A light-absorbing / heat-storing co-enhanced Li4SiO4-based thermal storage agent, its preparation method and application

Abstract

This invention discloses a light-absorbing / heat-storing co-enhanced Li4SiO4-based thermal energy storage agent, its preparation method, and its applications. The invention synthesizes an Fe-doped Li4SiO4-based thermal energy storage agent by wet mixing different lithium, silicon, and iron sources according to a specific mixture, followed by evaporation and high-temperature treatment. The preparation method of this invention is simple and easy to operate. The prepared Fe-doped Li4SiO4-based thermal energy storage agent maintained a stable energy storage density in multiple cycle energy storage tests. Furthermore, the thermal energy storage agent exhibits outstanding photothermal properties, maintaining a high absorption rate of the solar spectrum, providing a new application basis for the industrial application of thermochemical energy storage.

Description

Technical Field

[0001] This invention belongs to the field of thermochemical heat storage agent preparation technology, and more specifically, relates to a light absorption / heat storage co-enhanced Li4SiO4-based heat storage agent, its preparation method and its application. Background Technology

[0002] Solar energy, as the most abundant renewable and clean energy source in nature, has received widespread attention from various countries as energy demand continues to rise. Its industrial applications are expanding year by year, and its industrial application technologies are gradually maturing.

[0003] The main obstacle currently hindering solar power generation technology is the intermittent nature of solar radiation. In practical applications, the alternation of cloudy days and night makes it impossible for solar power plants to meet continuous power supply demands, leading to an imbalance between energy supply and demand and restricting the development of solar power generation technology. To address this, solar power plant energy storage systems have emerged. Energy storage technology stores the energy of solar radiation in a specific form within the system and releases it as heat during nighttime or cloudy / rainy days when solar radiation is weak, enabling uninterrupted thermal power generation from solar power plants.

[0004] Traditional thermal storage materials (heat transfer oil, molten salt, etc.) cannot meet the high operating temperatures of third-generation concentrated solar power (CSP) systems, which can reach up to 700°C. Furthermore, the corrosiveness of traditional thermal storage materials further restricts their development in the energy storage technology field. Thermochemical energy storage (TCES) is an energy storage technology suitable for long-term energy storage with low heat loss. Its principle is to achieve the cyclic storage / release of chemical and thermal energy through a reversible chemical reaction between the thermal storage material and specific substances. Currently, common thermochemical energy storage materials mainly include metal oxides, salts, and hydroxides.

[0005] Lithium orthosilicate (Li4SiO4) is a CO2 adsorbent material with high adsorption capacity (theoretically up to 0.367 g / g), low regeneration energy consumption (<750℃), and strong cycle stability, and has received widespread attention in the field of carbon capture in recent years. Thermochemical energy storage technology based on Li4SiO4 involves the reaction of Li4SiO4 with CO2 in a carbonization furnace to release heat, yielding Li2CO3 and Li2SiO3, which are stored in a specific material tank. Subsequently, during the energy supply phase, these are transferred to a calcining furnace to regenerate Li4SiO4 while simultaneously storing heat. In this circulating thermal storage project, the Li4SiO4 / Li2CO3 / Li2SiO3 material is continuously fluidized and circulated between the carbonization furnace, storage tank, and calcining furnace to achieve efficient and stable circulating thermal storage / release. Furthermore, the heat from the solid and gaseous phases is recovered through a coupled heat exchanger within the system to improve the overall system efficiency. Pure Li4SiO4 powder is white, which greatly limits the solar radiation absorption capacity of Li4SiO4-based thermal energy storage agents. Furthermore, unmodified Li4SiO4-based thermal energy storage agents lack strong industrial application suitability, specifically exhibiting low energy storage density and rapid performance degradation. Therefore, performance modification of Li4SiO4-based thermal energy storage agents to improve their light absorption and thermal storage properties is a necessary prerequisite for their practical application.

[0006] Currently, domestic and international research on Li4SiO4-based thermochemical thermal energy storage agents mainly includes: (1) research on the application potential of Li4SiO4-based materials in thermochemical energy storage (ApplEnergy 2017, 193, 74-83); (2) strengthening of Li4SiO4 / CO2 reaction system with K2CO3 additive (Energy Procedia 2017, 131, 94-100); (3) research on Li4SiO4 / CO2 / zeolite-based thermochemical thermal energy storage system (ApplEnergy 2019, 240, 1-5). The above research mainly focuses on the application potential of macroscopic Li4SiO4-based thermochemical thermal energy storage systems, while there are few reports on the modification methods of Li4SiO4-based thermochemical thermal energy storage materials. Summary of the Invention

