RU2146307C1 - Method of protecting plants from corrosion - Google Patents

Abstract

FIELD: heat and power engineering, particularly, protection from corrosion of steam-water circuits of turbine plants operating by cross-connection flow diagram. SUBSTANCE: method includes introduction into power plants of steam-water mixture with film-forming aliphatic amines of R-NH₂ type, where R is hydrocarbon radical with weight fraction of primary amines (C16-C18) in the amount of not less than 99%, and iodine number of not in excess of 2, and preservation for time required for sorption of amines on protected surfaces. The method provides for increase of protection from corrosion without decrease of temperature conditions that makes it possible not only combine in time of plant operation and operations for its protection from corrosion, but even protective effect due to use of higher sorption properties of plant components. EFFECT: higher efficiency. 8 cl, 2 dwg

Description

 The invention relates to the field of power engineering, and more specifically relates to a method of corrosion protection of steam-water paths of nuclear, thermal power plants and other power plants and is intended to prevent (or significantly slow down) the corrosion of metals in steam and water paths of equipment that can be used during repair work thermomechanical equipment or when withdrawing it to the reserve.

 A known method of protection against corrosion of steam-water paths of a turbine unit, which is used to preserve turbines that are put into reserve for a long time or for repair work.

 In accordance with this method, hot or dried air, or a working agent, is used to protect against corrosion, wherein hot air can be used using volatile corrosion inhibitors. When heated, the inhibitor is sublimated and transferred to conserved equipment, where it is precipitated with a film in contact with the cold metal surface of the protected tracts. As corrosion inhibitors, an amine-containing compound is used, for example, cyclohexylamine carbonate or nitrite dicyclohexylamine, to form a uniform film on the protected surfaces, they are treated in two directions with this mixture (E.Yu. Kostrikina, V.P. Pershantseva, O.V. Zamyatina, E.V. Kuznetsova, NK Mikhailov "Conservation of turbines by inhibited air". Energetik, N 9, 1983, S. 9-10).

 This method of corrosion protection is laborious, requires a constant energy consumption, as well as means for sealing the turbine to prevent leakage of the inhibitor into the surrounding space. In addition, this method of protection is used only on turbines taken into reserve, and excludes its use on turbine cylinders open during repair, which limits the scope of its use.

 The closest to the proposed technical essence and the achieved result is a method of corrosion protection of power plants, including the introduction of a steam-water mixture with octadecylamine into the installation, preservation of it for the time necessary for sorption of octadecylamine on the protected surfaces, and de-preservation of the installation using desalted deaerated water ( WO 93/06260, A1, 04/01/93).

 The disadvantages of this method is the inability to protect against corrosion at nominal parameters of the operating mode of the installation, since the aliphatic amines used in domestic practice have a low degree of purification and, most importantly, a high iodine number, so they begin to decompose at temperatures much lower than the operating ones and lose its protective properties.

 The technical result of the invention is to provide the possibility and increased protection against corrosion without reducing the temperature regime, which allows not only to combine the operation of the installation and the operations associated with its protection against corrosion, but also to enhance the protective effect through the use of increased sorption properties of the elements of the installation.

The technical result is achieved by the fact that in the method of corrosion protection of plants, comprising introducing into the plant a steam-water mixture with film-forming aliphatic amines of the R-NH _{2 type} , where R is the C ₁₆ -C ₁₈ hydrocarbon radical, preservation for the time required for the sorption of amines on protected surfaces with a mass fraction of primary amines (C ₁₆ ^o CC ₁₈ ) of at least 99% and an iodine number of not more than 2.

Optimal conditions for achieving a technical result:
- you can use amines that do not contain amino groups C ₈ , C ₁₀ , C ₁₂ , amides and nitriles;
- stearylamine octadecylamine, 1-amino-octadecane can be used as amines;
- before or after dosing of amines, ammonia, hydrazine and phosphates can be introduced into the steam-water mixture;
- preservation can be carried out until the specific sorption of amines of at least 3.2 mg / m ^{2 is} achieved;
- you can pre-wash the protected surfaces;
- washing can be carried out by introducing a steam-water mixture with amines;
- preservation can be carried out by mixing the steam-water mixture with amines in a dynamic mode;
- the introduction of the steam-water mixture can be carried out in the installation or in a dedicated installation unit - a pair: boiler-turbine.

The method is based on the use of aliphatic amines of the type R-NH ₂ , where R is the C ₁₆ -C ₁₈ hydrocarbon radical, which is used by treating the protected metal surfaces with an aqueous emulsion or steam containing an amine. After a certain time, depending on the initial concentration of the amine, surface area, surface contamination, kind of metals, a protective (hydrophobic) amine film forms on the metal surfaces, which protects the metal from parking corrosion. Along with this, due to the penetration of the amine to the metal, exfoliation of the existing deposits takes place, and deposits and corrosion products are displaced from the pores, cavities, cracks. Including corrosion-hazardous elements (chlorides, etc.), which are easily removed during repair and commissioning of equipment, which is a factor in increasing the efficiency of the equipment. By removing corrosive elements increases the reliability of the equipment due to a significant reduction in the likelihood of the formation of corrosion cracking of metal under voltage. The amine film is quite durable and provides protection against parking corrosion during the period of downtime and repair of equipment of the unit.

Use film-forming aliphatic amines of the type R-NH ₂ , where R is a hydrocarbon radical. The mass fraction of primary amines (C ₁₆ -C ₁₈ ) should be at least 99%, and the iodine number should be no more than 2. Such a high degree of purification of amines makes it possible to use them in the operating mode, i.e. at temperatures up to 600 ^o C, since the decomposition rate of amines of such a degree of purity and with such a small iodine number is quite low. The amines used should not contain the amino groups C ₈ , C ₁₀ , C ₁₂ , and impurities of amides and nitriles, which further increases their temperature stability.

