JP6766796B2 - How to sedate slag - Google Patents

Description

The present invention relates to a method of sedating slag.

When refining molten iron in a converter-type refining furnace, slag is generated during the refining process. Then, in such a refining process, a phenomenon (referred to as "forming") in which the slag expands due to the generated gas such as carbon monoxide (CO) gas occurs. If the amount of expansion due to forming is large, the slag overflows from the furnace body of the smelting furnace. Therefore, a method of calming or suppressing the forming of slag is being studied. As a method for sedating the forming of slag, a sedative is generally added to the formed slag.

Further, for example, Patent Document 1 discloses a method of adding a carbonaceous material within 3 minutes after the start of acid feeding by a top-blown lance as a method of suppressing slag forming.
Further, Patent Document 2 discloses a method of adjusting the acid feeding rate of the top blowing lance and the bottom blowing flow rate of the bottom blowing gas when the slag is formed, as a method of calming the forming of the slag.
Further, in Patent Document 3, as a method of calming the forming of slag in a reaction vessel different from that of a converter type smelting furnace, the slag is opened for degassing by inserting and removing the rod body from the upper part of the slag. A method of forming a hole is disclosed.

Japanese Patent No. 3888313 JP-A-2000-109923 Japanese Unexamined Patent Publication No. 10-183217

By the way, when the operation with intermediate slag is carried out in a converter type smelting furnace, it is necessary to form the slag to some extent in order to improve the slag. Therefore, in the refining treatment with intermediate slag, compared to the smelting treatment without intermediate slag, slag tends to be more likely to be ejected to the outside of the furnace except during the intermediate slag, so that the amount of sedative used is large. To increase. The refining process with intermediate slag has a lower cost than the normal smelting process without intermediate slag. However, if the amount of the sedative used increases, the cost increases, and from the viewpoint of cost, there is a possibility that the gain for performing intermediate scavenging cannot be sufficiently obtained. In addition, the inventory of sedatives may be exhausted, which may have an impact on operations.

Further, in Patent Document 1, since it is a method of suppressing slag forming in advance, it is not possible to deal with the case where forming actually occurs. Further, in Patent Document 2, since the correspondence is made during the blowing in which the acid feeding is carried out, it is not possible to deal with the forming of the slag generated in the standby state in which the blowing treatment is not carried out.

Therefore, the present invention has been made by paying attention to the above-mentioned problems, and provides a slag sedation method capable of sedating slag forming at a lower cost in a standby state in which a blowing process is not performed. The purpose is to do.

According to one aspect of the present invention, it is a method for squeezing slag in a converter type smelting furnace having a top-blown lance, in which molten iron and slag are contained in the furnace body of the smelting furnace, and oxygen is removed from the top-blown lance. Stagnation of slag, which is characterized by blowing gas into the furnace body from the top blowing lance when the slag in the furnace body is formed in a standby state in which the containing gas is not blown onto the molten iron. The method is provided.

According to one aspect of the present invention, there is provided a slag sedation method capable of sedating slag forming at a lower cost in a standby state where no blowing treatment is performed.

It is a schematic diagram which shows the converter type refining furnace. It is a graph which shows the use amount of the sedative in Example 1. FIG.

In the following detailed description, many specific details will be described by exemplifying embodiments of the invention to provide a complete understanding of the invention. However, it is clear that one or more embodiments can be implemented without such particular detail description. Also, for the sake of brevity, the drawings are schematic representations of well-known structures and devices.

<How to sedate slag>
(Dephosphorization of molten iron)
A slag sedation method according to an embodiment of the present invention will be described with reference to FIG. In the present embodiment, a converter type refining furnace 1 is used to perform a dephosphorization treatment, which is a refining treatment accompanied by intermediate slag.
As shown in FIG. 1, the smelting furnace 1 has a furnace body 11 and a top-blown lance 12. The furnace body 11 is a refining container in which a furnace port 111 having an opening is formed at the upper portion, and a refractory material is provided inside. A plurality of bottom blowing tuyere (not shown) are provided at the bottom of the furnace body 11, and an inert gas for stirring is blown into the furnace body 11 from the bottom blowing tuyere (not shown). The top blow lance 12 is a lance that can be raised and lowered in the vertical direction (vertical direction in FIG. 1). The top blowing lance 12 injects gas 2, which is oxygen gas supplied from a gas supply path (not shown) connected to the upper end side, from at least one nozzle hole formed at the lower end.

