CFD simulation of ash deposit formation in fixed bed biomass furnaces and boilers

In order to describe and predict the formation of ash deposits in biomass fired combustion plants, a mathematical model is being developed and implemented into the CFD code Fluent¿ as a post processing tool. At the present state of development the model covers the release of coarse ash particles and ash-forming vapours from the fuel bed, the transport to furnace and boiler surfaces and the deposition of particles and vapours. Changes in the flue gas composition due to chemical reactions are considered by performing thermodynamic equilibrium calculations in order to determine the gas phase composition. The build-up of the deposit layer depending on wall temperature, deposit porosity and chemical composition is also taken into account. First results of modelling deposit formation for the furnace and fire tube of a grate fired combustion unit (boiler capacity 440 kWth) show plausible results but have yet to be validated