Note: Descriptions are shown in the official language in which they were submitted.
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Process for producing liquid pig iron and/or primary
steel products
The invention relates to a process for
producing liquid pig iron and/or primary steel products
from charge materials formed by iron-oxide-containing
substances and additions if required, preferably in the
form of pieces and/or pellets, the charge materials
being reduced to iron sponge in a reducing zone, the
iron sponge being smelted in a fusion gasifying zone
supplied with dried solid carbon carriers and with
oxygen-containing gases, and a CO- and HZ-containing
reduction gas being generated, which gas is introduced
into the reducing zone, converted there and drawn off
as top gas from the reducing zone and subjected to gas
scrubbing, and if required is supplied to a consumer as
export gas. The invention also relates to a plant for
carrying out the process according to the invention.
It is known that, for gasifying in fusion
gasifiers, to improve the energy balance of the latter
carbon carriers have to be dried from an average
moisture content (<_ 15~). Without drying, hindrances
to the transport of the carbon carriers occur, and the
endothermic effect of the moisture content causes a
deterioration in the energy balance and an influence on
the composition of the gas generated. Without drying
the carbon carriers to be gasified, the proportion of
reducing constituents in the gas generated can be
increased only by increasing the energy input, i.e.
increasing the amount of oxygen to be blown into the
fusion gasifier.
In Austrian Patent 380 697 it is proposed to
preheat coal with drawn-off blast-furnace gas. This
entails increased expenditure for the construction and
operation of such a plant, since additional influences
during the operation of the fusion gasifier, and of the
reduction furnace, have to be taken into account. What
is more, part of the energy of the blast-furnace gas is
used up in drying the coal and consequently reduces the
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efficiency of the plant.
EP 0 498 289 Al discloses a process for drying
coal supplied to fusion or coal gasifiers by using
excess energy produced in co-operation with a gas- and
steam-turbine power station. For this purpose, excess
energy is taken from an auxiliary unit and supplied to
a coal drier via a fluid by heat extraction. The
excess energy can in this case also be taken, inter
alia, from the top gas of a reduction furnace. What is
disadvantageous about this process is that the excess
energy, for example of the top gas, is supplied to the
actual drying medium via altogether a double heat
exchange. This requires increased expenditure for
setting up and operating such a plant and lessens the
efficiency due to the unavoidable heat losses during
heat exchange. What is also disadvantageous about the
proposed process is that a drier is used for the drying
of the coal. On the one hand, this requires increased
expenditure on equipment and operation, on the other
hand it involves heat losses of the dried and preheated
coal during its transport from the drier into the
gasifier.
The object of the present invention is
therefore to provide a process of the type mentioned at
the beginning which avoids or significantly reduces the
disadvantages specified above of the prior art.
In particular, the process is to ensure
effective, energy-utilizing coal drying and preheating,
and at the same time require lower expenditure on both
equipment and operation. The sensible heat of the
dried and heated carbon carriers is to be used in this
case for improving the energy balance of the fusion
gasifier.
This object is achieved according to the
invention by the top gas drawn off from the reducing
zone undergoing heat exchange with a gaseous heat
exchange fluid - before the said gas is scrubbed - and
by solid carbon carriers, which are intended for being
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supplied into the fusion gasifying zone, being dried
with the heated heat-exchange fluid.
Since the heated heat-exchange fluid is brought
directly into contact with the carbon carriers to be
dried, optimum energy utilization is ensured. By
appropriate arrangement of the heat-exchanging and
drying operation in close proximity to each other, line
losses can be kept low.
It is expedient if an inert gas or inert gas
mixture, which, under the conditions of the drying of
the carbon carriers, behaves in a chemically inert
manner with respect to the latter and to the reduction
gas, is used as the heat-exchange fluid.
In an advantageous embodiment, nitrogen, in
particular industrial nitrogen, as obtained from an
air-separation plant, is used for this. Such
industrial nitrogen is preferred, since, on account of
its negligible oxygen content, higher drying
temperatures can be achieved, and consequently
altogether less heat-exchange fluid is required. In
addition, large amounts of oxygen, and consequently an
air-separation plant, are generally required in any
case for the smelting reduction process. Therefore,
nitrogen is readily available and inexpensive.
According to a further advantageous embodiment,
cooled and cleaned process gas, which is expediently
formed from CO- and HZ-containing reduction gas, for
example from a partial flow of the export gas, is used
as the heat-exchange fluid.
