A coupling refrigeration system of liquid ammonia subcooling and propylene subcooling

Abstract

The application belongs to the field of refrigeration and discloses a liquid ammonia subcooling and propylene subcooling coupled refrigeration system, which comprises a low-pressure compressor, a high-pressure compressor connected with the low-pressure compressor, a condenser connected with the high-pressure compressor, an outlet of the condenser comprising a secondary branch and a main branch, a throttle valve connected with the secondary branch, an inlet pipe of a cold side of an economizer connected with the throttle valve, an outlet pipe of the cold side of the economizer in communication with a pipeline between the low-pressure compressor and the high-pressure compressor, an inlet pipe of a hot side of the economizer connected with the main branch, a main throttle valve connected with the outlet pipe of the hot side of the economizer, an inlet of a cold side of an evaporator connected with the main throttle valve, a storage tank connected with an inlet of a hot side of the evaporator, a first bypass pipe having one end connected with the condenser and the other end connected with the main throttle valve, and a second bypass pipe having one end connected with an outlet of a cold side of the evaporator and the other end connected with an inlet of the high-pressure compressor. The application can realize free switching of liquid ammonia subcooling and propylene subcooling conditions, effectively reduce medium volatilization and maintain stable pressure of the storage tank.

Description

Technical Field

[0001] This invention relates to the field of refrigeration technology, and more particularly to a coupled refrigeration system of liquid ammonia subcooling and propylene insulation. Background Technology

[0002] With the increasing global demand for new energy sources, ammonia, due to its low-carbon characteristics, has become a viable alternative fuel for the shipping industry. Ammonia is an environmentally friendly fuel with zero carbon emissions during combustion. Liquid ammonia has an energy density as high as 13.6 MJ / L; the energy of 1 liter of liquid ammonia is equivalent to the energy of 4.5 liters of high-pressure liquid hydrogen or 1200 liters of atmospheric-pressure hydrogen, making it a representative fuel leading the zero-carbon era. Against this backdrop, the global maritime trade in liquid ammonia is expected to show a steady growth trend in the coming years. Liquid ammonia has low storage and transportation costs, and the largest existing ocean-going vessels capable of carrying liquid ammonia have a capacity of up to 93,000 m³. 3 However, due to factors such as ship rocking and heat leakage, liquid ammonia can evaporate, easily causing environmental pollution and economic losses.

[0003] Furthermore, the demand for propylene, as an important chemical raw material, is also increasing. Currently, shipyards are developing gas carriers capable of transporting both liquid ammonia and propylene to meet the growing transportation needs of various types of raw materials. However, liquid ammonia and propylene, being cryogenic liquids, require solutions to address the issue of heat-induced evaporation losses during transportation and delivery. Existing marine refrigeration systems cater to a single type of medium, and when the transported medium changes, the refrigeration performance of these systems struggles to adapt to the new refrigeration requirements, leading to decreased cooling efficiency and a range of potential risks. Summary of the Invention

[0004] The purpose of this invention is to provide a coupled refrigeration system of liquid ammonia subcooling and propylene insulation, which can effectively reduce the volatilization of different media during transportation and shore-based delivery.

[0005] The technical solution provided by this invention is as follows:

[0006] A coupled refrigeration system for liquid ammonia subcooling and propylene insulation includes:

[0007] Low-pressure compressor;

[0008] A high-pressure compressor, wherein the inlet of the high-pressure compressor is connected to the outlet pipeline of the low-pressure compressor;

[0009] A condenser, the inlet of which is connected to the outlet pipeline of the high-pressure compressor, the outlet of which includes a main branch and a secondary branch;

[0010] A throttle valve, the inlet of which is connected to the secondary branch pipeline;

[0011] An economizer includes a cold-side inlet pipe, a cold-side outlet pipe, a hot-side inlet pipe, and a hot-side outlet pipe. The cold-side inlet pipe is connected to the outlet pipe of the throttle valve, the cold-side outlet pipe is connected to the pipe between the low-pressure compressor and the high-pressure compressor, and the hot-side inlet pipe is connected to the main branch pipe.

