JPH0857256A - Ammonia decomposition apparatus - Google Patents

Abstract

PURPOSE: To efficiently decompose ammonia while enabling safe treatment at the time of the mixing with oxygen by combining an ammonia removing cylinder with a decomposition cylinder equipped with a catalyst such as Ni or the like generating heat upon the contact with oxygen and a heat generation detection means. CONSTITUTION: The decomposition cylinder 8 connected to an ammonia gas supply pipe 10 and packed with ammonia gas decomposition catalysts 4, 5 and having a heater 3 arranged thereto, the ammonia removing cylinder 14 connected to the outlet part of the decomposition cylinder 8 and a bypass pipe 16 branched from the supply pipe 10 and connected to the ammonia removing cylinder 14 are provided. The decomposition cylinder 8 is packed with the catalyst 4 generating heat in the presence of oxygen among the ammonia decomposition catalysts on at least the upstream side thereof and a thermometer 6 detecting generated heat is attached to the packed part of the catalyst 4. When generation of heat is detected at the time of the mixing of oxygen with the ammonia gas, the supply of the ammonia gas to the decomposition cylinder 8 is stopped and, at the same time, the supply pipe 10 is changed over to the bypass pipe 16 to supply the ammonia gas to the ammonia removing cylinder 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ammonia decomposing device, and more particularly to an ammonia decomposing device capable of detecting when oxygen is mixed in ammonia gas to be treated and at the same time reliably preventing the risk of explosion or the like. Decomposing device

[0002]

2. Description of the Related Art Conventionally, as a method of decomposing ammonia,
Ammonia or a gas containing ammonia, for example,
A decomposition catalyst in which a metal such as nickel, iron, palladium or platinum is supported on an inorganic carrier such as alumina, and 600
A method in which ammonia is decomposed into nitrogen and hydrogen by contacting at a high temperature such as ˜900 ° C. is generally used. And since these decomposition catalysts are relatively efficient as far as the decomposition of ammonia is concerned, the production of nitrogen and hydrogen,
Alternatively, it is widely used in various industries for the purpose of purifying gas by decomposing ammonia contained in exhaust gas as a harmful component.

[0003]

However, both ammonia and hydrogen produced by its decomposition are flammable. Especially, when hydrogen has a wide combustion range and oxygen is likely to be mixed, ignition occurs. Temperature (about 550 ℃)
It is dangerous to carry out the decomposition operation of ammonia at a high temperature exceeding 10 ° C. For this reason, if there is a possibility that oxygen will be mixed into the disassembly cylinder to some extent and enter the explosion range, it is necessary to accurately detect this and take appropriate safety measures.

As a means for detecting oxygen mixed in the gas, there is generally a method using a gas chromatograph or various oxygen analyzers, but not only are both complicated in structure and operation and expensive, In the case of gas such as ammonia, there is a possibility that oxygen contamination may be missed due to a failure due to corrosion of the detection end. On the other hand, when the mixture of oxygen is detected, the introduction of ammonia gas into the decomposition cylinder is stopped, but for example, exhaust gas continuously discharged from the semiconductor manufacturing process cannot be released into the atmosphere as it is, Depending on the situation, there is a problem that the manufacturing apparatus must be temporarily stopped.

[0005]

The present inventors have devised an ammonia decomposing device capable of decomposing ammonia efficiently and, at the same time, reliably detecting oxygen if it is mixed and safely treating gas. As a result of repeated studies to obtain the above, it was found that these objects can be achieved by combining an ammonia removal column with a decomposition column equipped with a catalyst and a heat generation detection unit that generate heat by contacting with oxygen such as nickel. Was completed. That is, the present invention is a decomposition tube connected to an ammonia gas supply pipe, filled with a catalyst for ammonia decomposition, and connected to a decomposition tube provided with a heater and an outlet side of the decomposition tube. An ammonia removing cylinder and a bypass pipe branching from the ammonia gas supply pipe and connected to the removing cylinder are provided, and among the catalysts for ammonia decomposition, at least the upstream side of the gas depends on the presence of oxygen. The ammonia decomposing apparatus is characterized in that it is filled with a catalyst that generates heat and a thermometer for detecting heat generation is attached to the filled portion of the catalyst. INDUSTRIAL APPLICABILITY The apparatus of the present invention is applied to the decomposition and purification of ammonia alone or ammonia mixed with nitrogen, hydrogen, a rare gas, etc. (hereinafter collectively referred to as ammonia gas).

