JP6989121B2 - Manufacturing method of chemical heat storage material and chemical heat storage material - Google Patents

Description

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

In recent years, reduction of fossil fuel use has been required by carbon dioxide emission regulations, and in addition to energy saving in each process, it is necessary to promote the use of waste heat. As a means of using waste heat, water is used 100. Hot water heat storage below ℃ is known. However, in hot water heat storage, (1) heat storage for a long time is impossible due to heat dissipation loss, and (2) a large amount of water is required because the amount of exposed heat is small, and it is difficult to make the heat storage facility compact. , (3) There are problems such as the output temperature is unsteady according to the usage fee and gradually decreases.
A chemical heat storage material can be mentioned as a highly efficient heat storage technology. Since the chemical heat storage method involves chemical changes such as adsorption and hydration of substances, the amount of heat storage per unit mass is higher than that of the heat storage method using latent heat or sensible heat of the material itself (water, molten salt, etc.). Proposed chemical heat storage methods include an air-solid reaction method between a solid material (chemical heat storage material) and water vapor or carbon dioxide, ammonia absorption into a metal salt (ammine complex formation reaction), and a reaction by adsorption and desorption of organic substances such as alcohol. Has been done. Considering the load on the environment and the convenience of the device, the air-solid reaction method is the most advantageous. As chemical heat storage materials used in the air-solid reaction method, calcium oxide and magnesium oxide, which are alkaline earth metal oxides, are used in the air-solid reaction system with water vapor, and calcium oxide and lithium silicate are used in the air-solid reaction system with carbon dioxide. Are known. Patent Document 1 describes a chemical heat storage material containing a lithium silicate-based compound.

As a means for effectively utilizing high-temperature waste heat (600 ° C or higher) generated from the iron-making industry, alloy-based latent heat storage technology and chemical heat storage technology using carbon dioxide as a reaction medium are being studied. The chemical heat storage technology has the advantage of having a higher heat storage density than the latent heat storage technology.

WO2016 / 043224A1

600 ° C. or more lithium silicate as materials capable heat storage operation in the temperature range (lithium orthosilicate .Li ₄ SiO _4.) Has but although carbon dioxide absorption reaction using the heat output operation proceeds at 600 ° C. or higher, the reaction Due to the speed limitation, it is difficult to operate the heat output quickly, which is a problem for practical use. Therefore, in order to use this material as a chemical heat storage material, it is required to speed up the heat output operation and lower the temperature.

In order to solve the above problems, according to one means of the present invention, the chemical heat storage material is a halide and / or hydroxide of at least one metal selected from the group consisting of an alkali metal and an alkaline earth metal. The product was added to lithium silicate.

Further, it is desirable that the amount of at least one metal selected from the group consisting of the alkali metal and the alkaline earth is 0.1 mol% or more and 50 mol% or less with respect to the lithium silicate.
Further, it is desirable that the metal is lithium, sodium, potassium, magnesium or strontium.

Further, according to another aspect of the present invention, the chemical heat storage material contains lithium silicate to which LiCl and / and NaCl is added.

According to another aspect of the present invention, a method for producing a chemical heat storage material, the Li ₄ SiO _4, and shall have the step of adding a LiCl or / and NaCl by physical mixing.

According to the present invention, it is possible to provide a chemical heat storage material capable of realizing a heat output operation at a lower temperature and a method for producing the same.

It is a figure which shows the mass change by the temperature under the carbon dioxide atmosphere of a chemical heat storage material. It is a figure (2) which shows the mass change by the temperature under the carbon dioxide atmosphere of a chemical heat storage material. It is a figure (3) which shows the mass change by the temperature under the carbon dioxide atmosphere of a chemical heat storage material. It is the figure which compared the heat storage operation temperature range, and the heat output density of a chemical heat storage material.

Hereinafter, embodiments and examples of the present invention will be described, but the embodiments of the present invention are not limited to the embodiments and examples described below.

In order to solve the above problems, the present inventors have conducted various studies and found that alkali metal halides, alkaline earth metal halides and / or alkali metal hydroxides are added to the lithium silicate to form carbon dioxide. It was confirmed that the carbon absorption reaction activity was improved, and it was found that a chemical heat storage material capable of realizing a heat output operation at 500 ° C., which is lower than the conventional material, can be manufactured.

In this embodiment, attention is paid to CO ₂ absorption capacity and CO ₂ selectivity of the conventional CO ₂ Li composite oxide has been studied as an absorbent. In particular LiCl against Li ₄ SiO ₄ ^[1] that reversibly react with CO ₂ by the following equation at 600 ° C. or higher, and evaluate the impact of the reactivity with CO ₂ by the addition of NaCl. In addition, the effects of the addition methods were evaluated using two different addition methods.

