WO2018091920A1

WO2018091920A1 - Hydrocarbon separation process and apparatus

Info

Publication number: WO2018091920A1
Application number: PCT/GB2017/053475
Authority: WO
Inventors: Terence Ronald Tomlinson; Zak Richard LOFTUS
Original assignee: Costain Oil Gas and Process Ltd
Current assignee: Costain Oil Gas and Process Ltd
Priority date: 2016-11-18
Filing date: 2017-11-17
Publication date: 2018-05-24
Anticipated expiration: 2019-05-18
Also published as: GB201908738D0; GB201619578D0; GB2556878A; GB2571676A

Abstract

This invention relates to a process, and apparatus for effecting such a process, for the cryogenic fractionation of gaseous hydrocarbon feeds to extract and recover the valuable heavier components thereof. The invention is particularly concerned with a process for efficient recovery of ethane and heavier components from a natural gas feed.

Description

HYDROCARBON SEPARATION PROCESS AND APPARATUS

This invention relates to a process, and apparatus for effecting such a process, for the cryogenic fractionation of gaseous hydrocarbon feeds to extract and recover the valuable heavier components thereof. The invention is particularly concerned with a process for efficient recovery of ethane and heavier components from a natural gas feed. The process is not limited to the recovery of paraffinic compounds such as ethane found in natural gas, but also, for example, to olefins such as ethylene often found in gases associated with petroleum refining or petrochemicals manufacture.

Processes to effect recovery of ethane and heavier components from natural gas typically utilise a combination of heat exchange, turbo-expansion, phase separation and fractionation steps. The use of turbo-expansion of a gaseous stream produces work, which can be used to drive a compressor to supplement residual gas compression, and by removing energy from the expanded gas a low temperature expanded gas stream is produced.

EP 1 ,1 14,808 discloses a process for the separation of heavier hydrocarbons from a gaseous feed using a two fractionation column system, the configuration of which is shown in Figure 1. In this process the high-pressure gaseous feed (7 MPa) is partially condensed and separated, and the gaseous and liquid components are expanded to a lower pressure (3.5 MPa) prior to being fed into the first fractionation column. Work expansion of the gaseous component from the separator prior to feeding into the first fractionation column can be used to drive a compressor.

Specifically, in the system shown in Figure 1 , a gaseous feed stream (2) is cooled and partially condensed in heat exchanger (4). The partially condensed feed (6) is separated in a separator (8) to give a liquid stream (48) and a gaseous stream (10). The gaseous stream (10) is work expanded in an expander (12) and the expanded stream (14) fed to a first fractionation column (16). The liquid stream (48) is expanded through a valve (50), and fed to the first fractionation column (16). The liquid stream (36) from the bottom of the first fractionation column (16) is subcooled in a heat exchanger (20), expanded through a valve (40), rewarmed in heat exchanger (20) and fed to a second fractionation column (54). The gaseous stream (18) from the first fractionation column (16) is subcooled in a heat exchanger (20) and separated in second separator (24), from which the liquid stream (26) provides reflux to the first and second fractionation columns (16 and 54), and the gaseous stream (62) is used to provide cooling in the heat exchangers (20 and 4) then combined with a separated lights stream (56) from the second fractionation column (54).

EP1 137616 discloses a process for the separation of heavier hydrocarbons from a gaseous feed using a two fractionation column system. In this process the high-pressure gaseous feed (7 MPa) is partially condensed and separated, and the gaseous and liquid components are expanded to a lower pressure (2.5 MPa) prior to being fed into the first fractionation column. Specifically, in the system shown in Figure 5, a gaseous feed stream (2) is cooled and partially condensed in heat exchanger (4). The partially condensed feed (6) is separated in a separator (8) to give a liquid stream (10) and a gaseous stream (14). The gaseous stream (14) is work expanded in an expander (16) and the expanded stream (18) fed to a first fractionation column (24). The liquid stream (10) is expanded through a valve (12), and the expanded stream (20) is combined with the expanded stream (18) from the gas fraction and fed to the first fractionation column (24). The liquid stream (26) from the bottom of the first fractionation column (24) is expanded through a valve (28), rewarmed in two heat exchangers (32, 4) and fed to a second fractionation column (38). The separated lights stream (48) from the second fractionation column (38) is cooled in a heat exchanger (32) and separated in second separator (52), from which the liquid stream (54) is pumped (56) and provides reflux to the second fractionation column (38) and another portion of the liquid stream (54) is pumped (59), cooled in a heat exchanger (32) and provides reflux to the first fractionation column. The gaseous stream from the second separator (52) is warmed in two heat exchangers (32 and 4) and compressed in a compressor (76) to produce a compressed stream (78). The gaseous stream (64) from the first fractionation column (24) is warmed in two heat exchangers (32, 4) and combined with the compressed stream (78) then further compressed in a compressor (82).

As demonstrated by the above processes, where a fractionation column is used in hydrocarbon separation systems, the pressure is let down from line pressure (normally around 7 MPa) using expanders prior to feeding to the fractionation column. This avoids the common problem that when a mixture of gases approaches its critical point (critical temperature and pressure) distillation becomes problematic and separation efficiency is reduced. For example, US 2010/0050688 discloses a process for the separation of hydrocarbons from a high pressure gaseous feed whereby the demethaniser (i.e. the fractionation column) is operated at a maximum pressure of 550 psi (3.8 MPa) in order to avoid distillation problems.

Thus, where work expansion of a high-pressure gaseous stream is provided, this is typically done prior to feeding the stream into a fractionation column in order to take advantage of the let-down in pressure understood to be necessary to achieve sufficient separation in the fractionation column.

Nonetheless, there remains a need for gas separation systems which provide reduced energy usage whilst maintaining good separation efficiency.

It has surprisingly been found that by not letting down the pressure of the feed into the first fractionation column of a two or three column hydrocarbon separation system, and providing work expansion of process gases after this, the total energy requirement of a hydrocarbon separation process may be reduced.

Thus, according to one aspect of the invention there is provided a process for the separation of a heavier hydrocarbon fraction from a high-pressure gaseous feed comprising a mixture of hydrocarbons, which process comprises:

(a) cooling the high-pressure gaseous feed to produce a first high-pressure condensed stream;

(b) feeding the first high-pressure partially condensed stream to a first fractionation column at a pressure greater than 6.0 MPa and recovering from the first fractionation column a first liquid stream higher in heavier and a first gaseous stream lower in heavier hydrocarbons, wherein reboil is provided to the first fractionation column;

(c) expanding at least a portion of said first liquid stream higher in heavier hydrocarbons to produce a first expanded stream and feeding at least a portion of said first expanded stream to a second fractionation column;

(d) recovering process energy by work expanding at least a portion of the first gaseous stream lower in heavier hydrocarbons to produce an expanded partially condensed stream and feeding at least a portion of said expanded partially condensed stream to the second fractionation column;

(e) recovering a separated lights stream lower in heavier hydrocarbons from said second fractionation column;

(f) recovering said heavier hydrocarbon fraction as a bottoms stream from said second fractionation column.

