A liquefied gas carrier non-condensable gas treatment device and control method

Abstract

The application provides a liquefied gas ship non-condensable gas treatment device and a control method. The treatment device is provided with a high-pressure liquid storage heat exchange tank. The liquid cargo composition and the non-condensable gas can be separated in the high-pressure liquid storage heat exchange tank. The temperature of the non-condensable gas and the liquid cargo vapor mixture is further reduced. The concentration of the liquid cargo evaporation gas contained in the top non-condensable gas mixture is greatly reduced when the mixture is discharged. The liquid cargo evaporation gas in the top mixed gas is more converted into liquid by cooling and falls to the bottom. The waste of effective liquid cargo is reduced. At the same time, the non-condensable gas is gathered at the top of the high-pressure liquid storage heat exchange tank. The partial pressure of the liquid surface at the bottom is reduced. The exhaust pressure of the compressor is reduced at the same liquid cargo condensation temperature. The power consumption is reduced. The economy of the whole system is improved.

Description

Technical Field

[0001] This invention relates to the field of liquefied gas carrier technology, and in particular to a device and control method for treating non-condensable gases on liquefied gas carriers. Background Technology

[0002] Liquefied petroleum gas (LPG) carriers are primarily used for transporting LPG. Because LPG is stored at temperatures below ambient during transport, it continuously evaporates into flash vapor. This flash vapor contains not only the normal propane and ethane components found in the cargo tanks, but also a certain amount of methane and nitrogen. During the reliquefaction process using a reliquefaction unit, the compressor pressurization and seawater cooling methods cannot condense and liquefy the methane and nitrogen for return to the tanks. This causes a small amount of non-condensable gases generated in the cargo tanks to accumulate in the gas-liquid separator after the condenser. Over time, the accumulation of non-condensable gases in the gas-liquid separator increases, leading to higher compressor discharge pressure and increased compressor power consumption. If the top gas is discharged after only a slight increase in pressure within the condenser and subsequent gas-liquid separator, a large amount of ethane and propane vapor will be released during the discharge of non-condensable gases, resulting in significant waste of the LPG cargo.

[0003] To balance the increased power consumption of the compressor in the reliquefaction system with the problem of a significant amount of liquid being carried away during the non-condensable gas emission process, foreign liquid manufacturers WGS and TGE have adopted a method of setting a higher non-condensable gas emission pressure in the gas-liquid separator after the condenser. This slightly increases the concentration of non-condensable gases during emission, but it also increases the power consumption of the compressor. Furthermore, due to the increased compressor pressure ratio, the compressor discharge temperature also increases significantly.

[0004] LGE removes the non-condensable gas from the top of the gas-liquid separator after the condenser and uses a dedicated heat exchanger and gas-liquid separator to process it. This method effectively reduces the compressor's discharge pressure and power consumption, and significantly reduces the effective liquid components carried by the discharged non-condensable gas. However, the addition of a heat exchanger and the need for an additional gas-liquid separator significantly increases the system's investment cost and complexity. Summary of the Invention

[0005] This invention addresses the problem of high effective liquid content in non-condensable gases emitted from liquefied gas (LNG) reliquefaction systems on LPG carriers, leading to increased compressor pressure and power consumption due to the accumulation of non-condensable gases during discharge. The invention discloses a non-condensable gas treatment device for LPG carriers. It separates the non-condensable gas-containing condensate from the condenser into a gas-liquid mixture and utilizes a partially throttled, low-temperature two-phase liquid to cool the separated non-condensable gas with a high liquid content. The cooled two-phase liquid mixture is then introduced into the gas-liquid separator to prevent liquid from being drawn into the compressor's third-stage inlet. Furthermore, the gas-liquid separator can be connected to both the compressor's second-stage and first-stage inlets via valves, further reducing the temperature of the liquid mixture in the two-phase mixture.

