JPS61231078A - Method of storing heat - Google Patents

Abstract

PURPOSE:To store heat at a high heat storing density and low heat storing loss, by storing heat by taking advantage of the vapor transfer CONSTITUTION:A dil, heat-storing soln. 40 having a concn. of C2 which has been transferred with a pump 21 from a heat-storing.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a heat storage method, and particularly to a heat storage method that uses a liquid heat storage agent to reduce heat storage loss.

[Background of the invention]

Heat storage methods include (1) storage in the form of thermal motion (1) use of sensible heat (also called use of specific heat capacity), (2) use of latent heat, stored in the form of chemical energy (3) use of reaction heat and use of dilution heat of concentrated liquid. (4) There are various methods of utilizing concentration difference energy and their combinations.

In general, sensible heat utilization is easy to operate, but has the disadvantage that the heat storage density (the amount of heat stored per heat storage agent) is smaller than other methods.

In addition, although indirect heat utilization has a high heat storage density, there is a limit to the heat storage temperature. Generally, high temperature heat storage of 200 to 5 ooc is targeted.

Concentration difference energy utilization, which uses only dilution heat, has a low heat storage density, so a method that combines this with latent heat utilization is advantageous.

Therefore, as a heat storage method in fields such as air conditioning, hot water supply, and heating and drying, a method that uses latent heat in combination with dilution heat is preferably used.

There are two ways to utilize latent heat: (A) a method that utilizes the heat of vaporization when a liquid evaporates, and (B) a method that utilizes the heat of fusion when a solid becomes a liquid. Since the latent heat of vaporization is larger than the heat of fusion, it is more advantageous to utilize the heat of vaporization.

Water, which has a large latent heat of vaporization, is used as the substance to be vaporized. In this method, heat is used to evaporate water and convert it into water vapor, but since the volume of water vapor is large, it is generally adsorbed or absorbed by a solid or liquid heat storage agent.
It is stored in a smaller volume.

Zeolite adsorption methods and absorption methods using calcium chloride water salts are methods for retaining water vapor with solid heat storage agents (for example, Japanese Patent Application Laid-Open No. 51-43387). There are problems such as low efficiency.

On the other hand, the method of retaining water vapor with a liquid heat storage agent allows easier contact with water vapor and has better heat exchange efficiency than a solid heat storage agent. Examples of liquid heat storage agents include salts such as lithium bromide aqueous solution (for example, Frozen 34-496, pages 22 to 25) used in absorption refrigerators, sulfuric acid, sodium hydroxide, and acid and alkali aqueous solutions.

For example, proc is a heat storage system using a liquid heat storage agent.
, Engineering Converter
There is a conventional example described in s 6ngconf 14 th 41. This conventional heat storage system will be explained with reference to FIG.

In the figure, the system includes a water tank 100. Heat storage liquid (lithium bromide aqueous solution) tank 500. It is composed of a water heat exchanger 200 having heat transfer tubes 210 and a heat storage liquid heat exchanger 600 having heat transfer tubes 610. Water 10 is circulated between a water tank 100 and a water heat exchanger 200 by a pump 11. On the other hand, a heat storage liquid tank 500 and a heat storage liquid heat exchanger 60
The heat storage liquid 20 is circulated by the pump 21 between 0 and 0.

Next, heat storage and heat output (cold heat generation) in this system
The operation will be explained using the water vapor pressure diagram shown in FIG. 5 in addition to FIG. 4.

In the figure, the horizontal axis is temperature and the vertical axis is water vapor pressure, and shows the water vapor pressure lines of water and heat storage liquid. The difference in water vapor pressure between the two causes heat storage and cold heat generation (heat output).

In the heat storage operation, first, the heat exchanger tube 6 is
The heat storage liquid sprinkled on the surface of 10 is heated at a temperature Tg, and the water is evaporated at a temperature TMc to change the heat storage liquid from a concentration Cs% to a concentration Ct.
% (point G in Figure 5). The water vapor 30 generated therein enters the water heat exchanger 200 connected to the heat storage liquid heat exchanger 600, is cooled by outside air, etc. in the heat transfer tube 210, and is condensed at the temperature TLC to become water (fifth 0 points in the figure). The pressure inside the Pazen exchanger is Pg, which is equal to the saturated vapor pressure of water at temperature TLC. In the above manner, the heat at temperature TmC0 is recovered as latent heat of vaporization by changing the phase of water, and is stored as a concentration difference in the heat storage liquid.

