Five-membered eutectic molten salt heat storage material with high stability, wide temperature range and high energy storage density as well as preparation method and application of five-membered eutectic molten salt heat storage material

Abstract

The invention discloses a pentabasic eutectic molten salt heat storage material with high stability, wide temperature range and high energy storage density and a preparation method and application thereof, and the pentabasic eutectic molten salt heat storage material is prepared from the following raw materials in percentage by mass: 32.58% of Na2CO3, 31.89% of K2CO3, 6.33% of NaF, 11.22% of KF and 17.98% of NaCl. The melting point of the quinary eutectic molten salt heat storage material is 511 DEG C, the phase change enthalpy is 195.6 J / g, the average specific heat capacity at 650-750 DEG C is 1.63 J / (g.K), and the decomposition temperature can reach 800 DEG C. The high-stability multi-element eutectic fused salt provided by the invention can provide an excellent heat transfer / heat storage medium for the fields of solar photo-thermal power generation, industrial waste heat recovery, fused salt heat pump heat storage, power plant peak regulation and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of molten salt heat storage materials, and in particular to a five-element eutectic molten salt heat storage material having high stability, a wide temperature range and high energy storage density, and a preparation method and use thereof. Background Art

[0002] Heat storage technology is an effective means to solve the problem of time-space mismatch between supply and demand of new energy. Due to its advantages of low cost and high safety, molten salt heat storage technology has become the most widely used heat storage technology. However, the operating temperature of traditional industrial molten salt systems is below 600°C, resulting in a narrow temperature range. At the same time, the existing molten salt system has a low specific heat, which together lead to low heat storage density of the system. Therefore, it is urgent to develop a new molten salt system that takes into account high stability, wide temperature range and high energy storage density. Summary of the invention

[0003] The purpose of the present invention is to provide a five-element eutectic molten salt heat storage material having high stability, wide temperature range and high energy storage density, as well as a preparation method and use thereof, so as to improve the stability and energy storage density of the molten salt system.

[0004] To achieve the above object, the present invention adopts the following technical solution:

[0005] A five-element eutectic molten salt heat storage material with high stability, wide temperature range and high energy storage density, wherein the raw materials are composed of the following components by mass percentage: 32.58% Na 2 CO 3 31.89% of K 2 CO 3 , 6.33% NaF, 11.22% KF, 17.98% NaCl.

[0006] The five-element eutectic molten salt heat storage material has a melting point of 511°C, a phase change enthalpy of 195.6 J / g, an average specific heat capacity of 1.63 J / (g·K) at 650-750°C, and a decomposition temperature of 800°C.

[0007] A method for preparing a five-element eutectic molten salt heat storage material having high stability, wide temperature range and high energy storage density, comprising the following steps:

[0008] S1, predict the eutectic composition and melting point of five-component eutectic molten salt based on thermodynamic principles and Newton-Raphson method;

[0009] S2, weigh Na in proportion to the predicted value obtained in step S1 2 CO 3 , K 2 CO 3 , NaF, KF, and NaCl are mixed to obtain a mixed molten salt;

[0010] S3, drying the mixed molten salt obtained in step S2 to obtain dried molten salt from which moisture has been removed;

[0011] S4, grinding the dried molten salt obtained in step S3 to obtain a uniformly mixed dried molten salt;

[0012] S5, placing the uniformly mixed dried molten salt obtained in step S4 in a heater, heating it, cooling it, and then crushing it to obtain a eutectic molten salt material.

[0013] The step S1 specifically includes:

[0014] S11, based on the existing binary phase diagram and physical property parameters, build a binary system database, including the binary system melting point T Eij , phase change enthalpy H fij , molar ratio X Eij , activity coefficient Y ij , interaction parameter q ij ;

[0015] S12, based on the binary system database constructed in step S11, using thermodynamic principles and the Newton-Raphson method, combined with the thermophysical property data of the single-component molten salt, calculate the eutectic composition and melting point of the five-component molten salt; jointly solve the following equations of the five components to obtain the eutectic composition and melting point of the five-component molten salt:

[0016]

[0017] In the formula, i represents component i, is the partial molar excess Gibbs energy of component i in the quinary system, R is the gas constant, T is the absolute temperature, X i is the molar proportion of component i in the quinary system, H mi is the solid-liquid phase change enthalpy of component i, T mi is the melting point of component i, ΔC pi is the difference in specific heat capacity between the liquid and solid states of component i at the melting point;

[0018] In the above formula Calculated by the following formula:

[0019] G ij =R*T'*[-X i *ln(1-X j *q ij )-X j *ln(1-X i *q ji )]

[0020]

[0021]

[0022] In the formula, n is the total number of components, G ij is the excess Gibbs energy of the binary system, G is the excess Gibbs energy of the quinary system, q ij is the interaction parameter of the binary system, X j is the molar percentage of component j in the quinary system.

[0023] In the step S12, the thermophysical property data of the single-component molten salt is obtained by experiments, manuals or software.

[0024] In step S3, drying is performed in a muffle furnace at 350° C. for 24 hours.

