WO2014125057A1

WO2014125057A1 - Process for charging a burden with high zinc content in a blast furnace installation

Info

Publication number: WO2014125057A1
Application number: PCT/EP2014/052877
Authority: WO
Inventors: Marc Solvi; Guy Thillen; Paul Tockert; Lionel Hausemer; Jean-Paul Simoes; Ludivine Piezanowski
Original assignee: Paul Wurth S.A.
Priority date: 2013-02-15
Filing date: 2014-02-14
Publication date: 2014-08-21
Also published as: LU92150B1; TW201437376A

Abstract

The present invention describes a method for treating a Zn contaminated material in a blast furnace installation comprising a blast furnace charged with a traditional burden of iron ore and coke, a gas cleaning unit, and lateral top gas extraction uptakes connected between an upper top cone of said blast furnace and said gas cleaning unit, said method comprising the following steps: a. Providing Zn contaminated material, b. Charging said Zn contaminated material in a central area of a raw material feeding zone of a blast furnace in addition to the traditional burden of iron ore and coke, c. Reducing the Zn contaminated material in the blast furnace so as to obtain a Zn enriched gas, d. Extracting a Zn enriched gas from the blast furnace, e. Treating said extracted Zn enriched gas in the gas cleaning unit.

Description

PROCESS FOR CHARGING A BURDEN WITH HIGH ZINC CONTENT IN A

BLAST FURNACE INSTALLATION

Technical Field

[0001 ] The present invention generally relates to a blast furnace installation, in particular a process for charging a burden with high Zinc content, ie. A Zn contaminated material in a blast furnace installation.

Background Art

[0002] In a blast furnace, iron oxides are reduced and the resulting iron is melted. Approximately 70% of the global steel production involves the use of blast furnaces.

[0003] Zinc is present in the blast furnace as a constituent of the sinter charge in the form of oxides (ZnO), ferrite (ZnO.Fe2O3), silicates (2 ZnO.SiO2) and sulphide (ZnS).

[0004] Reduction, vaporization, condensation, oxidation and circulation of zinc occur in the blast furnace. Zinc oxide is easily reduced in the furnace at temperatures higher than the melting (420°C) and boiling (907°C) points. At temperatures between 907°C and 1000°C, it sublimates and moves to the upper zones of the blast furnace.

[0005] ZnO(s) + C→ Zn_(g) + CO_(g) (1 )

[0006] Part of the volatilized Zn gas reacts with water vapor (steam) and carbon dioxide (equation (2)) in order to form zinc oxide. The other volatilized Zn gas condenses (equation 3). This leads to deposits under the form of fine particles at the refractory of the non-cooled upper part of the blast furnace shaft profile forming dense and heavy crusts.

[0007] Zn_(g) + H₂O(CO₂)→ ZnO +H₂(CO) (2)

[0008] Zn_(g) -> Zn (solid) (3)

[0009] These crusts prevent the uniform distribution of gases and adversely affect the thermodynamic equilibrium of the blast furnace process. This could lead to the collapse of the tuyeres and excess coke is consumed to reduce the Zn accumulated in the furnace.

[0010] The above zinc reactions are influenced by the following blast furnace operating factors:

• gas distribution and pressure,

• temperature of the reaction and

• the specific gas consumption.

[001 1 ] Furthermore, zinc is highly gasified at the temperature zone of 900°C and 1 100°C, which results in the lowering of the temperature in the concerned zones of the blast furnace. Consequently, it is estimated that a surplus of about 1 1 kg of coke is consumed for every kilogram of zinc released.

[0012] Oxidized zinc (ZnO) penetrates into the regions with large surface areas such as pores, cracks, masonry and bricks enclosure (linings). Because the linear expansion of oxidized zinc is higher than that of the refractory - chamotte, oxidized zinc causing severe damage.

[0013] Part of the reduced zinc in the lower part of the shaft, shoulder and hearth of the blast furnace dissolves in the iron and flows through the molten iron. When the crust of zinc oxide falls into the molten metal, zinc is absorbed into the pig iron. The remaining part of the gasified zinc is deposited on the iron oxides of the incoming charge in the form of ferrite.

[0014] Zn_(g) + FeO(Fe₃O₄)+ CO₂→ ZnO.FeO(Fe₃O₄) +CO (3)

[0015] Through this process, greater quantity of zinc moves back with the furnace burden to the zone of reduction, thus creating a recirculation system.