[0006] To achieve the above and other related objectives, the present invention provides a treatment apparatus for non-condensable gases on liquefied gas carriers, the treatment apparatus comprising:

[0007] A high-pressure liquid heat exchange tank, the side wall of which is connected to the reliquefaction system condenser via a pipeline, for collecting the gas-liquid mixture discharged from the reliquefaction system condenser. The liquid in the gas-liquid mixture includes high-pressure liquid condensate, and the gas includes non-condensable gas and liquid vapor.

[0008] A steam condenser is installed at the top of the high-pressure liquid heat exchange tank. One end of the condensing pipe is connected to the bottom of the high-pressure liquid heat exchange tank, and the other end is connected to the inlet of the steam condenser. The high-pressure liquid condensate at the bottom of the high-pressure liquid heat exchange tank flows through the throttling valve in the condensing pipe to achieve pressure and temperature reduction, and then enters the steam condenser. This creates a low-temperature environment at the top of the high-pressure liquid heat exchange tank, causing the liquid vapor in the gas at the top of the high-pressure liquid heat exchange tank to be cooled and converted into liquid, falling to the bottom of the high-pressure liquid heat exchange tank to form high-pressure liquid condensate.

[0009] Preferably, the high-pressure liquefied cargo condensate includes liquid propane and ethane, the non-condensable gases include methane and nitrogen, and the liquefied cargo vapor includes gaseous propane and ethane.

[0010] Preferably, the high-pressure liquid storage heat exchange tank is provided with an isolation net in the middle, which allows liquid and gas to pass through and prevents the gas in the upper part from mixing with the gas on the bottom liquid surface.

[0011] Preferably, the top of the high-pressure liquid storage heat exchange tank is connected to a vent via a pipe equipped with an exhaust valve to release residual non-condensable gases in the upper part of the high-pressure liquid storage heat exchange tank.

[0012] Preferably, the outlet of the steam condenser is connected to a high-pressure gas-liquid separator. After flowing through the steam condenser, the high-pressure liquid condensate absorbs heat and is converted into a gas-liquid mixture. The gas-liquid mixture includes liquid propane and ethane and gaseous propane and ethane. The gas-liquid mixture is separated into liquid and gas by the high-pressure gas-liquid separator to prevent the liquid from being sucked into the compressor.

[0013] Preferably, the outlet of the high-pressure gas-liquid separator is connected to three branches, with the first, second, and third branches respectively equipped with first, second, and third control valves; the first branch is connected to the inlet of the three-stage compressor; the second branch is connected to the inlet of the low-pressure gas-liquid separator, and the outlet of the low-pressure gas-liquid separator is connected to the inlet of the first-stage compressor; the third branch is connected to the top inlet of the low-pressure liquid storage heat exchange tank.

[0014] Preferably, a liquid subcooler is provided at the bottom of the low-pressure liquid storage heat exchange tank. The inlet of the liquid subcooler is connected in parallel to the condenser pipeline through a pipeline, and the outlet of the liquid subcooler is connected to the liquid cargo tank through a pipeline equipped with a flow regulating valve to realize the return of high-pressure liquid cargo condensate.

[0015] Preferably, the upper sidewall of the low-pressure liquid storage heat exchange tank is also connected in parallel to the condenser pipeline through a pipeline equipped with a flow regulating valve, so as to introduce the high-pressure liquid condensate into the interior of the low-pressure liquid storage heat exchange tank, forming a liquid at the bottom and a gaseous liquid at the top. The low-pressure liquid storage heat exchange tank also has a top outlet, through which the gas from the high-pressure gas-liquid separator and the gaseous liquid from the high-pressure liquid condensate are discharged and further discharged to the secondary compressor.

