3. TO IMPROVE THE EFFICIENCY
Q= K*A *d T
Efficiency of heat transfer is maximum when dT tends
to zero.
By raising the temperature of feed water in stages we
achieve a low dT at every stage.
Average temperature of at which heat is added also
increases and gives better efficiency.
4. RANKINE CYCLE
The four processes of an ideal Rankine
cycle are as follows:
Process1-2: Isentropic compression in a
pump. Here the working fluid is pumped
from low to high pressure.
Process2-3: Constant pressure heat addition
in the boiler. In this process, the high-
pressure liquid is added to the boiler and is
heatedat constant pressure to become a dry
saturated vapour.
5. RANKINE CYCLE
Process 3-4 : Isentropic
expansion in a turbine. The dry
saturated vapour expands through
the turbine resulting in the
generation of power.
Process 4 -1: Constant pressure
heat rejection in a condenser. Wet
vapour is condensed at a constant
pressure to become a saturated
liquid.
8. Regenerative Rankine cycle
ADVANTAGES
THERMAL EFFICIENCY INCREASES
REDUCED STEAM FLOW TO CONDENSER
DIFFICULTY IN PASSING LARGE VOL OF STEAM
THROUGH LAST STAGE IN LP TURBINE IS REDUCED –
BLADE HEIGHT TOBE INCREASED TO ACCOMMODATE
HIGH SPE.VOL OF STEAM.
DECREASE IN STEAM FLOW AT TURBINE EXHAUST -
SMALLER CONDENSER , LPH’S, HPH’S.
REDUCED SIZE RESULTS IN SAVING CAPITAL
INVESTMENT.
9. WHY FW HEATERS IN POWER PLANT
Heating the feed Water.
Increasing the cycle efficiency.
Reduction in fuel consumption.
DESIGN CODE OF FW HEATERS
HEI,ASME SEC VIII DIV-1 IBR
10. FEEDWATER HEATERS
A feedwater heater is a heat exchanger used to pre-
heat water delivered to steam generating boiler in the
regenerative Feed Heating System.
Steam is extracted from the steam turbine at various
stage.
This results in higher cycle efficiency by increasing the
temperature of the feed water and by reducing the
amount of energy lost in the condenser.es and used to
heat the feed water
11. Feed-water heaters can be Open and Closed heat
exchangers.
Open heat exchangers.
An open feedwater heater is a direct-contact heat
exchanger in which extracted steam is allowed to mix
with the feedwater.
This kind of heater will normally require a feed pump
at both the feed inlet and outlet since the pressure in
the heater is between the boiler pressure and
the condenser pressure.
A deaerator is a special case of the open feedwater
heater which is specifically designed to remove non-
condensable gases from the feedwater.
12. Closed heat exchangers.
Closed feedwater heaters are typically shell and tube
heat exchngers where the feedwater passes throughout
the tubes and is heated by turbine extraction steam.
These do not require separate pumps before and after
the heater to boost the feedwater to the pressure of the
extracted steam as with an open heater.
13. ADVANTAGES OF FW HEATERS
Fuel consumption reduces
Preheating improves the thermodynamic efficiency of the
system.
reduces plant operating costs and also helps to avoid thermal
shock to the boiler metal when the feedwater is introduced
back into the steam cycle.
Reduce heat losses in the condenser
Lower emissions as fuel use is reduced due to improve heat
rate.
Decrease the plant heat rate & hence increases the plant
efficiency.
14. Zones of heaters
De Superheating Zone.
cools the superheated steam to the point that the
steam is saturated.
Condensing Zone.
Maximum heat transfer occurs
Sub Cooling Zone.
Condensed steam cooled by feed water by convective
heat transfer method
17. Pipe lines connected to HP heaters
Feed water inlet line
Feed water outlet line
Condensate outline
Bleed Steam line ( Extraction steam line)
Shell Zone Drain & Vent (Operating vent & startup
vent).
