Large-temperature-difference high-temperature fused salt and water heat exchange steam production system and control method

Abstract

The invention discloses a large-temperature-difference high-temperature fused salt and water heat exchange steam production system and a control method. The system comprises a fused salt storage tank, a high-pressure hot water storage tank, a fused salt-water / steam heat exchanger and a steam pocket, the fused salt-water / steam heat exchanger is of a multi-shell-pass spiral coil pipe type heat exchanger structure. A plurality of limiting inner barrels are arranged in a shell barrel to form annular cavities of different levels, a plurality of heat transfer pipes are connected in parallel and wound around a central pipe or the wall of an upper-level fiber inner barrel to form spiral coil pipes, and a plurality of sets of spiral coil pipes are arranged in the annular cavities respectively. A shell side fused salt liquid inlet, a shell side fused salt liquid outlet, a pipe side water inlet and a pipe side steam outlet are formed in the shell cylinder body; the fused salt-water / steam heat exchanger is connected with an outlet and an inlet of the fused salt storage tank and further connected with a water outlet and an inlet of the high-pressure hot water storage tank. High-temperature thermal shock damage of the heat exchanger and pipeline blockage caused by fused salt solidification can be effectively eliminated, membrane boiling of water is inhibited, the heat transfer efficiency is high, and system operation is safe and reliable.

Description

Technical Field

[0001] The present invention relates to the technical field of molten salt heat storage, and in particular to a large temperature difference high temperature molten salt and water heat exchange steam production system and a control method under the condition of an inlet and outlet temperature difference of 600-650°C high temperature molten salt above 370°C. Background Art

[0002] High-temperature molten salt is widely used in the fields of heat storage and peak-shaving combined heat and power generation, heat pump power storage, deep peak-shaving of thermal power plants, and solar thermal power generation. At present, molten salt heat storage uses solar salt, which has the defects of melting point as high as 220℃, easy freezing and blocking of pipelines, maximum operating temperature within 570℃, small heat storage temperature difference, and low heat storage density. In recent years, with the technological progress of low-melting-point and high-decomposition-temperature molten salt composite heat storage materials, molten salt composite materials with melting point ≤180℃ and decomposition temperature ≥600℃, such as sodium nitrate, potassium nitrate, sodium nitrite, potassium nitrite, sodium carbonate, calcium carbonate, and calcium chloride, have been successfully developed and are expected to be applied.

[0003] The heat exchange between high-temperature molten salt and water to produce high-pressure steam is an important application direction of molten salt heat storage technology. In order to improve the thermal utilization efficiency of molten salt, the inlet and outlet temperature difference of the molten salt in the heat exchanger should be increased as much as possible. However, the outlet temperature of the molten salt in the heat exchanger is limited by the melting point of the molten salt. If the temperature is too low, the liquid molten salt will solidify and block the pipeline. The large heat transfer temperature difference has high requirements for the heat exchanger's stress resistance. The traditional U-tube heat exchanger can no longer meet the demand.

[0004] Chinese invention patent application CN115406283A discloses a single high-temperature molten salt energy storage device, including a heat exchange device, a pressure stabilizing device and a molten salt circulation pipeline. The heat exchange device includes a shell, a cooling medium pipeline and a heating medium pipeline; the cooling medium pipeline and the heating medium pipeline are arranged in the shell, and the pressure stabilizing device includes a molten salt circulation pump and a pressure stabilizing tank. The pressure stabilizing tank, the molten salt circulation pump and the shell are connected end to end through the molten salt circulation pipeline. However, this technology is mainly used to solve the water impact problem in the heat exchanger, and cannot solve the thermal stress damage to the molten salt heat exchanger caused by large temperature differences.

[0005] Chinese invention patent application CN117739724A discloses a high-temperature molten salt heat release system, in which the input end of the hot salt tank is connected to the air outlet end of the heat storage system, and the output end is connected to the steam molten salt heat exchanger and the adjacent hot salt tank; the hot inlet end of the steam molten salt heat exchanger is connected to the hot salt tank, the hot outlet end is connected to the reheater outlet header and the thermal system respectively, and the air inlet end is connected to the air supply system; the hot inlet end of the feed water molten salt heat exchanger is connected to the steam molten salt heat exchanger, the hot outlet end is connected to the thermal system, and the cold outlet end is connected to the cold salt tank , the water inlet is connected to the water supply system; although this technology solves the problem of small molten salt utilization temperature range by setting the heat inlet end to be connected to the hot salt tank, the heat outlet end to be connected to the boiler low-temperature reheater outlet header and the thermal system respectively, and the air inlet end of the steam molten salt heat exchanger to the air supply system, it mainly uses the unit steam to heat the molten salt to store heat during the steam consumption off-peak period, and uses high-temperature molten salt to heat the feed water for external steam supply during the steam consumption peak period. It cannot solve the thermal stress damage to the molten salt heat exchanger caused by large temperature difference. Summary of the invention

[0006] In view of the problem that heat shock damage to a heat exchanger is easily caused under high-temperature molten salt above 600°C and large temperature difference heat exchange conditions above 370°C, the present invention provides a large temperature difference, high temperature and high pressure molten salt-water / steam heat exchange system and its operation method, which can effectively eliminate high-temperature thermal shock damage to the heat exchanger and molten salt solidification clogging of pipelines, inhibit film boiling of water, have high heat transfer efficiency, and ensure safe and reliable system operation.

[0007] The large temperature difference in the present invention refers to a temperature difference of more than 370° C., the high temperature refers to a temperature of more than 600° C., and the high pressure refers to a pressure of 10-15 MPa.

