WO2010040735A2

WO2010040735A2 - Methods of treating a hydrocarbon stream and apparatus therefor

Info

Publication number: WO2010040735A2
Application number: PCT/EP2009/062954
Authority: WO
Inventors: Adekunle Adeyelure; Dirk Willem Van Der Mast
Original assignee: Shell Internationale Research Maatschappij B.V.
Priority date: 2008-10-08
Filing date: 2009-10-06
Publication date: 2010-04-15
Also published as: WO2010040735A3

Abstract

A hydrocarbon stream (710) is separated in a cyclonic expansion and separation device (100) into a primary methane enriched component stream (110) and one or more methane depleted streams (120, 130). At least one of these methane depleted streams (120, 130) is separated in a first gas/liquid separator (200) to provide an overhead first methane rich stream (210) and a first methane lean stream (220). The overhead first methane rich stream (210) is expanded in a first expansion device (300) to provide an expanded first methane rich stream (310), which is fed to a separating column (400) at a first feeding level. The expanded first methane rich stream (310) is separated in a separating column (400) to provide a second methane enriched component stream (410) and a second methane depleted component stream (420).

Description

METHODS OF TREATING A HYDROCARBON STREAM AND APPARATUS

THEREFOR

The present invention provides a method and apparatus for treating a hydrocarbon stream, to provide two or more hydrocarbon component streams .

A natural gas stream is a common example of a hydrocarbon stream to be treated, in which case the two hydrocarbon component streams may be formed of a methane- rich stream suitable for liquefaction into Liquefied Natural Gas (LNG) and a methane-lean stream suitable for the preparation of Liquefied Petroleum Gas (LPG) . Natural gas is a useful fuel source, as well as being a source of various hydrocarbon compounds. It is often desirable to liquefy natural gas in a liquefied natural gas (LNG) plant at or near the source of a natural gas stream for a number of reasons. As an example, natural gas can be stored and transported over long distances more readily as a liquid than in gaseous form because it occupies a smaller volume and does not need to be stored at high pressure.

Usually, natural gas, comprising predominantly methane, enters an LNG plant at elevated pressures and is pre-treated to produce a purified feed stream suitable for liquefaction at cryogenic temperatures. The purified gas is processed through a plurality of cooling stages using heat exchangers to progressively reduce its temperature until liquefaction is achieved. The liquid natural gas is then further cooled and expanded to final atmospheric pressure suitable for storage and transportation . In addition to methane, natural gas usually includes some heavier hydrocarbons and impurities, including but not limited to carbon dioxide, sulphur, hydrogen sulphide and other sulphur compounds, nitrogen, helium, water, other non-hydrocarbon acid gases, ethane, propane, butanes, C₅+ hydrocarbons and aromatic hydrocarbons. These and any other common or known heavier hydrocarbons and impurities either prevent or hinder the usual known methods of liquefying the methane, especially the most efficient methods of liquefying methane. Most known or proposed methods of liquefying hydrocarbons, especially liquefying natural gas, are based on reducing as far as possible the levels of at least most of the heavier hydrocarbons and impurities prior to the liquefying process.

Hydrocarbons heavier than methane and usually ethane are typically condensed and recovered as natural gas liquids (NGLs) from a natural gas stream. The methane is usually separated from the NGLs in a high pressure scrub column, and the NGLs are then subsequently fractionated in a number of dedicated distillation columns to yield valuable hydrocarbon products, either as products steams per se or for use in liquefaction, for example as a component of a refrigerant. WO 2006/089948 discloses a method and system for cooling a natural gas stream and separating the cooled stream into various fractions. A cyclonic expansion and separation device is used to separate a methane enriched fraction of natural gas into a methane rich substantially gaseous fluid fraction and a methane depleted substantially liquid fluid fraction. The methane rich substantially gaseous fluid fraction is passed to a compressor for gas export, while the methane depleted substantially liquid fluid fraction comprising the heavier hydrocarbons and the remaining methane is passed directly to a fractionation column for separation into a methane rich substantially gaseous fraction and a methane lean substantially liquid fraction.

Although the method and system of WO 2006/089948 can achieve the separation of export gas from the natural gas stream to provide a methane lean substantially fluid fraction, such as LPG, there is a need to improve the extraction process utilising the cyclonic expansion and separation device. For instance, higher specification LNG is required by law in certain countries, such that the extraction of certain C2+ hydrocarbons should be improved. It is an object of the present invention to address the above problem by providing a method of and apparatus for treating a hydrocarbon stream to provide two or more component streams, such as a primary methane enriched component stream, and a second methane depleted component stream. If the hydrocarbon stream is a natural gas stream, the primary methane enriched component stream can be suitable for liquefaction into LNG and the second methane depleted stream can be a source of LPG.

In a first aspect, the present invention provides a method of treating a hydrocarbon stream, such as a natural gas stream, to provide two or more hydrocarbon component streams, comprising at least the steps of:

(a) providing a hydrocarbon stream;

(b) separating the hydrocarbon stream in a cyclonic expansion and separation device into a primary methane enriched component stream and one or more methane depleted streams; - A -

(c) separating at least one of the one or more methane depleted streams in a first gas/liquid separator to provide an overhead first methane rich stream and a first methane lean stream; (d) expanding the overhead first methane rich stream in a first expansion device to provide an expanded first methane rich stream;

(e) feeding the expanded first methane rich stream to a separating column at a first feeding level; and (f) separating the expanded first methane rich stream in a separating column to provide a second methane enriched component stream and a second methane depleted component stream.

