JPH06159965A - Latent heat medium and heat collecting and accumulating system using the same - Google Patents

Abstract

PURPOSE:To effectively use an inorganic latent heat accumulating material low in cost and high in heat accumulation density, so far regarded as diffucult to use because of supercooling and phase separation problems, by a method in which a latent heat accumulating material is gelled to form a latent heat medium in which supercooling preventing agent and phase separation preventing agent are dispersed uniformly. CONSTITUTION:Preferably gelling agent is added to a heat accumulating material 10 which is sealed in a capsule 40 in order to gel the material 10, and core forming agent and phase separation preventing agent 30 are dispersed in the material 10 so that a capsule type latent heat medium 3 is finally formed. By this, effect to prevent supercooling and phase separation of the latent heat medium can be improved so much as to prevent degradation due to aging. Thus, an unused heat collecting and accumulating system using an inorganic latent heat accumulating material, which has been regarded unpractical, can be realized. According to this system, a direct contact heat exchange with unused heat by using a capsule type latent heat medium 3 can be realized, and further, staying time of the latent heat medium can be adjusted. As a result, as a difference of heat exchanging heat can be minimized, a heat exchanger 2 can be made compact.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a latent heat storage medium using a latent heat storage material capable of storing various kinds of heat energy at high density and a heat recovery heat storage system using the latent heat storage medium. In particular, the present invention relates to a latent heat storage material that can eliminate supercooling and phase separation at the time of phase change, which is a problem when the difference in heat exchange temperature is small due to unused heat utilization, and a heat recovery heat storage system using the latent heat medium.

[0002]

2. Description of the Related Art Up to now, the heat of river water and sewage has not been used because it is difficult to recover the heat because it is close to the ambient temperature. Further, in recent years, together with the increase in energy consumption, global warming due to an increase in the amount of released carbon dioxide has become a problem, and energy saving measures have been demanded as a part of measures against it. As a specific means for that purpose, a heat recovery system has been proposed that recovers the heat of the above-mentioned river water or sewage and uses it as a heat pump heat source for heating and cooling or hot water supply (for example, Air Conditioning and Sanitary Engineering Volume 63 No. 8, Recent District Heating and Cooling Plans and Waste Heat Utilization, p.651-656, etc.). In a conventional system, heat of river water, sewage, etc. is recovered by water through a heat exchanger, and the temperature of the water is increased (that is, sensible heat), and the hot water is stored in a heat storage water tank to store heat. When using
The hot water is heated to a required temperature via a heat pump or the like and supplied to a building or a house as hot water for heating.

On the other hand, in a small-scale building or the like, in order to miniaturize the heat storage water tank, it has been proposed to use a latent heat storage material such as calcium chloride hexahydrate which utilizes a phase (solid-liquid) change instead of water (for example, Japanese Patent Publication No. 3-54151), which has been partially commercialized.

[0004]

In the heat recovery heat storage system described above, particularly in the recovery of unused heat of river water, sewage, etc., the temperature is as low as about 10 ° C. in winter, for example, and many There are challenges. That is, a small temperature difference (for example, 1 ° C, this is 1/3 of a normal heat exchanger), and the temperature rise on the water side that can be recovered and recovered is also small (for example, 3 ° C, this is the normal temperature). 1/2). for that reason,
First, the heat exchanger becomes larger in proportion to the heat exchange temperature difference (3 times)
To do. Also, since the flow rate of the heat transport water increases in inverse proportion to the rise in the temperature of the recovered water, the heat transport pipe has a larger diameter (1.4 times),
Water supply power will also increase (double). Furthermore, since the temperature rise (temperature difference) of the recovered water is small, the heat storage water tank is also enlarged (doubled) in order to store a large amount of water in the heat storage.

