JP3423204B2 - How to remove scale - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to a chemical plant, a plating industry facility, a leather manufacturing facility, a metal manufacturing facility, a metal mining facility, a food manufacturing facility, a pharmaceutical manufacturing facility, a textile industry facility, a paper pulp industry facility, a dyestuff industry. Wastewater treatment equipment used for treatment of various industrial wastewater represented by equipment, power generation equipment, electronic industrial equipment, machinery industrial equipment, printing plate making equipment, glass manufacturing equipment, photographic treatment equipment, etc., and solids used in the wastewater treatment equipment The present invention relates to a method for removing scale attached to a catalyst. More specifically, the present invention relates to a method for effectively removing scale that causes an increase in pressure loss in the wastewater treatment equipment, blockage inside the equipment, deterioration of heat exchanger performance, deterioration of activity of a solid catalyst, and the like.

[0002]

2. Description of the Related Art When a wastewater treatment equipment is operated for a long period of time, the scale adheres strongly to the heat exchanger of the wastewater treatment equipment, the pipes near the heater, the reactor, and / or the solid catalyst, and the treatment equipment becomes blocked. In some cases, it may be difficult to continue the operation due to increase in pressure loss, decrease in performance of heat exchanger, decrease in activity of solid catalyst, and the like. In many cases, such a scale accumulates calcium, magnesium, iron, aluminum, silicon, etc. contained in wastewater as sparingly water-soluble salts, hydroxides, oxides, etc. Is.
As an example of such a scale removal method, chemical cleaning with an inorganic acid such as sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid or an organic acid such as citric acid, glycolic acid, formic acid or oxalic acid can be mentioned. However, cleaning with these acids has the following problems, respectively. First, in sulfuric acid, the sulfate ion forms a salt that is sparingly soluble in calcium ion and water, so that the scale removal efficiency becomes low. Hydrochloric acid
Since there are materials that cause stress corrosion cracking due to chloride ions, they are often unsuitable for equipment materials. Since nitric acid, phosphoric acid, and organic acids are regulated to discharge nitrogen, phosphorus, and COD, the used cleaning liquid cannot be discharged as it is, and further treatment is required.

[0003]

DISCLOSURE OF THE INVENTION The present invention uses the above-mentioned acid in the removal of the scale strongly adhered to the waste water treatment equipment and / or the solid catalyst, particularly the one mainly containing calcium. It is an object of the present invention to solve the problems of chemical cleaning treatment, and an object thereof is to provide a method for efficiently removing scale even when sulfuric acid, which has relatively few problems, is used as an acid.

[0004]

Means for Solving the Problems As a result of intensive studies conducted by the present inventors to solve the above problems, as a scale remover, a pH of an aqueous solution of sulfuric acid containing ammonium ions was added.
By supplying an aqueous solution of 0 to 3 into the wastewater treatment equipment and / or bringing it into contact with the solid catalyst, the scale strongly adhered to the wastewater treatment equipment and / or the solid catalyst is removed economically, highly efficiently and safely. I found that I could do it. The present invention has been completed based on this finding.

The present invention is specified as follows.

(1) In a method for removing scale in a wastewater treatment apparatus using a scale remover, the scale remover is an aqueous solution containing sulfate ions and ammonium ions, and the pH of the aqueous solution is 0 to 0. 3. A method for removing scale, characterized in that

(2) In the method for removing scale attached to a solid catalyst using a scale removing agent, the scale removing agent is an aqueous solution containing sulfate ions and ammonium ions, and the pH of the aqueous solution is 0 to 0. 3. A method for removing scale, characterized in that

(3) The method for removing scale according to the above (1) or (2), which is carried out under the conditions of a temperature of 5 to 370 ° C. and a pressure at which the scale removing agent retains a liquid phase.

(4) The sulfuric acid ion concentration in the scale removing agent is 1,000 to 200,000 mg / L, the ammonium ion concentration is 10 to 75,000 mg / L, and the molar amount of ammonium ion is relative to the molar concentration of sulfate ion. The concentration ratio (molar concentration of ammonium ion / sulfuric acid ion) is from 0.01 to 2.0 (1) to
The method for removing scale according to any one of (3).

