Process for the recovery of ethane and heavier hydrocarbon components from methane-rich gases

• US 4,203,742 A
• Filed: 10/31/1978
• Issued: 05/20/1980
• Est. Priority Date: 10/31/1978
• Status: Expired due to Term

• Current Assignee: Stone & Webster Engineering Corporation (Brookfield Asset Management Incorporated)
• Original Assignee: Stone & Webster Engineering Corporation (Brookfield Asset Management Incorporated)
• Inventors: Agnihotri, Chaitanya B.
• Primary Examiner(s): Yudkoff, Norman
• Application Number:
  US05/956,324
• Time in Patent Office: 567 Days
• Field of Search: 62/38, 62/39, 62/40, 62/23, 62/24, 62/27, 62/28
• US Class Current: 62/621
• CPC Class Codes: C07C 7/00 Purification; Separation; Use of additives working-up undefined gaseous mixtures obtained by cracking hydrocarbon oils C10G70/00
• CPC Class Codes: C07C 7/005 Processes comprising at least two steps in series
• CPC Class Codes: C07C 7/04 by distillation
• CPC Class Codes: C07C 9/06 Ethane
• 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 2235/60 the fluid being (a mixture of) hydrocarbons
• 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 2270/12 External refrigeration with liquid vaporising loop
• CPC Class Codes: F25J 2270/60 Closed external refrigeration cycle with single component refrigerant [SCR], e.g. C1-, C2- or C3-hydrocarbons
• 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 is disclosed for the recovery of ethane and heavier hydrocarbons from a methane-rich gas utilizing an expander, a high pressure demethanizer tower with flashed and expanded vapor and liquid streams, as coolants in heat exchange relationship with the processed hydrocarbon vapors.

Claims

1. A process for recovering ethane and heavier hydrocarbons from a methane-rich gas which comprises:

(a) passing said gas through a series of at least two indirect cooling stages whereby partial liquefaction of said gas takes place,

(b) separating the liquid and remaining vapors leaving each indirect cooling stage,

(c) vaporizing a portion of each of the liquids so formed by passing said liquids through pressure reduction stages,

(d) separating the vapors from the liquids remaining,

(e) passing the vapor from the last cooling stage through an expansion turbine whereby part of said vapor is liquefied,

(f) separating said liquid and remaining vapor,

(g) passing the liquid remaining after the last liquid pressure reduction stage in heat exchanger relation with a portion of the already partly cooled feed vapor thereby vaporizing a portion of said liquid and forming therefrom a mixture of vapor and liquid, and

(h) passing said mixture of vapor and liquid, the liquid from the separator after the expansion turbine and the liquid from the separator following the first liquid pressure reduction stage as separate feed streams to a demethanizer tower, said tower operating at a pressure level intermediate the inlet feed gas pressure and the pressure at the outlet of the expansion turbine.

2. The process of claim 1 wherein the feed gas is dried prior to passage through the first cooling stage.

3. The process of claim 1 wherein the vapor and liquid formed from liquid in step (g) are separated and fed as separate streams to the demethanizer tower.

4. The process of claim 1 wherein the temperatures of the feed streams to the demethanizer tower are in the range of from about -140°

F. to about -50°

F. and the pressure in said tower is maintained at a level intermediate the pressure of the first liquid pressure reduction stage and the pressure at the outlet of the expansion turbine.

5. The process of claim 4 wherein the vapors from the top of the demethanizer tower are passed in heat exchange relationship with a portion of the gas feed.

6. The process of claim 4 wherein the vapors from the expansion turbine and the vapor from the separation following the last liquid pressure reduction stage are mixed and the mixture is passed in heat exchange relationship in sequence with a portion of the vapors to the last feed vapor cooling stage and a portion of the vapors to another cooling stage.

7. The process of claim 4 wherein the vapors from the separator following the first pressure reduction stage are passed in heat exchange relationship with a portion of the feed gas to the first cooling stage.

8. The process of claim 4 wherein a portion of the feed gas is cooled using refrigeration produced external to the process.

9. The process of claim 8 wherein the feed gas is cooled by refrigerant which is evaporated at progressively lower temperatures.

10. The process of claim 8 wherein the refrigerant is substantially propylene.

11. The process of claim 4 wherein the liquids from the separators following the expansion engine and the second liquid pressure reduction stage are separately withdrawn from their respective separators by means of pumps.

12. The process of claim 4 wherein the first feed fed to the demethanizer tower is introduced at a temperature of about -137°

F.

13. The process of claim 4 wherein said second feed mixture fed to the demethanizer tower is introduced at a temperature of about -57°

F.

14. The process of claim 4 wherein said third feed fed to the demethanizer tower is introduced at a temperature of about -50°

F.

15. The process of claim 4 wherein the demethanizer tower is maintained at a pressure of about 350 to about 450 psia.

16. The process of claim 15 wherein said demethanizer tower pressure is about 410 psia.

17. The process of claim 4 wherein the pressure of the gas at the inlet to the expansion turbine is about 700 psia.

18. The process of claim 4 wherein the pressure of the gas at the outlet of the expansion turbine is about 210 psia.