Fuel Loading of a Fluidized Bed Combustor Burning Bituminous Coal, Peat or Wood Chips

Report, 1997

Characterisation of gas- and particle phases in the combustion chamber of a commercial size circulating fluidized bed (CFB) boiler has been carried out during tests with three different fuels: bituminous coal, peat and wood chips, for typical operating conditions of a CFB boiler. The evaluation of the test results aims at presenting data on the fuel loading in parallel with the vertical profiles of oxygen concentration to be used for validation of models and for modelling of the fuel loading. The measurements show that the char loading during peat combustion is 13% of the amount found during coal combustion. Wood combustion results in even less char, only 3.5% of the concentration during coal combustion. For all fuels, more than 80% of the mass of char is retained in the lower part of the combustion chamber, below 2 meter from the bottom plate. The oxygen concentration profiles show large variations over the cross section for all three fuels, explained as an effect of insufficient penetration of secondary air in combination with partial plugging of some of the secondary air nozzles. In the peat and wood cases some of the variation over the cross section is caused by the high volatile content of the fuel in combination with a fuel supply from only one of the furnace walls.