| Fossil fuel combustion is the main contributor to increase atmospheric CO2concentration, an important greenhouse gas that leads to global climate change. Now governments and the scholars in the world develop the new technology of CO2emissions and has achieved preliminary results. Chemical looping combustion (CLC) has been recognized as a promising technology with high efficient use of energy and inherent separation of CO2. And CLC of metal oxygen carrier is verified by the pilot tests. In this paper, aiming at the existing problem of Ca-based oxygen carrier in CLC, the related experiments are conducted through the methods of modification, molding, adding lime and hematite, and Ca-based oxygen carriers are characterized by a variety of characterization methods. Finally,1kW interconnected fluidized bed reactor for Ca-based oxygen carrier is built and operated.Firstly, the experimental research of CLC is carried out in the fixed bed reactor, investigating the reactions between CH4and Ca-based oxygen carrier with Ni-Fe mixed catalyst,. Ni-Fe mixed catalysts can greatly improve the reactivity of CaSO4reduction reaction. With the increase of temperature, the conversion of the oxygen carrier increases significantly. CH4concentration and mass of oxygen carrier affect the reduction reaction obviously, however the particle size has a little effect on the reduction. Meanwhile the mechanisms of sulfur release, carbon deposition and combustible gas are analyzed, and the long-time reduction-oxidation test proves the feasibility of CaSO4/CaS as an oxygen carrier.Secondly, CLC of methane with lime addition to CaSO4as an oxygen carrier is carried out in a laboratory fluidized bed reactor. The increase of lime mass gives rise to an increase in the conversion of CaSO4. Moreover, the more lime mass results in a lower sulfur release rate. The lime particle size has no major effect on the conversion of CaSO4. During the cyclic test, the average desulphurization rate of lime is up to78.77%.Thirdly, the char-based CLC with Fe2O3addition to CaSO4as oxygen carriers is conducted in a laboratory fluidized bed reactor. Fe3O4as catalyst could decrease the activation energy of CaSO4reduction and increase the reaction rate. The higher temperature would enhance the gasification rate of char, the reaction rate of the reaction with CaSO4and char gasification products, the carbon conversion, CO2selectivity formation and CO2yield increase. Moreover, the temperature is higher, the peak value of SO2is greater. And the time of peak of SO2is delayed with the increase of temperature because of the inhibition effect of Fe2O3. Fe/S ratio has a little effect on the conventional product gas composition. During the cyclic test, the conversion decreases gradually, SO2cumulative rate firstly decreases and then increases. The SO2cumulative rate during the reduction is obviously less than oxidation.Furthermore, using Taguchi robust design method for optimization of oxygen carrier extrusion conditions and the favorable oxygen carriers are comprehensively studied in a fixed bed reactor. The experimental results show that SB powder enhances both mechanical strength and conversion of CaSO4.Finally, a1kW interconnected fluidized bed reactor of chemical looping combustion for Ca-based oxygen carrier is successively designed and built, then cold and hot experiments are carried on at normal pressure. Quick start as well as easy and stable operation of the cold is found under most conditions, and no gas leakages between the FR and AR are detected. Chemical looping combustion of CH4in a1kW bed reactor system with Ca-based oxygen carrier is achieved with high fuel conversion to CO2and H2O. The results show that CaSO4/CaS suits as an oxygen carrier in addition to the mechanical properties and reduction rate needs to be improved. |
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