A cold-heat combined supply system based on NMP waste liquid purification and a control strategy

Abstract

The present application belongs to the technical field of heat pump system, and particularly relates to a cold-heat combined supply system based on NMP waste liquid purification and a control strategy. The cold-heat combined supply system comprises a cascade cold-heat combined supply subsystem and a waste liquid purification device, the waste liquid purification device comprises an evaporation tank and a condensation tank; the cascade cold-heat combined supply subsystem comprises a cascade cold-water heat pump unit, a heat supply module and a cold supply module; the cascade cold-water heat pump unit generates cold energy at a cold energy end and generates heat at a heat end by compressing refrigerant; the cold supply module brings the cold energy at the cold energy end into circulating chilled water through heat exchange; the heat supply module brings the heat at the heat end into circulating condensing water through heat exchange; the waste liquid in the evaporation tank flows into the condensation tank after forming steam at the top of the evaporation tank after absorbing heat, and the steam is condensed into liquid state in the condensation tank. The present application has compact structure, can efficiently and safely supply heat and cold to the waste liquid purification process at the same time, and reduces heat supply and cold supply energy consumption and cost.

Description

Technical Field

[0001] This invention belongs to the field of heat pump system technology, and particularly relates to a combined cooling and heating system and control strategy based on NMP waste liquid purification. Background Technology

[0002] In the lithium-ion battery manufacturing process, N-methylpyrrolidone (NMP) serves as a solvent, effectively fusing key components such as binders, electrode active materials, and conductive agents together, making it one of the crucial materials in lithium battery manufacturing. In traditional lithium-ion battery manufacturing, used NMP waste liquid needs to be packaged and transported from the battery manufacturing plant to a specialized factory for recycling and purification using dedicated equipment, enabling the reuse of the NMP waste liquid after impurity removal.

[0003] The process requires a boiler to generate high-temperature steam for distillation, followed by condensation using low-temperature cold water supplied by refrigeration equipment, ultimately yielding pure liquid NMP.

[0004] Current technology utilizes gas-fired or electric boilers to generate high-temperature steam for heating, while low-temperature chilled water also requires additional refrigeration. These two processes require separate heating and cooling systems, which are complex in structure, occupy a large area, and have high energy consumption, resulting in substantial operating costs. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a combined heating and cooling system based on NMP waste liquid purification. This system has a compact structure and can efficiently and safely provide heating and cooling to the NMP waste liquid purification process simultaneously, while reducing energy consumption and costs for heating and cooling.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A combined cooling and heating system based on NMP waste liquid purification includes a cascaded combined cooling and heating subsystem and an NMP waste liquid purification device. The NMP waste liquid purification device includes one or more parallel evaporator-condenser tank sets, each set containing one evaporator and one condenser. The cascaded combined cooling and heating subsystem includes a cascaded chilled water heat pump unit, a heating module, and a cooling module. The cascaded chilled water heat pump unit compresses the refrigerant to generate cooling on the cooling side and heat on the heating side. The cooling module heats the refrigerant through heat exchange... The cooling capacity from the cooling end is carried into the circulating chilled water. As the chilled water flows through the condenser, heat exchange occurs, bringing the heat from the condenser back to the cooling end. The heating module carries the heat from the heating end into the circulating condensate through heat exchange. As the condensate flows through the evaporator, heat exchange occurs, bringing the cooling capacity from the evaporator back to the heating end. After absorbing heat, the NMP waste liquid in the evaporator forms NMP vapor at the top of the evaporator and flows into the condenser. The NMP vapor condenses into liquid NMP in the condenser.

[0008] Preferably, the cooling module includes a chilled water pump and a heat exchanger; each condenser is connected in parallel to the main inlet and main outlet pipes of the NMP waste liquid purification device through its own chilled water branch pipes; the main inlet pipe of the NMP waste liquid purification device is installed on the high-temperature side of the heat exchanger; the inlet end of the chilled water pump is connected to the main outlet pipe of the NMP waste liquid purification device, and the outlet end of the chilled water pump is connected to the main inlet pipe of the NMP waste liquid purification device.

[0009] Preferably, the cascade chilled water heat pump unit includes a first compressor group, a second compressor group, a first cascade heat exchanger, and a second cascade heat exchanger; the first cascade heat exchanger has a first condensing pipe and a first evaporating pipe that are coupled to each other; the outlet end of the first compressor group is connected to the first condensing inlet pipe; the inlet end of the first compressor group is connected to the first condensing outlet pipe; the first condensing outlet pipe is located on the low-temperature side of the heat exchanger; the second cascade heat exchanger has a second condensing pipe and a hot water pipe that are coupled to each other; the outlet end of the second compressor group is connected to the second condensing inlet pipe; the inlet end of the second compressor group is connected to the first evaporating outlet pipe; the second condensing outlet pipe is connected to the first evaporating inlet pipe.

[0010] Preferably, the heating module includes a flash tank, a hot water pump, and a third compressor; the flash tank has a water inlet at its upper part, a water outlet and a water supply port at its bottom, and an air outlet at its top; the evaporator has an air inlet at its upper part and a water outlet at its bottom; a hot water outlet pipe is connected to the water inlet of the flash tank, and a hot water inlet pipe is connected to the water outlet of the flash tank; a hot water pump is installed on the hot water inlet pipe; the air outlet of the flash tank is connected to the air inlet of the third compressor; the air outlet of the third compressor is connected to the air inlet of each evaporator, and the water outlet of each evaporator is connected to the water supply port of the flash tank.

[0011] Preferably, the heating module also includes a three-way regulating valve and terminal heating equipment; the inlet of the three-way regulating valve is connected to the outlet of the third compressor, the first outlet of the three-way regulating valve is connected to the inlet of each evaporator, the second outlet of the three-way regulating valve is connected to the inlet of the terminal heating equipment; and the outlet of the terminal heating equipment is connected to the water supply port of the flash tank.

[0012] Preferably, the cooling module further includes terminal cooling equipment, a third electric valve, and a fourth electric valve; the inlet pipe of the terminal cooling equipment is connected to the main inlet pipe of the NMP waste liquid purification device; the outlet pipe of the terminal cooling equipment is connected to the main outlet pipe of the NMP waste liquid purification device; and the third electric valve and the fourth electric valve are respectively installed on the inlet pipe and the outlet pipe of the terminal cooling equipment.