[0008] The purpose of the present invention is achieved through the following technical solutions:

[0009] A large temperature difference, high temperature and high pressure molten salt-water / steam heat exchange system, comprising a molten salt storage tank, a high pressure hot water storage tank, a molten salt-water / steam heat exchanger and a steam drum; the molten salt-water / steam heat exchanger is a multi-shell spiral coil heat exchanger structure; in the shell body, a plurality of limiting inner cylinders are arranged with a central tube as the center, and an annular cavity connected at both ends is formed between the first limiting inner cylinder and the central tube, between two adjacent limiting inner cylinders, and between the outermost limiting inner cylinder and the shell body, a plurality of heat transfer tubes are connected in parallel and wound around the central tube or the upper-level fiber inner cylinder wall to form a spiral coil, and a plurality of groups of spiral coils are wound around the central tube or the upper-level fiber inner cylinder wall to form a spiral coil. The tubes are respectively arranged in the annular cavity; the shell cylinder is provided with a shell side molten salt liquid inlet, a shell side molten salt liquid outlet, a tube side water inlet and a tube side steam outlet; the molten salt-water / steam heat exchanger is connected to the outlet and inlet of the molten salt storage tank through the shell side molten salt liquid inlet and the shell side molten salt liquid outlet, respectively, and is connected to the water outlet and inlet of the high-pressure hot water storage tank through the tube side water inlet and the tube side steam outlet; the tube side steam outlet is also connected to the steam drum; electric heaters are provided in the molten salt storage tank and the high-pressure hot water storage tank; one end of each set of spiral coils is connected to the tube side water inlet, and the other end is connected to the tube side steam outlet.

[0010] To further achieve the purpose of the present invention, preferably, the molten salt inlet pipe and the molten salt outlet pipe of the molten salt-water / steam heat exchanger are respectively provided with a first molten salt valve and a second molten salt valve; the water inlet pipe and the outlet pipe of the molten salt-water / steam heat exchanger respectively connected to the water outlet and the inlet of the high-pressure hot water storage tank are respectively provided with a second hot water valve and a first hot water valve; the pipe connecting the outlet pipe of the molten salt-water / steam heat exchanger and the steam drum is provided with a first steam pipeline valve; the pipe connecting the steam drum and the inlet of the high-pressure hot water storage tank is provided with a second steam pipeline valve.

[0011] Preferably, a molten salt pump and a hot water circulation pump are respectively provided on the molten salt inlet pipe and the water inlet pipe of the molten salt-water / steam heat exchanger.

[0012] Preferably, a water replenishment valve and a water replenishment pump are provided on the water inlet pipe of the high-pressure hot water storage tank.

[0013] Preferably, the molten salt inlet pipe and the molten salt outlet pipe are respectively installed with a first temperature measuring point and a second temperature measuring point, and a molten salt mass flow meter is also installed in the molten salt inlet pipe of the molten salt-water / steam heat exchanger.

[0014] Preferably, the top of the shell cylinder is provided with an exhaust port, and the bottom is provided with a molten salt discharge port.

[0015] Preferably, the pipes provided with the exhaust port and the molten salt discharge port are provided with an exhaust valve and a molten salt discharge valve respectively.

[0016] Preferably, a steam outlet valve is installed on the upper part of the steam drum; a water inlet pipe pressure gauge and a steam outlet pressure gauge are installed on the outlet and water inlet pipes of the molten salt-water / steam heat exchanger respectively; the number of the limiting inner cylinders is 2-4; the spiral coil can withstand a pressure of 10-15MPa.

[0017] The control method of the large temperature difference, high temperature and high pressure molten salt-water / steam heat exchange system is as follows: the deoxygenated water in the high pressure hot water storage tank is first electrically heated and then sent into each group of spiral coils to preheat the molten salt-water / steam heat exchanger. When the pressure of the deoxygenated water is heated to 4-6MPa, the high temperature molten salt of 600-650°C is sent into the shell side molten salt liquid inlet of the molten salt-water / steam heat exchanger. The high temperature molten salt in the shell side exchanges heat with the deoxygenated water in the spiral coil, the outlet temperature of the molten salt is controlled at 200-230°C, and the water in the spiral coil is heated to form steam of 10-15MPa; the steam enters the steam drum.

[0018] Preferably, part of the steam is extracted from the steam drum and enters the high-pressure hot water storage tank to convert the normal temperature deoxygenated water into high-pressure saturated water; when the system stops running, the drain valve and the molten salt drain valve are opened to discharge and collect the high-temperature liquid molten salt from the molten salt-water / steam heat exchanger.

[0019] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0020] 1) According to the prior art, since the temperature of the molten salt is not high and the heat transfer temperature difference is not large, the traditional U-tube heat exchanger structure is generally used. However, this heat exchanger is difficult to withstand the long-term normal operation of the molten salt at an inlet high temperature of 600°C and a large temperature difference of more than 370°C; the present invention adopts a plurality of heat transfer tubes in parallel to be wound around the central tube or the inner tube wall of the upper-level fiber to form a spiral coil, and multiple groups of spiral coils are respectively arranged in the annular cavity. The spiral coil structure has a free contraction characteristic and can expand and contract autonomously with the temperature difference, which can effectively suppress the influence of large temperature difference thermal stress.

