1. Drain rate, or the rate at which melt is removed from the furnace, should be higher than the production rate in order to prevent a build up of liquid levels in the hearth. 2. On cast time refers to the amount of time that tap holes remain open to drain liquid from the furnace. A longer on cast time supports achieving a higher drain rate than the production rate. 3. If drain rate is not higher than production rate, high liquid levels in the hearth can negatively impact burden descent and gas distribution patterns in the furnace.

1. Drain rate vs on cast time
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A K Mistry

2. Drain rate(melt out per unit time) vs cast on time(time for
which all available active tap hole remain open)
Production rate(process)αDrain rate(casting)
on cast time support to achieve higher drain rate than production rate
raceway
Hearth coke grid
tapping
Formation of melt of
right temperature and
fluidity.
Strong coke to retain
voids for rivulets.
Syphoning of melt need
strong and sufficient length
of tap hole
Evacuation of melt
should more than charging.
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A K Mistry

3. Charging rate = Production rate
Drain rate should more than production rate
• Charging Rate
depends on:
– Oxygen amount at
tuyeres
• Wind
• Oxygen
• Moisture
– Fuel Rate
• Decrease in fuel rate
leads to increase in
production
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A K Mistry

4. Liquid management-few facts to know
 Liquid Fe & Slag collect in the furnace hearth below the tuyeres.
 We have a finite storage capacity in hearth.(only 25 to 30% of hearth volume available to
hold metal and slag. Hearth is column of coke and metal slag trickles through void in form of
rivulets. Slag takes 75% space compare to metal(Tata less slag volume can take care of less
tapping time)
 Fe & Slag don’t mix (Slag has a specific weight of 2.4t/m3, Fe 7.2t/m3)
 Viscosity of slag is 10times more compare to metal.(Evacuation of slag is concern for the fce
running with high slag volume)
 Flooding and loading to consider with respect to evacuation of liquid which also effect tuyer
parameters.(burden optimisation, blowing parameters, change in gas utilisation,
productivity)
 The blast furnace is tapped 8-14 times per day.
 The average duration of a cast is 90-180 mins and in this time about 1/3 of the furnace
content is transformed to molten metal.
 Tapping from diametric tap hole give symmetric cohesive.
 The liquid levels in the hearth has two major effects on the process.
1. High liquid levels will result in poor burden decent
2. Disruption of the gas distribution pattern(more fuel leads more slag less metal and
hence drain rate to increase)
GAS BURDEN
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5. Tapping Strategies
• Alternate taphole practice
– Large furnaces
– Constant liquid level
– High productivity, consistent
quality
• Single taphole operation
– Smaller furnaces
– Varying liquid level (effect on
burden descent)
– Productivity limited
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6. illustration of a taphole thermal footprint- vital tool to achieve desirable
drainage rate and health of taphole area
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7. High Residual Liquid Levels and its effects
• Increase CO/CO2
• Higher wall temperature
• Lower centre temperature
• Higher top temperature
• Charging rate decreases
• Higher in wall temperatures
• Lower cohesive zone in centre
• Increased heat flux
• Root of cohesive zone elevated
• Raceway blocked with slag filled
coke column
• Signs of peeling furnace at tuyere
• Slag level at tuyeres = higher blast
pressure
• Iron level high
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8. Poor Drainage causes loss in production
Poor burden descent
• Too high blast pressure: decrease
blast
• Poor hearth drainage: cast, open
2nd tap hole, open with bigger
drill diameter
• Too hot furnace (means high
position of cohesive zone): cool
down with additional moisture
injection
• Too many fines in burden:
eliminate sources of fines e.g.
poor quality burden materials
Burden weight
Upward force by
blast
Upward force by
liquid
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9. Casting and Burden Descent
Charging speed
slows as furnace
hearth fills
Increased speed of
burden descent as
liquids are tapped
Descending so fast that the
charging system is unable to
keep up – stockline lost
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10. Effect of High Liquid Levels
Top temperature increasing as filling
slows down.
Burden descent slows down due to not casting
furnace, then speeds up and even loses
stockline when the furnace is cast.
Blast pressure increasing and then
decreasing due to holding liquids in
the hearth
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11. Calculation of the Filling Rate
• Furnace Produces 6600 t/day = 4.6 t/min
• Slag Rate = 250 kg/THM
• HM density = 7.2 t/m3
• Slag density = 2.4 t/m3
• Hearth voidage = 20%
• Hearth Diameter = 10.8 m
• Taphole to tuyere height = 3.9 m
• After taphole is closed, how long will it be until liquids have reached the tuyeres?
• Iron volume = (4.6/7.2) = 0.64 m3/min
• Slag volume = ((250/1000x4.6)/2.4) = 0.48 m3/min
• Total volume accumulated liquids = (0.64+0.48) = 1.12 m3/min
• Area of hearth = πr2 = (3.14 x (10.8/2)2) = 91.6m2
• Storage capacity of hearth = (20%x91.6x3.9) = 71.5 m3
• Time until liquid at tuyeres = (71.5/1.12) = 64 minutes
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12. Deadman Voidage & Production Rate
• Reduction of deadman voidage causes an
effect on hearth liquid levels, even when the
furnace is casting.
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13. Where we fit? We like to consider a maximum liquids
throughput rate (m3/m2 hearth/24 hours)
This depends on whether it is a single or multiple taphole operation.Multiple taphole operation
can handle upto 22 - 23 m3/m2/24h like at JSW3 and 4. Single taphole probably more like 18
m3/m2/24h If you work out the volume of liquids that your casting operations can handle, based
on previous higher productivity periods, then you can generate a graph like below for your
particular furnace.
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14. A K Mistry

