WO2000070101A1 - 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 - Google Patents

Abstract

The invention relates to a method and installation for utilising residual material which contains iron, heavy metals and optionally iron ore. In said method, the following take place: residual material and optionally the iron ore is introduced into a smelting cyclone (1) with a backflow and a base opening which has a narrowed section. Reducing agents and oxygen are additionally introduced into the smelting cyclone (1) and are subjected to swirling. Iron is reduced at least to FeO in the smelting cyclone (1), heavy metals are reduced to metals in the smelting cyclone (1) and are converted into the gas phase by evaporation. The resulting gas which optionally contains heavy metals, the partially reduced iron and the slag are transferred to a furnace (5) which is directly adjacent. Energy, in electrical form is then supplied to said furnace (5), preferably using a direct electric arc. Reducing agents and oxygen, or oxygen-enriched air is then introduced into the furnace (5) and the iron is completely reduced and melted in the furnace (5). The evaporated heavy metals are condensed outside the furnace (5), whereby the iron can be subjected to further processing and a deposition of the residual materials is avoided.

Description

 METHOD AND INSTALLATION WITH MELT / REDUCTION CYCLE AND

COUPLED SUB-OVEN FOR RECYCLING IRON AND

HEAVY METAL RESIDUES AND / OR IRON FINE

The invention relates to a method and a plant for the recycling of iron and heavy metal-containing residues and possibly iron ore.

A major problem of the iron and steel producing industry lies in the constantly accumulating amounts of iron and heavy metal-containing residues, such as furnace dust, sludge, mill scale and the like, which are only accessible for recycling with great effort and are therefore usually landfilled without being dumped to take advantage of their valuable content.

From an ecological and economic point of view, there is a need to separate the iron present in the residues from its accompanying metals and to return it to the iron or steel production process.

A method of the type described at the outset is the INMETCO method. Here iron-rich metallurgical residues are agglomerated with solid reducing agents to form unburned, so-called "green" pellets and reduced in a rotary hearth furnace, the heavy metals evaporating, extracted with the exhaust gas and then melted in a melting furnace or optionally hot briquetted.

The disadvantages of this process lie in the need for a pretreatment stage in which the residues are agglomerated, and in the reduction and melting process carried out separately, as a result of which the energy for heating the residues has to be applied twice and a separate exhaust system is required in each case.

In a process described in DE-A-44 39 939, residues are melted in a melting cyclone, the heavy metals are evaporated and separated from the exhaust gas after oxidation as a dust fraction. The remaining slag is further depleted of heavy metals in a sub-furnace by blowing up reducing gas and oxygen and is subsequently used as a raw material for cement or rock wool production. However, the iron is not processed in this process, which means that an essential part of the residues remains unused.

A problem with the production of pig iron is the presence of fine ore in relatively large quantities, which is difficult to handle in the reduction and melting process. So The fine ore is usually reduced in fluidized bed reactors, which involve a great technical outlay. The introduction of the reduced fine ore into a smelting furnace also requires apparatuses with complex equipment, the service life of which is extremely limited due to the wear caused by the reactivity of the sponge iron.

From US-A-5,639,293 it is known to carry out a pre-reduction of iron ore by swirling the iron ore particles with oxygen and a reducing gas in a melting cyclone and to collect the melted iron particles in a metallurgical vessel below the melting cyclone and by blowing oxygen through a central one to finish reducing the lance projecting from the melting cyclone and adding fuel, whereby a reducing gas is formed which rises into the melting cyclone and, after reaction with the iron ore, is sucked off together with the resulting gases at the upper end of the melting cyclone.

Due to the cooling effect of the oxygen lance projecting centrally through the melting cyclone into the melting vessel according to US Pat. No. 5,639,293, the pre-reduced iron ore in the melting cyclone can become dull.

A device for reducing and smelting 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 enters a metallurgical vessel immediately below the melting cyclone, in which the final reduction takes place with the formation of a process gas from coal and oxygen blown onto the slag / metal layer and the complete melting of the iron takes place. The reducing process gas is partially burned with oxygen and in this way provides the heat necessary for the melt and the reduction both in the melting vessel and in the melting cyclone. The exhaust gases are drawn off at the top opening of the melting cyclone.

