Research Papers: Gas Turbines: Heat Transfer

Evaporative Cooling of Gas Turbine Engines

[+] Author and Article Information
Cyrus B. Meher-Homji

Bechtel Corporation,
Houston, TX

Aeroderivative engines typically operate at higher inlet Mach numbers resulting in higher inlet temperature depressions.

This approach is very data intensive with file sizes exceeding 60 MB.

There are several considerations other than just calculating the intake temperature static depression caused by air acceleration to Mach numbers of 0.5 to 0.8. There is also some heating (although small—of the order of 1 °C) due to the condensation that occurs and also due to heat transfer from the number 1 bearing, etc.

Contributed by the Heat Transfer Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received January 18, 2013; final manuscript received March 1, 2013; published online June 24, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 135(8), 081901 (Jun 24, 2013) (12 pages) Paper No: GTP-13-1019; doi: 10.1115/1.4023939 History: Received January 18, 2013; Revised March 01, 2013

There are numerous gas turbine applications in power generation and mechanical drive service where power drop during the periods of high ambient temperature has a very detrimental effect on the production of power or process throughput. Several geographical locations experience very high temperatures with low coincident relative humidities. In such cases media evaporative cooling can be effectively applied as a low cost power augmentation technique. Several misconceptions exist regarding their applicability to evaporative cooling, the most prevalent being that they can only be applied in extremely dry regions. This paper provides a detailed treatment of media evaporative cooling, discussing aspects that would be of value to an end user, including selection of climatic design points, constructional features of evaporative coolers, thermodynamic aspects of its effect on gas turbines, and approaches to improve reliability. It is hoped that this paper will be of value to plant designers, engineering companies, and operating companies that are considering the use of media evaporative cooling.

Copyright © 2013 by ASME
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Fig. 1

Representation of power boost by inlet air cooling

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Fig. 2

Media type evaporative cooler (courtesy CCJ, [8])

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Fig. 3

Typical inverse variation of relative humidity with ambient dry bulb temperature during the day

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Fig. 4

Data for Riyadh showing the relationship between DBT and WBT. At 40 °C, a wet bulb depression of approximately 21 °C is available.

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Fig. 5

Data for Rio, Brazil showing the relationship between DBT and WBT. At 36 °C, a wet bulb depression of approximately 7 °C is available.

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Fig. 6

Database showing hourly bin data of DBT versus RH for one year

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Fig. 7

GT output power for different combinations of RH and DBT with media evaporative cooling (evaporative cooler efficiency = 90%)

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Fig. 8

Selection of design point for gas turbine inlet air cooling system showing insensitivity to evaporative cooler evaporative efficiency. All DBT values shown are greater than 41.6 °C.

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Fig. 9

Selection of design point for gas turbine inlet air cooling system (evaporative cooling) shown with actual site data; DBT values shown greater than 35 °C

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Fig. 10

Relative humidity versus DBT for Phoenix, AZ

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Fig. 11

Relative humidity versus DBT for Riyadh, Saudi Arabia showing significant evaporative cooling potential for the year

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Fig. 12

Relative humidity versus DBT for Houston, TX

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Fig. 13

Representation of power boost in % for different dry bulb temperatures and relative humidities, assuming evaporative cooling with evaporative cooling efficiency of 90%

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Fig. 14

Representation of ECDH over 12 months by daily period of 3 h

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Fig. 15

Representation of ECDH at different time of the day as function of wet bulb depression in increments of 0.56 °C (1 °F)

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Fig. 16

ECDH as function of MWBT for different databases for a hot and dry location and a warm and humid region

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Fig. 17

Psychrometric chart indicating evaporative cooling LM2500+ simple cycle

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Fig. 18

LM2500+ G4 (simple cycle) (a) without evaporative cooling (above) and (b) with evaporative cooling

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Fig. 19

Cycle flow schematic Frame 6B combined cycle (no evaporative cooling) with condensing steam turbine. Net power 53 MW.

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Fig. 20

Frame 6B combined cycle with evaporative cooling. Net power 56,108 kW.

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Fig. 21

Chart to estimate approximate water flow requirements for varying gas turbine airflow rates and temperature depressions ranging from 5 °C to 15 °C

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Fig. 22

Comparison of new media with scaled media [8]

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Fig. 23

Microbiological fouling of media [8]




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