A non-isothermal integrated model of coal-fired traveling grate boilers

Abstract

The aim of this study is to develop a mathematical model for coal combustion in traveling grate boilers. The model contains a “bed-model” part and a “furnace-model” part. Within the description of the “bed-model”, a non-isothermal particle model is proposed, in order to accommodate temperature gradients within combusting particles. The “bed-model” is then coupled with the “furnace-model” based on an integrated grid. To verify the model, an experimental fixed-bed furnace has been set up to simulate combustion in a real chain grate stoker. Concentrations of gas species at the bed surface have been measured. Predicted results are in reasonable agreement with experimental data. This has provided a basis for studying the effect of major parameters influencing boiler behavior, for optimizing combustion conditions. These factors have included the excess air ratio and particle diameter. The results show that there is an optimum excess air ratio required for optimized combustion and that smaller coal particle sizes (in the range of 0.02–0.04 m) enhance ignition and burnout properties of the fuel. It appears essential during operation to monitor and control excess air ratios and particle diameters carefully controlled.