RU2668303C1 - System and method for liquefying of natural gas (options) - Google Patents

Abstract

FIELD: oil, gas and coke-chemical industries.

SUBSTANCE: invention relates to the field of liquefying natural gas. Natural gas liquefaction system (1) includes first expander (3) that produces energy by using natural gas under pressure as a gaseous material, first cooling unit (11, 12), distillation unit (15), first compressor (4) for compressing the gaseous material from which the heavy components are partially or completely removed by the distillation unit, by using the energy produced in the first expander, and liquefying unit (21).

EFFECT: as a result of using the energy produced by the expander by expanding the gaseous material, the pressure on the compressor outlet increases, and the required cooling capacity of the refrigerator decreases.

31 cl, 3 tbl, 10 dwg

Description

FIELD OF THE INVENTION

The invention provides a system and method for liquefying natural gas in order to produce liquefied natural gas by cooling natural gas.

State of the art

Natural gas produced in gas fields is liquefied in a liquefaction plant so that the gas can be stored and transported in liquid form. Cooled to approximately -162 degrees Celsius, liquid natural gas has a significantly reduced volume compared to gaseous natural gas, and high pressure is not required for its storage. At the same time, in the process of liquefying natural gas, impurities such as water, acid gases and mercury, which are contained in the produced natural gas, are removed and after heavy components having relatively higher freezing points (C5 + hydrocarbons, such as benzene, pentane and other heavy hydrocarbons, natural gas liquefies.

A variety of technologies have been developed to liquefy natural gas, including technologies based on expansion processes that use expansion valves and turbines, and heat transfer processes that use low-boiling refrigerants (such as light hydrocarbons, including methane, ethane and propane). For example, a particular known system for liquefying natural gas (see Patent Document 1) includes a cooling unit for cooling natural gas from which impurities are removed, an expansion unit for isentropic expansion of the cooled natural gas, a distillation unit for distilling natural gas, the pressure of which decreases in the expansion unit to a lower level than the critical pressures of methane and heavier components, a compressor for compressing distilled gas from a distillation unit through using the output shaft from the expander and a liquefaction unit for liquefying the distilled gas compressed by the compressor through heat exchange with mixed refrigerant.

Background Documents

Patent documents

Patent Document 1: US Patent No. 4065278.

SUMMARY OF THE INVENTION

The problem solved by the invention

In a traditional system for liquefying natural gas, such as the system described in Patent Document 1, the desired pressure at the outlet of the compressor (or the pressure of the source gas that is introduced into the liquefaction unit) should be as high as possible so that the load on the liquefaction unit is reduced (in particular, its main heat exchanger), and the efficiency of the liquefaction process reached its maximum.

In order to increase the pressure at the compressor outlet, a correspondingly large energy is required. However, in the traditional design, where the source gas cooled by the cooling unit is expanded by means of an expander, the energy produced by the expander is limited and insufficient to increase the pressure at the compressor outlet to the desired level.

In a traditional design, since the feed gas must be cooled before it expands in the expander, a relatively large capacity of the cooling unit is required, and this increases the capital costs and operating costs of the cooling unit.

In the traditional design, since the cooling of the source gas results in the formation of condensation products, it is necessary to install a separator for separating the gas and liquid phases in order to separate (remove) the condensation products from the source gas before the source gas is introduced from the cooling unit into the expander. In addition, since the temperature of the feed gas at the outlet end of the compressor is high, a significant temperature difference occurs between the intermediate inlet point of the liquefaction unit and the refrigerant, so that a corresponding high power is required for the cooling unit.

Given such problems of the prior art, the main objective of the present invention is to provide a system and method for liquefying natural gas, by which the pressure at the outlet end of the compressor can be increased by using the energy produced in the expander by expanding the source gas, and Minimize the cooling capacity required by the cooling unit.

Means of solving the problem

According to a first aspect of the present invention, there is provided a system (1) for liquefying natural gas, which cools natural gas for producing liquefied natural gas, comprising: a first expander (3) for generating energy by expanding natural gas under pressure as a gaseous material; a first cooling unit (11, 12) for cooling a gaseous material having a reduced pressure by expansion in a first expander; a distillation unit (15) for reducing the content or removal of the heavy component contained in the gaseous material by distilling the gaseous material cooled by the first cooling unit; a first compressor (4) for compressing the gaseous material from which the heavy components are partially or completely removed by means of a distillation unit, by using the energy produced in the first expander; a second heat exchanger for exchanging heat between the gaseous material that is introduced into the first compressor and the gaseous material compressed by the first compressor, and a liquefying unit (21) for liquefying the gaseous material compressed by the first compressor by heat exchange with a refrigerant.

According to a first aspect of the present invention, a system for liquefying natural gas provides an increase in the pressure at the outlet of the first compressor and a decrease in the cooling capacity required for the first cooling unit by utilizing the energy produced by the first expander by expanding the gaseous material before it is cooled by the first cooling block.

According to a second aspect of the present invention, there is provided a system for liquefying natural gas, further comprising a heat exchanger (69) for heat exchange between the gaseous material that is introduced into the distillation unit and the upper fraction from the distillation unit.

According to a second aspect of the present invention, even when the temperature of the gaseous material that is introduced into the liquefaction unit is less than the lower limit of the corresponding interval, the temperature of the gaseous material can be set near the temperature at the inlet end of the liquefaction unit by heating the upper fraction from the distillation unit during heat exchange with the gaseous material that is introduced into the distillation unit.

According to a third aspect of the present invention, there is provided a system for liquefying natural gas, further comprising a second heat exchanger (79) for exchanging heat between the gaseous material that is introduced by the first compressor and the gaseous material compressed by the first compressor.

According to a third aspect of the present invention, even when the temperature of the gaseous material that is compressed by the first compressor and introduced into the liquefaction unit exceeds the upper limit of the corresponding interval, the temperature of the gaseous material can be set near the temperature at the inlet end of the liquefaction unit by cooling the gaseous material from the first compressor during heat exchange with gaseous material that is introduced into the first compressor.

In the claims, a method for cooling a supplied natural gas is provided, comprising the steps of:

a) reduce the pressure of the supplied natural gas to produce a gaseous material having a reduced pressure;

b) removing heavy components from the gaseous material having a reduced pressure to produce an upper fraction and a lower fraction;

c) cooling the upper fraction to produce a cooled upper fraction;

d) separating the cooled upper fraction into a gas phase component and a liquid phase component;

e) increase the pressure of the gas-phase component to produce compressed gaseous material; and

f) conduct heat exchange between the gas phase component and the compressed gaseous material to produce at least a cooled compressed gaseous material.

Preferably, the method further comprises cooling the gaseous material having a reduced pressure from step a) before removing the heavy components in step b).

Preferably, the method further comprises at least partially liquefying the cooled compressed gaseous material from step f).

Preferably, the method further comprises cooling the compressed gaseous material from step e) before step f).

Preferably, the upper fraction is cooled in step c) by introducing the upper fraction into the warm region of the coil-type heat exchanger.

Preferably, the cooled compressed gaseous material of step f) is further cooled by introducing the cooled compressed gaseous material into the intermediate region of a coil-type heat exchanger.

Preferably, the removal of heavy components in step b) is carried out in a distillation unit.

Preferably, the method further comprises recirculating the liquid phase component from step d) to the distillation unit.

Preferably, the method further comprises the step of conducting heat exchange between the upper fraction from step b) and the gaseous material having a reduced pressure before carrying out step c).

Preferably, step f) comprises a heat exchange step between the gas phase component from step d), the compressed gaseous material from step e), and the gaseous material having a reduced pressure from step a).

