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Vapour Power Cycles
UNIT 10 VAPOUR POWER CYCLES
Structure
10.1 Introduction
Objectives
10.2 The Carnot Vapour Cycle
10.3 Rankine Cycle
10.4 Actual Vapour Power Cycle
10.5 The Ideal Reheat Rankine Cycle
10.6 The Ideal Regenerative Rankine Cycle
10.6.1 Open Feed Water Heater
10.6.2 Closed Feed Water Heater
10.7 Binary Vapour Cycle
10.8 Summary
10.9 Key Words
10.10Answers to SAQs
10.1 INTRODUCTION
In any thermodynamic process, the use of working fluid gas or vapour is an essential
working medium to convert heat into work. A cycle, which continuously converts
heat into work is called the power cycle. In a power cycle, the working fluid performs
the various processes, which are suction, compression, expanding, condensing, etc.
All these processes are performed repeatedly to generate the work or converting heat
in to work. If the steam is alternatively vaporised and condensed, then the working
cycle is called vapour power cycle.
There are various types of working fluids available such as steam, sodium, potassium
and mercury. Some working fluids are used at high temperatures and some are at low
temperatures. The steam is the mostly used working fluid in the vapour power cycles.
The steam has the various desirable characteristics such as low cost, easy availability
and high enthalpy of vaporization.
In this unit we will be discussing about the vapour power cycles, which are mostly
used for steam power plants. The steam power plants are classified as coal plants,
nuclear plants, natural gas or geothermal plants, depending on the type of fuel used to
supply the heat to generate the steam.
Objectives
After studying this unit, you should be able to
describe the various vapour power cycles,
explain the various fuels used in the power plants, and
understand the concept of power cycle.
10.2 THE CARNOT VAPOUR CYCLE
The Carnot vapour cycle is used as an ideal power cycle for steam power plants.
Consider an ideal Carnot cycle as shown is the Figure 10.1. Here the working fluid is
water, in the cyclic process 1-2, water is heated reversibly and isothermally in a
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boiler, in the process 2-3 it is expanded isentropically in a turbine, in the process 3-4,
then expanded water is condensed reversibly and isothermally in a condenser and
finally in the process 4-1, the fluid is compressed isentropically by a compressor to
the initial state.
Error!
Figure 10.1 : Carnot Cycle on P-V and T-S Diagram
The four Carnot cycle processes are :
Isothermal heat addition from process 1-2,
Isentropic expansion of steam in an expander from process 2-3,
Isothermal heat rejection in the condenser from process 3-4, and
Isentropic compression of a mixture of vapour and liquid from process4-1.
By considering 1 kg of water as working fluid for a vapour power cyclic process
Heat added = Q1, which is shown on T-S diagram as area (1-2-2-1-1) = T1S,
S= change in entropy.
Heat added = Q2, area (3-2-1-4-3) on T-S diagram = T2S
Net Work done = W= Q1 Q2 = T1ST2S= (T1 T2) S
Thermal efficiency of the cycleWork done
Heat added=
1 2
1 1
1Q Q QW
Q Q
2
1Q
= = =
2 2
1 1
1 1T TS
T S T
= =
2
1
1thT
T = .
Limitations of Carnot Cycle
Carnot vapour power cycle is an ideal cycle, efficiency of which is
independent of the working substance 2Carnot1
1T
T
=
. But it is extremely
difficult to operate in practice because of the following reasons :
(a) It is difficult to compress a wet vapour isentroprically to thesaturated state as required by the process (4-1).
(b) It is difficult to control the quality of the condensate coming out ofthe condenser so that the state 4 is exactly obtained.
(c) The efficiency of the Carnot cycle is correctly attached by thetemperature T1 at which heat is transferred to the working fluid.
Since the temperature of steam is only 374oC, therefore, if the
T
S
s
1
4 3
2
1 2T1
T2
O
P
V
43
1 2
O
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cycle is to be operated in the wet region, the maximum possible
temperature is severely limited.
(d) Isentropic compression of a vapour requires more work due to itshigh specific volume thereby reducing the work ratio.
(e) Isothermal heat addition after the saturated vapour line is verydifficult to achieve as it involves heat addition at the same time
expansion of steam.
