A molten salt pipeline anti-freezing and blocking device and a control method thereof

Abstract

The application discloses a molten salt pipeline anti-freezing and anti-blocking device and a control method thereof. The molten salt pipeline anti-freezing and anti-blocking device comprises a main molten salt pipeline, a plurality of auxiliary molten salt pipelines, and a temperature monitoring unit. Any auxiliary molten salt pipeline comprises an auxiliary pipeline body and a heating unit. The heating unit is used for heating the auxiliary pipeline body and the molten salt in the auxiliary pipeline body. The inlet and outlet of the auxiliary pipeline body are connected to the upstream end and the downstream end of the main molten salt pipeline through on-off valves respectively. The heating unit is connected to the temperature monitoring unit. The temperature monitoring unit is used for detecting the temperature of the auxiliary pipeline body and the molten salt in the auxiliary pipeline body, and starting and stopping the heating unit and controlling the heating power. The application realizes the flow of molten salt between the main molten salt pipeline and the auxiliary molten salt pipeline, improves the operation reliability of the molten salt pipeline system, and reduces the shutdown and operation safety problems caused by the local freezing and blocking of the main molten salt pipeline.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of high-temperature molten salt application, and in particular to a molten salt pipeline anti-freezing and anti-blocking device and a control method thereof. BACKGROUND

[0002] A solar thermal power station usually adopts binary molten salt as a heat transfer working medium. When a whole heat absorption-heat storage-power generation system is in operation, the molten salt in a cold molten salt storage tank is transported to a solar heat collector by a molten salt pump, absorbs heat energy to increase temperature, and enters a hot molten salt storage tank. Then, the high-temperature molten salt flows into a molten salt steam generator from the hot molten salt storage tank, heats cold water to generate superheated steam, drives a steam turbine to operate and generate power, and the molten salt with reduced temperature flows back to the cold molten salt storage tank.

[0003] The molten salt pipeline of the solar thermal power station is long and complex, and different degrees of heat loss will occur under different climates, outdoor environmental conditions and operation modes, thereby bringing potential freezing risks, causing damage to valves and other equipment and safety problems of the whole system.

[0004] In order to solve these problems, people have proposed various methods such as steam preheating, air heating and electric heating to maintain the temperature of the main molten salt pipeline above the freezing point of the molten salt. For example, a fast salting system and a molten salt process system applying the same, and a fast salting method (publication number: CN 111068585A) in the prior art, which adopts an electric resistance heating unit to heat and melt the frozen molten salt in the predetermined pipeline, and an induction heating unit to heat and melt the frozen molten salt in the predetermined equipment, so as to achieve the purpose of fast salting. An induction heater system for electric heating pipeline (authorized publication number: CN103202096B) proposes to install an induction heating coil outside the pipeline system to achieve rapid heating of the pipeline. A preheating and anti-freezing method for a molten salt energy storage and transmission pipeline of a solar thermal power station (publication number: CN 102563280A) proposes to preheat the molten salt energy storage and transmission pipeline by hot air, and to prevent freezing by using an electric trace heating method. Compared with the original steam heating method, this method has low investment and operation cost, less failure, simple equipment, short heating time, and can reach the starting temperature of the transmission pipeline device in a short time. A high-temperature molten salt transmission pipeline preheating and anti-freezing electric heater (publication number: CN106131986A) proposes to wrap an electric heating pipe around the outer wall of the high-temperature molten salt transmission pipeline or to lay the electric heating pipe parallel to the high-temperature molten salt transmission pipeline to achieve anti-freezing and heating insulation of the molten salt pipeline. This method can reach the starting temperature of the transmission pipeline device in a short time, and effectively preheats and prevents freezing of the high-temperature molten salt transmission pipeline.

[0005] But the above technical scheme is to heat the main molten salt pipeline by electricity, mainly to lay the heat tracing cable on the outer surface of the molten salt pipeline, and the arrangement mode and shape of the heat tracing cable are changed according to the shape of the pipeline and the auxiliary equipment on the pipeline, but on the one hand, due to the long main molten salt pipeline, the power consumption is large, on the other hand, when the local part of the main molten salt pipeline is locally changed in diameter, direction, arranged with valve and other auxiliary equipment, the flow resistance is high, the local heat loss is large, and the problem of frozen blocking of the molten salt in the local pipeline will occur, which affects the safe operation of the whole system, and in serious cases, it may cause pipeline damage and cracking, equipment shutdown and other hazards, and the existing method of laying heat tracing cable outside the pipeline cannot effectively prevent and solve these operation safety problems, therefore, how to improve the operation reliability of the molten salt pipeline system and even the economy and safety of solar thermal power generation is a problem that must be faced. SUMMARY

[0006] The purpose of the present application is to provide a molten salt pipeline anti-freezing device to solve the problem of frozen blocking risk of the main molten salt pipeline and ensure the operation reliability of the molten salt pipeline system, realize rapid heating of the molten salt in the local pipeline, reduce the shutdown caused by local frozen blocking and operation safety problems.

