KR20100039353A - Method and system for producing lng - Google Patents

Abstract

A method is described for production of LNG from an incoming feed gas (1) on an onshore or offshore installation, and it is characterised by the following steps: 1) the feed gas is led through a fractionation column (150) where it is cooled and separated in an overhead fraction with a reduced content of pentane (C5) and heavier components, and a bottom fraction enriched with heavier hydrocarbons, 2) the overhead fraction from the fractionation column is fed to a heat exchanger system (110) and is subjected to a partial condensation to form a two-phase fluid, and the two-phase fluid is separated in a suitable separator (160) into a liquid (5) rich in LPG and pentane (C3-C5) which is re-circulated as cold reflux to the fractionation column (150), while the gas (6) containing lower amounts of C5 hydrocarbons and hydrocarbons heavier than C5 is exported for further processing in the heat exchanger system (110) for liquefaction to LNG with a maximum content of ethane and LPG 3) the cooling circuit for liquefaction of gas in the heat exchanger system comprises an open or closed gas expansion process with at least one gas expansion step. A system for carrying out the method is also described.

Description

METHOD AND SYSTEM FOR PRODUCING LNG

The invention relates to an optimal method for producing LNG on a fixed or floating offshore installation, as can be seen in the preamble of the independent claim 1.

The invention also provides a fractionation column for supplying a feed gas, a heat exchanger system for cooling and partially condensing an upper gas stream from the fractionation column, a separator for separating a two-phase stream from the heat exchanger system, and A mechanism for returning from the separator to the fractionation column and for supplying this liquid as reflux to the upper part of the column, and for supplying gas to the heat exchanger system for further cooling and liquefaction of the separator from the LNG. It relates to a system for performing the method, including.

The present invention aims to use a closed gas expansion process for liquefying natural gas, wherein the gas is first fed through a fractionation column so that the gas is cooled and the reduced content of pentane (C5) and The upper fraction with heavy components, and the lower fraction, rich in heavy hydrocarbons, are separated, and the fractionation column reflux is also produced as an integrated part of the system for liquefaction that partially condenses the upper gas. By carrying out the liquefaction according to the invention, the production of liquefied gas with maximum content of ethane and LPG (liquid petroleum gas) results in an unstable / volatile liquid with a high content of ethane, LPG and pentane, which increases the efficiency of the gas expansion process. Incidental production of is achieved while minimizing.

In particular, the present invention includes methods and systems for liquefying natural gas or other hydrocarbon gases from a gas field or gas / oil field, which is the movement of gas from a source to a market. It is suitable to liquefy the gas in order to facilitate this. This is particularly relevant for sea oil / gas fields.

In this context, natural gas means a mixture of hydrocarbons whose essential part consists of methane. Natural gas is usually liquefied by significantly cooling the gas to condense it and make it liquid. LPG means liquid petroleum gas containing propane and butane (C4, C4 component).

It is an object of the present invention to provide a liquefaction of energy efficient gases while at the same time simple process so that the apparatus can be used at sea, in particular on floating installations. Incidental production of condensate is minimized during liquefaction and efficiency is maximized (minimizing the need for fuel gas).

The method according to the invention is characterized by the following steps:

1) passing the feed gas through a fractionation column 150 to cool it and separating the upper fraction with reduced content of pentane (C5) and heavy components and the lower fraction enriched with heavier hydrocarbons;

2) The top fraction from the fractionation column is fed to the heat exchanger system 110, partially condensed to form a two-phase fluid, and the two-phase fluid is transferred to LPG and pentane (C3-C5) in a suitable separator 160. Separated into an abundant liquid (5) and a gas (6) containing a small amount of C5 hydrocarbons and heavier hydrocarbons than C5, and the liquid (5) is recycled to a fractionation column (150) as cold reflux, Feeding the gas (6) for further processing in a heat exchanger system (110) for liquefaction with LNG having a maximum content of ethane and LPG; And

3) a cooling circuit for liquefaction of gas in the heat exchanger system comprising an open or closed gas expansion process having at least one gas expansion step.

Preferred embodiments of the method are defined in the dependent claims 2-10.

