JP2817604B2 - Exhaust gas treatment method in gas phase siliconizing equipment for steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas-phase siliconizing method for enriching the surface layer of a steel sheet or the entire steel sheet with Si for the purpose of improving the magnetic properties or the corrosion resistance, heat resistance and oxidation resistance of the steel sheet. In (chemical vapor deposition), the present invention relates to a method for treating exhaust gas exhausted from a siliconizing furnace constituting a gas-phase siliconizing apparatus.

[0002]

2. Description of the Related Art As a method for producing a high silicon steel sheet, a gas phase siliconizing treatment method is known. This method uses Si which is easy to roll.
By subjecting a steel sheet with relatively low content to gas phase siliconizing treatment,
enriched i, a method of obtaining a high silicon steel sheet having excellent magnetic characteristics and the like, for example, in JP-A No. 62-227078 and JP-63-26324 Patent like, the steel sheet SiCl ₄ is mol
In a non-oxidizing gas atmosphere containing 5 to 35% by fraction, a siliconizing treatment is continuously performed at a temperature of 1023 to 1200 ° C,
High silicon steel sheet is obtained. Usually, in this siliconizing treatment, SiCl ₄ gas is used as a raw material gas for supplying Si, and this SiCl ₄ reacts with the steel sheet according to the following reaction formula, and Si penetrates into the steel sheet, and a large amount of reaction by-products occurs. Of FeCl ₂ (ferrous chloride) is generated. SiCl ₄ + 5Fe → Fe ₃ Si + 2FeCl ₂ ↑

[0003] The FeCl ₂ is exhausted from the siliconizing furnace as part of the exhaust gas. FeCl ₂ in exhaust gas is 102
At 3 ° C. or higher, it is in a gaseous state, but is exhausted from the furnace, the temperature drops, and the liquid phase turns into a crystalline solid phase. For this reason, when the exhaust gas comes into contact with a low-temperature wall surface such as a pipe of the exhaust unit, the FeCl ₂ crystallizes and grows on the wall surface and is firmly deposited on the wall surface. The amount of the deposited FeCl ₂ increases with the elapse of the processing time, and eventually the piping of the exhaust part is closed, so that it is practically impossible to continue the siliconizing treatment.

Japanese Patent Application Laid-Open No. 63-24021 discloses an exhaust gas treatment apparatus for removing FeCl ₂ in exhaust gas as described above, in which an exhaust gas is fed to a primary cooler of a heat exchanger type.
An apparatus has been proposed in which FeCl ₂ is precipitated in the form of fine powder by cooling to a temperature lower than the melting point (670 ° C.) of Cl ₂ , and this is collected by a filter device.

[0005]

However, this exhaust gas treatment apparatus is of a so-called heat exchanger type in which a primary cooler for precipitating FeCl ₂ in a fine powder form cools the exhaust gas by contacting the exhaust gas with a heat transfer wall. Therefore, there is a problem that FeCl ₂ is crystallized on the tube wall of the heat exchanger and solidly deposited, thereby blocking the gas flow path in the vessel. In this case, the siliconizing treatment is continuously performed for a long time. Can not do.

An object of the present invention, the exhaust gas can be prevented from FeCl ₂ contained in the exhaust gas exhausted from the siliconizing treatment furnace, deposited on the wall surface of the exhaust gas treatment system for closing the gas passage It is to provide a processing method.

[0007]

Means for Solving the Problems The present inventors have studied a method of solidifying FeCl ₂ in exhaust gas without crystallization on the wall surface of a gas flow path, and as a result, as a result, exhausted gas from a siliconizing furnace. It has been found that when quenched exhaust gas containing SiCl ₄ and FeCl ₂ is quenched in an air stream, FeCl ₂ is solidified into a fine powder. The present invention has been made based on such knowledge, and the characteristic configuration is as follows.

(1) In an exhaust gas treatment method in an apparatus for subjecting a steel sheet to gas-phase siliconizing treatment by bringing a non-oxidizing gas containing SiCl ₄ into contact with the steel sheet, SiCl ₄ and FeCl ₂ exhausted from a siliconizing furnace are removed. Exhaust gas containing 1
It is guided into a gas mixing cooler without contacting a solid wall surface of 023 ° C. or less, and cooled by mixing with a non-oxidizing gas or a non-oxidizing gas containing SiCl ₄ at a lower temperature than the exhaust gas in the gas mixing cooler, Mixing average temperature 67
FeCl in the gas by using a mixed gas of less than 0 ° C.
_2. An exhaust gas treatment method in a gas-phase siliconizing treatment apparatus for a steel sheet, wherein ₂ is solidified into a fine powder.

