Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Method and Installation with Smelting and Reduction
Cyclone and a Coupled Lower Furnace For Utilising
Residual Material Containing Iron and Heavy Metals
and Optionally Iron Ore
The invention aerates to a process and a plant for
utilizing iron-containing and heavy-metal-containing
remainder materials and, if appropriate, iron ore.
A major problem of the iron- and steelmaking industry
is the continuous production of quantities of iron-
containing and heavy-metal-containing remainder
materials, such as for example furnace dusts, sludges,
rolling scale and the like, which are only available
for reuse with considerable outlay and therefore are
generally landfilled without the benefit being
extracted from their materials of value.
For ecological and economic reasons, there is a need to
separate the iron which is present in the remainder
materials from its accompanying metals and to return it
to the iron- or steelmaking process.
One process of the type described in the introduction
is the INMETCO process. In this process, iron-rich
metallurgical remainder materials are agglomerated with
solid reducing agents to form unburned, so-called
"green" pellets and are reduced in a rotary hearth
furnace, so that the heavy metals are vaporized, are
extracted with the off-gas and are then melted down or
optionally hot-briquetted in a melting furnace.
The drawbacks of this process are the need for a
pretreatment stage, in which the remainder materials
are agglomerated, and in the separately carried out
reduction and melting process, with the result that the
energy to heat up the remainder materials has to be
applied twice and a dedicated off-gas system is
required for each stage.
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In a process which is described in DE-A-44 39 939,
remainder materials are melted down in a melting
cyclone, the heavy metals are vaporized and are
separated out of the off-gas as a dust fraction after
oxidation has taken place. The levels of heavy metals
in the slag which remains are further depleted in a
lower furnace by blowing on reducing gas and oxygen and
the slag is then used as a starting material for the
production of cement or rockwool. However, in this
process the iron is not reused, and consequently a
significant constituent of the remainder materials
remains unused.
One problem in the production of pig iron is the fine-
ore content, of which there are relatively high levels
and which is difficult to handle during the reduction
and smelting process. Consequently, the reduction of
the fine ore usually takes place in fluidized bed
reactors, which entail high levels of technical outlay.
Introducing the reduced fine ore into a melting furnace
also requires complex apparatus, the service life of
which is greatly restricted on account of the wear
caused by the reactivity of the iron sponge.
It is known from US-A-5,639,293 to carry out
preliminary reduction of iron ore by making the iron-
ore particles turbulent using oxygen and a reducing gas
in a melting cyclone and collecting the melted iron
particles in a metallurgical vessel beneath the melting
cyclone and then fully reducing them by blowing in
oxygen by means of a lance which projects centrally
through the melting cyclone and adding fuel, leading to
the formation of a reduction gas which rises into the
melting cyclone and, after it has reacted with the iron
ore, is extracted at the upper end of the melting
cyclone together with off-gases which form.
The cooling action of the oxygen lance which projects
centrally through the melting cyclone into the melting
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vessel in accordance with US-A-5,639,293 may lead to
skull formation of the prereduced iron ore.
A device for reducing and melting down iron ore is
described in EP-A-0735146. According to EP-A-0 735 146,
iron ore is reduced and melted in a melting cyclone and
passes into a metallurgical vessel which directly
follows beneath the melting cyclone and in which, while
a process gas forms from coal which is blown onto the
slag/metal layer and oxygen which is blown in, the
final reduction and the complete melting of the iron
take place. The reducing process gas is partially burnt
with oxygen and, in this way, supplies the heat
required for the melting and reduction both in the
melting vessel and in the melting cyclone. The off-
gases are extracted at the upper opening of the melting
cyclone.
To separate slag and pig iron, the molten material
first has to be transferred into a settling vessel,
since in these known devices there is in each case only
one tapping hole in the lower vessel.
On account of the open melting cyclone base and the
associated lack of return flow in the melting cyclone,
the countercurrent guidance and the associated
turbulence of the reduction gas with respect to the
iron-ore particles leads to an increased level of
dusting, and this is made even worse by entrained slag
particles and leads to considerable discharges of
particles from the melting cyclone with the off-gas
which is discharged from the melting cyclone at the
top.