In a further aspect, the present invention provides an apparatus for treating a hydrocarbon stream, said apparatus comprising at least:

- a cyclonic expansion and separation device comprising a first inlet for a hydrocarbon stream and two or more outlets, said two or more outlets comprising a first outlet for a primary enriched methane component stream and a second outlet for a secondary methane depleted stream, said second outlet connected to the first inlet of a first gas/liquid separator;

- a first gas/liquid separator comprising at least a first inlet for the secondary methane depleted stream and a first outlet for a first methane rich stream, said first outlet connected to a first inlet of a first expansion device;

- a first expansion device comprising a first inlet for the first methane rich stream and a first outlet for an expanded first methane rich stream, the first outlet connected to the first inlet of a separating column; and - a separating column comprising a plurality of inlets and a plurality of outlets, said inlets comprising a first inlet for the expanded first methane rich gaseous stream and said outlets comprising a first outlet for a second methane enriched component stream and a second outlet for a second methane depleted component stream.

Embodiments and examples of the present invention will now be described by way of example only and with reference to the accompanying non-limited drawings in which:

Figure 1 is a diagrammatic scheme of a method of and apparatus for treating a hydrocarbon stream according to one embodiment;

Figure 2 is a diagrammatic scheme of a method of and apparatus for treating a hydrocarbon stream according to a second embodiment; and

Figure 3 is a diagrammatic scheme of a method of and apparatus for treating a hydrocarbon stream according to a third embodiment . For the purpose of this description, a single reference number will be assigned to a line as well as a stream carried in that line.

The present invention employs a cyclonic expansion and separation device in combination with a separating column, suitable as part of an NGL extraction line-up and process. One or more methane depleted streams from the cyclonic expansion and separation device are passed to a first gas/liquid separator to provide an overhead first methane rich stream from a first methane lean stream and a separate first methane lean stream. Separating the methane depleted streams provides an overhead first methane rich stream which improves separation of the hydrocarbon components in the separating column. Referring to the drawings, Figure 1 shows a method of and apparatus 1 for treating a hydrocarbon stream according to a first embodiment.

The hydrocarbon feed stream may be any suitable hydrocarbon stream such as, but not limited to, a hydrocarbon-containing gas stream able to be cooled. One example is a natural gas stream obtained from a natural gas or petroleum reservoir. As an alternative the natural gas stream may also be obtained from another source, also including a synthetic source such as a Fischer-Tropsch process .

Usually such a hydrocarbon feed stream is comprised substantially of methane. Preferably such a hydrocarbon feed stream comprises at least 50 mol% methane, more preferably at least 80 mol% methane. Although the method disclosed herein is applicable to various hydrocarbon streams, it is particularly suitable for natural gas streams to be subsequently liquefied. As the skilled person readily understands how to liquefy a hydrocarbon stream, this is not discussed herein in detail. Depending on the source, the hydrocarbon stream may contain one or more non-hydrocarbons such as H2O, N2, CO2, Hg, H2S and other sulfur compounds.

If desired, the hydrocarbon stream may be pre-treated before use, either as part of a hydrocarbon treatment process, or separately. This pre-treatment may comprise reduction and/or removal of non-hydrocarbons such as CO2 and H2S or other steps such as early cooling and pre- pressurizing . As these steps are well known to the person skilled in the art, their mechanisms are not further discussed here.

Thus, the term "hydrocarbon stream" as used herein also includes a composition prior to any treatment, such treatment including cleaning and/or dehydration, as well as any composition having been partly, substantially or wholly treated for the reduction and/or removal of one or more compounds or substances, including but not limited to sulfur, sulfur compounds, carbon dioxide and water. Preferably, a hydrocarbon stream to be used herein undergoes at least the minimum pre-treatment required to subsequently allow liquefaction of the hydrocarbon stream. Such a requirement for liquefying natural gas is known in the art.

A hydrocarbon stream commonly also contains varying amounts of hydrocarbons heavier than methane such as ethane, propane, butanes and pentanes, as well as some aromatic hydrocarbons. The composition varies depending upon the type and location of the hydrocarbon stream such as natural gas. Hydrocarbons heavier than butane generally need to be removed from natural gas to be liquefied for several reasons, such as having different freezing or liquefaction temperatures that may cause them to block parts of a methane liquefaction plant. In addition, the desired specification of the LNG may require the removal of or a reduction in the proportion of certain components. C2-C4 hydrocarbons can be extracted and used as a source of natural gas liquids (NGLs) such as LPG and/or refrigerant.

NGLs comprise: Liquefied Petroleum Gas (LPG), which predominantly comprises propane (C3) and butane (C4); and condensate, which predominantly comprises C5+ fractions. LPG is a high-value byproduct of LNG manufacture. Returning to Figure 1, a hydrocarbon feed stream 10 is provided. The hydrocarbon feed stream 10 is normally provided at ambient temperature, although this can be pre-cooled. The hydrocarbon feed stream 10 can be heat exchanged with one or more further streams by passing it through a first heat exchanger 500. The heat exchangers used herein can be of any type known in the art, such as plate and fin or shell and tube. Kettle heat exchangers are preferred. The one or more further streams which can cool the hydrocarbon feed stream 10 are discussed in greater detail below.

