JP4655717B2 - Thermal storage method, thermal storage device - Google Patents

Description

  The present invention relates to a heat storage method and a heat storage device. More specifically, the present invention relates to a heat storage method and apparatus that uses latent heat accompanying the phase change of the heat storage agent.

  Conventionally, a heat storage method using a eutectic mixture composed of two components as a heat storage agent and utilizing latent heat associated with a phase change of the heat storage agent is known.

  When the heat storage agent is formed at a composition ratio (eutectic composition) that causes eutectic in this method, the two components that form the heat storage agent gradually lower the temperature from the liquid state, and the temperature finally reaches the eutectic point. The phenomenon that no phase change occurs (crystals do not occur) even when the temperature reaches 1 so-called supercooling may occur, which is a problem from the viewpoint of heat storage efficiency.

  As a method for solving this problem of supercooling, a method of adding a nucleation material into a heat storage agent is known (Patent Document 1). According to this method, when the temperature of the heat storage agent reaches the eutectic point, this nucleation material becomes the nucleus of crystallization, and the heat storage agent changes from the liquid phase to the solid phase, thereby suppressing supercooling. I can do things.

  However, in this method, it is necessary to add a material completely different from the eutectic two-component to the heat storage agent as a nucleation material, so that the process of generating the heat storage agent becomes complicated, and furthermore, this nucleation Due to the fact that the capacity of the heat storage agent itself is reduced by the amount of the added material, there is a problem that the heat storage capacity of the entire heat storage agent is reduced. Furthermore, although supercooling can be suppressed, it is difficult to completely prevent it.

By the way, in recent years, the heat storage agent is formed as a composition in which the composition ratio of the two components forming the heat storage agent is shifted from the composition ratio (eutectic composition) at which the eutectic point is generated (for example, patent document). 2) Even when a heat storage agent having a composition deviating from the eutectic composition is used, the problem of supercooling can occur.
JP-A-56-84784 Japanese Patent Application Laid-Open No. 11-257885

  The present invention has been made in view of such a situation, and in storing heat using latent heat accompanying the phase change of the heat storage agent, a phase change from a liquid phase to a solid phase occurs even at a temperature below the freezing point. The main object is to provide a heat storage method and apparatus that do not cause a so-called supercooling phenomenon, and thus are more efficient than conventional ones.

In order to solve the above problems, the present invention provides a heat storage agent by forming a eutectic mixture composed of a plurality of components into a composition shifted from the eutectic composition in which the eutectic is generated , and the heat storage agent is used as a heat medium. Heat exchange is performed, and a state value or a physical property value that changes according to the phase state of the heat storage agent is measured, and based on the measured state value or physical property value, the solid phase is crystallized in advance among the components constituting the heat storage agent. The solid phase fraction of one component to be discharged is calculated, the flow rate of the heating medium is controlled, and the solid phase is always left without changing all of the one component to the liquid phase. The present invention relates to a heat storage method, wherein the one component is continuously melted and solidified while performing solid phase fraction control so that the one component functions as a nucleus when solidifying .

Moreover, this invention is accommodated in the thermal storage tank in which the thermal storage agent in which the eutectic mixture which consists of a several component was formed in the composition shifted from the eutectic composition in which a eutectic produces was accommodated, and the said thermal storage tank Measured by the heat exchanging means for exchanging heat between the heat accumulating agent and the heat medium, the measuring means for measuring the state value or the physical property value changing according to the phase state of the heat accumulating agent accommodated in the heat accumulating tank, and the measuring means Based on the obtained state value or physical property value, the solid phase ratio of one component that crystallizes the solid phase in advance among the components constituting the heat storage agent is calculated, and the solid phase ratio does not become 0 (zero) Solid phase fraction control means for controlling the solid phase fraction so that the solid phase always remains and the remaining solid phase functions as a nucleus when the one component coagulates , Heat whose solid fraction fraction control means adjusts the flow rate of the heat medium About the heat storage apparatus characterized by having a body flow rate adjusting means.

