JPH0528752B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an absorption liquid for absorption refrigerators, particularly when water is used as a refrigerant, an absorption liquid for absorption refrigerators made of a mixture of lithium halide and lithium nitrate that does not cause crystallization even at low temperatures. Related to absorption liquid. [Prior Art] Absorption refrigerators perform refrigeration by directly consuming high-temperature thermal energy, and are widely used from the standpoint of efficient and rational use of thermal energy. This absorption refrigerator has excellent refrigeration efficiency, which will be briefly explained below. A schematic diagram is shown in FIG. 4 as an example of an absorption refrigerator. The low concentration absorption liquid that has absorbed the vapor refrigerant is heated by the heating source 1 in the high temperature generator 2 and sent to the separator 4.
The refrigerant evaporates and the absorption liquid is concentrated to become a highly concentrated absorption liquid. Next, the high concentration absorption liquid is sent to the heat exchanger 6,
It exchanges heat with the low-concentration absorption liquid coming from the low-temperature absorber 13, is cooled, and is introduced into the absorber 13. The low-temperature, high-concentration absorption liquid is dispersed in the absorber 13, cooled by the cooling pipe 17, and then transferred to the evaporator 16.
It absorbs the vapor refrigerant from the liquid and becomes a low concentration absorption liquid.
It is then sent to the high temperature generator 2 via the heat exchanger 6 by the circulation pump 19 and recycled in this manner. On the other hand, the high-temperature vapor refrigerant evaporated from the separator 4 is introduced into the condenser 18, cooled by the cooling pipe 17, and condensed into liquid. Next, the liquid refrigerant is supplied to the evaporator 16 and evaporated to a low temperature, and the latent heat of evaporation cools the water passing through the cold water pipe 15 into cold water. This vapor refrigerant is absorbed into a high concentration absorption liquid in the absorber 13. The cold water is also used for indoor cooling. Conventionally, water has been used as a refrigerant and lithium bromide as an absorbent. An example of the operation cycle will be explained with reference to the Duehring diagram of an aqueous lithium bromide solution shown in FIG. FIG. 2 shows the relationship between temperature and vapor pressure using lithium salt concentration and water as parameters, and shows the cycle operation state of the absorption liquid using cycles ABCD. As an example, the straight line AD has a density of 62.5
% by weight, the straight line BC indicates the parameters for a concentration of 63.5% by weight. In the high temperature generator 2, the low concentration absorption liquid of lithium bromide sent by the circulation pump 19 is heated, the vapor refrigerant is expelled, and the liquid becomes a high concentration absorption liquid. That is, the absorption liquid is at point A (concentration) in Figure 2.
62.5% by weight) to point B. Further, the vapor refrigerant is cooled by the cooling pipe 17 in the condenser 18, and becomes liquid at point E. The condensation heat generated at that time is either discarded to the cooling tower via the water medium, or
or directly disposed of by air. on the other hand,
The high concentration absorption liquid is cooled from point B to point C in the absorber 13, and is then cooled from point B to point F from the evaporator 16.
It absorbs vapor refrigerant at a temperature of 5℃ and is diluted at point D.
(concentration: 62.5% by weight). At this time, in the evaporator 16, the water flowing into the cold water pipe 15 is cooled and turned into cold water, which is used for cooling the room. Further, in the absorber 13, the highly concentrated absorption liquid absorbs the vapor refrigerant to generate heat, and the heat is passed through the cooling pipe 17 as an aqueous medium or air and is disposed of in the cooling tower or the outside air. In addition, the diluted low concentration absorption liquid is heat exchanged with the high concentration absorption liquid in the heat exchanger 6, and the high temperature generator 2
, heated from point D to point A, and recycled. However, in such conventional known technology, the refrigerant evaporation temperature in the evaporator 16 is 5°C (point F).
In order to satisfy the conditions for cooling the absorption liquid that absorbs the refrigerant in the absorber 13 to a temperature of 50°C, for example, the air cooling condition, the concentration of the low concentration absorption liquid (point D) should be 62.5% by weight, and the high concentration absorption liquid should be set to 62.5% by weight. It must be ensured that crystallization does not occur in liquid state C. In order to prevent the absorption liquid from crystallizing, it should not overlap with the crystallization line X-X' of state C of the high concentration absorption liquid. For that purpose, in state C, the concentration difference (Δc) is 1% by weight at 63.5% by weight.