[0012] The main throttle valve, wherein the hot-side outlet pipe is connected to the inlet pipe of the main throttle valve;

[0013] An evaporator, wherein the cold-side inlet of the evaporator is connected to the outlet pipe of the main throttle valve, and the cold-side outlet of the evaporator is connected to the low-pressure compressor pipe;

[0014] A storage tank, the outlet of which is connected to the hot-side inlet pipe of the evaporator, and the hot-side outlet of the evaporator is connected to the inlet pipe of the storage tank;

[0015] The first bypass pipe is connected at one end to the outlet of the condenser and at the other end to the inlet of the main throttle valve;

[0016] The second bypass pipe is connected at one end to the cold side outlet of the evaporator and at the other end to the inlet of the high-pressure compressor.

[0017] In some embodiments, during the liquid ammonia subcooling cycle, liquid ammonia is stored in the storage tank, the first bypass pipe and the second bypass pipe are disconnected, the outlet of the condenser is connected to the inlet of the throttle valve and the hot-side inlet pipe of the economizer, and the cold-side outlet of the evaporator is connected to the inlet of the low-pressure compressor.

[0018] In some embodiments, during the propylene cold-keeping cycle, propylene is stored in the storage tank, the first bypass pipe and the second bypass pipe are connected, the throttle valve, the economizer and the low-pressure compressor are bypassed, the outlet of the condenser is connected to the inlet of the main throttle valve, and the cold-side outlet of the evaporator is connected to the inlet of the high-pressure compressor.

[0019] In some implementations, the ratio of the flow rate of the secondary branch to the flow rate of the primary branch is in the range of 1:9 to 3:7.

[0020] In some embodiments, a transfer pump is also included, which is disposed on the pipeline between the outlet of the storage tank and the hot-side inlet of the evaporator.

[0021] In some embodiments, the working fluid at the outlet of the low-pressure compressor is mixed with the working fluid at the cold-side outlet pipe, resulting in a temperature reduction.

[0022] In some embodiments, the working fluid temperature decreases after passing through the throttle valve and the economizer before entering the main throttle valve.

[0023] The technical advantages of this invention are as follows:

[0024] (1) The coupled refrigeration system of liquid ammonia subcooling and propylene insulation can meet the subcooling requirements of liquid ammonia at -40℃ and the insulation requirements of propylene at 12℃, so as to realize the switching between the high efficiency of liquid ammonia subcooling and propylene insulation requirements. It also has a very good coupled refrigeration capability to meet the refrigeration requirements of different media and avoid the refrigeration effect of the refrigeration system deteriorating.

[0025] (2) This invention sets up a throttling valve and an economizer between the condenser and the main throttling valve. After passing through the condenser, the refrigerant is divided into two streams, a main stream and a secondary stream. The secondary stream (secondary branch) is depressurized and cooled after passing through the throttling valve, and exchanges heat with the main stream (main branch) in the economizer. The temperature of the main stream is reduced, which can effectively reduce the temperature of the main stream refrigerant, reduce the temperature of the refrigerant entering the main throttling valve, and reduce the temperature of the refrigerant entering the evaporator. This increases the liquid phase fraction of the refrigerant entering the evaporator after throttling, thereby improving the efficiency of the subcooling system. The refrigerant from the secondary stream (the cold-side outlet refrigerant of the economizer) flows back to the inlet of the high-pressure compressor, which can reduce the suction temperature of the high-pressure compressor, reduce the load of the high-pressure compressor, reduce the system power consumption, and eliminate the interstage cooler between the low-pressure compressor and the high-pressure compressor. This optimizes the interstage cooler's dependence on cooling water, reduces the impact of the external environment on the interstage cooling effect, and enhances the system's anti-interference capability.

