Main Condensate & Feed Systems

References• Required

– Introduction to Naval Engineering (Ch. 9-10)

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.

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.

Main Condenser

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

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

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

in

in

out

Q

Q

W

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

Main Feed System• Purpose: to deaerate, preheat, store, and

transport water from DFT to the boiler or S/G

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)

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)

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

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

Makeup-and-Excess Feed System

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

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

Automatic Combustion Control (ACC) System

Feedwater Control System (FCS)

Differential Control System of MFP (DCS)

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

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.

Questions?