Molten salt heat storage system and method for removing calcium and magnesium impurities in molten salt on line

Abstract

The invention discloses a fused salt heat storage system and method for removing calcium and magnesium impurities in fused salt on line, and relates to the technical field of fused salt heat storage. According to the fused salt heat storage system, the reactor is arranged in the communicating pipeline between the heating device and the heat exchanger, and the calcium and magnesium removing reagent is arranged in the reactor. When the molten salt heat storage system is operated, the calcium and magnesium removal reagent can selectively react or adsorb magnesium ions and calcium ions in high-temperature molten salt, but basically does not react with a molten salt main body, so that the aim of removing impurities of the calcium ions and the magnesium ions in the molten salt on line is fulfilled; the storage tank corrosion problem caused by magnesium ion and calcium ion impurities is effectively inhibited, and the operation safety and the service life of the fused salt heat storage system are improved. After the molten salt heat storage system provided by the invention runs for 3 months, the content of calcium and magnesium ions in the molten salt can be lower than 0.01%, and the removal amount exceeds 99%; and after one year of operation, the content of calcium and magnesium is kept to be lower than 0.01%, and the storage tank is not obviously corroded.

Description

Technical Field

[0001] This invention relates to the field of molten salt thermal energy storage technology, and in particular to a molten salt thermal energy storage system and method for online removal of calcium and magnesium impurities from molten salt. Background Technology

[0002] Molten salt thermal energy storage technology, as a core solution supporting low-carbon energy systems such as concentrated solar power (CSP) and flexible peak shaving in thermal power, has been applied on a large scale globally. Among them, binary mixed molten salt (commonly known as "solar salt") composed of 60wt% sodium nitrate (NaNO3) and 40wt% potassium nitrate (KNO3) has become the mainstream thermal storage medium accounting for over 80% of commercial CSP plants due to its wide temperature range, low melting point, and high thermal stability. However, the purity of commercial-grade solar salt used in actual projects is typically only around 99%, with residual impurities mainly being magnesium nitrate (0.5%~1.2% Mg(NO3)2) and calcium nitrate (0.1%~0.3% Ca(NO3)2). Especially in salt lake-rich regions like Qinghai in my country, the magnesium ion concentration in the raw materials is extremely high, resulting in magnesium impurity content in the purified sodium nitrate and potassium nitrate reaching 0.8%~2.5%.

[0003] Although calcium nitrate and magnesium nitrate constitute a relatively small proportion of solar salt, they pose a serious threat to the long-term safe operation of molten salt thermal storage systems. Thermodynamic analysis shows that within the normal operating temperature range of solar salt (290~600℃), pure NaNO3 and KNO3 are relatively inert, and their Gibbs free energy for corrosion reactions with carbon steel or stainless steel tank materials is greater than zero, theoretically indicating no tendency for spontaneous corrosion. However, the thermal stability of magnesium nitrate and calcium nitrate is significantly lower than that of the main salt components: when the temperature exceeds 400℃, magnesium nitrate begins to thermally decompose, generating magnesium oxide (MgO) and highly oxidizing nitrogen dioxide (NO2) and oxygen (O2); although calcium nitrate thermodynamically decomposes significantly above 700℃, its decomposition temperature can be significantly reduced in actual tank atmospheres due to factors such as low NO2 partial pressure and local activity variations. On the one hand, both NO2 and oxygen O2 can react with steel storage tanks to cause oxidation corrosion. On the other hand, the generated MgO and CaO have extremely strong water absorption properties and readily absorb moisture from the air to form magnesium hydroxide and calcium hydroxide. Under high temperature conditions, these hydroxides can further react with the storage tank to regenerate oxides and release water vapor, thus forming a cycle of "water absorption - corrosion - oxide regeneration". This makes the oxides essentially act as catalysts that continuously promote corrosion.

