Note: Descriptions are shown in the official language in which they were submitted.
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Gas Purging Device for Metallurgical Melting Pots
DESCRIPTION
The invention pertains to a gas purging device for
metallurgical melting vessels. Numerous variations of gas
purging devices as well as corresponding gas purging
elements, particularly gas purging plugs, have been known and
used for many years.
Discrete gas purging plugs can be realized with so-called
directional or non-directional porosity. "Directional
porosity" is achieved, for example, with channels that extend
in the flushing element. "Non-directional porosity" can be
achieved with a porous refractory material that has
corresponding gas permeability.
Gas flushing devices can be installed into a refractory
lining of a metallurgical melting vessel that forms a wall or
the bottom of the vessel. However, they may also be realized
in the bottom or a wall in-situ, for example, as described in
EP 0 560 834 Bl.
Gas flushing elements primarily serve for conducting gas.
However, a gas flushing device of this type may also conduct
gas/solid mixtures in certain instances.
The gases used may be inert gases, for example, when flushing
ladles. However, it is also known to flush with oxygen, for
example, in electric furnaces.
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All gas flushing/purging devices are subjected to significant
wear, particularly a chemical/corrosive attack. This is the
reason why these gas purging devices need to be replaced
regularly.
The left part of Figure 1 shows a conventional gas purging
device. A so-called gas purging lance L is guided into the
bottom region H of an electric furnace from outside, wherein
said lance is held on the outer casing A of the vessel with
the aid of washers B and mounted by means of a flange.
Subsequently, a well nozzle S is placed over the lance L and
a mass is filled between the well nozzle and the lance. The
well nozzle S is subsequently walled in with bricks M and the
bottom H is then lined with a furnace mass.
Once the gas purging device is worn out (indicated with a
broken line in Figure 1), the entire purging device needs to
be cleared. This leads to the situation illustrated in the
left part of Figure 2. A new gas flushing device is
subsequently installed as described above.
This method is very time-consuming and nearly the entire
hearth mass of the bottom needs to be cleared, particularly
up to the outer casing A.
Consequently, it is an object of the invention to develop a
gas purging device that can be replaced faster and cheaper
when it is worn out.
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The invention proposes to separate the parts of the gas
purging device that are subject to particular wear, i.e., the
parts of the gas flushing device that are situated adjacent
to the molten metal or the parts situated at the gas outlet
end, from the parts arranged upstream thereof, i.e., in the
direction of the gas inlet end.
When an exchange is required, individual parts of the gas
purging device may remain and only the actually worn zones or
worn parts are replaced.
According to another aspect, the actual flushing element is
realized in a monolithic mass in the section that is situated
adjacent to the wall of the melting vessel. This mass
simplifies the alignment of the flushing element during the
installation of the flusher. This mass can also be cleared
and replaced more easily when the flushing device is torn
down. The mass may be arranged, in turn, in a permanent
receptacle that is not exchanged when the flusher (purging
element) is replaced.
According to its most general embodiment, the invention
pertains to a gas purging device for metallurgical melting
vessels with the following characteristics:
-a gas purging brick is arranged in an upper cylindrical
receptacle with its end on the gas outlet side and in a lower
cylindrical receptacle with its adjacent section, and
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-an annular space provided at least between the lower
receptacle and the gas purging brick is filled with a mass,
wherein
-the gas purging brick, the receptacles and the mass are made
of a refractory ceramic material.
In this context, the term "cylindrical" merely refers to a
body that is open on opposite sections and serves for
accommodating another body, wherein this term does not imply
any other geometric restrictions.
The lower receptacle is not subjected to wear in the normal
operating state and can be enclosed with refractory bricks or
a refractory mass (hearth mass) that also remains as a
permanent lining when a replacement is required. Its serves
for receiving a refractory ceramic mass, for example, a
ramming mass, which simultaneously serves for adjusting the
purging element (gas purging brick) when it is aligned in the
lower receptacle and embedded in the mass. The upper
cylindrical receptacle is situated adjacent to and
practically forms an extension of the lower receptacle
(referred to the flow direction of a gas or the direction
toward the molten metal). This upper receptacle may have, for
example, a circular inside cross section and encloses the
purging device in a more or less direct fashion such that it
forms a mechanical guide as well as a protection against
chemical attacks.
The gas purging element may be arranged in the upper
receptacle (i.e., on the "hot side") flush or with slight
clearance. It
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may be fixed in the upper receptacle by means of an adhesive
or mortar.
The gas purging brick usually extends over the entire length
(height) of the upper and the lower receptacle. It may also
protrude the upper receptacle by a short distance (when
mounted). The gas connection and, if applicable, a gas
distribution chamber for distributing gas to individual
channels or pores are situated on the other end.
