5a - Boiler Construction Continued -Internals - Superheaters Locked
Transcript of 5a - Boiler Construction Continued -Internals - Superheaters Locked
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MainPlant
Boilers
MainPlant
Boilers
Feed water in
Economiser
Steamdrum
Waterdrum
Superheater
Downcomers
Risers
Risers
Furnace
Casing
Superheated
steam out
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Steam DrumSteam Drum
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The steam drum is designed to separate the steam from the
steam/water emulsion produced in the riser tubes.
It is important to ensure that no water is carried over into
the superheater. Separation is carried out by:-
Horizontal perforated plates acting as baffles.
A dry pipe situated at the top of the drum with slots
cut in to help prevent the passage of water. The dry
pipe carries the steam away from the drum to the
superheater.
The feed water pipe is submerged below the normal
working water level of the boiler.
Steam Drum InternalsSteam Drum Internals
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CycloneSeparators
CycloneSeparators
Used in some makes
of boiler to give
improved separation of
steam/water.
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Cyclone SeparatorsCyclone Separators
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Steam DrumSteam Drum
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Steam DrumSteam Drum
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Super-heatersSuper-heaters
The ESD III boiler
has an external
superheater that
uses the thermalenergy of the
combustion gasses
after passing
through the screen
wall
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Superheater tubes are subject to very high temperatures
(510C) and full boiler pressure (65 bar) and are, therefore,
highly stressed.
Materials: Chrome/molybdenum steel.
Tube Diameter 53mmThe superheater tubes are welded on to stub pipes on the
headers, which are external to the gas passage.
The tube bends are supported by lugs which are welded tothe screen wall riser tubes in order to remove heat.
SuperheatersSuperheaters
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The superheater is set up as three separate banks of tubes.
The two top banks (furthest from the furnace) are set up asthe primary superheater.
The lower bank (closest to the furnace) is the secondary
superheater.ALL steam flow from the boiler drum must pass through
ALL sections of the superheater continuously.
It is important to maintain maximum flow through thesuperheater at all times in order to prevent overheating.
SuperheatersSuperheaters
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SuperheatersSuperheaters
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SuperheatersSuperheaters
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SuperheatersSuperheaters
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Steam Temperature ControlSteam Temperature Control
Air Attemporation
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Steam Temperature ControlSteam Temperature Control
ESD II
Gas Flow Control
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Steam Temperature ControlSteam Temperature Control
((AttemporationAttemporation))
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Superheat
Flow
SuperheatSuperheat
FlowFlow
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Superheat FlowSuperheat Flow
Primary Superheater Contra flow
Secondary Superheater Parallel Flow
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AttemporatorAttemporator
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AttemporatorAttemporator
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Water SprayWater Spray AttemporationAttemporation
Feed water sprayed into steam path
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Some of the superheated steam is de-superheated in order
to supply cooled saturated steam for lower quality heatingpurpose e.g.
Steam/steam generators. Evaporators. De-aerators. Air
heaters. etc.
There are two main ways of de-superheating:-
Via a cooling coil in the water drum of the boiler.
Via a water spray de-superheater.
De-superheatersDe-superheaters
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Spray De-superheaterSpray De-superheater
De-superheatedoutlet
Superheatedinlet
Drain
Feed
water inlet
Feed
water flow
control
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In order to improve the efficiency of the combustion
process and the overall efficiency of the boiler the
combustion air is pre-heated. This can be done in threeways:-
A tube type air heater using de-superheated steam.
A rotary heat exchanger (Ljungstrom)
A double casing fitted round the boiler.
Air HeaterAir Heater
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The combustion air is passed from the forced draught fan
into a double casing surrounding the furnace and
superheater.
The air is first heated by waste heat passing through the
riser tube wall and the refractory.
The air then passes through a tube type heat exchanger that
uses de-superheated steam to increase the temperature to
about 120C before the air passes to the burner registers.
Note that monowall boilers do not normally have double
casings.
Double Casing & Air HeaterDouble Casing & Air Heater
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Ljungstrom Air HeaterLjungstrom Air Heater
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