Darling Downs - Australia's biggest combined-cycle power station

Using Queensland’s rich source of coal seam gas (CSG) reserves, the Darling Downs Power Station is set to become Australia’s largest combined-cycle power station.

When operational, the $780 million 630 megawatt (MW) gas-fired power station will produce enough power to supply the equivalent of 400,000 Queensland homes. Poised to take advantage of Origin Energy’s CSG reserves in the area around Roma and Chinchilla, the power station will be located near Braemar, 40 kilometres west of Dalby.

Promoting CSG development

In November last year, construction started on the gas-fired power station.

Fuel for the power station will initially be drawn from Origin’s Spring Gully coal seam methane gas reserves 80 km northeast of Roma and later from its Talinga CSG fields in the Walloon Coal Measures. Recently, Origin Energy announced plans to invest a further $360 million to expand its CSG production at Spring Gully.

CSG will be processed at the Spring Gully processing plant and then transported through an existing gas pipeline to Wallumbilla. A new $90 million 200 km pipeline will be constructed from Wallumbilla to the new Darling Downs Power Station site.

In February this year, Origin secured $900 million for the development of the Darling Downs Power Station and ongoing CSG projects. The development will become one of the lowest cost power stations in the National Electricity Market, in part because Origin directly owns the CSG reserves that will fuel the power station, but also because, the power station is expected to have a low life cycle cost, including both construction and long-term maintenance costs.

Spurring the development of ‘economic powerhouses’

Not only is the Darling Downs Power Station poised to break records in terms of running cost, but Queensland Premier Anna Bligh has said that CSG projects, including the Darling Downs Power Station, have yielded approximately $1 billion worth of development across Queensland, benefiting the regional economy.

“We expect this investment to continue at more than $160 million a year and this means local jobs and a further boost to our regional economy,” Ms Bligh said. “This Origin power station and associated CSG developments alone will create an average of 440 jobs during the construction phases, and up to 55 jobs when operational.”

“Many of these regional communities have been hit hard by drought in recent years and the rich source of energy in the Surat Basin has the potential to turn towns like Dalby, Miles and Chinchilla into economic powerhouses.”

Providing a myriad of environmental benefits

Powered by CSG, the power station is estimated to emit about half the greenhouse emission of a conventional power station and have broader environmental benefits, according to Queensland Premier Anna Bligh.

“Coal seam gas is a clean energy source and when this station is online, it will produce 2.5 million tonnes per annum less than a conventional power station of its size – which is the equivalent of taking 600,000 cars off the road,” she said.

The environmental benefits of the gas-fired power station also extend to saving water. Since the power station uses air cooled technology, it will use less than 3 per cent of the water a conventional water cooled coal-fired power station would use, or about 200 megalitres (ML) versus 8,000 ML a year.

Additionally, unlike natural gas, which is trapped by specific geological conditions, since CSG is held in place by water, pumping out water is part of the CSG production process. Origin plans to develop a 9 ML/day reverse osmosis water treatment plant as part of the broader project. However, one of the project’s bigger challenges has revolved around the pre-treatment of this water, which has high coal fine loads.

Pre-treatment involves micro- and ultra-filtration, with a settling pond prior to the reverse osmosis reaction that exposes the water to the atmosphere and allows some heavier minerals to precipitate out. There are a range of different markets for this water, from supplying local councils with potable supplies to nearby industrial markets, including coal washing. Ultimately however, the projects’ broader environmental benefits are particularly important given the considerable impact of the drought on Queensland in recent years.

“Accelerating the development of the Darling Downs Power Station ensures we are able to select the site and sequence of development that will create the most economically attractive project for Origin. The development of the power project will accelerate the development of our coal seam gas resources, and, together with our peaking power stations at Roma (80 MW) and Mt Stuart (288 MW) and off-take rights from the Wambo peaking Power Station (450 MW), create a diverse and competitive portfolio of generation to support our electricity retail business in Queensland,” said Origin’s Managing Director Grant King.

When completed in 2010, the Darling Downs Power Station is likely to bring a range of other benefits that go beyond
just the gas industry, giving the drought-affected regional economy two boosts: by bringing jobs to the region and providing another source of water.

Origin contracted a consortium of GE and CH2M Hill to construct the power station. GE will supply three Frame 9E gas turbines with a capacity of 120 MW each and a steam turbine of 270 MW capacity. CH2M Hill will undertake engineering and construction activities and supply of the balance of plant.

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