Nitrogen Rejection Unit System and Method for Low Nitrogen Concentration Feeds
OwnerRichard B. Hopewellinventor
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Abstract
A system and methods for removing nitrogen from a natural gas or liquid natural gas stream. More particularly, a system and method for removing nitrogen from a natural gas feed stream that uses a two-column system with a first column operating at a pressure that is lower than the operating pressure of the second column. A first nitrogen-enriched vapor stream from the first column is compressed and cooled and the resulting stream is then directed to the second column, which produces a second nitrogen-enriched vapor stream and a second methane-enriched liquid stream. Cooling in the system is provided in heat exchangers that warm a first methane-enriched liquid stream from the first column and the second methane-enriched liquid stream from the second column.
Claims24
A system for removing nitrogen from a natural gas fluid stream comprising:
- a. a feed stream heat exchanger configured to receive and cool the natural gas fluid stream;
- b. a first expansion device configured to receive and expand fluid from the feed stream heat exchanger;
- c. a first feed stream separation device configured to receive expanded fluid from the first expansion device, said first feed stream separation device including a vapor outlet and a liquid outlet;
- d. a first column in fluid communication with the liquid and vapor outlets of the first feed stream separation device and configured to operate at a first operating pressure, said first column including a first column vapor outlet and a first column liquid outlet and configured to so that a first nitrogen-enriched vapor stream exits the first column vapor outlet and a first methane-enriched liquid stream exits the first column liquid outlet;
- e. a first compressor configured to receive and compress the first nitrogen-enriched vapor stream;
- f. a first after-cooler configured to receive the compressed first nitrogen-enriched vapor stream from the first compressor;
- g. a second expansion device configured to received fluid from the first after-cooler;
- h. a second column in fluid communication with the second expansion device and configured to operate at a second operating pressure, where the second operating pressure is greater than the first operating pressure, said second column including a second column vapor outlet and a second column liquid outlet and configured so that a second nitrogen-enriched vapor stream exits the second column vapor outlet and a second methane-enriched liquid stream exits the second column liquid outlet;
- and
- i. said feed stream heat exchanger in fluid communication with the second column vapor outlet and the first and second column liquid outlets and configured to warm nitrogen-enriched fluid and methane-enriched fluid to provide refrigeration within the feed stream heat exchanger.
A method for removing nitrogen from a natural gas fluid feed stream comprising the steps of:
- directing a feed stream to a first column, wherein the first column operates at a first operating pressure;
- separating the feed stream into a first nitrogen-enriched vapor and a first methane-enriched liquid in the first column;
- compressing and cooling the first nitrogen-enriched vapor;
- directing the compressed and cooled first nitrogen-enriched vapor to a second column, wherein the second column operates at a second operating pressure that is greater than the first operating pressure;
- separating the first nitrogen-enriched vapor into a second nitrogen-enriched vapor and a second methane-enriched liquid in the second column;
- venting the second nitrogen-enriched vapor from the second column;
- and
- combining the first methane-enriched liquid from the first column and the second methane-enriched liquid from the second column so as to form a product methane-enriched liquid stream.
Dependencies are inferred from the claim text.