A resistive molten salt heater for avoiding over-temperature risk and its usage method

Abstract

The present invention discloses a resistive molten salt heater for avoiding over-temperature risks and its usage method. The resistive molten salt heater includes a housing, a mixing tank, a temperature regulating pipeline, and a plurality of temperature measuring elements. A plurality of electric heating tubes are inserted inside the housing, and a molten salt outlet and a molten salt inlet are respectively arranged at two ends of the housing; the mixing tank protrudes and is arranged at a position of the housing close to the molten salt outlet, and the mixing tank is communicated with the inside of the housing; the outlet end of the temperature regulating pipeline penetrates through the mixing tank and extends into the inside of the housing, and a molten salt switch valve, a molten salt regulating valve, and a check valve are sequentially arranged on the temperature regulating pipeline from upstream to downstream. The outlet end of the temperature regulating pipeline transports the molten salt to different positions of the mixing tank through a plurality of branch pipelines. By arranging a mixing tank for mixing low-temperature molten salt and high-temperature molten salt at the outlet end of the electric heater, the present invention avoids the over-temperature risks of the electric heater under extreme working conditions or frequent variable load working conditions, reduces the number of trips during its non-operating conditions, and reduces the possibility of high-temperature thermal decomposition of the internal molten salt.

Description

Technical Field

[0001] The present invention relates to the technical field of molten salt electric heating, and particularly relates to a resistive molten salt heater for avoiding over-temperature risks and a using method thereof. Background Art

[0002] The molten salt electric heater is one of the key devices of the molten salt thermal energy storage system. It has strong scalability and can be utilized in scenarios such as the construction of large new energy bases for wind, light, heat, and storage, the flexibility transformation of thermal power plants, and heat storage and heating on the user side. According to different heating methods, molten salt electric heaters mainly have three forms: resistive, electrode type, and electromagnetic induction type. Among them, the resistive type is a heating method that uses an electric current passing through a resistance wire to release heat to heat the molten salt, and has the advantages of low price, wide application, and mature technology.

[0003] Engineering requirements state that the temperature of the heating tubes inside the molten salt heater cannot exceed a certain limit. Otherwise, the risks of internal resistance wire fusing and external molten salt thermal decomposition are greatly increased, resulting in situations such as electric heating tripping and the scrapping of the entire electric heating tube. This is mainly because the heat transfer efficiency between the electric heating tube and the molten salt is low. When the electric load or molten salt flow rate changes frequently, rapidly, and significantly, the molten salt cannot timely carry away the heat generated by the electric heating tube, leading to a sharp increase in the internal temperature of the electric heating. The excessive temperature greatly increases the risk of the resistance wire melting. On the other hand, since the molten salt flows slowly inside the electric heater, mainly presenting a laminar flow state, and there are no means of disturbing the flow inside the electric heater, the temperature difference between the molten salt boundary layer and the tube wall temperature is not large. When the tube wall temperature rises, the risk of molten salt thermal decomposition also increases significantly, having a certain potential safety hazard. Taking solar salt (potassium nitrate + sodium nitrate), which has the largest engineering application scale, as an example, when the molten salt temperature exceeds 600 °C, serious thermal decomposition will occur, affecting the normal operation of the electric heater. Summary of the Invention

[0004] The present invention aims to at least solve one of the technical problems in the related art to some extent.

[0005] For this purpose, an embodiment of the present invention provides a resistive molten salt heater for avoiding over-temperature risks and a using method thereof.

[0006] On the one hand, the present invention provides a resistive molten salt heater for avoiding over-temperature risks, including:

[0007] A housing, multiple electric heating tubes are inserted inside the housing, and the electric heating tubes are supported and fixed by support plates fixed at both ends to the inner wall of the housing. Molten salt outlets and molten salt inlets are respectively arranged at both ends of the housing;

[0008] A mixing tank, the mixing tank protrudes and is arranged at a position of the housing close to the molten salt outlet, and the mixing tank is communicated with the inside of the housing;

[0009] A temperature control pipeline, the inlet end of the temperature control pipeline is connected to the molten salt inlet, the outlet end of the temperature control pipeline passes through the mixing tank and extends into the interior of the housing, a molten salt switch valve, a molten salt regulating valve and a check valve are sequentially arranged upstream and downstream on the temperature control pipeline, and the outlet end of the temperature control pipeline transports molten salt to different positions of the mixing tank through a plurality of branch pipelines;

[0010] A plurality of temperature measuring elements, which are used to measure the temperature of the molten salt flowing through the mixing tank and then flowing to the molten salt outlet.

