A flash vapor reliquefaction system

Abstract

The application provides a flash vapor reliquefaction system. The flash vapor reliquefaction system realizes three-stage compression, one-stage condensation and two-stage intermediate cooling. The liquefied LPG is cooled by two stages in the supercooling process, so that the heat exchange temperature difference of the LPG working medium in the heat exchange process is reduced, and the irreversible loss is reduced. The working medium after the stage cooling and heat absorption vaporization enters the two-stage compressor and the three-stage compressor respectively, so that the refrigeration flow of the working medium entering the two-stage compressor in the cycle is reduced, and the power consumption in the compression process is reduced. The working medium after the first throttling and heat absorption vaporization is mixed with the working medium after the two-stage compression, and the gas working medium at the outlet of the two-stage compressor is cooled, so that the working temperature of the three-stage compressor is reduced, the three-stage compressor is protected, and the system is more energy-saving and stable and reliable to realize the reliquefaction function of the flash vapor.

Description

Technical Field

[0001] This invention relates to the fields of marine engineering and refrigeration technology, specifically to a flash vapor reliquefaction system. Background Technology

[0002] With the continuous growth of global energy demand, liquefied petroleum gas (LPG), as an important energy and chemical feedstock, has seen increasing attention paid to the safety and efficiency of its transportation and storage. In the shipping sector, the reliquefaction of LPG vapor is a crucial step in ensuring the safe transport and effective utilization of LPG by ships.

[0003] Currently, there are numerous systems on the market for treating and reliquefying LPG or liquid ammonia flash vapor. These systems are structurally and multifunctionally designed according to the specific characteristics of ships to adapt to the limited space on board. Among them, systems utilizing multi-stage compressors for compression cycles are one of the mainstream technologies for LPG vapor reliquefaction on ships. These systems mainly include two types: two-stage compression with complete cooling between stages and two-stage compression with incomplete cooling between stages.

[0004] However, despite technological advancements in existing LPG reliquefaction systems, several significant problems remain. Specifically, current systems typically only perform intercooling once during the multi-stage compressor compression and intercooling process. This design results in an excessively large heat exchange temperature difference between the LPG after pressurization and liquefaction and the LPG after throttling and vaporization during the intercooling process. This large temperature difference not only increases irreversible losses but also leads to a significant increase in system energy consumption.

[0005] Furthermore, in existing systems, the gas compressed in the second stage often directly enters the third stage, without sufficient cooling in the intermediate stages. This design results in a higher intake temperature for the third-stage compressor, which worsens the compressor's operating conditions, increases the compressor's operating load, and raises the risk of failure.

[0006] Therefore, in order to optimize the compression and cooling process, reduce the heat exchange temperature difference, reduce irreversible losses in the system, improve the operating conditions of the compressor, and reduce energy consumption and failure rate, this application provides a flash vapor reliquefaction system. Summary of the Invention

[0007] Given that existing technologies for LPG or liquid ammonia flash vapor suffer from large heat exchange temperature differences during compression and cooling, leading to irreversible losses, high energy consumption, and deterioration of compressor operating conditions, this application provides a flash vapor reliquefaction system. This flash vapor reliquefaction system utilizes the operating characteristics of a three-stage compressor to achieve a refrigeration cycle system with three-stage compression, one-stage condensation, and two-stage intercooling. The liquefied LPG undergoes subcooling through two-stage cooling, reducing the heat exchange temperature difference of the LPG working fluid and minimizing irreversible losses. The working fluid, after staged cooling and heat absorption vaporization, enters the second and third stage compressors respectively, thereby reducing the refrigeration flow rate of the working fluid entering the second stage compressor and reducing power consumption during compression. The working fluid after the first throttling and heat absorption vaporization mixes with the working fluid after the second stage compression and cools the gas working fluid at the outlet of the second stage compressor, lowering the operating temperature of the third stage compressor and protecting it. This allows the system to achieve flash vapor reliquefaction in a more energy-efficient, stable, and reliable manner.

