NMP waste liquid purification cold and heat combined supply system and control method based on heat load

Abstract

The invention belongs to the technical field of heat pump systems, and particularly relates to an NMP waste liquid purification cold and heat combined supply system and a control method based on heat loads. In the system, an NMP waste liquid purification device comprises an evaporation tank and a condensation tank; the cascade type cold water heat pump unit comprises a cooling capacity end and a heat end. The cold supply module brings cold energy of the cold energy end into circulating chilled water through heat exchange, the chilled water is subjected to heat exchange when flowing through the condensation tank, and heat in the condensation tank is brought back and sent to the cold energy end. The heat supply module brings heat of the heat end into circulating condensate water through heat exchange, the condensate water is subjected to heat exchange when flowing through the evaporation tank, and cold in the evaporation tank is brought back and sent to the heat end. After the waste liquid in the evaporation tank absorbs heat, NMP steam is formed at the top of the evaporation tank and then flows into a condensation tank, and the NMP steam is condensed into liquid NMP in the condensation tank; the cold supply module further comprises a supercooling protection unit. 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 an NMP waste liquid purification cold-heat combined supply system and a control method based on heat 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 recycled and 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 low-temperature cold water provided by a refrigeration device for condensation to finally obtain pure liquid NMP.

[0004] The prior art 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 need to supply heat and cold respectively, and the structure of the separate heat supply system and cold supply system is complex, occupies a large area, and the energy consumption of the heat supply system and cold supply 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 heat supply system and the cold supply system so that they can timely meet the cooling capacity and heat required in the NMP waste liquid purification process, and at the same time, minimize the electric energy consumption, has become a difficult problem to be solved. SUMMARY

[0005] The purpose of the application is to overcome the shortcomings of the prior art, and provide an NMP waste liquid purification cold-heat combined supply system which can efficiently supply heat and cold for the NMP waste liquid purification process while minimizing electric energy consumption.

[0006] To achieve the above purpose, the application adopts the following technical solutions: The application discloses a NMP waste liquid purification cold-heat combined system, which comprises a cascade cold-heat combined subsystem and a NMP waste liquid purification device, wherein the NMP waste liquid purification device comprises one or more sets of evaporation-condensation tank sets in parallel, each set of evaporation-condensation tank sets comprises one evaporation tank and one condensation tank; the cascade cold-heat combined 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 end and generates heat at a heat end; the cold supply module brings the cold energy at the cold end into circulating chilled water through heat exchange, and the chilled water exchanges heat when flowing through the condensation tank, so that the heat in the condensation tank is brought back and sent to the cold end; the heat supply module brings the heat at the heat end into circulating condensation water through heat exchange, and the condensation water exchanges heat when flowing through the evaporation tank, so that the cold energy in the evaporation tank is brought back and sent to the heat end; after absorbing heat, NMP waste liquid in the evaporation tank forms NMP vapor at the top of the evaporation tank and then flows into the condensation tank, and the NMP vapor is condensed into liquid NMP in the condensation tank; the cold supply module further comprises a supercooling protection unit, which brings part of the heat in the heat supply module into the chilled water.

[0007] Preferably, the cold supply module comprises a chilled water pump and a heat exchanger; each condensation tank is connected in parallel to a total water inlet pipe and a total water outlet pipe of the NMP waste liquid purification device through a chilled water branch pipeline; the total water inlet pipe of the NMP waste liquid purification device is arranged on the high-temperature side of the heat exchanger; the water inlet end of the chilled water pump 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 is connected to the total water inlet pipe of the NMP waste liquid purification device.

[0008] Preferably, the cascade cold water heat pump unit comprises a first compressor group, a second compressor group, a first cascade heat exchanger and a second cascade heat exchanger; the first cascade heat exchanger is provided with a first condensation pipeline and a first evaporation pipeline which are coupled to each other; the outlet end of the first compressor group is connected to the first condensation inflow pipeline; the inlet end of the first compressor group is connected to the first condensation outflow pipeline; the first condensation outflow pipeline is arranged on the low-temperature side of the heat exchanger; the second cascade heat exchanger is provided with a second condensation pipeline and a hot water pipeline which are coupled to each other; the outlet end of the second compressor group is connected to the second condensation inflow pipeline; the inlet end of the second compressor group is connected to the first evaporation outflow pipeline; the second condensation outflow pipeline is connected to the first evaporation inflow pipeline.

[0009] Preferably, the heat supply module comprises a flash tank, a hot water pump and a third compressor; the upper part of the flash tank is provided with a water inlet end, the bottom of the flash tank is provided with a water outlet end and a water supplement port, and the top of the flash tank is provided with a gas outlet; the upper part of the evaporation tank is provided with an air inlet, and the bottom of the evaporation tank is provided with a water outlet; the hot water outlet pipeline is connected with the water inlet end of the flash tank, and the hot water inlet pipeline is connected with the water outlet end of the flash tank; the hot water inlet pipeline is provided with a hot water pump; the gas outlet of the flash tank is connected with the air inlet end of the third compressor; the air outlet end of the third compressor is connected with the air inlets of the evaporation tanks, and the water outlets of the evaporation tanks are connected with the water supplement port of the flash tank.

[0010] Preferably, the heat supply module further comprises a first three-way regulating valve and an end heat utilization device; the air inlet end of the first three-way regulating valve is connected with the gas outlet of the third compressor, the first air outlet end of the first three-way regulating valve is connected with the air inlets of the evaporation tanks, and the second air outlet end of the first three-way regulating valve is connected with the air inlet of the end heat utilization device; the water outlet of the end heat utilization device is connected with the water supplement port of the flash tank.

[0011] Preferably, the heat supply module further comprises a condensate recovery tank and a condensate recovery pump; the water outlets of the end heat utilization device and all the evaporation tanks are connected with the water inlet of the condensate recovery tank, and the water outlet of the condensate recovery tank is connected with the water supplement port of the flash tank; the condensate recovery pump is arranged on the pipeline between the water outlet of the condensate recovery tank and the water supplement port of the flash tank.

[0012] Preferably, the cooling module further comprises an additional cold source and a cold water supplement pump; the branch water pipe of the additional cold source is connected in parallel with the total water inlet pipe and the total water outlet pipe of the NMP waste liquid purification device; the cold water supplement pump is arranged on the branch water pipe of the additional cold source; the supercooling protection unit comprises a temperature rising water pump and a second heat exchanger; the total water outlet pipe of the waste liquid purification device at the water inlet end of the chilled water pump is arranged through the low temperature side of the second heat exchanger; the hot water outlet pipeline of the second cascade heat exchanger is connected with the water inlet pipeline arranged through the high temperature side of the second heat exchanger; the water inlet end of the flash tank is connected with the water outlet pipeline arranged through the high temperature side of the second heat exchanger; and the high temperature side water outlet pipeline of the second heat exchanger is provided with a temperature rising water pump.

