EA016149B1 - Method and apparatus for recovering and fractionating a mixed hydrocarbon feed stream - Google Patents

Abstract

A condensed mixed hydrocarbon feed stream (10), recovered from an initial feed stream (8), is fractionated into one ore more fractionated streams. In this process, the condensed mixed hydrocarbon feed stream (10) is separated into at least a first part-feed stream (20) and a second part-feed stream (30). The first part- feed stream (20) is passed into a first gas/liquid separator (14), to provide at least a first fractionated stream in the form of a first gaseous overhead stream (40). A first bottom liquid stream (50) provided by the first gas/liquid separator (14) is passed into a second gas/liquid separator (22) to provide at least a second fractionated stream in the form of a second gaseous overhead stream (70), which is cooled by heat exchange (26) against the second part-feed stream (30).

Description

FIELD OF THE INVENTION

The present invention relates to a method and apparatus that are designed to separate a mixed hydrocarbon stream from a feed stream, such as a natural gas stream, and fractionate the mixed hydrocarbon feed stream into one or more fractionated streams.

State of the art

Natural gas is a useful source of fuel, as well as a source of various hydrocarbon compounds. Gas is produced for distribution through a piping system located at or near the gas source. Sometimes natural gas is first liquefied in a natural gas liquefaction (LNG) plant located at or near the source of the natural gas stream, which is done for a number of reasons. For example, natural gas is easier to store and move over long distances in the form of a liquid, rather than in a gaseous form, since it takes up a small volume in the form of a liquid and does not need to be stored at high pressures.

Typically, natural gas, mainly containing methane, enters the LNG plant at elevated pressures and is pre-treated to obtain a purified feed stream suitable for the specified purpose. In the event of subsequent liquefaction, the purified feed stream should be suitable for liquefaction at cryogenic temperatures. The purified gas is treated during several stages of cooling using heat exchangers in order to gradually reduce the temperature until liquefaction is achieved. Further, liquefied natural gas is further cooled and expanded to a final atmospheric pressure suitable for storage and transportation.

In addition to methane, natural gas usually contains some heavier hydrocarbons and impurities, including carbon dioxide, sulfur, hydrogen sulfide and other sulfur compounds, nitrogen, helium, water and other non-hydrocarbon gases, ethane, propane, butanes, C ₅ ⁺ hydrocarbons and aromatic hydrocarbons.

These and other common or known heavier hydrocarbons and impurities either impede the use of conventional known methods for liquefying methane or prevent their use, which is especially true for the most effective methods of liquefying methane. Most, if not all, known or proposed methods for liquefying hydrocarbons, especially liquefying natural gas, are based on reducing, as necessary, the levels of at least most of the heavier hydrocarbons and impurities before carrying out the liquefaction process.

Hydrocarbons are heavier than methane and usually ethane is recovered from the feed stream by partially condensing the feed stream, thereby forming a mixed condensed hydrocarbon feed stream, which is subsequently separated from the feed stream. In the case of a feed stream formed by natural gas, a feed stream of mixed condensed hydrocarbons is isolated in the form of so-called gas condensate liquids.

The mixed hydrocarbon feed stream containing HCL is often fractionated to produce valuable hydrocarbon products either as product streams per se or as products intended for use in a process. For example, if this process is a liquefaction process, hydrocarbon products can be used as a component of a cooling agent.

Fractionation usually involves the separation of one or more C ₂ ⁺ hydrocarbon streams from a mixed hydrocarbon stream, in particular as part of a multi-column system and gas condensate liquid (GLC) recovery structure.

Specialists in the field under consideration are aware of the use of two or more gas / liquid separators in series in the separation of HCL. In one example, the HCL recovery unit produces one stream with a higher content of heavier hydrocarbons, the stream is subsequently used either alone or in a separate place, or the block is further divided into streams with a higher content of specific heavier hydrocarbons. The fractionation of the stream with a higher content of heavier hydrocarbons can be performed in one or more additional gas / liquid separators (known in the art), for example, in a distillation column.

A distillation column using one or more columns can produce separate streams of certain heavier hydrocarbons. For example, if there are several columns, each column can be designed to produce a separate hydrocarbon stream, for example, a stream with a high content of ethane, a stream with a high content of propane, a stream with a high content of butane and a stream with a high content of C ₅ ⁺ , and the latter stream is sometimes also called stream of light condensates. Propane, butane, C ₅ ⁺ hydrocarbons (and, if desired, ethane) are sometimes called gas condensate liquids (GKZh) and their use is known.

- 1 016149

An example of a distillation column as a conventional distillation column used to isolate the SCL is described in I8 2004/0079107 A1.

In another example, the HCL recovery unit may comprise a distillation column which, as a whole, produces separate streams of certain heavier hydrocarbons, such as the hydrocarbons mentioned above.

Thus, the allocation of HCL usually includes the stages of cooling, condensation and separation into fractions, which require significant cooling costs and other energy costs. It is desirable to isolate HCG from a natural gas stream most effectively in terms of energy consumption or with minimal energy consumption for cooling.

