GB2581519A

GB2581519A - Process to remove benzene and other heavies for the prevention of freezing in cryogenic gas separations

Info

Publication number: GB2581519A
Application number: GB1902436.3A
Authority: GB
Inventors: Bigger Kathryn; Walter Thomas
Original assignee: Linde GmbH
Current assignee: Linde GmbH
Priority date: 2019-02-22
Filing date: 2019-02-22
Publication date: 2020-08-26
Also published as: GB201902436D0

Abstract

Method for separating a light hydrocarbon liquid product S from a gaseous feed mixture F1 comprising hydrocarbons comprising: cooling the gaseous feed mixture by means of a first heat exchanger 112, partly separating 130 the gaseous feed mixture into a first vapour fraction V1 and a first liquid fraction L1, further cooling the first vapour fraction by means of a second heat exchanger 114, partly separating the first vapour fraction into a second vapour fraction V2 and a second liquid fraction L2, expanding the second vapour fraction in an expander 150 and feeding the expanded second vapour fraction to a first portion of a fractionation section 160. Preferably the cold residue R1 from the fractionation section is used as a refrigerant for any or all of the heat exchange systems wherein any or all of the heat exchange system may comprise the use of an external refrigerant. Ideally the gaseous feed mixture comprises at least one of methane, ethane, propane, butanes, pentanes, olefinic hydrocarbons such as ethylene, propylene, and C4 to C6+ olefins or other C2 to C6+ hydrocarbons. The first phase separator may be a separator vessel or a separator column. Processing unit for the above method is disclosed.

Description

Process to Remove Benzene and Other Heavies for the Prevention of Freezing in Cryogenic Gas Separations

BACKGROUND OF THE INVENTION

The invention relates to a method and process to prevent freezing of heavier components, while potentially reducing power consumption, during cryogenic separations of gasous feed that primarily contains light hydrocarbons and other light combustible gases. Such gas is commonly used as fuel gas. For certain applications, it is desirable to separate components of this gas using cryogenic separation to recover those components that have commercial value which is greater than the fuel value, and to improve the combustion quality of the remaining fuel gas. /5

This gas can be a mixture of natural gas and/or off-gas from refinery units, petrochemical plants, or olefins plants and will be referred to as gaseous feed in this discussion. The gaseous feed typically consists of light paraffinic hydrocarbons such as methane, ethane, propane, butanes, and pentanes, olefinic hydrocarbons such as ethylene, propylene, and C4 to C6+ olefins, other C2 to C6+ hydrocarbons, hydrogen, nitrogen, carbon monoxide, carbon dioxide, and water vapor. The gaseous feed can contain varying levels of all the mentioned components, but need not contain all of these components. The gaseous feed can also contain various contaminants, such as heavy metals and sulfur compounds, for example mercury, arsenic, mercaptans, and hydrogen sulfide.

Certain constituents of the gaseous feed normally must be removed prior to cryogenic processing, such as carbon dioxide, heavy metals such as mercury, sulfur compounds, and water vapor. Prior to introducing the feed gas to the cryogenic separation process, the gaseous feed will be processed to remove these contaminants. Treating to remove these components is not the subject of the present invention and will not be discussed any further.

Also, it is desirable to remove or at least sufficiently reduce the concentration of some heavier hydrocarbons, which are critical as they tend to freeze at cryogenic processing temperatures. This is important for example in the context of fractionating, as such critical heavier hydrocarbons can freeze out during fractionation. For example, some heavier hydrocarbons in the gaseous feed, especially aromatics such as benzene, toluene, ethyl benzene, or xylene, or other 09+ components, have relatively high freezing points, and must be reduced to extremely low concentration levels to prevent freezing and plugging of process equipment in the context of cooling and liquefaction steps.

