Cofiring Alternate Fuels in Coal Fired Cyclone Boilers

Cofiring of unconventional fuels in coal-fired cyclone boilers has provided utilities with the opportunity to accomplish numerous objectives including fuel cost savings, fuel diversification, customer support, and a reduction in such airborne emissions as oxides of nitrogen and sulfur dioxide. Unconventional fuels employed in cyclone boilers have included wood and wood waste, tire-derived fuel (TDF), waste paper and plastics, refuse-derived fuel (RDF), and a host of other industrial materials. Unconventional fuel has been introduced into the cyclone blended with coal, and it has also been introduced separately, in the secondary air system. Extensive parametric testing has been perfonned at the Allen Fossil Plant (ALF) of TVA during 1994 and 1995, firing combinations of wood waste with both eastern bituminous coal and western bituminous coal; and firing combinations of wood waste and TDF with western bituminous coal. These tests, supported by the Electric Power Research Institute, addressed the impact of cofiring and trifiring unconventional fuels with coal on fuel handling systems, the ability of the unit to achieve capacity, the ability of the boiler to operate in a stable manner, the impact of these fuels on boiler efficiency, the impact of these fuels on various other combustion and operation parameters such as temperatures, and the impact of these fuel blends on such airborne emissions as sulfur dioxide, oxides of nitrogen, and opacity. Blends fired have included up to 20 percent wood, and up to 15 percent wood with 5 percent TDF. This paper reviews the results of these parametric tests at the ALF facility. It identifies key technical findings of the test program. It demonstrates the significant impacts of cofiring in the areas of operations and environmental control. It documents the opportunities and issues associated with cofiring and trifiring alternate fuels with coal, and highlights key issues that must be addressed on a site-specific basis.