[0007] To address the bottlenecks encountered by Li4SiO4-based materials in thermochemical thermal storage applications, this invention aims to provide a light-absorbing / heat-storage co-enhanced Li4SiO4-based thermal storage agent, its preparation method, and its application. This invention yields a dark-colored Li4SiO4-based thermochemical thermal storage agent synthesized using a single-step method. Different lithium, silicon, and iron sources are wet-mixed in a specific ratio, then evaporated, and finally synthesized under high-temperature conditions to obtain an Fe-doped Li4SiO4-based thermal storage agent. The Fe-doped thermal storage agent of this invention exhibits significantly improved heat storage and light absorption performance, making it suitable for use in solar thermal storage devices. The specific technical solution of this invention is described below.

[0008] Application of a light-absorbing / heat-storing co-enhanced Li4SiO4-based thermal energy storage agent as a thermochemical energy storage material in solar collectors

[0009] It is used as an Fe-doped Li4SiO4-based thermal storage agent.

[0010] In this invention, the light-absorbing / heat-storing co-enhanced Li4SiO4-based thermal storage agent is prepared by the following method:

[0011] (1) Weigh a certain amount of lithium source, silicon source and iron source and place them in a beaker. Add an appropriate amount of solvent to disperse them fully to obtain a precursor solution;

[0012] (2) The prepared precursor solution was placed in a water bath and evaporated to dryness to obtain precursor powder;

[0013] (3) The precursor powder is placed in a muffle furnace and calcined at high temperature, and then ground in a mortar to obtain heat storage agent powder.

[0014] In step (1) above, the lithium source, silicon source, and iron source comprise two groups, namely lithium acetate, alkaline silica sol, ferric citrate, and lithium carbonate, silicon dioxide, and ferric oxide; the solvent is water or anhydrous ethanol. More preferably, in step (1) above, lithium oxalate, 30wt% alkaline silica sol, and ferric citrate are fully dissolved in deionized water to obtain a precursor solution; when preparing a heat storage agent using lithium oxalate, ferric citrate, and silica sol as precursors, the three are mixed evenly in deionized water to achieve a diffusion level at the molecular level, and then evaporated to dryness to obtain a uniformly dispersed precursor solid, which is beneficial for the full reaction between the precursors.

[0015] In step (1) above, the molar ratio of lithium in the lithium source, silicon in the silicon source, and iron in the iron source is (3.4-3.9):1:(0.05-0.2). More preferably, the molar ratio is 3.7:1:0.1.

[0016] In step (2) above, the heating temperature is 85℃~95℃.

[0017] In step (2) above, calcination is carried out in an air atmosphere at a temperature of 800℃~950℃ for a time of 240min~360min.

[0018] The Li4SiO4-based thermal storage agent prepared via the synthesis route described in this invention has the following advantages:

[0019] The Fe-doped Li4SiO4-based thermal storage agent obtained by this invention exhibits uniformity across the entire wavelength range of 300 nm to 800 nm in solar spectrum.

[0020] It has high absorption rate, and its average absorption rate across the entire solar spectrum is significantly improved compared to pure Li4SiO4 thermal storage agent.

[0021] 2. The Fe-doped Li4SiO4-based thermal storage agent obtained by this invention exhibits a faster heating rate than pure Li4SiO4 under both high-intensity and low-intensity light irradiation conditions.

[0022] 3. The Fe-doped Li4SiO4-based thermal energy storage agent obtained by this invention has excellent cyclic energy storage stability, which can be maintained at around 450 kJ / kg, and no sharp performance degradation phenomenon was found.

[0023] 4. The Fe-doped Li4SiO4-based heat storage agent obtained by this invention has a higher absorption rate for light in the wavelength range of <500nm, and its light absorption and heat storage temperature can reach about 79.1℃. Attached Figure Description

[0024] Figure 1 These are the X-ray diffraction patterns of the Fe-doped Li4SiO4-based thermal storage agents prepared in Examples 1 and 2.

[0025] Figure 2 shows the change in energy storage density of the Fe-doped Li4SiO4-based thermal energy storage agents prepared in Examples 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 as a function of cycle number (thermal storage: 700℃ / 100% N2 / 20min; thermal release: 650℃ / 100% CO2 / 20min). Figures 2a-2j These correspond to Examples 1 through 10, respectively.

[0026] Figure 3 shows the near-infrared-visible-ultraviolet absorption performance curves of the Fe-doped Li4SiO4-based thermal storage agents prepared in Examples 3, 5, and 11; whereby... Figure 3a , 3b 3c corresponds to Embodiment 3, Embodiment 5 and Embodiment 11, respectively.