[0007] Based on the above purpose, the technical scheme of the present application is as follows:

[0008] A molten salt pipeline anti-freezing device, comprising a main molten salt pipeline, and a plurality of auxiliary molten salt pipelines, a temperature monitoring unit, any of the auxiliary molten salt pipelines comprising an auxiliary pipeline body and a heating unit, the heating unit being used for heating the auxiliary pipeline body and the molten salt in the auxiliary pipeline body, the inlet and outlet of the auxiliary pipeline body being communicated with the upstream end and downstream end of the main molten salt pipeline through on-off valves respectively, the heating unit being connected with the temperature monitoring unit, the temperature monitoring unit being used for detecting the temperature of the auxiliary pipeline body and the molten salt in the auxiliary pipeline body and controlling the start-stop and heating power of the heating unit.

[0009] In the area where the main molten salt pipeline has large heat loss and is prone to frozen blocking risk, auxiliary molten salt pipelines are added, the frozen blocking risk area of the main molten salt pipeline is not fixed, and each frozen blocking risk area corresponds to an auxiliary molten salt pipeline, and a heating unit is arranged in each auxiliary molten salt pipeline, the heating unit maintains the temperature of the auxiliary molten salt pipeline not lower than the melting temperature of the molten salt, when the temperature of the molten salt in the main molten salt pipeline is low and needs to be quickly raised, that is, when there is frozen blocking risk or problem in the area of the main molten salt pipeline, the inlet valve and outlet valve of the auxiliary molten salt pipeline are opened, so that the molten salt passes through the auxiliary molten salt pipeline, the system runs normally, the operation reliability of the molten salt pipeline system is improved, the rapid heating of the molten salt in the local pipeline of the main molten salt pipeline is realized, and the shutdown and operation safety problems caused by the local frozen blocking of the main molten salt pipeline are reduced.

[0010] As a further solution, the heating unit comprises a pipe-external heating unit and a pipe-internal heating unit, the pipe-external heating unit is a heating cable laid on the auxiliary pipe body, and the pipe-internal heating unit comprises a heating element connected to the auxiliary pipe body and arranged inside the auxiliary pipe body.

[0011] The added auxiliary molten salt pipe adopts the "double heating" mode of conventional molten salt pipe electric heat tracing and direct internal heating of the pipe, which can improve the molten salt heating efficiency, reduce the heating power consumption, and improve the heating uniformity compared with the single pipe-external indirect heating method.

[0012] As a further solution, the molten salt pipe anti-freezing and blocking device further comprises an insulation layer wrapped on the pipe-external heating unit.

[0013] The insulation layer is used for heat preservation to reduce the heat loss of the pipe-external heating unit.

[0014] As a further solution, the heating element comprises a plurality of first heating elements and a plurality of second heating elements, the first heating elements are movably connected to the auxiliary pipe body, and the second heating elements are fixedly connected to the auxiliary pipe body.

[0015] The heating element can be movably connected to the auxiliary pipe body or fixedly connected to the auxiliary pipe body.

[0016] As a further solution, the molten salt pipe anti-freezing and blocking device further comprises heat dissipation fins connected to the first heating elements and the second heating elements.

[0017] The heat dissipation fins fixed on the first heating elements are movably connected to the auxiliary pipe body, and the heat dissipation fins increase the heat dissipation area and disturb the medium to improve the heat dissipation efficiency; the heat dissipation fins fixed on the second heating elements increase the heat dissipation area and are fixedly connected to the auxiliary pipe body.

