JPH07239159A - Absorption refrigerator and absorption liquid for absorption refrigerator - Google Patents

Abstract

(57) [Abstract] [Purpose] Suppression of corrosion of the metal material of an absorption refrigerator by incorporating an alkali metal hydroxide and an aluminum compound in an aqueous solution of a lithium halide which is an absorption liquid. [Structure] Lithium halide as an absorption medium (eg Li
60 wt% of Br) and alkali metal hydroxide (eg L
An aqueous solution containing iOH) and an aluminum compound (eg :) is used as the absorbing liquid. Alternatively, an aqueous solution containing at least one oxo acid salt (eg, nitrate, molybdate, borate, etc.) in the aqueous solution is used as the absorbing liquid. According to the present invention, the local corrosion that causes the corrosion trouble in the absorption refrigerator can be prevented and the corrosion rate of the constituent materials can be suppressed, so that the absorption refrigerator having extremely high corrosion resistance can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an absorption refrigerating machine having excellent corrosion resistance by corroding a steel material, which is a main constituent material of the absorption refrigerating machine, by a corrosion inhibitor (inhibitor) contained in the absorption liquid. And a composition of an absorbent used in the absorption refrigerator.

[0002]

2. Description of the Related Art Generally, 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.

In the past, the most commonly used inhibitors are oxo acid salt oxidants. Chromates, nitrates, molybdates, tungstates, borates, and phosphates are known as general oxidizing agents. These oxidizing agents are used in combination with alkali metal hydroxide, which is a pH adjusting agent, and the oxidation action forms an oxide film on the material surface to prevent corrosion of the constituent materials.

Therefore, when an oxidizing agent having a strong oxidizing power is used as an inhibitor in order to enhance the anticorrosion property, local corrosion becomes a problem. In addition, when molybdate having weak oxidizing power was used, it was difficult to secure a necessary concentration because the solubility in the absorbing solution was small, and the film forming power was insufficient.

In order to make up for the drawbacks of these oxidizing agents, JP-A-1
In No. 92386, an absorbing solution using a nitrate and a molybdate together is mentioned. This composite inhibitor was able to form an iron oxide film containing Mo and enhance the anticorrosion effect. However, the temperature of the absorbing liquid is 220
If the temperature rises above ℃, the problem of local corrosion occurs.

[0006]

SUMMARY OF THE INVENTION In the above-mentioned prior art, a strong oxidant and a weak oxidant are combined in a concentration within a specific range to control the oxidative power and film forming ability as an inhibitor. As a result, it was possible to form a stable anticorrosion coating composed of molybdenum oxide and iron oxide on the surface of the iron-based material that is the main constituent material of the refrigerator. Therefore,
With this stable anticorrosion coating, corrosion due to local coating destruction can be suppressed, and the corrosion resistance reliability of the refrigerator is improved. However, the absorption of this complex inhibitor is 220 ° C.
At the above temperature, the oxidizing power rapidly increases, causing local destruction of the anticorrosion coating. Therefore, when the temperature of the absorbing liquid becomes higher, there arises a problem in the corrosion resistance of the iron-based material.

An object of the present invention is to provide an absorption refrigerating machine having excellent corrosion resistance and high reliability by forming an anticorrosive film on the surface of the structural material depending on the absorbing solution used, and an absorbing solution for the absorption refrigerating machine. is there.

[0008]

SUMMARY OF THE INVENTION The above-mentioned object is to provide an absorption refrigerating machine using water as a refrigerant and an aqueous solution of lithium halide as an absorbing solution, and an aqueous solution of lithium halide as a main component and a small amount of alkali metal hydroxide and halogen. This is achieved by enclosing an aqueous solution containing aluminum iodide as an absorbent.

The absorbing solution uses lithium halide (lithium bromide LiBr alone or lithium bromide as a main component and at least one of lithium chloride and lithium iodide) as an absorbing medium, and alkali metal hydroxide is used. It is preferable that the composition contains 0.01 to 1.0% by weight, an aluminum halide of 0.005 to 0.5% by weight (preferably 0.02 to 0.3% by weight), and the balance is water. Further, the alkali metal hydroxide is a lithium compound LiO.
It is preferably H. Aluminum halides include aluminum chloride, aluminum bromide and aluminum iodide, and at least one of them is contained.

That is, by forming a composite film of aluminum oxide and iron oxide on the surface of the iron-based material by the absorbing liquid containing the aluminum compound, the reliability of the corrosion resistance of the refrigerator is significantly improved.

Further, by adding a small amount of an oxo compound which is an oxidizing agent to the above absorbing solution, an anticorrosive film can be effectively formed in a shorter time. Examples of the oxidant include chromate, nitrate, molybdate, tungstate, phosphate, borate and the like. Addition amount is 0.0
05-0.5 wt% is desirable.

