Field and CFD Study of Fuel Distribution in Pulverized Fuel (PF) Boilers

The article presents both field and CFD results of a new concept of a mechanical pulverized fuel (PF) distributor. The goal of the study was to improve the pulverized coal-air mixture separation in PF boilers where the fuel preparation and feeding system was operated in a combined coal and biomass grinding conditions. The numerical analysis was preceded after a field study, where measurements were carried out in a pulverized coal-fired (PC) boiler equipped with a technology of NO_x reduction by means of primary methods. Proper distribution of a pulverized coal-air mixture to the individual burners is one of the fundamental tasks of the combustion systems where the primary methods are implemented to control the NO_x emission. Problems maintaining the proper distribution of fuel to the burners related primarily to the boilers where the coal and biomass co-grinding is used. Changing the load of coal-mills and fuel type at the same time (i.e., different types of biomass) could result in less effective separation of pulverized fuel particles in PF distributors. Selection of an appropriate construction of a distributor will allow the better control of the combustion process which results in decreased NO_x emission while keeping the proper combustion efficiency, i.e., less unburned carbon (UBC) in the fly ash. The results of the field measurements made it possible to create a CFD distribution base model, which was used for the analysis of a new splitter construction to be used in a PF distributor. Subsequent analysis of the numerical splitter enables precise analysis of its construction, including the efficiency of separation and the prediction of conveying of the coal and biomass particles.