Cryogenic gas plant

• US 4,496,380 A
• Filed: 07/07/1983
• Issued: 01/29/1985
• Est. Priority Date: 11/24/1981
• Status: Expired due to Fees

• Current Assignee: Shell Oil Company (Shell Plc)
• Original Assignee: Shell Oil Company (Shell Plc)
• Inventors: Harryman, John M.
• Primary Examiner(s): Sever, Frank
• Application Number:
  US06/511,448
• Time in Patent Office: 572 Days
• Field of Search: 62/23, 62/24, 62/31, 62/32, 62/34, 62/42, 62/27, 62/28, 62/29, 62/30, 62/41, 62/42
• US Class Current: 62/630
• CPC Class Codes: F25J 2200/02 in a single pressure main column system
• CPC Class Codes: F25J 2200/30 using a side column in a single pressure column system
• 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 2230/08 Cold compressor, i.e. suction of the gas at cryogenic temperature and generally without afterstage-cooler
• CPC Class Codes: F25J 2230/60 the fluid being hydrocarbons or a mixture of hydrocarbons
• 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 3/0233 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 substantially all of the C₃ and heavier components and a major portion of the C₂ component from a natural gas stream using a cryogenic process. The process uses a rectifying column in combination with a fractionating column to separate the C₂ and heavier components with the reflux for the rectifying column being supplied by compressing a small portion of the overheads and condensing it via heat exchange with the overheads stream.

Claims

1. A process for separating ethane and heavier components from a natural gas stream utilizing a cryogenic plant having a cold feedstream, said process comprising:

retrofitting said process to include a rectifier section upstream of a demethanizer;

introducing the cold feedstream into the rectifier section to recover ethane from the feedstream stream and withdrawing the methane through the overhead stream;

passing 1 to 17 percent of the overhead stream back to the top of said rectifier as a reflux stream, the pressure of said reflux stream being increased above the pressure of said overhead stream and then condensed;

directly introducing the bottoms of said rectifier as the feed to a demethanizer column;

directly returning the top stream of said demethanizer as a bottom feed to said rectifier;

withdrawing substantially all of said ethane and heavier components from the bottom of said demethanizer.

2. The process of claim 1 wherein the condenser is cooled by the top stream of said rectifier.

3. The process of claim 1 wherein the rectifier section and demethanizer column are separate vessels.

4. The process of claim 1 wherein the rectifier section and demethanizer are part of a common vessel.

5. The process of claim 1 and in addition reboiling at least a portion of liquid in the demethanizing column.

6. The process of claim 5 wherein at least two side reboilers and a bottom reboiler are used.

7. The process of claim 1 wherein a portion of the liquid in the rectifier section is reboiled.

8. The process of claim 1 wherein the feedstream has a temperature of between -100°

F. and -175°

F. and a pressure of between 250 and 450 pounds per square inch.