JPS61217514A - Production of preliminary dephosphorizing agent - Google Patents

Abstract

PURPOSE:To produce a granular preliminary dephosphorizing agent easily and inexpensively by sucking and removing the molten slag of soda ash refining by an ejector and adding soda ash-contg. powder to the slag in the mid-way of suction. CONSTITUTION:The aperture at the bottom end of a suction pipe 3 of an ejector type slag sucking and discharging device 1 which ejects a high-pressure gas such as air from a high-pressure gas ejection pipe 4 into a discharge pipe 2 consisting of a pipe closed at one end and branched with the pipe 3 is brought near to the molten slag 7 generated by molten iron refining by the soda ash refining agent to suck the slag. The sucked slag is removed through a suction area 8. The soda ash-contg. collected dust 6 from a powder adding pipe 5 is ejected and added to the sucked slag 7 by using a carrier gas. The solidification of the slag 7 liquid drops is thereby accelerated to prevent clogging. The granular dephosphorizing agent 12 having adequate components are efficiently formed and are recovered into a recovering boxy 11 provided with an air filter 13 and an exhauster 14 through a lead-out pipe 10 from a scattering area 9.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention provides a method for producing a soda ash-based preliminary dephosphorizing agent. This invention relates to a method for producing a granular, inexpensive preliminary dephosphorizing agent that has been subjected to a dephosphorizing treatment.

(Conventional technology) After tapping and before charging into the converter, the hot metal is subjected to preliminary treatments such as desilicification, dephosphorization, and desulfurization, and the slag generated in each of these preliminary treatments is completely removed before being transferred to the converter. So-called slagless refining, which involves refining tax coal, has recently attracted attention in terms of refining efficiency and alloy reduction rate, and has been put into practice in some cases.

In such hot metal pretreatment, the hot metal tapped from the blast furnace is separated from the blast furnace slag on the blast furnace gutter, first subjected to gutter desiliconization treatment using a desiliconizing agent such as iron oxide, and then usually placed in another container, For example, after being transferred to a mixer car, ladle, etc., it undergoes desulfurization and dephosphorization.

Dephosphorization agents used in hot metal pretreatment are roughly divided into lime-based and soda ash (Na2CO3)-based dephosphorization agents, but CaO and Fe
Compared to a lime-based dephosphorizing agent made of 2O3, a soda ash-based dephosphorizing agent has a shorter reaction time and higher dephosphorizing efficiency, so it has superior performance as a dephosphorizing agent.

However, soda ash-based dephosphorizing agents are expensive and the treatment of the generated slag is complicated, so they have not been widely put into practical use.

The present inventors first desilicated the hot metal to sufficiently reduce the Si content, then injected soda ash to perform the dephosphorization treatment, and recovered and reused the soda ash from the generated slag. (Japanese Patent Application Laid-Open No. 57-35604). The main purpose of this is to prevent expensive soda ash from reacting with St in the hot metal, resulting in loss of dephosphorizing agent. Although the basic unit of refining agent could be reduced by collecting and reusing it, a large amount of soda ash had to be added and replenished.

As a method for reducing the amount of dephosphorizing agent used in hot metal dephosphorization, there is a two-step dephosphorization method in which primary dephosphorization is performed continuously following desiliconization treatment on the blast furnace gutter, and then secondary dephosphorization is performed in a vessel. was proposed (Japanese Unexamined Patent Publication No. 58-48614). This is a method in which primary dephosphorization is performed in a short period of time using a small amount of dephosphorizing agent in a high phosphorus region, and then dephosphorization is carried out in a low phosphorous region over a sufficient amount of time using a sufficient amount of dephosphorizing agent to reach the target value. Therefore, compared to conventional methods, the basic unit of dephosphorizing agent required to obtain the same dephosphorizing rate is reduced, so this method is particularly suitable for dephosphorizing using expensive soda ash-based dephosphorizing agents. To explain in more detail, primary dephosphorization in planted soil is a reaction in a relatively high phosphorus concentration range, so dephosphorization proceeds efficiently with a very small amount of dephosphorizing agent, and most of the phosphorus is removed from the hot metal at this stage. be done.