[0021] 2) The present invention adopts a multi-shell-pass design. In the shell cylinder, a plurality of limiting inner cylinders are arranged with the central tube as the center interval. An annular cavity connected at both ends is formed between the first limiting inner cylinder and the central tube, between two adjacent limiting inner cylinders, and between the outermost limiting inner cylinder and the shell cylinder. Each annular cavity is provided with a group of spiral coils, which ensures sufficient and rapid heat exchange between the molten salt in the shell pass and the deoxygenated water in the tube pass, thereby enhancing the convective heat transfer of the molten salt.

[0022] 3) For high-temperature molten salt above 600°C, if it directly enters the heat exchanger to exchange heat with water, if the temperature of the heat exchanger itself is at room temperature, it will cause a huge thermal shock to the heat exchanger, resulting in stress damage to the heat exchanger. The present invention uses an electric heater to heat the deoxygenated water in the high-pressure hot water storage tank and pressurize it, and then passes it into the molten salt-water / steam heat exchanger. When the pressure of the deoxygenated water is controlled to about 4MPa, the heated high-pressure deoxygenated water can preheat the molten salt-water / steam heat exchanger by about 170°C, which can effectively offset the thermal stress damage impact caused by the high-temperature molten salt on the molten salt-water / steam heat exchanger when the system is started, and ensure that the system operates effectively for a long time.

[0023] 4) The solidification temperature of molten salt is usually below 170°C. When the low temperature of molten salt is below 170°C, the molten salt will become solid and block the pipeline. The present invention controls the outlet temperature of the molten salt through countercurrent heat exchange between molten salt and water. Moreover, the outlet molten salt of the molten salt heat exchanger directly enters the molten salt heating tank and no longer exchanges heat with water, which greatly reduces the risk of molten salt solidification blocking the pipeline.

[0024] 5) When the system is running, the inlet deoxygenated water is directly mixed with steam to form high-temperature water above 4MPa, which enters the molten salt-water / steam heat exchanger to exchange heat with the high-temperature molten salt, greatly reducing the heat transfer temperature difference in the heat exchange process, thereby inhibiting the film boiling of water and improving the heat transfer efficiency.

[0025] 6) The present invention effectively solves the problem of reliable operation of the molten salt-water / steam heat exchanger with a high inlet temperature of 600°C and a large temperature difference of 370°C or above, solves the damage of the heat exchanger to the thermal shock caused by the large temperature difference and high temperature, and improves the heat transfer efficiency and the reliability and safety of the system, and has good practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a composition diagram of a large temperature difference high temperature molten salt and water heat exchange steam production system.

[0027] Figure 2 for Figure 1 Schematic diagram of the structure of the molten salt-water / steam heat exchanger.

[0028] Figure 3 for Figure 2 Schematic diagram of the spiral coil structure.

[0029] The figure shows: molten salt storage tank ST1, high-pressure hot water storage tank ST2, molten salt-water / steam heat exchanger H, steam drum BD, molten salt pump P1, hot water circulation pump P2, make-up water pump P3, first molten salt valve V1, second molten salt valve V2, first steam pipeline valve V3, second steam pipeline valve V4, first hot water valve V5, second hot water valve V6, make-up water valve V7, drain valve V8, molten salt drain valve V9, steam outlet valve V10, steam outlet pressure gauge PI1, water inlet pipe pressure gauge PI2, molten salt mass flowmeter F, first temperature measuring point T1 and second temperature measuring point T2, shell cylinder 1, center tube 2, first limit inner cylinder 3, second limit inner cylinder 4, third limit inner cylinder 5, molten salt drain port 6, exhaust port 7, shell side molten salt liquid inlet 8, shell side molten salt liquid outlet 9, tube side water inlet 10, tube side steam outlet 11. DETAILED DESCRIPTION

[0030] In order to better understand the present invention, the present invention is further described below in conjunction with the accompanying drawings and embodiments, but the embodiments of the present invention are not limited thereto.

[0031] Aiming at high-temperature molten salt above 600℃ and large temperature difference heat exchange conditions above 370℃, the present invention develops a molten salt-water / steam heat exchanger with high heat transfer efficiency and resistance to large temperature difference stress, and eliminates high-temperature thermal shock damage to the heat exchanger and molten salt solidification clogging of the pipeline. It is a technical key to promote the engineering application of low-melting-point and high-decomposition-temperature molten salt composite heat storage materials.

[0032] The core feature of the present invention lies in the development of the molten salt-water / steam heat exchanger structure, and for the first time, a multi-shell spiral coil heat exchanger structure is developed; in the shell cylinder, multiple limiting inner cylinders are arranged with the center tube as the center interval, and annular cavities connected at both ends are formed between the first limiting inner cylinder and the center tube, between two adjacent limiting inner cylinders, and between the outermost limiting inner cylinder and the shell cylinder, and multiple heat transfer tubes are connected in parallel around the center tube or the wall of the upper-level fiber inner cylinder to form a spiral coil, and multiple groups of spiral coils are respectively arranged in the annular cavity; the shell cylinder is provided with a shell side molten salt liquid inlet, a shell side molten salt liquid outlet, a tube side water inlet, and a tube side steam outlet. At the same time, the heat exchange system of the present invention has a molten salt-water / steam heat exchanger structure in which the tube side inlet is water and the outlet is steam. Such a structure enables the molten salt-water / steam heat exchanger to be connected to the outlet and inlet of the molten salt storage tank through the shell side molten salt liquid inlet and the shell side molten salt liquid outlet, respectively, and to be connected to the water outlet and inlet of the high-pressure hot water storage tank through the tube side water inlet and the tube side steam outlet, respectively.

