feed water heaters - central board of irrigation and power · extraction connection to heaters ......

Feed Water Heaters

Sankar BandyopadhyayEmail : sankarbando1956@gmail.com

Feed water Heating

Advantage by Heater in Rankine Cycle

Effect of no. of feed-water heaters on thermal efficiency of the cycle

Terminal temperature difference (TTD) =

inlet steam saturation temperature -Feedwateroutlet temperature

Drains cooler approach (DCA) = shell drains outlet temperature - feedwater inlet temperature

Feedwater temperature rise (TR) = feedwateroutlet temperature - feedwater inlet temperature

Vital Measures of an Operating Heater

Zones of Feed Water Heaters

Horizontal Feed Water Heater

Horizontal Feed Water Heater

Vertical Feed Water Heater

Vertical Feed Water Heater Channel Down

Drain inletExtraction steam inlet

FW outlet

FW inletDrain outlet

HP Heater

HP Heater

HP Heater

Low pressure feedwater heater

UNIT SIZE (MW) Number of Heaters

0 – 50 3 – 5

50-100 5 or 6

100-200 5 - 7

Over 200 6 - 8

Low pressure feed water heater

No of extractio n

Steam extractio n

stages

Connection to Extraction steam pr, kg/cm2

Extraction steam temp,

0C

Steam flow T/hr

Ist -HPT 9 HPH-7 30 337 88

2nd -CRH 12 / CRH HPH-6 / Deaerator 26.2 314 77

3rd -IPT 15 HPH-5 / Deaerator

11.96 433 16.2

4th - IPT 18 LPH-4 6.47 368 26

5th – IPT 21 LPH-3 2.78 252 23

6th - IPH 23 LPH-2 1.28 172 28

7th - LPT 25 LPH-1 0.28 40-50 12.6

Extraction Connection To Heaters

TTD - Terminal Temperature Difference

TTD = TS - FW OUTLET TEMP TS saturation temperature corresponding to shell pressure

DCA

TR

PRESSURE DROP

Key Performance Indicator

Sensible heat transfer

Latent

heat transfer

Sensible heat transfer

Drain Cooling Zone

Condensing

Zone

Desuper heating Zone

TTD

DC A

Ts

Extn

FW

FW

Drain

Thermal profile in different zones of H P HEATER

High TTD Causes Effects

Tube fouling/Plugging

Non condensable gases

(Air) blanketing

Bled steam flow

Heater concerned Flooding

Tube leakage

Level control

Subsequent heater

Turbine steam flow

Low shell pressure Excessive venting

Feedwater outlet temperature [0C]

Terminal difference [0C]

30-110 2.8

110 -148.9 5.6

148.9 – 204.4 8.3

204.4 – 273.9 11.1

TTD and Feed Water temp

DCA = Drain out let temp - FW inlet temp

Drain Cooling Approach - DCA

HIGH - DCACauses Effects

LCV malfunction •Tube fouling/Plugging

•Bled steam flow

•Low water level

•Heater concerned •Subsequent heater •Drain cooler inlet not submerged

Temperature Profile of a closed Feed water Heater

NTHR – Net Turbine Heat Rate

NTHR – Net Turbine Heat Rate

NTHR – Net Turbine Heat Rate

NTHR – Net Turbine Heat Rate

Temperature Rise

TR = FW outlet temp - FW inlet temp

LOW TRCauses Effects

TTD high Bled steam flow DCA high Heater concerned Subsequent heater Turbine steam flow

Sample Calculation for Feedwater Heater

Terminal Temperature (TTD) TTD = t sat – t fw out = 252.8- 251.1 =1.7 0C.

Drain Cooler Apporach Temperature (DCA) DCA = t drains - t fw in = 202.8- 194.3 = 8.5 0C..

Temperature Rise (TR) TR = t fw out – t fw in = 251.1-194.3 = 56.8 0C Extraction Steam Flow = (Qe) = [Qf (hfw out – hfw in) + Qdrain in (hdrains out- hdrains in)] / (hext – hdrainsout ) Where: Qf = Feed Flow; Qdrain in = Drain Inlet flow; h fw out = Feed Water Enthalpy at HPH Out.; hfw in = Feed Water Enthalpy at HPH in hdrains out = Enthalpy of Drain Out; hdrains in = Enthalpy of Drain In hext = Enthalpy of Extraction Steam

751.2* (259.7 – 196.8)+0 Qe = ------------------------------------- = 90.2 t/hr

(729.4 – 205.95)

• Air accumulation • Steam side fouling • Water side fouling • Drainage defects • Parting plane leakage

DETERIORATION

Air accumulation

• Increased TTD • Possible elevation of steam-to-heater

temperature • Reduced temperature rise of feed water or

condensate. • 0.5 % steam is venting inevitable for good

venting

Steam side fouling

• Progressive increase of TTD • Drain temperature unaffected • Reduced feed water temperature rise • Eventual tube failure due to mechanical

weakening • Accumulation of debris in the heater shell.

Water side fouling

• Gradual increase of TTD. • Oil

– LPT bearing oil through seals – Deposition occurs in HP heaters, worst hit at

highest pressure heater.

Drainage defects

• Damaged flsahbox internals • Reduced orifice opening • Enlarged orifice opening • Heater drain CV/ bypass valve

malfunction.

Parting plane leakage

• Short circuiting of FW • TTD high • DCA high • TR less

HP Heater Performance Report - 210 MW

Sr. No Parameter Unit Test Data

HPH - 5 HPH - 6 HPH - 7

1 Unit Load MW 178 178 178

2 FW Flow t/hr 649 649 649

3 HPH - Extr. Temp (Htr End) Deg C 200 335 390

4 HPH - Extr. Press (Htr End) kg/cm2 (a) 14.5 29 36

5 FW Inlet Temp Deg C 165 180 215

6 FW Outlet Temp Deg C 180 215 232

7 HPH Drain outlet Temp Deg C 150 200 240

8 Drain inlet Temp to HPH Deg C 200 240 --

TTD Deg C 15.8 15.9 11.0

DCA Deg C -15.0 20.0 25.0

Extraction Flow to HPH t/hr 12.9 43.8 23.7

FW Temp rise in HPH Deg C 15.0 35.0 17.0

Partition Plane

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