Biomass Cofiring in Coal-Fired Boilers
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DOE/EE-0288 Leading by example, saving energy and Biomass Cofiring in Coal-Fired Boilers taxpayer dollars Using this time-tested fuel-switching technique in existing federal boilers in federal facilities helps to reduce operating costs, increase the use of renewable energy, and enhance our energy security Executive Summary To help the nation use more domestic fuels and renewable energy technologies—and increase our energy security—the Federal Energy Management Program (FEMP) in the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, assists government agencies in developing biomass energy projects. As part of that assistance, FEMP has prepared this Federal Technology Alert on biomass cofiring technologies. This publication was prepared to help federal energy and facility managers make informed decisions about using biomass cofiring in existing coal-fired boilers at their facilities. The term “biomass” refers to materials derived from plant matter such as trees, grasses, and agricultural crops. These materials, grown using energy from sunlight, can be renewable energy sources for fueling many of today’s energy needs. The most common types of biomass that are available at potentially attractive prices for energy use at federal facilities are waste wood and wastepaper. The boiler plant at the Department of Energy’s One of the most attractive and easily implemented biomass energy technologies is cofiring Savannah River Site co- fires coal and biomass. with coal in existing coal-fired boilers. In biomass cofiring, biomass can substitute for up to 20% of the coal used in the boiler. The biomass and coal are combusted simultaneously. When it is used as a supplemental fuel in an existing coal boiler, biomass can provide the following benefits: lower fuel costs, avoidance of landfills and their associated costs, and reductions in sulfur oxide, nitrogen oxide, and greenhouse-gas emissions. Other benefits, such as decreases in flue gas opacity, have also been documented. Biomass cofiring is one of many energy- and cost-saving technologies to emerge as feasible for federal facilities in the past 20 years. Cofiring is a proven technology; it is also proving to be life-cycle cost-effective in terms of installation cost and net present value at several federal sites. Energy-Saving Mechanism Biomass cofiring projects do not reduce a boiler’s total energy input requirement. In fact, in a properly implemented cofiring application, the efficiency of the boiler will be the same as it was in the coal-only operation. However, cofiring projects do replace a portion of the non- renewable fuel—coal—with a renewable fuel—biomass. Cost-Saving Mechanisms Overall production cost savings can be achieved by replacing coal with inexpensive biomass fuel sources—e.g., clean wood waste and waste paper. Typically, biomass fuel supplies should cost at least 20% less, on a thermal basis, than coal supplies before a cofiring project can be economically attractive. U.S. Department of Energy Energy Efficiency Internet: www.eere.energy.gov/femp/ and Renewable Energy No portion of this publication may be altered in any form without Bringing you a prosperous future where energy prior written consent from the U.S. Department of Energy, Energy is clean, abundant, reliable, and affordable Efficiency and Renewable Energy, and the authoring national laboratory. Federal Technology Alert Payback periods are typically To make economical use of captive investment of $850,000 was between one and eight years, wood waste materials—primarily required, resulting in a simple and annual cost savings could bark and wood chips that are payback period for the project range from $60,000 to $110,000 unsuitable for making paper—the of less than four years. The net for an average-size federal boiler. U.S. pulp and paper industry has present value of the project, These savings depend on the cofired wood with coal for evaluated over a 10-year analysis availability of low-cost biomass decades. Cofiring is a standard period, is about $1.1 million. feedstocks. However, at larger- mode of operation in that indus- Test burns at SRS have shown that than-average facilities, and at try, where biomass fuels provide the present stoker boiler fuel han- facilities that can avoid disposal more than 50% of the total fuel dling equipment required no costs by using self-generated input. Spurred by a need to reduce modification to fire the biomass/ biomass fuel sources, annual fuel and operating costs, and coal mixture successfully. No fuel- cost savings could be signifi- potential future needs to reduce feeding problems were experi- cantly higher. greenhouse gas emissions, an enced, and no increases in main- increasing number of industrial- tenance are expected to be needed Application and utility-scale boilers outside at the steam plant. Steam plant the pulp and paper industry are Biomass cofiring can be applied personnel have been supportive being evaluated for use in cofiring only