Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B08—CLEANING
  • B08B—CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
  • B08B3/00—Cleaning by methods involving the use or presence of liquid or steam
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
  • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
  • C23G1/14—Cleaning or pickling metallic material with solutions or molten salts with alkaline solutions
  • C23G1/19—Iron or steel
• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
  • G21F9/00—Treating radioactively contaminated material; Decontamination arrangements therefor
  • G21F9/001—Decontamination of contaminated objects, apparatus, clothes, food; Preventing contamination thereof

Definitions

• the invention relates to a method for cleaning a container, in particular a steam generator in a nuclear power plant, iron oxide located in the container being dissolved by a complexing acid.
• a cleaning method is known from DE-A 1 517 406 with which scale is removed from metal surfaces.
• scale can contain iron oxide, it consists primarily of calcium compounds.
• a saline solution containing, for example, a salt of nitrilotriacetic acid is used to remove scale.
• Ammonia is also used to adjust the pH.
• the known solution works passivating and decomposing. The main thing that decomposes is scale. The passivation is a protection of the cleaned surface by a layer to be applied. The surface is specifically oxidized. Otherwise, the dissolution temperature of the salt is not exceeded in the known. So there is not a fully dissolved salt.
• the known method removes scale and not iron oxide.
• the solution used has a passivating effect. This means that an iron oxide protective layer is built up.
• a process for removing iron oxide is known from CA-A 1 062 590.
• An acid is used, which may be mixed with hydrazine.
• a multi-stage process the so-called Mark III process, is also known, which is carried out alternately in the acidic and in the neutral range. This complex cleaning process takes a lot of time and causes very high costs.
• the invention was therefore based on the object of specifying a method for cleaning a container, in particular a steam generator, which, with very good effectiveness, minimizes attacks by the cleaning chemicals on the materials of the container and the lines, by not bringing any aggressive acids into contact with the surface. It is not intended to build up a protective layer of oxides, but rather to dissolve iron oxide. The chemicals used should always be completely dissolved in a solution for better effectiveness.
• the object is achieved according to the invention in that a salt solution which is produced from an acid which is a complexing agent, from a volatile alkalizing agent and from a reducing agent and which has an alkaline reducing effect is introduced into the container in such a way that the saline solution for a predetermined period of time at a temperature between 150 ° C and 250 ° C and below the decomposition temperature of the anionic part of the salt solution for the purpose of forming an iron complex in the container, and that the dissolved iron complex is then removed by emptying the container.
• the iron complexation and thus the cleaning of the container takes place with great effectiveness in the alkaline range.
• the acid, or its anionic part causes the complex formation.
• the volatile alkalizing agent raises the pH of the cleaning solution to the alkaline range.
• the cleaning solution therefore has a reducing and not passivating effect. So no protective layer is built up, but iron oxide is removed.
• the reducing conditions caused by the reducing agent are necessary, on the one hand, to reduce trivalent iron to divalent iron and, on the other hand, to reduce harmful effects of the cleaning solution on the metal surfaces of the container.
• the desired iron complexation in the alkaline range is made possible.
• a temperature below the dissolution temperature of a salt that is, a temperature at which the salt is not completely dissolved, is unsuitable for complex formation.
• the pH value of the cleaning solution is of crucial importance for optimal cleaning efficiency. A pH value that is too low would lead to a high removal of base metal from unalloyed and low-alloyed materials in the container. If the pH is too high, the iron solubility is greatly reduced.
• Optimal cleaning success with low base metal removal on unalloyed and low-alloy materials is achieved with the cleaning method according to the invention at a pH between 9.0 and 9.5 and at a temperature between 170 ° C and 220 ° C.
• the advantage is achieved that in only one process step and with great effectiveness, the container is freed from iron oxide deposits without the surfaces of the container and the supply pipes being attacked or even damaged by acids. Containers and pipes are not attacked by the alkaline chemical solution.
• the cleaning process according to the invention can be carried out 40 times faster and causes only a tenth of the costs incurred there.
• nitrilotriacetic acid which is known per se, is used as the complex-forming acid.
• Suitable volatile alkalizing agents are preferably ammonia, hydrazine, morpholine or a mixture of the substances mentioned. Hydrazine, for example, is used as the reducing agent. Hydrazine can thus act as a volatile alkalizing agent and as a reducing agent.
• the dissolved salt is adjusted to a pH greater than 9.6 by a further addition of volatile alkalizing agent and then metered into the container.
• the optimum pH value for cleaning which is between 9.0 and 9.5, is adjusted by partially evaporating the volatile alkalizing agent and water in the container. This pH value control advantageously prevents complex formation and thus removal in the mostly very long supply line to the container, which would result in reduced cleaning performance in the container itself.
• the pH is to be controlled via the composition of the metered solution and the duration of the evaporation of the alkalizing agent.
• the evaporation process advantageously results in homogeneous mixing of the solution in the container.
• part of the solution in the container is evaporated for a limited time. This creates a flow within the container, which leads to even better contact between the cleaning solution and the surfaces to be cleaned.
• alkalizing agents e.g. Hydrazine
• the dissolved salt to be dosed is degassed, for example, before dosing and 0.1% to 5% hydrazine is added to it as a reducing agent. Hydrazine is also regularly metered into the container during cleaning, so that a hydrazine concentration of 10 to 500 milligrams per gram is set there.
• the container is emptied.
• the container is pressed empty, for example by an inert gas, in particular by nitrogen or water vapor. This prevents iron oxide from being formed again by penetrating atmospheric oxygen.
• a possible proportion of copper in the deposits in the container does not interfere with the method according to the invention as long as it is less than 10%.
• the copper can then be removed after the iron oxide has been removed in accordance with the invention.
• the advantage of the invention is that containers, in particular steam generators of a nuclear power plant, can be reliably freed of iron oxide deposits in a short time and at low cost while protecting the metal surfaces. Particularly in the case of nuclear power plants, a particular advantage can be seen in the fact that only a downtime of approximately 12 hours is required for a complete cleaning of a steam generator.
• impurities which are introduced and deposited in the form of salts in the container in continuous operation are effectively removed.
• damage to the low and unalloyed base metals by etching is also excluded.
• the chemicals required for the process according to the invention cause considerably lower costs than other cleaning processes.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Life Sciences & Earth Sciences (AREA)
• General Engineering & Computer Science (AREA)
• High Energy & Nuclear Physics (AREA)
• Food Science & Technology (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
• Detergent Compositions (AREA)

Applications Claiming Priority (2)

Publications (2)

Family

ID=6314830

Family Applications (1)

Country Status (7)

Cited By (2)

Families Citing this family (11)

Family Cites Families (10)

• 1987
  • 1987-11-19 DE DE8787117112T patent/DE3771859D1/de not_active Expired - Lifetime
  • 1987-11-19 ES ES87117112T patent/ES2023397B3/es not_active Expired - Lifetime
  • 1987-11-19 EP EP87117112A patent/EP0273182B1/de not_active Expired - Lifetime
  • 1987-11-27 CA CA000552956A patent/CA1316799C/en not_active Expired - Lifetime
  • 1987-11-27 JP JP62301393A patent/JPS63143276A/ja active Granted
  • 1987-11-30 KR KR1019870013507A patent/KR950013495B1/ko not_active Expired - Lifetime
• 1991
  • 1991-03-14 US US07/669,032 patent/US5164015A/en not_active Expired - Lifetime

Also Published As

Similar Documents

Legal Events