1996-1997 indexDistributed December 3, 1996
Studies explore commercial uses for power plant ash
Two studies underway at Brown University are trying to find commercial uses for the 50 million tons of high-carbon fly ash piling up annually at the nation's power plants.
PROVIDENCE, R.I. -- High-carbon coal ash is velvety soft, but it's a hard nut for utilities to swallow.
Two new studies at Brown are designed to describe the ash's properties and consider commercial options for the almost 50 million tons of the dark powdery material that ends up trapped by power-plant filters and precipitators nationwide each year.
One study is funded primarily by a three-year, $400,000 grant from the Department of Energy. Brown engineers are working with colleagues from New England Power (NEP) and Princeton University to test the highest of the high-carbon ash from NEP plants. The researchers want to produce a detailed understanding of its abilities to absorb other substances. They are exploring novel uses for the ash as an absorbent material to snare pollutants at manufacturing sites or to trap substances in contaminated soil or water.
Activated carbon in powdered or granular form is used in a range of filters and other materials to trap pollutants. Because large amounts of high-carbon ash are produced by utilities each year, the researchers think the material could one day be sold commercially at a fraction of the cost of activated carbon now in use.
"A large commercial market exists for activated carbon," said Robert Hurt, one of the study leaders and an engineering professor at Brown. "The key is to generate a reliable stream of material with a high carbon content to make it a substitute for activated carbon and to identify special niche applications where fly ash can successfully compete with the more expensive commercial activated carbons."
Two NEP plants in Massachusetts produce a total of 350,000 tons of high-carbon ash per year. The utility is one of the few in New England that produces large amounts of the ash. However, NEP is recognized nationally for developing uses for the material.
Peter Calvert, NEP's ash and product development specialist, says NEP is committed to finding markets for its high-carbon ash within the next three years. Because NEP plants sit in highly populated areas, the utility cannot store large amounts of the ash on site. "We expect to come out of this research with a body of knowledge needed to find commercial outlets for all of our different ash streams," Calvert said.
Before the Clean Air Act of 1990 forced power plants to install what are called "low-NOx" burners to cut smokestack emissions of nitric oxide, a smog precursor, coal-burning utilities provided a steady flow of their ash as a substitute for Portland cement and silica in concrete production. Adding fly ash to concrete enhances its properties. But the combustion-related changes made by utilities raised the carbon content of coal ash greatly at many power plants. That made the ash unsuitable for any use outside landfill disposal, which approaches $20 a ton in New England.
In the other Brown study, Hurt and fellow Brown engineer Eric Suuberg are testing samples of high-carbon ash from utilities nationwide. They are trying to determine why the high-carbon ash makes a lousy concrete additive, how power plants might change the combustion process to make the ash suitable for concrete, or how ash might be treated to prepare it for concrete production. The study is funded by a three-year, $300,000 grant from the Electric Power Research Institute (EPRI), a private organization.
Brown researchers, particularly Yu-Ming Gao, a post-doctoral researcher, are credited with developing new laboratory methods to test the suitability of ash in concrete. Many forms of carbon exist in the ash. Each has an impact on the ash's suitability. "If you can define a material's characteristics, you can identify promising applications for it," Suuberg said. "An eventual goal is to understand the coupling of the combustion process with the nature of the carbon created in the ash. This could tell us how to control the variability of the carbon. That's a key to opening up markets for its use."
Making coal combustion more complete to avoid the carbon-in-ash problem is the topic of separate research led by Hurt. "Burning out" the carbon is a question of economics, he said. There are only so many changes a utility can afford to make to existing boilers to raise carbon "burn out" efficiency. At some point, a small amount of carbon will have to be thrown away with the ash.######