Method for producing iron ore agglomerates for use in direct reduction reactors and agglomerate products

Abstract

A method for producing iron ore agglomerates for use in a direct reduction furnace includes dispersing nanomaterials in a binder, combining the resulting mixture with iron ore fines and / or steelmaking by-products and additives, adjusting the moisture content, performing agglomeration, hardening the agglomerates, and applying a surface coating to mitigate sticking in the direct reduction furnace.

Description

[Technical Field]

[0001] The present invention belongs to the field of mining and metallurgical technology and relates to a method for producing iron ore agglomerates for use in direct reduction (DR) reactors, with the aim of using them as an alternative to the conventionally used pellets and lumps. [Background technology]

[0002] Direct reduction reactors are characterized by the reduction of iron ore to metallic iron within the reactor without melting the charge. The resulting solid metal product is called sponge iron (also known as direct reduced iron (DRI)) and can be hot briquetted to obtain hot briquette iron (HBI).

[0003] Direct reduction processes are an alternative to using a blast furnace to produce an intermediate product with the same basic function as the pig iron produced by a blast furnace. Both intermediate products (pig iron and sponge iron) are intended to be used in the production of steel in steel mills, with sponge iron being used in electric arc furnaces. The best-known direct reduction processes are Midrex, HyL, Armco, H.Iron, SL-RN, and Purofer.

[0004] To optimize the performance of the direct reduction reactor and obtain a high quality end product (sponge iron), the iron ore agglomerates fed must have specific physical, chemical and metallurgical properties.

[0005] The current state of the art offers several ore agglomeration techniques for application in reduction furnaces, however, none of these techniques has been able to produce agglomerates with the specific metallurgical properties required for optimal performance in direct reduction reactors, such as those provided by the present invention.

[0006] Patent BR102019023195-5 by Vale SA describes an agglomerate of iron ore fines for use as a replacement for metal charge in a blast furnace, but unlike the present invention, it is not directed to the production of agglomerates with specific properties intended for feeding into direct reduction reactors such as Midrex and HyL. Patent BR102019023195-5 also uses fluxes and raw materials different from those used in the present invention. Furthermore, the patent does not include the coating application step required in the present invention.

[0007] Patent No. BR112014005488-6 by Vale SA describes a process for obtaining agglomerates, but differs from the present invention in the following respects: (i) the raw materials used, (ii) the absence of a coating step, (iii) application to agglomerates obtained by pelletizing techniques (e.g., minipellets), and (iv) the product according to the patent does not have the physical and chemical requirements required for application in a direct reduction process.

[0008] Patent application BR102022006033-9 by Vale SA describes a process for obtaining agglomerates, but differs from the present invention in the following respects: (i) the raw materials used, (ii) the use of microwaves for reduction, (iii) the use of biomass as a reducing agent, and other differences. This document BR102022006033-9 describes a process for obtaining a reducing agent using microwave technology and biomass. The obtained pre-reduced agglomerates (metallic iron content >60%) are merely an intermediate stage intended for future application in different reactors.

[0009] The master's thesis "Desenvolvimento de briquetes autorredutores com agente de recobrimento" (Development of self-reducing briquettes using coating agents) published by Kleiton Goncalves Lovati in 2019 describes a process for producing self-reducing briquettes using coating agents such as dolomitic limestone, bentonite, serpentine, and steelmaking slag. The present invention is a product different from that document and cannot be considered self-reducing briquettes. Self-reducing briquettes are composed of iron ore and a large amount of carbonaceous material, which gives them self-reducing properties. These briquettes are used in reduction and melting technologies (e.g., Corex, Finex, Hismelt, Tecnored, Oxicup) and are different from the present invention, which is directed to direct reduction technologies (e.g., Midrex, HyL, Fastmet, Jindal, etc.).

[0010] The master's thesis "Development of a methodology to assess the reoxidation tendency of iron ore pellets reduced in a direct reduction process with gas" (Development of a methodology to assess the reoxidation tendency of iron ore pellets reduced in a direct reduction process with gas) published by Renata Goncalves Penna in 2010 describes the impact of degradation of iron ore pellets in a direct reduction process. This document relates to a different agglomeration process and is clearly distinct from the present invention: it focuses on pellets produced by a high-temperature agglomeration process above 1300°C, whereas the present invention is directed to a low-temperature agglomeration process carried out at a temperature of about 250°C.

[0011] Direct reduction agglomerates are required to have a high iron content (more than 60%) and a low content (less than 10%) of harmful elements (Na2O, SiO2, and Al2O3) compared to blast furnace processes. Furthermore, direct reduction agglomerates are required to have low disintegration and a high metallization content (more than 90%) compared to blast furnace products.

