1 Chaker - Evaporative Cooling of Gas Turbine Engines

Mustapha Chaker

Cyrus B. Meher-Homji

Bechtel Corporation,

Houston, TX

Evaporative Cooling of GasTurbine EnginesThere are numerous gas turbine applications in power generation and mechanical driveservice where power drop during the periods of high ambient temperature has a verydetrimental effect on the production of power or process throughput. Several geographi-cal locations experience very high temperatures with low coincident relative humidities.In such cases media evaporative cooling can be effectively applied as a low cost poweraugmentation technique. Several misconceptions exist regarding their applicability toevaporative cooling, the most prevalent being that they can only be applied in extremelydry regions. This paper provides a detailed treatment of media evaporative cooling, dis-cussing aspects that would be of value to an end user, including selection of climaticdesign points, constructional features of evaporative coolers, thermodynamic aspects ofits effect on gas turbines, and approaches to improve reliability. It is hoped that this pa-per will be of value to plant designers, engineering companies, and operating companiesthat are considering the use of media evaporative cooling. [DOI: 10.1115/1.4023939]

1 Introduction

Gas turbine output is a strong function of the ambient air tem-perature with power output dropping by 0.50.9% for every 1 Crise in ambient temperature (0.30.5% per 1 F). There is also aconcurrent heat rate increase of about 5%.

Aeroderivative gas turbines exhibit even a greater sensitivityto ambient temperature conditions. A representation of thepower boost capability for given inlet cooling potential for dif-ferent types of gas turbines is shown in Fig. 1. The drop in per-formance due to high ambient temperatures can be furtheraggravated with gas turbine recoverable and unrecoverable per-formance deterioration due to several factors as presented inMeher-Homji et al. [1].

To recover the power lost due to high ambient temperature, it isadvantageous to deploy power augmentation technologies such asevaporative cooling. This technology has been considered as asimple and cost-effective method to increase power output andalso improve thermal efficiency.

This paper presents a detailed review of evaporative coolingtechnology covering the thermodynamics and practical aspectsrelating to design and operation.

Several papers have been published to address the media typeevaporative cooling [24].

2 Overview of Media Evaporative Cooling

Traditional media-based evaporative coolers have been widelyused in the gas turbine industry for several decades, especially inhot arid areas. The basic principle of evaporative cooling is that aswater evaporates, it cools the air because of the latent heat ofvaporization.

Traditional evaporative coolers are described in detail by John-son [2,3].

Evaporative cooler effectiveness is given by

E T1DB T2DBT1DB T2WB (1)

where T1 is the inlet temperature of evaporative cooler, T2 is theexit temperature of evaporative cooler, DB is the dry bulb, WB isthe wet bulb.

A typical value for effectiveness is 8590%.The temperature drop assuming an effectiveness of 0.9 is given

by

DTDB 0:9 T1DB T2WB (2)

A psychometric chart can be used to obtain the value of the wetbulb temperature (WBT). The exact power increase depends onthe particular machine type, site altitude, and ambient conditions.

The presence of a media type evaporative cooler inherently cre-ates a pressure drop of approximately 2.54 cm (1 in.) water gauge(WG) [5] that results in a drop in turbine output. As a rough ruleof thumb, a 2.54 cm (1 in.) WG increase in inlet duct losses willresult in a 0.350.48% drop in power and a 0.12% increase in heatrate. These numbers would be somewhat higher for an aeroderiva-tive machine. Increases in inlet duct differential pressure willcause a reduction of compressor mass flow and engine operatingpressure. Increase in inlet differential pressure results in a reduc-tion of the turbine expansion ratio.

Water quality requirements for media evaporative coolers [2]are, less stringent than those required for direct fog cooling

Fig. 1 Representation of power boost by inlet air cooling

Contributed by the Heat Transfer Committee of ASME for publication in theJOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received January18, 2013; final manuscript received March 1, 2013; published online June 24, 2013.Editor: David Wisler.

Journal of Engineering for Gas Turbines and Power AUGUST 2013, Vol. 135 / 081901-1CopyrightVC 2013 by ASME

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systems [6]. Media type cooling requires more water for blowdown and water quality problems can lead to the removal ofmedia pads more frequently than the normal time frame. In somecases, media has been replaced by fogging systems as describedby Ingistov and Chaker [7]. Media evaporative cooling systemshave successfully been used in industry for several years. Thebasic layout of a media type system is shown in Fig. 2.

Media-based coolers typically have low installation and operat-ing costs when compared to chilling systems. Operation costsare low due to the inherent simplicity of the system and limitedauxiliary equipment needed. Potable water can be used especiallyif a drift eliminator is utilized to minimize risks of water carry-over. Typically media change out is required every 35 years,depending on the quality of water used, media deterioration, andnumber drying cycles.

