RU2554736C2 - Method of purifying multi-phase hydrocarbon flow and installation intended therefore - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: group of inventions relates to a method and an installation for the purification of a multi-phase hydrocarbon flow. The multi-phase hydrocarbon flow is purified with obtaining a purified liquid hydrocarbon flow, such as a flow of liquefied natural gas. The multi-phase hydrocarbon flow is supplied into the first gas-liquid separator, in which the said flow is divided under the first pressure into a hydrocarbon vapour flow of the first separator and the lower flow of the first separator. The lower flow of the first separator is then divided in the second gas-liquid separator under the second pressure, which is lower than the first pressure, with the formation of a hydrocarbon vapour flow of the second separator and a purified hydrocarbon flow. The hydrocarbon vapour flow of the second separator is subjected to compression in a compressor for the upper flow, which results in obtaining a stripping vapour flow, which is supplied into the first gas-liquid separator.

EFFECT: group of inventions is aimed at the creation of the method and installation for obtaining the purified liquid hydrocarbon flow, which does not require the application of cold in the upper gaseous flow for the creation of an irrigation flow.

17 cl, 2 dwg, 1 tbl

Description

The group of inventions relates to a method and apparatus for purifying a multiphase hydrocarbon stream.

The method and installation provide a purified liquid hydrocarbon stream. An additional low pressure fuel gas stream may be produced.

A common source of a multiphase hydrocarbon stream is a natural gas stream or a multiphase stream obtained from natural gas, for example, the formation of a multiphase stream containing a vapor phase and a liquid phase by cooling and / or changing the pressure of the natural gas. The methods described in the application can thus be used to produce a purified liquid hydrocarbon stream in the form of liquefied natural gas (LNG).

Natural gas is a valuable source of fuel, while at the same time being a source of various hydrocarbon compounds. Often, for various reasons, it is desirable to liquefy natural gas at a liquefied natural gas plant near or near a source of natural gas stream. For example, natural gas can be more easily stored and transported over long distances in the form of a liquid than in a gas form, since the liquid form takes up a smaller volume and does not require storage under high pressure.

As a rule, natural gas containing predominantly methane is fed to the LNG plant at elevated pressures and pre-treated in order to obtain a purified feed stream suitable for liquefaction at cryogenic temperatures. The purified gas is processed at several stages of cooling using heat exchangers to gradually reduce its temperature until liquefaction occurs. Liquid natural gas is then further cooled and expanded to a final atmospheric pressure, which is convenient for storage and transportation. Steam generated by flash evaporation during each expansion can be used as a source of fuel gas.

Some hydrocarbon streams, such as natural gas, may contain significant amounts of nitrogen, and therefore, unless special measures are taken to remove at least a portion of the nitrogen from the hydrocarbon stream, the fuel gas and liquefied hydrocarbon stream produced may contain undesirably high nitrogen levels. Many specifications for LNG require less than 1 mole in the final product. % nitrogen.

US 2008/0066493 discloses a method for purifying liquefied natural gas to form a liquid natural gas stream with a reduced content of components having low boiling points, such as nitrogen (N ₂ ). The method includes expanding a liquefied natural gas to form an expanded multiphase fluid and introducing a multiphase fluid into the column downstream of the gas-liquid contact section, whereby a bottoms liquid stream with a reduced content of components with low boiling points and an upper gaseous stream enriched are obtained low boiling components such as nitrogen. The bottoms liquid stream is sent to the flash unit. The upper gaseous stream, enriched with components with low boiling points, is heated in the heat exchanger and then compressed to the pressure of the fuel gas, resulting in a fuel gas. A recycle stream is separated from the fuel gas, which at least partially condenses in the heat exchanger against the overhead gas stream enriched with low boiling point components and is introduced into the column above the gas-liquid contacting section as an irrigation stream. In a number of embodiments of US 2008/0066493, a second gaseous stream (from the flash unit) is also heated in the heat exchanger, which is then compressed to the fuel gas pressure and added to the recycle stream.

Thus, at least part of the cold contained in the overhead gaseous stream is used to re-condensate the recycle stream to form irrigation, and this cold cannot be used to cool any other process stream anywhere else in the process.

In its first aspect, the present invention provides a method for purifying a multiphase hydrocarbon stream to form. purified liquid hydrocarbon stream, which (method) includes at least the stage of:

- the creation of a multiphase hydrocarbon stream from natural gas, which (multiphase hydrocarbon stream) contains a vapor phase and a liquid phase;

- supply of a multiphase hydrocarbon stream to the first gas-liquid separator;

- separation of the multiphase hydrocarbon stream in the first gas-liquid separator at the first pressure with the formation of the hydrocarbon vapor stream of the first separator containing hydrocarbons and nitrogen, and the lower stream of the first separator;

- separation of the lower stream of the first separator in the second gas-liquid separator at the second pressure with the formation of the hydrocarbon vapor stream of the second separator and the purified liquid hydrocarbon stream in the form of LNG, the second pressure being lower than the first pressure;

- compression of the hydrocarbon vapor stream of the second separator in the compressor of the overhead stream with the formation of the steaming steam stream; and

- supply of the steaming steam stream to the first gas-liquid separator at a vertical level below the level at which a multiphase hydrocarbon stream is introduced into the first gas-liquid separator.

In another aspect of the present invention, there is provided an apparatus for purifying a multiphase hydrocarbon stream comprising a liquid phase and a vapor phase, resulting in a purified liquid hydrocarbon stream in the form of LNG, which (installation) contains at least:

- means for creating a multiphase hydrocarbon stream from natural gas, which includes at least one liquefaction section and one or more expansion devices for the hydrocarbon stream;

a first gas-liquid separator for receiving a multiphase hydrocarbon stream and separating it into a hydrocarbon vapor stream of a first separator containing hydrocarbons and nitrogen, and a lower stream of a first separator, said first gas-liquid separator having a first inlet for supplying a multiphase hydrocarbon stream to a first gas-liquid separator, a first outlet for outputting a hydrocarbon steam stream of a first separator from a first gas-liquid separator, a second exit for outputting a lower stream a first separator from the first gas-liquid separator and a second inlet located vertically lower than the specified first inlet to supply a stripping steam stream to the first gas-liquid separator;

- a second gas-liquid separator, designed to receive the lower stream of the first separator and separate it into a hydrocarbon vapor stream of the second separator and a purified liquid hydrocarbon stream in the form of LNG, and the specified second gas-liquid separator has a first inlet in fluid communication with the second outlet of the first gas-liquid separator, for supplying the lower stream of the first separator to the second gas-liquid separator, the first outlet for outputting the hydrocarbon steam stream of the second separator from the second g zozhidkostnogo separator and a second output for outputting purified liquid hydrocarbon stream from the second gas-liquid separator;

- an expansion device for the lower stream, located between the second outlet of the first gas-liquid separator and the first inlet of the second gas-liquid separator, to reduce the pressure of the lower stream of the first separator; and

- a head-stream compressor designed to compress the hydrocarbon steam stream of the second separator to form a stripping steam stream, which (the head stream compressor) has an inlet in fluid communication with the first outlet of the second gas-liquid separator to receive a hydrocarbon vapor stream of the second separator and an output in communication in fluid with a second inlet of the first gas-liquid separator for outputting the steaming steam stream.