  Further, in the heat storage device, the state value or physical property value measured by the measuring means may be any of temperature, liquid phase conductivity, mixed phase conductivity, viscosity, pH, and sound velocity.

  According to the method of the present invention, first of all, since the composition of the heat storage agent is shifted from the eutectic composition in which the eutectic is generated (that is, the eutectic point is not used), the solid phase Can be controlled by the composition of the heat storage agent.

  Second, since the composition is shifted from the eutectic composition, the temperature falls between the eutectic temperature and the solidification start temperature (liquidus) of the component that crystallizes the solid phase in advance. Accordingly, the temperature also decreases while the component crystallizes (solidifies). As a result, the apparent specific heat becomes "liquid phase specific heat x liquid phase ratio + solid phase specific heat x solid phase ratio + solidification latent heat of components to be crystallized in advance x phase change amount" and below the liquidus line Compared to simple sensible heat utilization, the heat storage capacity can be increased.

  Furthermore, according to the method of the present invention, thirdly, the solid phase fraction is always maintained so that the solid phase always remains without making all of one of the components that crystallize the solid phase in advance as a liquid phase. Since one of the components is continuously melted and solidified while controlling, the solid phase (that is, the solid) that always remains functions as a nucleus when the component solidifies, and thus the solidification start temperature ( A phenomenon in which a solid phase does not occur even when reaching the liquidus), that is, supercooling can be completely prevented. In other words, the method of the present invention does not require the use of a nucleation material as in the invention disclosed in Patent Document 1, and uses a conventional heat storage agent as it is to control the solid phase fraction. Therefore, it is possible to prevent overcooling, which is a conventional problem.

  The same effect as the method of the present invention can be obtained by the apparatus of the present invention.

  Hereinafter, a heat storage method and a heat storage device of the present invention will be described in detail with reference to the drawings.

(1) Heat storage method FIG. 1 is a state diagram of a heat storage agent used in the heat storage method of the present invention. In addition, the horizontal axis | shaft of this figure shows the mole fraction of the component b, and a vertical axis | shaft shows temperature.

  The two components a and b constituting the heat storage agent used in the present invention are dissolved in a liquid phase state and separated into two solid phases which are not mixed in a solid phase state, and mixed crystallization is performed. When the eutectic composition is used, the eutectic point at which the melting point becomes the minimum value causes a eutectic reaction in which the entire solution simultaneously changes to the solid phase as if it were a pure liquid, and the entire solution changes to the solid phase. Until the temperature is kept constant.

That is, in the state diagram shown in FIG. 1, the liquidus line A in the figure shows the crystallization temperature (freezing point) of component a, and the liquidus line B in the figure shows the crystallization temperature of component b ( Freezing point). Moreover, the area | region of the code | symbol I in a figure is an area | region of a liquid phase state of the components a and b, and the code | symbol II is an area | region of the mixed state of the liquid phase (component a + component b) and the solid phase of the component a. Symbol III is a region in the mixed state of the liquid phase (component a + component b) and the solid phase of component b, and the region of symbol IV indicates a region in the solid phase state for both components a and b. The symbol X in the figure the eutectic point, X ₀ represents the eutectic composition.

The method of the present invention, for example Upon using the heat storage agent that shows a state diagram as shown in FIG. 1, characterized in that the composition shifted from the eutectic composition occurs eutectic point X (e.g., the composition of X ₁₎ Have.

Therefore, in the heat storage agent having a X ₁ composition deviated from eutectic composition X _0, as described above, from the temperature T ₁ of the Figure 1 lowering the temperature gradually until the temperatures T ₁ to T ₂ are a liquid phase (region I), component when the temperature reaches T ₂ b is started to crystallize and remain in the liquid phase for component a (region II). When the temperature is further lowered and the temperature reaches T ₃ , not only component b but also component a starts to crystallize, and the temperature is maintained at T ₃ until all of component a and component b are completely crystallized. When the component a and the component b are all in a solid phase and then further cooled, the temperature decreases in the solid state. In the temperature _{T 4} a, b are both a solid phase.