To separate slag and pig iron, the melt must first be transferred to a settling vessel, since in these known devices only one tap opening is provided in the lower vessel.

Due to the open melting cyclone bottom and the associated non-existing backflow in the melting cyclone, the countercurrent flow and the associated swirling of the reducing gas with respect to the iron ore particles result in a increased degree of dusting, which is further deteriorated by entrained slag particles and leads to a considerable discharge of particles from the melting cyclone with the exhaust gas discharged upwards from the melting cyclone.

The invention aims at eliminating these disadvantages and has as its object to create a method and a system which make it possible to use iron and heavy metal-containing residues, in particular from the iron and steel producing industry, and optionally iron ore in an environmentally friendly manner - while avoiding landfilling - To be processed, whereby the iron can be recycled, ie steel production benefits. Furthermore, only a single exhaust gas stream is generated, which saves system costs and minimizes emissions and increases the possible efficiency of energy recovery.

According to the invention, this object is achieved by the combination of the following features: the residues and, if appropriate, the iron ore are introduced into a melting cyclone with backflow, reducing agents and oxygen are additionally introduced and swirled into the melting cyclone,

Iron is reduced to at least FeO in the melting cyclone,

Heavy metals are reduced to metals in the melting cyclone and converted into the gas phase by evaporation, the resulting gas, which may contain heavy metals, the partially reduced iron and the slag are transferred to a directly coupled furnace, energy is supplied to the furnace, and reducing agents are added to the furnace and brought in oxygen or oxygen-enriched air,

- Iron is completely reduced and melted in the furnace, and

- The evaporated heavy metals are deposited outside the furnace.

The terms “iron”, “iron-containing”, “heavy metal” and “heavy-metal-containing” each encompass both the respective metals in oxidized, for example oxidic, form and in reduced, ie metallic, form, both oxidized and reduced, as just one of the two, the exact meaning of which is clear from the context. "Reduction to FeO" always means a reduction from trivalent to divalent iron, for example from Fe ₂ O to 2 FeO, but also from 3 Fe O ₃ to 2 Fe ₃ O ₄ (ie to Fe ₂ O ₃ »FeO).

Furthermore, by using a melting cyclone with backflow, which is caused by a constriction in the melting cyclone bottom, a low degree of dusting is possible. The iron and heavy metal-containing residues and possibly the iron ore achieve a longer residence time in the melting cyclone due to the backflow and are only transferred to the furnace in the liquid or gaseous state. Even if the melting cyclone is arranged above the furnace, slag particles are prevented from entering the melting cyclone by the constriction. In addition, there is only one outlet opening provided in the bottom of the melting cyclone, so that particles cannot be discharged by means of a gas flowing up through the melting cyclone. According to the invention, all materials and gases charged in the melting cyclone are forced to pass into the furnace, so that they can be efficiently finished there. This also results in the advantage of a single exhaust gas stream, namely from the furnace, which is accordingly simple and inexpensive to treat.

Fine ore can also advantageously be used as an iron-containing residue, in particular with a proportion of very fine particles that originate from ore processing or from abrasion from a pelletizing device.

The introduction of reducing agents, which are advantageously introduced in solid, liquid or gaseous form, and oxygen, preferably technical oxygen or oxygen-enriched air, takes place horizontally, preferably tangentially, in the vertically arranged melting cyclone, as a result of which the processes of mass and heat transfer take place very quickly. Reducing agents and oxygen are added in such controlled amounts that the heavy metals are converted into the gas phase by evaporation in a metallic state during the melting process and the iron is reduced at least to the divalent iron oxide FeO.

The heavy metal-containing gas, the partially reduced iron and the slag are transferred from the melting cyclone into the furnace by means of a connecting line which is arranged between the bottom opening of the melting cyclone and a furnace immediately following the melting cyclone, preferably through the ceiling or through a side wall of the furnace, and optionally via a maximum of one intermediate chamber arranged on the wall of the furnace, which separates the melting zone from the Reduction zone allowed in the furnace. The intermediate chamber, into which the connecting line opens, can also be designed as a furnace exhaust line.

