JPH083722A - Waste gas treatment - Google Patents

Abstract

PURPOSE:To prevent the accumulation of Fel2 in a waste gas and to conduct continuous siliconization by introducing a waste gas from a siliconizing furnace while kept at high temp. into a cooling tower and surrounding the waste gas with a low-temp. cooling nonoxidizing gas to cool the waste gas. CONSTITUTION:A steel sheet 21 is brought into contact with a nonoxidizing gas contg. SiCl4 in a continuous siliconizing furnace 1 and siliconized in the vapor phase. The waste gas contg. the SiCl4 and FeCl2 generated in the furnace is passed through a waste gas duct 2 consisting of a discharge cylinder 2a, insulating material 2b and duct heater 2c, heated to a temp. higher than the 1023 deg.C b.p. of FeCl2 and introduced into the upper part of a primary cooling tower 3. A nonoxidizing gas kept at a temp. lower than the m.p. (at 672 deg.C)of FeCl2 m.p. (at 672 deg.C) of FeCl2 is blown from plural slit nozzles 6 into a cylindrical part 3a at the upper part of the tower 3 to form a spiral flow along the inner wall surface, and the waste gas is cooled out of contact with the inner wall surface and sent downward. The waste gas is mixed with a cooling nonoxidizing gas in the lower conical part 3b, cooled to a temp. below the m.p. of FeCl2, and the FeCl2 is solidified into fine powder and separated in a dust collector 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating exhaust gas generated in an apparatus for vapor phase siliconizing a steel sheet by bringing the steel sheet into contact with a non-oxidizing gas containing SiCl ₄ .

[0002]

2. Description of the Related Art As a method for producing a high silicon steel sheet, a vapor phase siliconizing method has been known. This method is
This is a method for obtaining a high-silicon steel sheet having excellent magnetic properties and the like by enriching Si by subjecting a steel sheet, which has a relatively small content and can be easily rolled, to a vapor-phase immersion silicon treatment.

For example, in the technology disclosed in Japanese Patent Laid-Open No. 227078 and Japanese Patent Laid-Open No. 63-263324, SiCl ₄ (silicon tetrachloride) is used as a steel sheet in a mole fraction of 5 to 3
1023 in a non-oxidizing gas atmosphere containing 5%
Silicidation is continuously performed at a temperature of up to 1200 ° C to obtain a high silicon steel sheet.

Usually, in this siliconizing process, SiCl ₄ gas is used as a raw material gas for supplying Si. This SiCl ₄ is
Si reacts with the steel sheet according to the following reaction formula, Si permeates into the steel sheet, and a large amount of FeCl ₂ (ferrous chloride) is generated as a reaction product.

[0005]

Embedded image This FeCl ₂ is exhausted from the siliconizing furnace as part of the exhaust gas. Although FeCl ₂ in the exhaust gas is in a vapor phase state at 1023 ° C. or higher, it is exhausted from the furnace and its temperature lowers, and then becomes a crystalline solid phase through a liquid phase. Therefore, when the exhaust gas comes into contact with a low temperature wall surface such as a pipe of the exhaust section, FeCl ₂ crystallizes and grows on the wall surface, and is hard deposited on the wall surface. This FeCl
The deposition amount of ₂ increases with the lapse of processing time, and eventually the piping of the exhaust part is blocked, making it impossible to continue the siliconizing process.

[0006] In the technique disclosed in Japanese Patent Laid-Open No. 63-24021, as an exhaust gas treating apparatus for removing FeCl ₂ in exhaust gas as described above, the exhaust gas is a primary cooler of a heat exchange system and the exhaust gas has a melting point of FeCl ₂ . An apparatus has been proposed in which FeCl ₂ is precipitated in the form of fine powder by cooling to a temperature of (670 ° C.) or lower and is collected by a filter device.

[0007]

However, in the method for treating exhaust gas based on the technique disclosed in Japanese Patent Laid-Open No. 63-24021, the exhaust gas of the primary cooler is deposited in order to deposit FeCl ₂ in the form of fine powder. Since it is a heat exchange method of cooling by contacting the heat transfer wall, FeCl ₂ crystallizes and solidly deposits on the tube wall of the heat exchanger, etc., and the gas flow path inside the vessel is blocked by FeCl _{2 and} it continues for a long time. Then, there was a problem that the siliconizing treatment cannot be carried out.