Feed Water box Drain & vent lines.
18. FEED WATER HEATER PERFORMANCE
Three Variables are used to monitor feed water
heaters efficiency.
•Heater TTD or Terminal temp Difference.
•Heater DCA or Drain Cooler Approach.
•Feed Water heater Temp rise= TFWO-TFWI.
19. TTD OR TERMINAL TEMP DIFFERENCE
Difference between the saturation temperature at the
operating pressure of the inlet steam to the heater and
the temperature of the feed water leaving the heater.
For more cycle efficiency TTD value should be more.
An increase in TTD indicates a reduction in heat transfer
while a decrease is an improvement.
For the best performance , heaters are designed to get
TTD 3 to 5 Deg.C at full operating capacity.
TTD = TSAT - TFWO
20. High TTD indicates:
Excessive venting (worn vents, altered set point, vent
malfunctioning)
Excessive make up
High water level (tube leaks, improper setting)
Non condensable gases on shell side
Excessive tube bundle pressure drop (excessive
number of tubes plugged, tubes folded internally)
21. DCA OR DRAIN COOLER APPROCAH
Heater DCA how close the drain outlet temp to feed water inlet
temperature
DCA infers the condensate levels present within a feed water heater.
An increasing DCA temperature difference indicates the level is
decreasing. severe damage to the tubes and other internals such as
plates and baffles.
Decreasing DCA indicates a rise in level, good for Drain Cooling zone.
DCA high, corrective action to restoring the water level to proper
range from a level that is too low.
DCA= TDCO - TFWI
22. High DCA temperature indicates:
Drain cooler inlet not submerged
Low drain water level (improper setting, excessive FW
heater drain bypass – bypass valve left open - bypass
valve malfunctioning / leaking)
Excessive tube bundle pressure drop (excessive
number of tubes plugged / tubes folded internally)
Feed water heater bypassed
FW heater bypass valve leaking
23. FEED-WATER TEMPERATURE RISE (TR) is the
difference between the feed-water outlet temperature
and the feed-water inlet temperature. A properly
performing heater should meet the manufacturer’s
design specifications, provided the level controls are
up to the task.
TR = Tout – Tin
Tin = saturation temperature of the extraction steam
Tout = feed-water outlet temperature
24. Level of heaters.
Higher the condensate level is lower the performance
of heater & vice versa
Heater level is always maintained between 30-50%.
25. FEED WATER HEATER IMPACT ON THERMAL
PERFORMANCE
1 Deg.C in TTD, 0.033% increase in heat rate.
1 Deg.C in DCA,0.01% increase in heat rate.
Increasing TTD & DCA cause increased heat rate and reduced
electrical output.
27. DEAERATOR
Deaerator removes dissolved gases mainly dissolved oxygen
and other non-condensable gases from boiler feed water.
Dissolved Oxygen causes pitting type corrosion in feed
water systems.
DEAERATION PROCESS
Mechanical Deaeration
Chemical Deaeration
28. DEAERATOR
Mechanical Deaeration
Water is heated by steam within a few degree of its saturation temperature
according to deaerator operating pressure.
Approx. 97-98% of dissolved gases released with the steam & escaped from
the vents of deaerator.
Chemical Deaeration
Remainder 2-3% of dissolved gases removed by scrubbing the water with the
steam & addition of oxygen scavenger chemicals.
N2H4 + O2 → N2 + 2H2O
Venting is critical and necessary for the effective removal of dissolved gases
like oxygen and other non-condensable gases such as carbon dioxide.
29. DEAERATOR
Why steam is used as a purge gas in deaerator?
It doesn’t contaminate the water.
Only a small quantity of steam is venting from deaerator.
Most of the steam condenses and becomes the part of
deaerator water.
It heats the boiler feed water up to the saturation
temperature, so that solubility of unwanted dissolved gases
are decreases.