The first heat exchanger 500 cools the hydrocarbon feed stream to provide a cooled hydrocarbon stream 530, for example at a temperature below -25 ⁰C. Such cooling improves the subsequent separation into methane enriched and methane depleted component streams, enhancing the recovery of the second methane depleted component stream. In an optional embodiment not shown in Figure 1, the cooled hydrocarbon stream 530 can be further cooled in a chiller .

The cooled hydrocarbon stream 530 can then be passed to an inlet separation device 700, such as a gas/liquid separation device, where it is separated into a hydrocarbon stream 710 and a second methane lean stream 720, which can contain substantially all of any liquids present. The hydrocarbon stream 710 is then passed to an inlet 102 of a cyclonic expansion and separation device (CESD) 100.

The hydrocarbon stream 710 should be at high pressure, preferably at a pressure greater than 30 bar. Pressures around 90 bar are more preferred in order to reduce power consumption by requiring less re-compression of the methane enriched component stream product. At pressures around the lower end of this range, mechanical refrigeration may be employed to minimise the pressure loss and power requirement for compression. Consequently, the hydrocarbon stream 710, or the hydrocarbon feed stream 10 can be compressed to provide a stream under the appropriate pressure.

Cyclonic expansion and separation devices are known in the art, and are, for instance, described in

WO 2000/23757 and WO 2006/089948. Such devices provide a low temperature separation process with thermodynamics similar to a turboexpander, combining the process steps of expansion, cyclonic gas/liquid separation and recompression into a compact, tubular device with no moving parts. In contrast to a turboexpander, which transforms pressure to shaft power, the cyclonic expansion and separation device achieves a similar pressure drop by transforming pressure into kinetic energy.

The Twister™ Supersonic Separator (Twister B. V., Rijswijk, the Netherlands) is one example of a commercially available cyclonic expansion and separation device . CESDs are advantageous, particularly compared to turboexpanders, because they do not have any rotating parts, eliminating lubrication systems and maintenance programs, and can have overall availabilities in excess of 98%, with a near instant start-up. Returning to Figure 1, the CESD 100 comprises vanes in a vortex generator portion which impart a swirling motion to the hydrocarbon stream 710. The hydrocarbon stream 710 is then expanded to supersonic velocity, for instance using a laval nozzle, resulting in a reduction in temperature and pressure. If the temperature is reduced below the boiling point of a component, it will condense resulting in the formation of microscopic liquid droplets. These droplets may comprise the heavier hydrocarbons. The swirling motion of the gas creates centrifugal forces sufficient to move the microscopic droplets to the wall of the CESD 100. A CESD having an annular configuration with openings in the wall can provide the separation of the gas from the liquid component, the latter passing through the openings in the wall of the CESD into the annular space. The velocity of the gas and the liquid components can be reduced in a diffuser stage, thereby providing recompression to recover a portion, such as 65-80%, of the original pressure .

The CESD 100 produces a primary methane enriched component stream 110 at a first outlet 104 and a secondary methane depleted stream 120 at a second outlet 106.

The hydrocarbon stream preferably has a temperature below -25 ⁰C. At lower inlet temperatures the mid-CESD temperature will be lower, such that propane losses in the primary methane enriched component stream 110 decrease. If a higher specification product is required, the CESD inlet temperature should be less than -45 ⁰C, such as about -50 ⁰C. A portion of the required cooling can be achieved by heat exchanging the CESD outlet streams against the hydrocarbon feed stream 10. If necessary, this can be supplemented with a C3 refrigerant system to provide a -35 to -45 ⁰C inlet temperature. The use of a mixed refrigerant cooling system or an LNG source can lower the inlet temperature still further, for example to -50 ⁰C or below. The primary methane enriched component stream 110, is a gaseous stream, and can be passed to the first heat exchanger 500, where it is heated against one or more first auxiliary streams, to recover its cold and provide a heated methane enriched component stream 510. In the embodiment shown in Figure 1, the one or more first auxiliary streams can comprise the hydrocarbon feed stream 10, which is cooled by the primary methane enriched component stream 110 to provide the cooled hydrocarbon stream 530, and ultimately lower the temperature of the hydrocarbon stream 710 at the inlet 102 of the CESD 100.

The heated methane enriched component stream 510 can provide a major portion of the export gas. The heated methane enriched component stream 510 can be passed to a combiner 1400, which can be any device known in the art for combining one or more fluid streams, to provide a combined methane enriched component stream 1410. This combined stream 1410 can subsequently be cooled by first cooler 1700, such as an air or water cooler, and passed on as cooled methane enriched component stream 1710. The cooled methane enriched component stream 1710 can be sent for export as sales gas and/or further processing, such as liquefaction in a liquefaction unit to produce LNG. It is preferred to produce sales gas at a pressure of approximately 55 bara, such that if necessary, the heated methane enriched component stream 510 may be required to be compressed to an appropriate level prior to being passed to the combiner 1400.

The second outlet 106 of the CESD provides the secondary methane depleted stream 120. The secondary methane depleted stream 120, as well as comprising condensation droplets of the heavier hydrocarbons, will also contain slip-gas. The secondary methane depleted stream 120 is passed to an inlet 204 of a first gas/liquid separator 200. The first gas/liquid separator 200 provides an overhead first methane rich stream 210, which can be a gaseous stream, at a first outlet 204, and a first methane lean stream 220, which can be a liquid stream, at a second outlet 208.

