Study of the evolution of particle size distributions and its effects on the oxidation of pulverized coal

This paper discusses the factors influencing the evolution of particle size during the combustion of pulverized coal, as well as their consequences for the interpretation of burnout curves. A detailed experimental characterization of the evolution of the particle size distribution (PSD) of a pulverized coal (anthracite) burned under realistic conditions in an entrained flow reactor is presented and used as the reference data for the subsequent analysis. The data show evidence for particle fragmentation at relatively short times (or, equivalently, high unburnt fractions). The formation of fragments comparable in size to the parent coal/char particles is modeled with a simple fragmentation scheme, which results in an improved reproduction of the PSD's evolution. The effects of fragmentation on the burnout curves are then studied in detail. An enhancement of their curvature is observed, which results in a better fit of the experimental data; in particular, the high conversion range, where the largest discrepancies between predictions and measurements are usually found, is well reproduced with this “extended” model. Simultaneously, the increase of specific surface caused by particle fragmentation causes an increase in the conversion rate, and a smaller total conversion time. To fit the experimental data, new optimal kinetic parameters are calculated. Finally, the potential relevance of fragmentation in the simulation of industrial pf plants is discussed.