In order to reduce the partially reduced iron present in the melt in the form of divalent iron oxide, solid reducing agent, preferably coal or carbon-containing wastes (which are at least partly formed by fine particles), is blown into the melt with oxygen or oxygen-enriched air. These substances can be blown in using under-bath blowers or using lances that are immersed in the slag layer floating on the molten iron metal. For this purpose, the oven is provided with openings for the lances. The injection nozzles are expediently located in part below the metal bath level and are connected to supplies for reducing agents and / or oxygen. The lances can be arranged in the furnace in any manner known to those skilled in the art.

Due to the difference in density, the reduced metal droplets settle at the bottom of the furnace in the molten iron metal, which, like the slag, can advantageously be separated continuously or discontinuously from the furnace using its own tap hole.

In addition to the pre-reduced iron and heavy metal-containing residues and possibly iron ore melted and pre-reduced in the melting cyclone, a portion of coarse fraction can be charged directly into the furnace, preferably via a suitable feed opening into the furnace, for example in the ceiling or in a side wall of the Oven.

In order to maintain the temperature required for tapping slag and pig iron melt, energy is supplied to the furnace, which also prevents premature separation of the heavy metals in the region of the furnace. The energy is preferably supplied to the melt in the form of electrical energy, for example via a direct arc. The supply of the electrical energy by means of at least one electrode protruding into the furnace has proven to be particularly advantageous, both direct current and alternating current being possible.

The evaporated heavy metals are subjected to post-combustion together with the furnace exhaust gas directly at the gas outlet, as a result of which the heavy metals are converted into a solid oxidic form which, after separation from the remaining exhaust gas, can be further processed in a precipitation device. If the products originating from the melting cyclone, namely heavy metal-containing gas and melt, are first introduced into an intermediate chamber, the heavy metal-containing gas is introduced into the furnace exhaust gas, which is withdrawn from the furnace via the intermediate chamber, in this intermediate chamber, whereupon the further treatment of the gases done together.

The melting cyclone, the furnace vessel above the metal mirror and, if applicable, the intermediate chamber are expediently equipped with evaporative cooling, as a result of which the radiant heat from the furnace and the melting cyclone are used to evaporate cooling water and can thus be obtained in the form of steam, which can be used in an iron and steel mill to save energy . Exhaust gas cooling carried out after the afterburning of the heavy metal-containing gas and the furnace exhaust gas serves the same purpose, preferably in a steam boiler.

Advantageously, the heat inherent in the exhaust gas can also be used in whole or in part in a heat exchanger into which the exhaust pipe of the furnace opens, the heated air being able to be fed to a dryer which contains suitable iron and heavy metal-containing moist residues or, respectively, for use in the melting cyclone Sludge dries.

The invention is explained in more detail below with reference to exemplary embodiments shown in the drawing, with FIGS. 1 to 4 showing preferred embodiments of the system according to the invention in a schematic representation.

1 coal, oxygen and iron- and heavy metal-containing residues and possibly iron ore in the form of dust are introduced into a vertically arranged melting cyclone 1. The introduction takes place in such a way that the swirling and the associated mass and heat transfers take place very quickly according to the invention, as a result of which the melting and pre-reduction process as a whole has a high space-time yield. The controlled delivery of the substances to be introduced into the melting cyclone 1 is carried out by a metering device (not shown) known to the person skilled in the art. The substances are blown horizontally, preferably tangentially, into the melting cyclone 1 via a plurality of openings, which can be distributed over the entire melting cyclone jacket. In the interior 2 of the melting cyclone 1 there is a reduction of the iron and heavy metal-containing residues and possibly of the iron ore, with iron being reduced at least to FeO and the heavy metals to the metal. Furthermore, a melting of the reduced iron-containing material and a transfer of the heavy metals into the gas phase is effected quickly and efficiently due to a cyclone-specific backflow.

