Iron ore pellet

Abstract

The invention relates to iron ore pellets. Pellets comprising particulate iron ore and 0.05% to 1.0% by weight of an organic binder are described. The use of such pellets in the production of steel in an electric arc furnace is also described.

Description

[0001] This application is a divisional application of Chinese patent application filed on April 18, 2018, with application number “201880032924.6” and invention title “Iron Ore Pelletizing”. The original application was the Chinese national phase application of international application PCT / GB2018 / 051010. Technical Field

[0002] The present invention relates to iron ore pellets used in electric arc furnaces and methods for producing steel from such pellets. Background Technology

[0003] The production of briquettes from granular iron ore and other metallic ores is well known in the art. Typically, binders such as cement or clay are used to bind such granules together to form briquettes.

[0004] Such lumps are used in blast furnaces or direct iron reduction (DRI). The lumps are designed to be strong enough to allow them to be successfully conveyed and used within the blast furnace. The lumps must be able to maintain their integrity to pass through the blast furnace into the melting furnace; otherwise, the performance of the blast furnace or DRI equipment may be adversely affected. A problem associated with using cement or clay is that this increases the amount of silica in the iron and slag produced at the end of the process.

[0005] The high strength required for such clumps limits the use of more expensive binders, such as starch or polyvinyl alcohol (PVA).

[0006] An electric arc furnace, for example, heats a loaded material using an electric arc between two graphite electrodes. An electric arc is formed between the loaded material and the electrodes. The load is heated by the current passing through it and the radiant energy released by the electric arc, and can reach temperatures up to 3000°C.

[0007] Electric arc furnaces are typically used to produce steel from scrap metal. They typically use shredded scrap (from large household appliances, automobiles, or other lightweight steel) or large pieces of scrap (steel beams). The problem with using scrap metal is that the quality of the steel feed (and the steel produced from it) is usually poor. The steel often requires the addition of relatively expensive sponge iron or pig iron. The current cost of scrap metal is approximately $280 per tonne, while sponge iron is typically more expensive.

[0008] The applicant recognizes that using a cheaper iron source would make steel production using an electric arc furnace cheaper. One problem with using alternative sources, such as iron ore, is that the iron ore needs to be reduced to iron. This is typically not done in an electric arc furnace. However, the applicant recognizes that this alternative source can be used if iron ore pellet scrap can be used and a reducing atmosphere is used in the electric arc furnace.

[0009] The production of pellets for electric arc furnaces presents different challenges compared to conventional pellets used in blast furnaces. The pellets need to be heavy enough to penetrate the slag layer at the top of the furnace. However, they must also be porous enough to allow the iron ore within the pellets to react with the reducing atmosphere inside the furnace to produce iron. The iron is then mixed with scrap metal to produce the desired steel in the electric arc furnace. The bonds holding the particles together should also be weak enough to allow the particles to melt and disperse uniformly into the molten metal.

[0010] The use of granular materials increases the surface area of ​​the iron oxides, allowing them to react more effectively with a reducing atmosphere. Furthermore, the inventors realized that if an organic binder is used, it is burned off within the furnace's heat, increasing the porosity of the pellets and making them even more readily react with a reducing atmosphere. The cost of iron ore pellets is typically 100% higher than the spot price of iron ore (currently, the cost of pellets is approximately US$120 per ton). Therefore, this method reduces the price of steel produced by an electric arc furnace.

[0011] In addition, choosing cheaper reducing gases can also help reduce the cost of producing steel using electric arc furnaces. Summary of the Invention

[0012] This invention provides pellets comprising granular iron ore and less than 1.5% by weight of a binder. The binder is typically an organic binder. As mentioned above, organic binders have the advantage that they are typically removed by heat in a furnace to increase the porosity of the material within the furnace. The diameter of the granular material is typically 4 mm or smaller, more typically less than 1 mm, or less than 500 micrometers, or less than 100 micrometers. This can be determined by its ability to pass through a sieve. Typically, at least 10% by weight of the granular material is able to pass through a 100 μm sieve before being formed into pellets. More typically, a 30 μm or 20 μm sieve size is used to sieve the material. At least 50%, 80%, or 100% of the material can pass through the sieve.

[0013] It should be noted that the term "ball" includes objects commonly referred to as balls, rods, or pencil leads. Balls typically have a maximum average diameter of 20 mm, more commonly 16 mm or 15 mm, a minimum average diameter of 2 mm, particularly 5 mm, or an average diameter of 10 mm to 12 mm. These objects share the common characteristic of being a compacted form of material and are primarily distinguished by their size and shape.

[0014] The binder can be a polymer binder and can be selected from organic resins, such as polyacrylamide resins, methyl phenolic resins, or phenolic varnish resins; and / or polysaccharides, such as starch, hydroxyethyl methylcellulose, gum arabic, guar gum, or xanthan gum. Polysaccharides can be used as thickeners. Hydroxyethyl methylcellulose (MHEC) has been found to have a particularly good shelf life. It can be mixed with organic resins.