The present invention relates to the recovery of C2 to 06+ hydrocarbons, including paraffins and/or olefins, from the gaseous feed described above. These C2 to 06+ hydrocarbons will be referred to as light hydrocarbon liquids in this discussion. Such light hydrocarbon liquid recovery advantageously uses prior art turboexpander processes, including expansion of cooled feed gases followed by fractionation. Relevant prior art turboexpansion processes are described in U.S. Patent No. 4,157,904, 4,171,964, 4,617,039, 4,869,740, 4,895,584, 6,278,035, 6,311,516, and 7,544,272. As mentioned above, for certain gas compositions, especially gases containing low solubility critical heavier hydrocarbons such as benzene and other aromatics, and/or 09+ hydrocarbon components, freezing out of these components in colder portions of fractionating sections is highly problematic. Benzene is of particular concern in this context, as it has low solubility and a relatively high freezing point in the liquid phase of light hydrocarbons. Actual temperatures at which such freezing out occurs especially depends on the concentration of these components within a feed gas, as well as the concentration of other components within the gas. As an example, for a representative stream at typical pressure and composition for the process of this invention, benzene is predicted to freeze at the following temperatures, depending upon the concentration of benzene: Concentration of Benzene Freezing Temperature Freezing Temperature (molar ppm) at 17.2 bara at 250 psia 1.0 mol 943 -83°C -117°F 1,000 ppm (molar) -124°C -192°F ppm (molar) -152°C -242°F The stream composition in the above example is approximately 30% hydrogen, 32% methane, 4% nitrogen, with the balance 02 to 06 hydrocarbons, including benzene.

In the prior art, it has been attempted to remove these components by ambient temperature adsorption upstream of the turboexpander process using regenerative fixed bed or solvent, or by cryogenic distillation either upstream or downstream of the 02 to 06+ recovery process, i.e. via sequential cryogenic distillation.

The object of the invention is to facilitate removal of light hydrocarbon liquids from gaseous feed mixtures, especially feed gas that originates as off-gas from refinery units, petrochemical plants, olefins plants, and/or from natural gas in an integrated fashion, while preventing the conditions that could lead to the freezing of benzene or other critical low solubility components.

This object is achieved by a method comprising the method steps of claim 1 and a processing unit comprising the features of claim 14. Advantageous embodiments are the subject matter of the dependent claims.

DESCRIPTION OF THE INVENTION

According to the invention, there is provided a method for separating a light hydrocarbon liquid product from a gaseous feed mixture comprising the features of claim 1. The gaseous feed mixture can comprise any one or more of methane, 02 to C6+ hydrocarbons, and critical freeze out C5-C9+ hydrocarbons such as benzene. It may also comprise any one or more of nitrogen, hydrogen and carbon monoxide. The method comprises the following steps: cooling the gaseous feed mixture from a first temperature level to a second temperature level by means of a first heat exchange, at least partly separating the gaseous feed mixture into a first vapor fraction and a first liquid fraction by means of a first phase separator, the first liquid fraction comprising a larger concentration of heavier hydrocarbons than the first gaseous fraction, further cooling the first vapor fraction by means of a second heat exchange to a third temperature level, the third temperature level being lower than the second temperature level, at least partly separating the first vapor fraction into a second vapor fraction and a second liquid fraction by means of a second phase separator, - expanding the second vapor fraction in an expander and feeding the expanded second vapor fraction to a first portion of a fractionation section. Expendiently, the separating of the gaseous feed mixture into a first vapor fraction and a first liquid fraction is conducted at temperatures high enough to avoid any risk of freezing.

The method according to the invention is highly effective in preventing the freezing of hydrocarbons that have low solubility at cryogenic temperatures, such as benzene and other aromatics, applicable for any combination of subzero processing temperature and concentration of components that have a tendancy to freeze due to low solubility, while potentially reducing power consumption.

Advantageously, the method further comprises the steps of -extracting a cold residue gas from the first portion of the fractionation section and using the cold residue gas as refrigerant for the heat exchange systems, - extracting a light hydrocarbon liquid product from a second portion of the fractionation section.

Utilizing the invention, it is possible to effectively redirect heavier hydrocarbons which are critical regarding freeze out, especially benzene, to relatively warm portions of a fractionating section. This can also be utilized to reduce the power consumption required for refrigeration of the feed gas. By efficiently reducing the concentration of these components in the colder sections, problems associated with freezing out of such components, such as plugging of equipment, can be minimized or even completely avoided. At the same time, these components can be readily recovered in light hydrocarbon liquid (02 to 06+) stream extracted from the fractionation section. Once the critical freezing components are recovered in the liquid product, these light hydrocarbon liquids will no longer be subjected to subzero temperatures and the potential for freezing will be eliminated. If it is desired to selectively remove the freezing components from the 02 to 06+ liquid for product purity requirements, such separation would take place downstream of this process and is not the subject of this invention.

The invention is especially advantageous in that power consumption necessary for refrigeration of feed gases containing such heavier components can be significantly reduced over prior art solutions.

