A dual-tank molten salt energy storage nitrogen sealing system and a method for operating the same

Abstract

The application belongs to the technical field of fused salt energy storage, and specifically discloses a double-tank fused salt energy storage nitrogen sealing system and an operation method thereof, which comprises: a fused salt storage tank unit, including a low-temperature fused salt storage tank for storing low-temperature fused salt and a high-temperature fused salt storage tank for storing high-temperature fused salt, and the low-temperature fused salt storage tank and the high-temperature fused salt storage tank are both provided with a gas phase pressure monitoring device, an automatic exhaust pipeline and a manual exhaust pipeline; a nitrogen sealing unit, including a nitrogen preparation device, a nitrogen buffer device and a nitrogen supplement pipeline; a double-tank gas phase balance unit, including a gas phase balance pipeline and a temperature control device, the gas phase balance pipeline connects the gas phase zones of the low-temperature fused salt storage tank and the high-temperature fused salt storage tank, and the temperature control device is used for adjusting the temperature of the flowing gas between the two tanks. The application can ensure the pressure balance of the double tanks, inhibit the oxidation and deterioration of the fused salt, realize the recycling of nitrogen, avoid the temperature abnormality problem caused by the direct entry of high-temperature nitrogen into the low-temperature storage tank, and improve the safety of the fused salt storage tank.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of molten salt energy storage, in particular to a double-tank molten salt energy storage nitrogen sealing system and an operation method thereof. BACKGROUND

[0002] Wind power and photovoltaic power generation have great volatility and instability. With large-scale grid connection of wind and solar renewable energy power generation in China, the daily operation of the power grid has been greatly impacted. In order to ensure the safe and stable operation of the power grid, more and stronger peak shaving and frequency modulation capabilities are required from thermal power units. Now the relevant departments have put forward higher and more stringent index requirements for the minimum power output, load change rate, start-stop peak shaving, coal consumption, etc. of coal-fired units. At present, thermal power units are gradually changing from traditional main power sources to basic and regulating power sources that bear the bottom supply and peak shaving and frequency modulation functions for the power system.

[0003] Molten salt energy storage uses molten salt as the energy storage medium. Currently, a double-tank system is commonly used in engineering applications, i.e., two molten salt storage tanks are set, one at low temperature and the other at high temperature. The low-temperature tank is at 160-200℃, and the high-temperature tank is at 350-420℃. Molten salt energy storage has many advantages such as strong peak shaving capability, suitability for large-scale application, long service life, economic benefits, safety and environmental protection, and low cost, and is an economic and feasible technical approach to greatly improving the deep peak shaving and frequency modulation capability of coal-fired units. It has a broad market application prospect, and currently extensive technical research and engineering application demonstration are being conducted on molten salt energy storage coupled with coal-fired units in China. The commonly used commercial molten salts are solar salt (binary salt, 40% KNO3-60% NaNO3) and Hitec molten salt (ternary salt, 53% KNO3-7% NaNO3-40% NaNO2), both of which are relatively mature nitrate systems. The binary salt has relatively stable chemical properties, and the molten salt storage tank does not need special nitrogen sealing. The ternary salt has a lower melting point than the binary salt and is more commonly used in molten salt energy storage of coal-fired units. Since the ternary salt contains a large amount of sodium nitrite, if not sealed with nitrogen, a large amount of air will exist in the gas phase zone of the storage tank. The air contains oxygen, and the sodium nitrite in the ternary salt is easily oxidized to form sodium nitrate in a molten state for a long time in contact with air, which causes the binary molten salt to deteriorate, thereby affecting the heat storage performance and safe and stable operation of the entire energy storage system.

[0004] A Chinese patent with publication number CN120140968A discloses a molten salt energy storage system with a seal, which is provided with a set of nitrogen supply devices for conveying nitrogen to high-temperature molten salt storage tanks and low-temperature molten salt storage tanks. The top gas phase zones of the high-temperature molten salt storage tanks and the low-temperature molten salt storage tanks are connected by a balance pipeline. In the molten salt heat storage mode, low-temperature molten salt is pumped from the low-temperature molten salt storage tank, heated by electric heating or steam heating, and then sent into the high-temperature molten salt storage tank. The molten salt level in the high-temperature molten salt storage tank gradually rises, and the gas phase volume correspondingly decreases, causing the nitrogen pressure in the gas phase zone to increase. On the contrary, the molten salt level in the low-temperature molten salt storage tank gradually decreases, and the nitrogen pressure decreases accordingly. As a result, the nitrogen pressure in the gas phase zone of the high-temperature molten salt storage tank is higher than that in the gas phase zone of the low-temperature molten salt storage tank, and the nitrogen in the high-temperature molten salt storage tank flows into the low-temperature molten salt storage tank through the balance pipeline. Since the working temperature of the high-temperature molten salt storage tank is much higher than that of the low-temperature molten salt storage tank, the nitrogen temperature in the gas phase zone of the former is also much higher than that of the latter. The high-temperature nitrogen from the high-temperature molten salt storage tank entering the low-temperature molten salt storage tank will cause the nitrogen temperature in the gas phase zone of the low-temperature molten salt storage tank to slowly rise, and there will be a local high-temperature zone at the gas inlet of the low-temperature molten salt storage tank. The long-term direct contact between the gas and the liquid in the tank will even further cause the molten salt temperature in the low-temperature molten salt storage tank to gradually increase, which will have two serious consequences:

[0005] First, the working temperature of the low-temperature molten salt storage tank will increase, which will require the design temperature of the tank to be increased synchronously, and thus a material with a higher temperature resistance will be required for the tank, which will inevitably increase the cost of the low-temperature molten salt storage tank. At the same time, the increase in temperature may accelerate the aging of the sealing elements of the tank and increase the thermal stress of the tank, reducing the safety of the system operation. Second, the reduction of the working temperature difference between the high-temperature molten salt and the low-temperature molten salt will reduce the heat storage efficiency of the system to some extent. The increase in the molten salt temperature in the low-temperature storage tank will reduce the temperature difference (i.e., the heat storage temperature difference) of the molten salt in the "low-temperature-high-temperature" cycle, directly reducing the heat storage density of the system. If the molten salt temperature is higher than the design value for a long time, it may also exacerbate the corrosion reaction between the molten salt and the inner wall of the tank, shorten the service life of the molten salt and the maintenance cycle of the tank, and further increase the operation and maintenance cost of the system. SUMMARY

[0006] The present application provides a dual-tank molten salt energy storage nitrogen sealing system, which aims to ensure pressure balance between the two tanks while avoiding the temperature abnormality problem caused by the direct entry of high-temperature nitrogen into the low-temperature storage tank, thereby improving the safety of the molten salt storage tank.

[0007] The present application is implemented by the following technical solution: a dual-tank molten salt energy storage nitrogen sealing system, comprising:

[0008] The molten salt storage tank unit comprises a low-temperature molten salt storage tank for storing low-temperature molten salt and a high-temperature molten salt storage tank for storing high-temperature molten salt, and the low-temperature molten salt storage tank and the high-temperature molten salt storage tank are each provided with a gas phase pressure monitoring device, an automatic exhaust pipeline and a manual exhaust pipeline;

[0009] The nitrogen sealing unit comprises a nitrogen preparation device, a nitrogen buffer device and a nitrogen supplement pipeline, the nitrogen preparation device is communicated with the nitrogen buffer device, the nitrogen buffer device is connected to the top gas phase area of the low-temperature molten salt storage tank and the high-temperature molten salt storage tank through the nitrogen supplement pipeline, and a valve assembly controlled in linkage with the gas phase pressure monitoring device is arranged on the nitrogen supplement pipeline;

[0010] The double-tank gas phase balance unit comprises a gas phase balance pipeline and a temperature control device, the gas phase balance pipeline communicates the gas phase areas of the low-temperature molten salt storage tank and the high-temperature molten salt storage tank, and the temperature control device is arranged on the main pipeline of the flow path of the gas phase balance pipeline and used for adjusting the temperature of the flowing gas between the two tanks.

[0011] Compared with the prior art, the scheme has the following advantages and beneficial effects:

[0012] 1. In the scheme, the low-temperature molten salt storage tank and the high-temperature molten salt storage tank are provided with a nitrogen sealing system in the gas phase, which can inhibit the oxidation of ternary molten salt.

[0013] 2. In the scheme, the low-temperature molten salt storage tank and the high-temperature molten salt storage tank are each provided with a gas phase pressure monitoring device, when the monitoring value is lower than the set threshold value, the linkage valve assembly on the nitrogen supplement pipeline is automatically opened, nitrogen is supplemented to the gas phase area of the storage tank through the nitrogen buffer device, and the storage tank is always maintained in a slightly positive pressure state. The design can prevent the formation of negative pressure due to the excessively low gas phase pressure caused by the change of the molten salt liquid level (such as the decrease of the molten salt in the low-temperature tank during heat storage and the decrease of the molten salt in the high-temperature tank during heat release), thereby avoiding the leakage of external air into the storage tank and the reaction (such as the oxidation of molten salt and the mixing of impurities affecting the heat transfer efficiency) of the molten salt with the leaked air, and preventing the risk of the collapse of the wall structure of the storage tank caused by negative pressure, so that the molten salt storage tank has higher safety. While ensuring the pressure balance of the double tanks, the scheme can effectively avoid the temperature abnormality problem caused by the direct entry of high-temperature nitrogen into the low-temperature storage tank, and improve the safety of the molten salt storage tank.