[0025] In step S4, the grinding method is: using a planetary ball mill, the rotation speed is set to 700 r / min, the grinding time is 4 hours, and after taking out the sample, it is ground using an agate mortar.

[0026] In the step S5, the heater is a muffle furnace, and heating is performed at 700° C. for 4 hours.

[0027] The five-element eutectic molten salt heat storage material is used as a heat transfer / heat storage medium.

[0028] The heat transfer / heat storage medium is used in solar thermal power generation, industrial waste heat recovery, molten salt heat pump heat storage or power plant peak regulation.

[0029] Beneficial effects: The present invention proposes a five-element molten salt heat storage material that combines high stability, wide temperature range and high energy storage density, which can provide an excellent heat transfer / heat storage medium for solar thermal power generation, industrial waste heat recovery, molten salt heat pump heat storage and power plant peak regulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a flow chart of the preparation method of the present invention;

[0031] Figure 2 is a heat flow curve diagram of the molten salt material prepared in an embodiment of the present invention;

[0032] Figure 3 is a specific heat capacity curve diagram of the molten salt material prepared in an embodiment of the present invention;

[0033] Figure 4 3 is a thermogravimetric curve of the molten salt material prepared in the embodiment of the present invention. DETAILED DESCRIPTION

[0034] The technical solution of the present invention will be described clearly and completely below in conjunction with the embodiments and drawings. Obviously, the described embodiment is only one implementation of the present invention, not all implementations. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] Example

[0036] like Figure 1 This embodiment provides a five-element eutectic molten salt heat storage material and a preparation method thereof, the material raw materials include Na 2 CO 3 , K 2 CO 3 , NaF, KF, NaCl. The preparation method comprises the following steps:

[0037] (1) Based on the principles of thermodynamics and the Newton-Raphson method, the eutectic composition and melting point of the five-component eutectic molten salt are predicted, including:

[0038] (1.1) Based on the existing binary phase diagrams and physical property parameters, a binary system database is constructed, including the binary system melting point T Eij , phase change enthalpy H fij , molar ratio X Eij , activity coefficient Y ij , interaction parameter q ij .

[0039] In this embodiment, T Eij , X Eij , H fij , Y ij ,q ij The parameters are shown in Table 1 below:

[0040] Table 1

[0041]

[0042]

[0043] In this embodiment, Y ij ,q ij The parameters are shown in Table 2 below:

[0044] Table 2

[0045]

[0046] (1.2) Based on the binary system database, the eutectic composition and melting point of the multicomponent molten salt are calculated by using the thermodynamic principles and the Newton-Raphson method, combined with the thermophysical property data of the single-component molten salt. The thermophysical property data of the single-component molten salt are obtained by experiments, manuals or software. The eutectic composition and melting point of the five-component molten salt can be obtained by combining and solving the following equations of the five components:

[0047]

[0048] In the formula, is the partial molar excess Gibbs energy of component i in the quinary system, R is the gas constant, T is the absolute temperature, X i is the molar proportion of component i in the quinary system, H mi is the solid-liquid phase change enthalpy of component i, T mi is the melting point of component i, ΔC pi is the difference in specific heat capacity between the liquid and solid states of component i at the melting point. Calculated by the following formula:

[0049] G ij =R*T*[-X i *ln(1-X j *q ij )-X j *ln(1-X i *q ji )]

[0050]

[0051]

[0052] In the formula, n is the total number of components, G ij is the excess Gibbs energy of the binary system, G is the excess Gibbs energy of the quinary system, q ij is the interaction parameter of the binary system, X j is the molar percentage of component j in the quinary system.

[0053] The phase change enthalpy H of the single-component molten salt in this embodiment is mi , the melting point of component i itself is T mi , the specific heat capacity difference between the liquid and solid states of component i at the melting point ΔC pi As shown in Table 3 below:

[0054] Table 3

[0055]

[0056] The five-element eutectic components and melting points solved in this example are shown in Table 4 below:

[0057] Table 4

[0058]

[0059] (2) Weigh Na in proportion to the predicted value 2 CO 3 , K 2 CO 3 , NaF, KF, NaCl (the error between the actual weighing value and the theoretical value of each component is within 5wt%), and mixed to obtain a mixed molten salt, totaling 10g;

[0060] (3) Place the mixed molten salt in an alumina crucible and place the crucible in a muffle furnace. The heating rate of the muffle furnace is 10°C / min. After heating to 350°C, keep the temperature for 24 hours. After cooling to room temperature, take out the sample;

[0061] (4) Place the dried and cooled sample in a ball mill and grind it using a planetary ball mill. The speed of the ball mill is set to 700 r / min and the ball milling time is set to 4 hours;

[0062] (5) The uniformly mixed dried molten salt is placed in a muffle furnace. The heating rate of the muffle furnace is 10°C / min. After heating to 700°C, the temperature is kept at this temperature for 4 hours. After cooling to room temperature, the sample is taken out and ground with an agate mortar to obtain a uniformly mixed and anhydrous five-element eutectic molten salt heat storage material.