[0026] (3) During the transport of liquid ammonia and shore-based barge transport, the liquid ammonia subcooling cycle or propylene cold insulation cycle is operated. The ship's own liquid cargo pump is used to draw liquid ammonia or propylene from the bottom of the storage tank of the transport ship into the evaporator to cool it to 5-10°C below the saturation temperature and then flow it back to the storage tank to reduce the temperature of liquid ammonia or propylene inside the storage tank, thereby reducing the volatilization of liquid ammonia and propylene during the transport of liquid ammonia and shore-based transport. Attached Figure Description

[0027] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0028] Figure 1 This is a schematic diagram of the coupled refrigeration system of liquid ammonia subcooling and propylene insulation provided in the embodiments of this application;

[0029] Figure 2 This is a schematic diagram illustrating the operating principle of liquid ammonia subcooling provided in a specific embodiment of this application;

[0030] Figure 3 This is a schematic diagram illustrating the operating principle of propylene cold preservation provided in a specific embodiment of this application.

[0031] Explanation of icon numbers:

[0032] 1. Low-pressure compressor; 11. Inlet pipe; 12. Outlet pipe; 2. High-pressure compressor; 21. Inlet pipe; 22. Outlet pipe; 3. Condenser; 31. Outlet pipe; 4. Throttling valve; 5. Economizer; 51. Cold-side inlet pipe; 52. Cold-side outlet pipe; 53. Hot-side inlet pipe; 54. Hot-side outlet pipe; 6. Main throttle valve; 7. Evaporator; 71. Cold-side inlet; 72. Cold-side outlet; 73. Hot-side inlet; 74. Hot-side outlet; 10. Transfer pump; 20. Storage tank; 30. First bypass pipe; 40. Second bypass pipe. Detailed Implementation

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, 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.

[0034] To keep the drawings concise, only the parts relevant to the invention are shown schematically in each figure, and they do not represent the actual structure of the product. Furthermore, for ease of understanding, in some figures, only one of components with the same structure or function is shown schematically, or only one is labeled. In this document, "one" can mean not only "only one" but also "more than one".

[0035] It should also be further understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0036] In this document, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0037] Furthermore, in the description of this application, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0038] In one embodiment of this application, such as Figure 1As shown, a coupled refrigeration system for liquid ammonia subcooling and propylene insulation includes a low-pressure compressor 1, a high-pressure compressor 2, a condenser 3, a throttle valve 4, an economizer 5, a main throttle valve 6, an evaporator 7, a storage tank 20, a first bypass pipe 30, and a second bypass pipe 40. The inlet of the high-pressure compressor 2 is connected to the outlet pipe of the low-pressure compressor 1. The inlet of the condenser 3 is connected to the outlet pipe of the high-pressure compressor 2, and the outlet of the condenser 3 includes a main branch and a secondary branch. The inlet of the throttle valve 4 is connected to the secondary branch pipe. The economizer 5 includes a cold-side inlet pipe 51, a cold-side outlet pipe 52, a hot-side inlet pipe 53, and a hot-side outlet pipe 54. The cold-side inlet pipe 51 is connected to the outlet pipe of the throttle valve 4, and the cold-side outlet pipe 52 is connected to the low-pressure compressor 1. The pipeline between the high-pressure compressor 1 and the high-pressure compressor 2 is connected; the hot-side inlet pipe 53 is connected to the main branch pipeline; the inlet of the main throttle valve 6 is connected to the hot-side outlet pipe 54; the cold-side inlet 71 of the evaporator 7 is connected to the outlet pipeline of the main throttle valve 6, and the cold-side outlet 72 of the evaporator 7 is connected to the pipeline of the low-pressure compressor 1; the outlet of the storage tank 20 is connected to the hot-side inlet 73 of the evaporator 7, and the hot-side outlet 74 of the evaporator 7 is connected to the inlet pipeline of the storage tank 20; one end of the first bypass pipe 30 is connected to the outlet of the condenser 3, and the other end is connected to the inlet of the main throttle valve 6; one end of the second bypass pipe 40 is connected to the cold-side outlet 72 of the evaporator 7, and the other end is connected to the inlet of the high-pressure compressor 2.