[0013] This invention also provides a control strategy for a combined cooling and heating system based on NMP waste liquid purification, which controls the aforementioned combined cooling and heating system based on cooling load, including the following steps:

[0014] S1, with the exhaust valve, the third electric valve and the fourth electric valve all closed, start the combined cooling and heating system and adjust the load of each compressor in the first compressor group to P1;

[0015] S2, real-time monitoring of the load, first chilled water temperature T1, second chilled water temperature T2, and third chilled water temperature T3 of each compressor in the first compressor group; wherein, the second chilled water temperature T2 is the chilled water temperature in the main inlet pipe of the NMP waste liquid purification device near the NMP waste liquid purification device; the third chilled water temperature T3 is the chilled water temperature in the main outlet pipe of the NMP waste liquid purification device near the NMP waste liquid purification device; the first chilled water temperature T1 is the chilled water temperature in the main outlet pipe of the NMP waste liquid purification device near the high-temperature side of the heat exchanger;

[0016] S3, based on the first chilled water temperature T1, controls the valve opening of the third and fourth electric valves, the load of each compressor in the first compressor group, and the valve opening of each outlet end of the three-way regulating valve, to ensure that the load of each compressor in the first compressor group is above P0 and the first chilled water temperature is 0 < T1′ ≤ T1 ≤ T1″; where P0 < P1, P0 represents the critical load, T1′ represents the first water temperature threshold, and T1″ represents the second water temperature threshold.

[0017] Preferably, S3 includes the following: if the current first chilled water temperature T1 > T1″, then the third electric valve and the fourth electric valve are closed to increase the load of each compressor in the first compressor group.

[0018] Preferably, S3 includes the following: if the current first chilled water temperature T1′≤T1≤T1″, the first chilled water temperature T1 continuously decreases during the previous Δt time period, and the load of each compressor in the current first compressor group is above P1, then the load of each compressor in the current first compressor group is reduced; if the first chilled water temperature T1′≤T1≤T1″, the first chilled water temperature T1 continuously decreases during the previous Δt time period, and the load of each compressor in the current first compressor group is less than P1, then the valve opening of the third electric valve and the fourth electric valve is increased; if the current first chilled water temperature T1′≤T1≤T1″, then the first chilled water temperature T1 continuously decreases during the previous Δt time period, and the load of each compressor in the current first compressor group is less than P1, then the valve opening of the third electric valve and the fourth electric valve is increased; if the current first chilled water temperature T1′≤T1≤T1″, then the first chilled water temperature T1′≤T1″ is above P1, then the first chilled water temperature T1′≤T1″ is above P1. If the first chilled water temperature T1 continuously rises during the preceding Δt time period, and the load of each compressor in the first compressor group is above P1, then if both the third and fourth electric valves are open, the valve openings of the third and fourth electric valves will be reduced; if both the third and fourth electric valves are closed, the load of each compressor in the first compressor group will be increased; if the first chilled water temperature T1′≤T1≤T1″, and the first chilled water temperature T1 continuously rises during the preceding Δt time period, and the load of each compressor in the first compressor group is less than P1, then the load of each compressor in the first compressor group will be increased.

[0019] Preferably, S3 includes the following: if the current first chilled water temperature T1 < T1′ and the load of each compressor in the current first compressor group is above P1, then the load of each compressor in the current first compressor group is reduced; if the current first chilled water temperature T1 < T1′ and the load of each compressor in the current first compressor group is less than P1, then the valve opening of the third electric valve and the fourth electric valve is increased.

[0020] The beneficial effects of this invention are as follows:

[0021] (1) Compared with the separate refrigeration and heating equipment in the prior art, the combined cooling and heating system based on NMP waste liquid purification of the present invention has a compact structure and a small footprint. The electrical energy used to power the compressor in the combined cooling and heating system is simultaneously converted into the cooling and heating required by the NMP waste liquid purification device, thereby improving the energy utilization rate in the NMP waste liquid purification process and reducing the energy consumption and cost of heating and cooling.

[0022] (2) The present invention provides a combined cooling and heating system based on NMP waste liquid purification. The cascade thermodynamic cycle can divide the large total temperature difference into two segments through a condenser-evaporator. The cooling capacity of the high-temperature stage is used to bear the condensation load of the low-temperature stage, thereby obtaining a lower cooling temperature. In a combined cooling and heating system, a large temperature difference is generated between the cooling end and the heating end.

[0023] (3) The present invention provides a combined cooling and heating system based on NMP waste liquid purification. After prioritizing the NMP waste liquid purification device, the system can also send the excess cooling and heating energy to the end-use cooling / heating equipment. After being used by the NMP waste liquid purification device (and the end-use cooling / heating equipment), the remaining small amount of energy can be recovered again through the circulating water (i.e., low-temperature hot water and high-temperature chilled water) into the cascade combined cooling and heating system. This makes the cooling and heating energy generated by the entire combined cooling and heating system consuming electrical energy (to power the compressor) highly efficient and basically does not emit additional heat or cold to the surrounding environment, thus saving energy and protecting the environment.

[0024] (4) The combined cooling and heating system based on NMP waste liquid purification of the present invention can flexibly adjust the cooling and heating capacity used for the end cooling / heating equipment to ensure that the cooling and heating capacity generated by the combined cooling and heating system is preferentially used to meet the real-time changes in the cooling and heating capacity of the NMP waste liquid purification device, thereby improving the purification efficiency of NMP waste liquid and ensuring the safe operation of the cascade combined cooling and heating system.

[0025] (5) The control strategy of the combined cooling and heating system based on NMP waste liquid purification of the present invention ensures that each compressor is in the on state during operation, so that each compressor can quickly respond to the load change demand, thereby improving the response rate and adjustment flexibility of the entire combined cooling and heating system.

[0026] (6) The control strategy of the present invention ensures that the load of each compressor is in a healthy state, which can improve the life of the compressor and the entire combined cooling and heating system and reduce the operation and maintenance cost of the combined cooling and heating system.

[0027] (7) The control strategy of this invention is based on cooling capacity, while the cooling capacity required by the NMP waste liquid purification device changes in real time. This change will cause the first chilled water temperature T1 to change with a lag. If the cooling capacity that cannot be consumed by the NMP waste liquid purification device in time exists in the combined cooling and heating system, the first chilled water temperature T1 will be too low, causing the combined cooling and heating system to malfunction and shut down. Therefore, the control strategy of this invention, while providing sufficient cooling capacity to the NMP waste liquid purification device, also needs to ensure that the cooling capacity that cannot be consumed by the NMP waste liquid purification device in time does not cause the first chilled water temperature T1 to be too low. Furthermore, because the cooling capacity required by the NMP waste liquid purification device changes in real time, it is not feasible to know the cooling capacity requirement in advance and then accurately adjust the cooling capacity of the combined cooling and heating system. The most ingenious aspect of the control strategy in this invention lies in using the change in the first chilled water temperature T1 to measure the real-time changing cooling demand of the NMP waste liquid purification device. By directly controlling the first chilled water temperature T1 between the first water temperature threshold T1′ and the second water temperature threshold T1″, it is ensured that the cooling capacity supplied to the NMP waste liquid purification device is sufficient, and the combined cooling and heating system will not fail and shut down. Avoiding failure and shutdown also further extends the lifespan of the combined cooling and heating system.