[0016] The present invention also provides a control method for the above-mentioned processing device, comprising the following steps:

[0017] The gas-liquid mixture from the reliquefaction system condenser enters the high-pressure liquid storage heat exchange tank. The liquid in the gas-liquid mixture includes high-pressure liquid cargo condensate, and the gas includes non-condensable gas and liquid cargo vapor gas. The high-pressure liquid cargo condensate located at the bottom of the high-pressure liquid storage heat exchange tank flows through the throttling valve in the condensation pipeline to achieve pressure and temperature reduction, and then enters the steam condenser. This creates a low-temperature environment in the upper part of the high-pressure liquid storage heat exchange tank, causing the liquid cargo vapor gas in the upper part of the high-pressure liquid storage heat exchange tank to be cooled and converted into liquid, falling to the bottom of the high-pressure liquid storage heat exchange tank to form high-pressure liquid cargo condensate.

[0018] As non-condensable gases carried from the reliquefaction system condenser continuously enter the high-pressure liquid storage heat exchange tank, the non-condensable gases in the upper part of the high-pressure liquid storage heat exchange tank will accumulate and increase in concentration, eventually causing the pressure in the high-pressure liquid storage heat exchange tank to rise. At this time, the exhaust valve opens, and the non-condensable gases with lower temperature and higher concentration in the upper part of the high-pressure liquid storage heat exchange tank are discharged to the vent. Subsequently, the pressure in the high-pressure liquid storage heat exchange tank decreases, and after it drops to the set value, the exhaust valve closes.

[0019] Preferably, the method further includes the following steps:

[0020] The outlet of the steam condenser is connected to a high-pressure gas-liquid separator. After flowing through the steam condenser, the high-pressure liquid condensate absorbs heat and is converted into a gas-liquid mixture. The gas-liquid mixture is then separated into gas and liquid by the high-pressure gas-liquid separator.

[0021] When the reliquefaction system performs three-stage compression, the gas at the outlet of the high-pressure gas-liquid separator is discharged to the inlet of the three-stage compressor through the first branch. At this time, the first control valve is opened and the second and third control valves are closed, so that the pressure in the high-pressure gas-liquid separator is consistent with the pressure at the inlet of the three-stage compressor, and the liquid in the steam condenser evaporates under the pressure corresponding to the inlet of the three-stage compressor.

[0022] When the reliquefaction system performs primary compression, the second control valve opens and the first and third control valves close. The gas from the high-pressure gas-liquid separator outlet is discharged to the low-pressure gas-liquid separator through the second branch. The gas separated by the low-pressure gas-liquid separator enters the primary compressor.

[0023] When the reliquefaction system performs secondary compression, the third control valve is opened and the first and second control valves are closed. The gas at the outlet of the high-pressure gas-liquid separator is discharged to the low-pressure liquid storage heat exchange tank through the third branch.

[0024] As described above, the present invention provides a treatment apparatus and control method for non-condensable gases on liquefied gas carriers. The treatment apparatus is equipped with a high-pressure liquid storage heat exchange tank, which enables the separation of liquefied cargo components and non-condensable gases within the tank. It further reduces the temperature of the mixture of non-condensable gases and liquefied cargo vapor, thereby significantly reducing the concentration of liquefied cargo vapor contained in the top non-condensable gas mixture during discharge. This causes more of the liquefied cargo vapor in the top mixture to cool and condense into liquid, falling to the bottom and reducing the waste of effective liquefied cargo. Simultaneously, because the non-condensable gases accumulate at the top of the high-pressure liquid storage heat exchange tank, the partial pressure on the bottom liquid surface is reduced. Under the same liquefied cargo condensation temperature, the compressor's discharge pressure is reduced, power consumption is decreased, and the overall system economy is improved. Attached Figure Description

[0025] Figure 1 The diagram shows the component connections of the processing device of the present invention.

[0026] Component designation explanation

[0027] 1-High-pressure liquid heat exchange tank; 2-Isolation net; 3-Exhaust valve; 4-Throttle valve; 5-Steam condenser; 6-High-pressure gas-liquid separator; 7-First control valve; 8-Second control valve; 9-Low-pressure gas-liquid separator; 10-Third control valve; 11-Low-pressure liquid heat exchange tank; 12-Liquid subcooler; 13-Flow regulating valve; 14-Flow regulating valve. Detailed Implementation

[0028] 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.

