Effect of secondary air injection on the combustion efficiency of sawdust in a fluidized bed combustor

Abstract

Agricultural wastes like bagasse, paddy husks, sawdust and groundnut shells can be effectively used as fuels for fluidized bed combustion; otherwise these biomass fuels are difficult to handle due to high moisture and fines content. In the present work the possibility of using sawdust in the fluidized bed combustor, related combustion efficiencies and problems encountered in the combustion process are discussed. The temperature profiles for sawdust with an increase in fluidizing velocity along the vertical height above the distributor plate indicate that considerable burning of fuel particles is taking place in the freeboard zone rather than complete burning within the bed. Therefore, an enlarged disengagement section is provided to improve the combustion of fines. The temperature profiles along the bed height are observed at different feed rates. The feed rate of sawdust corresponding to the maximum possible temperature was observed to be 10.2 kg/h. It is observed that 50-60% excess air is optimal for reducing carbon loss during the burning of sawdust. The maximum possible combustion efficiency with sawdust is 99.2% and is observed with 65% excess air

Investigation of the Vortexing Effect on Sawdust Combustion in a Fluidized Bed Combustor

“…The CO emission decreases with a higher bed temperature , and excess oxygen. ,, Additionally, the staged combustion mode can reduce the CO emission with a higher secondary air ratio. , Currently, the disadvantages of fluidized bed combustion that uses sawdust are due to its higher CO emission. These CO emissions are generally larger than 2000 ppm. ,− Even under good combustion conditions that are increased by adjusting the operating variables, the CO concentration is still much higher than 100 ppm. According to the regulations of the Taiwan Environmental Protection Agency (EPA), the minimum emission of CO for an incinerator is 100 ppm and the CO emission is corrected to 11% residual oxygen on a dry basis.…”