Main Condensate & Feed Systems We Love Engineering!

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

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

Main Condensate System

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 Condenser

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

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

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 Stores feed (provides NPSH for MFBP) 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) 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

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

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

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