JP2011162809A - Method for desulfurizing molten iron - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique enabling to apply a treatment for optimizing an injecting condition of a lime-based desulfurizing agent, based on the result in which the injecting yield during the desulfurizing treatment, is assumed in on-line. <P>SOLUTION: In a method for desulfurizing molten iron, in which the desulfurizing treatment of the molten iron is performed by stirring the molten iron and the lime based desulfurizing agent with an impeller 4 dipped into the molten iron while placing the lime based desulfurizing agent on the molten iron 3 held in a vessel 2 and further, by injecting the lime based desulfurizing agent 7 through a top-blowing lance 5 which is separated and arranged a tip on the molten iron bath surface from the upper part of the vessel; the exhaust gas temperature is measured on the way of a duct 15 for introducing the dust generated from the molten iron bath surface during desulfurizing treatment together with the exhaust gas into a dust-collecting facility 12, and the injecting yield of the injected lime based desulfurizing agent, is successively assumed based on the exhaust gas temperature and the molten iron temperature, and the condition of the desulfurizing treatment is adjusted so as to improve the injected yield. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a desulfurization treatment method capable of efficiently performing desulfurization of hot metal using a container equipped with a mechanical stirring device.

The hot metal discharged from the blast furnace usually contains a high concentration of sulfur (S), which adversely affects the quality of the steel, so in the process from hot metal to molten steel depending on the required quality of the steel. A desulfurization process is performed. Various technologies have been put to practical use for desulfurization treatment, and these desulfurization treatments are roughly classified into hot metal desulfurization and molten steel desulfurization.
In hot metal desulfurization, inexpensive desulfurization agents mainly composed of lime (CaO) (hereinafter referred to as lime-based desulfurization agents) are widely used. When a lime-based desulfurizing agent is added to the hot metal, a reaction represented by the reaction formula CaO + S → CaS + O occurs, and desulfurization of the hot metal proceeds. In order to promote the desulfurization reaction, a technique of performing mechanical stirring has been put into practical use.

  In conventional desulfurization by mechanical stirring, when adding a lime-based desulfurizing agent to the hot metal, the lime-based desulfurizing agent is dropped freely on the bath surface (hereinafter referred to as “placement”) and immersed in the hot metal. Stirring is performed using a stirring blade (hereinafter referred to as impeller). In this technique, the lime-based desulfurizing agent agglomerates in the process of being caught in the hot metal by stirring with an impeller, so that the contact area between the lime-based desulfurizing agent and the hot metal (hereinafter referred to as reaction interface area) is reduced. is there. If the reaction interfacial area decreases, the progress of the desulfurization reaction is hindered.

Therefore, in order to increase the reaction interface area and increase the efficiency of the desulfurization treatment, a technique for suppressing the aggregation of the lime-based desulfurization agent has been studied.
For example, Patent Document 1 discloses a technique in which a lime-based desulfurizing agent is sprayed onto a hot metal bath surface through a top blowing lance together with a carrier gas. In this technique, a lime-based desulfurizing agent is sprayed at a high speed from an upper blowing lance to enter the hot metal. By performing high-speed spraying (hereinafter referred to as projection), the particles of the lime-based desulfurizing agent are dispersed and enter the hot metal, so that the aggregation of the lime-based desulfurizing agent is suppressed and the reaction interface area is expanded. However, there is a problem that the region where the lime-based desulfurizing agent is dispersed excessively expands or shrinks depending on the projection conditions such as the projection amount and position of the lime-based desulfurizing agent and the flow velocity of the carrier gas.

  When the area where the projected lime-based desulfurizing agent is dispersed excessively increases, the amount of lime-based desulfurizing agent scattered around the area increases, resulting in a decrease in the yield of the projected lime-based desulfurizing agent (hereinafter referred to as “projected yield”), and desulfurization. The processing efficiency is reduced. Moreover, when the area | region which the projected lime type | system | group desulfurization agent disperse | distributes excessively shrinks, a lime type | system | group desulfurization agent will aggregate in a hot metal, and will cause the fall of a projection yield and by extension the efficiency reduction of a desulfurization process.

