JP2000026846A - Aqueous solution composition for absorption type heat pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a composition which relaxes a crystallization line without reducing the water-vapor absorption performance by adding calcium nitrate to an aqueous solution composition for an absorption type heat pump which includes lithium bromide as its absorbent component and uses water as its coolant. SOLUTION: Calcium nitrate is preferably added to lithium bromide in a mol ratio of 0.1-0.5 (mol of calcium nitrate when the total mol of lithium bromide and calcium is 1). At 275 K of crystallization temperature, for example, in LiBr aqueous solution, crystallization occurs at the concentration of 61%. When 0.2 mol of Ca(NO3)2 is added to 0.8 mol of LiBr, however, crystallization does not occur up to the high concentration of 71%. If the system contains LiBr as the main component, this inversion also can be applied to absorbents of LiBr-LiI system, LiBr-LiCl system and LiBr-LiI-LiCl system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a working medium composition used for an absorption heat pump, and more specifically to an aqueous solution for an absorption heat pump containing water as a refrigerant and lithium bromide as a component of an absorbent. Composition. Note that, in this specification, the term absorption heat pump has a broad meaning, that is, an absorption refrigerator for utilizing the obtained cold water and a narrow sense absorption heat pump for utilizing the obtained hot water, unless otherwise specified. Shall mean both.

[0002]

2. Description of the Related Art An absorption heat pump is basically composed of a regenerator, as shown in FIG.
It comprises a condenser, an evaporator, and an absorber, of which the evaporator and the absorber are housed in a container maintained at a predetermined vacuum. An operation example in the case of using an aqueous solution containing water as a refrigerant and an absorbent (LiBr or the like) as a working medium will be described. The absorbing liquid diluted by absorbing water vapor in the absorber evaporates water in the absorbing liquid by heating with an external heat source in the regenerator, while the absorbing liquid itself is concentrated, and the absorbing ability of water vapor is restored. .

[0003] In the condenser, water vapor evaporated in the regenerator is condensed by a heat exchanger with an external cooling fluid (usually water). This condensed water is then sent to a lower pressure evaporator, where an external cold heat source (usually water)
From the heat, which evaporates and evaporates at a much lower temperature and lower pressure than the regenerator. On the other hand, the absorbent concentrated in the regenerator is sent to the absorber, where it is diluted by absorbing the evaporated and vaporized refrigerant vapor (water vapor) in the evaporator, and the diluted absorbent is circulated to the regenerator.

Here, regarding the transfer of heat between the heat pump and the outside, the following four types are performed simultaneously, and the balance is achieved as a whole. (1) Receiving high-temperature heat from outside with a regenerator. (2) Applying slightly high-temperature heat (condensation latent heat) to the outside with a condenser. (3) Pumping low-temperature heat (evaporation latent heat) from the outside with an evaporator (= derived from the term heat pump). (4) Applying medium temperature heat (absorption heat) to the outside with an absorber.

When this is used as a refrigerator (also referred to as a chiller), cold heat obtained from the evaporator is used for cooling.
At the same time, unnecessary heat generated in the condenser and absorber must be removed with cooling water. That is, when the absorption heat pump as shown in FIG. 1 is used as a water cooler, the cooled water is sent to the secondary side for use. The heated cooling water is sent to the cooling tower.

In a heat pump (also called a water heater) in a narrow sense, the heat obtained by a condenser and an absorber is used for heating. At the same time, the evaporator must provide heat of evaporation from hot wastewater. That is, when the absorption type heat pump as shown in FIG. 1 is used as a water heater, heated hot water is sent to the secondary side for use. Pumps low-temperature heat from low-temperature heat source water. Above, among the absorption heat pump,
This is one of the most basic single-effect types.In the double-effect type, heat efficiency is improved by utilizing the heat of condensation of refrigerant vapor generated in the regenerator, and the amount of heating in the regenerator is significantly reduced. Can be.

