The prediction of particle size distribution during pulverized fuel combustion using SEM and CFD methods and its impact on ash deposition rates

In most studies on modeling ash deposition, mineral inclusions are equally distributed among injected coal particles. However, computer controlled scanning electron microscopy (CCSEM) analyses reveal that, depending on the fuel, a substantial portion of inorganic material is excluded from the fuel matrix. The assumption that each coal particle has the same amount of mineral inclusions is not justified or valid. SEM investigations of a bituminous coal show that the mineral matter content strongly increases as particle diameter decreases. Moreover, the particle’s true density varies significantly for coal particles and excluded minerals. It is well known that particle diameter and density are crucial parameters when predicting ash deposition phenomena. Therefore, this study presents an in-depth characterization of mineral matter distribution in a high-volatile bituminous coal. A detailed fuel injection method for numerical simulations is proposed. The comparison of simulation results with experimentally determined particle size distributions and deposition rates confirms the validity of the modelling approach presented here. Obtained results show the significance of a proper fuel definition and injection when using computational fluid dynamics (CFD). The impaction rate on the deposition probe decreases when excluded minerals are considered in the model. The reason for this is the over-prediction of the remaining ash particle size distribution when applying ANSYS Fluent standard models. Consequently, neglecting mineral distribution could lead to wrong conclusions and is one of the crucial steps when predicting pulverized fuel (pf) combustion with ash deposition or developing sticking criteria.     «

In most studies on modeling ash deposition, mineral inclusions are equally distributed among injected coal particles. However, computer controlled scanning electron microscopy (CCSEM) analyses reveal that, depending on the fuel, a substantial portion of inorganic material is excluded from the fuel matrix. The assumption that each coal particle has the same amount of mineral inclusions is not justified or valid. SEM investigations of a bituminous coal show that the mineral matter content strongly...     »