Preparation Of New Calcium-based Composite Absorbents By Impregnation And Tar Reforming Investigation

The calcium-based sorption enhanced biomass gasification technology can make full use of clean and renewable biomass energy to produce high concentration of H2-containing syn gas.At the same time,the pre-combustion capture of greenhouse gas CO2 plays an important role in improving energy efficiency and coping with global climate change.A key issue for research and application of this technology is to retain good activity of carbon dioxide capture high mechanical strength and efficiency to eliminate biomass gasification tars.In this investigation,a new method of synthesizing calcium-based composite absorbent(Ca-Al-Fe)based on impregnation method is proposed.The physical and chemical characteristics of the new absorbent and the influence of the key preparation parameters on its physical and chemical properties are studied including the cyclic carbonation activity and the mechanical strength of the absorbent.And the preparation method of new type calcium complex absorbent and optimization of preparation parameters were clarified.Tar components of toluene,1-methyl-naphthalene steam reforming experiments were conducted to verify the advantages of new composite absorbent over other calcium-based absorbents.The effects of reforming reaction conditions on the removal of tar were also investigated,and the optimal operating conditions were obtained,which will provided valuable informations for the application of this technology.The impregnation method of the new composite calcium-based absorbent Ca-Al-Fe is mainly divided into two steps:First,CaO and aluminum precursor are coupled,and then the resulting solid is mixed with iron precursor.The key preparation parameters of the impregnation method were studied,including calcium precursor,impregnating solvent and calcination temperature.The optimal conditions were found to be calcium acetate,isopropanol and 900 ?.Chemical and physical properties of the new composite calcium-based absorbent Ca-Al-Fe were characterized.The chemical composition of the new absorbent mainly includes CaO,mayenite and brownmillerite,and oxygen free species chemical structure.In the multi-cycle CO2 absorption carbonation reaction,the new absorbent did not appear to reduce its activity,the stability of the reaction significantly increased,because mayenite effectively inhibited sintering of CaO.The mechanical strength of the new absorbent is significantly improved.Toluene and 1-methylnaphthalene were used to carry out the reforming experiments,in order to verify the advantages of new absorbents over other calcium-based absorbents for tar removal and examine the optimal operating conditions.Compared with conventional CaO,tar conversion rate of toluene and 1-methylnaphthalene increased by 65.1%and 54.8%respectively.At the same time,the coke deposition on absorbent-surface decreased by 65.4%and 82.5%respectively.In the presence of a new type of absorbent,the main reaction pathways of toluene and 1-methylnaphthalene are dehydrogenation reaction and methyl fragmentation reaction respectively.Operating reaction conditions have significant impacts on tar reforming.Reducing reaction temperature,the amount of iron loading,H2O/C molar ratio is not favorable for tar removal and inhibiting carbon deposition.The use of granular new absorbent resulted in better tar reforming effect,initially verifying the feasibility of using new absorbent in fluidized bed reactors.In the presence of a new type of absorbent Ca-AI-Fe,toluene-optimized reforming reaction conditions were 700 ?,the loading of iron was 10%,the molar ratio of H2O/C was 2.0.The optimum conditions for the reforming reaction of 1-methylnaphthalene were 800?,the loading of iron was 10%,and the molar ratio of H2O/C was 2.0.