The formula also claims a method of cooling the supplied natural gas, comprising the steps of:

a) reduce the pressure of the supplied natural gas to produce a gaseous material having a reduced pressure;

b) removing heavy components from the gaseous material having a reduced pressure to produce an upper fraction and a lower fraction;

c) conduct heat exchange between the gaseous material having a reduced pressure, and the upper fraction to produce at least the upper fraction, over which the heat exchange is carried out;

d) cooling the upper fraction, over which the heat exchange is carried out, to produce a cooled upper fraction;

e) separating the cooled upper fraction into a gas phase component and a liquid phase component;

f) increase the pressure of the gas-phase component to produce compressed gaseous material; and

g) cool the compressed gaseous material.

Preferably, the method further comprises cooling the gaseous material having a reduced pressure from step a) before removing the heavy components in step b).

Preferably, the compressed gaseous material is cooled in step g) by introducing the compressed gaseous material into one or more heat exchangers.

Preferably, the removal of heavy components in step b) is carried out in a distillation unit.

Preferably, the method further comprises recirculating the liquid phase component from step e) to the distillation unit.

The formula also claims a method for cooling the supplied natural gas, comprising the steps of:

a) reduce the pressure of the supplied natural gas to produce a gaseous material having a reduced pressure,

b) removing heavy components from a gaseous material having a reduced pressure to produce an upper fraction and a lower fraction,

c) cooling the upper fraction to produce a cooled upper fraction,

d) separating the cooled upper fraction into a gas phase component and a liquid phase component,

e) increase the pressure of the gas phase component to produce compressed gaseous material, and

f) conduct heat exchange between the gaseous material having a reduced pressure from the step preceding step b) and the compressed gaseous material to produce at least a compressed gaseous material over which heat exchange has been performed, the method further comprising cooling the gaseous material having a reduced pressure from the step a) before the heat transfer in step f).

The formula also claims a method for cooling the supplied natural gas, comprising the steps of:

a) reduce the pressure of the supplied natural gas to produce a gaseous material having a reduced pressure,

b) removing heavy components from the gaseous material having a reduced pressure in the distillation unit to produce an upper fraction and a lower fraction,

c) cooling and partially liquefying the upper fraction to produce a cooled upper fraction,

d) separating the cooled top fraction to produce a gas phase component and a liquid phase component,

e) recycle the liquid phase component into the distillation unit,

f) conduct heat exchange between a gaseous material having a reduced pressure and a gas-phase component to produce at least a gaseous component over which heat exchange is carried out, and

g) increasing the pressure of the gas-phase component over which heat exchange is carried out to produce compressed gaseous material, the method further comprising cooling the gaseous material having a reduced pressure in step a) before conducting heat exchange in step f).

The formula also claims a method for cooling the supplied natural gas, comprising the steps of:

a) reduce the pressure of the supplied natural gas to produce a gaseous material having a reduced pressure,

b) removing heavy components from a gaseous material having a reduced pressure to produce an upper fraction and a lower fraction,

c) increase the pressure of the upper fraction to produce compressed gaseous material, and

d) heat exchange is conducted between the upper fraction and the compressed gaseous material to produce at least cooled compressed gaseous material, the method further comprising cooling the gaseous material having a reduced pressure from step a) to step b).

The formula also claims a method for cooling the supplied natural gas, comprising the steps of:

a) reduce the pressure of the supplied natural gas to produce a gaseous material having a reduced pressure,

b) removing heavy components from a gaseous material having a reduced pressure to produce an upper fraction and a lower fraction,

c) increase the pressure of the upper fraction to produce compressed gaseous material, and

d) conduct heat exchange between the upper fraction and the compressed gaseous material to produce at least cooled compressed gaseous material, the method further comprising cooling the compressed gaseous material from step c) before conducting heat transfer in step d).

The formula also claims a system for liquefying the supplied natural gas, comprising:

a first expander to reduce the pressure of the supplied natural gas to produce a gaseous material having a reduced pressure,

a distillation unit for removing heavy components from a gaseous material having a reduced pressure to produce a top fraction and a bottom fraction,

a first heat exchanger for cooling the upper fraction to produce a cooled upper fraction,

the first separating the gas and liquid phases of the tank for separating the cooled upper fraction into a gas phase component and a liquid phase component,

 a first compressor for compressing the gas phase component to produce compressed gaseous material, and

a second heat exchanger for exchanging heat between the gas phase component and the compressed gaseous material.

Preferably, the system further comprises a first cooling unit for cooling a gaseous material having a reduced pressure before being introduced into the distillation unit.

Preferably, the system further comprises a second cooling unit for cooling the compressed gaseous material before being introduced into the second heat exchanger.

Preferably, the first heat exchanger is a warm region of a coil-type heat exchanger.

Preferably, the system further comprises a third heat exchanger for cooling the compressed gaseous material after the compressed gaseous material passes through the second heat exchanger, the third heat exchanger being an intermediate region of the coil type heat exchanger.

Preferably, the system further comprises a conduit for recycling the liquid phase component from the first reservoir separating the gas and liquid phases as a return stream to the distillation unit.

Preferably, the system further comprises a fourth heat exchanger for exchanging heat between the upper fraction from the distillation unit and the gaseous material having a reduced pressure.

Preferably, the second heat exchanger is configured to exchange heat between the gas phase component, the compressed gaseous material, and the gaseous material having a reduced pressure.

Preferably, the first expander is configured to generate energy, and the first compressor is configured to use the energy generated by the first expander.

The formula also claims a system for liquefying the supplied natural gas, comprising:

a first expander to reduce the pressure of the supplied natural gas to produce a gaseous material having a reduced pressure,

a distillation unit for removing heavy components from a gaseous material having a reduced pressure to produce a top fraction and a bottom fraction,

a first heat exchanger for exchanging heat between the upper fraction and a gaseous material having a reduced pressure to form at least an upper fraction over which heat exchange is carried out,

a second heat exchanger for cooling the upper fraction, over which the heat exchange is carried out, for the production of the cooled upper fraction,

the first separating the gas and liquid phases of the tank for separating the cooled upper fraction into a gas phase component and a liquid phase component,

 a first compressor for compressing the gas phase component to produce compressed gaseous material.

Preferably, the system further comprises a first cooling unit for cooling a gaseous material having a reduced pressure before being introduced into the distillation unit.

The formula also claims a system for liquefying the supplied natural gas, comprising:

a first expander to reduce the pressure of the supplied natural gas to produce a gaseous material having a reduced pressure,

a first cooling unit for cooling a gaseous material having a reduced pressure to produce a cooled gaseous material having a reduced pressure,

a distillation unit for removing heavy components from the cooled gaseous material having a reduced pressure to produce an upper fraction and a lower fraction,

a warm region of a coil-type heat exchanger for cooling the upper fraction to produce a cooled upper fraction,

the first separating the gas and liquid phases of the tank for separating the cooled upper fraction into a gas phase component and a liquid phase component,

a piping system for recycling a liquid phase component to a distillation unit,

a first compressor for compressing the gas phase component to produce compressed gaseous material,

a first cooling unit for cooling the compressed gaseous material to produce a cooled compressed gaseous material,

a third heat exchanger for exchanging heat between the cooled compressed gaseous material, and a gas-phase component for the production of additionally cooled compressed gaseous material, and

an intermediate region of a coil-type heat exchanger for at least partially liquefying an additionally cooled compressed gaseous material.

Effect of the invention

As can be understood from the above description, the liquefaction system for liquefying natural gas according to the present invention provides an increase in pressure at the outlet of the compressor by utilizing the energy produced by the expander by expanding the gaseous material, and reducing the cooling capacity required for the cooling unit.

Brief Description of the Drawings

FIG. 1 is a diagram illustrating a liquefaction process in a natural gas liquefaction system shown as a first embodiment of the present invention;

FIG. 2 is a diagram illustrating a liquefaction process in a conventional system for liquefying natural gas, given as a first example for comparison;

FIG. 3 is a diagram illustrating a liquefaction process in a conventional system for liquefying natural gas, given as a second example for comparison;

FIG. 4 is a diagram illustrating a liquefaction process in a natural gas liquefaction system shown as a first modification of a first embodiment;

FIG. 5 is a diagram illustrating a liquefaction process in a natural gas liquefaction system shown as a second modification of the first embodiment;

FIG. 6 is a diagram illustrating a liquefaction process in a natural gas liquefaction system shown as a third modification of the first embodiment;

FIG. 7 is a diagram illustrating a liquefaction process in a natural gas liquefaction system shown as a fourth modification of the first embodiment.