US Pat. No. 7,051,553 describes a conventional gas separation process in which the feed gas stream is cooled and then the liquids condensed from the cooled gas are expanded and fractionated in a distillation column to separate residual components from the desired heavier components. US Pat. No. 7,051,553 also discloses a two-column GCG separation unit comprising an absorber and a distillation column, whereby a second reflux stream containing cooled top gas of the distillation column is directed to the absorber. The cooling of the gas taken from above from the distillation column is carried out by a separate cooling device, which requires separate energy consumption.

US Pat. No. 6,116,050 describes methods for separating and separating propane, propylene, and C ₃ ⁺ hydrocarbons from a feed gas, which is done in order to produce gas for piping and to produce a liquid product. In these methods, successive first and second distillation columns and a self-cooling system are used, with respect to which it is believed that it improves the separation efficiency in the first column. The cooled feed gas is separated in a raw material separator, and then the vapors and liquids from the raw material separator are fed to the first column. Part of the liquids flows directly through the line to the first column, and the remaining part is heated using a vapor from the second column taken from above before being introduced into the first column through the same line.

Disclosure of the invention

The purpose of the present invention is to improve the efficiency of separation and subsequent separation into fractions of the feed stream of mixed hydrocarbons obtained from the feed stream.

According to one aspect, the present invention provides a method for separating a mixed hydrocarbon feed stream from a feed stream, such as a natural gas stream, and separating the mixed hydrocarbon feed stream into one or more fractionated streams, said method comprising at least the following stages:

(a) ensure the availability of the feed stream;

(b) partially condensing the feed stream, thereby forming a partially condensed feed stream;

(c) dividing the partially condensed feed stream into a gaseous top flow stream from the top and the mixed condensed hydrocarbon feed stream;

(d) separating the feed stream of the mixed condensed hydrocarbons into at least a first part of the feed stream and a second part of the feed stream;

(e) pass the first part of the feed stream into the first gas / liquid separator through the first inlet of the first gas / liquid separator, which is done in order to obtain at least the first fractioned stream in the form of a first gaseous stream taken from above and the first taken from below fluid flow;

(e) passing a first, bottom-drawn fluid stream into a second gas / liquid separator in order to obtain at least a second fractionated stream in the form of a second gaseous top-off stream and a second bottom-off liquid stream; and (g) cooling the second gaseous stream taken from above by heat exchange with the second part of the feed stream, resulting in a warmer second part of the feed stream;

(h) a warmer second part of the feed stream is passed into the first gas / liquid separator at a level which in the direction of gravity is below the level of the first inlet.

According to another aspect, the present invention provides a device for separating a mixed hydrocarbon feed stream from an initial feed stream and separating a mixed hydrocarbon feed stream into one or more fractionated streams, said device comprising at least the following:

a pre-cooling heat exchanger for cooling the feed stream to obtain a partially condensed feed stream; a gas / liquid feed separator for separating a partially condensed feed stream into a gaseous stream taken from above and a condensed mixed hydrocarbon stream;

flow divider designed to separate the feed stream of mixed condensed

- 2 016149 hydrocarbons, at least in the first part of the feed stream and the second part of the feed stream;

a first gas / liquid separator for receiving a first portion of the feed stream through the first inlet of the first gas / liquid separator and for obtaining at least a first fractioned stream in the form of a first gaseous stream taken from above and a first liquid taken from below;

a second gas / liquid separator for receiving a first liquid stream taken from below and for obtaining at least a second fractionated stream in the form of a second gas stream taken from above and a second liquid stream taken from below;

a heat exchanger for receiving a second part of the feed stream and a second gaseous stream taken from above and to produce a cooled second gaseous stream taken from above and a warmer second part of the feed stream; and a second inlet leading to the first gas / liquid separator and intended to let a warmer second part of the feed stream into the first gas / liquid separator, wherein the second inlet is located at a level which in the direction of gravity is lower than the level of the first inlet.

Next, examples and embodiments of the present invention will be described with reference to the accompanying non-limiting drawings, in which FIG. 1 is a diagram of a C ₂ ⁺ separation method and FIG. 2 is a diagram of an implementation of the method shown in FIG. 1, in the LNG production unit.

In this description, a single reference position will denote both the line and the stream flowing in this line.

In the embodiments described herein, the cooling of the second gaseous top-off stream from the second gas / liquid separator is achieved by using a portion of the cold of the feed stream of the mixed condensed hydrocarbons, rather than having some separate cooling device implying separate energy costs, or not combining it with a cooling system or circuit, associated with the liquefaction process.

Thus, cold from another source, such as cooling the (preliminary) hydrocarbon stream, such as natural gas, by a separate cooling agent, system or cooling circuit, does not need to be diverted for use in the separation and fractionation of a mixed hydrocarbon stream, for example in GKZH, thereby increasing the efficiency of other processes or sections of the liquefaction plant, such as the installation of producing LNG.

By cooling the second gaseous stream taken from above, a warmer second part of the feed stream is generated which can still enter the first gas / liquid separator or can be used differently. Introducing the mixed hydrocarbon feed stream fraction into the first gas / liquid separator at a higher temperature (which was preceded by using some part of the cold to cool the second gaseous stream taken from above from the second gas / liquid separator) reduces the energy consumption from a heat source such as a reboiler , for the operation of the first gas / liquid separator.

