Process for producing metal from metal ores

The invention concerns a process for producing metal from metal ores, in particular crude or pig iron from iron ore, wherein the ore which contains metal oxides is brought into contact with a reducing gas which contains carbon and/or hydrogen from solid, carbon-bearing and/or hydrocarbon-bearing substances obtained at least partially from plastic waste. According to the invention, the carbon-bearing and/or hydrocarbon-bearing substances are injected in comminuted fluidized form as an agglomerate into the air flow in the hearth of the metallurgical shaft or pit furnace, in particular a blast furnace. The apparatus includes a first shut-off device that is closed when blockages of the plastic material occur in the transport conduit or the lance, a second shut-off device that is closed when hot air penetrates into the transport conduit and/or the lance by reverse flow, and a third shut-off device that is closed when compressed air is supplied to a lance for cooling.

CROSS-REFERENCE TO RELATED APPLICATION
 This application claims the priority of Patent Application No. 19859354.6
 filed on Dec. 22, 1998 in Germany, the subject matter of which is
 incorporated herein by reference.
 FIELD OF THE INVENTION
 The Invention concerns a process and an apparatus for producing metal from
 metal ores, in particular crude or pig iron from iron ore, in which the
 ore which contains metal oxides is brought into reaction contact with a
 reducing gas which contains carbon and/or hydrogen (and possibly compounds
 thereof) and which was previously obtained from solid, carbon-bearing
 and/or hydrocarbon-bearing substances.
 BACKGROUND OF THE INVENTION
 It is known that the ore which for the major part comprises metal oxides
 (being various ones, even in the case of iron) must be subjected to a
 reduction procedure before the metal can be obtained. That reduction
 operation is effected by means of carbon and possibly hydrogen--or also
 compounds thereof--which are contained in a reducing gas which is caused
 to act on the metal ore.
 The reduced metal ore then passes into a smelting procedure. In that case,
 the gas required for the reduction operation is obtained in the region of
 the reducing and smelting procedure itself, by carbon-bearing substances
 (for example coke, coal, oil, natural gas) being added to the zone of the
 metal which has already been reduced and heated, whereby, with the
 addition of oxygen (in the air), they are broken up or converted in
 carbon-bearing gas which is fed to the preceding reduction operation.
 The conventional blast furnace process is known in that respect, in which
 both reduction of the metal ore and also formation of the reducing gas as
 well as subsequent smelting liquifaction of the metal occur in the blast
 furnace--progressively in a downward direction. In that blast furnace
 process, among additive substances, coke is possibly mixed with the iron
 ore, as a carbon carrier. It is known for oil or carbon also to be
 injected by way of lances into the air flow in the region of the hearth of
 the blast furnace for better control of the blast furnace process and to
 save on coke, the consumption of coke thereby also being reduced. This
 material (oil or coal dust) which is additionally injected must be
 introduced in very finely distributed form in order to ensure clean
 adequate gasification. Two articles in the journal "Stahl and Eisen", No 4
 of Feb. 25, 1985, pages 211-220 contain summaries relating to the
 injection of coal dust into blast furnaces. The injection of coal dust was
 forced upon operators in particular in the course of rising oil prices. In
 that respect it was found that when adopting the injection procedure,
 because of the short time available of about 10 ms, good results, more
 specifically almost complete gasification of the coal dust, were achieved
 only with grain sizes of below 0.1 mm., even if tests were also
 successfully carried out with some installations, using larger grain
 sizes.
 It has also already been proposed that, instead of injecting oil and coal
 dust, other carbon-bearing waste substances such as, for example, dried
 sewage sludge or other carbon-bearing waste such as refuse, waste paper,
 lignite, as well as waste from wood, plastic material, rubber or the like
 can be introduced (DE-A 29 35 544). In regard to appropriate tests or
 results however, all that was put forward were assumptions as to the
 manner in which such substances are to be introduced into the blast
 furnace. DE-A 41 04 252 also proposes introducing plastic-bearing waste
 substances into a blast furnace in a fine-grain or dust form by way of the
 tuyeres, with the introduction of sewage sludge (dust capable of trickle
 flow) being referred to by way of example. It is expressly emphasized that
 this process also requires that the substance, which is to be injected, be
 of a fine-grain nature.
