Japanese group urges SA to re-examine IGCC technology for power stations

South Africa should reconsider Integrated (coal) Gasification Combined Cycle (IGCC) technology for future power stations, because refinements in the technology have greatly increased its efficiency and rendered its previous evaluation obsolete. So argues Mitsubishi Hitachi Power Systems (MHPS) Africa, the local subsidiary of the Japanese large-scale thermal power generation systems manufacturing group.

“In the Integrated Resource Plan (IRP) 2010, the evaluation of IGCC was based on pre-2009 IGCC technologies. So the performance of IGCC was undervalued and by a considerable margin,” points out MHPS Africa sales and business development head David Milner. “The IRP considers it as no more efficient than other technologies and as having higher costs; this perspective was not changed in last year’s draft update. “But IGCC is now by far the most efficient coal-based electricity-generation technology in the world.”

Worldwide, IGCC has been under development since the late twentieth century. It involves the integration of two already well established, but previously unlinked, technologies – coal gasification and gas turbines. “Gasification, for example, is done by Sasol,” he explains. “But, instead of converting the resulting syngas [synthetic gas] into petrol, as Sasol does, we feed the syngas to gas turbines to generate electricity. “The main effect of this is an overall generating cycle efficiency that is much higher than using the traditional boiler and steam turbine, and increased efficiency means much lower carbon dioxide emissions.”

Moreover, a gas turbine has a very high availability than a steam turbine, while the availability of the coal gasification plant is about the same as that for a conventional coal-fired boiler. Thus, an IGCC plant will have the equivalent availability as the usual combination of a boiler and steam turbine.

The company delivered a demonstration plant in Japan, which operated from 2007 to 2013, and which was subsequently upgraded to, and is now operated as a commercial plant. “The main competing technology is Circulating Fluid Bed (CFB),” states Milner. “A CFB power station has an efficiency of 35%; Eskom’s new Medupi and Kusile power plants will likely have 38% to 39% efficiency. “Our 250 MW IGCC unit has an efficiency of 42%, while for our 540 MW unit the efficiency is expected to reach 48%. “Consequently, carbon dioxide emissions are between 20% and 30% lower.

This technology comes automatically with gas-cleaning technology. It is very efficient at separating out anything hazardous,” adds MHPS Africa chief technology officer Dietmar Breuer. “No South African power station today has state-of-the-art cleaning systems. IGCC is clean technology, in respect of environmental compliance.”

The company’s IGCC reference plant in Japan, which is located in an urban area and had to achieve low emissions, achieved a cut in carbon dioxide emissions of 10% to 20%, produced 60% less ash and used 30% less water than the state-of-the-art Ultra Super Critical (or USC) conventional technology. “The ash from a conventional boiler is fly ash, with limited uses,” notes Milner. “But ICGG plants produce molten slag ash instead, which can be used to build pavements and roads and in the manufacture of concrete.”

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