Compressor-Energized Refrigerant Isolation Valves

Description

CLAIM OF PRIORITY

This application claims the benefit of U.S. Provisional Application No. 63/724,154, filed Nov. 22, 2024, the contents of which are hereby incorporated by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to processes and systems for cooling or liquefying gases. More particularly, the present disclosure relates to an improved mixed refrigerant system and method for cooling or liquefying gases.

BACKGROUND

Natural gas and other gases are liquefied for storage and transport. Liquefaction reduces the volume of the gas and is typically carried out by chilling the gas through indirect heat exchange in one or more refrigeration cycles. For example, natural gas and other gases may be chilled through indirect heat exchange with a mixed refrigerant. During the indirect heat exchange, as the natural gas gets chilled, the mixed refrigerant becomes warmed and loses its capacity to chill.

Generally, warmed mixed refrigerant will be recycled in a liquefaction system by recooling the mixed refrigerant. This may be done in a cooling system/circuit that is in fluid communication with the liquefaction system. Typically, within the cooling system, a warmed mixed refrigerant may be passed through a series of separation vessels, compressors, and condensers until it has been sufficiently cooled to a high pressure stream to return to the liquefaction system.

In some cooling systems, part of the system/circuit may be separated from the remainder of the system/circuit with valves, for instance, isolation valves. For example, systems including multiple closed refrigerant compression loops may need to separate the loops from one another for safety and/or maintenance purposes. Generally, isolation valves used in liquefaction and cooling systems are energized by instrument air with solenoid-based control of the air supply. Such valves may be prone to solenoid failure and/or loss of instrument air, risking the isolation valve to fail closed. By closing at an inappropriate time, parts of the system may come into contact with cold refrigerant from the liquefaction exchanger, thus embrittling piping, vessels, and/or compressor casings. Additionally, other risks associated with valve failure may include overpressurization of the system, an increase in the required flare size, and/or a “blocked outlet” scenario.

Therefore, there is a need for improved systems and methods for cooling a mixed refrigerant.

SUMMARY OF THE DISCLOSURE

There are several aspects of the present subject matter which may be embodied separately or together in the methods, devices and systems described and claimed below. These aspects may be employed alone or in combination with other aspects of the subject matter described herein, and the description of these aspects together is not intended to preclude the use of these aspects separately or the claiming of such aspects separately or in different combinations as set forth in the claims appended hereto.

In one aspect, a system for cooling mixed refrigerant is provided. The system includes a feed line and at least one compression circuit. The compression circuit includes a first separation vessel in fluid communication with the feed line, a first compressor in fluid communication with the first separation vessel, a first condenser in fluid communication with the first compressor, and a first isolation valve. The isolation valve is configured to be opened using the pressure differential across the first compressor. The system also includes an outlet portion, wherein the outlet portion includes an outlet condenser, an outlet separation vessel, and an outlet line.

In another aspect, a method of cooling a mixed refrigerant is provided. The method includes passing the mixed refrigerant through a first compression circuit. The first compression circuit includes a first separation vessel, a first compressor, a first condenser, and a first isolation valve, wherein the first isolation valve is configured to be opened using the pressure differential across the first compressor.

In one aspect, a system for liquefying natural gas is provided. The system includes a liquefaction system and a mixed refrigerant cooling system. The mixed refrigerant cooling system includes a feed line configured to receive low pressure mixed refrigerant from the liquefaction system and at least one compression circuit. A first compression circuit includes a first separation vessel in fluid communication with the feed line, a first compressor in fluid communication with the first separation vessel, a first condenser in fluid communication with the first compressor, and a first isolation valve configured to be opened using the pressure differential across the first compressor. The mixed refrigerant cooling system also includes an outlet configured to return a high pressure mixed refrigerant to the liquefaction system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an embodiment of a mixed refrigerant cooling system of the disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

A more detailed description of the system and method in accordance with the present disclosure is set forth below. It should be understood that the description below of specific systems and methods is intended to be exemplary, and not exhaustive of all possible variations or applications. Thus, the scope of the disclosure is not intended to be limiting and should be understood to encompass variations or embodiments that would occur to persons of ordinary skill.

