CHAPTER
10
Vapor and Combined Power Cycles
10-1 The Carnot Vapor Cycle
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
FIGURE10-1T-s diagram of two Carnot vapor cycles.
TH
TC
WNET
QH
QC
H
C
H
CH
T
T
T
TQW
1
1
max
max
(1)
(2)
Operating principles
10-2 Rankine Cycle: The Ideal Cycle for Vapor Power Cycles
• Operating principles• Vapor power plants• The ideal Rankine vapor power cycle• Efficiency
– Improved efficiency - superheat
QQININ
QQOUTOUT
WWTURBINETURBINE
WWPUMPPUMP
The conventional vapor power plant
QQININ
QQOUTOUT
WWTURBINETURBINE
WWPUMPPUMP
High temperature heat addition.
High temperature heat addition.
Low temperature heat rejection
Low temperature heat rejection
Work input to compress working fluid
Work input to compress working fluid
Turbine to obtain work by expansion of working fluid.
Turbine to obtain work by expansion of working fluid.
The conventional vapor power plant
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
FIGURE 10-2The simple ideal Rankine cycle.
A hypothetical vapor power cycle
Assume a Carnot cycle operating between Assume a Carnot cycle operating between two fixed temperatures as shown.two fixed temperatures as shown.
TT
ss
11
22 3
4
All processes are internally reversible.All processes are internally reversible.All processes are internally reversible.All processes are internally reversible.
ss
TT
11
22
33
44
3*3*
4*4*
The ideal Rankine cycle
All processes are internally reversible.All processes are internally reversible.All processes are internally reversible.All processes are internally reversible.
ss
TT
11
22
33
44
3*3*
4*4*
Reversible constant pressure heat rejection (4 1)
Reversible constant pressure heat rejection (4 1)
Reversible constant pressure heat addition (2 3)
Reversible constant pressure heat addition (2 3)
Isentropic compression (1 2)
Isentropic compression (1 2)
Isentropic expansion to produce work (3 4) or (3* 4*)
Isentropic expansion to produce work (3 4) or (3* 4*)
The ideal Rankine cycle
The ideal Rankine cycle(h-s diagram)
hh
ss
44
33
22WOUT
QH
QC11
WIN
s
43
12
43
hhQ
hhW
hhW
H
IN
OUT
H
NET
Q
W (3)
hh
ss
44
33
22WOUT
QH
QC11
WIN
Rankine cycle efficiency
Isentropic process, s = constant
All accessible states lieto the right of the process (1 2).
p11
ss
hh
p2
2
ss11 = s = s22
CVe
e
ei
i
i
j j
jCV smsmT
Q
dt
dS
N
i
iiCSCS pekehmWQdt
tdE
1
)(
Ideal Turbine WorkIdeal Turbine Work
(4)
• Steady state.• Constant mass flow• Isentropic Expansion (s = Constant)
– Adiabatic and reversible– No entropy production
• No changes in KE and PE– Usual assumption is to neglect KE and PE
effects at inlet and outlet of turbine.
Ideal turbine work
N
i
iiCSCS pekehmWQdt
tdE
1
)(
43 hhm
WOut
(4)
(5)
Ideal turbine work
12 hhm
WIN
121 PPvm
WIN
(6)
(7)
Work of Compression
hh
ss
44
3*3*
22WOUT
QH
QC11
WIN
Increased average temperature of heat addition
Increased average temperature of heat addition
Improved Rankine cycle efficiency
2*3
124*3
hh
hhhh
0*3
h
(8)
(9)
Improved Rankine cycle efficiency
10-3 Deviation of Actual Vapor Power Cycles from Idealized Ones
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.FIGURE 10-4(a) Deviation of actual vapor power cycle from the ideal Rankine cycle. (b) The effect of pump and turbine irreversibilities on the ideal Rankine cycle.
The Improved Rankine Cycle
10-4 How Can We Increase the Efficiency of the Rankine Cycle
Raising the average temperature of heat addition
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.FIGURE 10-6The effect of lowering the condenser pressure on the ideal Rankine cycle.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.FIGURE 10-7The effect of superheating the steam to higher temperatures on the ideal Rankine cycle.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.FIGURE 10-8The effect of increasing the boiler pressure on the ideal Rankine cycle.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
FIGURE 10-9A supercritical Rankine cycle.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
FIGURE 10-10T-s diagrams of the three cycles discussed in Example 9–3.
