JP2023147105A - Ammonia treatment method and device - Google Patents

Abstract

To provide a method and a device for detoxifying ammonia in exhaust gas by decomposing it to into water and nitrogen.SOLUTION: A method for detoxifying ammonia by decomposing it into water and nitrogen includes: adjusting a target gas containing NH3 and O2 to a prescribed temperature; making the target gas flow into a first catalyst layer 12 including a catalyst that promotes a chemical reaction in which NH3 is oxidized with oxygen; and making an exiting gas from the first catalyst layer flow into a second catalyst layer 15 including a catalyst which is composed to be capable of promoting a chemical reaction in which nitrogen or nitrogen oxide is generated by oxidizing N3 and a chemical reaction in which nitrogen is generated by oxidizing nitrogen oxide with NH3; and controlling at least one selected from a group consisting of a ratio of NH3 to O2 in the target gas flowing into the first catalyst layer, an amount of the target gas flowing into the first catalyst layer, and a temperature of the target gas flowing into the first catalyst layer so that HN3 is contained in the gas flowing into the second catalyst layer.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for making ammonia harmless and an apparatus for the same. More specifically, the present invention relates to a method of decomposing ammonia NH ₃ into water H ₂ O and nitrogen N ₂ to render it harmless, and an apparatus therefor.

In fields where ammonia is stored and used, such as ammonia fuel ships, ammonia transport ships, ammonia fuel storage bases, ammonia tanks for denitrification equipment in power plants, and ammonia cooling/refrigeration equipment, tanks and pipes are purged with nitrogen, etc. When this happens, a large amount of ammonia is emitted. In the treatment of ammonia-containing wastewater, such as food and drinking water manufacturing wastewater, chemical factory wastewater, plating wastewater, semiconductor component manufacturing wastewater, domestic wastewater, etc., a large amount of ammonia is discharged in, for example, a dispersion tower.

In order to prevent large amounts of ammonia, a harmful substance, from being released into the atmosphere, ammonia is decomposed and rendered harmless. Various proposals have been made regarding methods for making ammonia harmless.

For example, Patent Document 1 discloses a NH ₃ processing method for removing liquid ammonia (NH ₃ ) remaining in a tank, in which after the liquid NH 3 in the tank is vaporized, the generated NH ₃ gas contains oxygen. a step of mixing gases, a step of heating the _NH3 -containing gas mixed in the step, and a step of bringing the heated _NH3- containing gas into contact with a catalyst to decompose the _NH3 into nitrogen and water; A liquid remaining in a tank, comprising a step of measuring the gas temperature before and after the decomposition step with the catalyst, and controlling the mixing ratio of NH ₃ and oxygen-containing gas based on the measured value. Discloses a method for treating ammonia.

Patent Document 2 discloses a decomposition cylinder connected to an ammonia gas supply pipe, filled with a catalyst for decomposing ammonia, and provided with a heater, and connected to an outlet side of the decomposition cylinder. It is equipped with an ammonia removal cylinder and a bypass pipe branched from the ammonia gas supply pipe and connected to the removal cylinder. This invention discloses an ammonia decomposition apparatus characterized in that it is filled with a catalyst that generates heat, and that a thermometer for detecting heat generation is attached to a portion filled with the catalyst.

Patent Document 3 discloses a method for producing hydrogen using a catalyst that decomposes ammonia in a gas containing ammonia, oxygen, and hydrogen into hydrogen, in which a plurality of oxygen-containing gas inlets are provided in a reactor, and the oxygen is split. A method for decomposing ammonia is disclosed.

Japanese Patent Application Publication No. 2004-216300 Japanese Patent Application Publication No. 8-57256 Japanese Patent Application Publication No. 2010-215457

The following is an example of the oxidation reaction of ammonia with oxygen O ₂ that occurs when ammonia is decomposed in the presence of a catalyst.
4NH ₃ + 5O ₂ → 4NO + 6H ₂ O (1)
4NH ₃ + 7O ₂ → 4NO ₂ + 6H ₂ O (2)
2NH ₃ + 2O ₂ → N ₂ O + 3H ₂ O (3)
4NH ₃ + 3O ₂ → 2N ₂ + 6H ₂ O (4)
4NH ₃ + O ₂ → 4H ₂ + 2N ₂ + 2H ₂ O (5)

The following chemical reactions involve the products of the above oxidation reactions (nitrogen oxides, hydrogen).
4NH ₃ + 4NO + O ₂ → 4N ₂ + 6H ₂ O (6)
8NH ₃ + 6NO ₂ → 7N ₂ + 12H ₂ O (7)
2NH ₃ + NO + NO ₂ → 2N ₂ + 3H ₂ O (8)
2NH ₃ + 3N ₂ O → 4N ₂ + 3H ₂ O (9)
2NO + O ₂ → 2NO ₂ (10)
2H ₂ + O ₂ → 2H ₂ O (11)

The temperature at which the oxidation reaction of ammonia with oxygen tends to proceed varies somewhat depending on the catalyst used, but is generally said to be as follows. It is said that the chemical reaction represented by formula (4), which can change ammonia into harmless nitrogen and water, tends to proceed at, for example, 300 to 350°C. It is said that the chemical reactions represented by formulas (1) and (2) tend to proceed at temperatures of 350° C. or higher, for example. It is said that the chemical reaction represented by formula (4) hardly progresses below 300°C. Even if the temperature is strictly controlled at 300 to 350°C to promote the chemical reaction represented by formula (4), the chemical reaction represented by formula (1), formula (2), or formula (3) is small. It progresses quickly. The oxidation reaction of ammonia is exothermic. If a large amount of ammonia and oxygen are supplied to the catalytic reactor, the chemical reaction may proceed too much, creating hot spots in the catalyst layer and causing sintering and deterioration of the catalyst. Therefore, it is necessary to prepare a catalytic reactor that can withstand high temperatures or a catalytic reactor that has a high cooling capacity. When the ammonia concentration in the catalyst layer increases in an attempt to increase the amount of ammonia detoxified, the temperature of the catalyst layer increases, making side reactions more likely to occur, and reducing nitrogen oxides (NO, NO, etc.) contained in the exhaust gas of the catalytic reactor. ₂ , N ₂ O) tends to increase. Nitrogen oxides are harmful substances that affect the environment.

