A circulation system and a circulation processing method

Abstract

The present disclosure relates to a circulating system and a circulating processing method. The circulating system comprises: a circulating system of desalted water and chilled water, the circulating system comprising: a compressed air unit for preparing compressed air; a desalted water preparation unit in communication with the compressed air unit, for providing desalted water at a first temperature as a first cooling medium to the compressed air unit to cool the compressed air to a second temperature; while the temperature of the desalted water is raised to a third temperature; a chilled water unit in communication with the compressed air unit, for pre-cooling chilled water return water of a chiller unit using the gas discharged by the compressed air unit as a second cooling medium. The circulating system of the present disclosure cools the compressed air by desalted water, pre-cools the chilled water return water using the gas discharged by the compressed air unit, can realize the cascade utilization of the cold energy of the compressed air, improve the energy utilization rate, and at the same time can reduce the refrigeration load of the chiller unit and reduce the power consumption of the chiller unit.

Description

Technical Field

[0001] This disclosure relates to the field of industrial energy comprehensive utilization technology, and in particular to a recycling system and recycling method. Background Technology

[0002] In modern chemical, electronics, pharmaceutical, and food and beverage companies engaged in continuous production, compressed air, demineralized water, and chilled water are three key utilities. The energy consumption of the preparation systems corresponding to these three media often accounts for a major portion of the total energy consumption in the company's production area. Currently, these three systems are designed and operated independently in most companies' production areas. This independent operation mode leads to a mismatch in energy quality between systems, resulting in a significant waste of low-grade heating and cooling energy. Summary of the Invention

[0003] To overcome the problems existing in related technologies, this disclosure provides a cyclic system and a cyclic processing method.

[0004] According to embodiments of this disclosure, a cyclic system is provided, comprising: Compressed air unit, used to generate compressed air; A demineralized water preparation unit, connected to the compressed air unit, is used to provide demineralized water at a first temperature to the compressed air unit as a first cooling medium, so as to cool the compressed air to a second temperature; at the same time, the temperature of the demineralized water is raised to a third temperature. The chilled water unit, connected to the compressed air unit, is used to pre-cool the chilled water return water using the gas discharged from the compressed air unit as a second cooling medium. In some embodiments, the compressed air unit includes an air compressor, a cooler, and a dryer connected in sequence; The demineralized water preparation unit includes a raw water tank, a first heat exchanger, a reverse osmosis membrane module, and a demineralized water tank connected in sequence. The outlet of the demineralized water tank is connected to the dryer to form a first loop, so as to provide the dryer with demineralized water at the first temperature; the dryer is connected to the inlet of the first flow passage of the first heat exchanger to provide the first heat exchanger with demineralized water at the third temperature as a heat exchange medium for preparing demineralized water. The raw water tank is connected to the inlet of the second flow passage of the first heat exchanger to input raw water into the second flow passage, and the outlet of the second flow passage is connected to the reverse osmosis membrane module; after the raw water is heated by the heat exchange medium, it forms raw water at a fourth temperature, and the raw water at the fourth temperature is input into the reverse osmosis membrane module for desalination treatment to form desalinated water at the fourth temperature, and the desalinated water is input into the desalination tank; The outlet of the first flow path is connected to the desalination water point to form a second loop.

[0005] In some embodiments, the inlet of the first flow passage is provided with a first bypass, which is connected to the demineralized water tank to input a portion of the demineralized water at the third temperature into the demineralized water tank.

[0006] In some embodiments, the compressed air unit further includes a user-end exhaust end for discharging compressed air after use by the user end; The chilled water unit includes a compressed air receiving end, which is connected to the user end exhaust end and is used to receive compressed air after use by the user end. The chilled water unit also includes a chilled water return pipeline, a chiller unit, and a second heat exchanger; The compressed air receiving end is connected to the inlet of the third flow passage of the second heat exchanger, the outlet of the third flow passage of the second heat exchanger is connected to the atmospheric discharge pipeline, the chilled water return pipeline is connected to the inlet of the fourth flow passage of the second heat exchanger, and the outlet of the fourth flow passage of the second heat exchanger is connected to the chiller unit, forming a third loop. The compressed air used by the user end is used as the second cooling medium to cool the chilled water return water, and is discharged through the third flow passage; the chilled water return water output from the chilled water return water pipeline is cooled by the second cooling medium through the fourth flow passage of the second heat exchanger and then input into the chiller unit.

[0007] In some embodiments, a second bypass is provided between the inlet and outlet of the fourth flow passage. If the exhaust temperature at the user end exhaust end does not meet the heat exchange conditions, the inlet of the fourth flow passage of the second heat exchanger is closed or the second bypass is opened.

[0008] In some embodiments, the demineralized water preparation unit further includes a third heat exchanger; The outlet of the chiller unit is connected to the inlet of the fifth connecting passage of the third heat exchanger, the outlet of the fifth connecting passage of the third heat exchanger is connected to the chilled water return pipeline, the reverse osmosis membrane module is connected to the inlet of the sixth connecting passage of the third heat exchanger, and the outlet of the sixth connecting passage of the third heat exchanger is connected to the demineralized water tank; the demineralized water at the fourth temperature output by the reverse osmosis membrane module is cooled by the sixth connecting passage and then output to the demineralized water tank; the chilled water output from the outlet of the chiller unit serves as the third cooling medium to cool the demineralized water at the fourth temperature flowing through the sixth connecting passage.

[0009] In some embodiments, the circulation system further includes a control unit, which includes a controller and a data management platform; The controller is connected to the compressed air unit, the demineralized water preparation unit, and the chilled water unit via signal connection. It is used to collect the operating data of the first loop, the second loop, and the third loop, and to control the operation of the compressed air unit, the demineralized water preparation unit, and the chilled water unit according to the scheduling parameters provided by the data management platform. The data management platform is used to generate scheduling parameters based on the data collected by the controller and the scheduling model, and to send the scheduling parameters to the controller.

[0010] In some embodiments, the scheduling model includes: The determination module is used to determine the maximum recoverable cold capacity of each loop based on the operating parameters of each node in the first loop, the second loop, and the third loop. The optimization module is used to determine the optimal flow control parameters and optimal valve opening control parameters for the first loop, the second loop, and the third loop based on the maximum recoverable cold capacity, the optimization objective, and the constraints.

