One-Parameter Model for the Oxidation of Pulverized Bituminous Coal Chars

Abstract

In this study, the oxidation of 22 bituminous coal chars is modeled with (i) an individual activation energy for each char and (ii) constant activation energy for all the chars. Modeled burnout profiles, from 0 to 75% of burnout, are compared to experimental measurements from a 4 m isothermal plug flow reactor operating at temperatures and heating rates typical of pulverized fuel industrial combustion. The fuel and the gas rates are chosen such that temperature gradients in the radial direction and along the centerline of the reactor are minimized. In this study, the objective is to predict the burnout profiles with a model suitable for the comprehensive computational fluid dynamics (CFD) modeling of pulverized fuel boilers. Therefore, a power law model that takes into account external diffusion and apparent kinetics is used. The kinetic parameters that are used in the model are determined with a suggested multivariable optimization method. The results show that the experimental burnout profiles of the 22 individual chars are not predicted with a significantly higher accuracy using separately determined activation energy for each char than they were using a constant activation energy for all the chars. Thus, only one fuel specific parameter (i.e. the pre-exponential factor) is needed to model the burnout profiles. These findings are in agreement with some previous studies but are important considering the significant amount of experimental data and the large number of coal chars investigated using a systematic approach.