RU2516176C2 - Inhibitor of carbonic acid corrosion for steam boilers of low and medium pressure aminat pk-2 - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to inhibitors of corrosion of carbon steels in acidic and neutral oxygen-containing water solutions. Inhibitor includes, wt.p.: morpholine 10-12, cyclohexylamine 8-10, dimethylaminoethanol 15-20, water - the remaining part.

EFFECT: reduction in rate of corrosion of equipment and pipelines of steam-condensate tract due to neutralisation of carbonic acid with simultaneous increase of heat carrier pH.

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Description

The invention relates to carbon steel corrosion inhibitors in acidic and neutral oxygen-containing aqueous solutions, which are widely used in medium and high pressure steam generating plants.

Currently, the amination method is used at power facilities, which consists in treating boiler water with ammonia, the effectiveness of which is due to such ammonia properties as high volatility and good neutralizing ability (see copyright certificate SU No. 120277, class C23F 11/00, 01.01.1959) .

However, for equipment made of copper-containing alloys, the use of ammonia at recommended concentrations of 500-1000 μg / l (especially in the presence of a residual oxygen content) limits the effectiveness of this method and the reliability of equipment protection due to a sharp increase in the corrosion rate.

Neutralizing amines as inhibitors of carbon dioxide corrosion have advantages over ammonia, widely used in the power industry, which is widely used in thermal power plants. Neutralizing amines are slightly volatile, which reduces their losses in the steam-water tract. Unlike ammonia, they do not cause corrosion of copper-containing alloys.

For the selection and effective use of amines, it is necessary to have information on the properties of these compounds in relation to the operating conditions of steam generating plants. Such properties primarily include the neutralizing ability with respect to carbon dioxide, heat resistance, volatility (characterized by distribution coefficients between water and steam), as well as the ability to inhibit corrosion of structural materials.

Molecules of any amines in which, like ammonia, contain one atom of trivalent nitrogen capable of forming three covalent bonds, in aqueous solutions function as monobasic bases:

B + H ₂ O = BH ⁺ + OH ^-

where B are neutralizing amine molecules.

The neutralizing properties of amines are quantified by the hydrolysis constant of the above reaction:

K _G = C _{BH +} C _OH- / C _B

The ratio of the equilibrium concentrations of amine in the vapor and liquid phases under phase transition conditions (during evaporation, condensation) is determined by the distribution coefficient:

$${\mathrm{TO}}_P=C_B^{P\mathrm{BUT}R}/C_B^F$$

It is known to use 1,4-tetrahydrooxazine (morpholine) as a corrosion inhibitor. Morpholine is used to inhibit the corrosion of carbon steel, aluminum, nickel, brass, silver, as well as to regulate the pH in the condensate-feeding path. Morpholine is also used to inhibit the corrosion of natural gas pipelines (Altsybeeva A.I., Levin S.Z. Metal corrosion inhibitors. - L .: Chemistry, 1968, p.143).

When morpholine is used in a two-phase vapor-water system, its concentration in the liquid phase is significantly higher than that of other amines (Cr <1), therefore, its neutralizing effect will manifest itself immediately in the initial sections of the vapor-condensate tract, which is an advantage of this amine. However, the low neutralizing ability of morpholine significantly limits the effectiveness of this amine.

Cyclohexylamine has a high neutralizing ability. But unlike morpholine, most of cyclohexylamine remains in the non-condensed fraction of steam, while its distribution between the liquid and vapor phases is largely dependent on temperature.

Compositions obtained by mixing morpholine and cyclohexylamine can provide a more uniform alkalization along the path and increase the effectiveness of preventing carbon dioxide corrosion. However, in oxygen-containing aqueous media, these amines as corrosion inhibitors are not so effective and do not prevent ulcerative (local) corrosion. (J. Bregman. Corrosion inhibitors. - L .: Chemistry, 1966, p. 47).

The closest to the invention in technical essence and the achieved result is a carbon dioxide corrosion inhibitor for medium and high pressure steam generating plants, including morpholine and cyclohexylamine (see application EP No. 0215655, class C02F 5/10, 03.25.1987).

