Salt injection construction method for trough type heat collection system

Abstract

The application discloses a kind of trough type heat collection system salt injection construction method, including molten salt tank for trough type heat collection system and salt storage tank, and the upper and lower parts of salt storage tank are respectively provided with feeding mechanism and heating mechanism, rotating device is installed outside fine filter box and is used to rotate filter filler layer, so that the liquid molten salt flowing through siphon internal persistence and filter filler layer different filter surface are continuously filtered impurities;Gas extraction assembly is arranged on the temporarily airtight salt storage tank, and the finished product liquid molten salt in the salt storage tank is discharged into the salt storage tank in a self-suction manner under the cooperation of siphon, gas extraction pipe and air valve, the setting of coarse filter cover and fine filter box filter filler layer ensures that the finished product liquid molten salt in molten salt tank can be continuously filtered impurities, and the solid molten salt in molten salt tank is added without directly affecting the finished product liquid molten salt in salt storage tank.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of molten salt utilization of a solar thermal power station, and particularly relates to a molten salt injection construction method for a trough type heat collection system. BACKGROUND

[0002] In the injection step of the molten salt in the solar thermal power station, the solvent water is injected first, then the solid molten salt is added and heated to 300 DEG C, the temperature of the liquid molten salt after heating is maintained at 270 DEG C, and a small amount of solid molten salt is gradually added, the liquid molten salt is heated to 350 DEG C again, the quantitative solid potassium nitrate is synchronously added, and the finished product is discharged, as described in the 'New Energy Solar Thermal Power Station Molten Salt System Commissioning and Operation Research' by Ye Liangzhong.

[0003] For example, a Chinese patent with the publication number CN105268378A discloses a molten salt system and a method for applying the molten salt system, the system includes a feeding system, a molten salt tank system, a combustion heating system and a salt storage tank system; the molten salt tank system includes a molten salt tank, which is a horizontal cylindrical shape and can rotate independently around the axis, the left end surface of the molten salt tank is provided with a feeding pipe connected with the inner cavity of the molten salt tank, and the right end surface of the molten salt tank is provided with a liquid outlet pipe connected with the inner cavity of the molten salt tank; the molten salt after melting can automatically overflow to the salt storage tank from the upper layer of the molten salt tank, without external power equipment such as a pump, and the structure is simple and practical.

[0004] For example, a Chinese patent with the publication number CN109011696B discloses a purification device for insoluble impurities in molten salt, which includes a separation column filled with adsorbent, the particles of the adsorbent have a pore structure for adsorbing the insoluble impurities in the molten salt, and the particles of the adsorbent have gaps for the molten salt to pass through; the patent describes the shortcomings of the existing bubble method for removing the impurities in the molten salt in the background art.

[0005] However, the above scheme has the following disadvantages: the liquid molten salt automatically overflowing into the salt storage tank in the Chinese patent with publication number CN105268378A is not subjected to impurity filtering treatment, and the adsorption area of the adsorbent in the Chinese patent with publication number CN109011696B is limited, which is difficult to ensure continuous and efficient impurity filtering in the face of tons of liquid molten salt, and at the same time, the liquid outlet pipe connection mode through the inner cavity between the salt dissolving tank and the salt storage tank cannot avoid the gas mixed when the feeding system feeds towards the salt dissolving tank and the floating dust impurities on the surface of the solid molten salt directly entering into the salt storage tank through the liquid outlet pipe, and when the addition amount of the solid salt in the salt dissolving tank is large, the connection of the liquid outlet pipe has an impact on the temperature maintenance of the finished liquid molten salt in the salt storage tank, how to improve the salt injection construction method to ensure that the finished liquid molten salt in the molten salt tank is continuously filtered and then discharged into the salt storage tank in a self-suction manner, and at the same time, the addition of the solid molten salt in the molten salt tank will not have a direct impact on the finished liquid molten salt in the salt storage tank. SUMMARY

[0006] The purpose of the present application is to provide a salt injection construction method for a trough-type heat collection system to solve the problems in the above background art.

