Biomass Cofiring

A couple of UFTO utilities have expressed an interest in biomass cofiring, so I followed up with Sandia and also found some other resources also which you may find useful.


First, the new National Energy Technology Lab website for global climate change has a lot of information on the subject:


The 1995 UFTO report on Sandia had this brief summary on the Combustion Research Facility (CRF) that Sandia operates at its Livermore CA site…

“Over 1000 Sandia employees are located in facilities in Livermore California, and operate several special facilities, one of which is the Combustion Research Facility, the only one of its kind in DOE. Can handle industrial scale burners to 3 million BTU/hour. It is a “user facility” and outside visitors and users are encouraged. Partnerships with industry include GM, Cummins and Beckman Instruments and many others. Developed a number of specialized flame/combustion observational, measurement and diagnostic techniques. Provided fuel blending strategies to midwest utilities to meet SOx requirements. The Burner Engineering Research Laboratory is a user facility for industrial burner manufacturers.”


The CRF “Multifuel Combustor” website is currently under construction:


The CRF continues to be a significant contributor to combustion science, and in particular has amassed a major database of the combustion characteristics of over 50 different biomass fuels, most recently in the context of cofiring with coal. This work has been funded mostly by DOE, and includes information on emissions, carbon burnout, ash, and corrosion/deposition.

They’re also doing extensive computer modeling of coal, biomass and coal-biomass cofiring combustion. The coal modeling is under EPRI sponsorship, so that work is available to EPRI members. The dedicated biomass boiler modeling (stokers, etc.) is publicly available. The intellectual property issues associated with the coal-biomass cofiring are currently being sorted out, but it will be at least available to EPRI members and possibly to everyone.

For addition information, contact:

Larry Baxter 925-294-2862;
Sandia National Labs, Livermore, CA


Larry has generously supplied a copy of a brand new overview paper. Here are the first couple of pages. I have the complete 8 page overview as a (100k) Word document, which I can send on request. Larry has a more detailed article that he is willing to send to interested parties. Also, see below for some earlier reports, and a link to an upcoming American Chemical Society meeting session.



Larry Baxter, Allen Robinson, Steve Buckley and Marc Rumminger Sandia National Labs, Livermore CA

March 2000

This document presents guidelines for cofiring biomass with coal in coal-fired boilers. These guidelines are based on the results from pilot- and commercial-scale tests using a variety of biomass fuels and coals. Guidelines are offered in each of six general areas of major concern when cofiring biomass with coal: (1) fuel preparation and handling; (2) pollutant emissions; (3) ash deposition and deposit properties; (4) fuel burnout; (5) corrosion; and (6) fly ash utilization. For each of these areas, a brief statement of the issue and a brief guideline are summarized. More detailed information can be found at the cited website and in the references.

Summary of Cofiring Guidelines

We believe the following guidelines are generally valid, but there are specific instances where each of them is not valid. The discussions in the literature and web site provide the background to determine when such instances arise.

Fuel should generally be prepared and transported using equipment designed specifically for that purpose rather than mixed with coal and simultaneously processed.

Wood-coal blends generally reduce NOx emissions. This reduction is traced to lower fuel nitrogen content and higher volatile yields from biomass. SOx is nearly always reduced proportional to the reduction in total fuel sulfur associated with combining biomass with coal.

Deposition rates from blends of coal and biomass vary strongly with the type of biomass fired. Most wood-coal blends reduce both the rate of deposition and the difficulty managing the deposits. Some biomass-coal blends, in particular high alkali and high chlorine fuels, severely increase deposition problems.

Complete conversion of the carbon in biomass fuels requires that the fuel be processed to small particle sizes and be moderately dry. Particles generally need to be less than 3 mm (1/8 inch) to completely combust. Fuels that pass through a quarter-inch screen are generally dominated by particles less than 1/8 inch. High moisture contents (greater than 40%) and high particle density both significantly increase the time required to completely combust the particles.

Fuel chlorine and alkali concentrations should be limited to less than one fifth of the total fuel sulfur on a molar basis to avoid corrosion problems. This limit should be applied to the fuel composition as fired through any single burner except in the rare case of rapid and complete mixing of in the furnace.

Fly ash from wood-coal cofiring generally does not significantly degrade fly ash performance as a concrete additive. However, strict interpretation of current standards for inclusion of fly ash in concrete preclude mixed ashes, including biomass-coal ashes. Fly ash from many herbaceous fuels may negatively impact concrete properties.


Concerns regarding the potential global environmental impacts of fossil fuels used for power generation and other energy supplies are increasing in the U.S. and abroad. One means of mitigating these environmental impacts is increasing the fraction of renewable and sustainable energy in the national energy supply. Traditionally, renewable energy sources struggle to compete in open markets with fossil energy due to low efficiencies, high cost, and high technical risk.

Cofiring biomass with coal in traditional coal-fired boilers (subsequently referred to as cofiring) represents one combination of renewable and fossil energy utilization that derives the greatest benefit from both fuel types. Cofiring capitalizes on the large investment and infrastructure associated with the existing fossil-fuel-based power systems while requiring only a relatively modest investment to include a fraction of biomass in the fuel. When proper choices of biomass, coal, boiler design, and boiler operation are made, traditional pollutants (SOx, NOx, etc.) and net greenhouse gas (CO2, CH4, etc.) emissions decrease. Ancillary benefits include increased use of local resources for power, decreased demand for disposal of residues, and more effective use of resources. These advantages can be realized in the very near future with very low technical risk. However, improper choices of fuels, boiler design, or operating conditions could minimize or even negate many of the advantages of burning biomass with coal and may, in some cases, lead to significant damage to equipment. This document reviews the primary fireside issues and guidelines for implementing coal-biomass cofiring.

