A cooling system for fluids with variable operating condition regulation function

Abstract

This invention relates to a cooling system for fluids with variable operating condition regulation. The cooling system includes an expander, a compressor driven by an electric motor with adjustable speed, a controller, and a sensing device. The sensing device is configured to detect the temperature of the fluid and / or the cooling medium. The controller can receive data from the sensing device and control the speed of the electric motor based on the data. Thus, when the required cooling capacity of the cooled fluid and / or the cooling capacity provided by the refrigerant changes, the controller can adjust the speed of the electric motor to ensure that the temperature of the cooled fluid remains at a predetermined value. In particular, the control is achieved through PID regulation, which has the advantages of simple control, safety and reliability, and rapid adjustment. This allows the cooling system of this invention to adjust the cooling capacity accordingly to changes in operating conditions, achieving variable operating condition regulation of the cooling capacity from 0% to 100%.

Description

Technical Field

[0001] This invention relates to the field of LNG storage and transportation, and more particularly to a system for handling evaporated gases in LNG ships, especially a cooling system for fluids with variable operating condition regulation function. Background Technology

[0002] With the rapid development of the economy, society, and modern industry, energy utilization and environmental pollution have become global concerns. Faced with increasingly stringent environmental requirements, the international energy strategy is accelerating its transformation, and the development and application of clean fuels have become an important direction for energy strategy. Natural gas, with its low pollutant emissions and relatively low cost, has seen its share in international energy supply increase year by year, and the rapid growth in global natural gas consumption demand is expected to continue until 2040. Compared to pipeline transportation of natural gas, maritime LNG (liquefied natural gas) transportation does not require long pipelines and can flexibly transport natural gas to various parts of the world, thus offering advantages in flexibility and diversification of production and destination. With the continued rapid growth of natural gas trade, the global LNG shipping industry will also develop rapidly, with an estimated 600 new large LNG carrier orders expected by 2030.

[0003] Given the unique physicochemical properties of LNG, even with well-insulated cargo tanks, LNG can still absorb heat from external sources during transport, leading to vaporization. This vaporization increases pressure in the cargo tanks, potentially damaging their structure. Directly releasing the vapor into the atmosphere also causes direct economic losses and contributes to greenhouse gas emissions. Therefore, a cooling system is necessary to address this vaporization. This system re-condenses and liquefies the vapor in the cargo tanks, reducing the likelihood of further evaporation, lowering transportation costs, and improving the safety of LNG transport. It is a crucial high-value-added piece of equipment for large LNG carriers and bunkering vessels. Similar challenges exist in onshore LNG storage facilities.

[0004] However, current LNG evaporative gas cooling systems, from a technological perspective, suffer from several drawbacks. The mixed reliquefaction method leads to complex processes and difficult maintenance, and propane and other working gases are highly explosive, posing a significant risk of leakage. While the nitrogen expansion reliquefaction method uses an inert gas as a refrigerant, offering higher safety, it requires numerous auxiliary devices such as evaporative gas compressors, nitrogen generators, and evaporative gas heaters, resulting in long installation and commissioning cycles and high maintenance costs. Furthermore, the pressure and temperature within LNG storage facilities are constantly fluctuating due to various factors, including changes in external temperature, the volume of LNG entering and leaving the facility, and corresponding temperature variations. Therefore, there is an urgent need to develop an LNG cooling system with a highly safe, reliable, and adaptable control method. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a cooling system with variable operating condition regulation for a fluid, preferably liquefied natural gas. The cooling system includes a cooling circuit for cooling the fluid, and the cooling circuit includes:

[0006] A compressor is used to compress the refrigerant in a cooling system, thereby increasing the pressure of the refrigerant.

[0007] A cooler is used to cool the compressed refrigerant.

[0008] An expander is used to expand a cooled refrigerant.

[0009] An electric motor can drive a compressor to compress the refrigerant. The speed of the electric motor is adjustable, especially continuously variable.

[0010] A heat exchanger is used to generate heat exchange between a cooled fluid and an expanded refrigerant.