The provision of the first gas/liquid separator 200 advantageously separates the secondary methane depleted stream 120 into at least two fractions, a preferably overhead, first methane rich stream 210 and a preferably bottoms, first methane lean stream 220 which may comprise heavier hydrocarbons. This separation step allows the methane rich fraction 210 to be passed to a separating column 400 at a different, preferably higher level from that of the methane lean heavier hydrocarbon fraction 220, improving the efficiency of the separation.

The overhead first methane rich stream 210 is passed to the inlet 302 of a first expansion device 300, such as a Joule-Thomson valve, to provide an expanded first methane rich stream 310 at the outlet 304 of the first expansion device 300.

The expanded first methane rich stream 310 is then fed to a separating column 400, such as a fractional distillation column, at a first inlet 402 having a first feeding level. The separating column 400 provides a second methane enriched component stream 410, preferably as an overhead stream, at a first outlet 416. A second methane depleted component stream 420 can also be provided, preferably as a bottoms stream.

The separating column 400 is preferably a deethaniser fractional distillation column. The separating column is preferably configured to minimise the loss of propane and heavier hydrocarbon components in the second methane enriched component stream 410 overhead, and to keep the methane and ethane in the bottoms stream to a minimum to provide a low vapour pressure. The separating column 400 may further comprise a reboiler unit 1800. The reboiler unit 1800 is fed by second methane depleted component stream 420, which exits the separation column at second outlet 418. The reboiler unit 1800 heats the second methane depleted component stream 420, a portion of which can be returned to the separating column 400 as a return methane depleted stream 1820. The remaining portion of the second methane depleted component stream 420 is removed from the reboiler 1800 as continuing second methane depleted component stream 1810. This stream can comprise propane and heavier hydrocarbon components ("C3+ hydrocarbons") . Continuing second methane depleted component stream 1810 can be provided for export or passed to a another unit, such as a de-butaniser column, for further treatment to provide a crude Liquefied Petroleum Gas (LPG) stream overhead and a C5+ component stream bottoms fraction, such as a stabilised condensate stream. The crude LPG stream can then be fractionated into appropriate commercial specification streams.

In order to provide extraction of the desired components from the hydrocarbon stream, a sharp distinction between the light components to become product gas and the heavy components to be extracted in the separating column 400 is desired. For instance, if the separating column 400 is a demethaniser column, then C2+ hydrocarbons should be extracted in the column to provide an overhead second methane enriched component stream 410 and second methane depleted component stream 420 comprising the C2+ hydrocarbons. Similarly, if the separating column 400 is a deethaniser column, then the C3+ hydrocarbons should be extracted and exit the column in the second methane depleted component stream 420. In order to provide extraction of the heavier hydrocarbon components, a lean liquid reflux should be created in the separation column 400 to absorb the lightest component which is to be extracted and removed from the separating column 400 in the second methane depleted component stream 420. Such a reflux can be created from the hydrocarbon stream 710. At least a part of this stream can be removed as a side-stream as first part hydrocarbon stream 730, and passed to a second heat exchanger 900 where it is cooled against one or more second auxiliary streams to provide a second cooled hydrocarbon stream 910. The heat exchange in the second heat exchanger 900 can be carried out against the second methane enriched component stream 410 to provide a heated second methane enriched component stream 920.

The second cooled hydrocarbon stream 910 can then be expanded in a fourth expansion device 1000, such as a Joule-Thomson valve, to provide an expanded hydrocarbon stream 1010. The expanded hydrocarbon stream 1010 can be passed to the separating column 400 at a sixth feeding level at or higher than the first feeding level of the expanded first methane rich stream 310, to provide a reflux stream.

The heated second methane enriched component stream 920 from the second heat exchanger 900 can be passed to the first heat exchanger 500 where its cold is extracted to cool the hydrocarbon feed stream 10. The heated second methane enriched component stream 920 leaves the second heat exchanger 900 as further heated second methane enriched component stream 540.

The further heated second methane enriched component stream 540 can be fed to a third gas/liquid separator 1500 to provide an overhead second methane enriched component stream 1510, which can be a gaseous stream and a second gas/liquid separator bottoms stream 1520, which can be a liquid stream. The overhead second methane enriched component stream 1510 can be fed to a first compressor 1600, where it is compressed to provide a compressed second methane enriched component stream 1610, at substantially the same pressure as the heated methane enriched component stream 510. The level of compression required will vary, for instance depending upon the pressure drop in the CESD 100. If expansion within the CESD 100 is deeper to provide greater extraction, the first compressor 1600 duty will be higher. The compressed second methane enriched component stream 1610, and the heated methane enriched component stream 510 can be combined in combiner 1400 to provide the combined methane enriched component stream 1410, for instance at a sales gas pressure of approximately 55 bara.

Returning to the inlet separation device 700, this provides a second methane lean stream 720, preferably as a bottoms stream, which can be a liquid stream. The second methane lean stream can be passed to a third expansion device 800, such as a Joule-Thomson valve, to provide an expanded second methane lean stream 810, which can be fed to the separating column 400 at a third feeding level, which is lower than the first feeding level of the expanded first methane rich stream 310.