[0007] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0008] A salt injection construction method for a trough-type heat collection system, comprising a molten salt tank and a salt storage tank for the trough-type heat collection system, a feeding mechanism and a heating mechanism are respectively arranged on the upper and lower parts of the salt storage tank, and the method further comprises the following steps:

[0009] A salt storage tank is installed below the molten salt tank, and a siphon pipe is installed to insert the inlet and outlet ends of the siphon pipe into the molten salt tank and the low-temperature salt storage tank, respectively;

[0010] A coarse filter cover is installed on the liquid inlet end of the siphon pipe and used for preliminary filtering of the liquid molten salt, and a fine filter box is installed on the middle part of the top end of the siphon pipe close to the salt storage tank side and used for secondary filtering of the liquid molten salt;

[0011] The fine filter box is sealed and filled with replaceable filter filler layers, and the filter filler layers have a filter surface larger than the flow area of the siphon pipe;

[0012] A rotating device is installed on the outside of the fine filter box and used for rotating the filter filler layers, so that the liquid molten salt flowing through the inside of the siphon pipe is continuously filtered by different filter surfaces of the filter filler layers;

[0013] An air extraction assembly is arranged on the salt storage tank, and when the salt storage tank is in a gas-tight state, the air extraction assembly extracts air, the finished liquid molten salt in the molten salt tank is sucked under the negative pressure suction of the siphon pipe, and after being double-filtered by the coarse filter cover and the fine filter box, the finished liquid molten salt is continuously discharged into the salt storage tank.

[0014] Preferably, the inside bottom end surface of the molten salt tank is located higher than the highest liquid level of the inside of the salt storage tank, and the liquid inlet end of the siphon pipe is higher than the liquid outlet end, and the liquid outlet side wall of the molten salt tank has an inner groove part.

[0015] Preferably, the fine filter box is detachably inserted into the inner groove part, and the upper and lower end surfaces of the insertion end of the fine filter box have flow-through pipe openings, and the flow-through pipe openings of the upper and lower end surfaces are communicated with the liquid discharge side of the siphon pipe.

[0016] Preferably, the fine filter box has a ring structure, and a filter ring frame is rotatably arranged in the annular cavity of the inner wall of the fine filter box, and the filter filler layer is arranged inside the filter ring frame, and the liquid molten salt discharged from the siphon pipe to the flow-through pipe opening of the upper end surface of the insertion side of the fine filter box sequentially passes through the filter ring frame, the filter filler layer, and the flow-through pipe opening of the lower end surface, and then is injected into the salt storage tank through the liquid outlet end of the siphon pipe.

[0017] Preferably, the upper and lower flow-through surfaces of the filter ring frame are concave hole structures and are used to increase the flow-through area of the liquid molten salt, the flow-through pipe opening of the upper end surface of the insertion side of the fine filter box is in sealed communication with the liquid discharge side of the siphon pipe through a valve body, the gap between the inner groove part and the fine filter box is filled with a removable temporary heat preservation filling layer, and the bottom end cross section of the fine filter box is an inner concave structure for gathering liquid molten salt to the liquid discharge port of the siphon pipe, and a drainage inclined arc plate with decreasing thickness towards the liquid discharge port of the siphon pipe is arranged at the inner concave structure.

[0018] Preferably, a heat preservation wire group is embedded in the inside of the drainage inclined arc plate, which heats the liquid molten salt above the drainage inclined arc plate to prevent solidification, and the heat preservation wire group is connected to an external temperature control switch and an external power source.

[0019] Preferably, the rotating device includes a protruding cavity block arranged on the outer side wall of the fine filter box, a rotatable heat-resistant gear body is prearranged in the inside of the protruding cavity block, an annular gear slot is arranged on the outer side ring wall of the filter ring frame and is engaged with the heat-resistant gear body, a drive motor is arranged on the outside of the protruding cavity body, the output shaft end of the drive motor is connected to the heat-resistant gear body through a sealing bearing hole prearranged on the protruding cavity body, and the output shaft end of the drive motor drives the filter filler layer in different regions inside the filter ring frame to continuously filter the liquid molten salt discharged from the siphon pipe through the cooperation of the heat-resistant gear body and the annular gear slot.

[0020] Preferably, the filter filler layer is arranged in zones on the filter ring frame, and the air extraction assembly includes an air extraction pipe and an air vent valve arranged on the salt storage tank, when the air extraction pipe extracts air from the salt storage tank, the air vent valve is in airtight state, after the liquid molten salt in the molten salt tank is sucked into the salt storage tank by the siphon pipe, the air suction end of the air extraction pipe is closed, and the air vent valve is opened, under the principle of siphon, the siphon pipe continuously sucks and discharges the liquid molten salt.

