Phase diagram of CaSO reductive decomposition by H and CO

The CaSO reductive decomposition is an interesting issue in both the reduction zone of fluidized bed combustors (FBCs) for coal combustion and the fuel reactor of chemical-looping combustion (CLC) system. Under CO or H atmosphere, CaSO is reduced to CaS and CaO, together with the releases of gas sulfides, which causes environmental pollutions. To lessen sulfur release, it is important to figure out the chemical stability of CaSO reductive decomposition. Thus, the chemical stability of CaSO/CaS/CaO under CO or H atmosphere was studied in consideration of SO, COS and HS emissions. The results show that regions I (VI), II (V), and III (IV) are the stability fields of CaSO, CaS and CaO, respectively. The range for CaO stability is increasing with reaction temperature and partial pressures of CO and HO. Within the reaction temperature range of 800 and 1,000 °C, when the CaSO-CO-H reaction system reaches the triple equilibrium point, the main gas sulfur released is SO, followed by HS, while COS generation is much smaller. In a real reaction system, when the values of real P/P (P/P), P, P (P), P (P) and T fall into Region I (IV), or II (V), the final product should be CaSO or CaS, and the sulfur release from CaSO reduction can be controlled.