Negative pressure suction nitrogen protection device

Abstract

This utility model relates to the field of polymer material processing technology, specifically a negative pressure suction nitrogen protection device. The device includes a liquid raw material storage tank, an intermediate metering mixing tank, an extruder and an extruder hopper, and is equipped with a two-stage series nitrogen-driven vacuum generation unit, a nitrogen circulation heating and pressurization circuit, and a vacuum storage and purification circuit. Nitrogen is utilized in stages through the two-stage vacuum generator, reducing nitrogen consumption; heat from high-temperature waste gas is recovered using a heat storage heat exchanger to preheat and pressurize the nitrogen, achieving energy saving and consumption reduction. The device can control the oxygen content in the tank at an extremely low level, avoiding material oxidation and degradation and moisture contamination, while also reducing the impact of temperature fluctuations on the material. This device has a high degree of structural integration and low operating cost, and is suitable for the safe transportation and protection of liquid raw materials such as thermoplastic polyurethane that are sensitive to moisture and oxygen.

Description

Technical Field

[0001] This utility model relates to the field of polymer material processing technology, specifically to a negative pressure suction nitrogen protection device. Background Technology

[0002] Polymer materials, especially liquid raw materials such as thermoplastic polyurethane (TPU) prepolymers, polyamide (PA) melts, and polyesters, are highly susceptible to the effects of oxygen and moisture in the air during storage, transportation, and subsequent processing. Oxygen can lead to oxidative degradation, molecular weight reduction, yellowing, and deterioration of mechanical properties, while moisture can trigger hydrolysis, affecting melt processing performance and even causing product spoilage. These problems are particularly prominent in the production of polymer materials, especially high-performance engineering plastics and specialty resins, directly affecting the stability, reliability, and service life of the final product.

[0003] Traditional methods of conveying liquid materials, such as pumping or simple negative pressure suction, often fail to effectively isolate the material from ambient air, resulting in continuous exposure of the material to oxygen and moisture during transport. To address this issue, the industry typically employs inert gas protection measures, such as filling critical equipment like storage tanks, intermediate metering tanks, and extruder hoppers with nitrogen to create a protective atmosphere. However, existing technologies have several shortcomings in achieving both negative pressure suction and nitrogen protection.

[0004] Many existing inert gas protection systems require frequent vacuuming and nitrogen purging cycles, or continuous replenishment of large amounts of fresh nitrogen to maintain the inert environment inside the equipment. This operating mode often results in huge nitrogen consumption, significantly increasing production operating costs. In the processing of polymer materials, liquid raw materials usually need to be heated to maintain fluidity. Therefore, the gas extracted from heated metering tanks or hoppers (including nitrogen and a small amount of material volatiles) carries a large amount of heat. Existing systems usually directly discharge these high-temperature waste gases through condensers and vacuum pumps, failing to effectively recover and utilize this sensible heat, resulting in serious energy waste. Simple vacuuming and refilling with room-temperature nitrogen may not completely remove oxygen and moisture from the equipment, especially in cases of complex equipment structures and dead zones in the piping, which may lead to localized high oxygen and moisture content, affecting the protection effect on sensitive materials. After vacuuming a high-temperature material tank, directly filling it with a large amount of room-temperature nitrogen may cause a sudden drop in the internal temperature, impacting the temperature stability of the material. In high-humidity environments, such rapid cooling can also cause residual moisture in the injected nitrogen to condense into droplets on the inner wall of the equipment, introducing new moisture contamination. Traditional negative pressure suction systems may require a separate mechanical vacuum pump or the use of a less efficient Venturi vacuum generator. These solutions often do not adequately consider the cascade utilization of the driving medium and the optimization of overall efficiency, resulting in low system integration, relatively high energy consumption, and potential risks of oil contamination.

[0005] Therefore, developing an integrated device that can efficiently utilize nitrogen, effectively recover waste heat, ensure stable transport and protection of materials in a high-purity nitrogen environment, and reduce operating costs and environmental impact is an urgent technological need in the field of polymer material processing, especially for the production of sensitive liquid raw materials. Utility Model Content

[0006] In view of the shortcomings of the prior art, the purpose of this utility model is to provide a negative pressure suction nitrogen protection device, which achieves efficient negative pressure suction, high-purity nitrogen protection, energy saving and consumption reduction and environmental protection in the process of liquid material transportation by integrating a two-stage series nitrogen-driven vacuum generation unit, a heat storage heat exchanger and a nitrogen circulation and heat recovery circuit.

