Energy Exploitation of High-Temperature Geothermal Sources in Volcanic Areas—a Possible ORC Application in Phlegraean Fields (Southern Italy)

Angelo Algieri

doi:10.3390/en11030618

Abstract

This work aims to investigate the energy performances of small-scale Organic Rankine Cycles (ORCs) for the exploitation of high temperature geothermal sources in volcanic areas. For this purpose, a thermodynamic model has been developed, and a parametric analysis has been performed that considers subcritical and transcritical configurations, and different organic fluids (isobutane, isopentane, and R245ca). The investigation illustrates the significant effect of the temperature at the entrance of the expander on the ORC behaviour and the rise in system effectiveness when the internal heat exchange (IHE) is adopted. As a possible application, the analysis has focused on the active volcanic area of Phlegraean Fields (Southern Italy) where high temperature geothermal reservoirs are available at shallow depths. The work demonstrates that ORC systems represent a very interesting option for exploiting geothermal sources and increasing the share of energy production from renewables. In particular, the investigation has been performed considering a 1 kg/s geothermal mass flow rate at 230 °C. The comparative analysis highlights that transcritical configurations with IHE guarantee the highest performance. Isopentane is suggested to maximise the ORC electric efficiency (17.7%), while R245ca offers the highest electric power (91.3 kWel). The selected systems are able to fulfil a significant quota of the annual electric load of domestic users in the area.

Highlights

The development and exploitation of renewable sources are today considered fundamental steps towards overcoming the energy “trilemma” of affordability, supply security, and environmental protection [1,2,3]
The organic working fluid is compressed by a pump (1-2 process) it results have been adopted to evaluate the possible use of geothermal-driven Organic Rankine Cycles (ORCs) to fulfill the is preheated (2-3) and vaporised (3-4) in the evaporator
The analysis has focused on the Phlegraean Fields caldera area (Southern Italy) to evaluate the possible exploitation of high temperature geothermal sources for electric production

Summary

Introduction

The development and exploitation of renewable sources are today considered fundamental steps towards overcoming the energy “trilemma” of affordability, supply security, and environmental protection [1,2,3]. The positive influence of the renewable sources promotion on local development opportunities, employment prospects, and social cohesion is expected. For this purpose, different actions have been proposed in the last decades to support the exploitation of alternative energies and to reduce the adoption of fossil fuels and the consequent greenhouse gas emissions (i.e., Kyoto Protocol, Paris Climate Agreement, etc.) [4,5,6]. The most recent statistical data provided by the International Energy Agency (IEA) show that the worldwide gross inland consumption in 2015 was equal to 109,124 TWh, and the share from renewable sources was 11.6% [7]. The target of the EU-28 by 2020 is at least a share of 20%

Objectives

Methods

Results

Conclusion