[0012] The present invention relates to a method for producing cold iron ore agglomerates for use in a direct reduction (DR) reactor, which has the following advantages compared to processes known in the prior art: 1. Control of the porosity of the agglomerate by adding organic additives and curing at a slightly high temperature (by burning the added organic matter). 2. Control of compaction degree by reducing the compaction pressure and bulk density of the agglomerates. 3. Application of enriched feedstock (ore feedstock with high iron content). 4. Application of binder(s). 5. Standard size agglomerates affecting the properties of the final product. 6. Agglomerates with high physical resistance (including weather resistance) to long-distance transportation and handling. 7. Agglomerates that generate little fine powder in the reduction reactor and have a high metallization rate. 8. Reduction of CO2 emissions due to curing occurring at room temperature or low temperature.

[0013] The porosity of this type of agglomerate is important for downstream use in a direct reduction reactor, and to this end, control of porosity and compaction is an essential differentiating factor in imparting the product properties required for use in a direct reduction reactor.

[0014] Control of porosity allows, for example, gases to enter and exit the internal structure of the agglomerates during the direct reduction process without compromising their physical quality, i.e., collapse. If the porosity is not controlled, the durability of the product will be significantly impaired, and it will not be able to meet the minimum performance standards required for the process.

[0015] The compaction of the agglomerates can be controlled by adjusting the process conditions, improving the agglomerate finish and using additives (chemical or mineral) to ensure optimum porosity.

[0016] Therefore, the present invention is significantly different from the known literature in the prior art because the importance of porosity in the direct reduction products of the present invention has been confirmed through bench scale tests and basket tests in the direct reduction process at some customers.

[0017] With regard to production materials, it should be noted that the possibility of using mixtures of various binders aims, among other things, to reduce the content of harmful components (Na2O, SiO2 and Al2O3) in the agglomerate products. Summary of the Invention

[0018] A general object of the present invention is to provide a novel process for producing iron ore agglomerates with high metallurgical performance for use as a replacement for lumps and pellets in direct reduction reactors. The main properties of the resulting agglomerates are high physical strength, low fines generation and high metallization during operation in the direct reduction reactor.

[0019] Another object of the present invention is to provide a more sustainable process for the reduction of CO2 emissions in the mining-metallurgical production chain.

[0020] In a preferred embodiment, the present invention is a method for producing iron ore agglomerates for use as a replacement for lump ore and pellets in a direct reduction furnace, comprising the steps of: a) dispersing 0.05-2 wt% of nanomaterials in a binder to obtain a "binding mixture"; b) mixing 1-10% of the binding mixture obtained in step a) with 70-99% of iron ore fines and / or steelmaking by-products and 0-5% of chemical and / or mineral additives having properties that promote plasticity and / or improve the porosity of the agglomerates; c) adjusting the water content in the mixture to 0 to 25% by weight; d) carrying out the agglomeration process by briquetting or extrusion; e) hardening the agglomerates; f) applying a coating to the surface of the agglomerates to reduce the sticking phenomenon in the direct reduction reactor A method is disclosed that includes:

[0021] The invention will now be explained in detail with reference to the following figures. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 shows a simplified block diagram of a process for producing agglomerates according to the present invention for use in a direct reduction reactor. [Figure 2] FIG. 2 is a comparative diagram showing the progress of the results of the disintegration test of the obtained agglomerates. [Figure 3] FIG. 3 shows an image of the agglomerates obtained by the process according to the invention after the application of a coating aimed at mitigating the sticking phenomenon. [Figure 4] FIG. 4 shows images of agglomerates (DRI) obtained after basket testing in an industrial-scale direct reduction reactor. [Figure 5]FIG. 5 shows a graph containing data on the metallization and carburization of agglomerates (DRI) obtained from various briquette samples subjected to basket testing in the Midrex and HyL reactors. [Figure 6] FIG. 6 shows a graph containing data on the disintegration under reduction of agglomerates (DRI) obtained from various briquette samples subjected to basket tests in the Midrex and HyL reactors. DETAILED DESCRIPTION OF THE INVENTION

[0023] While the present invention may take various forms, preferred embodiments are shown in the drawings and will become apparent from the following detailed description, which is to be understood as being for the purpose of illustrating the principles of the invention and is not intended to limit the invention to that which has been shown and described.

[0024] The requirements of the present invention are illustrated by the following examples, but are not limited thereto. The materials and methods disclosed herein may incorporate various details and procedures without departing from the scope of the invention. Unless otherwise specified, all parts and percentages given below are by weight.