[0011] In some embodiments, the scheduling model further includes a feedforward feedback control module, used to adjust the flow rate of the outlet of the desalination tank according to the temperature feedforward data of the raw water, and to adjust the diversion ratio of the first bypass according to the fourth temperature of the raw water at the outlet of the second flow path of the first heat exchanger.

[0012] According to embodiments of this disclosure, a loop processing method is provided, executed by the loop system of the above embodiments, the loop processing method comprising: Control the compressed air unit to generate compressed air; The demineralized water preparation unit is controlled to provide demineralized water at a first temperature as a first cooling medium to the compressed air unit, so that the compressed air will be cooled to a second temperature; at the same time, the temperature of the demineralized water will be raised to a third temperature. The chilled water unit is controlled to use the gas discharged from the compressed air unit as a second cooling medium to pre-cool the chilled water return water.

[0013] The technical solution provided in this disclosure may include the following beneficial effects: By cooling compressed air with demineralized water and pre-cooling chilled water return water with the gas discharged from the compressed air unit, the cascade utilization of compressed air cooling energy can be achieved, improving energy efficiency. At the same time, it can reduce the cooling load of the chiller unit and reduce the power consumption of the chiller unit.

[0014] It should be understood that the above general description and the following detailed description are merely exemplary and explanatory, and do not limit this document. Attached Figure Description

[0015] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure.

[0016] Figure 1 This is a schematic diagram of a cyclic system according to an exemplary embodiment; Figure 2 This is a flowchart illustrating a cyclic system according to an exemplary embodiment; Figure 3 This is a schematic diagram of a first flow path and a second flow path according to an exemplary embodiment; Figure 4 This is a schematic diagram illustrating a third flow path and a fourth flow path according to an exemplary embodiment; Figure 5 This is a schematic diagram illustrating a fifth flow path and a sixth flow path according to an exemplary embodiment; Figure 6 This is a schematic diagram illustrating different medium temperatures in summer and winter according to an exemplary embodiment; Figure 7 This is a flowchart illustrating a control unit according to an exemplary embodiment; Figure 8 This is a flowchart illustrating a loop processing method according to an exemplary embodiment. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without creative effort are within the scope of protection of this disclosure. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this disclosure can be arbitrarily combined with each other.

[0018] In continuous production enterprises, compressed air, demineralized water, and chilled water are the three key common engineering media, and the energy consumption of the preparation systems corresponding to these three media often accounts for the majority of the total energy consumption of the enterprise's production plant. Currently, these three systems are designed and operated independently in most enterprises' production plants. This independent operation mode leads to a mismatch in energy quality between systems, resulting in a large amount of low-grade heating and cooling energy being wasted.

[0019] In compressed air systems, air compressors consume electricity to produce compressed air, which then needs to be dried to remove moisture. Common refrigerated dryers require an additional refrigeration compressor (power consumption of approximately 2-5 kW / (m³ / min)), while adsorption dryers require high-temperature regeneration gas, which is even more energy-intensive. After being used by the user, the exhaust temperature of the compressed air is typically only 5-15°C, containing a large amount of low-grade cold energy, but it is often directly discharged into the atmosphere, resulting in waste.

[0020] In desalination systems, desalination is primarily achieved through reverse osmosis (RO) technology. The core equipment, the RO high-pressure pump, is a major power consumer (approximately 3-5 kWh / m³). The performance of the RO membrane is significantly affected by the influent temperature; for every 1°C decrease in influent temperature, desalination output decreases by approximately 3%, while for every 1°C increase, it decreases by approximately 0.5%. The optimal influent temperature range for RO membrane systems is 15-25°C. However, raw water (tap water or surface water) temperatures vary greatly with the seasons, reaching above 30°C in summer and below 5°C in winter, leading to low RO system efficiency.

[0021] In chilled water systems, electrically driven chiller units generate chilled water at 5-12°C for process equipment or air conditioning. Chiller units are among the largest power consumers in a factory, and their energy consumption is closely related to the chilled water return temperature. For every 1°C increase in the chilled water return temperature, the chiller unit's Coefficient of Performance (COP) decreases by approximately 2-3%.

[0022] This independent operation mode leads to a mismatch in energy quality between systems, resulting in a significant waste of low-grade heating and cooling energy. Therefore, a technology is needed to integrate and utilize compressed air systems, demineralized water systems, and chilled water systems in a coordinated manner.

[0023] This disclosure provides a circulating system including a compressed air unit 10, a demineralized water preparation unit 20, and a chilled water unit 30. The compressed air unit 10, used to prepare compressed air, is connected to the demineralized water preparation unit 20. The demineralized water in the demineralized water preparation unit 20 has a relatively low temperature and can be used as a first cooling medium for the compressed air unit 10 to cool the compressed air to a second temperature, while simultaneously raising the temperature of the demineralized water to a third temperature. The compressed air unit 10 is also connected to the chilled water unit 20. The gas discharged from the compressed air unit 10 has a low temperature and can be used as a second cooling medium to pre-cool the chilled water return water in the chilled water unit 30. Thus, this disclosure achieves cascade utilization of compressed air cooling energy by using demineralized water to cool the compressed air and pre-cooling the chilled water return water using the gas discharged from the compressed air unit, improving energy efficiency and reducing the cooling load and power consumption of the chiller unit.

[0024] According to an exemplary embodiment of this disclosure, such as Figure 1 As shown, this embodiment provides a circulation system, including a compressed air unit 10, a demineralized water preparation unit 20, and a chilled water unit 30.

[0025] In some embodiments, the compressed air unit 10 is used to generate compressed air. The compressed air obtained in the initial stage of generation is at a high temperature (e.g., between 120°C and 150°C) and needs to be further cooled before being provided to the user.

