INLET AND EXHAUST SYSTEM

 

GENERAL INFORMATION:

Gas turbine performance and reliability are a function of the quality and cleanliness of the

inlet air entering the turbine. Therefore, for optimum operation, it is necessary to treat the

atmospheric air entering the turbine and filter out the contaminants. The air inlet system, with

its specially designed equipment and ducting, modifies the quality of the air under various

temperature, humidity and contamination conditions, and makes it more suitable for use in

the unit. For the system drawing, please refer to ventilation system paragraph.

Hot exhaust gases produced as a result of combustion in the turbine are attenuated in the

exhaust system ducting before being released to the atmosphere or to a waste heat recovery

unit. These exhaust emissions must meet certain environmental standards for cleanliness and

acoustic levels, depending on site location.

AIR INLET:

The air inlet system consists of an elevated air inlet compartment and inlet ducting with

silencers connected to the turbine inlet plenum. This system combines the function of filtering

and silencing the inlet air with the function of directing the air into the turbine compressor.

Inlet air enters the inlet compartment and flows through the parallel overhead ducting, with

built- in acoustic silencers and filtration units, to the inlet plenum and then into the turbine

compressor. The elevated ducting arrangement provides a compact system and minimizes

entrance of dust which settles near the ground level.

All the external and internal surface areas exposed to air flow are coated with a protective

corrosion- preventive primer.

INLET COMPARTMENT:

The inlet compartment, an all-weather enclosure, is located off-base and connects to the inlet

ducting. This compartment contains a self-cleaning filtration system. The self-cleaning filter

system contains high efficiency media filter cartridges that are cleaned sequentially by pulses of

pressurized air during turbine operation. Compressor discharge air from the gas turbine compressor is supplied to the self-cleaning inlet filters for use as pulse air during the cleaning

cycle. The filtration unit is required to provide adequate protection for the turbine unit against

the environmental conditions at the turbine site. To ensure that this protection is maintained,

proper filtration maintenance is required.

INLET DUCTING:

The inlet compartment, an all-weather enclosure, is located on a raised support structure,

removed from the gas turbine. The air inlet duct work connects the inlet compartment to the

inlet plenum. It includes the acoustically-treated plenum at the gas turbine compressor inlet, a

90 degree elbow, a silencer module and sections of inlet ducting.

Silencing is provided by the use of vertical baffles, consisting of acoustically perforated sheets

of encapsulated low-density insulating material. In addition, the interior wall of the ducting and

plenum chamber are lined with the same type of covering. The vertical parallel baffles are

specifically tuned to eliminate the fundamental compressor tone as well as attenuating the

noise of other frequencies. The perforated sheet used in the silencers and line ducts is made of

steel and requires no maintenance. The inlet support structure are made of galvanized carbon

steel with multiple coats of protective paint.

EXHAUST SYSTEM:

Hot exhaust gases produced as the result of combustion are sent to the discharge duct. These

exhaust emissions must meet certain environmental standards of cleanliness and acoustic

levels, depending on site location. The exhaust duct is provided with an expansion joint and an

external insulation to avoid heat dissipation In the exhaust section, the gases that have been

used to power the turbine wheels are redirected and released to customer Heat Recovery

Steam Generator. One component of the system is the exhaust plenum, on which an

expansion joint and transition duct are vertically mounted, extending from the side of the

turbine base. A silencing section is installed between the transition duct and the exhaust duct

system.

Exhaust Plenum:

The exhaust plenum is a rectangular boxlike structure into which the turbine exhaust gases are

discharged before being ducted to the silencers and then vented to the atmosphere. Located

at the aft end of the turbine base, it encloses the exhaust frame, diffuser and turbine vanes. A

wrapper covers the top and side and serves to enlarge the plenum volume, forcing the exhaust

gases out of the side opening into the transition duct. Insulation placed inside the plenum

provides thermal and acoustical protection.

COUPLING

 

GENERAL INFORMATION:

The basic functions of the flexible gear type couplings used on this turbine are to:

a. connect two rotating shafts in order to transmit torque from one to the other,

b. compensate for all three types of misalignment (parallel, angular and a combination of

both),

c. compensate for any axial movement of the shafts so that neither exerts an excessive

thrust on the other.

Parallel misalignment is when the two connected shafts are parallel, but not on the same

straight line. Angular misalignment occurs when two shafts are on the same straight line but

their center lines are not parallel. Combined misalignment occurs when the shafts are neither

parallel nor on the same straight line. Axial movement is when one or both shafts are displaced

along their axis (center line).