FIG. 8 is a diagram illustrating a liquefaction process in a natural gas liquefaction system shown as a second embodiment of the present invention;

FIG. 9 is a diagram illustrating a liquefaction process in a natural gas liquefaction system shown as a first modification of a second embodiment;

FIG. 10 is a diagram illustrating a liquefaction process in a natural gas liquefaction system shown as a fifth modification of the first embodiment.

Description of Preferred Embodiments

Preferred embodiments of the present invention are described below with reference to the accompanying drawings.

 (First Embodiment)

FIG. 1 is a diagram illustrating a liquefaction process in a natural gas liquefaction system shown as a first embodiment of the present invention. Table 1, which will be given below, presents the simulation results of the liquefaction process in a system for liquefying natural gas. Similar results are presented in tables 2-12. Table 1 presents the temperature, pressure, flow rate, and molar composition of the natural gas that is liquefied at each of the various points of the liquefaction system according to the first embodiment. In Table 1, columns (i) - (ix) represent the values at the corresponding points of the fluidizing system 1, indicated by the corresponding Roman numbers (i) - (ix) in FIG. one.

Natural gas containing from about 80 to 98 mol% of methane is used as a gaseous material or a source gas. The gaseous material also contains at least C5 + hydrocarbons constituting at least 0.1 mol%, or BTX (benzene, toluene, xylene), constituting at least 1 molar part per million and being heavy Components. Components of a gaseous material that are not methane are illustrated in column (i) of Table 1. The term “gaseous material” as used herein means a material that does not have to be present in gaseous form, but may also be in liquid form. after various stages of liquefaction.

In this liquefaction system 1, gaseous material is sent to the dewatering unit 2 through line L1 and is free of moisture to prevent problems caused by ice formation. The gaseous material entering the dewatering unit 2 has a temperature of approximately 20 degrees Celsius, a pressure of approximately 5830 kPa (abs.), And a flow rate of approximately 720000 kg / h. The dewatering unit 2 may consist of columns that are filled with a desiccant (such as a molecular sieve), and it can reduce the moisture content of the gaseous material to less than 0.1 molar parts per million. The dewatering unit 2 may consist of any other known devices that are capable of setting the moisture content of the gaseous material below a desired level.

Although not discussed in detail below, additional known devices may be used in the fluidizing system 1 to carry out the preliminary process steps that precede the process step in the dewatering unit 2, such as a separation unit for separating natural gas condensate, an acid gas separating unit for removing acidic gases, such as carbon dioxide and hydrogen sulfide, and a mercury separating unit for mercury removal. Typically, gaseous material enters the dewatering unit 2, from which impurities are separated by using such devices. The gaseous material that is sent to the dewatering unit 2 is pre-treated so that the carbon dioxide (CO ₂ ) content is less than 50 molar parts per million, the hydrogen sulfide content (H ₂ S) is less than 4 molar parts per million, sulfur content is less than 20 mg / Nm ³ and the mercury content is less than 10 ng / Nm ³ .

The source of gaseous material may not be limited to any particular source, but may be, not exclusively, shale gas, gas from dense sand reservoirs and methane in the compressed state remaining in the roof of coal interlayers. Gaseous material may come not only from a source, such as a gas field, through a pipeline, but also from storage tanks.

Gaseous material from which water is separated in the dewatering unit 2 is sent to the first expander 3 through line L2. The first expander 3 consists of a turbine, which reduces the pressure of the natural gas entering it, and produces power (or energy) in the process of expansion of natural gas in isentropic conditions. When the expansion stages (first expansion stage) in the first expander 3 are carried out, the pressure and temperature of the material are reduced. The first expander 3 has a common shaft 5 with the first compressor 4 (which will be discussed later), so that the energy produced by the first expander 3 can be used as an energy source for the first compressor 4. If the rotation speed of the first expander 3 is less than the rotation speed of the first compressor 4, a suitable speed-increasing gear train can be installed between the first expander 3 and the first compressor 4. The first expander 3 reduces the temperature of the gaseous material to approx izitelno 8.3 degrees Celsius and reduces the pressure to about 4850 kPa (abs.), respectively. Typically, the pressure of the gaseous material that is discharged from the first expander 3 is in the range of 3000 kPa (abs.) To 5500 kPa (abs.) (30 bar (abs.) To 55 bar (abs.)) Or more preferably the range from 3500 kPa (abs.) to 5000 kPa (abs.) (from 35 bar (abs.) to 50 bar (abs.)).

Gaseous material from the first expander 3 is sent to the refrigerator 11 through a pipe L3. A cooling unit (first cooling unit) is formed by attaching the next refrigerator 12 to the downstream end of the refrigerator 11. The gaseous material is cooled by stepwise heat exchange with refrigerant (first cooling stage) in the first cooling unit 11, 12. The temperature of the gaseous material that is cooled by means of the first cooling unit 11, 12, is in the range of -20 to -50 degrees Celsius or more preferably in the range of -25 to -35 degrees Celsius. If the gaseous material that is introduced into the liquefaction system 1 has a relatively high pressure of, for example, more than 100 bar (abs.), The first cooling unit 11, 12 may not be present, since the temperature of the gaseous material at the outlet of the first expander 3 is relatively low , making, for example, -30 degrees Celsius. The possibility of eliminating the cooling unit on the upstream side of the distillation unit 15 extends equally to the embodiments illustrated in FIG. 5-7, which will be discussed later.

According to the present embodiment, the system uses pre-cooled propane-based mixed refrigerant (P-CX). The gaseous material is pre-cooled in the first cooling unit 11, 12 by using propane as a refrigerant, and then subjected to supercooling to an extremely low temperature in order to liquefy the gaseous material in the refrigeration cycle using mixed refrigerant, as will be discussed below. Propane as a refrigerant (PX) having medium pressure (DM) and low pressure (LP) is used to cool the gaseous material in a plurality of stages (two stages according to the illustrated embodiment) in the first cooling unit 11, 12. Although this is not illustrated in the drawings, the first cooling unit 11, 12 forms part of a well-known refrigeration cycle including compressors and condensers for propane as a refrigerant.

The liquefaction system 1 does not have to be a P-CX based system, but a cascade system can be used in which many separate refrigeration cycles are formed by using appropriate refrigerants (such as methane, ethane and propane) having different boiling points, the system based on double mixed refrigerant (DLC), which uses a mixed medium, such as a mixture of ethane and propane for the pre-cooling process, and a cascaded system based on mixed fluid (CTC), in which various mixed refrigerants are used separately for individual cycles of pre-cooling, liquefaction and subcooling, as well as other features.

Gaseous material from the refrigerator 12 is sent to the distillation unit 15 through line L4. The pressure of the gaseous material at this point should be less than the critical pressure of methane and heavier components through expansion in the first expander 3 and other optional processes. The distillation unit 15 is mainly a distillation column, inside of which numerous plates are installed, from which the heavy components of the gaseous material are removed at the stage of distillation. The liquid that makes up the heavy components is discharged through line L5 connected to the lower end of the distillation column of the distillation unit 15. The liquid which makes up the heavy components and which is discharged from the distillation unit 15 through line L5 has a temperature of about 177 degrees Celsius, and a flow rate of approximately 20,000 kg / h. The term “heavy components” means components, such as benzene, which have high freezing points, as well as components having lower boiling points, such as C5 + hydrocarbons. The pipeline L5 includes a recirculation unit, including a reboiler 16, which heats a part of the liquid discharged from the bottom of the distillation column of the distillation unit 15 by heat exchange with steam (or oil) entering the reboiler 16 from an external source, and the heated liquid is recycled back to the distillation block 15.