The root cause of these problems is that water is used as the heat medium for heat exchange and heat storage, and improvement of the heat medium used is an important solution. However, if the conventional latent heat storage material is used as a heat medium as it is, the following problems occur. For example, the latent heat storage material of inorganic salts such as calcium chloride hexahydrate, sodium sulfate decahydrate, lithium chlorate trihydrate, etc., compared to organic systems such as polyethylene glycol and paraffin,
While it has the advantages of being inexpensive and having a large latent heat of fusion during phase change, it has problems of supercooling and phase separation. That is, supercooling is a phenomenon in which solidification heat does not occur unless it is cooled to a temperature significantly lower than the melting point. For example, the calcium chloride hexahydrate disclosed in Japanese Patent Publication No. 3-54151 has a difference in supercooling temperature.
It can reach 20 ℃. Therefore, since the temperature difference is small in the heat recovery from river water or sewage, it cannot be taken out without solidifying in the heat storage tank due to supercooling. In addition, phase separation is a phenomenon in which a solid that is first solidified during solidification has a higher density than an unsolidified liquid and thus precipitates, and the liquid and the solid are separated. As a result, the rate of unsolidification increases with each repetition, and the latent heat of phase change that can be taken out substantially decreases.

As a countermeasure against supercooling and phase separation, there is a method of adding various supercooling inhibitors and phase separation inhibitors to the latent heat storage material. However, repeated use causes deterioration over time in which their preventive effects are reduced, and when filled in capsules or the like, the life of the medium is shortened, which is a serious problem. An object of the present invention is to solve the above problems and provide an inexpensive inorganic latent heat storage material that prevents supercooling and phase separation from occurring.

Still another object of the present invention is to provide an unused heat recovery heat storage system capable of heat recovery, heat transportation and heat storage with a relatively low temperature difference using such an inorganic latent heat storage material. Especially.

[0008]

In order to solve the above-mentioned problems, the present inventors have conducted various experiments and data analysis to determine the cause of the deterioration with time of the effects of the supercooling inhibitor and the phase change inhibitor. investigated. As a result, the cause of deterioration of these effects over time is that the inhibitor coagulates and precipitates due to the difference in density between the heat storage material and the inhibitor, etc. due to repeated solidification and melting, and separates from the heat storage material. It revealed that. Further, it was found that, especially when the capsules were filled, the flow was restricted, so that the capsules were easily separated and deteriorated with time.

Therefore, the present inventors can prevent the aggregation and sedimentation of the heat storage material by gelling the heat storage material and uniformly dispersing the supercooling prevention agent and the phase separation prevention agent therein. I found out that. The invention of the present application is based on the findings, and basically, an inorganic latent heat storage material that utilizes latent heat at the time of solid-liquid change is gelated in an agar form,
Disclosed is a latent heat medium in which a solid-liquid change occurs due to heat exchange, in which a nucleating agent for preventing supercooling is dispersed. As a result, the heat recovery heat storage system that recovers the heat of the river water or sewage through the latent heat storage material and stores the heat can eliminate the above-described effect of preventing supercooling and phase separation, and also the latent heat. The deterioration of the effect of the medium with time was eliminated.

It is a preferred embodiment that the inorganic latent heat storage material is made into a gel form and a nucleating agent or a phase separation inhibitor is dispersed therein to form a capsule type latent heat medium enclosed in a capsule. The present invention further discloses, as a heat recovery means, a system in which the above capsule type latent heat medium is brought into direct contact with unused heat such as sewage or river water, and the latent heat medium is transported and stored in a heat storage tank. As a result, the heat exchanger can be downsized and the heat transport power can be reduced, or the pipe diameter can be reduced and the heat storage tank can be downsized.

The inorganic latent heat storage material which is the object of the present invention is preferably used.
A good example is Ca by recovery temperature (melting temperature).
Cl₂・ 6H₂O (melting temperature: 29 ° C), Na₂SO_Four・ 10H₂O (32 ° C),
LiClO₃・ 3H₂O (8 ° C), Na₂S₂O₃・ 5H₂O (50 ℃), Na₂HPO_Four 
・ 12H₂O (35.5 ℃) etc. In addition, LiNO₃・ 3H₂O, Ca
(NO₃)₂・ 4H₂O, Al (NO₃)₂・ 9H₂O, Na₂CO₃・ 10H₂O, FeCl ₃
・ 6H₂O and water can also be used. In addition, the melting temperature
Na to change ₂SO_Four(31%), NaCl (13%), KCl (16
%), H₂Inorganic heat storage agent such as mixed system of O (40%) (melting temperature: 4 ° C)
Is also effective.