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The scale according to the present invention is not particularly limited as long as it is attached in the wastewater treatment equipment and / or on the solid catalyst, but the present invention is not limited to the scale containing calcium as one of the main components. On the other hand, it is particularly effective. When the inorganic components in the scale are converted to oxides, the present invention provides
It is effective when the proportion of calcium oxide is 1 to 100% by weight, and more effective when it is 5 to 100% by weight. If the amount is less than 1% by weight, the scale containing calcium can be sufficiently removed without using the method of the present invention. Further, according to the method of the present invention, even if the scale contains magnesium, iron, aluminum, silicon, etc., they can be removed without any problem.

The scale removing agent according to the present invention is an aqueous solution containing sulfate ions and ammonium ions and having a pH of 0 to 3, and the pH of the aqueous solution is preferably 0.5 to 2.
8 and more preferably 1.0 to 2.5. p
When H is less than 0, the processing equipment is corroded and the solid catalyst is deteriorated. When the pH exceeds 3, ammonium ions react with the oxygen-containing gas supplied into the wastewater treatment apparatus and the dissolved oxygen in the scale removing agent and are consumed, so that a sufficient effect may not be obtained. The concentration of sulfate ion is not particularly limited, but it is preferably 1,000 to 200,000 m as the one in which sulfuric acid is completely ionized in an aqueous solution.
g / L, more preferably 5,000-40,000 mg
/ L. If the sulfate ion concentration is less than 1,000 mg / L, the effect of the present invention cannot be sufficiently obtained, and 200,000 m
If the concentration exceeds g / L, the viscosity of the scale removing agent is too high, which hinders the supply into the apparatus, which is not preferable. The ammonium ion concentration is not particularly limited, but is preferably 100 to 75,000 mg / L, more preferably 500 to 15,000 mg / L. When the ammonium ion concentration is less than 100 mg / L, 15,
If it exceeds 000 mg / L, the effect of the present invention cannot be sufficiently obtained, which is not preferable. The ratio of the ammonium ion molar concentration to the sulfate ion molar concentration (ammonium ion molar concentration / sulfate ion molar concentration) is not particularly limited, but is preferably 0.01 to 2.0,
It is more preferably 0.05 to 1.8, still more preferably 0.5 to 1.5. If the ratio of the molar concentration of ammonium ion to the molar concentration of sulfate ion is less than 0.01 or exceeds 2.0, the effect of the present invention cannot be sufficiently obtained, which is not preferable.

The scale remover according to the present invention may contain a corrosion inhibitor, a cleaning aid and the like. Further, as the scale remover according to the present invention, if it is an aqueous solution containing sulfate ion and ammonium ion and having a pH of 0 to 3, other compounds or ions such as alkali metal salt, nitric acid, phosphoric acid, organic acid and the like. May be contained, and the wastewater having a pH of 0 to 3 containing a sulfate ion and an ammonium ion may be included. A liquid containing sulfate ions and ammonium ions having a pH of more than 3, such as waste water, is partially treated with various equipment such as waste water treatment equipment to reduce the pH to 3 or less. It can also be used for removing the scale adhering to the wastewater treatment apparatus and the solid catalyst according to the present invention. The pH in this case is 3
Equipment for lowering below is not particularly limited, but is preferably the wastewater treatment apparatus according to the present invention. Also, the pH
It is also possible to use a cation exchange resin to adjust the pH of a liquid having a value of 3 or more, such as waste water, to 3 or lower, and use it for removing the scale adhering to the waste water treatment apparatus and / or the solid catalyst according to the present invention. In this case, the cation exchange resin may be regenerated by using the treated water obtained by the wastewater treatment in the wastewater treatment facility.

The scale removing agent according to the present invention is not particularly limited, but can be reused many times,
Ammonia can be detoxified by treating ammonia using the wastewater treatment facility as exemplified in the present invention.