10-5 The Ideal Reheat Rankine Cycle
Assume a Carnot cycle operating between Assume a Carnot cycle operating between two fixed temperatures as shown.two fixed temperatures as shown.
TT
ss
11
22 3
4
A hypothetical vapor power cycle
A hypothetical vapor power cycle with superheat
Superheating the working fluid raises the Superheating the working fluid raises the average temperature of heat addition.average temperature of heat addition.
TT
ss
11
22
3
4
TTH,2H,2
TTH,1H,1
A hypothetical vapor power cycle: A Rankine cycle with superheat
s
T
d
b
c
T
HT
HT
Superheating the working fluid raises the average Superheating the working fluid raises the average temperature with a reservoir at a higher temperature.temperature with a reservoir at a higher temperature.
a
The extra expansion via reheating to state “d” allows a greater enthalpy to be released between states “c” to “e”.
ss
TT
f
a
b
c
p1
p2
d
e
HT
CT
The Rankine cycle with reheat
QOUT
WWININ
aa
bb
eeff
QQHH
WWOUTOUT
QQCC
ccdd
Single stage reheat. Workproduced in both turbines.Single stage reheat. Workproduced in both turbines.
The reheat cycle
Reheat Cycle Efficiency
cdab
faedcb
dcba
afedcb
hhhh
hhhhhh
WWW
)()(
(1)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
FIGURE 10-11The ideal reheat Rankine cycle.
Example 1
Example - 1: A Carnot cycle
To begin our analysis of Rankine cycle operations, consider a To begin our analysis of Rankine cycle operations, consider a steady Carnot cycle (a-b-c-d-a) with water as the working fluidsteady Carnot cycle (a-b-c-d-a) with water as the working fluidoperating between to given temperature limits as shown. The operating between to given temperature limits as shown. The given data are that the boiler pressure is 500 psi (pgiven data are that the boiler pressure is 500 psi (paa = 500 psi) and = 500 psi) and
the condenser temperature is 70the condenser temperature is 70o o F (TF (Tcc = 70 = 70oo F). Determine the F). Determine the
work outputwork output, , thermal efficiencythermal efficiency,, irreversibility irreversibility, and , and work ratiowork ratio..
b
cd
a TT11
TT22
T
s
aa bb
ccdd
T1
T2
p1
p2
Example 1 - Given data
a 500
b 500
c 530
d 530
State TR
Ppsi
hBTU/lbm
sBTU/lbm-R
x
Example 1 - Computed data
a 927 500 449 0.6487 0
b 927 500 1204 1.4634 1
c 530 0.361 774 1.4634 0.698
d 530 0.361 342 0.6487 0.288
State TR
Ppsi
hBTU/lbm
sBTU/lbm-R
x
Example 1 - Process quantities
Process HBTU/lbm
WBTU/lbm
QBTU/lbm
SBTU/lbm-R
Q/TBTU/lbm-
R
s
BTU/lbm-R
a-b 755 0 755 0.8147 0.8147 0b-c -430 430 0 0 0 0c-d -432 0 -432 -0.8147 -0.8147 0d-a 107 -107 0 0 0 0Net 0 323 323 0 0 0
To get the above process quantities, the First Law for open systemsTo get the above process quantities, the First Law for open systemshas been used assuming KE and PE effects are negligible. Thehas been used assuming KE and PE effects are negligible. Theentropy production was obtained from an entropy balance for anentropy production was obtained from an entropy balance for anopen system. Note that the cyclic heat equals the cyclic work as open system. Note that the cyclic heat equals the cyclic work as required by the First Law and that entropy production is zero as required by the First Law and that entropy production is zero as required by the Clausius Equality.required by the Clausius Equality.
