Transcript Main Condensate & Feed Systems

Main Condensate &
Feed Systems
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Objectives
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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
Main Condensate System
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Provides condensation phase of the main
steam cycle
Condenses steam from turbines to liquid
Pumps condensate from main condenser to
the Main Feed System
Main Condensate System
Main Condenser
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Indirect, shell-and-tube, cross flow heat
exchanger
Maintained at vacuum of 25-29” Hg
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How is the vacuum initiated & maintained?
Two flow paths through condenser
Condensate collects in hotwell
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Provides NPSH to condensate pumps
Main Condenser
Main Seawater System (MSW)
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Provides cooling water for main condenser
to condense steam
Scoop Injection System
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Used at higher speeds (> 8 knots)
Uses ship’s speed and scoop to cause flow
Not on SSN/SSBN’s
MSW Pump
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Used when going slow or astern
All SSN/SSBN’s
Main Condensate Pumps
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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
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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
Main Feed System
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Purpose: to deaerate, preheat, store, and
transport water from DFT to the boiler or S/G
Deaerating Feed Tank (DFT)
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Preheats feed using 150# Auxiliary Steam
Stores feed (provides NPSH for MFBP)
Deaerates feed (removes dissolved air)
Deaerating Feed Tank (DFT)
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Operation
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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
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Main Feed Booster Pump (MFBP)
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Main Feed Pump (MFP)
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Single-stage centrifugal pump
Provides NPSH to MFP
Multi-stage centrifugal pump
Raises feed pressure > S/G pressure
Feedwater Control Valve
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Regulates quantity of feed flow to S/G
Makeup-and-Excess Feed
System
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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
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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
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Uses closed loop feedback principle of
operation
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Measure actual output
Compare actual output with desired output
Compute necessary correction signal
Correct actual output
Automatic Boiler / S/G Level
Control System
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Automatic Combustion Control (ACC)
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Feedwater Control System (FCS)
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Maintains boiler’s steam drum pressure by controlling
rate of combustion (air/fuel)
Regulates flow of feedwater to boiler to maintain level
Diff Control System of MFP (DCS)
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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
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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
Boiler Chemistry Control
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High temperature water and steam at
neutral pH can be very corrosive
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Holes in piping
Chemicals are added to the water to ensure
pH stays low (basic)
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Must analyze for proper levels of these chemicals to
ensure corrosion prevented.
Can’t have too much – will cause fouling and scale
deposits
Questions?