JPH0975915A - Treating system of ammonia nitrogen - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simple treating system in which gives no so large adverse effect on the operation of the whole system including a process to convert ammonia after stripping into nitrogen in one stage and a process to discharge ammonia nitrogen. SOLUTION: This system includes a process to add alkali to a waste water containing ammonia nitrogen to convert the ammonia nitrogen into ammonia, a process to strip ammonia from the waste water discharged from the process, a process to convert the obtd. ammonia into nitrogen by the reaction with oxygen in the presence of a solid catalyst, and a process to use the heat generated in the oxidation process. By this method, ammonia nitrogen of high concn. which is not practically treated by a single process of a conventional biological nitrification and denitrification process can be treated, and the treatment of this method is simple compared to an ammonia stripping multistage oxidation- reduction method. Especially, when this method is used in a thermal power station, a waste liquid containing high concn. ammonia nitrogen can be treated by the utilities within the range not to influence the total thermal balance in the power station or the operation of equipments.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system for treating ammonia nitrogen, and more particularly to a system for treating waste liquid containing ammonia nitrogen generated in a thermal power plant.

[0002]

2. Description of the Related Art Ammonia nitrogen is regulated as a BOD component, but when the concentration of this ammonia nitrogen is about 100 mg / liter like sewage, it is generally converted to nitrogen by the bionitrification denitrification method. And is processing. However, some of the wastewater discharged from chemical plants, thermal power plants, etc. contains high-concentration ammonia nitrogen of 1000 mg / liter or more, and the load is too large in the general biochemical nitrification denitrification method. And practical processing cannot be performed.

As a system for treating a high concentration of ammonia nitrogen, for example, after ammonia nitrogen is stripped as ammonia, the ammonia is treated in a multi-step process consisting of primary oxidation, reduction and secondary oxidation to produce nitrogen. A conversion human waste treatment system has been proposed (Kou Isao: "Catalyst water treatment technology", water production technology, Vol.
19, No. 4, 63 (1993)).

In this system, platinum is added in the primary oxidation process.
Pt / Al supported on alumina carrier ₂O_ThreeUse catalyst
Therefore, part of the ammonia is converted into nitrogen oxides (mainly N
O), and a separate reduction step and treatment for this NO treatment.
And a secondary oxidation step is required. In the reduction process,
Bypass some of the tripped ammonia to the primary
Add vanadium oxide to the exhaust gas from the oxidation process
V / TiO supported on titania carrier₂N in the presence of a catalyst
O is reduced and converted to nitrogen. That is, in the reduction process
Ammonia reduction denitration is performed, and excess is generated in this reduction process.
The resulting ammonia is treated in the next secondary oxidation step. This
Like conventional processing systems, they consist of many processes.
However, its control was not easy.

[0005]

An object of the present invention is to provide a processing system capable of solving the above-mentioned problems of the prior art, namely, a method in which stripped ammonia is converted into nitrogen in a single stage and ammonia nitrogen is used. The objective is to provide a simple treatment system that does not significantly affect the operation of the entire system including the system that discharges.

[0006]

As a result of earnest research in view of the above problems, the inventors of the present invention were able to convert stripped ammonia into nitrogen in a single stage by providing a predetermined ammonia oxidation step. The present invention has been completed by finding that an ammonia nitrogen treatment system that can perform specific and simple treatment can be obtained.

That is, the present invention comprises a step of adding an alkali to wastewater containing ammonia nitrogen to convert the ammonia nitrogen into ammonia, and a step of stripping ammonia from the wastewater discharged in the step. An ammoniacal nitrogen treatment system comprising an oxidation step of reacting the obtained ammonia with oxygen in the presence of a solid catalyst to convert it into nitrogen, and a step of utilizing heat generated in the oxidation step. is there.

Further, the present invention is a system for treating ammonia nitrogen generated in a thermal power plant, which comprises adding alkali to wastewater containing ammonia nitrogen to convert the ammonia nitrogen into ammonia. A first preheating step of preheating waste water discharged from the step with a heat source in the power plant, a step of stripping ammonia from the preheated waste water with steam or air, and the obtained ammonia as a heat source in the power station And a step of utilizing the heat generated in the oxidation step, a second preheating step of preheating with the above step, an oxidation step of reacting preheated ammonia with oxygen in the presence of a solid catalyst to convert into nitrogen, and a step of utilizing heat generated in the oxidation step. The feature is the ammonia nitrogen treatment system.