One further stream is passed to separating column 400, obtained from the first methane lean stream 220 from the first gas/liquid separator 200. The first methane lean stream 220 is first expanded in a second expansion device 600 to match the pressure of the separating column 400 and provide an expanded first methane lean stream 610. The expanded first methane lean stream 610 can then be passed to the first heat exchanger 500 and the cold generated in the expansion step can be advantageously used to provide cooling to the hydrocarbon feed stream 10. The expanded first methane lean stream 610 leaves the first heat exchanger 500 as heated first methane lean stream 520. The heated first methane lean stream 520 can be passed to the separating column 400 at a second feeding level, which is lower than the first feeding level of the expanded first methane rich stream 310.

The heated first methane lean stream 520 comprises a heavier stream fraction at a higher temperature than the expanded first methane rich stream 310. By adding the heated first methane lean stream 520 at a lower feeding level than the first feeding level, a second source of heat is provided to the separating column 400, advantageously removing a portion of the reboiler duty.

Table 1 summarises one embodiment of the scheme of Figure 1 using a "lean" hydrocarbon feed stream 10, comprising 89.1 mol% methane, 4.4 mol% ethane, 2.6 mol% propane, 0.2 mol% i-butane, 0.8 mol% n-butane, 0.3 mol% i-pentane, 0.2 mol% n-pentane, 0.2 mol% n-hexane, 0.1 mol% n-heptane, 0.1 mol% n-octane and 2.0 mol% carbon dioxide. Table 1 provides vapour fraction, temperature and pressure data for a selection of the streams shown in Figure 1. Table 1 : Stream data for the scheme of Figure 1

Figure 2 discloses a second embodiment of the method and apparatus described herein. The scheme of Figure 2 is a modification of the scheme of Figure 1 in which the cyclonic expansion and separation device 100 provides a primary methane enriched component stream 110 and two, rather than one, methane depleted streams 120, 130 as secondary and tertiary streams. This is achieved by providing an additional expansion zone within the CESD, known as a "2-stage CESD". WO 2000/23757 discloses a CESD with multiple secondary component streams. Particular reference is made to Figure 2 and page 22, line 22 to page 23, line 7 of this document. The ternary methane depleted stream 130 is withdrawn from the CESD 100 after the first expansion zone, and is therefore similar in nature to the secondary methane depleted stream 120 of the embodiment of Figure 1.

One advantage of the method and apparatus 1 disclosed herein is that by providing a first expansion zone in the CESD to generate the ternary methane depleted stream 130 and a second expansion zone in the CESD to generate the secondary methane depleted stream 120, the methane enrichment of the primary methane enriched component stream 110 is increased due to the liquefaction and separation of more of the C2+ components in the second flash step.

In a similar manner to the embodiment of Figure 1, the primary methane enriched component stream 110 exiting the CESD 100 is used to cool the hydrocarbon feed stream 10, thereby providing the heated methane enriched component stream 510.

Similarly to the embodiment of Figure 1, the heated methane enriched component stream 510 is passed to a combiner 1400, to provide a combined methane enriched component stream 1410 suitable for export as sales gas and/or further processing, such as liquefaction in a liquefaction unit to produce LNG. The combiner 1400 merges the heated methane enriched component stream 510 with a cooled second methane enriched component stream 1610, provided by a second cooler 1900, such as an air or water cooler. Second cooler 1900 is supplied by the compressed second methane enriched component stream 1610, which is provided in a similar manner to the embodiment of Figure 1.

Returning to the cyclonic expansion and separation device 100, two methane depleted streams exit second and third outlets 106, 108 of the CESD 100 as secondary and ternary methane depleted streams 120, 130 respectively. The secondary methane depleted stream 120 is passed directly to a first inlet 202 of the first gas/liquid separator 200, in a similar manner to the embodiment of Figure 1. The secondary methane depleted stream 120, is at a lower temperature and pressure than the ternary methane depleted stream 130 because it has undergone a second expansion in CESD 100. The ternary methane depleted stream 130, which is at a higher temperature and pressure than the secondary methane depleted stream 120, is expanded in a fifth expansion device 1200 to provide an expanded ternary methane depleted stream 1210. The expansion cools the ternary methane depleted stream. The expanded ternary methane depleted stream 1210 can then be passed to a second inlet 206 of the first gas/liquid separator 200. The cooling of the ternary methane depleted stream 120 to provide the expanded methane depleted stream 1210 allows this stream to be passed to the first gas/liquid separator at a lower temperature, thereby improving the separation.

In a similar manner to the embodiment of Figure 1, the first gas liquid separator provides an overhead first methane rich stream 210 at a first outlet 204 which is then expanded and passed to the separating column 400, such as a fractional distillation column, at the first inlet 402 having the first feeding level.

The first methane lean stream 220 is expanded and then heated before being passed to the separating column 400 at the second feeding level, which is lower than the first feeding level of the expanded first methane rich stream 310, as described for the embodiment of Figure 1. The remaining streams have similar functions and designations as those streams of the same reference numeral discussed in the embodiment of Figure 1.

One advantage of utilising a two-stage CESD 400 is that due to the double expansion stages, the hydrocarbon stream 710 undergoes two flashing operations, generating a more methane enriched (i.e. C2+ lean) primary methane enriched component stream 110.