[0014] 3. When the gas phase pressure monitoring device detects that the pressure of the storage tank reaches the upper threshold value, the linkage valve assembly automatically closes the nitrogen supplement, so as to avoid the continuous increase of the pressure; at the same time, the automatic exhaust pipeline provided in the system can be opened to release pressure when the pressure exceeds the limit, and the manual exhaust pipeline serves as an emergency backup, thereby forming double overpressure protection of “automatic prevention and control + manual bottom-up”, which prevents the mechanical damage of the storage tank body, the flange sealing surface and other components caused by excessively high pressure, and prolongs the service life of the storage tank.

[0015] The automatic exhaust pipeline can cope with the normal overpressure scene in daily operation, and the manual exhaust pipeline is used when the automatic system fails (such as valve jamming, sensor abnormality), to avoid the safety risk caused by the failure of a single exhaust path and improve the safety redundancy of the system under extreme working conditions.

[0016] 4. In addition, the gas phase balance pipeline of the double-tank gas phase balance unit connects the gas phase zones of the two tanks. When the system stores or releases heat, causing the liquid level of the molten salt in the two tanks to change, such as when storing heat, the high-temperature tank molten salt increases, the gas phase pressure rises, the low-temperature tank molten salt decreases, and the gas phase pressure decreases. The gas phase nitrogen in the high-pressure side storage tank can flow to the low-pressure side storage tank through the gas phase balance pipeline, achieving dynamic pressure balance of the two tanks. This process does not require additional nitrogen to maintain stable pressure in the two tanks, and the nitrogen in the low-temperature molten salt storage tank and the high-temperature molten salt storage tank can be recycled, greatly reducing the amount of nitrogen used, avoiding the repeated consumption of nitrogen caused by "two tanks each nitrogen" in traditional systems, and reducing the amount of nitrogen used from the source.

[0017] 5. The valve assembly of the nitrogen supplement pipeline is interlocked with the gas phase pressure monitoring device, and nitrogen supplement is started only when the pressure of both tanks is below the threshold value (i.e. after balancing, it is still not possible to maintain a slight positive pressure). The nitrogen buffer device can stabilize the nitrogen output pressure, avoid frequent start-stop or excessive nitrogen supply of the nitrogen preparation device, further reduce the energy consumption and nitrogen waste of the nitrogen preparation device, and significantly reduce the nitrogen procurement and energy consumption costs of the system in the long run.

[0018] 6. In this scheme, under the heat storage working condition, the high-temperature gas phase nitrogen in the high-temperature molten salt storage tank flows to the low-temperature molten salt storage tank, and needs to pass through the temperature regulation device (such as a solid heat accumulator) on the gas phase connection main pipeline. The device can absorb the excess heat of the high-temperature nitrogen, avoiding the direct entry of high-temperature gas into the low-temperature tank and the formation of a large temperature difference between the low-temperature molten salt, reducing the invalid heat loss caused by "high-temperature gas phase heating low-temperature molten salt" in the low-temperature tank; under the heat release working condition, the low-temperature gas phase nitrogen in the low-temperature tank flows to the high-temperature tank, and the temperature regulation device releases the stored heat to preheat the low-temperature gas, avoiding the direct entry of low-temperature gas into the high-temperature tank and the formation of a large temperature difference between the high-temperature molten salt, reducing the energy loss of "low-temperature gas phase cooling high-temperature molten salt" in the high-temperature tank. That is, a temperature regulation device (such as a solid heat accumulator) is arranged on the gas phase balance pipeline, fully utilizing the working temperature difference of the nitrogen in the gas phase zones of the low-temperature molten salt storage tank and the high-temperature molten salt storage tank, and the nitrogen flowing through the solid heat accumulator is cyclically heated and cooled, without the need for additional heat sources or cold sources, to solve the temperature regulation problem of the nitrogen flowing back and forth between the two storage tanks.

[0019] Temperature fluctuations that are too large can cause local crystallization and decomposition of the molten salt, affecting the heat transfer and heat storage performance of the molten salt. The temperature regulation device stabilizes the temperature of the gas flowing between the two tanks, indirectly ensuring the uniformity of the molten salt temperature in the storage tank, avoiding the deterioration of the molten salt quality caused by abnormal gas temperature, and ensuring the stability of the heat efficiency of the system in long-term operation.

[0020] 7. Finally, the combination design of the nitrogen preparation device and the nitrogen buffer device in this scheme can avoid the pressure fluctuation of the nitrogen preparation device due to "instant nitrogen supplement demand": the nitrogen buffer device can store a certain amount of nitrogen, and when two tanks need to be quickly supplemented with nitrogen, nitrogen can be directly taken from the buffer device without waiting for the immediate output of the nitrogen preparation device, ensuring stable nitrogen supplement pressure and avoiding pressure fluctuations of the storage tank due to unstable nitrogen supply, making the molten salt storage tank more secure.

[0021] Further, it further comprises a storage tank preheating unit, which comprises a preheating fan, a preheating air heater, an in-tank gas discharge pipeline and a preheating gas supplement pipeline, the preheating fan and the in-tank gas discharge pipeline, preheating air heater, preheating gas supplement pipeline form a nitrogen internal circulation heating loop, which is used for preheating the low-temperature molten salt storage tank and the high-temperature molten salt storage tank before filling with molten salt.

[0022] Beneficial effect: After the high-temperature molten salt storage tank and the low-temperature molten salt storage tank are built and accepted, they need to be fully preheated before being filled with molten salt for the first time. If not preheated, directly filling with high-temperature molten salt can easily cause the molten salt to solidify, and the thermal shock and thermal stress generated by high-temperature molten salt on the tank body may cause damage to the tank body.

[0023] Further, the in-tank gas discharge pipeline comprises a first in-tank gas discharge pipeline and a second in-tank gas discharge pipeline which are in communication with each other, and the preheating gas supplement pipeline comprises a first preheating gas supplement pipeline and a second preheating gas supplement pipeline which are in communication with each other; one end of the first in-tank gas discharge pipeline and one end of the second in-tank gas discharge pipeline respectively extend into the lower part of the low-temperature molten salt storage tank and the high-temperature molten salt storage tank;

[0024] One end of the first preheating gas supplement pipeline and one end of the second preheating gas supplement pipeline respectively extend into the upper part of the low-temperature molten salt storage tank and the upper part of the high-temperature molten salt storage tank;

[0025] The preheating fan and the preheating air heater are connected in series on the in-tank gas discharge pipeline and the preheating gas supplement pipeline.

[0026] Beneficial effects: The first tank gas discharge pipeline extends into the lower part of the low-temperature molten salt storage tank, and the first preheating gas supplement pipeline extends into the upper part thereof. The second tank gas discharge pipeline and the second preheating gas supplement pipeline correspond to the same layout of the high-temperature molten salt storage tank. During preheating, the preheating fan extracts low-temperature nitrogen from the lower part of the storage tank (the lower part of the tank is prone to deposition due to high density, and the temperature is usually lower than that of the upper part), and after being heated into high-temperature nitrogen by the preheating air heater, the high-temperature nitrogen is supplemented from the upper part of the storage tank. The high-temperature nitrogen diffuses upward due to small density, gradually mixes with the low-temperature gas in the tank, and exchanges heat with the upper and middle regions of the tank wall. As the cycle progresses, the low-temperature gas in the lower part of the tank is continuously extracted and heated, forming a three-dimensional circulation path of cold extraction in the lower part, heat supplement in the upper part, and convection in the whole tank, completely eliminating the temperature dead angle (such as the bottom of the storage tank and the lower half of the tank wall, which are difficult to heat in the traditional layout) of the upper part of the tank wall, and meeting the strict requirements of molten salt filling on uniform preheating of the tank wall.

[0027] The lower space of the molten salt storage tank is close to the tank bottom (after subsequent molten salt filling, it is the molten salt liquid level area), and the upper part is the gas phase area. The lower part of the tank can directly bring the low-temperature nitrogen near the tank bottom into the heating circuit, avoiding the long-term existence of the low-temperature area at the tank bottom, which leads to insufficient thermal stress at the tank bottom. The upper part of the tank can make the high-temperature nitrogen exchange heat with the upper gas phase area of the tank wall first, and then diffuse downward, matching the operating state of the gas phase in the upper part and the liquid phase in the lower part of the storage tank, and laying a foundation for the temperature stability of the gas phase area after subsequent molten salt filling.

[0028] Further, the preheating fan is provided with at least two, and the two preheating fans are arranged in parallel with each other.

[0029] Beneficial effects: Two preheating fans are connected in parallel to form a one-for-one redundancy. When the main fan fails, it can be quickly switched to the standby fan to avoid temperature fluctuations in the tank wall caused by preheating interruption and ensure continuous and stable preheating.

[0030] Further, the automatic exhaust pipeline is provided with a normally open manual shut-off valve and an automatic exhaust valve. The normally open manual shut-off valve is kept open during normal system operation, and the automatic exhaust valve is automatically opened when the tank pressure reaches a set value. The manually operated exhaust pipeline is provided with a normally closed manual shut-off valve, which is kept closed during normal system operation.

[0031] Beneficial effects: The automatic exhaust valve of the automatic exhaust pipeline can automatically exhaust when the tank pressure is out of limit. The normally open manual shut-off valve is normally open to ensure the reliability of the automatic exhaust function, and can be manually cut off in an abnormal situation. The normally closed manual shut-off valve of the manual exhaust pipeline is normally closed to avoid misoperation. The double design covers both normal and extreme overpressure scenarios to prevent overpressure damage to the storage tank.

[0032] The normally open manual shutoff valve is normally open, which eliminates the risk of automatic exhalation valve failure caused by valve closure, ensures smooth automatic exhaust path when the pressure exceeds the limit in daily operation, and maintains stable pressure without manual intervention. The normally closed manual shutoff valve is normally closed, which avoids accidental opening of the manual exhaust line during normal operation, reduces nitrogen leakage, waste and energy loss, and prevents external air from entering the storage tank through the manual line.

