JPH11142012A - Absorption refrigerator and absorption liquid for absorption refrigerator - Google Patents

Abstract

(57) [Problem] In a conventional inhibitor, when the temperature of an absorbing solution becomes higher, local corrosion occurs on the surface of an iron-based material, so that corrosion resistance becomes a problem. SOLUTION: Lithium halide (eg, L
In an absorption refrigerator using an aqueous solution of iBr (65% by weight of iBr) as an absorbent, an aqueous solution containing lithium halide as a main component and a small amount of an alkali metal hydroxide (eg, LiOH) and aluminum nitrate is used as the absorbent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an absorption refrigerator having excellent corrosion resistance by preventing steel, which is a main component of the absorption refrigerator, from being corroded by a corrosion inhibitor (inhibitor) contained in an absorption liquid. It relates to the composition of the absorption refrigerator.

[0002]

2. Description of the Related Art In general, an absorption refrigerator uses lithium bromide as an absorption medium and water as a refrigerant. Since lithium bromide is highly corrosive, it is necessary to add an appropriate inhibitor to the absorbing solution in order to suppress the corrosion of the constituent metal materials.

[0003] Hitherto, an inhibitor widely used is an oxidizing agent for oxo acid salts. Chromates, nitrates, molybdates, tungstates, borates and phosphates are known as common oxidants, and lithium salts of these are often used in absorption refrigerators. . These oxidizing agents are used in combination with an alkali metal hydroxide, which is a pH adjuster, and form an oxide film on the surface of the material by the oxidizing action to prevent corrosion of the components.

[0004] Then, when an oxidizing agent having a strong oxidizing power was used as an inhibitor in order to enhance the corrosion protection, local corrosion became a problem. Further, when molybdate having weak oxidizing power was used, it was difficult to secure a necessary concentration because of low solubility in the absorbing solution, and the film forming power was insufficient.

To compensate for the disadvantages of these oxidizing agents, Japanese Patent Application Laid-Open
In -92386, an absorbing solution using a combination of nitrate and molybdate is mentioned. With this composite inhibitor, a film of iron oxide containing Mo could be formed and the anticorrosion effect could be enhanced. However, when the temperature of the absorbing solution is 220
When the temperature exceeded ℃, a problem of local corrosion occurred.

[0006]

In the above prior art, the oxidizing power as an inhibitor and the ability to form a film are controlled by combining a strong oxidizing agent and a weak oxidizing agent in a specific concentration range. As a result, a stable anticorrosion film composed of molybdenum oxide and iron oxide could be formed on the surface of the iron-based material that is a main constituent material of the refrigerator. Therefore,
This stable anti-corrosion film can suppress corrosion due to local film destruction, and the corrosion resistance of the refrigerator has been improved. However, this complex inhibitor has an absorption liquid of 220 ° C.
When the above occurs, the oxidizing power rapidly increases, and local destruction of the anticorrosion film occurs.

[0007] For this reason, when the temperature of the absorbing solution becomes higher, a problem arises in the corrosion resistance of the iron-based material.

An object of the present invention is to provide an absorption refrigerator having excellent corrosion resistance and high reliability without the need to control the concentration of an inhibitor after the formation of an anticorrosion film on the surface of a structural material by using an absorbing solution to be used. It is to provide the absorption refrigerator.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide an absorption refrigerator using water as a refrigerant and an aqueous solution of lithium halide as an absorbing solution. This is achieved by enclosing an aqueous solution containing

The absorbing solution uses lithium halide (lithium bromide LiBr alone or lithium bromide as a main component and contains at least one of lithium chloride LiCl and lithium iodide LiI) as an absorbing medium, and contains an alkali metal. hydroxide 0.1-1.0 wt% aluminum nitrate Al (NO _{3) 3} 0.005 to 1.0% by weight (preferably 0.05 to 0.2 wt%), with the balance being water Are preferred. Further, the alkali metal hydroxide is preferably a lithium compound LiOH.

That is, by forming a two-layer film of a lithium salt and an iron oxide containing aluminum on the surface of an iron-based material with an absorbing solution containing aluminum nitrate, the reliability of the refrigerator in terms of corrosion resistance is remarkably improved.

[0012] Further, the above object is to provide a closed circulation system mainly composed of a regenerator, a condenser, an evaporator, and a heat exchanger mainly composed of a steel material. In an absorption refrigerator that obtains cold by repeating concentration, refrigerant dilution, and heat exchange, a two-layer coating of an aluminum compound containing lithium and the like and an iron oxide is formed on at least the surface of a component part of the equipment that is in contact with the absorption liquid. Can also be achieved.

