The effect of coal type on thermal balance in a dense phase of a circulating fluidized bed combustor

Abstract

The results of experimental investigations of the effect of coal type on the thermal balance during early stages in a dense phase of a circulating fluidized bed combustor (CFBC) are presented in this paper. The experimental investigations were performed in a laboratory-scale CFBC. Five coals with three size classes (small 0.5-0.63 mm, medium 2-3.1 mm, and large 7.1-8 mm) were tested. The electrical heating system was used to ensure that the riser has a constant temperature (850°C) before the experiments. Mean velocity was 12 m/s. Oxygen concentration was 5%. During the experiments the temperature in the dense phase in the lower part of the riser and the gas concentrations of CO and CO2 were measured continuously. On the temperature histories measured, it can be seen that after feeding the coal batch into the hot CFBC, the temperature in the dense phase decreases, after reaching a minimum value and increases back again. The experimental results were compared to each other on the basis of the maximum temperature drop after feeding the coal batch. It was concluded that the temperature drop depends slightly on coal size and mainly on coal type and its mechanical and physical structure. The temperature drop slightly increases when the particle size of the coal batch increases. The strongest influence on the temperature drop in the dense phase of the CFBC shows the volatile content of the original coal and the temperature drop is directly proportional to the volatile content.