Biomass cofiring: status and prospects 1996

Biomass cofiring: status and prospects 1996

Fuel Processing Technology 54 Ž1998. 127–142 Biomass cofiring: status and prospects 1996 Evan E. Hughes a a,) , David A. Tillman b Electric Power...

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Fuel Processing Technology 54 Ž1998. 127–142

Biomass cofiring: status and prospects 1996 Evan E. Hughes a

a,)

, David A. Tillman

b

Electric Power Research Institute, Palo Alto, CA, USA b Foster Wheeler EnÕironmental,6 6 6, USA

Abstract Cofiring of biomass in coal-fired boilers has been tested and demonstrated in a number of utility installations including Allen, Kingston and Colbert Fossil Plants of TVA; Shawville Generating Station of PenelecrGPU; Steam Plant a2 of Tacoma Public Utilities; King Station of Northern States Power; Greenidge Station of New York State Electric and Gas; Plants Hammond, Mitchell, and Yates of Georgia Power; Plant Kraft of Savannah Electric; Jeffries Station of Santee Cooper; and several other installations. All types of combustion technologies have been used to cofire biofuels with coal including cyclone boilers, wall-fired and tangentially-fired pulverized coal boilers, fluidized-bed boilers, and stoker-fired boilers. Capacities used in cofiring tests and commercial applications have ranged from 50 MW to ) 500 MW. Supporting these tests and demonstrations have been fundamental studies and experiments on biofuel safety issues, blended biofuelrcoal storage and transport, pulverizer issues, fuel chemistries associated with blending, and related concerns. This activity in cofiring has resulted from utility interest in customer service and customer support in a deregulated utility environment, the potential for niche situations where blending of biofuel achieves fuel cost savings, and the potential for environmental benefit Že.g., NO x , SO 2 , and fossil CO 2 reductions.. The cofiring programs have resolved some issues, and have demonstrated that biofuel use, with coal, in large utility boilers can be beneficial for both the utility and its customers. Further, the cofiring programs have led to the development of a significant database concerning biofuel properties, boiler performance when cofiring biofuels, and combustion mechanisms when cofiring biofuels with coal. This database has been coupled with computer programs to evaluate certain issues associated with blending, such as ash behavior related to slagging or fouling. The cofiring programs have also defined certain issues that remain unresolved, at least in part. These issues include Ž1. the influence of cofiring on ash properties and flyash sales; Ž2. the influence of cofiring on boiler slagging and fouling problems; Ž3. the influence of fuel blending on pulverizer performance; Ž4. the maximum percentage of cofiring as a function of materials handling and combustion technologies; and Ž5. the required characteristics of biofuel particles to achieve defined project-specific goals such as avoiding derate, achieving

)

Corresponding author.

0378-3820r98r$19.00 Published by Elsevier Science B.V. PII S 0 3 7 8 - 3 8 2 0 Ž 9 7 . 0 0 0 6 4 - 7

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E.E. Hughes, D.A. Tillmanr Fuel Processing Technology 54 (1998) 127–142

dispatch, achieving NO x control, producing a coproduct from oversized particles, and otherwise meeting customer-service, environmental and economic goals. Published by Elsevier Science B.V. Keywords: Biofuel; Cofiring; Coal

1. Introduction Biofuels, a diverse group of energy sources ranging from wood waste and agribusiness waste to crops grown for energy Žsee Table 1., have long been used to generate process steam and electricity in industrial applications. Selectively, utilities and independent power producers ŽIPPs. have used biofuels, particularly wood waste, to generate electricity in small, stand-alone generating stations typically with - 50 MWe of capacity. In more recent years, utilities have become interested in cofiring biofuels with coal and other fossil fuels, applying wood waste and other solid forms of biomass to high efficiency, higher capacity, generating plants. The Electric Power Research Institute ŽEPRI. initiated a program to commercialize cofiring across a broad range of utility generating stations in 1992. Cofiring refers to the practice of introducing biofuels as a supplementary energy source in high efficiency utility boilers. Boiler technologies where cofiring has been practiced, tested, or evaluated, include pulverized coal ŽPC. boilers of both wall fired and tangentially fired designs, coal-fired cyclone boilers, fluidized-bed boilers, and spreader-stokers.

Table 1 List of biomass and waste fuels potentially useful to utilities Names of fuels Sawdust bark Bark Right-of-way trims Hybrid poplar trees Short rotation willow Eucalyptus trees Switchgrass Wheat straw Rice hulls Rice straw Sugarcane wastes Orchard prunings Walnut shells Grape pumice Railroad cross ties Cardboard

Paper Sewage sludge Pulprpaper sludge Scrap tires Waste plastic Waste paper Refuse ŽMSW. RDF Peat Baseline fossil fuels a. Lignites b. Coals c. CWS d. Fuel oil e. Oil–water slurry f. Natural gas

Key fuel properties

Representative values for sawdust

Name Size distribution Moisture Ash Heat content, wet Volatile matter Sulfur ŽS. Nitrogen ŽN. Potassium ŽK. Chlorine ŽCl.

