Co-firing of Coal with Biomass and Waste in Full-scale Suspension-fired Boilers

The energy policy in Denmark has for many years focused on lowering the net CO2 emission from heat and power production by replacing fossil fuels by renewable resources. This has been done by developing dedicated grate-fired boilers for biomass and waste fuels but also by developing coal-based suspension-fired boilers to accept still higher fractions of biomass or waste material as fuels.

This last development has been challenging of many reasons, including pre-treatment of fuels, and solving potential emission and operational problems during the simultaneous development of supercritical steam cycles with steam temperatures close to 600°C, providing power efficiencies close to 50% [Hein, 2008].

For 25 years the CHEC (Combustion and Harmful Emission Control) Research Centre at DTU Chemical Engineering, has attained a leading role in research, supporting power producing industry, plant owners and boiler manufacturers to optimize design and operation and minimize cost and environmental impact using alternative fuels in suspension fired boilers.

Our contribution has been made via a combination of full-scale measuring campaigns, pilot-scale studies, lab-scale measurements and modeling tools. The research conducted has addressed many issues important for co-firing, i.e. fuel processing, ash induced boiler deposit formation and corrosion, boiler chamber fuel conversion and emission formation, influence on flue gas cleaning equipment and the utilization of residual products.

This paper provides an overview of research activities, aiming at increasing biomass shares during co-firing in suspension, conducted in close collaboration with the Danish power industry. The research has lead to an improved understanding of the alternative fuels interaction with coal in the boiler chamber.

Further, the applied research has provided results with implications for operation of milling and burner equipment, appropriate fuel mixing strategies, minimization of ash deposit formation and corrosion, minimization of NO formation, appropriate operation of SCR catalyst equipment and utilization of residual products. © Tsinghua University Press, Beijing and Springer-Verlag Berlin Heidelberg 2012.