Overview and some issues related to co‐firing biomass and coal

Abstract

Low heating values, variable chemical compositions, peculiar physical properties, high investment cost and insecurity of biomass feedstocks supply limit the applications of biomass for energy and other processes. Co-firing biomass and coal has potential for the development of biomass-to-energy capacity with significant economic, environmental, and social benefits. However, co-firing is not straightforward, and some questions need to be addressed due to the differences in chemical compositions and physical properties of biomass and coal. This paper highlights key issues related to co-firing, including reactor types, feeding, hydrodynamics, ash sintering, fouling, and corrosion, based on previous studies, as well as calculations and analysis. Direct co-firing is the most common option for biomass and coal co-firing currently, mostly due to relatively low investment needed to turn existing coal power plants into co-firing plants. For direct co-firing, the physical characteristics and chemical compositions of the fuel entering the combustors or gasifiers are critical to an optimum operation. Any biomass mixed with coal needs to have acceptable physical properties. More research is needed on co-firing biomass and coal, including work on: preparation, handling, storage, and feeding of biomass feedstocks (e.g. drying, torrefaction, pelletization); co-firing mechanisms; hydrodynamic analysis of co-firing combustors and gasifiers; boiler/gasifier capacity, slagging, fouling, corrosion, efficiency, reliability, fuel flexibility; lower emissions and gas cleaning; catalyst poisoning; investment and operating costs.Les applications de la biomasse pour les procédésénergétiques et d'autres procédés sont limités par les faibles pouvoirs calorifiques, des compositions chimiques variables, des propriétés physiques particulières, des coûts d'investissementélevés et l'insécurité quantà l'approvisionnement en biomasse comme matière première. La co-alimentation biomasse-charbon est potentiellement intéressante pour la transformation de la biomasse enénergie, avec des avantageséconomiques, environnementaux et sociaux significatifs. Toutefois, la co-alimentation n'est pas simple et certaines questions se posent du fait des différences dans les compositions chimiques et les propriétés physiques de la biomasse et du charbon. On souligne dans cet article les principaux aspects entrant dans la co-alimentation, notamment le type de réacteurs, l'alimentation, l'hydrodynamique, le frittage des cendres, l'encrassement et la corrosion, d'après desétudes antérieures ainsi que des calculs et analyses. La co-alimentation directe est l'option la plus commune pour la co-alimentation biomasse-charbon, principalement en raison de l'investissement relativement faible requis pour transformer les centralesélectriques alimentées au charbon actuelles en centrales hybrides. Pour la co-alimentation directe, les caractéristiques physiques et les compositions chimiques du fioul entrant dans les chambres de combustion et les gazéifieurs sont critiques pour un fo...

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