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The beneficial uses of coal ash

World Coal,


Savannah Cooper, Worldwide Recycling Equipment Sales, explains how coal ash does not necessarily have to be disposed of as hazardous industrial waste; and can in fact be recycled and put to good use.

 

Beneficial use is the utilisation of a material that provides benefits to the environment, human health or the economy. In most cases, the beneficial use of a material replaces the use of an alternative material or conserves natural resources. The extraction of raw materials from the earth consumes energy, generates greenhouse gases and limits the availability of virgin natural resources, in addition to having a detrimental effect on water resources. The recycling and reuse of waste materials helps to decrease these unfortunate impacts.

Coal ash, also known as coal combustion waste (CCW) and coal combustion residue (CCR), is mostly made up of basic minerals, such as iron, silica, aluminum and calcium. With approximately 130 million tpa produced, coal ash makes up the second largest stream of industrial waste in the US.

Coal ash is disposed of in approximately 2000 facilities across the country – in over 600 wet ash ponds and over 300 dry landfills at power plants, in at least 100 offsite dry landfills, 750 inactive dumps and hundreds of abandoned and inactive mines.

An estimated 36% of the coal ash waste generated by utilities in 2007 was disposed of in dry landfills, which are often located onsite at the power plant where the coal was burned. However, the dry storage of coal ash can be hazardous. The dry ash can be dispersed by wind and blown into adjacent plots of land as “fugitive dust,” a carcinogen-heavy dust that can cause major health issues when inhaled. Dry landfills are also hazardous to groundwater, especially when they are not properly lined.

Wet coal ash storage consists of ash mixed with water and stored in large pounds, which are known as “surface impoundments,” “ponds” or “lagoons.” Wet disposal is the most common ash disposal method. Wet ash storage consists of constructing a large pond and filling it with coal ash slurry, allowing the water to drain and evaporate from the ash over time.

In 2007, wet storage accounted for 21% of coal ash disposal in the U.S. Unfortunately, the toxic substances contained in coal ash can migrate into water sources near the ponds, dissolving and seeping into the ground as “leachate.” This unseen stream of heavy metals and contaminants often makes its way into groundwater, exposing fish and wildlife to toxic substances such as arsenic.

Fortunately, there is another way to dispose of coal ash. Roughly 40% of the coal ash produced each year is recycled and beneficially reused. Coal ash is commonly reused as structural fill or fill for abandoned mines, as the top layer on unpaved roads, as an agricultural soil additive and as an ingredient in concrete, wallboard and school running tracks. Every year, approximately 11.5 million t of coal ash are used in structural fills, such as highway embankments or the foundations of buildings.

Coal ash can be reused in two forms: encapsulated or unencapsulated. Unencapsulated ash is in a loose or unbound particulate or sludge form. Encapsulated ash is bound into products such as wallboard, concrete, roofing materials and bricks. There are numerous environmental benefits to the use of encapsulated coal ash, including reduced greenhouse gas emissions, the conservation of energy, decreased land disposal and a limited need to mine and process virgin materials.

Encapsulated coal ash is the key to safe use. The US Environmental Protection Agency (EPA) uses a technology at hazardous waste landfills that ensures that, if toxic waste comes into contact with moisture, the toxic elements are bound at the molecular level into insoluble compounds that will not allow the toxic elements to leach out and contaminate nearby water sources. This same technology is used to encapsulate coal ash in concrete. When encapsulated, coal ash can be used to make bowling balls, concrete and bricks; the coal ash in these products is fully encapsulated, preventing the contaminants within the ash from leaking out.

In January of this year, the US EPA agreed to finalise its first-ever coal ash regulations by December, 2014. A month later, in February 2014, the EPA determined that coal ash and other CCRs are safe for use in concrete as a substitute for Portland cement. These new regulations have prompted plant owners to seek additional ways to dispose of or recycle coal ash.

Worldwide Recycling Equipment Sales, LLC, supplies a full range of equipment to dry, sort and move coal ash. The company’s dryer systems are designed specifically to dry coal ash, making the material easier to transport and handle. Dryers can be designed and built to best suit customer’s specific project needs.

The Vulcan® Fly Ash Drying System consists of a 48 ft long x 9 ft dia. rotary drum and is powered by four 50 hp, 208/230/460 V, 3-phase electric motors. This unit comes equipped with a 72,000 CFM pulse jet baghouse and includes two compressed air tanks for pulse jet cleaning. During the process, fly ash is fed into the rotary dryer. After passing through the dryer, the dried material is discharged to a transfer conveyor for further sorting and separation. The vapour from the process is pulled through a cyclone that is specifically designed to deal with the fine dust, as well as a high-temperature baghouse, which removes all fine particulates from the vapour stream.

The reuse of coal ash protects air and water, as well as lowers greenhouse gas emissions by reducing carbon inputs into cement. By using drying, calcining and thermal desorption equipment, it is possible to put an end to some of the hazards presented by coal ash.

Written by Savannah Cooper. Edited by Sam Dodson

Read the article online at: https://www.worldcoal.com/power/28082014/putting-coal-ash-to-good-use-1260/


 

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