CFB - Multi-fuel design features and operating experience

摘要

Over the recent years, the fuels for industrial combustion plants have changed dramatically. Environmental issues and economical drivers contribute to the shift from fossil fuels towards increasing utilisation of various biomasses and wastes. The chemical and physical properties of these fuels pose a variety of challenges on plant design, all the way from fuel handling to flue gas treatment. The combustion system is the part of the plant which meets most of the fuel related challenges. Natural, wood-based biomasses have been used as large-scale fuel since industrialisation. The basic challenge of combusting high-moisture biofuels with excellent efficiency has been solved by fluidised bed combustion systems already more than a quarter of a century ago. The basic chemical composition of natural biomasses may include elements like sodium and potassium, which contribute to a more challenging behaviour in combustion system. Alkali enrichment in the bed material and related risks of agglomeration have been typical issues coming up while increasing the share of biofuels. In general, operating methods have been developed also to overcome these issues. The more the biofuels are exposed to human influence, the more complex the fuel behaviour. Currently, operators and manufacturers are facing issues from handling mechanical impurities in recovered fuels to the effect of harvesting methods on the chemistry of fuels of agricultural origin. Especially, various recovered fuels are often rich in corrosive compounds that are seen only in negligible concentrations in natural fuels. Corrosion mechanisms are being intensively studied, and significant progress has been made during recent years. Metso Power's in-house experience and results of numerous other research organisations are incorporated in the latest design features to meet the increasing fuel-based challenges.