[0028] (8) The control strategy of the present invention also satisfies the condition that the load of each compressor is in a healthy state, and prioritizes reducing the load of each compressor to reduce the power consumption of the entire combined cooling and heating system; under these conditions, the excess cooling capacity is then supplied to the terminal cooling equipment. That is, the control strategy of the present invention can not only meet the real-time changing cooling demand of the NMP waste liquid purification device in a timely manner and improve the NMP waste liquid purification efficiency, but also minimize the power consumption during system operation; and through flexible adjustment measures, the unused heat / cooling capacity of the NMP waste liquid purification device can be utilized (supplied to the terminal heating / cooling equipment), and the lifespan of the entire combined cooling and heating system is greatly improved.

[0029] (9) The seven specific control methods in the control strategy of this invention cover all situations that may occur in the entire combined cooling and heating system, and are effective for dynamic fluctuations around the ideal temperature T. * The first chilled water temperature (i.e., T1′≤T1≤T1″) was also dynamically adjusted preventively, further reducing the adverse effects of lag changes in the first chilled water temperature on "dynamically stabilizing the first chilled water temperature at the ideal temperature," and maximizing the control of the first chilled water temperature within the ideal first water temperature threshold T1′ and second water temperature threshold T1″ range. Preventive dynamic adjustments were also made to the first chilled water temperature already between the first water temperature threshold T1′ and the second water temperature threshold T1″, further improving the response speed of the entire combined cooling and heating system to changes in cooling capacity at the next moment. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the overall structure of the combined cooling and heating system of the present invention. Detailed Implementation

[0031] To make the technical solution of the present invention clearer and more explicit, the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Solutions derived by those skilled in the art through equivalent substitution and conventional reasoning of the technical features of the present invention without creative effort all fall within the protection scope of the present invention.

[0032] Example 1

[0033] like Figure 1 The diagram shows the overall structure of a combined cooling and heating system for NMP waste liquid purification according to the present invention, including a cascaded combined cooling and heating subsystem and an NMP waste liquid purification device. The NMP waste liquid purification device is used to purify NMP (N-methylpyrrolidone) from the NMP waste liquid by first evaporating and then condensing it; the cascaded combined cooling and heating subsystem is used to simultaneously provide heat and cold to the NMP waste liquid purification device for evaporation and condensation.

[0034] The NMP waste liquid purification unit comprises one or more parallel evaporator-condenser sets. Each evaporator-condenser set includes one evaporator (ET) and one condenser (CT). The tops of the evaporator (ET) and condenser (CT) are connected. The bottom of the condenser (CT) has an extraction port (not shown in the diagram) for obtaining purified liquid NMP after condensation. After absorbing heat, the NMP waste liquid in the evaporator (ET) forms NMP vapor at the top. Due to the pressure difference, the NMP vapor automatically flows into the condenser (CT). The NMP vapor condenses into liquid NMP within the condenser (CT).

[0035] The NMP waste liquid purification unit in this implementation consists of only one evaporator-condenser unit.

[0036] The cascade combined cooling and heating subsystem includes a cascade chilled water heat pump unit, a heating module, and a cooling module. The cascade chilled water heat pump unit generates cooling at one end (the cooling end) and heat at the other end (the heating end) by compressing refrigerant through a compressor. The cooling module transfers the cooling from the cooling end into the circulating chilled water through heat exchange. The chilled water undergoes heat exchange as it flows through the condenser tank (CT), bringing the heat from the condenser tank back to the cooling end. The heating module transfers the heat from the heating end into the circulating condensate through heat exchange. The condensate undergoes heat exchange as it flows through the evaporator tank (ET), bringing the cooling from the evaporator tank back to the heating end.

[0037] The cooling module includes a chilled water pump PUMP1 and a heat exchanger H1. Each condenser tank (CT) is connected in parallel to the main inlet and outlet pipes of the NMP waste liquid purification unit via its own chilled water branch pipes. The main chilled water inlet pipe of the NMP waste liquid purification unit supplies chilled water to all condenser tanks (CT), and the chilled water flowing out of all condenser tanks (CT) eventually flows into the main outlet pipe of the NMP waste liquid purification unit. The main inlet pipe of the NMP waste liquid purification unit is located on the high-temperature side of the heat exchanger H1; the inlet of chilled water pump PUMP1 is connected to the main outlet pipe of the NMP waste liquid purification unit, and the outlet of chilled water pump PUMP1 is connected to the main inlet pipe of the NMP waste liquid purification unit.

[0038] Optionally, the cooling module also includes a chilled water flow meter F1 installed on the main outlet pipe of the NMP waste liquid purification unit to measure the chilled water flow rate on the main outlet pipe of the NMP waste liquid purification unit.

[0039] The cascade heat pump unit includes a first compressor group COMP1, a second compressor group COMP2, a first cascade heat exchanger FH1, and a second cascade heat exchanger FH2. The first cascade heat exchanger FH1 has a coupled first condenser pipe and a coupled first evaporator pipe. The outlet end of the first compressor group COMP1 is connected to the first condenser inlet pipe of the first cascade heat exchanger FH1, and the inlet end of the first compressor group COMP1 is connected to the first condenser outlet pipe of the first cascade heat exchanger FH1. The first condenser outlet pipe is located on the low-temperature side of heat exchanger FH1. The second cascade heat exchanger FH2 has a coupled second condenser pipe and a hot water pipe. The outlet end of the second compressor group COMP2 is connected to the second condenser inlet pipe of the second cascade heat exchanger FH2, and the inlet end of the second compressor group COMP2 is connected to the first evaporator outlet pipe of the first cascade heat exchanger FH1. The second condenser outlet pipe is connected to the first evaporator inlet pipe.

[0040] The first refrigerant circulates in the first condenser pipe, while the second refrigerant circulates in the second condenser pipe and the first evaporator pipe.

[0041] In this embodiment, the first refrigerant is R134a or R515b, and the second refrigerant is R245fa or R1233zd(E).

[0042] Both the first compressor group COMP1 and the second compressor group COMP2 contain more than one compressor connected in series, and the compressors in each compressor group have the same model.

[0043] Optionally, the cascade chilled water heat pump unit also includes a first storage tank TIN1, a first electric valve MV1, a second storage tank TIN2, and a second electric valve MV2. The first storage tank TIN1 and the first electric valve MV1 are both located on the first condensate outlet pipe; the second storage tank TIN2 and the second electric valve MV2 are both located on the second condensate outlet pipe. The electric valves are used to control whether the refrigerant circulates on their respective pipes and the refrigerant flow rate. The first storage tank TIN1 and the second storage tank TIN2 are used to store the corresponding refrigerant.

