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SNIST (JNTUH) – M.Tech (Therm.Engg)SNIST (JNTUH) – M.Tech (Therm.Engg)
GAS TURBINE POWER PLANTGAS TURBINE POWER PLANT
Dr. VIJAYA BHASKAR SIRIVELLA
Professor in Mechanical Engineering
Sreenidhi Inst. of Sci. & Tech., Hyderabad
Syllabus: GAS TURBINE PLANT
Cogeneration. Combined cycle power
plant, Analysis, Waste heat recovery,
IGCC power plant, Fluidized bed
combustion, Advantages, Disadvantages
Gas turbines have been used for electricity generation in the
periods of peak electricity demand
Gas turbines can be started and stopped quickly enabling
them to be brought into service as required to meet energy
Small unit sizes and their low thermal efficiency restricted
the opportunities for their wider use for electricity generation.
The Thermal efficiency of the gas turbine is 20 to 30% compared with the
modern steam power plant 38 to 40%.
In future it is possible to construct efficiencies in and around 45%.
Following are the fields of Gas Turbine applications:
Power Generation Aviation
Oil and Gas industry Marine Propulsion
A Gas Turbine is used in aviation and marine fields because it is self
contained, light weight not requiring cooling water and fit into the overall
shape of the structure.
It is selected for the power generation because of its simplicity, lack of
cooling water, needs quick installation and quick starting.
It is used in oil and gas industry because of cheap supply of fuel and low
Limitations of the gas turbine:
1. They are not self starting
2. low efficiencies at part loads
3. non reversibility
4. Higher rotor speeds
5. Low overall plant efficiency.
Gas turbine plant is defined as “ in which the principle of the prime mover
is of the turbine type and the working medium is a permanent gas”.
Simple gas turbine plant consists of
Auxiliary devices like starting device, lubricating pump, fuel pump, oil
system and duct system.
The working fluid is compressed in a compressor which is generally
rotary, multistage type.
Heat is added to the compressed fluid in the combustion chamber .
This high energy fluid at high temperature and pressure then expands in the
turbine thereby generating power.
Part of the energy generated is consumed in driving the compressor and
accessories and the rest is utilized in electrical energy.
GAS TURBINE POWER PLANTS CLASSIFICATION
1.By Application: Jet Propulsion
Air craft Prop-Jets
Peak Load Unit
Stand by Unit
Stationary End of Transmission Line Unit
Base Load Unit
GAS TURBINE POWER PLANTS CLASSIFICATION
3.According to Arrangement:
4.According to combustion:
Advantages of Gas Turbine Power Plants over Diesel Plants
Work developed per kg of air is more than diesel plant
Less vibrations due to perfect balancing and no reciprocating parts
Less space requirements
Capital cost is less
Higher mechanical efficiency
Running speed of the turbine is large
Lower installation and maintenance costs
Torque characteristics of turbine plants are better than diesel plant
Ignition and lubrication systems are simpler
Specific Fuel Consumption (SFC) does not increase with time in gas
turbine plant as rapidly in diesel plants
Poor quality fuel can be used
Light weigh with reference to Weight to power ratio is less for gas turbine
Smoke less combustion is achieved in gas power plants
Disadvantages of Gas Turbine Power Plants over Diesel Plants
Poor part load efficiency
Special metals and alloys are required for different components
Special cooling methods required for cooling of turbine blades
Thermal efficiency is low
Wide operating speeds the fuel control is difficult
Needs to have speed reduction devices for higher operating speeds of
Difficult to start a gas turbine compared to diesel engine
Manufacturing of blades is difficult and costly
Same output gas turbines produces the five times the exhaust gases than
Advantages of Gas Turbine Power Plants over Steam Plants
No ash handling
Low capital cost and running costs
Space requirement is less
Fewer auxiliaries are used
Can be built relatively quicker
Can brought on load quickly to support peak loads
Thermal efficiency of the gas turbine is higher than steam when
working on top temperature (>5500
Gas turbine plants quite economical for short running hours
Storage of fuel is smaller and handling is easy.