FIG. 2 shows an enthalpy curve of the amount of heat when the temperature is lowered from a temperature T ₁ at which the two components a and b constituting the heat storage agent together form a liquid phase to a temperature T ₄ at which the two components a and b both form a solid phase. FIG.

In the present invention, the amount of heat less than the temperature T ₂ in this enthalpy curve is used. For example, when the use temperature range is T ₃ or more and less than T ₂ , the amount of heat between T ₃ ′ and T ₂ and the use temperature. When the range is T ₄ or more and less than T _2, the amount of heat between T _{4 and} T ₂ is the heat capacity capable of storing the heat storage agent.

Here, in the method of the present invention, as described above, not only the heat storage agent having a composition shifted from the eutectic composition in which the eutectic is generated, but also one of the crystallization of the solid phase in advance. components, i.e. without all components b, the liquid phase in the case of the heat storage agent composition X ₁ shown in FIG. 1, always solid phase while the solid phase fraction controller so that the state remains, Specifically, characterized in that in the case where the heat storage agent and measuring target composition X ₁ shown in FIG. 1 is a temperature, which while controlling the temperature below T _2, is continuously melting and solidifying the component b It is said.

By controlling the temperature below T ₂ (that is, not raising the temperature to T ₂ ), the solid phase of component b can always remain in the heat storage agent, and as a result, supercooling can be prevented. It is. Here, the temperature T ₂ is lower than T ₂ (not including T ₂ ) because the temperature T ₂ is the liquidus temperature (melting point of the component b) in the composition X ₁ , and the solid phase is reached when the temperature T ₂ is reached. This is because all the nuclei for crystallization of the component b disappear when cooling, and supercooling occurs.

  Here, in order to carry out the method of the present invention, it is necessary to know the solid fraction of the heat storage agent in almost real time, but this method is not particularly limited, and the temperature of the heat storage agent shown above is not limited. Other properties that change according to the solid phase fraction of the heat storage agent, such as the conductivity of the liquid phase of the heat storage agent, the conductivity of the mixed phase of the heat storage agent (mixture of liquid phase and solid phase), the viscosity of the heat storage agent, The solid phase fraction of the heat storage agent may be known from pH, the speed of sound transmitted through the heat storage agent (sound speed), and the like.

  In the method of the present invention, the means for controlling the solid phase fraction of the heat storage agent within a predetermined range as described above is not particularly limited. For example, the heat storage method is used for exhaust gas, hot drainage, etc. When the heat is recovered from the heat medium of about 100 to 200 ° C., by controlling the flow rate of the heat medium and the heat storage agent itself, the solid phase fraction of the heat storage agent is controlled as a result. (Details are described in the apparatus of the present invention below).

Further, the component constituting the heat storage agent used in the method of the present invention is not particularly limited. For example, component a is magnesium chloride hexahydrate (MgCl ₂ · 6H ₂ O) and component b is A combination of magnesium nitrate hexahydrate (Mg (NO ₃ ) ₂ .6H ₂ O) (eutectic point 59.1 ° C.), component a as ammonium chloride (AlCl 3), component b as sodium chloride (NaCl) (Eutectic point 93 ° C.), component a as bismuth (Bi) and component b as lead (Pb) (eutectic point 125 ° C.), and the like. It can be suitably used when recovering warm heat from a heat medium of about 100 to 200 ° C. such as exhaust gas and warm waste water.

And, as described above, the method of the present invention can completely prevent the occurrence of supercooling by controlling the solid phase fraction so that not all of the components constituting the heat storage agent become a liquid phase. When selecting the components constituting the heat storage agent, it is not necessary to consider “easiness of supercooling”, and therefore the components can be selected only by considering “heat storage capacity”. That is, the degree of freedom in designing the heat storage agent can be improved. Specifically, for example, as components a magnesium chloride hexahydrate _(MgCl 2 · _6H 2 O) and a component b of magnesium nitrate hexahydrate _{(Mg (NO 3) 2 ·} 6H 2 O) Although the heat storage agent has a large heat storage capacity but is also supercooled, it is difficult to use it as a heat storage agent. However, in the method of the present invention, it can be used without any problems.