The invention aims to eliminate these drawbacks and
sets the object of providing a process and a plant
which make it possible to process iron-containing and
heavy-metal-containing remainder materials, in
particular from the iron- and steelmaking industry,
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and, if appropriate, iron ore in an environmentally
friendly manner - avoiding landfill - so that the iron
can be utilized, i.e. can be used beneficially for
steelmaking. Furthermore, only a single off-gas flow is
generated, thus saving plant costs and minimizing
emissions, as well as increasing the possible
efficiency of energy recovery.
According to the invention, this object is achieved by
the combination of the following features:
- the remainder materials and, if appropriate, the
iron ore are introduced into a melting cyclone
with return flow,
- reducing agents and oxygen are additionally
introduced into the melting cyclone and are made
turbulent,
- in the melting cyclone, iron is reduced at least
to FeO,
- in the melting cyclone, heavy metals are reduced
to form metals and are converted into the gas
phase by vaporization,
- the resulting gas, which may contain heavy metals,
the partially reduced iron and the slag are
transferred into a directly coupled furnace,
- energy is supplied to the furnace,
- reducing agents and oxygen or oxygen-enriched air
are introduced into the furnace,
- iron is fully reduced and partially melted in the
furnace, and
- the vaporized heavy metals are precipitated
outside the furnace.
The meaning of the terms 'iron", 'iron-containing",
"heavy-metal" and "heavy-metal-containing" in each case
encompass both the corresponding metals in oxidized,
for example oxidic, form, and in reduced, i.e.
metallic, form, and specifically both in oxidized and
reduced form and in only one of the two forms; the
precise meaning becomes clear from the context.
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In this context, the term "reduction to Fe0" is always
to be understood as meaning reduction from trivalent to
divalent iron, i.e. from FeZ03 to 2Fe0, but also from
3Fe~03 to 2Fe304 ( i . a . to Fe203~Fe0) .
Furthermore, the use of a melting cyclone with return
flow, which is effected by a constriction in the base
of the melting cyclone, allows a low level of dusting
to be achieved. The iron-containing and heavy-metal-
containing remainder materials and, if appropriate, the
iron ore, on account of the return flow, achieve a
longer residence time in the melting cyclone and are
transferred into the furnace only in the liquid or
gaseous state. Even when the melting cyclone is
arranged above the furnace, slag particles are
prevented from entering the melting cyclone by the
constriction. Moreover, there is only one outlet
opening, which is provided in the bottom of the melting
cyclone, so that particles cannot be discharged by
means of a gas flowing upward through the melting
cyclone. According to the invention, all the materials
and gases which have been introduced into the melting
cyclone are forced to move into the furnace, where they
can be fully processed efficiently. This also has the
advantage of a single off-gas flow, namely from the
furnace, which accordingly can be treated easily and
inexpensively.
It is advantageously also possible to use fine ore as
iron-containing remainder material, in particular with
a proportion of extremely fine particles which
originate from the ore beneficiation or from the fines
from a pelletizing device.
The introduction of reducing agents, which are
advantageously introduced in solid, liquid or gaseous
form, and oxygen, preferably industrial-grade oxygen or
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oxygen-enriched air, takes place horizontally,
preferably tangentially, into the vertically arranged
melting cyclone, with the result that the mass transfer
and heat exchange operations proceed very quickly.
Reducing agents and oxygen are added in controlled
quantities which are such that the heavy metals, during
the melting operation, are converted into the gas phase
by being vaporized in the metallic state, and the iron
is reduced at least to divalent iron oxide FeO.
The heavy-metal-containing gas, the partially reduced
iron and the slag are transferred into the furnace from
the melting cyclone by means of a connecting line which
is arranged between the bottom opening of the melting
cyclone and a furnace which directly follows the
melting cyclone, preferably through the top or through
a side wall of the furnace, and, if appropriate, via at
most one intermediate chamber which is arranged on the
wall of the furnace and allows particularly effective
separation of the melting zone from the reduction zone
in the furnace. The intermediate chamber into which the
connecting line opens may also be designed as a furnace
off-gas line.
To reduce the partially reduced iron which is present
in the form of divalent iron oxide in the molten
material to form metallic iron, solid reducing agent,
preferably coal or carbon-containing waste materials
(which are at least partially formed by fine
particles), is blown into the molten material with
oxygen or oxygen-enriched air. The step of blowing in
these substances may take place via below-bath blowing
nozzles or via lances which penetrate into the slag
layer floating on the molten metallic iron. For this
purpose the furnace is provided with openings for the
lances. The blowing nozzles are expediently partly
below the level of the metal bath and are connected to
feeds for reducing agents and/or oxygen. The lances may
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be arranged in the furnace in any manner which is known
to the person skilled in the art.
