KR101236863B1 - Method for separating a fraction rich in c2+ from liquefied natural gas - Google Patents

Abstract

The present invention relates to a method for separating C ₂₊ -rich fractions from liquefied natural gas (LNG).

a) partially evaporating the liquefied natural gas 1 '(E2),

b) separating the partially evaporated natural gas (2) into a first C ₁ -rich gas fraction (4) and a first C ₂₊ -rich liquid fraction (3),

c) rectifyingly separating the first C ₂₊ -rich liquid fraction (3) into a second C ₁ -rich gas fraction (8) and a second C ₂₊ -rich liquid fraction (10) ( T) step,

d) liquefying (E1) the first C ₁ -rich gas fraction 4 again, and

e) providing at least one partial stream 6 of said again liquefied C ₁ -rich gas fraction 5 to a rectifying separation device T as a reverse flow.

Description

Method for separating C2 + -rich fractions from liquefied natural gas {METHOD FOR SEPARATING A FRACTION RICH IN C2 + FROM LIQUEFIED NATURAL GAS}

The present invention relates to a method for separating C ₂₊ -rich fractions from liquefied natural gas (LNG).

Conventional methods can be provided, for example, when the heating value of the liquefied natural gas does not correspond to the desired specification of the pipeline network to which the liquefied natural gas is to be supplied. In such cases, liquefied natural gas is added with components that lower the heating value, for example nitrogen, or components that cause the heating value to be separated from the liquefied natural gas. The second alternative described above is described in detail below.

US-A 5,114,451 discloses a homogeneous method for the separation of C ₂₊ -rich or C ₃₊ -rich fractions from liquefied natural gas (LNG), in which the separation method differs from those realized to date. The partial flow of the C ₁ -rich gas fraction obtained in the rectification separation device of (liquefied) natural gas is liquefied again and provided as a return flow to the rectification separation device. The remaining flow of the C ₁ -rich gas fraction is compressed to the desired delivery pressure or pipeline pressure only after the separation of the partial flow forming the aforementioned reverse flow. The process described in US Pat. No. 5,114,451 can raise the ethane yield to an economically advantageous value, but such a rise possibility can only be achieved by using at least one cost intensive compressor.

US-A 3,420,068 also discloses a similar method for separating C ₂ -rich fractions from liquefied natural gas. In this case, the methane-rich gas fractionation recompression process, which was obtained inside the apparatus for the commutation of partially evaporated natural gas, was omitted, but the results could only reach average ethane yields. .

An object of the present invention, C ₂₊ -, and can reduce the investment and operating costs for the process at the same time which increases the yield of classification rich, particularly in the compression of the methane-enriched gas classification can be omitted, C _{2 It} provides a way to separate a rich fraction from liquefied natural gas (LNG).

In order to solve the above problems, including the processing steps as shown below, C _{2 +} - a method for separating the rich classification from liquefied natural gas (LNG) is proposed:

a) partially evaporating liquefied natural gas,

b) separating the partially evaporated natural gas into a first C ₁ -rich gas fraction and a first C ₂₊ -rich liquid fraction,

separating by rectification expression in a rich liquid category, - a rich liquid classification second of _{C 1 - - c) C 2} + in the first rich gas classification and C _{+ 2} of the second

d) liquefying the first C ₁ -rich gas fraction again, and

e) providing at least one partial flow of said again liquefied C ₁ -rich gas fraction as a counter flow to a rectifying separator.

In contrast to the method mentioned at the outset, in the method according to the invention, the first C ₁ -rich gas fraction obtained inside the device for separating partially evaporated natural gas is liquefied again and at least partially in a rectifying separation device. It is provided as a reverse flow. In this case the cooling necessary to liquefy the first C ₁ -rich gas fraction is only by means of a liquid natural gas stream which is heated up to the boiling point. Since the C ₁ -rich gas fraction provided as a counter flow to the rectifying separator has a relatively low ethane content, the heavier components of the ethane and the upper products of the rectifying separator are again washed by the rectifying separator. whereby the yield of C _{2 +} is elevated to a desired level.

