Patent Application
20230160632
The present invention relates to the storage and transportation of liquefied gases. Specifically, the present invention relates to the management and the re-liquefaction and subcooling of boil off gas of different liquefied gases that are alternatively stored and/or transported in the same facility.
Liquefied gases, such as liquefied ethane or liquefied natural gas (LNG), are typically stored in atmospheric tanks at saturated conditions, when being transported by liquefied gas carriers such as a floating transportation vessel. In the tanks liquefied gas evaporates due to the unavoidably imperfect insulation of the tanks. This evaporated gas is known as boil off gas (BOG). While it is possible to use some of the BOG for powering engines of the gas carrier, normally not all BOG can be utilized in this way. Therefore, liquefied gas carriers have a BOG management system for re-liquefying the BOG, in order to avoid a pressure build-up in the tanks, or venting of BOG into the atmosphere. Such BOG management systems are known; see US 20140102133 A1, for example.
For different gases there are large differences in temperature of the liquefied gas stored at saturated conditions in atmospheric tanks. For example, the temperature level in a tank for liquefied ethane is around -90° C., whereas the temperature level in a tank for LNG is around -160° C. Known BOG management systems are generally not able to re-liquefy different gases having a huge difference in the saturation temperatures at atmospheric pressure and requiring a huge difference in the cold temperature of the refrigerant fluid used for re-liquefaction.
Currently, large gas carriers being able to transport up to 180,000 m3 are planned to be built. Surplus ethane, which is a sub-product from shale gas in the US, is transported by such carriers from North America to Europe, for example. However, it is desirable that ethane carriers, whose construction requires a huge investment, are also able to transport LNG to provide a higher degree of flexibility, especially in case of uncertain market conditions.
Therefore, an objective of the present invention is to provide a liquefaction and subcooling system that is able to efficiently work at different temperature levels, in particular the liquefaction and subcooling system should be suitable for use in a boil off gas management system for re-liquefying and subcooling boil off gas.
Provided are a liquefaction and subcooling system for liquefying and subcooling different first and second gases having different saturation temperatures at a given pressure, a boil off gas management system, and a method for liquefying and subcooling different first and second gases having different saturation temperatures at a given pressure according to the independent claims. Dependent claims and the following descriptions relate to preferred embodiments.
The liquefaction and subcooling system for liquefying different first and second gases having different saturation temperatures at a given pressure, comprises a refrigeration device operable to alternatively provide a refrigerant fluid at a first and a second cold temperature that correspond to different liquefaction temperatures of the first and second gases, a subcooling arrangement coupled to the refrigeration device such that the refrigerant fluid is supplied to the subcooling arrangement at its cold temperature, the subcooling arrangement having first and second subcoolers for exchanging heat between a gas to be liquefied and/or subcooled and the refrigerant fluid, wherein, when the gas to be liquefied and/or subcooled is the first gas, the refrigeration device is configured to provide the refrigerant fluid at the first cold temperature and the subcooling arrangement is configured to guide the refrigerant fluid and the gas to be liquefied and/or subcooled through the first subcooler; and, when the gas to be liquefied and/or subcooled is the second gas, the refrigeration device is configured to provide the refrigerant fluid at the second cold temperature and the subcooling arrangement is configured to guide the refrigerant fluid and the gas to be liquefied and/or subcooled through the second subcooler. The term ‘liquefaction temperature’ is used herein to indicate the cryogenic temperature necessary to liquefy a gas at given pressure. After liquefaction (or already after a prior compression stage) a liquid state of the gas is obtained, which may further be cooled below the liquefaction temperature, i.e. which may be subcooled. Thus, generally the process includes liquefaction and/or subcooling. For the sake of simplicity the expression “gas to be liquefied and/or subcooled” is used, with the meaning that the subcooling part of this expression relates to the (re-)liquefied gas, i.e. the part “gas to be subcooled” in the expression means that the (re-)liquefied gas (in the liquid state) is subcooled (cooled below the liquefaction temperature, cooled below the condensation temperature).
The liquefaction and subcooling system can in particular be used in a boil off gas (BOG) management system of a storage or transportation device for liquid gas at atmospheric temperature, i.e. in a BOG management system for a tank for liquid gas. While in a BOG management system the gas is ‘re-liquefied’, the terms ‘liquefied’, ‘liquefying’, and ‘liquefaction’ are used throughout this application for simplicity and since the prior state of the gas is not essential for carrying out the invention.
