JP2018058920A - Chemical thermal storage medium for chemical heat pump, and production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a chemical thermal storage medium for a chemical heat pump, stable for a long period, having high reactivity, capable of preventing deterioration of the chemical thermal storage medium even when being used at a high temperature; and to provide a production method.SOLUTION: In a chemical thermal storage medium for a chemical heat pump, mainly composed of calcium oxide, and containing calcium oxide and a sintering auxiliary of metal oxide, the content of calcium oxide is 92-97 wt%, the mass ratio between calcium oxide and the sintering auxiliary of metal oxide is 15-35, a specific surface area is 8-13 m/g, and a breaking load is 90 N or more.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a chemical heat storage material for a chemical heat pump and a manufacturing method.

  Until now, various heat storage technologies have been developed to recover exhaust heat generated from various industrial processes. In a method using sensible heat (specific heat) of a substance, a temperature difference from the cooling or heating of the substance to the accumulation of heat to return to normal temperature is used as energy. This method is low in cost because it directly heats concrete or the like without using a heat storage material, but has the disadvantage that the volumetric efficiency is low and the temperature level is not constant.

  Moreover, in the method using the latent heat of a substance, the energy until the substance is frozen (solidified) to store heat and melted to become a liquid, or vice versa, is used. In this method, the amount of heat storage is large, and heat energy at a constant temperature can be obtained. However, since a special heat storage material is used, it is more expensive than sensible heat.

  On the other hand, in recent years, a chemical heat pump (CHP) using a chemical change of a substance has been proposed. Unlike a mechanical heat pump, a chemical heat pump reversibly stores heat and outputs heat with a specific chemical material. In addition, the system recovers exhaust heat generated from various industrial processes without requiring input of electric energy or the like.

  The characteristics of the chemical heat pump are that it has a high heat storage density, a small heat loss during heat storage, a heat storage at room temperature, and a higher heat dissipation temperature than the heat storage temperature. On the other hand, it is necessary to pay attention to the fact that there are many reactions at high temperatures, and the heat resistance and heat insulation of the container are required, the safety of the reaction material is ensured, the deterioration over time, the reaction and the stability of repetition are ensured.

  Patent Document 1 is an invention of a heat storage structure that improves a heat storage heat dissipation rate and repeated durability by disposing a chemical heat storage material in a partition wall of a honeycomb structure made of a material having good thermal conductivity. Further, Patent Document 2 discloses a chemical heat storage material molded body in which a chemical heat storage material particle is supported on a porous body formed by heating a resin so that the reactivity is hardly lowered even when used repeatedly, and a method for manufacturing the same. It is invention of this. Patent Document 3 is an invention of a chemical heat storage material mainly composed of quicklime having a large number of pores and a method for producing the same, and is an invention in which a chemical heat storage material can be repeatedly used.

  However, Patent Document 1 does not pay attention to the configuration of the chemical heat storage material itself used for the chemical heat pump. Moreover, although patent document 2 considers about the average particle diameter of the chemical thermal storage material used for a chemical heat pump, it is not paying attention to the structure other than that. Patent Document 3 found that quick lime has a large number of pores, and the durability is repeatedly increased, but does not pay attention to other configurations.

JP2013-124823A Japanese Patent No. 5586262 Japanese Patent No. 2539480

  Conditions required for chemical heat storage materials used in chemical heat pumps include higher performance of heat storage materials, improved safety, and cost reduction. Specific contents of high performance include improved reactivity, high heat storage density, long life (repeated durability), and expanded application conditions.

  The present invention has been made in view of such circumstances, has high reactivity, can prevent deterioration of the chemical heat storage material even when used at high temperatures, and stable chemical heat storage material for chemical heat pumps for a long period of time, and An object is to provide a manufacturing method.