[0026] In some embodiments, the demineralized water preparation unit 20 is used to prepare demineralized water. The demineralized water produced by the demineralized water preparation unit 20 has a low temperature and can be used as the first cooling medium of the compressed air unit 10. The demineralized water preparation unit 20 is connected to the air compression unit 10, and the demineralized water produced at the first temperature is delivered to the compressed air unit 10. Using the demineralized water as a cooling medium, the compressed air is cooled to a second temperature, which can then be used by the user end. Simultaneously, the demineralized water absorbs heat from the compressed air and heats up to a third temperature. Note that the terms "first" and "second" are only used to distinguish different objects and do not represent a sequential order, primary or secondary relationship, or quantity limitation.

[0027] In one example, the temperature of the demineralized water produced by the demineralized water preparation unit 20, i.e., the first temperature, is between 5°C and 12°C. Using the demineralized water as a cooling medium, the dew point of the compressed air can be lowered to the second temperature, which can be below -40°C. After absorbing the heat from the compressed air, the demineralized water can be heated to the third temperature, which can be between 15°C and 25°C.

[0028] In some embodiments, the chilled water return water is the chilled water that has absorbed heat and heated up before being delivered to the user end for use and then flows back. The energy consumption of the chiller unit is related to the chilled water return water temperature; the higher the chilled water return water temperature, the higher the energy consumption of the chiller unit and the lower the coefficient of performance (COP). The gas discharged from the compressed air unit 10 is compressed air that has been used at the user end, and its temperature is low, so it can be used as a second cooling medium to pre-cool the chilled water return water. By connecting the chilled water unit 30 to the compressed air unit 10, the gas discharged from the compressed air unit 10 can be delivered to the chilled water unit 30 to pre-cool the chilled water return water.

[0029] In one example, the chilled water temperature provided by the chilled water unit 30 is between 5°C and 7°C, the chilled water return temperature is between 10°C and 15°C, and the temperature of the gas discharged by the compressed air unit 10 is between 5°C and 15°C. After heat exchange, the chilled water return temperature can be reduced by 2°C to 5°C.

[0030] According to an exemplary embodiment of this disclosure, such as Figure 2As shown, the compressed air unit 10 includes an air compressor 11, a cooler 12, and a dryer 13 connected in sequence. The air compressor 11 is used to prepare compressed air in the initial stage, which has a relatively high temperature, approximately between 120°C and 150°C. Therefore, the compressed air in the initial stage needs to be cooled down before it can be delivered to the user end. The cooler 12 is installed after the air compressor and can therefore be called a post-cooler. It is used to initially cool down the compressed air in the initial stage. The dryer 13 is used to dry and further cool the initially cooled compressed air to prepare compressed air with a second temperature.

[0031] The desalination preparation unit 20 includes a raw water tank 21, a first heat exchanger 22, a reverse osmosis membrane module 23 (RO membrane module), and a desalination tank 24 connected in sequence. The raw water tank 21 is used to hold raw water. The first heat exchanger 22 can be a plate heat exchanger. The raw water undergoes heat exchange through the first heat exchanger 22. The reverse osmosis membrane module 23 is used to desalinate the raw water after heat exchange to obtain desalinated water. The desalination tank 24 is used to hold the desalinated water after desalination by the reverse osmosis membrane module.

[0032] In one example, air compressor 11 can be a screw air compressor with a power of 315kW, a discharge capacity of 55m³ / min, and a discharge temperature of 105°C. Dryer 13 can be a closed-loop cooling dryer with a processing capacity of 55m³ / min, using demineralized water as the cooling medium, and designed with an outlet dew point temperature of -45°C. The dew point temperature refers to the temperature at which, under constant air pressure and water vapor content, humid air is uniformly cooled until the water vapor in the air just reaches saturation and begins to condense into liquid water droplets. The RO membrane module can be two-stage: a first-stage brackish water membrane (Dow BW30-400) and a second-stage seawater membrane (SW30-400), with a total water production capacity of 80m³ / h.

[0033] In some embodiments, the outlet of the demineralized water tank 24 is connected to the dryer 13 to form a first loop, so as to provide demineralized water at a first temperature to the dryer 13. Figure 3As shown, the dryer 13 is connected to the inlet of the first flow path of the first heat exchanger 22 to provide demineralized water at a third temperature to the first heat exchanger 22 as the heat exchange medium for preparing demineralized water. The raw water tank 21 is connected to the inlet of the second flow path of the first heat exchanger 22 to input raw water into the second flow path, and the outlet of the second flow path is connected to the reverse osmosis membrane module 23. After heat exchange through the heat exchange medium, the raw water forms raw water at a fourth temperature, which is input to the reverse osmosis membrane module 23 for desalination treatment to form demineralized water at a fourth temperature. The demineralized water is input to the demineralized water tank 24, and the outlet of the first flow path is connected to the demineralized water usage point to form a second loop. By using the first heat exchanger and the demineralized water at the third temperature as the heat exchange medium, the raw water temperature can be adjusted to the optimal feed water temperature range of the reverse osmosis membrane module, ensuring the efficient operation of the reverse osmosis membrane module and the stability of the permeate flow.

[0034] In some embodiments, the first circuit and the second circuit may be referred to as the first cold energy utilization circuit and the second cold energy utilization circuit, respectively.

[0035] In some embodiments, when the raw water temperature exceeds a high temperature setting value, the demineralized water at the third temperature can be used as a cooling medium for preparing demineralized water to cool the raw water input into the second flow path; when the raw water temperature is lower than a low temperature setting value, the demineralized water at the third temperature can be used as a heating medium for preparing demineralized water to heat the raw water input into the second flow path.

[0036] In one example, the air compressor 11 generates compressed air at 105°C, which is cooled to 40°C by the cooler 12 and then enters the dryer 13. The demineralized water tank 24 stores demineralized water at 10°C (demineralized water at the first temperature), which is pumped into the dryer 13 at a flow rate of 18 m³ / h as the first cooling medium, so that the dew point temperature of the compressed air at the outlet of the dryer 13 can reach -45°C (compressed air at the second temperature). After absorbing heat, the demineralized water can be heated to 22°C (demineralized water at the third temperature).

