EA029627B1 - Method and apparatus for producing a liquefied hydrocarbon stream - Google Patents

Abstract

A cryogenic hydrocarbon composition, obtained by subjecting a raw liquefied hydrocarbon stream to a pressure reduction step, is first separated into a vaporous reject stream and a liquid stream. The liquid stream is discharged in the form of the liquefied hydrocarbon stream. The vaporous reject stream is recompressed, partially condensed by indirectly heat exchanging the compressed vapour stream against an auxiliary refrigerant stream, and separated. The condensed fraction is revaporized and combusted in a gas turbine. The vapour fraction, which generally has a higher nitrogen content and a lower heating value than the condensed fraction, is combusted in a combustion device other than a gas turbine. The auxiliary refrigerant stream is formed by a slip stream of the liquefied hydrocarbon stream.

Description

The invention relates to a method and apparatus for producing a stream of liquefied hydrocarbons.

Liquefied natural gas (LNG) is an economically important example of such a cryogenic hydrocarbon stream. Natural gas is an applicable source of fuel, as well as a source of various hydrocarbon compounds. It is often desirable to liquefy natural gas in a liquefied natural gas plant located at or near the source of the natural gas stream for a number of reasons. As an example, natural gas can be stored and transported over long distances more easily as a liquid than as a gas, because it takes up less space and does not need to be stored at high pressure.

Document UO 2006/120127 describes the process of LNG separation and installation for it. Liquefied natural gas in liquid form is sent to the separation unit, where they receive a stream of LNG purified from nitrogen and steam enriched with nitrogen. The separation unit uses two columns. An LNG stream liquefied in a liquefier is first separated in a first column operating at a pressure of about 1.25 bar, to obtain a nitrogen-depleted liquid and an upper gas stream. The upper gas stream is again compressed to a pressure of about 4 bar and passed into the second column, where any amount of residual methane is re-condensed. The recondensed methane is withdrawn as a liquid from the second column and mixed with the nitrogen-depleted liquid from the first column to form an LNG-free nitrogen stream. Nitrogen gas is removed from the top of the second column, which allows the use of nitrogen contained in natural gas, with a degree of technical purity.

Cooling or the mentioned re-condensation of methane in the second column is provided by the nitrogen cycle, independent of the liquefier, which uses a liquid refrigerant, the nitrogen content of which is more than 80 mol.%.

The disadvantage of the aforementioned LNG separation process is that an independent refrigeration cycle is required, which entails capital costs, as well as operating costs. In addition, as the re-condensed methane is added to the purified LNG stream, the need to maintain the nitrogen concentration in the purified LNG stream below the standard required for technical LNG increases.

The present invention relates to a method for producing a liquefied hydrocarbon stream comprising the following:

a cryogenic hydrocarbon composition is obtained, having in its composition the nitrogen and methane-containing liquid phase, with an initial pressure of from 1 to 2 bar abs .;

phase out the cryogenic hydrocarbon composition in a flash separator at a first separation pressure of 1 to 2 bar abs. return steam flow and liquid flow;

divert the liquid stream from the separator instantaneous evaporation in the form of a liquefied stream of hydrocarbons;

compressing the return steam flow in the instantaneous evaporation compressor to a pressure above 2 bar abs., thus obtaining a flow of compressed steam;

a partially condensed intermediate stream is formed from the compressed steam, and the partially condensed intermediate stream contains a condensed fraction and a vapor fraction as a result of partial condensation of the compressed vapor stream, wherein the partial condensation includes the indirect heat exchange of the compressed vapor stream with the auxiliary refrigerant stream formed by blowing off a liquefied hydrocarbon stream, by passing heat from at least part of the stream and compressed steam into the auxiliary refrigerant flow;

separating the condensed fraction from the vapor fraction in a gas-liquid separator at a second separation pressure;

the vapor fraction is removed from the gas-liquid separator, while the said vapor fraction has the first calorific value;

burning the vapor fraction in a combustion device other than a gas turbine; remove the condensed fraction from the gas-liquid separator;

re-evaporating the condensed fraction, whereby the condensed fraction is converted into a fully evaporated stream having a second calorific value that is higher than the first calorific value;

the fully vaporized gas stream is burned in the gas turbine.

Another aspect of the present invention relates to an apparatus for producing a liquefied hydrocarbon stream, comprising

a cryogenic supply line connected to a source of a cryogenic hydrocarbon composition including a nitrogen and methane-containing liquid phase;

a flash evaporator made with the possibility of obtaining a cryogenic hydrocarbon composition and separating the cryogenic hydrocarbon composition into a liquid stream and a return vapor stream;

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a liquid hydrocarbon product line connected in fluid to the bottom of the flash separator for diverting said liquid stream in the form of a liquefied stream of hydrocarbons from the flash evaporator;

a return steam line, fluidly connected to the top of the flash separator, for diverting said return steam flow from the flash evaporator;

an instant evaporation compressor located in the return steam line to compress the return steam flow and result in this flow of compressed steam;

a condenser placed in the return steam line further along the stream after the instantaneous evaporation compressor, configured to receive a stream of compressed steam and form a partially condensed intermediate stream from a stream of compressed steam, the said partially condensed intermediate stream containing a condensed fraction and a steam fraction configured to make contact at least between a portion of the flow of compressed steam and the flow of auxiliary refrigerant for wasps indirect heat exchange;

an auxiliary refrigerant supply line extending between the line of the liquid hydrocarbon product and the condenser, for the flow of the liquid hydrocarbon product to the condenser;

gas-liquid separator, located further along the stream after the condenser and configured to receive the condensed fraction and vapor fraction;

a vapor fraction withdrawal line connected in fluid with the upper part of the gas-liquid separator, made with the possibility of receiving the vapor fraction from the gas-liquid separator;

a device for combustion, other than a gas turbine, connected in fluid with a gas-liquid separator via a vapor fraction removal line, designed to receive and burn the exhaust vapor fraction;

a condensed fraction withdrawal line connected in fluid with the lower part of the gas-liquid separator, made with the possibility of receiving the condensed fraction from the gas-liquid separator;

a gas turbine connected in fluid with a gas-liquid separator via a condensed fraction withdrawal line, designed to receive and incinerate the condensed fraction withdrawn;

a device for re-evaporation, placed on the line of removal of the condensed fraction between the gas-liquid separator and the gas turbine and configured to convert the condensed fraction into a fully evaporated stream before burning in the gas turbine.

Later in this document, the invention will be further illustrated using examples and with reference to the drawings, which schematically represent:

in fig. 1 is a process flow diagram illustrating a method and apparatus according to an embodiment of the invention;

in fig. 2 illustrates an embodiment of a pressure reduction system for use in the present invention;

in fig. 3 is a process flow diagram illustrating a method and apparatus according to another embodiment of the invention;

in fig. 4 is a process flow diagram depicting a method and apparatus according to another embodiment of the invention;

in fig. 5 is a process flow diagram in which an embodiment corresponding to FIG. 3, used in combination with the selected liquefier;

in fig. 6 is a process flow diagram in which an embodiment corresponding to FIG. 4, used in combination with the selected liquefier; and

in fig. 7 is a flow chart of the process in which the embodiment corresponding to FIG. 4, is used using a special type of flash separator.

In these figures, the same item numbers will be used to refer to the same or similar elements. In addition, a single position number will be used to identify the pipe or line and the flow moving along the specified line.

The present description concerns the production of a liquefied hydrocarbon stream, such as, for example, a stream of liquefied natural gas. The cryogenic hydrocarbon composition is first separated into a vapor return stream and a liquid stream. The liquid stream is withdrawn as a liquefied hydrocarbon stream. The return steam flow is compressed again, partially condensed as a result of the indirect heat exchange of the compressed steam flow with the auxiliary refrigerant flow and separated. The condensed fraction is re-evaporated and burned in a gas turbine. The specified fuel gas vapor stream is identified as a high quality fuel gas stream.

The vapor fraction, which in general has a higher nitrogen content and lower calorific value than the condensed fraction, is burned in a combustion device other than a gas turbine. In connection with the present description and the condensed fraction, the indicated top is 2 029627

It is called low quality fuel gas. Poor quality in this context means having a calorific value that is lower than the calorific value of a high-quality fuel gas vapor stream that is burned in a gas turbine.

The auxiliary refrigerant flow is preferably formed from the discharge of a liquefied hydrocarbon stream. No high degree of separation of methane and nitrogen in the intermediate condensed stream formed from the return vapor stream is required, since both the vapor fraction and the condensed fraction are burned. Considering the above, the vapor fraction should not be free from methane, while the condensed fraction is associated with less stringent nitrogen requirements than if it were added to a liquefied hydrocarbon stream.

Thus, the proposed method and device do not require the presence of a full nitrogen return unit, since a flow of combustible fuel gas is produced instead of a released stream of nitrogen.

The proposed method and device can preferably be applied, for example, if the initial liquefied stream contains nitrogen in the range from 1 to 7 mol.%. However, the greatest benefit is obtained in cases where the initial liquefied stream contains more than 3 mol.% Of nitrogen, since in such cases a relatively large amount of vapor return gas is produced, which flows per unit time, from which a liquefied hydrocarbon stream is obtained at the maximum content of lower-boiling components, such as nitrogen, in liquefied natural gas sold on an industrial scale. A large amount of steam return gas flowing per unit of time usually contains too much nitrogen to use as fuel in gas turbines, and it usually exceeds the factory requirements for fuels if gas turbines are used to drive refrigeration cycles in the liquefier.