Thermal efficiencyThermal efficiency
Work ratioWork ratio
428.0755
323
HQ
W
249.0430
107
Turbine
in
W
Wr
Example 1 - Thermal efficiency and back work ratio
Example 2
Example 2 - A Rankine cycle without superheat
A Rankine cycle with water as the working fluid operates betweenA Rankine cycle with water as the working fluid operates betweenthe same limits as in Example l, pthe same limits as in Example l, paa = 500 psi and a condensing = 500 psi and a condensing
temperature of 70temperature of 70oo F. Assuming all processes to be internally F. Assuming all processes to be internally reversible, determine the work output, efficiency, entropy reversible, determine the work output, efficiency, entropy production, work ratio.production, work ratio.
TT
ss
aabb
ccdd
T1
T2
pa
pd
Example 2 - Computed data
a 927 500 39.5 0.0745 0
b 927 500 1204 1.4634 1
c 530 0.361 774 1.4634 0.698
d 530 0.361 38.0 0.0745 0
State TR
Ppsi
hBTU/lbm
sBTU/lbm-R
x
Example 2 - Process quantities
Process HBTU/lbm
WBTU/lbm
QBTU/lbm
SBTU/lbm-R
Q/TBTU/lbm-
R
s
BTU/lbm-R
a-b 1164.5 0 1164.5 1.3889 1.3889 0b-c -430 430 0 0 0 0c-d -736 0 -736 -1.3889 -1.3889 0d-a 1.5 -1.5 0 0 0 0Net 0 428.5 428.5 0 0 0
Work output =Work output = 428.5 BTU/lbm428.5 BTU/lbmThermal efficiency =Thermal efficiency = 36.8%36.8%Work ratio = Work ratio = 0.00350.0035Entropy production = Entropy production = 00
Example 3
Example 3 - Effect of irreversibility in the turbine and pump
A Rankine cycle operates between the same limits as above and A Rankine cycle operates between the same limits as above and has pump and turbine efficiencies of 80%. Determine the work has pump and turbine efficiencies of 80%. Determine the work output, efficiency, work ratio, and entropy production. Assume output, efficiency, work ratio, and entropy production. Assume the condensing and ambient temperatures to be the same.the condensing and ambient temperatures to be the same.
T1
T2
ss
aa bb
ccdd
pa
pd
c’c’
a’a’
TT
Example 3 - Computed data
The states at a’ and c’ are determined via the First Law for an The states at a’ and c’ are determined via the First Law for an open system and the definition of isentropic efficiency for turbinesopen system and the definition of isentropic efficiency for turbinesand pumps as appropriate.and pumps as appropriate.
State TR
Ppsi
hBTU/lbm
sBTU/lbm-R
x
a 530 500 39.5 0.0745 …a’ 530 500 39.9 0.0753 …b 927 500 1204 1.4364 1c 530 0.3631 774 1.4364 0.698c’ 530 0.3631 860 1.6262 0.780d 530 0.3631 38.0 0.0745 0
Example 3 - Process quantities
Process hBTU/ lbm
WBTU/ lbm
QBTU/ lbm
sBTU/lbm-R
Q/ TBTU/lbm-R
s
BTU/lbm-R
(a’-a) (0.4) (0) (0.4) (0.0008) (0.0008) (0)a-b 1164 0 1164 1.3881 1.3881 0(b-c’) (-430) (0) (0) (0) (0) (0)b-c -344 344 0 0.1628 0 0.1628c-d -822 0 -822 -1.5517 -1.5517 0(d-a’) (1.5) (-1.5) (0) (0) (0) (0)d-a 1.9 -1.9 0 0.008 0 0.0008Net 0 342 342 0 -0..1636 +0.1636
Isentropic processes are determined prior to actual processes whereIsentropic processes are determined prior to actual processes where
irreversibility is involved.irreversibility is involved.
