JP7067413B2 - How to inspect refractories in atmospheric furnaces and how to manufacture reduced iron - Google Patents

Description

The present invention relates to a method for inspecting refractories of an atmospheric furnace and a method for producing reduced iron.

In the iron manufacturing process, iron oxide dust (hereinafter referred to as "dust") containing iron oxide as a main component is generated as a by-product. The dust is recovered by a recovery device and used as a material for reduced iron.

For the reduction of iron oxide, an atmosphere furnace including a heating chamber, a refractory material arranged around the heating chamber, and an iron skin arranged outside the refractory material is used. Refractory materials are damaged by the operation of the furnace, so it is necessary to inspect the refractory materials on a regular basis. On the other hand, since the refractory cannot be observed from outside the furnace, it is necessary to suspend the operation of the furnace in order to measure the thickness of the refractory.

As a method of inspecting refractories in ladle and hot metal pot, a method of estimating the degree of damage of refractories from the temperature of the iron skin has been proposed.

Japanese Patent Application Laid-Open No. 2009-19249 states that the temperature of the iron skin of a ladle containing molten steel is measured with an infrared radiation thermometer, and the measured temperature or the measured temperature rise rate is equal to or higher than the preset thresholds. Discloses a method for preventing steel leakage in a ladle, which issues an alarm and adds a refractory elution inhibitor to the slag existing on the molten steel in the ladle.

In JP2013-244515, the surface temperature of the iron skin of the ladle is measured with an infrared radiation thermometer, and the maximum temperature among the measured surface temperatures is from the time when the molten steel was supplied to the continuous casting machine last time. A method for preventing steel leakage in a ladle, which inspects and repairs the fireproof material of the lining of the ladle when the temperature threshold required from the relationship between the time until the molten steel is received and the iron skin temperature is exceeded. Is disclosed.

In Japanese Unexamined Patent Publication No. 2008-127619, the residual thickness to be repaired for the fireproof material is set in advance, and after the continuous use time of the hot metal pot reaches 10 hours or more, the iron skin temperature of the hot metal pot is measured and iron is used. Disclosed is a method for determining whether or not a hot metal pot needs to be repaired, in which a fireproof material is inspected when the skin temperature is 300 ° C. or lower and has a predetermined relationship with the residual thickness to be repaired.

Japanese Patent Application Laid-Open No. 2000-171173 describes the internal space of a duct that guides gas generated in a metal smelting furnace to a dust recovery device, a thermometer for measuring the temperature of the inner wall surface of the duct, and the temperature of the outside air, and various types of heat. A deposit dust thickness detecting device including a calculator for calculating the thickness of dust adhering to the inner wall of a duct based on a transfer coefficient, a heat conduction coefficient, and a temperature measurement value is disclosed.

Japanese Unexamined Patent Publication No. 2009-19249 Japanese Unexamined Patent Publication No. 2013-24515 Japanese Unexamined Patent Publication No. 2008-127619 Japanese Unexamined Patent Publication No. 2000-171173

As described in JP-A-2009-192949, JP-A-2013-244515, and JP-A-2008-127619, it is conceivable to estimate the degree of damage to the refractory from the temperature of the iron skin. However, according to the investigation by the present inventors, no significant correlation was found between the residual thickness of the refractory and the temperature of the iron skin in the atmosphere furnace. Further, even when the adhered dust thickness detecting device in the duct described in Japanese Patent Application Laid-Open No. 2000-171173 was used, no significant correlation was found between the residual thickness of the refractory and the temperature of the iron skin.

An object of the present invention is to provide a method for appropriately inspecting the state of refractories in an atmosphere furnace. Another object of the present invention is to improve the operating efficiency of the atmospheric furnace and the production efficiency of reduced iron by appropriately checking the state of the refractory of the atmospheric furnace.

A method for inspecting a refractory material of an atmosphere furnace according to an embodiment of the present invention is an atmosphere furnace including a heating chamber, a refractory material arranged around the heating chamber, and an iron skin arranged outside the refractory material. In the method of inspecting the refractory, the step of measuring the temperature of the iron skin while the atmosphere furnace is in operation, the residual thickness of the refractory at the place where the temperature was measured, and the refractory formed in the refractory. A step of measuring the thickness of the infiltrated layer, a step of determining the damage rate of the refractory based on the residual thickness of the refractory and the thickness of the infiltrated layer, and the damage rate and the temperature of the iron skin. It is provided with a step of obtaining a correspondence relationship, a step of determining a reference temperature corresponding to a predetermined reference damage rate from the correspondence relationship, and a step of checking whether the temperature of the iron skin is lower than the reference temperature.

