JPH10309437A - Ammonia decomposition treatment apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly efficient ammonia decomposition treatment apparatus for ammonia-containing waste gas in the treatment facility in a thermal power plant and the like. SOLUTION: In an ammonia decomposition treatment apparatus to treat a waste gas 1 containing ammonia, oxygen, and steam by two-step catalyst layers 2, 3 installed in a front stage and in a rear stage, a concentration sensor 4 to detect the concentration of nitrogen oxide in the treated gas and an injection means to previously divides and injects the part of the waste gas 1 to catalyst layer 3 in the rear stage are installed in the outlet side of the catalyst layer 3 in the rear stage and a control means 7 to divide and inject waste gas 1 as to keep the concentration of nitrogen oxide at a prescribed concentration by the concentration sensor 4 is also installed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel ammonia decomposition treatment apparatus which treats ammonia contained in an ammonia-containing exhaust gas to convert it into nitrogen gas and water and renders it harmless.

[0002]

2. Description of the Related Art As an ammonia-containing exhaust gas, for example, there are exhaust gases from thermal power generation equipment, human waste treatment equipment, sewage treatment equipment, food production equipment, coke oven gas production equipment, and the like.
Ammonia in these exhaust gases is a harmful substance to the environment and has a bad effect such as corroding the piping system of such equipment. Therefore, studies have been made on the removal of ammonia from the exhaust gases.

A system for removing ammonia in exhaust gas is disclosed, for example, in Japanese Patent Application Laid-Open No. 54-197857.
As described in the publication, ammonia in an ammonia stripping gas is oxidatively decomposed by a catalyst. It has been proposed that generated nitrogen oxides (NO, NO ₂ , N ₂ O) are reacted with residual ammonia with a reduction catalyst to convert them into N ₂ and H ₂ O as shown in the following formula.

[0004]

## EQU1 ## 12NH + 13O ₂ ⇒ 2N ₂ + 2NO + 2NO ₂ + 2N _{2
O + 18HO 4NH 3 + 6O 2} ⇒ 2NO + 2NO 2 + 6H 2 O 8NH 3 + 4NO + 2NO 2 + 2O 2 ⇒ 7N 2 + 12H 2
O 8NH ₃ + 4NO + 4NO ₂ + 2N ₂ O + O ₂ ⇒ 6N ₂ +
4N ₂ O + 12H ₂ O As described above, the conventionally used ammonia decomposition treatment method renders NO and NO ₂ harmless by residual ammonia, but does not remove N ₂ O. It is necessary to react ammonia with NO and NO ₂ in equimolar amounts. Therefore, there is a problem that ammonia (NH ₃ ) or NO, NO ₂ , N ₂ O is discharged if the concentration ratio of these two is unbalanced. In particular, there is a problem that N ₂ O is not removed by the reduction catalyst.

[0005]

As described above, the conventional ammonia decomposition treatment method has a problem that ammonia and nitrogen oxides are discharged due to its complicated structure.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide an ammonia decomposition treatment apparatus for efficiently detoxifying ammonia and nitrogen oxides.

[0007]

The gist of the present invention to achieve the above object is as follows.

[1] In an ammonia decomposition treatment apparatus for treating an exhaust gas containing ammonia, oxygen and water vapor in a two-stage catalyst layer comprising a former stage and a latter stage, the nitrogen oxide concentration of the processing gas is detected at the exit of the latter stage catalyst layer. A concentration sensor;
Injection means for splitting a part of the exhaust gas in advance and splitting and injecting it into the subsequent catalyst layer is provided, and control means capable of splitting and injecting the exhaust gas so that the nitrogen oxide concentration by the concentration sensor becomes a predetermined concentration is provided. Ammonia decomposition treatment equipment.

[2] In the ammonia decomposition treatment apparatus, the former stage of the two-stage catalyst layer is an ammonia oxidation catalyst, and the latter stage is a nitrogen oxidation-reduction catalyst.

[3] In the above ammonia decomposition treatment apparatus, the catalysts of the front and rear catalyst layers are composed of a catalyst containing Ti and Ag and one or more of Fe, Mn, Zn, Mo, V and W.

[4] The catalyst of the preceding catalyst layer contains Ti and Ag and one or more of Fe, Mn, Zn, Mo, V and W, and the catalyst of the latter catalyst layer is Ti and Mo,
The ammonia decomposition treatment apparatus is constituted by a catalyst containing at least one of V and W.

