Low temperature evaporation heat pump double effect evaporation system and method of operation thereof

Abstract

The application provides a low-temperature evaporation heat pump double-effect evaporation system and an operation method thereof, and can solve the problem of low heat utilization rate of single-effect evaporation in the prior art. The single-effect evaporation unit comprises a single-effect evaporation tank, and the double-effect evaporation unit comprises a double-effect evaporation tank and a vertical tube heat exchanger. The refrigerant heat pump system comprises a compressor, a cold-side heat exchanger, a single-effect heat exchanger and a throttling element. The single-effect heat exchanger heats the raw liquid in the single-effect evaporation tank. A raw liquid system is used to deliver the raw liquid to the single-effect evaporation tank and the double-effect evaporation tank. A vacuum pumping system is connected to the single-effect evaporation tank and the double-effect evaporation tank. A distilled water system is used to discharge distilled water. Single-effect secondary steam generated by the single-effect evaporation tank is connected to the vertical tube heat exchanger, exchanges heat with the raw liquid in the double-effect evaporation tank, is condensed into distilled water, and is discharged into the distilled water system. Double-effect secondary steam generated by the double-effect evaporation tank is condensed into distilled water in the cold-side heat exchanger and is discharged into the distilled water system.

Description

Technical Field

[0001] This invention relates to the field of low-temperature evaporation, specifically to a low-temperature evaporation heat pump dual-effect evaporation system and its operation method. Background Technology

[0002] Evaporation and concentration technology is commonly used for industrial wastewater reduction, resource recovery, and the concentration of high-salt and high-organic-content raw materials. Existing evaporation technologies have evolved from single-effect evaporation to multi-effect evaporation, and then to mechanical vapor recompression evaporation, with the core goal of reducing energy consumption, mitigating scaling and corrosion, and improving operational stability.

[0003] Multi-effect evaporation reduces the consumption of live steam and cooling water by using the secondary steam generated in the previous effect as the heat source for the next effect. However, multi-effect evaporation usually still requires external live steam as the initial heat source, and the system has many supporting facilities and occupies a large area. Under the condition of increased wastewater concentration and viscosity, the heat transfer coefficient of the subsequent evaporator decreases, the temperature difference between each effect is not easy to maintain, and the concentration treatment efficiency is limited.

[0004] Mechanical vapor recompression evaporators increase enthalpy by compressing secondary steam and recycling heat, exhibiting good energy-saving potential. However, under complex operating conditions such as zero wastewater discharge, heat exchanger scaling, increased boiling point of the concentrate, and fluctuations in the raw liquid's operating conditions can lead to a decrease in evaporation or even shutdown. Furthermore, when using raw wastewater to cool the secondary superheated steam, the condensate temperature is high, compressor control becomes complex, and system stability is affected.

[0005] Low-temperature vacuum evaporators lower the boiling point of the raw liquid by creating a vacuum, allowing it to evaporate at a lower temperature. This helps reduce the risk of coking, scaling, and corrosion, and also reduces the need for external steam and cooling water. However, conventional low-temperature evaporators are mostly single-effect evaporators, and the waste heat from the secondary steam is not fully utilized, leaving room for improvement in heat utilization efficiency. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a low-temperature evaporative heat pump dual-effect evaporation system and its operation method, which can solve the problem of low waste heat utilization rate in existing single-effect evaporation systems and also improve the problem of easy coking and scaling on the heat exchange surface.