[0033] In the present invention, multiple heat transfer tubes are connected in parallel and wound around a central tube or the inner tube wall of an upper-level fiber to form a spiral coil. Multiple groups of spiral coils are respectively arranged in annular cavities. The spiral coil structure has a free shrinkage characteristic and can expand and contract autonomously with temperature differences, thereby effectively suppressing the influence of thermal stress due to large temperature differences.

[0034] The present invention proposes to set a high-pressure hot water storage tank with electric heating in the molten salt / steam heat exchange system to preheat the heat exchanger when the system is started, reduce the thermal shock damage of the high-temperature molten salt to the heat exchanger when the system is started, reduce the heat exchange temperature difference between the molten salt and water / steam during operation, inhibit the film boiling heat transfer of water, and improve the heat transfer efficiency and reliability of the heat exchanger.

[0035] As for the various pumps and valves, pressure gauges and temperature test points provided in conjunction with the molten salt storage tank, high-pressure hot water storage tank, molten salt-water / steam heat exchanger and steam drum, they can all be obtained by experiments based on the above-mentioned structural features and in combination with the purpose of the present invention.

[0036] like Figure 1 As shown, a large temperature difference, high temperature and high pressure molten salt-water / steam heat exchange system is mainly composed of a molten salt storage tank ST1, a high pressure hot water storage tank ST2, a molten salt-water / steam heat exchanger H and a steam drum BD. The molten salt inlet pipe and the molten salt outlet pipe of the molten salt-water / steam heat exchanger H are connected to the outlet and inlet of the molten salt storage tank ST1; the water inlet pipe and the outlet pipe of the molten salt-water / steam heat exchanger H are respectively connected to the water outlet and inlet of the high pressure hot water storage tank ST2; the outlet pipe of the molten salt-water / steam heat exchanger H is also connected to the steam drum BD; electric heaters are provided in the molten salt storage tank ST1 and the high pressure hot water storage tank ST2.

[0037] The large temperature difference, high temperature and high pressure molten salt-water / steam heat exchange system also includes a molten salt pump P1, a hot water circulation pump P2, a water supply pump P3, a first molten salt valve V1, a second molten salt valve V2, a first steam pipeline valve V3, a second steam pipeline valve V4, a first hot water valve V5, a second hot water valve V6, a water supply valve V7, a drain valve V8, a molten salt drain valve V9 and a steam outlet valve V10, etc.; the molten salt inlet pipeline and the molten salt outlet pipeline of the molten salt-water / steam heat exchanger H are respectively provided with a first molten salt valve V1 and a second molten salt valve V2, and the molten salt inlet pipeline and the molten salt outlet pipeline are also respectively installed with a first temperature measuring point T1 and a second temperature measuring point T2, and a molten salt mass flowmeter F is also installed in the molten salt inlet pipeline of the molten salt-water / steam heat exchanger H. The water inlet pipe and outlet pipe of the molten salt-water / steam heat exchanger H, which are respectively connected to the water outlet and inlet of the high-pressure hot water storage tank ST2, are respectively provided with a second hot water valve V6 and a first hot water valve V5. The outlet pipe of the molten salt-water / steam heat exchanger H is also connected to the drum BD, and a first steam pipeline valve V3 is provided on the connecting pipe; the drum BD is connected to the inlet of the high-pressure hot water storage tank ST2, and a second steam pipeline valve V4 is provided on the connecting pipe. The molten salt inlet pipe and water inlet pipe of the molten salt-water / steam heat exchanger H are respectively provided with a molten salt pump P1 and a hot water circulation pump P2. The water inlet pipe of the high-pressure hot water storage tank ST2 is provided with a water replenishment valve V7 and a water replenishment pump P3; the top of the molten salt-water / steam heat exchanger H is provided with an emptying valve V8, and the bottom is provided with a molten salt drain valve V9. A steam outlet valve V10 is installed on the top of the drum BD. The water inlet pressure gauge PI1 and the steam outlet pressure gauge PI2 are installed on the outlet and water inlet pipes of the molten salt-water / steam heat exchanger H. The molten salt pump P1 needs to withstand high temperatures above 650°C; the hot water circulation pump P2 and the water supply pump P3 need to withstand pressures above 15MPa; the first molten salt valve V1, the second molten salt valve V2, the drain valve V8, and the molten salt drain valve V9 need to withstand high temperatures; the first steam pipeline valve V3, the second steam pipeline valve V4, the first hot water valve V5, the second hot water valve V6, the water supply valve V7, and the steam outlet valve V10 all need to withstand high pressures.