Work output = 342 BTU/lbm Thermal efficiency = 29.4%Work ratio = 0.0054 Entropy production = 0.1636
BTU/lbm-R
Example 3 - Comparison
Example 1Carnot
Example 2Basic Rankine
Example 3Pump and Turbine
IrreversibilityWork 323 428.5 342
Work Ratio 0.249 0.0035 0.0054Thermal Efficiency 42.8% 36.8% 29.4%Entropy Production 0 0 0.1636
Example 4
Example 4 - Superheat
An internally reversible Rankine cycle is determined by specifyingAn internally reversible Rankine cycle is determined by specifyinga maximum temperature of 800a maximum temperature of 800o o F, a quality at the turbineF, a quality at the turbinedischarge of 0.9, and a minimum condensing temperature of 70discharge of 0.9, and a minimum condensing temperature of 70ooF.F.Compare the Compare the thermal efficiencythermal efficiency with that of a with that of a Carnot cycleCarnot cycleoperating between the same temperature limits.operating between the same temperature limits.
ss
bb
aa
ccddpd
paTT
Example 4 - Given and computed data
Process HBTU/lbm
WBTU/lbm
QBTU/lbm
a-b 1391 0 1391b-c -441.5 441.5 0c-d -950 0 -950d-a 0.5 -0.5 0Net 0 441
Example 4 - Thermal efficiency
Thermal efficiencyThermal efficiency
The Carnot efficiency
316.01391
441
579.01230
53011
H
CC
T
T
Example 5
Example 5 - The reheat cycle
f
a
b
c
pa pc
ss
d
e
TT Fo800
CT
Fo70
90.0cx
90.0ex
Example 5 - Given and computed data
The state at “c” has the same as the pressure specified in Example 4.The state at “c” has the same as the pressure specified in Example 4.This determines state “b”. State “a” is determined via the usualThis determines state “b”. State “a” is determined via the usualapproximation for an incompressible liquid under going processapproximation for an incompressible liquid under going processf-a.f-a.
Example 5 - Process quantities
Process HBTU/lbm
WBTU/lbm
QBTU/lbm
a-b 1315 0 1315b-c -264 264 0c-d 336 0 336d-e -442 442 0e-f -950 0 -950f-a 5 -5 0Net 0 701 701
Work output = 701 BTU/lbmWork output = 701 BTU/lbmThermal efficiency = 701/(1315+336) = 0.424Thermal efficiency = 701/(1315+336) = 0.424Carnot efficiency = 1-(530/1260) = 0.579Carnot efficiency = 1-(530/1260) = 0.579
Example 6
0.2
0.22
0.24
0.26
0.28
0.3
300 350 400 450 500 550 600 650 700
Pupper (psia)
Variation of the (First Law) cycle efficiency with a variationof the pressure of heat addition in a basic Rankine cycle with no super heat. The condenser pressure was assumed to be 14 psia.
5623
124653
6532
214653
)()(
hhhh
hhhhhh
WWW
TT
ss
1
2
3
5
6
4
p2
pmiddle
0.2
0.22
0.24
0.26
0.28
0.3
0 100 200 300 400 500 600
Pmiddle (psia)
Pup = 400 psia
Pup = 500 psia
Pup = 600 psia
The variation of cycle efficiency of a Rankine cycle with onestage of reheat as a function of the pressure at which reheat isdone. Pup is the pressure of high temperature heat addition.
Key terms and concepts
Cycle efficiencyRankine cycle with reheat
Rankine cycle with regenerationWork ratio
10-6 The Ideal Regenerative Rankine cycle
Another technique to raise the average temperature of the heat addition process.
Overview
• Review - The reheat cylce
• The Rankine Cycle with regeneration– Open and closed feedwater heaters
• Example
The Reheat Cycle
• Reheating the expanding fluid with primary heat source is made at inter-mediate points in the expansion process.
• Net effect is to raise the average expansion temperature of the turbine without raising the temperature of the heat source.
The Reheat Cycle
The extra expansionThe extra expansionallows a greater enthapyallows a greater enthapyto be released betweento be released betweenstates 3 to 4.states 3 to 4.
Here one additionalHere one additionalreheat process hasreheat process hasbeen added.been added.
The extra expansionThe extra expansionallows a greater enthapyallows a greater enthapyto be released betweento be released betweenstates 3 to 4.states 3 to 4.
Here one additionalHere one additionalreheat process hasreheat process hasbeen added.been added.
TT
s
1
2
3
5
6
4
p2
p1
5623
124653
6532
214653
)()(
hhhh
hhhhhh
WWW
TT
s
1
2
3
5
6
4
p2
p1
The Rankine cycle with regeneration
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
FIGURE 10-14The first part of the heat-addition processin the boiler takesplace at relatively low temperatures.
