JP5389525B2 - Ammonia decomposition cylinder - Google Patents

Description

  The present invention relates to an ammonia decomposition cylinder. More specifically, the present invention relates to an ammonia decomposition cylinder that decomposes ammonia into nitrogen and hydrogen by bringing an exhaust gas containing ammonia into contact with an ammonia decomposition catalyst under heating.

  Various harmful components are used in manufacturing plants for various chemical products including semiconductor manufacturing plants. Prior to releasing exhaust gas containing various harmful components from these factories into the atmosphere, the concentration should be less than the TLV-TWA (time-weighted average exposure limit concentration) defined for each harmful component. It is necessary to remove and purify harmful components from the exhaust gas.

  For example, exhaust gas containing 10 to 40% by volume of ammonia is discharged from the downstream of the gallium nitride (GaN) compound semiconductor manufacturing process at a flow rate of several tens to several hundreds of liters per minute. Since ammonia has a TLV-TWA of 25 ppm and has a unique irritating odor, it is necessary to remove the ammonia concentration below the TLV-TWA when the exhaust gas is released into the atmosphere.

  As a method for efficiently treating such a large amount of ammonia, as shown in Patent Documents 1 to 3, an exhaust gas containing ammonia is brought into contact with an ammonia decomposition catalyst under heating to decompose the ammonia into nitrogen and hydrogen. There is a way. As the ammonia decomposition catalyst, for example, a catalyst in which nickel, iron, palladium, platinum, or ruthenium is supported on an inorganic carrier is used.

As an apparatus for performing the above-mentioned ammonia decomposition treatment, there is an ammonia decomposition cylinder having a cylindrical shape provided with an exhaust gas introduction port, an ammonia decomposition catalyst filling part, a treated gas discharge port, and a heater on the outer wall.
JP-A-8-57256 JP-A-8-84910 JP 2000-233177 A

In recent years, with the increase in production of GaN-based compound semiconductors, the amount of ammonia discharged from semiconductor manufacturing plants has increased, and as a result, the ammonia decomposition cylinder has to be enlarged.
However, the above-mentioned ammonia decomposition reaction is an endothermic reaction, and a part of the heat applied from the heater to the catalyst is consumed in the decomposition reaction, and it is difficult for heat to be transmitted to the catalyst at a part away from the heater. Therefore, when the inside of the cracking cylinder is heated only by the heater on the outer wall, and the exhaust gas containing ammonia is circulated through the cracking cylinder, the temperature of the catalyst at the center of the cylinder does not rise as much as the catalyst at the periphery of the cylinder wall. The larger the ammonia decomposition cylinder, the greater the temperature difference of the catalyst between the cylinder center and the cylinder wall periphery.

  Here, if the catalyst around the outer wall is heated to an appropriate temperature, the temperature of the catalyst in the center of the cracking cylinder does not rise sufficiently, and the ability to decompose the original ammonia of the catalyst is not fully exhibited. Conversely, if the catalyst in the center of the cracking cylinder is heated to an appropriate temperature, the heater set temperature needs to be significantly higher than in the above case, resulting in increased power consumption in the heater and moreover the heater. Inconvenience that the life of the battery becomes shorter.

  Therefore, the problem to be solved by the present invention is, for example, in the case of using an ammonia decomposition cylinder having a large inner diameter even in the treatment of exhaust gas containing a high concentration of ammonia discharged from the GaN compound semiconductor manufacturing process. Even if it exists, it is providing the apparatus which the catalyst in a cracking cylinder is fully heated and can fully exhibit the capability to decompose | disassemble ammonia.

  As a result of intensive studies to solve these problems, the present inventors have made a decomposition in addition to the heater installed on the outer wall of the decomposition cylinder as usual so that the catalyst in the entire ammonia decomposition cylinder is heated sufficiently and uniformly. By installing another heater inside the cylinder, it was found that at least the catalyst on the outlet side in the decomposition cylinder reaches the target temperature almost uniformly, and the catalyst can fully exhibit the ability to decompose ammonia. The ammonia decomposition cylinder of the invention was reached.

  That is, the present invention relates to an ammonia decomposition cylinder having a cylindrical shape having an inlet for exhaust gas containing ammonia, a filling portion for an ammonia decomposition catalyst, an outlet for treated gas, and a heater on the outer wall, and further comprising the decomposition cylinder The ammonia decomposition cylinder is characterized in that a container containing a cylindrical heater is installed inside the cylinder so that the central axis of the decomposition cylinder is the same.

  According to the present invention, even when decomposing high-concentration ammonia discharged from a GaN-based compound semiconductor manufacturing process or when decomposing ammonia with an ammonia decomposing cylinder having a large inner diameter, at least an outlet in the decomposing cylinder Since the ammonia decomposition catalyst packed on the side reaches the target temperature almost uniformly, the ammonia decomposition catalyst can fully demonstrate its ability to decompose ammonia without wasting power consumption by the heater. It was.