[0033] The normally open manual shutoff valve can be closed during maintenance of the automatic exhalation valve, and the normally closed manual shutoff valve can be opened for exhaust during debugging, maintenance and other abnormal conditions, balancing the stability of normal operation and the flexibility of special conditions.

[0034] Further, the nitrogen supplement pipeline includes a first nitrogen supplement pipeline and a second nitrogen supplement pipeline;

[0035] The nitrogen inlet pipeline is connected between the inlet end of the nitrogen buffer device and the nitrogen preparation device, and the nitrogen supply pipeline is connected to the outlet end of the nitrogen buffer device; the nitrogen supply pipeline is connected to one end of the first nitrogen supplement pipeline and the second nitrogen supplement pipeline;

[0036] The other end of the first nitrogen supplement pipeline and the second nitrogen supplement pipeline is respectively connected to the top gas phase zone of the low-temperature molten salt storage tank and the high-temperature molten salt storage tank; the valve assembly is installed on the first nitrogen supplement pipeline and the second nitrogen supplement pipeline;

[0037] The valve assembly includes an electric valve, a pressure reducing valve and a manual shutoff valve, and the electric valve is electrically connected to the gas phase pressure monitoring device; when the gas phase pressure monitoring device detects that the gas phase pressure of the low-temperature molten salt storage tank or the high-temperature molten salt storage tank is lower than the first pressure threshold, the corresponding electric valve is opened to supplement nitrogen to the low-temperature molten salt storage tank or the high-temperature molten salt storage tank;

[0038] When the gas phase pressure monitoring device detects that the gas phase pressure of the low-temperature molten salt storage tank or the high-temperature molten salt storage tank reaches the second pressure threshold, the corresponding electric valve is closed to stop supplementing nitrogen; the second pressure threshold is greater than the first pressure threshold.

[0039] Beneficial effect: The first nitrogen supplement pipeline and the second nitrogen supplement pipeline are separately arranged, which cooperates with the interlocking control of the corresponding electric valve and the gas phase pressure monitoring device to independently adjust the nitrogen supplement amount of the low-temperature tank and the high-temperature tank, realizes precise independent control of the pressure of the double tanks, and ensures that each maintains a slight positive pressure state.

[0040] The pressure reducing valve can stabilize the pressure output by the nitrogen buffer device within a set range, avoid the fluctuation of the nitrogen supply pressure, prevent the sudden rise and fall of the tank pressure, and protect the electric valve and other components from high pressure impact.

[0041] The manual shutoff valve as a backup of the electric valve can manually cut off the nitrogen supplement when the electric valve fails or is being repaired, the first and second nitrogen supplement pipelines are independently controlled to avoid mutual interference, and the double protection mechanism reduces the risk of nitrogen leakage or pressure out of control.

[0042] By setting the threshold values of P1 (lower limit of nitrogen supplement) and P2 (upper limit of nitrogen supplement), the electric valve is only opened for nitrogen supplement when necessary, avoiding excessive consumption of nitrogen, and in combination with the pressure stabilizing effect of the nitrogen buffer device, the frequent start and stop of the nitrogen preparation device is reduced, and the system energy consumption is reduced. For different pressure requirements of the low-temperature tank and the high-temperature tank, the P1 and P2 threshold values of each can be independently set (such as the high-temperature tank requiring slightly higher pressure due to high temperature), to realize differentiated nitrogen supplement control and meet the sealing requirements of the double tanks under different working conditions.

[0043] Further, the first pressure threshold value is 100 Pa-500 Pa, and the second pressure threshold value is 100 Pa-300 Pa larger than the first pressure threshold value.

[0044] Beneficial effect: The first pressure threshold value of 100 Pa-500 Pa can accurately maintain the slight positive pressure of the storage tank, effectively isolating the entry of external air; the second pressure threshold value is 100 Pa-300 Pa larger than the first pressure threshold value, which avoids excessive nitrogen supplement leading to pressure fluctuations and reserves safety space for pressure regulation, ensuring that the pressure of the storage tank is always in a safe range.

[0045] The threshold difference of 100 Pa-300 Pa can prevent the electric valve from being frequently started and stopped due to small errors of the pressure monitoring device or instantaneous fluctuations of the system pressure, prolong the service life of the valve, and at the same time ensure the smoothness of the pressure regulation process, avoiding impact on the storage tank.

[0046] Further, the gas phase balance pipeline includes a first gas phase balance pipeline, a second gas phase balance pipeline, and a bypass gas phase balance pipeline, one end of the first gas phase balance pipeline is in communication with the top gas phase zone of the high-temperature molten salt storage tank, and the other end of the first gas phase balance pipeline is in communication with the temperature regulation device; one end of the second gas phase balance pipeline is in communication with the top gas phase zone of the low-temperature molten salt storage tank, and the other end of the second gas phase balance pipeline is in communication with the temperature regulation device;

[0047] The bypass gas phase balance pipeline is connected with the first gas phase balance pipeline and the second gas phase balance pipeline at both ends;

[0048] Valves are connected to the first gas phase balance pipeline, the second gas phase balance pipeline, and the bypass gas phase balance pipeline, and during normal operation, the valve on the bypass gas phase balance pipeline is in a closed state, and the valves on the first gas phase balance pipeline and the second gas phase balance pipeline are in an open state;

[0049] In the heat storage working phase, the high-temperature gas in the high-temperature molten salt storage tank flows into the temperature regulating device through the gas phase balance pipeline to release heat and reduce temperature, and then flows into the low-temperature molten salt storage tank.

[0050] In the heat release working phase, the low-temperature gas in the low-temperature molten salt storage tank flows into the temperature regulating device through the gas phase balance pipeline to absorb heat and increase temperature, and then flows into the high-temperature molten salt storage tank.

[0051] Beneficial effect: The gas phase balance pipeline cooperates with the temperature regulating device, the high-temperature gas flows into the corresponding storage tank after being cooled in the heat storage and being heated in the heat release, avoiding the damage of tank wall thermal stress and the loss of molten salt invalid heat caused by too large temperature difference, and ensuring the system thermal efficiency.

[0052] When normally operating, the main road valve is opened to realize the gas phase connection between the two tanks, balance the pressure difference caused by the change of molten salt liquid level through the natural flow of gas, reduce the nitrogen supplement frequency, and reduce the nitrogen consumption.

[0053] The bypass pipeline is connected in parallel with the temperature regulating device, which can be opened when the temperature regulating device is overhauled or fails to temporarily maintain the gas phase balance between the two tanks; the valves of the main road and the bypass are independently controlled to adapt to different working conditions and avoid system shutdown caused by single point failure.

[0054] The gas flow direction design in the heat storage or heat release phase matches the heat release / heat absorption function of the temperature regulating device to ensure accurate and efficient temperature regulation of the gas, and the pipeline is connected to the gas phase area at the top of the storage tank to avoid interference of gas flow with the stability of molten salt liquid level.

[0055] Further, the temperature regulating device is a solid heat accumulator, which is internally provided with a plurality of heat exchange pipes, and the plurality of heat exchange pipes adopt any one of the following structural forms:

[0056] Form one: the plurality of heat exchange pipes are all U-shaped heat exchange pipes, and each U-shaped heat exchange pipe is distributed in a serpentine shape in the solid heat accumulator;

[0057] Form two: the plurality of heat exchange pipes are all straight pipes, and each straight pipe is arranged in an interval in the solid heat accumulator;

[0058] The solid heat accumulator is filled with a solid heat storage medium.

[0059] Beneficial effect: In this scheme, the form structure of the heat exchange pipe can be any one, which can be a straight pipe structure arranged in parallel and interval, or a serpentine arrangement in a U-shaped structure, the plurality of heat exchange pipes increase the contact area of the gas and the solid heat storage medium, the high-temperature gas is quickly released in the heat storage, and the low-temperature gas is efficiently absorbed in the heat release, ensuring that the temperature of the circulating gas between the two tanks accurately matches the working condition of the corresponding storage tank, avoiding the safety risk and heat loss caused by temperature difference.

[0060] The solid heat storage medium (such as magnesium oxide, steel, etc.) has large heat storage capacity and strong thermal stability, can stably store and release heat for a long time, is not affected by gas flow fluctuation, guarantees continuous and reliable temperature regulation effect, and meets the long-term operation requirement of the system.

[0061] The design of filling the solid heat storage medium in the solid heat storage device can strengthen the heat conduction efficiency of the heat storage medium, fix the position of the heat exchange pipe, avoid pipe vibration or damage caused by gas flow impact, prolong the service life of the temperature regulation device, and reduce the maintenance cost.

