Development in biomass preparation for suspension firing towards higher biomass shares and better boiler performance and fuel rangeability

Suspension-firing enjoys the great popularity in biomass-fired heat and power generation. Since it has the strictest requirement on fuel quality and particle size, cares must be taken in biomass handling. This paper reviews, combined with concrete cases, the development in biomass preparation methods for suspension-firing: the processes and their impacts on critical issues in biomass suspension-firing. The first-generation preparation method, based on raw biomass, was successfully used for biomass suspension co-firing at low shares and nowadays is mainly used for other combustion technologies, due to the large particles it produces. The second-generation method, based on biopellets, is commonly used in existing suspension-firing plants. It can reduce biomass particle size to 85% < 1 mm (maximum 3 mm), ensuring good ignition and particle burnout. 100% biomass suspension-firing is mainly for high-quality biomass and often uses additives to mitigate corrosion. To improve fuel rangeability, the third-generation method will be prevailing. It includes extra thermal pre-treatment for increasing the energy density and grindability of the feedstock. Suspension-firing trials of torrefied biopellets are performed at several power plants. It is too costly in the present energy market and can be promoted by a future regulatory condition change in favor of alternative solid fuel sources.