Octa was asked to carry out a Health Check and subsequently to provide Project Management Services for Mighty River Power’s new $482 million 82MW geothermal power station at Ngatamariki, approx 20km NE of Taupō. The project involved construction of 4 x 22MW binary cycle (pentane) air-cooled turbine generator units installed in a greenfields development. The project had four main elements, each with a different procurement methodology but generally based on FIDIC Conditions of Contract:
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Power Station – a $185m EPC contract with Ormat, an Israeli company.
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Steamfield pipework – a $20m Design-Build contract with Hawkins Infrastructure.
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220kV Transmission line – a $12.5m fully designed (traditional-type) contract with Electrix to take electricity from the new power station to the grid (a distance of approx 8.5km including crossing SH5 and the Waikato River).
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Geothermal well drilling – a $155m time and materials contract with MRP’s Drilling Business Unit utilising an Icelandic drilling company to drill production and injection wells.
In addition, a number of long lead items such as steam field pipe, bends and valves, 11/220kV step up transformers and transmission poles were directly procured.
The production wells are drilled to a depth of around 3000m to tap into high pressure/high temperature “brine” at about 20barg (300psi) and 280oC. This is brought to the surface where the brine is “flashed off” to steam which, with remaining brine, is passed through multiple closed circuit heat exchangers. This vaporises the pentane to a gas which passes in a “closed loop” through the turbine/generator unit. The steam is then condensed and the brine pumped back down injection wells to a depth of about 3500m. This is a sustainable process given around 99% of the brine is re-injected.
Construction started on site in October 2011 and the first generation from Unit 1 fed power to the national grid on 22 March 2013 with all four units generating by June 2013. The sustainable nature of the power generation with recirculation of the brine is a key feature of the project.
