JPS6084379A - Thermal energy storage material - Google Patents

Abstract

PURPOSE:To provide a thermal energy storage material having excellent long- term stability and an excellent effect of inhibiting solid-liquid separation, consisting of Na2SO4.10H2O, a supercooling inhibitor and a specified solid-liquid separation inhibitor. CONSTITUTION:2-4wt% supercooling inhibitor (e.g. borax), 2-15wt% hydrated CaSO4 (e.g. III type CaSO4, alpha or beta type CaSO4.1/2H2O) as a solid-liquid separation inhibitor, optionally 0.5-10wt% thickener (e.g. finely divided amorphous silica) and 0.2-1.0mol (per mol of Na2SO4) of a melting point modifer (e.g. NaCl) are blended with Na2SO4.10H2O.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses sodium sulfate decahydrate (Na2SO410H
20) Concerning a heat storage material with excellent long-term stability. In particular, the present invention relates to a heat storage material characterized by adding hydrated calcium sulfate as a solid-liquid separation inhibitor.

Hydrous gold chloride, which has latent heat due to phase changes of melting and solidification;
The idea of using objects to store thermal energy has been known for a long time. According to the study results reported so far, it has been pointed out that there are two problems in the practical application of heat storage using this method. The first is that these hydrated salt compounds often do not undergo a phase change of melting or solidification at the melting point or freezing point, and exhibit a so-called supercooling phenomenon. Therefore, in order to cause a phase change at a constant temperature, it is necessary to prevent supercooling. As a method for preventing such supercooling, for example, US Pat.
7.664 specifies a supercooling inhibitor of Na2SO4.101120 and shite borax (Na2B407-10HzO
) is described. This Na2
B40y・10H20(7) Crystal HaNn2804-1O
H20o) in an epitaxial relationship with the crystal,
Na2B407-10H20 crystal is Na2804.1
'0H20(7) When present in a supersaturated solution, Na28
There is a report that it is effective in promoting crystal precipitation of 04/10H20 and preventing supercooling (Industrial & Medium Engineering Chemistry).
and Engi-neering chemis
try Vol 44 I+1808~tato,i
'b1952). Also, Ca0I! 2.6■20 supercooling inhibitor and (, TeBa(OH)2.Ba(OH)2-8
A method in which H20 or the like is used (Japanese Patent Publication No. 5B-9596) and a method in which BaI2. There are some substances that do not have an epitaxial relationship with 6H20, and the relationship between crystal form and nucleation is not necessarily clear.

The second problem is that solid-liquid separation occurs due to precipitation of anhydrous salts produced during the phase change process. For example, N
a2SO4・10■20 decomposes at 824℃ and 1. Anhydrous salt is produced, and this anhydrous salt settles to the bottom of the liquid. This is 3
When cooled to below 24°C, the anhydrous salt in the surface layer condenses and becomes Na.
2804.10H20, but since these crystals cover the surface, condensation is suppressed in the anhydrous bottom. Therefore, it is necessary to prevent precipitation of anhydrous salts. Generally, solid-liquid separation inhibitors are used to prevent sedimentation, but as heat storage materials, long-term stability must be maintained.Organic materials such as natural rubber and synthetic polymers are gradually hydrolyzed. Or it may be decomposed by living organisms, which is not preferable. For inorganic materials, a method using a porous support (% Kosho 58-6
108), a method using a clay-type substance having sheath-like particles as a thixotropic agent (JP-A-58-84687), a method using ultrafine silicic anhydride (8102) powder (
Chemical Week August 1 issue 84 negative, 1978) have been proposed. However, these are natural products that are produced only in specific regions or are expensive, and there are problems in putting them into practical use economically from the point of view of energy conservation, which is the original purpose of heat storage materials. Furthermore, in terms of effectiveness, repeating the cycle of heat storage and release over a long period of time tends to gradually reduce the viscosity and cause solid-liquid separation, so it cannot be said to be sufficient.

In view of the above-mentioned current situation, the present inventors
As a result of repeated studies on heat storage materials with excellent long-term stability that are mainly composed of H20, it was discovered that the stability was significantly improved by adding hydrated calcium sulfate as a solid-liquid separation inhibitor. It has been completed.

To explain the present invention, hydratable calcium sulfate is a calcium sulfate dihydrate (calcium sulfate dihydrate) that undergoes a hydration reaction in water.
It refers to calcium sulfate, which becomes CaSO4.2H20). It is also well known that the following double salts are formed in an aqueous solution of sodium sulfate, as described, for example, in Michio Sekiya, "Gypsum" (Gihodo, 1965), p. 104.

