The performance and operation economics of co-fired biomass boilers

Almost every co-fired power plant in Finland is pursuing to increase the use of biomass fuels due to environmental and economical reasons. However, co-firing conventional fuels with risky biomass and recycled fuels poses many new challenges to power plant operators. The challenges might have great influence on the total economy of the plant. The balance between the positive and the negative aspects of the use of biomass is most often based on the economical reasons at the power plants. Variable costs of a biofuel-fired boiler depend not only on the procurement costs of the fuels, but also on the operability of fuel feed and combustion process, i.e. on the total operability of the boiler. It is not necessarily economical to use the cheapest fuel available, if the effects on the boiler operation are significant. Poor usability of the fuel mainly results from the problems in the fuel feed, unstable combustion process or from harmful behaviour of the ashes. Combustion and co-firing properties of fuel blends have been studied both in VTT Processes’ test facilities and in industrialscale fluidised bed boilers. Recently performance monitoring and operation economics study of two Finnish biomass fired boilers were conducted. Some of the results of that project will be described in this paper. The developed monitoring methods of boiler operation and economics work as new tools to support the power plant operators in daily fuel and process related decision-making.