Energy-saving NMP vacuum rectification negative pressure air extraction system

Abstract

The utility model relates to an energy -saving NMP vacuum rectification negative pressure air -exhaust system, including air -cooled roots vacuum pump, main air inlet pipeline, primary condenser, connecting pipeline, screw dry vacuum pump and secondary condenser, the air -inlet of air -cooled roots vacuum pump is connected air -inlet main valve through main air inlet pipeline, the air outlet of air -cooled roots vacuum pump is connected primary condenser, the air inlet of screw dry vacuum pump is connected through connecting pipeline primary condenser, the air outlet of screw dry vacuum pump is connected secondary condenser. The utility model is not influenced by the change of environment temperature and cooling water temperature, and the air -exhaust performance is more stable, and the energy consumption is lower, and there is no waste liquid, and there is no waste gas cost emission, improves the purity and quality of product.

Description

Technical Field

[0001] This utility model relates to the field of chemical equipment technology, and in particular to an energy-saving NMP vacuum distillation negative pressure extraction system. Background Technology

[0002] N-Methylpyrrolidone (NMP) is an organic solvent that plays a crucial role in lithium-ion battery production, primarily used as a solvent for positive electrode slurry and a process medium. Its high solubility, low toxicity, and recyclability make it an irreplaceable chemical material in the lithium-ion battery industry. The NMP production process involves mixing γ-butyrolactone and methylamine in a specific ratio (typically a molar ratio of 1:1.1~1.5), heating the mixture to 200~250℃ in a reactor to generate a mixed solution of NMP and water. Subsequent processing includes three steps: vacuum dehydration, vacuum removal of light components, and high-vacuum distillation. The high-vacuum distillation process purifies the crude NMP solution after dehydration, removing water, unreacted methylamine, γ-butyrolactone (GBL), and other byproducts (such as N-methylsuccinimide) to obtain a high-purity (≥99.5%) NMP product. See also... Figure 1 A complete NMP distillation process is currently mainly produced in industrial production using a three-tower continuous distillation method. The process mainly includes a three-stage vacuum distillation tower, a three-stage condenser system, three sets of vacuum systems, and condensate recovery and treatment equipment.

[0003] Current NMP distillation vacuum systems have the following drawbacks:

[0004] (1) Poor vacuum stability: Currently, the vacuum equipment used in the NMP production distillation process is mostly the low-cost and low-efficiency liquid ring vacuum system. The liquid ring vacuum system uses a liquid ring vacuum pump as the vacuum equipment. The liquid ring vacuum pump usually uses water as the working fluid. When the working fluid water temperature is high, it will greatly affect the pumping performance of the liquid ring vacuum pump. Due to the changes in ambient temperature, cooling water temperature and working fluid temperature, the pumping performance of the liquid ring vacuum pump changes greatly. The fluctuation of ambient temperature will cause the vacuum degree to deviate, making it difficult to guarantee the production of NMP and the quality of the product.

[0005] (2) Low product purity: NMP distillation usually requires a high vacuum range of 20~10 kPa or higher. When the working fluid temperature reaches about 35°C in summer, the pumping speed and working vacuum of the liquid ring vacuum pump are difficult to meet the requirements of NMP distillation process, which affects the purity of NMP products.

[0006] (3) High energy consumption and low efficiency: The pumping efficiency of liquid ring vacuum pump is relatively low. The working fluid accounts for more than 70% of the suction chamber of liquid ring vacuum pump, and the volume utilization rate is relatively low. Moreover, the pumping efficiency is less than 60% when the working vacuum is 20~10kpa. Therefore, to obtain a certain pumping volume, a larger vacuum pump must be selected, which increases the power consumption.

[0007] (4) High pollution control costs: When the liquid ring vacuum pump is working, the working fluid is in direct contact with the pumped medium. The possible media in the pumped gas will dissolve into the working fluid. Therefore, the working fluid of the liquid ring vacuum pump must be replaced regularly. Otherwise, the pumping performance of the liquid ring vacuum pump will be affected. The treatment cost of chemical waste liquid generated by the mixing of working fluid and waste gas is high.