Compared to the prior art technique of ambient temperature adsorption, the invention leads to a significant simplification in the equipment required. For example, a reduction of the number of pieces of equipment can be achieved, since the adsorbent process usually requires a number of vessels for contacting gas with the adsorbent (either multiple fixed beds or adsorber columns) and additional components for adsorbent regeneration, such as vessels and heat exchangers. Furthermore, the invention has a reduced energy consumption in that it eliminates the need for heating and cooling during adsorbent regeneration. Also, waste streams can be essentially eliminated according to the invention, while adsorbent regeneration, as used in the prior art, produces waste gas streams, the disposal of which can be problematic. Also, operating expenses are reduced, as, according to the invention, there is no need for replacement or change out of adsorbent material.

Compared to cryogenic distillation processes installed sequentially to the C2 to C6+ recovery process, as also practiced in the prior art, the invention renders possible a significant reduction of necessary pieces of equipment, as distillation columns and associated heat exchangers, vessels, and pumps can be eliminated. Energy consumption is also reduced by eliminating reboilers and condensers.

All in all, implementing the present invention reduces operating complexity compared to any of the prior art operating processes discussed above.

Advantageously, the method further comprises selectively feeding the first liquid fraction to a second portion of the fractionation section, the temperature level of which is higher than that of the first portion. In some cases, it is of further advantage to reheat the first liquid fraction by means of a third heat exchange before feeding this first liquid fraction to the second portion of the fractionation section. Hereby, it can be ensured that fractions of the feed mixture containing elevated levels of critical heavier hydrocarbons, such as benzene, are processed in warmer portions of a fractionating section, so that there is no danger of freezing out of these components and the power consumption is reduced.

The method of the invention further advantageously comprises feeding at least part of the second liquid fraction to the first and/or the second portion of the fractionation section.

Expediently, the first heat exchange and the second heat exchange are performed in a single heat exchanger system or a multitude of heat exchanger systems, these heat exchanger systems especially comprising one or more brazed aluminium heat exchangers and may additionally comprise of one or more shell and tube heat exchangers.

This process advantageously makes use of prior art, in which a cold residue gas is extracted from the fractionation section and used as a refrigerant for the first and/or the second heat exchange. Hereby, costs for providing cold process streams for cross exchange with feed gas mixture to be cooled down are significantly reduced.

Expediently, the heat exchange system comprises the prior art of using one or more levels of an external refrigerant, the temperature of which is tailored to match the process temperature closely. Hereby, the efficiency of a heat exchanger system can be enhanced, leading to lower energy consumption.

According to a preferred embodiment, the first phase separator is provided as a separator vessel or a separator column. While separator vessels provide a low cost means for separation of feed gas mixtures for most applications, the use of separator columns can be advantageous in case of feed gas mixtures with higher contents of benzene and/or other critical freezing hydrocarbons.

According to a further preferred embodiment, a liquid stream extracted from the fractionation section, is recycled to the gaseous feed stream. This is especially advantageous in the case of higher concentrations of benzene or other critical freezing hydrocarbon species in the feed gas stream, as the freezing temperature of the feed stream can be decreased, thus minimizing the danger of freezing out in a separator, brazed aluminum heat exchanger, or column into which the feed gas stream is subsequently fed. This effect is due to the fact that the tendency of such critical hydrocarbons to freeze can be reduced in case of the presence of other, uncritical heavier hydrocarbons, which condense, but do not freeze in relevant temperature regions (for benzene the critical temperature region can range from -83°C to -152°C (-117°F to -242°F), at benzene concentrations ranging from 100 ppm to 1.0 molc/0). These uncritical heavier hydrocarbons have the effect of maintaining potentially critical hydrocarbon species in a state of solution, whereby a washing out or separation of these critical species during further processing is facilitated.

