A float nozzle was designed and developed for use with large-scale industrial circulating fluidized bed (CFB) boilers. The gas distributor equipped with the float 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.