[0008] One embodiment of this application provides a flash vapor reliquefaction system, including a primary compressor, a medium-pressure liquid storage heat exchange tank, a secondary compressor, a tertiary compressor, a condenser, a high-pressure liquid storage heat exchange tank, a subcooling heat exchanger, a first throttling valve, a coil evaporator, and a gas-liquid separator;

[0009] The inlet of the first-stage compressor is connected to the outlet of the fuel tank. The outlet of the first-stage compressor is connected via a pipe to the top of the medium-pressure liquid heat exchange tank and the inlet of the second-stage compressor. The outlet of the second-stage compressor is connected via a pipe to the inlet of the third-stage compressor and the top of the gas-liquid separator. The outlet of the third-stage compressor is connected via a pipe to the inlet of the condenser. The outlet of the condenser is connected via a pipe to the high-pressure liquid heat exchange tank. The bottom of the high-pressure liquid heat exchange tank is connected via a pipe to the inlet of the subcooling heat exchanger. The outlet of the subcooling heat exchanger is connected to the inlet of the first throttle valve. The outlet of the first throttle valve is connected to the inlet of the fuel tank. The inlet of the coil evaporator is connected to the bottom of the gas-liquid separator, and the outlet of the coil evaporator is connected to the middle of the gas-liquid separator.

[0010] In one embodiment, the coil evaporator and the gas-liquid separator are disposed inside the high-pressure liquid storage heat exchange tank.

[0011] In one embodiment, the low-temperature gas discharged from the top of the gas-liquid separator is mixed with the compressed gas discharged from the secondary compressor.

[0012] In one embodiment, the flash vapor reliquefaction system further includes a second throttle valve and a third throttle valve. The bottom of the high-pressure liquid storage and heat exchange tank is connected to the inlet of the second throttle valve and the inlet of the third throttle valve. The outlet of the second throttle valve is connected to the medium-pressure liquid storage and heat exchange tank. The outlet of the third throttle valve is connected to the gas-liquid separator.

[0013] In one embodiment, the outlet of the second throttle valve is located below the liquid level line inside the medium-pressure liquid storage heat exchange tank.

[0014] In one implementation, the medium-pressure liquid storage heat exchange tank, the condenser, the high-pressure liquid storage heat exchange tank, the subcooling heat exchanger, the first throttling valve, the second throttling valve, the third throttling valve, the coil evaporator, and the gas-liquid separator are modularly constructed within a single skid.

[0015] In one embodiment, the subcooling heat exchanger is disposed inside the medium-pressure liquid storage heat exchange tank.

[0016] As described above, the flash vapor reliquefaction system of this application has the following beneficial effects:

[0017] The flash vapor reliquefaction system of this application utilizes the operating characteristics of a three-stage compressor to achieve a refrigeration cycle system with three-stage compression, one-stage condensation, and two-stage intercooling. The liquefied LPG undergoes subcooling through two-stage cooling, reducing the heat exchange temperature difference of the LPG working fluid and minimizing irreversible losses. The working fluid, after absorbing heat and vaporizing in the staged cooling process, enters the third and second stages of the compressor respectively, thereby reducing the refrigeration flow rate of the working fluid entering the second stage of compression and reducing the power consumption of the refrigeration unit during compression. The working fluid after the first throttling and heat absorption vaporization mixes with the working fluid after the second stage compression and cools the gas working fluid at the outlet of the second stage compressor, lowering the operating temperature of the third-stage compressor and protecting it. This allows the system to achieve flash vapor reliquefaction in a more energy-efficient, stable, and reliable manner. Attached Figure Description

[0018] Figure 1 The diagram shown is a schematic representation of the flash vapor reliquefaction system according to an embodiment of the present invention.