The object of the present invention is to prevent catalyst deterioration caused by hot spots, suppress the increase in nitrogen oxides contained in exhaust gas even when ammonia concentration is high, and decompose NH ₃ into H ₂ O and N ₂ so that they are harmless. The purpose of this invention is to provide a method and apparatus for the same purpose.

[1] Adjusting the gas to be treated containing NH ₃ and O ₂ to a predetermined temperature,
A gas to be treated whose temperature has been adjusted to a predetermined temperature is caused to flow into a first catalyst layer including a catalyst configured to promote a chemical reaction of oxidizing _NH3 with oxygen;
Next, the outflow gas from the first catalyst layer is used to promote a chemical reaction in which _NH3 is oxidized with oxygen to produce nitrogen or nitrogen oxides, and a chemical reaction in which _NH3 is oxidized with nitrogen oxides to produce nitrogen. into a second catalyst layer containing a catalyst configured to
The ratio of NH ₃ to O ₂ in the gas to be treated flowing into the first catalyst layer, the amount of gas to be treated flowing into the first catalyst layer so that the gas flowing into the second catalyst layer contains NH ₃ and adjusting and controlling at least one selected from the group consisting of the temperature of the gas to be treated flowing into the first catalyst layer.
A method of decomposing ammonia into nitrogen and water to make it harmless.

[2] The second catalyst layer includes a first stage catalyst layer containing a catalyst configured to promote a chemical reaction in which _NH3 is oxidized with nitrogen oxides to generate nitrogen, and _NH3 is oxidized with oxygen. a post-catalyst layer that includes a catalyst configured to promote a chemical reaction that generates nitrogen or nitrogen oxides and a chemical reaction that generates nitrogen by oxidizing _NH3 with nitrogen oxides. , the method described in [1].

[3] The method according to [1] or [2], further comprising flowing a gas to be treated containing NH ₃ and O ₂ into the second catalyst layer together with the outflow gas from the first catalyst layer.

[4] Allowing a portion of the gas to be treated to flow into the first catalyst layer to pass from the inlet side of the first catalyst layer to the outlet side of the first catalyst layer without touching the catalyst contained in the first catalyst layer. The method according to [1] or [2], further comprising:

[5] The catalyst contained in the first catalyst layer promotes the chemical reaction of oxidizing _NH3 with oxygen to generate nitrogen or nitrogen oxides and the chemical reaction of oxidizing _NH3 with nitrogen oxides to generate nitrogen. A catalyst configured to be able to oxidize _NH3 with oxygen, or a catalyst configured to be able to promote a chemical reaction that generates nitrogen or nitrogen oxides, [1] to [ The method described in any one of [4].

[6] A temperature adjustment mechanism configured to adjust the temperature of the gas to be treated containing NH ₃ and O ₂ to a predetermined temperature;
a first catalyst layer including a catalyst configured to allow a gas to be treated adjusted to a predetermined temperature to flow therein and promote a chemical reaction that oxidizes _NH3 ;
The outflow gas from the first catalyst layer flows in and promotes the chemical reaction of oxidizing _NH3 to produce nitrogen or nitrogen oxides and the chemical reaction of oxidizing _NH3 with nitrogen oxides to produce nitrogen. a second catalyst layer containing a catalyst configured to allow NH ₃ and O ₂ in the gas to be treated flowing into the first catalyst layer such that NH ₃ is contained in the gas flowing into the second catalyst layer; , the amount of the gas to be treated flowing into the first catalyst layer, and the temperature of the gas to be treated flowing into the first catalyst layer can be adjusted and controlled. including a control device,
A device that decomposes ammonia into nitrogen and water, rendering it harmless.

[7] The second catalyst layer includes a first catalyst layer including a catalyst configured to promote a chemical reaction that oxidizes _NH3 with nitrogen oxides to generate nitrogen, and a first catalyst layer that oxidizes _NH3 with oxygen. a post-catalyst layer that includes a catalyst configured to promote a chemical reaction that generates nitrogen or nitrogen oxides and a chemical reaction that generates nitrogen by oxidizing _NH3 with nitrogen oxides. , the device according to [6].

[8] The device according to [6] or [7], further comprising a first catalyst layer bypass pipe configured to allow the gas to be treated containing NH ₃ and O ₂ to bypass the first catalyst layer.

[9] The first catalyst layer allows a part of the gas to be treated to flow in to pass from the inlet side of the first catalyst layer to the outlet side of the first catalyst layer without touching the catalyst contained in the first catalyst layer. The device according to [6] or [7], which includes a through tube configured to be able to perform the same operation.

[10] The catalyst contained in the first catalyst layer promotes the chemical reaction of oxidizing _NH3 with oxygen to generate nitrogen or nitrogen oxides and the chemical reaction of oxidizing _NH3 with nitrogen oxides to generate nitrogen. A catalyst configured to be able to oxidize _NH3 with oxygen, or a catalyst configured to be able to promote a chemical reaction that generates nitrogen or nitrogen oxides, [6] to [ 9].

