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Beneficial use of Fly Ash: An environmental win for water, CO2 and energy savings

September 14, 2016   By Susan Jackson in Power Delivery

Reclaiming coal ash at Santee Cooper’s now retired Grainger Generating Station site.

Coal combustion products (CCP) are the minerals that remain once coal is burned to generate electricity.

Fly ash, one of the largest groups of CCPs, is a fine powdery material that years ago would “fly” out of a power plant’s stacks. Today’s power plants collect more than 99.99 percent of the fly ash. Fly ash can be used as mineral filler in paints and shingles. It can also be used to make stuccos and mortars and even bowling balls. The largest application is for the production of concrete.

Santee Cooper has a long history of beneficial use of CCPs. In 2005, fly ash from Santee Cooper’s Winyah Generating Station was to make concrete for building Charleston’s Ravenel Bridge in Charleston.

The beneficial use of ash is a great way to reduce landfill disposals and to remove ash from ash ponds. Santee Cooper has recycled more than 325,000 tons of fly ash from Cross Generating Station in 2015 and 2016 to date, that otherwise would have gone into a landfill.

At Winyah Generating Station, over 125,000 tons of fly ash were recycled in that same time period. At the now demolished Grainger Generating Station, more than 630,000 tons of ash have been beneficially used from old ash ponds, which will be converted to wetlands.

Un-encapsulated ash is removed from a pond and then used in the concrete industry where it is encapsulated, so any metals are chemically bound. Fly ash chemically reacts with cement during the hydration process and then becomes an integral part of the new crystalline structure. So, the encapsulated use of fly ash is a very good alternative to sending ash to the landfills or ponds.

Fly ash can also function as a partial replacement for supplement for Portland cement because fly ash and Portland cement share similar chemical properties, mostly high amounts of silica and alumina.

When fly ash is used to replace cement in concrete, it preserves natural resources by replacing materials that would otherwise be mined to manufacture cement. There are energy savings by avoiding the need to extract and process other raw materials what would have been used instead of ash, another big environmental win.

Second, the use of fly ash instead of Portland cement creates a stronger and more durable concrete. Longer life means less material and energy will be used to repair or replace concrete structures.

Third, for each ton of cement produced, more than a ton of carbon dioxide (C02) is emitted. So when a ton of cement production is replaced with a ton of fly ash, those greenhouse gases are eliminated. Beneficial use of fly ash in concrete reduces U.S. greenhouse gas emissions by about 13 million tons each year.

Fourth, when fly ash is used to replace cement in the production of concrete less water is used in the process. Estimates indicate that concrete made with fly ash requires between 3 to 10 percent less water to produce than concrete made with Portland cement.

Lastly, when fly ash is used in concrete, the potential for leaching of heavy metals constituent to groundwater is greatly reduced. Even if a cement structure is demolished, the metals in coal ash will not leach. In 2014, the EPA released a report supporting the beneficial use of fly ash in concrete.

Overall environmental savings in landfill space, raw materials, reduced CO2 emissions and reduced water usage are significant. All of this adds up to a sustainable and solid environmental practice.