Cofiring Biomass and Coal 

for Fossil Fuel Reduction and 

Other Benefits—Status of North 

American Facilities in 2010

David Nicholls and John Zerbe

United States 

Department of 

Agriculture

Forest Service

Pacific Northwest 

Research Station

General Technical Report 

PNW-GTR-867

August 2012

DEPAR TMENT OF AGRICULT URE
Authors

David Nicholls is a forest products technologist, Alaska Wood Utilization and 

Development Center, 204 Siginaka Way, Sitka, AK 99835; and John Zerbe is 

a volunteer, Forest Products Laboratory, One Gifford Pinchot Dr., Madison, 

WI 53726. 

Cover photo of Seattle by Tom Iraci.

The Forest Service of the U.S. Department of Agriculture is dedicated to the principle of 

multiple use management of the Nation’s forest resources for sustained yields of wood, 

water, forage, wildlife, and recreation. Through forestry research, cooperation with the 

States and private forest owners, and management of the National Forests and National 

Grasslands, it strives—as directed by Congress—to provide increasingly greater service 

to a growing Nation.

The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and 

activities on the basis of race, color, national origin, age, disability, and where applicable, 

sex, marital status, familial status, parental status, religion, sexual orientation, genetic 

information, political beliefs, reprisal, or because all or part of an individual’s income 

is derived from any public assistance program. (Not all prohibited bases apply to all 

programs.) Persons with disabilities who require alternative means for communication of 

program information (Braille, large print, audiotape, etc.) should contact USDA’s TARGET 

Center at (202) 720–2600 (voice and TDD). To file a complaint of discrimination, write 

USDA, Director, Office of Civil Rights, 1400 Independence Avenue, SW, Washington, DC 

20250–9410 or call (800) 795–3272 (voice) or (202) 720–6382 (TDD). USDA is an equal 

opportunity provider and employer.
Abstract

Nicholls, David; Zerbe, John. 2012. Cofiring biomass and coal for fossil fuel 

reduction and other benefits–Status of North American facilities in 2010. Gen. 

Tech. Rep. PNW-GTR-867. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 22 p. 

Cofiring of biomass and coal at electrical generation facilities is gaining in importance as a means of reducing fossil fuel consumption, and more than 40 facilities 

in the United States have conducted test burns. Given the large size of many coal 

plants, cofiring at even low rates has the potential to utilize relatively large volumes 

of biomass. This could have important forest management implications if harvest 

residues or salvage timber are supplied to coal plants. Other feedstocks suitable for 

cofiring include wood products manufacturing residues, woody municipal wastes, 

agricultural residues, short-rotation intensive culture forests, or hazard fuel removals. Cofiring at low rates can often be done with minimal changes to plant handling 

and processing equipment, requiring little capital investment. Cofiring at higher 

rates can involve repowering entire burners to burn biomass in place of coal, or 

in some cases, repowering entire powerplants. Our research evaluates the current 

status of biomass cofiring in North America, identifying current trends and success 

stories, types of biomass used, coal plant sizes, and primary cofiring regions. We 

also identify potential barriers to cofiring. Results are presented for more than a 

dozen plants that are currently cofiring or have recently announced plans to cofire. 

Keywords: Cofiring, coal, biomass, fossil fuel, harvest residues.
Contents

1 Introduction

4 Objectives

4	 Past Cofiring (Pre-2000)

8 Case Study Briefs

8 Case 1: Coal Plant Repowering for Biomass (Portsmouth, New Hampshire)

8 Case 2: Coal Plant Repowering for Biomass (Shadyside, Ohio)

9 Case 3: Coal Plant Repowering for Biomass (Ontario, Canada)

9 Case 4: High-Rate Cofiring (Colorado Springs, Colorado)

10 Case 5: Cofiring With Agricultural Residues (Chillicothe, Iowa)

11 Discussion

11 Efforts in 2010 

15	 Summary on the Status of Cofiring Facilities

15 Metric Equivalents

16 Glossary

17 References
1

Cofiring Biomass and Coal for Fossil Fuel Reduction and Other Benefits

Introduction

Cofiring of biomass and coal presents a significant opportunity to address recent 

social, economic, and environmental incentives to reduce fossil fuel consumption 

for power generation in the United States. Coal plants are among the largest point 

source producers of nonrenewable carbon dioxide (CO2), and coal remains a significant energy source in the United States, with more than 1.1 billion tons consumed 

in 2008. More than 92 percent of this was used by the electric power sector (US 

DOE-EIA 2009). 

One of the most easily implemented biomass (material derived from plant matter) energy technologies is cofiring with coal in existing coal-fired boilers (US DOE 

2004). Biomass can provide numerous benefits when used as a fuel to supplement 

coal, including potentially lower fuel costs, lower landfill disposal costs, and reduce 

emission of sulfur dioxide (SO2) and oxides of nitrogen (NOx) (US DOE 2004). 

Other environmental benefits of cofiring may be more difficult to evaluate. The 

subject of carbon neutrality and biomass has become quite controversial lately, with 

some studies supporting the conclusion that cofiring results in net life-cycle greenhouse gas (GHG) reductions versus burning coal alone. For example, Mann and 

Spath (2001) estimated that cofiring rates of 5 and 15 percent would reduce equivalent CO2 emissions from burning coal alone by 5.4 and 18.2 percent, respectively. 