In preferred embodiments, the first high-pressure partially condensed stream is fed to the first fractionation column at a pressure of no more than 7.5 MPa. Preferably, the first high-pressure partially condensed stream is fed to the first fractionation column at a pressure of at least 6.5 MPa. For example, in particularly preferred embodiments, the first high-pressure partially condensed stream is fed to the first fractionation column at a pressure of from 6.75 MPa to 7.25 MPa.

Despite the first fractionation column operating at a pressure level typically believed to inhibit efficient separation in the fractionation column, an increased proportion of the first partially condensed stream exits the first fractionation column in the gas phase as compared to a system comprising a separator (for example, as shown in Figure 1 ). Therefore, an increased proportion of the feed can be work expanded in order to recover an increased amount of energy from the let-down of the high-pressure feed in comparison to typical systems.

As is commonly known to the skilled person, the work expansion of a stream, as referred to herein, will be understood to refer to the expansion of a stream whereby energy is recovered from the expansion. For example, the expansion may use a turbo expander. It will also be understood that the expander may be a single expander or a system of expanders (for example, a turbo expander system) and the actual quantity and configuration of expanders may vary.

"Heavier hydrocarbons" or a "heavier hydrocarbon fraction" as referred to herein, and as recovered as a bottoms stream from the second fractionation column, will be understood to mean a hydrocarbon fraction having an average molecular mass/boiling point higher than the separated lights fraction recovered from the top of the second fractionation column.

Preferably, the heavier hydrocarbon fraction will comprise C₂+ hydrocarbons, for example ethane, ethylene and heavier molecules. For example, the heavier hydrocarbon fraction may include all hydrocarbons with the exception of methane.

Where a stream is generally "expanded", this will be understood to include work expansion as described previously, or expansion by any other means. For example, expansion where energy recovery is not required will typically comprise expansion through a valve (e.g. a Joule-Thomson valve).

It will additionally be understood that expanders will generally have a bypass, which can be used to address bottlenecks in the system. In preferred embodiments, the first high-pressure partially condensed stream in part (a) is fed directly to the first fractionation column. In this way, the full line pressure of the feed stream may be maintained and utilised for energy recovery by work expansion.

As used herein, the term "fed directly", or "passed directly" in relation to a stream will be understood to mean that the stream will not be purposefully processed over the specified interval. For example, a stream fed directly from one part of the process to another will not be split or separated and will not be heated, cooled, expanded or compressed. Minor or trivial operations on the stream will be understood not to be excluded by the term "directly", as will changes to the stream which result from the passage of the stream inherently. For example, withdrawal of samples for analysis or minor temperature and/or pressure change (e.g. as a result of imperfect insulation of the stream) are not considered as processing of the stream for the purposes of feeding a stream "directly".

Preferably, cooling of the high-pressure gaseous feed in part (a) is provided, at least in part, by heat exchange with at least a portion the first expanded stream in part (c). By integrating the first expanded stream into the cooling requirement of the feed stream, the overall refrigeration requirement may be reduced, lowering the total process energy requirement. In some embodiments, at least a portion of the first expanded stream in part (c) is fed directly to the second fractionation column. Preferably, at least a portion of the first expanded stream in part (c) is used to cool the high-pressure gaseous feed in heat exchange and then fed directly to the second fractionation column. In other embodiments, the first expanded stream may be split and/or integrated into the process in any other manner.

Preferably, part (c) comprises expanding at least a substantial portion of said first liquid stream higher in heavier hydrocarbons to produce the first expanded stream. In some preferred embodiments, part (c) comprises feeding at least a substantial portion of the first expanded stream to the second fractionation column.

A "substantial portion" as referred to herein will be understood to mean more than 50 % of the volumetric flow of a stream, preferably at least 60 %, more preferably 70 %, even more preferably 80 %, for example 90 % or 95 %. In particularly preferred embodiments, a "substantial portion" will comprise the entire volumetric flow of the stream in question.

It will be appreciated that where only a portion of a stream is expanded, this may refer to separation of the stream and expansion of a separated part of the stream. For example this may refer to the use of an expander bypass as mentioned previously.

Preferably, part (d) comprises recovering process energy by work expanding at least a substantial portion of the first gaseous stream lower in heavier hydrocarbons to produce the expanded partially condensed stream. In preferred embodiments, part (d) comprises feeding at least a substantial portion of the expanded partially condensed stream to the second fractionation column.

In some embodiments, at least a portion of the expanded partially condensed stream in part (d) is fed directly to the second fractionation column. However, it will be understood that the expanded partially condensed stream may be split, integrated into other parts of the process (to provide cooling, for example) and/or fed into the second fractionation column at multiple positions.

The first and second fractionation columns may be any suitable columns. For example, the quantity of trays in each fractionation column may vary and can be provided in any suitable quantity and configuration.

It will be understood that the first fractionation column will operate at a pressure of greater than 6.0 MPa, and that the operating pressure will vary according to the pressure of the feed into the column as described previously. In some embodiments, the first fractionation column may comprise a condenser for providing reflux to an upper part of the column. It will be appreciated that any suitable condenser may be used. For example, a portion of the first gaseous stream may be partially condensed and separated, with the resultant liquid fraction being fed to an upper part of the first fractionation column. In other embodiments the first fractionation column will not comprise a condenser.

As a result of the expansion of the gaseous and liquid streams recovered from the first fractionation column, it will be appreciated that the second fractionation column will operate at a lower pressure than the first fractionation column. The second fractionation column may operate at any suitable pressure, but in preferred embodiments, the second fractionation column will operate at a pressure of from 1.5 MPa to 5.0 MPa, preferably from 2.5 MPa to 4.5 MPa, more preferably from 3.0 to 4.0 MPa, for example 3.5 MPa. Reboil may be provided to the first and second fractionation columns by any suitable means. By providing reboil to the first fractionation column, there will be an increase in the proportion of the first partially condensed stream exiting the first fractionation column in the gas phase. In this way, an increased amount of energy may be recovered during work expansion of the first gaseous stream.

In preferred embodiments, reboil to the first fractionation column is provided, at least in part, by heat exchange with the high-pressure gaseous feed. For example, reboil may be provided by one or more side reboilers, wherein a stream is withdrawn from the side of the fractionation column, heated and partially vapourised, and fed back into the column. Integrating reboil streams in order to provide cooling to the gaseous feed leads to a reduction of the overall refrigeration requirement, lowering the total process energy requirement. In other embodiments, reboil may be provided to the first fractionation column by a standalone reboiler or by alternative heat integration.

Preferably, reboil to the second fractionation column is provided, at least in part, by heat exchange with the high-pressure gaseous feed. For example, reboil may be provided by one or more side reboilers as described above.

