boilers accessories Presentation

8/7/2019 boilers accessories Presentation

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CONTENT Introduction

Economizer

Air Preheaters Superheaters


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INTRODUCTION

During combustion process 25% of heat

remain in exhaust gases, it means only

75% is utilized by boiler and remaining

goes to atmosphere through exhaust

gases. This loss can be reduced by

using equipment like Economizer,

Airpreheater and Superheters. It also help to increase the thermal

efficiency


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ECONOMIZER


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It is a feed water heater which use heat

from exhaust gases.

Application of economizer depend onvarious factors like

Gain in efficiency

Size of power plant in terms of power

generation

Exhaust gas temp.


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Required feed water temperature

Types of fuel used

Heat transfer surface should beminimum

It must be able to extract maximum

possible heat from exhaust gases.

There should be uniform water flow in

order to avoid steam formation


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TYPES OF ECONOMIZERS

Plain tube type

Gilled tube type


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PLAIN TUBE TYPE


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It consist of series of cast iron tubes,

located in the path of boiler and

chimney.

When the exhaust gases passed

through these tubes heat transfer take

place from gases to feed water.

Tubes are made of cast iron in order toprevent corrosive action of flue gases.


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GILLED TUBE TYPE


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In case of gilled tube type economizer

rectangular gill is cast on the bare wall

of tubes, by doing so high efficiency and

reduction in size can be obtained.

Cast iron gill tube can be use upto 50

bar working pressure, if working

pressure is more than 50 bar steel tubeis used.


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AIR PREHEATERS


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Exhaust gases coming out of

economizer is further utilized for

preheating the air before to the

combustion chamber.

1% boiler efficiency increase

corresponding to 20 degree temp.

Increase of air.


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Main objective of air preheater are

Improved combustion

Successful use of low grade carbonfuel

Increase thermal efficiency

Saving fuel consumption


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TYPES

Recuperative

Tubular Air Heater

Plate type Airheater Regenerative


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RECUPERATIVEPLATE TYPE AIRHEATER


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It consist of number of rectangular

plates, the space between two plates is

near about 1.5 to 2.5cm, flue gases and

air pass through these space and henceheat transfer take place.

Plate type Airheater is more expensive

as compare to tubular type because offlatness and maintenance cost.


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TUBULAR TYPE AIR HEATER


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In this type of air heater flue gas passes

through nobler of tubes and air is

passed over the outer surface of tube

and hence heat transfer take place.

Horizontal baffle is provided in order to

increase time of contact.


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Regenerative type


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In this type of air preheater transfer ofheat from hot gases to air take place intwo stage.

In first stage heat from hot gasestransfer to packing of heater where itgets accumulated or store, this stage isknown as heating period, during second

stage heat from packing transfer to airand thus packing gets cooled; this stageis known as cooling stage or period.


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SUPERHEATERS


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Main function of super heater is to

remove last trace of moisture from

saturated steam coming out of boiler

and increase the temperatureSufficiently above saturation

temperature.

Superheaters increase overall efficiency,and make use of exhaust gases to

remove the moisture content


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Materials used for super heater must

have following properties

High temperature strength

High creep, high resistance to

oxidation

Carbon steel and chromium-

molybdenum alloy normally used.


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Superheat temperature control

Tem. Control is necessary in order to

avoid over stressing of superheater

tubes, this is accomplished by using

combined type superheaters, one part ofwhich is located in furnace wall while

other in convection part.


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Common method of controlling the

temperature are

Bypassing the furnace gas around

superheaters

Tilting burner in the furnace

Gas recirculation etc.

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