GB2556878A

GB2556878A - Hydrocarbon separation process and apparatus

Info

Publication number: GB2556878A
Application number: GB1619578.6A
Authority: GB
Inventors: Ronald Tomlinson Terence; Joseph Finn Adrian; Richard Loftus Zak
Original assignee: Costain Oil Gas and Process Ltd
Current assignee: Costain Oil Gas and Process Ltd
Priority date: 2016-11-18
Filing date: 2016-11-18
Publication date: 2018-06-13
Also published as: GB2571676A; WO2018091920A1; GB201908738D0; GB201619578D0

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. The process comprises (i) cooling the high-pressure gaseous feed to produce a first high-pressure partially condensed stream, (ii) feeding that to a first fractionation column 8 at a pressure greater than 0.6 MPa and recovering a first liquid stream higher in heavier hydrocarbons and a first gaseous stream lower in heavier hydrocarbons, where reboil is provided to the first fractionation column, (iii) 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 it to a second fractionation column 16, (iv) 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 it to the second fractionation column, (v) recovering a separated lights stream lower in heavier hydrocarbons from the second fractionation column 16, and (vi) recovering the heavier hydrocarbon fraction as a bottoms stream from the second fractionation column 16.

Description

(54) Title of the Invention: Hydrocarbon separation process and apparatus Abstract Title: Hydrocarbon separation process and apparatus (57) 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 comprises (i) cooling the high-pressure gaseous feed to produce a first high-pressure partially condensed stream, (ii) feeding that to a first fractionation column 8 at a pressure greater than 0.6 MPa and recovering a first liquid stream higher in heavier hydrocarbons and a first gaseous stream lower in heavier hydrocarbons, where reboil is provided to the first fractionation column, (iii) 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 it to a second fractionation column 16, (iv) 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 it to the second fractionation column, (v) recovering a separated lights stream lower in heavier hydrocarbons from the second fractionation column 16, and (vi) recovering the heavier hydrocarbon fraction as a bottoms stream from the second fractionation column 16.

At least one drawing originally filed was informal and the print reproduced here is taken from a later filed formal copy.

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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 1,114,808 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

-2through 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).

As demonstrated by the above process, 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 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

-3separation 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).

-4Therefore, 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.

-5As 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 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.

-6It 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

-7fractionation 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

-8both 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 highpressure lights stream. Preferably, energy for the compression of the separated lights stream is provided, at least in part, by work expansion ofthe 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 ofthe 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

-9least 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 highpressure gaseous feed and optionally the recycle stream are passed.

-10According 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 highpressure 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.

-11 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.

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.

In the embodiment shown in Figure 2, a high-pressure gaseous feed (2) at a pressure of 7.0 MPa is cooled and partially condensed in the primary heat exchanger (4) to produce

-12 a first high-pressure partially condensed stream (6). The first high-pressure partially condensed stream (6) is fed to the upper portion of a first fractionation column (8) at a pressure of 7.0 MPa. A first liquid stream (18) higher in heavier hydrocarbons and a first gaseous stream (10) lower in heavier hydrocarbons are withdrawn from the first fractionation column (8).

The first liquid stream (18) is expanded across a valve (20) to produce a first expanded stream, which may also be partially condensed. A portion of the first expanded stream (22) may be fed directly to a second fractionation column (16). A portion (24) may also be fed to the primary heat exchanger (4) where this stream is partially vaporised to provide cooling to the high-pressure gaseous feed, producing partially vaporised stream (26) which is then fed to the second fractionation column (16). It will be appreciated that the split between streams 22 and 24 may include any suitable variation in flow ratios, including total flow to either stream.

The first gaseous stream (10) is work expanded in a turbo expander (12) to form an expanded partially condensed stream (14), which is fed to an upper part of the second fractionation column (16).

A liquid stream (84) is withdrawn from a tray part way up the first fractionation column (8) and fed to the primary heat exchanger (4), where it is partially vaporised and fed back to the first fractionation column (8) as a partially condensed stream (86) in order to provide reboil.

Refrigeration for cooling the high-pressure gaseous feed (2) or to any other part of the process may be supplemented by mechanical refrigeration. In this embodiment, a cold liquid propane refrigerant stream (88) is evaporated in the primary heat exchanger (4) to a produce refrigerant vapour stream (90).

A separated lights stream (30) is withdrawn from the top of the second fractionation column. The separated lights stream is heated in a secondary heat exchanger (20) and in the primary heat exchanger (4), where cooling is provided to the high-pressure

-13gaseous feed. The warmed lights stream (34) is compressed in an expander brake (36) and cooled to give a gas stream (42), which is compressed in a compressor (44) and cooled to give a gas product stream (54). The compressor after cooling is typically against ambient air or cooling water.