[0016] Because of these negative effects of zinc on the operation of a blast furnace, the maximum level of zinc charged into the furnace is generally 0.12-0.16 kg/t of hot metal or 0.01 % of the ferrous charge, although operations with Zn loads of up to 0.5 kg Zn/t hot metal have been reported in US 201 1/0041652 or in Luxembourg and Lorraine with the use of Minett ore.

[0017] Nevertheless, some of the gasified Zn leaves the furnace with the blast furnace gas, also referred to as top gas, a by-product of blast furnace operation. The top gas is generally also fed through a gas cleaning unit before it is used further. The gasified Zn is also recuperated in the gas cleaning unit plant under the form of ZnO mostly. Indeed on modern blast furnaces, it is common practice to recover at least 85% of the dust at the primary stage (dry) of the gas cleaning plant (GCP), i.e. axial (or tangential cyclone) whereas the rest of the dust is washed out or filtered in the secondary stage of the GCP, i.e. in a scrubber resulting in a sludge or in a bag filter resulting in dust.

[0018] Measurements show that the dust recovered at the cyclone of the primary stage has a relatively low Zn content, whereas the scrubber sludge or bag filter dust has a higher Zn content (up to 16 wt% dry basis).

[0019] Generally the dust of the primary stage (low in Zn) can be integrally recycled at the sinter plant.

[0020] The problem is about avoiding to have to dump these sludges or bag filter dusts, containing a fair concentration of Zn and iron.

[0021 ] The sludges may be treated in a separate facility as described for example in EP 1 797 207, wherein the sludge is treated in a multiple hearth furnace and Fe and Zn are very efficiently recovered. The only downfall of this is that a separate recycling plant with a multiple hearth furnace has to be constructed and operated.

Technical Problem

[0022] It is thus an object of the present invention to provide a method for treating a Zn contaminated material in a blast furnace installation.

[0023] This object is achieved by a process as claimed in claim 1 . General Description of the Invention

[0024] In particular there is proposed a method for treating a Zn contaminated material (Zn enriched burden) in a blast furnace installation comprising a blast furnace charged with a traditional burden of iron ore and coke, a gas cleaning unit, and lateral top gas extraction uptakes connected between an upper top cone of said blast furnace and said gas cleaning unit, said method comprising the following steps: a. Providing Zn contaminated material

b. Charging said Zn contaminated material in addition to the traditional burden of iron ore and coke, in a central area of a raw material feeding zone of a blast furnace

c. Reducing the Zn contaminated material in the blast furnace d. Extracting a Zn enriched gas from the blast furnace,

e. Treating said extracted Zn enriched gas in the gas cleaning unit

[0025] This method thus allows to increase the acceptable zinc load to the blast furnace considerably without effecting the blast furnace operation negatively and harming the blast furnace structure. This method allows to treat basically any Zn contaminated material in a blast furnace installation including sintered high Zn iron ore without affecting the operation of the blast furnace negatively.

[0026] Surprisingly, it has been found that if the Zn contaminated material is feed to a central area of the raw material feeding zone, the Zn does not affect the performance of the blast furnace. It has been found that the Zn contained in the material will first be reduced to gaseous Zn and then oxidised to very small particles of mostly ZnO that will easily be taken up by the gas extraction and sent to the cleaning unit.

[0027] The Zn contaminated material comprising Zn under the form of oxide (ZnO), ferrite (ZnO.Fe2O3), silicate (2 ZnO.SiO2), sulphide (ZnS) and/or carbonate (ZnCO) or mixtures thereof is charged into the blast furnace in addition to the traditional burden of iron ore and coke. The separate charging of Zn rich materials allows adapting the Zn input according to the requirements of blast furnace operation and productivity goals. In case of operational problems, the Zn input can immediately be reduced and can be increased during periods of optimal blast furnace performance. Also based on availability, the recycling of Zn rich materials can be limited in time. Low Zn load periods can follow after high Zn load periods in order to allow the blast furnace to regenerate if required. The normal blast furnace raw material logistics will not be disturbed by the separate charging of Zn rich materials.