An opening 3 in the bottom 4 of the melting cyclone 1 is formed by a constriction, which causes the backflow in the interior 2 of the melting cyclone 1 and thus enables a minimal degree of dusting.

The melting cyclone 1 is in direct connection with a furnace 5 arranged below the melting cyclone 1. The melt products and the heavy metal-containing gas enter 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 floating on the metal bath 7, which are separated from the furnace 5 via tap openings 9 and 10. Furthermore, the furnace 5 according to this embodiment has three electrodes 11, 11 ', 11 ", which dip into the slag layer 8 from above and which supply the energy required for maintaining a liquid slag 8 and a metal bath 7 in the form of arcs For example, the electrodes 11, 11 ', 11 "are operated with alternating current, but operation with direct current would also be possible, the furnace 5 having only one electrode 11.

Reducing agent and / or oxygen is introduced into the furnace 5 via under-bath injection nozzles 12 in a side wall 13 of the furnace 5 or in the base 14. The injection nozzles 12 are preferably arranged in part below the metal bath level.

In addition, a lance 15 for blowing in coal and oxygen is provided in the embodiment according to FIG. 1, which projects obliquely into the furnace 5 through the side wall 13 of the furnace 5 and dips into the slag layer 8 with its lower end.

In addition, a feed 16 opens into the furnace 5 for a coarse fraction of a reducing agent or a residue that can be introduced.

The iron-containing melt introduced into the furnace 5 from the melting cyclone 1 is completely reduced in the slag layer 8 with the aid of the reducing agent and oxygen, and the liquid iron is separated into the metal bath 7. When leaving the furnace 5, air is supplied to the exhaust gas and afterburning 21 is initiated. A part of the increased energy content of the exhaust gas is transferred to water in a waste heat boiler 17, the heat content of the exhaust gas being used to generate steam. A turbine generator 18 is used as an example for the further use of the steam, which is used to generate electricity. However, other possible uses of the steam generated are also conceivable, for example use in a metallurgical plant for cooling purposes, etc.

Following the boiler 17, the cooled exhaust gas is fed to a filter 19, in which the condensed heavy metals which accumulate as dust are separated from the remaining exhaust gas.

The preferred embodiment shown in FIG. 2 differs from the one illustrated in FIG. 1 by the manner in which the heavy metal-containing gas and the melting material from the melting cyclone 1 are introduced into the furnace 5. In this embodiment, the connecting line 6 opens into the side wall 13 of the furnace 5. The reducing agent and the oxygen are introduced into the furnace 5 exclusively via under-bath injection nozzles 12. The further treatment of the exhaust gas after it has left the furnace 5 is not shown further; it can also be carried out as shown in FIG. 1.

According to FIG. 3, the connecting line 6 opens into an intermediate chamber 20, which is optionally widened (shown in dashed lines), so that the heavy metal-containing gas from the melting cyclone 1 does not have to flow through the furnace 5 and the melting material is already on the way through the reducing furnace exhaust gas the furnace 5 is further reduced. In this embodiment of the system according to the invention, the lance 15 used to blow in the reducing agent and oxygen projects into the furnace 5 from above. However, it can also protrude over a side wall 13 in the furnace 5.

FIG. 4 shows the arrangement of melting cyclone 1 and furnace 5 described in FIG. 1, but the heat inherent in the exhaust gas is only partially used in the waste heat boiler 17. The still hot exhaust gas is heat exchanged in a recuperator 22 and then passed in a cooled state into the filter 19, where the described separation of the heavy metals takes place. The air heated in the recuperator 22 is fed to a dryer 23 which serves to dry moist residues and sludges for use in the melting cyclone 1. The process sequence according to the invention is set out in the examples 1, 2 and 3 below. The quantities given below relate to a ton of feed mix without coal or surcharges (lime).