By then discharging the slag and performing full-scale dephosphorization in the container, the load of this secondary dephosphorization can be significantly reduced, and as a result, the total amount of dephosphorization agent used in the converter furnace is reduced to about 2/3 of the conventional amount. The phosphorus concentration can be reduced to the target value before blowing. Furthermore, in general, during dephosphorization, Si in the hot metal reacts with the dephosphorizing agent, reducing the basicity of the slag and deteriorating the slag properties. However, since the primary dephosphorization in the above method is a continuous process, the influence of St is small, and therefore the amount of dephosphorizing agent used for basicity adjustment is reduced, which also reduces the basic unit. contributes to

In the above two-step dephosphorization method, the -second dephosphorization is carried out in a high phosphorus region where the reaction efficiency is extremely high, and furthermore, since it is followed by refining such as secondary dephosphorization and desulfurization, this second step is expensive. There is no need to use soda ash; a refining agent mixed with some impurities can suffice for the purpose.
It is advantageous to use the cheapest possible material.

Furthermore, secondary dephosphorization is usually carried out in planted soil. Methods for adding refining agents to hot metal flowing through the planting soil include the overlay method, blasting method (top spraying method), and injection method (method in which the lance is immersed and injected), but the durability of the equipment and The blasting method, which has excellent reaction efficiency, is most frequently used. In this blasting method, the refining agent is added by spraying from above, so if the refining agent is in the form of fine powder, most of it will immediately float to the top of the hot metal without reacting, reducing the refining efficiency. Therefore, the refining agent is preferably in the form of particles with a particle size of about 2 to 2 (1+n), taking into account the ability to penetrate into the hot metal and the ease of handling during transportation.

However, since conventional dephosphorizing agents are often added by injection, they are often in the form of fine powder, and granulating this requires a granulation process, which is costly.

Under such circumstances, it is still desired to supply an inexpensive granular dephosphorizing agent suitable for primary dephosphorization (preliminary dephosphorization) of hot metal from soda ash-based materials with high dephosphorization efficiency.

Attempts have been made to manufacture inexpensive refining agents using various types of slag and dust generated within steelworks (e.g., JP-A-50-160115, JP-A-58-16).
No. 010, No. 5B-64307, Special Publication No. 54-410
No. 05, see No. 55-21812). However, since most of these methods produce finely powdered refining agents, a granulation process is required to granulate them, and even methods that produce granular refining agents require expensive granulating agents such as water glass. However, many methods are aimed at producing desiliconizing agents. Therefore, there has been no method for manufacturing granular dephosphorizing agents from slag or dust at low cost without requiring a granulation process.

On the other hand, in the above-mentioned slagless refining, the slag generated in each hot metal pretreatment process may interfere with the next refining process, cause rephosphorization,
In principle, slag is removed after each treatment to avoid resulfurization. In particular, when charging the slag into the converter, complete removal of the slag is required to prevent impurities in the pretreated slag from being reduced in the converter and entering the molten steel. Also,
Similarly, complete slag removal is required to clean molten steel during tapping from a converter.

Conventionally, the means for removing these sludge was by scraping,
Alternatively, in the case of a ladle or converter, the usual method was to stop tapping or tapping just before residual pig iron or residual steel became low and slag was involved, and to discharge the slag together with the residual pig iron or residual steel. However, especially in the case of slagless refining,
It is necessary to remove slag quickly and as completely as possible in each hot metal pretreatment process, but with the slag scraping method, as the amount of slag decreases, the hot metal is also scraped out at the same time as slag scraping, making it possible to completely remove slag. Moreover, since it takes time to remove the slag, the effects of the slagless refining described above cannot be fully demonstrated.

