Hydrocarbon gas separation process

• US 5,890,377 A
• Filed: 11/04/1997
• Issued: 04/06/1999
• Est. Priority Date: 11/04/1997
• Status: Expired due to Term

• Current Assignee: ABB Randall Corp. (ABB Limited)
• Original Assignee: ABB Randall Corp. (ABB Limited)
• Inventors: Foglietta, Jorge Hugo
• Primary Examiner(s): CAPOSSELA, RONALD C
• Application Number:
  US08/963,770
• Time in Patent Office: 518 Days
• Field of Search: 62/621, 62/619
• US Class Current: 62/621
• CPC Class Codes: F25J 2200/02 in a single pressure main column system
• CPC Class Codes: F25J 2200/50 using multiple (re-)boiler-condensers at different heights of the column
• 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 2270/90 External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration
• CPC Class Codes: F25J 2290/80 Retrofitting, revamping or debottlenecking of existing plant
• 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 separating the components of a feed gas containing methane and heavier hydrocarbons is shown in which a recycle stream is used to satisfy the heat requirements of the process while at the same time providing a reflux to a demethanizer column to improve product recovery. The inlet gas stream is fed to a separator without first splitting the stream. A first vapor portion and a first liquid portion are produced by the separator with the first vapor portion being supplied, after expansion, to the demethanizer column at an intermediate feed position. The first liquid portion from the separator is expanded and supplied to the demethanizer column at a relatively lower feed position. Overhead vapor is removed from the column and compressed to a higher pressure. The resulting compressed recycle stream is cooled sufficiently to substantially condense it and is supplied as reflux to the demethanizer column at a top feed position.

Claims

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

feeding an inlet gas stream to a demethanizer column to produce therefrom an overhead vapor stream and a liquid bottom fraction;

compressing the overhead vapor stream from the column to form a compressed recycle stream;

utilizing the compressed recycle stream to satisfy heat requirements of the demethanizer column sufficient to satisfy a desired heat balance for the demethanizer column while extracting refrigeration from the process;

condensing the compressed recycle stream to form a reflux and supplying the reflux to the demethanizer to control product recovery from the process.

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

feeding an inlet gas stream to a demethanizer column to produce therefrom an overhead vapor stream containing predominantly methane and a bottom fraction containing predominately C₂ and C₂⁺ components;

compressing the overhead vapor stream to form a compressed recycle stream;

cooling the compressed recycle stream sufficiently to substantially condense it to a reflux stream by reboiling the demethanizer column while simultaneously satisfying heat requirements of the column;

supplying the condensed reflux stream to the demethanizer column as a top feed to thereby control product recovery from the process.

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

feeding an inlet gas stream to a separator, without first splitting the inlet gas stream, the separator producing a first vapor portion and a first liquid portion therefrom;

supplying the first vapor portion, after expansion, to a demethanizer column at an intermediate feed position;

expanding the first liquid portion to form an expanded stream and supplying the expanded stream to the demethanizer column at a relatively lower feed position;

removing an overhead vapor stream from the demethanizer column;

compressing the overhead vapor stream to a higher pressure and thereafter dividing the stream into a volatile residue gas fraction and a compressed recycle stream;

cooling the compressed recycle stream sufficiently to substantially condense it while reboiling the demethanizer and supplying the condensed stream as reflux to the demethanizer column at a top feed position.

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

feeding an inlet gas stream to a separator, without first splitting the inlet gas stream, the separator producing a first vapor portion and a first liquid portion therefrom;

supplying the first vapor portion, after expansion, to a demethanizer column at an intermediate feed position;

expanding the first liquid portion to form an expanded stream and supplying the expanded stream to the demethanizer column at a relatively lower feed position;

removing an overhead vapor stream from the demethanizer column;

compressing the overhead vapor stream to a higher pressure and thereafter dividing the stream into a volatile residue gas fraction and a compressed recycle stream;

cooling the compressed recycle stream sufficiently to substantially condense it while simultaneously providing heat to reboil the demethanizer column;

expanding the cooled compressed recycle stream to a lower pressure and supplying it to the demethanizer at a top feed position.

5. The process of claim 4, further comprising the steps of:

cooling the inlet gas stream under pressure to provide a cooled stream entering the separator.

6. The process of claim 5, wherein the compressed recycle stream is cooled sufficiently to substantially condense it by contact with the side reboilers provided as a part of the demethanizer column.

7. The process of claim 6, wherein the compressed recycle stream is further cooled in an additional cooling step and is thereafter expanded to approximately the pressure of the demethanizer column prior to being supplied to the column at the top feed position.

8. The process of claim 7, wherein the overhead vapor stream removed from the top of the demethanizer is passed in countercurrent flow to the inlet gas stream in a heat exchanger whereby the overhead vapor stream is warmed and the inlet gas stream is cooled prior to entering the separator.

9. A process for separation of a gas stream containing methane, C₂ components, C₃ components and heavier components, the process comprising the steps of:

cooling an inlet gas stream under pressure, prior to splitting the inlet gas stream, to provide a partially condensed, cooled stream;

separating the partially condensed, cooled stream in a high pressure separator into a first vapor portion and a first liquid portion;

expanding the first vapor portion in a turboexpander to further cool the stream and introducing the expanded stream to a demethanizer column at an intermediate feed position;

expanding the first liquid portion from the separator and directing the expanded liquid portion to the demethanizer column at a relatively lower feed position;

removing an overhead vapor stream from the demethanizer column;

passing the overhead vapor stream in countercurrent flow to the inlet gas stream in a heat exchanger to warm the overhead vapor stream and cool the inlet gas stream;

compressing the overhead vapor stream to a higher pressure and thereafter dividing the stream into a volatile residue gas fraction and a compressed recycle stream;

cooling the compressed recycle stream sufficiently to substantially condense it by contacting it with side reboilers provided as a part of the demethanizer column;

further cooling the compressed recycle stream;

expanding the cooled compressed recycle stream to a lower pressure and supplying it to the demethanizer at a top feed position.