Fused salt potential energy recovery process

Abstract

The present application relates to molten salt system technical field, disclose a molten salt potential energy recovery method, including the following operation: through molten salt pump send molten salt in molten salt tank to the middle of falling film tube, until the molten salt fills up entire molten salt heat exchange system;Then close the channel of molten salt in molten salt tank into molten salt pump, the molten salt of falling film tube is connected to the output port of molten salt pump, forms the closed loop of molten salt pump to falling film tube again to molten salt pump, the output lift of molten salt pump is changed into the output lift after the work of molten salt potential energy is offset, let molten salt circulate in molten salt pump to falling film tube;Through the method of the application, the problem of energy loss from the falling film tube to the molten salt tank during the existing molten salt circulation process can be solved.

Description

Technical Field

[0001] This invention relates to the field of molten salt heat exchange system technology, and more specifically to the technology of recovering potential energy of molten salt during the circulation process within the system. Background Technology

[0002] In the process of concentrating chemical products in the form of solutions or concentrates, such as the evaporation process of caustic soda, multiple heat exchange processes using molten salt are usually required. During the heat exchange process, there is usually a height difference between the heat exchange equipment and the molten salt tank. During the heat exchange process, molten salt needs to be pumped from the molten salt tank to the heat exchange equipment. The entire system of molten salt heat exchange consisting of pipelines and equipment is called a molten salt heat exchange system.

[0003] like Figure 1 The diagram shows an existing molten salt heat exchange system, including a molten salt tank B4 for storing molten salt. Molten salt is pumped through the molten salt tank B4 into a molten salt furnace B2 for heating, and then enters a falling film tube B1 that uses molten salt as a high-temperature heat exchange medium. The high-temperature molten salt exchanges heat with the target liquid in the falling film tube B1. After heat exchange, the molten salt becomes low-temperature molten salt and flows directly back into the molten salt tank B4 through the return pipe B3. The molten salt pump B5 then extracts molten salt from the molten salt tank B4, realizing the flow and circulation of molten salt.

[0004] During this process, due to the height difference between the falling film tube B1 and the molten salt tank B4, and the presence of other equipment between them, the greater the height difference between the falling film tube and the molten salt tank becomes with the addition of other equipment. In existing molten salt systems, the height difference between the falling film tube and the molten salt tank is tens of meters.

[0005] When pumping molten salt, the molten salt pump needs to pump the molten salt, which has zero kinetic energy in the molten salt tank; that is, each pumping operation requires the molten salt pump to maintain the same head. However, after the molten salt undergoes heat exchange in the falling film tube, the molten salt at the higher position in the falling film tube possesses significant gravitational potential energy. Currently, the molten salt is directly returned to the lower molten salt tank from the higher falling film tube via a return pipe, resulting in significant potential energy loss during the return process. Therefore, the existing molten salt system does not effectively utilize the substantial potential energy gained during the molten salt return process, leading to significant energy waste.

[0006] In addition, when molten salt flows back from the high-level falling film pipe to the low-level molten salt tank, the upper end of the return pipe is connected to the equipment, while the lower end of the return pipe is freely suspended in the molten salt tank. When the molten salt flows from the upper end to the lower end of the return pipe, its potential energy will cause an imbalance in the pressure between the upper and lower parts of the return pipe, which will further cause the return pipe to vibrate violently. The return pipe is in a state of vibration for a long time, which can easily cause leakage at the connection of the return pipe, and even cause the pipe wall to crack easily. Summary of the Invention

[0007] The present invention aims to provide a method for recovering molten salt potential energy, thereby recovering the potential energy of molten salt at high altitudes during the molten salt circulation process and reducing energy consumption.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: providing a method for recovering molten salt potential energy, comprising the following steps: Step 1: Fill the molten salt heat exchange system with molten salt: Use a molten salt pump to send the molten salt in the molten salt tank to the falling film tubes until the molten salt fills the entire molten salt heat exchange system; Step 2, switch to potential energy utilization loop: close the channel for molten salt in the molten salt tank to enter the molten salt pump, and connect the molten salt outlet of the falling film tube to the output port of the molten salt pump to form a closed loop from the molten salt pump to the falling film tube and then to the molten salt pump. Step 3, change the output head of the molten salt pump: reduce the output head of the molten salt pump to the output head after offsetting the work done by the potential energy of the molten salt; Step 4, Molten Salt Circulation: Keep the output head of the molten salt pump from Step 3 at a reduced operating state, allowing the molten salt in the potential energy utilization circuit to circulate in the molten salt pump to the falling film tube.