Zhang et al. (2010) found that life-cycle GHG emissions (measured in grams of CO2

per kilowatt [kW]-hour) for wood pellet combustion were less than 10 percent of 

those for two coal types used in Canada. In contrast, other studies suggest no net 

cumulative emission reductions by 2050 if biomass were to replace coal in powerplants (Manomet Center for Conservation Science 2010), and suggest that in some 

cases, biomass fuels can be more carbon positive (produce more carbon) than fossil 

fuels (Johnson 2009). Clearly, the issue of atmospheric carbon and implications on 

forest biomass is controversial, with yet unanswered questions. Additional research 

could help provide quantitative answers to these questions, especially considering 

the global dimensions associated with forest management, atmospheric emissions, 

and power generation to meet increased worldwide energy demands.

Despite this controversy, biomass cofiring has been a proven opportunity for 

coal facilities for more than a decade (Hughes 2000). Many U.S. coal facilities have 

at least performed cofiring trials, and cofiring is expected to be important for the 

foreseeable future. Further, equitably valuing the entire range of benefits of cofiring biomass with coal could further help to frame this debate, because numerous 

“externalities” and impacts of coal burning have not yet been valued (Faiij et al. 

1998), including: 

Many U.S. coal facilities 

have at least performed 

cofiring trials, and 

cofiring is expected to 

be important for the 

foreseeable future.
2

GENERAL TECHNICAL REPORT PNW-GTR-867

• Reductions in sulfur emissions (vs. burning coal only)

• Reductions in NOx emissions under most combustion scenarios

• Reductions in mercury emissions (Mentz et al. 2005)

• Reductions of landfill material (when cofiring municipal waste, construction debris, or other biomass material that would otherwise be landfilled, or 

when larger amounts of ash from coal must be landfilled for disposal)

Many coal plants can be “re-tooled” for biomass cofiring at a very reasonable 

cost. An important consideration for managers who are considering wood-coal 

cofiring is whether to cofire at low rates (with minimal capital investment) versus 

cofiring at higher rates (with greater capital investment). At low cofiring rates, 

expenses can be limited to minor mixing and blending of wood fuel with coal, often 

performed using a front-end loader. Cyclone boilers also offer low-cost opportunities for cofiring, typically in the range of $50 per kW of installed biomass capacity 

(NREL 2000). Higher cofiring rates often require a relatively modest investment of 

typically $50 to $300 per kW of installed biomass capacity (Baxter and Koppejan, 

n.d.), and in pulverized coal (PC) systems this is typically $150 to $300 per kW 

(NREL 2000). 

Cofiring at high rates (e.g., 10 percent of energy value) often involves separate 

wood fuel storage, handling, and injection systems. In this case, the capital and 

operating costs of retrofitting must be weighed against the expected benefits (De 

and Assadi 2009). In the case of larger coal facilities, a 10-percent cofiring rate 

(based on energy value) can be substantial. For example, the Drax facility in England expects to cofire 10 percent of a total coal capacity of 4,000 megawatt (MW) 

(resulting in 400 MW of energy from biomass) (Saimbi and Hart 2010). Some 

practical considerations for cofiring at high rates and repowering with biomass 

include the need for larger fuel storage areas, the potential need for wood fuel 

drying systems, and more powerful fans owing to the relatively low bulk density of 

wood fuels. 

Three general techniques are most often used when cofiring biomass and coal 

(Tillman 2000):

• Blend biomass and coal in the fuel handling system (then feed into boiler) 

• Prepare biomass separately from coal, then inject into boiler (with no 

impact on coal delivery)

• Gasify biomass, creating producer gas that is then combusted in a boiler to 

provide steam or hot water directly or used with an integrated gasification 

combined cycle (IGCC) system. 

An important 

consideration for 

managers who are 

considering wood-coal 

cofiring is whether 

to cofire at low rates 

(with minimal capital 

investment) versus 

cofiring at higher 

rates (with greater 

capital investment).
3

Cofiring Biomass and Coal for Fossil Fuel Reduction and Other Benefits

Worldwide, nearly 200 coal facilities have conducted test burns with biomass 

(IEA 2010). In the United States, more than 40 coal plants have conducted test 

burns. Numerous fuel types have been evaluated including wood chips, sawdust, 

switchgrass, and urban wood wastes (IEA 2010). However many of these test burns 

occurred at least 10 years ago, and were for limited amounts of biomass with shortduration test burns. Because many coal plants are aging and near replacement, 

cofiring with biomass could be an excellent “bridge” strategy to quickly reduce 

GHGs for a given facility whether or not coal would be used in the future. Further, 

the large size of many coal facilities could result in relatively large volumes of 

biomass utilization even at relatively low rates of cofiring. For example, it has been 

estimated that if all coal plants in the state of Colorado cofired at even a rate of 1 

percent energy value, then 53 MW of wood energy capacity would be added (about 

the size of a large wood energy installation) (Sourcewatch 2010).

Salvage biomass material, including salvage timber from fires or insect infestation, represents a significant resource for cofiring. However, important considerations would be the economics of transporting material to coal plants as well as 

the need to include merchantable timber (for higher value nonfuel use) as part of 

salvage operations. With 33 coal plants and significant acreages of beetle-killed 

timber, Colorado could be well-positioned to pursue cofiring opportunities. Use of 

salvage timber could become an important bridge strategy for coal plants as they 

pursue other, longer term fuel supplies.

Some large-scale regions are proposing wholesale shifts away from coal in 

favor of other fuels, e.g., the province of Ontario, Canada (see case study 3). The 

Netherlands is also making wholesale shifts toward cofiring. Here, cofiring has 

been conducted in at least six locations, and fuel sources have included wood 

pellets, demolition waste, sewage sludge, and chicken manure (vanRee et al. 2000). 