More than 30 mol.% Of the steam return stream and / or more than 30 mol.% Of the partially condensed intermediate stream may consist of nitrogen. This nitrogen content would be too high to meet the fuel gas requirements for most gas turbines. Then, the proposed method and device can preferably be used to re-condense the fraction of the return vapor stream to obtain a condensed fraction, less than 30 mol.% Of which consists of nitrogen, so that after re-evaporation it can be used to power the gas turbine with fuel.

If the nitrogen content is still too high for the selected gas turbine, the condensed fraction (preferably after re-evaporation) can be mixed in a certain ratio with another fuel gas to bring the fuel in compliance with the standards. In such cases, the invention achieves a positive effect, consisting in the fact that the requirements for the preparation of mixtures are less stringent than in the case if the fuel gas contained more than 30 mol.% Of nitrogen.

The re-evaporated condensed fraction may need to be compressed to meet the specified pressure specifications for the gas turbine fuel gas. Alternatively, the condensed fraction can be injected, for example, using a liquid pump, before re-evaporation, so that the condensed fraction can be re-evaporated at a pressure that is already high enough to meet the fuel pressure standards for the gas turbine in which re-evaporated condensed fraction.

The cryogenic hydrocarbon composition can be obtained by subjecting the initial liquefied hydrocarbon stream to treatment at the stage of pressure reduction.

The cryogenic hydrocarbon composition can be obtained from the liquefier. Such a liquefier may be part of the refrigerant circuit for recycling refrigerant flow. The refrigerant circuit may include a refrigerant compressor connected to the refrigerant compressor drive and adapted to compress the refrigerant flow; and a cryogenic heat exchanger configured to establish contact for the implementation of indirect heat exchange between the hydrocarbon stream and the refrigerant loop of the circuit, resulting in the initial liquefied stream is formed from the hydrocarbon stream containing the supercooled hydrocarbon stream. The liquefier may additionally include a pressure reduction system placed further along the flow after the cryogenic heat exchanger and communicating with it via a liquid medium, to receive the initial liquefied flow and lower the pressure of the initial liquefied flow. A drain line can fluidly connect a pressure reduction system with a cryogenic heat exchanger to establish a fluid message for the original liquefied flow that passes from the cryogenic heat exchanger to the pressure reduction system, with the flash evaporator further downstream of the pressure reduction system and fluidly communicates with it to receive a cryogenic hydrocarbon composition from a pressure reduction system. Accordingly, the gas turbine, in which the condensed fraction is re-evaporated and burned, drives the refrigerant compressor in the refrigerant circuit in the liquefier. The gas turbine is preferably selected from the group consisting of gas turbines based on an aircraft engine.

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Therefore, the present method may suitably include recirculating the refrigerant flow in the liquefier, including moving the compressor refrigerant and compressing said refrigerant flow in the refrigerant compressor. The hydrocarbon stream can be condensed and subcooled, including indirectly exchanging said hydrocarbon stream with a refrigerant stream in a liquefier, resulting in an initial liquefied stream at a liquefaction pressure above 2 bar abs. The initial liquefied stream can be carried out through the stage of pressure reduction, thus obtaining a cryogenic hydrocarbon composition, which has a nitrogen and methane-containing liquid phase. Accordingly, the refrigerant compressor is driven by the said gas turbine, in which the fully evaporated condensed fraction is burned.

The blowout for forming the auxiliary refrigerant stream is preferably formed from a portion of the liquefied hydrocarbon stream. The advantage of using an otduv liquefied hydrocarbon stream for this purpose is that it can be carried out relatively easily at an existing plant without the need to suspend or modify any part relating to the source of the cryogenic hydrocarbon composition. In addition, it is the coldest flow, easily accessible at the factory, without the need to provide a specially designed cooling cycle for it, and, as a rule, it is there in large quantities.

The auxiliary return refrigerant line respectively extends between the condenser and the flash separator. In this case, the auxiliary refrigerant stream containing heat from at least a part of the compressed vapor stream can be passed in the direction of the instantaneous evaporation separator and into it so that a semi-open refrigeration cycle is formed.

Preferably, the pump is placed in the auxiliary refrigerant line, through which the blowout of the liquefied hydrocarbon stream can be pumped into the condenser.

FIG. 1 illustrates an embodiment of the invention. A cryogenic hydrocarbon composition, which has a nitrogen and methane-containing liquid phase, is fed via line 8 of cryogenic feedstock. The source of the cryogenic hydrocarbon composition is not a limitation of the invention in its broadest definition, but for completeness, one of the embodiments is displayed in which the cryogenic hydrocarbon composition is supplied from the source as a liquefier 100

Such liquefier 100, as a rule, is provided higher upstream from line 8 of cryogenic feedstock. Liquefier 100 may have a fluid message with line 8 of cryogenic feedstock through pressure reduction system 5, which communicates with liquefier 100 via drain line 1. Pressure reduction system 5 is located downstream of the cryogenic heat exchanger 180 and adapted to receive and reduce pressure the original liquefied stream coming from the main cryogenic heat exchanger 5.

The pressure reduction system 5 may comprise a dynamic unit, such as a turbine-expander, a static unit, such as a Joule-Thomson valve, or a combination thereof. An example of a pressure reduction system 5 with a Joule-Thomson valve 7 connected in series with the expander turbine 6 is shown in FIG. 2. When using an expander turbine, it can optionally be movably connected to an energy source. Numerous configurations are possible and known to the person skilled in the art.

In the exemplary embodiment shown in FIG. 1, liquefier 100 encloses a refrigerant circuit 101 for recycling refrigerant. The refrigerant circuit 101 includes a refrigerant compressor 160 connected to a refrigerant compressor drive 190 in the form of a movable mechanical engagement. The refrigerant compressor 160 is adapted to compress the spent refrigerant stream 150 and discharge the refrigerant in an overpressure state to the compressed refrigerant line 120. In line 120 of the compressed refrigerant in the refrigerant circuit 101, typically at least one return heat exchanger 124 is provided. The return heat exchanger 124 is adapted to remove heat from the pressurized refrigerant flow transported through the compressed refrigerant line 120 to the external environment, either to the air or in a pond such as a lake, river, or sea.

Liquefier 100 typically contains a refrigerant cooler configured to cool an overpressure refrigerant coming from a compressed refrigerant line 120, from which heat is returned to the return heat exchanger 124. A cooled refrigerant stream is obtained from the refrigerant refrigerant 131.

Liquefier 100 additionally includes a cryogenic heat exchanger 180 connected to the outlet port of the refrigerant compressor 160 via a line 120 of compressed refrigerant. In the embodiment shown in FIG. 1, the cryogenic heat exchanger 180 also performs the function of the refrigerant cooler discussed in the previous paragraph, but this is not a requirement of the invention. The cryogenic heat exchanger is generally configured to establish contact for the implementation of indirect heat exchange between the stream 110 of hydrocarbons and the refrigerant of the refrigerant circuit 101.

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A spent refrigerant line 150 connects the cryogenic heat exchanger 180 to the main suction side of the refrigerant compressor 160. The cooled refrigerant line 131 is in fluid communication with the spent refrigerant line 150 through the cold side of the cryogenic heat exchanger 180. The hydrocarbon stream 110 flows along the warm side of the cryogenic heat exchanger 180. The cold side and the warm side are in heat exchange contact with each other.

The return refrigerant main line 133 establishes a fluid message between the cooled refrigerant line 131 and the cold side of the cryogenic heat exchanger 180. The return refrigerant main line 133 is in fluid communication with the spent refrigerant line 150 through the cold side and the heat exchange with the hot side. The main control valve 134 of the refrigerant is built into the main line 133 of the return refrigerant.

The cryogenic heat exchanger 180 receives the refrigerant flow in an overpressure state from the main line 133 of the return refrigerant through the main control valve 134 of the refrigerant and leads to the compressor 160 of the refrigerant. Thus, the cryogenic heat exchanger 180 forms part of the refrigerant circuit 101.

The cryogenic heat exchanger 180 may be provided in any suitable form, including a printed circuit heat exchanger, a plate-fin type heat exchanger, optionally in a cold room configuration, or a shell-and-tube type, such as a spiral heat exchanger or coil heat exchanger.

A specific non-limiting example of a liquefier and its refrigerant circuit based on a shell-and-tube type heat exchanger comprising a refrigerant compressor and a cryogenic heat exchanger is shown in FIG. 5 and 6. These figures will be described in detail below.

Referring again to the invention, it can be seen that the instantaneous evaporation separator 50 is adapted to receive a cryogenic hydrocarbon composition 8, optionally, downstream from the pressure reduction system 5 and is in fluid communication with it, if such a system is provided. Depending on the separation requirements, the flash evaporator 50 may be provided as a simple drum that separates the vapor from the liquid phases into one equilibrium stage (such as shown in Fig. 1), or a more complex distillation column. Non-limiting examples of features are disclosed in US Patents 5,421,165, 5,893,274, 6,0148,669, 6,105,391, and the publication of application 2008/0066492 prior to issuing a US patent.