The system according to the invention is characterized in that the cooling system used for the cooling, condensation and liquefaction of the gas in the heat exchanger system comprises an open or closed gas expansion process with at least one gas expansion step. The system preferably is rich in hydrocarbons having a normal boiling point lower than butane (C4) and mostly butane in the upper gas stream of the system, and components rich in normal boiling points higher than C6 and C6 in most of the bottom products of the fractionation column. And designed to separate the feed gas.

Liquefaction of natural gas may be performed with the use of a gas expansion process, in which the refrigerant proceeds through a processing circuit based on compression, cooling, expansion, and heat exchange with the fluid to be subsequently cooled. For example, for the liquefaction of natural gas, gaseous compressed refrigerant, usually nitrogen or methane, can be used, which is pre-cooled and then expanded across an expansion valve or turboexpander. Gas expansion produces very cold gases, or mixtures of gases and liquids, which are then used to liquefy natural gas and precool the compressed refrigerant gas. The gas expansion process is relatively simple and therefore very suitable for offshore installations. However, this process has a somewhat lower efficiency compared to more advanced processes, for example mixed refrigerant circulation processes, thus requiring a lot of compression equipment and a lot of energy.

In order to produce LNG, gas is generally required to have a relatively high content of methane. However, most feed gases will also contain some heavy hydrocarbons such as ethane, propane, butane, pentane and the like. In general, there are several requirements regarding the content of heavy hydrocarbons in liquefied gas:

The specific energy content per cubic meter of liquefied gas should generally not exceed the sales specification provided.

The content of pentane (C5) and hydrocarbons larger than C5, and aromatic compounds in the liquefied gas should be kept below prescribed limits to prevent freezing in the cooling process.

The simplest way to limit the content of heavy hydrocarbons in liquefied gas is to partially condense the gas and then separate the condensed liquid from the gas, which is further cooled for liquefaction. This separation is usually carried out as an integrated part of the cooling process, typically at temperatures between 0 ° C and -60 ° C. The separated condensate can be reheated as part of the cooling process using refrigeration potential.

In large terrestrial LNG plants (so-called "base load" plants), most of the propane and heavy hydrocarbons are usually removed before or as part of liquefaction, and in many cases also a substantial portion of ethane. This is to meet sales specifications and to produce and sell valuable ethane, LPG, and condensate / naphtha. Comprehensive processes typically use cold fractionation columns as part of the cooling process and as separate units outside the cooling system.

However, for offshore LNG production, it is not desirable to manipulate products other than liquid natural gas. However, if oil or condensate is also produced, it may be possible to separate the condensate for stabilization and drain it with other oils and / or condensates. However, stabilized condensate will generally consist of C6 + with relatively low content of pentane and light components. Hydrocarbons that are lighter than C6 cannot usually be stored or safely moved without cooling or under pressure. Some separated hydrocarbons or condensates can be used as fuel, but it is desirable to retain these components in the LNG product. Due to the possibility of subsequent blending into smaller LNG capacities and larger LNG capacities, they may be suitable for producing liquefied natural gas with significantly larger, and preferably maximum, heavy hydrocarbons in the ocean.

The present invention represents considerable optimization for marine applications, and especially on floating units, where a relatively simple and robust gas expansion process is used for the liquefaction of natural gas, liquefied gas maximized by maximizing the content of ethane and LPG At the same time, the amount of hydrocarbons heavier than methane separated as 2-products in the liquefaction process is minimized while the energy efficiency of this process is increased.

The installation comprising the system according to the invention can thereby be simply constructed and installed on board floating offshore installations, where space is often a limiting factor.

Reference to known techniques and other literature, and comparisons with the present invention:

Reference is first made to EP-1.715.267, which describes a method comprising cooling a natural gas and passing it through a fractionation column to separate the gas into an upper fraction and a lower fraction. The bottom fraction is rich in heavy hydrocarbons, which are discharged from the system. The upper fraction cools and forms a two-phase fluid, which is separated in the separator. The liquid phase is recycled to the fractionation column while the gas phase is further fed to a heat exchange system. Cooling of the upper fraction is carried out with an independent cooler. The EP patent concludingly describes a traditional and well known distillation process.

In addition, set-up is a standard procedure in a so-called “base load” LNG plant, where both the cooler 5 and the chiller 11 (see the drawings of the EP patent above) are part of a plant's pre-cooling plant. This is usually done as a multistage propane cooling plant. However, the setup in the EP patent does not integrate the fractionation column and the downstream LNG condensation process as the present invention aims. Integration here means that the two systems are tightly connected together and function as one system, where the material stream and / or energy stream flows in both ways between the systems.

