Process and system for continuous pre-reduction of a solid granular material

Abstract

The present invention relates to solid agglomerates for use in siderurgical reduction furnaces. In this context, the present invention provides a process for continuous pre-reduction of a solid granular material (10), comprising the steps of: (i) continuously feeding a solid granular material (10) into a reactor (20); and (ii) pre-reducing the solid granular material (10) by means of injecting pre-reduction gas (30) into the reactor (20) as the solid granular material (10) goes through the reactor (20), wherein the pre-reduction gas (30) comes from a siderurgical self-reduction furnace (40). The present invention further provides a system associated with the method described above.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to siderurgical processes. More specifically, the present invention relates to processes and systems for reusing gases from siderurgical furnaces.BACKGROUND OF THE INVENTION

[0002] Classical processes for obtaining primary iron from iron oxides are known in the state of the art. Traditionally, the blast furnace is used as a reduction reactor, producing pig iron. Additionally, there are direct reduction reactors, which produce sponge iron (Direct reduced iron - DRI). In these processes, the most common ferrous raw materials are sinter, pellets, and granulated iron ore.

[0003] The blast furnace is a shaft reactor that operates in a countercurrent mode. Ore in the form of sinter, pellets, and granulate, along with reducing agents (coke / coal) and fluxes (limestone, etc.), is sequentially loaded through the upper part of the furnace to form intercalated layers of ferrous charge and reducing agent. Preheated air is introduced into the lower part of the blast furnace through tuyeres located in the area above the crucible (combustion zone). Auxiliary fuels such as Pulverized Coal Injection (PCI) are used along with the blown air. The reaction between the heated air and the carbon in the coke / coal in the combustion zone generates reduction gas that ascends the reactor, promoting the transfer of energy from the hot gases to the solid charge, the reduction of the iron ore to metallic iron, and the formation of hot metal, in addition to the formation of a slag phase.

[0004] Some more modern furnaces use self-reduction agglomerates, which offer much more favorable conditions for reduction. Such equipment is called self-reduction furnaces. The closer contact between the iron oxide and the carbonaceous material provides favorable reaction kinetics, since the diffusion path of CO into the pellet is reduced. Thus, the reduction gas generation and oxide reduction reactions, shown below, occur within the agglomerate itself.         2MeO (s) + C (s) → 2Me (s) + CO 2(g)         CO 2(g) + C (s) → 2CO (g)         MeO (s) + CO (g) → Me (s) + CO 2(g)

[0005] In this sense, the agglomerate itself effectively establishes a semi-closed system in which the atmosphere remains reducing throughout the period in which carbon is available within it. Thus, self-reduction agglomerates act as mini-reactors.

[0006] The exhaust gases from self-reduction furnaces typically have a higher CO / CO 2 ratio than those from blast furnaces, resulting in greater reducing power.

[0007] Currently, some industrial processes utilize the gas from self-reduction furnaces to generate electricity through their combustion. However, the use of this reducing power of the gas in metal oxide reduction applications has not been explored.

[0008] The proposed invention solves the problems from the state of the art described above in a simple and efficient manner.SUMMARY OF THE INVENTION

[0009] The primary objective of the present invention is to provide a process and a system for the continuous pre-reduction of a solid granular material that utilizes the reducing potential of the gases from a siderurgical self-reduction furnace, rich in fuels and reduction gases.

[0010] The secondary objective of the present invention is to utilize the waste gases in other processes, such as post-combustion and reuse of the remaining calorific value.

[0011] In order to achieve the objectives described above, the present invention provides a process for the continuous pre-reduction of a solid granular material, comprising the steps of (i) continuously passing a solid granular material through a reactor and (ii) pre-reducing the solid granular material by means of injecting pre-reduction gas into the reactor as the solid granular material goes through the reactor, wherein the pre-reduction gas comes from a siderurgical self-reduction furnace.

[0012] The present invention also provides a system for the continuous pre-reduction of a solid granular material. The system comprises a pre-reduction reactor that is fed by the exhaust gas from a siderurgical self-reduction furnace. The solid granular material passes continuously through the reactor and is pre-reduced by the pre-reduction gas.BRIEF DESCRIPTION OF THE FIGURES

[0013] The detailed description shown below refers to the attached figure and its respective reference numerals. Figure 1 illustrates a process flowchart according to a preferred embodiment of the present invention.DETAILED DESCRIPTION OF THE INVENTION

[0014] It should be noted, first of all, that the following description will be based on a preferred embodiment of the invention, as will be apparent to anyone skilled in the art. However, the invention is not limited to this particular embodiment.

