JPS6334386B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a lithium bromide aqueous solution, its concentration,
This invention relates to a closed circulation absorption refrigerator that performs cooling through repeated refrigerant dilution and heat exchange. Closed circulation absorption refrigerators use water as the refrigerant and a concentrated aqueous solution of lithium bromide as the absorption liquid. As shown in the principle diagram in Fig. 1, this refrigerator has a regenerator 1, a condenser 2, an evaporator 3, an absorber 4, and circulates absorption liquid 6, 6a, 6b and refrigerant 7 between them. Pumps 8 and heat exchanger 5
Each part operates as follows. (A) Evaporator 3 Cold water 12 flows through the tubes of the evaporator tube bundle of the evaporator 3, and refrigerant 7 is spread outside the tubes, and the latent heat of evaporation removes heat from the cold water. (B) Absorber 4 Lithium bromide aqueous solution has significantly lower vapor pressure than water at the same temperature, and can absorb water vapor generated at considerably lower temperatures. In the absorber 4, the refrigerant evaporated in the evaporator 3 is absorbed by a lithium bromide aqueous solution (absorbing liquid) 6 sprinkled on the outer surface of the tube bundle of the absorber, and the absorbed heat generated at this time is cooled by cooling water 13 passing through the tubes. be done. (C) Regenerators 1a, 1b The concentration of the dilute solution 6b that has absorbed the refrigerant in the absorber 4 decreases, and its absorption capacity becomes weaker. Then, a part of the solution is sent to the high-temperature regenerator 1a by the solution circulation pump 8, heated by the high-temperature steam 11, etc., the refrigerant vapor 10 is evaporated and separated, and the solution is concentrated.
a returns to the absorption liquid 4. Furthermore, a part of the dilute solution 6b discharged from the absorber 4 is sent to the low temperature regenerator 16 by the solution circulation pump 8, where it is heated and concentrated by the refrigerant vapor 10 generated in the high temperature regenerator 1a, and the concentrated solution 6a is sent to the absorber 4. Return. (D) Condenser 2 The refrigerant vapor 10 separated in the regenerator 1 is cooled by the cooling water 9 flowing through the pipes in the condenser 2.
It is condensed and liquefied and returned to the evaporator 3. (E) Heat exchanger 5 The low-temperature dilute solution 6b flowing from the absorber 4 to the regenerator 1 is preheated by the high-temperature concentrated solution 6 flowing from the regenerator 1 to the absorber 4, thereby reducing the regenerator heating amount. (F) Pump 8 The pump 8 circulates the concentrated solution 6a, dilute solution 6b, and refrigerant 7. The absorber 4, the regenerator 1 and the pump 8 have the same function as the compressor of a compression refrigerator. Absorption liquid 6, 6a
and 6b circulate between the regenerator 1 and the absorber 4 via the heat exchanger 5 during refrigerator operation. Generally, the higher the concentration of the absorption liquid, the higher the refrigeration efficiency, so the regenerator 1 needs to be maintained at a higher temperature in order to concentrate the absorption liquid. On the other hand, the higher the temperature and concentration of the lithium bromide aqueous solution, the more corrosive it becomes to steel and copper, which are the constituent materials of the refrigerator. Therefore, it is essential to add an inhibitor to the absorption liquid to prevent corrosion. By the way, most of the inhibitors that have been put into practical use so far are chromate salts, and some molybdate salts have also been used, but they are limited to only a few because of their poor solubility at low temperatures. ing. All of the above inhibitors were oxidizing agents, and were of the type that suppressed corrosion by forming a dense protective film on the iron surface. However, it has been difficult to provide complete corrosion protection for all of the several types of refrigerator constituent materials. That is, the above-mentioned inhibitors not only have no anticorrosive effect on copper-based materials, but also sometimes even promote corrosion. Another drawback was that the copper ions eluted at that time precipitated on the surface of the iron, making the iron more susceptible to corrosion due to the potential difference between the two metals. In addition, organic inhibitors that have a corrosion-preventing effect on copper-based materials not only cause stability problems in regenerators that are exposed to high temperatures of 160°C or higher during refrigeration operation, but also cause problems with the corrosion of the most severely corroded iron in the regenerator. The drawback was that it had a poor anticorrosive effect on other types of materials. An object of the present invention is to provide a closed circulation type absorption refrigerator which has excellent corrosion resistance against a lithium bromide aqueous solution. Another object of the present invention is to provide a closed circulation absorption refrigerator which has excellent corrosion resistance and high cooling efficiency. The closed circulation absorption refrigerator of the present invention includes a regenerator,