As a quick method for removing slag, Japanese Patent Application Laid-Open No. 160868/1983 proposes a method of vacuum suction while scraping up the slag in the ladle. This method prevents molten slag from adhering to the pipe wall after vacuum suction and clogging the pipe.
Immediately after suction, water is poured to solidify and crush the slag, and the slag is recovered in the form of a slurry. However, this method is more dangerous than discharging water over hot metal, such as steam explosion, and cannot be carried out in a factory with many workers.Therefore, this method can only be used to remove slag from a pig iron mixing car. In addition, a large amount of water is required to cool the high-temperature slag with water, which increases the scale of the equipment, and the sensible heat of the high-temperature slag is not utilized at all, resulting in an energy loss.

Moreover, since the recovered slag is in the form of a slurry, it is normally discarded as is after solid-liquid separation, and requires steps such as drying in order to be reused.

(Problems to be Solved by the Invention) As mentioned above, at present, granular dephosphorizing agents suitable for preliminary dephosphorization of hot metal, especially gutter dephosphorization by blasting, cannot be obtained from by-product materials in steel works. There is no way to easily and inexpensively manufacture it with fewer steps.

On the other hand, the slag generated during preliminary refining of hot metal or converter refining can be quickly and completely removed, and the sensible heat of the slag can be used effectively to reuse the slag for some purpose. There is a need for a method for collecting slag in the form of sludge.

(Means for Solving the Problems) The present inventors have previously proposed a simple and quick method for producing molten slag without the need for water using an ejector method that utilizes the suction force generated when surrounding air is drawn in by jetting high-speed airflow. proposed a suction slag removal device (Japanese Patent Application No. 58-156426), and as an improvement thereof, the molten slag being sucked by the suction slag removal device was In order to improve the granulation properties of molten slag, it was proposed to collect the solid slag in granular form by adding a powdered basic substance and sucking out the molten slag (Japanese Patent Application No. 164629/1982).
.

Further research on the ejector method revealed that the molten slag waste produced during hot metal refining using a soda ash-based refining agent can be used in iron manufacturing instead of adding basic substance powder as described above. Even when soda ash-containing powder such as dust collected in-house was added, the adhesion prevention effect was almost the same, and the granulation properties were also good. Moreover, the recovered slag is granular with uniform particle size and contains a large amount of soda ash due to contamination with collected dust, etc., and also contains a moderate amount of iron oxide. The present invention was completed based on the discovery that a composition and properties that are extremely suitable as a pharmaceutical agent can be obtained.

Here, the present invention provides that when slag produced by hot metal refining using a soda ash-based refining agent is suctioned and sludge-removed by an ejector-type suction-slag device using high-pressure gas as a driving source, soda ash is contained in the slag during suction. A method for producing a pre-dephosphorizing agent, comprising adding powder and collecting particulate matter from the suction slag device.

(Function) Hereinafter, the present invention will be explained in more detail with reference to the accompanying drawings. In the present invention, % is by weight unless otherwise specified.

The accompanying drawing is a schematic diagram showing an example of an ejector-type suction slag device used for producing a dephosphorizing agent according to the method of the present invention. This suction sludge discharge device was developed in the above-mentioned Japanese Patent Application No. 59-1646.
Since the device is almost the same as that described in Japanese Patent Application No. 164629/1988, please refer to the specification of Japanese Patent Application No. 164629/1983 for details of the device.

To briefly explain the ejector-type dry suction sludge removal device shown in the attached drawing, this sludge removal device l:
Discharge pipe 2 consisting of a tube with one end closed through which a high-speed gas flow flows
, a suction pipe 3 that communicates with and branches from this discharge pipe, a high-pressure gas jet pipe 4 that penetrates the closed end surface of the discharge pipe 2 and is inserted into the discharge pipe, and a pipe wall that penetrates and opens into the molten slag suction area. It consists of a powder jet addition pipe 5. The powder addition pipe 5 is for transporting the collected dust 6 contained in a container communicating therewith by means of a carrier gas, and injecting it into the slag removal device.

