Lesson 05 - Main Steam Cycle
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Introduction • •
Parts of the Main Steam Cycle Four Phases of the cycle • •
•
Definitions of each phase Components involved with phases Press-temp relationships
Parts of Main Steam Cycle •
• • • •
•
Steam Generator (nuclear) or Boiler (conventional) Turbines Condenser Main Condensate Pumps Deaerating Feed Tank / Reserve Feed Tanks Main Feed Pumps
Main Steam Cycle
Background • •
Cycle used is a Rankine cycle P-v and T-s Diagrams • •
• •
Trace the points of cycle Provide graphical understanding of cycle
Four phases of cycle Conventional vs. Nuclear
Rankine Cycle T-s Diagram
1-2: 2-3: 3-4: 4-1:
P-v Diagram
Feed Phase (∆ Q=0, ∆ S=0), Win Generation Phase (∆ P=0), Qin Expansion Phase (∆ Q=0, ∆ S=0), Wout Condensation Phase (∆ P=0), Qout
Generation Phase Conventional •
Boiler (1200 # steam) •
•
•
Fuel burned to produce heat -> transferred to water which boils to steam Steam collects in steam drum (saturated)
Superheater • •
Increase temp of steam and dries steam Three reasons for superheating? • • •
Minimize erosion (dry steam better for blading) Minimize corrosion (less chemicals entrained) Maximize ∆ T (Carnot efficiency)
Boiler and Superheater
Generation Phase Nuclear •
Reactor (Rx) Plant •
•
Fission in Rx core transforms nuclear energy to thermal energy
Steam Generator • • • •
Water Space U-tubes Steam Space Moisture Separators
Reactor Plant
Expansion Phase • •
• •
Steam travels down main steam piping Turbines convert thermal energy -> mechanical energy (nozzles) and then work (blading) -> turn rotor/shaft Pressure drops as steam goes through Work performed on turbine blading • •
Main Engines (ME) -> propulsion Ship’s Service Turbine Generators (SSTG) -> electricity
Condensation •
Vacuum 26-29” Hg •
•
Air Ejectors - use 150# steam to establish initial vacuum and remove air Maintained by condensation •
•
volume of water << volume of steam -> contraction
Why vacuum? •
•
•
Ease of steam recovery (“pulls” steam into MC) More work out of turbines (larger ∆ P and ∆ T) Ease of conversion to water
Condensation •
Main Condenser • •
•
•
Large, indirect, cross-flow, shell-and-tube HX Seawater used to condense steam
Hotwell - holding area for condensate water at 80-100 F (lowest temp in cycle) Main Condensate Pumps - send condensate to the DFT at 20-30 psi (suction side is lowest pressure in cycle)
Main Condenser
Feed Phase •
Deaerating Feed Tank (DFT) • •
Direct-type HX (Aux Steam used) Purposes • • •
•
•
preheats feed storage/surge volume removes dissolved oxygen to minimize corrosion
FYI: RFT’s often used instead
Main Feed Pump •
Supplies feed water to Steam Generator (must be high pressure to overcome pressure)
Deaerating Feed Tank
Putting It All Together
Your Drawing • • • • • • • •
Boiler/Steam Generator Superheater Turbine Condenser Main Condensate Pumps Main Feed Pumps DFT/RFT Economizer
Questions ?
Introduction • •
Parts of the Main Steam Cycle Four Phases of the cycle • •
•
Definitions of each phase Components involved with phases Press-temp relationships
Parts of Main Steam Cycle •
• • • •
•
Steam Generator (nuclear) or Boiler (conventional) Turbines Condenser Main Condensate Pumps Deaerating Feed Tank / Reserve Feed Tanks Main Feed Pumps
Main Steam Cycle
Background • •
Cycle used is a Rankine cycle P-v and T-s Diagrams • •
• •
Trace the points of cycle Provide graphical understanding of cycle
Four phases of cycle Conventional vs. Nuclear
Rankine Cycle T-s Diagram
1-2: 2-3: 3-4: 4-1:
P-v Diagram
Feed Phase (∆ Q=0, ∆ S=0), Win Generation Phase (∆ P=0), Qin Expansion Phase (∆ Q=0, ∆ S=0), Wout Condensation Phase (∆ P=0), Qout
Generation Phase Conventional •
Boiler (1200 # steam) •
•
•
Fuel burned to produce heat -> transferred to water which boils to steam Steam collects in steam drum (saturated)
Superheater • •
Increase temp of steam and dries steam Three reasons for superheating? • • •
Minimize erosion (dry steam better for blading) Minimize corrosion (less chemicals entrained) Maximize ∆ T (Carnot efficiency)
Boiler and Superheater
Generation Phase Nuclear •
Reactor (Rx) Plant •
•
Fission in Rx core transforms nuclear energy to thermal energy
Steam Generator • • • •
Water Space U-tubes Steam Space Moisture Separators
Reactor Plant
Expansion Phase • •
• •
Steam travels down main steam piping Turbines convert thermal energy -> mechanical energy (nozzles) and then work (blading) -> turn rotor/shaft Pressure drops as steam goes through Work performed on turbine blading • •
Main Engines (ME) -> propulsion Ship’s Service Turbine Generators (SSTG) -> electricity
Condensation •
Vacuum 26-29” Hg •
•
Air Ejectors - use 150# steam to establish initial vacuum and remove air Maintained by condensation •
•
volume of water << volume of steam -> contraction
Why vacuum? •
•
•
Ease of steam recovery (“pulls” steam into MC) More work out of turbines (larger ∆ P and ∆ T) Ease of conversion to water
Condensation •
Main Condenser • •
•
•
Large, indirect, cross-flow, shell-and-tube HX Seawater used to condense steam
Hotwell - holding area for condensate water at 80-100 F (lowest temp in cycle) Main Condensate Pumps - send condensate to the DFT at 20-30 psi (suction side is lowest pressure in cycle)
Main Condenser
Feed Phase •
Deaerating Feed Tank (DFT) • •
Direct-type HX (Aux Steam used) Purposes • • •
•
•
preheats feed storage/surge volume removes dissolved oxygen to minimize corrosion
FYI: RFT’s often used instead
Main Feed Pump •
Supplies feed water to Steam Generator (must be high pressure to overcome pressure)
Deaerating Feed Tank
Putting It All Together
Your Drawing • • • • • • • •
Boiler/Steam Generator Superheater Turbine Condenser Main Condensate Pumps Main Feed Pumps DFT/RFT Economizer
Questions ?
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