In some embodiments, reboil to the second fractionation column is provided, at least in part, by external heating, for example reboil to the second fractionation column may be provided, at least in part, by heating the bottoms stream in part (e) to produce a heated bottoms stream, and feeding at least a portion of said heated bottoms stream to a lower part of the second fractionation column.

It will be understood that reboil to the second fractionation column may be provided by both heat exchange and external heating as described previously, or may be provided by only one of these. Alternatively, reboil to the second fractionation column may be provided by any other standalone reboiler or alternative heat integration.

It will be appreciated that the light hydrocarbons in the separated lights stream will typically be rewarmed and compressed to a suitable pressure for export. Thus, in preferred embodiments, the separated lights stream is compressed to produce a high- pressure lights stream. Preferably, energy for the compression of the separated lights stream is provided, at least in part, by work expansion of the first gaseous stream in part (d). For example, the separated lights stream may be compressed using an expander brake coupled to an expander through which the first gaseous stream is expanded in part (d).

In some embodiments, the separated lights stream will be compressed in one or more compressors in addition to or instead of the compression provided by work expansion of the first gaseous stream. Nonetheless, it will be appreciated that any suitable number and configuration of compressors may be incorporated for the compression of the separated lights stream. In some embodiments, the separated lights stream is cooled following compression. For example, compressor after cooling may comprise cooling against ambient air or cooling water.

In preferred embodiments, reflux to the second fractionation column is provided by cooling, subcooling and expanding a recycle stream comprising a portion of the separated lights stream and feeding this subcooled and expanded recycle stream into the top of the second fractionation column. It will nonetheless be appreciated that reflux may be provided from other sources and may comprise more than one reflux stream. The cooling and/or subcooling of the recycle stream may be provided by any suitable means, for example mechanical refrigeration or heat exchange with other process streams. Preferably, the cooling and/or subcooling of the recycle stream is provided, at least in part, by heat exchange with the separated lights stream. Preferably, the recycle stream will comprise at least a portion of the high-pressure lights stream. Alternatively, the recycle stream may be split from the separated lights stream at any point prior to compression or from between individual compression stages at an intermediate pressure.

It will be appreciated that where heat is transferred between streams by heat exchange, any suitable heat exchanger may be used. In the present method, any suitable number and configuration of heat exchangers may be used.

Preferably, one or more heat exchangers in the system will be configured to process more than two streams. For example, all heat exchange with the high-pressure gaseous feed may take place in a single primary heat exchanger. Alternatively, more than one heat exchanger may be used for providing heating or cooling to the high-pressure gaseous feed and/or any other streams.

It will be appreciated that the entire cooling requirement of the process may be provided by integration of process streams and heat exchange therebetween. Nonetheless, in some embodiments, cooling is provided to one or more streams by mechanical refrigeration. The mechanical refrigeration may comprise any suitable system or configuration. For example, the mechanical refrigeration may comprise a single refrigerant at a single pressure stage, a single refrigerant at multiple pressure stages, a multicomponent refrigerant at a single pressure stage, a multicomponent refrigerant at multiple pressure stages, a combination thereof or any other mechanical refrigeration arrangement.

In preferred embodiments, where mechanical refrigeration is included, a refrigerant stream will provide cooling to process streams by heat exchange. Preferably, the refrigerant stream will be integrated into a heat exchanger, through which the high- pressure gaseous feed and optionally the recycle stream are passed.

It will be appreciated that the precise composition of the heavier hydrocarbons recovered from the second fractionation column may be varied as necessary by varying the processing steps and conditions preceding the second fractionation column.

In some preferred embodiments, the process further comprises feeding at least a portion of the expanded partially condensed stream to a wash column and recovering from the wash column a wash column heavy stream higher in heavier hydrocarbons and a wash column lights stream lower in heavier hydrocarbons, and feeding at least a portion of the wash column heavy stream to the second fractionation column.

Preferably, in embodiments where the wash column is present, the heavier hydrocarbon fraction will comprise C₃₊ hydrocarbons, for example propane, propylene and heavier molecules. For example, the heavier hydrocarbon fraction may comprise any hydrocarbons with the exception of methane and ethane.

As described previously, the expanded partially condensed stream contains a larger proportion of the lighter hydrocarbon fraction from the feed stream than where a separator is used in place of the first fractionation column. By including the wash column in the process, a larger proportion of a lighter hydrocarbon fraction, such as a Ci or C₂ fraction may be removed from the feed prior to the second fractionation column, which may lead to increased efficiency of separation.

It will be understood that the wash column referred to herein will be a fractionation column. The wash column may be any suitable column. For example, the quantity of trays in the wash column may vary and can be provided in any suitable quantity and configuration.

The wash column may operate at any suitable pressure, but in preferred embodiments, the wash column will operate at a pressure of from 1.5 MPa to 5.5 MPa, preferably from 2.5 MPa to 5.0 MPa, more preferably from 3.5 to 4.5 MPa, for example 4.0 MPa. The second fractionation column will typically operate at a lower pressure than the wash column, and may be any suitable pressure. In preferred embodiments where the wash column is present, the second fractionation column will operate at a pressure of from 1.0 MPa to 5.0 MPa, preferably from 1.5 MPa to 4.0 MPa, more preferably from 2.0 to 3.0 MPa, for example 2.5 MPa.

It will be appreciated that, where a portion of the expanded partially condensed stream or first expanded stream is fed to the second fractionation column, this may refer to a portion of the respective streams that is first fed to the wash column and subsequently fed to the second fractionation column as part of the wash column heavy stream. Preferably, the process comprises feeding at least a substantial portion of the expanded partially condensed stream to the wash column.

In some preferred embodiments, the process comprises feeding at least a portion of the first expanded stream to the wash column. Preferably at least a portion of the first expanded stream is fed to the wash column at a lower position than the expanded partially condensed stream is fed to the wash column. As discussed, by the use of a high pressure fractionation, the expanded partially condensed stream contains a greater proportion of the feed material. In this way, by feeding the expanded partially condensed stream to the wash column at a higher position than the first expanded stream, the amount of lighter hydrocarbons, for example C₁ and C₂ hydrocarbons, dissolved in the wash column liquids may be reduced. This may lead to a reduction in the lighter hydrocarbons carried to the second fractionation column, increasing separation efficiency. Nonetheless, it will be understood that at least a portion of the first expanded stream may partially or substantially bypass the wash column and be fed to the second fractionation column.

Preferably, the process comprises feeding at least a substantial portion of the wash column heavy stream to the second fractionation column.