Sawdust - 0.25 in. 40–50% green weight 1–3% green weight 4000–5000 Bturlb 80–90% dry 0.02 lbrMMBtu 0.2 lbrMMBtu 0.1 lbrMMBtu 0.01 lbrMMBtu

Ultimate analysis Proximate analysis Ash analysis Trace element analysis Sieve tray analysis Baseracid ratio Ash fusion temperatures Slagging index Grindability index

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The initial EPRI cofiring investigations Ž1979–1986. concerned municipal waste-toenergy projects, situations where utilities were considering the prospects for cofiring fuel made from municipal solid waste. The EPRI cofiring program, based initially upon that earlier work with refuse derived fuel ŽRDF. developed from municipal solid waste ŽMSW., changed and expanded as utility interest moved from MSW to wood and other cleaner, more uniform fuels. That program has expanded, addressing technical and non-technical issues alike, defining technical and economic barriers to biofuel utilization, and considering economic barriers to biomass cofiring in coal-fired boilers. Resulting has been the development of an extensive database concerning methods for successfully applying cofiring to utility boilers. 1.1. Rationale for biomass cofiring in utility boilers Initially, cofiring was seen as a means for reducing greenhouse gas emissions from fossil energy generation, largely in response to voluntary commitments made by individual electric utilities to the US Government in response to the Rio Conference. Carbon dioxide ŽCO 2 . from fossil fuel combustion is considered to be a greenhouse gas, because it adds carbon from rock to the CO 2 in the global atmosphere. CO 2 from biomass is not considered as a net addition of greenhouse gas because the carbon is already in the atmosphere. Initial analysis by Foster Wheeler Environmental ŽFoster Wheeler., supported by the Tennessee Valley Authority ŽTVA. and EPRI, confirmed that fossil CO 2 reductions could well be achieved by cofiring. Those savings come not only from displacement of coal, but also from displacement of materials being sent to landfill that ultimately decompose and form both CO 2 and another, more powerful greenhouse gas: methane ŽCH 4 .. During the initial year of the TVArEPRI study by Foster Wheeler, there emerged more powerful motivating factors driving the commercialization of cofiring: Ža. providing services to customers who produce by-products and wastes such as sawdust, shaving, and other biomass wastes; assisting such customers in converting wastes into useful residues in a manner that eliminates the cost of landfill disposal; Žb. providing utilities with fuels that can be blended with coal to reduce both the sulfur content and, increasingly importantly, the fuel-bound nitrogen content when both are quantified in lb pollutantr10 6 Btu fuel; Žc. providing utilities with fuel diversity and stability, permitting blending to achieve both environmental and economic blends to enhance plant dispatch. There are less-quantifiable motivating factors also encouraging some utilities toward cofiring: environmental image, managing environmental externalities, and other noneconomic considerations. These become significant only if a cofiring project is otherwise attractive. 1.2. Technical and economic barriers to cofiring In performing investigations and testing of cofiring, EPRI, TVA, Foster Wheeler, and other utilities such as Tacoma Public Utilities, Northern Indiana Public Service

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ŽNIPSCO., New York State Electric and Gas ŽNYSEG., PenelecrGPU, Southern Company, Santee Cooper, and others have identified numerous technical and economic barriers to cofiring. These barriers include Žfor example.: Ža. biofuel procurement practices to obtain low-cost fuels in a long term reliable manner; Žb. the impact of biofuel cofiring on ash composition and ability to sell flyash; Žc. the trade-off between the impact of biofuels on emissions and fuel cost, relative to the impact of biofuels on boiler efficiency and plant net station heat rate in BturkW h. 1.3. Addressing the issues EPRI has developed a significant program to evaluate and demonstrate cofiring, addressing the issues and barriers identified and testing different technical approaches. With Foster Wheeler and with participating utilities, EPRI has developed a significant database concerning fuel properties, fuel processing requirements and technologies, and cofiring experience. The database contains information derived from both testing and commercial practice. At the same time, this EPRI program has identified unresolved issues that must be addressed if cofiring is to be more broadly applied.