The method and apparatus of the present invention prevent catalyst deterioration caused by hot spots and suppress an increase in nitrogen oxides contained in exhaust gas even in situations where ammonia concentration increases, while converting _NH3 into _H2O . It can be decomposed into _N2 and rendered harmless.
When reaction heat is likely to be generated mainly on the entrance side of the catalyst layer, the progress of the chemical reaction in the first catalyst layer is suppressed as much as possible to prevent the first catalyst layer from reaching a high temperature that would cause catalyst deterioration. The gas to be treated is made to flow additionally into the second catalyst layer so that the gas flowing into the second catalyst layer contains _NH3 , and the ammonia oxidation reaction at high temperature in the first catalyst layer is performed. A chemical reaction to detoxify nitrogen oxides that may be generated using ammonia and a chemical reaction to detoxify undecomposed ammonia are performed in the second catalyst layer. This prevents catalyst deterioration due to hot spots, and suppresses an increase in nitrogen oxides contained in exhaust gas even if side reactions increase.

The method and device of the present invention are suitable for detoxifying large amounts of ammonia, and are suitable for detoxification of large amounts of ammonia, for example, ammonia fuel ships, ammonia transport ships, ammonia fuel storage bases, ammonia tanks for denitrification equipment in power plants, ammonia cooling and freezing equipment, etc. It can be used in fields that store and utilize ammonia-containing wastewater, such as food and drinking water production wastewater, chemical factory wastewater, plating wastewater, semiconductor parts manufacturing wastewater, and domestic wastewater.

1 is a diagram showing an example of an ammonia detoxification device used in the present invention. 1 is a diagram showing an example of an ammonia detoxification device used in the present invention. 1 is a diagram showing an example of an ammonia detoxification device used in the present invention. 1 is a diagram showing an example of an ammonia detoxification device used in the present invention. 1 is a diagram showing an example of an ammonia detoxification device used in the present invention. It is a figure showing an ammonia detoxification device used in a comparative example.

The method of the present invention decomposes ammonia into nitrogen and water to render it harmless.

In the method of the present invention, first, a gas to be treated containing NH ₃ and O ₂ is adjusted to a predetermined temperature.
The gas to be treated can be obtained, for example, by mixing a gas containing NH ₃ and a gas containing O ₂ . Examples of NH3 _- containing gas include ammonia fuel ships, ammonia transport ships, ammonia fuel storage bases, ammonia tanks for denitrification equipment in power plants, fields where ammonia is stored and used such as ammonia cooling and freezing equipment, food and drinking water. Gases discharged from fields that treat ammonia-containing wastewater such as manufacturing wastewater, chemical factory wastewater, plating wastewater, semiconductor component manufacturing wastewater, and domestic wastewater can be used. When NH ₃ is dissolved in a liquid, or when NH ₃ is adsorbed on a solid, it can be vaporized using a stripping tower, a vaporizer, or the like. For example, air can be used as the O ₂ -containing gas. The mixing ratio of NH ₃ and O ₂ and the controlled temperature can be set by the control method described below. Temperature adjustment can be performed by a known method, for example, using a temperature adjustment device such as a heater, a heat exchanger, or a cooler. As the heat transfer medium used to adjust the temperature of the gas to be treated, the gas flowing out from the second catalyst layer and/or the gas flowing out from the first catalyst layer may be used.

In the method of the present invention, a gas to be treated whose temperature has been adjusted to a predetermined temperature is allowed to flow into the first catalyst layer. The first catalyst layer includes a catalyst (hereinafter sometimes referred to as an ammonia oxidation catalyst) configured to promote a chemical reaction of oxidizing NH ₃ with oxygen.

The ammonia oxidation catalyst contained in the first catalyst layer is, for example, a chemical reaction that oxidizes _NH3 with oxygen to produce nitrogen oxides (e.g., formulas (1), (2), (3), etc.). A catalyst configured to be able to promote a chemical reaction that generates nitrogen by oxidizing _NH3 with oxygen (for example, formulas (4), (5), etc.) Mention may be made of catalysts.
Examples of the components of the ammonia oxidation catalyst include catalyst components containing noble metals such as platinum, iridium, rhodium, palladium, and ruthenium, and catalyst components in which the noble metals are supported on a carrier such as alumina, silica, zirconia, titania, and ceria. , catalyst components containing alloys, nitrides, carbides, oxides or composite oxides of transition metals such as iron, cobalt, nickel and molybdenum, catalyst components containing oxides of rare earth metals such as lanthanum, cerium and neodymium. , a catalyst component containing vanadium oxide, tungsten oxide, molybdenum oxide, manganese oxide, iron oxide, cobalt oxide, nickel oxide, perovskite type oxide, etc.

The first catalyst layer may be used to promote a chemical reaction (for example, formulas (6), (7), (8), etc.) that generates nitrogen by oxidizing _NH3 with nitrogen oxide, as necessary. A catalyst configured to reduce nitrogen oxides (hereinafter sometimes referred to as a nitrogen oxide reduction catalyst) may be included.

As a component of the nitrogen oxide reduction catalyst, for example, a catalyst containing an oxide of titanium (Ti) and at least one oxide selected from the group consisting of tungsten (W), vanadium (V), and molybdenum (Mo). components (mainly catalysts that reduce NO and NO ₂ ), catalyst components containing zeolite (catalysts that mainly reduce NO and NO ₂ ), SiO ₂ and Al ₂ O ₃ such as β-zeolite and mordenite. For example, a catalyst component formed by supporting an iron element on a carrier containing iron (catalyst that mainly reduces N ₂ O; see, for example, Japanese Patent Application Laid-Open No. 8-57262).