[0062] Further, a method for operating the double-tank molten salt energy storage nitrogen sealing system, the method comprising the following steps:

[0063] Nitrogen sealing control: the pressure in the storage tank is detected in real time by the gas phase pressure monitoring device, when the pressure is lower than the first threshold value, the nitrogen supplement pipeline is opened to supplement nitrogen into the storage tank, when the pressure reaches the second threshold value, the nitrogen supplement is stopped, when the pressure exceeds the exhaust threshold value, the exhaust is performed through the automatic exhaust pipeline to maintain the micro-positive pressure of the storage tank;

[0064] Double-tank balance: the gas phase balance pipeline is used to connect the gas phase zones of the low-temperature molten salt storage tank and the high-temperature molten salt storage tank, the gas circulation is driven by the pressure difference between the two tanks, and the temperature of the circulating gas is adjusted by the temperature regulation device;

[0065] Storage tank preheating and salt injection: before the first filling of molten salt, the low-temperature molten salt storage tank and the high-temperature molten salt storage tank are first subjected to nitrogen replacement and inner wall preheating treatment, and then the storage tanks are subjected to salt injection;

[0066] The steps of the storage tank preheating and salt injection include:

[0067] Firstly, the air in the low-temperature molten salt storage tank and the high-temperature molten salt storage tank is subjected to nitrogen replacement, in the nitrogen replacement process, the preheating fan is started to replace the air in the outlet pipeline and the inlet pipeline of the preheating fan with nitrogen;

[0068] Secondly, the low-temperature molten salt storage tank is preheated, the low-temperature molten salt storage tank is preheated by the nitrogen internal circulation heating loop, the heating power is increased step by step with the tank wall temperature, and the preheating is stopped when the tank wall temperature reaches the standard;

[0069] Thirdly, molten salt is injected into the low-temperature molten salt storage tank, after the preheating of the low-temperature molten salt storage tank is completed, the molten salt melted by high-temperature heating is injected into the low-temperature molten salt storage tank;

[0070] Fourthly, the high-temperature molten salt storage tank is preheated, after the low-temperature molten salt storage tank is injected with salt, the high-temperature molten salt storage tank is preheated by the nitrogen internal circulation heating loop, the heating power is increased step by step with the tank wall temperature, and the preheating is stopped when the tank wall temperature reaches the standard;

[0071] In the fifth step, the molten salt is injected into the high-temperature molten salt storage tank, and after the preheating of the high-temperature molten salt storage tank is completed, the molten salt in the low-temperature molten salt storage tank is heated by the molten salt heating device and then injected into the high-temperature molten salt storage tank.

[0072] Beneficial effects: Nitrogen sealing control is realized through three-stage pressure control of "nitrogen supplement-nitrogen stop-gas exhaust", the micro-positive pressure of the storage tank is accurately maintained, the external air is completely isolated, the molten salt oxidation and the damage of the storage tank negative pressure are avoided, and the overpressure risk is prevented.

[0073] The double-tank balance utilizes the pressure difference to drive the gas circulation, and cooperates with the temperature regulation device to adjust the gas temperature, so as to eliminate the heat loss and tank wall thermal stress caused by the temperature difference between the double tanks, and ensure the molten salt quality and the long-term thermal efficiency stability of the system.

[0074] The storage tank preheating and salt injection replace the air first and then the tank is heated in stages to prevent the damage of the tank wall thermal shock; the preheating and salt injection process of the double tank are adapted to the characteristics of the double tank to avoid the molten salt from freezing by contacting the cold tank wall, and to ensure the safety and smoothness of the first molten salt filling.

[0075] The process of the present scheme is closely connected from nitrogen replacement, preheating, salt injection to double-tank balance switching, which not only meets the safety requirements of the first start, but also adapts to the changes of the subsequent heat storage-heat release working conditions through pressure dynamic regulation and gas circulation, and improves the overall operation reliability of the system. In addition, the nitrogen recycling in the present scheme can effectively reduce the nitrogen supplement amount, and the step-by-step heating avoids energy waste; the double-tank operation and working condition switching logic are clear, which reduces the manual intervention, and reduces the operation and maintenance difficulty and cost. BRIEF DESCRIPTION OF DRAWINGS

[0076] The drawings described herein are used to provide further understanding of the embodiments of the present application, constitute a part of the present application, and do not constitute a limitation on the embodiments of the present application. In the drawings:

[0077] Figure 1 is a structural schematic diagram of an embodiment of a double-tank molten salt energy storage nitrogen sealing system of the present application;

[0078] Figure 2 is Figure 1 is a local enlarged view of A in FIG. 6;

[0079] Figure 3 is a structural schematic diagram of another embodiment of a double-tank molten salt energy storage nitrogen sealing system of the present application;

[0080] Figure 4 is a structural schematic diagram of an embodiment of a double-tank molten salt energy storage nitrogen sealing system of the present application after adding a storage tank preheating unit.

[0081] Markings and corresponding component names in the drawings:

[0082] 1. Low-temperature molten salt storage tank; 11. First automatic exhaust pipeline; 12. First manual exhaust pipeline; 13. First pressure transmitter; 14. First nitrogen supplement pipeline; 15. First electric valve; 16. First pressure reducing valve; 17. First tank gas exhaust pipeline; 18. First preheating gas supplement pipeline;

[0083] 2. High-temperature molten salt storage tank; 21. Second automatic exhaust pipeline; 22. Second manual exhaust pipeline; 23. Second pressure transmitter; 24. Second nitrogen supplement pipeline; 25. Second electric valve; 26. Second pressure reducing valve; 27. Second tank gas exhaust pipeline; 28. Second preheating gas supplement pipeline;

[0084] 3. Nitrogen generator; 4. Nitrogen storage tank; 41. First pressure gauge; 42. Third pressure transmitter; 43. Safety valve; 44. Nitrogen inlet pipeline; 45. Nitrogen supply pipeline;

[0085] 5. Temperature control device; 51. Heat exchange pipe; 52. Solid heat storage medium; 53. First gas phase balance pipeline; 54. Second gas phase balance pipeline; 55. First temperature measuring point; 56. Second temperature measuring point; 57. Bypass gas phase balance pipeline; 6. Preheating air blower;

[0086] 61. Second pressure gauge; 7. Preheating air heater; 71. Third temperature measuring point. DETAILED DESCRIPTION

[0087] In order to make the object, technical scheme and advantages of the present application clearer, further detailed description will be given below in combination with examples and drawings, and the schematic implementation mode and its description of the present application are only used for explaining the present application, and not as a limitation to the present application.

[0088] As an embodiment of the present application, as shown in Figure 1 the present embodiment provides a double-tank molten salt energy storage nitrogen sealing system, which comprises:

[0089] A molten salt storage tank unit, which comprises a low-temperature molten salt storage tank 1 for storing low-temperature molten salt and a high-temperature molten salt storage tank 2 for storing high-temperature molten salt, and the low-temperature molten salt storage tank 1 and the high-temperature molten salt storage tank 2 are both provided with a gas phase pressure monitoring device, an automatic exhaust pipeline and a manual exhaust pipeline; in the present embodiment, a normally open manual shut-off valve and an automatic exhaust valve are arranged on the automatic exhaust pipeline, the normally open manual shut-off valve is kept open when the system is normally running, and the automatic exhaust valve is automatically opened to exhaust when the tank pressure reaches a set value; a normally closed manual shut-off valve is arranged on the manual exhaust pipeline, and the normally closed manual shut-off valve is kept closed when the system is normally running;

[0090] The nitrogen sealing unit comprises a nitrogen preparation device, a nitrogen buffer device and a nitrogen supplement pipeline. The nitrogen preparation device is communicated with the nitrogen buffer device. The nitrogen buffer device is connected to the top gas phase area of the low-temperature molten salt storage tank 1 and the high-temperature molten salt storage tank 2 through the nitrogen supplement pipeline. A valve assembly controlled in linkage with a gas phase pressure monitoring device is arranged on the nitrogen supplement pipeline.

[0091] The double-tank gas phase balance unit comprises a gas phase balance pipeline and a temperature control device 5. The gas phase balance pipeline communicates the gas phase areas of the low-temperature molten salt storage tank 1 and the high-temperature molten salt storage tank 2. The temperature control device 5 is arranged on the main pipeline of the flow path of the gas phase balance pipeline and is used to adjust the temperature of the flowing gas between the two tanks.

[0092] In an embodiment, the low-temperature molten salt storage tank 1 is a cylindrical vertical atmospheric pressure storage tank and is used to store low-temperature molten salt. The automatic exhaust pipeline on the low-temperature molten salt storage tank 1 is a first automatic exhaust pipeline 11. The manual exhaust pipeline on the low-temperature molten salt storage tank 1 is a first manual exhaust pipeline 12. The first automatic exhaust pipeline 11 is provided with a normally open manual shutoff valve and an automatic exhaust valve. The normally open manual shutoff valve is in a normally open state. Unauthorized closing of the normally open manual shutoff valve is strictly prohibited. The automatic exhaust valve is used to protect against safety risks caused by excessive pressure in the tank. When the pressure in the tank reaches a set pressure value P4 of the automatic exhaust valve, the automatic exhaust valve is automatically opened to exhaust the excess nitrogen in the tank to the atmosphere and then automatically returns to the closed state.

[0093] The first manual exhaust pipeline 12 is provided with a normally closed manual shutoff valve. The normally closed manual shutoff valve is opened by hand to exhaust the gas in the tank. The normally closed manual shutoff valve is generally opened only during the debugging, starting, maintenance and other abnormal operation of the low-temperature molten salt storage tank 1 and must be closed during the normal operation of the low-temperature molten salt storage tank 1.

[0094] The high-temperature molten salt storage tank 2 is a cylindrical vertical atmospheric pressure storage tank and is used to store high-temperature molten salt. The automatic exhaust pipeline on the high-temperature molten salt storage tank 2 is a second automatic exhaust pipeline 21. The manual exhaust pipeline on the high-temperature molten salt storage tank 2 is a second manual exhaust pipeline 22. The second automatic exhaust pipeline 21 is also provided with a normally open manual shutoff valve and an automatic exhaust valve. The second manual exhaust pipeline 22 is also provided with a normally closed manual shutoff valve. The working principles and operation control modes of the second automatic exhaust pipeline 21 and the second manual exhaust pipeline 22 are the same as those of the first automatic exhaust pipeline 11 and the first manual exhaust pipeline 12 on the low-temperature molten salt storage tank 1, which will not be described herein.

