JPH01252875A - Vapor absorbing medium - Google Patents

Abstract

PURPOSE:To obtain an excellent vapor absorbing performance in a absorbing medium and make it possible to use it stably by using a medium to absorb vapor which includes at least one kind of nitrate selected from nitrates of alkali metal and nitrates of alkaline earth metal. CONSTITUTION:As a vapor absorbing medium the water solution of a nitrate of alkali metal, water solution of alkaline earth metal, and the water solution of a mixture of a nitrate of alkali metal and nitrate of alkaline earth metal are used. As a nitrate of alkali metal lithium nitrate, sodium nitrate, and potassium nitrate are, for instance, used. As a nitrate of alkaline earth metal calcium nitrate, magnesium nitrate, strontium nitrate, etc. are, for instance, used. Those nitrates are used individually or in a combination of more than two nitrates. The vapor absorbing medium in the invention has not only an excellent vapor absorbing capability but also a very low corrosiveness for metal materials and it is used preferably as a working medium for vapor absorbing in a chemical heat pump of absorption type, its refrigerator, etc.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a novel water vapor absorption medium.

More specifically, the present invention is suitable for use as a working medium in absorption chemical heat pumps, refrigerators, etc.
The present invention relates to a water vapor absorbing medium that is less corrosive to metal materials and has good water vapor absorption ability.

Conventional technology Conventionally, in absorption chemical heat pumps and refrigerators, aqueous solutions such as lithium bromide, lithium chloride, sulfuric acid, and sodium hydroxide have been used as working media for absorbing water vapor. Lithium chloride aqueous solution is often used.

However, these aqueous solutions generally have the disadvantage of being highly corrosive to metal materials, causing stress corrosion cracking in metal materials at high temperatures, and in particular, lithium bromide aqueous solutions, which are commonly used, solidify at high temperatures. It cannot be said to be economically advantageous because it easily generates a phase and is subject to restrictions on the applicable temperature.Moreover, lithium and bromine are relatively expensive elements.

Furthermore, since conventional working media are usually single-component aqueous solutions, the relationship between water vapor pressure, temperature, and concentration is fixed to one type, which is inconvenient in terms of equipment design.

Therefore, there is a strong need to develop a relatively inexpensive working fluid that is less corrosive to metal materials even at higher temperatures, such as 150°C or higher, has excellent water vapor absorption performance, and can be used stably in operation. Problems to be Solved by the Invention The present invention overcomes the drawbacks of such conventional water vapor absorption media, and provides a medium that is less corrosive to metal materials and has good water vapor absorption even at high temperatures of 150'O or higher. The purpose of the present invention is to provide a relatively inexpensive water vapor absorption medium that has high performance, is operationally stable, and can be suitably used as a working medium for absorption chemical heat pumps and refrigerators. It has been done.

Means for Solving the Problems As a result of intensive research to develop a water vapor absorption medium with excellent performance, the inventors have found that alkali metal nitrates, alkaline earth metal nitrates, and mixed aqueous solutions thereof are good. Based on this knowledge, we discovered that the mixed aqueous solution exhibits excellent water vapor absorption performance and low metal corrosion at high temperatures, and that the relationship between water vapor pressure, temperature, and concentration can be adjusted over a wide range by appropriately selecting the component composition. Based on this, the present invention has been completed.

That is, the present invention provides a water vapor absorption medium containing at least one selected from alkali metal nitrates and alkaline earth metal nitrates.

The present invention will be explained in detail below.

As the water vapor absorption medium of the present invention, an aqueous alkali metal nitrate solution, an aqueous alkaline earth metal nitrate solution, and a mixed aqueous solution of an alkali metal nitrate and an alkaline earth metal nitrate are used. Preferred examples of the alkali metal nitrate include lithium nitrate, sodium nitrate, potassium nitrate, etc., and each of these may be used alone, or
You may use two or more types in combination. Preferable examples of alkaline earth metal nitrates include calcium nitrate, magnesium nitrate, and strontium nitrate, and each of these may be used alone or in combination of two or more.

Furthermore, in the present invention, a mixture of one or more types of alkali metal nitrates and one or more types of alkaline earth metal nitrates can be used.

When comparing the water vapor absorption performance of single component aqueous solutions of alkali metal nitrates and alkaline earth metal nitrates in terms of boiling point rise (water vapor pressure drop) of the aqueous solutions at the same molar concentration and the same temperature, K<Ha<Li <Ca
<Mt> Magnesium nitrate and the like have a higher water vapor absorption performance than lithium bromide, which has been widely used in the past.

