Control method of NMP waste liquid purification cold and heat combined supply system based on cooling load

Abstract

The invention belongs to the technical field of heat pump systems, and particularly relates to a control method of an NMP waste liquid purification cold and heat combined supply system based on a cold load. The cold and heat combined supply system based on NMP waste liquid purification comprises a cascade type cold water heat pump unit, a heat supply module, a cold supply module and an NMP waste liquid purification device. The control method comprises the steps that after the cold and heat combined supply system based on NMP waste liquid purification is started, loads of all compressors in the first compressor group are adjusted to be initial loads; and the load of each compressor in the first compressor group and the heat supply amount to the tail end heat utilization equipment are monitored and adjusted in real time, so that the heat supply amount to the NMP waste liquid purification device is equal to the cold supply amount, the load of each compressor in the first compressor group is higher than the critical load, and the water outlet temperature of the high-temperature side of the heat exchanger is within the set threshold value range. According to the invention, electric energy loss can be reduced as much as possible, and heat and cold can be efficiently supplied to the purification process of the NMP waste liquid.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of heat pump systems, and particularly relates to a control method for a cold-heat combined supply system for NMP waste liquid purification based on cold load. BACKGROUND

[0002] In the lithium ion battery manufacturing process, N-methyl pyrrolidone (NMP for short) as a solvent can effectively fuse key components such as binders, electrode active materials and conductive agents together, and is one of the key materials in lithium battery manufacturing. In the traditional lithium ion battery manufacturing process, the used NMP waste liquid needs to be transported from the battery manufacturing factory to the professional factory through filling, and is purified by special equipment to realize the reuse of the NMP waste liquid after impurities are removed.

[0003] This process needs a boiler to generate high-temperature steam for distillation, and a refrigeration device to provide low-temperature cold water for condensation to finally obtain pure liquid NMP.

[0004] The existing technology uses a gas boiler or an electric boiler to generate high-temperature steam for heating, and low-temperature cold water also needs to be obtained by additional refrigeration. Two processes are needed for heating and cooling respectively, and the structure of the separate heating system and cooling system is complex, occupies a large area, and the energy consumption of the heating system and cooling system is high, and the operation cost is huge. Moreover, the cooling capacity required in the NMP waste liquid purification process may change in real time, for example: a new tank of NMP waste liquid needs to be purified; or the purification of a tank of NMP waste liquid has just ended, and there is no new NMP waste liquid to be purified. Therefore, how to control the heating system and the cooling system so that they can meet the cooling capacity and heating capacity required in the NMP waste liquid purification process in time and reduce the power consumption as much as possible has become a difficult problem to be solved. SUMMARY

[0005] The purpose of the application is to overcome the shortcomings of the existing technology, and provide a control method for a cold-heat combined supply system for NMP waste liquid purification based on cold load, which can efficiently supply heat and cold to the NMP waste liquid purification process while reducing power consumption as much as possible.

[0006] To achieve the above purpose, the application adopts the following technical solutions: A kind of NMP waste liquid purification cold-heat combined system control method based on cold load, the application of a kind of NMP waste liquid purification cold-heat combined system based on, including cascade cold water heat pump unit, heating module, cooling module and NMP waste liquid purification device;Cascade cold water heat pump unit includes first compressor group and first cascade heat exchanger;Cooling module includes heat exchanger;Heating module includes end heat using equipment;Heat exchanger low-temperature side pipeline is provided with first compressor group, and heat exchanger low-temperature side pipeline is arranged in first cascade heat exchanger;First cascade heat exchanger is used to send the heat generated by the work of first compressor group and the heat of heat exchanger low-temperature side into NMP waste liquid purification device and end heat using equipment;Heat exchanger high-temperature side is used to supply cold to NMP waste liquid purification device;Control method includes the following steps: Step 1, after starting a kind of NMP waste liquid purification cold-heat combined system based on, the load of each compressor in first compressor group is adjusted to initial load P1; Step 2, real-time monitoring and adjusting the load of each compressor in first compressor group and the heat supply to end heat using equipment, so that the heat supply to NMP waste liquid purification device is equal to the cooling capacity, the load of each compressor in first compressor group is above critical load P0, and the outlet water temperature of heat exchanger high-temperature side is within the set threshold range;Wherein P0

[0007] Preferably, NMP waste liquid purification device contains more than one evaporation tank and condenser;Cascade cold water heat pump unit further includes second compressor group and second cascade heat exchanger;The heat exchanger low-temperature side pipeline arranged in first cascade heat exchanger is called first condensing pipeline, and first cascade heat exchanger is arranged with first condensing pipeline and first evaporation pipeline coupled with each other;Second cascade heat exchanger is arranged with second condensing pipeline and hot water pipeline coupled with each other, and second condensing pipeline is communicated with first evaporation pipeline;First compressor group is arranged at the inlet of first condensing pipeline of first cascade heat exchanger, and second compressor group is arranged at the inlet of second condensing pipeline of second cascade heat exchanger;Heating module further includes flash tank, hot water pump, third compressor and three-way regulating valve;Hot water pipeline is provided with flash tank and hot water pump, and the top gas outlet of flash tank is communicated with the gas inlet of third compressor;The gas outlet of third compressor is communicated with the gas inlet of three-way regulating valve, the first gas outlet of three-way regulating valve is communicated with the gas inlet of each evaporation tank, and the second gas outlet of three-way regulating valve is communicated with the gas inlet of end heat using equipment;The water outlet of end heat using equipment and the water outlet of each evaporation tank are both communicated with the water supplement port of flash tank.

[0008] Preferably, the cooling module includes a chilled water pump; each condensing tank is connected in parallel to the main water inlet pipe and the main water outlet pipe of the NMP waste liquid purification device through its own chilled water branch pipe, the main water inlet pipe of the NMP waste liquid purification device is arranged on the high-temperature side of the heat exchanger, and the water inlet and water outlet of the chilled water pump are respectively connected to the main water outlet pipe and the main water inlet pipe of the NMP waste liquid purification device; the chilled water flowing into the main water inlet pipe of the NMP waste liquid purification device cools the high-temperature side of the heat exchanger and brings the cold energy into the condensing tank after heat exchange, and the chilled water flowing out of the main water outlet pipe of the NMP waste liquid purification device brings the heat in the condensing tank into the high-temperature side of the heat exchanger.

[0009] Preferably, the cooling module also includes a terminal cooling device, a third electric valve and a fourth electric valve; the water inlet pipe and the water outlet pipe of the terminal cooling device are respectively connected to the main water inlet pipe and the main water outlet pipe of the NMP waste liquid purification device, and the third electric valve and the fourth electric valve are respectively provided on the water inlet pipe and the water outlet pipe of the terminal cooling device.

[0010] Preferably, the water vapor flows out from the first gas outlet end of the three-way regulating valve and enters each evaporation tank to release heat and then condenses into condensed water, which then flows out from the water outlet of the evaporation tank; the NMP waste liquid in the evaporation tank absorbs heat and forms NMP vapor at the top of the evaporation tank and flows into the condensation tank, and the NMP vapor is cooled and condensed into liquid NMP in the condensation tank.