Also in Europe, several circulating fluidized bed (CFB) combustors have been 

established, representing opportunities for cofiring coal with numerous fuel types 

and particle sizes (Zabetta et al. 2009). These and other developments in Europe 

and Canada can provide examples for the United States to emulate.

Several technical challenges associated with cofiring have been identified, and 

work is ongoing to identify practical solutions. For example, pulverizing wood 

particles for use in PC burners can pose some technical challenges (Prinzing and 

Hunt 1998). Other operational challenges can include (Baxter and Koppejan 2004):

Because many coal 

plants are aging and 

near replacement, 

cofiring with biomass 

could be an excellent 

“bridge” strategy to 

quickly reduce GHGs 

for a given facility 

whether or not coal 

would be used in 

the future.
4

GENERAL TECHNICAL REPORT PNW-GTR-867

• Stable, high-quality fuel supplies

• Fuel handling and storage

• Potential increases in corrosion

• Decreases in overall efficiency

• Ash deposition and ash marketing issues

• Control of moisture content

• Impacts on selective catalytic reduction (SCR) performance

• Overall economics

Objectives

Three objectives of this report are to:

Review the status of cofiring biomass and coal in North America, determining how many plants are still cofiring today on an ongoing basis; 

includes woody biomass and other cellulosic materials.

Determine which facilities are actually cofiring today (or have concrete 

plans for cofiring).

Include a discussion about cofiring trends in North America and future 

opportunities to use woody biomass.

Past Cofiring (Pre-2000) 

Early test burns with wood and coal (mostly in the 1990s) evaluated a variety of 

feedstocks, including wood chips, tires, urban wood wastes, agricultural residues, 

and others (tables 1, 2, and 3). They also considered several coal combustion 

systems, including stokers, PC, and cyclone burners. Most of these tests were 

short-term trials only, often lasting just a few days or weeks. Further, most of these 

tests considered relatively low cofiring rates. Results of these tests indicated the 

general feasibility of cofiring with wood and coal at low rates, but also revealed 

some challenges. For example, pulverizing wood particles for use in PC burners 

can pose some technical problems (Prinzing and Hunt 1998). Other studies have 

found that successful cofiring in PC systems requires wood particle sizes of 1/16 

inch or smaller (Gold and Tillman 1996). Numerous test burns of coal and biomass 

were conducted in the 1990s as part of collaboration between the Electric Power 

Research Institute (EPRI) and the U.S. Department of Energy (Tillman 2001). 

These tests investigated the feasibility of cofiring with a number of different feedstocks under various operating conditions and different coal burning technologies. 

Numerous test burns 

of coal and biomass 

were conducted in 

the 1990s as part of 

collaboration between 

the Electric Power 

Research Institute and 

the U.S. Department 

of Energy.
5

Cofiring Biomass and Coal for Fossil Fuel Reduction and Other Benefits

Other cofiring tests of this same era include:

Seward Station (Pennsylvania). This study evaluated wood sawdust cofiring with 

separate injection from coal in wall-fired PC systems. Wood was cofired at up to 

7 percent energy value (15 percent by mass), with only minor decreases in boiler 

efficiency (Battista et al. 2000). Capital costs for cofiring with separate injection 

were held to less than $200 per kW (energy from wood).

Table 1—Test burns at selected U.S. powerplants started prior to 2001

Location	 Name	 Boiler type	 Output	 Primary fuel	 Cofired fuels	 Cofire duration

Gadsden, Gadsden Steam Tangentially 60 MW Pulverized coal Switchgrass 4 weeks

 Alabama Plant No. 2 fired burner

Madison, Blount Street Station Wall-fired 100 MW Pulverized coal Switchgrass —

 Wisconsin burner

Ashland, Bay Front Station Grate 44 MW Coal Wood, shredded

 Wisconsin rubber, railroad ties

Chesterton, Bailey Generating Cyclone burner 160 MW Pulverized coal Urban wood waste, 300 hours 

 Indiana Station No. 7 petroleum coke (57 test burns)

Dresden, Dunkirk Steam Tangentially 90 MW Pulverized coal Willow wood 6 months

 New York Station No. 1 fired burner

Dresden, Greenridge Generating Tangentially 108 MW Pulverized coal Wood chips —

 New York Station No. 6 fired burner

Lake Michigan, Michigan City Cyclone 469 MW Pulverized coal Urban wood waste 6 tests (over

 Indiana Generating Station No. 12 5 days)

Memphis, T.H. Allen Plant Cyclone 272 MW Pulverized coal Sawdust 24 tests (each 3 to

 Tennessee 6 hours long)

Johnstown, Shawville Generating Wall-fired 138 MW Pulverized coal Ground wood 7 days (3 to 4

 Pennsylvania Station No. 2 hours each) 

Tampa, Gannon Generating Cyclone 165 MW Pulverized coal Paper pellets 21 days

 Florida Station

Tuscumbia, Colbert Fossil Plant No. 1 Front wall fired 182 MW Pulverized coal Sawdust —

 Alabama

Pittsburgh, Natl. Inst. Occ. Stoker grate 55,000 lb Coal Wood chips —

 Pennsylvania Safety & Health per hr

Pittsburgh, Pittsburgh. Travelling grate 42,000 lb Coal Wood chips 16 test burns (up

 Pennsylvania Brewing Co per hr to 16 hours each)

Pittsburgh, Seward Generating Wall fired 32 MW Pulverized coal Sawdust —

 Pennsylvania Station No. 12

Prewitt, Escalante Generating Tangentially 250 MW Pulverized coal Waste paper sludge 2-year duration

 New Mexico Station No. 1 fired

Stillwater, King Generating Cyclone 560 MW Pulverized coal Kiln-dried wood, 2-year duration

 Minnesota Station No. 1 petroleum coke

Tacoma, City of Tacoma Steam Bubbling 18 MW Coal Wood, refuse-

 Washington Plant No. 2 fluidized bed derived fuel —

— = No information available.

