JP2009024250A - Cleaning method and rust remover for iron-based device or iron-based device member - Google Patents

Abstract

The present invention provides a cleaning method capable of easily cleaning and removing rust generated on an iron-based device or an iron-based member such as a heat sterilizer made of stainless steel.
An iron-based device or an iron-based device member is cleaned using a mixed aqueous solution containing oxalic acid and an alkali metal oxalate salt or ammonium oxalate and having a pH adjusted to 1 to 4.
[Selection figure] None

Description

  The present invention relates to a cleaning method capable of effectively removing iron-based rust generated in an iron-based device or an iron-based device member, and a rust removal cleaner suitably used for the cleaning.

  The main purpose of food packaging is to prevent the growth and contamination of microorganisms. For this purpose, heat sterilization by retort (a type of autoclave) is not only for canning and bottling, but also for retort food. Is also widely practiced.

  When the retort sterilization is repeatedly performed on the food-filled sealed container, there is a problem that brown rust is formed on the wall surface of the stainless steel sterilizer or the conveyor surface. When such rust occurs, rust adheres to the bottom part and flange part of the container subjected to retort sterilization, thereby deteriorating its appearance characteristics and impairing the commercial value.

As a method of preventing foreign matter from adhering and accumulating on the wall and conveyor of a stainless steel sterilizer, the hot water for sterilization supplied into the sterilizer is purified with water containing magnesium phosphate or phosphate glass. Hot water for sterilization of a water treatment agent comprising an agent, an alkali metal component, an alumina component, and a phosphate component, and comprising a phosphate ion-releasing glass or a treatment agent comprising phosphoric acid or a water-soluble phosphate Means have been proposed in which the hot water for sterilization is purified by adding it (see Patent Documents 1 to 3).
Patent Document 4 proposes a derusting liquid comprising an aqueous oxalate solution such as potassium oxalate, sodium oxalate, or ammonium oxalate.

JP 2001-276846 A JP 2001-340893 A JP 2005-199148 A JP 59-31898 A

  In the methods described in Patent Documents 1 to 3, since sprinkling occurs in hot water used for retort sterilization (oil residue), a purifier is added to the hot water for sterilization, This is to prevent the formation of dusty floating substances. That is, in these methods, the oil residue is a calcium salt or transition metal salt (for example, an iron salt) of a higher fatty acid derived from a higher fatty acid adhering to the surface of a container or the like to be sterilized. Attention is paid to the prevention of adhesion and accumulation of foreign substances on the apparatus wall surface and conveyor by supplying phosphate or the like as a cleaning agent into the hot water for sterilization.

  However, by supplying the cleaning agent as described above to the hot water for sterilization, it is possible to prevent brown rust from occurring on the wall surface and piping of the sterilizer to some extent. Of course, once such rust occurs, it is difficult to remove the rust by supplying the cleaning agent. Rust can be removed by washing with a strong acid, but such means causes significant corrosion of the apparatus and the conveyor and cannot be used at all. Moreover, cleaning with a detergent such as a cleanser takes time and is not only a cause of wear of the apparatus, but in a sealed structure such as a retort sterilizer, it is necessary to disassemble the apparatus. It is impossible for practical use.

  In addition, the derusting liquid proposed in Patent Document 4 is used to remove rust by cathodic reduction by electrolysis using this as an electrolytic solution, and is applicable to a large apparatus such as a retort sterilizer. In addition, if such a derusting liquid is not electrolyzed and is simply flowed into the apparatus, there is almost no rust removal effect.

  Accordingly, an object of the present invention is to provide a cleaning method capable of easily cleaning and removing rust generated on an iron-based device such as a heat sterilizer made of stainless steel or an iron-based member and difficult to remove.

  According to the present invention, an iron-based device or an iron-based device member is cleaned using a mixed aqueous solution containing oxalic acid and an alkali metal oxalate or ammonium oxalate and having a pH adjusted to a range of 1 to 4. There is provided a cleaning method characterized in that it is performed.