[0028] The Zn contaminated material is thus charged in a central area of the raw material feeding zone of the blast furnace. This area has preferably a radius from about 0.5 m to 2.5 m, more preferably less than 2 m and most preferably less than 1 .75 m and advantageously less than 1 ,5 m. The addition of high Zn content material in the centre of the blast furnace leads to a concentration of Zn vapours in the centre of the blast furnace thus avoiding the contact of these vapours with the cold walls. By this way condensation of Zn and build-up of skulls on the walls can be avoided.

[0029] The radius of this central area of the raw material feeding zone should advantageously be not more than 1/3, preferably not more than ¼, more preferably not more than 1/5, and most preferably 1/6 of the radius of the blast furnace, measured at the level where the raw material is fed into the blast furnace.

[0030] With the above described method, it is possible to treat burdens with a total Zn content of > 0,75 kg Zn/t of molten iron/ hot metal, preferably > 1 kg Zn/t, more preferably > 1 .5 kg Zn/t, even more preferably > 2 kg Zn/t, most preferably > 2.5 kg Zn/t and advantageously > 3 kg Zn/t or 0.2% of the ferrous charge. The Zn content of the total burden should however be < 50 kg Zn/t of molten iron/ hot metal, preferably <40 kg Zn/t, more preferably < 30 kg Zn/t, even more preferably < 20 kg Zn/t, most preferably < 15 kg Zn/t and advantageously <10 kg Zn/t.

[0031 ] These values expressed in kg Zn/t of molten iron/ hot metal can easily be approximated as wt% of the total charge of the blast furnace by dividing by 1500 and multiplying by 100.

[0032] The Zn contaminated material preferably also contains iron (Fe) under different form. The content of iron is preferably > 15 wt%, more preferably > 20 wt%, even more preferably > 25 wt%, most preferably > 30 wt%, and advantageously > 40 wt%. Any iron contained in the Zn contaminated material will of course be reduced and melted in the blast furnace. The method thus allows to recycle any iron contained in the Zn contaminated material.

[0033] Zn contaminated materials that have a fine granulometry (diameter > 10 mm : 5.00 wt% max, diameter < 0.15 mm : 35.00 wt% max) like dusts from Electric Arc Furnaces or iron ore concentrate should be compacted or pelletized before they are fed into the blast furnace as otherwise a high percentage of the material would be transferred directly i.e. without properly reacting to the gas cleaning unit. [0034] The compacting of the material may be made by any known process i.e. by briquetting, pelletizing or sintering.

[0035] Zn contaminated materials that have a high carbon content (more than 5% wt of the dry material) like dusts and dried sludge from the gas-cleaning unit of a blast furnace may also be treated by the above method. They should however be decarbonised before being charged in the central area of the raw material feeding zone of a blast furnace. Indeed, the dust and sludge of the gas cleaning unit of a blast furnace contain between 21 and 51 wt% of carbon.

[0036] Care must be taken to have less than about 5 wt% of carbon, preferably less than about 4 wt% of carbon, more preferably less than about 3 wt% of carbon, even more preferably less than about 2 wt% of carbon and most preferably less than about 1 % of carbon in the decarbonised material.

[0037] Such a decarbonisation can be achieved by any known method (i.e. a burning process < 500 °C).

[0038] The decarbonised material may then be compacted, especially if it the granulometry of the material is too fine to be charged directly in the blast furnace. The compacting may be realized by any known method, preferably by briquetting, pelletizing or sintering so that it can be fed more efficiently in the blast furnace. In a preferred embodiment, the decarbonised Zn contaminated material is enclosed in a consumable container respectively wrapped in metal foil or the like before it is introduced in the blast furnace.

[0039] The removal of carbon from such a Zn contaminated material is important as too much remaining carbon in the compacted Zn contaminated material may lead to the disintegration of the pellets, briquettes and the like and thus creation of fines. Indeed, the carbon may react with the ZnO contained in the Zn contaminated material and form CO gas. This CO can again react with FeO which might also be contained in the Zn contaminated material and create CO2. The formation of gases inside the compacted material may lead to a pressure increase in the compacted material and result in the explosion of the latter. Such a disintegration of the compacted material should be minimized as it is desired that the Zn contaminated material goes down in the shaft of the blast furnace, as it is in this zone where ZnO is be reduced and vaporized for removal together with the top gas. If this is not the case, the smaller particles or fines may directly flow out of the blast furnace again together with the top gas and may lead to higher dust quantities or to the creation of scaffolds or accretions at the walls of the blast furnace.

