Process for natural gas liquefaction

1. A process for the offshore liquefaction of a natural gas feed produced in association with offshore crude oil production, the process-comprising:

(a) contacting the natural gas feed with a biphasic non-flammable refrigerant at a temperature T 1 , wherein the biphasic non-flammable refrigerant operating in a closed loop vapor compression cycle accounts for a first portion of a total electrical load;

(b) contacting the natural gas feed with a first gaseous refrigerant operating in a closed loop compressor loaded single expander cycle at a temperature T 2 ;

(c) expanding the refrigerated natural gas feed using an expansion device to form a flash gas stream and a liquefied natural gas stream; wherein T 1 and T 2 satisfy the inequality T 1 ≧T 2 , wherein at least a portion of the first gaseous refrigerant following contact with the natural gas feed is expanded in a isentropic process and used to further cool the natural gas feed; and wherein the first gaseous refrigerant operating in a closed loop compressor loaded expander cycle accounts for a second portion of the total electrical load, wherein the second portion of the total electrical load is at least 65% of the total electrical load; wherein the liquefaction takes place in one cryogenic heat exchanger; and wherein at least a portion of the biphasic refrigerant contacts the natural gas feed upstream of the cryogenic heat exchanger.

2. The process of claim 1 , wherein the biphasic non-flammable refrigerant is a liquid-gaseous refrigerant.

3. The process of claim 1 , wherein the biphasic non-flammable refrigerant operates in the closed loop vapor compression cycle in a low pressure level kettle.

4. The process of claim 3 , wherein the vapor compression cycle is electric motor driven.

5. The process of claim 1 , wherein the first gaseous refrigerant comprises substantially nitrogen.

6. The process of claim 1 , wherein the closed loop compressor loaded single expander cycle is gas turbine driven.

7. The process of claim 1 , wherein the natural gas feed is pre-treated to recover any less volatile hydrocarbons that is present in the natural gas feed prior to the liquefaction process.

8. The process of claim 7 , wherein the less volatile hydrocarbons are returned to a crude production facility for management.

9. The process of claim 1 , wherein a separate LPG stream is recovered in addition to the liquefied natural gas stream.

10. The process of claim 1 , wherein ethane, propane and butane are retained in the liquefied natural gas stream.

11. The process of claim 1 , wherein the expansion device is selected from the group consisting of:

an expansion valve,

a liquid turbine with a liquid outlet followed by an expansion valve,

a flashing expander, and

a turboexpander.

12. The process of claim 1 , wherein more than one pressure of the flash gas stream is:

(1) returned to the cryogenic heat exchanger,

(2) warmed, and

(3) fed to a flash gas compressor.

13. The process of claim 1 , wherein the natural gas feed undergoes dehydration and mercury removal prior to liquefaction.

14. The process of claim 13 further comprising:

compressing the flash gas stream to at least the pressure of the natural gas feed after dehydration and mercury removal; and

mixing the flash gas stream with the natural gas feed.

15. The process of claim 14 , wherein the step of mixing the flash gas stream with the natural gas feed further includes:

compressing mixed flash gas stream and natural gas feed in at least one stage of compression prior to forming a liquefied natural gas stream.

16. The process of claim 1 , wherein the flash gas stream is recycled for use as a second gaseous refrigerant in the liquefaction process, contacting the natural gas feed at a temperature T 3 , wherein T 2 and T 3 satisfy the inequality T 2 ≧T 3 .

17. The process of claim 1 , wherein at least a portion of the biphasic refrigerant contacts the natural gas feed upstream of, and only upstream of, the cryogenic heat exchanger.