[0007] This utility model is achieved using the following technical solution:

[0008] A negative pressure nitrogen protection device for material intake includes a liquid raw material storage tank, an intermediate metering mixing tank, an extruder, and an extruder hopper; the liquid raw material storage tank is connected to the intermediate metering mixing tank via a differential pressure self-holding valve A, and the intermediate metering mixing tank is connected to the extruder hopper via a differential pressure self-holding valve B; the extruder hopper is connected to the extruder; it also includes:

[0009] A two-stage series nitrogen-driven vacuum generation unit includes a secondary nitrogen-driven vacuum generator and a primary nitrogen-driven vacuum generator. The exhaust port of the secondary nitrogen-driven vacuum generator is connected to the gas supply port of the primary nitrogen-driven vacuum generator. The pipeline connecting the intermediate metering mixing tank to the vacuum port of the primary nitrogen-driven vacuum generator is connected to the vacuum port of the primary nitrogen-driven vacuum generator. The pipeline connecting the extruder hopper to the vacuum port of the secondary nitrogen-driven vacuum generator is connected to the vacuum port of the secondary nitrogen-driven vacuum generator.

[0010] The nitrogen circulation heating and pressurization circuit includes a circulating fan, a heat storage heat exchanger, and a nitrogen pressurization main pipe. The exhaust port of the primary nitrogen-driven vacuum generator is connected to the inlet of the circulating fan, the outlet of the circulating fan is connected to the shell-side inlet of the heat storage heat exchanger, and the shell-side outlet of the heat storage heat exchanger is connected to the nitrogen pressurization main pipe. The nitrogen pressurization main pipe is equipped with a one-way valve, and the nitrogen pressurization main pipe branches downstream of the one-way valve to the gas supply ports of the liquid raw material storage tank, the intermediate metering mixing tank, and the extruder hopper, respectively.

[0011] The exhaust heat storage purification circuit includes a condenser and a vacuum pump; the exhaust pipe of the intermediate metering mixing tank and the exhaust pipe of the extruder hopper are both connected to the tube side inlet of the heat storage heat exchanger, the tube side outlet of the heat storage heat exchanger is connected to the inlet of the condenser, and the outlet of the condenser is connected to the inlet of the vacuum pump.

[0012] The heat storage heat exchanger is a shell-and-tube heat exchanger, and its shell side is filled with a liquid phase heat storage medium.

[0013] Specifically, the two-stage series nitrogen-driven vacuum generation unit is the core component of this device to achieve efficient negative pressure material suction. It includes a two-stage nitrogen-driven vacuum generator and a one-stage nitrogen-driven vacuum generator.

[0014] Both nitrogen-driven vacuum generators are jet pumps utilizing the Venturi effect. Their basic structure consists of a high-pressure nozzle, a suction chamber, and a diffuser, with no moving mechanical parts inside. High-pressure nitrogen, as the working fluid, expands rapidly through the high-pressure nozzle, creating a localized low pressure within the suction chamber, thereby drawing in and carrying away the evacuated medium. This non-contact vacuuming method avoids oil contamination.

[0015] The key to this device lies in connecting the exhaust port of the secondary nitrogen-driven vacuum generator in series with the gas supply port of the primary nitrogen-driven vacuum generator. The pure high-pressure nitrogen from the nitrogen source first drives the secondary vacuum generator, and its exhaust gas still has a certain kinetic energy, which can be directly used as the driving gas source for the primary vacuum generator, realizing the cascade utilization of driving nitrogen and significantly improving the overall utilization efficiency of nitrogen energy.

[0016] The piping connecting the intermediate metering mixing tank to the vacuum port of the primary nitrogen-driven vacuum generator is mainly used to maintain the suction negative pressure of the intermediate metering mixing tank. The piping connecting the extruder hopper to the vacuum port of the secondary nitrogen-driven vacuum generator is used to establish a deeper suction negative pressure for the extruder hopper, adapting to the operating conditions of the extruder hopper near the high-temperature processing area. All connecting pipes are equipped with control valves, which can flexibly adjust the on / off state and flow rate of the suction.

