Characteristics of a modified bell jar nozzle designed for CFB boilers

Abstract

One of the most important factors for trouble free operation of CFB boilers is the pressure drop of the gas distributor. The pressure drop characteristic of the gas distributor depends on the nozzles used. A modified bell jar nozzle was designed and developed for use with large-scale industrial circulating fluidized bed (CFB) boilers. The nozzle consists of a vertically tapered tube with a larger end at the top, a float which is free to move within the tube and a cover with holes. The pressure drop characteristics of the nozzle were measured experimentally by using different floats and moving out the float respectively. The gas distributor equipped with the modified bell jar nozzle has a unique pressure drop characteristic. It has a higher resistance than other nozzles which results in the formation of an effective barrier against backflow at low boiler loads, which results from the pressure fluctuation caused by bubble burst and solids coming from the recycle system. In addition, it has a relatively low pressure drop at high or full boiler loads, which can greatly reduce the energy cost of the primary air fan.