The nucleating agent dispersed in the latent heat storage material of the present invention
The degree of effect varies depending on the latent heat storage material used.
Various soluble strontium salts (oxide stringent)
Water, stringent dioxide, stringent dioxide 8 water
Salt, strontium chloride hexahydrate, strontium phosphate,
Strontium hydroxide, etc.) and various barium salts (phosphoric acid 1
Barium hydrogen, barium dihydrogen phosphate, barium phosphate, pi
Barium rophosphate, barium phosphite, barium oxalate
Aluminum, barium metaborate, etc.), Na_FourP₂O₇・ 10H ₂O,
Na₂B_FourO₇・ 10H₂O, KClO, Na₂SiF₆, K₂SiF₆, BaSiF₆Or
Calcium silicate, silicic anhydride, silicon carbide, calcium carbonate
Um or the like can be used. Also, the physical core
As particles, aluminum powder, carbon powder, powder adsorbent, carbon
Black, molecular sieves, diatomaceous earth, borax, zebra
Effective use of powder materials such as olite and fiber materials
be able to. The amount of nucleating agent added depends on the combination.
However, if it is less than 0.5% by weight, the number of nuclei is small.
It is not possible to destroy the supercooling sufficiently, and the effect of preventing supercooling is insufficient.
It will be a minute. On the other hand, if the content exceeds 10% by weight, the nucleating agents will be mixed together.
As the particles become coarser and the supercooling prevention effect decreases,
Since the relative filling amount of the heat storage material is reduced, the latent heat amount is reduced.
Will end up. Therefore, the amount of nucleating agent added is 0.5 to 10
Amount% is suitable.

The phase-separation-preventing agent also has different effects depending on the latent heat storage material used, but hydroxyethyl cellulose,
Bentonite, polyacrylic acid, polyethylene oxide, starch paste, wood pulp and the like can be effectively used. As a gelling agent for gelling the latent heat storage material for realizing the present invention, a natural organic polymer such as gelatin, starch,
Cross-linked starch, cellulose polymer and the like can be effectively used. As a synthetic polymer, polyvinyl alcohol
, Polyacrylic acid, polyethylene oxide, polyacrylamide, polymethacrylamide, polyhydroxyalkyl methacrylate, polyethylene glycol
, Acrylonitrile grafted hydrolyzate, acrylic acid grafted product, polyvinyl pyridine, carboxymethyl cellulose and the like can be effectively used. The addition amount of the gelling agent is slightly different depending on the combination, but if it is less than 0.5% by weight, the mixture of the latent heat agent and the gelling agent becomes uneven,
The gel formation becomes insufficient, and the supercooling preventive agent and the phase separation preventive agent settle and do not disperse uniformly. On the other hand, if the amount exceeds 10% by weight, the gel structure is destroyed and the gelling action is adversely decreased. At the same time, the relative amount of the latent heat storage material is reduced, and the amount of latent heat is reduced. Therefore, the appropriate amount of gelling agent added is 0.5 to 10% by weight.

[0014]

First, preferably, the gelling agent is added to the heat storage material enclosed in a capsule to form a gel, and the nucleating agent or the phase separation inhibitor is dispersed therein to form a capsule type latent heat medium. Constitute. By doing so, the effect of preventing overcooling of the latent heat medium and phase separation can be improved and deterioration over time can be eliminated, so that heat such as unused heat using an inorganic latent heat storage material that has been difficult to use until now. A recovery heat storage system can be realized. Of course, it is also possible to use it as a heat exchange medium as it is without encapsulating it.

In this system, it is possible to adjust the residence time of the latent heat medium by directly contacting heat exchange with the unused heat using the above capsule type latent heat medium. Therefore, the difference in heat exchange temperature can be reduced, and the heat exchanger can be downsized. Further, since the latent heat medium itself is transported, heat can be transported at a high density, so that the transport power can be reduced and the pipe diameter can be reduced. Further, since the latent heat medium is stored in the heat storage tank, heat can be stored at a high density, so that the heat storage tank can be downsized.

