Extending the capabilities of CFD codes to assess ash related problems

This paper discusses the application of FLUENT? in theanalysis of grate-fired biomass boilers. A short description of theconcept used to model fuel conversion on the grate and the couplingto the CFD code is offered. The development and implementation ofa CFD-based deposition model is presented in the reminder of thepaper. The growth of deposits on furnace walls and super heatertubes is treated including the impact on heat transfer rates determinedby the CFD code. Based on the commercial CFD code FLUENT?,the overall model is fully implemented through the User DefinedFunctions. The model is configured entirely through a graphical userinterface integrated in the standard FLUENT? interface. The modelconsiders fine and coarse mode ash deposition and stickingmechanisms for the complete deposit growth, as well as an influenceon the local boundary conditions for heat transfer due to thermalresistance changes. The model is applied to the straw-fired Masnedøboiler. Results are in good qualitative agreement with bothmeasurements and observations at the plants