[0021] Preferably, the siphon pipe and the filter ring frame are made of heat-resistant ceramic material, the depth of the recess part is 20-30 cm, the thickness of the wall of the surface where the recess part is located is 15-25 cm, the wall of the surface where the recess part is located is made of metal heat-conducting material, the other wall of the recess part contacts with the liquid molten salt and transfers heat to the metal heat-conducting material, and the metal heat-conducting material finally keeps the side where the fine filter box is inserted warm through the temporary heat insulation filling layer.

[0022] Compared with the prior art, the beneficial effects of the present application are that the finished liquid molten salt in the salt storage tank is discharged into the salt storage tank in a self-suction manner under the cooperation of the siphon pipe, the air suction pipe and the air valve, the setting of the coarse filter cover and the filter filler layer in the fine filter box ensures that the finished liquid molten salt in the molten salt tank can be continuously filtered, and the solid molten salt in the molten salt tank does not directly affect the finished liquid molten salt in the salt storage tank. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The figure is a flowchart of the salt injection construction method of the present application.

[0024] Figure 2 The figure is a schematic diagram of the overall structure of the present application.

[0025] Figure 3 The figure is a schematic diagram of the fine filter box region. Figure 1 The figure is a schematic diagram of the fine filter box region.

[0026] Figure 4 The figure is a schematic diagram of the filter ring frame in a half-sectioned state and the position cooperation of the drainage inclined arc plate.

[0027] In the figure: 1, siphon pipe; 2, coarse filter cover; 3, fine filter box; 4, filter filler layer; 5, recess part; 6, flow-through pipe opening; 7, filter ring frame; 8, valve body; 9, temporary heat insulation filling layer; 10, drainage inclined arc plate; 11, heat preservation wire group; 12, external temperature control switch; 13, external power supply; 14, protruding cavity block; 15, heat-resistant gear body; 16, ring-shaped gear groove; 17, driving motor; 101, molten salt tank; 102, salt storage tank; 201, air suction pipe; 202, air valve. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application.

[0029] Please refer to Figures 1-4 The present application provides a technical solution:

[0030] Embodiment one:

[0031] A kind of trough type heat collection system salt injection construction method, including molten salt tank 101 for trough type heat collection system and salt storage tank 102, the upper and lower parts of salt storage tank 102 are provided with feeding mechanism and heating mechanism respectively, feeding mechanism and heating mechanism refer to the existing Chinese patent with publication number CN105268378A, and feeding mechanism and heating mechanism are also in the existing trough type heat collection system about "new energy photothermal power station molten salt salt system debugging and operation research" carry out invisible disclosure, not described repeatedly, also include the following steps:

[0032] S1: install salt storage tank 102 below the side of molten salt tank 101, and install siphon 1 so that its inlet and outlet ends are inserted into molten salt tank 101 and low-temperature salt storage tank 102 respectively;

[0033] S2: install coarse filter cover 2 at the liquid inlet end of siphon 1 and use it to preliminarily filter large-particle impurities in liquid molten salt, coarse filter cover 2 is composed of ceramic perforated plate, the aperture is 0.25mm, and the preliminarily filters large-particle impurities in the inhaled liquid molten salt, and install fine filter box 3 at the middle of the top end of siphon 1 close to the side of salt storage tank 102 and use it to secondarily filter small-particle impurities less than 0.25mm in liquid molten salt;

[0034] S3: sealably fill replaceable filter filler layer 4 in fine filter box 3, the porosity of filter filler layer 4 is 0.4-0.55, the selection of filter filler layer 4 can be quartz sand, activated carbon particles, alumina particles, etc., which needs to be adaptively selected according to the type of molten salt to avoid reaction between liquid molten salt and selected filter filler layer 4 to form impurities, and the specific selection of filter filler layer 4 type for which molten salt is paired is the existing technology disclosed in patent no. CN109011696B, not described repeatedly, and filter filler layer 4 has a filter surface larger than the flow area of siphon 1;