[0027] Figure 4 shows the performance of the Fe-doped Li4SiO4-based thermal storage agents prepared in Examples 3 and 5 under strong lamp radiation (1618 W / m²). 2 The temperature rise curve under ( ); where Figure 4a ,4b These correspond to Examples 3 and 5, respectively.

[0028] Figure 5 shows the performance of the Fe-doped Li4SiO4-based thermal storage agents prepared in Examples 3 and 5 under weak lamp radiation (752 W / m²). 2 The temperature rise curve under ( ); where Figure 5a , 5b These correspond to Examples 3 and 5, respectively. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0030] This invention provides a synthetic route for a light / thermal co-enhanced Li4SiO4-based thermal storage agent, comprising the following steps:

[0031] (1) Weigh a specific amount of lithium source, silicon source and iron source and place them in a beaker. Add an appropriate amount of deionized water to dissolve them completely to obtain a precursor solution.

[0032] (2) The prepared precursor solution was placed in a water bath and evaporated to dryness to obtain precursor powder;

[0033] (3) After calcining the precursor powder at 800℃~950℃ for 240 min~360 min, grind it in a mortar to obtain Fe-doped Li4SiO4-based heat storage agent.

[0034] In step (1), the lithium source, silicon source and iron source consist of two groups, namely lithium oxalate, 30wt% alkaline silica sol, iron citrate and lithium carbonate, silicon dioxide and ferric oxide, and the molar ratio of Li:Si:Fe is set to (3.4-3.9):1:(0.05-0.2).

[0035] In step (2), a water bath at 85-95℃ is used to heat and dry the product.

[0036] In step (3), the calcination atmosphere is an air atmosphere. Example 1

[0037] (1) 8.67g lithium oxalate (Li2C2O4, Maclean's reagent) and 2.45g ferric citrate (FeC6H5O7, Sinopharm)

[0038] Add the reagent powder and 10g of alkaline silica sol (30 wt%, Shandong Yousuo Chemical) to deionized water and stir until fully dissolved.

[0039] (2) The prepared solution was placed in a water bath and evaporated to dryness to obtain precursor powder;

[0040] (3) The precursor powder was calcined at 850°C for 300 min to obtain Fe-doped Li4SiO4-based heat storage agent. Example 2

[0041] (1) Take 6.83g of lithium carbonate (Li2CO3, Sinopharm reagent) and 0.4g of ferric oxide (Fe2O3, Sinopharm reagent).

[0042] The powder and 3g of silicon dioxide (SiO2, Guoyao Reagent) were added to anhydrous ethanol and stirred until homogeneous;

[0043] (2) The obtained suspension was placed in a water bath and evaporated to dryness to obtain precursor powder;

[0044] (3) The precursor powder was calcined at 850°C for 300 min to obtain Fe-doped Li4SiO4-based heat storage agent.

[0045] Furthermore, the parameters for Examples 3-7 are shown in Table 1. Parameters not listed in the table are the same as those for Example 1.

[0046] Table 1

[0047] Example Lithium source / quality Silicon source / quality Iron source / quality The mixture in step (1) Example 3 Lithium oxalate / 9.44g Silica sol / 10g Ferric citrate / 1.23g Deionized water Example 4 Lithium oxalate / 9.05g Silica sol / 10g Ferric citrate / 1.84g Deionized water Example 5 Lithium carbonate / 6.56g Silica / 3g Ferric oxide / 0.6g Anhydrous ethanol Example 6 Lithium carbonate / 6.28g Silica / 3g Ferric oxide / 0.8g Anhydrous ethanol Example 7 Lithium oxalate / 10.46g Silica sol / 9g Ferric citrate / 1.23g Deionized water Example 8 Lithium oxalate / 10.71g Silica sol / 8g Ferric citrate / 2.45g Deionized water Example 9 Lithium carbonate / 7.57g Silica / 2.7g Ferric oxide / 0.4g Anhydrous ethanol Example 10 Lithium carbonate / 7.76g Silica / 2.4g Ferric oxide / 0.8g Anhydrous ethanol Example 11 lithium oxalate silica sol - Deionized water

[0048] Experimental Results Analysis

[0049] The Fe-doped Li4SiO4-based thermal storage agents prepared in Examples 1, 2, 8, and 9 were analyzed by X-ray diffraction (XRD), and the results are as follows: Figure 1 As shown, obvious Li4SiO4 and LiFeO2 diffraction peaks can be observed, confirming the effective doping of Fe.