In the present invention,
(1) performing washing with the mixed aqueous solution under heating at 60 to 130 ° C .;
(2) After washing with the mixed aqueous solution, post-treatment with a strong alkaline aqueous solution having a pH of 12 or more,
(3) prior to washing with the mixed aqueous solution, pretreatment with a strong alkaline aqueous solution having a pH of 12 or more;
(4) preparing a mixed aqueous solution by adding a mixed solid containing oxalic acid and an alkali metal oxalate or ammonium oxalate to water;
(5) The iron-based device is a heat sterilizer,
Is preferred.

According to the present invention, there is also provided a powder or solid form rust remover comprising a mixture of an alkali metal oxalate and an oxalic anhydride or oxalic acid dihydrate.
In the above rust remover,
(A) consisting of a mixture of 100 parts by weight of sodium oxalate and 80-120 parts by weight of oxalic anhydride,
Or (b) consisting of a mixture of 100 parts by weight of sodium oxalate and 120-160 parts by weight of oxalic acid dihydrate,
The pH of the aqueous solution is reduced to about 1 to 4 by introducing such a powder or solid form rust removal detergent into 100 parts by weight of water in an amount of about 0.1 to 1 part by weight. Since it can be adjusted, it can be used as a cleaning liquid for cleaning the iron-based device or the iron-based device member.

  FIG. 2 shows an IR spectrum when the brown rust formed on the surface of the stainless steel conveyor in the retort sterilizer is scraped off, dried and subjected to IR analysis by the KBR method. According to FIG. 2, brown rust is a complex salt of iron oxide, a small amount of manganese dioxide, and silicate, and such a complex salt contains fatty acid iron and fatty acid calcium generated from fatty acids present in the apparatus. It is presumed that it adhered as an adhesive and solidified and stabilized over time to become an ore.

  In the present invention, the rust can be easily decomposed and removed by using a mixed aqueous solution of oxalic acid and alkali metal oxalate or ammonium oxalate prepared at a pH of 1 to 4 as a cleaning solution. Such decomposition of rust is due to the reducing power of oxalic acid, and in order to fully exhibit the reducing power of oxalic acid and avoid corrosion, the pH is in the range of 1 to 4 with an alkali metal oxalate. It is adjusted to. In the present invention in which cleaning is performed using the reducing power of oxalic acid, the mixed aqueous solution only needs to be immersed in the wall surface of an iron-based device, and thus can be easily applied to cleaning of a closed-system retort sterilizer. can do.

  According to the cleaning method of the present invention, by performing cleaning with the above mixed aqueous solution in the range of 60 to 130 ° C., decomposition of rust is promoted, and cleaning can be performed in a short time.

  Moreover, in this invention, after washing | cleaning by said mixed aqueous solution or prior to washing | cleaning, it can wash | clean more efficiently by performing post-processing or pre-processing using strong alkaline aqueous solution whose pH is 12 or more. . In other words, the post-treatment using a strong alkaline aqueous solution converts the rust decomposition product into a colloidal substance and floats it in the liquid, thus preventing reattachment and allowing it to be easily discharged out of the apparatus. It becomes possible. In addition, the pretreatment using the strong alkaline aqueous solution partially hydrolyzes the rust component to make it bulky, brittle and easily detached from the surface of the apparatus, and promptly proceeds with the reduction with oxalic acid in the mixed aqueous solution. To help.

  In addition, a powder or solid-state cleaning agent comprising a mixture of an alkali metal oxalate salt and an oxalic acid anhydride salt or an oxalic acid dihydrate is easy to handle and is equivalent to about 0.1 to 1% oxalic acid with respect to water. Since it is possible to easily adjust the cleaning liquid having a pH of 1 to 4 by adding the weight, it is possible to effectively remove rust by using the cleaning liquid.

