Monday, 13 September

Deloitte Energy Excellence Award for the New Zealand Power Plant

The Nga Awa Purua Geothermal Power Station, a NZ$430-million joint venture between Mighty River Power and the Tauhara North No.2 Trust, was named Project of the Year at the inaugural Deloitte Energy Excellence Awards last week. The plant was officially opened by the PM John Key in May.

The geothermal fluid at 300 oC is provided is extracted from a depth of 2500 metres using eight production wells (200-2500 m). The average geothermal production is 65 kg/second/well. The majority of the fluid is reinjected using 5 injection wells (3000 m deep). The company reported that each well took about 40 days to drill. The fluid was transported to the plant in steel pipes of 1200-mm diameter and 30 mm wall thickness.

The plant is a triple flash plant with a single-shaft turbine using three expansion stages. The plant was constructed by Sumitomo of Japan with the turbine and the generator provided by the Fuji Electric Systems. This is reportedly the largest single casing geothermal steam turbine in the world, capable of providing 139MW (gross). A wet cooling tower is used to cool the condensers. Air is driven through the coling tower using 10 fans that are at 10-m in diameter and spin at a speed of 99 rpm. The cooling tower has a footprint of 165m x 20m. The following is a picture taken during the construction of the cooling tower:

The power station will produce enough electricity to meet 3% of New Zealand’s electricity needs. The Mighty River Power chief executive Doug Heffernan says that with the addition of Nga Awa Purua, around 14% of New Zealand’s electricity supply now comes from geothermal energy.

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