Further, the present invention is a system for treating ammonia nitrogen generated in a thermal power plant, which comprises adding alkali to wastewater containing ammonia nitrogen to convert the ammonia nitrogen into ammonia. And a step of stripping ammonia from wastewater discharged in the step, and using the obtained ammonia in a denitration step, an ammonia nitrogen treatment system.

Hereinafter, the present invention will be described in detail. The wastewater to be treated by the present invention, that is, as the wastewater containing ammonia nitrogen, is not particularly limited, thermal power generation treatment plant, a chemical plant, for example, an amine production plant, wastewater discharged from a food production plant, and the like, Examples include activated sludge wastewater, wastewater such as human waste or sewage, and it is also effective for equipment cleaning wastewater (so-called unsteady wastewater) of thermal power plants.

Examples of ammonia nitrogen in these wastewaters include ammonium ions, amine compounds, amide compounds, amino acid compounds and the like. The amine compound may be any of primary amine, secondary amine, and tertiary amine ammonium salt, and is not particularly limited. More specifically, examples thereof include methylamine, dimethylamine, trimethylamine, propylamine, ethylenediamine, alkylamine, ethanolamine and the like, and aromatic and heterocyclic compounds such as aniline and pyridine. Examples of the amide compound include formamide, acetamide, methylpropionamide, ethylformamide, dimethylformamide, dimethylacetamide and the like. Amino acid compounds include glycine, alanine, valine,
Examples thereof include aromatic compounds such as leucine, serine, cysteine, aspartic acid, glutamic acid, and arginine, aliphatic compounds, and heterocyclic compounds.

However, the ammonia nitrogen in the present invention is not limited to the above compounds. Further, ammonia nitrogen in the waste water may be present as a single compound or may be contained in plural kinds, and is not particularly limited.
In the ammonia nitrogen treatment system of the present invention, first, alkali is added to wastewater containing ammonia nitrogen to convert the ammonia nitrogen into ammonia. This conversion to ammonia is shown by the following reaction formula. _{^{NH 4 + + OH - → NH}} 3 + H 2 O

The alkali may be any of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, calcium hydroxide and the like, and is not particularly limited. Further, the usage form thereof may be an aqueous solution, a slurry, or the like. Next, ammonia remaining in the wastewater discharged in the above step is stripped, but before that, it is preferable to collect sludge of heavy metals such as Fe, Ni, V, and Zn using a thickener or the like. Although ammonia is produced by the above process, some ammonia is also desorbed in thickener.

The stripping can be effectively carried out by adding an alkali to the waste water to adjust the pH of the solution to 10 or more, preheating the solution if necessary, and blowing in steam or air. Through this stripping step, ammoniacal nitrogen is recovered as ammonia gas. Stripping can be performed by a usual gas-liquid contact method using a bubble column, a packed column, a plate column, or the like. Chemical plants and thermal power plants are equipped with facilities to adjust the pH of wastewater by adding alkali to treat other wastewater such as BOD, COD, heavy metals, and fluorine, and improve or combine them. It is possible to use. Further, in thermal power plants and chemical plants, there are various heat sources and air sources such as steam, flue gas, and heated air, and it is easy to heat waste water and strip by blowing air. Since the stripping rate of ammonia increases as the temperature increases, stripping can be promoted by using the heat source.
Therefore, it can be said that the present invention is particularly effective when implemented in a chemical factory or a thermal power plant.

It is preferable that the ammonia converted using the alkali, the ammonia discharged from the thickener and the stripped ammonia are further preheated to 200 ° C. or more in the preheating step. As the heat source, the heat source in the power plant as described above, that is, steam, flue gas, heated air or the like can be used. In addition to that, LNG,
Combustion gas such as propane or kerosene may be used as a heat source.

