Transcript TURBINES - AIMES, Srinivas Integrated Campus,Mukka

‘Turbo Machine’ is defined as a
device that extracts energy from a
continuously
flowing fluid by the dynamic
action of one
or more rotating
elements .
The prefix ‘turbo’ is a Latin word
meaning
‘spin’ or ‘whirl’ implying
that turbo
machines
rotate
in
some way.
Types of Turbines
1.
2.
3.
Steam Turbines
Gas Turbines (Combustion Turbines)
Water (Hydraulic) Turbines
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Steam Turbines

A steam turbine is mainly used as an ideal prime mover in
which heat energy is transformed into mechanical energy in
the form of rotary motion.

A steam turbine is used in
1.
2.
3.
Electric power generation in thermal power plants.
Steam power plants.
To propel the ships, submarines.
In steam turbines, the heat energy of the steam is first
converted into kinetic (velocity) energy which in turn is
transformed into mechanical energy of rotation and
then drives the generator for the power generation.
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Based on action of steam or type of
expansion:
1.
2.
3.
Impulse or velocity or De Laval turbine
Reaction or pressure or Parson’s turbine
Combination turbine
Based on number of stages:
1.
Single stage turbine
2. Multi-stage turbine
Based on type of steam flow:
1.
Axial flow turbine
2. Radial flow turbine
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. The steam is made to
fall in its pressure by
expanding in a nozzle.
Due to this fall in
pressure,
a
certain
amount of heat energy is
converted into kinetic
energy, which sets the
steam to flow with a
 The
rapidly
moving particles of the steam enter the
greater
velocity.
rotating part of the turbine, where it undergoes a
change in the direction of motion, which gives rise
to a change of momentum and therefore a force.
This constitutes the
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force of the turbine.

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Impulse Turbines (De Laval
Turbine)
In this type of turbine, steam is
initially expanded in a nozzle from high
pressure to low pressure. High velocity
jet of steam coming out of the nozzle is
made to glide over a curved vane, called
‘Blade’.
The jet of steam gliding over the blade gets
deflected very closely to surface. This
causes the particles of steam to suffer a
change in the direction of motion, which gives
rise to a change of momentum and therefore a
force, which will be centrifugal in nature.
Resultant of all these centrifugal forces
acting on the entire curved surface of the
blade causes it to move.
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Q
VH
NOZZLE
PH
HIGH PRESSURE
STEAM
A
EXHAUST
STEAM
R
VL
P
PL
C
Velocity
Variation
Pressure
Variation
B
TURBINE
SHAFT
MOVING
BLADES
Schematic of Impulse Turbine
Nozzle
Rotor
Blades
Pressure-Velocity diagram in Impulse
Turbine
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Principle of working In this type of turbine, the
high pressure steam does
not initially expand in the
nozzle as in the case of
impulse
turbine,
but
instead directly passes
onto the moving blades.
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Blade shapes of reaction turbines are
designed in such a way that the steam
flowing between the blades will be
subjected to the nozzle effect. Hence,
the pressure of the steam drops
continuously as it flows over the
blades causing, simultaneous increase
in the velocity of the steam.
Reaction force:
is due to the change in
momentum relative velocity
of the steam while passing
over the blade passage.
Centrifugal force:
is the force acting on the
blade due to change in
radius of steam entering
and leaving the turbine.
Resultant force:
is the resultant of Reaction
force and Centrifugal force.
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Fixed Blade
Moving Blade
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Difference between Impulse & Reaction Turbines
Impulse Turbine
Reaction Turbine
The steam expands (pressure
drops) completely in nozzles or in
the fixed blades
The steam expands both in the
fixed and moving blades
continuously as it flows over them
The blades have symmetrical
profile of uniform section
The blades have converging
(aerofoil) profile
The steam pressure while passing
over the blades remains constant
The steam pressure while passing
over the blades gradually drops
Because of large initial pressure
Because of gradual pressure drop,
drop, the steam and turbine speeds the steam and turbine speeds are
are very high
low
The nozzles are fitted to the
The fixed blades attached to the
diaphragm (the partition disc
casing serve as nozzles
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Impulse Turbine
Reaction Turbine
Power is obtained only
due to the impulsive force
of the incoming steam
Power is obtained due to
impulsive force of
incoming steam as well as
reaction of exit steam
Suitable for small capacity Suitable for medium &
of power generation &
high capacity power
occupies less space per
generation and occupies
unit power
more space per unit power
Efficiency is lesser
Efficiency is higher
Compounding is
Compounding is not
necessary to reduce
necessary
speed
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Compounding of Impulse Turbines
As the complete expansion of steam takes in one stage
(i.e., the entire pressure drop from high pressure to low
pressure takes place in only one set of nozzles), the turbine
rotor rotates at very high speed of about 30,000 rpm
(K.E. is fully absorbed).
High speed poses number of technical difficulties like
destruction of machine by the large centrifugal forces
developed, increase in vibrations, quick overheating of
blades, impossibility of direct coupling to other
machines, etc.
To overcome the above difficulties, the expansion of
steam is performed in several stages.
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Utilization of the high pressure energy of
the steam by expanding it in successive
stages is called Compounding.
Methods of Compounding:
Velocity compounding (Curtis Impulse Turbine)
Pressure compounding
Pressure-velocity compounding
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Velocity compounding
Comprise of nozzles and two or more
rows
of moving blades arranged in
series. In
between
two
rows
of
moving blades, one set of guide (fixed)
blades are suitably
arranged.

