Study On Steam Gasification Characteristics Of Typical Biomass And The Correlative Mechanism Analysis

As the only carbon-containing renewable energy,biomass has the characteristics of wide distribution,abundant reserves,and low price.Biomass gasification is one of the most promising technologies,which can convert the energy in biomass into gases that are easy to store,transport and burn.The coverage of biomass is very wide,and the characteristics of different types of biomass are quite different.However,the researches on different types of biomass gasification are not enough,and more attention is paid to the biomass pyrolysis or char gasification reaction,while too little researches focus on the overall biomass gasification process of differnert types.In this study,the steam gasification characteristics of different type biomass was investigated,the weight loss characteristics and product composition of steam gasification were studied at the same time,and the liquid-liquid extraction method was introduced to try to separate useful components from the gasification tar.First,13 biomass materials including straws,shells and woods were selected,and the weight loss characteristics of the non-isothermal gasification process were explored on the steam thermogravimetric analyzer;the key weight loss parameters and reactivity were determined through the weight loss curves;with the aid of correlation analysis,the influence of feedstock properties on key characteristic parameters was explored;combined with the Coats-Redfern method,homogeneous model and shrinking nucleus model were selected to calculate the kinetic parameters of biomass steam gasification process.The biomass steam gasification process can be divided into two stages: pyrolysis and char gasification.The reactivity of the pyrolysis stage is positively correlated with cellulose content,volatile content and H/C value,and is negatively related to lignin content and biomass crystallization.The reactivity of char gasification stage is mainly positively correlated with the catalytic index and fixed carbon content,while it is negatively correlated with the volatile matter and ash content.The homogeneous model can describe the pyrolysis stage more accurately,while the shrinking nucleus model is more suitable for describing the char gasification stage.There is an obvious kinetic compensation effect between the activation energy and the pre-exponential factor.Then,a bench test of steam gasification reaction was carried out on a fixed bed gasification system to investigate the gasification characteristics of different types of biomass,and the correlation analysis between gasification performance and raw material characteristics was carried out;the influence of the steam inlet and temperature on the gasification performance and product characteristics was also explored.Shell biomass has the best steam gasification performance,followed by wood biomass,and straw biomass is the worst.Gasification performance is mainly positively correlated with catalytic index,volatile matter and fixed carbon content,and negatively correlated with ash content and crystallinity.The type of biomass has a great influence on gasification performance.Increasing the steam inlet can effectively promote tar cracking and reduce the heavy components in gasification tar;however,excessive steam inlet will reduce the gasification performance and affect the quality of synthesis gas.Increasing temperature can greatly improve the gasification performance of biomass and promote the conversion of oxygen-containing ketones and phenols in tar to aromatic hydrocarbons;but rising temperature can also cause the condensation of hydrocarbons in tar to heavy components,is not conducive to the subsequent removal of tar.Finally,the liquid-liquid extraction method was used to explore the separation characteristics of phenolic substances in gasified tar.Several typical biomass depolymerization model compounds were used to investigate the extraction efficiency of ethyl acetate and dichloromethane for phenol;then the pyrolysis wood tar was used to verify the experiment results;then related experiment was carried out on the gasification tar.Ethyl acetate has higher selectivity to phenol than dichloromethane.The composition of pyrolyzed wood tar is complex and the phenol content is high,and ethyl acetate has a good extraction efficiency for phenols in washed wood tar.The tar obtained at lower temperature contains more phenolic substances.As the temperature increases,phenolic substances decrease a lot,and ethyl acetate has a limited selectivity to phenolic substances in gasification tar.