JPS5818325B2 - Beta Gatatankakeisono Lenzokuseizohouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for continuously producing β-type silicon carbide, and more specifically, a raw material obtained by mixing silica powder, carbon powder, and a carbon-based binder and molding the mixture into granules is used as a starting raw material. The present invention relates to a method for continuously producing β-type silicon carbide.

Conventionally, silicon carbide has been industrially produced in a discontinuous Acheson type electric resistance furnace.

This manufacturing method connects the electrodes fixed at both ends of the furnace with a carbon resistance core, fills the surrounding area with a mixture of silica and carbon, supplies electricity to this resistance core to cause a heating reaction, and then In this method, the side wall of the furnace is removed and the hard α-type silicon carbide crystal lumps produced are recovered.

Therefore, much labor was required for the crushing and sorting work after collection, and the workability was extremely poor.

In addition, there are unresolved industrial hygiene and pollution problems due to dust and bad odors, and there are many other drawbacks, such as the long furnace downtime, extremely low furnace operating efficiency, and the difficulty of recovering exhaust CO gas. had.

On the other hand, microcrystalline β-type silicon carbide has different chemical and physical properties from α-type silicon carbide, and is used as a filler and binder for silicon carbide refractories and as a deoxidizing agent for metallurgy. Furthermore, due to the fine particle size that is difficult to obtain with α-type silicon carbide, many uses such as polishing abrasives and matting agents have been developed in recent years, and the demand for them is increasing.

Various attempts have been made to continuously produce β-type silicon carbide, such as West German Patent Nos. 1 and 1.
According to No. 86,447, a reaction tube composed of concentric double tubes, a heating element installed only in the innermost tube, and an outer wall of the reaction tube are used to constantly discharge CO gas out of the reaction area. A manufacturing method using a special device in which a plurality of diagonal holes are provided is disclosed.

However, this method has drawbacks as described later, and is difficult to implement.

This is because, according to the method described in the above West German patent,
In order to prevent the starting material from melting in the reaction zone or from silica grains fusing together and forming lumps, the surfaces of silica grains are wetted with a sticky liquid and sprinkled with carbon powder. .

Therefore, the air permeability of the raw material is extremely poor, it is easily affected by precipitates, and the thermal conductivity is extremely low because radiation heat transfer is severely inhibited in the reaction zone).

Further, the device has a heating element in the innermost part, and the raw material is charged into the outer periphery of the heating element.

Therefore, a horizontal temperature gradient occurs in the reaction zone, making it difficult to uniformly heat the raw materials and obtain a uniform product.

As mentioned above, a method for continuously producing β-type silicon carbide economically and on an industrial scale has not yet been known.

From this point of view, the inventors of the present invention previously filed a patent application filed in 1973-
No. 126425 proposes an invention relating to a method for continuous production of β-type silicon carbide using silica and carbon as starting materials.

According to the invention, when using a carbon material with relatively low reactivity, the reactivity is improved by finely pulverizing the carbon material, and further, by mixing and molding silica powder and a carbon-based binder, S is an intermediate product generated during the melting and agglomeration of raw materials by silica particles and the production reaction of silicon carbide.
This makes it possible to prevent the raw material from clumping together due to the adhesion of precipitates from iO gas.

However, since the carbon-based binder softens and melts before reaching the carbonization temperature, the adhesive action of the binder causes the forming raw materials to form into lumps before being heated to the high temperature required for the SiC production reaction. The shape of the molding raw material may be damaged when the binder softens and melts, and the gas permeability deteriorates, making it difficult for the SiC production reaction to proceed. In some cases, long-term stable continuous operation was difficult.

The present invention relates to an improvement of the method previously invented and patented by the present inventors, and its purpose is to smoothly lower the dead weight of the charged material in the heating furnace and maintain stable furnace conditions. It is an object of the present invention to provide a method for continuously producing β-type silicon carbide with low power consumption.

