Thermal Decomposition Of Biomass:Kinetic Methods And Interactions

An adequate understanding of the kinetics of thermal decomposition for biomass materials is fundamental for the research of forest fires and the design of energy systems.This work focuses on kinetic methods and thermal decomposition of biomass materials.On the one hand,the kinetic optimization method based on a search algorithm has been widely applied in kinetic analysis,and its performance has been commonly concerned.This work attempts to improve the kinetic optimization method from three aspects.The thermogravimetric(TG)experimental data of pine bark under nitrogen atmosphere are used to evaluate the performance of the kinetic optimization method.On the other hand,combustible materials usually appear as mixtures in forest fires.However,the interaction during thermal decomposition of flammable forest mixtures has been scarcely studied.This work analyzes the thermal decomposition of non-mixed and mixed forest fuels.The thesis is summarized as follows:(1)The kinetic optimization method is combined with traditional kinetic methods.The Kissinger method is used to preliminarily evaluate the activation energy of the reaction steps corresponding to the DTG(first derivative of a TG curve)peaks,the model-free methods are used to compare the activation energy values for different sub-reactions,while the two-point method is used to preliminarily evaluate the lower limits of activation energy and pre-exponential factor for the first reaction step.The results show that based on this method,the genetic algorithm(GA)calculation performs more efficiently than the calculation by using a blind range.(2)Based on the kinetic compensation effect and peak temperature,a kinetic optimization method named ETp method is proposed.The results show that the method is efficient,stable,robust,and user-friendly.The method is generally applicable to many kinetic models and reaction mechanisms.Therefore,the method is suitable for the thermo-chemical processes of a wide variety of materials.(3)The genetic algorithm has been widely used in the kinetic study for a longtime.Recently,other search algorithms have been introduced into this field.This work compares the performance of 20 search algorithms to guide the selection of search algorithms for kinetic analysis.Many of the search algorithms have been barely used in kinetic analysis.The results show that the shuffled complex evolution(SCE)is very suitable for kinetic optimization methods.Besides.the ETp method performs better than the previous kinetic optimization method for all of the 20 search algorithms.(4)The interactions in biomass-biomass,biomass component-biomass component,and biomass-soil mixtures during thermal decomposition are investigated.The TG experimental data under nitrogen and air show that the interaction among some biomass components is strong,the interaction between biomass and soil is weak,and the interaction among biomass materials is unobvious.A three-step and four-step mechanism are established to model the pyrolysis and combustion process of pure biomass and soil materials.Then,the thermal decomposition of biomass-biomass and biomass-soil mixtures are described by additive models.Finally,a method is proposed for estimating the effects of interactions on kinetic mechanisms.The results suggest that the interactions during the thermal decomposition of some biomass-soil mixtures promote lignin degradation and suppress char oxidation under air atmosphere.