The process according to the invention is thus
not restricted to the use of nitrogen or export gas as
the heat-exchange fluid. In principle, every process-
derived gas can be used as a heat-exchange fluid,
provided that, as specified above, it behaves in an
adequately inert manner. Furthermore, the gas to be
used as the heat-exchange fluid must be adequately
clean, in particular free from dust.
The drying of the solid carbon carriers
advantageously takes place in a way known per se by a
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counterflow process. In this way, the heat content of
the heat-exchange fluid can be utilized in a
particularly energy-saving manner. Other drying
processes, which operate for instance by the cross- or
uniflow process, can also be used however.
Expediently used as the solid carbon carriers
to be dried, or intended for use in the fusion
gasifying zone, are carbon carriers in piece form, in
particular coal and/or coke in piece form and/or
carbon-containing pellets and/or carbon-containing
briquettes.
The piece size of the carbon carriers is in
this case about 8 to 50 mm. Smaller or larger piece
sizes are, on the one hand, not appropriate for the
requirements of the fusion gasifying zone, but in
particular with smaller piece sizes there is no longer
adequate gas permeability of the carbon carriers, with
larger piece sizes a homogeneous drying effect of the
process according to the invention is no longer
ensured.
According to a preferred embodiment of the
process according to the invention, the heat-exchange
fluid is circulated between the heat-exchanging
operation and the drying operation. Since the heat-
exchange fluid emerging from the drying of the carbon
carriers is laden with a certain dust burden, it is
expediently subjected to gas scrubbing after the drying
step.
Those amounts of heat-exchange fluid which are
lost from the cycle either during the drying operation
or in the gas scrubbing are replaced by a continuous
supply of heat-exchange fluid into the cycle.
According to a further advantageous embodiment
of the process according to the invention, the top gas
is dedusted in the hot state, in particular is hot
filtered, before it undergoes heat exchange with the
heat-exchange fluid. Since the top gas emerging from
the reducing zone is laden with a high dust burden, the
known problems of clogging and plugging of the heat
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exchanger may result from this. These problems can be
effectively obviated by hot deducting of the top gas.
The temperature of the heat-exchange fluid,
after it has undergone heat exchange with the top gas,
is expediently adjusted to a permissible temperature
range. This temperature range is dependent on the type
of coal used and is about 100 - 200 °C.
The adjusting of this temperature range
advantageously takes place by supplying a partial flow
of heat-exchange fluid which has not undergone heat
exchange into the heated heat-exchange fluid, the
temperature of the resulting mixed gas being measured
and the supply of heat-exchange fluid which has not
undergone heat exchange being controlled in dependence
on this.
The invention also relates to a plant which is
suitable for carrying out the process according to the
invention.
Such a plant for producing liquid pig iron
and/or primary steel products from charge materials
formed by iron-oxide-containing substances, and
additions if required, preferably in the form of pieces
and/or pellets, having a reduction reactor for iron
oxide-containing substances, a fusion gasifier, a
supply line connecting the fusion gasifier to the
reduction reactor for a reduction gas formed in the
fusion gasifier, the supply line being provided with a
gas-cleaning device, having a feed line connecting the
reduction reactor to the fusion gasifier for the
reduction product formed in the reduction reactor,
having a top-gas removal line, leading from the
reduction reactor and provided with a scrubber, having
a charging bunker for solid carbon carriers, having a
feed line for solid carbon carriers connecting the
charging bunker to the fusion gasifier, having supply
lines for oxygen-containing gases opening into the
fusion gasifier and a run-off for pig iron and slag,
provided on the fusion gasifier, is characterized in
that in the top-gas removal line there is provided a
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heat exchanger and the heat exchanger is connected on
the output side to the charging bunker via a line for
heated heat-exchange fluid and the heat exchanger is
provided on the input side with a supply line for heat
s exchange fluid.
By means of this plant according to the
invention it is possible for the first time to use the
sensible heat of the top gas without appreciable heat
losses for drying the solid carbon carriers intended
for the fusion gasifier. In addition, the plant
according to the invention makes it possible for the
first time to do without a separate drier for the solid
carbon carriers, since the drying is carried out
directly in the charging bunker. This also makes it
15~ possible for the first time to use the sensible heat of
the dried and heated carbon carriers in the fusion
gasifier for improving the energy balance of the
latter, since heat losses which occur during transport
from a drier into the charging bunker likewise no
longer occur.
