Method for introducing metal-containing feed into an ironmaking process

Abstract

A method for introducing a metal-containing feed (4) into an ironmaking process, the method comprising the steps of pre-drying iron-containing sludge to a moisture content of 15 to 30% (w / w) by means of a drying device, mixing the pre-dried iron-containing sludge with a binder material to obtain particles having a particle size of less than 4 mm and drying the particles to a maximum of 3% (w / w) moisture, thereby forming a metal-containing feed (4), characterized in that the metal-containing feed is subsequently injected into a cyclone portion (10) of a metallurgical vessel (1).

Description

[0001] The present invention relates to a method for introducing a metalliferous feed in an ironmaking process, the method comprising the steps of pre-drying iron-containing sludge to a moisture content of 15 to 30% (w / w) by means of a drying device, preferably a filter press, mixing the pre-dried iron-containing sludge with a binder material to obtain particles having a particle size of less than 4 mm and drying the particles to a maximum of 3% (w / w) moisture, thereby forming a metalliferous feed.

[0002] The present invention also relates to a metalliferous feed material for use in an ironmaking process and a method of producing such a metalliferous feed material.

[0003] The process of converting sludge into pellets is known in the field of food and feed production. The preparation of pellets, also called granular material, pellets or granules, is also known in the steel industry. Typically, this is produced in the form of sintered and pelletized material.

[0004] Iron-containing sludges such as basic oxygen furnace steelmaking sludge or BOS-sludge are by-products of the steelmaking process and contain iron. Typically, such sludges contain moisture varying from about 20% (w / w) to about 40% (w / w). In current practice, such sludges are either recycled via sintering plants or exported as waste and stored.

[0005] However, in steelmaking sites using alternative ironmaking processes such as smelting reduction vessels, such as TataSteel's Hlsarna process, a sintering plant is no longer needed. Sintered bodies cannot be used in the Hlsarna process because they cannot be transported by pneumatic transport. Therefore, the iron-containing BOS-sludge cannot be recycled through the sintering plant, leaving waste storage as the only option that is not up to par. The inventors involved in the search for a more environmentally friendly solution found this to be an unacceptable option and began to think about better ways that reflect the idea of ​​a circular economy.

[0006] It is therefore an object to provide a method capable of recycling such waste material from the steelmaking process and turning this material into something that can be fully utilized in an alternative ironmaking process. Furthermore, it is an object of the invention to enable the obtained material to be transported by a pneumatic transport system. Another object is to be able to store the recycled material in silos for later use. Yet another object is to reduce the amount of dust (entrained dust) in the process, so that the amount of dust in the direct environment of the steelworks is reduced and both the workers and nearby residents have a healthier environment resulting in a better quality of life.

[0007] Thus, a method of introducing a metalliferous feed in an ironmaking process is provided, wherein the method comprises the steps of pre-drying iron-containing sludge to a moisture content of 15 to 30% (w / w) by means of a drying device, mixing the pre-dried iron-containing sludge with a binder material to obtain particles having a particle size of less than 4 mm and drying the particles to a maximum of 3% (w / w) moisture, thereby forming a metalliferous feed, wherein the metalliferous feed is subsequently injected into a cyclone portion of a metallurgical vessel. Tests have demonstrated that the metalliferous feed so formed has very advantageous properties as will be explained below and can be injected into a cyclone portion of a metallurgical vessel without any further adjustments.

[0008] As a first step, the iron-containing sludge is pre-dried by a drying device, preferably a filter press, to an amount of 15 to 30% (w / w) moisture. Pre-drying the iron-containing sludge is important. However, if this process is not well controlled and the iron-containing sludge has too low a moisture content, it can cause the sludge to re-oxidize, which can be the case when BOS-sludge is used. This is an undesirable process, as the sludge can be used in the iron-making process only in a reduced form. The moisture content should be between 15-30% (w / w) and preferably between 20 and 25% (w / w) moisture. The inventors note that 20% (w / w) moisture or less is possible if the sludge is mixed within 0 to 72 hours and preferably within 0 to 24 hours of pre-drying (second step) to avoid the re-oxidation process. Iron-containing sludge containing 20 to 25% (w / w) moisture is preferred, as the inventors have found that it optimizes the particle size for use in the iron-making process, and it requires a smaller amount of binder material. Iron-containing sludge may be used to contain iron in the form of hematite (Fe2O3), magnetite (Fe3O4), wüstite (FeO) or iron (Fe).