It should be noted herein that the lines, conduits, piping, passages and similar structures and the corresponding streams are sometimes both referred to by the same element number set out in the figures.

Reference numerals that are introduced in the specification in association with a drawing figure may be repeated in one or more subsequent figures for shared elements or components without additional description in the specification in order to provide context for other features.

In the claims, letters are used to identify claimed steps (e.g. a., b. and c.). These letters are used to aid in referring to the method steps and are not intended to indicate the order in which the claimed steps are performed, unless and only to the extent that such order is specifically recited in the claims.

Generally, natural gas and other gases may be liquefied by chilling the gas through indirect heat exchange with pre-cooled mixed refrigerant. During liquefaction of natural or other gases, the mixed refrigerant becomes warmed as a result of the indirect heat exchange. The mixed refrigerant may be cooled and reused in the system by passing the warmed mixed refrigerant through a cooling system/cycle.

An embodiment of the cooling system 10 is shown in FIG. 1. Generally, the cooling system 10 may cool a low pressure warmed mixed refrigerant by passing it through a series of separation vessels, compressors, and condensers. The vessels, compressors, and condensers may be in fluid communication with one another via a plurality of lines/conduits. Additionally, the lines/conduits may include openable/closable valves to control flow of the mixed refrigerant throughout the system 10.

In an embodiment, the vessels, compressors, condensers, and lines/conduits may be arranged to create a closed refrigerant compression loop. The cooling system 10 may include one or more compression loops. For example, a compression loop may include at least one separation vessel, compressor, and condenser. In an embodiment, as shown in FIG. 1, cooling system 10 may include a first compression loop 12a and a second compression loop 12b.

The compression loops in the cooling system may be separated by isolation valves. As shown in FIG. 1, compression loops 12a and 12b are separated from one another by isolation valve 14. Additionally, compression loop 12b may be separated from the remainder of the cooling system 10 by isolation valve 16. In an embodiment, isolation valve 16 separates compression loop 12b from lines/conduits returning mixed refrigerant to a liquefaction system. For example, the liquefaction system can be any of the systems described in U.S. Pat. Nos. 10,502,483; 10,345,039; 9,441,877; 10,480,851, 11,428,463; 11,408,673; and U.S. Publication 2022/0373255, all of which are hereby incorporated by reference herein. Other liquefaction systems known in the art may also be used. In another embodiment, isolation valve 16 may separate cooling loop 12b from another compression loop (not shown).

In an embodiment, the isolation valves 14 and 16 use the differential pressure across the compressor(s) to open and close. For example, the isolation valves 14 and 16 use the refrigerant compressor's differential pressure to keep the isolation valve open while the compressor is running (when the safest position is for the valve to stay open), and for the valve to still be forced closed when the compressor shuts down (when the safest position is for the valve to be closed).

A more detailed description of the isolation valves and the cooling system is provided below.

Referring to FIG. 1, a low pressure mixed refrigerant (LPMR) enters cooling system 10 through feed line 18. The LPMR travels through feed line 12 to a separation vessel 20. For example, separation vessel 20 may be a suction drum.

In an embodiment, feed line 18 may be made of two different materials. For example, an upstream portion 19a of feed line 12 may be made of a stainless-steel piping and a downstream portion 19b may be made of a carbon steel piping. The terms “downstream” and “upstream” refer to locations of devices and components of a system based on the direction of flow of the LPMR received from the liquefaction system at an inlet end 15 of the cooling system to an outlet end 17 of the cooling system returning a high pressure mixed refrigerant (HPMR) to the liquefaction system. The stainless-steel portion 19a may accommodate cryogenic conditions. By transitioning from stainless-steel to carbon steel, manufacturing and maintenance costs of the system 10 may be reduced. In another embodiment, feed line 18 may be made of a single material that can accommodate the mixed refrigerant.

