JPH07324838A - Aqueous solution composition for absorption heat pump - Google Patents

Abstract

(57) [Summary] [Composition] An aqueous solution composition containing water as a refrigerant and iodide as an absorbent component or an aqueous solution composition containing iodide and a nitrate, wherein the aqueous solution composition contains sodium thiosulfate (N
a ₂ S ₂ O ₃₎ absorption heat as a constituent material of stainless steel-based material, characterized by comprising the addition of - Toponpu aqueous solution composition. INDUSTRIAL APPLICABILITY In an absorption liquid containing iodide as an absorbent component, and an aqueous solution composition for absorption heat pump containing nitrate in the absorption liquid, sodium thiosulfate is added thereto to produce free iodine itself. It is possible to effectively prevent the corrosion of the stainless steel material, which is a material for various devices constituting the absorption heat pump.

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 in an absorption heat pump, and more specifically, it is used in an absorption heat pump composed of a stainless steel material. The present invention relates to an aqueous solution composition containing water as a refrigerant and iodide as an absorbent component or an aqueous solution composition containing iodide and a nitrate.

[0002]

BACKGROUND OF THE INVENTION Absorption heat - as the working medium used in Toponpu, heretofore water and ammonia (NH _3: refrigerant)
There have been proposed various things such as a combination of water and a halide and a combination of water and a halide, but in Japan, in reality, a system consisting exclusively of water and lithium bromide (“water- LiBr ”system is used, and a combination of water and ammonia (NH ₃ : refrigerant) is rarely used except in special cases because it is dangerous.

Among these, among the systems consisting of a combination of water and a halide, for example, a system consisting essentially of water and lithium bromide, in order to downsize the apparatus or cool it by air, the It is necessary to increase the concentration of lithium bromide, but then lithium bromide will crystallize out, and it has been difficult to reduce the size to a certain extent or to cool it by air. In order to improve this crystal limit, it has been proposed to add zinc bromide or zinc chloride to this aqueous solution of water and lithium bromide, but in a system in which these are added, the aqueous solution itself becomes acidic and extremely Not only does it show strong corrosiveness, but a dilute solution of about 10% by weight or less causes precipitation due to the formation of zinc hydroxide.

The absorption type heat pump basically comprises a regenerator, a condenser, an evaporator, an absorber and pipes connecting them, and these respective devices and pipes are made of mild steel or other carbon steel material, copper. , Cupronickel and other copper materials,
It is composed of various materials, and recently, it has been considered to use a stainless steel material as an alternative material when the carbon steel material cannot be used. Among these materials, the carbon steel-based materials that constitute the regenerator that functions at a high temperature, and the stainless steel-based materials described above, have the problem of corrosion with respect to the crystallization of the absorbent component and the formation of precipitates. Along with the problem, sufficient consideration must be given.

In the absorption type heat pump, it is necessary to keep the whole system in a completely airtight state in order to maintain the smooth operation, which is also very important for the corrosion protection of the system. However, when water is used as the refrigerant and lithium bromide, lithium chloride, etc. are used as the absorbent, this working medium is soft steel, etc., which is the main constituent material of the above-mentioned equipment constituting the absorption heat pump. It is corrosive to ferrous materials, and as a result, it is usually an inhibitor for corrosion prevention.
Is essential. As the inhibitor, for example, chromates such as lithium chromate, molybdates such as lithium molybdate, tungstates, nitrites, nitrates, azols, amines, etc. have been proposed. There is.

By the way, Japanese Patent Publication No. 5-28751 proposes a new absorption liquid for an absorption refrigerating machine, which has an improved crystallization limit in a working medium composed of water and a halogenated salt, and has an odor as a component. Lithium iodide, lithium iodide, lithium chloride, and lithium nitrate are used, and the ratio of each of these components is set within a predetermined range so that, for example, the concentration of the absorbent component in the aqueous solution is 63.6 wt% and the crystallization temperature is 0.5.
It has been shown that a crystallization temperature of 1.9 ° C. can be obtained at a temperature of 62.0 wt%.

When using this new working medium,
It is still necessary to give sufficient consideration to corrosion prevention. For example, in Japanese Patent Laid-Open No. 1-174588,
In particular, "lithium halide salt aqueous solution containing lithium iodide or the like" has been pointed out as an absorbent having strong corrosiveness, and countermeasures for using this have been studied.

According to this publication, in this absorbing solution, the conventional inhibitor alone was not sufficient for the corrosion inhibiting effect, but this problem was solved by adding an antimony compound, especially diantimony trioxide. The effect of the added antimony compound is to reduce the liberated halogen to ions and suppress the liberation of halogen, and the added antimony compound is adsorbed on the surfaces of copper and steel materials in the absorber. It is pointed out that there are two points: to form a dense protective film and prevent the elution of iron and steel.