According to EP-1.715.267, the refrigeration work, which cools the top fraction and produces a reflex for the so-called fractionation column, is clearly not the same cooling circuit that performs further cooling and condensation of natural gas, but clearly outside. Resulting from the cooling process.

International patent application WO-2005 / 071333 describes a well known double gas expansion used for liquefying boil off gase from a storage tank for LNG. Indeed, these evaporating gases only contain methane and nitrogen.

Patent publications US 2006/0260355 A1 and US Pat. No. 6,662,589 describe systems which are similar in appearance to the invention but in fact very different from the invention. The system in the above-mentioned publication includes a process for simultaneously liquefaction of natural gas and recovery / separation of components heavier than methane, ie ethane and heavier components, where ethane, LPG and heavy components are sold. Fractionated into product, the liquefied gas has a very reduced content of ethane and heavy components. This is achieved by feeding the feed gas to the fractionation column, where the feed gas is brought into contact with the ethane rich reflux so that the fractionation column brings the feed in a greatly reduced amount of top gaseous fraction with components heavier than methane and heavier than methane. Separated into a liquid stream from the very rich bottoms. The ethane rich reflux is produced by cooling and condensing the ethane rich stream where the gas is partially condensed from the fractionation column and also recycled from the fractionation train for fractionation of the bottom fraction from the fractionation column.

Patent publications US Pat. No. 6,401,486, US Pat. No. 6,742,358 and WO 2006/115597 A2 describe systems for simultaneously performing liquefaction of natural gas and recovery / separation of components heavier than methane, ie ethane and heavier components. The method is also significantly different from and more than the present invention in which the feed gas is first cooled in heat exchanger (s) for liquefaction of the gas and by heat exchange with flash-expanded separated liquid and fluid from the bottom of the column. Complex. In addition, all or part of the feed gas stream is expanded through a turboexpander or Joule-Thompson expansion valve before proceeding to the fractionation column.

Patent publications US 2006/0260355 A1, US Pat. No. 6,662,589, US Pat. No. 6,401,486 and US Pat. No. 6,742,358 relate to processes for minimizing the content of ethane, LPG and heavy hydrocarbons in liquefied gases, while The invention includes systems and methods for maximizing the content of methane, ethane and LPG in liquefied gas. US Patent Application 2006/0260355 A1, US Pat. No. 6,662,589, US Pat. No. 6,401,486 or US Pat. No. 6,742,358 are incorporated to accommodate rich reflux in C3-C5 from liquefied heat exchanger (s) for the production of LNG. The increase in energy efficiency with which a gas expansion process can be achieved using a separation column is not described.

DE Patent No. 10205366 describes a process for simultaneously performing liquefaction of natural gas and recovery / separation of components that are heavier than ethane, where the separated LPG and heavy components are fractionated into a product for sale. This is achieved by first partially cooling the feed gas in a condensation plant for the liquefaction of natural gas, then feeding the cooled feed gas into a fractionation column that is brought into contact with ethane-rich reflux to produce a heavier component of heavier than ethane in the fractionation column. Upper gaseous fraction with ethylene and components heavier than ethane are achieved by separation into a liquid stream from the bottom, which is very rich. Ethane-rich reflux is produced by partial condensation of gas from the fractionation column and then contacting the C4 / C5 stream in a second fractionation column, where the C4 / C5 fraction is used for fractionation of the bottom product from the first fractionation column. Recycled from the fractionation train. In other words, DE patent 10,205,366 includes a process for minimizing the content of LPG, and heavy hydrocarbons in liquefied gas, while the present invention includes systems and methods for maximizing the content of LPG in liquefied gas. Patent publication DE 10,205,366 describes the increase in energy efficiency achievable in a gas expansion process using an integrated separation column containing C3-C5 rich reflux from liquefied heat exchanger (s) for the production of LNG. Not.

US Pat. No. 4,690,702 describes an LNG method wherein the feed gas is first pre-cooled in a cooling plant for LNG production, and then fed to the first fractionation column and brought into contact with the cooled ethane rich reflux, wherein the ethane rich Reflux is recycled from the second fractionation column to fractionate the bottoms stream from the first column. The patent does not include a system in which C3-C5 rich reflux for a fractionation column is achieved by partially condensing the top gas product from the fractionation column as an integrated part of the LNG process.

