Research On Oxidative Pyrolysis,Combustion Characteristics And Prediction Model Of Typical Biomass

While the biofuel market is booming,its fire safety failings need to be addressed urgently.Fire accidents related to biomass raw materials and pellets occur frequently,which endanger social security and also cause environmental pollution.The fire accident is not only related to the type and form of biomass but also closely related to the characteristics and mechanism of its oxidative pyrolysis and combustion.The study of behaviors and mechanisms of biomass oxidative pyrolysis and combustion is the basis for predicting the occurrence and development of biomass fires,which is helpful for the in-depth understanding of the mechanism of combustion and is conducive to the development of relevant combustion models.Focusing on the characteristics and mechanism of biomass oxidative pyrolysis and combustion,the research work was carries out as following:Characterization and kinetics of typical biomass oxidative pyrolysis.The oxidative pyrolysis properties of typical biomass powders are analyzed by the STA 6000.It is found that the oxidative pyrolysis process of biomass powder can be divided into four stages:moisture and light volatiles release,devolatilization and(hemi)cellulose decomposition,carbon oxidation and lignin decomposition,and carbonaceous residue degradation.On this basis,the oxidative pyrolysis process of biomass powder and pellets fuel is comparatively studied by the thermogravimetric analyzer-Fourier transform infrared,and the reaction mechanism and kinetic parameters are solved by using the model-free method.The oxidative pyrolysis process,kinetic parameters,reaction mechanism,thermodynamic parameters and gaseous products of biomass powders and pellets are found to be different.The reason is that the physical structure and density of biomass raw materials are changed by molding.Besides,the chemical composition changes of biomass pellets due to slight pyrolysis during the molding process of pelletization.The analysis of various parameters in the oxidative pyrolysis process of biomass powders and pellets can better understand the combustion process and provide a reasonable pyrolysis sub-model for the combustion.Studying on the typical biomass combustion characteristics.The combustion characteristics of biomass powder under different external radiation conditions are studied in detail by the cone calorimeter,and the linear relationship between the ignition time and external radiation is established to predict the critical heat flow of biomass powder.Based on the Petrella method,all of the biomass powders studied are found to have a high risk to flashover.On this basis,the combustion characteristics of biomass powder and pellets were compared and analyzed,and it is found that pellets have longer preheating time and combustion duration,and the intermediate risk to flashover.Analysis of gas toxicity found that biomass powders have higher toxicity in burnout stage,while pellets have higher gas toxicity in preheat stage.Prediction of mass loss in biomass oxidative pyrolysis.Based on the purpose of simplifying the experimental operation and predicting the mass loss of biomass oxidative pyrolysis with basic data,the artificial neural network(ANN)method is introduced to solve the complicate nonlinear relationships.Considering the effect of heating rate on biomass oxidative pyrolysis process,one prediction of mass loss is established by heating rate and temperature change.Besides,considering the close relationship between the chemical composition of biomass and its oxidative pyrolysis process,the other prediction model is established by using the results of proximate analysis and ultimate analysis.Both established models show an excellent agreement between predicted and experimental data.The MIV algorithm is employed to analyze the sensitivity of each input parameter,and the result is:temperature>volatile matter>fixed carbon>carbon>nitrogen>moisture>hydrogen>oxygen>sulfur>ash.Prediction of heat release rate(HRR)from biomass combustion.The first is to consider the influence of external radiation on the HRR of biomass combustion,and establish a prediction model of it.On this basis,considering the influence of chemical composition on the HRR of biomass,the HRR prediction model based on industrial analysis and thermophysical parameters is developed.Meanwhile,the sensitivity of each input parameter to the combustion heat release rate is obtained by means of the MIV algorithm:time>thermal conductivity>heat of decomposition>volatile matter>density>emissivity>ash>specific heat capacity>moisture>activation energy>fixed carbon.The established prediction model can efficiently and conveniently obtain the results of biomass combustion heat release rate,so as to evaluate its fire risk.