JPH09276655A - Treatment of exhaust gas containing high concentration ammonia and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device capable of controlling/adjusting the concentration and temperature of ammonia guided into a catalytic layer and a treating method by which it is possible to decompose ammonia into nitrogen and water and not generate a nitrogen oxide using the device. SOLUTION: In a treating method for decomposing an exhaust gas containing enriched ammonia by catalytic oxidation, an exhaust gas is mixed with a gaseous oxidizing agent, then the concentration of ammonia is diluted to at least, 0.1% and not more than 2%, and the temperatures of the exhaust gas when introduced into a catalytic layer 14 range from 180 to 250 deg.C. Thus the exhaust gas is brought into contact with a catalyst. A gas for dilution should preferably be part of gas, exhausted from the catalytic layer 14, which is used after cooling and by circulation.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to highly concentrated ammonia obtained by separating and concentrating ammonia-containing wastewater discharged from the electric power industry, chemical industry, electronic industry, metal surface treatment industry, human waste treatment plant, etc. by a steam stripping method or the like. The present invention relates to a treatment method and treatment device for exhaust gas discharged as exhaust gas containing gas or exhaust gas directly containing high-concentration ammonia.

[0002]

2. Description of the Related Art As a method for treating exhaust gas containing a high concentration of ammonia having a concentration of about 5 to 20% discharged from an ammonia stripping method or the like, in the prior art, the ammonia concentration and the catalyst layer are adjusted so as not to generate nitrogen oxides. No adjustment is made to the temperature and the temperature of the gas to be treated. For example,
In JP-A-2-245285, the stripped ammonia-containing gas is heated to 250 to 350 ° C. and introduced into the catalyst layer. In this temperature range, in the exhaust gas containing high-concentration ammonia, the temperature further rises on the catalyst surface, the generation of nitrogen oxides remarkably occurs, and the treated gas cannot be directly discharged to the atmosphere. It was necessary to provide an absorption tower for absorbing oxides. Further, in JP-A-3-258388, the processing gas discharged from the catalyst layer is returned to the lower portion of the stripping tower and used as a carrier gas for stripping. However, ammonia is used so as to suppress the generation of nitrogen oxides. Since the concentration and the temperature of the gas to be treated are not adjusted, when high-concentration ammonia is introduced into the catalyst layer, the temperature in the catalyst layer rises due to the heat of oxidation reaction, which causes a large amount of nitrogen oxides. is there. In Japanese Patent Laid-Open No. 7-116650, the ammonia-containing gas discharged from the stripping tower is also catalytically oxidized, but this is not a method for suppressing the production of nitrogen oxides.

[0003]

When the high-concentration ammonia gas is introduced into the catalyst layer, the temperature of the catalyst layer rises due to the heat generated during the oxidation of ammonia, and the nitrogen oxide generation reaction is promoted. . In the conventional technique, it is necessary to attach a device for removing the generated nitrogen oxides, which directly leads to an increase in the cost of the treatment device for the high-concentration ammonia-containing gas. In addition, the oxidative decomposition of ammonia includes the following three reactions. That is, 1) NH ₃ +3/4/4 O ₂ −− → 1 / 2N ₂ + 3 / 2H ₂ O 2) NH ₃ + 5 / 4O ₂ −− → NO + 3 / 2H ₂ O 3) NH ₃ + 7 / 4O ₂ −− → NO ₂ + 3 / 2H ₂ O The higher the reaction temperature, the more accelerated the reactions 2) and 3). The present invention provides a method and apparatus for controlling and adjusting the concentration and temperature of ammonia in a gas to be treated introduced into a catalyst layer, which provides a situation where reaction 1) is selectively promoted, and 2).
It is an object to suppress the reactions of 3) and 3).