[0009] The advantages of this solution are: 1. Potential energy is converted into kinetic energy, and potential energy is rationally recovered and utilized, reducing system energy loss and lowering the head requirement of the molten salt pump.

[0010] This scheme converts the potential energy of molten salt into kinetic energy. When the molten salt descends to the position of the molten salt pump, it carries its own kinetic energy due to the influence of potential energy. When it enters the molten salt pump, the output power of the pump can be reduced. In other words, this method allows the molten salt pump to operate at a lower power. The energy reduction of the molten salt pump is just made up by the kinetic energy of the returning molten salt. In this way, when the molten salt pump pumps molten salt, it can achieve the head requirement that was originally required from the molten salt tank to the falling film tube with a small head, ultimately achieving low energy consumption of the system. This method also recovers the molten salt potential energy that was originally lost, resulting in higher energy utilization.

[0011] 2. It avoids severe vibration of the pipeline and extends the service life of the pipeline system.

[0012] By connecting the return pipe to the input end of the molten salt pump, the molten salt at both the upper and lower ends of the pipe is constrained by the consistency of molten salt flow. Both ends of the pipe are also fixedly connected, which greatly eliminates vibration and avoids the problem of easy damage to the pipeline system.

[0013] 3. This solution avoids the impact of molten salt on the molten salt tank. After the return pipe is added to the output end of the molten salt pump, the molten salt no longer passes through the molten salt tank. The molten salt tank is only used for replenishing and temporarily storing molten salt, thus avoiding the problem of the molten salt tank being impacted.

[0014] Preferably, in step one, heat is continuously supplied to the molten salt before it enters the falling film tube. A molten salt furnace is set between the molten salt pump and the falling film tube. The molten salt is continuously heated by the molten salt furnace until it reaches the standard temperature before entering the falling film tube, thus achieving continuous heat exchange of the molten salt and eliminating the need to heat the molten salt separately outside the molten salt heat exchange system.

[0015] Preferably, step one also includes venting the molten salt heat exchange system. A buffer tank is connected to the outlet of the falling film tube, and an venting valve is installed on the buffer tank. During the molten salt filling process, the gas of the molten salt heat exchange system is continuously discharged from the buffer tank. When the molten salt level in the buffer tank reaches the specified level, it indicates that the gas discharge of the molten salt heat exchange system is complete.

[0016] Only after all pipes and equipment in the molten salt heat exchange system are filled with the required amount of molten salt will the molten salt level in the buffer tank reach the specified level, indicating that the next step can proceed.

[0017] Preferably, between steps three and four, a preliminary test run is also included: a test run pipeline is connected between the output port of the molten salt pump and the outlet pipeline of the buffer tank. A test run valve is installed on the test run pipeline. During the test run, the test run valve is opened, and the molten salt passes through the molten salt pump and returns directly to the inlet of the molten salt pump from the test run pipeline. If the molten salt pump can maintain normal operation, the test run valve is closed, allowing the molten salt pump to be reconnected to the potential energy utilization circuit.

[0018] Adding a trial run step ensures that the molten salt pump is working properly before connecting it to the potential energy utilization circuit, thus avoiding the need to repair all equipment in the potential energy utilization circuit if the molten salt pump malfunctions.

[0019] Preferably, in step four, a frequency converter for controlling the motor output power is connected to the motor of the molten salt pump, and the output head of the molten salt pump is reduced by reducing the frequency through the frequency converter.

[0020] To reduce the output energy consumption of the molten salt pump, replacing it with a smaller power molten salt pump would require installing an additional bypass pipeline to connect to the molten salt pump, resulting in a larger investment in equipment. This solution still uses the original molten salt pump, but through frequency conversion by a frequency converter, the molten salt pump is put into a low-power operating state. The reduced head is compensated by the recovered potential energy, which allows the energy consumption of the molten salt pump to be detected.