Must be as follows. In this way, if the concentration difference is 1% by weight or less, the amount of circulation of the absorption liquid must be increased, resulting in a decrease in the coefficient of performance (amount of heat absorbed in the evaporator Q _E /amount of heating in the generator Q _G ). Refrigeration efficiency decreases. Furthermore, at this concentration, when the operation of the refrigerator is stopped, the temperature of the absorption liquid drops to the outside temperature, which may cause crystallization. Therefore, operating the refrigeration cycle under these conditions is extremely dangerous. [Problems to be Solved by the Invention] As mentioned above, when a lithium bromide aqueous solution is used as an absorption liquid for an absorption refrigerator, at a refrigerant evaporation temperature of 5°C and an absorption liquid temperature of 50°C, the lithium bromide absorption liquid has a high concentration of 63.5°C. When it reaches % by weight, it cannot be used because it crystallizes in the absorber, and if you try to lower the concentration of the absorption liquid to prevent crystallization, absorb the vapor refrigerant at a low temperature, and air cool the low-temperature absorption liquid, The temperature difference between the absorption liquid and the outside air (35°C) becomes small, and the cooling efficiency for cooling the absorption liquid decreases, or air cooling becomes impossible. When using a water cooling system, cooling water supply equipment is required, which has the disadvantage of being subject to restrictions on equipment cost and installation location. Furthermore, cooling water is expensive, making it unsuitable for home air conditioning from the point of view of saving water. In addition, in order to improve the drawbacks of the lithium bromide-water system and increase the temperature difference between the evaporator and absorber, other absorbing liquids were investigated. When zinc bromide and zinc chloride are added to this system, the solution becomes acidic and exhibits extremely strong corrosive properties, and dilute solutions (10% by weight or less) produce precipitates due to the formation of zinc hydroxide. Additionally, systems in which calcium bromide is added have strong corrosive properties, and the addition of lithium hydroxide as a corrosion inhibitor has the disadvantage of producing precipitates. Other materials being studied include lithium thiocyanate and ethylene glycol, but they are not suitable for practical use because of their poor heat resistance. In this way, water-lithium bromide based absorption liquids have not been satisfactory for absorption refrigerators. In issue 502 (1969) of the magazine "Frozen", a water-lithium bromide-lithium chloride absorption liquid was introduced, and in issue 614 (1978), lithium nitrate was added to the water-lithium bromide absorption liquid as a corrosion inhibitor. Experimental examples for each are disclosed. However, none of these documents describes any measures for lowering the crystallization temperature of the absorption liquid. An object of the present invention is to provide an absorption liquid for an absorption refrigerator that has a high concentration and a low crystallization temperature. [Means for Solving the Problems] In order to achieve the above object, the absorption liquid for an absorption refrigerator of the present invention is used in an absorption refrigerator consisting of a generator, a condenser, an evaporator, and an absorber. The absorption liquid includes lithium bromide, lithium chloride, and lithium nitrate in a weight ratio of lithium bromide to 1:1.
Lithium chloride 0.05~0.50: Lithium nitrate 0.05~
It is characterized by being an aqueous solution that is mixed at a ratio of 0.50 and dissolved in water, which is a refrigerant. More preferably, 1 part of lithium bromide contains 1 part of lithium chloride.
It is an aqueous solution of 0.2-0.3 and 0.1-0.3 of lithium nitrate.
If it deviates from this range, the crystallization temperature of a solution exhibiting the same vapor pressure increases as it deviates from this range, making it unsuitable as an absorption liquid. [Function] The absorption liquid of the present invention is an aqueous solution of a mixture of lithium bromide, lithium chloride and lithium nitrate, and has a crystallization temperature lower than that of an aqueous solution of lithium bromide alone. Figure 3 shows the relationship between the vapor pressure and crystallization temperature of an aqueous solution when the solution temperature is 50°C. Curve 1 shows a mixed aqueous solution of lithium bromide, lithium chloride and lithium nitrate according to the present invention, and curve 2 shows a conventional aqueous solution of lithium bromide alone. The crystallization temperature of an aqueous solution at a vapor pressure of 6.5 mmHg at a refrigerant water evaporation temperature of 5°C corresponds to point A on straight line 1 for the aqueous solution of the present invention and point B on curve 2 for an aqueous solution of lithium bromide alone. Temperatures are 14°C and 33°C. That is, by using the aqueous solution of the present invention, it is possible to lower the crystallization temperature by 19°C compared to an aqueous solution of lithium bromide alone. As mentioned above, an aqueous solution of lithium bromide alone has a high crystallization temperature and has a limited solubility. Therefore, when using this aqueous solution of lithium bromide alone, it is necessary to lower the absorption temperature by using a low concentration lithium bromide aqueous solution, which reduces the difference between the absorption temperature and the outside temperature, and cools the absorption liquid in air. It is difficult to do so. Further, Table 1 shows the solution properties of the mixed aqueous solution of lithium bromide, lithium chloride, and lithium nitrate of the present invention. In addition, as a comparative example, the solution characteristics of an aqueous solution of lithium bromide alone are also shown. From Table 1, the crystallization temperature of the aqueous solution of the present invention is clearly lower than that of the comparative aqueous solution relative to the concentration.