The process according to the invention thus makes it possible to reach a ethane-yield ratio of 90% or more through economical rational processing. The value is in the range of ethane-gain rates that can be achieved by the complex method according to US Pat. No. 5,114,451, but is much higher than the value in the method according to US Pat. No. 3,420,068.

Further refinements of the method according to the invention and of the subject matter of the dependent claims are described in detail below with reference to the embodiment shown in FIGS. 1 and 2.

As shown in FIG. 1, the liquefied natural gas cooled below the freezing point, pumped to a pressure of 15 to 30 bar by a pump P1, is transferred from the LNG storage vessel S through a line 1 through a heat exchanger ( E1). Inside the heat exchanger, the liquefied natural gas is heated to near boiling point for the C ₁ -rich gas fraction 4, which is described in more detail below, to be cooled and then liquefied again. The difference from the boiling point is typically 5 ° C., up to 20 ° C.

The heated natural gas is then provided via line 1 'to an additional heat exchanger E2, in which the second C ₁ -rich gas fraction to be cooled 8 -below in the additional heat exchanger. Described in more detail in-heated and partially evaporated.

The partially evaporated natural gas stream is provided via line 2 to separator D1. In the interior of the separator wherein the partially natural gas stream evaporated in the separator (D1), the first of C ₁ it is discharged through from the upper line (4) is separated into rich liquid category-rich gas classification and the first of the C _{2 +} . C _{+ 2} of the first-rich fluid classification pump 3 to the separation column (T) for via a line 3, which is provided therein, and then is provided to the commutation type separator.

As an alternative to separator D1 shown in FIG. 1, a rectification column may be provided in which the separation of the partially evaporated natural gas 2 is carried out therein. In this case the partially evaporated natural gas stream 2 is fed into a sump of the rectification column. The required column reverse flow can be implemented by the flow exiting from the line 6 described later or by the flow exiting the heat exchanger E2 and before the valve c from the line 8 described later. Can be. Such a refinement of the method according to the invention can significantly increase the C ₂ -yield, resulting in a reduction in the loss of heating gas.

The internal column (T) for separating the above-described C _{2 +} - rich liquid category (3) a second of the C ₁ - rich gas classification and C _{2 +} a 2 - a process of separation by rectification expression in a rich liquid classification runs The second C ₁ -rich gas fraction is withdrawn via line 8 at the top of the separation column T. The separating column T may have a bottom and / or a packing.

C _{2 +} in the above-described second-rich fluid classification control valve (e) is N atural G (is discharged from the sump of the separation column (T) for via a line 10 provided therein so-called NGL as L iquids ) Is discharged from the process as a classification and, in some cases, provided for further use. One partial flow of the fraction is partially evaporated inside the heat exchanger E3 and provided to the separation column T as a Reboiler-flow through line 11.

Inside the commutation type separator (T) is preferably natural gas (2) evaporating the partially first of C ₁ - to rich liquid category 3-rich gas classification 4 and C _{2 +} in the first The separation process takes place at a higher pressure than in the separator D1 to be separated. In this case, a pressure of preferably 15 to 25 bar is realized inside the separation device or separator D1, and preferably a pressure of 30 to 40 bar is realized inside the rectifying separation device T. A pump P3 may be provided in line 3 to overcome the pressure difference between separator D1 and separation column T.

The first C ₁ -rich gas fraction 4 obtained when separating the partially evaporated natural gas stream 2 and exiting the line 4 from the top of the separator D1 is subjected to the natural gas stream to be heated. Via line sections 5 and 6 after being liquefied again in heat exchanger E1 and pumped to a prevailing pressure inside said separation column T by pump P2-in this case In the line section 6 a control valve d is provided-a rectifying separation device T, preferably as a back flow to the upper region of the rectifying separation device.

