Study On The Chemical Structure Evolution And Reactive Mechanism Of CO₂/H₂O On Biomass Char

China’s biomass energy reserves are huge but underutilized.The development of biomass energy is conducive to the establishment of a sustainable energy system.Biomass and coal are quite different in material properties.Studying the mechanism of CO2/H2O on the structure evolution and reactivity of pure biomass char is beneficial to the understanding of the engineering application of biomass oxy-fuel combustion technology.This dissertation takes typical biomass rice straw as the research object,the tubular furnace reactor was used to conduct biomass char experiments,and the influence laws of characteristic parameters such as char yield and reaction rate in the process of biomass devolatilization were investigated.Fourier Transform Infrared spectroscopy(FTIR)technology and Raman spectroscopy(Raman)were used to characterize biomass char in detail,and the evolution of the micro-chemical structure of biomass char was explored.A thermogravimetric analyzer(TGA)was used to analyze the combustion reactivity of biomass char,revealing the influence of CO2 atmosphere,H2O atmosphere and CO2/H2O mixed atmosphere on the microchemical structure evolution and reactivity mechanism of biomass char.The results indicate:(1)Under the CO2/H2O mixed atmosphere and the corresponding separate atmosphere,the yield of biomass char decreases with the increase of the final temperature of the reaction,and the difference in char yield is more obvious when the temperature reaches 700℃ or higher.When the temperature range is 700℃～1000℃,the char yield of separate CO2 and H2O atmospheres at the same final reaction temperature will decrease with the increase of the partial pressure ratio.At the same reaction final temperature and partial pressure ratio,the char yield of H2O atmosphere is lower than that of CO2 atmosphere,which can promote the progress of biomass char reaction.The effect of CO2/H2O mixed atmosphere on the reaction of biomass char is more obvious than that of CO2 and H2O alone.(2)The content of oxygen-containing functional groups in the biomass char prepared by CO2 atmosphere and H2O atmosphere is more than that in pure N2 atmosphere.With the addition of CO2 and H2O,the chemical structure of biomass char becomes more poly condensed.And with the increase of temperature,the organic carbon chain structure in biomass char gradually decreases.Compared with CO2,H2O promotes the condensation polymerization of the small aromatic ring system in biomass char,which makes the structure of biomass char more orderly.The CO2/H2O mixed atmosphere has a stronger consumption effect on the small and medium aromatic ring system of biomass char,and the polycondensation effect on the small and medium aromatic ring system of biomass char is more obvious.(3)The temperature range required for the maximum weight loss of biomass char in the CO2/H2O mixed atmosphere is more inclined to the low temperature section than the pure N2 atmosphere,the CO2 atmosphere alone,and the H2O,atmosphere alone.The CO2/H2O mixed atmosphere has a synergistic effect at high temperature,which makes the biomass char combustion reactivity index Tindex lower than the biomass char combustion reactivity index Tindex at low temperature.Moreover,the relationship between biomass char and the combustion reactivity index Tindex function under different CO2 partial pressures and different H2O partial pressures has a high degree of fit,and the degrees of fit are all above 0.9.