By Steve Blankenship
The use of cement, concrete and wallboard increased dramatically over the past decade, generating a proportionate jump in demand for coal combustion products (CCPs). In the same period, sale of fly ash, bottom ash, boiler slag and flue gas desulfurization (FGD) materials increased 50 percent. Yet less than a third of these products find their way to the marketplace. The remaining two-thirds – 74 million tons in 1999 – must be disposed of, generally at plant sites or in mines from which the coal came. It’s a situation the American Coal Ash Association (ACAA) believes can and should change.
“The beneficial use of coal combustion products is one of the great untold success stories of the electric utility industry,” says Raul Deju, president of ISG Resources, a major marketer of CCPs. He has a point. In 1999, more than 33 million tons of CCPs were recycled. By comparison, a paltry 4.6 million tons of aluminum was recycled, and only a million tons of that was from beverage cans. Still, two-thirds of the aluminum produced is recycled – twice the recycling ratio of CCPs.
The four CCPs are almost always used in combination; the exception being wallboard (gypsum), the production of which consists solely of FGD material. The largest single application of CCPs is for making cement, concrete and grout (see table). Wallboard represents the second largest use, followed closely by road construction and materials used for blasting grit and roofing granules.
Ash marketers such as ISG have developed new uses as well. Fly ash is now being marketed as a mineral filler for the manufacture of roofing shingles and carpet backing, and as a high quality soil modifier for peanut growers. The newest fly ash based technologies now being commercialized include cellular concrete, rapid setting concrete patch material, and acid resistant concrete.
Increasing the Market
Addressing the American Coal Ash Association in San Antonio, Tx. in January, Deju said a goal should be established by which the use of CCPs would match the recycling rate of aluminum by 2010. Achieving a CCP recycle rate comparable to aluminum would have dramatic benefits: avoided disposal costs combined with improved public and regulatory image. “Expanding CCP use may also help persuade regulators that harsher disposal controls aren’t necessary,” said Deju. Reaching this goal will require finding uses for more than 35 million tons of CCPs, an increase of 3.5 million tons per year over the next decade.
Deju believes that expansion can be achieved by investment in marketing networks that ensure reliable availability of CCPs for those who need them. He also believes parties interested in the issue should help develop technologies that ensure CCPs are suitable for their intended traditional applications and that any negative effects of pollution control technologies, such as NOx reduction, are properly addressed.
Deju also thinks utilities and coal producers should help develop new technologies that use large volumes of CCPs in new applications. “They can invest in manufacturing facilities that create CCP-based products – such as wallboard, blocks, and various bagged products.”
Although recycling is considered a fundamental tenet of environmental stewardship, the industry’s ability to recycle CCPs could be harmed by more restrictive environmental controls. In a regulatory determination announced in April 2000, EPA determined reuse of CCPs does not warrant regulatory oversight, but left the door open to greater regulation of CCP disposal operations. But a few weeks later, EPA nearly issued a rule that would have regarded the disposal of CCPs as hazardous wastes under RCRA. At the last minute, the agency reaffirmed its position that CCPs are non-hazardous. Still, such indecisiveness creates fears that EPA could be moving to increase the physical requirements for landfills, ponds and mine fills.
Environmental regulations also have the potential to lower the quality of the products the power industry is trying to recycle. John Ward, vice president for combustion coal product marketer ISG Resources, notes several challenges. For instance, as utilities have implemented low NOx burners, many power plants have seen the residual carbon content in their ash increase. Residual carbon in ash interferes with air entrainment in concrete, making the fly ash less desirable in one of its primary markets. Even more challenging is the growing number of SCR units being installed. These units can contaminate fly ash with ammonia, which poses problems for concrete workers and creates a potential for leaching from fly ash disposal operations.
More than two-thirds of the CCPs Entergy produces are sold. Shown is the company’s four-unit White Bluff plant in Arkansas. Photo courtesy of Entergy.
Numerous technologies are under development to address the residual carbon and ammonia issues. ISG, for instance, has begun installing two different systems on power plants it serves. One introduces a solid reagent to fly ash that removes ammonia completely. The other introduces a liquid reagent to fly ash that binds with residual carbon so that its effects on concrete are negated.
Local Regulations Can Impact Sales
Wholesale generator Reliant Energy Mid-Atlantic owns and operates 17 coal-fired units at seven sites in Pennsylvania, burning bituminous coal with heating values ranging from 12,000 to 13,000 Btu/lb. The ash runs from 12 to 15 percent and sulfur from 1.38 to 1.85 lbs/MMBtu.
Dan Yost is the company’s ash marketing specialist. He notes that Pennsylvania’s regulations affecting the use of CCPs are quite possibly the most restrictive in the nation. “Some ash uses don’t require individual permitting, but many do,” says Yost. “Individual permits are required and each application is judged on a separate basis. The regulatory changes make it more difficult to use these products beneficially.”
Nonetheless, the company’s sale of ash product reached 35 percent in 1998 – well above the national average of 28 percent for that year. Helping Yost’s efforts was the need for materials to prevent ground subsidence in a Pennsylvania mine. Mine fill is a significant and highly valuable use for all four coal combustion products.
Reliant Mid-Atlantic is presently selling 28 percent of the ash products produced – 1.3 million tons of fly ash, 175,000 tons of bottom ash, 40,000 tons of scrubber sludge, and 94,000 tons of gypsum to markets typically within a 30 mile distance of its plants. Because the fly ash is very dusty, water is added before it is hauled. Ash is mixed with 10 to 15 percent water for transport to end-use locations. In the winter, bottom ash must be kept dry to prevent freezing.