[0004] Currently, the removal of calcium and magnesium impurities from molten salt mainly relies on upstream raw material purification processes, such as recrystallization, solvent extraction, or ion exchange. However, these methods are costly, complex, and difficult to completely eliminate trace impurities. Moreover, existing molten salt thermal storage systems generally lack the ability to purify the molten salt injected into the system online during operation. Therefore, it is urgent for those skilled in the art to develop a technical solution that can remove calcium and magnesium impurities in real time, efficiently, and safely under normal operating conditions of molten salt thermal storage systems, in order to suppress the generation of corrosive gases at the source and ensure the long-term stable operation of the system. Summary of the Invention

[0005] The main objective of this invention is to propose a molten salt thermal storage system and method for online removal of calcium and magnesium impurities from molten salt, aiming to solve the problem that existing molten salt thermal storage systems are unable to remove calcium and magnesium impurities from molten salt in a real-time, efficient, and safe manner.

[0006] To achieve the above objectives, the present invention proposes an online molten salt thermal storage system for removing calcium and magnesium impurities from molten salt, comprising a low-temperature molten salt storage tank, a heating device, a high-temperature molten salt storage tank, and a heat exchanger connected in sequence by a connecting pipeline, wherein the heat exchanger and the low-temperature molten salt storage tank are connected by a connecting pipeline to form a circulation pipeline. At least one reactor is provided in the connecting pipeline between the heating device and the heat exchanger. The reactor is equipped with a calcium and magnesium removal reagent, which is used to contact the high-temperature molten salt during the molten salt circulation process and remove calcium and / or magnesium ion impurities therein.

[0007] In one embodiment, the location of the reactor in the connecting pipeline between the heating device and the heat exchanger includes: A reactor is installed in the pipeline section between the heating device and the high-temperature molten salt storage tank; and / or, A reactor is installed in the pipeline section between the high-temperature molten salt storage tank and the heat exchanger.

[0008] In one embodiment, the molten salt is a nitrate mixture containing potassium nitrate and sodium nitrate.

[0009] In one embodiment, the calcium and magnesium removal agent comprises a silicon dioxide-containing material.

[0010] In one embodiment, the amount of the calcium and magnesium removal reagent added is 3 to 10 times the total mass of calcium and magnesium impurities contained in the molten salt, wherein the mass of the calcium and magnesium impurities is calculated as calcium nitrate and magnesium nitrate, respectively.

[0011] In one embodiment, the particle size of the silica-containing material is 5-100 mm; and / or, The silica-containing material contains at least 90% silica by mass; and / or, The silicon dioxide-containing material is quartz.

[0012] In one embodiment, the reactor is provided with a replaceable component for containing the calcium and magnesium removal reagent.

[0013] In one embodiment, the molten salt thermal storage system for online removal of calcium and magnesium impurities from molten salt further includes a gas supply system connected to the reactor for introducing inert gas into the reactor and carrying out the gas generated by the reaction of the calcium and magnesium removal reagent with the calcium and magnesium impurities out of the reactor.

[0014] This invention proposes a method for online removal of calcium and magnesium impurities from molten salt. The method utilizes the molten salt thermal storage system described in the aforementioned technical solution to remove calcium and magnesium impurities from molten salt. The method includes the following steps: The online molten salt thermal storage system for removing calcium and magnesium impurities from molten salt is activated, allowing the molten salt to circulate through the reactor.

[0015] In one embodiment, the step of activating the online molten salt thermal storage system for removing calcium and magnesium impurities from the molten salt, and circulating the molten salt through the reactor, includes: Turn on the online molten salt thermal storage system for removing calcium and magnesium impurities from the molten salt, and allow the molten salt to circulate through the reactor; Turn on the gas supply system and introduce inert gas into the reactor.