 SUMMARY OF THE INVENTION
 Taking the known process as set forth in the opening part of this
 specification as its basic starting point, the object of the invention is
 to make plastic waste, including in organically and/or inorganically
 contaminated form, useable as a supply for the constituents of the
 reducing gas. Plastic waste occurs constantly in large amounts and
 represents a serious disposal problem. It occurs mostly if not exclusively
 in solid form, either as packaging waste--which is frequently heavily
 contaminated--or as offcuts or the like in the course of the production of
 plastic articles.
 Accordingly the invention provides that the carbon-bearing and/or
 hydrocarbon-bearing substances, at least partially comprising plastic
 material, which in the process of the general kind set forth in the
 opening part of this specification are supplied to obtain the reducing
 gas, are injected in comminuted fluidised form as an agglomerate into the
 air flow in the hearth of the metallurgical shaft or pit furnace, in
 particular a blast furnace. That is effected by way of lances which
 project into the shaft furnace and which are connected to a transport
 conduit. The plastic material to be injected is fed to the lances by way
 of that transport conduit. In the event that, contrary to expectation,
 blockages should occur or hot air should blow back out of the blast
 furnace into the lance and thus into the transport conduit, a plurality of
 shut-off or check devices are proposed in the transport conduit, so that
 the transport conduit is not only protected but immediate resumption of
 overall operation of the installation and injection of the plastic
 materials occurs. To dissolve blockages of the plastic material in the
 transport conduit, there are provided a first and third shut-off device,
 while a second shut-off device is provided to prevent reverse
 transportation of plastic material or blow-back of the hot gas masses from
 the blast furnace into the transport conduit. The mode of operation
 thereof is set forth in greater detail in the claims but in particular
 also in the specific description.
 To dissolve blockages in the transport conduit, the invention makes use of
 the fact that the pressure in the transport conduit is a pressure which is
 4 to 6 times atmospheric pressure. If therefore the pressure in the
 interior of the transport conduit is reduced to atmospheric pressure
 (about 1 bar) by way of a vent opening, a very great pressure and suction
 effect is applied to the blockages which are released and conveyed out of
 the system from the transport conduit.
 So that the injection lances which project into the blast furnace do not
 overheat when the injection installation in a stopped condition, there is
 provided a connection for compressed air which is always activated.
 Further advantageous configurations of the invention are set forth in the
 claims.

DETAILED DESCRIPTION OF THE INVENTION
 Referring to FIG. 1. shown therein is a blast furnace 1 which is of the
 usual structure and which in the lower hearth region has a plurality of
 nozzles or tuyeres 20 (see FIG. 3) which are distributed uniformly around
 the periphery and to which air 3 heated in an air heater 4 is fed by way
 of a conduit 5 and a ring conduit or manifold 2. In addition the air 3 can
 also be enriched with oxygen 3a (O.sub.2). For the sake of simplicity,
 only one nozzle 20 is indicated in FIG. 1.
 Some or all of the nozzles 20 have one or more lances 18, by way of which
 the additional fuel can be injected. In the previously known blast
 furnaces, the additional fuel was either coal dust or oil, whereby it was
 possible to achieve an improved operating performance for the blast
 furnace 1 and a saving on coke. The usual number of nozzles 20 of the
 tuyere arrangement is for example 32 and each nozzle is of a diameter of
 for example 140 mm. In regard to the feed of coal dust or oil, there are
 usually two lances which are of a diameter of typically 12 or 8 mm. In the
 present case there is in each nozzle 20 only one lance 18 for the feed of
 fluidised plastic material, and it is for example of a diameter of 28 mm.
 In the tuyere arrangement, either all lances 18 can be supplied with
 fluidised plastic material, or the nozzles 20 are equipped in a mixed or
 hybrid fashion, that is to say some nozzles have for example two oil
 lances while other nozzles 20 are in turn equipped with a plastic material
 lance 18. It is however desirable for the distribution of plastic material
 lances 18 and oil lances to be uniform around the periphery of the tuyere
 arrangement.