[0007] The technical solution is as follows: a low-temperature evaporative heat pump dual-effect evaporation system, characterized in that it includes: A single-effect evaporation unit includes a single-effect evaporation tank, the bottom of which is connected to a single-effect circulation pump; The double-effect evaporation unit includes a double-effect evaporator and a vertical tube heat exchanger disposed within the double-effect evaporator; The refrigerant heat pump system includes a compressor, a cold-side heat exchanger, a first-effect heat exchanger, and a throttling element connected by pipelines. The first-effect heat exchanger is installed inside the first-effect evaporator and is used to heat the raw liquid inside the first-effect evaporator. The raw material system is connected to the first-effect evaporator and the second-effect evaporator respectively, and is used to supply raw materials to the first-effect evaporator and the second-effect evaporator; The vacuum system, connected to the first-effect evaporator and the second-effect evaporator, is used to maintain the vacuum level within the system; the distilled water system is used to discharge distilled water. The steam outlet of the first-effect evaporator is connected to the inlet of the vertical tube heat exchanger in the second-effect evaporator, so that the first-effect secondary steam generated by the first-effect evaporator can be directly connected to the vertical tube heat exchanger. After the first-effect secondary steam exchanges heat with the raw liquid in the second-effect evaporator, it is condensed into distilled water and discharged into the distilled water system. The steam outlet of the second-effect evaporator is connected to the cold-side heat exchanger, so that the second-effect secondary steam generated by the second-effect evaporator is condensed into distilled water in the cold-side heat exchanger and discharged into the distilled water system.

[0008] Furthermore, the compressor is an air-suspension compressor, the first-effect heat exchanger is a falling film heat exchanger installed inside the first-effect evaporator, the top of the first-effect evaporator is provided with a film distributor, and the first-effect evaporator is also connected to a separation tank.

[0009] Furthermore, the film distributor is positioned above the heat exchange tubes of the falling film heat exchanger to evenly distribute the raw liquid onto the inner wall of the heat exchange tubes, allowing the raw liquid to flow downwards in a thin film along the inner wall of the heat exchange tubes and exchange heat with the refrigerant outside the tubes; the separation tank is positioned downstream of the first-effect evaporator to perform gas-liquid separation of the liquid at the bottom of the first-effect evaporator, and the steam outlet of the separation tank is connected to the inlet of the vertical tube heat exchanger in the second-effect evaporator.

[0010] Furthermore, the inlet of the first-effect circulating pump is connected to the bottom of the first-effect evaporator, and the outlet of the first-effect circulating pump is connected to the film distributor. The first-effect circulating pump drives the raw liquid to circulate between the first-effect evaporator and the film distributor, so that a continuous and uniform liquid film is maintained on the inner wall of the heat exchange tube, which enhances heat exchange while reducing the occurrence of coking and scaling on the heat exchange surface.

[0011] Furthermore, the compressor's exhaust port is connected to the refrigerant inlet of the first-effect heat exchanger, the refrigerant outlet of the first-effect heat exchanger is connected to the refrigerant inlet of the cold-side heat exchanger through the throttling element, and the refrigerant outlet of the cold-side heat exchanger is connected to the compressor's suction port. The refrigerant flows sequentially through the compressor, the first-effect heat exchanger, the throttling element, and the cold-side heat exchanger, forming a closed refrigerant circulation loop. This transfers the condensation heat of the second-effect secondary steam absorbed in the cold-side heat exchanger to the first-effect heat exchanger for heating the raw liquid, thus realizing the recycling of heat within the system.

[0012] Furthermore, the heat exchange tubes of the vertical tube heat exchanger are vertically arranged, and the tube-side outlet of the vertical tube heat exchanger is connected to the distilled water system. The distilled water formed by the condensation of the secondary steam in the heat exchange tubes flows into the distilled water system by gravity, without the need for additional transportation power, and can avoid the accumulation of condensate in the tube side, which would affect the heat exchange effect; the distilled water outlet of the cold-side heat exchanger is connected to the distilled water system.

[0013] Furthermore, the ratio of raw liquid supplied by the raw liquid supply system to the first-effect evaporator and the second-effect evaporator is 0.8:1 to 1.2:1.

[0014] Furthermore, the first-effect evaporator and the second-effect evaporator are each equipped with a discharge pump to discharge the concentrated liquid after evaporation and concentration; the vacuum system is connected to the gas phase space of the first-effect evaporator and the second-effect evaporator through pipelines to discharge the non-condensable gas in the system to the atmosphere.

