Characteristics of CaS–CaO Oxidation for Chemical Looping Combustion with a CaSO₄-Based Oxygen Carrier

Abstract

The oxidation of CaS to a CaSO 4 oxygen carrier suffers SO 2 release. To capture SO 2 released, an amount of CaO particles was mixed with CaS particles. Isothermal kinetics of the CaS–CaO oxidation reaction has been conducted in a thermogravimetric reactor combined with a Frourier transform infrared spectroscopy (FTIR) analyzer. The effects of the reaction temperature, O 2 concentration, and molar ratio of CaO/CaS on CaSO 4 generation and SO 2 emission were investigated. The chemical compositions, morphology structures, and element distributions on the surfaces of solid residuals were characterized by FTIR and scanning electron microscopy–energy-dispersive X-ray spectroscopy instruments. The results show that the oxidation products of CaS species are mainly composed of CaSO 4 . A small amount of SO 2 is released from CaS oxidation, causing losses of the oxygen carrying capacity of a CaSO 4 -based oxygen carrier. Using a CaO additive in the CaS oxidation process reduces SO 2 liberation, improves the CaSO 4 selective yield, but results in an increase in remaining CaS species in solid residues. There is a general positive correlation between the remaining percentage of CaS species and the SO 2 selective yield. The SO 2 liberation varies with the reaction temperature, O 2 concentration, and CaO/CaS molar ratio. At 900 °C, a CaO/CaS molar ratio of 1, and 5% O 2, SO 2 released from CaS oxidation is completely trapped by the CaO additive.