1. Generation of Most Eligible Steam for Rankine Cycle
P M V Subbarao
Professor
Mechanical Engineering Department
Means to AchieveQualities of Working Fluid Preferred by Sir Carnot …..

3. Reheating : A Means to implement High Live Steam Pressure
Supercritical
593/6210C
593/5930C
565/5930C
565/5650C
538/5650C
Improvement in Efficiency, %
538/5380C

4. Classification of Rankine Cycles

5. More Bottlenecks to Achieve Supercritical Steam Cycle
3sub
4sub T 2 1 s

6. Quality and Saturated Liquid-Vapor (Wet) Mixture
Now, let’s review the constant pressure heat addition process for water shown in Figure.
The state 3 is a mixture of saturated liquid and saturated vapor.
How do we locate it on the T-v diagram?
To establish the location of state 3 a new parameter called the quality x is defined as

7. Adiabatic Expansion of Steam
The liquid in the LP turbine expansion flow field is seen to progressively appear, with lowering pressure, in four forms, namely as:
A fine mist (or fog) suspended in the steam;
As a water stream running in rivulets along the casing (mainly OD);
As a water film moving on the surface of the blades (mainly stator; not particularly evident on the rotor blades owing to centrifugal-flinging action);
As larger droplets created when the water flowing along the surface of the blades reaches the trailing edge.

8. More Bottlenecks to Achieve Supercritical Steam Cycle
3sub
4sub T 2 1 s

9. Ill Effects of High Pressure Cyclesx
Pressure, MPa

10. Old Last Stage LP Blade

11. Modified Loss Region

12. Why should steam condense during Adiabatic Expansion?????

13. Thermodynamic Characterization of Working Fluid

15. Philosophical Recognition of Working Fluid
Organic Substances must be selected
in accordance to the heat source
temperature level (Tcr < Tin source)

17. Progress in Steam Rankine Cycle
Year
1907
1919
1938
1950
1958
1959
1966
1973
1975 MW 5 20 30 60
120
200
500
660
1300
p,MPa
1.3
1.4
4.1
6.2
10.3
16.2
15.9
24.1
Th oC
260
316
454
482
538
566
565
Tr oC --
FHW 2 3 4 6 7 8
Pc,kPa
13.5
5.1
4.5
3.4
3.7
4.4
5.4
h,%
~17
27.6
30.5
35.6
37.5
39.8
39.5 40

18. Reheating of Steam to Enhance Quality at the Turbine Exit
Single Turbine drum

19. Analysis of Reheat Cycle
Consider reheat cycle as a combination of Rankine cycle and horn cycle.
Cycle = Cycle ’-1 + Cycle 4’ ’.
Therefore, 4’ 6

20. Analysis of the Reheat Cycle
4’ 6

21. Clues to Achieve Double Benefit
Consider the ratio of
Define Increment in efficiency

22. Selection of Reheat Pressure
pmax= 15 MPa
Tmax= 550 0C
Tsat= C

23. Effect of Reheat Pressure on New Tm,in
pmax= 15 MPa
Tmax= 550 0C
Tsat= C

24. Effect of Reheat Pressure
Dh,%
1.0
0.2
0.4
0.6
0.8
~0.3
prh/pmax

25. Optimal Selection of Reheat Point

26. Reheating : A Means to implement High Live Steam Pressure
Supercritical
593/6210C
593/5930C
565/5930C
565/5650C
538/5650C
Improvement in Efficiency, %
538/5380C

27. Super Critical Cycle ~ 1990

28. Ultra Supercritical Installations of The World

29. Double Reheat Ultra Super Critical Cycle8

30. Reheater Pressure Optimization for Double Reheat Units
97bar
110bar
69bar

31. 21st century Rankine Cycles
Improvement in Efficiency, %

32. Super Critical Cycle of Year 2005

33. Double Reheat Super Critical Plants
Net efficiency on natural gas is expected to reach 49%.
Net efficiency on coal is expected to reach 47%.