[0016]

EXAMPLES The present invention will be described below with reference to examples. First, an example of the latent heat medium will be shown. [Example 1] As a heat storage agent, calcium chloride hexahydrate (CaCl
₂ -6H ₂ O) is heated and melted at 40 ° C, and strontium chloride hexahydrate (SrCl ₂ -6H ₂ O) as a nucleating agent is added thereto in an amount of 1% by weight,
While adding 5% by weight of gelatin as a gelling agent,
After stirring for a minute, a latent heat medium gelled in a state where the nucleating agent was uniformly dispersed in the heat storage agent was prepared in a 50 cc beaker. [Example 2] A gelled latent heat medium was prepared in a 50 cc beaker in the same manner as in Example 1 except that polyvinyl alcohol was used as a gelling agent. [Example 3] The gelled heat storage agent prepared in Example 2 was
A columnar capsule made of polystyrene having a diameter of 10 mm and a thickness of 0.5 mm was filled to prepare a capsule-shaped latent heat medium. [Comparative Example 1] Calcium chloride hexahydrate (CaCl
₂ -6H ₂ O) was heated and melted at 40 ° C to prepare a heat storage agent in a 50cc beaker. [Comparative Example 2] Calcium chloride hexahydrate (CaCl 2 as a heat storage agent
₂ -6H ₂ O) is heated and melted at 40 ° C, and strontium chloride hexahydrate (SrCl ₂ -6H ₂ O) as a nucleating agent is added thereto in an amount of 1% by weight and stirred, and a heat storage agent is added in a 50cc beaker. Created in. [Performance Evaluation Method as Latent Heat Medium] 10 ° C. for the latent heat medium of Examples 1 to 3 and the heat storage agents of Comparative Examples 1 and 2
The change of the supercooling temperature difference at the time of solidification was measured, with one cycle consisting of a heat radiation operation of cooling to solidify and heating to heat to 50 ° C. and melting. Here, the supercooling temperature difference is the solidification (melting) temperature of calcium chloride hexahydrate 29
The difference between ° C and the solidification temperature of the actually prepared heat storage agent in the cycle test. It can be evaluated that the smaller the difference, the more effectively the nucleating agent works.

[0017]

[Table 1] [Performance Evaluation Result] Table 1 shows the test results of the latent heat mediums of Examples 1 to 3 and the heat storage agents of Comparative Examples 1 and 2 which were prepared by the above method and subjected to the performance evaluation test. In the table, the actual measured values of the first and 50th supercooling temperature differences are shown.

As a result, in Comparative Example 1 containing only the heat storage agent, the difference in supercooling temperature was as large as 18 ° C., and in Comparative Example 2 in which the nucleating agent was added, the difference in supercooling temperature was as small as 2 ° C. at the first time. , At the 50th time, the subcooling temperature difference was
It becomes as large as 17 ℃. On the other hand, in the latent heat mediums of Examples 1, 2 and 3 which are the present invention, the difference in supercooling temperature is as small as 2 ° C. and does not change until the 50th time. In Examples 1 and 2, the gelling agent was changed, but the difference between the two was small and the supercooling temperature difference was small. Examples 4 and 5 show the difference between the beaker state and the capsule state, but there is no difference between them, and it was demonstrated that the effect of the present invention is the same even in the capsule state.

From the above examples, it was found that the latent heat medium using the gelling agent of the present invention does not deteriorate due to supercooling and has stable performance even in the capsule state or long-term use. Next, an embodiment of a heat recovery heat storage system using the above-described latent heat medium according to the present invention as a heat exchange medium will be described with reference to FIGS. FIG. 1 shows a cycle diagram of a heat recovery heat storage system according to the present invention, and FIG. 2 shows a sectional view of a capsule type heat medium filled with a latent heat storage material used in the heat recovery heat storage system. A capsule type latent heat medium (hereinafter referred to as latent heat medium) 3 and a carrier fluid 4 are mixed and stored in the heat storage tank 1, and the latent heat medium 3 and the carrier fluid 4 are stored between the heat storage tank 1 and the heat exchanger 2. A transport pump 5 for transporting together is provided. The heat storage tank 1 and the heat exchanger 2 are connected by a heat insulating pipe 8 which is practically insulated.

The carrier fluid 4 is a fluid whose main component is water or oil used for a heat source such as the heat pump 11 and to which additives such as a corrosion inhibitor are added if necessary. The heat source fluid 7 is a fluid having a low temperature level near the ambient temperature such as river water, sewage, seawater, etc., which is supplied from the heat source 6 by the pump 9. The heat source fluid 7 is sent from the heat source 6 to the heat exchanger 2 by the pump 9. The heat source fluid 7 is in direct contact with the latent heat medium 3 in the heat exchanger 2 in a flowing state, gives heat to the inorganic latent heat storage material in the capsule, is cooled, and is then returned to the heat source 6.