  Patent Document 2 discloses an appropriate projection condition for improving the projection yield in the desulfurization treatment of hot metal in which a lime-based desulfurization agent is projected while performing mechanical stirring. Since this technique optimizes the static projection conditions, it is necessary to determine the optimal conditions prior to the desulfurization process based on parameters that can be known in advance. However, it is impossible to cope with the transition of the projection yield caused by dynamically varying parameters that cannot be assumed in advance, such as the amount of slag brought in from the previous process, and the change in stirring power due to impeller melt damage. As a result, there is a problem that variations in projection yield cannot be suppressed.

  In addition, in order to evaluate the projection yield with the conventional technique, it is necessary to analyze the molten iron and slag S concentration before and after the desulfurization treatment and investigate the mass balance, and thus it takes a long time to calculate the projection yield. For this reason, it is impossible to grasp the projection yield in real time during the desulfurization process and take measures for improving the yield.

JP 2005-179690 A JP 2007-247045

  It is an object of the present invention to provide a technique that makes it possible to estimate a projection yield online during a desulfurization process and to perform a treatment for optimizing the projection condition of the lime-based desulfurization agent based on the result. To do.

  The inventors focused on the fact that when the lime-based desulfurizing agent is projected onto the hot metal, the temperature of the exhaust gas generated by the desulfurization process changes. The relationship between the exhaust gas temperature and the lime-based desulfurization agent projection yield was investigated in detail. On the other hand, it is conventionally known that there is a correlation between the temperature of the hot metal and the temperature of the exhaust gas. Thus, it has been found that the projection yield can be estimated by using the temperature of the hot metal individually measured before the desulfurization treatment and the temperature of the exhaust gas continuously measured during the desulfurization treatment.

The present invention has been made based on such knowledge.
That is, the present invention places a lime-based desulfurizing agent on hot metal held in a container, and stirs the hot metal and the lime-based desulfurizing agent with an impeller immersed in the hot metal, while the tip from above the container is on the hot metal bath surface. In a hot metal desulfurization treatment method in which hot metal desulfurization treatment is performed by projecting a lime-based desulfurization agent through an upper blowing lance that is spaced apart, the dust generated from the bath surface of the hot metal during the desulfurization treatment is collected together with exhaust gas. The temperature of the exhaust gas is measured in the middle of the duct leading to, and the projected yield of the projected lime-based desulfurization agent is continuously estimated based on the temperature of the exhaust gas and the temperature of the hot metal, and the desulfurization treatment is performed to improve the projected yield. This is a hot metal desulfurization method for adjusting the conditions.

In the desulfurization treatment method of the present invention, the projection yield (%) is the following (using exhaust gas temperature T _G (° C.), hot metal temperature T _M (° C.), and preset constants A, B and C ( It is preferable to estimate by equation (1).
Projection yield (%) = A × T _G + B × T _M + C (1)
Here, the constants A, B, and C are constants obtained by performing multiple regressions for each desulfurization apparatus on the relationship between the projection yield, the exhaust gas temperature, and the hot metal temperature obtained in advance in each desulfurization treatment facility.

  In order to improve the projection yield of the lime-based desulfurizing agent, the parameters that can be adjusted during the desulfurization treatment of the hot metal held in the container are the flow rate of the carrier gas, the projection speed of the lime-based desulfurizing agent, the rotational speed of the impeller, The position of the upper blowing lance in the radial direction of the container, the height of the upper blowing lance, etc. By calculating the projection yield based on the above equation (1), monitoring the transition of the calculated value and adjusting one or more of these parameters as necessary, the projection yield can be improved. Plan.