[0008] Therefore, this invention proposes an energy-saving NMP vacuum distillation negative pressure pumping system to solve the above problems. Summary of the Invention

[0009] The purpose of this invention is to overcome the above-mentioned shortcomings and provide an energy-saving NMP vacuum distillation negative pressure pumping system that is not affected by changes in ambient temperature and cooling water temperature, and has more stable pumping performance, lower energy consumption, no waste liquid, no waste gas emissions, and better quality assurance for NMP purity.

[0010] The purpose of this utility model is achieved as follows:

[0011] An energy-saving NMP vacuum distillation negative pressure pumping system includes an air-cooled Roots vacuum pump, a main inlet pipe, a primary condenser, connecting pipes, a screw dry vacuum pump, and a secondary condenser. The inlet of the air-cooled Roots vacuum pump is connected to the main inlet valve through the main inlet pipe. The exhaust port of the air-cooled Roots vacuum pump is connected to the primary condenser. The primary condenser is connected to the inlet of the screw dry vacuum pump through the connecting pipes. The exhaust port of the screw dry vacuum pump is connected to the secondary condenser.

[0012] The connecting pipe between the primary condenser and the screw dry vacuum pump is equipped with a first check valve, a nitrogen sealing device, a nitrogen purging device, a solvent flushing device, a vacuum gauge, and a thermometer.

[0013] The screw dry vacuum pump is connected to a second check valve, which is connected to a flow meter, a regulating valve, and a pressure gauge; the first-stage condenser is connected to a first liquid storage tank via a solenoid valve, and the second-stage condenser is connected to a second liquid storage tank via a solenoid valve.

[0014] The inlets of the air-cooled Roots vacuum pump, the first-stage condenser, the screw dry vacuum pump, and the second-stage condenser are connected to the cooling water inlet via cooling water flow control valves, and the outlets of the air-cooled Roots vacuum pump, the first-stage condenser, the screw dry vacuum pump, and the second-stage condenser are connected to the cooling water outlet; the drain ports of the first and second liquid storage tanks are connected to the condensate outlet via automatic drain solenoid valves.

[0015] The air-cooled Roots vacuum pump, inlet main valve, pressure transmitter, screw dry vacuum pump, and various solenoid valves and level controllers are all connected to the PLC electrical control system, which receives data and controls the start and stop of the pump.

[0016] An energy-saving NMP vacuum distillation negative pressure pumping system, wherein a pressure transmitter is installed on the main air inlet pipe.

[0017] An energy-saving NMP vacuum distillation negative pressure extraction system, wherein the nitrogen sealing device is connected to the connecting pipeline via a solenoid valve.

[0018] An energy-saving NMP vacuum distillation negative pressure purging system, wherein the nitrogen purging device is connected to the connecting pipeline via a solenoid valve and a manual valve.

[0019] An energy-saving NMP vacuum distillation negative pressure pumping system, wherein the solvent flushing device is connected to the connecting pipeline via a solenoid valve and a manual valve.

[0020] An energy-saving NMP vacuum distillation negative pressure pumping system, wherein the first liquid storage tank is equipped with a level gauge with high and low liquid level controllers.

[0021] An energy-saving NMP vacuum distillation negative pressure pumping system, wherein the second liquid storage tank is equipped with a level gauge with high and low liquid level controllers.

[0022] An energy-saving NMP vacuum distillation negative pressure evacuation system, wherein the first liquid storage tank and the second liquid storage tank are connected to the PLC electrical control system via an electromagnetic venting valve.

[0023] Compared with the prior art, the beneficial effects of this utility model are:

[0024] This invention provides an energy-saving NMP vacuum distillation negative pressure pumping system. Through a series architecture of an air-cooled Roots vacuum pump and a screw dry vacuum pump, combined with two-stage condensation recovery, intelligent frequency conversion control and multiple safety protection designs, it solves the problems of high energy consumption, large amount of waste liquid and unstable vacuum of traditional liquid ring pumps. It achieves reduced energy consumption, zero pollution emissions, doubled vacuum stability, improved product purity and quality assurance, and significantly reduced maintenance costs in the NMP distillation process. Attached Figure Description

[0025] Figure 1This is a schematic diagram of the complete NMP distillation process.

[0026] Figure 2 This is a schematic diagram of the structure of this utility model.