In addition, it was found that an improvement in separation efficiency and a further decrease in any thermal power taken from an external source can be achieved due to the arrival of a warmer second part of the feed stream into the first gas / liquid separator at a height along the separator that is lower than the height at which the first part of the feed stream enters the first gas / liquid separator.

Typically, the feed stream essentially consists of methane. Preferably, the feed stream contains at least 60 mol% of methane, more preferably at least 80 mol% of methane.

The term “mixed hydrocarbon feed stream” as used herein refers to a feed stream containing methane and one or more hydrocarbons selected from the group consisting of ethane, propane, butanes, pentanes and C ₆ ⁺ hydrocarbons.

The mixed hydrocarbon feed stream may come from any suitable source. Preferably, the mixed hydrocarbon feed stream is obtained from the feed stream. The feed stream may be any suitable hydrocarbon stream, such as, but not limited to, a hydrocarbon containing gas stream to be cooled. One example is a natural gas stream obtained from natural gas or an oil reservoir. Alternatively, the feed stream can also be obtained from another source, for example, from a refinery and / or an artificial source, such as the Fischer-Tropsch process.

As used herein, the term C ₂ ⁺ refers to one or more components selected from the group consisting of ethane, propane, butanes, pentanes and the C ₆ ⁺ hydrocarbons.

Similarly, the term C ₃ ^{+ as} used herein refers to one or more components,

- 3 016149 selected from the group consisting of propane, butanes, pentanes and C ₆ ⁺ hydrocarbons.

The terms C ₄ ⁺ and so on are defined similarly, starting with butanes and so on.

Each gas / liquid separator of the present invention may contain one or more columns, and one or each of such columns may produce separate liquid streams from certain heavier hydrocarbons, such as ethane, propane and so on.

Any fractionating a stream or a separate stream from the _C2 ^+, C3 ^+, C4 ⁺ and so on may still contain a small (less than 10 mol.%) Methane; it is preferred that each such stream contains more than 80 mol%, more preferably more than 95 mol% of one or more of the components defined above.

Dividing a stream, such as a feed stream, into two or more parts of the stream can be performed using any suitable stream divider, which can be a separate unit or a simpler line separation, such as a T-shaped assembly.

Although the method of the present invention is applicable to various feed hydrocarbon-containing feed streams, it is especially advisable to liquefy natural gas streams. Since a specialist in the field under consideration will easily understand how to liquefy a stream of hydrocarbons, here this issue will be considered without details.

In FIG. 1 shows a simplified and general scheme 1 of a method for separating one or more C ₂ ⁺ hydrocarbon streams from a mixed hydrocarbon feed stream isolated from a feed stream, such as natural gas. The circuit of FIG. 1 may be part of a liquefied natural gas plant 2, which is shown in FIG. 2.

In FIG. 1 illustrates a method and apparatus for separating one or more C ₂ ⁺ hydrocarbon streams from a feed stream, such as natural gas. This device comprises means for separating a mixed hydrocarbon feed stream 10 from a feed stream 8;

a flow divider 36 for separating a mixed hydrocarbon feed stream 10 into at least a first part 20 of the feed stream and a second part 30 of the feed stream;

a first gas / liquid separator 14 for receiving the first portion 20 of the feed stream and producing at least a first gaseous top flow 40 and a first bottom fluid flow 50;

a second gas / liquid separator 22 for receiving a first liquid stream 50 taken from below and receiving at least a second gas stream taken from above 70 and a second liquid stream taken from below 80; and a heat exchanger 26 for receiving a second portion 30 of the feed stream and a second gaseous top flow stream 70 and to produce a cooled second gaseous top flow stream 70a and a warmer second portion 30b of the feed stream.

Illustrated in FIG. 1, the method includes at least the following steps: a mixed hydrocarbon feed stream 10 is obtained from the feed stream 8; separating the mixed hydrocarbon feed stream 10 at least into a first portion 20 of the feed stream and a second portion 30 of the feed stream;

passing the first part of the feed stream into the first gas / liquid separator 14 in order to obtain at least a first gaseous top flow 40 and a first bottom fluid flow 50;

pass the first, taken from below, the flow of liquid 50 into the second separator 22 gas / liquid in order to obtain at least a second gaseous taken from above the flow of 70 and the second taken from the bottom of the flow of liquid 80; and cooling the second gaseous stream 70 taken from above by heat exchange with the second part 30 of the feed stream.

The first and second gas / liquid separators may be any separators, such as a distillation column, adapted to produce at least one gaseous stream, typically having an increased content of one or more lighter hydrocarbons, and at least one liquid stream, typically having an increased content of one or more heavier hydrocarbons. An example of such a separator is methane removal unit adapted to receive the overhead stream with a high content of methane and a liquid stream with a high content of one or more C ⁺ _2, located in the bottom or close to it. Similarly, ethane removal devices and a propane removal device and so on are known in the art.

