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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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