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

Abstract

The present application belongs to the technical field of heat pump system, and particularly relates to a NMP waste liquid purification cold-heat combined supply system and a control method based on heat load. In the system, the NMP waste liquid purification device comprises an evaporation tank and a condensation tank; the cascade cold water heat pump unit comprises a cold end and a heat end; the cold supply module brings the cold quantity of the cold end into the circulating chilled water through heat exchange, and the chilled water exchanges heat when flowing through the condensation tank, bringing the heat of the condensation tank back and sending it into the cold end; the heat supply module brings the heat of the heat end into the circulating condensation water through heat exchange, and the condensation water exchanges heat when flowing through the evaporation tank, bringing the cold quantity of the evaporation tank back and sending it into the heat end; after the waste liquid in the evaporation tank absorbs heat, NMP vapor is formed at the top of the tank and 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. The present application can efficiently supply heat and cold for the NMP waste liquid purification process while minimizing the loss of electric energy.

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 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 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 power consumption, 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 an NMP waste liquid purification cold-heat combined supply system, which can efficiently supply heat and cold to the NMP waste liquid purification process while minimizing power consumption.

[0006] To achieve the above purpose, the application adopts the following technical solutions:

[0007] 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.

[0008] 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.

[0009] 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.

[0010] 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.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] 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:

[0015] 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;

[0016] 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 the first ideal temperature interval, and the high-temperature hot water temperature fluctuates within the second ideal temperature interval;

[0017] 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

[0018] 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.

[0019] 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:

[0020] Q1=[C×(T2-T3)+(h1-h2)]×ρ×f2; Q2=[(COP-1) / (1+COP)]×Q1; Q3=Q1; Q4=Q3-Q2; q=Q4 / (C×△T);

[0021] 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

[0022] The beneficial effects of the present application are:

[0023] (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 the advantages of compact structure, small occupied area, and the electric energy for supplying power to 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.

[0024] (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 refrigerating 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.

[0025] (3) The NMP waste liquid purification cold and heat combined supply system can send the excess heat into the end heat using 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 being used by the NMP waste liquid purification device and the end heat using equipment 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 supplying power to 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, which is energy-saving and environment-friendly.

[0026] (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.

[0027] (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.

[0028] (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.

[0029] (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.

[0030] (8) The control method of the 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 equipment. That is, the control method of the 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 equipment), which also greatly improves the service life of the entire combined cooling and heating system.

[0031] (9) In the control method of the 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.

[0032] (10) The control method of the 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 while ensuring that the current heat demand of the NMP waste liquid purification device 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

[0033] Figure 1 It is a schematic diagram of the overall structure of a NMP waste liquid purification combined cooling and heating system of the application. DETAILED DESCRIPTION

[0034] In order to make the technical solutions of the application clearer and more explicit, the application will be described in detail below with reference to the drawings. Obviously, the described embodiments are only part of the embodiments of the 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 application without creative labor, and the solutions fall within the protection scope of the application.

[0035] Example 1

[0036] As Figure 1 shown, it is a whole structure schematic diagram of the NMP waste liquid purification cold-heat combined system of the application, including cascade cold-heat combined subsystem and NMP waste liquid purification device. The NMP waste liquid purification device is used for purifying 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 for providing heat and cold to the NMP waste liquid purification device to evaporate and condense.

[0037] The NMP waste liquid purification device contains one or more than one parallel evaporating-condensing tank set. One evaporating-condensing tank set contains one evaporating tank ET and one condensing tank CT, the top of the evaporating tank ET and the top of the condensing tank CT are connected, and 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; under the influence of 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.

[0038] The NMP waste liquid purification device in the embodiment contains only one evaporating-condensing tank set.

[0039] 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) through compression of refrigerant by a compressor; the cold supply module brings the cold from the cold end into circulating chilled water through heat exchange, and the chilled water exchanges heat when flowing through the condensing tank CT, bringing the heat from the condensing tank CT back to the cold end; the heat supply module brings the heat from the heat end into circulating condensing water through heat exchange, and the condensing water exchanges heat when flowing through the evaporating tank ET, bringing the cold from the evaporating tank ET back to the heat end.

[0040] 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 arranged therein, the total water inlet pipe of the NMP waste liquid purification device provides chilled water for all the condensing tanks CT, and the chilled water flowing out of all the 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 in 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.