(1) In order to achieve the above object, the chemical heat storage material for chemical heat pump of the present invention is a chemical heat storage material for chemical heat pump whose main component is calcium oxide, and is a sintering aid for calcium oxide and metal oxide. The content ratio of the calcium oxide is 92 to 97 wt%, the mass ratio of the calcium oxide to the sintering aid for the metal oxide is 15 to 35, the specific surface area is 8 to 13 m ² / g, and the breaking load is It is characterized by 90N or more.

  Thereby, since the content rate of the calcium oxide which is a main component is 92-97 wt%, since there is enough density of the material which produces a thermal storage reaction, it has sufficient thermal storage density. In addition, since the mass ratio with the sintering aid is 15 to 35, the melting point of calcium oxide is lowered and the bonding of the particles proceeds and the breaking load increases, but the bonding of the particles does not proceed too much and the specific surface area decreases. Hateful. Therefore, it is excellent in durability against repeated strain due to expansion / contraction, and can be highly reactive as a chemical heat storage material.

  (2) Moreover, the chemical heat storage material for a chemical heat pump of the present invention is characterized in that the sintering aid is MgO. Thereby, it is excellent in the durability with respect to the repeated distortion by expansion / contraction at the time of high temperature use, and can make reactivity high as a chemical heat storage material. Since MgO is readily available, it can be manufactured at low cost.

(3) Further, the chemical heat storage material for chemical heat pump of the present invention is characterized in that pores serving as communication holes are formed, and the average diameter of the pores is 40 to 60 μm. Thereby, since the communication hole is formed, a porous body having fine pores is formed, a flow path of H ₂ O (water or water vapor) and other substances is secured, and the reaction to the inside of the chemical heat storage material is performed. The reactivity can be increased. Moreover, it has sufficient breaking strength.

  (4) Further, the chemical heat storage material for chemical heat pump of the present invention is characterized in that pores serving as communication holes are formed, and the porosity of the pores is 25 to 45%. Thereby, it has sufficient fracture strength and reactivity.

  (5) Moreover, the manufacturing method of the chemical heat storage material for chemical heat pumps of this invention is a manufacturing method of the chemical heat storage material for chemical heat pumps whose main component is calcium oxide, Comprising: Ca content rate is 92-97 wt in oxide conversion %, And a step of preparing calcium carbonate containing a sintering aid for metal oxide and having a mass ratio of Ca content in terms of oxide and content of the sintering aid of 15 to 35, and A step of heating the prepared calcium carbonate at a heating rate of 1 to 15 ° C./min, a step of heat-treating the heated calcium carbonate at a temperature of 700 to 1000 ° C. for 0 to 5 hours, and It is characterized by including. Through such a process, a chemical heat storage material for a chemical heat pump having a configuration in which fine pores are maintained can be easily manufactured by controlling the bonding of particles to an appropriate range while suppressing crystal grain growth. . As a result, the obtained chemical heat storage material for chemical heat pumps has sufficient durability against repeated strain due to expansion / contraction during high temperature use while maintaining sufficient reactivity.

  According to the present invention, as a chemical heat storage material, it is excellent in durability against repeated strain due to expansion / contraction during high temperature use, and can be highly reactive.

It is a table | surface which shows the composition of each sample. (A) is a table | surface which shows the relationship between the holding time of the heat processing in the temperature of 900 degreeC of each sample, and a fracture load. (B) is the graph. (A) is a table | surface which shows the relationship between the holding time of the heat processing at the temperature of 900 degreeC of each sample, and a specific surface area. (B) is the graph. (A) is a table combining FIG. 2 (a) and FIG. 3 (a). (B) is a graph showing the relationship between the specific surface area of each sample at a temperature of 900 ° C. and the breaking load. (A) is a table | surface which shows the relationship between the temperature in the retention time of 3 hours of each sample, and a destruction load. (B) is the graph. (A) to (c) are all 10,000 times SEM photographs of Sample 1. (A) to (c) are all 10,000 times SEM photographs of Sample 2. (A) to (c) are all SEM photographs of 10000 times that of Sample 3. (A) to (c) are all SEM photographs of 10000 times that of Sample 4. (A) to (c) are all 10,000 times SEM photographs of Sample 5. It is a table | surface which shows the composition and characteristic of each sample.

