ABSTRACT
The term ‘cofiring’, in general, refers to co-combustion of two different fuels. Cofiring of biomass with coal in conventional coalfired boilers represents a combination of renewable and fossil energy utilization that derives the greatest benefits from both fuel types. It capitalizes on the large investment and infrastructure associated with the existing fossil-fuel-based power systems, while requiring only a relatively modest investment to include a fraction of biomass in the fuel mix. When proper choices of biomass, coal, boiler design, and boiler operation are made, gaseous pollutants (SOx, NOx, etc.) and net greenhouse gas emissions (primarily CO2) decrease in a reliable and cost-effective manner. Cofiring can be realized in a relatively short time frame with relatively low technical risk. However, improper choices of fuels,
boiler design, or operating conditions could minimize or even negate many of the advantages of burning biomass with coal and may, in some cases, lead to significant damage to equipment. In many countries, cofiring is one of the most economic technologies available to achieve CO2 reduction on a significant scale. Replacing an existing fossil fuel in a large power plant is often preferred over building a new but somewhat smaller dedicated biomass plant, because economies-of-scale effects make that larger plants can accommodate additional unit operations (e.g., superheaters, economizers, reheaters, etc.) to improve on thermal and electrical conversion efficiencies. Therefore, cofiring in large thermal power stations can lead to an overall saving of fuels in comparison to independent fossil and biomass plants. Further, better use of existing flue gas-cleaning facilities present in such large-scale installations can be made.