The object of the invention is also achieved by a processing unit comprising the features of claim 14.The processing unit according to the invention is configured and adapted for separating light hydrocarbon liquids from a gaseous feed mixture which contains but is not limited to methane, C2 to C6+ hydrocarbons, critical freeze out hydrocarbons, and may contain nitrogen, hydrogen, and carbon monoxide. The processing unit comprises a first heat exchanger system adapted for cooling the gaseous feed mixture from a first temperature level to a second temperature level, a first phase separator adapted for at least partly separating the gaseous feed mixture into a first vapor fraction and a first liquid fraction, the first liquid fraction comprising a larger concentration of heavier hydrocarbons than the first vapor fraction, a second heat exchanger system configured and adapted for further cooling the first vapor fraction to a third temperature level, the third temperature level being lower than the second temperature level, a second phase separator configured and adapted for at least partly separating the first vapor fraction into a second vapor fraction and a second liquid fraction, an expander configured and adapted for expanding the second vapor fraction a fractionating section comprising at least a first colder portion and a second warmer portion, configured and adapted to process the expanded second vapor fraction in the first colder portion and the first liquid fraction in the second, warmer portion.

Again, expendiently, the separating of the gaseous feed mixture into a first vapor fraction and a first liquid fraction is conducted at temperatures high enough to avoid any risk of freezing.

Advantageously, the processing unit further comprises - a means for extracting a cold residue gas from the first portion of the fractionation section and using the cold residue gas as refrigerant for the heat exchange systems, and - a means for extracting a light hydrocarbon liquid product from the second portion of the fractionation section, where the liquid product contains the freezing components such as benzene that have been diverted from the cryogenic sections.

Preferably, the processing unit is further adapted to perform the method of any one of the method claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the invention will now be described with reference to the accompanying figures.

Figure 1 shows a first preferred embodiment of a processing unit, with which the invention can advantageously be implemented, Figure 2 shows a second preferred embodiment of a processing unit, with which the invention can advantageously be implemented, Figure 3 shows a third preferred embodiment of a processing unit, with which the invention can advantageously be implemented, and Figure 4 shows a fourth preferred embodiment of a processing unit, with which the invention can advantageously be implemented.

The embodiment that will be most suitable for a particular application will depend upon the feed conditons and composition as well as the product specifications and can be determined on a case-by-case basis via optimization or trial and error. Furthermore, the most suitable configuration may also be a combination or hybrid of one or more of the preferred embodiments.

In Figure 1, a first preferred embodiment of a processing unit for implementing the invention is generally designated 100. It comprises a heat exchanger system 110, a refrigeration system 120, a first phase separator 130, a second phase separator 140, an expander unit 150 and a fractionation section 160. In the embodiment of Figures 1 and 2, the phase separators are provided as separator vessels. Be it noted that phase separators will be referred to simply as separators in the following.

Heat exchanger system 110 can advantageously be provided as one or more brazed aluminium heat exchangers, and may also include one or more shell and tube heat exchangers, and serves to cool down the feed gas mixture by means of cross exchange with a number of cold process streams. The Refrigeration system 120 serves to augment this cooling down of the feed gas mixture by means of an additional, external refrigeration, which can make one or more passes through heat exchanger system 110.

The process pressures and temperatures described in the following are representative of typical conditions; however the actual pressures and temperatures can vary depending upon the optimum conditions for the given feed composition, feed and product pressures, and the level of critical freezing components contained in the gaseous feed mixture.

A dry and treated gaseous feed mixture Fl, in the following just referred to as feed mixture, containing components such as methane, C2 to C6+ hydrocarbons including freezing components such as benzene, and may contain nitrogen, hydrogen, and carbon monoxide, is cooled down from a first temperature level to a second temperature level in a first section 112 of heat exchanger system 110. At this second temperature level, feed mixture Fl is partially condensed. As an example, the feed mixture initially has a pressure of around 54.5 bar (791 psia) and a temperature of around 44°C (111°F), and is cooled down to -25°C (-13°F) in the first section 112 of heat exchanger 110, essentially maintaining the same pressure less hydraulic losses.

The feed mixture Fl thus cooled down to the second temperature level is fed to first separator 130, where it is at least partially separated into a first vapor fraction V1 and a first liquid fraction L1. The second temperature level is chosen such that an appreciable portion of the heavier hydrocarbons within the feed mixture, such as benzene, especially a portion typically greater than 90%, condenses but is not subject to freezing. At the same time, the second temperature level ensures that a relatively small portion of lighter hydrocarbons, especially C2 to 03 hydrocarbons, condenses.

Vapor fraction V1 is then further cooled down to a third temperature level in a second section 114 of heat exchanger system 110, so that it again at least partly condenses. The third temperature level is, as an example, around -76°C (-105°F). Be it noted that the third temperature level, which is highly dependant upon the gaseous feed pressure and compositon, will be selected to effect the optimum level of condensation of the C2 and heavier components remaining in first vapor fraction V1. The pressure of the vapor fraction V1 typically remains unchanged except for hydraulic losses, at around 54 bar (783 psia) in this example.

