REMOVAL OF H2S FROM COAL-GAS USING LIMESTONE - KINETIC CONSIDERATIONS

The calcium carbonate contained in limestone becomes thermodynamically capable of sorbing hydrogen sulfide from high-pressure coal gas at temperatures above 600-degrees-C, typically well below the calcination temperature. Limestone can be used more effectively as a sorbent for hydrogen sulfide in high-temperature gas-cleaning applications if it is prevented from undergoing calcination since calcium oxide may sinter rapidly. For large (millimeter) sized particles typically used in gas cleaning, sintering of uncalcined limestone was found to be insignificant in the temperature range 750-900-degrees-C. Poor conversion of the solid upon reaction with H2S is caused by sintering of the CaS product layer, which can be seen from scanning electron microscopy photographs. Sintering of CaS is rapid in an atmosphere that contains CO2, but is slow under N2 or H-2. The kinetics of CaS sintering under CO2 was determined for the temperature range 750-900-degrees-C.