That is, aluminum nitrate is added as an inhibitor to an absorbing solution mainly composed of lithium halide, and the absorbing solution is sealed in an absorption refrigerator, and aluminum containing lithium is preliminarily brought into contact with the absorbing solution on the surface of the constituent member. By forming a two-layer film of the compound and the iron oxide, the corrosion resistance of the refrigerator is significantly improved.

The two-layer film of the lithium-containing aluminum compound and iron oxide is formed in advance by a preliminary operation of a refrigerator, or a refrigerator using a material having the two-layer film formed on the surface in advance is used. Is achieved effectively. The object can be achieved even in a normal operation using the absorbing solution containing aluminum nitrate.

Next, the formation process of the above-mentioned two-layer film of the lithium-containing aluminum compound and iron oxide and its anticorrosion performance will be described.

Since the absorption liquid for the absorption refrigerator is mainly composed of lithium halide, the aqueous solution is weakly acidic and the metal material corrodes violently by halide ions. The concentration of lithium halide is 45 to 70% by weight, and the highest concentration regenerator uses an aqueous solution of 60 to 65% by weight.

The alkali added to the aqueous solution has the function of changing the pH of the absorbing solution from weakly acidic to alkaline, thereby reducing the corrosiveness of the absorbing solution. That is, by controlling the alkali concentration, the surface potential of the iron-based material is increased, and the passivation phenomenon is increased, so that the corrosion rate of the iron-based material is reduced. An alkali metal hydroxide is used for adjusting the alkali concentration. The addition amount is 0.1 to 1.0% by weight, and particularly preferably 0.1 to 0.3% by weight. Further, the solubility of iron oxide in an alkaline aqueous solution decreases, and the passivation film on the iron surface hardly dissolves, so that the protection effect of the base iron is maintained and the amount of corrosion is reduced.

It is considered that aluminum nitrate is dissociated in an aqueous solution of lithium halide as follows.

[0019]

## STR1 ## is considered to _{Al (NO 3) 3 → Al} 3+ + NO 3- ... ( Formula 1) corrosion by the reaction of the following two steps on the surface of the ferrous material is in progress.

[0020]

Embedded image Fe + 2H ₂ O → Fe (OH) ₂ + H ₂ (Formula 2)

[0021]

Embedded image Fe (OH) ₂ → Fe ₃ O ₄ + 2H ₂ O (Formula 3) Aluminum ions contained in the absorbing solution are adsorbed on iron hydroxide generated on the iron surface. The aluminum ions act as a catalyst to promote the reaction of chemical formula ₃ in which Fe ₃ O ₄ is generated, so that a dense oxide film having excellent adhesion of Fe ₃ O ₄ is formed and the anticorrosion effect is enhanced. In addition, the aluminum ions themselves adsorbed on the iron hydroxide also form a complex salt with the surrounding lithium ions and hydroxide ions, etc.,
It has a two-layer structure.

[0022]

(Example 1) LiBr 65% by weight, LiOH 0.1 to 1.0% by weight, Al (NO ₃ ) ₃ 0.0
1 to 50% by weight using an absorbing solution contained in the range of 0.5 to 1.0% by weight.
A corrosion test was performed at 80 ° C. for 200 hours. Table 1 shows the average corrosion rate and the form of corrosion of the carbon steel at that time together with comparative examples.

[0023]

[Table 1]

The lowest corrosion rate of the present invention is 56 mg /
dm ² is smaller than that of the comparative example by about a half, and the corrosion form is also general corrosion, and the inhibitor effect of aluminum nitrate is clear. 1 and 2 show the results obtained by measuring the surface of the carbon steel at that time by Auger spectroscopy and X-ray analysis. From these measurement results, it is understood that a double-layered film of an oxide of iron and an aluminum compound is present on the carbon steel surface.

Example 2 The corrosion rate of the present invention was 150 mg / dm ² or less even at a high temperature, which is almost the same value as when Li ₂ MoO ₄ of the comparative example was added. However, Li ₂ MoO ₄ and L ₂
Compared to the corrosion mode of the comparative example in which iNO ₃ is added, the corrosion mode is local corrosion, and the present invention is a preferable overall corrosion, and the effect of aluminum nitrate as an inhibitor is clear.

(Embodiment 3) FIG. 3 shows a system diagram of an absorption refrigerator according to one embodiment of the present invention. Example 1
No. 2 which has a particularly high anticorrosive effect was used as the absorbing liquid according to the present invention used in the above items 2 and 2.