On the other hand, in the heat exchanger 2, the solid latent heat storage material in the capsule is melted, and the heat obtained from the heat source fluid 7 is stored in the capsule at high density as the latent heat of fusion of the latent heat storage material. The latent heat medium 3 filled with the latent heat material in a liquid state is mixed with the carrier fluid 4 and carried in the heat insulating pipe 8 and stored in the heat storage tank 1. Corresponding to the heat demand side, only the carrier fluid 4 is sent to the heat pump 11 to be heated to a required temperature and supplied as a heat source for heating a building or the like. Where the heat pump
If the latent heat medium 3 and the carrier fluid 4 are mixed and flown to 11, it is possible to reduce the diameter of the pipe between them.

The heat exchanger 2 has a structure in which the capsule 3 is in direct contact with the heat source fluid 7 while flowing in the container and descends while exchanging heat. On the other hand, in the heat storage tank 1, the capsule is filled in the carrier fluid 4, and while the capsule 3 is sent to the heat exchanger 2 by the pump 5, the capsule moves in the tank by the piston flow. The carrier fluid 4 is sent to the heat pump 11 through the strainer 8 in the tank, while the capsule 3 is the heat pump.
It is structured so that it cannot be sent to 11.

Although the heat source fluid 7 and the latent heat medium 3 may indirectly exchange heat in the heat exchanger 2, when the heat is directly exchanged, the latent heat is generated between the heat storage tank 1 and the heat exchanger 2. It is better to provide a device for separating the medium 3 and the carrier fluid 4 so that only the latent heat medium 3 can be contacted by the heat source fluid 7 for heat exchange. here,
The latent heat medium 3 may be densely filled in the heat exchanger 2 to exchange heat with the heat source fluid 7 in a substantially stationary state (including piston flow). However, the heat exchange performance can be improved by reducing the filling amount of the latent heat medium and exchanging heat with the latent heat medium in a flowing state, and at the same time, when the heat source fluid is dirty, such as sewage, the capsule surface of the latent heat medium becomes dirty. It has the effect of making it hard to attach and improving the stain resistance.

The filling state of the latent heat medium 3 in the heat storage tank 1 is also the same as above. That is, the heat storage tank 1 may be densely filled with the latent heat medium 3 and heat may be exchanged in a substantially stationary state (including the piston flow), but the latent heat medium may be exchanged in a fluid state by reducing the filling amount of the latent heat medium. The better the heat exchange performance,
The load response of the heat storage tank is improved. Depending on the object, scale, or purpose, it is advantageous to fill the heat storage tank 1 and the heat exchanger 2 with the latent heat medium 3 separately and not circulate the latent heat medium 3 between them. In this case, two or more heat exchangers are installed and the solidification and the melting are alternately performed in a batch type, but the transport pump 5 has an effect that an inexpensive pump can be used.

In the above, the case where the heat is recovered from the heat source fluid 7 and used as the heat source of the heat pump 11 for the purpose of heating in the winter, etc., the latent heat storage material in the capsule is the heat exchanger 2.
And the solidification occurs in the heat storage tank 1. On the other hand, the heat source fluid 7 for river water or sewage is used as a refrigerator (heater) for the purpose of cooling in summer.
The same equipment as the pump can be used.)
The phase change of the latent heat storage material in the capsule is reversed, solidification occurs in the heat exchanger 2 and melting occurs in the heat storage tank 1, but the configuration and operation of the heat recovery system are the same as in winter.

The above heat recovery works effectively when the latent heat storage material in the capsule does not have supercooling or phase separation. In the present invention, the supercooling preventive agent 20 and the phase separation preventive agent 30 are uniformly dispersed in the gelled latent heat storage material 10 shown in FIG. 2 and encapsulated in a capsule shell 40 such as a resin. Is particularly effective. The diameter of the capsule is
The size of 0.5 to 30 mm is suitable for flow and transportation. The shape of the capsule changes depending on the type of heat source fluid and the purpose of use. For example, when using a latent heat medium in a stationary state (including piston flow), conversely the flow is restricted, such as a cylindrical type or a rectangular shape. The non-spherical shape may be good.

