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

Building Products from Fly Ash and CO2

Our friends at Materials Technology Ltd. have shared with me the following information about the significant progress they’re making to turn ash into useful materials using Supercritical CO2. Especially noteworthy is the fact that the CO2 is expected to come from the power plant flue gas, and thus represents significant sequestration of CO2 at the same time. Note the information presented on CO2 separation methods.

The original UFTO note about this work appeared on January 1, 1997 – available in the UFTO website database.

Here is the abstract of a paper they will present at the Green Chemistry Conf, Jun 30 – July 2 in Washington (conference details are attached below).


Roger Jones, President and CEO,
Materials Technology Ltd, 14525 Rim Rock Road, Reno, NV 89511;
Frank G. Baglin, Prof of Physical Chemistry, Univ of Nevada – Reno,
Bruce A. Salisbury, Plant Engineer, Four Corners Power Plant,
Arizona Public Service, P.O. Box 355, Fruitland, NM 87416.


Coal-fired electric power plant wastes, portland cement, calcium oxide and supercritical carbon dioxide (CO2) are feedstocks to make low-cost, superior roofing shingles, wallboard and other fiber-reinforced products. Flue-gas CO2, recovered using thermally-driven, gas-stripping techniques(1), is permanently bound into the products as carbonates, reducing atmospheric pollution and its contribution to global warming.

The purpose of this patented technology is to produce profitable building products and many other useful things using cemented “dusty” wastes treated with supercritical CO2 (2,3). Products are shaped from a paste made of quick lime, a small amount of portland cement, foamed fly ash and fiberglass reinforcement. Once hydrated, they are treated with supercritical CO2 (preferably recovered from flue gas) to react the hydroxide components, forming carbonates and water and reducing alkalinity to about neutral.

The process has four important advantages:

– Capital required is low (three-year plant and equipment payback).
– Parasitic energy loss to the power plant is low or non-existent.
– There is a sufficiently high value-added component in final products to offset the logistics costs of raw materials and finished goods.

Production of cementitious goods and gas separation technologies are well-settled. Practical gas-separation technologies can be subdivided into four broad categories (4):

Membrane separation followed by distillation
Membrane absorption
The appropriate technology depends upon feed stream composition and thermodynamics and upon required quantities of carbon dioxide. In our planned implementation, we will use propylene carbonate absorption. CO2 stripping will occur after sulfur and nitrogen scrubbing.

Forming fiber-reinforced cementitious products like wallboard and roof shingles is also settled technology. Presently, fiberglass reinforced cementitious products demand costly alkali-resistant or plastic-coated glass to prevent alkali-silica reaction. Supercritical carbonation technology allows use of low-cost e-glass instead.

With the exception of foaming agents, fiber reinforcement and portland cement, all raw materials are available on site. The lightweight building products (in this case, fiberglass reinforced roofing shingles and fiberglass reinforced wallboard) are made by cementing foamed fly ash (about 53,000 tons annually for this plant) with calcium oxide (quick lime) and a small amount of portland cement. Both products will be made on continuous lines. After cementing, the products are subjected to treatment with supercritical CO2, again, in a continuous process. The CO2 forms carbonates and carbonated zeolites and reduces the alkalinity of the product to about neutral (pH 7). This permits incorporation of low-cost e-glass fibers without fear of subsequent, harmful alkali-silica reaction. The reinforcement is in the form of both continuous and chopped fiber.

An analysis of the relative inputs to the prototype shingle compared with competing roofing products was made and the results appear in the chart at left (5).

Based on costs of raw materials and energy, our studies indicate that we will be able to sell these waste-based products at pricing points below those of the lowest-priced competing products.

These products are examples of practical, solid-waste-feedstock, chemically bonded ceramics. Many other products can be produced in a similar manner, sequestering large quantities of solid waste and CO2 while offsetting manufacture of products using more energy-intensive systems that increase atmospheric CO2. Examples of such systems include thermoplastics, metals, composites, ceramics and forest products.

As industrial infrastructure in the developed countries ages and requires replacement or renovation, it will be wise to consider supercritical CO2 treated chemically bonded ceramics to reduce energy, raw materials and atmospheric pollution. For developing countries, the benefits are even greater.

In a developing economy, the creation of new industrial infrastructure requires huge investments in transportation systems for feedstocks, raw materials and components. Investment is also required to develop primary, secondary and tertiary manufacturing capacity as well as power plants and facilities to dispose of all types of plant wastes at all levels. Supercritical CO2 chemically bonded ceramic technology reduces much of this investment. Wastes and CO2 simply replace most feedstocks. Ancillary benefits arise from reduction of capital and energy needed to harvest, mine, or otherwise produce raw materials and transport them and intermediate raw materials for secondary or tertiary manufacturing.