In preferred embodiments, at least a portion of the wash column heavy stream is expanded before being fed to the second fractionation column. Preferably, the expanded wash column heavy stream is heated before being fed to the second fractionation column. It will be appreciated that any suitable heating may be used. In more preferred embodiments, cooling of the high-pressure gaseous feed in part (a) is provided, at least in part, by heat exchange with the expanded wash column heavy stream. Preferably, cooling of the high-pressure gaseous feed in part (a) is provided, at least in part, by heat exchange with the wash column lights stream. It will be appreciated that by integrating the cooling of the gaseous feed stream with heating the expanded wash column heavy stream or wash column lights stream, or other process streams, the overall refrigeration requirement may be reduced, lowering the total process energy requirement. Preferably, at least a portion of the separated lights stream is cooled to produce a partially condensed separated lights stream which is fed to a separator to produce a second separated lights stream and a separated heavy stream, wherein at least a portion of the separated heavy stream is fed to the an upper part of the second fractionation column to provide reflux to the second fractionation column. In preferred embodiments, at least a portion of the separated heavy stream is subcooled and fed to an upper part of the wash column to provide reflux to the wash column.

It will nonetheless be appreciated that reflux to the second fractionation column or wash column may be provided from other sources and may comprise more than one reflux stream. In particular, it will be understood that the separated heavy stream may be used to provide reflux separately to either the second fractionation column or wash column, or to both. In some preferred embodiments, reflux to the wash column is provided by cooling, subcooling and expanding a recycle stream, the recycle stream comprising at least a portion of the separated lights stream and/or the wash column lights stream, and feeding the subcooled and expanded recycle stream into an upper part of the wash column.

Preferably, cooling of the separated lights stream is provided, at least in part, by heat exchange with the wash column lights stream and/or the wash column heavy stream and/or the second separated lights stream.

In preferred embodiments, subcooling of the separated heavy stream is provided, at least in part, by heat exchange with the wash column lights stream and/or the wash column heavy stream and/or the second separated lights stream.

Preferably, cooling of the high-pressure gaseous feed in part (a) is provided, at least in part, by heat exchange with the second separated lights stream.

It will be appreciated that the light hydrocarbons recovered from the process will typically be compressed to a suitable pressure for export. Compression of the light hydrocarbons may be performed in any suitable way with any suitable compressor configuration. In preferred embodiments, at least a portion of the wash column lights stream is combined with the second separated lights stream and compressed to produce a high pressure lights stream.

Preferably, energy for the compression of process streams, for example the wash column lights stream, the second separated lights stream or a combination thereof, may be provided, at least in part, by work expansion of the first gaseous stream in part (d). For example the wash column lights stream, the second separated lights stream or a combination thereof, may suitably be compressed using an expander brake coupled to an expander through which the first gaseous stream is expanded in part (d).

The wash column heavy stream may suitably be fed to the second fractionation column substantially without combining with other process streams. Nonetheless, in some embodiments at least a portion of the first expanded stream is combined with the wash column heavy stream before being fed to the second fractionation column.

It will be appreciated that a portion of the first expanded stream may be fed directly to the wash column, or may directly bypass the wash column and be fed to the second fractionation column. Nonetheless, in some preferred embodiments, at least a portion of the first expanded stream is fed to a second separator to produce a light intermediate stream and a heavy intermediate stream, wherein the light intermediate stream is fed to the wash column and the heavy intermediate stream is combined with the wash column heavy stream and/or fed to the second fractionation column. The heavy and/or light intermediate streams may preferably be cooled in heat exchange with the wash column lights stream and/or the wash column heavy stream and/or the second separated lights stream. According to another aspect of the invention there is provided an apparatus for the separation of a heavier hydrocarbon fraction from a high-pressure gaseous feed comprising a mixture of hydrocarbons, which apparatus comprises;

(a) means for cooling the high-pressure gaseous feed to produce a first high- pressure partially condensed stream;

(b) a first fractionation column and means for feeding the first high-pressure partially condensed stream directly thereto at a pressure greater than 6.0 MPa, wherein the first fractionation column comprises means for providing reboil;

(c) means for recovering from the first fractionation column a first liquid stream higher in heavier hydrocarbons and a first gaseous stream lower in heavier hydrocarbons;

(d) a second fractionation column;

(e) a first expander configured to expand at least a portion of the first liquid stream higher in heavier hydrocarbons to produce a first expanded stream, means for feeding at least a portion of said first expanded stream to the second fractionation column;

(f) a second expander configured to recover process energy by work expanding at least a portion of the first gaseous stream lower in heavier hydrocarbons to produce an expanded partially condensed stream, and means for feeding at least a portion of said expanded partially condensed stream to the second fractionation column;

(g) means for recovering from said second fractionation column a separated lights stream lower in heavier hydrocarbons;

(h) means for recovering from said second fractionation column said heavier hydrocarbon fraction as a bottoms stream. It will be appreciated that the first and second fractionation columns, the expanders and other elements of the apparatus or configurations of the apparatus may be as described previously herein. In some preferred embodiments, the apparatus further comprises a wash column and means for feeding at least a portion of the expanded partially condensed stream to the wash column; means for recovering from the wash column a wash column heavy stream higher in heavier hydrocarbons and a wash column lights stream lower in heavier hydrocarbons; and means for feeding at least a portion of the wash column heavy stream to the second fractionation column.

It will be appreciated that in preferred embodiments the wash column and other elements of the apparatus or configurations of the apparatus comprising a wash column may be as described previously herein.

By providing an apparatus comprising means to feed the first high-pressure partially condensed stream directly to the first fractionation column, pressure let down of the feed is avoided. In this way, a larger proportion of the high-pressure feed (the vapour fraction from the first fractionation column) may be passed through a work expander to recover an increased amount of process energy.

According to another aspect of the invention there is provided the use of reboil to increase the proportion of a heavier hydrocarbon fraction exiting a fractionation column in the gaseous phase in a process for the separation of a heavier hydrocarbon fraction from a mixture of hydrocarbons.

According to another aspect of the invention, there is provided a process for the separation of a heavier hydrocarbon fraction from a high-pressure gaseous feed comprising a mixture of hydrocarbons, which process comprises:

(a) cooling the high-pressure gaseous feed to produce a first high-pressure partially condensed stream;

(b) feeding the first high-pressure partially condensed stream to a first fractionation column at a pressure greater than 6.0 MPa and recovering from the first fractionation column a first liquid stream higher in heavier hydrocarbons and a first gaseous stream lower in heavier hydrocarbons, wherein reboil is provided to the first fractionation column;

(d) recovering process energy by work expanding at least a portion of the first gaseous stream lower in heavier hydrocarbons to produce an expanded partially condensed stream and feeding at least a portion of said expanded partially condensed stream to a wash column;

(d-ii) recovering from the wash column a wash column heavy stream higher in heavier hydrocarbons and a wash column lights stream lower in heavier hydrocarbons and feeding at least a portion of the wash column heavy stream to a second fractionation column;

It will be appreciated that the steps of the process may suitably be as described previously herein.

