3-D numerical simulation for co-firing of torrefied biomass in a pulverized-fired 1 MWth combustion chamber

Abstract

Torrefaction process is a promising technology for changing the chemical and physical properties of biomass so, that it can be used in existing pulverized fuel firing systems. A numerical 3-D simulation to study the combustion behaviour of torrefied biomass in a pulverized-fired furnace has been carried out. In the model different reaction kinetics for devolatilization and char oxidation of three biomass components, namely hemicellulose, cellulose and lignin, have been applied. The reaction kinetic parameters for pyrolysis and char oxidation were determined by experimental work using thermogravimetric analysis (TGA). In numerical studies three different fuel blends were examined, which include pure coal, ∼9% and ∼17% (thermal basis) torrefied sawdust in coal. Gas concentrations, temperature distribution, pyrolysis and char reactions were analyzed along the 1 MWth combustion chamber. The numerical investigation suggests that the torrefied biomass can be used as a substitute fuel for coal without modifications in the co-firing system. However, the case-study with the highest biomass substitute leads to an incomplete decomposition of the lignin component, due to coarser biomass particles and decreased char reaction rates.