[0016] The technical solution of this invention achieves online removal of calcium and / or magnesium ion impurities from molten salt by setting a reactor in the connecting pipeline between the heating device and the heat exchanger, specifically in the pipeline between the heating device and the high-temperature molten salt storage tank, or between the high-temperature molten salt storage tank and the heat exchanger. During molten salt circulation, the calcium and magnesium removal reagent selectively reacts with or adsorbs magnesium and calcium ions in the high-temperature molten salt, while reacting minimally with the molten salt itself. This achieves the goal of online removal of calcium and magnesium ion impurities from the molten salt, effectively suppressing tank corrosion caused by these impurities and improving the operational safety and service life of the molten salt thermal storage system. After three months of operation, the calcium and magnesium ion content in the molten salt was below 0.01%, with a removal rate exceeding 99%. After one year of operation, the calcium and magnesium content remained below 0.01%, and no significant corrosion was observed in the storage tank. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0018] Figure 1 A schematic diagram of an embodiment of the molten salt thermal storage system for online removal of calcium and magnesium impurities from molten salt provided by the present invention; Figure 2 This is a schematic diagram of yet another embodiment of the molten salt thermal storage system for online removal of calcium and magnesium impurities from molten salt provided by the present invention; Figure 3 This is a schematic diagram of a reactor for online removal of calcium and magnesium impurities from molten salt, as provided by the present invention.

[0019] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0022] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0023] Binary mixed molten salt (commonly known as "solar salt") composed of 60 wt% sodium nitrate (NaNO3) and 40 wt% potassium nitrate (KNO3) has become the mainstream thermal storage medium, accounting for over 80% of commercial solar thermal power plants, due to its wide temperature range, low melting point, and high thermal stability. However, the purity of commercial-grade solar salt used in actual projects is usually only around 99%, with residual impurities mainly being magnesium nitrate (0.5%~1.2% Mg(NO3)2) and calcium nitrate (0.1%~0.3% Ca(NO3)2). Especially in salt lake-rich areas such as Qinghai in my country, the magnesium ion concentration in the raw materials is extremely high, and the magnesium impurity content in the purified sodium nitrate and potassium nitrate can reach 0.8%~2.5%.

[0024] Although calcium nitrate and magnesium nitrate constitute a relatively small proportion of solar salt, they pose a serious threat to the long-term safe operation of molten salt thermal storage systems. Thermodynamic analysis, as detailed in Table 1, shows that within the normal operating temperature range of solar salt (290~600℃), pure NaNO3 and KNO3 are relatively inert, and their Gibbs free energy for corrosion reactions with carbon steel or stainless steel tank materials is greater than zero, theoretically indicating no tendency for spontaneous corrosion. However, the thermal stability of magnesium nitrate and calcium nitrate is significantly lower than that of the main salt components: when the temperature exceeds 400℃, magnesium nitrate begins to thermally decompose, producing magnesium oxide (MgO) and highly oxidizing nitrogen dioxide (NO2) and oxygen (O2); although calcium nitrate thermodynamically decomposes significantly above 700℃, its decomposition temperature can be significantly reduced in actual tank atmospheres due to factors such as low NO2 partial pressure and local activity variations. On the one hand, both NO2 and oxygen O2 can react with steel storage tanks to cause oxidation corrosion. On the other hand, the generated MgO and CaO have extremely strong water absorption properties and readily absorb moisture from the air to form magnesium hydroxide and calcium hydroxide. Under high temperature conditions, these hydroxides can further react with the storage tank to regenerate oxides and release water vapor, thus forming a cycle of "water absorption - corrosion - oxide regeneration". This makes the oxides essentially act as catalysts that continuously promote corrosion.

[0025] Table 1 Gibbs free energy of decomposition only of NaNO3, KNO3, Mg(NO3)2 and Ca(NO3)2

[0026] Currently, the removal of calcium and magnesium impurities from molten salt mainly relies on upstream raw material purification processes, such as recrystallization, solvent extraction, or ion exchange. However, these methods are costly, complex, and difficult to completely eliminate trace impurities. More importantly, existing molten salt thermal storage systems generally lack the ability to purify the molten salt injected into the system online during operation. Once impurities enter the circulation loop with the molten salt, their decomposition products will continue to accumulate, leading to irreversible corrosion of critical equipment such as storage tanks, pipelines, and heat exchangers, severely shortening system lifespan, and even causing safety accidents such as leaks. Therefore, there is an urgent need to develop a technical solution that can remove calcium and magnesium impurities in real time, efficiently, and safely under normal operating conditions of molten salt thermal storage systems, in order to inhibit the generation of corrosive gases from the source and ensure the long-term stable operation of the system. However, no effective solution has yet been found in the existing technology that integrates impurity removal functionality into the molten salt circulation pipeline to achieve "online purification."