[0011] The refrigerant operates in a closed loop in the cooling circuit. After being compressed in the compressor, the refrigerant is cooled by the cooler and then expanded by the expander, which reduces the pressure and temperature. After that, it absorbs heat from the cooled fluid in the heat exchanger to reduce the temperature of the cooled fluid. The refrigerant, after absorbing heat, then enters the compressor to be compressed.

[0012] The cooling system also includes a controller and a sensor. The sensor is configured to detect the temperature of the fluid and / or the coolant. The sensor and the motor are connected to the controller, which is able to receive data from the sensor and control the motor speed based on the data.

[0013] Furthermore, the sensing device can be installed on at least one of the following: the inlet pipe section of the expander, the pipe section between the expander outlet and the heat exchanger, the outlet pipe section of the cooled fluid of the heat exchanger, and the outlet pipe section of the refrigerant of the heat exchanger.

[0014] Furthermore, the controller has a preset value for the temperature-related values ​​of the refrigerant or the cooled fluid at the location where the sensor is installed. When the actual value measured by the sensor differs from the preset value, the controller adjusts the motor speed through PID control to regulate the circulation speed of the refrigerant in the cooling circuit and thus adjust the cooling capacity provided by the cooling circuit until the actual value is the same as the preset value. In particular, when the actual value is greater than the preset value, the controller increases the motor speed, and when the actual value is less than the preset value, the controller decreases the motor speed.

[0015] Furthermore, the temperature-related values ​​can be the temperature value detected by a single sensor, the rate of change of the temperature value detected by a single sensor, the difference between the temperature values ​​detected by multiple sensors, or the rate of change of the difference between the temperature values ​​detected by multiple sensors.

[0016] Furthermore, the flow direction of the fluid in at least a portion of the heat exchanger is opposite to the flow direction of the expanded refrigerant; wherein the refrigerant is an inert gas, preferably He, N2, H2 or Ne, or a mixture of at least two of He, N2, H2 and Ne; wherein the fluid is liquefied natural gas, carbon dioxide, hydrogen or helium, or a mixture of at least two of liquefied natural gas, carbon dioxide, hydrogen or helium.

[0017] Furthermore, the cooling circuit also includes a regenerative heat exchanger, in which the refrigerant flowing out of the heat exchanger exchanges heat with the refrigerant before entering the expander; the heat exchanger and the regenerative heat exchanger are installed in an insulation device.

[0018] Furthermore, the number of compressors is at least two, and the at least two compressors are arranged in series and / or parallel in the cooling circuit, so that the refrigerant flows through the at least two compressors in series and / or parallel, wherein a cooler is provided at the outlet of each compressor; the refrigerant expands in the expander so that the expander outputs energy, and at least one of the at least two compressors can receive the energy output by the expander; at least one of the at least two compressors can be driven by an electric motor.

[0019] Furthermore, at least one of the at least two compressors can be configured in a coaxial manner with the electric motor and the expander, such that the at least one compressor is driven by the energy output from the electric motor and the expander.

[0020] Furthermore, the number of expanders is at least two, and the at least two expanders are arranged in series and / or parallel in the cooling circuit, so that the refrigerant flows through the at least two expanders in series and / or parallel.

[0021] Furthermore, the compressor is an axial flow compressor or a centrifugal compressor, and the expander is an axial flow expander or a centrifugal expander.

[0022] Furthermore, the expander is provided with a bypass branch, one end of which is connected to the inlet of the expander and the other end of which is connected to the outlet of the expander. Preferably, a regulating valve is provided on the bypass branch to regulate the refrigerant flowing from the expander inlet to the expander outlet via the bypass branch. In particular, one end of the bypass branch is connected to a pipe section upstream of the heat exchanger at the expander inlet, and the other end of the bypass branch is connected to a pipe section downstream of the heat exchanger at the expander outlet.

