Investigation on lateral dispersion characteristics of fuel particles in dense phase zone of a large-scale circulating fluidized bed boiler under combustion conditions

Abstract

The dispersion characteristics of fuel particles in the dense phase zone in circulating fluidized bed (CFB) boilers have an important influence on bed temperature distribution and pollutant emissions. However, previous research in literature was mostly on small-scale apparatus, whose results could not be applied directly to large-scale CFB with multiple dispersion sources. To help solve this problem, we proposed a novel method to estimate the lateral dispersion coefficient (Dx) of fuel particles under partial coal cut-off condition in a 350 MW supercritical CFB boiler based on combustion and dispersion models. Meanwhile, we carried out experiments to obtain the Dx in the range of 0.1218–0.1406 m2/s. Numerical simulations were performed and the influence of operating conditions and furnace structure on fuel dispersion characteristics was investigated, the simulation value of Dx was validated against experimental data. Results revealed that the distribution of bed temperature caused by the fuel dispersion was mainly formed by char combustion. Because of the presence of intermediate water-cooled partition wall, the mixing and dispersion of fuel and bed material particles between the left and right sides of the furnace were hindered, increasing the non-uniformity of the bed temperature near furnace front wall.