[0029] In the detailed description of embodiments of the present invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged and not to scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. In actual fabrication, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0030] For ease of description, spatial relation terms such as “below,” “under,” “lower than,” “below,” “above,” and “upper” may be used herein to describe the relationship between one element or feature shown in the accompanying drawings and other elements or features. It will be understood that these spatial relation terms are intended to include directions other than those depicted in the drawings for the device in use or operation. Furthermore, when a layer is referred to as being “between” two layers, it can be the only layer between the two layers, or there may be one or more layers in between. The phrase “between” as used herein includes both endpoint values.

[0031] In the context of this application, the structure described above the first feature may include embodiments in which the first and second features are formed in direct contact, or embodiments in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact.

[0032] 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.

[0033] like Figure 1 As shown, the present invention provides a device for treating non-condensable gases on liquefied gas ships, specifically comprising:

[0034] A high-pressure liquid storage heat exchange tank 1 is provided. The side wall of the high-pressure liquid storage heat exchange tank 1 is connected to the reliquefaction system condenser through a pipeline to collect the gas-liquid mixture discharged from the reliquefaction system condenser. The liquid in the gas-liquid mixture includes high-pressure liquid condensate (liquid propane and ethane), and the gas includes non-condensable gases (methane and nitrogen) and liquid vapor (gaseous propane and ethane).

[0035] It should be noted that the main components of the high-pressure liquefied petroleum gas condensate include propane and ethane, while the main components of the non-condensable gases include methane and nitrogen. Because liquefied petroleum gas (LPG) evaporates flash vapor during transportation, which includes the aforementioned gases, propane and ethane can be condensed into liquids after liquefaction. Methane and nitrogen, with relatively lower liquefaction temperatures, remain gaseous after condensation and mix with the liquid propane and ethane to form a gas-liquid mixture that enters the high-pressure storage heat exchange tank. Existing technology directly introduces this gas-liquid mixture into a gas-liquid separator. While this achieves separation of liquid propane and ethane, some gaseous propane and ethane mix with the non-condensable gases during the process. When this mixture is discharged, propane and ethane are also discharged, resulting in significant waste. Therefore, this invention adds a high-pressure storage heat exchange tank to achieve complete separation of the liquefied components (propane and ethane) and non-condensable gases within the high-pressure storage heat exchange tank.

[0036] Furthermore, the high-pressure liquid storage heat exchange tank 1 is provided with an isolation net 2 in the middle. The isolation net 2 allows liquid and gas to pass through and prevents the gas at the top from mixing with the gas on the bottom liquid surface. The pipeline connecting the high-pressure liquid storage heat exchange tank 1 to the condenser of the reliquefaction system is located between the isolation net and the bottom liquid surface.

[0037] Furthermore, a steam condenser 5 is provided at the upper part of the high-pressure liquid heat exchange tank 1. One end of the condensing pipe is connected to the bottom of the high-pressure liquid heat exchange tank 1, and the other end is connected to the inlet of the steam condenser 5. The high-pressure liquid condensate at the bottom of the high-pressure liquid heat exchange tank 1 flows through the throttle valve 4 in the condensing pipe to achieve pressure and temperature reduction, and then enters the steam condenser 5. This creates a low-temperature environment at the upper part of the high-pressure liquid heat exchange tank 1, causing the liquid vapor in the gas at the upper part of the high-pressure liquid heat exchange tank 1 to be cooled and converted into liquid, falling to the bottom of the high-pressure liquid heat exchange tank 1 to form high-pressure liquid condensate. Here, if the high-pressure liquid condensate at the bottom is directly introduced into the steam condenser 5, the temperature cannot reach the required cooling level. Therefore, it is necessary to further cool it through the throttle valve 4 to achieve the condensation effect. During the process, the opening degree of the throttle valve 4 can be controlled to control the degree of cooling.