[0044] The heating module includes a flash tank (TANK1), a hot water pump (PUMP2), and a third compressor (COMP3). The flash tank (TANK1) has a water inlet at its top, a water outlet and a water supply port at its bottom, and an air outlet at its top. The evaporator (ET) has an air inlet at its top and a water outlet at its bottom. The hot water outlet of the second cascade heat exchanger (FH2) is connected to the water inlet of the flash tank (TANK1), and the hot water inlet of the second cascade heat exchanger (FH2) is connected to the water outlet of the flash tank (TANK1). A hot water pump (PUMP2) is installed on the hot water inlet of the second cascade heat exchanger (FH2). The air outlet of the flash tank (TANK1) is connected to the air inlet of the third compressor (COMP3). The air outlet of the third compressor (COMP3) is connected to the air inlet of each evaporator (ET), and the water outlet of each evaporator (ET) is connected to the water supply port of the flash tank (TANK1).

[0045] Optionally, the heating module also includes a three-way regulating valve (TWV), a dew point sensor (not shown in the figure), and a terminal heating device (HET). The inlet of the three-way regulating valve (TWV) is connected to the outlet of the third compressor (COMP3), the first outlet of the three-way regulating valve (TWV) is connected to the inlet of each evaporator (ET), and the second outlet of the three-way regulating valve (TWV) is connected to the inlet of the terminal heating device (HET). The outlet of the terminal heating device (HET) is connected to the water supply port of the flash tank (TANK1). Each evaporator (ET) is equipped with a dew point sensor. The first outlet of the three-way regulating valve (TWV) controls the flow rate of water vapor entering the evaporator (ET) based on the dew point measured by the dew point sensor inside the evaporator (ET). All remaining water vapor is sent to the terminal heating device (HET).

[0046] The top of the flash tank TANK1 is equipped with an exhaust valve EV. When the cascade combined cooling and heating system is operating, the exhaust valve EV is normally closed. It only opens to release pressure when the pressure difference between the inlet and outlet of the flash tank TANK1 exceeds a pressure threshold, ensuring the safety of the flash tank TANK1. When the cascade combined cooling and heating system is not operating, the exhaust valve EV opens to connect with the external environment, ensuring that non-condensable gases inside the flash tank TANK1 are discharged to the outside environment, preventing blockage of the flash tank TANK1's outlet.

[0047] In this embodiment, the pressure threshold of the pressure difference between the water inlet and the air outlet of the flash tank TANK1 is 100 kPa.

[0048] Optionally, the cooling module also includes a terminal cooling unit (CET), a third electric valve (MV3), and a fourth electric valve (MV4). The inlet pipe of the terminal cooling unit (CET) is connected to the main inlet pipe of the NMP waste liquid purification device; the outlet pipe of the terminal cooling unit (CET) is connected to the main outlet pipe of the NMP waste liquid purification device; the third electric valve (MV3) and the fourth electric valve (MV4) are respectively installed on the inlet and outlet pipes of the terminal cooling unit (CET).

[0049] Heat exchange equipment (HET) and cooling exchange equipment (CET) can be used in other stages of a lithium-ion battery manufacturing plant. For example, high-temperature steam is required in processes such as coating ovens in lithium-ion battery manufacturing plants, and this high-temperature steam can be provided by heat exchange equipment (HET).

[0050] The working process of a combined cooling and heating system based on NMP waste liquid purification in this embodiment is described below:

[0051] When a combined cooling and heating system based on NMP waste liquid purification starts working, the exhaust valve EV is closed, and both the first electric valve MV1 and the second electric valve MV2 are opened. After startup, if the third electric valve MV3 and the fourth electric valve MV4 are opened simultaneously, the chilled water will flow not only through each condenser tank CT, but also through the terminal cooling equipment CET. That is, the cooling capacity of the chilled water is used not only to cool the condenser tanks CT, but also to cool the terminal cooling equipment CET. The high-temperature chilled water flowing out from each condenser tank CT and the terminal cooling equipment CET is collected into the main outlet pipe of the NMP waste liquid purification unit. The chilled water pump PUMP1 provides circulation power, and after heat exchange and cooling on the high-temperature side of the heat exchanger H1, it becomes low-temperature chilled water and flows back into the main inlet pipe of the NMP waste liquid purification unit.

[0052] The temperature range of the low-temperature chilled water is 5–10 degrees Celsius; in this embodiment, it is 7 degrees Celsius. The temperature range of the high-temperature chilled water is 15–20 degrees Celsius; in this embodiment, it is 16 degrees Celsius.

[0053] The low-temperature first refrigerant flows through the low-temperature side of heat exchanger H1 and is heated up. It then flows into the first compressor group COMP1, where it is compressed and heated up to become a high-temperature first refrigerant. It then enters the first condenser pipe in the first cascade heat exchanger FH1, where it exchanges heat with the second refrigerant flowing through the first evaporator pipe in the first cascade heat exchanger FH1. After cooling down, it becomes a low-temperature first refrigerant and flows out of the first cascade heat exchanger FH1, flowing through the low-temperature side of heat exchanger H1 again and circulating continuously.

[0054] In this embodiment, the temperature range of the low-temperature first refrigerant is 10 to 12 degrees Celsius; the temperature range of the high-temperature first refrigerant is 60 to 70 degrees Celsius.

[0055] The low-temperature second refrigerant is heated after flowing through the first evaporator pipe in the first cascade heat exchanger FH1. It then flows into the second compressor group COMP2, where it is compressed and heated and pressurized to become a high-temperature second refrigerant. It then enters the second condenser pipe in the second cascade heat exchanger FH2, where it exchanges heat with the hot water flowing through the hot water pipe in the second cascade heat exchanger FH2 and is cooled to become a low-temperature second refrigerant. It then flows out of the second cascade heat exchanger FH2 and flows through the first evaporator pipe in the first cascade heat exchanger FH1 again, continuously circulating.

[0056] In this embodiment, the temperature range of the low-temperature second refrigerant is 60–65 degrees Celsius; the temperature range of the high-temperature second refrigerant is 125–140 degrees Celsius.

[0057] Powered by the hot water pump PUMP2, the low-temperature hot water at the bottom of the flash tank TANK1 is heated to high-temperature hot water after flowing through the hot water pipeline in the second cascade heat exchanger FH2. After the high-temperature hot water enters the flash tank TANK1 and is depressurized, part of it becomes water vapor at the top of the flash tank TANK1, and part of it becomes low-temperature hot water stored at the bottom of the flash tank TANK1. After the water vapor flows out from the top of the flash tank TANK1, it enters the third compressor COMP3 and is compressed and increased in enthalpy to become high-temperature steam.

