In Situ Gasification Chemical Looping Combustion of Coal Using the Mixed Oxygen Carrier of Natural Anhydrite Ore and Calcined Limestone

The utilization of CaSO4-based oxygen carrier suffers the deactivation problem caused by sulphur loss. To capture the gas sulphides and to improve the stability of CaSO4 oxygen carrier, calcined limestone was introduced into the fuel reactor of Chemical Looping Combustion (CLC). Kinetic behaviors and thermodynamics of the combined process of coal gasification and oxygen carrier reduction using the mixed oxygen carrier CaSO4-CaO under different atmospheres were investigated. The effects of reaction temperature, gasification intermediate, and molar ratio of CaO to CaSO4 on gas sulphide emissions, CO2 generation, and distribution of other gas emissions and characterization of solid products are taken into account. It is found the CaO-based additive evidently suppressed the sulphur emissions, and improved both chemical reaction rate and CO2 generation efficiency. The sulfation products, both CaS and CaSO4, can be used as oxygen carrier later. The optimum reaction parameters are evaluated and obtained in terms of gas sulphide emissions, CO2 capture, other gas releases and maintenance of oxygen transfer capability.