Transcript MAIN STEAM CYCLE - IHMC Public Cmaps (3)

An Introduction
To
Marine Steam Propulsion Plant
[Source: US Navy]
Four Phases of Steam
Cycle
Generation
 Expansion
 Condensation
 Feed

GENERATION (Boilers)
SG/ Boiler
Economizer
Superheater
GENERATION

Boiler
– fuel is converted to heat
– largest and heaviest part of steam plant
– heat is transferred via conduction to water in
the metal tubes
– some of this water becomes steam

Steam drum
– as steam is generated it collects in the upper
portion of the boiler
– steam collecting in the steam drum is called
saturated steam
GENERATION

Super heater
– saturated steam does not contain enough
thermal energy to make the turbines operate
efficiently
– uses heat from the burner section of the boiler
to increase the temperature of the steam
– superheated steam is also dryer which helps
prevent erosion of the turbine blades and main
feed pumps
GENERATION

Economizer
– improves efficiency in the steam plant
– uses thermal energy that would go up the
stack to preheat feedwater before the steam
drum
– nest of tubes located between the generating
tubes of the boiler and the stack
EXPANSION (Turbines)
Reduction
Gears
HP
Turbine
M ain
Shaft
LP
Turbine
EXPANSION
Turbines
 High pressure/high temperature steam
goes from the superheater outlet to the
high pressure turbine of the main engine

– this is where expansion begins
– superheated steam expands in the turbine
and is converted to mechanical energy to
turn the rotor
EXPANSION
– energy conversion takes place in two steps in
each stage of turbine blades
– first the steam passes through the nozzles which
increase the steam’s velocity
– this kinetic energy is then converted into work
by the turbine blades
– after steam leaves the HP turbine it still has
thermal energy
– steam undergoes the same process in the LP
turbine
CONDENSATION
(Condenser, MCP, AEC)
Condenser
M U Feed
Tank
Condensate
Pump
Air Ejector
Condenser
CONDENSATION

Main Condenser
– large sealed container that serves as an indirecttype shell and tube heat exchanger
– cool seawater flows through thousands of
internal tubes
– steam from the exhaust of the LP turbine flows
over these tubes and heat is removed from the
steam, condensing the steam in to a liquid
(Condensate)
– The condensing action of the steam creates and
maintains a vacuum in the condensers
CONDENSATION

Main condensate pump
– one or two stage centrifugal pump,
electrically driven
– moves condensate from the hotwell through
the main air ejector condenser to the
deaerating feed tank
– pump is drawing a suction on the water in
the hotwell
– lowest pressure in the system occurs here
CONDENSATION

Air ejector condenser
– shell and tube heat exchanger
– two functions


removes latent heat from the auxiliary steam
being discharged by the air ejector
transfers heat from the steam to the condensate
to preheat it before it enters the deaerating feed
tank
FEED (DFT, MFBP, MFP)
DFT
Feed
Pump
Booster
Pump
FEED PHASE
The Deaerating feed tank is the
beginning of the feed phase
 Direct type heat exchanger - three
functions

– feed is heated by auxiliary steam and then
falls to the lower section - causing the
oxygen held in solution to be removed
– heats feed and maintains proper temperature
of water
– storage tank for heated oxygen free
feedwater
FEED PHASE
Feedwater goes from deaerating tank to
main feed boost pump(MFBP)
 MFBP

– one or two stage double suction centrifugal
pump
– installed below the DFT
– discharges into the suction side of the main
feed pump (MFP)
FEED PHASE

MFP
– Large Multistage Centrifugal pumps (steam or
electrically driven)
– delivers feedwater in sufficient amounts and
develops enough pressure to force the water
into the boiler against the pressure of the steam
drum
MACHINERY PLANT
LAYOUT
No two ships are exactly alike
 Machinery is arranged in various ways as
space and weight permit
 Generally speaking

– Propulsion machinery is usually on two
levels


condensers and main reduction gear on
lower level
propulsion turbines and pinion gears are on
upper level
MACHINERY PLANT
LAYOUT
– Low pressure turbine exhaust is directly
above the condenser
– Boilers are on the lower and upper levels
along the centerline of the ship
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