Patent Application
20250154621
The present invention pertains to the field of mining-metallurgical technologies and refers to a process of iron ore agglomerate production for application in direct reduction (DR) reactors, thereby replacing the pellets and lumps traditionally used.
Direct reduction reactors are characterized by reducing iron ore to metallic iron without melting the burden in the reactor. The metallic product obtained in the solid phase is called sponge iron (a.k.a. DRI—Direct Reduced Iron), which can be hot briquetted, thereby obtaining the Hot Briquetted Iron (HBI).
The direct reduction process is an alternative to using the blast furnace for manufacturing an intermediate product with the same basic functions as pig iron produced by the blast furnace. Both intermediate products (pig iron and sponge iron) are intended for use in the steelworks for the production of steel, with sponge iron being used in electric furnaces. The best-known direct reduction processes are Midrex, HyL (Hayata y Lamina), Armco, H. Iron, SL-RN, and Purofer.
In order to ensure an optimized performance of direct reduction reactors, as well as a high-quality final product (sponge iron), the iron ore agglomerate to be fed needs to have specific physical-chemical-metallurgical characteristics.
The current state of the art provides for some ore agglomeration technologies for application in reduction furnaces. However, none of such technologies results in agglomerates with specific metallurgical characteristics for optimized performance in a direct reduction reactor, as provided by the present invention.
Vale S. A.'s patent BR102019023195-5 describes an agglomerate of iron ore fines to replace metallic burdens in blast furnaces, unlike the present invention, which produces agglomerates with specific characteristics to feed direct reduction reactors, such as Midrex and HyL. Furthermore, patent BR102019023195-5 uses fluxes and inputs other than those from the present invention. Moreover, said patent does not have coating application steps, as required in the present invention.
Patent BR112014005488-6, also in the name of Vale S. A., describes a process for obtaining agglomerates that, in several aspects, differs from the present invention, including (i) raw materials employed, (ii) lack of a coating stage, (iii) application to agglomerates obtained by pelletizing technology (e.g., mini pellets), and (iv) the product subject to the patent does not have physical and chemical requirements for application in the direct reduction process.
Patent application BR102022006033-9, also in the name of Vale S. A., describes a process for obtaining agglomerates that differs from the present invention in terms of (i) the raw materials employed, (ii) the use of microwaves for reduction, (iii) the use of biomass as a reducer, and other differences. Document BR102022006033-9 describes a process for obtaining reduced material through microwave technology and biomass. The resulting pre-reduced agglomerate (metallic Fe>60%) is only an intermediate step for future application in different reactors.
The master's thesis entitled “Desenvolvimento de briquetes autorredutores com agente de recobrimento” (Development of self-reducing briquettes with coating agent), published in 2019 by Kleiton Gonçalves Lovati, describes a process for obtaining self-reducing briquettes that use coating agents such as dolomitic limestone, bentonite, serpentinite, and steelmaking slag. The present invention differs from this document as it is a different product and cannot be considered a self-reducing briquette. Self-reducing briquettes are composed of iron ore and a significant amount of carbonaceous material so as to provide them with their self-reducing characteristic. They are specifically used in Reduction and Fusion technologies (e.g., Corex, Finex, Hismelt, Tecnored, Oxicup), unlike the present invention, whose focus is on Direct Reduction technologies (e.g., Midrex, HyL, Fastmet, Jindal, etc.).
The master's thesis entitled “Desenvolvimento de metodologia para avaliação à tendência à reoxidação de pelotas de minério de ferro reduzidas em processo de redução direta a gás” (Development of a methodology to evaluate the reoxidation tendency of iron ore pellets reduced through direct gas reduction process), published by Renata Gonçalves Penna in 2010, describes the effect of degradation of iron ore pellets in a direct reduction process. Distinguishing itself from the present invention, this document pertains to a dissimilar agglomeration process. Specifically, the document focuses on pellets generated through a hot agglomeration process (>1300° C.), whereas the present invention deals with cold agglomeration carried out at a temperature of approximately 250° C.
In direct reduction agglomerates, the iron content has to be higher (>60%) and the deleterious content (Na2O, SiO2, and Al2O3) lower (<10%) when compared to the blast furnace process. Furthermore, it is essential that agglomerates for direct reduction need to have low disintegration and high metallization content (>90%) when compared to blast furnace products.
The present invention relates to a process for producing cold iron ore agglomerate for use in direct reduction (DR) reactors, which presents the following benefits when compared to processes known in the prior art:
The porosity for this type of agglomerate is critical for its subsequent application in direct reduction reactors. To this end, control of porosity and degree of compaction are the differentiating and essential factors that can promote the necessary properties of the product for its use in direct reduction reactors.