The upper fraction from the distillation unit 15, which is composed of the light components of the gaseous material, consists mainly of methane having a low boiling point, and this gaseous material is introduced into the liquefaction unit 21 via line L6 and cooled in the pipe systems 22a and 22b. The gaseous material that is led into the L5 pipeline has a temperature of about −45.6 degrees Celsius and a pressure of about 4700 kPa (abs.). The gaseous material freed from the heavier components in the distillation unit 15 contains less than 0.1 mol% of C5 + and less than 1 molar part per million BTX (benzene, toluene and xylene). As it passes through the piping systems 22a and 22b, the gaseous material is cooled to approximately −65.2 degrees Celsius, and then sent from the liquefaction unit 21 to the first gas and liquid phase separating tank 23 through the pipeline L7.

As will be discussed later, in the liquefaction system 1, the liquefaction unit 21 is primarily a main heat exchanger, and this heat exchanger is a coil-type heat exchanger comprising a shell and coils of heat exchange tubes through which gaseous material and refrigerant are transported. In the liquefaction unit 21, a warm region Z1, which is located in the lower part of the block, is used to receive mixed refrigerant and has the highest temperature level (interval), an intermediate region Z2, which is located in the intermediate part of the block and has a lower temperature than the warm region Z1, and the cold region, which is located in the upper part of the block, is intended for the release of liquefied gaseous material and has the lowest temperature. According to a first embodiment, the warmer region Z1 is constituted by the warmer region Z1a on the high temperature side and the less warm region Z1b on the low temperature side. The piping systems 22a and 22b, as well as the piping systems 42a, 51a, and 42b and 51b through which the mixed refrigerant passes, comprise tube bundles located in the warmer region Z1a and the less warm region Z1b, respectively. According to the illustrated embodiment, the temperature of the warmer region Z1a is about −35 degrees Celsius on the upstream side (inlet side) of the gaseous material to be cooled, and about −50 degrees Celsius on the downstream side (inlet) of the gaseous material. The temperature of the less warmer region Z1b is about −50 degrees Celsius on the upstream side of the gaseous material and about −135 degrees Celsius on the downstream side of the gaseous material. The temperature of the intermediate region Z2 is about −65 degrees Celsius on the upstream side of the gaseous material and about −135 degrees Celsius on the downstream side of the gaseous material. The temperature of the cold region Z3 is about −135 degrees Celsius on the upstream side of the gaseous material, and about −155 degrees Celsius on the downstream side of the gaseous material. The temperatures on the upstream side and the downstream side of each region are not limited to the values presented above, and the temperature in each of these parts can vary within a predetermined range of, for example, ± 5 degrees Celsius).

The first gas and liquid phase separating tank 23 separates the liquid phase component (condensate) of the gaseous material, and this liquid, which is mainly hydrocarbons, is returned to the distillation unit 15 by means of a recirculation pump 24 installed in the pipeline L8. The gas-phase component of the gaseous material obtained in the first gas and liquid phase separating tank 23 and consisting mainly of methane is sent to the first compressor 4 through line L9. Gaseous material is passed through line L8 at a flow rate of approximately 83,500 kg / h and is passed through line L6 at a flow rate of approximately 780,000 kg / h. The first gas and liquid phase separating tank 23 can also be cooled by using mixed refrigerant or ethylene refrigerant.

The first compressor 4 is a single-stage centrifugal compressor having turbine blades for compressing gaseous material and mounted on a common shaft 5 with a first expander 3. Gaseous material compressed by the first compressor 4 (first compression stage) is introduced into the liquefaction unit 21 through line L10. The gaseous material that is released by the first compressor 4 into the L10 pipeline has a temperature of approximately -51 degrees Celsius and a pressure of approximately 5500 kPa (abs.). The gaseous material introduced into the liquefaction unit 21 is compressed by the first compressor 4 to a pressure preferably exceeding at least 5171 kPa (abs.).

The pipeline L10 is connected to the pipeline system 30, which is located in the warm region Z1b of the fluidizing unit 21, and the upstream end of this pipeline system 30 is connected to the pipeline system 31 in the intermediate region Z2, and then to the pipeline system 32, which is located in the cold region Z3. After liquefaction and supercooling during the flow through the pipeline systems 31 and 32, natural gas is sent for storage to a liquefied natural gas (LNG) tank, which is not illustrated in the drawings, through an expansion valve 33 installed in the pipeline L11. The gaseous material processed in the liquefaction step acquires a temperature of -162 degrees Celsius and a pressure of approximately 120 kPa (abs.) At the downstream end of the expansion valve 33.

The gaseous material flowing through the liquefaction unit 21 is cooled by a refrigeration cycle using mixed refrigerants. According to the illustrated embodiment, each of the mixed refrigerants may contain nitrogen as a complement to a mixture of hydrocarbons containing methane, ethane and propane, but it may also have a different well-known composition, provided that the required cooling capacity can be achieved.

In the liquefaction unit 21, the high-pressure (VD) mixed refrigerant (CX) is sent to the refrigerant separator 41 via a conduit L12. The mixed refrigerant, which constitutes the liquid phase component in the refrigerant separator 41, is introduced into the liquefaction unit 21 through line L13, and then flows upward in the liquefaction unit 21 through line systems 42a and 42b located in warm regions Z1a and Z1b, respectively, and line system 43 located in the intermediate region Z2. The mixed refrigerant then expands in the expansion valve 44 installed in the pipe L14, and partially undergoes rapid evaporation.

After passing through expansion valve 44, the mixed refrigerant is discharged downward (so that its flow is opposite to the flow of gaseous material in the liquefaction unit 21) from the spray manifold 45 installed in the upper part of the intermediate region Z2. The mixed refrigerant discharged from the spray manifold 45 flows downward, and heat is exchanged with the intermediate tube bundle formed by the piping systems 31, 43 and 52 (the latter piping system will be discussed later), which are located in the intermediate region Z2, and with the lower bundle tubes formed by the piping systems 22a, 22b, 30, 42a, 42b, 51a and 51b (the last two piping systems will be discussed later), which are located in the warm region Z1.

The mixed refrigerant, which makes up the gas phase of the refrigerant separator 41, is introduced into the fluidizing unit 21 through line L15, and then flows upward in the fluidizing unit 21 by flowing through piping systems 51a and 51b located in warm regions Z1a and Z1b, piping system 52 in the intermediate area Z2 and a piping system 53 located in the cold area Z3. The mixed refrigerant then expands in the expansion valve 54 installed in the pipe L16, and partially undergoes rapid evaporation.

The mixed refrigerant, which is passed through expansion valve 54, is cooled to a temperature below the boiling point of methane (in this case, approximately -167 degrees Celsius) and is discharged downward from the spray manifold 55 located in the upper part of the cold region Z3 (or flows in the opposite direction with respect to the flow of gaseous material in the fluidizing unit 21). The mixed refrigerant discharged from the atomization manifold 55 flows downward and is exchanged with the upper tube bundle formed by the piping systems 32 and 53, which are located in the cold region Z3, and after mixing with the mixed refrigerant which is discharged from the atomizer manifold 45, located below, flows down, and in this case, heat is exchanged with an intermediate tube bundle formed by pipeline systems 31, 43 and 52, which are located in the intermediate region Z2, and the lower m of tubes formed pipe systems 22a, 22b, 30, 42a, 42b, 51a and 51b, which are disposed in the warm region Z1.

The mixed refrigerant discharged from the spray manifolds 45 and 55 is ultimately discharged through line L17 connected to the lower end of the liquefaction unit 21 as a gaseous mixed refrigerant (CX) having a low pressure (LP). The mixed refrigerant devices that are installed in the liquefaction unit 21 (such as the refrigerant separator 41) form part of the well-known mixed refrigerant cycle, and the mixed refrigerant discharged into the L17 line is returned to the refrigerant separator 41 via the L12 line after passing through the compressors and capacitors.