Embodiments are further described by way of example only with reference to the accompanying non-limiting drawings, of which:

figure 1 is a diagrammatic diagram of a method and apparatus for purifying a multiphase hydrocarbon stream according to one embodiment; and

figure 2 is a diagrammatic diagram of a method and apparatus for liquefying a stream of hydrocarbon feedstock, comprising a method and apparatus for purifying a multiphase hydrocarbon stream.

For the purposes of this description, the same reference number will be assigned to both the line and the stream carried on that line.

The methods and installations disclosed in the application offer an improvement in the separation of multiphase flow components in two successive stages in two gas-liquid separators operating at different pressures. The hydrocarbon vapor stream of the second separator from the second gas-liquid separator is compressed in the head-stream compressor and returns to the first gas-liquid separator in the form of a steaming steam stream.

The present invention can successfully propose a method and apparatus for purifying a multiphase hydrocarbon stream, whereby a purified liquid hydrocarbon stream can be obtained that does not require the use of cold in the overhead gaseous stream to create an irrigation stream.

In the method and installation of the present invention, stripping steam is successfully used in the first gas-liquid separator, which is formed by compressing the vapor stream from the second gas-liquid separator, to enhance the separation of components. Obtaining stripping steam from the second gaseous stream allows the use of a second gaseous stream to improve the separation of components without the need for re-condensation of its or its part.

Thus, the cold in the hydrocarbon vapor stream of the first separator, which in US 2008/0066493 was necessary to create irrigation in order to achieve the desired efficiency in the separation of components, in this case released for use for any other purpose. Naturally, the invention does not exclude the possibility that the irrigation stream can still be created (using cold from the hydrocarbon vapor of the first separator and / or from the external refrigerant) and be used to further improve separation of the components. But this is completely optional. In some embodiments, an irrigation stream, such as that used in US 2008/0066493, is not required.

One or more devices for expanding the hydrocarbon stream, as well as the first and second gas-liquid separators, can form part of the LNG flash system. Similarly, lowering the pressure of at least a partially liquefied hydrocarbon stream to create a multiphase hydrocarbon stream and subsequent separation in the first and second gas-liquid separators can form part of the process of instant flash LNG evaporation.

Accordingly, the formation of a multiphase hydrocarbon stream from natural gas may include the following steps:

- creating a stream of hydrocarbon feed from a natural gas stream at elevated pressure;

- separation of the ongoing hydrocarbon stream from the hydrocarbon stream;

- supplying an ongoing stream to the cooling and liquefaction section, where it is cooled and at least partially liquefied, resulting in at least partially liquefied hydrocarbon stream;

- supplying at least a partially liquefied hydrocarbon stream to the inlet of at least one device for expanding the hydrocarbon stream and reducing there the pressure of at least a partially liquefied hydrocarbon stream, resulting in a multiphase hydrocarbon stream.

A multiphase stream may comprise a vapor phase and a liquid phase. The purified liquid hydrocarbon stream obtained according to the present invention, in particular obtained in the form of LNG, may have technical characteristics that allow it to evaporate and be used as a network gas.

Not intending to be bound by the following explanation by analogy, the applicant believes that the head-stream compressor delivers the compression heat to the hydrocarbon vapor stream of the second separator and, thus, acts as a special reboiler that produces a steam-vapor stream at a higher pressure and temperature than pressure and temperature hydrocarbon steam stream of the second separator, for the first gas-liquid separator. This steaming vapor stream enhances the separation of components with a lower boiling point, such as nitrogen, from the expanded hydrocarbon stream in the first gas-liquid separator. Lower boiling components are discharged into the hydrocarbon vapor stream of the first separator.

If the hydrocarbon vapor stream of the first separator is not pure nitrogen, but also contains a certain set of hydrocarbons, this stream can be used as fuel gas. Thus, the method may further include:

- extracting the low pressure fuel gas stream (LP) from the hydrocarbon vapor stream of the first separator; and

- the flow of low pressure fuel gas to the combustion device at a fuel gas pressure not exceeding the pressure of the hydrocarbon gas stream of the first separator. The first pressure of the first gas-liquid separator may be equal to or higher than the pressure of the fuel gas. Neither the hydrocarbon vapor stream of the first separator, nor the low pressure fuel gas stream are predominantly compressed before being used in the combustion device.

In US 2008/0066493, nitrogen (N2) and other vaporous constituents that separate in the column are compressed and released into the high pressure fuel gas stream. Table 1 of US 2008/0066493 discloses an example in which a feed stream of natural gas with a nitrogen content of 3.05 mol. % is processed, giving a stream of liquefied natural gas with a nitrogen content of 0.65 mol. % and fuel gas with a nitrogen content of 24 mol. % However, high nitrogen fuel gas streams can pose significant problems when used on gas fuel turbines, which are commonly used to drive compressors or generators in any liquefaction plant. For example, many turbines running on air-derived gas are currently unable to withstand the nitrogen content of their fuel gas above 15%.

In this regard, in preferred embodiments of the present methods and installations, the hydrocarbon vapor stream of the first separator is used as a low pressure fuel gas stream. Fuel gas with large amounts of nitrogen can still be used as low pressure fuel gas, for example, for stoves, boilers and / or dual-fuel diesel engines.

For the purposes of use in this application, the expression "low pressure" in the low pressure fuel gas stream is close in meaning to the "high pressure" fuel gas stream that is required for the operation of gas turbines. In the present description, low pressure fuel gas may be under pressure in the range of 2 to 15 bar (abs) and, more specifically, from 2 to 10 bar (abs). High pressure fuel (HP) can be at a pressure of 15 bar (abs) or higher, typically in the range of 15 to 40 bar (abs) and, more specifically, from 20 to 30 bar (abs).

The first gas-liquid separator can be successfully operated at a suitable or higher pressure of the fuel gas, so that the hydrocarbon vapor stream of the first separator can be successfully provided at a sufficiently high pressure, which does not require compression or significant compression before use. For this reason, it is preferable to choose such a first pressure of the gas-liquid separator so as to obtain a hydrocarbon vapor stream of the first separator at a pressure equal to or higher than the predetermined pressure of the fuel gas.

