FR2488149A1 - Gas magnetic dust filter - having central core with coil and ring filter for magnetic and non-magnetic particles - Google Patents

Abstract

The dust separator consists of a vessel (3) with a gas inlet (1) and outlet (2). The centre of the vessel contains a filter (4) and a central core (5) which can produce a magnetic field in the filter. The core has a coil (7) carrying a current from the supply (13). The dusty gas passes through the passages (12) in the filter where the magnetic particles are held and the non magnetic particles are retained in the filter. The filters may also be assembled in parallel banks connected to a hopper.

Description

 The present invention relates to a method for treating gaseous waste leaving a steelmaking furnace, a reduction pellet making furnace, etc., as well as an apparatus for practicing said method and more particularly relates to a method and apparatus for treating such waste gases using a magnetic separation process.

 Steel furnaces, such as blast furnaces, converters, arc furnaces, cupola furnaces, etc., as well as reduction pellet furnaces produce gaseous waste which contains gases such as: carbon dioxide, carbon dioxide, nitrogen, hydrogen, etc., as well as iron oxide dust, for example Fe3O, FezO3, etc., and oxide dust. non-ferrous metals, for example ZnO, MnO, etc. Since such gaseous waste can not be discharged into the surrounding atmosphere without contaminating it, the aforementioned dusts (which will be referred to hereinafter by the generic term dust, intended that is, that the dust from a steelmaking furnace, etc., contains both iron oxides and nonferrous metal oxides) is recovered in a collection apparatus. Since these dusts, directly discharged into the atmosphere, cause secondary pollution, some treatment is usually carried out before discharge. In recent years, there has been an increasing attempt to reuse them, for example by reducing them for use as a raw material in the manufacture of steel, or for recovering zinc, zinc oxides, etc.

However, this treatment requires a large installation, which is therefore storytelling. On the other hand, since the dusts are composed of iron oxides, non-ferrous metal oxides and other geographically and physically mixed components in the form of an integrated mass, it has been found extremely difficult to separate them, and only by involving excessively high separation costs so that such separation into individual components is not carried out commonly. In the present situation where the conservation of resources is a widely recognized objective, it is quite desirable to have a simple separation and recovery process.

 To satisfy such a desire, a method has been proposed which consists of separating iron dust and iron dioxides by direct contact with solid particles in a high temperature atmosphere, and then cooling the gas in a drawn stream to ensure agglomeration of a non-ferrous metal to effect separation (Japanese Patent Application No.

50440/1980). However, this method has drawbacks because it requires a large installation and the separation capacity is low for the expenses incurred.

 Depending on such circumstances, it has therefore been sought to develop a simple method of separation, and an apparatus for its implementation, which eliminate the disadvantages mentioned above. The inventors have discovered that the dust, once trapped in a collector, is a complicated mixture in which different components are nested within one another and therefore can not be separated by a single magnetic action, and have, besides the dust , when they are still in a flue before entering the dust collector, and when they are knocked into a hopper, are in the state where the components are in a floating condition and relatively independent of each other and can be easily separated by the magnetic action, which resulted in the development of the present invention.

 Accordingly, the invention relates to a novel method for magnetically separating dust, as well as an apparatus for carrying out said method. The method according to the invention consists in generating a magnetic field gradient in a gaseous waste pipe leaving a steel-making furnace, etc., in separating magnetic dust (which comprises dusts consisting of magnetic materials and of dust consisting of magnetic materials and non-magnetic materials affixed thereto) of the dust contained in the gaseous waste cooled by selective adsorption, and then to retain the resulting non-magnetic dust in a dust collector; the invention further relates to a dust separation apparatus which is characterized in that there are provided a plurality of magnetically permeable cylindrical bodies, each of which has an inner surface on which there is disposed, with the possibility of removal, a magnetic field gradient, in the waste gas conduit, or a magnetically permeable cylindrical body whose outer surface is provided, with possibility of removal, of a magnetic field gradient forming material, in at least a portion of the waste gas duct, the magnetic dust contained in the gaseous waste being stopped by adsorption of said dust on the outer surface or the inner surface of each of said cylindrical bodies and then the magnetic field gradient forming material being removed from each of said cylindrical bodies to suppress the magnetic field, in favor thus recovering the dust from the outer surface or the inner surface of each of said cylindrical bodies.