[0017] The nitrogen circulation heating and pressurization circuit is used to realize the recycling and preheating of inert gas, effectively reducing nitrogen consumption and improving the overall inert protection effect. It mainly consists of a circulating fan, a heat storage heat exchanger and a nitrogen pressurization main pipe.

[0018] The mixed gas discharged from the primary nitrogen-driven vacuum generator is connected to the inlet of the circulating fan. The circulating fan pressurizes the gas and drives it to circulate stably throughout the entire circuit.

[0019] The low-temperature circulating nitrogen gas output by the circulating fan is sent into the shell side of the heat storage heat exchanger. During the flow, it fully absorbs the heat stored in the shell side and is preheated to the appropriate operating temperature.

[0020] After being heated, the nitrogen gas flows through the shell-side outlet of the regenerative heat exchanger into the nitrogen pressurization main pipe. A one-way valve is installed inside the main pipe to effectively prevent backflow of gas and ensure unidirectional gas delivery. After passing through the one-way valve, the gas flow is split into multiple streams, which are respectively connected to the gas replenishment points of the liquid raw material storage tank, the intermediate metering mixing tank, and the extruder hopper, completing the tank venting and pressure stabilization and providing inert gas protection throughout the process.

[0021] The extraction and heat storage purification circuit mainly completes the initial air replacement and periodic large-flow gas extraction operations of the system, and simultaneously completes waste heat recovery and gas impurity purification. Its components include a heat storage heat exchanger, a condenser and a vacuum pump.

[0022] The extraction pipelines from the intermediate metering mixing tank and the extruder hopper are connected to the tube-side inlet of the regenerative heat exchanger, and control valves are installed on the pipelines. During initial system replacement or periodic deep extraction operations, the high-temperature gas containing volatiles extracted from the tank and hopper enters the tube side of the heat exchanger, transferring its own heat to the heat storage medium inside the shell side, thus completing waste heat recovery and storage.

[0023] After the heat is released, the low-temperature mixed gas flows out from the tube side of the heat storage heat exchanger and enters the condenser to complete secondary cooling. This promotes the condensation and liquefaction of water vapor and volatile organic components contained in the gas, removes various impurities from the gas, and comprehensively protects the stable operation of the downstream vacuum pump equipment.

[0024] The clean gas, after being condensed and purified, is introduced into a vacuum pump. The vacuum pump establishes a deep vacuum environment in the system to meet the initial replacement vacuum requirements of the equipment. Finally, the qualified exhaust gas is uniformly transported to a dedicated treatment area for discharge.

[0025] The heat storage heat exchanger is the core heat exchange and energy storage component of this device. It adopts a shell-and-tube structure and consists of an outer shell, an internal tube bundle, and various fluid communication ports. The shell-side cavity of the equipment is filled with a liquid-phase heat storage medium, which can be heat transfer oil, pure water, or a high-boiling-point organic medium. Relying on its special structure and filling medium, it can achieve bidirectional operation of heat storage and heat release in different time periods.

[0026] During the operation of the exhaust heat storage purification circuit, the high-temperature process gas flows through the tube side of the heat exchanger, and the heat is quickly transferred through the tube wall to the shell side stationary heat storage medium, thus completing the heat storage and accumulation.

[0027] When the nitrogen circulation heating and pressure replenishment circuit is working, low-temperature circulating nitrogen is introduced into the shell side of the heat exchanger to fully exchange heat with the liquid phase heat storage medium that has already stored sufficient heat, and quickly complete the heating operation.

[0028] This structural design enables dynamic control of heat storage and release, achieving efficient energy recycling within the system and continuously ensuring a stable and uniform temperature for pressurized nitrogen.

[0029] In addition, to further improve the overall material handling efficiency, the liquid raw material storage tank is equipped with a stirring structure for homogenizing and mixing the material, and a heating jacket is installed on the outside of the tank to achieve constant temperature control of the material; the intermediate metering mixing tank is also equipped with a heating jacket to meet the requirements of constant temperature transportation of the material throughout the process; the inlet of the secondary nitrogen-driven vacuum generator is connected to an industrial high-purity nitrogen source through a dedicated pipeline.

[0030] Compared with the prior art, the beneficial effects of this utility model are:

[0031] (1) This device adopts a two-stage series nitrogen-driven vacuum generation unit, which realizes the cascade utilization of driving nitrogen, significantly improves the nitrogen driving efficiency, and thus greatly reduces the consumption of high-pressure nitrogen. At the same time, the heat in the high-temperature waste gas is recovered through the heat storage heat exchanger and used to preheat the circulating pressurized nitrogen, realizing the secondary utilization of energy and further reducing the system's operating energy consumption.

