Emission of carbon dioxide (CO2) during coal-based power generation is generally acknowledged as one of the major contributions to global warming and its management has become central to coal’s future, says technology and project management company Mitsibushi Hitachi Power consultant and technology specialist Vinesh Raijcoomar.
Although most energy scenarios predict an increase in the share of renewables, in absolute numbers, fossil fuels will continue to meet most energy needs for the foreseeable future.
Raijcoomar notes that, for South Africa, the reality is that coal is abundant, a local resource, reliable and less expensive than most other energy options and will therefore remain an important part of the energy future. Based on economics and the need for development, most developing countries will use fossil fuels as their main source of energy, despite the calls to decrease the dependence.
With the use of coal projected to continue to grow, he states that a low carbon pathway for coal is essential if climate and development objectives are to be met.
CO2 capture and utilisation (CCU) is considered a potential pathway, among other emissions mitigation options, to achieving greenhouse-gas emissions reduction. The use of “captured” CO2 as a feedstock in the chemicals industry for the synthesis of chemical products and fuel, offers an option for climate mitigation while producing a product that has economic value.
Further, he states that the focus is on addressing emissions instead of trying to get rid of a fuel which has economic advantages. Technical analysis shows that the dual strategy of improving generation efficiency coupled with CCU is the best option for advanced coal power generation systems.
A hybrid concept for the recycling of CO2 focused on the fuel pathway is presented as a potential opportunity for South Africa. “Hybrid energy concepts use a range of power generation technologies integrated with CCU technologies that contribute to climate change mitigation,” he adds.
Hybrid power approaches are becoming increasingly important for power generation and energy storage to respond to energy fluctuations of renewables sources such as solar and wind.
Coal Quality and Role of Beneficiation
Coal is used in industry mainly in combustion, gasification, carbonisation and liquefaction processes. African research and development organisation the Council for Scientific and Industrial Research coal processing engineer Johan de Korte notes that each of these processes requires coal of a specific quality. Raw coal as mined can usually not be used directly.
The beneficiation or processing of raw coal involves crushing of the coal, screening the coal into specific size ranges and subjecting the coal to dense-medium separation. De Korte adds that this will upgrade the coal to a specific ash content or heat value as well as correct size range required by a specific industrial process.
In the Mpumalanga coalfields, the best coals have been mined out and the remaining coal is of an ever-decreasing quality. “A number of mines are now re-mining the pillars left by previous bord-and-pillar mining operations. There is further a growing trend to reprocess discard coal from previous operations to recover low- grade thermal coal.”
Water is required in the coal processing process but is becoming more difficult to supply and dry processing of coal is being implemented at some mines.
The decline in the quality of raw coal makes the control of coal product quality increasingly difficult and the beneficiation of raw coal more important.