KR20160134348A - The System and Method for Carbon Dioxide Separation from Natural Gas before Gas Liquefaction Process - Google Patents

Abstract

A system and a method for removing carbon dioxide of a natural gas according to the present invention can perform a phase change on (can solidify) and separate carbon dioxide by performing heat exchange on a natural gas including carbon dioxide under carbon dioxide solidification temperature conditions according to pressure of a natural gas obtained from a gas field. Accordingly, since high concentration carbon dioxide can be treated, energy can be reduced, an equipment size can be minimized compared to a conventional scheme, and space utilization can be improved. Moreover, the system and the method can be flexibly applied with respect to a change in the composition of carbon dioxide of a gas field, so applicability according to a gas field is high. Furthermore, carbon dioxide can be separated after being solidified, so a volume reducing effect is ensured. In addition, solidified carbon dioxide is melted in a solid state and is directly sublimated into a gas, so surrounding heat is absorbed and temperature can be rapidly reduced. Besides, moisture does not remain during sublimation, so solidified carbon dioxide can be easily treated as a coolant. The system and the method according to the present invention remove carbon dioxide from a natural gas during a pretreating process of a natural gas liquefying process. The method comprises the steps of: solidifying carbon dioxide included in a natural gas provided from a gas field (well) by supplying the natural gas to a heat exchanger; separating the solidified carbon dioxide from the natural gas; and pre-cooling the natural gas by supplying the solidified carbon dioxide separated from the natural gas to a refrigerant of a first cooling means in the natural gas liquefying process.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a system and a method for separating carbon dioxide from natural gas,

The present invention relates to a system and a method for separating carbon dioxide from a natural gas, and more particularly, to a system and a method for separating and removing carbon dioxide from a natural gas in a pretreatment process of a natural gas liquefaction process .

Liquefied natural gas (hereinafter referred to as "LNG") is a colorless and odorless transparent liquid obtained by drilling natural gas containing methane as a main component from a gas field and cooling it to about -162 DEG C, Compared to natural gas, it has a volume of about 1/600.

In addition, LNG is considered to be the best eco-friendly fossil fuel in comparison with coal and petroleum because it has the minimum carbon dioxide (CO ₂ ) emission per unit of combustion and high efficiency, and the demand for it is rapidly increasing worldwide.

The natural gas drilled in the offshore or onshore gas field contains foreign substances such as carbon dioxide (CO ₂ ), acid gases such as hydrogen sulfide (H ₂ S), and water (H ₂ O). Acidic gases such as carbon dioxide and hydrogen sulfide cause equipment corrosion or transport pipe corrosion in the processing of natural gas and moisture forms a gas hydrate in the cryogenic process of natural gas, which causes equipment breakage. Therefore, these foreign substances must be separated and removed from the natural gas prior to the liquefaction process of the natural gas.

Conventionally, in order to remove such carbon dioxide, a membrane separation method using a separation membrane, a method of absorbing carbon dioxide into an absorption solvent in an absorption tower, or a method of adsorbing the same to an adsorbent, or the like, In the pretreatment process.

The most widely applied method is a combination of a membrane and an amine process. It is not sophisticated by supplying natural gas as a separation membrane, but after removing a large amount of carbon dioxide firstly, it is supplied to an amine process to a low concentration It removes the carbon dioxide contained in natural gas.

The absorption method, particularly the absorption method using an amine solution as an absorbent, is the most efficient and most widely used because it can finely separate carbon dioxide.

Future gas drilling and production is expected to be more demanding at sea than onshore plants, and it is already in the trend. In particular, marine medium-sized gas fields often contain a large amount of carbon dioxide. LNG-FPSO (LNG-Floating, Production, Storage, Offloading), a marine plant structure that floats on the ocean and drills, , Hereinafter referred to as 'FLNG'), there is a restriction on energy and space due to the characteristic of FLNG. Therefore, it is necessary to improve the processing ability of the FLNG than the conventional single amine process. However, in order to treat such a high concentration of carbon dioxide, the FLNG has a high ignition risk because it is a heat-collecting process requiring a lot of heat at a high temperature in the amine regeneration process.

