FLUIDISATION BED
COMBUSTION (FBC) BOILERS
GUIDE
PROF : XYZ
BY
ISAAC JOHN
INTRODUCTION
 Viable alternative
 Multiple benefits
 compact boiler design, fuel flexibility,
 higher combustion efficiency and reduced emission
of pollutants SOx and NOx.
 Fuels
 coal, washery rejects, rice husk, bagasse & other
agricultural wastes.
 Capacity range- 0.5 T/hr to over 100 T/hr.
HISTORY: A NEW WAY TO BURN
0ne afternoon more than a decade ago, a British engineer named Douglas
Elliott tapped a bit of coal, ground to crumbs in a kitchen blender, into a tin
can mounted on the wall. Below the can was an ordinary small open
fireplace – ordinary, that is, at a casual glance.
For instead of burning coals, a red- hot bed of sand gently undulated like
simmering lava. As the coal trickled out of the can onto the glowing bed
below, each crumb exploded into flame with a pop and a blue-white flare. It
burned only about two pounds of coal an hour, but the little fireplace glowed
fiercely, delivering much more warmth than its size suggested.
FLUIDISATION
 The operation through which fine solids are transformed into a fluid
like state through contact with either a gas or a liquid.
 A process similar to liquefaction whereby a granular material is
converted from a static solid-like state to a dynamic fluid-like state.
This process occurs when a fluid (liquid or gas) is passed up through
the granular material.
MECHANISM OF FLUIDISED BED
COMBUSTION
TYPES OF FLUIDISED BED
COMBUSTION BOILERS
There are three basic types of fluidized bed combustion
boilers:
1.Atmospheric classic Fluidized Bed Combustion System
(AFBC)
2.Atmospheric circulating (fast) Fluidized Bed Combustion
system (CFBC)
3.Pressurized Fluidized Bed Combustion System (PFBC)
ATMOSPHERIC FLUIDISED BED
COMBUSTION SYSTEM (AFBC)
 Crushed coal size 1 – 10 mm
 Velocity of fluidising air –
1.2 to 3.7 m /sec.
 Narrow temperature range 800oC to 850oC.
 Unit Size-25MWe
 Thermal Efficiency-30%
GENERAL ARRANGEMENTS OF
AFBC BOILERS
AFBC boilers comprise of following systems:
i)
Fuel feeding system

Under bed pneumatic feeding

Over bed feeding
ii) Air Distributor
iii) Bed & In-bed heat transfer surface
iv) Ash handling system

Bottom ash removal

Fly ash removal
Many of these are common to all types of FBC boilers
CIRCULATING FLUIDISED BED
COMBUSTION SYSTEM (CFBC)
 Crushed coal size 6 – 12 mm
 Velocity of fluidising air –
3.7 to 9 m/sec
 Solid recycle – 50 to 100 kg
per kg of fuel burnt
 Unit Size - 250-300MWe
 Thermal Efficiency-40%
PRESSURISED FLUIDISED BED
COMBUSTION SYSTEM (PFBC)
 Temperature – 860 C
 Pressure- 16-18bars
 Flue gases expanded in
gas turbine
 Used for cogeneration
 Unit Size-80MWe
 Thermal Efficiency-40%
RETROFITTING OF FBC SYSTEMS
TO CONVENTIONAL BOILERS
 Retrofitting fluidized bed coal fired combustion
systems to conventional boilers has been
 Carried out successfully both in India and abroad.
 The important aspects to be considered in retrofit
projects are:
a) Water/steam circulation design
b) Furnace bottom-grate clearance
c) Type of particulate control device
d) Fan capacity
e) Availability of space.
COMPARISON BETWEEN STOKER
AND FLUIDISED BED COMBUSTION
S.No
STROKER
FBC
1
TRAVELLING/FIXED
GRATE
FLUIDISED BED WITH AIR BOX
SYSTEM
2
BED EVAPORATER IS
NOT APPLICABLE
BED EVAPORATER WILL BE
INTRODUCED
3
BED SUPER HEATER
IS NOT APPLICABLE
BED SUPER HEATER SHALL
BE INTRODUCED
4
ONLY OVER BED
FEEDING SYSTEM
UNDER/OVER BED FEEDING
SYSTEM IS POSSIBLE
5
BED ASH HOPPER
WITH SUBMERGE
BELT CONVEYOR
6
PRIMARY AIR SYSTEM
NOT APPLICABLE
BED ASH DRAIN WITH
COOLER AND PNEUMATIC /
MECHANICAL CONVEYING
SYSTEM
PRIMARY AIR SYSTEM IS
REQUIRED FOR FUEL
TRANSPORTION IN TO BED
ADVANTAGES OF FBC BOILERS
1. High Efficiency
2. Reduction in Boiler Size
3. Fuel Flexibility
4. Ability to Burn Low Grade Fuel
5. Ability to Burn Fines
6. Pollution Control
7. Easier Ash Removal – No Clinker Formation
8. No Slagging in the Furnace-No Soot Blowing
9. Provisions of Automatic Coal and Ash
Handling System
10.High Efficiency of Power Generation
CONCLUSIONS





Decreasing electricity prices and improving
environmental protection
Clean energy
More flexible than conventional plants
Reduced emissions and Improved combustion
Research and development is required in order to
improve the FBC technology.
THANK YOU