32. LP HEATERS
There are 4*100% capacity, horizontal type, U-type LP heaters
equipped.
Designated as LP Heater -8A/7A > LP Heater 8B/7B > LP Heater -
6 >LP heater-5 respectively in the order along the direction of
water flow.
33. Types of Feed water heaters
LPH-5 DESIGN SPECIFICATIONS
S.NO. ITEMS UOM DESIGN
1 TYPE Horizontal U tube heat exchanger
2 PRESSURE IN SHELL SIDE MPa 0.6
3 PRESSURE IN TUBE SIDE MPa 4.2
4 MAX ALL.WORKING PR IN SHELL SIDE MPa 0.612
5 MAX ALL. WORKING PR IN TUBE SIDE MPa 4.28
6 TEMP IN SHELL SIDE I/L & O/L ℃ 242/124.8
7 TEMP IN TUBE SIDE I/L & O/L ℃ 119.2/137.3
8 SHELL SIDE SV SET PR MPa 0.6
9 TUBE SIDE SV SET PR MPa 4.2
10 WORKING MEDIUM IN SHELL SIDE Steam and water
11 WORKING MEDIUM IN TUBE SIDE Condensate water
34. Types of Feed water heaters
LPH-6 DESIGN SPECIFICATIONS
S.NO. ITEMS UOM DESIGN
1 TYPE Horizontal U tube heat exchanger
2 PRESSURE IN SHELL SIDE MPa 0.6
3 PRESSURE IN TUBE SIDE MPa 4.2
4 MAX ALL.WORKING PR IN SHELL SIDE MPa 0.612 @150 ℃
5 MAX ALL. WORKING PR IN TUBE SIDE MPa 4.28 @ 150 ℃
6 TEMP IN SHELL SIDE I/L & O/L ℃ 1874.7/106.1
7 TEMP IN TUBE SIDE I/L & O/L ℃ 100.5/119.2
8 SHELL SIDE SV SET PR MPa 0.6
9 TUBE SIDE SV SET PR MPa 4.2
10 WORKING MEDIUM IN SHELL SIDE Steam and water
11 WORKING MEDIUM IN TUBE SIDE Condensate water
35. Types of Feed water heaters
LPH-7A & 7B DESIGN SPECIFICATIONS
S.NO. ITEMS UOM DESIGN
1 TYPE Horizontal U tube heat exchanger
2 PRESSURE IN SHELL SIDE MPa 0.6
3 PRESSURE IN TUBE SIDE MPa 4.2
4 MAX ALL.WORKING PR IN SHELL SIDE MPa 0.612 @ 150 ℃
5 MAX ALL. WORKING PR IN TUBE SIDE MPa 4.28 @ 150 ℃
6 TEMP IN SHELL SIDE I/L & O/L ℃ 126/86.9
7 TEMP IN TUBE SIDE I/L & O/L ℃ 81.3/100.5
8 SHELL SIDE SV SET PR MPa 0.6
9 TUBE SIDE SV SET PR MPa 4.2
10 WORKING MEDIUM IN SHELL SIDE Steam and water
11 WORKING MEDIUM IN TUBE SIDE Condensate water
36. LPH-8A & 8B DESIGN SPECIFICATIONS
S.NO. ITEMS UOM DESIGN
1 TYPE Horizontal U tube heat exchanger
2 PRESSURE IN SHELL SIDE MPa 0.6
3 PRESSURE IN TUBE SIDE MPa 4.2
4 MAX ALL.WORKING PR IN SHELL SIDE MPa 0.612 @ 150 ℃
5 MAX ALL. WORKING PR IN TUBE SIDE MPa 4.28 @ 150 ℃
6 TEMP IN SHELL SIDE I/L & O/L ℃ 85.4/52.9
7 TEMP IN TUBE SIDE I/L & O/L ℃ 47.3/81.3
8 SHELL SIDE SV SET PR MPa 0.6
9 TUBE SIDE SV SET PR MPa 4.2
10 WORKING MEDIUM IN SHELL SIDE Steam and water
11 WORKING MEDIUM IN TUBE SIDE Condensate water
37. HP HEATERS
There are 3*100% capacity, horizontal type, U-type LP heaters
equipped.