[0058] In this embodiment, the temperature of the low-temperature hot water is 110 degrees Celsius; the temperature of the water vapor at the top of the flash tank TANK1 is 115 degrees Celsius; the temperature of the high-temperature hot water is 120 degrees Celsius (in a closed system, the high-temperature hot water temperature can be maintained at 120 degrees Celsius by pressure); and the temperature of the high-temperature steam is 130 degrees Celsius.

[0059] The three-way regulating valve (TWV) adjusts the valve openings of the first and second outlets based on the dew point measured by the dew point sensor inside the evaporator (ET). This allows a portion of the high-temperature steam to heat the evaporator (ET), while the remaining portion heats the end-user heating equipment (HET). After being heated, the high-temperature steam cools and liquefies into condensate, flowing out from the outlets of each evaporator (ET) and the end-user heating equipment (HET). It then enters the bottom of the flash tank (TANK1) through the water inlet, becoming low-temperature hot water.

[0060] Compared to separate refrigeration and heating equipment in existing technologies, the combined cooling and heating system based on NMP waste liquid purification in this embodiment has a compact structure and a small footprint. Furthermore, the electrical energy used to power the compressor in the combined cooling and heating system is simultaneously converted into the cooling and heating required by the NMP waste liquid purification device, thereby improving the energy utilization rate during the NMP waste liquid purification process and reducing the energy consumption and cost of heating and cooling.

[0061] This embodiment presents a combined cooling and heating system based on NMP waste liquid purification. The cascade thermodynamic cycle uses a condenser-evaporator to divide the large total temperature difference into two segments. The high-temperature stage's cooling capacity is used to handle the low-temperature stage's condensation load, thus achieving a lower cooling temperature. This creates a large temperature difference between the cooling and heating ends within the combined cooling and heating system. The difference between the first and second refrigerants also serves to assist in dividing the temperature difference in this embodiment's combined cooling and heating system.

[0062] This embodiment of a combined cooling and heating system based on NMP waste liquid purification allows for the supply of cooling and heating to the NMP waste liquid purification device after prioritizing the NMP waste liquid purification device. Excess cooling and heating can then be sent to end-user cooling / heating equipment. Furthermore, the small amount of energy remaining after being used by the NMP waste liquid purification device (and end-user cooling / heating equipment) is recycled back into the cascade combined cooling and heating system through circulating water (i.e., low-temperature hot water and high-temperature chilled water). This ensures that the cooling and heating generated by the electrical energy consumed by the entire combined cooling and heating system (to power the compressor) are utilized efficiently, with virtually no additional heat or cold emissions to the surrounding environment, resulting in energy conservation and environmental protection.

[0063] This embodiment of a combined cooling and heating system based on NMP waste liquid purification can flexibly adjust the cooling and heating capacity used for end-user cooling / heating equipment to ensure that the cooling and heating capacity generated by the combined cooling and heating system is preferentially used to meet the real-time changes in cooling and heating demand of the NMP waste liquid purification device, thereby improving the purification efficiency of NMP waste liquid and ensuring the safe operation of the cascade combined cooling and heating system.

[0064] According to technical personnel, the combined cooling and heating system based on NMP waste liquid purification in this embodiment has a 50% smaller footprint and a 150% higher energy efficiency compared to the existing technology that requires separate refrigeration and heating equipment in the NMP waste liquid purification process.

[0065] Example 2

[0066] When the cooling capacity of a combined cooling and heating system (CCHP) for NMP waste liquid purification is fixed, the heating capacity of the CCHP is approximately 1.5 to 2 times the cooling capacity. This means that not all the heating capacity can be used for the evaporator (ET). The "cooling load-based" principle requires the CCHP to prioritize the cooling capacity for the condenser (CT). Furthermore, the production volume of NMP waste liquid is variable and directly affected by the addition, reduction, and start-up / shutdown of the production line. Therefore, the cooling capacity required by all condensers (CT) in the NMP waste liquid purification unit is always variable; it can even change abruptly (e.g., a new tank of NMP waste liquid needs purification, or the purification of a tank of NMP waste liquid has just ended and there is no new NMP waste liquid to purify).

[0067] Therefore, the cooling capacity of a combined cooling and heating (CCHP) system generally exceeds the total cooling capacity required by all condensers (CTs) in the NMP waste liquid purification unit. Furthermore, the CCHP system needs to respond promptly to changing cooling demands, increasing the supplied cooling capacity when demand increases and decreasing the supplied cooling capacity or sending excess cooling to the end-user cooling equipment (CET) when demand decreases. Correspondingly, excess heat supplied by the CCHP system is promptly sent to the end-user heating equipment.

[0068] This embodiment provides a control strategy for a combined cooling and heating system based on NMP waste liquid purification, used to control a combined cooling and heating system based on NMP waste liquid purification as described in Embodiment 1 based on the cooling load:

[0069] S1, with the exhaust valve EV, the third electric valve MV3 and the fourth electric valve MV4 all closed, a combined cooling and heating system based on NMP waste liquid purification is started, and the load of each compressor in the first compressor group COMP1 is adjusted to the initial load P1.

[0070] S2, real-time monitoring of the load, first chilled water temperature T1, second chilled water temperature T2, and third chilled water temperature T3 of each compressor in the first compressor group COMP1; wherein, the second chilled water temperature T2 is the chilled water temperature in the main inlet pipe of the NMP waste liquid purification device near the NMP waste liquid purification device; the third chilled water temperature T3 is the chilled water temperature in the main outlet pipe of the NMP waste liquid purification device near the NMP waste liquid purification device; the first chilled water temperature T1 is the chilled water temperature in the main outlet pipe of the NMP waste liquid purification device near the high-temperature side of the heat exchanger H1.

[0071] S3, based on the first chilled water temperature T1, controls the valve opening of the third electric valve MV3 and the fourth electric valve MV4, the load of each compressor in the first compressor group COMP1, and the valve opening of each outlet end of the three-way regulating valve TWV, to ensure that the load of each compressor in the first compressor group COMP1 is above P0 and the first chilled water temperature is 0 < T1′ ≤ T1 ≤ T1″, where P0 < P1, P0 represents the critical load, T1′ represents the first water temperature threshold, and T1″ represents the second water temperature threshold.

[0072] In this embodiment, T1′=5℃, T1″=8℃; P0 is 50% of the full load, and P1 is 53% of the full load.

[0073] S3 includes the following:

[0074] ①If the current first chilled water temperature T1 > T1″, then close the third electric valve MV3 and the fourth electric valve MV4 to increase the load of each compressor in the first compressor group COMP1.

[0075] Because the cooling capacity required for NMP waste liquid purification is uncertain and may change abruptly, it is impractical to calculate the required cooling capacity in real time and then control the combined cooling and heating system to provide the corresponding cooling capacity.

