2 gas turbine_ air inlet system

Dr. Walid Abdelghaffar

Dr. Walid AbdelghaffarGas Turbine- Air Inlet System

Gas turbines applications

• Aircraft• Power plants• Standby equipment• Boat and ship propulsion• Gas pipeline compressor drives• Railroad (have been used but are not common)• Automotive (extensive experimentation in the past)

• Heavy mobile equipment (experimentation)

Simplified Air-Flow Turbine Diagram


Major Gas Turbine Components


When the turbine starting system is actuated ambient air is drawn through the air inlet plenum assembly by the Compressor through Variablecompressor Inlet Guide Vanes (IGVs).

The inlet casing is located at the forward end of the gas turbine. Its prime function is to uniformly direct air into the compressor. The inlet casing also supports the No. 1 bearing assembly.


Basic Turbine Operation


Comparison of Events in Gas Turbine and Piston Engines


The axial flow gas turbine is one of the most common gas turbine engine designs.

The figure shows the simplified airflow through an axial flow gas turbine.

As you can see from the red flow lines, the air flows in a straight or axial path from one end of the gas turbine to the other.

Axial Flow Design


The purpose of the engine case in an axial flow gas turbine engine is to house and protect internal engine parts.

The engine case usually consists of two parts, a top half and a bottom half.

This type of construction allows easy access to the internal engine parts.

Axial Flow Design


•Another main component of a gas turbine engine is the air inlet system. •Air is delivered to the gas turbine engine air inlet through the air inlet system. •The purpose of the air inlet system is to carry clean, dry air to the compressor with minimum turbulence and energy loss.

•The outside covering of the air inlet system is called ducting and is usually made of galvanized or stainless steel.•The exterior of the ducting and the inlet support structure should be painted to protect them from damage caused by corrosion.•Salt air will quickly corrode any unprotected exterior surfaces.

Air Inlet System: Purpose


Air intake system

The air intake system ensures that clean air is provided to the gas turbine. To achieve this, air filter are installed in the intake to filter the air.The type of air intake system is dependent in the environmental condition encountered at the gas turbine location. Special challenges are posed when a gas turbine is installed on an offshore platform, close to the ocean, in a desert or dusty location, or in an arctic environment. The intake system become more complicated if intake cooling (to increase power at high ambient temperatures) is required, or if icing condition may occur.


Air intake system

A typical intake system is shown in Fig. Note that in this design, the air intake is positioned above the enclosure both to save space and to place the intake in a higher position where the air may be cleaner. The intake is designed to allow the installation of intake cooling and/or anti-icing. The first stage of filtration is a stainless steel screen to prevent entry of major debris. The main filtration is achieved by a series of cylindrical filters mounted inside the air intake.

Typical Air Intake System(Courtesy General Electric)


Air intake system

Air FiltrationAir FiltrationIn the past, many filter systems were based on inertial filtering which consisted of a series of vanes that deflected the air to separate the contaminants, using centrifugal force. The current approach is to use many small cylindrical filters such as the ones shown in Fig. In this system, compressed air is used to backflow individual filters and dislodges the dust that has collected on them. These “pulse cleaning systems” are commonly called “huff and puff”, and operate automatically, based on pressure differential. They work well in both dusty and cold weather conditions

Pulse Cleaning Filter (Courtesy Donaldson Filters)Pulse Cleaning Filter (Courtesy Donaldson Filters)


Air intake system

Inlet CoolingInlet CoolingInlet cooling systems that decrease the temperature of the inlet air and thereby increase power output have been available for a long time but are now seeing renewed interest. They are based on the principle of evaporative cooling. When water evaporates, it requires a large amount of latent heat, which is provided by the warmer air. The result is a drop in air temperature.Various methods are used today:

• Spray cooling where air is sprayed into the intake in fine droplets• Fog cooling where a very fine fog is produced using a high

pressure spray• Special evaporative pads

A New Gas Turbine Cycle for Economical Power Boosting

(WAC System : Water Atomizing Cooling)


Water Atomizing Cooling

Concept of WAC System:

3) The rest of water reduces compressor work through evaporating and cooling compressor internal air.

2) Injected water fog reduces gas turbine inlet air temperature due to evaporation, which results in air

flow rate increase.