[0013] The application also provides a control method based on heat load, which is used for controlling the NMP waste liquid purification cold and heat combined supply system as described above, and comprises the following steps: S1, closing the exhaust valve, starting the cold and heat combined supply system based on NMP waste liquid purification, and adjusting the load of each compressor in the first compressor group to the initial load P1; S2, real-time monitoring the load of each compressor in the first compressor group, the first chilled water temperature T1, the second high-temperature steam temperature T2, the third condensate water temperature T3 and the high-temperature hot water temperature T4; by adjusting the load of each compressor in the first compressor group, the valve opening degree of the outlet of the first three-way regulating valve and the power of the cold water pump, the load of each compressor in the first compressor group is in a healthy state, the first chilled water temperature T1 fluctuates within a first ideal temperature interval, and the high-temperature hot water temperature fluctuates within a second ideal temperature interval; Wherein, the second high-temperature steam temperature T2 is the high-temperature steam temperature at the outlet of the third compressor; the third condensate water temperature T3 is the condensate water temperature at the outlet of the evaporating tank; the first chilled water temperature T1 is the water temperature of the chilled water in the total outlet water pipe of the NMP waste liquid purification device close to the high-temperature side of the first heat exchanger; the high-temperature hot water temperature T4 is the temperature of the high-temperature hot water at the inlet of the flash tank; the healthy state means that the load of the compressor is above the critical load P0, 0

[0014] Preferably, in S2, the following is included: if the current high-temperature hot water temperature T4 < T4, then close the second gas outlet end of the first three-way regulating valve and increase the load of each compressor in the first compressor group; if the current high-temperature hot water temperature T4 '≤ T4≤ T4, the high-temperature hot water temperature T4 continuously rises in the previous △t time period, and the load of each compressor in the current first compressor group is all above P1, then reduce the load of each compressor in the current first compressor group; if the current high-temperature hot water temperature T4 '≤ T4≤ T4, and the high-temperature hot water temperature T4 continuously rises in the previous △t time, and the load of each compressor in the current first compressor group is all less than P1, then increase the valve opening of the second gas outlet end of the first three-way regulating valve; if the current high-temperature hot water temperature T4 '≤ T4≤ T4, the high-temperature hot water temperature T4 continuously falls in the previous △t time period, and the load of each compressor in the current first compressor group is all above P1, if the valve of the second gas outlet end of the first three-way regulating valve is opened, then reduce the valve opening of the second gas outlet end of the first three-way regulating valve; if the valve of the second gas outlet end of the first three-way regulating valve is closed, then increase the load of each compressor in the first compressor group; if the current high-temperature hot water temperature T4 '≤ T4≤ T4, and the first chilled water temperature T1 continuously falls in the previous △t time, and the load of each compressor in the current first compressor group is all less than P1, then increase the load of each compressor in the first compressor group; if the current high-temperature hot water temperature T4 > T4, and the load of each compressor in the current first compressor group is all above P1, then reduce the load of each compressor in the current first compressor group; if the current high-temperature hot water temperature T4 > T4, and the load of each compressor in the current first compressor group is all less than P1, then increase the valve opening of the second gas outlet end of the first three-way regulating valve.

[0015] Preferably, in S2, the following is included: adjust the power of the cold water pump to make the additional cold source pass through the water supply flow rate q to add the additional cold quantity Q4 into the current cooling module: Q1=[C×(T2-T3)+(h1-h2)]×ρ×f2; Q2=[(COP-1) / (1+COP)]×Q1; Q3=Q1; Q4=Q3-Q2; q=Q4 / (C×△T); Wherein, Q1 represents the heat demand of the current NMP waste liquid purification device; C represents the specific heat capacity of water; f2 represents the current high-temperature steam flow entering all evaporation tanks; h1 represents the specific enthalpy of water vapor at the current T2 temperature; h2 represents the specific enthalpy of saturated water at the current T2 temperature; Q2 represents the corresponding refrigerating capacity of the cascade cold water heat pump unit under the condition that the heating capacity is Q1; COP represents the energy efficiency coefficient of the cascade cold water heat pump unit; the first heat Q3 represents the cold demand of the current NMP waste liquid purification device; △T represents the temperature difference of the inlet and outlet water of the additional cold source ECS; when the water supply flow rate q=0, the current high-temperature hot water temperature T4>T4''' and the valve opening degree of the first gas outlet end of the first three-way regulating valve is maximum, if the first chilled water T1

[0016] The beneficial effects of the present application are: (1) Compared with the separate refrigeration equipment and heating equipment in the prior art, the NMP waste liquid purification cold and heat combined supply system has a compact structure and small footprint, and the electric energy used for power supply of the compressor 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.

[0017] (2) The NMP waste liquid purification cold and heat combined supply system can divide a larger total temperature difference into two sections through a condensation evaporator, use the high-temperature refrigeration capacity to bear the condensation load of the low-temperature level, and obtain a lower refrigeration temperature, so as to generate a cold end and a heat end with a huge temperature difference in a cold and heat combined supply system.

[0018] (3) The NMP waste liquid purification cold and heat combined supply system can send the excess heat into the end heat equipment after the cold and heat supply of the NMP waste liquid purification device is preferentially met, the cold capacity lacking in the NMP waste liquid purification device is provided by the additional cold source, and a small amount of energy remaining after the NMP waste liquid purification device and the end heat equipment are used is recovered to the cascade cold and heat combined supply system through the circulating water (i.e. condensation water and high-temperature chilled water) again, so that the cold and heat generated by the consumed electric energy (for power supply of the compressor) of the entire cold and heat combined supply system is efficiently utilized, and additional heat emission or cold emission to the surrounding environment is basically avoided, thereby achieving energy saving and environmental protection.

[0019] (4) The cold-heat combined supply system based on NMP waste liquid purification can flexibly adjust the heat for the end heat-using equipment, so that the generated heat of the cold-heat combined supply system is preferentially used to meet the real-time change of the heat demand of the NMP waste liquid purification device, the additional cold provided by the additional cold source is only used to meet the real-time change of the cold change 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.

[0020] (5) The control method based on heat load of the application can ensure that each compressor is in an open state during operation, so that each compressor can quickly respond to the change demand of the load, and the response rate and the flexibility of adjustment of the entire cold-heat combined supply system are improved.

[0021] (6) The control method of the application ensures that the load of each compressor is in a healthy state, so that the service life of the compressor and the entire cold-heat combined supply system is improved, and the operation and maintenance cost of the cold-heat combined supply system is reduced.

[0022] (7) The control method of the application is based on heat, and the heat required by the NMP waste liquid purification device is real-time changeable, which will cause a lag change in the high-temperature hot water temperature T4; if the heat that cannot be consumed by the NMP waste liquid purification device in time exists in the cold-heat combined supply system, the high-temperature hot water temperature T4 will be too high to cause the cold-heat combined supply system to stop working; therefore, the control method of the application needs to ensure that the heat that cannot be consumed by the NMP waste liquid purification device in time cannot make the high-temperature hot water temperature T4 too high while providing enough heat for the NMP waste liquid purification device. Moreover, because the heat required by the NMP waste liquid purification device is real-time changeable, it is not feasible to know the heat demand first and then accurately adjust the heat supply of the cold-heat combined supply system. In the control method of the application, the most creative part is to use the change of the high-temperature hot water temperature T4 to measure the real-time change of the heat demand of the NMP waste liquid purification device, and to directly control the high-temperature hot water temperature T4 in the second ideal temperature range, so as to ensure that the heat supplied to the NMP waste liquid purification device is sufficient and the cold-heat combined supply system will not stop working. Avoiding the stop working also further prolongs the service life of the cold-heat combined supply system.