Although single-component aqueous solutions of the alkali metal nitrates and alkaline earth metal nitrates mentioned above also have excellent water vapor absorption performance,
In the case of a single component, the relationship between water vapor pressure-temperature-concentration is fixed, and the degree of freedom in designing equipment using the working medium is small. On the other hand, in a multicomponent aqueous solution containing two or more types of nitrates, the relationship between water vapor pressure, temperature, and concentration can be adjusted over a wide range by appropriately selecting the component composition, allowing a greater degree of freedom in equipment design. In addition, when it becomes an anhydrous salt, its melting point decreases.
It has the advantage of effectively preventing the formation of a solid phase in the working medium at high temperatures and high concentrations.

Suitable examples of such multi-component aqueous solutions are shown below.

[0.5Li・0.5Mtl・Nitrate aqueous solution [0.4L
i・0.3N*content 0.31 []・Nitrate aqueous solution [0,6
1i・0.2Nx Salary 0.2K] ・Nitrate aqueous solution [(
0,5Li-0,1Cs)・0.2N1・0. []・Nitrate aqueous solution (0,6Li-0,2Ni・(0,1-6
, 11)]・Nitrate aqueous solution (numbers are mole fractions) The boiling point increase degree of the [0,5Li・0,5 Mtl nitrate aqueous solution is almost the same as that of the lithium bromide aqueous solution.

Such a single-component aqueous solution or a multi-component aqueous solution is made to exist as a working medium in the steam generation region inside an absorption chemical heat pump or refrigerator to efficiently absorb the required water vapor, and then is sent to a regenerator. It is then heated and concentrated. In this manner, when the medium is used, absorption and release (dilution and concentration) of water vapor are repeated, so its concentration is constantly changing.

In addition, the single-component aqueous solution and multi-component aqueous solution are less corrosive to metal materials than conventional working media, and are particularly less corrosive at high temperatures, so they can be used as water vapor absorption media for chemical heat pumps and the like at temperatures above 150°C. It can also be applied to temperatures of

Effects of the Invention The water vapor absorption medium of the present invention is a single-component aqueous solution containing one selected from alkali metal nitrates and alkaline earth metal nitrates, or a multi-component aqueous solution containing two or more of them, and has good properties. In addition to having excellent water vapor absorption ability, it is extremely less corrosive to metal materials than conventional ones, and is suitably used as a working medium for water vapor absorption in absorption type chemical heat pumps and refrigerators. In addition, since the water vapor absorption medium has low corrosiveness to metal materials even at high temperatures, it can be stably used in various applications that require heating above 150°C, which was previously considered impossible, and is economical in thermal energy. It is also of high value from the standpoint of practical use.

Furthermore, when a multi-component aqueous solution containing several types of nitrates is used as the water vapor absorption medium of the present invention, the relationship between water vapor pressure - temperature - concentration can be adjusted more widely than in conventional solutions, and even if extremely concentrated, Since the anhydrous salt has a low melting point, it has the advantage that it is difficult to form a solid phase even at high concentrations. Furthermore, there is no need to use expensive bromine, and the amount of expensive lithium used can be relatively reduced, so it is economically advantageous.

Example Next, the present invention will be explained in more detail with reference to Examples.

EXAMPLE In order to investigate the water vapor absorption performance of nitrate aqueous solutions, various nitrate aqueous solutions having the following compositions were prepared, and the relationship between their concentration and boiling point was determined and shown in graphs in FIGS. 1 to 4.

(1) K nitrate aqueous solution (2) Na nitrate aqueous solution (3) Li nitrate aqueous solution (4) Na nitrate aqueous solution (5) [0,6Li・0.2Kg・0.2K] nitrate aqueous solution (6) [(0,5Li・o, tCa)・0.
2Km・0.2K] Nitrate aqueous solution (7) [(0,5Li・0,1 Mg)・0.2Km
・0.2K] Nitrate aqueous solution (8) [0.6Li・0.2Ns・(0.1K・O, l
Nitrate aqueous solution (9) [0,6Li・0.2Ns・(0,IK-0,1
Nitrate aqueous solution (10) [0.5Li・0.5Mg1 Nitrate aqueous solution (If) [0.4Li・0.3C・0.3Mg1
Nitrate aqueous solution (H) [0,4Li, 0.3KM, 0.3K] Nitrate aqueous solution (13) [0,4Ha, 0.3C, 0.
3M (] Nitrate aqueous solution (numbers are mole fractions) Figure 1 shows the case of an aqueous solution containing a single component of nitrate,
In the figure, the horizontal axis shows the molar fraction of H and O in the solution, and the vertical axis shows the boiling point ('K) at each concentration.