In the present invention, the ammonia decomposition cylinder is a cylinder having an inlet and an outlet for gas, usually a cylindrical cylinder filled with a catalyst for ammonia decomposition, and its inlet is an ammonia gas supply pipe. Connected with. The decomposition cylinder has corrosion resistance to ammonia, and there is no particular limitation on the material as long as it can withstand a high operating temperature of, for example, about 1000 ° C., but generally a metal having corrosion resistance is used. For example, stainless steel, Inconel (INCO Co., nickel-chromium alloy) and the like are preferable in terms of good property and availability. The decomposition cylinder may be one cylinder filled with a catalyst for decomposing ammonia, and
A plurality of cylinders may be connected in series and each may be filled with a catalyst for decomposing ammonia, but usually one cylinder is filled with a catalyst.

In the present invention, the decomposition cylinder is filled with a catalyst for decomposing ammonia into nitrogen and hydrogen, and at least the upstream side of the gas generates heat due to the presence of oxygen (hereinafter referred to as exothermic catalyst). Is filled. The exothermic catalyst produces heat that can be detected by a thermometer even if oxygen is present at a concentration sufficiently lower than the lower limit (about 5%) of the oxygen concentration that forms an explosive mixture with hydrogen generated by decomposition. Examples thereof include nickel-, iron- and copper-based catalysts and the like.Usually, an inorganic carrier such as alumina, silica, silica-alumina, aluminosilicate, diatomaceous earth, etc. Is 5 to 50 wt
%, Preferably 10 to 50 wt%. Among these, nickel-based catalysts have high decomposition efficiency of ammonia, and are sensitive to the presence of low-concentration oxygen such as 500 to 1000 ppm to trap oxygen and generate remarkable heat at the same time. Particularly preferred.

In the present invention, the catalyst for decomposing ammonia may be an exothermic catalyst as a whole including the downstream side, and whether or not the downstream side has a small heat generation even if it contacts oxygen. A catalyst that generates almost no heat (hereinafter referred to as a non-heat generating catalyst) may be filled. Non-exothermic catalysts are mainly noble metal-based catalysts such as platinum, palladium and ruthenium. Platinum, palladium or ruthenium or the like is added to the above-mentioned inorganic carrier such as α-alumina or γ-alumina with respect to the entire catalyst. It is supported so as to be about 1 to 5 wt%. When using both an exothermic catalyst and a non-exothermic catalyst, the amount of the exothermic catalyst that is filled upstream is the amount of heat that can be reliably detected by the thermometer even with the low concentration of oxygen as described above. However, for example, the filling length in the disassembling cylinder is usually 10 mm or more, preferably 30 mm or more.

The contact temperature between the ammonia gas and the catalyst is usually about 600 to 900 ° C. for both the exothermic catalyst and the non-exothermic catalyst, but among the non-exothermic catalysts, the ruthenium type catalyst is 300 to 500 ° C. Since it has excellent decomposition performance even at a relatively low temperature, that is, in a temperature range lower than the ignition temperature of a mixed gas of oxygen and hydrogen, it is more preferable in terms of safety and the like.

In the present invention, in order to monitor the presence (mixing) of oxygen, a thermometer is attached on the upstream side of the decomposition tube, that is, at the filling portion of the exothermic catalyst. It is preferable that the thermometer is attached at a position where the heat generation of the catalyst due to the reaction with oxygen can be accurately detected, and the detection end is inserted in the catalyst layer of the decomposition cylinder. There are no particular restrictions on the type of thermometer, but thermocouple type thermometers, resistance type thermometers, expansion type thermometers, etc., which have high sensitivity and high durability, can be used as they are or as protective tubes. It is inserted and attached. It is also possible to connect an alarm device and various control devices to the thermometer for the purpose of automatically monitoring the heat generation.In this case, the thermometer is a thermocouple type thermometer or resistance type thermometer. Etc. are suitable.

