Experimental Study On Cyclic Reaction Characteristics Of K/Mg And Cu Modified Iron-based Oxygen Carriers In Chemical Looping Combustion

The continuous development of the world economy has led to the increasing consumption of fossil fuels,and the large amount of greenhouse gas CO₂ emissions has exacerbated the further deterioration of the global environment.China as the world's second largest economy,has become a major energy consumption,but China's inherent resource endowment has decided that China's energy consumption structure is dominated by coal.Therefore,the development of coal-based solid fuel carbon emission reduction technology has important practical significance.Chemical looping combustion as a new type of combustion,can be simple and low energy consumption to achieve the separation and capture of CO₂,which has been widespread concern.Oxygen carrier as the basic elements of chemical looping combustion,and iron-based oxygen carrier because of its wide range of sources and environmentally friendly,so this paper to iron-based oxygen carrier as a research object for experimental research.In this paper,K₂CO₃/MgO modified iron-based oxygen carrier and Fe/Cu composite oxygen carrier were prepared by coprecipitation.Al₂O₃ was used as inert carrier.In the early stage,the prepared fresh oxygen carriers were subjected to cold wear test on a small fluidized bed to study the wear resistance of each series of oxygen carriers.And the preparation of coal char and pine semi-coke for the subsequent fixed bed cycle test to prepare.Then two series of iron-based oxygen carriers with different proportions of MgO and CuO were added respectively.The primary reduction reaction with CH₄ was carried out on the thermogravimetric analyzer to study the primary reduction conversion of the oxygen carrier.And the multicycle reaction of oxygen carrier with coal char and pine semi coke was carried out in a fixed bed system,and the reactivity of oxygen carrier under the multi-cycle conditions was studied,including carbon conversion rate and CO₂ capture efficiency.The XRF characterization of K₂CO₃/MgO modified iron-based oxygen carriers was also carried out,and the loss of K elements in oxygen carriers after 15 cycles was studied.Finally,The microstructures and phase composition of two series of oxygen carriers were characterized by SEM and XRD respectively.The results show that the higher the addition ratio of MgO,the better the wear resistance of the oxygen carrier,especially to reduce the loss of K elements have a positive significance at the same time.However,the addition of MgO also delayed the activity of the oxygen carrier at the beginning of the reaction,so that the reaction rate of the oxygen carrier was slightly delayed.In the multi-cycle reaction,the carbon conversion efficiency and CO₂ capture efficiency of 5% MgO were the best,which had a positive effect on the maintenance of oxygen carrier activity.In the Fe/Cu composite oxygen carrier,the weight loss of 6Fe1Cu3 Al was the highest,and the primary reduction conversion rate,carbon conversion rate and CO₂ capture efficiency were the best.Therefore,the proportion of Cu should not be added too high,from the SEM analysis,the high proportion of Cu can lead to the surface sintering of oxygen carrier under the condition of multi cycle,thereby reducing the oxygen carrier activity to maintain.XRD analysis showed that CuO and Fe₂O₃ reacted to produce CuFe₂O₄ and CuFe₂O₄ with spinel structure,which had positive effect on the oxygen transport rate of oxygen carrier.