Effect of particle size distribution on agglomeration/defluidization during fluidized bed combustion

Abstract

This study focused on the effect of particle size distribution (PSD) on agglomeration and defluidization in a fluidized bed. The four PSDs studied were narrow, Gaussian, binary and flat. The experimental variables studied included the gas velocity, the operating temperature, the Na concentration and the addition of Ca. The defluidization time decreased with increasing operating temperature and Na concentration, and these effects were independent of the sand bed's PSD. In contrast, the defluidization time increased with increasing gas velocity for all PSDs. Comparing the four PSDs, the narrow and Gaussian distributions had higher defluidization times when using operating temperatures of 700°C and 800°C, gas velocities of 0.163m/s and 0.187m/s, and Na concentrations of 0.5% and 0.7%. However, the flat and binary distributions had lower defluidization times under these conditions because they had poor fluidized quality. Thus, the PSD apparently affects the agglomeration and defluidization properties of a sand bed. However, if the system operates at extreme conditions (e.g., high operating temperature, poor mixing and high Na concentration), the PSD's influence on agglomeration will decrease. According to TGA/DTA results, there were two melting points in the agglomerate: 575°C and 782°C. This result confirmed that the liquid-phase eutectic species were formed at the incineration temperature (700–900°C).