A stepwise cooling carbon dioxide refrigeration system

Abstract

The application discloses a step-by-step cooling carbon dioxide refrigeration system, which is composed of a compressor, a compression cooler, a re-cooler, a cooler, an evaporator, a throttling device, a working medium pipeline, a cooling pipeline, an adjusting valve, a low-temperature pipeline and a temperature sensor, the compression cooler is in close contact with the outer wall of the compression cavity / cylinder of the compressor, the temperature sensor is arranged on the exhaust pipe of the compressor, the compressor is connected with the cooler, the re-cooler, the throttling device and the evaporator through the working medium pipeline to form a closed refrigeration system, and the closed refrigeration system is filled with proper working medium, the cooling fluid in the cooling pipeline flows through the re-cooler, the compression cooler and the cooler in sequence, the working state of the adjusting valve is controlled by the temperature sensor, and the fluid in the low-temperature pipeline flows through the evaporator, so that the compression process of the carbon dioxide is strengthened by the compression cooler, the cooling process of the carbon dioxide is strengthened by the added re-cooler, and the energy efficiency ratio and the operation reliability of the carbon dioxide refrigeration system are obviously improved.

Description

Technical Field

[0001] This invention relates primarily to the technical field of refrigeration equipment and systems, particularly a staged cooling carbon dioxide refrigeration system. Background Technology

[0002] Currently, the main synthetic refrigerants used in commercial and industrial refrigeration equipment, including R32, are being gradually replaced. Expanding the use of natural refrigerants such as carbon dioxide in refrigeration equipment has become an inevitable choice in this new round of refrigerant replacement aimed at reducing GWP (Global Greenhouse Potential). Carbon dioxide has a critical temperature of 31.1℃, therefore transcritical cycle carbon dioxide refrigeration technology is widely used, and its performance is improved through measures such as recovering expansion work, regulating exhaust pressure, and reducing cooling fluid temperature. Although these improvements have significantly enhanced the performance of carbon dioxide refrigeration systems, their overall energy efficiency ratio (EER) is still significantly lower than that of synthetic refrigerant refrigeration systems such as R32. This presents a significant challenge to the role of carbon dioxide in this new round of refrigerant replacement and to the widespread application of carbon dioxide refrigeration systems.

[0003] The compression process is the main power-consuming process in a carbon dioxide refrigeration system. Strengthening cylinder cooling can shift the compression process from a traditional isentropic to an isothermal process, significantly reducing compression work. This is because the compression work in an isothermal process is theoretically only 1 / k of that in an isentropic process, where k is the adiabatic index of the gas, and carbon dioxide has an adiabatic index of 1.3. When the cooling fluid is at a low temperature, the temperature of the working fluid entering the throttling element can be significantly reduced, helping to increase the refrigeration capacity of the system. However, if it is used to directly cool the cylinder, it can easily cause the carbon dioxide in the cylinder to fall below its critical temperature, resulting in partial condensation or liquefaction, as with traditional working fluids like R32, damaging the compressor. If the cooling fluid is used to sequentially cool the working fluid before the throttling element, in the compression cylinder, and discharged from the compressor, it can both enhance the cooling of the working fluid before it enters the throttling element with a low-temperature fluid and adjust the temperature of the fluid cooling the cylinder to a suitable value. This increases the refrigeration capacity, reduces compression work, and prevents carbon dioxide condensation or liquefaction in the cylinder, effectively solving the problem that the energy efficiency ratio of carbon dioxide refrigeration systems is significantly lower than that of traditional working fluids like R32. Summary of the Invention

[0004] Therefore, this invention, taking into account the low critical temperature of carbon dioxide, designs a staged cooling carbon dioxide refrigeration system. It is equipped with heat exchangers such as a compressor cooler, a cooler, and a recooler. The cooling fluid flows sequentially through the recooler, compressor cooler, and cooler, while the working fluid in the system simultaneously flows sequentially through the compressor cooler, cooler, and recooler. This staged cooling of the working fluid before the throttling element, in the compression cylinder, and at the compressor discharge point ensures that the working fluid is cooled step-by-step. The fluid with the lowest temperature first passes through the added recooler, further cooling the working fluid before it enters the throttling element. After the recooler, the fluid temperature is adjusted to a suitable value before flowing through the added compressor cooler to enhance the compression process of cooling the carbon dioxide, while also preventing condensation or liquefaction of carbon dioxide in the cylinder. Finally, the fluid after the compressor cooler flows through the cooler to cool the working fluid discharged from the compressor, and the working fluid exiting the cooler enters the recooler for further cooling. This effectively improves the refrigeration capacity and reduces compression work, significantly improving the energy efficiency ratio and operational reliability of the carbon dioxide refrigeration system, which is beneficial for the widespread application of carbon dioxide refrigeration technology.