[0023] Implementing this invention provides the following advantages: The cooling system for fluids according to this invention, which features variable operating condition adjustment, includes a compressor driven by an electric motor with adjustable speed, a controller, and a sensing device. The sensing device is configured to detect the temperature of the fluid and / or the cooling medium. The controller receives data from the sensing device and controls the motor speed based on this data. Therefore, when the required cooling capacity of the cooled fluid and / or the cooling capacity provided by the refrigerant changes, the motor speed is adjusted to ensure that the temperature of the cooled fluid remains at a predetermined value. In particular, the control is achieved through PID regulation, which offers advantages such as simple control, safety, reliability, and rapid adjustment. This allows the cooling system of this invention to adjust the cooling capacity accordingly to changes in operating conditions, achieving variable operating condition adjustment of the cooling capacity range from 0% to 100%. Attached Figure Description

[0024] To more clearly illustrate the technical solution of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is the control flowchart of the present invention.

[0026] Figure 2 This is a system diagram of Embodiment 1 of the present invention.

[0027] Figure 3 This is a system diagram of Embodiment 2 of the present invention.

[0028] Figure 4 This is a system diagram of Embodiment 3 of the present invention.

[0029] Figure 5 This is a system diagram of Embodiment 4 of the present invention.

[0030] Reference numerals: 1. Compression and expansion unit; 2. Compression device; 3. Cooler; 4. Insulation device; 5. Regenerative heat exchanger; 6. Heat exchanger; 7. First motor; 8. Second motor; 9. Controller; 10. Regulating valve of bypass branch; 11. Sensing device; C1. First-stage compressor; C2. Second-stage compressor; C3. Third-stage compressor; E1. Expander; L1. Fluid inlet pipe section; L2. Fluid outlet pipe section. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] To solve the above-mentioned technical problems, the present invention proposes a cooling system for fluids with variable operating condition adjustment, wherein the fluid is preferably liquefied natural gas, carbon dioxide, hydrogen or helium, or a mixture of at least two of liquefied natural gas, carbon dioxide, hydrogen or helium.

[0033] The cooling system includes a cooling circuit for cooling the fluid, and a refrigerant is provided in a closed loop in the cooling circuit. The refrigerant is an inert gas, preferably He, N2, H2 or Ne, or a mixture of at least two of He, N2, H2 and Ne.

[0034] Example 1:

[0035] like Figure 2 As shown, the cooling circuit of the cooling system includes:

[0036] The compressor is used to compress the refrigerant in the cooling system. In this embodiment, the compressor adopts a three-stage series compression method, that is, it includes a first-stage compressor C1, a second-stage compressor C2, and a third-stage compressor C3. For the refrigerant, the first-stage compressor C1, the second-stage compressor C2, and the third-stage compressor C3 are arranged in series. That is to say, the refrigerant passes through the first-stage compressor C1, the second-stage compressor C2, and the third-stage compressor C3 in sequence. Thus, the refrigerant is pressurized by each stage of the compressor, thereby increasing the pressure of the refrigerant step by step.

[0037] Cooler 3 cools the refrigerant after compression by the compressor. In this embodiment, cooler 3 includes three independent cooler modules, each connected to the outlet of the first-stage compressor C1, the second-stage compressor C2, and the third-stage compressor C3, respectively, to cool the refrigerant at the outlet of each compressor stage. As the refrigerant is compressed in the compressor, its volume decreases, increasing both its pressure and temperature. Therefore, by installing a cooler module at the outlet of each compressor stage, the temperature of the refrigerant can be lowered. The cold source in the cooler can be ambient temperature cooling water or ambient temperature air. Thus, the refrigerant at normal temperature and pressure (not referring to normal temperature and pressure relative to ambient temperature, but to the relative state of the refrigerant circulating in the cooling circuit; the same applies to high temperature, low temperature, medium pressure, high pressure, and low pressure mentioned below) is compressed by the first-stage compressor C1 into a high-temperature, medium-pressure refrigerant, then cooled by the cooler 3 into a normal-temperature, medium-pressure refrigerant, then compressed by the second-stage compressor C2 into a high-temperature, sub-high-pressure refrigerant, then cooled by the cooler 3 into a normal-temperature, sub-high-pressure refrigerant, then compressed by the third-stage compressor C3 into a high-temperature, high-pressure refrigerant, and finally cooled by the cooler 3 into a normal-temperature, high-pressure refrigerant.