  Next, embodiments of the present invention will be described with reference to the drawings.

[Configuration of chemical heat storage material for chemical heat pump]
The chemical heat storage material for a chemical heat pump of the present invention is composed of a sintering aid of CaO and a metal oxide and other impurities. The main component is calcium oxide, and the content of calcium oxide is 92 to 97 wt%. The sintering aid is included in an amount such that the mass ratio of calcium oxide and sintering aid is 15 to 35. In the present embodiment, the sintering aid is MgO, which has an effect of improving the bonding force between CaO crystal particles during heat treatment. When the content ratio of calcium oxide and the mass ratio of calcium oxide and sintering aid are in such a range, CaO crystal particles are appropriately bonded to achieve high strength.

Moreover, the chemical heat storage material for chemical heat pump is preferably formed with pores serving as communication holes, and the average diameter of the pores is 40 to 60 μm. A chemical heat storage material for a chemical heat pump needs to secure a flow path for H ₂ O (water or water vapor) or other substances when performing an exothermic reaction or an endothermic reaction. Since the chemical heat storage material for chemical heat pump of the present invention has pores as communication holes, a porous body having fine pores is formed, and a flow path for H ₂ O (water or water vapor) or other substances is formed. Secured.

  Therefore, it can be made to react to the inside of a chemical heat storage material, and reactivity can be made high. Further, if the average diameter of the pores is larger than 60 μm, the fracture strength is lowered, and if it is smaller than 40 μm, the reactivity is lowered. The chemical heat storage material for chemical heat pump of the present invention has sufficient fracture strength and reactivity since the average diameter of the pores is 40 to 60 μm.

  Moreover, the chemical heat storage material for a chemical heat pump is preferably formed with pores serving as communication holes and a porosity of 25 to 45%. If the porosity is larger than 40%, the fracture strength is lowered, and if it is less than 25%, the reactivity is lowered. The chemical heat storage material for chemical heat pump of the present invention has a sufficient fracture strength and reactivity since the porosity of the pores is 25 to 45%.

Moreover, the chemical heat storage material for chemical heat pumps of the present invention has a specific surface area of 8 to 13 m ² / g. In chemical heat storage materials for chemical heat pumps, since the entry and exit of substances and heat occurs on the surface of the material, both the exothermic reaction and the endothermic reaction progress faster as the surface area increases. Since the chemical heat storage material for chemical heat pump of the present invention has such a high specific surface area, it has high reactivity as a chemical heat storage material.

Moreover, the chemical heat storage material for chemical heat pumps of the present invention has a breaking load of 90 N or more. A chemical heat storage material for chemical heat pumps combines with H ₂ O and expands when undergoing an exothermic reaction. When endothermic reaction occurs, it decomposes and H ₂ O is released and contracts. Moreover, since the chemical heat storage material for chemical heat pumps is used at a high temperature, it is expanded by the heat. When the breaking load is small, the chemical heat storage material is destroyed by the repetition of expansion / contraction as described above, and the heat storage function is lowered. Since the chemical heat storage material for a chemical heat pump of the present invention has such a high strength, the chemical heat storage material is excellent in durability against repeated strain due to expansion / contraction during high temperature use, and can prevent deterioration of the chemical heat storage material.

  In this way, chemical heat storage materials for chemical heat pumps that have high reactivity as chemical heat storage materials while being excellent in durability against repeated strain due to expansion / contraction during high temperature use efficiently recover waste heat from factories and automobiles. It is preferably used to Since it has high reactivity, exhaust heat generated from various industrial processes can be efficiently recovered, and since it has excellent durability, it can be used for a long time.