The liquefaction and subcooling system according to the invention advantageously allows the use of a single cold production system (refrigeration device) that is common for the liquefaction of different gases, in particular for the management of different boil off gases. Specifically, the rotating machinery is common and the refrigerant is common, and switching between the different gases can be done by a simple set of on/off valves.
According to this solution, the provision of two different subcoolers allows to liquefy different gases. The liquefaction and subcooling system may simply be switched between the two situations. This implies that a tank facility for liquid gas (e.g. on a gas carrier vessel) can be used for different gases without the need of having to provide different re-liquefaction and BOG management systems for each of the gases, only the subcooling arrangement has to be changed.
Preferably, the first subcooler is configured for heat exchange between the first gas to be liquefied and/or subcooled and the refrigerant fluid being at the first cold temperature, and the second subcooler is configured for heat exchange between the second gas to be liquefied and/or subcooled and the refrigerant fluid being at the second cold temperature. Specifically, the subcoolers are selected or designed to enable a large heat exchange at the respective temperature level for each of the gases. This allows to overcome mechanical constraints imposed on the subcoolers (heat exchangers) by the operation at different temperature levels, i.e. to overcome the problem that a heat exchanger designed to operate at a certain temperature may not be suitable to operate effectively at a different temperature. The first and second subcoolers are used alternatively. The first and the second subcoolers are essentially heat exchangers, and may be one of the following types: a shell and tube heat exchanger, a plate in shell heat exchanger, or a plate fin heat exchanger, preferably plate fin heat exchangers are used.
According to an embodiment the liquefaction and subcooling system can comprise a multi-stream heat exchanger, in which a heat exchanger of the refrigeration device is formed, and in which the first and second subcoolers are formed by separate conduits.
According to an embodiment the subcooling arrangement can include a combined subcooler formed by a heat exchanger in which the first and second subcoolers are formed by separate conduits.
According to an embodiment the first and second subcoolers can be separate heat exchangers. Preferably the two separate heat exchangers are of two different types selected from the following types: shell and tube heat exchangers, plate in shell heat exchangers, and plate fin heat exchangers.
According to an embodiment the first and/or second subcoolers can be formed by plate fin heat exchangers.
According to an embodiment the refrigerant fluid can be selected from helium, nitrogen, methane, ethane, neon, or a combination thereof. According to an embodiment the first cold temperature can be in the range of -120° C. to -85° C., preferably -115° C., and the second cold temperature can be in the range of -183° C. to -155° C., preferably -178° C. Preferably the difference between the first and second cold temperatures is at least 30° C., preferably at least 40° C., most preferably at least 50° C. Preferably the difference between the first and second cold temperatures is in the range of 30° C. - 100° C., more preferably in the range of 40° C. - 80° C., most preferably in the range of 50° C. - 70° C.
According to an embodiment the first gas can be ethane and the second gas can be natural gas. The same principles can be applied to ammonia carriers or LPC carriers.
The boil off gas management system comprises one of the preceding liquefaction and subcooling systems, wherein the liquefaction and subcooling system is arranged to re-liquefy and/or subcool boil off gas.
The method for liquefying different first and second gases having different saturation temperatures at a given pressure comprises providing a refrigeration device operable to alternatively provide a refrigerant fluid at a first and a second cold temperature that correspond to different liquefaction temperatures of the first and second gases, and, when the gas to be liquefied and/or subcooled is the first gas, operating the refrigeration device to provide the refrigerant fluid at the first cold temperature and guiding the gas to be liquefied and/or subcooled through a first subcooler for heat exchange with the refrigerant fluid, and, when the gas to be liquefied and/or subcooled is the second gas, operating the refrigeration device to provide the refrigerant fluid at the second cold temperature and guiding the gas to be liquefied and/or subcooled through a second subcooler for heat exchange with the refrigerant fluid.
It is noted that any features described above in connection with the liquefaction and subcooling system do also apply to the method according to the present invention.