[0012]

DETAILED DESCRIPTION OF THE INVENTION
In an ammonia decomposition treatment apparatus for treating an exhaust gas containing ppm of ammonia, oxygen and water vapor in a two-stage catalyst layer comprising a former stage and a latter stage, a part of the exhaust gas is divided in advance at the entrance of the former stage catalytic layer and divided into the former stage and the latter stage. The injection is divided into the middle of the catalyst layer, and the concentration of nitrogen oxide at the outlet of the catalyst layer at the subsequent stage is detected by a sensor, and the injection amount of the exhaust gas to be split and injected at the subsequent stage is controlled based on the detected concentration.

In the pre-stage catalyst layer of the present invention, Ti and Ag
And an ammonia oxidation catalyst containing one or more of Fe, Mn, Zn, Mo, V, and W, and the resulting nitrogen oxide is reduced by a known catalyst layer comprising Ti, Mo, and V at the subsequent stage.

In the former catalyst layer, NH ₃ is oxidized and decomposed to form nitrogen oxides. However, the former catalyst layer of the present invention is also characterized in that the generation of N ₂ O is small. Since N ₂ O cannot be completely removed in the subsequent catalyst layer, it is necessary to suppress its generation in the former catalyst layer.

In the two-stage catalyst layer, the catalysts of the first and second catalyst layers include Ti and Ag, and Fe,
It may include one or more of Mn, Zn, Mo, V, and W.

The ammonia treatment apparatus according to the present invention includes a thermal power generation facility, a sewage treatment facility, a human waste treatment facility, an amine production facility,
Ammonia-containing exhaust gas discharged from food production equipment can be efficiently treated. The ammonia concentration is preferably in the range of 100 to 30,000 ppm.

Further, the catalyst of the two-stage catalyst layer may be 300 to
The catalyst activity can be recovered very easily only by heat treatment at 600 ° C.

The preferred embodiment of the catalyst used in the first catalyst layer of the ammonia decomposition treatment apparatus of the present invention is 100 to 3
It is a catalyst for oxidatively decomposing exhaust gas containing 0.00000 ppm of ammonia, equivalent amount or more of oxygen, and water vapor. As the oxide carrier, at least one of titania, alumina, silica, and zeolite is used. The catalytically active components formed on the surface layer are Ti and Ag, Fe, Zn, M
o, V, and W.

Next, a preferred embodiment of the ammonia decomposition catalyst preferably has a specific surface area of usually 10 to 500 m ² / g. In addition, there is a tendency that as the specific surface area is larger, the ammonia resolution is increased.

A feature of the ammonia decomposition treatment apparatus of the present invention is that exhaust gas is oxidatively decomposed in the first catalyst layer and then introduced into the second catalyst layer.

In the latter catalyst layer, the nitrogen oxide concentration at the outlet of the latter catalyst layer is detected by a sensor, and an ammonia-containing exhaust gas (raw material gas) slightly smaller than the amount corresponding to the nitrogen oxide concentration is dividedly injected into the latter catalyst layer. To prevent outflow of nitrogen oxides.

In the present invention, it is preferable that the first and second catalyst layers are combined with different types of catalysts. However, the first and second catalyst layers may be formed of the same type of catalyst.

The temperature at which the exhaust gas contacts the two-stage catalyst layer is 3
The temperature is from 00 to 600 ° C, preferably from 350 to 500 ° C.
Outside this temperature range, the performance of removing ammonia and the performance of removing nitrogen oxides in the exhaust gas are undesirably reduced.

The gas hourly space velocity of the exhaust gas in contact with the two-stage catalyst layer is preferably in the range of 1,000 to 100,000 h- ¹ . The pressure of the exhaust gas may be atmospheric pressure, but is not particularly limited.

The ammonia decomposition catalyst of the present invention recovers its catalytic activity by performing a heat treatment. After the recovery, the same ammonia removal performance as in the initial stage is obtained. In addition,
The heat treatment temperature is preferably from 300 to 600C.

The reaction of the ammonia decomposition catalyst in the first catalyst layer of the present invention is an oxidative decomposition reaction. In the latter catalyst layer, the reaction of nitrogen oxide is a reduction reaction with ammonia injected in portions.

The above NO and NO ₂ are mixed with ammonia at 1/1.
And in the presence of oxygen,

[0028]

## EQU2 ## It is converted into harmless N ₂ and H ₂ O such as 4NH ₃ + 4NO + O ₂ ⇒4N ₂ + 6H ₂ O.

[0029]

EXAMPLES The present invention will be described based on examples.

Embodiment 1 FIG. 1 is a schematic diagram of an ammonia decomposition treatment system according to an embodiment of the present invention.

