Process for separating Nitrogen from a natural gas stream with Nitrogen stripping in the production of liquefied natural gas

• US 20110289963A1
• Filed: 04/16/2010
• Published: 12/01/2011
• Est. Priority Date: 04/16/2010
• Status: Active Grant

• Current Assignee: Black & Veatch International Company (Black & Veatch Corporation)
• Original Assignee: Black & Veatch Corporation
• Inventors: Price, Brian C.
• Granted Patent: US 10,113,127 B2
• Time in Patent Office: Days
• US Class Current: 62/620
• CPC Class Codes: C10L 3/105 of nitrogen
• CPC Class Codes: F25J 1/0047 using an "external" refrigerant stream in a closed vapor compression cycle F25J1/0221, F25J1/0225 take precedence
• CPC Class Codes: F25J 2200/02 in a single pressure main column system
• CPC Class Codes: F25J 2200/04 in a dual pressure main column system
• CPC Class Codes: F25J 2200/70 Refluxing the column with a condensed part of the feed stream, i.e. fractionator top is stripped or self-rectified
• CPC Class Codes: F25J 2200/78 Refluxing the column with a liquid stream originating from an upstream or downstream fractionator column
• CPC Class Codes: F25J 2205/04 in the feed line, i.e. upstream of the fractionation step
• CPC Class Codes: F25J 2210/06 Splitting of the feed stream, e.g. for treating or cooling in different ways
• CPC Class Codes: F25J 2215/04 Recovery of liquid products
• CPC Class Codes: F25J 2220/62 Separating low boiling components, e.g. He, H2, N2, Air
• CPC Class Codes: F25J 2260/20 Integration in an installation for liquefying or solidifying a fluid stream
• CPC Class Codes: F25J 2270/12 External refrigeration with liquid vaporising loop
• CPC Class Codes: F25J 2270/66 Closed external refrigeration cycle with multi component refrigerant [MCR], e.g. mixture of hydrocarbons
• CPC Class Codes: F25J 3/0209 Natural gas or substitute natural gas
• CPC Class Codes: F25J 3/0233 separation of CnHm with 1 carbon atom or more
• CPC Class Codes: F25J 3/0257 separation of nitrogen from air F25J3/04, production of nitrogen in general C01B21/00

Abstract

A mixed single refrigerant process for separating a nitrogen gas stream from a natural gas stream containing nitrogen to produce a nitrogen gas stream from a liquefied natural gas stream wherein the separated nitrogen gas stream is used as a refrigerant for the natural gas stream and wherein the mixed refrigerant provides cooling for the process.

Claims

1. A single mixed refrigerant process for separating a nitrogen gas stream from a natural gas stream containing nitrogen to produce the nitrogen gas stream and a liquefied natural gas stream, the process consisting essentially of:

a) cooling the natural gas stream in a single mixed refrigerant heat exchanger to produce a cooled natural gas stream;

b) separating the natural gas stream in a separator and recovering a concentrated methane rich liquid stream and a concentrated nitrogen rich vapor stream from the separator;

c) further cooling the concentrated methane rich liquid in the heat exchanger and recovering a first liquefied natural gas stream from the heat exchanger;

d) passing the first liquefied natural gas stream to a nitrogen stripping column;

e) passing the concentrated nitrogen vapor stream to the nitrogen stripping column;

f) recovering a product liquefied natural gas from a lower portion of the nitrogen stripping column; and

,

g) recovering an overhead nitrogen stream from near the top of the nitrogen stripping column and passing the overhead nitrogen stream to the heat exchanger as a refrigerant.

2. The process of claim 1 wherein the concentrated nitrogen vapor stream is passed from the separator to heat exchange in a nitrogen stripping tower reboiler to cool the concentrated nitrogen vapor stream.

3. The process of claim 1 wherein overhead nitrogen stream is further cooled by heat exchange with the concentrated nitrogen vapor stream.

4. The process of claim 1 wherein the separator is a distillation column.

5. The process of claim 1 wherein a cooled natural gas stream containing a methane rich liquid stream and a nitrogen rich vapor stream is withdrawn from the heat exchanger and split into a first portion and a second portion with the first portion being charged to a lower portion of the distillation column and the second portion being returned to the heat exchanger for further cooling and then withdrawn downstream of the point at which the first portion was withdrawn.

6. The process of claim 6 wherein at least a portion of a bottom stream from the high pressure distillation column is passed into the heat exchanger at a point downstream from the point at which the second portion is withdrawn from the heat exchanger.