Investigation Of Cu-based Oxygen Carrier With The Presence Of Coal Ash In Chemical Looping Process

With the development of industrial and the improvement of people's life standards,more and more carbon dioxide has been released from the combustion of coal,petroleum,and natural gas,which has become one of the major causes of the increasingly serious greenhouse effect.Therefore,reducing CO₂ emissions has become a hot topic in the world today.Chemical-looping combustion?abbreviated as CLC?is proposed as a novel combustion method that can efficiently capture CO₂.Compared with the traditional technology,the advantages of CLC was inherent CO₂ separation,lower energy consumption and cost.At first,the concentration of CLC technology mainly focused on chemical looping combustion systems using gaseous fuels.However,compared with gaseous fuels,solid-fuel fuels,as a more general and cheaper main energy source,are also one of the major sources of CO₂ emissions.The chemical looping oxygen uncoupling?CLOU?has been proposed as a derivative CLC technology based on the CLC using solid fuel.However,during the chemical looping cycle involving solid fuels,solid fuel ash will be produced in the fuel reactor and recycled to the air reactor through the solids.Although ash can be separated by a cyclone,it is inevitably deposited in the reaction system because its density is much lower than that of the oxygen carrier.Therefore,how the solid fuel ash reacts with the oxygen carrier and affects the performance of the oxygen carrier is a subject worthy of study.Here,the potential interaction between different coal ash and CuO/MgAl₂O₄oxygen carriers in the CLC/CLOU process was studied experimentally in this paper.The impact factors including the types of coal ash,coal ash content and cycle times were evaluated.XRF,XRD,BET-BJH and SEM-EDS techniques were used to characterize the changes in oxygen carriers containing coal ash,and the effects of the presence of ash on the kinetics of oxygen uncoupling reactions were also evaluated in detail.The study obtained the following results:?1?It was found that the presence of coal ash contained Fe₂O₃ in the oxygen carrier could significantly promote the redox reaction of the oxygen carrier.During the CLC process based on Cu-based oxygen carrier,owing to some of the coal ash?S2Y and S1H?containing a certain amount of Fe₂O₃ which acted as an active oxygen carrier in the CLC process,it caused the sample after mixing has stronger redox ability than pure oxygen carrier..?2?It was found that the presence of coal ash contained Al₂O₃ in the oxygen carrier could significantly inhibit the decoupling of the oxygen carrier.In the CLOU process based on the Cu-based oxygen carrier,the presence of ash will lead to a significant decrease in the oxygen oxygen evolution rate of the oxygen carrier during the oxygen uncoupling process.The most probable reason is that a large amount of Al₂O₃ in the coal ash will consume free CuO in the reaction.As a result,oxygen-inert CuAl₂O₄ is generated,resulting in a significant decrease in the oxygen-releasing and oxygen-absorbing capacity of the oxygen carrier.As the ash content increases,the degree of ashing of the sample increases,and the oxygen release ability of the oxygen carrier gradually decreases.As the number of cycles increases,the above effects become more serious.?3?It was found that the presence of coal ash in the oxygen carrier resulted in a significant changes in the oxygen release kinetics.In the oxygen uncoupling process based on the Cu-based oxygen carrier,the oxygen release activation energy of the oxygen carrier has been significantly increased due to the presence of ash,making the oxygen uncoupling more difficult,and the type of oxygen release reaction changed from the shrinking-core model to a nucleation growth model.