As discussed above, the gaseous material that is introduced into the liquefaction system 1 is effectively liquefied after the expansion stage, the cooling stage, the distillation stage, the compression stage, and the liquefaction stage are processed. This liquefaction system can be applied, for example, to a standard-loaded liquefaction plant for the production of liquefied natural gas (LNG), which is mainly methane, from the gaseous material produced in the gas field.

Table 1 No. (i) (ii) (iii) (iv) (v) (vi) (vii) (viii) (ix) Vapor phase fraction 1.00 1.00 1.00 0.00 0.93 0.00 1.00 1.00 0.00 Temperature (° C) 20.08 8.32 -42.58 177.19 -65.24 -65.24 -65.24 -50.99 -161.55 Pressure (kPa) 5830.00 4850.00 4700,00 4705.00 4,400.00 4,400.00 4,400.00 5483.00 120.00 Molar flow rate (kmol / h) 42000 42000 45020 313 45020 3334 41686 41686 41700 Mass flow rate (kg / h) 719619 719619 783504 19764 783504 83548 699948 699948 698733 Molar fraction Nitrogen 0.008199590 0.000033626 0,008260844 Methane 0.949952502 0,043508871 0.956667221 Ethane 0.024998750 0,032339550 0,024931118 Propane 0.009999500 0.143654595 0,009076200 Butane 0.001999900 0.165149865 0,000793571 n-butane 0.001999900 0.232835468 0,000268518 Isopentane 0,000499975 0,066891831 0.000001710 n-Pentane 0,000499975 0.067093928 0.000000817 n-hexane 0,000599970 0,080591893 0.000000000 Benzene 0,000499975 0,067159786 0.000000000 Toluene 0.000099995 0.013432078 0.000000000 p-xylene 0.000049998 0,006716040 0.000000000 n-heptane 0,000499975 0,067160391 0.000000000 n-octane 0.000099995 0.013432079 0.000000000

 (The first and second examples are for comparison)

FIG. 2 and 3 are diagrams illustrating liquefaction processes in conventional systems for liquefying natural gas, given as a first and second example for comparison with a first embodiment of the present invention. In conventional systems for liquefying natural gas 101 and 201, parts corresponding to parts of the liquefying system according to the first embodiment are denoted by the same reference numerals. Tables 2 and 3 represent the temperature, pressure, flow rate, and molar fractions of the gaseous material in fluidizing systems in the first and second examples for comparison, respectively. It should be noted that the liquefaction system 201 in the second example for comparison is a system based on the prior art described in patent document 1 (US patent No. 4065278).

As illustrated in FIG. 2, in the liquefaction system 101 according to the first example, for comparison, there is no first expander 3 and a first compressor 4 that are used in the liquefaction system 1 according to the first embodiment, and the gaseous material discharged from the dehydration unit 2 is sent to the refrigerator 110 through line L101. The cooling unit is formed by connecting the refrigerator 11 and the refrigerator 12 to the downstream end of the refrigerator 110 in series connection, so that the gaseous material is sequentially cooled during heat exchange in three refrigerators 110, 11 and 12, in which propane is used as the refrigerant, having high pressure (VD), medium pressure (DM) and low pressure (ND), respectively. The gaseous material discharged from the refrigerator 12 through the downstream end has a temperature of about −34.5 degrees Celsius and a pressure of about 5680 kPa (abs.). The gaseous material is then subjected to pressure reduction during the expansion process in the expansion valve 113 in the pipe L4, and then introduced into the distillation unit 15.

In the liquefaction system 101, a gaseous material that forms a gas-phase component in the first gas and liquid phase separating tank 23 and consists mainly of methane is introduced into the piping system 31 located in the intermediate region Z2 of the liquefying unit 21, through the pipeline L102. The gaseous material that is discharged from the first gas and liquid phase separating tank 23 into the pipeline L12 has a temperature of approximately −65.3 degrees Celsius and a pressure of approximately 4400 kPa (abs.).

table 2 No. (i) (ii) (iii) (iv) (v) (vi) (vii) (viii) Vapor phase fraction 1.00 0.99 1.00 0.00 0.93 0.00 1.00 0.00 Temperature (° C) 20.08 -34.50 -42.58 176.73 -65.25 -65.25 -65.25 -161.56 Pressure (kPa) 5830.00 5680,00 4700,00 4705.00 4,400.00 4,400.00 4,400.00 120.00 Molar flow rate (kmol / h) 42000 42000 45020 314 45020 3334 41686 41700 Mass flow rate (kg / h) 719619 719619 783488 19624 783454 83495 699951 696348 Molar fraction Nitrogen 0.008199590 0,000072318 0,008260784 Methane 0.949952502 0.064051796 0.956622861 Ethane 0.024998750 0.031841875 0.024947225 Propane 0.009999500 0.129428030 0.009100267 Butane 0.001999900 0.161816482 0,000796567 n-butane 0.001999900 0.231738008 0,000270095 Isopentane 0,000499975 0,066667173 0.000001771 n-Pentane 0,000499975 0,066846201 0.000000423 n-hexane 0,000599970 0,080282498 0.000000003 Benzene 0,000499975 0,066901980 0.000000003 Toluene 0.000099995 0.013380485 0.000000000 p-xylene 0.000049998 0,006690243 0.000000000 n-heptane 0,000499975 0,066902427 0.000000000 n-octane 0.000099995 0.013380486 0.000000000

[0091]

As illustrated in FIG. 3, the liquefaction system 201 in the second example for comparison is an improvement of the liquefaction system 101 in the first example for comparison, and there are a first expander 3 and a first compressor 4. However, unlike the first expander 3, which is used in the liquefaction system 1 according to in the first embodiment, the expander 3 is located on the downstream side of the cooling unit (which in this case comprises three refrigerators 110, 11 and 12). In the liquefaction system 201, gaseous material discharged from the refrigerator 12 is directed to a separator 213, where it is separated into gaseous and liquid components. The gaseous material that forms the gas phase component in the separator 213 is sent to the expander 3, where it expands, and then sent to the distillation unit 15 through the pipeline L204. A portion of the gaseous material that forms the liquid component in the separator 213 is discharged into the pipeline L205, in which the expansion valve 214 is installed. The liquid that expands in the expansion valve 214 is then sent to the distillation unit 15 through the pipeline L204 together with the gaseous material from the expander 3.

[0092]

The liquefaction system 201 is similar to the system according to the first embodiment, if it is considered that part which is located downstream relative to the distillation unit 15, and the gaseous material that is discharged into the pipeline L10 by the compressor 4, has a temperature of approximately -54.7 degrees Celsius, and a pressure of approximately 5120 kPa (abs.).

[0093]

Table 3 No. (i) (ii) (iii) (iv) (v) (vi) (vii) (viii) (ix) Vapor phase fraction 1.00 1.00 1.00 0.00 0.94 0.00 1.00 1.00 0.00 Temperature (° C) 20.08 -45.36 -44.83 208.13 -64.56 -64.56 -64.56 -54.74 -161.59 Pressure (kPa) 5830.00 4705.00 4700,00 4705.00 4,400.00 4,400.00 4,400.00 5120.00 120.00 Molar flow rate (kmol / h) 42000 41783 44200 302 44200 2500 41700 41700 41700 Mass flow rate (kg / h) 719619 709009 764342 19107 764342 63861 700471 700471 694674 Molar fraction Nitrogen 0.008199590 0.000051871 0.008259333 Methane 0.949952502 0.053398407 0.956509212 Ethane 0.024998750 0,032075932 0,024927984 Propane 0.009999500 0.133750785 0,009066826 Butane 0.001999900 0.153843084 0,000893180 n-butane 0.001999900 0.230805233 0,000340430 Isopentane 0,000499975 0,069219794 0.000002448 n-Pentane 0,000499975 0,069480324 0.000000589 n-hexane 0,000599970 0.083472642 0.000000000 Benzene 0,000499975 0.069560398 0.000000000 Toluene 0.000099995 0.013912204 0.000000000 p-xylene 0.000049998 0.006956102 0.000000000 n-heptane 0,000499975 0.069561020 0.000000000 n-octane 0.000099995 0.013912205 0.000000000

[0094]

As can be understood by comparing the first and second comparative examples with the present invention, the liquefaction system 1 according to the present invention provides increased energy production by expanding the gaseous material having a higher temperature and higher pressure, since the first expander 3 is located on the upstream side the first cooling unit 11, 12, compared with the fluidizing system 201 according to the second example, which has an expander 3 located on the lower downstream of the cooling unit 110, 11, 12. As a result, the first compressor 4 may be driven with increasing power (or the pressure at the outlet of the first compressor 4 may increase), so that the pressure of the gaseous material introduced into the fluidizing unit 21, may increase, and the efficiency of the liquefaction process in the liquefaction unit 21 may preferably increase.