On account of the difference in density, the reduced
metal droplets settle at the bottom of the furnace in
the molten metallic iron, and like the slag can
advantageously be tapped separately from the furnace,
continuously or discontinuously, via a dedicated
tapping hole.
In addition to the iron-containing and heavy-metal-
containing remainder material(s), which has/have been
melted down and prereduced in the melting cyclone, and,
if appropriate, iron ore, some coarse fraction may be
charged directly to the furnace, preferably via a
dedicated feed which opens into the furnace, for
example in the top or a side wall of the furnace.
To maintain the temperature which is required in order
to tap off slag and molten pig iron, energy is supplied
to the furnace, and this also prevents premature
separation of the heavy metals in the region of the
furnace. The energy is preferably supplied in the form
of electrical energy, for example via a direct arc, to
the molten material. It has proven particularly
advantageous for the electrical energy to be supplied
by means of at least one electrode projecting into the
furnace; both direct current and alternating current
are possible.
The evaporated heavy metals, together with the furnace
off-gas, are afterburned directly at the gas outlet,
with the result that the heavy metals are converted
into a solid oxidic form which, after separation from
the remaining off-gas in a precipitation device, can be
fed for further processing.
If the products originating from the melting cyclone,
namely heavy-metal-containing gas and molten material,
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are firstly introduced into an intermediate chamber,
the heavy-metal-containing gas is introduced into the
furnace off-gas, which is extracted from the furnace
via the intermediate chamber, in this intermediate
chamber, whereupon the further treatment of the gases
takes place jointly.
The melting cyclone, the furnace vessel above the metal
level and, if appropriate, the intermediate chamber are
expediently equipped with evaporation cooling, with the
result that the radiant heat from the furnace and the
melting cyclone can be used to evaporate cooling water
and can therefore be recovered in the form of steam,
which can be used to save energy within a metallurgical
plant.
The same purpose is served by off-gas cooling,
preferably in a steam boiler, carried out following the
afterburning of the heavy-metal-containing gas and the.
furnace off-gas.
The utilization of the heat which is inherent to the
off-gas may advantageously also take place completely
or partially in a heat exchanger into which the off-gas
line of the furnace opens, it being possible to feed
the heated air to a dryer which dries iron-containing
and heavy-metal-containing, wet remainder materials or
slurries which are suitable for use in the melting
cyclone.
The invention is explained in more detail below with
reference to exemplary embodiments which are
illustrated in the drawing, in which Fig. 1 to 4 show
diagrammatic views of preferred embodiments of the
plant according to the invention.
In accordance with Fig. 1, coal, oxygen and iron-
containing and heavy-metal-containing remainder
materials and, if appropriate, iron ore in the form of
dust are introduced into a vertically arranged melting
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cyclone 1. The introduction takes place in such a
manner that the turbulence and the associated mass and
heat transfer processes in accordance with the
invention take place very quickly, with the result that
the melting and prereduction process overall has a high
space-time yield. The controlled release of the
substances which are to be introduced into the melting
cyclone 1 is effected by a metering device, which is
not shown but is known to the person skilled in the
art . The substances are blown into the melting cyclone
1 horizontally, preferably tangentially, via a
plurality of openings, which may be distributed over
the entire jacket of the melting cyclone.
Reduction of the iron-containing and heavy-metal-
containing remainder materials and, if appropriate, of
the iron ore takes place in the interior 2 of the
melting cyclone 1, iron being reduced at least to Fe0
and the heavy metals being reduced to the metal.
Furthermore, melting of the reduced iron-containing
material and conversion of the heavy metals into the
gas phase is achieved quickly and efficiently on
account of a cyclone-specific return flow.
An opening 3 in the bottom 4 of the melting cyclone 1
is formed by a constriction which causes the return
flow in the interior 2 of the melting cyclone 1 and
therefore allows minimal dusting to be achieved.
The melting cyclone 1 is directly connected to a
furnace 5 which is arranged beneath the melting cyclone
1. The melted products and the heavy-metal-containing
gas pass into the furnace 5 from above via a connecting
line 6.
