The Hindu Business Line : From sub- to super-critical, a power jump

New Delhi: Coal-based power stations have been a bugbear for ‘green’ lobby groups. But thermal generators are now beginning to clean up their act. Fossil fuel-fired power generation’s most perceptible and by far the biggest environmentally-sensitive measure is the move from the sub-critical to super-critical technology.

Steam turbines based on super-critical technology use less energy and generate higher pressure for greater efficiency than the traditional plants, thus leading to higher power generation from the same quantity of fuel even while reducing environmental pollution substantially.

Much of the thermal capacity additions, including the plants being set up by the country’s largest power generator, NTPC Ltd, and private players, would be in the form of super-critical units of 660/800 MW rating. Also, all the 4,000 MW Ultra Mega Power Projects on the anvil would use this technology.

Currently, about 55 per cent of the country’s 140,907 MW installed capacity is based on sub-bituminous coal, with the entire coal-based generation capacity implemented with sub-critical technology. On the basis of India’s weighted average operating Station Heat Rate, generation efficiency of sub-critical technology coal-based power plants is 30.05 per cent. As a result of the super-critical parameters, operational efficiencies of the projects will be higher than the current levels, with the difference in efficiency working out to over 5 per cent, according to experts.

Marking a shift in technology parameters, the country’s largest power equipment-maker, Bharat Heavy Electricals Limited (BHEL), has entered into a technology transfer agreement with Alstom for design and manufacture of large super-critical boilers.

Apart from the shift to super-critical sets, clean coal technology is another area where action has begun and Integrated Gasification Combined Cycle (IGCC) is rapidly emerging as one of the most promising technologies in power generation. IGCC uses low-quality solid and liquid fuels and is able to meet the most stringent emission requirements and reduces greenhouse gases. The Centre has approved a special grant of Rs 300 crore for the first 182 MW IGCC plant being set up at Vijaywada in Andhra Pradesh.

An IGCC plant uses technology that turns coal into gas. It then removes impurities from the coal gas before it is combusted. This results in lower emissions of sulphur-dioxide, particulates and mercury. It also results in improved efficiency compared to conventional pulverised coal.

Scheduled to be commissioned by October 2011. BHEL and Andhra Pradesh Power Generation Corporation Limited (APGENCO) have jointly invested in this Rs 950-crore project. Though IGCC technology is used in low-ash coal in many advanced countries, this plant will perhaps for the first time use it in high-ash coal. The main problem, though, for IGCC is its extremely high capital cost.

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