  According to the present invention, it is possible to estimate the projection yield online during the desulfurization process, and to take measures for optimizing the projection conditions of the lime-based desulfurization agent based on the result. That is, since the projection yield can be estimated during the desulfurization process, a measure for improving the projection yield can be performed during the desulfurization process. Moreover, since the progress of desulfurization of hot metal can be estimated from the projection yield, the projection amount of the lime-based desulfurizing agent can be increased or decreased according to the target value of the S content after the desulfurization treatment. Therefore, excessive use of the lime-based desulfurizing agent can be suppressed.

1 is a layout diagram schematically showing an example of an apparatus to which a desulfurization treatment method of the present invention is applied. It is a graph which shows the relationship between the performance value of a projection yield, and a calculated value. It is a graph which shows the relationship between a projection ratio and the actual value of a projection yield. It is a graph which shows transition of the calculated value of the temperature of an exhaust gas, and a projection yield. It is a graph which shows the other example of transition of the calculated value of the temperature of an exhaust gas, and a projection yield.

FIG. 1 is an arrangement diagram schematically showing an example of an apparatus to which the desulfurization treatment method of the present invention is applied, and shows an example in which a ladle type hot metal ladle is used as a container 2 for containing hot metal 3. About the shape of the container 2, since a desulfurization process is performed with the container provided with the mechanical stirring apparatus, the ladle-type container 2 as shown in FIG. 1 is suitable. However, the present invention can also be applied to a torpedo car.
The hot metal 3 discharged from the blast furnace is received by a hot metal ladle or torpedo car mounted on the carriage 1 and further conveyed to a mechanical stirring device. When it is received by a torpedo car, it is preferably transferred to a ladle type container prior to the desulfurization treatment. Moreover, the component of the hot metal 3 used as the object of the desulfurization process which concerns on this invention is not specifically limited. For example, the desulfurization treatment method of the present invention can also be applied to hot metal previously subjected to desiliconization treatment or dephosphorization treatment.

Below, the example which uses a hot metal ladle as the container 2 is demonstrated.
The mechanical stirrer includes a refractory impeller 4 for immersing in the hot metal 3 accommodated in the hot metal ladle 2 and stirring the hot metal 3. The impeller 4 is moved up and down in the vertical direction by a lifting device (not shown) and rotated around a shaft 4a by a rotating device (not shown). Further, an upper blowing lance 5 for projecting the lime-based desulfurizing agent 7 onto the hot metal 3 accommodated in the hot metal pan 2 is installed. Further, a charging port 6 for placing the lime-based desulfurizing agent 7 on the bath surface of the hot metal 3 accommodated in the hot metal ladle 2 is also provided. That is, it is possible to project and place the lime-based desulfurizing agent 7 together.

A duct 15 that guides the exhaust gas to the dust collection facility 12 is installed above the hot metal ladle 2 to supply dust generated during the desulfurization process to the dust collection facility 12 together with the exhaust gas.
The top blowing lance 5 is connected to a supply device comprising a hopper 8 for storing the powdery lime-based desulfurizing agent 7 and a cutting device 9 for cutting out a predetermined amount of the lime-based desulfurizing agent 7 from the hopper 8. In addition, a powdery lime-based desulfurizing agent 7 can be appropriately projected from the top blowing lance 5 together with the conveying gas as needed. It is also possible to supply only the transport gas from the top blowing lance 5.

The inlet 6 is connected to a supply device comprising a hopper 10 for storing a powdery lime-based desulfurizing agent 7 and a rotary feeder 11 for cutting out a predetermined amount of the lime-based desulfurizing agent 7 from the hopper 10. The powdery, granular or massive lime-based desulfurization agent 7 can be appropriately placed from the inlet 6 as needed.
The temperature T _M (° C.) of the hot metal 3 is measured at an arbitrary position before the carriage 1 arrives at the mechanical stirring device. After measuring the temperature of the hot metal 3, the position of the carriage 1 is adjusted so that the position of the impeller 4 substantially coincides with the center of the hot metal pan 2. Next, the impeller 4 is lowered and immersed in the hot metal 3, and then the impeller 4 starts to rotate. When the rotation of the impeller 4 reaches a predetermined number of revolutions, the cutting device 9 is activated to project the lime-based desulfurizing agent 7 accommodated in the hopper 8 from the top blowing lance 5 onto the hot metal 3 together with the carrier gas.