Line 90 of the liquid hydrocarbon product is fluidly connected to the bottom of the flash evaporator 50. Line 90 of a liquid hydrocarbon product connects flash separator 50 to a cryogenic storage tank 210. An optional cryogenic pump (not shown) may be present in line 90 of a liquid hydrocarbon product to facilitate the movement of any liquid hydrocarbon product withdrawn from the flash separator 50 to the cryogenic storage tank 210.

Line 64 return steam is connected in fluid with the upper part of the separator 50 instantaneous evaporation. The instant evaporation compressor 260 is located on the return steam line 64 to compress the return steam flow from the instant evaporator separator 50. Condenser 35 is located on line 64 of the return steam downstream from instant evaporation compressor 260. This portion of the return steam line will be referred to as line 70 of the compressed steam flow.

The condenser 35 is configured to receive a stream of compressed steam and form a partially condensed intermediate stream from a stream of compressed steam. The condenser is configured to establish contact for the implementation of indirect heat exchange between at least a portion of the flow of compressed steam and the flow of an auxiliary refrigerant.

An aftercooler 69 may be provided in the compressed steam flow line 70 between the flash evaporator 260 and the condenser 35. The aftercooler is adapted to recover heat from the compressed vapor to the external environment (for example, by exchanging heat with external air flow or external water flow).

Such an aftercooler is recommended in embodiments of the invention in which the temperature of the compressed steam flow, as discharged from the flash compressor, exceeds the temperature of the outside air and / or outside water, so that at least some of the heat added to the steam in the instant compressor evaporation, can be returned to the external environment.

Heat exchanger 65 for cold recovery may optionally be provided in return steam line 64, and as a result, the return steam is supplied to flash evaporator 260 at the flash temperature of the compressor intake, which is higher than the temperature at which the return steam is removed from separator 50 instantaneous evaporation in line 64 of the return steam. In this case, the cold contained in the return steam in the return steam line 64 is retained in the cold recovery flow 66, as a result of heat exchange with the cold recovery flow 66, until the return vapor is compressed in the instant evaporation compressor 260.

In one of the embodiments of the invention, the cold recovery stream 66 may comprise or consist of a side stream formed from the hydrocarbon stream 110 in the liquefier 100.

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The resulting cooled sidestream can be combined, for example, with a cryogenic hydrocarbon composition in line 8 of a cryogenic feedstock. Thus, the implementation of heat exchange to recover the cold in the heat exchanger 65 to recover the cold adds the rate of formation of a cryogenic hydrocarbon composition.

In another embodiment of the invention, the cold recovery stream 66 may contain or consist of a refrigerant stream recycled to the liquefier 100, resulting in the refrigerant stream (or exhausting) condensing or supercooled. For example, the blowout of the compressed refrigerant can be removed from the line 120 of the compressed refrigerant and cooled using the return steam line 64.

In yet another embodiment of the invention, the cold recovery flow 66 may comprise or consist of additional cooled return steam in line 70 of a compressed vapor flow, preferably in that part of line 70 of a compressed vapor flow that extends between the after-cooler 69 and condenser 35, through which the compressed vapor is passed from the compressor 260 instantaneous evaporation into the condenser 35. In this case, the load on the condenser 35, required from the auxiliary refrigerant stream 132, will decrease.

The auxiliary refrigerant stream is supplied from the auxiliary refrigerant supply line 132, which extends between the liquid hydrocarbon product line 90 and the condenser 35. As shown in the example, the liquefied hydrocarbon product line 90 is split into the auxiliary refrigerant supply line 132 and the main product line 91. The auxiliary return refrigerant line 138 extends between the condenser 35 and the flash separator 50 and is adapted to return the auxiliary refrigerant containing the heat obtained from the pressurized vapor stream back to the flash evaporator 50. The auxiliary refrigerant check valve 135 is located on the auxiliary refrigerant supply line 132. An optional auxiliary refrigerant pump (not shown) may optionally be provided in the auxiliary refrigerant supply line 132.

The gas-liquid separator 33 is located downstream from the condenser 35. The steam fraction withdrawal line 80 is fluidly connected to the upper part of the gas-liquid separator 33, and the condensed fraction withdrawal line 40 is fluidly connected to the lower part of the gas-liquid separator 33. The gas turbine 320 is connected to fluid with a gas-liquid separator using the line 40 removal of the condensed fraction. A combustion device 220, other than a gas turbine, is fluidly connected to a gas-liquid separator via a vapor fraction removal line 80.

Combustion device 220 may include multiple combustion units. It may include, for example, one or more of the following units: furnace, boiler, afterburner, dual-fuel diesel engine, or their combinations. The boiler and the dual-fuel diesel engine can preferably be connected to an electrical power generator.

The device 285 for re-evaporation is placed in the line 40 for withdrawing the condensed fraction between the gas-liquid separator 33 and the gas turbine 320. The device for re-evaporation is configured to bring the condensed fraction in the line 40 for discharging the condensed fraction into contact with the heating fluid 286 to implement indirect heat exchange, whereby during operation, heat is transferred from the heating fluid 286 to the condensed fraction located in the outlet line 40 is condensed Noah fraction. Optionally, the compressor 360 of the fuel gas is placed in the line 40 removal of the condensed fraction between the device 285 for re-evaporation and the gas turbine 320.

Heat exchanger 85 for recovering cold may optionally be provided in line 80 for discharging the vapor fraction to recover the cold contained in the vapor fraction before burning it in the combustion device 220. Heat exchanger 85 for cold recovery is designed to bring the vapor fraction in line 80 of the vapor fraction into contact with the cold recovery stream 86 in order to effect indirect heat exchange. In the course of operation, heat is transferred from the cold recovery stream 86 of the steam fraction located in the 80 branch of the steam fraction. Said cold recovery heat exchanger 85 may be referred to as a second cold recovery heat exchanger in embodiments of the invention in which a cold recovery heat exchanger 65 is provided in the return steam line 64. In such embodiments of the invention, the heat exchanger 65 for cold recovery in the return steam line 64 may be called the first heat recovery exchanger for cold recovery.

The device described above can be used in the method described as follows.

The cryogenic hydrocarbon composition 8, which has a nitrogen and methane-containing liquid phase, is supplied at an initial pressure in the range from 1 to 2 bar abs. and initial temperature. Making the supply of the cryogenic hydrocarbon composition 8 may include passing the hydrocarbon stream 110 through the liquefier 100. The hydrocarbon stream 110 may be condensed and supercooled in the liquefier 100. The condensation and overcooling of the hydrocarbon stream 110 preferably includes the indirect heat exchange of the hydrocarbon stream 110 with chla-

The dagent in the liquefier 100. The supercooled liquefied hydrocarbon stream thus formed is called the initial liquefied stream. Therefore, the initial liquefied stream is formed from the hydrocarbon stream as a result of condensation and subsequent subcooling of the hydrocarbon stream.

For example, in such a liquefier 100, the hydrocarbon stream 110 enclosing the hydrocarbon-containing vapor source may undergo heat exchange with the primary refrigerant stream, for example, in a cryogenic heat exchanger 180, resulting in a fluidization of the original vapor stream of the feed stream to produce an initial liquefied stream inside the discharge line 1. Then, the desired cryogenic hydrocarbon composition can be obtained from the initial liquefied stream 1. The initial liquefied stream can be removed from the liquefier 100 via the discharge line 1. Cryogenic coal Euro hydrogen composition 8 can be obtained from the initial liquefied stream, for example, when passing the initial liquefied stream through the stage of pressure reduction in the system 5 pressure reduction. At this stage of pressure reduction, the pressure can be reduced from the liquefaction pressure to the initial pressure.

The cryogenic hydrocarbon composition 8 is then subjected to phase separation into the vapor return stream 64 and the liquid stream 90 at a first separation pressure of 1 to 2 bar abs. Accordingly, the specified phase separation is carried out in the separator 50 flash evaporation. Return steam 64 comprises most of any instantaneous vapor evaporation, preferably all that vapor that formed during the pressure reduction stage. Liquid stream 90 is drawn off in the form of a liquefied hydrocarbon stream, which may be a stream of liquefied natural gas, provided that the methane content is at least 81 mol%. Liquid stream 90 is typically sent to a cryogenic storage tank 210.

The return steam stream 64 is removed from the separator 50 of flash evaporation and then compressed in the flash evaporator 260 to a pressure higher than 2 bar abs., Thereby obtaining a stream 70 of compressed steam.

Stream 70 of compressed steam is passed to condenser 35. If after-cooler 69 is provided in line 70 of a stream of compressed steam, stream 70 of compressed steam is passed through after-cooler 69 as the stream passes to condenser 35. In after-cooler 69, heat returns from the compressed steam to the external environment (for example, as a result of heat exchange with external air flow or external water flow). Compressed steam 70 is removed from the optional after-cooler 69 at a cooling temperature close to the external temperature, for example, 2 ° C. above the external temperature. It is believed that the external temperature is the temperature of the external environment (air or water) to which heat returns.

In the condenser 35, a partially condensed intermediate stream is formed from the compressed vapor 70 as a result of the partial condensation of the compressed vapor stream. The partially condensed intermediate stream contains the condensed fraction 40 and the vapor fraction 80. Partial condensation includes the indirect heat exchange of the compressed vapor stream 70 with the auxiliary refrigerant stream 132 formed by blowing out the liquid stream 90. During the embodiment of the indirect heat exchange, the heat passes at least from a portion of the stream 70 of compressed steam to the stream 132 of the auxiliary refrigerant. It is estimated that only about 0.2% of the liquid stream 90 is required as an auxiliary refrigerant stream 132. In the General case, from 0.05 to 0.40% of the liquid stream 90 may be required as the auxiliary refrigerant stream 132.

