1. Fluidized Bed Combustion Systems M.RAJAVEL, SDGM / R&D/PCPS
Welcome
Fluidized Bed Combustion Systems By
M.RAJAVEL, SDGM / R&D/PCPS
BHEL, TRICHY -14

2. What is Fluidization ? Fluidized Bed When Buoyancy Force balances
FLUIDISED BED BOILER
When
Buoyancy Force
balances
Gravity Force
Buoyancy Force
Gravity Force
AIR
FUEL
ASH

3. Why call it Fluidized Bed ?
Light object Floats ; Heavier ones Sink
(Fixes Fuel Size)
AIR
AIR

4. Why call it Fluidized Bed ?
Horizontality Maintained
(Fixes Ash drain mechanism from Bed)
ASH
ASH
ASH
Fixed Bed
Fluidised Bed

5. Why call it Fluidized Bed ? Pressure drop is  Bed Height
(Fixes Fan Power)
Umf P B A B A
Flow / Velocity
AIR
AIR

6. What is Fluidization ? Fixed Bed When Gravitational Force
STOKER FIRED BOILER
Buoyancy Force
When
Gravitational Force
is predominant
ASH
FUEL
Upto 25mm
AIR

7. Why call it Fluidized Bed ?
FLUIDISED BED BOILER
A Bed of Solid Particles exhibit the
properties of a FLUID namely:
Lighter objects float heavier ones sink
Pressure drop is  Bed Height
Horizontality maintained
hence termed as Fluidized Bed
AIR
FUEL
ASH

8. How does a Fluidized Bed work ?
The Bed of solid particles have to be retained at that size:
Combustion Temperature has to be well below ash fusion temperature
Heat transfer walls are enclosed
Ash does not fuse - no slagging
Heat transfer by Gas / Particles Convection & Radiation
Fuel size upto 10mm - No PULVERISING
Ash soft amorphous state - less erosion
FLUIDISED BED BOILER
FUEL
AIR
ASH

9. How does a Fluidized Bed work ?
When Fuel is injected into a Fluidized Bed of solid particles which is heated to Ignition Temperature of Fuel, it burns imparting heat to the entire bed
Fuel Combustion takes place due to the heat available in the Bed Ash - millions of
IGNITORS
Fuel of any Quality can be fired
FLUIDISED BED BOILER
FUEL
AIR
ASH

10. How does a Fluidized Bed work?
Combustion of Solid Fuel leaves behind Ash. Finer fraction carried by flue gas, coarser fraction replenishes the bed solid inventory and excess is drained out by drain pipes
Ash is dry and granular and is easily handled.
FLUIDISED BED BOILER
FUEL
AIR
ASH

11. Summary of Combustion Technologies
PNEUMATIC
TRANSPORT
FIXED
BED
FLUIDIZED
BED
PRESSURE DROP
GAS FLOW/VELOCITY

12. Technology Comparison
STOKER
(FIXED BED)
FLUIDISED – BED FIRING
PULVERISED FIRING
(ENTRAINED BED)
FBC
GAS
GAS
GAS
FUEL
FUEL
AIR
AIR
FUEL
FUEL
AIR
ASH
ASH
AIR
ASH
Vel
m/s
m/s
m/s
6000 m m
50 m
Par 
1600  C
1600  C
Temp
850 C

13. Advantages of Fluidized Bed Combustion Boilers
Low combustion temperature- <900 DegC lead to less Nox emission.
Sulphur present in coal can be recovered in-situ by adding limestone. SOx emission can be reduced >90%
S + O2  SO2
CaO + SO2 +1/2 (O2) --> CaSO4
Poor quality coal/lignite, coal washery rejects, containing ash >70%, can be used.
Biomass fuel can be fired either independently or in combination with fossil fuels.

14. Advantages of Fluidized Bed Combustion Boilers
FBC Boilers can be operated in all loads without sacrificing combustion efficiency.
Fuel of size less than 6 m.m. is used in FBC boilers and hence need not be pulverised as does in P.F. Boilers.
No moving grate or burners in FBC boilers.
Ash does not fuse at 900 DegC and hence soot blowers are not required.
High combustion efficiency of fuel due to higher residence time and entire surface area of fuel in contact with air.

15. Stoker fired boiler

16. Stoker Fired Boilers
Moving Component (Travelling Grate) in the high temperature Furnace zone
Combustion temperature °C; heat transfer in furnace by Flame Radiation
Fuel Ignited by the already burning Fixed Bed
Fuel Combustion time limited to grate travel length - hence fuels of poorer quality than design do not burn fully
Due to grate cooling requirements a minimum air quantity is required - hence excess air is high at part loads
Very low relative movement between Fuel and Air

17. Fluidised Bed Combustion Boilers
Atmospheric pressure Fluidised Bed Combustion Boilers (AFBC)
Pressurised Fluidised Bed Combustion Boilers (PFBC) I

18. Atmospheric Fluidised Bed Combustion Boilers
Bubbling Fluidised Bed Combustion Boilers (BFBC)
Circulating Fluidised Bed Combustion Boilers (CFBC) I

19. 10 t/hr BFBC Prototype Boiler - 1977
FBC Test Facilities
10 t/hr BFBC Prototype Boiler
BFBC Test Facility-1986
Combustion Test Rig-1979
(90 t/hr Hot water)

