A novel cyclic process using CaSO 4 /CaS pellets for converting sulfur dioxide to elemental sulfur without generating se
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I. INTRODUCTION
GAS streams containing high levels of sulfur dioxide are generated from nonferrous metal smelters, coal-burning power plants, and integrated-gasification, combined-cycle, desulfurization units.[1–4] The sulfur dioxide in the flue gas from the power plant is scrubbed, generating wastes that need to be discarded.[5,6] Nonferrous smelters convert the sulfur dioxide to sulfuric acid, but there are often few attractive markets for the sulfuric acid, and thus, its production is driven by the need to fix the pollutant byproduct rather HONG YONG SOHN, Professor of Metallurgical Engineering and Adjunct Professor of Chemical and Fuels Engineering, is with the University of Utah, Salt Lake City, UT 84112-0114. Contact e-mail: hysohn@mines. utah.edu BYUNG-SU KIM, formerly Graduate Student, Department of Metallurgical Engineering, University of Utah, is Senior Researcher, Recycling Research Center, Korea Institute of Geoscience & Mineral Resources, Daejeon, Korea 305-350. Manuscript submitted December 4, 2001. METALLURGICAL AND MATERIALS TRANSACTIONS B
than to make a marketable commodity.[7,8,9] The current trend in the sulfide-smelting industry is to use increasingly high oxygen enrichment in the process gas to reduce the heavy energy load to heat nitrogen to the process temperature and reduce the volume of the process gas.[3] As a consequence, the modern sulfide-smelting technologies produce highstrength sulfur-dioxide gas streams. As an example, the new Kennecott copper converting process in Utah (near Salt Lake City, UT) generates a steady stream of off-gas containing 35 to 45 pct sulfur dioxide.[3,10,11] For conversion to sulfuric acid, however, this stream must be diluted to 10 to 14 pct sulfur-dioxide concentration.[2,9,12,13] Therefore, it would be highly desirable to develop an alternative process to directly treat sulfur-dioxide streams without dilution. Technology exists to condense sulfur-dioxide gas to liquid, but the market for liquid sulfur dioxide is even more limited than for sulfuric acid. Conversion to elemental sulfur would have many advantages because it is highly inert as a solid, and its long distance transportability VOLUME 33B, OCTOBER 2002—711
calcium-sulfide pellets that were obtained by the hydrogen reduction of calcium-sulfate pellets and reacted repeatedly up to ten cycles. The reduction kinetics of calcium-sulfate pellets with hydrogen gas is reported in the accompanying Part II.[15]
II. EXPERIMENTAL Experiments were carried out in a typical TGA apparatus described elsewhere.[13,14,16] The reactor was an INCONEL* *INCONEL is a trademark of Special Metals Corp., Huntington, WV.
Fig. 1—Equilibrium composition for the reaction of 1 mol of CaS with 1 mol of SO2 at a total pressure of 0.85 atm.
is excellent. A number of other processes for converting sulfur dioxide directly to elemental sulfur have been suggested previously and developed, but all these processes have either been discontinued or never been commercialized because of their complexities or costliness. The literature
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