According to a preferred embodiment of the
plant according to the invention, the charging bunker
is connected by means of a return line to the supply
line of the heat-exchange fluid. This makes it
possible to circulate the heat-exchange fluid largely
without volume losses.
In an advantageous way, the return line
connecting the charging bunker to the supply line has a
gas-cleaning device, in particular a gas scrubber.
Since the heat-exchange fluid leaving the charging
bunker has a certain dust burden and a moisture
content, it is advantageous to dedust the heat-exchange
fluid before entry into the heat exchanger and to expel
the moisture from the cycle. This also has the effect
that a blower arranged in this line is protected from
the abrasive action of entrained dust.
According to a further feature of the plant
according to the invention, in the top-gas removal line
there is provided upstream of the heat exchanger a hot-
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gas filter, in order to dedust the top gas before its
entry into the heat exchanger and to avoid the problems
resulting from such a dust burden, such as for example
plugging and blockages of the heat exchanger.
The plant according to the invention
expediently has a temperature bypass line which
contains a control valve and connects the line for
heat-exchange fluid to undergo heat exchange to the
line for heated heat-exchange fluid. In dependence on
the desired final temperature of the heat-exchange
fluid, the mixture of the two heat-exchange fluid flows
is controlled by means of the control valve.
The process according to the invention, and the
plant according to the invention, are explained in more
detail below with reference to the exemplary embodiment
schematically represented in Figure 1. v
A reduction reactor designed as a shaft furnace
1, i.e. its reducing zone 2, is charged from above, via
a supply line 3, with iron-oxide-containing charge
materials in piece form, such as ore 4, if required
with uncalcined additions 5. The shaft furnace 1 is in
connection with a fusion gasifier 6, in which a
reduction gas is generated from carbon carriers and
oxygen-containing gas, is supplied via a supply line 7
to the shaft furnace 1 and flows through the latter in
counterflow with respect to the charge materials 4, 5.
In the supply line 7 there is provided a gas-cleaning
device 8. For temperature adjustment, the reduction
gas has cooled reduction gas added to it (not shown).
Undried, solid carbon carriers 10 in piece form
are fed from a storage bunker 9 into a charging bunker
11, where they are dried. The dry carbon carriers 12
are fed via a feeding means 13 into the fusion gasifier
6, or the fusion gasifying zone 14 of the latter.
The fusion gasifier 6 has supply lines 15 for
oxygen-containing gases. In the fusion gasifier 6,
molten pig iron 16 and molten slag 17 collect
underneath the fusion gasifying zone 14 and are tapped
via a run-off 18.
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The charge materials 4, 5 partly or fully
reduced to iron sponge in the shaft furnace l, in the
reducing zone 2 of the latter, are supplied to the
fusion gasifier 6 via one or more feed lines 19, for
example by means of feed screws. The upper part of the
shaft furnace 1 is adjoined by a removal line 20 for
the top gas produced in the reducing zone. This top
gas is directed to a gas-cleaning means, designed as a
scrubber 21, for the purpose of being freed from
residual dust and water vapour.
The top gas cleaned in the scrubber 21, after
COZ elimination if required (not shown), is available
to a further consumer as export gas.
Provided upstream of the scrubber 21 in the
top-gas removal line 20 is a heat exchanger 22, to
which heat-exchange fluid is supplied via a supply line
23 by means of a blower 24 arranged therein. Arranged
upstream of the heat exchanger 22 in the top-gas
removal line 20 is a hot-gas filter 25, by which the
top gas is dedusted before its entry into the heat
exchanger 22.
Heated heat-exchange fluid is supplied via a
line 26 to the lower part of the charging bunker 11.
The cooled heat-exchange fluid is drawn off from the
charging bunker 11 via a return line 27, supplied to a
gas scrubber 28, drawn off from the latter and re-
introduced into the supply line 23.
From the supply line 23 there branches off a
temperature bypass line 29, via which the admixing of
cold heat-exchange fluid into the line 26 is controlled
by means of a control valve 30 located in the said
bypass line.
The invention is not restricted to the
exemplary embodiment represented in Figure 1, but also
covers all means known to a person skilled in the art
which can be used for implementing the invention.