The invention can be more fully understood by the subsequent description, in which reference is made to the accompanying drawings, wherein:
In
In the refrigeration device a working circuit 12 of the refrigerant fluid is formed. The working circuit 12 comprises a compression section, an expansion section and a heat exchanger section. The compression section is formed by three compressors 14, 16, 18 which are driven by motors 20, 22, 24 over driving shafts, for example. More generally any number of compressors may be used, i.e. the compression section may generally comprise any number of compression stages. The compressors 14, 16, 18 may be of the centrifugal compression type. After each of the compressors 14, 16, 18 coolers 26, 28, 30 are included in the working circuit 12 for cooling the refrigerant fluid after each compression stage to ambient temperatures. The coolers 26, 28, 30 are supplied with a cooling fluid over conduits as indicated by arrows 32, 34, 36. Air, water or, on a maritime vessel, sea water may be used as cooling fluid, for example.
The expansion section is formed by an expansion turbine 38, which may be of the centripetal expansion type. More generally it is possible that the expansion section is formed by more than one expansion turbine. The expansion turbine 38 is driven by a motor 24, which in the embodiment shown in
The heat exchanger section of the refrigeration device 10 is formed by a heat exchanger 42, in which heat is exchanged between the compressed refrigerant fluid downstream the compression section and upstream the expansion section and the expanded refrigerant fluid downstream of the expansion section and upstream the compression section. In this way the compressed refrigerant fluid that is cooled by cooler 30 to be essentially at ambient temperature is cooled down to a low (cryogenic) temperature by exchanging heat with the refrigerant fluid that downstream the expansion section (expansion turbine 38) is at its lowest temperature before being guided through the heat exchanger 42. To facilitate understanding of the different embodiments, an oval line is drawn around the conduits between which heat is exchanged and a reference sign is attached to the line to indicate the corresponding heat exchanger. This is the case for the heat exchanger 42 of the refrigeration device as well as for the first and second subcoolers 70, 72 introduced below.
It should be noted that the specific structure of the refrigeration device 10 is not essential for implementing the invention. Key point is that the refrigeration device can be operated such that the refrigerant fluid may be provided at different cold temperatures. In the exemplary embodiment shown in
Additionally, a by-pass valve 44 may be provided that allows the refrigerant fluid to by-pass the heat exchanger 42 via a conduit.
In the subcooling arrangement 50 a flow of the gas to be liquefied and/or subcooled is provided at an inlet 52, passed through the subcooling arrangement for cooling, and leaving the subcooling arrangement at an outlet 54 preferably in a fluid state. The subcooling arrangement 50 has two different flow paths for the gas to be liquefied and/or subcooled, a first flow path 56 and a second flow path 58. The flow path taken by the gas to be liquefied and/or subcooled can be chosen by switching valves accordingly. Specifically, the gas to be liquefied and/or subcooled flows through the first flow path 56, when valves 60, 62 are open and valves 64 and 66 are closed. The gas to be liquefied and/or subcooled flows through the second flow path 58, when valves 64, 66 are open and valves 60, 62 are closed.
The gas to be liquefied and/or subcooled will typically be provided in compressed form and may at least partially be in a liquid state. In particular the BOG will normally be guided through a compression stage before being fed to the inlet 52 by a BOG management system.
In the first flow path 56 a first subcooler 70 is provided and in the second flow path 58 a second subcooler 72 is provided. The first subcooler 70 is configured to efficiently exchange heat between the first gas to be liquefied and/or subcooled and the refrigerant fluid being at the first cold temperature. The second subcooler 70 is configured to efficiently exchange heat between the second gas to be liquefied and/or subcooled and the refrigerant fluid being at the second cold temperature. The first and the second subcoolers 70, 72 are heat exchangers, preferably plate fin heat exchangers.
Specific to the embodiment shown in
When the gas to be liquefied and/or subcooled is the first gas, the refrigerant fluid is provided at the first cold temperature and the gas is guided through the first flow path 56, which includes the conduits in the multi-stream heat exchanger 100 that form the first subcooler 70. When the gas to be liquefied and/or subcooled is the second gas, the refrigerant fluid is provided at the second cold temperature and the gas is guided through the second flow path 58, which includes the conduits in the multi-stream heat exchanger 100 that form the second subcooler 72. In both cases a valve 108 should be open, wherein this valve 108 controls the flow of the refrigerant fluid to the conduit 104 which is guided through the first and second subcooler 72.
Additionally, a by-pass valve 68 may be provided that allows to directly connect the inlet 52 with the outlet 54, which, for example, is helpful when performing maintenance of the multi-stream heat exchanger 100.