Figure 3 discloses a third embodiment of the method and apparatus described herein. In a similar manner to the embodiment of Figure 2, a two-stage CESD is utilised which provides a primary methane enriched component stream 110 and secondary and ternary methane depleted streams 120, 130. The scheme of Figure 3 differs from that of Figure 2 in that an external reflux unit fed from the separating column 400, and particularly the second methane enriched component stream 410, is provided. In this embodiment, the second methane enriched component stream 410, which can exit the separator 400 as an overhead stream, is passed to a third heat exchanger 1100 where it is cooled against a fourth auxiliary stream to provide a first cooled second methane enriched component stream 1120. The first cooled second methane enriched component stream 1120 can be passed to a second gas/liquid separator 1300, where it is separated to provide an upper second methane enriched component stream 1310 and a reflux stream 1320, as a bottoms stream. The reflux stream 1320 is fed to the separator column at a fifth feeding level, which is above the first feeding level of the expanded first methane rich stream 310.

The upper second methane enriched component stream 1310 is passed to the second heat exchanger 900 where it is heated against the first part hydrocarbon stream 730, withdrawn from the hydrocarbon stream 710, to provide heated second methane enriched component stream 920, which is then treated as described above for Figures 1 and 2.

The first part hydrocarbon stream 730 is cooled in the second heat exchanger 900 against a second auxiliary stream, such as the upper second methane enriched component stream 1310 to provide a second cooled hydrocarbon stream 910. The second cooled hydrocarbon stream 910 can be passed to a fourth expansion device 1000 to provide an expanded hydrocarbon stream 1010. The expanded hydrocarbon stream 1010 can be passed to the third heat exchanger 1100, where is heated against a second auxiliary stream, such as the second methane enriched component stream 410 from the separation column 400, to provide a heated hydrocarbon stream 1110. The heated hydrocarbon stream 1110 is then fed to the separating column 400.

Depending upon on the degree of heating provided to the expanded hydrocarbon stream 1010 in the third heat exchanger 1100, the resulting heated hydrocarbon stream 1110 can be fed to the separating column 400 at a fourth feeding level which can be above, below or at the level of the first feeding level of the expanded first methane rich stream 310. For instance, if the second auxiliary stream such as the second methane enriched component stream 410, is partially condensed, the fourth feeding level can be below the first feeding level as shown in Figure 3. Alternatively, the fourth feeding level may be at or above the first feeding level of the expanded first methane rich stream 310.

The remaining streams have similar functions and designation as those streams of the same reference numeral discussed in the embodiment of Figure 1 and Figure 2.

The embodiment shown in Figure 3 has the advantages of: reducing any losses from the second methane enriched component stream 410 by cooling this stream in the third heat exchanger 1100 and providing a reflux to the column. This embodiment is particularly preferred for use with lean hydrocarbon feed streams at higher pressures, such as around 90 bara; and having a low reboiler duty and larger separating column reflux stream, particularly when compared with corresponding processes utilising turboexpanders .

These advantages are related to the separating column bypass of the primary methane enriched component stream which results in a lower methane content and therefore higher ethane content. These effects combine to produce an overall improvement of the heat integration. The higher ethane content of the second methane enriched component stream 410 (when compared to the corresponding turboexpander process) increases the flux ratio, while the propane content is lower. The composition of the separating column 400 feed streams originating from the CESD facilitates improved extraction such that the second methane enriched component stream 410 is leaner. Table 2 summarises one embodiment of the scheme of Figure 3 using a "lean" hydrocarbon feed stream 10, comprising 89.1 mol% methane, 4.4 mol% ethane, 2.6 mol% propane, 0.2 mol% i-butane, 0.8 mol% n-butane, 0.3 mol% i-pentane, 0.2 mol% n-pentane, 0.2 mol% n-hexane, 0.1 mol% n-heptane, 0.1 mol% n-octane and 2.0 mol% carbon dioxide. Table 2 provides vapour fraction, temperature and pressure data for a selection of the streams shown in Figure 1.

Table 2 : Stream data for one embodiment of the scheme of Figure 3

The method and apparatus disclosed herein will now be further described with reference to the following non- limiting Examples. Example 1

The apparatus 1 of Figure 1 was supplied with "lean" and "rich" hydrocarbon feed streams 10 with compositions shown in Table 3.1.

Table 3.1: Hydrocarbon feed compositions

Table 3.2 details the composition of the product gas i.e. cooled methane enriched component stream 1710, for a cyclonic expansion and separation device inlet temperature of -30 ⁰C, for "lean" and "rich" hydrocarbon feed streams 10 defined above at pressures of 90 bar, and at 60 bar. Table 3.2: Product gas compositions for lean and rich hydrocarbon feed streams under two pressure regimes

"Lean " hydrocarbon "Rich " hydrocarbon feed stream feed stream

Feed 90 60 90 60 pressure/bar

Component/ mol%

Methane 94.6 93.4 93.1 92.0

Ethane 2.8 3.6 4.0 5.0

Propane 0.7 0.9 1.0 1.1 i-Butane 0.0 0.0 0.1 0.1 n-Butane 0.1 0.1 0.1 0.1 i-Pentane 0.0 0.0 0.0 0.0 n-Pentane 0.0 0.0 0.0 0.0 n-Hexane 0.0 0.0 0.0 0.0 n-Heptane 0.0 0.0 0.0 0.0

CO₂ 1.7 1.9 1.3 1.5

It is apparent from a comparison of tables 3.1 and 3.2 that the method and apparatus disclosed herein is successful in extracting C₂+ hydrocarbons, particularly C3+ hydrocarbons from the hydrocarbon feed streams to provide methane enriched component streams. Example 2

The apparatus 1 of Figure 2 was supplied with "lean" and "rich" hydrocarbon feed streams 10 with compositions shown in Table 3.1 above.