[0019] Component designation explanation

[0020] 10, Fuel tank; 20, First-stage compressor; 30, Second-stage compressor; 40, Third-stage compressor; 50, Medium-pressure liquid storage heat exchange tank; 51, Subcooling heat exchanger; 60, High-pressure liquid storage heat exchange tank; 61, Coil evaporator; 62, Gas-liquid separator; 70, Condenser; 81, First throttle valve; 82, Second throttle valve; 83, Third throttle valve. Detailed Implementation

[0021] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0022] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0023] With the development of the shipping industry, the safe and efficient utilization of fuels such as liquefied petroleum gas (LPG) or ammonia vapor has become an important technological requirement. Existing LPG vapor reliquefaction systems on the market mainly rely on multi-stage compressors for compression cycles to achieve vapor condensation and liquefaction. However, these systems have several shortcomings in the compression and cooling processes. On the one hand, the intermediate cooling process often only occurs once, resulting in an excessively large temperature difference in heat exchange between the LPG and the throttled vaporized LPG during the subcooling process, increasing irreversible losses and energy consumption. On the other hand, the gas after the second-stage compression directly enters the third-stage compression without necessary intermediate cooling, leading to excessively high inlet temperatures for the third-stage compressor and deteriorating its operating conditions.

[0024] Therefore, existing LPG reliquefaction systems still need improvement in terms of efficiency and energy consumption. In particular, for applications such as shipping, which have high requirements for energy consumption and efficiency, developing a high-efficiency and energy-saving reliquefaction system is of great significance.

[0025] To address the aforementioned deficiencies, this application provides a flash vapor reliquefaction system. The following embodiments will provide a detailed description.

[0026] This embodiment provides a flash vapor reliquefaction system, such as Figure 1As shown, the flash vapor reliquefaction system includes a primary compressor 20, a medium-pressure liquid storage heat exchange tank 50, a secondary compressor 30, a tertiary compressor 40, a condenser 70, a high-pressure liquid storage heat exchange tank 60, a subcooling heat exchanger 51, a first throttle valve 81, a coil evaporator 61, and a gas-liquid separator 62. The inlet of the first-stage compressor 20 is connected to the outlet of the fuel tank 10 via a pipeline; the outlet of the first-stage compressor 30 is connected to the top of the medium-pressure liquid storage heat exchange tank 50 via a pipeline, and the outlet of the first-stage compressor 30 is connected to the inlet of the second-stage compressor 30 via a pipeline; the outlet of the second-stage compressor 30 is connected to the inlet of the third-stage compressor 40 via a pipeline, and the outlet of the second-stage compressor 30 is connected to the top of the gas-liquid separator 62 via a pipeline; the outlet of the third-stage compressor 40 is connected to one side inlet of the condenser 70 via a pipeline; one side outlet of the condenser 70 is connected to the high-pressure liquid storage heat exchange tank 60 via a pipeline; the bottom of the high-pressure liquid storage heat exchange tank 60 is connected to the inlet of the subcooling heat exchanger 51 via a pipeline; the outlet of the subcooling heat exchanger 51 is connected to the inlet of the first throttle valve 81; the outlet of the first throttle valve 81 is connected to the inlet of the fuel tank 10; the inlet of the coil evaporator 61 is connected to the bottom of the gas-liquid separator 62, and the outlet of the coil evaporator 61 is connected to the middle of the gas-liquid separator 2. The flash vapor reliquefaction system of this embodiment performs three-stage compression, one-stage condensation and two-stage subcooling on the flash vapor generated in the fuel tank 10, and then sends the lower temperature LPG back to the fuel tank 10. The exhaust temperature of the three-stage compressor 40 is reduced and the mass flow rate of the two-stage compressor 30 is reduced, which realizes high-efficiency and low-cost reliquefaction of flash vapor, and reduces the intake temperature of the three-stage compressor 40, thus protecting the compressor.

[0027] In an optional embodiment, the coil evaporator 61 and the gas-liquid separator 2 are disposed inside the high-pressure liquid storage heat exchange tank 60. Gas-liquid separation and natural convection heat exchange are carried out by gravity to cool the liquid inside the high-pressure liquid storage heat exchange tank 60, thereby realizing the temperature and pressure control of the gas-liquid two-phase LPG inside the high-pressure liquid storage heat exchange tank 60, thereby adjusting the condensation pressure of the flash vapor reliquefaction system and the outlet pressure of the three-stage compressor 40, and reducing the energy consumption of the compressor.

