Dual column nitrogen producing air separation unit with split kettle reboil and integrated condenser-reboiler

Patent metadata

Field	Value
Publication number	US-11674750-B2
Application number	US-202117234080-A
Country	US
Kind code	B2
Filing date	Apr 19, 2021
Priority date	Jun 4, 2020
Publication date	Jun 13, 2023
Grant date	Jun 13, 2023

Abstract

Enhancements to a dual column, nitrogen producing cryogenic air separation unit are provided. Such enhancements include an improved air separation cycle that uses multiple condenser-reboilers and recycles a portion of the vapor from one or more of the condenser-reboilers to the incoming feed stream and or the compressed purified air streams to yield improvements in such dual column, nitrogen producing cryogenic air separation units. The multiple condenser-reboilers preferably include an integrated condenser-reboiler arrangement comprising a heat exchanger having a set of nitrogen condensing passages, a first set and second set of boiling passages, and a phase separator.

First claim

What is claimed is:

1. An air separation unit comprising:
a distillation column system comprises a higher pressure column and a lower pressure column linked in a heat transfer relationship via an integrated condenser-reboiler arrangement;
a main air compression system configured for receiving a stream of incoming feed air and producing a compressed air stream;
an adsorption based pre-purifier unit configured for removing impurities from the compressed air stream and producing the compressed, purified air stream; and
a main heat exchange system configured to cool the compressed and purified air stream to temperatures suitable for fractional distillation;
wherein the higher pressure column is configured to receive a cooled, compressed, purified air stream and produce a nitrogen enriched overhead and an oxygen-enriched kettle stream;
wherein the lower pressure column is configured to produce a lower pressure nitrogen product stream, an overhead stream and an oxygen-enriched bottoms;
wherein the integrated condenser-reboiler arrangement is configured to condense a portion of the nitrogen enriched overhead from the higher pressure column against a split kettle stream from the higher pressure column to produce a liquid nitrogen stream, a recycle stream and a vaporized boil off stream;
wherein the split kettle stream comprises a first kettle stream and a second kettle stream and wherein the first kettle stream is fed into a bottom portion of the integrated condenser-reboiler arrangement and partially vaporized in the integrated condenser-reboiler arrangement with the vapor portion forming the recycle stream, and wherein the second kettle stream is vaporized or partially vaporized in the integrated condenser-reboiler arrangement to form the vaporized boil off stream that is directed to or released into the lower pressure column;
wherein another portion of the nitrogen enriched overhead from the higher pressure column is taken as a high pressure nitrogen product stream;
wherein the distillation column system further comprises another condenser-reboiler distinct from the integrated condenser-reboiler, the another condenser-reboiler is operatively associated with the lower pressure column and configured to condense the nitrogen overhead from the lower pressure column against the oxygen bottoms from the lower pressure column to produce a nitrogen reflux stream for the lower pressure column and a waste stream;
wherein the integrated condenser-reboiler arrangement further comprises:
a heat exchanger shell;
a first set of boiling passages disposed within the heat exchanger shell and configured to partially vaporize the first kettle stream;
a second set of boiling passages disposed within the heat exchanger shell and configured to vaporize or partially vaporize the second kettle stream to form the vaporized boil off stream; and
a phase separator in fluid communication with the first and second set of boiling passages;
wherein the first kettle stream is partially vaporized in the first set of boiling passages with the resulting two phase boil off stream directed to the phase separator;
wherein the phase separator is configured to separate the two phase boil off stream into the second kettle stream and the recycle stream; and
wherein the recycle stream from the integrated condenser-reboiler arrangement is directed to the main heat exchange system where it cools the compressed and purified air stream via indirect heat exchange to produce a warm recycle stream and the warm recycle stream is directed to the main air compression system.