[0007] By the way, various types of working medium have been proposed as the working medium used in the absorption heat pump. However, in Japan, actually, a system consisting exclusively of water and lithium bromide ("" Water-LiBr ”). The water-LiBr system has been widely used in the past because of its excellent stability, corrosiveness, price, and the like, but has a performance limit based on the crystal limit. The LiBr concentration of a commonly used absorbing solution is as high as 60 to 65 wt%,
Since the liquid temperature is also 60 ° C. or lower, crystallization occurs during the summer time when the cooling load is high or during an emergency stop, and the operation becomes impossible due to, for example, adhesion to the regenerator or the inner wall of the absorber and a blockage of a pipe connecting them. There is danger.

[0008] Therefore, if the above crystal limit is relaxed, that is, if there is no crystal precipitation even at a high concentration of the absorbent, the following many performance improvements can be expected. First,
The concentration range of the absorbing solution can be expanded. As a result, the circulation amount of the solution is reduced, and the size of the solution pump can be reduced and power consumption can be reduced. Further, since the temperature difference between the concentrated solution and the dilute solution in the solution heat exchanger is widened, the solution heat exchanger is reduced in size or the heat recovery rate is improved, and the work performance (cop) is further improved. Second
In addition, since the temperature of the absorbing solution can be increased in the absorber,
The absorber that occupies a large part of the machine can be downsized. If the mitigation effect is large, the possibility of air cooling comes out. For the same reason, when used as a water heater, higher temperature hot water is obtained. Third, since the evaporation temperature of the evaporator can be reduced, cold water of lower temperature can be obtained as a water heater, and a lower temperature heat source of lower temperature can be used as a water heater.

For these reasons, various attempts have been made to relax the crystal limit (crystallization line), and various proposals have been made. However, those which can sufficiently withstand practical use have not yet been developed. For example, it has been proposed to add zinc bromide or zinc chloride to an aqueous solution of this system. However, in the system to which zinc bromide or zinc chloride is added, the solution itself becomes acidic, and not only exhibits extremely strong corrosiveness, but also forms a precipitate accompanying the formation of zinc hydroxide in a dilute solution of about 10% by weight or less. Would.

In this regard, Japanese Patent Publication No. Sho 61-52738 discloses that in a system comprising water and lithium bromide, lithium iodide is added to lithium bromide, and the amount of lithium bromide is 70- By setting 99 mol% and lithium iodide to 1 to 30 mol%, the vapor pressure drop is larger and the crystallization temperature is lower than that of an aqueous solution of lithium bromide. It is possible to suppress the occurrence of problems such as improvement and solidification of the absorbing solution.

In Japanese Patent Publication No. 5-28749,
In an absorption liquid used for an absorption refrigerator including a generator, a condenser, an evaporator, and an absorber, lithium bromide, lithium iodide and lithium chloride contain lithium bromide in a weight ratio of 1:
Lithium iodide 0.1 to 1.0: lithium chloride 0.05
An absorption solution for an absorption refrigerator comprising an aqueous solution obtained by dissolving an absorbent containing a mixture mixed at ~ 0.50 in water as a refrigerant has been proposed, whereby an absorption solution having a high concentration and a low crystallization temperature has been proposed. It has been provided. Patent No. 2750
No. 834 (JP-A-9-14784) lowers the crystal deposition temperature of the absorbing solution by adding cesium halide.

[0012]

SUMMARY OF THE INVENTION The present inventor has proposed water-Li
The composition of the Br-based absorbent was investigated in more detail, and measured and examined from various viewpoints.By mixing calcium nitrate with the water-LiBr-based absorbent, without lowering the water vapor absorption performance, The present inventors have found that the crystallization line can be effectively relaxed, and have reached the present invention.

[0013] That is, the present invention provides a water-LiBr aqueous solution composition for an absorption heat pump containing a specific component called calcium nitrate, so that the crystallization line can be formed without lowering the water vapor absorption performance. It is an object of the present invention to provide a practically extremely effective aqueous composition for an absorption heat pump, which is moderated (that is, the solubility of the absorbent is increased and the crystallization temperature of the absorbing liquid is lowered).