[0015] For example, the total amount of the binder may be 1.0 wt%, 0.8 wt%, 0.6 wt%, 0.5 wt%, at least 0.05 wt%, at least 0.1 wt%, or at least 0.2 wt%. When used in combination, the amount of polysaccharide relative to the resin may be from 0.1 wt% to 0.5 wt% of polysaccharide relative to 0.5 wt% to 0.1 wt% of resin.

[0016] Polyvinyl alcohol (PVA) can be used in amounts from 0% to 0.3% by weight, particularly from 0.1% to 0.2% by weight, as a substitute for or other adhesives. Typically, when needed, PVA is added in addition to other adhesives to improve uncured and cured strength.

[0017] Examples of starch include, for example, wheat starch, corn starch, and barley starch. More typically, starch is potato starch because it is relatively inexpensive.

[0018] Polyvinyl alcohol is commercially produced from polyvinyl acetate by reacting it with sodium hydroxide in a process known as saponification, which replaces the acetate groups of the acetate ester with hydroxyl groups. Partial saponification means that some acetate groups have been replaced by hydroxyl groups, thus forming at least partially saponified polyvinyl alcohol residues.

[0019] Typically, PVA has a saponification degree of at least 80%, usually at least 85%, at least 90%, at least 95%, at least 99%, or 100%. PVA is commercially available from, for example, Kuraray Europe GmbH in Germany. It is typically used as an aqueous solution. PVA can be modified to include, for example, sodium hydroxide content.

[0020] Typically, when in solution, PVA binders have an active polymer content of 12% to 13% and a pH in the range of 4 to 6.

[0021] Acetylated phenolic resins are alkali-catalyzed phenol-formaldehyde resins, in which the formaldehyde to phenol ratio is greater than 1 (usually about 1.5). Phenolic varnishes are phenol-formaldehyde resins, in which the formaldehyde to phenol molar ratio is less than 1.

[0022] Typically, no additional binders, such as inorganic binders like clay, are added to granular materials.

[0023] Trace amounts of surfactants such as SLS (sodium lauryl sulfate) can be added to improve the wetting of iron driven by the additive.

[0024] Typically, iron ore originates from tailings or dust from sources such as electric arc furnaces. The ore can be magnetite (Fe3O4) or hematite (Fe2O3). Iron ore may contain naturally occurring contaminants.

[0025] Granular iron ore can have a moisture content of less than 50%, more typically less than 30% or less than 25%. Typically, the moisture content is at least 2% by weight, at least 5% by weight, or 10% by weight.

[0026] Typically, biaxial mixing is used to agglomerate the mixture. Generally, a press or extruder is used to form pellets.

[0027] Waterproofing agents can be used to enhance the weather resistance of pellet materials. Waterproofing agents can be combined with granular materials (e.g., by spraying) or applied as a layer on the outer surface of the pellets. Examples of waterproofing agents include, for instance, styrene-acrylate copolymers and bitumen emulsions.

[0028] The pellets may additionally contain up to 20% by weight of carbonaceous material. This carbonaceous material can be, for example, coke, carbon black, peat, or coal. The coal can be of any grade, including lignite, sub-bituminous coal, bituminous coal, steam coal, or anthracite. The carbonaceous material is typically granular and may have the particle size defined above for iron particles.

[0029] The pellets may contain less than 15% by weight, less than 10% by weight, or less than 5% by weight of carbonaceous material.

[0030] Pellets are typically cold-formed, for example, without sintering before being placed in a furnace, or heated to above 60°C, above 40°C, or 30°C.

[0031] A method for producing steel is also provided, which includes heating pellets according to the invention in a furnace such as an electric arc furnace. Typically, the pellets are heated in a reducing atmosphere to convert the iron ore into iron to be incorporated into the steel. The reducing atmosphere can be, for example, hydrogen, shale gas, or other natural gas. Hydrogen is typically produced as a byproduct of processing fossil fuels. Shale gas is natural gas found trapped within shale formations. In the United States, it has become an increasingly important source of natural gas, and there is growing interest in potential gas-bearing shale formations that have spread to other parts of the world. It has become a relatively inexpensive source of natural gas. Alternative sources of natural gas include, for example, natural gas deposits from the North Sea gas fields off the coast of the United Kingdom.

[0032] This method typically involves mixing pellets with scrap metal. Generally, the total amount of pellets plus scrap metal is up to 50% by weight of iron ore pellets. More typically, the amount of pellets used is less than 40% by weight, less than 30% by weight, less than 20% by weight, or at least 5% by weight.

