Heat exchange system of single-tank fused salt heat storage evaporator

Abstract

The utility model discloses a heat exchange system of a single-tank fused salt heat storage evaporator. The heat exchange system comprises a heat exchange pipe arranged in a fused salt tank and a group of electric heaters uniformly distributed at intervals along the circumferential direction, the electric heater surrounds the outer side of the heat exchange tube and is used for heating the fused salt in the fused salt tank; a flow guide fence is arranged between the heat exchange tube and the electric heater; the diversion fence is opened up and down and surrounds the outer side of the heat exchange tube; the space inside the flow guide fence is a low-temperature area, and the space between the molten salt tank and the flow guide fence is a high-temperature area; the electric heater is located in the high-temperature area, and the heat exchange pipe is located in the low-temperature area. A water inlet of the heat exchange pipe is connected to a water outlet of a water feeding pump through a water inlet pipeline, and a water inlet of the water feeding pump is connected to a water outlet of a water supply device. When the molten salt releases heat, the density difference between the cold molten salt and the hot molten salt can be utilized to form pressure difference, the molten salt is promoted to flow, and natural circulation of the molten salt in the molten salt tank is achieved.

Description

Technical Field

[0001] The utility model relates to the technical field of molten salt energy storage, in particular to a heat exchange system of a single-tank molten salt heat storage evaporator. Background Art

[0002] Molten salt energy storage is a technology that converts chemical energy into thermal energy, and then into electrical energy or other medium thermal energy; its basic principle is to heat the molten salt to a high temperature and store thermal energy (taking ternary salt as an example, when the storage temperature is 535°C, 1 ton of molten salt can store about 120kWh of thermal energy). When electrical energy or other medium thermal energy is needed, the thermal energy is converted into electrical energy or other medium thermal energy. The core of molten salt energy storage is the high-temperature melting property of salts, which enables energy to be converted and stored at high temperature and high thermal efficiency. It is highly flexible, can respond quickly to energy fluctuations, and smoothly maintain system stability. As an advanced high-temperature energy storage technology, molten salt energy storage has the advantages of low cost and no pollution. In addition to the field of solar thermal power generation, it has broad application prospects in the fields of heating, steam supply, and flexible transformation of thermal power units.

[0003] Traditional molten salt heat storage technology mainly adopts the method of heat storage in a cold and hot double tank system (hot molten salt tank and cold molten salt tank). When storing heat, the molten salt in the cold molten salt tank is heated, and the heated molten salt is introduced into the hot molten salt tank; when releasing heat, the molten salt in the hot molten salt tank is led out for heat exchange, and the molten salt after the heat exchange is returned to the cold molten salt tank. At present, the application of double tank molten salt heat storage technology is relatively mature, but it has the disadvantages of high investment cost, long investment recovery period, large equipment footprint, cumbersome operation and management, slow steam production speed, and difficult maintenance. In view of this, many manufacturers have begun to study single tank molten salt heat storage technology. For example, Chinese patent 201610168408.9 discloses a single tank internal replacement hot valley electric hot water boiler for molten salt heat storage; it adopts a single tank built-in heat exchange solution, so that the heated molten salt flows in the molten salt tank, and realizes heat exchange with the heat exchange tube in the molten salt tank, thereby effectively saving material costs. However, the hot water boiler divides the interior of the molten salt tank into a low-temperature zone, an electric heating zone, a heat exchange zone and a low-temperature suction zone, and realizes the flow circulation of the molten salt in the molten salt tank by setting a molten salt pump and a molten salt transmission pipeline. The overall volume is large, and the solidification point of the molten salt is usually 120-220°C. The molten salt transmission pipeline has the risk of solidification and freezing, and the subsequent maintenance cost is high. Utility Model Content

[0004] In order to overcome the above-mentioned problems existing in the prior art, the present application provides a heat exchange system of a single-tank molten salt heat storage evaporator. The heat exchange system of the present application includes an electric heater and a heat exchange tube arranged inside the molten salt tank, and a guide fence arranged between the electric heater and the heat exchange tube; wherein the guide fence is opened at the top and bottom, and surrounds the outside of the heat exchange tube, dividing the inside of the molten salt tank into a high temperature zone and a low temperature zone, so that when the molten salt releases heat, the density difference between the cold and hot molten salts can be used to form a pressure difference, promote the flow of molten salt, and realize the natural circulation of molten salt inside the molten salt tank. At this time, there is no need to set up a molten salt pump and pipeline separately, and there is no risk of molten salt solidification and freezing; in addition, most of the equipment of the heat exchange system is arranged inside the molten salt tank, and the overall structure is compact, which can reduce the footprint of the evaporator, reduce investment costs, and facilitate later maintenance.