Other advantages and characteristics of the invention will be highlighted, in the remainder of the description, given by way of non-limiting example, with reference to the appended drawings in which:
FIG. 1 is a vertical sectional view showing a first embodiment of the dust separation apparatus according to the present invention;
FIG. 2 is a sectional view of the apparatus of FIG. 1 taken on the line II-II;
FIG. 3 is a perspective view, partially broken away, of a second embodiment of the dust separation apparatus according to the present invention;
FIG. 4 is a perspective view, partly cut away, of the cylindrical body involved in the second embodiment;
FIG. 5 is a partial perspective view showing another embodiment of the cylindrical body; ;
FIG. 6 is a diagram giving an example of practice of the present invention;
FIG. 7 is a diagram giving an example of the installation in the vicinity of the separation apparatus;
FIG. 8 gives a series of photomicrographs showing an example of the dust condition in the gaseous waste pipe, a being a photograph of Fie304, Fe203, etc. dust. with a magnification of x 10000, while b is a dust photograph of ZnO, etc., with a magnification of 30000.

The dust to be separated in accordance with the present invention is dust contained in gaseous waste from the steel-making furnaces, etc., mentioned above, and contains components such as
Fe, FeO, Fe3O4, Fe2O3, ZnO, MnO, SiO2, CaO, NiO, Au2O3, PbO,
Cr 2 O 3, CdO, MgO, Na 2 O, K 2 O, NaCl, KCl, etc., and although the composition of the dust varies depending on the particular type of steelmaking furnace, etc., and the operating conditions of the furnace the present invention may be applied to any dusts provided that they contain a magnetic component such as magnetite (fie304, etc., and a non-magnetic component.

The gaseous waste leaving the steel-making furnace is generally at a high temperature, for example 1000 ° C. or more, and it contains non-ferrous metals such as zinc, lead, etc., in the form of steam; in the case of a beam, during the combustion of a combustible gas leaving the steel-making furnace in a combustion tower, they become oxide-based dusts as described above. Then the gaseous waste is cooled in a cooling tower to about 2000C. This is because, if the temperature is above about 3000C, the magnetization of the magnetic materials is reduced and is therefore not advantageous.In the course of this process, iron oxides and non-ferrous metal oxides become crystals with their particular shapes and they pass into the channel of gaseous waste.

For example, Fe3O4, Fe2O3, etc. have the spherical shape shown in FIG. 8 (a), while ZnO takes the form of needles having a length of 1 or more, as shown in FIG. 8 (b). The magnetic separation is carried out by establishing in the duct in which the dust passes a magnetic field gradient and by adsorbing the magnetic components. In a small installation or laboratory equipment, a magnet can be placed in a flue so that the dust containing a high concentration of magnetic materials can be attracted by the magnetic force, but for best performance, it is better to use a magnetic separation apparatus such as that shown for example in Figures 1 and 2.

 More particularly, in the magnetic separation apparatus shown in FIGS. 1 and 2, there is provided inside a cylindrical container 3 provided with an inlet 1 and an outlet 2 of gaseous waste, a hollow filter 4 of annular shape, and a device for generating magnetic field 5 comprising an iron core surrounded by a coil 7 is placed in the hollow part of the filter. When an electric current is applied to the coil 7 from a current source 13, a magnetic field is generated around the coil 7 and filtering agents 8 of the filter 4 which are now in the magnetic field are united In these conditions, when the waste gas containing the dust is introduced into the filter container 3 via the inlet 1 and coming from a flue or other duct 9, the gaseous waste passes through the liquefaction. the gap between the filter container 3 and an inner container 10, then they pass through the filtering agents 8 through holes 11a formed in a pole piece 11 of the filter 4, and they pass through holes 12a d a pole piece 12 placed on the output side, and they are finally discharged via the outlet orifice 2. In this case, since the gaseous waste passes through the filtering agents 8 which are magnetized, magnetic particles contained in the dust, such as Fe, Fe304, etc., are selectively adsorbed on the surface of the filtering agents 8 by the magnetic action produced. On the other hand, non-magnetic dusts, for example non-ferrous metal oxides, are not adsorbed, but pass through filtering agents 8 and are discharged through outlet 2. Accordingly; as a result of this selective adsorption of magnetic dust, the dust discharged from the plant now contains a high concentration of non-magnetic oxides.

 Figures 3 and 9 show the second embodiment of the magnetic separation apparatus according to the invention; 102 has been designated by a chamber placed at a distance in a horizontal duct 101 for the passage of gaseous waste from a steel-making furnace, etc., and a number of cylindrical bodies 104 are arranged vertically through a raised bottom. 103 of said chamber and projecting downwards in the waste gas conduit.