For this reason, studies on the two-stage amine process are active. Since the waste heat can be operated in a low-temperature process, the process can safely treat carbon dioxide up to about 15 mol% without high temperature treatment. However, There is a problem that the size of the apparatus becomes large due to the solution flow at a high concentration, and CAPEX and OPEX increase.

Further, in the process of liquefying natural gas, a refrigerant cycle that provides a cold source for cooling natural gas to about -162 占 폚 requires a large amount of electric power to occupy about 30% or more of the total energy of the gas plant, There is a growing demand for ways to save money.

Korean Patent Publication No. 10-2009-0006934 (Published Jan. 16, 2009)

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a method for effectively separating and removing carbon dioxide (CO ₂ ) contained in natural gas coming from a gas field, And to provide a system and method for removing carbon dioxide from a natural gas having a high space efficiency.

According to an aspect of the present invention, there is provided a method for removing carbon dioxide from a natural gas in a pretreatment process of a natural gas liquefaction process, comprising the steps of supplying natural gas supplied from a gas well to a heat exchanger to solidify the carbon dioxide contained in the natural gas step; Separating the solidified carbon dioxide and natural gas; And supplying the solidified carbon dioxide separated from the natural gas to the refrigerant of the first cooling means of the natural gas liquefaction process to pre-cool the natural gas.

Preferably, the step of solidifying the carbon dioxide and supplying the separated natural gas to the amine absorption tower to remove the acidic gas secondarily.

Preferably, the step of solidifying the carbon dioxide may solidify the natural gas containing carbon dioxide by cooling the carbon dioxide to below the triple point temperature of the carbon dioxide in the heat exchanger.

Preferably, the step of solidifying the carbon dioxide and the step of separating the solidified carbon dioxide from the natural gas include cooling the natural gas in the heat exchanger to liquefy the carbon dioxide, wherein the liquefied carbon dioxide is decompressed And can be cooled and supplied to the first cooling means in a solid state.

Preferably, the natural gas passing through the amine absorption tower is fed to the first cooling means of the natural gas liquefaction process and heat exchanged with the solidified carbon dioxide to receive pre-cooling of LNG production.

According to another aspect of the present invention, there is provided a system for removing carbon dioxide from a natural gas in a pretreatment process of a natural gas liquefaction process, the natural gas drilled from the gas field is cooled to below the triple point of carbon dioxide, heat transmitter; And a first cooling means for precooling the natural gas in a liquefaction process for liquefying the natural gas into which the carbon dioxide has been separated and removed to produce LNG.

Preferably, the refrigerant in the first heat exchanger is cooled in the heat exchanger and may be used by supplying phase-change carbon dioxide.

Preferably, the heat exchanger may cool the natural gas below the triple point of the carbon dioxide to solidify the carbon dioxide, and supply the solidified carbon dioxide to the refrigerant of the first heat exchanger.

Preferably, the heat exchanger further includes a fluid injection means for cooling the natural gas to a carbon dioxide critical point to liquefy the carbon dioxide, and to decompress and cool the liquefied carbon dioxide to supply solid phase carbon dioxide to the first heat exchanger .

According to the present invention, the natural gas including carbon dioxide can be heat-exchanged with the carbon dioxide solidification temperature condition depending on the pressure of the natural gas drilled from the gas field, so that the carbon dioxide can be separated by phase change or solidification, The carbon dioxide can be effectively and precisely separated and the processing ability can be improved.

Therefore, it is possible to treat carbon dioxide at a high concentration, so that it has the effect of saving energy, minimizing the equipment size and increasing the space utilization compared with the conventional technology, and applying it flexibly to changes in the carbon dioxide composition of the gas field, .

In addition, the solidified carbon dioxide melts in the solid state and sublimates to the gas, so that it absorbs the surrounding heat and can rapidly lower the temperature. Since the solidified carbon dioxide does not leave moisture at the time of sublimation, it is easy to handle as a coolant.

1 is a PT state diagram of carbon dioxide.
2 is a conceptual diagram of a system for removing carbon dioxide in natural gas according to an embodiment of the present invention.
3 is a conceptual diagram of a system for removing carbon dioxide from natural gas according to another embodiment of the present invention.

