JP7537471B2 - How to recover iron - Google Patents

Description

The present invention relates to a method for recovering iron.

Various types of slag are generated during the steelmaking process, and this slag contains impurities (oxides of Si, P, Mn, Al, etc.) and iron. This iron is recovered and reused as an iron source.

Patent Document 1 discloses a method for utilizing an iron source recovered from steelmaking slag by crushing steelmaking slag, magnetically separating it, scattering the small-diameter iron nuggets onto the surface slag of the molten iron in a ladle or torpedo car after the molten iron pretreatment, allowing the nuggets to bind and be incorporated, and then charging the nuggets into a converter or electric furnace together with the molten iron for decarburization and refining. With this method, the nuggets can be added without scattering, no slag foaming occurs when they are added, the iron is recovered in the molten steel during decarburization and refining, and the iron source can be utilized efficiently without adversely affecting the load of subsequent refining.

Patent Document 2 discloses a method for continuously or intermittently feeding a cold iron source into molten iron at a predetermined feeding density V (feeding rate per unit time and unit feeding area) during at least one of molten iron desiliconization and dephosphorization processes. This method is said to enable the amount of cold iron source used to be increased without reducing the yield of the cold iron source in the molten iron treatment.

Patent Document 3 discloses a technique for suppressing slag foaming during dephosphorization or desiliconization by supplying an oxygen source to molten iron, in which slag-adhering metal recovered from the slag generated during the dephosphorization of molten iron is added on top. This method suppresses slag foaming and allows stable desiliconization without using a sedative or changing the amount of oxygen gas supplied. It also says that the recovered metal can be effectively used as an iron source.

JP 2009-144179 A JP 2016-188403 A JP 2006-241535 A

However, in the technology of Patent Document 1, in order to prevent the iron nuggets from reacting with the molten iron and forming the slag, the iron nuggets are bonded to the surface of the slag after the molten iron pretreatment and are incorporated into the slag. If the slag after the molten iron pretreatment is then deslagged before being charged into a converter or electric furnace, the iron nuggets will be deslagged together with the slag and will not be retained in the molten iron. Furthermore, omitting the deslag process increases the refining load in the converter, which results in a significant increase in refining costs, particularly when melting high-grade steel, which requires low levels of impurities.

In the technology of Patent Document 2, the cold iron source is added during the hot metal desiliconization process or hot metal dephosphorization process, so depending on the type of cold iron source, slopping or the like may occur during the process, causing problems such as reduced productivity due to interruptions to the process and a low yield of the added cold iron source. In particular, Patent Document 2 describes that bullion recovered from slag generated in the refining process through one or more of the processes of crushing, classification, and magnetic separation can be used as the cold iron source, but the use of such bullion is prone to slopping.

The technology of Patent Document 3 also involves adding a metal to which slag adheres during dephosphorization or desiliconization treatment, which is performed by supplying an oxygen source to molten iron. This technology involves adding metal to open the slag produced during the dephosphorization or desiliconization treatment, forming an escape route for CO gas generated during the treatment, and suppressing slag foaming. Therefore, the metal that can be used is limited to a shape that can break through the slag and reach the molten iron surface. In other words, fine-grained metal cannot be used. Also, if the metal contains a large amount of iron oxide, the iron oxide reacts with the carbon in the molten iron to generate CO gas, which can actually promote foaming. In this respect, the metal that can be used is also limited.

Therefore, the present invention was made with a focus on the above problems, and aims to provide a method for recovering iron that suppresses an increase in refining load and the occurrence of slag foaming and slopping during processing, and can recover granular ingots with a good yield.

According to one aspect of the present invention, there is provided a method for recovering iron contained in powdered ingot, the method including: a slag removal process for removing slag floating on the surface of molten iron contained in a molten iron transport vessel; and an addition process for top-adding the powdered ingot to the molten iron in the molten iron transport vessel after the slag removal process, in which in the addition process, the powdered ingot is top-added at an arbitrary charging rate of 0.1 t/(min· ^m2 ) or more and 2.0 t/(min· ^m2 ) or less during an initial period from the start of charging until the amount of the powdered ingot charged reaches 1 t, and after the initial period of charging, the powdered ingot is top-added at an arbitrary charging rate of 0.1 t/(min· ^m2 ) or more and 3.0 t/(min· ^m2 ) or less.

