Dynamic Behavior of Biomass Ash Deposition in a 25 kW One-Dimensional Down-Fired Combustor

As a CO2-neutral renewable energy, biomass combustion is encouraged to reduce global-warming gas emissions in China. The severe fouling and slagging problem because of high alkali and alkaline earth metal contents still limit the applications of self-sustained biomass power plants. It is essential to study the dynamic behavior of ash deposition in pure biomass combustion. In this paper, three kinds of biomass, saw dust, wheat straw, and corn stover, were burned in a 25 kW one-dimensional down-fired furnace. Three different sampling probe temperatures (550, 600, and 650 degrees C) and four different sampling time periods were chosen, while the deposited ash mass, collection efficiency, deposition morphology, and deposit composition were studied. The results indicate that the deposition mass, collection efficiency, and deposition area all achieve a minimum at an intermediate temperature of 600 degrees C. Highly reactive potassium plays an important role in the ash deposition process, causing a higher deposition rate of wheat straw than corn stover. The results under different sampling time periods indicate that the depositing rate exhibits a trend of a "fast slow fast slow" process. Finally, the governing mechanisms are speculated on the basis of the experimental data, such as deposit morphology and elemental composition.