Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Method and Device for Cleaning Slag
The invention relates to a method and a device for purifying slag from a
nonferrous metal (NE)
or iron alloy production process.
Such methods and devices are fundamentally known in the prior art, also for
said production
processes. For this purpose ¨ as shown in Figure 2 ¨ the slag arising during
said production
processes is typically continuously conducted via a slag intake channel 112
into a settling
furnace 110 and heated and metallurgically treated therein. The treatment is
used for the purpose
of reducing the metal component still contained in the slag. After the
treatment and a
corresponding dwell time of the slag in the settling furnace 110, a part of
the metals contained in
the slag settles as a metal alloy or as a mat, for example, as a copper mat,
on the bottom of the
settling furnace. The original slag thus decomposes into a metal alloy and a
first residual slag.
The metal alloy is poured off via a metal outlet channel 111 of the settling
furnace 110, while the
first residual slag, which typically floats on the metal alloy, is tapped via
a slag outlet channel
114 from the first settling furnace 110.
Document EP 0 627 012 Al discloses a method for desulfurization of iron melts,
which is to be
applied by means of a slag both for crude iron and also for cast iron.
Document US 4,720,837 A discloses a ladle furnace device for refining molten
steel. In this case,
liquid steel and a slag former are introduced into the ladle furnace device.
The slag former is
slagged by electric arc heating in the ladle, whereby the liquid steel is
purified by means of the
slag.
The purification of slag from an NE or iron alloy production process
traditionally ends at this
point. The remaining first residual slag still has a metal component of? 0.5
wt.%, however. This
still relatively high metal component no longer meets modem requirements for
environmental
protection, in particular if toxic heavy metal components are still contained
in the first residual
slag.
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The invention is based on the object of refining a known method and a known
device for
purifying slag from an NE or iron alloy production process such that the slag
is less
environmentally harmful, and in particular the metal component in the slag is
reduced further.
This object is achieved by the method according to Claim 1. Accordingly, the
first residual slag
is tapped in a ladle, the composition of the first residual slag is analyzed,
and finally at least one
gaseous medium is introduced onto or into the first residual slag for the
metallurgical-physical
reaction to form a second residual slag in the ladle, wherein the gaseous
medium is selected as a
function of the analyzed individual composition of the first residual slag,
and the second residual
slag is transported in the ladle to a second settling furnace; and pouring off
the second residual
slag from the ladle into the second settling furnace, and the second residual
slag remains for a
predetermined dwell time in the second settling furnace and becomes calmer
therein, and the
decomposition of the second residual slag during the dwell time into a second
metal alloy and a
third residual slag, wherein the second metal alloy settles on the bottom of
the second settling
furnace and the third residual slag floats on the second metal alloy.
The term "analyze" typically means taking a sample from the slag and analyzing
the respective
present metallurgical/chemical composition of sample. The analysis can
possibly occupy a
longer period of time, and therefore the results of the analysis are only
available at the end of this
period of time. The composition of the sample ascertained on the basis of the
analysis then
possibly no longer accurately corresponds to the composition of the slag at
the end of said period
of time, because further material introductions into the slag can have taken
place in the
meantime. The term "analyzing" in the meaning of the invention therefore
possibly furthermore
also includes a prognosis, to what extent the composition of the slag will
presumably change
during the analysis period of time, for example, because of further
introductions into the slag
which have occurred during this period of time.
The term "ladle furnace" is used here in the meaning of a slag treatment
station (STS).
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The gaseous medium in the meaning of the invention is either a gas or a
gaseous carrier
medium in combination with dusty or fine-grained materials; keyword: carbon
injection. The
introduction of the gaseous medium is used to intensify an intended (chemical)
reaction, for
example, for homogenization or better mixing of the slag or for generating
turbulence in the
slag. The gas or the gaseous carrier medium can be an inert gas or carbon
dioxide.