3 Climatic and Psychrometric Aspects of EvaporativeCooling and a Review of Climatic Databases

3.1 Climate Evaluation Issues. A major obstacle faced bygas turbine users in analyzing the potential for evaporative cool-ing is that there is sparse climatic data available in a form thatusers can make a decision on the benefits of evaporative cooling.The obstacle may be broken into three factors:

Operators cannot easily locate the appropriate weather datafor their site. Much of the data is available at a plant site maybe based on average data points with no representation of thevalues of coincident dry temperature and relative humidity.These data are invaluable when evaluating any evaporativecooling solution.

Even when some appropriate data are available through web-sites or other sources, the data tables and information are notin a format to enable an operator to rapidly access the poten-tial of evaporative cooling. The data have to be considerablymassaged and numerically analyzed before a meaningful esti-mate can be made of cooling potential at the site.

There are a wide variety of databases, each providing specifictypes of climatic data.

The authors are aware of several locations where evaporativecooling was not considered due to the general perception that the

location was a high humidity region. While it is axiomatic thatevaporative cooling is more effective in desert-like regions, acareful climatic analysis will often show that considerable coolingpotential even in coastal high humidity regions. In some mechani-cal drive applications, even moderate power boosts of turbinescan have significant economic benefits. For example, an offshoreplatform in the Arabian Gulf (envisioned as a high humidityregion) utilizing mechanical drive gas turbines was able to utilizefog evaporative cooling and derive significant benefit to the plat-form operation [9].

Chaker et al. [10,11] have provided a detailed analysis of theevaporative cooling potential in terms of equivalent degree cool-ing hours (ECDH) for a large number of sites in the U.S. and forinternational locations. Equivalent cooling degree hours is a mea-sure of the evaporative cooling potential available, in terms of theproduct of the degrees of cooling available and the hours forwhich they are available. McNeilly [12] has provided a detailedstudy on the importance of accurate climatic data when evaluatinggas turbine inlet cooling projects.

3.2 Relationship Between Relative Humidity and AmbientDry Bulb Temperature. There are numerous problems and diffi-culties when modeling climatic dataseveral of which derivefrom the concept of averaging of data. One example of this isusing averaged data of wet and dry bulb temperature. Any dataused for climatic analysis for an evaporative cooler must reflectcoincident web bulb (WB) and dry bulb (DB) conditions. It is ad-visable that the sites temperature profile for a full year of hourlydata with the 20 years being represented wet and dry bulb coinci-dent temperatures be considered in the analysis. These data can beused to generate evaporative cooling degree hour (ECDH) num-bers for each hour of the year and allow a turbine operator tomake a very detailed and accurate analysis of potential powergain from wet media evaporative cooling.

High relative humidity conditions do not occur with high drybulb temperatures. A typical pattern of variation of dry bulb andwet bulb temperature over a day is depicted in Fig. 3. As can beseen, during the afternoon hours, there is a considerable differencebetween the wet bulb and dry bulb temperatures. It is this spreadthat allows the use of evaporative cooling.

A common mistake made by users is to take the reported highrelative humidity and temperature for a given month and base thedesign on these. The problem is that the high relative humiditygenerally occurs time-coincident with the lowest temperature andthe lowest relative humidity occurs with the highest temperatureas shown in Fig. 3 below. This mistake results in the erroneous

Fig. 2 Media type evaporative cooler (courtesy CCJ, [8])Fig. 3 Typical inverse variation of relative humidity with ambi-ent dry bulb temperature during the day

081901-2 / Vol. 135, AUGUST 2013 Transactions of the ASME


conclusion that very little evaporative cooling can be accom-plished and has historically been the underlying cause of themaxim that evaporative cooling is not possible in so-called highhumidity regions.

The dry bulb versus wet bulb relationship for a dry region(Riyadh, Saudi Arabia) is shown in Fig. 4. This represents anextremely dry area with cooling potentials of as high as 28 Cbeing available.

Corresponding data from what is considered a high humidityregion is shown in Fig. 5.

While it is true that the available cooling is lower than a lowhumidity region, there is still a valuable cooling potential of78 C available during the times when ambient temperatures arehigh, which can result in power boosts of around 5%.

3.3 Selection of Climatic Design Point. The decision as towhich power augmentation approach should be deployed shouldtake into consideration the characteristic of the gas turbine, theimportance and nature of the augmented power, the coolingpotential and psychrometrics of the site, the payback period, andthe advantages and disadvantage of each technology. With evapo-rative coolers, the question as to the selection of the design pointis illustrated using Fig. 6, which shows a historical database of

ambient dry bulb temperature (DBT) and relative humidity (RH)for a particular site. As is quite typical the coincident humiditiesat higher ambient temperatures are low, but considerable scatterin the RH exists at a temperature of say 30 C.