[0027] in:

[0028] 1. Air-cooled Roots vacuum pump; 2. Main inlet pipe; 3. Main inlet valve; 4. Pressure transmitter; 5. First-stage condenser; 6. Connecting pipe; 7. First check valve; 8. Nitrogen sealing device; 9. Nitrogen purging device; 10. Solvent flushing device; 11. Vacuum gauge; 12. Thermometer; 13. First liquid storage tank; 14. Screw dry vacuum pump; 15. Second check valve; 16. Flow meter; 17. Regulating valve; 18. Pressure gauge; 19. Second-stage condenser; 20. Second liquid storage tank; 21. PLC electrical control system. Detailed Implementation

[0029] To better understand the technical solution of this utility model, a detailed description will be provided below in conjunction with relevant illustrations. It should be understood that the specific embodiments described below are not intended to limit the specific implementation of the technical solution of this utility model, but are merely possible implementations of the technical solution of this utility model. It should be noted that the descriptions of the positional relationships of the components herein, such as component A being located above component B, are based on the relative positions of the components in the illustrations and are not intended to limit the actual positional relationships of the components. Example

[0030] See Figure 2 , Figure 2 A schematic diagram of the structure of this utility model has been drawn. As shown in the figure, an energy-saving NMP vacuum distillation negative pressure pumping system includes an air-cooled Roots vacuum pump 1, a main inlet pipe 2, a primary condenser 5, a connecting pipe 6, a screw dry vacuum pump 14, and a secondary condenser 19. The inlet of the air-cooled Roots vacuum pump 1 is connected to the main inlet valve 3 through the main inlet pipe 2. The exhaust port of the air-cooled Roots vacuum pump 1 is connected to the primary condenser 5. The primary condenser 5 is connected to the inlet of the screw dry vacuum pump 14 through the connecting pipe 6. The exhaust port of the screw dry vacuum pump 14 is connected to the secondary condenser 19.

[0031] The main air intake pipe 2 is equipped with a pressure transmitter 4. The function of the pressure transmitter is to pre-set different evaporation vacuum pressures according to the negative pressure vacuum distillation process and control the air-cooled Roots vacuum pump to operate at a certain frequency through PLC and frequency converter to meet the pumping volume and working vacuum degree or pressure required by different distillation stages of the system.

[0032] The connecting pipe 6 between the primary condenser 5 and the screw dry vacuum pump 14 is equipped with a first check valve 7, a nitrogen sealing device 8, a nitrogen purging device 9, a solvent flushing device 10, a vacuum gauge 11, and a thermometer 12. The nitrogen sealing device 8 is connected to the connecting pipe 6 via a solenoid valve. The nitrogen purging device 9 is connected to the connecting pipe 6 via a solenoid valve and a manual valve. The solvent flushing device 10 is connected to the connecting pipe 6 via a solenoid valve and a manual valve.

[0033] The screw dry vacuum pump 14 is connected to a second check valve 15, which is connected to a flow meter 16, a regulating valve 17, and a pressure gauge 18.

[0034] The first-stage condenser 5 is connected to the first liquid storage tank 13 via a solenoid valve. The first liquid storage tank 13 is equipped with a liquid level gauge with a high and low liquid level controller.

[0035] The secondary condenser 19 is connected to the second liquid storage tank 20 via a solenoid valve. The second liquid storage tank 20 is equipped with a level gauge with high and low liquid level controllers.

[0036] The inlets of the air-cooled Roots vacuum pump 1, the first-stage condenser 5, the screw dry vacuum pump 14, and the second-stage condenser 19 are connected to the cooling water inlet via cooling water flow control valves, and the outlets of the air-cooled Roots vacuum pump 1, the first-stage condenser 5, the screw dry vacuum pump 14, and the second-stage condenser 19 are connected to the cooling water outlet, respectively; the drain ports of the first liquid storage tank 13 and the second liquid storage tank 20 are connected to the condensate outlet via automatic drain solenoid valves, respectively.