<Cleaning liquid>
In the present invention, a mixed aqueous solution containing oxalic acid and an alkali metal oxalate or ammonium oxalate is used as the cleaning liquid. As explained above, oxalic acid in this cleaning solution (mixed aqueous solution) is a component that chemically decomposes rust components by its reducing power, while alkali metal oxalate and ammonium oxalate decompose oxalic acid. Without adjusting the pH. As such an alkali metal oxalate salt that is a pH adjusting component, sodium oxalate or potassium oxalate is usually preferable from the viewpoint of easy availability and low cost.

  The pH of the cleaning liquid is adjusted to 1 to 4, particularly 2 to 3, with an alkali metal oxalate salt or ammonium oxalate (hereinafter sometimes referred to as an oxalate-based auxiliary). It is necessary to perform rust removal without causing corrosion of an iron-based substrate such as stainless steel or steel plate to which rust is attached. That is, when the pH is lower than the above range, even if rust removal can be effectively performed by oxalic acid present in a large amount, corrosion of the iron-based substrate becomes significant. Moreover, when pH is larger than the said range, the reducing power of oxalic acid will not fully be exhibited, and rust removal will become difficult.

  In the present invention, the cleaning liquid as described above can be used as a cleaning liquid by previously mixing a predetermined amount of oxalic acid and an oxalate-based auxiliary agent with water to obtain a mixed aqueous solution having the above pH. If necessary, an acid (anhydride or hydrated salt) powder and an oxalate-based auxiliary (anhydride or hydrated salt) powder are mixed with a binder, if necessary, to obtain a powder or solid form cleaning agent (hereinafter, solid cleaning) It is effective to use it as a cleaning liquid by introducing it into water circulated to a sterilizer or the like.

As the oxalate-based auxiliary, alkali metal oxalate is particularly preferable from the viewpoint of safety. For example, powder of alkali metal oxalate and anhydrous oxalate (C ₂ H ₂ O ₄ ) or oxalate The solid detergent consisting of a mixture with acid dihydrate (C ₂ H ₂ O ₄ · 2H ₂ O) is easy to handle and quickly dissolves in water, so the pH is easily within the above range. A certain cleaning liquid can be adjusted, and rust removal can be performed efficiently.

  In the present invention, the solid detergent most preferably used is a mixture of 100 parts by weight of sodium oxalate and 80 to 120 parts by weight of anhydrous oxalic acid salt, or 100 parts by weight of sodium oxalate, and 120 to It consists of a mixture with 160 parts by weight of oxalic acid dihydrate. Solid detergents composed of these mixtures are effective for removing rust. For example, a cleaning liquid having a pH of 1 to 4 is formed by adding 0.1 to 1 part by weight in 100 parts by weight of water. Therefore, it can be effectively washed by putting it in water circulated to a sterilizer or the like.

  Moreover, although said solid cleaning agent can also be used with a powder form, generally it is preferable at points, such as handleability and a conveyance property, that it is solidified using a suitable quantity of binders. Such a binder is preferably a carbohydrate-based water-soluble polymer such as carboxymethylcellulose (CMC), starch, or alginic acid, and the amount of such a binder should be as small as possible.

<Washing>
In the present invention, it is preferable to perform pretreatment using a strong alkaline aqueous solution having a pH of 12 or more prior to cleaning with the above cleaning solution. That is, by this pretreatment, for example, the following general reaction formula (1):
Fe ₂ (SiO ₃ ) ₃ + H ₂ O + NaOH
→ Na ₂ (SiO ₃ ) [solution] + Fe (OH) ₃ ↓ (1)
Accordingly, the iron silicate component in the rust is hydrolyzed, so that the rust on the iron-based substrate surface becomes bulky, brittle and easily detached from the substrate surface, and the cleaning with the cleaning liquid is effectively performed. Can do.

  The strong alkaline aqueous solution as described above is not particularly limited as long as the pH is 12 or more, but an aqueous solution of sodium hydroxide or potassium hydroxide is generally used. In this case, sodium carbonate is accompanied by generation of carbon dioxide, so care must be taken.

