New methods for NO_x emission reduction in fluidised bed combustion: CFD modelling results from a stationary fluidised bed boiler

Fortum and VTT have developed new air staging methods to reduce primary NOx emission from stationary fluidized bed combustion (SFB). These methods are based on the appropriate choice of secondary (and tertiary) air vertical position depending on the mode of operation and on the optimization of low furnace air distribution, which can be controlled by additional air feed into the near bed region. Computational fluid dynamics (CFD) equipped with specific models for SFB combustion was systemically applied to investigate alternative options for air system design and air distribution in a SFB furnace firing a fuel mixture of forest based-biomass and peat. Based on the results of CFD optimum concepts can be realised.