1) Gas turbine power plants work by compressing air, mixing it with fuel and igniting it to spin a turbine. The turbine powers a generator and compressor. 2) Open cycle plants draw in air, exhaust it out. Closed cycle plants circulate a working fluid. Improving open cycle efficiency involves regeneration, reheating, or intercooling. 3) Combining gas turbines with steam plants improves efficiency by using exhaust heat to generate steam. Combining with diesels involves turbocharging, a gas generator, or a compound engine configuration.

1. POWER PLANT ENGINEERING
Gas turbine plant
Suryakanth L G
Asst. Prof Mechanical Dept
NMREC, Hyderabad

2. History of Gas Turbine…
The first gas turbine for power generation became operational
in 1939 in Switzerland.
It was developed by the company Brown Boveri.
 They were therefore used to provide power at peak loads.
 After world war II, gas turbine developed rapidly. It therefore
soon became the primary choice for many applications.

3. GAS TURBINE POWER PLANT
Working principle :
 Air is compressed(squeezed) to high
pressure by a fan-like device called the
compressor.
 Then fuel and compressed air are mixed
in a combustion chamber and ignited.
 Hot gases are given off, which spin the
turbine wheels.
 Most of the turbine’s power runs the
compressor. Part of it drives the
generator/machinery.
 At present, thermal efficiencies of 45%
,max. temp is about 10000C and at
present the maximum gas turbine size
limitation is about 30 to 40 MW.

4. Efficiency is 20 to 30% whereas that of steam power plant is 38 to 48%.
Major Applications of Gas Turbine
1. Aviation(self contained, light weight don’t require cooling)
2. Power Generation
3. Oil and Gas industry(cheaper supply of fuel and low installation cost)
4. Marine propulsion
 Gas turbines burn fuels such as oil, nature gas and pulverized( powdered) coal.
 Instead of using the heat to produce steam, as in steam turbines, gas turbines use
the hot gases directly to turn the turbine blades.
Gas turbines have three main parts:
i) Air compressor
ii) Combustion chamber
iii) Turbine

5. SIMPLE GAS TURBINE
A simple gas turbine consists of
 Turbine
 A compressor mounted on the same shaft
 A combustor
 Auxiliaries such as starring device, lubrication pump, fuel system, oil
system etc

6. ENERGY FLOW DIAGRAM
 The air brings in minute amount of energy
 Compressor adds considerable amount of energy
 Fuel carries major input to cycle
 Sum of fuel & compressed air energy leaves combustor to enter
turbine
 In turbine smallest part of entering energy goes to useful output,
largest part leaves in exhaust.

7.  Advantages of Gas turbine power plants.
 Compact design, high speed and high power.
 Storage of fuel requires less area and handling is easy.
 The cost of maintenance is less.
 It is simple in construction. There is no need for boiler,
condenser and other accessories as in the case of steam power
plants.
 Cheaper fuel such as kerosene , paraffin, benzene and powdered
coal can be used which are cheaper than petrol and diesel.
 Gas turbine plants can be used in water scarcity areas.
 Less pollution and less water is required
 Simple lubrication system.
 The gas turbine can be driven at a very high speed i.e 40000 rpm.

8. Disadvantages of gas turbine power plant
1. 66% of the power developed is used to drive the
compressor. Therefore the gas turbine unit has a low
thermal efficiency.
2. The running speed of gas turbine is in the range of
(20,000 to 80,000 rpm) and the operating temperature is
as high as 1100 – 12600C. For this reason special metals
and alloys have to be used for the various parts of the
turbine.
3. High frequency noise from the compressor is
objectionable.
4. Starting of the plant is not as simple as diesel plants.
5. Compare to other power plant, the overall efficiency of
this plant is quite low.
6. In summer, oxygen starvation may occur.

9. GAS TURBINE POWER PLANTS IN INDIA

10. TYPES OF GAS TURBINE POWER PLANTS
The gas turbine power plants can be classified mainly into
two categories. These are :open cycle gas turbine power
plant and closed cycle gas turbine power plant.
1. Open Cycle Gas Turbine Power Plant
In this type of plant the atmospheric air is charged into the
combustor through a compressor and the exhaust of the
turbine also discharge to the atmosphere.
2. Closed Cycle Gas Turbine Power Plant
In this type of power plant, the mass of air is constant or
another suitable gas used as working medium, circulates
through the cycle over and over again.