Note that a predetermined amount of the lime-based desulfurizing agent 7 may be put on the bath surface of the molten iron 3 from the hopper 10 before or after the impeller 4 is immersed.
While the lime-based desulfurizing agent 7 is projected, the temperature T _G (° C.) of the exhaust gas is continuously measured by the thermocouple 13 and transmitted from the data logger 14 to a computer (not shown). The computer calculates the projection yield of the lime-based desulfurizing agent 7 from the following equation (1) based on the temperature T _G (° C.) of the exhaust gas and the temperature T _M (° C.) of the hot metal 3 and displays the calculated value on the screen. indicate.
Projection yield (%) = A × T _G + B × T _M + C (1)
Here, the constants A, B, and C are constants obtained by performing multiple regression for each desulfurization apparatus on the relationship between the projection yield, the exhaust gas temperature, and the hot metal temperature obtained in advance in each desulfurization treatment facility.

  The worker of the desulfurization process monitors the transition of the calculated value of the projected yield displayed on the screen, and takes measures to improve the projected yield when the calculated value falls below a preset threshold value. The parameters to be adjusted for the treatment are (a) carrier gas flow velocity, (b) lime-based desulfurization agent projection speed, (c) impeller rotation speed, (d) top blowing lance position in the container radial direction, ( e) The height of the top lance.

Thus, by adjusting the treatment conditions during the desulfurization treatment, the projection yield can be improved.
Further, when projecting the lime-based desulfurizing agent 7, an amount that can be determined that the lime-based desulfurizing agent 7 necessary for desulfurization is present in the molten iron 3 from the calculated value of the projection yield is projected. Therefore, optimization of the projection amount of the lime-based desulfurizing agent 7 can be achieved.

  After the projection of the lime-based desulfurizing agent 7 is completed and stirring is performed for a predetermined time, the rotational speed of the impeller 4 is gradually reduced. When the rotation of the impeller 4 is stopped, the impeller 4 is raised and waited above the hot metal ladle 2. And the slag produced | generated by the desulfurization process floats up, the bath surface of the hot metal 3 is covered, and a desulfurization process is complete | finished in the still state. After the desulfurization treatment is completed, the slag is discharged from the hot metal ladle 2 and conveyed to the refining process.

  As described above, according to the present invention, by calculating the projected yield of the lime-based desulfurizing agent 7, it is possible to take a measure for improving the projected yield during the desulfurization process. Moreover, since the required amount of the lime-based desulfurizing agent 7 can be estimated from the projection yield, the projection amount can be optimized.

Preliminary experiments were performed using the apparatus shown in FIG. 1, and the constants A, B, and C of equation (1) were determined by multiple regression of the relationship between the projection yield of lime-based desulfurization agent, the temperature of exhaust gas, and the temperature of hot metal. . As a result, A = −0.271, B = 0.221, and C = −153.973 were obtained.
Subsequently, the hot metal desulfurization process was performed using the apparatus shown in FIG. The hot metal before and after the desulfurization treatment and the S concentration of slag were analyzed, and the actual value of the projection yield was obtained from the mass balance. On the other hand, during the desulfurization treatment, the temperature of the exhaust gas and the temperature of the hot metal were measured, and the projection yield was calculated from equation (1). The relationship between the actual value of the projection yield and the calculated value is shown in FIG. As shown in FIG. 2, the actual value of the projection yield and the calculated value are in a relationship that can be approximated by a linear function. That is, the projection yield can be accurately estimated from the exhaust gas temperature and the hot metal temperature.