In particular, when used as a low-pressure fuel, the hydrocarbon vapor stream of the first separator of the present invention may contain N ₂ in a wide range, for example in the range from 30 to 95 mol. % N ₂ and, more preferably, from 60 to 95 mol. %

Thus, the present invention can be successfully used to create a low pressure fuel gas stream suitable for use in combustion devices, such as furnaces or incinerators, or, for example, in dual-fuel diesel engines that can be used for power plant generators. The low pressure fuel gas stream may be released from the hydrocarbon vapor stream of the first separator by heating. The hydrocarbon vapor stream of the first separator can be directed to any suitable heat exchange device in which it can be used to cool the process stream. The process stream can mainly come in the form of a part of natural gas in order to cool this part of natural gas.

In order to obtain a high-pressure fuel gas stream suitable for use as a gas turbine fuel, the purification method and installation disclosed in the application may be included in a method for liquefying a hydrocarbon feed stream and a corresponding installation. High pressure fuel gas may be released from the hydrocarbon stream prior to liquefaction. This is advantageous because the hydrocarbon feed stream may have a low nitrogen content compared with the low pressure fuel gas stream released from the hydrocarbon vapor stream of the first separator. In addition, the hydrocarbon feed stream is a high pressure stream, so there is no need for additional compression of a portion of this stream to be used as a fuel gas stream. Thus, there is no need for a compressor for high pressure fuel gas. If necessary, if the hydrocarbon feed stream is under too high a pressure, the pressure of the released fuel gas can be (but not necessarily) reduced before being used as fuel.

In addition, the method disclosed in the application has the advantage that it eliminates the use of a gaseous stream produced by expanding a liquefied hydrocarbon stream as a high pressure fuel gas stream. Such gaseous streams produced by stepwise gas-liquid separation, such as flash flash operations, would have to have a higher content of lower boiling components, such as nitrogen, compared to the liquid product produced by the separator.

Turn to the drawings. Figure 1 shows the method and installation 1 for purification of multiphase hydrocarbon stream 145 according to the first embodiment. Multiphase hydrocarbon stream 145 is formed from natural gas. Multiphase hydrocarbon stream 145 contains vapor and liquid phases. Below, with reference to FIG. 2, one more example of how a multiphase hydrocarbon stream 145 can be created is discussed in more detail.

The multiphase hydrocarbon stream 145 is supplied to the first inlet 148 of the first gas-liquid separator 150. The first gas-liquid separator 150 produces the hydrocarbon vapor stream 205 of the first separator as an upper stream at the first outlet 151 and a lower stream 155a of the first separator, which is a liquid stream, at the second outlet 152 at or near the bottom of the first gas-liquid separator 150. The first gas-liquid separator 150 may be in the form of a separation column such as a fractionating or distillation column. The first gas-liquid separator 150 is preferably in the form of a nitrogen separation column. The hydrocarbon vapor stream 205 of the first separator generally contains hydrocarbons, typically methane and nitrogen.

The separation is carried out at a first pressure, which preferably lies in the range of 2 to 10 bar (abs), in order to achieve an even lower nitrogen content in the liquid hydrocarbon stream, which would remain applicable as a low pressure fuel gas stream.

To improve separation in the first gas-liquid separator 150, a steaming steam stream 185a is supplied to the second inlet 149. The second inlet 149 typically comprises a steam inlet device known to those skilled in the art. The second inlet 149 is predominantly located at a vertical level lower than the level of the first inlet 148, in order to ensure efficient distillation of lighter components of the hydrocarbon mixture, such as nitrogen, from the liquid phase of the multiphase hydrocarbon stream to the vapor phase. Typically, the first inlet 148 may comprise an intake manifold known to those skilled in the art.

In one of the preferred embodiments, the first gas-liquid separator 150 comprises a contact zone, advantageously comprising contact enhancing means 154, such as trays or packing, for improving separation. The contact enhancing means 154 is advantageously located vertically between the first and second inputs 148, 149.

The contact enhancement means may include a plurality of plates arranged one above the other, the configuration of which may allow the liquid phase to flow horizontally along each plate and flow to the next plate, while the vapor phase will bubble through the openings in the plates. This increases the contact area between the liquid and vapor phases. Alternatively, the contact enhancing means may consist of a nozzle. The contact zone of the nozzle acts similarly to the plates in the case of the nozzle, which can be both structured and structureless, increasing the contact area between the liquid and vapor phases.

The hydrocarbon vapor stream 205 of the first separator may contain hydrocarbons and greater than or equal to 30 mol. % stock N ₂ . Preferably, the hydrocarbon vapor stream 205 of the first separator has a pressure lower than or equal to 10 bar (abs).

The low pressure fuel gas stream 215 may be obtained from the hydrocarbon vapor stream 205 of the first separator. The hydrocarbon vapor stream 205 of the first separator may, for example, be directed to a fuel gas heat exchanger 210, where it is heated by a heating stream 355, resulting in the formation of a low pressure fuel gas stream 215, for example at a pressure of about 5 or 6 bar (abs). At the same time, the heating stream is cooled and converted into a cooled heating stream 365.

The fuel gas heat exchanger 210 may be a heater, such as an external heater, in which case the heating stream 355 may be supplied as ambient air or external water to form a cooled heating stream 365 in the form of a stream of chilled air or chilled water. The cooled heating stream 365 can be used as an intermediate stream to quickly cool another stream. However, in preferred embodiments, heating stream 355 is supplied as a process stream that requires cooling, resulting in an additional cooled process stream. In this way, the cold energy of the hydrocarbon vapor stream 205 of the first separator can be effectively used to provide cooling of the process stream in unit 1, for example, a hydrocarbon stream or a refrigerant stream. An example related to the embodiment of FIG. 2 is provided.

The low pressure fuel gas stream 215 may contain greater than or equal to 30 mol. % amount of N ₂ . The low pressure fuel gas stream 215 may then be routed to the low pressure fuel gas network. 1 shows a low pressure fuel gas stream 215 directed directly to one or more low pressure fuel gas consumers 220, such as a combustion device, such as a stove, boiler, or dual fuel diesel engine. Such combustion devices, as is known to those skilled in the art, are typically capable of withstanding high levels of nitrogen in low pressure fuel gas.

The bottom stream 155a of the first separator from the first gas-liquid separator 150 may be supplied to the first inlet 158 of the second gas-liquid separator 160. The second gas-liquid separator 160 operates at a second pressure that is lower than the first pressure used to provide separation in the first gas-liquid separator 150. The second pressure is mainly lower than 4 bar (abs), but even more preferably below 2 bar (abs). Preferably, the second pressure may be equal to or close to atmospheric pressure. In accordance with the teachings of the present disclosure, “equal to or close to atmospheric pressure” preferably implies a pressure between 1 and 1.3 bar (abs).

If the pressure drop between the first and second gas-liquid separators 150, 160 is not enough to provide a suitable second pressure, the first stream of the first separator 155a can be passed through the device for expanding the lower stream, which supplies the (expanded) lower stream 155b of the first separator to the first inlet 158 of the second gas-liquid separator 160 at a second pressure.

