KR102379711B1 - Method of cooling boil off gas and an apparatus therefor - Google Patents

Abstract

A method for cooling a boil off gas stream from a liquefied ethane cargo on a floating transport vessel, the method comprising at least:
compressing the boil off gas stream from the liquefied ethane cargo in two or more stages of compression comprising at least a first stage and a final stage to provide a compressed BOG effluent stream, the first compression the stage has a first stage discharge pressure, the final compression stage has a final stage suction pressure and one or more intermediate, optionally cooled, compressed BOG streams are provided between successive stages of compression;
cooling the compressed BOG effluent stream with respect to the one or more first coolant streams to provide a cooled compressed first BOG stream;
cooling the cooled compressed first BOG stream with respect to the at least one second coolant stream to provide a cooled compressed second BOG stream;
cooling the cooled compressed second BOG stream relative to the third coolant stream to provide a cooled compressed third BOG stream;
expanding a portion of the cooled compressed third BOG stream to a pressure between the first stage outlet pressure and the final stage inlet pressure to provide an expanded cooled first BOG stream;
using the expanded and cooled first BOG stream as a third coolant stream to provide an expanded and heated first BOG stream; and
using the expanded and heated first BOG stream as a second coolant stream.

Description

Boil-off gas cooling method and device therefor

FIELD OF THE INVENTION The present invention relates to a method and apparatus for cooling, in particular reliquefaction, of boil off gas (BOG) from liquefied ethane cargo on a floating transportation vessel and apparatus therefor.

Liquefied gas carriers and barges and floating transport vessels are capable of transporting a variety of cargoes in a liquefied state. In the present context, liquefied cargo is wholly or substantially ethane, generally >90% ethane, or >95%, or >96%, or >97% or >98% or >99% ethane. Ethane is a useful product source for a variety of industrial processes.

Ethane may be extracted from natural gas production, fracking, or may be produced from crude oil refining. As a result, ethane may be associated with a plurality of other components, particularly methane. It is often desirable to liquefy ethane in a liquefaction plant at or near a source of ethane, as ethane is more readily stored and stored over long distances (generally beyond normal pipeline distances) in gaseous form than in liquid. Because it can be transported, ethane occupies a smaller volume and may not need to be stored at high pressure as it does not need to be stored at high pressure.

Long-distance transport of liquefied ethane cargoes, which have a boiling point of about -87° C. when measured at 1 atmosphere, is carried out by ocean-going cargoes having one or more storage tanks for holding the liquefied ethane cargo. tanker) in a suitable liquefied gas carrier. These storage tanks may be insulated and/or pressurized tanks. During the loading of tanks and storage of liquefied ethane cargoes, gases may be generated due to evaporation of the cargoes. This vaporized cargo gas is known as boil off gas (BOG). In order to prevent the build-up of BOG in the tank (resulting in pressure build-up problems), a system may be provided on the carrier that can reliquefy the BOG and return it to the storage tank in a condensed state. This can be achieved by compression and cooling of the BOG against a cold source. Since ethane has a critical temperature of 32.18 °C at a pressure of 47.7 barg, seawater at a similar temperature would not be suitable as a primary cold source. In many systems, the compressed BOG is cooled and condensed against a secondary refrigerant.

Methods and apparatus are known for reliquefying BOG, where conventional liquefied cargoes can be defined as 'pure'. However, liquefied ethane transported as cargo on a floating transport vessel may contain concentrations of other components above a de minimus level and may gradually increase. This may be due, at least in part, to the increasing sourcing of 'impure' ethane from new sources or new industrial processes.

One of the other possible components is propane. However, since propane has a boiling point of about -40°C when measured at 1 atmosphere, the method and apparatus needed to reliquefy ethane/propane BOG will achieve essentially reliquefaction of any propane portion of the BOG.

One other possible component is nitrogen. It is generally not practical to attempt to reliquefy any nitrogen in BOG on floating transport vessels, as its boiling point is about -196° C. as measured at 1 atmosphere. Thus, nitrogen is generally considered to be at least a major component of these parts of BOG, which are defined as "in-condensable", ie it can never (substantially) condense on floating transport vessels. However, nitrogen is a relatively 'safe' gas.

Another major possible component considered in liquefied ethane cargoes is methane. Methane has a boiling point of about -162 °C to -163 °C when measured at 1 atmosphere. This boiling point is significantly lower than the boiling point of ethane, measured at 1 atmosphere. As such, methane has heretofore been regarded as a "non-condensable" component of typically liquefied cargoes, i.e. may be condensable (i.e. reliquefied), but with reasonable CAPEX and/or CAPEX for floating transport vessels. Or particularly special methods that may not be OPEX are required. Thus, since conventional LPG BOG reliquefaction methods and apparatus are not capable of reliquefying methane, relatively small amounts of methane in liquefied cargoes such as wholly or substantially propane (i.e. LPG) or the like have hitherto been: It was vented to the atmosphere.

However, methane is considered one of the 'greenhouse gases', which is increasingly preferably not vented to the atmosphere.

Also, as liquefied ethane is expected to have an increased amount of methane concentration in cargo, it is now expected that more and more types of ethane will be transported as liquefied ethane.

Moreover, it is a particular disadvantage of methane that even a small concentration of methane in the liquefied cargo makes the amount of methane in the BOG unequal. For example, at a concentration of only 0.5 mol % in the liquid phase, BOG of liquefied ethane cargo can induce 25 mol % methane.

Accordingly, it may not be possible to reliquefy all of the components of boil off gas from liquefied ethane cargoes, particularly liquefied ethane cargoes including lighter components such as methane present in concentrations exceeding 0.1 mole %. These non-condensable components may be returned to vapor phase liquefied ethane cargo storage tanks, but will accumulate boil off gas in a closed system and thereby increase in concentration over time. Moreover, as the concentration of the non-condensable components of the boil off gas increases, the volume of the boil off gas that cannot be recondensed will increase, thereby reducing the effective capacity of the reliquefaction system.

As noted above, other alternatives to ventilation of non-condensable components such as methane, which may be a greenhouse gas, are environmentally and commercially undesirable.

WO2012/143699A relates to a method and apparatus for reliquefying BOG from a liquefied cargo of a floating transport vessel, wherein the liquefied cargo has a boiling point greater than -110° C. at 1 atmosphere and may contain non-condensable BOG components The cooled vent stream is compressed, cooled and then heat exchanged with a portion of the expanded BOG stream. It is particularly suitable for liquefied cargoes with boiling points greater than -110° C. when measured at 1 atmosphere, but with an improved cooling method, in particular boil off gas from liquefied ethane cargo under reasonable OPEX and CAPEX - in particular such cargo They need to provide a way to reliquefy as much as possible – including increasing rates of lighter components such as methane.