  FIG. 3 is a graph showing the relationship between the projection ratio and the actual value of the projection yield. The projection ratio indicates the ratio of the projected lime-based desulfurizing agent to the total amount of addition of the lime-based desulfurizing agent (that is, the total of the projected lime-based desulfurizing agent and the lime-based desulfurizing agent placed on top). As is apparent from FIG. 3, the projection yield tends to decrease as the projection ratio increases. However, it is possible to improve the projection yield by reducing the flow rate of the carrier gas.

  FIG. 4 is a graph showing the transition of the exhaust gas temperature and the calculated value of the projection yield according to equation (1) during the desulfurization process from the start of rotation of the impeller to the end of rotation. As apparent from FIG. 4, when the projection of the lime-based desulfurizing agent is started, the temperature of the exhaust gas rises. Further, the higher the exhaust gas temperature, the lower the calculated value of the projection yield. The average projection yield calculated during this period was 63.2%. On the other hand, the actual value of the projection yield obtained from the mass balance of S was 61.8%. In other words, the projection yield could be estimated with high accuracy using equation (1).

FIG. 5 is a graph showing another example of the transition of the exhaust gas temperature and the calculated value of the projection yield according to the equation (1) during the desulfurization process from the start of rotation of the impeller to the end of rotation. In this example, after the start of lime-based desulfurization agent projection, the flow rate of the carrier gas when the temperature of the exhaust gas rises and the projection yield decreases and falls below the threshold (ie 60%). It was changed ^{(17Nm 3 / min → 10Nm 3} / min). As a result, the calculation value of the projection yield after decreasing the flow velocity of the carrier gas increased to about 75%. The average value of the projection yield calculated during the period from the start of rotation of the impeller to the end of rotation was 71.2%. On the other hand, the actual value of the projection yield obtained from the mass balance of S was 72.1%. In other words, even when the desulfurization conditions were changed during the desulfurization treatment, the projection yield could be accurately estimated using the equation (1).

  Projection yield can be estimated online during the desulfurization treatment, and a process for optimizing the projection conditions of the lime-based desulfurization agent can be performed based on the result, which has a remarkable industrial effect.

1 cart 2 hot metal pan 3 hot metal 4 impeller
4a Shaft 5 Top blowing lance 6 Input port 7 Lime-based desulfurization agent 8 Hopper 9 Cutting device
10 Hopper
11 Rotary feeder
12 Dust collection equipment
13 Thermocouple
14 Deterlogger
15 Duct

Claims (2)

  A lime-based desulfurizing agent is placed on the hot metal held in the container, and the hot metal and the lime-based desulfurizing agent are stirred by an impeller immersed in the hot metal, while the tip from above the container is placed on the hot metal bath surface. In the hot metal desulfurization treatment method of performing desulfurization treatment of the hot metal by projecting a lime-based desulfurization agent through an upper blowing lance that is spaced apart, dust generated from the bath surface of the hot metal during the desulfurization treatment is collected together with exhaust gas. The temperature of the exhaust gas is measured in the middle of a duct leading to a dust facility, and the projection yield of the projected lime-based desulfurizing agent is continuously estimated based on the temperature of the exhaust gas and the temperature of the hot metal, and the projection yield is calculated. A desulfurization treatment method for hot metal, wherein the desulfurization treatment conditions are adjusted so as to improve. The projection yield (%) is estimated by the following equation (1) using the exhaust gas temperature T _G (° C.), the hot metal temperature T _M (° C.), and preset constants A, B, and C. The hot metal desulfurization treatment method according to claim 1.
Projection yield (%) = A × T _G + B × T _M + C (1)
Here, the constants A, B, and C are constants obtained by performing multiple regressions for each desulfurization apparatus on the relationship between the projection yield, the exhaust gas temperature, and the hot metal temperature obtained in advance in each desulfurization treatment facility.

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