[0011] Preferably, step 2 further includes the following steps S2 and S3: S2, real-time monitoring of the load of each compressor in the first compressor group, the first chilled water temperature T1, the second chilled water temperature T2, and the third chilled water temperature T3; Among them, the first chilled water temperature T1 refers to the outlet water temperature on the high-temperature side of the heat exchanger; the second chilled water temperature T2 refers to the temperature of the chilled water in the total water inlet pipe of the NMP waste liquid purification device close to the NMP waste liquid purification device; the third chilled water temperature T3 refers to the temperature of the chilled water in the total water outlet pipe of the NMP waste liquid purification device close to the NMP waste liquid purification device; S3, controlling the valve openings of the third electric valve, the fourth electric valve, and the outlet ends of the three-way regulating valve, as well as the load of each compressor in the first compressor group, based on the first chilled water temperature T1, so that the heating and cooling capacities supplied to the NMP waste liquid purification apparatus are equal, the load of each compressor in the first compressor group is above the critical load P0, and the first chilled water temperature 0<T1´≤T1≤T1´; wherein T1´ represents the first water temperature threshold, and T1´´ represents the second water temperature threshold.

[0012] Preferably, in S3, the following is further included: if the current first chilled water temperature T1'≤T1≤T1'', the first chilled water temperature T1 continuously decreases in the previous △t time period, and the load of each compressor in the current first compressor group is greater than P1, then the load of each compressor in the current first compressor group is reduced; if the first chilled water temperature T1'≤T1≤T1'', and the first chilled water temperature T1 continuously decreases in the previous △t time, and the load of each compressor in the current first compressor group is less than P1, then the valve opening of the third and fourth electric valves is increased; if the current first chilled water temperature T1'≤T1≤T1'', the first chilled water temperature T1 continuously increases in the previous △t time period, and the load of each compressor in the current first compressor group is greater than P1, if the third and fourth electric valves are both open, then the valve opening of the third and fourth electric valves is reduced; if the third and fourth electric valves are both closed, then the load of each compressor in the first compressor group is increased; if the first chilled water temperature T1'≤T1≤T1'', and the first chilled water temperature T1 continuously increases in the previous △t time, and the load of each compressor in the current first compressor group is less than P1, then the load of each compressor in the first compressor group is increased.

[0013] Preferably, in S3, the following is further included: if the current first chilled water temperature T1'≤T1≤T1'', the first chilled water temperature T1 continuously decreases in the previous △t time period, and the load of each compressor in the current first compressor group is greater than P1, then the load of each compressor in the current first compressor group is reduced; if the first chilled water temperature T1'≤T1≤T1'', and the first chilled water temperature T1 continuously decreases in the previous △t time, and the load of each compressor in the current first compressor group is less than P1, then the valve opening of the third and fourth electric valves is increased; if the current first chilled water temperature T1'≤T1≤T1'', the first chilled water temperature T1 continuously increases in the previous △t time period, and the load of each compressor in the current first compressor group is greater than P1, if the third and fourth electric valves are both open, then the valve opening of the third and fourth electric valves is reduced; if the third and fourth electric valves are both closed, then the load of each compressor in the first compressor group is increased; if the first chilled water temperature T1'≤T1≤T1'', and the first chilled water temperature T1 continuously increases in the previous △t time, and the load of each compressor in the current first compressor group is less than P1, then the load of each compressor in the first compressor group is increased.

[0014] Preferably, in S3, the heat supply to the NMP waste liquid purification device is equal to the cold supply, and the following is further included: adjusting the valve opening of each gas outlet end in the three-way regulating valve, so that the first gas outlet end supplies the first heat Q3 to the evaporation tank in the NMP waste liquid purification device, and the second gas outlet end supplies the second heat Q4 to the terminal heat using equipment; The first heat Q3 and the second heat Q4 are calculated using the following formula: Q1=C×f1×(T3-T2);EX=Q1 / n / W;Q2=(1+COP) / (COP-1);Q3=Q1;Q4=Q2-Q3; Wherein, Q1 represents the cold demand of the current NMP waste liquid purification device; C represents the specific heat capacity of water; f1 represents the chilled water flow in the total water outlet pipe or the total water inlet pipe of the NMP waste liquid purification device; EX represents the expected operation capacity percentage of a single compressor in the first compressor group; n represents the number of compressors in the first compressor group; W represents the rated refrigerating capacity of the compressors in the first compressor group; Q2 represents the corresponding heating capacity of the cascade cold water heat pump unit under the condition of the refrigerating capacity being Q1; and COP represents the energy efficiency coefficient of the cascade cold water heat pump unit.

[0015] The present application has the following beneficial effects: (1) Compared with the separate refrigeration equipment and heating equipment in the prior art, the cold and heat combined supply system based on NMP waste liquid purification has a compact structure and small footprint, and the electric energy used for powering the compressors in the cold and heat combined supply system is converted into the cold and heat required by the NMP waste liquid purification device, thereby improving the electric energy utilization rate in the NMP waste liquid purification process and reducing the heating and cooling energy consumption and cost.

[0016] (2) The cold and heat combined supply system based on NMP waste liquid purification has a cascade thermodynamic cycle which can divide a large total temperature difference into two sections through a condenser-evaporator, and use the refrigerating capacity of the high-temperature stage to bear the condensing load of the low-temperature stage, so as to obtain a lower refrigerating temperature, thereby generating a cold end and a heat end with a huge temperature difference in the cold and heat combined supply system.

[0017] (3) The cold and heat combined supply system based on NMP waste liquid purification can send the excess cold and heat to the terminal cold / hot equipment after the cold and heat are preferentially used for the NMP waste liquid purification device, and a small amount of energy remaining after being used by the NMP waste liquid purification device (and the terminal cold / hot equipment) can be recovered to the cascade cold and heat combined supply system through the circulating water (i.e. low-temperature hot water and high-temperature chilled water), so that the cold and heat generated by the electric energy (used for powering the compressors) consumed by the entire cold and heat combined supply system are efficiently utilized, and additional heat emission or cold emission to the surrounding environment is basically avoided, thereby achieving energy saving and environmental protection.

[0018] (4) The cold and heat combined supply system based on NMP waste liquid purification can flexibly adjust the cold and heat used for the terminal cold / hot equipment, so as to ensure that the cold and heat generated by the cold and heat combined supply system are preferentially used for the NMP waste liquid purification device with real-time changes in the cold and heat demand, thereby improving the purification efficiency of the NMP waste liquid and ensuring the operation safety of the cascade cold and heat combined supply system.

[0019] (5) The control method of the application ensures that each compressor is in an open state during operation, so that each compressor can quickly respond to changes in load demand, improving the response rate and flexibility of the entire combined cooling and heating system.

[0020] (6) The control method of the application ensures that the load of each compressor is in a healthy state, which can improve the service 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.