Supercritical CO2-treated chemically bonded ceramics rely upon proven, practical technology to produce valuable products from solid waste feedstocks. Capital requirements are lower than conventional production systems, particularly when considering cradle-to-grave economics. Parasitic energy loss to producers is essentially none. Profit margins are high, because most products can be produced with low-cost or no-cost feedstocks.


2 United States Patent 5,518,540 issued May 21, 1996, Cement Treated with High-pressure CO2

3 United States Patent 5,690,729 issued November 27, 1997, Cement Mixtures with Alkali-Intolerant Matter and Method for Making Same

4 21 unpublished papers on methodology for practical recovery of food-grade CO2 from power plant flue gases, Carnegie Mellon University, Professor W.T. Berg, Senior Design Project, March 6, 1996


The 2nd Annual Green Chemistry and Engineering Conference: Global Perspectives
June 30 – July 2, 1998
National Academy of Sciences, Washington, D.C.

The Conference is cosponsored by the American Chemical Society, Committee on Environmental Improvement, Division of Environmental Chemistry, Division of Industrial & Chemical Engineering, American Institute of Chemical Engineers, Chemical Manufacturers Association, Council for Chemical Research, National Institute of Standards and Technology, National Research Council, National Science Foundation, Engineering Directorat, the U.S. Department of Energy and the U.S. Environmental Protection Agency, Office of Pollution Prevention & Toxics and Office of Research and Development.

Details, registration form and complete program available at:

Contact Dianne Ruddy at the ACS for further information at
(202) 872-4402, or e-mail

Resonant Shock

See UFTO Note Jan 15, 1998 for background on this remarkable development–turns ash of any kind, tailings, and dirt, into excellent building materials–cheaply and easily–using shock compaction.

The company, Resonant Shock Compaction, is making excellent progress. Here are two items they’ve just sent me (I’ve made no changes):

1. Large Block Testing Program — invitation to participate.
2. Abstract of their paper at recent DOE FETC 3rd annual Conference on Unburned Carbon on Utility Fly Ash.

Proposed Large Block Testing
RSC Compaction Technology
University of Denver


Public Service Company of Colorado and others are interested in testing the RSC technology beyond tests conducted in 1997 using coal combustion by-product (CCB) mixes to make parts for potential construction applications. This testing will test the RSC technology and its ability to fabricate large block parts.

Test Program Participants:

The following are defined as “test program participants,” Boral Material Technologies, Cat Construction Inc., McDonald Farms Enterprises, Public Service Company of Colorado, RSC LLC, Tri-State Generation & Transmission, UtiliCorp United, University of Denver, VFL Technologies, Wallace Industries; and Nuclear Fuel Industries/Stoller Corp. These parties are willing to fund this test program in which large parts will be fabricated for laboratory and field testing. All program participants will share equally in test data without regard to their monetary contribution toward the test program.

Test Objective:

The test objective is to measure strength and durability of large blocks fabricated from CCB mixes compacted by the RSC technology. These large blocks will be approximately 36″ by 48″ by up to 10″ thick. The test program will compare properties of the large blocks with smaller test blocks fabricated and tested in 1997 and 1998.

It is proposed that the following number of quality blocks be fabricated from the following mixes:

(4 Blocks) Cherokee bottom ash and Cherokee No. 4 silo ash
(1 Block) Cameo combination silo/bottom ash
(1 Block ) FGD material from Craig and bottom ash from Hayden
(1 Block) Bottom ash from Nucla and other materials
(1 Block) Bottom ash from Clark Station and Class C ash from Comanche
(1 Block) Mojave bottom ash and fly ash
(1 Block) Japanese bottom ash and fly ash (NFI/Stoller)


The existing RSC machine at the University of Denver will be used. Four more air cushions and associated pneumatics will be installed to fabricate large blocks. A vacuum lifting device will be installed to safely move the large blocks. The vacuum lifting device will enable the same mold to be used repeatedly with minimum cycle time. A low cost curing chamber will be constructed to accelerate block curing to approximately 24 hours. Cement mixers and batch scales will be rented to prepare mixes and core drilling services will be hired to produce cores for laboratory testing.

A single mold that can fabricate the blocks will be provided and upon completion of the program, the mold will become property of RSC LLC.

