JPWO2012105414A1 - Gas superheater and superheater assembly - Google Patents

Abstract

[Problem] In a zinc reduction method for producing corrosive and reactive gases, especially high-purity silicon, it is possible to heat the raw material silicon tetrachloride gas to a target temperature of 900 to 1,100 ° C with precise control A gas superheater and a superheater assembly are provided. [Solution] A plurality of heat generating tubes each containing a heat generating element are arranged in a longitudinal direction in an outer tube having a gas inlet and a gas outlet.

Description

  The present invention relates to, for example, a gas superheater and a superheater assembly used to heat a heated gas introduced into an electric furnace to a high temperature.

In recent years, a zinc reduction method for producing high-purity polycrystalline silicon by reducing silicon tetrachloride with metallic zinc has attracted attention as a method for producing polycrystalline silicon as a raw material for silicon solar cells.
In the zinc reduction method, silicon tetrachloride and zinc as raw materials are vaporized at 900 to 1,100 ° C. and heated to cause a gas phase reduction reaction.

  Since silicon tetrachloride has a boiling point of 58 ° C, it can be vaporized relatively easily. However, it reacts violently with water and is corrosive. Care should be taken in handling such as selection.

  By the way, Patent Document 1 discloses a gas heater that obtains a high-temperature gas by heating a metal resistor to a high temperature by direct energization and bringing the gas into direct contact with the metal resistor that has reached a high temperature.

However, when a corrosive gas such as silicon tetrachloride is heated, there is a problem that the metal resistor is corroded by the gas.
On the other hand, in Patent Document 2, a heating element including a heat generating part formed in a spiral shape and an electrode terminal taken out from the heat generating part in a protective tube disposed through the inner wall of the furnace, A gas heating device is disclosed that is inserted so as to be located inside the furnace.
In this gas heating apparatus, gas or air is guided to a heat generating portion formed in a spiral shape and heated, and the heated gas or air is discharged into the furnace.
Since this gas heating device has a structure in which the heat generating part penetrates the furnace inner wall, the maximum length of the heat generating part is limited by the thickness of the furnace inner wall, and as a result, sufficient control of the heating temperature is achieved. There is a problem that it is difficult.

JP 2003-297527 A JP 2003-185353 A

  The present invention has been made in order to solve the conventional problems in a gas superheater for heating a gas supplied to a reactor or the like to a high temperature, and its purpose is to provide a corrosive and reactive gas. It is an object of the present invention to provide a gas superheater and a superheater assembly that can be heated under strictly control to a target temperature of 900 to 1,100 ° C.

  In particular, according to the present invention, in the zinc reduction method for producing high-purity silicon, it is possible to heat the raw material silicon tetrachloride gas to a target temperature of 900 to 1,100 ° C. while strictly controlling it and supplying it to the reduction reactor. An object of the present invention is to provide a gas superheater and a superheater assembly.

In order to achieve the above object, a gas superheater according to the present invention comprises:
A gas superheater for heating a gas to a high temperature,
The gas superheater,
An outer tube having a gas inlet and a gas outlet;
A plurality of heat generating tubes disposed in the longitudinal direction of the outer tube, and containing a heat generating element therein;
It is characterized by comprising at least.

According to such a gas superheater, there is no possibility of corrosion because the heating element does not contact the gas.
Here, it is preferable that a side plate in which a hole for inserting the heat generating tube is formed in advance is disposed at both ends of the outer tube, and the heat generating tube is inserted into the hole.

If formed in this way, the heating energy can be effectively used and the heating tube can be held in a stable posture.
Furthermore, the heating tube is formed longer than the entire length of the outer tube,
A heating tube having a length longer than that of the outer tube may be extended from one end of the outer tube to the other end.
Alternatively, the heating tube is less than half the length of the outer tube,
The exothermic tube having a length of half or less may be inserted from both ends of the outer tube to the vicinity of the center of the outer tube.

Since the design can be easily changed in this way, it is possible to select either one of insertion from one side or both sides depending on the length of the heat generating tube.
In the present invention, it is preferable that an external heating means is disposed on the outer periphery of the outer tube.

Thus, if an external heating means is arrange | positioned, since it can heat by an inner side and an outer side, a heating effect is favorable.
Furthermore, the heating element is preferably a resistance heating element made of metal or ceramic.

