Kinetic and structural studies of calcium-based sorbents for high-temperature coal-gas desulfurization

The absorption of H2S by large particles of limestone, dolomitic limestone and dolomite (average mass-radius of 0.40 mm) was tested under simulated coal gases. Below the calcination temperature of CaCO3 (about 900 degrees C under 1 bar of CO2), complete conversion of the calcium carbonate to calcium sulfide can only be achieved with dolomite. Above the calcination temperature of CaCO3, the conversion to CaS is complete for all three sorbents in about one hour when 10,000 ppm H2S is present in the gas phase. Large particles of limestone thus appear to be a suitable sorbent for high-temperature coal-gas desulfurization (above about 900 degrees C). A mathematical model based on the kinetic information collected in this work predicts the desulfurization performance of a packed or moving bed of limestone particles. Finally, a low-temperature regeneration scheme for the spent sorbent (CaS) in which sulfur can be subsequently recovered as the element is suggested.