[0023] (8) The control method of the present application also meets the condition that the load of each compressor is in a healthy state, and preferentially reduces the load of each compressor to reduce the power consumption of the entire combined cooling and heating system; under the premise of meeting these conditions, the excess heat is supplied to the end heat using equipment. That is, the control method of the present application not only can meet the real-time heat demand of the NMP waste liquid purification device, 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 unused heat of the NMP waste liquid purification device is utilized (supplied to the end heat using equipment), which also greatly improves the service life of the entire combined cooling and heating system.

[0024] (9) In the control method of the present application, all situations that may occur in the entire combined cooling and heating system are covered, and preventive dynamic adjustment is also made for the high-temperature hot water temperature T4 that dynamically fluctuates in the second ideal temperature range, further reducing the adverse effects of the lagging change of the high-temperature hot water temperature T4 on the "stabilization of the high-temperature hot water temperature in the second ideal temperature range", and maximizing the control of the high-temperature hot water temperature in the second ideal temperature range. Preventive dynamic adjustment is also made for the high-temperature hot water temperature that is already in the second ideal temperature range, which further improves the response speed of the entire combined cooling and heating system to the heat supply change at the next moment.

[0025] (10) The control method of the present application can calculate the heat Q1 supplied to the current NMP waste liquid purification device (i.e. supplied to all evaporation tanks) and the required additional cold Q4 in the combined cooling and heating system in a timely manner while ensuring that the current NMP waste liquid purification device heat demand is met, ensuring that the supply amount of the additional cold Q4 can meet the demand of the NMP waste liquid purification device, and further reducing the adverse effects of the lagging change of the high-temperature hot water temperature T4 on the "dynamic stabilization of the high-temperature hot water temperature T4 in the second ideal temperature range" and the "dynamic stabilization of the first chilled water temperature T1 in the first ideal temperature range". BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is a schematic diagram of the overall structure of a NMP waste liquid purification combined cooling and heating system of the present application. DETAILED DESCRIPTION

[0027] In order to make the technical solutions of the present application clearer and more explicit, the present application will be described in detail below with reference to the drawings. Obviously, the described embodiments are only part of the embodiments of the present application, not all embodiments. Those skilled in the art can make equivalent substitutions and common inferences to the technical features of the technical solutions of the present application without creative labor, and the solutions fall within the protection scope of the present application.

[0028] Example 1 AsFigure 1 As shown, it is a whole structure schematic diagram of the NMP waste liquid purification cold-heat combined system, including a cascade cold-heat combined subsystem and an NMP waste liquid purification device. The NMP waste liquid purification device is used to purify NMP (N-methyl pyrrolidone) from NMP waste liquid by evaporating and then condensing the NMP waste liquid. The cascade cold-heat combined subsystem is used to provide heat and cold to the NMP waste liquid purification device to evaporate and condense.

[0029] The NMP waste liquid purification device contains one or more sets of evaporating-condensing tank sets in parallel. Each set of evaporating-condensing tank set contains one evaporating tank ET and one condensing tank CT, and the top of the evaporating tank ET and the top of the condensing tank CT are connected. The bottom of the condensing 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 evaporating tank ET forms NMP vapor at the top of the evaporating tank ET. Due to the pressure difference, the NMP vapor will automatically flow into the condensing tank CT. The NMP vapor is condensed into liquid NMP in the condensing tank CT.

[0030] The NMP waste liquid purification device in the embodiment contains only one set of evaporating-condensing tank set.

[0031] The cascade cold-heat combined subsystem includes 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 at one end (cold end) and heat at the other end (heat end) by compressing refrigerant through a compressor. The cold supply module brings the cold from the cold end into circulating chilled water through heat exchange. The chilled water exchanges heat when flowing through the condensing tank CT, brings the heat from the condensing tank CT back and sends it into the cold end. The heat supply module brings the heat from the heat end into circulating condensing water through heat exchange. The condensing water exchanges heat when flowing through the evaporating tank ET, brings the cold from the evaporating tank ET back and sends it into the heat end.

[0032] The cold supply module includes a chilled water pump PUMP1 and a first heat exchanger H1. Each condensing 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 the chilled water branch pipe line. The total water inlet pipe of the NMP waste liquid purification device provides chilled water for all condensing tanks CT. The chilled water from all condensing 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 at the high temperature side of the first 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.

[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 first 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 first three-way valve TWV1, a dew point sensor (not shown in the figure), and a terminal heat utilization device HET. The gas inlet end of the first three-way valve TWV1 is connected with the gas outlet of the third compressor COMP3, the first gas outlet end of the first three-way valve TWV1 is connected with the gas inlets of the evaporation tanks ET, and the second gas outlet end of the first three-way valve TWV1 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 first three-way valve TWV1 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 cooling supply module further comprises an additional cold source ECS and a make-up water pump PUMP4. The branch water pipe of the additional cold source ECS is connected in parallel to the total water inlet pipe and the total water outlet pipe of the NMP waste liquid purification device; the make-up water pump PUMP4 is arranged on the branch water pipe of the additional cold source ECS. The additional cold source ECS and the make-up water pump PUMP4 are used cooperatively to provide additional cold quantity, which is combined with the cold quantity generated by the cold end of the cascade cold water heat pump unit to supply cooling for the NMP waste liquid purification device.

[0043] Optionally, the cooling supply module further comprises a water supply flow meter F1 arranged on the branch water pipe of the additional cold source ECS, which is used to measure the water supply flow of the additional cold source ECS.

[0044] Optionally, the cooling supply module further comprises a supercooling protection unit composed of a temperature rising water pump PUMP5 and a second heat exchanger H2. The total water outlet pipe of the NMP waste liquid purification device at the water inlet end of the chilled water pump PUMP1 is arranged through the low temperature side of the second heat exchanger H2; the hot water outlet pipe of the second cascade heat exchanger FH2 is connected in communication with the water inlet pipe arranged through the high temperature side of the second heat exchanger H2; the water inlet end of the flash tank TANK1 is connected in communication with the water outlet pipe arranged through the high temperature side of the second heat exchanger H2; and the temperature rising water pump PUMP5 is arranged on the water outlet pipe of the high temperature side of the second heat exchanger H2.

[0045] Optionally, the supercooling protection unit further comprises a second three-way valve TWV2, which comprises two water inlet ends and one water outlet end and is arranged on the water outlet pipe of the high temperature side of the second heat exchanger H2, wherein one water inlet end of the second three-way valve TWV2 is connected in communication with the water inlet pipe of the high temperature side of the second heat exchanger H2.

