Vapour power cycle a

 By:
Naphis ahmad
Assistant professor
JIT, Barabanki
12/31/2016 Jhangirabad institute of technology 1

 Operating principles
 Vapor power plants
 The ideal Rankine vapor power cycle
 Efficiency
◦ Improved efficiency - superheat

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Jhangirabad institute of technology 3

 Assume a Carnot cycle operating between
 two fixed temperatures as shown.
T
s
1
2 3
4

All processes are internally reversible.
s
T
1
2
3
4
3*
4*
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All processes are internally reversible.
s
T
1
2
3
4
3*
4*
Reversible constant
pressure heat rejection
(4  1)
Reversible constant
pressure heat addition
(2  3)
Isentropic
compression
(1  2)
Isentropic
expansion to
produce work
(3  4) or
(3*  4*)
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h
s
4
3
2
WOUT
QH
QC1
WIN
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s
43
12
43
hhQ
hhW
hhW
H
IN
OUT



H
NET
Q
W
 (3)
h
s
4
3
2
WOUT
QH
QC1
WIN
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FIGURE 10-6
The effect of lowering the condenser pressure on the ideal Rankine cycle.
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FIGURE 10-7
The effect of superheating the steam to higher temperatures on the ideal Rankine cycle.
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FIGURE 10-8
The effect of increasing the boiler pressure on the ideal Rankine cycle.
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FIGURE 10-10
T-s diagrams of the three cycles discussed in Example 9–3.
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Superheating the working fluid raises the
average temperature of heat addition.
T
s
1
2
3
4
TH,2
TH,1
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s
T
d
b
c
T
HT
HT
Superheating the working fluid raises the average temperature with a reservoir at a
higher temperature.
a
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The extra expansion via reheating to state “d” allows a
greater enthalpy to be released between states “c” to
“e”.
s
T
f
a
b
c
p1
p2
d
e
HT
CT
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FIGURE 10-11
The ideal reheat Rankine cycle.
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The first part of the heat-addition process in the boiler takes place at relatively low
temperatures.
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The ideal regenerative Rankine cycle with an open feedwater heater.
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FIGURE 10-16
The ideal regenerative Rankine cycle with a closed feedwater heater.
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FIGURE 10-17
A steam power plant with one open and three closed feedwater heaters.
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 Reheat (multiple stages)
 Regeneration (multiple extractions)
 Nearly ideal heat addition
◦ Constant temperature boiling for water

 Heat transfer characteristics of steam and water permit
external combustion systems
 Compression of condensed liquid produces a favorable
work ratio.

 The Rankine cycle with reheat and regeneration is
advantageous for large plants.
 Small plants do not have economies of scale
◦ Internal combustion for heat addition.
◦ A different thermodynamic cycle

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A simple process-heating plant.
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An ideal cogeneration plant.
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FIGURE 10-22
A cogeneration plant with adjustable loads.
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Combined gas–steam power plant.
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Mercury–water binary vapor cycle.
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A steam turbine is a prime mover in which
potential energy is converted into kinetic energy
and then to Mechanical energy.
Potential Energy
Kinetic energy
Mechanical Energy
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Jhangirabad institute of technology
34
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Description of common types of Turbines.
1. Impulse Turbine.
2. Reaction Turbine.
The main difference between these two turbines
lies in the way of expanding the steam while it
moves through them.
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In the impulse turbine, the steam expands in
the nozzles and it's pressure does not alter as it
moves over the blades.
In the reaction turbine the steam expanded
continuously as it passes over the blades and
thus there is gradually fall in the pressure
during expansion below the atmospheric
pressure.
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ENTRANCE
HIGH THERMAL ENERGY
HIGH PRESSURE
LOW VELOCITY
STEAM INLET
EXIT
LOW THERMAL ENERGY
LOW PRESSURE
HIGH VELOCITY
STEAM EXHAUST
PRESSURE
VELOCITY
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Simple impulse Turbine.
It the impulse turbine, the steam expanded within
the nozzle and there is no any change in the steam
pressure as it passes over the blades
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NOZZLE
STEAM
CHEST
ROTOR
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VELOCITY
PRESSURE
TURBINE
SHAFT
DIRECTION OF SPIN
ENTRANCE
HIGH VELOCITY
STEAM INLET
REPRESENTS MOVING
IMPULSE BLADES
EXIT
LOW VELOCITY
STEAM EXHAUST
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Reaction Turbine
In this type of turbine, there is a gradual pressure drop
and takes place continuously over the fixed and moving
blades. The rotation of the shaft and drum, which
carrying the blades is the result of both impulse and
reactive force in the steam. The reaction turbine consist
of a row of stationary blades and the following row of
moving blades
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The fixed blades act as a nozzle which are attached inside
the cylinder and the moving blades are fixed with the rotor
as shown in figure
When the steam expands over the blades there is
gradual increase in volume and decrease in pressure. But
the velocity decrease in the moving blades and increases in
fixed blades with change of direction.
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Because of the pressure drops in each stage, the number of
stages required in a reaction turbine is much greater than in
a impulse turbine of same capacity.
It also concluded that as the volume of steam
increases at lower pressures therefore the diameter of the
turbine must increase after each group of blade rings.
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STEAM CHEST
ROTOR
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46
TURBINE
SHAFT
DIRECTION OF SPIN
ENTRANCE
HIGH PRESSURE
HIGH VELOCITY
STEAM INLET
REPRESENTS MOVING
REACTION BLADES
EXIT
LOW PRESSURE
LOW VELOCITY
STEAM EXHAUST
PRESSURE
VELOCITY
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Compounding in Steam Turbine.
The compounding is the way of reducing the wheel or rotor
speed of the turbine to optimum value.
Different methods of compounding are:
1.Velocity Compounding
2.Pressure Compounding
3.Pressure Velocity Compounding.
In a Reaction turbine compounding can be achieved only by
Pressure compounding.
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Velocity Compounding:
There are number of moving blades separated by rings of fixed
blades as shown in the figure. All the moving blades are keyed
on a common shaft. When the steam passed through the nozzles
where it is expanded to condenser pressure. It's Velocity
becomes very high. This high velocity steam then passes
through a series of moving and fixed blades. When the steam
passes over the moving blades it's velocity decreases. The
function of the fixed blades is to re-direct the steam flow
without altering it's velocity to the following next row moving
blades where a work is done on them and steam leaves the
turbine with allow velocity as shown in diagram.
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Velocity Compounding
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Pressure Compounding:
These are the rings of moving blades which are keyed on a
same shaft in series, are separated by the rings of fixed
nozzles.
The steam at boiler pressure enters the first set of
nozzles and expanded partially. The kinetic energy of the
steam thus obtained is absorbed by moving blades. The
steam is then expanded partially in second set of nozzles
where it's pressure again falls and the velocity increase the
kinetic energy so obtained is absorbed by second ring of
moving blades.
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Pressure Compounding
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Pressure velocity compounding:
This method of compounding is the combination of two
previously discussed methods. The total drop in steam
pressure is divided into stages and the velocity obtained in
each stage is also compounded. The rings of nozzles are fixed
at the beginning of each stage and pressure remains constant
during each stage as shown in figure. The turbine employing
this method of compounding may be said to combine many of
the advantages of both pressure and velocity staging By
allowing a bigger pressure drop in each stage, less number
stages are necessary and hence a shorter turbine will be
obtained for a given pressure drop.
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Reaction turbine pressure compounding
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Vapour power cycle a

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