[0027] Based on the above background, please refer to Figure 1 and Figure 2This invention proposes an online molten salt thermal storage system for removing calcium and magnesium impurities from molten salt, comprising a low-temperature molten salt storage tank, a heating device, a high-temperature molten salt storage tank, and a heat exchanger connected in sequence by a connecting pipeline, wherein the heat exchanger and the low-temperature molten salt storage tank are connected by a connecting pipeline to form a circulation pipeline. At least one reactor is provided in the connecting pipeline between the heating device and the heat exchanger. The reactor is equipped with a calcium and magnesium removal reagent, which is used to contact the high-temperature molten salt during the molten salt circulation process and remove calcium and / or magnesium ion impurities therein.

[0028] The technical solution of this invention achieves online removal of calcium and / or magnesium ion impurities from molten salt by setting a reactor in the connecting pipeline between the heating device and the heat exchanger, specifically in the pipeline between the heating device and the high-temperature molten salt storage tank, or between the high-temperature molten salt storage tank and the heat exchanger. During molten salt circulation, the calcium and magnesium removal reagent selectively reacts with or adsorbs magnesium and calcium ions in the high-temperature molten salt, while essentially not reacting with the molten salt bulk, thereby achieving online removal of calcium and magnesium ion impurities from the molten salt. This effectively suppresses tank corrosion caused by magnesium and calcium ion impurities, improving the operational safety and service life of the molten salt thermal storage system. After three months of operation, the calcium and magnesium ion content in the molten salt was below 0.01%, with a removal rate exceeding 99%; after one year of operation, the calcium and magnesium content remained below 0.01%, and no significant corrosion was observed in the storage tank.

[0029] It should be noted that the provision of at least one reactor in the connecting pipeline between the heating device and the heat exchanger means that only one reactor or multiple reactors can be installed in the connecting pipeline between the heating device and the heat exchanger, both of which are within the scope of protection of this invention. For example, in one embodiment of this invention, only one reactor is installed in the connecting pipeline between the heating device and the heat exchanger, and the amount of calcium and magnesium removal reagent used in the reactor is controlled to balance the effectiveness of removing calcium and magnesium impurities with the modification cost.

[0030] It should be noted that the technical solution of this invention does not impose specific limitations on the material of the reactor, as long as the reactor can ensure that the solar salt is within the normal operating temperature range. For example, the same material as the high-temperature molten salt storage tank can be used. The technical solution of this invention also does not limit the way the calcium and magnesium removal reagent is placed in the reactor, as long as the calcium and magnesium removal reagent is fixed in the reactor and does not flow out with the molten salt. For example, please refer to [link to relevant documentation]. Figure 3In one embodiment of the present invention, the reactor has a containment cavity for accommodating the calcium and magnesium removal reagent, which is contained within the containment cavity and does not flow out with the molten salt. When the molten salt flows through the reactor, impurities selectively react with the calcium and magnesium removal reagent components in the reactor containment cavity to generate solid calcium / magnesium silicates, which are then fixed within the reactor, thereby enabling the outflowing molten salt to remove calcium and magnesium impurities online.

[0031] In embodiments of the present invention, the location of the reactor in the connecting pipeline between the heating device and the heat exchanger includes: A reactor is installed in the pipeline section between the heating device and the high-temperature molten salt storage tank; and / or, A reactor is installed in the pipeline section between the high-temperature molten salt storage tank and the heat exchanger.