1) Gas turbine power augmentation with water injection

atomized at compressor inlet

4) Evaporated water can increase turbine work due to the same principles of steam injection into combustor.



WAC System Schematic

Spray Nozzle

Inlet Duct

Feed Water (Demineralized)

Atomizing AirFuel

HRBCompressor Turbine


Benefits of WAC for Gas Turbines


1) Increased Capacity

2) Improved Efficiency

3) Good Application for Peaking Generation

4) More Effective Use of Base Capacity

5) On Demand, on Line Operability

6) Reduced NOx Emission Level and NH3 Consumption

7) Compressor Washing Effect



Mechanism

C T

TC

C T

� Inlet Air

Cooling

CompressorMass FlowIncrease

� CompressorInter-cooling

Compressor Work Decrease

� Steam

Injection Larger Specific Heat

Total

6%

2%

2%

10%

PowerIncrease

Turbine Mass Flow Increase

WAC System Mechanism


Spe

cific

Hum

idity

(kg/

kgD

A)

Dry Bulb Temperature

100%R.H.Psychometric Chart

23 30

A (Ambient Condition)

C

60%R.H.

Equi - Wet Bulb Temperature

B

Evaporationin

Compressor

Evaporationin Inlet Duct

(Compressor Inlet)



Calculated Evaporation Profile in Compressor

0102030

405060708090

100

1 2 3 4 5 6 7 8 9 1011121314151617Compressor Stage Number

(Axial Position)Atmosphere

Inlet DuctIGV

Tota

l Eva

pora

tion

Rat

e (%

)

Machine : F9EComp.Inlet Temp. : 15�Droplet Size : 10μm



WAC Test Facility (1/2)

Water Fog from Water Spray Nozzles



Water Atomization Technology for WAC

1) Water droplets must evaporate completely in compressor stages within the residential time of approximately 0.02 seconds.

2) Hitachi has developed new water atomization nozzlewhich can make water droplets fine enough to meet

WAC system requirements.




S (Entropy)

Heat Cycle ComparisonT

(Tem

pera

ture

)

TurbineWork

Turbine Work

Compressor Work

CompressorWork

Inlet Air Cooling

Normal Breton cycle

Breton cycle with WAC



Power Increment Characteristics of WACAmbient Condition : 30�,60%R.H.

Water Injection : 1% to Air Ratio

(1) 6%

(2) 2%

(3) 2%

85

100

0 5 23

30

Pow

er (%

)

Ambient Temperature (�)

(Wet Bulb Temp.)

(Dry Bulb Temp.)

A

B

C

Power Increment

Rated

NormalOperation

WAC Operation



WAC Validation Test Plant

Heat Recovery Steam Generator

No.2&3 Gas Turbine

No.1 Gas Turbine

Cooling System

No.2&3

Steam Turbine




Water & Air Header



Spray Nozzle Header


Compressor Inlet



Example of WAC Validation Test Results

0

2

4

6

8

10

0 0.2 0.4 0.6 0.8Water Flow Rate (%)

Pow

er In

crem

ent (

%)

0.0

0.5

1.0

1.5

2.0

2.5

0 0.2 0.4 0.6 0.8Water Flow Rate (%)

Ther

mal

Effi

cien

cy(%

rela

tive)

Test Condition1) Ambient Condition : 33.9 C, 53%RH2) Load : 95.4 MW

(+) 7.7%(+) 2.1%

0.63%0.63%



15:45 16:00 16:15

TCI

TCD

Fuel flow

TEX

Gen. power

630 l / min653 l / min

26.2�

22.6�353.1

�343.5

� 339.2�539.4

�536.6

�

102.5MW106.5MW

107.5MW

Water Flow Rate : 105 l / min (0.45%)

Water Spray on

Water Spray off

Measured transient behavior of GT performance


Hitachi WAC System Validation

4) All GT operating conditions were good during WAC operation.

3) Thermal efficiency was also improved by 2.1% on relative value basis.

2) Test results showed 7.7% power increase at 0.63%

water injection.

1) WAC system validation test was completed successfully

using 130MW simple cycle power station.



The formation of ice in the air intake or on the first few stages of the compressor can occur if a combination of temperature and humidity takes place (see Fig).If chunks of ice are ingested into the compressor, major damage can result including catastrophic destruction of the compressor section balding.