[0050] The cyclic thermal storage performance of the Fe-doped Li4SiO4-based thermal storage agents prepared in Examples 1-10 under specific thermal storage conditions was tested using a dual-temperature-controlled fixed-bed reactor. The thermal storage conditions were: thermal storage temperature 700℃, thermal storage time 20 min, and atmosphere of 100 vol.% N2; the exothermic conditions were: exothermic temperature 650℃, holding time 20 min, and atmosphere of 100 vol.% CO2. The cycle test was performed 10 or 15 times. The mass of CO2 adsorbed in each cycle was calculated based on the difference in adsorbent mass before and after each cycle. The energy storage density was calculated using the heat of reaction (ΔH = -94 kJ / kg). The change in energy storage density with increasing cycle number was illustrated graphically. The results are shown below. Figures 2a-2jAs shown, the horizontal axis represents the number of heat storage-exothermic cycles, and the vertical axis represents the energy storage density. It can be seen that the energy storage densities of the heat storage agents prepared by lithium oxalate, silica sol, and ferric citrate (Examples 1, 3, 4, 7, and 8) are generally higher than those prepared by lithium carbonate, silicon dioxide, and ferric oxide (Examples 2, 5, 7, 9, and 10). The Fe-doped Li4SiO4-based heat storage agent prepared in Example 3 has the highest energy storage density, which remains at approximately ~450 kJ / kg. It is noteworthy that the heat storage agents prepared in all 10 examples exhibit excellent cyclic energy storage stability, without any drastic performance degradation.

[0051] Ultraviolet-visible-near-infrared absorption tests were performed on Examples 3, 5, and 11, and the test results are as follows: Figure 3a , 3b As shown in Figure 3c, the samples in Examples 3 and 5 exhibited similar absorbance trends. Specifically, an absorbance peak (>50%) appeared near a wavelength of 300 nm, followed by a gradual decrease in absorbance with increasing wavelength. The absorbance then increased again around 350 nm, before decreasing again near 500 nm, and this decrease continued thereafter. In contrast, Example 11, lacking Fe doping, had a very low absorbance. Specifically, it only exhibited some absorbance for light radiation with wavelengths <500 nm, and the absorbance gradually decreased with increasing wavelength, reaching a maximum of only 5.1%. Therefore, it can be concluded that the Fe-doped Li4SiO4-based thermal storage agent possesses stronger light absorption performance compared to pure Li4SiO4.

[0052] High-intensity lamp illumination temperature rise tests were conducted on Examples 3 and 5 (light source distance 17.5cm, power 1618W), and the temperature change curves over time are shown below. Figure 4a and 4b As shown, it can be observed that the temperature changes of the two samples first rise sharply and then rise slowly. The final temperature of the sample in Example 3 is ~79.1℃, and the final temperature of the sample in Example 5 is ~75.2℃.

[0053] Low-intensity lamp illumination temperature rise test was conducted on Examples 3 and 5 (light source distance 25cm, power 752W), and the temperature change curves over time are shown below. Figure 5a and 5b As shown, it can be observed that the temperature changes of the two samples first rise sharply and then rise slowly. The final temperature of the sample in Example 3 is ~69.4℃, and the final temperature of the sample in Example 5 is ~63.6℃.

Claims

1. The application of a light-absorbing / heat-storing co-enhanced Li4SiO4-based thermal energy storage agent as a thermochemical energy storage material in solar collectors, characterized in that, It is an Fe-doped Li4SiO4-based thermal storage agent; the light absorption / thermal storage co-enhanced Li4SiO4-based thermal storage agent is prepared by the following method: (1) Weigh a certain amount of lithium source, silicon source and iron source and place them in a beaker. Add an appropriate amount of solvent to disperse them fully to obtain a precursor solution; (2) The prepared precursor solution was placed in a water bath and evaporated to dryness to obtain precursor powder; (3) The precursor powder is calcined at high temperature in a muffle furnace and then ground in a mortar to obtain the heat storage agent powder; wherein: In step (1), the lithium source, silicon source and iron source are lithium acetate, alkaline silica sol and iron citrate, respectively; the molar ratio of lithium in the lithium source, silicon in the silicon source and iron in the iron source is (3.4-3.9):1:(0.05-0.2).

2. The application as described in claim 1, characterized in that, In step (1), the solvent is water or anhydrous ethanol.

3. The application as described in claim 1, characterized in that, In step (2), the heating temperature is 85℃~95℃.

4. The application as described in claim 1, characterized in that, In step (2), calcination is carried out in an air atmosphere at a temperature of 800℃~950℃ for a time of 240 min~360 min.

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