Further, the above-mentioned object is a closed circulation system mainly composed of a regenerator, a condenser, an evaporator and a heat exchanger whose main materials are steel materials, and the absorption liquid enclosed in the circulation system is In an absorption refrigerator that obtains refrigeration by repeating concentration, refrigerant dilution and heat exchange, it is also achieved by forming a composite film of aluminum oxide and iron oxide at least on the surface of the component member of the device that is in contact with the absorption liquid. it can.

That is, a mixture of aluminum halide or an oxo compound which is an oxidizing agent is added as an inhibitor to an absorption liquid containing lithium halide as a main component, and the absorption liquid is sealed in an absorption refrigerating machine to be absorbed in advance. By forming a composite oxide film of aluminum oxide and iron oxide on the surface of the component that is in contact with the liquid, the corrosion resistance of the refrigerator is significantly improved.

The composite oxide film containing aluminum is formed in advance by preliminary operation of the refrigerator, or
Alternatively, it can be effectively achieved by constructing a refrigerator using a material having the composite oxide film formed on its surface in advance. The object can be achieved even in the normal operation with the absorbing liquid containing the aluminum halide.

[0015]

Since the absorption liquid for the absorption refrigerator is mainly composed of lithium halide, its aqueous solution is weakly acidic, and the metal ions are severely corroded by the halide ions. An aqueous solution having a lithium halide concentration of 55 to 70% by weight, preferably 60 to 67% by weight is used.

The alkali added to the above-mentioned 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 passivation phenomenon of iron becomes strong, and the surface potential changes from a base potential to a noble potential and corrosion is reduced. An alkali metal hydroxide is used to adjust the alkali concentration,
~ 1.0 wt% is added. Particularly, 0.1 to 0.3% by weight is desirable. Furthermore, the solubility of iron oxide in the alkaline aqueous solution decreases, and the passive film on the iron surface becomes difficult to dissolve, so that the protective effect of the base iron is maintained and the amount of corrosion decreases.

It is considered that aluminum halide is dissociated as follows in a lithium halide aqueous solution.

[0018]

[Chemical 1]

This aluminum ion is hydrolyzed by the following reaction in a lithium halide aqueous solution.

[0020]

[Chemical 2]

It is considered that at the same time that the reaction of Chemical formula 2 is proceeding, the corrosion of the surface of the iron-based material is proceeding by the following two-step reaction.

[0022]

Embedded image Fe + 2H ₂ O → Fe (OH) ₂ + H ₂ (Chemical formula 3)

[0023]

[Chemical formula 4] Fe (OH) ₂ → Fe ₃ O ₄ + 2H ₂ O (Chemical formula 4) Aluminum ions in the absorbing solution are taken in as an oxide of aluminum by the reaction of Chemical formula 2 in the oxide film formed on the iron surface. . Since the oxide film containing aluminum has excellent adhesion to the metal, it has a high corrosion inhibiting effect and produces a dense and stable film. Therefore, it is considered that the effect of preventing local destruction is high. Further, it is considered that the aluminum ion is contained in the absorbing solution, whereby the reaction of Chemical formula _{4 in} which Fe ₃ O ₄ is produced by the catalytic action of the aluminum ion is promoted.

Further, by adding an oxo acid salt, which is an oxidizing agent, to this absorbing solution, the oxidation of the surface of the steel material is promoted to effectively form an anticorrosion film containing an oxide of aluminum in a shorter time. can do.

[0025]

【Example】

(Example 1) LiBr 65 wt%, LiOH 0.01-
160% with an absorbent containing 1.0% by weight, AlBr ₃ 0.005 to 0.5% by weight and oxo acid salts (nitrates, molybdates and borates) in the range 0 to 0.5% by weight. A corrosion test was performed at 200C for 200 hours. Table 1 shows the average corrosion rate and the corrosion morphology of the carbon steel at that time together with comparative examples.

[0026]

[Table 1]

The corrosion rate of the present invention is 15.5 mdd or less, which is a quarter or less than that of the comparative example, and the corrosion mode is general corrosion, and the effect as an inhibitor of aluminum salt is clear.

(Example 2) LiBr 65 wt%, LiO
H0.01~1.0 weight%, AlBr ₃ 0.005~0.5
Corrosion tests were carried out at 230 ° C. for 200 hours with absorbers containing by weight and oxoacid salts (nitrates, molybdates and borates) in the range 0-0.02% by weight. Table 2 shows the average corrosion rate and the corrosion morphology of the carbon steel at that time together with comparative examples.

[0029]

[Table 2]

The corrosion rate of the present invention is 40 md even at high temperature.
In comparison with the comparative example in which molybdate and nitrate are added, which is smaller than d and less than one-third of that of the comparative example, the corrosion mode of the present invention is preferable general corrosion, and the corrosion mode of the aluminum salt The effect as an inhibitor is clear.