  As described above, it is needless to say that the pretreatment is effective at higher temperatures in order to promote hydrolysis, but in practice, for example, the pretreatment should be performed at a temperature of about 70 to 95 ° C. The pretreatment time may be an appropriate time depending on the size of the iron-based substrate to be treated and the degree of rust.

  After the pretreatment that is performed as necessary, the above-described cleaning liquid is used for cleaning. By washing with such a washing solution, for example, according to the following general reaction formulas (2a) to (2d), iron components such as iron oxide and manganese components such as manganese oxide react with oxalic acid to form an oxalate complex. Removed from the surface.

Oxalate complexation of manganese component [MnO ₂ ] :
MnO ₂ ²⁻ + C ₂ O ₄ ²⁻ + Na ⁺ + H ⁺
→ Na ₃ [Mn (C ₂ O ₄ ) ₃ ] (↑ CO ₂ ) (2a)

First iron oxalate and oxalate complexation of iron component :
Fe (OH) ₃ + C ₂ O ₄ ² + + H ⁺
→ Fe ₃ (C ₂ O ₄ ) ₂ (↑ CO ₂ ) (2b)
Fe ₂ O ₃ + C ₂ O ₄ ²⁻ + H ⁺
→ Fe ₃ (C ₂ O ₄ ) ₂ (↑ CO ₂ ) (2c)
Fe ₃ (C ₂ O ₄ ) ₂ + Na ₂ C ₂ O ₄ + H ⁺
→ Na ₃ [Fe (C ₂ O ₄ ) ₃ ] (↑ CO ₂ ) (2d)

  In the present invention, in order to promote the oxalate chloride and complexation reaction of manganese or iron by reduction of oxalic acid as described above, and to perform cleaning effectively, it is preferable to perform such cleaning under heating, For example, cleaning may be performed by heating the cleaning liquid to 60 to 130 ° C., particularly 75 to 95 ° C. By performing the cleaning under heating in this manner, the cleaning can be performed in a short time.

Furthermore, in the present invention, it is preferable to perform a post-treatment using a strong alkaline aqueous solution after washing as described above. That is, due to the washing as described above, some of the salts and complexes produced by the reduction of oxalic acid have poor solubility and remain as precipitates in the liquid. Moreover, this precipitate has a specific gravity that is considerably heavier than that of water, has poor buoyancy, and may reattach to the substrate surface. However, when the post-treatment as described above is performed, the low-solubility complex is oxidized to form a floating colloidal precipitate and can be easily removed. The formation mechanism and composition of such colloidal precipitates have not been clearly elucidated, but it is presumed that the colloidal precipitate is probably a complex structure as shown in the following formula (3).
aNa _x [Mn (C ₂ O ₄ ) ₃ ] · b [Fe (C ₂ O ₄ ) ₃ ] · cFe ₂ O ₃ · dFe (OH) ₃ (3)

  The strong alkaline aqueous solution used for the post-treatment is preferably a liquid having a pH of 12 or more, as in the pre-treatment described above, whereby the floating colloidal precipitate as described above is formed. It is formed quickly and can be discharged in a short time.

  Cleaning using the above-described cleaning liquid can be easily performed by immersing an iron-based base material for rust removal in each liquid. For example, in a sterilization apparatus such as a retort sterilization apparatus, circulating water is used. It is preferable to adjust the pH by adding to the solution so that the washing can be performed continuously.

  FIG. 1 shows the structure of a retort sterilizer in which the above-described cleaning method of the present invention is suitably implemented.

  That is, FIG. 1 shows a schematic structure of a hydrostatic pressure pressurization type continuous retort sterilizer used for heat sterilization of a food-filled hermetically sealed package. This sterilizer includes a vertical cylindrical sterilization chamber 1 and The inlet-side water tower 2 and the outlet-side water tower 3 are arranged on both sides of the sterilization chamber 1, and each of the inlet-side water tower 2 and the outlet-side water tower 3 has a tubular structure with an inverted U-order shape. Yes.