Ammonia-containing exhaust gas 1 (NH ₃ concentration 10,
000 ppm, steam 40%, residual air) is introduced into the pre-stage catalyst layer 2 at a catalyst layer temperature of 350 ° C. In this case, the ammonia-containing exhaust gas 1 is divided in advance at the inlet of the pre-catalyst layer 2.

The ammonia-containing exhaust gas is applied to the pre-catalyst layer 2 (oxide carrier and Ag and Fe catalysts) at an SV of 20,000.
/ H, the oxidative decomposition reaction proceeds to produce nitrogen and H ₂ O in the product gas, 10 ppm of unreacted NH ₃ of air pollutants and nitrogen oxides (NO + NO ₂ :
(1,000 ppm, N ₂ O: 20 ppm).

The gas generated in the first catalyst layer 2 has a reaction temperature of 35
At 0 ° C., the latter catalyst layer 3 (Ti carrier, Mo and V catalyst)
At an SV of 20,000 / h.

A nitrogen oxide concentration sensor 4 is provided at the outlet of the latter catalyst layer 3, and NO and NO generated by the sensor are provided.
The amount of ammonia-containing exhaust gas, which is slightly smaller than the amount corresponding to NO ₂ (NH ₃ : 9500 ppm), is controlled by the control device 7 and dividedly injected from the injection port 5.

The nitrogen oxides in the product gas react with NH ₃ and are converted into H ₂ O and nitrogen. The exhaust gas after conversion is N
H ₃ : 5 ppm, NO + NO ₂ : 30 ppm, N ₂ O: 2
It becomes a detoxifying gas consisting of 5 ppm of residual air, and is released from the detoxifying gas outlet 6 into the atmosphere.

As described above, it can be seen that the present embodiment has a lower NH ₃ and NO ₂ concentration at the outlet of the latter catalyst layer, especially a lower N ₂ O concentration, than the comparative example described later.

[Comparative Example 1] Ammonia concentration 8000p
pm, a steam concentration of 30%, and an ammonia-containing gas consisting of residual air were introduced into an oxidation catalyst layer consisting of a Pt / Al ₂ O ₃ catalyst at a reaction temperature of 270 ° C. and passed through the catalyst layer at an SV of 10,000 / h to oxidize. As a result, unreacted NH ₃ : 2
50 ppm, NO + NO ₂ : 360 ppm, N ₂ O: 4,
900 ppm of residual air gas was obtained.

The NH ₃ was added to ammonia-containing gas to the gas: Passing in Fe / Al in the catalyst layer of the reaction temperature 350 ° C. containing ₂ O ₃ SV5,000 / h as 370ppm was reduced, NH _3: 20 ppm , NO + NO ₂ : 2
0ppm, N ₂ O: 4,500ppm process gas is obtained.

Example 2 10 g of a titania carrier powder crushed to 0.5 to 1.0 mm and fired at 500 ° C.
Was impregnated with a solution of 3.2 g of silver nitrate (AgNO ₃ ) dissolved in 10 ml of distilled water. This was dried at 120 ° C. for 1 hour and fired at 500 ° C. for 1 hour.

[0040] impregnated with the solution of ferrous _{(FeSO 4 · 7H 2 O)} 0.29g sulfuric acid in distilled water to Ag with titania carrier after firing. This is dried at 120 ° C. for 1 hour, 50
It was calcined at 0 ° C. for 2 hours to obtain a completed catalyst.

This catalyst is Ti-Ag-Fe,
/ Ag (molar ratio = 1 / 0.15) and Ti / Fe (molar ratio = 1 / 0.05). This catalyst is designated as A.

10 g of the calcined titania carrier powder was impregnated with a solution of 3.6 g of AgNO ₃ dissolved in 10 ml of distilled water, and dried and calcined in the same manner as described above.

The zinc sulfate Ag with titania carrier _{(ZnSO 4 · 7H 2 O)} 0.3g was impregnated with a solution prepared by dissolving in distilled water after firing, the same dry, and the finished catalyst calcined to. This catalyst is Ti-Ag-Zn, and Ti / Ag
(Molar ratio = 1 / 0.15), Ti / Zn (molar ratio = 1 / 0.1)
0.05). This catalyst is designated as B.

10 g of the calcined titania carrier powder was impregnated with a solution of 3.2 g of AgNO ₃ dissolved in 10 ml of distilled water, and dried and calcined in the same manner as described above.

[0045] 3 ammonium molybdate Ag with titania carrier after firing _{[(NH 4) 6 Mo 7 O} 24 · 5H 2 O ].
A solution prepared by dissolving 0 g in distilled water was impregnated, dried and calcined in the same manner as described above to obtain a finished catalyst. This catalyst is Ti-Ag-M
o, Ti / Ag (molar ratio = 1 / 0.15), Ti
/ Mo (molar ratio = 1 / 0.05). This catalyst is
And

10 g of the calcined titania carrier powder was impregnated with a solution of 3.2 g of AgNO ₃ dissolved in 10 ml of distilled water, and dried and calcined in the same manner as described above.

