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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 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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ESP Raping Mechanism

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p g

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Thank you

Documents

116986044 Air Pre Heating