A method for producing reduced iron according to an embodiment of the present invention uses an atmosphere furnace including a heating chamber, a refractory material arranged around the heating chamber, and an iron skin arranged outside the refractory material. A method for producing reduced iron, in which the step of measuring the temperature of the iron skin during operation of the atmosphere furnace, the residual thickness of the refractory, and the thickness of the infiltrated layer formed on the refractory are measured. A step of determining the damage rate of the refractory based on the residual thickness of the refractory and the thickness of the infiltrating layer, and a step of determining the correspondence between the damage rate and the temperature of the iron skin. From the correspondence, the step of determining the reference temperature corresponding to the predetermined reference damage rate, the step of checking whether the temperature of the iron skin is lower than the reference temperature, and the step of reducing iron oxide in the heating chamber. It has a process.

According to the present invention, the state of the refractory of the atmosphere furnace can be appropriately inspected. In addition, this makes it possible to produce reduced iron with high efficiency.

FIG. 1 is a flow chart showing a method for inspecting a refractory material of an atmosphere furnace according to an embodiment of the present invention. FIG. 2 is a schematic diagram of a rotary hearth furnace, which is an example of an atmosphere furnace. FIG. 3 is a cross-sectional view taken along the line III-III of FIG. FIG. 4 is a diagram for explaining the iron skin temperature measuring step and the refractory thickness measuring step. FIG. 5 shows the damage rate of the refractory when the damage rate is (initial thickness of the refractory-residual thickness of the refractory) / (initial thickness of the refractory) without considering the infiltrating layer. It is a scatter diagram which shows the relationship between a refractory temperature and a refractory temperature. FIG. 6 is a plot of the scatter plot of FIG. 5 with different marks for the refractory material in which the infiltrating layer is formed and the refractory material in which the infiltrating layer is not formed. FIG. 7 is a scatter diagram showing the relationship between the damage rate of the refractory and the iron skin temperature when the damage rate is determined in consideration of the thickness of the infiltrated layer.

The present inventors investigated the state of the refractory of the atmosphere furnace in detail and obtained the following findings. The refractory material of the atmosphere furnace has a region where dust adheres to the surface and a region where dust does not adhere. In the region to which dust is attached, a layer deteriorated by infiltration of dust (hereinafter referred to as "infiltration layer") may be formed. The infiltrated layer has lower heat insulating performance (higher thermal conductivity) than the refractory material in which the infiltrated layer is not formed. Therefore, in order to evaluate the degree of damage to the refractory, it is necessary to consider not only the residual thickness of the refractory but also the thickness of the infiltrating layer.

The present invention has been completed based on the above findings. Hereinafter, a method for inspecting a refractory material of an atmosphere furnace according to an embodiment of the present invention will be described.

FIG. 1 is a flow chart showing a method for inspecting a refractory material of an atmosphere furnace according to an embodiment of the present invention. This method includes a step of predetermining a reference temperature as a reference for inspection (step S1) and a step of checking whether the temperature of the iron skin is lower than the reference temperature (step S2).

The atmosphere furnace to be inspected in the present embodiment includes a heating chamber, a refractory material arranged around the heating chamber, and an iron skin arranged outside the refractory material. The atmosphere furnace means a furnace other than a furnace in which a refractory material comes into direct contact with hot metal, molten steel, etc. (specifically, a blast furnace, a converter, a hot metal furnace, a molten steel furnace). The word "atmosphere" of an atmosphere furnace does not necessarily mean a replacement atmosphere, and a furnace used in an atmosphere atmosphere is also included in the "atmosphere furnace" of the present embodiment.

The atmosphere furnace is, for example, a heating furnace, an annealing furnace, or the like. Further, the intake pipe connected to the converter is also the "intake pipe" of the present embodiment in the sense that there is a high temperature space (heating chamber) surrounded by the refractory and the refractory does not come into direct contact with the hot metal or molten steel. Included in "Atmosphere Furnace".

FIG. 2 is a schematic view of a rotary hearth furnace 1 which is an example of an atmosphere furnace. The rotary hearth furnace 1 includes an annular hearth 11 that rotates in a horizontal plane, and a furnace body 12 that covers the hearth 11.

