A circulating molten salt heat extraction system
By utilizing the circulating molten salt heat recovery system, which combines the circulation of molten salt buffer tanks and tubular reactors, the problem of heat management in medium-sized experimental devices at high temperatures was solved, achieving efficient heat exchange and temperature control.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- MERYER TECHNOLOGIES CO LTD
- Filing Date
- 2025-08-04
- Publication Date
- 2026-07-10
Smart Images
Figure CN224474986U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to a circulating molten salt heat recovery system suitable for medium-sized experimental reactors, belonging to the field of chemical heat exchange technology. Background Technology
[0002] The reactors in experimental setups typically operate isothermally. If the reaction is significantly exothermic, the catalyst must be diluted or the released heat rapidly removed to maintain a constant catalyst bed temperature within the reactor. Using inert materials to dilute the catalyst to maintain a constant catalyst bed temperature is only suitable for relatively small catalyst loads. If the catalyst load is large, an excessively large diameter of the reaction tubes hinders the rapid transfer of heat to the reactor wall, leading to a sharp rise in the catalyst bed temperature. Using small-diameter tubular reactors to remove reaction heat is widely used in experimental and industrial reactors. For tubular reactors, to uniformly remove heat from each reaction tube, the heat removal medium must be a fluid. Thermal oil is commonly used as a heating medium, but practice has shown that its heat removal efficiency is poor, and its operating temperature is typically limited to 350°C, making it unsuitable for high-temperature reaction systems. Saturated water vaporization is effective for heat removal, but if the reaction temperature exceeds the critical temperature of water, cooling water or saturated water vaporization cannot be used. Molten salts are suitable for use at higher temperatures, and there are precedents for using molten salts as heating media. Therefore, it is essential to develop a system that uses molten salt to extract heat from the reactor at a higher temperature. Summary of the Invention
[0003] The technical problem to be solved by this utility model is to provide a circulating molten salt heat recovery system suitable for a medium-sized experimental device tubular reactor.
[0004] To address the aforementioned problems, this utility model provides a circulating molten salt heat recovery system, comprising a molten salt buffer tank. The molten salt buffer tank is divided into a reflux side and a salt injection side by a partition. The salt injection side is equipped with a salt injection port and a reactor salt injection pump. The reflux side is equipped with a reflux side salt injection port and a molten salt cooler salt injection pump. The outlet of the reactor salt injection pump is connected to the inlet of the shell side of a tube reactor via a reactor molten salt injection pipe. The outlet of the shell side of the tube reactor is connected to the reflux side of the molten salt buffer tank via a reactor molten salt outflow pipe and a reactor molten salt pressure balancing valve. The outlet of the molten salt cooler salt injection pump is connected to the shell side inlet of the molten salt cooler. The shell side outlet of the molten salt cooler is connected to the salt injection side of the molten salt buffer tank. The top of the molten salt cooler is equipped with a tube side water inlet and a steam outlet, and the bottom of the molten salt cooler is equipped with a tube side outlet. The tube side steam / condensate flow port is connected to the bottom of the steam condenser via a tube side steam / condensate flow pipe.
[0005] Preferably, the molten salt buffer tank is equipped with at least two electric heaters so that if one of them fails, the other can be used to heat and melt the salt to remove the faulty heater for repair. The electric heater located on the salt injection side is the salt injection side electric heater, and the electric heater located on the reflux side is the molten salt reflux side electric heater.
[0006] Preferably, the molten salt buffer tank is equipped with a reflux side temperature measuring thermocouple and a salt injection side temperature measuring thermocouple, respectively. The salt injection side electric heater, the reflux side electric heater, and the corresponding salt injection side temperature measuring thermocouple and reflux side temperature measuring thermocouple form a control loop to heat the molten salt in the buffer tank to above the molten salt melting temperature (147°C) before salt is injected into the shell side of the tubular reactor.
[0007] Preferably, a bottom-side thermocouple is provided at the bottom of the shell side of the tubular reactor, and molten salt inlet and outlet thermocouples are respectively provided at the inlet and outlet of the shell side. The molten salt circulation flow rate of the reactor injection pump depends on the heat of reaction to be extracted and the allowable temperature rise of the molten salt. The flow rate of the injection pump is controlled by the temperature difference between the molten salt inlet thermocouple and the molten salt outlet thermocouple. The reactor molten salt outflow pipe delivers the heated molten salt to the reflux side of the molten salt buffer tank. The outlet of the shell side of the tubular reactor is higher than the inlet. When the unit is shut down and begins to return salt to the molten salt buffer tank, the reactor molten salt pressure balancing valve is used to balance the gas phase pressure of the shell side of the tubular reactor, the reflux pipe, and the molten salt buffer tank to ensure smooth salt return. The upper end of the reflux pipe is connected to the top shell side outlet of the reactor, and the other end is connected to the top opening flange of the molten salt buffer tank.