The present invention addresses these problems by the use of a triple cooled and compressed BOG stream. In this way, the triple cooling stream will condense previously uncondensed components, and may be reliquefied and subsequently returned to the liquid liquefied ethane cargo tank. The triple cooled and compressed BOG stream provides a source of increased cooling duty compared to a heat exchange medium such as seawater, allowing reliquefaction of lighter components in the BOG stream.

Thus, for a given number of compression stages, the method and apparatus disclosed herein provide increased content of lighter components, such as methane, without the need to add additional compression stages or increase the aeration of previously contemplated non-condensable components. Allows transport of liquefied ethane cargoes with In other words, the method and apparatus described herein allow for expanding a compression system having a given number of compression stages into cargoes having components that typically cannot be reliquefied or condensed.

In a first aspect, the present invention provides a method for cooling a boil off gas stream from a liquefied ethane cargo on a floating transport vessel, the method comprising at least the following steps:

compressing the boil off gas stream from the liquefied ethane cargo in two or more stages of compression including at least a first stage and a final stage to provide a compressed BOG effluent stream, the first compression the stage has a first stage discharge pressure, the final compression stage has a final stage suction pressure and one or more intermediate, optionally cooled, compressed BOG streams are provided between successive stages of compression;

cooling the compressed BOG effluent stream with respect to the one or more first coolant streams to provide a cooled compressed first BOG stream;

cooling the cooled compressed first BOG stream with respect to the at least one second coolant stream to provide a cooled compressed second BOG stream;

cooling the cooled compressed second BOG stream relative to the third coolant stream to provide a cooled compressed third BOG stream;

expanding a portion of the cooled compressed third BOG stream to a pressure between the first stage outlet pressure and the final stage inlet pressure to provide an expanded cooled first BOG stream;

using the expanded and cooled first BOG stream as a third coolant stream to provide an expanded and heated first BOG stream; and

using the expanded and heated first BOG stream as the second coolant stream or a second coolant stream.

That is, the expanded and cooled first BOG stream is used as a third coolant stream in a heat exchanger/exchanger with respect to the cooled and compressed second BOG stream, wherein the heat exchanger/exchanger is indirectly, more preferably, directly to provide a cooled and compressed third BOG stream and an expanded and heated first BOG stream as a heated third coolant stream that can be used as a primary or secondary second coolant stream.

That is, the expanded and heated first BOG stream is used as a primary or secondary second coolant stream in a heat exchanger/exchanger with respect to the cooled and compressed first BOG stream, wherein the heat exchanger/exchanger A second cooled compressed BOG stream and a first expanded additional heated BOG stream are provided as coolant streams.

As used herein, terms such as “first,” “second,” “third,” “fourth,” etc., except where explicitly stated otherwise, refer to concatenation or It is intended to indicate a relationship. That is, there may be one or more other steps or processes or locations between the “second” feature and the “third” feature. These terms are used to clarify the different nature or existence of an associated feature in or in a stream, and the invention is not limited by these terms.

For the avoidance of doubt, the second coolant stream (ie, the expanded and heated first BOG stream) is at a lower temperature than the cooled, compressed first BOG stream; the third coolant stream (ie, the expanded and cooled first BOG stream) is at a lower temperature than the cooled, compressed second BOG stream; and the third coolant stream is at a lower temperature than the second coolant stream.

According to another embodiment, the method comprises:

combining the expanded heated first BOG stream as a heated second coolant stream with an intermediate compressed BOG stream, such as the first or second intermediate compressed BOG stream, preferably the first intermediate compressed BOG stream. include

According to another embodiment of the present invention, cooling the compressed BOG effluent stream with respect to one or more first coolant streams to provide a cooled compressed first BOG stream;

cooling the compressed BOG effluent stream relative to the first refrigerant stream as the first refrigerant stream to provide a cooled compressed first BOG stream.

That is, the first refrigerant stream is used as one of the one or more first refrigerant streams in a heat exchanger/exchanger with respect to the compressed BOG effluent stream, wherein the heat exchanger/exchanger is heated as a heated first refrigerant stream. provided a first refrigerant stream and a cooled, compressed first BOG stream.

According to another embodiment of the present invention, cooling the compressed BOG effluent stream with respect to one or more first coolant streams to provide a cooled compressed first BOG stream;

precooling the compressed BOG effluent stream with respect to the precooled coolant stream as a first coolant stream to provide a precooled compressed BOG stream;

cooling the precooled compressed BOG stream relative to the first refrigerant stream as the first refrigerant stream to provide a cooled compressed first BOG stream.

That is, the pre-cooled coolant stream is used as one of the one or more first coolant streams in a heat exchanger/exchanger with respect to the compressed BOG effluent stream, wherein the heat exchanger/exchanger is heated as a heated first coolant stream. A precooled coolant stream and a precooled compressed BOG stream are provided.

That is, the first refrigerant stream is used as one of the one or more first coolant streams in a heat exchanger/exchanger for the precooled and compressed BOG stream, wherein the heat exchanger/exchanger is a heated first coolant stream. to provide a heated first refrigerant stream and a cooled compressed first BOG stream.

According to another embodiment of the present invention, the pre-cooled coolant flow may be part of an open pre-cooled coolant system or a closed pre-cooled coolant system. The pre-cooled coolant stream may be selected from a water stream, an air stream or a pre-cooled refrigerant stream, preferably a water or air stream. Typically, if an open pre-cooled coolant circuit is used, the pre-cooled coolant stream may be selected from a seawater stream and an ambient air stream. Typically, if a closed pre-cooled coolant circuit is used, the pre-cooled coolant stream may be selected from the pre-cooled refrigerant stream.

According to another embodiment of the present invention, cooling of the effluent stream precooled and compressed with respect to the precooled coolant stream is performed in a precooled heat exchanger such as a shell and tube heat exchanger or a plate heat exchanger.

According to another embodiment of the present invention, the one or more first coolant streams comprise a first refrigerant stream, such as a first refrigerant comprising a single refrigerant or a mixture of refrigerants. The first refrigerant must be capable of condensing ethane at (i) at the discharge pressure of the compression system and at the discharge temperature of the compression system or (ii) at the discharge pressure of the compression system and at the temperature of the pre-cooled and compressed BOG stream. The first refrigerant comprises one or more organic compounds comprising a fluorinated hydrocarbon mixture R-410A, ammonia, and in particular hydrocarbons and fluorinated hydrocarbons such as propane, propylene, difluoromethane and pentafluoromethane can do.

According to another embodiment of the present invention, cooling of the compressed BOG effluent stream or precooled and compressed effluent stream with respect to the first refrigerant stream is performed in an exhaust heat exchanger such as a shell and tube heat exchanger, a plate heat exchanger or an economizer. .

According to another embodiment of the present invention, all compressed BOG effluent streams are cooled with respect to one or more primary coolant streams.

In one embodiment of the invention, the liquefied ethane cargo comprises >0.1 mole % methane. In practice, a liquefied ethane cargo may contain >0.4 mol % methane, including >0.5 mol %, 0.6 mol %, > 0.7 mol %, > 0.8 mol %, >0.9 mol % and >1.0 mol % methane. there is. The present invention extends to a liquefied ethane cargo having from 1 to 5 mole % methane, optionally >5 mole % methane.

