Abstract The sulfur values are recovered from calcium sulfate principally in the form of sulfur dioxide by a two-stage reduction process. The calcium sulfate to be decomposed and the reducing gases pass countercurrently through the two-stage system in which the solids are maintained in a fluidized state. Temperatures within the range of from about 600* C. to about 900* C. may be employed. Steam may be condensed out of the product gas stream to provide a product gas containing a major proportion of sulfur dioxide and a minor proportion of carbon dioxide. The calcium sulfate is first reduced to calcium sulfide and is then further reduced in the second stage to calcium oxide. Sand may be mixed with the calcium sulfate being decomposed in order to minimize agglomeration of the solids.
The process of claim 1 in which the temperature in each stage is maintained at from about 600* C. to about 900* C.
Claim 2
Dependent Claim
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The process of claim 1 in which the reducing gases are passed upwardly through each stage at a velocity sufficient to maintain said calcium solids in a fluidized state.
Claim 3
Dependent Claim
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The process of claim 1 in which steam is present in step c in an amount of from about 2 to about 6 moles per mole of reducing gas.
Claim 4
Dependent Claim
137 words
A process for converting calcium sulfate which comprises: a. drying gypsum to a substantially anhydrous form, b. contacting the substantially anhydrous gypsum with hydrogen sulfide in a first stage at a temperature of from 600* C. to about 900* C. to form calcium sulfide and a gas stream containing sulfur dioxide, c. recovering the sulfur-dioxide-containing gas stream, d. contacting said calcium sulfide with gas selected from the group consisting of hydrogen, carbon monoxide, methane, natural gas, primary reform gas and mIxtures thereof, and from about 2 to 6 moles of steam per mole of said gas in a second stage at a temperature of from 600* C. to 900* C. to form calcium oxide and a hydrogen-sulfide-containing gas stream, e. recovering said hydrogen-sulfide-containing gas stream and recycling said hydrogen sulfide stream for use in said first stage.