Electrolyzer for iron production using improved iron oxide feeder

Abstract

The present invention relates to an apparatus (1) for producing iron through the reduction of iron ore by electrolytic reaction, in which the means for feeding iron ore comprises a twin screw feeder (32) arranged to discharge iron ore powder (46) into an electrolyte feed pipe (31) upstream of an electrolyte chamber (6).

Description

[Technical field]

[0001] The present invention relates to an apparatus for producing iron by an electrolytic process. [Background technology]

[0002] Currently, steel can be produced on an industrial scale through two main production routes. The production route most commonly used today is the production of pig iron in a blast furnace by using a reducing agent, mainly coke, to reduce the iron oxide. This process consumes about 450 to 600 kg of coke per metric ton of pig iron. This process releases significant amounts of CO2, both in the production of coke from coal in the coking plant and in the production of pig iron.

[0003] The second main route involves the so-called "direct reduction process". Among them are processes by the brands MIDREX, FINMET, ENERGIRON / HYL, COREX, FINEX, etc., in which sponge iron is produced in the form of HDRI (high-temperature direct reduced iron), CDRI (low-temperature direct reduced iron) or HBI (high-temperature briquetted iron) by direct reduction of an iron oxide support. Sponge iron in the form of HDRI, CDRI and HBI is usually further processed in an electric arc furnace. Even if this second route emits less CO2 than the previous one, it still emits some and depends on more carbon fossil fuels.

[0004] Current developments are therefore focused on methods that make it possible to produce iron that emits less or no CO2 and is carbon neutral.

[0005] A known alternative method for producing steel from iron ore is based on electrochemical technology. In such technology, iron is produced from the iron oxide using an electrolysis unit comprising two electrodes (anode and cathode) connected to a current source, an electrolyte circuit, and iron oxide entering the electrolysis unit. The anode and cathode are constantly immersed in a circulating electrolyte to ensure good electrical conduction between said electrodes. The electrolysis reaction produces a pure iron plate and gaseous oxygen on the cathode. The iron plate thus obtained may then be melted in an electric furnace with other elements such as carbon-containing materials and scrap to produce steel.

[0006] The continuous and automated supply of iron oxide to the electrolyte is a critical component. The supply system must supply the iron oxide solid particles at the rate of their consumption by the electrolyte. Loss of control of the iron oxide content in the electrolyte reduces the faradaic yield and therefore adversely affects the productivity of the cell. One such control problem results from the propension of iron oxide, which becomes pasty and sticky when wet, especially when placed on a metal surface.

[0007] One solution is to stir the iron oxide with the liquid before feeding it into suspension in the electrolyte, but this leads to the entrapment of air into the liquid, which should be avoided due to neutralization of the alkalinity by carbonation from atmospheric carbon dioxide. Moreover, if such stirring is done manually, this action is dangerous due to the close proximity to the alkaline electrolyte. Summary of the Invention [Problem to be solved by the invention]

[0008] It is therefore an object of the present invention to ameliorate the shortcomings of the prior art by providing an improved oxide delivery apparatus which is capable of automatically discharging iron oxide powder in an electrolyte in a precisely controlled manner whilst preventing any air contact with the powder. It is also an object of the present invention to provide such an apparatus which is easy to manufacture and cost effective. [Means for solving the problem]

[0009] For this purpose, the device of the invention comprises a casing which contains a gas-permeable anode plate and a cathode plate, both facing each other and separated by an electrolytic solution (electrolyte) chamber. The casing further includes a degassing unit with a gas recovery section extending along the side of the gas-permeable anode plate opposite the chamber, the casing is provided with a means for circulating electrolyte in an electrolyte chamber having an electrolyte inlet and an electrolyte outlet, and a means for supplying iron ore to the electrolyte chamber, the means for supplying iron ore to the electrolyte chamber comprising a twin screw supply section arranged to discharge iron ore powder into an electrolyte supply pipe in fluid communication with the electrolyte inlet, the twin screw supply section having two parallel screws arranged inside a barrel, maintaining a shaft distance A between them, the two screws rotating in opposite directions while engaged with each other, the barrel extending from the screw rotation drive means to a discharge opening immersed in the electrolyte flowing through the electrolyte supply pipe, the barrel comprising an iron ore powder supply opening connected to the iron ore powder supply means.