20. AFBC Technology Development
1981 : First 12 t/h Commercial Boiler commissioned
1984 : First 10 MW power plant for Washery Rejects
1987 : First 10 MW power plant for Straw
1992 : First 20 MW (100 t/h) power plant for Rejects and Char
2000 : Largest boiler in operation of 180 t/h (45 MW)
2002 : Export of 17 MW Boilers to PT IBR Indonesia
2003 : Largest Boiler (300 t/hr) offered
2006 : Design of 120 MW Boiler ready
2008 : 3x18 MW Order from PT KPP, Indonesia
2009 : 2 X 180 t/hr BFBC Boiler order from JSPL, Angul
66 Boilers Contracted Over 2.5 million operating hours

21. Schematic of AFBC Boiler
Drum
S H I
Eco
Coal
Bunker
DESH
Air Heater
EVA
S H II
E S P
Main
Steam
Ash
Feeder
Air
Distributor
I D Fan
P A Fan
F D Fan
Schematic of AFBC Boiler

22. Presentaion on FBC boilers
AFBC Components 1 2 3 4 5 6 7 8 9 10
1 Steam Drum
2 Bed Superheater
3 Bed Evaporator
4 Convection Superheater
5 Economiser
6 Windbox
7 Air Distributor Plate
8 Hot Air Duct
9 Cold Air Duct
10 Air Preheater
8th June

23. Compartment – Unique Operational feature

25. Presentaion on FBC boilers
Flow Diagram of CFBC Boiler - Separate FBHE
DRUM
Spiess
Valve
SECONDARY AIR
ID Fan

26. CFB Process Advantages

28. Major Milestone -CFBC Technology Development
1995 : First CFBC boiler of capacity 175 TPH contracted
1995 : Utility size 2x125 Mwe capacity plant order received from
Surat Lignite plant (SLPP)
2003 : RVUNL, Rajasthan -2x125 Mwe plant using high sulphur content
lignite (6%)
2005 : First 2x250 MW CFBC power plant order received from
NLC,Neyveli.
2008 : Export order received from New Calidonia to supply TPH steam generator
28 CFBC Boilers Contracted .

29. Typical Fuel analysis ( Assam Coal)
Proximate
Moisture %
4.50
Volatile Matter
39.58
Ash
3.77
Fixed Carbon
52.15
HHV
kcal/kg
7792
Ultimate
Carbon
78.36
Hydrogen
5.04
Sulphur
2.57
Nitrogen
0.98
Oxygen
4.78

30. Chemical composition of fuel ash (Assam Coal) and limestone:
Silica (SiO2) %
56.70
4.90
Aluminium Oxide(Al2O3)
15.0
1.20
Iron Oxide (Fe2O3)
17.90
1.00
Titanium Oxide (TiO2)
0.80
Calcium Oxide (CaO)
1.70
53.70
Magnesium Oxide (MgO)
1.60
0.50
Sodium Oxide (Na2O)
3.50
Potassium Oxide (K2O)
2.60
0.10
Carbon di Oxide (CO2) -
37.00

31. C.
ASH ANALYSIS 1.
Silica (SiO2) (%)
51.08
48.42
52.38
48.15
52.56 2.
Alumina (Al2O3) (%)
14.83
13.84
15.73
13.66
15.97 3.
Iron Oxide (Fe2O3) (%)
18.60
25.16
15.31
26.14
14.36 4.
Titania (TiO2) (%)
1.30
1.04
1.42
0.96
1.49 5.
Phosphoric Anhydride(P2O5) (%)
0.26
0.19
0.32
0.16
0.37 6.
Lime (CaO) (%)
2.04
1.73
2.18
1.68
2.25 7.
Magnesia (MgO) (%)
0.51
0.41
0.65
0.73 8.
Sulphuric Anhydride(SO3) (%)
8.82
7.08
9.09
6.81
9.91 9.
Sodium Oxide (Na2O) max (%)
0.10
0.31
10.
Potassium Oxide (%)
2.41
2.03
2.66
1.97
2.76 D.
ASH FUSION RANGE (under reducing atmosphere)
Initial Deformation Temp.(IDT) oC
1075
1050
1100
Hemispherical Temp oC
1125
1150
FusionTemp oC
1175
1200

34. Supercritical 600 MWe CFBC Boiler- Baima, China
Research on supercritical CFB was started in A demonstration of 600MWe supercritical CFB was initiating in 2006 supported by government.
The first demonstration in Baima was approved in 2008, that shall be commissioned in 2011
Steam T : 571℃/569℃
Steam P : 25.4MPa
Steam Flow: 1900t/h，
Boiler efficiency: 92%
SO2 : <300mg/Nm3，
Nox : <200mg/Nm3，
Generation efficiency:42%

35. Design of 600MWe Supercritical CFB Boiler ,
Design features:
Vertical tube design with partial rifle tube ;
Mass flow rate is 1400kg/m2s
6 cyclones with 6 external heat exchangers (EHEs);
Bottom ash drained from both two side walls through roller type ash cooler;

36. Design Feature:
Benson vertical tube water membrane, mass flow 800kg/M2S.
Twin furnace (with total cross section 15x28m2 and 55 m height) divided by a partition water wall.
Six cyclones with inner diameter 9m.
six external heat exchanger (EHE).
In furnace superheater panels.
The LT SH and LT RH in second pass.
The HT RH , the MT SH located in EHEs.
There are two options for the cyclone selection –steam cooled and insulated.
Water jacketed rotary ash cooler is used bed ash 2011.

37. Arrangement of 600MWe supercritical CFB Boiler of Tsinghua’s Design

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