Modelling of the Separated Geothermal Water Flow Between Te Mihi Flash Plants

Abstract

The development of the Te Mihi sector of the Wairakei geothermal field includes two large flash/separation plants to supply steam to the Te Mihi and Poihipi power plants. The plants produce large quantities (6500 t/h) of separated water which has to be flowed in a controlled manner to the low pressure flash separators of the Te Mihi power station. The steamfield also has to receive and reinject the water from the Te Mihi station after the second flash stage. Dynamic modelling of the water flows was carried out for operating and upset conditions. It was found that these qualities of fluid had high momentum and this produced oscillations in the water levels between the flash plants during upsets. Operating states with only one plant operating were examined. This included the effects of cooling in dead legs. The reinjection lines were also modelled for water hammer and vapour separation. The modelling showed the two flash plants could be operated effectively as a single plant even with the large geographic separation between the vessels. Operating experience is compared to the modelling.