For the design of a media evaporative cooling system, themedia is maintained wet and the makeup water is a function of theevaporation and blowdown. The system is, therefore, designed interms of water consumption for the most severe conditions. Amore important and interesting question is that for an ambienttemperature of 30 C, what coincident relative humidity should beconsidered to determine the power boost of the gas turbine.

As shown in Fig. 7 an evaporatively cooled LM6000PF engineat 30 C would vary in output from 36 MW when the RH is 80%to a power of 41 MW when the RH is 20%. Often the mostappropriate RH to be considered may be the median RH at thattemperature so that 50% of the points are above it and 50% below.In a media evaporative cooling system, the selection of the designpoint will impact the available power considered in the projecteconomics and have a minimal impact on the evaporative coolerhardware design.

Sizing of a gas turbine cooling system is generally based onhistorical weather psychrometric data, mainly temperature andcoincident relative humidity. Each cooling technology has condi-tions/characteristics related to specific design criteria to maximizepower output, economics, and investment return.

There are two parts to this fundamental issue:

The impact on the design of the cooling system. For mediabased cooling systems, where the media is kept wet withwater, this issue becomes less important as the evaporationrate will be governed by the actual site relative humidity.

Fig. 4 Data for Riyadh showing the relationship between DBTand WBT. At 40 C, a wet bulb depression of approximately21 C is available.

Fig. 5 Data for Rio, Brazil showing the relationship betweenDBT and WBT. At 36 C, a wet bulb depression of approximately7 C is available.

Fig. 6 Database showing hourly bin data of DBT versus RH forone year

Fig. 7 GT output power for different combinations of RHand DBT with media evaporative cooling (evaporative coolerefficiency590%)

Journal of Engineering for Gas Turbines and Power AUGUST 2013, Vol. 135 / 081901-3


The impact on the power boost that can be derived. This is anextremely important point to be considered as the project eco-nomics are often related to the power augmentation levelattainable. In evaporative cooling systems, selection of con-servative relative humidities (i.e., higher humidities that areactually expected) would result in a conservative estimationof power (lower power boost).

In media type evaporative cooling systems there are two issuesthat impact the design as described in Chaker and Meher-Homji[13]the evaporative cooling efficiency and the selection of thecoincident relative humidity. The selection of design points for aparticular location (Fig. 8) along with the wet bulb depressionattainable for varying levels of media evaporative cooling effi-ciency are shown for the 41.6 C DBT point. It can be seen thatthe impact of media evaporative cooling efficiency (variedbetween 85%, 90%, and 95%) is relative small compared to theselection of the coincident RH point. Actual site data for the samelocation are shown in Fig. 9 with the design point dry bulb tem-perature superimposed on it. It can be seen that there is a higherwet bulb depression (WBD) available for this site and with thisdesign point, the power boost derived will be underestimated.(i.e., a more conservative approach).

4 Evaporative Cooling Degree Hours

4.1 Evaporative Cooling Available in Different ClimaticRegions. It is known that evaporative cooling technology workswell in hot and dry areas. This technology can boost the gas

turbine power significantly as the relative humidities are quite lowfor several dry bulb temperatures as shown in the Figs. 10 and 11below. These figures, which represent hourly data for a year, werederived from Typical Meteorological Year (TMY) databases [13]and, consequently, include coincident bin data of 20 years. It canbe seen that most of the cooling occurs at high temperature andlow relative humidity with a few hours at low temperature andhigh relative humidity. In such hot and dry locations, the powerboost can be comparable to that obtained from a more costly andcomplicated mechanical chiller system [13].

Even the most humid environments allow for up to 8 C (15F)of evaporative cooling during the hotter part of the day. The termrelative humidity refers to the moisture content in the airrelative to what the air could hold at that temperature. In con-trast absolute humidity is the absolute amount of water vapor inthe air (normally expressed in unit mass of water vapor per unitmass of air).

The moisture-holding capacity of air depends on its tempera-ture. Warmer air can hold more moisture than cooler air. Conse-quently, relative humidity is highest during the cool morning andevening hours and lowest in the hot afternoon hours. This sectionfocuses on the availability of evaporative cooling in selected highhumidity regions.

A plot of relative humidity versus DBT in a humid regionsuch as Houston, TX is shown in Fig. 12. Considerable coolingpotential exists when the ambient temperature is above 35 C and

Fig. 8 Selection of design point for gas turbine inlet air cool-ing system showing insensitivity to evaporative cooler evapora-tive efficiency. All DBT values shown are greater than 41.6 C.