[0032] (2) This device can achieve high-standard negative pressure vacuuming. Combined with preheated circulating nitrogen for pressure replenishment and replacement, it can effectively control the oxygen content in the tank and hopper to an extremely low level. Preheated nitrogen helps to improve replacement efficiency and reduce the risk of condensation. The transportation, metering and storage of liquid materials in a low-oxygen and low-humidity environment can effectively inhibit the oxidative degradation, hydrolysis and yellowing of polymer materials, thereby ensuring the stability and superiority of the appearance, mechanical properties and processing performance of the final product. The pressurized nitrogen is preheated to 50~60℃ by the heat exchanger before entering the tank and hopper, which can effectively avoid the cold shock caused by filling the high-temperature material or tank with room temperature nitrogen, and maintain the stability of the material temperature. At the same time, the preheated nitrogen is not easy to condense on the inner wall of the equipment, avoiding the introduction of new moisture pollution. Before entering the vacuum pump, the extracted gas will be deeply cooled by the condenser, effectively recovering the water vapor and volatile organic compounds, reducing the emission of harmful substances, reducing the impact on the environment, and extending the service life of the vacuum pump. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the structure of the negative pressure suction nitrogen protection device of this utility model;

[0034] In the diagram: 1. Liquid raw material storage tank; 2. Intermediate metering mixing tank; 3. Extruder; 4. Extruder hopper; 5. Secondary nitrogen-driven vacuum generator; 6. Primary nitrogen-driven vacuum generator; 7. Heat exchanger; 8. Condenser; 9. Vacuum pump; 10. Circulating fan; 11. Storage tank agitator; 12. Storage tank heating jacket; 13. Metering mixing tank heating jacket; 14. Differential pressure self-holding valve A; 15. Differential pressure self-holding valve B; 16. Nitrogen inlet pipe; 17. Nitrogen pressure replenishment main pipe; 18. Metering mixing tank exhaust port pipe; 19. Extruder hopper exhaust port pipe; 20. Vacuum port pipe for secondary nitrogen-driven vacuum generator; 21. Vacuum port pipe for primary nitrogen-driven vacuum generator; 22. Check valve. Detailed Implementation

[0035] To make the objectives and technical solutions of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings.

[0036] Example 1

[0037] This utility model device is used in thermoplastic polyurethane (TPU) production lines for feeding, metering, and protecting liquid polyurethane prepolymers, with a focus on nitrogen protection, heat recovery, and energy-saving effects.

[0038] like Figure 1 The specific configuration of the device in this embodiment is as follows:

[0039] Material Piping: Liquid raw material storage tank 1 serves as the main storage tank, equipped with an internal tank agitator 11 and an external tank heating jacket 12 to maintain suitable temperature and flowability of the liquid polyurethane prepolymer. Liquid raw material storage tank 1 is connected to intermediate metering mixing tank 2 via differential pressure self-holding valve A14. Intermediate metering mixing tank 2 serves as a buffer metering device, equipped with an external metering mixing tank heating jacket 13 for heating the material. Intermediate metering mixing tank 2 is connected to extruder hopper 4 via differential pressure self-holding valve B15. Extruder hopper 4 directly feeds material to extruder 3.

[0040] Nitrogen-driven vacuum generation unit: A high-pressure pure nitrogen source is connected to the gas supply port of the secondary nitrogen-driven vacuum generator 5 via nitrogen inlet pipe 16. The exhaust port of the secondary nitrogen-driven vacuum generator 5 is connected in series with the gas supply port of the primary nitrogen-driven vacuum generator 6.

[0041] Vacuum connection: The top evacuation port of the intermediate metering mixing tank 2 is connected to the vacuum port of the primary nitrogen-driven vacuum generator 6 via a control valve-equipped inlet pipe 21. The top evacuation port of the extruder hopper 4 is connected to the vacuum port of the secondary nitrogen-driven vacuum generator 5 via a control valve-equipped inlet pipe 20.

