Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Metallurgical melting and processing unit
Description
The invention relates to a metallurgical melting and
processing unit, in particular an essentially cylindrical
vessel for accommodating and processing a non ferrous metal
melt.
These metallurgical units/vessels include the following
in particular:
Peirce-Smith converters, Teniente converters, Noranda
reactors, copper refining furnaces.
The basic design of such units for melting metals and for
accommodating and processing metal melts is as follows:
- The vessel/furnace is of an essentially cylindrical
shape and the longitudinal axis of the cylinder
extends essentially horizontally when the vessel is
in the operating position. This is illustrated in
Figure 1 in the case of a Peirce-Smith converter.
- The vessel has an outer metal casing and an inner
refractory lining.
- The vessel is provided with several nozzles which run
from outside through the metal casing of the furnace
and through the inner refractory lining into the
actual furnace space, to enable a processing gas such
as air to be injected into the metal melt.
- in this connection, the nozzles respectively the
nozzle openings are disposed adjacent to one another
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spaced at a distance apart in the longitudinal
direction of the longitudinal axis of the vessel. In
other words, the nozzles are disposed along a line
of the cylindrical casing, the line extending parallel
to the cylinder axis. The axis of the nozzles usually
extends in a plane perpendicular to the cylinder axis.
Up to a hundred of such processing nozzles may be
disposed in one of these units.
If a non-advantageous flow profile of the melt is
established in the area of the nozzles or due to fluctuating
gas pressure for example, the melt is able to penetrate
the nozzles. In the region of the nozzle orifices/nozzle
openings, chemical reactions can lead to solids being
deposited, for example deposits of magnetite (Fe304). This
can lead to a successive "clogging" of the processing
nozzles as the free nozzle cross-section becomes smaller.
At a prevailing gas pressure, this can reduce the gas
throughput per unit of time. Productivity decreases.
It is not always possible to increase the gas pressure by
using compressors.
In this connection, a known approach is to clean the nozzles
manually or mechanically with the aid of a ram device. The
original cross-section for the gas circulation is restored
again as a result. However, this can cause damage to the
refractory lining around the nozzle openings and hence
premature wear in this area.
It is an object of the invention to propose a vessel for
smelting metal, accommodating and
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processing a metal melt, in particular a non ferrous metal
melt, in which the nozzle area incorporating the nozzles
remains fully functional for longer periods. In this
connection, it should also be possible to retrofit existing
units.
In achieving this objective, the invention is based on the
following knowledge.
Figure 2 illustrates a cross-section through a part of a
wall of a Peirce-Smith converter (illustrated in Figure
1) in the nozzle area, and a nozzle 10 may be seen extending
from the outside through a metal casing 12 and a refractory
lining 14 into an area of the converter in which a metal
melt 50 is disposed.
Figures 1 and 2 illustrate the converter in a position
referred to as the "operating position". Accordingly, the
nozzle 10 extends essentially horizontally in this position
and in a plane perpendicular to the likewise essentially
horizontally oriented longitudinal axis L-L of the
converter. The opening region 10m extends slightly beyond
the refractory lining 14 (in the case of a new installation
illustrated by way of example here).
A plurality of such nozzles 10 are disposed on the
longitudinal face of the converter spaced at a distance
apart from one another along an imaginary straight line,
as schematically indicated in Figure 1.
Via the nozzles 10, which have an internal diameter of 5
cm for example, the processing gas (air in this embodiment)
is introduced into the melt 50, where it leaves the nozzle
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in the form of relatively large bubbles 52 and rises.
The bubbles are released from the nozzle in the region of
the top part of the opening of the nozzle. During the course
of the treatment process, a flow of melt 50 forms, as
indicated by the arrows in Figure 2. The non-advantageous
profile of the flow of melt in the vicinity of the nozzle
opening and the pressure of the melt acting on the nozzle
opening lead to melt penetration into the nozzle and the
formation of solid deposits 10a at the bottom region of
the nozzle opening, as schematically indicated in Figure
2. Due to the relatively large gas bubbles, the interface
between the gas and liquid phase is relatively small.
Furthermore, the dwell time of the large gas bubbles in
the melt is short. Both factors lead to a low level of
efficiency of the air introduced. In practice, therefore,
it is necessary to introduce considerable quantities of
air through the nozzles into the melt, which means long
processing times and hence higher costs. Although using
air with a higher proportion of oxygen shortens processing
times, it leads to extreme temperature peaks in the region
of the nozzle openings, thereby significantly increasing
wear of the refractory lining 14. This simultaneously
increases the risk of infiltration into the refractory
lining 14 and/or deposits 10a in the opening region 10m
of the nozzles 10.