Due to the above reasons, it is not possible to achieve the high efficiency as
derived the Carnot vapour cycle.
10.3 RANKINE CYCLE
Rankine cycle is simplest and an ideal cycle for vapour power cycles. Rankine cycle
has four components and four thermodynamic processes. So each one of process
takes place in each component. The four components are shown in Figure 10.2
Boiler
Turbine
Pump
Q1
Wp
WT
Q2Condenser
|
4
1
2
3
(a) Rankine Cycle Components and System
Boiler Pressureh
3
4
2
1
Condenser Pressure
S
T1
23
4
S
3
WorkSuppliedto feedpump
1
2
4
v
P
Figure 10.2(b) : Rankine Cycle on T-S, p-v and h-s Diagram
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The four process takes places in rankine cycle are :
The process 1-2 is isentropic expansion in the turbine,
The process 2-3 is isobaric reversible heat rejection in the condenser,
The process 3-4 is a reversible adiabatic compression takes place in thepump, and
The process 4-1 is a isobaric heat addition process in the boiler.
To analyse and determine the efficiency of rankine cycle by taking working fluid as
water (1 kg) flowing through all the components of rankine cycle system. By
observing the rankine cycle in P-V, T-S and H-S diagrams as shown in Figure 10.2(b)
for calculating the efficiency of the rankine cycle.
The heat supplied = Q1 = (h1 h3) Wp
Where Wp = (h4 h3) is called pump work per kg steam.
The heat rejected into the condenser = Q2 = (h2 h3)
Net work done per kg of steam W= Q1 Q2 = WTWP = (h1 h3) Wp
Where WT= turbine work
Rankine cycle efficiency1
Network done
Heat suppliedR
W
Q= = =
1 2
1 3
( )
( )
pR
p
h h W
h h W
=
When pump work is negligible value, the Rankine cycle efficiency will be,
1 2
1 3
( )
( )R
h h
h h =
The expression of thermal efficiency can also be developed by introducing
thermodynamic mean temperature of heat addition. Thermodynamic mean
temperature of heat addition
1 4 1 4
1 4 1
Heat added
Change in entropyR
h h h h
S S S S 3
= = =
If pump work is neglected then
1 3
1 3av
h hTS S
=
The Rankine efficiency becomes
21Rav
T
T =
1 22
1 3
1RS S
Th h
=
10.3.1 Specific Steam Consumption (SSC)
Definition
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The specific steam (fluid) consumption is defined as the steam consumed in a
power plant to produce one unit power (kW).
Mathematically it is denoted as,
Steam Consumption/hrSSC = = kg/s/kW = kg/kWs
Net Power Output
1 2
3600
kg/kWhrh h=
Relative Efficiency
It is the ratio of Thermal Efficiency to the Rankine Efficiency
threl
R
=
Thermodynamic Variables
The thermodynamic variables which influence the efficiency and output
of Rankine cycle are :
By increasing the steam pressure at inlet to turbine is calledpressure at throttle condition.
By increasing the temperature of steam at inlet to turbinecalled temperature at throttle condition.
By decreasing the steam pressure at exhaust.
Effect of Pressure at Throttle Condition
By observing the Figure 10.3, you will notice that, by increasing the steam
pressure at inlet to turbine, keeping the minimum temperature and keeping the
exhaust pressure is assumed constant. Some increase in efficiency of the cycleis observed.
Figure 10.3 : Effect of Admission Pressure at Inlet to Turbine
Cycle 1-2-3-4-5-6-1 is for inlet pressure P and cycle 1-2-3-4-5-6-1 is forhigher inlet pressurep. From the figure we observe that at higher-pressurep,work done is reduced by the hatched area (1-2-2-6-1) but increased by the area(4-4-5-1-6-5-4). Both the areas are almost equal but at higher-pressure heatrejected is less by the amount of area 2-2-2-2. Therefore the efficiency isincreased.
Effect of Temperature
When the initial temperature of the steam increases, what effect it is going to
give on the efficiency of the power plant can be found.