[0021] Preferably, in step one, the inlet end of the molten salt pump is further provided with a pressure compensation mechanism. The pressure compensation mechanism includes a bushing and a bushing. The bushing is fixedly installed outside the output shaft of the molten salt pump, and the bushing is fixedly sleeved on the output shaft of the molten salt pump. The inner wall of the bushing and the outer wall of the bushing are both provided with spiral grooves. The bushing and the bushing abut against each other, and a molten salt channel for molten salt to pass through is formed between the bushing and the bushing.

[0022] A molten salt pump's structure consists of a motor driving an output shaft, which in turn drives an impeller, pumping molten salt from a molten salt tank. The output shaft needs radial restraint above the impeller connection to prevent rotational vibration; therefore, a dynamic seal is required at the output shaft support location. This creates a molten salt chamber above the seal and a pumping chamber at the impeller. If the pumping pressure in the pumping chamber is too high, the molten salt will cause pressure shocks to the heat exchange equipment, potentially damaging it. Conversely, if the pumping pressure is too low, it will be insufficient to achieve the expected pumping head.

[0023] In this solution, a pressure compensation mechanism replaces the original dynamic seal structure. If the pumping chamber pressure is within the expected range, the sleeve with spiral grooves is fixed to the output shaft, and the bushing with spiral grooves is fixed outside the sleeve. The sleeve and bushing abut against each other, and the spiral grooves between the sleeve and bushing form a spiral channel. Driven by the output shaft, the molten salt in the spiral channel will have a pumping pressure towards the pumping chamber. Since the pumping chamber also has a pressure, this pumping pressure will eliminate the pumping pressure in the direction of the pumping chamber, resulting in less leakage from the bushing and sleeve to the molten salt chamber. Therefore, the sealing effect is better than the original dynamic seal structure without pumping force.

[0024] In addition, this solution can also achieve pressure balance between the molten salt chamber and the pumping chamber, as detailed below: When the pressure in the pumping chamber is too low, the molten salt in the molten salt chamber is pumped into the pumping chamber from the spiral groove formed between the bushing and the bushing under the spiral extrusion and pushing force generated by the rotation of the bushing, thus replenishing the pressure in the molten salt chamber.

[0025] When the pressure in the pumping chamber is too high, the pumping chamber first overcomes the pumping force of the rotating bushing, and then the molten salt overflows from the pumping chamber, i.e., the impeller, into the molten salt chamber, thereby relieving the pressure in the pumping chamber and reducing the pressure in the pumping chamber.

[0026] Therefore, when the pumping chamber pressure is within the normal range, the pressure compensation mechanism provides a sealing effect. When the pumping chamber pressure is unbalanced, the pressure compensation mechanism helps maintain the pumping chamber pressure within the normal range and eliminates pressure fluctuations.

[0027] Preferably, the spiral grooves on the inner wall of the bushing and the outer wall of the bushing have opposite spiral directions and the same width. With the spiral grooves on the inner wall of the bushing and the outer wall of the bushing in opposite directions, the bushing and bushing abut against each other. When neither rotates, they form a sealed cavity. This allows for a relatively sealed state at the pump output shaft where the bushing is located while adjusting the input and output pressures of the molten salt pump. The identical width of the spiral grooves also facilitates predictability of pressure adjustment and makes manufacturing the bushing and bushing structure more convenient.

[0028] Preferably, in step two, a three-way valve is connected between the molten salt pump inlet, the buffer tank outlet, and the molten salt tank, and the three-way valve is used to switch the connection between the molten salt pump inlet and the buffer tank outlet or the molten salt pump inlet.

[0029] A three-way valve is used to switch between the molten salt pump inlet, buffer tank outlet, and molten salt tank, requiring only one switching component, thus reducing the number of equipment parts.

