CaSO4 is an attractive oxygen carrier for chemical looping combustion（CLC） because of its high oxygen capacity and low price. The utilization of a CaSO4 oxygen cartier suffers the problems of sulfur release, and dea...CaSO4 is an attractive oxygen carrier for chemical looping combustion（CLC） because of its high oxygen capacity and low price. The utilization of a CaSO4 oxygen cartier suffers the problems of sulfur release, and deacti- vation caused by sulfur loss. With respect to the fact that partial sulfur release could be recaptured and then recycled to CaSO4 by CaO sorbent, the mixture of CaSO4-CaO can be treated as an oxygen carrier. Thermodynamics of CaSO4 and CaSO4-CaO reduction by CO have been investigated in this study. The sulfur migrations, including the sulfur migration from CaSO4 to gas phase, mutual transformation of sulfur-derived gases and sulfur migration from gas phase to solid phase, were focused and elucidated. The results show that the releases of S2, S8, COS and CS2 from CaSO4 oxygen carrier are spontaneous, while SO2 can be released at high reaction temperatures above 884 ℃. SO2 is the major emission source of sulfur at low CO/CaSO4 molar ratios, and COS is the major part of the byproducts as soon as the ratio exceeds 4 at 900℃. Under CO atmosphere, all the sulfur-derived gases, SO2, S2, S8 and CS2, involved are thermodynamically favored to be converted into COS substance, and are spontaneously absorbed and solidified by CaO additive just into CaS species, which may be recycled to CaSO4 as oxygen carrier in the air reactor. But high reaction temperatures and high CO2 concentrations are adverse to sulfur capture.展开更多
基金Supported by the National Natural Science Foundation of China（Nos.51306084, 51374004）, the Scientific and Technological Leading Talent Projects in Yuunan Province, China（No.2015HA019） and the Natural Science Foundation of Kunming University of Science and Technology, China（No.KKZ3201352030）.
文摘CaSO4 is an attractive oxygen carrier for chemical looping combustion（CLC） because of its high oxygen capacity and low price. The utilization of a CaSO4 oxygen cartier suffers the problems of sulfur release, and deacti- vation caused by sulfur loss. With respect to the fact that partial sulfur release could be recaptured and then recycled to CaSO4 by CaO sorbent, the mixture of CaSO4-CaO can be treated as an oxygen carrier. Thermodynamics of CaSO4 and CaSO4-CaO reduction by CO have been investigated in this study. The sulfur migrations, including the sulfur migration from CaSO4 to gas phase, mutual transformation of sulfur-derived gases and sulfur migration from gas phase to solid phase, were focused and elucidated. The results show that the releases of S2, S8, COS and CS2 from CaSO4 oxygen carrier are spontaneous, while SO2 can be released at high reaction temperatures above 884 ℃. SO2 is the major emission source of sulfur at low CO/CaSO4 molar ratios, and COS is the major part of the byproducts as soon as the ratio exceeds 4 at 900℃. Under CO atmosphere, all the sulfur-derived gases, SO2, S2, S8 and CS2, involved are thermodynamically favored to be converted into COS substance, and are spontaneously absorbed and solidified by CaO additive just into CaS species, which may be recycled to CaSO4 as oxygen carrier in the air reactor. But high reaction temperatures and high CO2 concentrations are adverse to sulfur capture.