[0005] To achieve the aforementioned objectives, the present invention provides a staged cooling carbon dioxide refrigeration system. This system includes a compressor (1), a compressor cooler (2), a recooler (3), a cooler (4), an evaporator (5), a throttling device (6), a working fluid pipeline (7), a cooling pipeline (8), a regulating valve (9), a low-temperature pipeline (10), and a temperature sensor (11). The compressor cooler (2) is in close contact with the outer wall of the compressor (1)'s compression chamber / cylinder. The temperature sensor (11) is located on the compressor (1)'s exhaust pipe. The refrigeration system is connected as follows: the compressor (1) exhaust port is connected to the cooler (4) inlet, and the cooler (4) outlet is connected to the recooler (3) inlet and outlet. The outlet of the cooler (3) flows through the throttling device (6) and is connected to the inlet of the evaporator (5). The outlet of the evaporator (5) is connected to the suction port of the compressor (1). The working fluid pipeline (7) is filled with an appropriate amount of working fluid. The inlet of the cooling pipeline (8) is connected to port a of the regulating valve (9). Ports c and b of the regulating valve (9) are connected to the fluid inlets of the cooler (4) and the recooler (3) respectively. The fluid outlet of the recooler (3) is connected to the fluid inlet of the compression cooler (2). The fluid outlet of the compression cooler (2) is also connected to the fluid inlet of the cooler (4). The fluid outlet of the cooler (4) is connected to the outlet of the cooling pipeline (8). The working state of the regulating valve (9) is controlled by the temperature sensor (11). The fluid in the low-temperature pipeline (10) flows through the evaporator (5).

[0006] The ratio of the heat exchange area of ​​the recooler (3) to the heat exchange area of ​​the cooler (4) is 0.15 to 0.75.

[0007] The ratio of the heat exchange area of ​​the compression cooler (2) to the heat exchange area of ​​the cooler (4) is 0.01 to 0.3.

[0008] The working fluid suitable for this refrigeration system is carbon dioxide, or other fluids with a critical temperature below 40°C.

[0009] The compression cooler (2) is a cooling coil wound around the outside of the compression chamber, or a cylinder outer wall jacket welded from steel plates, or a cast double-walled cylinder body, or a cooling jacket formed by the cylinder body and cylinder liner.

[0010] The recooler (3) and cooler (4) can be two independent heat exchangers, or an integral structure heat exchanger with multiple fluid / working fluid inlets and outlets. The heat exchanger structure can be plate type, shell and tube type, or coaxial tube type, etc.

[0011] The compressor (1) is a piston type, or screw type, or scroll type, or rolling piston type, or centrifugal type compressor.

[0012] This refrigeration system is suitable for single-stage compression, two-stage compression, supplementary compression, or cascade refrigeration systems.

[0013] The throttling device (6) is a throttling pipe, a throttling valve, or a throttling orifice plate, or it can be a pressure energy recovery device such as an ejector or an expander.

[0014] The cooling fluid applicable to this refrigeration system is liquid such as water or gas such as air. When the air is cooled, the compressor cooler (2) can be cooled indirectly by connecting the heat transfer fluid to the air radiator, or the air can be cooled directly by passing over the outer surface of the compression chamber / cylinder without the compressor cooler (2).