〔Example〕

An aqueous solution of lithium bromide: lithium chloride: lithium nitrate in a mixed weight ratio of 1:0.25:0.25 was used as the absorption liquid, and was used in the above-mentioned absorption refrigerator shown in FIG. 4 for refrigeration operation. According to the Duering diagram of the mixed aqueous solution in Figure 1, lithium bromide - lithium chloride -
The cycle GHIJ in the operation cycle state using a mixed aqueous solution of lithium nitrate is shown. FIG. 1 shows the relationship between temperature and vapor pressure in the same way as the operating cycle state explained using the Düring diagram of FIG. 2 described above. The conditions for the absorption liquid to absorb vapor refrigerant (steam) are as follows: vapor refrigerant temperature: 5°C, absorption liquid temperature: 50°C, concentration difference (Δc) of the absorption liquid before and after absorbing the vapor refrigerant.
2.5% by weight, and operate in the same manner as in the case of using lithium bromide alone. In the high temperature generator 2, the low concentration absorbent liquid (64.2% by weight) is heated from point G to point H, water evaporates and becomes high concentration absorbent liquid (66.7% by weight). Next, absorber 1
3, the high-concentration absorbent liquid is cooled to point I and absorbs the evaporated water (point L, 5°C, vapor pressure 6.5 mmHg), and the low-concentration absorbent liquid (64.2
% by weight). Furthermore, the low temperature absorption liquid is at point J.
It is heated from to point G and recycled. At this time, the water in the cold water pipe 15 is cooled to cold water using a low-temperature vapor refrigerant in the evaporator 16, and is used for cooling or the like. The temperature in the absorber of the three-component mixed absorption liquid of the present invention does not overlap the crystallization line Y-Y' as shown at points I and J, and the absorption liquid temperature is higher than the crystallization temperature.
Lithium bromide, lithium chloride, and lithium nitrate in the aqueous solution do not precipitate, and the absorption liquid is completely in an aqueous solution state. On the other hand, in the recycling operation of the lithium bromide alone aqueous solution shown in FIG.
It overlaps with the crystallization line X-X' and cannot be operated, and a concentration range of only 1% by weight can be obtained. However, by using the absorption liquid of the present invention, the concentration range can be set to 2.5% by weight under the same conditions, and the absorption refrigerator can be operated without any trouble under air cooling conditions. [Effects of the Invention] The absorption liquid for an absorption refrigerator of the present invention is composed of an aqueous solution of a mixture of lithium bromide, lithium chloride, and lithium nitrate in a weight ratio of 1:0.05 to 0.50:0.05 to 0.50, respectively. Crystallization temperature is low,
Lithium halide and lithium nitrate in the aqueous solution do not crystallize during the operating cycle of the refrigerator.
Air-cooled absorption refrigerators, which have been difficult to put to practical use in the past, can be operated very safely and without any problems, and chilled water can be efficiently obtained and used for cooling, freezing, etc.

[Brief explanation of the drawing]

Figure 1 is a Duering diagram of the lithium bromide-lithium chloride-lithium nitrate 3-component mixed absorption liquid of the present invention, Figure 2 is a Duering diagram of a conventional lithium bromide water absorption liquid, and Figure 3 is a Duering diagram of the absorbent liquid. FIG. 4 shows a correlation curve between vapor pressure of an aqueous solution and crystallization temperature at 50° C., and a schematic diagram of a refrigerator. 2... High temperature generator, 4... Separator, 6... Heat exchanger, 13... Absorber, 15... Cold water pipe, 16...
...Evaporator, 17...Cooling pipe, 18...Condenser.

Claims (1)

[Claims] 1. In an absorption liquid used in an absorption refrigerator consisting of a generator, a condenser, an evaporator, and an absorber, the absorption liquid contains lithium bromide, lithium chloride, and lithium nitrate in a weight ratio of 1:1:1:1. lithium
An absorption liquid for an absorption refrigerator, characterized in that it is an aqueous solution obtained by mixing lithium nitrate in a ratio of 0.05 to 0.50 and dissolving it in water, which is a refrigerant.