The resulting ammonia (preheated ammonia) is then oxidized with oxygen to nitrogen and water. The oxygen may be oxygen in the air, for example oxygen in the air from the air preheater in the power plant system, or oxygen from the TO plant (deep cold air separation device). The reaction formula is as follows. 4NH ₃ + 3O ₂ → 2N ₂ + 6H ₂ O In this oxidation step, ammonia is converted to nitrogen in the presence of a solid catalyst. The solid catalyst may be any as long as it can selectively convert ammonia into nitrogen and water, but an oxide such as copper or molybdenum is supported on titanium oxide, alumina, silica-alumina, zeolite or the like. It is preferable to use the above catalysts. Particularly, the addition of cobalt, tin, tungsten, manganese, cerium or the like to these catalysts improves the catalytic activity and is more effective.

The preferred reaction temperature in the oxidation step is 200 to 400 ° C., though it depends on the space velocity (SV) of the gas. At lower temperatures than this, the oxidation rate of ammonia is small, and at high temperatures, nitrogen oxides are generated, so reduction and secondary oxidation are required, and the characteristics of the present invention are impaired. As a reaction method that can be used in the oxidation step, for example, a reaction method usually used for waste gas treatment, specifically, a fixed bed flow method and the like can be mentioned. Space velocity of gas (gas amount /
The amount of the catalyst) is preferably 100 to 100,000 / h, and particularly preferably 1000 to 10,000 / h. Further, the air supply amount is preferably equal to or more than the equivalent amount required for converting ammonia into nitrogen.

Reaction heat is generated in this oxidation step, but in order to improve the heat balance of the entire plant, the generated heat is used by means such as using a heat exchanger or returning it to a flue. The generated heat can be used, for example, as a heat source for reheating exhaust gas from the desulfurizer. In the ammonia nitrogen treatment system of the present invention, it is also possible to treat the nitrogen content in the waste water after stripping to about 100 mg / liter and biochemically treat the remaining nitrogen content. By providing the biochemical treatment process in this way, the burden of the ammonia stripping and oxidation process can be reduced.

In the biochemical treatment process, the nitrogen content is preferably converted into nitrogen in a two-step process. In this case, in the first step, the nitrogen content is converted to nitric acid and nitrite nitrogen by the action of nitrifying bacteria under aerobic conditions, and in the second step, COD components (organic substances) or methanol are converted under anaerobic conditions. It converts nitric acid and nitrite nitrogen into nitrogen by the action of denitrifying bacteria with such nutrients.

In addition to the system described above, when the present invention is applied to a thermal power plant, it is also possible to apply a treatment system that does not have an oxidation step. In a thermal power plant, in order to make nitrogen oxides in combustion gas (flue gas) generated in a boiler harmless, ammonia is added and nitrogen is converted (denitration) at about 350 ° C. Therefore, the stripped ammonia can be used in the denitration step without being oxidized.
By this denitration step, excess ammonia adheres to the air heater, dust collector, etc. in the subsequent stage in the form of ammonium salt, but when the adhered ammonium salt is washed,
Since wastewater containing a high concentration of ammonia nitrogen of several g / liter is discharged, this wastewater can also be treated by this system or the system described above.

[0021]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited to these examples. Example 1 In this example, ammonia nitrogen was treated according to the system configuration diagram shown in FIG.

Waste liquid 1 of pH 1.6 containing 2 g / liter of ammonia nitrogen discharged from an air heater, a dust collector, a condenser, etc. of a 1000 MW coal-fired power plant is stored in a storage tank 2
From 84 to 84 t / d to the pH adjusting tank 3 continuously,
200 wt% of 0 wt% sodium hydroxide solution 4
Ammonia 5 was generated by addition at kg / h. The waste liquid after generating ammonia 5 was led to thickener 6 and sludge 7 of heavy metals was recovered.

Next, the overflow liquid 8 from the thickener 6 was introduced to the top of a tray type ammonia stripper 9, and air 10 was supplied from the bottom of the tower at 3,500 m ³ N / h to strip ammonia. At this time, the flue gas 12 at 290 ° C. was introduced into the heat exchanger 11 in the stripper 9 at 16,100 m ³ N / h to heat the temperature of the waste liquid to 50 ° C.

