DK152766B - CORROSION INHIBITOR FOR WATER Vapor condensate systems, AND PROCEDURES FOR INHIBITING CORROSION SEED SYSTEMS - Google Patents

Description

The invention relates to a corrosion inhibitor for water-vapor condensate systems and a method for corrosion control in water vapor condensate systems and other aqueous systems in which the mineral content is relatively low, by means of this inhibitor.

In particular, the invention relates to a method of preventing corrosion in water vapor condensate systems in the form of the use of methoxypropylamine in combination with hydrazine to control water vapor condensate systems or other low solids aqueous systems.

Condensate corrosion protection is an ever-growing phenomenon in the operation of aquifers. In these energy-conscious times, increasing the amount and quality of condensate will result in water and heat savings. the total boiler system.

in historical terms, the effect of dissolved gases, such as oxygen and carbon dioxide, have been two of the main factors leading to condensate corrosion. To understand the role of oxygen and carbon dioxide in corrosion, one must understand the electrochemical nature of corrosion. Pure water has very little effect on pure iron, but this situation rarely occurs. In most circumstances, there is a tendency for iron to dissolve in water and two electrons are released for each atom that dissolves. These electrons are transferred to hydrogen ions present in water and the ions are reduced to elemental gaseous hydrogen. Any effect ceases at this stage if the hydrogen remains on the surface of the metal because a protective coating is formed which interferes with the passage of electrons. However, any agent which increases the number of hydrogen ions present in the water or which will remove the protective film serves to increase the rate of corrosion.

When carbon dioxide dissolves, it reacts with water to form carbonic acid, which supplies additional active hydrogen to the system. Iron displaces the hydrogen from this acid. When oxygen is also present in the water, a two-fold reaction takes place. Some molecules of oxygen are combined with the displaced hydrogen, thus exposing the metal to a fresh attack. Other oxygen molecules are combined with iron ions to form insoluble rust compounds.

A greater corrosive influence than the mere dissolving tendency of iron is the existence of a heterogeneous surface in commercial iron and steel due to the presence of superficial defects which tend to form galvanic element with the adjacent base metal. Electrons are released from the anodes of these galvanic elements to the hydrogen ions at the adjacent cathodic surface, thereby increasing the corrosive area and accelerating the corrosion rate.

The first corrosion product can be converted to ferric oxide which exhibits only a loose adhesion and which makes the corrosion even more pronounced by blocking areas so that oxygen can be accessed. These areas become anodic and galvanic iron oxide elements are produced. The iron during the oxide precipitation is then dissolved and crater formation is developed. As a result, there is an attack of carbon dioxide, thereby reducing the metal thickness and thereby forming grooves in the metal.

For the systems that allow, film-forming amines will provide condensate corrosion protection against both oxygen and carbon dioxide. However, many industrial systems cannot withstand film-forming amines and must make use of neutralizing amines.

The ideal neutralizing amine should exhibit the following characteristics: 1. The distribution ratio should be so high that a significant amount of the neutralizing amine supplied to the boiler will be found in the condensate. This will reduce the loss of neutralizing amine via blowout.

2. The distribution ratio should not be too high to minimize losses from aeration and venting. The distribution ratio is the ratio of the amount of amine in the vapor phase to the amount of amine in the liquid phase.

3. The value of the basicity should be moderately high or very high so that the amine will effectively neutralize the entire amount of carbon dioxide present.

4. The neutralizing amine should have sufficient hydrolytic and thermal stability that it will not degrade to ammonia and other compounds in the boiler or to superheated or saturated steam.

5. The neutralizing amine should be a water-soluble liquid for ease of dosing.

Such neutralizing amines as cyclohexylamine and morpholine have been used, but they exhibit several disadvantages. P.eks. For example, cyclohexylamine has a high distribution ratio and, as a result, significant amounts of cyclohexylamine escape from the system through the vent valve. Morpholine, on the other hand, has a low value of the basicity, which means that more morpholine is required to obtain high values of pH in the condensate system, and it also has a very low distribution ratio, which means that significant amounts thereof are lost via blowout.

The corrosion inhibitor of the invention eliminates the above-mentioned disadvantages of cyclohexylamine and morpholine in that it contains methoxypropylamine, which has a very desirable distribution ratio and a rather high basicity value, and in which the hydrazine acts as an oxygen scavenger.

During operation, corrosion inhibitor concentrations of 22 to 1000 mg / l, preferably 85 to 100 mg / l, should be maintained in the water vapor condensate system. The corrosion inhibitor should contain from approx. 85% to approx. 99% methoxypropylamine and from approx. 1% to approx. 15% of the oxygen corrosion inhibitor. The corrosion inhibitor of the invention can be supplied to the water vapor condensate system treated by conventional liquid supply means or it can be supplied to the boiler feed water or directly to the water vapor supply lines.