Na2504-CaS04NazSO4-CaSO4-
4H202Na2804-Ca804-2H20Na2
504-5CiaSO4-3H20 Therefore, Na2SO
When hydrated calcium sulfate is added to a 4-H2O-based mixture and stirred, CB 804.2H20 and/or the above-mentioned double salt are produced.

Since the double salt crystals of Oa, 804., 2H20 and /Mt produced are fine needle-like crystals, these are intertwined and fill the entire system to form a matrix. The matrix thus formed has the effect of preventing solid-liquid separation. By the way, the hydration reaction or double salt formation reaction of hydratable calcium sulfate in water as described above involves a process of dissolution of calcium sulfate → reaction → precipitation of dihydrate or double salt, so it takes time to complete the reaction. It takes.

Therefore, after adding hydrated calcium sulfate to the Na2SO4-[20 system, it is necessary to continue stirring and mixing until a certain amount of dihydrate or double salt precipitates, thereby increasing the viscosity of the slurry. This part of the precipitated crystals prevents unreacted calcium sulfate from settling, and therefore the crystals are uniformly precipitated in the system. It is desirable to add a thickener to prevent precipitation of unreacted calcium sulfate. Particularly desirable thickeners include silica-based thickeners, which can be prepared in the C system by adding amorphous silica imitation powder or by mixing sodium silicate and sulfuric acid. There is a method of producing polymerized silicic acid. Both have the effect of increasing the viscosity of the Na2SO4-H2O thread and preventing the precipitation of unreacted calcium sulfate, and also have the effect of acting as solid-liquid separation inhibitors, thereby further improving stability.

In addition, if the solid Cn804.2) II20 shown above or Fukusio is dissolved in water or a mixture of sodium sulfate and water, a matrix will not be formed and it is not suitable as a heat storage material33.
As the sodium sulfate in the main body of the present invention, bamboo, sodium acid decahydrate or anhydrous sodium sulfate and water are used.
The zO/Na 2804 molar ratio is in the range of 10 to I5. If the amount of water added is small within this range, then Na 280
If the amount of condensate is insufficient, the amount of heat storage will decrease, and if the amount is larger than this range, the concentration of Na 2804 will decrease, which is not preferable. Tejaborax (NazB407-10H20) is effectively used as a supercooling inhibitor, and the amount added is 2 to 4% by weight. Examples of filtrate phase calcium sulfate used as a solid-liquid separation inhibitor include hydratable anhydrous calcium sulfate (■ type CaSO4),
α-type and β-type hemihydrate calcium sulfate (α-type and β-type C
A 804.1/2H20) is used in an amount of 2 to 15% by weight, preferably 3 to 7% by weight in the heat storage material composition.
If the amount added is less than this range, the amount is too small and the formation of the matrix is insufficient, resulting in a low anti-separation effect, which is not preferable. If it exceeds this range, there is no problem in terms of matrix formation, but it is not preferable because the concentration of Na2SO4 decreases and the amount of heat storage decreases. As the amorphous silica fine powder optionally added as a thickener, an amorphous silica fine powder produced by a dry method or a wet method is used, and is commonly known as white carbon. These are commercially available product names such as Aerosil ■ (manufactured by Nippon Aerosil), Toxy ■ Lu (manufactured by Tokuyama 1F Tatsu M), Nip Seal (manufactured by Nippon Silica), Thyroid ■ (manufactured by Fuji Davison Chemical), etc., and are easily available. . The amount added is 0.5 to 10% by weight, preferably 1 to 7M. If the amount is less than this range, it is too small and the thickening effect is low, so it is not preferable, and if it exceeds this range, the concentration of NB2804 will decrease. This is not preferable because it reduces the amount of heat stored in the rice and increases the cost. In addition, when producing polymerized silicic acid by mixing sodium silicate and sulfuric acid, hydraulic lath or sodium metasilicate is used as the sodium silicate, and in the case of hydraulic lath, it is preferable to dilute it to about tit by weight. . It is also desirable that the sulfuric acid concentration be low. The mixing method of sodium silicate and sulfuric acid is to add sodium silicate to sulfuric acid, that is, by neutralizing from the acidic side, it is easier to obtain polymerized silicic acid with a thickening effect, compared to the reverse addition method. is also desirable. The amounts of sodium silicate and sulfuric acid added are such that the mixing of the two will result in neutrality, and the addition of 5i
The amount added is in the same range as the above-mentioned amorphous silica fine powder in terms of 0.02.