The first vapor fraction V1 thus cooled down to this third temperature level is then fed to second separator 140, where it is at least partly further separated into a second vapor fraction V2 and a second liquid fraction L2. A major portion of the C2 and heavier components that did not condense in first separator 130 will condense and be separted into second liquid fraction L2, while a major portion of the methane and lighter components will be contained in second vapor fraction V2.

Second vapor fraction V2 is then fed into expander unit 150, which can especially be provided as a turboexpander, where it is cooled down further, and then into a colder portion 162 of fractionating section 160.

The second liquid fraction L2 is advantageously split, and can then be fed into a warmer portion 164 as well as the cooler portion 162 of fractionating section 160. Be it noted that the warmer portion 164 and colder portion 162 of fractionating section 160 are indicated purely schematically in Figure 1 and the further Figures. The temperature levels of portions 162 and 164 of fractionating section 160 will be highly dependant upon the gaseous feed composition and the product specfications. The warmest temperature in portion 164 will normally be close to ambient temperature, while the coldest temperature in portion 162 will be at the cryogenic level.

The first liquid fraction L1, which contains a high concentration of heavier hydrocarbons, such as benzene, is fed only into the warmer portion 164 of fractionating section 160.

By the process as described above, the concentration of critical freezing heavier hydrocarbons in second vapor fraction V2 and also in second liquid fraction L2 is significantly reduced over prior art solutions.

From the warmer portion 164 of fractionation section 160 a stream S of 02 to C6+ liquid hydrocarbons, including the critical freezing components such as benzene, is extracted, for example at temperatures around 19°C (66°F) and a pressure of around 19 bar (280 psia). A flow of cold residue gas R1 is extracted from the colder portion 162 of fractionating section 160, and fed back into heat exchanger system 110 as a cold process stream for cross exchange with feed mixture Fl, typically at temperatures of around -128°C ( -198°F) and a pressure of 17 bar (255 psia). The cold residue stream R1 contains close to 100% of the methane and lighter components that were present in the feed mixture, and can also contain small to trace percentages of 02 to 03 hydrocarbons that were present in the feed.

In Figure 2, a second embodiment of a processing unit for implementing the invention is shown and generally designated 200. Be it noted that in this and further embodiments components or streams corresponding to those of the embodiment of Figure 1 or respective other previous embodiments will not again be described in detail, and the same reference numerals will be used throught the figures. Additional reference numerals will only be provided for components or streams not included in the embodiment of Figure 1 or any other previous embodiment.

This embodiment according to Figure 2 differs from the first embodiment in that a control valve 210 to reduce the stream pressure is provided for the first liquid fraction L1. Furthermore, first liquid fraction L1 is reintroduced into a third section 116 of heat exchanger system 110, where it is reheated by cross exchange with warmer process streams. First liquid fraction Li is then fed to the warmer portion 164 of fractionation section.

it is possible to combine the embodiments of Figures 1 and 2 in one unit by installing components to allow operation in either embodiment. This will allow the unit to be flexible to operate optimially under a variety of feed conditions.

A third embodiment is shown in Figure 3, and generally designated 300. As can be seen, this embodiment differs from that of Figure 1 and 2 in that first separator 130, formerly provided as a separator vessel, is replaced by a separation column 330. As can be seen in Figure 3, feed mixture Fl can, simultaneously or selectively, be fed into different regions of separator column 330. Such a separator column is advantageously used in case of higher concentrations of critical freezing components in the feed mixture Fl, or in case lower concentrations of such critical components are desired in the outlet, i.e. in first vapor fraction V1 of first separator column 330.

According to the embodiment of Figure 3, it is also possible to selectively heat or cool first liquid fraction L1 in a third section 116 of heat exchanger system 110. Also, in addition or alternatively to feeding first liquid phase L1 (containing most of the critical freezing hydrocarbons such as benzene) into the warmer portion 164 of fractionation section 160 (designated fraction L1a in Figure 3), it is also possible to extract it as a product from the system (fraction Lib).

Furthermore, according to the embodiment as shown in Figure 3, a liquid stream L3 from the warmer portion 164 of fractionation section 160 is fed to separator column 330 to provide reflux allowing for the separation of components in separation column 330.