Thus, if the first gas / liquid separator is a methane removal device, the first liquid taken from below will be a C ₂ ⁺ hydrocarbon stream. If the second gas / liquid separator is an ethane removal device, then the second liquid flow taken from below will be a C ₃ ⁺ hydrocarbon stream, and the second gas flow taken from above

- 4 016149 will preferably contain more than 60 mol.% Ethane, more preferably more than 85 and even more preferably more than 90 mol.% Ethane.

In more detail, in FIG. 1 shows a feed stream 8 containing natural gas, which is cooled in a pre-cooling heat exchanger 32 in order to obtain a cooled and partially condensed feed stream 8a. The pre-cooling heat exchanger 32 may comprise one or more heat exchangers arranged in parallel or in series or combining both of these locations, as is known in the art. The cooling is carried out using the first coolant stream 100, which is heated in the pre-cooling heat exchanger 32 and a heated coolant stream 100a is formed.

This cooling of the feed stream 8 may be part of a liquefaction process, such as a pre-cooling step including a cooling propane circuit, which will be described later in the discussion of FIG. 2, or may be a separate process.

The cooling of the feed stream 8 may include reducing the temperature of the feed stream 8 to values less than 0 ° C, for example, values in the range from -10 to -40 ° C.

The cooled feed stream 8 passes to a feed gas / liquid separator, such as a scrub column 34 operating in a manner known per se in the art at pressures in excess of atmospheric pressure. In the scrub column 34, a condensed mixed hydrocarbon feed stream 10 and a gaseous top stream 110 are obtained. The methane content of the gaseous top stream 110 is typically greater than or equal to 80 mol%. Usually it is a stream with a higher methane content compared to the cooled feed stream 8a.

The mixed hydrocarbon feed stream 10 contains methane and one or more C ₂ ⁺ hydrocarbons. Typically, the proportion of methane in the feed stream of mixed hydrocarbons is 30-50 mol.%, With a significant proportion of ethane and propane and the proportion of each of these substances is 5-10 mol.%.

It is usually desirable to isolate any amount of methane from the feed stream of mixed hydrocarbons (for use as fuel or the like, so that it can be liquefied in LNG plant 2 and provided as additional LNG) and produce one or more of the following streams: stream C ₂ , stream C ₂ ⁺ , stream C3 ⁺ , stream C4 ⁺ and so on, or a combination thereof. The method of the present invention is useful for separating any one or more of the C ₂ ⁺ streams as pure streams or streams of combined components.

In FIG. 1, flow divider 36 separates the mixed hydrocarbon feed stream 10 into a first part 20 of a feed stream and a second part 30 of a feed stream. The separation of the feed stream 10 of mixed hydrocarbons may be based on any ratio of mass and / or volume and / or flow rate. The ratio may be based on the size or capacity of subsequent parts, systems or blocks, or the size, capacity or temperature of the second part 30 of the feed stream and the capacity of the heat exchanger 26 (to be discussed later). In general, the first part 20 of the feed stream is from 20 to 70% by weight, preferably from 30 to 50% by weight, and more preferably 40% by volume of the mixed hydrocarbon feed stream 10.

The first part 20 of the feed stream passes through the valve 12 to obtain the first part 20a of the reduced pressure feed stream, which then enters the first gas / liquid separator, such as the first distillation column 14, with the first feed stream part 20a passing through the first inlet, located on top of the first distillation column 14 or near the top. Typically, the first part 20a of the reduced pressure feed stream is a mixed phase stream, and the first distillation column 14 is adapted to separate the gaseous phase and the vapor phase to obtain a first gaseous top flow 40 and a first bottom flow 50 of the liquid.

The nature of the streams obtained in the first distillation column 14 may be different depending on the size and type of the distillation column, its operating conditions and operation parameters, which is known in the art. For the structure shown in FIG. 1, it is desirable that the first gaseous top-off stream 40 has an increased methane content, preferably more than 90 mol% of methane is present in stream 40. This methane-rich stream 40 can be added to other parts of the liquefaction plant to obtain, for example, additional LNG, or it can be used as fuel.

Also, the first distillation column 14 comprises a first reboiler 17 and a return flow 60 taken from below, which usually takes the form of a return flow of steam of a reboiler, as is known in the art.

The first liquid stream 50 taken from below mainly consists of C ₂ ⁺ hydrocarbons, for example of more than 90 or more than 95 mol.% Ethane and heavier hydrocarbons. The first bottom fluid stream 50 is cooled by one or more atmospheric cooling devices, such as a water and / or air cooling device 16, after which the flow passes through the valve 18 to produce a first underpressure liquid stream 50a from the bottom, which flows through the inlet hole 42 in a second gas / liquid separator, such as a second dis

- 5 016149 distillation column 22. And again, the type, size and performance of the second distillation column 22, as well as its operating conditions and operating parameters, will control the nature of the streams obtained in the second distillation column 22.

In the construction shown in FIG. 1, the second distillation column 22 produces a second gaseous top-off stream 70 containing predominantly ethane, preferably more than 85 or more than 90 mol% of ethane, and produces a second bottom-off stream 80 of liquid, generally containing more than 98% propane and heavier hydrocarbons. Also, the second distillation column 22 comprises a reboiler 27 and a return stream 90 of steam of the reboiler.