[0038] like Figure 2 As shown, the molten salt-water / steam heat exchanger H is a multi-shell spiral coil heat exchanger structure; in the shell body 1, a plurality of limiting inner cylinders are arranged with the central tube 2 as the center, and an annular cavity with two ends connected is formed between the first limiting inner cylinder and the central tube, between two adjacent limiting inner cylinders, and between the outermost limiting inner cylinder and the shell body 1, as shown in FIG. Figure 3As shown, multiple heat transfer tubes are connected in parallel and wound around the central tube or the inner wall of the upper-level fiber tube to form a spiral coil. Multiple groups of spiral coils are respectively arranged in the annular cavity. The shell cylinder 1 is provided with a molten salt drain port 6, an exhaust port 7, a shell-side molten salt liquid inlet 8, and a shell-side molten salt liquid outlet 9. The top of the molten salt-water / steam heat exchanger H is equipped with an exhaust port 7. After the operation is completed, the exhaust port 7 is opened to connect to the outside world to ensure that the molten salt-water / steam heat exchanger H is connected to the atmosphere, so that the molten salt drain port 6 arranged at the bottom of the molten salt-water / steam heat exchanger H can discharge the remaining liquid molten salt; the drain valve V8 and the molten salt drain valve V9 are respectively arranged on the pipes of the exhaust port 7 and the molten salt drain port 6. One end of the spiral coil is connected to the tube-side water inlet 10, and the other end is connected to the tube-side steam outlet 11. Preferably, the molten salt-water / steam heat exchanger H is a 2-4-stage shell-side structure, such as Figure 2 The molten salt-water / steam heat exchanger H shown is a 4-stage shell structure, a first-stage annular space is formed between the central tube and the first limiting inner tube 3, a second-stage annular space is formed between the first limiting inner tube 3 and the second limiting inner tube 4, a third-stage annular space is formed between the second limiting inner tube 4 and the third limiting inner tube 5, and a fourth-stage annular space is formed between the third limiting inner tube 5 and the shell cylinder 1. The molten salt enters the molten salt-water / steam heat exchanger H from the molten salt liquid inlet 8 on the shell side of the shell cylinder 1, flows through the fourth-stage annular space, the third-stage annular space, the second-stage annular space, the first-stage annular space in sequence, and finally flows out from the shell side molten salt liquid outlet 9. The high-temperature liquid molten salt flows outside the spiral coil in the annular space, and the deoxygenated water flows in the inner tube of the coil, and the molten salt and the deoxygenated water are countercurrent heat exchange. The deoxygenated water flows in the tube, and by selecting the appropriate tube inner diameter size and tube wall thickness, it can withstand a pressure of 10-15MPa. The spiral coil structure can reduce the influence of large temperature difference stress. The spiral flow of deoxygenated water in the tube can enhance boiling heat transfer and inhibit the influence of film boiling heat transfer. Countercurrent heat exchange can improve the heat transfer efficiency of the heat exchanger.

[0039] When the system is started, power is turned on in the molten salt storage tank ST1 to heat the molten salt to 600-650°C, the first molten salt valve V1 and the second molten salt valve V2 are closed, the drain valve V8, the molten salt drain valve V9, the first steam pipeline valve V3, the second steam pipeline valve V4 and the steam outlet valve V10 are closed, the first hot water valve V5, the second hot water valve V6 and the water supply valve V7 are opened, and the water supply pump P3 is started to send deoxygenated water at room temperature into the high-pressure hot water storage tank ST2 and the pipe process of the molten salt-water / steam heat exchanger H. After the deoxygenated water is filled, the water supply valve V7 is closed and the water supply pump P3 is shut down. The electric heater of the high-pressure hot water storage tank ST2 is turned on to heat the deoxygenated water, and the hot water circulation pump P2 is started until the deoxygenated water is heated to saturated hot water of 4-6MPa, and the electric heater of the high-pressure hot water storage tank ST2 is stopped. The molten salt-water / steam heat exchanger H is preheated by deoxygenated hot water. On the one hand, it prevents the high-temperature molten salt from thermally shocking the heat exchanger. On the other hand, increasing the inlet water temperature can reduce the heat transfer temperature difference of the molten salt-water / steam heat exchanger H and reduce the influence of temperature difference stress.

[0040] When the system is running, close the first hot water valve V5, open the first steam pipeline valve V3 and the second steam pipeline valve V4, open the first molten salt valve V1, the second molten salt valve V2 and the water supply valve V7, and start the water supply pump P3. The high-temperature molten salt from the molten salt storage tank ST1 flows in the shell side of the molten salt-water / steam heat exchanger H, and the deoxygenated water from the high-pressure hot water storage tank ST2 flows in the tube side. After heat exchange with the high-temperature molten salt, 10-15MPa steam is formed and flows into the drum BD. If the superheat of the steam needs to be increased, the electric heater in the drum BD can be started to heat the steam, and the steam outlet valve V10 is opened to provide steam for the user. Part of the steam flows into the high-pressure hot water storage tank ST2, and is directly mixed with the normal temperature deoxygenated water sent from the water supply pump P3 to form 4-6MPa saturated hot water, which is sent to the tube side of the molten salt-water / steam heat exchanger H through the hot water circulation pump P2.

[0041] When the system stops, turn off all the electric heaters in the system, shut down the molten salt pump P1, hot water circulation pump P2 and water supply pump P3, close the first molten salt valve V1, the second molten salt valve V2, the first steam pipeline valve V3, the second steam pipeline valve V4, the steam outlet valve V10, the second hot water valve V6, and the water supply valve V7. Open the drain valve V8 and the molten salt drain valve V9 to discharge the high-temperature liquid molten salt from the molten salt-water / steam heat exchanger H and collect it.

[0042] Example 1

[0043] When the system is started, power is turned on in the molten salt storage tank ST1 to heat the molten salt to 600°C, the first molten salt valve V1 and the second molten salt valve V2 are closed, the drain valve V8, the molten salt drain valve V9, the first steam pipeline valve V3, the second steam pipeline valve V4 and the steam outlet valve V10 are closed, the first hot water valve V5, the second hot water valve V6 and the water supply valve V7 are opened, and the water supply pump P3 is started to send deoxygenated water at room temperature into the high-pressure hot water storage tank ST2 and the pipe process of the molten salt-water / steam heat exchanger H. After the deoxygenated water is filled, the water supply valve V7 is closed and the water supply pump P3 is shut down, the electric heater of the high-pressure hot water storage tank ST2 is turned on to gradually heat the deoxygenated water, and the hot water circulation pump P2 is started to send hot water into the pipe process of the heat exchanger H, and circulate it between the molten salt-water / steam heat exchanger H and the high-pressure hot water storage tank ST2 to preheat the molten salt-water / steam heat exchanger H. When the pressure of the steam outlet pressure gauge PI2 is 4 MPa, the electric heater of the high-pressure hot water storage tank ST2 is stopped.

