CONTENTS INTRODUCTION

OBJECTIVE

CIRCUIT DIAGRAM

OPERATION/WORKING PRINCIPLE

CALCULATIONS

ADVANTAGES

DISADVANTAGES

APPLICATIONS

REFERENCES

INTRODUCTION A Regenerative air preheater is a type of air preheater used in

thermal power plants to preheat the steam generator's

combustion air with the hot flue gas from the steam generator. 

The types of Regenerative Air Preheaters are

1. Bisector

2. Trisector

3. Qudrasector

Here the discussion is carried on the Trisector Air Preheater.

OBJECTIVEMainly there are two types of Air Preheaters

1. Recuperative Air Preheater

2. Regenerative Air Preheater

The main objective of this project is to prove that the efficiency of

regenerative air pre heater is more, when compared to the

recuperative air pre heater.

It is to say that the Trisector type of Regenerative air pre heater is

more advantageous than Bisector type.

CIRCUIT DIAGRAM OF BOILERSteam generator

Burner

Sec

onda

ry a

ir Air preheater

FD-Fans

Excess Air

Electricprecipitator

Intermed. Fly-ash bunker

Fly ash

Flue gas

Coal bunker

Coal mill

Pu

lveri

zed

fuel

Prim

ary

air

CIRCUIT DIAGRAM OF AIR PREHEATER

WORKING PRINCIPLEAir Preheater is a device which is designed to heat the air

before the combustion process.

The purpose of Air Preheater is to recover the heat from

the flue gases which are obtained from the boiler thus

increases the thermal efficiency of the boiler.

Due to the discontinuous action taking place in the air pre

heater, it is so called as regenerative air pre heater.

TRISECTOR AIR PREHEATERThere are three sections in

the Trisector Air Preheater.

Flue Gases

Primary Air

Secondary Air

Flue gases are sent through

the chimney through

Induced Draft(ID) Fan.

FLUE GASES

SECONDARY

AIR

PRIMARY

AIR

Primary Air (PA) is used to dry the fine particles of pulverized coal, which is then forced into the furnace with the help of PA fan, from the gravimetric coal feeder.

Secondary Air (SA) is used to supply sufficient oxygen for complete combustion of fuel and this is done with the help of Forced Draft (FD)fan.

Primary Air occupies 1/6th part of the Air Preheater.

Flue gases occupies 1/2nd part of the Air Preheater.

Secondary Air occupies 1/3rd part of the Air Preheater.

Sealings in air pre heater

Temperature at inlet conditions:• Flue gas – 3600 c• Air temperature – 35o c

Exit Temperature:• Flue gas – 1400 c• Air temperature – 180o c

CALCULATIONS

1)

2)

3)

[(Fraction of primary air x Inlet air temperature of primary air sector)

+(Fraction of secondary air x Inlet air

temperature of secondary air sector)]

=Weighted air

in temperature

4)

5) Convective heat transfer takes place in air preheater i.e.

q = hA (t2 – t1)

6) Area of Cross section occupied of flue gas, PA and SA systems:

i) Gas flow area = 25.94 m2

ii) Primary air flow area = 8.96 m2

iii) Secondary air flow area = 14.62 m2

ADVANTAGESTrisector Air Preheater provides both

Primary and Secondary Air sections in a single plate.

Due to the presence of Primary section immediate to the Flue Gas path, complete drying up of coal particles takes place.

It has quick response with variation of loads.

DISADVANTAGESLeakages are more, but this can be avoided

up to some extent by perfect sealing system.

Constructional cost for regenerative air

preheater is more when compared to

recuperative type.

APPLICATIONSIt is used where in waste heat recovery is

possible for increase in efficiency of

particular device.

Hence it is installed in every thermal power

station.

REFERENCESMaterial provided by KTPS.

Thermal Engineering By R.K.Rajput, 6th

Edition, published by Laxmi Publications.

Heat And Mass Transfer By

C.P.Kothandaraman and S.Subramanyan, 6th

Edition.

Heat And Mass Transfer By R.K.Rajput.