Fig. 9 Selection of design point for gas turbine inlet air cool-ing system (evaporative cooling) shown with actual site data;DBT values shown greater than 35 C

Fig. 10 Relative humidity versus DBT for Phoenix, AZ

Fig. 11 Relative humidity versus DBT for Riyadh, Saudi Arabiashowing significant evaporative cooling potential for the year



even at the lower temperatures (for example, between 2030 C);considerable scatter exists in the relative humidity indicating thatevaporative cooling potential exists.

In several mechanical drive operations such as liquefied naturalgas (LNG), excess power can directly translate to increased LNGproduction and the economic benefits of this can be significant.The power boost for different DBT and RH conditions for a typi-cal gas turbine with a powertemperature lapse rate of 0.7%/C isshown in Fig. 13. In examining the graph, at temperatures around40 C, even humidities of 6080%, will result in power boost ofaround 24% which can be very significant in mechanical driveapplications.

4.2 Evaporative Cooling Degree Hours (ECDH)Calculations. The evaporative cooling degree hours (ECDH) isdefined as a number (C-hours) that defines the total amount ofcooling that can be derived in a given time period [10,11]. Thetotal ECDH is arrived at by summing the ECDHs derived daily,monthly, or yearly at a given location.

The ECDH is chosen with a lower limit of minimum wet bulbtemperature (MWBT) varying between 7.2 C (45 F) and 12.8 C(55 F). The MWBT depends on the airflow velocity at the

compressor bellmouth for a given gas turbine1 and is selected inorder to avoid the possibility of inlet icing. In Fig. 14 below, theminimum wet bulb temperature was set at 7.2 C (45 F). This

Fig. 12 Relative humidity versus DBT for Houston, TX

Fig. 13 Representation of power boost in % for different drybulb temperatures and relative humidities, assuming evapora-tive cooling with evaporative cooling efficiency of 90%

Fig. 14 Representation of ECDH over 12 months by dailyperiod of 3h

Fig. 16 ECDH as function of MWBT for different databases fora hot and dry location and a warm and humid region

Fig. 15 Representation of ECDH at different time of the day asfunction of wet bulb depression in increments of 0.56 C (1 F)

1Aeroderivative engines typically operate at higher inlet Mach numbers resultingin higher inlet temperature depressions.



means that the ECDH is calculated as the difference between thecoincident dry bulb temperature and the wet bulb temperaturemultiplied by the number of hours that this difference exists ifthe WBT is above 7.2 C (45 F). If the WBT is below 7.2 C(45 F) and the DBT is above 7.2 C (45 F), the ECDH is equal tothe difference between DBT and 7.2 C (45 F) multiplied by thenumber of hours of occurrence. If the DBT is below 7.2 C(45 F), the calculation is not done and no evaporative cooling isderived.

By knowing the ECDH at a given location, a gas turbine opera-tor can easily compute the kW-hours of capacity available by theuse of power augmentation compared to the situation if there wasno power augmentation. In order to do this, the ECDH numberwould be multiplied by the turbine specific kW/C cooling num-ber. This can be obtained from the gas turbine original equipmentmanufacturers (OEMs) curves. For example, if the ECDH is80,000 degree-hours, then a gas turbine such as the LM6000 thathas a power lapse rate of approximately 537 kW/C, the kW-hoursgained would be 80,000 537 0.9 38,664,000 kW-h, where0.9 is the cooling effectiveness.

A representation of ECDH over 12 months and the hours of theday in which they occur is depicted in Fig. 14. As can be seen, theECDH between the months of April and October are over 2000and the majority of these occur in the afternoon high demandpower period where there is a high wet bulb depression. A barchart showing the wet bulb depression (in increments of 0.56 C)during this time is shown in Fig. 15.

ECDH data can also be examined more closely to account fordifferences in energy market values at different times of the year.For example, study of data could provide an estimate of the reve-nue stream during the hot summer months alone. An economicevaluation can then be developed on a month-by-month basisknowing the site-specific economic criteria.

Meteorological conditions can vary dramatically from year toyear for a given site but the approach presented here represents areasonable estimate of what can be expected for any given yearwith inlet cooling.

Very often, hourly bin weather data for a location in which agas turbine cooling system to be installed are not available. In thiscase, one would have to look for available weather databases forthe close location to the site under consideration. Differentaspects should be considered when deciding on the use of a givenweather database. This includes geographical conditions such asthe distance between the weather station and location of the gasturbine, altitude, and relative distance from sea, which canconsiderably affect the relative humidity and, consequently, theWBD.