[0076] We determine whether the current cooling capacity of the combined cooling and heating system (CCHP) is sufficient to meet the cooling requirements of the NMP waste liquid purification unit by real-time monitoring of the first chilled water temperature T1. We aim to keep the first chilled water temperature T1 as constant as possible at the ideal temperature T. * , where T1′≤T * The temperature ≤T1″ indicates that the current cooling capacity of the combined cooling and heating system is sufficient to meet the cooling requirements of the NMP wastewater purification unit. Therefore, when the current first chilled water temperature T1 > T1″, we believe that the cooling capacity currently provided by the combined cooling and heating system is far from meeting the cooling requirements of the NMP wastewater purification unit. Therefore, regardless of whether the third electric valve MV3 and the fourth electric valve MV4 are open, we keep the fourth electric valve MV4 and the fourth shut-off valve SV closed at this time, and increase the load of each compressor in the first compressor group COMP1 in order to quickly increase the cooling capacity of the combined cooling and heating system.

[0077] In this embodiment, T * =7℃.

[0078] ② If the current first chilled water temperature T1′≤T1≤T1″, the first chilled water temperature T1 continuously decreases during the previous Δt time period, and the load of each compressor in the current first compressor group COMP1 is above P1, then reduce the load of each compressor in the current first compressor group COMP1.

[0079] If the current first chilled water temperature T1′≤T1≤T1″, we believe that the cooling capacity currently provided by the combined cooling and heating system can basically meet the cooling capacity requirements of the NMP waste liquid purification unit. However, on the one hand, the change in the first chilled water temperature T1 caused by the change in the cooling capacity requirements of the NMP waste liquid purification unit is lagging; on the other hand, in order to respond to the cooling demand in a timely manner, we need to ensure that all compressors in the first compressor group COMP1 are running; furthermore, we need to ensure that the load of each running compressor in the first compressor group COMP1 is maintained above P0, so that the compressors are in a healthy state, extending the service life of the compressors and the entire combined cooling and heating system.

[0080] In practice, technicians assign health state loads to each operating compressor in the first compressor group COMP1 after considering the health states of each compressor in the second compressor group COMP2 and the third compressor group COMP3. Therefore, as long as each compressor in the first compressor group COMP1 is in a healthy state, then the second compressor group COMP2 and the third compressor group COMP3 are naturally in a healthy state.

[0081] It should be noted that if the temperature of the first chilled water, T1, drops below 0 degrees Celsius, the chilled water in the main outlet pipe of the NMP waste liquid purification unit near the high-temperature side of heat exchanger H1 will freeze, causing the combined cooling and heating system based on NMP waste liquid purification to shut down. Similarly, if the load on each compressor in the first compressor group COMP1 is consistently less than P0, each compressor in COMP1 will also fail and shut down, causing the combined cooling and heating system to shut down as well.

[0082] Therefore, we make preventative adjustments based on the trend of the first chilled water temperature T1 during the preceding Δt time period: if the first chilled water temperature T1 continues to decrease during the preceding Δt time period, to prevent the cooling capacity from increasing further in the next moment, i.e., to prevent the first chilled water temperature T1 from continuing to decrease or even rapidly dropping to 0 degrees Celsius, we need to reduce the cooling capacity. However, considering that the load of each compressor in the current first compressor group COMP1 is still above P1, we reduce the load of each compressor in the current first compressor group COMP1, saving power consumption while reducing the cooling capacity.

[0083] ③ If the first chilled water temperature T1′≤T1≤T1″, and the first chilled water temperature T1 continuously decreases within the first Δt time, and the load of each compressor in the current first compressor group COMP1 is less than P1, then increase the valve opening of the third electric valve MV3 and the fourth electric valve MV4.

[0084] We believe that the cooling capacity currently provided by the combined cooling and heating system can basically meet the cooling capacity requirements of the NMP waste liquid purification unit. However, the cooling capacity may continue to increase in the future, exceeding the cooling capacity requirements, which means that the unused cooling capacity of the NMP waste liquid purification unit will increase.

[0085] Since the load of each compressor in the first compressor group COMP1 is already less than P1, further reducing the load of each compressor in the first compressor group COMP1 may cause the load of each compressor in the first compressor group COMP1 to reach P0, which is the limit of the compressor's healthy state. Therefore, our preventive adjustment is to increase the valve opening of the third electric valve MV3 and the fourth electric valve MV4 to send more of the unused cooling capacity of the NMP waste liquid purification unit into the terminal cooling equipment CET, so as to avoid the subsequent drop of the first chilled water temperature T1 to 0 degrees Celsius.

[0086] ④ If the current first chilled water temperature T1′≤T1≤T1″, the first chilled water temperature T1 continuously rises during the previous Δt time period, and the load of each compressor in the current first compressor group COMP1 is above P1, if both the third electric valve MV3 and the fourth electric valve MV4 are open, then the valve opening of the third electric valve MV3 and the fourth electric valve MV4 is reduced; if both the third electric valve MV3 and the fourth electric valve MV4 are closed, then the load of each compressor in the first compressor group COMP1 is increased.

[0087] We believe that the cooling capacity currently provided by the combined cooling and heating system is basically sufficient to meet the cooling demand of the NMP waste liquid purification unit. However, the cooling demand may continue to increase in the next moment. Therefore, our precautionary adjustments are as follows: when the terminal cooling equipment CET is already in use, in order to save the power consumption of the compressors, we will reduce the valve opening of the third electric valve MV3 and the fourth electric valve MV4 to reduce the cooling demand of the terminal cooling equipment CET; when the terminal cooling equipment CET is not in use, we will increase the load of each compressor in the first compressor group COMP1 to increase the cooling capacity of the combined cooling and heating system in the next moment.

[0088] ⑤ If the first chilled water temperature T1′≤T1≤T1″, and the first chilled water temperature T1 continuously rises within the first Δt time period, and the load of each compressor in the first compressor group COMP1 is less than P1, then increase the load of each compressor in the first compressor group COMP1.

[0089] We believe that the cooling capacity currently provided by the combined cooling and heating system can basically meet the cooling capacity requirements of the NMP waste liquid purification unit. However, the cooling capacity requirements may continue to increase in the next moment. Considering that the load of each compressor in the first compressor group COMP1 is currently less than P1, in order to ensure that the compressors are in good condition, our precautionary adjustment is to increase the load of each compressor in the first compressor group COMP1.

[0090] ⑥ If the current first chilled water temperature T1 < T1′, and the load of each compressor in the current first compressor group COMP1 is above P1, then reduce the load of each compressor in the current first compressor group COMP1.