The temperature level of the heat source fluid varies depending on the type of heat source and the season (purpose). For example, river water and sewage,
During the heating period in winter, the temperature is around 10 ° C, which is higher than the outside temperature, so it can be used as a heat source for heating, but in the summer, the cooling period is around 17 ° C, which is lower than the outside temperature, so it can be used as a cooling source for cooling. Even the heat source has different temperatures depending on the season. Therefore, since the melting temperature of the latent heat storage material filled in the capsule to be used is different,
It is necessary to select a latent heat storage material according to the purpose and target.

[0028]

According to the present invention, the latent heat storage material is gelled and used as a latent heat medium in which a supercooling inhibitor and a phase separation inhibitor are uniformly dispersed. Inorganic latent heat storage material with low heat storage density and high heat storage density, which was considered difficult to use, can be used efficiently. As a result, it is possible to realize a heat recovery heat storage system suitable for recovering unused heat, which has a heat exchanger using the latent heat medium and a heat storage tank. This system is capable of downsizing heat exchangers, improving stain resistance, downsizing heat storage tanks, reducing transport power, and downsizing pipes.

[Brief description of drawings]

FIG. 1 is a cycle diagram of a heat recovery heat storage system using a heat medium according to the present invention.

FIG. 2 is a cross-sectional view of a capsule-type heat medium used in the heat recovery heat storage system.

[Explanation of symbols]

 1 ... Heat storage tank 2 ... Heat exchanger 3 ... Capsule type heat medium 4 ... Carrier fluid 6 ... Heat source 7 ... Heat source fluid 10 ... Latent heat storage material 11 ... Heat pump 20 ... Supercooling inhibitor 30 ... Phase separation inhibitor 40 ... Capsule shell

Claims (11)

[Claims] 1. A heat exchange characterized in that a nucleating agent for preventing supercooling is dispersed in a latent heat storage material that utilizes latent heat at the time of solid-liquid change by gelling with a gelling agent. A latent heat medium that changes solid-liquid. 2. A capsule-shaped latent heat medium comprising the latent heat medium according to claim 1 enclosed in a capsule container. 3. A natural organic polymer such as gelatin, starch, cross-linked starch, or cellulose polymer is used as a gelling agent for gelling the latent heat storage material. The latent heat medium described. 4. A gelling agent for gelling a latent heat storage material, such as polyvinyl alcohol, polyacrylic acid, polyethylene oxide, polyacrylamide, polymethacrylamide, polyhydroxyalkylmethacrylate.
The latent heat medium according to claim 1 or 2, wherein a synthetic polymer such as a polyester, a polyethylene glycol, an acrylonitrile grafted hydrolyzate, an acrylic acid grafted product, polyvinyl pyridine, or carboxymethyl cellulose is used. 5. The latent heat medium according to claim 1 or 2, further comprising a phase separation inhibitor. 6. The latent heat medium according to claim 5, wherein hydroxyethyl cellulose, bentonite, polyacrylic acid, polyethylene oxide, starch paste, and wood pulp are used as the phase separation inhibitor. 7. A heat recovery system comprising a heat exchanger having a structure in which the latent heat medium according to claim 1 is directly contacted with a heat source fluid for heat exchange. 8. The heat recovery system according to claim 8, further comprising a heat exchanger having a structure for performing direct contact heat exchange of the latent heat medium in a fluid state. 9. A heat recovery heat storage system comprising a heat storage tank having a structure in which the latent heat medium according to claim 1 is used as a heat storage material to directly exchange heat with a heat recovery fluid. 10. A heat storage tank having a structure for directly contacting heat exchange of a latent heat medium in a fluid state.
10. The heat recovery heat storage system described in 10. 11. A heat storage tank for storing the latent heat medium according to claim 1 and a carrier fluid, a heat exchanger for directly or indirectly exchanging heat with a heat source fluid using the latent heat medium, A heat recovery heat storage system characterized in that a means for circulating and transporting a latent heat medium together with a carrier fluid is provided between the heat storage tank and the heat exchanger.