The scale removal by bringing the scale removing agent of the present invention into contact with the solid catalyst is usually carried out while the solid catalyst is filled in the waste water treatment equipment. However, it is also possible to extract the solid catalyst from the wastewater treatment device and transfer it into another container or device for implementation.

The temperature at which the descaling agent is fed into the wastewater treatment equipment and / or in contact with the solid catalyst is
Although not particularly limited, it is usually 5 to 370 ° C., preferably 10 to 280 ° C., more preferably 30 to 16 ° C.
The temperature is 0 ° C, more preferably 50 to 120 ° C. In addition,
The scale removing agent is generally supplied below the design temperature of the wastewater treatment equipment. If the temperature is lower than 5 ° C, the scale removing agent may freeze. If the temperature exceeds 370 ° C., the cost of the device will be high.

The pressure for supplying the scale removing agent into the waste water treatment equipment is usually a pressure at which the scale removing agent holds the liquid phase.

The supply of the scale removing agent according to the present invention can be carried out without supplying a gas, but an inert gas such as nitrogen gas or helium gas or an oxygen-containing gas is supplied for the purpose of cleaning effect by bubbling. You can also do it. In particular, the supply of the oxygen-containing gas is often preferable because an oxide film is often formed on the surface of the device material. The oxygen-containing gas is not particularly limited as long as it is a gas containing oxygen gas, and examples thereof include air, oxygen-enriched gas, pure oxygen gas, and factory exhaust gas. It is advantageous in cost to use air as the oxygen-containing gas. The gas supply amount is not particularly limited as long as the scale removing agent is concentrated and the salt in the scale removing agent is not deposited.

The waste water treatment apparatus according to the present invention is not particularly limited, but the present invention is not limited to the COD component or the nitrogen component in the waste water containing oxygen (for example, air, oxygen-enriched gas, oxygen gas, etc.). ) Wastewater treatment equipment that decomposes or removes it by reacting with oxygen, ozone, hydrogen peroxide, nitrite, etc., and wastewater treatment equipment that reduces and removes nitrate radicals in wastewater using methanol, hydrogen, ammonia, etc. as reducing agents. Can be applied. The present invention particularly preferably includes, in those wastewater treatment apparatuses, oxygen in a gas containing oxygen (eg, air, oxygen-enriched gas, oxygen gas, etc.) in the presence of a solid catalyst for COD components and nitrogen components in wastewater. A catalytic wet oxidation treatment device that reacts with ozone, an ozone oxidation wastewater treatment device that decomposes or removes COD components and nitrogen components in wastewater by reacting with ozone,
It is effective to apply it to a wastewater treatment apparatus or the like that decomposes or removes COD components and nitrogen components represented by ammonia in wastewater by reacting with hydrogen peroxide and / or nitrite in the presence of a solid catalyst.

The material of the wastewater treatment equipment according to the present invention is, for example, stainless steel, hastelloy, titanium or the like, and is not particularly limited.

The solid catalyst according to the present invention is any solid catalyst having durability and activity in wastewater treatment and sufficient durability in scale removal in the acidic scale removing agent of the present invention. Although catalysts are also targeted, titanium, silicon, zirconium, and
A compound insoluble or sparingly soluble in water of at least one element selected from the group consisting of iron, cobalt, nickel, manganese, tungsten, cerium, copper, silver, gold, platinum, palladium, rhodium, ruthenium, and iridium. It is a solid catalyst containing. The shape of the solid catalyst according to the present invention is not particularly limited, such as granules, pellets, and integral structures such as honeycombs.

The wastewater treated by the wastewater treatment apparatus according to the present invention is not particularly limited, but is preferably wastewater containing a nitrogen-containing compound such as ammonia and / or ammonium ion. Therefore, it is often effective for drainage of power generation equipment, which often contains a nitrogen-containing compound such as ammonia and / or ammonium ion, drainage of electronic industrial equipment such as a semiconductor factory. When the wastewater treated by the wastewater treatment equipment is wastewater containing nitrogen-containing compounds such as ammonia and / or ammonium ions, the wastewater can be used as it is as a scale remover, or a scale remover can be prepared based on the wastewater. This makes it possible to reduce the cost related to scale removal.