[0015] A method for operating a low-temperature evaporative heat pump double-effect evaporation system, applied to the aforementioned low-temperature evaporative heat pump double-effect evaporation system, includes the following steps: The raw liquid is supplied to the first-effect evaporator and the second-effect evaporator respectively; Start the vacuum system to put the first-effect evaporator and the second-effect evaporator into a vacuum evaporation state; The raw liquid in the first-effect evaporator is heated by the heat exchanger of the first-effect heat pump system, so that the first-effect evaporator generates first-effect secondary steam. The primary effect secondary steam is directly delivered to the vertical tube heat exchanger in the secondary effect evaporator, so that the primary effect secondary steam exchanges heat with the raw liquid in the secondary effect evaporator and condenses into distilled water, and the raw liquid in the secondary effect evaporator is heated to generate secondary effect secondary steam. The secondary steam from the double-effect heat pump system is delivered to the cold-side heat exchanger of the refrigerant heat pump system and condensed into distilled water. Distilled water formed by the condensation of secondary steam from the first effect and distilled water formed by the condensation of secondary steam from the second effect are discharged into the distilled water system.

[0016] Furthermore, by maintaining the vacuum level in the first-effect evaporator and the second-effect evaporator through a vacuum system, the boiling point of the raw liquid in the first-effect evaporator and the second-effect evaporator is reduced to 30℃~40℃. The raw liquid achieves low-temperature evaporation under vacuum negative pressure conditions, which can avoid coking, scaling and thermal degradation of materials caused by high-temperature evaporation, and reduce system energy consumption.

[0017] In the low-temperature evaporative heat pump dual-effect evaporation system of the present invention, the first-effect evaporation unit uses the condensation heat released by the heat pump hot side as the raw liquid heating source, and the second-effect evaporation unit uses the secondary steam generated by the first-effect evaporation unit as the heating source. The heat of the secondary steam in the second effect is absorbed by the heat exchanger on the cold side of the heat pump. After the refrigerant evaporates, it returns to the heat pump cycle. The system realizes two-stage utilization and recycling of heat. The second-effect evaporation does not require a separate steam heat source, which significantly improves the heat utilization rate and the evaporation capacity per unit of electricity consumption is greater. The system only uses electricity as the input energy and does not require an external steam source or external cooling water. It has fewer supporting facilities and is convenient to install and use.

[0018] In this invention, the secondary steam of the first effect does not pass through an intermediate heat exchanger and directly enters the tube side of the vertical shell-and-tube heat exchanger of the second effect as a heating source. This eliminates the intermediate heat exchanger and corresponding pipeline valves in conventional double-effect systems, making the system structure compact and the secondary steam flow of the first effect shorter. This can reduce the equipment footprint and manufacturing costs, and reduce heat loss caused by intermediate heat exchange links.

[0019] The first-effect evaporation unit of this invention employs forced heat exchange in conjunction with a circulating pump. The circulating pump drives the raw liquid to circulate continuously within the tank, creating a continuous liquid scouring effect on the heat exchange surface of the first-effect heat exchanger, thus improving heat transfer efficiency and significantly reducing coking and scaling deposits on the heat exchange surface. The second-effect evaporation unit uses vertical tube heat exchange. The secondary steam from the first effect enters the tube side for heat exchange and condensation under the combined action of gravity and vacuum. The condensate flows downward along the tube side and is discharged by gravity, ensuring smooth drainage. The vacuum system maintains a low-temperature boiling environment, allowing the raw liquid to evaporate at a lower temperature, mitigating coking, scaling, and corrosion problems caused by high temperatures. The combination of these two elements contributes to the long-term operational stability of the system. Attached Figure Description

[0020] Figure 1 This is a system block diagram of the low-temperature evaporative heat pump dual-effect evaporation system in the embodiment. Detailed Implementation

[0021] Example: Reference Figure 1 This embodiment provides a low-temperature evaporative heat pump dual-effect evaporation system, including a first-effect evaporation unit and a second-effect evaporation unit. The system utilizes heat in stages through a refrigerant heat pump system. The first-effect evaporation unit adopts a falling film heat exchanger 105, and the refrigerant heat pump system adopts an air-suspension compressor 303. The first-effect evaporation unit is also equipped with a film distributor 106 and a separator tank 107.