FIG. 3 is a cross-sectional view taken along the line III-III of FIG. The furnace body 12 includes a refractory material 122 arranged around the heating chamber 121, and an iron skin 123 arranged outside the refractory material 122. The refractory material 122 is, for example, a refractory brick, a pouring material, a spraying material, a ceramic fiber, or the like.

The furnace body 12 is defined in a plurality of regions in the circumferential direction, and the heating chamber 121 is maintained at a different temperature for each region. Iron oxide M (FIG. 2) is charged onto the hearth 11. The iron oxide M passes through a plurality of regions of the furnace body 12 as the hearth 11 rotates, and is heated and reduced in the heating chamber 121 of each region. As a result, iron oxide M is gradually reduced to produce reduced iron.

[Reference temperature determination step (step S1)]
With reference to FIG. 1 again, the description of the method for inspecting the refractory of the atmosphere furnace according to the present embodiment will be continued. More specifically, the step (step S1) in which the reference temperature to be the reference for inspection is determined in advance is the iron skin temperature measuring step (step S1-1) and the fireproof material thickness measuring step (step S1-2). , The damage rate calculation step (step S1-3), the correspondence relationship acquisition step (step S1-4), and the reference temperature determination step (step S1-5) are included. Hereinafter, each step will be described in detail.

FIG. 4 is a diagram for explaining the iron skin temperature measuring step (step S1-1) and the refractory thickness measuring step (step S1-2). As shown in FIG. 4, the refractory material 122 is damaged by the operation of the atmosphere furnace, but the rate of damage varies from place to place. Further, dust D may be attached to the surface of the refractory material 122, and the infiltration of the dust D causes the infiltration layer 122b to be formed on the refractory material 122. FIG. 4 shows a case where the dust D adheres to the entire surface of the refractory material 122, but depending on the location, the dust D may not adhere to the refractory material 122, and the infiltration layer 122b is formed. It may not be.

[Iron skin temperature measurement step (step S1-1)]
First, the temperature of the iron skin during operation of the atmosphere furnace is measured. Specifically, the temperatures T (x ₁ ), T (x ₂ ), ..., T (x _n ) of the iron skin 123 were measured at the locations x ₁ , x ₂ , ..., X _n , and the measured locations and temperatures. And record. The temperature of the iron skin 123 can be measured by, for example, an infrared radiation thermometer. The temperature of the iron skin 123 may be measured by a thermocouple, a resistance thermometer, or the like.

[Refractory thickness measurement step (step S1-2)]
Next, the residual thickness of the refractory and the thickness of the infiltrated layer at the place where the temperature was measured are measured. The thickness measurement can be performed, for example, when the operation of the atmosphere furnace is interrupted (for example, at the time of periodic inspection). It is preferable that the interval between the iron skin temperature measuring step (step S1-1) and the thickness measuring step (step S1-2) is as short as possible.

Specifically, the residual thicknesses B (x ₁ ), B (x ₂ ), ..., B (x _n ), and infiltration of the refractory 122 at the locations where the temperature was measured x ₁ , x ₂ , ..., X _n . The thicknesses B ₂ (x ₁ ), B ₂ (x ₂ ), ..., B ₂ (x _n ) of the layer 122b are measured and recorded. The thickness can be measured, for example, by removing the refractory material 122 from the furnace body and applying a measure or the like from the side surface. The region 122a in which the infiltrating layer is not formed and the infiltrating layer 122b can be distinguished from each other by appearance.

At this time, it is preferable to collect as much data as possible (that is, it is preferable to increase n). Further, the temperature measurement step (step S1-1) and the refractory thickness measurement step (step S1-2) may be repeated until a sufficient number of data are collected.

[Damage rate calculation step (step S1-3)]
The damage rate of the refractory is determined based on the residual thickness of the refractory and the thickness of the infiltrated layer. Since the thermal properties of the infiltrated layer 122b and the region 122a other than the infiltrated layer are different, in order to evaluate the degree of damage of the refractory material 122, not only the residual thickness of the refractory material 122 but also the thickness of the infiltrated material 122b is used. This is because it needs to be taken into consideration.

Specifically, of the residual thickness B (x ₁ ), B (x ₂ ), ..., B (x _n ), and the infiltration layer 122b of the refractory 122 for each location x ₁ , x ₂ , ..., X _n . Refractory damage rates E (x ₁ ), E (x ₂ ), ..., E (x _n ) based on thickness B ₂ (x ₁ ), B ₂ (x ₂ ), ..., B ₂ (x _n ). ).

