Optimum operation of a novel ejector assisted flash steam cycle for better utilization of geothermal heat

Abstract

Dual flash steam cycle (DFSC) is a proven technology to produce power from hot geothermal water. However, in a DFSC, substantial exergy destruction occurs during the two flashing processes. A good amount of thermal energy is also lost with the saturated water exiting the low-pressure vapour separator (LPVS). In the present study, saturated water exiting the high-pressure vapour separator (HPVS) of the geothermal flash steam cycle is used as the motive stream of an ejector. The ejector enhances the pressure of the steam exiting the high-pressure turbine. The steam exits the diffuser of the ejector at a two-phase state. The dry saturated vapour separated from this two-phase steam is expanded through a low-pressure turbine to produce some power output. It is observed that the use of the ejector helps to reduce the exergy loss with the mass of geothermal water entering into the injection well. For 210 °C geo-fluid temperature, the maximum achievable power output of the flash steam cycle with ejector (FSCWE) is 6.67% higher compared to that of the baseline DFSC. While delivering the maximum power at said geo-fluid temperature, the use of the ejector also reduces the levelized cost of electricity (LCOE) by 4.5% compared to that of the baseline cycle.