Cofiring of Coal and Fossil Fuels is a Way to Decarbonization of Heat and Electricity Generation (Review)
G. A. Ryabov
Abstract
Cofiring of coal and biomass has been demonstrated to be a promising solution to the problem of partial decarbonization of electricity and heat generation. This technology meets the aims of sustainable development of the world community and complies with the UN documents on environment protection and control of greenhouse gas emission. The properties of biomass, which largely determine the selection of one or another solution for its cofiring with fossil fuels, are discussed. The biomass pretreatment, which makes the biomass properties closer to the coal properties, is important. The pretreatment techniques, including leaching, pelletization, torrefaction, and steam explosion, are examined. Data are presented on the process solutions in the form of direct or indirect combustion (gasification followed by combustion). The greatest share of biomass in cofiring can be attained with fluidized bed (FB) and circulating fluidized bed (CFB) technologies. Circulating fluidized bed boiler, their performance indicators, and the problems arising in their operation (such as slagging, bed agglomeration, fouling and corrosion of heating surfaces) are presented. It has been found that, compared to the conventional technology, the oxygen supported cofiring of coal and biomass in a CFB boiler can considerable reduce the recorded CO2 emission. The prospects are discussed concerning the application cofiring technologies in Russia, where huge reserves of unused wood and plant waste are available. It is demonstrated that requirements to reduce the carbon footprint in products may be an additional drive for the implementation cofiring technologies. However, this requires additional research and engineering activities, including studies of biomass pretreatment, safety of cofiring facilities, formation and control of harmful emission, especially during combustion in an oxygen environment with CO2 recirculation, the effect of biomass components (such as alkaline elements and chlorides) on the formation of deposits on heating surfaces, their corrosion, and bed agglomeration.