[0025] The main approach of the present invention is a method for producing iron ore agglomerates for use as a replacement for lump ore and pellets in direct reduction furnaces, comprising the steps of: a) dispersing 0.05-2 wt% of nanomaterials in a binder to obtain a "binding mixture"; b) mixing 1-10% of the binding mixture obtained in step a) with 70-99% of iron ore fines and / or steelmaking by-products and 0-5% of chemical and / or mineral additives having properties that promote plasticity and / or improve the porosity of the agglomerates; c) adjusting the water content in the mixture to 0 to 25% by weight; d) carrying out the agglomeration process by briquetting or extrusion; e) hardening the agglomerates; f) A step of applying a coating to the surface of the agglomerates to reduce the sticking phenomenon during direct reduction The present invention relates to a method comprising:

[0026] The agglomerate production process, represented by the block diagram shown in Figure 1, preferably begins with dispersing 0.05 to 2 wt% of nanomaterial(s) in the binder under mechanical agitation, relative to the amount of binder used in the mixture. Nanomaterials used in step a) include carbon nanotubes, exfoliated graphite, functionalized microsilicates, tubular nanosilica, tubular halloysite, carbon nanofibers, graphene, etc.

[0027] The binder used in step a) may consist of sodium silicate, vegetable tar, pitch, starch, phenolic resin, molasses, etc. These binders are used to bind the particles together by adhesion and / or chemical interaction and can be used alone or in combination to improve the durability of the agglomerate product.

[0028] Step b) of the present invention involves adding 1-10% of the binding mixture obtained in step a) to 70-99% by weight of iron ore fines and / or steelmaking by-products and 0-5% by weight of chemical and / or mineral additives, followed by mixing in an intensive mixer for up to 4 minutes. Additives used as plasticizers include bentonite, pitch, tar, starch, and hydrated lime, which have the property of increasing plastic conformation in the subsequent agglomeration step. Porosity-forming substances, such as pitch, tar, phenolic resin, glucose, starch, molasses, glycerin, carboxymethylcellulose (CMC), and biomass, are also used as additives, which increase the porosity of the agglomerates after hardening.

[0029] The iron ore fines and steelmaking by-products used in step b) of the present invention contain more than 60% total iron (Fe total It is preferable that the by-products have a SiO2 content of less than 5%, an Al2O3 content of less than 2%, a granulometry of 98% less than 6 mm, and a maximum moisture content of 25%. Steelmaking by-products that can be used include pellet fines, direct reduced iron (DRI) fines, sludge, scale, etc. Since the quality of these by-products can vary from steel mill to steel mill, when using them as raw materials, they must meet the above quality standards and be confirmed by prior laboratory testing.

[0030] Step c) of the present invention consists in adjusting the moisture content of the mixture by adding water to obtain an optimum moisture content of 0-25% suitable for the agglomeration process.

[0031] Step d) of the present invention relates to an agglomeration process, which can be carried out by briquetting or extrusion.

[0032] For agglomeration by extrusion, the optimum moisture content is 8-25%. The strength and porosity of the green agglomerate are controlled during the manufacturing process by adjusting the negative pressure in a device known as an extruder, in addition to the blending of binders and additives. The resulting extrudates are cylindrical rods with diameters of 5-50 mm and lengths of 50-200 mm.

[0033] For agglomeration by briquetting, the moisture content of the mixture is preferably 1-7%. The briquetting process is carried out in a roller press with an appropriate cavity, resulting in pillow-shaped briquettes measuring 15-50 mm x 10-40 mm x 5-25 mm. By properly controlling the shape and dimensions, as well as the raw materials and process conditions used, agglomerates with higher mechanical strength are obtained, which exhibit superior performance.

[0034] In the briquetting process, it is important to adjust the pressure and speed of the rollers, control the distance between the rollers (maintain a minimum gap to prevent the formation of open and burred briquettes), and manage the feed rate. This allows for a briquetting rate of 3.8 g / cm 3 Briquettes are obtained that have a bulk density of less than 1000 kJ / g, a compaction degree of about 50% or less than 50%, and meet the desired metallurgical properties.

[0035] Roller pressure and speed are controlled by changing the amperage of the briquetting machine, but the adjustment method varies depending on the machine. It is difficult to set a predetermined amperage range because it can vary significantly depending on the type, brand, and capacity of the briquetting machine. Therefore, the optimal control method, which is applicable and reproducible across different machines, is to calculate the linear force, with a recommended value of 15–30 kN / cm. Higher amperage increases the particle-to-particle force, which increases compaction (packing and bulk density) and reduces porosity. However, it is necessary to find an optimal balance between compaction, bulk density, porosity, and physical quality of the agglomerates.