  One pipe 2 a of the inverted U-shaped inlet side water tower 2 extends to a position lower than the sterilization chamber 1, communicates with the bottom of the sterilization chamber 1 through the inlet side bottom chamber 5, and the other pipe 2b is an entrance into which a lower part is opened and a package (not shown) to be sterilized is introduced, and a water storage tank 6 is provided at the lower end.

  Moreover, one pipe 3a of the outlet side water tower 3 extends to a position lower than the sterilization chamber 1, communicates with the bottom of the sterilization chamber 1 through the outlet side bottom chamber 7, and the other pipe 3b The lower opening is an outlet through which a package (not shown) to be sterilized is discharged, and a water storage tank 8 is provided at the lower end.

  In the sterilization apparatus as described above, a conveyor belt conveyor 10 is stretched endlessly by a predetermined roller from the inlet side water tower 2 to the sterilization chamber 1 and the outlet side water tower 3, and this belt conveyor 10 performs sterilization treatment. The package to be introduced is introduced into the inlet-side water tower 2 and discharged through the sterilization chamber 1 and the outlet-side water tower 3.

  In such a sterilizer, water supply pipes (not shown) are provided at the upper ends of the inlet-side water tower 2 and the outlet-side water tower 3, water is supplied from these upper ends, and water is stored at the bottom of the sterilization chamber 1. It is supposed to be. That is, as shown in the drawing, one pipe 2 a of the inlet-side water tower 2, the inlet-side bottom chamber 5, the bottom of the sterilization chamber 1, the outlet-side bottom chamber 7, and one pipe 3 a of the outlet-side water tower 3 are filled with water. The water that has been filled and overflowed in the pipes 2a and 3a flows into the water storage tanks 6 and 8 from the pipes 2b and 3b.

  The sterilization chamber 1 is provided with a heating member such as a band heater on the outer wall or the like, so that water at the bottom is heated by hot water. By this heating, the upper part of the hot water in the sterilization chamber 1 is pressurized by water vapor and air, and the package passing through the sterilization chamber 1 is sterilized by heating. Usually, the heat sterilization temperature in the sterilization chamber 1 is about 80 to 135 ° C. In this case, since the inside of the sterilization chamber 1 is in a pressurized state, it is possible to effectively prevent troubles due to an increase in the internal pressure of the heated package.

  In addition, it is preferable that the water supplied from the upper end of the inlet side water tower 2 is heated to an appropriate temperature. By preheating the package that passes through the one pipe 2a, The heat sterilization effect can be enhanced. The water supplied from the upper end of the outlet-side water tower 3 is preferably at a relatively low temperature. The packaging body is primarily cooled by the pipe 3a, and the cooling water is sprayed by the pipe 3b. By performing the next cooling, the package that has been sterilized by heating can be quickly and efficiently cooled.

  In the other pipe 2b of the inlet-side water tower 1, it is preferable to perform rough cleaning by spraying warm water on the package by spraying or the like. This is because it is possible to reduce the mixing of oil and the like into the water introduced into the sterilization chamber 1.

Further, although not shown, a drainage valve is provided at the inlet side bottom chamber 5 and the outlet side bottom chamber 7 or at the bottom of the sterilization chamber 1 so that water in the sterilization chamber 1 can be drained appropriately. It has become.
In addition, unlike the tower-type continuous retort sterilizer described above, there is also a horizontal continuous retort sterilizer in which the sterilization chamber is a floor horizontal type. In this type, the part to be sterilized is immersed in pressurized hot water. Is the majority.