The present invention has been made in order to solve the above-mentioned problems of the prior art, and since FeCl ₂ does not deposit, exhaust gas treatment, and consequently, silicidation treatment, can be performed continuously for a long time. It is intended to provide a way.

[0009]

The exhaust gas cooling method according to the present invention is a method for treating exhaust gas generated in an apparatus for vapor phase siliconizing a steel sheet by bringing the steel sheet into contact with a non-oxidizing gas containing SiCl _4. Therefore, 1. The exhaust gas containing SiCl ₄ and FeCl ₂ exhausted from the siliconizing furnace is maintained at a temperature of 1023 ° C. or higher, the upper part is formed into a cylindrical shape, and the lower part is gradually reduced from the inner diameter of the cylindrical part in a conical shape. 1. A step of leading from above to the cooling tower formed in 1. Introducing a cooling non-oxidizing gas having a temperature lower than the melting point of FeCl ₂ by a plurality of blowing nozzles provided in the cooling tower cylindrical portion to form a swirling flow along the inner wall surface of the cooling tower, and the high temperature SiCl ₄ and FeCl _2. A step of cooling the exhaust gas containing ₂ without contacting the inner wall of the cooling tower. The exhaust gas cooled in the cooling tower cylinder is guided to the cone of the cooling tower and mixed with a non-oxidizing gas for cooling whose swirling radius is narrowed and the flow velocity is increased, and the exhaust gas temperature is set to a temperature below the melting point of FeCl _{2 in} the exhaust gas. Of solidifying FeCl ₂ in the form of fine powder,
It is composed of and.

[0010]

[Function] SiCl ₄ and FeCl generated in the siliconizing furnace
Exhaust gas having a temperature of 1023 ° C. or higher including ₂ is introduced into a cylindrical portion that constitutes the upper part of the cooling tower. In the cylindrical part, the non-oxidizing gas for cooling having a temperature lower than the melting point of FeCl ₂ is discharged from a plurality of blowing nozzles provided at regular intervals along the inner peripheral surface of the cylindrical part. Since it is supplied so as to form a swirling flow along, the exhaust gas introduced into the cylindrical portion is hindered by the flow of the cooling non-oxidizing gas,
The cylindrical part moves downward without being rapidly cooled by touching the wall surface of the cylindrical part.

Since the peripheral portion of the exhaust gas is in contact with the cooling non-oxidizing gas at the same time, the temperature of the exhaust gas gradually decreases from the outside.

When the exhaust gas entrained in the cooling non-oxidizing gas reaches the conical portion of the cooling tower, the swirling diameter gradually decreases, so that the swirling flow velocity of the cooling non-oxidizing gas increases. The exhaust gas is mixed and stirred with a cooling non-oxidizing gas and the exhaust gas, and further cooling is promoted to reach a temperature below the melting point (672 ° C.) of FeCl _{2 at} the end.

For this reason, FeCl ₂ contained in the exhaust gas is solidified into a fine powder, and is discharged from the lower end of the conical portion of the cooling tower in a state of being contained in the exhaust gas.

Then, after the temperature is further lowered by the secondary cooler, fine particles of FeCl _{2 in} the exhaust gas are recovered through the dust collector, and the gas after dust removal is sent to the blowing nozzle and used for cooling the exhaust gas.

[0015]

EXAMPLE An exhaust gas treatment method according to an example of the present invention will be described with reference to FIG. FIG. 1 is an explanatory diagram showing the equipment configuration when implementing this exhaust gas treatment method. SiCl ₄ generated when the steel plate 21 was vapor-phase siliconized in the continuous siliconization furnace 1 and
High-temperature exhaust gas containing FeCl ₂ at a temperature of about 1200 ° C is used for the hearth
It is discharged to the primary cooling tower 3 through the exhaust gas duct 2 installed at.