[0010] The device of the invention may also include the following optional features, taken into account by the techniques individually or in all possible combinations: -The screw is arranged parallel to the gravitational force; - The electrolyte supply pipe is arranged perpendicular to the screw; - The surfaces of the two screws are smooth. -The two screws are twin concave coarse screws; - the ratio of the screw diameter (D) to the screw pitch (B) of each screw is in the range between 0.8 and 1.2; the barrel has a roughened inner surface and is disposed in mechanical contact with the screw; -The barrel is under nitrogen atmosphere, - the iron ore powder supply means comprises a pinch valve; -The equipment is powered by renewable energy.

[0011] Other characteristics and advantages of the present invention will become apparent in the following description, given by way of indication and in no way limiting, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a longitudinal section of an apparatus according to the invention including a twin screw feed section shown diagrammatically. [Diagram 2] FIG. 1 is a front view of a twin screw feeder positioned to discharge iron ore powder into an electrolyte supply tube. [Diagram 3] FIG. 2 is a perspective view of the ends of the two screws of a twin screw feed section. [Figure 4] FIG. 2 is a front view of two intermeshing screws of a twin screw feed section. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] First, it should be noted that in the figures, like reference numerals refer to like elements regardless of the figure they feature in and regardless of the form of those elements. Similarly, if elements are not specifically referenced in one of the figures, their reference can be readily found by referencing them in another figure.

[0014] It should also be noted that the figure represents primarily one embodiment of the subject matter of the invention, but other embodiments may exist that correspond to the definition of the invention.

[0015] The present invention refers to an apparatus 1 provided for the production of iron metal (Fe) through the reduction of iron ores, in particular containing hematite (Fe2O3) and other iron oxides or hydroxides, by electrolytic reactions. Said chemical reactions are well known and are described in particular in the case of hematite by the following equation (1):

number

[0016] It is therefore envisaged that the electrolysis reaction releases gases - mainly oxygen - which must be extracted from the device 1 .

[0017] With reference to FIG. 1, the device 1 comprises a casing 4 extending along a longitudinal axis X along which the electrolysis reaction takes place. Said casing 4 is defined by a base plate 20, a cover plate 13 and two side plates 21. In addition, the casing comprises a gas-permeable anode plate 2 intended to be completely immersed in an electrolytic solution (electrolyte) 5, and a cathode plate 3, both plates facing each other and kept at the required distance by means of fastening means (not shown in this figure). The casing 4 also comprises an electrolyte chamber 6 extending longitudinally between the anode plate 2 and the cathode plate 3 up to an exhaust chamber 22. The device 1 finally comprises a power supply (not shown) connected to the anode plate 2 and the cathode plate 3.

[0018] In a preferred embodiment, the power source uses renewable energy, defined as energy collected from renewable sources that are naturally replenished on human timescales, including sources such as sunlight, wind, rain, tides, waves, and geothermal heat. In an embodiment, the use of nuclear-derived electricity can be utilized, as it does not release the CO2 produced. This further limits the CO2 footprint of the iron production process.

[0019] To produce iron by electrolysis reaction, an electrolyte 5, preferably an aqueous solution such as, for example, aqueous sodium hydroxide, flows through the casing 4 in the electrolyte chamber 6 while the apparatus 1 is in operation. The apparatus 1 therefore comprises means for circulating the electrolyte, for example an electrolyte circuit managed in the casing 4 and connected to an inlet 24 and an outlet 25, both fluidly connected to the electrolyte chamber 6. Iron ore is introduced into the apparatus 1 as a powder suspension in the electrolyte 5 through the inlet 24, as will be further explained.

[0020] During the electrolysis reaction, the oxidized iron is reduced to iron by reaction (1), and the reduced iron is deposited on the cathode plate 3, while gaseous oxygen is released inside the casing 4. Since this gas is an electrical insulator, it interferes with the good operation of the electrolysis reaction and must be continuously vented outside the casing 4.

