Air nozzle design criteria for protection against the backflow of solids in CFB boilers

The article provides the most important criteria that have to be taken into account in the design of the air distributor of a circulating fluidized-bed (CFB) boiler equipped with the low-pressure drop air nozzles. Special consideration is given to the issues of prolonging the service life of the grid and improving the boiler availability that involves the reduction of an inert material backflow to the air plenum chamber. In this regard, a new criterion for the kinetic energy of the outlet air stream was proposed, which was then used for developing a primary air nozzle design alternative to the arrowhead nozzle, with increased aerodynamic drag force. On the example of the CFB-1300 supercritical 466 MWe circulating fluidized bed boiler, the results of the implementation of the new-design nozzle are shown, where the bed material backflow problem has been totally eliminated.