[0011] In some embodiments, the low-temperature molten salt flowing out of the branch pipeline forms a jet and mixes with the main-path molten salt in the mixing tank.

[0012] In some embodiments, the opening degree of the molten salt regulating valve is adjusted according to the indicated temperature of the temperature measuring element. When the indicated temperature of the temperature measuring element exceeds the safety value, the opening degree of the molten salt regulating valve is increased.

[0013] In some embodiments, the electric heating tube is a U-shaped electric heating tube.

[0014] In some embodiments, the support plate is provided with through holes for the electric heating tubes to pass through.

[0015] In some embodiments, the mixing tank is an annular protrusion arranged at a position of the housing close to the molten salt outlet.

[0016] In some embodiments, a plurality of partition plates are arranged in the mixing tank.

[0017] In some embodiments, a plurality of the temperature measuring elements are uniformly arranged along the inner wall of the housing at a position between the mixing tank and the molten salt outlet.

[0018] In some embodiments, it further includes a wiring cavity, and one end of the electric heating tube for external wiring is inserted into the interior of the wiring cavity.

[0019] On the other hand, the present invention proposes a method for using a resistive molten salt heater to avoid over-temperature risks, including the following steps:

[0020] Under stable operating conditions, close the molten salt switch valve and the molten salt regulating valve. The low-temperature molten salt enters the molten salt heater from the molten salt inlet, flows through the electric heating tube and is heated, and then forms high-temperature molten salt and flows out from the molten salt outlet;

[0021] Under frequent load-changing operating conditions, open the molten salt switch valve and the molten salt regulating valve. The main-path molten salt enters the molten salt heater from the molten salt inlet, and the branch molten salt enters the mixing tank from the molten salt inlet through the temperature control pipeline and mixes with the main-path molten salt. When the indicated temperature of the temperature measuring element exceeds the safety value, increase the opening degree of the molten salt regulating valve to increase the flow rate of the low-temperature molten salt flowing out of the branch pipeline.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] When the resistive molten salt heater of the present invention frequently changes the load, by injecting low-temperature molten salt into the mixing tank, the turbulent state of the molten salt is enhanced, the heat transfer between the molten salt and the pipe wall is strengthened, the temperatures of the molten salt and the pipe wall are timely reduced, and the stable operation of the electric heater is ensured.

[0024] The resistive molten salt heater of the present invention is applicable to the working conditions where the electric load or the molten salt flow rate frequently changes greatly, and can avoid the risk of overheating, reduce the number of abnormal trippings, and reduce the possibility of thermal decomposition of the internal molten salt. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The above and / or additional aspects and advantages of the present invention will become apparent and be readily understood from the following description of the embodiments in conjunction with the drawings, wherein:

[0026] Figure 1 is a schematic structural diagram of the resistive molten salt heater for avoiding the overheating risk of the present invention;

[0027] Figure 2 is Figure 1 a view along the A-A section in

[0028] Figure 3 is Figure 1 a view along the B-B section in

[0029] DESCRIPTION OF THE REFERENCE NUMERALS

[0030] Wiring cavity 1, housing 2, support plate 3, electric heating tube 4, molten salt inlet 5, molten salt outlet 6, temperature measuring element 7, temperature regulating pipeline 8, check valve 9, molten salt switch valve 10, molten salt regulating valve 11, mixing tank 12, partition plate 13, branch pipeline 14. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0032] The resistive molten salt heater for avoiding the overheating risk and its usage method according to the embodiments of the present invention will be described below with reference to the drawings.

[0033] As Figures 1-3 shown, the resistive molten salt heater for avoiding the overheating risk of the present invention includes a housing 2, a mixing tank 12, a temperature regulating pipeline 8, a wiring cavity 1 and a plurality of temperature measuring elements 7.

[0034] At both ends of the housing 2, a molten salt inlet 5 and a molten salt outlet 6 are respectively provided. As Figure 1 shown, the molten salt inlet 5 is provided at the lower right side of the housing 2, and the molten salt outlet 6 is provided at the upper left side of the housing 2. The main path molten salt flowing through the housing 2 is pumped into the housing 2 from the molten salt inlet 5 under the action of a power pump. The main path molten salt flows from the right side to the left side of the housing 2 on the shell side and finally flows out from the molten salt outlet 6.