[0095] In an embodiment, the nitrogen buffer device is a nitrogen storage tank 4. The nitrogen preparation device is a nitrogen generator 3. The nitrogen supplement pipeline comprises a first nitrogen supplement pipeline 14 and a second nitrogen supplement pipeline 24.

[0096] The nitrogen inlet pipeline 44 is in communication between the inlet end of the nitrogen buffer device (i.e., the nitrogen storage tank 4) and the nitrogen preparation device (i.e., the nitrogen generator 3), and the nitrogen supply pipeline 45 is in communication with the outlet end of the nitrogen buffer device; the nitrogen supply pipeline 45 is in communication with one end of the first nitrogen supplement pipeline 14 and the second nitrogen supplement pipeline 24, and in the embodiment, the nitrogen supply pipeline 45 is in communication with the first nitrogen supplement pipeline 14 and the second nitrogen supplement pipeline 24 through a three-way pipe;

[0097] The other end of the first nitrogen supplement pipeline 14 and the second nitrogen supplement pipeline 24 is respectively in communication with the top gas phase zone of the low-temperature molten salt storage tank 1 and the high-temperature molten salt storage tank 2; that is, in the embodiment, the nitrogen generator 3 is used to prepare industrial nitrogen, and the qualified nitrogen prepared is transported to the nitrogen storage tank 4 for buffering through the nitrogen inlet pipeline 44, and the nitrogen storage tank 4 is in communication with the top of the low-temperature molten salt storage tank 1 through the nitrogen supply pipeline 45 and the first nitrogen supplement pipeline 14, and is in communication with the top of the high-temperature molten salt storage tank 2 through the nitrogen supply pipeline 45 and the second nitrogen supplement pipeline 24;

[0098] In the embodiment, the nitrogen inlet pipeline 44 is sequentially provided with a manual shut-off valve and a check valve, the nitrogen supply pipeline 45 is provided with a manual shut-off valve, and the first nitrogen supplement pipeline 14 and the second nitrogen supplement pipeline 24 are both provided with a valve assembly; the valve assembly in the embodiment includes an electric valve, a pressure reducing valve and a manual shut-off valve, and the electric valve is electrically connected with the gas phase pressure monitoring device; when the gas phase pressure monitoring device detects that the gas phase pressure of the low-temperature molten salt storage tank 1 or the high-temperature molten salt storage tank 2 is lower than the first pressure threshold P1, the corresponding electric valve is opened to supplement nitrogen to the low-temperature molten salt storage tank 1 or the high-temperature molten salt storage tank 2;

[0099] When the gas phase pressure monitoring device detects that the gas phase pressure of the low-temperature molten salt storage tank 1 or the high-temperature molten salt storage tank 2 reaches the second pressure threshold, the corresponding electric valve is closed to stop supplementing nitrogen; specifically, in the embodiment, the valve assembly on the first nitrogen supplement pipeline 14 includes a first electric valve 15, a first pressure reducing valve 16 and a manual shut-off valve arranged in sequence, and the valve assembly on the second nitrogen supplement pipeline 24 includes a second electric valve 25, a second pressure reducing valve 26 and a manual shut-off valve arranged in sequence; when the molten salt energy storage and nitrogen sealing system in the embodiment is running, the manual shut-off valves on the nitrogen inlet pipeline 44, the nitrogen supply pipeline 45, the first nitrogen supplement pipeline 14 and the second nitrogen supplement pipeline 24 are all in an open state;

[0100] In the embodiment, the gas phase pressure detection device arranged on the low-temperature molten salt storage tank 1 includes a first pressure transmitter 13, and the gas phase pressure detection device arranged on the high-temperature molten salt storage tank 2 includes a second pressure transmitter 23; the first pressure transmitter 13 and the second pressure transmitter 23 are electrically connected with the first electric valve 15 and the second electric valve 25 respectively to realize interlocking control.

[0101] When the first pressure transmitter 13 detects that the gas phase pressure measurement value of the low-temperature molten salt storage tank 1 is lower than the first pressure threshold P1, it indicates that the gas phase pressure of the low-temperature molten salt storage tank 1 is too low, and in order to prevent the problem of external air leakage into the storage tank caused by the negative pressure phenomenon inside the low-temperature molten salt storage tank 1, the first electric valve 15 is opened to make the first nitrogen supplement pipeline 14 in a flow state, nitrogen is supplemented to the low-temperature molten salt storage tank 1, and the working pressure of the low-temperature molten salt storage tank 1 is ensured to always maintain a slight positive pressure operation; when the first pressure transmitter 13 detects that the gas phase pressure measurement value of the low-temperature molten salt storage tank 1 reaches the second pressure threshold P2, the first electric valve 15 is closed, and the nitrogen supplement to the low-temperature molten salt storage tank 1 is stopped, so as to prevent the working pressure of the low-temperature molten salt storage tank 1 from being too large to damage the storage tank;

[0102] The second pressure threshold is greater than the first pressure threshold, and specifically, in the embodiment, the first pressure threshold is 100 Pa-500 Pa, and the second pressure threshold is greater than the first pressure threshold by 100 Pa-300 Pa.

[0103] The second electric valve 25 and the second pressure transmitter 23 on the high-temperature molten salt storage tank 2 form a interlocking control relationship, and the control mode of opening and closing is completely same as that of the first electric valve 15, which will not be described here.

[0104] In an embodiment, a third pressure transmitter 42, a safety valve 43 and a first pressure gauge 41 are sequentially installed on the top of the nitrogen storage tank 4, so that the gas source pressure can be monitored in real time, the overpressure can be automatically relieved, and the pressure data can be double-verified to ensure the safety and stability of the nitrogen source; the second pressure gauges 61 are installed on the pipelines between the two preheating fans 6 and the preheating air heater 7, so that the air pressure can be monitored, the air path blockage or fan failure can be assisted to be investigated, and the preheating efficiency and equipment safety can be ensured.

[0105] In an embodiment, the gas phase balance pipeline includes a first gas phase balance pipeline 53, a second gas phase balance pipeline 54 and a bypass gas phase balance pipeline 57, one end of the first gas phase balance pipeline 53 is in communication with the top gas phase zone of the high-temperature molten salt storage tank 2, and the other end of the first gas phase balance pipeline 53 is in communication with the temperature control device 5; one end of the second gas phase balance pipeline 54 is in communication with the top gas phase zone of the low-temperature molten salt storage tank 1, and the other end of the second gas phase balance pipeline 54 is in communication with the temperature control device 5; in the embodiment, the flow path formed between the first gas phase balance pipeline 53, the temperature control device 5 and the second gas phase balance pipeline 54 is a main pipeline, that is, the temperature control device 5 is arranged on the main pipeline of the flow path of the gas phase balance pipeline, and the bypass gas phase balance pipeline 57 is a branch pipeline.

[0106] The bypass gas phase balance pipeline 57 is connected in parallel with the temperature regulating device 5, two ends of the bypass gas phase balance pipeline 57 are connected with the first gas phase balance pipeline 53 and the second gas phase balance pipeline 54 respectively, and valves are connected on the first gas phase balance pipeline 53, the second gas phase balance pipeline 54 and the bypass gas phase balance pipeline 57, the valves are manual shut-off valves, and the valve on the bypass gas phase balance pipeline 57 is in a closed state in normal operation, and the valves on the first gas phase balance pipeline 53 and the second gas phase balance pipeline 54 are in an open state;

[0107] In the heat storage working phase, the high-temperature gas in the high-temperature molten salt storage tank 2 flows into the low-temperature molten salt storage tank 1 after being cooled by the temperature regulating device 5 through the gas phase balance pipeline;

[0108] In the heat storage working phase, the high-temperature gas in the high-temperature molten salt storage tank 2 flows into the low-temperature molten salt storage tank 1 after being cooled by the temperature regulating device 5 through the gas phase balance pipeline;

[0109] In one embodiment, as shown in Figure 1 and Figure 3 The temperature regulating device 5 is a solid heat accumulator, and a plurality of heat exchange pipes 51 are arranged in the solid heat accumulator, and the plurality of heat exchange pipes 51 adopt any one of the following structural forms:

[0110] Form one: the plurality of heat exchange pipes 51 are all U-shaped heat exchange pipes, and each U-shaped heat exchange pipe is arranged in a serpentine shape in the solid heat accumulator;

[0111] Form two: the plurality of heat exchange pipes are all straight pipes, and each straight pipe is arranged in an interstitial manner in the solid heat accumulator;

[0112] The solid heat accumulator is filled with a solid heat storage medium 52, and the solid heat storage medium 52 can be at least one of magnesium oxide, steel, concrete, sand and other solid mediums.

[0113] In one embodiment, as shown in Figure 1 and Figure 2 The plurality of heat exchange pipes 51 are straight pipes, and the plurality of heat exchange pipes 51 are arranged in a planar and interstitial manner, the interstices between the heat exchange pipes 51 are filled with the solid heat storage medium 52, and two ends of the plurality of heat exchange pipes 51 and the solid heat storage medium 52 form a gas buffer cavity with the upper part and the lower part of the fixed heat accumulator, and the gas is distributed into the plurality of heat exchange pipes 51 for heat exchange in the gas buffer cavity.

[0114] In another embodiment, as shown in Figure 3As shown, the solid heat accumulator in the embodiment also has a plurality of heat exchange pipes 51, and the solid heat accumulator is also filled with fixed heat storage medium, but the solid heat accumulator in the embodiment is different from the solid heat accumulator in the above-mentioned embodiments in that the plurality of heat exchange pipes 51 in the solid heat accumulator in the embodiment is in a U-shaped heat exchange pipe structure, the plurality of heat exchange pipes 51 forms a U-shaped multi-pipe-pass heat exchange pipe, and the plurality of heat exchange pipes 51 is distributed in a serpentine shape, so that the heat exchange area can be increased, and thus the heat exchange efficiency can be improved.