According to another aspect of the invention, there is provided an apparatus for the separation of a heavier hydrocarbon fraction from a high-pressure gaseous feed comprising a mixture of hydrocarbons, which apparatus comprises;

(a) means for cooling the high-pressure gaseous feed to produce a first high- pressure condensed stream;

(d) a second fractionation column and a wash column;

(f) a second expander configured to recover process energy by work expanding at least a portion of the first gaseous stream lower in heavier hydrocarbons to produce an expanded partially condensed stream, and means for feeding at least a portion of said expanded partially condensed stream to the wash column;

(f-ii) means for recovering from the wash column a wash column heavy stream higher in heavier hydrocarbons and a wash column lights stream lower in heavier hydrocarbons;

(f-iii) means for feeding at least a portion of the wash column heavy stream to the second fractionation column;

(g) means for recovering from said second fractionation column a separated lights stream lower in heavier hydrocarbons; and

(h) means for recovering from said second fractionation column said heavier hydrocarbon fraction as a bottoms stream.

It will be appreciated that the first and second fractionation columns, the wash column, the expanders and other elements of the apparatus or configurations of the apparatus may be as described previously herein.

Typically, when separating a heavier hydrocarbon fraction from a mixture of hydrocarbons, it will be desirable to minimise the proportion of the heavier hydrocarbon fraction exiting a fractionation column in the gaseous phase, i.e. to minimise loss of the heavier fraction into the lighter fraction. As described herein, using reboil in an unusual way to increase the proportion of a heavier hydrocarbon fraction exiting a fractionation column in the gaseous phase allows increased energy recovery, leading to a more efficient separation process.

Embodiments of the invention will now be described in more detail with particular reference to the accompanying drawings of which: Figure 1 shows a prior art process for the separation of heavier hydrocarbons from a gaseous hydrocarbon feed comprising a two column arrangement.

Figure 2 shows an embodiment of the present invention, wherein a high-pressure gaseous feed is fed directly into a first fractionation column and process energy is recovered by work expansion of the gaseous fraction therefrom.

Figure 3 shows an embodiment of the present invention comprising a wash column, wherein a high-pressure gaseous feed is fed directly into a first fractionation column and process energy is recovered by work expansion of the gaseous fraction therefrom.

Figure 4 shows another embodiment of the present invention comprising a wash column, wherein a high-pressure gaseous feed is fed directly into a first fractionation column and process energy is recovered by work expansion of the gaseous fraction therefrom. Figure 5 shows a different prior art process for the separation of heavier hydrocarbons from a gaseous hydrocarbon feed comprising a two column arrangement.

In the embodiment shown in Figure 2, a high-pressure gaseous feed (202) at a pressure of 7.0 MPa is cooled and partially condensed in the primary heat exchanger (204) to produce a first high-pressure partially condensed stream (206). The first high-pressure partially condensed stream (206) is fed to the upper portion of a first fractionation column (208) at a pressure of 7.0 MPa. A first liquid stream (218) higher in heavier hydrocarbons and a first gaseous stream (210) lower in heavier hydrocarbons are withdrawn from the first fractionation column (208).

The first liquid stream (218) is expanded across a valve (292) to produce a first expanded stream, which may also be partially condensed. A portion of the first expanded stream (222) may be fed directly to a second fractionation column (216). A portion (224) may also be fed to the primary heat exchanger (204) where this stream is partially vaporised to provide cooling to the high-pressure gaseous feed, producing partially vaporised stream (226) which is then fed to the second fractionation column (216). It will be appreciated that the split between streams 222 and 224 may include any suitable variation in flow ratios, including total flow to either stream.

The first gaseous stream (210) is work expanded in a turbo expander (212) to form an expanded partially condensed stream (214), which is fed to an upper part of the second fractionation column (216).

A liquid stream (284) is withdrawn from a tray part way up the first fractionation column (208) and fed to the primary heat exchanger (204), where it is partially vaporised and fed back to the first fractionation column (208) as a partially condensed stream (286) in order to provide reboil.

Refrigeration for cooling the high-pressure gaseous feed (202) or to any other part of the process may be supplemented by mechanical refrigeration. In this embodiment, a cold liquid propane refrigerant stream (288) is evaporated in the primary heat exchanger (204) to a produce refrigerant vapour stream (290).

A separated lights stream (230) is withdrawn from the top of the second fractionation column. The separated lights stream is heated in a secondary heat exchanger (220) and in the primary heat exchanger (204), where cooling is provided to the high-pressure gaseous feed. The warmed lights stream (234) is compressed in an expander brake (236) and cooled to give a gas stream (242), which is compressed in a compressor (244) and cooled to give a gas product stream (254). The compressor after cooling is typically against ambient air or cooling water.

A recycle stream (252) is split from the cooled and compressed lights stream (250) and fed to the primary heat exchanger (204) where it is cooled and partially condensed. This cooled and partially condensed recycle stream (256) is then fed to the secondary heat exchanger (220) where the stream is subcooled and fully condensed. The subcooled and condensed recycle stream (258) is then expanded across a valve (260) to the same pressure as the second fractionation column (216) and the subcooled and expanded recycle stream (262) is fed to the top of the second fractionation column (216) as reflux.

A bottoms stream (276) comprising the heavier hydrocarbon fraction (C₂+) is drawn from the bottom of the second fractionation column (216). The bottoms stream (276) is heated in a heater (278) and a portion of the heated bottoms stream (280) is fed to a lower part of the second fractionation column (216) to provide reboil. A liquid product stream (282), comprising the remainder of the heated bottoms stream, is removed for further processing.

Reboil to the second fractionation column is also provided by three liquid streams (264, 268, 272) drawn from trays part way up the second fractionation column (216), fed to the primary heat exchanger (204) where they are partially vaporised, and then fed back to the second fractionation column (216) as partially vaporised streams (266, 270, 274). It will be appreciated that, while in this embodiment reboil is provided by both the heated bottoms stream (280) and reboil streams (264, 268, 272), reboil could be provided by only one of these systems, or by an alternative system.

In the embodiment shown in Figure 3, a high-pressure gaseous feed (302) at a pressure of 7.0 MPa is cooled and partially condensed in the primary heat exchanger (304) to produce a first high-pressure partially condensed stream (306). The first high-pressure partially condensed stream (306) is fed to the upper portion of a first fractionation column (308) at a pressure of 7.0 MPa. A first liquid stream (310) higher in heavier hydrocarbons and a first gaseous stream (314) lower in heavier hydrocarbons are withdrawn from the first fractionation column (308). The first liquid stream (310) is expanded across a valve (312) to produce a first expanded stream (320), which may also be partially condensed. The first expanded stream (320) is fed to a lower part of a wash column (324).