[0021] (7) The control method of the application is based on cold energy, and the cold energy 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 cold energy 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 method of the application not only provides sufficient cold energy for the NMP waste liquid purification device, but also ensures that the cold energy that cannot be consumed by the NMP waste liquid purification device in time cannot make the first chilled water temperature T1 too low. Moreover, because the cold energy required by the NMP waste liquid purification device changes in real time, it is not feasible to know the cold energy demand first and then accurately adjust the cooling capacity of the combined cooling and heating system. In the control method of the application, the most creative aspect is to use the change of the first chilled water temperature T1 to measure the real-time change of the NMP waste liquid purification device cold energy demand, and to directly control the first chilled water temperature T1 between the first water temperature threshold T1' and the second water temperature threshold T1'', so as to ensure that the cold energy supplied to the NMP waste liquid purification device is sufficient and the combined cooling and heating system will not malfunction and shut down. Avoiding malfunction and shutdown also further prolongs the service life of the combined cooling and heating system.

[0022] (8) The control method of the application also meets the condition of reducing the load of each compressor to reduce the power consumption of the entire combined cooling and heating system under the condition that the load of each compressor is in a healthy state. Under these conditions, the excess cold energy is supplied to the end cooling equipment. That is, the control method of the application not only meets the real-time change of the cold energy demand of the NMP waste liquid purification device, improves the NMP waste liquid purification efficiency, and reduces the power consumption during system operation as much as possible; and by flexibly adjusting the measures, the heat / cold energy not used by the NMP waste liquid purification device is utilized (supplied to the end heat / cold equipment), which also greatly improves the service life of the entire combined cooling and heating system.

[0023] (9) The seven specific control modes in the control method of the present invention cover all situations that may occur in the entire combined cooling and heating system. Preventive dynamic adjustments are also made to the first chilled water temperature that dynamically fluctuates around the ideal temperature T* (i.e., T1´≤T1≤T1´´), further reducing the adverse effects of the hysteresis change of the first chilled water temperature on the "dynamic stabilization of the first chilled water temperature at the ideal temperature", and controlling the first chilled water temperature to the greatest extent possible within the range of the ideal first water temperature threshold T1´ and the second water temperature threshold T1´´. Preventive dynamic adjustments are also made to the first chilled water temperature that is 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 the cooling capacity at the next moment.

[0024] (10) The control method of the present invention can timely calculate the heat Q3 (i.e., the heat Q4 supplied to the current NMP waste liquid purification device) and the heat Q4 supplied to the terminal heat-using equipment HET in the combined cooling and heating system, while ensuring that the cooling capacity demand of the current NMP waste liquid purification device is met. This ensures that there will not be too much heat that is not used by the NMP waste liquid purification device accumulated in the combined cooling and heating system, further reducing the adverse effect of the hysteresis change of the first chilled water temperature on the "dynamic stabilization of the first chilled water temperature at the ideal temperature", so that the first chilled water temperature can more stably and dynamically fluctuate around the ideal temperature T*. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the overall structure of the combined cooling and heating system of the present invention. DETAILED DESCRIPTION

[0026] In order to make the technical solution of the present invention clearer and more specific, the present invention is clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Ordinary technicians in this field, without making any creative work, make equivalent substitutions for the technical features of the technical solution of the present invention and solutions derived from conventional reasoning all fall within the scope of protection of the present invention.

[0027] Example 1 like Figure 1 Figure 2 shows the overall structure of a combined cooling and heating system for NMP waste liquid purification according to the present invention, comprising 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 evaporating and then condensing the NMP waste liquid. The cascaded combined cooling and heating subsystem is used to simultaneously provide heat and cooling to the NMP waste liquid purification device for evaporation and condensation.

[0028] The NMP waste liquid purification device comprises one or more sets of evaporation-condensation tank sets in parallel. Each set of evaporation-condensation tank set comprises an evaporation tank ET and a condensation tank CT, the top of the evaporation tank ET and the top of the condensation tank CT are connected, and the bottom of the condensation tank CT is provided with an extraction port (not shown in the figure) for obtaining the purified liquid NMP after condensation. After absorbing heat, the NMP waste liquid in the evaporation tank ET forms NMP vapor at the top of the evaporation tank ET; under the influence of pressure difference, the NMP vapor automatically flows into the condensation tank CT; and the NMP vapor is condensed into liquid NMP in the condensation tank CT.

[0029] The NMP waste liquid purification device in the embodiment comprises only one set of evaporation-condensation tank set.

[0030] The cascade cold and heat 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 quantity at one end (cold quantity end) and heat at the other end (heat quantity end) through compression of refrigerant by a compressor. The cold supply module brings the cold quantity at the cold quantity end into circulating chilled water through heat exchange, and the chilled water exchanges heat when flowing through the condensation tank CT, bringing the heat in the condensation tank CT back and sending it into the cold quantity end. The heat supply module brings the heat at the heat quantity end into circulating condensing water through heat exchange, and the condensing water exchanges heat when flowing through the evaporation tank ET, bringing the cold quantity in the evaporation tank ET back and sending it into the heat quantity end.

[0031] The cold supply module comprises a chilled water pump PUMP1 and a heat exchanger H1. Each condensation tank CT is connected in parallel to the total water inlet pipe and the total water outlet pipe of the NMP waste liquid purification device through a chilled water branch pipe. The total water inlet pipe of the NMP waste liquid purification device provides chilled water for all condensation tanks CT, and the chilled water flowing out of all condensation tanks CT finally flows into the total water outlet pipe of the NMP waste liquid purification device. The total water inlet pipe of the NMP waste liquid purification device is arranged in the high-temperature side of the heat exchanger H1; the water inlet end of the chilled water pump PUMP1 is connected to the total water outlet pipe of the NMP waste liquid purification device, and the water outlet end of the chilled water pump PUMP1 is connected to the total water inlet pipe of the NMP waste liquid purification device.

[0032] Optionally, the cold supply module further comprises a chilled water flow meter F1 arranged on the total water outlet pipe of the NMP waste liquid purification device, for measuring the chilled water flow on the total water outlet pipe of the NMP waste liquid purification device.

[0033] The cascade cold water heat pump unit comprises 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 is provided with a first condensing pipeline and a first evaporating pipeline which are coupled to each other. The outlet end of the first compressor group COMP1 is connected to the first condensing inflow pipeline of the first cascade heat exchanger FH1, and the inlet end of the first compressor group COMP1 is connected to the first condensing outflow pipeline of the first cascade heat exchanger FH1. The first condensing outflow pipeline is provided in the low-temperature side of the heat exchanger H1. The second cascade heat exchanger FH2 is provided with a second condensing pipeline and a hot water pipeline which are coupled to each other. The outlet end of the second compressor group COMP2 is connected to the second condensing inflow pipeline of the second cascade heat exchanger FH2, and the inlet end of the second compressor group COMP2 is connected to the first evaporating outflow pipeline of the first cascade heat exchanger FH1. The second condensing outflow pipeline is connected to the first evaporating inflow pipeline.

[0034] The first condensing pipeline circulates the first refrigerant, and the second condensing pipeline and the first evaporating pipeline circulate the second refrigerant.

[0035] In the embodiment, the first refrigerant is R134a or R515B, and the second refrigerant is R245fa or R1233zd(E).

[0036] The first compressor group COMP1 and the second compressor group COMP2 each comprise one or more than one compressor connected in series, and the compressors in each compressor group are of the same type.

[0037] Optionally, the cascade cold water heat pump unit further comprises 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 arranged on the first condensing outflow pipeline, and the second storage tank TIN2 and the second electric valve MV2 are arranged on the second condensing outflow pipeline. The electric valves are used to control the circulation and flow rate of the refrigerant in the pipelines, and the first storage tank TIN1 and the second storage tank TIN2 are used to store the corresponding refrigerants.