The second gas-liquid separator 160 produces the hydrocarbon vapor stream 175 of the second separator in the form of an overhead stream at the first outlet 161 and a purified liquid hydrocarbon stream 165 at the second outlet 162. The second gas-liquid separator 160 may be a suitable flash unit.

The purified liquid hydrocarbon stream 165, which may be an LPG stream, if the source of the multiphase hydrocarbon stream 145 is natural gas, may be produced at or near atmospheric pressure. The purified liquid hydrocarbon stream 165 may be directed to a storage tank 170, for example, to a storage tank of a cryogenic type.

The hydrocarbon vapor stream 175 of the second separator is directed to the overhead compressor 180, where it is compressed to form a steaming steam stream 185. The overhead compressor 180 can be mechanically driven by the actuator 190 of the overhead compressor, such as a gas turbine, steam turbine and / or electric motor . The stripping steam stream 185 may in some cases be mixed with the additional stripping steam stream 235 to form a combined stripping steam stream 185a before the latter is directed to the second inlet 149 of the first 185 gas-liquid separator 150 to improve separation therein. The steam stripping stream 185 is produced at a certain third pressure, which, as a rule, should be equal to or slightly higher than the first pressure, for example, the first pressure plus a possible pressure loss between the discharge end of the compressor 180 for the upper stream and the second inlet 149 of the first gas-liquid separator 150. Third pressure may be, for example, 0-2 bar (abs) above the first pressure.

Additional steaming steam stream 235 may contain the vaporized product from the cryogenic storage tank. In the case of cryogenic storage of the purified liquid hydrocarbon, some degree of evaporation of the purified liquid hydrocarbon in the storage tank 170 can be expected due to imperfect thermal insulation and temperature fluctuations. Evaporated vapor can be removed as vaporized gas stream 195. Evaporated gas stream 195 may be supplied to the evaporated gas compressor 230, where it is compressed to form a compressed vaporized gas stream 235 for use as an additional vaporized vapor stream. The evaporated gas compressor 230 may be driven by the evaporator gas compressor drive 240, such as a gas or steam turbine and / or electric motor.

In one alternative embodiment, not shown in FIG. 1, an additional stripping steam stream 235 may be introduced directly into another separate inlet of the first gas-liquid separator 150. The final choice of where the additional stripping steam stream 235 should be supplied to the first gas-liquid separator may determined by the composition and temperature of the additional stripping steam stream 235, such as a stream of compressed vaporized gas.

In one preferred embodiment, the method disclosed in the application can be used as part of a liquefaction process for a hydrocarbon feed stream, in which case the multiphase hydrocarbon stream to be treated can be formed by cooling and / or changing the pressure of the hydrocarbon feed stream. The hydrocarbon feed stream may be any suitable gas stream that needs to be cooled and liquefied, but typically it is a natural gas stream obtained from natural gas or oil deposits. Alternatively, the hydrocarbon feed stream may be obtained from any other source, including a synthetic source such as a Fischer-Tropsch process.

Typically, a natural gas stream is a hydrocarbon composition consisting mainly of methane. Advantageously, the hydrocarbon feed stream contains at least 50 mol. % and. more preferably at least 80 mol. % methane.

Hydrocarbon compositions such as natural gas may also contain non-hydrocarbon components such as H ₂ O, N ₂ , CO ₂ , Hg, H ₂ S and other sulfur compounds, and the like. Before cooling and possibly liquefying, natural gas can be pretreated if desired. This pre-treatment may include reducing the content and / or removing undesirable components such as CO ₂ and H ₂ S, or other operations such as early cooling, pre-compression, and the like. Since all of these operations are well known to those skilled in the art, they will not be discussed further here.

Thus, the expression “hydrocarbon feed stream” may include compositions without any previous treatment, which may be cleaning, dehydration and / or washing, as well as any composition that has been partially, substantially or completely processed to reduce the content and / or removing one or more compounds or substances, including (but not limited to) sulfur, sulfur compounds, carbon dioxide, water, Hg and one or more C ₂ + hydrocarbons.

Depending on the source, natural gas may contain different amounts of heavier hydrocarbons than methane, such as ethane, propane and butanes, and possibly smaller amounts of pentanes and aromatic hydrocarbons. The composition varies depending on the type and location of the gas.

Traditionally heavier hydrocarbons than methane are removed to some extent from the hydrocarbon feed stream prior to liquefaction for several reasons, such as the fact that they have different freezing and liquefaction temperatures, which can lead to their blocking of parts of the methane liquefaction plant, or to provide the desired technical conditions for liquefied product. C2 + hydrocarbons can be separated from the hydrocarbon feed stream, or their content can be reduced using a demethanizer that produces a methane-rich upper hydrocarbon stream and a methane-depleted lower stream containing C2 + hydrocarbons. The methane-depleted bottom stream can then be sent to other separators, resulting in flows of liquefied petroleum gas (LPG) and condensate.

After separation, the hydrocarbon stream thus obtained can be further cooled, preferably liquefied. Cooling can be carried out using a number of methods known in the art. A hydrocarbon stream is passed against one or more refrigerant streams in one or more refrigerant circuits. Such a refrigerant circuit may comprise one or more refrigerant compressors to compress at least a partially vaporized refrigerant stream, resulting in a compressed refrigerant stream. The compressed refrigerant stream may then be cooled in a refrigeration device such as an air or water cooler, resulting in a refrigerant stream. Refrigerant compressors can be powered by one or more gas and / or steam turbines and / or electric motors.

The hydrocarbon stream may be cooled in one or more stages. Initial cooling, also called pre-cooling or auxiliary cooling, can be carried out using pre-cooling refrigerant, for example a mixed refrigerant, a pre-cooling refrigerant circuit in one or more pre-cooling heat exchangers, whereby a pre-cooled hydrocarbon stream can be obtained. The pre-cooled hydrocarbon stream is mainly partially liquefied, in particular at a temperature below 0 ° C.

Such pre-cooling heat exchangers could include a pre-cooling step along with possible subsequent cooling carried out in one or more main heat exchangers to liquefy a fraction of the hydrocarbon stream in one or more main cooling and / or supercooling stages.

Thus, two or more cooling stages can be involved, each of which consists of one or more stages, parts, etc. For example, at each cooling stage, one to five heat exchangers can be used. The hydrocarbon stream or its fraction and / or refrigerant may not pass through all and / or through similar heat exchangers of any cooling stage.

In one embodiment, the hydrocarbon may be cooled and liquefied using a process comprising two or three cooling steps. The pre-cooling step is intended primarily to reduce the temperature of the hydrocarbon feed stream below 0 ° C, usually in the range from -20 to -70 ° C.

The main cooling step is advantageously separated from the pre-cooling step. In other words, the main cooling stage includes one or more separate main heat exchangers. The main cooling stage is mainly intended to reduce the temperature of the hydrocarbon stream, usually at least a portion of the hydrocarbon stream cooled in the pre-cooling stage to a temperature below -100 ° C.