Obviously, further structures or elements may be included in the working circuit 12 and/or the first and second flow paths 56, 58, such as a surge valve, flow meters, pressure sensors and the like.
The difference between the embodiments of
The heat exchanger 42 of the refrigeration device is formed by a regular counter current heat exchanger 200. The first and second subcoolers 70, 72 of the subcooling arrangement 50 are formed as a combined subcooler (combined heat exchanger) 202. The combined subcooler 202 is basically a heat exchanger which combines heat exchangers that constitute the first and second subcoolers 70, 72. The combined subcooler 202 is separate from the counter current heat exchanger 200, i.e. the combined subcooler 202 is dedicated for subcooling. Several valves 204, 206, 208 are arranged in the working circuit 12 for controlling the flow of the refrigerant fluid to and from the combined subcooler 202 and the counter current heat exchanger 200.
The combined subcooler 202 is provided in the working circuit 12 between the expansion and heat exchanger sections of the refrigeration device 10, i.e. downstream of the expansion turbine 38 and upstream of the counter current heat exchanger 200. The refrigerant fluid is guided from the outlet conduit 40 of the expansion section through valve 204 into a single inlet 210 for refrigerant fluid of the combined subcooler 202. The first and second subcoolers 70, 72 are formed by means of two separate conduits in the combined subcooler 202. These two separate conduits are arranged to exchange heat with the refrigerant fluid which is guided through the combined subcooler 202 by another conduit. The two separate conduits form part of the first and second flow paths 56, 58, respectively.
When the gas to be liquefied and/or subcooled is the first gas, the refrigerant fluid is provided at the first cold temperature and the gas to be liquefied and/or subcooled is guided through the first flow path 56, which includes the conduits in combined subcooler 202 that form the first subcooler 70. When the gas to be liquefied and/or subcooled is the second gas, the refrigerant fluid is provided at the second cold temperature and the gas to be liquefied and/or subcooled is guided through the second flow path 58, which includes the conduits in the combined subcooler 202 that form the second subcooler 72. In both cases a valve 204 should be open, wherein this valve 204 controls the flow of the refrigerant fluid to the inlet 210 for refrigerant fluid of the combined subcooler 202.
The difference between the embodiments of
The heat exchanger 42 of the refrigeration device is formed by regular counter current heat exchanger 300. The first and second subcoolers 70, 72 of the subcooling arrangement are formed as two separate subcoolers (heat exchangers) that are also separate from the counter current heat exchanger 300. That is, the first subcooler 70 is formed by first heat exchanger 302 and the second subcooler 72 is formed by a second heat exchanger 304, the second heat exchanger 304 is separate from the first heat exchanger 302. Several valves 306, 308, 310, 312, 314 are arranged in the working circuit 12 for controlling the flow of the refrigerant fluid to and from first and second heat exchangers 302, 304 and the counter current heat exchanger 300.
The first and second heat exchangers 302, 304 are provided in parallel in the working circuit 12 between the expansion and heat exchanger sections of the refrigeration device 10, i.e. downstream the expansion turbine 38 and upstream the counter current heat exchanger 300. A valve 306 controls the flow of refrigerant fluid to the first heat exchanger 302 and another valve 308 controls the flow of refrigerant fluid to the second heat exchanger 304.
When the gas to be liquefied and/or subcooled is the first gas, the refrigerant fluid is provided at the first cold temperature and the gas to be liquefied and/or subcooled is guided through the first flow path 56, which includes the first heat exchanger 302 that forms the first subcooler 70. When the gas to be liquefied and/or subcooled is the second gas, the refrigerant fluid is provided at the second cold temperature and the gas to be liquefied and/or subcooled is guided through the second flow path 58, which includes the second heat exchanger 304 that forms the second subcooler 72. In the first case (first gas to be liquefied and/or subcooled), the valve 306 controlling the flow of refrigerant fluid to the first heat exchanger 302 is open while the valve 308 controlling the flow of refrigerant fluid to the second heat exchanger 304 is closed, and vice versa for the second case (second gas to be liquefied and/or subcooled).
While the invention has been described in terms of embodiments and examples in the preceding specification, the scope of the present invention is restricted by the appended claims not by specific embodiments of the specification. It should be noted that elements of the different embodiments may be combined even if not explicitly stated.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20315135.2 | Apr 2020 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/025117 | 3/29/2021 | WO |
