Ash Transformations in the Real-Scale Pulverized Coal Combustion of South African and Colombian Coals

Abstract

In this work, the formation of ash particles in the combustion of South African Klein Kopie coal and a Colombian coal was studied by measuring the ash particle characteristics upstream of the electrostatic precipitator (ESP) at a 510 MWe pulverized coal fired power plant. We measured the ash particle mass size distributions in the size range 0.01-50 µm using low-pressure impactors and pre-cutter cyclones. Also, samples were collected for computer controlled scanning electron microscopy (CCSEM) with a cyclone with an aerodynamic cut-diameter of about 1 µm. The cyclone-collected samples were analyzed with standard CCSEM procedure by depositing the particles on a filter, and by embedding the particles in epoxy hence acquiring the cross-section analysis of the sample. All major mineral classes in both coals were found to undergo extensive coalescence during combustion. Iron, calcium and magnesium rich particles resulting from the decomposition of pyrite, calcite and dolomite were found to coalesce with quartz and aluminosilicate particles. The size distributions of the fly ash determined with CCSEM and low-pressure impactor-cyclone sampler were found to be similar.