Then, the condensed fraction 40 is separated from the vapor fraction 80 in the gas-liquid separator 33 at the second separation pressure. Preferably, the vapor fraction and the condensed fraction coexist in gas-liquid separator 33 and undergo separation, being in the same thermodynamic equilibrium between said vapor fraction and the condensed fraction, being inside the gas-liquid separator 33. In general, this can be achieved if the gas-liquid separator 33 is designed as drum without any internal elements for the implementation of gas-liquid contact, such as plates or nozzle, which, by virtue of this, yaet is substantially a single theoretical stage.

The vapor fraction 80 is removed from the gas-liquid separator 33, usually as a vapor phase at its dew point. The vapor fraction 80, as withdrawn from the gas-liquid separator 33, has a first calorific value. The vapor fraction 80 is burned in a combustion device 220.

The condensed fraction 40 is also withdrawn from the gas-liquid separator 33, but as a liquid phase at its boiling point. Then the condensed fraction 40 is re-evaporated in the device 285 for re-evaporation. Re-evaporation involves bringing the condensed fraction 40 into contact with a heating fluid 286 for indirect heat exchange, whereby heat is transferred from the heating fluid 286 to the condensed fraction 40. During re-evaporation, the condensed fraction 40 turns into a fully evaporated stream having a second calorific value. Upon completion of re-evaporation, the condensed fraction 40 is completely in the vapor phase. Fully evaporated stream generated from the condensed fraction 40 is burned in a gas turbine 320.

The auxiliary load of cold transmitted by the flow of the auxiliary refrigerant 132 to the condenser 35 can be changed by adjusting the check valve 135 of the auxiliary refrigerant.

refrigerant charge. Various control strategies are possible. For example, the auxiliary refrigerant control valve 135 is functionally connected to an optional level controller 37 placed in the gas-liquid separator 33 to establish a constant liquid level in the gas-liquid separator 33 by controlling the degree of partial condensation of the compressed vapor 70 that takes place in the condenser 35. Another example includes that the auxiliary refrigerant control valve 135 is functionally connected to an optional temperature sensor (not shown) located between the condensate om 35 and the gas-liquid separator 33 to establish a constant temperature of the partially condensed intermediate stream.

A suitable value specified for the temperature sensor may be based on the desired nitrogen content in the condensed fraction 40, which is related to the composition of the fuel gas for the gas turbine 320. The remaining nitrogen remains in the vapor fraction. The discharge temperature of the original liquefied stream located in the discharge line 1 can be adjusted to ensure that the total amount of available thermal energy available in the return pair 64 and / or partially condensed intermediate flow satisfies the requirement imposed on the combined fuel gas for the chamber ( chambers) 220 of the combustion and gas turbine (s) 320. For example, if the return pair 64 has too much heat energy, the temperature of the drain can be lowered to reduce the amount of methane, which It evaporates at the stage of pressure reduction in the system 5 pressure reduction. The distribution of nitrogen between the vapor fraction 80 and the condensed fraction 40 is controlled by the auxiliary cold load.

The nitrogen content in the liquid stream 90 can be maintained within the standards throughout the drain temperature range assumed during the work, by correctly selecting and determining the size of the flash evaporator 50 at the design stage.

The first and second calorific values determine the amount of heat that can be generated when a mole of fuel gas is burned. This can be either the so-called "high" calorific value, or the "low" calorific value, if the same conditions are used to compare the two calorific values. Preferably, a "low" calorific value is used to compare the two calorific values, since this is closest to the combustion conditions used in the invention. The calorific value can be determined using the standard ΆδΤΜ Ό3588-98, applied without regard to the composition of the steam fraction 80 and / or the condensed fraction 40. As a result of the separation in the cooled gas-liquid separator 33, the second calorific value (related to the condensed fraction 40) is higher than the first calorific value (related to the steam fraction 80). However, since the partially condensed intermediate stream consists essentially of two components, methane and nitrogen, the first and second calorific values unambiguously reflect the nitrogen content in the vapor fraction 80 and in the condensed fraction 40, respectively.

The vapor fraction 80 is combusted in a combustion device 220, preferably at a first pressure of fuel gas that is not higher than a second separation pressure. Thus, the compressor can be eliminated, since the pressure in the vapor fraction 80 should not increase. Preferably, the vapor fraction 80 is burned in a combustion apparatus at a pressure of from 2 to 15 bar abs., More preferably, at a pressure of from 2 to 6 bar abs.

The condensed fraction 40 may need to be injected to a second fuel gas pressure that is higher than the second separation pressure. If the fuel gas compressor 360 is located on the condensed fraction removal line 40 between the re-evaporator 285 and the gas turbine 320, the fully evaporated stream can optionally be compressed in the fuel gas compressor 360 to the second pressure of the fuel gas before burning the fully evaporated gas turbine 320. The second pressure of the fuel gas is generally higher than the second separation pressure and is preferably adapted to meet the pressure requirements of the fuel gas imposed by This gas turbine 320.

The pressure reducing valve 245 can optionally be placed in the condensed fraction withdrawal line 40 between the gas-liquid separator 33 and the re-evaporation device 285. This allows you to once evaporate a certain amount of condensed fraction 40 before passing the condensed fraction 40 through the device 285 for re-evaporation first by passing the condensed fraction 40 through the pressure reducing valve 245, and then carrying out indirect heat exchange of the condensed fraction 40 with the heating fluid 286. In this case A lower temperature of the heating fluid 286 is achieved when it is withdrawn from the device 285 for re-evaporation, and / or more cold contained in the condensed fraction 40, it can be removed into the heating fluid 286. The pressure reduction valve 245 controls the temperature of the evaporating flow removed from the device 285 for re-evaporation. The pressure reduction valve 245, respectively, may be functionally connected to the first temperature sensor 247 located in the condensed fraction discharge line 40 downstream of the re-evaporator 285, whereby the valve position is controlled according to the first temperature signal generated by first sensor 247 temperature. If the pre- 8 029627

An optional fuel gas compressor 390 is installed, the first temperature sensor, respectively, is placed in the condensed fraction withdrawal line 40 between the re-evaporation unit 285 and the optional fuel gas compressor 390. The adjustable value of the first target temperature for the specified control circuit can be set a few degrees lower, for example, 2 ° C below the temperature of the heating fluid 286 at the inlet of the device 285 for re-evaporation. Preferably, the temperature of the condensed fraction 40 at the outlet of the device for re-evaporation is in the range from external temperature to a value 10 ° C below the external temperature in order to effectively obtain the greatest positive effect from the cold present in the condensed fraction 40.

The second separation pressure is preferably higher than the first separation pressure. The second separation pressure, respectively, may be from 2 to 22 bar abs., Preferably from 5 to 22 bar abs., More preferably from 5 to 15 bar abs. The second separation pressure at the upper end of the range from 2 to 22 bar abs. contributes to the partial condensation of the compressed stream 70 and to ensure the presence of an interval for greater pressure drop in the optional pressure reducing valve 245 and / or maintaining a higher pressure even after the pressure reducing valve 245, resulting in savings on the compression load of the fuel gas in the optional fuel gas compressor 360. The pressure at the lower end of the range contributes to the separation efficiency in the gas-liquid separator 33 and has less impact on the compression process of the vapor fraction 80, which should be burned in the combustion device 220 at a relatively low pressure, usually less than 15 bar abs. In the proposed range from 5 to 15 bar abs. for the second separation pressure, a proper balance is achieved between the beneficial and adverse effects, summarized earlier in this paragraph.

It has been found that a typical pressure drop of 1.0 to 4.0 bar on the optional pressure reducing valve 245 is adequate under normal conditions.

In some embodiments of the invention, the second separation pressure is in the range of 5 to 8 bar abs., Said pressure most often satisfies the requirements for a low pressure fuel gas flow suitable for supplying vapor fraction 80 to the combustion device 220 without the need for additional compression. You can choose a higher pressure if the combustion device 220 is located at a relatively large distance from the first gas-liquid phase separator and / or when the vapor fraction 80 is designed to pass through one or more heat exchangers 85 to recover the cold. In such circumstances, an additional pressure drop can be expected during the supply of the stripping gas to the combustion device 220. In one of the embodiments of the invention, the second separation pressure is about 6.5 bar abs.

Cryogenic hydrocarbon composition 8 can be obtained from deposits of natural gas or oil, or from coal seams. Alternatively, the cryogenic hydrocarbon composition 8 can also be obtained from another source, including, for example, a synthetic source such as the Fischer-Tropsch process. Preferably, the cryogenic hydrocarbon composition 8 contains at least 50 mol.% Methane, more preferably at least 80 mol.% Methane. The preferred initial temperature below -130 ° C can be achieved by passing the hydrocarbon stream 110 through the liquefaction system 100. An embodiment of passing the hydrocarbon stream 110 through the liquefaction system 100 will be described in more detail below.