[0022] The single-effect evaporation unit includes a single-effect evaporator 101 and a falling film heat exchanger 105 disposed inside the single-effect evaporator 101. The falling film heat exchanger 105 includes multiple vertical falling film heat exchange tubes. The falling film heat exchanger 105 is installed inside the single-effect evaporator 101. A film distributor 106 is provided on the top of the single-effect evaporator 101. The film distributor 106 is located above the falling film heat exchange tubes and is used to evenly distribute the raw liquid to the inner wall surface of each falling film heat exchange tube. After the raw liquid flows out from the film distributor 106, it flows downward in a thin film along the inner wall of the heat exchange tube. The high-temperature refrigerant of the refrigerant heat pump system flows on the outside of the heat exchange tube and transfers heat to the raw liquid film on the inner wall of the tube through the tube wall, causing the raw liquid to evaporate. The first-effect evaporator 101 is also connected to a separation tank 107, which is used to separate the liquid discharged from the bottom of the first-effect evaporator 101. The steam outlet of the separation tank 107 is connected to the inlet of the vertical tube heat exchanger 202 in the second-effect evaporator to separate the steam entrained in the incompletely evaporated liquid and improve the steam recovery rate. A first-effect evaporator 101 is connected to a first-effect circulating pump 103 at its bottom. The inlet of the first-effect circulating pump 103 is connected to the bottom of the first-effect evaporator 101, and the outlet of the first-effect circulating pump 103 is connected to a film distributor 106 through a pipeline. This drives the raw liquid to circulate between the first-effect evaporator 101 and the film distributor 106, ensuring that the inner wall of the heat exchange tube is always covered by a uniform liquid film, improving heat exchange efficiency and inhibiting scaling. In this embodiment, a falling film heat exchanger is used, where the raw liquid flows in a thin film state. The thin liquid film results in low thermal resistance, high coefficient, and small evaporation temperature difference, making it particularly suitable for processing heat-sensitive materials. A first discharge pump 104 is also provided at the bottom of the first-effect evaporator 101 to discharge the concentrated liquid after evaporation and concentration.

[0023] In this embodiment, the double-effect evaporation unit includes a double-effect evaporator 201 and a vertical tube heat exchanger 202 disposed within the double-effect evaporator 201. The double-effect evaporator 201 is a vertical container structure. The vertical tube heat exchanger 202 consists of multiple vertically arranged heat exchange tubes. The tube-side inlet of the vertical tube heat exchanger 202 is connected to the steam outlet of the first-effect evaporator 101 via a pipeline. The first-effect secondary steam generated by the evaporation of the raw liquid in the first-effect evaporator 101 directly enters the tube side of the vertical tube heat exchanger 202, flows inside the tubes, and transfers heat through the tube walls to the raw liquid inside the second-effect evaporator 201 outside the tubes, causing the second-effect raw liquid to be heated and evaporated to generate second-effect secondary steam. After releasing heat in the tube side, the first-effect secondary steam condenses into distilled water. The condensate is discharged from the tube-side outlet and enters the distilled water system 400. A second discharge pump 203 is provided at the bottom of the double-effect evaporator 201 for discharging the concentrate. By directly utilizing the secondary steam of the first effect, the intermediate heat exchanger is eliminated, simplifying the system structure and avoiding heat loss in the intermediate heat exchange links. In the vertical tube heat exchanger 202, the secondary steam of the first effect condenses inside the tubes, and the condensate flows out naturally downwards by gravity, ensuring smooth drainage and preventing liquid accumulation that could affect the heat exchange efficiency.