Heat exchangers for use as two or more pre-cooling heat exchangers and main heat exchangers are well known in the art. Pre-cooling heat exchangers are preferably shell-and-tube heat exchangers.

At least one of the main heat exchangers is mainly the bobbin type cryogenic heat exchanger known in the art. In some cases, the heat exchanger may contain one or more cooling sections in its housing, and each cooling section can be considered as a cooling stage or as a separate heat exchanger with respect to other cooling positions.

In another embodiment, one or both of the pre-cooling refrigerant streams and any main refrigerant stream can be passed through one or more heat exchangers, preferably through the two or more pre-cooling heat exchangers mentioned above and the main heat exchanger, resulting in cooled refrigerant streams.

If the refrigerant is a mixed refrigerant in a mixed refrigerant circuit, such as a pre-refrigerant circuit or a main refrigerant circuit, it can be formed from a mixture of two or more components selected from the group consisting of nitrogen, methane, ethane, ethylene, propane, propylene, butanes, pentanes, etc. Separate or overlapping refrigerant circuits or other refrigerant circuits may use one or more other refrigerants.

The pre-cooling circuit may comprise pre-mixed refrigerant. The main refrigerant circuit may comprise a mixed main refrigerant. The mixed refrigerant or mixed refrigerant stream, as it is called in the application, contains at least 5 mol. % of two different components. More preferably, the content in the mixed refrigerant is two or more components from the group consisting of: nitrogen, methane, ethane, ethylene, propane, propylene, butanes and pentanes.

The typical composition of the mixed refrigerant for pre-cooling may be as follows:

Methane (C1) 0-20 mol.% Ethan (C2) 5-80 mol.% Propane (C3) 5-80 mol.% Bhutan (C4) 0-15 mol%

In total, the composition contains 100 mol.%.

The typical composition of the mixed refrigerant for main cooling may be as follows:

Nitrogen 0-10 mol.% Methane (C1) 30-70 mol.% Ethan (C2) 30-70 mol.% Propane (C3) 0-30 mol.% Bhutan (C4) 0-15 mol%

In total, the composition contains 100 mol.%.

In yet another embodiment, a pre-chilled hydrocarbon stream, such as a pre-chilled natural gas stream, can be further cooled to form at least partially (preferably completely) a liquefied hydrocarbon stream, such as an LNG stream. Further cooling may be carried out at the main cooling stage. The purified liquid hydrocarbon stream obtained using the method and installation described in the application is preferably stored in one or more storage tanks. The fully liquefied hydrocarbon stream is predominantly somewhat supercooled. Further cooling, for example at the main cooling stage or at a separate supercooling step, may thus include supercooling of the liquefied hydrocarbon stream.

After liquefaction, at least partially (preferably fully), the liquefied hydrocarbon stream can be expanded to form a multiphase hydrocarbon stream, which can be further processed in accordance with the method and installation described in the application.

FIG. 2 shows a second embodiment of a plant in which a compressed hydrocarbon feed stream 85 is refined, cooled, at least partially liquefied and expanded, resulting in a multiphase hydrocarbon stream 145 used in the purification process disclosed in the application. A more detailed description of the multiphase hydrocarbon stream 145 can be obtained in the following stages:

- creating at least partially (preferably completely) liquefied hydrocarbon stream 115; and

expanding at least partially (preferably completely) the liquefied hydrocarbon stream 115 in one or more devices 120, 140 to form a multiphase hydrocarbon stream 145 as an expanded hydrocarbon stream.

At least partially (preferably completely) liquefied hydrocarbon stream 115 can be obtained in stages:

- creating a stream of 105 hydrocarbon feedstocks;

- dividing the hydrocarbon feed stream 105 into a high pressure fuel gas stream 107 and an ongoing hydrocarbon stream 108;

at least partial (preferably complete) liquefaction of the ongoing hydrocarbon stream 108 by cooling at least a portion of the ongoing hydrocarbon stream 108 in one or more heat exchangers 110a, 110b, resulting in at least partially (preferably completely) liquefied hydrocarbon stream 115.

The high pressure fuel gas stream 107 may have one or both of: a nitrogen content below 15 mol. % and pressure above 15 bar (abs). High pressure fuel gas stream 107 can be successfully supplied to one or more consumers 300, such as gas turbines.

To separate the hydrocarbon feed stream 105 into an ongoing hydrocarbon stream 108 and a high pressure fuel gas stream 107, a device 80 may be provided for separating the feed stream. The device 80 for separating the feed stream preferably has an inlet 78 for the inlet of the hydrocarbon feed stream 105, a first outlet 81 for the high pressure fuel gas stream 107 and a second outlet 82 for the continued hydrocarbon stream 108.

In some embodiments, the implementation of the stage of at least partial (preferably complete) liquefaction may include:

pre-cooling at least a portion of the ongoing hydrocarbon stream 108 in one or more pre-cooling heat exchangers 110a against the pre-cooling refrigerant in the pre-cooling refrigerant circuit, resulting in a pre-cooled hydrocarbon stream 113; and

at least partial (preferably complete) liquefaction of at least a portion 113b of the pre-cooled hydrocarbon stream 113 in one or more main cooling heat exchangers 110b against the main cooling refrigerant circulating in the main cooling refrigerant circuit, resulting in at least partially (preferably fully) liquefied hydrocarbon stream 115.

These embodiments may further include the steps of:

- feeding part 113b of the pre-cooled hydrocarbon stream 113 to the fuel gas heat exchanger 210 as a heating stream 355;

- cooling said portion 113b of the pre-chilled hydrocarbon stream in the fuel gas heat exchanger with the hydrocarbon vapor stream 205 of the first separator, resulting in a cooled process stream 365;

- feeding the cooled process stream 365 to one or more devices 120, 140 to expand hydrocarbon streams.

Thus, the installation may include one or more stages 110 for cooling and at least partially (preferably completely) liquefying the ongoing hydrocarbon stream 108 to obtain a partially, preferably completely liquefied hydrocarbon stream 115. These one or more stages 110 of cooling mainly have an inlet 109 for an ongoing hydrocarbon stream 108 in fluid communication with a second outlet 82 of the raw material stream separation device 80 and an outlet 112 for at least partially (preferred completely) liquefied hydrocarbon stream 115 connected to the inlet 118 of one or more devices 120, 140 for expanding hydrocarbon streams.

The hydrocarbon feed stream 85, which may be natural gas, is supplied as a compressed stream, typically under pressure, in the range of 30 to 90 bar (abs). The hydrocarbon feed stream 85 may be supplied to the acid gas removal section 90. The acid gas removal section 90 reduces the content of acid gases, such as carbon dioxide and hydrogen sulfide, in the hydrocarbon feed stream 85 using known methods, resulting in a purified hydrocarbon stream 95.