34. Advanced 700 8C Pulverised Coal-fired Power Plant Project

35. FUTURE ULTRA SUPERCRITICAL PLANT – UNDER DEVELOPMENT
EFFICIENCY 55 %

36. Steam Generation : Explore more Causes for Wastageh
x=s

37. Look for More Opportunities to Reduce Wastage

38. Follow the Steam Path : Early Stage

39. Follow the Steam Path : Middle Stage

40. Follow the Steam Path : End Stage

41. Follow the Steam Path : The End

42. Save Wastage thru Recycling !?!?

43. Regeneration Cycle with Mixer (Open Feed Water Heater)

44. Synthesis of Rankine Cycle with OFWH5 6 T 6’ 4
p2=p6 3 2 1 7

45. Regeneration Cycle with Mixer (Open Feed Water Heater)

46. Analysis of mixing in OFWH

47. Analysis of mixing in OFWH
Constant pressure mixing process h6 y
Consider unit mass flow rate of steam thru the turbine h2
(1-y) h3
Conservation of energy:

48. Analysis of Regeneration through OFWH

49. Optimal Location of FWH

50. Performance of OFWH Cycle
~ 12MPa
htotal
pbleed, MPa

51. Gross Workoutput of bleed Steam
~ 12MPa
wbleed
pregen, MPa

52. Workoutput of bleed Steam
wbleed
y, MPa

53. More Work output with more bleed Steams
wbleed
y pregen, MPa

54. Progress in Rankine Cycle Power Plants
Year
1907
1919
1938
1950
1958
1959
1966
1973
1975 MW 5 20 30 60
120
200
500
660
1300
p,MPa
1.3
1.4
4.1
6.2
10.3
16.2
15.9
24.1
Th oC
260
316
454
482
538
566
565
FHW -- 2 3 4 6 7 8
Pc,kPa
13.5
5.1
4.5
3.4
3.7
4.4
5.4
h,%
~17
27.6
30.5
35.6
37.5
39.8
39.5 40

55. Open (Direct Contact) Feed Water Heater

56. An Impractical Efficient Model for Power Plant
Turbine B SG
Yj-11,hbj-1
yj, hbj
Yj-2,hbj-2 C
OFWH
OFWH
OFWH C
1 ,hf (j)
1- yj
hf (j-1)
1- yj – yj-1
hf (j-2)
1- yj – yj-1- yj-2
hf (j-3)
n number of OFWHs require n+1 no of Pumps…..
The presence of more pumps makes the plant unreliable…

57. Closed Feed Water Heater (Throttled Condensate)

58. Closed Feed Water Heater (Throttled Condensate)

59. Control of Entropy Generation due to Liquid Heating

60. Effect of no of feed water heaters on thermal efficiency and work output of a regeneration cycle
Specific Work Output

61. Heater Selection and Final Feedwater Temperature
In order to maximize the heat rate gain possible with ultra-supercritical steam conditions, the feedwater heater arrangement also needs to be optimized.
In general, the selection of higher steam conditions will result in additional feedwater heaters and a economically optimal higher final feedwater temperature.
In many cases the selection of a heater above the reheat point (HARP) will also be warranted.
The use of a separate desuperheater ahead of the top heater for units with a HARP can result in additional gains in unit performance.

62. Typical Single Reheat Heater Cycle with HARP

63. Effect of Final Feedwater Temperature and Reheat Pressure on Turbine Net Heat Rate

64. Double Reheat Cycle with Heater above Reheat Point

66. More FWHs for a Selected Bleed Points

67. New Circuits of Desuperheater for Preheating of Feedwater in Steam Power Plants

68. New Circuits of Desuperheater for Preheating of Feedwater in Steam Power Plants

69. New Circuits of Desuperheater for Preheating of Feedwater in Steam Power Plants

70. Efficiency of Danish Coal-Fired Power Plants
Continuous development resulted around the mid 80's in an average efficiency of 38% for all power stations, and best values of 43%.
In the second half of the 1990’s, a Danish power plant set a world record at 47%.

71. Average efficiency, specific coal usage, CO2 emissionsh
Indian Coal Plants:
Efficiency of modern coal power plant = 34-36%
Efficiency of old power plant = 20-30%

72. Expectations from Modern Steam Generator for Higher Efficiency
High Main Steam Pressure.
High Main Steam Temperature.
Double Reheat & Higher Regeneration.
Metal component strength, stress, and distortion are of concern at elevated temperatures in both the steam generator and the steam turbine.
In the steam generator’s heating process, the tube metal temperature is even higher than that of the steam, and concern for accelerated corrosion and oxidation will also influence material selection.