[0039] like Figure 2 As shown, in the liquid ammonia subcooling cycle, liquid ammonia is stored in storage tank 20. The first bypass pipe 30 and the second bypass pipe 40 are disconnected. The outlet pipe 31 of condenser 3 is connected to the inlet of throttle valve 4 and the hot-side inlet pipe 53 of economizer 5. The cold-side outlet 72 of evaporator 7 is connected to the inlet of low-pressure compressor 1. In the liquid ammonia subcooling cycle, the outlet of storage tank 20 is connected to the inlet of transfer pump 10, the outlet of transfer pump 10 is connected to the hot-side inlet 73 of evaporator 7, and the hot-side outlet 74 of evaporator 7 is connected to storage tank 20. Transfer pump 10 draws liquid ammonia or propylene from the bottom of storage tank 20 into evaporator 7, cools it to a certain temperature, and then flows back to storage tank 20 to reduce the temperature of liquid ammonia or propylene inside storage tank 20, thereby achieving the purpose of cold preservation and pressure maintenance.

[0040] like Figure 2As shown, in the liquid ammonia subcooling cycle, the outlet pipe 12 of the low-pressure compressor 1 merges with the cold-side outlet pipe 52 from the economizer 5 and is then connected to the inlet pipe 21 of the high-pressure compressor 2; the outlet of the high-pressure compressor 2 is connected to the inlet pipe of the condenser 3; the outlet pipe 31 of the condenser 3 is divided into a secondary stream and a main stream. The secondary stream and the throttle valve 4 are connected to the cold-side inlet pipe 51 of the economizer 5, and the main stream is connected to the hot-side inlet pipe 53 of the economizer 5. The hot-side outlet pipe 54 is connected to the main throttle valve 6. The cold-side outlet pipe 52 of the economizer 5 is connected to the outlet pipe 12 of the low-pressure compressor 1. The outlet of the main throttle valve 6 is connected to the cold-side inlet 71 of the evaporator 7, and the cold-side outlet 72 of the evaporator 7 is connected to the inlet pipe 11 of the low-pressure compressor 1.

[0041] The liquid ammonia subcooling cycle of the present invention is a two-stage compression refrigeration system. The refrigerant passes through two-stage compressors, condenser 3, throttle valve 4, economizer 5, and main throttle valve 6 in sequence to reach a low temperature state before entering evaporator 7 to exchange heat with liquid ammonia and then returning to the compressor, completing one closed refrigeration cycle. The liquid ammonia exchanges heat with the refrigerant in evaporator 7 to reach a cold state before entering storage tank 20 to reduce the temperature of liquid ammonia inside storage tank 20.

[0042] The cooling capacity of evaporator 7 comes from the refrigeration cycle, which employs a two-stage compression refrigeration cycle. Low-pressure refrigerant, after being compressed by low-pressure compressor 1, mixes with medium-pressure, low-temperature refrigerant from the cold-side outlet pipe 52 of economizer 5, causing its temperature to drop before entering high-pressure compressor 2. After compression by high-pressure compressor 2, it becomes a high-temperature, high-pressure state. After condensation by condenser 3, it becomes a medium-high-temperature, high-pressure state. A small portion of the refrigerant enters the expansion valve 4 via a secondary branch. The expansion valve 4 throttles and cools the refrigerant flowing out of the secondary branch before it enters the cold-side inlet pipe 51 of economizer 5. The main stream... The refrigerant enters the hot-side inlet pipe 53 of the economizer 5 through the main branch. The secondary refrigerant absorbs heat through throttling and evaporation, thereby lowering the temperature of the main refrigerant. After the secondary refrigerant is rewarmed, it flows out from the cold-side outlet pipe 52 and mixes with the refrigerant from the low-pressure compressor 1 before flowing back to the high-pressure compressor 2. The main refrigerant becomes a medium-low temperature and high-pressure refrigerant after being cooled by the secondary refrigerant. Then, it enters the main throttling valve 6 through the hot-side outlet pipe 54 and is throttled to a low-temperature and low-pressure state. It vaporizes and absorbs heat in the evaporator 7, providing subcooling capacity for liquid ammonia. After being rewarmed, it flows back to the low-pressure compressor 1.