[0009] As a second step, the pre-dried iron-containing sludge is mixed with a binder material to obtain particles with a particle size of less than 4 mm. The binder is preferably an organic binder as this will prevent additional slag formation during the ironmaking process. Suitable binder materials are cellulose derivatives, preferably A cellulose based long chain polyelectrolyte available from Nouryon. Good results are achieved using a binder material added in an amount of 0.2-0.4% (w / w). Below 0.2% (w / w), the integrity of the material is insufficient, making it unsuitable for pneumatic transport as the material will break apart. Above 0.4% (w / w), the particles become too large and too heavy for pneumatic transport. A suitable mixer is an Eirich intensive mixer, rotating at a speed of 1000 to 1500 rpm. It was found that a particle size (diameter) of less than 4 mm is the desired particle size for pneumatic transport purposes, and the inventors prefer a particle size of less than 3 mm. The desired particle size is achieved if the pre-dried sludge is mixed for less than 60 seconds, preferably less than 45 seconds. It should be noted that the particle size diameter mentioned in this patent application is the maximum particle size diameter of the particles. Optionally, the particles can be filtered to ensure that the maximum particle size diameter is less than 4 mm.

[0010] The granules obtained, also called microgranules or pellets, have very advantageous properties since they can be stored in silos and since in a subsequent step they are dried, they are at least partially protected from reoxidation, which means that the calorific value of the partially pre-reduced iron oxide (FeO) is maintained.

[0011] The particles are then dried to a maximum of 3% (w / w) moisture, thereby forming a metal-containing feed. Preferably, the maximum moisture content is 2% (w / w). Drying significantly improves the handling of the particles, especially in pneumatic transport systems. Preferably, this drying step is performed by a belt dryer. This has the main advantage that heat from the factory's own environment can be used efficiently. This heat is lost under normal processing conditions. Dust emissions are also significantly reduced, resulting in a better environmental situation for workers and people near the steel plant. Another advantage of using a belt dryer is that the particles will become stronger and less prone to breakage. Therefore, they are easy to transport. The inventors have found that drying also improves the strength of the particles. When the particles enter the dryer, they have a strength of about 7Nm / pellet. This increases to more than 20Nm / pellet when leaving the dryer. A suitable device for measuring the strength of the pellets is the EirichTAXT texture analyzer. A suitable method for measuring the strength of the pellets is ISO 4700:2015. Instead of a belt dryer, a drum dryer can also be used as an alternative.

[0012] As a final step, the metalliferous feed is then injected into the cyclone of the metallurgical vessel. Due to the chemical composition and physical properties obtained after the steps described above, the pellets are ready to be injected into the metallurgical vessel as metalliferous feed. The melting properties are also extremely important. Since the iron-containing sludge also contains a certain amount of calcium (about 10%), the melting behavior of the pellets is optimized. However, if the chemical composition of the iron-containing sludge is less optimized, carbon (coke) can be added to improve the melting behavior. For the same purpose, flux materials (such as limestone) can also be added.

[0013] Using this method has the additional advantage that there are no gaseous compounds such as SO x or NO x The metal-bearing feed is usually injected at a much smaller particle size (as a powder), and this powder can also clog together making the ironmaking process less optimal.

[0014] Preferably, the metallurgical vessel is a smelting reduction vessel. Such a smelting reduction vessel has a good track record of reducing emissions such as CO2. It is therefore a preferred choice for mitigating climate change and reducing the amount of carbon dioxide. We now find that due to global warming, the beaches near IJmuiden are reaching temperatures that used to belong to places like Ipanema Beach. Unfortunately for some, the famous lady does not want to move.

[0015] Preferably, the metal-bearing feed is injected into the cyclone of the metallurgical vessel by a pneumatic transport system. The usual way to introduce metal-bearing feed is via pneumatic transport, since metal-bearing powders are injected under current processing conditions. By pelletizing the material, it is also possible to pneumatically transport the material and introduce it into the cyclone of the metallurgical vessel while avoiding the blockages mentioned above. The pellets can also be stored in a silo for the next batch. This also means that no further adjustments to existing equipment are required.

[0016] The invention will be further elucidated hereinafter with reference to the accompanying drawing of an exemplary embodiment of an apparatus operating according to the inventive method (not limiting with respect to the appended claims).

[0017] In the attached picture:

[0018] Figure 1 showing a metallurgical vessel with a cyclone section;

[0019] Whenever the same reference numbers are used in the drawings, these numbers refer to the same parts.

[0020] Figure 1The basic elements required for making iron according to the process disclosed in patent application EP-A-0 726 326 are described, wherein a vessel 1 has a cyclone 10 applied on top of the vessel 1. Figure 1 A metalliferous feed 4 is shown being injected into a smelting cyclone 10 at the top of the vessel 1. The metalliferous feed 4 is now molten and partially pre-reduced, after which it drips into the vessel 1 and forms molten iron 2. In addition Figure 1 Shown are a molten iron bath 2, a slag layer 3, carbonaceous material introduction points 5 and oxygen containing gas introduction points 7, an iron outlet 8, a slag outlet 9 and a reaction gas outlet 11. For the present invention only the point of introduction of the metal containing feed 4 is important.