[0044] When the system is running, close the first hot water valve V5, open the first steam pipeline valve V3 and the second steam pipeline valve V4, open the first molten salt valve V1, the second molten salt valve V2 and the water supply valve V7, and start the water supply pump P3. The 600℃ high-temperature molten salt from the molten salt storage tank ST1 flows in the shell side of the molten salt-water / steam heat exchanger H, and the 4MPa saturated deoxygenated water from the high-pressure hot water storage tank ST2 flows in the tube side and exchanges heat with the 600℃ high-temperature molten salt. Adjust the first molten salt valve V1 to control the mass flow rate of the molten salt, so that the value of the molten salt outlet temperature T2 of the molten salt-water / steam heat exchanger H is 230℃, and the temperature difference between the inlet and outlet of the molten salt is 370℃. Adjust the second hot water valve V6 to make the value of the steam outlet pressure gauge PI1 of the molten salt-water / steam heat exchanger H 10MPa, and the 10MPa steam enters the drum BD. If the superheat of the steam needs to be increased, the electric heater in the drum BD can be started to heat the steam, and the steam outlet valve V10 can be opened to provide steam for the user. Adjust the second pipeline steam valve V4 to make part of the steam flow into the high-pressure hot water storage tank ST2, and directly mix with the normal temperature deoxygenated water sent from the water supply pump P3 to form 4MPa saturated hot water, which is sent to the pipe side of the molten salt-water / steam heat exchanger H through the hot water circulation pump P2.

[0045] When the system stops, turn off all the electric heaters in the system, shut down the molten salt pump P1, hot water circulation pump P2 and water supply pump P3, close the first molten salt valve V1, the second molten salt valve V2, the first steam pipeline valve V3, the second steam pipeline valve V4, the steam outlet valve V10, the second hot water valve V6, and the water supply valve V7. Open the drain valve V8 and the molten salt drain valve V9 to discharge the high-temperature liquid molten salt from the molten salt-water / steam heat exchanger H and collect it.

[0046] Example 2

[0047] When the system is started, power is turned on in the molten salt storage tank ST1 to heat the molten salt to 620°C, the first molten salt valve V1 and the second molten salt valve V2 are closed, the drain valve V8, the molten salt drain valve V9, the first steam pipeline valve V3, the second steam pipeline valve V4 and the steam outlet valve V10 are closed, the first hot water valve V5, the second hot water valve V6 and the water supply valve V7 are opened, and the water supply pump P3 is started to send deoxygenated water at room temperature into the high-pressure hot water storage tank ST2 and the pipe process of the molten salt-water / steam heat exchanger H. After the deoxygenated water is filled, the water supply valve V7 is closed and the water supply pump P3 is shut down. The electric heater of the high-pressure hot water storage tank ST2 is turned on to gradually heat the deoxygenated water, and the hot water circulation pump P2 is started to send hot water into the pipe process of the molten salt-water / steam heat exchanger H, and circulate between the molten salt-water / steam heat exchanger H and the high-pressure hot water storage tank ST2 to preheat the molten salt-water / steam heat exchanger H. When the pressure of the steam outlet pressure gauge PI2 is 5 MPa, the electric heater of the high-pressure hot water storage tank ST2 is stopped.

[0048] When the system is running, close the first hot water valve V5, open the first steam pipeline valve V3 and the second steam pipeline valve V4, open the first molten salt valve V1, the second molten salt valve V2 and the water supply valve V7, and start the water supply pump P3. The 620℃ high-temperature molten salt from the molten salt storage tank ST1 flows in the shell side of the molten salt-water / steam heat exchanger H, and the 5MPa saturated deoxygenated water from the high-pressure hot water storage tank ST2 flows in the tube side and exchanges heat with the 620℃ high-temperature molten salt. Adjust the first molten salt valve V1 to control the mass flow rate of the molten salt, so that the value of the molten salt outlet temperature T2 of the molten salt-water / steam heat exchanger H is 210℃, and the temperature difference between the inlet and outlet of the molten salt is 410℃. Adjust the second hot water valve V6 to make the value of the steam outlet pressure gauge PI1 of the molten salt-water / steam heat exchanger H 12MPa. The 12MPa steam enters the drum BD. If the superheat of the steam needs to be increased, the electric heater in the drum BD can be started to heat the steam, and the steam outlet valve V10 can be opened to provide steam for the user. Adjust the second pipeline steam valve V4 to make part of the steam flow into the high-pressure hot water storage tank ST2, and directly mix with the normal temperature deoxygenated water sent from the water supply pump P3 to form 5MPa saturated hot water, which is sent to the pipe side of the molten salt-water / steam heat exchanger H through the hot water circulation pump P2.

[0049] When the system stops, turn off all the electric heaters in the system, shut down the molten salt pump P1, hot water circulation pump P2 and water supply pump P3, close the first molten salt valve V1, the second molten salt valve V2, the first steam pipeline valve V3, the second steam pipeline valve V4, the steam outlet valve V10, the second hot water valve V6, and the water supply valve V7. Open the drain valve V8 and the molten salt drain valve V9 to discharge the high-temperature liquid molten salt from the molten salt-water / steam heat exchanger H and collect it.