The gas outlet side of the decomposition tube is connected to the inlet of the ammonia removal tube, and at the same time, the inlet of this removal tube is also directly connected to the ammonia gas supply pipe to the decomposition pipe by a bypass pipe. . The removal column may be either dry type or wet type as long as it can surely remove ammonia in the gas, but a dry type removal column is generally preferable because of its simple structure and compact manufacturing of the entire apparatus.
The dry type removing agent is not particularly limited as long as it can remove ammonia gas efficiently, but activated carbon or an inorganic carrier carrying a copper (II) salt or the like is preferable, for example, , Copper sulfate as pentahydrate per 100 parts by weight of activated carbon such as palm shell charcoal and charcoal.
80 parts by weight, or, for example, alumina,
Ordinary catalyst carriers such as silica, silica-alumina and zirconia or heavy metal oxides such as copper oxide and manganese oxide are used as carriers, on which carbonates and nitrates as copper (II) salts,
Inorganic and organic salts such as sulfate, hydrochloride, formate, acetate and oxalate are added to 100 parts by weight of the above carrier.
Those supported in an amount of 3 to 80 parts by weight are preferable. The treatment temperature in the removal tube is usually room temperature, and heating or cooling is not particularly required.

During normal operation of the ammonia decomposing device, the decomposed gas discharged from the ammonia decomposing cylinder is guided to the removing cylinder, and the undecomposed ammonia remaining in the gas is removed. On the other hand, when oxygen is mixed in the ammonia gas supplied to the decomposition tube for some reason and heat generation due to the reaction between oxygen and the catalyst is detected, the supply of ammonia gas to the decomposition tube is stopped and the bypass pipe The ammonia is removed by the scavenger, and the danger of oxygen contamination in the decomposition gas is eliminated, and the emission of harmful gas to the atmosphere is prevented. It When using the removal cylinder filled with the dry type removing agent as described above, heating or cooling is not particularly required, and the decomposition cylinder is not only used in the residual ammonia in the decomposition gas discharged from the decomposition cylinder, but also in the case of an abnormality due to oxygen mixture. Ammonia that is directly led without passing through can be removed as it is within a predetermined time.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The apparatus of the present invention is illustrated in the drawings and will be described more specifically. FIG. 1 is a flow sheet of the ammonia decomposing apparatus of the present invention. In FIG. 1, an exothermic catalyst 4 is provided on the upstream side as a catalyst for decomposing ammonia, and an exothermic catalyst 4 is provided on the downstream side inside a cylindrical tube having a gas inlet 1 and an outlet 2 and a heater 3 disposed outside. The non-exothermic catalyst 5 is filled in each, the thermometer 6 is inserted in the filled portion of the exothermic catalyst 4, the alarm device 7 is connected to the thermometer 6 to form the ammonia decomposition tube 8, and the inlet of the decomposition tube 8 1 is connected to an ammonia gas supply pipe 10 via a valve 9, while the outlet 2 is connected to an inlet 15 of a removing cylinder 14 filled with an ammonia removing agent 13 by a connecting pipe 12 in which a valve 11 is interposed, Further, the inlet 15 is connected to the ammonia gas supply pipe 10 by a bypass pipe 16, and a valve 17 is provided in the middle of the bypass pipe 16 to form the ammonia decomposing apparatus of the present invention as a whole.

The ammonia decomposing device is operated while the decomposition tube 8 is heated to a predetermined temperature by the heater 3. For example, an ammonia-containing exhaust gas discharged from a semiconductor manufacturing process or the like enters a decomposition tube 8 via a supply pipe 10, a valve 9 and a gas inlet 1, and first, an exothermic catalyst 4 charged upstream and then non-heat generation. By coming into contact with the catalyst 5, most of the ammonia is decomposed into nitrogen and hydrogen.
Subsequently, this decomposed gas enters the removing cylinder 14 from the outlet 2 via the connecting pipe 12 and the inlet 15 in which the valve 11 is interposed,
While in contact with the remover 13, undecomposed ammonia remaining in the decomposed gas is surely removed, detoxified and discharged to the outside.

