Note: Descriptions are shown in the official language in which they were submitted.
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Process for producing molten pig iron
The invention relates to a process for producing molten
pig iron, raw materials formed by iron ore, preferably
in the form of pieces and/or pellets, and, if
appropriate, additives, preferably limestone and/or
dolomite, being reduced to iron sponge in a reduction
zone, and the iron sponge being smelted in a fusion/
gassification zone with addition - of solid carbon
carriers and oxygen-containing gases to give molten pig
iron, and a reduction gas, which is at least partially
introduced into the reduction zone, being converted
therein and taken off as top gas, and slag being
formed. The invention further relates to a plant for
carrying out the process.
Such a process is known from DE PS 35 03 493. In this
process, a direct reduction shaft furnace is fed,
together with iron ore, with a carbon carrier which at
least partially reduces again those constituents of the
reduction gas which have been oxidized by the reduction
of the iron ore. This measure is intended, on the one
hand, to prevent the agglomeration of iron ore
particles and/or iron sponge particles, but mainly to
improve the heat balance of the fusion gassifier, so
that its effect on the direct reduction shaft furnace
is such that the quantity of gas containing CO and Hz
and thus the quantity of reduction gas are diminished.
The diminution of the quantity of reduction gas in a
direct reduction shaft furnace is, however, no longer
up to date. A substantial part of the economics of a
system consisting of fusion gassifier and direct
reduction shaft furnace results from the fact that the
top gas taken off from the direct reduction shaft
furnace can, if appropriate after gas scrubbing, be
used again as reduction gas and/or as calorifically
utilizable gas. Diminution of the quantity of reduction
gas thus also impairs the economics of such a process.
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In the reduction of some iron ores, the problem arises
that the interstitial volume per tonne of ore of the
charge in the bed of the raw materials does not suffice
for passing the quantity of reduction gas required for
the ore reduction through the reduction shaft. This can
have a number of causes: a high bulk density, or small
mean grain size of the ore, a broad grain size
distribution or a large proportion of fines, or
pronounced grain disintegration of the ore particles or
pellets during the reduction, or due to mechanical
stress. The interstitial volume is here to be
understood as the volume of the voids in a bed. An
unduly small interstitial volume results in
insufficient and/or fluctuating metallization of the
iron sponge since, in addition to the unduly small
quantity of reduction gas, the gas distribution within
the reduction shaft is also non-uniform. In fact,
channels can form within the bed, in which the
reduction gas flows preferentially, while other regions
obtain a gas flow which is no longer adequate, or none
at all.
In addition, the non-uniform gas distribution also
leads to a non-uniform temperature distribution in the
bed, which adversely affects the calcination of the
additives, such as limestone and/or dolomite, contained
in the raw materials. Since the metallization and/or
calcination, which has not been achieved in the direct
reduction shaft furnace, must eventually be completed
in the fusion-gassifier, this also leads to a reduction
in the smelting performance of the fusion-gassifier and
to a plant operation which is altogether unstable.
EP 0,623,684 A has disclosed a process in which waste
materials and residues containing coal dust and iron in
the metallic form and oxide form are separately
collected and agglomerated in three groups in
accordance with their composition, the first group
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mainly containing iron in the oxide form, the second
group mainly containing iron in the metallic form and
the third group mainly containing carbonaceous
substances. These are utilized by feeding the
substances of the first group to the reduction zone and
those of the second and third groups to the fusion
gassification zone.
The use of, in particular, agglomerates containing iron
oxide in the reduction zone is, however, not a suitable
method for increasing the voidage in the bed, since
these agglomerates tend to lead to grain disintegration
and have an unduly low mechanical stability.
It is the object of the invention to provide a process,
in which a quantity of reduction gas, increased as
compared with the state of the art, can be passed
through the reduction shaft and a degree of
metallization and calcination, which is both increased
and made more uniform, of the iron sponge and the
additives respectively, is achieved owing to a gas
distribution which has been made more uniform.
According to the invention, this object is achieved in
such a way that, together with the raw materials,
further lumpy additives, which are substantially inert
under the reaction conditions of~the reduction zone,
are fed to the reduction zone.
In this connection, "inert" is to be understood as an
essentially chemical inertness, that is to say the
further additives react with the reduction gas and to
the raw materials only to a negligible degree or not at
all. Moreover, "inert" is also to be understood as
being essentially completely resistant to thermal and
mechanical stresses. The expulsion of small quantities
of gases such as COZ and/or HZO is, however, possible.