The purified hydrocarbon stream 95, which will be depleted in acidic gases, may then be directed to a natural gas liquid extraction (LPG) plant, possibly through a dryer (not shown). In an LPG extraction plant 100, at least a portion of any natural gas liquids, such as propane, butanes and pentanes, together with heavier hydrocarbons, can be removed using, for example, one or more wash columns. The LPG extraction unit 100 produces a hydrocarbon feed stream 105 that may be depleted in natural gas liquids.

FIG. 2 shows a hydrocarbon feed stream 105 supplied to an input 78 of a feed stream separation device 80, where it is separated into a high pressure fuel gas stream 107 at a first outlet 81 and an ongoing hydrocarbon stream 108 at a second outlet 82.

In one alternative embodiment, not shown in FIG. 2, the high pressure fuel gas stream 107 may be withdrawn from the hydrocarbon feed stream 85 and / or the purified hydrocarbon stream 95 instead of the hydrocarbon feed stream 105. The sampling point of the high pressure fuel gas stream 107 is determined in accordance with the composition of the hydrocarbon mixture. For example, if the hydrocarbon mixture initially contains little acid gas, the high pressure fuel gas stream 107 may be taken from the hydrocarbon feed stream 85 and the pressure will decrease in a valve type device 106 located on line 107 in order to meet the pressure requirements for the fuel as desired high pressure.

Alternatively (not shown), the high pressure fuel gas stream may be diverted from the LPG extraction unit at a lower pressure if the LPG extraction unit is operated at a lower pressure. In this case, energy consumption for useless re-compression of part of the hydrocarbon feed stream 105, which is planned to be extracted as fuel gas, can be avoided.

The high pressure fuel gas stream 107 may then be supplied to the high pressure fuel gas network or, as shown in FIG. 2, directly to one or more high pressure fuel gas consumers 300, such as gas turbines. Gas turbines can mechanically drive compressors, such as compressors in the refrigerant circuit.

The continuing hydrocarbon stream 108 from the second outlet 82 of the raw material separation device 80 may then be supplied to a cooling and liquefaction section 110 where this stream is cooled and at least partially (preferably completely) liquefied. The liquefaction section 100 produces at least partially (preferably completely) liquefied hydrocarbon stream 115 at a first outlet 112. Such liquefaction sections are well known in the art, for example from US Pat. No. 6,370,910.

The liquefaction section 110 shown in FIG. 2 includes first and second cooling steps. The first cooling stage includes one or more pre-cooling heat exchangers 110a that cool the ongoing hydrocarbon stream 108 against the pre-cooling refrigerant in the pre-cooling refrigerant circuit (not shown). One or more pre-cooling heat exchangers 110a produce a pre-cooled hydrocarbon stream 113.

The pre-chilled hydrocarbon stream 113 may be supplied to a device 70 for separating the pre-chilled stream, in which case it (optionally) can be divided into (ongoing) pre-chilled hydrocarbon stream 113b and the process stream used as heating stream 355.

The pre-chilled hydrocarbon stream 113 or the continuing pre-chilled hydrocarbon stream 113b is directed to a second cooling stage. The second cooling stage includes one or more main cooling heat exchangers 110b, which at least partially (preferably completely) liquefy the pre-cooled hydrocarbon stream 113 or at least partially its continuing portion 113b against the main cooling refrigerant in the main cooling refrigerant circuit (not shown ) One or more main cooling heat exchangers 110b produce at least partially (preferably completely) liquefied hydrocarbon stream 115.

In one alternative embodiment, the LHG extraction section 100 may be located somewhere in the liquefaction section 110, and not in front of it, as shown in FIG. In this case, the apparatus 80 for separating the feed stream may also be located in the liquefaction section 110. It would be preferable that both the LPG extraction section 100 and the feed stream separation device 80 are located upstream from the place where the complete feed condensation takes place. A suitable position for this, as a rule, is the position before the second stage of cooling.

At least partially (preferably completely), the liquefied hydrocarbon stream 115 may be supplied to the inlet 118 of one or more devices 120, 140 for expanding the hydrocarbon streams, for example two or more expansion devices in a row where the pressure of the stream decreases sequentially, resulting in an output 142 a multiphase hydrocarbon stream 145 is obtained. In one of the embodiments shown in FIG. 2, at least partially (preferably completely) liquefied hydrocarbon stream 115 may be supplied to the first device 120 to expand the hydrocarbon stream, which may be a turbine in which the dynamic expansion of the stream occurs, resulting in an expanded hydrocarbon stream 125. The dynamic energy generated by the dynamic expansion is at least partially (preferably completely) liquefied hydrocarbon stream 115 in the first expansion device 120 can be recovered, for example, by mechanically actuating an electric generator 130 or some other device, such as a compressor (not shown).

The expanded hydrocarbon stream 125 may then be directed to a device 60 for separating the expanded hydrocarbon stream, resulting in the formation of an expanded hydrocarbon "satellite" (blow) stream 305 and an (ongoing) expanded hydrocarbon stream 125b. The (ongoing) expanded hydrocarbon stream 125b may then be passed through a second expansion device 140, such as a Joule-Thomson valve, in which the stream expands to form a multiphase hydrocarbon stream 145.

In the embodiment of FIG. 2, the heating stream 355, after being cooled in the fuel gas heat exchanger 210 to form a cooled heating stream 365, is part of a suitable shape stream 145. In this case, after the necessary pressure relief, for example in the expander or Joule-Thomson device 121, the cooled heating stream 365 may be injected into the (ongoing) expanded hydrocarbon stream 125b to be supplied to the second hydrocarbon stream expansion device 140, as already described. In some embodiments, it may be useful to re-combine the cooled heating stream 365 with the liquefied hydrocarbon stream 115 upstream of the expansion device 120 so that these streams can be expanded together.

In the embodiment of FIG. 2, the heating stream 355 is supplied in the form of a satellite stream (“satellite stream”) discharged from the pre-cooled hydrocarbon stream 113 using the device 70 for separating the pre-cooled stream. However, the heating stream can also be obtained at different pressures from other sources, including, but not limited to, the LPG extraction section 100 or the fractionation cascade (not shown), which is usually installed to fractionate the LPG product obtained from the LPG extraction section.

In another group of embodiments, the pre-chilled hydrocarbon stream may not separate at all, in which case the heating stream 355 consists of a completely different process stream, such as a (tangled) refrigerant stream or an intermediate cooling fluid stream.

A multiphase hydrocarbon stream 145 may be supplied to a first inlet 148 of a first gas-liquid separator 150a, in which the stream is separated into vapor and liquid fractions in the same way as in FIG. The vapor stream 205 of the first separator exits from the top of the first gas-liquid separator 150a through the first outlet 151 located there. The lower stream 155a of the first separator, which is a liquid stream, exits the second outlet 152 at or near the bottom of the first gas-liquid separator 150a. The combined steam vapor stream 185a is supplied to the second inlet to the second inlet 149 of the gas-liquid separator 150a, which is located downstream of the first inlet 148. The second inlet 149 may be located above the second outlet 152.

