Heavy hydrocarbon removal system for lean natural gas liquefaction
AssigneeAir Products and Chemicals, Inc.
InventorsFei Chen, Mark Julian Roberts, Christopher Michael Ott, Annemarie Ott Weist
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Abstract
A system and method for integrated heavy hydrocarbon removal in a liquefaction system having a lean natural gas source. An economizer located between a main cryogenic heat exchanger and a reflux drum is provided to cool an overhead vapor stream against a partially condensed stream. In addition, pressure of the natural gas feed stream is maintained into a scrub column. A pressure drop is provided by a valve located between the economizer and the reflux drum on a partially condensed stream withdrawn from the cold end of the warm section of the main cryogenic heat exchanger.
Claims12
A method of steady state operation of a system for liquefying natural gas, the method comprising:
- (a) performing a closed-loop compression sequence on a warm first refrigerant stream withdrawn from a warm side of a main heat exchanger, the compression sequence comprising compressing and cooling the warm first refrigerant stream to produce at least one cooled, compressed first refrigerant stream;
- (b) withdrawing a natural gas feed stream from a natural gas feed source at a source pressure;
- (c) introducing the natural gas feed stream into a scrub column at a scrub column pressure, the scrub column having a top section and a bottom section;
- (d) separating the natural gas feed stream in the scrub column into a methane-rich vapor fraction, collected as a first overhead vapor stream at a top end of the scrub column, and a heavy hydrocarbon-enriched fraction, collected as a first bottoms liquid stream at a bottom end of the scrub column;
- (e) withdrawing the first bottoms liquid stream from the scrub column, the first bottoms liquid stream being a heavy hydrocarbon enriched natural gas stream;
- (f) withdrawing the first overhead vapor stream from the scrub column, the first overhead vapor stream being a methane-enriched natural gas stream;
- (g) introducing at a warm end of a warm section of a main heat exchanger, the first overhead vapor stream into a natural gas circuit, and each of the at least one cooled-compressed first refrigerant stream into a refrigerant circuit;
- (h) in at least one of the refrigerant circuits, withdrawing and reducing a pressure of an overhead refrigerant stream to produce a reduced pressure overhead refrigerant stream and introducing the reduced pressure overhead refrigerant stream into a cold side of the main heat exchanger;
- (i) providing indirect heat exchange between the warm side and the cold side of the main heat exchanger;
- (j) producing a product stream from the natural gas circuit at a cold end of the main heat exchanger, the product stream being at least partially liquefied;
- (k) withdrawing a two-phase natural gas stream from the natural gas circuit at a cold end of the warm section of the main heat exchanger;
- (l) reducing a pressure of the two-phase natural gas stream to form a reduced pressure two-phase natural gas stream;
- (m) introducing the reduced pressure two-phase natural gas stream into a reflux drum at an intermediate natural gas temperature;
- (n) separating the reduced pressure two-phase natural gas stream into a reflux drum liquid stream and a reflux drum vapor stream;
- (o) introducing the reflux drum vapor stream into the natural gas circuit at a location in the main heat exchanger that is closer to a cold end of the main heat exchanger than the cold end of the warm section;
- (p) increasing a pressure of the reflux drum liquid stream and introducing the reflux drum liquid stream into the top section of the scrub column;
- and
- (q) providing indirect heat exchange between the reflux drum vapor stream and the two-phase natural gas stream by which the two-phase natural gas stream is cooled against the reflux drum vapor stream.
Dependencies are inferred from the claim text.