[0046] The function of the supercooling protection unit is to make part of the high temperature hot water about to enter the water inlet end of the flash tank TANK1 circulate in the high temperature side of the second heat exchanger H2, so that the high temperature chilled water about to enter the high temperature side of the first heat exchanger H1 is further heated through heat exchange of the second heat exchanger H2, thereby preventing the first compressor group COMP1 from stopping (i.e. the whole cold and heat combined supply system stops working) due to too low temperature of the first chilled water T1. The temperature of the first chilled water T1 is the water temperature of the chilled water in the total water outlet pipe of the NMP waste liquid purification device near the high temperature side of the first heat exchanger H1.

[0047] The end heat equipment HET can be equipment in other links of the lithium ion battery manufacturing plant. For example, the coating oven and other process links of the lithium ion battery manufacturing plant also need high temperature steam, which can be provided by the end heat equipment HET.

[0048] Optionally, the heat supply module further comprises a condensate recovery tank TANK2 and a condensate recovery pump PUMP3. The water outlet of the end heat utilization device HET and the water outlets of all the evaporation tanks ET are connected to the water inlet of the condensate recovery tank TANK2, and the water outlet of the condensate recovery tank TANK2 is connected to the water supplement inlet of the flash tank TANK1; the condensate recovery pump PUMP3 is arranged on the pipeline between the water outlet of the condensate recovery tank TANK2 and the water supplement inlet of the flash tank TANK1.

[0049] Optionally, a vapor flow meter F2 is arranged at the first gas outlet end of the first three-way valve TWV1 to measure the flow of high-temperature vapor entering all the evaporation tanks ET.

[0050] Optionally, a water supplement flow meter F3 is arranged at the water outlet of the condensate recovery tank TANK2 to measure the flow of condensate from the condensate recovery tank TANK2 back to the flash tank TANK1; and a fourth flow meter F4 is arranged at the gas outlet of the flash tank TANK1 to measure the flow of vapor discharged from the gas outlet of the flash tank TANK1.

[0051] The cold-heat combined supply system of the embodiment is a closed system, and the condensate obtained after all the evaporation tanks ET and / or the end heat utilization device HET are used needs to be returned to the flash tank TANK1 to ensure normal operation of the system. However, the condensate pressure is relatively small, and when the pipeline between the water supplement inlet of the flash tank TANK1 and the water outlet of the evaporation tank ET is relatively long, the resistance will be relatively large, and the condensate cannot be directly returned to the flash tank TANK1. Therefore, the existence of the condensate recovery tank TANK2 and the condensate recovery pump PUMP3 can ensure that the condensate is stably and smoothly recovered to the flash tank TANK1. The condensate is first temporarily stored in the condensate recovery tank TANK2, the power of the condensate recovery pump PUMP3 is adjusted, the flow from the water outlet of the condensate recovery tank TANK2 is made equal to the flow of vapor discharged from the gas outlet of the flash tank TANK1, the condensate is stably returned to the flash tank TANK1, and the pressure in the flash tank TANK1 is maintained. The condensate recovery process is not unstable, and the water in the flash tank TANK1 is not subjected to a large impact, which further improves the safety of the cold-heat combined supply system of the embodiment.

[0052] Optionally, an additional water inlet and an additional water outlet are arranged on the flash tank TANK1 (not shown in the figure), and the additional water inlet and the additional water outlet are usually closed. When the temperature inside the flash tank TANK1 exceeds a set threshold, the additional water inlet is opened to introduce low-temperature pure water, and the flow is adjusted to ensure that the flash tank TANK1 does not overheat; when the liquid level in the flash tank TANK1 exceeds a set threshold, the additional water outlet is opened to drain water.

[0053] The working process of the NMP waste liquid purification cold-heat combined supply system of the embodiment is described below. At the beginning of the operation of the NMP waste liquid purification cold-heat combined power system, the exhaust valve EV is closed, and the first electric valve MV1 and the second electric valve MV2 are both opened. After the operation starts, the chilled water not only flows through each condenser CT, but also flows through the additional cold source ECS, that is, the cold energy in the chilled water and the additional cold energy provided by the additional cold source ECS are used together to cool the condenser CT. The original high-temperature chilled water flowing out of each condenser CT and the additional low-temperature chilled water flowing out of the additional cold source ECS are mixed to form high-temperature chilled water in the NMP waste liquid purification device total water outlet pipe, so that the water temperature of the high-temperature chilled water is not too high, so as to ensure the condensation efficiency of the NMP waste liquid purification device. The high-temperature chilled water is provided with circulating power by the chilled water pump PUMP1, and after heat exchange and cooling in the high-temperature side of the first heat exchanger H1, it becomes low-temperature chilled water, and then flows into the NMP waste liquid purification device total water inlet pipe again.

[0054] 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 15-30 degrees Celsius; in this embodiment, it is X degrees Celsius.

[0055] The low-temperature first refrigerant flows through the low-temperature side of the first heat exchanger H1, is then compressed in the first compressor group COMP1, and becomes high-temperature first refrigerant after being compressed and pressurized, 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, and is cooled to become low-temperature first refrigerant, and then flows out of the first cascade heat exchanger FH1, and flows through the low-temperature side of the first heat exchanger H1 again and continuously circulates.

[0056] In this 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.

[0057] The low-temperature second refrigerant flows through the first evaporating pipe of the first cascade heat exchanger FH1, is then compressed in the second compressor group COMP2, and becomes high-temperature second refrigerant after being compressed and pressurized, and then enters the second condensing pipe of the second cascade heat exchanger FH2, exchanges heat with the hot water flowing through the hot water pipe of the second cascade heat exchanger FH2, and is cooled to become low-temperature second refrigerant, and then flows out of the second cascade heat exchanger FH2, and flows through the first evaporating pipe of the first cascade heat exchanger FH1 again and continuously circulates.

[0058] 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 125-130 degrees Celsius.

[0059] 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 is heated to high-temperature hot water. The high-temperature hot water enters the flash tank TANK1 and is decompressed, and 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. The water vapor flows out of the top of the flash tank TANK1 and enters the third compressor COMP3 to be compressed to high-temperature steam.

[0060] In this embodiment, the temperature of the low-temperature hot water is 105°C; the temperature of the water vapor at the top of the flash tank TANK1 is 115°C; the temperature of the high-temperature hot water is 120°C (in a closed system, the temperature of the high-temperature hot water can be maintained at 120°C by pressure); and the temperature of the high-temperature steam is 130°C.

[0061] The first three-way valve TWV1 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, which flows out of the water outlet of each evaporation tank ET and the water outlet of the end-use heat equipment HET, respectively, and enters the bottom of the flash tank TANK1 from the water supplement port of the flash tank TANK1 to become low-temperature hot water.

[0062] Compared with the separate refrigeration equipment and heating equipment in the prior art, the NMP waste liquid purification cold and heat combined supply system in this embodiment has a compact structure and a small footprint. The electric energy used to power the compressor in the cold and heat combined supply system is converted into the cold and heat required by the NMP waste liquid purification device at the same time, which improves the electric energy utilization rate in the NMP waste liquid purification process and reduces the heating and cooling energy consumption and cost.