4.3 Use of Equivalent Cooling Degree Hour (ECDH)Numbers. Many types of weather databases are available. Thisincludes typical or representative modified weather databasessuch as Typical Meteorological Year (TMY), EngineeringWeather Data (EWD), International Station Meteorological Cli-mate Summary (ISMCS), and exact bin data collected over theyears such as Integrated Weather Surface (IWS) hourly observa-tions. The typical and representative databases are developedbased on methodologies that reject extreme (very rare) weatherconditions. The newly developed databases such as TMY3 appearto be more reliable. The IWS data include exact (actual) data col-lected for a specific year.

A comparison between typical/representative weather data(TMY2, TMY3, and EWD) and exact hourly bin data (IWS) col-lected over the last five years is compared in terms of ECDH. Thiscomparison is done for two locations with different climaticprofiles:

warm and humidHouston, TX hot and dryPhoenix, AZ

The analysis shows the expected results that would be derivedif a project were developed using a specific database versus theactual results that would have been achieved over the time framebased on actual historical data. The data were examined for miss-ing data and other errors and corrections made using standard

Fig. 17 Psychrometric chart indicating evaporative cooling LM25001 simple cycle



metrological techniques. Calculations were then made for ECDHvalues2.

The yearly ECDH is plotted in Fig. 16, respectively, as a func-tion of applied MWBT. This figure confirms the general tendencyof underestimation of the ECDH by the typical/representativeweather databases when compared with the actual collected bindata (IWS data) independent of imposed MWBT.

It is important to note that even though the total ECDH numberis relatively low for Houston (approximately 25,000 C-h at a

MWBT of 15 C) evaporative cooling benefits will be significantduring the high dry bulb temperature conditions when the coinci-dent relative humidity is low.

In a hot and dry climate such as Phoenix, AZ, and as expected,there is a sizable ECDH cooling potential as shown in Fig. 15. Fora MWBT of 10 C, there are over 80,000 ECDH.

For hot and dry weather conditions, evaporative cooling canboost the gas turbine power to a similar extent compared tomechanical chiller technology [13].

The tendency of underestimating the cooling potential based onrepresentative databases (TMY, EWD, and ISMCS) when com-pared to actual measured data (IWS data) can be seen in Fig. 16.

Fig. 18 LM25001 G4 (simple cycle) (a) without evaporative cooling (above) and (b) with evaporative cooling

2This approach is very data intensive with file sizes exceeding 60 MB.



5 Impact of Evaporative Cooling on Gas TurbineCycle

5.1 Evaporative Cooling Impact on Gas Turbine Cycle(Simple Cycle). In order to examine the impact of evaporativecooling on a gas turbine cycle, a LM2500 engine has been mod-eled with and without evaporative cooling. The starting ambientconditions 40 C and 40% RH and the final ending point afterevaporative cooling are plotted on a psychometric chart (seeFig. 17). As shown in Fig. 18, the engine produces 25,391 kWwithout evaporative cooling and 28,812 kW with evaporativecooling. The amount of water evaporated in the cooler is0.3546 kg/s. The figure shows all the key cycle parameters andthe fuel conditions. As expected the heat rate improves, but theamount of fuel consumed increases.

5.2 Evaporative Cooling Impact on Gas Turbine CombinedCycle. The impact of evaporative cooling on a combined cycle usexamined here. Two combined cycles based on a heavy dutyFrame 6B unit have been designed, one optimized for a situationwith evaporative cooling and one without. The following assump-tions are made:

number of pressure levels 2 condensing steam turbine water cooled plant

The cycle flow schematics are shown in Fig. 19 for the com-bined cycle configuration without the evaporative cooler and inFig. 20 with the evaporative cooler. The comparative performanceis shown in Table 1 below.

The power boost for range of gas turbine with and without ofevaporative cooling is shown in Table 2.

6 Practical Aspects Relating to Evaporative Cooling

Media type evaporative coolers should be placed after the filtersand should always have mist eliminators located downstream ofthe coolers.

6.1 Issues With Evaporative Media Coolers. The mainissue with evaporative media coolers is droplet carryover. Unlikefogging systems, the droplet sizes can be very large and ifentrained in the airstream can cause compressor erosion problems.However, with proper design of the system this can be minimized.Important design criteria include:

Design air velocities across the media should be kept moder-ate (below approximately 200 m/min).

Water distribution rates should be maintained between 0.7 to2 liters per second per square meter of surface area of the dis-tribution pad (this is a function of site humidity).

Downstream drift eliminators if used, will almost eliminaterisk of spray carryover.

Fig. 19 Cycle flow schematic Frame 6B combined cycle (no evaporative cooling) with condensing steam turbine. Net power53MW.