The refrigerant is subjected to recirculation in the circuit 101 of the refrigerant liquefier 100. Recirculating involves activating the refrigerant compressor 160 and compressing the refrigerant flow in the refrigerant compressor 160. The hydrocarbon stream 110 condenses and supercooled. Condensation and subcooling includes the implementation of indirect heat exchange of a stream of 110 hydrocarbons with a refrigerant in a liquefier 100. The supercooled stream of liquefied hydrocarbons that is formed in this way is called an initial liquefied stream. Therefore, the initial liquefied stream is formed from the hydrocarbon stream as a result of condensation and subsequent subcooling of the hydrocarbon stream.

Hydrocarbon stream 110 in any of the examples disclosed herein, can be obtained from deposits of natural gas or oil, or from coal seams. Alternatively, the cryogenic hydrocarbon composition 8 can also be obtained from another source, including, for example, a synthetic source such as the Fischer-Tropsch process. Preferably, the cryogenic hydrocarbon stream 110 contains at least 50 mol.% Methane, more preferably at least 80 mol.% Methane. The resulting liquid hydrocarbon product fed to line 90 of a liquid hydrocarbon product and / or collected in a cryogenic storage tank 210 is preferably a liquefied natural gas (LNG).

Depending on the source, hydrocarbon stream 110 may contain varying amounts of components other than methane and nitrogen, including one or more non-hydrocarbon components other than water, such as CO ₂ , Nd, H _2, and other sulfur compounds; and one or more hydrocarbons heavier than methane, in particular, such as ethane, propane and butane, and possibly smaller amounts of pentanes and aromatic hydrocarbons. Hydrocarbons with a molecular weight of at least equal to the mass of propane can be referred to as C ₃ + hydrocarbons in this document, and carbohydrates - 9 029627

genera with a molecular weight of at least equal to that of ethane can be referred to as C ₂ ⁺ hydrocarbons in this document.

If desired, hydrocarbon stream 110 may be pretreated to reduce the amount and / or remove one or more undesirable components, such as CO ₂ and H ₂ §, or it may be affected in other stages, such as pre-overpressure or the like. . Such stages are well known to the person skilled in the art and their mechanisms are not discussed further here. Thus, the composition of the hydrocarbon stream 110 varies depending on the type and location of the gas, as well as the pretreatment (s) used.

The initial liquefied stream is withdrawn from the liquefier 100 through the discharge line 1. The initial liquefied stream may contain nitrogen in the range from 1 to 7 and more than 81 mol.% Of methane. The temperature of the initial liquefied stream in the discharge line 1 can be approximately from -165 to -120 ° C. The cryogenic hydrocarbon composition 8 is obtained from an initial liquefied stream while passing an initial liquefied stream through a stage of pressure reduction in the system 5 of pressure reduction, as a result of which the pressure decreases from the liquefaction pressure to an initial pressure of 1 to 2 bar abs. Evaporation vapor is usually formed during this stage of pressure reduction.

The cryogenic hydrocarbon composition 8 contains a nitrogen and methane-containing liquid phase and is usually at a temperature below 130 ° C.

In many cases, the temperature of the initial liquefied stream in the discharge line 1 may be in the range from -160 to -145 ° C. Within this narrower range, the cold load required in the liquefaction system 100 is lower than if lower temperatures are desired, whereas the degree of supercooling at pressures above 15 bar abs. is high enough to avoid excessive vaporization of instantaneous evaporation when the pressure is reduced to an initial value of 1 to 2 bar abs.

The liquefaction system 100 in the present description has so far been depicted very schematically. It may be any suitable system and / or process for liquefying hydrocarbons, in particular, any process for liquefying natural gas to produce liquefied natural gas, and this invention is not limited to the specific choice of liquefaction system. Examples of suitable liquefaction systems use processes with a single refrigerant cycle (usually with one cycle on a mixed refrigerant — § MI — processes such as the P1CO process described in the work of the authors KI 1oopkep and R. Sybkyapkep presented in 1998 at the conference SakUSN (Dubai)), but a process with a single-component refrigerant is also possible, such as, for example, the VNR-SKS process. also described in the aforementioned paper by the authors Loibes and S'Npkbappkep); processes with a double refrigerant cycle (for example, the highly applied Rgorup-M1heb-YerGg1gleg1 process, often abbreviated as C3MI, such as described, for example, in US 4404008, or, for example, double-cycle processes with a mixed refrigerant — IMI; described in US Pat. No. 6,688,891; or, for example, processes with two cycles, in which each cycle of the refrigerant contains a one-component refrigerant); and processes based on three or more compressor units for three or more refrigeration cycles, an example of which is described in US Pat. No. 7,114,351.

Other examples of suitable liquefaction systems are described in US Pat. No. 5,832,745 (§11 11), US Pat. No. 6,295,833, US Pat.

Another suitable example of the IMI process is the so-called Ahepk υρυΕΠΝ process, such as, described, for example, in the work under the name 'ΕΕΙΝρυ: ΙΝΝΟ ΑΤίνΕνΕ RIOC88 TO NEVESE BPS SO8T8 "by R.-. World Gas Conference (Υοτίά Sak S'ophegepsa) in Tokyo, Japan (2003). Other suitable three-cycle processes include, for example, US Patent 6962060; document \ EO 2008/020044; US Patent 7127914; German patent application ΌΕ 3521060Α1; US Patent 5,669,234 (known in the industry as an optimized cascade process ); US Patent 6,253,574 (known in the industry as a cascade process with mixed fluid); US Patent 6,308,531; US Patent Application Publication No. 2008/0141711; Job Magc 1. Joiek e1 a1. NUBB BPS Rygosek, SacilesH 2002, Doha, Qatar (October 13–16, 2002). These proposals are intended to demonstrate the broad applicability of the invention and are not intended to represent an exclusive and / or exhaustive list of possibilities. Not all of the examples listed above use gas turbines (based on an aircraft engine) as the primary drives of the refrigerant compressors. It is clear that any actuators other than gas turbines can be replaced with a gas turbine to achieve some of the preferred benefits of the present invention.

An example in which the liquefaction system 100 is created based on, for example, C3MI or BF11 is briefly illustrated in FIG. 5 and 6. In both cases, it is chosen that the cryogenic heat exchanger 180 in the liquefaction system 100 is a spiral heat exchanger comprising a warm part comprising all pipes, including lower and upper pipe bundles for the hydrocarbon product

- 10 029627

(181 and 182, respectively), lower and upper tube bundles for LMK (183 and 184, respectively) and a bundle of 185 pipes for NMK. The cold part is formed from the side of the casing of the cryogenic heat exchanger 180.

The lower and upper beams 181 and 182 of the pipe for the hydrocarbon product fluidly connect the line 110 of the hydrocarbon stream to the drain line 1. At least one heat exchanger 115 precools the cooled hydrocarbon 180 above the stream 110 from the cryogenic heat exchanger 180 .

The refrigerant supplied in refrigerant circuit 101 will be referred to as “primary refrigerant” to distinguish it from other refrigerants that can be used in the liquefaction system 100, such as pre-cooling refrigerant 127, which can provide a cold load on the pre-cooled heat exchanger 115. The primary refrigerant in the present embodiment is a mixed refrigerant.

Refrigerant circuit 101 includes a spent refrigerant line 150 connecting the cryogenic heat exchanger 180 (in this case, the side 186 of the cryogenic heat exchanger casing 180) with the main suction side of the refrigerant compressor 160, and the compressed refrigerant line 120 connecting the refrigerant compressor 160 with the separator MC 128 One or more heat exchangers are provided in line 120 of the compressed refrigerant, including in this example at least one return heat exchanger 124. The MK separator 128 is reported in flow medium with a lower bundle of 183 LMK pipes through the 121 line of the light fraction of the refrigerant and with a bundle of NMK pipes through the 122 line of the heavy fraction of the refrigerant.

At least one pre-cooling heat exchanger 115 of the cooled hydrocarbon and at least one cooled pre-cooling pre-cooling heat exchanger 125 are cooled by the pre-cooling refrigerant (via lines 127 and 126, respectively). The same pre-cooling refrigerant can be distributed from the same pre-cooling refrigerant cycle. In addition, at least one heat exchanger 115 for pre-cooling the cooled hydrocarbon and at least one cooled heat exchanger 125 for pre-cooling the main refrigerant can be combined into one block of pre-cooling heat exchangers (not shown). As a non-limiting example, reference is made to US Patent 6,370,910.

In the transition zone between the upper (182, 184) and lower (181, 183) tube bundles of the NMC, the tube bundle 185 is in fluid communication with the NMK line 141. NMC line 141 is in fluid communication with the side 186 of the cryogenic heat exchanger casing 180 through the first NMC return line 143, in which the NMC places a check valve 144. Through the mentioned side 186 of the casing and under the heat exchange scheme with each of the lower bundle 181 of hydrocarbon product pipes and the lower LMK bundle of 183 tubes, as well as the CMB bundle of tubes 185, the first NCM return line 143 is connected by flow medium with line 1 50 exhaust refrigerant.

Above the upper beams 182 and 184 of pipes, near the upper part of the cryogenic heat exchanger 180, LMK, a beam of 184 pipes is in fluid communication with the line 131 of the refrigerant to be cooled. The main return refrigerant line 133 establishes a fluid message between the refrigerant line 131 and the cryogenic heat exchanger casing side 186 180. The main refrigerant control valve 134 is located on the main return refrigerant line 133. The main return refrigerant line 133 is in fluid communication with the exhaust refrigerant line 150 through the casing side 186 and the heat exchange circuit with each of the upper and lower hydrocarbon product tube bundles 182 and 181, respectively, as well as each of the LMC bundles 183 and tube 184 and NMK a bunch of 185 pipes.

