Experimental Study And Analyses Of O₂ -CO₂ Production Based On Chemical Looping Method

CO₂ emission from the combustion of fossil fuel is the main source of greenhouse gases. Oxy-combustion is a very promising CO₂ capture technology, which is particularly suited to the coal-dominated energy structure of China. However, the net efficiency of power station based on oxy-combustion will significantly decline due to the air separation unit. How to apply oxygen is a key barrier to the implementation of oxy-combustion. Presently all air separation technologies produce pure oxygen, thus have the disadvantages of heavy investment cost and high energy consumption. Based on the fact that an O₂-CO₂ mixed stream with O₂ concentration between 20-40% rather than pure oxygen is needed for oxy-combustion, this paper studied a chemical looping method that directly produces this kind of O₂-CO₂ mixed stream to reduce energy consumption.Co-based oxygen carrier particles were prepared by dipping method, then XRD were used to study their compositions and SEM were used to observe their micro-structures. TGA experiments were conducted to study their oxygen absorption and desorption characteristics under different temperatures and different O₂ concentrations. The results indicated that this kind of particles did not react with CO₂, and it had quite good react rate for both absorption and desorption process. A relation between O₂ equilibrium pressure and temperature were obtained by thermodynamic calculations and experimental data, and shrinking-core model were used to study the kinetic parameters. Co-based oxygen carrier had been doubted that it's had low melting point and thus easy to deactivate due to sintering. In reply to this doubt, 150 cycles of absorption and desorption were conducted under high temperatures required by the oxygen process, very high cyclical stability were observed without any deactivation. Experiments and theoretical analyses indicated that the SO₂ and NO in the flue gas would have no effect on Co-based oxygen carrier under process temperatures, thus validated the feasibility to use flue gas as the purge gas.Absorption and desorption experiments were also conducted in fixed-bed reactor, to study the effects of temperature and gas flow rate on the absorption and desorption characteristics. O₂-CO₂ mixed stream with O₂ concentration above 20% was produced continuously for 12 hours in two parallel fixed-bed reactors using gas switch, validated the feasibility of continuous O₂ production.O₂ production system and operation parameters suited to Co-based oxygen carrier were proposed based on thermodynamic equilibrium and heat analyses. Then work and heat consumed in the oxygen process were calculated by Aspen, the results showed significant advantage compared with cryogenic oxygen method. The quantity of Co-based oxygen carrier needed for oxygen process was estimated to check the feasibility on costs and mineral reserves.