The further additives thus do not tend to suffer grain
disintegration or increased erosion either due to the
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shock-like heating occurring on introduction into the
reduction zone or owing to the remainder of the bed
lying above them in the further course of the reaction.
The further additives migrate essentially unchanged
through the reduction zone. The interstitial volume per
tonne of ore in the bed is increased by the addition of
inert lumpy additives.
According to a preferred embodiment of the process
according to the invention, it is possible thereby to
pass an increased quantity of reduction gas from the
fusion gassification zone through the reduction zone.
The quantity of reduction gas is then about 5 to 50s,
preferably 20 to 40~, greater than the quantity
required for reducing the iron ore. Owing to the
increased interstitial volume, the formation of
channels and instances of caking within the bed is also
diminished and therefore the gas distribution is also
made more uniform, again with the result of an overall
enhanced and more uniform metallization and calcination
of the raw materials.
Advantageously, the further additives used are coke,
which is substantially inert under the reaction
conditions, and/or carriers of slag constituents, the
main constituents being Ca0 and/or Mg0 and/or SiOZ
and/or A1203.
Whereas it is explicitly demanded in the state of the
art described above that the coke charged to the direct
reduction shaft furnace reacts at least partially with
the reduction gas, this is not desired in this case
since the mean grain size of the further additives
should not change during the passage through the
reduction zone. Such a coke, as used according to the
invention, is rendered inert, for example, by a thin
layer of ash. In the case of the carriers of slag
constituents likewise used according to the invention,
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the problem of the reaction with the raw materials or
the reduction gas does not arise.
According to a preferred embodiment, quartz and/or slag
from a steel converter and/or a blast furnace and/or an
electric furnace and/or from the fusion gassification
zone are used as further additives.
In addition to the outstanding suitability of these
materials for the process according to the invention,
the use of slag also leads to the utilization of at
least a part of slags arising in the iron and steel
industry. Hitherto, these stags had either to be dumped
or, at best, could be used further in the building
materials industry.
Accordingly, the use of slag from a steel converter, in
particular a steel converter operated by the LD
process, is particularly preferred. These stags have an
especially low phosphorus content and therefore do not
cause any additional introduction of phosphorus into
the fusion gassification zone which follows the
reduction zone.
Advantageously, the mean grain size of the further
additives is 6 to 40 mm, preferably 10 to 25 mm. This
range of grain sizes essentially corresponds to that of
the remaining raw materials and therefore makes it
possible to enhance the gas permeability of the bed and
makes this more uniform.
According to a further advantageous embodiment of the
process according to the invention, the volume of the
further additives, relative to the total volume of all
the materials fed to the reduction zone, is 5 to 30%,
preferably 5 to 20%. In this range, there is an optimum
of gas permeability of the bed in the reduction zone,
the degree of metallization and/or calcination of the
raw materials, of the achievable reduction performance
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of the reduction zone and also of the smelting
performance of the fusion gassification zone.
The invention also relates to a plant for carrying out
a process for producing molten pig iron from raw
materials formed from iron ore, preferably in the form
of pieces and/or pellets and, if appropriate,
additives, preferably limestone and/or dolomite,
comprising a reduction reactor for iron ore, a fusion-
gassifier, a feed line, connecting the fusion gassifier
to the reduction reactor, for a reduction gas formed in
the fusion gassifier, one or more conveying lines,
connecting the reduction reactor to the fusion-
gassifier, for the reduction product formed in the
reduction reactor, a top gas discharge line starting
from the reduction reactor, a feed line, leading into
the fusion gassifier, for carbon carriers, and also
feed lines, leading into the fusion gassifier, for
oxygen-containing gases, and a tapping for pig iron and
slag provided on the fusion gassifier.
Such a plant is characterized in that a charging device
for the addition of further lumpy additives, which are
substantially inert under the reaction conditions
prevailing in the reduction reactor, is provided on the
reduction reactor.
According to a preferred embodiment, means for
controlling the volume flow of top gas taken off from
the reduction reactor are provided in the top gas
discharge line. These means can be designed as, for
example, an adjustable flap. By means of controlling
the volume flow of top gas, the volume flow of
reduction gas, increased according to the invention,
into the reduction reactor is at the same time also
adjusted.
