Process and installation for separation of a gas mixture containing methane by distillation

• US 6,578,379 B2
• Filed: 12/13/2001
• Issued: 06/17/2003
• Est. Priority Date: 12/13/2000
• Status: Active Grant

• Current Assignee: Technip-Coflexip
• Original Assignee: Technip-Coflexip
• Inventors: Paradowski, Henri
• Primary Examiner(s): CAPOSSELA, RONALD C
• Application Number:
  US10/013,838
• Publication Number:
  US 20020095062A1
• Time in Patent Office: 551 Days
• Field of Search: 626/22, 626/28, 626/57
• US Class Current: 62/622
• CPC Class Codes: F25J 2200/02 in a single pressure main column system
• CPC Class Codes: F25J 2200/76 Refluxing the column with condensed overhead gas being cycled in a quasi-closed loop refrigeration cycle
• CPC Class Codes: F25J 2205/04 in the feed line, i.e. upstream of the fractionation step
• CPC Class Codes: F25J 2240/02 Expansion of a process fluid in a work-extracting turbine (i.e. isentropic expansion), e.g. of the feed stream
• CPC Class Codes: F25J 2280/02 Control in general, load changes, different modes ("runs"), measurements
• CPC Class Codes: F25J 3/0209 Natural gas or substitute natural gas
• CPC Class Codes: F25J 3/0233 separation of CnHm with 1 carbon atom or more
• CPC Class Codes: F25J 3/0238 separation of CnHm with 2 carbon atoms or more

Abstract

A process and apparatus for separation of a gas mixture. A process and an installation for cryogenic separation of the constituents of a natural gas under pressure in a first phase separator in which the constituents of each phase are separated in a distillation column. Part of the gaseous fraction from the top of the column is recycled into the highest stage of the column. The process also includes branching of part of a first top fraction from the first phase separator. The process also includes separation of a first bottom fraction from the first separator, in a second separator.

Claims

1. A process for separation of a mixture cooled under pressure, containing methane and C₂ and higher hydrocarbons, into a methane-rich light fraction and a final heavy fraction rich in C₂ and higher hydrocarbons, the process comprising:

in a first stage, cooling the mixture under pressure,

separating the mixture, in a first flask, into a relatively more volatile first top fraction and a relatively less volatile first bottom fraction,

introducing the first bottom fraction into a middle part of a distillation column,

collecting in the lower part of the distillation column, the heavy fraction rich in C₂ and higher hydrocarbons as a second bottom fraction,

introducing, after pressure reduction in a turbine, the first top fraction, in an upper part of the distillation column,

collecting, in an upper part of the distillation column, a second methane-rich top fraction,

compressing and cooling the second top fraction to produce the light fraction, and

taking a first sample fraction from the light fraction;

in a second stage, cooling and liquefying the first sample fraction, and

introducing the cooled and liquefied first sample fraction into the upper part of the distillation column; and

in a third stage, subjecting the first bottom fraction to a number of sub-stages including heating, passage into a second flask, and separation into a relatively more volatile third top fraction, and a relatively less volatile third bottom fraction,

introducing the third bottom fraction into the middle part of the distillation column,

cooling and liquefying a third top fraction, and

introducing the cooled and liquefied third top fraction, after cooling and liquefaction, into the upper part of the distillation column.

2. The process according to claim 1, including removing a second sample fraction from the first top fraction, cooling and liquefying the second sample, and introducing the cooled and liquefied second sample fraction into the upper part of the distillation column.

3. The process according to claim 2, including:

cooling and partly condensing the second sample fraction,

separating the second sample fraction in a third flask into a fourth relatively more volatile top fraction,

cooling, liquefying, and introducing the fourth volatile top fraction into the upper part of the distillation column, heating and separating a fourth relatively less volatile bottom fraction in a fourth flask into a fifth relatively more volatile top fraction, cooling and introducing the fifth top fraction into the upper part of the distillation column, and heating a fifth relatively less volatile bottom fraction and sending the fifth bottom fraction into said second flask.

4. The process according to claim 3, wherein the upper part of the distillation column comprises at least two successive stages, the first of the two successive stages being the lowest, and including introducing the fifth top fraction above the first of the two successive stages.

5. The process according to claim 3, wherein the upper part of the distillation column comprises at least three successive stages, the first of the three successive stages being the lowest, and including introducing the fourth top fraction above the second of the three successive stages.

6. The process according to claim 2, wherein the upper part of the distillation column comprises at least two successive stages, the first of the two successive stages being the lowest, and including introducing the second sample fraction above the first of the two successive stages.

7. The process according to claim 6, including introducing the third top fraction in the first stage of the upper part of the distillation column.

8. The process according to claim 1, wherein the lower part of the distillation column comprises a number of stages connected, in pairs, to at least one lateral reboiler.

9. The process according to claim 1, including heating and compressing, the second top fraction, after it leaves the distillation column, to produce the methane-rich light fraction.

10. The process according to claim 1, wherein the upper part of the distillation column comprises at least three stages, the first of the three stages being the lowest, including introducing the first sample fraction in a lower part of the last of the three stages, and introducing the third top fraction below the last of the three stages.

11. The process according to claim 1, wherein the middle part of the distillation column comprises at least two successive stages, the first of the two successive stages being the lowest, and introducing the third bottom fraction into the first of the two successive stages, and introducing the first top fraction above the first of the two successive stages.

12. An apparatus for separation of a mixture cooled under pressure containing methane and C₂ and higher hydrocarbons, into a methane-rich light fraction and a heavy fraction rich in C₂ and higher hydrocarbons, comprising:

in a first stage including a distillation column in which the mixture cooled under pressure is present, means for separating the mixture, in a first flask, into a relatively more volatile first top fraction and a relatively less volatile first bottom fraction, the first bottom fraction being introduced into a middle part of the distillation column in which, in a lower part of the column, the final heavy fraction rich in C₂ and higher hydrocarbons are collected as the second bottom fraction, a turbine reducing pressure of the first top fraction for introducing, after the pressure reduction, the first top fraction into an upper part of the distillation column, for collecting a second methane-rich top fraction in the upper part of the distillation column, a compressor and cooler for compressing and cooling the second top fraction to produce the light fraction, and for taking a first sample fraction from the light fraction;

means, in a second stage, for introducing the first sample fraction, after cooling and liquefaction, into the upper part of the distillation column; and

in a third stage, means for subjecting the first bottom fraction to heating, passage into a second flask, and separation into a relatively more volatile third top fraction and a relatively less volatile third bottom fraction, wherein the third bottom fraction is introduced into the middle part of the distillation column, and the third top fraction is introduced into the upper part of the distillation column, after cooling and liquefaction.