windows-1256__wet compression.pdf

Mohsen Assadi

L U N D U N I V E R S I T Y

Inlet Air Cooling & Wet Compression

ETN- Brussels

2006-10-12

Prof. Mohsen Assadi 2

LUN D UN IVER SITY

Inlet Air Cooling - Overview

• Why do we need inlet air cooling?

• Cooling techniques available– A short description of its functionality and

applicability

– Operating experience and analysis (PG & PG I)

• No time left for questions - do not hesitate to stopme and ask your question while still in your head


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Why Do We Need Inlet Air Cooling?

• The general benefits associated with inlet cooling are:

– Decreases the work of compression

– Increase air density also means that the gas turbinecan operate with higher mass flow

– The compressor discharge temperature is beinglowered giving the possibility to burn more fuel in orderto reach the same TIT, hence increasing power output


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Potential enhancementInlet cooling techniques

Potential performance enhancement - GT10B

15000

17000

19000

21000

23000

25000

27000

0 10 20 30 40 50 60

Ambient temperature [C]

Pow

ero

utp

ut[

kW]

ISO conditions GT10B

Media based evaporative cooler, RH 60%

Media based evaporative cooler, RH 30%

Fogging, RH 60%

Fogging, RH 30%

Chiller, RH 60%

Chiller, RH 30%

Cooling notapplicable dueto icing risk

ISO

RH 60%

RH 30%

Chillers


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Cooling Techniques AvailableMedia based evaporative cooler

Wet compressionInlet fogging

Mechanical Chiller


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Cooling Techniques AvailableMechanical Chiller

• Mechanical chiller– Refrigerant cooling technique– Has cooling coils placed in the airstream– Consists of

• One huge fridge• Inlet coils• Cooling tower


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• Found in study– Performance

• Can cool the inlet air back to 15°C from any ambient condition– Great power output augmentation. 15% at 35°C and 50% RH

• The gas turbine will regain its original efficiency

– Economy• Expensive, High investment, and O&M costs• Construction time is 6-9 months and require a turbine down time

about 7-10 days

– Advantages• Not susceptible to ambient conditions

– Disadvantages• Large footprint, bulky construction, water tower• Require large face area across chilling coil• Added pressure drop in the air intake system


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Cooling Techniques AvailableMedia Based Evaporative Cooler

• Based on the principle of adiabatic saturation• Media where water and air interacts is

placed in the airstream– Water evaporates from the surface– The air is cooled by the latent heat of

vaporization• Consist of:

– Media based cooler unitDistribution padsMedia


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Cooling Techniques AvailableMedia Based Evaporative Cooler


• Usually have an effectiveness of 85-90 %• Increases the power output. 5 % at 35°C and 50% RH

– Economy• Investment cost is low. About 1 00 000 Euro• O&M is low. Media change every 3 year• Construction time: 30 days. Turbine down time 7-10 days

– Advantages• Low risk for overspray, Passive system• Potable water can be used• No integration with GT needed

– Disadvantages• The effectiveness is limited by ambient conditions• Added pressure drop in the air intake system


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Cooling Techniques AvailableInlet Fogging

• Based on the adiabatic saturationprocess

• Water is injected through nozzles

– Small droplets in the airstream

– Droplets evaporate and air iscooled

• Consists of

– Pump skid

– Nozzle rack


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Cooling Techniques AvailableInlet Fogging


• Effectiveness around 90-97 %• Increases the power output. 6 % at 35°C and 50% RH

– Economy• Investment cost is low. About 60 000 Euro• O&M is low. Nozzle replacement every 2nd year• Construction time: 20 days. Turbine down time 2-3 days

– Advantages• Achieves lower inlet temperature compared to media based evap.• Requires small footprint• No added pressure loss in air intake system

– Disadvantages• Integration with GT control system required• Demineralized water needed• Large droplet can cause erosion• Require inlet drain consideration & careful implementation


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EU Related Projects• Based on the adiabatic saturation process• Achieves cooling by

– Normal evaporative cooling– Intercooling effect in compressor

• Water is injected through nozzles– Small droplets in the air stream– Droplets evaporate and air is cooled

• Consist of:– Pump skid– Nozzle rack

Wet compressionrecommended location of

installation


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Cooling Techniques AvailableWet Compression

Power output vs. ambient temperature


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• Found in study Performance

Great power output augmentation. Increases by 10-15 %Great efficiency augmentation. Improves and regain efficiency by 1-3 %

Economy Investment cost about 3 00 000 Euro Low O&M costs. Nozzle replacements every 2-3 year Construction time: 30 days. Turbine down 5 days

AdvantagesMore independent of ambient conditions Can be placed downstream of media based cooler or inlet fogging

DisadvantagesMust be integrated with GT control systemGas turbine adjustments might be needed to adapt to new operating

conditions for compressor and combustor Risks associated with wet compression


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Wet Compression EvaluationResults

C - absolute velocity

W - relative velocity

Ca - axial velocity

U - blade rotational speed

• Velocity triangles

Axial velocity is lowered

Leads to off-design blade operation

Blade angles is no longer optimized to

the flow

Increased risk for stall and surge

Increased fouling is seen in the latter

stages. Increased incidence angles

can be the explanation

Rear stage


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• For a first time wet compression installation a couple of issues needsto be investigated

PulsationComponents life


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Operating Experiences

• Operating experience– Leading edge erosion seen. Worst at row 1 blades and

decreases downstream. In a 16 stage compressor, lastsigns of erosion can be seen at stage 12.

– Pitting corrosion is considered a medium risk if thesystem is not running constantly.

– Other potential risks have not been encountered orhave successfully been mitigated.


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Operating Experiences

• Erosion on inlet guide vane• Pitting corrosion potential


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Summation and Analysis• Media based evaporative cooler is well-known and proven technique

– Should be recommended for the present

• Inlet fogging is a cost-effective and promising technique but– Should be used on certain GT with enough inlet duct length

• Mechanical chillers– Great power output– Expensive and bulky installations. Inconvenient technique for medium

sized gas turbines.

• Absorption chillers– Great power output– Expensive and bulky installations. Promising technique if cheaper

• Wet compression– Great performance enhancement– Cost-effective and flexible. Involves a lot of unknown risks.– If risks can be mitigated, this technique is the best alternative


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windows-1256__wet compression.pdf

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