The amount of the nitrogen oxide reduction catalyst that can be contained in the first catalyst layer is not particularly limited, but the mass ratio of the nitrogen oxide reduction catalyst to the ammonia oxidation catalyst is preferably 99.99/0.01 or less, for example. is 99.9/0.1 or less, more preferably 99/1 or less. The lower limit of the mass ratio of the nitrogen oxide reduction catalyst to the ammonia oxidation catalyst is preferably 0.01/99.99, more preferably 0.1/99.9, and even more preferably 1/99.

The amount or space velocity of the gas to be treated flowing into the first catalyst layer can be adjusted by a control method described below.

The temperature in the first catalyst layer can be appropriately set depending on the characteristics, amount, etc. of the catalyst contained in the first catalyst layer.
When only an ammonia oxidation catalyst is used, the temperature in the first catalyst layer is preferably 150 to 300°C, more preferably 150 to 250°C. When using a mixed catalyst of an ammonia oxidation catalyst and a nitrogen oxide reduction catalyst, the temperature in the first catalyst layer is preferably 150 to 450°C, more preferably 200 to 400°C.
The temperature in the first catalyst layer is determined by the mixing ratio or each content of NH ₃ and O ₂ in the gas to be treated flowing into the first catalyst layer, the amount of gas to be treated flowing into the first catalyst layer, and the amount of gas flowing into the first catalyst layer. The temperature of the gas to be treated flowing into the first catalyst layer can be adjusted by using a heat insulating material, radiation fins, a jacket type heat exchanger, etc. that can be installed around the first catalyst layer.

The gas flowing out from the first catalyst layer may contain NH ₃ or may not contain NH ₃ . The amount of NH ₃ that may be contained in the gas flowing out from the first catalyst layer may be smaller than the amount of NH ₃ contained in the gas to be treated that has flowed into the first catalyst layer. The amount is preferably 20% by volume or less, more preferably 90% by volume or less, based on the amount of NH ₃ contained in the gas to be treated that has flowed into the catalyst layer.

The outflow gas from the first catalyst layer is then allowed to flow into the second catalyst layer. The second catalyst layer may be of a single-stage type, a two-stage type, or a three-stage type or more.

The single-stage second catalyst layer can promote the chemical reaction of oxidizing _NH3 with oxygen to generate nitrogen or nitrogen oxides and the chemical reaction of oxidizing _NH3 with nitrogen oxides to generate nitrogen. It includes a catalyst configured as follows. The catalyst included in the single-stage second catalyst layer may include, for example, a mixture of the ammonia oxidation catalyst and the nitrogen oxide reduction catalyst described above. The ratio of the ammonia oxidation catalyst to the nitrogen oxide reduction catalyst in the single-stage second catalyst layer is not particularly limited as long as the problems of the present invention can be solved. The mass ratio of the nitrogen oxide reduction catalyst to the ammonia oxidation catalyst is, for example, preferably 0.01/99.99 to 99.99/0.01, more preferably 0.1/99.9 to 99.9/0. .1, more preferably 1/99 to 99/1.

The two-stage second catalyst layer is configured to accelerate the chemical reaction of oxidizing _NH3 with nitrogen oxide, preferably nitrous oxide ( _N2O ) to produce nitrogen. A front catalyst layer containing a catalyst, a chemical reaction in which _NH3 is oxidized with oxygen to produce nitrogen or nitrogen oxides, and _NH3 is converted into nitrogen oxides, preferably nitrogen monoxide (NO) or nitrogen dioxide ( _NO2 ). and a latter catalyst layer including a catalyst configured to promote a chemical reaction that oxidizes to produce nitrogen. The catalyst included in the front catalyst layer may include, for example, the nitrogen oxide reduction catalyst described above. The catalyst included in the latter stage catalyst layer may include, for example, a mixture of the ammonia oxidation catalyst and nitrogen oxide reduction catalyst described above. The ratio of the ammonia oxidation catalyst to the nitrogen oxide reduction catalyst in the two-stage second catalyst layer is not particularly limited as long as the problems of the present invention can be solved. The mass ratio of the nitrogen oxide reduction catalyst to the ammonia oxidation catalyst is, for example, preferably 0.01/99.99 to 99.99/0.01, more preferably 0.1/99.9 to 99.9/0. .1, more preferably 1/99 to 99/1.

The temperature in the second catalyst layer (in the case of a two-stage type, each temperature in the first stage catalyst layer and the second stage catalyst layer) is the temperature of the catalyst contained in the second catalyst layer (in the case of a two-stage system, the first stage catalyst layer and the second stage catalyst layer). It can be set as appropriate depending on the characteristics, amount, etc. of each catalyst contained in the catalyst.
The temperature in the single-stage second catalyst layer is preferably 250 to 450°C, more preferably 300 to 400°C.
The temperature in the first catalyst layer of the two-stage second catalyst layer is preferably 250 to 450°C, more preferably 300 to 400°C.
The temperature in the latter catalyst layer of the two-stage second catalyst layer is preferably 250 to 450°C, more preferably 300 to 400°C.
The temperature in the second catalyst layer is determined by the amount of gas flowing into the second catalyst layer, the temperature of the gas flowing into the second catalyst layer, nitrogen oxides, ammonia and/or The amount of oxygen can be adjusted by adjusting the amount of oxygen, heat insulating material, heat radiation fins, jacket heat exchanger, etc. that can be installed around the second catalyst layer.

