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Plain steel pipes vs. advanced lances
Furnace tapping using oxygen steel pipes has not seen a significant change in over
100 years. Until now. Well-known problems related to the use of standard pipes as
well as wire filled lances in a Silicon furnace, include, but are not limited to:
• Inaccurate tool: pipe bends and flame is not focused, causing damages &
shortening the life of the taphole refractories, which adds cost and loss of
production.
• Increased Fe contamination of the Silicon produced, resulting in reduced revenue.
• Physically hard and unsafe to operate, as you need to push the pipe against the
taphole to keep it ignited.
• Safety: slow getting the job done, results in extended exposure to the operator in an
unsafe area of the furnace.
• Cost: high oxygen consumption & high lance consumption. Ceramic coating
needed to protect pipes from high tapping temperature.
• Time consuming and frustrating to connect one lance to another; increased waste
and cost. Screw joints many times result in labor injuries to arms and joints.
• Deteriorating taphole conditions resulting in gas blowing, with an impact on the
environment as well as operator health.
Many of these drawbacks are related to the use of primitive steel pipe oxygen lances.
One of these consequences appears when the lance has to be pressed against its attack
point. The pipe bends and more importantly, that pressure generates an undesired
radial combustion, speeds up lance consumption and generates an irregular
perforation. Thus, this effect lowers the lance’s capability to concentrate all its energy
at the attack point, wasting energy on its own consumption and tearing up undesired
zones of taphole refractories.
The basic concept of any thermal lance is that it generates a thermal energy flow from
Fe combustion contained in the steel of the lance itself. In order for this combustion to
take place, the Fe's ignition temperature must be reached and it must also be in
contact with high purity oxygen at the right pressure and flow rate. The flame at the
tip of the lance has a temperature of about 3 000C (5 400F). The kinetic energy of the
oxygen drags the combustion forward leaving only the tip of the lance lit; its effective
attack edge.
The plain steel pipe lance is a hollow tube, without inserts resulting in the steel
coming into contact with oxygen only in the internal wall of the tube. The thicker the
walls “the better”, as you are adding more Fe to the combustion. The new advanced
thermal lances on the other hand, have several specially designed internal ducts which
allow the oxygen to get in contact with both sides of its steel internal profiles. The
result is a significantly increased steel/oxygen contact surface in the important
combustion zone compared to the standard oxygen pipes. In addition, it cools the
section of the pipe not burning, extending its longevity in a taphole environment.
The oxygen pipe is ignited by heating its tip with a solid combustible mass already
ignited (i.e. burning coal), the pure oxygen increases the combustion, so that heat and
oxygen bounce against the outer wall of the oxygen pipe (see Figure 1).
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