CO-FIRING OF BIOMASS FUELS WITH COAL IN NEW AND RETROFIT STEAM AND UTILITY BOILERS

摘要

Biomass fuels are universally recognized to be a clean and renewable source of thermal energy. While a boiler can be designed to burn 100% biomass, the seasonal reliability of the fuel supply, and higher fuel transportation costs for these typically low energy density fuels, have tended to favor 100% biomass firing in smaller boilers. An alternative to firing biomass as the sole fuel in a smaller boiler is to co-fire it in larger, new and existing coal fired boilers at varied utilization levels, depending on the boiler design and biomass fuel composition. New, large scale steam and utility boilers can be designed to accommodate the unique fuel handling and combustion/fireside behavior of the particular biomass fuel, allowing relatively high levels of biomass to be co-fired. Similarly, existing large steam and utility boilers can be retrofitted to handle a wide range of biomass types and co-firing rates, with limitations based on the economics of the particular unit and fuel. The large number, totaling many thousands worldwide, and wide geographic dispersion of existing coal fired boilers presents an opportunity to utilize a range of local biomass fuels in these units at significant economic and environmental benefit. Environmental benefits from such use include lower NO{sub}x emissions as a consequence of biomass' typically lower fuel nitrogen content and higher moisture content, lower SO{sub}x emissions as a consequence of their typically low sulfur content, and reduced CO{sub}2 emissions/their designation as 'CO{sub}2 neutral' fuels owing to their renewable nature, potentially giving rise to CO{sub}2 and/or tax credits.