The ejection pipe 4 is connected to a supply source (not shown) of high-pressure gas (e.g., pressure ta air), such as a compressor, and the tip of the ejection pipe 4 is preferably slightly above the extension of the central axis of the suction pipe 3. It has reached the retracted position. When high-pressure gas is ejected from the ejection pipe 4, a high-speed airflow is generated inside the ejection pipe 2,
This airflow entrains the air in the suction pipe 3 and is ejected from the outlet of the discharge pipe 2. As the air in the suction tube is drawn in, surrounding air is sucked in from the lower end of the suction tube 3, generating suction wind into the suction tube, and generating an upward air current, that is, a suction force inside the suction tube.

When the ejector-type suction slag device 1 having such a configuration is brought close to the molten slag 7 from above, the molten slag is sucked in together with the surrounding air, and after being transported upward in the suction pipe 3 in the form of droplets by an upward air current, When the slag drops enter the discharge pipe 2, they collide with the high-speed airflow from the ejector 4, changing the course of the slag droplets and causing them to be blown away. That is, 8 is a slag suction area, and 9 is a slag blow-off area. The slag droplets solidify before being discharged from the outlet of the discharge pipe and are recovered as granular slag.

In the method of the present invention, collected dust containing soda ash is injected from the powder addition pipe 5 using a carrier gas to promote coagulation of slag droplets and prevent clogging caused by droplets adhering to the pipe wall. In addition to promoting granulation, the composition of the resulting granular slag is adjusted to an appropriate component as a dephosphorizing agent. The opening position of this powder addition pipe 5 is within the slag suction area (i.e.
before it is blown away), and as shown in the figure, the discharge pipe 2
It may be opened substantially parallel to the bottom of the ejection pipe 4 by penetrating the closed end face of the suction pipe, or it may be opened at a further lower position, that is, through the pipe wall of the suction pipe.

However, the illustrated position has the advantage of increasing the ejector effect due to the high-speed airflow within the discharge pipe.

In order to facilitate recovery of the granular slag, that is, the dephosphorizing agent, discharged from the outlet of the discharge pipe, in the illustrated example, a discharge pipe 10 is provided following the outlet of the discharge pipe 2 of the suction slag device 1.
The discharged dephosphorizing agent is guided to the collection box 11 through the outlet pipe 10, and the granular dephosphorizing agent 12 is separated from the airflow and deposited in the collection box 11. It is preferable to install an air filter 13 to separate dust entrained in the airflow from the collection box, and an exhaust air ta 14 to promote discharge of the airflow.

According to the method of the present invention, a dephosphorizing agent is produced by adding powder with an ejector-type suction/slag device, draining and granulating molten slag as described above. To achieve this objective, it is necessary that both the molten slag and the powder have a composition that is compatible with the production of dephosphorizing agents.

Specifically, the molten slag is Na 2 Co 3 or N
It is necessary to contain a large amount of a2O, and it is preferable that the slag has been sufficiently formed. In this sense, preferred molten slag is desulfurization slag produced by preliminary dephosphorization of hot metal using a soda ash-based refining agent in a ladle before charging into a converter. Since such preliminary desulfurization is carried out by stirring the hot metal by mechanical means, the resulting slag is sufficiently slaged and also contains a considerable amount of unreacted soda ash. However, when a dephosphorizing agent is produced according to the present invention by sucking and discharging such desulfurizing slag, 80% of the slag goes into the dephosphorizing agent, but the preliminary dephosphorizing treatment of hot metal is performed as described above. Usually, dephosphorization and desulfurization are carried out in the planted soil, and then full-scale dephosphorization and desulfurization are carried out in a ladle, so the mixing of 8 minutes into the dephosphorization agent does not pose much of a problem. Generally, the slag used in the present invention is Na 2
Any slag containing about 20% or more, preferably about 40% or more of CO3 may be used, and any slag other than the above may be used as long as it contains CO3. However, since it is necessary to contain soda ash, slag produced by refining hot metal with a soda ash-based refining agent is used.

On the other hand, as the powder to be added to the slag during suction, a powder containing soda ash as a main component is used for the purpose of producing a soda ash-based dephosphorizing agent.