The absorbing solution 6 is heated and concentrated in the high-temperature regenerator 1a to separate water vapor 14. The steam 14 heats and concentrates the dilute solution 6b through the heat exchanger of the low-temperature regenerator 1b and enters the condenser 2, where it is cooled by the cooling water 15 to become water. This water becomes the refrigerant 11. The refrigerant 11 is pressure-fed to the evaporator 3 by the refrigerant pump 8b and is sprayed on the evaporating pipe 9.
Since the inside of the evaporator is maintained at a reduced pressure of several mmHg, the sprayed refrigerant 11 evaporates to become steam again. The cold water 10 passing through the inside of the evaporating tube 9 is cooled by the latent heat of evaporation at this time, and is used for cooling.

The vapor of the evaporated refrigerant 11 enters the absorber 4, where the concentrated solution 6a concentrated in the high temperature regenerator 1a is sprayed and absorbed therein. The concentrated solution 6a generates heat when absorbing the water vapor, which is cooled by the cooling 13 passing through the cooling pipe 12 to become the diluted solution 6b. The dilute solution 6b is sent by the pump 8a and returns to the high temperature regenerator 1a and the low temperature regenerator 1b through the heat exchanger 5. The recirculation pipe 16 of the high-temperature regenerator is provided with a valve 17b during refrigeration operation.
Is closed and not used.

When the high-temperature regenerator 1a is operated alone to form an anticorrosion film on the inner wall, the valves 17a and 17c are closed, the valve 17e is opened, and the inside of the high-temperature regenerator 1a becomes empty. After confirmation, a certain amount of the film forming liquid is introduced from the valve 17e, the valve 17e is closed, and then the valve 17b is opened, the high temperature regenerator is operated and heated, and the film forming liquid is circulated using the recirculation pipe 16. The water vapor 14 generated at this time is returned to water in the condenser 2 to form the refrigerant 11.
This refrigerant 11 is supplied to a valve 17 d using a refrigerant supply pipe 18.
And supply it into the high temperature regenerator 1a.

As a result, the film formation concentration in the high-temperature regenerator 1a is kept constant, and an anticorrosion protective film composed of a two-layer structure film of an aluminum compound and iron oxide is formed on the inner surface of the high-temperature regenerator and the piping. This makes it possible to form a film having an extremely excellent anticorrosion effect on the inner wall of the high-temperature regenerator, which is the most corrosive in the absorption refrigerator.

[0031]

According to the present invention, it is possible to prevent local corrosion, which is a cause of corrosion problems in the absorption refrigerator, and to suppress the corrosion rate of the constituent materials, thereby providing an absorption refrigerator having extremely high corrosion resistance.

[Brief description of the drawings]

FIG. 1 shows a temperature of 180 ° C., 20 ° C. in an absorbing solution to which the present invention is added.
It is a characteristic view showing the result of having measured Auger spectroscopy analysis of the carbon steel surface after immersion for 0 hours.

FIG. 2: 180 ° C., 20 ° C. in an absorbing solution to which the present invention has been added.
It is a characteristic view showing the result of having measured the X-ray analysis of the carbon steel surface after immersion for 0 hours.

FIG. 3 is a system diagram of an absorption refrigerator of one embodiment of the present invention.

[Explanation of symbols]

1a: High temperature regenerator, 1b: Low temperature regenerator, 2: Condenser, 3
... Evaporator, 4 ... Absorber, 5 ... Heat exchanger, 16 ... Coating liquid recirculation pipe, 17a, 17b, 17c, 17d, 17e
... Valve, 18 ... Refrigerant supply pipe.

Claims (7)

[Claims] An absorption refrigerator comprising an aqueous solution containing lithium halide as a main component and an alkali metal hydroxide and aluminum nitrate as an absorbing solution. 2. The absorption refrigerator according to claim 1, wherein the hydroxide of the alkali metal is lithium hydroxide. 3. The method according to claim 1, wherein the concentration of the alkali metal hydroxide is 0.1 to 0.1.
1.0% by weight, and the concentration of aluminum nitrate is 0.00
3. The absorption refrigerator according to claim 1, wherein the amount is 5 to 1.0% by weight. 4. An absorption refrigerator using an absorbing solution containing 65% by weight of lithium halide, wherein said absorbing solution has a corrosion rate of 100 when immersed in carbon steel at 180 ° C. for 200 hours.
An absorption refrigerator having a mg / dm ² or less. 5. An absorption liquid for an absorption refrigerator comprising lithium halide as a main component and a small amount of an alkali metal hydroxide and aluminum nitrate. 6. An absorption refrigerator having a structure in which a double-layer film of an aluminum compound and iron oxide is formed on the surface of a component for an absorption refrigerator. 7. An absorption refrigerator having a two-layer film of an aluminum compound and iron oxide formed on the surface of a component.