[0018] Corresponding to the above-mentioned molten salt pipe anti-freezing and blocking device is a control method of the molten salt pipe anti-freezing and blocking device, the control method comprises the following steps:

[0019] S1: evaluating a region of the main molten salt pipe with high risk of freezing and blocking;

[0020] S2: according to the evaluation result in step S1, adding an auxiliary molten salt pipe in the region of the main molten salt pipe with high risk of freezing and blocking;

[0021] S3: judging the working state of the main molten salt pipeline, when the main molten salt pipeline works abnormally, controlling the opening of the auxiliary molten salt pipeline switch valve, and making the molten salt flow between the auxiliary molten salt pipelines;

[0022] S4: monitoring the temperature of the molten salt in the auxiliary pipeline body, and controlling the heating unit according to the molten salt temperature of the auxiliary molten salt pipeline;

[0023] S5: judging the working state of the main molten salt pipeline, when the main molten salt pipeline works normally, controlling the closing of the auxiliary molten salt pipeline switch valve, and making the molten salt flow between the main molten salt pipelines;

[0024] S6: repeating steps S3, S4 and S5 to realize the switching and flowing of the molten salt between the main molten salt pipeline and the auxiliary molten salt pipeline.

[0025] As a further scheme, the heating unit of the molten salt pipeline anti-freezing and blocking device comprises a pipe outer heating unit and a pipe inner heating unit, and the specific operation mode and control process are as follows:

[0026] (1) The pipe outer heating unit: it must be in a hot standby state regardless of whether the molten salt passes through the auxiliary molten salt pipeline, so that the temperature of the pipeline body is not lower than the set temperature;

[0027] (2) The pipe inner heating unit: when there is no molten salt passing through the auxiliary molten salt pipeline, its control method is consistent with that of the pipe outer heating unit; the specific control method is shown in S41;

[0028] (3) The pipe inner heating unit: when there is molten salt passing through the auxiliary molten salt pipeline, there are two cases: the auxiliary molten salt pipeline is only used as a temporary pipeline for passing, and the molten salt is not heated and warmed, and its control method is consistent with that of the pipe outer heating unit; the molten salt needs to be warmed on line, and the heating power and heating switch need to be controlled according to the inlet temperature, outlet temperature and target temperature of the molten salt.

[0029] In combination with the above specific operation and control mode, step S4 in the method further comprises the following specific steps:

[0030] S41: monitoring the temperature of the outer wall surface of the auxiliary pipeline body, and setting an outer wall surface reference temperature, when the temperature of the outer wall surface of the auxiliary pipeline body is lower than the outer wall surface reference temperature, starting the pipe outer heating unit and the pipe inner heating unit; when the temperature of the outer wall surface of the auxiliary pipeline body is higher than the outer wall surface reference temperature, closing the pipe outer heating unit and the pipe inner heating unit;

[0031] S42: When the auxiliary molten salt pipeline's switch valve is opened, the molten salt flows in the auxiliary pipeline, the temperature of the molten salt is monitored, the target temperature of the molten salt is set, the target temperature is higher than the outer wall surface reference temperature, and the inlet molten salt temperature and the outlet molten salt temperature of the auxiliary molten salt pipeline are measured in real time;

[0032] S43: When the inlet molten salt temperature of the auxiliary molten salt pipeline is equal to or higher than the target temperature, the control of the pipe-in-pipe heating unit is realized based on the method of step S41; when the inlet molten salt temperature of the auxiliary molten salt pipeline is lower than the target temperature, the heating power of the pipe-in-pipe heating unit is calculated, and the heating power is the product of the flow of the molten salt working medium, the specific heat capacity of the molten salt working medium, and the temperature difference, and the temperature difference is the difference between the inlet molten salt temperature and the target temperature of the molten salt;

[0033] S44: When the outlet molten salt temperature of the auxiliary molten salt pipeline is equal to or higher than the target temperature, the heating unit in the auxiliary molten salt pipeline is controlled to be closed.