[0038] Expander E1 is used to expand the cooled refrigerant. The inlet of expander E1 is fluidly connected to cooler 3 to expand the refrigerant at room temperature and high pressure that has been compressed by a three-stage compressor and cooled by a cooler. In expander E1, the volume of the room temperature and high pressure refrigerant increases, resulting in a decrease in pressure and temperature. Thus, the room temperature and high pressure refrigerant is transformed into a low temperature and low pressure refrigerant through expansion in expander E1.

[0039] Here, to cool the fluid, particularly LNG, the cooling circuit includes a heat exchanger 6. The fluid enters the heat exchanger 6 through a fluid inlet pipe section L1 and then exits through a fluid outlet pipe section L2. In the heat exchanger 6, a low-temperature, low-pressure refrigerant with cryogenic capabilities exchanges heat with the fluid being cooled. Specifically, the fluid being cooled transfers heat to the low-temperature, low-pressure refrigerant, further reducing the temperature of the fluid. The heat exchanger 6 can be a multi-flow heat exchanger; for example... Figure 2 As shown, in at least a portion of the heat exchanger 6, the flow direction of the fluid is opposite to that of the refrigerant, that is, the two transfer heat in the heat exchanger 6 in a relatively counter-current flow manner, which can improve the efficiency of heat transfer and improve the cooling effect on the fluid being cooled.

[0040] Meanwhile, since the low-temperature, low-pressure refrigerant in heat exchanger 6 still maintains a relatively low temperature after absorbing heat from the cooled fluid, a regenerative heat exchanger 5 is further installed. In the regenerative heat exchanger 5, the refrigerant output from heat exchanger 6 is used to cool the ambient-temperature, high-pressure refrigerant at the inlet of expander E1, thereby further reducing the inlet temperature of expander E1 and achieving energy savings. Similarly, as... Figure 2 As shown, in at least a portion of the regenerative heat exchanger 5, the flow direction of the ambient temperature, high-pressure refrigerant at the inlet of the expander E1 is opposite to the flow direction of the refrigerant output from the heat exchanger 6. That is, the two flow in a counter-current manner to transfer heat in the regenerative heat exchanger 5, which improves heat transfer efficiency and cooling effect. To prevent the cooled fluid and refrigerant from emitting cold energy to the external environment, an insulation device 4 is installed. The regenerative heat exchanger 5 and the heat exchanger 6 are housed within the insulation device 4, effectively isolating the low-temperature cooled fluid and refrigerant from heat exchange with the external environment, thus improving the overall cooling system efficiency.

[0041] Thus, the refrigerant flows sequentially through the first-stage compressor C1, cooler 3, the second-stage compressor C2, cooler 3, the third-stage compressor C3, cooler 3, regenerator 5, expander E1, heat exchanger 6, and regenerator 5, before returning to the inlet of the first-stage compressor C1, completing one cycle in the cooling circuit. This repeated cycle provides continuous cryogenic cooling to the fluid being cooled.

[0042] The primary compressor C1, secondary compressor C2, and tertiary compressor C3 can be axial flow compressors and / or centrifugal compressors, and the expander E1 can be an axial flow expander or a centrifugal expander.

[0043] Since the compressor converts external energy into the internal energy of the compressed gas, it requires external power to operate. In this embodiment, the cooling circuit also includes a first motor 7 and a second motor 8. The first motor 7 drives the first-stage compressor C1, and the second motor 8 drives the second-stage compressor C2 and the third-stage compressor C3. Specifically, as... Figure 2 As shown, the secondary compressor C2, the tertiary compressor C3, and the second motor 8 are connected by a common rotating shaft, so that only one second motor 8 is used to drive the secondary compressor C2 and the tertiary compressor C3.

