Analysis of nitrogenous compounds in the effluent streams from a fluidized bed coal gasification reactor

Abstract

A Texas lignite and a New Mexico subbituminous coal were gasified with steam and oxygen in a pilot-scale fluidized bed reactor at pressures from 770 kPa to 830 kPa, and temperatures form 795°C to 980°C. The make gas passed through a cyclone separator, and then a venturi scrubber in which condensable and water-soluble compounds were removed. The gasifier effluents (spent char, cyclone fines, tar, wastewater, and dry make gas) were analyzed for nitrogenous compounds. For both coals, 6–12% of the nitrogen in the feed was retained in the spent char, with greater quantities being retained in the subbituminous coal char. Of the nitrogen volatilized from both coals, roughly 5% appeared in the tar, less than 0.2% appeared in the dry make gas as ammonia and NO x, and the balance appeared in the wastewater as ammonia (60%), hydrolyzable nitrogenous compounds and possibly cyanate (10–15%), thiocyanate (1%), cyanide (0.5%), and other compounds (3–10%). The average concentration of NO x in the dry gas was 7 ppm for lignite. No NO x data for subbituminous coal were obtained. Reactor conditions (temperature, pressure, steam-to-carbon feed ratio) had no measurable effect on the production rates of nitrogenous compounds over the range of conditions investigated.