[0036] Step e) of the present invention involves curing the agglomerates, and can be carried out in a gas oven, electric oven, infrared oven, electromagnetic oven, or at room temperature. The temperature conditions and curing time for each type of oven are determined by the type of binder or binder mixture used. When the binder is pure sodium silicate, conditions of 100 to 550°C for 10 to 30 minutes are recommended for an electric oven, infrared oven, or gas oven. When using an electromagnetic oven using electromagnetic waves, the curing time is 2 to 15 minutes. When curing at room temperature, the curing time can reach a maximum of 15 days.

[0037] In step f), an additional layer of chemical or mineral additives is applied by dipping, spraying, or other techniques to minimize agglomerate sticking in the direct reduction reactor. These additives include bauxite, bentonite, serpentine, cement, magnesium hydroxide, limestone, or combinations thereof. The amount of coating used is 1 to 10 kg per ton of agglomerate. The coating is applied in a water suspension.

[0038] The iron ore agglomerates produced according to the present invention have physical, chemical and metallurgical properties that allow them to be used as a replacement for pellets and lump ore in direct reduction reactors, thereby improving the efficiency and productivity of the entire metallurgical chain. The properties of the final agglomerates are as follows: High iron content (Fe>60%) Low content of harmful components (Na2O, SiO2 and Al2O3<5%) Low decay rate (<10%, can reach values ​​below 5%) High metallization rate (>90%, can reach 99.5%)

[0039] The superior performance of the agglomerates obtained according to the present invention in the direct reduction reactor is due to three important factors that are tightly controlled throughout the process: The compression rate is less than 50%. Bulk density is 3.8g / cm 3 is less than. Porosity is over 40% and has a network of connected pores.

[0040] The porosity of this type of agglomerate is important for downstream use in the direct reduction reactor. Control of the porosity allows, for example, gases to enter and exit the internal structure of the agglomerate during the direct reduction process without degrading its physical quality. If the porosity is not controlled, the durability of the product during reduction will be significantly impaired, it will not meet the minimum performance requirements for the process, and it will lead to the generation of fines due to collapse, which will have a negative impact on the process in the direct reduction reactor.

[0041] Figure 2 shows a comparative graph of the progression of disintegration rates obtained throughout the research and development (R&D) process conducted to optimize the present invention. Figure 2A shows agglomerates obtained from a prior art process, with high disintegration rates of 40-65%. Figure 2B shows the progress in the early stages of the R&D process, with disintegration rates of 20-30%. Figure 2C shows agglomerates obtained by the process described in the present invention, with disintegration rates of less than 10%.

[0042] The degree of particle compaction directly affects the level of agglomerate collapse in the direct reduction reactor and also contributes to improving the metallization rate. Agglomerates with lower density have a higher porosity, which allows for a more uniform (gentler) gas ingress and egress during metallurgical operations in the direct reduction reactor, as described above.

[0043] The present invention allows achieving optimal parameters of compaction and porosity through the adjustment of agglomeration conditions, the improvement of the agglomerate finish and the use of chemical or mineral additives to increase porosity. [Example]

[0044] The process described in this invention was followed to produce iron ore fines agglomerates for specific use in direct reduction reactors.

[0045] The iron ore fines used were pellet feed with an Fe content of 68.5% and a particle size of less than 0.15 mm, totaling 96% by weight. Sodium silicate and nanomaterials were used as binders. Starch and hydrated lime were used as additives. Briquetting was selected as the agglomeration process, and pillow-shaped briquettes with dimensions of 25 x 20 x 15 mm were produced.

[0046] The amperage used in the briquetting machine varied between 30 and 40 amps, corresponding to a linear pressure of 15.7 to 29.4 kN / cm. The briquettes were cured in a gas furnace at a temperature range of 250 to 350°C for 30 minutes. After curing, the briquettes were subjected to a coating process with sprayed cement.

[0047] The resulting briquettes were subjected to chemical, physical, and metallurgical tests to verify the quality of the final agglomerates, as shown in Figure 3. The chemical and physical quality test results for several briquette samples are shown in Table 1 below.

[0048] [Table 1]

[0049] Figure 4 shows images of DRI agglomerates obtained from basket tests conducted in commercial reactors at Midrex and HyL. Quality data on these DRI agglomerates are also shown, including the metallization and carbonization rates (Figure 5) and the rate of disintegration under reduction (Figure 6).

[0050] While only specific embodiments of the present invention have been shown and described above by way of example, those skilled in the art will recognize that various omissions, substitutions, and changes may be made thereto without departing from the spirit and scope of the present invention. The embodiments described herein are to be considered in all respects as illustrative only and are not to be construed as limiting.