[0028] In an optional embodiment, the low-temperature gas discharged from the top of the gas-liquid separator 2 is mixed with the compressed gas discharged from the secondary compressor 30, which reduces the temperature of the inlet gas entering the tertiary compressor 40 and optimizes the working state of the tertiary compressor 40.

[0029] In an optional embodiment, the flash vapor reliquefaction system further includes a second throttle valve 82 and a third throttle valve 83. The bottom of the high-pressure liquid storage heat exchange tank 60 is connected to the inlet of the second throttle valve 82, and the outlet of the second throttle valve 82 is connected to the medium-pressure liquid storage heat exchange tank 50. Simultaneously, the bottom of the high-pressure liquid storage heat exchange tank 60 is connected to the inlet of the third throttle valve 83, and the outlet of the third throttle valve 83 is connected to the gas-liquid separator 2. The LPG liquid at the bottom of the high-pressure liquid storage heat exchange tank 60 enters the medium-pressure liquid storage heat exchange tank 50 through the second throttle valve 82 and the high-pressure liquid storage heat exchange tank 60 through the third throttle valve 83, performing staged cooling on the LPG liquid condensed by the condenser 70. This reduces the consumption of liquid LPG in the medium-pressure liquid storage heat exchange tank 50 and lowers the load on the secondary compressor 30.

[0030] In an optional embodiment, the outlet of the second throttle valve 82 is located below the liquid level line inside the medium-pressure liquid storage heat exchange tank 50. The second throttle valve 82 is introduced into the liquid inside the medium-pressure liquid storage heat exchange tank 50. By driving the liquid flow, the heat exchange effect between the internal liquid and the subcooling heat exchange is enhanced, the heat exchange temperature difference of the subcooling heat exchanger 51 is reduced, the subcooling of LPG entering the fuel tank 10 is increased, and the vaporization of the liquid entering the fuel tank 10 is reduced.

[0031] In an optional embodiment, the medium-pressure liquid storage heat exchange tank 50, condenser 70, high-pressure liquid storage heat exchange tank 60, subcooling heat exchanger 51, first throttle valve 81, second throttle valve 82, third throttle valve 93, coil evaporator 61, and gas-liquid separator 62 are connected by pipelines according to the above connection relationship and can be modularly constructed in a skid.

[0032] In an optional embodiment, the subcooling heat exchanger 51 is disposed inside the medium-pressure liquid storage heat exchange tank 50, and the subcooling heat exchanger 51 is located below the liquid level line of the total pressure liquid storage heat exchange tank 50.

[0033] The principle of the flash vapor reliquefaction system in this embodiment is as follows:

[0034] The LPG vapor discharged from the top of fuel tank 1 is drawn into and compressed by the first-stage compressor 20. After mixing with and cooling the vapor discharged from the top of the medium-pressure liquid storage heat exchange tank 50, it enters the inlet of the second-stage compressor 30 and is compressed for the second time. The gas discharged from the outlet of the second-stage compressor 30 is mixed with and cooled by the vapor discharged from the top of the gas-liquid separator 62 and enters the inlet of the third-stage compressor 40 and is compressed for the third time. The high-temperature and high-pressure gas discharged from the outlet of the third-stage compressor 40 is cooled and condensed by the condenser 70. The liquefied LPG enters the high-pressure liquid storage heat exchange tank 60 and exchanges heat with the low-temperature LPG in the coil evaporator 61 inside it, and the temperature is initially reduced. A portion of the LPG at the bottom of the high-pressure liquid storage heat exchange tank 60 enters the gas-liquid separator 2 and the coil evaporator 61 through the third throttle valve 83, where it cools down, absorbs heat, and vaporizes, thus cooling the LPG inside the high-pressure liquid storage heat exchange tank 60. Another portion of the LPG at the bottom of the high-pressure liquid storage heat exchange tank 60 enters the medium-pressure liquid storage heat exchange tank 50 through the second throttle valve 82, where it cools down, absorbs heat, and vaporizes, thus cooling the LPG inside the subcooling heat exchanger 51. The last portion of LPG at the bottom of the high-pressure liquid storage heat exchange tank 60 is further subcooled in the subcooling heat exchanger 51, then throttled down through the first throttle valve 81, and finally returns to the fuel tank 10, thus completing the reliquefaction cycle.