[0015] The present invention therefore provides a process for the continuous pre-reduction of a solid granular material 10, the flowchart of which is illustrated in Figure 1. In a first step, the process of the present invention comprises the step of continuously passing a solid granular material 10 through a reactor 20. Preferably, the solid granular material 10 is iron ore. Such solid granular material 10 may include a wide variety of particle sizes, including fine and ultrafine. Alternatively, solid granular material 10 is a solid agglomerate, such as a self-reduction briquette.

[0016] Preferably, reactor 20 is a rotating cylindrical reactor or any other reactor capable of pre-reducing solid granular material 10.

[0017] In a second step, the process of the present invention comprises the step of pre-reducing the solid granular material 10 by injecting pre-reduction gas 30 into the reactor 20 as the solid granular material 10 goes through the reactor 20. The pre-reduction gas used in the step of pre-reducing the solid granular material 10 comes from a siderurgical self-reduction furnace 40, which ensures a reducing atmosphere favorable to the pre-reduction of the solid granular material 10, due to the CO / CO 2 ratio present in the composition of the exhaust gas from this type of furnace. Preferably, the mass ratio of CO / CO 2 present in the composition of the gas from the siderurgical self-reduction furnace 40 varies from 1.5 to 3. Thermodynamically, this ratio may be sufficient to achieve satisfactory degrees of metallization.

[0018] In addition to the high amount of CO in its composition, the gas from the siderurgical self-reduction furnace 40 has an exhaust temperature in the range of 600 to 800 °C, which is sufficient for pre-reduction of the solid granular material 10. Thus, the gas from the siderurgical self-reduction furnace 40 can be injected directly into the reactor 20 without the need for a cooling / heating system. It is worth noting that in blast furnaces the temperature of the outlet gases can vary between 100 and 200 °C, which makes it difficult to use them in pre-reduction processes.

[0019] Preferably, the step of continuously passing the solid granular material 10 through a reactor 20 comprises continuously moving the solid granular material 10 from a first end of the reactor 20 toward a second end of the reactor 20. In this scenario, the first end of the reactor 20 is an inlet end for the solid granular material 10, while the second end of the reactor 20 is an outlet end for the solid granular material 10.

[0020] Still preferably, the first end of reactor 20, where the solid granular material is added, is the gas outlet end after pre-reduction. The second end of reactor 20 is an inlet end for pre-reduction gas 30 coming from the siderurgical self-reduction furnace 40. Thus, the pre-reduction gas 30 preferably passes through reactor 20 in countercurrent with the solid granular material 10, favoring the transfer of heat and mass between the two materials and, therefore, improving the efficiency of the pre-reduction process. Furthermore, there is the possibility of using auxiliary fuels in order to minimize the loss of energy efficiency of the top gas throughout the pre-reduction process.

[0021] Preferably, after the step of pre-reducing the solid granular material 10 inside the reactor 20, the exhaust gas that leaves the pre-reduction system can be used in another application, such as reusing its remaining calorific value through post-combustion. The heat generated can be used in a wide variety of applications within the siderurgical plant.

[0022] Preferably, after the step of pre-reducing the solid granular material 10 inside the reactor 20, it is directed directly to the siderurgical self-reduction furnace 40 for material reduction.

[0023] Alternatively, comminution, separation, and / or magnetic concentration techniques can be used, followed by a step of agglomerating the pre-reduced material, for its subsequent destination to the reduction furnace. This option allows (i) avoiding the generation of agglomerate fines during pre-reduction, caused by crystalline transformations resulting from phase transformations, and / or (ii) a possible low iron concentration (if the solid granular material is, for example, iron ore or iron agglomerate) in the pre-reduced agglomerate.

[0024] Alternatively, it is possible to pre-reduce materials to fine / ultrafine particle sizes and then perform agglomeration.

[0025] The present invention further provides a system associated with the method described above, the system comprising reactor 20 and siderurgical self-reduction furnace 40, wherein a solid granular material 10 passes continuously through the interior of reactor 20 and is pre-reduced by a pre-reduction gas 30 originating from siderurgical self-reduction furnace 40.

