| Abstract |
Ngati Tuwharetoa Geothermal Assets Limited (NTGAL) supplies about 340-t/h of raw geothermal steam and 15-t/h of clean steam to the adjacent pulp, paper and timber mills from the Kawerau steamfield. Mighty River Power (MRP) operates the steamfield on behalf of NTGAL. MRP also operates its own 100 MW geothermal power station that was commissioned in 2008; this plant is known as KGL (Kawerau Geothermal Limited). Geothermal process steam has been supplied to the mills since 1957. The steam is used in the pulp and paper process, for timber drying and for co-generation. Some of the steam is used in heat exchangers to generate clean process steam. An innovative technique developed by Norske Skog Tasman (NST) uses stripped geothermal condensate as feedwater for the heat exchangers. The industrial direct use at Kawerau accounts for about 56% of all New Zealand’s direct geothermal heat use and is the largest industrial direct use in the world. The steamfield is, however, increasingly being used for electricity production. Recently there has been renewed interest in the use of geothermal steam for industrial processes and NTGAL is working with existing and new users to provide geothermal energy in different forms. In 2010 NTGAL constructed a purpose-designed, high reliability, heat plant to supply clean steam to SCA’s tissue mill. It also uses the NST condensate stripping process to generate feedwater; the process has been further refined. NTGAL constructed pipelines to supply separated geothermal water (SGW) and steam to a new binary power plant commissioned by NST in December 2012. The SGW used is a by-product of the steam supply and some was previously discharged to the Tarawera River without the heat being extracted. For the first 50 years of its operation the Kawerau steamfield supplying the mills was contained within an area of around one square kilometre. To increase the steam supply, and because production is moving to the south, in 2013 a new separation plant was commissioned south of the mills. The plant has a capacity of 200 t/h of steam and is fed by a well drilled in 1980 but not used in the interim. Two new reinjection wells have also been drilled out to the northwest. A total of 7 km of pipelines have been constructed to connect the new wells and separation plant, greatly increasing the extent of the working steamfield. |