US Pat. No. 7,010,937 describes a system for simultaneously performing liquefaction of natural gas and recovery / separation of components heavier than methane. According to the patent, the gas feed is pre-cooled and partially condensed so that the liquid stream can be separated in the separator, where this liquid stream is fractionated in the first fractionation column to generate a top gas, which is the second fractionation. Cooled to form a reflux for the column. The gas flow from the separator is expanded across the gas expander and fed to the second fractionation column. As such, the US patent has little in common with the present invention as defined in the following claims.

Description of the invention:

The invention will be described in more detail with reference to the accompanying drawings:

1 shows a first embodiment showing main components and main functions.

2 shows another embodiment of the present invention.

Figure 3 illustrates another embodiment of the present invention that includes further stabilization of the heavy hydrocarbons (condensates) that are separated.

Figure 4 illustrates in detail the invention carried out using a dual gas expansion process.

Figure 5 illustrates the invention carried out using a hybrid cooling circuit with a gas expansion loop and a liquid expansion loop.

6 shows an example of a high and low temperature curve (composite curve) for a conventional nitrogen expansion cycle.

Figure 7 shows an example of a high temperature curve and a low temperature curve (composite curve) for the nitrogen expansion cycle obtained using the present invention.

8 shows a comparison of the curves shown in FIGS. 6 and 7.

Referring to FIG. 1, the system for the optimized liquefaction of gas comprises at least the following major components:

An inlet gas stream (1) to be cooled and liquefied,

A fractionation column 150 which cools the inlet gas and separates it into an upper fraction (2) with reduced content of pentane and heavy components, and a lower fraction (3) rich in heavy hydrocarbon components,

A system 110 of heat exchanger which cools the inlet gas and partially condenses it for the separation of heavy hydrocarbons and for further cooling and liquefaction,

A product stream 11 comprising cooled and liquefied gas,

A product stream 3 comprising mainly pentane and heavy hydrocarbons, and

A cooling system for cooling and liquefying gas, comprising a gaseous refrigerant stream 20, at least one cycle compressor 100, at least one aftercooler 130 and at least one gas expander 120. .

The cleaned inlet feed gas 1, for example methane rich hydrocarbon gas, is first supplied to the fractionation column 150, where the gas is cooled in contact with the colder reflux fluid. During the countercurrent contact with the cooling and low temperature fluids, the feed gas is reduced content of the upper fraction (2) with a hydrocarbon having a molecular weight greater than pentane (C5), and a hydrocarbon-rich lower with a molecular weight greater than C6 and C6. Fraction (3). The upper fraction 2 from the fractionation column then proceeds to a heat exchanger system 110 where the gas is cooled and partially condensed so that the resulting two-phase fluid 4 can be separated in a suitable separator 160. . LPG and pentane (C3-C5) -rich liquid (5) separated in separator (160) is recycled to fractionation column (150) as a low temperature reflux (see Her er det feil i originalteksten (150/160) men det). bør vaere opplagt for behandlende instans at dette er skrivefeil og at meningen ikke forandres]. As this fluid is produced by condensation by cooling, the reflux fluid 5 will have a lower temperature than the feed gas 1. Gas 6 from separator 160 further reduces the content of C5 hydrocarbons and hydrocarbons larger than C5. This gas then proceeds back to the heat exchanger system 110 for further cooling, condensation and sub-cooling. The liquefied gas 11 alternatively proceeds through a control valve 140 that controls the operating pressure and flows through the system.

In a preferred embodiment, the gas feed stream 10 is pre-cooled by a suitable external refrigerant, for example available air, water, sea water or a separate suitable refrigeration system / pre-cooling system. For the latter external cooling method, separate closed mechanical refrigeration systems with propane, ammonia or other suitable refrigerants are often used.