[0038] It should be noted that the upper gas in the high-pressure liquid heat exchanger includes non-condensable gases (methane and nitrogen) and liquid vapors (gaseous propane and ethane). Because their liquefaction temperatures differ significantly, the steam condenser only converts the liquid vapors to liquid state and does not liquefy the non-condensable gases, thus avoiding the problem of non-condensable gases mixing with the bottom liquid. Furthermore, the entire condensation process directly utilizes the high-pressure liquid condensate for heat absorption, eliminating the need for other condensing media and simplifying the entire system to the greatest extent possible.

[0039] Furthermore, the top of the high-pressure liquid heat exchange tank 1 is connected to a vent via a pipe equipped with an exhaust valve 3 to release residual non-condensable gases in the upper part of the high-pressure liquid heat exchange tank 1. As the non-condensable gases surrounding the steam condenser 5 are cooled, their concentration increases. As non-condensable gases carried from the reliquefaction system condenser continuously enter the high-pressure liquid heat exchange tank 1, the non-condensable gases in the upper part of the high-pressure liquid heat exchange tank 1 accumulate and their concentration increases, eventually causing the pressure in the high-pressure liquid heat exchange tank to rise. At this time, the exhaust valve 3 opens, and the non-condensable gases with lower temperature and higher concentration in the upper part of the high-pressure liquid heat exchange tank 1 are discharged to the vent. Subsequently, the pressure inside the high-pressure liquid heat exchange tank decreases, and after it drops to a set value, the exhaust valve 3 closes.

[0040] Furthermore, the outlet of the steam condenser 5 is connected to the high-pressure gas-liquid separator 6. After flowing through the steam condenser 5, the high-pressure liquid condensate absorbs heat and transforms into a gas-liquid mixture, which includes liquid propane and ethane and gaseous propane and ethane. The gas-liquid mixture is separated into liquid and gas by the high-pressure gas-liquid separator 6 to prevent liquid from being sucked into the compressor. The outlet of the high-pressure gas-liquid separator is connected to three branches. The first, second, and third branches are respectively equipped with first, second, and third control valves. The first branch is connected to the inlet of the three-stage compressor; the second branch is connected to the inlet of the low-pressure gas-liquid separator 9, and the outlet of the low-pressure gas-liquid separator is connected to the inlet of the first-stage compressor; the third branch is connected to the top inlet of the low-pressure liquid storage heat exchange tank 11. The three branches are connected to different compressor inlets, which can be flexibly selected according to the outlet pressure of the high-pressure gas-liquid separator.

[0041] When the reliquefaction system performs three-stage compression, the gas at the outlet of the high-pressure gas-liquid separator is discharged to the inlet of the three-stage compressor through the first branch. At this time, the first control valve 7 is opened and the second and third control valves are closed, so that the pressure in the high-pressure gas-liquid separator 6 is consistent with the pressure at the inlet of the three-stage compressor, and the liquid in the steam condenser evaporates at the pressure corresponding to the inlet of the three-stage compressor.

[0042] When the reliquefaction system performs primary compression, the second control valve 8 opens and the first and third control valves close. The gas from the outlet of the high-pressure gas-liquid separator is discharged to the low-pressure gas-liquid separator 9 through the second branch. The gas separated by the low-pressure gas-liquid separator 9 enters the primary compressor. Here, the low-pressure gas-liquid separator 9 plays a transitional role in reducing pressure to reach the working pressure of the primary compressor.

[0043] When the reliquefaction system performs secondary compression, the third control valve 10 is opened and the first and second control valves are closed. The gas from the outlet of the high-pressure gas-liquid separator 6 is discharged to the low-pressure liquid storage heat exchange tank 11 through the third branch. The lower part of the low-pressure liquid storage heat exchange tank 11 is equipped with a liquid subcooler 12. The inlet of the liquid subcooler 12 is connected in parallel to the condenser pipeline through a pipeline. The outlet of the liquid subcooler 12 is connected to the liquid cargo tank through a pipeline equipped with a flow regulating valve 13 to realize the return of high-pressure liquid cargo condensate.