In order to fully understand the operational advantages of the present invention and the objects attained by the practice of the present invention, reference should be made to the accompanying drawings, which illustrate preferred embodiments of the present invention, and to the contents of the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, like reference numerals refer to like elements throughout. The same reference numerals in the drawings denote like elements throughout the drawings. In addition, the following examples can be modified in various forms, and the scope of the present invention is not limited to the following examples.

1 is a P-T state diagram of carbon dioxide. As shown in the carbon dioxide state diagram of FIG. 1, the triple point of carbon dioxide is about -56.6 DEG C at about 5.18 bar. That is, the three phases (liquid phase, solid phase, and gas phase) exist at equilibrium at about -56.6 ° C. and 5.18 bar under the condition of low pressure, and they are not liquefied even when the gas temperature is lowered. .

Alternatively, the carbon dioxide is liquefied when the gaseous carbon dioxide is cooled, and when the gaseous carbon dioxide is further cooled or decompressed and cooled, the carbon dioxide is solidified.

On the other hand, the natural gas drilled from the gas field and supplied to the pretreatment process, including foreign substances such as acid gas (carbon dioxide, hydrogen sulfide, etc.) and water, is typically 20 to 80 bar, more typically 40 to 65 bar, to be.

Therefore, the pressure of the natural gas including carbon dioxide drilled from the gas field and supplied to the natural gas pretreatment process is in the range of liquefaction and solidification of the carbon dioxide. If the temperature is lowered to meet the solidification condition of the carbon dioxide at the supply pressure of the natural gas, Solidified and separated from natural gas. The liquefaction condition of natural gas is about -162 ° C at 1 atmospheric pressure and can not be liquefied within the liquefaction conditions of the carbon dioxide, so that only carbon dioxide can be separated without loss of hydrocarbon.

2 illustrates a system for removing carbon dioxide from natural gas according to an embodiment of the present invention. 3 illustrates a system for removing carbon dioxide from natural gas according to another embodiment of the present invention. 1, 2 and 3, respectively.

The present invention relates to an LNG-Floating Production Storage Offloading (LNG-FPSO) which floats on the sea to drill a gas from an undersea gas field and to perform purification, liquefaction production, storage and unloading, It can also be carried out on offshore plants as well as onshore gas plants that produce gas from offshore gas fields.

The carbon dioxide removal system of natural gas according to the present invention is a system for removing carbon dioxide contained in a natural gas in a pretreatment process of a natural gas liquefaction process, in which the natural gas drilled from the gas field (1) is cooled to remove carbon dioxide And a natural gas liquefaction process unit (30) for producing LNG by liquefying natural gas separated and discharged with carbon dioxide, wherein the natural gas liquefaction process unit (30) comprises a natural gas liquefaction process unit And a first cooling means 31 for performing pre-cooling of natural gas for liquefying natural gas.

 The stabilizer unit may further include a stabilization unit that removes solids such as mud that have been introduced with the natural gas before supplying the natural gas to the heat exchanger 10 of the pretreatment process.

The pretreatment step includes a step of removing an acidic gas such as carbon dioxide and hydrogen sulfide, a step of removing water (H ₂ O), a step of removing mercury (mercury), and the like. In the step of removing acid gas, Removing method.

According to the present invention, in order to separate carbon dioxide from the carbon dioxide separation process, the natural gas from which the solids are removed after being drilled in the gas field 1 by the heat exchanger 10 is supplied to the heat exchanger 10, The natural gas is cooled to separate the carbon dioxide by phase change, that is, solidification.

  The natural gas containing carbon dioxide supplied to the heat exchanger 10 should not be below the critical point pressure of carbon dioxide, i.e., about 73.8 bar. The natural gas supplied to the heat exchanger 10 within the pressure range is cooled to a triple point temperature or lower, that is, about -56.6 ° C or lower to solidify the carbon dioxide.

The temperature of the natural gas containing carbon dioxide cooled in the heat exchanger 10 must be cooled to a temperature at which the carbon dioxide solidifies according to the pressure of the natural gas supplied to the heat exchanger 10 and the pressure or decompression device is connected to a heat exchanger 10 so that the pressure of the natural gas supplied to the heat exchanger 10 can be kept constant.

