Optimization of binary geothermal power systems

Abstract

In this article, modeling and optimization of two different organic Rankine cycles (ORC) (Power Plant (a) with a recuperator and Power Plant (b) without a recuperator) utilizing geothermal brine (GB) are studied. The developed models for these ORCs include performance characteristics of different components obtained from two existing power plants. The power plants rely on dry cooling (air cooled condenser) and as such exhibit performance degradation for high ambient temperatures. The models are validated with measured data for one-year operation of each power plant. The optimal operations of these power plants are obtained maximizing the net power output. The optimization is performed in Aspen Plus®. Although in the literature it is suggested that for an ORC, the optimal performance is achieved with no superheat at the inlet of turbine, this statement only holds for low ambient temperatures. Our findings suggest that the optimal value of superheat is a monotonic increasing function of the ambient temperature; in hot days, high values of superheat provide the maximum power output. The new optimal operation boosts the annual power output of the cycles up to 9% in ORC (a) and up to 7% in ORC (b). Furthermore, the findings reveal that for a fixed total flow rate of GB in a year, an optimized operation of power plant increases the revenue by an additional 3.7 % compared to fixed flowrate of brine; this is achieved by a slightly higher flow rate of GB in the low and moderate ambient temperatures and no operation of the plant in the hot hours of the year. This can be economical if the shutdown is combined with plant maintenance.