Additional causes that contribute to water carryover that can beavoided by the use of an installation checklist include:

Incorrect media installationmedia is installed upside downor backwards.

Damaged mediausually damage occurs when media isreinstalled after it has been removed in the field. A commonarea of damage is at the media edge where the media isforced back into position. This often results in open cracksbetween media sections.

Media strips have excessive lateral misalignment resulting in3=4 in. or more gaps between media strips or a gap at the sidehousing.

Media not sealed against retainermedia must be firmlysealed against the media retainers that hold the top and sidesof the media on the downstream side of the cooler.

Uneven water distribution from the headerclogged distri-bution holes result in too much water being delivered tolocalized areas of the media.

There is distorted airflow throughout the evaporative cooler. There are scale deposits on the media.

Undetected carryover into the gas turbine compressor couldcause fouling of the compressor blades, and inlet guide vanes. Inextreme cases, first stage blade erosion can occur.

Media-based coolers are adaptable for using potable qualitywater. Once the water analysis has been evaluated and the bleedor blow down rate of the cooler has been calculated to maintainrecommended parameters, the system can operate with minimalintervention. Periodic inspection and water analysis should bedone on a recommended schedule. A preferred approach is to usea conductivity meter that could be tied into an alarm system. Thistype of instrumentation monitors the sump water quality and couldfacilitate the adjustment of blow down rates.

Demineralized water can be used with evaporative coolers, butit may react with stiffening agents in the media and could soften itto the point of collapse. If demineralized water is used, additionalsafeguards need to be taken in regard to the material used for thepiping and downstream components. Galvanized material shouldnot be used. The cooler housing and water piping should be con-structed of 304 stainless steel, and the media should be con-structed with increased stiffening agents. Typical water qualityrequirements for evaporative media coolers are shown in Table 3.

Modern media type evaporative coolers use media that is typi-cally 12 in. thick and that can attain a 90% evaporation efficiency.The life of media is a important factor to consider and the mediamay have to be replaced after five years with high quality mainte-nance but this life is a function of water quality. Air leakage

Fig. 20 Frame 6B combined cycle with evaporative cooling. Net power 56,108kW.

Table 1 Comparative performance of combined cycle plant

Net power and heat rate GT power ST power

No evap cooler 53,079 kW 34,589 kW 19,614 kW7784 kJ/kwhr

With evap cooler 56,108 kW 37,250 kW 20,011 kW7791 KJ/kWhr



around the sealing perimeter of the cooling media can produce airjet velocities up to 10 m/s, increasing the potential for carryover,which is why several users utilize a droplet eliminator after themedia section to avoid compressor erosion. This droplet eliminatorcan induce an additional pressure drop. The water chemistry mustbe carefully monitored and maintained to limit plugging of air pas-sages by organic and inorganic deposits. Physical inspection of themedia during outages is recommended as is the provision of view-ing windows both upstream and downstream of the media system.

6.2 Lowest Temperature for Cooling. Several OEMs pub-lish a combination of relative humidity and temperature at whichanti icing measures are turned on. With evaporative media andfogging applications the ending relative humidity is close to100%; temperatures as low as 10 C can be utilized3. However, tobe on the very conservative side, temperatures of 12.8 C havebeen considered. Many media evaporative coolers are designed toshut off when the ambient temperature reaches 15 C.

6.3 Water Required to Saturate Air for EvaporativeCooling. The required amount of water to cool the air to mini-mum wet bulb temperature (MWBT) of 15 C (solid lines) and

30 C (dashed lines) for a series of wet bulb depression (WBD)between 5 C and 15 C is shown in Fig. 21. This figure showsthat cooling the air, for example, from 45 C to 30 C requiresaround 5% more water than to cool the air from 30 C to 15 C.

6.4 Practical Aspects, Operations, and Inspection

6.4.1 Temperature Limitations. If the ECDH number is usedto compute kW-h boost over the year, it is important to note thatthis would imply that evaporative cooling is employed wheneverthere is even a 1 C depression. There are practical limitations thatduring the cooler months; freezing conditions may occur duringthe early morning hours that may cause evaporative cooling to beshut off. Several evaporative media cooling systems are designedto be shut down when the ambient temperature reaches 15 C.