[0042] The exhaust gas storage and purification circuit is connected as follows: Another exhaust port of the intermediate metering mixing tank 2 is connected to the tube-side inlet of the heat storage heat exchanger 7 via a metering mixing tank exhaust port pipe 18 with a control valve. Another exhaust port of the extruder hopper 4 is connected to the tube-side inlet of the heat storage heat exchanger 7 via an extruder hopper exhaust port pipe 19 with a control valve (merging with the metering mixing tank exhaust port pipe 18). The tube-side outlet of the heat storage heat exchanger 7 is connected to the inlet of the condenser 8. The outlet of the condenser 8 is connected to the inlet of the vacuum pump 9, and the outlet of the vacuum pump 9 is connected to the exhaust gas treatment system.

[0043] The nitrogen circulation heating and pressurization circuit is connected as follows: the exhaust port of the primary nitrogen-driven vacuum generator 6 is connected to the inlet of the circulating fan 10. The outlet of the circulating fan 10 is connected to the shell-side inlet of the heat regenerator 7. The shell-side outlet of the heat regenerator 7 is connected to the nitrogen pressurization main pipe 17. A one-way valve 22 is installed on the nitrogen pressurization main pipe 17. Downstream of the one-way valve 22, branches of the nitrogen pressurization main pipe 17 are connected to the gas supply ports of the liquid raw material storage tank 1, the intermediate metering mixing tank 2, and the extruder hopper 4, respectively.

[0044] Heat storage heat exchanger 7: It adopts a shell and tube heat exchanger, and its shell side is filled with heat transfer oil as the liquid phase heat storage medium.

[0045] In this embodiment, liquid polyurethane prepolymer of TPU is used as liquid raw material. This prepolymer needs to be stored and transported in a low humidity and low oxygen environment.

[0046] Phase 1: Initial System Replacement and Heat Storage

[0047] Close differential pressure self-holding valves A14 and B15. Close the valves on the vacuum port pipe 20 for the secondary nitrogen-driven vacuum generator and the vacuum port pipe 21 for the primary nitrogen-driven vacuum generator. Open the valves on the evacuation port pipe 18 of the metering mixing tank and the evacuation port pipe 19 of the extruder hopper. Turn on the vacuum pump 9 to evacuate the intermediate metering mixing tank 2 and the extruder hopper 4 to -0.08 MPa. At this time, the residual gas (initially air, then nitrogen) in the intermediate metering mixing tank 2 and the extruder hopper 4 enters the tube side of the regenerative heat exchanger 7 through the evacuation port pipes 18 and 19 of the metering mixing tank and the extruder hopper. The material temperature in the liquid raw material storage tank 1 is maintained at 60°C through the storage tank heating jacket 12; the material temperature in the intermediate metering mixing tank 2 is maintained at 80°C through the metering mixing tank heating jacket 13; and the material temperature (if any residue) in the extruder hopper 4 is maintained at 120°C. The extracted high-temperature gas exchanges heat with the heat transfer oil in the shell side of the heat exchanger 7 within the tube side, causing the heat transfer oil to heat up from the initial ambient temperature of 25°C to 70°C. When the pressure drops to -0.08 MPa, the vacuum pump 9 is shut off. The valve on the nitrogen pressurization main pipe 17 is opened, and nitrogen is introduced into the intermediate metering mixing tank 2 and the extruder hopper 4 through the one-way valve 22 and its downstream branch (fresh nitrogen can be used directly during initial purging, or it can be provided by the circulating heating and pressurization circuit). The above vacuuming → nitrogen charging steps are repeated 3 times until the oxygen content in the intermediate metering mixing tank 2 and the extruder hopper 4 is below 0.1%. During each evacuation, the high-temperature gas continuously heats the heat transfer oil. The valves on the metering mixing tank evacuation port pipe 18 and the extruder hopper evacuation port pipe 19 are closed, maintaining an atmospheric pressure nitrogen environment in the intermediate metering mixing tank 2 and the extruder hopper 4.

