Controlling the freeboard temperature applying a novel design of fluidized bed

Abstract

An experimental study on controlling the temperature of gases in the freeboard applying a novel fluidized bed configuration has been carried out. A bubbling fluidized bed reactor of 300mm ID is equipped with a jet pipe of 38.1mm ID to adopt the novel configuration. A part of air is fed through the jet pipe to be issued vertically near the bed surface creating a large fountain of particles in the freeboard. The remaining part of air is fed through the distributor plate to fluidize bed solids. A third stream of hot air at 300°C is introduced in the freeboard beyond the main bed to simulate a heat generation source. The hot air is evenly distributed over the reactor cross section using a special pipe. Due to contacting the hot air with the entrained particles, its temperature is dampened while the bed solids heat-up. After a certain period of time the bed temperature profile evens out. The obtained results demonstrate that the fountain particles are very effective in transporting heat from the freeboard gases to the bed that minimizes the temperature difference between them, i.e., better control of the freeboard temperature. The bed stabilizes at a higher temperature while the freeboard temperature is better controlled with increasing the jet velocity and with decreasing bed particles sizes. Moreover, by applying the novel configuration the freeboard temperature can be effectively controlled to a higher extent along the reactor height compared with the splashing zone of conventional operation.