[0004]

The above-mentioned object of the present invention can be achieved by the following method and apparatus for treating exhaust gas containing high-concentration ammonia. (1) In a treatment method of catalytically oxidizing and decomposing an exhaust gas containing high-concentration ammonia, a gaseous oxidizing agent is mixed with the exhaust gas, and the ammonia concentration is diluted to 0.1% or more and less than 2%, and the diluted exhaust gas is mixed. The method for treating high-concentration ammonia-containing exhaust gas, which comprises contacting the catalyst in the catalyst layer at a temperature of 180 to 250 ° C. when introduced into the catalyst layer. (2) The method for treating a high-concentration ammonia-containing exhaust gas according to (1), wherein the gaseous oxidant is any one of air, oxygen-enriched air, and pure oxygen. (3) Since the temperature at the time of introducing the gas to be treated, which is obtained by diluting the exhaust gas containing high-concentration ammonia with the air oxidant into the catalyst layer, is 180 to 250 ° C., the gas to be treated is discharged from the catalyst layer. The method for treating exhaust gas containing high-concentration ammonia according to (1) above, wherein a gas containing an oxidant heated by another external heat source is used while performing heat exchange with the gas. (4) In order to set the temperature at which the gas to be treated is introduced into the catalyst layer to 180 to 250 ° C., a part of the catalyst layer exhaust gas is cooled and the gas is circulated to produce the high-concentration ammonia-containing exhaust gas. The method for treating high-concentration ammonia-containing exhaust gas according to (1) above, wherein the exhaust gas is mixed with the high-concentration ammonia-containing exhaust gas in order to dilute.

(5) A catalyst layer filled with a catalyst, an inlet pipe for introducing a gas to be treated into the catalyst layer, and an exhaust pipe provided with a gas-gas heat exchanger for exchanging heat between the exhaust gas for the catalyst layer and the diluting gas. A gas for dilution introduction in which the treated gas treatment system consisting of, a blower for introducing a dilution gas containing a gaseous oxidant, and a heater for heating the dilution gas are placed in communication by a dilution gas introduction pipe. System, the dilution gas introduction pipe is passed through a gas-gas heat exchanger that exchanges heat between the catalyst layer exhaust gas and the dilution gas, and the dilution gas is passed through the dilution gas heater. An apparatus for treating a high-concentration ammonia-containing exhaust gas, which is for introducing a gas and is connected upstream of the catalyst layer to an introduction pipe for introducing a gas to be treated into the catalyst layer. (6) A gas introducing pipe containing a gaseous oxidant and a diluting gas introducing pipe connected to a conduit for exhaust gas containing high-concentration ammonia.
A catalyst layer filled with a catalyst, an introduction pipe for introducing a gas to be treated into the catalyst layer, an exhaust pipe for introducing an exhaust gas from the catalyst layer,
A blower, a gas circulation pipe branching from the discharge pipe and connected to the dilution gas introduction pipe is provided, and a gas cooling heat exchanger is provided on at least one of the discharge pipe and the gas circulation pipe. Equipment for treating exhaust gas containing concentrated ammonia.

(7) The treated gas treatment system is provided with a catalyst layer filled with a catalyst and a high temperature gas booster for circulating the treated gas diluted with a diluting gas through a circulation pipe. A target gas introduction pipe provided upstream of the catalyst layer of the circulation pipe, downstream of the high-temperature gas booster, upstream of the dilution gas introduction pipe intake port, branched from the circulation pipe, and a valve A processing gas processing system comprising a processing gas discharge pipe provided with a gas-gas heat exchanger for exchanging heat between the catalyst layer exhaust gas and the dilution gas, and a blower for introducing the dilution gas also serving as a gaseous oxidant. A part of the conduit is passed through a gas-gas heat exchanger for exchanging heat between the exhaust gas for the catalyst layer and the diluent gas in order to preheat the diluent gas introduced before being connected to the circulation conduit. Dilution gas supply consisting of And a start-up bypass provided with a start-up heater between the gas inlet for dilution and the gas inlet for dilution of the circulation line. .

(8) The diluent gas supply line equipped with a blower for introducing a diluent gas that also serves as the gaseous oxidant passes through the gas-gas heat exchanger for heat exchange with the processing gas, and A heat exchange pipe for passing through the inside of the catalyst layer and forming a pipe line connected to the gas to be treated introduction pipe, and a portion of the pipe line passing through the inside of the catalyst layer for exchanging heat between the catalyst layer and the dilution gas. The treatment apparatus for high-concentration ammonia-containing exhaust gas according to (7) above.

