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Research Papers: Gas Turbines: Industrial & Cogeneration

Investigation of Cooling Effectiveness of Gas Turbine Inlet Fogging Location Relative to the Silencer

[+] Author and Article Information
Jobaidur R. Khan1

Energy Conversion and Conservation Center,  University of New Orleans, New Orleans, LA 70148-2220jrkhan@uno.edu

Ting Wang

Energy Conversion and Conservation Center,  University of New Orleans, New Orleans, LA 70148-2220twang@uno.edu

Mustapha Chaker

 BECHTEL Corporation, Houston, TX 77056mchaker@bechtel.com

1

Corresponding author.

J. Eng. Gas Turbines Power 134(2), 022001 (Dec 16, 2011) (9 pages) doi:10.1115/1.4004044 History: Received April 12, 2011; Revised April 13, 2011; Published December 16, 2011; Online December 16, 2011

The output and efficiency of gas turbines are reduced significantly during the summer, especially in areas where the daytime temperature reaches as high as 50°C. Gas turbine inlet fogging and overspray has been considered a simple and cost-effective method to increase the power output. One of the most important issues related to inlet fogging is to determine the most effective location of the fogging device by determining (a) how many water droplets actually evaporate effectively to cool down the inlet air instead of colliding on the wall or coalescing and draining out (i.e., fogging efficiency), and (b) quantifying the amount of nonevaporated droplets that may reach the compressor bellmouth to ascertain the erosion risk for compressor airfoils if wet compression is to be avoided. When the silencer is installed, there is an additional consideration for placing the fogging device upstream or downstream of the silencer baffles. Placing arbitrarily the device upstream of the silencer can cause the silencer to intercept water droplets on the silencer baffles and lose cooling effectiveness. This paper employs computational fluid dynamics (CFD) to investigate the water droplet transport and cooling effectiveness with different spray locations such as before and after the silencer baffles. Analysis on the droplet history (trajectory and size) is employed to interpret the mechanism of droplet dynamics under influence of acceleration, diffusion, and body forces when the flow passes through the baffles and duct bent. The results show that, for the configuration of the investigated duct, installing the fogging system upstream of the silencer is about 3 percentage points better in evaporation effectiveness than placing it downstream of the silencer, irrespective of whether the silencer consists of a single row of baffles or two rows of staggered baffles. The evaporation effectiveness of the staggered silencer is about 0.8 percentage points higher than the single silencer. The pressure drop of the staggered silencer is 6.5% higher than the single silencer.

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Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Different types of silencers

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Figure 2

Fog nozzle manifold operating in the inlet duct of a GE-7EA gas turbine [7]

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Figure 3

Gas turbine inlet duct showing different subdomains and postprocessing planes

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Figure 4

Dimension of the domain

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Figure 5

Meshed computational domain consisting of a mix of 231,000 structured and unstructured cells

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Figure 6

Droplet-wall interaction models [22]

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Figure 7

Temperature distributions for different cases on different axial planes

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Figure 8

Temperature distributions for different cases on the longitudinal midplane along the duct. (The gaps are due to the plane cutting through a silencer baffle, which is not included in the computational domain. The circles in each figure show the cross-sectional temperature distribution at the compressor bellmouth inlet.)

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Figure 9

Velocity vectors for different silencers (circulation is shown by arrows)

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Figure 10

Air pathlines surrounding the silencer’s staggered baffles

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Figure 11

Static pressure distribution across the baffles

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Figure 12

Droplet traces colored by the droplet Reynolds number surrounding the silencer baffles

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Figure 13

DPM concentration for mid-horizontal plane for the cases where fogging is applied upstream of the silencer

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