The harness around the flash evaporator 50 and the gas-liquid separator 33 shown in FIG. 5 corresponds to the harness shown in FIG. 3. The harness around the flash evaporator 50 and the gas-liquid separator 33 shown in FIG. 6 corresponds to the harness shown in FIG. 4. In both cases, the auxiliary refrigerant line, with its upstream end, is fluidly connected to the liquid hydrocarbon product line 90, and the downstream end to the condenser 35 end. An optional auxiliary refrigerant pump 96 is located on the auxiliary refrigerant supply line 132. The auxiliary return refrigerant line 138, with its upper end upstream, is in fluid communication with the auxiliary refrigerant supply line 132 through the condenser 35. In the embodiments shown in FIG. 5 and 6, line 138 of the auxiliary return refrigerant, with its lower end of the flow, is ultimately connected to the flash separator 50.

The use of a blowout from a liquid hydrocarbon product stream has the advantage that the amount of additional equipment to be installed is minimal. For example, no additional auxiliary refrigerant compressor and auxiliary refrigerant condenser will be required, which would be the case if a separate independent auxiliary refrigerant cycle were proposed.

The refrigerant in the liquefier 100 is recycled in the refrigerant circuit 101, whereby the spent refrigerant 150 is compressed in the refrigerant compressor 160 to produce

- 11 029627

compressed refrigerant 120 from spent refrigerant 150. Heat is removed from the compressed refrigerant withdrawn from the refrigerant compressor 160 using one or more heat exchangers that are provided in the compressed refrigerant line 120, including at least one return heat exchanger 124. As a result, this results in partially condensed compressed refrigerant, which is subjected to phase separation in the MK separator 128 into a light fraction 121 of the refrigerant, consisting of vapor components of the partially condensed compressed x adagenta and heavy refrigerant fraction 122, consisting of the liquid components of the partially condensed compressed refrigerant.

The refrigerant light fraction 121 is passed successively through the lower LMK beam 183 and the upper LMK beam 184 through a cryogenic heat exchanger 180, while the heavy refrigerant fraction 122 is passed through the LMC beam 185 through a cryogenic heat exchanger 180 into the transition zone. When passing through the indicated tube bundles, the respective refrigerant fractions, light and heavy, are cooled by the light and heavy refrigerant fractions, which evaporate from the casing side 186, again producing the spent refrigerant 150, which completes the cycle. At the same time, hydrocarbon stream 110 passes through a cryogenic heat exchanger 180 successively through the lower beam 181 for hydrocarbons and the upper beam 182 for hydrocarbons and liquefies, evaporating the heavy fraction of the refrigerant, and is supercooled due to evaporation of the light fraction of the refrigerant.

Preferably, evaporator 285 is placed in line 70 of compressed steam between instantaneous evaporation compressor 260 and upstream from gas-liquid separator 33 so that heating fluid 286 can be supplied as compressed vapor stream 70. Examples of such embodiments of the invention in which the condensed fraction 40 undergoes indirect heat exchange with at least a portion of the compressed vapor stream 70, which leads to complete evaporation of the condensed fraction 40, are shown in FIG. 3 and 4. As a result, the cold load required from the auxiliary refrigerant 132 in the condenser 35 to generate the same degree of condensation becomes smaller.

FIG. 3 and 4, it is also illustrated that flash evaporator 260 and optional fuel gas compressor 360 can share one compressor drive 290. These compressors can be made in the form of two separate compressor housings on a common drive shaft, or in reality they can be two compressor steps within one housing.

FIG. 4 shows a special group of embodiments of the invention in which a flow divider 75 is provided in the compressed steam flow line 70, whereby the compressed steam flow line 70 is divided into the first branch 71 and the second branch 72. The first branch 71 is configured to supply the first portion of the compressed flow the steam in the gas-liquid separator 33, and the second branch 72 are configured to supply the second part of the compressed steam flow to the same gas-liquid separator 33. The flow divider 70 only divides the incoming stream 70 of the compressed steam into two parts of the composition and in the same phase. The flow divider 70 may be a pipe connection in the form of a simple T-shaped connection, preferably in conjunction with a flow dividing control valve 76 in one of the branches, first or second.

The condenser 35 is placed in the first branch 71. Preferably, the optional heat exchanger 85 for cold recovery is also located in the first branch 71, so that the first part of the compressed steam flow is used as the cold recovery medium 86 indicated in the general form in FIG. 1. A device 285 for re-evaporation can be placed in the second branch 72 in such a way as to use the second part of the compressed steam flow as the heating fluid 286, shown generally in FIG. one.

In the embodiment of the invention illustrated in FIG. 4, compressed steam stream 70 is split into a first portion of a compressed vapor stream and a second portion of a compressed vapor stream. The first part of the compressed steam flow is withdrawn from the flow divider 75 and fed to the gas-liquid separator 33 through the first branch 71, while the second part of the compressed steam flow is withdrawn from the flow divider 75 and fed to the gas-liquid separator 33 via the second branch 72. Both parts, the first part of the flow The compressed steam and the second part of the compressed steam flow have the same composition and are in the same phase as the compressed steam 70. A portion of the compressed steam flow 70, from which heat is passed into the auxiliary refrigerant flow 132, is formed from the first part of the compressed steam flow. However, before passing heat from the first part of the compressed vapor stream to the auxiliary refrigerant stream 132, the first part of the compressed steam stream is subjected to indirect heat exchange with the vapor fraction 80 leaving the gas-liquid separator 33 in the heat exchanger 85 for cold recovery. Further along the course of the flow, after the said heat exchange has been accomplished, the vapor fraction 80 is warmer than in the zone between the gas-liquid separator 33 and the heat exchanger 85 for cold recovery. It can then be burned in a combustion device 220, as previously explained herein.

Referring again to FIG. 4, it can be seen that a portion of the compressed vapor stream, which undergoes indirect heat exchange with the condensed fraction 40 in the re-evaporation unit 285, is formed from the second portion of the compressed vapor stream. Thus, the partially condensed pro 12 029627

interstitial flow, which is sent to the gas-liquid separator 33, is formed by combining the first and second parts of the compressed stream.

The splitting of the flow of compressed steam is preferably carried out with a regulated ratio of dividing the flow. The ratio of the flow division corresponds to the ratio of the mass flow rates in the second branch 71 and the line 70 of compressed steam. The flow division ratio can be adjusted in accordance with the signal of the temperature of the vapor fraction 80 coming from the gas-liquid separator 33 discharged from the heat exchanger 85 to recover the cold before burning. This temperature is preferably maintained at a predetermined design value by adjusting the flow division ratio, and thus it will be possible to achieve a certain degree of cold recovery from the vapor fraction 80 regardless of changes in the flow rate of the vapor fraction 80. The flow rate of the first part of the compressed vapor flow, which functions cold recovery fluid is effectively matched to the available flow rate of the vapor fraction 80. For this purpose, in line 80 of the vapor fraction m A second temperature sensor 77 can be provided between the heat recovery exchanger 85 for cold recovery and the combustion device 220, which is electronically connected to the flow control valve 76 so that the position of the flow control valve 76 is adjusted using the temperature signal generated in the second temperature sensor 77 . The adjustable value of the second target temperature for the specified control circuit can be set a few degrees lower, for example, 2 ° C below the temperature of the fluid 86 for cold recovery at the inlet of the heat exchanger 85 for cold recovery. If the temperature of the vapor fraction 80 at the outlet of the heat exchanger 85 for cold recovery is still below the second target temperature, the flow dividing ratio can be adjusted upwards (for example, by decreasing the degree of opening for the flow in the flow dividing control valve 76). Additional control strategies known to the person skilled in the art can be implemented to avoid a temperature jump in the heat exchanger 85 to recover the cold while controlling for the outlet temperature.

Preferably, the temperature of the vapor fraction 80 at the outlet of the heat exchanger 85 for cold recovery is in the range from external temperature to a value at most 10 ° C below the external temperature in order to achieve the greatest degree of cold recovery from the vapor fraction 80.

Calculations of the material and heat balance were made using the Pro2 simulation program to demonstrate the feasibility of the implementation of the proposed methods and devices. In tab. 1-4 show the results for the embodiments based on FIG. 7. In the embodiment corresponding to FIG. 7, the expanded flash evaporation separator system described previously in US Pat. No. 6,014,869, the contents of which are incorporated herein by reference, is embodied. The instantaneous evaporation separator 50 in this case comprises a gas-liquid contact device (for example, in the form of a nozzle or a set of contact plates), a lower inlet device 52 connected to a boiler 55, and an upper inlet device 53. The flow 66 for cold recovery consists of a side stream natural gas of the same composition as the initial liquefied gas stream 1. It should be noted that for clarity, most of the auxiliary refrigerant supply line 132 and the auxiliary return refrigerant line 138 are not drawn. Only the end portions near the condenser 35 and the flash evaporator 50 are shown, and it should be understood that the end portions of the auxiliary refrigerant supply line 132 are interconnected, as well as the end portions of the auxiliary refrigerant supply line 138.