The damage rate E (x _k ) (k = 1, 2, ..., N) can be obtained, for example, from the following equation. The damage rate E (x _k ) may be obtained from an equation other than this equation.
E (x _k ) = (A- (B (x _k ) -κB ₂ (x _k ))) / A
However, κ = 1-λ ₁ / λ ₂
Here, A is the initial thickness of the refractory 122, B (x _k ) is the residual thickness of the refractory 122, B ₂ (x _k ) is the thickness of the infiltration layer 122b, and λ ₁ is the heat of the refractory 122. Conductivity, λ ₂ is the thermal conductivity of the infiltrated layer 122b.

[Correspondence relationship acquisition process (step S1-4)]
Find the correspondence between the damage rate and the temperature of the iron skin. Specifically, the damage rate E (x _k ) (k = 1, 2, ..., N) obtained in step S1-3 and the iron skin temperature T (x _k ) (k =) measured in step S1-1. Regression analysis is performed from the pair with 1, 2, ..., N) to obtain the correspondence T (E).

The correspondence T (E) is not limited to this, but can be, for example, a linear function of the damage rate E. In this case, in the correspondence relationship acquisition step (step S1-4), the constants d and e in the following equation are obtained.
T (E) = E × d + e

[Reference temperature determination step (step S1-5)]
Finally, the reference temperature corresponding to the predetermined reference damage rate is determined from the correspondence relationship obtained in step S1-4. Specifically, since the correspondence relationship T (E) between the damage rate of the refractory and the iron skin temperature was obtained in step _S1-4 , the iron when the reference damage rate Ec is obtained from this correspondence relationship T (E). The skin temperature T (E _c ) is calculated and used as the reference temperature T _c . The standard damage rate E _c is a standard damage rate that requires repair of refractories. The reference damage rate _Ec depends on the temperature of the heating chamber of the atmosphere furnace and the type of refractory, but can be, for example, 70%.

When the correspondence T (E) is a linear function of the damage rate E described above, the reference temperature T _c can be obtained from the following equation.
T _c = E _c × d + e

[Inspection process (step S2)]
Periodically measure the temperature of the iron skin and check if the temperature of the iron skin is less than the reference temperature T _c .

The specific operation is not limited to this, but when the temperature of the iron skin exceeds the reference temperature T _c , the refractory material may be repaired when the operation of the atmosphere furnace is interrupted next time. Alternatively, when the temperature of the iron skin reaches the reference temperature T _c or higher, emergency measures such as filling a refractory material from outside the furnace or cooling the iron skin with water may be taken.

[Effect of this embodiment]
The method of inspecting the refractory of the atmosphere furnace according to the embodiment of the present invention has been described above. In the present embodiment, the damage rate E of the refractory is obtained in consideration of the infiltrated layer formed on the refractory, and the reference damage rate E is obtained from the correspondence relationship T (E) between the damage rate E and the temperature T of the iron skin. The reference temperature T _c corresponding to _c is obtained. According to the present embodiment, by considering the infiltrated layer, the correspondence relationship T (E) between the damage rate E and the temperature T of the iron skin can be obtained more accurately, and an appropriate reference temperature T _c can be determined. be able to. Further, once the reference temperature T _c is determined, the inspection can be performed only by measuring the iron skin temperature and comparing it with the reference temperature from the next time onward. As a result, the state of the refractory material of the atmosphere furnace can be inspected appropriately and with high efficiency. In addition, this makes it possible to produce reduced iron with high efficiency.

Hereinafter, the present invention will be described in more detail by way of examples. The present invention is not limited to this embodiment.

For the skirt part (the part around the hearth of the outer wall of the furnace body) of the rotary hearth furnace (heating chamber temperature of about 1400 ° C), the temperature of the iron skin, the residual thickness of the fireproof material, and the thickness of the infiltration layer are determined. Measured before and after regular repair of the furnace. 10 points were measured for each repair, and data for a total of 110 points was acquired for 11 repairs.

FIG. 5 shows the damage rate of the refractory when the damage rate is (initial thickness of the refractory-residual thickness of the refractory) / (initial thickness of the refractory) without considering the infiltrating layer. It is a scatter diagram which shows the relationship between a refractory temperature and a refractory temperature. As shown in FIG. 5, when the infiltrated layer was not taken into consideration, no significant correlation was found between the damage rate of the refractory and the iron skin temperature, and it was difficult to determine the reference temperature.

