This document describes the Rankine cycle process used in steam power plants. It discusses key components like the boiler, turbine, pump and condenser. It establishes the saturated liquid and vapor lines that form the steam dome on a temperature-entropy diagram. It also describes ways to improve the thermal efficiency of the Rankine cycle, such as increasing the boiler pressure, superheating steam, using regeneration to preheat feedwater, and implementing reheating in multi-stage turbines. Regenerative cycles use extracted steam from turbines to preheat liquid feedwater prior to the boiler in closed or open feedwater heaters.

1. RANKINE CYCLE

2. Constant Pressure Process

3. Many Constant Pressure Processes
• If all of the saturated liquid
states are connected, the
saturated liquid line is
established.
• If all of the saturated vapor
states are connected, the
saturated vapor line is
established.
• These twolines intersect at
the critical point and form
what is often called the
“steam dome.”

4. Many Constant Pressure Processes
• If all of the saturated liquid
states are connected, the
saturated liquid line is
established.
• If all of the saturated vapor
states are connected, the
saturated vapor line is
established.
• These twolines intersect at
the critical point and form
what is often called the
“steam dome.”

5. Critical Point
• The region to the left of
the saturated liquid line
and below the critical
temperature is called
the compressed liquid
region.
• The region to the right
of the saturated vapor
line and above the
critical temperature is
called the superheated
region.
• At temperatures and
pressures above the
critical point, the phase
transition from liquid to
vapor is no longer
discrete.

7. BOILER
TURBINE
PUMP
CONDENSER
qin
wout
qout
win
1
3
42
Simplify the Power Plant

8. Vapor-cycle power plants
T
s
1
2
3
4
qin
win qout
wout

9. Thermal Efficiency
• Thermal efficiency can be
improved by
Lowering the condensing
pressure
(lower condensing
temperature, lower TL)
T
s
1
2
3
4
(a) lower pressure(temp)

10. Thermal Efficiency
• Thermal efficiency can be
improved by
Superheating the steam to
higher temperature
s
s
T
1
2
(b) Superheating

11. Thermal Efficiency
• Increasing the boiler pressure
(increase boiler temperature,
increase TH)
s
T
1
2
3
4
( c) increase pressure
Low quality,
high moisture content
Thermal efficiency can be
improved by

12. Rankine-cycle power plants
T
s
1
2
3
4
qin
win qout
wout

13. Equivalent Carnot Model of Rankine Model
smin smax
Tm,out
Tm,in

14. Reheating
• The optimal way of increasing the boiler pressure but not increase the
moisture content in the exiting vapor is to reheat the vapor after it exits from a
first-stage turbine and redirect this reheated vapor into a second turbine.
boiler
high-P
turbine
Low-P
turbine
pump
condenser
1
2
3
4
5
6
T
s
1
2
3 5
6
4
high-P
turbine
low-P
turbine

15. Regeneration
• From 2-2’, the temperature at 2 is very low, therefore, the heat addition process is
at a lower temperature and therefore, the thermal efficiency is lower.
• Use regenerator to heat up the liquid (feed water) leaving the pump before sending
it to the boiler, therefore, increase the averaged temperature (efficiency as well)
during heat addition in the boiler.
T
s
1
2
2’
3
4
Lower temp
heat addition
T
s
1
2
3
4
5
6
7
Use regenerator to heat up the feedwater
higher temp
heat addition
Extract steam from
turbine to provide
heat source in the
regenerator

16. RegenerativeCycle
• Improve efficiency by increasing feed water temperature before it enters the
boiler.
• Open feed water: Mix steam with the feed water in a mixing chamber.
• Closed feed water: No mixing.
Pump 24
Pump 1
Open
FWH
boiler
condenser1
23
5
6
7
1
2
3
4
5
6
7
T
s
Open FWH
(y) (1-y)
(y)
(1-y)

17. Closed Feedwater Heaters
• the closed feed water heater in which heat is transferred from the
extracted steam to the feed water without any mixing taking place.
• The two streams now can be at different pressure, since they do
not mix.