[0044] The refrigerant expands in expander E1, doing work on expander E1 and causing it to rotate, thus outputting mechanical energy. To utilize the energy output from expander E1 to improve system efficiency, such as... Figure 2As shown, the expander E1, the first motor 7, and the first-stage compressor C1 are mounted on the same rotating shaft to form an integrated compression-expansion unit 1. This allows the mechanical energy output from the first motor 7 and the expander E1 to be jointly delivered to the first-stage compressor C1 via this common rotating shaft, thereby improving energy efficiency. Alternatively, the expander E1 can also be mounted on the same rotating shaft as the second-stage compressor C2 and / or the third-stage compressor C3 to form an integrated compression-expansion unit, while the first-stage compressor C1 is driven solely by an electric motor; or two expanders can be arranged in series or parallel, each coaxially with a compressor to form an integrated compression-expansion unit to drive the compressor. It should be noted that an integrated compression-expansion unit can include a coaxially rotating compressor and expander, or it can include a coaxially rotating compressor, expander, and electric motor.

[0045] A further alternative, in order to improve the cooling capacity of the cooling circuit, may include multiple compressors, multiple expanders, and three or more electric motors, with three or more compressors and two or more expanders. The multiple compressors may be arranged in series, in parallel, or in a series-parallel combination. Specifically, each compressor may be driven by an electric motor alone, or by a combination of an electric motor and an expander on the same shaft, thereby forming a cryogenic evaporative gas cooling system with a more powerful cooling capacity.

[0046] like Figure 2 As shown, a bypass branch pipe is also provided in the cooling circuit. Specifically, the upstream end of the bypass branch pipe is connected to the pipe section between the cooler 3 and the regenerator 5, and the downstream end of the bypass branch pipe is connected to the pipe section located between the regenerator 5 and the inlet of the first-stage compressor C1. This partially delivers the high-pressure refrigerant after three-stage compression to the inlet of the first-stage compressor C1 for anti-surge backflow and pressure and temperature regulation during startup. Further, to achieve the desired regulation effect, a regulating valve 10 is preferably provided on the bypass branch pipe to regulate the refrigerant flowing from the inlet of expander E1 to the outlet of expander E1 via the bypass branch pipe, or in other words, to regulate the refrigerant flowing from the three-stage compressed refrigerant to the inlet of the first-stage compressor C1 via the bypass branch pipe, especially regulating the flow rate or pressure. This allows for direct regulation and control of the amount of refrigerant flowing to expander E1 and increases the flow rate of the refrigerant in the three-stage compressor. Therefore, when surge occurs in the compressor or expander, the regulating valve 10 can be opened to adjust the operating state of the compressor or expander, eliminate the surge phenomenon, and prevent the compressor or expander from being damaged or even destroyed due to surge. Specifically, when the cooling system starts, the regulating valve 10 is fully open; when the cooling system is running stably, the regulating valve 10 is fully closed.

[0047] Because the cooling demand of the fluid being cooled changes continuously under the influence of various factors, and the cooling capacity provided by the refrigerant in the cooling circuit also changes continuously under the influence of various factors, the operating conditions of the cooling circuit are constantly changing. In order to ensure that the cooling circuit can provide a reliable and stable cooling effect to the fluid being cooled under changing conditions, the cooling system of the present invention also has the ability to adjust the variable operating conditions.

