Hot Gas Clean‐Up with Dolomites: Effect of Gas Composition on Sulfur Removal Activity

Abstract

In this study high temperature desulfurization performance of dolomite was investigated for coal‐derived gases. Experimental results indicated that dolomite was active and could be effectively used for gas desulfurization at temperatures greater than 1023 K. However, due to thermodynamic equilibrium restrictions, in the presence of water vapour the H2S concentration could not be reduced below 150–200 ppmv by dolomite. Thermodynamics predicts that water vapour can adversely affect the chemical equilibrium between H2S and calcium oxide. The presence of CO2 in the gas stream did not have a suppressing effect on the sulfidation reactions, whereas it tended to depress the calcination of CaCO3 to CaO. During the dolomite‐based sulfur removal process, both the water‐gas shift and reverse water‐gas shift reactions could also occur depending on the reacting gas compositions. The Boudouard reaction could take place and proceed at 1023 K depending on the CO/CO2 ratio in the feed stream. This was dictated by the thermodynamic characteristics of the reaction. COS formation was observed due to the reactions taking place between H2S and CO/CO2 during H2S removal by dolomite. Trace amounts of methyl mercaptan were also detected in the reactor effluent gases during H2S removal. Methyl mercaptan formation might be attributed to the reactions taking place between H2S, H2, and CO and/or CO2.