[0034] The beneficial effects realized by the present application are:

[0035] The auxiliary molten salt pipeline is installed in the area where freezing is prone to occur on the main molten salt pipeline and the place where heat dissipation loss is large, which is beneficial to improve the temperature of the local molten salt, reduce the risk of freezing of the valve and the pipeline, and facilitate non-stop maintenance and accident handling of the risk area where local freezing has occurred;

[0036] The auxiliary molten salt pipeline is realized by combining the pipeline external heating and the pipeline internal heating, which is beneficial to quickly improve the temperature of the molten salt and reduce the risk of freezing caused by the decrease of the temperature of the molten salt during abnormal operation of the system. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 It is a schematic diagram of the auxiliary molten salt pipeline of the embodiment of the present application;

[0038] Figure 2 It is a fixed frame of the auxiliary molten salt pipeline system of the embodiment of the present application;

[0039] Figure 3 It is a pipe-in-pipe heating unit of the embodiment of the present application;

[0040] Figure 4 It is a pipe-in-pipe heating unit fixedly installed in the auxiliary pipeline body (horizontal row) of the embodiment of the present application;

[0041] Figure 5 It is a pipe-in-pipe heating unit fixedly installed in the auxiliary pipeline body (vertical row) of the embodiment of the present application;

[0042] Figure 6 It is a pipe-in-pipe heating unit movably connected and installed in the auxiliary pipeline body (horizontal row) of the embodiment of the present application;

[0043] Figure 7 The in-pipe heating unit of the embodiment of the present application is movably connected and installed in the auxiliary pipe body (longitudinal column) ;

[0044] Figure 8 A specific implementation diagram of the embodiment of the present application.

[0045] Wherein: 100, main molten salt pipe, 101, non-frozen area of the main molten salt pipe, 102, frozen area of the main molten salt pipe, 103, non-frozen area of the main molten salt pipe, 4, valve of the main molten salt pipe, 5, inlet valve, 6, outlet valve, 7, auxiliary pipe body, 8, out-pipe heating unit, 9, in-pipe heating unit, 10, temperature monitoring unit, 11, support hanger, 12, base, 13, heating element, 14, heating element protective sleeve, 15, heat dissipation fin, 16, sealing bearing, 17, transmission device, 18, driving motor. DETAILED DESCRIPTION

[0046] As shown in Figure 1 The added auxiliary molten salt pipe includes an auxiliary pipe body 7, heating units (8, 9), a temperature monitoring unit (10), and molten salt switch valves (4, 5, 6). The heating units in the auxiliary molten salt pipe include an out-pipe heating unit 8 and an in-pipe heating unit 9. The out-pipe heating unit 8 is installed on the outer surface of the auxiliary pipe body 7, and the in-pipe heating unit 9 is installed inside the auxiliary pipe body 7. The temperature monitoring unit can also be referred to as a temperature monitoring and control unit.

[0047] As shown in Figure 2 The auxiliary molten salt pipe is composed of an auxiliary pipe body 1, a thermal insulation layer, a thermal insulation layer shell, and a fixing frame. The auxiliary pipe body is made of corrosion-resistant steel pipe material. The thermal insulation layer is composed of at least one layer of heat insulation material. The fixing frame can have a structure form of a support hanger 11 and a base 12, or other common support and fixing structure forms.

[0048] The out-pipe heating unit 8 in the auxiliary molten salt pipe contains a heating element-heating cable, which is arranged in the same way as the existing general molten salt pipe electric heat tracing arrangement.

[0049] The out-pipe heating unit 8 in the auxiliary molten salt pipe uses the temperature monitoring unit 10 to realize the display and control of the outer surface temperature of the auxiliary pipe body. The control mode is as follows: the initial outer surface temperature T30 of the auxiliary pipe body is set to be the melting point temperature of the molten salt + 50℃. When the T3 temperature is lower than T30, the out-pipe heating unit 8 starts to work. When the T3 temperature reaches or exceeds T30 + 10℃, the out-pipe heating unit 8 stops working.

[0050] The in-pipe heating unit 9 in the auxiliary molten salt pipe mainly comprises a heating element 13, a heating element protective sleeve 14 and a heat dissipation fin 15, wherein the heating element is arranged in the heating element protective sleeve, and the heat dissipation fin is welded to the outer surface of the heating element protective sleeve.

[0051] The in-pipe heating unit 9 in the auxiliary molten salt pipe is provided with a temperature monitoring unit 10 to display and control the temperature of the molten salt. Figure 3 The control mode is as follows: the temperatures T1 and T2 of the molten salt at the inlet and outlet of the auxiliary molten salt pipe are measured in real time, the target heating temperature T20 of the molten salt is set, the required heating power theoretical value P0 is calculated according to the inlet temperature T1 and the target temperature T20, and the heating power is set according to the value, the value of P0 is equal to the flow rate of the molten salt working medium * the specific heat capacity of the molten salt working medium * (T20-T1); when the outlet temperature T2 is equal to or higher than the target temperature T20, the in-pipe heating unit 9 stops working.