According to one aspect of the present invention, a method for recovering iron is provided that can suppress an increase in refining load and the occurrence of slag foaming and slopping during processing, and can recover powdered or granular ingots with a high yield.

1A is an explanatory diagram showing a method for recovering iron according to one embodiment of the present invention, in which (A) is an explanatory diagram showing a slag removal process, (B) is an explanatory diagram showing an addition process, and (C) is an explanatory diagram showing a discharge process.

In the following detailed description, an embodiment of the present invention will be described with reference to the drawings. In the description of the drawings, identical or similar parts are given the same or similar reference numerals, and duplicate explanations will be omitted. The drawings are schematic and may differ from the actual product. In addition, the embodiments shown below are examples of devices and methods for embodying the technical concept of the present invention, and the technical concept of the present invention does not specify the materials, structure, arrangement, etc. of the components as described below. The technical concept of the present invention may be modified in various ways within the technical scope defined by the claims.

<Iron recovery method>
The iron recovery method according to the present embodiment will be described. In the present embodiment, first, a slag removal process is performed to remove slag 3 floating on the surface of molten pig iron 2 contained in a molten pig iron transport vessel (FIG. 1(A)). The molten pig iron transport vessel is, for example, a mixed iron car 1 that contains molten pig iron 2 tapped from a blast furnace and transports it to the next process. On the surface of the molten pig iron 2 contained in the mixed iron car 1, desiliconization slag (slag 3) generated by a desiliconization treatment performed in a blast furnace casthouse or the like floats. In the slag removal process, for example, the mixed iron car 1 containing the molten pig iron 2 is transported to a slag removal facility, and slag removal is performed in the slag removal facility. Slag removal is performed, for example, by tilting the torpedo car 1 to the extent that the molten iron 2 does not flow out, and scraping the slag 3 out of the furnace through the throat 10 of the torpedo car 1 with a hoe-shaped slag dragger 4.

In addition, the slag removal process is preferably performed so that the thickness of the slag 3 floating on the surface of the molten pig iron 2 is 200 mm or less. It is preferable not to remove the slag so that the molten pig iron surface is exposed, and it is more preferable that the thickness of the slag 3 after slag removal is 40 mm or more. If the molten pig iron surface is exposed, the temperature of the molten pig iron 2 is likely to drop, and as described below, the added powdered ingots pass through the slag 3, creating a moderate resistance, which reduces the effect of suppressing the rapid reaction between the powdered ingots and the molten pig iron.

Furthermore, it is preferable that the freeboard of the molten iron transport vessel after the slag removal process (the height from the bath surface of the molten iron 2 to the upper end of the mouth of the molten iron transport vessel (the upper end of the throat of the torpedo car 1)) is 0.8 m or more. As described later, the powdered metal added in the addition process passes gradually through the slag 3 and then dissolves in the molten iron 2, during which some reactions such as the generation of CO gas occur, which may cause mild slag foaming. By making the freeboard 0.8 m or more, the powdered metal can be dissolved while maintaining a mild slag foaming state.

After the slag removal process, an addition process is carried out in which powdered ingots 6 are added to the molten iron 2 in the molten iron transport vessel (Figure 1 (B)). When the molten iron transport vessel is a torpedo car 1, the torpedo car 1, which was tilted during slag removal, is returned to a vertical position, and the powdered ingots 6 are added from the ingot injection equipment 5 installed above the throat of the torpedo car 1. Examples of the method of adding the powdered ingots 6 include cutting the powdered ingots 6 stored in a hopper with a feeder, transporting them to the upper part of the mouth of the molten iron transport vessel by a conveyor, and adding them by free fall from there.

The powdered metal 6 may be obtained, for example, by crushing steelmaking slag and magnetically separating it. The powdered metal 6 may also be obtained by crushing and classifying iron-containing dust generated during refining or metal attached to steelmaking equipment. In addition, it is preferable to install the metal injection equipment 5 in the same building as the slag removal equipment, since this allows the addition process to be carried out immediately after the slag removal process is completed without having to move the torpedo car 1.