T
S
3
p
4
4
15
O
65 p
2 2
2 2
6
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As shown in Figure 10.4, if we increase the temperature of a steam from T1 to
T1 at inlet of turbine, the work done will be increased by the amount of shaded
area 1-1-2-2-1. The heat supplied to the steam is also increased by the amountof
area 2-2-2-2-2. Therefore, the net efficiency of the cycle increases withincreases in degree of super heat.
T
3
S
1
O
Figure 10.4 : Rankine Cycle with Super Heat
Example 10.1A Steam power plant has steam at a Pressure of 40 bar and temperature 400
oC
and exhausted in to a condenser where, a pressure of 0.05 bar is maintained.
The mass flow rate of steam is 160 kg/sec. Determine :
The Rankine Cycle Efficiency
Rankine Engine Efficiency
Power Developed
Specific Steam Consumption
The Heat rejected into the Condenser per hour
Carnot Efficiency
Solution
P1 = 40 bar, t1 = 400oC, Pb = 0.05 bar, ms = 160 kg/sec.
From steam tables :
h1 = 3215.7 kJ/kg, s1 = 6.773 kJ/kgK,
s1 = s2 = sf2 +x2sfg2, Pb = 0.05 bar,
sf2 = 0.476 kg/kgK, sfg2 = 7.919 kg/kgK
Substituting the values
6.773 = 0.476 +x2 (7.919)
x2 = 0.795
h2 = hf2 +x2hfg2
h2 = 137.8 + 0.795 (2423.7)
h2 = 2064.64 kJ/kg
v3 = vf2= 1.005 10 3 m3/kg
(a) Rankine Cycle Efficiency1 2
1 3
( )
( )
pR
p
h h W
h h W
=
2 2
4
1
2 2
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(40 0.05)(3215.7 2064.64)
(10)
(40 0.05)(3215.7 137.8)
(10)
=
(1151.06 3.99)
(3077.9 3.99)
=
1147.07
3073.91=
0.37 37%R = =
(b) Rankine engine efficiency 1 2
1 3
( )
( )
h h
h h
=
(1151.06)
(3077.9)=
0.3739 37.39%= =
Note : Rankine engine efficiency is almost equal to Rankine efficiency.
Therefore in Rankine cycle efficiency, pump work is neglected.
(c) Power Developed Work done per kgsm=
1 2160 ( )h h=
160 (1151.6)=
= 184256 kW = 184.256 MW
(d) Specific steam consumption1 2
3600
( )h h=
3600
1151.6=
= 3.125 kg/hr.kW
(e) Heat rejected in the condenser 2 2( )sQ m h h3= =
160 (3077.9)=
= 422464 kJ/s
(f) Carnot efficiency 2
1
(273 32.9) 305.91 1 1
(273 250.3) 523.3
C
T
T
+ = = =
+
1 0.584 0.416 or 41.6%= =
SAQ 1
(a) Explain the working of Carnot cycle with the aid ofPVand T-Sdiagram.
(b) Explain the differences in Carnot cycle and Rankine cycle used in steampower plants.
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10.4 ACTUAL VAPOUR POWER CYCLE
Actual Vapour Power cycle is different than ideal Rankine cycle by observing
various irreversibilitys associated with components of the two systems. The ideal
and actual vapour power cycles are shown in the Figure 10.5. It can be observed that
the deviations of the actual pumps and turbines from the ideal isentropic ones can be
properly accounted for by using adiabatic efficiencies. Which are defined as :
2 1
2 1
iPP
G a
h hW
W h h = =
3 4
3 4
a aT
i i
W h h
W h h
= =
T
S
1
Irreversibilityin the Pump
O
Pressure Dropin the Boiler
2
4
3
Ideal Cycle
Irreversibilityin the Turbine
Pressure Dropin the CondenserActual Cycle
Figure 10.5 : Comparison of Actual and Ideal Vapour Power Cycles
T2 a
S
3
O
2 i
4 i1 4 a
Figure 10.6 : Effect of Pump and Turbine Irreversibilities on the Ideal Rankine Cycle
The various effects of irreversibilities associated with pumps and turbine on the ideal
Rankine cycle is as shown in Figure 10.6. In which 2 i, 4i are the isentropic exit states
of the pump and turbine and 2a, 4a are the actual exit states of the pump and turbine.
