Nga Awa Purua Geothermal Power Plant

The Nga Awa Purua Geothermal Power Station is a new $430 million 140 MW geothermal development near Taupo and houses the world’s largest single-shaft geothermal turbine. It forms part of a significant geothermal expansion programme being undertaken by Mighty River Power. Nga Awa Purua, with the existing Rotokawa and Kawerau power stations and a planned station at Ngatamariki, are intended to create 500 megawatts of renewable geothermal energy by 2012, helping Mighty River's strategy of developing renewable and sustainable power generation.

Beca was involved in the $300 million 100MW Kawerau Geothermal power plant, and the same team was engaged as sub-consultant to Hawkins Construction to provide structural, civil, geotechnical, architectural and fire engineering design services on this significant project.

The civil and structural design included the turbine hall building, the turbine and generator table support structure, cooling tower, reinforced concrete shafts and pits, steam field equipment and balance of plant and pipe rack elevated support structures, extensive site development, including roads, site drainage, storm water and thermal water retention ponds, potable water reticulation, and on site sewage treatment.

Beca's geotechnical engineers worked with Hawkins to pile construction in what were difficult ground conditions. Weak volcanic soils, aggressive groundwater and high temperatures, and susceptibility to liquefaction meant that 30m deep bored piles were needed to support the plant structures, which included the generator and turbine weighing a combined 325 tonnes, and the turbine hall.

Previous experience on the Kawerau project meant that Beca had already developed a good understanding of the relevant plant processes. Using the 3D design tool Revit®, the team was able to produce an integrated design to address the complex needs of the generating equipment and balance of plant.