[0048] like Figure 2 As shown, the cooling system includes a sensing device 11, specifically a temperature sensor. The sensing device 11 is located at the outlet of the expander E1, specifically on the pipe section between the outlet of the expander E1 and the heat exchanger 6, to detect the temperature of the low-temperature, low-pressure refrigerant at the outlet of the expander E1. In the cooling system of this invention, when the state of the cooled fluid in the heat exchanger 6 changes, such as a change in flow rate or temperature, i.e., a change in cooling demand (for example, an increase in cooling demand), the operating conditions of the refrigerant remain temporarily unchanged. However, during heat exchange in the heat exchanger 6, the increased cooling demand of the fluid, while the cooling capacity of the refrigerant remains unchanged, directly results in a rise in the temperature of the refrigerant exiting the heat exchanger 6. Therefore, when the refrigerant flow rate and velocity in the cooling loop remain unchanged, the temperature of the refrigerant at the outlet of the expander E1 rises, further reducing the cooling capacity provided, thus worsening the cycle. Similarly, a decrease in cooling demand will cause the temperature of the refrigerant at the outlet of expander E1 to drop, a decrease in cooling supply will cause the temperature of the refrigerant at the outlet of expander E1 to rise, and an increase in cooling supply will cause the temperature of the refrigerant at the outlet of expander E1 to drop.

[0049] The cooling system also includes a controller 9, which is connected to a sensor 11 and can receive data detected by the sensor 11. The controller 9 is also connected to the first motor 7 and the second motor 8. Based on the data from the sensor 11, the controller 9 can control the rotational speeds of the first motor 7 and the second motor 8, thereby changing the flow rate of the refrigerant in the cooling circuit, i.e., the circulation rate. This allows adjustment of the amount of refrigerant flowing through the heat exchanger 6 per unit time, thus regulating the cooling capacity provided by the cooling circuit to the cooled fluid, ensuring sufficient, reliable, and stable cooling. When adjusting, the controller 9 can control the rotational speeds of the first motor 7 and the second motor 8 based on the temperature value detected by a single sensor 11, the rate of change of the temperature value detected by the single sensor 11 (the derivative of the temperature value), or both the temperature value detected by the single sensor 11 and its rate of change.

[0050] To ensure the cooling circuit provides appropriate cooling capacity to match the cooling demand of the fluid being cooled, thereby improving the efficiency of the cooling circuit, a predetermined value SP is set in the controller 9. When the actual value PV measured by the sensor 11 differs from the predetermined value SP, the controller 9 adjusts the speed of the first motor 7 and the second motor 8 through PID control, thereby adjusting the circulation speed of the refrigerant in the cooling circuit and adjusting the cooling capacity provided by the cooling circuit until the actual value PV matches the predetermined value SP. In particular, the predetermined value can also be adjusted manually or automatically, especially when the state of the fluid during storage or the refrigerant changes, such as when the temperature rises. When it is clear that the cooling demand of the fluid or the cooling capacity supplied by the refrigerant has changed, the predetermined value can be adjusted manually or automatically to adapt to the change in cooling demand or cooling capacity supplied.

[0051] Specific adjustment methods are as follows: Figure 1 As shown, after a change in cooling demand and / or cooling supply, the sensor 11 acquires the actual value PV detected by the monitoring point. When the actual value PV is different from the predetermined value SP, it indicates that the cooling demand and cooling supply are mismatched. The controller 9 then uses a PID control method to adjust the speed of the first motor 7 and the second motor 8. Here, the speed or rotation frequency of the first motor 7 and the second motor 8 is continuously variable. Specifically, for example, when the actual value PV is greater than the predetermined value SP, the controller 9 increases the speed of the first motor 7 and the second motor 8, and when the actual value PV is less than the predetermined value SP, the controller 9 decreases the speed of the first motor 7 and the second motor 8 until the actual value PV is the same as the predetermined value SP, which indicates that the cooling demand and cooling supply are matched.

[0052] The PID control method has the advantages of simple control, safety and reliability, and rapid adjustment. It enables the cooling system to adjust the cooling capacity according to changes in operating conditions, achieving variable operating condition adjustment of the cooling capacity from 0 to 100%. This allows the power consumption of the cooling system to match the cooling demand, thereby improving energy efficiency.

[0053] Example 2:

[0054] The arrangement in Example 2 is as follows Figure 3 As shown, the parts that are the same as in Embodiment 1 will not be described again here. Embodiment 2 differs from Embodiment 1 in that the sensing device 11 is arranged on the outlet pipe of the refrigerant in the heat exchanger 6 to detect the temperature of the refrigerant after absorbing heat from the cooled fluid in the heat exchanger 6. Therefore, at this monitoring point, it is also possible to reflect whether there is a match between the required cooling capacity and the supplied cooling capacity.