[0038] The heat supply module comprises a flash tank TANK1, a hot water pump PUMP2, and a third compressor COMP3. The upper portion of the flash tank TANK1 is provided with a water inlet end, the bottom of the flash tank TANK1 is provided with a water outlet end and a water supplement port, and the top of the flash tank TANK1 is provided with a gas outlet. The upper portion of the evaporation tank ET is provided with a gas inlet, and the bottom of the evaporation tank ET is provided with a water outlet. The hot water outlet pipeline of the second cascade heat exchanger FH2 is connected with the water inlet end of the flash tank TANK1, and the hot water inlet pipeline of the second cascade heat exchanger FH2 is connected with the water outlet end of the flash tank TANK1. The hot water inlet pipeline of the second cascade heat exchanger FH2 is provided with the hot water pump PUMP2, and the gas outlet of the flash tank TANK1 is connected with the gas inlet end of the third compressor COMP3. The gas outlet end of the third compressor COMP3 is connected with the gas inlets of the evaporation tanks ET, and the water outlets of the evaporation tanks ET are connected with the water supplement ports of the flash tank TANK1.

[0039] Optionally, the heat supply module further comprises a three-way regulating valve TWV, a dew point sensor (not shown in the figure), and a terminal heat utilization device HET. The gas inlet end of the three-way regulating valve TWV is connected with the gas outlet of the third compressor COMP3, the first gas outlet end of the three-way regulating valve TWV is connected with the gas inlets of the evaporation tanks ET, and the second gas outlet end of the three-way regulating valve TWV is connected with the gas inlet of the terminal heat utilization device HET. The water outlet of the terminal heat utilization device HET is connected with the water supplement port of the flash tank TANK1. Each evaporation tank ET is provided with a dew point sensor, and the first gas outlet end of the three-way regulating valve TWV controls the water vapor flow entering the evaporation tank ET according to the dew point measured by the dew point sensor in the evaporation tank ET, and the rest of the water vapor is sent into the terminal heat utilization device HET.

[0040] The top of the flash tank TANK1 is provided with an exhaust valve EV, which is usually closed when the cascade heat and cold combined supply system is working. Only when the pressure difference between the water inlet end and the gas outlet of the flash tank TANK1 exceeds the pressure threshold, the exhaust valve EV opens to release pressure, so as to ensure the safety of the flash tank TANK1. When the cascade heat and cold combined supply system is not working, the exhaust valve EV is opened to communicate with the external environment, so as to ensure that the non-condensable gas in the flash tank TANK1 is discharged to the external environment, avoiding the blockage of the gas outlet of the flash tank TANK1.

[0041] In this embodiment, the pressure threshold of the pressure difference between the water inlet end and the gas outlet of the flash tank TANK1 is 100 kpa.

[0042] Optionally, the cold supply module further comprises a CET, a third electric valve MV3 and a fourth electric valve MV4. The inlet pipe of the CET is connected to the NMP waste liquid purification device total inlet pipe; the outlet pipe of the CET is connected to the NMP waste liquid purification device total outlet pipe; the third electric valve MV3 and the fourth electric valve MV4 are respectively arranged on the inlet pipe and the outlet pipe of the CET.

[0043] The HET and the CET can be devices in other links of the lithium ion battery manufacturing factory. For example, the coating oven and other process links of the lithium ion battery manufacturing factory also need high-temperature steam, and the high-temperature steam can be provided by the HET.

[0044] The working process of the cold and heat combined supply system based on NMP waste liquid purification in the embodiment is described as follows: When the cold and heat combined supply system based on NMP waste liquid purification starts to work, the exhaust valve EV is closed, and the first electric valve MV1 and the second electric valve MV2 are both opened. After starting to work, if the third electric valve MV3 and the fourth electric valve MV4 are both opened, the chilled water will not only flow through the condensers CT, but also flow through the CET, that is, the cold energy in the chilled water is used not only to supply cold to the condensers CT, but also to supply cold to the CET. The high-temperature chilled water flowing out of the condensers CT and the CET is collected in the NMP waste liquid purification device total outlet pipe, and the circulating power is provided by the chilled water pump PUMP1, the high-temperature chilled water is cooled by heat exchange in the high-temperature side of the heat exchanger H1 to become low-temperature chilled water, and then flows into the NMP waste liquid purification device total inlet pipe again.

[0045] The temperature range of the low-temperature chilled water is 5-10 degrees Celsius; in the embodiment, it is 7 degrees Celsius. The temperature range of the high-temperature chilled water is 15-20 degrees Celsius; in the embodiment, it is 15 degrees Celsius.

[0046] The low-temperature first refrigerant flows through the low-temperature side of the heat exchanger H1, is heated, and then flows into the first compressor group COMP1 to be compressed, heated and pressurized to become high-temperature first refrigerant, and then enters the first condensing pipe of the first cascade heat exchanger FH1, exchanges heat with the second refrigerant flowing through the first evaporating pipe of the first cascade heat exchanger FH1, is cooled to become low-temperature first refrigerant, and then flows out of the first cascade heat exchanger FH1, flows through the low-temperature side of the heat exchanger H1 again and continuously circulates.

[0047] In the embodiment, the temperature range of the low-temperature first refrigerant is 10-12 degrees Celsius; the temperature range of the high-temperature first refrigerant is 60-70 degrees Celsius.

[0048] The low-temperature second refrigerant flows through the first evaporation pipeline in the first cascade heat exchanger FH1, and then is heated. The low-temperature second refrigerant flows into the second compressor group COMP2, is compressed, and then is heated and pressurized to become high-temperature second refrigerant. The high-temperature second refrigerant enters the second condensation pipeline in the second cascade heat exchanger FH2, exchanges heat with the hot water flowing through the hot water pipeline in the second cascade heat exchanger FH2, and then is cooled to become low-temperature second refrigerant. The low-temperature second refrigerant flows out of the second cascade heat exchanger FH2, and then flows through the first evaporation pipeline in the first cascade heat exchanger FH1 again, and continuously circulates.

[0049] In the embodiment, the temperature range of the low-temperature second refrigerant is 60-65 degrees Celsius; and the temperature range of the high-temperature second refrigerant is 125-140 degrees Celsius.

[0050] The circulating power is provided by the hot water pump PUMP2. The low-temperature hot water at the bottom of the flash tank TANK1 flows through the hot water pipeline in the second cascade heat exchanger FH2, and then is heated to become high-temperature hot water. The high-temperature hot water enters the flash tank TANK1, is decompressed, and then part of the high-temperature hot water becomes water vapor and is located at the top of the flash tank TANK1, and part of the high-temperature hot water becomes low-temperature hot water and is stored at the bottom of the flash tank TANK1. The water vapor flows out of the top of the flash tank TANK1, enters the third compressor COMP3, is compressed, and then is heated to become high-temperature steam.

[0051] In the embodiment, the temperature of the low-temperature hot water is 105 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 temperature of the high-temperature hot water can be maintained at 120 degrees Celsius by pressure); and the temperature of the high-temperature steam is 130 degrees Celsius.