Example 1 :

1000 kg / h of iron and heavy metal-containing residues, which had a composition shown in Table 1, and 105 kg / t of coal with 1 12 NmVt of conveying air were introduced into the melting cyclone and swirled with 260 NmVt of oxygen. 5.4 NmVt of fuel gas (natural gas) were supplied to ignite the solid / gas mixture in the melting cyclone and to maintain an ignition flame.

Table 1

Das teilreduzierte Eisen wurde danach im Reduktionsofen mit 182 kg/t Kohle und 36 NmVt Sauerstoff fertigreduziert und aufgeschmolzen. Die Förderluftmenge für die durch Lanzen oder Düsen eingeblasenen Feststoffe betrug 45 NmVt. Der Strombedarf des Ofens betrug 320 kWh/t.

The partially reduced iron was then completely reduced in the reduction furnace with 182 kg / t coal and 36 NmVt oxygen and melted. The conveying air volume for the solids blown through lances or nozzles was 45 NmVt. The electricity requirement of the furnace was 320 kWh / t.

576 kg / t of molten metal, 130 kg / t of slag and a dedusted amount of exhaust gas of 12140 NmVt were obtained. 24 kg / t of heavy metal dust was separated from the exhaust gas. Furthermore, 737 kWh / t of electricity was generated by using the waste heat in a steam generator.

The composition of the molten metal, the slag, the exhaust gas and the separated dust is shown in Table 2. For Examples 2 and 3, product compositions were found which were in the same range. Table 2

Beispiel 2:

Example 2:

A quantity of 1000 kg / h of iron and heavy metal-containing residues and iron ore - the composition of the feed mixture is shown in Table 1 - was introduced into the melting cyclone with 56 kg / t of coal using 106 NmVt of conveying air and vortexed with 270 NmVt of oxygen. 5.1 NmVt of fuel gas were supplied. The amount of reducing agent (coal) introduced into the furnace was 151 kg / t, 30 NmVt in oxygen and 38 NmVt in conveying air. The electricity requirement was 268 kWh / t.

480 kg / t of molten metal, 125 kg / t of slag, 1,100 NmVt of dedusted exhaust gas and 36 kg / t of heavy metal-containing dust were obtained. Electricity production was 684 kWh / t.

Example 3:

1000 kg / h iron ore (composition: Table 1) with 290 kg / t coal and a conveying air quantity of 136 NmVt were used as the input product. Furthermore, 336 NmVt oxygen and 55 kg / t lime were introduced into the melting cyclone. The amount of fuel gas was 6.5 NmVt.

To reduce the iron, 197 kg / t coal with 49 NmVt conveying air and 38 NmVt oxygen were fed into the furnace. The electricity requirement was 348 kWh / t.

The products produced were 625 kg / t molten metal, 139 kg / t slag, 15760 NmVt dedusted exhaust gas and 22 kg / t dust. 945 kWh / t of electricity were generated.