These problems can be avoided by a design of the type
illustrated in Figure 3. Whilst the shape, disposition and
number of nozzles 10 may remain. essentially unchanged, the
metal melting unit proposed by the invention is equipped
with additional gas flushing devices 20, which are disposed
underneath the nozzles 10 in an operating/working position
of the unit. The gas flushing devices 20
=
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are used to introduce a gas into the metal smelt 50 in such
a way that it rises adjacent to the refractory lining and
in such a way that it is subsequently flushed around one
or more nozzle openings 10m. "Flushed around" means that
the gas leaving the gas flushing devices 20 (for example
an inert gas such as argon) is directed towards the nozzle
opening(s) 10m and passes the nozzle openings 10m as close
as possible in front or along said nozzles.
It has been found that the occurrence of deposits in the
nozzle in the area of the nozzle opening thus being
prevented or significantly reduced. The continual flushing
(purging) around the nozzle opening ensures that a
homogeneous velocity profile is created in the vicinity
of the nozzle opening. The melt flow is advantageously
affected in such a way that the melt does not get into the
nozzle opening at all or does so to only a slight degree,
and is no longer there to form deposits. Furthermore, the
relatively small gas bubbles 54 introduced via the gas
flushing device 20 lead to a melt-gas mixture, the density
of which is lower than that of the pure melt. Consequently,
the process gas (air or air-oxygen mixture) is able to
penetrate the melt more deeply at the same intake pressure,
which leads to a better dispersion (distribution) of the
process gas. The time the air bubbles remain in the melt
is also increased as a result so that, overall, a
significantly improved reaction behaviour is established
between the air bubbles 52 and the melt, thereby resulting
in a more efficient use of the process gas.
In its most general embodiment, the invention relates to
a metallurgical melting and processing unit with the
following features:
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- a cylindrical shape with a longitudinal axis which
extends essentially horizontally when the unit is in
an operating position,
- an outer metal casing,
- an inner refractory lining,
- several nozzles running from outside through the metal
casing and refractory lining for introducing a
processing gas into the metal melt via corresponding
nozzle openings,
- the nozzles are disposed mutually adjacent and at a
distance to each other along the longitudinal face
of the unit (in the direction of the longitudinal axis
of the unit),
in the operating position of the unit, one or more
gas flushing devices are disposed underneath the
nozzles, through which a gas can be introduced into
the metal melt so that it rises adjacent to the
refractory lining and flows along one or more nozzle
openings.
The arrangement and design of the nozzles as well as of
the gas flushing devices may be realized in different ways.
As mentioned above, the nozzle openings in known furnaces
of the described type usually lie adjacent to one another
along an imaginary straight line. In the case of such a
nozzle layout, the invention proposes that a co-operating
(corresponding) gas flushing device be disposed underneath
every nozzle. In other words, every nozzle is assigned a
separate gas flushing device so that fine gas bubbles can
be selectively directed from a gas flushing device towards
the opening region of a co-operating nozzle.
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Alternatively, a gas flushing device may also co-operate
with a group of nozzles.
This is specifically an option if the gas flushing device
selected is one which has an end face at the gas outlet
end which extends across a larger surface area, for example
has a length spanning two or three adjacently disposed
nozzles.
Figure 4 illustrates such an embodiment (a view from the
interior towards the refractory lining 14) of a converter
of the type illustrated in Figure 1, but based on the design
proposed by the invention with gas flushing devices 20
underneath the nozzles 10.
As may be seen, ten nozzles 10 are disposed in a horizontal
row and there is a space respectively between adjacent
nozzles 10.
Disposed underneath the nozzle row by approximately a
nozzle diameter are seven gas flushing devices 20, and each
gas flushing device 20 has a rectangular end face 20m at
the gas outlet end. The size of the gas flushing devices
20 is such that the gas discharged from a gas flushing device
20, for example nitrogen, can be selectively directed to
two nozzles 10 disposed above.
Of course, the gas flushing devices 20 may have a different
geometry, especially in the region of the end face at the
gas outlet end and may have a circular end face, for example.
However, also in this embodiment, one gas flushing device
20 may be provided for one nozzle 10 or alternatively also
one (bigger) gas flushing unit for
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several nozzles 10, for example.
The layout of the gas flushing devices 20 is the same as
the nozzle row in Figure 1 so that the gas outlet surfaces
of the gas flushing devices 20 are mounted along an
imaginary straight line lying parallel with the axis of
the converter. It is likewise possible for the gas flushing
devices 20 to be positioned offset from one another at
different heights in the refractory lining 14.
As illustrated in Figure 3, the gas flushing devices 20
are installed such that they extend through the metal casing
12 and refractory lining 14 in the same way as the nozzles
10.
As explained above, the purpose and function of the gas
flushing devices 20 is to direct the finest possible gas
bubbles in front of the opening region of the nozzles 10
in order to influence the melt flow there in order to prevent
melt entering the nozzle and deposits being formed in the
nozzle and to make better use of the process gas.
