Research Papers

Discussion of Some Myths/Features Associated With Gas Turbine Inlet Fogging and Wet Compression

[+] Author and Article Information
Ting Wang, Jobaidur R. Khan

Energy Conversion & Conservation Center,
University of New Orleans,
New Orleans, LA 70148

1Present address: Department of Mechanical Engineering, University at Buffalo, Buffalo, NY 14260-1660.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF THERMAL SCIENCE AND ENGINEERING APPLICATIONS. Manuscript received January 28, 2015; final manuscript received July 2, 2015; published online November 17, 2015. Assoc. Editor: Srinath V. Ekkad.

J. Thermal Sci. Eng. Appl 8(2), 021001 (Nov 17, 2015) (9 pages) Paper No: TSEA-15-1034; doi: 10.1115/1.4031360 History: Received January 28, 2015; Revised July 02, 2015

Gas turbine (GT) inlet fogging and overspray (high-fogging) have been considered the most cost-effective means of boosting a GT's total power output, especially under hot or dry weather conditions. The result of employing fogging or overspray is indisputably clear—total power output is increased; however, development of the theory and explanation of the phenomena associated with fogging and overspray are not always consistent and are sometimes misleading and incorrect. This paper focuses on reviewing several interesting features and commonly discussed topics, including (a) entropy production of water evaporation, (b) the effect of centrifugal force on water droplets, and (c) whether water droplets can survive the journey in the compressor and enter the combustor. Furthermore, three turbine myths that fogging/overspray increases the air density in the compressor, reduces the compressor power consumption, and noticeably enhances the GT efficiency are examined and discussed. Some common mistakes in describing the compressor work are identified and corrected. A newly constructed multiphase T–s diagram is used to explain the physics of water droplet evaporation process and corresponding entropy production during wet compression.

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Fig. 1

Effect of increased ambient temperature on GT efficiency and output power per unit mass flow rate (i.e., specific work) [9]

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Fig. 2

Different fog/overspray cooling processes in the air-intake duct and in the compressor [9]

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Fig. 3

A qualitative T–s diagram illustration of different phases during a wet compression (not to scale)

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Fig. 4

(a) T–s diagram with actual data for all the species. Liquid droplet evaporation at four representative pressures are taken from four compressor stages (St.) in Ref. [22]. Note: The air-only line almost coincides with the mixture line. (b) Magnified view of dry and wet compression processes in the region of nearly coincided paths.

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Fig. 5

Density variation in an eight-stage axial compressor with fogging/overspray [22]

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Fig. 6

Control volume for (a) dry compression and (b) wet compression

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Fig. 7

Theoretical representation of overspray and/or interstage spray cases. The shaded area represents the double compression work due to the interstage spray [22].

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Fig. 8

Thermal efficiency variations under different fogging and ambient conditions [9]

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Fig. 9

Reduction of droplet diameter for nonequilibrium cases [29]




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