Combustion in a fluidised catalyst bed (FCB) is an alternative to plasma-assisted coal combustion, which is performed at a temperature of over 1,200 degrees Celsius. FCB combustion occurs in a metal reactor filled with catalyst balls, which circulate at high speed under air blasts and a temperature of 600 to 750 degrees Celsius. The volatile compounds contained in the fuel combust on the surface of the catalyst, thus reducing the emissions of incomplete oxidation (i.e., combustion without flame) products. The higher the content of volatile compounds (coal tar, carbon dioxide, methane) in the fuel, the more efficient the combustion process. Finally, this technology does not require the use of equipment for after-treatment of gases, which is why it might reduce the cost of ‘clean’ coal-fired power generation.
Scientists from the Institute of Catalysis at the SB RAS decided to try out the FCB technology during the co-combustion of brown coal and biomass (pine sawdust). “Combustion in a fluidised catalyst bed is by itself a clean technology: the resulting emissions of toxic substances, such as carbon monoxide or nitrogen and sulphur oxides, never exceed the permissible limits. The use of biomass makes the process even more carbon neutral: plants absorb carbon dioxide in the course of their growth, so carbon dioxide emissions produced by the combustion of plant biomass are not added to the overall CO2 balance,” Yury Dubinin, candidate of chemical sciences and one of the authors of the study, is quoted as saying by the Institute of Catalysis.
The experiment has shown that the FCB process reaches maximum efficiency at a temperature of 750 degrees Celsius and a 3:1 ratio of sawdust to coal in terms of volume, as the degree of fuel combustion goes up to 99.6% in these conditions. Meanwhile, carbon dioxide emissions and nitrogen oxide emissions drop by 36% and 29% respectively compared to plasma-assisted coal combustion without the use of biomass. Moreover, no sulphur oxide emissions were detected during the experiment even though the content of sulphur oxides in brown coal is 12%.
The researchers believe that the FBC technology can be used with not only coal and biomass but also other fuels, such as oil shales and tar sands. For that reason, the technology could be employed in regions facing issues with the deliveries of conventional energy resources.