When powdered metal 6 is added to the molten iron transport vessel after slag removal, the added powdered metal 6 spreads out horizontally on the surface of the slag 3 in the shape of an upside-down dish and accumulates on the surface of the slag 3. The powdered metal 6 then settles within the slag 3, and is gradually absorbed into the molten iron 2 starting from the bottom and dissolved there. The passage of the added powdered metal 6 through the slag 3 provides a moderate resistance to the settling of the powdered metal 6, preventing a sudden reaction between the powdered metal 6 and the molten iron 2. On the other hand, if powdered metal 6 is added when the thickness of slag 3 floating on the surface of the molten iron 2 is large, such as when slag removal is not performed, the time it takes for the powdered metal 6 to settle in the slag 3 is too long, and the powdered metal 6 does not reach the surface of the molten iron by the time the molten iron 2 is discharged from the molten iron transport vessel, resulting in a reduced addition yield.

The charging speed of the powdered ingot 6 is set to an arbitrary speed of 0.1 t/(min· ^m2 ) to 2.0 t/(min· ^m2 ) in the initial charging period from the start of charging until the amount of powdered ingot 6 charged reaches 1 t. The charging speed of the powdered ingot 6 in the initial charging period is preferably set to an arbitrary speed of 0.1 t/(min· ^m2 ) to 1.0 t/(min· ^m2 ). Furthermore, in the period after the initial charging period (the period when the amount of powdered ingot 6 charged exceeds 1 t), the charging speed of the powdered ingot 6 is set to an arbitrary speed of 0.1 t/(min· ^m2 ) to 3.0 t/(min· ^m2 ). The charging speed of the powdered metal 6 is the mass (t (metric ton)) of the powdered metal 6 charged per minute per ^m2 of the area over which the powdered metal 6 falls. If the charging speed is less than 0.1 t/(min· ^m2 ), the added powdered metal 6 may not settle in the slag 3 and may be trapped on the surface of the slag 3. On the other hand, if the charging speed is more than 3.0 t/(min· ^m2 ), the powdered metal 6 piled up at the top may sinter as it is, preventing melting. Conversely, if the powdered metal 6 does not pile up at the top and settles in large amounts in the molten pig iron 2, slag foaming may occur.

Furthermore, if the charging speed is 2.0 t/(min· ^m2 ) or more, particularly in the initial charging period when the charging amount is up to 1 t, a large amount of the granular ingot 6 will settle in the molten pig iron 2, increasing the possibility of severe slag foaming. However, if the granular ingot 6 charged in the initial charging period spreads out like an upside-down dish, the granular ingot 6 will not settle all at once in the molten pig iron 2 even if the charging speed is increased thereafter, so it is possible to increase the charging speed after the initial charging period. However, if the charging speed is increased too much, problems such as slag foaming will occur even when the charging amount is more than 1 t, so the charging speed is set to 3.0 t/(min· ^m2 ) or less.

The powdered metal 6 preferably has a particle size of 0.5 mm to 5 mm. If the particle size is smaller than 0.5 mm, dust may be generated, which may reduce the yield of the molten iron 2. On the other hand, if the particle size is larger than 5 mm, the powdered metal 6 may penetrate the molten iron 2 with too much force, which may cause slag foaming.

Furthermore, the repose angle of the powdered ingot 6 is preferably 40° or less. Here, the repose angle is the angle that the powder layer surface makes with the horizontal plane when the powder is deposited in a gravitational field to form a free surface. The injection method is often used to measure the repose angle, but other methods such as the discharge method and tilt method can also be used. In the injection method, a tray is first prepared below the funnel at a certain distance, and the sample is poured into the funnel and deposited on the tray at a certain speed. The repose angle is then measured when the sample leaks from the tray and the deposited powder forms a certain mountain. In the discharge method, a small hole is made in the bottom of a container filled with the sample, and the sample is discharged from the container. The repose angle is measured from the slope formed by the powder remaining in the container after the sample has been discharged. In the tilt method, the sample is filled into a cylindrical container or the like, the container is tilted, and the repose angle is measured from the slope formed by the powder in the container.

If the angle of repose of the powdered metal 6 is greater than 40°, the powdered metal 6 after addition will not spread over the slag 3, but will pile up upwards and become more likely to be sintered as is. It is preferable that the moisture content of the powdered metal 6 be 8% or less. If the powdered metal 6 contains more than 8% moisture, not only will reactions such as steam explosions be possible, but the particles will also be more likely to adhere to each other, resulting in a larger angle of repose.

