A Sophisticated Model to Predict Ash Inhibition during Combustion of Pulverized Char Particles

摘要

Final burnout of char particles from practical fuels such as coal and biomass occurs in the presence of a large ash component. Also, newly utilized coal resources, such as those from India, often contain much larger ash fractions than have traditionally been utilized. Similarly, lignin-rich residues from biochemical processing of biomass often contain high ash fractions and have been shown to burn slowly. In the past, the inhibitory influence of ash on pulverized coal particle combustion has been most frequently modeled using an ash film model, though such films are rarely found when examining partially combusted particles. Conversely, previous EDX probing has suggested that mineral components exposed on the surface of burning pulverized coal particles frequently diffuse back into the char matrix, whose effects can be modeled as an ash dilution effect. To explore the implications of these different ash inhibition models on the temporal evolution of char combustion during burnout, we have developed a new model that considers the possibility of an ash film effect, an ash dilution effect, or some arbitrary combination of the two effects acting in tandem, which is the most realistic scenario. This new model predicts that ash content will have a significant impact on the char burnout rate, and the specific rate is dependent on whether an ash film or ash dilution effect is most prominent. Comparison against experimental data suggests that the ash dilution effect has a larger role than development of an ash film during combustion of pc chars.