[0095]

The liquefaction system 1 according to the illustrated embodiment provides an additional advantage of reducing the required cooling capacity of the cooling unit (and, as a result, the refrigerator 110 in the second example may be omitted for comparison), since the temperature of the gaseous material is reduced by expanding the gaseous material in the first expander 3, due to the fact that the first expander 3 is located on the upstream side of the first cooling unit 11, 12. In the fluidizing system Related 1 according to the illustrated embodiment may be omitted tank (separator 213) separating a gas and a liquid phase, which separates the condensate and the gaseous material is located between the cooling unit and the expander 3.

 (First, second, and third modifications of the first embodiment)

FIG. 4-6 are diagrams illustrating liquefaction processes in natural gas liquefaction systems shown as second, third, and fourth modifications of the first embodiment, respectively. In liquefaction systems, which are illustrated in FIG. 4, 5 and 6, the parts corresponding to the parts of the liquefaction system 1 according to the first embodiment (as well as other modifications) are denoted by the same reference numbers and are excluded from the subsequent discussion, except for those issues that will be discussed later.

As illustrated in FIG. 4, in the liquefaction system 1 according to the first modification, a heat exchanger 69 is installed between conduit L4 and conduit L9. Thus, the gaseous material, which is separated in the first gas-liquid phase separating tank 23 as a gas-phase component and flows through the pipeline L9, is heated during heat exchange with the gaseous material flowing from the cooling unit 12 to the distillation unit 15 through the pipeline L4, before being introduced into the first compressor 4. Gaseous material compressed by the first compressor 4 is introduced into the liquefaction unit 21 through line L10. The downstream end of the pipeline L10 is connected to the piping system 30 located in the warm region Z1, where the highest temperature is observed in the fluidizing unit 21. The piping system 30 forms a bundle of tubes that is located in the warm region Z1, together with the piping system 22, in which introduces the upper fraction from the distillation unit 15, as well as the piping system 42 and the piping system 51, through which the mixed refrigerant flows.

Due to this design, according to the first modification of the first embodiment, even when the temperature level of the gaseous material that is introduced into the liquefaction unit 21 through the pipeline L10 should be less than the lower limit of the corresponding interval, the temperature of the gaseous material can be raised to an appropriate level by heat exchange in the heat exchanger 69. In other words, according to a first modification of the first embodiment, the temperature of the gaseous material in the pipe L10 after c Atium can be installed near the temperature at the point of introduction (piping system 30) in the fluidizing unit 21 (preferably with a deviation of less than 10 degrees Celsius) so that the heat load on the fluidizing unit 21 can be reduced (or thermal stress can be minimized) )

The design of the heat exchanger 69 according to the first modification can be freely changed, provided that the temperature of the gaseous material in the pipeline L10 after compression can be set near the temperature at the point of introduction of the fluidizing unit 21. For example, in the fluidizing system 1 according to the second modification illustrated in FIG. 5, a heat exchanger 69 is installed between conduit L4 and conduit L10. The gaseous material compressed by the first compressor 4 and flowing through line L10 is cooled during heat exchange with the gaseous material flowing through line L4 before being introduced into the liquefaction unit 21. According to the second modification, since the gaseous material heated by the heat exchanger 69 is introduced into the liquefaction unit 21 without the intervention of a device such as a first compressor 4, the temperature of the gaseous material that is introduced into the liquefaction unit 1 can be easily controlled.

As illustrated in FIG. 6, in a fluidizing system according to a fourth modification, a heat exchanger 69 is installed between conduit L4 and conduit L6. Thus, the gaseous material, which is separated as the upper fraction from the distillation unit 15 and flows through the pipeline L6, is heated during heat exchange with the gaseous material flowing through the pipeline L4 before being introduced into the fluidizing unit 21 (pipeline system 22). In particular, according to the fourth modification, even when the gaseous material is natural gas (low calorie gas) containing at a relatively low level heavy components (heavy hydrocarbons), as illustrated in table 1, and the temperature of the gaseous material that flows through the pipeline L6 after stage distillation may be less than the lower limit of the corresponding interval, and the temperature of the gaseous material can be raised to an appropriate level through heat transfer the heat exchanger 69.

 (Fourth Modification of the First Embodiment)

FIG. 7 is a diagram illustrating a liquefaction process in a natural gas liquefaction system shown as a fifth modification of the first embodiment. In a fluidizing system, which is illustrated in FIG. 7, the parts corresponding to the parts of the liquefaction system 1 according to the first embodiment (including corresponding modifications) are denoted by the same reference numbers and are excluded from the subsequent discussion, except for those issues that will be discussed later.

The fourth modification is similar to the third modification, but additionally includes a heat exchanger 79 installed between line L9 and line L10. The refrigerator 80, which uses propane having a low pressure (LP) as a refrigerant (PX), is additionally installed in the L10 line. As a result, the gaseous material discharged from the first compressor 4 is cooled in a heat exchange process with the gaseous material flowing through the pipeline L9 before being introduced into the liquefaction unit 21. The downstream end of the pipeline L10 is connected to the pipeline system 31 located in the intermediate region Z2 .

According to a fourth modification, gaseous material discharged from the first compressor 4 can be introduced into the intermediate region Z2. Thus, the tube bundle in the warm region Z1 can be formed by three piping systems 22, 42 and 51, and the tube bundle in the intermediate region Z2 can be formed by three piping systems 31, 43 and 52. As a result of this, according to the fourth modification, when the fluidizing unit 21 formed by using a coil heat exchanger, the design of the piping systems in the warm region Z1 and the intermediate region Z2 can be optimized (by evenly distributing the piping systems between different regions) in comparison with a construction according to the third modification such that the excessively large size of the fluidizing unit 21 is prevented. In the fifth refrigerator 80, propane is used as a refrigerant in the same way as the first and second refrigerators 11 and 12 according to the illustrated embodiment, and other types of air coolers can also be used cooling or water cooling.

(Fifth modification of the first embodiment)

FIG. 10 is a diagram illustrating a liquefaction process in a natural gas liquefaction system shown as a second modification of a first embodiment of the present invention. In a fluidizing system, which is illustrated in FIG. 10, the parts corresponding to the parts of the liquefaction system 1 according to the first embodiment (including corresponding modifications) are denoted by the same reference numbers and are excluded from the subsequent discussion, except for those issues that will be discussed later.

The fifth modification is similar to the fourth modification, which is discussed above, but there is no fifth refrigerator 80 according to the fourth modification, and a heat exchanger 100 is additionally installed between the pipe L6 leading from the distillation unit 15 and the pipe L10 leading from the first compressor 4. As a result, the gaseous material discharged from the first compressor 4 into the pipeline L10 is cooled by gaseous material (upper fraction), which is discharged from the distillation unit 15 into the pipeline L6, instead cooling by the fifth refrigerator 80, and introduced into the heat exchanger 79 similarly to the system according to the fourth modification. In this case, the gaseous material discharged from the distillation unit 15 is introduced into the liquefaction unit 21 through the pipeline L6 after heat exchange, and then cooled by the piping system 22. Due to this design, according to the fifth modification, the gaseous material is cooled by the fifth refrigerator 80, as in the system according to the fourth an embodiment, may be supplemented or replaced by heat exchange in the heat exchanger 100. According to the eighth embodiment, there is no heat exchanger 69 that was used as agreed about the fifth embodiment, but it is also possible such a configuration in which gaseous material discharged from the distillation unit 15 into the pipe L6 is introduced into the heat exchanger 100 through the heat exchanger 69.