The method for treating exhaust gas containing high-concentration ammonia according to the present invention comprises treating exhaust gas containing high-concentration ammonia with a diluent gas containing a gaseous oxidant so that the ammonia concentration becomes 0.1% or more and less than 2%. By diluting and adjusting the temperature of the gas introduced into the catalyst layer to 180 to 250 ° C., the NO _x generation amount in the catalyst layer can be maintained at a sufficiently low temperature, and ammonia can be decomposed in a stable state. It was achieved through research based on the finding of this.
That is, when the ammonia concentration in the gas to be treated is 2% or more, the catalyst layer temperature rises due to the heat of ammonia oxidation, and a high concentration of NO _x components is generated. Further, when the ammonia concentration is 0.1% or less, the problem of NO _x generation is eliminated, but the amount of heat of oxidation of ammonia is small, and therefore a large amount of external heating is required to proceed the decomposition of ammonia in the catalyst layer, Running costs are high. For this reason, the ammonia concentration in the gas to be treated is set to 0.1% or more and less than 2%, and in consideration of the progress of the reaction in the catalyst layer, the temperature of the gas to be introduced to the catalyst layer is set to 180 to 250. By adjusting the temperature to 0 ° C., the oxidation heat of ammonia can be efficiently used, and a high ammonia decomposition rate can be obtained in a stable state in a region where the amount of NO _x generated is small.

As the diluent gas of the present invention, it is possible to use air or a mixed gas of air and a circulating gas. When the ammonia concentration of the ammonia-containing gas is high, air is used as the diluent gas. However, it is necessary to heat a large amount of dilution air with a heat exchanger and a heater, which is disadvantageous in terms of cost. However, when the air is preheated by exchanging heat with the heated exhaust gas from the catalyst layer in a heat exchanger, or when a heat exchange pipe is provided in the catalyst layer and air is preheated through it, the heat cost is reduced. In particular, in the latter case, the catalyst layer can be cooled to suppress its temperature rise, exhaust gas having a higher ammonia concentration can be treated, and the ammonia-containing gas can be treated at a temperature close to the reaction temperature. Can be mixed with. Further, a part of the heated exhaust gas discharged from the catalyst layer is circulated,
If air of a gaseous oxidant is mixed with this and used as a diluting gas, there is an advantage that energy saving can be achieved because there is little heat loss because no additional heating device is required.

However, as described above, when a part of the exhaust gas is circulated, as a practical problem, the ammonia concentration in the diluted gas to be treated is 0.1% so that the reaction proceeds in the catalyst layer. Although the range is less than 2%, there is a problem that the temperature in the catalyst layer rises too much. In particular, in such a case where the exhaust gas whose temperature has risen is circulated and used, as a result, the heat of reaction accumulates in the catalyst layer, so the temperature in the catalyst layer rises too much. Therefore, the circulating gas needs to be cooled. For this purpose, it is preferable to pass a heat exchanger for cooling the gas, and such a heat exchanger is sometimes called a gas cooler. The cooling heat exchanger may be provided in the exhaust pipe through which the exhaust gas from the catalyst layer passes, or in the circulation pipe branched from the exhaust pipe, or in both.
When it is provided in the exhaust pipe, there is an advantage that the temperature of the exhaust gas to the outside is lowered and it is environmentally preferable.

The catalyst layer may take the form of a conventional packed reaction layer or honeycomb catalyst layer. As the catalyst, titanium oxide, zirconium oxide, alumina, cordierite, Fe, Co, Ni and C, which are effective for oxidative decomposition of ammonia, are used.
It is possible to use a metal-supported catalyst such as u, Pt, Ag, Mo, V, Mn or the like, or a pellet-shaped or spherical catalyst obtained by complex-oxidizing the metal oxide. A blower is used to send the gas, but this includes not only a fan type but also a compressor type.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The treatment of exhaust gas containing high-concentration ammonia according to the present invention will be described with reference to the apparatus shown in FIG. In FIG. 1, a sample ammonia gas 1 and dilution air 2 are introduced from the lower part of a reaction tank B provided with a catalyst layer A filled with a honeycomb catalyst, and the mixture gas and the catalyst layer are passed through the catalyst layer A. A is heated by a heater from the outside. Temperature measuring means (C for inlet and D for outlet) are respectively provided at the inlet and the outlet of the catalyst layer A to measure the inlet temperature and the outlet temperature and control the supply amounts of the sample ammonia gas 1 and the dilution air 2.
The sample ammonia gas 1 and the dilution air 2 are oxidatively decomposed while passing through the catalyst layer A, and are discharged out of the system as a processing gas 3 which is preferably composed of nitrogen gas and steam gas.