[0055] The control method of Example 2 is the same as that of Example 1, such as... Figure 1 As shown, it will not be elaborated upon here.

[0056] Example 3:

[0057] The arrangement in Example 3 is as follows Figure 4 As shown, the parts that are the same as in Embodiment 1 will not be described again here. The difference between Embodiment 3 and Embodiment 1 is that the sensing device 11 is arranged on the inlet pipe of the refrigerant in the expander E1 to detect the temperature of the refrigerant at the inlet of the expander E1. Therefore, at this monitoring point, it is also possible to reflect whether there is a match between the required cooling capacity and the supplied cooling capacity.

[0058] The control method in Example 3 is the same as that in Example 1, such as... Figure 1 As shown, it will not be elaborated upon here.

[0059] Example 4:

[0060] The arrangement in Example 4 is as follows Figure 5 As shown, the parts that are the same as in Embodiment 1 will not be described again. Embodiment 4 differs from Embodiment 1 in that the sensing device 11 is directly arranged on the fluid outlet pipe section L2 of the heat exchanger 6 to detect the temperature of the refrigerant in the fluid outlet pipe section L2 of the heat exchanger 6. Therefore, at this monitoring point, it is also possible to detect whether there is a match between the cooling demand and the cooling supply.

[0061] The control method in Example 4 is the same as that in Example 1, such as... Figure 1 As shown, it will not be elaborated upon here.

[0062] Although in the above embodiment, the sensor 11 is arranged at only one monitoring point, alternatively, two or more sensor 11 can be arranged in the cooling system at different locations to monitor changes in the cooling demand of the fluid or the cooling capacity supplied by the refrigerant more quickly. For example, sensor 11 can be arranged at the refrigerant inlet and outlet of the heat exchanger, thereby enabling real-time monitoring of the temperature changes of the refrigerant and the temperature difference between the refrigerant at the inlet and outlet of the heat exchanger, and detecting changes in the operating conditions of the refrigerant more quickly and rapidly; or sensor 11 can be arranged at the fluid inlet and outlet of the heat exchanger, thereby enabling real-time monitoring of the fluid temperature changes and the temperature difference between the fluid at the inlet and outlet of the heat exchanger, and detecting changes in the operating conditions of the fluid more quickly and rapidly. Furthermore, when the controller makes adjustments, it can use PID control to regulate the motor based on data from a single sensor (including temperature value, rate of change of temperature value, etc.), or based on the differences between multiple sensors, or based on data from a single sensor (including temperature value, rate of change of temperature value, etc.), the differences between multiple sensors, and / or the rate of change of the differences between multiple sensors (the derivatives of the differences between multiple sensors). Specifically, to achieve a simple, fast, and safe adjustment method, even though multiple sensors are installed in the cooling system, the controller can adjust based on data from only one sensor when performing control and regulation; or, under different conditions, it can use data from different individual sensors for adjustment, but under a given condition, it can only use data from one sensor.

[0063] Implementing this invention provides the following advantages: The cooling system for fluids according to this invention, which features variable operating condition adjustment, includes an expander, a compressor driven by an electric motor (the motor speed is adjustable), a controller, and a sensing device. The sensing device is configured to detect the temperature of the fluid and / or the cooling medium. The controller receives data from the sensing device and controls the motor speed based on this data. Therefore, when the required cooling capacity of the cooled fluid and / or the cooling capacity provided by the refrigerant changes, the motor speed is adjusted to ensure that the temperature of the cooled fluid remains at a predetermined value. In particular, the control is achieved through PID regulation, which offers advantages such as simple control, safety, reliability, and rapid adjustment. This allows the cooling system of this invention to adjust the cooling capacity accordingly to changes in operating conditions, achieving variable operating condition adjustment within a cooling capacity range of 0-100%.