[0037] In one example, the optimal feed water temperature for the reverse osmosis membrane module 23 is between 15°C and 25°C. The high-temperature setting for the raw water temperature is set to 25°C, and the low-temperature setting is set to 15°C. In summer, when the raw water temperature reaches 30°C, which is much higher than the high-temperature setting, the demineralized water heated to 22°C serves as the cooling medium for the raw water. After passing through the first heat exchanger 22, the temperature of the 30°C raw water drops to 20°C (the fourth temperature raw water), which is exactly within the optimal temperature range of the reverse osmosis membrane module 23. In winter, when the raw water temperature drops to 8°C, which is much lower than the low-temperature setting, the demineralized water heated to 22°C serves as the heating medium for the raw water. After passing through the first heat exchanger 22, the temperature of the 8°C raw water rises to 15°C (the fourth temperature raw water), which is exactly within the optimal temperature range of the reverse osmosis membrane module 23.

[0038] In some embodiments, the point of use for demineralized water can be an external production unit, where the demineralized water is consumed and used and is not recycled back.

[0039] In some embodiments, the outlet of the first flow path is provided with two branches, one of which is connected to the demineralized water tank 24 to reuse a portion of the demineralized water from the outlet of the first flow path to the demineralized water tank 24, and the other is connected to the demineralized water point to send a portion of the demineralized water from the outlet of the first flow path to the demineralized water point.

[0040] In some embodiments, such as Figure 2 As shown, the inlet of the first flow path is equipped with a first bypass, which is connected to the demineralized water tank 24 to input a portion of the demineralized water at the third temperature into the demineralized water tank 24. The flow ratio of the first bypass can be adjusted according to actual conditions. The larger the flow ratio of the first bypass, the smaller the flow rate of the demineralized water at the third temperature entering the first flow path.

[0041] In one example, the flow ratio of the first bypass is 0.6. 60% of the demineralized water output from the dryer 13 is input to the demineralized water tank 24 through the first bypass, and 40% of the demineralized water is input to the first flow passage to exchange heat with the raw water.

[0042] In some embodiments, the compressed air unit 10 further includes a user-end exhaust end 14 for discharging compressed air used by the user end, and the chilled water unit 30 includes a compressed air receiving end 31 connected to the user-end exhaust end 14 for receiving compressed air used by the user end. Figure 2 and Figure 4 As shown, the chilled water unit 30 also includes a chilled water return pipe 32, a chiller unit 33, and a second heat exchanger 34. The compressed air receiving end 31 is connected to the inlet of the third flow passage of the second heat exchanger 34, and the outlet of the third flow passage of the second heat exchanger 34 is connected to the atmospheric discharge pipe. The chilled water return pipe 32 is connected to the inlet of the fourth flow passage of the second heat exchanger 34, and the outlet of the fourth flow passage of the second heat exchanger 34 is connected to the chiller unit 33, forming a third loop. The compressed air used by the user end is used as the second cooling medium to cool the chilled water return and is discharged through the third flow passage. The chilled water return output from the chilled water return pipe 32 is cooled by the second cooling medium through the fourth flow passage of the second heat exchanger 34 and then input to the chiller unit 33.

[0043] In one example, chiller unit 33 can be a screw chiller with a cooling capacity of 650 kW and a COP of 4.5. The third heat exchanger 34 can be a shell-and-tube heat exchanger with a heat exchange area of ​​30 m², the shell side being the exhaust gas from the user-end exhaust port 14 (flow rate 50 m³ / min), and the tube side being the chilled water return water (flow rate 100 m³ / h). This heat exchanger only operates when the exhaust gas temperature at the user-end exhaust port is lower than the chilled water return water temperature.

[0044] In some embodiments, the third flow path may also be referred to as the cold side of the second heat exchanger 34, and the fourth flow path may also be referred to as the hot side of the second heat exchanger 34. The cold side and the hot side are distinguished according to the relative temperature of the flow medium in the two paths. The third loop may also be referred to as the third cold energy utilization loop.

[0045] In some embodiments, the second heat exchanger 34 may be a gas-water heat exchanger, with one side of the gas-water heat exchanger used for the flow of compressed air, i.e., the third flow passage, and the other side of the gas-water heat exchanger used for the flow of chilled water return water, i.e., the fourth flow passage.

[0046] In some embodiments, the compressed air unit 10 employs a water-cooled cooler 12, which is connected to the chiller unit 33 of the chilled water unit 30. The chilled water output from the chiller unit 33 is used as the cooling medium for the cooler 12 to reduce the exhaust temperature of the air compressor 11 and improve the cold energy grade of the air entering the dryer 13.

[0047] In one example, the cooler 12 can be a plate heat exchanger with a heat exchange area of ​​20 m² and a chilled water flow rate of 30 m³ / h, cooling the compressed air to 40°C.

[0048] In some embodiments, a second bypass is provided between the inlet and outlet of the fourth flow path. If the exhaust temperature at the user-end exhaust end 14 does not meet the heat exchange conditions, the inlet of the fourth flow path of the second heat exchanger 34 is closed or the second bypass is opened. When the inlet of the fourth flow path of the second heat exchanger 34 is closed, the exhaust from the user-end exhaust end 14 cannot enter the second heat exchanger 34, thus cutting off the heat exchange medium source for the chilled water return. When the second bypass is opened, the chilled water return can bypass the second heat exchanger 34 and be directly delivered to the chiller unit 33 for treatment, avoiding ineffective heat exchange. Even without pre-cooling the chilled water return, the total power consumption of the system is still significantly lower than that of a traditional independent system because the raw water inlet temperature of the reverse osmosis membrane module 23 has been adjusted to the optimal temperature range.

[0049] In some embodiments, when the exhaust temperature of the user-end exhaust terminal 14 is higher than or equal to the chilled water return temperature, the inlet of the fourth communication passage of the second heat exchanger 34 is closed or the second bypass is opened.

[0050] In one example, such as Figure 6 As shown, the exhaust temperature of the user end exhaust 14 in summer is about 12℃, and the chilled water return temperature is about 12℃. Since the two temperatures are close, there is no significant cold energy available in the exhaust. Therefore, the inlet of the fourth connecting passage of the second heat exchanger 34 should be closed or the second bypass should be opened to avoid ineffective heat exchange and waste of resources.

