Main Condensate & Feed Systems

1. Main Condensate & Feed Systems We Love Engineering!

2. Objectives • Components of Main Condensate System and purposes of each • Components of Main Feed System and purposes of each • Operation of Automatic Control Systems • Interrelationship of systems during operations

3. Main Condensate System • Provides condensation phase of the main steam cycle • Condenses steam from turbines to liquid • Pumps condensate from main condenser to the Main Feed System

4. Main Condensate System

5. 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

6. Main Condenser

7. 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’s • MSW Pump • Used when going slow or astern • All SSN/SSBN’s

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

11. Deaerating Feed Tank (DFT) • Preheats feed using 150# Auxiliary Steam • Stores feed (provides NPSH for MFBP) • Deaerates feed (removes dissolved air)

12. 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)

13. More Components • Main Feed Booster Pump (MFBP) • 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

14. 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

15. Makeup-and-Excess Feed System

16. 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

17. 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

18. Automatic Combustion Control (ACC) System

19. Feedwater Control System (FCS)

20. Differential Control System of MFP (DCS)

21. 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

22. Boiler Chemistry Control • High temperature water and steam at neutral pH can be very corrosive • Holes in piping • Chemicals are added to the water to ensure pH stays low (basic) • Must analyze for proper levels of these chemicals to ensure corrosion prevented. • Can’t have too much – will cause fouling and scale deposits

23. Questions?