The apparatus shown in FIG. 6 is for explaining the treatment of the high-concentration ammonia-containing exhaust gas of the present invention when at least a part of the exhaust gas is circulated for use as a diluent gas. In FIG. 6, the exhaust gas 1 containing high-concentration ammonia is a line a for introducing ammonia.
The mixed gas with the circulating gas from the line g, which is a circulation pipe described later, is introduced into the catalyst layer A as the gas to be treated from the line b. The exhaust gas from the catalyst layer A passes through a line d which is an exhaust pipe, passes through a gas cooler K, and is cooled. External air is introduced into the gas cooler K for cooling. In the line d after the gas cooler K, air 2 which is a gaseous oxidant
Is introduced. After that, the line g is branched at the branch point k after passing through the blower H. A part of the cooled exhaust gas is branched to the line g, connected to the line a for introducing ammonia described above, and the circulating gas is mixed with the high-concentration ammonia-containing exhaust gas 1. The exhaust gas not circulated at the branch point k is released to the outside. In the above description, the location where the blower H is installed and the location where the dilution air 2 is introduced are determined in consideration of the gas distribution relationship, and the air 2 may be near the location where the circulating gas is mixed with the line a. The location shown in the figure is better due to the magnitude of the suction pressure. The structure and operation of the device of FIGS. 2 to 5 will be explained in the examples given below.

[0014]

【Example】

Example 1 With the simple apparatus shown in FIG. 1, the decomposition was performed using a gas formed from commercially available ammonia gas as the exhaust gas containing high-concentration ammonia. Ammonia gas 1 was mixed with dilution air 2 in the lower part of reaction tank B to adjust the ammonia concentration to 1%. The catalyst filled in the catalyst layer A is platinum on the honeycomb carrier.
A noble metal such as paradigm was carried, and the size was 30 mm and the height was 50 mm. The flow rate of the mixed gas of the dilution air 2 and the ammonia gas 1 is GHS.
The V was adjusted to 10,000 hr ^-1 . The catalyst and mixed gas were heated in an electric furnace (heater). The temperature of the electric furnace was controlled so that the inlet temperature became an appropriate temperature. Set the inlet temperature of the catalyst layer A, the outlet temperature and the ammonia decomposition rate corresponding thereto, it showed the production rate of the NO _x in Table 1. When the concentration of ammonia in the mixed gas is 1%,
In the temperature range of 250 ° C., ammonia can be decomposed with high efficiency, and the production rate of NO _x can be suppressed low.

[0015]

[Table 1]

Comparative Example 1 An ammonia decomposition experiment was conducted under the same conditions as in Example 1 except that the concentration of ammonia in the mixed gas of Example 1 was changed to 2%. The results are shown in Table 2. When the concentration of ammonia is high,
The surface temperature of the catalyst rises, promoting the production of NO _x ,
It was not possible to obtain a temperature condition in which the concentration of O _x was suppressed to a low level and a high ammonia decomposition rate was obtained.

[0017]

[Table 2]

Example 2 Assuming ammonia stripping using steam, catalytic oxidative decomposition of ammonia in the presence of water vapor was carried out using the apparatus shown in FIG. The device shown in FIG.
The structure and function are the same as those of the apparatus shown in FIG. 1 except that the steam 2 is blown together with the dilution air 2 and the ammonia gas 1 from the lower part of the reaction tank B. The concentration of water vapor 4 in the mixed gas is 39%, and the concentration of ammonia 1 is 1
%, And the air concentration was set to 60%. Catalyst and GHSV
Under the same conditions as in Example 1 and Comparative Example 1, an ammonia decomposition experiment was conducted. The results are shown in Table 3. It can be seen from Table 3 that, in the case of the present Example 2, the temperature of the catalyst layer 2 can be kept uniform in the presence of water vapor, and it is easy to suppress the production of NO _x . From the results of Example 2, it can be seen that the method for treating a high-concentration ammonia-containing exhaust gas of the present invention is effective for the high-concentration ammonia-containing exhaust gas containing a large amount of water vapor, which is discharged from the ammonia stripping apparatus.