[0021] For this purpose, the casing 4 contains a degassing unit 7 with a gas collection section 8 extending longitudinally along the opposite side 27 of the anode plate 2 to the electrolyte chamber 6. This gas collection section 8 is a compartment arranged to be filled with electrolyte 5 and located between the anode plate 2 and the cover plate 13. Said gas collection section 8 is therefore arranged to collect gas leaking through the anode plate 2.

[0022] As illustrated in Fig. 1, the degassing unit 7 also comprises an electrolyte recirculation section 28, which extends in series with the gas recovery section 8 up to a gas outlet 29 managed by the casing 4. The electrolyte recirculation section 28 is arranged to be at least partially filled with electrolyte 5. In addition, said recirculation section 28 is in fluid connection with the electrolyte chamber 6. When the device 1 is in operation, the recirculation section 28 allows the electrolyte 5 flowing from the gas recovery section 8 to be redirected towards the electrolyte chamber 6, for example via an elbow duct 30 fluidly connected to the electrolyte chamber 6, adjacent to the anode plate 2.

[0023] 1, in accordance with the present invention, the means for feeding iron ore to the electrolyte chamber 6 comprises a twin screw feed 32 positioned on an electrolyte supply pipe 31 in fluid connection with the electrolyte inlet 24. The twin screw feed 32 traverses a wall 33 of the electrolyte supply pipe 31 and discharges the iron ore powder into the electrolyte flow 5.

[0024] 2, the twin screw feeder 32 comprises two output shafts 35, 36 arranged parallel to each other, maintaining a constant shaft distance between them and rotating in opposite directions, and a gearbox 34. The gearbox 34 transmits the torque obtained from a drive motor 37 connected to the gearbox 34 through the output shafts 35, 36 to the two screws 38, 39.

[0025] The bases of the two screws 38 , 39 are connected to the output shafts 35 , 36 , and the free parts 42 , 43 opposite the bases are immersed in the electrolyte 5 flowing through the electrolyte supply pipe 31 .

[0026] The two screws 38, 39 are arranged in parallel within the barrel 40 and maintain a shaft distance between them. Thus, the two screws 38, 39 rotate in opposite directions within the barrel 40 while engaging with each other.

[0027] The barrel 40 extends from the gearbox 34 to a discharge opening 41 immersed in the electrolyte 5. The free parts 42, 43 of the two screws 38, 39 are located at the discharge opening 41. The dimensions of the barrel 40 are adapted to those of the two screws 38, 39, with a small mechanical clearance between the screws 38, 39 and the barrel 40, due to the low free surface of the electrolyte 5. The electrolyte 5 can thus rise in the barrel 40 at least to the level of the wall 33 of the electrolyte supply pipe 31, thereby defining a dry conveying region and a wet conveying region and allowing the discharge of the iron oxide powder into the electrolyte 5 in a non-agglomerated state.

[0028] The inner surface of the barrel 40 is advantageously roughened and edged with counter-rotating helices to provide high friction with the two counter-rotating screws 38, 39. This makes it possible to prevent bridges and cavities from forming.

[0029] The barrel 40 is provided with an iron feed opening 44 through which iron oxide powder 46 is discharged into the interior of the barrel 40 onto the surfaces of the two counter-rotating screws 38, 39, so that the iron oxide powder 46 is conveyed to the discharge opening 41.

[0030] The iron feed opening 44 is connected to a valve 45, for example a pinch valve, through which iron oxide powder 46 is fed to the iron feed opening 44.

[0031] The iron feed opening 44 is located above the maximum level of the electrolyte in the barrel 40 during operation. Such a position allows the dispersion of the iron oxide powder in the electrolyte under gentle mixing conditions after being conveyed by the two screws 38, 39, thus avoiding agglomeration of the powder. These conditions achieve wetting of the powder by ensuring maximum exposure to the electrolyte.

[0032] The amount of iron oxide powder 46 discharged into the electrolyte 5 is controlled by a command means (not shown) according to the rate at which the iron oxide is consumed by electrolysis.