[0037] The air-cooled Roots vacuum pump 1, the main inlet valve 3, the pressure transmitter 4, the screw dry vacuum pump 14, and each solenoid valve and liquid level controller are all connected to the PLC electrical control system 21. The first liquid storage tank 13 and the second liquid storage tank 20 are connected to the PLC electrical control system 21 through the electromagnetic air breaker valve. The PLC electrical control system 21 receives data and controls the start and stop.

[0038] Specific implementation examples:

[0039] (1) Core pump set structure

[0040] An air-cooled Roots vacuum pump is used as the main pump. The air inlet is connected to the distillation column via the main pipeline. The pipeline is equipped with a pressure transmitter and a pneumatic / electric main valve.

[0041] The screw dry vacuum pump is used as a backing pump, and its inlet is connected to the exhaust end of the air-cooled Roots vacuum pump.

[0042] Pump set ratio: The air intake ratio of the main pump to the backing pump is 5:1.

[0043] (2) Condensation recovery module

[0044] First-stage condenser: Located at the exhaust port of the air-cooled Roots vacuum pump, it performs three functions:

[0045] It condenses more than 80% of condensable gases, reducing the load on the backing pump;

[0046] The pump body is cooled by circulating cooling gas through a return pipe.

[0047] Reduce the intake air temperature to below 45℃ (to meet the screw pump requirement of ≤60℃);

[0048] Secondary condenser: Located at the exhaust port of the screw dry vacuum pump, equipped with a condensate recovery tank to achieve near-zero emissions of waste gas.

[0049] (3) Safety protection components (located in the connecting pipeline between the two pumps)

[0050] Check valve: Prevents condensate from flowing back when the machine is stopped;

[0051] Nitrogen sealing device: to prevent chemical media from corroding the screw pump bearings and seals;

[0052] Solvent flushing device: Regularly removes chemical buildup in the pump chamber;

[0053] Nitrogen purging device: Removes residual solvent.

[0054] (4) Intelligent control system

[0055] The pressure transmitter monitors the pipeline pressure and adjusts the Roots pump speed via PLC and frequency converter.

[0056] Cooling water interlock: Cooling water pressure / flow must be verified before startup; the machine will automatically shut down if any abnormality is detected.

[0057] The operation process of an energy-saving NMP vacuum distillation negative pressure pumping system in this embodiment is as follows:

[0058] (1) Startup process:

[0059] Start the cooling water system → Start the screw back pump → After the pressure reaches the set value, the PLC starts the Roots main pump;

[0060] (2) Operation control:

[0061] The pressure transmitter provides real-time data feedback, and the PLC dynamically adjusts the frequency of the Roots pump.

[0062] (3) Condensate recovery:

[0063] The condensate from the first-stage condenser is stored in the collection pipe and automatically discharged after the liquid level reaches the target.

[0064] The secondary condenser deeply captures residual exhaust gas;

[0065] (4) Maintenance operations:

[0066] Regularly initiate the solvent flushing → nitrogen purging process to prevent pump blockage.

[0067] Working principle:

[0068] This invention relates to an energy-saving NMP vacuum distillation negative pressure pumping system, employing a cartridge-type vacuum device composed of a series combination of a first-stage air-cooled Roots vacuum pump and a first-stage screw dry vacuum pump. The system primarily consists of the air-cooled Roots vacuum pump and the screw dry vacuum pump connected in series, meeting the vacuuming requirements of different working pressures in the NMP three-stage distillation column. Because the suction chambers of the air-cooled Roots vacuum pump and the screw dry vacuum pump do not require working fluid or lubricating oil, they are insensitive to the pumped medium. Furthermore, the pumping performance of the vacuum pump is unaffected by the air temperature of the pumped gas and is also insensitive to the cooling water temperature, making its pumping performance virtually unaffected by external interference. The air-cooled Roots vacuum pump, due to its high permissible pressure differential, can meet the long-term reliable continuous operation of the NMP distillation process at any pressure point from 100 kPa to 10 kPa. Moreover, the pump chamber is dry and oil-free, which is very beneficial to the pumped gas, resulting in a longer service life and better reliability. In the NMP distillation process, from atmospheric pressure to a vacuum of 10 kPa, the pumping efficiency of this new type of ear-shaped energy-saving air-cooled Roots screw dry vacuum pumping system can reach more than 85%, which is far superior to the original liquid ring vacuum pumping system.