Mold Design:

A single mold, designed to produce parts approximately 36″ by 48″ by up to 10″ thick will be designed by RSC LLC. Cost of the mold will be paid by test program participants. The mold will be designed for manual disassembly or ejection removal of parts. Testing will also address handling techniques (pins, bolts, lifting holes, etc.) for these test parts. The use of a vacuum lifting device will enable parts to be removed from the mold upon ejection for separate movement to the curing chamber.

Mix Design:

Each test participant will provide sufficient quantities of CCBs at no cost to the program. All costs of raw materials provided to RSC LLC will be borne by test program participants. Disposal of excess material will be arranged by PSCo. Each participant will work with RSC LLC to determine the appropriate mix design. New materials and/or mix designs will first be tested in the small mold to develop mix design for the large blocks.

Machine Operations:

Machine power settings, vibration, shock, acceleration, and period will be set to achieve large block strength and durability characteristics similar to previously fabricated small test blocks.


Block strength and durability will be determined by measurement of compressive strength, porosity, freeze-thaw cycling, and resonant frequency. These tests will be performed on core samples cut from the blocks. Test criteria are based upon the 1997 and 1998 testing of small test block fabricated from similar mixes. Machine parameters and mix composition will be optimized to achieve strong and durable blocks.

Upon completion of curing the blocks will be transported to the PSCo Arapahoe Plant where the test cores will be cut from the blocks for testing at the University of Denver and at Commercial Testing Laboratories (CTL). Participants will determine block performance by placing the blocks in field test conditions at their respective locations. Upon completion of the test program, sample cores or whole parts may be retained by RSC LLC, the University of Denver and/or program participants.

Additional test capabilities available through the University of Denver Environmental Materials Laboratory include acoustic pulse velocity and absorption, acoustic emission, surface porosity, SEM analysis, thermal properties, and TCLP.

Test Results:

Test data obtained from this program will be available to program participants. It is anticipated that test data will be used by program participants and others to identify potential market applications of the RSC technology for large blocks. If a participant requires test data for a specific mix to be treated with confidentiality, that data will be provided only to that participant. However, it is anticipated that the physical characteristics of the large blocks will be reported generically without regard to specific mix designs.

Material Handling Issues:

Material handling techniques used at the University of Denver will not represent anticipated production techniques. Raw materials will be delivered in drums and mixing performed by manually placing mix components into a cement mixer and manually placing the mix into the mold. Equipment for weighing, measuring and blending raw materials may be rented. A forklift and vacuum hoist will be used to move the block. Because of space limitations at the University, different mix designs will be scheduled to reduce on property storage of raw materials and facilitate movement of completed blocks.


The test program schedule will be mutually determined by test program participants. A draft schedule is attached.

Test Program Costs:

The test program participants have agreed to fund this test program for an amount not to exceed $50,000. A test agreement will be prepared in which each participant will indicate their participation and/or level of funding. Participants will additionally bear all costs associated with providing their mix materials to the program, and transportation of mix material and test blocks. PSCo will assist in the coordination of transportation of finished blocks to Arapahoe Station and in the disposal of excess materials.

Other Parties and Potential Recovering of Test Program Costs:

To reduce the test program costs for all participants and to encourage development of the RSC technology with other entities, if test data from this program attract other partners, then the test program participants will be reimbursed a prorated portion of their costs from future agreements in which the large block testing served as the catalyst. For example, each participant’s share will be calculated as a percent of the total program. If a future agreement is signed between RSC LLC and other entities in which the large block test program results enable the agreement to be executed, then each test program participant will receive a fractional share of the agreement value to reimburse them for their participation, up to the full value only of their actual costs. This repayment will be made within three years of the completion of the test program. If no large block agreement with an entity is executed by that time, the test program costs will be forgiven.

Proposed Estimated Budget $45,000 – $50,000.

Presentation at the DOE FETC 3rd Annual Conference
on Unburned Carbon on Utility Fly ASh.


⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭⎭University of Denver

Robert E. Pressey, Keith Wier, and David Frey, RSC LLC.


The RSC technology is a high-g particle packing and forming process that has been licensed for ten years to commercially manufacture refractories weighing up to 5000 pounds. The Public Service Company of Colorado has funded a program at the University of Denver to develop applications of RSC to forming high-carbon Class F fly ash and bottom ash into value-added blocks and panels to construct sound barriers, retaining walls, pond liners, and tilt-up building panels. The Environmental Materials Laboratory is providing test facilities to study RSC process dynamics and product characteristics.