From this figure, it can be seen that the boiling point of an aqueous solution containing nitrate is much higher than the boiling point of pure water (x-1,100°C), and its water vapor pressure is lowered by a considerable amount. Further, when comparing the same concentration, it can be seen that the effect of increasing the boiling point (decreasing the water vapor pressure) is larger in the order of K<Nx<Li<Mg. Furthermore, the boiling point increase of magnesium nitrate aqueous solution is
It was confirmed that it was larger than that of lithium bromide, which has been widely used in the past.

Figure 2 shows the case of a multi-component aqueous solution containing three types of lithium, sodium and potassium nitrates, and an aqueous solution in which a part of the lithium nitrate in this aqueous solution is replaced with calcium and magnesium nitrates. The case of an aqueous solution in which a part of potassium nitrate in a multi-component aqueous solution is replaced with calcium and magnesium nitrate is shown. The horizontal and vertical axes in these figures have the same meanings as in FIG.

From FIG. 2 and FIG. 3, it can be seen that by replacing lithium or potassium nitrate with calcium or magnesium nitrate, a greater effect of increasing the boiling point (reducing water vapor pressure) is brought about.

FIG. 4 shows the relationship between concentration and boiling point in various multicomponent aqueous solutions. The horizontal axis and pseudo-axis in this figure have the same meaning as in FIG. This figure shows that an aqueous solution containing an equimolar mixture of lithium nitrate and magnesium nitrate has a large effect of increasing the boiling point (decreasing water vapor pressure).

Next, in order to clearly show the drop in water vapor pressure of a nitrate aqueous solution, we will use the mole fraction of LO and the pressure ratio (p/P
) is shown in a graph in Figure 5.

Here, p is the water vapor pressure at the boiling point of various solutions, and P is the water vapor pressure of pure water at the same temperature. In FIG. 5, (14) shows a straight line according to Raoult's law, but the (p/P) of each solution is much more negative than that, and it can be seen that the water vapor absorption ability of the nitrate aqueous solution is quite large.

In addition, since the melting point of the anhydride in a multi-component aqueous solution is lower than that in the case of a single component, there is a side effect that makes it difficult for the solid phase to precipitate even at high temperatures and high concentrations. It was done.

Furthermore, in order to investigate the corrosivity of nitrate aqueous solutions to metal materials, small pieces of carbon steel were immersed for a long time below the boiling point in various aqueous solutions with boiling points of 150 to 170°C.
When the annual amount of corrosion was calculated from the weight loss, it was found to be 0.04
Track layer/year. This value is expected to be even lower under practical conditions in the absence of air. For comparison, similar measurements were performed on an aqueous lithium chloride solution.
However, the annual corrosion amount was 1.2+u+/year.

From this, it was found that the corrosiveness of the nitrate aqueous solution to metal materials is extremely low, and it can be used stably for a long time even at high temperatures of 150° C. or higher.

[Brief explanation of the drawing]

Figures 1, 2, 3, and 4 are graphs showing the relationship between the concentration (molar fraction of water) and boiling point in various nitrate aqueous solutions, and Figure 5 is a graph showing the relationship between the concentration (mole fraction of water) and boiling point in various nitrate aqueous solutions. It is a graph which shows the relationship between mole fraction) and p/P. Patent applicant: Director of the Agency of Industrial Science and Technology Kozo Iizuka Designated agent: Director of the Nagoya Institute of Industrial Science and Technology, Mitsuo Isoya 1 Figure 0 0.2 0.4 0.5 0,81. O
I(2C) mole fraction 4 Second figure 0 0.2 0.4 0.6 0.8 1
．． 0H2 () mole fraction 9 3 Figure I-(2C) mole fraction No. 4 Figure B 20 mole fraction

Claims (1)

[Claims] 1. A water vapor absorption medium comprising an aqueous solution containing at least one selected from alkali metal nitrates and alkaline earth metal nitrates.