[0064] The above-disclosed embodiments are merely a few preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, any equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A cooling system for a fluid with variable operating condition regulation function, the cooling system comprising a cooling circuit for cooling the fluid, the cooling circuit comprising: At least two compressors are arranged in series and / or parallel in the cooling circuit, such that the refrigerant flows through the at least two compressors in series and / or parallel to compress the refrigerant in the cooling system; wherein a cooler is provided at the outlet of each compressor to cool the compressed refrigerant; an expander is used to expand the cooled refrigerant; an electric motor is used to drive the compressor to compress the refrigerant, wherein the speed of the electric motor is adjustable; and a heat exchanger is used to generate heat exchange between the cooled fluid and the expanded refrigerant. The cooling system also includes a controller and a sensor. The sensor is configured to detect the temperature of the fluid and / or the cooling medium. The sensor and the motor are connected to the controller, which receives data from the sensor and controls the motor speed based on the data. Its features are: At least one of the at least two compressors receives energy output from the expander; and at least the other of the at least two compressors is driven by an electric motor. The expander is provided with a bypass branch. One end of the bypass branch is connected to the pipe section upstream of the heat exchanger at the expander inlet, and the other end of the bypass branch is connected to the pipe section downstream of the heat exchanger at the expander outlet. A regulating valve is provided on the bypass branch to regulate the refrigerant flowing from the expander inlet to the expander outlet via the bypass branch. The compressed refrigerant flows to the compressor inlet via the bypass branch.

2. The cooling system of claim 1, wherein, The speed of an electric motor is continuously variable.

3. The cooling system of claim 1, wherein, A sensing device is installed on at least one of the following: the inlet pipe section of the expander, the pipe section between the expander outlet and the heat exchanger, the outlet pipe section of the heat exchanger for the cooled fluid, and the outlet pipe section of the heat exchanger for the refrigerant.

4. The cooling system according to claim 3, characterized in that, The controller has a preset value for the temperature-related values ​​of the refrigerant or the cooled fluid at the location where the sensor is installed. When the actual value measured by the sensor differs from the preset value, the controller adjusts the speed of the motor until the actual value matches the preset value.

5. The cooling system according to claim 4, characterized in that, The controller uses a PID controller to adjust the motor speed; the preset value is set in a variable manner; when the actual value measured by the sensor is greater than the preset value, the controller increases the motor speed, and when the actual value measured by the sensor is less than the preset value, the controller decreases the motor speed.

6. The cooling system according to claim 4, characterized in that, Temperature-related values ​​include the temperature value detected by a single sensor, the rate of change of the temperature value detected by a single sensor, the difference between the temperature values ​​detected by multiple sensors, and / or the rate of change of the difference between the temperature values ​​detected by multiple sensors.

7. The cooling system according to claim 1, characterized in that, In at least a portion of the heat exchanger, the flow direction of the fluid is opposite to the flow direction of the expanded refrigerant; wherein the refrigerant is an inert gas; wherein the fluid is liquefied natural gas, carbon dioxide, hydrogen, or helium, or a mixture of at least two of liquefied natural gas, carbon dioxide, hydrogen, or helium.

8. The cooling system according to claim 7, characterized in that, The refrigerant is selected from He, N2 or Ne, or a mixture of at least two of the gases selected from He, N2 and Ne.

9. The cooling system according to claim 1, characterized in that, The cooling circuit also includes a regenerative heat exchanger, in which the refrigerant flowing out of the heat exchanger exchanges heat with the refrigerant before entering the expander; the heat exchanger and the regenerative heat exchanger are installed in an insulation device.

10. The cooling system according to claim 1, characterized in that, At least one of the at least two compressors can be configured in a coaxial manner with the electric motor and the expander, such that the at least one compressor is driven by the energy output from the electric motor and the expander.

11. The cooling system according to claim 1, characterized in that, The number of expanders is at least two, and the at least two expanders are arranged in series and / or parallel in the cooling circuit, so that the refrigerant flows through the at least two expanders in series and / or parallel.

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