System and method for liquefied petroleum gas recovery

• US 6,658,893 B1
• Filed: 09/17/2002
• Issued: 12/09/2003
• Est. Priority Date: 05/30/2002
• Status: Active Grant

• Current Assignee: Propak Systems Limited (Mcpike Investments Limited)
• Original Assignee: Propak Systems Limited (Mcpike Investments Limited)
• Inventors: Mealey, W. Brent
• Primary Examiner(s): Doerrler, William C.
• Application Number:
  US10/244,612
• Publication Number:
  US 20030221447A1
• Time in Patent Office: 448 Days
• Field of Search: 626/17, 626/19, 626/20, 626/21
• US Class Current: 62/620
• 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 2205/02 using simple phase separation in a vessel or drum
• 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 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 3/0242 separation of CnHm with 3 carbon atoms or more

Abstract

An improved process for recovery of liquefied petroleum gas from a raw natural gas feed stream, capable of achieving ultra high propane recovery yields, thereby separating substantially all of the propane and heavier hydrocarbon components from a predominantly methane and ethane feed gas stream. The process includes steps to liquefy all of the propane and heavier components and part of the methane and ethane components by cooling, condensing, and absorption. The residual feed gas containing the methane and ethane components, being the final gaseous product stream. The liquefied portion of the feed is separated and then fractionated in a distilling unit to produce a propane and heavier product stream. The distilling unit overhead vapors are cooled and condensed in two steps to provide reflux for the top of the deethanizer and for the feed gas absorption.

Claims

1. A process for recovery of liquefied petroleum gas from a feed stream, the process comprising:

passing said feed stream through an indirect heat exchanger;

separating said feed stream into a first vapor fraction and a first liquid fraction;

transferring said first liquid fraction to said indirect heat exchanger;

transferring said first vapor fraction to a direct heat exchanger absorber column;

transferring said first liquid fraction to a distilling unit;

distilling said first liquid fraction in said distilling unit to yield a second vapor fraction and a second liquid fraction;

cooling said second vapor fraction in said indirect heat exchanger;

separating said second vapor fraction into a third vapor fraction and a third liquid fraction;

returning substantially all of said third liquid fraction to said distilling unit;

passing said third vapor fraction through the indirect heat exchanger, at least a portion of said third vapor fraction condensing to a liquid phase;

decreasing pressure of said third vapor fraction such that at least a portion of said liquid phase flashes;

transferring said third vapor fraction to said direct heat exchanger absorber column such that said third vapor fraction mixes with said first vapor fraction, yielding a fourth vapor fraction and a fourth liquid fraction;

transferring said fourth liquid fraction to said indirect heat exchanger;

transferring said fourth liquid fraction to said distilling unit to distill said fourth liquid fraction; and

transferring said fourth vapor fraction to said indirect heat exchanger, such that, the feed stream exchanges heat with the first liquid fraction, the fourth vapor fraction and the fourth liquid fraction, all four streams being in parallel, and the third vapor fraction exchanges heat with the fourth vapor fraction and the fourth liquid fraction, all three streams being in parallel, and the second vapor fraction exchanges heat with the fourth vapor fraction and the fourth liquid fraction, all three streams being in parallel, wherein heat is exchanged between the feed stream and the fourth liquid fraction, after the fourth liquid fraction has exchanged with the third vapor fraction, and then with the second vapor fraction.

2. The process for recovery of liquefied petroleum gas according to claim 1, wherein the second vapor fraction exchanges heat with the fourth vapor fraction, the first liquid fraction and the fourth liquid fraction, all four streams being in parallel.

3. The process for recovery of liquefied petroleum gas according to claim 1, wherein said feed stream exchanges heat with the first liquid fraction, the fourth vapor fraction and the fourth liquid fraction in a first section of said indirect heat exchanger and the third vapor fraction exchanges heat with the fourth vapor fraction and the fourth liquid fraction in a second section of said indirect heat exchanger.

4. The process for recovery of liquefied petroleum gas according to claim 3, wherein said second vapor fraction exchanges heat with the fourth vapor fraction and the fourth liquid fraction in said second section of said indirect heat exchanger.

5. The process for recovery of liquefied petroleum gas according to claim 3, wherein said second vapor fraction exchanges heat with the fourth vapor fraction, the first liquid fraction and the fourth liquid fraction in said first section of said heat exchanger.

6. The process for recovery of liquefied petroleum gas according to claim 1, wherein said distilling unit is a deethanizer.

7. The process for recovery of liquefied petroleum gas according to claim 1, wherein said direct heat exchanger is a packed column or trayed column.

8. The process for recovery of liquefied petroleum gas according to claim 1, wherein said first vapor fraction is expanded in an expander turbine prior to transferring to said direct heat exchanger.

9. The process for recovery of liquefied petroleum gas according to claim 1, wherein said distilling unit is maintained at a substantially higher pressure than said direct heat exchanger.

10. The process for recovery of liquefied petroleum gas according to claim 3, wherein said indirect heat exchanger comprises two indirect heat exchangers, corresponding to said first and second sections.

11. The process for recovery of liquefied petroleum gas according to claim 1, wherein said indirect heat exchanger comprises one plate-fin exchanger.