Research On The Mechanism Of Pyrolysis Of Sawdust Biomass To Produce Highly Reducing Gas

In the past few decades,the consumption of fossil fuels around the world has increased sharply.With the continuous emission of a large amount of greenhouse gases and environmental pollutants such as SOx and NOx,more and more environmental problems have become increasingly prominent.How to make full use of biomass,wind energy,solar energy and nuclear energy and other clean energy to reduce greenhouse gas emissions such as CO₂has become the focus of social attention.The research group is carrying out the magnetization roasting of iron tailings.How to obtain high reducing gas and conform to the green development direction is the key to the successful application of this technology.In this work,a large number of fir and bamboo which were planted in Shaoguan,Guangdong Province were studied.The basic properties of fir sawdust and bamboo sawdust and the influencing factors of reducing gas production by pyrolysis were explored,and the pyrolysis kinetics was analyzed.The main research results are as follows:（1）Fir sawdust and bamboo sawdust are mainly composed of five elements C,H,O,N,and S,in which the mass ratios of C and O elements are more than 40%.The two kinds of biomass have high volatile content,about 75%,and the fixed carbon content is about 16%,which has good potential for biochar preparation.The cellulose,hemicellulose and lignin contents of the two were different,and the three-stage pyrolysis mechanism was followed in the pyrolysis process.The maximum weight loss occurred in the temperature range of250～400°C,and the main pyrolysis gases were CO,CO₂ and CH4.（2）Increasing pyrolysis temperature of biomass under the condition of moisture content below 40%is conducive to the preparation of reducing gas.At 700°C,the addition of 4%Na2CO3 catalyst can significantly increase the proportion of H2 in pyrolysis gas from less than 15%to more than20%,while the proportion of CO decreases,and the total reducing gas content remains basically unchanged.Cellulose,xylan and lignin were used to prepare simulated fir sawdust samples and simulated bamboo sawdust samples.Single factor experiments were carried out under the same reaction conditions to further explore the influence of biomass raw material composition on the production of reductive gases.The results showed that the change trend of pyrolysis gas of the two simulated biomasses was the same as that of the primary substance in most cases,but the difference between them was not as obvious as that of the primary substance,which is due to the lack of covalent bonds between cellulose,xylan,and lignin in the mixed samples,resulting the interaction of the three was not significant.However,the H₂content of the pyrolysis gas of the mixed sample is larger than real sample,which is mainly because the mixed sample lacks sufficient porosity,which inhibits the volatilization and diffusion of the gas and promotes the occurrence of secondary reactions.（3）Thermogravimetric analysis was carried out on the dried samples of fir sawdust and bamboo sawdust at heating rates of 10,20,and 40 K·min^-1,the pyrolysis activation energies were calculated by KAS,FWO and Friedman method.The results show that fir sawdust and bamboo sawdust have a good linear fit when the pyrolysis conversion rate is 0.1～0.7.The Coats-redfern method and master-plots method were used for linear fitting,and the calculation shows that the two biomass pyrolysis processes are in line with the series reaction model,with the increase of the heating rate,the reaction order shows a downward trend,and goes to the first order.The calculation results of the activation energy of fir sawdust are 126.52～135.43k J·mol^-1,and bamboo sawdust are 112.39～118.75 k J·mol^-1.The pyrolysis activation energy of fir sawdust is slightly higher than that of bamboo sawdust.