[0005] The technical solution of this application is:

[0006] The heat exchange system of a single-tank molten salt heat storage evaporator comprises a heat exchange tube arranged inside a molten salt tank and a group of electric heaters evenly spaced along the circumferential direction; the electric heater surrounds the outside of the heat exchange tube and is used to heat the molten salt in the molten salt tank; a guide fence is arranged between the heat exchange tube and the electric heater; the guide fence is opened at the top and bottom and surrounds the outside of the heat exchange tube; the space inside the guide fence is a low-temperature zone, and the space between the molten salt tank and the guide fence is a high-temperature zone; the electric heater is located in the high-temperature zone, and the heat exchange tube is located in the low-temperature zone; the water inlet of the heat exchange tube is connected to the water outlet of a water supply pump through a water inlet pipe, and the water inlet of the water supply pump is connected to the water outlet of a water supply device.

[0007] Compared with the prior art, the heat exchange system of the single-tank molten salt heat storage evaporator of the present application includes an electric heater and a heat exchange tube arranged inside the molten salt tank, and a guide fence arranged between the electric heater and the heat exchange tube; wherein the guide fence is opened at the top and bottom and surrounds the outside of the heat exchange tube, dividing the inside of the molten salt tank into a high-temperature zone and a low-temperature zone, so that when the molten salt releases heat, the density difference of the cold and hot molten salts can be used to form a pressure difference to promote the flow of the molten salt (when the molten salt releases heat, the molten salt in the low-temperature zone will exchange heat with the heat exchange tube, heating the water in the heat exchange tube into steam, at this time the temperature of the molten salt drops, and the density As the temperature increases, it flows to the bottom of the molten salt tank, while the molten salt in the high temperature area flows to the top of the molten salt tank due to its relatively high temperature and low density. After the high-temperature molten salt accumulates on the top of the molten salt tank, it will enter the diversion fence from the opening above the diversion fence to form a natural flow loop), thereby realizing the natural circulation of the molten salt inside the molten salt tank. At this time, there is no need to set up additional molten salt pumps and pipelines, and there is no risk of molten salt solidification and freezing. In addition, most of the equipment of the heat exchange system is arranged inside the molten salt tank, and the overall structure is compact, which can reduce the footprint of the evaporator, reduce investment costs, and facilitate later maintenance.

[0008] As an optimization, in the heat exchange system of the aforementioned single-tank molten salt heat storage evaporator, the water supply device includes a raw water tank, a pure water tank, and a water purifier disposed between the raw water tank and the pure water tank; the water purifier is used to purify the water in the raw water tank to output pure water; the water inlet of the water supply pump is connected to the water outlet of the pure water tank through a water outlet pipe. After the water in the raw water tank is treated by the water supply device, the water quality can meet the GB / T1576-2018 standard, thereby ensuring the safety and stability of the operation of the heat exchange system.

[0009] As an optimization, in the heat exchange system of the aforementioned single-tank molten salt heat storage evaporator, the heat exchange tube is fixed on the central tube plate, and the water inlet and outlet of the heat exchange tube are both led out from the central tube plate; the central tube plate is detachably connected to the upper cover plate of the molten salt tank. Therefore, when the heat exchange tube is damaged and needs to be replaced, the central tube plate can be directly lifted up and the heat exchange tube can be pulled out from the top without cutting the molten salt tank body, which is very convenient for maintenance. Furthermore, two lifting rings are symmetrically provided on the top of the central tube plate. Therefore, during later maintenance, the lifting rope can be loaded into the lifting ring, and then the central tube plate can be lifted and moved using a crane, which is more convenient to operate. Furthermore, a safety valve is provided at the water inlet of the heat exchange tube. When the pressure exceeds the setting value of the safety valve, the safety valve automatically jumps to ensure the reliability of the heat exchange system.