The number of compression stages is not a limiting factor of the present invention. Optionally, the method comprises three or four stages of compression.

Optionally, although it is desirable to provide fully condensed boil off gas as a cooled, compressed first BOG stream, the present invention provides for fully condensed boil off gas after the boil off gas has been cooled with respect to one or more first coolant streams. expanded in a way that is not possible.

The present invention overcomes the difficulties of using certain types of heat exchange, in particular certain types of heat exchanger, and more specifically, conventional shell and coil economizers where temperature access is limited by the composition of the fluid within the shell. . If the composition of the fluid in the shell can be a single component, ie a sufficiently 'pure' gas, its cooling for the expanded portion of compressed BOG is well known and widespread. However, this cooling duty is reduced in multi-component mixtures, and especially in multi-component mixtures with significant differences in boiling points such as ethane and methane. Thus, the present invention improves the coefficient of performance of the cooling cycle of liquefied ethane cargoes containing significant amounts of methane, i.e., the present invention provides cargoes that are currently considered de minimus (e.g., 0.1 mol % or less methane), and permit operation with cargoes containing cargoes with much higher methane contents (eg, greater than about 0.4 or 0.4 or 0.5 mole % methane).

The present invention also seeks to maintain the use of current onboard equipment and devices with known OPEX and CAPEX, rather than introducing and researching methods of using new equipment with new operating requirements.

Accordingly, in accordance with another embodiment of the present invention, cooling of the cooled and compressed first BOG stream with respect to the second coolant stream is performed in the economizer.

According to another embodiment of the present invention, both the cooled and compressed first BOG stream is cooled with respect to the second coolant stream.

According to another embodiment of the present invention, both the cooled and compressed second BOG stream is cooled with respect to the third coolant stream.

In another embodiment of the present invention, the method comprises:

providing a gas vent stream from the cooled compressed first BOG stream;

expanding a portion of the cooled compressed third BOG stream to form a fourth coolant stream;

cooling the gaseous vent stream relative to the fourth coolant stream to provide a cooled vent stream and a heated fourth coolant stream.

In this way, the present invention may further provide for increased reliquefaction of previously considered 'non-condensables' or 'non-condensable' components in the compressed BOG.

Preferably, the heated fourth coolant stream is used as the BOG recycle stream or can be used as the BOG recycle stream. Therefore, the method is

The method may further comprise combining the heated fourth coolant stream with an intermediate compressed BOG stream, such as the first or second, preferably intermediate compressed first BOG stream.

Optionally, the method of the present invention comprises:

and separating the cooled vent stream to provide a vent vent stream and a cooled vent BOG return stream.

Optionally, the method of the present invention comprises:

expanding the cooled aerated BOG return stream to provide an expanded cooled aerated BOG return stream;

and passing the expanded cooled vent BOG return stream to a storage tank.

Optionally, the method of the present invention comprises:

expanding the cooled aerated BOG return stream to provide an expanded cooled aerated BOG return stream;

heat exchanging the expanded cooled vent BOG return stream with respect to the vent vent stream to provide a heat exchanged vent BOG return stream, a cooled vent vent stream, and an additional vent vent stream;

expanding the cooled vent vent stream to provide an expanded cooled vent vent stream;

and passing the heat exchanged vent BOG return stream and the expanded cooled vent vent stream to a storage tank.

Optionally, the compression stages are compression stages of a multi-stage compressor.

cooling the cooled compressed first BOG stream with respect to the at least one second coolant stream to provide a cooled compressed second BOG stream; Optionally, the cooled and compressed first BOG stream is cooled entirely or substantially relative to a second coolant stream comprising only the expanded and heated first BOG stream. Preferably, both of the second coolant streams comprise the expanded and heated first BOG stream. That is, the cooled and compressed first BOG stream may be cooled relative to one or more other second coolant streams, but these are secondary compared to the cooling provided by use of the expanded and heated first BOG stream. or minor.

Optionally, the expanded heated first BOG stream used as the second coolant stream comprises both liquid and gaseous phases. That is, there is no need to separate into separate gaseous and liquid phases prior to use as the second coolant stream.

Preferably, the liquid phase and gas phase of the first expanded and heated BOG stream used as the second coolant stream are separated during cooling of the cooled, compressed first BOG stream. This is preferably an apparatus, preferably an economizer, which allows the cooled and compressed first BOG stream to be cooled.

According to a second aspect of the present invention, there is provided an apparatus for cooling a boil off gas stream from a liquefied ethane cargo of a floating transport vessel comprising a plurality of components, the apparatus comprising at least:

A compression system for compressing a boil off gas stream from a liquefied ethane cargo, the compression system comprising two or more compression stages comprising at least a first stage and a final stage to provide a compressed BOG discharge stream; , intermediate, optionally cooled, compressed BOG streams provided between successive compression stages;

one or more first heat exchangers for cooling the compressed BOG effluent stream to provide a cooled compressed first BOG stream;

one or more second further cooling the cooled compressed first BOG stream relative to the mixed bed coolant stream to be separated in the one or more second heat exchangers to provide a cooled compressed second BOG stream heat exchangers;

one or more third heat exchangers for further cooling the cooled compressed second BOG stream to provide a cooled compressed third BOG stream.

Optionally, the device as defined herein is operable using the method as defined herein.

Preferably, the second heat exchanger is an economizer.

According to a further aspect of the present invention there is provided a floating transport vessel for liquefied ethane cargo having an apparatus as defined herein or operating a method as defined herein.

The present invention is applicable to any floating transport vessel for liquefied ethane cargo. The present invention relates to cargo in storage tanks as well as in floating transport vessels that maintain liquid phase in cargo at generally atmospheric pressure by reducing the temperature by completely refrigeration of liquefied ethane cargo storage tanks at reduced temperature and increased pressure versus atmosphere. It can be utilized on these ships which are kept in liquid phase by combination.

To obtain the advantages of the method and apparatus disclosed herein, the use of economizers is not required. However, in certain embodiments, heat exchangers such as economizers may be placed between successive compression stages, such as between a first stage and a second stage, to cool the intermediate compressed BOG streams. When three or more compression stages are present, heat exchangers such as economizers or intercoolers such as seawater intercoolers that allow cooling of intermediate compressed BOG streams may be provided between the second and final stages of compression. can

For example, an intercooler may be positioned between the second compression stage and the third compression stage. Alternatively, the economizer may be positioned between the first and second stages as well as the second and third compression stages. In the economizer, the expanded, optionally further cooled portion of the cooled compressed BOG stream may be heat exchanged with an intermediate compressed BOG stream. In a further embodiment, the expanded and optionally further cooled portion of the cooled compressed BOG stream may be heat exchanged with an optionally further cooled portion of the cooled compressed effluent stream. This leads to further improvements in the coefficient of performance and increased cooling, in particular reliquefaction capacity.