[0063] The NMP waste liquid purification cold and heat combined supply system in this embodiment can divide a large total temperature difference into two sections by a condenser-evaporator, use the high-temperature refrigeration capacity to bear the condensing load of the low-temperature stage, and obtain a lower refrigeration temperature. In a cold and heat combined supply system, a cold end and a heat end with a large temperature difference are generated, and the difference between the first refrigerant and the second refrigerant is also to assist the cold and heat combined supply system in this embodiment to divide the temperature difference.

[0064] The cold and heat supply of the NMP waste liquid purification cold-heat combined supply system can be sent to the end cold / heat equipment after the NMP waste liquid purification device is preferentially satisfied, and a small amount of energy remaining after being used by the NMP waste liquid purification device (and the end cold / heat equipment) can be recovered to the cascade cold-heat combined supply system again through the circulating water (i.e., low-temperature hot water and high-temperature chilled water), so that the cold and heat generated by the entire cold-heat combined supply system consumed by the electric energy (for power supply of the compressor) are efficiently utilized, and additional heat discharge or cold discharge to the surrounding environment is basically avoided, energy saving and environmental protection are achieved.

[0065] The NMP waste liquid purification cold-heat combined supply system can flexibly adjust the cold and heat for the end cold / heat equipment, so that the generated cold and heat of the cold-heat combined supply system is preferentially used for the NMP waste liquid purification device with real-time changes of the cold and heat demand, the purification efficiency of the NMP waste liquid is improved, and the operation safety of the cascade cold-heat combined supply system is ensured.

[0066] 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 NMP waste liquid purification cold-heat combined supply system has a reduced land occupation area by 80%, a reduced power consumption by 30%, and an increased purification efficiency of the NMP waste liquid by 50%.

[0067] Embodiment 2 When the cold-heat combined supply system based on NMP waste liquid purification preferentially satisfies the heat demand of the evaporation tank ET in the NMP waste liquid purification device, that is, the heat supply is equal to the heat demand, the cold supply of the cold-heat combined supply system is about 1 / 3-1 / 2 of the heat supply. However, according to the heat conservation law, in the NMP waste liquid purification device, the heat and cold required by the same amount of NMP waste liquid in the purification process at the same time are the same regardless of the real-time changes of the heat demand. This leads to that the cold supplied by the cold-heat combined supply system cannot satisfy the cold demand of the NMP waste liquid purification device, so the additional cold source is provided to supply additional cold in the embodiment, so as to ensure that the NMP vapor in the condensation tank CT in the NMP waste liquid purification device is efficiently condensed.

[0068] In addition, 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. That is, the heat required by all evaporation tanks ET 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 at present; or the purification of a tank of NMP waste liquid is just completed, and there is no new NMP waste liquid to be purified at present).

[0069] Therefore, the heat supply of the cold-heat combined supply system is generally greater than the total heat required by all the evaporation tanks ET in the NMP waste liquid purification device; and we need the cold-heat combined supply system to respond to the changing heat demand in time, and increase the cold supply when the heat demand increases, and reduce the heat supply or send the excess heat into the end heat using equipment HET when the cold demand decreases. Correspondingly, the additional cold source ECS of the cold-heat combined supply system also needs to provide the corresponding additional cold in time, together with the cold produced by the cold end of the cascade cold water heat pump unit, to supply all the condensers CT of the NMP waste liquid purification device.

[0070] The embodiment provides a control method based on heat load, which is used for controlling an NMP waste liquid purification cold-heat combined supply system as described in embodiment 1 based on heat load: S1, close the exhaust valve EV, start an NMP waste liquid purification cold-heat combined supply system, and adjust the load of each compressor in the first compressor group COMP1 to the initial load P1.

[0071] S2, real-time monitor the load of each compressor in the first compressor group COMP1, the first chilled water temperature T1, the second high-temperature vapor temperature T2, the third condensate water temperature T3 and the high-temperature hot water temperature T4; by adjusting the load of each compressor in the first compressor group COMP1, the valve opening degree of the outlet of the first three-way valve TWV1 and the power of the cold water pump PUMP4, the load of each compressor in the first compressor group COMP1 is in a healthy state, the first chilled water temperature T1 fluctuates within the first ideal temperature interval, and the high-temperature hot water temperature fluctuates within the second ideal temperature interval.

[0072] Wherein, the second high-temperature vapor temperature T2 is the high-temperature vapor temperature at the outlet of the third compressor COMP3; the third condensate water temperature T3 is the condensate water temperature at the water outlet of the evaporation tank ET; the first chilled water temperature T1 is the water temperature of the chilled water in the NMP waste liquid purification device total water outlet pipe close to the high-temperature side of the first heat exchanger H1; the high-temperature hot water temperature T4 is the temperature of the high-temperature hot water entering the water inlet end of the flash tank TANK1; the healthy state means that the load of the compressor is above the critical load P0, 0

[0073] In the embodiment, T1´=5℃, T1´´=8℃, T4´=120℃, T4´´=125℃; P0 is 50% of the full load, and P1 is 53% of the full load.

[0074] Include the following in S2: ① If the current high-temperature hot water temperature T4 is less than T4'', the second outlet port of the first three-way regulating valve TWV1 is closed, and the load of each compressor in the first compressor group COMP1 is increased.

[0075] Because the amount of heat required by the NMP waste liquid purification unit is uncertain and may change suddenly, it is impractical to calculate the heat required in real time and then control the combined cooling and heating system to provide the corresponding heat.

[0076] We monitor the high-temperature hot water temperature T4 in real time to determine whether the current heat supply of the combined cooling and heating system can meet the heat demand of the NMP waste liquid purification device. We hope that the high-temperature hot water temperature T4 can be kept as constant as possible at the ideal temperature T * , where T4´≤T * ≤T4´´, which means that the current heat supply of the combined cooling and heating system can fully meet the heat demand of the NMP waste liquid purification device. However, considering that the high temperature hot water temperature T4 is difficult to always maintain the ideal temperature T * Since the temperature remains unchanged, we settle for the next best option: stabilizing the high-temperature hot water temperature T4 within the second ideal temperature range. Therefore, when the current high-temperature hot water temperature T4 is less than T4´´, we believe that the heat currently provided by the combined cooling and heating system is far from meeting the heat requirements of the NMP waste liquid purification unit. Therefore, regardless of whether the second outlet of the first three-way regulating valve TWV1 is open, we keep the second outlet of the first three-way regulating valve TWV1 closed and increase the load on each compressor in the first compressor group COMP1 to rapidly increase the heat supply of the combined cooling and heating system.

[0077] In this embodiment, T * =123℃.

[0078] ② If the current high-temperature hot water temperature T4´≤T4≤T4´´, the high-temperature hot water temperature T4 continues to rise during the previous △t 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 high-temperature hot water temperature T4'≤T4≤T4'', we consider that the heat provided by the combined cooling and heating system can basically meet the heat demand of the NMP waste liquid purification device. On the one hand, the change of the high-temperature hot water temperature T4 caused by the change of the heat demand of the NMP waste liquid purification device is lagging; on the other hand, in order to respond to the heat demand in time, we need to ensure that all the compressors in the first compressor group COMP1 are turned on; in addition, we need to 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 and heating system.