[0032] Using the technical solution of this invention, the reactor can be placed in the pipeline section between the heating device and the high-temperature molten salt storage tank, or in the pipeline section between the high-temperature molten salt storage tank and the heat exchanger, or simultaneously in both pipeline sections. When the reactor is placed in these pipeline sections, the molten salt is at a high temperature. At this high temperature, the calcium and magnesium removal reagent can selectively react with or adsorb magnesium and calcium ions in the high-temperature molten salt, while essentially not reacting with the bulk molten salt. This achieves the purpose of online removal of magnesium and calcium ions from the molten salt, effectively suppressing tank corrosion caused by magnesium and calcium ion impurities.

[0033] In embodiments of the present invention, the molten salt is a nitrate mixture comprising potassium nitrate and sodium nitrate. The molten salt can be exemplary, for example, solar salt (60wt% NaNO3 + 40wt% KNO3).

[0034] In embodiments of the present invention, the molten salt is a nitrate mixture containing potassium nitrate and sodium nitrate, and the calcium and magnesium removal agent comprises a silicon dioxide-containing material.

[0035] Thermodynamic calculations show that, at the same temperature, the Gibbs free energy of the reaction between calcium nitrate / magnesium nitrate and silicon dioxide (SiO2) is much negative than the Gibbs free energy of the decomposition of calcium nitrate / magnesium nitrate alone. The specific Gibbs free energies of the reaction are shown in Table 2.

[0036] Table 2. Gibbs free energies for the decomposition of Mg(NO3)2 and Ca(NO3)2 alone, and for the reactions of Mg(NO3)2, Ca(NO3)2, KNO3, and NaNO3 with SiO2.

[0037] Based on the Gibbs free energy in Table 2, it can be seen that calcium nitrate and magnesium nitrate react more readily with SiO2 in the presence of SiO2. Therefore, the technical solution of this invention, by setting up a reactor containing silica material, allows calcium nitrate and magnesium nitrate impurities in the molten salt to preferentially react with SiO2 in the calcium and magnesium removal reagent during the flow of high-temperature molten salt, generating NO2, O2, and insoluble calcium / magnesium silicate, while hardly reacting with the molten salt matrix (NaNO3+KNO3). Furthermore, the generated calcium / magnesium silicate adheres to the surface of the calcium / magnesium removal reagent particles and does not enter the molten salt matrix, thereby achieving the purpose of online removal of calcium and magnesium ion impurities from the molten salt.

[0038] In an embodiment of the present invention, the molten salt is a nitrate mixture containing potassium nitrate and sodium nitrate, and the amount of calcium and magnesium removal reagent added is 3 to 10 times the total mass of calcium and magnesium impurities contained in the molten salt, wherein the mass of the calcium and magnesium impurities is calculated as calcium nitrate (Ca(NO3)2) and magnesium nitrate (Mg(NO3)2), respectively.

[0039] In embodiments of the present invention, the particle size of the silica-containing material is 5-100 mm. Exemplarily, silica-containing materials with particle sizes of 5 mm, 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm, or 100 mm can be selected. Using silica-containing materials within the above particle size range as calcium and magnesium removal agents results in finer particle sizes, larger specific surface areas, and exposed surface active sites, which is beneficial for promoting the reaction between silica and calcium and magnesium ion impurities in the molten salt. Preferably, the particle size of the silica-containing material is 5-50 mm.

[0040] In embodiments of the present invention, the mass percentage of silicon dioxide in the silicon dioxide-containing material is not less than 90%. This setting is beneficial to accelerating the reaction rate between SiO2 and calcium and magnesium ion impurities in the molten salt.

[0041] In embodiments of the present invention, the silica-containing material is quartz. When the molten salt is a mixture of nitrates containing potassium nitrate and sodium nitrate, quartz is chosen as the calcium and magnesium impurity remover. This material is abundant, inexpensive, and helps control costs, and is easy to process into the desired particle size. Furthermore, natural quartz (especially high-purity quartz sand) can achieve a SiO2 content of over 99%, with extremely low impurity content, thus avoiding the introduction of new impurities.