Several magnets in the form of elongated bars have been designated by 105, each of which can slide upwards and downwards in each cylindrical body 104, the insertion and retraction operations of the magnets being carried out ensuring the winding and unwinding of a cable (not shown) via uprights 106 which are provided vertically on the bottom of register 103, manual operating handles 108 which are fixed on a frame 107 placed horizontally on the uprights 106 and rotating rollers 109 which are each directly connected to the corresponding handle.

Several angles have been designated by 110 which are each mounted on the frame 107 in parallel and at intervals so that each angle is in contact with the cylindrical bodies 104 of a row. A cover 103a serves to cover the raising and lowering mechanism of said magnets 105. A control window 111 is designated on the side of a chamber 102. Windproof plates 112 are provided below the cylindrical bodies 104 to prevent the penetration of gaseous waste and hoppers 113 are placed at the base of the apparatus, the upper part of each hopper being provided with a basket 114 for collecting dust.

In the structure described above, the cylindrical body 104 may have a horizontal cross section of any suitable shapes, for example circular as indicated on the
Fig. 4 (a), or square as shown in FIG. 4 (b), etc. However, this body must be formed of a nonmagnetic material which must have magnetic permeation properties so that the magnet 105 introduced into said body can adsorb magnetic materials found in gaseous waste passing on the outer surface of the body. cylindrical 104 by a magnetic permeation action through the cylindrical body 104; Materials having this property of magnetic permeation include aluminum, plastics, brass, natural or synthetic rubbers, etc. The magnet to be introduced into each cylindrical body 104 is constituted, for example, as the show partially broken away perspective views of FIGS. 4 (a) and 4- (b), numerous magnetic blocks 105a which are stacked vertically on a centrally located suspension bar 116 and that identical poles are directed towards each other (this is that is, a pole to a north pole and a south pole to a south pole), with the interposition of armatures 105b for producing an extension of the magnetic field.

 In the dust separation apparatus described above, when gaseous waste from a steelmaking furnace, etc., enters the chamber 102 via the inlet 101a in the indicated horizontal direction. by the arrow, the gaseous waste is directed towards the outlet 115, but their passage is impeded by the windproof plates 112 during this period, and only the particles of magnetic materials contained in the gutters and entrained by the gaseous waste are stopped by adsorption on the outer surface of the cylindrical bodies under the effect of the magnetic force generated by each magnet 105 introduced into the corresponding cylindrical body, said cylindrical bodies being arranged vertically in the chamber 102.

On the other hand, the non-magnetic materials that have not been stopped leave the chamber 102 via the outlet 115 and are stopped in a known dust collection device, such as a bag filter. , not shown in the figures. Accordingly, by controlling the accumulation of particles of magnetic material adsorbed on the outer surface of said cylindrical bodies 104, the operation is carried out, when the amount of adsorbed material is sufficiently high, so as to rotate the rollers 109 through the handles 108 for winding the cables 107a on the rollers 109 in order to get the magnets 105 out of the cylindrical bodies 104 to suppress the magnetic field, so that the magnetic dust then falls by gravity. The angles 110 placed in contact with the cylindrical bodies 104 are subjected to percussion, for example by means of a hammer, to detach the magnetic dust still retained. The magnetic dust thus removed is collected in the baskets 114 provided at the top of each hopper 113.

 With the dust separation apparatus corresponding to the example described above, the magnetic dusts are adsorbed on the magnets indirectly via the magnetically permeable and non-magnetic bodies (cylindrical bodies), so that the gaseous waste and the magnets are not in direct contact with each other in the gas conduit and, therefore, when recovering these adsorbed magnetic dusts, a simple operation of moving the magnets away from the non-magnetic materials allows an efficient separation, since said dusts are not adsorbed directly onto the magnetic surfaces.

Fig. 5 is a perspective view showing another embodiment of the cylindrical body used in the dust separation apparatus according to the present invention; in this case, a cylindrical body 104 is provided on its outer surface with a series of magnetic blocks 105a stacked with the interposition of frames 105b, in the same manner as described above, to form a magnet 105 which is under the shape of a U-shaped column, which is removably mounted in the direction indicated by the arrows
P and P '. Waste gaseous pass through the cylindrical body 104 in the direction indicated by an arrow Q so that the body adsorbs magnetic dust on its inner surface; for the separation and recovery of magnetic dust, the magnet 105 is removed from the cylindrical body 104 by other mechanical means. In the example considered, if the cylindrical body 104 is formed of a flexible material such as cloth, soft plastics, etc., the cylindrical body 104 is in the form of a bellows and the magnet is arranged. 105 around its outer surface as shown in FIG. 5, which increases in correspondence the surface available for the adsorption of magnetic dust. Alternatively, it is of course possible to make the cylindrical body using a non-flexible material such as aluminum, etc., as described above.

