Combustion of Dola Char In

AFBC & CFBC Systems

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Dola Char AnalysisComposition Weight Char - I Char -II

Carbon % 47.19 25.8

Hydrogen % 1.27 0.4

Moisture % 5.87 0.6

Oxygen % 0.02 N.D

Sulphur % 0.0 0.2

Nitrogen % 0.26 0.2

Ash % 45.39 72.8

GCV Kcal/kg 4302 1900

OEG INDIA

Char -I -Imported coal used in Sponge Iron-25% Iron in Dola CharChar – II-Indian coal used in Sponge Iron-45% Iron in Dola Char

Size of Fuel

Recommended Coal-100% Less than 10mm-Fines (<1mm) limited to maximum of 30%

Dola Char-100% Less than 8mm-Iron content in char limited to maximum of 0.5% on weight basis

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Coal used for AFBC & CFBC

Composition Indonesian Indian Coal Coal Fines

% weight %weight % weight

Carbon 46.13 35 44.85

Hydrogen 3.02 2.1 1.79

Oxygen 16.1 9.82 2.65

Moisture 28.0 4.7 11.13

Sulphur 0.2 0.7 1.15

Nitrogen 1.35 0.58 1.88

Ash 5.2 47.1 36.55

GCV ( ADB ) 5600 3200 4200

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Multi Fuel FiringAFBC

-50% Coal + 50% Dola Char-10% Coal + 90% Dola Char-20% Coal + 20% Coal Fines + 60% Dola Char

CFBC

-50% Coal + 25% Dola Char + 25% Washer Rejects-30% Coal + 50% Dola Char + 20% Coal Fines

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Dola Char

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Dola Char & Slag

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Pretreatment of Dola Char

The impurities in Dola Char are separated by

-Magnetic Pulley installed as Head Pulley of a Conveyor System

-Over Band Magnetic Separator

-Gravity Separator for removal of stone and slag

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Magnetic Pulley

The material is discharge on the belt by the feeder. The magnetic roll is enveloped by the conveyor. The para and magnetic ingredients remains stuck to the belt whereas non magnetic ingredients passes freely at the end of the conveyor

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Over Band Magnetic Separator

This is a self cleaning magnetic separator installed in cross section to initial conveyor for removing iron from a combination of dola char and coal

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Gravity Separator

Gravity Separator is used to remove the stones or heavier particles present in Dola char. This is installed in circuit after removing iron

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Mode of Feeding Char to BunkerCASE I : Unit having single or two Bunker

-Dola char alone or a combination of coal & char is fed onto initial conveyor for iron separation and after screening and crushing, it is transferred to one of the bunker-The second bunker is filled with recommended coal

CASE II : Unit having three Bunker

-Dola char alone is fed directly onto initial conveyor for iron separation and then to one bunker-A combination of Dola Char and Coal to second bunker-Only recommended coal to third bunker

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Recommendations for DolaChar firingAdditional Drain Points-Bed ash generation is vey high due to high unburnable content in dolachar. The bed ash has to drained almost continuously. More number of drains are required if more percentage of dolachar used

Control of Iron in Bed-Irrespective of bed height increase, certain amount of bed ash must be removed continuously for control of Iron in bed ash. The bulk density of bed ash to be restricted to 1.0gm/cc

Control of Iron in bed by adding fresh bed material -The iron containing bed ash must be restricted to less than 5% for better combustion and to avoid slagging of bed ash above fuel feed points. To avoid clinker formation, addition of iron free sieved bed ash can be used or use of high ash content coal is a solution for controlling bed ash chemistry

Bed Ash Recycling-The drained bed ash must be sieved for removal of larger size particles and also for the iron containing bed. After the screen, a mechanised iron removal arrangement is required

OEG INDIA

OEG INDIA