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An Over view of
Air Pre Heaters, Soot Blowers and
Electro Static PrecipitatorsTraining & Development
Dr KC Yadav, Director,
Jindal Institute of Power Technology
Training & Development
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Air Pre Heaters
Dr. K.C. Yadav, Head,
Training & Development
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Purpose
It recovers the heat from the boiler flue gas and
increase the temperature of combustion air (PA & SA),
which in turn increases the thermal efficiency of the
boiler.
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Air HeaterAir heater is a heat exchanger in whichair temperature is raised by
transferring heat from other fluids suchas flue gas.
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Advantages of Air Heaters
Stability of combustion is improved by use of hot air.
Intensified and improved combustion.
Burning poor quality fuel efficiently.
Less unburnt fuel particle in flue gas thus complete
combustion is achieved.
Intensified combustion permits faster load variation.
In the case of pulverized coal combustion, hot air can beused for drying the coal as well as for transporting the
pulverized coal to burners.
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Types of Air heaters
Air heaters can be classified as:
A. RecuperativeB. Regenerative
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RECUPERATIVE
In Recuperative type-heating medium is onone side and air is on the other side of tubeor plate and the heat transfer is by
conduction through the material, whichseparates the media. These are of staticconstruction and hence there is only nominalleakage through expansion joints, accessdoors, casings etc
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REGENERATIVE
In Regenerative type the heating medium
flows through a closely packed matrix to
raise its temperature and then air is passed
through the matrix to pick-up the heat.
Either the matrix or the hoods are rotated to
achieve this and hence there is slight leakage
through sealing arrangements at the moving
surfaces
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Recuperative
1. Tubular Air heater
This usually consists of large number of
steel tubes of 40 to 65 mm dia eitherwelded or expanded into the tube
plates at the end. Either gas or air may
be allowed to flow through the tube.
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Tubular Type APH
Tubular pre heaters consist of straight tube bundles
which pass through the outlet ducting of the boiler andopen at each end outside of the ducting. Inside the
ducting, the hot furnace gases pass around the preheater tubes, transferring heat from the exhaust gas tothe air inside the pre heater. Ambient air is forced by afan through ducting at one end of the pre heater tubesand at other end the heated air from inside of the tubesemerges into another set of ducting, which carries it tothe boiler furnace for combustion.
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Problems inTubular Type APH
The tubular preheater ductings for cold and hot air require more
space and structural supports than a rotating preheater design.
Further, due to dust-laden abrasive flue gases, the tubes outsidethe ducting wear out faster on the side facing the gas current.
Many advances have been made to eliminate this problem such
as the use of ceramic and hardened steel.
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Recuperative
2. Plate Type Air heater
These comprise of parallel plates which
provide alternate passage for gas and air3. Steam Air Preheater
This does not utilize the heat from boilerflue gas and hence does not improve boiler
efficiency.
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Regenerative
1. Ljungstrom Type
The heat transfer elements are rotated at a
constant speed and they pass alternately
through gas and air passes.
2. Davidson/Rothemuhle Type
This type is the same as the Ljungstrom type-except that the matrix element is stationary
and the air gas hoods rotate.
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Stationary-Plate Regenerative Air Pre Heater
The heating plate elements in this type of regenerative air
preheater are also installed in a casing, but the heating plate
elements are stationary rather than rotating. Instead the air ducts
in the preheater are rotated so as to alternatively expose sections
of the heating plate elements to the upflowing cool air.
There are rotating inlet air ducts at the bottom of the stationary
plates similar to the rotating outlet air ducts at the top of the
stationary plates.
Stationary-plate regenerative air preheaters are also known as
Rothemuhle preheaters.