According to the present invention, a raw material obtained by mixing silica powder, carbon powder, and a carbon-based binder and forming it into granules is charged into the heating furnace from above a vertical electric resistance type indirect heating furnace, In the continuous production method of β-type silicon carbide, in which a SiC production reaction is caused by indirect heating in the heating furnace, and a SiC product is taken out from below the heating furnace, a high-temperature reaction that occurs as a by-product during the SiC production reaction in the heating furnace. A carbonization furnace into which generated gas can be introduced is connected, and the raw material formed into granules is charged into the carbonization furnace, and SiC
The carbon-based binder in the raw material is carbonized by contacting with the high-temperature reaction product gas produced as a by-product during the production reaction, and then discharged from the carbonization furnace, and then charged into the heating furnace. Heat to within the temperature range of 2100°C
The above object can be achieved by a method for continuously producing β-type silicon carbide, which is characterized by causing an iC production reaction.

Next, the present invention will be explained in detail.

According to the present invention, a raw material obtained by mixing silica powder, carbon powder, and a carbon-based binder and forming the mixture into granules is used.

It is important that the shaped raw material always maintains its initial shape in the heating furnace. It is necessary to carbonize the binder.

The reason is that the carbon-based binder used in the present invention is used for the purpose of improving the crushing strength of the molded raw material in a high temperature range. It exhibits bonding strength by carbonizing in a high temperature range.

Therefore, if the molded raw material is used without carbonizing the carbon-based binder, the carbon-based binder will soften and melt in the heating furnace, so that the molded raw material will be softened and melted in the heating furnace due to the adhesive action of the softened and melted binder. The raw materials stick to each other and form clumps, which prevents the raw materials from falling smoothly under their own weight.

Further, if the softening and melting is significant, the initial shape is damaged by the weight of the raw materials stacked on top, gas permeability is significantly deteriorated, and the silicon carbide production reaction becomes difficult to proceed.

However, before charging the shaped raw material into the heating furnace, it is necessary to first heat it to at least the carbonization temperature of the binder,
By carbonizing the carbon-based binder, the raw material becomes a carbon-bonded state with excellent thermal and strength properties, and the raw material becomes lumpy and deformed due to softening and melting of the carbon-based binder in the heating furnace. can be prevented.

According to the present invention, the temperature at which the carbon-based binder contained in the molded raw material is carbonized is 400°C.
It is preferable to set it as above.

According to the present invention, carbon-based binders such as coal tar, petroleum tar, wood tar, coal tar pitch, petroleum pitch, wood cool pitch, asphalt, molasses, phenolic resin, pulp waste liquid, and those having effects equivalent to these can be used. You can use things to your advantage.

According to the present invention, as the silica powder, pulverized silica stone or silica sand can be advantageously used, and as the carbon powder, pulverized petroleum coke, pitch coke, or anthracite can be advantageously used.

According to the present invention, a carbonization furnace capable of introducing high-temperature reaction product gas that is produced as a by-product during the SiC production reaction is connected to the heating furnace, and a raw material formed into granules is charged into the carbonization furnace to produce SiC. It is necessary to carbonize the carbon-based binder in the raw material by bringing it into contact with the high-temperature reaction product gas produced as a by-product during the reaction.

In the present invention, the reason why the carbon-based binder in the raw material is carbonized by bringing the raw material shaped into particles into contact with the high-temperature reaction product gas that is produced as a by-product during the SiC production reaction is because of the reaction that occurs as a by-product during the SiC production reaction. The generated gas is 90
This is because it has an extremely high temperature of 0° C. or higher and a large amount of sensible heat, and by effectively utilizing this sensible heat of the reaction product gas, thermal efficiency can be significantly improved.

In addition, in the present invention, the reason why the carbonization furnace is connected to the heating furnace, which can introduce the high temperature reaction product gas that is produced as a by-product during the SiC production reaction, is that the reaction product gas that is produced as a by-product during the SiC production reaction is mainly CO gas and SiO gas. However, in the present invention, the high-temperature reaction product gas that is brought into contact with the raw material is CO gas, and by connecting the carbonization furnace to the heating furnace, the high temperature state can be efficiently maintained without oxidizing the CO gas. This is because the coal can be introduced into the furnace as it is.