[0052] The three-way regulating valve TWV adjusts the valve opening degree of the first gas outlet and the second gas outlet according to the dew point measured by the dew point sensor in the evaporation tank ET, so that part of the high-temperature steam is used to heat the evaporation tank ET, and the other part of the high-temperature steam is used to heat the end-use heat equipment HET. After heating, the high-temperature steam is liquefied into condensed water, and then flows out of the water outlet of each evaporation tank ET and the water outlet of the end-use heat equipment HET, respectively. The condensed water enters the bottom of the flash tank TANK1 through the water supplement port of the flash tank TANK1, and becomes low-temperature hot water.

[0053] Compared with the separate refrigeration equipment and heating equipment in the prior art, the cold and heat combined supply system based on NMP waste liquid purification in the embodiment has a compact structure and a small footprint. In the cold and heat combined supply system, the electric energy used to power the compressor is converted into the cold and heat required by the NMP waste liquid purification device, thereby improving the electric energy utilization rate in the NMP waste liquid purification process and reducing the heating and cooling energy consumption and cost.

[0054] The cold-heat combined supply system based on NMP waste liquid purification of the embodiment can split a large total temperature difference into two sections through a condenser-evaporator, use the refrigerating capacity of a high-temperature stage to bear the condensing load of a low-temperature stage, and obtain a lower refrigerating temperature, so as to generate a cold end and a heat end with a huge temperature difference in a cold-heat combined supply system, and the difference between the first refrigerant and the second refrigerant is also to assist the cold-heat combined supply system of the embodiment to split the temperature difference.

[0055] The cold-heat combined supply system based on NMP waste liquid purification of the embodiment can supply cooling and heating after preferentially meeting the NMP waste liquid purification device, can send excess cold and heat to the end cold / hot equipment, and can recycle a small amount of energy remaining after being used by the NMP waste liquid purification device (and the end cold / hot equipment) to the cascade cold-heat combined supply system through circulating water, so that the cold and heat generated by the cold-heat combined supply system are efficiently utilized, and additional heat emission or cold emission to the surrounding environment is basically avoided, thereby achieving energy saving and environmental protection.

[0056] The cold-heat combined supply system based on NMP waste liquid purification of the embodiment can flexibly adjust the cold and heat for the end cold / hot equipment, so that the cold and heat generated by the cold-heat combined supply system is preferentially used to meet the real-time change of the cold and heat demand of the NMP waste liquid purification device, the purification efficiency of the NMP waste liquid is improved, and the operation safety of the cascade cold-heat combined supply system is ensured.

[0057] According to the verification of the technical personnel, compared with the refrigeration equipment and heating equipment separately set up for the NMP waste liquid purification process in the prior art, the cold-heat combined supply system based on NMP waste liquid purification of the embodiment reduces the occupied area by 50%, reduces the power consumption by 60%, and increases the purification efficiency of the NMP waste liquid by 100%.

[0058] Embodiment 2 When the cooling capacity of a cold-heat combined supply system based on NMP waste liquid purification is constant, the heating capacity of the cold-heat combined supply system is about 1.5-2 times the cooling capacity, which leads to that the heating capacity cannot be used for all the evaporation tanks ET, and the "cold load-based" requires the cold-heat combined supply system to preferentially meet the cooling capacity for the condensation tank CT. Because the yield of the NMP waste liquid is not fixed and is directly affected by the increase / decrease and start / stop of the production line, the cooling capacity required by all the condensation tanks CT in the NMP waste liquid purification device is not fixed, and even can be mutated (for example, a new tank of NMP waste liquid needs to be purified, or the purification of a tank of NMP waste liquid is just completed and no new NMP waste liquid needs to be purified).

[0059] Therefore, the cooling capacity of the combined cooling and heating system is generally greater than the total cooling capacity required by all condensers CT in the NMP waste liquid purification device. We need the combined cooling and heating system to respond to the changing cooling capacity in time. When the cooling capacity demand increases, the cooling capacity supplied increases. When the cooling capacity demand decreases, the cooling capacity supplied decreases or the excess cooling capacity is sent to the end-use cold equipment CET. Correspondingly, the excess heating capacity of the combined cooling and heating system is sent to the end-use hot equipment HET in time.

[0060] The embodiment provides a control method of a combined cooling and heating system based on NMP waste liquid purification based on cold load, which is used for controlling a combined cooling and heating system based on NMP waste liquid purification as described in Embodiment 1 based on cold load: S1, under the condition that the exhaust valve EV, the third electric valve MV3 and the fourth electric valve MV4 are all closed, starting a combined cooling and heating system based on NMP waste liquid purification, and adjusting the load of each compressor in the first compressor group COMP1 to an initial load P1.

[0061] S2, real-time monitoring of the load of each compressor in the first compressor group COMP1, the first chilled water temperature T1, the second chilled water temperature T2 and the third chilled water temperature T3; wherein the second chilled water temperature T2 is the water temperature of the chilled water in the NMP waste liquid purification device total water inlet pipe close to the NMP waste liquid purification device; the third chilled water T3 temperature is the water temperature of the chilled water in the NMP waste liquid purification device total water outlet pipe close to the NMP waste liquid purification device; the first chilled water T1 temperature refers to the heat exchanger H1 high temperature side outlet water temperature, which is also the water temperature of the chilled water in the NMP waste liquid purification device total water outlet pipe close to the heat exchanger H1 high temperature side.

[0062] S3, controlling the valve opening degree of the third electric valve MV3 and the fourth electric valve MV4 and the load of each compressor in the first compressor group COMP1 according to the first chilled water temperature T1, to ensure that the load of each compressor in the first compressor group COMP1 is above P0 and the first chilled water temperature 0

[0063] In this embodiment, T1´=5℃, T1´´=8℃; P0 is 50% of full load, and P1 is 53% of full load.

[0064] In S3, the following contents are included: If the current first chilled water temperature T1 > T1´´, then the third electric valve MV3 and the fourth electric valve MV4 are closed, and the load of each compressor in the first compressor group COMP1 is increased.

[0065] Because the cooling capacity required by the NMP waste liquid purification device is uncertain and may change suddenly, it is not practical to calculate the cooling capacity required at the current time and then control the combined cooling heating system to provide the corresponding cooling capacity.

[0066] We determine whether the current cooling capacity of the combined cooling heating system can meet the cooling capacity requirement of the NMP waste liquid purification device by monitoring the first chilled water temperature T1 in real time. We hope that the first chilled water temperature T1 can be kept as constant as possible at the ideal temperature T*, where T1´ ≤ T* ≤ T1´´, which means that the current cooling capacity of the combined cooling heating system can fully meet the cooling capacity requirement of the NMP waste liquid purification device. Therefore, when the current first chilled water temperature T1 > T1´´, we believe that the current cooling capacity provided by the combined cooling heating system cannot meet the cooling capacity requirement of the NMP waste liquid purification device, so we keep the fourth electric valve MV4 and the fourth stop valve SV closed regardless of whether the third electric valve MV3 and the fourth electric valve MV4 are open or not, and increase the load of each compressor in the first compressor group COMP1 to rapidly increase the cooling capacity of the combined cooling heating system.

