1300 Tonne Mixer Section
(Steel Making Department Pakistan Steel).
(Steel Making Department Pakistan Steel).
The Hot metal (molten pig iron) is supplied to steel making department from different tappings of Blast Furnaces, stored in 1300 Tonne Mixer.
1300
Tonne Mixer section is located in the charging aisle of LD-Converters of steel
making department.
As the tapping schedule of
Blast furnace does not match with the charging of steel making converters, Mixer
acts as a reserve stock of molten pig iron at steel making department. Besides it
equalizes the varying temperature and chemical composition of different tappings
of Blast furnaces and helps the LD-Converter operators to set the operating parameters
for steady pace of production cycle.
There
are two railway tracks for transportation and receiving the hot metal from
Blast Furnaces of Iron Making Department to Steel Making Department.
Mixer is made in cylindrical shape with the
length to diameter ratio of around 1:3.
Mixer
rests on special pads fastened on a strong reinforced-concrete foundation and
when being tilted, it turns on its horizontal axes with the aid of rollers. The
rollers are mounted in cast steel frames attached to the shell of the Mixer. A
huge rocker arm and pinion system allows mixer tilt for pouring out hot metal.
As
per project the safety lining of 1300 tonne Mixer is
of heat insulating fireclay bricks which diminishes the heat loss to the
surroundings. The roof is lined with heavy duty fireclay bricks and inner working lining (900 mm thick)
is made up of two layers of Magnesite
bricks.
The permanent pre- heating burners are
provided at both the end faces and nozzle of the Mixer to keep the temperature
of hot metal intact. As per project design, for Phase- ii expansion to 2.2 million
tone, a premise adjacent to existing Mixer was left for installation of second
1300 Tonne Mixer.
Capital Repair of 1300 Tons Mixer.
The campaign lining
life of Mixer is about 0.9 million tons hot metal holding cycle and after that Mixer is stopped for Capital repair for
about two months.
The
main causes for stopping Mixer for relining are collapse of roof fire clay
brick work, wearing of slag line and tap hole zone which need improvement. In
order to enhance the lining life, safety and improve the service condition of
hot metal Mixer, the conventional brickwork has been replaced with monolithic
lining in developed countries.
Capital
repair of Mixer is a labour and material intensive project. The refractory demolishing
and relining work is carried out by R. R. Dept. Pakistan Steel. During capital repair
of Mixer, besides the relining work, the electrical, mechanical, heat &
power equipments and automation instruments pertaining to mixer operation are
repaired and overhauled.
Hot metal mixer plays important role in
achieving pace of production and quality in the Steel making shops which are
operating without Torpedo vessels and computer aided dynamic models.
Sulfur and silica are harmful components in Mixer
slag. The unwanted Mixer
Slag is skimmed off from Hot Metal Ladles before dispatching the hot metal to
converter to prevent its passage into the LD- Converter.
As
per demand of Converter operator, hot metal is poured out from 1300 tonne Mixer
into a refractory lined ladle positioned under the Mixer spout on a weigh scale platform. The Mixer Section has
arrangements for weighing hot metal, temperature measuring and taking samples
for hot metal analysis.
Technical specifications of Hot metal for steel making.
As per Pakistan Steel’s specifications, the
average Physical temperature of hot metal poured out of
Mixer should not be less than 1320 ºC and the Chemical composition is kept controlled within the limits as under:
-
Carbon not less than 4%
-
Si :
0.4 – 0.8%
-
Mn : 0.5 – 1.0%
-
P : 0.2% max
-
S : 0.04% max
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