Chemical Looping Combustion Characteristics Of Low-cost Oxygen Carriers Prepared By Spray-drying Method On Large Scale

The CO₂ produced by the burning of fossil fuels is the main cause of the greenhouse effect.Chemical Looping Combustion（CLC）is an innovative combustion method that can realize capture of CO₂ produced by the combustion of fossil fuels with low energy consumption.Oxygen Carrier（OC）is the core of chemical looping combustion technology.Many OC preparation methods in experimental scale have disadvantages such as complex preparation process,low single-shot yield,and high raw material cost,which are difficult to meet the requirements of large-scale preparation.In this work,development of batch production process for cheap OC and investigation of long period performance of cheap OC were studied,which mainly includes the followings.Firstly,the pilot scale spray drying method with hematite and copper ore as raw materials for oxygen carrier was explored.A variety of spray drying parameters,such as air inlet temperature,solid content and additive content,were optimized,and the spherical Cu20Fe80OC was successfully synthesized.Subsequently,the characteristics of Cu20Fe80 OC with coal were studied in in situ gasification chemical looping combustion（i G-CLC）process via batch fluidized bed reactor,and the effects of temperature,oxygen/fuel ratio,coal type and cyclic tests on the performance of oxygen carrier were investigated.It was found that the reaction rate increased with the increase of temperature,peroxidation coefficient and the decrease of coal rank.SEM characterization showed that the spherical shape of OC was maintained,and no sintering phenomenon on the surface was observed before and after the cycle.Considering the preparation process,raw material cost and reactivity of oxygen carrier,the composite metal oxide OC prepared by spray drying method with cheap ore as raw material has the potential to be applied in industrial CLC device.Furthermore,the preparation scale of spray drying process was further expanded,and the large-scale production of cheap composite OC was preliminarily realized by building an industrial-scale spray drying granulation platform.At the same time,montmorillonite was introduced into the OC raw material as an inert carrier to improve the stability of OC particles under long-term cycles.Through 100 redox cycles in thermogravimetric analyzer（TGA）,considering the stability,weight loss and reaction rate of OC,the oxygen carrier modified with10 wt.%montmorillonite（named Cu Fe10M）had the best performance.Subsequently,the i G-CLC experiment of Cu Fe10M OC and coal was carried out for 100 cycels in batch fluidized bed reactor.The results showed that the CO₂ concentration and oxygen transfer rate showed a trend of first rising and then falling within 100 cycles.The XRD results proved the stability of the CuFe10MOC chemical composition within 100 cycles.The SEM results found that the surface morphology of the oxygen carrier changed within 100 cycles,and surface sintering occured after 100 cycles.Finally,based on the optimized montmorillonite modification ratio（10 wt.%）,the use of cheap industrial waste red mud as the raw material of OC was further considered.Four oxygen carriers modified by montmorillonite,which were based on red mud or ore and,were prepared by spray drying in batches.100 redox cycles were also carried out in TG,and it was found that the red mud-based OCs had a high utilization rate of active ingredients.Subsequently,the Cu Red10M OC（copper ore,red mud and montmorillonite as raw materials）was subjected to30 cycles in batch fluidized bed.The results showed that Cu Red10M always had higher CO₂yield and combustion efficiency than Cu Fe10M,which may be due to the larger specific surface area and the existence of Na⁺in red mud.In the XRD patterns,the Na element was detected in the form of Na Al Si O₄ compound,which effectively alleviated the volatilization of alkali metal Na during the cycles.