[0051] In one example, such as Figure 6 As shown, the exhaust temperature at the user-side exhaust end 14 is relatively low in winter, approximately 6℃, while the chilled water return temperature is approximately 10℃. Since the exhaust temperature at the user-side exhaust end 14 is lower than the chilled water return temperature, the heat exchange conditions are met, and the second heat exchanger 34 is put into normal operation, while the second bypass remains closed. After heat exchange, the chilled water return temperature drops to a suitable temperature (e.g., 7.5℃), reducing the load on the chiller unit and resulting in significant energy savings.

[0052] In some embodiments, such as Figure 5 As shown, the demineralized water preparation unit 20 also includes a third heat exchanger 25. The outlet of the chiller unit 33 is connected to the inlet of the fifth connecting passage of the third heat exchanger 25, and the outlet of the fifth connecting passage of the third heat exchanger 25 is connected to the chilled water return pipe 32. The reverse osmosis membrane module 23 is connected to the inlet of the sixth connecting passage of the third heat exchanger 25, and the outlet of the sixth connecting passage of the third heat exchanger 25 is connected to the demineralized water tank 24. The demineralized water at the fourth temperature output by the reverse osmosis membrane module 23 is cooled through the sixth connecting passage and then output to the demineralized water tank 24. The chilled water output from the outlet of the chiller unit 33 serves as the third cooling medium to cool the demineralized water at the fourth temperature flowing through the sixth connecting passage. By using the chilled water produced by the chiller unit to further cool the demineralized water produced by the reverse osmosis membrane module, the cold storage density of the demineralized water tank can be increased.

[0053] In some embodiments, the third heat exchanger 25 may be a plate heat exchanger.

[0054] In some embodiments, the fifth flow passage may also be referred to as the cold side of the third heat exchanger 25, and the sixth flow passage may also be referred to as the hot side of the third heat exchanger 25. The cold side and the hot side are distinguished according to the relative temperature of the flow medium in the two passages.

[0055] In one example, the demineralized water output from the reverse osmosis membrane module 23 has a fourth temperature range of 20°C to 25°C. Directly storing it in the demineralized water tank 24 would raise the water temperature inside the tank, reducing the cold energy storage density. The chilled water output from the outlet of the chiller unit 33 has a temperature range of 5°C to 7°C. The chilled water produced by the chiller unit 33 can reduce the 20°C to 25°C demineralized water output from the reverse osmosis membrane module 23 to 10°C to 15°C. The demineralized water reduced to 10°C to 15°C is then stored in the demineralized water tank 24. The temperature inside the demineralized water tank 24 can be stabilized at 8°C to 10°C, providing higher-grade cold energy for compressed air drying, thereby further reducing the outlet flow rate requirement of the demineralized water tank.

[0056] In some embodiments, such as Figure 2 As shown, the circulating system also includes a control unit 40, which comprises a controller 41 and a data management platform 42. The controller 41 is signal-connected to the compressed air unit 10, the demineralized water preparation unit 20, and the chilled water unit 30, and is used to collect operating data from the first, second, and third loops, and control the operation of the compressed air unit 10, the demineralized water preparation unit 20, and the chilled water unit 30 according to the scheduling parameters provided by the data management platform 42. The data management platform 42 is used to generate scheduling parameters based on the data collected by the controller 41 and the scheduling model, and then sends the scheduling parameters to the controller 41.

[0057] In some embodiments, the controller 41 may be an edge controller, the data management platform 42 may be a cloud platform, and the scheduling model may also be called a cold energy cascade utilization optimization model.

[0058] In some embodiments, temperature sensors, flow sensors, regulating valves, and pump frequency converters are installed on the first, second, and third circuits. The controller is communicatively connected to the temperature sensors, flow sensors, regulating valves, and pump frequency converters on each circuit to collect relevant data in real time and perform local control.

[0059] In some embodiments, the scheduling model includes a determination module and an optimization module. The determination module is used to determine the maximum recoverable cooling capacity of each loop based on the operating parameters of each node in the first, second, and third loops. The optimization module is used to determine the optimal flow control parameters and optimal valve opening control parameters for the corresponding first, second, and third loops based on the maximum recoverable cooling capacity, optimization objectives, and constraints. The maximum recoverable cooling capacity is theoretically the maximum recoverable cooling capacity of each loop. The determination module can also be called a cooling energy grade matching submodule, and the optimization module can also be called a multi-objective optimization submodule. The flow control parameters determine the operating parameters of the corresponding pump inverter, and adjusting the pump inverter parameters controls the fluid flow rate at the corresponding location. The valve opening control parameters determine the opening value of the regulating valve for the corresponding bypass (first bypass or second bypass), controlling the flow split ratio of the corresponding bypass.

[0060] In some embodiments, the nodes of the first loop are the compressed air inlet of the dryer 13, the user-end exhaust end 14, the water outlet of the demineralized water tank 24, and the cooling medium outlet of the dryer 13, and the corresponding operating parameters are, in order, the inlet compressed air temperature of the dryer 13 (…). ), Dryer 13 outlet compressed air temperature ( ), the temperature of the deionized water before it enters the dryer 13 ( ), the temperature of the deionized water after leaving the dryer 13 ( The nodes of the second loop are the inlet of the first flow path, the outlet of the first flow path, the inlet of the second flow path, and the outlet of the second flow path of the first heat exchanger 22, respectively. The corresponding operating parameters are, in order, the temperature of the demineralized water entering the first heat exchanger 22 after heating. ), the temperature at which the demineralized water leaves the first heat exchanger 22 ( ), the temperature of the raw water entering the first heat exchanger 22 ( ), the temperature of the raw water leaving the first heat exchanger 22 ( The nodes of the third loop are the inlet, outlet, inlet, and outlet of the third flow path of the second heat exchanger 34, and the corresponding operating parameters are the temperature of the compressed air exhaust from the user end exhaust end 14 entering the second heat exchanger 34, respectively. ), the temperature of compressed air exhaust leaving the second heat exchanger 34 ( ), the temperature of chilled water return entering the second heat exchanger 34 ( ), the temperature of the chilled water return water leaving the second heat exchanger 34 ( ).

