On Friday, South African state-owned power utility Eskom, announced that its Lethabo coal-fired power plant has returned to full operation following an extended planned outage where major work was done on the turbine, boiler pressure parts, ash handling and condenser.

[quote]The station, located between Vereeniging in Gauteng and Sasolburg in the Free State, is currently running all six of its generating units, producing an excess of 3,400MW of power, the utility said in a company statement.

Coal-fired resources

Nicknamed the ZLED-station (Zero-Liquid-Effluent-Discharge), the plant utilises low grade and low quality coal as fuel for its power generation process, making it a unique plant compared to the other existing coal-fired plants in the country.

Eskom explained: “The coal burnt has an average calorific value of about 16 MJ/kg. Very few power stations can burn this quality of coal, with most boilers requiring coal fuel of values in excess of 20 MJ/kg.

“At full load, the power station consumes about 50,000 tonnes of fuel per day, enough to fill 1,500 trucks carrying 33 tonnes each.

“The ash content of the coal ranges between 35% and 42%, which means that the power station produces approximately 20,000 tonnes of ash per day. After mining operations, the open pit is filled with spoils and over burden, which was removed during mining.”

Environmental consideration

The ash debris can accumulate to as much as 50 metres above ground level, which are then covered with 350mm of fertile soil and revegetated.

“Rehabilitation involves the covering of the ash dumps with fertile soil and the planting of grass and trees. Although other Eskom stations burn coal of a better quality with lower ash content, they still produce ash (fly ash), in smaller volumes though,” the utility added.

The utility noted in the statement: “Eskom is committed to integrated environmental management to conserve the country’s heritage and resources. It is with this commitment in mind that all power stations have a programme in place for the rehabilitation and revegetation of the ash disposal sites.

“This means that the whole station is a closed system and no water from our processes is allowed to leave the power station premises. An extensive water recycling and cleaning desalination is in place."