[0050] Example 3

[0051] When the system is started, power is supplied to the molten salt storage tank ST1 to heat the molten salt to 650°C, the first molten salt valve V1, the second molten salt valve V2, the drain valve V8, the molten salt drain valve V9, the first steam pipeline valve V3, the second steam pipeline valve V4 and the steam outlet valve V10 are closed, the first hot water valve V5, the second hot water valve V6 and the water supply valve V7 are opened, the water supply pump P3 is started to send the normal temperature deoxygenated water into the high-pressure hot water storage tank ST2 and the pipe course of the heat exchanger H, after the deoxygenated water is filled, the water supply valve V7 is closed and the water supply pump P3 is shut down, the electric heater of the high-pressure hot water storage tank ST2 is turned on to gradually heat the deoxygenated water, and the hot water circulation pump P2 is started to send the hot water into the pipe course of the heat exchanger H, and circulate between the heat exchanger H and the high-pressure hot water storage tank ST2 to preheat the heat exchanger H. When the pressure of the steam outlet pressure gauge PI2 is 6MPa, the electric heater of the high-pressure hot water storage tank ST2 is stopped.

[0052] When the system is running, close the first hot water valve V5, open the first steam pipeline valve V3 and the second steam pipeline valve V4, open the first molten salt valve V1, the second molten salt valve V2 and the water supply valve V7, and start the water supply pump P3. The 620℃ high-temperature molten salt from the molten salt storage tank ST1 flows in the shell side of the molten salt-water / steam heat exchanger H, and the 6MPa saturated deoxygenated water from the high-pressure hot water storage tank ST2 flows in the tube side and exchanges heat with the 650℃ high-temperature molten salt. Adjust the first molten salt valve V1 to control the mass flow rate of the molten salt, so that the value of the molten salt outlet temperature T2 of the molten salt-water / steam heat exchanger H is 200℃, and the temperature difference between the inlet and outlet of the molten salt is 450℃. Adjust the second hot water valve V6 to make the value of the steam outlet pressure gauge PI1 of the molten salt-water / steam heat exchanger H 15MPa. The 15MPa steam enters the drum BD. If the superheat of the steam needs to be increased, the electric heater in the drum BD can be started to heat the steam, and the steam outlet valve V10 can be opened to provide steam for the user. Adjust the second pipeline steam valve V4 to make part of the steam flow into the high-pressure hot water storage tank ST2, and directly mix with the normal temperature deoxygenated water sent from the water supply pump P3 to form 6MPa saturated hot water, which is sent to the pipe side of the molten salt-water / steam heat exchanger H through the hot water circulation pump P2.

[0053] When the system stops, turn off all the electric heaters in the system, shut down the molten salt pump P1, hot water circulation pump P2 and water supply pump P3, close the first molten salt valve V1, the second molten salt valve V2, the first steam pipeline valve V3, the second steam pipeline valve V4, the steam outlet valve V10, the second hot water valve V6, and the water supply valve V7. Open the drain valve V8 and the molten salt drain valve V9 to discharge the high-temperature liquid molten salt from the molten salt-water / steam heat exchanger H and collect it.

[0054] From above Figure 1-3 As can be seen from Examples 1-3, the large temperature difference, high temperature and high pressure molten salt-water / steam heat exchange system of the present invention has the following characteristics:

[0055] 1) The traditional U-tube heat exchanger structure is difficult to withstand the long-term normal operation of molten salt at an inlet high temperature of 600°C and a large temperature difference of more than 370°C; the present invention adopts a plurality of heat transfer tubes in parallel to be wound around the central tube or the inner tube wall of the upper-level fiber to form a spiral coil, and multiple groups of spiral coils are respectively arranged in the annular cavity. The spiral coil structure has the characteristic of free contraction, can expand and contract autonomously with the temperature difference, and can effectively suppress the influence of thermal stress due to large temperature difference.

[0056] 2) The present invention adopts a multi-shell-pass design. In the shell cylinder, a plurality of limiting inner cylinders are arranged with the central tube as the center interval. An annular cavity connected at both ends is formed between the first limiting inner cylinder and the central tube, between two adjacent limiting inner cylinders, and between the outermost limiting inner cylinder and the shell cylinder. Each annular cavity is provided with a group of spiral coils, which ensures sufficient and rapid heat exchange between the molten salt in the shell pass and the deoxygenated water in the tube pass, thereby enhancing the convective heat transfer of the molten salt.

[0057] 3) The present invention utilizes an electric heater to heat the deoxygenated water in the high-pressure hot water storage tank and pressurize it, and then passes it into the molten salt-water / steam heat exchanger. When the pressure of the deoxygenated water is controlled to about 4 MPa, the heated high-pressure deoxygenated water can preheat the molten salt-water / steam heat exchanger by about 170°C, which can effectively offset the thermal stress damage impact of the high-temperature molten salt on the molten salt-water / steam heat exchanger when the system is started, thereby ensuring that the system operates effectively for a long time.

[0058] 4) The present invention controls the outlet temperature of the molten salt through countercurrent heat exchange between the molten salt and water, and the outlet molten salt of the molten salt heat exchanger directly enters the molten salt heating tank without exchanging heat with water, which greatly reduces the risk of molten salt solidification and clogging the pipeline.

[0059] 5) When the system is running, the inlet deoxygenated water is directly mixed with steam to form high-temperature water above 4MPa, which enters the molten salt-water / steam heat exchanger to exchange heat with the high-temperature molten salt, greatly reducing the heat transfer temperature difference in the heat exchange process, thereby inhibiting the film boiling of water and improving the heat transfer efficiency.

