Exergy and Energy Analysis of a Dry Steam Power Plant with Heller Condenser

Abstract

Geothermal power plants are widely used in Larderello region, Tuscany, due to its favourable geological characteristics. The geothermal fluid available at Larderello can be considered as a dry steam, since it contains about 95% of steam at relatively high temperature (200°C), and about 5% of non-condensable gases, mainly carbon dioxide. Due to its thermodynamic properties, the geothermal fluid is currently used in a Dry Steam power plant, where it is directly expanded in turbine. In this paper, some modifications to the structure of the plant are proposed and the plant is modelled using the software EES®. In the model, the geo-fluid flow is ideally separated in two flows, respectively water vapour flow and carbon dioxide flow, treating separately the expansion and the compression processes. Energy and exergy analysis are performed, and the results show a good agreement with the results presented in the literature, where the geo-fluid is modelled as a single flow. Since the water flow rate for the condensing process is significant, the possibility of recovering work through a Heller system is considered. The results show that 85% of the power required for the pumping of the condensing water can be provided by this Heller system

Keywords

• Dry steam power plant, Geothermal energy, Exergy analysis, Heller condenser

References

1. R. DiPippo. Geothermal Power Plants: Principles, Applications, Case Studies and Environmental Impact, 2 nd Ed. Burlington, MA: Elsevier, 2008.
2. J.E. Ahern, The Exergy Method of Energy System Analysis, Hoboken, NJ: John Wiley and Sons, 1980.
3. M. Moran, Availability Analysis: A Guide to Efficient Energy Usage, Englewood Cliffs, NJ: Prentice-Hall, 19 T. J. Kotas, The exergy method of thermal plant analysis, New York: Krieger, 1995.
4. A. Bejan, G. Tsatsaronis, M. Moran, Thermal Design and Optimization, New York: Wiley Interscience, 19 J. Szargut, D.R. Morris, F.R. Stewart, Exergy analysis of themal, chemical and metallurgical processes, London, UK: Taylor and Francis, 1998.
5. M. Kanoglu, Exergy Analysis of a dual-level binary geothermal power plant. Geothermics, 31, 709–724, 200 G. Bodvarsson, D.E. Eggers, The exergy of thermal power, Geothermics, 1, 93–95, 1972.
6. R. DiPippo, D.F. Marcille, Exergy Analysis of Geothermal Power Plants, Geothermal Resources Council Transactions, 8, 47-52, 1984.
7. R DiPippo, Second law assessment of binary plants generating power from low-temperature geothermal fluids, Geothermics, 33, 565–586, 2004.
8. M. Yari, Exergetic analysis of various types of geothermal power plants, Renewable Energy, 35, 112–121, 2010.

9. C. Coskun, Z. Oktay, I. Dincer, Performance evaluations of a geothermal power plant, Applied Thermal Engineering, 31, 4074–4082, 2011.
10. H. Ganjehsarabi, A. Gungor, I. Dincer, Exergetic performance analysis of Dora II geothermal power plant in Turkey, Energy, 46, 101–108, 2012.
11. N. Bettagli, G. Bidini, Larderello-FarinelloValleSecolo geothermal area: exergy analysis of the transportation network and of the electric power plants, Geothermics, 25, 3-16, 1996.
12. Engineering Equation Solver, Academic Version V603, www.fchart.com, 2013.
13. UNEP - United Nations Environment Program (Accessed 2011, February 21). Cooling towers: Energy Efficiency Guide for Industry in Asia – Available: http://www.energyefficiencyasia.org/docs/ee_module s/Chapter-Cooling%20Towers.pdf
14. Italian Ministry of Environment, DLgs. 152/2006 attachment 5, Table 3.
15. GEA EGI Co. Ltd. (Accessed 2011, February 21), GEA Heat Exchangers, Indirect dry cooling system (Heller system). Available: http://www.geaenergytechnology.com/opencms/opencms/egi/en/cool ing/drycooling/
16. A. Balogh, Z. Szabo, The Advanced HELLER System – Technical Features and Characterisctics. EPRI Conf. on Advanced cooling Strategies/Technologies, Sacramento, CA, 2005.