Designated as HP Heater-3 > HP Heater-2 > HP Heater-1
respectively in the order along the direction of water flow.
38. HPH-3 DESIGN SPECIFICATIONS
S.NO. ITEMS UOM DESIGN
1 TYPE Horizontal U tube heat exchanger
2 PRESSURE IN SHELL SIDE MPa 2.55
3 PRESSURE IN TUBE SIDE MPa 29
4 MAX ALL.WORKING PR IN SHELL SIDE MPa 2.55
5 MAX ALL. WORKING PR IN TUBE SIDE MPa 29
6 TEMP IN SHELL SIDE I/L & O/L ℃ 493/227
7 TEMP IN TUBE SIDE I/L & O/L ℃ 227/247
8 SHELL SIDE SV SET PR MPa 2.55
9 TUBE SIDE SV SET PR MPa 29
10 WORKING MEDIUM IN SHELL SIDE Steam and water
11 WORKING MEDIUM IN TUBE SIDE water
39. HPH-2 DESIGN SPECIFICATIONS
S.NO. ITEMS UOM DESIGN
1 TYPE Horizontal U tube heat exchanger
2 PRESSURE IN SHELL SIDE MPa 4.70
3 PRESSURE IN TUBE SIDE MPa 29
4 MAX ALL.WORKING PR IN SHELL SIDE MPa 4.70
5 MAX ALL. WORKING PR IN TUBE SIDE MPa 29
6 TEMP IN SHELL SIDE I/L & O/L Deg.C 358/262
7 TEMP IN TUBE SIDE I/L & O/L Deg.C 262/282
8 SHELL SIDE SV SET PR MPa 4.70
9 TUBE SIDE SV SET PR MPa 29
10 WORKING MEDIUM IN SHELL SIDE Steam and water
11 WORKING MEDIUM IN TUBE SIDE water
40. HPH-1 DESIGN SPECIFICATIONS
S.NO. ITEMS UOM DESIGN
1 TYPE Horizontal U tube H.E
2 PRESSURE IN SHELL SIDE MPa 7.35
3 PRESSURE IN TUBE SIDE MPa 29
4 MAX ALL.WORKING PR IN SHELL SIDE MPa 7.35
5 MAX ALL. WORKING PR IN TUBE SIDE MPa 29
6 TEMP IN SHELL SIDE I/L & O/L Deg.C 420/290
7 TEMP IN TUBE SIDE I/L & O/L Deg.C 290/310
8 SHELL SIDE SV SET PR MPa 7.35
9 TUBE SIDE SV SET PR MPa 29
10 WORKING MEDIUM IN SHELL SIDE Steam and water
11 WORKING MEDIUM IN TUBE SIDE water
41. HPH-1,2 & 3 OPERATING PARAMETERS
S.NO.
DESCRIPTION UOM HPH-3 HPH-2 HPH-1
1 Working pressure in shell side MPa 2.167 3.794 6.115
2 Working pressure in tube side MPa 20.68 20.68 20.68
3 HP heater inlet temp tube side ◦C 182.5 216.5 247.2
4 HP heater outlet temp tube side ◦C 216.5 247.2 278.5
5 HP heater inlet temp shell side ◦C 470 330.7 394.8
6 HP heater outlet temp shell side ◦C 188.1 222.1 252.8
46. Problems in FW Heaters
Flashing in heaters
change in state of liquid to vapour.
o If the liquid drains are not sub cooled enough , any one
of these pressure drops could result in flashing and
two phase flow.
o Two phase flow is known to cause problems to piping ,
tubing, the cage& the shell.
47. Fouling
Deposition of any undesired material on heat transfer
surfaces.