The baked titania carrier with Ag was impregnated with a solution of 0.12 g of ammonium vanadate (NH ₄ VO ₃ ) dissolved in distilled water, dried and calcined in the same manner as above to obtain a finished catalyst.

This catalyst is Ti-Ag-V, and Ti / Ag-V
Ag (molar ratio = 1 / 0.15), Ti / V (molar ratio = 1
/0.05). This catalyst is designated as D.

10 g of the calcined titania carrier powder was impregnated with a solution of 3.2 g of AgNO ₃ dissolved in 10 ml of distilled water, and dried and calcined in the same manner as described above.

The ammonium tungstate in Ag with titania carrier after firing _{[(NH 4) 10 W 1 2} O 41 · 5H 2 O ] 0.25g was impregnated with a solution prepared by dissolving in distilled water, the same drying , And calcined to obtain a finished catalyst. This catalyst is Ti-
Ag-V, Ti / Ag (molar ratio = 1 / 0.1
5), Ti / V (atomic ratio = 1 / 0.05). This catalyst is designated as E.

10 g of the calcined titania carrier powder
Was immersed in a solution of diamine nitroplatinum [Pt (NO ₃ ) ₂ (NH ₃ ) ₂ ] so that the Pt amount was 1% by weight. Drying and baking were performed as described above.

This catalyst is Pt-Al (known catalyst). This catalyst is referred to as Comparative Example Catalyst X.

The catalysts A to D and Comparative Example Catalyst X were installed at the center of a quartz reaction tube having an inner diameter of 19 mm and a length of 300 mm. As a simulated exhaust gas of ammonia, a gas obtained by mixing and diluting ammonia into helium was used. Was introduced into the quartz reaction tube and brought into contact with the catalyst.

The change in the ammonia concentration before and after the reaction was measured as an index of the catalyst performance. To measure ammonia concentration,
An ammonia detector tube (sulfuric acid absorbent) was used. The reaction conditions are as follows.

Ammonia concentration: 10,000 ppm, water vapor concentration: 40%, reaction temperature with remaining air: 400 ° C., gas hourly space velocity: 30,000 h- ¹ (supply amount of gas per unit time, unit catalyst volume), Catalyst amount: 10 ml.

Table 1 shows the performance of Catalysts A to E and Comparative Catalyst X. As is clear from the table, it can be seen that the catalysts A to E have a lower ammonia (NH ₃ ) concentration at the outlet of the catalyst layer than the catalyst X of the comparative example.

Although the NO and NO ₂ concentrations are higher than those of the catalyst X, they are removed by the latter catalyst layer. On the other hand, N ₂ O
Since is not removed in the latter catalyst layer, it is necessary to suppress the generation in the former catalyst layer, and it has been found that the catalysts A to E have a remarkable suppression effect as compared with the catalyst X.

[0058]

[Table 1]

[0059] Example 3 TiO ₂ slurry 10g and ammonium molybdate _{[(NH 4) 6 Mo 7 O} 24 · 4
0.78g and 120 ° C. The mixture slurry 0.21g of ammonium metavanadate (NH ₄ VO ₃₎ of H ₂ O],
It is dried for 2 hours and then calcined at 500 ° C. for 2 hours to obtain an oxide powder. 2% of graphite was added to this powder and kneaded well, and the mixture was tableted to a height of 5 mmφ × 5 mm by a tableting machine to obtain a finished catalyst.

In the experiment, this catalyst was used after being crushed to 0.5 to 1 mm. This catalyst is Ti-Mo-V,
Ti / Mo (molar ratio = 1 / 0.12) and Ti / V (molar ratio = 1 / 0.05). This catalyst is designated as F.

[0061] 0.78g and ammonium tungstate of TiO ₂ slurry 10g and ammonium molybdate mixed slurry 120 ° C. of 0.5g of _{[(NH 4) 10 W 12 O} 41 · 5H 2 O ], and dried for 2 hours, Next, the powder is fired at 500 ° C. for 2 hours to obtain an oxide powder. 2% of graphite was added to this powder and kneaded well, and the mixture was tableted to a height of 5 mmφ × 5 mm to obtain a finished catalyst.

In the experiment, the catalyst was used in an amount of 0.5 to 1.0 mm.
And used. This catalyst is Ti-Mo-W, and has Ti / Mo (molar ratio = 1 / 0.12), Ti / W
(Molar ratio = 1 / 0.05). This catalyst is designated G.