In the furnace 5 there are a metal bath 7 (iron bath)
and a slag layer 8 which floats on the metal bath 7,
and these constituents are removed separately from the
furnace 5 via tapping holes 9 and 10. Furthermore,
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according to this embodiment, the furnace 5 has three
electrodes 11, 11', 11" which are immersed in the slag
layer 8 from above and supply the energy which is
required to maintain a liquid slag 8 and a metal bath 7
S in the form of arcs. In this example, the electrodes
11, 11', 11" are operated with alternating current,
although operation with direct current would also be
possible, in which case the furnace 5 would have only
one electrode 11.
Reducing agent and/or oxygen is introduced into the
furnace 5 via below-bath blowing nozzles 12 in a side
wall 13 of the furnace 5 or in the bottom 14. Some of
the blowing nozzles 12 are preferably arranged below
the metal bath level.
In addition, in the embodiment shown in Fig. 1 there is
a lance 15 for blowing in coal and oxygen, which
projects obliquely into the furnace S through the side
wall 13 of the furnace 5 and the lower end of which is
immersed in the slag layer 8.
Moreover, a feed 16 for a coarse fraction of a reducing
agent or a remainder material which can be introduced
if appropriate opens into the furnace 5.
The iron-containing molten material which is introduced
into the furnace 5 from the melting cyclone 1 is fully
reduced in the slag layer 8 with the aid of the
reducing agent and the oxygen, and the liquid iron is
separated out into the metal bath 7.
On emerging from the furnace 5, air is fed to the off-
gas and afterburning 21 is initiated. Some of the
energy content of the off-gas, which has been increased
in this way, is transferred to water in a heat recovery
steam generator 17, the heat content of the off-gas
being used to generate steam. An example for the
further use of the steam is a turbine generator 18
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which is used for current generation. However, other
possible uses for the steam which is generated are also
conceivable, for example use in the metallurgical plant
for cooling purposes, etc.
Following the boiler 17, the cooled off-gas is fed to a
filter 19, in which the condensed heavy metals, which
are in the form of dust, are separated from the
remaining off-gas.
The preferred embodiment illustrated in Fig. 2 differs
from the embodiment illustrated in Fig. 1 with regard
to the way in which the heavy-metal-containing gas and
the melted material from the melting cyclone 1 are
introduced into the furnace 5. In this embodiment, the
connecting line 6 opens out in the side wall 13 of the
furnace 5. The reducing agent and the oxygen are
introduced into the furnace 5 only via below-bath
blowing nozzles 12. The further treatment of the off-
gas after it leaves the furnace 5 is not shown in
further detail; it may take place in the same way as
that shown in Fig. 1.
In accordance with Fig. 3, the connecting line 6 opens
out in an intermediate chamber 20, which is designed as
an optionally widened (as illustrated by dashed lines)
off-gas line, so that the heavy-metal-containing gas
from the melting cyclone 1 does not need to flow
through the furnace 5, and the melted material is
already reduced further on the way into the furnace 5
by the reducing furnace off-gas . In this embodiment of
the plant according to the invention, the lance 15
which is used to blow in reducing agent and oxygen
projects into the furnace S from above. However, it may
also project through a side wall 13 into the furnace 5.
Fig. 4 shows the arrangement of melting cyclone 1 and
furnace 5 which is described in Fig. 1, but in this
case the heat which is inherent to the off-gas is only
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partially utilized in the heat recovery steam generator
17. The off-gas which is still hot undergoes heat
exchange in a recuperator 22 and is then, in the cooled
state, passed into the filter 19, where the above-
described separation of the heavy metals takes place.
The air which is heated in the recuperator 22 is fed to
a dryer 23 which is used to dry wet remainder materials
and slurries for use in the melting cyclone 1.
The process sequence according to the invention is
explained with reference to the following Examples 1, 2
and 3. The quantity data are in each case based on one
tonne of charge mixture without coal or additives
(lime) .
Example 1:
1000 kg/h of iron-containing and heavy-metal-containing
remainder materials, which had a composition as shown
in Table 1, and 105 kg/t of coal were introduced into
the melting cyclone with 112 m3/t (s.t.p.) of deliver
air, and were made turbulent using 250 m3/t (s.t.p.) of
oxygen. 5.4 m3/t (s.t.p.) of fuel gas (natural gas)
were supplied in order to ignite the solid/gas mixture
in the melting cyclone and to maintain a pilot flame.