However, this corrosion inhibitor has a complex multicomponent composition, which includes, in addition to morpholine and cyclohexylamine, a number of components. The technology for producing this composition is complex. In addition, studies have not determined the effectiveness of the effect of this inhibitor on local corrosion.

The problem to which the present invention is directed, is to create a carbon dioxide corrosion inhibitor that effectively protects the steel metal structures of medium and high pressure steam generating plants, including from local (pitting) corrosion. Moreover, this corrosion inhibitor can be used to protect against heat exchange equipment made of carbon and low alloy steels and copper alloys.

The technical result consists in the fact that it is possible to reduce the corrosion rate of the equipment and pipelines of the vapor condensate path due to the neutralization of carbon dioxide while increasing the pH of the coolant.

This problem is solved, and the technical result is achieved due to the fact that the carbon dioxide corrosion inhibitor for steam boilers of medium and high pressure includes morpholine and cyclohexylamine, while the corrosion inhibitor additionally contains dimethylaminoethanol in the following ratio, wt.h .:

morpholine 10-12 cyclohexylamine 8-10 dimethylaminoethanol 15-20 Water rest.

The combination of several amines allows one to obtain a reagent with the best neutralizing properties, which ensure reliable operation of the equipment due to the uniform distribution of the inhibitor along the path of medium and high pressure steam generating units.

In the course of the studies, it was found that the cause of the processes of carbon dioxide corrosion in the path of medium and high pressure steam generating plants is carbon dioxide, which is formed as a result of hydrolysis and decomposition of the bicarbonate and carbonate component of the alkalinity of boiler water. Medium-pressure steam boilers are usually fueled with water softened by sodium cation or H cation. Water always contains bicarbonate ions (alkalinity) in an amount depending on the alkalinity of the raw water and the fraction of condensate return.

High-pressure steam boilers are fed partially or completely with demineralized water; therefore, the content of carbonate and bicarbonate ions is negligible in the added water. However, bicarbonates additionally enter the feed water with suction cups in the condensers of the steam generating units.

Carbon dioxide, carried away with steam, when dissolved in the condensate lowers the pH and leads to corrosion with hydrogen depolarization. Carbon dioxide corrosion of a metal leads to an increase in its brittleness, the appearance of tears and ulcers on the pipes of heat exchangers and connecting pipelines.

An experimental study of the properties of neutralizing amines for the operating conditions of medium and high pressure boilers was carried out on a semi-industrial bench simulating the operating conditions of steam generating plants.

Before starting the experiment, pre-weighed samples of the studied structural materials were loaded into the container. During the experiment, water of the required composition heated to a predetermined temperature flowed through the container with a certain speed. At the end of the experiment, the samples were removed from the container, subjected to electrochemical etching and weighed again. The corrosion rate was determined by weight loss.

Considering that the quality of feed water and condensate of TPPs is strictly regulated by the standards of PTE, the experiments were conducted on waters of the appropriate composition. The temperature regime of the studies was chosen in accordance with the temperature regime of the condensate and feed paths of medium and high pressure boilers.

Given that in medium- and high-pressure boilers, high-temperature sections of the condensate path are subjected to the greatest corrosion, a given temperature of 250 ° C was chosen for research.

Results of corrosion tests for condensate path conditions of medium and high pressure boilers. For comparison, part of the experiments was carried out without dosing of reagents and with dosing of ammonia. The inhibitor was prepared by mixing the components of the active base, consisting of morpholine, cyclohexylamine and dimethylaminoethanol, and dissolving them in purified water. The results of the experiments are shown in table 1

Table 1 Example The composition of the active base The ratio of components, parts by weight The dose of the active base, mg / l Corrosion rate, mm / year The percentage of ingibaniya, st / lat.% Article 20 Brass L 68 one No inhibitor - 0.85 0.1 - 2 Ammonia 1,0 0.2 0.05 76.5 / 50 3 Morpholine 3.0 20,0 0,045 0.015 94.7 / 85 Cyclohexylamine 6.0 Dimethylaminoethanol 26 four Morpholine 6.0 20,0 0.04 0.008 95.3 / 92 Cyclohexylamine 9.0 Dimethylaminoethanol twenty 5 Morpholine 12 20,0 0.025 0.008 97.1 / 92 Cyclohexylamine 8.0 Dimethylaminoethanol 15.0 6 Morpholine 16,0 20,0 0,035 0.008 96.1 / 92 Cyclohexylamine 9.0 Dimethylaminoethanol 10.0

