By-Product Sulfur from the Stabilization of Coal Solid Wastes
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BY-PRODUCT SULFUR FROM THE STABILIZATION OF COAL SOLID WASTES A.J. GOKHALEa and G. BURNETb a. Department of Chemical Engineering, Zachary Hall, Texas A&M University, College Station, TX 77843. b. Ames Laboratory, U.S.D.O.E. and Department of Chemical Engineering, Iowa State University, Ames, IA 50011. Received 2 November, 1988; refereed ABSTRACT A stabilization process for coal cleaning and coal combustion-related wastes has been developed that uses the energy derived from the fuel contained in the coal cleaning wastes. The wastes are pulverized, when necessary, formed into granules in a rotary pan agglomerator, and then fired to a sintering temperature. The result is a readily disposable product that is highly resistant to environmental degradation. Granules of refuse only, and of refuse/fly ash and refuse/FGD sludge mixtures have been investigated. About 90 wt% of the sulfur in the refuse/sludge mixtures is evolved as SO2 during the combustion/sintering portion of the process. Studies using a microreactor system have shown the generation of SO2 to be a function of temperature and to parallel the decomposition of the sulfur-containing compounds present. Based on laboratory tests, SO2 concentrations of 4-8 vol% are predicted in the S0 2 -rich off-gases. By-product sulfur recovery from the off-gases appears practical and attractive using current technology that is proven and well established. INTRODUCTION Disposal of coal cleaning and of coal combustion wastes is a significant problem for many
coal producers and utilities. Difficulties have stimulated research on acceptable alternatives to current disposal practices. Work in the U.S. and elsewhere has focused on easier and safer disposal through pretreatment of the wastes, and on utilization of the wastes as by-products. About one-third of the coal consumed by U.S. utilities each year receives some cleaning before it is burned. The cleaning results in an annual production of wastes in excess of 100-million tons. Subsequent combustion of the coal produces other environmentally troublesome solid wastes, primarily ash and flue gas desulfurization sludge. About 70-million tons of ash and 30-million tons (dry basis) of sludge are produced each year and, as power stations under construction or planned come on line, these amounts will increase significantly. DISPOSAL OF COAL SOLID WASTES Myriad federal, state, and local regulations in the United States have been promulgated in recent years to control the siting, construction, and operation of solid waste disposal facilities. Consideration is given to water and air quality, land and aquatic wildlife, vegetation, aesthetics, and regional concerns. The most common method of disposal is the use of landfill sites which are not only costly but mar the landscape and consume large amounts of land area. Most of the cleaning is performed on Eastern and Midwestern bituminous coals to remove unwanted clay, pyrite, and other impurities. About one-fourth of the run-of-the-mine coal will be rejected as cleaning refuse and will be dispos
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