[0044] Furthermore, the upper sidewall of the low-pressure liquid storage heat exchange tank 11 is also connected in parallel to the condenser pipeline through a pipeline equipped with a flow regulating valve 14, so as to introduce the high-pressure liquid condensate into the interior of the low-pressure liquid storage heat exchange tank 11, forming a liquid at the bottom and a gaseous liquid at the top. The low-pressure liquid storage heat exchange tank 11 also has a top outlet, through which the gas from the high-pressure gas-liquid separator 6 and the gaseous liquid from the high-pressure liquid condensate are discharged and further discharged to the secondary compressor.

[0045] Here, the low-pressure liquid heat exchange tank 11 serves as a transitional pressure reduction mechanism to reach the working pressure of the secondary compressor; at the same time, it also plays a role in regulating the internal pressure of the high-pressure liquid heat exchange tank 1. When the internal pressure of the high-pressure liquid heat exchange tank 1 is too high, it can be diverted to the low-pressure liquid heat exchange tank 11 through the pipeline to achieve the effect of pressure regulation.

[0046] Based on the above processing device, the present invention also provides a control method, the control method comprising the following steps:

[0047] The gas-liquid mixture from the reliquefaction system condenser enters the high-pressure liquid storage heat exchange tank 1. The liquid in the gas-liquid mixture includes high-pressure liquid cargo condensate (liquid propane and ethane), and the gas includes non-condensable gases (methane and nitrogen) and liquid cargo vapor gas (gaseous propane and ethane). The high-pressure liquid cargo condensate located at the bottom of the high-pressure liquid storage heat exchange tank 1 flows through the throttling valve 4 in the condensation pipeline to achieve pressure and temperature reduction, and then enters the steam condenser 5, thereby creating a low-temperature environment in the upper part of the high-pressure liquid storage heat exchange tank 1. This causes the liquid cargo vapor gas in the gas in the upper part of the high-pressure liquid storage heat exchange tank to be cooled and converted into liquid, falling to the bottom of the high-pressure liquid storage heat exchange tank to form high-pressure liquid cargo condensate.

[0048] As non-condensable gases carried from the reliquefaction system condenser continuously enter the high-pressure liquid storage heat exchange tank 1, the non-condensable gases in the upper part of the high-pressure liquid storage heat exchange tank will accumulate and increase in concentration, eventually causing the pressure in the high-pressure liquid storage heat exchange tank to rise. At this time, the exhaust valve 3 opens, and the non-condensable gases with lower temperature and higher concentration in the upper part of the high-pressure liquid storage heat exchange tank 1 are discharged to the vent. Subsequently, the pressure in the high-pressure liquid storage heat exchange tank decreases, and after it drops to the set value, the exhaust valve 3 closes.

[0049] Furthermore, the outlet of the steam condenser 5 is connected to the high-pressure gas-liquid separator 6. After flowing through the steam condenser 5, the high-pressure liquid condensate absorbs heat and is converted into a gas-liquid mixture. The gas-liquid mixture includes liquid propane and ethane and gaseous propane and ethane. The gas-liquid mixture is separated into liquid and gas by the high-pressure gas-liquid separator 6 to prevent the liquid from being sucked into the compressor.

[0050] Furthermore, when the reliquefaction system performs three-stage compression, the gas at the outlet of the high-pressure gas-liquid separator 6 is discharged to the inlet of the three-stage compressor through the first branch. At this time, the first control valve 7 is opened, and the second and third control valves 8 and 10 are closed, so that the pressure in the high-pressure gas-liquid separator is consistent with the pressure at the inlet of the three-stage compressor, and the liquid in the steam condenser evaporates under the pressure corresponding to the inlet of the three-stage compressor.

[0051] When the reliquefaction system performs primary compression, the second control valve 8 opens, and the first and third control valves 7 and 10 close. The gas from the outlet of the high-pressure gas-liquid separator 6 is discharged to the low-pressure gas-liquid separator 9 through the second branch. The gas separated by the low-pressure gas-liquid separator 9 enters the primary compressor.

