Process and system for liquefying natural gas

• US 6,324,867 B1
• Filed: 05/18/2000
• Issued: 12/04/2001
• Est. Priority Date: 06/15/1999
• Status: Expired due to Term

• Current Assignee: Mobil Oil Corporation (Exxon Mobil Corporation)
• Original Assignee: Exxonmobil Oil Corporation (Exxon Mobil Corporation)
• Inventors: Ryberg, Brett L., Smith, Bruce K., Phan, Luan D., Fanning, Robert A.
• Primary Examiner(s): CAPOSSELA, RONALD C
• Application Number:
  US09/574,940
• Time in Patent Office: 565 Days
• Field of Search: 626/11, 626/12, 626/13, 629/12, 607/28
• US Class Current: 62/613
• CPC Class Codes: F25J 1/0022 Hydrocarbons, e.g. natural gas
• CPC Class Codes: F25J 1/0052 by vaporising a liquid refrigerant stream
• CPC Class Codes: F25J 1/0055 originating from an incorporated cascade
• CPC Class Codes: F25J 1/0087 Propane; Propylene
• CPC Class Codes: F25J 1/0216 using a C3 pre-cooling cycle
• CPC Class Codes: F25J 1/0236 providing refrigeration for different processes treating not the same feed stream
• CPC Class Codes: F25J 1/0283 Gas turbine as the prime mechanical driver
• CPC Class Codes: F25J 1/0292 Refrigerant compression by cold or cryogenic suction of the refrigerant gas
• CPC Class Codes: F25J 2220/64 Separating heavy hydrocarbons, e.g. NGL, LPG, C4+ hydrocarbons or heavy condensates in general
• CPC Class Codes: Y10S 62/912 External refrigeration system

Abstract

A natural gas liquefaction system and process wherein excess refrigeration available in a typical natural gas liquefaction system is used to cool the inlet air to gas turbines in the system to thereby improve the overall efficiency of the system. A cooler is positioned in front of the air inlet of each gas turbine; and coolant (e.g. water) is flowed through each of the coolers to cool the ambient air as it flows into the gas turbines. The water, in turn, is cooled with propane taken from a refrigerant circuit in the system which, in turn, is used to initially cool the natural gas which is to be liquefied.

Claims

1. A method for processing natural gas to produce liquefied natural gas, said method comprising the steps of:

(a) cooling said natural gas in one or more heat exchangers using a first refrigerant from a first refrigerant circuit in which said first refrigerant is compressed in a first compressor driven by a first gas turbine having a first inlet air stream; and

(b) liquefying said natural gas using a second refrigerant, which second refrigerant is compressed in a second compressor driven by a second gas turbine having a second inlet air stream,

wherein at least one of said first and second inlet air streams is cooled with said first refrigerant from said first refrigerant circuit.

2. The method of claim 1 wherein at least one of said first and second inlet air streams is cooled to a temperature of no lower than about 5°

C. (41°

F.).

3. The method of claim 1 wherein said first refrigerant is propane.

4. A method for improving the efficiency of a process for producing liquefied natural gas, said process comprising the steps of (a) cooling said natural gas in one or more heat exchangers using a first refrigerant from a first refrigerant circuit in which said first refrigerant is compressed in a first compressor driven by a first gas turbine having a first inlet air stream and (b) liquefying said natural gas using a second refrigerant, which second refrigerant is compressed in a second compressor driven by a second gas turbine having a second inlet air stream, said method comprising cooling at least one of said first and second inlet air streams with said first refrigerant from said first refrigerant circuit.

5. The method of claim 4 wherein at least one of said first and second inlet air streams is cooled to a temperature of no lower than about 5°

C. (41°

F.).

6. The method of claim 4 wherein said first refrigerant is propane.

7. A system for liquefying natural gas comprising:

a first refrigerant circuit of a first refrigerant for initially cooling said natural gas;

a first compressor for compressing said first refrigerant as said first refrigerant flows through said first refrigerant circuit;

a first gas turbine for driving said first compressor, said first gas turbine having a first inlet air stream;

a second refrigerant circuit of a second refrigerant for liquefying said natural gas;

a second compressor for compress said second refrigerant as said second refrigerant flows through said second refrigerant circuit; and

a second gas turbine for driving said second compressor, said second gas turbine having a second inlet air stream,

wherein at least one of said first and second inlet air streams is cooled with said first refrigerant from said first refrigerant circuit.

8. The system of claim 7 wherein at least one of said first and second inlet air streams is cooled to a temperature of no lower than about 5°

C. (41°

F.).

9. The system of claim 7 wherein said first refrigerant is propane.