The expanded hydrocarbon satellite stream 305 is further expanded using a Joule-Thomson valve 310 and the thus expanded hydrocarbon satellite stream 315 is passed through an irrigation condenser 320 to re-condensate a portion of the vapor at the top of the first gas-liquid separator 150a. The irrigation capacitor 320 may be located at a level between the first inlet 148 and the first outlet 151, supplying irrigation, enhancing the separation of the lighter components of the multiphase hydrocarbon stream. As is known to those skilled in the art, an external capacitor may be used in place of the internal capacitor 320.

Additionally, the expanded hydrocarbon satellite stream 315 is heated in the condenser 320, resulting in the formation of a heated hydrocarbon satellite stream 325, which can be directed to the (expanded) lower stream 155b of the first separator. The (expanded) bottom stream of the first separator 155b transporting the heated hydrocarbon from the heated hydrocarbon satellite stream 325 may be supplied to the inlet 158 of the second gas-liquid separator 160 in the form of a combined stream 155 s, which is shown in FIG. 1 and its description above regarding the flows, discharged from the second gas-liquid separator 160 and their subsequent processing.

Returning again to the gas-liquid separator 150a, it should be noted that it may contain two zones with contact enhancing means (154a, 156a) formed, for example, by plates or nozzles that improve the separation and removal of nitrogen. The first zone of these two zones is located between the first input 148 and the second input 149 in the same way as in the embodiment of FIG. The second zone of these two zones 156a is located between the first exit 151 of the first hydrocarbon vapor stream separator 205 and the first input 148 for multiphase hydrocarbon stream 145. The second zone 156a should be below the condenser 320 or below the irrigation inlet from the external condenser, which allows the use of irrigation formed during the condensation of hydrocarbon vapor on the condenser 320.

The hydrocarbon vapor stream 205 of the first separator exiting the first outlet 151 can be directed to a fuel gas heat exchanger 210, where this stream is heated from a heating stream 355, resulting in a low pressure fuel gas stream 215 and a cooled heating stream 365. If a heating stream is supplied in the form of a process stream, part of the cold energy of the hydrocarbon vapor stream 205 can be used to cool this process stream, allowing it to bypass one or more main exchangers 110b, thereby increasing thermal efficiency.

As already mentioned above, the heating stream 355 may also be a process stream in the form of a refrigerant stream, such as a pre-cooling refrigerant stream and / or main cooling refrigerant stream. In this case, part of the cold energy of the hydrocarbon vapor stream 205 of the first separator can be returned to one or both cooling stages 110 by cooling the refrigerant.

The advantages of the method and installation disclosed in the application will become apparent from the following non-limiting example.

Example

This example compares the nitrogen contents in different streams generated from the natural gas hydrocarbon feed stream 105 in accordance with the production scheme of FIG. 2 with three comparative examples calculated according to the embodiment of FIG. 3 from the above US 2008/0066493.

The nitrogen contents in the hydrocarbon feed stream 105 consisting of natural gas, the high and low pressure fuel gas streams 107, 215, respectively, the vaporized gas stream 195 and the LPG stream 165, and together with additional data for the scheme disclosed in the application of FIG. 2 were calculated. presented in the table below under the heading "Invention".

In the embodiment of FIG. 3, in US 2008/0066493, a high pressure fuel gas stream is supplied via line 34a from the overhead 25 from the top 10u of the column 10 'after heat exchange and compression together with the overhead 42 of the flash evaporator 101 after heat exchange and compression. It is noted that the pipeline 33, which only flows from heat transfer and compression of the overhead 25 from the upper part 10u of the column 10 ', was not able to supply sufficiently high pressure fuel gas, as a result of which, in this comparative example, this gas was taken from the pipeline 34a. In the absence of a check valve on line 34, pipelines 33 and 34a must communicate with each other in fluid.

US 2008/0066493 does not disclose the corresponding low pressure gas fuel stream. In accordance with the teachings of this comparative example, it was assumed that the low pressure fuel gas stream was taken from a conduit 25 transferring the overhead from the top 10u of the column 10 '. The vaporized gas stream is located in line 22.

The data calculated according to the modified diagram of FIG. 3 in US 2008/0066493 are shown in the table below under the headings Comparison 1, Comparison 2, and Comparison 3. “Comparison 1” is a comparison with the method according to FIG. 2 disclosed in the application, taken with the same natural gas feed stream, low pressure fuel stream, high pressure fuel stream, vaporized gas stream and production rates of LPG streams. “Comparison 2” is a comparison with the method according to FIG. 2 disclosed in the application, taken at the same natural gas flow rates and the calorific value of low pressure and high pressure fuel gas. "Comparison 3" is a comparison with the method according to the disclosed in the application of figure 2, taken at the same speeds of the feed streams of natural gas and the speeds of the LPG flows and the calorific value of low pressure fuel gas.

It clearly follows from the table below that the method and installation disclosed in the application remove nitrogen in the low pressure fuel gas stream 215 and at the same time produce an LPG stream 165 and high pressure fuel gas stream 107 with an acceptable low nitrogen content.

Table Invention Comp. 1 Comp. 2 Comp. 3 Mol .. the proportion of N ₂ in the feed stream of natural gas 0.056 0.056 0.056 0.056 Mol .. the proportion of N ₂ in the flow of high-pressure fuel gas 0.056 0.248 0.285 0.298 Mol .. the proportion of N ₂ in the flow of fuel gas low pressure 0.805 0.418 0.409 0.445 Mol .. the proportion of N ₂ in the vaporized gas stream 0.223 0.154 0.141 0.154 Mol .. the proportion of N ₂ in the purified liquid hydrocarbon stream 0.009 0.006 0.005 0.006 Calorific value of low pressure fuel gas flow 64 234 65 64 Specific power / (kV / tons of gas and oil gas per day) 14.8 14.2 14,4 14.3 Net power / (kM / tonne of gas-engineered gas / day) 14.6 13.9 14.1 14.1 Production within 340 business days / million tons / year 3.60 3.60 3.56 3.60

It will be apparent to those skilled in the art that the present invention can be practiced in a variety of different ways without departing from the scope of the appended claims.