In the single-stage second catalyst layer, the temperature of the gas flowing into the second catalyst layer can be adjusted to a predetermined temperature before flowing into the second catalyst layer, if necessary.
In the two-stage second catalyst layer, if necessary, the gas flowing into the first catalyst layer may be adjusted to a predetermined temperature before flowing into the first catalyst layer, and/or the gas flowing into the second catalyst layer may be adjusted to a predetermined temperature. The temperature can be adjusted to a predetermined value before flowing into the latter stage catalyst layer.
The temperature adjustment of the gas flowing into the second catalyst layer or the temperature adjustment of the gas flowing into the first catalyst layer and/or the second catalyst layer can be performed by a known method, such as using a heater, a heat exchanger, a cooling device, etc. This can be done using a temperature control device such as a container. The gas to be treated may be used as a heat transfer medium used to adjust the temperature of the gas flowing into the second catalyst layer or the temperature of the gas flowing into the first catalyst layer and/or the second catalyst layer.

The gas flowing into the second catalyst layer (in the case of a two-stage type, the first stage catalyst layer) is made to contain NH ₃ . In order to make the gas flowing into the second catalyst layer (the first catalyst layer in the case of a two-stage type) contain NH ₃ , for example, NH ₃ and O ₂ are contained together with the gas flowing out from the first catalyst layer. additionally allowing the gas to be treated to flow into the second catalyst layer, and allowing a portion of the gas to be treated to flow into the first catalyst layer from the inlet side of the first catalyst layer without touching the catalyst contained in the first catalyst layer; The reaction conditions in the first catalyst layer may be adjusted such that NH ₃ is included in the gas flowing out from the first catalyst layer.

In the method of the present invention, the amount or ratio of NH ₃ and O ₂ contained in the gas to be treated flowing into the first catalyst layer, so that NH ₃ is contained in the gas flowing into the second catalyst layer, The method includes adjusting and controlling at least one selected from the group consisting of the amount of the gas to be treated flowing into the catalyst layer and the temperature of the gas to be treated flowing into the first catalyst layer. In addition to these, the amount of gas to be treated that is additionally introduced into the second catalyst layer, the temperature of the gas to be treated that is additionally introduced into the first catalyst layer, or the average temperature of the first catalyst layer may be adjusted and controlled. I can do it.
This control includes temperature and/or ammonia concentration on the inlet side of the first catalyst layer, temperature and/or ammonia concentration on the outlet side of the first catalyst layer, temperature and/or ammonia concentration on the outlet side of the second catalyst layer, etc. It is preferable to measure and perform the measurement based on those measured values.
Temperature and/or ammonia concentration can be measured by known instruments. In addition to temperature and ammonia concentration, NO concentration, NO ₂ concentration, N ₂ O concentration, O ₂ concentration, etc. can be further measured and control can be performed by taking these measured values into consideration.

The amount of NH ₃ contained in the gas flowing into the second catalyst layer is preferably at least a sufficient amount to reduce nitrogen oxides that may be generated in the first catalyst layer. Since nitrogen oxides may also be generated in the second catalyst layer, it is more preferable that the amount is at least sufficient to reduce nitrogen oxides that may be generated in the first catalyst layer and the second catalyst layer. On the other hand, since it is desired that the gas flowing out from the second catalyst layer does not substantially contain _NH3 and nitrogen oxides, the amount of _NH3 contained in the gas flowing into the second catalyst layer is It is preferable that the amount of NH ₃ remaining after subtracting the amount of NH ₃ required for the reduction of the substance is equal to or less than the amount that can be decomposed in the second catalyst layer.

Hereinafter, the apparatus of the present invention will be explained with reference to the drawings.
(first form)
The apparatus of the present invention shown in FIG. 1 for decomposing ammonia into nitrogen and water to render it harmless includes a temperature control mechanism, a first catalyst layer 12, a second catalyst layer 15, and a control device 17.

The temperature adjustment mechanism is configured to be able to adjust the temperature of the gas to be treated containing NH ₃ and O ₂ to a predetermined temperature. In FIG. 1, a first heat exchanger 9 and a heater 10 are provided, which are configured to perform heat exchange between the gas to be treated and the second catalyst layer exhaust gas.
The gas to be treated containing NH ₃ and O ₂ is obtained by mixing NH ₃ -containing gas A and O ₂ -containing gas B in a mixer 5 .
The supply amounts of NH ₃ -containing gas A and O ₂ -containing gas B can be adjusted by the opening degree of each control valve. The amount of the second catalyst layer exhaust gas supplied to the first heat exchanger 9 can be adjusted by the opening degree of the control valve installed in the first heat exchanger bypass pipe 3. You can adjust the amount of heat. If the first heat exchanger 9 alone can adequately control the temperature, there is no need to provide the heater 10.

The first catalyst layer 12 includes a catalyst configured such that a gas to be treated whose temperature is adjusted to a predetermined temperature flows thereinto to promote a chemical reaction of oxidizing NH ₃ with oxygen. The catalyst configured to be able to promote the chemical reaction of oxidizing _NH3 with oxygen is as described above. The first catalyst layer 12 may include a catalyst configured to promote the chemical reaction of oxidizing NH ₃ with nitrogen oxides, if necessary.
The amount of gas to be treated flowing into the first catalyst layer can be adjusted by the opening degree of the control valve installed in the first catalyst layer inflow pipe 2 or the opening degree of the control valve installed in the first catalyst layer bypass pipe 1. In order to stably perform the chemical reaction in the first catalyst layer 12, the amount of the gas to be treated that flows in through the first catalyst layer inflow pipe 2 is determined based on the amount of gas to be treated that flows in through the first catalyst layer bypass pipe 1. Preferably, the amount remains substantially constant even if the amount changes.