When oxygen is mixed in the ammonia gas due to fluctuations in conditions in the semiconductor manufacturing process and other abnormal causes, the oxygen in the gas entering the decomposition tube 8 reacts with the exothermic catalyst 4 such as nickel. At the same time as being trapped, heat is generated. This heat generation is detected by the thermometer 6 and transmitted to the alarm device 7. Here, the valve 9 at the inlet of the disassembling cylinder 8 and the valve 11 of the connecting pipe 12 are closed, and the bypass pipe 16
The valve 17 is opened, and the ammonia gas is introduced from the supply pipe 10 through the bypass pipe 16 directly to the removal cylinder 14, where it comes into contact with the removal agent 13 to remove ammonia, and is purified and discharged to the outside. In the above-mentioned device, it goes without saying that the alarm device 7 and each switching valve can be interlocked to automatically switch gases by mixing oxygen.

In the present invention, when the ammonia gas to be treated contains harmful components other than ammonia, it may be directly introduced into the decomposition tube, but if possible, it is common to remove the harmful components in advance. Is preferred. For example, when ammonia gas is an exhaust gas discharged from a semiconductor manufacturing process and contains silane as a harmful component, copper oxide is used as a silane removing agent on the upstream side of the decomposition tube.
It is desirable to provide a detoxifying cylinder filled with soda lime or the like, pass ammonia gas through the detoxifying cylinder to remove silane, and then introduce the ammonia decomposing tube.

[0017]

The device of the present invention has the following excellent features. Ammonia is efficiently decomposed and the remaining undecomposed ammonia is surely removed by the removing cylinder. Since the ammonia decomposition catalyst that generates heat by contacting with oxygen is used, it is possible to accurately detect the mixing of oxygen when an abnormality occurs due to heat generation. When oxygen is mixed, the supply of ammonia gas to the decomposition tube is stopped, and it is guided to the removal tube without heating, so there is no danger of ignition and it is safe, and ammonia is removed by the remover, which pollutes the environment. There is nothing to do. Oxygen detection does not require a complicated and expensive analyzer, the structure of the entire device is simple and compact, and it can be installed in a limited space such as a clean room of a semiconductor manufacturing factory.

[0018]

[Brief description of drawings]

FIG. 1 is a flow sheet of an ammonia decomposing device.

[Explanation of symbols]

 1, 15 Inlet 2 Outlet 3 Heater 4 Exothermic catalyst 5 Non-exothermic catalyst 6 Thermometer 7 Alarm device 8 Decomposition cylinder 9, 11, 17 Valve 10 Supply pipe 12 Communication pipe 13 Remover 14 Removal pipe 16 Bypass pipe

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location B01J 23/46 M 23/755

Claims (8)

[Claims] 1. A decomposition tube connected to an ammonia gas supply pipe, which is filled with a catalyst for ammonia decomposition and which is connected with a heater, and is connected to an outlet side of the decomposition tube. Of the catalyst for ammonia decomposition, an ammonia removing cylinder and a bypass pipe branched from the ammonia gas supply pipe and connected to the removing cylinder are provided.
An ammonia decomposing apparatus characterized in that at least an upstream side of the gas is filled with a catalyst that generates heat due to the presence of oxygen, and a thermometer for detecting heat generation is attached to a filling portion of the catalyst. 2. The decomposition apparatus according to claim 1, wherein the upstream side of the decomposition cylinder is filled with a catalyst that generates heat due to the presence of oxygen, and the downstream side is filled with a non-exothermic catalyst. 3. The decomposition apparatus according to claim 2, wherein the catalyst that generates heat due to the presence of oxygen is a nickel-based catalyst. 4. The decomposition apparatus according to claim 2, wherein the non-exothermic catalyst is a platinum, palladium or ruthenium-based catalyst. 5. The decomposition apparatus according to claim 1, wherein an alarm device is connected to a thermometer for detecting heat generation. 6. The decomposition apparatus according to claim 1, wherein the ammonia removing cylinder is a dry-type removing cylinder having a removing agent filled therein. 7. The decomposition apparatus according to claim 6, wherein the removing agent is an inorganic carrier or activated carbon supporting a copper (II) salt. 8. The decomposition apparatus according to claim 1, wherein the ammonia gas is an ammonia-containing exhaust gas discharged from a semiconductor manufacturing process.