[0052] The in-pipe heating unit 9 in the auxiliary molten salt pipe can be installed on the auxiliary pipe body of the auxiliary molten salt pipe by sealing welding, and the arrangement mode of the in-pipe heating unit can be horizontal (as shown in Figure 4 ) or vertical (as shown in FIG. 5).

[0053] More specifically, as shown in Figure 6 , Figure 7 the in-pipe heating unit 9 in the auxiliary molten salt pipe can be connected to the auxiliary pipe body in a bearing sealing movable connection mode, so that the heating element protective sleeve and the heat dissipation fin in the in-pipe heating unit 9 can rotate freely in the auxiliary pipe body, so as to strengthen the heat exchange between the molten salt and the in-pipe heating unit.

[0054] The auxiliary molten salt pipe is provided with a molten salt inlet valve 5 and an outlet valve 6, when the molten salt inlet valve 5 of the auxiliary molten salt pipe is opened, the molten salt can enter the auxiliary molten salt pipe for online heating, and then enter the main molten salt pipe through the opened outlet valve 6.

[0055] More specifically, a valve 4 is arranged on the main molten salt pipe, the valve has adjustable opening degree and can be completely closed. When all the molten salt needs to pass through the auxiliary path and the main molten salt pipe parallel to the auxiliary path needs to be cut off, the valve 4 can be closed after the inlet valve 5 is opened; when all the molten salt needs to pass through the main molten salt pipe and the auxiliary pipe body 7 parallel to the main molten salt pipe needs to be cut off, the inlet valve 5 and the outlet valve 6 can be closed after the valve 4 is opened.

[0056] The present application proposes to arrange the auxiliary pipe at a specific position and region of the main molten salt pipe, which can improve the safety and reliability of the whole photothermal power generation system, and reduce the risk of freezing and plugging of the molten salt pipe, especially the molten salt pipe connected with the cold salt tank, and the shutdown accident caused by freezing and plugging.

[0057] This invention proposes a "dual heating" method on the added auxiliary pipe body 7, which combines conventional molten salt pipe electric heating with direct heating inside the pipe. Compared with the single method of indirect heating outside the pipe, this method can improve the heating efficiency of molten salt, reduce the energy consumption of heating electricity, and improve the uniformity of heating.

[0058] The present invention proposes an in-tube heating unit that can realize online and rapid heating of molten salt during the flow process, which can quickly increase the temperature of molten salt in the tube, ensure that the molten salt has a high internal energy or enthalpy value during the flow process in the tube, and reduce the possibility of solidification and phase change.

[0059] The protective sleeve and heat dissipation fins of the heating element in the tube heating unit proposed in this invention, which are in direct contact with the molten salt, can rotate under the drive of a motor. On the one hand, the heat exchange effect is increased by disturbance, collision and friction between the molten salt and the fins. On the other hand, the thrust can be generated to increase the movement speed of the molten salt, reduce the flow resistance in the tube, and enhance the heat exchange.

[0060] The tube heating unit proposed in this invention can determine the heating power according to the set molten salt temperature, the inlet molten salt temperature, and the flow rate. By adjusting the power, on-demand heating and controllable heating can be achieved, thereby increasing the molten salt temperature.

[0061] The following is combined with Figure 8 The implementation process of this invention will be described in detail:

[0062] like Figure 8 As shown, auxiliary pipelines are added upstream and downstream of the freezing risk zone 2 of the main molten salt pipeline 1, and a valve 4 is installed on the main molten salt pipeline near the inlet valve 5 of the auxiliary pipeline system. The auxiliary pipeline system includes an inlet valve 5 and an outlet valve 6. The inlet valve 5 is connected to the upstream of the freezing risk zone 2 of the main molten salt pipeline 1, and the outlet valve 6 is located downstream of the freezing risk zone 2.

[0063] Heating cables are laid throughout the auxiliary pipelines of the pipeline auxiliary system, in the same manner as typical molten salt pipeline electric heat tracing. Heating power and temperature are controlled in three zones based on the molten salt temperature and pipeline shape. Figure 8 External heating units 8-1, 8-2, and 8-3 are located within the tubes.