The first gaseous stream (314) is work expanded in a turbo expander (316) to form an expanded partially condensed stream (318), which is fed to a higher part of the wash column (324) than the first expanded stream. A liquid stream (390) is withdrawn from a tray part way up the first fractionation column (308) and fed to the primary heat exchanger (304), where it is partially vaporised and fed back to the first fractionation column (308) as a partially condensed stream (392) in order to provide reboil. Refrigeration for cooling the high-pressure gaseous feed (302) or to any other part of the process may be supplemented by mechanical refrigeration. In this embodiment, a cold liquid propane refrigerant stream (394) is evaporated in the primary heat exchanger (304) to a produce refrigerant vapour stream (396). A wash column heavy stream (326) is withdrawn from the bottom of the wash column (324). The wash column heavy stream is expanded across a valve (328) and is heated in a secondary heat exchanger (332), and in the primary heat exchanger (304) before being fed to a second fractionation column (338). A wash column lights stream (364) is withdrawn from the top of the wash column (324). The wash column lights stream (364) is heated in the secondary heat exchanger (332), and in the primary heat exchanger (304) before being combined with a compressed lights stream (378) to give a combined lights stream (380). The combined lights stream (380) is compressed in a compressor (382) and cooled in a cooler (386) to give a gas product stream (388). The compressor after cooling is typically against ambient air or cooling water. A separated lights stream (348) is withdrawn from the top of the second fractionation column (338). The separated lights stream (348) is cooled in the secondary heat exchanger (332) and fed to a separator (352), from which a second separated lights stream (370) and a separated heavy stream (354) are withdrawn. The second separated lights stream (370) is warmed in the secondary heat exchanger (332) and the primary heat exchanger (304), then compressed in a first stage compressor (376) and combined with the heated wash column lights stream (368) to produce the combined lights stream (380). The separated heavy stream (354) is split and a first portion is pumped (356) to provide a reflux stream (358) to the top of the second fractionation column (338). A second portion of the separated heavy stream (354) is pumped (359) and subcooled in the secondary heat exchanger (332) to provide a subcooled reflux stream (362) to the top of the wash column (324).

A bottoms stream (340) comprising the heavier hydrocarbon fraction (C₃+) is drawn from the bottom of the second fractionation column (338). The bottoms stream (340) is heated in a heater (342) and a portion of the heated bottoms stream (346) is fed to a lower part of the second fractionation column (338) to provide reboil. A liquid product stream (344), comprising the remainder of the heated bottoms stream, is removed for further processing.

Figure 4 shows an embodiment arranged substantially as for Figure 3, with the exception that the first expanded stream (320) is fed to a second separator (400) to produce a light intermediate stream (402) and a heavy intermediate stream (404). The light intermediate stream (402) and heavy intermediate stream (404) are cooled in the primary heat exchanger (304) and the secondary heat exchanger (332). The cooled light intermediate stream (410) is fed to a lower part of the wash column than the expanded partially condensed stream (318). The cooled heavy intermediate stream (412) is combined with the expanded wash column heavy stream to produce a combined heavy stream (430).

Operation of the system shown in Figure 2 is further illustrated by the Material Balance data in Table 1. Table 3 shows Material Balance data for operation of the system shown in Figure 3 and Table 4 shows Material Balance data for operation of the system shown in Figure 4. Table 2 shows Material Balance data for operation of the prior art system shown in Figure 1 and Table 5 shows Material Balance data for operation of the prior art system shown in Figure 5.

The data in Tables 1 and 2 shows that the embodiment of the process of the present invention shown in Figure 2 has a total power input of 12,490 kW, for an ethane recovery of 95 %, as compared to 13,318 kW for the prior art system shown in Figure 1.

This represents a power saving of 828 kW (6.2 %), which may be largely attributed to the operation of the first fractionation column at high-pressure and the resultant ability to route a larger proportion of the high-pressure feed to work expansion, leading to increased energy recovery. For example, Table 2 shows that in the prior art system of Figure 1 , only 44 % of the mass flow of the high-pressure feed is routed to the work expander inlet. Conversely, in the system of the present invention, as shown in the embodiment of Figure 2, 75 % of the mass flow of the high-pressure feed is routed to the work expander inlet. Similarly, the data in Tables 3, 4 and 5 shows that the embodiments of the process of the present invention shown in Figures 3 and 4 have respective total power inputs of 8,837 kW and 8,671 kW, for a propane recovery of 99.6%, as compared to 1 1 ,492 kW, for a propane recovery of 96.7%, for the system shown in Figure 5. This represents a power saving of 2,655 kW (23.1 %) and 2,821 kW (24.5%) , which may be at least partially attributed to the operation of the first fractionation column at high-pressure and the resultant ability to route a larger proportion of the high-pressure feed to work expansion, leading to increased energy recovery. For example, Table 5 shows that in the system of Figure 5, only 78 % of the mass flow of the high-pressure feed is routed to the work expander inlet. Conversely, in the system of the present invention, as shown in the embodiments of Figures 3 and 4, 81 % of the mass flow of the high-pressure feed is routed to the work expander inlet.

Claims

1. A process for the separation of a heavier hydrocarbon fraction from a high- pressure gaseous feed comprising a mixture of hydrocarbons, which process comprises:

(e) recovering a separated lights stream lower in heavier hydrocarbons from said second fractionation column; (f) recovering said heavier hydrocarbon fraction as a bottoms stream from said second fractionation column.

2. The process of Claim 1 , wherein the first high-pressure partially condensed stream is fed to the first fractionation column at a pressure of no more than 7.5 MPa.

3. The process of Claim 1 or Claim 2, wherein the first high-pressure partially condensed stream is fed to the first fractionation column at a pressure of at least 6.5

MPa.

4. The process of any one of the preceding claims, wherein the first high-pressure partially condensed stream is fed to the first fractionation column at a pressure of from 6.75 MPa to 7.25 MPa.

5. The process of any one of the preceding claims, wherein the first high-pressure partially condensed stream in part (a) is fed directly to the first fractionation column.

6. The process of any one of the preceding claims, wherein cooling of the high- pressure gaseous feed in part (a) is provided, at least in part, by heat exchange with at least a portion the first expanded stream in part (c).

7. The process of any one of the preceding claims, wherein part (c) comprises expanding at least a substantial portion of said first liquid stream higher in heavier hydrocarbons to produce the first expanded stream.

8. The process of any one of the preceding claims, wherein part (c) comprises feeding at least a substantial portion of the first expanded stream to the second fractionation column.

9. The process of any one of the preceding claims, wherein part (d) comprises recovering process energy by work expanding at least a substantial portion of the first gaseous stream lower in heavier hydrocarbons to produce the expanded partially condensed stream.

10. The process of any one of the preceding claims, wherein part (d) comprises feeding at least a substantial portion of the expanded partially condensed stream to the second fractionation column.

1 1. The process of any one of the preceding claims, wherein at least a portion of the expanded partially condensed stream in part (d) is fed directly to the second fractionation column.

12. The process of any one of the preceding claims, wherein at least a portion of the first expanded stream in part (c) is fed directly to the second fractionation column.