[0024] The refrigerant heat pump system includes an air-suspended compressor 303, a falling film heat exchanger 105, a cold-side heat exchanger 302, and a throttling element. The air-suspended compressor 303 has high operating efficiency, low vibration, and long service life. The air-suspended compressor 303 uses gas bearings to support the rotor, and the rotor has no contact friction during operation, so no lubricating oil is required. Its oil-free operation mode solves the problem of difficult oil return that is easy to occur in traditional oil-filled compressors in low-temperature evaporative heat pump systems. It can reduce the risk of heat exchange efficiency reduction or even compressor damage caused by the accumulation of lubricating oil in the refrigerant circuit. After the high-temperature and high-pressure refrigerant is discharged from the exhaust port of the air-suspension compressor 303, it enters the outside of the tube of the falling film heat exchanger 105 through the refrigerant inlet, releasing heat to heat the original liquid film inside the tube. The condensed refrigerant flows out from the refrigerant outlet of the falling film heat exchanger 105, and after being throttled and depressurized by the throttling element, it enters the cold-side heat exchanger 302 through the refrigerant inlet, absorbing the heat of the secondary steam of the second effect. After absorbing heat and evaporating into low-temperature and low-pressure gas, the refrigerant flows out from the refrigerant outlet of the cold-side heat exchanger 302 and returns to the suction port of the air-suspension compressor 303. This cycle repeats, forming a refrigerant circulation loop. The refrigerant heat pump system simultaneously heats the original liquid of the first effect and condenses and recovers the secondary steam of the second effect.

[0025] The raw liquid inlet system 500 is connected to the first-effect evaporator 101 and the second-effect evaporator 201 respectively. The raw liquid is fed into the first-effect evaporator 101 and the second-effect evaporator 201 at a ratio of 1:1. The equal ratio of the raw liquid inlet can ensure that the evaporation load of the two effects is basically balanced, which is conducive to the stable operation of the system and the overall evaporation efficiency. When the properties of the raw liquid or the evaporation load changes, the ratio of the raw liquid inlet can be adjusted to 0.8:1 to 1.2:1 to maintain the load matching between the first-effect evaporation unit and the second-effect evaporation unit. The vacuum system 600 is connected to the gas phase space of the first-effect evaporator 101 and the second-effect evaporator 201 via gas phase pipelines to maintain the vacuum level within the system. Under vacuum negative pressure conditions, the boiling point of the raw liquid is reduced to 30℃~40℃, enabling low-temperature evaporation. Low-temperature evaporation avoids coking and scaling problems caused by high-temperature evaporation and also reduces the system's energy consumption. The concentration rate of the raw liquid can reach 70%~95%, depending on the quality and specific gravity of the raw liquid. At the same time, the vacuum system 600 discharges the accumulated non-condensable gases in the system to the atmosphere, ensuring the system's heat transfer efficiency and evaporation efficiency. The distilled water system 400 collects distilled water produced by the condensation of the tube side of the vertical tube heat exchanger 202 and the condensation of the cold-side heat exchanger 302. The tube side outlet of the vertical tube heat exchanger 202 and the distilled water outlet of the cold-side heat exchanger 302 are connected to the distilled water system 400, and the two distilled water streams are discharged together.