The second C ₁ -rich gas fraction obtained inside the rectifying separation device T is discharged via line 8 at the top of the separation column T and is applied to the natural gas stream 1 ′ to be heated. With respect to the heat exchanger E2, at least partly, but preferably completely liquefied, is provided to the pump collection vessel D2 via a line 8 'in which a control valve c is arranged. The pump collection vessel D2 is again liquefied C ₁ -not provided as backflow to the separation column T via a line section 7 with a control valve b arranged therein. A rich first fractional partial flow is provided.

C _{2 +} from the pump collection vessel (D2) - depleted LNG- product classification is pumped by a pump (P4) to the desired delivery pressure or pipeline pressure - the pressure is usually in the range of 50 to 150 bar - The control valve a is likewise withdrawn from the process via a line 9 provided therein.

Rectification type separator (T) is obtained in the interior of the second body through the line 10 from the sump of the column (T) for the separated C _{2 +-case} to be separated-enriched liquid category C ₂ / C ₃ The process preferably proceeds as shown in FIG.

₂ of a second in C 2 ₊ - rich fluid classification rectified formula C ₂ / C ₃ (the second) in the internal column (T) for separation subjected to a separation process. The C ₃₊ -rich LPG-product fraction is withdrawn from line sump 18 from the sump of separation column T ′, optionally provided for further processing or use. One partial flow of the fraction is partially evaporated inside the heat exchanger E5 and provided to the separation column T 'as a reboiler-flow through line 19.

C ₂ / C ₃ -enriched gaseous fraction exits the line 12 at the top of the separation column T 'and is connected to the separation column T via the line 13 to the side boiling vessel E4 ( After condensing at least partially inside the side boiling vessel, it is provided to the pump collection vessel D3 via line 14.

The condensed C ₂ / C ₃ -rich fraction is fed from pump collection vessel D3 to pump P5 via line 15 and pumped by the pump to the desired delivery pressure. The secondary flow of the pumped fraction is provided as a reverse flow on top of the separating column T 'via line 16 and control valve f, while the main flow of the pumped fraction is line 17 Through the process, and in some cases provided for further use or treatment.

Alternative C ₂ / C ₃ -separation processes can also be realized as an alternative to the treatment mode described with reference to FIG. 2, for example, gaseous top product fractionation is withdrawn from vessel D3.

C _{2 +} - in the improvement of the process according to the invention for separating the rich classification from liquefied natural gas, first for ₂ C 2 ₊ - rich fluid classification separating device (T ') the resulting first the processing flow from the of C _{2 +} - rich fluid against classification and / or the first of the C _{2 +} - a method of cooling for at least one of the liquid discharged from the classification type rectification separation under a rich supply of liquid jet system is proposed.

In particular C _{2 +} of the second-a rectifying formula C ₂ / C ₃ rich fluid classification 10-separation device (T ') when passing through the rectification formula C ₂ / C ₃ - separating device (T' ), the C ₂ / C ₃ obtained in the internal-to manner, preferably pressureless storage temperature is cooled with respect to the rich liquid category (3) a rich gas classification 12 in the internal heat exchanger C _{2 +} in the first Cooling is recommended.

The heat exchanger necessary for such a manner can be provided, for example, between the pump P3 and the separation column T. In order to realize a pressureless storage condition, a temperature of about -100 ° C. is required for gas fractionation consisting mainly of ethane and obtained at the top of the rectified C ₂ / C ₃ -separation device (T ′). Do. An advantage in this treatment is that the forced cooling process in the whole process-in other words the cooling below ambient temperature-or-the compression process with thermodynamically identical effects-can be omitted.

As described with reference to the method shown in FIGS. 1 and 2, when all process flows enter the liquid state (flow 1) and are discharged back to the liquid state (flows 9 and 10 or 9, 17 and 18), eventually all The cooling process starts with the process of cooling the used LNG below the freezing point.

C _{2 +} - in the process according to the invention for separating the rich classification from liquefied natural gas (LNG), there can be realized a high ethanol yield at the same time with the use of cost-intensive compressor can be omitted.