[0064] The auxiliary pipeline body of the auxiliary pipeline system is equipped with four sets of internal heating units, namely internal heating units 9-1, 9-2, 9-3 and 9-4; the heating element protective sleeves and heat dissipation fins of internal heating units 9-1 and 9-4 can rotate under the combined action of sealed bearing 16, transmission device 17 and drive motor 18; internal heating units 9-2 and 9-3 are directly welded and fixed to the auxiliary pipeline body of the auxiliary pipeline system.

[0065] The start-stop and work of the pipe outer heating units 8-1, 8-2, 8-3 and the pipe inner heating units 9-1, 9-2, 9-3, 9-4 are completed by the temperature monitoring unit 10, and the specific monitoring control process is as follows:

[0066] (1) The pipe outer heating units 8-1, 8-2, 8-3: whether or not there is molten salt passing through the auxiliary molten salt pipeline, they must be in a hot standby state so that the temperature of the pipeline body is not lower than the set temperature;

[0067] (2) The pipe inner heating units 9-1, 9-2, 9-3, 9-4: when there is no molten salt passing through the auxiliary molten salt pipeline, the control method is consistent with that of the pipe outer heating units, and the specific control method is shown in S41;

[0068] (3) The pipe inner heating units 9-1, 9-2, 9-3, 9-4: when there is molten salt passing through the auxiliary molten salt pipeline, there are two cases: the auxiliary molten salt pipeline is only used as a temporary pipeline for passing through, and it is not heated to warm the molten salt, and the control method is consistent with that of the pipe outer heating units; the molten salt needs to be warmed online, and the heating power and heating switch need to be controlled according to the inlet temperature, outlet temperature and target temperature of the molten salt.

[0069] The specific control method includes steps S1-S6:

[0070] S1: evaluating the region of the main molten salt pipeline where the risk of freezing and blocking is high;

[0071] S2: according to the evaluation result in step S1, auxiliary molten salt pipelines are added in the region of the main molten salt pipeline where the risk of freezing and blocking is high;

[0072] S3: judging the working state of the main molten salt pipeline, and when the main molten salt pipeline works abnormally, controlling the opening of the switch valve of the auxiliary molten salt pipeline, and making the molten salt flow between the auxiliary molten salt pipelines;

[0073] S4: monitoring the temperature of the molten salt in the auxiliary pipeline body, and controlling the heating unit according to the molten salt temperature of the auxiliary molten salt pipeline;

[0074] Wherein S4 includes specific steps S41-S44:

[0075] S41: monitoring the outer wall surface temperature of the auxiliary pipeline body, and setting an outer wall surface reference temperature, when the outer wall surface temperature of the auxiliary pipeline body is lower than the outer wall surface reference temperature, starting the pipe outer heating unit and the pipe inner heating unit; when the outer wall surface temperature of the auxiliary pipeline body is higher than the outer wall surface reference temperature, closing the pipe outer heating unit and the pipe inner heating unit; that is, when there is no molten salt passing through the auxiliary pipeline, the pipe inner heating unit and the pipe outer heating unit are controlled together, the pipe outer heating is started, the pipe inner heating is started, the pipe outer heating temperature control issues a closing instruction, and the pipe inner heating is also closed;

[0076] S42: When the auxiliary molten salt pipeline switch valve is opened, the molten salt flows in the auxiliary pipeline, the temperature of the molten salt is monitored, the target temperature of the molten salt is set, the target temperature is higher than the outer wall surface reference temperature, and the inlet molten salt temperature and the outlet molten salt temperature of the auxiliary molten salt pipeline are measured in real time;

[0077] S43: When the inlet molten salt temperature of the auxiliary molten salt pipeline is equal to or higher than the target temperature, the control of the inner and outer tube heating units is realized based on the method of step S41; when the inlet molten salt temperature of the auxiliary molten salt pipeline is lower than the target temperature, the heating power of the inner tube heating unit is calculated, and the heating power is the product of the flow of the molten salt working medium, the specific heat capacity of the molten salt working medium, and the temperature difference, and the temperature difference is the difference between the inlet molten salt temperature and the target temperature of the molten salt;

[0078] S44: When the outlet molten salt temperature of the auxiliary molten salt pipeline is equal to or higher than the target temperature, the heating unit in the auxiliary molten salt pipeline is controlled to be closed.

[0079] S5: The working state of the main molten salt pipeline is judged, and when the main molten salt pipeline works normally, the switch valve of the auxiliary molten salt pipeline is controlled to be closed, and the molten salt flows between the main molten salt pipelines;

[0080] S6: Steps S3, S4, and S5 are repeated to realize the switching and flowing of the molten salt between the main molten salt pipeline and the auxiliary molten salt pipeline.