[0035] S4: install rotating device outside fine filter box 3 and use it to rotate filter filler layer 4, so that the liquid molten salt flowing in siphon 1 continuously filters impurities on different filter surfaces of filter filler layer 4;

[0036] Saltification step:

[0037] (1) inject 15 tons of water into molten salt tank 101;

[0038] (2) open the outlet valve of the cooling water pump and start the cooling water pump, then form a closed loop of cooling water, and then start the fan, water pump, agitator and electric heater of molten salt tank 101;

[0039] (3) start adding solid molten salt to molten salt tank 101, start the belt conveyor, and add 30 tons of molten salt to molten salt tank 101, pay attention to observe the dissolution of molten salt during the adding process to ensure that all the added molten salt is dissolved;

[0040] (4) Control the heating rate of the liquid molten salt in the molten salt tank 101 to 20℃ / h by controlling the start-stop of the electric heater of the molten salt tank 101, until heated to 300℃, and the heating temperature is adjusted adaptively according to the selected type of solid-state molten salt;

[0041] (5) Add 20 tons of solid-state molten salt to the molten salt tank 101, and observe the material inlet of the molten salt tank 101 and the temperature of the molten salt in the molten salt tank 101 at the same time during the adding process; the temperature of the liquid molten salt needs to be maintained at 270℃ during the adding process, and the adding process needs to be stopped when the temperature of the liquid molten salt in the molten salt tank 101 reaches 250℃, and the adding process needs to be continued after the temperature rises;

[0042] (6) Maintain the temperature of 270℃ in the molten salt tank 101, start the empty tube preheating of the molten salt furnace, and continue until the empty tube preheating is completed;

[0043] (7) After turning off the electric heater of the molten salt tank 101, turn on the molten salt circulating pump, heat the molten salt by the molten salt furnace, heat the molten salt in the molten salt tank 101 to 350℃, and start preheating the molten salt pipeline of the molten salt system.

[0044] (8) Keep circulating and add 30 tons of molten salt to the tank, and when the temperature in the tank reaches 350℃, the start-up stage is completed;

[0045] S5: Set an air extraction assembly on the salt storage tank 102, and when the salt storage tank 102 is in airtight state, specifically, set an externally controlled air valve on the liquid discharge side of the salt storage tank 102 to ensure that the salt storage tank 102 is in airtight state when the air extraction assembly is extracting air, and the finished liquid molten salt in the molten salt tank 101 is sucked into the salt storage tank 102 through secondary filtration under the negative pressure suction of the siphon tube 1 when the air extraction assembly is extracting air. For details, refer to the siphon principle: the liquid at the highest point in the tube moves to the lower tube opening under the action of gravity, a negative pressure is generated inside the U-shaped tube, causing the liquid at the high tube opening to be sucked into the highest point, forming a siphon phenomenon.

[0046] Example Two:

[0047] Based on example one, it is further explained that the position of the bottom end face inside the molten salt tank 101 is higher than the highest liquid level inside the salt storage tank 102, and the height of the liquid inlet end of the siphon tube 1 is higher than that of the liquid discharge end, and the molten salt tank 101 has an inner groove part 5 with an opening facing horizontally outward on the liquid outlet side wall;

[0048] The fine filtration box 3 can be detachably inserted into the inner groove part 5, and the upper and lower end faces of the fine filtration box 3 have flow-through tube openings 6, the fine filtration box 3 and the flow-through tube openings 6 are made of ceramic high-temperature resistant composite material, and the upper and lower end faces of the flow-through tube openings 6 are connected to the liquid discharge side of the siphon tube 1.

[0049] Example Three:

[0050] Further illustrated on the basis of the embodiment two, the fine filter box 3 is a ring structure, and a filter ring frame 7 is sealingly and rotatably arranged in the annular cavity of the inner wall of the fine filter box 3. The filter filler layer 4 is arranged inside the filter ring frame 7. The liquid molten salt flowing through the flow-through pipe orifice 6 at the upper end surface of the insertion side of the fine filter box 3 is sequentially subjected to the filter ring frame 7, the filter filler layer 4, and the flow-through pipe orifice 6 at the lower end surface, and then is injected into the salt storage tank 102 through the discharge port of the siphon pipe 1;

