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Waste gases from smelters are increasingly being used for power production in South Africa, according to Clarke Energy, the service provider for Tronox’s Namakwa Sands smelter
South Africa has numerous metal ore smelters across the country that process metals from minerals. These smelters, particularly in the steel and ferro alloys industries often produce an off- gas during the process of refining the ore. Ordinarily, the waste gas would be burned in a flare to yield carbon dioxide and steam and the energy wasted to the atmosphere. However, power plants are now extracting electrical energy before releasing carbon dioxide and steam to the atmosphere.
High power needs and rising energy costs present a major challenge to the industry. Some furnace gases created as a by-product during processes serve as an attractive fuel for power generation. In addition to the economic benefit, using these gases reduce emissions and dependence on the grid, said Clarke Energy in a recent press release.
Metallurgical production processes produce large volumes of special gases. The three different process stages in steel production provide a number of different gas types: coke gas, blast furnace gas and converter gas.
Coke gas is a by-product of industrial coke production from coal created by high-temperature pyrolytic distillation of coking coal. Blast furnace gas is a by-product of blast furnace operations where iron ore is reduced with coke into metallic iron. Converter gas is created from pig iron during the steel production process. Ferro-alloys and calcium carbide furnaces also produce combustible gases.
The combustion behaviour of furnace gases places considerable demands on engine design. This technology is however developed and being successfully deployed in South Africa at a number of sites. Tronox’s Namakwa Sands smelter in the Western Cape uses waste gases generated from its two open arc titanium melting furnaces for power production. The gas engine power plant operates on waste gas produced and incorporates eight GE J620 gas engines and is the second largest furnace gas-fuelled power plant in South Africa. The engines produce electricity and heat through cogeneration giving high process efficiency, said Clarke Energy, the service provider for the plant.