[0026] The operation method of the low-temperature evaporative heat pump double-effect evaporation system in this embodiment is as follows: The raw liquid system delivers the raw liquid to the first-effect evaporator and the second-effect evaporator according to the set ratio; the air-suspension compressor starts and runs, and the high-temperature refrigerant flows outside the heat exchange tubes of the first-effect falling film heat exchanger and releases heat; the raw liquid is evenly distributed on the inner wall surface of each falling film heat exchange tube through the film distributor, flows downward in a thin film state, and evaporates to generate secondary steam; the secondary steam generated by the first-effect evaporation unit enters the tube side of the second-effect vertical tube heat exchanger directly through the pipeline, exchanges heat with the raw liquid outside the tubes of the second-effect, and the raw liquid in the second-effect evaporates to generate secondary steam, and the secondary steam in the first-effect condenses into distilled water; the secondary steam in the second-effect enters the cold side heat exchanger. The heat exchanger absorbs heat from the refrigerant and condenses it into distilled water; the liquid discharged from the bottom of the first-effect evaporator enters the separator for gas-liquid separation; the first-effect circulating pump pumps the unevaporated raw liquid back to the film distributor for circulating evaporation; the distilled water formed by the condensation of the second-effect secondary steam and the second-effect secondary steam are both discharged into the distilled water system; when the concentrate in the first-effect or second-effect evaporator reaches the preset liquid level, preset density, or preset concentration ratio, the concentrated liquid after evaporation is discharged through its respective discharge pump; the vacuum system runs continuously to maintain the system vacuum and remove non-condensable gases, keeping the boiling point of the raw liquid in the first-effect and second-effect evaporators at 30℃~40℃, achieving low-temperature evaporation.

[0027] In this embodiment, the air-suspension compressor operates without oil, which can eliminate the risk of oil return difficulties and improve the reliability and service life of the system; the falling film heat exchanger has a high heat transfer coefficient and a small evaporation temperature difference, and together with the film distributor, it ensures uniform liquid film distribution and high heat exchange efficiency. The configuration in this embodiment is particularly suitable for working conditions that are sensitive to lubricating oil contamination or for application scenarios that require high heat transfer efficiency.

[0028] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0029] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A low-temperature evaporative heat pump dual-effect evaporation system, characterized in that, include: A single-effect evaporation unit includes a single-effect evaporation tank, the bottom of which is connected to a single-effect circulation pump; The double-effect evaporation unit includes a double-effect evaporator and a vertical tube heat exchanger disposed within the double-effect evaporator; The refrigerant heat pump system includes a compressor, a cold-side heat exchanger, a first-effect heat exchanger, and a throttling element connected by pipelines. The first-effect heat exchanger is installed inside the first-effect evaporator and is used to heat the raw liquid inside the first-effect evaporator. The raw material system is connected to the first-effect evaporator and the second-effect evaporator respectively, and is used to supply raw material to the first-effect evaporator and the second-effect evaporator; The vacuum system, connected to the first-effect evaporator and the second-effect evaporator, is used to maintain the vacuum level within the system; the distilled water system is used to discharge distilled water. The steam outlet of the first-effect evaporator is connected to the inlet of the vertical tube heat exchanger in the second-effect evaporator, so that the first-effect secondary steam generated by the first-effect evaporator can be directly connected to the vertical tube heat exchanger. After the first-effect secondary steam exchanges heat with the raw liquid in the second-effect evaporator, it is condensed into distilled water and discharged into the distilled water system. The steam outlet of the second-effect evaporator is connected to the cold-side heat exchanger, so that the second-effect secondary steam generated by the second-effect evaporator is condensed into distilled water in the cold-side heat exchanger and discharged into the distilled water system.

2. The low-temperature evaporative heat pump dual-effect evaporation system according to claim 1, characterized in that: The compressor is an air-suspension compressor, the first-effect heat exchanger is a falling film heat exchanger installed inside the first-effect evaporator, the top of the first-effect evaporator is provided with a film distributor, and the first-effect evaporator is also connected to a separation tank.

3. The low-temperature evaporative heat pump double-effect evaporation system according to claim 2, characterized in that: The film distributor is located above the heat exchange tubes of the falling film heat exchanger and is used to evenly distribute the raw liquid to the inner wall of the heat exchange tubes, so that the raw liquid flows downward along the inner wall of the heat exchange tubes in a thin film and exchanges heat with the refrigerant outside the tubes; the separator is located downstream of the first-effect evaporator and is used to perform gas-liquid separation of the liquid at the bottom of the first-effect evaporator. The steam outlet of the separator is connected to the inlet of the vertical tube heat exchanger in the second-effect evaporator.

