CHEMICAL DESULFURIZATION OF COAL: PARTITIONING SULFUR TO zyxwv GAS AS H,S John M. Stencel, James K. Neathery, and Jidong Yang Center for Applied Energy Research University of Kentucky Lexington, KY 40511 Keywords: Coal desulfurization, gasification, phosphoric &id INTRODUCTION The yields and characterisitics of products from mild temperature gasification or pyrolysis of coal have been evaluated extensively in fundamental and process development efforts. At 5OO0C, the following has been presented as representing the sulfur product distribution from US bituminous coals (1,2) zyxw : Total sulfur in gas = 0.31 x zyxw SCm, Total sulfur in tar = 0.06 x zyxw S, Total sulfur in solid = 0.61 x Stoa,. This type of distribution is affected by factors such as coal type, sulfur content and form, particle size, heating rates, temperature of pyrolysis, reactor and process design, and the type of reactants to which the coal is subjected. For example, increasing the pyrolysis residence time usually decreases the sulfur content in the char and increases the tar and gas yields and their Sulfur content. As indicated above, and in other mild temperature gasification studies of low-to-high sulfur coals at temperatures between 400- 825OC (3-5), the coal sulfur was distributed nonselectively to all products. As a consequence, the upgrading required to meet environmental regulations has to be applied to more diverse products than the coal from which the products were derived. The severity of such upgrading, and the severity to which coal has to be treated to release all of its sulfur, depends on the chemical form of the sulfur. Recent analytical efforts have begun to define these sulfur forms in coal, the most refractory organic species of which are thiophenic in nature (6,7). In the current study, the mild temperature pyrolysis of Illinois basin coals mixed with phosphoric acid under continuous-feed, bench-scale fluidized bed conditions at 500'C is reported. The extent of sulfur removal and its partitioning to gas as H,S are discussed in relation to its chemical form in the coal. Swelling characteristics of coal/acid mixtures are also discussed relative to operation of the fluidized bed reactor. EXPERIMENTAL The two coal samples (labelled as VA and VB) were obtained from the Illinois Basin Coal Sample Program and were both from the Springfield seam (Indiana V), but were sampled at different locations in the seam and at different times. Their composition is presented in Table 1. The coals were admixed with 50% strength, reagent grade phosphoric acid to attain coa1:acid weight ratios of 1.0:0.65 and 1.0:0.96 or with water to produce a coal-only sample having a coa1:acid ratio of 1.O:O. These mixtures were dried at 2OO0C in a nitrogen purged furnace then vacuum dried at the same temperature. The dried samples were stored in sealed containers subsequent t o purging with argon until they were treated in a bench-scale reactor. A schematic Of the fluidized bed reactor system is presented in Figure 1. The reactor had a 7.6 cm diameter and was 100 cm in height. Dried coals were loaded into a pressurized hopper located on a precision screw feeder. Coal was dropped from the screw outlet of the feeder into a eductor line which led to the bottom of the gasifier. Gasification tests were as long as four hours in duration with average coal feeds of 0.1-0.3 kg/h. 438