[0035] A plurality of electric heating tubes 4 are inserted inside the housing 2. The plurality of electric heating tubes 4 are fixedly supported inside the housing 2 by a support plate 3. There are a plurality of support plates 3, and both ends of the support plate 3 are fixed on the inner wall of the housing 2, so as to fixedly support the plurality of electric heating tubes 4 inside the housing 2. In some embodiments, the support plate 3 has through holes for the electric heating tubes 4 to pass through, and the through holes of the support plate 3 are used to limit the position of the electric heating tubes 4. It can be understood that a plurality of through holes can be provided on the support plate 3, some through holes are used to limit the position of the electric heating tubes 4, and the remaining through holes are used for the molten salt to pass through. The wiring ends of the electric heating tubes 4 are inserted into the wiring cavity 1. Inside the wiring cavity 1, the electric heating tubes 4 are wired to the outside. During the operation of the electric heating tubes 4, current flows through the resistance wires inside the electric heating tubes 4 to generate heat, and the heat is transferred from the inside to the outside to the outer molten salt. Preferably, the electric heating tubes 4 are U-shaped electric heating tubes 4. The bottom of the U-shaped electric heating tubes 4 extends into the left side position of the housing 2, and the ends of the U-shaped electric heating tubes 4 extend into the wiring cavity 1 to be wired to the outside.

[0036] The temperature control pipeline 8 is a branch of the low-temperature molten salt flowing in from the molten salt inlet 5. The inlet end of the temperature control pipeline 8 is connected to the molten salt inlet 5, and the outlet end of the temperature control pipeline 8 passes through the mixing tank 12 and extends into the interior of the housing 2. A molten salt shut-off valve 10, a molten salt regulating valve 11, and a check valve 9 are sequentially arranged on the upstream and downstream of the temperature control pipeline 8. The upstream inlet end of the temperature control pipeline 8 is connected to the molten salt inlet 5, and the downstream outlet end of the temperature control pipeline 8 passes through the outer wall of the mixing tank 12 and extends into the interior of the housing 2. The branch molten salt flows in from the molten salt inlet 5, flows out through the temperature control pipeline 8, and mixes with the main path molten salt in the mixing tank 12 to reduce the temperature of the main path molten salt. It can be understood that the pressure drop of the branch molten salt flowing from the molten salt inlet 5 to the mixing tank 12 is less than that of the main path molten salt flowing from the molten salt inlet 5 to the mixing tank 12. Therefore, after the branch molten salt flows out of the temperature control pipeline 8, it forms a jet flow, disturbing the main path molten salt, thereby increasing the turbulent state of the molten salt, strengthening the heat exchange between the molten salt and the pipe wall, timely reducing the temperature of the molten salt and the pipe wall, and ensuring the stable operation of the electric heater. A molten salt shut-off valve 10, a molten salt regulating valve 11, and a check valve 9 are arranged on the pipeline of the temperature control pipeline 8. Among them, the molten salt shut-off valve 10 is arranged close to the molten salt inlet 5 for opening and closing the temperature control pipeline 8; the check valve 9 is arranged close to the mixing tank 12 for preventing the molten salt flowing through the temperature control pipeline 8 from flowing back; the molten salt regulating valve 11 is arranged between the molten salt shut-off valve 10 and the check valve 9 for adjusting the flow rate of the molten salt flowing through the temperature control pipeline 8. It can be understood that the flow rate of the molten salt flowing through the temperature control pipeline 8 is adjusted by adjusting the opening of the molten salt regulating valve 11.

[0037] The outlet end of the temperature control pipeline 8 is connected to a plurality of branch pipelines 14. The low-temperature molten salt flowing out of the branch pipelines 14 forms a jet flow and mixes with the main path molten salt in the mixing tank 12. The low-temperature molten salt flowing through the temperature control pipeline 8 is transported to different positions of the mixing tank 12 through the plurality of branch pipelines 14, so that the low-temperature molten salt is mixed more evenly with the high-temperature molten salt of the main path, and the high-temperature molten salt of the main path is cooled faster and more evenly.

[0038] The mixing tank 12 protrudes and is arranged at a position of the housing 2 close to the molten salt outlet 6, and the mixing tank 12 communicates with the interior of the housing 2. After the branch molten salt flows out through the temperature control pipeline 8, it flows out from the branch pipeline 14 at the downstream outlet end of the temperature control pipeline 8 and flows towards the mixing tank 12; the main path molten salt flows into the interior of the housing 2 from the molten salt inlet 5 end and flows towards the mixing tank 12 from right to left. The low-temperature branch molten salt and the high-temperature molten salt of the main path are mixed and heat-exchanged in the mixing tank 12, so that the temperature of the high-temperature molten salt of the main path is reduced, avoiding the risk of over-temperature of the high-temperature molten salt.