[0041] 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 at 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.

[0042] The first condensing pipeline circulates the first refrigerant, and the second condensing pipeline and the first evaporating pipeline circulate the second refrigerant.

[0043] In the embodiment, the first refrigerant is R134a or R515b, and the second refrigerant is R245fa or R1233zd(E).

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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 has a small pressure, and when the pipeline between the water supplement inlet of the flash tank TANK1 and the water outlet of the evaporation tank ET is long, the resistance will be 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, further improving the safety of the cold-heat combined supply system of the embodiment.

[0060] 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.

[0061] The working process of the NMP waste liquid purification cold-heat combined supply system of the embodiment is described below.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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 to become high-temperature hot water; the high-temperature hot water enters the flash tank TANK1 and is decompressed, part of which becomes water vapor at the top of the flash tank TANK1, and part of which becomes low-temperature hot water stored at the bottom of the flash tank TANK1; the water vapor flows out from the top of the flash tank TANK1 and enters the third compressor COMP3 to be compressed to high-temperature steam.

[0069] In the embodiment, the temperature of the low-temperature hot water is 105℃; the temperature of the water vapor at the top of the flash tank TANK1 is 115℃; the temperature of the high-temperature hot water is 120℃ (in a closed system, the temperature of the high-temperature hot water can be kept at 120℃ by pressure); and the temperature of the high-temperature steam is 130℃.

[0070] 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 from 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.

[0071] 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 the embodiment has a compact structure and a small footprint, and 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, thereby improving the electric energy utilization rate in the NMP waste liquid purification process and reducing the heating and cooling energy consumption and cost.

[0072] The NMP waste liquid purification cold and heat combined supply system in the embodiment can divide a larger 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, so as to generate a cold end and a heat end with a huge temperature difference in a cold and heat combined supply system, and the difference between the first refrigerant and the second refrigerant is also to assist the cold and heat combined supply system in the embodiment to divide the temperature difference.

[0073] 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.

[0074] 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.

[0075] 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%.

[0076] Embodiment 2

[0077] 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 law of conservation of heat, in the NMP waste liquid purification device, the heat and cold required in the purification process of the same amount of NMP waste liquid at the same time are the same regardless of the real-time changes of the heat demand. This leads to the fact that the cold supplied by the cold-heat combined supply system cannot meet the cold demand of the NMP waste liquid purification device, so in this embodiment, an additional cold source is used to provide additional cold to ensure that the NMP vapor in the condensation tank CT in the NMP waste liquid purification device is efficiently condensed.

[0078] In addition, the yield of 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; or the purification of a tank of NMP waste liquid has just been completed, and there is no new NMP waste liquid to be purified at present).

[0079] 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 when the heat demand increases, the cold supply is increased; when the cold demand decreases, the heat supply is reduced or the excess heat is sent to the end heat using equipment HET. 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 generated 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.

[0080] The embodiment provides a heat load-based control method for controlling an NMP waste liquid purification cold-heat combined supply system as described in Embodiment 1 based on a heat load:

[0081] 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 an initial load P1.

[0082] 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 a first ideal temperature interval, and the high-temperature hot water temperature fluctuates within a second ideal temperature interval.

[0083] In the embodiment, T1'=5°C, T1''=8°C, T4'=120°C, and T4''=125°C; P0 is 50% of the full load, and P1 is 53% of the full load.

[0084] In the embodiment, T1'=5°C, T1''=8°C, T4'=120°C, and T4''=125°C; P0 is 50% of the full load, and P1 is 53% of the full load.

[0085] In S2, the following is included:

[0086] ① If the current high-temperature hot water temperature T4 < T4´´, then close the second gas outlet end of the first three-way regulating valve TWV1, and increase the load of each compressor in the first compressor group COMP1.

[0087] Because the heat required by the NMP waste liquid purification device is uncertain and may suddenly change, it is not practical to calculate the heat required at the current time and then control the combined cooling heating system to provide the corresponding heat.