[0015] This invention presents a staged cooling carbon dioxide refrigeration system. Based on the low critical temperature of carbon dioxide, a compressor cooler is added to enhance the cooling effect during the compression process, making it closer to isothermal compression and effectively reducing compression work. The compressor exhaust, after being strongly cooled, enters a cooler for further cooling, and then flows through an added recooler for further cooling. This significantly reduces the temperature of the high-pressure carbon dioxide before it enters the throttling device, effectively improving its refrigeration capacity. The cooling fluid, after passing through the recooler and having its temperature adjusted to a suitable value, enters the compressor cooler, effectively preventing the fluid temperature from becoming too low. A cooling fluid regulating valve controlled by a temperature sensor is added to regulate the fluid flow rate into the compressor cooler, comprehensively preventing the risk of carbon dioxide condensing into liquid due to over-cooling in the compression chamber, thus improving operational reliability. Therefore, this staged cooling carbon dioxide refrigeration system, by cooling carbon dioxide gas in stages through a compressor cooler, cooler, and recooler, significantly improves the energy efficiency ratio and operational reliability of the carbon dioxide refrigeration system, strongly promoting its widespread application. Attached Figure Description

[0016] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0017] Figure 1 This is a system configuration diagram of Embodiment 1 of the present invention.

[0018] Figure 2 This is a system configuration diagram of Embodiment 2 of the present invention.

[0019] Figure 3 This is a system configuration diagram of Embodiment 3 of the present invention.

[0020] Figure 4 This is a system configuration diagram of Embodiment 4 of the present invention.

[0021] Figure 5 This is a system configuration diagram of Embodiment 5 of the present invention.

[0022] Figure 6 This is a system configuration diagram of Embodiment Six of the present invention.

[0023] Explanation of the labels in the diagram:

[0024] 1—Compressor, 2—Compressor Cooler, 3—Recooler, 4—Cooler, 5—Evaporator, 6—Throttling element, 7—Working fluid line, 8—Cooling line, 9—Regulating valve, 10—Cryogenic line, 11—Temperature sensor, 12—Dual-flow cooler, 13—Air-cooled radiator, 14—Economy unit, 15—Intercooler

[0025] Example 1

[0026] refer to Figure 1This embodiment is a carbon dioxide refrigeration system with three heat exchangers and staged cooling, mainly applicable to chiller units and low-temperature refrigeration units in centralized air conditioning systems. The refrigeration system includes a compressor (1), a compressor cooler (2), a recooler (3), a cooler (4), an evaporator (5), a throttling device (6), a working fluid pipeline (7), a cooling pipeline (8), a regulating valve (9), a low-temperature pipeline (10), and a temperature sensor (11). The compressor cooler (2) is tightly wound with copper or stainless steel pipes around the outer wall of the cylinder of the compressor (1). To increase heat exchange performance, thermally conductive materials such as silicone grease or butter can be applied appropriately between the outer surface of the pipe and the outer wall of the cylinder. The temperature sensor (11) is placed on the exhaust pipe of the compressor (1) to sense the exhaust temperature. The temperature sensor (11) and the regulating valve (9) actuator are connected by a signal transmission cable. During operation, the temperature signal can be transmitted to the regulating valve (9) in real time. The refrigeration system is connected as follows: the exhaust port of the compressor (1) is connected to the inlet of the cooler (4), and the cooling system is connected to the inlet of the cooler (4). The outlet of the recooler (4) is connected to the inlet of the recooler (3). The outlet of the recooler (3) flows through the throttling device (6) and then connects to the inlet of the evaporator (5). The outlet of the evaporator (5) is connected to the suction port of the compressor (1). The working fluid pipeline (7) is filled with an appropriate amount of carbon dioxide. The inlet of the cooling pipeline (8) is connected to port a of the regulating valve (9). Ports c and b of the regulating valve (9) are connected to the fluid inlets of the cooler (4) and the recooler (3) respectively. The fluid outlet of the recooler (3) is connected to the fluid inlet of the compression cooler (2). The fluid outlet of the compression cooler (2) is also connected to the fluid inlet of the cooler (4). The fluid outlet of the cooler (4) is connected to the outlet of the cooling pipeline (8). The working state of the regulating valve (9) is controlled by the temperature sensor (11). The fluid in the low-temperature pipeline (10) flows through the evaporator (5). The fluid in the cooling pipeline (8) and the low-temperature pipeline (10) is water or a low-freezing-point liquid.

[0027] The recooler (3) is a shell-and-tube heat exchanger, while the cooler (4) and evaporator (5) are both plate heat exchangers. The ratio of the heat exchange area of ​​the recooler (3) to that of the cooler (4) is approximately 0.3.

[0028] The ratio of the heat exchange area of ​​the compressor cooler (2) to the heat exchange area of ​​the cooler (4) is approximately 0.15.

[0029] The compressor (1) is a piston type, and the throttling device (6) is an electric expansion valve.