[0040] The ferrous residues in an integrated plant can be subdivided into two groups, those with low Zn content which can be mixed to the traditional burden of iron ore and coke and recycled to the blast furnace. However those with high Zn content have to be dumped because the charging of those residues into the blast furnace would lead to operational problems. The following table gives typical compositions for representatives of both groups.

[0041 ] The aim of the present method is to modify the behaviour of the Zn in the blast furnace by central charging the high Zn content materials so that the negative effects of Zn can be minimized or at best be avoided. The result of the present method will be that the residues that are dumped today because of their high Zn content, can be recycled into the blast furnace with the central charging technique described herein.

[0042] A brief calculation example based on a blast furnace producing of 5000 t hot metal/d allows understanding the difference between normal operation and high Zn load operation. For the normal operation, it is supposed that only the sinter dust and the BF gas cleaning dust (see first two columns of the table above) are recycled. For the case with Zn rich material charging in the centre, also the sludges from the blast furnace and the Basic Oxygen Furnace (BOF) gas cleaning plants are be recycled (see last two columns of the table above). The results of the calculation are shown in the following table:

[0043] The additional recycling of BF and BOF sludges leads to a dramatic increase (+ 1 466% !) of the Zn input into the BF. It is known from BF operation experience that such high Zn inputs cannot be handled with the normal operation as skull formation in the shaft would be the consequence. The charging of high Zn materials to the centre avoids such skull formations efficiently.

[0044] This method is especially useful to treat the dust and sludge from the gas cleaning unit of a blast furnace although other Zn contaminated material (like sinter dust, BOF sludge, BOF dust, electric arc furnace dust...) may be used.

[0045] It must be noted that - according to this embodiment - the quantity of dust/sludge of the gas-cleaning unit, which has to be finally dumped, is much reduced, as part of it is recycled in the blast furnace. The dust/sludge to be dumped is equivalent to the quantity of the Zn input in the other raw materials charged in the blast furnace. It is estimated that the quantity of dust/sludge of the gas-cleaning unit to be finally dumped or otherwise treated is about 5 times lower than in conventional operation. [0046] According to a further preferred embodiment, the extracting of Zn enriched gas from the blast furnace from may be made from a central zone in an upper part of the blast furnace, separately from lateral top gas extraction uptakes of the blast furnace and treated in an auxiliary gas cleaning unit.

[0047] This central zone in the upper portion of the blast furnace may preferably be up to about 1 m above the level of the burden in the central area of the raw material feeding zone to about 1 m below the level of the burden in the central area of the raw material feeding zone, and preferably in the vicinity of a vertical axis of the blast furnace.

[0048] The dust/sludge of the auxiliary gas-cleaning unit has a higher concentration of Zn than the dust/sludge of the gas-cleaning unit. The Zn content may even be high enough that this dust/sludge can be sold or given free of charge to a third company for further treatment to extract Zn by a conventional process.

[0049] The Zn contaminated material is advantageously charged in the furnace with a multiple hopper Bell Less Top. In case a so called "3 Hopper Bell Less Top" as described in WO2007082633 is used, one hopper may be dedicated to this Zn contaminated material. This would have the advantage that almost no time is lost for charging the conventional raw materials. On the other hand this Zn contaminated material may be mixed to large centre coke, which would promote permeability of the centre chimney.

[0050] According to another aspect of the present invention, there is proposed a blast furnace installation to treat a Zn contaminated material.

[0051 ] The blast furnace installation comprises a blast furnace, a gas cleaning unit and lateral top gas extraction uptakes connected between an upper topcone of said blast furnace and said gas cleaning unit, a centre material unit for feeding an optionally compacted, optionally decarbonised Zn contaminated material in a central area of a raw material feeding zone, a central gas uptake conduit, said central gas uptake conduit having an uptake opening arranged in the vicinity of a vertical axis of the blast furnace, in an upper portion of said blast furnace for extracting gas from an axial region of said blast furnace; and an auxiliary gas cleaning unit connected to said central gas uptake conduit for cleaning gas extracted via said central gas uptake conduit. [0052] According to an aspect of the present invention, the blast furnace installation further comprises a central gas uptake conduit having a lower uptake opening arranged in the vicinity of a vertical axis of the blast furnace, in an upper portion of the blast furnace for extracting gas from an axial region of the blast furnace; and an auxiliary gas cleaning unit connected to the central gas uptake conduit for cleaning gas extracted via the central gas uptake conduit.