(2) In an exhaust gas treatment method in an apparatus for subjecting a steel sheet to gas-phase siliconizing treatment by bringing a non-oxidizing gas containing SiCl ₄ into contact with the steel sheet, SiCl ₄ and FeCl ₂ exhausted from the siliconizing furnace are removed. Exhaust gas containing 1
It is guided into a gas mixing cooler without contacting a solid wall surface of 023 ° C. or less, and cooled by mixing with a non-oxidizing gas or a non-oxidizing gas containing SiCl ₄ at a lower temperature than the exhaust gas in the gas mixing cooler, Mixing average temperature 67
FeCl in the gas by using a mixed gas of less than 0 ° C.
₂ is solidified into a fine powder, and then the FeC
After removal of the l _2, wherein at least a portion of the mixed gas, immersion phase gas of steel sheet characterized by using as the gas to be mixed with the exhaust gas to cool the exhaust gas exhausted from the siliconizing treatment furnace Exhaust gas treatment method in silicon treatment equipment.

[0010]

When the FeCl _{2 in the} gas phase is cooled in a gas stream, it becomes fine mist in a liquid phase, and when further cooled, the mist becomes a fine powdery solid in the gas stream as it is. Such fine powdered FeCl ₂ does not crystallize and grow even when it comes into contact with a low-temperature wall surface or the like, and even if it temporarily adheres to the wall surface, it is blown off by an air current and does not deposit. Therefore, FeCl ₂ exhaust gas exhausted from the furnace
Is introduced into a gas mixing cooler without contacting with a solid wall surface having a boiling point of 1023 ° C. or less, and a cooling gas is mixed in the gas mixing cooler to reach a temperature of less than 670 ° C. which is the melting point of FeCl _{2 in} a gas stream. When cooled, FeCl ₂ in the exhaust gas is solidified into a fine powder in the air stream, and does not crystallize and deposit on the wall surface of the exhaust gas channel. Fine powder F
eCl ₂ is directly pneumatically sent along with the airflow, and can be easily removed by a filter or the like.

The details of the present invention will be described below with reference to the drawings. FIG. 1 shows the outline of the exhaust gas treatment method of the present invention.
1 is a siliconizing furnace, 2 is a gas mixing cooler, 3 is a cooling gas mixing section, and 4 is a cooling gas supply pipe. Exhaust gas exhausted from the siliconizing furnace 1 is a non-oxidizing gas (A
an inert gas such as r or He or N ₂ or a mixed gas thereof) containing SiCl ₄ not used in the siliconizing reaction and FeCl ₂ as a reaction by-product at 1023 ° C.
This is the above high-temperature gas. Exhaust gas exhausted from the siliconizing furnace is maintained at a high temperature of 1023 ° C. or higher and guided to a gas mixing cooler 2 without contacting a solid wall surface of 1023 ° C. or lower, and a cooling gas is mixed in the gas mixing cooler. As a result, it is cooled in a gas stream to a temperature lower than 670 ° C., which is the melting point of FeCl ₂ .

A cooling gas supply pipe 4 is provided in the gas mixing cooler 2.
The cooling gas is supplied at a relatively low temperature (lower than the exhaust gas) through the cooler wall, and the cooling gas flows from the cooler wall surface toward the center or along the cooler wall surface.
High-temperature exhaust gas is prevented from directly touching the cooler wall. The method of supplying the cooling gas into the cooler is described in, for example, FIG.
As shown in FIG. 5, slit-shaped outlets 6 (5a are headers) capable of blowing out the cooling gas at high speed along the inner wall surface of the cooler are provided at several locations in the circumferential direction of the cooler.
The entire inner wall of the cooler may be covered with the swirling flow of the cooling gas by the cooling gas blown from the cooling gas. Further, as shown in FIG. 3, gas may be blown from the entire wall surface (5b is a header) toward the center.

[0013] Thus, the cooler wall is covered with the cooling gas,
By cooling FeCl ₂ in the exhaust gas to a temperature lower than its melting point in an air stream, the FeCl ₂ is solidified into a fine powder in the air stream, and the FeCl ₂ is not crystallized and deposited on the wall surface. The fine powder of FeCl ₂ is directly pneumatically sent along with the airflow, and collected and removed by a downstream filter or the like. Further, even if FeCl _{2 in the} form of fine powder temporarily adheres to the wall surface of the cooler or the gas passage, it is blown off by the air current and does not accumulate.

As the cooling gas, a non-oxidizing gas (A
An inert gas such as r or He or N ₂ or a mixed gas thereof) or a non-oxidizing gas containing SiCl ₄ is used. Further, the mixed gas average temperature after mixing the cooling gas with the exhaust gas needs to be lower than 670 ° C. which is lower than the melting point of FeCl ₂ . This is because if the average temperature of the mixed gas does not fall below 670 ° C., gaseous FeCl ₂ remains in the exhaust gas, which crystallizes on the wall of the gas passage downstream of the gas mixing cooler to form a solid. It is.