In a preferred embodiment, the fractionation column 150 and separator 160 are characterized in that the complete system (fractionation column 150 and reflux separator 160) divides the components in the normal boiling point region (NBP) of -120 ° C to 60 ° C. Operate at pressures and temperatures that can create a split point. This may correspond, for example, to the light main component for separation, which is butane (C4) with a normal boiling point of −12 ° C. to 0 ° C., and the heavy main component which is a C6 component with a boiling point of 50 ° C. to 70 ° C. The upper gas stream 6 of the system will then be rich in most butanes (C4) and hydrocarbons having a normal boiling point lower than butane. The bottom product (3) from the fractionation column will be rich in components with a normal boiling point higher than most of C6 and C6, and pentane (C5, NBP = 28-36 ° C.) is contained in the gas product of the system and in the bottom product of the fractionation column. It is a distributed transition component.

Cooling and condensation of the feed gas in the heat exchange system 110 is provided by a closed or open gas expansion process. A refrigerant 21 comprising a gas or a mixture of gases (eg, pure nitrogen, methane, a hydrocarbon mixture, or a mixture of nitrogen and hydrocarbons) at high pressure, preferably 3 to 10 MPa, is supplied to the heat exchange system 110. And a cooling process is disclosed that cools to a temperature between 0 ° C. and −120 ° C., but this refrigerant stream is primarily in gaseous form at prevailing pressure and temperature 31. The pre-cooled refrigerant 31 proceeds to the gas expander 121 where the gas expands to a low pressure of 5% to 40% of the inlet pressure, preferably 10% to 30% of the inlet pressure, whereby the coolant Is mainly gaseous. Gas expanders are generally expansion turbines called turboexpanders, but other types of expansion equipment for gases, such as valves, may be used. The flow of precooled coolant expands at high isentropic efficiency in the gas expander 121, which significantly lowers the temperature. In certain embodiments of the invention, some liquids may be separated at this expansion, but this is not a requirement for the process. The cold stream of coolant 32 then proceeds back to heat exchanger 110 where it is used to cool and alternatively condense the cooled, condensed, sub-cooled gas and other warm inlet refrigerant.

After the cold refrigerant stream 32 has been heated in the heat exchange system 110, the refrigerant will be present as the gas stream 51, which in a closed loop embodiment is again compressed in an appropriate manner for recycling, and an external refrigerant, for example Cooled with air, water, sea water or a suitable refrigeration unit.

Alternatively, the cooling system will use a refrigerant 21 composed of a gas or a mixture of gases at a high pressure obtained from a suitable source, for example from a feed gas being treated and cooled in an open embodiment. The open embodiment also includes the low pressure refrigerant stream 51 being used for other purposes, or mixed with the feed gas to be compressed and treated and cooled again in a suitable manner.

In a preferred embodiment, the recovery of the refrigerant stream 51 proceeds from the heat exchanger 110 to a separate compressor 101 driven by the expansion turbine 121. In this way, expansion work is used and the energy efficiency of the process is improved. After the compressor 101, the coolant is further cooled in the heat exchanger 131 before the stream is further compressed in the cycle compressor 100. The cycle compressor 100 may be one or more units, alternatively one or more stages per unit. The cycle compressor may also be equipped with an internal cooler 132 between the compressor stages. The compressed refrigerant 20 is then cooled by heat exchange using a suitable external refrigerant, for example air, water, sea water or a suitable separate refrigeration cycle, in the aftercooler 130 to compress the refrigerant 21 in a closed loop. As reused.

In one preferred embodiment, the system of heat exchanger 110 is one heat exchanger (so-called multi-stream heat exchanger) comprising a number of different "warm" and "cold" streams in the same unit.

2 shows an alternative embodiment, wherein the multi-stream heat exchangers are connected together in such a way that the necessary heat exchange between the cold and warm streams can be carried out. 2 illustrates a heat exchange system 110 that includes several heat exchangers in series. However, the present invention is not related to the specific type of heat exchanger or the number of heat exchangers, but may be carried out in several different types of heat exchange systems capable of manipulating the required number of hot and cold process streams.

3 illustrates an alternative embodiment, wherein fractionation column 150 further includes reboilers to further improve separation (clear division of light and heavy components) and also to reduce the volatility of the bottom fraction in the column. 135). It can be used to directly produce stable condensate at ambient temperature and atmospheric pressure.

