The document describes the key components and operation of a circulating fluidized bed (CFB) boiler. The CFB boiler combusts crushed coal between 20-50mm in size using fluidized air. Unburnt coal is returned to the furnace through a cyclone separator. The main components are the furnace, cyclone separator, back pass, and air preheater. In the furnace, coal is combusted and limestone is added to reduce SOx emissions. The cyclone separator separates unburnt particles from flue gas. Heat from flue gas is transferred in the back pass to produce steam. The air preheater improves efficiency by preheating combustion air.

1. CFB Boiler Process
(Circulating Fluidized Bed )

2. What is Boiler?
• A closed vessel or arrangement of vessels and tubes,
together with a furnace or other heat source, in which
steam or vapor is generated from water to drive turbines
or engines.
• In this section, the fuel is combusted, and huge amount
of heat energy is released, which is then absorbed by the
water wall containing many tubes, the mode of heat
transfer is mostly radiation and partially convection. This
unit contains the complex arrangement of primary and
secondary air inlets, coal feeding, returned coal feeding,
flue gas outlet, bottom ash discharge mechanism and so
on. The boiler in this power plant was CFB subcritical
boiler
1- Pulverized Coal Boiler
2- Circulating Fluidized Bed Boiler

3. Pulverized Coal Boiler
PC Boiler operates on powdered Coal or Coal
dust.
PC boiler needs desulphurization unit for Sox
reduction.
There is no return of Ash and unburnt Coal to
Furnace.
PC boiler needs pulverizer for pulverizing of
Coal.

4. Circulating Fluidized Bed Boiler
CFB Boiler operates on crushed coal of (20mm-
50mm) particle.
For SOx reduction limestone is fed with
fluidized air.
Unburnt Coal is returned back to Furnace
through Cyclone separator.
CFB Boiler needs crusher for crushing of coal to
required size.

5. Parameter of Boiler
Boiler type Subcritical boiler Superheated steam
temperature
541⁰C
Steam flow 1105t/h Flue gas temp at the
Outlet of ESP
147⁰C
Steam pressure 17.4 MPa SOx Emission limit 850 mg/Nm3
Steam Temperature: 541 ͦ C NOx Emission limit 510 mg/Nm3
Bed temperature 823⁰C Coal Consumption 279.71t/h
Feedwater temperature 281⁰C Limestone Consumption 19.38t/h
Feedwater pressure 20.7MPa
Superheated steam
pressure
17.1MPa

7. Main components of CFB Boiler
1-Furnace
2-Cyclone Separator
3-Back pass
5-Air preheater
6-Ash Handling system

8. Furnace
• A Furnace is a closed vessel in which Fluid (generally
water) is heated. The water on high temperature
converts into Steam
• The closed area or closed vessel where combustion
takes place.
• Feeding of Coal directly into Furnace wall through Coal
feeder.
• Fluidized air enters from bottom of furnace.
• Combustion air enters in the upper portion of furnace.
• In furnace 29 High Super Heater Panels and 4 Evaporator
Panels.
• Bottom ash removes from bed of the furnace and passes
through the ash cooler.
• Flue gas goes out from outlet of furnace and enters into
the Cyclone Separator.
• Feeding of Limestone powder with compressed air by air
blowers.

13. Cyclone Separator
• It is closed vessel which is made to produce Cyclone.
• Flue gas enters cyclone and centrifugal force
produces.
• Which separates unburnt heavy particle of coal from
flue gases.
• Unburnt particle of coal rests in Seal pot and then
through return duct feed to Furnace.
• Flue gas goes out through Vortex Finder.

14. Cyclone separator Loop seal

15. HP Fluidizing Air fan

16. Back Pass
• The Back pass is the low temperature closed
vessel.
• There are three different types of tubes in
Back pass.
Super Heater
Re-Heater
Economizer
Economizer
Re-Heater
Super Heater

18. Economizer
• Economizer raises the temperature of Feed
water of Highest Pressure to saturation
temperature.
• Which is done by transferring of heat of flue
gases.
• The gases leaving the Super heater/ Re-
heater still have enough heat to transfer.

19. Super Heater
• Super Heater is used to convert saturated steam
into Super heated or dry steam.
Re-Heater
• Re-heaters are same like super heaters.
• They used to heat low temp steam to increase
thermal efficiency.
• The steam pressure is low as compared to Super
heater.

21. Steam drum
A steam drum is a standard feature of the boiler water pipes. It is a reservoir of
water/steam at the upper end of the tube of water. Drums keep the steam produced
in the water tubes and act as a phase separator for mixed steam/water. The density
difference between hot and cold water helps in the accumulation of -water/and
“hot” saturated steam into the steam drum.
Since it contains both the water and steam, at first the water from feed water pump
is passed through the economizer and then it is pumped to the steam drum, from
where it goes into the water wall via down-comers, and then the water is naturally
raised in the water tubes where it transforms into the steam, later on the steam in
raised getting further heated and goes into the steam drum via risers and finally
steam in directed towards the back pass to get sufficient temperature, so that it can
be supplied to HP turbine.

23. Steam drum down commers

24. Air preheater have four zone one is for
flue gases, two zones for secondary air
and one zone for Primary air, and it is
used to preheat the primary and
secondary air, this equipment extracts
heat from the flue gases reuse the that
heat to preheat the air which ultimate
improves the efficiency of turbine.
1. Primary air fan (A+B)
2. Secondary air fan (A+B)
3. Exhaust or flue gases
Air preheater

26. Coal feeding System
Coal bunker
Coal feeder
Chute
The coal from the conveyer belts, come across the coal plough
which directs the coal into the chute which leads to the coal
bunker, from the coal bunker the coal drops in the gravimetric
coal feeder, through which the required amount of coal is feed in
the furnace via different chutes and scrapper mechanism.
Coal Feeding Points For Furnace: 08 (Front Side)
Coal Feeding Points For Furnace: 04 (Rear Side)

29. Limestone feeding system
• Lime stone leading from lime
silos come across in limestone
feeders through compressed air,
which directs limestone in coal
chute
• The purpose of lime stone
feeding is to reduce sox

31. Sand feeding
• Silica sand feeding in furnace
bed for coal combustion
efficiency
• Original bed material and
sand can be used as startup
bed material. Sand used as
furnace bed material it absorb
heat and ignite coal.
Underground
Hopper
Bucket elevator
Capacity: 10t/h
Bed Material
Bin
Capacity:
10t/h
Pneumatic Conveying
2 sets
Boiler

33. Burner
• A furnace burner works by taking the air
ad fuel mixture and burning it to create
heat which is distributed inside furnace
• The oil gun of air duct burner is
activated firstly to heat bed temperature
to the ignition temperature of coal when
boiler is started. Air duct burner is
equipped with ignition device and flame
detector which are to ensure the safety
of ignition. And oil gun equipped on the
bed is used in the normal combustion or
under emergency condition.

34. Ash handling
• Initially ash collect at bottom
furnace through ash cooler to
reduce temperature and
come across bucket chain
conveyer, bucket elevator to
Ash bin tank.

36. AIR/FLUE GAS SYSTEM
CFB
Boiler
Cyclone
3 sets
Air
Preheater
Back
pass
Ash coolers
Coal
Bunker
Primary Air Suction
Secondary Air Suction
Fluidizing Air Suction
Primary Air
Secondary Air
Fluidizing
Air
Sand
Limestone