2 ReferencesRequiredIntroduction to Naval Engineering (Ch. 9-10)
3 ObjectivesComprehend 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.
5 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.
7 Main Condenser Indirect, shell-and-tube, cross flow heat exchanger Maintained at vacuum of 25-29” HgHow is the vacuum initiated & maintained?Two flow paths through condenserCondensate collects in hotwellProvides NPSH to condensate pumps
8 Main Condensate PumpsCentrifugal pumps, either steam or electrical power (subs all electrical)Usually 2 pumps per condenserCheck valve on discharge of pump to prevent backflowLowest pressure in MS cycle at suction of pumps
9 Condensate Depression Amount of subcooling of condensate in the hotwell of the main condenserIf too little (< 2oF), then cavitation of condensate pumps can occurIf too much (> 5oF), then lose efficiency (since condensate must be reheated later)Controlled by regulating MSW flow
10 Main Seawater System (MSW) Provides cooling water for main condenser to condense steamScoop Injection SystemUsed at higher speeds (> 8 knots)Uses ship’s speed and scoop to cause flowNot on SSN/SSBN/SSGN’sMSW PumpUsed when going slow or asternAll SSN/SSBN/SSGN’s
11 Main Feed SystemPurpose: to deaerate, preheat, store, and transport water from DFT to the boiler or S/G
12 Deaerating Feed Tank (DFT) Preheats feed using 150# Auxiliary SteamProvides NPSH for MFBPProvides a surge volume to compensate for changes in steam demand.Deaerates feed (removes dissolved air)
13 Deaerating Feed Tank (DFT) Operation150# Aux Steam enters in for heatingCondensate sprayed in thru nozzles (foglike)Baffles collect condensate/condensed steam and directed to atomizer assemblyAtomizer uses high-velocity steam to redirect condensate-> remove last gases (scrubbing)
14 More Components Main Feed Booster Pump (MFBP) Main Feed Pump (MFP) Single-stage centrifugal pumpProvides NPSH to MFPMain Feed Pump (MFP)Multi-stage centrifugal pumpRaises feed pressure > S/G pressureFeedwater Control ValveRegulates quantity of feed flow to S/G
15 Makeup-and-Excess Feed System During normal operations, necessary to add/remove water from steam cycleSystem stores feed and provides it if neededDFT level control system provides controlIf level low, make-up feed valve openedIf level high, excess feed valve opened
17 Automatic Boiler / S/G Level Control System Uses closed loop feedback principle of operationMeasure actual outputCompare actual output with desired outputCompute necessary correction signalCorrect actual output
18 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 levelDiff Control System of MFP (DCS)Maintains feedwater supply pressure above steam drum pressure
22 Interrelation of Systems Answering AA2/3 -> OOD orders AAIIOpen throttles -> steam flow -> steam pressureACC system air & fuel to combustion rateFWC system feed to match steam flowDCS of MFP speed of MFP to discharge pressure
23 Take Away Classify the main condenser Describe the two methods of providing cooling to the Main CondenserDefine condensate depression. Discuss the impact of condensate depression on system operation and efficiencyDescribe the purposes of the main feed systemDescribe the purposes and operation of the DFTDescribe 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.