2. Biomass cofiring experience The electric utility industry initiated an evaluation of biomass cofiring to address the issues involved. At the time of EPRI program initiation, some utilities already had commercialized cofiring in niche applications. Through the EPRI program, and parallel utility programs, additional experience has been obtained. 2.1. Commercial cofiring experience Biomass cofiring has been commercialized in niche applications by such utilities as Tacoma Public Utilities, Northern States Power, and Southern Company. The commercial operation within Southern Company is at Georgia Power’s Plant Yates. The Tacoma project was a repowering of the Tacoma Steam Plant a2 by adding two fluidized-bed boilers fired with locally available wood waste, RDF, and coal. The plant uses two 25 MWe Žgross. turbines, each fired by a single boiler. The wood fuel is locally available hog fuel. Northern States Power initiated cofiring in 1987 at its King Station, a 550 MWe cyclone boiler fired with subbituminous coal. This cofiring application accepts finely divided wood waste from Andersen Windows, and firs it in the cyclones using the secondary air system for fuel transport. Customer service was the driving factor in this project. At Plant Yates, cofiring involves mixing low percentages of wood waste with coal on the coal pile. Since Yates is a PC-based station, the wood waste Žfine sawdust. and coal are transported together through the coal handling system and the pulverizers enroute to the boilers. The commercial experience has revealed some of the opportunities, and some of the technical barriers, associated with cofiring. Opportunities in the area of customer support

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have been demonstrated. Barriers identified have included fuel procurement issues, fuel quality issues, ash quality issues related to flyash sales, and limits to the percentage of biofuel that can be fired in given configurations. 2.2. Cofiring testing experience Cofiring tests, which constitute the heart of the EPRI program and the parallel utility programs, have extended the applicability of cofiring within utilities. Table 2 lists many of the key cofiring tests conducted or underway in the cofiring field. Note that some plants such as the Allen Fossil Plant ŽALF. of TVA have been tested extensively, using both eastern and western coals as the base fuel. Note also that plants such as the Shawville Generating Station of Penelec have cofired a variety of woody biofuels including sawdust, right-of-way trimmings ŽROW., and hybrid poplar. Significant additional test experience has been acquired by Southern Company, Santee Cooper, Duke Power, and several other utilities where biofuels exist in potentially plentiful supply. 2.2.1. Summary of the Allen Fossil Plant test experience The ALF test experience of TVA, EPRI, and Foster Wheeler is the most extensive program for moderate-level wood waste cofiring in cyclone boilers. Biofuelrcoal blends of up to 20% wood waster80% coal have been burned. The coal type has varied between an eastern high-sulfur coal and a Utah bituminous coal. At times tires have been incorporated into the fuel blend. The experience has shown that biofuels can accomplish the following: Ø achieve a trade between boiler efficiency and fuel cost Ø reduce SO 2 emissions, particularly when wood is fired with eastern coal Ø reduce NO x emissions through a variety of mechanisms Ø reduce fossil CO 2 emissions through fuel displacement Ø achieve customer service and fuel diversity goals This experience has been summarized in other papers. The test programs have been sufficiently successful that the plant is now ŽJuly 1996. in precommercial testing of wood cofiring over extended time periods. 2.2.2. Summary of the Kingston and Colbert Fossil Plant test experiences Kingston Fossil Plant ŽKIF. is based upon tangentially-fired PC technology. TVA tested low percentage cofiring at this installation, limiting the percentage of green Žwet. sawdust introduced into the coal supply to less than 5% Žby weight.. Colbert Fossil Plant ŽCOF. is based upon wall-fired PC technology. TVA also tested cofiring at this installation successfully at low levels, focusing upon levels up to 5% by mass. The KIF and COF experiences demonstrated that pulverizers could perform adequately at these low percentages of wood cofiring, and that the boilers could operate at capacity in a stable fashion. Indications of both tests were that 5% Žby weight. may be an approximate limit for transporting wood through ball mills or bowl mills, due to pulverizer performance and fuel fineness.

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Descriptive title and approximate date

Organizations Performers

Commercial operations cofiring sander dust with coal in a cyclone boiler at NSP Ž1987–present. Cofiring forest debris from Hurricane Hugo in a pulverized coal boiler at Santee Cooper Ž1990. Commercial coalrbiomass fluidized-bed combustion at Tacoma Ž1991–present. Waste wood cofiring tests at Plant Hammond, pulverized coal boiler of Georgia Power Ž1992. Tire-derived fuel cofiring test in a wall-fired grate-equipped PC boiler Ž1992. Cofiring of low percentage of wood at the Colbert wall-fired PC boiler of TVA Ž1992. Cofiring of low percentage of wood at the Kingston tangential-fired PC Boiler of TVA Ž1993, 1994.

Report reference Funders

Northern States Power

Northern States Power

Power Ž ;1990., EPRI Conference 1992 and 1993

Santee Cooper Electric Coop. ŽSouth Carolina.

Santee Cooper Electric Coop. ŽSouth Carolina.

Power Ž1993. SERBEP Ž1992.

Tacoma Public Utilities

Tacoma Public Utilities

Power Ž ;1993.

Georgia Power and Southern Company Services ŽSCS.

SCS and Georgia Power

EPRI Conference 1993 in Washington, DC ŽTR-103146, 12r93.