Source: International Energy Administration-Task 32 [2010]. Cofiring database http://www.ieabcc.nl/database/cofiring.php.
6

GENERAL TECHNICAL REPORT PNW-GTR-867

Bailly Station (Indiana). This cofiring work included test burns of “triburn 

blends” of biomass, petroleum coke, and coal. Triburn cofiring resulted in (1) 

increased boiler efficiency, (2) reduced fuel costs, and (3) reduced emissions of 

NOx, mercury, and CO2 (Hus and Tillman 2000). Here, up to 30 percent of coal was 

replaced with petroleum coke and wood waste.

Shawville Station (Pennsylvania). This test fire program evaluated the effect 

of low-percentage wood cofiring (up to 3 percent by weight) on operating characteristics of 138-MW and 190-MW PC boilers. Three percent wood cofiring resulted 

in negative impacts in pulverizing, which led to reductions in boiler capacity for 

wall-fired and tangentially fired systems (Hunt et al. 1997). Alternatively, a separate 

injection system could be used for wood (bypassing the coal pulverizer). 

Gadsden Station (Alabama). This facility has evaluated switchgrass cofiring as part of a comprehensive evaluation of farm production issues, pilot-scale 

cofiring, and full-scale firing (Boylan et al. 2000). This research found that, even 

at cofiring rates of 5 percent switchgrass by mass in PC boilers, separate injection from coal is preferred. Other research at the Gadsden Station has considered 

cofiring coal with green wood chips. Test parameters included particle size of 

wood chip and the presence of pine foliage in the fuel mixture (Boylan et al., n.d.; 

Boylan 1996). 

Table 2—Cofiring tests at full-scale utility boilers (pre-2001)

Location	 Name	 Boiler type	 Primary fuel	 Cofired fuels	 Cofire date

Minnesota Northern States Power Cyclone boiler Coal Sander dust Started 

 in 1987

South Carolina Santee Cooper Electric Pulverized coal boiler Pulverized coal Forest debris from 1990

 Hurricane Hugo

Georgia Plant Hammond Pulverized coal boiler Pulverized coal Waste wood 1992

Tennessee Kingston plant Tangentially fired Pulverized coal Wood (low 1993, 

 Valley Authority pulverized coal boiler percentage) 1994

Tennessee Colbert plant Wall-fired pulverized Pulverized coal Wood (low 1992

 Valley Authority coal boiler percentage)

Tennessee Cyclone boiler Coal Wood (up to 20 1995

 Valley Authority percent by mass)

Savannah Electric Pulverized coal boiler Pulverized coal Wood (high 1993

 boiler percentage)

New York State NYSEG Pulverized coal boiler Pulverized coal Wood (10 percent 1994

 boiler by heat)

Madison Gas University of Wisconsin Wall-fired, grate-equipped, Pulverized coal Switchgrass 1996

 and Electric pulverized coal boiler boiler

Tacoma, Tacoma Public Utilities Fluidized bed boiler Coal Biomass Started

 Washington in 1991

Source: Sami et al. 2001. 
7

Cofiring Biomass and Coal for Fossil Fuel Reduction and Other Benefits

Tennessee Valley Authority (Allen, Kingston, and Colbert Stations). Cofiring tests were conducted at three coal facilities owned by the Tennessee Valley 

Authority. It was found that cofiring at 10 to 15 percent heat input for PC systems 

would require separate wood preparation systems and wood fuel burners (Gold and 

Tillman 1996). 

Dunkirk Station (New York). A short-rotation willow production model has 

been developed in New York, having a goal of providing biomass feedstock for 

cofiring. Heller et al. (2004) found that when cofiring 10 percent willow, the system 

net energy ratio increases by 8.9 percent while the net global warming potential 

decreases by 7 to 10 percent. Net SO2 emissions are reduced by 9.5 percent. Tharakan et al. (2005) stressed the importance of biomass tax credits, given that the 

production cost of willow feedstock is more than twice that of coal.

Blount St. Station (Wisconsin). This trial consisted of cofiring switchgrass at 

a 50-MW coal burner in Madison, Wisconsin. Cofiring levels varied between 4.3 

and 10.2 percent heat input of switchgrass, resulting in decreases in combustion 

efficiency of only about 1 percent (versus 100 percent coal) (Tillman 2001). An 

important benefit of switchgrass cofiring is the potential decrease in NOx emissions, which were reduced about 31 percent owing to switchgrass cofiring (Aerts 

and Ragland 1997).

