Study On The Effects Of Different Ash Components During Carbothermal Reaction Of SiO₂ And Fe₂O₃

The current situation of coal-based energy structure in China leads to the serious problem of carbon emission and pollution.Therefore,it is urgent to demand the efficient and clean utilization of coal.The complexity of the structure of the solid fuel makes the various technologies based on solid fuels.So,it is necessary to have a deep understanding of solid fuels,especially coal and biomass,and the mechanism of minerals in the process of high temperature.In this paper,the influence of main minerals on the reaction process of coal and other solid fuels is studied in the background of coal gasification and chemical looping combustion.First,to investigate the carbothermal reduction of silicon-containing minerals in high temperature,the pure SiO₂,synthetic ash and high-silica coal ash mixed with graphite was heated in the tube furnace under different temperature.The results showed that Fe₂O₃promoted the carbothermal reaction of SiO₂,and the production of Fe_xSi_y improved the condition of SiO₂ reduction.CaO has inhibitory effect on the reduction of SiO₂.CaO reacts with SiO₂ and Al₂O₃ to form dense Ca-Al-Si eutectic in low temperature,and the reduction of it is more difficult than SiO₂.Al₂O₃ mainly exists in the form of amorphous phase and eutectic,and has little effect on the carbothermal reaction of SiO₂.Then,the effects of ash on Fe₂O₃ reduction were investigated.By adding different kinds of ash in Fe₂O₃,fixed-bed experiment was carried out with different carbon content.The reduction of Fe₂O₃ takes precedence over the reaction between Fe₂O₃ and minerals in ash in the case of sufficient carbon.When carbon is insufficient,Fe₂O₃ began to interact with different minerals in ash,generate a variety of composite iron compounds,such as MgFe₂O₄,Fe₂SiO₄,CaFe₂O₄ and Ca₂Fe₂O₅,the formation of these compounds could hinder carbothermal reaction process of Fe₂O₃.Finally,the chemical looping of Fe-based oxygen carriers was carried out in fixed bed by reciprocating the atmosphere.In the circulation,the effect of different ash components on the efficiency of Fe-based oxygen carriers was studied by changing the ash species,temperature and ash content.Different minerals shows different effects.K,Na,etc.significantly improve the reaction activity of Fe₂O₃,while SiO₂ reacts with Fe₂O₃ to form Fe₂SiO₄ which is difficult to be reduced.In addition,both the reaction temperature and ash content influence the reduction of Fe₂O₃.