[0030] Preferably, the three-way valve is installed in such a way that the valve body is fixedly installed in the molten salt tank, one inlet of the three-way valve is directly connected to the molten salt tank, the other inlet of the three-way valve is connected to the outlet of the buffer tank through a return pipe, the switching rod of the three-way valve extends outside the molten salt tank, and a heat-resistant sealing ring is used to seal the switching rod and the molten salt tank.

[0031] The valve body of the three-way valve is fixedly installed in the molten salt tank, and the switching rod of the three-way valve extends outside the molten salt tank. A heat-resistant sealing ring is used to seal the switching rod and the molten salt tank. By placing the switching rod outside the molten salt tank, when it is necessary to switch the three-way valve, the operation can be performed only outside the molten salt tank, avoiding the need for special operations to open the molten salt tank.

[0032] In this application, the molten salt tank is only a device for storing molten salt, and can be replaced with any device that can store molten salt. The falling film tube is used for heat exchange for the concentration of alkali solution. Any device that uses molten salt for heat exchange is also applicable in this method. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the existing molten salt circulation loop connection; Figure 2 This is a schematic diagram of the potential energy utilization loop connection in this method; Figure 3 This is a schematic diagram of the installation structure of the molten salt pump where the pressure compensation mechanism is located; Figure 4 for Figure 3 Schematic diagram of the assembly structure of the medium pressure compensation mechanism components.

[0034] The reference numerals in the accompanying drawings include: falling film pipe 1; buffer tank 2; molten salt furnace 3; test valve 4; pumping pipeline 5; return pipeline 6; molten salt pump 7; pressure compensation mechanism 71; bushing 711; bushing 722; output shaft 72; molten salt chamber 73; molten salt chamber inlet 74; pumping chamber 75; molten salt tank 8; three-way valve 9. Detailed Implementation

[0035] The present invention will be further described in detail below through specific embodiments, but the embodiments are not limited thereto. Unless otherwise specified, the technical means used in the following embodiments are conventional means well known to those skilled in the art.

[0036] like Figure 2 As shown, the potential energy utilization loop structure involved in this method includes a molten salt tank 8 and a molten salt pump 7. The molten salt pump 7 is placed inside the molten salt tank 8. The output end of the molten salt pump 7 is connected to the molten salt furnace 3 and the falling film pipe 1 in sequence through the pumping pipe 5. The outlet of the falling film pipe 1 is connected to the buffer tank 2. The inlet of the molten salt pump 7, the outlet of the buffer tank 2, and the molten salt tank are connected by a three-way valve. The three-way valve 9 is installed inside the molten salt tank 8. The three-way valve 8 switches the connection between the inlet of the molten salt pump 7 and the outlet of the buffer tank 2 or between the molten salt tank 8. The buffer tank 2 and the three-way valve 9 are connected by a return pipe 6.

[0037] Based on the above potential energy utilization loop, the following method is used to recover potential energy: Step 1: Fill the molten salt heat exchange system with molten salt. Molten salt in the molten salt tank 8 is pumped to the molten salt furnace via molten salt pump 7 to replenish its temperature, ensuring it reaches the required heat exchange temperature. The heated molten salt then enters the falling film tube 1, where the liquid alkali is heated and concentrated. The process continues until the entire molten salt heat exchange system is filled. During filling, molten salt pump 7 operates at its rated head. To pump the molten salt to a height of 20 meters, the pump must have an output head greater than 20 meters. The specific output head of the pump selected depends on the distance between the molten salt tank and the falling film tube.

[0038] Step 2: Switch to potential energy utilization loop: Close the channel for molten salt in molten salt tank 8 to enter molten salt pump 7, and connect the molten salt in return pipe 6 to the output port of molten salt pump 7 to form a closed loop from molten salt pump 7 to falling film pipe 1 and then to molten salt pump 7. Step 3: Change the output head of molten salt pump 7: Change the output head of molten salt pump 7 to the output head after offsetting the work done by the potential energy of molten salt; molten salt flows from the falling film pipe to the molten salt tank. Considering energy loss, the utilization rate of the gravitational potential energy of molten salt is about 40%, that is, the energy loss rate of molten salt is about 60%. Therefore, the molten salt pump can pump at 60% of the original output head. For example, if the height of the molten salt tank from the falling film pipe is 20 meters, it is only necessary to select an output head of 12 meters for the molten salt pump.