An absorption liquid consisting of an aqueous lithium bromide solution sealed in a closed circulation system consisting of a condenser, evaporator, absorber, and heat exchanger is condensed, refrigerant diluted, and heat exchanged repeatedly. In a closed circulation absorption refrigerator (hereinafter simply referred to as a refrigerator) for obtaining (a) a borate; (b) a triazole compound selected from benzotriazole and tolyltriazole; In the present invention, B ₄ O ₇ ^-2 ions in the inhibitor oxidize the surface of a member made of iron or an iron alloy, forming a dense passive film mainly composed of Fe ₃ O ₄ , and further oxidizing the film. It is presumed that a hardly soluble film consisting of a Fe-C ₆ H ₄ N ₃ H complex is formed on the surface of the steel, imparting a corrosion inhibiting effect. On the other hand, for members made of copper or copper alloys, the triazole compound in the inhibitor acts, and the following formula (R is HorCH _3. ) It is thought that it forms a hardly soluble film shown in the following formula and imparts a corrosion inhibiting effect. Although the present invention is effective for single-effect closed circulation absorption refrigerators, it is particularly effective for double-effect closed circulation absorption refrigerators. This is because the inhibitor has superior solubility compared to molybdate inhibitors and the like, so there is no need for it to precipitate or precipitate even when the absorbing liquid is at a low temperature. The borates (a) as inhibitors used in the present invention are borates of alkali metals such as sodium, lithium, potassium, etc., among which disodium tetraborate is particularly preferred. In the present invention, in addition to the borate, benzotriazole (C ₆ H ₄ N ₃ H) is used as an inhibitor that is stable even at high temperatures encountered by the absorption liquid during refrigeration operation and exhibits a sufficient anticorrosion effect over a long period of time. and triazole (CH ₃ C ₆ H ₃ N ₃ H). The amount, that is, the concentration, of the borate and triazole compound in the absorption liquid is a concentration sufficient to prevent corrosion of iron-based and copper-based materials in a well-balanced manner. Borate is practically in the range of 0.1-1.0% by weight. The borate dissociates in solution, producing borate ions. It is thought that borate ions form precipitates that are poorly soluble in metal ions and their hydroxides. In particular, it appears to react easily with corrosion products of iron (in this case iron hydroxide), forming extremely sparingly soluble compounds. In the absorption liquid containing LiBr, iron ions eluted by corrosion become corrosive products such as iron hydroxide, which react with the borate ions mentioned above to form a precipitate film on the iron surface, causing corrosion. Shows suppressive action. Although this film is relatively thick, it has many defects and therefore does not have a sufficient corrosion inhibiting effect. On the other hand, triazole compounds such as benzotriazole (BAT) react with Fe ²⁺ eluted from iron in a solution free of dissolved oxygen, forming a dense, poorly soluble polymeric film of Fe()-BTA. It has the effect of inhibiting corrosion. However, the Fe()-BTA film is very thin, and this alone does not have a sufficient corrosion inhibiting effect. Therefore, we considered combining borate and BTA, thereby creating a composite film of Fe()-BTA and borate deposited on the iron surface, and the synergistic effect of these deposits significantly increases the corrosion inhibiting effect. I found it. In this case, BTA reacts quickly with Fe ²⁺ eluted from iron, while borate produces a corrosion product of ferrous iron and forms a deposited film after reacting with this, so it reacts faster than BTA. The reaction is a little slow. Therefore, when used as a mixed inhibitor, a dense film of Fe()-BTA is formed on the iron surface, and on top of that a film consisting of a deposited film of iron corrosion products and borate, and a mixture of both. is formed, and it is thought that a high corrosion inhibition effect can be obtained. On the other hand, triazole compounds such as benzotriazole and tolyltriazole have low solubility in water, and in particular,
Their solubility in concentrated lithium bromide aqueous solution is very low, and the solubility in 55% lithium bromide aqueous solution (room temperature) is about 0.13-0.15%. Therefore, if the concentration of the triazole compound is higher than this, the surrounding Depending on the temperature conditions, it may precipitate when the refrigerator is stopped, and its accumulation may cause problems such as nozzle clogging. Therefore, in practical terms
0.001-0.12% by weight, preferably 0.005-0.1% by weight
range is effective. In the present invention, 5-50 ml/surfactant such as octyl alcohol can be added to the absorption liquid to increase the thermal efficiency of the absorber, so that the inhibitor of the present invention is not extracted. . In the refrigerator of the present invention, the circulation component made of a copper-based material such as copper or copper alloy removes some or all of the copper oxide generated and attached to the surface that comes into contact with the absorption liquid. , is preferably removed before enclosing the absorption liquid. In this way, when components from which copper oxide is removed are used, it is possible to improve the cooling effect of the refrigerator. According to the research conducted by the present inventors, the triazole compound (b) in the composite inhibitor reacts with copper ions in the absorption liquid to form compounds such as -C ₆ H ₄ N ₃ Cu-, and some precipitates are formed. It was confirmed that it was generated and attached to piping. Therefore, the present