Thermodynamic and economic analysis for the pre-feasibility study of a binary geothermal power plant

Abstract

Maximum power output and thermal conversion efficiency are the goals of ORC thermodynamic analysis. Co-optimization of energetic performance and system cost is needed for pre-feasibility design analysis. This paper presents a pre-feasibility design investigation for a binary geothermal power plant using a typical geothermal resource in New Zealand. Thermodynamic and economic analyses were conducted for key cycle design options, a range of working fluids and component selection parameters. The net electrical power output (Wnet) and the ratio of Wnet to total Purchased Equipment Cost (PEC) are used as the objective function to select the most thermo-economical designs. Three working fluids n-pentane, R245fa and R134a are investigated. The thermodynamic analysis shows that the net electrical power output (Wnet) of cycle design achieves a maximum level at a certain optimum turbine inlet pressure and mass flow rate of working fluid. The 2-stage designs produce higher Wnet and thermal and exergy efficiencies than the 1-stage designs. Economic comparison indicates that the type of working fluid and cycle configuration have a great effect on economic performance as measured by PEC. The profitability analysis was conducted for the top three options. The results indicate that a standard Rankine cycle with a 2-stage turbine using n-pentane is the most thermo-economical design for the particular brine resource and re-injection conditions.