Development of an Advanced Air System in a Biomass Boiler, 2001 Engineering / Finishing & Converting Conference Proceedings

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Problems associated with poor combustion in biomass boilers are often related to inadequate mixing of the combustible gases with air. The existing boiler defined in this document required the ability to follow variable steam loading in the mill while maintaining the mill header at acceptable levels. Also, considerations about decreasing the CO, Nox, and particulate by 30% to acceptable levels at the boiler exit while decreasing the exit O2 in the flue gas were reviewed. Since hundreds of thousands of dollars of modifications were being considered, process modeling was used to simulate gas flow and gas phase combustion to minimize risks by improving the air systems design.

The mathematical model developed was used to simulate the flow, heat transfer, and combustion in the biomass boiler of the proposed Under Grate and Over Fire Air (OFA) systems. The resulting model was investigated by boiler personals with years of experience to suggest refinements in subsequent models. Operational cases were evaluated with design loads, different OFA nozzle arrangements, and with and without the addition of an arch. The process simulation showed distributions of velocity, temperature, chemical species concentrations, and heat flux and confirmed the optimum placement, number, and size of OFA nozzles.