With such a configuration, heat generation efficiency is good and temperature adjustment is easy.
Further, in the present invention, a substantially semicircular rectifying plate is disposed on the inner wall of the outer tube at a predetermined interval, and the rectifying plates adjacent to each other are arranged on one side of the inner wall of the outer tube. It is preferable that they are alternately arranged on the side and the other side.

  With such a configuration, the heated gas flowing inside collides with the rectifying plate and the flow path is changed, so that a long flow path for the gas in the outer tube can be secured, and the entire gas is uniformly heated. be able to.

In the present invention, it is preferable that the material of the outer tube and the heating tube is quartz.
Furthermore, in the present invention, the heated gas is preferably silicon tetrachloride.
Moreover, it is preferable that the superheater coupling body of the present invention is configured by connecting a plurality of the above gas superheaters.

According to the gas superheater and superheater assembly of the present invention, the gas supplied to the reactor or the like can be heated while strictly controlling to the target temperature.
Further, even when a corrosive gas is heated, a heating element such as a coil is not corroded by the gas.

  Furthermore, since the length of the heat generating part can be set freely, the control of the heating temperature is easy.

FIG. 1 is an exploded perspective view showing a main part of a gas superheater according to an embodiment of the present invention. 2A is a schematic cross-sectional view in a state where the gas superheater of FIG. 1 is assembled, and FIG. 2B is a cross-sectional view in the direction of the line BB in FIG. 2A. FIG. 3 is a perspective view showing another aspect of the side plate shown in FIG. FIG. 4 is a schematic front view of a gas superheater according to another embodiment of the present invention. FIG. 5 is a schematic cross-sectional view of a gas superheater according to still another embodiment of the present invention. FIG. 6 is a schematic cross-sectional view of a gas superheater according to still another embodiment of the present invention.

Hereinafter, the gas superheater concerning the present invention is explained based on a drawing.
FIG. 1 is an exploded perspective view of a gas superheater according to an embodiment of the present invention, and FIG. 2A is a schematic cross-sectional view of the assembled gas superheater of FIG. (B) is a schematic sectional drawing of the BB line direction of FIG. 2 (A). In this embodiment, the gas to be heated is silicon tetrachloride used for producing high-purity polycrystalline silicon.

  The gas superheater 10 of the present embodiment includes a substantially cylindrical outer tube 2, a plurality of (four in this embodiment) heat generating tubes 4 disposed at both ends projecting from the outer tube 2, It has a plurality of heating elements 6 housed inside the heating tube 4. Further, both end portions of the outer tube 2 are sealed by the side plates 8 and 8 after the heating tube 4 is accommodated.

A gas inlet 2a and a gas outlet 2b are formed at both ends of the outer tube 2, respectively.
Further, one side plate 8 disposed at each end of the outer tube 2 may be used, but in order to maintain strength, an inner closing plate 8a and an outer closing plate 8b, as in the side plate 8 ′ shown in FIG. It is also possible to adopt a structure in which a heat insulating material such as a ceramic fiber blanket is loaded between them.

  Quartz, silicon carbide, silicon nitride, etc. having corrosion resistance and heat resistance can be used as the material of the outer tube 2, the heating tube 4, and the side plate 8 (8 '). Quartz is suitable when the gas to be handled is silicon tetrachloride as in this embodiment.

  The number of heating tubes 4 and heating elements 6 accommodated in the outer tube 2 is normally 2 to 10, but this number is not particularly limited and is appropriately determined according to the required heat capacity. In the illustrated example, the respective heat generating tubes 4 are arranged substantially equally apart.

  The exothermic tube 4 has a length in which both end portions 4a and 4b project to the outside through both side plates 8 and 8, and the heating element 6 extends from either one of the projecting end portions 4a and 4b. Is inserted into the heat generating tube 4 and accommodated.

  The heating element 6 can be a resistance heater such as Kanthal alloy, nickel chrome alloy, or silicon carbide. As the shape of the heater, a coil shape, a rod shape, a spiral shape, a cylindrical shape, or the like can be used as appropriate. The outer tube 2 containing the heat generating tube 4 is usually installed horizontally, but can also be installed vertically or obliquely depending on the installation space.