Impact the thermal & mechanical performance of heat
exchangers.
Increases the thermal resistance & lowers the heat
transfer coefficient of heat exchangers.
Impedes the fluid flow , accelerates corrosion &
increase the pressure drop across heat Exchangers.
Particulate / Sedimentation Fouling, Corrosion fouling
, Chemical Fouling & Freezing Fouling.
48. Fouling
Initial Two phase Mixture & Hammering.
Tubes Failure Due to Wrong Operation.
Level Fluctuation & Leakages.
Overfeeding of steam& Feed water
Operating the heaters above the parameters & design
parameters.
49. Precautions
Operate the LP& HP Heaters as per SOP.
Take Utmost Caring during initial charging.
Do not operate the heaters beyond the operating
pressure & temperature.
Conduct routine preventive maintenance.
Bypass the LP & HP heaters Boilers Hydraulic tests.
50. PROBABLE REASONS RECOMMENDED MEASURES
Air blanketing of Tubes due to
insufficient venting.
Ensure proper venting and check for
the tube leakage, if any.
Deviations in operating flow
conditions and other process
parameters.
Maintain flow and other parameters
within their design limits
Excessive level build- up resulting in
the submergence of parts of tubes,
which will
reduce available heat transfer area.
Maintain liquid level within the
normal limits
Fouling of the Tube surface Periodic inspection & proper cleaning
of the tubes.
REASONS FOR REDUCTION IN FEED WATER HEATER
PERFORMANCE
51. FUNCTION OF DEAERATOR
Extraction from:
Auxiliary Steam Header & 4th extraction.
Function:-
As Feed Water Storage Tank
As Feed Heater( Direct Mixing Type)
To Provide NPSH to BFP
AS Deaerator (To remove Dissolved O2,CO2 which is harmful to the System
due to its corrosive attack on the metal).
The vendors of deaerators usually gives guarantee of less than 7 ppb of
dissolved oxygen in boiler feed water.
52. DEAERATOR SPECIFICATIONS
S.NO. ITEMS UOM DESCRIPTION/VALUES
1 TYPE SPRAY TYPE
2 EFFECTIVE CAPACITY M3
240 (6 min of feed water outflow at
VWO)
3 DESIGN TEMP OF SHELL Deg.C 220
4 MAX OPERATING TEMP Deg.C 182
5 MAX ALL.WORKING PR Mpa 1.3 Mpa @ 220 Deg.C
6 HYDRAULIC TEST PR Mpa 1.95 @ 20-50 Deg.C
7 WORKING PRESSURE Mpa 0.147~1.105
8 WORKING MEDIA STEAM,WATER
Operating Conditions at TMCR
1 WORKING PRESSURE Mpa 0.977
2
HEATING STM FLOW FROM TUR 4TH
EXTR
TPH 100.87
3 NML DRAIN FLOW FROM HPH-3 TPH 348.28
4 CONDENSATE I/L FLOW TPH 1443.7
5 FW O/L FLOW TPH 1892.9
6 CONDENSATE INLET TEMP Deg.C 137.3
7 FW O/L TEMP Deg.C 178.9
54. D/A & ITS CONNECTIONS
D/A EMER DRAIN
MIV TO IBD -13.7 M
EL
D/A OVERFLOW
MIV & MOV-27
M EL
D/A ATM DRN MIV
D/A CHEMICAL DOSING MIV
MDBFP
SUCTION
TAPPING
TDBFP-1A BP
SUC TAPPING
TDBFP-1B BP
SUC TAPPING
MANHOLE
62. DEAERATOR
Henry’s Law (scrubbing with oxygen free steam):
The amount of dissolved gases present in
water is directly proportional to the partial pressure of
that gas in the vapour space above the water/gas
interface.
Charles’Law (oxygen solubility vs temperature):
The solubility of oxygen decreases as
the temperature of water increases.
