GAS_TURBINE_POWER_PLANT

1. IUBAT- International University of Business Agriculture and Technology
Founded 1991 by Md. Alimullah Miyan
COLLEGE OF ENGINEERING AND TECHNOLOGY(CEAT)
LECTURE SLIDE - 2
Course Title: Power Plant Engineering
Course Code : MEC 403
Course Instructor: Engr. Md. Irteza Hossain

2. Gas Turbine Power Plant

3. GAS TURBINES
• Invented in 1930 by Frank Whittle
• Patented in 1934
• First used for aircraft propulsion in 1942 on Me262 by
Germans during second world war
• Currently most of the aircrafts and ships use GT engines
• Used for power generation
• Manufacturers: General Electric, Pratt &Whitney, SNECMA,
Rolls Royce, Honeywell, Siemens – Westinghouse, Alstom
• Indian take: Kaveri Engine by GTRE (DRDO)

4. Gas turbine power plant
 Gas turbine:
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.

5. Gas turbine power plant…
 Gas turbine:
Description:
 Gas turbines burn fuels such as oil,
nature gas and pulverised(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

6. Gas turbine power plant…
 Gas turbine:
Air compressor:
 The air compressor and turbine are
mounted at either end on a common
horizontal axle(shaft), with the
combustion chamber between them.
 Gas turbines are not self starting. A
starting motor initially drives the
compressor till the first combustion of
fuel takes place, later, part of the
turbine’s power runs the compressor.
 The air compressor sucks in air and
compresses it, thereby increasing its
pressure.

7. Gas turbine power plant…
 Gas turbine:
Combustion chamber:
 In the combustion chamber, the
compressed air combines with fuel and
the resulting mixture is burnt.
 The greater the pressure of air, the better
the fuel air mixture burns.
 Modern gas turbines usually use liquid
fuel, but they may also use gaseous fuel,
natural gas or gas produced artificially
by gasification of a solid fuel.
Note :
 The combination of air compressor and
combustion chamber is called as gas
generator.

8. Gas turbine power plant…
 Gas turbine:
Turbine:
o The burning gases expand rapidly and
rush into the turbine, where they cause
the turbine wheels to rotate.
o Hot gases move through a multistage gas
turbine.
o Like in steam turbine, the gas turbine
also has fixed(stationary) and
moving(rotor) blades.
o The stationary blades guide the moving
gases to the rotor blades and adjust its
velocity.
o The shaft of the turbine is coupled to a
generator or machinery to drive it.

9. Gas turbine power plant…
 Applications of gas turbine:
 Gas turbines are used to drive pumps, compressors and high speed cars.
 Used in aircraft and ships for their propulsion. They are not suitable for
automobiles because of their very high speeds.
 Power generation(used for peak load and as stand-by unit).
Note :
 Gas turbines run at even higher temperatures than steam turbines, the
temperature may be as high as 1100 – 12600C.
 The thermal efficiency of gas turbine made of metal components do not
exceed 36%.
 Research is underway to use ceramic components at turbine inlet
temperature of 13500C or more, and reach thermal efficiencies over 40% in a
300 kW unit.

10. Layout of a gas turbine power plant

11. Layout of gas turbine power plant…
 Starting motor:
 Gas turbines are not self starting.
They require a starting motor to
first bring the turbine to the
minimum speed called coming –in
speed, for this purpose a starting
motor is required.
 Low pressure compressor(LPC):
 The purpose of the compressor is
to compress the air. Air from the
atmosphere is drawn into the LPC
and is compressed.
Intercooler:
The air after compression in the LPC
is hot. It is cooled by the intercooler.
The intercooler is circulated with
cooling water.

12. Layout of gas turbine power plant…
 High pressure compressor(HPC):
 The air from the intercooler enters
the HPC where it is further
compressed to a high pressure.
The compressed air passes
through a regenerator.
 Regenerator(Heat exchanger):
 The air entering the combustion
chamber(CC) for combustion
must be hot. The heat from the
exhaust gases is picked up by the
compressed air entering the
combustion chamber.
 Combustion chamber:
The fuel(natural gas, pulverized coal,
kerosene or gasoline) is injected into the
combustion chamber.
The fuel gets ignited because of the
compressed air.
 The fuel along with the compressed air
is ignited sometimes with a spark plug.

13. Layout of gas turbine power plant…
 High pressure compressor(HPC):
 The air from the intercooler enters
the HPC where it is further
compressed to a high pressure.
The compressed air passes
through a regenerator.
 Regenerator(Heat exchanger):
 The air entering the combustion
chamber(CC) for combustion
must be hot. The heat from the
exhaust gases is picked up by the
compressed air entering the
combustion chamber.
 Combustion chamber:
The fuel(natural gas, pulverized coal,
kerosene or gasoline) is injected into
the combustion chamber.
The fuel gets ignited because of the
compressed air.
 The fuel along with the compressed
air is ignited sometimes with a spark
plug.

