General surface activation function model for intrinsic reaction kinetics of char conversion.

Thermal analysis has been widely used to determine the intrinsic reaction kinetics (IRK) of char conversion, but there are still two major problems to be solved. Problem (a) is that the ignition temperature T ig values of coal and low-temperature pyrolysis char obtained by thermal analysis are approximately 200–300 °C lower than those obtained in boiler-like environment reactors. The high-temperature (1400 °C) pyrolysis chars produced in an entrained flow reactor were used to solve problem (a). A differential scanning calorimetry (DSC) inflection point method (DIPM) based on Semenov's thermal explosion theory was developed to obtain the T ig of char combustion at different heating rates β s. The effect of β on T ig was described by an exponential function. Eliminating the influence of the β on T ig obtained the limiting ignition temperature, which was in line with that obtained in boiler-like environment reactors, and problem (a) was solved. Problem (b) lacks a general kinetic model that can obtain a consistent IRK between nonisothermal (NON) and isothermal (ISO) experiments, and it has no uncertain parameters in the reaction mechanism function f (X). A general surface activation function model (GSAFM) based on f (X) = 1- X with variable kinetic parameters was developed to obtain the IRK of char conversion. The results showed that the GSAFM predicted char NON and ISO combustion best among the evaluated approaches, including extensively used model-free methods, such as FWO and KAS, and the isothermal surface activation function model with fixed kinetic parameters. GSAFM could obtain a consistent IRK between NON and ISO experiments, and it was further verified as a simple and general theoretical method that could be used to obtain the IRK of solid fuel (coal/biomass chars) combustion or gasification. This study could provide new insight into the IRK of char conversion. [ABSTRACT FROM AUTHOR]