Basic principle of Operation
A gas turbine operates by:
1. Continuously drawing in fresh air
- Point 1,
2. Compressing this air to a higher
pressure - Point 2
3. Adding and burning fuel in the
compressed air to increase its
4. Directing the high pressure high
temperature air to an expansion
Point 3 - that converts the gas
energy to the mechanical energy of
a rotating shaft.
5. The resulting low pressure, lower
temperature gases are discharged to
atmosphere or HRSG – Point 4
• Air Inlet – filters and directs the air into to the compressor.
• Compressor – axial flow. Draws air in and compresses it to a higher
pressure and temperature. Consists of rotor assembly, stator casings,
rotating and stationary blades.
• Combustors – multiple combustion chambers where fuel and air are
mixed and burned to provide the heat energy to the turbine. Directs the
combustion gases to the
• Turbine – converts the hot gas kinetic energy into rotational shaft power.
• Exhaust – directs the high temperature, low pressure, gases to
atmosphere or to a
• heat recovery steam generator (HRSG)
• Auxiliary Support Systems: Controls, Lubrication Oil, Hydraulics, Cooling
and Sealing Air and others required for the operation, control and
protection of the turbine.
• IGV permits fast, smooth
acceleration of the turbine
without compressor surge.
• A hydraulic cylinder mounted
on a base cross member
actuates the IGV through a
large ring gear and multiple
small pinion gears.
• Gear & Rack Material: Stainless
IGV Material: Cr-Ni-Cd ,C-450
•Rotor - bolted design of individual stage wheels/disks and stub shafts as a
bolted assembly. Forward stub shaft contains the #1 bearing rotor journal,
thrust (bearing) collar and 60 tooth speed ring. Rotor blades attached via slots
in the outside diameter or each wheel.
• Inlet guide vanes – variable IGVs direct the air onto the first row of rotating
• Blades - Limit amount of entering air during startup and shutdown to prevent
surge/pulsations. Control air flow during turbine operation to help control
On startup & shutdown the VIGV’s are closed – 26 to 30 degree angle
when below approximately 80% speed.
Full Open position is typically 84 to 89 degree angle
• Each rotating row of blades (airfoils)
increases the velocity of the incoming air
raising its kinetic energy. Attach to rotor
via dovetail fits.
• The stationary row of blades (vanes) act
as diffusers converting the kinetic energy
to a pressure increase and guides the air
onto the next stage of rotating blades.
Mounted to the casings inside diameter.
• Extraction ports for pulsation protection
with compressor bleed valves and for
cooling/sealing air supply.
• Combustion chambers.
• Fuel nozzles.
• Cross -fire tubes.
• Transition pieces.
• Combustion liners.
• Spark plugs (2 nos. at no.1&10)
• Flame detectors (4 nos at no 2,37&8)
Reverse Flow type Combustors
Air flow through the chambers is on the outside of the liners and is counter flow in
relation to the hot gas flow . Serves to cool the liners and transition pieces and
preheats the air to be used for combustion
• Serves to inject fuel, atomizing air and gas fuel
into each chamber. Fuel and air are mixed at
the fuel nozzle tip
• located with each chamber. Contains the
combustion flame. Have cooling and
mixing holes to enhance the fuel
combustion reaction and to cool
(dilution air) the combustion gases prior
to entering the transition piece and
turbine section. Liners are cooled with
the compressor discharge air flowing on
the outside and for some designs the
inside diameter is cooled via slots in the
• Material : Hastelloy X
• Crossfire tubes: Interconnect the individual chambers to facilitate
lighting of each chamber at initial ignition at 1 or 2 chambers.
• Flow Sleeve – located inside each chamber. The liners are located
inside the flow sleeves. Flow sleeves direct compressor discharge
air along the outside of the liners. Provides insulation barrier
between the liner and combustion chamber.
• Transition Piece and seals – directs the combustion gases from
the liner to the first stage turbine nozzle. Quantity – 1 per
• Spark plug – igniters – quantity 2. Electric arc igniter used to
ignite the fuel at startup. Once flame is established these shut off.
Power supplied from igniter transformers at 15,000 to 20,000
volts. Need only 1 to light off (fire) the turbine.
• Flame detectors – UV. Detect the presence of flame in the
monitored chambers. Typically 4 are used per unit. Primary
function is for startup and shutdown to indicate flame. Also used
for flameout protection during full operation. Need at least 2 out
of 4 functional to operate the turbine.
Turbine Section-Hot Gas Path
• 3 stages of stationary nozzles and rotating
• Buckets (Stage 1, 2, 3) – convert the high
velocity (kinetic) energy from the nozzles into
rotational mechanical shaft energy. Buckets are
attached to the turbine wheels via a dovetail (fir
• Stationary Nozzles (Stage 1, 2, 3) – convert the
high pressure gases into high velocity (kinetic)
energy jets that impinge on the turbine buckets
• Owing to high temp , The need for better materials spurred in
the field of alloys and manufacturing techniques, One of the
earliest of these was Nimonic ( 50% nickel and
20% chromium with additives such
as titanium and aluminium. )
• The development of superalloys in the 1940s and new
processing methods such as vacuum induction melting in the
1950s greatly increased the temperature capability of turbine
• Further processing methods like hot isostatic
pressing improved the alloys used for turbine bladoften
use nickel-based superalloys that
incorporate chromium, cobalt, and rheniumes and increased
turbine blade performance. Modern turbine blades.
• A major breakthrough was the development of directional
solidification (DS) and single crystal (SC) production methods.
These methods help greatly increase strength against fatigue
and creep by aligning grain boundaries in one direction (DS)
or by eliminating grain boundaries all together (SC).
• Another major improvement to turbine blade material
technology was the development of thermal barrier
coatings (TBC). Where DS and SC developments improved
creep and fatigue resistance, TBCs improved corrosion and
oxidation resistance, both of which become greater concerns
as temperatures increased.
• The first TBCs, applied in the 1970s, were aluminide coatings.
Improved ceramic coatings became available in the 1980s.
• Another strategy to improving turbine blades and increasing
their operating temperature, aside from better materials, is to
cool the blades. There are three main types of cooling used in
gas turbine blades; convection, film, and transpiration cooling.
While all three methods have their differences, they all work
by using cooler air (often bled from the compressor) to
remove heat from the turbine blades.
• The blades are coated with the TBC they will have, and then
cooling holes are machined as needed, which gives further
higher temperature sustenanace, thus creating a complete
Cooling and Sealing Air
• Bearing cooling and sealing
• Cooling of internal turbine parts subjected to
• Cooling of turbine outer shell and exhaust
• Pulsation protection
• Providing air supply for air operated valves
• Providing air for auxiliary requirements