[0115] In one embodiment, a temperature measuring point is arranged on each of the gas phase balance pipelines at the outlet and the inlet of the solid heat accumulator, which are respectively a first temperature measuring point 55 and a second temperature measuring point 56, and the first temperature measuring point 55 and the second temperature measuring point 56 are both provided with a temperature sensor to realize real-time monitoring of the temperature of the gas flow. During normal operation of the molten salt energy storage nitrogen sealing system, the valve on the bypass gas phase balance pipeline 57 should be in a closed state, and the valves on the first gas phase balance pipeline 53 and the second gas phase balance pipeline 54 should both be in an open state, so as to ensure that the gas phase area of the low-temperature molten salt storage tank 1 and the gas phase area of the high-temperature molten salt storage tank 2 and the pipelines connected thereto are in a communication state, so that the gas phase working pressures of the two storage tanks can always be dynamically self-balanced.

[0116] When the liquid levels of the low-temperature molten salt storage tank 1 and the high-temperature molten salt storage tank 2 are both maintained unchanged, that is, the low-temperature molten salt pump and the high-temperature molten salt pump are both stopped, the pressures and temperatures of the gas phase areas of the low-temperature molten salt storage tank 1 and the high-temperature molten salt storage tank 2 will gradually reach self-balance, that is, finally the gas phase pressures of the two storage tanks are the same, and the gas phase temperatures are consistent with the temperatures of the molten salts stored in the respective storage tanks.

[0117] When the molten salt energy storage system performs heat storage work, the low-temperature molten salt pump is used to continuously extract the low-temperature molten salt in the low-temperature molten salt storage tank 1, heat the low-temperature molten salt to high temperature through a molten salt heating device (such as an electric heater or a steam heater, which heats the molten salt by electricity or steam), and then send the low-temperature molten salt into the high-temperature molten salt storage tank 2, so that the liquid level of the molten salt in the low-temperature molten salt storage tank 1 gradually decreases, the gas phase volume correspondingly increases, and the gas phase pressure decreases, while the liquid level, the gas phase volume, and the gas phase pressure of the high-temperature molten salt storage tank 2 change in the opposite direction, so that the gas phase pressure of the high-temperature molten salt storage tank 2 is greater than that of the low-temperature molten salt storage tank 1, and a certain pressure difference is formed between the gas phase pressures of the two storage tanks. Under the action of the pressure difference, the high-temperature nitrogen gas in the gas phase area of the high-temperature molten salt storage tank 2 will first flow into the solid heat accumulator through the first gas phase balance pipeline 53. In the solid heat accumulator, the high-temperature nitrogen gas releases heat to the solid heat storage medium 52 through the heat exchange pipes 51, and the solid heat storage medium 52 stores all the heat released by the high-temperature nitrogen gas. After releasing heat and being cooled, the high-temperature nitrogen gas becomes low-temperature nitrogen gas, which then flows into the gas phase area of the low-temperature molten salt storage tank 1 through the second gas phase balance pipeline 54.

[0118] When the molten salt energy storage system is in exothermic operation, a high-temperature molten salt pump continuously draws high-temperature molten salt from the high-temperature molten salt storage tank 2. After being cooled by a molten salt exothermic device (such as a heat exchanger, which uses the heat released by the molten salt to heat water or steam), the molten salt is sent to the low-temperature molten salt storage tank 1. This causes the molten salt level in the high-temperature molten salt storage tank 2 to gradually decrease, and its gas phase volume to increase accordingly, resulting in a decrease in gas phase pressure. However, the changes in molten salt level, gas phase volume, and gas phase pressure in the low-temperature molten salt storage tank 1 are exactly the opposite of those in the high-temperature molten salt storage tank 2. This leads to a decrease in the low-temperature molten salt level. The gas phase pressure of molten salt storage tank 1 is greater than that of high-temperature molten salt storage tank 2, resulting in a certain pressure difference between the two tanks. Under the action of the pressure difference, the low-temperature nitrogen in the gas phase zone of the low-temperature molten salt storage tank 1 will first flow by gravity into the solid heat accumulator through the second gas phase balance pipeline 54. In the solid heat accumulator, the solid heat storage medium 52 will release the stored heat to the low-temperature nitrogen through the heat exchange tube 51. After absorbing heat and heating up, the low-temperature nitrogen becomes high-temperature nitrogen. The high-temperature nitrogen then flows by gravity into the gas phase zone of the high-temperature molten salt storage tank 2 through the first gas phase balance pipeline 53.

[0119] During the molten salt heat storage and release process, since the gas phase zones of the high-temperature molten salt storage tank 2 and the low-temperature molten salt storage tank 1 are connected, the gas phase pressure of the two tanks will always reach a dynamic self-balance. Nitrogen circulates back and forth between the two tanks. As long as the tanks do not leak, there is no need to add nitrogen to the tanks during daily operation, which greatly reduces the amount of nitrogen used.

[0120] By setting up a solid-state heat accumulator, the temperature of nitrogen gas traveling between the two tanks can be effectively controlled through the heat storage and release process of the solid-state heat accumulator. This ensures that the gas phase temperature of the two tanks changes little and remains within a suitable temperature range, avoiding overheating of the gas phase in the low-temperature molten salt tank 1 and the formation of large temperature differences between the gas and liquid phases of the two tanks, which would affect the safe operation of the tanks and the thermal efficiency of the energy storage system.

[0121] In one embodiment, such as Figure 4 As shown, the dual-tank molten salt energy storage nitrogen sealing system in this embodiment also includes a tank preheating unit. The tank preheating unit includes a preheating fan 6, a preheating air heater 7, a tank gas discharge pipeline, and a preheating gas supply pipeline. The preheating fan 6, the tank gas discharge pipeline, the preheating air heater 7, and the preheating gas supply pipeline form a nitrogen internal circulation heating circuit, which is used to preheat the low-temperature molten salt storage tank 1 and the high-temperature molten salt storage tank 2 before filling them with molten salt.

[0122] In one embodiment, such as Figure 4As shown, in the embodiment, the in-tank gas discharge pipeline includes a first in-tank gas discharge pipeline 17 and a second in-tank gas discharge pipeline 27 which are in communication with each other, and the preheating gas supplement pipeline includes a first preheating gas supplement pipeline 18 and a second preheating gas supplement pipeline 28 which are in communication with each other; one end of the first in-tank gas discharge pipeline 17 and one end of the second in-tank gas discharge pipeline 27 extend into the lower part of the low-temperature molten salt storage tank 1 and the high-temperature molten salt storage tank 2 respectively;

[0123] One end of the first preheating gas supplement pipeline 18 and one end of the second preheating gas supplement pipeline 28 extend into the upper part of the low-temperature molten salt storage tank 1 and the high-temperature molten salt storage tank 2 respectively; in the embodiment, valves are installed at positions close to the low-temperature molten salt storage tank 1 and the high-temperature molten salt storage tank 2 respectively for the first in-tank gas discharge pipeline 17 and the second in-tank gas discharge pipeline 27 and the first preheating gas supplement pipeline 18 and the second preheating gas supplement pipeline 28; the preheating fan 6 and the preheating fan heater 7 are connected in series on the in-tank gas discharge pipeline and the preheating gas supplement pipeline; in the embodiment, the preheating fan 6 is provided with at least two fans which are connected in parallel with each other; the preheating fan 6 is usually configured in a one-for-one standby mode; the preheating fan heater 7 can not be provided; the heating source can be electricity or high-temperature flue gas, etc.

[0124] In one embodiment, a third temperature measuring point 71 is arranged on the pipeline between the preheating fan heater 7 and the preheating gas supplement pipeline; a temperature sensor is installed at the third temperature measuring point 71 to realize real-time monitoring of the gas temperature, accurately control the preheating gas temperature, avoid the thermal shock of the tank wall, and reduce energy waste.

[0125] In the embodiment, valves are installed on the outlet and inlet pipelines of the preheating fan 6; a check valve is further installed on the pipeline between the outlet of the preheating fan 6 and the valve arranged at the outlet thereof; and the second pressure gauge 61 is located between the check valve and the valve arranged at the outlet of the preheating fan 6.

[0126] In one embodiment, the application further discloses a running method of the dual-tank molten salt energy storage nitrogen sealing system.

[0127] Nitrogen sealing control: the pressure in the storage tank is detected in real time by the gas phase pressure monitoring device; when the pressure is lower than the first threshold value, the nitrogen supplement pipeline is opened to supplement nitrogen into the storage tank; when the pressure reaches the second threshold value, the nitrogen supplement is stopped; when the pressure exceeds the exhaust threshold value, the automatic exhaust pipeline is used to exhaust to maintain the micro-positive pressure of the storage tank;

[0128] Double-tank balance: the gas phase balance pipeline is used to make the gas phase zones of the low-temperature molten salt storage tank 1 and the high-temperature molten salt storage tank 2 communicate, the gas circulation is driven by the pressure difference between the two tanks, and the circulating gas temperature is adjusted by the temperature regulating device 5;

[0129] Storage tank preheating and salt injection: before the first filling of molten salt, the low-temperature molten salt storage tank 1 and the high-temperature molten salt storage tank 2 are first subjected to nitrogen replacement and inner wall preheating treatment, and then the storage tanks are subjected to salt injection;

[0130] The steps of the storage tank preheating and salt injection include:

[0131] Firstly, the air in the low-temperature molten salt storage tank 1 and the high-temperature molten salt storage tank 2 is subjected to nitrogen replacement, and in the nitrogen replacement process, the preheating fan 6 is started to make the air in the outlet pipeline and the inlet pipeline of the preheating fan 6 all replaced by nitrogen; Specifically:

[0132] Nitrogen replacement of the air in the double tanks (the high-temperature molten salt storage tank 2 and the low-temperature molten salt storage tank 1): firstly, the valves on the bypass gas phase balance pipeline 57, the first gas phase balance pipeline 53 and the second gas phase balance pipeline 54 are opened, then the valve on the first manual exhaust pipeline 12 at the top of the low-temperature molten salt storage tank 1 is closed, after that, the valve on the second manual exhaust pipeline 22 at the top of the high-temperature molten salt storage tank 2 is opened, and finally, the nitrogen generator 3 is started to inject nitrogen into the nitrogen storage tank 4, the first electric valve 15 is opened to continuously input nitrogen into the low-temperature molten salt storage tank 1 through the nitrogen storage tank 4 and the first nitrogen supplement pipeline 14, the gas in the low-temperature molten salt storage tank 1 is discharged into the high-temperature molten salt storage tank 2 through the second gas phase balance pipeline 54, the bypass gas phase balance pipeline 57 and the first gas phase balance pipeline 53, and the gas in the high-temperature molten salt storage tank 2 is discharged to the external atmospheric environment through the second manual exhaust pipeline 22.

