This document discusses the performance calculation and monitoring of feedwater heaters in thermal power plants. There are three key variables used to monitor feedwater heater efficiency: terminal temperature difference (TTD), drain cooler approach (DCA), and feedwater temperature rise (TR). The TTD measures how close the outlet water temperature is to the saturation temperature, and a higher TTD indicates poorer performance. The DCA measures how close the drain outlet temperature is to the inlet water temperature, and a higher DCA can cause damage. These variables are calculated and trended monthly to monitor heater performance and identify any issues.

1. Performance Calculation of
FEED WATER HEATER
in Thermal Power Plant
Shivaji Choudhury

2. Purpose of feedwater heaters
in a thermal power plant
 They provide efficiency gains in the
steam cycle by increasing the initial
water temperature to the boiler, so
there is less sensible heat addition
which must occur in the boiler.

3. FEEDWATER HEATERS IN POWER
CYCLE

4. Performance of feedwater heaters
Three variables are used to monitor
feedwater heaters efficiency.
 The heater Terminal Temperature
Difference or TTD .
 The heater Drain Cooler Approach or
DCA .
 Feedwater temperature rise (TR)

5. Terminal temperature difference -
TTD
 The heater Terminal Temperature
Difference or TTD is a measure of
how close the outlet feedwater
temperature is to the feedwater
heater saturation temperature.

6. Terminal temperature difference -
TTD
 The TTD is a measure of the heat transfer
capability of the feedwater heater.
 The higher the TTD is above design, the
poorer the performance of the heater.
 Actual measurements should be compared
with controlled performance tests at various
power levels to determine if serious changes
are occurring.
 If the TTD is substantially higher than normal
for the existing conditions, the heater has
problems.

7. Drain Cooler Approach- DCA
 The heater Drain Cooler Approach or
DCA is a measure of how close the
heater drain outlet temperature is to
the feedwater inlet temperature.

8. DCA low
 The DCA temperature is a critical factor in
the assurance of a long service life for a
closed feedwater heater.
 If the actual drains approach is at or
slightly better (lower) than the designated
value, the drains cooling zone should be in
good physical condition

9. DCA High
 If the DCA temperature is too high for the existing
power level, a serious operating condition exists.
 This condition threatens to do severe damage to the
tubes and other internals, such as the drains cooling
zone end plate and baffles. Rapid heater destruction
may follow, especially in a horizontal heater.
 Corrective action usually consists of restoring the
water level to the proper range from a level that is
too low.
 Failure to do so can allow flashing to develop
destructive velocities and rapid erosion in the drains
cooling zone.

10. Feedwater Heater performance
Calculations
1. Drain Cooler Approach temperature
difference (DCA)
2. Feedwater heater Terminal
Temperature Difference (TTD)
3. Feedwater temperature rise (TR)

11. 1.Drain Cooler Approach
temperature difference (DCA)
 Input variables
TDO = Heater drain out temp ( in deg C)
TFWI=Feedwater inlet temp ( in deg C)
 calculation for DCA
DCA= TDO-TFWI ( unit in deg C)

12. 2.Calculation for TTD
2.1.Input variables
Tag no unit description Design
data
PES Kg/cm2 Press extn
stm to
heater
TFWO Deg c Temp FW
heater out

13. 2.2.Calculation for TTD
 TSATES = saturation temperature of
the steam at the extraction inlet
pressure( PES) as found in the ASME
steam tables ( Unit deg C)
 TTD calculation ( unit deg C)
TTD = TSATES –TFWO

14. 3.Feedwater temperature rise
(TR)
 • Feedwater temperature rise (TR) =
feedwater outlet temperature minus
feedwater inlet temperature

15. monitoring
 The TTD and DCA for each heater
should be determined and trended on
a monthly basis.

16. HP Heaters -500 MW

17. LP heaters -500 MW

18. Feedwater Heater Responses
problem TR TTD DCA
Inadequate
vent
Decrease Increase Increase
Level increase Decrease Increase Decrease
Level decrease Increase Decrease Increase
Tube fouling Decrease Increase Increase
Tube Leak Decrease Increase Increase
High FW flow Decrease Increase Increase
Plugged tubes Decrease Increase Increase

19. Feedwater Heater Impact on
Thermal Performance
 1°C increase in top heater TTD,
0.033% increase in heat rate.
 1°C increase in DCA, 0.01% increase
in heat rate.
 Increasing TTD and DCA cause
increased heat rate and reduced
electrical output.

20. Thank you