[0042] In an embodiment of the invention, the reactor is equipped with a replaceable component for containing the calcium and magnesium removal reagent. After the molten salt thermal storage system is operational, during the molten salt circulation process, the calcium and magnesium removal reagent selectively reacts with or adsorbs magnesium and calcium ions in the high-temperature molten salt, while reacting almost entirely with the molten salt matrix (NaNO3 + KNO3). The generated calcium silicate / magnesium silicate adheres to the surface of the calcium and magnesium removal reagent particles and does not enter the molten salt matrix. Because the reactor is replaceable, the calcium and magnesium removal reagent can be easily removed from the reactor, achieving the purpose of removing magnesium and calcium ions from the molten salt. Furthermore, by making the reactor replaceable, the amount of calcium and magnesium removal reagent particles in the reactor can be easily adjusted according to the impurity detection results of the molten salt during actual operation.

[0043] In an embodiment of the present invention, the molten salt thermal storage system for online removal of calcium and magnesium impurities from molten salt further includes a gas supply system. The gas supply system is connected to the reactor and is used to introduce an inert gas into the reactor, carrying away the gas generated by the reaction of the calcium and magnesium removal reagent with the calcium and magnesium impurities. The reaction of the calcium and magnesium removal reagent with the calcium and magnesium impurities produces NO2 and O2. Both NO2 and O2 can react with steel storage tanks to cause oxidation corrosion. By introducing an inert gas (such as nitrogen) into the reactor, the NO2 and O2 generated in the reactor can be removed, reducing the oxidation corrosion problem of the storage tank.

[0044] This invention proposes a method for online removal of calcium and magnesium impurities from molten salt. The method utilizes the molten salt thermal storage system described in the aforementioned technical solution to remove calcium and magnesium impurities from molten salt. The method includes the following steps: The online molten salt thermal storage system for removing calcium and magnesium impurities from molten salt is activated, allowing the molten salt to circulate through the reactor.

[0045] The method for removing calcium and magnesium impurities from molten salt online, as provided by this invention, allows molten salt to circulate through the reactor during the operation of the molten salt thermal storage system. The calcium and magnesium impurities in the reactor react with the calcium and magnesium ions in the molten salt. After a period of molten salt circulation, the calcium and magnesium ion impurities in the molten salt can be effectively removed, reducing the oxidation and corrosion problems of the storage tank.

[0046] In an embodiment of the present invention, the step of activating the online molten salt thermal storage system for removing calcium and magnesium impurities from the molten salt and circulating the molten salt through the reactor includes: Turn on the online molten salt thermal storage system for removing calcium and magnesium impurities from the molten salt, and allow the molten salt to circulate through the reactor; Turn on the gas supply system and introduce inert gas into the reactor.

[0047] Using the above technical solution, during the operation of the molten salt thermal storage system, molten salt circulates through the reactor. Calcium and magnesium ion impurities in the molten salt react with the calcium and magnesium removal reagent. The resulting solid products adhere to the surface of the reagent, while the generated NO2 and O2 gases are discharged with the inert gas. Compared to molten salt thermal storage systems without inert gas, introducing inert gas helps to further improve the oxidation and corrosion problems of the molten salt thermal storage system.

[0048] The technical solution of the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0049] Example 1 A method for removing calcium and magnesium impurities from molten salt online, employing the following molten salt thermal storage system (e.g.) Figure 1 The molten salt thermal storage system includes a low-temperature molten salt storage tank, a heating device, a high-temperature molten salt storage tank, a reactor, and a heat exchanger, which are connected in sequence via connecting pipelines. The heat exchanger is connected to the low-temperature molten salt storage tank to form a circulation pipeline. All tanks and pipelines in the system are made of 347H stainless steel. The molten salt thermal storage system uses solar salt (NaNO3-KNO3) as the thermal storage medium, and its operating temperature is between 290℃ and 580℃. The amount of molten salt used in the system is 5000t, and the total content of calcium and magnesium impurities (calcium nitrate and magnesium nitrate) in the molten salt (i.e., the sum of the mass percentages of calcium nitrate and magnesium nitrate in the molten salt based on the total mass of the molten salt) is measured to be 0.9%. The reactor is equipped with a calcium and magnesium removal reagent, the amount of which is 4.5% of the total mass of the molten salt, and the calcium and magnesium removal reagent is made of quartz particles (10 mm in diameter) with a silica content of not less than 99.9%. The method for removing calcium and magnesium impurities from molten salt online includes the following steps: (1) Start the online molten salt heat storage system for removing calcium and magnesium impurities from molten salt, so that the molten salt circulates through the reactor and the temperature of the molten salt in the reactor pipeline section is about 560°C; (2) Turn on the gas supply system and introduce nitrogen into the reactor.