[0088] We determine whether the current heat supply of the combined cooling heating system can meet the heat demand of the NMP waste liquid purification device by monitoring the high-temperature hot water temperature T4 in real time. 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 heating system can fully meet the heat demand of the NMP waste liquid purification device. Considering that the high-temperature hot water temperature T4 is difficult to maintain at the ideal temperature T * without change, we settle for keeping the high-temperature hot water temperature T4 as stable as possible within the second ideal temperature interval. Therefore, when the current high-temperature hot water temperature T4 < T4´´, we believe that the current heat supply of the combined cooling heating system is far from meeting the heat demand of the NMP waste liquid purification device, so we keep the second gas outlet end of the first three-way regulating valve TWV1 closed regardless of whether it is already open, and increase the load of each compressor in the first compressor group COMP1 to rapidly increase the heat supply of the combined cooling heating system.

[0089] In this embodiment, T * = 123℃.

[0090] ② 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 first compressor group COMP1 is currently above P1, then reduce the load of each compressor in the first compressor group COMP1.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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´´.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] If 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.

[0103] Regardless of 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 in a healthy state above P1 at present, 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.

[0104] If 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.

[0105] 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 case ⑤, after processing, the load of each compressor in the first compressor group COMP1 can be gradually increased to a healthy state.

[0106] In S2, based on the above seven cases, 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, thereby ensuring the purification efficiency of the NMP waste liquid purification device:

[0107] Q1=[C×(T2-T3)+(h1-h2)]×ρ×f2; Q2=[(COP-1) / (1+COP)]×Q1; Q3=Q1; Q4=Q3-Q2; q=Q4 / (C×△T);

[0108] Where Q1 represents the heat demand of the current NMP waste liquid purification unit, in 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 flow meter F2, in m³ / s. 3 / s; h1 represents the specific enthalpy of water vapor at the current temperature T2, in kJ / kg; h2 represents the specific enthalpy of saturated water at the current temperature T2, in 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 performance of the cascade chiller-heat pump unit, which is obtained by actual measurement by each manufacturer, and this value is usually 2 to 3; the first heat Q3 represents the cooling capacity requirement of the current 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.

[0109] 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 air outlet of the first three-way regulating valve TWV1 is at its maximum, if the first chilled water T1<T1´, then the heating water pump PUMP5 is turned on. At this time, the heating supply of the combined cooling and heating system is too large, so that even without an additional cold source ECS to provide additional cooling capacity, the temperature of the first chilled water T1 is still too low. In order to prevent the first chilled water T1 from freezing due to a sudden drop in temperature to 0 degrees Celsius or below in 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, that is, directly uses the high-temperature hot water (T4>T4´´) to raise the temperature of the first chilled water T1, which also further ensures the safe operation of the entire combined cooling and heating system.

[0110] Optionally, to ensure the safe operation of the third compressor COMP3, the third compressor COMP3 will be shut down when the outlet temperature exceeds a set threshold.

[0111] In this implementation, the set threshold for the outlet temperature of the third compressor COMP3 is 132 degrees Celsius.

[0112] The total time consumed for starting up the compressor and adjusting the load to the required value is much longer than that for directly adjusting the load of the started compressor to the required value. The control method based on the heat load of the present embodiment ensures that each compressor is in an open state during operation, so that each compressor can quickly respond to the change in load demand, thereby improving the response rate and flexibility of the entire combined cooling and heating system.

[0113] The control method of the present embodiment ensures that the load of each compressor is in a healthy state, thereby improving the service life of the compressor and the entire combined cooling and heating system, and reducing the operation and maintenance cost of the combined cooling and heating system.

[0114] The control method of the present embodiment is based on heat, and the heat required by the NMP waste liquid purification device changes in real time. This change causes 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, thereby causing the combined cooling and heating system to malfunction and shut down. Therefore, the control method of the present 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. Furthermore, because the heat required by the NMP waste liquid purification device changes in real time, it is not feasible to know the heat demand in advance and then accurately adjust the heat supply of the combined cooling and heating system. In the control method of the present embodiment, the most creative aspect is that the change in the high-temperature hot water temperature T4 is used to measure the real-time change in the heat demand of the NMP waste liquid purification device, and the high-temperature hot water temperature T4 is directly controlled to be within the second ideal temperature range, so as to ensure that the heat 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.

[0115] Under the guidance of the control method described above, the control method of the present embodiment also satisfies 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 these conditions, the excess heat is supplied to the end heat utilization equipment.

[0116] That is, the control method of the present embodiment not only meets the real-time change in the heat demand of the NMP waste liquid purification device in time, improves the NMP waste liquid purification efficiency, and reduces the power consumption during system operation as much as possible, but also utilizes the unused heat of the NMP waste liquid purification device (supplies the end heat utilization equipment), thereby greatly improving the service life of the entire combined cooling and heating system.