<Washing>
In the continuous heat sterilizer having the above-described structure, for example, the sterilization chamber 1, the inlet-side water tower 2, the outlet-side water tower 3, the walls of the water storage tanks 6 and 8, the conveyor 10, and the like are made of stainless steel, particularly in contact with water. As the sterilization with hot water is repeated, brown rust may be generated in the area where the water is applied, and when water with a lot of iron and silicic acid is supplied, these inorganic substances are deposited as brown structures over time. There are things to do. In such a case, the cleaning method of the present invention is carried out to remove rust.

  In addition, while carrying out heat sterilization with hot water, floating substances, oil residue, etc. are generated in the hot water, and these not only adhere to the packaging container to be sterilized but damage the appearance and reduce the commercial value. Since it also becomes a factor of rusting, generally, a purifier as proposed in Patent Documents 1 to 3 described above is regularly supplied into hot water.

  By the way, in order to carry out the cleaning method of the present invention for the sterilization apparatus having the structure described above, the sterilization chamber 1 is hydraulically sealed, so that the above-described cleaning liquid or solid cleaning agent is passed through the upper ends of the inlet side water tower 2 and the outlet side water tower 3. It may be supplied from the part until a predetermined pH is reached. Further, the cleaning liquid or the like can be directly supplied to the water tank 6 or the water tank 8 until a predetermined pH is reached. Therefore, when carrying out the cleaning method of the present invention, for example, it is preferable to monitor the pH in the inlet side bottom chamber 5 and the outlet side bottom chamber 7 and the water storage tanks 6 and 8 in the sterilization chamber 1. In addition, the pre-treatment and the post-treatment using the strong alkaline aqueous solution may be performed by supplying the strong alkaline aqueous solution in the same manner as described above. After washing, the liquid may be appropriately discharged from the inlet side bottom chamber 5 and the outlet side bottom chamber 7.

  By the way, when the cleaning method of the present invention is carried out, carbon dioxide gas is generated. When cleaning is performed in a state where the sterilization chamber 1 is sealed as in the above-described apparatus, the internal pressure rises, and during the cooling process, carbon dioxide gas is liquid. It may be dissolved in it and become a reduced pressure state. Therefore, in this cleaning, it is preferable to keep the inside of the sterilization chamber 1 in an open system by opening a valve or the like.

The invention is illustrated by the following experimental example.
In carrying out the following experiment, for the retort sterilization apparatus having the structure shown in FIG. 1 in which retort sterilization was repeatedly performed, a conveyor substrate (made of SUS) with brown rust was cut into small pieces having a width of about 3 cm, and a sample It was a piece.

<Experimental example 1>
The rusted portion on the surface of the sample piece was scraped off, IR analysis was performed by the KBr method, and the IR chart is shown in FIG.
From FIG. 2, the rust component is a complex salt of iron oxide, a small amount of manganese dioxide, and silicate, and this complex salt is presumed to have adhered via fatty acid iron or fatty acid calcium.

<Experimental example 2>
Solid detergents consisting of sodium oxalate powder, oxalic anhydride powder and mixed powder, with different addition amounts of sodium oxalate powder, were prepared, and using this solid detergent, pH 1, 3, 4, 6, 8 A mixed aqueous solution of 10 and 12 oxalic acid and sodium oxalate each having a solid content of 0.5% was prepared.
Each mixed aqueous solution was kept at 95 ° C., and the sample piece was immersed in each for 2.5 hours, the state of the sample piece surface and the presence or absence of corrosion were observed, and the state of the mixed aqueous solution was also observed. The results were as follows.

