System and process for liquefying high pressure natural gas
First Claim
Patent Images
1. A process for liquefying a natural gas stream having a pressure greater than about 500 psig in a mixed refrigerant process to produce a liquefied natural gas product, the method comprising:
- a) cooling the natural gas stream in a heat exchanger in the mixed refrigerant process to a first temperature less than about −
40_F. to produce a cooled natural gas stream;
b) passing the cooled natural gas stream to a liquids separation zone to produce a first gas stream and a first liquids stream;
c) passing the first liquids stream to a methane separation tower at a temperature less than about −
40°
F. and at a pressure less than about 650 psig to produce a second gas stream comprising methane and a second liquids stream containing natural gas liquids;
d) passing the first gas stream to a turbo expander to reduce the pressure of the first gas stream to a pressure less than about 650 psig to produce a reduced pressure gas stream and passing the reduced pressure gas stream to the methane separation vessel;
e) driving a compressor with the turbo expander;
f) passing the second gas stream to the compressor and compressing the second gas stream to a pressure of at least about 500 psig to produce a compressed gas stream; and
, g) passing the compressed gas stream to the heat exchanger for liquefaction at a pressure of at least about 500 psig to produce the liquefied natural gas.
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Abstract
A system and a method for efficiently removing natural gas liquids from a natural gas stream at an elevated pressure and liquefying the natural gas stream at an elevated pressure by use of a turbo expander and a compressor.
116 Citations
23 Claims
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1. A process for liquefying a natural gas stream having a pressure greater than about 500 psig in a mixed refrigerant process to produce a liquefied natural gas product, the method comprising:
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a) cooling the natural gas stream in a heat exchanger in the mixed refrigerant process to a first temperature less than about −
40_F. to produce a cooled natural gas stream;
b) passing the cooled natural gas stream to a liquids separation zone to produce a first gas stream and a first liquids stream;
c) passing the first liquids stream to a methane separation tower at a temperature less than about −
40°
F. and at a pressure less than about 650 psig to produce a second gas stream comprising methane and a second liquids stream containing natural gas liquids;
d) passing the first gas stream to a turbo expander to reduce the pressure of the first gas stream to a pressure less than about 650 psig to produce a reduced pressure gas stream and passing the reduced pressure gas stream to the methane separation vessel;
e) driving a compressor with the turbo expander;
f) passing the second gas stream to the compressor and compressing the second gas stream to a pressure of at least about 500 psig to produce a compressed gas stream; and
,g) passing the compressed gas stream to the heat exchanger for liquefaction at a pressure of at least about 500 psig to produce the liquefied natural gas.
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2. The method of claim 1 wherein the first temperature is from about −
- 40 to about −
120°
F.
- 40 to about −
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3. The method of claim 1 wherein the first liquids stream is passed to the methane separation tower at a temperature from about −
- 40 to about −
120°
F.
- 40 to about −
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4. The method of claim 1 wherein the methane separation tower has an overhead temperature from about −
- 100 to about −
150°
F. and operatesat a pressure less than about 650 psig.
- 100 to about −
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5. The method of claim 1 wherein the second liquid stream is passed to a fractionator to produce a third gas stream and a stream comprising natural gas liquids.
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6. The method of claim 5 wherein the third gas stream is cooled, liquefied and pumped to combination with the compressed gas stream.
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7. The method of claim 1 wherein the compressor is also driven by a motor.
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8. The method of claim 1 wherein the reduced pressure gas stream is passed to a second separation zone to produce a third gas stream and a third liquid stream with the third gas stream being passed to the compressor and the third liquid stream being passed to the methane separation tower.