[0067] In this embodiment, T* = 7℃.

[0068] If the current first chilled water temperature T1´ ≤ T1 ≤ T1´´, the first chilled water temperature T1 has been continuously decreasing in the previous △t time period, and the load of each compressor in the first compressor group COMP1 is greater than P1, then the load of each compressor in the first compressor group COMP1 is reduced.

[0069] If the current first chilled water temperature T1´ ≤ T1 ≤ T1´´, we believe that the current cooling capacity provided by the combined cooling heating system can basically meet the cooling capacity requirement of the NMP waste liquid purification device. However, on the one hand, the change of the first chilled water temperature T1 caused by the change of the cooling capacity requirement of the NMP waste liquid purification device is lagging; on the other hand, in order to respond to the cooling requirement in a timely manner, we need to ensure that each compressor in the first compressor group COMP1 is turned on; furthermore, we hope that the load of each turned-on compressor in the first compressor group COMP1 is maintained above P0, so that the compressor is in a healthy state, prolonging the service life of the compressor and the entire combined cooling heating system.

[0070] The health state load set by the technician for each open compressor in the first compressor group COMP1 is obtained after considering the health state of each compressor in the second compressor group COMP2 and the health state of the third compressor COMP3. Therefore, as long as each compressor in the first compressor group COMP1 is in a healthy state, the second compressor group COMP2 and the third compressor COMP3 are naturally in a healthy state.

[0071] It should be noted that if the first chilled water temperature T1 falls below 0 degrees Celsius, the chilled water in the NMP waste liquid purification device total outlet pipe near the high temperature side of the heat exchanger H1 will freeze, resulting in shutdown of the combined cooling heating system based on NMP waste liquid purification. When the load of each compressor in the first compressor group COMP1 is less than P0 for a long time, each compressor in the first compressor group COMP1 will also be damaged and shut down, resulting in shutdown of the combined cooling heating system.

[0072] Therefore, we combine the change trend of the first chilled water temperature T1 in the previous △t time period to make preventive adjustments: if the first chilled water temperature T1 continues to drop in the previous △t time period, in order to avoid the cooling capacity continuing to increase at the next moment, that is, to avoid the first chilled water temperature T1 continuing to drop or even rapidly drop to 0 degrees Celsius, we need to reduce the cooling capacity. However, considering that the load of each compressor in the first compressor group COMP1 is still above P1, we reduce the load of each compressor in the first compressor group COMP1, thereby saving the power consumption while reducing the cooling capacity.

[0073] ③ If the first chilled water temperature T1' ≤ T1 ≤ T1'', and the first chilled water temperature T1 continues to drop in the previous △t time, and the load of each compressor in the first compressor group COMP1 is less than P1, then the valve opening of the third electric valve MV3 and the fourth electric valve MV4 is increased.

[0074] We believe that the cooling capacity currently provided by the combined cooling heating system can basically meet the cooling capacity demand of the NMP waste liquid purification device, but the cooling capacity at the next moment may continue to increase to exceed the cooling capacity demand, that is, the cooling capacity that the NMP waste liquid purification device does not use is increased.

[0075] Because the load of each compressor in the first compressor group COMP1 has been less than P1 at this time, we reduce the load of each compressor in the first compressor group COMP1 again, which may cause the load of each compressor in the first compressor group COMP1 to be P0, that is, at the limit of the healthy state of the compressor, so our preventive adjustment is to increase the valve opening of the third electric valve MV3 and the fourth electric valve MV4 to send more cold energy that is not used by the NMP waste liquid purification device into the end cold equipment CET to avoid the subsequent first chilled water temperature T1 falling to 0 degrees Celsius.

[0076] ④If the current first chilled water temperature T1' ≤ T1 ≤ T1'', the first chilled water temperature T1 constantly rises in the previous △t time period, and the load of each compressor in the first compressor group COMP1 is above P1 at present, if the third electric valve MV3 and the fourth electric valve MV4 are both open, then reduce the valve opening of the third electric valve MV3 and the fourth electric valve MV4; if the third electric valve MV3 and the fourth electric valve MV4 are both closed, then increase the load of each compressor in the first compressor group COMP1.

[0077] We believe that the cold energy provided by the combined cooling and heating system at present can basically meet the cold energy demand of the NMP waste liquid purification device, but the cold energy demand may continue to increase at the next moment, so our preventive adjustment is to reduce the valve opening of the third electric valve MV3 and the fourth electric valve MV4 to reduce the cooling amount of the end cold equipment CET in the case that the end cold equipment CET has participated in cooling; in the case that the end cold equipment CET has not participated in cooling, we choose to increase the load of each compressor in the first compressor group COMP1 to increase the cooling capacity of the combined cooling and heating system at the next moment.

[0078] ⑤If the first chilled water temperature T1' ≤ T1 ≤ T1'', and the first chilled water temperature T1 constantly rises in the previous △t time, and the load of each compressor in the first compressor group COMP1 is less than P1 at present, then increase the load of each compressor in the first compressor group COMP1.

[0079] We believe that the cold energy provided by the combined cooling and heating system at present can basically meet the cold energy demand of the NMP waste liquid purification device, but the cold energy demand may continue to increase at the next moment, and considering that the load of each compressor in the first compressor group COMP1 is less than P1 at present, in order to ensure that the compressor is in a healthy state, our preventive adjustment is to increase the load of each compressor in the first compressor group COMP1.

[0080] If the current first chilled water temperature T1 < T1' and the load of each compressor in the current first compressor group COMP1 is greater than P1, then the load of each compressor in the current first compressor group COMP1 is reduced.

[0081] Regardless of whether the end cold-using equipment CET participates in cold-using, we believe that the cold energy currently provided by the combined cooling and heating system has far exceeded the cold energy demand of the NMP waste liquid purification device, and the load of each compressor in the current first compressor group COMP1 is greater than P1, which is a healthy state. Therefore, we reduce the cold energy provided by the combined cooling and heating system by reducing the load of each compressor in the current first compressor group COMP1 to avoid the first chilled water temperature from falling below 0°C.

[0082] 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 the valve opening of the third electric valve MV3 and the fourth electric valve MV4 is increased.

[0083] Based on the analysis of ⑥, in order to avoid the first chilled water temperature from falling below 0°C and to ensure the health status 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 cold energy that is not used by the NMP waste liquid purification device to the end cold-using equipment CET.

[0084] In S3, the first heat Q3 and the second heat Q4 are calculated using the following formula: Q1 = C x f1 x (T3 - T2); EX = Q1 / n / W; Q2 = (1+COP) / (COP-1); Q3 = Q1; Q4 = Q2-Q3; wherein Q1 represents the cold energy demand of the current NMP waste liquid purification device, unit: kW; C represents the specific heat capacity of water, which is 4.18 kJ / (kg·℃); f1 represents the chilled water flow rate measured by the chilled water flow meter F1, unit: kg / s; EX represents the expected operating capacity percentage of a single compressor in the first compressor group COMP1; n represents the number of compressors in the first compressor group COMP1; W represents the rated refrigerating capacity of the compressors in the first compressor group COMP1; Q2 represents the corresponding heating capacity of the cascade cold water heat pump unit under the condition that the refrigerating capacity is Q1; COP represents the energy efficiency coefficient of the cascade cold water heat pump unit, which is measured by each manufacturer, and the value is usually 2-3; the first heat Q3 also represents the heat demand of the current NMP waste liquid purification device; and the second heat Q4 also represents the heat supplied to the end heat-using equipment HET.