Typically, high-carbon test specimens formed by the RSC process have a compressive strength of 2000 to 5000 psi. Even specimens made from stoker fired ash containing 30% LOI measured 2500 psi. RSC is a robust technology that is tolerant of a wide range of carbon, calcium oxide, and calcium sulfate.

The RSC machine at the Environmental Materials Laboratory is a commercial sized unit capable of compacting 2000 pound parts. Laboratory test specimens are nominally 10 pounds but a mold to make 500 to 1000 pound panels has been designed. Large ash-based blocks and panels will be made for field testing.

Based upon Resonant Shock Compaction of Public Service Company of Colorado Cherokee Plant Class F fly ash and bottom ash this past year, it appears that the RSC technology can compact high-carbon ash into construction blocks, panels, or aggregate that pass many ASTM concrete and masonry strength and durability standards. These standards include compressive strength of 3000 to 5000 psi, sodium sulfate aggregate durability, face fired masonry water absorption, and freeze-thaw 300 cycle tests. These tests were performed by an ASTM certified commercial laboratory.

Papers at the last three DOE FETC Conferences on Unburned Carbonaceous Material on Utility Fly Ash reported that the highest valued ash utilization (cement admixture) is “at risk” because low NOx combustion technology often increases ash carbon content above the ASTM 618 limit of 6%, and the industry preference for 3% or lower. There is considerable effort underway to modify combustion processes to reduce ash carbon content and other efforts to increase alternative high-volume use options for high-carbon ash such as structural fill, agricultural soil amendments, and mine stabilization. Ash use is also limited by transportation cost to market and seasonal demand by the construction industry. Reduced ash use in concrete results in increased cement consumption and an associated one ton of CO2 for each ton of cement clinker produced.

Current research and development is focused on PSCo Cherokee Class F fly ash containing sodium carbonate flue gas conditioning agents and bottom ash, Valmont Class F fly ash and bottom ash, Comanche Class C fly ash, and Hayden bottom ash mixed with fly ash which has been conditioned with limestone ( flue gas desulfurization conditioned fly ash). Other tests include similar ashes, high carbon stoker ash (30% LOI), and circulating fluid bed ash containing highly reactive residual calcined calcium oxide with calcium sulfate.

The RSC market goal is to provide an alternative high-volume, high-valued product utilization of coal combustion products in partnership with electric utilities, ash brokers, construction companies, and manufacturers of concrete blocks, panels, and bricks. Acceptance of RSC ash-based construction materials is predicated upon successfully demonstrating the strength and durability of these products and obtaining the construction industry certifications from the International Conference of Building Officials, National Evaluation Service (ICBO NES).

Large blocks and panels will be made at the Environmental Materials Laboratory for testing in real applications. A transportable commercial plant will be built. Marketing studies have been performed by MBA students at the University of Denver Daniels School of Business. A preliminary conceptual design including capital and operating costs has been completed. Projected capital and operating costs are quite low.

Several electric utilities, environmental contractors, construction companies, and block manufacturers are participating in evaluation of the RSC technology to convert ash into construction blocks and panels. Waste clay and mine tailings are also being tested independently and in combination with ash. Specific products of interest to these parties are low cost highway sound barriers, retaining walls. pond liners, and tilt-up building walls. Test specimens containing greater than 50% bottom ash can be sawed, screwed, and nailed like wood.
⎭The University of Denver, Environmental Materials Laboratory, RSC LLC, and several electric utilities, are continuing studies to understand the unique properties of the RSC formed ash-based products. High-carbon ash formed into high strength products by the RSC process appear to be stronger than conventionally formed high-carbon ash products. RSC particle packing and high-g compaction of fly ash, bottom ash, and binder only requires about 10% water. This bonding process is being studied.

Acoustic velocity absorption and scanning electron microscopy have been used to measure ash and RSC product characteristics. A scanning optical microscopy densitometer system has been developed to measure product porosity. Acoustic velocity will be measured to correlate with product integrity. Differential scanning calorimetry and wide line proton nuclear magnetic resonance can provide information on ash-cement hydration.

The US Department of Energy has funded similar studies of the RSC technology at the University of Denver, Environmental Materials Laboratory to compact and stabilize radioactive and heavy metal contaminated soils. These studies have been conducted in cooperation with the DOE Rocky Flats Environmental Test Site, the DOE Argonne National Laboratories, and the DOE Mixed Waste Focus Area. Preliminary results have shown that RSC compacted soils have lower toxicity leach rates than other methods.