Table 4.1 details the composition of the product gas i.e. cooled methane enriched component stream 1710, for a cyclonic expansion and separation device inlet temperature of -30 ⁰C, for the "lean" and "rich" hydrocarbon feed streams 10 at pressures of 90 bar, and at 60 bar.

Table 4.1: Product gas compositions for lean and rich hydrocarbon feed streams under two pressure regimes

"Lean " hydrocarbon "Rich " hydrocarbon feed stream feed stream

Feed 90 60 90 60 pressure/bar

Component /mo1%

Methane 94.3 93.4 93.4 91.9

Ethane 3.0 3.7 3.9 5.0

Propane 0.8 0.9 1.0 1.2 i-Butane 0.0 0.0 0.1 0.1 n-Butane 0.1 0.1 0.1 0.1 i-Pentane 0.0 0.0 0.0 0.0 n-Pentane 0.0 0.0 0.0 0.0 n-Hexane 0.0 0.0 0.0 0.0 n-Heptane 0.0 0.0 0.0 0.0

CO₂ 1.7 1.9 1.3 1.5

It is apparent from a comparison of the data in tables 3.1 and 4.1 that the method and apparatus disclosed herein is successful in extracting C₂+ hydrocarbons, particularly C3+ hydrocarbons from the hydrocarbon feed streams to provide methane enriched component streams . Example 3

The effectiveness of the method and apparatus utilising 1-stage and 2-stage CESDs are compared in Tables 5.1 and 5.2 below, which show the propane losses, as a mole% of the feed stream, for 1-stage and 2-stage cyclonic expansion and separation devices respectively, - Z O Qo — at an inlet temperature of -30 ⁰C, for "lean" and "rich" hydrocarbon feed streams 10 as defined in Table 3.1 at pressures of 90 bara, and at 60 bar.

Table 5.1: Propane losses (as mole% of the hydrocarbon feed stream) for 1-stage CESD

"Lean " hydrocarbon "Rich " hydrocarbon feed stream feed stream

Feed 90 60 90 60 pressure/bar

Propane loss/mol% of feed stream

Primary stream 9.3 13.0 6.9 8.4 (*D

Secondary stream 12.5 19.0 8.7 11.0 (*2)

Combined primary 21.8 32.0 15.6 19.4 and overhead (*3)

*1 primary methane enriched component stream 110

*2 Secondary methane depleted stream 120

*3 Second methane enriched component stream 410

Table 5.1 shows the extent of the propane extraction from the hydrocarbon stream 710, as measured in the primary methane enriched component stream 110 and the secondary methane depleted stream 120. The 1-stage CESD and the separation column successfully extracted in excess of 15% of the propane content of the hydrocarbon feed stream 10. Similar behaviour was observed for other CESD inlet temperatures. Table 5.2: Propane losses (as mole% of the hydrocarbon feed stream) for 2-stage CESD

*1 primary methane enriched component stream 110

*2 Secondary methane depleted stream 120

*3 Second methane enriched component stream 410

*4 Ternary methane depleted stream 130

Table 5.2 shows the extent of the propane extraction from the hydrocarbon stream 710, as measured in the primary methane enriched component stream 110 and the secondary methane depleted stream 120. The 2-stage CESD and the gas/liquid separator 200 successfully extracted in excess of about 15% of the propane content of the hydrocarbon feed stream 10. Similar behaviour was observed for other CESD inlet temperatures.

A comparison of the values in Tables 5.1 and 5.2 shows that the 2-stage CESD has a lower percentage propane in both the primary methane enriched component stream 110 and the secondary methane depleted stream 120 In the 2-stage CESD, the combined primary and overhead stream (second methane enriched component stream 410) is also combined with the ternary methane depleted stream 130 making the propane losses when viewed as a percentage of the hydrocarbon stream higher than the 1-stage CESD. Other inlet temperatures showed similar behaviour.

Thus, the 2-stage CESD can provide a leaner gas product than the 1-stage CESD because less propane is lost to the primary methane enriched component stream 110 and the secondary methane depleted stream 120. The embodiment of Figure 1 can provide propane recoveries of 90% at all CESD inlet pressures for both lean and rich hydrocarbon feed streams. The embodiment of Figure 2 can provide increased propane recoveries of 94% because the primary methane enriched component stream is leaner than that of the embodiment of Figure 1. The additional reflux unit in the embodiment of Figure 3 can still further increase propane recoveries to 98%.

The person skilled in the art will understand that the present invention can be carried out in many various ways without departing from the scope of the appended claims. For instance, the introduction of a reflux stream, as described in the embodiment of Figure 3 could be applied to the scheme of Figure 1, which utilises a 1- stage cyclonic expansion and separation device.

Claims

C L A I M S

1. A method of treating a hydrocarbon stream, to provide two or more hydrocarbon component streams, comprising at least the steps of:

(a) providing a hydrocarbon stream; (b) separating the hydrocarbon stream in a cyclonic expansion and separation device into a primary methane enriched component stream and one or more methane depleted streams;

(c) separating at least one of the one or more methane depleted streams in a first gas/liquid separator to provide an overhead first methane rich stream and a first methane lean stream;

(d) expanding the overhead first methane rich stream in a first expansion device to provide an expanded first methane rich stream;

(e) feeding the expanded first methane rich stream to a separating column at a first feeding level; and

(f) separating the expanded first methane rich stream in a separating column to provide a second methane enriched component stream and a second methane depleted component stream.

