Main Condensate

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Main Condensate Feed Systems

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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

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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

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Main Condensate System
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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

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Main Condenser
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Main Seawater System (MSW)

• Provides cooling water for main condenser to
  condense steam
• Scoop Injection System
• Used at higher speeds (gt 8 knots)
• Uses ships speed and scoop to cause flow
• Not on SSN/SSBNs
• MSW Pump
• Used when going slow or astern
• All SSN/SSBNs

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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

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Condensate Depression

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

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Main Feed System

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

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Deaerating Feed Tank (DFT)

• Preheats feed using 150 Auxiliary Steam
• Stores feed (provides NPSH for MFBP)
• Deaerates feed (removes dissolved air)

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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-gt remove last gases (scrubbing)

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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 gt S/G pressure
• Feedwater Control Valve
• Regulates quantity of feed flow to S/G

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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

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Makeup-and-Excess Feed System
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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

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Automatic Boiler / S/G Level Control System

• Automatic Combustion Control (ACC)
• Maintains boilers 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

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Automatic Combustion Control (ACC) System
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Feedwater Control System (FCS)
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Differential Control System of MFP (DCS)
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Interrelation of Systems

• Answering AA2/3 -gt OOD orders AAII
• Open throttles -gt steam flow -gt 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

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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.
• Cant have too much will cause fouling and
  scale deposits

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Questions?