4. The low-temperature evaporative heat pump double-effect evaporation system according to claim 2, characterized in that: The inlet of the first-effect circulating pump is connected to the bottom of the first-effect evaporator, and the outlet of the first-effect circulating pump is connected to the film distributor. The first-effect circulating pump drives the raw liquid to circulate between the first-effect evaporator and the film distributor.

5. The low-temperature evaporative heat pump dual-effect evaporation system according to claim 1, characterized in that: The compressor's exhaust port is connected to the refrigerant inlet of the first-effect heat exchanger, the refrigerant outlet of the first-effect heat exchanger is connected to the refrigerant inlet of the cold-side heat exchanger through the throttling element, and the refrigerant outlet of the cold-side heat exchanger is connected to the compressor's suction port. The refrigerant flows sequentially through the compressor, the first-effect heat exchanger, the throttling element, and the cold-side heat exchanger, forming a refrigerant circulation loop.

6. The low-temperature evaporative heat pump double-effect evaporation system according to claim 1, characterized in that: The heat exchange tubes of the vertical tube heat exchanger are arranged vertically, and the tube outlet of the vertical tube heat exchanger is connected to the distilled water system. The distilled water formed by the condensation of the secondary steam in the heat exchange tubes is discharged into the distilled water system by gravity. The distilled water outlet of the cold-side heat exchanger is connected to the distilled water system.

7. The low-temperature evaporative heat pump double-effect evaporation system according to claim 1, characterized in that: The ratio of raw liquid supplied by the raw liquid supply system to the first-effect evaporator and the second-effect evaporator is 0.8:1 to 1.2:

1.

8. The low-temperature evaporative heat pump double-effect evaporation system according to claim 1, characterized in that: The first-effect evaporator and the second-effect evaporator are each equipped with a discharge pump to discharge the concentrated liquid after evaporation and concentration; the vacuum system is connected to the gas phase space of the first-effect evaporator and the second-effect evaporator through pipelines to discharge the non-condensable gas in the system to the atmosphere.

9. A method for operating a low-temperature evaporative heat pump double-effect evaporation system, characterized in that, The method applied to the low-temperature evaporative heat pump dual-effect evaporation system according to any one of claims 1 to 8 includes the following steps: The raw liquid is supplied to the first-effect evaporator and the second-effect evaporator respectively; Start the vacuum system to put the first-effect evaporator and the second-effect evaporator into a vacuum evaporation state; The raw liquid in the first-effect evaporator is heated by the heat exchanger of the first-effect heat pump system, so that the first-effect evaporator generates first-effect secondary steam. The primary effect secondary steam is directly delivered to the vertical tube heat exchanger in the secondary effect evaporator, so that the primary effect secondary steam exchanges heat with the raw liquid in the secondary effect evaporator and condenses into distilled water, and the raw liquid in the secondary effect evaporator is heated to generate secondary effect secondary steam. The secondary steam from the double-effect heat pump system is delivered to the cold-side heat exchanger of the refrigerant heat pump system and condensed into distilled water. The distilled water formed by the condensation of the first-effect secondary steam and the distilled water formed by the condensation of the second-effect secondary steam are discharged into the distilled water system.

10. The operation method of the low-temperature evaporative heat pump double-effect evaporation system according to claim 9, characterized in that: By maintaining the vacuum level in the first-effect evaporator and the second-effect evaporator through a vacuum system, the boiling point of the raw liquid in the first-effect evaporator and the second-effect evaporator is reduced to 30℃~40℃, and the raw liquid achieves low-temperature evaporation under vacuum negative pressure conditions.

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