[0008] Preferably, the inner diameter of the reaction tubes in the tubular reactor is 22-50 mm to facilitate the transfer of reaction heat.
[0009] Preferably, the shell-side outlet of the molten salt cooler is also connected to the air connection at the top of the molten salt buffer tank via a pressure balancing valve, ensuring that the molten salt in the shell side and pipelines can smoothly return to the molten salt buffer tank when the unit is shut down and salt is returned. The molten salt cooler is a shell-and-tube heat exchanger, installed vertically. Based on the density difference of water at room temperature and saturation temperature, the water level added at room temperature is calculated to ensure that at saturation temperature, the water level rises to the upper tube sheet due to thermal expansion, allowing the molten salt entering the shell side to fully exchange heat with the saturated water in the tube side.
[0010] Preferably, the molten salt cooler is provided with an external heater for heating the water in the tubes to a preset saturation temperature before the molten salt enters.
[0011] Preferably, the molten salt cooler is equipped with a molten salt cooler tube-side level gauge.
[0012] Preferably, the bottom of the molten salt cooler is provided with a molten salt cooler bottom temperature measuring thermocouple.
[0013] Preferably, the steam condenser is a shell-and-tube heat exchanger, with an outlet at the top. The outlet is connected to a saturated water pressure control system, including a nitrogen pressure reducing valve, a pressure gauge, and a back pressure valve. The pressure control system formed by the nitrogen pressure reducing valve and the back pressure valve maintains the vapor phase pressure in the tube side of the steam condenser and the tube side of the molten salt cooler at the same level as the saturation pressure of the saturated water, ensuring that the water in the tube side of the molten salt cooler is always saturated.
[0014] The volume of the molten salt buffer tank must ensure that after the pumped molten salt fills the reactor shell space, the molten salt cooler shell side space, and related pipelines, the remaining molten salt in the buffer tank can still submerge the heater to prevent it from burning dry and being damaged; it must also ensure that there is enough space to ensure that when the molten salt in the reactor shell side, the molten salt cooler shell side, and related pipelines returns to the buffer tank during shutdown, it will not overflow.
[0015] The heat exchange area of the molten salt cooler, the saturated water temperature, the circulating molten salt flow rate, and the molten salt temperature after cooling should all be considered comprehensively to reasonably determine the equipment load.
[0016] The steam condenser is positioned above the molten salt cooler. The pipe connecting the steam outlet at the top of the molten salt cooler to the steam inlet at the bottom of the steam condenser should be appropriately enlarged to ensure that the vaporized steam from the heat exchange between saturated water and hot molten salt smoothly enters the steam condenser, while also ensuring that the condensate returns to the vapor phase space at the top of the molten salt cooler via the same pipe. The heat exchange capacity of the steam condenser should be appropriately over-designed to prevent steam from flowing out of the condenser.
[0017] All molten salt pipelines must be heated to the operating temperature of the molten salt, and the heating process must be preheated before the salt is injected to prevent the molten salt from cooling, solidifying, and clogging the pipelines.
[0018] Hot molten salt, at a temperature comparable to the reaction temperature, is injected into the bottom shell of the reactor. The molten salt, having absorbed the heat of the reaction and increased in temperature, flows out from the top shell and returns to the molten salt buffer tank. A circulating pump built into the buffer tank then injects the high-temperature molten salt into the bottom shell of the molten salt cooler, where it exchanges heat with the saturated water in the cooler tubes. Utilizing the latent heat of vaporization of the saturated water, the temperature of the high-temperature molten salt is reduced to the required temperature. The cooled molten salt returns to the buffer tank, is reheated by a heater, and then injected back into the reactor shell for heat recovery. The steam generated from the vaporization of the saturated water in the cooler tubes enters the steam condenser located above through connecting pipes. After condensation in the condenser, the condensate flows back to the top vapor phase space of the cooler tubes by gravity, forming a closed-loop cycle of vaporization-condensation-revaporization, thus achieving the purpose of cooling the molten salt. The upper vapor phase outlet of the steam condenser is connected to a nitrogen constant pressure system. Nitrogen enters through pressure reduction and is then discharged by a back pressure valve at a pressure higher than the system pressure. This maintains the vapor phase pressure in the molten salt cooler tubes consistent with the saturated water pressure, ensuring that the water in the molten salt cooler tubes is always saturated.
