Scientists aim for clean energy from dirty coal...

BROWN coal has been condemned as being polluting and inefficient, but a series of scientific advances are spectacularly improving its attractiveness, according to the Cooperative Research Centre for Clean Power from Lignite (CRC CPL). JULIAN CRIBB reports.
Scientists aim for clean energy from dirty coal... Scientists aim for clean energy from dirty coal... Scientists aim for clean energy from dirty coal... Scientists aim for clean energy from dirty coal... Scientists aim for clean energy from dirty coal...

While Australia has centuries' worth of black coal and natural gas still to exploit, it has an even greater bounty of brown coal, or lignite.

Estimates range from 400-600 years' supply in Victorian and South Australian beds alone, says CRC CPL chief executive Dr Peter Jackson.

The CRC's Mechanical Thermal Expression (MTE) technology removes more than 70% of the water from the brown coals, resulting in huge greenhouse savings for power stations, according to Jackson.

MTE dries the coal by a process of mild heating and squeezing, reducing it to a state far more suitable as feed for efficient power generation. It may also prove useful in removing salt from SA lignite, making it a cleaner fuel.

"Using our technology to dry coal for a new "state of the art" supercritical power station, greenhouse gas emissions can be reduced by more than 30% compared to today's power stations," Jackson said.

"Reductions exceeding 40% will be achieved ifthe dry coal is fed to the next generation of integrated coal gasification combined cycle (IGCC) plants."

Drying brown coal in this way could save nine million tonnes of carbon dioxide a year if applied to remove half of the lignite water in the feed to existing power stations, he said.

CRC researchers have successfully demonstrated the MTE process in a one tonne per hour pilot plant, and are helping partners to develop a larger 15tph pilot plant. The next step would be a commercial-scale 200tph demonstration plant.

The research has also found potential uses for the large amount of water removed from the coal by MTE, such as for power station cooling and ash pond water, therefore helping to reduce power station demand for fresh water.

As a bridge between improving existing power station performance and the "holy grail" of zero emissions through IGCC, the CRC is exploring two high efficiency technologies:

  • upgrading or retrofitting existing pulverised fuel plants with coal pre-drying or repowering with a gasification unit
  • new supercritical or ultra-supercritical pulverised fuel plants with coal pre-drying.
  • In the 10-year quest for zero emissions from lignite the CRC is planning to pursue two other options in the proposed CRC for Clean Utilisation of Lignite:

  • Oxy-fuel pulverised fuel combustion, with carbon dioxide and water vapour flue gas recycle to the furnace, and carbon dioxide sequestration following condensation of the water in the furnace flue gas
  • Oxygen-fuelled gasification, coupled with carbon dioxide separation and sequestration, and combustion of hydrogen in a combined cycle (IGCC) gas turbine.
  • While the CRC is not actively exploring liquid transport fuels production from brown coal, Jackson said that this was a potential spin-off from the oxy-fuel gasification route to meet Australia’s declining indigenous oil supply.

    "It looks as if it may be cheaper to convert Victorian brown coal to liquid fuel than to convert natural gas. This would produce an extremely clean diesel fuel, with no polluting emissions – but it wouldn't make particularly good gasoline. Using another route you can capture the carbon.

    "But all these technologies rely on our ability to capture and sequester carbon dioxide to achieve zero or near-zero greenhouse gas emissions."

    For the coming half-century, Australia's energy strategy – and economic prosperity – turns on the issue of carbon storage. The task of finding where and how to store the nation's surplus carbon dioxide sits in the in-tray of Dr Peter Cook, chief executive of the CO2CRC.

    Professor Julian Cribb FTSE is a science journalist and communicator.

    Tomorrow - removing pollution through carbon sequestration.

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