Power Plant Selection in Mighty River Power Develpment Projects

Abstract

This paper compares different energy conversion rates for some geothermal power plant cycles. These are being implemented at two high temperature, liquid dominated reservoirs; Kawerau and Rotokawa.
The power plant cycle selected for the first development is a dual flash, condensing steam turbine; however, optimisation with higher pressures and enthalpies resulted in a triple flash, condensing steam turbine for the second development. This will be the largest single cylinder geothermal steam turbine in the world. The project is currently under construction with commercial operation scheduled for the first half of 2010.
The environmental consent process in New Zealand provides a fixed average fluid extraction rate and an instantaneous maximum. Geothermal fluid conditions, (including; enthalpy, non-condensable gas content and chemistry) were defined from well test results and reservoir modelling. The owners’ financial model has been used to provide key metrics for selection of the plant cycle giving the maximum revenue from the consented geothermal fluid flow, considering life cycle costs. In one example, the selected triple flash cycle developed 6 MW more than a comparable dual flash cycle.