[0019] This invention utilizes the good heat extraction effect of saturated water vaporization and the suitability of molten salt for use at higher temperatures, providing a system for extracting heat from a reactor using molten salt at higher temperatures. Attached Figure Description
[0020] Figure 1 A schematic diagram of the circulating molten salt heat extraction system provided by this utility model. Detailed Implementation
[0021] To make this utility model more apparent and understandable, preferred embodiments are described in detail below with reference to the accompanying drawings.
[0022] Example
[0023] like Figure 1As shown, this utility model provides a circulating molten salt heat recovery system, which includes a molten salt buffer tank 1. The molten salt buffer tank 1 is divided into a reflux side and a salt injection side by a partition 2. The salt injection side is provided with a salt injection port 6 and a reactor salt injection pump 3. The reflux side is provided with a reflux side salt injection port 7 and a molten salt cooler salt injection pump 10. The outlet end of the reactor salt injection pump 3 is connected to the inlet of the shell side 11 of the tubular reactor 12 through a reactor molten salt injection pipe 17. The outlet of the shell side 11 of the tubular reactor is connected to the reflux side of the molten salt buffer tank 1 through a reactor molten salt outflow pipe 18 and a reactor molten salt pressure balancing valve 16. The outlet end of the molten salt cooler salt injection pump 10 is connected to the shell side inlet of the molten salt cooler 20. The shell side outlet of the molten salt cooler 20 is connected to the salt injection side of the molten salt buffer tank 1. The molten salt cooler 20 has a tube-side water inlet 23 and a steam outlet at the top, and a tube-side outlet at the bottom. The tube-side steam / condensate flow port is connected to the bottom of the steam condenser 25 through the tube-side steam / condensate flow pipe 26. The shell-side outlet of the molten salt cooler 20 is also connected to the air connection at the top of the molten salt buffer tank 1 through the molten salt cooler pressure balancing valve 19.
[0024] The molten salt buffer tank 1 is equipped with at least two electric heaters so that if one heater fails, the other can be used to melt the salt and remove the faulty heater for repair. The electric heater located on the salt injection side is the salt injection side electric heater 4, and the electric heater located on the reflux side is the molten salt reflux side electric heater 8. The reflux side and salt injection side of the molten salt buffer tank 1 are respectively equipped with a reflux side temperature measuring thermocouple 9 and a salt injection side temperature measuring thermocouple 5.
[0025] The bottom of the shell side 11 of the tubular reactor is equipped with a bottom temperature measuring thermocouple 13, and the inlet and outlet of the shell side 11 are equipped with a reactor molten salt inlet temperature measuring thermocouple 14 and a reactor molten salt outlet temperature measuring thermocouple 15, respectively. The inner diameter of the reaction tubes of the tubular reactor 12 is 22-50 mm.
[0026] The molten salt cooler 20 is equipped with an external heater 24. The molten salt cooler 20 is equipped with a tube-side level gauge 22. The bottom of the molten salt cooler 20 is equipped with a bottom temperature measuring thermocouple 21.
[0027] The steam condenser 25 is a tube heat exchanger with an outlet at the top. The outlet is connected to a saturated water pressure control system, including a nitrogen pressure reducing valve 27, a pressure gauge 29, and a back pressure valve 28.