11. OPEN CYCLE GAS TURBINE POWER PLANT
AND ITS CHARACTERISTICS
Gas turbines usually operate on an open
cycle. Air at ambient conditions is drawn
into the compressor, where its
temperature and pressure are raised.
The high pressure air proceeds into the
combustion chamber, where the fuel is
burned at constant pressure. The high-
temperature gases then enter the
turbine where they expand to
atmospheric pressure while producing
power output.
Some of the output power is used to
drive the compressor.
The exhaust gases leaving the turbine
are thrown out (not re-circulated),
causing the cycle to be classified as an
open cycle.

12.  The ideal cycle that the
working fluid undergoes in the
closed loop is the Brayton
cycle. It is made up of four
internally reversible
processes:
 1-2 Isentropic
compression;(No change in
entropy)
 2-3 Constant-pressure heat
addition;
 3-4 Isentropic expansion;
 4-1 Constant-pressure heat
rejection.
 The T-s diagrams of an ideal
Brayton cycle.
P-v and T-s diagrams of Brayton cycle

13. Entropy
 The term entropy was first used by Rudolf clausius to state the
second law of thermodynamics. Entropy is the extensive property
of the system and its unit of measurement is J/K.
 The measure of a system’s thermal energy per
unit temperature that is unavailable for doing useful work.
Because work is obtained from ordered molecular motion, the
amount of entropy is also a measure of the molecular disorder,
or randomness of a system.
 The various causes of the increase in entropy of the system are
@ Due to external interaction.
@ Internal changes in the system.
 dS = δq/T
Where dS is the change in entropy,
δq is the heat added to the system.

14. METHODS OF IMPROVEMENT OF THERMAL
EFFICIENCY OF OPEN CYCLE GAS TURBINE PLANT
1. Regeneration
2. Reheating
3. Intercooling

15. REGENERATION
 The exhaust gasses from
the turbine carry a large
quantity of heat with them
since their temperature is
far above the ambient
temperature.
 They can be used to heat
air coming from the
compressor there by
reducing the mass of fuel
supplied in the combustion
chamber.
Gas turbine with regenerator

16. T-S DIAGRAM FOR THE UNIT
 2’-3: heat flow into
compressed air (heat
exchanger)
 3-4: heat taken in from
combustion fuel.
 6:Temp of exhaust
gases.

17.  Regenerative Cycle has
more efficiency than
simple cycle only at
lower pressure ratios.
 Above certain pressure
ratio limit, the efficiency
of cycle drops since in
that case regenerator
will cool the
compressed air instead
of heating it.
THERMAL EFFICIENCY V/S PRESSURE RATIO GRAPH

18. REHEATING
 The output of gas turbine
can be improved by
expanding the gasses in two
stages with a reheater
between the two.
 The H.P. turbine drives the
compressor and the LP
turbine provides useful
power output.
Gas turbine with reheater

19. T-S DIAGRAM FOR THE UNIT
1-2’: Compression
2’-3: C.C (heating)
3’-4’: Turbine(Expansion)
4’-5: Reheater(heating)
5-6’: Turbine(Expansion)

20.  Net Work output
increases.
 Thermal Efficiency
Decreases.
THERMAL EFFICIENCY V/S PRESSURE RATIO GRAPH

21. INTERCOOLING
 A compressor in a gas
turbine cycle utilizes the
major percentage of
power developed by the
gas turbine.
 The work required by
the compressor can be
reduced by compressing
the air in two stages and
incorporation a
intercooler between the
two.

22. T-S DIAGRAM FOR THE UNIT
 1-2’: LP compression
 2’-3: Intercooling
 3-4’: H.P. compression
 4’-5: C.C. Combustion
chamber(heating)
 5-6’: T(Turbine) –Expansion
 The heat supplied when
intercooling is used is
greater than with no
intercooling.

23. THERMAL EFFICIENCY V/S PRESSURE RATIO GRAPH
 Work Ratio is
increased
 Thermal efficiency
decreases but it
increases at high
pressure ratio.

24. CLOSED CYCLE GAS TURBINE POWER PLANT
AND ITS CHARACTERISTICS
 The compression and
expansion processes
remain the same, but
the combustion process
is replaced by a
constant-pressure
heat addition process
from an external source.
 The exhaust process is
replaced by a constant-
pressure heat
rejection process to the
ambient air.