[0039] Step 4, Molten Salt Circulation: Keep the output head of molten salt pump 7 in the reduced working state as in Step 3, so that the molten salt in the potential energy utilization circuit circulates from molten salt pump 7 to falling film tube 1.

[0040] Before the molten salt enters the falling film tube 1, heat is continuously supplied to the molten salt. The molten salt is continuously heated by the molten salt furnace 3 until it reaches the standard temperature before entering the falling film tube 1. The standard temperature here is the temperature at which the molten salt melts. In practical applications, the standard temperature is appropriately about 10% higher than the melting temperature.

[0041] A buffer tank 2 is connected to the outlet of the falling film tube 1. An exhaust valve is installed on the buffer tank 2. During the molten salt filling process, the gas of the molten salt heat exchange system is continuously discharged from the buffer tank 2. When the molten salt level in the buffer tank 2 reaches the specified level, it indicates that the gas discharge of the molten salt heat exchange system is complete.

[0042] A test pipeline is connected between the output port of the molten salt pump 7 and the outlet pipeline of the buffer tank. A test valve 4 is installed on the test pipeline. During the test, the test valve 4 is opened, and the molten salt returns directly to the inlet of the molten salt pump through the test pipeline. If the molten salt pump can maintain normal operation, the test valve 4 is closed, and the molten salt pump is reconnected to the potential energy utilization circuit.

[0043] The inlet end of the molten salt pump is also equipped with a pressure compensation mechanism to balance the pressure at the inlet end of the molten salt pump.

[0044] A frequency converter is connected to the motor of the molten salt pump to control the output power of the motor. The output head of the molten salt pump is reduced by reducing the frequency through the frequency converter.

[0045] When maintenance is required, first shut down the system, guide the molten salt in the falling film tube 1 and molten salt furnace 3 back to the molten salt tank 8, and then carry out maintenance.

[0046] In this embodiment, the molten salt pump 7 is electrically connected to a frequency converter for controlling the output power of the molten salt pump. During the potential energy recovery process, the frequency converter reduces the frequency to reduce the output power of the molten salt pump. Through testing, by controlling the speed of the molten salt pump through frequency conversion, the load of the molten salt pump is reduced by 30%-40% during the operation with potential energy recovery. This reduces the energy consumption of the molten salt pump.

[0047] The valve body of the three-way valve 9 is fixedly installed in the molten salt tank 8. The switching rod of the three-way valve 9 extends outside the molten salt tank 8, and a heat-resistant sealing ring is used to seal the switching rod and the molten salt tank.

[0048] like Figure 3 and Figure 4As shown, the pressure compensation mechanism 71 used in this scheme includes a bushing 711 and a bushing 722. The bushing 711 is fixedly installed on the housing outside the output shaft of the molten salt pump 7, and the bushing 722 is fixedly sleeved on the output shaft of the molten salt pump. The inner wall of the bushing 711 and the outer wall of the bushing 722 are both provided with spiral grooves. The bushing 711 and the bushing 722 abut against each other, and a molten salt channel for molten salt to pass through is formed between the bushing 711 and the bushing 722.

[0049] In this embodiment, a pressure compensation mechanism replaces the original sealing device. The bushing 722 with spiral grooves is fixed to the output shaft 72, and the bushing 711 with spiral grooves is fixed outside the bushing 722. The spiral grooves on the bushing 722 and the bushing 711 cooperate to form a sealed spiral channel. When the bushing 722 rotates driven by the output shaft 72, the molten salt in the spiral channel experiences a pumping pressure towards the pumping chamber. Since the pumping chamber also has pressure, this pumping pressure eliminates the pumping pressure in the direction of the pumping chamber, resulting in less leakage from the bushing and bushing into the molten salt chamber. Therefore, the sealing effect is superior to the original dynamic seal structure without pumping force.