Depending on the individual composition of the first residual slag and
according to the
desired chemical and/or metallurgical-physical reaction, the at least one
gaseous medium is
selected such that it causes its agglomeration of metal particles in the slag,
a reduction of the
slag, and/or an oxidation of the slag.
Due to the claimed ladle treatment, the first residual slag originally
supplied to the ladle is
converted into a second residual slag. This second residual slag is already
less harmful from
an environmental aspect than the first residual slag, because a part of the
undesired
components still contained in the first residual slag was separated by said
treatment, either by
vaporization or by conversion/settling into a heavy metal phase, which settles
later on the
bottom of the second settling furnace.
In one aspect the present invention resides in a method for purifying slag, as
arises in a non-
ferrous or iron alloy production process, having the following steps: heating
and treating the
slag in a first settling furnace to obtain a first metal alloy and a first
residual slag, tapping the
first residual slag into a ladle; analyzing the composition of the first
residual slag; and
introducing at least one gaseous medium onto or into the first residual slag
for the
metallurgical-physical reaction to form a second residual slag in the ladle,
wherein the at
least one gaseous medium is selected as a function of the analyzed individual
composition of
the first residual slag, transporting the second residual slag in the ladle to
a second settling
furnace; and pouring off the second residual slag from the ladle into the
second settling
furnace, wherein the second residual slag remains for a predetermined dwell
time in the
second settling furnace and becomes calmer therein, and wherein decomposition
of the
second residual slag during the dwell time into a second metal alloy and a
third residual slag,
wherein the second metal alloy settles on the bottom of the second settling
furnace and the
Date Recue/Date Received 2021-07-08
3a
third residual slag floats on the second metal alloy; wherein heat energy is
supplied to the
second residual slag in the second settling furnace via a plurality of
electrodes, which
protrude into the slag of the second settling furnace.
In one aspect the present invention resides in a method for purifying slag, as
arises in a non-
ferrous or iron alloy production process, having the following steps: heating
and treating the
slag in a first settling furnace to obtain a first metal alloy and a first
residual slag, tapping the
first residual slag into a ladle; analyzing the composition of the first
residual slag; and
introducing at least one gaseous medium onto or into the first residual slag
for the
metallurgical-physical reaction to form a second residual slag in the ladle,
wherein the at
least one gaseous medium is selected as a function of the analyzed individual
composition of
the first residual slag, transporting the second residual slag in the ladle to
a second settling
furnace; and pouring off the second residual slag from the ladle into the
second settling
furnace, wherein the second residual slag remains for a predetermined dwell
time in the
second settling furnace and becomes calmer therein, and wherein decomposition
of the
second residual slag during the dwell time into a second metal alloy and a
third residual slag,
wherein the second metal alloy settles on the bottom of the second settling
furnace and the
third residual slag floats on the second metal alloy; wherein the third
residual slag only has a
metal component of less than 0.5 wt.%.
Two figures are appended to the description, wherein
Figure 1 shows the device according to the invention; and
Figure 2 shows a device according to the prior art.
The invention will be described in greater detail hereafter with reference to
Figure 1 in the
form of exemplary embodiments.
Date Recue/Date Received 2021-07-08
3b
The invention begins according to Figure 1 where the prior art described above
with
reference to Figure 2 stops, namely upon the tapping of the first residual
slag from the first
settling furnace 110 via the slag outlet channel 114 into the ladle 120.
Date Recue/Date Received 2021-07-08
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The tapping of the first residual slag from an NE or iron alloy production
process into a ladle
120, which is fundamentally known from the iron and steel industry, firstly
causes the inflow of
slag, which still takes place continuously into the first settling furnace
110, to be interrupted,
because the tapping of the first residual slag takes place discontinuously. A
transition into so-
called "batch operation" thus takes place. The use of the ladle 120 to receive
the first residual
slag offers the advantage that the ladle is already innately best suitable as
a transportation and
treatment vessel for the further treatment of the first residual slag. It thus
typically has lance
accesses in the cover, lateral injection options, or bottom purging plugs,
each for introducing
gaseous media.