However, the addition of lithium iodide as a component of the absorbent therefor utilizes the characteristics of lithium iodide itself as a compound, so during the operation of an absorption heat pump using this, Rather than returning the released and generated iodine to the original iodine ion, it is necessary to suppress the release and generation of iodine itself, and it is desirable to eliminate it if it can be generated.

From this point of view, the present inventors have proposed various aqueous solution compositions using water as a refrigerant and a halide containing an iodine compound such as lithium iodide as an absorbent. As a result of continuing various observations, iodine was easily liberated in the aqueous solution composition, and this was remarkable particularly when nitrate was contained, and free iodine in the aqueous solution containing lithium iodide was We have found the facts that significantly promote crevice corrosion of submerged stainless steels, but these facts justify the need to control the liberation of iodine itself.

Based on these facts, an aqueous solution composition used in an absorption heat pump having a stainless steel material as a constituent material and containing water as a refrigerant and iodide as an absorbent component, the aqueous solution composition. By adding sodium bisulfite (NaHSO ₃ ) as a reducing agent to the above, a method for suppressing or eliminating iodine liberation and generation itself has been developed and previously proposed (Patent application Hei 5-346533), and while further studying and pursuing from the same viewpoint, they have found that there is an additive component which is equivalent to or more effective than this, and arrived at the present invention.

[0012]

That is, the present invention is
Specific addition to an aqueous solution composition using water as a refrigerant and containing iodide as an absorbent component or an aqueous solution composition containing iodide and nitrate, which is used in an absorption heat pump having a stainless steel-based material as a constituent material. By including the components, it is possible to suppress or eliminate iodine liberation and generation as much as possible, to prevent corrosion of the stainless steel material used there, and to avoid the above-mentioned drawbacks. It is intended to provide an aqueous solution composition.

[0013]

The present invention provides an aqueous solution composition or iodide containing water as a refrigerant and iodide as an absorbent component, which is used in an absorption heat pump having a stainless steel material as a constituent material. In an aqueous solution composition containing nitrate, the aqueous solution composition contains sodium thiosulfate (N
adding a ₂ S ₂ O _3), absorption heat, characterized in that formed by incorporating - is intended to provide a Toponpu aqueous solution composition. Here, the term "absorption-type heat pump" is used not to mean a heat pump in a narrow sense but to mean a heat pump in a broad sense including a refrigerator.

In this case, the sodium thiosulfate (Na
₂ S ₂ O ₃ ) suppresses the liberation of iodine itself, thereby preventing corrosion of the stainless steel-based material used in the absorption heat pump for a long period of time.
Further, this sodium thiosulfate (Na ₂ S ₂ O ₃ ) is relatively soluble in the aqueous solution composition, and is also advantageous in this respect. The addition amount of this sodium thiosulfate (Na ₂ S ₂ O ₃ ) is The solubility of the components is possible, but can be appropriately set depending on the amount of iodide added to the aqueous solution, the amount of this and the nitrate, and the like.

In the present invention, the target "aqueous solution composition containing iodide as an absorbent component" or "aqueous solution composition containing iodide and nitrate as an absorbent component" is water-lithium iodide. System, water-lithium bromide-lithium iodide system, water-lithium iodide-lithium nitrate system, water-lithium bromide-lithium iodide-lithium chloride-lithium nitrate system and the like. Among these systems, especially in the case of a system containing lithium iodide and lithium nitrate, since lithium nitrate has an oxidizing power and tends to generate free iodine as it is, addition of sodium thiosulfate according to the present invention is not recommended. More effective.

[0016]

EXAMPLES Examples of the present invention will be described below, but it goes without saying that the present invention is not limited to these examples. First,
As the absorbing liquid composition, "60% LiXs + 0.2% LiO
Prepare a basic aqueous solution of "H",
a ₂ S ₂ O ₃ was added to adjust its concentration. Where L
iXs is LiBr: LiI: LiCl: Li in a molar ratio.
NO ₃ = 100: 75: 41: 25. In this case, the LiOH is added to keep the solution alkaline with low corrosiveness with respect to stainless steel.

The concentration of the additive component Na ₂ S ₂ O ₃ was adjusted as follows. Some I in basic aqueous solution
^- is present as ^- is oxidized I _3. Then, this basic solution is titrated with Na ₂ S ₂ O ₃ to reduce I ₂ in the solution by the following chemical reaction to obtain a titration end point solution. Both I ₂ and Na ₂ S ₂ O ₃ in the solution at this point are 0 ppm, but when Na ₂ S ₂ O ₃ is further added to this solution,
This results in a Na ₂ S ₂ O ₃ containing solution in which I ₂ is not present. ^{_{2S 2 O 3 2- + I 3}} - = 3I - +
S ₄ O ₆ ^2-

On the other hand, as a stainless steel test piece, SU
S304 steel (Cr: 18.25%, Ni: 8.53%,
C: 0.05%, Si: 0.49%, P: 0.0300
%, Mn: 0.85%, S: 0.006%, balance: F
e) is prepared, and a clearance test piece [inner and outer diameters of each is 10
mm / 20 mm of the annular surfaces are in contact with each other. Metal / metal-clearance (gap)]. In the present example, the test piece as such a "clearance" test piece is formed even in the case of stainless steel in a gap between metals or the like, and an air-concentration difference occurs in the gap to form an oxygen concentration battery. , Insufficient oxygen supply at the joint and the bottom of the deposit becomes an anode, causing corrosion (crevice corrosion)
Is due to progress.