[0030] When the carbon dioxide refrigeration system is working, the compressor (1) circulates carbon dioxide through the cooler (4), recooler (3), throttling device (6) and evaporator (5) in sequence, and then it is sucked in by the compressor (1) to complete the working cycle of the working fluid; the fluid in the cooling pipe (8) flows through the regulating valve (9), recooler (3), compression cooler (2) and cooler (4) in sequence. The working state of the regulating valve (9) is controlled by the temperature sensor (11) to bypass the fluid to the fluid inlet of the cooler (4) according to a certain ratio; the control logic of the regulating valve (9) is: let the exhaust temperature be T, and the control target be T0. T0 is usually any value between 60℃ and 80℃. When T deviates from T0, the flow opening of port b and port c is adjusted by the regulating valve (9) to make T approach T0.

[0031] Example 2

[0032] refer to Figure 2 This embodiment is a carbon dioxide refrigeration system with two heat exchangers and staged cooling, mainly suitable for applications such as chiller units in centralized air conditioning systems. Compared with Embodiment 1, a dual-flow cooler (12) replaces the recooler (3) and the cooler (4). ， The dual-flow cooler (12) and evaporator (5) are shell and tube type, the compressor (1) is piston type, and its cylinder block and cylinder liner form a cooling jacket together. The throttling element (6) is a thermostatic expansion valve.

[0033] Example 3

[0034] refer to Figure 3 This embodiment is a carbon dioxide refrigeration system with staged cooling without a recooler, which is mainly suitable for applications such as chiller units in centralized air conditioning. Compared with the first embodiment, the recooler (3) is omitted, the cooler (4) and evaporator (5) are both shell and tube type, the compressor (1) is screw type, and the throttling device (6) is a thermostatic expansion valve; the temperature sensor (11) is moved to the cooling pipe at the inlet of the compressor cooler (2), and the working state of the regulating valve (9) is controlled by the fluid temperature at the inlet of the compressor cooler (2). At the same time, the outlet of the compressor cooler (2) is directly connected to the outlet pipe of the cooling pipe (8).

[0035] Example 4

[0036] refer to Figure 4This embodiment is an air-cooled, staged cooling carbon dioxide refrigeration system, mainly suitable for applications such as chiller units in centralized air conditioning systems. Compared with the first embodiment, the recooler (3) and regulating valve (9) are omitted. The cooler (4) and evaporator (5) are both air-cooled finned types, the compressor (1) is a scroll type, and the throttling device (6) is an electric expansion valve. An external air-cooled radiator (13) is added, which is connected to the compressor cooler (2) through the cooling pipe (8). The fluid in the cooling pipe (8) is a low-boiling-point medium, which, similar to the heat pipe principle, transfers the heat absorbed by the compressor cooler (2) to the air-cooled radiator (13) and dissipates it into the air. The temperature sensor (11) is moved to the compressor exhaust pipe, and the working state of the fan motor of the air-cooled radiator (13) is controlled by the exhaust temperature.

[0037] Example 5

[0038] refer to Figure 5 This embodiment is a carbon dioxide quasi-two-stage compression refrigeration system with three heat exchangers and staged cooling, which is mainly suitable for applications such as chiller units and low-temperature refrigeration units in centralized air conditioning. Compared with the first embodiment, the compressor (1) is a screw compressor with a gas injection port, and the recooler (3), cooler (4) and evaporator (5) are all shell and tube type. An economizer (14) is added to the working fluid pipeline between the compressor (1), recooler (3) and evaporator (5). Two throttling devices (6-1) and (6-2) are set from the recooler (3) to the evaporator (5). The recooler (3) is connected to the inlet of the economizer (14) through the throttling device (6-1). The upper outlet of the economizer (14) is connected to the gas injection port of the compressor (1), and the lower outlet of the economizer (14) is connected to the inlet of the evaporator (5) through the throttling device (6-2).