10.5 THE IDEAL REHEAT RANKINE CYCLE
Earlier we have explained that increasing the steam pressure at inlet to turbine and
decreasing the steam pressure at exhaust will increase the thermal efficiency of
Vapour Power cycle. In this system the moisture problem will be encountered at the
final stage of the turbine. To over come this problem the ideal reheat and
Regenerative cycle procedures will be used. In practice reheat and regeneration both
are used for improve the overall efficiency of the vapour power cycles.
The reheat Rankine cycle is shown in Figure 10.7. In this cycle extra low pressure
turbine is added. In reheat Rankine cycle; the steam which is collected from the HP
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turbine is reheated with the help of fine gases in the boiler furnace. Then the reheated
steam is sent to the LP turbine and the regular power cycle. The two turbines are used
here because reheating is done at higher pressures only. The reheating can be done
two or more stages, which will be determined by economical consideration.
Advantages of Reheat Cycles
Reheated steam eliminated the erosion and corrosion to the blades of theturbine,
Turbine output will be increased,
th will be increased,
Final dryness fraction is improved,
Nozzle and blade efficiencies are increased, and
Specific steam consumption is decreased.
Efficiency Calculation of Reheat Cycle
The total heat added per kg of steam
Q = (h1 h5) + (h3 h2) wP kJ/kg
Work done = W= (h1 h2) + (h3 h4) wP kJ/kg
where, wP = Pump work = h6 h5
Efficiency of reheat cycle1 2 3 4
1 5 3 2
( ) ( )
( ) ( )
p
p
h h h h wW
Q h h h h w
+ =
+
Figure 10.7 : Reheat Cycle Equipment
6
Condenser
Reheater
Feed Pump5
1
2
3
L. P TurbineH. P Turbine
|
4
|
T
S
3
O
6
2
4
5
1
h
S
3
O
P2
4
2
1
P3
P1
Figure 10.8 : Reheat CycleExample 10.2
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A Rankine cycle operates between pressures of 80 bar and 0.1 bar. The
maximum cycle temperature is 600oC. If the steam turbine and condensate
pump efficiencies are 0.9 and 0.8, respectively, calculate the specific work and
thermal efficiency. Relevant steam table extract is given below :
Specific Volume
(m3/kg)
Specific Enthalpy
(kJ/kg)
Specific Entropy
(kJ/kg K)
P
(bar)
T
(oC)
vf vg hf hfg hg sf sfg sg
0.1 45.84 0.0010103 14.68 191.9 2392.3 2584.2 0.6488 7.5006 8.1494
80 29.51 0.001385 0.0235 1317 1440.5 2757.5 3.2073 2.5351 5.7424
80 bar, 600oC v 0.486 m
3/kg
Super heat h 3642 kJ/kg
Table s 7.0206 kJ/kg
T
1
2
S
5
3
4
p1 = 80 bar
p2 = 0.1 bar
Figure 10.9
Solution
Refer to Figure 10.9
At 80 bar, 600oC
h1 = 3642 kJ/kg
s1 = 7.0206 kJ/kg
Since s1 = s2
2 27.0206 2f fgs x s= +
20.6488 7.5006x= +
27.0206 0.6488
0.857.5006x
= =
Now, 2 2 2 2f fgh h x h= +
191.9 0.85 2392.3 2225.36 kJ/kg= + =
Actual turbine work turbine 1 2( )h h=
0.9 (3642 2225.36) 1275 kJ/kg= =
Pump work2( ) 1 2
( )f pv p p=
5
3100.0010103 (80 0.1) 8.072 kJ/kg10
= =
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Actual pump workpump
8.072 8.07210.09 kJ/kg
0.8= = =
Specific work (Wnet) = 1275 10.09 = 1264.91 kJ/kg
Thermal efficiency net
1
W
Q=
1 1 4fQ h h=
4 3 Pump workf fh h= +
191.9 10.09 202 kJ/kg= + =
Thermal efficiency1264.91
0.368 or 36.8%3642 202
th = =
Example 10.3
In a Rankine cycle, the steam of inlet to turbine is saturated at a pressure of 35
bar and the exhaust pressure is 0.2 bar.Determine :
(a) The pump work,
(b) The turbine work,
(c) The Rankine efficiency,
(d) The condenser heat flow, and
(e) The dryness at the end of the expansion.
