Suspension-to-wall heat transfer in a 12-MW(th) circulating fluidized-bed combustor

An experimental investigation was carried out to study the effects of operating parameters on the local suspension-to-wall heat transfer in the combustor of a 12-MW(th) circulating fluidized-bed (CFB) boiler. The heat transfer coefficients were measured with a conduction-type heat flux meter at five different vertical levels. The measurements covered a range of superficial gas velocities from 4 to 6 m/s, a bulk bed temperature from 800 to 850 degrees C and a suspension density from 6 to 70 kg/m(3) for 270-mu m silica sand particles. The heat transfer coefficient for the membrane wall in the combustion chamber of the CFB boiler was in the range of 100 to 180 W/m(2) K for the range of operating conditions employed in this work. The beat transfer coefficient decreased with increasing height and increased with increasing bulk bed temperature, superficial gas velocity and suspension density. Based on the experimental data, a simple correlation is proposed for predicting the suspension-to-membrane wall heat transfer coefficient. The results were analysed and compared with the experimental data of other workers.