Air PreHeater In thermal power plant

5/21/2018 Air PreHeater In thermal power plant

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AIR PREHEATER

Air Pre-heater is an auxiliary equipment forsteam boilers. It is a heat exchanger that

absorbs heat from exit flue gas in boilersand transfers the heat to the cold air. Inutility and process boilers it is used to heat

the air required for combustion purposeand to dry and transport coal.


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TYPES OF AIR PRE HEATERS RECUPERATIVE

-Tubular Heater

-Plate Type Heater-Steam Coiled Heater

REGENERATIVE

-Ljungstrom Air Pre Heater


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RECUPERATIVE AIR PREHEATER-

In Recuperative type Air Preheater two fluids flow atdifferent temperatures in a space separated by a solid

partition. Heat is transferred by Convection &Conduction through the separating wall.

Tubular Air Preheater, Plate Type Air Preheater &

Steam Coil Air Preheater (SCAPH).


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TUBULAR APH

Advantages:

Not having any moving parts.Small Nominal leakages of air to gas.

No auxiliary power consumption.

ProblemsLarge for thermal duty.Difficult to clean.Do not allow replacement of damaged heating surface.The ductings for cold and hot air require additionalspace and structural supports compared with theLjungstrom design


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Ljungstrom Air Pre Heater

In Regenerative type Air Preheater, one heating surface

is exposed at certain intervals of time first to a hotfluid and then to a cold one. The surface of theRegenerative Air Preheater first removes heat from thehot fluid and is itself heated in the process, then the

surface gives up this heat to the cold f luid


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Application - Air Pre Heater

To heat fresh air usingheat of flue gas for :

Primary Air :

To remove moisture frompulverized coal

Secondary Air :

To assist combustion inboiler

Air Pre Heater,

Vertical Inverted, Trisector


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COMPONENTS OF RAPH Rotor Rotor Post Modules

Heating elements Bearings Housing Connecting Plates

Sealing Arrangements Drive units Cleaning devices Safety Devices


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HEATING ELEMENTS

End Height OfHeatingElements

Material Description ofElements

Hot 300mm Carbon Steel Double

Corrugated

Inter-1 800mm Carbon Steel DoubleCorrugated

Inter-2 800mm Carbon Steel DoubleCorrugated

Cold 300mm Corrosion resistance steel Notched Plate


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THRUST BEARING-


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AIR PRE HEATER

SEALING ARRANGEMENT

Radial Seals

Axial Seals Bypass Seals

Rotor Post Seals


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Sealing system


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Ljungstrom Regenerative Air Preheater (RAPH)

Advantages: Significant reduction in overall size and weight.

Easy and economic replacement of heating surfacewith separate cold end and hot end packs.

Problems High Air leakages resulting high fan power.

Dust carry over to furnace is high causing ash erosionof boiler tubes in burner panels

Baskets are subjected to abrasive wear , hencefrequent replacement of the baskets are required.

Prone to air heater fire , the problem is aggravatedduring oil firing


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Air PreHeater In thermal power plant