City of Ames, Iowa State University

EPRI TR-103851, 12r94

TVA

South Carolina E&G, Penelec, Centerior TVA

EPRI Meeting 12r93

TVA, Foster Wheeler

TVA

EPRI Meetings 12r93 and 11r94

E.E. Hughes, D.A. Tillmanr Fuel Processing Technology 54 (1998) 127–142

Table 2 Tests of cofiring in full-size utility coal-fired boilers

South Carolina E&G

South Carolina E&G

South Carolina E&G 1994

Savannah Electric and SCS

Savannah Electric and SCS

Power Ž1995.

TVA, Foster Wheeler

TVArEPRI

NYSEG

NYSERDA, NYSEG, ESEERCO

TVA, Foster Wheeler

TVArEPRI

TVA, Foster Wheeler

TVArEPR

GPUrPenelec, Foster Wheeler

State of PA, DOErPETC, EPRI, GPUrGenco

Madison Gas and Electric, University of Wisconsin Duke Power

EPRI, DOE’s Great Lakes Reg. Biomass Prog., MG&E, others Duke Power

Foster Wheeler 12r94, EPRI Gray Cover 7r96 NYSERDA Report No. 96-01 ŽJanuary 1996. EPRI Gray Cover 5r96

Foster Wheeler Report and Paper 5r96 EPRI Gray Cover 7r96

EPRI Meeting 6r96 EPRI Meeting 6r96

E.E. Hughes, D.A. Tillmanr Fuel Processing Technology 54 (1998) 127–142

Plasticrfiber waste cofired in a PC boiler Ž1993. High-percentage wood cofiring in a pulverized coal boiler at Savannah Electric Ž1993. Wood cofiring up to 20% by mass in a Cyclone boiler at TVA ŽAugust 1994. Mid-percentage Ž10% by heat. cofiring in a pulverized coal boiler at NYSEG Ž1994. Wood and tire trifiring with coal up to 15% by mass at Cyclone boiler at TVA ŽAugust 1995. Wood cofiring up to 20% by mass in a Cyclone boiler at TVA ŽDecember 1995. Wood preparation Žsawdust, right-of-way, and poplar. and cofiring in a PC boiler Ž1995. Switchgrass cofiring in a wall-fired, grateequipped PC boiler in Madison, WI Ž1996. Preliminary test of plastics, mill residues cofired in a PC boiler Ž1996.

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2.2.3. ShawÕille Generating Station test experience PenelecrGPU, along with Foster Wheeler, EPRI, and the US DOE’s Pittsburgh Energy Technology Center ŽPETC., tested low percentage cofiring at the Shawville Generating Station in north-central Pennsylvania. Unique aspects about these tests included the fact that Shawville uses both tangentially-fired and wall-fired boilers, and all of its units are equipped with low NO x burners. Further, Shawville is a plant where pulverizer capacity is the limiting factor in plant capacity to a significant extent. The tests at Shawville demonstrated that sawdust, right-of-way trimmings ŽROW., and hybrid poplar materials could be cofired successfully in PC boilers at low Žnominally 3% by mass. percentages. Boiler stability and operability were not, in any way, compromised. Efficiency was not significantly impacted. At the same time, ROW and hybrid poplar materials, being more fibrous than the sawdust, did cause difficulties with the pulverizers, reducing their capacities either through feeder speeds in the case of the table feeders to the ball mills in the wall-fired boiler, or mill outlet temperatures in the case of the paddle-fed bowl mills in a corner-fired boiler. 2.2.4. Plant Hammond test experience The Southern Company has conducted extensive cofiring testing at Plant Hammond. These tests have been conducted in a wall-fired PC boiler equipped with ball-and-race pulverizers. Wood percentages in the total fuel mix have ranged from 9.7% to 13.5%. This experience highlighted certain features: Ža. boiler efficiency losses were modest when cofiring wood; Žb. unburned combustibles were higher when cofiring than when firing coal; Žc. mill amps increased modestly when cofiring; Žd. mill fineness decreased modestly when cofiring; Že. positive impacts of cofiring on emissions were not apparent, due to some unique circumstances: SO 2 did not decrease, NO x decreased only slightly, and opacity increased. The boiler was operated at full capacity during the tests, and no derating was experienced. When superheat temperatures fell, fuel gas recirculation was employed to maintain acceptable levels of this parameter. 2.2.5. Plant Kraft test experience Southern Company also tested cofiring at higher percentages of wood in the 55 MWe Boiler a2 at Plant Kraft of Savannah Electric. That boiler, a tangentially-fired unit, was equipped with a separate wood feeding system directing a flow of dry sawdust into the exhauster of a bowl mill. ŽThis bowl mill was not run during the cofiring mode, and all of the coal was fed through the other mill to the other level, or row, of burners during cofiring.. Wood and coal were cofired, with coal being fired in one row of burners and wood being fired in the other row of burners. During some experiments natural gas also was fired. These tests demonstrated that high percentage wood cofiring in PC boilers could be successful if wood is fired separately from fossil fuels. 2.2.6. Other test experience A review of each individual cofiring test is beyond the scope of this paper. However, it is important to note that NYSEG has successfully cofired wood waste in a tangentially-fired PC boiler of 108 MWe capacity. NYSEG fired the wood separately from the