The present invention is applied to an ammonia decomposition cylinder, particularly an ammonia decomposition cylinder having an inner diameter of 150 mm or more, in which exhaust gas containing ammonia is brought into contact with an ammonia decomposition catalyst under heating to decompose ammonia into nitrogen and hydrogen.
Hereinafter, although the ammonia decomposition cylinder of this invention is demonstrated based on FIGS. 1-3 , this invention is not limited by these.
FIGS. 1 and 2 are vertical sectional views showing examples of the ammonia decomposition cylinder of the present invention. FIG. 3 is a horizontal sectional view taken along the line aa ′ of FIG.

As shown in FIGS. 1 and 2 , the ammonia decomposing cylinder of the present invention includes an introduction port 1 for exhaust gas containing ammonia, a filling portion 2 for ammonia decomposition catalyst, a discharge port 3 for treated gas, and a heater 4 on the outer wall. Ammonia decomposing cylinder having a cylindrical shape, and further comprising a container 5 containing a cylindrical heater 4 'installed in the decomposing cylinder so that the central axis of the decomposing cylinder is the same. It is a disassembly cylinder. In the present invention, the container 5 is installed so that the contact area with the filling portion 2 of the ammonia decomposition catalyst becomes large so that the ammonia decomposition catalyst can be sufficiently heated.

Containers in the ammonia decomposition column of the present invention, as shown in FIG. 1, not preferable that the outer shape is cylindrical.

  The gap between the outer wall 6 of the disassembly cylinder and the container 5 is preferably 150 mm or less, and more preferably 120 mm or less. When the gap between the outer wall 6 of the decomposition cylinder and the container 5 exceeds 150 mm, the temperature difference between the ammonia decomposition catalyst in the part farthest from the heater and the ammonia decomposition catalyst in the heater peripheral part becomes large, causing inconvenience in the decomposition of ammonia. There is a fear.

  The outer diameter of the container 5 is preferably not less than 1/4 times and not more than 3/4 times the inner diameter of the disassembly cylinder. When the outer diameter of the container is smaller than 1/4 times the inner diameter of the decomposition cylinder, the area of the wall surface of the container is too small, so that the heating effect on the ammonia decomposition catalyst from the heater in the container is small. The temperature may not rise sufficiently. When the outer diameter of the container is larger than 3/4 times the inner diameter of the cracking cylinder, the ammonia cracking catalyst filling portion becomes narrow, and ammonia may not be efficiently decomposed.

  Moreover, it is preferable that the container 5 is a structure which coat | covers a heater and prevents ammonia which is corrosive gas from contacting a heater. As such a configuration, for example, as shown in FIGS. 1 and 2, the container can be formed in a bag shape with one end closed, and a heater can be installed therein.

  In the present invention, the constituent material of the container and the peripheral member (member for fixing the container to the disassembly cylinder) is preferably a corrosion-resistant material, such as SUS316, SUS316L, Inconel, Hastelloy, etc. The same material as that of the outer wall can be used. The thickness of the container is usually 1 to 5 mm. Furthermore, in order to heat the ammonia decomposition catalyst efficiently, the container preferably has a structure that penetrates from the uppermost part to the lowermost part of the filling part of the ammonia decomposition catalyst.

  In the ammonia decomposition cylinder of the present invention, the temperature at a predetermined location inside the decomposition cylinder may be further measured. For example, as shown in FIG. 2, a narrow tube 7 made of stainless steel or the like having a hole with a diameter of about 3 to 7 mm in the upper lid of the ammonia decomposition cylinder and having one end closed at the hole is closed. Is welded in a direction to enter the inside of the decomposition cylinder, and the thermocouple 8 can be inserted until the tip of the thermocouple 8 reaches a position where the temperature is desired to be measured.

The ammonia decomposition catalyst filled in the ammonia decomposition cylinder of the present invention is, for example, a catalyst in which nickel, iron, palladium, platinum, and ruthenium are supported on an inorganic carrier.
These shapes and sizes are not generally limited by the specifications of the ammonia decomposition cylinder, the distribution conditions of the exhaust gas, and the like. However, it is usually a spherical shape, a cylindrical shape, or the like, and in the case of a spherical shape, the diameter ranges from 2 to 12 mm, and in the cylindrical shape (pellet), the diameter ranges from 1 to 10 mm and the height ranges from about 2 to 10 mm.