While travelling through feed line 12, a portion of the LPMR stream may exit the system 10 via blowdown line 11. For example, a portion of the LPMR stream may travel through line 11 and pass through valve 13. In an embodiment, the stream exiting system 10 through blowdown line 11 may be collected or flared. Blowdown line 11 may be located in upstream portion 19a of feed line 12. In other words, blowdown line 11 may be located upstream the transition from stainless-steel piping to carbon steel piping. By placing blowdown line 11 upstream of the transition from stainless-steel piping to carbon steel piping, the remainder of system 10 (including piping, vessels, and compressor casings) may be protected from cryogenic temperatures.

After entering separation vessel 20, the LPMR stream is separated to a liquid component and a vapor component. The separated liquid component is collected in the bottom of the vessel 20. In an embodiment, the liquid component may be removed from the vessel through an outlet at or near the bottom of the vessel. The separated vapor component may include a low pressure vapor. The vapor stream exits the vessel 20 through line 22 and travels to compressor 24, where the stream is compressed.

The compressed stream then travels through line 26 to condenser 28, where the stream is condensed and cooled. In an embodiment, line 26 may include an outlet line 27 with a valve 29. Outlet line 27 may be used to depressurize line 26. For example, valve 29 may be a pressure safety valve. Valve 29 may include a pressure sensor. In instances where the pressure sensor senses the pressure within line 26 is too high after the stream exits compressor 24, valve 29 can be opened to direct a portion of the stream through line 27. The stream exiting system 10 through outlet line 27 may be collected or flared.

After travelling through condenser 28, the condensed stream may exit condenser 28 via line 30 and travel towards isolation valve 14. In some embodiments, line 30 may include a valve 32, such as a check valve, located upstream from isolation valve 14. Check valve 32 may prevent backflow of the stream. Additionally, in some embodiments, the condensed stream may be recirculated through the first loop 12a via recirculation line 34. For example, the stream may travel through line 34, through a valve 35, to merge with the upstream portion 19b of feed line 18. Valve 35 may be an automatic safety valve. In some embodiments, valve 35 may be associated with a sensor.

After travelling through isolation valve 14, the stream may travel to separation vessel 38 via line 36. In an embodiment, the separation vessel 38 may be a suction drum. After entering separation vessel 38, the stream is separated to a liquid component and a vapor component. The separated liquid component including medium pressure mixed refrigerant (MPMR) is collected in the bottom of the vessel 38. The MPMR may be returned to the liquefaction system via line 40 located at or near the bottom of the vessel 38.

The separated vapor component exits the vessel 38 through line 42 and travels to compressor 46, where the stream is compressed. In an embodiment, both compressor 24 and compressor 46 may be singly driven by the same driver 25. In another embodiment, compressor 24 and compressor 46 may be driven by separate drivers. In another embodiment, the system may include a single compressor configured to accommodate both compression loops 12a and 12b.

While travelling through line 42, a portion of the stream may exit the system 10 via blowdown line 44. For example, a portion of the stream may travel through line 44 and pass through valve 45. In an embodiment, the stream exiting system 10 through blowdown line 42 may be collected or flared.

After compression, the compressed stream then travels through line 48 to enter condenser 50, where the stream is condensed and cooled. In an embodiment, condenser 50 may be a desuperheater. The cooled stream then travels through line 52 towards isolation valve 16. In some embodiments, line 52 may include a valve 53, such as a check valve, located upstream from isolation valve 16. Check valve 53 may prevent backflow of the stream.

In an embodiment, line 52 may include an outlet line 54 with valve 55. Outlet line 54 may be used to depressurize line 52. For example, valve 55 may be a pressure safety valve. Valve 55 may include a pressure sensor. In instances where the pressure sensor senses the pressure within line 52 is too high after the stream exits condenser 50, valve 55 can be opened to direct a portion of the stream through line 54. The stream exiting system 10 through outlet line 54 may be collected or flared.

Additionally, after travelling through condenser 50, the condensed stream may be recirculated through the second loop 12b via recirculation line 56. For example, the stream may travel through line 52, through line 56, and through a valve 57 to merge with line 36. Valve 57 may be an automatic safety valve.