[0085] Optionally, in order to ensure the safe operation of the third compressor COMP3, when the outlet temperature of the third compressor COMP3 exceeds a set threshold, the third compressor COMP3 is shut down.

[0086] In this embodiment, the set threshold value of the outlet temperature of the third compressor COMP3 is 132 degrees Celsius.

[0087] Turning on a shut-down compressor and then adjusting its load to the required value takes far longer than simply adjusting an already-started compressor to the required load. The control method of this embodiment ensures that each compressor is always on during operation, allowing each compressor to quickly respond to changing load demands, thereby improving the response rate and adjustment flexibility of the entire combined cooling and heating system.

[0088] The control method of this embodiment ensures that the load of each compressor is in a healthy state, thereby increasing the life of the compressor and the entire combined heating and cooling system and reducing the operation and maintenance cost of the combined heating and cooling system.

[0089] The control method of this embodiment is based on cooling capacity, and the cooling capacity required by the NMP waste liquid purification device changes in real time. This change causes the first chilled water temperature T1 to change with hysteresis. If cooling capacity that cannot be consumed promptly by the NMP waste liquid purification device remains 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 method of this embodiment, while providing sufficient cooling capacity for the NMP waste liquid purification device, also needs to ensure that the cooling capacity that cannot be consumed promptly by the NMP waste liquid purification device 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 first determine the cooling capacity demand and then precisely adjust the cooling capacity of the combined cooling and heating system. The control method of this embodiment is highly innovative in that it uses changes in the first chilled water temperature T1 to measure the real-time 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'', sufficient cooling capacity is ensured for the NMP waste liquid purification device and the combined cooling and heating system is prevented from shutting down due to failures. Avoiding shutdowns further extends the life of the combined cooling and heating system.

[0090] Under the guidance of the control method mentioned above, the control method of this embodiment also meets the requirement of reducing the load of each compressor to reduce the power consumption of the entire combined heating and cooling system while ensuring that the load of each compressor is in a healthy state; when these prerequisites are met, the excess cooling capacity is supplied to the terminal cooling equipment.

[0091] That is, the control method of the embodiment not only can meet the real-time change of the cold demand of the NMP waste liquid purification device in time, improve the NMP waste liquid purification efficiency, and reduce the power consumption in the system operation process as much as possible; and through flexible adjustment measures, the heat / cold not used by the NMP waste liquid purification device is utilized (supplied to the end heat / cold equipment), which also greatly improves the service life of the whole cold-heat combined supply system.

[0092] The seven specific control modes in the control method of the embodiment cover all situations that may occur in the whole cold-heat combined supply system, and the first chilled water temperature dynamically fluctuating around the ideal temperature T* (i.e., T1´≤T1≤T1´´) is also prevented from dynamic adjustment, which further reduces the adverse effects of the lagging change of the first chilled water temperature on the dynamic stabilization of the first chilled water temperature at the ideal temperature, and maximizes the control of the first chilled water temperature within the ideal first water temperature threshold T1´ and the second water temperature threshold T1´´. The first chilled water temperature within the first water temperature threshold T1´ and the second water temperature threshold T1´´ is also prevented from dynamic adjustment, which further improves the response speed of the whole cold-heat combined supply system to the cooling capacity change at the next moment.

[0093] The control method of the embodiment can calculate the heat Q3 (i.e., supplied to all the evaporation tanks ET) and the heat Q4 supplied to the end heat equipment HET in the cold-heat combined supply system for the current NMP waste liquid purification device in time while ensuring that the current NMP waste liquid purification device cold demand is met, which ensures that there is no excessive heat not used by the NMP waste liquid purification device accumulated in the cold-heat combined supply system, further reduces the adverse effects of the lagging change of the first chilled water temperature on the dynamic stabilization of the first chilled water temperature at the ideal temperature, and makes the first chilled water temperature more stably fluctuate around the ideal temperature T*.

[0094] According to the verification of the technical personnel, the control method of the embodiment reduces the power consumption of the whole cold-heat combined supply system by 70% compared with the prior art, increases the NMP waste liquid purification efficiency by 120%, and reduces the operation and maintenance cost by 70%.

[0095] The technologies, shapes and configurations not described in detail in the present application are all known technologies. It should be pointed out that the above is only a preferred embodiment of the present application, and is not used to limit the present application. The components or steps in the embodiment of the present application can be decomposed and / or recombined, which should be regarded as equivalent solutions of the present application, and should fall within the protection scope of the present application.

Claims

1. A method for controlling a combined cooling and heating system for NMP waste liquid purification based on cooling load, characterized in that: A combined cooling and heating system based on NMP waste liquid purification is used, comprising a cascade chiller heat pump unit, a heating module, a cooling module, and an NMP waste liquid purification device; the cascade chiller heat pump unit comprises a first compressor group COMP1 and a first cascade heat exchanger FH1; the cooling module comprises a heat exchanger H1; the heating module comprises a terminal heat-using device HET; the first compressor group COMP1 is provided on the low-temperature side pipeline of the heat exchanger H1, and the low-temperature side pipeline of the heat exchanger H1 is passed through the first cascade heat exchanger FH1; the first cascade heat exchanger FH1 is used to transfer heat generated by the work of the first compressor group COMP1 and heat on the low-temperature side of the heat exchanger H1 to the NMP waste liquid purification device and the terminal heat-using device HET; the high-temperature side of the heat exchanger H1 is used to provide cooling for the NMP waste liquid purification device; and a control method comprises the following steps: Step 1: After starting a combined cooling and heating system based on NMP waste liquid purification, the load of each compressor in the first compressor group COMP1 is adjusted to an initial load P1; Step 2: Monitor and adjust the load of each compressor in the first compressor group COMP1 and the heat supply to the terminal heat-consuming equipment HET in real time, so that the heat supply to the NMP waste liquid purification device is equal to the cooling capacity, the load of each compressor in the first compressor group COMP1 is above the critical load P0, and the outlet water temperature on the high-temperature side of the heat exchanger H1 is within the set threshold range; where P0 < P1.

2. A method for controlling a cold load-based NMP waste liquid purification cold and heat combined supply system according to claim 1, characterized in that: The NMP waste liquid purification device includes one or more evaporation tanks ET and condensation tanks CT; the cascade chiller heat pump unit also includes a second compressor group COMP2 and a second cascade heat exchanger FH2; the low-temperature side pipeline of the heat exchanger H1 arranged in the first cascade heat exchanger FH1 is recorded as the first condensation pipeline, and the first cascade heat exchanger FH1 is provided with a first condensation pipeline and a first evaporation pipeline coupled to each other; the second cascade heat exchanger FH2 is provided with a second condensation pipeline and a hot water pipeline coupled to each other, and the second condensation pipeline is connected to the first evaporation pipeline; the first compressor group COMP1 is provided at the inlet of the first condensation pipeline of the first cascade heat exchanger FH1, and the second compressor group COMP2 is provided at the inlet of the second condensation pipeline of the second cascade heat exchanger FH2. At the inlet of the condensation pipeline; the heating module also includes a flash tank TANK1, a hot water pump PUMP2, a third compressor COMP3 and a three-way regulating valve TWV; a flash tank TANK1 and a hot water pump PUMP2 are provided on the hot water pipeline, and the top air outlet of the flash tank TANK1 is connected to the air inlet end of the third compressor COMP3; the air outlet end of the third compressor COMP3 is connected to the air inlet end of the three-way regulating valve TWV, the first air outlet end of the three-way regulating valve TWV is connected to the air inlet of each evaporation tank ET, and the second air outlet end of the three-way regulating valve TWV is connected to the air inlet of the terminal heat equipment HET; the water outlet of the terminal heat equipment HET and the water outlet of each evaporation tank ET are both connected to the water supply port of the flash tank TANK1.