Bellefield Boiler (Pennsylvania). Urban wood waste (construction debris) was 

cofired with coal in an underfeed stoker boiler using blends of 20 to 40 percent 

wood by volume (Cobb et al. 2004). The wood component consisted mainly of 

pallets, trim ends of framing lumber, trim ends of trusses, and minor amounts of 

plywood and particleboard. Combustion efficiency decreased only slightly even 

with 40 percent wood volume. However some assistance was needed to help maintain flow of the 40 percent blend so that wood was not unevenly distributed on the 

Table 3—United States powerplants cofiring with biomass (2001)

Heat input

Facility	 Company	 City/county	 State	 Capacity	 from biomass

- - - Megawatt - - -

6th Street Alliant Energy Cedar Rapids Iowa 85 7.7

Bay Front Xcel Energy Ashland Wisconsin 76 40.3

Colbert Tenn. Valley Auth. Tuscumbia Alabama 190 1.5

Gadsden 2 Alabama Power Co. Gadsden Alabama 70 <1.0

Greenridge AES Dresden New York 161 6.8

C.D. McIntosh, Jr. City of Lakeland Polk Florida 350 <1.0

Tacoma Steam Plant Tacoma Public Utilities Tacoma Washington 35 44.0

Willow Island 2 Allegheny Power Pleasants West Virginia 188 1.2

Yates 6 and 7 Georgia Power Newnan Georgia 150 <1.0

Source: Haq 2002.
8

GENERAL TECHNICAL REPORT PNW-GTR-867

grate. Also an increase in slagging was noticed with the 40 percent wood blend 

(Cobb et al. 2004). 

Northern Indiana Public Service Company (Indiana). Cofiring in this 

cyclone burner system was done with 1,000 tons of urban wood waste and kilndried wood waste (sawdust). Wood was screened to 1⁄2 inch in size, then blended 

with coal for cofiring at 6.5 percent energy value (Tillman 2001). Cofiring with 

wood resulted in a 9.5 percent decrease in NOx emissions and only minor reductions in boiler efficiency (approx. 0.5 percent). 

Case Study Briefs

Case 1: Coal Plant Repowering for Biomass 

(Portsmouth, New Hampshire)

At the Schiller Generating Station in New Hampshire, a 50-MW coal burner has 

been retrofitted to burn entirely wood in a circulating fluidized bed (CFB) boiler, 

while two other 50-MW units still burn coal. The biomass plant plans to earn 

350,000 renewable energy credits (RECs) annually, which could be sold to power 

companies in Connecticut and Massachusetts. Sale of these credits could be worth 

an estimated $15 million per year, helping to shorten the payback period of the 

repowering project, which cost an estimated $75 million (Peltier 2007). The new 

CFB boiler fueled by wood emits about 75 percent less NOx, 98 percent less SO2, 

and 90 percent less mercury than the coal boiler used previously (Peltier 2007). 

Given the flexibility of this CFB system, coal can be burned when needed. However 

the primary fuel source is to be 400,000 tons of whole-tree chips and clean, lowgrade wood. The wood energy facility was commissioned in December 2006.

Case 2: Coal Plant Repowering for Biomass (Shadyside, Ohio)

The Burger powerplant in Shadyside, Ohio, was planning to cofire wood pellets 

and agricultural biomass pellets with coal in two 156-MW units. This facility was 

expected to be “biomass-ready” by late 2012, with retrofits costing $200 million, 

and could burn biomass to produce up to 312 MW. Cofiring with up to 20 percent 

low-sulfur coal might also have been allowed (Renewable Energy World 2009). 

Eventually the plant was to be operated as a closed-loop bioenergy facility, with 

biomass fuel being obtained from dedicated energy plantations (Holly 2009). Under 

one scenario, woody and agricultural biomass would be pressed into cubes, which 

would later be pulverized for cofiring with coal. After much preliminary work, 

including obtaining construction permits, this project was cancelled by power producer First Energy because of falling prices for electricity (Cartledge 2010). Instead, 

plans call for permanently shutting down two of the coal units by the end of 2010.
9

Cofiring Biomass and Coal for Fossil Fuel Reduction and Other Benefits

Case 3: Coal Plant Repowering for Biomass (Ontario, Canada)

The Ontario, Canada, provincial government is planning to phase out all coal-based 

electrical generation from Ontario Power Generation (OPG) by the end of 2014 

(Marshall et al. 2010). Ontario Power Generation operates five fossil fuel power 

stations (total installed capacity of 8,177 MW), of which four are coal powered. 

Although provincial mandates are expected to motivate some conversions to natural 

gas (Murray 2010), OPG is also giving serious consideration to wood pellets for 

replacing substantial portions of their coal load. In 2008, test burns were conducted 

at the Atikokan Generating Station to evaluate the feasibility of powering a 227-

MW coal (lignite) boiler with wood pellets (Marshall et al. 2010). As of September 

2010, negotiations were underway for purchasing renewable power generated from 

the Atikokan facility. When repowering is completed, close to 99,000 tons of wood 

pellets per year will be required (Austin 2010). 

Other facilities (i.e., the Nanticoke Station) have begun plant preparations for 

firing with biomass, including a 50-MW injection system for introducing agricultural and woody biomass fuels into commercial-scale systems. Future work by OPG 

for increased biomass use includes:

• Evaluating fuel supplies (for agriculture residues and woody biomass) 

• Evaluating transportation logistics 

• Evaluating unloading and fuel storage requirements (as well as 

safety measures)

• Analyzing complete GHG life cycle of biomass fuels versus coal 

The Ontario powerplants under consideration for phasing out coal are:

• Atikokan Station (211 MW)

• Lambton Station (1,920 MW)

• Nanticoke Station (3,640 MW)

• Lakeview Station (1,140 MW)

• Thunder Bay Station (310 MW) planned conversion from coal to natural gas

Case 4: High-Rate Cofiring (Colorado Springs, Colorado)

Colorado Springs Utility is planning to continuously blend about 15 percent biomass (energy value) with 85 percent coal in one of their burners, utilizing more than 

100,000 tons of wood per year. Cofiring will occur within a 140-MW capacity coal 

burner, where nearly 20-MW of energy will be from wood. The wood is expected 

to come from a pellet plant in Colorado where a “microchip” product (approx. 1/2 

inch by 5/8 inch maximum dimension) will be produced. After delivery to the Colorado Springs coal facility, wood will be further processed in a hammermill grinder 

to a maximum dimension of about 1/16 inch, then mixed with the PC (Meikle 2010). 

