THE CENTRAL PARTICLE MODE IDENTIFICATION AND ITS FORMATION MECHANISMS DURING PULVERIZED COAL COMBUSTION

摘要

The present work proposes an updated version of the previous method for identification of the central mode, which is based on mass fraction size distributions of the Al in particle samples. A general central mode is generated from pulverized coal combustion in a drop tube furnace (DTF) and two full-scale boilers. These results confirm the generality and effectiveness of this method in particle mode identification. It is proposed that the central mode is produced by heterogeneous condensation/adsorption of vaporized species on fine residual ash particles. To elucidate the origins of these fine residual ash particles, sized and density-separated coal fractions from one bituminous coal are burnt in the DTF under different conditions. The results show that char fragmentation, the combustion of original fine coal particles and the transformation of excluded minerals all contribute to the formation of the central particle mode.