[0081] For the outer tube heating units 8-1, 8-2, and 8-3, the initial auxiliary pipeline body outer surface temperature T30 is set to be the melting point temperature of the molten salt + 50℃, and T3-8-1, T3-8-2, and T3-8-3 thermocouples are installed in the areas where the outer tube heating units 8-1, 8-2, and 8-3 are located, respectively, and when the temperature value measured by any one of the three thermocouples is lower than T30, the outer tube heating unit where the thermocouple is located starts to work; when the temperature value measured by any one of the three thermocouples reaches or exceeds T30+10℃, the outer tube heating unit where the thermocouple is located stops working.

[0082] For the in-pipe heating units 9-1, 9-2, 9-3, 9-4, the temperature monitoring unit 10 is used to realize the display and control of the molten salt temperature, and the control mode is: the molten salt temperatures T1 and T2 at the inlet and outlet of the auxiliary molten salt pipeline are measured in real time, the target heating temperature T20 of the molten salt is set, and the monitoring control device 10 calculates the required total heating power P0 according to the inlet temperature T1 and the target temperature T20; that is, the total power of the in-pipe heating units 9-1, 9-2, 9-3, 9-4 is P0, and the sub-power of each heating section is automatically allocated according to the resistance and length of the heating element, and the value of P0 is equal to the flow rate of the molten salt working medium * the specific heat capacity of the molten salt working medium * (T20-T1), and when the outlet temperature T2 is equal to or higher than the target temperature T20, the in-pipe heating units 9-1, 9-2, 9-3, 9-4 stop working.

[0083] In combination with the above-mentioned auxiliary road system device, the operation process of the entire auxiliary road system is as follows: when the system is normally working, the valve 4 is fully opened, the valves 5 and 6 are closed, the freezing point of the molten salt is 230 DEG C, the surface temperature of the auxiliary pipeline body in the auxiliary road system is set to 280 DEG C, the in-pipe heating units 9-1, 9-2, 9-3, 9-4 are started to ensure that the auxiliary road system is in a hot standby state.

[0084] When the frozen blockage risk area is found: the molten salt flow resistance increases, the molten salt temperature drops rapidly, the power consumption of the external heat preservation heating cable rises, and the molten salt temperature in the molten salt pipeline needs to be raised, the valves 5 and 6 are opened, the valve 4 is closed, the target temperature T20 of the molten salt is set to 300 DEG C, the inlet temperature T1 of the molten salt entering the auxiliary molten salt pipeline is 280 DEG C, the molten salt mass flow rate is 100 kg / s, and the specific heat is 1300 J / kg.k; then the total power of the in-pipe heating units 9-1, 9-2, 9-3, 9-4 is 2600 kw, and when the outlet temperature T2 is equal to or higher than the target temperature T20, that is, 300 DEG C, the in-pipe heating units 9-1, 9-2, 9-3, 9-4 stop working.

[0085] When the frozen blockage risk area is removed, the valve 4 is opened, the valves 5 and 6 are closed, and the system is normally working, and the auxiliary molten salt pipeline is set to a hot standby state according to the foregoing method.

[0086] The auxiliary pipeline of the present application is added, and the molten salt pipeline anti-freezing and heat preservation method of in-pipe and external combined heating is used in the pipeline auxiliary road, which not only has the function of the original molten salt pipeline conveying medium, but also increases the online direct rapid heating function, improves the heating efficiency, directly raises the operating temperature of the molten salt while conveying the molten salt, avoids the freezing and frozen blockage of the molten salt, and has the advantages of simple process, high reliability and strong operability.

[0087] Finally, it should be noted that the above-mentioned embodiments illustrate rather than limit the application, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims.

