Designing a new bell-type primary air nozzle for large-scale circulating fluidized bed boilers

Abstract

The design of energy efficient engineering systems is crucial for sustainable operation when economic and environmental consequences are considered. Circulating Fluidized Bed (CFB) boilers, which are among the major contributors to world electricity production, are still increasing in numbers and unit sizes. Primary air nozzles are key components of CFB boilers that may decrease energy consumption and increase energy efficiency, and they need to be carefully designed. There are certain types of nozzles commonly used in the air distribution grate, but even minor design improvements on the nozzle can significantly decrease the pressure loss. This work is about optimizing the bell-type primary air nozzle used in the Turkish lignite-fired ÇAN Thermal Power Plant (CTPP), which has two 160 MWe CFB boilers, through computational fluid dynamics (CFD). Initially, the bell-type nozzle was designed newly by changing the inner head holes geometry. After that, the nozzle geometry was optimized by changing the orifice size and angle to decrease the pressure drop, increase the orifice velocity outlet, and flow uniformity through CFD simulations. With the optimum nozzle geometry, the velocity at the outlet orifices was increased, and a decrease of 2.86 kPa was achieved in the total pressure loss. Furthermore, when the nozzle orifices were designed downwardly with an angle of 105°, pressure drop across the nozzle decreased by 7.6 %, and the uniformity index increased by 2 % at the outlet orifices. Using the bell-type primary air nozzle, which is newly designed, in the CTPP boiler not only will save 2.26 GWh/year of energy consumption but also minimize the backflow risk in the boiler operation.