[Method for producing chemical heat storage material for chemical heat pump]
Next, the manufacturing method of the chemical heat storage material for chemical heat pumps comprised as mentioned above is demonstrated. First, the Ca content in terms of oxide is 92 to 97 wt%, and includes a sintering aid for metal oxide, and the mass ratio of the Ca content in terms of oxide and the content of the sintering aid is 15 Prepare calcium carbonate which is ~ 35. The sintering aid may be added to calcium carbonate so as to have such a ratio, or a mineral such as limestone having such a ratio may be used. The average particle diameter of the calcium carbonate used as a material is appropriately selected depending on the size of the reactor. The particle size distribution is preferably sharp from the viewpoint of securing a flow path for H ₂ O (water or water vapor) or other substances.

  Then, the prepared calcium carbonate is heated at a heating rate of 1 to 15 ° C./min. Next, it heat-processes by hold | maintaining the temperature of the heated calcium carbonate at 700 to 1000 degreeC for a fixed time. By increasing the temperature at such a temperature increase rate and performing a heat treatment at an optimum temperature, it is possible to produce calcium oxide having a large specific surface area while suppressing crystal grain growth. That is, a chemical heat storage material for a chemical heat pump having high reactivity can be manufactured.

  The holding time of the heat treatment step is 0 hour to 5 hours. By setting the holding time in such a range, the bonding of crystal grains can be controlled in an appropriate range. Since the bonding of the crystal particles does not proceed excessively, the porous body has a configuration in which fine pores are maintained, and the specific surface area can be maintained. Moreover, it can be set as sufficient destruction load because the coupling | bonding of a crystal grain advances to some extent. That is, a chemical heat storage material for chemical heat pumps that has high reactivity as a chemical heat storage material and has sufficient durability against repeated strain due to expansion / contraction during high temperature use can be easily produced. Note that the heat treatment holding time is 0 hour means that the temperature lowering control is started immediately after reaching the target temperature.

[Example]
Based on said manufacturing method, the chemical heat storage material for chemical heat pumps was produced using the calcium carbonate (limestone) which has a composition of the table | surface of FIG. The specific surface area, fracture load, average pore diameter, and porosity of the obtained chemical heat storage material were measured. For measurement of the specific surface area, a fluid type specific surface area automatic measuring device (Flowsorb 2305) manufactured by Shimadzu Corporation was used. For the measurement of the breaking load, particles after decarboxylation were selected within a range of 7 to 10 mm, and the load when the particles were broken was used with a push-pull gauge manufactured by Aiko Engineering. The average diameter and porosity of the pores were measured by a mercury intrusion method (JIS R1655, JIS R1634). Here, the average diameter means the median pore diameter based on the specific surface area.

In addition, the reactivity and durability of chemical heat storage materials for chemical heat pumps were measured. The reactivity was measured using a thermogravimetric analyzer, the material was classified at 710 to 1000 μm, the material was heated at a rate of 100 to 500 ° C. at 5 ° C./min, and the weight change due to the reaction was measured. From the reaction formula, CaO + H ₂ O Ｃａ Ca (OH) ₂ , the theoretical value of the weight change with respect to the input amount of CaO was calculated, and the value obtained by dividing the measured weight change by the theoretical value was defined as the reaction rate. The reactivity was evaluated based on the fact that this reaction rate was 80% or more. Durability was judged on the basis that the reactivity test was carried out five times in succession and the reactivity was not lowered as compared with the first. The results are shown at the right end of the table of FIG. Sample 1 had a reaction rate of 85%, and no decrease in the reaction rate was observed in five consecutive tests. However, although the reaction rate of sample 5 was as good as 95%, a decrease in the reaction rate was observed in five consecutive tests.

  FIG. 2A is a table showing the relationship between the heat treatment holding time and the breaking load at a temperature of 900 ° C. for each sample. (B) is the graph. According to this, it can be seen that the fracture load tends to increase as the heat treatment time increases. This is thought to be because the necking of the crystal particles proceeds as the heat treatment time increases.