[0021] Experiments were conducted to investigate the size distribution and compressive strength of several pellets. The pellets were produced using a two-step mixing procedure using a 5L Eirich mixer. First, the BOS-sludge and binder (Peridur 300D) were loaded together and mixed at 2000 rpm for 45 seconds to ensure good homogenization. Second, the material was mixed at 500 rpm for 45 seconds to achieve stable pelletization. The amount of moisture in the BOS sludge and the binder content were varied. The table shows the particle size distribution indicators for the tested parameters.

[0022]

[0023] The flowability study of the granules filtered under different particle sizes (3mm, 1mm, 0.4mm) using the Hosokawa powder tester showed that the maximum particle size should be less than 4mm, preferably less than 3mm so as to enable smooth pneumatic injection. Therefore, the granules should preferably have a D90 less than 4mm, more preferably less than 3mm. Granules with larger particle sizes can be optionally removed by a filter. D10 should preferably be greater than 0.5 to avoid being carried away. The mechanical resistance of the granules was tested by a drop test to determine the optimized binder content. 500g of each sample was selected from mature granules (dried from the original moisture in the air) and dropped 2 times from a height of 2m. The particle size distribution of the granules before and after was similar for all granules, indicating good mechanical resistance even when the binder content was 0.2%. In general, a lower binder content is desired because it will reduce the total cost of the granules. Sample 4 also undergoes a flat plate compression test of the original granules and the dried granules. The average diameters of the original granules and the dried granules are 2.4 and 2.7mm, respectively. The average rupture forces for the original (15 to 30% moisture) and dried (up to 3% moisture) pellets were 4.65 and 18.05 N, respectively. Thus, the dried pellets are much stronger and more suitable for pneumatic transport and storage.

[0024] Although the present invention is discussed above with reference to the exemplary embodiments of the present invention, the present invention is not limited to these specific embodiments, which can be varied in many ways without departing from the present invention. Therefore, the exemplary embodiments discussed should not be used to interpret the attached claims to be strictly consistent with them. On the contrary, the embodiments are only intended to interpret the wording in the attached claims, and are not intended to limit the claims to these exemplary embodiments. Therefore, the scope of protection of the invention should be interpreted only in accordance with the attached claims, wherein these exemplary embodiments should be used to resolve possible ambiguities in the wording of the claims.

Claims

1. A method for introducing a metal-containing feed (4) into an ironmaking process, the method comprising the following steps: Pre-drying iron-containing sludge by a drying device to a moisture content of 20 to 25% (w / w), mixing the pre-dried iron-containing sludge with an organic binder material to obtain particles with a particle size of less than 4 mm and drying the particles to a maximum of 3% (w / w) moisture, thereby forming a metalliferous feed (4), characterized in that the metalliferous feed (4) is then injected into a cyclone portion (10) of a metallurgical vessel (1) by a pneumatic transport system.

2. The method according to claim 1, characterized in that the metallurgical vessel (1) is a smelting reduction vessel.

3. A method according to any one of claims 1-2, characterised in that the binder material is a cellulose derivative.

4. The method according to any one of claims 1-2, characterized in that the binder material is added in an amount of 0.2% to 0.4% (w / w).

5. The method according to any one of claims 1-2, characterized in that the particle size of the obtained particles is less than 3 mm.

6. Process according to any one of claims 1-2, characterised in that the moisture content of the dried granules is maximum 2% (w / w).

7. The method according to any one of claims 1 to 2, characterized in that the granules are dried by means of a belt dryer.

8. A method for producing a metal-containing feed material (4) suitable for pneumatic transport for use in an ironmaking process, characterised in that the method comprises the following steps: Pre-drying the iron-containing sludge by a drying device to a moisture content of 20 to 25% (w / w), mixing the pre-dried iron-containing sludge with an organic binder material to obtain particles having a particle size of less than 4 mm and drying the particles to a maximum of 3% (w / w) moisture, thereby forming a metal-containing feed (4), and characterized in that the metal-containing feed is pneumatically transportable.

9. A metalliferous feed material (4) suitable for pneumatic transport for an ironmaking process, obtained by the process of claim 8, characterised in that the metalliferous feed material (4) comprises iron-containing sludge and also has a particle size of less than 4 mm, an organic binder material content of between 0.2 and 0.4% (w / w) and a moisture content of a maximum of 3% (w / w), and in that the metalliferous feed material is pneumatically transportable.

10. The metal-containing feed material (4) for an ironmaking process according to claim 9, characterized in that the metal-containing feed material (4) contains carbon and / or limestone.

11. A metalliferous feed material (4) for an ironmaking process according to claim 9 or 10, characterised in that the binder material is a cellulose derivative.

12. A metal-containing feed material (4) for an ironmaking process according to claim 9 or 10, characterised in that the particle size is less than 3 mm.

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