[0043] like Figure 3 As shown, in the propylene cold storage cycle, propylene is stored in the storage tank 20, the first bypass pipe 30 and the second bypass pipe 40 are connected, the throttle valve 4, the economizer 5 and the low-pressure compressor 1 are bypassed, the outlet pipe 31 of the condenser 3 is connected to the inlet of the main throttle valve 6, and the cold side outlet 72 of the evaporator 7 is connected to the inlet of the high-pressure compressor 2.

[0044] like Figure 3As shown, in the refrigeration cycle under propylene insulation conditions, the low-pressure compressor 1, the expansion valve 4, and the economizer 5 are bypassed. The inlet of the high-pressure compressor 2 is connected to the cold-side outlet 72 of the evaporator 7, the outlet pipe 22 of the high-pressure compressor 2 is connected to the condenser 3, the outlet pipe 31 of the condenser 3 is connected to the main expansion valve 6, the outlet of the main expansion valve 6 is connected to the cold-side inlet 71 of the evaporator 7, and the cold-side outlet 72 of the evaporator 7 is connected to the inlet of the high-pressure compressor 2.

[0045] In the propylene cold insulation cycle, the outlet of storage tank 20 is connected to the inlet of transfer pump 10, the outlet of transfer pump 10 is connected to the hot-side inlet 73 of evaporator 7, and the hot-side outlet 74 of evaporator 7 is connected to storage tank 20. The cooling capacity comes from the refrigeration cycle, which is a single-stage compression refrigeration cycle. The low-pressure refrigerant is compressed by high-pressure compressor 2 into a high-temperature, high-pressure refrigerant, condensed by condenser 3 into a medium-high-temperature, high-pressure refrigerant, and then throttled by main throttling valve 6 into a low-temperature, low-pressure refrigerant. It vaporizes and absorbs heat in evaporator 7 to provide the cooling capacity for propylene cold insulation, and then flows back to high-pressure compressor 2 after rewarming.

[0046] In this embodiment, by setting the throttle valve 4 and the economizer 5, the temperature of the mainstream refrigerant can be effectively reduced, the temperature of the refrigerant entering the main throttle valve 6 can be reduced, and the temperature of the refrigerant entering the evaporator 7 can be reduced, thereby improving the efficiency of the subcooling system. The refrigerant in the cold side outlet pipe 52 of the economizer 5 flows back to the high-pressure compressor 2, which can reduce the suction temperature of the high-pressure compressor 2, reduce the load of the high-pressure compressor 2, and eliminate the interstage cooler between the low-pressure compressor 1 and the high-pressure compressor 2, reducing the impact of the external environment on the interstage cooling effect and enhancing the anti-interference capability of the system.

[0047] Compared to conventional two-stage compression refrigeration systems, the coupled refrigeration system of liquid ammonia subcooling and propylene insulation in this embodiment eliminates the compressor interstage cooler and also optimizes the interstage cooler's dependence on cooling water.

[0048] Under the premise of requiring a system evaporation temperature of -40℃, compared with the conventional two-stage compression refrigeration system, the novel coupled refrigeration system of liquid ammonia subcooling and propylene insulation in this embodiment can reduce the suction temperature of the high-pressure compressor, reduce system power consumption, reduce the refrigerant temperature entering the main throttling valve 6, and increase the liquid phase fraction of the refrigerant entering the evaporator 7 after throttling.

[0049] The beneficial effects of this invention are as follows:

[0050] (1) The coupled refrigeration system of liquid ammonia subcooling and propylene insulation has the ability to freely switch between liquid ammonia subcooling mode and propylene insulation mode.

[0051] (2) By setting up a throttle valve and an economizer, the suction temperature of the high-pressure compressor can be effectively reduced from 8°C to -7°C, and the power consumption of the high-pressure compressor is reduced by 28.72%.