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coal, in one corner burner of the furnace. They did not blend the biofuel with the coal and did not introduce the wood into the pulverizer. In these tests at Greenidge Station, NYSEG fired wood at up to 10% of the heat input to the boiler. With wet sawdust, this test program documented NO x reductions as a function of biofuel cofiring; however, when dry wood waste was cofired with coal these reductions did not occur. The 10% Žheat basis. level was achieved only on dry sawdust. With green Žwet. sawdust the level achieved was close to 5% by heat. Santee Cooper had a significant cofiring program over an 8-month period, with up to 8% wood Žby weight. in the fuel blend. This program was initiated to manage the downed timber and wood waste generated by Hurricane Hugo. During this program, the wood was received in chip form, mixed with coal on the belt feeding the crusher, and then the mix was fed to Riley Atritta pulverizers. Atritta mills, which operate much like fine hammermills, have significant capability to handle biofuels. 2.2.7. Lessons learned from cofiring tests A number of significant lessons have been learned from the cofiring tests conducted by TVA, Penelec, Southern Company, and other utilities. Given, in all tests, the need to maintain plant capacity, these lessons include the following. Ø Cofiring can be performed at moderate and high percentages in cyclone boilers, with significant environmental benefits and site-specific boiler efficiency and economic impacts. Ø Cofiring can be performed at low percentages in PC boilers with potentially beneficial economic impacts depending upon the site and its local fuel supply conditions. Ø Cofiring in PC boilers, with the feeding of wood through the pulverizer, is typically limited by pulverizer performance; and pulverizer performance can vary as a function of the biofuel fired. Ø Cofiring in PC boilers 3–10% Žmass basis. input of biofuel in the blend may require separate fuel feeding Že.g., feeding not involving the coal pulverizers. depending upon the boiler and the capacity of the existing pulverizers, the type and condition of the biofuel being fired, and the type of pulverizer being used Žball-and-race, bowl, Atritta mill.. These tests also document the site-specific nature of biomass cofiring with coal. They have been limited to date by the selection of biofuel: clean wood waste. Very little, if any, experience has been gained with other biofuels. One particularly significant test will be conducted this year Ž1996., cofiring switchgrass with coal at the Blount Street Station of Madison Gas and Electric. That project involves MG & E and the University of Wisconsin as the primary participants, with Wisconsin Power and Light, EPRI, and Foster Wheeler providing support to the program. Outside funding of the Madison project is being provided by EPRI and DOE’s Great Lakes Regional Biomass Energy Program. 2.3. Additional studies and databases deÕeloped for biofuel cofiring A number of additional studies have been conducted Žsee representative list in Table . 3 , leading to an extensive database on cofiring experience and expertise. These studies

136

Descriptive title and approximate date

Organizations Performers

RDF cofiring in utility boilers and performance calculations via ‘RDFCOAL’ Ž ; 1985. RDF cofiring update Ž1996. Strategic analysis of biomassrwaste fuels for utilities, and ‘BIOPOWER’ Calculations Ž1993. Wood fuel sources, transportation and costrsupply for cofiring at TVA plants Ž1992–1995. Case studies of wood cofiring concepts and costs for TVA power plants Ž1993. Conceptual designs and costs for cofiring wood in systems based on natural-gas fired gas turbines Ž1993. Wood reburn for NO x control in coal-fired boilers: lab tests and rough economics Ž1994. Wood reburn concept designrcost for NO x control in TVA cyclone-fired boiler Ž1995. Woodrcoal blends: storage and cold-flow tests simulating bin feed for cyclone boilers Ž1994. Fuel characteristics of mill residues for TVA cofiring Ž1994.

Report reference Funders

MRI, Iowa State University, EPRI

EPRI, DOEr Argonne

EPRI CS-5754, 6r88

Iowa State University Appel, SFA Pacific, EPRI

EPRI EPRI, NYSERDA, DOErSERBEP

EPRI Ž ;9r96. EPRI TR-102773, 12r93; -774, 3r95

University of Tennessee

TVA, EPRI

University of Tennessee 8r93, EPRI ;8r96

Ebasco Žnow Foster Wheeler.

EPRI, TVA, DOErSERBEP

EPRI Gray Cover 4r94

Ebasco Žnow Foster Wheeler.