The natural gas on the gaseous phase of the natural gas cooled to -56.6 ° C or lower in the heat exchanger 10 is supplied to the natural gas liquefaction unit 30 and is produced as LNG. The gaseous natural gas separated and discharged from the heat exchanger 10 may be further removed from the acidic gas such as carbon dioxide and hydrogen sulfide through the amine absorption tower (not shown) before being supplied to the liquefaction unit 30. Further, it can be supplied to the liquefaction processing unit 30 after the water removal step, the mercury removal step and the NGL extraction step are further performed.

Alternatively, the heat exchanger 10 may include a coolant supply line provided in the heat exchanger 10 to supply natural gas containing carbon dioxide into the heat exchanger 10, supply the coolant to the coolant supply line, The solid carbon dioxide is condensed in the coolant supply line to form a bond or the coolant supply line is provided in the form of a coil outside the heat exchanger 10 to supply the coolant to the heat exchanger 10 ) On the inner wall surface. Thereafter, the cooled natural gas is discharged, and the solid carbon dioxide is heated by supplying the coolant to the coolant supply line to be vaporized and discharged.

The refrigerant supplied through the refrigerant supply line can be supplied from a refrigerant cycle for liquefaction of a natural gas liquefaction process that liquefies natural gas to produce LNG (liquefied natural gas). For example, the refrigerant supplied from the natural gas liquefaction process can be separated into a mixed refrigerant (C3MR) cycle and a propane refrigeration cycle of a mixed refrigerant cycle, a propane, ethane or ethylene and methane refrigeration cycle of a Cascade process, Such as propane, mixed refrigerant, ethylene, methane, nitrogen, etc., and the refrigeration cycle may be obtained from a line branched from APCI Corporation, Linde Corp., ConocoPhillips, Shell, and others.

The concentration of carbon dioxide in the natural gas supplied to the natural gas liquefaction unit 30 is 50 ppm or less.

In the natural gas liquefaction unit 30, liquefied natural gas is produced to produce LNG. In order to cool the natural gas to a liquefaction temperature of about -162 ° C, multi-stage cooling means are arranged. Among the multi-stage cooling means, in particular, it may include an initial cooling of the natural gas, for example, a first heat exchanger 31 for precooling the natural gas before it reaches the liquefaction temperature.

The solidified carbon dioxide separated and discharged from the heat exchanger 10 is supplied to the first heat exchanger 31 and provided as the refrigerant of the first heat exchanger 31 to cool the natural gas supplied to the natural gas liquefaction process unit 30 .

Generally, the temperature of the natural gas supplied to the natural gas liquefaction unit 30 is about 40 DEG C, and in the precooling step, it is cooled to about -40 DEG C with a pure refrigerant cycle like a propane refrigeration cycle. In the case of propane refrigerant, -42 ° C.

The temperature of the solidified carbon dioxide is about -56.6 ° C or less. Since it is a pure state, the natural gas can be precooled. When the solidified carbon dioxide is subordinate to the triple point, that is, about 5.18 bar and -56.6 ° C, It is easy to handle as a coolant.

The carbon dioxide is cooled to -56.6 ° C or lower in the heat exchanger 10 to be solidified in the form of snow, compressed into dry ice, and supplied to the first heat exchanger 31 to perform heat exchange with the natural gas in indirect contact form, .

Alternatively, as shown in FIG. 3, the carbon dioxide is cooled in the heat exchanger 10 at a temperature below the critical point of carbon dioxide, that is, at a temperature of about 31.1 ° C. or less, particularly about a triple point temperature, ie, -56.6 ° C., After the natural gas and the carbon dioxide in the liquid phase are separated and discharged, the carbon dioxide in the liquid phase can be injected into the first heat exchanger 31 while being reduced in pressure and cooled through the fluid injection means 32 to be supplied as solid carbon dioxide.

The fluid injection means 32 may be a valve, a nozzle, or the like, and the liquefied carbon dioxide may be phase-changed into a solid phase by a Joule-Thomson effect.