inventors conducted various studies based on the idea that cooling efficiency could be further improved by removing this deposit, and as a result, succeeded in discovering the above-mentioned present invention. did. In the present invention, copper oxides may be removed before the refrigerator is assembled, or may be removed by pickling or the like after assembly and before filling the absorption liquid. As a method for removing copper oxide, a known method can be used. For example, in addition to the above-mentioned pickling, it can be carried out by a method using an aqueous solution of its salt (eg, sodium nitrate, sodium sulfate, etc.), a mechanical method such as sandplast, or a reduction method. Practically, the simplest method is a method using an aqueous solution of an acid or its salt, such as sodium nitrate (hereinafter simply referred to as pickling method). Here, as the acid, for example, hydrochloric acid,
Inorganic acids such as nitric acid, hydrobromic acid, sulfuric acid, phosphoric acid,
Typical examples include organic acids such as citric acid, and their salts, such as lithium bromide, sodium chloride, lithium nitrate, sodium sulfate, and sodium phosphate. in short,
Known acids and salts thereof that have the effect of reacting with and dissolving copper oxides can be used. Nitric acid and lithium bromide are most preferred in consideration of dissolving and removing copper oxides on the surface of copper-based materials and their effects on iron-based materials. The higher the acid concentration, the more corrosive it becomes, so for practical purposes,
A range of 0.5 to 1.0% is suitable. When using an aqueous salt solution, the higher the concentration, the more preferable it is. Generally, 20% or more is appropriate. Further, the higher the pickling temperature, the shorter the cleaning time, but since the corrosive action becomes more severe, it is practically preferable to use a temperature between room temperature and 80°C, and a circulation time of 10 minutes or more is sufficient to achieve the purpose. Generally, about 10 to 30 minutes is preferable. It is desirable to thoroughly wash with water immediately after pickling. In the present invention, when pickling is performed after assembling the refrigerator, the acid is circulated in the circulation system, the pickling is replaced with water, the water is thoroughly washed, and when the washing water becomes around neutrality, the water is drained. good. In this case, the above-mentioned triazole compound as an inhibitor may be added to the acid or salt solution, which is extremely convenient since it is possible to form an anti-corrosion film at the same time as removing the copper oxide. It is most desirable to remove substantially all of the copper oxide, but even if this is not the case, at least the residual copper oxide reacts with the triazole compound to form a precipitate that is removed from the absorption liquid jetting nozzle (14 in Figure 1).
It is necessary to remove it to the extent that it does not become substantially occluded. The amount varies depending on the structure of the refrigerator, the size of the nozzle, etc. Although the constituent materials of the refrigerator differ slightly depending on the type of heat source such as gas, combustion gas such as kerosene, or steam, the present invention shows its efficiency for all of these models, and in particular, the material of the refrigerator is shown to be effective for all of these models. The effect is remarkable for refrigerators that are used at a high rate. Furthermore, the absorbent liquid of the present invention is free from pollution concerns compared to absorbent liquids using chromate or the like. Next, examples will be described in detail. Examples 1 to 10 62% by weight of lithium bromide is added to an aqueous solution in which prescribed amounts of disodium tetraborate and benzotriazole are dissolved.
and 0.2% by weight of lithium hydroxide to prepare an absorption liquid. Using this absorption liquid, a corrosion test was conducted on carbon steel (SS-41), oxygen-free steel (OFCuT), and 7:3 Cypronickel (CNTF-3) at 160°C in vacuum for 200 hours. The amount of corrosion at that time is shown in the table. The refrigerator used here is a steam-fired dual-effect closed circulation type absorption refrigerator shown in FIG. Also,
For comparison, the table also shows the test results of absorption solutions without additives, with disodium tetraborate and benzotriazole added alone, and with absorption solutions containing conventionally used inorganic inhibitors. In the conventional example, sharp and deep pitting corrosion occurs and the amount of corrosion varies, so the average value of 10 specimens was used.
On the other hand, in the example, the specimen was covered with a uniform thin yellow-black film after the test. All of the additives added alone are less corrosive than those without additives, but no sufficient effect is observed. As is clear from the table, the amount of corrosion in the example was greater than that in the conventional example using only an inorganic inhibitor.
has been significantly reduced. In particular, the effect in preventing corrosion of copper-based materials is remarkable. The effect on iron-based materials is also clear, and if the structure of the equipment is taken into account, it can be said that the anti-corrosion effect on both materials is well balanced. In particular, for iron-based materials, borate is 0.1 to 0.8
% and triazole compounds have a high anticorrosive effect at 0.06% or more.