It is believed that the cryogenic hydrocarbon composition 8 consists of a stream 66 for recovering the cold and an initial liquefied stream 1 coming from the pressure reducing system 5. The remainder of FIG. 7 corresponds to FIG. four.

To perform the calculations, it is additionally assumed that the return steam 64 located between the heat exchanger 65 for cold recovery and the instant evaporation compressor 260 comprises the vapor from the instant evaporation separator 50 together with the stripping gas stream from the cryogenic storage tank 210. Additionally, it is assumed that the control valve 77 of the steam bypass channel, the control valve 88 of the steam recirculation, the valve 14 of the recirculation and the external control valve 73 of the steam flow are closed and are in an empty state.

Tab. 1 and 2 correspond to the same version of the calculation, within which the second separation pressure falls in the range from 4 to 8 bar abs. This is called a low pressure mode. Tab. 3 and 4 correspond to another version of the calculation, which refers to the high pressure mode.

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Table 1

Low pressure mode

No stream one 1a 1b eight 60 66 90 138 Pressure (bar abs.) 74.8 74.2 9.88 1.05 1.05 9.88 1.12 1.50 Temperature (° C) -155 -163 -164 -167 -167 -157 -163 -134 Flow rate (kg / s) 211 211 211 218 19.4 6.65 198 0.30 Nitrogen (mol%) 3.93 3.93 3.93 3.93 41.4 3.93 1.09 1.09 Methane (mol%) 95.7 95.7 95.7 95.7 58,6 95.7 98.5 98.5 C ₂ + (mol.%) 0.39 0.39 0.39 0.39 0.00 0.39 0.42 0.42

table 2

Low pressure mode

No stream eight 40 64 70 71 71a 71b 72 80 90 132 138 230 240 Pressure (bar abs.) 1.05 6.50 0.85 7.50 7.50 7.00 6.50 7.00 6.50 1.12 2.00 1.50 1.00 3.00 Temperature (° C) - 167 -162 -27 +31 +31 -131 -142 -169 -162 -163 -163 -134 -159 -172 Flow rate (kg / s) 218 19.6 23.7 23.7 3.48 3.48 3.48 20.3 4.12 198 0.30 0.30 3.20 19.6 Nitrogen (mol%) 3.93 29.0 36.8 36.8 36.8 36.8 36.8 36.8 86.4 1.09 1.09 1.09 17.3 29.0 Methane (mol%) 95.7 71.0 63.2 63.2 63.2 63.2 63.2 63.2 13.6 98.5 98.5 98.5 82.7 71.0 C ₂₊ (mol.%) 0.39 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.42 0.42 0.42 0.00 0.00

Table 3

High pressure mode

No stream one 1a sixteen eight 60 66 90 138 Pressure (bar abs.) 74.8 74.2 9.88 1.05 1.05 9.73 1.12 1.50 Temperature (° C) -155 -163 -164 -167 -167 -157 -163 -128 Flow rate (kg / s) 210 210 210 217 19.4 6.58 198 0.49 Nitrogen (mol%) 3.93 3.93 3.93 3.93 41.6 3.93 1.11 1.11 Methane (mol%) 95.7 95.7 95.7 95.7 58.4 95.7 98.5 98.5 C ₂ + (mol.%) 0.39 0.39 0.39 0.39 0.00 0.39 0.42 0.42

Table 4

High pressure mode

No stream eight 40 64 70 71 71a 71b 72 80 90 132 138 230 240 Pressure (bar abs.) 1.05 16.5 0.85 17.5 17.5 17.0 16.5 17.0 16.5 1.12 2.00 1.50 1.00 9.50 Temperature (° C) - 167 -135 -27 +31 +31 -125 -127 -140 -135 -163 -163 -128 -160 -144 Flow rate (kg / s) 217 12.5 23.5 23.5 8.18 8.18 8.18 15.3 10.9 198 0.49 0.49 4.32 12.5 Nitrogen (mol%) 3.93 19.3 36.9 36.9 36.9 36.9 36.9 36.9 62.9 1.09 1, P 1, P 18.9 19.3 Methane (mol%) 95.7 80.7 63.1 63.1 63.1 63.1 63.1 63.1 37.1 98.5 98.5 98.5 81.1 80.7 C ₂₊ (mol.%) 0.39 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.42 0.42 0.42 0.00 0.00

In another version of the calculation, the second separation pressure falls in the range from 10 to 20 bar abs. This affects the pressure drop achievable on the pressure reduction valve 245, which in turn affects the cold load that is achievable in the re-evaporation device 285. And, of course, on the expenditure of additional energy of compression. It can be seen that the temperature at which the phase separation is performed in the gas-liquid separator 33 can be higher in the indicated pressure range. Despite this, a larger volume of liquid hydrocarbon stream should be used as an auxiliary refrigerant stream.

The low pressure mode option calculated in this example provides low quality fuel gas, which is removed from heat exchanger 85 to recover the cold at a pressure of 5.00 bar abs. and a temperature of 22 ° C; and re-evaporated condensed fraction, which is 14 029627

Toru take away from the device 285 for re-evaporation at a pressure of 3.00 bar abs. and a temperature of 25 ° C. The latter can be used as high-quality fuel gas.

The high pressure mode option calculated in this example provides low quality fuel gas, which is removed from heat exchanger 85 to recover the cold at a pressure of 5.00 bar abs. and a temperature of 28 ° C; and the re-evaporated condensed fraction, which is withdrawn from the device 285 for re-evaporation at a pressure of 9.00 bar abs. and a temperature of 19 ° C. The latter can be used as high-quality fuel gas.

In both low pressure and high pressure regimes, the final composition of the inventory of liquefied hydrocarbons collected in the cryogenic storage tank 210 is as follows: 0.83 mol% nitrogen; 98.74 mol.% Methane and 0.43 mol.% C ₂ +, while C ₂ + indicates all hydrocarbons having a mass corresponding to the mass of ethane and above. A stream of liquefied hydrocarbons passed through the main product line 91 to the cryogenic storage tank 210 contains slightly more nitrogen than the stock of liquefied hydrocarbons collected in the cryogenic storage tank 210.

In any of the examples above, the preferred liquefaction pressure range, in which the initial liquefied stream is withdrawn to the discharge line 1 from the liquefier 100, is from 15 to 120 bar abs., More preferably from 15 to 90 bar abs. or from 45 to 120 bar abs. Most preferably, the range for the liquefaction pressure is from 45 to 90 bar abs. In case the initial liquefied stream consists of at least 80 mol.% Of methane and nitrogen, the preferred temperature range for the initial liquefied stream in discharge line 1 can be from -165 to -120 ° C.

In any of the examples above, it is assumed that the vapor fraction 80 contains in the range from 30 to 90 mol.% Nitrogen, preferably in the range from 30 to 80 mol.% Nitrogen or in the range from 45 to 90 mol.% Nitrogen, preferably in the range from 45 to 80 mol.% nitrogen, most preferably from 50 to 80 mol.% nitrogen. To achieve a nitrogen content in the range from 50 to 80 mol.%, Such as, for example, about 60 mol.%, A sufficient amount of methane must be re-condensed from the stream 70 of compressed steam. This can be done, for example, using the pressure of the stream 70 of compressed steam in the range from 4 to 8 bar abs. and by reaching a temperature of partially condensed intermediate stream in the range from -150 to -135 ° C. The temperature range may have higher boundary points if the pressure is above 8 bar abs.

In addition, the condensed fraction 40, as a rule, contains up to 30 mol.% Of nitrogen and at least 5 mol.%, Preferably at least 10 mol.%. Striving for lower values will be associated with a greater cold auxiliary load, whereas this is not necessary for typical gas turbines and, specifically, for gas turbines based on an aircraft engine.

Compressors that form part of the hydrocarbon liquefaction process in the liquefaction system 100, specifically, any refrigerant compressor, including refrigerant compressor 160, can be powered by a suitable drive 190 of any type of compressor, including any type selected from the group consisting of a gas turbine, a steam turbine turbines and electric motor, as well as their mutual combinations. In general, this also applies to the compressor refrigerant drive 190.

The gas turbine can be selected from the group of so-called industrial gas turbines or from the group of so-called gas turbines based on an aircraft engine. The group of gas turbines on the basis of an aircraft engine includes: Κοίΐδ Kousee TGSSH 60, KV211, or 6761, as well as Seiyet1 E1es1ps LM8100TM, LM6000, LM5000 and LM2500, as well as any variants of them (for example, LM2500 +).

Accordingly, the gas turbine 320, in which the condensed fraction 40 is ultimately burned, is driven by the refrigerant compressor 190, which is in mobile engagement with the refrigerant compressor 160. Gas turbine 320 may drive refrigerant compressor 160.

Typically, the second pressure of the fuel gas is chosen in the range from 15 to 75 bar abs., More preferably in the range from 45 to 75 bar abs. A typical predetermined fuel gas pressure for the most traditional types of industrial gas turbines is from about 15 to about 25 bar abs., On average. However, the latest generation of industrial gas turbines requires a relatively high fuel gas pressure, such as, for example, in the range of 35 to 45 bar abs. To meet fuel gas pressure requirements of typical gas turbines based on an aircraft engine, a range of 45 to 75 bar abs is recommended.