Advantageously, a discharge line branches off from the
reduction gas feed line which connects the fusion-
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gassifier to the reduction reactor and through which
that proportion of the reduction gas is withdrawn which
is not fed to the reduction reactor. Preferably, a
pressure control instrument is provided in this
discharge line, which instrument is usually preset to a
defined pressure, so that reduction gas is removed from
the system when this pressure is exceeded.
Advantageously, the charging device for the further
additives includes a weighing device, by means of which
the desired quantitative ratio relative to the
remaining raw materials is adjusted.
The process according to the invention is explained in
more detail below by reference to an illustrative
embodiment:
Raw materials in the shaft, without inert material:
150 tonne/hour of ore
15 tonne/hour of limestone
10 tonne/hour of dolomite
157,000 m3/hour of reduction gas
Voidage: about 45s
Degree of metallization of the Fe sponge: about 800
Degree of calcination of the additives: about 80%
Derived characteristic process data:
Reduction gas/m3 of charge: ~ about 2050
m3
Reduction gas/tonne of ore or pellets: about 1050
m3
Raw materials in the shaft with inert material:
140 tonne/hour of ore
5.5 tonne/hour of dolomite
28.5 tonne/hour of LD slag
166,000 m3/hour of reduction gas
Voidage: about 450
Degree of metallization of the Fe sponge: > 900
Degree of calcination of the additives: > 85%
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Derived characteristic process data:
Reduction gas/m3 of charge: about 2050 m3
Reduction gas/tonne of ore or pellets: about 1180 m3,
that is to say
specifically
about 12% more
gas
Gas volumes refer in each case to the standard state,
that is to say 273.15 K and 101,325 Pa.
The invention is explained in more detail below by
reference to an illustrative embodiment shown in the
drawing in Figure 1, the drawing illustrating, in a
diagrammatic representation, a preferred embodiment of
the plant for carrying out the process according to the
invention.
Lumpy raw materials containing iron oxide, such as ore
4, if appropriate with uncalcined additives 5, such as
limestone and/or dolomite, are charged from above via a
feed line 3 to a reduction reactor designed as a shaft
furnace 1, that is to say into the reduction zone 2
thereof. The shaft furnace 1 is connected to a fusion-
gassifier 6, in which a reduction gas is generated from
carbon carriers and oxygen-containing gas, which
reduction gas is fed via a feed line 7 to the shaft
furnace 1 and flows through the~latter in counter-
current to the raw materials 4, 5.
Moreover, further additives 8 are introduced into the
reduction reactor 1 by means of a charging device 9.
The charging device is fitted with a weighing device,
by means of which the quantitative ratio or the volume
ratio of the further additives 8 relative to the raw
materials 4, 5 is controlled.
The fusion gassifier 6 has a feed line 10 for solid
lumpy carbon carriers 11 and feed lines 12 for oxygen-
containing gases. In the fusion gassifier 6, molten pig
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iron 14 and molten slag 15 accumulate below the fusion-
gassification zone 13 and are tapped via a tapping 16.,
The raw materials 4, 5, partially or wholly reduced to
iron sponge in the shaft furnace 1 in the reduction
zone 2 are fed to the fusion gassifier 6 via one or
more conveying lines 17, for example by means of
conveyor screws. The upper part of the shaft furnace 1
is adjoined by a discharge line 18 for the top gas
formed in the reduction zone 2. The top gas discharge
line 18 contains means 19, for example an adjustable
flap, for controlling the volume flow of the top gas
taken off from the shaft furnace 1. The means 19
provided in the top gas discharge line 18 also control
the volume of the reduction gas introduced via the
reduction gas feed line 7 into the shaft furnace 1.
From the reduction gas feed line 7, a discharge line 20
branches off, through which reduction gas which is not
passed into the reduction reactor 1 is taken off. The
discharge line 20 can contain a pressure control
instrument 21. The pressure control instrument 21 is
usually preset to a defined pressure, so that reduction
gas is removed from the system when this pressure is
exceeded.
The volume of the reduction gas fed to the shaft
furnace 1 is controlled by the interaction of the
pressure control instrument 21 and the means 19 for
controlling the volume flow.
The invention is not restricted to the illustrative
embodiment shown in Figure 1, but also comprises all
means known to those skilled in the art, which can be
utilized for carrying out the invention.