[0053] In addition to the conventional lateral top gas extraction uptakes, which are arranged at a distance from the vertical axis of the blast furnace, the present invention provides a central gas uptake conduit. Whereas, the conventional lateral top gas extraction uptakes extract gas from a lateral region of the blast furnace, the central gas uptake conduit extracts gas from an axial region of the blast furnace, i.e. the vicinity of a vertical axis of the blast furnace, thus allowing a more selective extraction of gas from the furnace.

[0054] Particularly, said auxiliary gas cleaning unit is a gas cleaning unit dedicated to treating zinc or zinc containing components contained in said gas extracted via said central gas uptake conduit.

[0055] Preferably, the uptake opening of the central gas uptake conduit is arranged in the top cone or throat region of the blast furnace, preferably at the level of the base of the top cone, that is below the openings of the lateral top gas extraction uptakes.

[0056] The extraction of gas from an axial upper region of the blast furnace allows extracting gas with high Zn concentration. Indeed, it has been found that the Zn concentration in top gas is highest in this axial upper region, due to the fact that there are the zones of higher gas velocities and higher gas temperatures.

[0057] A dedicated gas extraction in the axial region of the blast furnace thus permits the extraction of a gas much richer in Zn than an average top gas through the traditional lateral top gas extraction uptakes would be.

[0058] The Zn rich gas collected through the central gas uptake conduit is then fed through an auxiliary gas cleaning unit, which is preferably specifically adapted to collect Zn rich dust or sludge.

[0059] When compared to a traditional gas cleaning unit, the auxiliary gas cleaning unit is fed with a gas richer in Zn and thus produces dry flue dust and/or sludge that is also expected to be richer in Zn. Such an "enriched" sludge is a product with an added value as it can easier be exploited in a dedicated recycling unit or sold to a specialized company.

[0060] By enabling an improved extraction of Zn from the blast furnace, it is possible to raise the limit of Zn load in the charge material. Indeed, it is even possible to feed Zn rich sludge back into the blast furnace and thus extract the residual iron in the dust or sludge.

[0061 ] It should also be noted that the central gas uptake conduit and the auxiliary gas cleaning unit allow the recycling of Zn rich by products at reduced cost when compared to recycling plants with multiple hearth furnaces.

[0062] According to a preferred embodiment, the blast furnace is provided with a central gas uptake conduit that is arranged and formed so as to serve as centre material feeding pipe, which is connected to a material hopper and to the auxiliary gas cleaning unit. Indeed, such a centre material feeding pipe is in some blast furnace installations used to feed further charge material, generally coke, into the blast furnace.

[0063] In case of an existing blast furnace installation, which is already provided with a centre material feeding pipe, such an installation may thus be easily adapted for use with the present invention. Indeed, the existing centre material feeding pipe may be used as central gas uptake conduit and additionally be connected to an auxiliary gas cleaning unit.

[0064] It is also worth noting that such a centre material feeding pipe / central gas uptake conduit would be self-cleaning. Indeed, any Zn deposits on the inner walls of the pipe would be abraded while coke or any other charge material is fed through the pipe.

[0065] According to another preferred embodiment, the blast furnace is provided with a central gas uptake conduit that is arranged and formed within or on a probe reaching into the blast furnace. Such a probe may e.g. be an above burden probe or an in burden probe.

[0066] It should also be noted that the uptake opening of the central gas uptake conduit may be arranged above the burden level within the blast furnace. Alternatively, it may be arranged below the burden level within the blast furnace. [0067] The uptake opening of the central gas uptake conduit may be arranged in a central zone in the upper portion of the blast furnace. This central zone may preferably be up to about 1 m above the level of the burden in the central area of the raw material feeding zone to about 1 m below the level of the burden in the central area of the raw material feeding zone, and preferably in the vicinity of a vertical axis of the blast furnace.