[0063] The molten salt heat storage material prepared in this embodiment was subjected to performance tests, including melting point, decomposition temperature, specific heat capacity, and latent heat of phase change. The melting point, latent heat of phase change, and specific heat capacity were tested using a differential scanning calorimeter (DSC), and the decomposition temperature was tested using a thermogravimetric analyzer (TG).

[0064] The heat flow curve test results of the five-element eutectic molten salt heat storage material are as follows Figure 2 As shown, Figure 2 There are two peaks: the first peak is around 100℃, which is due to the removal of water absorbed by the sample; the second peak is the melting peak of the sample. This shows that the prepared molten salt is a eutectic molten salt, and the melting temperature is 511℃.

[0065] The melting point and phase change enthalpy of the five-element eutectic molten salt heat storage material are as follows Figure 2 As shown, the specific heat capacity is Figure 3 The decomposition temperature is shown as Figure 4 The test data are summarized in Table 5 below:

[0066] Table 5

[0067]

[0068] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A five-element eutectic molten salt heat storage material with high stability, wide temperature range and high energy storage density, characterized in that: According to mass percentage, its raw materials are composed of the following components: 32.58% Na2CO3, 31.89% K2CO3, 6.33% NaF, 11.22% KF, and 17.98% NaCl.

2. According to claim 1, a five-element eutectic molten salt heat storage material having high stability, wide temperature range and high energy storage density, characterized in that: The five-element eutectic molten salt heat storage material has a melting point of 511°C, a phase change enthalpy of 195.6 J / g, an average specific heat capacity of 1.63 J / (g·K) at 650-750°C, and a decomposition temperature of 800°C.

3. A method for preparing a five-element eutectic molten salt heat storage material having high stability, wide temperature range and high energy storage density as described in claim 1, characterized in that: The following steps are involved: S1, predict the eutectic composition and melting point of five-component eutectic molten salt based on thermodynamic principles and Newton-Raphson method; S2, according to the predicted value obtained in step S1, weigh Na2CO3, K2CO3, NaF, KF, and NaCl in proportion, and mix them to obtain a mixed molten salt; S3, drying the mixed molten salt obtained in step S2 to obtain dried molten salt from which moisture has been removed; S4, grinding the dried molten salt obtained in step S3 to obtain a uniformly mixed dried molten salt; S5, placing the uniformly mixed dried molten salt obtained in step S4 in a heater, heating it, cooling it, and then crushing it to obtain a eutectic molten salt material.

4. The method for preparing a five-element eutectic molten salt heat storage material having high stability, wide temperature range and high energy storage density according to claim 3, characterized in that: The step S1 specifically includes: S11, based on the existing binary phase diagram and physical property parameters, build a binary system database, including the binary system melting point T Eij , phase change enthalpy H fij , molar ratio X Eij , activity coefficient Y ij , interaction parameter q ij ; S12, based on the binary system database constructed in step S11, using thermodynamic principles and the Newton-Raphson method, combined with the thermophysical property data of the single-component molten salt, calculate the eutectic composition and melting point of the five-component molten salt; jointly solve the following equations of the five components to obtain the eutectic composition and melting point of the five-component molten salt: In the formula, i represents component i, is the partial molar excess Gibbs energy of component i in the quinary system, R is the gas constant, T is the absolute temperature, X i is the molar proportion of component i in the quinary system, H mi is the solid-liquid phase change enthalpy of component i, T mi is the melting point of component i, ΔC pi is the difference in specific heat capacity between the liquid and solid states of component i at the melting point; In the above formula Calculated by the following formula: G ij =R*T*[-X i *ln(1-X j *q ij )-X j *ln(1-X i *q ji )] In the formula, n is the total number of components, G ij is the excess Gibbs energy of the binary system, G is the excess Gibbs energy of the quinary system, q ij is the interaction parameter of the binary system, X j is the molar percentage of component j in the quinary system.

5. The method for preparing a five-element eutectic molten salt heat storage material having high stability, wide temperature range and high energy storage density according to claim 4, characterized in that: In the step S12, the thermophysical property data of the single-component molten salt is obtained by experiments, manuals or software.

6. The method for preparing a five-element eutectic molten salt heat storage material having high stability, wide temperature range and high energy storage density according to claim 3, characterized in that: In step S3, drying is performed in a muffle furnace at 350° C. for 24 hours.

7. The method for preparing a five-element eutectic molten salt heat storage material having high stability, wide temperature range and high energy storage density according to claim 3, characterized in that: In step S4, the grinding method is: using a planetary ball mill, the rotation speed is set to 700 r / min, the grinding time is 4 hours, and after taking out the sample, it is ground using an agate mortar.

8. The method for preparing a five-element eutectic molten salt heat storage material having high stability, wide temperature range and high energy storage density according to claim 3, characterized in that: In the step S5, the heater is a muffle furnace, and heating is performed at 700° C. for 4 hours.

9. Use of the five-element eutectic molten salt heat storage material according to claim 1 as a heat transfer / heat storage medium.

10. The use according to claim 9, characterized in that: The heat transfer / heat storage medium is used in solar thermal power generation, industrial waste heat recovery, molten salt heat pump heat storage or power plant peak regulation.

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