Preferably, the cooling of the second gaseous top-off stream 70 results in the condensation of at least a portion, preferably the entire second gaseous top-off stream. In particular, the condensed fraction can be used as reflux stream 70b for the second gas / liquid separator 22. Thus, in one embodiment of the present invention, the method corresponding to the present invention further includes the following steps:

(i) separating the cooled second gaseous top-off stream 70a obtained in step (g) into two or more fractions (70b, 70c) and (k) passing at least one of these fractions (70b) back into the second gas separator 22 / liquid, preferably in the form of a reflux stream.

If the second gas / liquid separator 22 is a distillation column, for example an ethane removal device, a fraction of the second gaseous stream taken from above can be used in step (s) to obtain reflux for the distillation column.

Typically, the second gaseous top-off stream 70 is cooled in a separate or external cooling device, as shown in I8 7051553 B2 or using a pre-cooling heat exchanger 32. The use of the former requires a separate energy source, and the use of the latter takes part of the cooling capacity of the pre-cooling heat exchanger 32 from cooling the feed stream 8. Both of these situations reduce the efficiency of the LNG plant. Also, both situations create a complex combination of fractionation design and the remainder of the liquefaction plant.

Preferably, the temperature of the second part 30 of the feed stream (from the mixed hydrocarbon feed stream 10) after passing through the valve 24 to obtain the second part 30a of the reduced pressure feed stream is sufficiently low, for example, in the range of 0 to −50 ° C., which is necessary for cooling the second gaseous flow taken from above from the top 70 in the heat exchanger 26. The heat exchanger 26 may be one or more heat exchangers arranged in parallel, sequentially or combining both of these location. In embodiments of the invention, heat exchanger 26 may be referred to as a reflux heat exchanger.

The cold second portion 30a of the reduced pressure feed stream draws off the heat of the second gaseous top stream 70 to at least partially condense, preferably completely condensate, the second gaseous top stream 70 in the heat exchanger 26 and obtain at least partially condensed second stream 70a . Thus, the cooling of the second gaseous flow taken from above from the top 70 is carried out without the need for a separate cooling source, which makes the SCL recovery design shown in FIG. 1, independent of any cooling system.

Stream divider 44 may separate at least partially condensed second stream 70a into reflux stream 70b and product stream 70c. Product stream 70c may be in the form of a separate product stream intended for use outside the liquefaction plant, or in the form of a coolant, or in the form of a component of a coolant for a liquefaction plant, for example, as a mixed coolant, as is known in the art.

As a result of the heat exchange of the second gaseous top stream 70 and the second part 30a of the feed stream, a warmer second part 30b of the feed stream is also obtained, which can be directed to the first distillation column 14 preferably between the first inlet 38 for the first part 20a of the feed stream and the bottom drawn back flow 60, for example, through the inlet 39 of the first distillation column 14, while in the direction of gravity, the inlet 39 is located below the first inlet from verst 38. The bottom return flow 60 may be fed back to the first distillation column 14 through the return flow inlet 41.

The construction shown in FIG. 1 is intended to separate streams 40, 70 C ₁ and C ₂ from the feed stream 10 of mixed hydrocarbons, resulting in the formation of a stream of 80 C ₃ '. However, this design can be similarly applied, for example, to obtain a stream of C ₁ and a stream of a mixture of C _2/3 , and the remainder will be a stream of C ₄ ⁺ . All such configurations and designs are known to the person skilled in the art of GCG isolation.

Thus, the process of the present invention is equally applicable for use with two other gas / liquid separators with a mixed hydrocarbon feed stream.

- 6 016149 births and is adapted to receive other product flows. In addition, the method of the present invention is applicable to a structure comprising more than two gas / liquid separators when more than three product streams are produced, for example, separate C ₃ , C ₄ and C5 ⁺ streams.

In addition, the second part 30 of the feed stream can be divided into two or more fractions in order to cool other gaseous top-off streams (such as streams from a propane removal device and so on), thereby further reducing or eliminating the need for separate cooling devices or heat exchangers for each top stream.

In the embodiment shown in FIG. 1, the mixed hydrocarbon feed stream 10 is obtained from the feed stream 8 by dividing the feed stream 8 into a mixed hydrocarbon feed stream 10 and a gaseous top-off stream 110. In practical situations, the latter is often a methane-rich stream.

The source gaseous top-off stream 110 can be supplied to a gas distribution system to use this stream with a high methane content in the form of gas on the market. However, before being fed to the gas distribution system, the source gaseous top-off stream 110 may undergo other processing steps, for example, undergo additional processing to change composition and / or cooling, preferably liquefaction, to produce a cooled stream of hydrocarbons, preferably LNG.

Thus, the present invention further provides a method for cooling an initial feed stream, such as a hydrocarbon stream, natural gas, said method comprising at least the following steps:

(ί) passing the feed stream through a feed separator in order to produce a gaseous top stream with a high methane content and a condensed mixed hydrocarbon feed stream;

(i) cooling, preferably liquefying, the initial gaseous stream taken from above to obtain a cooled, preferably liquefied, stream of hydrocarbons; and (ΐϊϊ) separating one or more C ₂ ⁺ hydrocarbons from the condensed mixed hydrocarbon stream using the method defined herein.

