Experimental Study On The Effects Of Modified Bauxite On The Pyrolysis And Gasification Of Biomass

Biomass,as a kind of renewable energy,has attracted much attention for its advantages of environmental friendliness and abundant reserve.Pyrolysis and gasification are two common utility patterns of biomass.However,the by-product of tar is inevitable in the process of pyrolysis and gasification,and it is easy to cause corrosion and pollution of downstream pipelines and equipment.The catalytic cracking of tar and improving components of gas production can be achieved by adding additives during pyrolysis and gasification.In this paper,modified bauxite was used as an additive to conduct the experimental study on biomass pyrolysis and gasification.Initially,the weight loss characteristics of rice straw and bauxite were investigated with different reaction atmosphere,heating rates and mixing proportion by thermogravimetric analyzer.The weight loss characteristics of rice straw and bauxite were analyzed,and the ignition point and burnout temperature of rice straw were calculated by the formula in combustion science.Secondly,according to the weight loss characteristics,pyrolysis of rice straw was studied in the fixed bed reactor in order to study the effects of impregnating materials,impregnation concentration and reaction temperature.The effect of different impregnant on the improvement of gas production characteristics of rice straw was studied so as to select the ones with better performance.Yet the concentration of impregnating solution and reaction temperature was investigated.The results indicate that the CuCl₂ and Ni（NO₃）₂ modified bauxite has obvious improvement on the pyrolysis gas production of rice straw.The CuCl₂ modified bauxite has the best performance in improving the low heating value of rice straw pyrolysis gas.The effective coating of bauxite multiplies with the concentration increase of impregnating solution,and the amount of pyrolysis gas rises correspondingly.The catalytic cracking of tar is promoted with the increasing of the reaction temperature in the range of 650 ^oC and 800 ^oC,which also increases the gas production and the low heating value of pyrolysis gas.Finally,on the basis of the above experimental studies,the gasification experiments of rice strew was performed in a bubbling fluidized bed with the modified bauxite as bed material.The effects of modified materials,equivalent ratio（ER）and reaction temperature were investigated.The results show that the modified bauxite with Cu performs the best in improving the gasification characteristics.Comparing with the control group,the low heating value of gasification gas increases by 14.3%,and the conversion efficiency of fixed carbon increases by17.91%.The best gasification performance is obtained at the ER of 0.3,with the low heating value of product gas 4.51MJ/Nm³ and the conversion efficiency of fixed carbon 84.62%.In the range of 600 ^oC⁷50 ^oC,the activity of the modified bed material increases with the reaction temperature,as well as the lower concentration of tar in the gas production.The concentration of tar in the gasification gas is only 10.59g/Nm³ at 750 ^oC.Furthermore,operation time has an influence on the composition of the modified bauxite.As the experiment progress,the content of active substances decreases,while the content of K₂O and other substances increases.The content of active materials in the modified bauxite tends to be stable after 12 hours,while no carbon deposition is found during the whole operation process of the bubbling fluidized bed.