13. The process of any one of the preceding claims, wherein at least a portion of the first expanded stream in part (c) is used to cool the high-pressure gaseous feed in heat exchange and then fed directly to the second fractionation column.

14. The process of any one of the preceding claims, wherein reboil to the first fractionation column is provided, at least in part, by heat exchange with the high- pressure gaseous feed.

15. The process of any one of the preceding claims, wherein the separated lights stream is compressed to produce a high-pressure lights stream.

16. The process of Claim 15, wherein energy for the compression of the separated lights stream is provided, at least in part, by work expansion of the first gaseous stream in part (d).

17. The process of any one of the preceding claims, wherein reflux to the second fractionation column is provided by cooling, subcooling and expanding a recycle stream, the recycle stream comprising at least a portion of the separated lights stream, and feeding the subcooled and expanded recycle stream into the top of the second fractionation column.

18. The process of Claim 17, wherein cooling and/or subcooling of the recycle stream is provided, at least in part, by heat exchange with the separated lights stream.

19. The process of any one of the preceding claims, wherein cooling of the high- pressure gaseous feed is provided, at least in part, by heat exchange with the separated lights stream.

20. The process of any one of the preceding claims, wherein reboil to the second fractionation column is provided, at least in part, by heat exchange with the high- pressure gaseous feed.

21. The process of any one of the preceding claims, wherein reboil to the second fractionation column is provided, at least in part, by external heating.

22. The process of any one of the preceding claims, wherein reboil to the second fractionation column is provided, at least in part, by heating the bottoms stream in part (e) to produce a heated bottoms stream, and feeding at least a portion of said heated bottoms stream to a lower part of the second fractionation column.

23. The process of any one of the preceding claims, wherein cooling is provided, at least in part, by mechanical refrigeration.

24. The process of any of the preceding claims, further comprising feeding at least a portion of the expanded partially condensed stream to a wash column and recovering from the wash column a wash column heavy stream higher in heavier hydrocarbons and a wash column lights stream lower in heavier hydrocarbons, and feeding at least a portion of the wash column heavy stream to the second fractionation column.

25. The process of Claim 24 where not dependent on Claim 10, wherein the process comprises feeding at least a substantial portion of the expanded partially condensed stream to the wash column.

26. The process of Claim 24 or Claim 25, wherein the process comprises feeding at least a portion of the first expanded stream to the wash column, preferably at a lower position than the expanded partially condensed stream is fed to the wash column.

27. The process of any one of Claims 24 to 26, comprising feeding at least a substantial portion of the wash column heavy stream to the second fractionation column.

28. The process of any one of Claims 24 to 27, wherein at least a portion of the wash column heavy stream is expanded before being fed to the second fractionation column.

29. The process of Claim 28, wherein the expanded wash column heavy stream is heated before being fed to the second fractionation column.

30. The process of Claim 29, wherein cooling of the high-pressure gaseous feed in part (a) is provided, at least in part, by heat exchange with the expanded wash column heavy stream.

31. The process of any one of Claims 24 to 30, wherein cooling of the high-pressure gaseous feed in part (a) is provided, at least in part, by heat exchange with the wash column lights stream.

32. The process of any one of Claims 24 to 31 , wherein at least a portion of the separated lights stream is cooled to produce a partially condensed separated lights stream which is fed to a separator to produce a second separated lights stream and a separated heavy stream, wherein at least a portion of the separated heavy stream is fed to the an upper part of the second fractionation column to provide reflux to the second fractionation column.

33. The process of Claim 32, wherein cooling of the separated lights stream is provided, at least in part, by heat exchange with the wash column lights stream and/or the wash column heavy stream and/or the second separated lights stream.

34. The process of Claim 32 or Claim 33, wherein at least a portion of the separated heavy stream is subcooled and fed to an upper part of the wash column to provide reflux to the wash column.

35. The process of Claim 34, wherein the subcooling of the separated heavy stream is provided, at least in part, by heat exchange with the wash column lights stream and/or the wash column heavy stream and/or the second separated lights stream.

36. The process of any one of Claims 24 to 35, wherein cooling of the high-pressure gaseous feed in part (a) is provided, at least in part, by heat exchange with the second separated lights stream.

37. The process of any one of Claims 32 to 36, wherein at least a portion of the wash column lights stream is combined with the second separated lights stream and compressed to produce a high pressure lights stream.

38. The process of any one of Claims 24 to 37, wherein reflux to the wash column is provided by cooling, subcooling and expanding a recycle stream, the recycle stream comprising at least a portion of the separated lights stream and/or the wash column lights stream, and feeding the subcooled and expanded recycle stream into an upper part of the wash column.

39. The process of any one of Claims 24 to 38, wherein at least a portion of the first expanded stream is combined with the wash column heavy stream before being fed to the second fractionation column.

40. The process of any one of Claims 24 to 39, wherein at least a portion of the first expanded stream is fed to a second separator to produce a light intermediate stream and a heavy intermediate stream, wherein the light intermediate stream is fed to the wash column and the heavy intermediate stream is combined with the wash column heavy stream and/or fed to the second fractionation column.

41. Apparatus for the separation of a heavier hydrocarbon fraction from a high- pressure gaseous feed comprising a mixture of hydrocarbons, which apparatus comprises;

(a) means for cooling the high-pressure gaseous feed to produce a first high- pressure condensed stream; (b) a first fractionation column and means for feeding the first high-pressure partially condensed stream directly thereto at a pressure greater than 6.0 MPa, wherein the first fractionation column comprises means for providing reboil;

(d) a second fractionation column;

42. The apparatus of Claim 41 , wherein the second expander is a turbo expander.

43. The apparatus of Claim 41 or 42, additionally comprising means for cooling the high-pressure gaseous feed in heat exchange with at least a portion of the first expanded stream in part (e).

44. The apparatus of Claim 41 to 43, wherein the means for feeding at least a portion of said first expanded stream to the second fractionation column in part (e) comprises means for feeding at least a portion of said first expanded stream directly to the second fractionation column.

45. The apparatus of any one of Claims 41 to 44, wherein the first expander in part (e) is configured to expand at least a substantial portion of the first liquid stream higher in heavier hydrocarbons to produce a first expanded stream.

46. The apparatus of any one of Claims 41 to 45, wherein the second expander in part (f) is configured recover process energy by work expanding at least a substantial portion of the first gaseous stream lower in heavier hydrocarbons to produce an expanded partially condensed stream.

47. The apparatus of any one of Claims 41 to 46, wherein the means for providing reboil to the first fractionation column comprises means for providing reboil by heat exchange with the high-pressure gaseous feed.

48. The apparatus of any one of Claims 41 to 47, additionally comprising at least one compressor configured to compress the separated lights stream to produce a high pressure lights stream.

49. The apparatus of Claim 48, wherein energy for the compression of the separated lights stream is provided, at least in part, by work expansion of the first gaseous stream in part (f).