Claims (10)

C ₂₊ -Method for separating fraction rich from liquefied natural gas (LNG), a) partially evaporating the liquefied natural gas 1 '(E2), b) separating the partially evaporated natural gas (2) into a first C ₁ -rich gas fraction (4) and a first C ₂₊ -rich liquid fraction (3) (D1), c) rectifyingly separating the first C ₂₊ -rich liquid fraction (3) into a second C ₁ -rich gas fraction (8) and a second C ₂₊ -rich liquid fraction (10) ( T) step, d) reliquefying (E1) said first C ₁ -rich gas fraction (4), and e) providing at least one partial stream 6 of the reliquefied C ₁ -rich gas fraction 5 to the rectifying separation device T as a return flow, C _{2+ -Method} for separating rich fractions from liquefied natural gas (LNG). The method of claim 1, Re-liquefying (E1) of the first C ₁ -rich gas fraction 4 is carried out at the time of heat exchange with the liquefied natural gas 1 to be evaporated, C _{2+ -Method} for separating rich fractions from liquefied natural gas (LNG). 3. The method according to claim 1 or 2, The separation process inside the rectifying separation device T comprises a first C ₁ -rich gas fraction 4 and a first C ₂₊ -rich liquid fraction 3 of the partially evaporated natural gas 2. Characterized in that the pressure is higher than the separation process made in the separator (D1) to be separated by a), C _{2+ -Method} for separating rich fractions from liquefied natural gas (LNG). The method of claim 3, wherein The separation process inside the separator D1 separating the partially evaporated natural gas 2 into a first C ₁ -rich gas fraction 4 and a first C ₂₊ -rich liquid fraction 3 It is made in the pressure range of 15 to 25 bar, the separation process made in the rectifying separation device (T) is characterized in that it is made in the pressure range of 30 to 40 bar, C _{2+ -Method} for separating rich fractions from liquefied natural gas (LNG). The method of claim 1, The partial stream 7 of the again liquefied C ₁ -rich gas fraction 5, which is not supplied as a reverse flow to the rectifying separator T, is the second C obtained inside the rectifying separator T. Characterized in that it is combined with ₁ -rich gas fraction 8, 8 ', C _{2+ -Method} for separating rich fractions from liquefied natural gas (LNG). The method of claim 1, The second C ₁ -rich gas fraction 8 obtained inside the rectifying separation device T is at least partially reliquefied (E), and the reliquefaction process is carried out with the liquefied natural gas 1 'to be evaporated. Characterized in that at the time of heat exchange, C _{2+ -Method} for separating rich fractions from liquefied natural gas (LNG). The method of claim 1, The resulting process streams from the separation device of the second C ₂₊ -rich liquid fraction 10 are applied to the first C ₂₊ -rich liquid fraction 3 and / or to the first C _{2. +} -Cooled to at least one liquid fraction 13 discharged from said rectifying separator T under the supply of a rich liquid fraction 3 C _{2+ -Method} for separating rich fractions from liquefied natural gas (LNG). The method of claim 1, The second C ₂₊ -rich liquid fraction 10 is separated inside the rectifying C ₂ / C ₃ -separating device T 'and condensed at the top of the C ₂ / C ₃ -separating device T'. Water is produced inside the side boiling vessel E4 with respect to the at least one liquid fraction 13 discharged from the rectifying separator T under the supply of the first C ₂₊ -rich liquid fraction 3. Made, C _{2+ -Method} for separating rich fractions from liquefied natural gas (LNG). The method of claim 1, C ₂₊ of the second-interior - (- rich fluid classification 10 is rectified formula C ₂ / C ₃ separator (T) separator T) is separated from the inside, the rectification formula C ₂ / C ₃ ' The C ₂ / C ₃ -rich gas fraction 12 obtained in the above is cooled to the first C ₂₊ -rich liquid fraction 3 at the time of heat exchange, C _{2+ -Method} for separating rich fractions from liquefied natural gas (LNG). The method of claim 1, The step (D1) of separating the partially evaporated natural gas (2) into the first C ₁ -rich gas fraction (4) and the first C ₂₊ -rich liquid fraction (3) is a separator or rectification. Characterized in that inside the column, C _{2+ -Method} for separating rich fractions from liquefied natural gas (LNG).

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