Assume flow rate of 9.5 kg/sec.
SolutionPressure and condition of steam, at inlet of turbine
p1 = 35 bar, x1 = 1,
Exhaust pressurep2 = 0.2 bar
Flow rate = 9.5 kg/sec
5 1
23
4
S
T
35 bar
0.2 bar
Figure 10.10
From steam table
At 35 barh1 = hg1 = 282 kJ/kg,
sg1 = 6.1228 kJ/kg KAt 0.2 bar
hf= 251.5 kJ/kg, hfg = 235.4 kJ/kg,
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vf= 0.001017 m3/kg, sf= 0.8321 kJ/kg K, sfg = 7.0773 kJ/kg K
(a) The pump work
Pump work 4 3( ) fp p v=
5(35 0.2) 10 0.001017=
33.54 10 J/kg or 3.54 kJ/kg=
Also 4 3 Pump work 3.54f fh h = = kJ/kg
4 251.5 3.54 255.04 kJ/kgfh = + =
Now power required to drive the pump
9.5 3.54 33.63 kW= =
(b) The turbine work
1 2 2 2 2f fgs s s x s= = +
26.1228 0.8321 7.0773x= +
26.1228 0.834
0.7477.0773
x
= =
2 2 2 2f fgh h x h= +
251.5 0.747 2358.4 2013 kJ/kg= + =
Turbine work 1 2( )m h h= &
9.5 (2802 2013) 7495.5 kW= =
It may be noted that pump work (33.63 kW) is very small as compared
to the turbine work (7495.5 kW).(c) The Rankine efficiency
1 2rankine
1 2
2802 20130.3093 or 30.93%
2802 251.5f
h h
h h
= = =
(d) The condenser heat flow
The condenser heat flow 2 3( ) 9.5 (2013 251.5)fm h h= = &
16734.25 kW=
(e) The dryness at the end of expansionx2 :
The dryness at the end of expansion,x2 = 0.747 or 74.7%.
10.6 THE IDEAL REGENERATIVE
RANKINE CYCLE
The practical ideal regenerative Rankine cycle is achieved by extracting steam from
the high-pressure turbine at various parts and is used for heating the feed water. The
device where the feed water is heated is known as regenerator. The regenerator also
de-operates the feed water, which is necessary to prevent corrosion in the boiler?
The feed water heaters of regenerators are classified as open feed water heater andclosed feed water heater.
Open Feed Water Heater
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6 )
6 )
)
As shown in Figure 10.9 the simple open feed water heater and the T-S
diagram, it is explained that the working of regenerative cycle with various
components.
Considern kg of Steam flowing from the boiler to the turbine. After expansion
ofn kg of steam of expanded to condenser pressure and leaves the turbine at
states-3. After condensation to states-4. Condensate water is enter to the heater
maintained at same pressure (n m) kg of condensate mixed with m kg of
taken out steam and the mixture come out at stage-6. Latent heat of taken out
steam has been used to heat the feed water upto saturation temperaturecorresponding to taken out steam pressure. Then n kg of heated condensate is
pumped to the boiler where heating starts from state-7. This cycle is not ideal
cycle as mixing in feed water heater is not reversible. However with infinite
number of taken out steam parts (bleedings), the mixing process become
reversible and theoretically Carnot efficiency can be attained. The mass of bled
steam (m) can be determined by energy balance and mass balance equations
applied to feed heater.
This gives :
2 5( ) (mh n m h n h+ =
h5 = h4 if pump work is neglected.
Then, 2 4( ) (mh n m h n h+ =
Knowing h2, h4 and h6, m can be determined.
Total work done 1 2 2 3( ) ( ) (W n h h n m h h= = +
Heat supplied = Q1 = (h1 h6) neglecting pump work
The efficiency of regenerative cycle is
1 2 2 3
1 6( )h h
( ) ( ) ( )n h h n m h h + = .