[0010] As an optimization, in the heat exchange system of the aforementioned single-tank molten salt heat storage evaporator, the guide fence is composed of four guide plates connected end to end in sequence to form a square. In this case, the structure is simple and convenient for mass production. Furthermore, two support rods are respectively provided on both sides of the guide fence, and the support rods are fixed to the bottom of the molten salt tank. It is easy to assemble and has high installation firmness.

[0011] As an optimization, in the heat exchange system of the aforementioned single-tank molten salt heat storage evaporator, the number of electric heaters is 6, and each electric heater is provided with 2 D thermocouples. When it is detected that the central molten salt temperature of the electric heater tube exceeds the set temperature value, the electric heater automatically stops heating, thereby ensuring the service life of the electric heater. Furthermore, the electric heater is fixed on the upper cover plate of the molten salt tank. At this point, the installation is convenient and easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a schematic diagram of the heat exchange system structure of a single-tank molten salt heat storage evaporator in an embodiment of the present application (a top view of the molten salt tank after removing the upper cover plate);

[0013] Figure 2 It is a schematic diagram of the internal structure of the molten salt tank in the embodiment of the present application;

[0014] Figure 3 It is a structural schematic diagram of a single-tank molten salt heat storage evaporator in an embodiment of the present application;

[0015] Figure 4 yes Figure 3 Structural schematic diagram of a single-tank molten salt heat storage evaporator.

[0016] The markings in the attached drawings are: 1-molten salt tank, 101-salt injection port, 102-salt discharge port, 103-upper cover plate; 2-heat exchange tube; 3-electric heater, 301-D thermocouple; 4-A thermocouple; 5-diversion fence; 6-water pump; 7-water supply device, 701-raw water tank, 702-pure water tank, 703-water purifier; 8-desuperheater, 801-B thermocouple, 802-C thermocouple, 803-pressure sensor, 804-desuperheating water regulating valve, 805-steam regulating valve; 9-liquid level gauge; 10-exhaust pipe; 11-center tube sheet; 12-lifting ring; 13-insulation layer; 14-safety valve; 15-support rod; 16-bypass valve; 17-flow meter; 18-heat-using equipment. DETAILED DESCRIPTION

[0017] The present application is further described below in conjunction with the accompanying drawings and embodiments, but they are not intended to limit the present application.

[0018] Example (see Figure 1 and Figure 2 ):

[0019] The heat exchange system of the present application is the core component of a single-tank molten salt heat storage evaporator. In this embodiment, the heat exchange system of the single-tank molten salt heat storage evaporator includes a heat exchange tube 2 arranged inside the molten salt tank 1 and 6 electric heaters 3 evenly spaced along the circumference (each electric heater 3 is provided with 2 D thermocouples 301; when the molten salt temperature at the center of the electric heater tube is detected to exceed 450°C, the electric heater 3 automatically stops heating); the electric heater 3 surrounds the outside of the heat exchange tube 2, and is used to heat the molten salt in the molten salt tank 1; 8 A thermocouples 4 are evenly spaced inside the molten salt tank 1, which are used to monitor the temperature of the molten salt in different areas of the molten salt tank 1 in real time (when the molten salt temperature detected by one of the A thermocouples 4 exceeds the operating temperature of 410°C, the electric heater 3 automatically stops heating); a diversion fence 5 is provided between the heat exchange tube 2 and the electric heater 3 ( Figure 2 In order to clearly display the heat exchange tube 2, the guide fence 5 is made transparent); the guide fence 5 is opened at the top and bottom, and surrounds the outside of the heat exchange tube 2; the space inside the guide fence 5 is a low-temperature zone, and the space between the molten salt tank 1 and the guide fence 5 is a high-temperature zone; the electric heater 3 is located in the high-temperature zone, and the heat exchange tube 2 is located in the low-temperature zone; the water inlet of the heat exchange tube 2 is connected to the water outlet of the water supply pump 6 through a water inlet pipe, and the water inlet of the water supply pump 6 is connected to the water outlet of the water supply device 7.