[0052] When the reliquefaction system performs secondary compression, the third control valve 10 is opened and the first and second control valves 7 and 8 are closed. The gas at the outlet of the high-pressure gas-liquid separator is discharged to the low-pressure liquid storage heat exchange tank 11 through the third branch.

[0053] In summary, this invention provides a treatment device and control method for non-condensable gases on liquefied gas carriers. The treatment device includes a high-pressure liquid storage heat exchange tank, which enables the separation of liquefied cargo components and non-condensable gases within the tank. It further reduces the temperature of the mixture of non-condensable gases and liquefied cargo vapor, significantly lowering the concentration of liquefied cargo vapor contained in the top non-condensable gas mixture during discharge. This results in more of the liquefied cargo vapor in the top mixture being cooled and converted into liquid, falling to the bottom and reducing waste of effective liquefied cargo. Simultaneously, because the non-condensable gases accumulate at the top of the high-pressure liquid storage heat exchange tank, the partial pressure on the bottom liquid surface is reduced. Under the same liquefied cargo condensation temperature, the compressor's discharge pressure is lowered, power consumption is reduced, and the overall system economy is improved.

[0054] 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 device for treating non-condensable gases on liquefied gas ships, characterized in that, The processing device includes: A high-pressure liquid heat exchange tank, the side wall of which is connected to the reliquefaction system condenser via a pipeline, for collecting the gas-liquid mixture discharged from the reliquefaction system condenser. The liquid in the gas-liquid mixture includes high-pressure liquid condensate, and the gas includes non-condensable gas and liquid vapor. A steam condenser is installed at the top of the high-pressure liquid heat exchange tank. One end of the condensation pipe is connected to the bottom of the high-pressure liquid heat exchange tank, and the other end is connected to the inlet of the steam condenser. The high-pressure liquid condensate at the bottom of the high-pressure liquid heat exchange tank flows through the throttling valve in the condensation pipe to achieve pressure and temperature reduction, and then enters the steam condenser, thereby creating a low-temperature environment at the top of the high-pressure liquid heat exchange tank. This causes the liquid vapor in the gas at the top of the high-pressure liquid heat exchange tank to be cooled and converted into liquid, falling to the bottom of the high-pressure liquid heat exchange tank to form high-pressure liquid condensate. The outlet of the steam condenser is connected to a high-pressure gas-liquid separator. The outlet of the high-pressure gas-liquid separator is connected to a first, second, and third branch. The third branch is connected to the top inlet of the low-pressure liquid storage heat exchange tank. A liquid subcooler is installed at the bottom of the low-pressure liquid storage heat exchange tank. The inlet of the liquid subcooler is connected in parallel to the condensation pipeline through a pipeline. The outlet of the liquid subcooler is connected to the liquid cargo tank through a pipeline equipped with a flow regulating valve to realize the return flow of high-pressure liquid cargo condensate. The upper sidewall of the low-pressure liquid storage heat exchange tank is also connected in parallel to the condensation pipeline through a pipeline equipped with a flow regulating valve to introduce high-pressure liquid cargo condensate into the interior of the low-pressure liquid storage heat exchange tank.

2. The apparatus for treating non-condensable gases on liquefied gas carriers according to claim 1, characterized in that: High-pressure liquefied cargo condensate includes liquid propane and ethane, non-condensable gases include methane and nitrogen, and liquefied cargo vapors include gaseous propane and ethane.

3. The apparatus for treating non-condensable gases on liquefied gas carriers according to claim 2, characterized in that: The high-pressure liquid storage heat exchange tank is equipped with an isolation net in the middle. The isolation net allows liquid and gas to pass through and prevents the gas in the upper part from mixing with the gas on the bottom liquid surface.

4. The apparatus for treating non-condensable gases on liquefied gas carriers according to claim 2, characterized in that: The top of the high-pressure liquid storage heat exchange tank is connected to a vent via a pipe equipped with an exhaust valve to release the residual non-condensable gas in the upper part of the high-pressure liquid storage heat exchange tank.