The second catalyst layer 15 is configured to be able to promote the chemical reaction of oxidizing _NH3 to produce nitrogen or nitrogen oxides and the chemical reaction of oxidizing _NH3 with nitrogen oxides to produce nitrogen. Contains a catalyst. As described above, a catalyst configured to be able to promote a chemical reaction that oxidizes _NH3 to generate nitrogen or nitrogen oxides and a chemical reaction that oxidizes _NH3 with nitrogen oxides to generate nitrogen is used. belongs to. The apparatus shown in FIG. 1 is configured such that the gas to be treated flowing in through the first catalyst layer bypass pipe 1 and the gas flowing out from the first catalyst layer 12 flow into the second catalyst layer 15. A mixing tank may be provided to mix the gas to be treated flowing in through the first catalyst layer bypass pipe 1 and the gas flowing out from the first catalyst layer 12. The mixing tank may be provided with stirring means (for example, a static stirring device) to make the mixed gas more uniform. Although the mixing tank can be expected to have the effect of preventing the gas to be treated flowing in through the first catalyst layer bypass pipe from flowing back into the first catalyst layer, a check valve or the like may be separately provided.

The measurement mechanism measures physical property values necessary for monitoring the operating state of the device of the present invention. In the apparatus shown in FIG. 1, the temperature and/or ammonia concentration on the inlet side of the first catalyst layer, the temperature and/or The ammonia concentration and the temperature and/or ammonia concentration on the outlet side of the second catalyst layer can be measured. The measurement mechanism may be configured to be able to further measure NOx concentration, _O2 concentration, etc. in addition to temperature and ammonia concentration.

The control device 17 shown in FIG. 1 controls the ratio and/or amount of NH ₃ and O ₂ contained in the gas to be treated to flow into the first catalyst layer based on the measured value by the measurement mechanism. It is configured to be able to control the amount of gas to be treated, the temperature of the gas to be treated flowing into the first catalyst layer, and the amount of gas to be treated flowing into the second catalyst layer. The goal of the control in the controller 17 is to ensure that the gas flowing into the second catalyst layer contains NH 3 , preferably the gas flowing into the second catalyst layer contains NH ₃ and the gas flowing into the second catalyst layer contains NH ₃ . Preferably, the gas flowing into the second catalyst layer contains _NH3 , and the gas flowing into the second catalyst layer does not cause high temperature conditions such as hot spots to occur in the first catalyst layer, and the exhaust gas 13 substantially free of NOx and/or _NH3 .

In the apparatus shown in Fig. 1, in order to ensure that the gas flowing into the second catalyst layer contains NH ₃ , the opening of the control valve installed in the first catalyst layer inflow pipe 2 or the bypass of the first catalyst layer is controlled. A control device 17 instructs the opening degree of a control valve installed in the pipe 1. Although not shown in FIG. 1, the catalytic reactor 11 may have, for example, heat radiation fins, a jacket type heat exchanger, etc. in order to adjust each temperature in the first catalyst layer and the second catalyst layer. .

(Second form)
The device of the present invention shown in FIG. 2 for decomposing ammonia into nitrogen and water to render it harmless has the following features, except that a through pipe 1a is installed in the first catalyst layer instead of the first catalyst layer bypass pipe 1. It has the same configuration as the device shown in FIG. A part of the gas to be treated that has flowed into the catalytic reactor 11 through the first catalyst layer inflow pipe 2 passes through the through pipe 1a and is transferred to the first catalyst layer without touching the catalyst contained in the first catalyst layer. It passes from the inlet side to the outlet side of the first catalyst layer, and the remainder flows into the first catalyst layer, contacts the catalyst, causes a chemical reaction, and can be discharged from the first catalyst layer. This causes the gas flowing into the second catalyst layer to contain NH ₃ . Since the gas to be treated that flows in through the through pipe 1a is warmed by the heat generated by the chemical reaction in the first catalyst layer, the gas that flows into the second catalyst layer has few temperature variations.

(Third form)
The apparatus of the present invention shown in FIG. 3 for decomposing ammonia into nitrogen and water to render it harmless includes a reactor 11, a first reactor 11a provided with a first catalyst layer 12, and a second catalyst layer 15. A second heat exchanger 6 (an additional temperature control mechanism) is installed between the first reactor 11a and the second reactor 11b, and the measurement mechanism is connected to the second catalyst layer. The device has the same configuration as the device shown in FIG. 1 except that it is configured to further measure the temperature and/or ammonia concentration on the inlet side of the device. The second heat exchanger 6 is configured to be able to exchange heat between the gas to be treated and the gas scheduled to flow into the second catalyst layer. The amount of gas supplied to the second heat exchanger 6 can be adjusted by the opening degree of the control valve installed in the second heat exchanger bypass pipe 4, and the amount of heat exchanged in the second heat exchanger 6 can be adjusted. The environment for the chemical reaction in the second catalyst layer 15 can be adjusted by the second heat exchanger 6.