2. The method of claim 1, further comprising the step of:

(g) heating the primary methane enriched component stream by heat exchanging against an auxiliary stream in a first heat exchanger to recover its cold against the auxiliary stream to provide a heated methane enriched component stream.

3. The method of claim 1 or claim 2, further comprising the step of: (h) expanding the first methane lean stream of step (c) in a second expansion device to provide an expanded first methane lean stream;

(i) heating the expanded first methane lean stream in a first heat exchanger to provide a heated first methane lean stream; and

(j) feeding the heated methane lean stream in the separating column by passing the heated methane lean stream to the separating column at a second feeding level lower than the first feeding level.

4. The method of any of the preceding claims, further comprising at least the steps of:

(I) providing a hydrocarbon feed stream;

(II) heat exchanging the hydrocarbon feed stream in a first heat exchanger to provide a cooled hydrocarbon stream;

(III) separating the cooled hydrocarbon stream in an inlet separation device to provide the hydrocarbon stream and a second methane lean stream.

5. The method of claim 4, in which in step (II) the hydrocarbon feed stream is heat exchanged against the primary methane enriched component stream in the first heat exchanger to recover the cold of the primary methane enriched component stream to provide the cooled hydrocarbon stream and a heated methane enriched component stream.

6. The method of claim 4 or claim 5, further comprising the steps of:

(IV) expanding the second methane lean stream in a third expansion device to provide an expanded second methane lean stream; and (V) feeding the expanded second methane lean stream in the separating column at a third feeding level which is lower than the first feeding level.

7. The method of claim 5 or claim 6, further comprising the steps of:

(VI) cooling a fraction of the hydrocarbon stream against a second auxiliary stream to provide a second cooled hydrocarbon stream; and

(VII) expanding the second cooled hydrocarbon stream to provide an expanded hydrocarbon stream.

8. The method of claim 7, further comprising the steps of:

(VIII) heating the expanded hydrocarbon stream by heat exchange against a third auxiliary stream in a third heat exchanger to provide a heated hydrocarbon stream; and

(IX) feeding the heated hydrocarbon stream in the separator column at a fourth feeding level at or higher than the first feeding level.

9. The method of claim 7, further comprising the steps of:

(VIII) heating the expanded hydrocarbon stream by heat exchange against a partially condensed third auxiliary stream in a third heat exchanger; and

(IX) feeding the heated hydrocarbon stream in the separator column at a fourth feeding level which is below the first feeding level.

10. The method of claim 7, further comprising the step of:

(VIII) feeding the expanded hydrocarbon stream in the separating column at a sixth feeding level which is at the first feeding level or higher.

11. The method of any one of the preceding claims, further comprising the steps of: - heating the second methane enriched component stream in a second heat exchanger to provide a heated second methane enriched component stream;

- further heating the heated second methane enriched component stream in a first heat exchanger to provide a further heated second methane enriched component stream.

12. The method of claim 10 or claim 11, further comprising the steps of:

- cooling the second methane enriched component stream in a third heat exchanger to provide a first cooled second methane enriched component stream;

- separating the first cooled second methane enriched component stream in a second gas/liquid separator to provide an upper second methane enriched component stream and a reflux stream; and

- passing the reflux stream to the separating column.

13. The method of claim 12, further comprising the steps of:

- heating the upper second methane enriched component stream in a second heat exchanger to provide a heated second methane enriched component stream; and

- heating the heated second methane enriched component stream in a first heat exchanger to provide a further heated second methane enriched component stream.

14. The method of any one of the preceding claims wherein the cyclonic expansion and separation device provides a secondary methane depleted stream and a ternary methane depleted stream in step (b) ; and the secondary methane depleted stream is separated in the first gas/liquid separator in step (c) .

15. The method of claim 14, further comprising the steps of: - expanding the ternary methane depleted stream in a fifth expansion device to provide an expanded ternary methane depleted stream; and

- separating the expanded ternary methane depleted stream in the first gas/liquid separator in step (c) .

16. An apparatus for treating a hydrocarbon stream, said apparatus comprising at least:

- a cyclonic expansion and separation device comprising a first inlet for a hydrocarbon stream and two or more outlets, said two or more outlets comprising a first outlet for a primary enriched methane component stream and a second outlet for a secondary methane depleted stream, said second outlet connected to the first inlet of a first gas/liquid separator; - a first gas/liquid separator comprising at least a first inlet for the secondary methane depleted stream and a first outlet for a first methane rich stream, said first outlet connected to a first inlet of a first expansion device; - a first expansion device comprising a first inlet for the first methane rich stream and a first outlet for an expanded first methane rich stream, the first outlet connected to the first inlet of a separating column; and

- a separating column comprising a plurality of inlets and a plurality of outlets, said inlets comprising a first inlet for the expanded first methane rich gaseous stream and said outlets comprising a first outlet for a second methane enriched component stream and a second outlet for a second methane depleted component stream.

17. An apparatus according to claim 16, wherein the cyclonic expansion and separation device further comprises a third outlet for a ternary methane depleted stream, said third outlet connected to a first inlet of a fifth expansion device, and further comprising: - a fifth expansion device comprising a first inlet for the ternary methane depleted stream and a first outlet for an expanded ternary methane depleted stream, said first outlet connected to a second inlet of the first gas/liquid separator.