Next, in the cold heat generation operation, the concentrated heat storage liquid 20 with a concentration of C% is sent from the heat storage liquid tank 500 into the heat exchanger 600 for heat storage liquid by the pump 21, and at the same time it is sprayed onto the surface of the heat transfer tube 610. Cool it down. Then, since the heat storage liquid 20 has a low water vapor pressure, it absorbs the water vapor in the container and generates heat, and since the container is sealed, the vapor pressure inside the container becomes Pc.
down to. On the other hand, when water 10 is sent from the water tank 100 to the water heat exchanger 200 using the pump 11 and sprayed on the surface of the heat exchanger tube 2100, evaporation occurs because the inside of the vessel is in a vacuum, and the heat exchanger tube 210 absorbs the latent heat of evaporation. Deprived and cooled. The generated water vapor 31 is absorbed into the heat storage liquid 20, and the heat storage liquid is diluted to maintain a balance between the amount of water vapor and the heat storage liquid. I degree Ct
becomes. The heat storage liquid 20 on the surface of the heat exchanger tube 610 is cooled by the outside air or the like in the heat exchanger tube 610, and the heat generated when absorbing water vapor is removed and the temperature reaches TbC. The internal pressure of the heat storage liquid heat exchanger 600 at that time is the concentration C of the heat storage liquid 20 after dilution.
At 1%, the temperature Tt decreases to the water vapor pressure Pc in the state of C (point A in FIG. 5). Therefore, the temperature of the water evaporated in the heat exchanger tubes 210 of the water heat exchanger 200 decreases to the saturation temperature Tc of water at the internal pressure Pc (point E in FIG. 5). Through this operation, the concentrated heat storage liquid is diluted by water vapor absorption, so that the temperature T
The cold energy of c is generated and used for air conditioning, etc.

The above heat storage system has many advantages over solid heat storage agents, but the heat storage density and the resulting cold temperature are
It greatly affects the concentration and water vapor pressure characteristics of the heat storage liquid, and in the case of low temperature heat storage, it cannot be concentrated to a high concentration, so there are disadvantages that the heat storage density is small and the cold temperature does not drop.

[Purpose of the invention]

An object of the present invention is to provide a heat storage method that has a high heat storage density and can generate cold heat at a lower temperature.

[Summary of the Invention] The present inventors conducted various studies to achieve the above object, and as a result, they came to the following findings.

Contents (1) to (3) of this knowledge will be explained based on FIG.

(1) Improving heat storage density Considering that heat storage occurs due to the latent heat of vaporization of water vapor and the heat of dilution of the heat storage liquid, the best way to increase the heat storage density is to concentrate the heat storage liquid to a higher concentration. Since the high concentration of the liquid has a large dilution heat and a large water vapor absorption capacity, the heat storage amount (heat storage density) of the heat storage liquid becomes large. Therefore, even if heat at the same temperature is used, the heat storage liquid can be concentrated to a higher concentration.

This means that during heat storage (at a place with high water vapor pressure and temperature), the heat storage liquid with a concentration of 02' has a higher concentration of C than in Figure 3.
It can be concentrated up to s (>Cs).

(2) The basic strategy for generating a temperature Tc' lower than low-temperature cold heat generation is shown in Figure 3. must be large.

(8) High-performance heat storage method (1) Improving heat storage density (2) In order to generate low-temperature cold heat, the water vapor pressure difference between the heat storage liquid with low vapor pressure and the medium with high vapor pressure must be kept small during heat storage, and when cold heat is generated ( It is important to operate the water vapor pressure so that it increases when the water vapor pressure and temperature are low. This means that the water vapor pressure gradient of the medium should be small, and that of the heat storage liquid should be conversely large.

By doing so, even if the same temperature difference (TiTc) is used, a high concentration (TiTc) can be achieved by using a heat storage liquid with a high gradient.
Cs→Cs), improving the heat storage density, and generating cold heat at a lower temperature (Tc→Ta').Furthermore, by using a medium with a low gradient, cold heat at a lower temperature can be obtained.

The present invention has been made based on such knowledge, and is configured to provide a heat storage method for storing heat by moving steam based on a vapor pressure difference between a substance with a low vapor pressure and a substance with a high vapor pressure. The heat storage method is characterized in that the rate of change in vapor pressure of the substance with low vapor pressure in response to a change in temperature is greater than the rate of change in vapor pressure in response to a change in temperature of the substance with high vapor pressure.

In the above configuration of the present invention, as a method for relatively changing the rate of change in vapor pressure according to temperature change between a substance with a low vapor pressure and a substance with a high vapor pressure, the water vapor pressure gradient of the substance with a low vapor pressure is increased. and/or methods for lowering the water vapor pressure gradient of substances with high vapor pressure.

As a method for increasing the water vapor pressure gradient of substances with low vapor pressure, there is a method of using salts such as calcium chloride and lithium chloride, mixtures thereof, and alkaline solutions such as sodium hydroxide.

Conversely, methods for reducing the water vapor pressure gradient of substances with high water vapor pressure include using Freon, n-hexane, or dichloropentane instead of water, or using magnesium chloride or zinc chloride, which have a small water vapor pressure gradient, instead of water. There is a method of using a dilute aqueous solution of as an intermediate heat storage liquid.

[Embodiments of the invention]

Next, one embodiment of the present invention will be explained in detail using FIGS. 1 and 2. Note that the same parts as in the prior art are given the same reference numerals, and the explanation thereof will be omitted.