T
S
O
6 2
4
5
1
7
(n m)
P1
P2
Pb
m
n kg
3
6
Condenser
(n m) kg
Feed Pump
5|
2
3
Turbine
4
|
Feed heater7
n kg
Feed Pump
Boiler
1
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Figure 10.11 : A Simple Regenerative Cycle
Closed Feed Water Heater
In the Ideal closed feed water heater, the feed water is heated to the exit
temperature of the extracted steam, which leaves the heater below the exit
temperature of the extracted steam because a temperature difference of at least
a few degrees is required for any effective heat transfer to take place. The
condensed steam is then pumped to the feed water time or routed to another
heater or to the condenser through a device called a trap, which allows theliquid to be throttled to a lower pressure region but traps the vapour.
Advantages
Average temperature of heat addition to the cycle is increased.
The thermal stresses in the boiler are reduced.
Thermal efficiency will be increased.
The condenser capacity is reduced.
The hotter feed prevents the condensation of sulphur dioxide gases on
economiser.
Disadvantages
Cost of the plant increases.
Work done per kg of steam is reduced due to which boiler capacity isincreased for a given output.
10.7 BINARY VAPOUR CYCLE
In the vapour power cycles most commonly used working fluid is water. But at high
temperatures to get the high efficiency of vapour power cycle, some other working
fluids are used. At high temperatures a few working fluids are used, which are
mercury, sodium, potassium and sodium-potassium mixtures. Among these, only
mercury has been used in practice.
For the best performance, the working fluid should have the following characteristics
:
High Critical temperature and safe maximum pressure,
Low triple point temperature,
Condenser pressure which is not too low,
High enthalpy of vaporization,
Good heat transfer characteristics, and
Inert, easy availability at low cost.
To increase the efficiency of Cornot cycle, with an increase in initial temperature or
with the decrease in exit temperature of the fluid. At the normal pressure of 12 bar,
the saturation temperature for water and mercury are 187oC, 560
oC, respectively.
The highest temperature achieved in a power plants is about 550 600oC. Therefore
mercury is a better working fluid in the high temperature range, because its
vaporization pressure is relatively low. Mercury vapour at high temperature with low
pressure which avoid the difficulties connected with high pressure.
To get the high thermal efficiency of the power plant, by using two working fluidssuch as water and mercury, the binary vapour cycle has been developed. The power
cycle, which is a combination of two cycles, one in the high temperature region and
the other in the low temperature region, called the binary vapour cycle. In this cycle,
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the condenser of the high temperature cycle called the tapping cycle serves as the
boiler of the low temperature cycle, termed the bottom cycle. Mercury water binary
vapour cycle with
T-S diagram is as shown in Figure 10.12.
Cycle Efficiency Calculation
For calculation the efficiency of binary vapour power cycle, we must draw the
temperature (T), entropy (S) diagram. In this diagram it consist of mercury
cycle and steam cycle. The mercury leaves the condenser as saturated liquidand steam leaves as the saturated vapour. The mercury cycle 1-2- 2-3-4-1 isnamed as topping cycle and steam cycle 5-6-6-7-8-5 as bottoming cycle. Themercury leaves the condenser as saturated liquid and steam leaves as the
saturated vapour. The condensed mercury liquid is pumped back to its boiler
with the help of mercury pump. The evaporated steam is super heated in the
boiler, after being sent to economizer. It is then expanded isentropically in
steam turbine to a point 6, finally the steam is condensed in the steam
condenser upto point 7 and pumped to the steam boiler.