[0020] When the molten salt releases heat, the molten salt in the guide fence 5 will exchange heat with the heat exchange tube 2, heating the water in the heat exchange tube 2 into steam. At this time, the temperature of the molten salt drops, the density increases, and it flows to the bottom of the molten salt tank 1. The molten salt in the high-temperature zone flows to the top of the molten salt tank 1 due to its relatively high temperature and low density. After the high-temperature molten salt turns at the top of the molten salt tank 1, it will enter the guide fence 5 from the opening above the guide fence 5, thus forming a natural flow loop, realizing the natural circulation of the molten salt inside the molten salt tank 1. At this time, there is no need to set up a molten salt pump and pipeline separately, and there is no risk of molten salt solidification and freezing.

[0021] In this embodiment, the water supply device 7 includes a raw water tank 701, a pure water tank 702, and a water purifier 703 disposed between the raw water tank 701 and the pure water tank 702 (the water inlet 703 includes multiple filters, a high-pressure pump and a reverse osmosis unit, and uses multi-stage filtration and reverse osmosis principles to purify the water in the raw water tank 701 to output pure water); a raw water pump is disposed between the raw water tank 701 and the water purifier 703; the water inlet of the water supply pump 6 is connected to the water outlet of the pure water tank 702 through a water outlet pipe; the water inlet of the raw water tank 701 is connected to natural water; and a water quality detector is disposed on the water purifier 703. The water quality after being treated by the water supply device 7 can meet the GB / T1576-2018 standard, thereby ensuring the safety and stability of the evaporator operation. Furthermore, a time-controlled switch is also disposed in the water supply device 7, which is used to control the water supply device 7 to be turned on during the off-peak period. The water outlet pipe is provided with a flow meter 17 for real-time monitoring of the flow of pure water in the pipe; when the detected flow is less than the set value, it means that the molten salt energy storage has been fully utilized, and the water supply pump 6 needs to be controlled to stop working. Furthermore, the pure water tank 702 is provided with a liquid level switch for controlling the liquid level of the pure water tank 702.

[0022] Furthermore, the water outlet of the water supply pump 6 is connected to a bypass pipeline, and the other end of the bypass pipeline is connected to the pure water tank 702; the bypass pipeline is provided with a bypass valve 16. Therefore, when the water supply pump 6 is adjusted to the minimum safe working flow rate, which is still higher than the pure water flow rate required by the molten salt tank 1 (in this embodiment, the minimum safe working flow rate is 250kg / h), the bypass valve 16 can be opened to allow part of the water to return to the pure water tank 702 to reduce the water supply flow rate, thereby achieving that the pure water flow rate input into the molten salt tank 1 is less than the minimum safe working flow rate of the water supply pump 6, and ensuring that the water supply pump 6 will not be damaged.

[0023] In this embodiment, the heat exchange tube 2 is fixed on the central tube sheet 11, and the water inlet and outlet of the heat exchange tube 2 are both led out from the central tube sheet 11; the central tube sheet 11 is detachably connected to the upper cover plate 103 of the molten salt tank 1 (connected by flanges). Therefore, when the heat exchange tube 2 is damaged and needs to be replaced, the central tube sheet 11 can be directly lifted up and the heat exchange tube 2 can be pulled out from the top without cutting the tank body of the molten salt tank 1, which is very convenient for maintenance. Further, two lifting rings 12 are symmetrically provided on the top of the central tube sheet 11. Therefore, during later maintenance, the lifting rope can be loaded into the lifting ring 12, and then the central tube sheet 11 can be lifted and moved using a crane, which is more convenient to operate. Further, a safety valve 14 is provided at the water inlet of the heat exchange tube 2. When the pressure exceeds the set value of the safety valve 14, the safety valve 14 automatically jumps, ensuring the reliability of the heat exchange system.

