Power Engineering, March 2000, pgs 46-50
Innovation Takes CCBs from Liabilities to Assets
 Electric Utilities in the United States Annually Generate more than 100 Million Tons of High-volume coal combustion by-products (CCB) including fly ash, bottom ash, boiler slag and flue-gas desulfurization (FGD) sludge. Historically, about 25 percent of the high-volume by-products have been used as construction material or for other applications, leaving 75 percent for deposit in landfills, according to EPRI statistics. There are many markets for CCBs, depending on the chemical composition of the ash, and research and development efforts are discovering more. Some utilities have found creative ways to dispose of most or all of their ash, and as competition increases the need to trim expenses more coal plants will undoubtedly seek ways to turn their ash into a marketable product, rather than expensive waste for disposal.
Ash Strategies
Baltimore Gas and Electric Co. has been working to find "creative and environmentally sound methods" of managing fly ash for more than a decade. "We have been able to recycle 100 percent of the ash we produce," said Ron Lowman, BGE Fossil Energy vice president. "We manage a full portfolio of ways to market our ash for beneficial uses. Some of our efforts include using ash to reclaim sand and gravel mines, constructing highway embankments and business parks, and backfilling utility trenches.
 The utility recently completed a new coal ash processing facility at its Brandon Shores/H.A. Wagner complex in Maryland. The facility, designed and operated by Separation Technologies Inc., processes coal ash for use in concrete. (See Figure
to the Right)
Master Builders Inc. is working to sell the ash to ready-mixed concrete producers along the Washington-Baltimore-Philadelphia corridor.
"This partnership with STI allows us an opportunity to refine and enhance our admixture technology," said Mike Shydlowski, Master Builders president and CEO. "We continue to work on innovative chemistries to exploit the benefits of coal ash so we can help provide an energy-efficient solution for producing high performance concrete."
The ash separation facility segregates high-carbon and low-carbon ash. The low-carbon ash can be used in concrete mix, and the higher-carbon ash can be re-burned or used in other beneficial projects.
"There are numerous environmental and financial advantages to installing an ash separation technology. STI is converting a by-product into a high-quality construction material, while at the same time reducing the utility's operating costs," said Joseph Teves, STI chairman. The ash facility at Brandon Shores is designed to process 400,000 tons of ash annually. The technology is in use at several of the nation's largest power plants.
Commonwealth Edison has been recycling about 87 percent of its CCBs to keep them out of landfills. The utility is currently providing ash from its coal-fired generating plants to be used as fill material for the Lewis University Airport near Joliet, Ill. The five-to-seven-year project will bring the utility's ash recycling total to approximately 90 percent.
"ComEd realized long ago that recycling coal ash could help the environment and make sound business sense," said Mary O'Toole, ComEd environmental services manager. "We're keeping millions of tons of waste out of landfills, and that helps us earn savings on disposal costs." The ash can save money for its users as well. The Lewis University Airport expects to save almost $10 million dollars by using ash as fill material.
"What we've done at ComEd is enhance our facilities and practices to improve the marketability of our coal ash. By looking at the life of the product as a whole, we use it much more efficiently and create much less waste," said Marion Madeja, ComEd's fossil fuels life cycle manager.
American Electric Power has been saving landfill space and protecting shorelines by recycling coal ash from its Mountaineer Plant into honeycomb-shaped Seabee blocks for erosion control projects. The plant produces about 280,000 tons of coal ash annually, some of which is converted into blocks by Environmental Solutions Inc. of Richmond, Va. Environmental Solutions developed the blocks, which have been used in numerous projects for customers including the Army Corp. of Engineers and the U.S. Navy.
The Seabee's honeycomb shape makes it preferable to rip-rap, a traditional erosion material made of rocks. Unlike rock, which is easily washed away by waves, the Seabees' smooth, interlocking design holds them in place. The honeycomb design disperses returning waves, and instead of washing away, sand is deposited in the Seabees' holes, building up a dune in front of the Seabees to further bond the seal.
Seabees use about 27 percent coal ash and are produced in either four- or eight-inch thick blocks. The blocks weigh from 25 to 70 pounds and cost $2 to $3 each.
Ash Improvements
Pittsburgh Mineral and Environmental Technology Inc. (PMET) and Hosokawa Micron Power Systems are working together to commercialize a new process for producing low-carbon fly ash with Hosokawa's particle sizing and classification equipment. The PMET Process reduces the carbon content of the ash and improves ash pozzolanity.