[0068] A primary stage of the auxiliary gas cleaning unit may comprise a cyclone for removing gross particles from the extracted gas. It has been found that Zn generally tends to condensate to the finer particles. The gross particles removed from the extracted gas thus generally have low concentration of Zn. Such gross particles may therefore be more easily recycled, e.g. by feeding them back into the blast furnace.

[0069] A second stage of the auxiliary gas cleaning unit may comprise a dry gas cleaning unit, e.g. an electrobag filter, downstream of the cyclone for removing flue dust from the extracted gas. As the Zn generally tends to stick to the finer particles, such flue dust would be particularly rich in Zn. The use of electrobag filters has the advantage that the flue dust remains dry and therefore uses less volume than wet sludge would do.

[0070] The second stage of the auxiliary gas cleaning unit may also comprise a scrubber downstream of the cyclone for removing sludge from the extracted gas. For the same reasons explained above the removed sludge is rich in Zn.

[0071 ] Alternatively the auxiliary gas cleaning unit may comprise a venturi ejector for the removal of fine particles from the extracted gas. Such a venturi ejector, which comprises the injection of water, allows separating Zn rich dust from the gas by using the phenomenon of different exit velocities of the gas and the water. The fine dust particles are then removed as sludge..

[0072] Furthermore, the ejector permits to drive the gas back to the blast furnace. According to an embodiment of the invention, the installation further comprises a return conduit between the auxiliary gas cleaning unit and the blast furnace for feeding cleaned gas back into the blast furnace. The cleaned gas, which has been stripped of its high Zn content, may thus be fed back into the blast furnace.

[0073] The cyclone may be connected to the return conduit for feeding back gross particles removed by the cyclone into the return conduit for introduction into the blast furnace. Gross particles, which are poor in Zn may therefore be fed back into the blast furnace and the residual iron therein may be extracted. In this configuration, the gross particles and gas are entrained by a second ejector placed below the cyclone.

[0074] According to an embodiment of the invention, the installation may further comprise a recirculation conduit between the dry gas cleaning unit and the central gas uptake conduit for feeding flue dust removed by the dry gas cleaning unit back into central gas uptake conduit. Re-circulation of cold flue dust containing fine Zn particles into the central gas uptake conduit upstream of the cyclone, scrubber or dry gas cleaning unit allows for hot Zn extracted from the blast furnace to condensate on the recirculated colder flue dust, thereby increasing further the Zn concentration of the particles.

[0075] According to a further embodiment of the invention, a combustion chamber is arranged in the central gas uptake conduit for heating the extracted gas fed to the auxiliary gas cleaning unit. Such a combustion chamber allows re- evaporation of the Zn deposited on the bigger particles and a quick oxidation of the Zn to ZnO, which may then be easier to separate as dust in the off-gas. This combustion can also avoid a condensation of the Zn on the inner face of the pipes.

[0076] It should be noted that, although the present application generally mentions zinc (Zn), this is understood to encompass zinc-containing molecules such as e.g. zinc oxide (ZnO).

Brief Description of the Drawings

[0077] Preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Fig. 1 is a cross-section through a traditional blast furnace;

Fig. 2 is a cross-section through a portion of a blast furnace installation with an auxiliary gas cleaning unit according to a first embodiment of the invention; Fig. 3 is a cross-section through a portion of a blast furnace installation with an auxiliary gas cleaning unit according to a second embodiment of the invention;

Fig. 4 is a cross-section through a portion of a blast furnace installation with an auxiliary gas cleaning unit according to a third embodiment of the invention;

Fig. 5 is a cross-section through a portion of a blast furnace installation with an auxiliary gas cleaning unit according to a fourth embodiment of the invention;

Fig. 6 is a cross-section through a portion of a blast furnace installation with an auxiliary gas cleaning unit according to a fifth embodiment of the invention;

Fig. 7 is a cross-section through a portion of a blast furnace installation with an auxiliary gas cleaning unit according to a sixth embodiment of the invention;

Fig. 8 is a cross-section through a portion of a blast furnace installation with an auxiliary gas cleaning unit according to a seventh embodiment of the invention;