[0061] In some embodiments, in the determining module, the operating parameters of each node in the first loop, second loop, and third loop are respectively substituted into the average heat transfer temperature calculation formula to calculate the average heat transfer temperature of the first loop, second loop, and third loop. The formula is: This formula is calculated based on the arithmetic mean of the relatively hot and cold fluid inlet and outlet temperatures on both sides of the heat exchanger / dryer. It is based on the average heat exchange temperatures of the first, second, and third loops, as well as the ambient temperature. ), calculate the efficiency of the corresponding loop ( The formula for calculating efficiency is: By incorporating the efficiency of each loop and the inlet temperatures of both sides of each loop into the formula for calculating the maximum recoverable cooling capacity, the maximum recoverable cooling capacity of the first, second, and third loops is calculated. The formula for calculating the maximum recyclable cold energy is: ,in, This represents the mass flow rate of the fluid on the cold side of the loop. The isobaric specific heat capacity of the cold-side fluid in the loop. This refers to the temperature at which the hot-side fluid enters the heat exchanger / dryer in this circuit. The temperature of the cold-side fluid entering the heat exchanger / dryer in the loop is: the hot-side fluid in the first loop is compressed air, and the cold-side fluid is demineralized water; the hot-side fluid in the second loop is demineralized water after heating, and the cold-side fluid is raw water; the hot-side fluid in the third loop is chilled water return, and the cold-side fluid is compressed air exhaust.

[0062] In some embodiments, the determining module updates all input parameters at a set time interval (e.g., 1 minute) and recalculates the values ​​of each loop. The calculation results are transmitted to the optimization module in real time.

[0063] In some embodiments, the optimization module can employ Non-dominated Sorting Genetic Algorithm II (NSGA-II) to perform the optimization function, with the optimization objective set as minimizing total system energy consumption and maximizing total cold energy utilization. The goal is to maximize the demineralized water output, and the constraints can be adaptively set according to actual conditions. Under this optimization objective and constraints, the NSGA-II algorithm is used to output the optimal flow control parameters for the outlet of the demineralized water tank 24 in the first loop, the optimal valve opening control parameters for the first bypass in the second loop, the optimal valve opening control parameters for the second bypass in the third loop, and the optimal flow control parameters for the connection path between the chiller unit 33 and the cooler 12.

[0064] In one example, the total cold energy utilization rate is the ratio of the sum of the actual recovered cold energy of each loop to the sum of the theoretical maximum recoverable cold energy of each loop, and its formula is: , This indicates the actual amount of cold energy recovered. This represents the theoretical maximum recoverable cold energy.

[0065] In one example, the constraints could be that the temperature of the demineralized water at the outlet of dryer 13 does not exceed 25°C, the temperature of the raw water entering the reverse osmosis membrane module 23 is not lower than 12°C and not higher than 25°C, the temperature of the chilled water return water is not lower than 5°C, and the actual recovered cold energy of each loop does not exceed the theoretical maximum recoverable cold energy of the corresponding loop.

[0066] In some embodiments, the scheduling model further includes a feedforward feedback control module. The feedforward feedback control module is used to adjust the flow rate at the outlet of the desalination tank 24 based on the raw water temperature feedforward data, and to adjust the flow ratio of the first bypass based on the fourth temperature of the raw water at the outlet of the second flow path of the first heat exchanger. The temperature feedforward data refers to the temperature of the raw water in the raw water tank 21, i.e., the temperature of the raw water before heat exchange.

[0067] In one example, the feedforward feedback control module can employ a proportional-integral-derivative (PID) control algorithm, with a control period set to 1 minute and a proportional coefficient ( The integral time is set to 0.8. The time is set to 30 seconds, and the derivative time is ( The time limit is set to 5 seconds. The values ​​of each parameter in this algorithm can be customized according to actual needs; there are no restrictions on this.

[0068] In some embodiments, when the feedforward temperature data of the raw water is lower than the optimal temperature range of the reverse osmosis membrane module 23 (e.g., 15°C to 25°C), it indicates that the raw water does not need cooling but needs preheating. In this case, the flow rate at the outlet of the desalination tank 24 is reduced so that the desalination water absorbs less heat in the dryer 13, and the temperature rise of the desalination water is reduced (e.g., the temperature of the desalination water after heating is controlled between 15°C and 18°C). When the feedforward temperature data of the raw water is higher than the optimal temperature range of the reverse osmosis membrane module 23, it indicates that the raw water needs a large amount of precooling. In this case, the flow rate at the outlet of the desalination tank 24 is increased so that the desalination water fully absorbs the heat of the compressed air in the dryer 13 (e.g., the temperature of the desalination water after heating is controlled between 22°C and 25°C), and carries more cooling energy into the first heat exchanger 22.

[0069] In some embodiments, when the raw water temperature at the outlet of the second flow path of the first heat exchanger 22 is lower than the optimal temperature range of the reverse osmosis membrane module 23, the flow ratio of the first bypass is increased to reduce the flow rate of demineralized water entering the first heat exchanger 22, allowing more heated demineralized water to bypass directly to the demineralized water tank 24, reducing the cooling amount of the raw water, preventing the raw water from entering the RO membrane module at too low a temperature, and ensuring that the reverse osmosis membrane module 23 operates within the optimal temperature range; when the raw water temperature at the outlet of the second flow path of the first heat exchanger 22 is higher than the optimal temperature range of the reverse osmosis membrane module 23, the flow ratio of the first bypass is decreased to increase the flow rate of demineralized water entering the first heat exchanger 22, allowing more heated demineralized water to be used for precooling the raw water, reducing the raw water temperature to the optimal temperature range of the reverse osmosis membrane module 23, and improving the water production efficiency of the reverse osmosis membrane module 23.