The Ontario, Canada, 

provincial government 

is planning to phase 

out all coal-based 

electrical generation 

from Ontario Power 

Generation by the 

end of 2014.
10

GENERAL TECHNICAL REPORT PNW-GTR-867

A potentially significant advantage of burning low-moisture beetle-killed wood is 

that it is already close to the British Thermal Unit (BTU) value of some low-rank 

coals. For example, coal mined in Wyoming has an average of only 8,600 BTU 

per pound, only somewhat greater than that expected from the beetle-killed wood 

(Sourcewatch 2010). 

The plant renovations needed to receive, store, process and inject biomass 

separately from coal at the Colorado Springs plant are expected to cost about $10 

million (Anon. 2010). An important aspect of this project is the separate fuel injection systems needed for coal and wood. As of June 2010, design and engineering 

plans have been finalized and a contractor chosen for this work (Meikle 2010). 

Although the Colorado Springs project is expected to allow high cofiring rates, 

lower cofiring rates of biomass are possible as well. These projects typically do not 

require expensive capital improvements because the wood and coal can be mixed 

together and burned through a common injection system. Typically, costs for low 

percentage cofiring range from about $50 to $300 per installed kilowatt of biomass 

(National Renewable Energy Lab 1999). 

There are many coal-burning plants in the northern Rocky Mountain region, 

some of which could be within economical transportation distances of beetle-killed 

wood. For example, Colorado has 33 coal-fired powerplants (at 14 locations) totaling 

more than 5,300 MW of generating capacity (Sourcewatch 2010). However, other 

wood fuel sources could be available along Colorado’s Front Range to supplement 

beetle-killed material (Ward et al. 2004).

Case 5: Cofiring With Agricultural Residues (Chillicothe, Iowa)

In 2000 and 2001, the Chariton Valley Biomass Project completed successful test 

burns over a 2-month period, 26 days of which some switchgrass was burned 

(Amos 2002). Cofiring test objectives included (1) evaluating impacts on boiler 

performance (including slagging, fouling, and/or corrosion), (2) evaluating impacts 

on flue gas emissions, and (3) evaluating fuel handling and processing systems, 

including particle size reduction and dust control.

More than 1,269 tons of switchgrass were combusted to achieve a 3 percent heat 

input for the 725-MW plant. On several single days, more than 100 tons of switchgrass were burned. An advantage of using switchgrass as the cofiring fuel is that 

relatively low power requirements were needed to reduce particle sizes for use in a 

PC system (compared to wood cofiring). In the Chillicothe test burns, switchgrass 

particles were typically less than 1/16 inch in thickness and burned quickly in the 

PC burner (even though some particles were greater than 1 inch in length) (Amos 

2002). A disadvantage of cofiring with switchgrass is the potential for corrosion 

resulting from chlorine contents higher than that of coal. 
11

Cofiring Biomass and Coal for Fossil Fuel Reduction and Other Benefits

Discussion

Efforts in 2010 

In the past few years, numerous coal plants have announced plans to cofire with 

biomass, with several plants making serious moves in this direction (table 4). Several different scales, technology types, and biomass resources are being explored. 

Many of these efforts are aimed at either cofiring at high levels or repowering an 

entire coal plant to run on biomass. Several cofiring options are available to coal 

facilities, including the following:

• Cofire at low biomass rates with little equipment modification

• Cofire at higher biomass rates with equipment upgrades

• Convert/repower individual coal burners to be fired with biomass 

• Convert/repower entire coal plants to be fired with biomass

• Cofire with torrefied wood

Repowering and high-rate cofiring—

Current cofiring efforts seem to be focusing more on repowering entire units, or 

cofiring at high rates. Current efforts include burning more than 300 MW of biomass at one location (Burger Plant, Ohio). The motivation for some of these efforts 

is the need to upgrade older coal plants to meet air quality regulations, and cofiring 

with biomass is viewed as one means of achieving this goal, even if a capital investment for retrofitting is needed. Cofiring at high rates could offer opportunities to 

use large volumes of biomass quickly (e.g., hurricane debris or beetle-killed timber); 

however, potential problems in fuel supply could arise given that biomass residues 

often have a limited useful “shelflife.”

Key issues for cofiring biomass at high rates and/or repowering could include 

the following:

• Securing long-term fuel contracts for potentially large amounts of biomass

• Identifying the form of fuel that is best suited to the coal plant

• Acquiring capital needed to modify fuel receiving yard, and fuel handling 

and injection systems

• Processing fuel efficiently when cofiring at PC facilities

• Influencing coal plant operations (e.g., power requirements for fans, stack 

emissions)

• Addressing potential lack of local support

• Addressing higher levelized costs of electricity (and potential resistance 

from ratepayers)
12

GENERAL TECHNICAL REPORT PNW-GTR-867 Table 4—Summary of current (2010) activity—coal plant conversions and repowering Name	 Location	 Operator	 Cofire fuel	 Description/status Mount Poso Bakersfield, Red Hawk Energy Agricultural and Expected conversion date is September 2010 Cogeneration Plant California residential waste Boardman Plant Boardman, Portland General Torrefied wood or Planning to operate coal plant until 2020, Oregon Electric other biomass then close

Schiller Station Portsmouth, Public Service Co. Wood In operation since December 2006; burns approx. 