In addition to the above, melting point regulators may be added as necessary. Examples include NaC/, KO/? , N
H40,/', NaN03t (Which inorganic salt is used,
The amount added is 0.2 to i per 1 mol of Na2804,
.

The amount is in the molar range necessary to obtain the desired melting point.

As explained above, the method of the present invention has a remarkable effect of suppressing solid-liquid separation and dramatically improves stability, which greatly contributes to the practical application of heat storage materials.

Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples in any way. The heat of fusion was measured as follows. That is, heat storage i
The heat of fusion was calculated from the temperature change of the hot water by putting 80 F into a polyethylene sachet and putting it into 800 F hot water in a dewar bottle.

Example 1 Anhydrous sodium sulfate 81.60 parts Water 52.1 parts Sodium chloride 6.50 parts α-Gypsum hemihydrate 6.75 parts After stirring the above mixture at 30°C for 130 minutes, 8 parts of borax was added to make it viscous. A composition was obtained. After being left at about 80° C. for one day, this material became a solid substance with no thixotropy, and no floating ice was observed.

Example 2 Anhydrous sodium sulfate 87.27 parts Water 57.08 parts After stirring the above-mentioned platform at 85° C. for 80 minutes, part B of borax was added to obtain a viscous composition. After being left at 85°C for one day, this product became a solid with no fold change, and no floating ice was observed, and the heat of fusion was measured and showed a value of 49.6 CaJ/S'.

Example 3 85.29 parts of anhydrous sodium sulfate and 54.97 parts of water were stirred for 80 minutes in the same manner as in Example 2, and then 8 parts of borax was added to obtain a viscous composition. After being left for one day, this product was even harder than the composition of Example 2, and the heat of fusion was measured and showed a value of 48.7 Cat/f.

Example 4 86.47 parts of anhydrous sodium sulfate and 56.80 parts of water were stirred for 80 minutes in the same manner as in Example 2, and then 8 parts of borax was added to obtain a viscous composition. After leaving this thing for one day, 40℃-1θ
C temperature cycles were performed 28 times to observe changes in hardness and heat of fusion. The results are shown in Table 1 along with comparative examples.

Example 5 Anhydrous sodium sulfate 88.78 parts Water 52.1 parts Thorium chloride 694 parts Alpha hemihydrate gypsum 4.22 parts After stirring the above mixture at 25°C for 80 molecules tJJ, 3 parts of borax was added to form a viscous composition. I got something. When this product was left at about 25° C. for one day, it became a solid with no fold degeneration. This composition was subjected to a temperature cycle of 35°C = 10°C 28 times to observe changes in hardness and heat of fusion. The results are shown in Table 1 together with Comparative Example ♂.

Example 6 Finely powdered silica was added to Aerosil “200” (8 bottles of American 5L M
) was prepared using the same composition and method as in Example 5, except for the above, and as a result, a product with sufficient hardness and no floating ice was obtained.

This composition was subjected to 28 temperature cycles of 35° C. to 210° C., and the hardness, state of floating ice formation, and heat of fusion were measured. Table 1 shows the results.

Example 7 80.15 parts of anhydrous sodium sulfate was added to 4164 parts of 1.54 Wt sulfuric acid in a ladle at 30°C with stirring, and then 10.20 parts of 3 waterproof glass/water-1/l were gradually added. Shitko. Additionally, 6.40 parts of sodium chloride and 6 parts of α-hemihydrate gypsum.
After adding 55 parts of borax and stirring for 20 minutes, 3 parts of borax was added and stirring was continued for 60 minutes. This composition has a temperature of about 1 at Bθ°C.
After being left in the sun, it became solid and no floating ice was observed.

Comparative Example 1 Anhydrous sodium sulfate 42.76 parts The above composition was prepared and subjected to a temperature cycle of 40°C':10°C 12 times to observe changes in hardness and heat of fusion. The results are shown in Table 1 along with Examples.

Table 1

Claims (1)

[Claims] In a heat storage material composition that uses sodium sulfate decahydrate as a raw moon and consists of a supercooling inhibitor and a solid-liquid separation inhibitor, 2 to 15% by weight of hydratable calcium sulfate (as a solid-liquid separation inhibitor)
A heat storage material characterized in that the heat storage material is added to the heat storage material composition.