PRODUCTION OF NEW BIOMASS/WASTE-CONTAINING SOLID FUELS

Abstract

CQ Inc. and its industry partners--PBS Coals, Inc. (Friedens, Pennsylvania), American Fiber Resources (Fairmont, West Virginia), Allegheny Energy Supply (Williamsport, Maryland), and the Heritage Research Group (Indianapolis, Indiana)--addressed the objectives of the Department of Energy and industry to produce economical, new solid fuels from coal, biomass, and waste materials that reduce emissions from coal-fired boilers. This project builds on the team's commercial experience in composite fuels for energy production. The electric utility industry is interested in the use of biomass and wastes as fuel to reduce both emissions and fuel costs. In addition to these benefits, utilities also recognize the business advantage of consuming the waste byproducts of customers both to retain customers and to improve the public image of the industry. Unfortunately, biomass and waste byproducts can be troublesome fuels because of low bulk density, high moisture content, variable composition, handling and feeding problems, and inadequate information about combustion and emissions characteristics. Current methods of co-firing biomass and wastes either use a separate fuel receiving, storage, and boiler feed system, or mass burn the biomass by simply mixing it with coal on the storage pile. For biomass or biomass-containing composite fuels to be extensively used in the U.S., especially in the steam market, a lower cost method of producing these fuels must be developed that is applicable to a variety of combinations of biomass, wastes, and coal; economically competitive with current fuels; and provides environmental benefits compared with coal. During Phase I of this project (January 1999 to July 2000), several biomass/waste materials were evaluated for potential use in a composite fuel. As a result of that work and the team's commercial experience in composite fuels for energy production, paper mill sludge and coal were selected for further evaluation and demonstration in Phase II. In Phase II (June 2001 to December 2004), the project team demonstrated the GranuFlow technology as part of a process to combine paper sludge and coal to produce a composite fuel with combustion and handling characteristics acceptable to existing boilers and fuel handling systems. Bench-scale studies were performed at DOE-NETL, followed by full-scale commercial demonstrations to produce the composite fuel in a 400-tph coal cleaning plant and combustion tests at a 90-MW power plant boiler to evaluate impacts on fuel handling, boiler operations and performance, and emissions. A circuit was successfully installed to re-pulp and inject paper sludge into the fine coal dewatering circuit of a commercial coal-cleaning plant to produce 5,000 tons of a ''composite'' fuel containing about 5% paper sludge. Subsequent combustion tests showed that boiler efficiency and stability were not compromised when the composite fuel was blended with the boiler's normal coal supply. Firing of the composite fuel blend did not have any significant impact on emissions as compared to the normal coal supply, and it did not cause any excursions beyond Title V regulatory limits; all emissions were well within regulatory limits. SO{sub 2} emissions decreased during the composite fuel blend tests as a result of its higher heat content and slightly lower sulfur content as compared to the normal coal supply. The composite fuel contained an extremely high proportion of fines because the parent coal (feedstock to the coal-cleaning plant) is a ''soft'' coal (HGI > 90) and contained a high proportion of fines. The composite fuel was produced and combustion-tested under record wet conditions for the local area. In spite of these conditions, full load was obtained by the boiler when firing the composite fuel blend, and testing was completed without any handling or combustion problems beyond those typically associated with wet coal. Fuel handling and pulverizer performance (mill capacity and outlet temperatures) could become greater concerns when firing composite fuels which contain higher percentages of high-moisture biomass materials, such as paper sludge and some wood wastes.