[0069] This invention employs a single-stage air-cooled Roots vacuum pump as the main pump, and utilizes a cooler at the exhaust port of the air-cooled Roots vacuum pump to condense and capture the condensable gas discharged from the pump. Over 80% of the condensable gas is condensed by this cooler, resulting in the gas flow rate entering the backing screw dry vacuum pump being less than 20% of the intake flow rate. Therefore, a smaller backing screw dry vacuum pump can be matched with the main pump. Considering the high compression ratio of the air-cooled Roots vacuum pump, the intake ratio of the main pump (air-cooled Roots vacuum pump) to the backing screw dry vacuum pump is 5:1 or even greater. The original process system used a liquid ring vacuum pump with a pumping capacity of 2200 m³ / h, whose motor power consumption was about 75 kW. Using an energy-saving air-cooled Roots screw dry vacuum system with the same pumping capacity, the motor power of the two vacuum pumps was 18.5 + 18.5 = 37 kW. In actual use, the energy consumption of the motor of the energy-saving air-cooled Roots screw vacuum system was more than 50% lower than that of the liquid ring vacuum system.

[0070] In addition, an atmospheric condenser and condensate recovery tank are installed at the exhaust port of the screw dry vacuum pump. This can capture and recover almost 100% of the condensable chemical gases discharged from the vacuum system, which can reduce environmental pollution, reduce chemical loss, and improve production efficiency.

[0071] The primary condenser has a triple function. First, it condenses and captures the condensable gas discharged from the gas-cooled Roots vacuum pump, with a capture efficiency of over 80%. This significantly reduces the flow rate of condensable gas entering the backing screw dry vacuum pump, allowing for the selection of a smaller backing screw dry vacuum pump and greatly reducing the investment and operating costs of the entire vacuum system. Secondly, the cooled gas discharged from the gas-cooled Roots vacuum pump is then circulated back into the pump chamber of the gas-cooled Roots vacuum pump through cooling gas return pipes located on both sides of the condenser and the pump body. This utilizes the pressure difference between the inside of the vacuum pump and the exhaust port to effectively cool the heat-generating components inside the gas-cooled Roots vacuum pump, thus ensuring the safe, reliable, and stable operation of the gas-cooled Roots vacuum pump at a working vacuum of 100~1kPa. Thirdly, it lowers the inlet temperature of the screw vacuum pump. The maximum allowable inlet temperature of the screw vacuum pump is 60℃, and the gas temperature drops by 45℃ after being cooled by the exhaust port cooler of the gas-cooled Roots vacuum pump, providing a guarantee for the safe operation of the screw dry vacuum pump.

[0072] The screw dry vacuum pump is the backing pump of the air-cooled Roots vacuum pump. The two are matched with a certain suction capacity. Its function is to promptly remove the exhaust gas after the gas discharged from the air-cooled Roots vacuum pump has been condensed and captured by the cooler. This can reduce the exhaust pressure of the air-cooled Roots vacuum pump. Moreover, the two stages in series can also improve the pumping efficiency of the air-cooled Roots vacuum pump at high inlet pressure, making the operation of the air-cooled Roots vacuum pump more stable.

[0073] Check valves, nitrogen sealing devices, solvent flushing devices, and nitrogen purging devices are respectively installed on the connecting pipes between the exhaust end of the air-cooled Roots vacuum pump cooler and the inlet end of the screw dry vacuum pump.

[0074] The function of the check valve is to prevent the backflow of condensate from the exhaust end of the screw dry vacuum pump when it stops, ensuring safe operation of all vacuum pumps in the vacuum system when restarted.

[0075] The function of the nitrogen sealing device is to prevent the chemical medium pumped during operation from causing chemical corrosion to the high-speed precision parts such as bearings and lip seals inside the two end covers of the suction chamber of the screw dry vacuum pump, thus protecting the screw dry vacuum pump.