[0051] The upper and lower flow-through surfaces of the filter ring frame 7 are concave hole structures and are used to increase the flow-through area of the liquid molten salt. The filter ring frame 7 can also be made of high-temperature ceramic material. The flow-through pipe orifice 6 at the upper end surface of the insertion side of the fine filter box 3 is sealingly communicated with the discharge side of the siphon pipe 1 through a valve body 8. The valve body 8 is a high-temperature molten salt valve produced by Shanghai Yahu Valve Industry Co., Ltd. and is used to adjust the opening and closing of the discharge side of the siphon pipe 1, thereby controlling the opening and closing of the inlet end of the molten salt liquid in the fine filter box 3. The gap between the recess portion 5 and the fine filter box 3 is filled with a removable temporary heat preservation filling layer 9. The temporary heat preservation filling layer 9 is made of ceramic particles with a diameter of 1 cm. A detachable cover plate is matched with the opening portion of the recess portion 5. The cover plate is not shown and is symmetrically arranged in two halves, which facilitates the combined installation and sealing of the opening portion of the recess portion 5. Meanwhile, the rotary control end of the valve body 8 can be designed to be extended outside the opening portion of the recess portion 5 and penetrate through the reserved port of the cover plate, thereby avoiding the sliding of the temporary heat preservation filling layer 9. The bottom end cross section of the fine filter box 3 is an inner concave structure for gathering the liquid molten salt to the discharge port of the siphon pipe 1. Meanwhile, a drainage inclined arc plate 10 with a decreasing thickness towards the discharge port of the siphon pipe 1 is arranged at the inner concave structure.

[0052] The heat preservation wire group 11 is embedded in the drainage inclined arc plate 10. The heat preservation wire group 11 is made of symmetrically arranged electric heating wires. The working temperature of the heat preservation wire group 11 is greater than the solidification temperature of the selected molten salt. The heat preservation wire group 11 heats the liquid molten salt above the drainage inclined arc plate 10 to avoid solidification. Meanwhile, the heat preservation wire group 11 is connected with an external temperature control switch 12 and an external power supply 13.

[0053] The rotating device comprises a convex cavity block 14 arranged on the outer side wall of the fine filter box 3, a rotatable heat-resistant gear body 15 is prearranged in the interior of the convex cavity block 14, an annular groove is prearranged on the inner ring wall of the filter ring frame 7, and the outer side wall of the annular groove and the interior cavity of the convex cavity block 14 are in communication, an annular gear slot 16 is arranged on the outer side ring wall of the filter ring frame 7 and is engaged with the heat-resistant gear body 15, a driving motor 17 is arranged outside the convex cavity block 14, the power supply end of the driving motor 17 is connected with an external power supply, the output shaft end of the driving motor 17 is connected with the heat-resistant gear body 15 through a sealing bearing hole prearranged on the convex cavity block 14, and the output shaft end of the driving motor 17 drives the filter filler layer 4 in different regions in the interior of the filter ring frame 7 to continuously filter the liquid molten salt discharged from the siphon pipe 1 through the cooperation of the heat-resistant gear body 15 and the annular gear slot 16.

[0054] In another embodiment, the annular region in the interior of the filter ring frame 7 is divided into four regions, and the filter filler layers 4 with gradually decreasing particles are sequentially arranged in the four regions, and the filter filler layers 4 with different particle diameters have different gaps between the particles, so that the liquid molten salt passing through the fine filter box 3 is filtered through different gaps.

[0055] In another embodiment, the annular region in the interior of the filter ring frame 7 is divided into four regions, and the selection of the filter filler layers 4 in the four regions is obtained through the existing authorized Chinese patent with the patent announcement number CN109011696B, and details are not described herein.