[0048] Phase 2: First-stage material feeding

[0049] Ensure the valves on the metering mixing tank evacuation port pipe 18, the extruder hopper evacuation port pipe 19, and the secondary nitrogen-driven vacuum generator vacuum port pipe 20 are closed. Open the valve on the primary nitrogen-driven vacuum generator vacuum port pipe 21. Turn on the nitrogen source; high-pressure nitrogen enters the secondary nitrogen-driven vacuum generator 5 supply port via nitrogen inlet pipe 16. The secondary nitrogen-driven vacuum generator 5 operates, and its exhaust drives the primary nitrogen-driven vacuum generator 6. The vacuum port of the primary nitrogen-driven vacuum generator 6 evacuates the intermediate metering mixing tank 2 through the primary nitrogen-driven vacuum generator vacuum port pipe 21, reducing its internal pressure to -0.08 MPa. The gas extracted by the primary nitrogen-driven vacuum generator 6 (containing nitrogen and a small amount of organic matter, at approximately 80°C) enters the shell side of the heat exchanger 7 via the primary nitrogen-driven vacuum generator 6 exhaust port → circulating fan 10. At this time, the circulating nitrogen flowing in the shell side passes through the heated heat transfer oil, absorbing heat and rising to approximately 55°C. After being heated, nitrogen gas flows through the nitrogen pressurization main pipe 17 and through the one-way valve 22 and its downstream branches into the gas inlets of the liquid raw material storage tank 1, the intermediate metering mixing tank 2, and the extruder hopper 4. The negative pressure inside the intermediate metering mixing tank 2 causes the differential pressure self-holding valve A14 to open automatically, allowing liquid raw material to flow from the liquid raw material storage tank 1 into the intermediate metering mixing tank 2. When the liquid level in the intermediate metering mixing tank 2 reaches its upper limit, the nitrogen source is shut off (stopping the operation of the secondary nitrogen-driven vacuum generator 5 and the primary nitrogen-driven vacuum generator 6). The gas inlet valve of the intermediate metering mixing tank 2 is opened (preheated nitrogen gas is introduced through the nitrogen pressurization main pipe 17 to break the vent), and the differential pressure self-holding valve A14 closes. The first stage of material intake is complete.

[0050] Phase 3: Second-stage material feeding

[0051] Ensure the valves on the metering mixing tank vent pipe 18, the extruder hopper vent pipe 19, and the primary nitrogen-driven vacuum generator vacuum port pipe 21 are closed. Open the valve on the secondary nitrogen-driven vacuum generator vacuum port pipe 20. Turn on the nitrogen source; high-pressure nitrogen enters the secondary nitrogen-driven vacuum generator 5 supply port via nitrogen inlet pipe 16. The secondary nitrogen-driven vacuum generator 5 operates, and its vacuum port evacuates the extruder hopper 4 through the secondary nitrogen-driven vacuum generator vacuum port pipe 20, reducing its internal pressure to -0.08 MPa. The gas extracted by the secondary nitrogen-driven vacuum generator 5 (containing nitrogen and high-temperature TPU volatiles, temperature 120~150℃) flows through the secondary nitrogen-driven vacuum generator 5 exhaust port → primary nitrogen-driven vacuum generator 6 supply port → primary nitrogen-driven vacuum generator 6 exhaust port → circulating fan 10 → heat exchanger 7 shell side. At this time, the shell-side nitrogen is reheated and replenished to each replenishment port via the nitrogen pressurization main pipe 17. The negative pressure inside extruder hopper 4 causes the differential pressure self-holding valve B15 to open automatically, allowing material to flow from the intermediate metering mixing tank 2 into extruder hopper 4. When the liquid level in extruder hopper 4 reaches its upper limit, the nitrogen supply is shut off. The air replenishment valve of extruder hopper 4 is opened (preheated nitrogen is introduced through the nitrogen pressurization main pipe 17 to break the air vent), and the differential pressure self-holding valve B15 closes. The second stage of material feeding is complete.

[0052] Phase 4: Continuous feeding and replenishment of material in the extruder

[0053] Extruder 3 continuously feeds material from the bottom of extruder hopper 4. When the liquid level in extruder hopper 4 drops to the lower limit, stage 2 is automatically triggered. When the liquid level in intermediate metering mixing tank 2 drops to the lower limit, stage 1 is automatically triggered.

[0054] Phase 5: Regular full replacement and heat storage replenishment

[0055] After every 24 hours of operation, repeat the vacuuming and nitrogen purging steps of Phase 1 twice to ensure gas purity and compensate for heat loss from the heat storage medium.