The company has been a proactive CCP marketer. It is working with a new technology to produce a lightweight aggregate formed from mixing scrubber sludge with fly ash. The company has also added capability to load pneumatic tankers and special chutes to load cement trucks as well as a system to remove the pyrites from the bottom ash.
“Most countries consider these products a national asset providing extremely cost-effective materials for a variety of uses,” says Yost. “We need to view them that way too. In many cases, our combustion by-products have provided customers with construction material at one-third the cost,” says Yost. “So far as our electricity customers are concerned, anything we can do to reduce disposal cost adds to the bottom line. Any income from the sale of the material and the avoidance of disposal cost improves the total cost to produce energy. The most expensive part of running a coal- fired plant is the fuel, so the by-product stream could be used against that cost.”
Already at the Two-thirds Mark
Entergy operates 3,887 MW of coalfired capacity: four units in Arkansas and one unit near Lake Charles, Louisiana. All coal is Powder River Basin sub-bituminous, with heat values ranging from 8,500 to 8,850 Btu/lb. Ash ranges from 4 to 5.5 percent with sulfur varying from 0.2 to 0.4 percent. The company sells 76,000 tons of fly ash per year and approximately 17,000 tons of bottom ash.
Entergy is already operating at the enviable two-thirds recycling rate, marketing close to 65 percent of the total ash volume produced at its coal plants in Arkansas and Louisiana to markets as far away as 300 miles from the plant sites. Transportation is primarily by truck, with some by rail or barge. The ash for which there is a market is sold to ISG. The remaining ash is land-filled on site.
Rather than being placed in landfills, ash can be marketed and used in safe and productive ways, often taking the place of other virgin materials so they can be left for future use, says Jim Mutch, vice president, environmental support.
Neither weather nor any other natural factor represents significant problems in the handling and storage of waste products according to Entergy. “We think the overall way we handle these by-products keeps us competitive because it helps us better manage the cost of our operations,” says Mutch. “Our marketers are continually looking for new applications for the product, which in turn enhances our competitive edge.”
AEP annually produces more than five million tons of fly ash, 1.2 million tons of bottom ash, 250,000 tons of boiler slag and 1.2 million tons of scrubber material. Fly ash is typically sold within a 150-mile radius of the plant. Sale within a 25-mile radius from the plant is typical for bottom ash, boiler slag and scrubber material. The majority of the company’s CCPs are delivered by truck, and products not used for beneficial purposes are deposited in regulated on-site disposal facilities.
AEP uses various methods to enhance marketability of its coal combustion products. The company is implementing a technology developed by ISG that mitigates the effect of unburned carbon (LOI) in fly ash intended for use in concrete. The process uses a liquid reagent to bind with unburned carbon particles and hinder their impact on the concrete mix. Carbon isn’t removed, but its effects on air entrainment are minimized and concrete producers are better able to control their concrete mixes. The technology also renders some ash products usable for the first time without having any impact on the quality of finished concrete.
CCP handling methods vary from plant to plant depending on individual site constraints, state agency regulations, and economics. As a general rule, methods incorporating the latest technologies to reduce wear on handling equipment and promote free flow of CCP materials have also been found to be cost effective.
Most handling problems are associated with dust and moisture. Regulating moisture content of the ash is always a delicate balancing act since water added to control dusting can also increase the propensity of the ash to stick to equipment surfaces. Through testing, the optimum moisture content can be determined for controlling dust and reducing the buildup of material in truck beds and other equipment. When CCPs are transported on public roads, particular attention must be paid to dust control and spill prevention.
AEP regularly reviews disposal capacity for each facility to assure that it is enough to meet projected needs. Additional disposal space is developed as required.
The remote location of Public Service of New Mexico’s San Juan plant, in the San Juan Basin of northeastern New Mexico, makes it difficult to market the substantial supply of CCPs the plant produces. “We are currently marketing fly ash,” says Al Putzig, manager of technical projects/fuels. “And we’re trying to market the other byproducts also. Our biggest obstacle to marketing is the long truck haul to rail access. Once loaded on trains, the markets are several hundred miles distant.” A very small number of customers are close enough to take delivery by truck.
With a combined generating capacity of almost 1,800 MW, San Juan’s four coal-fired units annually produce 420,000 tons of bottom ash, 1.7 million tons of fly ash, and 280,000 tons of FGD material. The mine-mouth facility takes its coal from two nearby mines. The sub-bituminous coal has a heating value of 9,300 Btu/lb, an ash content of 25 percent and a sulfur content of 0.83 percent sulfur. Coal is delivered to the plant in 200-ton capacity off-road haulers.
The coal supplier is paid to haul the unsold byproducts back to the San Juan Mine for mine backfilling. The San Juan Mine is adjacent to the plant and the ash is placed in the open dragline pits as the mine progresses. “We are currently assessing the merit of fly ash classification,” says Putzig. “Classification would allow our fly ash to replace cement in concrete production and significantly expand the market and value of our fly ash. Currently the fly ash is used in road bed or soil stabilization and other low grade product uses.”
San Juan’s principal problem is the shear volume of ash to be handled. The station was designed for a lower ash content but a favorable coal price has resulted in higher ash content. Since 1995, the plant has shifted more of coal deliveries from the La Plata Mine and taken less from the San Juan Mine. The La Plata Mine has a lower strip ratio but higher ash content.
“The sale of our byproducts provides a revenue stream to help offset the cost of coal,” says Putzig. “Sales of fly ash in recent years have only amounted to less than two percent of our total production. Our marketing goal is to increase sales by ten fold if we can justify the installation of the classifier. If we decide against a classifier, our marketing goals are more modest but still target two or three times our current sales.”