The dephosphorization treatment is a pretreatment for efficiently performing the subsequent decarburization treatment, and is performed by the following process divided into a plurality of steps.
In the dephosphorization treatment, first, the molten iron 3 is charged into the furnace body 11 (charge step). The molten iron 3 is hot metal ejected from a blast furnace, and may be subjected to a simple desiliconization treatment such as cast bed desiliconization or a desulfurization treatment in advance. The slag generated in the dephosphorization step may be left in the furnace body 11 as described later. Further, the furnace body 11 may be charged with a cold iron source such as scrap in advance.

After the charging step, the gas 2 is blown from the top blowing lance 12 to perform a blowing process, whereby a process of mainly removing silicon (Si) in the molten iron 3 is performed (desiliconization step). The desiliconization step is performed while the inert gas for stirring is blown from a plurality of bottom blowing tuyere provided at the bottom of the furnace body 11. The desiliconization step is performed until the amount of gas 2 set according to the Si concentration of the molten iron 3 before the dephosphorization treatment and the desiliconization reaction efficiency is sprayed. Further, in the desiliconization step, the molten slag 4 is formed on the bath surface of the molten iron 3 by the oxidation reaction of Si in the molten iron 3 and the slag pre-loaded in the furnace body 11. Further, in the desiliconization step, it is necessary to stably form the slag during the treatment in order to improve the fluidity of the slag in the intermediate slag removal step described later. For the control of slag forming, a method generally used in dephosphorization treatment with intermediate slag can be used. For example, in the control of slag forming, the height of the slag 4 in the furnace body 11 is measured with a slag level meter, and the SiO ₂ concentration with respect to the CaO concentration (mass%) in the slag is determined according to the measurement result. It is carried out by adjusting the ratio of (mass%), CaO / SiO ₂ ), the acid feeding rate from the top-blown lance 12, the lance height of the top-blown slag 12, and the like, or by adding a stagnation agent. The slag level meter may be any as long as it can measure the height of the slag 4 in the vertical direction (vertical direction in FIG. 1), and for example, a microwave type level meter may be used.

After the desiliconization step, a slag treatment for discharging a part of the slag 4 contained in the furnace body 11 is performed (intermediate slag removal step). In the intermediate slag removal step, the slag 4 is discharged from the furnace port 111 of the furnace body 11 while tilting the furnace body 11. For example, in the case of one example of FIG. 1, the slag 4 on the bath surface of the molten iron 3 is discharged from the furnace port 111 by tilting the furnace body 11 so as to rotate clockwise. The discharged slag 4 is housed in a slag pot, which is a pot-shaped container arranged below the furnace body 11. Then, in the intermediate slag removal step, after a predetermined amount of slag is discharged, the furnace body 11 is tilted, and the furnace port 111 shown in FIG. 1 is brought to a state (also referred to as a "true state") in the vertical direction. The slag processing is completed by returning.

After the intermediate slag removal step, a predetermined amount of CaO-based medium solvent such as quicklime or limestone is put into the furnace body 11, and gas 2 is blown from the top blowing lance 12 to perform a blowing process, whereby the main component in the molten iron 3 is A treatment for removing phosphorus (P) is performed (dephosphorization step). In the dephosphorization step, as in the desiliconization step, the treatment is performed while the inert gas for stirring is blown from the plurality of bottom blowing tuyere provided at the bottom of the furnace body 11. The dephosphorization step is carried out until the amount of gas 2 set according to the P concentration of the molten iron 3 before the dephosphorization treatment and the dephosphorization reaction efficiency is sprayed. Further, in the dephosphorization step, molten slag 4 is formed on the bath surface of the molten iron 3 by the slag remaining in the slag removal treatment and the added CaO-based medium solvent.

After the dephosphorization step, a hot water discharge process is performed in which the molten iron 3 is discharged from the furnace body 11 while leaving the slag 4 (hot water discharge step). In the hot water discharge step, the furnace body 11 is tilted to the opposite side of the tilting direction in the intermediate slag discharge step, and the molten iron 3 is discharged from the hot water discharge hole (not shown) formed on the side wall of the furnace body 11. The discharged molten iron 3 is housed in a hot metal pot, which is a pot-shaped container arranged below the furnace body 11. The hot water discharge process ends when the molten iron 3 of the furnace body 11 is discharged to the outside of the furnace body 11. When the hot water discharge process is completed, the slag 4 floating on the bath surface of the molten iron 3 remains in the furnace body 11. Then, the remaining slag 4 is continuously used in the desiliconization step in the next dephosphorization treatment.
The dephosphorization treatment is carried out by the above series of processes.