A further embodiment is shown in Figure 4 and generally designated 400. This embodiment differs from that of Figure 3 in that a fourth liquid stream L4 is recycled to the feed mixture Fl. Providing such a recycled liquid stream, which contains a relatively large fraction of heavier hydrocarbons other than the critical freezing hydrocarbons, is advantageous in case of higher concentrations of critical freezing species in the feed stream in that the freezing temperature of the feed stream can be decreased, thus minimizing the danger of freezing out in the first separator column 330. This effect is due to the fact that the tendency of freezing components to become insoluble can be reduced by the presence of other heavier hydrocarbons, which condense, but do not freeze, in relevant temperature regions. These heavier hydrocarbons have the effect of maintaining the critical hydrocarbon freezing components in a state of solution, whereby a washing out or separation of these critical species is facilitated.

According to the embodiment as shown in Figure 4, there is also provided a third separator 180, positioned between the first and the second separator, i.e. between separator colum 330 and separator vessel 140. First vapor fraction V1 is fed into third separator 180 after having been further cooled in a first portion 114a of the second heat exchange of heat exchanger system 110. In third separator 180, the first vapor fraction is separated into an intermediate vapor fraction V1.5 and an intermediate liquid fraction L1.5.

Intermediate vapor fraction V1.5 is fed, after further cooling in a second portion 114b of the heat exchanger system 110, into second separator 140, and the intermediate liquid fraction L1.5 is recycled into separator column 330 as reflux. By means of such a third separator 180, the concentration of critical freezing hydrocarbons within the intermediate vapor fraction V1.5 and then second vapor fraction V2 can be further reduced, further minimizing the risk of freezing out within the cold portion 162 of fractionation section 160.

Using either stream L3 in embodiment 3 or stream L1.5 in embodiment 4 as reflux to separator column 330 may be more advantageous in terms of effectiveness of facilitating the separation of components and/or energy efficiency, depending upon the stream composition and thermal conditions. Determination of which reflux stream is more advantageous can be found via optimization on a case-by-case basis.

