Experimental And Theoretical Study On Pyrolysis Model Parameters Of Solid Combustibles

For solid combustibles, pyrolysis is the critical and the first step in their thermal conversion process. The pyrolysis process of solid combustibles is highly complex,involving a series of physical effects such as heat and mass transfer and complex chemical reaction kinetics, as well as the mutual coupling between these two effects.Pyrolysis behavior of solid combustibles determines the subsequent combustion, fire spread stages. By summarizing and analyzing the pyrolysis model of solid combustible materials as well as the pyrolysis model parameters,and understanding the pyrolysis mechanisms, researchers can look deeply into these physical and chemical effects from the mechanism perspective, which is beneficial to the understanding of the fire dynamics mechanism and is helpful in developing relevant fire models. It is the basis of the entire fire research.Focusing on the pyrolysis model and the parameters of solid combustibles,following research works were carried out in present paper:Studying on the method for solving pyrolysis model parameters of fire combustibles. A typical lignocellulosic combustible-rape straw pyrolysis is studied.Pyrolysis characteristics and gas evolution of this multicomponent combustibles are investigated using thermogravimetric-infrared spectroscopy technique. The variation of activation energies with the conversion rate is solved by using three model-free methods based on non-isothermal kinetics, and the reaction mechanism of the pyrolysis process is analyzed via the generalized master-plots method. Then, considering the pyrolysis of multiple components, the independent parallel reactions model coupled to particle swarm optimization (PSO) is presented to solve the kinetic and stoichiometric parameters. The accuracy and predictability of the pyrolysis model parameters are further proved by cross-validation.Investigating on co-pyrolysis parameters of solid combustibles. Pyrolysis characteristics and kinetics of two kinds of common solid combustible materials -lignocellulosic combustible rape straw and macro-molecule polymer combustible waste tire under different heating rates and mixing ratios are investigated. It is found that co-pyrolysis process is different from the pyrolysis of single materials and could be divided into four stages. The theoretical and experimental TG and DTG curves show that slight synergistic effect occurred during co-pyrolysis. The pyrolysis index of solid combustible materials is calculated. By analyzing these various parameters, the co-pyrolysis process of fire combustibles can be understood much deeply, which will be helpful in providing valuable references to the development of related fire models.Investigating on pyrolysis model parameters of solid combustible based on sensitivity analysis. Box-Behnken design with Sobol variance decomposition are presented to analyze the global sensitivity of the model parameters. Experiments are carried out based on Box-Behnken design, mass loss and reaction heat are chosen as the model response variables. Best-fit regression models correlated explanatory variables with the responses are presented. F-test, lack-of-ft test and residues normal probability plots and other statistical means demonstrated the reliability and accuracy of derived models. Finally, global sensitivity analysis is carried out based on Sobol method. Results show that for the model of mass loss, the importance of the three input factors follows the order as: temperature> mixing ratio> heating rate; while for the model of reaction heat, it turned to be temperature> heating rate> mixing ratio. In addition, the first-, second- and total-order sensitivity indices proposed can be used to quantitatively quantify the influence of the input parameters and their interactions on the pyrolysis model. It is anticipated that our current work can provide guidance in the development of pyrolysis experiments and numerical simulations in the future.