[0033] A method for producing pellets according to the invention is also provided, comprising mixing granular iron ore with a binder of up to 0.3% by weight. The binder and iron ore can be as defined above. As mentioned above, biaxial batching is typically used to agglomerate the mixture. Typically, an extruder can be used to form pellets.

[0034] Depending on the required compaction amount, the compaction amount of the pellets can be varied, for example, by subjecting the mixture of granular iron ore and binder to a larger or smaller vacuum. A larger vacuum will increase the compaction of the pellets. Alternatively, this can be controlled by the amount of pressure used to form the pellets.

[0035] The present invention also provides a method for producing steel, comprising providing pellets according to the invention, optionally produced by the method for producing pellets according to the invention, conveying the pellets to an electric arc furnace and producing steel by the method of the invention.

[0036] Pelletizing can be produced at a location separate from where it is used. That is, pellets can be produced at a deposit containing, for example, iron ore powder, which is combined with a binder to form pellets, and then transported to an electric arc furnace at a geographically separate location. The transport can be, for example, by ship, road, or rail.

[0037] Alternatively, the binder can be mixed with granular iron ore in essentially the same location as the electric arc furnace before being placed into the furnace.

[0038] The pellets can be fed into the electric arc furnace via, for example, a conveyor belt or other suitable means for moving the pellets into the furnace. Detailed Implementation

[0039] The invention will now be described by way of example only.

[0040] Study on the reduction characteristics of cold-bonded iron ore pellets under blast furnace, direct reduction and submerged arc furnace conditions

[0041] Various samples were tested using the following methods:

[0042] The pellets are placed in a small Inconel reaction vessel and surrounded by activated carbon particles. The vessel is then sealed and placed inside a muffle furnace. The furnace is circulated at various temperatures and times to simulate conditions within a full-scale apparatus.

[0043] The condition of the sample was assessed as it cooled naturally to room temperature.

[0044] 1. Sample type: Unrefined ore, mainly hematite.

[0045] 16 mm × 16 mm pellets using a binder comprising a powdered methyl phenolic resin and a liquid polymer binder for uncured strength. Cold compressive strength > 5 kN.

[0046] Test cycle

[0047] a. 60°C / 30 minutes

[0048] b. 600°C / 2 hours

[0049] c. 1000°C / 1 hour

[0050] result:

[0051] a. The sample exhibits microcracks that are easily visible under a microscope. The sample also shows some magnetism, indicating that it has been reduced to magnetite.

[0052] b. The samples were significantly magnetic, and their size increased by 1% to 3% due to swelling cracking.

[0053] c. The sample hardens and its dimensions return to their original size.

[0054] 2. Sample type: Selected ore, mainly magnetite.

[0055] 16 mm × 16 mm pellets using a binder comprising a powdered methyl phenolic resin and a liquid polymer binder for uncured strength. Cold compressive strength > 6 kN.

[0056] Test cycle

[0057] a. 60°C / 30 minutes

[0058] b. 600°C / 2 hours

[0059] c. 1000°C / 1 hour

[0060] result

[0061] a. No changes were observed.

[0062] b. When studied under a microscope, the pellets are inherently vesicular.

[0063] c. Dimensional variation - small, 5% to 10%, highly porous

[0064] 3. Sample type: Mixed BF waste

[0065] 16 mm × 16 mm pellets using a binder comprising a liquid polymer binder. Cold compressive strength > 5 kN.

[0066] Test cycle

[0067] a. 60°C / 30 minutes

[0068] b. 1100°C / 1 hour

[0069] result

[0070] a. Color change and intensity loss.

[0071] b. Highly porous, with increased strength and signs of sintering bonding.

[0072] 4. Sample type: Mixed EAF dust

[0073] 32 mm × 32 mm pellets using an organic liquid binder.

[0074] Test cycle

[0075] a. 60°C / 30 minutes

[0076] b. 1000°C / 1 hour

[0077] result

[0078] a- No change was observed

[0079] b - Volume decreases by 25%. Strength change is minimal.

[0080] Example:

[0081] 5. The moisture content of low-grade hematite ore tailings with a size of 0 to 50 micrometers was found to be 20%.

[0082] Add 0.5% of anionic polyacrylamide powder in the 500-micron size range to the ore and mix in a high-shear mixer. Add trace amounts of surfactants such as SLS as an aid to the production process.

[0083] The pellets were extruded through a 15 mm orifice using vacuum extrusion and cut into pellet size.

[0084] The moisture content was 20% before extrusion and 16% after extrusion.

[0085] The curing time is 24 hours at 25°C.

[0086] Test results: Compressive strength > 250 kg / cm² 2

[0087] For ISO 4696-2 static RDI=36

[0088] 6. High-grade magnetite concentrate with a density of 2.3 tons / m³ 3 Up to 2.5 tons / m 3 The grade ranges from 0 micrometers to 100 micrometers, with a moisture content of 13% + / - 3%. When refined to pellet grade, it exhibits typical characteristics of many hematite ores.