 (Second Embodiment)

FIG. 8 is a diagram illustrating a liquefaction process in a natural gas liquefaction system shown as a second embodiment of the present invention. In a fluidizing system, which is illustrated in FIG. 8, the parts corresponding to the parts of the liquefaction system 1 according to the first embodiment are denoted by the same reference numbers and are excluded from the subsequent discussion, except for those issues that will be discussed later.

In the liquefaction system 1 according to the second embodiment, high-calorie gas containing 88 mol% of methane is used as the gaseous material. In this liquefaction system, gaseous material, which is separated as the upper fraction in the distillation unit 15, is directly introduced through line L19 into the first compressor 4, where it is compressed. The gaseous material is then pre-cooled in the piping system 22 in the warm region Z1 and sent to the first reservoir 23 separating the gas and liquid phases through the pipeline L21.

The first gas and liquid phase separating tank 23 separates the liquid phase component (condensate) of the gaseous material, and the liquid-shaped hydrocarbons forming the liquid phase component are returned to the distillation unit 15 through an expansion valve 89 installed in the pipeline L22. In this case, the gaseous material, consisting mainly of methane and forming a liquid-phase component in the first reservoir separating the gas and liquid phases 23, is sent to the pipeline system 31 in the liquefaction unit 21 through the pipeline

Since in the liquefaction system 1 according to the second embodiment, the first gas and liquid phase separating tank 23 is installed on the downstream side of the first compressor 4, and gaseous material discharged from the first compressor 4 is introduced into the first gas and liquid phase separating tank 23 system 22 located in the warm region Z1, the temperature of the gaseous material can be set near the temperature level of the warm region Z1 of the liquefaction unit 21. In addition, since the gaseous material is cooled in the warm region Z1 (piping system 22) of the fluidizing unit 21, and the gas-phase component discharged from the first gas and liquid phase separating tank 23 is introduced into the intermediate region Z2 (piping system 31), the temperature of the gaseous material can be set near the level temperature of the intermediate region Z2 of the fluidizing unit 21 is easy. In addition, since the gaseous material discharged from the first gas and liquid phase separating tank 23 can be compressed by the first compressor 4, there may be no recirculation pump 24 installed in the recirculation pipe (line L21), which passes from the first gas and liquid phase separating tank 23 to the distillation unit 15 according to some of the embodiments, including the first embodiment.

When liquefying the gaseous material in the liquefying unit 21, it is preferable to increase the pressure at the outlet of the compressor 4 (or increase the pressure of the gaseous material that is introduced into the liquefying unit 21). However, when the upper fraction from the distillation unit 15 is cooled in the fluidizing unit 21, it is separated in the first gas and liquid phase separating tank 23, and the separated gas phase component is compressed by the first compressor 4 before being introduced into the fluidizing unit 21, as is the case according to the first embodiment, since the temperature the gaseous material is increased by the first compressor 4, which precedes the liquefaction unit 21, depending on conditions such as composition, pressure and rate of introduction of the gaseous material, uro The temperature drop of the gaseous material may go beyond a suitable interval for introduction into the fluidizing unit 21 in such a way that the heat load on the fluidizing unit 21 can become excessive. This problem can be solved by changing the point of introduction of the gaseous material in the fluidizing unit 21, but this may not It will turn out in the case when the main heat exchanger is a type such as a coil heat exchanger, in which the point of introduction cannot be easily changed. Thus, if the gaseous material separated as the top fraction in the distillation unit 15 is sent directly to the first compressor 4 through the pipeline L19 where it is compressed, the gaseous material compressed by the first compressor 4 is cooled in the warm region Z1 of the compression unit 21, the cooled gaseous the material is separated in the first gas and liquid phase separating tank 23, and the separated gas-phase component of the gaseous material is introduced into the intermediate region Z2 (downstream of the relatively warm region Z1) of the liquefaction unit 21, as in the case of the present embodiment, the temperature of the gaseous material can be maintained within an appropriate interval (or the temperature of the gaseous material can be set near the temperature level at the point of introduction of the liquefied unit 21).

 (First Modification of the Second Embodiment)

FIG. 9 is a diagram illustrating liquefaction processes in natural gas liquefaction systems, which are provided as a first embodiment of the present invention. In liquefaction systems, which are illustrated in FIG. 9, the parts corresponding to the parts of the liquefaction system 1 according to the first embodiment are denoted by the same reference numbers and are excluded from the subsequent discussion, except for those issues that will be discussed later.

As illustrated in FIG. 9, the liquefaction system 1 according to the first modification includes a heat exchanger 69 located between conduit L4 and conduit L20, so that the gaseous material discharged from the first compressor 4 and passing through conduit L20 is heated during heat exchange with the gaseous material that flows through pipeline L4, and then introduced into the pipeline system located in the warm region Z1 of the liquefaction unit 21. According to a first modification of the second embodiment, the gaseous material is heated to heat exchanger 69, is introduced directly into the fluidizing unit 21 without the intervention of the first compressor 4, so that the temperature of the gaseous material which is introduced into the fluidizing unit 21 may be easily adjusted.

The position of the heat exchanger 69 according to the first modification of the second embodiment can be changed in various ways without deviating from the idea of the present invention, provided that the temperature of the gaseous material in the pipe L20 after compression can be set near the temperature at the point of introduction of the fluidizing unit 21.

The present invention is described in relation to specific embodiments, but these embodiments are merely examples and do not limit the present invention in any way. The various components of liquefaction systems and liquefaction methods for liquefying natural gas according to the present invention are not necessarily completely indispensable, but can be appropriately replaced and eliminated without deviating from the idea of the present invention.

Legend List

1 - liquefying system

2 - dewatering unit

3, 3a - the first expander

3b - second expander

4, 4a - the first compressor

4b - third compressor

5 - shaft

10, 11, 12 - the first refrigerator

15 - distillation unit

21 - sludge block

23 - the first separating gas and liquid phases of the tank

33 - expansion valve

41 - refrigerant separator

44 - expansion valve

45 - spray manifold

54 - expansion valve

55 - spray manifold

69 - heat exchanger

79- heat exchanger

80 - refrigerator

Z1 - warm area

Z2 - intermediate area

Z3 - cold area

Claims (87)