[0050] Results: After three months of operation, tests on the impurity content of the molten salt revealed that the calcium and magnesium ion content was below 0.01%, with a removal rate exceeding 98%. After one year of operation, the total calcium and magnesium ion content in the molten salt was below 0.01%, and no significant corrosion was observed in the storage tank.

[0051] Example 2 Compared to Example 1, the difference lies in that before operating the system, the total content of calcium and magnesium impurities (calcium nitrate and magnesium nitrate) in the molten salt is 1%, and the mass of quartz particles in the reactor is 6% of the mass of the molten salt. During the molten salt circulation process, the temperature of the molten salt flowing through the reactor is approximately 550°C.

[0052] Results: After three months of operation, tests on the impurity content of the molten salt revealed that the calcium and magnesium ion content was below 0.01%, with a removal rate exceeding 99%. After one year of operation, the total calcium and magnesium ion content in the molten salt was below 0.01%, and no significant corrosion was observed in the storage tank.

[0053] Example 3 Compared to Example 1, the difference lies in that before operating the system, the total content of calcium and magnesium impurities (calcium nitrate and magnesium nitrate) in the molten salt was 1.2%, and the mass of quartz particles in the reactor was 5% of the mass of the molten salt. During the molten salt circulation process, the temperature of the molten salt flowing through the reactor was approximately 560°C.

[0054] Results: After three months of operation, tests on the impurity content of the molten salt revealed that the calcium and magnesium ion content was below 0.01%, with a removal rate exceeding 99%. After one year of operation, the total calcium and magnesium ion content in the molten salt was below 0.01%, and no significant corrosion was observed in the storage tank.

[0055] Example 4 Compared to Example 3, the difference is that the step of introducing nitrogen gas into the reactor is omitted.

[0056] Results: After three months of operation, the impurity content of the molten salt was tested and found that the calcium and magnesium ion content in the molten salt was less than 0.01%, but the reactor containing quartz showed slight corrosion.

[0057] Example 5 Compared to Example 1, the difference lies in that the reactor is located in the pipeline section between the heating device and the high-temperature molten salt storage tank, and the molten salt thermal storage system is as follows: Figure 2 As shown.

[0058] Results: After three months of operation, tests on the impurity content of the molten salt revealed that the calcium and magnesium ion content was below 0.01%, with a removal rate exceeding 98%. After one year of operation, the total calcium and magnesium ion content in the molten salt was below 0.01%, and no significant corrosion was observed in the storage tank.

[0059] Example 6 The difference from Example 1 is that the quartz particles in the reactor have a particle size of 50 mm.

[0060] Results: After three months of operation, tests on the impurity content of the molten salt revealed that the calcium and magnesium ion content was below 0.01%, with a removal rate exceeding 98%. After one year of operation, the total calcium and magnesium ion content in the molten salt was below 0.01%, and no significant corrosion was observed in the storage tank.

[0061] Example 7 Compared to Example 1, the difference lies in that the total content of calcium and magnesium impurities (calcium nitrate and magnesium nitrate) in the molten salt before system operation is 1%; the particle size of the quartz particles in the reactor is 110 mm. During the molten salt circulation process, the temperature of the molten salt flowing through the reactor is approximately 550°C.

[0062] Results: After 3 months of operation, the impurity content of the molten salt was tested and found to be approximately 0.4%, with a removal rate of 60%. After one year of operation, the total calcium and magnesium ion content was 0.2%, and slight corrosion appeared in the storage tank.