Claims

Claims: 1. A process for recycling iron and heavy metal-containing residues and possibly iron ore, characterized by the combination of the following features: the residues and possibly the iron ore are introduced into a melting cyclone (1) with backflow, and reducing agent and oxygen are additionally introduced into the melting cyclone (1) introduced and swirled, - iron is reduced to at least FeO in the melting cyclone (1), Heavy metals are reduced to metals in the melting cyclone (1) and by Evaporation transferred into the gas phase, the resulting gas, which may contain heavy metals, the partially reduced Iron and the slag are transferred to a directly coupled furnace (5), the furnace (5) is given energy in electrical form, preferably via a direct one Arcing, fed into the furnace (5), reducing agents and oxygen or oxygen-enriched Air, Iron is completely reduced in the furnace (5) and melted, and the evaporated heavy metals are deposited outside the furnace (5). 2. The method according to claim 1, characterized in that the reducing agents are introduced in a solid, liquid or gaseous state. 3. The method according to claim 1 or 2, characterized in that coal or carbon-containing waste are used as reducing agents. 4. The method according to one or more of claims 1 to 3, characterized in that the reducing agents (which are at least partially formed by fine particles) and / or the oxygen via Unterbadeinblasdüsen (12) are introduced into the furnace (5). 5. The method according to one or more of claims 1 to 4, characterized in that the reducing agent and / or the oxygen are introduced into the furnace (5) via a lance (15) immersed in a slag layer (8). 6. The method according to one or more of claims 1 to 5, characterized in that iron and slag are tapped separately via tap openings (9 and 10) from the furnace (5). 7. The method according to one or more of claims 1 to 6, characterized in that the heavy metal-containing gas is burned directly at the gas outlet and the heavy metals are brought into a solid oxidic form and then separated. 8. The method according to one or more of claims 1 to 7, characterized in that exhaust gas is withdrawn from the furnace (5) and the heavy metal-containing gas is introduced into the exhaust gas withdrawn. 9. The method according to one or more of claims 1 to 8, characterized in that heat from the melting cyclone (1) is used to evaporate cooling water. 10. The method according to one or more of claims 1 to 9, characterized in that heat from the oven (5) is used to evaporate cooling water. 11. The method according to one or more of claims 1 to 10, characterized in that exhaust gas from the furnace (5) is combusted together with the heavy metal-containing gas and then cooled, with a water used for cooling being evaporated. 12. The method according to one or more of claims 1 to 11, characterized in that as iron-containing residue fine ore, in particular with a proportion of fine particles, preferably originating from iron ore processing and / or the abrasion from a pelletizing, is used. 13. Plant for the recycling of iron and heavy metal-containing residues and possibly iron ore using the method according to one or more of claims 1 to 12, characterized by the combination of the following features: - A melting cyclone (1) having a bottom opening (3) with a constriction and Has feeds for iron and heavy metal-containing residues and possibly iron ore which lead into the melting cyclone (1), - an oven (5) with a supply for electrical energy, preferably with at least one electrode (11, 11 ', 1 1 ") projecting into the oven (5), - Feeds for reducing agent and oxygen or oxygen-enriched air in the furnace (5), and - An exhaust pipe, which starts from the furnace (5) and leads to a precipitation device for escaping from the furnace (5) containing heavy metal gas. 14. Plant according to claim 13, characterized in that the furnace (5) is provided with injection nozzles (12) for reducing agents and / or oxygen, which are at least partially below the metal bath level in the furnace (5) and to which supplies for reducing agents and / or drive oxygen. 15. Plant according to one or more of claims 13 or 14, characterized in that the furnace (5) is provided with openings for lances (15) for blowing in reducing agent and or oxygen. 16. Plant according to one or more of claims 13 to 15, characterized in that in the furnace (5) opens a feeder (16) for a coarse fraction of a reducing agent or residue. 17. Plant according to one or more of claims 13 to 16, characterized in that a tap opening (9) for iron and a tap opening (10) for slag are provided in the furnace (5). 18. Plant according to one or more of claims 13 to 17, characterized in that a connecting line (6) between the bottom opening (3) of the melting cyclone (1) and the furnace (5) is arranged. 19. Plant according to one or more of claims 13 to 18, characterized in that on a wall (13) of the furnace (5) an intermediate chamber (20), which is optionally designed as an exhaust pipe, is arranged, in which the connecting line (6 ), which connects the bottom opening (3) with the oven (5), opens. 20. Plant according to one or more of claims 13 to 19, characterized in that the exhaust pipe of the furnace (5) opens into a heat exchanger, preferably in a steam boiler (17). 21. Plant according to claim 20, characterized in that from the heat exchanger leads a hot air line to a dryer (23), the sludge is supplied, which can be fed to the melting cyclone (1) as a residue via a transport line in the dried state. 22. Plant according to one or more of claims 13 to 21, characterized in that the melting cyclone (1) is equipped with a cooling device, preferably an evaporative cooling device. 23. Plant according to one or more of claims 13 to 22, characterized in that the furnace (5) above the metal mirror is equipped with a cooling device, preferably an evaporative cooling device. 24. Plant according to one or more of claims 13 to 23, characterized in that in the exhaust pipe from the furnace (5) or at the confluence thereof in the furnace (5) a post-combustion device (21) for emerging from the furnace (5) Exhaust gas is provided.