Table 1
Example 1 Example Example
2 3
Charge Unit Remainder- Remainder-Iron ore
mixture material mix material
1
without iron mix 2 with
ore iron ore
Chemical
analysis
-A1Z03 % by weight 0.67 0.90 0.63
-C % by weight 7.9 15.2 -
-Ca0 % by weight 5.5 5.1 3.0
-Fe % by weight 10.0 0.70 -
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-Fe0 % by weight 34.4 20.1 -
-Fe203 % by weight 31.7 46.7 90.6
-Mg0 % by weight 1.69 1.1 0.36
-Mn0 % by weight - 0.10 0.17
-K + Na % by weight 0.15 0.24 0.04
-C1 + F % by weight 0.80 0.13 -
-Pb + Zn % by weight 0.30 1.7 0.01
-Si02 % by weight 3.13 3.6 4.0
-S % by weight 0.15 0.10 0.05
-P % by weight 0.15 0.10 0.05
The partially reduced iron was then fully reduced and
partially melted in the reduction furnace with 182 kg/t
of coal and 36 m3/t (s.t.p.) of oxygen. The amount of
delivery air for the solids blown in through lances or
nozzles was 45 m3/t (s.t.p.). The current consumption
of the furnace was 320 kwh/t.
576 kg/t of molten metal, 130 kg/t of slag and a
dedusted off-gas quantity of 12,140 m3/t (s.t.p.) were
obtained. 24 kg/t of heavy-metal-containing dust was
separated out of the off-gas. Furthermore, 737 kWh/t of
current were generated by utilizing the waste heat in a
steam generator.
The composition of the molten metal, of the slag, of
the off-gas and of the separated dust is given in Table
2. Examples 2 and 3 resulted in product compositions
which lay within the same range.
Table 2
Molten metal
-C % by weight 2.0 - 3.0
-Mn % by weight < 0.2
-Si % by weight 0.1 - 0.2
-S % by weight < 0.09
-P % by weight < 0.08
Slag
-Fe0 % by weight 3.0 - 6.0
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-Ca0 % by weight 38 - 44
-Si02 % by weight 30 - 36
-Mg0 % by weight 7.0 - 12
-A1203 % by weight 5.0 - 10
Off-gas
-C02 % by volume 6.5 - 7.5
-02 % by volume 16 - 17
-Hz0 % by volume 1.0 - 1.5
-Nz + Ar % by volume Remainder
Dust
-Fe0 % by weight 30 - 75
-Zn0 % by weight 5 - 50
-Pb0 % by weight < 5.0
-Si02 % by weight < 5.0
-Ca0 % by weight < 7.0
Example 2:
A quantity of 1000 kg/h of iron-containing and heavy-
metal-containing remainder materials and iron ore - the
composition of the charge mixture is given in Table 1 -
with 56 kg/t of coal was introduced into the melting
cyclone by means of 106 m3/t (s.t.p.) of delivery air
and was made turbulent using 270 m3/t (s.t.p.) of
oxygen. 5.1 m3/t (s.t.p.) of fuel gas were supplied.
The amount of reducing agent (coal) introduced into the
furnace was 151 kg/t, the amount of oxygen was 30 m3/t
(s.t.p.) and the amount of delivery air was 38 m3/t
(s.t.p.). The current consumption was 268 kWh/t.
480 kg/t of molten metal, 125 kg/t of slag, 11,900 m3/t
(s.t.p.) of dedusted off-gas and 36 kg/t of heavy-
metal-containing dust were obtained. The current
production was 684 kWh/t.
Example 3:
The charge product used was 1000 kg/h of iron ore
(composition: Table 1) with 290 kg/t of coal and
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136 m3/t (s.t.p.) of delivery air. Furthermore, 336 m3/t
(s.t.p.) of oxygen and 55 kg/t of lime were introduced
into the melting cyclone. The amount of fuel gas was
6.5 m3/t (s.t.p. ) .
To reduce the iron, 197 kg/t of coal were fed to the
furnace with 49 m3/t (s.t.p.) of delivery air and
38 m3/t (s.t.p.) of oxygen. The current consumption was
348 kWh/t.
The products obtained were 625 kg/t of molten metal,
139 kg/t of slag, 15,760 m3/t (s.t.p.) of dedusted off-
gas and 22 kg/t of dust. 945 kWh/t of current were
generated.