[0024] In this embodiment, the guide fence 5 is composed of four guide plates connected end to end in sequence to form a square. In this case, the structure is simple and convenient for mass production. Furthermore, two support rods 15 are respectively provided on both sides of the guide fence 5, and the support rods 15 are fixed to the bottom of the molten salt tank 1. It is easy to assemble and has high installation firmness.

[0025] In this embodiment, the electric heater 3 is fixed on the upper cover plate 103 of the molten salt tank 1. In this case, the installation is convenient and easy to implement.

[0026] A specific application of the heat exchange system of the single-tank molten salt heat storage evaporator of this application:

[0027] A single-tank molten salt heat storage evaporator comprises a molten salt tank 1; the top of the molten salt tank 1 is provided with a salt injection port 101, and the bottom is provided with a salt discharge port 102 (for discharging molten salt when the evaporator is shut down or overhauled); and also includes the heat exchange system of the single-tank molten salt heat storage evaporator of the present application.

[0028] The evaporator can use low-valley electricity to heat the molten salt in the molten salt tank 1 during the off-peak period, and use the heat in the molten salt tank 1 to heat water to generate steam during the peak period, and deliver it to users (that is, the heating medium is pure water, and the product is steam; trace impurities in the water are allowed to deposit on the inner wall of the heat exchange tube 2, and the life of the heat exchange tube 2 can be determined by calculating the deposition amount); for example, it can be supplied to enterprises that require high-temperature steam in the production process of chemical industry, papermaking, etc., or supplied to small generators for power generation. The working principle is: during the off-peak period, the molten salt in the tank is heated by the electric heater 3; during the peak period, the high-temperature molten salt in the molten salt tank 1 is used to exchange heat with the heat exchange tube 2, and the water in the heat exchange tube 2 is heated by the molten salt to generate slightly superheated steam and delivered to the user, completing the molten salt heat release cycle.

[0029] As a specific embodiment of the evaporator: the outlet of the heat exchange tube 2 of the heat exchange system is connected with a desuperheater 8; the inlet and outlet of the desuperheater 8 are respectively provided with a B thermocouple 801 and a C thermocouple 802, which are used to monitor the temperature of the steam in the desuperheater 8 in real time, and the outlet of the desuperheater 8 is also provided with a pressure sensor 803, which is used to monitor the outlet pressure of the desuperheater 8 in real time; the water spray port of the desuperheater 8 is provided with a desuperheating water regulating valve 804; the inlet of the desuperheater 8 is provided with a safety valve 14, and the outlet is provided with a steam regulating valve 805; the outlet of the steam regulating valve 805 is connected to the heat-using device 18. The setting of the desuperheater 8 can ensure the temperature stability of the output steam. In the actual operation of the evaporator, the working temperature of its output steam can be set to slightly superheated (working pressure 1.0MPa, working temperature 190℃) to avoid serious water in the steam and ensure the quality of the steam. Two ultrasonic level gauges 9 are provided on the top of the molten salt tank 1 for real-time monitoring of the liquid level of the molten salt in the molten salt tank 1; an exhaust pipe 10 connected to the inside of the molten salt tank 1 is provided on the top of the molten salt tank 1. When the volume of the molten salt expands during heating, exhaust can be discharged through the exhaust pipe 10 to balance the internal and external pressures. The electric heater 3, D thermocouple 301, A thermocouple 4, water pump 6, water supply device 7, desuperheater 8, level gauge 9, bypass valve 16, flow meter 17 are electrically connected to the control module respectively.

