Thermochemical conversion: direct combustion

This chapter describes some fundamental theory about combustion within a framework of practical applications. The purpose of the combustion process is to release the energy of the biomass. In order to understand the conversion process in a quantitative way, one could analyze one-dimensional systems like a propagating front. The chapter considers the combustion of the remaining (porous) solid particles that are composed of carbon, with mass fraction YC, and inert ashes that are not converted. The shrinking density model, in which reaction takes place inside the particle, resulting in a density decrease, is considered. The general theory of surface conversion is explained by first looking at simple evaporation of a droplet. Finally, the emissions from biomass combustion and measures to reduce them are discussed.