Kinetic study of char combustion in a fluidized bed

Experiments were carried out with eight different chars in a batch fluidized bed reactor. The combustion rate was determined by measuring the CO and CO2 concentrations in the flue gas. Four models were tested, but only two well described the combustion rate for all tested chars. The effect of temperature and particle size on the combustion rate and the rate-controlling step (chemical or diffusion) were determined. With small particle size, the temperature dependence of reaction rate constant was determined and expressed by the Arrhenius equation, providing the apparent activation energy and the pre-exponential factor. The experiments were extended to larger particle size and the temperature dependence of the reaction rate constant was analysed. For the high volatile bituminous and subbituminous chars, the combustion process was under external diffusion control when the temperature was > 1073 and > 973 K and the size was > 3.15 and > 1.6 mm, respectively. For the anthracite, the combustion was not under diffusion control when the temperature was < 1173 K and the particle size was <4mm. Copyright (C) 1996 Elsevier Science Ltd.