[0039] Example 6

[0040] refer to Figure 6This embodiment is a two-stage compression refrigeration system for carbon dioxide with three heat exchangers and progressive cooling, mainly suitable for applications such as low-temperature refrigeration units. Compared with Embodiment 1, two compressors (1-1) and (1-2) are set up, as well as corresponding compressor coolers (2-1) and (2-2), and an intercooler (15) is added to the working fluid pipeline between compressors (1-1) and (1-2). Accordingly, the working fluid pipeline and cooling pipeline have been partially adapted. The working fluid pipeline changes as follows: the suction port of compressor (1-2) is connected to the outlet of evaporator (5), the discharge port of compressor (1-2) is connected to the inlet of intercooler (15), the outlet of intercooler (15) is connected to the inlet of compressor (1-1), and the discharge port of compressor (1-1) is connected to the inlet of cooler (4); the fluid in the cooling pipeline (8) flows through recooler (3) and cooler (4) respectively, and after flowing out of cooler (4), the pipeline is connected to the outlet of cooling pipeline (8), and after flowing out of recooler (3), the pipeline is divided into three paths, which flow through compressor cooler (2-1) and (2-2) and intercooler (15) respectively, and then converge and connect to the outlet of cooling pipeline (8).

Claims

1. A staged cooling carbon dioxide refrigeration system, characterized in that: The refrigeration system includes a compressor (1), a compressor cooler (2), a recooler (3), a cooler (4), an evaporator (5), a throttling device (6), a working fluid pipeline (7), a cooling pipeline (8), a regulating valve (9), a low-temperature pipeline (10), and a temperature sensor (11). The compressor cooler (2) is in close contact with the outer wall of the compression chamber / cylinder of the compressor (1), and the temperature sensor (11) is placed on the exhaust pipe of the compressor (1). The exhaust port of the compressor (1) is connected to the inlet of the cooler (4), the outlet of the cooler (4) is connected to the inlet of the recooler (3), and the outlet of the recooler (3) flows through the throttling device (6) and then connects to the evaporator (5). The inlet of the evaporator (5) is connected to the suction port of the compressor (1), and the working fluid pipeline (7) is filled with an appropriate amount of working fluid; the inlet of the cooling pipeline (8) is connected to the a port of the regulating valve (9), the c port and b port of the regulating valve (9) are connected to the fluid inlets of the cooler (4) and the recooler (3) respectively, the fluid outlet of the recooler (3) is connected to the fluid inlet of the compression cooler (2), the fluid outlet of the compression cooler (2) is connected to the fluid inlet of the cooler (4), the fluid outlet of the cooler (4) is connected to the outlet of the cooling pipeline (8), and the working state of the regulating valve (9) is controlled by the temperature sensor (11); the fluid in the low temperature pipeline (10) flows through the evaporator (5).

2. The carbon dioxide refrigeration system with staged cooling according to claim 1, characterized in that: The ratio of the heat exchange area of ​​the recooler (3) to the heat exchange area of ​​the cooler (4) is 0.15~0.

75.

3. The carbon dioxide refrigeration system with staged cooling according to claim 1, characterized in that: The ratio of the heat exchange area of ​​the compression cooler (2) to the heat exchange area of ​​the cooler (4) is 0.01~0.

3.

4. The carbon dioxide refrigeration system with staged cooling according to claim 1, characterized in that: The working fluid suitable for this refrigeration system is carbon dioxide, or other fluids with a critical temperature below 40°C.

5. A staged cooling carbon dioxide refrigeration system according to claim 1, characterized in that: The compression cooler (2) is a cooling coil wound around the outside of the compression chamber, or a cylinder outer wall jacket welded from steel plates, or a cast double-walled cylinder body, or a cooling jacket formed by the cylinder body and cylinder liner.

6. The carbon dioxide refrigeration system with staged cooling according to claim 1, characterized in that: The recooler (3) and the cooler (4) are two independent heat exchangers, or an integral structure heat exchanger with multiple fluid / working fluid inlets and outlets; the heat exchanger structure is a plate heat exchanger, or a shell-and-tube heat exchanger, or a coaxial heat exchanger.

7. A staged cooling carbon dioxide refrigeration system according to claim 1, characterized in that: The compressor (1) is a piston compressor, or a screw compressor, or a scroll compressor, or a rolling piston compressor, or a centrifugal compressor.

8. A staged cooling carbon dioxide refrigeration system according to claim 1, characterized in that: This carbon dioxide refrigeration system is suitable for single-stage compression, two-stage compression, supplemental compression, or cascade compression.

9. A staged cooling carbon dioxide refrigeration system according to claim 1, characterized in that: The throttling device (6) is a throttling pipe, or a throttling valve, or a throttling orifice plate, or an injector, or an expander.

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