Carbon consumption is a potential problem when cofiring biomass with coal. The links at left summarize and illustrate the issues associated with carbon burnout, some experimental highlights from laboratory investigations of burning rates, and conclusions regarding burnout. The general guideline for carbon burnout is:
Complete conversion of the carbon in biomass fuels requires that the fuel be processed to small particle sizes and be moderately dry. Particles generally need to be less than 3 mm (1/8 inch) to completely combust. Fuels that pass through a quarter-inch screen are generally dominated by particles less than 1/8 inch. Larger sizes, high moisture contents (greater than 40%) and high particle density all significantly increase the time required to completely combust the particles and may increase fly ash carbon content.