Guide (fixed) blades are fixed to
casing and are stationary.

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N – Nozzle
M – Moving Blade
F – Fixed Blade
Velocity Compounding (Curtis Impulse Turbine)
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Pressure compounding
• Consists
of two stage of nozzles
followed by two rows of moving blades.
Pressure Compounding
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Pressure-Velocity Compounding
(Combined Impulse Turbine)
A – Axial clearance, N – Nozzle, M – Moving Blade, F – Fixed Blade
Pi and Pe – Pressure at inlet & exit, Vi and Ve - Velocity at inlet & exit
Total pressure drop is divided into two stages & the total
velocity obtained in each
stage is also compounded
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A Gas turbine uses the hot gases of
combustion directly to produce the
mechanical power.
Fuels used - Kerosene, coal, coal gas,
bunker oil, gasoline, producer gas, etc.,
Classification:
1.
2.
Open cycle gas turbine
Closed cycle gas turbine
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Applications
Gas turbines are used in:
Electric power generation plants
Steel, oil and chemical industries
Aircrafts, Ship propulsion
Turbo jet and turbo-propeller engines like
rockets, missiles, space ships etc.,
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Open cycle gas turbine:
The entire flow of the working substance
comes from atmosphere and is returned
to the atmosphere back in each cycle.
Closed cycle gas turbine:
The flow of the working substance of
specified mass is confined within the cyclic
path. ( Air or Helium is the working
substance)
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Open cycle gas turbine
• COMPRESSOR:
draws in air and compress it before it is fed
into combustion chamber
• COMBUSTOR:
fuel is added to the compressed air and
burnt to produce high velocity exhaust gas
• TURBINE:
extracts energy from exhaust gas
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Difference between open & closed cycle turbine
Open cycle
Lesser thermal efficiency
Loss of working fluid
Bigger in size
Big compressor is needed
Possibility of corrosion of blades and
rotor
Economical
Exhaust gases from turbine exit to
atmosphere
Closed cycle
Higher
No loss of working
fluid
Smaller
Smaller one is
sufficient
Free from corrosion
Not economical
Fed back into the
cycle
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Pharmaceutical
Pharmaceutical
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Hospitals
Hospitals
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Pulp
Pulp and
and Paper
Paper
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It is a prime mover, which converts hydro
power (energy of water) into mechanical
energy and further into hydro-electric
power.
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Classification of Water Turbines
Based on action of water:
1.
2.
Impulse turbine – pelton wheel.
Reaction turbine – francis and kaplan.
Based on name of originator:
1.
2.
3.
Pelton turbine or Pelton wheel
Francis turbine
Kaplan turbine
Based on head of water:
1.
2.
3.
Low head turbine
Medium head turbine
High head turbine
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Pelton Turbine
(Pelton Wheel or Free Jet Turbine)
High head, tangential flow, horizontal
shaft, impulse turbine
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PELTON TURBINE
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Pelton Turbine Runner
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Only a part of the pressure energy of
the water is converted into K.E. and
the rest remains as pressure head.
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First, the water passes to the guide
vanes which guide or deflect the water
to enter the blades, called moving
blades, mounted on the turbine wheel,
without shock.
The water from the guide blades are
deflected on to the moving blades,
where its part of the pressure energy is
converted into K.E., which will be
absorbed by the turbine wheel. The
water leaving the moving blades will
be at a low pressure.
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The difference in pressure between the
entrance and the exit of the moving blades
is called Reaction pressure, which acts on
moving blades of the turbine wheel and
sets up the turbine wheel into rotation in
the opposite direction.
Examples: Francis turbine, Kaplan turbine,
Propeller turbine, Thompson turbine, Bulb
turbine.
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Francis Turbine
Mixed flow, medium head reaction turbine.
Consists of a spiral casing enclosing a
number of stationary guide blades fixed all
round the circumference of an inner ring of
moving blades (vanes) forming the runner,
which is keyed to the turbine shaft.
Radial entry of water along the periphery of
the runner and discharge at the center of the
runner at low pressure through the diverging
conical tube called draft tube.
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FRANCIS TURBINE
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Francis Inlet Scroll, Grand Coulee Dam
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Francis Runner,
Grand Coulee Dam
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FRANCIS TURBINE
& GENERATOR
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Kaplan Turbine
Axial flow, low head.
Similar to Francis turbine except the runner
and draft tube.
The runner (Boss or Hub) resembles with the
propeller of the ship, hence some times it is
called as Propeller turbine.
Water flows parallel to the axis of the shaft.
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(GUIDE VANE)
(RUNNER VANE)
(SCROLL CASING)
KAPLAN TURBINE
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Vertical Kaplan Turbine
(Courtesy: VERBUND-Austrian
Hydro Power)
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Propeller Turbine Runner
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Objectives