14. Layout of gas turbine power plant…
 High pressure turbine (HPT):
 In the beginning the starting
motor runs the compressor shaft.
 The hot gases(products of
combustion) expands through the
high pressure turbine.
 It is important to note that when
the HPT shaft rotates it infact
drives the compressor shaft which
is coupled to it. Now the HPT
runs the compressor and the
starting motor is stopped.
Note :
 About 66% of the power
developed by the gas turbine
power plant is used to run the
compressor.
Only 34% of the power developed by
the plant is used to generate electric
power.

15. Layout of gas turbine power plant…
 Low pressure turbine (LPT):
 The purpose of the LPT is to
produce electric power.
 The shaft of the LPT is directly
coupled with the generator for
producing electricity.
 The hot gases(products of
combustion) after leaving the
HPT is again sent to a combustion
chamber where it further
undergoes combustion.
 The exhaust gases after leaving
the LPT passes through the
regenerator before being
exhausted through the chimney
into the atmosphere.
 The heat from the hot gases is used
to preheat the air entering the
combustion chamber. This preheating
of the air improves the efficiency of the
combustion chamber.

16. Gas turbine power plant…
 Advantages of gas turbine power plant :
 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.
 Disadvantages of gas turbine power plant :
 66% of the power developed is used to drive the compressor. Therefore
the gas turbine unit has a low thermal efficiency.
 The running speed of gas turbine is in the range of (40,000 to 100,000
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.
 High frequency noise from the compressor is objectionable.

17. Compared to Steam-Turbine, Gas Turbine offers :
1. Greater Power for a given size and weight,
2. High Reliability,
3. Long Life,
4. More Convenient Operation.
5. Engine Start-up Time reduced from 4 hrs to less than 2 min…!!
Gas Turbine Power Plants – Advantages

18. Thermodynamic Cycles
Applications of Thermodynamics
Power
Generation
Refrigeration
Power Cycles Refrigeration Cycles
Engines
Devices / Systems used to
produce Net Power Output.
Refrigerators / Heat Pumps /
A.C.
Devices / Systems used to produce
Refrigeration Effect.
External
Heat is supplied to the Working Fluid
from an external source such as a Furnace
/ Geothermal Well / Nuclear Reactor, etc.
Internal
Heat is supplied to the Working Fluid
by burning the Fuel within the System
Boundaries.

19. Introduction
Thermodynamics Cycles
Gas Cycles Vapour Cycles
Working Fluid remains in Gaseous
Phase throughout the Cycle.
Working Fluid exists in Vapor
Phase during part of the Cycle, and
in liquid phase during remaining
part.

20. Thermodynamics Cycles
Closed Cycles Open Cycles
Working Fluid returns to Initial State at
the end of the cycle, and is
Recirculated.
Working Fluid is Renewed at the end of
each cycle, and thus us Non-
Recirculated.
Introduction

21. Made up of Four Internally Reversible processes:
Brayton Closed Cycle – Analysis
1-2 Isentropic Compression (in a Compressor)
2-3 Constant-Pressure Heat Addition
3-4 Isentropic Expansion (in a Turbine)
4-1 Constant-Pressure Hat Rejection

22. Brayton Closed Cycle – Analysis
Neglecting changes in Kinetic and Potential energies, the Energy Balance
for a Steady-Flow Process, on a Unit–Mass Basis :
in out in out exit inlet
q q w w h h
3 2 3 2
in P
q h h C T T
4 1 4 1
out P
q h h C T T
Thermal Efficiency of Ideal Brayton Cycle
:

23. Processes 1-2 and 3-4 are
Isentropic,
P2 = P3 and P4 = P1.
Brayton Closed Cycle – Analysis
Substituting and simplifying the equation :
, 1
1
1
th Brayton
p
r
2
1
p
P
r
P
where;

24. Brayton Closed Cycle – Analysis
, 1
1
1
th Brayton
p
r
, ,
th Brayton p
f r
Thermal Efficiency of an Ideal Brayton
Cycle depends on the Pressure Ratio of
the gas turbine and the Specific Heat
Ratio of the working fluid.
for γ = 1.4

25. Highest Temperature occurs at the end of the Combustion process (state 3), and
it is limited by the maximum temperature that the turbine blades can withstand.
Brayton Closed Cycle – Analysis
This limits the Pressure Ratios that can be used in the cycle.
For a fixed Turbine Inlet Temperature T3,
the Net Work Output per Cycle increases
with the Pressure Ratio, reaches a
maximum, and then starts to decrease,
Compromise between the Pressure
Ratio (thus the Thermal Efficiency)
and the Net Work Output.
Generally, the Pressure Ratio ranges from about 11 to 16.

26. Back Work Ratio
1
2
CompressorWork
BackWork Ratio
TurbineWork
Usually, more than one-half of the
Turbine Work Output is used to drive the
Compressor.
In contrast to Steam Power Plants, where Back Work Ratio is only a few percent.
..!!
This is due to :
1. Liquid is compressed in Steam Power Plants instead of a gas.
2. Steady-Flow Work is proportional to Sp. Volume of the working fluid.
Therefore, the turbines used in Gas-Turbine Power Plants are larger than those
used in Steam Power Plants of the same net power output…!!