[0052] (3) By setting up a throttling valve and an economizer, the working fluid temperature at the inlet of the main throttling valve is reduced, and the refrigerant temperature before the main throttling valve is reduced from 42℃ to 25℃. After throttling, the liquid phase fraction of the refrigerant entering the evaporator increases from 40% to 53.3%, which can effectively utilize the latent heat of vaporization of the liquid phase refrigerant, and the system COP is increased by 0.324.

[0053] (4) The interstage cooler between the low-pressure compressor and the high-pressure compressor was eliminated, which reduced the impact of the external environment on the interstage cooling effect and enhanced the system's anti-interference ability.

[0054] (5) After the economizer is installed, the refrigerant consumption of the system is reduced by 5%, which reduces the system investment cost and subsequent maintenance cost.

[0055] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A coupled refrigeration system for liquid ammonia subcooling and propylene insulation, characterized in that, Comprise: a low-pressure compressor; a high-pressure compressor, the inlet of which is connected with the outlet pipeline of the low-pressure compressor; a condenser, the inlet of which is connected with the outlet pipeline of the high-pressure compressor, and the outlet of which comprises a main branch and a secondary branch; a throttle valve, the inlet of which is connected with the secondary branch pipeline; an economizer, comprising a cold-side inlet pipe, a cold-side outlet pipe, a hot-side inlet pipe and a hot-side outlet pipe, the cold-side inlet pipe being connected with the outlet pipeline of the throttle valve, the cold-side outlet pipe being communicated with the pipeline between the low-pressure compressor and the high-pressure compressor, and the hot-side inlet pipe being connected with the main branch pipeline; a main throttle valve, the hot-side outlet pipe being connected with the inlet pipeline of the main throttle valve; an evaporator, the cold-side inlet of which is connected with the outlet pipeline of the main throttle valve, and the cold-side outlet of which is connected with the low-pressure compressor pipeline; a storage tank, the outlet of which is connected with the hot-side inlet pipeline of the evaporator, and the hot-side outlet of which is connected with the inlet pipeline of the storage tank; a first bypass pipe, one end of which is connected with the outlet of the condenser, and the other end of which is connected with the inlet of the main throttle valve; a second bypass pipe, one end of which is connected with the cold-side outlet of the evaporator, and the other end of which is connected with the inlet of the high-pressure compressor.

2. The coupled refrigeration system for liquid ammonia subcooling and propylene subcooling according to claim 1, wherein in the liquid ammonia subcooling cycle mode, the storage tank stores liquid ammonia, the first bypass pipe and the second bypass pipe are disconnected, the outlet of the condenser is communicated with the inlet of the throttle valve and the hot-side inlet pipe of the economizer, and the cold-side outlet of the evaporator is communicated with the inlet of the low-pressure compressor.

3. The coupled refrigeration system for liquid ammonia subcooling and propylene subcooling according to claim 1, wherein in the propylene subcooling cycle mode, the storage tank stores propylene, the first bypass pipe and the second bypass pipe are connected, the throttle valve, the economizer and the low-pressure compressor are bypassed, the outlet of the condenser is communicated with the inlet of the main throttle valve, and the cold-side outlet of the evaporator is communicated with the inlet of the high-pressure compressor.

4. The coupled refrigeration system for liquid ammonia subcooling and propylene subcooling according to claim 1, wherein the flow rate ratio of the secondary branch to the main branch is in the range of 1:9 to 3:

7.

5. The coupled refrigeration system for liquid ammonia subcooling and propylene subcooling according to claim 1, further comprising a delivery pump, which is arranged on the pipeline between the outlet of the storage tank and the hot-side inlet of the evaporator.

6. The coupled refrigeration system for liquid ammonia subcooling and propylene subcooling according to claim 1, wherein the temperature of the working medium mixed in the cold-side outlet pipe decreases after the working medium in the low-pressure compressor outlet is mixed with the working medium in the cold-side outlet pipe.

7. The coupled refrigeration system for liquid ammonia subcooling and propylene subcooling according to claim 1, wherein the temperature of the working medium entering the main throttle valve decreases after the working medium passes through the throttle valve and the economizer. ​ ​ ​ ​ ​ ​

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