The experiments with the dosing of ammonia were carried out at a concentration of 1 mg / l, which corresponds to the maximum allowable for medium and high pressure boilers according to the standards of PTE. However, corrosion inhibition during dosing of ammonia is negligible for carbon steel. In the presence of neutralizing amines for all ratios of components, a slowdown in steel corrosion was obtained. At the same time, the optimal ratio of amines was determined, at which the prevention of corrosion processes in high-temperature sections of the steam condensate path (boiler superheaters and surfaces of turbine blades) is maximum.

A significant slowdown in brass corrosion was also obtained by dosing neutralizing amines.

In addition, studies were conducted for the temperature regime of the condensate path and industrial consumers of a pair of medium and high pressure boilers at 160 ° C. The results of the experiments are given in table.2.

table 2 Example The composition of the active base The ratio of components, parts by weight The dose of the active base, mg / l Corrosion rate, mm / year The percentage of ingibaniya, st / lat.% Article 20 Brass L 68 one No inhibitor - - 0.7 0.1 - 2 Ammonia 1,0 0.15 0.06 78.6 / 40 3 Morpholine 3.0 20,0 0.05 0.006 92.9 / 94 Cyclohexylamine 6.0 Dimethylaminoethanol 26 four Morpholine 6.0 20,0 0.04 0.006 94.3 / 94 Cyclohexylamine 9.0 Dimethylaminoethanol twenty 5 Morpholine 12 20,0 0,025 0.004 96.4 / 96 Cyclohexylamine 8.0 Dimethylaminoethanol 15.0 6 Morpholine 16,0 20,0 0.05 0.004 92.9 / 96 Cyclohexylamine 9.0 Dimethylaminoethanol 10.0

Slowing down corrosion of samples of article 20 was observed both with the introduction of ammonia and with the dosing of amines. However, the greatest effectiveness in limiting corrosion for samples of article 20 in all three experiments was obtained with the ratio of components given in the claims. A decrease in the content of individual components below the specified limits or an increase above the specified limits leads to a decrease in the degree of protection.

Studies were also carried out for the conditions of the nutrient path of medium and high pressure boilers and heating the coolant to a temperature of up to 250 ° C. During corrosion tests simulating the working conditions of the nutrient tract, only the corrosion rate of samples from st.20 was determined. The quality of the feed water of medium-pressure boilers with a higher content of carbonate and bicarbonate ions was simulated as a heat carrier. The results of the experiments are given in table.3.

Table 3 Example The composition of the active base The ratio of components, parts by weight The dose of the active base, mg / l Corrosion rate, mm / year The percentage of ingibiriya,% Article 20 one No inhibitor - - 1,2 - 2 Ammonia 1,0 0.2 3 Morpholine 3.0 20,0 0,07 94.2 Cyclohexylamine 6.0 Dimethylaminoethanol 26 four Morpholine 6.0 20,0 0,055 95.4 Cyclohexylamine 9.0 Dimethylaminoethanol twenty 5 Morpholine 12 20,0 0,040 96.7 Cyclohexylamine 8.0 Dimethylaminoethanol 15.0 6 Morpholine 16,0 20,0 0,055 95.4 Cyclohexylamine 9.0 Dimethylaminoethanol 10.0

For the conditions of the feeding path of medium and high pressure boilers, the optimal ratio of amines has also been determined. An increase in the proportion of morpholine above the optimum due to its low neutralizing ability leads to a decrease in the effectiveness of the entire composition.

Thus, the use of the invention allows to increase the service life of equipment in steam generating installations of medium and high pressure.

Claims (1)

Carbon dioxide corrosion inhibitor for steam boilers of medium and high pressure, including morpholine and cyclohexylamine, characterized in that it additionally contains dimethylaminoethanol in the following ratio, wt.h .:
morpholine 10-12 cyclohexylamine 8-10 dimethylaminoethanol 15-20 water rest