Preferably, the source gaseous top-off stream is cooled without passing through the first gas / liquid separator. The specified stream can be cooled by passing through one or more heat exchangers, where there is the possibility of heat exchange with one or more cooling substances involved in one or more cooling cycles.

In FIG. 2 shows an LNG production unit 2, including a separation structure 1 shown in FIG. one.

In FIG. 2 shows the feed stream 8, which is cooled by three pre-cooling heat exchangers 46 (which are similar or equivalent to the pre-cooling heat exchanger 32 of FIG. 1) in order to obtain a cooled feed stream 8a, which is divided by a divider 29 into a first stream 9, which directly flows into the scrubbing column 34, and a second stream 9a, which enters the main cryogenic heat exchanger 23 to obtain a cooled feed stream 9b, which also enters the scrubbing columns 34 at a level above the level of the first stream 9.

In the scrub column 34, a condensed mixed hydrocarbon feed stream 10 is generated. A flow divider 36 separates this mixed stream 10 into a first part 20 of a feed stream and a second part 30 of a feed stream, the further course of which was previously described in the discussion of FIG. one.

Thus, the first part 20 of the feed stream passes through the valve to obtain the first part 20a of the reduced pressure feed stream, which then enters the first distillation column 14. In the distillation column 14, a first gaseous overhead stream 40 is produced, mainly consisting of methane and FIG. 2 denoted by C1, and a first liquid stream 50 taken from below, which, after cooling and expansion, enters the second distillation column 22.

In the second distillation column 22, a second gaseous top-off stream 70 is generated, which is cooled in the heat exchanger 26 by means of the second part 30a of the reduced pressure feed stream in order to obtain a cooled second top-off stream in the form of at least partially, preferably completely condensed, second stream 70a which is separated into reflux stream 70b and product stream 70c, which is mainly composed of ethane, and in FIG. 2 is denoted by C2.

Also in the second distillation column 22 produce a second bottom liquid stream 80 is withdrawn, which is a C ₃ ⁺ stream, which after the expansion can be directed to an optional gas / liquid separator, such as third distillation column 52 which, if desired, removing the installation is propane. In a third distillation column 52, a third can be produced

- 7 016149 top-off stream 140 (which after cooling may be a C3 product stream containing, for example, more than 95 mol%, preferably 99 mol% of propane) and a third bottom stream 130, which is a C ₄ ⁺ stream. The third bottom-withdrawn stream 130 may enter a fourth gas / liquid separator, which is the fourth distillation column 54, in which a fourth gaseous top-off stream 160 is produced (which, after cooling, may be a C4 product stream containing, for example, more than 95 mol%, preferably 99 mol% of butanes) and the fourth bottom stream 150, which is a C ₅ ⁺ stream (sometimes also called a light condensate stream).

In FIG. 2 shows a diagram of the separation of C ₂ ^+, which includes a number of separators intended to receive streams of C _s C _2, C _3, C ₄ and C ^_5+, which can be used as product streams or be used by methods known to those skilled in the art .

Meanwhile, the initial gaseous top-off stream 110 from the scrubbing column 34 may enter the main cryogenic heat exchanger 23 for further cooling. Typically, the cooling provided by the pre-cooling heat exchangers 46 can be considered as a pre-cooling step, and the cooling provided by the main cryogenic heat exchanger 23 can be considered as the main cooling step or the second cooling step.

Typically, the main cryogenic heat exchanger 23 is able to reduce the temperature of the source gaseous top-off stream 110 to values lower than -90 or -100 ° C, preferably to values that liquefy the source gaseous top-off stream 110. Such cooling may be provided in several ways known to the person skilled in the art area in question. One example is the use of cooling circuit 25 in a manner known in the art.

In the main cryogenic heat exchanger 23, a top flow 120 is generated which is preferably completely liquefied. If the feed stream 8 is natural gas, then typically the gaseous top stream 120 is LNG. In particular, in the present invention, the overall efficiency of the LNG production unit 2 is improved by reducing the complexity of combining the cooling needed for at least one top flow stream and other heat exchangers (such as pre-cooling heat exchanger 32, 46) or other heat exchangers.

In the table below 1 provides an overview of the estimates of compositions, phases, pressures, and temperatures of certain streams in various parts of the example process of FIG. 2. In these calculations, it was assumed that a warmer second portion 30b of the feed stream was supplied to the first distillation column 14 from the ninth of 12 trays, and a first portion 20 of the feed stream was fed to the first distillation column 14 from the first tray (top). The calculations showed that the purity C1 of the first gaseous top stream 40 is approximately 94% for a given feed stream 10 of mixed hydrocarbons with a first reboiler 17 having a power of 2.6 MW.

In the table below 2 contains the results of calculations similar to those performed for table. 1, with one exception, that the warmer portion 30b of the feed stream is supplied to the first distillation column 14 from the first tray at the same level as the first portion 20a of the feed stream. Compared to the table. 1, the purity C1 of the first gaseous stream taken from above decreased to about 90% with an increase in the power of the first reboiler 17 to 2.8 MW.

