99/00790 Effect of in-bed recirculation of particle on the design of heat transfer surface of dense phase zone in circulating fluidized bed

Abstract

The circulating fluidized bed combustion technology has been extensively developed in recent years all over the world. The size of fed coal ranges from 0 to 10 mm and the mean diameter of coal ranges from 2 mm to 3.5 mm leading to a the fluidized bed which consists of a dense phase zone (large particle bed) and a dilute phase zone (small particle bed). This means that the coal combustion fraction in the dense phase zone is large, so one must pay more attention to the heat balance calculation and amount of heat exchange surface area in the dense phase zone. If the heat exchange surface area is not sized correctly, the circulating fluidized bed boiler can not be operated in a steady manner. This paper analyses the heat balance and heat exchange surface design in the dense phase zone for a circulating fluidized bed boiler of 75 t/h steam capacity which is widely used in China. The effect of in-bed particle recirculation on the amount of heat exchange surface area in the dense phase zone is also described.