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JETBOX™- LATERAL THINKING DELIVERS
IMPROVED EAF PERFORMANCE
Europe's first installation of the new JetBOx™ oxy-fuel
burner system shows that simple ideas can deliver big results
In November 2000, Process Technology International
Inc. (PTI), in co-operation with Air Products PLC, installed
Europe's first JetBOx™ system into the Huta Zawiercie
130T electric arc furnace (EAF) in Poland.
Four oxy-fuel jet burners, installed in the groundbreaking
JetBOx™ mountings, replaced three conventional burners
and a slag door lance manipulator.
Now, after a year of full production, the new system has
shown significant performance improvements across a range
of key indicators (see Diagram X).
In the meantime, a second complete JetBOx™ system
has been installed in the ISCOR EAF in South Africa, a third
installation has been completed at Nucor Steel Hickman (USA),
two new orders have been received from China and very recently
another system successfully started up at Gallatin Steel
(USA); while PTI and Air Products PLC have recently announced
an agreement to market the new technology across Europe,
the Middle East and North Africa.
How it works
So what makes the new JetBOx™ technology different?
In summary, it applies a radically simple idea to solve
an old problem.
Conventional techniques involve the use of oxy-fuel burners/lances
located in the furnace's sidewall. These techniques then
apply an oxy-fuel flame to the scrap and a supersonic jet
of oxygen into the molten steel, to decarburise and supply
chemical energy. Carbon is then injected into the vicinity
of oxygen jet, assisting with slag foaming and reducing
FeO.
The big challenge is maintaining the oxygen's high velocity
to provide good oxygen penetration through the slag and
into the molten steel itself. A higher velocity means a
faster decarburisation rate and more efficient oxygen usage.
It's here that conventional burners/lances strike a problem:
the supersonic jet of oxygen has to travel a considerable
distance from the sidewall of the furnace to reach the metal
line. And that means it inevitably loses velocity on the
way - as much as 30% over a typical jet length of 1,750mm.
Past attempts to solve this problem have tended to focus
on maintaining jet velocity, for example increasing the
flow of oxygen through the jets, which has significant cost
and efficiency implications. An excessive use of oxygen
in the process can produce negative effects such as panel
flashback, refractory wear through oxidisation and higher
electrode consumption.
Another technique is to enclose the supersonic core of
the jets in a shrouding flame to reduce turbulence along
the edges. Without this protective flame, a supersonic jet
exiting a nozzle tends to "entrain" surrounding
gases, causing the jet to expand and lose velocity (see
Diagram Y).
Shrouded jets are now standard in many burner systems.
More than 200 PTI burners with the shrouded supersonic oxygen
feature have been installed on EAFs since 1995.
Lateral thinking
But these techniques only go so far. Significant velocity
is still lost across the distance the jet has to travel
from the sidewall to the metal line.
What PTI did with its JetBOx™ system was to apply
lateral thinking to the problem.
Shrouding the supersonic jet with an oxy-fuel flame can
maintain jet velocity over a longer distance, however the
basic rules of fluid dynamics still apply. So, the longer
the distance the jet has to travel, the lower the speed
at the end of the jet. It seems that the most efficient
technique is to use a shrouded supersonic oxygen jet but
reduce the distance the jet has to travel. A combination
of the two improves oxygen efficiency.
As Diagram Z shows, the JetBOx™ simply moves the supersonic
oxygen nozzle closer to the molten bath, by mounting it
in a special housing set away from the sidewall of the furnace.
This simple approach generates three major benefits.
First, it reduces the distance to the metal line by as
much as 50 percent over conventional mountings, allowing
the oxygen jet to intersect the molten steel in the supersonic
core region of the jet stream (see Diagram Z1). The supersonic
jet reaches the molten steel before it has had the chance
to lose a lot of its velocity, which means faster decarburisation
and more efficient oxygen usage.
Second, it means a more aggressive angle of attack can
be used without the risk of impinging on the refractory.
And third, it positions the JetBOx's™ carbon injection
pipe close to the molten bath for enhanced slag foaming.
The close proximity to the burner also helps to prevent
the injection port becoming plugged with slag.
Results at Huta Zawiercie
So how does all this translate into actual performance
benefits?
Data accumulated from Huta Zawiercie show significant improvements
across a range of criteria (see Diagram X), in particular
reduced power on time, increased speed and efficiency of
decarburisation, reduced electrode consumption and scrap
pre-heating with burners.
The JetBOx™ system increased the efficiency of chemical
energy utilisation, resulting in a substantial improvement
in performance.
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