As-combusted ash is introduced into a jet mill where the carbon is ground by particle-to-particle impact. (See Figure 2) In this process, ash is loaded at the top of the mill and falls down into the grinding chamber where pressurized air draws the particles into the center of the chamber to impact at high velocities, resulting in autogenous grinding. The lighter ground particles are carried upward toward a rotating classifier wheel and out of the mill, but denser particles fall back to the bottom for further grinding or discharge.
Carbon content of the ash product is achieved by controlling air velocity, classifier rotational speed and grinding time. The process treats all ashes regardless of initial carbon content or ash characteristics and removes both bound and unbound carbon.
Demonstrations have been performed on a large number of commercially generated utility coal ashes from around the world at Hosokawa's New Jersey facility. The demonstrations have shown that the process can consistently produce product ash with carbon contents of 3 to 4 percent while improving ash characteristics.
PP&L Inc. is helping build a golf course near York Haven by selling land at its Brunner Island plant and by providing a fly-ash product called Stabil-Fill to be used in constructing the golf course base. Stabil-Fill is produced by mixing hydrated lime with fly ash to create a material that is chemically stable and environmentally safe. The product develops higher strength than soil-based fill, according to Kathy Wildauer, PP&L Inc.'s community development director. It has been used as fill material in construction projects such as recreational fields and parking areas. The product was developed by PP&L Inc. with assistance from the state Department of Environmental Protection.
"Building a golf course would be an innovative use of Stabil-Fill that would benefit the community by providing a new recreational facility, creating jobs and generating tax revenues," Wildauer said. About 1.8 million tons of the ash product will be used in the project - the equivalent of the power plant's entire production of fly ash for nine years. Development of the golf course is ongoing over the nine-year period. PP&L is selling the land to Combustion Projects Management Inc., which will design, construct and operate the golf course.
| A pilot plant at Consol Energy's Research and
Development campus in Library, Pa. is producing aggregates from
mixtures of FGD sludge and pulverized coal fly ash using disk
pelletization and moderate temperature curing. Consol built the
pilot plant with co-funding by the U.S. DOE, Duquesne Light Co. and
SynAggs Inc. In its first six-week run last summer, the continuous
500 lb/hr plant produced nearly 150 tons of aggregates that meet
commercial specifications for use in construction. Testing
continues. |
| FGD BY-PRODUCT USES |
| Gypsum wallboard |
| Flowable fill material |
| Waste stabilization |
| Roadway/runway construction |
| Concrete admixture |
| Concrete block |
| Cement additive |
| Mine reclamation |
| Agricultural applications |
|
About two billion tons of aggregates - mostly natural - are used annually nationwide in everything from concrete blocks to highway construction. Manufactured aggregates eventually may play an important role in this market," said Frank Burke, Consol Research and Development vice president.
Consol began testing the process in 1997 in a laboratory research program funded by the company, SynAggs, the Ohio Coal Development Office, and the Illinois Clean Coal Institute. Aggregates from that program were used to construct a 72-ft. road test strip in Ohio and to manufacture concrete test blocks. Aggregates from the new pilot plant are being used to pave a larger road test strip in Pennsylvania and to make light- and medium-weight concrete test blocks.
"High-Btu coal is efficient and inexpensive for our customers, but some of it also has a high sulfur content. We are looking for a way for electric utility companies to turn an unwanted material - in this case scrubber sludge - into a useful and value-added product," Burke said. He estimates that over time the amount of wet FGD sludge generated by electric utilities could reach more than 40 million tons annually." Disposing of this material in a landfill or pond can cost a utility and its customers as much as $6 per ton of coal burned," Burke said. "Recycling FGD sludge into a saleable product would make the economics of scrubbing more attractive."
 Ash is loaded into the mill (A), and falls to the grind chamber (B). Pressurized air enters from nozzles positioned circumferentially around the grind chamber, drawing particles into the center of the chamber (C) where they impact at high velocities, resulting in autogenous grinding of the particles. The ground particles are carried upward toward a rotating classifier wheel (D) containing passages through which less dense particles of a selected size are drawn prior to exiting the mill. The denser particles fall back to the bottom for further grinding or discharge. Figure courtesy Hosokawa Micron Power Systems.
Power Engineering March, 2000
Author(s) : Ann Chambers
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