1. The method of cooling the supplied natural gas, comprising stages in which: a) reduce the pressure of the supplied natural gas to produce a gaseous material having a reduced pressure; b) removing heavy components from the gaseous material having a reduced pressure to produce an upper fraction and a lower fraction; c) cooling the upper fraction to produce a cooled upper fraction; d) separating the cooled upper fraction into a gas phase component and a liquid phase component; e) increase the pressure of the gas-phase component to produce compressed gaseous material; and f) conduct heat exchange between the gas phase component and the compressed gaseous material to produce at least a cooled compressed gaseous material. 2. The method according to claim 1, further comprising cooling the gaseous material having a reduced pressure from step a) before removing the heavy components in step b). 3. The method according to claim 1, further comprising at least partially liquefying the cooled compressed gaseous material from step f). 4. The method according to claim 1, further comprising cooling the compressed gaseous material from step e) before step f). 5. The method according to claim 1, in which the upper fraction is cooled in step c) by introducing the upper fraction into the warm region of the coil-type heat exchanger. 6. The method according to claim 5, in which the cooled compressed gaseous material of step f) is further cooled by introducing the cooled compressed gaseous material into the intermediate region of the coil-type heat exchanger. 7. The method according to claim 1, in which the removal of heavy components in step b) is carried out in a distillation unit. 8. The method according to claim 7, further comprising recycling the liquid phase component from step d) to the distillation unit. 9. The method according to claim 1, further comprising the step of conducting heat exchange between the upper fraction from step b) and the gaseous material having a reduced pressure, before carrying out step c). 10. The method according to claim 1, in which step f) comprises the step of conducting heat exchange between the gas phase component from step d), the compressed gaseous material from step e), and the gaseous material having a reduced pressure from step a). 11. A method of cooling the supplied natural gas, comprising stages in which: a) reduce the pressure of the supplied natural gas to produce a gaseous material having a reduced pressure; b) removing heavy components from a gaseous material having a reduced pressure to produce an upper fraction and a lower fraction, c) conduct heat exchange between the gaseous material having a reduced pressure, and the upper fraction to produce at least the upper fraction, over which the heat exchange is carried out, d) cool the upper fraction, over which the heat exchange is carried out, to produce a cooled upper fraction, e) separating the cooled upper fraction into a gas phase component and a liquid phase component, f) increasing the pressure of the gas phase component to produce compressed gaseous material, and g) cool the compressed gaseous material. 12. The method according to claim 11, further comprising cooling a gaseous material having a reduced pressure from step a) before removing heavy components in step b). 13. The method according to claim 11, in which the compressed gaseous material is cooled in step g) by introducing the compressed gaseous material into one or more heat exchangers. 14. The method according to claim 11, in which the removal of heavy components in step b) is carried out in a distillation unit. 15. The method according to 14, further comprising recycling the liquid phase component from step e) to the distillation unit. 16. A method of cooling the supplied natural gas, comprising stages in which: a) reduce the pressure of the supplied natural gas to produce a gaseous material having a reduced pressure, b) removing heavy components from a gaseous material having a reduced pressure to produce an upper fraction and a lower fraction, c) cooling the upper fraction to produce a cooled upper fraction, d) separating the cooled upper fraction into a gas phase component and a liquid phase component, e) increase the pressure of the gas phase component to produce compressed gaseous material, and f) conduct heat exchange between the gaseous material having a reduced pressure from the step preceding step b) and the compressed gaseous material to produce at least a compressed gaseous material over which heat exchange has been performed, the method further comprising cooling the gaseous material having a reduced pressure from the step a) before the heat transfer in step f). 17. A method of cooling the supplied natural gas, comprising stages in which: a) reduce the pressure of the supplied natural gas to produce a gaseous material having a reduced pressure, b) removing heavy components from the gaseous material having a reduced pressure in the distillation unit to produce an upper fraction and a lower fraction, c) cooling and partially liquefying the upper fraction to produce a cooled upper fraction, d) separating the cooled top fraction to produce a gas phase component and a liquid phase component, e) recycle the liquid phase component into the distillation unit, f) conduct heat exchange between a gaseous material having a reduced pressure and a gas-phase component to produce at least a gaseous component over which heat exchange is carried out, and g) increasing the pressure of the gas-phase component over which heat exchange is carried out to produce compressed gaseous material, the method further comprising cooling the gaseous material having a reduced pressure in step a) before conducting heat exchange in step f). 18. A method of cooling the supplied natural gas, comprising stages in which: a) reduce the pressure of the supplied natural gas to produce a gaseous material having a reduced pressure, b) removing heavy components from a gaseous material having a reduced pressure to produce an upper fraction and a lower fraction, c) increase the pressure of the upper fraction to produce compressed gaseous material, and d) heat exchange is conducted between the upper fraction and the compressed gaseous material to produce at least cooled compressed gaseous material, the method further comprising cooling the gaseous material having a reduced pressure from step a) to step b). 19. A method of cooling the supplied natural gas, comprising stages in which: a) reduce the pressure of the supplied natural gas to produce a gaseous material having a reduced pressure, b) removing heavy components from a gaseous material having a reduced pressure to produce an upper fraction and a lower fraction, c) increase the pressure of the upper fraction to produce compressed gaseous material, and d) conduct heat exchange between the upper fraction and the compressed gaseous material to produce at least cooled compressed gaseous material, the method further comprising cooling the compressed gaseous material from step c) before conducting heat transfer in step d). 20. A system for liquefying the supplied natural gas, comprising: a first expander to reduce the pressure of the supplied natural gas to produce a gaseous material having a reduced pressure, a distillation unit for removing heavy components from a gaseous material having a reduced pressure to produce a top fraction and a bottom fraction, a first heat exchanger for cooling the upper fraction to produce a cooled upper fraction, the first separating the gas and liquid phases of the tank for separating the cooled upper fraction into a gas phase component and a liquid phase component,  a first compressor for compressing the gas phase component to produce compressed gaseous material, and a second heat exchanger for exchanging heat between the gas phase component and the compressed gaseous material. 21. The system of claim 20 further comprising a first cooling unit for cooling a gaseous material having a reduced pressure before being introduced into the distillation unit. 22. The system of claim 20 further comprising a second cooling unit for cooling the compressed gaseous material before being introduced into the second heat exchanger. 23. The system of claim 20, wherein the first heat exchanger is a warm region of a coil-type heat exchanger. 24. The system of claim 23, further comprising a third heat exchanger for cooling the compressed gaseous material after the compressed gaseous material passes through the second heat exchanger, the third heat exchanger being an intermediate region of the coil type heat exchanger. 25. The system of claim 20, further comprising a pipeline for recycling the liquid phase component from the first reservoir separating the gas and liquid phases as a return stream to the distillation unit. 26. The system of claim 20, further comprising a fourth heat exchanger for exchanging heat between the upper fraction from the distillation unit and the gaseous material having a reduced pressure. 27. The system of claim 20, wherein the second heat exchanger is configured to exchange heat between a gas phase component, a compressed gaseous material, and a gaseous material having a reduced pressure. 28. The system of claim 20, wherein the first expander is configured to generate energy, and the first compressor is configured to use the energy generated by the first expander. 29. A system for liquefying the supplied natural gas, comprising: a first expander to reduce the pressure of the supplied natural gas to produce a gaseous material having a reduced pressure, a distillation unit for removing heavy components from a gaseous material having a reduced pressure to produce a top fraction and a bottom fraction, a first heat exchanger for exchanging heat between the upper fraction and a gaseous material having a reduced pressure to form at least an upper fraction over which heat exchange is carried out, a second heat exchanger for cooling the upper fraction, over which the heat exchange is carried out, for the production of the cooled upper fraction, the first separating the gas and liquid phases of the tank for separating the cooled upper fraction into a gas phase component and a liquid phase component,  a first compressor for compressing the gas phase component to produce compressed gaseous material. 30. The system of claim 29, further comprising a first cooling unit for cooling a gaseous material having a reduced pressure before being introduced into the distillation unit. 31. A system for liquefying the supplied natural gas, comprising: a first expander to reduce the pressure of the supplied natural gas to produce a gaseous material having a reduced pressure, a first cooling unit for cooling a gaseous material having a reduced pressure to produce a cooled gaseous material having a reduced pressure, a distillation unit for removing heavy components from the cooled gaseous material having a reduced pressure to produce an upper fraction and a lower fraction, a warm region of a coil-type heat exchanger for cooling the upper fraction to produce a cooled upper fraction, a first gas and liquid phase separating tank for separating the cooled upper fraction into a gas phase component and a liquid phase component, a piping system for recycling a liquid phase component to a distillation unit, a first compressor for compressing the gas phase component to produce compressed gaseous material, a first cooling unit for cooling the compressed gaseous material to produce a cooled compressed gaseous material, a third heat exchanger for exchanging heat between the cooled compressed gaseous material, and a gas-phase component for the production of additionally cooled compressed gaseous material, and an intermediate region of a coil-type heat exchanger for at least partially liquefying an additionally cooled compressed gaseous material.

Images