Two couplings are used on this turbine:

a. one connects the accessory drive gear with the turbine

shaft, and

b. the other connects the turbine shaft with the load equipment.

For specific and detailed information relevant to coupling refer to sub-supplier manual

enclosed in Auxiliary Equipment And Instrumentation volume 4 of this manual.

CONTINUOUSLY-LUBRICATED ACCESSORY GEAR COUPLING:

The coupling is a continuously-lubricated flexible gear-type device. It uses a hub of male teeth

fitted at each end of a distance piece. The male teeth mesh with the female teeth of a sleeve at

each end, to transmit the torque. The male teeth are crowned and can slide fore and aft within

the female spline.

This allows for all three types of misalignment.

The sleeve at the accessory gear end is bolted to a flange (hub) which has been shrink-fitted and keyed to the accessory gear shaft. The sleeve at the turbine end is bolted directly to the turbine rotor.

LOAD COUPLING:

The non-lubricated coupling consists of flexible diaphragms, adapter shafts and a centre shaft.

The adapter shaft, fitted to the ends of the centre shaft, includes flanges which interface with

the load compressor and the load turbine rotor shaft and also provide support for the flexible

diaphragms. The diaphragm sections provide the flexibility to compensate for the nominal

misalignment between the load equipment and the load turbine rotor, and permit axial

movement of the turbine relative to the load equipment.

GAS TURBINE GENERATOR UNIT (GTG UNIT)

 

PROCESS DESCRIPTION:

Gas turbine generators:

Power Generation Package (GTG) is composed of gas turbine and turbo generator. MP fuel gas is supplied from fuel gas unit is burnt in gas turbine to generate mechanical energy which is used to drive electrical generator.

Parts of Gas turbine generator:

The essential parts of Gas turbine generator are listed below

• Engine Air compression system

o Compressor stator

o Compressor rotor

• Combustion system

o Fuel nozzles

o Spark plugs

o Flame detector

• Turbine section

o H.P Turbine section

▪ Turbine casing

▪ First and second stage turbine nozzle

▪ First and second stage turbine wheel

▪ Bearings

o L.P Turbine section

▪ Transition duct

▪ First and second stage turbine casing

▪ L.P exhaust frame

▪ Discharge diffuser

▪ Exhaust plenum

▪ L.P rotor

▪ Bearings

• Auxiliary section

o Accessory gear

o Coupling

o Inlet and exhaust system

o Lube oil system

o Ventilation system

o Cooling and sealing air system

o Washing system

Engine air compression section:

The aerodynamic design of this section functions to achieve top performance while keeping the number of stages to a minimum. The primary purpose of the compressor section is to compress air for combustion. Air taken in through the inlet passes through successive stages of compressor rotor blades and compressor stator vanes and is compressed as it passes from one to the next. After passing through the 11 stages, the air has been compressed to a ratio of 17:1.

The position of the compressor IGV and VSVs are controlled as function of compressor speed by the control panel.

Major components of compressor section are:

• Compressor stator.

• Compressor rotor.

Combustion Section:

The combustion system is of the multi-can, reverse flow type, with six cans mounted on the compressor discharge casing. In each combustion chamber there are 5 fuel nozzles, each of them containing a premixing tube (where fuel gas and air mix together before the burning zone) and a central body with a diffusion fuel gas circuit.

The combustion section consists of:

• Six combustion chambers.

• Six transition pieces.

Turbine section:

The H.P. turbine section is directly coupled to the HP turbine rotor. It is a two-stage turbine with air cooled nozzles and buckets that were designed to obtain high efficiency over a wide power range.

The H.P. turbine section consists of:

• Turbine casing.

• First stage turbine nozzle.

• Second stage turbine nozzle.

• First and second stage turbine wheels.

The L.P. turbine section consists of:

• Transition duct.

• First and second stage turbine casing.

• L.P exhaust frame.

• Discharge diffuser.

• Exhaust plenum.

• L.P rotor.

• Bearings.

Auxiliary section:

The following are the auxiliary section involves in Gas Turbine Generator (GTG).

Accessory gears:

The accessory gear assembly is a gear box coupled directly to the turbine rotor and it is used to drive the turbine-driven accessory devices.The accessory gear, located on the base, contains the gear trains required to provide gear reductions to drive the accessory devices at required speeds.

Coupling:

The basic functions of the flexible gear type couplings used on this turbine are to:

a) Connect two rotating shafts in order to transmit torque from one to other.

b) Compensate for all three types of misalignment (parallel, angular and combination of both).

c) Compensate for any axial movement of the shafts so that neither exerts an excessive thrust on the other.