[0030] If the B thermocouple 801 detects that the temperature of the steam flowing out of the water outlet of the heat exchange tube 2 is not greater than the set temperature, the cooling water regulating valve 804 is closed; when the B thermocouple 801 detects that the steam flowing out of the water outlet of the heat exchange tube 2 exceeds the operating temperature, the cooling water regulating valve 804 is opened, and cooling water is sprayed into the interior of the desuperheater 8 to evaporate it into water vapor and mix it with the superheated steam inside. During this process, if the C thermocouple 805 detects that the outlet steam temperature of the desuperheater 8 is higher than the set temperature, the flow rate of the cooling water regulating valve 804 is increased until the C thermocouple 805 detects that the outlet steam temperature of the desuperheater 8 is lower than the set temperature, and then the cooling water regulating valve 804 is closed (in this embodiment, the set temperature is 190°C). When the B thermocouple 801 detects that the steam flowing out of the outlet of the heat exchange tube 2 is lower than the working temperature or the pressure sensor 803 detects that the outlet pressure is higher than the working pressure value, the flow of the feed water pump 6 is reduced. If the feed water pump 6 drops to the minimum safe working flow and still receives a signal to reduce the flow, the bypass valve 16 is controlled to open; when the pressure sensor 803 detects that the outlet pressure is lower than the working pressure value, the opening of the steam regulating valve 805 is reduced. (K-type thermocouples can be selected for the A, B, C, and D thermocouples)

[0031] The above general description of the utility model involved in this application and the description of its specific implementation method should not be understood as limiting the technical solution of the utility model. Based on the disclosure of this application, those skilled in the art can add, reduce or combine the disclosed technical features in the above general description or / and the specific implementation method (including examples) without violating the constituent elements of the utility model involved, to form other technical solutions within the scope of protection of this application.

Claims

1. The heat exchange system of a single tank molten salt heat storage evaporator is characterized by: The invention comprises a heat exchange tube (2) arranged inside a molten salt tank (1) and a group of electric heaters (3) uniformly spaced along the circumference; the electric heater (3) surrounds the outer side of the heat exchange tube (2) and is used to heat the molten salt in the molten salt tank (1); a flow guide fence (5) is arranged between the heat exchange tube (2) and the electric heater (3); the flow guide fence (5) is opened at the top and bottom and surrounds the outer side of the heat exchange tube (2); the space inside the flow guide fence (5) is a low temperature zone, and the space between the molten salt tank (1) and the flow guide fence (5) is a high temperature zone; the electric heater (3) is located in the high temperature zone, and the heat exchange tube (2) is located in the low temperature zone; the water inlet of the heat exchange tube (2) is connected to the water outlet of a water supply pump (6) through a water inlet pipe, and the water inlet of the water supply pump (6) is connected to the water outlet of a water supply device (7).

2. The heat exchange system of the single-tank molten salt heat storage evaporator according to claim 1 is characterized in that: The water supply device (7) comprises a raw water tank (701), a pure water tank (702), and a water purifier (703) disposed between the raw water tank (701) and the pure water tank (702); the water purifier (703) is used to purify water in the raw water tank (701); and the water inlet of the water supply pump (6) is connected to the water outlet of the pure water tank (702) via a water outlet pipe.

3. The heat exchange system of the single-tank molten salt heat storage evaporator according to claim 1 is characterized in that: The heat exchange tube (2) is fixed on the central tube plate (11), and the water inlet and the water outlet of the heat exchange tube (2) are both led out from the central tube plate (11); the central tube plate (11) is detachably connected to the upper cover plate (103) of the molten salt tank (1).

4. The heat exchange system of the single-tank molten salt heat storage evaporator according to claim 3 is characterized in that: Two hanging rings (12) are symmetrically arranged on the top of the central tube plate (11).

5. The heat exchange system of the single-tank molten salt heat storage evaporator according to claim 1 is characterized in that: The guide fence (5) is composed of four guide plates connected end to end in sequence to form a square.

6. The heat exchange system of the single-tank molten salt heat storage evaporator according to claim 5 is characterized in that: Two support rods (15) are respectively provided on both sides of the diversion fence (5), and the support rods (15) are fixed to the bottom of the molten salt tank (1).

7. The heat exchange system of the single-tank molten salt heat storage evaporator according to claim 3 is characterized in that: A safety valve (14) is provided at the water inlet of the heat exchange tube (2).

8. The heat exchange system of the single-tank molten salt heat storage evaporator according to claim 1 is characterized in that: The number of the electric heaters (3) is 6, and each electric heater (3) is provided with two D thermocouples (301).

9. The heat exchange system of the single-tank molten salt heat storage evaporator according to claim 8, characterized in that: The electric heater (3) is fixed on the upper cover plate (103) of the molten salt tank (1).

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