[0056] Comparative Example 1

[0057] Compared to Example 1, this system does not include the secondary nitrogen-driven vacuum generator 5, the primary nitrogen-driven vacuum generator 6, the circulating fan 10, the heat storage heat exchanger 7, the nitrogen pressurization main pipe 17, the one-way valve 22, or the condenser 8. Instead, it uses a separate mechanical vacuum pump, which is directly connected to the suction ports of the intermediate metering mixing tank 2 and the extruder hopper 4 via pipelines. Nitrogen protection is provided by an external high-pressure nitrogen cylinder, which directly supplies room-temperature fresh nitrogen to the gas supply ports of the liquid raw material storage tank 1, the intermediate metering mixing tank 2, and the extruder hopper 4 through a pressure reducing valve and a flow meter. There is no circulation or heat recovery function.

[0058] Close differential pressure self-holding valves A14 and B15. Turn on the mechanical vacuum pump and evacuate the intermediate metering mixing tank 2 and extruder hopper 4 to -0.08 MPa. Then turn off vacuum pump 9 and directly fill the intermediate metering mixing tank 2 and extruder hopper 4 with fresh nitrogen at room temperature through the nitrogen cylinder until atmospheric pressure is reached, repeating twice. Turn on vacuum pump 9 and evacuate the intermediate metering mixing tank 2 to -0.08 MPa, opening differential pressure self-holding valve A14 to suck up material. After material sucking is complete, turn off vacuum pump 9 and directly fill the intermediate metering mixing tank 2 with fresh nitrogen at room temperature to break the cavitation, closing differential pressure self-holding valve A14. Turn on vacuum pump 9 and evacuate the extruder hopper 4 to -0.08 MPa, opening differential pressure self-holding valve B15 to suck up material. After material sucking is complete, turn off vacuum pump 9 and directly fill the extruder hopper 4 with fresh nitrogen at room temperature to break the cavitation, closing differential pressure self-holding valve B15. The heating temperatures of the liquid raw material storage tank 1, the intermediate metering mixing tank 2, and the extruder hopper 4 are the same as in Example 1, and are maintained by the storage tank heating jacket 12 and the metering mixing tank heating jacket 13, respectively.

[0059] Example 1 and Comparative Example 1 were tested for continuous operation for 100 hours, and the results are shown in Table 1.

[0060] Table 1: Test results of continuous operation for 100 hours for Example 1 and Comparative Example 1

[0061]

[0062] As shown in Table 1, the oxygen content provided by this device in the intermediate metering mixing tank and extruder hopper is lower than that of the traditional system, indicating that it can provide a more thorough inert gas protective environment and effectively prevent the oxidative degradation of TPU prepolymer. The nitrogen consumption of this device is only about 20% of that of the traditional system. This is mainly attributed to the cascade utilization of driving nitrogen by the two-stage series nitrogen-driven vacuum generator and the recycling of nitrogen by the nitrogen circulation heating and pressurization circuit. The TPU-A processed by this device exhibits excellent stability in terms of MFR change rate, yellowing index change, and tensile strength retention rate, far superior to the traditional system. This indicates that the low-oxygen environment and stable temperature protection effectively inhibit molecular weight degradation, yellowing, and mechanical property deterioration of the material, ensuring product quality. This device can provide preheated and pressurized nitrogen at around 55℃, resulting in small temperature fluctuations in the material during negative pressure suction and void breaking, effectively avoiding the potential impact of cold shock on the material, and preventing condensation caused by temperature differences. In contrast, the traditional system uses room-temperature nitrogen, leading to larger temperature fluctuations in the material. Although this device includes components such as a circulating fan, the total energy consumption of the extraction stage is still lower than that of traditional mechanical vacuum pump solutions due to the high efficiency of waste heat recovery and nitrogen-driven operation. If the nitrogen procurement cost is converted into energy cost, the overall energy efficiency advantage becomes even more significant.