In the embodiment shown in FIGS. 1 and 2, a low-concentration heat storage liquid (for example, a dilute aqueous solution of magnesium chloride) with a low water vapor pressure gradient is used instead of water as the medium, and a high-concentration heat storage liquid with a large water vapor pressure gradient is used as the heat storage liquid. Concentrated heat storage liquid (aqueous solution of calcium chloride)
is used. Therefore, the straight line between the temperature and water vapor pressure of water as a medium shown in FIG. 5 becomes the straight line between the temperature and water vapor pressure of the intermediate heat storage liquid in FIG.

The heat storage method of this embodiment will be explained below by taking cold heat generation as an example.

In the heat storage operation, as shown in FIG. 1, the dilute heat storage liquid 40 sent by the pump 21 from the heat storage liquid tank 500 is sprayed onto the heat transfer tubes 610 of the heat storage liquid heat exchanger 600 until the temperature TI is reached.
It is heated with K, boiled with water, and concentrated to a concentration of C3.

Then, it is returned to the tank 500 and stored (G
point). The generated water vapor 30 is transferred to an intermediate heat storage liquid heat exchanger 40
0, where the pump 8 is pumped from the intermediate heat storage liquid tank 800.
It comes into contact with the intermediate heat storage liquid 80 sent in step 1 near the heat transfer tube 410 and is absorbed by the intermediate heat storage liquid. At the same time, the intermediate heat storage liquid is diluted and returned to the tank 800.

The absorbed heat (condensation heat and dilution heat) generated at that time is cooled by the outside air, and the temperature is maintained at Tx (point A' in FIG. 2).

The pressure during heat storage is Pi', which is equal to the water vapor pressure at the temperature of the diluted intermediate heat storage liquid (TL), and the heat storage pressure is lower than in the case of Fig. 5 (PHI'< PIE), and the heat storage liquid is heated to a higher temperature. It can be concentrated to a high concentration (C3>C2), increasing the heat storage density.

When cold heat is generated, the concentration C is
The concentrated heat storage liquid 40 of No. 3 is transferred to the heat exchanger tube 610 in the heat exchanger 600.
spray on the surface and cool it with outside air. Then, since the water vapor pressure of the heat storage liquid is low, it absorbs the water vapor inside the vessel and the pressure decreases. On the other hand, when the dilute intermediate heat storage liquid 80 is sent from the tank 800 to the heat exchanger 400 by the pump 81, evaporation occurs due to the low internal pressure, and the intermediate heat storage liquid is condensed, and its temperature decreases due to the latent heat of vaporization. The internal pressure at that time is the temperature Tt of the diluted concentration C,/ of the heat storage liquid 40.

is equal to the water vapor pressure of Pc'(<Pc) (point A in Figure 2). Therefore, the obtained cold temperature becomes the saturation temperature Tc' (point G' in Fig. 2) at the pressure Pa' of the intermediate heat storage liquid, which is significantly lower than the case shown in Fig. 5 (Tc'<Tc). can be achieved.

Although the above embodiments have been explained by taking cold heat generation as an example, a similar system can also be used for hot heat generation. In that case, the operating pressures during heat storage and heat generation are close to each other,
The effect of the difference in water vapor pressure gradient is smaller than in the case of cold generation.

Further, in the embodiments shown in FIGS. 1 and 2, an intermediate heat storage liquid is used instead of water, but the same effect can be obtained by using Freon or the like having a large gradient alone as described above.

Further, although the explanation has been made using a liquid heat storage agent, a solid heat storage agent having the same water pressure characteristics as the present invention can also have similar effects.

〔Effect of the invention〕

As explained above, according to the heat storage method according to the present invention, the heat storage agent can be concentrated to a higher concentration, thereby increasing the heat storage density. Therefore, relatively low-temperature heat can be stored, and the amount of heat storage agent per heat storage amount can be reduced, so that the device can be made more compact.

Furthermore, since the difference in vapor pressure and temperature between substances having different vapor pressures when generating cold heat is large, it has the unique effect of being able to generate cold heat at a lower temperature.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing the system of the heat storage method according to the present invention, FIG. 2 is a water vapor pressure diagram of the heat storage system shown in FIG. 1, and FIG. 3 is a water vapor pressure diagram showing the principle of the present invention. FIG. 4 is a system diagram showing a conventional heat storage system, and FIG. 5 is a water vapor pressure diagram of the heat storage system shown in FIG. 10...Water, 20...Heat storage liquid, 30...Steam,
100...Water tank, 200...Water heat exchanger, 2
10°610... Heat exchanger tube, 500... Heat storage liquid tank, 600... Heat exchanger for heat storage liquid.

Claims (1)

[Claims] 1. In a heat storage method that stores heat by moving vapor based on a vapor pressure difference between a substance with a low vapor pressure and a substance with a high vapor pressure, the rate of change in vapor pressure in response to a temperature change of the substance with a low vapor pressure is A heat storage method characterized by a rate of change in vapor pressure that is greater than the rate of change in vapor pressure in response to temperature changes in substances with high vapor pressure.