EPRI, TVA, DOErSERBEP

EPRI Gray Cover 7r96

REI, Foster Wheeler, University of Utah

DOErSERBEP, EPRI, NSF

REI Paper 1995 EPRI ;8r96

Foster Wheeler, REI

TVArEPRI

EPRI Gray Cover 5r96

REI, Foster Wheeler

TVArEPRI

EPRI Gray Cover 7r96

Foster Wheeler, TVA

TVArEPRI

EPRI Gray Cover 7r96

E.E. Hughes, D.A. Tillmanr Fuel Processing Technology 54 (1998) 127–142

Table 3 Studies of biomassrwastes cofiring

NEOS Foster Wheeler

DOErGLRBEP TVA,EPRI,DOE

GLRBEP Report EPRI Ž ;8r96.

Foster Wheeler

Union Electric, EPRI

EPRI Ž ;9r96.

Foster Wheeler

GPUrPenelec, EPRI

EPRI Gray Cover 10r95

Antares, NYSEG, NMPC, SUNY

EPRI TR-105250 11r95, NREL also

Iowa State University, IES, others

DOErNREL, EPRI, NYSEG, NMPC, others DOErNREL, EPRI, IES, others

DOErPETC

DOErPETC

ABB-CE, Duke Power

Duke Power, EPRI, American Plastics Council

EPRI Gray Cover 7r96

Foster Wheeler

NIPSCO, EPRI

EPRI soon Ž ;8r96.

Moll Associates

NIPSCO, EPRI

EPRI, soon Ž ;8r96.

NYSEG

EPRI, NYSERDSA, NYSEG

ESEERCO,

NREL Žalso an EPRI summary in TR-105854. PETC soon Ž ;8r96.

EPRI ;11r96

E.E. Hughes, D.A. Tillmanr Fuel Processing Technology 54 (1998) 127–142

Biomass fuel resources for Indiana Ž1994. Designs, costs and COFIRE1 spreadsheet Ž1995. Biomass resources and power plants for potential cofiring at Union Electric Ž1995. Wood resources and power plants for potential cofiring projects at Pennsylvania Electric Ž1995. Willow energy crop and wood cofiring feasibility in New York State Ž1995. Grass crops and wood crops for cofiring in a coal-fired power plant in Iowa Ž1995. Bench-scale test of switchgrass cofiring Ž1995. Lab ‘drop tube’ test and engineering study of waste plastic cofiring for a PC boiler Ž1995. Biomass cofiring prospects for Northern Indiana Public Service Ž1996. Biomass cofiring and CO 2 options for NIPSCO Wood fuel preparation at NYSEG: equipment selection and equipment tests Ž1996.

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and experiences include laboratory combustion tests, cold-flow biofuel performance tests, fuel characterizations, processing characterizations, resource characterizations, and cofiring case study conceptual engineering evaluations and cost estimates. These studies are incorporated into the database on cofiring being developed by EPRI and Foster Wheeler. 2.3.1. Laboratory combustion tests and cold-flow tests Pittsburgh Energy Technology Center ŽPETC. of DOE has conducted a short duration cofiring test in a laboratory-scale furnace simulating PC combustion. Those tests were designed to begin to assess the impact of switchgrass on boiler slagging and fouling. This test began to address the issues concerning firing switchgrass with coal in PC boilers, where the fuel particles exist in a dilute phase system. It serves as a precursor to future full-scale switchgrass tests such as the Madison Gas and Electric test this year Ž1996. at Blount Street Station in Madison, WI. Reaction Engineering International and the University of Utah, supported by Foster Wheeler, performed laboratory-scale tests using wood as a fuel in the application of reburn technology for NO x control. This test program, supported by EPRI and DOE Southeast Regional Biomass Energy Program, demonstrated the following: Ža. Wood fuels are as effective in reburn applications as either natural gas or coal; because they are solid, they can be transported well into the furnace before they pyrolyze to form the reactive volatiles Že.g., CH 3 . that drive the reburn reactions. Žb. Wood fuels in reburn applications can reduce NO x emissions by 50–70%, depending upon the initial concentrations of NO formed during combustion, the reburn stoichiometries employed, the reburn residence time, and the temperature profile in the furnace. The laboratory tests of wood reburn exemplify the potential use of low-nitrogen biofuels in special cofiring applications to achieve specific objectives in pollution control. Duke Power, with cofunding by Duke, EPRI and the American Plastics Council has investigated the cofiring properties of film plastics wastes. As part of this investigation, ABB-CE has conducted drop tube experiments defining some of the combustion properties of waste film plastics. These experiments relate the combustion of waste plastics to PC firing, in support of a cofiring program. Reaction Engineering International, under subcontract to Foster Wheeler in performance of the TVArEPRI studies also constructed a test bunker and performed extensive cold-flow test of woodrcoal blend storage and flow characteristics. These tests documented that wood, mixed with coal, improved the flowability of the fuel through the bunker. The wood did not stratify. Wood did not increase ratholing and it did not cause bridging in blends up to 30% woodr70% coal Žmass basis.. Further, the addition of wood to the fuel in the bunker did not increase the temperature of the fuel in the bunker above that associated with a 100% supply of coal in the bunker when such mixtures were stored for up to 30 days in the test unit. 2.3.2. Fuel characterization and resource studies In support of the cofiring program, Foster Wheeler has performed extensive fuel characterization and has developed an associated database regarding a vast array of