[0063] Comparative Example 1 Compared to Example 1, the difference is that the reactor of the provided molten salt thermal storage system does not contain quartz particles; the gaseous components in the reactor are removed only by introducing nitrogen into the reactor.

[0064] Results: After three months of operation, tests on the impurity content of the molten salt revealed that the total calcium and magnesium ion content was approximately 0.9%, showing no significant change. After one year of operation, the storage tank exhibited significant corrosion.

[0065] The above description is merely an exemplary embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention specification and drawings under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A molten salt thermal storage system for online removal of calcium and magnesium impurities from molten salt, characterized in that, It includes a low-temperature molten salt storage tank, a heating device, a high-temperature molten salt storage tank, and a heat exchanger connected in sequence through a connecting pipeline, and the heat exchanger is connected to the low-temperature molten salt storage tank through a connecting pipeline to form a circulation pipeline; At least one reactor is provided in the connecting pipeline between the heating device and the heat exchanger. The reactor is equipped with a calcium and magnesium removal reagent, which is used to contact the high-temperature molten salt during the molten salt circulation process and remove calcium and / or magnesium ion impurities therein.

2. The molten salt thermal storage system for online removal of calcium and magnesium impurities from molten salt as described in claim 1, characterized in that, The location of the reactor in the connecting pipeline between the heating device and the heat exchanger includes: A reactor is installed in the pipeline section between the heating device and the high-temperature molten salt storage tank; and / or, A reactor is installed in the pipeline section between the high-temperature molten salt storage tank and the heat exchanger.

3. The molten salt thermal storage system for online removal of calcium and magnesium impurities from molten salt as described in claim 1, characterized in that, The molten salt is a mixture of nitrates containing potassium nitrate and sodium nitrate.

4. The molten salt thermal storage system for online removal of calcium and magnesium impurities from molten salt as described in claim 3, wherein the calcium and magnesium removal reagent comprises a material containing silicon dioxide.

5. The molten salt thermal storage system for online removal of calcium and magnesium impurities from molten salt as described in claim 3, characterized in that, The amount of the calcium and magnesium removal reagent added is 3 to 10 times the total mass of calcium and magnesium impurities contained in the molten salt, wherein the mass of the calcium and magnesium impurities is calculated as calcium nitrate and magnesium nitrate, respectively.

6. The molten salt thermal storage system for online removal of calcium and magnesium impurities from molten salt as described in claim 4, characterized in that, The silica-containing material has a particle size of 5-100 mm; and / or, The silica-containing material contains at least 90% silica by mass; and / or, The silicon dioxide-containing material is quartz.

7. The molten salt thermal storage system for online removal of calcium and magnesium impurities from molten salt as described in claim 1, characterized in that, The reactor is equipped with replaceable components for containing the calcium and magnesium removal reagent.

8. The molten salt thermal storage system for online removal of calcium and magnesium impurities from molten salt as described in claim 1, characterized in that, It also includes a gas supply system, which is connected to the reactor and is used to introduce inert gas into the reactor and carry out the gas generated by the reaction of the calcium and magnesium removal reagent with calcium and magnesium impurities out of the reactor.

9. A method for removing calcium and magnesium impurities from molten salt online, characterized in that, The method for removing calcium and magnesium impurities from molten salt using the online removal system for molten salt according to any one of claims 1 to 8 includes the following steps: The online molten salt thermal storage system for removing calcium and magnesium impurities from molten salt is activated, allowing the molten salt to circulate through the reactor.

10. The method for online removal of calcium and magnesium impurities from molten salt as described in claim 9, characterized in that, The step of activating the online molten salt thermal storage system for removing calcium and magnesium impurities from the molten salt and circulating the molten salt through the reactor includes: Turn on the online molten salt thermal storage system for removing calcium and magnesium impurities from the molten salt, and allow the molten salt to circulate through the reactor; Turn on the gas supply system and introduce inert gas into the reactor.

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