After traveling through isolation valve 16, the stream travels through line 58 and into condenser 60. The condensed stream then travels through line 62 and into vessel 64, where it is separated into a HPMR liquid component and vapor component. The HPMR liquid component exits through the bottom of the vessel through line 66 and is returned to the liquefaction system. The HPMR vapor component exits the vessel 64 through line 68 at the top of the vessel and is returned to the liquefaction system. In an embodiment, the stream travelling through line 66 may be returned to vessel 38 via line 70. For example, the stream may travel through line 70 and valve 71 to enter vessel 38. The stream may be separated further into a liquid component and vapor component in vessel 38.

As discussed above, isolation valves 14 and 16 may separate compression loops/circuits in the cooling system 10. For example, isolation valve 14 separates the first loop 12a, including line 18, vessel 20, line 22, compressor 24, line 26, condenser 28, line 30 and line 34 from the remainder of the system 10, including second compression loop/circuit 12b. Isolation valve 16 separates second compression loop/circuit 12b, including line 36, separation vessel 38, line 42, compressor 46, line 48, condenser 50, line 52, and line 56, from the remainder of the system 10, including the components located downstream from isolation valve 16, as described.

In an embodiment, the isolation valves 14 and 16 may be spring-closed valves, which are energized to open using the pressure differential across the compressors. For example, isolation valve 14 is in communication with pressure tubing 15a and 15b. Pressure tubing 15a is connected at one end to line 22 and at another end to isolation valve 14. The pressure tubing 15a may communicate the pressure of line 22 with isolation valve 14. Pressure tubing 15b is connected at one end to line 26 and at another end to isolation valve 14 and may communicate the pressure of line 26 to the isolation valve. By communicating the pressure of the stream before and after the stream travels through the compressor 24 to the isolation valve 14, the differential pressure across the compressor may energize the valve to open. For instance, the valve is energized to open while the compressor is running (i.e., when it is safest for the valve to remain open) and the valve closes when the compressor 24 shuts down (i.e., when it is safest for the valve to be closed).

Similar to isolation valve 14, isolation valve 16 is in communication with pressure tubing 17a and 17b. Pressure tubing 17a is connected at one end to line 42 and at another end to isolation valve 16 and may communicate the pressure of line 42 to isolation valve 16. Pressure tubing 17b is connected at one end to line 48 and at another end to isolation valve 16 and may communicate the pressure of line 48 to the isolation valve 16. By communicating the pressure of the stream before and after the stream travels through the compressor 46 to the isolation valve 16, the differential pressure across compressor 46 may energize the valve to open. For instance, the valve is opened while the compressor 46 is running (i.e., when it is safest for the valve to remain open) and for the valve to close when the compressor 46 shuts down (i.e., when it is safest for the valve to be closed).

By using the differential pressure across the compressors 24 and 46 to open and close isolation valves 14 and 16, respectively, the risk of the valves failing closed when the compressor(s) is running is reduced. For example, in the event of a shutdown that requires depressuring of the separation vessel 38 via blowdown valve 45, compressors 24 and 46 will be shut down and then blowdown valve 45 will be opened. Unless, isolation valve 14 is closed, opening blowdown valve 45 will draw cold refrigerant from the liquefaction exchanger, thereby potentially embrittling the carbon steel piping, vessels, and compressor casings. Additionally, by including isolation valve 14 as described, the required flare size may be decreased. Furthermore, by using isolation valves that use the differential pressure across the compressors to open and close, the failure risk that other valve types (for instance, valves energized by instrument air with solenoid-based control of the air supply) may experience (i.e., solenoid failure, loss of instrument air, etc.) is removed. In some instances, by using the isolation valves as described herein, a “blocked outlet” case is no longer a credible scenario required in the design of pressure sensor valve 29.

There are several aspects of the present subject matter which may be embodied separately or together in the methods, devices, and systems described and claimed below. These aspects may be employed alone or in combination with other aspects of the subject matter described herein, and the description of these aspects together is not intended to preclude the use of these aspects separately or the claiming of such aspects separately or in different combinations as set forth in the claims appended hereto.

While the preferred embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made therein without departing from the spirit of the invention, the scope of which is defined by the appended claims.