Furthermore, it is preferable that the powdered ingot 6 satisfies the formulas (1) and (2). In the formulas (1) and (2), (%T.Fe) indicates the total Fe content (mass%) in the powdered ingot 6, and (%M.Fe) indicates the metallic Fe content (mass%) in the powdered ingot 6.
(%T.Fe)≧30% by mass...(1)
(%T.Fe)-(%M.Fe)≦25% by mass...(2)

If (%T.Fe) is less than 30% by mass, the amount of iron that can be recovered is small, and there is little benefit to recovering the iron source. In addition, (%T.Fe) - (%M.Fe) in formula (2) indicates the degree of oxidation of the iron contained in the powdered ingot 6; a small value indicates a large amount of metallic iron, and a large value indicates a large amount of iron oxide. If (%T.Fe) - (%M.Fe) is greater than 25% by mass, there is a large amount of iron oxide, and the carbon in the molten iron 2 reacts with the oxygen in the iron oxide to generate CO gas, making slag foaming more likely to occur.

As the powdered metal 6 satisfying the above-mentioned conditions, powdered metal obtained by crushing steelmaking slag and separating it by magnetic force is suitable.
After the adding step, a discharge step can be performed in which the molten pig iron 2 in the molten pig iron transport vessel is discharged to a molten pig iron charging ladle 7 (FIG. 1(C)). For example, in the discharge step, the torpedo car 1 to which the granular ingots 6 have been added is moved to a converter plant, and the molten pig iron 2 is discharged from the torpedo car 1 to a molten pig iron charging ladle 7, which is a ladle for charging the converter, in the raw material yard of the converter plant. The added granular ingots 6 gradually dissolve in the molten pig iron 2 during the period until the torpedo car 1 is moved to the converter plant, and the remaining granular ingots 6 are taken into the molten pig iron and melted during this discharge. That is, the melting of the granular ingots 6 progresses to a certain extent during the period from the removal of the desiliconization slag to the discharge, so that it is possible to prevent foaming from occurring due to a large amount of unmelted granular ingots reacting with the molten pig iron 2 all at once during the discharge.

In the iron recovery method according to this embodiment, after removing slag 3 floating on the surface of molten iron 2 contained in a molten iron transport vessel (e.g., torpedo car 1), powdered ingot 6 is added to the molten iron transport vessel. It is then preferable to discharge the molten iron 2 in the molten iron transport vessel into a molten iron charging ladle 7. By including these steps, it is possible to suppress an increase in refining load and the occurrence of slag foaming and slopping during processing, and to recover powdered ingot with a good yield. Furthermore, the effect is more pronounced by setting the addition rate and characteristics of powdered ingot 6 within the preferred ranges as described above.

<Modification>
Although the present invention has been described above with reference to specific embodiments, it is not intended that the invention be limited by these descriptions. By referring to the description of the present invention, other embodiments of the present invention including various modifications in addition to the disclosed embodiments will be apparent to those skilled in the art. Therefore, it should be understood that the embodiments of the invention described in the claims also include embodiments including these modifications described in this specification, either alone or in combination.

For example, in the above embodiment, the discharge step is performed after the addition step, but the present invention is not limited to such an example. For example, after the addition step and before the discharge step, a refining step may be performed in which a lance is immersed in the molten pig iron 2 in the molten pig iron transport vessel, and a gaseous oxygen source containing oxygen gas or a solid oxygen source such as iron oxide is blown into the molten pig iron 2 from the lance to perform a desiliconization process or a desiliconization and dephosphorization process. In the refining step, an inert gas or a cooling gas may be blown together with the gaseous oxygen source or solid oxygen source, as necessary. In the refining step, the slag 3 is stirred by immersing the lance and performing the process, so that the powdery ingot 6 added in the addition step and settling from the surface of the slag 3 into the slag 3 is taken into the molten pig iron 2, and the iron content can be recovered more.

In addition, in the above embodiment, the molten iron transport vessel is a torpedo car 1, but the present invention is not limited to such an example. For example, the molten iron transport vessel may be a ladle-type transport vessel.

Furthermore, in the above embodiment, in the discharging process, the molten iron 2 contained in the molten iron transport vessel is discharged into the molten iron charging ladle 7, but the present invention is not limited to such an example. In the discharging process, it is sufficient that the molten iron 2 is discharged from the molten iron transport vessel into a vessel to be used in the next process, and the molten iron 2 may be discharged into another vessel.

