The Effect Of Torrefaction On The Kinetics Characteristics Of Biomass Pyrolysiss、Gasfication And Combustion

Biomass has received much attention as the only carbon-neutral energy,but it`s industrialized standardization has been hampered by its irregularity and differences in biomass feedstock.For example,the pyrolysis characteristic parameters and reaction mechanism of different biomass are quite different,which is not conducive to the process optimization and reactor design of commercial-scale biorefineries.The biggest advantage that torrefaction is currently recognized is the conversion of biomass from different sources into more uniform biomass feedstock.Based on this,this work focused on the changes in the physical and chemical properties of different types of biomass after torrefaction,and the changes in thermochemical conversion characteristics such as pyrolysis,gasification and combustion.It also was studied that the changes in the uniform of different types of biomass and the correlation between the thermochemical properties of the material and the properties of the biomass material before and after torrefaction.The main works are shown as follows.Firstly,we selected 20 different kinds of biomass,including straw biomass: peanut straw,sesame straw,tobacco stem,rice straw,soybean straw,cotton straw,cornstalk,wheat straw;and shell biomass: peanut shell,rice husk,rape pod,pecan shell,bada wood shell,walnut shell;and woody biomass: camphor tree,sapele,eucalyptus,bamboo,poplar,willow.The samples torrefied at 270 ° C using a fixed bed system,and it was done the industrial analysis and elemental analysis of the raw and torrefied biomass.It was found that torrefaction can lower the oxygen content of biomass,increase the fixed carbon content,and increase the biomass calorific value.Torrefaction can improve the distribution of elements in biomass.After Torrefaction,the atomic ratio of hydrogen to carbon and oxygen to carbonin biomass is more uniform.The distribution of elements in biomass after torrefaction generates a certain degree of uniformity.Then,the thermogravimetric analyzer was used to study the effect of species and torrefaction on the pyrolysis characteristics of biomass.We analyzed the kinetics characteristic parameters of the biomass pyrolysis process.The relationship between species and the kinetics parameters of the biomass pyrolysis process was discussed,and the association of species with changes in the kinetics parameters of the biomass pyrolysis process was revealed.After torrefaction,the maximum weight loss rate of straw biomass pyrolysis was significantly reduced,but the maximum weight loss rate of woody biomass increased significantly.Regardless of the pyrolysis onset temperature,the pyrolysis offst temperature,and the maximum weight loss rate of pyrolysis,the raw and torrefied woody biomass was slightly higher than the shell biomass,and the straw biomass had the lowest pyrolysis onset temperature.The stability of cellulose in different kinds of biomass was different.The thermal stability of cellulose in woody biomass was the highest,followed by shell biomass and the thermal stability of cellulose in straw biomass was the worst.The standard deviation of the distribution of the pyrolysis onset temperature,the maximum weight loss rate,and the pyrolysis offset temperature in the pyrolysis characteristics of the biomass after torrefaction became smaller,so the torrefaction could make these pyrolysis characteristics became concentrated to some extent,so that a certain degree of uniform of the torrefied biomass was generated.After torrefaction,the maximum weight loss rate of biomass pyrolysis and its corresponding temperature had a obvious positive correlation with volatile,indicating that torrefaction could make distribution of the maximum weight loss rate of biomass pyrolysis and its corresponding temperature more regular,and so the biomass after torrefaction became more uniform.Next,the thermogravimetric analyzer was used to studied the effect of species and torrefaction on the gasfication characteristics of biomass.The kinetic parameters of the biomass gasfication process were analyzed and the relationship between the species and the kinetic parameters of the biomass gasfication process was discussed.And then the association of species with changes in the kinetic parameters of the gasfication process was revealed.For most biomass,the maximum weight loss rate and corresponding temperature and the complete gasification conversion temperature of the gasification stage after torrefaction were significantly increased.After torrefaction,the standard deviation of the distribution parameters of the woody biomass in the gasification process was smaller,and the uniformity of the gasification process of the woody biomass was enhanced after torrefaction.The standard deviation of the parameters of the woody biomass gasification was lower than that of the straw and shell biomass.and the homogeneity of the biomass of woody biomass was stronger than that of stalks and shells.Finally,the thermogravimetric analyzer was also used to studied the effect of species and torrefaction on the combustion characteristics of the biomass.The kinetic parameters of the biomass combustion process were analyzed,and the relationship between species and the kinetic parameters of the biomass combustion process was discussed.And then the association of species with changes in the kinetic parameters of the biomass combustion process was revealed.After torrefaction,the ignition temperature of straw biomass,shell biomass and woody biomass increased,but the comprehensive combustion characteristic of straw biomass,shell biomass and woody biomass index increased,and the burnout temperature of straw biomass,shell biomass and woody biomass also increased significantly.After torrefaction,the maximum burning rate of straw biomass decreased,while the maximum burning rate of woody biomass increased,and the maximum burning rate of shell biomass decreased partially and partially increased.It was found that the combustion mode of the raw and torrefied biomass in 200℃~550℃ was tha firstly the volatile was resolved and burned and then the volatile and fixed carbon simultaneously burned.After torrefaction,the standard deviation of the distribution of the kinetic parameters of the woody biomass combustion process all becames smaller,and torrefaction could effectively increased the uniformity of combustion characteristics of woody biomass.There was a strong positive correlation between biomass ignition temperature,maximum burning rate and its corresponding temperature with volatile after torrefaction,so torrefaction could effectively enhance the uniformity of biomass combustion process.