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Ljungstrm Air Pre Heaters
Th Lj t R ti Ai P h t P i i l
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1) Combined Cleaning
Device for Blowing
with
Steam or Compressed
Air and Washing with
Water
2) Rotor Drives
3) Axial Seal
Adjustable during
Boiler Operation
4) Radial Seal
Adjustable duringBoiler Operation
5) Guide Bearing
6) Rotor
7) Heating Elements in
Baskets
8) Hot Layer
(Material: Steel)
9) Cold Layer
(Material: Steel,
Corten or
Enameled Steel)
10) Intermediate Layer
(Material: Steel)
11) Pin Rack
The LjungstrmRegenerative Air Preheater Principle
The Ljungstrm air
preheater is a
regenerative heat
exchanger through
which flue gas and air
pass in countercurrent
flow.
The heat transfer surface
comprises thin, profiledheating
elements which are
contained in a rotor and
arranged parallel
to the direction of flow.
The rotor rotates at a
constant speed. During
each revolution theheating elements absorb
heat while rotating
through the flue gas side
and impart this stored
heat to the air when
rotating through the air
side.
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APH Driving Mechanism
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APH Driving Mechanism
APH Driving Mechanism
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APH Driving Mechanism
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APH Rotating Mechanism
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APH HeatingElements
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Dew point corrosion
Dew point corrosion occurs for a variety of reasons. The type of
fuel used, its sulfur content and moisture content are
contributing factors. However, by far the most significant cause
of dew point corrosion is the metal temperature of the tubes. Ifthe metal temperature within the tubes drops below the acid
saturation temperature, usually at between 190F (88C)and
230F (110C), but sometimes at temperatures as high as 260F
(127C), then the risk of dew point corrosion damage becomes
considerable.
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Regenerative Vs. Recuperative
Regenerative air heaters have the followingadvantages over recuperative ones (tubular):
1. Compact and hence save space and structure cost.
2. This is the type that can be economically used forhigh capacity boiler.
3. From the above two reasons, it is clear that initialcost as well as the operating cost can be keptminimum with regenerative air- heaters for highersize boilers.
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Regenerative Vs. Recuperative4. Less weight of metal permit economic usage of alloy
steel like corten steel.
5. Holes in the elements due to corrosion etc. will not
materially affect the performance of the heater.6. Deposit on the heat transfer surface does not
reduce the heat transfer.
7. Hot primary air for coal drying in mill is possible
with single air heater of tri-sector design. This alsohelps to make use of a cold primary air fan.
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Soot Blowers
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Long Retractable Soot Blowers are available in
various basic models designed for travel up to12.2 m. to suit the cleaning requirements of
different furnace sizes, heat recovery coil
arrangements etc. These blowers are availablewith single motor drive, dual motor drive and
non-rotating lance. They can be operated
electrically or pneumatically.
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The LRSB has one electric motor to move the lance in
and out, a second to rotate it - always in the same
direction. With no step-stop action at the end of travel,repeated cycles give an infinite number of double-helix
patterns. This minimizes danger of tube cutting or
erosion and ensures uniform cleaning of all surfaces.
Low rotating speed increases range and penetration of
cleaning, decreases wear, eliminates whip and permits
proper cleaning with faster traversing speeds. Rotating
and traversing speeds may be adjusted independentlyby speed-change gears or sprockets.
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Lance and feed pipe have no inaccessible parts to clog, corrode or
retard blowing-medium travel. Both are flanged for easy
maintenance. Feed pipe is ground and polished stainless steel toprevent binding and wear from carriage movement. Single exposed
stuffing box is easily repacked. Self-cleaning, low friction BHEL chain
drive needs no lubrication, and is easy to inspect and maintain. No
auxiliary carriage is needed or used. Method of support - never morethan two points - is tailored to the needs of each installation. Both
electric motors are stationary, away from hot furnace gases. Custom
built for BHEL they are totally enclosed, non-ventilated, 3-phase,
heavy-duty hoist type with special boiler room insulation and
protection against internal corrosion.
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APH Soot Blower
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APH Soot Blower
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Electro Static Precipitator
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ESP
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ESP
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ESP Roof
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ESP Roof
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ESP Roof
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ESP Bottom
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ESP Raping Mechanism
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p g
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ESP Raping Mechanism
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p g
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Thank you