The ammonia gas discharged from the stripper 9 together with the ammonia 5 and the ammonia from the thickener 6 is transferred to the heat exchanger 13 using the flue gas 12 for 2
It was heated to 90 ° C. and led to the oxidizer 14. As the oxidizer 14, the titanium oxide catalyst 1 carrying 10 wt% of copper oxide, 1 wt% of cerium oxide and 2 wt% of manganese oxide was used.
5 used in an amount of 0.35 m ³ was used. This oxidizer 1
As a result of reaction at about 300 ° C. in
The concentration of ammonia in the exhaust gas 16 at the outlet is 3 ppm, the concentration of nitrous oxide and nitrogen oxides is 1 ppm or less,
The temperature of the gas was 320 ° C.

This exhaust gas 16 is used as a reheating source of the exhaust gas 18 from the desulfurization device 17, so that the desulfurization device 17 can be used.
Of the exhaust gas and discharged from the chimney together with the exhaust gas 18. On the other hand, the waste water discharged from the bottom of the stripper 9 had a nitrogen content of 15 mg / liter and a BOD of 20 mg / liter, and sulfuric acid 20 was added and discharged so as to have a pH of 7 in the pH treatment tank 19 at the subsequent stage. The amount of flue gas 12 introduced into the heat exchanger 13 of 16,100 m ³ N / h was about 0.5% of the combustion exhaust gas of the entire power plant, and the influence on the heat balance of the power plant was negligible.

The reaction was carried out in the same manner except that an oxidizer 14 filled with an alumina catalyst supporting 1 wt% of platinum was used.
The ammonia concentration in 6 was 2 ppm, but the concentration of nitrous oxide was 5 ppm and the concentration of nitrogen oxides was 155 ppm.
Met.

Example 2 In this example, ammonia nitrogen was treated according to the system configuration diagram shown in FIG. 5
Waste liquid 1 of pH 1.7 containing 2.5 g / liter of ammonia nitrogen discharged from an air heater, dust collector, condenser, etc. of a 00 MW coal-fired power plant is stored in a storage tank 2 at 34 t /
At d, the solution was continuously introduced into the pH adjusting tank 3, and the calcium hydroxide slurry 21 having a concentration of 20 wt% was added at 40 kg / h to generate ammonia 5. The waste liquid after generating ammonia 5 was led to thickener 6 and sludge 7 was collected.

Next, the overflow liquid 8 from the thickener 6 was introduced into a bubble column type ammonia stripper 9, and steam 22 was supplied to the heat exchanger 11 from the bottom of the column to strip ammonia. At this time, the air 10 was supplied to the top of the stripper 9 at a rate of 1,800 m ³ N / h to accompany the stripped ammonia. Flue gas 1
By using the heat exchanger 13 utilizing 2, the mixed gas of ammonia 5, ammonia from the thickener 6 and stripped ammonia and air was heated to 280 ° C. and introduced into the oxidizer 14. As the oxidizer 14, a silica alumina catalyst 23 supporting 10 wt% of molybdenum oxide and 1 wt% of cerium oxide was filled in an amount of 0.18 m ³ and used. As a result of reaction at about 300 ° C. in the oxidizer 14, the exhaust gas 16 at the outlet of the oxidizer 14 has an ammonia concentration of 2 ppm and a nitrous oxide and nitrogen oxide concentration of 1
It was below ppm and the gas temperature was 320 ° C.

The exhaust gas 16 is used as a reheating source of the exhaust gas 18 from the desulfurization device 17,
Of the exhaust gas and discharged from the chimney together with the exhaust gas 18. On the other hand, the nitrogen content in the wastewater discharged from the bottom of the stripper 9 is 130 mg / liter, and the BOD is 180 mg.
/ Liter. Sulfuric acid 20 was added to this in a pH treatment tank 19 in the latter stage so as to have a pH of 7, and then introduced into an existing biochemical nitrification and denitrification tank 24, and discharged as residual nitrogen of 15 mg / liter and BOD of 18 mg / liter.

As the oxidizer 14, 0.5 wt% platinum
When the reaction was carried out in the same manner except that a titanium oxide catalyst supporting C was used, the ammonia concentration in the exhaust gas 16 at the outlet of the oxidizer 14 was 5 ppm, but the concentration of nitrous oxide was 22 ppm, Oxide concentration is 72
It was ppm.