[0080] The health state load set by the skilled person for each turned-on 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.

[0081] It should be noted that if the high-temperature hot water temperature T4 rises to more than T4'', it will cause the second compressor group COMP2 to shut down due to excessive temperature, thereby causing the combined cooling and heating system based on NMP waste liquid purification to shut down. 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 shut down due to damage, thereby causing the combined cooling and heating system to shut down.

[0082] Therefore, we combine the change trend of the high-temperature hot water temperature T4 in the previous△t time period to make preventive adjustments: if the high-temperature hot water temperature T4 continues to rise in the previous△t time period, in order to avoid the heat supply continuing to increase at the next moment, that is, to avoid the high-temperature hot water temperature T4 continuing to rise or even rapidly rising to more than T4'', we need to reduce the heat supply. 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 heat supply.

[0083] ③ If the current high-temperature hot water temperature T4'≤T4≤T4'', and the high-temperature hot water temperature T4 continues to rise 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 degree of the second gas outlet end of the first three-way regulating valve TWV1 is increased.

[0084] We think that the heat provided by the combined cooling and heating system can basically meet the heat demand of the NMP waste liquid purification device at present, but the heat demand may continue to increase in the next moment so as to exceed the heat demand, that is, the heat not used by the NMP waste liquid purification device is increased.

[0085] But 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, which may lead to the load of each compressor in the first compressor group COMP1 being P0, that is, being at the limit of the healthy state of the compressor, so our preventive adjustment is to increase the valve opening degree of the second gas outlet end of the first three-way regulating valve TWV1 to send more heat not used by the NMP waste liquid purification device into the end heat using equipment HET to avoid the subsequent high-temperature hot water temperature T4 exceeding T4´´.

[0086] ④If the current high-temperature hot water temperature T4´≤T4≤T4´´, the high-temperature hot water temperature T4 continuously decreases 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 valve of the second gas outlet end of the first three-way regulating valve TWV1 is opened, the valve opening degree of the second gas outlet end of the first three-way regulating valve TWV1 is reduced; if the valve of the second gas outlet end of the first three-way regulating valve TWV1 is closed, the load of each compressor in the first compressor group COMP1 is increased.

[0087] We think that the heat provided by the combined cooling and heating system can basically meet the heat demand of the NMP waste liquid purification device at present, but the heat demand may continue to increase in the next moment so as to exceed the heat demand, that is, the heat not used by the NMP waste liquid purification device is increased.

[0088] ⑤If the current high-temperature hot water temperature T4´≤T4≤T4´´, and the first chilled water temperature T1 continuously decreases in the previous△t time, and the load of each compressor in the first compressor group COMP1 is less than P1 at present, the load of each compressor in the first compressor group COMP1 is increased.

[0089] We think that the heat provided by the combined cooling and heating system can basically meet the heat demand of the NMP waste liquid purification device at present, but the heat demand may continue to decrease next time, 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.

[0090] ⑥If the current high-temperature hot water temperature T4>T4´´, and the load of each compressor in the first compressor group COMP1 is greater than P1 at present, then reduce the load of each compressor in the first compressor group COMP1.

[0091] No matter whether the end-use heat equipment HET participates in heat use, we think that the heat provided by the combined cooling and heating system has far exceeded the heat demand of the NMP waste liquid purification device at present, and the load of each compressor in the first compressor group COMP1 is greater than P1 at present, which is in a healthy state, so we reduce the heat supply of the combined cooling and heating system by reducing the load of each compressor in the first compressor group COMP1 at present, reduce the temperature of the high-temperature hot water temperature T4, and avoid the high-temperature hot water temperature T4 exceeding T4´´ for a long time to cause the combined cooling and heating system to shut down.

[0092] ⑦If the current high-temperature hot water temperature T4>T4´´, and the load of each compressor in the first compressor group COMP1 is less than P1 at present, then increase the valve opening of the second gas outlet end of the first three-way regulating valve TWV1.

[0093] Based on the analysis of ⑥, in order to avoid the high-temperature hot water temperature T4 exceeding T4´´ for a long time, and also to ensure the health status of each compressor in the first compressor group COMP1 at present, we increase the valve opening of the second gas outlet end of the first three-way regulating valve TWV1 to send more heat that is not used by the NMP waste liquid purification device into the end-use heat equipment HET. If the high-temperature hot water temperature T4´≤T4≤T4´´ next time, and the load of each compressor in the first compressor group COMP1 is less than P1 at present, then according to the situation ⑤, after processing, the load of each compressor in the first compressor group COMP1 can be gradually increased to a healthy state.

[0094] In S2, based on the above seven situations, the power of the cold water supplement pump PUMP4 can be adjusted according to the following formula, so that the additional cold source ECS supplies additional cold Q4 to the current cooling module through the water supply flow rate q, so that the first chilled water T1 is in the first ideal temperature interval, and the total cooling capacity of the NMP waste liquid purification device is ensured, so as to ensure the purification efficiency of the NMP waste liquid purification device: Q1=[C×(T2-T3)+(h1-h2)]×ρ×f2; Q2=[(COP-1) / (1+COP)]×Q1; Q3=Q1; Q4=Q3-Q2; q=Q4 / (C×△T); Where Q1 represents the heat 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·℃); f2 represents the high-temperature steam measured by the current steam flowmeter F2, unit: m 3 / s; h1 represents the specific enthalpy of water vapor at the current temperature T2, unit: kJ / kg; h2 represents the specific enthalpy of saturated water at the current temperature T2, unit: kJ / kg; Q2 represents the cooling capacity of the cascade chiller heat pump unit under the condition of heating capacity Q1; COP represents the coefficient of energy efficiency of the cascade chiller heat pump unit, which is obtained by actual measurement by each manufacturer and the value is usually 2-3; the first heat Q3 represents the current cooling capacity demand of the NMP waste liquid purification device; △T represents the inlet and outlet water temperature difference set by the additional cold source ECS; the water supply flow rate q is in kg / s and can be directly measured by the water supply flow meter F1.

[0095] In S2, when the water supply flow rate q = 0, the current high-temperature hot water temperature T4 > T4´´, and the valve opening of the first outlet port of the first three-way regulating valve TWV1 is at its maximum, if the first chilled water T1 < T1´, the warming water pump PUMP5 is turned on. At this point, the combined cooling and heating system's heat supply is too high, so that without the additional cooling source ECS providing additional cooling, the temperature of the first chilled water T1 remains too low. To prevent the first chilled water T1 from freezing due to a sudden drop in temperature to 0°C or below at the next moment, causing the entire combined cooling and heating system to shut down, the control method of this embodiment intervenes through the overcooling protection unit, directly using the overheated high-temperature hot water (T4 > T4´´) to raise the temperature of the first chilled water T1, further ensuring the safe operation of the entire combined cooling and heating system.