[0070] In one example, such as Figure 6 As shown, the raw water temperature in summer reaches as high as 30℃, far exceeding the optimal temperature range of the reverse osmosis membrane module 23, requiring a large amount of cold energy for pre-cooling. The control unit automatically adjusts its strategy based on the current operating conditions, increasing the outlet flow rate of the demineralized water tank 24 to maintain it at 18 m³ / h. This allows the demineralized water to fully absorb heat from the compressed air and heat up to 22℃, carrying more cooling energy into the first heat exchanger 22. The raw water temperature at the outlet of the second flow path of the first heat exchanger 22 is also far higher than the optimal temperature range of the reverse osmosis membrane module 23. Therefore, the flow ratio of the first bypass is set to 0.3, meaning only 30% of the heated demineralized water bypasses back to the demineralized water tank 24, while the remaining 70% enters the first heat exchanger 22 to exchange with the raw water, maximizing the use of the cooling energy in the heated demineralized water for pre-cooling the raw water. After this adjustment, the raw water temperature drops from 30℃ to 20℃ after heat exchange, which is exactly within the optimal temperature range of the reverse osmosis membrane module 23.

[0071] In one example, such as Figure 6As shown, the raw water temperature in winter is as low as 8℃, far below the optimal temperature range of the reverse osmosis membrane module 23. Therefore, a large amount of cold energy is not required for pre-cooling. To prevent the raw water from becoming too cold and causing a decrease in the permeate output of the reverse osmosis membrane module 23, the control unit 40 automatically adjusts its strategy based on the current operating conditions, reducing the outlet flow rate of the demineralized water tank 24 from 18 m³ / h in summer to 8 m³ / h. This allows the demineralized water to absorb less heat in the dryer 13, only raising its temperature to 16℃ (instead of the summer 22℃). This reduces the amount of cooling energy that can be introduced into the first heat exchanger 22. The raw water temperature at the outlet of the second flow path of the first heat exchanger 22 is also much lower than the optimal temperature range of the reverse osmosis membrane module 23. Therefore, the flow ratio of the first bypass is set to 0.7, meaning that 70% of the heated demineralized water is bypassed back to the demineralized water tank 24, and the remaining 30% enters the first heat exchanger 22 to exchange with the raw water. This reduces both the flow rate of demineralized water entering the heat exchanger and the average temperature difference within the heat exchanger, thereby reducing the cooling intensity on the raw water. After this adjustment, the raw water is gently raised from 8℃ to 15℃ (rather than being over-cooled), which is precisely within the optimal temperature range of the reverse osmosis membrane module, ensuring efficient operation and stable permeate flow.

[0072] In one example, such as Figure 7 As shown, the edge controller uses an industrial-grade ARM Cortex-A9 processor, runs a real-time Linux kernel, and supports protocols such as Modbus TCP / IP and PROFINET. It collects data at 1-second intervals, including the temperature of raw water tank 21, the inlet and outlet temperatures of demineralized water from dryer 13, the inlet and outlet temperatures of raw water and demineralized water on both sides of the first heat exchanger 22, the inlet and outlet temperatures of both sides of the second heat exchanger 34, the temperature of the demineralized water tank, the chilled water return temperature, the flow rate of demineralized water outlet, the flow rate of raw water tank, the demineralized water production, the flow rate of chilled water, the frequency of each pump inverter, the valve opening, the air compressor load, and the chiller unit load. This data is then uploaded to the cloud platform. The cloud platform (deployed on Alibaba Cloud ECS) receives the aggregated data (10-second average) uploaded by the edge controller every 5 minutes, runs the NSGA-II algorithm with a population size of 100 and 200 iterations, and outputs a Pareto front solution set. The edge controller selects the closest feasible solution based on the front solution set and the current operating conditions, and executes PID control. When the network is interrupted, the edge controller performs interpolation control based on the most recent week's optimized parameters stored locally to ensure continuous optimized operation of the system.

[0073] This embodiment provides a cyclic processing method, applied to the above embodiments, such as... Figure 8 As shown, the method includes: Step S110: Control the compressed air unit to generate compressed air.

[0074] In some embodiments, the air compressor 11 of the compressed air unit 10 is started to generate high-temperature compressed air. After the high-temperature compressed air is cooled by the cooler 12 of the compressed air unit 10, it is sent to the dryer 13 of the compressed air unit 10, and the compressed air produced by the dryer 13 is sent to the user end for use.

[0075] Step S120: Control the demineralized water preparation unit to provide demineralized water at a first temperature to the compressed air unit as the first cooling medium, so that the compressed air will be cooled to a second temperature; at the same time, the temperature of the demineralized water will be raised to a third temperature.

[0076] In some embodiments, the demineralized water at a first temperature in the demineralized water tank 24 of the demineralized water preparation unit 20 is transported to the dryer 13 of the compressed air unit 10 as a cooling medium for the dryer 13 to perform secondary cooling on the compressed air output from the cooler 12, so that it reaches a second temperature. At the same time, the demineralized water absorbs the heat of the compressed air and rises to a third temperature. The heated demineralized water is then transported to one side of the first heat exchanger 22 of the demineralized water preparation unit 20. Meanwhile, the raw water in the raw water tank 21 of the demineralized water preparation unit 20 is transported to the other side of the first heat exchanger 22, and the temperature of the raw water is adjusted to the optimal temperature range of the reverse osmosis membrane module 23 of the demineralized water preparation unit 20.

[0077] Step S130: Control the chilled water unit to use the gas discharged from the compressed air unit as a second cooling medium to pre-cool the chilled water return water.

[0078] In some embodiments, when the exhaust temperature of the user end exhaust end 14 of the compressed air unit 10 is lower than the chilled water return temperature, the exhaust and chilled water return of the chilled water unit 30 are respectively introduced into both sides of the second heat exchanger 34 for heat exchange, so that the chilled water return temperature is reduced before entering the chiller unit 33 of the chilled water unit 30. When the exhaust temperature of the user end exhaust end 14 is higher than or equal to the chilled water return temperature, the chilled water return flow of the second heat exchanger 34 is shut off or bypassed.

[0079] In one example, after the cyclic system and cyclic processing method according to the above embodiments have been running for 6 months, the statistical results are as follows:

[0080] In this example, the annual electricity savings of the circulating system disclosed herein compared to a traditional standalone system are: (1150-920)kW×8000h=1.84 million kWh, which translates to an annual saving of 1.104 million yuan based on an electricity price of 0.6 yuan / kWh. The system upgrade investment (piping, heat exchangers, valves, and control systems) is approximately 1.5 million yuan, with a payback period of approximately 1.36 years.