[0014]

SUMMARY OF THE INVENTION The present invention provides an aqueous solution composition for an absorption type heat pump containing water as a refrigerant and lithium bromide as an absorbent component, wherein the composition contains calcium nitrate. Provided is an aqueous solution composition for an absorption heat pump characterized by the following.

[0015]

According to the present invention, water is used as a refrigerant,
Increasing calcium nitrate [Ca (NO ₃ ) ₂ ] in an aqueous solution composition containing lithium bromide (LiBr) as an absorbent component, thereby alleviating the crystal precipitation line of the absorbent without lowering the water vapor absorption performance. Can be. In the present invention, the addition ratio of calcium nitrate is preferably 0.1 to 0.5 in terms of a molar ratio with respect to lithium bromide (when the total number of moles of lithium bromide and calcium nitrate is 1, when the total mole number thereof is 1). (Number of moles of calcium nitrate). Further, the aqueous solution composition of the present invention may be a LiBr-LiI system, Li
It is also applicable to Br-LiCl-based and LiBr-LiI-LiCl-based absorbents.

[0016]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but it is needless to say that the present invention is not limited to the examples.

FIG. 2 is a diagram comparing solubility lines of a solution containing various components with an aqueous LiBr solution as a basic composition. The concentration is shown on the horizontal axis, the temperature is shown on the vertical axis, and L containing Ca (NO ₃ ) ₂ , 1,3-propanediol, LiCl + ZnCl ₂ , and ethanolamine as additive components.
An iBr aqueous solution is shown. In FIG. 2, (1) LiBr +
In Ca (NO ₃ ) ₂ , the molar ratio of LiBr and Ca (NO ₃ ) ₂ is 0.8: 0.2, but the ratios of other components are as shown in the following (2) to (4). .

(2) LiBr + 1,3-propanediol has a weight ratio of LiBr / 1,3-propanediol = 3.
5 [Int J. Refrig. Vol. 20, No. 5,
pp. 319-325 (1997)]. (3) LiBr
+ LiCl + ZnCl ₂ is LiBr: Li in weight ratio
Cl: ZnCl ₂ = 3: 1: 4 [Refrigerate
ion Vol. 68, No. 789]. (4) LiBr +
Ethanolamine was LiBr / ethanolamine = 3.5 by weight ratio [“Journal of Chemical”
and Engineering Data "Vol.4
1, No. 2 (1996)].

In FIG. 2, the region on the left side of the solubility line is a region where the crystal can be operated without precipitation of crystals. However, in the case of LiBr aqueous solution, the concentration is 61% (mass%: the same applies hereinafter).
When the concentration is 75K and the concentration is 65%, crystal precipitation starts at 306K, and the operating temperature range is limited. In contrast, C
a (NO ₃ ) ₂ , 1,3-propanediol, LiCl +
In the case where ZnCl ₂ and ethanolamine are added, the solubility lines are all shifted largely to the right, and the operating temperature range is relaxed.

However, when 1,3-propanediol is contained, its stability is poor because it is an organic compound, and when it contains ZnCl ₂ , it is highly corrosive and becomes an acidic solution. Therefore, iron materials such as carbon steel are corroded, and considerable consideration is required even in the case of stainless steel. Further, when ethanolamine is contained, it is an organic compound, so that the stability is poor and the viscosity may be increased.

However, when Ca (NO ₃ ) _{2 according} to the present invention is contained, since it is a stable inorganic compound, it does not have the drawbacks of the above-mentioned organic compounds and has the corrosive properties of ZnCl ₂ . Since it has no problem, it is extremely effective as an additive component. In FIG. 2, for a crystal precipitation temperature of 275K,
LiBr aqueous solution, which is the basic composition, precipitates crystals at a concentration of 61%, but in the case of Ca (NO ₃ ) ₂ , no crystals precipitate up to a high concentration of 71%. This fact means that, for example, at a crystal deposition temperature of 275 K, the concentration of the absorbent can be as high as 71% by including Ca (NO ₃ ) ₂ .

