Fluidised bed combustion of biomass
Conference contribution, 2011
This is a short review on fluidised bed combustion of biomass. At present most biomass fuels are prepared from wastes, mainly originating from agriculture and forest. The transport of this voluminous material to a plant sets a limitation on the plant size, whose role then is mostly within industrial and heating systems. Co-combustion with fossil fuels amplifies the use of biomass combustion to utility boilers. Fluidized bed boilers are built for biomass combustion both in circulating and non-circulating mode. Combustion of biomass is a mixing problem, which is solved by stirring with secondary air in a sufficiently high combustion chamber. Once the volatiles are successfully burnt, the remaining emission of concern is nitrogen oxide, because the sulphur content in the fuel is low. The principal problem of biomass combustion is formation of deposits on heat transfer surfaces and bed agglomeration caused by high potassium and chlorine contents in some fuels. Modification of the bed material may help: alumina-silicates have shown to alleviate the agglomeration-sintering problem, typically encountered with silica sand as bed material.