FIG. 6 is a plot of the scatter plot of FIG. 5 with different marks for the refractory material in which the infiltrating layer is formed and the refractory material in which the infiltrating layer is not formed. FIG. 7 is a scatter diagram showing the relationship between the damage rate of the refractory and the iron skin temperature when the damage rate is obtained in consideration of the thickness of the infiltrated layer. Specifically, as described in the embodiment, E (x _k ) = (A- (B (x _k ) -κB ₂ (x _k ))) / A. The thermal conductivity of the infiltrated layer was calculated as 2.5 times the thermal conductivity of the refractory (κ = 0.6). As shown in FIG. 7, by considering the thickness of the infiltrated layer, a correlation can be found between the damage rate of the refractory and the iron skin temperature, and the damage rate can be controlled by the iron skin temperature. It became possible.

Specifically, the correspondence between the damage rate E and the temperature T of the iron skin was determined from FIG. 7 as T = E × 3.32 + 54.33. When the reference damage rate E _c is, for example, 70%, the reference temperature T _c is 286.73 ° C.

The embodiment of the present invention has been described above. The embodiments described above are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and the above-described embodiment can be appropriately modified and implemented within a range that does not deviate from the gist thereof.

1 rotary hearth furnace 11 hearth 12 hearth 121 heating chamber 122 refractory 123 iron skin

Claims (6)

A method for inspecting a refractory of an atmosphere furnace including a heating chamber, a refractory arranged around the heating chamber, and an iron skin arranged outside the refractory.
The step of measuring the temperature of the iron skin during the operation of the atmosphere furnace, and
A step of measuring the residual thickness of the refractory and the thickness of the infiltrating layer formed on the refractory at the place where the temperature was measured, and a step of measuring the thickness.
A step of determining the damage rate of the refractory based on the residual thickness of the refractory and the thickness of the infiltrating layer, and
The process of obtaining the correspondence between the damage rate and the temperature of the iron skin, and
From the above correspondence, the process of determining the reference temperature corresponding to the predetermined reference damage rate and
A method for inspecting a refractory material of an atmosphere furnace, comprising a step of inspecting whether the temperature of the iron skin is lower than the reference temperature. The method for inspecting a refractory material of an atmosphere furnace according to claim 1.
A method for inspecting a refractory material of an atmosphere furnace in which the damage rate E is obtained from the following formula.
E = (A- (B-κB ₂ )) / A
However, κ = 1-λ ₁ / λ ₂
Here, A is the initial thickness of the refractory, B is the residual thickness of the refractory, B ₂ is the thickness of the infiltrated layer, λ ₁ is the thermal conductivity of the refractory, and λ ₂ is the infiltration. The thermal conductivity of the layer. The method for inspecting a refractory material of an atmosphere furnace according to claim 1 or 2.
A method for inspecting a refractory material of an atmosphere furnace in which the reference temperature T _c is obtained from the following formula.
T _c = E _c × d + e
Here, E _c is the reference damage rate, and d and e are constants determined in the step of obtaining the corresponding relationship. The method for inspecting a refractory material of an atmosphere furnace according to any one of claims 1 to 3.
A method for inspecting a refractory of an atmosphere furnace, further comprising a step of repairing the refractory when the operation of the atmosphere furnace is interrupted next time when the temperature of the iron skin becomes equal to or higher than the reference temperature. The method for inspecting a refractory material of an atmosphere furnace according to any one of claims 1 to 4.
The atmosphere furnace is a method for inspecting refractories of an atmosphere furnace, which is a furnace used for reducing iron oxide. A method for producing reduced iron using an atmosphere furnace including a heating chamber, a refractory material arranged around the heating chamber, and an iron skin arranged outside the refractory material.
The step of measuring the temperature of the iron skin during the operation of the atmosphere furnace, and
A step of measuring the residual thickness of the refractory and the thickness of the infiltrating layer formed on the refractory, and
A step of determining the damage rate of the refractory based on the residual thickness of the refractory and the thickness of the infiltrating layer, and
The process of obtaining the correspondence between the damage rate and the temperature of the iron skin, and
From the above correspondence, the process of determining the reference temperature corresponding to the predetermined reference damage rate and
The process of checking whether the temperature of the iron skin is lower than the reference temperature, and
A method for producing reduced iron, comprising a step of reducing iron oxide in the heating chamber.

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