South Africa has been pioneering the use of fly ash in cement production for some time, opening the door for the country to reduce its carbon emissions while retaining a strong and innovative cement sector. Fly ash comprises the fine particles of coal ash that rise with flue gases from burning coal, and is usually removed by electrostatic precipitators or bag filters.
By incorporating fly ash – as well as ground-granulated blast furnace slag (GGBFS) – in its cements, AfriSam reduced its carbon emissions per ton of cement by over 30% between 2000 and 2018.
Hannes Meyer, cementitious executive at AfriSam, says: “The local sector has made great strides in reducing its carbon footprint. The use of fly ash creates more environmental benefits, including a reduction in the amount of coal ash that power stations must dump on the surface, of which almost two thirds of the ash produced worldwide disturbingly still ends up in ash ponds or landfill.
“Fly ash extends the volume of cement while adding valuable cementitious qualities to the final product,” he says. “This on its own reduces the amount of energy-intensive clinker that must be produced – thereby economising on the energy our plants must consume.”
More than that, he says, the use of fly ash can also replace the traditional non-renewable products in the manufacture of clinker. These include limestone and shale, which is mined at a considerable cost. AfriSam has been researching this area for some time, with exciting results.
“The use of fly ash in clinker production means less carbon dioxide is produced,” he says. “Usually, calcium carbonate in the limestone must first be converted to calcium oxide, and this generates carbon dioxide. The calcium in ash, however, has already been converted in calcium oxide and silicate form.”
He notes that the carbon tax needs to play a supportive role in gearing up the economy for a low-carbon future. “The danger of the tax rising to unsustainable levels in future, could have a detrimental impact on the cement sector’s global competitiveness and its capacity to retain or create jobs.”
He urges that revenues from the government’s recent carbon tax should be carefully channelled into incentivising this kind of innovation in the market; and highlights the strategic importance of this kind of research and development for the future of the South African economy.
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