Fuel Characteristics

The biomass fuels considered here range from woody (ligneous) to grassy and straw-derived (herbaceous) materials and include both residues and energy crops. Woody residues are generally the fuels of choice for coal-fired boilers while energy crops and herbaceous residues represent future fuel resources and opportunity fuels, respectively. Biomass fuel properties differ significantly from than those of coal and also show significantly greater variation as a class of fuels than does coal. As examples (see Figure 1 and Figure 2), ash contents vary from less than 1% to over 20% and fuel nitrogen varies from around 0.1% to over 1%. Other notable properties of biomass relative to coal are a generally high moisture content (usually greater than 25% and sometimes greater than 50% as-fired, although there are exceptions), potentially high chlorine content (ranging from near 0 to 2.5 %), relatively low heating value (typically about half that of hv bituminous coal), and low bulk density (as low as one tenth that of coal per unit heating value). These properties each affect design, operation, and performance of cofiring systems.


Published papers available on cofiring:

Robinson, A., Baxter, L. L., Freeman, M., James, R. and Dayton, D. (1998) “Issues Associated with Coal-Biomass Cofiring,” In Bioenergy ’98Madison, Wisconsin.

Robinson, (1998) “Interactions between Coal and Biomass when Cofiring,” In Twenty-Seventh Symposium (International) on Combustion Combustion Institute, Boulder, CO, pp. 1351-1359.

Baxter and Robinson (1999) In Biomass: A Growth Opportunity for Green Energy and Value-added Products, Vol. 2 (Eds, Overend, R. P. and Chornet, E.) Elsevier Science, Ltd., Oxford, UK, pp. 1277-1284.

Baxter and Robinson (1999) “Key Issues When Cofiring Biomass with Coal in pc Boilers,” In Pittsburgh Coal Conference Pittsburgh, PA.

Baxter, Robinson, and Buckley (2000) “The Potential Role of Biomass in Power Generation,” In Biomass for Energy and Industry: 1st World Conference and Technology Exhibition Seville, Spain, to be presented.

Baxter, (1997) “Biomass-Coal Cofiring: Imperatives and Experimental Investigations,” In 3rd Biomass Conference of the Americas Montréal, Ontario, Canada.

Baxter, (2000) “Cofiring Biomass in Coal Boilers: Pilot- and Utility-scale Experiences,” In Biomass for Energy and Industry: 1st World Conference and Technology Exhibition Seville, Spain, to be presented.

Buckley, (1997) “Feasibility of Energetic Materials Combustion in Utility Boilers: Pilot-scale Study,” In 1997 Spring Meeting of the Western States Section of the Combustion Institute Sandia National Laboratories’ Combustion Research Facility, Livermore, CA.

Junker, (1997) “Cofiring Biomass and Coal: Plant Comparisons and Experimental Investigation of Deposit Formation,” In Engineering Foundation Conference on the Impact of Mineral Impurities on Solid Fuel Combustion Kona, HI. Robinson, A., Baxter, L. L., Freeman, M., James, R. and Dayton, D. (1998) “Issues Associated with Coal-Biomass Cofiring,” In Bioenergy ’98Madison, Wisconsin.

Robinson, (1997) “Fireside Considerations when Cofiring Biomass with Coal in PC Boilers,” In Engineering Foundation Conference on the Impact of Mineral Impurities on Solid Fuel Combustion Kona, HI.

Robinson, (1997) “Ash Deposition and Pollutant Formation when Cofiring Biomass with Coal in PC Boilers,” In EPRI Coal Quality Conference Kansas City, MO.

Robinson, (1997) “Pollutant Formation, Ash Deposition, and Fly Ash Properties When Cofiring Biomass and Coal,” In Engineering Foundation Conference on the Economic and Environmental Aspects of Coal Utilization Santa Barbara, CA.


1998 Tech Review — Sandia Combustion Research

-Coal and Biomass Combustion
-Cofiring Biomass and Coal to Reduce CO2 Emissions from
Coal-Fired Utility Boilers
-Thermal Conductivity of Ash Deposits Formed in Utility Boilers
-Mineral Matter Evolution during Coal Char Burnout


1997 Tech Review — Sandia Combustion Research

Scroll down to — “Coal and Biomass Combustion”

-Carbon Burnout Kinetic Model Developed for Pulverized Coal Combustion;
-Ash Deposit Property Analysis
-Pollutant Formation and Ash Deposition When Cofiring Biomass and Coal
-Formation of Ash Deposits in Biomass-Fired Boilers
-Combustion Properties of Biomass Pyrolysis Oils


AUGUST 20-24, 2000
Washington DC.

Division of Fuel Chemistry:

· 1990 Clean Air Act Amendments: A 10-Year Assessment
· Inorganics in Fossil Fuels, Waste Materials, and Biomass:
Characterization, Combustion
· Waste Material Recycling for Energy and Other Applications
· Fossil Fuels and Global Climate/CO2 Abatement
· Solid Fuel Chemistry
· Chemistry of Liquid and Gaseous Fuels

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