[0019]

[Table 3]

Example 3 FIG. 3 shows an example of an apparatus used for carrying out catalytic oxidative decomposition of ammonia gas discharged from an ammonia stripping apparatus by the method for treating exhaust gas containing high-concentration ammonia according to the present invention. In FIG. 3, 15 through line a
Saturated steam containing ammonia at a concentration of 15% (composition: 15% ammonia, 85% steam) 360 Nm ³ /
Air is supplied at a flow rate of Hr (8000 Nm ³ / day) at 110 ° C., and is supplied to the catalyst layer A through the line b. On the other hand, the air 2 used as a diluent gas is compressed by the compressor E.
Room-temperature air is taken into the line f as a flow rate of 5,040 Nm ³ / Hr, preheated by heat exchange with the processing gas d via the heat exchanger F, enters the line g, and the air heater G moves to the line b. The temperature of the gas to be processed is raised to 180 to 220 ° C.

Diluted gas 2 heated from the air heater G and heated
Enters the line c and is uniformly mixed in the line b with the saturated steam containing the ammonia 1 sent through the line a, and the saturated steam containing exhaust gas containing the high concentration ammonia 1 from the line a is mixed with the ammonia concentration 1 Dilute to%. The flow rate and temperature of the gas in the line b are preferably 5,400 Nm ³ / Hr and 180 to 220 ° C. The ammonia-containing gas in the line b is oxidatively decomposed in the catalyst layer A, converted into nitrogen and water / detoxified, introduced into the heat exchanger F via the line d, cooled, and cooled as the process gas 3 via the line e. Can be released into the atmosphere.

Example 4 FIG. 4 shows another example of an apparatus used for carrying out catalytic oxidative decomposition of ammonia gas discharged from an ammonia stripping apparatus by the method for treating exhaust gas containing high-concentration ammonia according to the present invention. In FIG. 4, via line a,
Saturated steam containing 15% concentration of ammonia 1, which is the gas to be treated (composition is 15% ammonia and 85% steam), is sent at a flow rate of 360 Nm ³ / Hr (8000 Nm ³ / day) and a temperature of 110 ° C. Then, it is supplied to the catalyst layer A through the line b. The gas for diluting the saturated steam (exhaust gas) containing ammonia 1 to an ammonia concentration of about 1% or less is a mixed gas of the processing gas and heated air discharged from the catalyst layer A. The process gas for diluting the object to be processed is a high temperature gas booster H, a process gas take-out pipe e having a valve I, a heated air supply pipe h, and lines d, g, j having a line i having a heater J for start-up. The gas to be treated is diluted in the line b together with the heating air supplied from the heating air supply pipe h on the way through the circulation conduit consisting of c and b, and then returns to the catalyst layer A.

On the other hand, the air used as a diluting gas which also serves as a gaseous oxidant is taken into the line f by the compressor E at a flow rate of 600 Nm ³ / Hr by the compressor E, and heat-exchanged with the process gas via the heat exchanger F. Is preheated in, enters the line h (heated air supply pipe), and enters the circulation pipe line through which the dilution gas 2 circulates. The air flow rate of 600 Nm ³ / Hr supplied to this line f is 10,000 pp
It is an air flow rate containing three times the amount of oxygen necessary to oxidize ammonia in the gas to be treated of m. Ammonia concentration is about 1
The gas to be treated diluted to not more than 100% is supplied to the catalyst layer A via the line b and is oxidatively decomposed therein. The processing gas decomposed to an ammonia concentration of 10 ppm or less is introduced into the high temperature booster H via the line d. The high temperature gas booster H plays a role of circulating the processing gas in the system of the present invention. A part of the gas boosted by the high temperature booster H is taken out of the system through the operation of the valve I to a processing gas take-out pipe e having a valve I provided in the middle of the circulation line, and is used as an oxidant and a diluent gas. It exchanges heat with the air supplied as, and is discharged into the atmosphere after cooling.