[0035] In this process, the high-temperature, high-pressure steam exiting the third-stage compressor 40 discharges heat to the condenser 70, where the heat is carried away by cooling water passing through the other side of the condenser 70. The LPG vapor, after absorbing heat and vaporizing in the gas-liquid separator 62, is transported to the inlet of the third-stage compressor 40 through a pipe connected to its top, where it is compressed again. The LPG vapor, after absorbing heat and vaporizing in the medium-pressure liquid storage heat exchange tank 50, is transported to the inlet of the second-stage compressor 30 through a pipe connected to its top, where it is compressed again.

[0036] The flash vapor reliquefaction system in this embodiment employs a refrigeration cycle of three-stage compression, one-stage condensation, and two-stage intercooling. The liquefied LPG undergoes subcooling via two-stage cooling, reducing the heat exchange temperature difference of the LPG working fluid and minimizing irreversible losses. The working fluid, after heat absorption and vaporization during staged cooling, enters the second-stage compressor 30 and the third-stage compressor 40 respectively, thereby reducing the refrigeration flow rate of the working fluid entering the second-stage compressor and decreasing the power consumption of the refrigeration unit during compression. The working fluid after the first throttling and heat absorption vaporization mixes with the working fluid after the second-stage compression and cools the gas at the outlet of the second-stage compressor 30, lowering the operating temperature of the third-stage compressor 40 and protecting it. This allows the flash vapor reliquefaction system to achieve flash vapor reliquefaction in a more energy-efficient and stable manner.

[0037] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A flash vapor reliquefaction system, characterized in that, It includes a primary compressor, a medium-pressure liquid heat exchange tank, a secondary compressor, a tertiary compressor, a condenser, a high-pressure liquid heat exchange tank, a subcooling heat exchanger, a first throttling valve, a coil evaporator, and a gas-liquid separator; The inlet of the first-stage compressor is connected to the outlet of the fuel tank. The outlet of the first-stage compressor is connected via a pipe to the top of the medium-pressure liquid heat exchange tank and the inlet of the second-stage compressor. The outlet of the second-stage compressor is connected via a pipe to the inlet of the third-stage compressor and the top of the gas-liquid separator. The outlet of the third-stage compressor is connected via a pipe to the inlet of the condenser. The outlet of the condenser is connected via a pipe to the high-pressure liquid heat exchange tank. The bottom of the high-pressure liquid heat exchange tank is connected via a pipe to the inlet of the subcooling heat exchanger. The outlet of the subcooling heat exchanger is connected to the inlet of the first throttle valve. The outlet of the first throttle valve is connected to the inlet of the fuel tank. The inlet of the coil evaporator is connected to the bottom of the gas-liquid separator, and the outlet of the coil evaporator is connected to the middle of the gas-liquid separator. The coil evaporator and the gas-liquid separator are disposed inside the high-pressure liquid storage heat exchange tank; The low-temperature gas discharged from the top of the gas-liquid separator is mixed with the compressed gas discharged from the secondary compressor; It also includes a second throttle valve and a third throttle valve. The bottom of the high-pressure liquid storage and heat exchange tank is connected to the inlet of the second throttle valve and the inlet of the third throttle valve. The outlet of the second throttle valve is connected to the medium-pressure liquid storage and heat exchange tank. The outlet of the third throttle valve is connected to the gas-liquid separator. The subcooling heat exchanger is installed inside the medium-pressure liquid storage heat exchange tank.

2. The flash vapor reliquefaction system according to claim 1, characterized in that, The outlet of the second throttle valve is located below the liquid level line inside the medium-pressure liquid storage heat exchange tank.

3. The flash vapor reliquefaction system according to claim 1, characterized in that, The medium-pressure liquid storage heat exchange tank, the condenser, the high-pressure liquid storage heat exchange tank, the subcooling heat exchanger, the first throttling valve, the second throttling valve, the third throttling valve, the coil evaporator, and the gas-liquid separator are modularly constructed within a single skid.

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