The method and apparatus disclosed herein maintains the current number of compression stages and adds the necessary piping, valves and controllers to perform cooling of the cooled, compressed second BOG stream relative to the expanded portion of the cooled third BOG stream. It will be apparent that by doing so, it can be applied to a reference floating transport vessel as a retro-fit.

As used herein, the term “multiple stages of compression” defines two or more compression stages in series in a compression system. Each compression stage may be accomplished by one or more compressors. One or more compressors of each compression stage may be independent of the compressors of the other compression stages, such that they are driven separately. Alternatively, two or more stages of compression stages may utilize compressors that are linked, typically powered, by a single driver and drive shaft with optional gearing. These linked compression stages may be part of a multi-stage compressor.

The method and apparatus disclosed herein require at least two compression stages. After the first compression stage, each successive stage provides an increased pressure relative to the pressure at evacuation of the previous stage. The term “continuous stages” refers to pairs of adjacent compression stages, ie, stage (n) and the next (n+1) stage, where n is a whole number greater than zero. Consequently, successive stages are, for example, a first stage and a second stage or a second stage and a third stage or a third stage and a fourth stage. Intermediate compressed streams (and cooled intermediate compressed streams) refer to those streams connecting successive compression stages. The term "next compression stage" or "subsequent compression stage" as used in reference to a cooled intermediate compressed stream means that the higher number of the two successive stages defining the intermediate stream (and the higher pressure stage) ) means

The heat exchange steps may be indirect, wherein the two or more streams involved in the heat exchange are not in direct contact in isolation. Alternatively, the heat exchange may be direct, in which case two or more streams involved in the heat exchange may be mixed to thereby produce a combined stream.

According to another aspect of the present invention, there is provided a method for integrally designing an apparatus for cooling a boil off gas stream from a liquefied ethane cargo of a floating transport vessel comprising a plurality of components, the method comprising:

selecting a compression system for compressing the boil off gas stream from the liquefied ethane cargo, wherein the compression system comprises two or more compression systems comprising at least a first stage and a final stage to provide a compressed BOG discharge stream. stages, wherein intermediate, optionally cooled, compressed BOG streams are provided between successive compression stages;

selecting one or more first heat exchangers for cooling the compressed BOG effluent stream to provide a cooled compressed first BOG stream;

one or more second further cooling the cooled compressed first BOG stream relative to the mixed bed coolant stream to be separated in the one or more second heat exchangers to provide a cooled compressed second BOG stream selecting heat exchangers;

further cooling the cooled compressed second BOG stream to select one or more third heat exchangers to provide a cooled compressed third BOG stream.

Optionally, this method

running a process simulation on the device;

determining the effectiveness of the method;

changing a process variable in the process simulation; and

The method further includes repeating the process simulation.

According to a further aspect of the present invention, there is provided a method of designing a process for cooling a boil off gas stream from a liquefied ethane cargo of a floating transport vessel, said method comprising at least the following steps:

A compression system for compressing a boil off gas stream from a liquefied ethane cargo, the compression system comprising two or more compression stages comprising at least a first stage and a final stage to provide a compressed BOG discharge stream; , intermediate, optionally cooled, compressed BOG streams provided between successive compression stages;

one or more first heat exchangers for cooling the compressed BOG effluent stream to provide a cooled compressed first BOG stream;

one or more second further cooling the cooled compressed first BOG stream relative to the mixed bed coolant stream to be separated in the one or more second heat exchangers to provide a cooled compressed second BOG stream heat exchangers;

one or more third heat exchangers for further cooling the cooled compressed second BOG stream to provide a cooled compressed third BOG stream.

Optionally, this method

running a process simulation for the process;

determining the effectiveness of the method;

changing a process variable in the process simulation; and

The method further includes repeating the process simulation.

Design methods as discussed herein can be incorporated into computer aided processes for including the associated operating equipment and controls into the overall ship structure, and can incorporate the associated cost, capacity, and associated cost of operating parameters into the method and design. there is. The methods described herein may be encoded on a medium suitable for reading and processing on a computer. For example, code for performing the methods described herein may be encoded on a magnetic or optical medium that can be copied and read by a personal or mainframe computer. The methods can then be executed by a design engineer using a personal or mainframe computer.

Certain features of the invention and its design method may be described in terms of a set of numerical upper bounds and a set of numerical lower bounds. It should be understood that any ranges formed by any combination of these limits are contemplated as being within the scope of the invention. It is also contemplated that the overall design includes the selection of additional structures for use with the combinations specifically defined herein. The various structures operating parameters may be selected for limited or fixed criteria or may be selected for flexible or multiple operating applications within a vessel. Accordingly, the method of design is intended to cover alternatives, modifications and equivalents to the overall design of the ship and any off-board that fall within the spirit and scope of the present invention.

Embodiments of the present invention will now be described with reference to the accompanying drawings, which are by way of example only and non-limiting.

1 shows a schematic diagram of one known possible system for reliquefying boil off gas from a cargo tank in a carrier vessel.
2 shows a schematic diagram of a system for cooling boil off gas from a liquefied ethane cargo of a floating transport vessel, in particular a reliquefaction system, according to an embodiment of the present invention;
3a and 3b are economizer temperature profiles of temperature versus heat flow for a pure component BOG cooling system 3a and a broad boiling multicomponent mixture cooling system 3b.
4 shows a schematic diagram of a system for cooling boil off gas from a liquefied ethane cargo of a floating transport vessel, in particular a reliquefaction system, according to an embodiment of the present invention;

Floating reliquefaction systems draw vapor - also known as boil off gas - from one or more storage tanks and pass the boil off gas to a compressor, where the compressed vapor is used in the one or more coolants. can be cooled and condensed as a heat sink/refrigerant for For example, seawater may be used to precool, typically de-superheat, the compressed vapor in an open cycle pre-cooling circuit. The pre-cooled compressed vapor can then be further cooled relative to the refrigerant in a closed cycle refrigerant circuit.

These lighter components of compressed vapor that cannot be condensed with respect to the refrigerant are usually vented to the atmosphere or recycled to storage tanks in vapor form. Typically, liquefied cargoes are stored in storage tanks under one or both of reduced temperature (at atmospheric pressure) and increased pressure (atmospheric pressure).

1 shows a schematic diagram of a known system for reliquefying boil off gas from an ethane cargo. Currently, ethane cargo tends to be transported in repurposed ethylene carrier vessels. The liquefied ethane cargo is stored in a tank 50a that may be insulated and/or pressurized to keep the ethane in a liquefied state. For example, evaporation of ethane in the tank due to poor thermal insulation will result in the formation of ethane gas in the overhead space of tank 50a, which gas is commonly boil off gas (BOG). ) is called To prevent this gas build-up, the gas is removed from tank 50a as boil off gas stream 01a. All components are compressed and condensed before as many components as possible of the removed boil off gas are normally cooled and returned to tank 50a.