AntiAnti--Icing SystemsIcing SystemsAir intake system



Anti-icing systems may operate by:• Bleeding air from the compressor and injecting it into the front of the

compressor through the nose cone and the first few stator vanes • Installing heating coils in the air intake• Feeding heated air from some other source (such as the exhaust) into the

air intake• Introducing warm air into the gas turbine intake will reduce the capacity of

the unit, because warm air is less dense than cold air. The increase in air temperature means less mass will flow through the turbine. Because of this, anti-icing systems are activated only when icing conditions are present.


Anti-Icing System (Courtesy Rolls Royce)



The air inlet system controls the air quality and directs a steady flow of air to the compressor air inlet.

The amount and quality of air affects engine performance and reliability.

The air inlet system has two main assemblies:

· filter assembly· inlet ducting assembly

Air Inlet System: Main Assemblies


The first component of the air inlet system is the filter assembly.

The filter assembly consists of the following parts:

· weather louvers

· inlet screens

· filters( Contd. )

Filter Assembly


•The filter assembly separates moisture and particles such as dirt, dust, and insects from the inlet air. This prevents contamination and foreign object damage to the compressor. Weather Louvers, Screens, & Filters

•The purpose of the weather louvers is to prevent direct rainfall from entering the air inlet system.

Inlet screens, usually constructed of wire mesh, are designed toprevent large items and other contaminants from entering the compressor inlet.

•The inlet screens are located behind the weather louvers.Filters trap small particles of dust, dirt, and other contaminants to prevent them from entering the compressor section.

Filters are constructed of materials which meet the specific operating and climatic conditions of the gas turbine location.

Filter Assembly


The air inlet system controls the air quality and directs a steady flow of air to the compressor air inlet.

The amount and quality of air affects engine performance and reliability.

The air inlet system has two main assemblies:

· filter assembly· inlet ducting assembly

Air Inlet System: Main Assemblies


Air Filtering


The second main assembly in the air inlet system is the inlet ducting assembly which consists of the following parts:

· bypass door(s)

· inlet silencer

· trash screens

· air plenum

Inlet Ducting Assembly


Some air inlet systems have bypass doors located just downstream of the air filters.

The purpose of the bypass doors is to protect the air inlet from excessive differential pressure.

High differential pressure is usually caused by excessively dirty air inlet filters or some other abnormal blockage of the air inlet system restricting airflow through the filter.( Contd. )

Bypass Doors


Anytime the bypass doors are open during gas turbine operation, the engine is unprotected and is operating with unfiltered air.

Operating under these conditions reduces engine reliability and operating life.

Operators should take immediate action to determine why the bypass doors are open and take corrective action.

Bypass Doors


The inlet silencer is a baffle arrangement intended to quiet the noise vibration of the compressor blading.

Silencers are usually installed in both the air inlet system and the exhaust section of the gas turbine to reduce operating noise.

Silencing is accomplished by baffles covered with sound-absorbing material.

In some air inlet ducts, the interior walls of the ducting and air plenum chambers are also lined with this sound-absorbing material.( Contd. )

Silencers


Gas turbine operating noise is harmful to the human ear.

Silencers help but do not totally eliminate gas turbine noise.

If you work near a gas turbine that is operating, you should wear ear protection to avoid hearing loss.

Silencers


The trash screens are the next component in the inlet ducting assembly.

Trash screens prevent foreign objects from entering the compressor inlet.

Trash screens are installed downstream in the ducting before the compressor inlet. ( Cont. )

Trash Screens


•Access doors are provided to allow cleaning and servicing of the trash screens.

•Trash screens are constructed of stainless steel and should not require maintenance other than periodic cleaning and inspection.

Trash Screens


The final component in the duct assembly is the air plenum.

The purpose of the air plenum is to provide equal distribution of ducted air to the compressor inlet.

The air plenum is located just forward of the compressor inlet.

One of the most common types of compressor inlets is the bellmouthinlet.

Air Plenum

Air Plenum


The bellmouth inlet is a bell-shaped funnel with rounded shoulders that reduce air resistance.

A bellmouth inlet is designed to direct the outside air to the inlet guide vanes of the compressor.

In some gas turbines, the inlets are fitted with protective screens to prevent foreign objects from entering the compressor.

Bellmouth Compressor Inlet

Dr. Walid Abdelghaffar

2 gas turbine_ air inlet system

Documents