[0056] Embodiment four:

[0057] On the basis of embodiment one, the filter filler layer 4 is arranged in zones on the filter ring frame 7, the air extraction assembly includes an air extraction pipe 201 and a vent valve 202 arranged on the salt storage tank 102, the vent valve 202 can select a high-temperature-resistant electromagnetic valve 2L / US-50 produced by Ningbo Fenghua Xikou Naida Pneumatic Component Factory, when the salt storage tank 102 is in a gas-tight state, the vent valve 202 is in a closed state, and the air extraction pipe 201 is connected with the suction end of an external air extraction pump not shown, the air extraction pump can select an XGB series produced by Taizhou Yijia Electrical Machinery Co., Ltd., and the air extraction pump and the air extraction pipe 201 are connected through an electric shut-off valve not shown for opening and closing control of the passage, the power on and off ends of the electric shut-off valve and the air extraction pump are connected in series, when the air extraction pipe 201 extracts air from the salt storage tank 102, the selection of the vent valve 202 and the electric shut-off valve and the air extraction pump can be adjusted and replaced according to the actual size of the salt storage tank 102, which is not limited, and the power on and off ends of the air extraction pump and the vent valve 202 are connected with an external PLC power controller, the vent valve 202 is closed in a gas-tight state, the air extraction pipe 201 extracts air from the inside of the salt storage tank 102 through the air extraction pump and forms a negative pressure with a low pressure difference, while the gas pressure difference inside the molten salt tank 101 is normal, and the connection of the salt storage tank 102 to the liquid discharge pump is in a gas-tight closed state, so that after the siphon pipe 1 sucks the liquid molten salt inside the molten salt tank 101 into the salt storage tank 102, the suction end of the air extraction pipe 201 is closed, the vent valve 202 is opened, and the siphon pipe 1 continuously sucks and discharges the liquid molten salt under the principle of siphon, realizing the absorption of the finished liquid molten salt in the molten salt tank 101 into the salt storage tank 102 through the siphon pipe 1 without power.

[0058] Embodiment five:

[0059] On the basis of embodiment three, the siphon pipe 1 and the filter ring frame 7 are both made of heat-resistant ceramic material, the depth of the recessed groove part 5 is 20 cm, the thickness of the wall where the recessed groove part 5 is located is 15 cm, and the corresponding wall of the recessed groove part 5 is made of metal heat-conducting material, which can include any one of carbon steel and iron, and the other wall of the recessed groove part 5 contacts the liquid molten salt and transfers heat to the metal heat-conducting material, and the metal heat-conducting material finally transfers heat to the side of the fine filter box 3 inserted through the temporary heat preservation filler layer 9, thereby reducing the heat dissipation of the liquid molten salt in the fine filter box 3.

[0060] Embodiment six: different from embodiment five, the depth of the recessed groove part 5 is 30 cm, and the thickness of the wall where the recessed groove part 5 is located is 25 cm.

[0061] In another embodiment, the corresponding wall of the recessed groove part 5 is made of any one of wrought iron and copper.

[0062] The inside product liquid molten salt of the salt storage tank 102 is discharged into the salt storage tank 102 in a self-suction manner under the cooperation of the siphon 1, the air extraction pipe 201 and the air valve 202, the setting of the coarse filter cover 2 and the fine filter box 3 and the filter filler layer 4 ensures that the product liquid molten salt in the molten salt tank 101 can be continuously filtered, and the molten salt tank 101 and the salt storage tank 102 are connected only through the siphon 1, so that the addition of solid molten salt in the molten salt tank 101 does not directly affect the product liquid molten salt in the salt storage tank 102.

[0063] Finally, it should be noted that: the above only for the preferred embodiments of the present application, and not for limiting the present application, although the foregoing embodiments of the present application are described in detail, for those skilled in the art, it still can be modified, or part of the technical features of the equivalent replacement, within the spirit and principles of the present application, any modification, equivalent replacement, improvement, etc., should be included in the protection scope of the present application.