(2) Heat storage device Next, the device of the present invention will be described.

  FIG. 3 is a schematic diagram showing the configuration of the apparatus of the present invention.

  As shown in FIG. 3, the device 30 of the present application includes a heat storage tank 31 in which a heat storage agent formed by shifting a eutectic mixture composed of a plurality of components from a eutectic composition in which a eutectic is generated is contained. The heat exchange means 32 for exchanging heat with the heat storage agent accommodated in the heat storage tank 31 and the state value or physical property value that changes according to the phase state of the heat storage agent accommodated in the heat storage tank are measured. Of the solid phase of one component that crystallizes the solid phase in advance among the components constituting the heat storage agent based on the state value or the physical property value measured by the measurement unit 33 The control means 34 (the personal computer (PC) 34a for calculating the ratio of the solid phase and the flow rate of the heat medium) for controlling the solid phase fraction of the heat storage agent so that the ratio does not become 0 (zero). Heat medium flow rate adjusting means 34b to adjust; A heat storage agent flow controller 34c) for adjusting the flow rate of the heat storage agent, and an.

  The heat storage tank 31 is provided with a heat storage agent pipe 35 for circulating the heat storage agent accommodated between the heat storage tank 31 and the heat exchange means 32. Is provided with a heat storage agent pump 36 for circulating the heat storage agent. On the other hand, the heat exchange means 32 is also provided with a heat medium pipe 37 through which a substance (heat medium) that exchanges heat with the heat storage agent is circulated. The heat medium circulation means (not shown) generates heat. The medium is circulated. In addition, in FIG. 3, since the flow of a thermal storage agent and a heat medium is shown by the arrow, please refer.

  According to the apparatus, when the heat storage agent in the heat storage agent tank 31 stores heat, the temperature of the heat medium flowing through the heat medium pipe 37 is set to be higher than the melting point of the heat storage agent (specifically, For example, when the heat medium uses a heat medium of about 100 to 200 ° C. such as exhaust gas or warm waste water, the heat storage means 32 exchanges heat with the heat storage agent 32 (the temperature of the heat medium decreases). The temperature of the heat storage agent rises), and heat is stored in the heat storage agent in the heat storage tank 31. In this case, the ratio of the solid phase of the heat storage agent in the heat storage tank 31 gradually decreases and the ratio of the liquid phase increases as the temperature increases.

  Here, in the apparatus 30 of the present invention, since the measuring means 33 is provided on the heat storage agent pipe 35 through which the heat storage agent flows, the state value or physical property value (for example, the heat storage agent) of the heat storage agent is measured by the measurement means 33. And the like, and the ratio of the solid phase of the heat storage agent can be calculated from the measured value by the PC 34a of the control means 34 connected to the measurement means 33. Since the apparatus of the present invention can monitor the ratio of the solid phase of the heat storage agent in this way, when the ratio of the solid phase is likely to be 0 (zero), it is connected to the PC 34a and is used as the control means 34. The flow rate of the heat medium and the flow rate of the heat storage agent can be controlled using the heat medium flow rate adjustment unit 34b and the heat storage agent flow rate adjustment unit 34c. And by such control, it can prevent that all of a thermal storage agent turns into a liquid phase, and can prevent supercooling by this.

  In the device 30, when heat is radiated from the heat storage agent, a heat medium having a temperature lower than the temperature of the heat storage agent may be circulated in the heat medium pipe 37.

  The heat storage tank 31 in the device 30 of the present invention is not particularly limited as long as it functions as a container for storing a heat storage agent. Inside the heat storage tank 31, stirring / mixing means 31a for keeping the state of the heat storage agent uniform may be installed.