27. Functions of Air in Gas Turbines :
Brayton Closed Cycle – Analysis
1. Supplies the Necessary Oxidant for the combustion of the
fuel.
2. As a Coolant to keep the temp. of various components within safe
limits.
Drawing in more air than is needed for the complete combustion of the
fuel.
Air–Fuel Mass Ratio of 50 or above is common.
Treating the Combustion Gases as Air does not cause any appreciable
error.

28. Gas Turbine Power Plants – Applications
Two Major Application Areas :
1. Aircraft Propulsion
2. Electric Power Generation.
Electric Power Generation
Aircraft Propulsion

29. Actual Gas-Turbine Cycles
• For actual gas
turbines, compressor
and turbine are not
isentropic

30. Regenerative Brayton Cycle
For the Brayton cycle, the turbine exhaust temperature is greater than the
compressor exit temperature. Therefore, a heat exchanger can be placed
between the hot gases leaving the turbine and the cooler gases leaving the
compressor. This heat exchanger is called a regenerator or recuperator..

31. Gas Turbine Cycle – Intercooling
Net Work Output of Gas Turbine can be ↑ by ↓ the Compressor Work Input.
Multistage + Intercooling…!!!

32. Gas Turbine Cycle – Intercooling
Three Internally Reversible
processes:
1-c Isentropic Compression,
till Pr. is Pi
c-d Constant-Pressure Cooling,
↓ from Tc to Td
d-2 Isentropic Compression,
State 2.

33. Work Input per unit Mass Flow on the P–V Diagram : 1–c–d–2–a–b–1.
Gas Turbine Cycle – Intercooling
Without Intercooling : Single Stage Isentropic Compression from State 1 to State
2’.
Work Area ≡ 1–2’–a–b–1.
Crosshatched Area ≡ Reduction in work due to
Intercooling.

34. When using multistage compression, cooling the working fluid between the stages
will reduce the amount of compressor work required. The compressor work is
reduced because cooling the working fluid reduces the average specific volume of
the fluid and thus reduces the amount of work on the fluid to achieve the given
pressure rise.
To determine the intermediate pressure at which intercooling should take place to
minimize the compressor work, we follow the approach shown in Chapter 7.
For the adiabatic, steady-flow compression process, the work input to the
compressor per unit mass is4 3
2 4
1 3
1 2
= =
comp
w v dP vdP v dP vdP
0
Gas Turbine Cycle – Intercooling

35. This yields P P P
2 1 4
or, the pressure ratios across the two compressors are equal.
P
P
P
P
P
P
2
1
4
2
4
3
Inter cooling is almost always used with regeneration. During inter cooling the
compressor final exit temperature is reduced; therefore, more heat must be supplied
in the heat addition process to achieve the maximum temperature of the cycle.
Regeneration can make up part of the required heat transfer.
Gas Turbine Cycle – Intercooling

36. Brayton with Intercooling,
Reheat, & Regeneration
• For max performance

37. Gas Turbine Cycle – Reheat
For Metallurgical Reasons, the Temperature of the Gaseous Combustion Products
entering the turbine must be limited.
This temperature can be controlled by providing Air in Excess of the Amount
required to Burn the Fuel in the combustor.
As a consequence, the gases exiting the combustor contain Sufficient Air to
support the Combustion of Additional Fuel.
Gas Turbine Power Plants take advantage of the Excess Air by means of a
Multistage Turbine with a Reheat Combustor between the stages. With this
arrangement the Net Work per Unit of Mass Flow can be increased.
NOTE : Reheat is used for ↑ in Output Power.
It may not ↑ the Efficiency…!!

38. Gas Turbine Cycle – Reheat
After expansion from State 3 to State a in the first turbine, the gas is Reheated
at Constant Pressure from State a to State b.
The expansion is then completed in the second turbine from State b to State 4.

39. Gas Turbine Cycle – Intercooling + Reheat + Regenerator

40. Example 1
Inlet conditions to a Brayton cycle are 1 bar and 300 K. The cycle pressure ratio is 8.
The temperature at the inlet to the turbine is 1300 K. Calculate
a. The gas temperature at the exit of the compressor and turbine b. the back work
ratio c. the thermal efficiency
300 K
1300 K
rp =8

41. Example 2
300 K
1300 K
rp =8
In the plant of Example 1, let the compressor and the turbine have the isentropic
efficiencies of 0.8 and .85 respectively each. Calculate the performance parameters
of the cycle.
a. the back work ratio b. the thermal
efficiency c. the turbine exit temperature

42. Regeneration
• Use heat exchanger
called recuperator or
regenerator
• Counter flow

43. Regeneration
• Effectiveness
• For cold-air
assumptions

44. Determine the thermal efficiency of the gas turbine
described in the previous problem if a regenerator
having an effectiveness of 80percent is installed
Example 3

45. Brayton with Intercooling,
Reheat, & Regeneration

46. Example 4