Claims

Claims 1. Method for separating a light hydrocarbon liquid product (S) from a gaseous feed mixture (F1) comprising hydrocarbons, including the following steps: cooling the gaseous feed mixture (F1) from a first temperature level to a second temperature level by means of a first heat exchange, at least partly separating the gaseous feed mixture (F1) into a first vapor fraction (V1) and a first liquid fraction (L1), the first liquid fraction (L1) comprising a larger concentration of heavier hydrocarbons than the first vapor fraction (V1), such that the temperature of stream L1 is not cold enough to freeze any of the heavier components, further cooling the first vapor fraction (V1) by means of a second heat exchange to a third temperature level, the third temperature level being lower than the second temperature level, at least partly separating the first vapor fraction into a second vapor fraction (V2) and a second liquid fraction (L2), expanding the second vapor (V2) fraction in an expander (150) and feeding the expanded second vapor fraction (V2) to a first portion (162) of a fractionation section (160).
2. Method according to claims 1 and 3, further comprising extracting a cold residue gas (R1) from the first portion (162) of the fractionation section (160) and using the cold residue gas (R1) as refrigerant for any or all of the 25 heat exchange systems, wherein any or all of the heat exchange systems may comprise of the use of an external refrigerant, extracting a light hydrocarbon liquid product (S) from a second portion (164) of the fractionation section, where the liquid product contains the freezing or heavy components such as benzene and C6+ that have been diverted from the cryogenic sections.
3. Method according to claims 1 and 2, further comprising: feeding at least part of the second liquid fraction (L2) to the first portion (162) and/or the second portion (164) of the fractionation section (160), and selectively feeding the first liquid fraction (L1) to a second portion (164) of the fractionation section (160), such that the majority of the mass of components that have low solubility at cold temperatures are contained within the first liquid fraction (L1).
4. Method according to any one of the preceding claims, wherein the gaseous feed mixture (F1) comprises at least one of the following hydrocarbons: methane, ethane, propane, butanes, and pentanes, olefinic hydrocarbons such as ethylene, propylene, and C4 to C6+ olefins, other C2 to C6+ hydrocarbons.
5. Method according to any one of the preceding claims, wherein the gaseous feed mixture may comprise one or more of nitrogen, hydrogen, and carbon monoxide.
6. Method according to any one of the preceding claims, further comprising reducing the pressure via a control valve followed by reheating or further cooling the first liquid fraction (L1) by means of a third heat exchange prior to selectively feeding the first liquid fraction (L1) to the second portion (164) of the fractionation section 160.
7. Method according to any one of the preceding claims, wherein the first heat exchange, the second heat exchange, third heat exchange, and/or fourth heat exchange are performed in a single or a multitude of heat exchangers (110), especially comprising one or more brazed aluminium heat exchangers and also may contain one or more shell and tube heat exchangers.
8. Method according to any one of the preceding claims, wherein the first phase separator is provided as a separator vessel (130) or a separator column (330).
9. Method according to any one of the preceding claims, wherein the first liquid fraction (L1) is split into two streams, and the first stream (L1a) is fed to the second portion (164) of fractionation section (160) and the second stream (Lib) is extracted as a product from the process.
10. Method according to any one of the preceding claims, when the first phase separator is provided as a column (330), such that feed stream Fl can be cooled to a first temperature level in a first heat exchange, and then fed either simultaneously or selectively, into different regions of separator column (330).
11 Method according to any one of the preceding claims, when the first phase separator is provided as a column (330), such that an intermediate liquid stream (L3) from the second portion (164) of the fractionation section (160) is fed as reflux to the separator column (330).
12. Method according to any one of the preceding claims, when the first phase separator is provided as a column (330), such that the first vapor fraction (V1) can be cooled in a first portion of the second heat exchange (114a) and separated into a third vapor fraction (V1.5) and third liquid fraction (L1.5), whereby the third vapor fraction (V1.5) is further cooled in a second portion of the second heat exchange (114b) and sent to the second separator (140) to be separated into the second vapor fraction (V2) and second liquid (L2) fraction, and the third liquid fraction (L1.5) is fed as reflux to the separator column (330).
13. Method according to any one of the preceding claims, wherein a liquid stream (L4) extracted from the fractionation section is recycled to the gaseous feed mixture (F1).
14. Processing unit configured and adapted for separating a light hydrocarbon liquid product (S) from a gaseous feed mixture (F1) comprising hydrocarbons the processing unit comprising a first heat exchanging means (112) configured and adapted for cooling the gaseous feed mixture (F1) from a first temperature level to a second temperature level, a first phase separator (130,330) configured and adapted for at least partly separating the gaseous feed mixture (F1) into a first vapor fraction (V1) and a first liquid fraction (L1), the first liquid fraction comprising a larger concentration of heavier hydrocarbons than the first vapor fraction, and the temperature of stream L1 is not cold enough to freeze any of the heavier components, a second heat exchanging means (114) configured and adapted for further cooling the first vapor fraction (V1) to a third temperature level, the third temperature level being lower than the second temperature level, a second phase separator (140) configured and adapted for at least partly separating the first vapor fraction (V1) into a second vapor fraction (V2) and a second liquid fraction (L2), an expander (150) configured and adapted for expanding the second vapor fraction (V2), a fractionating section (160) comprising at least a first colder portion (162) and a second warmer portion (164), configured and adapted to process the expanded second vapor fraction (V2) in the first, colder portion (162), the first liquid fraction (L1) in the second, warmer portion (164).and the second liquid fraction (L2) to be divided between the first, colder portion (162) and the second, warmer portion (164).
15. Processing unit according to claim 14, further comprising a means for extracting and reheating the cold residue gas (R1) produced in the first cold section (162) of the fractionation section (160) to cool down the incoming feed stream (F1) and some or all process streams (V1, L1, V1.5), a means for providing external refrigeration to further cool down the feed (F1) and some or all process streams (V1, Li, V1.5), and a means for extracting a light liquid hydrocarbon product (S) containing freezing components such as benzene from the warmer portion (164) of the fractionation section (160).
16. Processing unit according to any one of claims 14 or 15, adapted to process a gaseous feed mixture comprising hydrocarbons such as methane, ethane, propane, butanes, and pentanes, olefinic hydrocarbons such as ethylene, propylene, and C4 to C6+ olefins, other C2 to C6+ hydrocarbons, and which feed mixture also may contain nitrogen, hydrogen, and carbon monoxide, for the purpose of preventing the freezing of hydrocarbons that have low solubility at cryogenic temperatures, such as benzene and other aromatics, while potentially reducing power consumption.
17. Processing unit according to any one of claims 14 to 16, further configured and adapted to perform the method of any one of claims 1 to 13.