Therefore, supplying the warmer second portion 30b of the feed stream to the distillation column 14 at a level lower than the level of the inlet 38 for the first portion 20a of the feed stream improves the separation efficiency of the first distillation column 14 while reducing the power of the reboiler of the first distillation column 14.

Table 1

Flow Phase Temperature Pressure Speed flow ν ₂ C1 from ₂ Sz 1C ₄ C _{4 5} ⁺ ° s MPa kilomol / s molar% 8 P 19,4 6.6 17.11 2.7 92.3 3,5 0.9 0.2 0.2 0.3 8a p / f -29.3 6.5 17.11 2.7 92.3 3,5 0.9 0.2 0.2 0.3 nine p / f -29.3 6.5 6.84 2.7 92.3 3,5 0.9 0.2 0.2 0.3 9b p / f -62.0 6.15 10.26 2.7 92.3 3,5 0.9 0.2 0.2 0.3 110 P -55.1 5.96 16.91 2.7 92.9 3.4 0.8 0.1 0.1 0,0 120 well -148.2 5.19 16.91 2.7 92.9 3.4 0.8 0.1 0.1 0,0 10 well -33.3 5.97 0.19 0.4 44.1 9.8 8.6 4.3 8.8 24.1 20a p / f -42.4 3,5 0.10 0.4 44.1 9.8 8.6 4.3 8.8 24.1 30a p / f -41.3 3.75 0.10 0.4 44.1 9.8 8.6 4.3 8.8 24.1 zo p / f 2,5 3,7 0.10 0.4 44.1 9.8 8.6 4.3 8.8 24.1 40 P -42.0 3,5 0.09 0.8 94.4 3.8 0.7 0.1 0.2 0,0 fifty well 129.3 3,51 0.10 0,0 1,0 14.9 15.3 7.8 16,2 44.8 fifty' well 43,2 2.75 0.10 0,0 1,0 14.9 15.3 7.8 16,2 44.8 80 well 156.0 2.77 0.09 0,0 0,0 0,0 17.4 9,4 19,4 53.7 70s well -2.6 3.6 0.02 0,0 6.0 89.0 5,0 0,0 0,0 0,0

P - steam, F - liquid

- 8 016149

table 2

Flow Phase Temperature Pressure Flow rate ν ₂ C1 C ₂ C ₃ 1C4 from _{4 5} ⁺ ° s MPa kilomol / s molar% 8 P 19,4 6.6 17.11 2.7 92.3 3,5 0.9 0.2 0.2 0.3 8a p / f -29.3 6.5 17.11 2.7 92.3 3,5 0.9 0.2 0.2 0.3 nine p / f -29.3 6.5 6.84 2.7 92.3 3,5 0.9 0.2 0.2 0.3 9b p / f -62.0 6.15 10.26 2.7 92.3 3,5 0.9 0.2 0.2 0.3 110 P -55.1 5.96 16.91 2.7 92.9 3.4 0.8 0.1 oh 1 0,0 120 well -148.2 5.19 16.91 2.7 92.9 3.4 0.8 0.1 0.1 0,0 10 mg W -33.3 5.97 0.19 0.4 44.1 9.8 8.6 4.3 8.8 24.1 20a p / f -42.4 3,5 0.10 0.4 44.1 9.8 8.6 4.3 8.8 24.1 30a p / f -41.3 3.75 0.10 0.4 44.1 9.8 8.6 4.3 8.8 24.1 ZOE p / f 2,5 3,7 0.10 0.4 44.1 9.8 8.6 4.3 8.8 24.1 40 P -16.4 3,5 0.09 0.7 89.9 6.4 1.8 0.4 0.5 0.2 fifty well 135.8 3,51 0.10 0,0 1,0 12.9 14.9 7.9 16.6 46.6 50a well 43,2 2.75 0.10 0,0 1,0 12.9 14.9 7.9 16.6 46.6 80 well 157.8 2.77 0.09 0,0 0,0 0,0 16.7 9.2 19,4 55.6 70s well -4.3 3.6 0.01 0,0 6.8 88.2 5,0 0,0 0,0 0,0

P - steam, F - liquid

Suitable process control for embodiments of the present invention may include a level control for the source gas / liquid separator 34, which controls the flow of the first feed stream portion 20 to the gas / liquid separator 14, for example, by controlling the setting of valve 12. Valve 24 can be controlled with using a flow regulator, the setting of which is determined by the pressure regulator for the second gas / liquid separator. Similarly, its setting can be determined by the level regulator on an optional vessel 21, designed to receive and release a cooled second stream taken from above. This is equivalent to a pressure regulator, since the level in the vessel is determined by the power of the condensation device, which performs condensation upon receipt of the stream 70a.

It is useful that in the illustrated embodiments of the present invention eliminated the complex combination of the extraction process GKZH with cooling systems of any corresponding installation for producing LNG.

One skilled in the art will appreciate that the present invention may be practiced in various ways without departing from the scope of the invention defined in the appended claims. For example, instead of natural gas, the feed stream can be formed from other types of gas, including petroleum gas.