[0117] 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.

[0118] 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 quantity 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 quantity 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".

[0119] 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.

[0120] 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, and 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 combined cooling and heating system for purifying NMP waste liquid, characterized in that: The NMP waste liquid purification device comprises one or more sets of evaporative-condensing tank sets in parallel, each set of evaporative-condensing tank sets comprising an evaporative tank ET and a condensing tank CT; the cascade cold-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 energy at a cold energy end and generates heat at a heat energy end; the cold supply module brings the cold energy at the cold energy end into circulating chilled water through heat exchange, and the chilled water exchanges heat when flowing through the condensing tank CT, bringing the heat in the condensing tank CT back and sending it to the cold energy end; the heat supply module brings the heat at the heat energy end into circulating condensed water through heat exchange, and the condensed water exchanges heat when flowing through the evaporative tank ET, bringing the cold energy in the evaporative tank ET back and sending it to the heat energy end; the NMP waste liquid in the evaporative tank ET forms NMP vapor at the top of the evaporative tank ET after absorbing heat, and then flows into the condensing tank CT, and the NMP vapor condenses into liquid NMP in the condensing tank CT; the cold supply module further comprises a supercooling protection unit that brings part of the heat in the heat supply module into the chilled water; 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 that are coupled to each other; the outlet end of the first compressor group COMP1 is in communication with the first condensing inflow pipeline; the inlet end of the first compressor group COMP1 is in communication with the first condensing outflow pipeline; the inlet end of the first compressor group COMP1 is in communication with the first condensing outflow pipeline; 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 that are coupled to each other, the outlet end of the second compressor group COMP2 is in communication with the second condensing inflow pipeline, and the inlet end of the second compressor group COMP2 is in communication with the first evaporating outflow pipeline; the second condensing outflow pipeline is in communication with the first evaporating inflow pipeline.

2. The NMP waste liquid purification combined cooling and heating system according to claim 1, characterized in that: The cold supply module comprises a chilled water pump PUMP1 and a heat exchanger H1; each condensing tank CT is connected in parallel to the NMP waste liquid purification device total water inlet pipe and the NMP waste liquid purification device total water outlet pipe through a chilled water branch pipeline provided therein; the NMP waste liquid purification device total water inlet pipe is provided in the high-temperature side of the heat exchanger H1; the water inlet end of the chilled water pump PUMP1 is in communication with the NMP waste liquid purification device total water outlet pipe, and the water outlet end of the chilled water pump PUMP1 is in communication with the NMP waste liquid purification device total water inlet pipe.

3. The NMP waste liquid purification combined cooling and heating system according to claim 2, characterized in that: The heat supply module comprises a flash tank TANK1, a hot water pump PUMP2 and a third compressor COMP3; the upper part 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 part 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 is communicated with the water inlet end of the flash tank TANK1, and the hot water inlet pipeline is communicated with the water outlet end of the flash tank TANK1; the hot water inlet pipeline is provided with the hot water pump PUMP2; the gas outlet of the flash tank TANK1 is communicated with the gas inlet end of the third compressor COMP3; the gas outlet end of the third compressor COMP3 is communicated with the gas inlets of the evaporation tanks ET, and the water outlets of the evaporation tanks ET are communicated with the water supplement port of the flash tank TANK1.

4. The NMP waste liquid purification combined cooling and heating system according to claim 3, characterized in that: The heat supply module further comprises a first three-way valve TWV1 and a terminal heat utilization device HET; the gas inlet end of the first three-way valve TWV1 is communicated with the gas outlet of the third compressor COMP3, the first gas outlet end of the first three-way valve TWV1 is communicated with the gas inlets of the evaporation tanks ET, and the second gas outlet end of the first three-way valve TWV1 is communicated with the gas inlet of the terminal heat utilization device HET; the water outlet of the terminal heat utilization device HET is communicated with the water supplement port of the flash tank TANK1.

5. The NMP waste liquid purification combined cooling and heating system according to claim 4, characterized in that: The heat supply module further comprises a condensate recovery tank TANK2 and a condensate recovery pump PUMP3; the water outlet of the terminal heat utilization device HET and the water outlets of all the evaporation tanks ET are communicated with the water inlet of the condensate recovery tank TANK2, and the water outlet of the condensate recovery tank TANK2 is communicated with the water supplement 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 supplement port of the flash tank TANK1.