Porosity control, for example, allows gases to enter and leave the internal structure of the agglomerate during the direct reduction process without compromising its physical quality, that is, disintegrating. Otherwise, the product's resistance is highly impacted, and the product fails to meet the minimum performance standards essential for the process.
Agglomerate compaction can be controlled by adjustments to process conditions, by improving the agglomerate finish and using additives (chemical or mineral) to ensure optimal porosity.
Therefore, the present invention greatly differs from the documents known in the state of the art since the importance of porosity for this direct reduction product was verified in bench-scale tests, as well as in basket tests in direct reduction process in some customers.
Regarding the production supplies, it is important to note that the potential utilization of a blend of various binders aims, among other objectives, to diminish the presence of deleterious substances (Na2O, SiO2, and Al2O3) in the agglomerated product.
The present invention's general objective is to provide a new production process for iron ore agglomerate with high metallurgical performance to replace lumps and pellets in direct reduction reactors. The main characteristics of the resulting agglomerate are high physical resistance, low generation of fines, and a high degree of metallization during operation in direct reduction reactors.
Another objective of the present invention is to provide a more sustainable process for the reduction of CO2 emissions in the mining-metallurgical production chain.
The present invention, in its preferred embodiment, discloses a production process for iron ore agglomerate to replace lumps and pellets in direct reduction furnaces comprising the following steps:
The present invention is described in detail based on the respective figures:
Although the present invention may be susceptible to different embodiments, the preferred embodiments are depicted in the figures and elucidated in the subsequent detailed discussion, where it should be understood that this description serves as an illustration of the principles of the invention and is not meant to constrain the present invention solely to what has been depicted and described here.
The matter required in the present invention will be expanded upon hereinafter, by way of example and not limitation, since the materials and methods disclosed herein may comprise different details and procedures without departing from the scope of the invention. Unless otherwise indicated, all parts and percentages disclosed below are per weight.
The main approach of this invention is related to a production process for iron ore agglomerate to replace lumps and pellets in direct reduction furnaces comprising the following steps:
The agglomerate production process, represented by the block diagram in
The binders used in step a) may consist of sodium silicate, vegetable tar, pitch, starch, phenolic resins, and molasses, among others. Such binders, used to link particles by adhesion and/or chemical interaction, can be used individually or combined to obtain better resistance of the agglomerated product.
Step b) of the process of the present invention consists of adding 1 to 10% of the binder mixture obtained in step a) to 70 to 99% per weight of iron ore fines and/or steel co-products, and 0 to 5% per weight of chemical and/or mineral additives and, then, mixing in an intensive mixer for no more than 4 minutes. The additives used as plasticizing agents consist of bentonite, pitch, tar, starch, and hydrated lime and have the property of increasing plastic conformation during the subsequent agglomeration step. Some porosity-forming substances are also used as additives, such as pitch, tar, phenolic resins, glucose, starch, molasses, glycerin, CMC (carboxy methyl cellulose), and biomass, which promote greater porosity in the agglomerate after curing.
The iron ore fines and steelmaking by-products used in step b) of the present invention's process preferably have Fetotal contents >60%, SiO2<5%, Al2O3<2%, granulometry 98%<6 mm, and maximum humidity of 25%. The steelmaking by-products used may consist of pellet fines, DRI (Direct Reduced Iron) fines, sludge, and scale, among others. The quality of such by-products may vary depending on the plant. Thus, their use as raw material is subject to compliance with the grades previously mentioned and through prior laboratory tests.
Step c) of this process consists of adjusting the humidity of the mixture by adding water to obtain the optimal moisture of 0 to 25%, as desired for the agglomeration step.
Step d) of the present invention refers to the agglomeration process that can be carried out by means of briquetting or extrusion.
For agglomeration via extrusion, the optimum moisture should be in the range of 8-25%. In addition to the incorporation of binders and additives, the strength and porosity of the green agglomerate are modulated in the production process by regulating the negative pressure within equipment known as extruders. The resulting extrudates are cylindrical rods of size 5-50 mm in diameter and 50-200 mm in length.
For briquetting agglomeration, the mixture should preferably contain between 1-7% moisture. The briquetting process takes place in a roller press with suitable cavities to obtain briquettes in pillow geometry measuring 15-50 mm×10-40 mm×5-25 mm. This geometry and adequate control of these dimensions, associated with the raw materials and process conditions used, result in agglomerates with greater mechanical resistance that generate excellent performance results.
