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

Bharat Heavy Electricals Limited TIRUCHIRAPALLI

Presentation on FBC Boilers

28th August 2012

Fluidized Bed Combustion SystemsBy

M.RAJAVEL, SDGM / R&D/PCPSBHEL, TRICHY -14

Welcome



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What is Fluidization ?

When

Buoyancy Force

balances

Gravity Force

Buoyancy Force

FLUIDISED BED BOILER

Fluidized Bed

FUEL AIR

ASH

Gravity Force



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Light object Floats ; Heavier ones Sink (Fixes Fuel Size)

AIR AIR

Why call it Fluidized Bed ?



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Horizontality Maintained(Fixes Ash drain mechanism from Bed)


ASH

ASHASH

Fixed Bed Fluidised Bed



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AIRAIR

Flow / Velocity

P

A

B A B

Pressure drop is Bed Height(Fixes Fan Power)

Umf




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What is Fluidization ?

When

Gravitational Force

is predominant

Buoyancy Force

STOKER FIRED BOILER

Fixed Bed

FUEL

AIR

ASH

Upto 25mm



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FUEL AIR

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

ASH



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How does a Fluidized Bed work ?


FUEL AIR

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

ASH



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How does a Fluidized Bed work ?


FUEL AIR

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 bedFuel Combustion takes place due to the heat available in the Bed Ash - millions of

IGNITORS

Fuel of any Quality can be fired

ASH



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FUEL AIR

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.

How does a Fluidized Bed work?

ASH



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Summary of Combustion Technologies

GAS FLOW/VELOCITY

PR

ES

SU

RE

D

RO

P

FIXED BED

FLUIDIZED BED

PNEUMATIC TRANSPORT



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Technology Comparison

2.3 - 3 m/s 1.2 - 6 m/s 4.6 - 6.1 m/sVel

6000 m 300 - 1000 m 50 mPar

FUEL FUEL

STOKER

(FIXED BED)

FLUIDISED – BED FIRING FBC

PULVERISED FIRING

(ENTRAINED BED)

AIR ASHASH ASH

FUELFUEL

AIRAIR

AIR

GAS GAS

GAS

Temp 1600 C 850 C 1600 C



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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.



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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.

•



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Stoker fired boiler



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Stoker Fired Boilers

Moving Component (Travelling Grate) in the high temperature Furnace zoneCombustion temperature 1400 - 1600°C; heat transfer in furnace by Flame RadiationFuel Ignited by the already burning Fixed BedFuel Combustion time limited to grate travel length - hence fuels of poorer quality than design do not burn fullyDue to grate cooling requirements a minimum air quantity is required - hence excess air is high at part loadsVery low relative movement between Fuel and Air



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Fluidised Bed Combustion Boilers

Atmospheric pressure Fluidised Bed Combustion Boilers (AFBC)

Pressurised Fluidised Bed Combustion Boilers (PFBC)

I



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Atmospheric Fluidised Bed Combustion Boilers

Bubbling Fluidised Bed Combustion Boilers (BFBC)

Circulating Fluidised Bed Combustion Boilers (CFBC)

I



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10 t/hr BFBC Prototype Boiler - 1977

FBC Test FacilitiesFBC Test Facilities

Combustion Test Rig-1979

BFBC Test Facility-1986

(90 t/hr Hot water)



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AFBC Technology DevelopmentAFBC 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



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CoalBunker

Feeder

P A Fan

E S P

Air Heater

EcoS H I

S H II EVA

Drum

Schematic of AFBC Boiler

I D Fan

AirDistributor

F D Fan

MainSteam Ash

DESH



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AFBC ComponentsAFBC Components

1 Steam Drum2 Bed Superheater3 Bed Evaporator4 Convection Superheater5 Economiser6 Windbox7 Air Distributor Plate8 Hot Air Duct9 Cold Air Duct10 Air Preheater

1

23

4

5

6

78

9

10



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Compartment – Unique Operational feature Compartment – Unique Operational feature



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Flow Diagram of CFBC Boiler - Separate FBHE

ID Fan

SpiessValve

DRUM

SECONDARY AIR



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CFB Process Advantages



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Major Milestone -CFBC Technology DevelopmentMajor 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 405 TPH steam generator

28 CFBC Boilers Contracted .



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Proximate

Moisture % 4.50Volatile Matter % 39.58Ash % 3.77Fixed Carbon % 52.15HHV kcal/kg 7792

Ultimate

Carbon % 78.36Hydrogen % 5.04Sulphur % 2.57Nitrogen % 0.98Moisture % 4.50Ash % 3.77Oxygen % 4.78

Typical Fuel analysis ( Assam Coal)



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Assam Coal Lime StoneSilica (SiO2) % 56.70 4.90

Aluminium Oxide(Al2O3) % 15.0 1.20

Iron Oxide (Fe2O3) % 17.90 1.00

Titanium Oxide (TiO2) % 0.80 1.00

Calcium Oxide (CaO) % 1.70 53.70Magnesium Oxide (MgO) % 1.60 0.50Sodium Oxide (Na2O) % 3.50 1.00

Potassium Oxide (K2O) % 2.60 0.10

Carbon di Oxide (CO2) % - 37.00

Chemical composition of fuel ash (Assam Coal) and limestone:



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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 0.37 0.73

8. Sulphuric Anhydride(SO3) (%) 8.82 7.08 9.09 6.81 9.91

9. Sodium Oxide (Na2O) max (%) 0.16 0.10 0.26 0.10 0.31

10. Potassium Oxide (%) 2.41 2.03 2.66 1.97 2.76

D. ASH FUSION RANGE (under reducing atmosphere)

1. Initial Deformation Temp.(IDT) oC 1075 1050 1100 1050 1100

2. Hemispherical Temp. oC 1125 1100 1150 1100 1150

3. FusionTemp. oC 1175 1150 1200 1150 1200



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Supercritical 600 MWe CFBC Boiler- Baima, China Research on supercritical CFB

was started in 2003. 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 : 25.4MPaSteam Flow: 1900t/h，Boiler efficiency: 92%SO2 : <300mg/Nm3，Nox : <200mg/Nm3，Generation efficiency:42%



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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;

Design of 600MWe Supercritical CFB Boiler ,



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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.



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



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Take Care of Our Environment

Thanks for Your Patient Listening

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

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