25. T-S DIAGRAM FOR CLOSED LOOP CYCLE TURBINE
1-2 : The air is compressed
isentropically from lower
pressure p1 to the upper
pressure p2, temp rising from T1
to T2.
2-3: Heat flows into the system
increasing its volume V2 to V3
and temp T2 to T3, pressure
remains constant at p2.
Heat received = mCp(T3-T2)
3-4: The air is expanded
isentropically from p2 to p1, and
temp T3 to T4, No heat flow
occurs.
4-5: Heat is rejected from the
system as volume decreases
from V4 toV1 and temp from T4
to T1, pressure remains constant
p1. Heat rejected= mCp(T4-T1)

26. MERITS AND DEMERITS OF CLOSED LOOP CYCLE
TURBINE OVER OPEN LOOP CYCLE TURBINE
Merits:
 Higher thermal efficiency
 Reduced size
 No contamination
 Improved heat
transmission
 Lesser Fluid friction
 No loss in working
medium
 Greater output
 Inexpensive fuel.
Demerits:
 Complexity
 Large amount of cooling
water is required.
 Dependent System
 Not economical for moving
vehicles as weight /kW
developed is high.
 Requires the use of very
large air heater.

27. Gas turbine fuels
Important properties:
It should have better
calorific value
Self lubrication property
Available at low cost
It’s volatility in
appreciable value
Well Purified

28. Various types:
Natural gas (for industrial applications)
High grade gasoline (for aircraft applications)
Kerosene (distillate oils)
Blast furnace gas of steel mills
Residual oils as residue
of crude oil
Heavy oils

29. STARTING OF A GAS TURBINE PLANT
The starting of a gas turbine plant is quite simple and quick.
 Oil pumps & intercooler water pumps are run up
 The starting motor is switched on.
 The fuel line is opened to the combustion chamber and the
charge is ignited.
 Fuel charge to the reheater is ignited.
 As both the shaft gain speed, the starting motor is
automatically switched off.
 Speed and voltage is adjusted
 Load can be built up on the alternator by governor gear
control.

30. COMBINATION OF GAS TURBINE CYCLES
Gas Turbine and Steam Power Plants:
The combination of gas-turbine-steam cycle aims at
utilizing the heat of exhaust gases from the gas turbine
thus, improve the overall plant efficiency.
The popular designs are:
 1. Heating feed water with exhaust gases.
 2. Employing the gases from a supercharged boiler to
expand in the gas turbine.
 3. Employing the gasses as combustion air in the steam
boiler.

31. HEATING FEED WATER WITH EXHAUST GASES.
 The output heat of the gas
turbine flue gas is utilized to
generate steam by passing it
through a heat recovery steam
generator (HRSG), so it can
be used as input heat to the
steam turbine power plant.
 This combination of two
power generation cycles
enhances the efficiency of the
plant.
 While the electrical efficiency
of a simple cycle plant power
plant without waste heat
utilization typically ranges
between 25% and 40%, a
CCPP can achieve electrical
efficiencies of 60% and more. Gas turbine gases used for feed
water heating.

32. EMPLOYING THE GASES FROM A SUPERCHARGED BOILER TO
EXPAND IN THE GAS TURBINE.
 The boiler furnace works under
a pressure of about 5 bars and
the gases are expanded in the
gas turbine, the exhaust being
used to heat feed water before
being discharged through the
stack.
 The heat transfer rate is very
high as compared to
conventional boiler due to high
pressure of gases, and smaller
size of steam generator is
needed.
 No need of forced draught fans
as the gases in furnace are
already under pressure.
 Overall improvement in heat
rate is 7%.
Supercharged Boiler

33. EMPLOYING THE GASES AS COMBUSTION AIR IN THE STEAM
BOILER.
 Exhaust gases are used
as preheated air for
combustion in the
boiler, results in5%
improvement in heat
rate.
 The boiler is fed with
supplementary fuel
and air, and is made
larger than
conventional furnace.
Exhaust heat recovery steam gas plant

34. COMBINED GAS TURBINE AND DIESEL POWER
PLANTS
 The performance of
diesel engine can be
improved by combining
it with exhaust driven
gas turbine.
Three combinations:
1. Turbo charging
2. Gas Generator
3. Compound engine

35. TURBO CHARGING
 This method is known
as supercharging.
 The exhaust of the
diesel engine is
expanded in the gas
turbine and the work
output of the gas
turbine is utilized to
run a compressor
which supplies the
pressurized air to the
diesel engine to
increase its output. Turbo charging

36. GAS GENERATOR
 The compressor which
supplies the
compressed air to the
diesel engine is not
driven from gas turbine
but from the diesel
engine through some
suitable device.
 The output of diesel
engine is consumed in
driving the air
compressor and gas
turbine supplies the
power.
Gas generator

37. COMPOUND ENGINE
 The air compressor is
driven from both diesel
engine and gas turbine
through a suitable
gearing and power
output is taken from the
diesel engine shaft.
Compound engine