 New Hampshire of NH 400,000 tons/year in fluidized bed boiler

E.J. Stoneman Cassville, DTE Energy Wood Plan to convert a 50 MW-coal plant entirely  Powerplant Wisconsin to woodHu Honua Station Hawaii Hu Honua Agricultural 24-MW facility burning local wood and 

 Bioenergy, LLC residues agricultural wastes

Bay Front Station Ashland, Xcel Energy Wood waste from After repowering, will burn biomass in all

 Wisconsin forest harvesting three boilers

Charter St. Madison, University of Various biomass Refire coal boilers with biomass or natural gas;  Heating Plant Wisconsin Wisconsin fuels install a new boiler to burn 100 percent biomassMitchell Steam Albany, Southern Company Woody biomass Plan to convert 163-MW coal plant to biomass Generating PlantR.E. Burger Plant Shadyside, First Energy Corp. Variety of biomass Plan to repower two coal units to biomass (up to

 Ohio (Ohio Edison) fuels 312 MW of total biomass energy)

Lakeview Station Ontario, Ontario Power Wood pellets, Plan to phase out coal generation in Ontario

 Canada agricultural residues by 2014

Lambton Station Ontario, Ontario Power Wood pellets, Plan to phase out coal generation in Ontario

 Canada agricultural residues by 2014

Nanticoke Station Ontario, Ontario Power Wood pellets, Plan to phase out coal generation in Ontario

 Canada agricultural residues by 2014

Atikokan Station Ontario, Ontario Power Wood pellets, Plan to phase out coal generation in Ontario

 Canada agricultural residues by 2014

Note: MW = megawatt. Source: Sourcewatch 2010.
13

Cofiring Biomass and Coal for Fossil Fuel Reduction and Other Benefits

Fluidized bed combustion—

In fluidized bed combustion (FBC) systems, material is burned in a bed of inert 

material (such as sand), that is “fluidized” by air movement. The FBC systems can 

be modified as circulating FBCs (CFBC), in which material is recirculated to the 

combustion chamber for further burning. Fluidized bed systems have generally 

been limited to sizes of less than 300 MW; however, they are now being designed 

for larger applications, including a 460-MW CFB in Lagisza, Poland (Jantti et al., 

n.d.), that could be scaled up to the 600- to 800-MW range at a later date. 

The FBC and CFBC systems are becoming important as older coal plants can 

be repowered, opening the possibility of cofiring with biomass over a wide range of 

conditions. Important advantages of FBC systems can include (Jantti et al., n.d.):

• Their ability to burn fuels over a wide range of moisture content, particle 

size, and density, potentially including coal, biomass, tire-derived-fuel, 

agricultural residues, and urban wood wastes 

• More efficient heat transfer during combustion results in lower combustion 

temperatures, in turn lowering NOx emissions 

• Lower costs for SO2 capture because limestone can be added directly to the 

fluidizing medium (Laursen and Grace 2002) at relatively low cost compared to installing postcombustion scrubbers

Coal plants that install FBC systems as part of retrofits or new plant construction could “open the door” for future use of biomass (even if no biomass is included 

initially). The Schiller, New Hampshire, repowering is an example of a dedicated 

biomass FBC unit. Here, one 50-MW FBC runs entirely on wood while the remaining two units operate on coal only (Peltier 2007). The FBC systems have numerous 

advantages related to their flexible-fuel capabilities that are likely to remain important in new coal plant projects, new wood energy projects, repowering projects, and 

combinations of these.

Pulverizing biomass materials—

Proper pulverizing biomass for use in PC systems is an important operational 

consideration. Test burns have shown that a maximum wood particle size of about 

1⁄4 inch is needed before being copulverized with coal (Prinzing and Hunt 1998). In 

test burns at Shawville Generating Station (Pennsylvania), biofuels were processed 

in a tub grinder followed by trammel screen to achieve this particle size. 

However, cofiring at high rates can pose operational challenges to PC systems. 

For example, when cofiring sawdust up to 8 percent energy value, grinding coal and 

wood together had negative effects on coal fineness (Savolainen 2003). Other studies found negative impacts on boiler capacity even when only a 3 percent sawdust 

blend was included (Prinzing and Hunt 1998). However many of the drawbacks 
14

GENERAL TECHNICAL REPORT PNW-GTR-867

of including biomass could be mitigated by using a separate fuel injection system 

(versus processing wood and coal together). At least one firm manufactures equipment capable of producing a “microchip” product where 96 percent of material 

is sized less than 0.25 inch maximum dimension (Enviva 2010). Further work is 

needed to assess the pulverizing properties of wide-ranging biomass materials 

(including hazard fuel materials, urban wood wastes, and agricultural residues) as 

well as optimal cofiring levels, impacts on boiler efficiency, and whether separate 

injection is needed. 

Pulverized coal facilities are common in Maryland, with 13 of the 16 coal 

facilities in the state being PC facilities (Princeton Energy Resources International 

2006). Several key issues associated with cofiring in PC systems have been identified:

• Possible interference with SCR emissions equipment when cofiring biomass

• Little capital investment requirements when cofiring at less than 2 percent 

of energy value

• Capital investments ranging from $150 to $400 per installed kW of bioenergy are likely when cofiring at greater than 2 percent energy value

• Cofiring with biomass was less financially attractive than burning only coal

Torrefied wood—

In the torrefaction process, wood is heated to 200 to 300 °C, driving off volatile 

compounds in an oxygen-free environment. The result is a darkened, brittle product 

that has a higher energy content per unit mass than the original biomass source. 