Claims

1. A control method of a molten salt pipeline freeze plug device, characterized by, The control method comprises the following steps: S1: evaluating a region of the main molten salt pipeline where the risk of freezing is high; S2: according to the evaluation result in step S1, adding auxiliary molten salt pipelines in the region of the main molten salt pipeline where the risk of freezing is high; any auxiliary molten salt pipeline comprises an auxiliary pipeline body and a heating unit; S3: judging the working state of the main molten salt pipeline; when the main molten salt pipeline works abnormally, opening the on-off valve of the auxiliary molten salt pipeline, and making the molten salt flow in the auxiliary molten salt pipeline; S4: monitoring the temperature of the molten salt in the auxiliary pipeline body, and controlling the heating unit according to the temperature of the molten salt in the auxiliary molten salt pipeline; the heating unit is used for heating the auxiliary pipeline body and the molten salt in the auxiliary pipeline body; S5: judging the working state of the main molten salt pipeline; when the main molten salt pipeline works normally, closing the on-off valve of the auxiliary molten salt pipeline, and making the molten salt flow in the main molten salt pipeline; S6: repeating steps S3, S4 and S5 to realize the switching and flowing of the molten salt between the main molten salt pipeline and the auxiliary molten salt pipeline; the heating unit of the molten salt pipeline anti-freezing device comprises an outer-pipe heating unit and an inner-pipe heating unit; step S4 further comprises the following specific steps: S41: monitoring the temperature of the outer wall surface of the auxiliary pipeline body, and setting a reference temperature of the outer wall surface; when the temperature of the outer wall surface of the auxiliary pipeline body is lower than the reference temperature of the outer wall surface, starting the outer-pipe heating unit and the inner-pipe heating unit; when the temperature of the outer wall surface of the auxiliary pipeline body is higher than the reference temperature of the outer wall surface, closing the outer-pipe heating unit and the inner-pipe heating unit; S42: when the on-off valve of the auxiliary molten salt pipeline is opened and the molten salt flows in the auxiliary pipeline, monitoring the temperature of the molten salt, setting a target temperature of the molten salt, and measuring the inlet molten salt temperature and the outlet molten salt temperature of the auxiliary molten salt pipeline in real time; the target temperature is higher than the reference temperature of the outer wall surface; S43: when the inlet molten salt temperature of the auxiliary molten salt pipeline is equal to or higher than the target temperature, controlling the outer-pipe heating unit and the inner-pipe heating unit according to the method in step S41; when the inlet molten salt temperature of the auxiliary molten salt pipeline is lower than the target temperature, calculating the heating power of the inner-pipe heating unit; the heating power is the product of the flow rate of the molten salt working medium, the specific heat capacity of the molten salt working medium, and the temperature difference; the temperature difference is the difference between the inlet molten salt temperature and the target temperature of the molten salt; S44: when the outlet molten salt temperature of the auxiliary molten salt pipeline is equal to or higher than the target temperature, controlling the heating unit in the auxiliary molten salt pipeline to be closed.

2. A molten salt piping freeze protection and blockage prevention device employing the control method of claim 1 for molten salt piping freeze protection and blockage prevention comprising a main molten salt piping, characterized by, The application further comprises several auxiliary molten salt pipes, a temperature monitoring unit, any of the auxiliary molten salt pipes comprises an auxiliary pipe body and a heating unit for heating the auxiliary pipe body and the molten salt in the auxiliary pipe body, the inlet and outlet of the auxiliary pipe body are connected to the upstream end and downstream end of the main molten salt pipe through on-off valves respectively, the heating unit is connected to the temperature monitoring unit, the temperature monitoring unit is used for detecting the temperature of the auxiliary pipe body and the molten salt in the auxiliary pipe body and starting and stopping the heating unit and controlling the heating power.

3. The fused salt piping freeze plug of claim 2 wherein, The heating unit comprises an external pipe heating unit and an internal pipe heating unit, the external pipe heating unit is a heating cable laid on the auxiliary pipe body, the internal pipe heating unit comprises a heating element connected to the auxiliary pipe body and arranged inside the auxiliary pipe body.

4. The fused salt piping freeze plug of claim 3 wherein, The application further comprises an insulation layer wrapped on the external pipe heating unit.

5. The molten salt piping freeze plug of claim 3, wherein, The heating element comprises several first heating elements and several second heating elements, the first heating elements are movably connected to the auxiliary pipe body, and the second heating elements are fixedly connected to the auxiliary pipe body.

6. The fused salt piping freeze plug of claim 5 wherein, The application further comprises several heat dissipation fins connected to the first heating elements and the second heating elements respectively.

7. The fused salt piping freeze plug of claim 5 wherein, The application further comprises a bearing, a transmission unit and a driving motor, the bearing is fixed to the auxiliary pipe body, the transmission unit is connected to the bearing, the driving motor is connected to the transmission unit, and the first heating elements are movably connected to the auxiliary pipe body through the bearing.

Images