[0033] The barrel 40 is airtight and maintained under a nitrogen atmosphere by means not shown, so that the dry iron oxide powder conveyed by the two screws is air-free and therefore any air contact with the electrolyte is avoided.

[0034] The twin screw feeder 32 is advantageously positioned parallel (perpendicular) to the gravitational pull, thereby providing gravity assistance for transporting the iron oxide powder into the electrolyte.

[0035] Advantageously, the electrolyte supply pipe 31 is arranged vertically to the twin screw supply 32 and then horizontally.

[0036] With reference to figures 3 and 4, the two screws 38, 39 are identical for an optimized joint. The two screws 38, 39 engage with each other and are maintained parallel to each other with a shaft distance A smaller than the diameter D of each screw 38, 39. The surfaces of the two screws 38, 39 are smooth and are preferably prepared by electrolytic polishing. The rotation of the two screws 38, 39 in opposite directions allows the two screws 38, 39 to finely expel the iron oxide powder into the electrolyte while being self-cleaning. Thus, the surface of the screws remains smooth while avoiding any powder agglomeration. The two screws 38, 39 are co-rotating to operate with a small pumping effect, thus limiting air vortexes. Preferably, the two screws 38, 39 are twin concave coarse screws and the roots 47 of the two screws 38, 39 are deep. Advantageously, the ratio of screw diameter (D) to screw pitch (B) of each screw (38, 39) is between 0.8 and 1.2. Below this range there is a risk of compressing the powder, but above this range there is no longer enough pressure for the forward movement of the powder.

Claims

1. An apparatus (1) for producing iron through the reduction of iron ore by an electrolytic reaction, said electrolytic reaction releasing a gas, the apparatus comprising a casing (4), the casing (4) comprising a gas-permeable anode plate (2) and a cathode plate (3), both of which are opposite each other and separated by an electrolyte chamber (6), The casing (4) further comprises a degassing unit (7) having a gas collection section (8) extending along the side of the gas-permeable anode plate (2) opposite the chamber (6), The casing (4) is provided with means (24, 25) for circulating an electrolyte (5) in an electrolyte chamber (6) having an electrolyte inlet (24) and an electrolyte outlet (25), and means for supplying iron ore to the electrolyte chamber (6), said means for feeding iron ore to said electrolyte chamber (6) comprises a twin screw feeder (32) arranged to discharge iron ore powder (46) into an electrolyte feed pipe (31) in fluid communication with an electrolyte inlet (24); The twin screw feeder (32) is provided with two parallel screws (38, 39) inside a barrel (40) and maintaining a shaft distance (A) between them, the two screws (38, 39) rotating in opposite directions while engaged with each other; The barrel (40) extends from the screw rotation drive means (34, 37) to a discharge opening (41) immersed in the electrolyte (5) flowing through the electrolyte supply pipe (31), and the barrel is provided with an iron ore powder supply opening (44), the iron ore powder supply opening (44) being connected to an iron ore powder supply means (45). Device.

2. 2. The device according to claim 1, wherein the screws (38, 39) are arranged parallel to the gravitational force.

3. 3. The device according to claim 2, wherein the electrolyte supply pipe (31) is arranged perpendicular to the screws (38, 39).

4. A device according to any one of claims 1 to 3, wherein the surfaces of the two screws (38, 39) are smooth.

5. An apparatus according to any one of the preceding claims, wherein the two screws (38, 39) are twin concave coarse screws.

6. A device according to any one of the preceding claims, wherein the ratio of the screw diameter (D) to the screw pitch (B) of each screw (38, 39) is in the range 0.8 to 1.

2.

7. The device according to any one of the preceding claims, wherein the inner surface of the barrel (40) is roughened and is placed in mechanical contact with the screws (38, 39).

8. The apparatus according to any one of claims 1 to 6, wherein the barrel (40) is under a nitrogen atmosphere.

9. Apparatus as claimed in any one of the preceding claims, wherein the iron ore powder supply means comprises a pinch valve (45).

10. 10. The device according to any one of claims 1 to 9, powered by renewable energy.

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