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biofuels including: bark, sawdust from mills in the Kingston and Allen Fossil Plant areas; wood waste from around the entire USA; treated wood products including railroad ties and telephone poles; crops and crop wastes such as alfalfa stems, switchgrass, rice hulls, rice straws, stone fruit pits, and other waste materials; and crops grown specifically for energy purposes including hybrid poplars. Characteristics include proximate analysis, ultimate analysis, chlorine content, higher heating value, ash elemental analysis, and trace metal content on a selective basis. These data also include physical properties such as specific gravity and bulk density. This database includes test data associated with cofiring tests, literature reviews, and information sent by other researchers. In addition to the characterizations of individual fuels, tests were performed concerning the behavior of ash from fuel blends. These tests assumed that the biofuel and coal ash products would be in intimate contact with each other; and these tests documented the eutectic effects of biofuel ash, with baseracid ratios ranging from 2.0 to 6.0, when combined with coal ash with baseracid ratios ranging from 0.15 to 0.6. The wood ash, if present in significant quantities, significantly depresses both ash fusion temperatures and T250 temperatures of the blended fuel. Resource studies have been performed by the University of Tennessee, Knoxville, under sponsorship from the TVArEPRI cofiring program. The analysis by the University shows fuel price sensitivity as a function of the quantity of biofuel required at any particular TVA power plant, using a complete GIS-based model with full details of roads, transportation costs, sites of wood sources and the specific site Žor sites. of the wood-consuming power plant Žor plants.. Further, resource studies performed for Penelec, Union Electric and EPRI by Foster Wheeler have also shown the plant-specific nature of fuel availability. A 50 mile change in location causes significant impacts on fuel supplyrcost curves. 2.3.3. Plant conceptual engineering case studies Several utilities have had case studies performed for a variety of plants. These case studies have led to the development of a series of cofiring spreadsheet methodologies for assessing the specific applicability of this technology at a given location. This methodology provides an initial screening tool which can be used to evaluate the cofiring potential of specific power plants. These case studies have typically involved developing a concept of materials handling, a profile of the boiler, expected combustion and environmental implications associated with cofiring, and a screening-level economic assessment of using biofuels with coal at candidate locations. These results are being made a part of Foster Wheeler’s COFIRE1 spreadsheet program for standardized screening of potential cofiring operations. 2.4. OÕerÕiew of cofiring status The commercial experience, plant test data, plant testing experience and the extensive study profile associated with past and current cofiring all contribute to the following overview of the status of cofiring as a biomass utilization technology.

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Ø Cofiring has emerged from niche applications to a broader commercial availability as a low-capital-cost means for using biofuels in existing generation systems. Although cofiring does not add generating capacity to a utility, cofiring can be implemented in a manner that does not reduce capacity and, simultaneously, it can be deployed where appropriate to achieve both economic and environmental benefits. Ø Cofiring feasibility is conditioned by the characteristics of the power plant being considered, the availability and price of biofuel within 50–100 miles of the plant, and the economic value of some environmental benefits associated with cofiring, such as the SO 2 and NO x reductions associated with cofiring at q10% Žmass basis. biofuel with coal. The potential for successful application of cofiring, on a purely commercial basis, is extremely site-specific. Ø The application of cofiring often has economic potential at low cofiring levels Že.g., - 5%, mass basis., depending primarily on the prospects for receiving acceptable biofuel at a delivered price well below that of the coal Ži.e., some 25¢ to 40¢r10 6 Btu below the coal price.. Ø The application of cofiring has environmental potential at moderate cofiring levels Že.g., 10–30%, mass basis., and can be particularly environmentally attractive if cofiring can be deployed economically and technically as a system that avoids the cost of installing and operating some other NO x control system. 3. Prospectus The prospectus for implementation of cofiring, as a dominant biomass utilization technology, involves resolving uncertainties and remaining issues, and then applying the cofiring concept where the driving forces and site-specific conditions are favorable. 3.1. Uncertainties and remaining issues There are several uncertainties and issues that remain, and which need to be resolved if cofiring is to be expanded. The following is a representative list of such issues. 1. Can the ASTM C-618 specification for Pozzolan be changed such that incorporation of modest amounts of biofuel in the blend of fuel going to a coal-fired boiler will not cause violation of the flyash as pozzolanic material specification? 2. What is the maximum particle size of wood, or any other biofuel, that can be fed to a given coal-fired boiler without impairing its performance, with particular attention to Ø type of boiler Žcyclone, wall-fired PC, T-fired PC, fluidized bed. Ø feed approach Žwith the coal—through the pulverizer, or separate feed. Ø type of biofuel Ø plant design 3. What are the consequences of cofiring high alkali herbaceous materials Ži.e., non-woody materials. together with coal, especially the consequences in terms of slagging and fouling, with particular emphasis on pulverized coal boilers? 4. What are the NO x implications of cofiring low-nitrogen biofuels at higher percentages, either derived from fuel blending or from reburning, if the boiler is specifically tuned and optimized around the specific biofuelrcoal blend?