[0050] The pressure compensation mechanism balances the pressure between the molten salt chamber and the pumping chamber, as follows: When the pressure in the pumping chamber 75 is too low, the molten salt chamber 73 receives molten salt through the molten salt chamber inlet 74. Under the pumping force generated by the rotation of the bushing 722, the molten salt is pumped from the spiral groove formed between the bushing 722 and the bushing 711 into the pumping chamber 75, thereby compensating for the pressure in the pumping chamber 75 and balancing the pressure between the pumping chamber 75 and the molten salt chamber 73.

[0051] When the pressure in the pumping chamber 75 is too high, the pumping chamber 75 first overcomes the pumping force of the rotating bushing 722, and then the molten salt flows from the spiral channel into the molten salt chamber 73, which causes the pumping chamber 75 to depressurize and achieves a balance between the pressure in the pumping chamber 75 and the pressure in the molten salt chamber 73.

[0052] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for recovering the potential energy of molten salt, characterized in that, Includes the following steps: Step 1: Fill the molten salt heat exchange system with molten salt: Use a molten salt pump to send the molten salt in the molten salt tank to the falling film tubes until the molten salt fills the entire molten salt heat exchange system; Step 2, switch to potential energy utilization loop: close the channel for molten salt in the molten salt tank to enter the molten salt pump, and connect the molten salt in the falling film tube to the inlet of the molten salt pump to form a closed loop from the molten salt pump to the falling film tube and then to the molten salt pump. Step 3, change the output head of the molten salt pump: change the output head of the molten salt pump to the output head after offsetting the work done by the potential energy of the molten salt; Step 4, Molten Salt Circulation: Keep the output head of the molten salt pump from Step 3 at a reduced operating state, allowing the molten salt in the potential energy utilization circuit to circulate in the molten salt pump to the falling film tube. In step one, a molten salt furnace is set between the molten salt pump and the falling film tube. The molten salt in the molten salt tank is first heated by the molten salt furnace to reach the expected temperature, and then the molten salt is introduced into the falling film tube. Step one also includes venting the molten salt heat exchange system, connecting a buffer tank between the falling film pipe and the return pipe, installing an vent valve on the buffer tank, and when the molten salt level in the buffer tank reaches the specified level during the molten salt filling process, proceeding to the next operation step. In step one, the inlet end of the molten salt pump is also provided with a pressure compensation mechanism. The pressure compensation mechanism includes a bushing and a bushing. The bushing is fixedly installed on the housing outside the output shaft of the molten salt pump, and the bushing is fixedly sleeved on the output shaft of the molten salt pump. The inner wall of the bushing and the outer wall of the bushing are provided with spiral grooves. The bushing and the bushing abut against each other, and a molten salt channel for molten salt to pass through is formed between the bushing and the bushing. The spiral grooves on the inner wall of the bushing and the outer wall of the bushing have opposite spiral directions and the same width. In step two, a three-way valve is connected between the molten salt pump inlet, the buffer tank outlet, and the molten salt tank. By switching the three-way valve, one of the following can be connected: between the molten salt pump inlet and the molten salt tank, or between the molten salt pump inlet and the buffer tank.

2. The molten salt potential energy recovery method according to claim 1, characterized in that: Between steps three and four, a preliminary test run is also included: a test run pipeline is connected between the output port of the molten salt pump and the outlet pipeline of the buffer tank. A test run valve is installed on the test run pipeline. During the test run, the test run valve is opened to allow molten salt to flow from the outlet of the molten salt pump through the test run pipeline and back to the inlet of the molten salt pump. If the molten salt pump works normally, the test run valve is closed and the aforementioned molten salt potential energy recovery step is started.

3. The molten salt potential energy recovery method according to claim 1, characterized in that: In step four, a frequency converter for controlling the motor output power is connected to the motor of the molten salt pump, and the output head of the molten salt pump is adjusted by the frequency converter.

4. The molten salt potential energy recovery method according to claim 1, characterized in that, The three-way valve is installed in such a way that the valve body is fixedly installed in the molten salt tank, the three ports of the three-way valve are respectively connected to the molten salt tank, the molten salt pump inlet and the return pipe, the switching rod of the three-way valve extends outside the molten salt tank, and the switching rod is sealed with a heat-resistant sealing ring between itself and the molten salt tank.

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