BASIC OXYGEN FURNACE
INTRODUCTION:-
BOF is the core of a steel plant and the tonnage
capacity of any steel plant is normally designated by the tonnage capacity of
its BOF or SMS. Basic Oxygen Furnace was added under modernization scheme of
DSP. It has a production capacity of 1.86 MT of stell per year. The BOF shop in
DSP consists of a newer mixer bay, one VAD unit, 3 converters, a lade treatment
section, which is intermediate between BOF and the CCP.
Hot
metal comes from the Blast Furnace to Furnace to the mixer bay of the BOF shop.
These mixers (2 in nos.) are of capacity 1300T. In the mixers a temperature of
about 1300-1400 degree Celsius is maintained. Mixers mixes the liquid metals of
two or more ladles comong from blast furnace and homogenizes the composition of
liquid iron to be charged in the BOF converters. Fuel for the mixers is a mixer
of coke oven gas and air in the ratio of 1:5. To measure the ladle temperature
of hot metal, the slag layer above is broken by anchor punch or by oxygen
lancing.
Each
converter has a capacity of 110-130T per heat
and due to nitrogen splashing, the average life of each of the converter
has increased from 500 heats to 1000 heats. The converter has tap hole for
tapping slag & steel. Each converter has its own lance system. Lance is
used in the converter for blowing the oxygen at a high pressure (42 kgf/cm2)
so as to form an emulsion on the surface of the metal which increases the
surface area to an extent; the separation of impurities takes place very fast,
thus giving the process unique distinction i.e. a very fast process for the
steel making. There are two lances for each converter operated by separate
lance carriages. The oxygen blowing rate is 450Nm3/min and the
blowing pressure is 16 bar from the top and 12 bar from the bottom.
Oxygen
is passed through the molten pig iron and thus steel is produced, as there is
reduction in carbon percentage. The charge consists of molten metal, cold pig
iron, steel scrap, lime, dolomite, bauxite, iron ore, mill scale etc. They have
got the facility to stir the mass by non reactive gas like argon or nitrogen
from bottom.
The quantity of
material required for the production of
one ton of steel:-
|
Hot metal
|
962 kg
|
|
Scrap
|
142 kg
|
|
Iron ore
|
29 kg
|
|
Dolomite
|
40 kg
|
|
Lime
|
120 kg
|
|
Limestone
|
15 kg
|
Tap to tap time in BOF:
|
Scrap charging
|
3 min
|
|
Hot metal charging
|
4 min
|
|
Oxygen blowing
|
18 min
|
|
Initial slag off
|
5 min
|
|
Sampling temp. measure
|
6 min
|
|
Final slag off
|
3 min
|
|
Tapping of steel
|
6 min
|
|
Reserve delays
|
57min
|
|
Total time
|
57 min
|
Tapping temperature at converter=17000C
Tap-pouring temperature =1640-16500C.
Total blowing time is 18 min
BOF gas rate=75Nm3/ton with Cv=2100kcal/m3
Slag obtained =250 kg/TMH
The composition of the molten metal of the BOF is as
follows:
·
Carbon:
4.1-4.3%
·
Phosphorous:
0.1-0.25%
·
Silicon:
0.65-0.85%
·
Manganese:
0.7-0.8%
·
Sulphur:
0.03-0.04%
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