(Sedation of slag)
Further, in the present embodiment, the slag 4 forming sedation treatment is performed in a series of processes. In this sedation treatment, when the molten iron 3 and the slag 4 are housed in the furnace body 11 and the slag 4 in the furnace body 11 is formed while the smelting furnace 1 is in the standby state, the furnace body is formed from the top blowing lance 12. This is done by blowing gas 2 into the 11. In this sedation treatment, the bubbles 2 of the formed slag 4 are physically destroyed by the gas 2 injected from the top-blown lance 12. The sedation treatment is performed in a state where the furnace body 11 is identified as shown in FIG.

Here, the standby state is a state in which the smelting process of blowing the oxygen gas 2 from the top lance 12 onto the molten iron 3 is not performed in the smelting furnace 1. That is, in the present embodiment, in the desiliconization step and the dephosphorization step, the state in which the gas 2 is injected from the top blowing lance 12 for the desiliconization and dephosphorization is the state in which the blowing process is performed. The other state is the standby state. In the present embodiment, as an example, it is assumed that the sedation treatment is performed from the end of the desiliconization step to the start of the intermediate slag removal step. In the above-mentioned desiliconization treatment, a blowing treatment is performed so as to form the slag 4 in the desiliconization step. Therefore, the forming of the slag 4 may proceed even during the waiting time when the blowing process in the desiliconization step is completed, and the slag 4 may be ejected from the furnace body 11.

The formation of the slag 4 in the sedation process is detected by using a slag level meter. Then, when the height of the slag 4 measured by the slag level meter becomes equal to or higher than a predetermined threshold value, a sign of ejection of the slag 4 from the furnace body 11 is detected, and the slag 4 is sedated.
Further, in the sedation treatment, it is preferable that the time for blowing the gas 2 from the top blowing lance 12 is within 30 s. When the gas 2 contains oxygen as in the present embodiment, by blowing the gas 2 for a long time, CO gas or the like is generated by the oxidation of carbon in the molten iron 3, and the forming of the slag 4 may further proceed. There is sex.

Further, in the sedation treatment, it is preferable that the injection speed of the gas 2 from the top blowing lance 12 is 30,000 Nm ³ / hr or more and 50,000 Nm ³ / hr or less. When the injection speed of the gas 2 from the top blowing lance 12 is less than 30,000 Nm ³ / hr, the injection speed of the gas 2 is low, so that the bubbles of the slag 4 are less likely to be destroyed, and a sufficient calming effect of forming can be obtained. May not be. Further, when the injection speed of the gas 2 from the top blowing lance 12 exceeds 50,000 Nm ³ / hr, the reaction between the oxygen-containing gas 2 and the carbon in the molten iron 3 is promoted, and CO gas or the like is newly generated. Because of the possibility, the sedative effect of forming may not be sufficiently obtained.

Further, in the sedation treatment, the gas 2 contains oxygen with respect to the bath surface height at which the lance height of the top blowing lance 12 is the height from the bath surface of the molten iron 3 in the furnace body 11 to the furnace port 111. If the height is 95% or more and 160% or less from the bath surface of the molten iron 3 in the furnace body 11, and if the gas 2 does not contain oxygen, the bath surface of the molten iron 3 in the furnace body 11 It is preferable to arrange the top blowing lance 12 so as to have a height of 60% or more and 160% or less. Here, the case where the gas 2 contains oxygen means the case where the oxygen concentration of the gas 2 is 80 vol% or more. The lance height of the upper blowing lance 12 is the height from the bath surface of the molten iron 3 in the furnace body 11 to the nozzle hole formed at the lower end of the upper blowing lance 12 and injecting the gas 2. If the lance height is less than the lower limit with respect to the bath surface height, forming is rather promoted. At that time, when the gas 2 contains oxygen, the forming is further promoted by the generation of CO gas due to the reaction with the molten iron 3, so the lower limit of the lance height is the case of the gas 2 containing no oxygen. It is higher than that. On the other hand, when the lance height exceeds 160% of the bath surface height, the distance between the top-blown lance 12 and the slag 4 becomes long, so that the forming calming effect of the slag 4 may not be sufficiently obtained. There is.
The sedation treatment is performed for a preset time or until the height of the slag 4 measured by the slag level meter becomes equal to or less than a predetermined value, and is completed. It should be noted that this predetermined value is a value at which it can be determined that the forming of the slag 4 has been sufficiently sedated.