[0060] 6) The present invention effectively solves the problem of reliable operation of the molten salt-water / steam heat exchanger with a high inlet temperature of 600°C and a large temperature difference of 370°C or above, solves the damage of the heat exchanger to the thermal shock caused by the large temperature difference and high temperature, and improves the heat transfer efficiency and the reliability and safety of the system, and has good practicality.

Claims

1. A large temperature difference, high temperature and high pressure molten salt-water / steam heat exchange system, characterized in that: It includes a molten salt storage tank, a high-pressure hot water storage tank, a molten salt-water / steam heat exchanger and a steam drum; the molten salt-water / steam heat exchanger is a multi-shell spiral coil heat exchanger structure; in the shell body, a plurality of limiting inner cylinders are arranged with the central tube as the center, and an annular cavity with two ends connected is formed between the first limiting inner cylinder and the central tube, between two adjacent limiting inner cylinders, and between the outermost limiting inner cylinder and the shell body, a plurality of heat transfer tubes are connected in parallel and wound around the central tube or the wall of the upper-level fiber inner cylinder to form a spiral coil, and a plurality of groups of spiral coils are arranged in the annular cavity respectively. ; The shell cylinder is provided with a shell side molten salt liquid inlet, a shell side molten salt liquid outlet, a tube side water inlet and a tube side steam outlet; the molten salt-water / steam heat exchanger is connected to the outlet and inlet of the molten salt storage tank through the shell side molten salt liquid inlet and the shell side molten salt liquid outlet respectively, and is connected to the water outlet and inlet of the high-pressure hot water storage tank through the tube side water inlet and the tube side steam outlet respectively; the tube side steam outlet is also connected to the steam drum; electric heaters are provided in the molten salt storage tank and the high-pressure hot water storage tank; one end of each set of spiral coils is connected to the tube side water inlet, and the other end is connected to the tube side steam outlet.

2. The large temperature difference, high temperature and high pressure molten salt-water / steam heat exchange system according to claim 1 is characterized in that: The molten salt inlet pipe and the molten salt outlet pipe of the molten salt-water / steam heat exchanger are respectively provided with a first molten salt valve and a second molten salt valve; the water inlet pipe and the outlet pipe of the molten salt-water / steam heat exchanger respectively connected to the water outlet and the inlet of the high-pressure hot water storage tank are respectively provided with a second hot water valve and a first hot water valve; the pipe connecting the outlet pipe of the molten salt-water / steam heat exchanger and the steam drum is provided with a first steam pipeline valve; the pipe connecting the steam drum and the inlet of the high-pressure hot water storage tank is provided with a second steam pipeline valve.

3. The large temperature difference, high temperature and high pressure molten salt-water / steam heat exchange system according to claim 1 is characterized in that: The molten salt inlet pipe and the water inlet pipe of the molten salt-water / steam heat exchanger are respectively provided with a molten salt pump and a hot water circulation pump.

4. The large temperature difference, high temperature and high pressure molten salt-water / steam heat exchange system according to claim 1 is characterized in that: The water inlet pipe of the high-pressure hot water storage tank is provided with a water replenishment valve and a water replenishment pump.

5. The large temperature difference, high temperature and high pressure molten salt-water / steam heat exchange system according to claim 1, characterized in that: The molten salt inlet pipe and the molten salt outlet pipe are respectively installed with a first temperature measuring point and a second temperature measuring point, and a molten salt mass flow meter is also installed in the molten salt inlet pipe of the molten salt-water / steam heat exchanger.

6. The large temperature difference, high temperature and high pressure molten salt-water / steam heat exchange system according to claim 1, characterized in that: The top of the shell cylinder is provided with an exhaust port, and the bottom is provided with a molten salt discharge port.

7. The large temperature difference, high temperature and high pressure molten salt-water / steam heat exchange system according to claim 6, characterized in that: The pipes provided with the exhaust port and the molten salt discharge port are respectively provided with an exhaust valve and a molten salt discharge valve.

8. The large temperature difference, high temperature and high pressure molten salt-water / steam heat exchange system according to claim 1, characterized in that: A steam outlet valve is installed on the upper part of the steam drum; a water inlet pipe pressure gauge and a steam outlet pressure gauge are installed on the outlet and water inlet pipes of the molten salt-water / steam heat exchanger respectively; the number of the limiting inner cylinders is 2-4; the spiral coil can withstand a pressure of 10-15MPa.

9. The control method of the large temperature difference, high temperature and high pressure molten salt-water / steam heat exchange system according to any one of claims 1 to 8, characterized in that: The deoxygenated water in the high-pressure hot water storage tank is first electrically heated and then sent to each group of spiral coils to preheat the molten salt-water / steam heat exchanger. When the pressure of the deoxygenated water is heated to 4-6MPa, the high-temperature molten salt of 600-650℃ is sent to the shell-side molten salt liquid inlet of the molten salt-water / steam heat exchanger. The high-temperature molten salt in the shell side exchanges heat with the deoxygenated water in the spiral coil. The outlet temperature of the molten salt is controlled at 200-230℃, and the water in the spiral coil is heated to form 10-15MPa steam; the steam enters the steam drum.

10. The control method of the large temperature difference, high temperature and high pressure molten salt-water / steam heat exchange system according to claim 9, characterized in that: Part of the steam in the steam drum is extracted into the high-pressure hot water storage tank to convert the normal temperature deoxygenated water into high-pressure saturated water; when the system stops running, the drain valve and the molten salt drain valve are opened to discharge and collect the high-temperature liquid molten salt from the molten salt-water / steam heat exchanger.

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