| Taking the Pyrolysis char of Miscanthus as the research object,the physicochemical structure of pyrolysis char prepared at different pyrolysis atmospheres(N2,He and CO2)and different pyrolysis temperatures were analyzed by Ultimate and proximate analysis,electron microscopy(SEM),isothermal nitrogen adsorption,Fourier transform infrared spectroscopy(FTIR)and Raman spectroscopy(Raman).The isothermal and non-isothermal gasification experiments of pyrolysis char were carried out by thermogravimetry(TG).The effects of different conditions(gasification temperature,gasification heating rate and gasification agent)on the gasification reaction characteristics of pyrolysis char prepared under different pyrolysis atmospheres and pyrolysis temperatures were investigated.And the kinetic parameters of the gasification reaction were solved by the model method and the iso-conversion method.The pyrolysis char under different pyrolysis atmospheres and different pyrolysis temperatures was prepared by a tube furnace.The yield analysis results of pyrolysis char showed that the yield of pyrolysis char decreased with the increase of pyrolysis temperature;at the same pyrolysis temperature,the yield of pyrolysis char prepared under nitrogen atmosphere was the highest,while in CO2,the yield of pyrolysis char prepared under the atmosphere is the lowest.Ultimate and proximate analysis showed that with the increase of pyrolysis temperature,the fixed carbon content of the pyrolysis char obtained under the three pyrolysis atmospheres(N2,He and CO2)increased,while the moisture and volatile matter content decreased.The pyrolysis char at 600℃ has the lowest O/C value.Scanning analysis by electron microscopy showed that the surface crack of the pyrolysis char was more prominent with the increase of pyrolysis temperature,the original surface structure was deepened,the surface roughness was increased,and the specific surface area was relatively increased.Low temperature nitrogen adsorption analysis showed that the micropore volume,micropore surface area and BET surface area of the pyrolysis char increased with the increase of pyrolysis temperature.Infrared analysis showed that with the increase of pyrolysis temperature,the content of hydroxyl-OH,aliphatic CH,olefin C=C and carboxyl C=O bond of pyrolysis char decreased continuously;tensile vibration band of carbonyl and olefin C=C moving toward a lower wavenumber confirms the development of aromatization.Raman analysis shows that with the increase of pyrolysis temperature,the proportion of pyrolysis focal lattice defect structure in pyrolysis char increases;the Raman spectrum is divided into five peaks,when the pyrolysis temperature is≥800℃,The degree of disorder in biomass char is reduced,the loss of organic functional groups,and the increase in aromatic ring structure and graphite structure.The isothermal and non-isothermal gasification experiments of pyrolysis char were carried out by thermogravimetric analyzer.The effects of different conditions on the gasification reaction characteristics of pyrolysis char prepared under different pyrolysis atmospheres and pyrolysis temperatures were investigated.The results show that the gasification reaction activity of the pyrolysis char obtained under the N2 atmosphere is not much different from that of the He atmosphere.The gasification reaction activity of the pyrolysis char obtained under the CO2 atmosphere is the worst;when the pyrolysis temperature is increased,The gasification reaction activity of pyrolysis char is reduced,and the higher the pyrolysis temperature,the higher the rate of decrease of gasification reaction activity of pyrolysis char;when the pyrolysis temperature is increased,the maximum weight loss rate of pyrolysis char gasification reaction increases.And the corresponding temperature shifts to the high temperature side.The higher the pyrolysis temperature,the larger the maximum reaction rate peak shifts to the right;When the gasification temperature increases,the pyrolysis char gasification rate increases,and the 1000℃ pyrolysis char has the greatest influence on the gasification rate.The pyrolysis char at 800℃ is followed by the minimum of 600℃ pyrolysis char.When the rate of gasification is increased,the reaction rate curve and the peak temperature of the reaction rate are all shifted to the high temperature side,the temperature range of the main reaction stage of the pyrolysis char is widened,the maximum weight loss rate is increased,the reaction is more intense,the S value is gradually increased,and the gasification reaction is promoted;Comparing the effects of different gasification agents on gasification reaction,the gasification characteristic temperature point of pyrolysis char in H2O atmosphere is lower than that of pyrolysis char under CO2 atmosphere,and the pyrolysis char-H2O gasification reaction activity is higher than pyrolysis char-CO2 gasification reaction activity.The kinetic parameters of the isothermal gasification and non-isothermal gasification reactions were calculated by the model method and the iso-conversion rate method of Ozawa.The results show that at the same pyrolysis temperature,the activation energy values of the pyrolysis char in the N2 and He atmospheres are not much different,and the activation energy of the pyrolysis char in the CO2 atmosphere is the highest;Under the same pyrolysis atmosphere,the higher the pyrolysis temperature,the higher the activation energy value,and the reaction is more difficult;the activation energy value and the pre-exponential factor have kinetic compensation effects.For non-isothermal gasification,the activation energy value of pyrolysis char decreases with the increase of conversion rate;Among the pyrolysis chars under different pyrolysis atmospheres,N2-600J has the lowest activation energy value and CO2-800J has the highest activation energy;Using the master-plot method to determine the mechanism function of the kinetic model shows that the pyrolysis gasification kinetics accords with the phase interface reaction mechanism. |
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