In the present invention, it is necessary to guide the exhaust gas exhausted from the siliconizing furnace 1 to the gas mixing cooler 2 without making contact with the solid wall below 1023 ° C. When the wall surface of the gas passage between the mixing coolers 2 is likely to be 1023 ° C. or less, it is necessary to heat the wall surface of the gas passage with a heater or the like.

The mixed gas of the exhaust gas and the cooling gas as described above recovers and removes fine powdered FeCl ₂ from the gas, and at least a part thereof is circulated again to the gas mixing cooler 2.
It is preferable to reuse it as a cooling gas for exhaust gas.

FIG. 4 shows the circulation flow of the cooling gas. The exhaust gas (mixed gas of the exhaust gas and the cooling gas) cooled by the gas mixing cooler 2 is further cooled by the secondary cooling device 7 to a low temperature, and then is filtered by the filter device 8 (eg, a bag filter) and the auxiliary filter device 9. The FeCl ₂ powder is removed, and a part of the FeCl ₂ powder is
Is supplied as cooling gas. Also, only the amount of exhaust gas discharged from the siliconizing furnace is
_After being sent to an exhaust gas treatment system including a ₄ recovery device 12 and a gas cleaning device 13 and completely recovering SiCl ₄ , it is released to the atmosphere. By providing such a circulation system, it is possible to economically treat the exhaust gas without replenishing the exhaust gas treatment system with new cooling gas. The above 2
As the secondary cooling device 7, since FeCl ₂ in the exhaust gas has already been pulverized, a conventional heat exchanger type can be used.

[0018]

【Example】

Example 1 In a continuous siliconizing furnace for producing a 6.5% Si steel strip shown in FIG. 5, a 3% Si steel strip is continuously siliconized to produce a 6.5% Si steel strip. At this time, the exhaust gas exhausted from the siliconizing furnace was introduced into the gas mixing cooler 2 shown in FIG. 6, and N ₂ was mixed as a cooling gas, and cooled until the average gas temperature after mixing reached 400 ° C. . The gas mixing cooler 2 shown in FIG. 6 has an outlet 6 (5a) capable of blowing a cooling gas at a high speed along the inner wall surface of the cooler at several places (three places) in the circumferential direction of the cooler as in the method shown in FIG. A header is provided, and the entire inner wall of the cooler is covered with a swirling flow of the cooling gas by the cooling gas blown out from the outlet 6. Further, as a comparative example, the exhaust gas exhausted from the siliconizing furnace was passed through a normal shell-and-tube heat exchanger shown in FIG. 7 and cooled to 200 ° C.

With respect to the above-mentioned examples of the present invention and comparative examples, the state of deposition of FeCl ₂ in the exhaust gas treatment system was compared. FIG. 8 shows the change in the differential pressure before and after the gas cooling device (the gas mixing cooler in FIG. 6 and the heat exchanger in FIG. 7) corresponding to the processing time, in the case where the normal heat exchanger in FIG. 7 is used. In this case, the differential pressure gradually increased with the passage of time, and eventually the exhaust gas could not be sucked, making it impossible to continue the siliconizing treatment. On the other hand, when the gas mixing cooler of FIG. 6 was used, the pressure difference did not change even after several tens of hours had elapsed, and the siliconizing treatment could be continuously performed for a long time.

FIG. 9 is a view showing a state in which the heat exchanger is removed at the time when exhaust gas suction cannot be performed and the inner surface of the gas passage tube is observed in the comparative example using the heat exchanger of FIG.
This shows the state of adhesion of eCl ₂ , and as shown in the figure, FeCl ₂ deposited and grown in a crystalline form was deposited thickly on the inner surface of the tube. In contrast, FIG.
Opened the gas mixing cooler and observed its inner wall surface.
Only fine powdery FeCl ₂ was slightly attached, and no hard crystalline deposit was observed. That is, in the present invention example using gas mixing cooler shown in FIG. 6, FeCl ₂ is pulverized in an air stream in the cooler, inside wall attachment FeCl ₂ is a crystalline, that to grow is prevented confirmed Was. FIG. 10 shows the particle size distribution of the FeCl ₂ powder collected from the exhaust gas. As shown in the figure, it can be seen that FeCl ₂ is a fine powder having an average of several μm.

Embodiment 2 In a continuous siliconizing furnace for producing a 6.5% Si steel strip shown in FIG. 5, a 3% Si steel strip is continuously siliconized to obtain a 6.5% Si steel strip. When manufacturing the, the exhaust gas was cooled and treated by the exhaust gas treatment device shown in FIG. 6 is used as the gas mixing cooler 2, exhaust gas exhausted from the siliconizing furnace 1 is introduced, and N ₂ is mixed as a cooling gas.
Cooled to 00 ° C. FIG. 11 shows the change in the furnace pressure of the siliconizing furnace and the change in the differential pressure before and after the gas mixing cooler during operation. According to this, there was no change in the furnace pressure and the differential pressure even when the siliconizing treatment was performed for a long time, and it was confirmed that the siliconizing treatment can be continuously performed for a long time according to the method of the present invention.