  When the ammonia contained in the exhaust gas is decomposed into nitrogen and hydrogen by the ammonia decomposition cylinder of the present invention, the temperature of the heater on the outer wall of the ammonia decomposition cylinder of the present invention and the heater in the container is increased, and the ammonia decomposition catalyst is heated. The ammonia is decomposed by introducing exhaust gas containing ammonia from the inlet of the ammonia decomposition cylinder. The temperature at which ammonia in the exhaust gas is decomposed by bringing it into contact with the ammonia decomposition catalyst varies depending on the type of catalyst and the flow conditions of the exhaust gas, and is usually from 300 ° C to 800 ° C. However, it is limited to a range narrower than the above, for example, under conditions such as the type of ammonia decomposition catalyst that is limited.

  For example, when an exhaust gas containing ammonia (10 to 40% by volume) discharged from a gallium nitride compound semiconductor manufacturing process is decomposed using a catalyst in which ruthenium is supported on an inorganic carrier, the contact temperature between the exhaust gas and the catalyst is 540. It is set so that it may become -700 degreeC, Preferably it is 550-650 degreeC. When the contact temperature between the exhaust gas and the catalyst is less than 540 ° C., there is a disadvantage that the decomposition rate of ammonia decreases. When the temperature exceeds 700 ° C., the heater deteriorates quickly and the life is shortened, the improvement of the decomposition rate of ammonia is small, the power consumption of the heater is increased, energy is wasted, and harmful nitrogen oxidation There is concern about the generation of things.

Since the ammonia decomposition cylinder of the present invention is configured as described above, the adverse effect of the endothermic reaction due to the ammonia decomposition reaction can be greatly reduced even in the decomposition treatment of high-concentration ammonia discharged from the gallium nitride compound semiconductor manufacturing process. And at least the temperature of the ammonia decomposition catalyst on the outlet side of the filling section can be kept relatively uniform. As a result, the ammonia decomposition catalyst can sufficiently exhibit the ability to decompose ammonia, and can efficiently decompose ammonia.
In the present invention, a preheater for heating exhaust gas can be provided before the ammonia decomposition cylinder, or a purification cylinder filled with an adsorbent such as activated carbon or zeolite can be provided after the ammonia decomposition cylinder. .

  EXAMPLES Next, although an Example demonstrates this invention concretely, this invention is not limited by these.

[Example 1]
(Production of ammonia decomposition cylinder)
An ammonia decomposing cylinder as shown in FIG. 1 having a cylindrical wall made of a stainless steel cylinder having an inner diameter of 300 mm and a height of 1840 mm was manufactured. As the container, a stainless steel container (container having a cylindrical outer shape) having an outer diameter of 150 mm, a height of 1660 mm, an upper end opened, and a lower end closed. Since the lowermost part of the catalyst filling part (height 1400 mm) was positioned 90 mm above the lowermost part of the container, the inner cylinder penetrated from the uppermost part to the lowermost part of the catalyst filling part. Further, a microsheath heater for heating the catalyst was installed on the entire outer wall of the outer cylinder and the part of the container facing the catalyst filling part. Moreover, the preheater for heating the gas before introduce | transducing into an ammonia decomposition cylinder was provided.

(Preparation and filling of ammonia decomposition catalyst)
An ammonia decomposition catalyst having a ruthenium loading of 2.0 wt% and a specific surface area of 20 m ² / g by impregnating a spherical α-alumina carrier having a particle diameter of about 3 mm with an aqueous ruthenium chloride solution and then hydrogen reduction. Got. This ammonia decomposition catalyst was filled in the gap between the outer wall of the ammonia decomposition cylinder and the container so that the filling length was 1400 mm. The packing density was 1.0 g / ml.
Further, two stainless steel thin tubes each having an outer diameter of 6.4 mm and a length of 1670 mm were prepared and three thermocouples were inserted so as to obtain the configuration shown in FIG. The insertion position of the tip of the thermocouple was set at a total of three locations of 100 mm, 500 mm, and 1300 mm from the top to the bottom of the catalyst filling portion.

(Ammonia decomposition test)
The set temperature of the heater of the preheater and the heater of the ammonia decomposition cylinder was set to 620 ° C., and nitrogen and hydrogen were introduced from the preheater to the ammonia decomposition cylinder at a flow rate of 225 L / min. As a result, the temperature of the tip portion of the thermocouple of the ammonia decomposition catalyst was stable around 600 ° C. Next, the introduced gas was changed, and nitrogen, hydrogen, and ammonia were each introduced from the preheater into the ammonia decomposition cylinder at a flow rate of 150 L / min.

  After introducing the gas consisting of nitrogen, hydrogen, and ammonia, the temperature at the tip of the thermocouple fluctuated temporarily, but finally stabilized at a substantially constant temperature. The treated gas was sampled at the discharge port of the ammonia decomposition cylinder, and the ammonia concentration was measured. These results are shown in Table 1. In Table 1, the temperatures at the 100 mm, 500 mm, and 1300 mm locations from the top to the bottom of the catalyst filling portion are respectively indicated as the thermocouple temperature, the thermocouple temperature, and the thermocouple temperature. Moreover, temperature shows the average value of the location.