The time for supplying the scale removing agent into the wastewater treatment equipment and / or the time for contacting with the solid catalyst are not particularly limited, but preferably 10 minutes to 200 hours, more preferably 1 to 100 hours, and further preferably 6 hours. ~ 30 hours. If it is less than 10 minutes, the scale is often insufficiently removed. Further, if it exceeds 200 hours, it is often uneconomical because the effect is not commensurate with the long washing time.

The flow rate at which the scale removing agent is supplied into the wastewater treatment equipment is not particularly limited, but is preferably 0.05 to 10 times, more preferably 0.2 to 2 times the design flowrate of the wastewater treatment equipment. . If it is less than 0.05 times, the effect of the present invention cannot be sufficiently obtained in many cases. Also,
If it exceeds 10 times, a large amount of scale remover is consumed, which is uneconomical.

When the solid catalyst is immersed in the scale removing agent in the container to remove the scale, the amount of the scale removing agent is
The amount of the solid catalyst is not particularly limited as long as it is sufficient to contact the scale removing agent, but preferably 1 to 1 of the volume of the solid catalyst.
50 times, more preferably 2 to 10 times the volume of the scale remover is used. If it is less than 1 time, the scale removal is often incomplete. If it exceeds 50 times, a large amount of scale remover is consumed, which is uneconomical.

[0025]

EXAMPLES The present invention will now be described in detail with reference to examples, but the present invention is not limited thereto.

Example 1 According to the flow shown in FIG. 1, COD (Cr) 20,000 to 22,000 containing the following inorganic elements and containing an organic acid as a main component.
The wastewater of mg / L was treated using the catalyst wet oxidation treatment device and the solid catalyst shown below, and further, the scale attached to the treatment device and the solid catalyst was removed. The details will be described below.

-Composition and properties of wastewater- Calcium 20-40mg / L Magnesium 10-20 mg / L Iron 5-10 mg / L Aluminum 0.1-1mg / L Silicon 1-5 mg / L The wastewater was treated as follows.

The drainage tank 4 regularly received drainage having the above composition.

The pump 3 boosts the drainage of the drainage tank 4 to 1
It was supplied into the apparatus at a flow rate of L / hr. In addition, line 1
After the air supplied from 0 was pressurized by the compressor 6, the flow rate control valve 9 controlled the flow rate to 74 NL / hr, and the air was mixed into the waste water through the line 11.

The gas-liquid mixture is heated by the heat exchanger 2, the pipe 12 and the heater 14 installed in the wet oxidation tower 1, and the wet oxidation tower filled with 1 liter of the solid catalyst while maintaining the temperature at 250 ° C. 1, and the waste water was subjected to wet oxidation treatment. The treated water obtained was cooled in the heat exchanger 2 via the line 13 and introduced into the gas-liquid separator 5. In the gas-liquid separator 5, the liquid level controller (L
The liquid level is detected by C), the liquid level control valve 7 is operated to maintain a constant liquid level, and the pressure controller (P
C) detects the pressure and activates the pressure control valve 8
It was operated so as to hold 0 kg / cm ² G.

Up to about 1,000 hours after the start of operation, the COD (Cr) of the treated water was stable at 200 mg / L, and the pressure gauge (PG) displayed 71 kg / cm ² G. . However, the COD (Cr) of the treated water was 850 mg / L after the operation for 2,000 hours, and the pressure gauge (PG) display was 75 kg / cm ² G. Here, as a result of stopping the apparatus and inspecting the inside, generation of scale was recognized on the inner wall of the heat exchanger 2, the inside of the wet oxidation tower 1 and the surface of the solid catalyst. As a result of the scale analysis, it was confirmed that calcium was the main component and contained magnesium, iron, aluminum and silicon little by little.

The scale attached to the waste water treatment equipment and the solid catalyst was removed by the method described below.

