Ind. Eng. Chem. Res. zyxwvu 1989,28, zyxwvu 27-33 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONML 27 maximum sorbent utilization efficiency. These pilot test results indicate that zyxwvuts SOz capture by entrained hydrated lime particles occurs by two different mechanisms: a gas/solid reaction mechanism for particles which do not interact with droplets; a gas/solid/droplet reaction mechanism for particles interacting with water droplets. Accordingly, the sorbent injection process performance may be improved by enhancing either of these two reaction mechanisms. The lime properties may be improved to enhance the sorbent’s intrinsic activity for the gas/solid reaction mechanism. The humidifier may be designed to provide increased particle-droplet interactions to promote the wet reaction. Registry No. zyxwvutsrqp SOz, 7446-09-5. Literature Cited Babu, M.; Forsythe, R. C.; Runyon, C. V.; Kanary, D. A.; Pennline, H. W.; Sarkus, T.; Thompson, J. zyxwvuts L. “Results of 1.0 MMBtu/Hour Testing and Plans for a 5 MW Pilot HALT Program for SOz Control”. Proceedings of the Third Annual Pittsburgh Coal Conference, Pittsburgh, PA, Sept 1986. Forsythe, R. C.; Kaiser, R. A. “Hydrate Addition at Low Tempera- ture: SOz Removal in Conjunction with a Baghouse”. Proceedings of the Second Annual Pittsburgh Coal Conference, Pittsburgh, PA, Sept 1985. Klingspor, J. “Kinetic and Engineering Aspects on the Wet-Dry FGD Process”. Licenciate Thesis, Lund Institute of Technology, Lund, Sweden, 1983. Statnick, R. M.; Burke, F. P.; Koch, B. J.; McCoy, D. C.; Yoon, H. “Status of Flue Gas Sorbent Injection Technologies”. Proceedings of the Fourth Annual Pittsburgh Coal Conference, Pittsburgh, PA, Sept 1987. Yoon, H.; Stouffer, M. R.; Rosenhoover, W. A.; Statnick, R. M. “Laboratory and Field Development of Coolside SO2 Abatement Technology”. Proceedings of the Second Annual Pittsburgh Coal Conference, Pittsburgh, PA, Sept 1985a. Yoon, H.; Ring, P. A.; Burke, F. P. “Coolside SOz Abatement Tech- nology: 1 MW Field Tests”. Proceedings of the Coal Technology ’85 Conference, Pittsburgh, PA, Nov 1985b. Yoon, H.; Theodore, F. W.; Burke, F. P.; Koch, B. J.; Corder, W. C. “Low Capital Cost, Retrofit SOz Control Technologies for High Surfur Coal Applications”. Proceedings of the 79th Annual Meeting of the Air Pollution Control Association, Minneapolis, MN, June 1986. Yoon, H.; Stouffer, M. R.; Rosenhoover, W. A.; Withum, J. A.; Burke, F. P. “Pilot Process Variable Study of Coolside Desulfurization“. Enuiron. Prog. 1988, 7, 2, 104-111. Received for review March 4, 1988 Revised manuscript received August 31, 1988 Accepted September 16, 1988 Evolution of Hydrogen Sulfide in a Fluidized Bed Coal Gasification Reactor Robert P. Ma, Richard M. Felder,* and James K. Ferrell Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695 The rates of evolution of hydrogen sulfide have been measured for the steam/oxygen gasification of a devolatilized Western Kentucky bituminous coal, a New Mexico subbituminous coal, and a Texas lignite in a pilot-scale fluidized bed reactor, and a phenomenological model has been formulated to correlate the results. The model assumes instantaneous devolatilization and partial combustion of the coal followed by rate-limited gasification of the char in a single well-mixed stage and includes kinetic correlations for the water gas shift reaction and char hydrodesulfurization. Estimated char reactivities agree well with results obtained in other studies, and the model predictions are generally satisfactory, especially considering the relative simplicity of the model. The results indicate that sulfur present in the coal as pyrite, mercaptans, aliphatic sulfides, and disulfides is converted completely, while sulfur in aryl sulfides and thiophenes is only partially converted. A substantial fraction of the sulfur converted during gasification is released in pyrolysis-50-70% for the sub- bituminous coal and 35-45% for the lignite. An Environmental Protection Agency sponsored study of the potential environmental impact of coal gasification operations has been under way since 1978 at North Car- olina State University. Several coal feedstocks have been gasified with steam and oxygen in a small (15-cm i.d.1 pilot-scale fluidized bed reactor operated by the faculty, students, and staff of the NCSU Department of Chemical Engineering (Felder et al., 1980; Ferrell et al., 1980). Results have been reported on the compositions of syn- thesis gas and waste streams from the gasifier (Ferrell et al., 1980, 1982a,b), and dynamic and steady-state models have been developed to correlate the observed rates of production of the principal product gas species with the operating conditions of the gasifier (Ma et al., 1988; Purdy et al., 1981,1984;Rhinehart et al., 1987a,b). Other studies have dealt with rates of evolution of nitrogen gases (Far- zam et al., 1985) and of volatile trace elements (Rudisill, * To whom correspondence should be addressed. 0888-58851891 2628-0027$01.50/0 1984). This paper reports on experimental and modeling studies of the evolution of hydrogen sulfide, the most prevalent sulfur-containing species in the synthesis gas. Coal generally contains iron pyrite (FeS2)and various divalent organic sulfurs, including, in descending order of thermal stability, thiophenes, aryl sulfides, cyclic sulfides, aliphatic sulfides, and aryl and aliphatic thiols (Attar, 1978). In a reducing atmosphere above about 500 “C, iron pyrite reacts with hydrogen to form hydrogen sulfide (Thompson and Tilling, 1924). All the organic sulfur species present in coal can also react with hydrogen to form hydrogen sulfide, with the reactivity of a species varying inversely with its thermal stability (Attar, 1978). Coal decomposition and secondary gasification reactions also lead to the formation of other sulfur gas species including carbonyl sulfide (COS), carbon disulfide, and various thiophenes and mercaptans. Studies of coal desulfurization chemistry have been reported by Zielke et al. (1954), Maa et al. (1975), Robinson (1976), Haldipur and Wheelock zyxwvutsr 0 1989 American Chemical Society