4 details the invention as applied in more developed embodiments, where a dual gas expansion process is used. In this embodiment, the compressed refrigerant stream 21 is first cooled to moderate temperatures. At this temperature, the coolant stream is divided into two parts, where one part 31 is obtained from the heat exchanger and expands in the gas expander 121 to the low pressure gas stream 32. The other portion 41 is further pre-cooled to expand to essentially the same pressure as the pressure in the stream 32 in the gas expander 122. The expanded low temperature coolant streams 32 and 42 are withdrawn to different inlet locations on the heat exchange system 110 and combined into one stream in this exchanger. The heated coolant 51 is then recovered by recompression. In another embodiment of the system in FIG. 3, the compressed coolant stream 20 in the dual gas expansion circuit is split into two streams in front of the heat exchanger 110 in a separate flow channel in the heat exchanger 110. It can be cooled to different temperatures.

The same applies to the heating of the recovered cold coolant streams 32, 42. This embodiment is in accordance with FIG. 3 in another respect.

Figure 5 illustrates in detail the invention carried out with the use of a hybrid cooling loop, wherein one refrigerant is used in both the pure gas phase and the pure liquid phase. In this embodiment, the closed cooling loop provides cooling of the feed gas in the heat exchange system 110. The cooling cycle is initiated by methane, or a mixture of methane and nitrogen, in which the methane constitutes at least 50% by volume, which is compressed into a compressed refrigerant stream 21 and after-cooled, where such refrigerant stream is Pre-cooled, at least a portion 31 of the refrigerant stream is used in the gas phase to expand across the gas expander 121, at least a portion 41 of the coolant stream condenses into liquid, and the valve or liquid expander 141 Inflates across.

It is emphasized that embodiments of the present invention are not limited to the cooling process described above, but can be used in conjunction with a gas expansion cooling process for the liquefaction of natural gas or other hydrocarbon gases, wherein the cooling mainly uses one or more expansion gas streams. Is achieved.

By carrying out the liquefaction of natural gas in accordance with the present invention, liquefaction has a maximum content of methane, ethane and LPG, but at the same time does not exceed the acceptable levels of pentane and heavier hydrocarbons having a normal boiling point above 50-60 ° C. The product of the gas is produced. At the same time, the incidental production of volatile hydrocarbons with significant amounts of ethane, propane and butane will be minimized or eliminated, which will make it difficult to operate on offshore installations for LNG production. At the same time, more liquefied natural gas will also be produced with less energy consumption than for similar cooling cycles arranged without a fractionation column to accept cold and LPG-rich reflux from the cooling process. See Her er det. skrivefeil i originaltekst].

The reasons why the energy consumption for a gas expansion process for liquefying natural gas is reduced in the present invention compared to a similar cooling process in which there is no integrated separation column has several aspects:

Heavy hydrocarbons which are essentially separated to prevent freezing during liquefaction will be condensed and will be separated at considerably higher temperatures than conventional methods, and much condensation is carried out in the fractionation column. This reduces energy losses in the cooling process where the cooling load is moved to a higher temperature range.

The heat exchange system 100 of the cooling process receives the gas liquefied as stream 2 (overhead gas stream in the fractionation column), which has a reduced temperature in relation to the actual gas feed stream 1. The gas expansion process is characterized by the warm cooling curve and the cold cooling curve being controlled by a large amount of gas used as the refrigerant. This gas stream forms a linear cooling curve. The reduced feed temperature to the heat exchanger forms a "break point" on the worm cooling curve (sum of streams cooled), making it possible to obtain a general decrease in the distance between the worm cooling curve and the cold cooling curve. This provides better temperature adaptation, reduced energy loss, and thus reduced energy consumption to drive the cooling process.

Preliminary analysis and comparison shows that the necessary compressor work per 1 kg of liquefied natural gas produced can be reduced by 5-15% for the gas expansion cycle performed according to the present invention compared to conventional methods.

FIG. 6 shows a warm cooling curve and a cold cooling curve (warm composite curve and cold composite curve) for a heat exchange system 110 performed according to the dual nitrogen expansion process as the present invention and cooling system. Ie the sum of all warm streams to be cooled and the sum of all cold streams to be heated). FIG. 7 shows the corresponding worm cooling curves and cold cooling curves for the corresponding cooling process with the same feed, but was performed in a conventional manner without a fractionation column. The curves look similar, but with the view of FIG. 8 showing sections and two systems in the same curve (skrivefeil i originaltekst), the "branch point" and better adaptation can be clearly identified.