6.4.2 Evaporative Cooler Inspections. Careful inspection ofthe evaporative cooler and examining several practical features isof importance in maintaining the operational reliability of an

Table 2 Power boost for range of gas turbines with and without evaporative cooling (DBT5 32 C; RH5 50%)

Id Gas turbine

Net powercooling-off

(KW)

Net powercooling on

(KW)

Powerboost(%)

Powerboost%/ C

Powerboost

KW/ C Id Gas turbineNet powercooling-off

Net powercooling on

Powerboost(%)

Powerboost%/ C

Powerboost

KW/ C

24 ABB GT 8 40,780 42,999 5.16 0.62 267.3 113 GE 9391 G 246,850 256,787 3.87 0.47 1197.2152 ABB GT 8C2 49,460 51,662 4.26 0.51 265.2 159 GE LM2500PE 18,790 19,717 4.70 0.57 111.625 ABB GT 11N 69,860 73,192 4.55 0.55 401.4 118 GE LM6000PC 32,250 35,846 10.03 1.21 433.2110 ABB GT 11N2 97,240 102,434 5.07 0.61 625.7 161 GE LM6000SPT 33,830 35,836 5.60 0.67 241.741 ABB GT 13D2 86,770 91,063 4.71 0.57 517.2 101 KWU V64.3A 60,040 62,718 4.27 0.51 322.670 ABB GT 13E2 139,000 146,234 4.95 0.60 871.5 43 KWU V94.2 125,960 132,335 4.82 0.58 768.118 Aln 501KB5 3,020 3,216 6.08 0.73 23.6 154 Mtsb 701 F 228,760 239,861 4.63 0.56 1337.521 Aln 571KA 4,440 4,755 6.61 0.80 37.9 169 PW ST6L-813 645 698 7.55 0.91 6.3129 Asig ASE40 2,620 2,748 4.64 0.56 15.4 137 Sol Taurus 4,200 4,472 6.08 0.73 32.8151 Asig ASE50A 2,990 3,211 6.88 0.83 26.6 132 Sol Saturn 970 1,038 6.55 0.79 8.248 EGT Typhoon 3,240 3,572 9.28 1.12 39.9 188 Sol Centaur 3,820 4,058 5.86 0.71 28.7145 EGT Typhoon 4,370 4,617 5.34 0.64 29.7 97 Sol Mars 9,120 9,647 5.46 0.66 63.533 EGT Tornado 5,230 5,528 5.38 0.65 35.8 189 Sol Titan 11,170 11,918 6.28 0.76 90.11 GE 5371 PA 22,150 23,604 6.16 0.74 175.1 44 TPM FT8 21,030 22,441 6.29 0.76 170.0133 GE 6561 B 34,290 36,101 5.02 0.60 218.1 13 TPM FT4C 24,210 26,140 7.38 0.89 232.5135 GE 7241 FA 148,580 157,157 5.46 0.66 1033.3 47 W251 B12 39,940 42,448 5.91 0.71 302.1148 GE 9171E 107,746 113,266 4.87 0.59 665.0 77 W501 D5A 103,860 109,496 5.15 0.62 679.0174 GE 9351 FA 227,478 239,886 5.17 0.62 1495.0 74 W701 F 197,080 207,467 5.01 0.60 1251.4

Table 3 Typical water quality for media evaporative coolers

Constituent PPM 610%

Calcium hardness (CaCO3) 50150Total alkalinity (CaCO3) 50150Chlorides (Cl)

evaporative cooler. There are several important things that shouldbe considered, including the following:

Verify there are no gaps between media segments that allowair and water droplets to bypass the cooler.

Verify there is no water bypassing the media because thatwould reduce efficiency.

Check water flow rates and distribution. Dry streaks on themedia are indicative of poor distribution.

Examine the walls of the air inlet house downstream of thedrift eliminator for streaking. Streaking can be caused byhigh air velocity, water bypassing the evaporative cooler,and/or a defective drift eliminator.

Examine media to see if it is mushy. If it is then considerreplacement and determine the root cause.

Check media differential pressure and trend this value. If scaling is noted, check water chemistry.

Check framing, drift eliminator, sump, piping, pumps, andsupport systems for corrosion. These should be repaired asnecessary.

Verify integrity of seals, gaskets, and caulking. Flush the sump and piping system thoroughly annually or

more frequently. Send samples of the media and water to the evaporative

cooler supplier annually for evaluation.

Comparison of new and scaled media is shown in Fig. 22.Microbiological fouling of media that can be very damaging isshown in Fig. 23.

Excellent details regarding inspection and commissioning ofevaporative coolers may be found in Grace [14].

7 Summary

The demand for gas turbine power augmentation during timesof high ambient temperature for the power generation andmechanical drive market has created an increasing emphasis onevaporative cooling. Media evaporative cooling is a relatively lowcost technology that can provide considerable power boost, espe-cially during hot climates when the coincident relative humidity islow. This paper has presented a detailed review of evaporativecooling in terms of the technology, thermodynamics, and aspectsof analysis and has also covered numerous practical checklistsand issues that are very important for ensuring the operationalreliability of such systems.