[0028] In this embodiment, the molten salt buffer tank 1 is equipped with two electric heaters, one on the salt injection side and one on the reflux side. The volume of the molten salt buffer tank must ensure that after the pumped molten salt fills the reactor shell space, the molten salt cooler shell-side space, and related pipelines, the remaining molten salt in the buffer tank can still submerge the heaters to prevent them from burning dry and being damaged; it must also ensure that there is enough space to prevent overflow when the molten salt in the reactor shell-side, molten salt cooler shell-side, and related pipelines returns to the buffer tank during shutdown. The molten salt buffer tank has two built-in molten salt transfer pumps, one for injecting heating / heat extraction molten salt into the reactor shell-side, and the other for delivering high-temperature molten salt to the molten salt cooler shell-side. Before starting the molten salt system, the buffer tank is filled with salt, and the heaters are started simultaneously. As the molten salt continues to melt, more salt is added until the appropriate liquid level is reached. The tubular reactor is placed inside the reactor shell-side. When loading the catalyst, the upper surface of the catalyst bed must be lower than the molten salt outlet at the top of the shell-side to ensure that the heat generated by the reaction can exchange heat with the molten salt in the shell-side in a timely manner. A thermocouple is installed at the bottom of the shell side to determine if the reactor shell temperature meets the requirements for salt injection. The shell is covered with sufficiently thick insulation material to prevent heat loss. Before injecting molten salt into the reactor shell, the reactor shell is preheated to above the molten salt's freezing point (147°C) using hot materials, leaving a margin, such as 160°C, before the hot molten salt is injected. The molten salt circulation flow rate depends on the amount of reaction heat to be removed and the allowable temperature rise of the molten salt. Before the reactor temperature reaches the required reaction temperature, the molten salt's role is to heat the reactor. When the catalyst bed in the reactor reaches the reaction temperature, the material entering the reactor reacts under the action of the catalyst, releasing a large amount of heat, thus raising the temperature of the catalyst and the material passing through. At this time, the high-temperature hot material transfers heat back through the reaction tube wall to the molten salt in the shell side, raising the temperature of the molten salt and thus removing the heat generated by the reaction. The heated molten salt flows out of the reactor shell from the top and enters the reflux side formed by the baffles inside the molten salt buffer tank. A pressure balancing valve is installed at the highest point of the molten salt outflow pipe near the reactor shell side, and connected to the top of the molten salt buffer tank via a pipeline. When the unit shuts down and begins to return salt to the buffer tank, the pressure balancing valve is opened. As the molten salt falls under its own weight in the pipe and on the reactor shell side, the hot gas at the top of the molten salt buffer tank fills the space created by the falling molten salt, balancing the pressure on both sides and allowing the molten salt to smoothly return to the buffer tank. During normal testing, the hot molten salt flowing back from the top of the reactor shell side to the molten salt buffer tank is then sent to the shell side of a shell-and-tube molten salt cooler by a molten salt cooling circulation pump. The low-temperature saturated water in the tubes is vaporized, and the latent heat of vaporization of the saturated water is used to lower the molten salt temperature to the reaction temperature. The steam generated by the vaporization of the saturated water enters a steam condenser located above the molten salt cooler. The condensate generated by the steam cooling flows back under its own weight along the connecting pipe between the two heat exchangers to the top of the tube side of the molten salt cooler. The molten salt cooler is installed vertically to facilitate the smooth discharge of vaporized steam. The steam condenser is installed vertically or at an angle to ensure that the steam condensate flows smoothly back to the molten salt cooler.The steam condenser should be appropriately over-designed to prevent steam from rising to the top of the tubes. The upper outlet of the steam condenser tubes is connected to a nitrogen pressure reducing valve and a system back pressure valve. The pressure of the saturated water vaporization / condensation system is set according to the required saturated water temperature. The molten salt cooler is equipped with an external heater to heat the soft water pre-added to the tubes to near its saturation temperature. The saturated water temperature must be determined to be higher than the freezing point of the molten salt (147°C) while also ensuring a suitable temperature difference between the molten salt being cooled and the saturated water. This effectively cools the high-temperature molten salt without causing difficulties in the manufacturing of the shell-and-tube heat exchanger due to excessive temperature differences. The molten salt cooler is equipped with a level gauge on the tubes and a water inlet on the upper end cap. Before use, soft water is added to the cooler tubes. The water level at room temperature is calculated based on the density difference between water at room temperature and saturation temperature. This ensures that at saturation temperature, the water level rises to the upper tube sheet due to thermal expansion, allowing the molten salt in the shell side to fully exchange heat with the saturated water in the tubes. A 200-400mm long straight cylindrical section, with dimensions matching the shell side, is added between the upper head and the upper tube sheet sealing flange. Even if water rises above the tube sheet due to vaporization in the tubes, there is sufficient space to separate the saturated water from the vaporized steam. The upper head of the molten salt cooler has a steam outlet, which is connected to the steam inlet at the bottom of the steam condenser via a pipe. Steam enters the steam condenser along this pipe, and condensate flows back to the upper tube sheet of the molten salt cooler tube side along the same pipe. Even if the returning condensate only enters part of the tubes, the same water level is maintained because all tubes are connected to the bottom head, forming a communicating vessel, thus not affecting the cooling of the shell-side molten salt. The molten salt cooler has an external heater. Before use, the water in the tubes must be preheated to saturation temperature, and the bottom temperature must be higher than the molten salt solidification temperature (147°C) before starting the molten salt cooling circulation pump. This prevents premature salt injection, which could cause molten salt solidification and block the pipes and equipment. A pressure balancing valve is also installed at the highest point of the molten salt outflow pipeline at the top of the molten salt shell side of the molten salt cooler, and is connected to the top of the molten salt buffer tank via a pipeline. When the unit is shut down and begins to return salt to the buffer tank, the pressure balancing valve is opened to balance the pressure in the buffer tank, the shell side of the molten salt cooler, and the return pipeline, allowing the molten salt in the shell side and pipelines to smoothly return to the buffer tank. All molten salt pipelines must be heat-traced and insulated according to the maximum operating temperature. By adjusting the saturated water temperature and the molten salt circulation flow rate into the cooler, the molten salt at the outlet of the molten salt cooler reaches the required temperature. The cooled molten salt flows back to the feed side of the molten salt buffer tank, where the temperature is readjusted by the heater, and then the circulating pump injects the molten salt that meets the temperature requirements into the bottom of the reactor shell side.