On the other hand, the amount of the air 2 supplied as the oxidizing agent and as the diluent gas is sufficient to be in the range of 1 to 5 times the equivalent amount capable of completely oxidizing the ammonia 1 contained in the line a. The air 2 supplied as an oxidant and as a diluent gas is taken into the line f by the compressor E at a flow rate of 600 Nm ³ / Hr as room temperature air and heated by the heat exchanger F, and is fed through the line h to the circulation pipe. Introduced to the road. The heater J is provided in the bypass line i and is used only at the start-up.

Example 5 FIG. 5 shows another example of an apparatus used for carrying out catalytic oxidative decomposition of ammonia gas discharged from an ammonia stripping apparatus by the method for treating exhaust gas containing high-concentration ammonia according to the present invention. . The device shown in FIG.
Compared with the device shown in FIG. 4, the device is the same as the device shown in FIG. 4 except that the structure of the device for preheating "air supplied as an oxidizing agent or diluent gas" by a heat exchange method is different. An example of the device of the present invention and its function will be described with reference to FIG. In FIG. 5, saturated steam containing ammonia 1 at a concentration of 150,000 ppm (composition is 15% ammonia and 85% steam), which is the gas to be treated, is supplied through line a to 360 Nm ³ / Hr (8000 Nm).
The gas is supplied at a flow rate of ³ / day) at a temperature of 110 ° C. and is supplied to the catalyst layer A via line b. The gas that dilutes the saturated steam containing ammonia to an ammonia concentration of 1% or less is preheated by heat exchange with the processing gas via the heat exchanger F in the line a, and further passes through the line h to pass through the catalyst layer A. The air for oxidation and dilution preheated through the heat exchange passage K provided inside and the processing gas discharged from the catalyst layer A.

The processing gas discharged from the catalyst layer A is
A line d, a line g for branching a process gas take-out pipe e having a high-temperature gas booster H and a valve I, a line j provided with a line i provided with a heater J for start-up, and a circulation line consisting of a line c and a line b. Street catalyst layer A
Return to In the line b on the way back to the catalyst layer A through this circulation line, the mixed gas of the gas to be treated 1 and the dilution air 2 flowing into the catalyst layer A via the line a is uniformly mixed.

In the catalyst layer A, the gas to be treated is "as an oxidizing agent and as a diluting gas" introduced through the line h.
The heat of the supplied air 3 is exchanged, whereby the reaction heat due to the oxidation reaction generated from the gas to be treated 1 is removed, and the temperature of the catalyst layer A is constantly suppressed to around 200 ° C. By keeping the temperature in the catalyst layer A constant at around 200 ° C., generation of NO _{x in} the catalyst layer A is suppressed and deterioration of the catalyst is suppressed. The detoxified process gas is introduced into the high-temperature gas booster H through the line d, and is pressurized to a pressure at which the gas is circulated through the circulation pipe line. A part of the pressure-increased processing gas is discharged to the outside of the system by operating the valve I, and most of the processing gas is returned to the circulation pipe system passing through the line g. The extracted processing gas 3 is introduced into the heat exchanger F through the line e, cooled, and then released into the atmosphere. The processing gas returned to the circulation pipe system passing through the line g is used as a dilution gas for the high-concentration ammonia-containing gas. As in the case of the fourth embodiment, the bypass line i
The heater J provided in the
Then, the temperature of the catalyst layer A is heated up to around 200 ° C. which is an ideal reaction temperature.

Example 6 A high-concentration ammonia-containing exhaust gas was treated using the apparatus shown in FIG. In the apparatus shown in FIG. 6, the gas cooler K is provided in the line d, which is an exhaust pipe that guides the exhaust gas from the catalyst layer A as described above, to cool the circulating gas. Ammonia concentration 20%, steam 8 from line a
Exhaust gas containing 0% high concentration ammonia is 100 ° C, 2.1
The gas is introduced at a flow rate of N · L / min, and a circulating gas at 182 ° C. is introduced at a flow rate of 119 N · L / min from the line g which is a circulation pipe, and mixed to produce a gas to be treated at 180 ° C. of 121.1N. Enter the catalyst layer A at a flow rate of liter / min. At the time of start-up, the start-up heater J consisting of an electric heater is passed for heating, but after the process is started, the start-up heater J
It does not pass through.

