Hydrocarbon gas separation process

• US 5,566,554 A
• Filed: 06/07/1995
• Issued: 10/22/1996
• Est. Priority Date: 06/07/1995
• Status: Expired due to Term

• Current Assignee: KTI Fish Incorporated
• Original Assignee: KTI Fish Incorporated
• Inventors: Ostaszewski, Ricardo J., Vijayaraghavan, Bharat
• Primary Examiner(s): Capossela, Ronald C.
• Application Number:
  US08/476,835
• Time in Patent Office: 503 Days
• Field of Search: 62/621
• US Class Current: 62/621
• CPC Class Codes: C10L 3/06 Natural gas; Synthetic natural gas obtained by processes not covered by C10G, C10K3/02 or C10K3/04 liquefying by pressure and cold treatment F25J
• CPC Class Codes: F25J 2200/02 in a single pressure main column system
• CPC Class Codes: F25J 2200/70 Refluxing the column with a condensed part of the feed stream, i.e. fractionator top is stripped or self-rectified
• CPC Class Codes: F25J 2205/04 in the feed line, i.e. upstream of the fractionation step
• CPC Class Codes: F25J 2220/66 Separating acid gases, e.g. CO2, SO2, H2S or RSH
• 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 2270/02 Internal refrigeration with liquid vaporising loop
• 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 for the recovery of components of a feed gas containing methane and heavier components utilizing a demethanizer wherein at least two separation stages are provided, in which at least a portion of the liquid condensate from the first separation is partially vaporized to provide a vapor component that, when directed to a first feed point on the demethanizer, preferably functions as an enhanced reflux stream in the demethanizer. Preferably, the first separation is conducted at a higher pressure than the second separation, and both separations are preferably conducted at pressures higher than the operating pressure of the demethanizer.

Claims

1. A process for separating components of a feed gas containing methane and heavier hydrocarbons, comprising the steps of:

condensing said feed gas to provide a first vapor component comprising vapor and a first liquid component comprising condensed liquid;

directing said first vapor component to a demethanizer; and

partially vaporizing at least a portion of said first liquid component to form a second vapor component and a second liquid component, said second vapor and liquid components being directed to different feed points on the demethanizer.

2. The process of claim 1 further comprising the steps of directing the second vapor component to the demethanizer in which, prior to being fed to the demethanizer, the second vapor component is partially or totally condensed to form a reflux agent, the pressure of said reflux agent being lowered by expansion and fed to the demethanizer.

3. The process of claim 2 in which said first liquid component is formed by steps that include cooling and separating the feed gas in one or more heat exchangers and in one or more separation stages.

4. The process of claim 1 in which the first and second vapor components have different compositions.

5. The process of claim 4 in which the first and second vapor components are partially condensed prior to introduction to the demethanizer.

6. The process of claim 1 in which the step of partially vaporizing the first liquid component includes the step of lowering the pressure of said first liquid component by :

expansion to provide an expanded first liquid component or heating said first liquid component or both, wherein the expansion step may either precede or follow the heating step.

7. The process of claim 1 in which the step of directing the second liquid component to the demethanizer includes expanding the second liquid component prior to being fed to the demethanizer.

8. The process of claim 1 in which the pressure of said first liquid component is higher than the pressure at which at least a portion of the first liquid component is partially vaporized to form the second vapor component and second liquid component.

9. The process of claim 1 in which the first vapor component is directed to a first point on the demethanizer and the second vapor component is directed to a second point on the demethanizer, said second point being higher than said first point.

10. The process of claim 1 in which said first vapor component is expanded to a lower pressure and ted into the demethanizer column at a first feed point.

11. The process of claim 1 additionally comprising the step of totally or partially condensing the first vapor component and feeding the resulting condensate to the demethanizer.

12. The process of claim 1 further comprising:

totally or partially condensing the first vapor component and feeding the resulting condensate to the demethanizer; and

totally or partially condensing the second vapor component and feeding the resulting condensate as a refluxing agent to the demethanizer.

13. The process of claim 1 further comprising:

totally or partially condensing the first vapor component and feeding the resulting condensate to the demethanizer; and

totally or partially condensing the second vapor component and feeding the resulting condensate to the demethanizer as a refluxing agent, wherein the refluxing agent is fed to the demethanizer at a higher point than the point at which the condensate from the first vapor component is fed.

14. A process for recovering components of a feed gas containing methane and heavier hydrocarbons comprising:

cooling said feed gas under a first pressure to provide a first vapor portion and a first liquid portion;

partially vaporizing at least a portion of said first liquid portion at a second pressure to provide a second vapor portion and a second liquid portion; and

directing said second vapor and liquid portions to the demethanizer, wherein said second pressure is lower than said first pressure.

15. A process for the recovery of components of a feed gas under high pressure containing methane and heavier components comprising:

cooling said feed gas under high pressure to form a liquid portion under said high pressure and a vapor portion under said high pressure;

directing said vapor portion under said high pressure through an expander such that the vapor portion partially condenses into a second liquid portion;

feeding said second liquid portion into said demethanizer column at a first feed point;

expanding at least part of said liquid portion under said high pressure to an intermediate pressure that is lower than said high pressure but higher than said low pressure, resulting in a flashed liquid portion;

passing said flashed liquid portion through a heat exchanger to vaporize at least part of said flashed liquid portion to produce a partially vaporized stream;

dividing said partially vaporized stream into at least two streams, wherein the first of said two streams comprises primarily vapors and the second of said two streams comprises primarily liquids; and

passing said first stream through a heat exchanger and expanding said first stream to said low pressure and then supplying said first stream as an enhanced reflux stream to said demethanizer column at a second feed point, said second feed point being above said first feed point, and expanding said second stream to said low pressure and supplying said second stream to said demethanizer at a third feed point.

16. The process of claim 15 in which said flashed liquid portion is placed in heat exchange relation with said feed gas or enhanced reflux stream to cool at least part of said feed gas or at least part of said reflux stream or a combination thereof.