A typical example of such powder is dust generated when soda ash is blown into hot metal in a container such as a pig iron mixing car to perform dephosphorization and desulfurization treatment. During this process, a large amount of Na2O, Na2C
O3 is generated, Na2O reacts with CO2 in the gas, and N
Since it becomes a 2 CO3, more than half, usually 60% or more, of the dust collected by the dust collector becomes Na 2 C03. Conventionally, 6 kg of such dust has been collected per ton of hot metal, and the current situation is that it requires a large amount of cost to dispose of it. When such collected dust is used in the present invention, since it contains a considerable proportion of iron oxide (e.g., about 30%) in addition to soda ash, a moderate amount of iron oxide is also added to the dephosphorizing agent produced. This further improves the dephosphorization efficiency and also provides a desiliconization effect. Therefore, from both the compositional advantage and the manufacturing cost of the dephosphorizing agent, it is preferable to use dust containing soda ash that is collected in steel plants, but other soda ash-based dusts are preferable. It goes without saying that powders such as these can also be used.

Although the term "collected dust" is used in the attached drawings and the following explanation for convenience, the powder added to the slag in the method of the present invention is not limited to collected dust collected in steel works, etc. do not have.

Next, the operating conditions of the method of the present invention will be briefly explained. High-pressure gas, for example, compressed air at a pressure of 5 kg/alI, is ejected from the ejection pipe 4 of the ejector-type sludge removal device 1 at a flow rate such that a high-speed airflow of about 0.5 to 1.5 matsuha flows into the ejector pipe 2. let Since the flow rate of the airflow in the discharge pipe varies depending on the pipe diameters of the discharge pipe and the ejection pipe, the flow rate is adjusted so as to obtain the desired flow velocity. The suction and removal of the molten slag 7 is carried out by bringing the sludge removal device l close to a suitable molten slag from above, but in order to suction the molten slag with a specific gravity of approximately 2 to 3, a suction air flow of 5 m/sec or more is required on the top surface of the slag. Therefore, if the flow rate of the air flow in the discharge pipe is within the above range, the distance between the lower end of the suction pipe and the upper surface of the slag should be 20 to 80 mm.
It is preferable to set it within the range of m+-.

Addition of collected dust is carried out by flowing a carrier gas (e.g. compressed air) at the flow rate through which it is conveyed and injected, and injecting it into the suction area along with this air flow.The amount of collected dust added is It is added in an amount sufficient to prevent the molten slag from adhering in the slag removal device and to granulate it, and is usually added at a ratio of 0.6 to 1 ton per ton of molten slag.

When the dephosphorizing agent is produced by the method of the present invention in this way, the dephosphorizing agent is granulated to a particle size of about 2 to 20 m5+ while removing the molten slag without causing clogging by adding the collected dust. can be obtained. As mentioned above, this dephosphorizing agent is added by the blasting method for gutter dephosphorization of hot metal, but of course it can also be used for other dephosphorizing processes. It can be adjusted by A small amount of collected dust is collected without being granulated by the air filter 13, but among the dust collected by the air filter or the granular dephosphorizing agent collected in the collection box 11, the particle size is too small. can be mixed with the collected dust 6 and reused, or can be used as a dephosphorizing agent added by blowing using the in-die excin method.

Next, the present invention will be explained with reference to Examples.

Desiliconizing agent mainly containing mill scale 40kg/V on the blast furnace gutter
The hot metal that has been desiliconized using 8-pig T is transferred to a pig iron mixer after being slaged, and is mixed with soda ash (Na 2 Co 395.9%, 5i02
1゜0%, T, Fe O, 2%, PO35%, So, 3
%) 15 kg/ton of hot metal was injected into the hot metal using the injection method to perform dephosphorization and blasting treatment. The following Table 1 shows the changes in hot metal components during these steps.

Table 1 Approximately half of the molten slag produced by this dephosphorization was removed from the pig iron mixer using a vacuum suction type removal device.