In the gas superheater 10 of FIG. 1, the heat generating tube 4 longer than the outer tube 2 is accommodated in the outer tube 2, but instead of this, two divided bodies can be arranged linearly.
That is, when the length of the heating element 6 or the heating tube 4 is limited, as shown in FIG. 5, two bottomed cylindrical heating tubes 14 with one end sealed in advance are prepared as a set. The end portions 14a on the closed side of the heat generating tubes 14 and 14 are inserted into the outer tube 2 from both sides in a substantially straight line, and the end portions 14b on the open side are inserted into the side plates 8 and 8 of the outer tube 2. It is also possible to have a structure protruding from the outside.
In FIG. 5, the end portions 14 a and 14 a on the closed side of the pair of heat generating tubes 14 and 14 are arranged adjacent to each other at a predetermined interval in the central portion of the outer tube 2. The separation distance between the end portions 14a of the heat generating tubes 14 adjacent to each other is not particularly limited, but it is preferable to secure about 1 to 10 cm.

On the other hand, as shown in FIGS. 2A and 2B, a plurality (four in the embodiment) of rectifying plates 16 are provided on the inner wall of the outer tube 2 with respect to the axial direction of the outer tube 2. Are arranged in a vertical direction. These rectifying plates 16 have a substantially semicircular shape, and in a cross-sectional view of the outer tube 2 provided with the rectifying plate 16, a space on the opposite side to the side where the rectifying plate 16 is provided is a substantially semicircular notch. Part 16a is formed.
The cutout portion 16 a may be arcuate and the shape is determined by the shape of the rectifying plate 16.
The heat generating tube 4 has a structure penetrating each rectifying plate 16, and the heat generating tube 4 and the rectifying plate 16 in the penetrating portion are integrated by fixing several points by welding. The gas passes through the inside of the outer tube 2 through the notch 16a.
It is preferable that the notch positions of the rectifying plates 16 adjacent to each other are alternated by 180 degrees. As a result, the gas passing therethrough changes the flow path while hitting the rectifying plate 16, and the passage distance in the outer tube 2 is ensured to be long, whereby heat exchange can be performed efficiently. The distance between the rectifying plates adjacent to each other is preferably 10 to 30 cm.

Quartz, silicon carbide, silicon nitride, or the like can be used as the material of the rectifying plate 16. Quartz is preferred when the gas to be handled is silicon tetrachloride.
Although the outer periphery of the outer tube 2 may be covered with a heat insulating material, in order to reduce heat dissipation loss and increase thermal efficiency, for example, as in the other embodiment shown in FIG. Preferably, the external heating means 20 is disposed in each of the defined areas and heated from the outside to the inside.

  By providing the external heating means 20 in this way, the heating capacity of the internal heat generating tube 4 can be set to be small accordingly, so that the heat exchanger can be made more compact than before. As the heating element of the external heating means 20, a resistance heater such as a cantal alloy, a nickel chromium alloy, or silicon carbide can be used.

The heating capacity of each region of the external heating means 20 is preferably larger on the gas inlet 2a side shown in FIG. 1 than on the gas outlet 2b side.
In the gas superheater 10 of the present embodiment, silicon tetrachloride gas to be heated is introduced into the outer tube 2 from the gas inlet 2a, and if the heating element 6 generates heat to a high temperature when energized, the heated gas is The temperature gradually increases and flows into the downstream side of the outer tube 2 while colliding with the rectifying plate 16, and finally reaches a temperature of 900 to 1,100 ° C. and is ejected to the outside from the gas outlet 2b.
Thereby, for example, if the gas superheater 10 is accommodated in a furnace or the like for producing polycrystalline silicon, silicon tetrachloride gas heated to a predetermined temperature can be supplied into the furnace.

  With such a configuration, there is no problem that the heating element 6 is corroded by the heated gas. Further, since the heat generating part does not have a structure that penetrates the furnace inner wall as in the conventional case, the length of the heat generating part is not limited by the thickness of the furnace inner wall, and can be designed to a free length.

The gas superheater 10 according to one embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment.
For example, two or three or more gas superheaters 10 described above can be connected as shown in FIG. By connecting the gas superheater 10 in this way to form the superheater assembly 30, it becomes possible to obtain a high-temperature gas by strictly controlling the temperature.

  Further, by employing the superheater coupling body 30, for example, corrosive and reactive gas can be heated under strictly control to a target temperature of 900 to 1,100 ° C. In particular, according to the present invention, in the zinc reduction method for producing high-purity silicon, it is possible to heat the raw material silicon tetrachloride gas to a target temperature of 900 to 1,100 ° C. while strictly controlling it and supplying it to the reduction reactor. is there.