The exhaust gas duct 2 comprises an exhaust gas exhaust pipe 2a, a heat insulating material 2b, a duct heater 2c, and an exhaust pipe receiving block 2d. In order to prevent clogging inside the exhaust gas discharge tube 2a, the length is shortened as much as possible, and the temperature drop of the exhaust gas during this period is minimized to reduce the boiling point of FeCl ₂ (1
The temperature is maintained above 023 ° C. The reason for installing the exhaust gas duct 2 in the hearth 1a is that the exhaust gas exhaust pipe 2
This is because the length of a is made as short as possible and the temperature drop of the exhaust gas is prevented. Since a part of the duct heat insulating material 2b constitutes the inner wall of the furnace, heat radiation from the exhaust gas duct 2 to the outside air is small. Further, the amount of heat radiated from the duct 2 can be reduced by increasing the outer surface temperature of the duct 2 with the duct heater 2c. In order to prevent the powder contained in the exhaust gas from adhering to the inner wall surface by smoothing it, a fine ceramic sleeve having excellent heat resistance and corrosion resistance is used for the exhaust gas discharge tube 2a. Silicon nitride, dense alumina, or dense mullite material is suitable for the material of the fine ceramics. In the present embodiment, high-alumina microdense mullite is used. Exhaust gas exhaust tube 2 composed of this ceramic sleeve
The lower end of a is supported by the discharge tube receiving block 2d. Since the load of the exhaust gas discharge cylinder 2a is applied to the upper surface of the discharge cylinder receiving block 2d, a fired product of a precast block having high temperature strength is used. The precast block is supported by a receiving plate 5 above the water cooling jacket 4 of the primary cooling tower 3 installed immediately below it. A thick plate of ordinary steel is used for the receiving plate 5.

The primary cooling tower 3 has a cylindrical portion 3a at the upper portion and a conical portion 3b at the lower portion, and is constituted by a steel water cooling jacket 4 having a double structure as a whole. Cylindrical part 3
A slit nozzle 6 for blowing cold air is provided on the inner surface of a in parallel with the cylindrical axis. The non-oxidizing gas for cooling is supplied from the slit nozzle 6 into the primary cooling tower 3,
Exhaust gas that has left the primary cooling tower 3 and is further cooled to 60 ° C. or less by the secondary cooler 7 is circulated and used as this cooling gas.

The blowing direction of the slit nozzle 6 is as shown in FIG.
2, which is a view taken along the line AA of FIG. 2, is in the tangential direction of the inner wall of the cylindrical portion 3a, and the blowing gas is
It is designed to flow along the inner wall. Therefore, the nozzle plate 8 is provided at the tip of the slit nozzle 6 so that the cooling gas flows more effectively along the wall surface. A plurality of slit nozzles 6 are provided on the inner peripheral surface of the cylindrical portion 3a along the circumferential direction, but the installation interval between them is smaller than the distance from the outlet to the point where the blown gas tries to separate from the inner wall surface. . That is, as shown in FIG. 3, the cooling gas blown out from the slit nozzle 6 having the width d has a uniform flow velocity V initially in the width direction of the slit nozzle 6, but for cooling the portion in contact with the inner wall surface 3c. The flow velocity of the gas becomes slower due to the resistance from the wall,
At the end, it becomes 0 (peeling point B). Inner wall surface 3c ahead
Flow is disturbed and the cooling gas leaves the wall. That is, the flow of the cooling gas is in the range surrounded by the dotted lines, and a turbulent flow region C due to the backflow is generated between this flow and the inner wall surface 3c. In such a state, the exhaust gas to be cooled comes into contact with such an inner wall surface, and the inner wall surface is corroded or deformed under the influence of heat. Therefore, the installation interval of the slit nozzle 6 is separated from the blowout port. It must be shorter than the distance L to the point B.

The distance L between the nozzles is the flow velocity of the air blown out from the nozzles.
V, nozzle width d, curvature of inner cylinder 3a, etc.
Therefore, it is necessary to make an experimental determination. Primary cooling tower 3
In the lower conical portion 3b of the, formed by the upper cylindrical portion 3a
The swirling flow exits while increasing the swirling speed due to the decrease of the turning radius.
Spilled into the mouth pipe. In the process, the central part of the primary cooling tower 3
The high-temperature furnace exhaust gas flowing from top to bottom is wound into a high-speed swirl flow.
Get caught. As a result, the exhaust gas exhaust pipe 2a is connected to the primary cooling tower.
The high-temperature furnace exhaust gas introduced into the interior of the primary cooling tower 3
Without touching the wall, the lower cone 3b can
About 40 g
It is rapidly cooled to 0 ° C. On the other hand, the primary cooling tower 3 itself
Does not come into direct contact with high temperature furnace exhaust gas, so heat and corrosion
Since it is not affected, ordinary steel can be sufficiently designed.
FeCl in the furnace exhaust gas during the rapid cooling process ₂But from the gas phase to fine powder
Precipitates as a solid phase. After mixing at the outlet of the primary cooling tower 3
The gas temperature of FeCl₂Below the melting point (672 ° C) of
Therefore, it is necessary to completely precipitate it as a solid phase. However, this
If the temperature is too low, the amount of return circulation gas increases and the
Blower 9, secondary cooler 7 and dust collector 10 have increased capacity
It is an uneconomical structure in terms of equipment. According to the method described above
Generated FeCl₂The fine powder has a flow velocity of about 30 m /
By taking more than s, the deposit in the piping downstream of the primary cooling tower 3
It was confirmed that the problems of accumulation and blockage do not occur.