 The separated magnetic dusts are, if desirable or necessary, again subjected to a magnetic separation, and the products obtained are used as medium to low-grade magnets, as raw materials for the manufacture of ferrite, rust-resistant paints, while the non-magnetic dusts are stopped in the dust collector from which it is possible to recover, for their use, metals such as zinc, lead, etc. The recovery of zinc, lead, etc., from the dust can be carried out in this case economically because zinc, lead, etc., exist with high concentrations in the dust because most of the magnetic materials have already been magnetically separated.

As a result, dusts that were previously discarded can be separated and recovered for commercial reuse, saving metal resources.

 As an example of practicing the present invention, reference will be made to the scheme of FIG. 6 a waste treatment application from an arc furnace. The gaseous waste from the arc furnace designated AF is introduced into a combustion tower FT where the CO carbon monoxide contained in the gases is shaken and where, simultaneously, iron and non-ferrous metals are oxidized.

Then, the gases are cooled to about 2000C in a cooling tower CT and they are introduced, via a conduit 209, into a magnetic separation apparatus M where the magnetic dust. are separated and where the remaining dust enters a dust collector C, under the impetus of a fan B, which allows to collect dust 213 containing a high concentration of ZnO. Then, the zinc contained in this dust 213 is recovered. On the other hand, the magnetic dust is channeled to a ME magnetic separation apparatus, and they are separated therein in the form of magnetic dust 214 containing a strong magnetic dust. concentration of magnetic components, and dust 215 containing a large part of the residual components, the first stresses 214 being used, for example, as medium to low quality magnets, as raw materials for the manufacture of ferrite, rust paints etc.

 In addition, the environment of the magnetic separation apparatus M according to this first embodiment can also be arranged as shown in FIG. 7.

More particularly, when a valve V1 is open, gaseous waste is introduced: via a conduit ~ 209 into the magnetic separation apparatus M where they are separated in the form of magnetic dust and non-magnetic dust , the latter being conveyed to a dust collector C via a valve V2. During the operation of the magnetic separation apparatus M, the valves V3, V4 and V5 are closed.

During the blow discharge of the magnetic dust deposited in the apparatus M, the valves V1 and V2 are closed while the valves V4 and V5 are open and the electric current applied to the coil is cut off, after which the valve V3 is opened to introduce a stream of air from an AT tank into the magnetic separation apparatus M, while the backwardly flowing gases pass through the valve V4 and enter a cyclone S or a filter S bag in which the dust 216 is stopped, the remaining dust passing through the valve V5 and entering the dust collector C. The pillows 215 are used as medium to low quality magnets, as raw materials for manufacturing ferrite, anti-rust paints, etc.

 Thus, the present invention is characterized by generating a magnetic field gradient in a waste gas conduit prior to a dust collection and dust separation phase using a magnetic force.

The reason why such a separation is possible is explained by the fact that the respective components of the dust, during their passage through the waste gas duct, and as is evidenced by the photographs of Figs. 8 (a) and 8 (b) are in a floating condition and relatively free without interfering with each other, and it is only in such a condition of freedom that separation by a magnetic force is possible. Floating conditions of the dust passing through the waste gas conduit were first discovered by the inventors and the present invention was derived from this discovery. Once the dust is collected, for example by a suitable collector, and the components The respective crystals are inter-mixed, the needle-shaped crystals are intricately interwoven with the spherical crystals, as shown in FIG. 8 (b), and it is no longer possible to effect a separation by a magnetic force.

 In addition, since the magnetic separation apparatus according to the present invention is provided with a structure such that non-magnetic and magnetically permeable elements, provided with removable magnets, are installed in a gas conduit, and since the magnetic components The dust content can be adsorbed on the surfaces of the elements without direct contact with the magnets, the advantage is obtained that the deposited compounds can be recovered very easily by removing the magnets magnetically permeable elements to suppress the magnetic field.

In addition, the separated dusts can be used in the state where they are obtained, or they can be regenerated and used in different applications, which makes it possible to efficiently exploit the dusts.

 The invention will be described more particularly with reference to the following example, but it goes without saying that the invention is not limited to this example.