[0133] In the nitrogen replacement process, the two preheating fans 6 are intermittently switched to operate (at this time, the preheating fan heater 7 does not operate), so that the air in the outlet and inlet pipelines of the two preheating fans 6 is all replaced by nitrogen. The nitrogen purity in the exhaust gas at the outlet of the second manual exhaust pipeline 22 is manually detected, and when the nitrogen purity reaches the specified requirement, the first electric valve 15 and the valves on the first gas phase balance pipeline 53 and the second gas phase balance pipeline 54 are closed, and the preheating fan 6 is stopped, thus the nitrogen replacement of the two storage tanks is completed.

[0134] Secondly, the low-temperature molten salt storage tank 1 is preheated, and the low-temperature molten salt storage tank 1 is preheated by the nitrogen internal circulation heating loop, the heating power increases with the tank wall temperature in steps, and the preheating is stopped when the tank wall temperature reaches the standard, specifically:

[0135] The low-temperature molten salt storage tank 1 is preheated, the valves on the first tank gas discharge pipeline 17 and the first preheating gas supplement pipeline 18 are opened, and the valves on the second tank gas discharge pipeline 27 and the second preheating gas supplement pipeline 28 are closed at the same time. One of the preheating air blowers 6 is selected as the main air blower, and the other is selected as the standby air blower. The valves on the outlet and inlet pipelines of the main preheating air blower 6 are opened, and the valves on the outlet and inlet pipelines of the standby preheating air blower 6 are closed at the same time. Then, the main preheating air blower 6 and the preheating air heater 7 are started in sequence. Nitrogen gas is circulated and pumped from the low-temperature molten salt storage tank 1 through the first tank gas discharge pipeline 17, and then is sent to the preheating air heater 7 after being pressurized by the preheating air blower 6. The heated nitrogen gas is returned to the low-temperature molten salt storage tank 1 through the first preheating gas supplement pipeline 18. The inner wall of the low-temperature molten salt storage tank 1 is continuously heated by the hot nitrogen gas, so that the temperature of the tank wall gradually increases. The heating power of the preheating air heater 7 will increase in steps as the temperature of the tank wall increases.

[0136] A plurality of temperature measuring points are arranged on the wall of the low-temperature molten salt storage tank 1. When all the temperature measuring points reach the predetermined temperature, the preheating air heater 7 is stopped first, then the preheating air blower 6 is stopped, and finally the valves on the first tank gas discharge pipeline 17 and the first preheating gas supplement pipeline 18 are closed.

[0137] In the third step, molten salt is injected into the low-temperature molten salt storage tank. After the low-temperature molten salt storage tank is preheated, molten salt that has been melted by high-temperature heating is injected into the low-temperature molten salt storage tank. Specifically, in the embodiment, after the low-temperature molten salt storage tank 1 is preheated, the molten salt that has been melted by high-temperature heating is injected into the low-temperature molten salt storage tank 1 through the temporary salt melting facility. The amount of molten salt injected should meet the design requirements.

[0138] In the fourth step, the high-temperature molten salt storage tank is preheated. After the low-temperature molten salt storage tank is filled with molten salt, the high-temperature molten salt storage tank is preheated by a nitrogen gas internal circulation heating loop. The heating power increases in steps as the temperature of the tank wall increases. When the temperature of the tank wall reaches the standard, the preheating is stopped. Specifically, after the molten salt is injected into the low-temperature molten salt storage tank 1, the valves on the second tank gas discharge pipeline 27 and the second preheating gas supplement pipeline 28 are opened. Then, the main preheating air blower 6 and the preheating air heater 7 are started in sequence. Nitrogen gas is circulated and pumped from the high-temperature molten salt storage tank 2 through the second tank gas discharge pipeline 27, and then is sent to the preheating air heater 7 after being pressurized by the preheating air blower 6. The heated nitrogen gas is returned to the high-temperature molten salt storage tank 2 through the second preheating gas supplement pipeline 28. The inner wall of the high-temperature molten salt storage tank 2 is continuously heated by the hot nitrogen gas, so that the temperature of the tank wall gradually increases. The heating power of the preheating air heater 7 will increase in steps as the temperature of the tank wall increases.

[0139] A plurality of temperature measuring points are arranged on the wall of the high-temperature molten salt storage tank 2. When all the temperature measuring points reach the predetermined temperature, the preheating air heater 7 is first stopped, then the preheating air blower 6 is stopped, and finally the valves on the second tank gas discharge pipeline 27 and the second preheating gas supplement pipeline 28 and the valves on the preheating air blower 6 inlet and outlet pipelines are closed;

[0140] In the fifth step, molten salt is injected into the high-temperature molten salt storage tank. After the preheating of the high-temperature molten salt storage tank is completed, the molten salt in the low-temperature molten salt storage tank is heated by the molten salt heating device and then injected into the high-temperature molten salt storage tank. Specifically,

[0141] The molten salt in the low-temperature molten salt storage tank 1 is extracted by using a low-temperature molten salt pump and then heated by the molten salt heating device and injected into the high-temperature molten salt storage tank 2. When the molten salt level in the high-temperature molten salt storage tank 2 reaches the set minimum working level, the low-temperature molten salt pump is stopped, the valve on the second manual exhaust pipeline 22 is closed, the valves on the first and second gas phase balance pipelines 53 and 54 are opened, and the valve on the bypass gas phase balance pipeline 57 is closed.

[0142] According to the measurement values of the first and second pressure transmitters 13 and 23, if the pressure measurement value is lower than the first pressure threshold P1, the first electric valve 15 is opened to supplement an appropriate amount of nitrogen into the low-temperature molten salt storage tank 1 or the second electric valve 25 is opened to supplement an appropriate amount of nitrogen into the high-temperature molten salt storage tank 2, until the first and second electric valves 15 and 25 are closed when the gas phase pressures of the low-temperature molten salt storage tank 1 and the high-temperature molten salt storage tank 2 both reach the second pressure threshold P2, and the nitrogen supplement into the two storage tanks is stopped.

[0143] In one embodiment, the opening set pressure value P4 of the automatic exhaust valve can be determined according to the following formula:

[0144] (P3+P0)*(V1-V) / (273.15+T1)+(P3+P0)*(V2+V) / (273.15+T2)=(P2+P0)*V1 / (273.15+T1)+(P2+P0)*V2 / (273.15+T2) (1)

[0145] P4=P3+ΔP (2)

[0146] In the formula, T1 is the lowest working temperature of the molten salt stored in the low-temperature molten salt storage tank, in units of ℃;

[0147] T2 is the highest working temperature of the molten salt stored in the high-temperature molten salt storage tank, in units of ℃;

[0148] P0 is the average atmospheric pressure in the local area for many years, in units of Pa;

[0149] P2 is the second pressure threshold, in units of Pa;

[0150] P3 is the gas phase pressure in the high-temperature molten salt storage tank and the low-temperature molten salt storage tank when the maximum molten salt heat release of the molten salt energy storage system, unit Pa;

[0151] ΔP is the pressure margin, unit Pa;

[0152] V is the effective volume of the molten salt energy storage system when the molten salt circulates to store and release heat, unit m 3 ;

[0153] V1 is the gas phase volume of the low-temperature molten salt storage tank corresponding to the maximum molten salt heat storage of the molten salt energy storage system, unit m 3 ;

[0154] V2 is the gas phase volume of the high-temperature molten salt storage tank corresponding to the maximum molten salt heat storage of the molten salt energy storage system, unit m 3 .

[0155] The solid heat accumulator heat storage Q is calculated according to the following formula:

[0156] Q = M / R / 1000 * [(P3 + P0) * (V2 + V) - (P2 + P0) * V2] / (273.15 + T2) * (T2 - T1) * C (3)

[0157] C is the specific heat capacity of nitrogen, kJ / (kg•℃); M is the molecular weight of nitrogen, taken as 28.01 g / mol; R is the universal gas constant, taken as 8.314 J / (mol•K).

[0158] Implementation case: T1 is 190℃, T2 is 420℃, P0 is 100000 Pa, P2 is 500 Pa (P1 is 300 Pa), V is 10000 m 3 , V1 is 12000 m 3 , V2 is 2000 m

[0159] P3 is calculated to be 33787.25 Pa using formula (1). ΔP is selected to be 1212.75 Pa, and P4 is calculated to be 35000 Pa using formula (2). C is 0.741 kJ / (kg•℃), and Q is calculated to be 1163395.19 kJ using formula (3).