Principle of the regenerative cycle
c
a
b
f
WWOUTOUT
WIN
QQHH
QQCCA higher feed water inletA higher feed water inlettemperature as a result oftemperature as a result ofheating from States a - b.heating from States a - b.
de
• Heating of some of the compressed liquid is done to raise the average temperature of heat addition.
• Heat is supplied after the liquid is compressed to a high pressure at State a.
Impacted processes
The T-s diagram for the regenerative cycle
TT
f
b
c
ssInternal heat transfer to feed water heater.Internal heat transfer to feed water heater.
e
d
a
• Turbines cannot be designed economically with internal heat exchangers.
• Condensation could occur in the turbine.
Not practical!
Practical considerations...
The practical regenerative cycle
5
QQ2-32-3 = 0 = 0
123
WW2,out2,out
WWIN,1IN,1
QQHH 6
WWIN,2IN,2
7
QQCC
4
WW1,out1,out
Feedwater heaterFeedwater heaterFeedwater heaterFeedwater heater
45
122,341,
762,651,
1
)1(
hhQ
hhyWandhhW
hhyWandhhW
H
ININ
OUTOUT
hh
ss
1
3
4
2
WOUT,1
QQHH
QQCC
WIN,1
5
6
7
WOUT,2WIN,2
(1 kg)
(y kg)
(1-y kg)
The h-s diagram for the regenerative cycle
Energy balances and thermal efficiency
45
12347665 )1()1(
hh
hhyhhhhyhh
hh
ss
1
3
4
2
WOUT,1
QQHH
QQCC
WIN,1
5
6
7
WOUT,2WIN,2
(1 kg)
(y kg)
(1-y kg)
Feedwater heaters
Open and Closed
Feedwater Heaters
Regeneration with an open feedwater heater
QQCC
Regeneration with Regeneration with an an open feedwateropen feedwater heater at the massheater at the massfraction rate of “y” fraction rate of “y” per unit mass of per unit mass of primary the flow primary the flow rate.rate.
Regeneration with Regeneration with an an open feedwateropen feedwater heater at the massheater at the massfraction rate of “y” fraction rate of “y” per unit mass of per unit mass of primary the flow primary the flow rate.rate.
QQHH
yy 1-y1-y
WWIN,1IN,1 WWIN,2IN,2
WWOUTOUT
yy
From the outletFrom the outletof the condenser of the condenser and first feedwaterand first feedwaterpump. (1-y kg.)pump. (1-y kg.)
From theFrom theturbine.turbine.(y kg.)(y kg.)
To the secondTo the second feedwater pump.feedwater pump.(1 kg.)(1 kg.)
1-y1-y
The open feedwater heater
Regenerative cycle with a closed feedwater heater
55
11
22 33
44
66
77 88
yy1-y1-y
yy
1-y1-y
QQHH QQCC
WWTT
Closed Closed feedwaterfeedwaterheaterheater
TrapTrap
CondenserCondenser
T-s diagram for a regenerative cycle with a closed feedwater heater
1
2
34
5
67
8
ss
TT
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
FIGURE 10-15The ideal regenerative Rankine cycle with an open feedwater heater.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
FIGURE 10-16The ideal regenerative Rankine cycle with a closed feedwater heater.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.FIGURE 10-17A steam power plant with one open and three closed feedwater heaters.
Example - Regeneration with a single extraction and an open feedwater heater
Example
A regenerative Rankine cycle with a single extraction A regenerative Rankine cycle with a single extraction provides saturated steam at 500 psi a the turbine inlet.provides saturated steam at 500 psi a the turbine inlet.Condensation takes place at 70Condensation takes place at 70oo F. One open regenerative F. One open regenerativefeedwater heater is included, using extracted steam at a feedwater heater is included, using extracted steam at a temperature midway between the limits of the cycle. temperature midway between the limits of the cycle. All processes are assumed to be internally reversible All processes are assumed to be internally reversible except that in the regenerative heater. Neglect KE and except that in the regenerative heater. Neglect KE and PE effects, and determine the thermal efficiency, PE effects, and determine the thermal efficiency, the internal irreversibility, and the extraction pressure. the internal irreversibility, and the extraction pressure. Assume steady operation.Assume steady operation.