[0039] In some embodiments, the mixing tank 12 is an annular protrusion arranged at a position of the housing 2 close to the molten salt outlet 6. A plurality of partition plates 13 are arranged in the mixing tank 12, as Figure 2 shown, and the mixing tank 12 is divided into a plurality of spaces by the partition plates 13. As Figure 3As shown in the figure, 4 partition plates 13 are evenly arranged in the mixed-flow tank 12. The 4 partition plates 13 divide the mixed-flow tank 12 into 4 spaces. The downstream outlet end of the temperature-regulating pipeline 8 is connected to 4 branch pipelines 14. The outlet ends of the 4 branch pipelines 14 respectively correspond to the 4 space positions where the mixed-flow tank 12 is divided. Thus, the low-temperature molten salt flowing out through the branch pipeline 14 is evenly transported to the 4 space positions of the mixed-flow tank 12 along the periphery, so that the low-temperature molten salt is evenly mixed with the high-temperature molten salt in the main path.

[0040] The temperature-measuring element 7 is used to measure the temperature of the molten salt flowing through the mixed-flow tank 12 and then flowing to the molten salt outlet 6. A plurality of temperature-measuring elements 7 are evenly arranged along the inner wall of the housing 2 at the position between the mixed-flow tank 12 and the molten salt outlet 6, that is, the temperature-measuring element 7 is arranged downstream of the mixed-flow tank 12 and close to the molten salt outlet 6, and is used to measure the temperature of the molten salt flowing out of the mixed-flow tank 12. The opening degree of the molten salt regulating valve 11 is adjusted according to the indicated temperature of the temperature-measuring element 7. When the indicated temperature of the temperature-measuring element 7 exceeds the safety value, the opening degree of the molten salt regulating valve 11 is increased.

[0041] For the resistive molten salt heater of the present invention, by arranging the temperature-regulating pipeline 8, the molten salt regulating valve 11 and the mixed-flow tank 12, when the outlet of the electric heating tube 4 exceeds the set temperature, there is no need to trip the electric heater for protection, avoiding the over-temperature risk of the electric heating tube 4; the low-temperature molten salt jet at the tail increases the turbulence degree of the molten salt at the tail of the electric heater, strengthens the convective heat transfer between the molten salt and the pipe wall, reduces the pipe wall temperature under the steady-state condition, and reduces the possibility of internal molten salt thermal decomposition.

[0042] The using method of the resistive molten salt heater for avoiding over-temperature risk of the present invention includes the following steps:

[0043] Under the stable working condition, close the molten salt switch valve 10 and the molten salt regulating valve 11. The low-temperature molten salt enters the molten salt heater from the molten salt inlet 5, flows through the electric heating tube 4 and is heated, and then forms high-temperature molten salt and flows out from the molten salt outlet 6;

[0044] Under the frequent variable load working condition, open the molten salt switch valve 10 and the molten salt regulating valve 11. The main-path molten salt enters the molten salt heater from the molten salt inlet 5, and the branch-path molten salt enters the mixed-flow tank 12 from the molten salt inlet 5 through the temperature-regulating pipeline 8 and is mixed with the main-path molten salt. When the indicated temperature of the temperature-measuring element 7 exceeds the safety value, increase the opening degree of the molten salt regulating valve 11 to increase the flow rate of the low-temperature molten salt flowing out from the branch pipeline 14.

