Process for LPG recovery

• US 4,507,133 A
• Filed: 09/29/1983
• Issued: 03/26/1985
• Est. Priority Date: 09/29/1983
• Status: Expired

• Current Assignee: Exxon Production Research Company (Exxon Mobil Corporation)
• Original Assignee: Exxon Production Research Company (Exxon Mobil Corporation)
• Inventors: Haliburton, James, Khan, Shuaib A.
• Primary Examiner(s): Sever, Frank
• Application Number:
  US06/537,127
• Time in Patent Office: 544 Days
• Field of Search: 62/23, 62/24, 62/27, 62/28, 62/29, 62/30, 62/32, 62/34, 62/36, 62/38, 62/39, 62/42, 62/43, 62/44, 62/31
• US Class Current: 62/621
• CPC Class Codes: C07C 7/09 by fractional condensation
• CPC Class Codes: F25J 2200/04 in a dual pressure main column system
• CPC Class Codes: F25J 2200/74 Refluxing the column with at least a part of the partially condensed overhead gas
• CPC Class Codes: F25J 2200/78 Refluxing the column with a liquid stream originating from an upstream or downstream fractionator column
• CPC Class Codes: F25J 2205/04 in the feed line, i.e. upstream of the fractionation step
• CPC Class Codes: F25J 2210/12 Refinery or petrochemical off-gas
• 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 2270/12 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 2270/90 External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration
• CPC Class Codes: F25J 2290/40 Vertical layout or arrangement of cold equipments within in the cold box, e.g. columns, condensers, heat exchangers etc.
• CPC Class Codes: F25J 3/0209 Natural gas or substitute natural gas
• CPC Class Codes: F25J 3/0219 Refinery gas, cracking gas, coke oven gas, gaseous mixtures containing aliphatic unsaturated CnHm or gaseous mixtures of undefined nature
• CPC Class Codes: F25J 3/0233 separation of CnHm with 1 carbon atom or more
• CPC Class Codes: F25J 3/0242 separation of CnHm with 3 carbon atoms or more

Abstract

An improved process is described for the separation and recovery of substantially all the propane and heavier hydrocarbon components in a hydrocarbon gaseous feedstream. In this process, the vapor stream from a deethanizer is cooled to liquefaction and contacted with a vapor phase from the hydrocarbon gaseous feedstream. The contact takes place within a direct heat exchanger, and the resulting vapor fraction, which is essentially ethane and methane, is the gaseous product of the process.

Claims

1. In a process for separating propane and heavier hydrocarbons from a gaseous feedstream containing hydrocarbon components of different boiling points wherein said feedstream is cooled and separated into a first vapor fraction and a first liquid fraction and said first liquid fraction is distilled in a deethanizer to form a second vapor fraction and a second liquid fraction, the improvement which comprises expanding and transferring said first vapor fraction to the lower portion of a direct heat exchanger, cooling said second vapor fraction to form a substantially liquefied stream, transferring at least a portion of said liquefied stream to the upper portion of said direct heat exchanger whereby said liquefied stream contacts said first vapor fraction to form a third vapor fraction and a third liquid fraction, returning said third liquid fraction to said deethanizer, and removing said third vapor fraction from said direct heat exchanger.

2. A process as described in claim 1 wherein said direct heat exchanger is a packed column.

3. A process as described in claim 1 wherein said direct heat exchanger is a tray column.

4. A process as described in claim 1 wherein said first vapor fraction is expanded in a turboexpander.

5. A process as described in claim 1 further comprising partially flashing said liquefied stream prior to transferring it to said direct heat exchanger.

6. A process for separating propane and heavier hydrocarbons from a gaseous feedstream containing hydrocarbon components of different boiling points which comprises:

(a) cooling and separating said feedstream into a first vapor fraction and a first liquid fraction;

(b) distilling said first liquid fraction is a deethanizer to form a second vapor fraction and a second liquid fraction;

(c) removing said second liquid fraction from said deethanizer as a liquid product;

(d) expanding said first vapor fraction and transferring it to the lower portion of a direct heat exchanger;

(e) cooling said second vapor fraction to form a third vapor fraction and a third liquid fraction;

(f) returning at least a portion of said third liquid fraction to said deethanizer as reflux;

(g) further cooling said third vapor fraction to form a substantially liquefied stream;

(h) transferring said liquefied stream to the upper portion of said direct heat exchanger whereby said liquefied stream contacts said first vapor fraction to form a fourth vapor fraction and a fourth liquid fraction;

(i) removing said fourth vapor fraction from said direct heat exchanger as a gaseous product; and

(j) returning said fourth liquid fraction to said deethanizer.

7. A process as described in claim 6 wherein said direct heat exchanger is a packed column.

8. A process as described in claim 6 wherein said direct heat exchanger is a tray column.

9. A process as described in claim 6 wherein said first vapor fraction is expanded in a turboexpander.

10. A process as described in claim 6 further comprising partially flashing said liquefied stream prior to transferring it to said direct heat exchanger.

11. A process as described in claim 6 further comprising combining at least a portion of said third liquid fraction with said third vapor fraction prior to further cooling said third vapor fraction.

12. A process as described in claim 6 further comprising transferring at least a portion of said third liquid fraction to said direct heat exchanger.

13. A process for separating propane and heavier hydrocarbons from a gaseous feedstream containing hydrocarbon components of different boiling points which comprises:

(a) cooling and separating said feedstream into a first vapor fraction and a first liquid fraction;

(b) distilling said first liquid fraction in a deethanizer to form a second vapor fraction and a second liquid fraction;

(c) removing said second liquid fraction from said deethanizer as a liquid product;

(d) expanding said first vapor fraction and transferring it to the lower portion of a direct heat exchanger;

(e) cooling said second vapor fraction to form a third vapor fraction and a third liquid fraction;

(f) removing said third vapor fraction as a gaseous product;

(g) returning at least a portion of said third liquid fraction to said deethanizer as reflux.

(h) transferring at least a portion of said third liquid fraction to the upper portion of said direct heat exchanger whereby said third liquid fraction contacts said first vapor fraction to form a fourth vapor fraction and a fourth liquid fraction;

(i) removing said fourth vapor fraction from said direct heat exchanger as a gaseous product; and

(j) transferring said fourth liquid fraction to said deethanizer.

14. A process as described in claim 13 wherein said direct heat exchanger is a packed column.

15. A process as described in claim 13 wherein said direct heat exchanger is a tray column.

16. A process as described in claim 13 wherein said first vapor fraction is expanded in a turboexpander.

17. A process as described in claim 13 further comprising partially flashing said third liquid fraction prior to transferring it to said direct heat exchanger.