[Table] Example 11 Benzotriazole to tolyltriazole 0.07
Absorbent liquids were prepared in the same manner as in Examples 1 to 9 above, except that the weight % was changed. As a result of a corrosion test on the above absorption liquid under the same conditions as in Examples 1 to 9, the amount of corrosion was 35mg/d for carbon steel.
m ² , copper is 17.0 mg/dm ² , cypronic is 3.0
mg/ ^dm2 . Example 12 To an aqueous solution with a lithium bromide concentration of 62% by weight and a lithium hydroxide concentration of 0.2% by weight, 25 ml of n-octyl alcohol and 9.1 g of disodium tetraborate were added.
(concentration 0.6% by weight), benzotriazole 960mg/
(concentration: 0.06% by weight) to prepare an absorption liquid. Carbon steel and oxygen-free copper specimens (each with a surface area of 12 cm ² ) were immersed in 10 ml of this solution, and the state of consumption of disodium tetraborate and benzotriazole was measured when the specimens were held at 160°C. The results were as shown in Figure 2. As shown by curve A, benzotriazole is slightly consumed after the start of the test, but the amount consumed is very small overall, and almost no extraction with n-octyl alcohol is observed. On the other hand, as shown by curve B, the amount of disodium tetraborate consumed is also very small. From these facts, it is recognized that the stability of the absorption liquid is excellent. In the actual machine, virtually no change in inhibitor concentration was observed after one year of operation. Example 13 A copper member was immersed in a pickling solution prepared by adding 0.05% by weight of benzotriazole to 3% HNO ₃ in advance, and heated to 50°C.
(liquid temperature) for 10 minutes to remove surface oxides. This copper member was mixed with 62% by weight of lithium bromide,
Corrosion tests were conducted on the model for 400 hours at 160° C. by immersing it in an absorption solution containing 0.2% by weight lithium hydroxide, 0.3% by weight disodium tetraborate and 0.05% by weight benzotriazole. As a result, the amount of corrosion was 1.8 mg/dm ² and the corrosion rate was 0.0005 mm/year. Further, tests were conducted by varying the liquid temperature during pickling from 20 to 80°C, but the results were almost the same. As is clear from the above examples, according to the present invention, since there is no contamination of the absorption liquid, troubles such as deposits adhering to piping or clogging of spray nozzles can be prevented. It can be seen that it exhibits a remarkable anticorrosive effect that can significantly reduce corrosion, and in addition, it can significantly suppress the consumption of the composite inhibitor in the absorption liquid and maintain a stable corrosion inhibiting effect. The refrigerator of the present invention can also be used as a heating device. When used as a heating device, it is operated as follows. That is, during heating operation, the warm/cool switching valve 14 is opened, the valve 15 is closed, the refrigerant switching valve 16 is further opened, and the valve 17 is closed. High temperature regenerators and condensers are used in heating systems. The refrigerant vapor 10 generated by heating in the high temperature regenerator 1a passes through the heating/cooling switching valve 15, enters the condenser 2, heats the cooling water 9, turns it into hot water, and uses this hot water for heating. The refrigerant generated in the condenser 2 passes through the refrigerant switching valve 17 and returns to the high temperature regenerator 1a to dilute the concentrated absorption liquid and is heated again to generate refrigerant vapor 10.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle of a closed circulation absorption refrigerator according to an embodiment of the present invention, and FIG. 2 is a graph showing changes over time in the inhibitor concentration in the absorption liquid. 1a...High temperature regenerator, 1b...Low temperature regenerator, 2
...Condenser, 3...Evaporator, 4...Absorber, 5...
...Heat exchanger, 6...Absorption liquid, 6a...Concentrated absorption liquid,
6b... Diluted absorption liquid, 7... Refrigerant, 8... Pump, 9... Cooling water, 10... Water vapor, 11... Steam, 12... Cold water, 13... Cooling water.

Claims (1)

[Claims] 1. Concentrating an absorption liquid consisting of an aqueous lithium bromide solution sealed in a closed circulation system configured by sequentially combining a regenerator, a condenser, an evaporator, an absorber, and a heat exchanger,
In a closed circulation absorption refrigerator that obtains refrigeration by repeated refrigerant dilution and heat exchange, the absorption liquid contains a sufficient amount of the following compounds (a) and (b) to substantially function as an inhibitor, ( A closed circulation absorption refrigerator comprising: a) a borate, and (b) a triazole compound selected from benzotriazole and tritriazole. 2 Concentrate the absorption liquid consisting of an aqueous lithium bromide solution sealed in a closed circulation system configured by sequentially combining a regenerator, condenser, evaporator, absorber, and heat exchanger,
In a closed circulation absorption refrigerator that obtains refrigeration through repeated refrigerant dilution and heat exchange, the absorption liquid contains a sufficient amount of the following compounds (a) to (c) to substantially function as an inhibitor, ( A closed circulation absorption refrigerator comprising: a) a borate; (b) a triazole compound selected from benzotriazole and tritriazole; and (c) octyl alcohol.