Sulfate ion concentration 10,000 mg / L, ammonium ion concentration 2,500 mg / L, pH 1.
2 、 Scale removal agent with temperature 20 ℃ 1 by pump 3
It was supplied into the apparatus at a flow rate of L / hr. In addition, line 1
The air supplied from 0 was pressurized by the compressor 6 and then mixed in the scale removing agent through the line 11 at a flow rate of 10 NL / hr. This gas-liquid mixture was heated by the heat exchanger 2, the pipe 12 and the heater 14 installed in the wet oxidation tower 1, and was introduced into the wet oxidation tower 1 while maintaining the temperature at 80 ° C. The solid catalyst with scale is
It was contacted with a scale removing agent in the wet oxidation tower 1. The scale removing agent passed through the wet oxidation tower 1 was cooled in the heat exchanger 2 through the line 13 and introduced into the gas-liquid separator 5. In the gas-liquid separator 5, the liquid level controller (LC) detects the liquid level, the liquid level control valve 7 is operated to maintain a constant liquid level, and the pressure controller (PC) detects the pressure. 9kg / cm ² G by operating the pressure control valve 8
Was operated to hold. In this way, the scale removing agent was supplied for 12 hours.

After the above scale removing operation, the inside of the apparatus was visually inspected, and as a result, the inner wall of the heat exchanger 2 and the wet oxidation tower 1 were found.
The scale adhering to the inside of the catalyst and the surface of the solid catalyst was removed. After this, as a result of performing wastewater treatment in the same manner as before scale removal, the COD (Cr) of the treated water was 200 mg / L.
And the display of the pressure gauge (PG) was 71 kg / cm ² G.

Comparative Example 1 First, the same wastewater as in Example 1 was treated for 2,000 hours in the same manner as in Example 1. The COD (Cr) of the treated water was 850 mg / L, and the pressure gauge (PG) display was 75 kg / cm ² G. Here, as a result of stopping the apparatus and inspecting the inside, generation of scale was recognized on the inner wall of the heat exchanger 2, the inside of the wet oxidation tower 1 and the surface of the solid catalyst. As a result of the scale analysis, it was confirmed that calcium was the main component and contained magnesium, iron, aluminum and silicon little by little.

Next, scale removal was carried out in the same manner as in Example 1 except that an aqueous solution of sulfuric acid having a sulfate ion concentration of 10,000 mg / L and containing no ammonium ion was used as the scale remover. After the above scale removal operation, the inside of the apparatus was visually inspected, and as a result, the scale attached to the inner wall of the heat exchanger 2, the inside of the wet oxidation tower 1 and the surface of the solid catalyst was reduced, but the scale was completely removed. Was not removed. As a result of analyzing the remaining scale, calcium was detected and other elements were not detected. After this,
As a result of performing wastewater treatment in the same manner as before scale removal, the COD (Cr) of the treated water was 480 mg / L, and the pressure gauge (P
The display of G) was 73 kg / cm ² G.

(Example 2) According to the flow shown in FIG. 1, wastewater having the following composition and properties was treated by using the catalytic wet oxidation treatment apparatus and the solid catalyst shown below, and further the treatment apparatus and The scale adhering to the solid catalyst was removed. The details will be described below.

Ammonia nitrogen 2,000 to 2,500 mg / L Sulfate ion 15,000 to 20,000 mg / L Calcium 10 to 20 mg / L Iron 1 to 2 mg / L pH 1.0 to 1.5 , Was carried out as follows for the purpose of removing ammoniacal nitrogen.

The above waste water was adjusted to pH 9 with sodium hydroxide.
It was adjusted to -10 and was regularly received in the drainage tank 4.

The pump 3 boosts the drainage of the drainage tank 4 to 1
It was supplied into the apparatus at a flow rate of L / hr. In addition, line 1
After the air supplied from 0 was pressurized by the compressor 6, the flow rate control valve 9 controlled the flow rate to 25 NL / hr and mixed it into the waste water through the line 11.