15. Blast furnace slag control
• Blast furnace slag consists of approx. 96% by weight of 4 main oxides,
CaO, SiO2, MgO and Al2O3
• The balance comprises of FeO, S, Alkali oxides, MnO etc.
• The properties of blast furnace slag is of compromise depending on
the relative quantity of the 4 main oxides.
• In general terms, the operating requirements of BF slag can be
summarised as follows:-
– 1.Low melting point
– 2. High fluidity
– 3. High S capacity
– 4. High K20 capacity
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16. HM Si and Slag LiquidusTemperature-important factor for desired
casting rate
• B2 = CaO
SiO2
• B3 = CaO + MgO
SiO2
• B4 = CaO + MgO
SiO2 + Al2O3
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17. Slag Volume
• In the bosh, liquid iron and slag percolate down through the coke bed
counter current to the ascending gas stream
• The lower the slag volume i.e. the less space between the coke liquid
taken up by slags, then there is more available space for liquid iron.
• It can be calculated that a reduction in slag volume by 10kg/tonne hot
metal creates sufficient extra space for approx. 3% more liquid iron,
• i.e. potentially increases hot metal output by approx. 3%.
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18. Pressure Tap Analysis
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19. Fce Casting data
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20. Cast Data Recording for better casting management
• Cast number
• Time start drilling
• Number of drills and/or oxygen lances used
• Time liquid started flowing
• Drill diameter used to open hole
• Taphole length
• Time slag over
• Time end cast
• Amount of clay used to close taphole
• Clay type used
• Dry or no dry cast
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21. conclusion-casting duration (time) is not important.
Yet casting (tapping) rate is a key process control parameter
A good casting rate will give you a stable and cost effective operation.
The casting rate you chose would need to satisfy the four requirements.
(1) First of all, the casting rate must be higher than your smelting rate. For example, you are
producing around 6600 thm/day. Your smelting rate is around 4.6 thm/min. Your casting rate
must be 4.6 thm/min or higher.
(2) Your casting rate must be slow enough to allow a good liquid drainage,
(3) Your casting rate must be slow enough not to erode the trough lining severely.
(4) Your casting rate must be slow enough to allow a good iron/slag separation
Note-concern would be delays in getting slag when iron casting rate is the same as iron
making rate. Here you must open another tap hole.We have experienced this and often
results in slag only being cast through the second hole. This can create problems of a mess on
the casthouse and lead to asymmetrical gas flow in the furnace, causing problems.
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22. Thanks for your time
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