Claims

1. A method for salt injection construction of a trough type heat collection system, comprising a molten salt trough for a trough type heat collection system and a salt storage tank, a feeding mechanism and a heating mechanism being respectively arranged on the upper and lower parts of the salt storage tank, characterized in that, Further comprising the following steps: S1, installing a salt storage tank below the side of the molten salt tank, and installing a siphon tube with its inlet and outlet ends inserted into the molten salt tank and the salt storage tank, respectively; S2, installing a coarse filter cover at the liquid inlet end of the siphon tube for primary filtration of the liquid molten salt, and installing a fine filter box near the side of the siphon tube close to the salt storage tank for secondary filtration of the liquid molten salt; S3, sealingly filling the fine filter box with replaceable filter filler layers, and the filter filler layers having a filter surface larger than the flow area of the siphon tube; S4, installing a rotating device outside the fine filter box for rotating the filter filler layers, so that the liquid molten salt flowing through the siphon tube continuously passes through different filter surfaces of the filter filler layers for impurity filtration; and S5, providing an air extraction assembly on the salt storage tank, when the salt storage tank is in airtight state, the air extraction assembly extracts air to suck the finished liquid molten salt in the molten salt tank into the salt storage tank through the siphon tube under the negative pressure suction of the siphon tube, and the liquid molten salt is double-filtered by the coarse filter cover and the fine filter box. The filter filler layers are arranged in zones on the filter ring frame, and the air extraction assembly includes an air extraction tube and an air valve provided on the salt storage tank, when the air extraction tube extracts air from the salt storage tank, the air valve is closed in airtight state, after the liquid molten salt in the molten salt tank is sucked into the salt storage tank by the siphon tube, the air extraction end of the air extraction tube is closed, and the air valve is opened, under the principle of siphon, the siphon tube continuously sucks and discharges the liquid molten salt.

2. The method of claim 1, wherein the method further comprises: The position of the bottom end surface of the molten salt tank is higher than the highest liquid level in the salt storage tank, and the height of the liquid inlet end of the siphon tube is higher than that of the liquid outlet end, and the liquid outlet side wall of the molten salt tank has an inner groove part.

3. The method of claim 2, wherein the method further comprises: The fine filter box is detachably inserted into the inner groove part, and the upper and lower end surfaces of the insertion end of the fine filter box have flow-through tube openings, and the flow-through tube openings of the upper and lower end surfaces are communicated with the liquid outlet side of the siphon tube.

4. The method of claim 3, wherein the salt is injected into the trench by a salt injection device. The fine filter box has a ring structure, and a filter ring frame is sealingly and rotatably arranged in the annular cavity of the inner wall of the fine filter box, the filter filler layers are arranged in the filter ring frame, and the liquid molten salt discharged into the upper end surface flow-through tube opening of the insertion side of the fine filter box through the siphon tube is sequentially filtered by the filter ring frame, the filter filler layers, and the lower end surface flow-through tube opening, and then injected into the salt storage tank through the liquid outlet end of the siphon tube.

5. The method of claim 4, wherein the method further comprises: The upper and lower flow-through surfaces of the filter ring frame are concave hole structures for increasing the flow-through area of the liquid molten salt, the upper end surface flow-through tube opening of the insertion side of the fine filter box is sealingly communicated with the liquid outlet side of the siphon tube through a valve body, the gap between the inner groove part and the fine filter box is filled with a removable temporary heat preservation filling layer, and the bottom end cross section of the fine filter box is an inner concave structure for gathering the liquid molten salt to the liquid outlet end of the siphon tube, and a drainage inclined arc plate with decreasing thickness towards the liquid outlet end of the siphon tube is arranged at the inner concave structure.

6. The method of claim 5, wherein the method further comprises: A heat preservation wire group is embedded in the drainage inclined arc plate for heating the liquid molten salt above the drainage inclined arc plate to prevent solidification, and the heat preservation wire group is connected with an external temperature control switch and an external power supply.

7. The method of claim 4, wherein the method further comprises: The rotating device comprises a convex cavity block arranged on the outer wall of the fine filter box, a rotatable heat-resistant gear body being prearranged inside the convex cavity block, an annular tooth groove being arranged on the outer ring wall of the filter ring frame and being engaged with the heat-resistant gear body, a driving motor being arranged outside the convex cavity block, the output shaft end of the driving motor being connected through a sealing bearing hole prearranged on the convex cavity block and the heat-resistant gear body, and the output shaft end of the driving motor driving the filter filler layer in different areas inside the filter ring frame to continuously filter the liquid molten salt discharged by the siphon through the cooperation of the heat-resistant gear body and the annular tooth groove.

8. The method of claim 5, wherein the method further comprises: The siphon and the filter ring frame are both made of heat-resistant ceramic material, the depth of the recess part is 20-30 cm, the thickness of the wall of the surface where the recess part is located is 15-25 cm, the wall of the surface where the recess part is located is made of metal heat-conducting material, the other wall of the recess part contacts with the liquid molten salt and transmits heat to the metal heat-conducting material, and the metal heat-conducting material finally transmits heat to the side where the fine filter box is inserted through the temporary heat preservation filler layer.

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