[0051] The scope of the present invention expressly includes all combinations of elements that perform the same function in substantially the same way to achieve the same results, and the substitution of elements in one described embodiment for elements in another embodiment is also fully intended and contemplated.

Claims

1. 1. A process for producing iron ore agglomerates for use in a direct reduction reactor, comprising: The following steps: a) dispersing 0.05 to 2 wt. % of nanomaterial in a binder to obtain a binding mixture; b) mixing 1-10% of the binding mixture obtained in step a) with 70-99% of iron ore fines and / or steelmaking by-products and 0-5% of additives in an intensive mixer; c) adjusting the water content in the mixture to 0 to 25% by weight; d) carrying out the agglomeration process by briquetting or extrusion; e) curing the agglomerates; f) applying a coating to the surface of the agglomerates to reduce the sticking phenomenon in the direct reduction furnace; A method comprising:

2. 2. The method of claim 1, wherein the nanomaterial used in step a) is selected from the group consisting of carbon nanotubes, exfoliated graphite, functionalized microsilicates, tubular nanosilica, tubular halloysite, carbon nanofibers and graphene.

3. 2. The method of claim 1, wherein the binder used in step a) is selected from the group consisting of sodium silicate, vegetable tar, pitch, starch, phenolic resins and molasses.

4. The iron ore fines and steelmaking by-products used in step b) have a total iron content of more than 60% and less than 5% SiO ２ Al content less than 2% ２ O ３ 2. The method of claim 1, having a content and a particle size distribution of 98% less than 6 mm.

5. 2. The method of claim 1, wherein the additive used in step b) is selected from the group consisting of bentonite, pitch, tar, hydrated lime, phenolic resin, glucose, starch, molasses, glycerin, carboxymethyl cellulose (CMC) and biomass.

6. 10. The method of claim 1, wherein the mixing in step b) is carried out in an intensive mixer for up to 4 minutes.

7. 2. The method of claim 1, wherein the agglomeration in step d) is carried out in an extruder producing cylindrical rod-shaped extrudates having a size of 5 to 50 mm in diameter and 50 to 200 mm in length.

8. 2. The method of claim 1, wherein the agglomeration in step d) is carried out in a roller press producing pillow-shaped briquettes having dimensions of 15-50 mm x 10-40 mm x 5-25 mm.

9. The agglomeration in step d) has a filling level of less than 50%, 3.8 g / cm ３ 10. The method of claim 1, wherein the method is carried out in a roller press to produce briquettes having a bulk density of less than 1000 kJ / cm, a porosity of more than 40% and interconnected pores.

10. 2. The method according to claim 1, wherein the agglomeration in step d) is carried out in a briquetting machine controlling the linear pressure in the range of 15 to 30 kN / cm.

11. 10. The method of claim 1, wherein the curing in step e) can be carried out in a gas, electric, infrared or electromagnetic oven or at room temperature.

12. 12. The method of claim 11, wherein the curing in a gas, electric or infrared oven is carried out at a temperature of 100 to 550° C. for 10 to 30 minutes.

13. 12. The method of claim 11, wherein the curing in the electromagnetic oven is carried out for 2 to 15 minutes.

14. 12. The method of claim 11, wherein curing at room temperature is carried out for up to 15 days.

15. 2. The method of claim 1, wherein the application of the coating agent in step f) is carried out by dipping or spraying using a chemical or mineral additive having surface coating properties selected from the group consisting of bauxite, bentonite, serpentine, cement, magnesium hydroxide, limestone, and combinations thereof.

16. 2. The method according to claim 1, wherein the amount of coating agent used in step f) is 1 to 10 kg per ton of agglomerates.

17. The iron ore agglomerates obtained from the method according to any one of claims 1 to 16 have optimum physical, chemical and metallurgical properties for use as a replacement for pellets and lumps in direct reduction furnaces, namely Fe content of more than 60%, no harmful elements (Na ２ O, SiO ２ and Al ２ O ３ ) content, less than 10% disintegration rate, more than 90% metallization rate, less than 50% loading, 3.8 g / cm ３ 1. Iron ore agglomerates characterized by having a bulk density of less than 1000 kJ / cm, a porosity of more than 40% and interconnected pores.

18. Fe content of 65.1-67.5%, harmful components less than 5% (Na ２ O, SiO ２ and Al ２ O ３ 18. Agglomerates according to claim 17, characterized in that they have a .alpha.-methyl-.beta.-methylpropional content, a disintegration rate of less than 5% and a metallization rate of 91.2 to 99.5%.

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