Example - Plant diagram
WWOUTOUT
QQCC
aa
dd
ee
cc
bbQQHH
yy 1-y1-y
WWIN,1IN,1 WWIN,2IN,2
gg ff
Example - T-s diagram
aabb
cc
ddee
ff
gg
yy
1-y1-y
11
1-y1-y
TT
ss
Example - Mass fraction at State “c”Example - Mass fraction at State “c”
The mass fraction of fluid extracted at State c is obtainedThe mass fraction of fluid extracted at State c is obtainedfrom the energy balance for an open system applied tofrom the energy balance for an open system applied tothe feedwater heater. the feedwater heater. Assume adiabatic mixingAssume adiabatic mixing..
aa bb
cc
ddee
ffgg
yy
1-y1-y
11
1-y1-y
TT
ss
gfc
gfccc
hhyyh
hmhmmhm
1
chy,
fhy,1gh
Example - Entropy balance for the feedwater heaterExample - Entropy balance for the feedwater heater
Apply the entropy balance for an open system to the Apply the entropy balance for an open system to the feedwater heater.feedwater heater.
fgcg
fcg
ssyssy
syyss
1
1
cc shy ,,
ff shy ,,1gg sh ,
Given DataSTATE T
RP
psih
BTU/ lbms
BTU/lbm-Rx
a 728.7 500 …b 500 1c 728.5d 530e 530 0f 530 …g 728.7 0
Example - Given data
Computed Data (From Tables)STATE T
RP
psih
BTU/ lbms
BTU/lbm-Rx
a 728.7 500 239.1 0.3940 …b 927 500 1204.4 1.4364 1c 728.5 41 1016 1.4364 0.835d 530 0.361 774 1.4364 0.698e 530 0.361 38 0.0745 0f 530 41 38.1 0.0745 …g 728.7 41 237.6 0.3940 0
Example - Computed data
Process QuantitiesProcess H
BTU/ lbmm mh
BTU/ lbm
WBTU/ lbm
a-b 965 1 965 0b-c -188 1 -188 188c-d -242 0.796 -193 193d-e -736 0.796 -586 0e-f 0.1 0.796 0.1 -0.1f-g 199.5 0.796 159c-g -778 0.204 -159
0
g-a 1.5 1 1.5 -1.5Net … … 0 379.4
Example - Process quantities
Process QuantitiesProcess Q
BTU/ lbmds
BTU/ lbm-Ryds
BTU/ lbm-R
Q/TBTU/lbm-R
BTU/lbm-R
a-b 965.3 1.0694 1.0694 1.0694 0b-c 0 0 0 0 0c-d 0 0 0 0 0d-e -586 -1.3889 -1.1056 -1.1056 0e-f 0 0 0 0 0f-g 0.3195 0.2543c-g
0-1.0694 -0.2180
0 0.0363
g-a 0 0 0 0 0Net 379.3 … 0 -0.0362 0.0363
Note the positive entropy production in Note the positive entropy production in the feedwater heater.the feedwater heater.Note the positive entropy production in Note the positive entropy production in the feedwater heater.the feedwater heater.
Example - Process quantities
393.0965
4.379
HQ
W
Note that regeneration has increased thermalNote that regeneration has increased thermalefficiency above that of the previous example at efficiency above that of the previous example at the expense of some work output per lbm of steam.the expense of some work output per lbm of steam.
Example - Thermal efficiency
Commercial steam-power plants
• Reheat (multiple stages)
• Regeneration (multiple extractions)
• Nearly ideal heat addition – Constant temperature boiling for water
Commercial steam-power plants
• Heat transfer characteristics of steam and water permit external combustion systems
• Compression of condensed liquid produces a favorable work ratio.
Commercial steam-power plants
• 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
10-7 Second-Law Analysis of Vapor Power Cycles
10-8 Cogeneration
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
FIGURE 10-20A simple process-heating plant.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
FIGURE 10-21An ideal cogeneration plant.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
FIGURE 10-22A cogeneration plant with adjustable loads.
10-9 Combined /gas-Vapor Power Cycles
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
FIGURE 10-24Combined gas–steam power plant.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
FIGURE 10-26Mercury–water binary vapor cycle.