(Fourth form)
In the device of the present invention shown in FIG. 4, which decomposes ammonia into nitrogen and water and renders it harmless, the second catalyst layer is changed to a front catalyst layer 15a and a rear catalyst layer 15b, and the measuring mechanism is connected to the front catalyst layer 15a and the second catalyst layer 15b. The device has the same configuration as the device shown in FIG. 1, except that it is configured to further measure the temperature and/or ammonia concentration on each outlet side of the rear catalyst layer 15b. In the front catalyst layer 15a, a reduction reaction of nitrogen oxides with ammonia is mainly performed.

(Fifth form)
The apparatus of the present invention shown in FIG. 5 for decomposing ammonia into nitrogen and water to render it harmless includes a reactor 11, a first reactor 11a provided with a first catalyst layer 12 and a first catalyst layer 15a, It is divided into a second reactor 11b provided with a second stage catalyst layer 15b, and a second heat exchanger 6 (an additional temperature control mechanism) is installed between the first reactor 11a and the second reactor 11b, and the measurement mechanism is The device has the same configuration as the device shown in FIG. 1 except that it is configured to be able to measure the temperature and/or ammonia concentration on the inlet side of the rear catalyst layer 15b and the temperature and/or ammonia concentration on the outlet side of the rear catalyst layer 15b. be.

(Example of catalyst production)
Fine silica powder was added to the chloroplatinic acid solution, stirred, and then evaporated to dryness on a sand bath. The dried product was calcined in air at 550° C. for 2 hours. The obtained calcined product was pulverized to obtain a powder of 0.05 wt% Pt.SiO ₂ which is ammonia oxidation catalyst I.
Calcined titanium oxide, ammonium metatungstate, ammonium metavanadate, and oxalic acid were mixed into a paste. The resulting paste was granulated. The granules were dried and then calcined at 500°C for 2 hours. The obtained calcined product was pulverized to obtain a powder of Ti/W/V=91/5/4 (atomic ratio), which is a nitrogen oxide reduction catalyst.
Next, the ammonia oxidation catalyst I powder, the nitrogen oxide reduction catalyst powder, and water were mixed to obtain a slurry. The mass ratio of the ammonia oxidation catalyst I to the nitrogen oxide reduction catalyst was set to 1/99. A honeycomb-shaped carrier was immersed in the obtained slurry, and then the liquid was drained. Then, it is dried at 120°C and fired at 500°C for 2 hours to produce a chemical reaction in which _NH3 is oxidized with oxygen to produce nitrogen or nitrogen oxides, and _NH3 is oxidized with nitrogen oxides to produce nitrogen. A honeycomb catalyst I configured to promote chemical reactions was obtained.

Mordenite powder was added to the chloroplatinic acid solution, stirred, and then evaporated to dryness on a sand bath. The dried product was calcined in air at 550° C. for 2 hours. The obtained calcined product was pulverized to obtain a 0.5 wt % Pt mordenite powder, which was ammonia oxidation catalyst II.
Ammonia oxidation catalyst II powder, silica sol, and water were mixed to obtain a slurry. The mixing ratio of the ammonia oxidation catalyst II powder and the silica sol was such that SiO ₂ was 20% of the dry mass of the slurry. A honeycomb-shaped carrier was immersed in the obtained slurry, and then the liquid was drained. Thereafter, the Honeycomb Catalyst II was dried at 120°C and calcined at 500°C for 2 hours to promote the chemical reaction of oxidizing _NH3 with oxygen to produce nitrogen or nitrogen oxides. Obtained.

(Example)
The following test was conducted using the apparatus shown in FIG. 1 in which the honeycomb catalyst I was installed in the second catalyst layer and the honeycomb catalyst II was installed in the first catalyst layer.
The temperature of the first catalyst layer is controlled to be between 150 and 250°C, the ammonia removal rate in the first catalyst layer is 100%, and the temperature of the second catalyst layer is between 250 and 500°C. Then, a part of the gas to be treated consisting of 3% ammonia/97% air prepared in mixer 5 (average value of the value set by the control = about 60%) is transferred to the first catalyst layer via the first catalyst layer inlet pipe. The remaining gas to be treated flows into the catalytic reactor 11 via the first catalyst layer bypass pipe and is mixed with the gas flowing out from the first catalyst layer, and the resulting mixed gas is passed through the second catalyst layer. It was allowed to flow into the layer.
The gas flowing into the second catalyst layer contained, on average, 1.2% ammonia and several thousand ppm of by-product nitrogen oxides. The gas flowing out from the second catalyst layer maintained NOx concentration <10 ppm and _NH3 concentration <5 ppm. No hot spots that would cause sintering occurred in the first catalyst layer and the second catalyst layer.

(Comparative example 1)
The following test was conducted using the apparatus shown in FIG. 6 in which the honeycomb catalyst II was installed in the catalyst layer 12b.
The temperature at the inlet of the catalyst bed was controlled to be between 150 and 250°C and the removal rate of ammonia in the catalyst bed was 100%, and a cover made of 3% ammonia/97% air was prepared in the mixer 5. Process gas was allowed to flow into the catalyst bed. The gas flowing out from the catalyst layer contained several thousand ppm of by-product nitrogen oxides. No hot spots that would cause sintering occurred in the catalyst layer.

(Comparative example 2)
The following test was conducted using the apparatus shown in FIG. 6 in which the honeycomb catalyst I was installed in the catalyst layer 12b.
The gas to be treated consisting of 3% ammonia/97% air prepared in the mixer 5 was allowed to flow into the catalyst layer while controlling the gas flowing out from the catalyst layer to have a NOx concentration <10 ppm and a _NH3 concentration <5 ppm. Ta. The average temperature of the catalyst layer exceeded 500°C, and catalyst deterioration due to sintering was progressing at hot spots.