  The heat exchange means 32 is not particularly limited as long as heat exchange can be performed between the heat storage agent in the heat storage tank 31 and the heat medium, and a conventionally known heat exchange device may be appropriately selected. It only has to be. In FIG. 3, heat storage and heat dissipation to the heat storage agent are performed by the same heat exchanging means 32, but two heat exchanging means are provided, and heat storage and heat dissipation are respectively different heat exchanging means. You may make it carry out by.

  The measuring means 33 in the device 30 of the present invention is a means for measuring a state value or a physical property value that changes in accordance with the phase state of the heat storage agent accommodated in the heat storage tank, and the actual measured state value or physical property. It can be appropriately selected and used according to the value.

  Regarding the physical properties measured by the means, not only the temperature that is the state value of the heat storage agent, but also the electrical conductivity of the liquid phase, which is the physical property value of the heat storage agent, and the conductivity of the mixed phase (liquid phase and solid phase) of the heat storage agent. , Viscosity and pH of the heat storage agent, speed of sound transmitted through the heat storage agent (sound speed), and the like. In other words, any physical property value can be used as long as it changes depending on the solid phase fraction of the heat storage agent. In particular, in the present invention, the composition of the heat storage agent is shifted from the composition causing the eutectic, so that the liquid phase and the solid phase coexist in the regions II and III of FIG. Since the composition of the liquid phase portion changes according to the change in the solid phase fraction, the physical property value that changes depending on the composition of the liquid phase can also be set as the measurement target.

  Specific examples of the measuring means 33 include various thermometers and thermocouples when the physical property to be measured is temperature, and the electrical conductivity when the physical property to be measured is a liquid phase or mixed phase conductivity. When the physical property to be measured is viscosity, a device that measures the power of the stirrer, a pH meter if the physical property to be measured is pH, and a sonic meter if the physical property to be measured is sound velocity, Can be mentioned.

  Further, the position of installing the measuring means 33 is not particularly limited as long as the apparatus of the present invention is used, but a place that is not easily affected by the heat exchanging means is desirable. For example, as shown in FIG. It is good to install on the piping 35 from 31 to the heat exchange means 32.

  The control means 34 in the apparatus 30 of the present invention calculates the ratio of the solid phase of the heat storage agent in the heat storage tank 31 based on the physical property value measured by the measurement means 33 so that this ratio does not become 0 (zero). There is no particular limitation as long as it is a means that can be controlled.

  For example, as shown in FIG. 3, a PC is used as a means for calculating the solid phase ratio of the heat storage agent, and a heat medium flow adjusting means 34b for adjusting the flow rate of the heat medium is used as means for controlling the ratio, and the heat storage agent. When the heat storage agent flow rate adjusting means 34c for adjusting the flow rate of the gas is used, in the PC, the measured value (Z) of the measuring means is converted into the solid phase ratio (Y), and the solid phase ratio Y is calculated based on this numerical value. The heat medium flow rate adjusting means 34b for adjusting the flow rate of the heat medium so as not to become 0 (zero) and the heat storage agent flow rate adjusting means 34c for adjusting the flow rate of the heat storage agent are controlled.

Here, the conversion from the signal from the measuring means 33 to the solid phase ratio follows the conversion determined based on the heat storage agent composition. For example, in the heat storage agent in which two substances having a eutectic state diagram as shown in FIG. 4 are mixed, a case where the target to be measured by the measuring means is a temperature will be described as an example. By inputting the state diagram into the PC 34a of the control means in advance, the lengths of the heat storage agent composition X ₁ and the line segments α and β in FIG. 4 when the measured temperature is T (= Z). The solid phase ratio Y is Y = α / (α + β).

Further, the conversion from pre-heat storage agent composition X ₁ to previously obtain the target object property values in liquidus (that solid phase come crystallized) a (Zcr), the signal from the measuring means 33 to the solid phase ratio Y It is also possible to directly control using the control means 34 so that the measured value does not become (Zcr). For example, it may be controlled so that the temperature is less than the Tcr (= Zcr) under the conditions of the heat storage agent composition _{X 1} in FIG. 4.