Example

The following examples illustrate the liquefaction of natural gas with 90.4% by volume of methane, and the present invention provides a solution for maximizing the amount of liquefied gas and at the same time minimizing the byproducts of unstable hydrocarbon liquids with high contents of ethane, propane and butane. Used. Stream data is shown in Figures 1, 2, 3, 4 or 5.

Claims (12)

As a method of producing LNG from the inlet feed gas (1) on land or offshore facilities,
1) the feed gas is passed through a fractionation column 150 to cool it and separated into a lower fraction enriched with heavier hydrocarbons and an upper fraction with reduced content of pentane (C5) and heavy components;
2) The upper fraction of the fractionation column is introduced into a heat exchanger system 110, partially condensed to form a two-phase fluid, and the two-phase fluid is LPG and pentane (C3-C5) in a suitable separator 160. This rich fluid (5) is separated into a gas (6) containing a small amount of C5 hydrocarbons and heavier hydrocarbons than C5, and the fluid (5) is recycled to the fractionation column (150) as cold reflux. Removing the gas (6) for further processing in a heat exchanger system (110) to liquefy the gas (6) with LNG having a maximum content of ethane and LPG;
3) a cooling circuit for liquefaction of gas in a heat exchanger system comprising an open or closed gas expansion process having at least one gas expansion step. The complete system (fractionation column 150) according to claim 1, wherein fractionation column 150 and separator 160 generate component splits / separation points in the normal boiling point range (NBP) of -12 ° C to 60 ° C. And reflux separator (160). The light major component for separation is butane (C4) having a normal boiling point of -12 ° C to 0 ° C, and the heavy key component is a C6 component having a boiling point of 50 ° C to 70 ° C. Whereby the top gas stream 6 of the system will comprise a significantly reduced content of n-butane and hydrocarbons having a normal boiling point lower than n-butane, and the reject stream of the system is mostly more than C6 and C6. A component having a high normal boiling point. 4. The fractionation column (150) and the separator (160) of claim 1, wherein the fractionation column (150) and the separator (160) are pentane (C5, NBP = 28-36 ° C) the system's top gas stream (6) and rejection of the system. Operating to be a transition component distributed in both streams (3). The temperature of the gas when the temperature of the feed gas is supplied to the heat exchanger system 110 is the temperature of the refrigerant gas stream at the hot end of the heat exchanger system (high temperature pinch). Reduced through fractionation column (150) to be lower than hot pinch point temperature. 6. The method according to claim 1, wherein the reboiler is connected to the fractionation column to reduce the vapor pressure of the bottom product. 7. The method according to any one of claims 1 to 6, characterized in that the heat exchanger for liquefaction (LNG production) comprises at least one multi-stream heat exchanger. 8. A method according to any one of the preceding claims, characterized in that it is carried out in a closed gas expansion process using one or more nitrogen expanders. The process according to any one of claims 1 to 8, which is carried out in a closed hybrid cooling process using methane / nitrogen as the coolant, wherein the coolant is used in both gas and liquid phases The cooling circuit comprises at least one gas expander and at least one device for expansion of the refrigerant in the liquid phase. 10. The process according to any one of claims 1 to 9, which is carried out in an open gas expansion process using one or more gas expanders, wherein a suitable high pressure gas is used as the cooling gas and a low pressure expanded gas is recycled for recirculation. Characterized in that it is not compressed but is used for other purposes. Fractionation column 150 for receiving feed gas, heat exchanger system 110 for cooling and partially condensing the top gas stream of the fractionation column, separator 160 for separating a two-phase stream from the heat exchanger system A mechanism for recirculating fluid from the separator to the fractionation column and introducing such fluid as reflux into the top portion of the column, and for supplying gas to the heat exchanger system for further cooling and liquefaction of gas from the separator to LNG. The cooling system used for cooling, condensation and liquefaction of a gas in a heat exchanger system, wherein the cooling system comprises an open or closed gas expansion process having at least one gas expansion step. A system for performing the method according to any one of the preceding claims. 12. The system according to claim 11, wherein the system separates the feed gas so that the upper gas stream (6) of the system is rich in most butanes (C4) and hydrocarbons having a normal boiling point lower than butane, and most of the bottom products in the fractionation column. And are designed to be rich in components having a normal boiling point higher than C6 and C6 of.

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