The gas containing the fine FeCl ₂ powder that has exited the primary cooling tower 3 is cooled by the secondary cooler 7 to the supply temperature (about 60 ° C. or less) to the slit nozzle 6 of the primary cooling tower 3. Needless to say, this temperature is set to be lower than the heat resistant temperature of the dust collector 10. Since the secondary cooler 7 cools the dust-containing gas, it is necessary to have a mechanism for removing the adhesion and deposition of FeCl ₂ fine powder on the heat exchange portion in the cooling process. The dust collector removes iron chloride fine powder in the gas. The gas that has passed through the dust collector 10 is the circulating blower 9
The pressure is increased by and is supplied to the slit nozzle 6 of the primary cooling tower 3 as a return circulation gas.

In the cooled gas, unreacted SiCl
Exhaust blower 1 part of the circulating gas because ₄ is included
In step 1, it is sent to the SiCl ₄ recovery facility for recovery.

[0022]

According to the present invention, a high temperature and corrosive exhaust gas containing a reaction product gas which becomes a solid at the final cooling temperature generated in the vapor phase silicon treatment equipment is used to block the flow path due to the precipitated solid during the cooling process. Can be cooled without causing problems.

Further, since the exhaust gas can be cooled and the reaction product can be removed separately from the recovery of the unreacted SiCl ₄ , the recovery of the SiCl ₄ can be carried out efficiently and continuously, so that the high concentration can be achieved. (Approximately 6.5%) Construction of a large-scale vapor-phase immersion silicon treatment equipment for commercial production for the production of silicon steel sheets has become possible.

[Brief description of drawings]

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

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is an explanatory diagram of an installation interval of blowing nozzles.

[Explanation of symbols]

 1 Continuous Silica Treatment Furnace 2 Exhaust Gas Duct 2a Exhaust Gas Exhaust Cylinder 2b Insulation Material 2c Duct Heater 2d Exhaust Cylinder Receiver Block 3 Primary Cooling Tower 3a Cylindrical Part 3b Conical Part 4 Water Cooling Jacket 5 Catch Plate 6 Slit Nozzle 7 Secondary Cooler 8 Nozzle Plate 9 Circulation blower 10 Dust collector 11 Exhaust blower

Claims (1)

[Claims] 1. A method for treating exhaust gas generated in an apparatus for vapor phase siliconizing a steel sheet by bringing the steel sheet into contact with a non-oxidizing gas containing SiCl ₄ , comprising the following steps: A method for treating high temperature exhaust gas containing SiCl ₄ and FeCl ₂ . 1. The exhaust gas containing SiCl ₄ and FeCl ₂ exhausted from the siliconizing furnace is maintained at a temperature of 1023 ° C. or higher, the upper part is formed into a cylindrical shape, and the lower part is gradually reduced from the inner diameter of the cylindrical part in a conical shape. A step of leading from above to the cooling tower formed in. 2. Introducing a cooling non-oxidizing gas having a temperature lower than the melting point of FeCl ₂ by a plurality of blowing nozzles provided in the cooling tower cylindrical portion to form a swirling flow along the inner wall surface of the cooling tower, and the high temperature SiCl ₄ and FeCl A step of cooling the exhaust gas containing ₂ without contacting the inner wall of the cooling tower. 3. The exhaust gas cooled in the cooling tower cylinder is guided to the cone of the cooling tower and mixed with a non-oxidizing gas for cooling whose swirling radius is narrowed and the flow velocity is increased, and the exhaust gas temperature is set to a temperature below the melting point of FeCl _{2 in} the exhaust gas. Step of solidifying FeCl ₂ in the form of fine powder.