The catalyst layer A is a catalyst chamber consisting of two layers, a layer filled with 2.4 liters of Fe / Mn pellets and a layer provided with 1.5 liters of Pt honeycomb, and the gas to be treated is contained in the catalyst layer A. As the oxidative decomposition of ammonia occurs, the temperature rises and the gas is discharged to the line d as 217 ° C. exhaust gas.
This exhaust gas is guided to a gas cooler K, and is heat-exchanged with air sent by a cooling fan at a flow rate of 20 ° C. and a flow rate of 500 Nl / min to be cooled to a temperature of 190 ° C. Air having a temperature of 20 ° C. is used as a gaseous oxidant from the line h in the exhaust gas.
It is introduced at a flow rate of 5 to 7.5 N · liter / min, and the mixed gas is sucked and sent by a circulation fan H. Although this gas has a flow rate in the range of 124.5 to 128.5 N · liter / min, it is branched into two, and one of the branched gas flows is 121.1 N · liter / min.
It is circulated to mix with the exhaust gas containing high-concentration ammonia as a circulating gas at a flow rate of min. The remaining branch gas flow is 5.5 to 9.5 N · liter / min.
Is exhausted at a flow rate of. By such a treatment, an ammonia decomposition rate of 99.9% or more is obtained, and NO in exhaust gas is
_{The x} concentration could be suppressed to 30 ppm or less. that's all,
According to the present invention, it is possible to decompose the high-concentration ammonia-containing gas with high efficiency, economically and safely while suppressing the deterioration of the catalyst by the method as described in the examples.

[0030]

As described above, in the case of decomposing a high-concentration ammonia-containing gas, the conventional undiluted method raises the temperature in the catalyst layer and increases the amount of NO _x generated, and further, the catalyst due to high temperature is used. Is severely deteriorated. According to the present invention,
0.1% with process gas and air circulating ammonia concentration
By diluting it to less than 2%, preferably 0.1 to 1%, and setting the temperature of the gas to be treated to 180 to 250 ° C., the high-concentration ammonia-containing gas can be decomposed with high efficiency, economically and safely. And the life of the catalyst can be extended.

[Brief description of drawings]

FIG. 1 High temperature of exhaust gas containing high-concentration ammonia according to the present invention
It is an explanatory view showing an example of a catalytic oxidation treatment method.

FIG. 2 is a schematic view of an apparatus that performs catalytic oxidative decomposition when water vapor is present in exhaust gas containing high-concentration ammonia.

FIG. 3 shows a schematic diagram of an apparatus used to perform catalytic oxidative decomposition of ammonia gas discharged from an ammonia stripping apparatus.

FIG. 4 shows a schematic diagram of another example of an apparatus used to carry out catalytic oxidative decomposition of ammonia gas discharged from an ammonia stripping apparatus.

FIG. 5: Dilution air is heat-exchanged in a catalyst layer,
FIG. 1 shows a schematic diagram of an apparatus used for performing catalytic oxidative decomposition of ammonia gas discharged from an ammonia stripping apparatus.

FIG. 6 is a flow sheet showing a method for treating exhaust gas containing high-concentration ammonia according to the present invention, in which exhaust gas from a catalyst layer is cooled and circulated as a diluent gas.

[Explanation of symbols]

 1 Ammonia gas (gas to be treated) 2 Dilution air 3 Treatment gas 4 Steam 5 Cooling air A Catalyst layer B Reaction tank C Inlet thermometer D Outlet thermometer E Compressor F Heat exchanger H Booster I Valve J Start-up heater K gas cooler a line (sample supply pipe) b line (sample introduction pipe) c line d line e line f line g line h line i line j line k branch point

Claims (8)