10 g of TiO ₂ slurry and iron nitrate (Fe
NO ₃ · 9H 120 mixed slurry of 1.84g of ₂ O)
C. for 2 hours and then calcined at 500.degree. C. for 2 hours to obtain an oxide powder. 2% of graphite was added to this powder and kneaded well, and the mixture was tableted to a height of 5 mmφ × 5 mm to obtain a finished catalyst.

In the experiment, this catalyst was used after being crushed to 0.5 to 1 mm. This catalyst is Ti-Fe, Ti
/ Fe (molar ratio = 1 / 0.12). This is designated as Comparative Example Catalyst Y.

The catalysts F and G and the comparative catalyst Y were placed at the center of the quartz reaction tube in the same manner as in Example 2, and a simulated ammonia exhaust gas and a simulated NO exhaust gas were mixed, and H ₂ O was added thereto. Then, gas was introduced into the quartz reaction tube and brought into contact with the catalyst.

Changes in the ammonia concentration and the NO concentration before and after the reaction were measured as indices of the catalyst performance. An ammonia detector tube (sulfuric acid absorbent) was used for measuring the ammonia concentration, and a NO detector tube (3.3'-dimethylbenzidine absorbent) was used for measuring the NO concentration. The reaction conditions are as follows.

Ammonia concentration: 960 ppm, NO concentration: 1,000 ppm, water vapor concentration: 40%, remaining air, reaction temperature: 400 ° C., gas space velocity: 30,000
h ~ ¹ , catalyst amount: 10 ml.

Table 2 shows the performance of the catalysts F and G and the catalyst Y of the comparative example. As is clear from Table 2, the catalysts F and G were compared with the comparative example catalyst Y in that the ammonia concentration, NO,
It was observed that the NO ₂ concentration and the N ₂ O concentration were low.

[0069]

[Table 2]

[0070]

According to the present invention, an ammonia-containing exhaust gas is introduced into a two-stage catalyst layer comprising a former stage and a latter stage to cause a decomposition reaction, and its concentration is detected by a nitrogen oxide sensor provided at an outlet of the latter catalyst layer. By dividing and injecting an ammonia-containing exhaust gas in an amount slightly smaller than the amount corresponding to the concentration into the subsequent catalyst layer, air pollutants such as ammonia and nitrogen oxides are efficiently removed, and environmental pollution by the exhaust gas is prevented. be able to.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an ammonia decomposition treatment system of the present invention.

[Description of Signs] 1 ... Ammonia-containing exhaust gas, 2 ... Pre-catalyst layer, 3 ... Post-catalyst layer, 4 ... Nitrogen oxide concentration sensor, 5 ... Injection port, 6 ...
Detoxifying gas outlet, 7 ... Control device.

 ──────────────────────────────────────────────────続 き Continued on front page (72) Inventor Yukio Murai 1-1-1 Uchikanda, Chiyoda-ku, Tokyo Inside Hitachi Plant Construction Co., Ltd. (72) Inventor Akio Tanaka 1-1-1, Uchikanda, Chiyoda-ku, Tokyo No. 14 Inside Hitachi Plant Construction Co., Ltd.

Claims (4)

[Claims] An ammonia decomposition treatment apparatus for treating an exhaust gas containing ammonia, oxygen and water vapor in a two-stage catalyst layer comprising a former stage and a latter stage, wherein a concentration for detecting a nitrogen oxide concentration of the processing gas at an exit of the latter stage catalyst layer. Control means for providing a sensor and injection means for splitting a part of the exhaust gas in advance and split-injecting it into a subsequent catalyst layer, and capable of split-injecting the exhaust gas so that the nitrogen oxide concentration by the concentration sensor becomes a predetermined concentration. An ammonia decomposition treatment apparatus, comprising: 2. The ammonia decomposition treatment apparatus according to claim 1, wherein the first stage of the two-stage catalyst layer is an ammonia oxidation catalyst, and the second stage is a nitrogen oxidation-reduction catalyst. 3. The catalyst of the front and rear catalyst layers is composed of a catalyst containing (1) Ti and Ag and (2) one or more of Fe, Mn, Zn, Mo, V and W. Ammonia decomposition treatment apparatus according to item 1. 4. The catalyst of the preceding catalyst layer comprises (1) Ti
And Ag, and (2) Fe, Mn, Zn, Mo, V, W
Wherein the catalyst of the latter catalyst layer comprises (3)
The ammonia decomposition treatment apparatus according to claim 1, comprising a catalyst containing Ti and (4) one or more of Mo, V, and W.