pH = 1;
The brown color on the surface of the sample piece disappeared and no corrosion was observed. Further, a black precipitate was observed in the mixed aqueous solution.
pH = 3;
The brown color on the surface of the sample piece disappeared and no corrosion was observed, and the surface of the sample piece was in the best condition. Further, a black precipitate was observed in the mixed aqueous solution.
pH = 4;
The brown color on the surface of the sample piece slowly disappeared and no corrosion was observed. Further, a black precipitate was gradually formed in the mixed aqueous solution.
pH = 5;
The brown color on the surface of the sample piece did not change and no corrosion was observed. No precipitate was found in the mixed aqueous solution.
pH = 6;
The brown color on the surface of the sample piece did not change and no corrosion was observed. No precipitate was found in the mixed aqueous solution.
pH = 8;
The brown color on the surface of the sample piece did not change and no corrosion was observed. No precipitate was found in the mixed aqueous solution.
pH = 10;
The brown color on the surface of the sample piece did not change and no corrosion was observed. No precipitate was found in the mixed aqueous solution.
pH = 12;
The brown color on the surface of the sample piece did not change and no corrosion was observed. No precipitate was found in the mixed aqueous solution.

  From the above results, it can be seen that a mixed aqueous solution having a pH of 1 to 4 is effective for rusting, and a solution having a pH of about 3 is optimal.

<Experimental example 3>
The mixed aqueous solution having a pH of 3 was maintained at 90 ° C., and the specimen was immersed for 15 hours for observation. As a result, compared with Experimental Example 2 in which the temperature of the mixed aqueous solution was maintained at 95 ° C., the browning rate was slightly reduced, but finally the brown color on the surface was completely eliminated. Further, no corrosion of the test piece surface was observed.
Further, the surface of the test piece was polished to give a mirror surface, and an experiment similar to the above was performed, but the mirror surface was not changed and no corrosion was observed.

<Experimental example 4>
A sodium hydroxide aqueous solution having a pH of 13 was maintained at 95 ° C., and the test piece was immersed in this aqueous solution for 15 hours, and then the test piece was immersed in a mixed aqueous solution having a pH of 3 under the same conditions as in Experimental Example 3. . As a result, it was recognized that the brown color decreased faster than Experimental Example 3.

<Experimental example 5>
Sodium carbonate was added to the mixed aqueous solution having a pH of 3 after the test in Experimental Example 1 to adjust the pH to 13, and the mixture was further heated to 95 ° C. for 1 hour. As a result, the black precipitate formed in the mixed aqueous solution was It turned into a particulate haze deposit and floated in the liquid.

The schematic sectional drawing which shows an example of the heat sterilizer with which the washing | cleaning method of this invention is implemented suitably. The figure which shows the IR chart of the rust produced | generated on the stainless steel conveyor board | substrate surface (experiment example 1).

Explanation of symbols

1: Heat sterilization chamber 2: Entrance side water tower 3: Exit side water tower

Claims (9)

  The iron-based device or the iron-based device member is cleaned using a mixed aqueous solution containing oxalic acid and an alkali metal oxalate salt or ammonium oxalate and having a pH adjusted to a range of 1 to 4. Cleaning method.   The cleaning method according to claim 1, wherein the cleaning using the mixed aqueous solution is performed under heating at 60 to 130 ° C.   The cleaning method according to claim 1 or 2, wherein after the cleaning using the mixed aqueous solution, the post-treatment is performed using a strong alkaline aqueous solution having a pH of 12 or more.   The cleaning method according to any one of claims 1 to 3, wherein a pretreatment is performed using a strong alkaline aqueous solution having a pH of 12 or more prior to the cleaning using the mixed aqueous solution.   The cleaning method according to any one of claims 1 to 4, wherein the mixed aqueous solution is prepared by adding a mixed solid containing oxalic acid and an alkali metal oxalate salt or ammonium oxalate to water.   The cleaning method according to claim 1, wherein the iron-based device is a heat sterilizer.   A powder or solid form rust remover comprising a mixture of an alkali metal oxalate and an oxalic anhydride or oxalic acid dihydrate.   The rust removal detergent according to claim 7, comprising a mixture of 100 parts by weight of sodium oxalate and 80 to 120 parts by weight of oxalic anhydride.   The rust removal detergent according to claim 7, comprising a mixture of 100 parts by weight of sodium oxalate and 120 to 160 parts by weight of oxalic acid dihydrate.

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