Description of Preferred Embodiments

[0078] A blast furnace installation comprises a blast furnace 10, as shown in Fig .1 , with a furnace shaft 12, which has in an upper region a furnace top cone 14 through which charge material is fed into the furnace shaft 12. Laterally in the roof 16 of the blast furnace top cone, openings are arranged for the connection of top gas extraction uptakes 18 leading top gas from the blast furnace to a conventional gas cleaning unit (not shown). A charging system 20 is arranged centrally above the furnace shaft 12 for feeding charge material into the blast furnace 10. Due to the central arrangement of the charging installation 20, the top gas extraction uptakes 18 are arranged off-centre in the roof 16 of the blast furnace. Although the charging system 20 shown in Fig .1 is of the bell-less top type, it should be noted that other installations, such as e.g. two- or three-bell systems, are equally possible and within the scope of the present invention. [0079] Fig.2 shows the top cone 14 of a blast furnace with a central gas uptake conduit 22 and an auxiliary gas cleaning unit 24. The central gas uptake conduit 22 has an uptake opening 26 arranged centrally at the base of the top cone 14 on the axis of the blast furnace 10. The central gas uptake conduit 22 is configured as a centre material feeding pipe connected to a material hopper (not shown) for feeding an additional charge material into the blast furnace in addition to the charge material fed from the charging system 20. The central gas uptake conduit 22 is further connected to the auxiliary gas cleaning unit 24, which comprises a cyclone 28 and a dry gas cleaning unit 30 in the form of an electrobag filter. In the cyclone 28, gross particles are removed from the extracted gas via a gross particle exit 32. Such gross particles have low concentration of Zn. In the dry gas cleaning unit 30, flue dust is removed from the extracted gas via dust exit 34. Such flue dust has high Zn concentration. The remainder of the extracted gas may be fed via feed pipe 36 to another installation (not shown) for further use.

[0080] Fig.3 shows the top cone 14 of a blast furnace with a central gas uptake conduit 22 and another auxiliary gas cleaning unit 24. The auxiliary gas cleaning unit 24 of Fig.3 comprises a scrubber 38 for removing sludge from the extracted gas via sludge exit 40. Such sludge has high Zn concentration.

[0081 ] Fig.4 shows the top cone 14 of a blast furnace with a central gas uptake conduit 22 and another auxiliary gas cleaning unit 24. The auxiliary gas cleaning unit 24 of Fig.4 comprises a venturi ejector 42 for removing sludge from the extracted gas via sludge exit 44. Such sludge has high Zn concentration. The auxiliary gas cleaning unit 24 of Fig.4 further shows a return conduit 46 for feeding cleaned gas back into the throat 14 of the blast furnace.

[0082] Fig.5 shows the top cone 14 of a blast furnace with a central gas uptake conduit 22 and another auxiliary gas cleaning unit 24. The auxiliary gas cleaning unit 24 of Fig.5 comprises a cyclone 28 for removing gross particles from the extracted gas via the gross particle exit 32 and a venturi ejector 42 for removing sludge from the extracted gas via sludge exit 44. Furthermore, this auxiliary gas cleaning unit 24 also comprises a return conduit 46 for feeding cleaned gas back into the throat 14 of the blast furnace. The gross particle exit 32 is connected to the return conduit 46 and feeds gross particles having low Zn concentration into the cleaned gas, which is fed back into the throat 14 of the blast furnace. A further venturi ejector 48 is provided in the return conduit 46 for entraining the gross particles.

[0083] Fig.6 shows the top cone 14 of a blast furnace with a central gas uptake conduit 22 and another auxiliary gas cleaning unit 24. The auxiliary gas cleaning unit 24 of Fig.6 comprises a cyclone 28 for removing gross particles from the extracted gas via a gross particle exit 32 and a dry gas cleaning unit 30 for removing flue dust from the extracted gas via dust exit 34. A recirculation conduit 50 is connected between the dust exit 34 and the central gas uptake conduit 22 for feeding the removed flue dust, which is high in Zn concentration, into the central gas uptake conduit 22 upstream of the cyclone 28. The flue dust is thereby further coated with Zn and forms bigger dust particles.

[0084] Fig.7 shows the top cone 14 of a blast furnace with another central gas uptake conduit 22 and an auxiliary gas cleaning unit 24. The central gas uptake conduit 22 of Fig.7 is formed within an above burden probe 52 and has its uptake opening 26 arranged centrally in the furnace throat 14 in the vicinity of the axis of the blast furnace 10. The central gas uptake conduit 22 is connected to an auxiliary gas cleaning unit 24 as shown in Fig.3.