In this respect, the nozzles and gas flushing devices are
significantly different from one another in terms of
construction and function. The nozzle has a large free
internal cross-section (e.g. > 500 mm2) through which the
gas flows. In the case of a gas flushing device, the gas
is conveyed along homogeneously extending individual
passages, each with a significantly smaller internal
cross-section (in particular < 50 mm2) or through a pore
structure.
Porosity may be said to be directed or non-directed.
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Non-directed porosity is similar to a sponge-type structure
where the gas seeks an irregular path through the ceramic
. base material of the gas flushing brick depending on the
pore structure. Such gas flushing devices with non-directed
porosity are known and will therefore not be described in
further detail here.
In the case of gas flushing devices 20 with directed
porosity, the gas is directed through the flushing element
via discrete gas passages with a selective flow direction.
It would also be possible to opt for a combination of
directed and non-directed porosity inside a gas flushing
device 20 or within a row of gas flushing devices 20.
In this case, the penetration depth of the process gas in
the smelt 50 can also be selectively adjusted. The process
gas is the gas fed through the nozzles 10.
The arrangement proposed by the invention results in a
reduction in temperature peaks and a largely homogenous
temperature profile of the melt in the area around the
nozzle opening.
Refractory wear is significantly reduced. Penetration of
the nozzle opening by melt and deposits in the nozzle
opening are significantly reduced. The overall nozzle
cross-section remains free for a longer period, requiring
no cleaning, and the process gas is introduced much more
constantly than is the case with the prior art. Down-time
of the unit is minimised.
In parallel, costs can be reduced. This also applies when
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additional gas flushing devices 20 are provided because
they have a considerable service life and the service life
of the nozzles 10 is also made significantly longer compared
with the prior art.
When the unit is in the working position with the nozzles
disposed horizontally as described above, it is possible
for the gas flushing devices 20 to be disposed so that the
projections of the longitudinal axis of the nozzles 10 and
gas flushing devices 20 form an acute angle between them
on a plane perpendicular to the longitudinal axis LL of
the unit, as illustrated in Figure 3, where the
corresponding angle is denoted by a and is approximately
30 .
The nozzles 10, like the gas flushing devices 20, are
usually disposed at the bottom part of the unit when it
is in its operating position, as may be seen from the
presentation of Figures 1 to 3.
The gas flushing device 20 illustrated in Figures 3 and
4 is a gas flushing brick which has a non-directed porosity
end to end, and the gas (in this instance nitrogen) is
directed via a gas intake line 22 and a gas distributor
chamber 26 disposed between the gas intake line 22 and the
porous refractory part 24. Such a gas flushing brick has
been part of the prior art for centuries but was used for
other applications.
In the illustration of Figure 3, the end face 20m of the
gas flushing device 20 at the gas outlet end lies flush
with the internal face of the refractory lining 14 but may
also project slightly beyond it into the metal melt
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50. In any case, the end face 20m at the gas outlet end
is in direct contact with the melt 50 during the flushing
operation.
When talking of large or small gas bubbles within the
context of the invention, this should specifically be taken
as meaning the following in quantitative terms.
The gas bubbles introduced into the metal melt 50 via the
gas flushing devices 20 typically have a bubble diameter
of < 10 mm.
Gas flushing devices 20 with directed porosity have gas
passages for this purpose, the free internal cross-section
of which for the gas transport is < 15 mm2, < 25 mm2 or
< 50 mm2 respectively.
Gas flushing devices 20 with non-directed porosity made
from porous refractory material may be designed so that
the gas permeability has the following values conforming
to EN 993-4 (1995): > 2 x 10-12 m2, > 15 x 10-12 m2, > 50
x 10-12 m2, < 200 x 10-12 m2.
The ratio between the mean diameter of the bubbles fed
through the nozzles 10 and the mean diameter of the bubbles
fed through the gas flushing device 20 is usually 10 : 1
to 200 : 1.
The quantities of gas introduced into the smelt via the
gas flushing devices 20 and the nozzles 10 are based on
similar relationships. For example, a gas quantity of 0.02
to 0.5 Nm3/min is introduced through every gas flushing
element 10 and 20 Nm3/min through every nozzle 10.
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In the case of a newly installed unit (as illustrated in
Figure 3), the shortest distance between the nozzles 10
and co-operating gas flushing devices 20 on the side of
the refractory lining facing the melt may be 2 to 100 cm,
for example 5 to 50 cm.
The angle a between the projection of the nozzle axis and
the projection of the axis of the co-operating gas flushing
device on a plane lying perpendicular to the longitudinal
axis L-L of the unit may be 10 - 80', preferably 10 -
40 .