In addition, it is preferable that the carbonization furnace is connected above the heating furnace.

According to the present invention, a rotary furnace such as a rotary kiln can be advantageously used as the carbonization furnace.

The reason why a rotary furnace is advantageous as the carbonization furnace is that the raw material and C
The form of contact with the O gas can be countercurrent, allowing for sufficient heat exchange, and by rotating the furnace, it is possible to prevent the raw material from coagulating into lumps due to softening and melting of the binder. The carbonization process can be carried out without damaging the initial shape because almost no load is applied.

According to the present invention, the raw material discharged from the carbonization furnace is charged into the heating furnace and heated to a temperature range of 1600-2100°C.

The reason why the temperature range is 1,600 to 2,100°C is that if the temperature is higher than 2,100°C, the generated β-type silicon carbide will crystallize and transform into α-type silicon carbide to form a sintered mass. This is because operation is difficult, and on the other hand, if the temperature is lower than 1600°C, the reaction rate is extremely slow and uneconomical.

According to the present invention, by using an electric resistance type indirect heating furnace, the horizontal temperature distribution of the raw materials and reaction products is made almost uniform, the local deviation of the reaction is reduced, and uniform products are obtained. You can get it easily.

Next, an example of a continuous manufacturing apparatus used in the method of the present invention will be explained with reference to the drawings.

As shown in FIG. 1, the manufacturing equipment used in the method of the present invention includes a vertical furnace 1 using electric resistance indirect heating, and a carbonization furnace 2 into which high-temperature reaction product gas produced as a by-product during the SiC production reaction can be introduced. It is a device consisting of

A cylindrical reaction tube 3 is provided in the center of the vertical furnace 1,
The central heating part of the reaction tube 3 is made of graphite, and the lower part thereof is made of refractory material 4.

A heating element 5 made of graphite is provided on the outer periphery of the central heating part of the reaction tube 3.
A heating element protection outer cylinder 6 made of graphite is also provided.

The heating element 5 is located in a space surrounded by the heating element protection outer cylinder 6 and the reaction cylinder 3, and a non-oxidizing gas is sealed in the space.

A heat insulating layer γ filled with a powder heat insulating material such as acetylene black or carbon black, which has excellent heat insulating properties, is provided on the outer periphery of the heating element protection outer cylinder 6.

The reaction temperature in the vertical furnace 1 is controlled by the vertical furnace 1.
Using a temperature measuring pipe 8 and a thermometer 9 provided on the side of the reactor tube 3, measure the temperature of the outer wall of the reaction tube 3 or the temperature near the center thereof, and correlate this measured value with the control circuit of the power supply or the load voltage. This can be done by

As the thermometer 9, a tip thermometer, a two-color thermometer, a radiation thermometer, etc. can be advantageously used.

A carbonization furnace 2 is provided above the vertical furnace 1.
The raw material charging inlet 10 of the carbonization furnace 2 is connected to the charging port 1 outlet 11 of the carbonization furnace 2 so as to correspond to each other.

The connecting portion between the carbonization furnace 2 and the vertical furnace 1 has an airtight structure so that the reaction product gas extracted from the vertical furnace 1 can be efficiently sent to the carbonization furnace 2.

In addition, an auxiliary heating means 1 for heating the inside of the carbonization furnace 2 when there is insufficient reaction product gas in the carbonization furnace 2 immediately after the start of operation, etc.
2 can be provided.

According to this manufacturing apparatus, the raw material formed into granules is cut out from the raw material hopper 13 provided at the upper part of the carbonization furnace 2 by the raw material cutting means 14 such as a rotary valve, and is sent to the bean paste of the carbonization furnace 2 through the chute 15. The CO gas is supplied and added to the carbonization furnace 2 while being in countercurrent contact with the high-temperature CO gas obliquely discharged from the vertical furnace 1, and moves downward in the carbonization furnace 2.

Next, the raw material discharged from the discharge port 11 of the coal furnace 2 is supplied to the vertical furnace 1, and as it descends inside the reaction tube 3, it is further subjected to force [
The product is heated and undergoes a reaction to generate SiC, is cooled in a cooling layer 11 provided with a water cooling jacket 16, and is discharged from a product discharge port 18.