After the above preparations, various experiments were carried out using the basic aqueous solution and the adjusted solution, all of which were carried out by the following method. After injecting each aqueous solution into a Teflon-lined titanium container (internal volume: 1 liter (1 liter)), the test piece of the above stainless steel was immersed in the aqueous solution (submerged surface area was SUS304: approximately 45c
m ² , Ti bolt: about 20 cm ² ), the container was capped and degassed using high-purity nitrogen gas, and then the inside was made into a nitrogen atmosphere and sealed.

Subsequently, the container is heated to bring the inside to a predetermined temperature, and this state is continued for a predetermined time until the natural potential (Es
p: The spontaneous change of the specimen that did not cause local corrosion) was measured to determine the maximum value (Esp, max), and the presence or absence of change of the stainless steel test piece was measured. The temperature and time in each test were 150 ° C. and 20 hours (1200 minutes), unless otherwise specified. In this case, the electrode potential (Electrode P
was measured and displayed by collating it with SCE (saturated sweet ko electrode potential) at room temperature.
The same applies to the display.

In addition, "clearance repassivation potential (E _R = E
_{R, CREV} ) ”was measured by the following measurement procedure. First, the electrode potential was set to -200 mV. While maintaining the SCE level, it was nobled at +10 mV / 10 min. From the time when the current of the test piece reached 10 mA (= 10000 μA),
After manipulating the potential so as to maintain this value for 10 hours,
The electric potential was made base at 10 mV / 60 min. In this way, the potential at which the current of the test piece became negative (-) for the first time was _defined as E _R (E _{R, CREV} ).

According to the above-mentioned method, with the use of the test aqueous solution having each Na ₂ S ₂ O ₃ concentration, the temporal changes of Esp, max and E _R (= E _R , _CREV ) at the temperature of 150 ° C. and the presence or absence of corrosion Was measured. The results are shown in FIGS. Of these, FIG. 1 shows E depending on the Na ₂ S ₂ O ₃ concentration.
sp, max and E _R, shows the change in _CREV, also, FIG. 2
FIG. 6 shows Esp, max at each concentration of Na ₂ S ₂ O _3.
And E _R , _CREV with time and the presence or absence of erosion depth (maximum erosion depth). Further, FIG. 7 compares the measurement results when an excess of NaHSO ₃ was added to the basic aqueous solution, in addition to the results shown in FIG.

As shown in FIG. 1, the E _R slightly fluctuates regardless of the Na ₂ S ₂ O ₃ concentration, but there is practically no change and the E _R is maintained at around -210 mV. In addition, in FIG.
The E _R is shown up to a Na ₂ S ₂ O ₃ concentration of 1000 ppm, but there is virtually no change after this concentration. On the other hand, Esp, max gradually decreases to a Na ₂ S ₂ O ₃ concentration of 600 ppm, and slightly increases thereafter, but it can be seen that there is practically no change.

Next, FIG. 2 shows a basic solution, that is, a solution at the end point of titration, in which the concentration of Na ₂ S ₂ O ₃ is 0 ppm. As shown, there is some change in the Esp value-
Approximately 390 mV, Esp. max is -380m
V. It was SCE. The Esp for E _R (-210mV). the difference between the max (E _R -Esp.max) 17
The test piece had no erosion, and the maximum erosion depth was 0 μm.

FIG. 3 shows that Na ₂ S ₂ O ₃ is added to the basic aqueous solution.
Was tested using a solution containing 150 ppm of H., but as shown in the figure, the spontaneous potential (Esp) in this case was
Shows a moderate upward trend over time,
Compared with the case of FIG.
max is -390 mV. It was SCE. E _R, (a 180mV about baser) significantly lower than even for _CREV, 12
Even after 00 minutes (20 hours), the test piece did not corrode,
The maximum erosion depth was zero (0 μm).

FIG. 4 shows that Na ₂ S ₂ O ₃ is added to the basic aqueous solution.
Is a case where the test is performed using a solution in which the amount of 300 ppm is present. As shown, spontaneous potential (Esp) in this case
Shows a moderate upward trend over time,
Compared with the case of FIG.
max is −410 mV. It was SCE. E _{R, CREV} -1
60 mV. Significantly lower than SCE (250 mV
Even after 1200 minutes (20 hours), the test piece has no erosion and the maximum erosion depth is zero (0 μm).
Met.