6. The combined cooling and heating system for purifying NMP waste liquid according to any one of claims 3-5, characterized in that: The cooling module further comprises an extra cold source ECS and a cold water supplement pump PUMP4; the branch water pipe of the extra cold source ECS 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 PUMP4 is arranged on the branch water pipe of the extra cold source ECS; the supercooling protection unit comprises 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 refrigeration water pump PUMP1 is arranged through the low temperature side of the second heat exchanger H2; the hot water outlet pipeline of the second cascade heat exchanger FH2 is communicated with the water inlet pipeline arranged through the high temperature side of the second heat exchanger H2; the water inlet end of the flash tank TANK1 is communicated with the water outlet pipeline arranged through the high temperature side of the second heat exchanger H2; the high temperature side water outlet pipeline of the second heat exchanger H2 is provided with the temperature rising water pump PUMP5.

7. A control method based on heat load, for controlling the NMP waste liquid purification combined cooling and heating system according to claim 6, comprising the following steps: S1, closing the exhaust valve EV, starting the 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 the initial load P1. S2, real-time monitoring 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 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 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 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 COMP3; the third condensate water temperature T3 is the condensate water temperature at the outlet of the evaporating tank ET; 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 H1; the high-temperature hot water temperature T4 is the temperature of the high-temperature hot water entering the inlet of the flash tank TANK1; the healthy state means that the load of the compressor is above the critical load P0, 0 8. The control method based on heat load according to claim 7, characterized by, In S2, the following contents are included: if the current high-temperature hot water temperature T4 is less than T4´´, the second outlet of the first three-way 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" and the previous If the high-temperature hot-water temperature T4 is constantly rising in the period t and the load of each compressor in the current first compressor group COMP1 is above P1, the load of each compressor in the current first compressor group COMP1 is reduced. If the current high-temperature hot water temperature T4' ≤ T4 ≤ T4" and the previous If the high-temperature hot water temperature T4 keeps rising within the time t, and the load of each compressor in the first compressor group COMP1 is less than P1, then the valve opening of the second gas outlet end of the first three-way regulating valve TWV1 is increased. If the current high-temperature hot water temperature T4' ≤ T4 ≤ T4", the previous If the high-temperature hot water temperature T4 continuously decreases in the period t and the load of each compressor in the first compressor group COMP1 is above P1, if the valve of the second outlet of the first three-way regulating valve TWV1 is opened, the valve opening of the second outlet of the first three-way regulating valve TWV1 is reduced; if the valve of the second outlet of the first three-way regulating valve TWV1 is 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 previous If the first chilled-water temperature T1 continuously decreases within t time and the load of each compressor in the first compressor group COMP1 is less than P1, the load of each compressor in the first compressor group COMP1 is increased. If the current high-temperature hot water temperature T4 is greater than T4´´, and the load of each compressor in the first compressor group COMP1 is greater than P1, the load of each compressor in the first compressor group COMP1 is reduced; If the current high-temperature hot water temperature T4 is greater than T4´´, and the load of each compressor in the first compressor group COMP1 is less than P1, the valve opening degree of the second outlet of the first three-way valve TWV1 is increased.

9. The control method based on heat load according to claim 7, characterized by, In S2, the following contents are included: Adjusting the power of the cold water pump PUMP4, so that the additional cold source ECS adds the additional cold quantity Q4 into the current cooling module through the water supply flow rate q: Q1 = [C x (T2 - T3) + (h1 - h2)] x p x f2; Q2 = [(COP - 1) / (1 + COP)] x Q1; Q3 = Q1; Q4 = Q3 - Q2; q = Q4 / (C x T); Q1 = C * f2 * (h1 - h2) + Q2 / COP - Q3 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 rate entering all evaporation tanks ET; 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; and Q3 represents the cold demand of the current NMP waste liquid purification device; T represents the water temperature difference set by the additional cold source ECS; When the water supply flow rate q is 0, the current high-temperature hot water temperature T4 is greater than T4´´, and the valve opening degree of the first outlet of the first three-way valve TWV1 is maximum, if the first chilled water T1 is less than T1´, the temperature increasing water pump PUMP5 is started.

Images