Note: Descriptions are shown in the official language in which they were submitted.
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The invention relates to a method of recovering metals
or metal alloys, in particular ferro-alloys, by reducing
metal oxides in a reduction zone formed by a coal bed
flowed through by a reducing gas, as well as a plant for
carrying out the method.
` In EP-A - 0 174 291 a method of melting metals, i.e.
copper, lead, zinc, nickel, cobalt and tin, of oxidic fine-
grain non-ferrous metal ores is described, wherein the
charging material is charged into a reduction zone formed
by a coal fluidized layer in a meltdown gasifier. When
passing this reduction zone, the oxidic charging material
is reduced to metal, which is collected in the lower part
of the meltdown gasifier.
It has shown that the method according to EP-A 0
174 291 may advantageously be used for reducing oxides
reacting with elementary carbon at temperatures below
1,000C, yet that problems may occur when recovering metals
and metal alloys, in particular ferro-alloys/ such as
ferro~manganese, ferro-chromium and ferrosilicon, which
are recoverable from their oxides only at temperatures
exceeding 1,000C using elementary carbon as the reducing
agent, since the period of contact of this oxidic charging
materlal which reacts at higher temperatures, with the
carbon particles forming the fluidized layer is relatively
; ; short.
The invention aims at avoiding these disadvanta~es and
difficulties and has as its object to provide a method and
a plant of the initially defined kind which make it possib-
le to produce metals and metal alloys, in particular ferro~
alloys, such as ~erro-manganese, ~erro-chromium and ferro-
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silicon of lumpy oxidic charging material in a meltdown
gasifier, wherein the metal has such a high a~finity to
oxygen that it reacts with elementary carbon at above
1,000C only.
With a method of the initially defined kind this
object is achieved according to the invention in that,
under the action of gravity, lumpy oxidic charging material
is guided through a static coal bed comprised of three
layers, wherein
- a bottom layer of degassed coal is provided, which
covers a liquid sump of reduced metal and slag,
- into a middle layer, oxygen or an oxygen-containing
gas is introduced so as to form a hot reducing gas
consisting essentially of CO, and
- into a top layer, combustion gases of carbon par-
ticles and oxygen or oxygen-containing gas are in-
.,
troduced.
Advantageously, lumpy oxidic charging material havinga grain size of from 6 to 50 mm, preferably 10 to 30 mm, is
used.
For forming the static bed layers, suitably coal
having a grain size of ~rom 5 to 100 mm, in particular 5 to
30 mm, is used.
According to a preferred embodiment, the thickness of
; the middle and top static bed layers is maintained between
1 and 4 m.
A further embodiment o~ the method according to the
invention in characterised in that dust-like carbon parti-
cles are separated from the off-gas passing the static bed
layers (reduction zones) and that these carbon particles,
_ ~ _
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preferably in the hot state, together with oxygen or oxy-
gen-containing gas are fed to burners directed into the top
static bed layer.
As the coal, preferably coal maintaining its lumpy
character after degassing is used, so that with a grain
size range of from 5 to 100 mm, preferably 5 to 30 mm,
utilized, at least 50 ~ of the degassed coal formed after
degassing is present within the original grain size range
of from 5 to 100 mm or 5 to 30 mm, respectively, and the
remainder is present as undersize grain.
The method according to the invention offers the ad-
vantage that all known advantages of the reduction pro-
cesses in shaft furnaces heated with fossile energy are
maintained, such as counterflow-heat exchange, metallurgi-
cal reaction with elementary carbon in the static bed,
which is necessary for the xeduction of oxides of non-
precious metals, as well as a good separation of metal and
slag. Coking or degassing of coal may be carried out with-
out the formation of tar and other condensable compounds.
The gas formed during the degassing of the coal acts as
additional reducing agent to the reduction gases formed
from the gasification of the degassed coal.
A particular advantage of the method consists in that
the reduction of oxides of non-precious elements, such as,
e.g., silicon, chromium, manganese, can be effected without
using electric energy. In the method according to the
invention, the energy required for degassing the coal is
controlled in a simple manner, because the undersize grain
(smaller than 5 mm) is discharged with the hot of~-gases of
0 the meltdown gasifier, separated, returned into the upper
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blowing-in zone of oxygen-containing gases and oxidized by
means of the oxygen-containing gases, heat being released.
The grain decomposition behaviour is tested such that
a grain fraction of from 16 to 20 mm is subjected to de
gassing for one hour in a chamber which has been pre-heated
to 1,400C. The volume of the chamber is 12 dm3. After
cooling by flushing with cold inert gas, the grain distri-
bution is determined.