Two couplings are used on this turbine:

• One connects the accessory drive gear with the turbine shaft.

• Other connects the turbine shaft with the load equipment.

Inlet and Exhaust system:

Gas turbine performance and reliability are a function of the quality and cleanliness of the inlet air entering the turbine. Therefore, for optimum operation, it is necessary to treat the atmospheric air entering the turbine and filter out the contaminants. The air inlet system, with its specially designed equipment and ducting, modifies the quality of the air under various temperature, humidity and contaminants.

Hot exhaust gases produced as a result of combustion in the turbine are attenuated in the exhaust system ducting before being released to the atmosphere or to a waste heat recovery unit.

Mineral Lube Oil System:

The gas turbine is lubricated by a closed loop, forced feed oil system which includes an oil tank, pumps, heat exchangers, filters, valves and miscellaneous devices which offer control and protection to the system. Lube oil from the system is circulated to the the four main turbine bearings, turbine accessories and driven load equipment.

Ventilation system:

The ventilation system provides ventilation to the auxiliary, auxiliary gear, turbine and coupling compartments to prevent over temperature condition and accumulation of hazardous gases.

Cooling and Sealing air system:

The cooling and sealing Air system supplies cooling air to the aft side of the second stage wheel space of H.P. turbine, the forward and aft sides of first and second stage wheel spaces of L.P. turbine, cooling for the L.P. turbine exhaust frame struts and sealing air for the lube oil seals of all the gas turbine bearing lube oil seals by means of the axial compressor fourth stage extraction.

Washing system:

The on-line / off-line washing is provided to clean axial compressor blades, removing deposists and ensuring the restoration of efficiency and it’s substantially composed of

• Water washing skid (or trolley) including,

o Washing solution tank.

o Washing fluid pump, driven by electric AC motor.

o Electric heater.

o Local control panel.

o Water washing drain water tank.

• Solenoid valves.

• Water washing on-line and off-line manifold.

HEAT RECOVERY STEAM GENERATOR UNIT(HRSG UNIT)

  Fig. HRSG (HEAT RECOVERY STEAM GENERATOR)

 

PROCESS DESCRIPTION

The Flue gas produced by the Power Generation is sent to the Heat Recovery Steam Generator(HRSG) with the purpose to recover the heat generated by the combustion of the MP Fuel Gas.

In case of insufficient exhaust from gas turbine and to provide an extra steam demand, 

supplementary firing shall supply the required duty. Fresh air firing facilities for cold start up and operation of HRSG without GTG exhaust gas are provided.

LP fuel gasfrom fuel gas unit is used for supplementary firing and fresh air firing. A HRSG Control 

System shall keep constant temperature and pressure of the steam produced by the HRSG. Steam 

flowrate will be controlled as per demand. The same system shall keep constant the level inside 

the steam drum with a level control in cascade with a flow control installed on the inlet BFW(Boiler Feed Water) line.

To maintain the salt concentration levels in the required range, blowdown facilities for the steam 

drum are provided. The continuous and intermittent blowdown are sent respectively to the Captive Power Plant(CPP) Continuous Blowdown Drum and Atmospheric KO Drum.

Fresh Air System:

Fresh air system is provided for operation of the HRSG in FA mode. The FA System consist of 

one forced draft fan with outlet damper isolating the FA system from the turbine exhaust gas.

The Fail position of the FA damper to HRSG is closed, which is provided with seal air to provide 

100% tightness. 

In TEG mode operation the FA damper is closed and the seal air valve is open.

  Burner and Ignition source:

There are two duct burners in the HRSG.

Both burners are fired with fuel gas within the burner turn down ratio. Burner 1 and Burner 2 has 

6 elements each. Burner 1 is located between the GT outlet and the combustion chamber inlet of 

the HRSG. Burner 2 is located between HP Superheater 1 and HP Evaporator 3.

Operating modes and their firing:

1. In Turbine Exhaust Gas mode, only three elements are fired. 

2. In FA mode, all the elements are fired. 

The Ignition gas is branched off from the main gas supply and is provided with the necessary 

equipment for control and safeguarding of the fuel gas supply to the ignition burner.

Instrument Air and Cooling Air System:

Instrument air is essential for the functioning of the burner. To safeguard the system, 3 pressure 

transmitters is provided to monitor the IA supply with 2 out of 3 pressure failure.

For cooling of the ignition burners, flame scanners, burner and boiler view port, ambient air is supplied by two cooling air fans.

The Supply of cooling air shall be available prior to start-up and during the normal functioning of all the operating modes.