Study On Pyrolysis Characteristics Of Biomass Briquette

As an renewable resource,biomass energy plays an irreplaceable role in the sustainable development of human society.If the raw biomass materials are combusted to obtain energy by the traditional way,it can cause many problems such as low thermal efficiency,labor intensity,environmental pollution and so on.Solid shaping and pyrolysis technologies are the most effective measures to convert biomass energy into high-grade clean energy.In this paper,based on the research of curing technology of biomass energy in the early stage of the research group,the reaction mechanism of pyrolysis of biomass briquette was studied.This paper mainly carried out the following work.(1)Based on the kinetic model of biomass pyrolysis and the microcosmic equation,the pyrolysis model of biomass briquette was established by the way of considering the comprehensive effect of material transfer and chemical kinetics.In addition,based on the time scale analysis,the heat transfer equation of the pyrolysis was nondimensionalized and parameter values of the equation were determined according to references.The heat transfer equation and chemical kinetics equation were used to simulate the model which the solving process was described by the flow chart.The variation regularity of temperature inside the biomass briquette which was simulated by the model during pyrolysis was compared with the experimental data of the reference and the result showed that the accuracy of model was favourable.(2)The pyrolysis behaviors of 4 kinds of biomass briquette(Poplar sawdust,pine sawdust,pine needles,mixture of poplar sawdust and peanut shell)were studied in a fixed bed reactor with different heating rate and different temperature.The study indicated that the pyrolysis was affected by the heating rate.The heating rate increased,the char yield decreased significantly and the tar yield increased obviously.The yield of the pyrolysis product was greatly influenced by the content of volatiles and ash of biomass briquette.The effect of final-temperature on the weight loss of samples was analyzed,and the result showed that the pyrolysis reaction mainly occurred during 300-500℃,and the reaction was completed after 500℃.The simulation of the weight loss was carried out on the pyrolysis model and the simulation results was compared with experimental datas,which showed that the pyrolysis model led to good agreements and could reflect the actual laws of the pyrolysis process of biomass briquette.(3)The characteristics of char were studied by Scanning Electron Microscopy(SEM),and the evolution of pore structure under different pyrolysis conditions was observed.The results of proximate analysis of chars showed that the fixed carbon content of the char decreased and the ash content of the char gradually increased when the heating rate increased.The higher the ash content of biomass raw material,the higher the carbon content of char that produced by pyrolysis.The SEM images showed that the surface structure of char was more complex with the increase of the temperature.In addition,it was observed that pore structure of char was mainly formed and enriched during 300~500℃,and in the meanwhile,the surface area of char increased rapidly.There was a wide range of molten structures on the surface pores at the later stage of the reaction.The SEM images also showed that the higher heating rate led to a stronger pyrolysis reaction and a more obvious pore structure evolution.(4)The composition of pyrolysis tar was analyzed by FTIR and GC-MS technology to investigate the composition variation of tar under different pyrolysis conditions.Carbonyl,hyydroxyl and aromatic groups were detected in tar by infrared spectral,and the results showed that the higher the heating rate,the higher the absorption intensity of functional groups.Main compounds,which contained phenolic compound,benzene derivative,ketones compound and ester compound,were separated and identified from pyrolysis tar by GC-MS analysis,and the results of GC-MS showed that the content of aromatic compounds and aliphatic compounds increased significantly while the content of furan and its derivatives decreased slightly with the increase of heating rate.