 In the present embodiment preparation and processing of the plastic
 material is effected in the following manner:
 From a plastic material preparation installation 6, comminuted plastic
 material is fed to a silo 7, in the form of an agglomerate of high
 specific surface area and with a grain size of 1 to 10 mm, preferably
 about 5 mm. The use of plastic material which results in an agglomerate
 with a bulk density of greater than 0.35 has proved itself worthwhile.
 Plastic material packaging cartons or the like are suitable for these
 purposes while for example plastic films or sheets, upon comminution
 thereof, result in a lower bulk density, so that special precautions must
 be taken prior to or upon injection, in order to be able to inject an
 adequate quantity.
 FIG. 1 shows an injection vessel 8 into which the plastic material
 agglomerate is introduced by way of a course grain sieve 14 and fluidised
 by the injection of a fluidisation gas by means of a blower 11 by way of
 conduits 12 and 13. With an injection vessel having a volume for example
 of 3 m.sup.3, about 2 to 25 m.sup.3 of fluidisation gas/h is required. The
 fluidised plastic material is then metered by way of a separate metering
 device 9, for example a mechanical screw-type metering device or a
 cell-wheel metering device, and uniformly fed by way of a conduit 10 to
 the appropriate lances 18 of the tuyere arrangement. In this case, the
 plastic material particles are conveyed by means of flying flow
 conveyance, that is to say with a high proportion of gas, for example with
 a ratio of 5 to 30 kg of plastic material per 1 kg of fluidisation gas. In
 the present example air under pressure is used as the fluidisation gas as
 there is no risk of explosion, due to the size of the plastic material
 particles of from 1 to 10 mm.
 The amount of plastic material injected can be varied over wide limits (for
 example 30-150 kg of plastic material/t pig iron). It was also found that,
 with equally good gasification, an amount of plastic material in
 comparison with oil, that is higher by a factor of 1.5, can be injected.
 If the injection amount of plastic material is above 70 kg/t pig iron,
 then O.sub.2 is preferably added to the air flow for the purposes of good
 gasification, as already mentioned above. For each kg of plastic
 material/t pig iron above the value of 70 kg/t pig iron, the air should be
 enriched with 0.05 to 0.1% O.sub.2 preferably 0.08%. For a good
 gasification effect the mixed air temperature from the air heater 4 is
 above 1100.degree. C. The injection pressure at the lances 18 is desirably
 0.5.times.10.sup.5 to 1.5.times.10.sup.5 Pa above the pressure in the
 blast furnace 1.
 As plastic material melts at relatively high temperatures--in contrast to
 coal dust or oil--there is the danger of the plastic material suffering
 from baking-on phenomena before Issuing from the injection lance 18 due to
 heat being radiated back from the nozzle. For that reason the flow speed
 of the gas with the plastic material particles in suspension must be
 sufficiently high, in comparison with the tube cross-section of the lance
 18, to prevent the plastic material from starting to melt or fuse on and
 thus suffer from baking phenomena in the lance 18 due to heat being
 radiated back. A suitable ratio of the flow speed to the lance
 cross-section is in the range of 20000 to 40000 l/sec.times.m, preferably
 about 25000 l/sec.times.m. If that ratio is too low, there is the risk of
 baking phenomena occurring, while if the value is too high, a excessive
 wear occurs in the lances 18. In addition, in all transport conduits,
 particularly in the connecting region 18a of the lances 18, it is
 necessary to avoid discontinuities, non-uniformities and constrictions in
 the flow configuration and radii of smaller than 1 m in the case of bends
 and curves.
 In the arrangement shown in FIG. 1 the metering effect is implemented by a
 separate metering device 9. Another construction is shown in FIG. 2 that
 can provide that fluidisation and metering in one operation. For that
 purpose a ball valve 19 is provided as the metering device in the lower
 region of the injection vessel. Fine setting is effected by way of the
 pressure setting and adjusting the amount of fluidisation gas. That
 construction however requires fast accurate regulation of the feed of air
 under pressure at the upper conduit 13 of the injection vessel 8 in
 dependence on the fluctuating internal pressure in the blast furnace 1.
 Therefore, at a suitable location in the blast furnace 1 a pressure sensor
 is provided which rapidly adjusts a valve in the conduit 13 by way of a
 regulating loop 17 in order to arrive at an accurate metering effect.