[0091] Regardless of whether the end-user cooling equipment (CET) participates in cooling, we believe that the cooling capacity currently provided by the combined cooling and heating system far exceeds the cooling capacity requirements of the NMP waste liquid purification unit. Currently, the loads of each compressor in the first compressor group COMP1 are all above P1, which is a healthy state. Therefore, we reduce the cooling capacity of the combined cooling and heating system by reducing the loads of each compressor in the first compressor group COMP1, thus preventing the first chilled water temperature from dropping below 0 degrees Celsius.

[0092] ⑦ If the current first chilled water temperature T1 < T1′, and the load of each compressor in the current first compressor group COMP1 is less than P1, then increase the valve opening of the third electric valve MV3 and the fourth electric valve MV4.

[0093] Based on the analysis of ⑥, in order to prevent the temperature of the first chilled water from dropping below 0 degrees Celsius, and in order to ensure the health of each compressor in the current first compressor group COMP1, we increase the valve opening of the third electric valve MV3 and the fourth electric valve MV4 to send more of the unused cooling capacity of the NMP waste liquid purification device into the terminal cooling equipment CET.

[0094] Optionally, to ensure the safe operation of the third compressor COMP3, the third compressor COMP3 will be shut down when the outlet temperature exceeds a set threshold.

[0095] In this implementation, the set threshold for the outlet temperature of the third compressor COMP3 is 132 degrees Celsius.

[0096] Turning on a shut-down compressor and then adjusting its load to the required value takes significantly longer than directly adjusting an already running compressor to the required load. This embodiment presents a control strategy for a combined cooling and heating system based on NMP waste liquid purification. By ensuring that each compressor is always running, each compressor can quickly respond to changes in load demand, improving the overall response rate and adjustment flexibility of the combined cooling and heating system.

[0097] The control strategy in this embodiment ensures that the load of each compressor is in a healthy state, which can improve the lifespan of the compressor and the entire combined cooling and heating system and reduce the operation and maintenance costs of the combined cooling and heating system.

[0098] The control strategy in this embodiment is based on cooling capacity. However, the cooling capacity required by the NMP waste liquid purification device changes in real time, causing a lag in the change of the first chilled water temperature T1. If the cooling capacity that cannot be consumed by the NMP waste liquid purification device in time exists in the combined cooling and heating system, the first chilled water temperature T1 will be too low, causing the combined cooling and heating system to malfunction and shut down. Therefore, the control strategy in this embodiment must provide sufficient cooling capacity to the NMP waste liquid purification device while ensuring that the cooling capacity that cannot be consumed by the NMP waste liquid purification device in time does not cause the first chilled water temperature T1 to be too low. Furthermore, because the cooling capacity required by the NMP waste liquid purification device changes in real time, it is not feasible to know the cooling capacity requirement in advance and then precisely adjust the cooling capacity of the combined cooling and heating system. The most innovative aspect of the control strategy in this embodiment lies in using the change in the first chilled water temperature T1 to measure the real-time changing cooling demand of the NMP waste liquid purification device. By directly controlling the first chilled water temperature T1 between the first water temperature threshold T1′ and the second water temperature threshold T1″, it is ensured that the cooling capacity supplied to the NMP waste liquid purification device is sufficient, and the combined cooling and heating system will not fail and shut down. Avoiding failure and shutdown also further extends the lifespan of the combined cooling and heating system.

[0099] Under the control strategy guiding principles mentioned above, the control strategy of this embodiment also satisfies the condition that the load of each compressor is in a healthy state, prioritizing the reduction of the load of each compressor to reduce the power consumption of the entire combined cooling and heating system; and only when these conditions are met will the excess cooling capacity be supplied to the terminal cooling equipment.

[0100] In other words, the control strategy of this embodiment can not only meet the real-time changing cooling demand of the NMP waste liquid purification device in a timely manner and improve the NMP waste liquid purification efficiency, but also minimize the power consumption during system operation; and through flexible adjustment measures, utilize the unused heat / cooling energy of the NMP waste liquid purification device (supplying it to the terminal heating / cooling equipment), and greatly extend the lifespan of the entire combined cooling and heating system.

[0101] The seven specific control methods in this embodiment cover all situations that may occur in the entire combined cooling and heating system, and address dynamic fluctuations around the ideal temperature T. *The first chilled water temperature (i.e., T1′≤T1≤T1″) was also dynamically adjusted preventively, further reducing the adverse effects of lag changes in the first chilled water temperature on "dynamically stabilizing the first chilled water temperature at the ideal temperature," and maximizing the control of the first chilled water temperature within the ideal first water temperature threshold T1′ and second water temperature threshold T1″ range. Preventive dynamic adjustments were also made to the first chilled water temperature already between the first water temperature threshold T1′ and the second water temperature threshold T1″, further improving the response speed of the entire combined cooling and heating system to changes in cooling capacity at the next moment.

[0102] According to technical personnel, the control strategy of this embodiment reduces the power consumption of the entire combined cooling and heating system by 70% and the operation and maintenance costs by 70% compared with the existing technology.

[0103] The technologies, shapes, and structures not described in detail in this invention are all well-known technologies. It should also be noted that the above are merely preferred embodiments of this invention and are not intended to limit the scope of the invention. The components or steps in the embodiments of this invention can be decomposed and / or recombined, and these decompositions and / or recombinations should be considered equivalent solutions to this application and should all fall within the protection scope of this invention.

