Main Steam Cycle

References Required – Introduction to Naval Engineering (pg 41-48) Recommended – Principles of Naval Engineering ( )

Objectives A. Comprehend the application of the laws of thermodynamics to determine the changes in state/energy which water undergoes in the basic steam cycle. B. Comprehend the purpose and safety issues of the various components and their effect on these energy and state changes. C. Comprehend the four phases of the basic steam cycle and know the components found in each.

Introduction What are the basic elements of a heat engine? Working Substance Generation (heat source) Expansion Rejection Pump

GenerationExpansion Pump Working Substance Basic Heat Engine Rejection

Steam Generator or Boiler Turbine Pump Working Substance The Main Steam Cycle Rejection Heat Added Work Out Heat Out Work On

Conventional Steam System

Typical Nuclear Steam Cycle Expansion Generation Condensing Feed

Background Cycle used is a Rankine cycle P-v and T-s Diagrams – Trace the points of cycle – Provide graphical understanding of cycle Conventional vs. Nuclear

Generation Phase - Conventional Boiler ( steam) – Watersides (steam) and Firesides (furnace) – 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

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 steam to establish initial vacuum and remove air – Maintained by condensation volume of water contraction – Why vacuum? Ease of steam recovery (“pulls” steam into MC) More work out of turbines (larger  P and  T)

Condensation Main Condenser – Large, indirect, cross-flow, shell-and-tube HX – Seawater used to condense steam Hotwell - holding area for condensate water at F (lowest temp in cycle) Main Condensate Pumps - send condensate to the DFT at 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

Rankine Cycle 4-1: Feed Phase (  Q=0,  S=0), W in 1-2: Generation Phase (  P=0), Q in 2-3: Expansion Phase (  Q=0,  S=0), W out 3-4: Condensation Phase (  P=0), Q out T-s Diagram

Putting It All Together

Take Away Draw a T-s Diagram of the Rankine Cycle, label the phases of the cycle and indicate the condition of the working fluid in each phase Draw and label a simple, one-line diagram of the main steam cycle Describe the energy conversions/phase changes occurring in each component of the steam cycle Describe the advantages of a super heater and deaerating feed tank in propulsion plants

Questions?