The gas-liquid mixture is heated by the heat exchanger 2, the pipe 12 and the heater 14 installed in the wet oxidation tower 1, and the wet oxidation tower filled with 1 liter of the solid catalyst while maintaining the temperature at 160 ° C. 1, and the waste water was subjected to wet oxidation treatment. The treated water obtained was cooled in the heat exchanger 2 via the line 13 and introduced into the gas-liquid separator 5. In the gas-liquid separator 5, the liquid level controller (L
The liquid level is detected by C), the liquid level control valve 7 is operated to maintain a constant liquid level, and the pressure controller (P
C) detects the pressure and operates the pressure control valve 8 to
It was operated so as to hold kg / cm ² G.

Up to about 2,000 hours after the start of operation, the result that the ammonia nitrogen concentration in the treated water was 10 mg / L or less was stably obtained, and the pressure gauge (PG) was 9.2 kg / cm.
² G was displayed. However, the ammonia nitrogen concentration was 50 mg / L after 4,000 hours of operation, and the pressure gauge (PG) display was 9.6 kg / cm ² G.
Here, as a result of stopping the apparatus and inspecting the inside, generation of scale was recognized on the inner wall of the heat exchanger 2, the inside of the wet oxidation tower 1 and the surface of the solid catalyst. The result of the scale analysis,
It was confirmed that calcium was the main component and a small amount of iron was included.

The scale attached to the waste water treatment equipment and the solid catalyst was removed by the method described below. The pH of the wastewater to be treated remains unadjusted (that is, pH 1.0 to
It was used as a scale remover (as it was at 1.5) and was supplied into the apparatus at a flow rate of 0.5 L / hr by the pump 3 at a temperature of 20 ° C. Further, the air supplied from the line 10 was pressurized by the compressor 6, and then mixed with the scale removing agent in the line 11 at a flow rate of 0.1 NL / hr. This gas-liquid mixture is applied to the heat exchanger 2, the pipe 12 and the wet oxidation tower 1.
It is heated by the heater 14 installed in the
It was introduced into the wet oxidation tower 1 while being maintained at 0 ° C. The scale-attached solid catalyst was brought into contact with the scale removing agent in the wet oxidation tower 1. The scale removing agent passed through the wet oxidation tower 1 was cooled in the heat exchanger 2 through the line 13 and introduced into the gas-liquid separator 5. In the gas-liquid separator 5, the liquid level controller (LC) detects the liquid level, the liquid level control valve 7 is operated to maintain a constant liquid level, and the pressure controller (PC) detects the pressure. The pressure control valve 8 was operated and operated so as to maintain 9 kg / cm ² G. In this way, the scale removing agent was supplied for 24 hours.

After the above scale removing operation, the inside of the apparatus was visually inspected, and as a result, the inner wall of the heat exchanger 2 and the wet oxidation tower 1 were found.
The scale adhering to the inside of the catalyst and the surface of the solid catalyst was removed. After that, as a result of performing wastewater treatment in the same manner as before scale removal, the ammonia nitrogen concentration in the treated water was 10 mg.
/ L or less, the display of the pressure gauge (PG) is 9.2 kg /
It became cm ² G.

Comparative Example 2 First, the same waste water as in Example 2 was treated in the same manner as in Example 2 for 4,000 hours. The ammonia nitrogen concentration in the treated water was 50 mg / L, and the pressure gauge (PG) display was 9.6 kg / cm ² G.
Here, as a result of stopping the apparatus and inspecting the inside, generation of scale was recognized on the inner wall of the heat exchanger 2, the inside of the wet oxidation tower 1 and the surface of the solid catalyst. The result of the scale analysis,
It was confirmed that calcium was the main component and a small amount of iron was included.

Next, scale removal was performed in the same manner as in Example 2 except that an aqueous solution of sulfuric acid having a sulfate ion concentration of 15,000 mg / L and containing no ammonium ion was used as the scale remover. After the scale removal operation described above,
As a result of visually inspecting the inside of the apparatus, the scales attached to the inner wall of the heat exchanger 2, the inside of the wet oxidation tower 1 and the surface of the solid catalyst were reduced, but were not completely removed. As a result of analyzing the remaining scale, calcium was detected and other elements were not detected. After this, as a result of performing wastewater treatment in the same manner as before scale removal, CO
D (Cr) was 30 mg / L, and the pressure gauge (PG) display was 9.4 kg / cm ² G.