[0081] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This disclosure is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the claims.

[0082] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this disclosure. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0083] Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first," "second," or "third" may explicitly or implicitly include at least one of that feature. In the description of this disclosure, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0084] It should be understood that the various forms of processes shown above can be used to rearrange, add, or delete steps. For example, the steps described in this disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this disclosure can be achieved, and this is not limited herein.

[0085] The specific embodiments described above do not constitute a limitation on the scope of protection of this disclosure. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

Claims

1. A cyclic system, characterized in that, The circulation system includes a demineralized water circulation system and a chilled water circulation system, the circulation system comprising: Compressed air unit, used to generate compressed air; A demineralized water preparation unit, connected to the compressed air unit, is used to provide demineralized water at a first temperature to the compressed air unit as a first cooling medium, so as to cool the compressed air to a second temperature; at the same time, the temperature of the demineralized water is raised to a third temperature. The chilled water unit is connected to the compressed air unit and is used to precool the chilled water return water using the gas discharged from the compressed air unit as a second cooling medium.

2. The cyclic system according to claim 1, characterized in that, The compressed air unit includes an air compressor, a cooler, and a dryer connected in sequence; The demineralized water preparation unit includes a raw water tank, a first heat exchanger, a reverse osmosis membrane module, and a demineralized water tank connected in sequence. The outlet of the demineralized water tank is connected to the dryer to form a first loop, so as to provide the dryer with demineralized water at the first temperature; the dryer is connected to the inlet of the first flow passage of the first heat exchanger to provide the first heat exchanger with demineralized water at the third temperature as a heat exchange medium for preparing demineralized water. The raw water tank is connected to the inlet of the second flow path of the first heat exchanger to input raw water into the second flow path, and the outlet of the second flow path is connected to the reverse osmosis membrane module; after the raw water is heated by the heat exchange medium, it forms raw water at a fourth temperature, which is input to the reverse osmosis membrane module for desalination treatment to form desalinated water at the fourth temperature, which is then input to the desalination tank; the outlet of the first flow path is connected to the desalination water point to form a second loop.

3. The circulation system according to claim 2, characterized in that, The inlet of the first flow passage is provided with a first bypass, which is connected to the demineralized water tank to input a portion of the demineralized water at the third temperature into the demineralized water tank.

4. The circulation system according to claim 2, characterized in that, The compressed air unit also includes a user-end exhaust end for discharging compressed air after use by the user end; The chilled water unit includes a compressed air receiving end, which is connected to the user end exhaust end and is used to receive compressed air after use by the user end. The chilled water unit also includes a chilled water return pipeline, a chiller unit, and a second heat exchanger; The compressed air receiving end is connected to the inlet of the third flow passage of the second heat exchanger, the outlet of the third flow passage of the second heat exchanger is connected to the atmospheric discharge pipeline, the chilled water return pipeline is connected to the inlet of the fourth flow passage of the second heat exchanger, and the outlet of the fourth flow passage of the second heat exchanger is connected to the chiller unit, forming a third loop. The compressed air used by the user end is used as the second cooling medium to cool the chilled water return water, and is discharged through the third flow passage; the chilled water return water output from the chilled water return water pipeline is cooled by the second cooling medium through the fourth flow passage of the second heat exchanger and then input into the chiller unit.

5. The circulation system according to claim 4, characterized in that, A second bypass is provided between the inlet and outlet of the fourth flow passage. If the exhaust temperature at the user end exhaust end does not meet the heat exchange conditions, the inlet of the fourth flow passage of the second heat exchanger is closed or the second bypass is opened.

6. The cyclic system according to claim 4, characterized in that, The demineralized water preparation unit also includes a third heat exchanger; The outlet of the chiller unit is connected to the inlet of the fifth connecting passage of the third heat exchanger, the outlet of the fifth connecting passage of the third heat exchanger is connected to the chilled water return pipeline, the reverse osmosis membrane module is connected to the inlet of the sixth connecting passage of the third heat exchanger, and the outlet of the sixth connecting passage of the third heat exchanger is connected to the demineralized water tank; the demineralized water at the fourth temperature output by the reverse osmosis membrane module is cooled by the sixth connecting passage and then output to the demineralized water tank; the chilled water output from the outlet of the chiller unit serves as the third cooling medium to cool the demineralized water at the fourth temperature flowing through the sixth connecting passage.

7. The circulating system according to claim 6, characterized in that, The circulation system also includes a control unit, which includes a controller and a data management platform; The controller is connected to the compressed air unit, the demineralized water preparation unit, and the chilled water unit via signal connection. It is used to collect the operating data of the first loop, the second loop, and the third loop, and to control the operation of the compressed air unit, the demineralized water preparation unit, and the chilled water unit according to the scheduling parameters provided by the data management platform. The data management platform is used to generate scheduling parameters based on the data collected by the controller and the scheduling model, and to send the scheduling parameters to the controller.

8. The circulation system according to claim 7, characterized in that, The scheduling model includes: The determination module is used to determine the maximum recoverable cold capacity of each loop based on the operating parameters of each node in the first loop, the second loop, and the third loop. The optimization module is used to determine the optimal flow control parameters and optimal valve opening control parameters for the first loop, the second loop, and the third loop based on the maximum recoverable cold capacity, the optimization objective, and the constraints.

9. The circulating system according to claim 8, characterized in that, The scheduling model also includes a feedforward feedback control module, which is used to adjust the flow rate of the outlet of the desalination tank according to the temperature feedforward data of the raw water, and to adjust the diversion ratio of the first bypass according to the fourth temperature of the raw water at the outlet of the second flow path of the first heat exchanger.

10. A cyclic processing method, characterized in that, The loop processing method is executed by the loop system according to any one of claims 1-9, and the loop processing method includes: Control the compressed air unit to generate compressed air; The demineralized water preparation unit is controlled to provide demineralized water at a first temperature as a first cooling medium to the compressed air unit, so that the compressed air will be cooled to a second temperature; at the same time, the temperature of the demineralized water will be raised to a third temperature. The chilled water unit is controlled to use the gas discharged from the compressed air unit as a second cooling medium to pre-cool the chilled water return water.

Images