| More attention is paid to reduce emissions of greenhouse gases such as carbon dioxide due to the frequent extreme weather caused by global warming in recent years. Concequently, carbon dioxide capture and storage technology has become a research hotspot. Chemical looping combustion (CLC) technology, characterized by CO2 inherent separation without extra energy consuming, low NOx emission and high efficient, is considered as a promising technology of carbon dioxide capture. Chemical looping combustion technology gives a new way to solve the problems of energy and the environment, while the oxygen carriers are the prerequisites to explore the process of chemical looping combustion. A series of investigations on the oxygen carriers for chemical looping combustion were carried out in this paper.Firstly, the mechanism of calcium sulfate pyrolysis and its reaction with reducibility gas (H2, CO) using double extrapolation was studied in this paper. Thirty kinds of common mechanism functions of and their corresponding kinetic parameters were presented using the precise temperature integral form. The most probable mechanism is evaluated to be nucleation and nuclei growth model, and their probable mechanism functions were G(α)=[-ln(1-α)]2, G(α)=[-ln(1-α)]1/3 and G(α)=[-ln(1-α)]1/2 respectively.The effects of temperature and partial pressure of reducing gas on the reaction between oxygen carrier and reducing gas were also investigated. The reactant components varied with the reaction temperature. The fractions of by-products CaO are increased with increasing temperature. However, the above reaction rate would be very low at low temperature; oxygen carrier particles show a good regeneration at a relatively low temperature and heating rate. To some extent, the higher reducing gas partial pressure was, the greater main reaction rate favored reactions. Reaction products were almost the calcium sulfide when the partial pressure of reducing gas reached a certain value, and then the reaction products and the reaction rate would not change with the partial pressure of reducing gas increasing.Based on the study on calcium sulfate oxygen carrier and its structure characteristics and reaction feature, the chemical and physical properties of calcium sulfate oxygen carrier were modified by different particle sizes of calcium carbonate. The experiment results showed that the reactivity and regeneration of calcium sulfate oxygen carriers modified by calcium carbonate were improved with less side reaction. The regeneration of the calcium sulfate oxygen carrier modified by the nano-calcium carbonate was better then unmodified oxygen carriers. When the acid treated calcium sulfate was modified by the calcium carbonate, the loss of calcium sulfate was very low after eight redox cycles.Considering the reaction rate of the solid fuels for chemical-looping combustion slower, calcium sulfate oxygen carrier was modified by three trace metallic oxides (ferric oxide, copper oxide and nickel oxide) using the wet impregnation method. The reaction rate of the modified calcium sulfate was improved. The reduced calcium sulfate was characterized by scanning electron microscopy (SEM) and XRD respectively on its surface morphology and physical form. It has been found that the main cause on higher reactive of oxygen carrier modified by metal oxides was attributed to its basic pore structure and surface properties, and also the catalyticaction of the metallic oxide.The fuel reactor, a high temperature fluidized bed with multiple angles jetting pipes, was designed in this paper. And the cold and heat flow characteristics of the oxygen carriers and solid fuel particles were researched in the reactor. The effect of temperature on the minimum fluidization velocity of particles was examined. Through experiment and empirical equation, the law that the minimum fluidization velocity of oxygen carrier particles increased with temperature decreasing was obtained. Also the minimum fluidization velocity of the oxygen carrier particles and coal particle binary system with the same particle size and different density was studied in this paper. The error between experiment value and calculate value become smaller with the mass ratio of coal particles and oxygen carriers increasing, due to the relatively larger difference of the density between two particles.
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