The inventors of the present invention conducted an example. In the example, the slag removal process, the addition process, and the discharge process were carried out on the torpedo car 1, which is a molten iron transport vessel, in the same manner as in the above embodiment, and the yield of the molten iron 2 was investigated. The yield of the molten iron 2 is the ratio of the mass of the molten iron 2 discharged in the discharge process to the sum of the mass of the molten iron 2 in the torpedo car 1 before the addition process (after the slag removal process) and the mass of the powdered ingot T.Fe added in the addition process.

In the embodiment, the slag removal step was performed until the thickness of the slag 3 reached 120 mm. Next, in the addition step, the powdered metal 6 was added under the condition that the charging speed was constant at 0.1 t/(min·m ² ) or more and 2.0 t/(min·m ² ) or less. Furthermore, in the period after the initial charging period when the charging amount exceeded 1 t, the charging speed was increased to 3.0 t/(min·m ² ). The powdered metal 6 was sieved to have a particle size range of 0.5 mm or more and 5 mm or less, an average particle size (mass average diameter) of 3.2 mm, and an angle of repose of 38° or less. Here, the angle of repose was measured by the injection method. The moisture content of the powdered metal 6 was 8 mass% or less. Furthermore, as comparative examples, the yield of molten iron 2 was investigated under conditions where the adding step and the unloading step were performed without performing the slag removing step (Comparative Example 1) and under conditions where the charging rate was more than 2.4 t/(min·m ² ) (Comparative Example 2). The other conditions in Comparative Examples 1 and 2 were the same as those in the examples.

From the results of the Examples and Comparative Examples, it was confirmed that the yield of the molten pig iron 2 in the Examples was improved by 4% compared to Comparative Example 1. In Comparative Example 2, in which the charging speed of the granular ingot 6 was more than 2.0 t/(min· ^m2 ), slag foaming occurred, which forced the interruption of addition in some cases, and the amount of the granular ingot 6 charged per torpedo car 1 was often less than 1000 kg. On the other hand, in the Examples in which the charging speed of the granular ingot 6 was 0.2 t/(min· ^m2 ) or more and 2.0 t/(min· ^m2 ) or less, it was confirmed that slag foaming was suppressed and the granular ingot 6 could be stably charged in an amount of 1000 kg or more.

REFERENCE SIGNS LIST 1 torpedo car 10 furnace throat 2 molten iron 3 slag 4 slag dragger 5 ingot charging equipment 6 powdered ingot 7 molten iron charging ladle

Claims (7)

A method for recovering iron contained in powdered or granular bullion, comprising the steps of:
a slag removing step of removing the slag floating on the surface of the molten iron contained in the molten iron transport vessel so that the thickness of the slag is 40 mm or more and 200 mm or less;
an addition step of top-adding the powdered metal to the molten iron in the molten iron transport vessel after the slag removal step;
Including,
This is an iron recovery method, in which, in the addition step, during the initial period from the start of addition until the amount of powdered bullion added reaches 1 ton, the powdered bullion is added from above at an arbitrary addition rate of 0.1 t/(min· ^m2 ) or more and 2.0 t/(min· ^m2 ) or less, and after the initial period of addition, the powdered bullion is added from above at an arbitrary addition rate of 0.1 t/(min· ^m2 ) or more and 3.0 t/(min· ^m2 ). 2. The method for recovering iron according to claim 1, wherein in the adding step, the powdered metal is added from above at an arbitrary charging rate of 0.1 t/(min·m ² ) to 1.0 t/(min·m ² ) in the initial charging stage. The method for recovering iron according to claim 1, wherein the powdered metal has a particle size of 0.5 mm or more and 5 mm or less, and an angle of repose of 40° or less. 4. The method for recovering iron according to claim 1, wherein the powdered or granular metal satisfies the formulas (1) and (2).
(%T.Fe)≧30% by mass...(1)
(%T.Fe)-(%M.Fe)≦25% by mass...(2)
(% T. Fe): Total Fe content (mass%) in the powdered metal
(%M.Fe): The content (mass%) of metallic Fe in the powdered metal The method for recovering iron according to claim 1 or 3, wherein the powdered metal is obtained by crushing steelmaking slag and separating it with magnetic force. The iron recovery method according to claim 1 or 3, wherein the freeboard of the molten iron transport vessel after the slag removal process is 0.8 m or more. The method for recovering iron according to claim 1 or 3 further comprises a refining step of immersing a lance in the molten iron in the molten iron transport vessel after the adding step to perform a desiliconization process or a desiliconization and dephosphorization process.

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