  FIG. 3A is a table showing the relationship between the heat treatment holding time and the specific surface area of each sample at a temperature of 900 ° C. (B) is the graph. This shows that the specific surface area decreases as the heat treatment time increases. Similarly to the above, it is considered that the necking of the crystal particles proceeds as the heat treatment time becomes longer.

  FIG. 4A is a table combining these. FIG. 4B is a graph showing the relationship between the specific surface area of each sample at a temperature of 900 ° C. and the breaking load. According to this, it can be seen that the fracture load decreases as the specific surface area increases. When combined with the above results, the specific surface area and the breaking load are in a trade-off relationship, and a long heat treatment time is advantageous in terms of breaking load but disadvantageous in terms of specific surface area.

  FIG. 5A is a table showing the relationship between the temperature and the breaking load at a holding time of 3 hours for each sample. (B) is the graph. According to this, it can be seen that the fracture load decreases as the heat treatment temperature increases. This is considered to be because when the heat treatment temperature is increased, the grain growth of the crystal grains is promoted, and the necking of the crystal grains is difficult to proceed.

  From the above results, it is important to consider the properties of the necessary heat storage material and determine the heat treatment time and heat treatment temperature at which the necessary properties are obtained. Also, the composition of the starting material is very important since the results vary greatly depending on the composition of the starting material.

  Next, an SEM photograph of the obtained chemical heat storage material was taken using a scanning electron microscope (SEM) (JSM-7001F) manufactured by JEOL.

  6 to 10 are 10,000 times SEM photographs of each sample. FIGS. 6A to 10A are SEM photographs when the heat treatment is held at 900 ° C. for 3 hours. Similarly, (b) is an SEM photograph when held at 900 ° C. for 24 hours, and (c) is an SEM photograph when held at 1000 ° C. for 3 hours.

  From observation of these SEM photographs, it can be seen that the grain growth of crystal grains does not progress much and the bonding of crystal grains progresses as the heat treatment time increases. Moreover, it turns out that the grain growth of a crystal grain is progressing when the heat processing temperature becomes high. That is, the mechanism that the heat treatment time and the heat treatment temperature that are assumed from the numerical values of the measurement results affect the properties (performance) of the chemical heat storage material can also be read from the SEM photograph.

  Based on the above considerations, the chemical heat storage material for chemical heat pump of the present invention is a chemical heat storage material having both high reactivity and high durability, and the method for producing the chemical heat storage material for chemical heat pump of the present invention has high reactivity. And a chemical heat storage material having both high durability.

Claims (5)

A chemical heat storage material for a chemical heat pump whose main component is calcium oxide,
Including sintering aids for calcium oxide and metal oxides,
The calcium oxide content is 92-97 wt%,
A mass ratio of the calcium oxide to the sintering aid of the metal oxide of 15 to 35,
A specific surface area of 8 to 13 m ² / g,
A chemical heat storage material for a chemical heat pump, wherein the breaking load is 90 N or more.   The chemical heat storage material for a chemical heat pump according to claim 1, wherein the sintering aid is MgO.   The chemical heat storage material for a chemical heat pump according to claim 1 or 2, wherein pores serving as communication holes are formed, and the average diameter of the pores is 40 to 60 µm.   The chemical heat storage material for a chemical heat pump according to any one of claims 1 to 3, wherein pores serving as communication holes are formed, and the porosity of the pores is 25 to 45%. A method for producing a chemical heat storage material for a chemical heat pump whose main component is calcium oxide,
The Ca content is 92 to 97 wt% in terms of oxide, and includes a sintering aid for metal oxide, and the mass ratio of Ca content in terms of oxide and the content of the sintering aid is 20 to 30. A step of preparing calcium carbonate,
Heating the prepared calcium carbonate at a heating rate of 1 to 15 ° C./min;
And a step of heat-treating the heated calcium carbonate at 700 to 1000 ° C. for 0 to 5 hours and performing a heat treatment.