Next, the hot metal is transferred to a ladle, and among the slag floating on top of the hot metal, large lumps and unslaged parts are first removed by the slag scraping method, and approximately 100% of the remaining approximately 1.5 tons is removed using the method of the present invention. According to the method, a granular dephosphorizing agent was produced by adding collected dust while removing the slag using two ejector-type suction and evacuation devices shown in the attached drawings. In each of the slag removal devices used, both the discharge pipe and the suction pipe were made of steel pipes with a diameter of 120L1m, and the length of the discharge pipe was 1200B.

The suction tube was 800+u+. As the ejector driving source, compressed air with a pressure of 5 kg/cd is supplied from the ejection pipe for 7 ONn.
? It was ejected at a flow rate of /+mtn/. From the powder addition pipe, dust (average composition: Fe 2
9.22%, Na2C0361,27%, SiO
20.80%, SO, 39%), the pressure is the same as above and the flow rate is 25Nn? /win/unit of compressed air was added as a carrier gas at a total rate of 100 kg/win. As shown in the illustrated example, the powder addition tube was inserted into the discharge tube so as to be substantially parallel (slightly upward) to the lower side of the discharge tube so as to enhance the ejector effect. The top of the collection box was sealed as shown in the figure, and an air filter and exhaust fan were installed.

Under the above conditions, the distance between the lower end of the suction tube and the upper surface of the molten slag was controlled to approximately 50 + + + m, and since the large lumps were removed by scraping first, there was no problem such as clogging in the tube, and the slag was removed for about 10 m. Suction and drainage were terminated at minute intervals. During this time, only molten slag adhered to the tube wall to a thickness of about 5 to 1511I11. Approximately 2 tons of particulate matter had accumulated in the collection box after the slag removal was completed. As a result of separating fine particles with a particle size of less than 21111 using a sieve, the average particle size was 5.
A granular dephosphorizing agent of sm was obtained. The composition of the obtained dephosphorizing agent is shown in the following Table 2 together with the composition of the dephosphorizing slag before adding the dust collection dust.

Using the dephosphorizing agent obtained in this example, a dephosphorizing test was conducted by adding 10 kg/ml of this dephosphorizing agent to hot metal in a test furnace. As is clear from the results shown in Table 3 below, it was confirmed that this dephosphorizing agent had sufficient phosphorizing ability as a preliminary dephosphorizing agent and also had a considerable desiliconizing effect. Furthermore, it was a better dephosphorizing agent than soda ash alone, with good slag-forming properties and little dust generation during the reaction.

Table 3: Fine particles with a particle size of less than 2IIIm separated from the collected material using a sieve are used by mixing them into the collected dust during the next slag removal operation, or are used as a dephosphorizing agent added by the injection method. I was able to do that.

(Effects of the Invention) As is clear from the above explanation, the method for producing a dephosphorizing agent of the present invention has the following effects.

■ By regenerating collected dust and molten slag, which were conventionally disposed of or recycled, by simple means, dephosphorizing agents can be obtained at a very low cost. ) can be recovered, and dust treatment and slag treatment can be eliminated or significantly reduced.

- Molten slag can be almost completely separated from hot metal, and adhesion to and clogging of the suction pipe can be prevented, so stable operation as a whole can be maintained.

(2) The resulting dephosphorizing agent is in the form of granules and has been subjected to primary dephosphorization, particularly by a blasting method, and the sensible heat of the molten slag is effectively utilized for granulation.

[Brief explanation of the drawing]

The accompanying drawing is a schematic diagram showing an example of an ejector-type suction slag device used for producing a dephosphorizing agent according to the method of the present invention.

Claims (2)

[Claims] (1) When removing slag by suction from slag produced by hot metal refining using a soda ash-based refining agent using an ejector-type suction slag device using high-pressure gas as a driving source, soda ash-containing powder is added to the slag during suction, A method for producing a pre-dephosphorizing agent, comprising collecting particulate matter from the suction and drainage device. (2) The method according to claim 1, wherein the soda ash-containing powder is collected dust collected during hot metal refining using a soda ash-based refining agent.