[0096] 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.

[0097] In this embodiment, the set threshold value of the outlet temperature of the third compressor COMP3 is 132 degrees Celsius.

[0098] 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. This embodiment's thermal load-based control method ensures that each compressor is always on during operation, enabling each compressor to quickly respond to changing load demands, thereby improving the overall response rate and adjustment flexibility of the combined cooling and heating system.

[0099] The control method of the embodiment 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.

[0100] The control method of the embodiment is based on heat, and the heat required by the NMP waste liquid purification device changes in real time. This change can cause the high-temperature hot water temperature T4 to change with a lag. If the heat that cannot be consumed by the NMP waste liquid purification device in time exists in the combined cooling and heating system, the high-temperature hot water temperature T4 will be too high, which can cause the combined cooling and heating system to stop working. Therefore, the control method of the embodiment needs to ensure that the heat that cannot be consumed by the NMP waste liquid purification device in time cannot make the high-temperature hot water temperature T4 too high while providing sufficient heat for the NMP waste liquid purification device. In addition, because the heat required by the NMP waste liquid purification device changes in real time, it is not feasible to know the heat demand first and then accurately adjust the heat supply of the combined cooling and heating system. In the control method of the embodiment, the most creative part is to use the change of the high-temperature hot water temperature T4 to measure the real-time change of the heat demand of the NMP waste liquid purification device, and to ensure that the heat supplied to the NMP waste liquid purification device is sufficient and the combined cooling and heating system will not stop working by directly controlling the high-temperature hot water temperature T4 in the second ideal temperature range. Avoiding stop working can further prolong the service life of the combined cooling and heating system.

[0101] Under the guidance of the control method mentioned above, the control method of the embodiment also meets the condition that the load of each compressor is in a healthy state, and reduces the load of each compressor to reduce the power consumption of the entire combined cooling and heating system. Under the condition that all the above-mentioned conditions are met, the excess heat is supplied to the end heat-using equipment.

[0102] That is, the control method of the embodiment not only can meet the real-time change of the heat 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, but also can utilize the heat that is not used by the NMP waste liquid purification device (supply the end heat-using equipment) through flexible adjustment measures, which can greatly improve the service life of the entire combined cooling and heating system.

[0103] The control method of the embodiment covers all situations that may occur in the whole combined cooling and heating system, and also performs preventive dynamic adjustment on the high-temperature hot water temperature T4 fluctuating in the second ideal temperature range, further reduces the adverse effects of the lagging change of the high-temperature hot water temperature T4 on the "high-temperature hot water temperature stably in the second ideal temperature range", and maximizes the control of the high-temperature hot water temperature in the second ideal temperature range. The preventive dynamic adjustment is also performed on the high-temperature hot water temperature already in the second ideal temperature range, and further improves the response speed of the whole combined cooling and heating system to the heat supply change at the next moment.

[0104] The control method of the embodiment can calculate the heat Q1 supplied to the current NMP waste liquid purification device (i.e. supplied to all evaporation tanks ET) and the required additional cold Q4 in the combined cooling and heating system in time while ensuring that the heat demand of the current NMP waste liquid purification device is met, ensures that the supply amount of the additional cold Q4 can meet the demand of the NMP waste liquid purification device, and further reduces the adverse effects of the lagging change of the high-temperature hot water temperature T4 on the "dynamic stabilization of the high-temperature hot water temperature T4 in the second ideal temperature range" and the "dynamic stabilization of the first chilled water temperature T1 in the first ideal temperature range".

[0105] According to the verification of the skilled person, the control method of the embodiment reduces the power consumption of the whole combined cooling and heating system by 50% and reduces the operation and maintenance cost by 40% compared with the prior art.

[0106] The technical, shape and structure parts not described in detail in the present application are all known technologies. It should be pointed out that the above is only the 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 the equivalent solutions of the present application, and should fall within the protection scope of the present application.

Claims

1. A NMP waste liquid purification cooling and heating combined supply system, characterized by: It includes a cascade cooling and heating subsystem and an NMP waste liquid purification device. The NMP waste liquid purification device includes one or more parallel evaporation-condensation tank sets, and each evaporation-condensation tank set includes an evaporation tank ET and a condensation tank CT; the cascade cooling and heating subsystem includes a cascade chiller heat pump unit, a heating module and a cooling module; the cascade chiller heat pump unit compresses the refrigerant to generate cooling at the cooling end and heat at the heating end; the cooling module brings the cooling at the cooling end into the circulating chilled water through heat exchange, and the chilled water undergoes heat exchange when flowing through the condenser tank CT, The heat in the condenser tank CT is brought back and sent to the cooling end; the heating module brings the heat from the heating end into the circulating condensing water through heat exchange. The condensing water undergoes heat exchange when flowing through the evaporator tank ET, bringing the cooling energy in the evaporator tank ET back and sending it to the heating end; after absorbing heat, the NMP waste liquid in the evaporator tank ET forms NMP vapor at the top of the evaporator tank ET and then flows into the condenser tank CT. The NMP vapor is cooled and condensed into liquid NMP in the condenser tank CT; the cooling module also includes an overcooling protection unit, which brings part of the heat in the heating module into the chilled water.

2. A NMP waste liquid purification cold and hot supply system according to claim 1, characterized in that: The cooling module includes a chilled water pump PUMP1 and a heat exchanger H1; 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 installed on the high-temperature side of the heat exchanger H1; the water inlet end of the chilled water pump PUMP1 is connected to the main 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 main water inlet pipe of the NMP waste liquid purification device.

3. A NMP waste liquid purification cold and hot combined supply system according to claim 2, characterized in that: The cascade chiller 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 is provided with a first condensing pipeline and a first evaporating pipeline coupled to each other; the outlet end of the first compressor group COMP1 is connected to the first condensing inlet pipeline; the inlet end of the first compressor group COMP1 is connected to the first condensing outflow pipeline; the first condensing outflow pipeline is provided on 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 coupled to each other, the outlet end of the second compressor group COMP2 is connected to the second condensing inflow pipeline, the inlet end of the second compressor group COMP2 is connected to the first evaporating outflow pipeline; the second condensing outflow pipeline is connected to the first evaporating inflow pipeline.

4. A NMP waste liquid purification cooling and heating combined supply system according to claim 3, characterized in that: The heating module includes a flash tank TANK1, a hot water pump PUMP2 and a third compressor COMP3; a water inlet is provided at the upper part of the flash tank TANK1, a water outlet and a water replenishing port are provided at the bottom of the flash tank TANK1, and an air outlet is provided at the top of the flash tank TANK1; an air inlet is provided at the upper part of the evaporator ET, and a water outlet is provided at the bottom of the evaporator ET; the hot water outlet pipeline is connected to the water inlet of the flash tank TANK1, and the hot water inlet pipeline is connected to the water outlet of the flash tank TANK1; a hot water pump PUMP2 is provided on the hot water inlet pipeline; 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 replenishing port of the flash tank TANK1.

