Analysis of Rankine Cycle with FWHs

P M V SubbaraoProfessor

Mechanical Engineering Department

I I T DelhiEngineering solution to Pure Thoughts ..…..

Regeneration Cycle with Open FWH

’

212111 smSsmS

mixmix smSS 23

515414 smmSsmmS mixmix

556 smSS mix

S

5smmix

1m

Synthesis of Rankine Cycle with OFWH

5

p2=p6

Analysis of OFWH

h3

h6y

h2

1-y

Conservation of energy:

326 1 hhyhy 2326 hhhhy

26

23

hhhhy

Analysis of Regeneration through OFWH

26

23

hhhhy

45 hhmQ in

171 hhymQOut

pumpscondbleednet WWWW

3412 & hhhh 0

pumpsW

7565 1 hhyhhymWWW condbleednet

45

7565 1hhm

hhyhhymin

net

Q

W

35

7565 1hh

hhyhhy

35

75

35

65 1hh

hhyhhhhy

16

13

26

23

hhhh

hhhhy

Performance of FWH Cycle

0.45

0.455

0.46

0.465

0.47

0.475

0.48

0.485

0.49

0 5 10 15 20

pregen, MPa

total

~ 12MPa

wbl

eed

020406080

100120140160180200

0 5 10 15 20

65 hhy

Workoutput of bleed Steam

pregen, MPa

~ 12MPa

0

200

400

600

800

1000

1200

1400

1600

0 0.1 0.2 0.3 0.4 0.5

wbl

eed

Workoutput of bleed Steam

0

200

400

600

800

1000

1200

1400

1600

0 0.1 0.2 0.3 0.4 0.5

wbl

eed

Workoutput of bleed Steam

Progress in Rankine CycleYear 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 15.9 24.1

Th oC 260 316 454 482 538 566 566 565 538

Tr oC -- -- -- -- 538 538 566 565 538

FHW -- 2 3 4 6 6 7 8 8

Pc,kPa 13.5 5.1 4.5 3.4 3.7 3.7 4.4 5.4 5.1

,% -- ~17 27.6 30.5 35.6 37.5 39.8 39.5 40

Open (Direct Contact) Feed Water Heater

                                   

Closed Feed Water Heater (Pumped Condensate)

Closed Feed Water Heater (Throttled Condensate)

Closed Feed Water Heater (Expanded Condensate)

Thermodynamic Analysis of A Power Plant

ANALYSIS OF ‘ith’ FEED WATER HEATER

• Mass entering the turbine is

STEAM TURBINE

n

iiSGcond ymm

1

1

yn,

hbn

yi,

hbi

y(i+1)

hb(i+1)

mie ,

hfi

mi,i,

hf(i+1)

STEAM IN

STEAM OUT

SGmSGm

Mass of steam leaving the turbine is

RESULTS

S.NO Pmax Tmax Tmin PminMpa oC oC Mpa ΔH = constant ΔT = constant Simulated

1 12.75 535 25.7 0.0033 43.4 47.6 50.642 23.5 540 26 0.0034 30.8 36.97 53.543 12.74 565 23.97 0.00298 44.39 46.72 51.24 15 550 40 0.0074 46.73 50.285 53.995 16.5 535 40 0.01 38.8 43.08 49.022

GENERATIONS = 5000 /// NO OF FEED HEATERS = 6 Thermal Efficiency

RESULTS

S.NO Pmax Tmax Tmin Pmin W bledsteam Popt

1 12.75 535 25.7 0.0033 234.2 7.28 , 4.88 , 3.42 , 3.09 , 1.326 , 0.2762 23.5 540 26 0.0034 302.093 12.74 565 23.97 0.00298 242.164 15 550 40 0.0074 270.35 16.5 535 40 0.01 249.589 5.293, 2.33, 1.096, 0.779, 0.651, 0.0674

7.28 , 4.88 , 3.42 , 3.09 , 1.326 , 0.276

5.3 , 2.23 , 1.096 , 0.779 , 0.651 , 0.06748.28, 4.88, 3.7792, 2.0907, 0.48, 0.2597

RESULTS

S.NO H2 Pmax Tmax Tmin Pmin THERMAL EFFICIENCYSimulated

1 1465 16.75 535 25.7 0.0033 49.192 1500 16.75 535 25.7 0.0033 49.0223 1550 16.75 535 25.7 0.0033 49.0224 1600 16.75 535 25.7 0.0033 49.022

NO OF FEED HEATERS = 6

Condenser

Block Diagram of A Large Steam Turbine Reheat Steam

HP

Main Steam

Steam for Reheating

IP

LPLP

CFWH 6 CFWH 5

OFWH 4

CFWH 2

CFWH 1

CFWH 3

Plow

Phigh

Regeneration cycle

Reheat-Regeneration cycle

Improvement in efficiency due to reheating in a reheat-regeneration cycle

Heater Selection and Final FeedwaterTemperature

• 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.

Typical Single Reheat Heater Cycle with HARP

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

Double Reheat Cycle with Heater above Reheat Point

Double Reheat Super Critical Plants

Net efficiency on natural gas is expected to reach 49%. Net efficiency on coal is expected to reach 47%.

Advanced 700 8C Pulverised Coal-fired Power Plant Project