Boiler
MercuryPump
MercuryTurbine
Mercury Cycle
Heat Exchanger
SteamTurbine
Condenser
SteamPump
Steam Cycle
SuperHeater
1
2 3
4
5
6
7
8
T
8
9
S
O
67
3
4
10
2
1
4
Steam Cycle
MercuryCycle
SaturationDome (steam)
5
Q
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Figure 10.12 : Mercury Water Binary Vapour Cycle
Let 1 kg of steam be evaporated in the mercury condenser and it requires mhgof
mercury vapour. Energy balance for mercury condenser can be written as :
2 3( ) 1 (hg f em h h h h= = )
or2 3
( )
( )
k fhg
h hm
h h
=
By neglecting pump work
2 2 1 ( ) 1hg fg f e fgm x h h h h = =
Network done per kg of steam,
Wnet = (Mercury turbine work) (Mercury pump work) + (Steam turbine work) (Steam pump work)
1 2 4 3 5 6 8 7( ) ( ) ( ) ( )hg hgm h h m h h h h h h= + +
If the pump work is neglected
net 1 2 5 6( ) (hgW m h h h h= + )
)
Heat supplied per kg of working fluid
1 4 5 10 9 8( ) ( ) (s hgQ m h h h h h h= + +
Heat rejected per kg of working fluid (steam)
6 7( )rQ h h=
Cycle efficiency, netcycles r T P
S S
Q Q WW W
Q Q SQ
= = = .
SAQ 2
(a) Briefly describe the working of Ideal reheat Rankine cycle. Also explainthe advantages of reheat Rankine cycle.
(b) What are the various types of feed water heaters used in the regenerativeRanking cycle. Explain its properties.
10.8 SUMMARY
In this unit we have studied about vapour power cycles. We have also studied aboutvarious working fluids used in the vapour power cycles and their effects. It explains
that in most of the steam power plants, Carnot vapour cycle is used as an Ideal cycle.
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Vapour Power Cycles
We have learned about improving the efficiency of vapor power cycles, by changing
the thermodynamic variables. The thermal efficiency of Rankine cycles increased by
(a) Increasing the average temperature at which heat is added to the cycle.
(b) Decreasing the average temperature at which heat is rejected to thecycle.
Finally, we conclude this unit explaining various advantages and disadvantage of
vapour power cycles used in steam power plants.
10.9 KEY WORDS
Working Fluid : Working medium (water, gas or vapour, etc.)
used for converting heat into work is known as
working fluid.
Power Cycle : A cycle which continuously converts heat into
work is called the power cycle.
Rankine Cycle : It is simplest and an ideal cycle for vapour
power cycles.
Thermodynamic Variables : Thermodynamic variables (pressure,
temperature, etc.) which influence the
efficiency and output of Rankine cycle.
Regenerator : The device, where the feed water is heated is
known as regenerator.
10.10 ANSWERS TO SAQs
Refer the preceding text for all the Answers to SAQs.
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Engineering Applications
FURTHER READING
Ajay Kumar and G. N. Shah, (2004), Thermal Engineering, Narosa Publishing
House, New Delhi.
E. Radhakrishnan, (2000), Fundamentals of Engineering Thermodynamics, Prentice-
Hall of India, Pvt. Ltd. New Delhi.
B. Commoner, (1974), The Closing Circle, A Bantam Book, New York.
E. Cook, (1976),Man, Energy, Society, W. H. Freeman and Co., USA.
A. P. Fraas, (1982),Engineering Evaluation of Energy Systems, McGraw Hill Book
Company, New York.
R. W. Haywood,Analysis of Engineering Cycles.
R. Natarajan, A. W. Henham, (1992),Lecture Notes of Indo-British Workshop on
Economics and Management of Energy Conversion and Use, Madras.
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Vapour Power Cycles
ENGINEERING APPLICATIONSUnit 7, Refrigeration, describes the various types of refrigeration system. Also, it
explains the different types of refrigerants used in the refrigeration system. It further
elaborates on air craft cooling system and steam jet refrigeration system with suitable
solved problems and examples.
Unit 8 deals with Reciprocating Compressors. It describes the working of
reciprocating compressors with net diagrams and also explains the efficiency
calculation of compressor.
Unit 9, Energy Management, deals with the management of various resources
available in the nature. It also explains the strategies of energy management and
elaborates on role and principles of energy conservations strategies. Finally, itdescribes the concept of energy efficiency and scope of energy audit.
Unit 10, Vapour Power Cycles, deals with various types of vapour power cycles used
in the steam power plants. It also describes the various types of working fluids used
in the vapour power plants. The limitations of the Carnot cycle and advantages of
vapour power cycles are also highlighted in this unit. Finally, it concludes with
explaining the working of Binary Vapour Cycle.