[Example 2]
In the production of the ammonia decomposition cylinder of Example 1, the ammonia decomposition cylinder was produced in the same manner as in Example 1 except that the inner diameter of the ammonia decomposition cylinder was changed to 200 mm and the outer diameter of the container was changed to 100 mm. An ammonia decomposition test was conducted in the same manner as in Example 1 except that this ammonia decomposition cylinder was used. The results are shown in Table 1.

[Example 3]
In the ammonia decomposition test of Example 1, the ammonia decomposition test was performed in the same manner as in Example 1 except that the flow rates of the gas composed of nitrogen, hydrogen, and ammonia were each changed to 120 L / min. The results are shown in Table 1.

[Comparative Example 1]
In the production of the ammonia decomposition cylinder of Example 1, an ammonia decomposition cylinder was produced in the same manner as in Example 1 except that no container was used. An ammonia decomposition test was conducted in the same manner as in Example 1 except that this ammonia decomposition cylinder was used. (Ammonia decomposition catalyst and its filling length are the same as in Example 1) The results are shown in Table 1.

[Comparative Example 2]
In the production of the ammonia decomposition cylinder of Example 2, an ammonia decomposition cylinder was produced in the same manner as in Example 2 except that no container was used. An ammonia decomposition test was conducted in the same manner as in Example 2 except that this ammonia decomposition cylinder was used. (Ammonia decomposition catalyst and its filling length are the same as in Example 2). The results are shown in Table 1.

In the ammonia decomposition treatment, an endothermic reaction occurs due to the contact between ammonia and the ammonia decomposition catalyst, and a rapid temperature drop occurs at a location on the inlet side away from the heater of the catalyst filling portion. In the embodiment of the present invention, as described above, In addition, the temperature rises at the outlet side of the catalyst filling portion, and the decomposition rate of ammonia can be prevented from decreasing. On the other hand, in the comparative example (conventional example), the temperature does not rise sufficiently on the outlet side of the catalyst filling portion, and it is impossible to prevent a decrease in the decomposition rate of ammonia. This situation is represented by the relationship between the position and the temperature of the catalyst shown in FIG. (The X-axis direction in FIG. 4 indicates the displacement from the inlet side (upstream side) to the outlet side (downstream side) of the catalyst filling portion.

  As described above, the ammonia decomposition cylinder of the present invention is a case where ammonia is decomposed by an ammonia decomposition cylinder having a large inner diameter even when high concentration ammonia discharged from the GaN compound semiconductor manufacturing process is decomposed. However, since the ammonia decomposition catalyst charged at least on the outlet side in the decomposition cylinder reaches the target temperature almost uniformly, it is possible to efficiently decompose ammonia without wasting power consumption by the heater. it can.

Vertical sectional view showing an example of the ammonia decomposition cylinder of the present invention Vertical sectional view showing an example of an ammonia decomposition cylinder other than FIG. 1 of the present invention Horizontal sectional view taken along the a-a 'section in FIG. The graph which shows the position of the catalyst in the case of ammonia decomposition in an Example and a comparative example, and the relationship of temperature

DESCRIPTION OF SYMBOLS 1 Introducing port of exhaust gas containing ammonia 2 Filling part of ammonia decomposition catalyst 3 Discharging port of treated gas 4 Heater 4 'heater 5 Container with built-in cylindrical heater 6 Outer wall of decomposition cylinder 7 For inserting thermocouple Narrow tube 8 Thermocouple

Claims (7)

  An ammonia decomposition cylinder having a cylindrical shape having an inlet for exhaust gas containing ammonia, a filling portion for an ammonia decomposition catalyst, a discharge port for treated gas, and a heater on the outer wall, and further inside the decomposition cylinder, An ammonia decomposing cylinder, wherein a container containing a cylindrical heater is installed so that the central axis of the decomposing cylinder is the same.   The ammonia decomposition cylinder according to claim 1, wherein the inner diameter of the decomposition cylinder is 150 to 350 mm, and the outer shape of the container is a cylindrical shape.   The ammonia decomposition cylinder according to claim 1, wherein the outer diameter of the container is not less than 1/4 times and not more than 3/4 times the inner diameter of the decomposition cylinder.   The ammonia decomposition cylinder according to claim 1, wherein a gap between the outer wall of the decomposition cylinder and the container is 150 mm or less.   The ammonia decomposition cylinder according to claim 1, wherein the container penetrates from the uppermost portion to the lowermost portion of the filling portion of the ammonia decomposition catalyst.   The ammonia decomposition cylinder according to claim 1, wherein the constituent material of the container is the same as that of the outer wall of the decomposition cylinder.   The ammonia decomposition cylinder according to claim 1, wherein the heater in the container is configured not to contact ammonia.

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