[0045] Specifically, under stable operating conditions, the molten salt can timely carry away the heat generated by the electric heating tube 4. There is no over-temperature risk for the high-temperature molten salt flowing out of the molten salt outlet 6, and there is no need for low-temperature molten salt to cool down the high-temperature molten salt in the main circuit. Therefore, at this time, the temperature adjustment pipeline 8 does not work, the molten salt switch valve 10 and the molten salt regulating valve 11 are closed. The low-temperature molten salt enters the molten salt heater from the molten salt inlet 5, flows through the electric heating tube 4 and is heated to form high-temperature molten salt and then flows out from the molten salt outlet 6. Under frequent load-changing operating conditions, the molten salt cannot timely carry away the heat generated by the electric heating tube 4. There is an over-temperature risk for the high-temperature molten salt flowing out of the molten salt outlet 6, and it is necessary to use low-temperature molten salt to cool and adjust the high-temperature molten salt in the main circuit. Therefore, at this time, the temperature adjustment pipeline 8 works, and the molten salt switch valve 10 and the molten salt regulating valve 11 are opened. The low-temperature molten salt is divided into two paths. One path of low-temperature molten salt enters the electric heater from the molten salt inlet 5, then flows through the electric heating tube 4, and finally flows out from the molten salt outlet 6 to form high-temperature molten salt. This path of low-temperature molten salt is the main-circuit molten salt. The other path of low-temperature molten salt enters the temperature adjustment pipeline 8 from the molten salt inlet 5, then forms a jet from the branch pipeline 14 and enters the mixing tank 12 to mix with the main-circuit molten salt to cool and adjust the high-temperature molten salt. This path of low-temperature molten salt is the branch molten salt. Observe the indicated temperature of the temperature measuring element 7. When the indicated temperature of the temperature measuring element 7 exceeds the safety value, increase the opening degree of the molten salt regulating valve 11 on the temperature adjustment pipeline, thereby increasing the flow rate of the low-temperature molten salt flowing out of the branch pipeline 14. By increasing the jet flow rate of the low-temperature molten salt at the tail of the electric heater, on the one hand, the flow rate of the low-temperature molten salt is quickly increased, and the temperature of the high-temperature molten salt in the main circuit is reduced. On the other hand, a jet is formed in the mixing tank 12, increasing the turbulence degree of the molten salt at the tail of the electric heater and strengthening the convective heat transfer between the molten salt and the wall of the electric heating tube 4, so that the molten salt can timely carry away the heat generated by the electric heating tube 4.

[0046] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms may be directed to different embodiments or examples. Moreover, the specific features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0047] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0048] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the claims and their equivalents.

Claims

1. A resistive molten salt heater for avoiding over-temperature risk, characterized in that, Comprising: A housing, inside which a plurality of electric heating tubes are inserted. The electric heating tubes are supported and fixed by support plates fixed at both ends to the inner wall of the housing. At both ends of the housing, a molten salt outlet and a molten salt inlet are respectively provided; A mixing tank, which protrudes at a position of the housing close to the molten salt outlet, and the mixing tank communicates with the inside of the housing. The mixing tank is an annular protrusion provided at a position of the housing close to the molten salt outlet, and a plurality of partition plates are provided inside the mixing tank; A temperature regulating pipeline, the inlet end of which is connected to the molten salt inlet, and the outlet end of which passes through the mixing tank and extends into the inside of the housing. A molten salt switch valve, a molten salt regulating valve and a check valve are sequentially arranged upstream and downstream on the temperature regulating pipeline. The outlet end of the temperature regulating pipeline transports the molten salt to different positions of the mixing tank through a plurality of branch pipelines. The low-temperature molten salt flowing out from the branch pipelines forms a jet and mixes with the main-path molten salt in the mixing tank; A plurality of temperature measuring elements, which are used to measure the temperature of the molten salt flowing through the mixing tank and then flowing to the molten salt outlet.

2. The resistive molten salt heater according to claim 1, characterized in that, Adjust the opening degree of the molten salt regulating valve according to the indicated temperature of the temperature measuring element. When the indicated temperature of the temperature measuring element exceeds the safety value, increase the opening degree of the molten salt regulating valve.

3. The resistive molten salt heater according to claim 1, characterized in that, The electric heating tube is a U-shaped electric heating tube.

4. The resistive molten salt heater according to claim 1, characterized in that, The support plate is provided with through holes for the electric heating tubes to pass through.

5. The resistive molten salt heater according to claim 1, characterized in that, A plurality of the temperature measuring elements are uniformly arranged along the inner wall of the housing at a position between the mixing tank and the molten salt outlet.

6. The resistive molten salt heater according to claim 1, characterized in that, It further includes a wiring cavity, and one end of the electric heating tube for external wiring is inserted into the inside of the wiring cavity.

7. A method for using a resistive molten salt heater for avoiding over-temperature risk, characterized in that, Using the resistive molten salt heater according to any one of claims 1-6, comprising the following steps: Under stable operating conditions, close the molten salt switch valve and the molten salt regulating valve. The low-temperature molten salt enters the molten salt heater from the molten salt inlet, is heated by flowing through the electric heating tubes, forms high-temperature molten salt and flows out from the molten salt outlet; Under frequent variable load conditions, open the molten salt switch valve and the molten salt regulating valve. The main-path molten salt enters the molten salt heater from the molten salt inlet, and the branch-path molten salt enters the mixing tank from the molten salt inlet through the temperature regulating pipeline and mixes with the main-path molten salt. When the indicated temperature of the temperature measuring element exceeds the safety value, increase the opening degree of the molten salt regulating valve to increase the flow rate of the low-temperature molten salt flowing out from the branch pipelines.

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