The boil off gas stream 01a may be passed to a compression system 60 , such as the two stage compressor shown in FIG. 1 comprising a first compression stage 65 and a second compression stage 75 . The two stage compression system 60 produces a compressed BOG discharge stream 06a, which can be passed to a pre-cooled heat exchanger 100, where the compressed BOG discharge stream 06a is a seawater stream. It is cooled with respect to (102). The precooled heat exchanger 100 produces a precooled compressed BOG stream 07a and a warmed seawater stream 104 . The pre-cooled heat exchanger 100 may de-superheat the compressed BOG effluent stream 06a.

The precooled and compressed BOG stream 07a may be passed to a refrigerant heat exchanger 250 , in which the precooled and compressed BOG stream 07a is cooled against a refrigerant stream 252 . The refrigerant must be capable of condensing the ethane at the discharge pressure of the compression system 60 . The refrigerant may be propane or propylene. Refrigerant stream 252 may be part of a refrigerant circuit (not shown) comprising refrigerant heat exchanger 250 , refrigerant compressor and refrigerant cooler. The refrigerant circuit may be a closed refrigerant system. Such refrigerant circuits, also called refrigerant packs, are well known.

Refrigerant heat exchanger 250 produces a cooled compressed BOG stream 08a and a heated refrigerant stream 254 . The cooled and compressed BOG stream 08a is an at least partially condensed stream comprising these components of the boil off gas possible at the outlet pressure of the second compression stage 75 of 'reliquefaction' to the refrigerant, ie condensation. .

'non-condensed', which is not reliquefiable for the refrigerant in this system and may contain both non-condensable and 'in-condensable' components as discussed herein Components may be removed from refrigerant heat exchanger 250 or an associated accumulator (not shown) located downstream of refrigerant heat exchanger 250 as vent stream 49 , which is a vapor stream. Vent stream 49 is typically expanded to atmospheric pressure and then vented to atmosphere.

The cooled compressed BOG stream 08a may be passed to a further heat exchanger 80 to provide a cooled return fluid stream 18, which is typically a fully condensed stream.

The cooled return fluid stream 18 may then be passed to a return pressure reducing device 22 such as an expander or Joule-Thomson valve to provide an expanded cooled return fluid stream 24 . . Typically, return depressurization device 22 converts the pressure of cooled return fluid stream 18 from or near the pressure of compressed BOG discharge stream 06a to a pressure close to the pressure of liquid ethane and BOG in tank 50a. , such as to a pressure just above the pressure of BOG in the tank sufficient to ensure adequate flow of the expanded cooled return fluid stream 24 into tank 50a. The pressure of the expanded cooled return fluid stream 24 is lower than the pressure of the outlet pressure of the first compression stage 65 .

Returning to the compression system 60 , a first compression stage 65 provides a first intermediate compressed BOG stream 02a , which is passed to a further heat exchanger 80 . The first intermediate compressed BOG stream 02a is then transferred to a further heat exchanger ( 80) for heat exchange against the expanded portion 8b of the cooled and compressed BOG stream 08a. A second stage 75 compresses the cooled first intermediate compressed BOG stream 03a to provide a compressed BOG effluent stream 06a.

Referring to Figure 3a, a graph shows a typical temperature profile for cooling of 'pure' material in a conventional shell and coil economizer with a line 'xxxx' representing the shell side and a line 'oooo' representing the tube or coil temperature. Since the shell-side temperature is 'flat', it can be seen that there is no change in the shell-side temperature as the heat flow increases. This represents the cooling of 'pure' substances such as pure ethane.

However, Figure 3b shows the temperature profile of the same economizer (and using the same line formats) for a multi-component mixture with 'broad boiling points', such as the difference in boiling points of ethane and methane. Figure 3b shows that it is difficult to obtain a constant temperature on the tube side. As the cleared efficiency decreases across all heat flows, in the case of multi-component mixtures, the cooling efficiency is dictated by the heavier components, reducing the potential cooling that can be achieved in this type of equipment.

Nevertheless, it is more preferable to continue using this type of equipment with its known CAPEX.

The methods and apparatus disclosed herein seek to provide improved methods and apparatus for reliquefying BOG. An embodiment of a method and apparatus according to the invention is disclosed in FIG. 2 . Where appropriate, the same stream and component names as those in FIG. 1 and the same reference numbers are used for corresponding streams and components in the remaining figures.

2 shows a liquefied ethane cargo storage tank 50 in a floating transport vessel, such as an ethane carrier. The liquefied ethane cargo may include ethane and methane. In order to cool or in particular reliquefy the vaporized cargo from the storage tank 50 , the boil off gas stream 01 comprising the vaporized cargo is passed to a compression system 60 having two or more compression stages. is passed The boil off gas stream 01 may have a pressure in the range of 0 to 500 kPa gauge (“BOG pressure”). Compression system 60 may be a multi-stage compressor comprising two or more stages. By "multi-stage compressor" it is meant that each compression stage of the compressor is driven by the same drive shaft. Alternatively, compression system 60 may include compressors driven independently for each of the compression stages. When compression system 60 is a multi-stage compressor, it is typically a reciprocating compressor.

Although the embodiment of FIG. 2 shows a compression system 60 having a first stage 65 and a second stage 70 and a third and final stage 75 , the method and apparatus described herein are also It is also applicable to compressors with stages or more than 3 stages. A first stage 65 and a final stage 75 of compression provide a low pressure stream and a high pressure stream, respectively, on their discharge.

A compression system 60 compresses the boil off gas stream 01 to provide a compressed BOG effluent stream 06 . The compressed BOG effluent stream 06 may have a pressure in the range of 1.5 to 3.2 MPa or more, for example up to 6 MPa (“final stage pressure”).

The compressed BOG effluent stream 06 is cooled to one or more first heat exchangers for one or more first coolant streams 202 , 302 to provide a cooled compressed first BOG stream 08 . It is cooled in the fields 200 and 300 . 2 , the compressed BOG effluent stream 06 may be passed to a pre-cooled heat exchanger 200 as one of the one or more primary heat exchangers. The compressed BOG effluent stream 06 is precooled relative to the precooled coolant stream as one of the one or more first coolant streams. The pre-cooling coolant stream 202 may be an air or water stream, such as an atmospheric or seawater stream. The pre-cooled heat exchanger 200 may be a shell and tube heat exchanger or a plate heat exchanger. A pre-cooled heat exchanger may non-superheat the compressed BOG effluent stream (06). The precooled heat exchanger 200 provides a precooled compressed BOG stream 07 and a heated precooled coolant stream 204 . Typically, seawater used as a pre-cooling coolant will have a temperature of +36°C or less, more typically +32°C or less.

