1. Main Condensate & Feed Systems

2. References
Required
Introduction to Naval Engineering (Ch. 9-10)

3. Objectives
Comprehend the purpose, principles of operation and key components of the main condensate system.
Comprehend the thermodynamic aspects associated with the main condensate system to include condensate depression.
Comprehend the purpose, principles of operation and key components of the main feed system.
Comprehend the purpose of automatic boiler control systems.
Know the purpose of routine water chemistry aboard ship.

5. Main Condensate System
Condenses exhaust steam from propulsion turbines and SSTGs for reuse in the boiler (S/G).
Pumps condensate from main condenser to the Main Feed System.
Provides a means of adding makeup water to the system.
Provides a means of removing excess water during periods of low demand.

6. Main Condenser

7. Main Condenser Indirect, shell-and-tube, cross flow heat exchanger
Maintained at vacuum of 25-29” Hg
How is the vacuum initiated & maintained?
Two flow paths through condenser
Condensate collects in hotwell
Provides NPSH to condensate pumps

8. Main Condensate Pumps
Centrifugal pumps, either steam or electrical power (subs all electrical)
Usually 2 pumps per condenser
Check valve on discharge of pump to prevent backflow
Lowest pressure in MS cycle at suction of pumps

9. Condensate Depression
Amount of subcooling of condensate in the hotwell of the main condenser
If too little (< 2oF), then cavitation of condensate pumps can occur
If too much (> 5oF), then lose efficiency (since condensate must be reheated later)
Controlled by regulating MSW flow

10. Main Seawater System (MSW)
Provides cooling water for main condenser to condense steam
Scoop Injection System
Used at higher speeds (> 8 knots)
Uses ship’s speed and scoop to cause flow
Not on SSN/SSBN/SSGN’s
MSW Pump
Used when going slow or astern
All SSN/SSBN/SSGN’s

11. Main Feed System
Purpose: to deaerate, preheat, store, and transport water from DFT to the boiler or S/G

12. Deaerating Feed Tank (DFT)
Preheats feed using 150# Auxiliary Steam
Provides NPSH for MFBP
Provides a surge volume to compensate for changes in steam demand.
Deaerates feed (removes dissolved air)

13. Deaerating Feed Tank (DFT)
Operation
150# Aux Steam enters in for heating
Condensate sprayed in thru nozzles (foglike)
Baffles collect condensate/condensed steam and directed to atomizer assembly
Atomizer uses high-velocity steam to redirect condensate-> remove last gases (scrubbing)

14. More Components Main Feed Booster Pump (MFBP) Main Feed Pump (MFP)
Single-stage centrifugal pump
Provides NPSH to MFP
Main Feed Pump (MFP)
Multi-stage centrifugal pump
Raises feed pressure > S/G pressure
Feedwater Control Valve
Regulates quantity of feed flow to S/G

15. Makeup-and-Excess Feed System
During normal operations, necessary to add/remove water from steam cycle
System stores feed and provides it if needed
DFT level control system provides control
If level low, make-up feed valve opened
If level high, excess feed valve opened

16. Makeup-and-Excess Feed System

17. Automatic Boiler / S/G Level Control System
Uses closed loop feedback principle of operation
Measure actual output
Compare actual output with desired output
Compute necessary correction signal
Correct actual output

18. Automatic Boiler / S/G Level Control System
Automatic Combustion Control (ACC)
Maintains boiler’s steam drum pressure by controlling rate of combustion (air/fuel)
Feedwater Control System (FCS)
Regulates flow of feedwater to boiler to maintain level
Diff Control System of MFP (DCS)
Maintains feedwater supply pressure above steam drum pressure

19. Automatic Combustion Control (ACC) System

20. Feedwater Control System (FCS)

21. Differential Control System of MFP (DCS)

22. Interrelation of Systems
Answering AA2/3 -> OOD orders AAII
Open throttles -> steam flow -> steam pressure
ACC system air & fuel to combustion rate
FWC system feed to match steam flow
DCS of MFP speed of MFP to discharge pressure

23. Take Away Classify the main condenser
Describe the two methods of providing cooling to the Main Condenser
Define condensate depression. Discuss the impact of condensate depression on system operation and efficiency
Describe the purposes of the main feed system
Describe the purposes and operation of the DFT
Describe the functions of the ACC, FCS and DCS.
Describe how the above systems function together for a change in ordered bell.
Describe, using pump curves, how a MFBP provides NPSH to the MFP.

24. Questions?