The invention furthermore comprises a plant for car-
rying out the method with a refractorily lined shaEt-shaped
meltdown gaslfier, which has, in its upper part, charging
openings for introducing coal and lumpy oxidic charging
m~t~:~ia~ w~l ~ a ~i~c~ye ~z~c~ ~or o~
wa~ ~ o~ ~he me~t~own yasi~ie~ 5~ein~ penetrate~ ~y s~pp~y
: ducts for coal and oxygen or oxygen-containing gas, respec-
: tively, and a lower section being provided for collecting
: molten metal and liquid slag. This plant is characterised ~ .
-~ in that, under formation of three superposed static bed
layers A, B, C
- in the region between the bottom static bed layer A
and t~ mi~lg ~t~ h~ ~ye~ B, ~ ~in~ of bloT~-in
pipes for oxygen or oxygen-containing g~s is pro-
vided and
- at a distance thereabove, in the region between the
middle static bed layer B and the top static bed
layer C, a ring of burners charged with carbon
particles and oxygen or oxygen-containing gas, re-
spectively, is provided.
Advantageously, a hot cyclone for separating carbon
particles from the off-gas is provided in the discharge
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duct for off-gas, and the discharge end of this hot cyclone
is in flow connection with the ring of burners.
The method and the plant of the invention for carrying
out the method are explained in more detail by way of the
drawing, which shows a schematic illustration of the melt-
down gasifier with additional means connected thereto.
A shaft-like meltdown gasifier denoted by 1 has a
refractory lining 2. The bottom region of the meltdown
gasifier serves for accommodating molten metal 3 and molten
slag 4. A tap opening for metal is denoted by 5, and a tap
opening for slag is denoted by 6. In the upper part of the
meltdown gasifier, a charging opening 7 for supplying lumpy
coal, as well as a charging opening 9 for lumpy oxidic
charging material are provided. Above the liquid sump 3, 4,
the static coal bed is formed~ i.e. a bottom layer A of
degassed coal which is not gas-passed, a middle layer B of
degassed coal provided thereabove and passed by gas, and a
top layer C of lumpy coal provided thereabove and passed by
gas.
The side wall of the meltdown gasifier 1 is penetrated
by blow-in pipes, i.e. by a ring of blow-in pipes 8 for
oxygen or oxygen-containing gases, respectively. These
pipes are arranged in the border region between the non-
~ gas-passed static bed layer A and the static bed layer B.
;~ At a distance thereabove, i.e. in the border region
between layer B and layer C, a ring of burners 10 pene-
trating the side wall of the meltdown gasifier 1 i5 pro-
vided, into which a mixture of dust-like carbon particles
and oxygen or oxygen-containing gas is introduced. From the
upper part of the meltdown gasifier, a discharge duct 11
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guides the off-gas formed to a hot cyclone 12.
Dust-like carbon particles suspended in the off-gas
are separated in the hot cyclone 12 and fed from the dis-
charge end of the hot cyclone 12, in which a dosing means
13 is provided, through a duct 14 to the burners 10
arranged in a ring. A duct for oxygen-containing gas
leading to the burners 10 is denoted by 15. With the dosing
means 13 the filling degree of the hot cyclone 12 can be
regulated and the separating effect of the hot cyclone 12
can be influenced. From the upper part of the hot cyclone
12 off-gas is discharged through duct 16.
Advantageously, the method according to the invention
is carried out such that coal and lumpy oxidic charging
material are commonly introduced through the charging open-
ings in the upper part of the meltdown gasifier 1. The coal
is degassed in the static bed layer C. The heat required
for degassing is provided, on the one hand, by the hot
reducing gases rising from the static bed layer B, and, on
the other hand, by combustion heat from the carbon partic-
20: les burned by means of oxygen-containin~ gases in the
: burners 10. The vertical extension of the layer C is selec-
ted such that the gas leaving layer C has a minimum tempe-
rature of 950C. Thereby it is ensured that tars and other
condensable compounds are cracked. Thus an obstruction of
the top static bed layer C becomes impossihle. In practice,
a layer thickness of from 1 to 4 m has proved to be ad-
vantageous for layer C. A vertical extension of from 1 to 4
m also proves to be advantageous for static bed layer B.
Coal degassed ln static bed layer C forms the static bed
layer B when it sinks down.
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The lumpy oxidic charging material is melted in static
bed layer B and reduced by the elementary carbon. The heat
required for melting and reducing is supplied by gassifying
hot degassed coal by means of oxygen-containing gases in~
troduced into the gasifier via the blow-in pipes 8. The
molten metal forming in static bed layer B and the molten
slag flow down and are collected and tapped below static
bed layer A.