 Fluidisation and metering of the plastic material particles can also be
 implemented by means of a pressure-tight cell-wheel lock assembly. In this
 case the injection vessel 8 can be omitted.
 FIG. 4 is an enlarged view of the portion, indicated at I in FIGS. 1 and 2.
 of the conduit 10 by way of which the plastic materials to be injected
 into the blast furnace 1, in particular plastic waste, in agglomerated
 form, are transported to the lance 18. Adjoining the fittings in the
 injection tower (including for example the metering device 9 but also for
 example the connection for the compressed air or the supply for flushing
 air/nitrogen) that transport conduit 10 is formed by a hose portion 21.
 Joined thereto is a shut-off block or unit 22 of the transport conduit 10
 and joined in turn to the shut-off block or unit 22 in the direction of
 the injection lance 18 is an essential lance fitting portion 23 including
 the injection lance 18.
 The shut-off block or unit 22 includes as a first shut-off device 24 a
 shut-off valve which is closed to eliminate blockages (will be referred to
 hereinafter). In addition, a vent conduit (opening) 25 extends in the
 shut-off block or unit 22 from the transport conduit 10. The vent conduit
 (opening) 25 has a shut-off valve 26.
 Connected to the shut-off block or unit 22 is the region of the transport
 conduit 10, which is also referred to hereinafter as the fitting portion
 23 of the lance. Disposed within that fitting portion 23 is a hose portion
 27 which connects the transport conduit 10 of the shut-off block or unit
 22 to a heat shut-off or check valve 28 as a second shut-off device.
 Joined to that second shut-off device is a third shut-off device 29 for
 shutting off the lance 18. Disposed downstream of the third shut-off
 device (as viewed from the shut-off block or unit 22) is a mouth portion
 30 by way of which compressed air can be injected by means of a connecting
 portion 31 into the lance 18 and thus into the blast furnace 1.
 The mode of operation of the above-described arrangement is as follows: if
 for any reason no plastic material or other reducing agent is being
 injected into the blast furnace, the shut-off device 29 is closed and the
 connection 31 is opened and compressed air is then blown into the lance,
 when the injection installation is in a stopped condition. The operation
 of injecting compressed air is implemented either manually or
 automatically whenever the transport of plastic materials to the lance is
 interrupted. The introduction of compressed air prevents the injection
 lance from heating up to an undesirably high degree, and heat damage is
 thus precluded. The connection 31 for the introduction of compressed air
 into the lance is opened whenever the feed of plastic materials to the
 lance is closed by the third shut-off device. The connecting portion 31
 itself essentially comprises a valve which is connected to a compressed
 air reservoir.
 In the event of pressure fluctuations in the tuyere--which may repeatedly
 and undesirably occur--a return flow of hot tuyere gas from the tuyere
 (blast furnace) into the lance and the injection system behind same can be
 prevented, the heat shut-off valve which is in the form of a non-return
 valve is provided as the second shut-off device. That heat shut-off valve
 can be a simple flap which permits the transport of material/air to the
 lance (and is therefore then opened), but it is automatically closed in
 the opposite direction by the reverse flow of material/gas.
 The plastic agglomerates which are to be injected into the blast furnace
 have a tendency to cause blockages in the conduit 10 depending on their
 grain shape and size and also their specific composition, which should be
 prevented as described hereinbefore. If such a blockage (plug) occurs, a
 rapid blockage-removal operation must be effected. The shut-off block or
 unit is designed for that purpose. In the event of a blockage occurring,
 after closure of the shut-off valves (first and/or third shut-off device),
 a vent fitting or the vent valve 26 is opened. That venting action is
 effected by way of the outside atmosphere, with the consequence that a
 pressure drop of nearly 4 to 6 bars is to be recorded between the
 transport conduit 10 by way of the vent conduit 25 while the total
 pressure drop by way of the conduit from the injection fittings to the
 injection lance is only about 0.5 to 0.8 bar. Due to the extremely high
 air pressure drop, a considerable pressure is applied to the plastic
 material causing the blockage, and that results in the abrupt removal of
 blockages in the transport conduit so that the transport conduit is then
 again available, after closure of the valve 26. for injection of the
 agglomerated plastic materials.