TEMPERATURES IN A FUEL PARTICLE BURNING IN A FLUIDIZED-BED - THE EFFECT OF DRYING, DEVOLATILIZATION, AND CHAR COMBUSTION

Intra-particle temperatures and the emissions of carbon dioxide, carbo n monoxide, and total hydrocarbons have been measured during devolatil ization and char combustion of large spheres (3-20 mm diameter) of sel ected fuels. The fuels range from a carbon-rich, bituminous coal to tw o different, sub-bituminous coals of very different moisture and ash c ontents, to a highly volatile and ash-rich sewage sludge and to beech wood with the highest volatile content. To obtain results under variou s fluidized bed combustor conditions and to independently change the g overning parameters, the experiments were performed in three different laboratory-scale fluidized bed combustors (FBCs). The beds' temperatu res varied between 700 and 950 degrees C, the oxygen partial pressure in the fluidizing gas varied from 0 to 21 kPa, the superficial gas vel ocity from 0.3 to 9 m/s, the voidage of the fluidized particles in the beds was usually 0.5 or 0.997, and the mean diameter of the fluidized particles was 200 or 900 mu m. A dynamic simulation model has been de veloped to describe the behavior of a single fuel particle during its lifetime in a combustor. The model considers drying, devolatilization, volatile and char combustion, external and internal heat and mass tra nsfer, and changing fuel properties. Calculated temperature profiles a nd emission data are in good agreement with observations. Copyright (C ) 1997 by The Combustion Institute