Claims

1. A combined cooling and heating system based on NMP waste liquid purification, characterized in that: The system includes a cascade combined cooling and heating subsystem and an NMP wastewater purification unit. The NMP wastewater purification unit comprises one or more parallel evaporator-condenser units, each containing one evaporator (ET) and one condenser (CT). The cascade combined cooling and heating subsystem includes a cascade chilled water heat pump unit, a heating module, and a cooling module. The cascade chilled water heat pump unit compresses the refrigerant to generate cooling on the cooling side and heat on the heating side. The cooling module transfers the cooling energy from the cooling side into the circulating chilled water through heat exchange. Heat exchange occurs in the condenser (CT), bringing the heat from the condenser (CT) back and sending it to the cooling end; the heating module uses heat exchange to bring the heat from the heating end into the circulating condensate. The condensate flows through the evaporator (ET) and undergoes heat exchange, bringing the cooling from the evaporator (ET) back and sending it to the heating end; after absorbing heat, the NMP waste liquid in the evaporator (ET) forms NMP vapor at the top of the evaporator (ET) and flows into the condenser (CT). The NMP vapor condenses into liquid NMP in the condenser (CT). The cooling module includes a chilled water pump (PUMP1) and a heat exchanger (H1); each condenser (CT) is connected in parallel to the main inlet and outlet pipes of the NMP waste liquid purification unit through its own chilled water branch pipes; the main inlet pipe of the NMP waste liquid purification unit is installed on the high-temperature side of the heat exchanger (H1); the inlet of the chilled water pump (PUMP1) is connected to the main outlet pipe of the NMP waste liquid purification unit, and the outlet of the chilled water pump (PUMP1) is connected to the main inlet pipe of the NMP waste liquid purification unit; The cascade chilled water heat pump unit includes a first compressor group (COMP1), a second compressor group (COMP2), a first cascade heat exchanger (FH1), and a second cascade heat exchanger (FH2). The first cascade heat exchanger (FH1) has a coupled first condenser pipe and a coupled first evaporator pipe. The outlet end of the first compressor group (COMP1) is connected to the first condenser inlet pipe; the inlet end of the first compressor group (COMP1) is connected to the first condenser outlet pipe; the first condenser outlet pipe is located on the low-temperature side of the heat exchanger (H1). The second cascade heat exchanger (FH2) has a coupled second condenser pipe and a hot water pipe. The outlet end of the second compressor group (COMP2) is connected to the second condenser inlet pipe, and the inlet end of the second compressor group (COMP2) is connected to the first evaporator outlet pipe; the second condenser outlet pipe is connected to the first evaporator inlet pipe. The heating module includes a flash tank (TANK1), a hot water pump (PUMP2), and a third compressor (COMP3). The flash tank (TANK1) has a water inlet at its top, a water outlet and a water supply port at its bottom, and an air outlet at its top. The evaporator (ET) has an air inlet at its top and a water outlet at its bottom. A hot water outlet pipe is connected to the water inlet of the flash tank (TANK1), and a hot water inlet pipe is connected to the water outlet of the flash tank (TANK1). A hot water pump (PUMP2) is installed on the hot water inlet pipe. The air outlet of the flash tank (TANK1) is connected to the air inlet of the third compressor (COMP3). The air outlet of the third compressor (COMP3) is connected to the air inlets of each evaporator (ET), and the water outlet of each evaporator (ET) is connected to the water supply port of the flash tank (TANK1).

2. The combined cooling and heating system based on NMP waste liquid purification according to claim 1, characterized in that: The heating module also includes a three-way regulating valve (TWV) and a terminal heat supply device (HET); the inlet of the three-way regulating valve (TWV) is connected to the outlet of the third compressor (COMP3), the first outlet of the three-way regulating valve (TWV) is connected to the inlet of each evaporator (ET), the second outlet of the three-way regulating valve (TWV) is connected to the inlet of the terminal heat supply device (HET); the outlet of the terminal heat supply device (HET) is connected to the water supply port of the flash tank (TANK1).

3. A combined cooling and heating system based on NMP waste liquid purification according to claim 1 or 2, characterized in that: The cooling module also includes a terminal cooling unit (CET), a third electric valve (MV3), and a fourth electric valve (MV4); the inlet pipe of the terminal cooling unit (CET) is connected to the main inlet pipe of the NMP waste liquid purification device; the outlet pipe of the terminal cooling unit (CET) is connected to the main outlet pipe of the NMP waste liquid purification device; the third electric valve (MV3) and the fourth electric valve (MV4) are respectively installed on the inlet and outlet pipes of the terminal cooling unit (CET).

4. A control strategy for a combined cooling and heating system based on NMP waste liquid purification, comprising controlling the combined cooling and heating system based on NMP waste liquid purification as described in claim 3 based on the cooling load, including the following steps: S1, with the exhaust valve (EV), the third electric valve (MV3) and the fourth electric valve (MV4) all closed, start the combined cooling and heating system and adjust the load of each compressor in the first compressor group (COMP1) to P1; S2, real-time monitoring of the load, first chilled water temperature T1, second chilled water temperature T2, and third chilled water temperature T3 of each compressor in the first compressor group (COMP1); wherein, the second chilled water temperature T2 is the chilled water temperature in the main inlet pipe of the NMP waste liquid purification device near the NMP waste liquid purification device; the third chilled water temperature T3 is the chilled water temperature in the main outlet pipe of the NMP waste liquid purification device near the NMP waste liquid purification device; the first chilled water temperature T1 is the chilled water temperature in the main outlet pipe of the NMP waste liquid purification device near the high-temperature side of the heat exchanger (H1); S3, based on the first chilled water temperature T1, controls the valve opening of the third electric valve (MV3) and the fourth electric valve (MV4), the load of each compressor in the first compressor group (COMP1), and the valve opening of each outlet end of the three-way regulating valve (TWV) to ensure that the load of each compressor in the first compressor group (COMP1) is above P0 and the first chilled water temperature is 0 < T1' ≤ T1 ≤ T1''; where P0 < P1, P0 represents the critical load, T1' represents the first water temperature threshold, and T1'' represents the second water temperature threshold.

5. The control strategy of a combined cooling and heating system based on NMP waste liquid purification according to claim 4, wherein S3 includes the following: if the current first chilled water temperature T1 > T1´´, then the third electric valve (MV3) and the fourth electric valve (MV4) are closed to increase the load of each compressor in the first compressor group (COMP1).

6. The control strategy of a combined cooling and heating system based on NMP waste liquid purification according to claim 4, wherein S3 includes the following: if the current first chilled water temperature T1´≤T1≤T1´´, the first chilled water temperature T1 continuously decreases during the previous Δt time period, and the load of each compressor in the current first compressor group (COMP1) is above P1, then the load of each compressor in the current first compressor group (COMP1) is reduced; If the first chilled water temperature T1´≤T1≤T1´´, and the first chilled water temperature T1 continuously decreases within the first Δt time, and the load of each compressor in the current first compressor group (COMP1) is less than P1, then increase the valve opening of the third electric valve (MV3) and the fourth electric valve (MV4). If the current chilled water temperature T1´≤T1≤T1´´, the chilled water temperature T1 continuously rises during the previous Δt time period, and the load of each compressor in the current first compressor group (COMP1) is above P1, then if both the third electric valve (MV3) and the fourth electric valve (MV4) are open, the valve opening of the third electric valve (MV3) and the fourth electric valve (MV4) will be reduced; if both the third electric valve (MV3) and the fourth electric valve (MV4) are closed, the load of each compressor in the first compressor group (COMP1) will be increased. If the first chilled water temperature T1´≤T1≤T1´´, and the first chilled water temperature T1 continuously rises within the first Δt time period, and the load of each compressor in the current first compressor group (COMP1) is less than P1, then the load of each compressor in the first compressor group (COMP1) is increased.

7. The control strategy of a combined cooling and heating system based on NMP waste liquid purification according to claim 4, wherein S3 includes the following: if the current first chilled water temperature T1 < T1', and the load of each compressor in the current first compressor group (COMP1) is above P1, then reduce the load of each compressor in the current first compressor group (COMP1). If the current chilled water temperature T1 < T1', and the load of each compressor in the current first compressor group (COMP1) is less than P1, then increase the valve opening of the third electric valve (MV3) and the fourth electric valve (MV4).

Images