50. The apparatus of Claim 48 or Claim 49, additionally comprising means for cooling the high pressure lights stream to produce a cooled high pressure lights stream, a third expander configured to expand at least a portion of said cooled high pressure lights stream to produce an at least partially condensed lights stream, and means for feeding said at least partially condensed lights stream to an upper part of the second fractionation column.

51. The apparatus of Claim 50, wherein the means for cooling the high pressure lights stream comprises means for cooling the high pressure lights stream in heat exchange with the separated lights stream.

52. The apparatus of any one of Claims 41 to 51 , wherein the means for cooling the high-pressure gaseous feed in part (a) comprises, at least in part, means for cooling the high-pressure gaseous feed in heat exchange with the separated lights stream.

53. The apparatus of any one of Claims 41 to 52, additionally comprising means for heating one or more reboil streams from the second fractionation column in heat exchange with the high-pressure gaseous feed.

54. The apparatus of any one of Claims 41 to 53, additionally comprising a reboiler attached to the second fractionation column wherein the reboiler makes use of external heating.

55. The apparatus of any one of Claims 41 to 54, additionally comprising means for heating the bottoms stream in part (h) to produce a heated bottoms stream, and means for feeding at least a portion of said heated bottoms stream to a lower part of the second fractionation column.

56. The apparatus of any one of Claims 41 to 55, wherein means for cooling comprises a mechanical refrigeration system.

57. The apparatus of any one of Claims 44 to 56, further comprising:

a wash column and means for feeding at least a portion of the expanded partially condensed stream to the wash column;

means for recovering from the wash column a wash column heavy stream higher in heavier hydrocarbons and a wash column lights stream lower in heavier hydrocarbons; and

means for feeding at least a portion of the wash column heavy stream to the second fractionation column.

58. The apparatus of Claim 57, wherein the means for feeding at least a portion of the expanded partially condensed stream to the wash column are configured to feed at least a substantial portion of the expanded partially condensed stream to the wash column.

59. The apparatus of Claim 57 or Claim 58, comprising means for feeding at least a portion of the first expanded stream to the wash column, preferably means for feeding at least a portion of the first expanded stream to the wash column at a lower position than the expanded partially condensed stream is fed to the wash column.

60. The apparatus of any one of Claims 57 to 59, wherein the means for feeding at least a portion of the wash column heavy stream to the second fractionation column are configured to feed at least a substantial portion of the wash column heavy stream to the second fractionation column.

61. The apparatus of any one of Claims 57 to 60, comprising a fourth expander configured to expand at least a portion of the wash column heavy stream before the wash column heavy stream is fed to the second fractionation column.

62. The apparatus of Claim 61 , comprising means for heating the expanded wash column heavy stream before the wash column heavy stream is fed to the second fractionation column.

63. The apparatus of Claim 62, wherein the means for cooling the high-pressure gaseous feed in part (a) comprises, at least in part, means for cooling the high-pressure gaseous feed in heat exchange with the expanded wash column heavy stream.

64. The apparatus of any one of Claims 57 to 63, wherein the means for cooling the high-pressure gaseous feed in part (a) comprises, at least in part, means for cooling the high-pressure gaseous feed in heat exchange with the wash column lights stream.

65. The apparatus of any one of Claims 57 to 64, comprising means for cooling at least a portion of the separated lights stream to produce a partially condensed separated lights stream;

means for feeding the partially condensed separated lights stream to a separator to produce a second separated lights stream and a separated heavy stream; and

means for feeding at least a portion of the separated heavy stream to an upper part of of the second fractionation column to provide reflux to the second fractionation column.

66. The apparatus of Claim 65, wherein cooling of the separated lights stream is provided, at least in part, by heat exchange with the wash column lights stream and/or the wash column heavy stream and/or the second separated lights stream.

67. The apparatus of Claim 65 or Claim 66, comprising means for cooling at least a portion of the separated heavy stream and means for feeding the cooled stream to an upper part of the wash column to provide reflux to the wash column.

68. The apparatus of Claim 67, wherein the means for cooling at least a portion of the separated heavy stream comprises, at least in part, means for cooling the separated heavy stream in heat exchange with the wash column lights stream and/or the wash column heavy stream and/or the second separated lights stream.

69. The apparatus of any one of Claims 57 to 68, wherein the means for cooling the high-pressure gaseous feed in part (a) comprises, at least in part, means for cooling the high-pressure gaseous feed in heat exchange with the second separated lights stream.

70. The apparatus of any one of Claims 65 to 69, comprising means for combining at least a portion of the wash column lights stream with the second separated lights stream and a compressor configured to compress the combined stream to produce a high pressure lights stream.

71. The apparatus of any one of Claims 57 to 70, comprising means for cooling the high pressure lights stream to produce a cooled high pressure lights stream, a third expander configured to expand at least a portion of said cooled high pressure lights stream to produce an at least partially condensed lights stream, and means for feeding said at least partially condensed lights stream to an upper part of the wash column.

72. The apparatus of any one of Claims 57 to 71 , comprising means for combining at least a portion of the first expanded stream with the wash column heavy stream before feeding the combined stream to the second fractionation column.

73. The apparatus of any one of Claims 57 to 72, comprising means for feeding at least a portion of the first expanded stream to a second separator;

means for withdrawing a light intermediate stream and a heavy intermediate stream from said second separator; and

means for feeding the light intermediate stream to the wash column and means for combining the heavy intermediate stream with the wash column heavy stream.

74. Use of reboil to increase the proportion of a heavier hydrocarbon fraction exiting a fractionation column in the gaseous phase in a process for the separation of a heavier hydrocarbon fraction from a mixture of hydrocarbons.

75. A process for the separation of a heavier hydrocarbon fraction from a high- pressure gaseous feed comprising a mixture of hydrocarbons, which process comprises:

(d-ii) recovering from the wash column a wash column heavy stream higher in heavier hydrocarbons and a wash column lights stream lower in heavier hydrocarbons and feeding at least a portion of the wash column heavy stream to a second fractionation column; (e) recovering a separated lights stream lower in heavier hydrocarbons from said second fractionation column;

76. The process of Claim 75, wherein the process is as further defined in any one of Claims 2 to 23 or 25 to 40.

77. Apparatus for the separation of a heavier hydrocarbon fraction from a high- pressure gaseous feed comprising a mixture of hydrocarbons, which apparatus comprises;

(b) a first fractionation column and means for feeding the first high-pressure partially condensed stream directly thereto at a pressure greater than 6.0 MPa, wherein the first fractionation column comprises means for providing reboil; (c) means for recovering from the first fractionation column a first liquid stream higher in heavier hydrocarbons and a first gaseous stream lower in heavier hydrocarbons;

(d) a second fractionation column and a wash column;

78. The apparatus of Claim 77, wherein the apparatus is as further defined in any one of Claims 42 to 56 or 58 to 73.