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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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Engineering Applications

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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Vapour Power Cycles

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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Vapour Power Cycles

(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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Vapour Power Cycles

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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Vapour Power Cycles

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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Vapour Power Cycles

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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Vapour Power Cycles

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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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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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.

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