EXAMPLE
In accordance with the scheme of FIG. 6, waste gas generated by an arc furnace for the manufacture of steel is cooled to about 2000C, and the magnetic separation apparatus shown in FIG. -1 to obtain magnetic dust A. High dust concentration B was then obtained by the dust collector and the dust A was again subjected to magnetic separation by another magnetic separation apparatus so as to obtain dust magnetic C and residual dust D after this new magnetic separation. The magnetization and composition of each batch of dust are shown in Table I below.

By way of a reference, the dust collected in the collector without operating the magnetic separation apparatus was also analyzed and their magnetization and composition in the array designated by (E) were used in the same table.

TABLE I

<tb><SEP> Lot <SEP> Magne- <SEP> Composition <SEP> f% <SEP> in <SEP> weight)
<tb><SEP> of <SEP> tisa
<tb> p <sep>SEP> Fe304 <SEP> Fe203 <SEP> ZnO <SEP> MnO <SEP> SiO2 <SEP><SEP> CaO <SEP> Other <SEP> Total <SEP>
<tb> sisters <SEP> (emu / g)
<tb><SEP> (E) <SEP> 25.1 <SEP> 30 <SEP> 20 <SEP> 15 <SEP> 4 <SEP> 6 <SEP> 5 <SEP> 20 <SEP> 100
<tb><SEP> (A) <SEP> 50.5 <SEP> 61 <SEP> 9 <SEP> 3 <SEP> 2 <SEP> 4 <SEP> 5 <SEP> 16 <SEP> 100
<tb><SEP> (B) <SEP> 4.3 <SEP> 5 <SEP> 29 <SEP> 25 <SEP> .5 <SEP> 8 <SEP> 5 <SEP> 23 <SEP> 100
<tb><SEP> (C) <SEP> 61.1 <SEP> 68 <SEP> 8 <SEP> 3 <SEP> 2 <SEP> 3 <SEP> 3 <SEP> 13 <SEP> 100
<tb><SEP> (D) <SEP> 1.9 <SEP> 1 <SEP> 19 <SEP> 5 <SEP> 5 <SEP> 16 <SEP> 16 <SEP> 38 <SEP> .100
<Tb>
Table I shows that, when using the magnetic separation apparatus according to the invention, there is a high concentration of iron oxides, especially Fe 3 O 4, in the magnetically separated dusts A, while there is a concentration of ZnO up to 25% in dust with a high concentration of ZnO B. treat the dust containing 25% ZnO by reduction using, for example, a rotary kiln to recover ZnO, Zn, etc., for reuse. Magnetic dust C showed, after a new magnetic separation operation, a Fe304 content of up to 68%, which allows them to be used as medium to low magnets, as raw materials for the production of ferrite.

 Of course, the present invention is not limited to the embodiments described and shown; it is capable of many variants accessible to those skilled in the art, depending on the intended applications and without departing from the spirit of the invention.

Claims (5)

 1. A process for magnetically separating dusts entrained in gaseous waste and containing iron oxides and non-ferrous metal oxides, characterized in that a magnetic field gradient is generated in a gaseous waste pipe, in that The dust entrained in the gaseous waste is separated in the form of magnetic dust and non-magnetic dust and the non-magnetic dust is stopped in a dust collector.  2. A method of magnetic separation according to claim 1, characterized in that the non-ferrous metal oxides are mainly constituted by zinc oxide.  3. Apparatus for separating dust entrained in gaseous waste containing magnetic materials by passing gaseous waste in a conduit in which a gradient of magnetic field is generated, characterized in that there is provided a plurality of cylindrical bodies magnetically permeable materials (104), each of which has an interior surface on which a magnetic field gradient forming material, in the waste gas conduit, or a magnetically permeable cylindrical body having a surface is provided, with possibility of removal, of a magnetic field gradient forming material, in at least a portion of the gaseous waste pipe, the magnetic dust contained in the gaseous waste being stopped by adsorption of said dust on the outer surface or the inner surface of each of said cylindrical bodies and then the magnetic field gradient forming material being removed from each of said cylindrical bodies to suppress the magnetic field, thereby allowing the recovery of dust from the outer surface or inner surface of each of said cylindrical bodies (104). ).  4. Apparatus for separating dust according to claim 3, characterized in that the material for forming the magnetically permeable cylindrical body (104) is a flexible material.  5. A dust separation apparatus according to claim 3, characterized in that the magnetic field gradient forming material is composed of magnetic blocks (105a) stacked in the form of a structure such that identical poles are directed one towards the other, with the interposition between them of a frame (105b).