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Underground coal gasification research
The underground coal gasification (UCG) pilot plant celebrated its first birthday on 20 January 2008. During the first year of operation, it produced more than 13 million cubic metres of gas, or enough to supply the heating and cooking requirements of 330 medium-sized houses.
Extensive monitoring of the environmental impact of operations has indicated no significant effects, but monitoring will continue to ensure that this remains the case. While the output of the plant is presently fairly modest (100kW of electricity), the engineering, procurement, and construction of a demonstration plant are under way to increase the scale by some forty-fold. This will see sufficient gas produced for co-firing into Majuba power station’s coal boilers and will prove the first gas production module.
The engineering, procurement, and construction of the demonstration plant are already under way, with plans to produce 70 000Nm3/h by mid-2009. Following approvals, production will proceed to 125 000Nm3/h by the end of 2009 and with approvals again to 625 000Nm3/h by the end of 2010. This gas will be co-fired with coal at the existing Majuba power station, until approvals are received for a new 350MW UCG-integrated gasification combined-cycle (IGCC) ultra-high-efficiency power station, which could potentially be commissioned in the 2012 timeframe.
In parallel with the research and development phases, a motivation is being compiled for a new 2 400MW commercial power station, which will be proposed to Eskom and stakeholders.
An EIA has also been commissioned for this new concept. It is proposed that the new power station shares gas with the existing Majuba power station, so as to maintain UCG gas production flexibility.
Eskom’s Corporate Services division is developing this project with UCG technology experts, Ergo Exergy Technologies Inc. (Canada), who are providing their proprietary eUCG technology.
UCG is ideally suited for complete extraction of both the solid and gaseous fuels from coal resources that are not destined for conventional mining to extract solid fuel.
Eskom's underground coal gasification demonstration
plant in the foregroung
Eskom has determined that UCG technology offers the following merits:
- UCG technology, in combination with a combined-cycle power station, significantly reduces the emissions footprint of a coal-fired power station.
- The overall resource utilisation efficiency is very high, especially when the gas is used for power generation in a combined-cycle power station. UCG as a mining technology also effectively extends South Africa’s coal reserves, by allowing extraction of coal previously disregarded as being unminable.
- The focus on “unminable” resources suggests minimal overlap with existing conventional mining houses, although conflict is possible with CBM developers.
- The broader geographic availability of coal suitable for UCG enables Eskom to position new coal generating plant far more strategically to support demand-side needs and stabilise the transmission network.
- The technology will increase Eskom operational flexibility and efficiency, by allowing the coal mine and power station to effectively integrate.
- The technology, on a large scale, offers the opportunity to reduce the cost of electricity from new coal-based power stations. It achieves this through an inherently simpler mining process, and a shorter resource-to-electricity production supply chain.
- It could be suitable for carbon capture.
The UCG technology is modular, and Eskom is already proving the first module. The modularity, availability, and relative simplicity of major plant components enable faster lead times than for conventional coal plant.
Eskom's UCG demonstration plant in the foreground, with
Majuba station in the background
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