(Embodiment 3) FIG. 1 is a system diagram of an absorption refrigerator according to an embodiment of the present invention. As the absorbent according to the present invention used in Examples 1 and 2, Nos. 2, 6 to 10 having a particularly high anticorrosive effect were used.

The absorbing liquid 6 is heated and concentrated in the high temperature regenerator 1a to separate the water vapor 14. The steam 14 passes through the heat exchanger of the low temperature regenerator 1b to heat and concentrate the diluted solution 6b and then 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 the refrigerant pump 8
It is pressure-fed to the evaporator 3 by b and is sprayed on the evaporation pipe 9. The sprayed refrigerant 11 evaporates into steam again because the inside of the evaporator is kept in a reduced pressure state of several mmHg. The cold water 10 passing through the inside of the evaporation pipe 9 is cooled by the latent heat of evaporation at this time, and this is used for cooling. The vaporized water vapor of the refrigerant 11 enters the absorber 4, where the concentrated liquid 6a concentrated in the high temperature regenerator 1a is sprayed and absorbed therein.
The concentrated liquid 6a generates heat when absorbing water vapor, but this is cooled by the cooling water 13 passing through the inside of the cooling pipe 12 to become the diluted liquid 6b. The dilute liquid 6b is sent by the pump 8a, passes through the heat exchanger 5, and the high temperature regenerator 1a and the low temperature regenerator 1b.
Return to. The recirculation pipe 16 of the high temperature regenerator is not used because the valve 17b is closed during the freezing operation.

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 is emptied. After confirming, introduce the film forming liquid to a certain level from the valve 17e, close the valve 17e,
Next, the valve 17b is opened, the high temperature regenerator is operated and heated, and the film forming liquid is circulated through the recirculation pipe 16.
At this time, the generated water vapor 14 is returned to water in the condenser 2 and used as the refrigerant 11. This refrigerant 11 is supplied into the high temperature regenerator 1a by using the refrigerant supply pipe 18 and opening the valve 17d. As a result, the concentration of the film forming liquid in the high temperature regenerator 1a is kept constant, and an anticorrosion protective film composed of a mixed film of aluminum oxide and iron oxide is formed on the inner surface of the high temperature regenerator and the pipe. As a result, a film having an extremely excellent anticorrosion effect can be formed on the inner wall of the high temperature regenerator, which is the most corrosive in the absorption refrigerator.

[0034]

As described above, according to the present invention, it is possible to prevent the local corrosion which is the cause of the corrosion trouble in the absorption refrigerating machine and to suppress the corrosion rate of the constituent materials, so that the absorption refrigerating machine having extremely high corrosion resistance can be obtained.

[Brief description of drawings]

FIG. 1 is a system diagram of an absorption refrigerator according to an 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 ... Film forming liquid recirculation piping, 17a, 17b, 17c, 17d, 17e
… Valve, 18… Refrigerant supply pipe.

Claims (11)

[Claims] 1. An absorption refrigerator comprising a lithium halide as a main component and an aqueous solution containing an alkali metal hydroxide and an aluminum compound as an absorbing liquid. 2. The absorption refrigerator according to claim 1, further comprising an oxo acid salt as an additive. 3. The alkali metal hydroxide is lithium hydroxide, and the aluminum compound is at least one kind of aluminum halide selected from aluminum chloride, aluminum bromide, and aluminum iodide. The absorption refrigerator according to claim 1. 4. The alkali metal hydroxide concentration is 0.01.
Is about 1.0% by weight, and the concentration of the aluminum compound is 0.0.
005-0.5% by weight.
Alternatively, the absorption refrigerator according to the item 3. 5. The oxo acid salt of the additive comprises at least one of chromate, nitrate, molybdate, tungstate, borate, and phosphate. Absorption refrigerator. 6. The additive oxoacid salt is lithium chromate,
Of lithium nitrate, lithium molybdate, lithium tungstate, lithium borate, and lithium phosphate,
The absorption refrigerator according to claim 5, wherein the absorption refrigerator comprises at least one type. 7. The concentration of the oxo acid salt as an additive is 0.005.
The absorption refrigerator according to any one of claims 2, 5 and 6, characterized in that it is 0.5% by weight. 8. An absorption refrigerator using an absorption liquid containing 65% by weight of lithium halide, wherein the absorption liquid has a corrosion rate of 20 md when immersed in carbon steel at 160 ° C. for 200 hours.
An absorption chiller characterized by being d or less. 9. An absorption liquid for an absorption chiller, which comprises lithium halide as a main component and contains a small amount of an alkali metal hydroxide and an aluminum compound. 10. A member for an absorption refrigerating machine, wherein an oxide film containing aluminum and iron is formed on a surface of a constituent material for the absorption refrigerating machine. 11. An absorption refrigerating machine, wherein an oxide film containing aluminum and iron is formed on the surfaces of the constituent members.