[0085] Fig.8 shows the top cone 14 of a blast furnace with a central gas uptake conduit 22 and an auxiliary gas cleaning unit 24 as generally shown in Fig.2. According to Fig.8, a combustion chamber 54 is provided in the central gas uptake conduit 22. Such a combustion chamber 54 is arranged for heating the extracted gas, thereby allowing oxidation of the Zn to ZnO, which is easier to separate.

[0086] It should be noted that, although many different combinations have been shown in Figures 2 to 8, these combinations are not exhaustive, indeed many other combinations are possible and well within the scope of the present invention.

Legend of Reference Numbers:

10 blast furnace 16 roof

12 furnace shaft 18 conventional top gas extraction 14 furnace top cone uptakes charging system 40 sludge exit central gas uptake conduit 42 venturi ejector auxiliary gas cleaning unit 44 sludge exit uptake opening 46 return conduit cyclone 48 further venturi ejector dry gas cleaning unit 50 recirculation conduit gross particle exit 52 above burden probe dust exit 54 combustion chamber feed pipe

scrubber

Claims

1 . A method for treating a Zn contaminated material in a blast furnace installation comprising a blast furnace charged with a traditional burden of iron ore and coke, a gas cleaning unit, and lateral top gas extraction uptakes connected between an upper top cone of said blast furnace and said gas cleaning unit, said method comprising the following steps:

a. Providing Zn contaminated material,

b. Charging said Zn contaminated material in a central area of a raw material feeding zone of a blast furnace in addition to the traditional burden of iron ore and coke,

c. Reducing the Zn contaminated material in the blast furnace so as to obtain a Zn enriched gas,

d. Extracting a Zn enriched gas from the blast furnace,

e. Treating said extracted Zn enriched gas in the gas cleaning unit.

2. The method according to claim 1 , wherein the Zn contaminated material is decarbonised before it is introduced into the blast furnace.

3. The method according to claim 1 or 2, wherein the Zn material is compacted before it is introduced into the blast furnace.

4. The method according to any of the preceding claims, wherein the Zn contaminated material is enclosed in a consumable container before it is charged in the blast furnace.

5. The method according to claim 4, wherein the consumable container comprises a metal foil.

6. The method according to any of the preceding claims, wherein the Zn contaminated material comprises sinter dust, BOF sludge, BOF dust, and/or electric arc furnace dust.

7. The method according to any of the preceding claims, wherein a Zn enriched gas is extracted from a central zone in an upper portion of the blast furnace, separately from lateral top gas extraction uptakes of the blast furnace and wherein said extracted Zn enriched gas is treated in an auxiliary gas cleaning unit.

8. A blast furnace installation comprising a blast furnace, a gas cleaning unit and lateral top gas extraction uptakes connected between an upper topcone of said blast furnace and said gas cleaning unit wherein a centre material feeding unit for feeding an optionally compacted, optionally decabruized Zn contaminated material in a central area of a raw material feeding zone of said blast furnace, a central gas uptake conduit, said central gas uptake conduit having an uptake opening arranged in the vicinity of a vertical axis of the blast furnace, in an upper portion of said blast furnace for extracting gas from an axial region of said blast furnace; and an auxiliary gas cleaning unit connected to said central gas uptake conduit for cleaning gas extracted via said central gas uptake conduit.

9. The installation according to claim 8, wherein said uptake opening of said central gas uptake conduit is arranged in the top cone or a throat region of said blast furnace.

10. The installation according to any of claims 8 or 9, wherein said uptake opening of said central gas uptake conduit is arranged at the level of the base of the top cone. .

1 1 . The installation according to any of claims 8 to 10, wherein said central gas uptake conduit is formed by a centre material unit comprising a material feeding pipe, said centre material feeding pipe being connected to a material hopper and to said auxiliary gas cleaning unit.

12. The installation according to any of claims 8 to 1 1 , wherein said central gas uptake conduit is within or on a probe reaching into said blast furnace.

13. The installation according to any of claims 8 to 12, wherein said uptake opening of said central gas uptake conduit is arranged above a level of burden within said blast furnace.

14. The installation according to any of claims 8 to 13, wherein said uptake opening of said central gas uptake conduit is arranged below a level of burden within said blast furnace.