Claims (14)

CLAIM 1. A method of separating a mixed hydrocarbon feed stream from an initial feed stream, such as a natural gas stream, and separating the mixed hydrocarbon feed stream into one or more fractionated streams and producing a liquefied hydrocarbon stream, which contains at least the following steps, which: (a) supplying the feed stream; (b) partially condensing the feed stream to obtain a partially condensed feed stream; (c) dividing the partially condensed feed stream into a gaseous feed stream taken from above and a feed stream of mixed condensed hydrocarbons; (ίί) liquefying at least a portion of the source gaseous top-off stream to produce a liquefied hydrocarbon stream; (d) separating the feed stream of the mixed condensed hydrocarbons into at least a first part of the feed stream and a second part of the feed stream; (e) passing the first part of the feed stream into the first gas / liquid separator through the first inlet of the first gas / liquid separator to obtain at least a first fractionated stream in the form of a first gaseous stream taken from above and a first liquid taken from below; (e) passing a first bottom-withdrawn liquid stream into a second gas / liquid separator to obtain at least a second fractionated stream in the form of a second gaseous stream taken from above and a second liquid taken from below; (g) cooling the second gaseous stream taken from above by heat exchange with the second part of the feed stream without using the cooling circuit associated with the liquefaction process, and a warmer second part of the feed stream is obtained; (h) a warmer second part of the feed stream is passed into the first gas / liquid separator at a level which in the direction of gravity is below the level of the first inlet. 2. The method according to claim 1, in which at least a portion of the source gas, taken from above - 9 016149 stream liquefied without passing at least part of the source of gaseous, taken from the top of the stream through the first gas / liquid separator. 3. The method according to any one of claims 1, 2, in which the source gaseous stream taken from above is a stream with a high content of methane. 4. The method according to any one of claims 1 to 3, which further comprises the following steps: (i) separating the cooled second gaseous top-off stream obtained in step (g) into two or more fractions and (k) passing at least one of these fractions back into the second gas / liquid separator, preferably in the form of a reflux stream. 5. The method according to any one of claims 1 to 4, in which the pressure of the second part of the feed stream is reduced to heat exchange with the second gaseous stream taken from above in step (g). 6. The method according to any one of claims 1 to 5, in which the first and second gas / liquid separators are distillation columns. 7. The method according to any one of claims 1 to 6, in which the specified warmer second part of the feed stream is passed into the first gas / liquid separator at a level between the first inlet and the bottom of the separator. 8. The method according to any one of claims 1 to 7, in which the reboiler stream is additionally removed from the first gas / liquid separator, the reboiler stream is heated to obtain a return flow taken from below and the return flow taken from below is fed back to the first gas / liquid separator, this warmer second part of the feed stream is passed into the first gas / liquid separator at a level between the first inlet and the return flow taken from below. 9. The method according to any one of claims 1 to 8, in which the second gaseous stream taken from above contains more than 60 mol.% Ethane, preferably more than 90 mol.% Ethane. 10. The method according to any one of claims 1 to 9, in which the first fluid taken from below is a C ₂ ⁺ hydrocarbon stream. 11. The method according to any one of claims 1 to 10, in which the second fluid stream taken from below is a C ₃ ⁺ hydrocarbon stream. 12. A device for separating a mixed hydrocarbon feed stream from an initial feed stream and separating a mixed hydrocarbon feed stream into one or more fractionated streams and producing a liquefied hydrocarbon stream, which contains at least the following: a pre-cooling heat exchanger for cooling the feed stream in order to obtain a partially condensed feed stream; a source gas / liquid separator for separating a partial condensed feed stream into a gaseous stream taken from above and a stream of condensed mixed hydrocarbons; one or more heat exchangers comprising a main cryogenic heat exchanger configured to heat exchange a source gaseous stream taken from above with one or more coolants circulating in one or more cooling cycles to liquefy at least a portion of the source gaseous stream taken from above; a flow divider for separating a feed stream of mixed condensed hydrocarbons into at least a first portion of the feed stream and a second portion of the feed stream; a first gas / liquid separator for receiving a first portion of the feed stream through the first inlet of the first gas / liquid separator and to obtain at least a first fractionated stream in the form of a first gaseous, flow taken from above and a first flow taken from below; a second gas / liquid separator for receiving a first liquid stream taken from below and obtaining at least a second fractionated stream in the form of a second gas stream taken from above and a second liquid taken from below; a heat exchanger designed to receive a second part of the feed stream and a second gaseous stream taken from above and produce a cooled second gaseous stream taken from above and a warmer second part of the feed stream without using a cooling circuit associated with the liquefaction process; and a second inlet to the first gas / liquid separator for letting a warmer second portion of the feed stream into the first gas / liquid separator, wherein the second inlet is located at a level which in the direction of gravity is lower than the level of the first inlet. 13. The device according to item 12, in which the main cryogenic heat exchanger is designed to receive the original gaseous stream taken from above, flowing along the path that does not pass through the first gas / liquid separator, and for further cooling the initial gaseous stream taken from above. - 10 016149 14. The device according to any one of paragraphs.11-12, which further comprises a pressure reducing valve located between the flow divider and the heat exchanger.