Claims (17)

1. A method for purifying a multiphase hydrocarbon stream to form a purified liquid hydrocarbon stream, wherein the method comprises at least the following steps:
- the creation of a multiphase hydrocarbon stream from natural gas, and this multiphase hydrocarbon stream contains a vapor phase and a liquid phase;
- the supply of a multiphase hydrocarbon stream to the first gas-liquid separator;
- separation of the multiphase hydrocarbon stream in the first gas-liquid separator at the first pressure with the formation of the hydrocarbon vapor stream of the first separator containing hydrocarbons and nitrogen, and the lower stream of the first separator;
- separation of the lower stream of the first separator in the second gas-liquid separator at the second pressure with the formation of a hydrocarbon vapor stream of the second separator and the purified liquid hydrocarbon stream in the form of liquefied natural gas (LNG), the second pressure being lower than the first pressure;
- compression of the hydrocarbon vapor stream of the second separator in the compressor for the upper stream with the formation of a steaming steam stream; and
- supplying a steaming steam stream to the first gas-liquid separator at a vertical level below the level at which a multiphase hydrocarbon stream is introduced into the first gas-liquid separator,
wherein the method further includes
- extracting the low pressure fuel gas stream (LP) from the hydrocarbon vapor stream of the first separator; and
- the flow of low pressure fuel gas to the combustion device at a fuel gas pressure not exceeding the pressure of the hydrocarbon vapor stream of the first separator. 2. The method of claim 1, wherein said compression of the hydrocarbon vapor stream of the second separator using an overhead compressor yields a stripping vapor stream at a third pressure that is equal to or higher than the first pressure. 3. The method according to p. 1, in which
The purified liquid hydrocarbon stream in the form of liquefied natural gas (LNG) is sent to a storage tank of the cryogenic type. 4. The method according to claim 3, wherein the first pressure of the first gas-liquid separator is equal to or higher than the fuel gas pressure and neither the hydrocarbon vapor stream of the first separator nor the low pressure fuel gas stream are compressed before being used in the combustion device. 5. The method of claim 3, wherein the combustion device is a combustion device selected from the group consisting of a furnace, a boiler, and a dual-fuel diesel engine. 6. The method of claim 3, wherein the step of extracting the low pressure fuel gas stream from the hydrocarbon vapor stream of the first separator comprises the following step:
- heating the hydrocarbon vapor stream of the first separator by a heating stream of a fuel gas heat exchanger to form a low pressure fuel gas stream and a cooled heating stream. 7. The method of claim 6, wherein the step of producing a multiphase hydrocarbon stream from said natural gas comprises:
- cooling a portion of the natural gas as said heating stream in a fuel gas heat exchanger with a hydrocarbon vapor stream of a first separator, thereby forming said cooled heating stream in the form of a cooled process stream. 8. The method according to p. 1, in which the hydrocarbon vapor stream of the first separator contains from 30 to 95 mol.% Nitrogen and / or has a pressure in the range from 2 to 15 bar (abs). 9. The method according to p. 1, in which the purified liquid hydrocarbon stream contains less than 1 mol.% Nitrogen. 10. The method of claim 1, wherein the step of producing a multiphase hydrocarbon stream from said natural gas comprises cooling and / or changing the pressure of the natural gas. 11. The method according to one of the preceding paragraphs, in which the operation of obtaining a multiphase hydrocarbon stream from the specified natural gas includes:
- the creation of a hydrocarbon feed stream from a natural gas stream at elevated pressure;
- separation of the ongoing hydrocarbon stream from the hydrocarbon stream;
- supplying an ongoing stream to the cooling and liquefaction section, where it is cooled and at least partially liquefied, resulting in at least partially liquefied hydrocarbon stream;
- supplying at least a partially liquefied hydrocarbon stream to the inlet of at least one device for expanding the hydrocarbon stream and reducing there the pressure of at least a partially liquefied hydrocarbon stream, resulting in a multiphase hydrocarbon stream. 12. The method according to claim 11, further includes the step of separating the hydrocarbon feed stream into a high pressure fuel gas stream and the above continuing hydrocarbon stream, wherein the high pressure fuel gas stream has one or both of the following characteristics: nitrogen content below 15 mol% and pressure above 15 bar (abs). 13. Installation for cleaning a multiphase hydrocarbon stream containing a liquid phase and a vapor phase to provide a purified liquid hydrocarbon stream in the form of liquefied natural gas (LNG), where the installation contains at least:
- means for creating a multiphase hydrocarbon stream from natural gas, which contains at least one liquefaction section and one or more devices for expanding the hydrocarbon stream;
a first gas-liquid separator for receiving a multiphase hydrocarbon stream and separating it into a hydrocarbon vapor stream of a first separator containing hydrocarbons and nitrogen, and a lower stream of a first separator, said first gas-liquid separator having a first inlet for supplying a multiphase hydrocarbon stream to a first gas-liquid separator, a first outlet for outputting a hydrocarbon steam stream of a first separator from a first gas-liquid separator, a second exit for outputting a lower stream a first separator from a first gas-liquid separator, a second inlet located vertically lower than the level of said first inlet, for supplying a stripping steam stream to the first gas-liquid separator;
- a second gas-liquid separator, designed to receive the lower stream of the first separator and separate it into a hydrocarbon vapor stream of the second separator and a purified liquid hydrocarbon stream in the form of LNG, and the specified second gas-liquid separator has a first inlet in fluid communication with the second outlet of the first gas-liquid separator, for supplying the lower stream of the first separator to the second gas-liquid separator, the first outlet for outputting the hydrocarbon steam stream of the second separator from the second g zozhidkostnogo separator and a second output for outputting purified liquid hydrocarbon stream from the second gas-liquid separator;
- an expansion device for the lower stream, located between the second outlet of the first gas-liquid separator and the first inlet of the second gas-liquid separator, to reduce the pressure of the lower stream of the first separator; and
- an overhead compressor for compressing a hydrocarbon vapor stream of a second separator to form a steaming vapor stream, wherein the compressor for an upper stream has an inlet fluidly communicating with a first outlet of a second gas-liquid separator for receiving a hydrocarbon vapor stream of a second separator, and an output, communicating in fluid with the second inlet of the first gas-liquid separator for outputting the steaming steam stream,
wherein the installation further comprises
- a combustion device operating at a fuel gas pressure not higher than the pressure of the hydrocarbon vapor stream of the first separator, and the design of which allows receiving low pressure fuel gas taken from the hydrocarbon stream of the first separator. 14. The installation according to p. 13, where one or more devices for expanding hydrocarbon streams are connected to the liquefaction section and located after it equipment for expanding at least partially liquefied hydrocarbon stream leaving the liquefaction section, resulting in a multiphase hydrocarbon stream, and said one or more devices for expanding hydrocarbon streams have an inlet for receiving at least a partially liquefied hydrocarbon stream and an outlet for discharging a multiphase hydrocarbon stream ka, while the specified output is connected to the first input of the first gas-liquid separator. 15. Installation according to p. 13, which further comprises
cryogenic-type storage tank for receiving a purified liquid hydrocarbon stream from a second gas-liquid separator. 16. Installation according to claim 15, in which there is no compressor between the first outlet of the first gas-liquid separator and the combustion device. 17. The installation according to claim 15 or 16, wherein the combustion device is a combustion device selected from the group consisting of a furnace, a boiler and a dual-fuel diesel engine.

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