[0031]

According to the present invention, it becomes possible to treat high-concentration ammonia nitrogen which cannot be practically treated by the conventional biological nitrification and denitrification method alone, and more easily than the ammonia stripping multistage redox method. Can be processed.
In particular, when the present invention is applied to a thermal power plant, a high-concentration ammonia nitrogen waste liquid can be treated with a utility within a range that does not affect the heat balance of the entire power plant or the operation of the equipment.

[Brief description of drawings]

FIG. 1 is a diagram showing a system configuration according to an embodiment of an ammoniacal nitrogen treatment system of the present invention.

FIG. 2 is a diagram showing a system configuration according to another embodiment of the ammonia nitrogen treatment system of the present invention.

[Explanation of symbols]

1 ... Waste liquid, 2 ... Storage tank, 3 ... pH adjusting tank, 4 ... Sodium hydroxide solution, 5 ... Ammonia, 6 ... Thickener, 7 ... Sludge, 8 ... Overflow liquid, 9 ... Stripper, 10
... air, 11 ... heat exchanger, 12 ... flue gas, 13 ... heat exchanger, 14 ... oxidizer, 15 ... titanium oxide catalyst, 16 ... exhaust gas, 17 ... desulfurization device, 18 ... exhaust gas, 19 ... pH adjusting tank , 20 ... Sulfuric acid, 21 ... Calcium hydroxide, 22 ... Steam, 23 ... Silica-alumina catalyst, 24 ... Biochemical nitrification / denitrification tank

Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location C02F 1/58 B01D 53/36 ZABF 3/30 ZAB B01J 23/84 311A (72) Inventor Kenji Baba Hitachi Ibaraki Prefecture 7-1, Omika-cho, Oita-shi, Ltd. Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Yukio Murai 1-1-14 Kanda, Uchida Plant Construction Co., Ltd., Chichida-ku, Tokyo (72) Inventor Tanaka Akio 1-1-14 Kanda, Chiyoda-ku, Tokyo Inside Hirit Plant Construction Co., Ltd.

Claims (8)

[Claims] 1. A step of adding an alkali to wastewater containing ammonia nitrogen to convert the ammonia nitrogen into ammonia, a step of stripping ammonia from the waste water discharged in the step, and the obtained ammonia. An ammoniacal nitrogen treatment system comprising an oxidation step of reacting with oxygen in the presence of a solid catalyst to convert it into nitrogen, and a step of utilizing heat generated in the oxidation step. 2. A system for treating ammonia nitrogen generated in a thermal power plant, which comprises adding alkali to wastewater containing ammonia nitrogen to convert the ammonia nitrogen into ammonia, and discharging the ammonia. The first preheating step of preheating the waste water to be recovered with the heat source in the power plant, the step of stripping ammonia from the pre-heated waste water with steam or air, and the pre-heating of the obtained ammonia with the heat source in the power station. 2, a preheating step, an oxidation step of reacting preheated ammonia with oxygen in the presence of a solid catalyst to convert into nitrogen, and a step of utilizing heat generated in the oxidation step. Ammonia nitrogen treatment system. 3. The ammonia nitrogen treatment system according to claim 2, wherein the heat source in the first preheating step and the second preheating step is any one of steam, flue gas and heated air. 4. The heat source in the first preheating step is any one of steam, flue gas and heated air, and the heat source in the second preheating step is combustion gas. The ammonia nitrogen treatment system described. 5. A step of biochemically treating the wastewater discharged from the stripping is provided,
The ammonia nitrogen treatment system according to claim 1 or 2. 6. The solid catalyst is a catalyst comprising at least one oxide of copper and molybdenum supported on at least one selected from the group consisting of titanium oxide, alumina, silica alumina and zeolite. The ammonia nitrogen treatment system according to claim 1 or 2. 7. The ammonia nitrogen treatment system according to claim 6, wherein the solid catalyst further contains at least one selected from the group consisting of cobalt, tin, tungsten, manganese, and cerium. 8. A system for treating ammonia nitrogen generated in a thermal power plant, which comprises adding an alkali to wastewater containing ammonia nitrogen to convert the ammonia nitrogen into ammonia, and discharging the ammonia. And a step of stripping ammonia from the wastewater to be treated, and the obtained ammonia is utilized in a denitration step, an ammonia nitrogen treatment system.