Its note on basic oxygen furnace which help in production of steel

1. ABHINAV QC SMS-II, BSP
B.S.P
Converter Steel Making
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2. The raw materials charged into the converter
• Liquid 'hot metal' from the blast furnace after specific pre-
treatments, i.e. desulfurization or dephosphorization
• Other iron-containing additions, essentially scrap and ore,
calculated so as to adjust the thermal balance and obtain the
required steel temperature
• The additions necessary to form a slag of appropriate
composition, involving mainly lime (CaO) and dolomitic lime (CaO-
MgO), usually in the form of 20 to 40 mm lumps
• Pure oxygen injected either through a multi-hole lance or through
bottom tuyeres
Inputs, Additions and Outputs
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3. • Liquid steel
• Exhaust gas rich in CO (about 80-90%), recovered through the
closed or suppressed combustion hood, and is often used in the
burners of the reheating furnaces
• Slag, poured out of the vessel after the steel
• Both gas and slag are valuable by-products, provided they are
properly recovered and stored
Output after completion of blowing
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4. SPECIFICATION
RAW MATERIAL SPECIFICATION DETAILS
Ferro manganese(high C) Mn- 70 % min, C 7.5 % max, SIZE : 25-50mm
Ferro –Silicon Si 70% min, SIZE : 25 -50mm
Ferro niobium Nb 63%min
Ferro-Vanadium V – 50 %min,SIZE : 25 -70mm
Ferro Chrome[ high carbon] Cr - 60 %min.,C- 8%max
Ferro Chrome [low C ] Cr – 60 %min,C - 0.2% max
Alluminum Cubes- 97%,Wire Al – 97%,Shots - 93 %min
Petro coke Fixed Carbon -99.0%min,Moisture 0.1%max,Ash –
0.5 % max Size : 2 -10mm
Silico-Manganese Mn 60%min,Si - 15%min,Size : 25 –50mm
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5. OXYGEN
OXYGEN IS SUPPLIED AT 16 Kg / cm2 PRESSURE & HAS A
PURITY OF 99.9 %.
TOTAL OXYGEN REQUIRED FOR HEAT IS AROUND 7000 M3/100t
ADDITION THROUGH WATER COOLED LANCE @ 400 – 450
M3/min.
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6.  HOT METAL
 TOTAL SCRAP
 TOTAL
 TOTAL LIME
 SILICO MANGANESE
 FERO SILICON
 FERO MANGANESE
 RAW DOLOMITE
 ALUMUNIUM
 NICKEL
 PETRO COKE
 COPPER
 OTHER FERRO ALLOYS
 SYNTHETIC SLAG
 IRON ORE
 CALCINED DOLO
 OXYGEN
 1038.5
 96.6
 1135.1
 44.7
 18.5
 0.7
 0.1
 0.6
 0.7
 0.04
 3.7
 0.04
 0.3
 1.1
 0.5
 27.7
 59.7CU METRE/TON
SPECIFIC CONSUMPTION[KG/TON STEEL]
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7. Scrap charging
Hot metal charging
Blowing
Deslagging and Sampling
Additional / Re-blow
Steel tapping
Additions during tapping.
Slag coating and final De-slagging.
Sequence of Operations
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8.  Scrap generated internally is used.
 Steel scrap is preferred over iron scrap.
Scrap Charging
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9. Hot metal charging
I. Hot metal is charged in the convertor
either directly or after processing at De-
Sulphurisation Unit.
II. In case of direct charging, raking is
done if excess mixer slag is present.
III. Hot metal to Scrap ratio is 85-88% to
12-15%.
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10. Hot metal charging
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11.  Before blowing is started Hot metal analysis,
temp. and weight along with scrap weight are
fed in the computer system.
 Computer predicts the total Oxygen and fluxes
required for the blow.
 Blowing is started by bringing the lance down
to a height of 2.5m above the bath level.
 Further the lance is slowly brought to working
height i.e. 1.6m.
Oxygen Blowing
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12.  Fluxes are added in required doses so that
slag formation takes place in the first 4-6 min.
of the blow.
 The flow rate of Oxygen is kept at 400-
450nm³/min during the blow.
 If the blow is going dry even after 4000nm³
Oxygen then the lance is lifted to assist slag
formation.
Oxygen Blowing
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13. Phases in
Jet Impingement Area
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14. A water-cooled lance is used to inject a high velocity
stream of oxygen onto the molten bath. Supersonic jets
are produced with convergent / divergent nozzles and
provide well defined and controlled penetration
characteristics in order to efficiently produce the desired
steelmaking reactions and to maximize lance life
(typically 200 to 400 heats). Lance tips have typically
from 3 to 5 holes.
Nozzles for Top-Blown Converters
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16. The hot metal charge is refined by rapid oxidation
reactions on contact with the injected oxygen with the
other elements present under conditions far removed
from thermodynamic equilibrium. The three most
important reactions are:
Post-combustion of CO into CO2 is only partial, i.e. only a
part of the present CO will oxidize into CO2. These
gaseous reaction products (CO and CO2) are evacuated
through the exhaust hood. The ratio CO2/(CO+CO2) is
called Post-Combustion Ratio (PCR).
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Important Reactions