For example, the first heat exchanger 21 exchanges solidified carbon dioxide with natural gas by indirect contact such as spraying and applying solid carbon dioxide to a pipe or tube through which natural gas is supplied and discharged, Lt; RTI ID = 0.0 > -40 C < / RTI >

The solidified carbon dioxide cooled by the natural gas can be discharged to the outside of the first heat exchanger 31 in a gaseous state and can be supplied to a customer requiring a low temperature carbon dioxide, for example, a process requiring an inert gas or a carbon capture & ) Technology, or by burning in a flare tower.

The natural gas that has been heat-exchanged with the solidified carbon dioxide can be further liquefied after being subjected to a liquefaction cycle (not shown), a subcooling cycle (not shown), and the like, and then transferred to the LNG storage tank.

As described above, according to the present invention, it is possible to treat even the high concentration of carbon dioxide by separating the carbon dioxide from the natural gas drilled in the gas field 1 into a solid state, And the power consumption of the refrigerant cycle of the natural gas liquefaction process can be reduced by providing carbon dioxide separated and discharged in a solid state as an example of cold heat of a natural gas liquefaction process.

It will be apparent to those skilled in the art that the present invention may be embodied in other specific forms without departing from the spirit or scope of the invention as defined in the appended claims. . Therefore, the above-described embodiments are to be considered as illustrative rather than restrictive, and the present invention is not limited to the above description, but may be modified within the scope of the appended claims and equivalents thereof.

1: Gas Well
10: Heat exchanger (Cooling Unit)
30: Purified Natural Gas Liquefaction Unit
31: a first cooling unit (Pre-Cooling Unit)
32: Fluid Jet Device
40: Amine Stream / Regeneration Column

Claims (9)

A method for removing carbon dioxide from a natural gas in a pretreatment process of a natural gas liquefaction process,
Supplying natural gas supplied from a gas well to a heat exchanger to solidify the carbon dioxide contained in the natural gas;
Separating the solidified carbon dioxide and natural gas; And
Supplying the solidified carbon dioxide separated from the natural gas to the refrigerant of the first cooling means of the natural gas liquefaction process to precool the natural gas. The method according to claim 1,
Further comprising the step of solidifying the carbon dioxide and supplying the separated natural gas to the amine absorption tower to remove the acid gas secondarily. The method of claim 2,
The step of solidifying the carbon dioxide
Wherein the natural gas containing carbon dioxide is cooled to a temperature below the triple point of carbon dioxide in the heat exchanger to solidify the carbon dioxide. The method of claim 2,
The step of solidifying the carbon dioxide and the step of separating the solidified carbon dioxide and the natural gas
And cooling the natural gas in the heat exchanger to liquefy carbon dioxide,
And the liquefied carbon dioxide is decompressed and cooled through a fluid injecting means to supply the liquefied carbon dioxide to the first cooling means in a solid state. The method according to claim 3,
Wherein the natural gas passing through the amine absorption tower is supplied to a first cooling means of a natural gas liquefaction process and is heat exchanged with solidified carbon dioxide to receive pre-cooling of LNG production. A system for removing carbon dioxide from natural gas in a pretreatment process of a natural gas liquefaction process,
A heat exchanger for cooling the natural gas drilled from the gas field to a temperature equal to or lower than the triple point of the carbon dioxide to phase-change and separate the carbon dioxide;
And a first cooling means for precooling natural gas in a liquefaction process for producing LNG by liquefying the natural gas from which the carbon dioxide has been separated and removed. The method of claim 6,
Wherein the refrigerant of the first heat exchanger is cooled in the heat exchanger and supplied with the phase-changed carbon dioxide. The method of claim 7,
The heat exchanger cools the natural gas to below the triple point of the carbon dioxide to solidify the carbon dioxide,
And the solidified carbon dioxide is supplied to the refrigerant of the first heat exchanger. The method of claim 7,
The heat exchanger cools the natural gas to below the carbon dioxide critical point to liquefy the carbon dioxide,
A fluid injection means for decompressing and cooling the liquefied carbon dioxide to supply solid phase carbon dioxide to the first heat exchanger;
Wherein the carbon dioxide removal system further comprises:

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