Claims
1. A circulating molten salt heat recovery system, characterized in that, The system includes a molten salt buffer tank (1), which is divided into a reflux side and a salt injection side by a partition (2). The salt injection side is equipped with a salt injection port (6) and a reactor salt injection pump (3). The reflux side is equipped with a reflux side salt injection port (7) and a molten salt cooler salt injection pump (10). The outlet of the reactor salt injection pump (3) is connected to the inlet of the shell side (11) of the tubular reactor (12) through the reactor molten salt injection pipe (17). The outlet of the shell side (11) of the tubular reactor is connected to the inlet of the shell side (11) of the tubular reactor (12) through the reactor molten salt outflow pipe (18) and the reactor molten salt inflow pipe (19). The molten salt pressure balancing valve (16) of the molten salt cooler is connected to the reflux side of the molten salt buffer tank (1); the outlet end of the molten salt cooler injection pump (10) is connected to the shell-side inlet of the molten salt cooler (20); the shell-side outlet of the molten salt cooler (20) is connected to the injection side of the molten salt buffer tank (1); the top of the molten salt cooler (20) is provided with a tube-side water inlet (23) and a steam outlet; the bottom of the molten salt cooler (20) is provided with a tube-side outlet; the tube-side steam / condensate flow port is connected to the bottom of the steam condenser (25) through the tube-side steam / condensate flow pipe (26).
2. The circulating molten salt heat recovery system as described in claim 1, characterized in that, The molten salt buffer tank (1) is equipped with at least two electric heaters. The electric heater located on the salt injection side is the salt injection side electric heater (4), and the electric heater located on the reflux side is the molten salt reflux side electric heater (8).
3. The circulating molten salt heat recovery system as described in claim 1 or 2, characterized in that, The molten salt buffer tank (1) is equipped with a reflux side temperature measuring thermocouple (9) and a salt injection side temperature measuring thermocouple (5) on the reflux side and the salt injection side, respectively.
4. The circulating molten salt heat recovery system as described in claim 1, characterized in that, The bottom of the shell side (11) of the tubular reactor is provided with a bottom temperature measuring thermocouple (13), and the inlet and outlet of the shell side (11) of the tubular reactor are respectively provided with a reactor molten salt inlet temperature measuring thermocouple (14) and a reactor molten salt outlet temperature measuring thermocouple (15).
5. The circulating molten salt heat recovery system as described in claim 1, characterized in that, The inner diameter of the reaction tube of the tubular reactor (12) is 22-50 mm.
6. The circulating molten salt heat recovery system as described in claim 1, characterized in that, The tube outlet of the molten salt cooler (20) is also connected to the gas connection at the top of the molten salt buffer tank (1) via the molten salt cooler pressure balancing valve (19).
7. The circulating molten salt heat recovery system as described in claim 1, characterized in that, The molten salt cooler (20) is provided with an external heater (24).
8. The circulating molten salt heat recovery system as described in claim 1, characterized in that, The molten salt cooler (20) is equipped with a molten salt cooler tube level gauge (22).
9. The circulating molten salt heat recovery system as described in claim 1, characterized in that, The bottom of the molten salt cooler (20) is provided with a molten salt cooler bottom temperature measuring thermocouple (21).
10. The circulating molten salt heat recovery system as described in claim 1, characterized in that, The steam condenser (25) is a shell-and-tube heat exchanger. The top of the shell-and-tube heat exchanger is provided with an outlet. The outlet is connected to a saturated water pressure control system, including a nitrogen pressure reducing valve (27), a pressure gauge (29), and a back pressure valve (28).