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5. What types of fuel receiving and processing systems are most cost-effective for given applications and locations. 6. Can economically attractive cofiring applications be configured to integrate biofuels with natural gas, incorporating landfill gas and sewage treatment gas into the family of biofuels and incorporating biomass into combined cycle combustion turbine plants without challenging the combustion turbine system to accept a gaseous fuel high in alkali andror particulates? The issues that exist today are more defined, and more focused, than the issues and uncertainties associated with the cofiring technology in 1991. Because they are more readily defined, they can be addressed through research, testing, and specific programs. On a broader basis, however, the overall utility business climate has also changed. The impending deregulation of utilities has created significant uncertainties associated with separating generation, transmission, and distribution functions into separate companies: GenCo’s, TransCo’s, and DisCo’s. There are more uncertainties associated with stranded investments, the changing face of environmental regulations, and related concerns. Utilities now are taking a shorter-term focus on new opportunities, and they are less able to spread risk throughout the entire operation. Cofiring must be implemented within this framework. 3.2. Potential for cofiring implementation The forces supporting cofiring include the fact that it is a low capital cost option that can be implemented in today’s uncertain world. These forces permit deployment of this technology in coal-fired generating stations where biofuel exists in significant quantities and at low costs in the vicinity of such power plants. Each case is unique, and must be evaluated on that basis. The forces encouraging broader deployment of cofiring in the next 5 years include, potentially: Ž1. environmental regulations, and set-asides, that encourage biofuel utilization as the most economically attractive alternative; Ž2. customer service implications associated with customer satisfaction in a deregulated utility economy; Ž3. an available supply of low cost biofuels, capable of competing with coal and natural gas in the fuels market. There are other forces which are specific to given utilities and given utility service areas. In the near term, however, despite all of the uncertainties associated with utility deregulation and the economic changes caused by political shifts at state and federal levels, cofiring of biofuels in coal-fired utility boilers appears to be a most promising technology for implementation of electric utilities.

4. EPRI role EPRI has selected wood cofiring as the major thrust of the EPRI biomass power program for reasons indicated above. This has enabled EPRI to focus on the fundamental questions of how small, how dry, how much to cofire, in what type of boiler, with what equipment and processes, and at what cost and benefitrcost ratio. Wood is a

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widely available waste material that is relatively easy to use; it is the easiest among the biofuels to handle and fire. Consequently, it is the best starting point for biofuel cofiring. Compared to ordinary municipal refuse, wood is clean and uniform. Compared to many biomass fuels, including agricultural residues and the potential energy crop herbaceous fuels such as switchgrass, wood is low in alkali and, consequently, less likely to cause problems of slagging and fouling due to ash chemistry. As the principal collaborative research organization of the US electric utility industry, EPRI has worked with a number of electric utility companies to define and conduct studies and field tests of biomass cofiring. Tables 2 and 3, above, document those studies and tests. Some of the tests involve alternate fuels that are not wood, nor even biomass. Nevertheless, these cofiring experiments are part of the EPRI biomass power program because they may compliment biomass fuel use, lead the way to eventual expansion of biomass use as a utility fuel, or involve similar topics, measurement, equipment and techniques. Waste materials are the biomass fuels of today, and cofiring of such fuels is a way for utilities to seize the opportunities they have today to distinguish themselves from other suppliers of bulk electricity by providing customer service in a cost-effective manner. Utilities own valuable assets which provide special combustion environments well-suited for the disposal of many combustible wastes that could otherwise become disposal problems for utility customers or provide sources of fuel for power generation systems run by customers or competitors. In the near-term future, EPRI plans to provide its funders with systematic analysis and interpretation of alternate fuels, their combustion properties, and the experience in burning them. Field tests cofunded by EPRI member companies, and using commercial utility boilers owned and operated by those companies, are and will continue to be the heart of the EPRI biomass program in 1996 and 1997. After 1997, EPRI expects that the test results will be sufficient to enable EPRI’s member companies to make their cofiring decisions and that the research role for EPRI can then move on to emphasize other biomass resources and processes: Ž1. potentially more abundant biomass fuel sources, such as woody crops grown for fuel as well as higher-value products, and Ž2. processes that are more advanced or problematic, such as combustion andror gasification of more difficult or more abundant biofuels. In keeping with the near-term focus of today’s cofiring tests, EPRI is also looking for ways to integrate the use of biomass fuels with the expected next generation of fossil fuel power plants, namely natural-gas-fired combustion–turbine power systems, especially combined cycle power plants.