[0047]

INDUSTRIAL APPLICABILITY Sulfate ion forms a salt which is sparingly soluble in calcium ion and water. Therefore, when an aqueous solution containing only sulfuric acid is used for scale removal, a new sparingly soluble salt will be generated even if the scale containing calcium as one of the main components dissolves due to the action of acid. Can't get However, when ammonium ions are present together with sulfate ions, particularly when the ratio of the ammonium ion molar concentration to the sulfate ion molar concentration (ammonium ion molar concentration / sulfate ion molar concentration) is 0.01 to 2.0. Is believed to solubilize the sparingly soluble salt of calcium. Therefore, it is considered that the scale can be removed efficiently even with an aqueous solution containing sulfuric acid.

According to the method of the present invention, in removing a scale containing calcium as one of the main components, the calcium content in the scale can be removed more efficiently than when a simple aqueous solution of sulfuric acid is used. . Sulfuric acid has relatively few problems as an acid used for chemical cleaning, and problems caused by using other acids, such as the risk of stress corrosion cracking of the material when hydrochloric acid is used, nitric acid or phosphorus It is possible to avoid the problem of treating the used scale removing agent due to emission control of nitrogen and phosphorus when using an acid, and the problem of treating the same used scale removing agent when using an organic acid.

The scale removing agent of the present invention is effective for removing magnesium, iron, aluminum, silicon, etc. in the scale, and can be widely used in addition to removing calcium.

Since the scale removing agent of the present invention can be easily reused or treated after use, it is possible to carry out scale removal at low cost.

When the wastewater to be treated is wastewater containing ammonium ions and sulfate ions, the wastewater is used as a scale removing agent by partially treating the ammonia and / or ammonium ions in the wastewater. can do. In particular, the wastewater to be treated has a pH of 0 to 3 containing ammonium ions and sulfate ions.
In the case of the waste water of No. 3, the waste water can be used as it is as a scale removing agent. Therefore, in these cases, the scale removal can be performed at a lower cost.

[Brief description of drawings]

FIG. 1 shows a flow of an example of a processing apparatus according to the present invention. 1. Wet oxidation tower 2. Heat exchanger 3. Drainage feed pump 4. Drainage tank 5. Gas-liquid separator 6. Compressor 7. Liquid level control valve 8. Pressure control valve 9. Flow control valve 10. Air line 14． heater

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Claims (3)

(57) [Claims] 1. A method for removing scale containing calcium as a main component in a wastewater treatment apparatus using a scale remover, wherein the scale remover is an aqueous solution containing sulfate ion and ammonium ion, and P of aqueous solution
H is Ri 0-3 der, sulfate ion concentration of more aqueous solution
Is 1,000 to 200,000 mg / L, ammonium
The ion concentration is 10 to 75,000 mg / L, and
Ammonium ion model for the molar concentration of sulfate ion.
Concentration ratio (molar concentration of ammonium ion / sulfuric acid ion)
The method for removing scale is characterized in that the molar concentration) is 0.01 to 2. 2. A wastewater treatment equipment using a scale removing agent
In the method for removing scale mainly composed of calcium attached to the solid catalyst, the scale removing agent is an aqueous solution containing sulfate ions and ammonium ions, and the pH of the aqueous solution is 0-3 der is, further the water
Sulfate ion concentration in the liquid is 1,000 to 200,000 m
g / L, ammonium ion concentration 10 to 75,000
mg / L, and the value for the molar concentration of sulfate ion
The molar ratio of ammonium ion (ammonium ion
(Molar concentration of sulphate / molar concentration of sulfate ion) is 0.01 to 2. 3. The method for removing scale according to claim 1 or 2, which is carried out under the conditions of a temperature of 5 to 370 ° C. and a pressure at which the scale removing agent holds a liquid phase.