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Wed May 25 18:57:19 SAST 2016

Eskom says it’s committed to conserving country’s heritage and resources

TMG Digital | 20 February, 2016 11:53
Uses of fly ash include brickmaking‚ dam building and as a cement extender during the manufacturing of cement. File photo
Image by: Gallo Images/iStock

Eskom says it is committed to integrated environmental management to conserve the country’s heritage and resources.

For this reason‚ all its power stations have a programme in place for the rehabilitation and re-vegetation of its ash disposal sites.

Eskom’s coal-fired power stations consume about 120-million tons of coal per annum‚ producing 25-million tons of ash‚ to supply the bulk of South Africa’s electricity.

A modern coal fired power station with a total output of 3‚ 600MW‚ it says‚ will consume about 50‚000 tons of coal every day. Depending on the coal quality‚ the heat and ash content‚ stations can produce around 17‚000 tons of ash per day.

Almost 90% of the ash produced in the generation process is called fly ash or pulverised fuel ash.

The reason for this is that the coal is pulverised into a very fine dust (rather like cake flour) before being fed into the boilers to ensure efficient combustion.

Larger particles of ash‚ called coarse ash‚ which make up the rest of the ash produced at the power station‚ drop down from the furnace and collect at the bottom in the ash hopper of the boiler.

The fly ash (also particulate matter) is removed from the flue gas stream (exhaust gases from the boiler) by means of electrostatic precipitators or bag filter systems.

After being removed from the collecting hoppers‚ the fly ash and coarse ash is stacked on huge dumps or ash dams (slurry dams)‚ the latter at older power stations. Flue Gas Conditioning (FGC) will be installed at Eskom’s new build coal-fired power station‚ Kusile‚ later also at Medupi‚ Eskom says.

It says rehabilitation involves the covering of the ash dumps with fertile soil and the planting of grass and trees.

“The areas are rehabilitated to the extent that it becomes a habitat for a variety of plant‚ animal and bird species. At some power stations‚ the ash is back-stacked onto the area from where the coal was mined (open cast mining). It is important to note that this area is filled up with spoils‚ overburden etc. before re-vegetation starts.

“Approximately 1.2-million tons of ash per year is sold to‚ amongst others‚ the cement industry where the ash is used as a cement extender. Fly ash is successfully used to enhance the quality and economy of concrete.

“Uses of fly ash include brickmaking‚ dam building and as a cement extender during the manufacturing of cement. Approximately 250 000 tons of ash from Lethabo Power Station‚ for instance‚ was exported to Lesotho for the Katse Dam project.” The electricity parastatal explains.


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