As described above, the method and apparatus of the present invention prevent catalyst deterioration caused by hot spots, suppress an increase in nitrogen oxides contained in exhaust gas even in situations where ammonia concentration increases, and reduce _NH3 can be decomposed into H ₂ O and N ₂ to render it harmless.

A: Ammonia
B: Air
1: First catalyst layer bypass pipe
1a: Through tube
2: First catalyst layer inflow pipe
3: First heat exchanger bypass pipe
4: Second heat exchanger bypass pipe
5: Mixer
6: Second heat exchanger
9: First heat exchanger
10: Heater
11: Catalytic reactor
11a: First catalytic reactor
11b: Second catalytic reactor
12: First catalyst layer
12b: Catalyst layer
13: Exhaust
14: Measuring instrument (thermometer/densitometer)
15: Second catalyst layer
15a: Front catalyst layer
15b: Later catalyst layer
17: Control device

Claims (10)

Adjusting the gas to be treated containing NH ₃ and O ₂ to a predetermined temperature,
A gas to be treated whose temperature has been adjusted to a predetermined temperature is caused to flow into a first catalyst layer including a catalyst configured to promote a chemical reaction of oxidizing _NH3 with oxygen;
Next, the outflow gas from the first catalyst layer is used to promote a chemical reaction in which _NH3 is oxidized with oxygen to produce nitrogen or nitrogen oxides, and a chemical reaction in which _NH3 is oxidized with nitrogen oxides to produce nitrogen. into a second catalyst layer containing a catalyst configured to
The ratio of NH ₃ to O ₂ in the gas to be treated flowing into the first catalyst layer, the amount of gas to be treated flowing into the first catalyst layer so that the gas flowing into the second catalyst layer contains NH ₃ and adjusting and controlling at least one selected from the group consisting of the temperature of the gas to be treated flowing into the first catalyst layer.
A method of decomposing ammonia into nitrogen and water to make it harmless. _The first catalyst layer includes a catalyst configured such that the second catalyst layer can promote a chemical reaction that oxidizes _NH3 with nitrogen oxides to generate nitrogen; or a second stage catalyst layer including a catalyst configured to promote a chemical reaction that generates nitrogen oxides and a chemical reaction that oxidizes NH ₃ with nitrogen oxides to generate nitrogen. The method described in 1. 3. The method of claim 1 or 2, further comprising flowing a gas to be treated containing _NH3 and _O2 into the second catalyst layer together with the outflow gas from the first catalyst layer. The method further includes passing a portion of the gas to be treated to flow into the first catalyst layer from the inlet side of the first catalyst layer to the outlet side of the first catalyst layer without touching the catalyst contained in the first catalyst layer. , the method according to claim 1 or 2. The catalyst contained in the first catalyst layer is a catalyst configured to promote a chemical reaction that oxidizes _NH3 with oxygen to produce nitrogen or nitrogen oxides, or oxidizes _NH3 with oxygen. Any one of claims 1 to 4, wherein the catalyst is configured to be able to promote a chemical reaction that produces nitrogen or nitrogen oxides and a chemical reaction that oxidizes _NH3 with nitrogen oxides to produce nitrogen. One of the methods mentioned above. a temperature adjustment mechanism configured to be able to adjust a gas to be treated containing NH ₃ and O ₂ to a predetermined temperature;
a first catalyst layer including a catalyst configured to allow a gas to be treated adjusted to a predetermined temperature to flow in and promote a chemical reaction of oxidizing _NH3 with oxygen;
Outflow gas from the first catalyst layer flows in and promotes the chemical reaction of oxidizing _NH3 with oxygen to produce nitrogen or nitrogen oxides and the chemical reaction of oxidizing _NH3 with nitrogen oxides to produce nitrogen. a second catalyst layer including a catalyst configured to allow the gas to flow into the first catalyst layer, and _NH3 in the gas to be treated flowing into the first catalyst layer so that the gas flowing into the second catalyst layer contains _NH3 ; At least one selected from the group consisting of the ratio of _O2 , the amount of gas to be treated flowing into the first catalyst layer, and the temperature of the gas to be treated flowing into the first catalyst layer can be adjusted and controlled. a configured control device;
A device that decomposes ammonia into nitrogen and water, rendering it harmless. _The first catalyst layer includes a catalyst configured such that the second catalyst layer can promote a chemical reaction that oxidizes _NH3 with nitrogen oxides to generate nitrogen; or a second stage catalyst layer including a catalyst configured to promote a chemical reaction that generates nitrogen oxides and a chemical reaction that oxidizes NH ₃ with nitrogen oxides to generate nitrogen. 6. The device according to 6. 8. The apparatus according to claim 6, further comprising a first catalyst layer bypass pipe configured to allow a gas to be treated containing _NH3 and _O2 to bypass the first catalyst layer. The first catalyst layer is configured so that a part of the gas to be treated flowing in can be detoured from the inlet side of the first catalyst layer to the outlet side of the first catalyst layer without touching the catalyst contained in the first catalyst layer. 8. The device of claim 6 or 7, comprising a through tube configured to. The catalyst contained in the first catalyst layer is a catalyst configured to promote a chemical reaction that oxidizes _NH3 with oxygen to produce nitrogen or nitrogen oxides, or oxidizes _NH3 with oxygen. Any one of claims 6 to 9, wherein the catalyst is configured to be able to promote a chemical reaction that produces nitrogen or nitrogen oxides and a chemical reaction that oxidizes _NH3 with nitrogen oxides to produce nitrogen. The device mentioned in one of the above.

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