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RESEARCH PAPERS

Performance Analysis and Optimization of Double-Flash Geothermal Power Plants

[+] Author and Article Information
Ahmet Dagdas

Department of Mechanical Engineering, Yildiz Technical University (YTU), 34349, Besiktas, Istanbul, Turkeydagdas@yildiz.edu.tr

J. Energy Resour. Technol 129(2), 125-133 (Oct 09, 2006) (9 pages) doi:10.1115/1.2719204 History: Received January 31, 2006; Revised October 09, 2006

One of the most important cycles for electricity generation from geothermal energy is the double-flash cycle. Approximately 25% of the total geothermal based electricity generation all over the world comes from double-flash geothermal power plants. In this paper, performance analysis of a hypothetical double-flash geothermal power plant is performed and variations of fundamental characteristics of the plant are examined. In the performance analysis, initially, optimum flashing pressures are determined, and energy and exergy values of the base points of the plant are calculated. In addition, first and second law efficiencies of the power plant are calculated. Main exergy destruction locations are determined and these losses are illustrated in an exergy flow diagram. For these purposes, it is assumed that a hypothetical double-flash geothermal power plant is constructed in the conditions of western Turkey. The geothermal field where the power plant will be built produces geofluid at a temperature of 210°C and a mass flow rate of 200kgs. According to simulation results, it is possible to produce 11,488kWe electrical power output in this field. Optimum first and second flashing pressures are determined to be 530kPa and 95kPa, respectively. Based on the exergy of the geothermal fluid at reservoir, overall first and second law efficiencies of the power plant are also calculated to be 6.88% and 28.55%, respectively.

Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

A simplified scheme of double-flash geothermal power plant

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Figure 2

T-s diagram of the double-flash geothermal power plant

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Figure 3

Optimum first flashing pressure of the double-flash geothermal power plant. Second flashing pressure is 100kPa.

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Figure 4

Optimum second flashing pressure of the double-flash geothermal power plant. First flashing pressure is 530kPa.

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Figure 5

Percentage loss in exergy (relative to pure saturated liquid water) as a function of temperature for various values of NaCl molality (18)

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Figure 6

Steam quality vs first flashing pressure (P9=95kPa)

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Figure 7

The variation of mass flow rate of the steam related to first flashing pressure (P9=95kPa)

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Figure 8

Overall first law efficiency of the power plant vs first flashing pressure (P9=95kPa)

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Figure 9

Overall second law efficiency of the power plant vs first flashing pressure (P9=95kPa)

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Figure 10

The variation of net power output of the plant related to first flashing pressure at different reservoir temperatures. The second flashing pressure is 95kPa.

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Figure 11

The optimal first flashing pressure vs the reservoir temperature (P9=95kPa)

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Figure 12

Variations of the second flashing pressures and overall net power output of the plant for different first flashing pressures (TR=210°C)

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Figure 13

Computed mass flow rate of the steam at the second flashing process vs second flashing pressures (P2=530kPa)

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Figure 14

The second law efficiency of the power plant vs the second flashing pressure (P2=530kPa)

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Figure 15

Exergy flow diagram of the double-flash geothermal power plant

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