A pre-cooled heat exchanger/exchanger 200 is optional in the methods and apparatus disclosed herein. This is advantageous because it reduces the cooling duty of subsequent cooling steps. However, rather than in an essential aspect, in an alternative embodiment, the compressed BOG effluent stream 06 may be passed directly to the effluent heat exchanger 300 via line 06', so the equipment shown at 210 is omitted. can be In such circumstances, the cooling capacity of the exhaust heat exchanger 300 will have to be increased to compensate for the absence of pre-cooling.

The pre-cooled and compressed BOG stream 07 may then be passed to an exhaust heat exchanger 300 as the other of the one or more first heat exchangers. The exhaust heat exchanger 300 cools the precooled and compressed BOG stream 07 relative to the first refrigerant stream 302 as the other of the one or more first refrigerant streams. The exhaust heat exchanger 300 provides a cooled compressed first BOG stream 08 and a heated first refrigerant stream 304 .

The first refrigerant stream 302 , the exhaust heat exchanger 300 and the heated first refrigerant stream 304 may be part of a first refrigerant system (not shown). This first refrigerant system comprises a first refrigerant compressor compressing the heated first refrigerant stream 304 to provide a compressed first refrigerant stream, and cooling the first refrigerant to provide a cooled, compressed first refrigerant stream. and a first refrigerant expansion device for expanding the cooled compressed first refrigerant stream to provide a first refrigerant stream (302). The first refrigerant system may be a closed system. The first refrigerant is a fluorinated hydrocarbon mixture R-410A as well as one or more organic compounds including one or more inorganic compounds such as ammonia, in particular hydrocarbons and propane, propylene, difluoromethane and pentafluoro may contain fluorinated hydrocarbons such as methane.

The cooled, compressed first BOG stream 08 may be a partially condensed, compressed BOG stream comprising these components of boil off gas which may be condensed with respect to the first refrigerant at the outlet pressure of the final compression stage. . Any non-condensed components may be removed from the exhaust heat exchanger 300 as a vent stream (not shown) or from an exhaust receiver (not shown) functioning as a gas/liquid separator located downstream of the exhaust heat exchanger 300. can Exhaust heat exchangers suitable for the separation of gas and liquid components are shell and tube heat exchangers in which the cooled and compressed BOG is located on the shell side.

Any exhaust receiver may be an accumulator and may operate to maintain a liquid seal in the exhaust heat exchanger 300 and/or maintain an exhaust pressure in the final compression stage 75 .

The exhaust heat exchanger 300 may be of a type that cannot adequately separate the vapor and condensed phases into separate streams, such as plate and fin type heat exchangers. In this situation, an exhaust receiver will be located downstream of the exhaust heat exchanger 300 to separate the non-condensed components as an vent stream.

The cooled and compressed first BOG stream 08 is then cooled a second time. This may be accomplished by passing the cooled, compressed first BOG stream 08 through a second heat exchanger 180 . The second heat exchanger 180 may be of any type, and an intermediate stage, in particular a first stage, an economizer for cooling the intermediate BOG streams 02 or 04 as well as the cooled and compressed first stream 08 . 2 is shown.

Cooling of the cooled compressed first BOG stream 08 is opposed to the second coolant stream to provide a cooled, compressed second BOG stream 34 . Optionally, a portion of the cooled compressed first BOG stream 08 may be used elsewhere prior to passing to the second heat exchanger 180 , although in the present invention, a portion of the cooled compressed first BOG stream 08 may be used. ) preferably all or substantially all of which is passed to the first heat exchanger 180 .

The action of the second coolant, described below, is to provide a cooled, compressed second BOG stream 34 . Again, a portion of this stream 34 may be used elsewhere, but preferably all or substantially all of the cooled compressed second BOG stream 34 is further cooled and compressed with the second BOG stream 34 . It passes through a third heat exchanger 195 for cooling to provide a cooled, compressed third BOG stream 35 .

The third heat exchanger 195 may be of any type, such as an economizer, but is preferably a countercurrent heat exchanger, such as a plate and fin heat exchanger known in the art.

In the present invention, a portion of the cooled compressed third BOG stream 35 is expanded to a pressure between the first stage discharge pressure and the final stage suction pressure to provide an expanded and cooled first BOG stream 33a. This action may be performed via a pressure reducing device 80 such as a Joule-Thomson valve or an expander in a manner known in the art.

The expanded and cooled first BOG stream (33a) is used as a third coolant in a third heat exchanger (195), wherein the heat exchange provides a cooled and compressed third BOG stream (35); The expanded and heated first BOG stream 33b as heated third coolant stream 33b, which may be indirectly or more preferably direct, is used as second coolant stream 33b. The expanded and heated first BOG stream/second coolant stream 33b is used in the third heat exchanger 195 to fully utilize the remaining cooling effect of the expanded and heated first BOG stream after use in the second coolant. It is not separated (to separate into gas/liquid phase) prior to use as stream 33b.

The expanded and heated first BOG stream/second coolant stream 33b is passed to a second heat exchanger 180 . Heat exchange with the cooled, compressed first BOG stream 08 provides a second cooled and compressed BOG stream 34 and heated second coolant in a second heat exchanger 180 . The heated second coolant may include vapor and liquid components conveniently separated in the second heat exchanger 180 and discussed hereinafter. A second heated coolant stream, which is a first expanded additional heated BOG stream, may be passed to an intermediate compressed BOG stream of suitable pressure. 2 , the heated second coolant stream is combined with the first intermediate compressed BOG stream 02 .

The portion of the third cooled compressed BOG stream 35 that is not used to provide the expanded cooled first BOG stream 33a is, in a manner known in the art, the expanded cooled BOG return stream 36 as It may be returned as a return stream to the cargo tank 50 via the decompression device 82 .

A special feature of the present invention is that the 'conventional' shell and tube economizer can be used as a second Still usable as heat exchanger 180 , the present invention can be achieved simply by adding a third heat exchanger 195 . This means that the entire BOG reliquefaction system is at least controlled by the existing level controllers in the second heat exchanger 180 to control the temperature that may occur with the use of different BOG compositions and different inter stage pressures. avoid potential problems.

Indeed, an improvement of 10 to 15% in the refrigeration capacity of the BOG reliquefaction method and apparatus for liquefied cargo exceeds the minimum level for ethane cargo containing methane (in liquid state) and even 0.4 or 0.5 mol % It makes methane possible. Such methane-containing liquefied ethane cargoes may become increasingly common where new or other sources of ethane are being provided, but the desire to purify the ethane (by reducing or eliminating any methane content) prior to shipping is cost prohibitive. It is not effective or, in some cases, not possible locally.

4 shows another embodiment of the method and apparatus of the present invention. In common with FIG. 2 , FIG. 4 shows a liquefied ethane cargo storage tank 50 , from which a boil off gas stream 01 comprising cargo vaporized from a first stage 65 , a second stage and An intermediate stage 70 and a third and final stage 75 are passed to a compression system 60 having three compression stages. A first stage 65 provides a first intermediate compressed BOG stream 02 which passes into a second heat exchanger 180 and a cooled first intermediate BOG stream that passes into an intermediate compression stage 70 . (03) and a second intermediate compressed BOG stream (04) passing into the suction of the final compression stage (75).