[0026] The system according to the present invention further comprises all the ducts necessary for connecting and transporting solid granular material and pre-reduction gas between reactor 20 and siderurgical self-reduction furnace 40.

[0027] Optionally, a magnetic separation step 50 is provided after the pre-reduction of the solid granular material 10 and before the entry of this material into the siderurgical self-reduction furnace 40 with the aim of concentrating the magnetic material and separating it from the gangue that originates from the magnetic material itself.

[0028] Thus, as explained above, the present invention primarily provides a process and system for the continuous pre-reduction of a solid granular material that utilizes the reducing potential of gases from a siderurgical self-reduction furnace, rich in fuels and reduction gases. As mentioned above, the gases from the self-reduction furnace have a favorable concentration of CO 2 compared to CO 2 and other compounds, ensuring the formation of a reducing atmosphere in the reactor. Furthermore, the gas outlet temperature from the self-reduction furnace meets the criteria for direct injection into the reactor, eliminating the need for gas heating systems.

[0029] Several variations affecting the scope of protection of the present application are permitted. Thus, it is emphasized that the present invention is not limited to the particular configurations / embodiments described above.

Claims

1. Process for continuous pre-reduction a solid granular material (10), comprising the steps of: continuously passing a solid granular material (10) through a reactor (20); and pre-reduction the solid granular material (10) by means of injecting pre-reduction gas (30) into the reactor (20) as the solid granular material (10) goes through the reactor (20); characterized in that the pre-reduction gas (30) comes from a siderurgical self-reduction furnace (40).

2. Process, according to claim 1, characterized in that the step of continuously passing a solid granular material (10) through a reactor (20) comprises continuously moving the solid granular material (10) from a first end of the reactor (20) toward a second end of the reactor (20).

3. Process, according to claim 2, characterized in that the first end of the reactor (20) is an inlet end for solid granular material (10) and an outlet end for pre-reduction gas (30) from the siderurgical self-reduction furnace (40).

4. Process, according to claim 2 or 3, characterized in that the second end of the reactor (20) is an outlet end for solid granular material (10) and an inlet end for pre-reduction gas (30) from the siderurgical self-reduction furnace (40).

5. Process, according to any one of claims 1 to 4, characterized by comprising an additional step of post-combustion of the pre-reduction gas (30) to generate heat after the step of pre-reduction the solid granular material (10) inside the reactor (20).

6. Process, according to any one of claims 1 to 5, characterized by comprising an additional step of directing the solid granular material (10), pre-reduced inside the reactor (20), to the siderurgical self-reduction furnace (40).

7. Process, according to any one of claims 1 to 6, characterized in that the reactor (20) is a rotating cylindrical reactor.

8. Process, according to any one of claims 1 to 7, characterized by comprising the additional step of comminuting the pre-reduced solid granular material (10).

9. Process, according to claim 8, characterized by comprising the additional steps of: separating and / or magnetically concentrating the comminuted material and / or fines and ultrafines generated in the pre-reduction step; and agglomerating the separated and / or concentrated material.

10. Continuous pre-reduction system for a solid granular material (10), comprising: a reactor (20); a siderurgical self-reduction furnace (40); wherein a solid granular material (10) passes continuously through the reactor (20); characterized in that the solid granular material (10) is pre-reduced by a pre-reduction gas (30) originating from the siderurgical self-reduction furnace (40).

11. System, according to claim 10, characterized in that the reactor (20) comprises a first end and a second end, wherein the continuous movement of the solid granular material (10) occurs from the first end toward the second end.

12. System, according to claim 11, characterized in that the first end of the reactor (20) is an inlet end for solid granular material (10) and an outlet end for pre-reduction gas (30) originating from the siderurgical self-reduction furnace (40).

13. System, according to claim 11 or 12, characterized in that the second end of the reactor (20) is an outlet end for solid granular material (10) and an inlet end for pre-reduction gas (30) coming from the siderurgical self-reduction furnace (40).

14. System, according to any one of claims 11 to 13, characterized in that the solid granular material (10) pre-reduced inside the reactor (20) is directed to the siderurgical self-reduction furnace (40).

Images