FIG. 3 is a graph showing the solubility curve of the LiBr + Ca (NO ₃ ) ₂ mixed salt aqueous solution, that is, the solubility curve when the amount of Ca (NO ₃ ) ₂ added to the LiBr aqueous solution as the basic composition is changed. It is. The horizontal axis shows the concentration and the vertical axis shows the temperature, and also shows the LiBr aqueous solution and Ca (NO ₃ ) ₂ aqueous solution. From FIG. 3, it is clear that the solubility line is shifted to the right by adding Ca (NO ₃ ) ₂ to the aqueous solution of the basic composition LiBr, and the crystal precipitation limit is greatly relaxed.

For example, at 290K, the concentration of LiBr aqueous solution is limited to 55%, but when 1 mol of Ca (NO ₃ ) ₂ is added to 9 mol of LiBr, the solution concentration becomes 66%.
%. Ca for LiBr
With an increase in the amount of (NO ₃ ) ₂ added, the working concentration is further relaxed, and can be increased to 70% or more. For example, at 290 K, Ca (N
When 2 mol of O ₃ ) ₂ is added, the solution concentration can be relaxed to a little over 72%.

FIG. 4 shows LiBr + at a temperature of 280K.
Ca (NO ₃₎ is a graph showing the solubility of ₂ mixed salt solution. In FIG. 3, it corresponds to the line A at a temperature of 280K. In FIG. 4, the horizontal axis represents the molar mixing ratio of Ca (NO ₃ ) ₂ , and the vertical axis represents the solution concentration. The mixing ratio = 0 is for the LiBr aqueous solution, and the mixing ratio = 1 is for the Ca (NO ₃ ) ₂ aqueous solution. It is.

As shown in FIG. 4, C
a (NO ₃ ) ₂ , solute [LiBr
+ Ca (NO ₃ ) ₂ ]. C
a (NO ₃ ) ₂ ], the crystallization line was improved by increasing the solution concentration, and the molar ratio of 0.1
A solubility of 5.4% and a molar ratio of 0.5 indicates 75%. Thereafter, it gradually decreases as the content ratio of Ca (NO ₃ ) ₂ ] increases, but the amount of Ca (NO ₃ ) ₂ and the molar ratio are 0.1.
5 shows a solubility equivalent to 69%, and a molar ratio of 0.7 shows the same solubility as in the case of a molar ratio of 0.1.

This is because an aqueous solution mainly composed of LiBr as an absorbent improves the solubility without lowering the water vapor absorption performance (ie, without lowering the water vapor absorption performance per total weight of solute (kg)). Considering the points that need to be performed, the fact of FIG. 4 shows that the inclusion of Ca (NO ₃ ) ₂ in LiBr preferably in the range of about 0.1 to 0.5 (molar ratio) It shows that the crystallization line can be improved and relaxed. in this way,
It is clear that the effect of relaxing the crystal crystallization line by adding Ca (NO ₃ ) ₂ in the present invention is an effective and excellent effect.

[0027]

According to the present invention, in the aqueous solution of the LiBr-based, LiBr-LiI-based, and LiBr-LiI-LiCl-based absorbents used in the absorption heat pump, even if the water-absorbing performance is not reduced, even if the concentration is high. Crystal precipitation can be avoided and the crystallization line can be effectively relaxed. Thereby, various advantages as described above can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a conventional absorption heat pump (single-effect type).

FIG. 2 is a diagram comparing solubility lines of a solution containing various components with an aqueous LiBr solution as a basic composition.

FIG. 3 is a diagram showing a solubility curve of a LiBr + Ca (NO ₃ ) ₂ mixed salt aqueous solution.

FIG. 4 LiBr + Ca (NO) at a temperature of 280 K
₃ ) Graph showing the solubility of _two mixed salt aqueous solutions.

[Explanation of symbols] Regenerator Condenser Evaporator Absorber

Claims (2)

[Claims] 1. An aqueous solution composition for an absorption heat pump, comprising water as a refrigerant and lithium bromide as an absorbent component, wherein the composition contains calcium nitrate. Aqueous composition. 2. The aqueous solution composition for an absorption heat pump according to claim 1, wherein the molar ratio of calcium nitrate to lithium bromide is 0.1 to 0.5.