The influence of fragmentation on the behavior of pyrite particles during pulverized coal combustion

Coal combustion is a complex series of reactions, dominated by transport mechanisms. A poorly understood aspect is the influence that fragmentation of excluded pyrite minerals has on the combustion thermal history and sulfur release. To explore this effect, fragmentation was incorporated into a mathematical model consisting of several stages, namely: heating up the particle, decomposition to pyrrhotite, fragmentation, and oxidization. A computational fluid dynamic (CFD) model was used to verify the heat and mass transfer predictions of the model. The model was then solved to simulate the particle heat and mass balance of a pyrite particle in a combustion environment. Fragmentation was found to increase particle temperature and sulfur release rate compared with a no fragmentation case, speeding up the particle temperature increase towards its melting point. Increased oxygen content in the bulk environment decreases the time required for a particle to reach its melting point and for complete sulfur release due to increased oxidation reaction rates. Model results also indicate that small pyrite particles need less time to reach both decomposition and melting temperatures; suggesting that smaller particles will spend more time in a molten state and react more completely. (c) 2010 Elsevier B.V. All rights reserved.