<Modification example>
Although the present invention has been described above with reference to specific embodiments, it is not intended to limit the invention by these descriptions. By reference to the description of the invention, one of ordinary skill in the art will appreciate other embodiments of the invention that include various modifications as well as the disclosed embodiments. Therefore, it should be understood that the embodiments of the invention described in the claims also include embodiments including these modifications described in the present specification alone or in combination.

For example, in the above embodiment, the sedation treatment is performed between the desiliconization step of the dephosphorization treatment including the intermediate slag removal step and the intermediate slag removal step, but the present invention is not limited to such an example. For example, in the same dephosphorization treatment as in the above embodiment, it may be performed between the dephosphorization step and the hot water discharge step. Further, not only the dephosphorization treatment as in the above embodiment, but also the refining furnace of the converter type, such as performing the dephosphorization treatment, the slag removal treatment, and the decarburization treatment in order for the refining furnace in the standby state in the operation. It may be applied in other refining processes using a furnace.

Further, in the above embodiment, oxygen is injected as gas 2 from the top-blown lance 12 in the sedation treatment, but the present invention is not limited to such an example. The gas 2 injected from the top-blown lance 12 may be a gas having a component other than oxygen. That is, in the sedation treatment, the gas 2 injected from the top-blown lance 12 may be a gas having a component other than oxygen or a gas containing oxygen and a component other than oxygen. In particular, if there is no problem in terms of equipment restrictions and a gas other than oxygen can be injected, an inert gas such as nitrogen gas may be injected as gas 2 in the sedation treatment. In this case, since the gas 2 does not react with the carbon in the molten iron 3, the injection speed from the top blowing lance 12 may be increased or the injection time may be extended as compared with the case where oxygen gas is used. ..

Further, in the above embodiment, oxygen is injected as gas 2 from the top blowing lance 12 in the blowing treatment of the desiliconization step and the dephosphorization step, but the present invention is not limited to such an example. The gas 2 injected from the top blowing lance 12 in the blowing process may contain oxygen and may contain components other than oxygen. Further, the powdery CaO-based medium solvent (limestone, quicklime, slag powder, etc.) may be sprayed from the top-blown lance 12 together with the gas 2.

Further, in the above embodiment, the forming of the slag 4 is sedated by blowing gas 2 from the top blowing lance 12 in the sedation treatment, but the present invention is not limited to such an example. For example, in the sedative treatment, in addition to blowing the gas 2 from the top blow lance 12, a sedative may be further added. As the sedative, a general sedative used for suppressing slag forming may be used, and for example, a carbonaceous material or the like can be used. By using gas 2 and a sedative in combination, the forming of slag 4 can be sedated in a shorter time.

<Effect of embodiment>
(1) The method for squeezing the slag 4 according to one aspect of the present invention is a method for squeezing the slag 4 in a converter-type smelting furnace 1 having a top-blown lance 12, and the molten iron 3 is placed in the furnace body 11 of the slag furnace 1. And when the slag 4 in the furnace body 11 is formed in a standby state in which the slag 4 is accommodated and the gas 2 containing oxygen is blown from the top blowing lance 12 onto the molten iron 3 in a standby state, the top blowing lance is formed. Gas 2 is blown into the furnace body 11 from 12.

According to the configuration of (1) above, the bubbles of the formed slag 4 are physically destroyed by the gas 2 injected from the top blowing lance 12, so that the slag is in a standby state where the blowing process is not performed. The forming can be calmed down. As a result, the amount of the sedative used can be reduced, and the cost required for the refining process can be reduced. That is, according to the configuration of (1) above, the slag forming can be calmed down at a lower cost in the standby state where the blowing process is not performed.

(2) In the configuration of (1) above, the time for blowing the gas 2 into the furnace body 11 is 30 s or less when the gas 2 is a gas containing oxygen.
According to the above configuration (2), the secondary combustion of CO gas is promoted by containing oxygen in the gas 2 used for sedation of forming. Then, the metal adhering to the inside of the furnace body 11 can be melted by the heat generated by the secondary combustion. Therefore, it is possible to reduce the risk of operation suspension due to the excessive amount of the metal adhering to the metal and to improve the production yield of the molten iron 3 by the molten metal. Moreover, since the FeO concentration in the slag 4 can be improved, the dephosphorization efficiency after the sedation treatment can be improved.