  The gas superheater 10 is not limited to heating silicon tetrachloride gas, and can be used as a superheater for various gases.

[Example 1]
Both ends of a quartz tube having an outer diameter of 308 mm, an inner diameter of 300 mm, and a length of 2,000 mm were sealed with a double quartz side plate 8 ′ filled with a ceramic fiber blanket. Four pairs (a total of eight) of heat generating tubes 4 made of quartz, each having an outer diameter of 80 mm and a length of 1,070 mm, were prepared inside the outer tube 2 formed as described above.
On the other hand, four semicircular rectifying plates 16 were arranged in the outer tube 2 with an interval of 200 mm. Then, four heat generating tubes 4 are inserted into the outer tube 2 from one side, and the heat generating tubes 4 penetrate the rectifying plate 16 so that the heat generating tubes 4 are fixed to the through portions of the rectifying plate 16 by welding. Attached.

As shown in FIG. 5, when four from the gas inlet 2 a side and four from the gas outlet 2 b side are arranged (in FIG. 5, two of the four are arranged in parallel, two of the four are The closed end portion 14 a side of the heat generating tubes 14 is inserted so as to be disposed at a substantially intermediate position of the outer tube 2.
Then, a spiral cantal heater (heating element 6) was inserted from the open end 14b of the heating tube 14. The heat capacity of the cantal heater (heating element 6) was 6.5 kw × 4 on the gas inlet 2a side and 3 kw × 4 on the gas outlet 2b side.

  Further, as shown in FIG. 4, an external heater (external heating means 20) composed of upper and lower divided four units was installed on the outer periphery of the outer tube 2. The capacity of the external heater (external heating means 20) was set to 20.5 kW in the two zones on the gas inlet side and 10 kW in the two zones on the gas outlet side.

  Each heater of the gas superheater configured as described above was energized, and silicon tetrachloride gas heated to 80 ° C. was introduced from the gas inlet 2a side at a flow rate of 600 kg / hr. The temperature on the gas outlet 2b side of the silicon tetrachloride gas was measured and found to be 970 ° C.

  It was confirmed that the gas superheater 10 of the present invention can obtain a high-temperature gas under a strict temperature control with a compact configuration.

2 Outer tube 2a Gas inlet 2b Gas outlet 4 Heat generating pipe 4a, 4b End 6 Heating element 8, 8 'Side plate 8a Inner closing plate 8b Outer closing plate 10 Gas superheater 14 Heating tube 14a Closed end 14b Open end Part 16 Current plate 16a Notch part 20 External heating means 30 Superheater coupling body

Claims (10)

A gas superheater for heating a gas to a high temperature,
The gas superheater,
An outer tube having a gas inlet and a gas outlet;
A plurality of heat generating tubes disposed in the longitudinal direction of the outer tube, and containing a heat generating element therein;
A gas superheater characterized by comprising at least.   The side plate in which a hole for inserting the heat generating tube is formed in advance at both ends of the outer tube, and the heat generating tube is inserted into the hole. The gas superheater described. The exothermic tube is formed longer than the entire length of the outer tube,
3. The gas overheating according to claim 1, wherein a heat generating tube having a length longer than that of the outer tube is extended from one end of the outer tube to the other end. 4. vessel. The exothermic tube is less than half the length of the outer tube,
3. The gas superheater according to claim 1, wherein the heat generating pipe having a length of less than half is inserted from both end portions of the outer cylindrical pipe to the vicinity of the center of the outer cylindrical pipe.   The gas superheater according to any one of claims 1 to 4, wherein external heating means is disposed on an outer periphery of the outer tube.   The gas heater according to any one of claims 1 to 5, wherein the heating element is a resistance heating element made of metal or ceramic.   A substantially semicircular rectifying plate is disposed on the inner wall of the outer tube at a predetermined interval, and the rectifying plates adjacent to each other are alternately arranged on one side and the other side of the inner wall of the outer tube. The gas superheater according to any one of claims 1 to 6, wherein the gas superheater is disposed in the inside.   The gas superheater according to any one of claims 1 to 7, wherein a material of the outer tube and the heating tube is quartz.   The gas superheater according to any one of claims 1 to 8, wherein the gas to be heated is silicon tetrachloride.   A superheater assembly comprising a plurality of the gas superheaters according to claim 1 connected to each other.

Images