Combustion and Slagging Behavior of Biomass Pellets Using a Burner Cup Developed for Ash-Rich Fuels

摘要

An innovative pellet burner cup ("BTC burner") designed to enable the burning of ash-rich fuels in small-scale boilers (30-40 kW) was evaluated, with respect to slagging behavior, combustion performance, and flue gas composition. The BTC burner features an open, flat-bottomed channel with air supply tubes on top of its lateral sides. The pellets are fed in horizontally, pushing the formed ash forward until it drops down into the ash pan. Eight different pelletized biomass fuels were combusted in the BTC burner, and no unscheduled stops occurred during the combustion tests. Conversely, seven of the eight fuel assortments caused unscheduled stops, because of slagging and/or piling-up of ash when burned in a conventional underfeed burner. The level of slagging in the BTC burner was considerably lower than in the underfeed burner, and the slag and ash were transported out of the burner cup without any complications. Combustion in the BTC burner cup also produced lower CO concentrations in the flue gas for all significantly sintering wood fuels and reed canary grass, and reduced NO emissions for all but one of the studied fuels. However, the BTC burner produced higher NO_2 and SO_2 levels than the underfeed burner for most assortments, and higher CO concentrations when burning corn stover with or without added lime. Further optimization of the BTC design will be required, particularly in order to minimize particle emissions.