Compression system 60 provides a compressed BOG effluent stream 06, which stream is one or more agents to be cooled relative to a first coolant that is seawater of seawater stream 202 in the manner previously described. One of the heat exchangers may be passed into a precooled heat exchanger 200 to provide a precooled and compressed BOG stream 07 .

The pre-cooled compressed BOG stream 07 may then be passed to the exhaust heat exchanger 300 as the other of the one or more first heat exchangers in the manner previously described. The exhaust heat exchanger 300 provides a cooled compressed first BOG stream 08 and a heated first refrigerant stream 304 .

The cooled, compressed first BOG stream 08 may be provided either directly or alternatively after passing through an exhaust receiver 305 as shown in FIG. 4 .

When the cooled, compressed BOG stream 08 is not fully condensed, a gaseous vent stream 51 that is also provided from the vent heat exchanger 300 as stream 51a and/or from the vent receiver 305 as stream 51b. ) exists. Although FIG. 4 shows the two streams 51a and 51b separately, these streams may be individually or in combination or without any distinction depending on the nature and structure of the exhaust heat exchanger 300 and the exhaust receiver 305 . can be provided. The provision of these streams or streams is known in the art.

The gas vent stream 51 may include both 'non-condensable' components and 'in-condensable' components. Components that may not be condensed are generally considered to be components that may never be substantially compressed and condensed within the boundaries and operating parameters of a particular floating transport vessel BOG cooling system, and relate primarily to nitrogen.

Usually, the main non-condensable component is considered to be methane, whose boiling point at 1 atmosphere is significantly lower than that of ethane, so that its condensation is generally again practical within the boundaries and operating parameters of a floating transport vessel. was considered not to be.

In WO 2012/143699A there is shown a method and apparatus for increasing the amount or rate of condensation of a gas vent stream in order to increase the recovery of the gas vent stream.

In the present invention, the method and apparatus, as shown by way of example in FIG. 4 , transfer a portion of the cooled and compressed third BOG stream 35 generally through a pressure reducing valve 87 to the cooled and compressed third BOG stream. passage of a portion of (35)—an amount that permits that portion of the cooled and compressed third BOG stream (35) to act as a fourth coolant (33c) in a fourth heat exchanger (197), such as a vent heat exchanger; and expanding to form a fourth coolant stream 33c by

The fourth heat exchanger 197 can be of any type, but is preferably a countercurrent heat exchanger such as a plate and fin arrangement. As shown in FIG. 4 , gaseous vent stream 51 may be cooled relative to fourth coolant stream 33c to provide a cooled vent stream 53 and a heated fourth coolant stream 38 .

Optionally, the heated fourth coolant stream 38 is a BOG recycle stream that can be passed to the second heat exchanger 180 , so that vapor therefrom can be used as part of the cooled first intermediate BOG stream 03 . .

Cooling of the gas vent stream 51 in the vent heat exchanger 197 may condense some of the components of the boil off gas that cannot be condensed in the exhaust heat exchanger 300 with respect to a first refrigerant such as propane or propylene. . The cooled vent stream 53 is typically an at least partially condensed stream.

In one embodiment, the cooled vent stream 53 may be passed to an vent stream decompression device 61 (dotted line), such as a Joule-Thomson valve or expander, where it expands Its pressure is reduced to provide an additional cooled vent stream 63 (dotted line). The expanded additional cooled vent stream 63 may have a pressure at or slightly higher than the pressure of the liquefied ethane cargo storage tank 50 , for example added to the expanded cooled BOG return stream 36 . may be returned to the tank to provide a combined expanded cooled BOG return stream 11 .

4, the cooled vent stream 53 may be passed to an vent stream separator 150, such as a gas/liquid separator. The vent stream separator 150 typically includes fully or substantially non-condensable components, which are typically a vapor stream, the vent effluent stream 55 , and these components of the boil off gas that has been condensed in the fourth heat exchanger 197 . to provide a cooled vent BOG return stream (57), which is a condensed stream. The pressure of the vent vent stream 55 may be reduced to a pressure suitable for return to storage tank 50, storage elsewhere, or venting, for example.

The cooled vent BOG return stream 57 may be passed through a vent return stream pressure reducing device 58 such as a Joule-Thomson valve or expander to provide an expanded cooled vent BOG return stream 59 . The expanded cooled vent BOG return stream 59 may be passed to the storage tank 50 , for example, by adding it to the expanded cooled BOG return stream 36 .

That portion of the cooled compressed third BOG stream 35 that is not passed to the decompression devices 80 and 87 to provide the third and fourth coolant streams 33a, 33c is the BOG return stream 10 This stream can be expanded to or near the pressure of the storage tank 50 as a cooled BOG return stream 36 expanded by means of a pressure reducing valve 82 . It can then be returned to the storage tank 50 .

Those skilled in the art will appreciate that the present invention may be practiced in many different ways without departing from the scope of the appended claims. For example, the present invention includes a combination of one or more optional or preferred features disclosed herein.

Claims (27)