Nomenclature

ASHRAE American Society of Heating and RefrigerationEngineers

CDH cooling degree hoursCCDH chiller cooling degree hours, C h (F h)

CTIT compressor target inlet temperature (with chiller)DBT dry bulb temperature, C

E evaporative cooler effectiveness (efficiency)ECDH evaporative cooling degree hours, C h (F h)EWD engineering weather data

GT gas turbineISMCS International Station Meteorological Climate

SummaryIWS Integrated Weather Surface

Fig. 22 Comparison of new media with scaled media [8]

Fig. 23 Microbiological fouling of media [8]



LNG liquefied natural gasLPM liters/minuteOEM original equipment manufacturer

OS overspray (water flow as a % of airflow rate)RH relative humidity, %

T temperature, CTMY typical meteorological yearWBT wet bulb temperature, CWBD wet bulb depression, C

MWBT minimum wet bulb temperature, C

References[1] Meher-Homji, C. B., Chaker, M., and Motiwalla, H., 2001, Gas Turbine Per-

formance Deterioration, Proceedings of the 30th Turbomachinery Symposium,Houston, TX, September 1720.

[2] Johnson, R. S., 1988, The Theory and Operation of Evaporative Coolers forIndustrial Gas Turbine Installations, International Gas Turbine and AeroengineCongress, Amsterdam, Netherlands, June 59, ASME Paper No. 88-GT-41.

[3] Johnson, R. S., 1994, Set Up and Operation of a Recirculating Wetted RigidMedia Evaporative Cooler Installed in a Gas Turbine Combustion Inlet Air Sys-tem, International Gas Turbine and Aeroengine Congress and Exposition, TheHague, Netherlands, June 1316.

[4] Hosseini, R., Beshkani, A., and Soltani M., 2007, Performance Improvementof Gas Turbines of Fars (Iran) Combined Cycle Power Plant by Intake AirCooling Using a Media Evaporative Cooler, Energ. Convers. Man. J., 48, pp.10551064.

[5] Jones, C., and Jacobs J. A., III, 2000, Economic and Technical Considerationsfor Combined-Cycle Performance-Enhancement Options, GE Power Systems,Schenectady, NY, Report No. GER-4200,

[6] Chaker, M., and Meher-Homji, C. B., 2007, Evaporative Cooling of GasTurbine Engines: Climatic Analysis and Application in High HumidityRegions, ASME Turbo Expo 2007: Power for Land, Sea, and Air (GT2007),Montreal, Canada, May 1417, ASME Paper No. GT2007-27866.

[7] Ingistov, S., and Chaker, M., 2011, Upgrade of the Intake Air Cooling Systemfor a Heavy-Duty Industrial Gas Turbine, Proceedings of ASME Turbo Expo2011, Vancouver Canada, June 610, GT2011-45398.

[8] Air Inlet System, Make it Right, 2010, Comb. Cycle J., 2Q(2010), pp. 2236.[9] Al-Amiri, A. M. M., Zamzam, M. M., Chaker, M. A., and Meher-Homji C. B.,

2066, Application of Inlet Fogging for Power Augmentation of MechanicalDrive Turbines in the Oil and Gas Sector, Proceedings of ASME Turbo Expo,Barcelona, Spain, May 811, Paper No. GT2006-91054.

[10] Chaker, M., Meher-Homji, C., Mee, T., and Nicholson, A., 2003, Inlet Foggingof Gas Turbine EnginesDetailed Climatic Analysis of Gas Turbine Evapora-tive Cooling Potential. ASME J. Eng. Gas Turb. Power, 125(1), pp. 300309.

[11] Chaker, M., and Meher-Homji, C. B., 2006, Inlet Fogging of Gas TurbineEnginesDetailed Climatic Analysis of Gas Turbine Evaporative CoolingPotential for International Locations, ASME J. Eng. Gas Turb. Power, 128(4),pp. 815825.

[12] McNeilly, D., 2000, Application of Evaporative Coolers for Gas TurbinePower Plants, International Gas Turbine and Aeroengine Congress, Munich,Germany, May 811, ASME Paper No. 2000-GT-303.

[13] Chaker, M., and Meher-Homji, C. B., 2011, Selection of Climatic DesignPoints for Gas Turbine Power Augmentation, Proceedings of ASME TurboExpo 2011, Vancouver, Canada, June 610, ASME Paper No. GT2011-46463.

[14] Grace, B., 2011, Benefits of Inspecting and Commissioning EvaporativeCoolers, accessed April 3, 2011, www.ccj-online.com/inspection-overhaul-and-upgrade-of-evaporative-cooler



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1 Chaker - Evaporative Cooling of Gas Turbine Engines

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