Claims

1. A negative pressure suction nitrogen protection device, comprising: The system comprises a liquid raw material storage tank (1), an intermediate metering mixing tank (2), an extruder (3), and an extruder hopper (4); the liquid raw material storage tank (1) is connected to the intermediate metering mixing tank (2) via a differential pressure self-holding valve A (14), the intermediate metering mixing tank (2) is connected to the extruder hopper (4) via a differential pressure self-holding valve B (15), and the extruder hopper (4) is connected to the extruder (3); characterized in that it further comprises: The two-stage series nitrogen-driven vacuum generation unit includes a secondary nitrogen-driven vacuum generator (5) and a primary nitrogen-driven vacuum generator (6). The exhaust port of the secondary nitrogen-driven vacuum generator (5) is connected to the gas supply port of the primary nitrogen-driven vacuum generator (6). The vacuum port pipe (21) of the intermediate metering mixing tank (2) to the primary nitrogen-driven vacuum generator is connected to the vacuum port of the primary nitrogen-driven vacuum generator (6). The vacuum port pipe (20) of the extruder hopper (4) to the secondary nitrogen-driven vacuum generator is connected to the vacuum port of the secondary nitrogen-driven vacuum generator (5). The nitrogen circulation heating and pressurization circuit includes a circulating fan (10), a heat storage heat exchanger (7), and a nitrogen pressurization main pipe (17); the exhaust port of the primary nitrogen-driven vacuum generator (6) is connected to the inlet of the circulating fan (10), the outlet of the circulating fan (10) is connected to the shell-side inlet of the heat storage heat exchanger (7), the shell-side outlet of the heat storage heat exchanger (7) is connected to the nitrogen pressurization main pipe (17), the nitrogen pressurization main pipe (17) is provided with a one-way valve (22), and the nitrogen pressurization main pipe (17) branches downstream of the one-way valve (22) to the gas supply ports of the liquid raw material storage tank (1), the intermediate metering mixing tank (2), and the extruder hopper (4); The vacuum storage and purification circuit includes a condenser (8) and a vacuum pump (9); the vacuum port pipe (18) of the intermediate metering mixing tank (2) and the vacuum port pipe (19) of the extruder hopper (4) are both connected to the tube side inlet of the heat storage heat exchanger (7), the tube side outlet of the heat storage heat exchanger (7) is connected to the inlet of the condenser (8), and the outlet of the condenser (8) is connected to the inlet of the vacuum pump (9); The heat storage heat exchanger (7) is a shell-and-tube heat exchanger, and its shell side is filled with liquid phase heat storage medium.

2. The negative pressure suction nitrogen protection device according to claim 1, characterized in that, The liquid-phase heat storage medium filled in the shell side of the heat storage heat exchanger (7) is at least one of heat transfer oil, water or high-boiling-point organic matter.

3. The negative pressure suction nitrogen protection device according to claim 1 or 2, characterized in that, The liquid raw material storage tank (1) is equipped with a tank agitator (11) inside and a tank heating jacket (12) outside, and the intermediate metering mixing tank (2) is equipped with a metering mixing tank heating jacket (13) outside.

4. The negative pressure suction nitrogen protection device according to claim 1 or 2, characterized in that, The gas supply port of the secondary nitrogen-driven vacuum generator (5) is connected to the nitrogen source through the nitrogen inlet pipe (16).

5. The negative pressure suction nitrogen protection device according to claim 1 or 2, characterized in that, The metering mixing tank exhaust port pipe (18), the extruder hopper exhaust port pipe (19), the secondary nitrogen-driven vacuum generator vacuum port pipe (20), and the primary nitrogen-driven vacuum generator vacuum port pipe (21) are all equipped with control valves.

6. The negative pressure suction nitrogen protection device according to claim 1 or 2, characterized in that, The vacuuming and heat storage purification circuit is used to evacuate the intermediate metering mixing tank (2) and the extruder hopper (4) during the initial replacement phase of the system, and to introduce the extracted high-temperature gas into the tube side of the heat storage heat exchanger (7) for heat recovery.

7. The negative pressure suction nitrogen protection device according to claim 1 or 2, characterized in that, The nitrogen temperature at the shell-side outlet of the heat storage heat exchanger (7) can reach 50~60℃.

8. The negative pressure suction nitrogen protection device according to claim 1 or 2, characterized in that, When the two-stage series nitrogen-driven vacuum generation unit evacuates the intermediate metering mixing tank (2) or the extruder hopper (4), the pressure inside the tank or hopper can be reduced to -0.08 MPa.

9. The negative pressure suction nitrogen protection device according to claim 1 or 2, characterized in that, After replacement, the oxygen content in the intermediate metering mixing tank (2) and the extruder hopper (4) can be lower than 0.5%.

10. The negative pressure suction nitrogen protection device according to claim 1 or 2, characterized in that, The device is used to achieve negative pressure feeding from the liquid raw material storage tank (1) to the intermediate metering mixing tank (2), and negative pressure feeding from the intermediate metering mixing tank (2) to the extruder hopper (4).

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