[0160] It should be noted that the above description of the disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features disclosed herein.

Claims

1. A dual-tank molten salt energy storage nitrogen sealing system, characterized in that, include: The molten salt storage tank unit includes a low-temperature molten salt storage tank for storing low-temperature molten salt and a high-temperature molten salt storage tank for storing high-temperature molten salt. Both the low-temperature molten salt storage tank and the high-temperature molten salt storage tank are equipped with a gas phase pressure monitoring device, an automatic exhaust pipeline and a manual exhaust pipeline. The nitrogen sealing unit includes a nitrogen preparation device, a nitrogen buffer device, and a nitrogen supply pipeline. The nitrogen preparation device is connected to the nitrogen buffer device. The nitrogen buffer device is connected to the top gas phase zone of the low-temperature molten salt storage tank and the high-temperature molten salt storage tank respectively through the nitrogen supply pipeline. The nitrogen supply pipeline is equipped with a valve assembly that is interlocked with the gas phase pressure monitoring device. The dual-tank gas phase balance unit includes a gas phase balance pipeline and a temperature control device. The gas phase balance pipeline connects the gas phase zones of the low-temperature molten salt storage tank and the high-temperature molten salt storage tank. The temperature control device is located on the main pipeline of the flow path of the gas phase balance pipeline and is used to regulate the temperature of the gas flowing between the two tanks.

2. The dual-tank molten salt energy storage nitrogen sealing system according to claim 1, characterized in that, It also includes a tank preheating unit, which includes a preheating fan, a preheating air heater, a tank gas discharge pipeline, and a preheating gas supply pipeline. The preheating fan, the tank gas discharge pipeline, the preheating air heater, and the preheating gas supply pipeline form a nitrogen internal circulation heating circuit, which is used to preheat the low-temperature molten salt storage tank and the high-temperature molten salt storage tank before filling them with molten salt.

3. The dual-tank molten salt energy storage nitrogen sealing system according to claim 2, characterized in that, The gas discharge pipeline inside the tank includes a first gas discharge pipeline inside the tank and a second gas discharge pipeline inside the tank that are interconnected. The preheated gas supply pipeline includes a first preheated gas supply pipeline inside the tank and a second preheated gas supply pipeline that are interconnected. One end of the first gas discharge pipeline inside the tank and one end of the second gas discharge pipeline inside the tank extend into the lower part of the low-temperature molten salt storage tank and the high-temperature molten salt storage tank, respectively. One end of the first preheating gas supply pipeline and one end of the second preheating gas supply pipeline extend into the upper part of the low-temperature molten salt storage tank and the upper part of the high-temperature molten salt storage tank, respectively. The preheating fan and the preheating air heater are connected in series in the gas discharge pipeline and the preheating gas supply pipeline inside the tank.

4. The dual-tank molten salt energy storage nitrogen sealing system according to claim 3, characterized in that, The preheating fan is provided in at least two units, and the two preheating fans are connected in parallel.

5. A dual-tank molten salt energy storage nitrogen sealing system according to claim 1, characterized in that, The automatic exhaust pipe is equipped with a normally open manual shut-off valve and an automatic exhalation valve. The normally open manual shut-off valve remains open during normal system operation, and the automatic exhalation valve automatically opens to exhaust air when the pressure inside the tank reaches a set value. The manual exhaust pipe is equipped with a normally closed manual shut-off valve, which remains closed during normal system operation.

6. The dual-tank molten salt energy storage nitrogen sealing system according to claim 1, characterized in that, The nitrogen supply pipeline includes a first nitrogen supply pipeline and a second nitrogen supply pipeline; The nitrogen buffer device is connected to the nitrogen preparation device by a nitrogen inlet pipeline, and the nitrogen buffer device is connected to a nitrogen supply pipeline at its outlet. The nitrogen supply pipeline is connected to one end of the first nitrogen replenishment pipeline and the second nitrogen replenishment pipeline. The other ends of the first nitrogen inlet pipeline and the second nitrogen inlet pipeline are respectively connected to the top gas phase zone of the low-temperature molten salt storage tank and the high-temperature molten salt storage tank; the valve assembly is installed on both the first nitrogen inlet pipeline and the second nitrogen inlet pipeline. The valve assembly includes an electric valve, a pressure reducing valve, and a manual shut-off valve. The electric valve is electrically connected to the gas phase pressure monitoring device. When the gas phase pressure monitoring device detects that the gas phase pressure of the low-temperature molten salt storage tank or the high-temperature molten salt storage tank is lower than a first pressure threshold, the corresponding electric valve opens, and nitrogen is added to the low-temperature molten salt storage tank or the high-temperature molten salt storage tank. When the gas phase pressure monitoring device detects that the gas phase pressure of the low-temperature molten salt storage tank or the high-temperature molten salt storage tank reaches the second pressure threshold, the corresponding electric valve closes and stops the replenishment of nitrogen; the second pressure threshold is greater than the first pressure threshold.

7. A dual-tank molten salt energy storage nitrogen sealing system according to claim 6, characterized in that, The first pressure threshold is 100Pa-500Pa, and the second pressure threshold is 100Pa-300Pa higher than the first pressure threshold.

8. A dual-tank molten salt energy storage nitrogen sealing system according to claim 1, characterized in that, The gas phase balance pipeline includes a first gas phase balance pipeline, a second gas phase balance pipeline, and a bypass gas phase balance pipeline. One end of the first gas phase balance pipeline is connected to the top gas phase zone of the high-temperature molten salt storage tank, and the other end of the first gas phase balance pipeline is connected to the temperature control device. One end of the second gas phase balance pipeline is connected to the top gas phase zone of the low-temperature molten salt storage tank, and the other end of the second gas phase balance pipeline is connected to the temperature control device. The bypass gas phase balance pipeline is connected in parallel with the temperature control device, and the two ends of the bypass gas phase balance pipeline are respectively connected to the first gas phase balance pipeline and the second gas phase balance pipeline. Valves are connected to the first gas phase balance pipeline, the second gas phase balance pipeline, and the bypass gas phase balance pipeline. During normal operation, the valve on the bypass gas phase balance pipeline is in the closed state, while the valves on the first gas phase balance pipeline and the second gas phase balance pipeline are in the open state. During the thermal storage operation, the high-temperature gas in the high-temperature molten salt storage tank enters the temperature control device through the gas phase balance pipeline to release heat and cool down, and then flows into the low-temperature molten salt storage tank. During the exothermic operation phase, the low-temperature gas in the low-temperature molten salt storage tank enters the temperature control device through the gas phase balance pipeline, absorbs heat and rises in temperature, and then flows into the high-temperature molten salt storage tank.

9. A dual-tank molten salt energy storage nitrogen sealing system according to claim 1, characterized in that, The temperature control device is a solid heat accumulator, which has multiple heat exchange tubes inside. The multiple heat exchange tubes adopt any of the following structural forms: Form 1: All heat exchange tubes are U-shaped heat exchange tubes, and each U-shaped heat exchange tube is distributed in a serpentine pattern within the solid accumulator; Form 2: All heat exchange tubes are straight tubes, and the straight tubes are arranged with gaps in the solid heat accumulator; The solid heat accumulator is filled with a solid heat storage medium.

10. A method for operating a dual-tank molten salt energy storage nitrogen sealing system, comprising operating the dual-tank molten salt energy storage nitrogen sealing system according to any one of claims 1-9, characterized in that, Includes the following steps: Nitrogen sealing control: The pressure inside the storage tank is monitored in real time by a gas phase pressure monitoring device. When the pressure is lower than the first threshold, the nitrogen supply pipeline is opened to supply nitrogen to the storage tank; when the pressure reaches the second threshold, nitrogen supply is stopped; when the pressure exceeds the exhaust threshold, the gas is exhausted through the automatic exhaust pipeline to maintain a slight positive pressure in the storage tank. Dual-tank balancing: The gas phase zones of the low-temperature molten salt storage tank and the high-temperature molten salt storage tank are connected by a gas phase balancing pipeline. The gas circulation is driven by the pressure difference between the two tanks, and the temperature of the circulating gas is regulated by a temperature control device. Tank preheating and salt filling: Before the first filling of molten salt, the low temperature molten salt storage tank and the high temperature molten salt storage tank are first purged with nitrogen and the inner wall is preheated, and then the storage tank is filled with salt. The steps for preheating and salting the storage tank include: The first step is to replace the air in the low-temperature molten salt storage tank and the high-temperature molten salt storage tank with nitrogen. During the nitrogen replacement process, the preheating fan is started so that all the air in the outlet and inlet pipes of the preheating fan is replaced with nitrogen. The second step is to preheat the low-temperature molten salt storage tank. First, the low-temperature molten salt storage tank is preheated through the nitrogen internal circulation heating circuit. The heating power increases stepwise with the tank wall temperature. Preheating is stopped when the tank wall temperature reaches the standard. The third step is to inject molten salt into the low-temperature molten salt storage tank. After the low-temperature molten salt storage tank has been preheated, molten salt that has been melted by high-temperature heating is injected into the low-temperature molten salt storage tank. The fourth step is to preheat the high-temperature molten salt storage tank. After the low-temperature molten salt storage tank is filled with salt, the high-temperature molten salt storage tank is preheated through the nitrogen internal circulation heating circuit. The heating power increases stepwise with the tank wall temperature. Preheating is stopped when the tank wall temperature reaches the standard. The fifth step is to inject molten salt into the high-temperature molten salt storage tank. After the high-temperature molten salt storage tank has been preheated, the molten salt in the low-temperature molten salt storage tank is heated by the molten salt heating device and then injected into the high-temperature molten salt storage tank.

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