Nitrogen rejection from natural gas integrated with NGL recovery
AssigneeAir Products and Chemicals, Inc.
InventorsRuth A. Davis, Donn M. Herron, James W. Pervier, Harvey L. Vines
Life of this patent
Estimating the term…
Abstract
A process is set forth for the recovery of methane, nitrogen and natural gas liquids (C.sub.2+) from a natural gas feed stream wherein the recovery can be made at high pressure by the integration of a nitrogen rejection stage including a heat pump driven distillation column and a natural gas liquids stage. Nitrogen can be rejected over a wide range of nitrogen concentration (approximately 1 to about 80%) of the feed stream.
Claims14
A process for the recovery at high pressure of a substantially pure nitrogen product, an ethane-rich product and a methane-rich product from a methane-containing feed stream wherein the feed stream has a variable concentration of nitrogen comprising:
- (a) cooling a high pressure methane-containing feed stream comprising a variable nitrogen concentration of approximately 1 to 80 volume percent and separating said stream into an ethane-rich fraction and a nitrogen-rich fraction;
- (b) heat exchanging the nitrogen-rich fraction against a methane-rich stream wherein both streams are at relatively high pressure and reducing the nitrogen-rich fraction in pressure at least in part through an expander before introducing said nitrogen-rich fraction into a first high pressure distillation column;
- (c) driving said column with a closed loop heat pump refrigerant which condenses an overhead reflux stream, condenses an intermediate reflux stream and vaporizes a reboil stream to said distillation column wherein a portion of the refrigeration for the reflux of the column is produced by expanding the refrigerant through an expansion turbine;
- (d) removing a high pressure, substantially pure nitrogen product as an overhead stream from said column and rewarming it against the closed loop refrigerant and portions of the feed stream;
- (e) removing a methane-rich bottom stream from said column and introducing said stream into a second distillation column as reflux to recover additional hydrocarbon;
- (f) introducing the ethane-rich fraction of step (a) into said second distillation column;
- and
- (g) removing a methane-rich product at high pressure from the top of said second column and an ethane-rich product from the bottom of said second column.
An apparatus comprising elements designed, sized and arranged for the recovery at high pressure of a substantially pure nitrogen prodct, an ethane-rich product and a methane-rich product from a methane-containing feed stream wherein the feed stream has a variable concentration of approximately 1 to 80 volume percent nitrogen, including:
- (a) heat exchange means for cooling said feed stream in order to partially condense the stream and to rewarm a methane-rich stream at high pressure;
- (b) phase separator means for separating an ethane-rich liquid phase fraction from a nitrogen-rich vapor phase fraction;
- (c) an expander for reducing the pressure and temperature on at least a portion of the nitrogen-rich fraction;
- (d) a first distillation column operated at high pressure for the separation of a substantially pure nitrogen product as an overhead stream and a methane-rich bottom stream;
- (e) a closed loop heat pump refrigeration cycle which drives the first distillation column, including an expansion turbine wherein a portion of the refrigeration for the reflux of said column is supplied;
- (f) a second distillation column for the separation of the ethane-rich fraction of clause (b) and the methane rich bottom stream of clause (d) into a methane-rich product and an ethane-rich product.
Dependencies are inferred from the claim text.