Although declining in Europe and Canada, cofiring biomass with coal is a subject of growing interest in Asia so work continues on developing the technology. This review facilitates the technology transfer ‘from West to East’. Biomass characteristics and the options for cofiring are described, of which direct cofiring is the most widely used method. Biomass pretreatment methods include washing and leaching, torrefaction, steam explosion, densification and pelletisation. Generally, pretreatment methods are combined such as the pelletisation of torrefied material. Agricultural residues are of interest for cofiring in Asia, partly to improve local air quality. However, compared to woody biomass, they have a higher concentration of chlorine, phosphorus, and alkali and alkaline earth elements, which result in slagging and fouling. The report discusses the latest developments in combustion related issues such as cofiring in CFB boilers, cogasification cofiring, oxyfuel cofiring and cofiring ratios. Oxyfuel cofiring of biomass, if combined with carbon capture and storage has the potential to result in negative emissions of CO2. Attention should be paid to biomass handling, storage and fire protection as it has a lower ignition temperature and is more explosive than coal. Computational fluid dynamics (CFD) is a powerful tool in the development of coal and biomass cofiring technologies for increased understanding, exploration of unfamiliar conditions, design, troubleshooting, and optimisation of combustion processes.
The impacts on emission controls and ash utilisation from cofiring are analysed. Cofiring biomass can help meet various Sustainable Development Goals including Goal 7 affordable and clean energy, Goal 9 industry innovation and infrastructure, Goal 12 ensure sustainable consumption and production, and Goal 13 climate action. However, government support, and favourable regulatory and environmental policies are still required for the widespread deployment of cofiring.
Technology Developments in the cofiring of biomass
Xing Zhang and Simone Meloni