Experimental Investigation On The Reduction Of Modified Calcium Sulfate Oxygen Carriers For Chemical Looping Combustion

With the rapid development of global economy,CO₂ emission arising from fossil fuel combustion increases year by year.The global warming caused by CO₂ emission has aroused worldwide attention,so it is urgent to develop technology of CO₂ emission reduction.Chemical looping combustion is an innovative combustion technology to achieve CO₂ separation.Oxygen carrier is a key compnent in the chemical looping combustion.Non-metallic oxygen carrier CaSO₄ has high oxygen ransfer capacity,low price and extensive source,but its activity is low.In this paper,new CaSO₄ oxygen carriers modified by active additives are prepared,and the reaction characteristics of these CaSO₄ oxygen carriers are studied.CaSO₄ oxygen carriers modified by the ternary eutectic salt were prepared by physical mixing and impregnation method,and the experiments about modified CaSO₄ oxygen carriers were carried out in a bench-scale fluidized-bed reactor.The effects of preparation process and addition techniques on the combustion characteristics of coal char were studied.After adding the ternary eutectic salt,the gasification rate of coal char and CaSO₄ reduction reactivity are significantly improved.The ternary eutectic salt has higher catalytic activity than alkali carbonate mixture of the same composition,which is mainly due to formation of new alkali carbonate?LiKCO₃ and LiNaCO₃?.The samples prepared by the physical mixing method and impregnation method show no significant difference in the combustion performance.The physical mixing method is slightly superior to the impregnation method,which mainly attributes to more simple preparation process of physical mixing method.In addition to the ternary eutectic salt,CaSO₄ oxygen carriers modified by by CuO or MnO₂ were prepared by physical mixing and impregnation method,and the experiments about the compound CaSO₄ oxygen carriers were carried out in thermo gravimetric analyzer?TGA?.The influences of addtion method,addition amount and temperature on the compound CaSO₄ oxygen carriers were investigated.The reaction activities of compound CaSO₄ oxygen carriers modified by by CuO or MnO₂ are greatly increased,and compound CaSO₄ oxygen carrier prepared by impregnation method gives high reactivity than that prepared by mechanical mixing method.The optimum amount of CuO is 5mol.%,and the best amount of MnO₂ is 10 mol.%.CuO/CaSO₄ and MnO₂/CaSO₄ compound oxygen carriers present high reaction activity at low reaction temperature.CuO/CaSO₄ and MnO₂/CaSO₄ compound oxygen carriers have almost the same reactivity.The reactivity of CuO/CaSO₄ oxygen carrier is always high in the whole reaction process;while the reactivity of MnO₂/CaSO₄ oxygen carrier in the initial stage of the reaction is really high,after which the reactivity continuously decreases.The difference of the reactivity between these two oxygen carriers is mainly related to the distribution of CuO or MnO₂ on CaSO₄ particles.