Synthesis of li ₄ SiO ₄ was a solid phase method. Material as Li ₂ CO ₃ and SiO ₂ molar ratio of 2: 1. The mixture was heated at 1000 ° C. 20 hours, the milled sample was Li ₄ SiO _4. Li ₄ against SiO _4, LiCl, NaCl in two impregnation method and physical mixing, the molar ratio of _{Li 4 SiO 4: NaCl = 5} : 1, Li 4 SiO 4: LiCl = 5: 1 and comprising as additives did. Added sample in the impregnation method, the case of adding LiCl LiCl / Li ₄ SiO _4, the added sample in the physical mixture shows as Li ₄ SiO ₄ + LiCl. A thermal balance (TG-DTA2000SE, manufactured by Netch Japan Co., Ltd.) was used to evaluate the reactivity with _{CO 2.} The reaction was heated from room temperature to 900 ° C at a heating rate of 10 ° C / min. As a reaction gas, 100 mL / min of _{N 2} gas was circulated up to 200 ° C. to dry the sample, and then 100 mL / min of _{CO 2 gas was circulated.} The sample weight at 200 ° C was used as the initial weight. The reaction conversion rate X [%] and the heat output density Q [kJ / kg] were defined by the following formulas 1 and 2.

Here, M _sample: sample molecular weight _{[g / mol], W ini} : Sample Initial Weight [mg], M _Li4SiO4: molecular weight of _{Li 4 SiO 4 [g / mol} ], ΔH: enthalpy of reaction [kJ / mol], A : a weight ratio of Li ₄ SiO ₄ contained per sample 1 kg.

Figure 1 shows the Li ₄ SiO ₄ LiCl, thermogravimetric change of synthesis by-added sample, respectively NaCl. Samples to which LiCl and NaCl have been added by the impregnation method _{absorb CO 2} immediately after _{CO 2} flow at 200 ° C, but since the weight decreases significantly from the initial weight at 700 ° C or higher, LiCl and NaCl are added by the impregnation method. In addition to the system oxide, it is considered that another compound is produced. Li ₄ SO ₄ results anything subjected to the same processing as impregnation method without adding respect, since it showed thermogravimetric change differ from the original Li ₄ SiO _4, and Li ₄ SiO ₄ by impregnation Is also supported by the production of different substances. On the other hand, the behavior of the physical mixture LiCl, samples with the addition of NaCl is definitive CO ₂ emission above 700 ° C. Although similar to Li ₄ SiO _4, CO ₂ absorption initiation temperature it is found that the low temperature. The temperature at the peak of the mass of Li ₄ Si ₄ O ₄ + LiCl was 645 ° C (Fig. 2). The temperature at the time of the mass peak of Li ₄ SiO ₄ + NaCl became 662 ° C.. Under the experimental conditions this time, it was found that the addition of LiCl and NaCl by physical mixing _{has the effect of lowering the CO 2 absorption temperature.}

We synthesized _{Li 4 SiO 4, Li 4 SiO} 4 + LiCl, Li 4 SiO 4 + 70% , respectively maximum reaction conversion of NaCl, 78%, was 81%. When considering this to calculate the thermal power density, Li ₄ SiO ₄ is 837 [kJ / kg], Li 4 SiO 4 + LiCl is 852 [kJ / kg], Li 4 SiO 4 + NaCl is 903 [kJ / kg] The heat output density was higher than that of the alloy-based latent heat storage material that can be operated for heat storage in this temperature range. The comparison result of the heat output density and the heat storage operation temperature range is shown in FIG.

In this example, to evaluate the effect of using different addition methods against Li ₄ SiO ₄ LiCl, the reactivity with CO ₂ by the addition of NaCl. Considered a result, LiCl and NaCl using impregnation method showed no reversibility such as a conventional Li ₄ SiO _4, the process itself of the impregnation method is likely to produce a material different from Li ₄ SiO ₄ Be done. _{On the other hand, the effect of lowering the CO 2} absorption start temperature by up to about 50 ° C was observed by adding LiCl and NaCl by physical mixing. Furthermore, it was found that these have a higher heat output density than alloy-based latent heat storage materials that can perform heat storage operations in the high temperature range.

INDUSTRIAL APPLICABILITY The present invention can be industrially used as a method for producing a chemical heat storage material and a scientific heat storage material.

Claims (5)

Chemical heat storage material of at least one metal halide compound was added to the lithium silicate is selected from the group consisting of alkali metals and alkaline earth metals. The chemistry according to claim 1, wherein the amount of at least one metal selected from the group consisting of the alkali metal and the alkaline earth is 0.1 mol% or more and 50 mol% or less with respect to the lithium silicate. Heat storage material. The chemical heat storage material according to claim 1, wherein the metal is lithium, sodium, potassium, magnesium or strontium. A chemical heat storage material containing lithium silicate to which LiCl or / and NaCl is added. The Li ₄ SiO _4, a manufacturing method of a chemical heat storage material comprising the step of adding LiCl or / and NaCl by physical mixing.

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