[Claims] 1. A treatment method for catalytically oxidatively decomposing an exhaust gas containing a high concentration of ammonia, wherein the exhaust gas is mixed with a gaseous oxidant and the ammonia concentration is 0.1% or more and 2% or more.
Treatment of a high-concentration ammonia-containing exhaust gas, which is characterized in that the exhaust gas diluted to less than 1 is brought into contact with the catalyst in the catalyst layer at a temperature of 180 to 250 ° C. when the diluted exhaust gas is introduced into the catalyst layer. Method. 2. The gas oxidant is any one of air, oxygen-enriched air, and pure oxygen.
The method for treating exhaust gas containing high-concentration ammonia according to 1. 3. The temperature at which the gas to be treated obtained by mixing and diluting the gaseous oxidizer with the high-concentration ammonia-containing exhaust gas is introduced into the catalyst layer is 180 to 250 ° C. The process gas is heat-exchanged with the exhaust gas of the catalyst layer, and a gas containing an oxidant heated by another external heat source is used as the gas containing the gaseous oxidant. A method for treating exhaust gas containing concentrated ammonia. 4. In order to set the temperature at which the gas to be treated is introduced into the catalyst layer to 180 to 250 ° C., a part of the exhaust gas from the catalyst layer is cooled, and the gas is circulated to produce the high concentration ammonia. The method for treating a high-concentration ammonia-containing exhaust gas according to claim 1, wherein the high-concentration ammonia-containing exhaust gas is mixed with the high-concentration ammonia-containing exhaust gas to dilute the high-concentration ammonia-containing exhaust gas. 5. A catalyst layer filled with a catalyst, an introduction pipe for introducing a gas to be treated into the catalyst layer, and an exhaust pipe provided with a gas-gas heat exchanger for exchanging heat between the exhaust gas for the catalyst layer and the diluting gas. The system for processing a gas to be treated, a blower for introducing a diluting gas containing a gaseous oxidant, and a heater for heating the diluting gas are connected by a diluting gas introducing pipe to provide a diluting gas introducing system. The dilution gas introduction pipe is made to pass through a gas-gas heat exchanger that exchanges heat between the catalyst layer exhaust gas and the dilution gas, and the dilution gas has passed through the dilution gas heater. The apparatus for treating high-concentration ammonia-containing exhaust gas, characterized in that the exhaust gas is introduced into the catalyst layer and is connected upstream of the catalyst layer to an introduction pipe for introducing the gas to be treated into the catalyst layer. 6. A gas introducing pipe containing a gaseous oxidizing agent and a diluting gas introducing pipe connected to a high-concentration ammonia-containing exhaust gas conduit, a catalyst layer filled with a catalyst, and an introduction introducing a gas to be treated into the catalyst layer. A pipe, an exhaust pipe for guiding the exhaust gas from the catalyst layer, a blower, a gas circulation pipe branched from the exhaust pipe and connected to the dilution gas introduction pipe, and a gas is provided in at least one of the exhaust pipe or the gas circulation pipe. An apparatus for treating exhaust gas containing high-concentration ammonia, which is provided with a heat exchanger for cooling. 7. The processing gas treatment system comprises a catalyst layer filled with a catalyst and a high temperature gas booster for circulating the processing gas diluted with a diluting gas into a circulation pipe. A target gas introduction pipe provided upstream of the catalyst layer of the circulation pipe, downstream of the high-temperature gas booster, and upstream of the dilution gas introduction pipe intake, branched from the circulation pipe, the valve and the valve. A gas for heat exchange between the catalyst layer exhaust gas and the dilution gas-a treated gas treatment system comprising a treated gas exhaust pipe provided with a gas heat exchanger, and a blower for introducing a diluent gas also serving as a gaseous oxidant, A part of the pipe is passed through a gas-gas heat exchanger for exchanging heat between the exhaust gas of the catalyst layer and the diluting gas in order to preheat the diluting gas introduced before being connected to the circulation pipe. Diluent gas supply system consisting of And a start-up bypass having a start-up heater provided between the processing gas intake port and the diluting gas intake port of the circulation pipe. 8. The diluting gas supply line equipped with a blower for introducing a diluting gas that also serves as the gaseous oxidant passes through a gas-gas heat exchanger that exchanges heat with the process gas, and then the catalyst. A pipe that passes through the inside of the layer and is connected to the gas to be treated introducing pipe, and a portion of the pipe that passes inside the catalyst layer is a heat exchange pipe for exchanging heat between the catalyst layer and the diluting gas. The apparatus for treating exhaust gas containing high-concentration ammonia according to claim 7, characterized in that.