 To comply with these requirements, stearylamine, octadecylamine, and highly purified 1-amino-octadecane can be used as amines.

 Preservation of thermal power equipment using these substances can be carried out at thermal and nuclear power plants of block type and thermal stations with cross-links.

 Figure 1 presents the scheme of conservation of equipment of a thermal power plant of block type. In this case, for the preservation, a standard unit operation scheme is used, including a boiler 1, a turbine 2, a condenser 3, regenerative heaters 4, 5, pumps 6, 7. The preservative is dosed to the suction of the feed pump.

 In FIG. 2 shows a scheme of conservation of equipment of thermal power plants with transverse connections. Such a scheme is used when the installation is working with a partial load. In this case, for preservation, the boiler 1, 2, 3 and the turbine 4, 5, 6 with auxiliary equipment are allocated to the unit using shutoff valves 7-14. According to this scheme, by switching reinforcement, any pair can be distinguished; boiler 1 - turbine 4, boiler 1 - turbine 5, etc.

Preservative reagent is dosed into the power plant path in front of the feed pump. The equipment can operate both at nominal parameters and in partial load mode. Preservation is carried out for the time necessary for the adsorption of these reagents on the internal surfaces of the equipment. The amount adsorbed on the surface of the reagent should be at least 3.2 mg / m ² .

 When using aliphatic amines for preservation, washing of the internal surfaces of the equipment from iron, copper and organosilicon deposits, chlorides, sulfates, oil products, etc. can be observed. In this case, it is necessary to carry out the conservation process taking into account the current data of the water-chemical regime. Dosing of the reagent is carried out in several stages, each time increasing its concentration in the steam-water tract. The washing products are removed through continuous purging of the boiler and through periodic purging of the lower points. For these purposes, it is not possible to briefly incorporate a block desalination plant into operation. The moment of completion of washing is stabilization of the parameters of the water-chemical mode of operation of the equipment.

 The treatment of the steam-water tract with preservative reagents may include the following sequence of operations: washing the internal surfaces of the equipment from iron oxide, copper-containing deposits and corrosive impurities, oil products and preservation of the power unit circuit. In this case, a decrease in the intensity of erosion-corrosion wear of the equipment and an increase in the efficiency of the unit during its operation are achieved. It is not necessary to de-preserve the equipment before start-up.

 The calculated concentration of amine in the working mixture depends on many factors: the area of the surfaces to be protected, the degree of contamination of the surfaces, the type of metal, the speed of the working medium, etc. For each specific item of equipment, this is a different value. Ultimately, this value is determined by the rate of sorption of the amine on the metal surface and is determined experimentally.

 The sorption rate for a particular equipment is accelerated or slowed by a change in amine concentration.

 The exposure time of the working mixture or its transportation (preservation time) is determined by the rate of decrease in the concentration of amine in the working mixture.

 The conservation process ends when there is a significant slowdown in the rate of decrease in the concentration of amine in the working mixture.

 The results of the studies show that the specific sorption of amine from a preservative on the protected surfaces of dissimilar metals is not the same and depends on many factors, primarily on the initial (calculated) concentration of amine in the preservative, temperature, speed, phase state of the working mixture in the equipment cavities, and the time to reach the maximum possible sorption of the reagent and its absolute value for dissimilar metals are significantly different. The effectiveness of the method will be higher if the initial concentration of the amine in the equipment is determined depending on the maximum possible specific sorption of it on the surface of a particular metal. It is equally important from the point of view of saving reagent and time costs that the end time of the formation of the protective film is determined by the moment of a significant decrease in the rate of sorption of the amine on the protected metal surface.

 Due to changes in the processes of hydrodynamics, boiling and condensation, the presence of a hydrophobic film on the metal surface for a considerable time increases the efficiency of the unit by 1-1.5%.

 The method allows, along with the conservation of the unit as a whole, to carry out element-by-element conservation of equipment.

 Thus, the invention provides an increase in the effectiveness of corrosion protection at nominal parameters of the operating mode of the installation.

 The technical result of the invention is to provide the possibility and increased protection against corrosion without reducing the temperature regime, which allows not only to combine the operation of the installation and the operations associated with its protection against corrosion, but also to enhance the protective effect through the use of increased sorption properties of the elements of the installation.

Claims (8)

1. A method of protecting against corrosion of power plants, including introducing into the installation a steam-water mixture with film-forming aliphatic amines of the R-NH _{2 type} , where R is the C ₁₆ -C ₁₈ hydrocarbon radical, preservation for the time required for the sorption of amines on the protected surfaces, different the fact that amines with a mass fraction of primary amines C ₁₆ -C _{18 of} at least 99% and an iodine number of not more than 2 are used. 2. The method according to claim 1, characterized in that the use of amines that do not contain amino groups C ₈ , C ₁₀ , C ₁₂ , amides and nitriles.  3. The method according to p. 1 or 2, characterized in that as amines use stearylamine, octadecylamine, 1-amino-octadecane. 4. The method according to any one of claims 1 to 3, characterized in that the preservation is carried out until the specific sorption of amines of at least 3.2 mg / m ^{2 is} achieved.  5. The method according to any one of claims 1 to 4, characterized in that the washing surfaces to be protected are preliminarily washed.  6. The method according to any one of claims 1 to 5, characterized in that the washing is carried out by introducing a steam-water mixture with amines.  7. The method according to any one of claims 1 to 6, characterized in that the preservation is carried out by mixing the steam-water mixture with amines in a dynamic mode.  8. The method according to any one of claims 1 to 7, characterized in that the introduction of the steam-water mixture is carried out in the installation or in a dedicated unit of the installation - a pair of boiler-turbine.

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