Because torrefied wood is brittle, it can be pulverized and burned with coal, rather 

than needing separate handling, processing, and injection systems. This can result 

in substantial equipment cost savings when cofiring at higher rates. Numerous agricultural residues, including straws and grasses can be torrefied in addition to woody 

biomass, improving combustion properties of coal systems (Bridgeman et al. 2008).

Torrefied wood has been successfully cofired with coal at a powerplant in 

Borselle, The Netherlands. Here torrefied wood was copulverized with coal up to 9 

percent of energy value in a PC boiler, resulting in no measurable effects or adverse 

system operation (Weststeijn 2004). Also in The Netherlands, a plant to produce 

torrefied wood pellets is under construction, with an initial capacity of 60,000 tons 

per year (R.I.S.I. 2010), with potential scale-up to 100,000 tons per year (Beckman 

2010). Torrified wood may be cofired at higher rates than traditional forms of wood, 

as it more closely resembles coal in many properties. The torrefaction process 

typically results in considerably less volume than the original feedstock. Thus, the 

energy density of torrified wood can be on the order of 30 percent higher 

(Tennessee Valley Authority 2010) and can be economically trucked greater 

Further work is 

needed to assess the 

pulverizing properties 

of wide-ranging 

biomass materials 

including hazard 

fuel materials, urban 

wood wastes, and 

agricultural residues.
15

Cofiring Biomass and Coal for Fossil Fuel Reduction and Other Benefits

Metric Equivalents

When you know:	 Multiply by	 To get

Inches 2.54 Centimeters

Pounds 453.59 Grams

Tons (U.S. short tons) 0.91 Metric tons or 

megagrams

British thermal units 1,055.06 Joules

Degrees Fahrenheit (°F) F-32/1.8 Degrees Celsius (°C)

distances than unprocessed wood. Recently, work has been initiated with wet or 

hydrothermal torrefaction. Loblolly pine (Pinus taeda L.) was treated using hot 

compressed water at 292 to 500 °F (200 to 260 °C). Generally the wet torrefaction 

process produces a product with higher energy density than the dry torrefaction 

process (Wei Yan et al. 2009). HM3 Energy, located in Gresham, Oregon, has 

tested cocombustion of torrefied wood and coal (using a 50/50 blended feed) for 

up to 2 hours at the Western Research Institute in Laramie, Wyoming. In the tests, 

designed to simulate a PC-fired utility boiler, no problems were encountered with 

fuel feeding or combustion, while providing substantial reductions in sulfur emissions (HM3E 2010).

Summary on the Status of Cofiring Facilities

Biomass is a significant renewable energy option for the United States (de Richter 

et al. 2009) and cofiring is perhaps the best short-term means of reducing CO2

emissions from coal-burning facilities. Numerous test burns have been conducted 

with biomass and coal under a variety of plant operating conditions. Although 

many of these tests were conducted over 10 years ago, there is now renewed interest in cofiring. Current initiatives are often at larger scales, involving conversion of 

coal burners or entire plants to biomass fuels. The potential biomass feedstocks are 

diverse and could include greater use of urban wood wastes or biomass salvaged 

from insect infestations, fire, and other agents. New technologies are also likely 

to play a role, especially with aging coal plants that may be replacing burners 

with biomass fuel. Fluidized bed burners allow for a wide variety of fuel types 

and could see increased use. Ultimately, financial incentives will guide the future 

direction of cofiring. This could include cap and trade legislation, greater use of 

renewable energy certificates, and environmental mandates to replace aging equipment. United States facilities can benefit from experiences and lessons learned 

from Europe, where considerable volumes of biomass have been cofired over the 

past decade.

The potential biomass 

feedstocks are diverse 

and could include 

greater use of urban 

wood wastes or 

biomass salvaged from 

insect infestations, 

fire, and other agents.
16

GENERAL TECHNICAL REPORT PNW-GTR-867

Glossary

co-fire—The use of a supplemental fuel in a boiler in addition to the primary fuel 

the boiler was originally designed to use (Fehrs and Donovan 1999).

fluidized bed combustion (FBC)—Combustion units that burn fuel in an airsuspended mass (or bed) of particles. Fluidized bed combustion benefits include 

fuel flexibility and the ability to combust fuels such as biomass or waste fuels 

(Babcock and Wilcox 2006).

hardgrove grindability index (HGI)—Empirically measures the relative difficulty 

of grinding coal to the particle size necessary for relatively complete combustion 

in a pulverized coal boiler furnace. To determine HGI, a 50-gram sample of 

coal is ground under a fixed load, after which the proportion that is less than 75 

microns is recorded (ACARP 2008).

megawatt (MW)—one million watts.

megawatt-hour (MW-hr)—A unit of energy equal to the work done by one 

[million] watts acting for 1 hour and equivalent to 3.6 x 109 joule (The Free 

Dictionary, 2012).

pulverized coal (PC) burner—Pulverized coal (PC) boilers are the most 

commonly used technology in cofiring operations, and in electricity production 

in general. PC boilers burn finely ground particles of coal in a suspension boiler 

within the combustion area (Princeton Energy Resources International, LLC. 

2006). 

super-critical (SC)—Pressures greater than 3,200 pounds per square inch (22.1 

MPa) (Babcock and Wilcox 2012).

selective catalytic reduction (SCR)—A technology for reducing certain nitrogen 

emissions from coal combustion. The SCR process consists of injecting ammonia 

(NH3) into boiler flue gas and passing the flue gas through a catalyst bed where 

the NOx and NH3 react to form nitrogen and water vapor (US DOE 1997).
17

Cofiring Biomass and Coal for Fossil Fuel Reduction and Other Benefits

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