  As the heat medium flow rate adjusting unit 34b and the heat storage agent flow rate adjusting unit 34c, for example, a flow rate adjusting valve or the like may be used.

  The configuration shown in FIG. 3 is a configuration that can be used when the heat storage agent always exhibits fluidity.

  FIG. 5 is a schematic view showing the configuration of another example of the apparatus of the present invention. When a state in which the heat storage agent does not exhibit fluidity occurs, as shown in FIG. 5, in the device 50 of the present invention, the heat storage tank 51 and the heat exchanging means 52 are the same device, and only the heat medium is used. It may be circulated. Further, the agitation / mixing means 51a may be installed in the heat storage tank 51 and operated only when the heat storage agent in the heat storage tank 51 shows a flow. The other means in the apparatus 50 (the measuring means 53, the personal computer 54a as the control means 54, the heat medium flow rate adjusting means 54b, and the heat medium pipe 57) are the same as those in the apparatus 30 of the present invention shown in FIG. Therefore, the description here is omitted.

It is a state figure of the thermal storage agent used for the thermal storage method of this invention. Temperatures T ₁ bicomponent a the secondary components a and b constituting the heat storage agent forms together liquid phase shown in FIG. 1, the enthalpy curve of heat when b is allowed to temperature drop to a temperature T ₄ which forms together solid phase FIG. It is the schematic which shows the structure of the apparatus of this invention. It is a figure explaining the control in the apparatus of this invention. It is the schematic which shows the structure of another example of the apparatus of this invention.

Explanation of symbols

30, 50 ... Thermal storage device 31, 51 ... Thermal storage tank 32, 52 ... Heat exchange means 33, 53 ... Measuring means 34, 54 ... Control means 34a, 54a ... Personal computer (PC)
34b, 54b ... Heat medium flow rate adjusting means 34c ... Heat storage agent flow rate adjusting means 35 ... Heat storage agent piping 36 ... Heat storage agent pumps 37, 57 ... Heat medium piping

Claims (4)

A eutectic mixture composed of a plurality of components is formed into a composition deviated from the eutectic composition in which the eutectic is generated to form a heat storage agent, the heat storage agent is heat exchanged with a heat medium, and the phase state of the heat storage agent Measures the changing state value or physical property value, and calculates the solid fraction of one component that crystallizes the solid phase ahead of the components constituting the heat storage agent based on the measured state value or physical property value and, by controlling the flow rate of the heat medium, without all of the one component and the liquid phase, always functions as a nucleus when the solid phase one component is solidified to the remaining is left a solid phase while the solid phase fraction controller as make, thermal storage method which comprises causing a continuous melting and solidifying said one component. The heat storage agent is any one of a mixture of magnesium chloride hexahydrate and magnesium nitrate hexahydrate, a mixture of ammonium chloride and sodium chloride, and a mixture of bismuth and lead. The described heat storage method. A heat storage tank containing a heat storage agent formed in a composition shifted from the eutectic composition in which the eutectic mixture of the plurality of components is formed;
Heat exchange means for causing heat exchange between the heat storage agent and the heat medium stored in the heat storage tank,
Measuring means for measuring a state value or a physical property value that changes according to the phase state of the heat storage agent accommodated in the heat storage tank;
Based on the state value or property value measured by the measuring means, wherein to calculate the solid fraction of one component to crystallize prior to the solid phase of the components constituting the heat storage agent, the solid phase ratio is 0 A solid phase fraction control means for controlling the solid fraction so that the solid phase always remains so that it does not become (zero), and the remaining solid phase functions as a nucleus when the one component coagulates ;
Consisting of
The heat storage device, wherein the solid phase fraction control means has a heat medium flow rate adjusting means for adjusting the flow rate of the heat medium . The heat storage device according to claim 3, wherein the state value or physical property value measured by the measuring means is any one of temperature, liquid phase conductivity, mixed phase conductivity, viscosity, pH, and sound velocity.

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