Less cooling water required for gas turbine plants compared to
Weight per H.P. is far less
Can be installed any where
Control of gas turbine is much easier.
Working Principle of Gas Turbine
Air is compressed(squeezed) to high pressure by a compressor.
Then fuel and compressed air are mixed in a combustion
chamber and ignited.
Hot gases are given off, which spin the turbine wheels.
Gas turbines burn fuels such as oil, natural gas and
Gas turbines have three main parts:
i) Air compressor
ii) Combustion chamber
November 5, 201716
Gas turbine power plant
The air compressor and turbine are mounted at
either end on a common shaft, with the combustion
chamber between them.
Gas turbines are not self starting. A starting motor
The air compressor sucks in air and compresses it,
thereby increasing its pressure.
November 5, 201717
Gas turbine power plant
In the combustion chamber, the compressed air
combines with fuel and the resulting mixture is
The greater the pressure of air, the better the fuel air
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.
November 5, 201718
Gas turbine power plant
Hot gases move through a multistage gas
Like in steam turbine, the gas turbine also has
stationary and moving blades.
The stationary blades
guide the moving gases to the rotor blades
adjust its velocity.
The shaft of the turbine is coupled to a
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
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.
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.
OPEN CYCLE GAS TURBINE POWER
PLANTAND ITS CHARACTERISTICS
Gas turbines usually operate on an open
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
Some of the output power is used to drive
The exhaust gases leaving the turbine are
thrown out (not re-circulated), causing the
cycle to be classified as an open cycle
November 5, 201721
Closed cycle gas turbine power plant
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
addition process from an
The exhaust process is
replaced by a constant-
pressure heat rejection
process to the ambient air.
Merits and Demerits of Closed Loop Cycle
Turbine over Open Loop Cycle turbine
Higher thermal efficiency
Improved heat transmission
Lesser Fluid friction
No loss in working medium
Large amount of cooling
water is required.
Not economical for moving
vehicles as weight /kW
developed is high.
Requires the use of very
large air heater.
Waste Heat Recovery
To improve the efficiency and
economic feasibility using Waste Heat
Recover exhaust gas waste heat in medium to
high temperature applications such as soaking
or annealing ovens, melting furnaces,
afterburners, gas incinerators, radiant tube
burners, and reheat furnaces.
Recuperators can be based on radiation,
convection, or combinations
Recuperators are constructed out of either
metallic or ceramic materials.
Heat exchange between
flue gases and the air
combustion air for
Waste heat stream on
The exhaust gasses
from the turbine carry a
large quantity of heat
with them since their
temperature is far
above the ambient
They can be used to
heat air coming from
the compressor there
by reducing the mass
of fuel supplied in the
Glass and steel melting
Time between the
reversals important to
Heat transfer in old
regenerators reduced by
Dust & slagging on surfaces
heat losses from the walls
Porous disk rotating
between two side-byside
Low to medium
temperature waste heat
Heat transfer efficiency
up to 85 %
Transfer up to 100
times more thermal
energy than copper
- sealed container
- capillary wick structure
- working fluid
Works with evaporation
Heat Pipe – Performance &
Lightweight and compact
No need for mechanical maintenance, input
power, cooling water and lubrication systems
Lowers the fan horsepower requirement and
increases the overall thermal efficiency of the
Can operate at 315 ◦C with 60% to 80% heat
A compressor utilizes
the major percentage of
power developed by the
The work required by the
compressor can be
reduced by compressing
the air in two stages and
intercooler between the
The output of gas
turbine can be
expanding the gasses
in two stages with a
reheater between the
The H.P. turbine
drives the compressor
and the LP turbine
provides useful power
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
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.
