THAT THE PARTICLES WILL DWELL IN THE PYROLYZER FOR ONLY A FEW SECONDS BEFORE LEAVING FOR THE FURNACE. THE LIGHT HYDROCARBONS EVOLVED WILL NOT HAVE TO BE SENT THROUGH A CYCLONE SEPARATOR BUT CAN BE DIRECTLY QUENCHED BY A TUBE BANK PLACED CLOSE TO THE BED. PHASE I WILL BE DIRECTED AT A CRITICAL EVALUATION OF THE CONCEPT, WITH PARTICULAR ATTENTION TO THE EFFECTS OF TRANSIT TIMES ON REDUCING OBJECTIONABLE POLYMERIZATION OF THE EVOLVED GASES AND VAPOR. PHASE II WILL BE DIRECTED AT DETERMINING KEY PARAMETERS IN A LABORATORY-SCALE EXPERIMENT. THE APPLICATION OF THE CONCEPT TO OIL SHALE RETORTING WILL ALSO BE EXAMINED.