at facilities with existing of the project. Emissions measure- applications. coal-fired boilers. The best oppor- ments made during initial testing tunities for economically attrac- showed level or reduced emissions tive cofiring are at coal-fired facili- Case Study Summary for all eight measured pollutants, ties where all or most of the fol- The U.S. Department of Energy’s and sulfur emissions are expected lowing conditions apply: (1) coal (DOE) Savannah River Site (SRS) to be reduced by 20%. Opacity prices are high; (2) annual coal in Aiken, South Carolina, has levels also decreased significantly. usage is significant; (3) local or installed equipment to produce The project will result in a reduc- facility-generated supplies of bio- “alternate fuel,” or AF, cubes from tion of about 2,240 tons per year mass are abundant; (4) local land- shredded office paper and finely in coal usage at the facility. fill tipping fees are high, which chipped wood waste. After a series means it is costly to dispose of of successful test burns have been Implementation Barriers biomass; and (5) plant staff and completed to demonstrate accept- For utility-scale power generation management are highly motivated able combustion, emissions, and projects, acquiring steady, year- to implement the project success- performance of the boiler and fuel round supplies of large quantities fully. As a rule, boilers producing processing and handling systems, of low-cost biomass can be diffi- less than 35,000 pounds per hour cofiring was expected to begin in cult. But where supplies are avail- (lb/hr) of steam are too small to 2003 on a regular basis. The bio- able, there are several advantages be used in an economically attrac- mass cubes offset about 20% of to using biomass for cofiring opera- tive cofiring project. the coal used in the facility’s two tions at federal facilities. For exam- traveling-grate stoker boilers. The ple, federal coal-fired boilers are Field Experiences project should result in annual coal typically much smaller than cost savings of about $112,000. Cofiring biomass and coal is a time- utility-scale boilers, and they tested fuel-switching strategy that Cost savings associated with avoid- are most often used for space is particularly well suited to a ing incineration or landfill disposal heating and process heat appli- stoker boiler, the type most often of office waste paper and scrap cations. Thus, they do not have found at coal-fired federal facili- wood from on-site construction utility-scale fuel requirements. ties. However, cofiring has been activities will total about $172,000 In addition, federal boilers needed successfully demonstrated and per year. Net annual savings from for space heating typically operate practiced in all types of coal the project, after subtracting the primarily during winter months. boilers, including pulverized- $30,000 per year needed to oper- During summer months, waste coal boilers, cyclones, stokers, ate the AF cubing facility, will be wood is often sent to the mulch and fluidized beds. about $254,000. An initial capital Federal Technology Alert market, which makes the wood • Economics is the driving factor. energy efficiency and renewable unavailable for use as fuel. Thus, Project economics largely deter- energy projects. Projects can be federal coal-fired boilers could mine whether a cofiring proj- funded through Energy Savings become an attractive winter mar- ect will be implemented. Performance Contracts (ESPCs), ket for local wood processors. This Selecting sites where waste Utility Energy Services Contracts, has been one of the driving fac- wood supplies have already or appropriations. Among these tors behind a cofiring demonstra- been identified will reduce resources is a Technology-Specific tion at the Iron City Brewery overall costs. Larger facilities “Super ESPC” for Biomass and in Pittsburgh, Pennsylvania. with high capacity factors— Alternative Methane Fuels (BAMF), those that operate at high loads which facilitates the use of bio- These are some of the major policy year-round—can utilize more mass and alternative methane and economic issues and barriers biomass and will realize fuels to reduce federal energy con- associated with implementing greater annual cost savings, sumption, energy costs, or both. biomass cofiring projects at assuming that wood supplies federal sites: are obtained at a discount in Through the BAMF Super ESPC, FEMP enables federal facilities • Permit modifications may be comparison to coal. This will to obtain the energy- and cost- required. Permit requirements also reduce payback periods. savings benefits of biomass and vary from site to site, but alternative methane fuels at no modifications to existing Conclusion up-front cost to the facility. More emissions permits, even for DOE FEMP, with the support of information about FEMP and limited-term demonstration staff at the DOE National Labor- BAMF Super ESPC contacts and projects, may be required for atories and Regional Offices, offers contract awardees is provided in cofiring projects.