A recycle stream (52) is split from the cooled and compressed lights stream (50) and fed to the primary heat exchanger (4) where it is cooled and partially condensed. This cooled and partially condensed recycle stream (56) is then fed to the secondary heat exchanger (20) where the stream is subcooled and fully condensed. The subcooled and condensed recycle stream (58) is then expanded across a valve (60) to the same pressure as the second fractionation column (16) and the subcooled and expanded recycle stream (62) is fed to the top of the second fractionation column (16) as reflux.

A bottoms stream (76) comprising the heavier hydrocarbon fraction (C₂+) is drawn from the bottom of the second fractionation column (16). The bottoms stream (76) is heated in a heater (78) and a portion of the heated bottoms stream (80) is fed to a lower part of the second fractionation column (16) to provide reboil. A liquid product stream (82), 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 (64, 68, 72) drawn from trays part way up the second fractionation column (16), fed to the primary heat exchanger (4) where they are partially vaporised, and then fed back to the second fractionation column (16) as partially vaporised streams (66, 70, 74). It will be appreciated that, while in this embodiment reboil is provided by both the heated bottoms stream (80) and reboil streams (64, 68, 72), reboil could be provided by only one of these systems, or by an alternative system.

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

-14The 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 10 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.

-15Table 1

00 00	Propane Refrigerant Return (HP/LP Stage)	o O _o o O —-k _l m \| 1 1 1 1 1 1 1 1 1 1 1 2 ^? - s
O LD o q, τ-i O pi Ln 1 1 1 1 1 1 1 1 1 1 1 Ο 1 Γ\Ι O v-5
ld 00	Propane Refrigerant In (HP/LP Stage)	oo — r*** _t~j t-η O _k T—1 1 1 1 1 1 1 1 1 1 1 1 1 -1 S o
Ή ς£> 00 Q p-1 ΟΊ υη ............ on i r\i o o m
Γ\Ι 00	Liquid Product	Ο Γ\1 O ' (Q f—) pj & omo^LD^LDLDom^c ό ^m 5 ¹⁰
Ln	Residue Gas	§ us S p § ° 2 § -^goooooooojr -Η ΓΜ
Γ\Ι ld	De- methaniser Reflux	o ° q τ^-1 O 00 r- o cn i_n ld ^unrfi^OOOOOOOOLj· m o LD LC O i
00 Ln	Subcooled Recycle	o O O - ri o 00 r- o « S S LD O LD LC O rH
ΓΝ m	Recycle Gas	o © O LD Ο O0 T- _o c σι oo r-.OLn________a o m en ld ^ίηΓη^{οααοαοαα}υ- LD O LD LC Ή τ—1
m	LP Residue Gas	S (η ?! S ⁰⁰ § 7- K §S33 mgooooooooo^ -H _m
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Claims

1. A process for the separation of a heavier hydrocarbon fraction from a highpressure 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;

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.

-184. 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 highpressure 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.

11. 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.

-1914. 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 highpressure 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 highpressure 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 highpressure 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.

-2024. Apparatus for the separation of a heavier hydrocarbon fraction from a highpressure gaseous feed comprising a mixture of hydrocarbons, which apparatus comprises;

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

(d) a second fractionation column;

25. The apparatus of Claim 24, wherein the second expander is a turbo expander.

26. The apparatus of Claim 24 or 25, 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).

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27. The apparatus of Claim 24 to 26, 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.

28. The apparatus of any one of Claims 24 to 27, 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.

29. The apparatus of any one of Claims 24 to 28, 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.

30. The apparatus of any one of Claims 24 to 29, 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.

31. The apparatus of any one of Claims 24 to 30, additionally comprising at least one compressor configured to compress the separated lights stream to produce a high pressure lights stream.

32. The apparatus of Claim 31, 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).

33. The apparatus of Claim 31 or Claim 32, 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.

34. The apparatus of Claim 33, 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.

-2235. The apparatus of any one of Claims 24 to 34, 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.

36. The apparatus of any one of Claims 24 to 35, additionally comprising means for

5 heating one or more reboil streams from the second fractionation column in heat exchange with the high-pressure gaseous feed.

37. The apparatus of any one of Claims 24 to 36, additionally comprising a reboiler attached to the second fractionation column wherein the reboiler makes use of external heating.

10

38. The apparatus of any one of Claims 24 to 37, 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.

39. The apparatus of any one of Claims 24 to 38, wherein means for cooling

15 comprises a mechanical refrigeration system.

40. 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.

Intellectual

Property

Office

Application No: GB1619578.6 Examiner: Mr Martin Price