METHODOLOGY OF PRE-FEASIBILITY STUDY FOR A BINARY GEOTHERMAL POWER PLANT UTILIZING LOW-MODERATE TEMPERATURE HEAT SOURCES

Abstract

The exploitation of low-medium temperature geothermal reservoirs in New Zealand is a potential resource that does not yet have mature commercial technology solutions. The development and exploration of the geothermal potential of New Zealand has been limited to high temperature resources due to the abundance of high temperature geothermal resources, the wide-spread availability of cheap hydro-generated electricity and the availability of natural gas (Hunt, 2006). This study describes the methodology used in a pre-feasibility study for a binary geothermal power plant utilizing a low-moderate temperature heat source. This pre-feasibility study can be a useful tool for decision making processes in the preliminary study.
The methodology is applied to an existing geothermal well located in the Taupo Volcanic Zone (TVZ) in New Zealand. Three common working fluids, namely: n-pentane, R245fa and R134a are analyzed. The cycle designs considered are standard (Std) and recuperative (Rec) cycles. The results of the analyses indicate that the Std designs using n-pentane and R245fa are feasible to be used for the geothermal well. The Std design using R245fa is more economical than the design using n-pentane, however the design using R245fa has a lower Energy Return on Investment (EROI) than the design using n-pentane. The present methodology can be utilized to estimate pre-feasibility of binary geothermal power plants using geothermal wells at the initial stage, reducing risk and indicating potential for further engineering investigations.