5. The apparatus for treating non-condensable gases on liquefied gas carriers according to claim 4, characterized in that... After passing through the steam condenser, the high-pressure liquid condensate absorbs heat and is converted into a gas-liquid mixture, which includes liquid propane and ethane as well as gaseous propane and ethane. The gas-liquid mixture is then separated into liquid and gas by a high-pressure gas-liquid separator to prevent liquid from being sucked into the compressor.

6. The apparatus for treating non-condensable gases on liquefied gas carriers according to claim 5, characterized in that: The first, second, and third branches are equipped with first, second, and third control valves, respectively; the first branch is connected to the inlet of the three-stage compressor; the second branch is connected to the inlet of the low-pressure gas-liquid separator, and the outlet of the low-pressure gas-liquid separator is connected to the inlet of the first-stage compressor.

7. The apparatus for treating non-condensable gases on liquefied gas carriers according to claim 6, characterized in that: The low-pressure liquid storage heat exchange tank also has a top outlet. The gas from the high-pressure gas-liquid separator and the gaseous liquid from the high-pressure liquid condensate that enter through the top outlet are discharged through the top outlet and further discharged to the secondary compressor.

8. The control method for the processing device according to claim 7, characterized in that, The steps include the following: The gas-liquid mixture from the reliquefaction system condenser enters the high-pressure liquid storage heat exchange tank. The liquid in the gas-liquid mixture includes high-pressure liquid cargo condensate, and the gas includes non-condensable gas and liquid cargo vapor gas. The high-pressure liquid cargo condensate located at the bottom of the high-pressure liquid storage heat exchange tank flows through the throttling valve in the condensation pipeline to achieve pressure and temperature reduction, and then enters the steam condenser. This creates a low-temperature environment in the upper part of the high-pressure liquid storage heat exchange tank, causing the liquid cargo vapor gas in the upper part of the high-pressure liquid storage heat exchange tank to be cooled and converted into liquid, falling to the bottom of the high-pressure liquid storage heat exchange tank to form high-pressure liquid cargo condensate. As non-condensable gases carried from the reliquefaction system condenser continuously enter the high-pressure liquid storage heat exchange tank, the non-condensable gases in the upper part of the high-pressure liquid storage heat exchange tank will accumulate and increase in concentration, eventually causing the pressure in the high-pressure liquid storage heat exchange tank to rise. At this time, the exhaust valve opens, and the non-condensable gases with lower temperature and higher concentration in the upper part of the high-pressure liquid storage heat exchange tank are discharged to the vent. Subsequently, the pressure in the high-pressure liquid storage heat exchange tank decreases, and after it drops to the set value, the exhaust valve closes.

9. The control method for the processing device according to claim 8, characterized in that, It also includes the following steps: The outlet of the steam condenser is connected to a high-pressure gas-liquid separator. After flowing through the steam condenser, the high-pressure liquid condensate absorbs heat and is converted into a gas-liquid mixture. The gas-liquid mixture is then separated into gas and liquid by the high-pressure gas-liquid separator. When the reliquefaction system performs three-stage compression, the gas at the outlet of the high-pressure gas-liquid separator is discharged to the inlet of the three-stage compressor through the first branch. At this time, the first control valve is opened and the second and third control valves are closed, so that the pressure in the high-pressure gas-liquid separator is consistent with the pressure at the inlet of the three-stage compressor, and the liquid in the steam condenser evaporates under the pressure corresponding to the inlet of the three-stage compressor. When the reliquefaction system performs primary compression, the second control valve opens and the first and third control valves close. The gas from the high-pressure gas-liquid separator outlet is discharged to the low-pressure gas-liquid separator through the second branch. The gas separated by the low-pressure gas-liquid separator enters the primary compressor. When the reliquefaction system performs secondary compression, the third control valve is opened and the first and second control valves are closed. The gas at the outlet of the high-pressure gas-liquid separator is discharged to the low-pressure liquid storage heat exchange tank through the third branch.

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