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
No need of forced draught fans as
the gases in furnace are already
Overall improvement in heat rate is
Employing the gases as combustion air in the
Exhaust gases are
used as preheated air
for combustion in the
boiler, results in 5%
improvement in heat
rate. The boiler is fed
fuel and air, and is
made larger than
Combined Gas Turbine and Diesel Power
The performance of
diesel engine can be
combining it with
exhaust driven gas
1. Turbo charging
2. Gas Generator
3. Compound engine
Turbo Charging / Supercharging
This method is known as
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
supplies the pressurized
air to the diesel engine to
increase its output.
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 air compressor is
driven from both
diesel engine and gas
turbine through a
suitable gearing and
power output is taken
from the diesel engine
Integrated Gasification Combined Cycle (IGCC)
Integrated Gasification Combined Cycle (IGCC) is
emerging as a best available technology to utilize low
quality or contaminated energy resources, coal or oil.
It can meet emission limits not achievable by other
conventional or advanced competing technologies.
In particular IGCC offers refiners the possibility of
reducing to zero the production of residual fuel oil, an
increasingly undesired product, while at the same time,
co-producing electricity, hydrogen and steam.
It also drastically cuts SO2 emissions.
Critical Factors for Selection of IGCC
IGCC is a capital-intensive technology.
Therefore, to exploit with maximum profit all the advantages
of this technology, it is important to optimize the design to
improve performance and reduce capital cost.
One important design aspect is the degree of integration
between the gas turbine and the air separation unit.
The choice of the optimum degree of integration can bring
substantial benefits in performance efficiency and capital
The selection of the best degree of integration to assure the
maximum profitability of IGCC.
The need of clean energy technologies has been in existence
since the first oil crisis more than 25 years ago.
IGCC is emerging today as one of the most promising
technologies to exploit low-quality solid and liquid fuels and
meet the most stringent emission limits.
How does IGCC work?
IGCC is a combination of two leading technologies.
The first technology is called coal gasification, which uses
coal to create a clean-burning gas (syngas).
The second technology is called combined-cycle, which is the
most efficient method of producing electricity commercially
The gasification portion of the IGCC plant produces a clean
coal gas (syngas) which fuels the combustion turbine.
Coal is combined with oxygen in the gasifier to produce the
gaseous fuel, mainly hydrogen and carbon monoxide.
The gas is then cleaned by a gas cleanup process.
After cleaning, the coal gas is used in the combustion turbine
to produce electricity.
As early as 1800, coal gas was made by heating coal in the absence of
Coal gas is rich in CH4
and gives off up to 20.5 kJ per liter of gas burned.
Coal gas or town gas, as it was also known became so popular that
most major cities and many small towns had a local gas house in which it
was generated, and gas burners were adjusted to burn a fuel that
produced 20.5 kJ/L.
A slightly less efficient fuel known as water gas can be made by reacting
the carbon in coal with steam.
C(s) + H2
O(g) → CO(g) + H2
(g) ( Ho
= 131.3 kJ/molrxn
Water gas burns to give CO2
O, releasing roughly 11.2 kJ per liter
of gas consumed.
Note that the enthalpy of reaction for the preparation of water gas is
positive, which means that this reaction is endothermic.
As a result, the preparation of water gas typically involves alternating
blasts of steam and either air or oxygen through a bed of white-hot coal.
The exothermic reactions between coal and oxygen to produce CO
provide enough energy to drive the reaction between steam
Water gas formed by the reaction of coal with oxygen and steam is
a mixture of CO, CO2
, and H2
. The ratio of H2
to CO can be increased
by adding water to this mixture, to take advantage of a reaction
known as the water-gas shift reaction.
CO(g) + H2
O(g) → CO2
(g) + H2
= -41.2 kJ/molrxn
The concentration of CO2
can be decreased by reacting the CO2
coal at high temperatures to form CO.
C(s) + CO2
(g) → 2 CO(g) Ho
= 172.5 kJ/molrxn
Water gas from which the CO2
has been removed is called
Synthesis gas can also be used to produce methane, or synthetic
natural gas (SNG).
CO(g) + 3 H2
(g) → CH4
(g) + H2
2 CO(g) + 2 H2
(g) → CH4
(g) + CO2