[0076] The gas discharged from the exhaust port cooler of the air-cooled Roots vacuum pump enters the screw dry vacuum pump through a connecting pipe. After compression within the pump chamber, the gas becomes a gas-liquid mixture. The nitrogen seal in the screw dry vacuum pump prevents condensation in the pumped gas from damaging the pump's seals. (Additional note: The pumped gas enters and exits the air-cooled Roots vacuum pump chamber in a pure gaseous state; therefore, the air-cooled Roots vacuum pump does not require nitrogen sealing protection, nor does it require solvent flushing or nitrogen purging processes.)

[0077] The purpose of the solvent flushing device is to address the accumulation of chemicals inside the screw dry vacuum pump after a period of operation. If these chemicals are not regularly removed, they can affect the normal operation of the screw dry vacuum pump and cause the rotor to seize up. This device can effectively clean the chemicals from the screw dry vacuum pump periodically, ensuring its long-term safe operation.

[0078] The purpose of the nitrogen purging device is to purge the solvent remaining in the pump chamber of the screw dry vacuum pump after solvent flushing, so that the pumping performance of the screw dry vacuum pump is not affected.

[0079] The secondary condenser installed at the exhaust port of the screw dry vacuum pump serves to deeply condense and capture condensable chemical gases that have not been completely condensed and captured by the system, reducing raw material waste, lowering the pollution caused by exhaust emissions, and achieving emission reduction and efficiency improvement for users. A liquid storage tank is installed at the lower end of the condenser to continuously recover and capture the condensate.

[0080] For operating conditions with the same gas volume requirements, the new energy-saving vacuum system can save 50% of energy compared to the existing liquid ring vacuum system, and the NMP distillation products have higher purity and better quality. Furthermore, the novel vacuum system is equipped with a waste gas capture device at the exhaust port, achieving zero emissions and reducing environmental pollution.

[0081] In addition to meeting the specific distillation process requirements of NMP, the vacuum system of this invention, with appropriate modifications, can become a comprehensive vacuum treatment system applicable to various industries such as chemical, pharmaceutical, and food processing. For example, it can be used in processes such as vacuum concentration, vacuum drying, and vacuum degassing; and can be equipped with a pre-condenser, a pre-condensate collection device, a high-precision dust collector, a post-condenser, and a post-condensate collection device.

[0082] Detailed operating procedures:

[0083] Power on the main power supply of the main control system for vacuum pumping, start with one key and open the main inlet valve of the vacuum system cooling water. Only after the cooling water pressure reaches the required value will the control system allow the main inlet valve of the vacuum system to be opened automatically. Then, the cooling water inlet valves of the two vacuum pumps and the cooling water of the two coolers (condensers) will be opened in sequence. If the flow rate is insufficient, the control will alarm and automatically stop the subsequent operation steps of the vacuum system.

[0084] After the cooling water pressure and flow rate are normal, the fore-stage screw dry vacuum pump automatically starts to pre-vacuum the distillation column. When the pressure transmitter value on the main inlet pipe of the vacuum system, i.e., the pressure inside the distillation column, reaches a certain set pressure value, the air-cooled Roots vacuum pump is automatically started by the PLC control system according to the frequency set in the process flow. When the vacuum pressure inside the distillation column reaches a certain required value, heating of the material inside the distillation column begins. Heating of the distillation column is generally achieved through high-temperature heat transfer oil in the jacket outside the column. When the material inside the distillation column reaches a certain temperature, under the negative pressure suction of the vacuum system, the internal material reaches saturation pressure and begins to evaporate. The evaporated gas is sucked into the vacuum system and passes through the condenser at the top of the distillation column. Most of the gas is condensed and captured, while the uncondensed gas re-enters the novel air-cooled Roots screw dry vacuum pump system. The screw dry vacuum pump always operates at a constant speed at the industrial frequency, and the air-cooled Roots vacuum pump can automatically allocate its operating frequency according to the system evaporation rate and the gas output of the condenser at the top of the distillation column, based on the set working pressure. The gas being pumped enters the suction compressor of the air-cooled Roots vacuum pump, is compressed, and then discharged into the cooler at the bottom of the pump. Most of the pumped gas is compressed and cooled into a liquid, and the condensate is stored in the collection pipe. When the condensate reaches a certain level, the control system automatically closes or opens the relevant valves to discharge the condensate in the storage tank into the appropriate storage and transportation equipment.

