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Research Papers: Gas Turbines: Cycle Innovations

Thermodynamic Analysis of Part-Flow Cycle Supercritical CO2 Gas Turbines

[+] Author and Article Information
Motoaki Utamura

 Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8552, Japanutamura@nr.titech.ac.jp

J. Eng. Gas Turbines Power 132(11), 111701 (Aug 12, 2010) (7 pages) doi:10.1115/1.4001052 History: Received April 21, 2009; Revised January 06, 2010; Published August 12, 2010; Online August 12, 2010

Cycle characteristics of closed gas turbines using supercritical carbon dioxide as a working fluid are investigated. It is found that an anomalous behavior of the physical properties of CO2 at the pseudocritical point may limit the heat exchange rate of a regenerative heat exchanger due to the presence of a pinch point inside the regenerative heat exchanger. Taking such a pinch problem into consideration, the cycle efficiency of the Brayton cycle is assessed. Its value is found to be limited to 39% degraded by 8% compared with the case without the pinch present inside. As an alternative, a part-flow cycle is investigated and its operable range has been identified. It is revealed that the part-flow cycle is effective to recover heat transfer capability and may achieve the cycle thermal efficiency of 45% under maximum operating conditions of 20 MPa and 800 K. Optimal combination of turbine expansion ratio and a part-flow ratio is 2.5 and 0.68, respectively. Parametric study is carried out. In neither compressor nor turbine, deteriorated adiabatic efficiency may affect cycle efficiency significantly. However, pressure drop characteristics of heat exchangers govern the cycle efficiency.

Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Variation in the fluid temperatures in a counterflow heat exchange

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Figure 2

Temperature difference profile under a constant physical property

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Figure 3

Behavior of the physical property of carbon dioxide in a pseudocritical state

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Figure 4

Temperature profile in heat exchanger using S-CO2 as a heating medium

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Figure 5

Temperature difference profile reduced from Fig. 4

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Figure 6

Part-flow cycle configuration

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Figure 7

Cycle efficiency as function of turbine expansion ratio

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Figure 8

Optimal part-flow ratio ψ

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Figure 9

T-s diagram under the operation condition optimized for the part-flow cycle

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Figure 10

Thermal efficiency as a function of the specific output

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Figure 11

Effect of temperature effectiveness on thermal efficiency

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Figure 12

Effect of pressure drop on thermal efficiency

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Figure 13

Effect of adiabatic efficiency

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Figure 14

Cycle thermal efficiency under the optimal choice of turbine expansion ratio

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Figure 15

Heat duty or work of component consisting of the CO2 cycle

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