(3) In the configuration of (1) or (2) above, the injection speed of the gas 2 injected from the top blowing lance 12 is set to 30,000 Nm ³ / hr or more and 50,000 Nm ³ / hr or less.
(4) In any of the above configurations (1) to (3), the lance height of the top-blown lance 12 is set to the height from the bath surface of the molten iron 3 to the furnace port 111 of the furnace body 11 with respect to the gas. When oxygen is contained in 2, it is 95% or more and 160% or less, and when gas 2 does not contain oxygen, it is 60% or more and 160% or less.
According to the configurations (3) and (4) above, the sedative effect of forming the slag 4 can be stably and sufficiently obtained.

Next, Example 1 performed by the present inventors will be described. In Example 1, dephosphorization treatment was performed in the same manner as in the above embodiment. In the dephosphorization treatment, when the forming of the slag 4 was detected between the desiliconization step and the intermediate slag removal step, a sedation treatment was performed. In the sedation treatment, a sedative was added in addition to the injection of the gas 2 from the top-blown lance 12 depending on the situation so that the slag 4 would not be ejected from the furnace body 11. Further, in Example 1, as a comparison, when the sedative treatment was performed, the dephosphorization treatment corresponding to the injection of the sedative agent without injecting the gas 2 from the top-blown lance 12 was also performed (Comparative Example).

In the sedation treatment of Example 1, a smelting furnace 1 having a heat size of 350 tons was used. The heat size is the maximum capacity of the molten iron 2 that can be refined in the refining furnace 1. Further, in the sedation treatment of Example 1, the gas 2 injected from the top-blown lance 12 is a gas containing 99.9 vol% of oxygen, and the injection speed (acid feeding speed) of this gas 2 is 30,000 Nm ³ / hr or more and 50,000 Nm. ^{It was set to 3} / hr or less, and the lance height of the top blowing lance 12 was set to 95% or more and 160% or less with respect to the bath surface height. In the sedation treatment of the embodiment performed under the above conditions, the flow velocity of the gas 2 on the bath surface of the slag 4 is 226 m / s or more under the calculation condition that the bath surface of the slag 4 and the lower end of the top blowing lance 12 are 0 mm. It is 328 m / s, and the dynamic pressure of the gas 2 is 0.04 MPa or more and 0.07 MPa or less.

FIG. 2 shows the average value of the amount (kg / t) of the sedative used for each Si concentration (mass%) before the dephosphorization treatment of molten iron 3 as a result in Example 1. The amount of the sedative used is the amount of the sedative used in the dephosphorization treatment per ton (t) of molten iron. That is, in the result of FIG. 2, the sedative agent used when the sedative treatment such as the desiliconization step or the dephosphorization step is not performed is also included in the amount used. In FIG. 2, the result indicated by "average" on the far right side indicates the average value of all the results in Example 1 and Comparative Example.
As shown in FIG. 2, in Example 1 in which the sedative treatment was performed in the same manner as in the above embodiment, it was confirmed that the amount of the sedative used was significantly reduced and the cost required for the dephosphorization treatment could be reduced. .. Further, in the example, since the slag 4 could be prevented from being ejected from the furnace body 11 in the standby state, it was confirmed that the forming could be sedated by the sedation treatment using the gas 2.

Next, Example 2 performed by the present inventors will be described. In Example 2, a nitrogen gas containing no oxygen was used as the gas 2, and the refining treatment was performed so that the lance height of the top-blown lance 12 was 60% or more and 160% or less with respect to the bath surface height. The other refining treatment conditions in Example 2 were the same as those in Example 1.
As a result of the refining treatment, it was confirmed that the amount of the sedative used in Example 2 can be significantly reduced as in Example 1.

1 Refining furnace 11 Furnace 111 Furnace 12 Top-blown lance 2 Gas 3 Molten iron 4 Slag

Claims (3)

A method for sedating slag in a converter-type smelting furnace with a top-blown lance.
When molten iron and slag are contained in the furnace body of the smelting furnace, and the slag in the furnace body is formed in a standby state in which a gas containing oxygen is blown onto the molten iron from the top blowing lance. , only write blowing a gas into the furnace body from the upper blowing lance,
A method for sedating slag, which comprises setting the injection speed of the gas injected from the top-blowing lance to be 30,000 Nm ³ / hr or more and 50,000 Nm ³ / hr or less . The method for sedating slag according to claim 1, wherein the time for blowing the gas into the furnace body is 30 s or less when the gas contains oxygen. The lance height of the top-blown lance is set with respect to the height from the bath surface of the molten iron to the furnace mouth of the furnace body.
If the gas contains oxygen, it should be 95% or more and 160% or less.
The method for sedating slag according to claim 1 or 2 , wherein when the gas does not contain oxygen, the content is 60% or more and 160% or less.

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