The flusher (gas purging element) may have a circular cross
section. However, gas flushing elements in the shape of
truncated cones or cuboid geometries may also be utilized.
When using a cuboid purging element, the upper receptacle
accordingly has a rectangular cross section.
In this context, the term "cylindrical receptacle" should be
understood in the form of an enclosure for a certain length
of the gas purging element regardless of its inside cross
section. The outside cross section may have an arbitrary
shape.
At least one receptacle may be realized in the form of a
pressed part. Pressed enclosure parts for the flushing
element are particularly tight and consequently wear-
resistant.
The purging element itself can be realized with directed or
non-directed porosity. Purging elements with directed
porosity are used, in particular, when purging electric
furnaces with oxygen. This can be achieved by realizing the
purging element with
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several tubular channels that extend in the axial direction
and consist, for example, of small metal or ceramic tubes.
The purging element may be equipped with an additional lance
(separate gas supply for purging element and lance) or
consist merely of a lance lined with refractory material.
The length of the upper receptacle is determined in
dependence on the respective application and the expected
wear, namely because only the upper receptacle should be
subsequently replaced.
According to one embodiment, the upper receptacle is at least
as long as the lower receptacle. However, the upper
receptacle may be up to four-times as long as the lower
receptacle referred to the axial direction of the flushing
element, i.e., in the flow direction of the gas. For example,
the upper receptacle is two-times to three-times as long as
the lower receptacle.
The upper receptacle may have a cross-sectional shape that
makes it possible to directly place the upper receptacle on
the lower receptacle. However, the upper receptacle may also
have a wall thickness that corresponds to the wall thickness
of the refractory mass introduced between the flushing
element and the lower receptacle as discussed below in the
description of the figures.
It usually suffices to realize the upper receptacle with an
outside cross section that is smaller than the outside cross
section of the lower receptacle. This means that the gas
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purging device has a stepped cross section as shown in the
right part of Figures 1, 2. However, it would also be
conceivable to realize embodiments, in which the upper
receptacle ends at a certain distance in front of the lower
receptacle or protrudes into the lower receptacle.
The described gas purging device can be installed into the
bottom or a wall of a metallurgical melting vessel. The term
"metallurgical melting vessel" includes all crucibles for
melting metal and for treating molten metal, respectively.
The gas purging device consequently is also suitable for
installation into the hearth bottom of an electric furnace,
for example, an electric arc furnace.
Other characteristics of the invention are disclosed in the
dependent claims as well as the remaining application
documents. This includes the multi-part design of one or both
receptacles.
One embodiment of the invention is described below with
reference to the figures that respectively show a schematic
section through the embodiment in the right part of Figures
1, 2.
The gas purging device comprises a total of four parts. A
lower receptacle 10 is initially inserted during the lining
process. This receptacle is a pressed, refractory enclosure
of annular shape. Subsequently, a purging brick 12 with
directed porosity (channels 20) is inserted via the outer
wall A through an opening 14 from below (from outside),
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and its section 12u is centered in the lower receptacle 10 as
well as the region situated thereunder with the aid of a
ramming mass. The gas outlet end 120 of the purging element
12 protrudes the lower receptacle 10 and the mass 16,
respectively. An upper receptacle 18 that is also realized
cylindrically analogous to the lower receptacle 10 is then
placed over the upper section 120 of the gas purging element,
wherein the upper receptacle has an inside cross section that
corresponds to the outside cross section of the gas purging
element 12. The upper receptacle 18 is aligned with the
annular channel, filled with the mass 16, between the lower
receptacle 10 and the purging element 12. The upper
receptacle 18 is twice as long as the lower receptacle 10.
The hearth mass H is ultimately introduced and the hearth
bottom is formed.
In an alternative variation of the embodiment shown, the
region underneath the lower receptacle 10 may also be
equipped with mounting elements B analogous to the state of
the art, for example, washers (as illustrated in the left
part of Figures 1, 2) in order to fix the purging elements 12
on the outer wall A of the melting vessel.
The time required for lining the gas purging device shown in
Figures 1, 2 is approximately one hour.
The time required for a lining process in accordance with the
state of the art that is illustrated in the left part of
Figures l, 2 is approximately 2.5 hours. Another advantage of
the gas flushing device according to the invention can be
seen in the fact that the lower receptacle 10 can remain when
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a replacement is required (Figure 2). In addition, the zones
of the hearth mass H that are situated adjacent to the outer
wall A can be largely preserved such that the required
quantity of new hearth mass is reduced.