According to one advantageous exemplary embodiment, the ladle 120 can also be
designed as a
ladle furnace or as a copper refining furnace/heating furnace and is best
suitable as such for
heating the first residual slag, to improve the metallurgical-physical
reaction of the first residual
slag with the gaseous medium. The residual slag is preferably heated using
electrodes 128, as
shown in Figure 1.
Furthermore, introduction ducts, i.e., a type of charging pipes, can be
provided in the ladle for
supplying additives, for example, reducing agents or slag formers, into the
first residual slag, also
to assist the metallurgical-physical reaction. For better mixing and
homogenization of the
residual slag, the gaseous medium can be introduced into the residual slag via
a purging lance
immersed from above into the slag, via lateral purging lances, or via bottom
plugs.
The first residual slag originally supplied into the ladle is converted by the
described treatment,
which preferably provides the generation of turbulence in the residual slag to
accelerate the
reaction, into a second residual slag. This second residual slag is already
less harmful from an
environmental aspect than the first residual slag, because due to said
treatment, a part of the
undesired components still contained in the first residual slag was separated,
for example, by
vaporization or by conversion/settling into a heavy metal phase.
To improve the second residual slag still further with respect to
environmental protection
aspects, however, in particular to enable settling of the heavy metal phase,
the method according
CA 03003784 2018-05-01
to the invention optionally furthermore provides that the ladle 120 having the
second residual
slag is transported, for example, with the aid of a carriage 130 or with the
aid of a crane (not
shown) to a second settling furnace 140, and the second residual slag is then
poured off from the
ladle 120 into the second settling furnace 140.
The pouring off is performed, for example, with the aid of a tipple 135 via a
slag inlet channel
142. In the second settling furnace 140, which is typically a reduction
furnace (submerged arc
furnace, SAF), the second residual slag is to come to rest by dwelling therein
for a predetermined
dwell time. During the dwell time, at least a part of the metals still
contained in the second
residual slag settles as the second metal alloy on the bottom of the second
settling furnace 140,
while a remaining third residual slag typically floats on the top of the
second metal alloy. After
the dwell time, the third residual slag can be tapped via a slag outlet
channel 144, for example,
into a bucket 150 or into a granulation. The second metal alloy, in contrast,
is tapped separately
via an outlet 146 from the third residual slag.
During its dwell time in the second settling furnace 140, the second residual
slag is preferably
kept at a constant temperature. For this purpose, heat energy can be
introduced into the second
settling furnace 140. This introduction of the heat energy preferably takes
place via a plurality of
small electrodes 148 having a diameter less than 900 mm, which protrude into
the slag of the
second settling furnace. The electrodes 148 can either be arranged along a
straight line or each
offset in relation to the straight line in a zigzag shape. The straight line
preferably extends along
or parallel to the longitudinal side of a preferably rectangular vessel of the
second settling
furnace. The plurality of small electrodes offers the advantage that they mix
or swirl the residual
slag less strongly than a single large electrode, and therefore enable better
heat conservation. The
second settling furnace 140 can be operated using direct current or
alternating current. In the case
of smaller slag introductions and therefore smaller dimensions of the second
settling furnace 140,
however, equipping it with 3 larger electrodes can have a simpler design and
be more cost-
effective.
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The third residual slag advantageously only still contains a metal component
of less than 0.5
wt.%, in particular of heavy metals, and is thus substantially more
environmentally friendly to
dispose of than the first or the second residual slag.
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List of reference numerals
100 device
110 first settling furnace
111 metal outlet channel of first settling furnace
112 slag inlet channel of first settling furnace
114 slag outlet channel of first settling furnace
120 ladle
128 electrodes of the ladle
130 crane or carriage
135 tipple
140 second settling furnace
142 slag inlet channel of second settling furnace
144 slag outlet channel of second settling furnace
146 metal outlet of second settling furnace
148 electrodes
150 bucket