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9. A process for liquefying a natural gas stream having a pressure greater than about 500 psig in a natural gas liquefaction process to produce a liquefied natural gas product, the process comprising:
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a) cooling the natural gas stream in a heat exchanger in the natural gas liquefaction process to a first temperature less than about −
40°
F. to produce a cooled natural gas stream;
b) passing the cooled natural gas stream to a liquids separation zone to produce a first gas stream and a first liquids stream;
c) passing the first liquids stream to a methane separation tower at a temperature less than about −
40°
F. and at a pressure less than about 650 psig to produce a second gas stream comprising methane and a second liquids stream containing natural gas liquids;
d) passing the first gas stream to a turbo expander to reduce the pressure of the first gas stream to a pressure less than about 650 psig to produce a reduced pressure gas stream and passing the reduced pressure gas stream to the methane separation tower;
e) driving a compressor with the turbo expander;
f) passing the second gas stream to the compressor and compressing the second gas stream to a pressure of at least about 500 psig to produce a compressed gas stream; and
,g) passing the compressed gas stream to the heat exchanger for liquefaction at a pressure of at least about 500 psig to produce the liquefied natural gas.
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10. The method of claim 9 wherein the first temperature is from about −
- 40 to about −
120°
F.
- 40 to about −
-
11. The method of claim 9 wherein the first liquids stream is passed to the methane separator at a temperature from about −
- 40 to about −
120°
F.
- 40 to about −
-
12. The method of claim 9 wherein the methane separator is at a temperature from about −
- 100 to about −
120°
F. and at a pressure less than about 650 psig.
- 100 to about −
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13. The method of claim 9 wherein the second liquid stream is passed to a fractionator to produce a third gas stream and a stream comprising natural gas liquids.
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14. The method of claim 13 wherein the third gas stream is cooled, liquefied and pumped to combination with the compressed gas stream.
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15. The method of claim 9 wherein the compressor is also driven by a motor.
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16. The method of claim 9 wherein the reduced pressure gas stream is passed to a second separative zone to produce a third gas stream and a third liquid stream with the third gas stream being passed to the compressor and the third liquid stream being passed to the methane separation tower.
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17. A system for liquefying a natural gas stream having a pressure greater than about 500 psig, the system comprising:
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a) a refrigeration unit adapted to cool the natural gas to a temperature sufficient to liquefy at least a major portion of the natural gas, the refrigeration unit having an intermediate gas outlet, an intermediate gas inlet and a product liquefied natural gas outlet;
b) a separator in fluid communication with the intermediate gas outlet and having a gas outlet and a liquids outlet;
c) a methane separator tower in fluid communication with the liquids outlet and having an overhead gas outlet, a bottom liquid outlet and a gas inlet;
d) a turbo expander in fluid communication with the gas outlet from the separator and the gas inlet to the methane separator tower; and
,e) a compressor driven by the turbo expander and in fluid communication with the overhead gas outlet and having a compressed gas outlet in fluid communication with the intermediate gas inlet.
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18. The system of claim 17 wherein the system further comprises a fractionator in fluid communication with the bottom liquid outlet and having a separated gas outlet and a natural gas liquids outlet.
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19. The system of claim 18 wherein the separated gas outlet is in fluid communication via a heat exchanger, a pump and a line with the intermediate gas inlet.
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20. The system of claim 17 wherein the refrigeration unit comprises a plurality of heat exchange zones.
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21. A process for efficiently separating natural gas liquids from a natural gas stream at a pressure greater than about 500 psig to produce a high pressure gas stream and a natural gas liquids stream, the process comprising:
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a) cooling the natural gas stream to a first temperature less than about −
40°
F. to produce a cooled natural gas stream;
b) passing the cooled natural gas stream to a liquids separation zone to produce a first gas stream and a first liquids stream;
c) passing the first liquids stream to a methane separation vessel at a temperature less than about −
40°
F. and at a pressure less than about 650 psig to produce a second gas stream comprising methane and a second liquids stream containing natural gas liquids;
d) passing the first gas stream to a turbo expander to reduce the pressure of the first gas stream to a pressure less than about 650 psig to produce a reduced pressure gas stream and passing the reduced pressure gas stream to the methane separation tower;
e) driving a compressor with the turbo expander; and
,f) passing the second gas stream to the compressor and compressing the second gas stream to produce a high pressure compressed gas stream.
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22. The process of claim 21 wherein the second liquid stream is passed to a fractionator to produce a third gas stream and a stream comprising natural gas liquids.
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23. The method of claim 21 wherein the reduced pressure gas stream is passed to a second separation zone to produce a third gas stream and a third liquid stream with the third gas stream being passed to the compressor and the third liquid stream being passed to the methane separation tower.
Specification