Under the sponsorship of the Pennsylvania Electric Company (Penelec), and with the support of EPRI, the U.S. Department of Energy, and the Pennsylvania Department of Conservation and Natural Resources, Penelec and Foster Wheeler Environmental Corporation conducted low percentage (3% by weight) wood cofiring tests at Units 2 and 3 of the Shawville Generating Station in November 1995. Unit 2 is a 138 MWe (gross) wall-fired pulverized coal boiler equipped with ball and race mills, table feeders, and low-NOx burners. Unit 3 is a 190 MWe (gross) tangentially-fired pulverized coal boiler equipped with bowl mills, paddle feeders, and low-NOx burners. There is no spare capacity in the pulverizing systems of either unit when operating under full load conditions.
This project was unique in a number of respects, expanding the knowledge and cofire experience base achieved in other previous projects (ref. 1). First, the project tested the use of blended biofuels in boilers equipped with low NOx burners. Additionally, three types of biofuel were tested: (1) mill waste sawdust, (2) utility right-of-way trimmings, and (3) harvested hybrid poplar. Biofuels were processed off-site, blended at a nearby coal blending yard, and then trucked to the unmodified Shawville Station on a “just-in-time” schedule basis. The off-site fuel preparation and blending operations provided an adequate supply of blended biofuel and coal to allow the project to meet its overall test objectives, and also provided much useful new data and information needed to help establish commercial processing facilities.
Plant operating technical objectives were to determine the impacts of using low percentage biofuel blends on boiler capacity, efficiency, stability, temperature, and air/solid waste emissions. Significant boiler capacity limitations were experienced on both units when cofiring 3 percent biomass blends. The 138 MWe boiler lost 8–10 MWe of capacity due to feeder limitations, and the 190 MWe boiler lost 15 MWe of capacity due to significant reductions in mill outlet temperatures. For both units, the 3 weight percent biofuel blends behaved like wet coal.
Significant new information was developed with respect to both fuel processing and plant performance issues. This paper describes the project and the test results and explores the CO2 mitigation impacts of firing blends of coal and biomass that are prepared off-site.