The nitrogen content in the liquid stream 90, as a rule, does not exceed the desired maximum of about 1.1 mol.%. In some embodiments of the invention, the amount of nitrogen in the stream 90 of liquid hydrocarbons is from 0.5 to 1 mol.%, Preferably as close as possible to 1.0 mol.%, If possible without exceeding the said maximum of about 1.1. mol.%.

This is a well-known phenomenon that the stripping gas is produced as a result of thermal evaporation due to the heat applied to the liquefied product, for example, as heat loss in storage tanks, when pumping LNG, as well as heat coming from the pumps of the LNG plant. In any of the examples and embodiments of the invention illustrated herein, the stripping gas may optionally be injected into return line 64.

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either upstream or downstream from flashline compressor 260 to affect phase separation in gas-liquid separator 33. This, respectively, may include collecting boil-off gas coming from a cryogenic storage tank 210, possibly from a boil-off supply line 230 gas, as illustrated, for example, in FIG. 5. Steam gas is produced by applying heat to at least some of the liquefied hydrocarbons, whereby a part of the methane-containing liquid phase present in the liquefied hydrocarbons evaporates to form the said stripping gas.

The person skilled in the art will appreciate that the present invention can be implemented in many different ways within the scope of the appended claims.

Claims (18)

CLAIM 1. A method of producing a stream of liquefied hydrocarbons, including operations in which provide a hydrocarbon composition, cooled to cryogenic temperatures and containing in its composition the nitrogen and methane-containing liquid phase, with an initial pressure of from 1 to 2 bar abs .; phase separation of the cryogenic hydrocarbon composition is carried out in an instantaneous evaporation separator at a first separation pressure of 1 to 2 bar abs. return steam flow and liquid flow; divert the liquid stream from the separator instantaneous evaporation in the form of a liquefied stream of hydrocarbons; compressing the return steam flow in the instantaneous evaporation compressor to a pressure above 2 bar abs., thus obtaining a flow of compressed steam; Partially condensed intermediate stream is formed from compressed steam as a result of partial condensation of a compressed vapor stream, said partial condensed intermediate stream containing a condensed fraction and a vapor fraction, and this partial condensation involves performing indirect heat exchange of the compressed vapor stream with the auxiliary refrigerant stream formed by part of the liquefied stream hydrocarbons by passing heat from at least part of the compressed vapor stream auxiliary refrigerant stream; separating the condensed fraction from the vapor fraction in a gas-liquid separator at a second separation pressure; the vapor fraction is removed from the gas-liquid separator, while the said vapor fraction has the first calorific value; burning the vapor fraction in a combustion device other than a gas turbine; remove the condensed fraction from the gas-liquid separator; re-evaporating the condensed fraction, whereby the condensed fraction is converted into a fully evaporated stream having a second calorific value that is higher than the first calorific value; the fully vaporized gas stream is burned in the gas turbine. 2. The method according to claim 1, further comprising passing the auxiliary refrigerant stream containing said heat from at least a part of the compressed steam flow towards and into the flash evaporator. 3. A method according to any one of the preceding claims, wherein said re-evaporation of the condensed fraction involves passing the condensed fraction through a pressure reduction valve and then performing indirect heat exchange of the condensed fraction with at least a portion of the compressed vapor stream, resulting in complete evaporation of the condensed steam fractions. 4. The method according to claim 3, further comprising operations in which the compressed steam flow is divided into the first part of the compressed steam flow and the second part of the compressed steam flow, wherein both the first part of the compressed steam flow and the second part of the compressed steam flow have same composition and phase as compressed steam; wherein a portion of the compressed vapor stream, from which heat is passed into the auxiliary refrigerant stream, is formed from said first portion of the compressed vapor stream, and wherein said portion of the compressed vapor stream, which is subjected to indirect heat exchange with the condensed fraction, is formed from the second portion of the compressed vapor stream. 5. The method according to claim 4, in which the said formation of a partially condensed intermediate stream from compressed steam further includes carrying out an indirect heat exchange of the first part of the compressed steam stream with the vapor fraction coming from the gas-liquid separator, to the said combustion of the vapor fraction in said combustion device. 6. The method according to claim 5, in which the said separation of the flow of compressed steam is carried out at a controlled flow separation ratio, wherein the method further includes controlling the flow separation ratio in accordance with the indicator of the temperature signal of the vapor fraction coming from the gas-liquid separator at implementation mentioned 7. A method according to any one of the preceding claims, wherein after re-evaporation of the condensed fraction and prior to burning the fully evaporated stream, the fully evaporated stream is compressed in the fuel gas compressor to a second fuel gas pressure that is higher than the second separation pressure and ranges from 15 to 75 bar abs. preferably to a second fuel gas pressure of between 45 and 75 bar abs. 8. A method according to any one of the preceding claims, wherein the vapor fraction is burned in said combustion device at a first fuel gas pressure not higher than the second separation pressure, preferably the vapor fraction is burned in said combustion device at a pressure of from 2 to 15 bar abs 9. A method according to any one of the preceding claims, wherein the second separation pressure is from 2 to 22 bar abs., Preferably from 5 to 22 bar abs., More preferably from 5 to 15 bar abs. 10. The method according to any of the preceding paragraphs, in which the liquid stream and the liquefied hydrocarbon stream contain less than 1.1 mol.% Nitrogen. 11. A process according to any of the preceding claims, in which more than 30 mol.% Of the partially condensed intermediate stream consists of nitrogen and less than 30 mol.% Of the condensed fraction discharged from the gas-liquid separator consists of nitrogen. 12. The method according to any one of the preceding claims, wherein the vapor fraction and the condensed fraction coexist in the same thermodynamic equilibrium between said vapor fraction and the condensed fraction and are subjected to separation in the same thermodynamic equilibrium state between said vapor fraction and the condensed fraction. 13. An apparatus for producing a liquefied hydrocarbon stream according to claim 1, comprising a cryogenic feed line connected to a source of hydrocarbon composition cooled to cryogenic temperatures and comprising a nitrogen and methane-containing liquid phase; an instant evaporation separator adapted to receive the hydrocarbon composition cooled to cryogenic temperatures and separate the hydrocarbon composition cooled to cryogenic temperatures into a liquid stream and a return vapor stream; a liquid hydrocarbon product line connected in fluid to the bottom of the flash separator for diverting said liquid stream in the form of a liquefied stream of hydrocarbons from the flash evaporator; a return steam line, fluidly connected to the top of the flash separator, for diverting said return steam flow from the flash evaporator; an instantaneous evaporation compressor placed in the return steam line to compress the return steam flow and result in this flow of compressed steam; a condenser placed in the return steam line further along the stream after the instantaneous evaporation compressor, configured to receive a stream of compressed steam and form a partially condensed intermediate stream from a stream of compressed steam, the said partially condensed intermediate stream containing a condensed fraction and a steam fraction configured to make contact at least between a portion of the flow of compressed steam and the flow of auxiliary refrigerant for wasps indirect heat exchange; an auxiliary refrigerant supply line, passing between the liquid hydrocarbon product line and the condenser, for a portion of the liquid hydrocarbon product stream to enter the condenser; gas-liquid separator, located further along the stream after the condenser and configured to receive the condensed fraction and vapor fraction; a vapor fraction withdrawal line connected in fluid with the upper part of the gas-liquid separator, made with the possibility of receiving the vapor fraction from the gas-liquid separator; a device for combustion, other than a gas turbine, connected in fluid with a gas-liquid separator via a vapor fraction removal line, designed to receive and burn the exhaust vapor fraction; a condensed fraction withdrawal line connected in fluid with the lower part of the gas-liquid separator, made with the possibility of receiving the condensed fraction from the gas-liquid separator; a gas turbine connected in fluid with a gas-liquid separator via a condensed fraction withdrawal line, designed to receive and incinerate the condensed fraction withdrawn; a device for re-evaporation, placed on the line of removal of the condensed fraction between the gas-liquid separator and the gas turbine and configured to convert the condensed fraction into a fully evaporated stream before burning in the gas turbine. 14. The device according to item 13, further comprising an auxiliary return line 15. Device according to any one of paragraphs.13, 14, in which the gas-liquid separator consists of a drum without internal elements forming the gas-liquid contact section. 16. Device according to any one of p-15, in which the line of return steam downstream from the compressor instantaneous evaporation is a stream line of compressed steam, with the above-mentioned device additionally includes a pressure reducing valve placed in the line of withdrawal of the condensed fraction between the gas-liquid separator and the device for re-evaporation; a flow divider placed in the line of compressed steam to divide the line of compressed steam into the first branch and the second branch, the first branch being located between the flow divider and the gas-liquid separator and the second branch located between the flow divider and the gas-liquid separator, while the condenser is placed in the first branch, and a device for re-evaporation is located in the second branch. - 16 029627 indirect heat exchange with the first part of the compressed steam flow, as a result of which the said steam fraction temperature is maintained at a given calculated value. 17. The device according to clause 16, further comprising a heat exchanger for recovery of cold, placed in the exhaust line of the vapor fraction above along the flow from the combustion chamber, while the heat exchanger for recovery of cold is placed in the first branch, in addition to the condenser. - 17 029627 the refrigerant passing between the condenser and the separator instantaneous evaporation and made with the possibility of returning auxiliary refrigerant containing heat obtained from the flow of compressed steam to the separator instantaneous evaporation. - 18 029627