[0022]

According to the present invention described above, the clogging of the exhaust gas treatment system due to the deposition of FeCl ₂ is prevented by pulverizing FeCl _{2 in} the exhaust gas exhausted from the siliconizing furnace in a gas stream. The siliconizing treatment can be performed continuously for a long period of time. In addition, since a part of the exhaust gas is circulated in the system and used as a cooling gas for the exhaust gas, economical exhaust gas treatment can be performed without supplying a cooling gas from outside the system.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an outline of an exhaust gas treatment method of the present invention.

FIG. 2 is an explanatory view showing an example of a method of introducing a cooling gas into a gas mixing cooler, where (a) is a horizontal cross section of the cooler,
(B) has shown the longitudinal cross section of the cooler.

3A and 3B are explanatory diagrams showing another example of a method of introducing a cooling gas into a gas mixing cooler, wherein FIG. 3A shows a horizontal cross section of the cooler, and FIG. 3B shows a vertical cross section of the cooler.

FIG. 4 is an explanatory view showing a circulation flow of a cooling gas when implementing the present invention.

FIG. 5 is an explanatory view showing a continuous siliconizing treatment apparatus for producing a 6.5% Si steel strip.

FIG. 6 is an explanatory view showing a gas mixing cooler used in an example of the present invention in Example 1, (a) is a horizontal cross section of the cooler,
(B) has shown the longitudinal cross section of the cooler.

FIG. 7 is an explanatory view showing a shell-and-tube heat exchanger used in a comparative example of Example 1.

FIG. 8 is a graph showing a change in a differential pressure before and after a gas cooling device according to a processing time in Example 1.

FIG. 9 is a drawing showing the state of adhesion of FeCl ₂ when the inner surface of the tube of the heat exchanger is observed in the comparative example of Example 1.

FIG. 10 is a graph showing the particle size distribution of FeCl ₂ powder collected from exhaust gas in Example 1.

FIG. 11 is a graph showing a change in furnace pressure of a siliconizing furnace and a change in differential pressure before and after a gas mixing cooler in Example 2.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Silicon-treatment furnace, 2 ... Gas mixing cooler, 3 ... Cooling gas mixing part, 4 ... Cooling gas supply pipe, 5a, 5b ... Header, 6 ...
Outlet, 7: Secondary cooling device, 8: Filter device, 9: Auxiliary filter device, 10, 11: Blower, 12: SiCl
₄ Recovery device, 13 Gas cleaning device

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Morihiro Wada 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Tsunehiro Yamaji 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan (72) Inventor Hirohisa Kashiji 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Katsuji Kasai 1-1-2, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (56) References JP-A-63-24021 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C23C 10/00, 10/06-10/08 C23C 10/14-10 / 16,10 / 28,12 / 00,16 / 24

Claims (2)

(57) [Claims] 1. An exhaust gas treatment method for an apparatus for subjecting a steel sheet to gas-phase siliconizing by bringing a non-oxidizing gas containing SiCl ₄ into contact with the steel sheet, the method including SiCl ₄ and FeCl ₂ exhausted from a siliconizing furnace. Exhaust gas
It is led into the gas mixing cooler without contacting the solid wall surface below ℃, and cooled by mixing with the non-oxidizing gas or the non-oxidizing gas containing SiCl ₄ at lower temperature than the exhaust gas in the gas mixing cooler. An exhaust gas treatment method in a gas phase siliconizing treatment apparatus for a steel sheet, wherein FeCl ₂ in the gas is solidified into a fine powder by using a mixed gas having an average temperature of less than 670 ° C. 2. An exhaust gas treatment method for an apparatus for subjecting a steel sheet to gas-phase siliconizing treatment by bringing a non-oxidizing gas containing SiCl ₄ into contact with the steel sheet, the method including SiCl ₄ and FeCl ₂ exhausted from a siliconizing furnace. Exhaust gas
It is led into the gas mixing cooler without contacting the solid wall surface below ℃, and cooled by mixing with the non-oxidizing gas or the non-oxidizing gas containing SiCl ₄ at lower temperature than the exhaust gas in the gas mixing cooler. By making the mixed gas having an average temperature of less than 670 ° C., the FeCl ₂ in the gas is solidified into a fine powder, and then the FeCl ₂ in the mixed gas is removed. Exhaust gas in a gas phase siliconizing apparatus for steel sheets, wherein the gas is used as a gas to be mixed with the exhaust gas.