In addition, the CO gas used for heating the forming raw material in the carbonization furnace 2 is discharged from the gas discharge port 1 provided above the carbonization furnace 2.
9 and can be effectively used for fuel, chemical reactions, etc.

Next, the present invention will be specifically explained with reference to Examples and Comparative Examples.

Examples 62 parts by weight of silica powder with a particle size of 50 to 80 mesh (hereinafter expressed in parts), petroleum coke powder with a particle size of 800 mesh or less (GL
38 parts of coke powder) and 10 parts of high pitch powder under 200 mesh were uniformly mixed and formed into pellets with an average particle size of 61 rLm using a pan-type granulator using a 1% CMC aqueous solution.

After drying this molding raw material, it was continuously charged into a manufacturing apparatus as shown in FIG. 1, and the product was recovered at an average rate of 65 kg/hr.

The results are shown in Table 1. The carbonization furnace in the production equipment used is a rotary kiln with a total length of 2.0 m and an inner diameter of 0.4 m, and a vertical furnace with a total length of 3.5 m and a reaction cylinder inner diameter of o, sm.
A Tanmann type furnace was used.

The heating temperature of the charging material in the lower part of the rotary kiln is 700°C, and the reaction temperature in the vertical furnace is 19°C.
The temperature was controlled at 50°C.

In the examples using the method of the present invention, the raw material showed smooth natural descent over a long period of time, and it was possible to carry out extremely smooth continuous operation.

Further, as can be seen from the results shown in Table 1, the thermal efficiency of the furnace and the yield of produced SiC were high, and the productivity was also extremely good.

Comparative Example A molding raw material similar to that used in the example was charged directly from the top of a vertical furnace using a manufacturing apparatus having the same structure as shown in FIG. 1 but without a carbonization furnace. The same operation as in the example was performed.

The results are shown in Table 1.

As mentioned above, if the forming raw material is directly charged into the vertical furnace without being carbonized, the falling of the raw material sometimes worsens during operation, and it is necessary to forcibly lower the raw material by poking, etc. The operation was intermittent, making it difficult to maintain stable continuous operation.

As explained above, the method of the present invention has the effect of allowing extremely stable continuous operation over a long period of time when producing β-type silicon carbide, and is extremely useful industrially.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a manufacturing apparatus used in an example of the present invention. 1... Vertical furnace, 2... Carbonization furnace, 3...
...Reaction tube, 4...Refractory, 5...
・Heating element, 6... Heating element protection outer cylinder, γ...
...Heat insulation layer, 8...Temperature measuring pipe, 9...
・Thermometer, 10... Raw material charging port of vertical furnace, 11
...Charge discharge port of carbonization furnace, 12...
Auxiliary heating means, 13... Raw material hopper, 14.
... Raw material cutting means, 15 ... Chute,
16... Water cooling jacket, 1γ... Cooling layer, 18... Product outlet, 19...
- Gas discharge port, 20...Non-oxidizing gas filling port.

Claims (1)

[Claims] 1. A raw material obtained by mixing silica powder, carbon powder, and a carbon-based binder and forming it into granules is charged into the heating furnace from above a vertical electric resistance type indirect heating furnace, and is heated in the heating furnace. In a method for continuous production of β-type silicon carbide in which a SiC production reaction is caused by indirect heating and a SiC product is taken out from below the heating furnace, a high-temperature reaction product gas that is produced as a by-product during the SiC production reaction is introduced into the heating furnace. A carbonization furnace consisting of a rotary furnace that can be used is connected, and the raw material formed into granules is charged into the carbonization furnace and brought into contact with the high-temperature reaction product gas that is produced as a by-product during the SiC production reaction. After the carbon-based binder is carbonized, it is discharged from the carbonization furnace, and then charged into the heating furnace, and heated to 1600 to 2100
1. A method for continuously producing β-type silicon carbide, which comprises heating within a temperature range of 0.degree. C. to cause a SiC production reaction.