A numerical model has been developed to simulate the various interacting physical processes that occur within any stoker-fired power boiler burning wood, refuse-derived fuel (RDF), coal, or other biomass fuel and operating at steady state. The processes modeled are three-dimensional turbulent gas flow, particle motion (including dispersion and re-entrainment), heterogeneous and homogeneous chemical reactions, and heat transfer. The purpose of this paper is to provide a detailed description of the model and to present an example of its use.

The model can be used as a cost-effective tool to assist in the design of original and retrofit power boiler equipment and in the diagnosis and resolution of boiler operating problems. The effects of modifying operational parameters or the physical arrangement of equipment can be quickly evaluated. Simulations can be used to optimize overfire air distribution and arrangement to produce a more uniform gas flow distribution within the furnace, resulting in more complete combustion and less particulate carryover.

As an example of the model’s capability, simulations were produced for a stoker-fired power boiler using wood, bark-pile reclaim, and waste-treatment sludge for fuel. The results show that changes in the air distribution and in the arrangement of operational overfire air ports can produce a significant reduction in carbon monoxide, unburned carbon loss, and particulate carryover, without increasing furnace exit gas temperature. Field modifications as a result of the modeling study have improved boiler operation and eliminated tube failures caused by flyash erosion.

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