[0089] Add 0.2% of a synthetic thickener (e.g., hydroxyethyl methyl cellulose with a high molecular weight) and 0.5% of a water-soluble phenolic varnish resin in powder form to the ore, and then mix in a high-shear mixer.

[0090] Gum, such as gum arabic, guar gum, and xanthan gum, can also be used, but they have been found to have a shorter shelf life in the field.

[0091] The pellets were extruded through a 15 mm orifice using vacuum extrusion and cut into pellet size.

[0092] After curing at 25°C for 24 hours, the strength of the pellets is >250 kg / cm². 2 .

[0093] The thermal stability at 550°C and 900°C was found to be:

[0094] 550°C / 1 hour - maintain >50% intensity

[0095] 900°C / 1 hour - maintain >60% intensity

[0096] PvOH can be added to the mixture at a rate of 0.1% to 0.2% to increase both uncured and cured strength to >400 kg / cm². 2 .

[0097] 7. Dust from electric arc furnaces originating from bag filters

[0098] The alternative binder is a 2% solution of high molecular weight MHEC. Add 5% to 10% and mix with a high-shear mixer.

[0099] This application also relates to the following aspects:

[0100] 1. A pellet comprising granular iron ore and 0.05% to 1.0% by weight, typically less than 0.3% by weight, of an organic binder.

[0101] 2. The pellets according to aspect 1, wherein the organic binder is a polymeric organic binder.

[0102] 3. The pellets according to aspect 1 or 2, wherein the organic binder is selected from polyacrylamide resin, methyl phenolic resin, phenolic varnish resin, polyvinyl alcohol, and polysaccharides.

[0103] 4. The pellets according to any one of the foregoing aspects, wherein the granular iron ore is magnetic.

[0104] 5. The pellets according to aspects 1 to 4, comprising a waterproofing agent.

[0105] 6. The pellets according to aspects 1 to 5 further contain up to 20% by weight of carbonaceous material.

[0106] 7. The pellets according to aspects 1 to 6, wherein the granular iron ore is capable of passing through a 100 µm mesh before pelletizing.

[0107] 8. A method for producing steel, comprising heating pellets according to aspects 1 to 7 in an electric arc furnace.

[0108] 9. The method according to aspect 8, wherein the pellets are heated in a reducing atmosphere.

[0109] 10. The method according to aspect 9, comprising heating in a reducing atmosphere containing hydrogen, shale gas or natural gas.

[0110] 11. The method according to aspects 8 to 10, including mixing with scrap metal.

[0111] 12. The method according to aspect 11, wherein the pellets plus scrap metal are formed from iron ore pellets up to 50% by weight.

[0112] 13. A method for producing pellets according to aspects 1 to 7, comprising mixing granular iron ore with a binder of up to 0.3% by weight.

[0113] 14. A method of producing steel, comprising providing pellets, optionally produced by the method according to aspect 13, as described in aspects 1 to 7, conveying the pellets to an electric arc furnace, and producing steel by the method according to aspects 8 to 13.

Claims

1. A method of producing steel comprising: providing cold formed pellets, the pellets comprising particulate iron ore and 0.05 to 1.0 wt% of an organic binder, the organic binder comprising a novolak resin and polyvinyl alcohol; producing the pellets by mixing particulate iron ore with the binder; delivering the pellets to an electric arc furnace; and producing steel by heating the pellets in the electric arc furnace, wherein the pellets are not sintered or heated above 40°C to form prior to being placed in the electric arc furnace.

2. The method of claim 1, wherein the pellets further comprise an organic binder selected from a polyacrylamide resin, a resol resin, and a polysaccharide.

3. The method of claim 1 or claim 2, wherein the particulate iron ore is magnetic.

4. The method of any one of claims 1 to 2, wherein the pellets comprise a water repellent selected from a styrene-acrylate copolymer and an asphalt emulsion.

5. The method of any one of claims 1 to 2, wherein the pellets additionally comprise up to 20 wt% of a carbonaceous material.

6. The method of any one of claims 1 to 2, wherein the particulate iron ore is capable of passing through a 100 pm mesh prior to pelletizing.

7. The method of any one of claims 1 to 2, wherein the pellets are heated under a reducing atmosphere.

8. The method of claim 7, wherein the reducing atmosphere comprises hydrogen, shale gas, or natural gas.

9. The method of any one of claims 1 to 2, comprising mixing the pellets with scrap metal.

10. The method of claim 9, wherein up to 50 wt% of the pellets plus scrap metal are formed from iron ore pellets.

11. The method of any one of claims 1 to 2, comprising mixing the particulate iron ore with up to 0.3 wt% of the binder.