A method of cooling a boil off gas stream (01) from a liquefied ethane cargo on a floating transport vessel, comprising:
The boil off gas stream (01) from the liquefied ethane cargo is subjected to at least two compression stages comprising at least a first stage (65) and a final stage (75) to provide a compressed BOG discharge stream (06). Compressing - the first compression stage (65) has a first stage discharge pressure, the final compression stage (75) has a final stage suction pressure and one or more intermediate compressed BOG streams (02, 03; 04) is provided between successive compression stages;
cooling the compressed BOG effluent stream (06) with respect to one or more first coolant streams (202, 302) to provide a cooled compressed first BOG stream (08);
cooling the cooled compressed first BOG stream (08) with respect to at least one second coolant stream to provide a cooled, compressed second BOG stream (34); and
cooling the cooled, compressed second BOG stream (34) relative to a third coolant stream to provide a cooled, compressed third BOG stream (35);
expanding a portion of the cooled compressed third BOG stream (35) to a pressure between the first stage outlet pressure and the final stage inlet pressure to provide an expanded cooled first BOG stream (33a);
using the expanded and cooled first BOG stream (33a) as a third coolant stream to provide an expanded and heated first BOG stream (33b); and
at least further comprising the step of using the expanded and heated first BOG stream (33b) as the second coolant stream.
A method of cooling a boil off gas stream from a liquefied ethane cargo on a floating transport vessel. The method of claim 1,
wherein the liquefied ethane cargo comprises > 0.1 mol % methane, or >0.5 mol % methane;
A method for cooling a boil off gas stream from a liquefied ethane cargo on a floating transport vessel. 3. The method of claim 1 or 2,
3 or 4 compression stages,
A method for cooling a boil off gas stream from a liquefied ethane cargo on a floating transport vessel. 3. The method of claim 1 or 2,
cooling of the cooled and compressed first BOG stream (08) with respect to the second coolant stream is performed in an economizer (180);
A method for cooling a boil off gas stream from a liquefied ethane cargo on a floating transport vessel. 3. The method of claim 1 or 2,
both the cooled and compressed first BOG stream (08) are cooled with respect to the second coolant stream;
A method for cooling a boil off gas stream from a liquefied ethane cargo on a floating transport vessel. 3. The method of claim 1 or 2,
both the cooled and compressed second BOG stream (34) are cooled relative to the expanded and cooled first BOG stream (33a);
A method for cooling a boil off gas stream from a liquefied ethane cargo on a floating transport vessel. 3. The method of claim 1 or 2,
providing a gas vent stream (51) from the cooled compressed first BOG stream (08);
expanding a portion of the cooled compressed third BOG stream (35) to form a fourth coolant stream (33c); and
cooling the gas vent stream (51) with respect to the fourth coolant stream (33c) to provide a cooled vent stream (53) and a heated fourth coolant stream (38);
A method for cooling a boil off gas stream from a liquefied ethane cargo on a floating transport vessel. 8. The method of claim 7,
expanding the cooled vent stream (53) to provide an expanded additional cooled vent stream (63); and
passing the expanded additional cooled vent stream (63) to a storage tank (50);
A method for cooling a boil off gas stream from a liquefied ethane cargo on a floating transport vessel. 8. The method of claim 7,
separating the further cooled vent stream (53) to provide a vent vent stream (55) and a cooled vent BOG return stream (57);
expanding the cooled aerated BOG return stream (57) to provide an expanded cooled aerated BOG return stream (59); and
passing the expanded cooled aerated BOG return stream (59) to a storage tank (50);
A method for cooling a boil off gas stream from a liquefied ethane cargo on a floating transport vessel. 3. The method of claim 1 or 2,
Cooling the compressed BOG effluent stream (06) with respect to one or more first coolant streams (202, 302) to provide a cooled compressed first BOG stream (08) comprising:
precooling the compressed BOG effluent stream (06) with respect to a precooled coolant stream (202) as a first coolant stream to provide a precooled compressed BOG stream (07); and
cooling the precooled compressed BOG stream (07) against a first refrigerant stream (302) as a first coolant stream to provide the cooled compressed first BOG stream (08);
A method for cooling a boil off gas stream from a liquefied ethane cargo on a floating transport vessel. 11. The method of claim 10,
wherein the pre-cooled coolant stream 202 is at least one of a seawater stream or an air stream;
A method for cooling a boil off gas stream from a liquefied ethane cargo on a floating transport vessel. 11. The method of claim 10,
The first refrigerant stream (302) is at least one selected from the group consisting of propane and propylene;
A method for cooling a boil off gas stream from a liquefied ethane cargo on a floating transport vessel. 3. The method of claim 1 or 2,
The compression stages (65, 75) are compression stages of a multi-stage compressor,
A method for cooling a boil off gas stream from a liquefied ethane cargo on a floating transport vessel. 3. The method of claim 1 or 2,
wherein both the second coolant streams comprise the expanded and heated first BOG stream (33b).
A method for cooling a boil off gas stream from a liquefied ethane cargo on a floating transport vessel. 3. The method of claim 1 or 2,
wherein the expanded and heated first BOG stream (33b) used as the second coolant stream comprises both liquid and gaseous phases;
A method for cooling a boil off gas stream from a liquefied ethane cargo on a floating transport vessel. 16. The method of claim 15,
the liquid phase and gas phase of the first expanded and heated BOG stream (33b) used as the second coolant stream are separated upon cooling of the cooled, compressed first BOG stream (08);
A method for cooling a boil off gas stream from a liquefied ethane cargo on a floating transport vessel. An apparatus for cooling a boil off gas stream (01) from a liquefied ethane cargo of a floating transport vessel comprising a plurality of components, the apparatus comprising:
A compression system (60) for compressing a boil off gas stream (01) from a liquefied ethane cargo, comprising at least a first stage (65) and a final stage (75) to provide a compressed BOG discharge stream (06) a compression system (60) comprising two or more compression stages, wherein intermediate compressed BOG streams (02, 03, 04) are provided between successive compression stages; and
at least one or more first heat exchangers (200, 300) for cooling the compressed BOG effluent stream (06) to provide a cooled compressed first BOG stream (08);
Further cooling the cooled compressed first BOG stream (08) with respect to the mixed-bed coolant stream (33b) to be separated in one or more second heat exchangers (180), whereby the cooled and compressed second BOG stream (34) is ) one or more second heat exchangers 180 ; and
one or more third heat exchangers (195) for further cooling the cooled, compressed second BOG stream (34) to provide a third, cooled, compressed BOG stream (35), and a decompression device (80) including,
The decompression device 80 expands a portion of the cooled compressed third BOG stream 35 to a pressure between a first stage outlet pressure and a final stage inlet pressure, so that the one or more third heat exchangers 195 ) for providing an expanded and cooled first BOG stream (33a) as a coolant in the ,
An apparatus for cooling a boil off gas stream from a liquefied ethane cargo of a floating transport vessel comprising a plurality of components. An apparatus for cooling a boil off gas stream (01) from a liquefied ethane cargo of a floating transport vessel comprising a plurality of components, the apparatus comprising:
A compression system (60) for compressing a boil off gas stream (01) from a liquefied ethane cargo, comprising at least a first stage (65) and a final stage (75) to provide a compressed BOG discharge stream (06) a compression system (60) comprising two or more compression stages, wherein intermediate compressed BOG streams (02, 03, 04) are provided between successive compression stages; and
at least one or more first heat exchangers (200, 300) for cooling the compressed BOG effluent stream (06) to provide a cooled compressed first BOG stream (08);
Further cooling the cooled compressed first BOG stream (08) with respect to the mixed-bed coolant stream (33b) to be separated in one or more second heat exchangers (180), whereby the cooled and compressed second BOG stream (34) is ) one or more second heat exchangers 180 ; and
one or more third heat exchangers (195) for further cooling the cooled, compressed second BOG stream (34) to provide a cooled, compressed third BOG stream (35);
The device is operable using the method according to claim 1 or 2,
An apparatus for cooling a boil off gas stream from a liquefied ethane cargo of a floating transport vessel comprising a plurality of components. 18. The method of claim 17,
The second heat exchanger 180 is an economizer,
An apparatus for cooling a boil off gas stream from a liquefied ethane cargo of a floating transport vessel comprising a plurality of components. having the device as defined in claim 17,
Floating transport vessel for liquefied ethane. using the method defined in claim 1 or 2,
Floating transport vessel for liquefied ethane. 12. The method of claim 11,
wherein the pre-cooled coolant stream (202) may be an atmospheric stream or a refrigerant stream;
A method for cooling a boil off gas stream from a liquefied ethane cargo on a floating transport vessel. delete delete delete delete delete

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