5. A NMP waste liquid purification cooling and heating combined supply system according to claim 4, characterized in that: The heating module also includes a first three-way regulating valve TWV1 and a terminal heat-using equipment HET; the air inlet end of the first three-way regulating valve TWV1 is connected to the air outlet of the third compressor COMP3, the first air outlet end of the first three-way regulating valve TWV1 is connected to the air inlet of each evaporator ET, and the second air outlet end of the first three-way regulating valve TWV1 is connected to the air inlet of the terminal heat-using equipment HET; the water outlet of the terminal heat-using equipment HET is connected to the water supply port of the flash tank TANK1.

6. A NMP waste liquid purification cooling and heating combined supply system according to claim 5, characterized in that: The heating module also includes a condensate recovery tank TANK2 and a condensate recovery pump PUMP3. The water outlet of the terminal heat equipment HET and the water outlets of all evaporation tanks ET are connected to the water inlet of the condensate recovery tank TANK2, and the water outlet of the condensate recovery tank TANK2 is connected to the water supply port of the flash tank TANK1; the condensate recovery pump PUMP3 is arranged on the pipeline between the water outlet of the condensate recovery tank TANK2 and the water supply port of the flash tank TANK1.

7. A NMP waste liquid purification cooling and heating combined supply system according to any one of claims 4 to 6, characterized in that: The cooling module also includes an additional cold source ECS and a cold water supplement pump PUMP4. The branch water pipes of the additional cold source ECS are connected in parallel to the main water inlet pipe and the main water outlet pipe of the NMP waste liquid purification device; the cold water supplement pump PUMP4 is arranged on the branch water pipe of the additional cold source ECS; the overcooling protection unit includes a warming water pump PUMP5 and a second heat exchanger H2, and the main water outlet pipe of the NMP waste liquid purification device at the water inlet end of the chilled water pump PUMP1 is passed through the low-temperature side of the second heat exchanger H2; the hot water outlet pipe of the second cascade heat exchanger FH2 is connected to the water inlet pipe passed through the high-temperature side of the second heat exchanger H2; the water inlet end of the flash tank TANK1 is connected to the water outlet pipe passed through the high-temperature side of the second heat exchanger H2; and a warming water pump PUMP5 is provided on the high-temperature side outlet pipe of the second heat exchanger H2.

8. A heat load-based control method for controlling the NMP waste liquid purification cooling and heating combined supply system according to claim 7, comprising the following steps: S1, close the exhaust valve EV, start a combined cooling and heating system based on NMP waste liquid purification, and adjust the load of each compressor in the first compressor group COMP1 to the initial load P1; S2, real-time monitoring of the load of each compressor in the first compressor group COMP1, the first chilled water temperature T1, the second high-temperature steam temperature T2, the third condensed water temperature T3, and the high-temperature hot water temperature T4; by adjusting the load of each compressor in the first compressor group COMP1, the valve opening of the outlet end of the first three-way regulating valve TWV1, and the power of the supplementary cooling water pump PUMP4, the load of each compressor in the first compressor group COMP1 is kept in a healthy state, the first chilled water temperature T1 fluctuates within a first ideal temperature range, and the high-temperature hot water temperature fluctuates within a second ideal temperature range; Among them, the second high-temperature steam temperature T2 is the high-temperature steam temperature at the outlet of the third compressor COMP3; the third condensed water temperature T3 is the condensed water temperature at the outlet of the evaporator ET; the first chilled water temperature T1 is the water temperature of the chilled water in the total outlet pipe of the NMP waste liquid purification device near the high-temperature side of the first heat exchanger H1; the high-temperature hot water temperature T4 is the temperature of the high-temperature hot water entering the water inlet of the flash tank TANK1; the healthy state means that the load of the compressor is above the critical load P0, 0<P0<P1; the first ideal temperature range is [T1´,T1´´], where T1´ represents the first water temperature threshold, T1´´ represents the second water temperature threshold, and 0<T1´; the second ideal temperature range is [T4´,T4´´], where T4´ represents the third water temperature threshold, T4´´ represents the fourth water temperature threshold, and 0<T4´.

9. The heat load-based control method according to claim 8, characterized in that: S2 includes the following: if the current high-temperature hot water temperature T4 is less than T4'', the second outlet port of the first three-way regulating valve TWV1 is closed, and the load of each compressor in the first compressor group COMP1 is increased; If the current high-temperature hot water temperature T4´≤T4≤T4´´, the high-temperature hot water temperature T4 has been rising in the previous △t 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; If the current high-temperature hot water temperature T4´≤T4≤T4´´, and the high-temperature hot water temperature T4 continues to rise during the previous △t period, and the load of each compressor in the current first compressor group COMP1 is less than P1, then increase the valve opening of the second outlet end of the first three-way regulating valve TWV1; If the current high-temperature hot water temperature T4´≤T4≤T4´´, the high-temperature hot water temperature T4 has been decreasing during the previous △t period, and the load of each compressor in the first compressor group COMP1 is greater than P1, if the valve at the second outlet end of the first three-way regulating valve TWV1 is open, the valve opening of the second outlet end of the first three-way regulating valve TWV1 is reduced; if the valves at the second outlet end of the first three-way regulating valve TWV1 are all closed, the load of each compressor in the first compressor group COMP1 is increased; If the current high-temperature hot water temperature T4´≤T4≤T4´´, and the first chilled water temperature T1 continues to decrease within the previous △t period, and the current 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; If the current high-temperature hot water temperature T4>T4´´, 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 current high-temperature hot water temperature T4>T4'', and the current load of each compressor in the first compressor group COMP1 is less than P1, the valve opening of the second outlet end of the first three-way regulating valve TWV1 is increased.

10. The heat load-based control method according to claim 8, characterized in that: Include the following in S2: Adjust the power of the supplementary cooling water pump PUMP4 so that the additional cooling source ECS can substitute the additional cooling capacity Q4 into the current cooling module through the water supply flow rate q: Q1=[C×(T2-T3)+(h1-h2)]×ρ×f2; Q2=[(COP-1) / (1+COP)]×Q1; Q3=Q1; Q4=Q3-Q2; q=Q4 / (C×△T); Where Q1 represents the current heat demand of the NMP waste liquid purification unit; C represents the specific heat capacity of water; f2 represents the current high-temperature steam flow rate entering all evaporation tanks ET; h1 represents the specific enthalpy of water vapor at the current temperature T2; h2 represents the specific enthalpy of saturated water at the current temperature T2; Q2 represents the cooling capacity of the cascade chiller heat pump unit under the condition of a heating capacity of Q1; COP represents the energy efficiency coefficient of the cascade chiller heat pump unit; the first heat Q3 represents the current cooling capacity demand of the NMP waste liquid purification unit; ∆T represents the inlet and outlet water temperature difference set by the additional cooling source ECS; When the water supply flow rate q=0, the current high-temperature hot water temperature T4>T4´´ and the valve opening of the first outlet end of the first three-way regulating valve TWV1 is the largest, if the first chilled water T1<T1´, the heating water pump PUMP5 is turned on.

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