Abstract
Emissions of contaminants and CO2 are becoming a relevant issue for the development of geothermal energy projects. Organic Rankine (ORC) Cycles present in this light particular appeal in the light of the possibility of total reinjection of the geothermal fluid resource including Non-Condensable Gases (NCGs). The Castelnuovo (IT) case study conditions are considered a saturated vapour resource at 10 bar pressure. The performance of the ORC cycle for power generation from this geothermal resource is evaluated through mass and energy balances, stepping up to exergy, Life Cycle Analysis (LCA) and Exergo-Environmental analyses (EEvA). The applied methodology allows to identify the most critical components of the system and to evaluate the environmental indicators of the system.
Highlights
Geothermal Energy is experiencing continuous growth in the last 50 years, having been acknowledged as an attractive renewable resource, whose utilization with a correct perspective can ensure sustainable development
The issues related to the environmental concerns related to the traditional exploitation of geothermal resources greatly increased the interest towards total reinjection geothermal powerplants
This technology belongs to binary power cycles, that are fed by a closed loop exploiting the heat only of the geothermal resource, which is completely reinjected avoiding the release of pollutants to the atmosphere
Summary
Geothermal Energy is experiencing continuous growth in the last 50 years, having been acknowledged as an attractive renewable resource, whose utilization with a correct perspective can ensure sustainable development. Even though most of the geo-fluid is water, a problem arises in connection with the presence of NonCondensable Gases (NCGs) Most of these are Carbon Dioxide (CO2), but minor constituents are present, such as H2S, CH4, NH3, and Boron. The Italian resource has typical CO2 levels from 2 to 8% or more, determining a greenhouse emission factor, in strict terms, in the range between 100 and 400 gCO2/kWh [8] This is a “natural” emission, part of which would probably reach the surface anyway because of natural fracture patterns [9]. For the above reasons, taking advantage of a favourable scheme of incentives applied by the Italian government for resources having such difficult conditions for utilization, a number of new operators on the power market are proposing new solutions for the conversion of geothermal energy: these are based on ORCs but include the complete reinjection (or mineralization) of CO2
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