3. A method for controlling a cold load-based NMP waste liquid purification cold and heat combined supply system according to claim 2, characterized in that: The cooling module includes a chilled water pump PUMP1; each condensing tank CT is connected in parallel to the main water inlet pipe and the main water outlet pipe of the NMP waste liquid purification device through its own chilled water branch pipe. The main water inlet pipe of the NMP waste liquid purification device is arranged on the high-temperature side of the heat exchanger H1. The water inlet and water outlet ends of the chilled water pump PUMP1 are respectively connected to the main water outlet pipe and the main water inlet pipe of the NMP waste liquid purification device; the chilled water flowing into the main water inlet pipe of the NMP waste liquid purification device cools the high-temperature side of the heat exchanger H1 after heat exchange and brings the cold energy into the condensing tank CT, and the chilled water flowing out of the main water outlet pipe of the NMP waste liquid purification device brings the heat in the condensing tank CT into the high-temperature side of the heat exchanger H1.

4. A method for controlling a cold load-based NMP waste liquid purification cold and heat combined supply system according to claim 3, characterized in that: The cooling module also includes a terminal cooling device CET, a third electric valve MV3 and a fourth electric valve MV4; the water inlet pipe and the water outlet pipe of the terminal cooling device CET are respectively connected to the main water inlet pipe and the main water outlet pipe of the NMP waste liquid purification device, and the third electric valve MV3 and the fourth electric valve MV4 are respectively provided on the water inlet pipe and the water outlet pipe of the terminal cooling device CET.

5. A method for controlling a cold load-based NMP waste liquid purification cold and heat combined supply system according to claim 3, characterized in that: After flowing out from the first outlet port of the three-way regulating valve TWV, the water vapor enters each evaporator ET, releases heat, and then condenses into condensed water, which then flows out from the water outlet of the evaporator ET. 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 is cooled in the condenser CT and condensed into liquid NMP.

6. A method for controlling a cold load-based NMP waste liquid purification cold and heat supply system according to claim 4, characterized in that: Step 2 also includes the following: S2 and S3: S2, real-time monitoring of the load of each compressor in the first compressor group COMP1, the first chilled water temperature T1, the second chilled water temperature T2 and the third chilled water temperature T3; Among them, the first chilled water temperature T1 refers to the outlet water temperature on the high-temperature side of the heat exchanger H1; the second chilled water temperature T2 refers to the temperature of the chilled water in the total water inlet pipe of the NMP waste liquid purification device close to the NMP waste liquid purification device; the third chilled water temperature T3 refers to the temperature of the chilled water in the total water outlet pipe of the NMP waste liquid purification device close to the NMP waste liquid purification device; S3, controlling the valve openings of the third electric valve MV3, the fourth electric valve MV4, and the outlet ends of the three-way regulating valve TWV, as well as the load of each compressor in the first compressor group COMP1, based on the first chilled water temperature T1, so that the heating and cooling capacities supplied to the NMP waste liquid purification device are equal, the load of each compressor in the first compressor group COMP1 is above the critical load P0, and the first chilled water temperature 0<T1´≤T1≤T1´; wherein T1´ represents the first water temperature threshold, and T1´´ represents the second water temperature threshold.

7. A method for controlling a cold load-based NMP waste liquid purification cold and heat supply system according to claim 6, characterized in that: S3 also includes the following: if the current first chilled water temperature T1>T1'', 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.

8. A method for controlling a cold load-based NMP waste liquid purification cold and heat supply system according to claim 6, characterized in that: S3 also includes the following: if the current first chilled water temperature T1´≤T1≤T1´´, the first chilled water temperature T1 has been decreasing during the previous Δt period, and the load of each compressor in the current first compressor group COMP1 is greater than P1, then reducing the load of each compressor in the current first compressor group COMP1; If the first chilled water temperature T1´≤T1≤T1´´, and the first chilled water temperature T1 continues to decrease within the previous △t period, and the load of each compressor in the first compressor group COMP1 is less than P1, the valve openings of the third electric valve MV3 and the fourth electric valve MV4 are increased; If the current first chilled water temperature T1´≤T1≤T1´´, the first chilled water temperature T1 has been rising in the previous △t period, and the load of each compressor in the current first compressor group COMP1 is greater than P1, if the third electric valve MV3 and the fourth electric valve MV4 are both open, the valve openings of the third electric valve MV3 and the fourth electric valve MV4 are reduced; if the third electric valve MV3 and the fourth electric valve MV4 are both closed, the load of each compressor in the first compressor group COMP1 is increased; If the first chilled water temperature T1´≤T1≤T1´´, and the first chilled water temperature T1 continues to rise within the previous △t time, 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.

9. A method for controlling a cold load-based NMP waste liquid purification cold and heat supply system according to claim 6, characterized in that: S3 also 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 reducing the load of each compressor in the current first compressor group COMP1; If the current first chilled water temperature T1<T1', and the current load of each compressor in the first compressor group COMP1 is less than P1, the valve openings of the third electric valve MV3 and the fourth electric valve MV4 are increased.

10. The method for controlling a cold load-based NMP waste liquid purification cold and heat supply system according to claim 6, wherein: In S3, the heating and cooling capacities supplied to the NMP waste liquid purification device are equal, and the following contents are also included: Adjust the valve opening of each outlet of the three-way regulating valve TWV so that the heat supplied from the first outlet to the evaporator ET in the NMP waste liquid purification device is the first heat Q3, and the heat supplied from the second outlet to the terminal heat device HET is the second heat Q4; The first heat quantity Q3 and the second heat quantity Q4 are calculated using the following formula: Q1=C×f1×(T3-T2); EX=Q1 / n / W; Q2=(1+COP) / (COP-1); Q3=Q1; Q4=Q2-Q3; Wherein, Q1 represents the current cooling demand of the NMP waste liquid purification device; C represents the specific heat capacity of water; f1 represents the chilled water flow rate in the main outlet pipe or the main inlet pipe of the NMP waste liquid purification device; EX represents the expected operating capacity percentage of a single compressor in the first compressor group COMP1; n represents the number of compressors in the first compressor group COMP1; W represents the rated cooling capacity of the compressors in the first compressor group COMP1; Q2 represents the heating capacity of the cascade chiller heat pump unit under the condition of cooling capacity Q1; COP represents the coefficient of energy efficiency of the cascade chiller heat pump unit.

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