The following examples are intended to illustrate the use of methoxypropylamine in combination with hydrazine as a water vapor condensate corrosion inhibitor, according to the technical teachings of the invention.

EXAMPLE 1

Distribution ratios of a number of neutralizing amines were calculated by preparing solutions of each amine having a concentration of 100 mg / l and adding 500 ml of this solution to a brine vessel which is slowly and uniformly heated so that 100 ml distillate is produced every 40 'minutes. Additional solution is manually added to the saline container every 5 'to every 10' minutes to maintain the solution in the 500 ml labeled saline container.

Each 100 ml aliquot of distillate is collected and the pH is determined until a constant pH is obtained for three consecutive aliquots. This is taken as evidence that equilibrium conditions are being established. At equilibrium, the brine and the final 100 ml are analyzed by gas chromatography to determine the amount of amine in each and every partition ratio (DR) calculated according to the following formula:

Similarly, the basicity value (Kfc>) or the measure of the amine's ability to react with carbon dioxide is calculated according to the formula:

where [BH +], [OH-] and [B °] are defined as: [BH +] = concentration of dissociated amine [OH]] = hydroxide concentration [B °] = concentration of free, undissociated amine

The results of these experiments and calculations are shown in Table 1.

TABLE 1 River properties

Mole- Distribution cool weight _Kh ratio

Cyclohexylamine 89 153 x 10 ”® 3.8

Morpholine 87 2.4 x 10 “0.4

Diethylamine Ethanol 117 52 x 10 10® 2.7 2-Amino, 2-methylpropanol 89 40 x 10 10® 0.3

Methoxypropylamine 89 130 x 10 ”® 1.0

Hydrazine 32 1.7 x 10 “EXAMPLE 2

The hydrolytic-thermal stability of various neutralizing amines is measured by a sample in which the neutralizing concentration of 1000 mg / l is autoclaved for 24 hours at 42.2 kg / cm 2 (254 ° C) and the final concentration of ammonia is measured. The results of this sample are given in Table 2.

TABLE 2

Amine mg / l NH3

Methoxypropylamine <1.0

Morpholine 1.6

Cyclohexylamine 3.3

Diethylaminoethanol * 2.4

Aminomethylpropanol 124.0 * Diethylaminoethanol is substantially degraded to diethylamine.

EXAMPLE 3

A condensate test system is used to evaluate neutralizing amines. This system includes a boiler capable of producing 45 kg / h of steam under a pressure of 14 kg / cm, pumps and metering means to control the composition of the boiler supplementary water, and cooling coils with temperature control means to condense the steam. The condensate is recycled via a test circuit where the corrosion rate is evaluated with metal pieces and corrosometer samples. The test water is distilled water containing <1 mg / 1 SO4, <1 mg / 1 Cl, <1 mg / 1 SIO2 and 10 mg / 1 CO2.

Table 3 lists the results of corrosion tests in this system.

TABLE 3

Corrosion rate /% reduction Concentration in relation to inhibitor pH tration to blank

Blind sample --- 0 0%

Cyclohexylamine 8.5 37.5 mg / l 48%

Morpholine 8.5 152 mg / l 73%

Methoxy-propylamine 8.5 106 mg / l 75% EXAMPLE 4

The condensate test system of Example 3 was used to demonstrate the effect of the addition of hydrazine to methoxypropylamine in the inhibition of corrosion.

TABLE 4 Amount of Inhibition Per

inhibitor Inhibit ppm of the access inhibitor pH in the systemic product

Blind sample --- · --- 0% 0.00% MPA 8.5 106 ppm 75% 0.71% 7% hydrazine / 93% MPA 8.5 61 ppm 83% 1.36% 15% hydrazine / 85% MPA 8.5 61 ppm 71% 1.16%

Hydrazine 8.5 22 ppm 19% 0.85% 1% hydrazine / 99% MPA 8.5 49.5 ppm 55% 1.11% * MPA = methoxypropylamine

Claims (4)

1. Corrosion inhibitor for water vapor condensate systems, characterized in that it consists essentially of methoxypropylamine and hydrazine. Corrosion inhibitor according to claim 1, characterized in that it contains between 1 and 15% by weight of hydrazine. A method of inhibiting corrosion in water vapor condensate systems, characterized in that a concentration of at least 22 mg / l of the corrosion inhibitor according to claims 1 and 2 is maintained. Process according to claim 3, characterized in that the corrosion inhibitor contains between 1 and 15% by weight of hydrazine.