2. An air separation unit comprising:
a distillation column system comprises a higher pressure column and a lower pressure column linked in a heat transfer relationship via an integrated condenser-reboiler arrangement;
a main air compression system configured for receiving a stream of incoming feed air and producing a compressed air stream;
an adsorption based pre-purifier unit configured for removing impurities from the compressed air stream and producing the compressed, purified air stream; and
a main heat exchange system configured to cool the compressed and purified air stream to temperatures suitable for fractional distillation;
wherein the higher pressure column is configured to receive a cooled, compressed, purified air stream and produce a nitrogen enriched overhead and an oxygen-enriched kettle stream;
wherein the lower pressure column is configured to produce a lower pressure nitrogen product stream, an overhead stream and an oxygen-enriched bottoms;
wherein the integrated condenser-reboiler arrangement is configured to condense a portion of the nitrogen enriched overhead from the higher pressure column against a split kettle stream from the higher pressure column to produce a liquid nitrogen stream, a recycle stream and a vaporized boil off stream;
wherein the split kettle stream comprises a first kettle stream and a second kettle stream and wherein the first kettle stream is fed into a bottom portion of the integrated condenser-reboiler arrangement and partially vaporized in the integrated condenser-reboiler arrangement with the vapor portion forming the recycle stream, and wherein the second kettle stream is vaporized or partially vaporized in the integrated condenser-reboiler arrangement to form the vaporized boil off stream that is directed to or released into the lower pressure column;
wherein another portion of the nitrogen enriched overhead from the higher pressure column is taken as a high pressure nitrogen product stream;
wherein the distillation column system further comprises another condenser-reboiler distinct from the integrated condenser-reboiler, the another condenser-reboiler is operatively associated with the lower pressure column and configured to condense the nitrogen overhead from the lower pressure column against the oxygen bottoms from the lower pressure column to produce a nitrogen reflux stream for the lower pressure column and a waste stream;
wherein the integrated condenser-reboiler arrangement further comprises:
an outer phase separator;
an inner condenser-reboiler disposed within the outer phase separator;
a first set of boiling passages disposed within the inner condenser-reboiler and configured to receive and partially vaporize the first kettle stream;
a second set of boiling passages disposed within the inner condenser-reboiler and configured to receive and vaporize or partially vaporize the second kettle stream to form the vaporized boil off stream; and
wherein the two phase boil off stream exiting the first set of boiling passages is released into the outer phase separator;
wherein liquid within the outer phase separator forms the second kettle stream and is directed to the second set of boiling passages while the vapor within the outer phase separator is recycled as the recycle stream; and
wherein the recycle stream from the integrated condenser-reboiler arrangement is directed to the main heat exchange system where it cools the compressed and purified air stream via indirect heat exchange to produce a warm recycle stream and the warm recycle stream is directed to the main air compression system.

3. The air separation unit of claim 2 , wherein the integrated condenser-reboiler arrangement is disposed within the lower pressure column.

4. The air separation unit of claim 2 , wherein the integrated condenser-reboiler arrangement is disposed outside the lower pressure column in a separate vessel.

Assignees

• Tuo Hanfei
• Xu Zhengrong
• Praxair Technology Inc

Inventors

• Tuo Hanfei
• Xu Zhengrong

Classifications

• F25J3/04412 Primary

  in a classical double column flowsheet, i.e. with thermal coupling by a main reboiler-condenser in the bottom of low pressure respectively top of high pressure column · CPC title

• F25J3/04303 Primary

  Lachmann expansion, i.e. expanded into oxygen producing or low pressure column · CPC title

• F25J3/0257

  separation of nitrogen (from air F25J3/04, production of nitrogen in general C01B21/00) · CPC title

• F25J2200/54

  in the low pressure column of a double pressure main column system · CPC title

• F25J3/04012

  by compression of warm gaseous streams; details of intake or interstage cooling (F25J3/04048 takes precedence; operation of compressors F25J3/04781; particular layout of compressors used in air fractionation units F25J3/04866) · CPC title