[0085] Uncondensed gas after passing through the air-cooled Roots vacuum pump cooler enters the screw dry vacuum pump through a connecting pipe. The gas experiences a temperature rise after being drawn in and compressed by the screw dry vacuum pump. Therefore, a condenser is installed at the exhaust port of the screw dry vacuum pump to further condense and re-capture the high-temperature gas-liquid mixture discharged from the pump. This achieves zero emissions of waste gas and complete capture of the condensate from the distillation tail gas, realizing a green economy characterized by energy saving, emission reduction, and increased efficiency.

[0086] The above are merely specific application examples of this utility model and do not constitute any limitation on the scope of protection of this utility model. All technical solutions formed by equivalent transformations or equivalent substitutions fall within the scope of protection of this utility model.

Claims

1. An energy-saving NMP vacuum distillation negative pressure pumping system, characterized in that: The system includes an air-cooled Roots vacuum pump (1), a main inlet pipe (2), a primary condenser (5), a connecting pipe (6), a screw dry vacuum pump (14), and a secondary condenser (19). The inlet of the air-cooled Roots vacuum pump (1) is connected to the main inlet valve (3) through the main inlet pipe (2). The outlet of the air-cooled Roots vacuum pump (1) is connected to the primary condenser (5). The primary condenser (5) is connected to the inlet of the screw dry vacuum pump (14) through the connecting pipe (6). The outlet of the screw dry vacuum pump (14) is connected to the secondary condenser (19). The connecting pipe (6) between the primary condenser (5) and the screw dry vacuum pump (14) is equipped with a first check valve (7), a nitrogen sealing device (8), a nitrogen purging device (9), a solvent flushing device (10), a vacuum gauge (11), and a thermometer (12). The screw dry vacuum pump (14) is connected to the second check valve (15), which is connected to the flow meter (16), the regulating valve (17), and the pressure gauge (18); the first-stage condenser (5) is connected to the first liquid storage tank (13) via a solenoid valve, and the second-stage condenser (19) is connected to the second liquid storage tank (20) via a solenoid valve. The inlets of the air-cooled Roots vacuum pump (1), the first-stage condenser (5), the screw dry vacuum pump (14), and the second-stage condenser (19) are connected to the cooling water inlet via cooling water flow control valves, and the outlets of the air-cooled Roots vacuum pump (1), the first-stage condenser (5), the screw dry vacuum pump (14), and the second-stage condenser (19) are connected to the cooling water outlet; the drain ports of the first liquid storage tank (13) and the second liquid storage tank (20) are connected to the condensate outlet via automatic drain solenoid valves. The air-cooled Roots vacuum pump (1), the main inlet valve (3), the pressure transmitter (4), the screw dry vacuum pump (14), and each solenoid valve and level controller are all connected to the PLC electrical control system (21), which receives data and controls the start and stop through the PLC electrical control system (21).

2. The energy-saving NMP vacuum distillation negative pressure pumping system according to claim 1, characterized in that: A pressure transmitter (4) is installed on the main air intake pipe (2).

3. The energy-saving NMP vacuum distillation negative pressure pumping system according to claim 1, characterized in that: The nitrogen sealing device (8) is connected to the connecting pipe (6) via a solenoid valve.

4. The energy-saving NMP vacuum distillation negative pressure pumping system according to claim 1, characterized in that: The nitrogen purging device (9) is connected to the connecting pipe (6) via a solenoid valve and a manual valve.

5. The energy-saving NMP vacuum distillation negative pressure pumping system according to claim 1, characterized in that: The solvent rinsing device (10) is connected to the connecting pipe (6) via a solenoid valve and a manual valve.

6. The energy-saving NMP vacuum distillation negative pressure pumping system according to claim 1, characterized in that: The first liquid storage tank (13) is equipped with a level gauge with high and low liquid level controllers.

7. The energy-saving NMP vacuum distillation negative pressure pumping system according to claim 1, characterized in that: The second liquid storage tank (20) is equipped with a level gauge with high and low liquid level controllers.

8. The energy-saving NMP vacuum distillation negative pressure pumping system according to claim 1, characterized in that: The first liquid storage tank (13) and the second liquid storage tank (20) are connected to the PLC electrical control system (21) via an electromagnetic venting valve.

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