Further, FIG. 5 and FIG. 6 show 600 ppm and 200 ppm of Na ₂ S ₂ O ₃ with respect to the basic aqueous solution, respectively.
When tested using a solution in which 0 ppm was present, both spontaneous potentials (Esp) were lower than those in the case of FIG. 4, and even after 1200 minutes (20 hours), there was no erosion on the test piece, and maximum erosion was observed. The depth was zero (0 μm).
Further, when comparing FIG. 5 and FIG. 6, after 500 minutes,
In the case of FIG. 6 (Na ₂ S ₂ O ₃ 2000 ppm), FIG.
It can be seen that the amount is still lower than the case of (Na ₂ S ₂ O ₃ 600 ppm), but further lowers.

FIG. 7 is a diagram showing the results when Na ₂ S ₂ O ₃ shown in FIG. 1 is used and the results when NaHSO ₃ is used. As is clear from FIG. 7, first N
Esp, m when aHSO ₃ is 0 ppm (end point of titration)
ax> E _R , while Na ₂ S ₂ O ₃ is 0 ppm
In the case of, Esp, max <E _R , and it is recognized that there is already a difference between the two at this point.

Next, E _R in the solution to which Na ₂ S ₂ O ₃ was added,
_CREV is about 50 mV base compared to that in the solution with _{NaHSO 3} . Also, excess Na of 600 ppm or more
Esp, max in the liquid added with ₂ S ₂ O ₃ is
Compared to that in a liquid containing approximately the same amount of aHSO ₃ ,
It is mV base. As a result, the difference between E _R , _CREV and Esp, max in this concentration range is about 80 mV larger in the solution containing Na ₂ S ₂ O ₃ .

[0030] Thus, Na ₂ S ₂ O _3, the absorption solution containing iodide as an absorbent component, also acts very effectively to the absorption solution containing nitrate thereto, excess Na ₂ S ₂
O ₃ makes the Esp and max even more basic than NaHSO ₃ . Thus, Na ₂ S ₂ O ₃ was added, and I ₂
It is clear that the reduced solution has excellent crevice corrosion resistance for stainless steel materials. When Na ₂ S ₂ O ₃ is used, compared to NaHSO ₃ ,
It shows that Esp is kept more _base and the difference between _ER and _CREV is larger, and it becomes a safer environment for stainless steel.

[0031]

INDUSTRIAL APPLICABILITY As described above, the present invention provides an absorbing solution containing iodide as an absorbent component, and an aqueous solution composition for an absorption heat pump containing nitrate in the absorbing solution, and sodium thiosulfate as a reducing agent. By adding (Na ₂ S ₂ O ₃ ), the generation of free iodine itself is prevented, and the corrosion of the stainless steel material, which is a material for various equipment constituting the absorption heat pump, is extremely effectively prevented. be able to. In addition, when Na ₂ S ₂ O ₃ is used as compared with NaHSO ₃ , Esp is kept more _base and the difference between E _{R and CREV} becomes larger, which provides a safer environment for stainless steel.

[Brief description of drawings]

FIG. 1 E _{SP, max} and E _{R, CREV of} excess Na ₂ S ₂ O ₃ concentration
FIG.

FIG. 2 is a view showing a change with time of a spontaneous potential at a Na ₂ S ₂ O ₃ concentration of 0 ppm.

FIG. 3 is a view showing a change with time of a spontaneous potential at a Na ₂ S ₂ O ₃ concentration of 150 ppm.

FIG. 4 is a graph showing a change over time in spontaneous potential at a Na ₂ S ₂ O ₃ concentration of 300 pmm.

FIG. 5 is a diagram showing a change over time in the spontaneous potential at a Na ₂ S ₂ O ₃ concentration of 600 pm.

FIG. 6 is a view showing a time-dependent change in spontaneous potential at a Na ₂ S ₂ O ₃ concentration of 2000 pmm.

FIG. 7: Excess Na ₂ S ₂ O ₃ concentration and excess NaHSO ₃
The figure which shows the influence which it has on concentration E _{SP, max} and E _{R, CREV} .

Claims (2)

[Claims] 1. An aqueous solution composition containing water as a refrigerant and iodide as an absorbent component, wherein sodium thiosulfate is added to the aqueous solution composition as a constituent material. Aqueous solution composition for absorption heat pump. 2. A constituent material of a stainless steel material characterized in that an aqueous solution composition containing iodide and nitrate as an absorbent component with water as a refrigerant is obtained by adding sodium thiosulfate to the aqueous solution composition. An aqueous solution composition for absorption heat pumps.