17. These oxides combine
with previously charged
fluxes, e.g. lime and
dolomite, to form a liquid
slag which floats on the
surface of the metal bath.
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2
5

18. De-Siliconisation
[Si] + 2(FeO) + 2(CaO) = (2CaO.SiO2) + 2[Fe]
SiO2(Silica) is a very stable oxide and hence
its reversal does not take place.
Hot metal with low Si content is preferred to
decrease lime consumption and minimize
slag volume. High Si in hot metal has an
adverse impact on converter lining.
Reactions during Blowing
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19. De-Phosphorisation
2[P]+5(FeO)+3(CaO) = (3CaO.P2O5) + 5[Fe]
For effective removal of Phosphorous
slag of high basicity and low
temperature are favourable.
De-Phosphorisation increases with
increasing FeO % in slag.
Reactions during Blowing
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20. Manganese Removal
[Mn] + (FeO) = (MnO) + [Fe]
De-Carburization
[C] + [O]  CO gas
[ ].. Dissolved in steel
( ).. Dissolved in slag
Reactions during Blowing
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21. De-Sulphurisation
[S] + (CaO) = (CaS) + [O]
For removal of Sulphur, slag of high basicity,
high bath temp. and reducing condition are
favourable. Since BOF steel making is not a
reducing process Sulphur removal is only to
the extent of 30 – 40 %. Higher Slag volume
has a positive effect on Sulphur reduction,
but this in turn adversely effects the
converter life. Hence hot metal having high
S% is not desirable in BOF process.
Reactions during Blowing
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22. 2/28/2023 22
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Changes in
Metal
Composition
during Blowing

23. Changes in the slag composition during the blow
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24. Metal Sample is taken and analyzed at
shop floor lab.
Aim bath analysis is as follows:
 C% 0.10 – 0.15
 P% 0.025 max.
Aim bath temperature is 1660-1680ºC
Slag sample is also taken and
analyzed in XRF.
Deslagging and Sampling
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25. %CaO = 43.0 – 47.0
%SiO₂ = 12.0 – 15.0
%MgO = 10.0 – 14.0
%Al₂Oɜ = 0.7 – 1.1
%MnO = 1.0 – 2.5
%P₂O5 = 1.0 – 2.0
%S = 0.05 – 0.15
%T.Fe = 12.0 – 18.0
Basicity = 3.0 – 3.8
Typical Slag analysis
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26.  2nd blow/Re-blow is given after checking
bath analysis & temperature.
 Factors affecting 2nd blow/re-blow are:
 Bath temperature
 Bath Carbon and Phosphorous
 Steel grade being tapped
 Routing of steel before casting
Additional blow / Re-blow
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27. Ladle is examined for any metallic jam.
Ladle temperature is taken before
placement for tapping.
Once tapping is started the ladle is
kept in such a position that the metal
stream does not hit the side walls of
the ladle.
Steel tapping
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28. Ferro-alloy additions are started
after 1/3rd of the ladle is filled.
Final slag is arrested using conical
refractory ball (DART) which is
inserted into the tap-hole from the
mouth of the converter.
Steel tapping
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29. At the end of tapping the converter is
coated with the slag remaining inside the
vessel.
0.5 T Calcined Dolo is added prior to Slag
coating.
For this Nitrogen is used at a pressure of
8-10Kg.
This coating is done for 3-5min.
After coating remaining slag is taken out
and the converter is ready for next
charging.
Slag Coating and final De-slagging.
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30. Stages of the Oxygen Top Blowing Process
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