In the briquetting process, it is crucial to regulate the pressure and speed of the rollers, control the distance between rollers (maintaining a minimal gap to prevent the formation of open briquettes and/or those with burrs), and oversee the feeding rate. This is done to achieve a briquette with a bulk density below 3.8 g/cm3 and a compaction degree around or less than 50%, aligning with the desired metallurgical properties.
The pressure and speed of the rollers are controlled by changing the amperage of the briquetting machine, with each machine having a different type of adjustment. It is not possible to define pre-determined amperage ranges, as this can vary greatly depending on the type, brand, and capacity of the briquetting machine. Therefore, a control that is best applied and can be replicated for different machines is through the calculation of linear force, whose recommended value is 15 to 30 KN/cm. The higher the amperage, the greater the force of particle approximation and, consequently, the greater the compaction (packing and bulk density) and the lower the porosity. However, an optimum point between compaction, bulk density, porosity, and the physical quality of the agglomerate is required.
Step e) of the present production process comprises curing the agglomerate, which can be done through gas furnaces, electric, infrared, electromagnetic furnaces or at room temperature. The temperature conditions and curing time in the different types of furnaces will be determined by the type of binder or mixture of binders used. If the binder is pure sodium silicate, 10 to 30 minutes at 100 to 550° C. is recommended for electric, infrared, or gas furnaces. For microwave-based electromagnetic furnaces, the time would be 2 to 15 min. For curing at room temperature, time adds up to 15 days.
In step f), an additional layer of chemical or mineral agent is applied through methods such as immersion, spray, or alternative technologies, aiming to minimize the sticking of agglomerates within the direct reduction reactors. These additives can be bauxite, bentonite, serpentinite, cement, magnesium hydroxide, limestone, and combinations thereof. The coating agent dosage per ton of agglomerate varies between 1 and 10 kg. The coating is disposed in suspension in water for application.
The iron ore agglomerate produced via the present invention has physical, chemical, and metallurgical attributes that allow it to substitute pellets and lumps in direct reduction furnaces, thus resulting in enhanced efficiency and productivity within the metallurgical chain. The characteristics of the final agglomerate are:
The exceptional performance of the agglomerates derived from the present invention within direct reduction reactors is attributable solely to three critical factors meticulously regulated throughout the process:
The porosity for this type of agglomerate is critical for its subsequent application in direct reduction reactors. Porosity control, for example, allows gases to enter and leave the internal structure of the agglomerate during the direct reduction process without compromising its physical quality. Otherwise, the product's resistance during reduction is highly impacted, and the product will not have the minimum performance required in the process, thus generating fines through disintegration, which is detrimental to the process in direct reduction reactors.
The compaction degree of the particles directly influences the level of disintegration of the agglomerates in direct reduction reactors, in addition to improving the degree of metallization. Less dense agglomerates have greater porosity, allowing gases to enter and exit more homogeneously (less abruptly) during the metallurgical operation within a direct reduction reactor, as previously mentioned.
The present invention allows optimal parameters of compaction degree and porosity to be achieved through adjustments in agglomeration conditions, improvement of the agglomerate finish and use of additives (chemical or mineral) to improve porosity.
Agglomerates of iron ore fines for specific use in direct reduction reactors were produced according to the process described by the present invention.
A total of 96% per weight of pellet feed with Fe content=68.5% and particle size <0.15 mm were used as iron ore fines. Sodium silicate and nanomaterial were used as binders. The additives used were starch and hydrated lime. The agglomeration process of choice was briquetting, and pillow-shaped briquettes were produced in the following dimensions: 25×20×15 mm.
The amperage used in the briquetting machine varied between 30 and 40 Å, corresponding to a linear force in the order of 15.7 to 29.4 KN/cm. The briquettes were cured in a gas furnace for 30 min, in a temperature range of 250-350° C. After curing, the briquettes underwent the coating stage through sprayed cement.
The resulting briquettes, as shown in
Therefore, while only specific embodiments of the present invention have been illustrated, it should be recognized that a person skilled in the art can make various omissions, substitutions, and modifications without deviating from the essence and extent of the present invention. The described embodiments should be considered in all respects only as illustrative and not restrictive.
It is expressly provided that all combinations of elements that perform the same function in substantially the same way to achieve the same results are within the scope of the invention. Substitutions of elements from one described embodiment to another are also fully intended and contemplated.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1020230002650 | Jan 2023 | BR | national |
| 1020230256260 | Dec 2023 | BR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/BR2023/050498 | 12/26/2023 | WO |
