Effects of reinjection temperature on thermodynamic performance of dual-pressure and single-pressure geothermal ORCs

Abstract

The geothermal water reinjection temperature should keep at a high level to avoid silica oversaturation but the permissible reinjection temperature varies with geothermal source characteristics. The reinjection temperature directly affects geothermal source and working fluid temperature profiles, and then affects the organic Rankine cycle (ORC) thermodynamic performance. This work optimized the evaporation temperatures for dual/single-pressure ORCs using isopentane as working fluids to maximize the net power outputs and analyzed the effects of the reinjection temperature on ORC thermodynamic performance. The net power output of a dual-pressure ORC decreases with increasing permissible reinjection temperature. The low-temperature geothermal heat can be more efficiently used by a low-pressure evaporation in a dual-pressure ORC than a single-pressure ORC, but the benefit in power output for a dual-pressure ORC over a single-pressure ORC is lower for higher reinjection temperatures. The evaporation exergy destruction rates for dual-pressure ORCs are considerably lower than single-pressure ORCs for higher reinjection temperatures and geothermal water inlet temperatures.