Geothermal power plant case study for a new ORC plant including CO2 reinjection

A closed-loop ORC power plant layout including complete gas reinjection for the geothermal location of Castelnuovo Val di Cecina, Italy is proposed and analysed. The reservoir conditions correspond to a live steam field, with relevant contents of CO2 and acid gases in the resource. The proposed solution includes complete reinjection of the non-condensable gases, using an intercooled compressor train to reinject the gas at suitable depth within the condensate stream. A subcritical single-pressure ORC using R245fa or R1233zd(E) is taken as the reference case and optimized conditions for efficiency and power are determined. The effect of the CO2 content in the resource is investigated and discussed. The calculations include the piecewise solution of the main heat exchanger; a detailed exergy balance and exergoeconomic analysis is done, allowing the evaluation of the final cost of electricity, and the contributions to this last of capital costs and of irreversibilities in the process.