US 5,390,499 AGranted

Process to increase natural gas methane content

AssigneeLiquid Carbonic Corporation

InventorsGeorge D. Rhoades, Robert J. Golueke

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Abstract

The present invention is directed to a process for purifying natural gas to provide a liquified natural gas product which is substantially pure methane. In the process, a natural gas feed stream is introduced into indirect countercurrent heat exchange in a first heat exchanger to cool the natural gas to below the dew point of ethane and higher hydrocarbons so as to separate the feed stream into a gas which is substantially pure methane and liquid which contains the ethane and higher hydrocarbons. The liquid/gas mixture is transferred to a separator where the gas occupies the head space of the separator and the liquid occupies the bottom of the separator. A gas fraction is removed from the top of the separator and is introduced into countercurrent heat exchange with liquid nitrogen in a second heat exchanger so as to liquefy the substantially pure methane gas. Liquid nitrogen is introduced into a third heat exchanger where the liquid nitrogen is mixed with a recycled portion of nitrogen vapor is mixed with a recycled portion of nitrogen vapor exiting from the second heat exchanger to provide a liquid nitrogen feed stream for the second heat exchanger.

Claims13

Dependent claims

A process for purifying natural gas comprising:

(a) introducing a natural gas feed stream into indirect countercurrent heat exchange in a first heat exchanger to cool said natural gas to the dew point of C.sub.2 and higher hydrocarbons so as to provide a mixture consisting of a gas which is substantially pure methane and a liquid containing C.sub.2 and higher hydrocarbons;
(b) transferring said mixture to a separator;
(c) removing a gas fraction from the top of said separator and introducing said gas fraction to a second heat exchanger into countercurrent heat exchange with liquid nitrogen so as to provide a purified liquid methane product,
(d) introducing liquid nitrogen into a third heat exchanger where said liquid nitrogen is mixed with a recycle portion of gaseous nitrogen exiting from said second heat exchanger to provide a liquid nitrogen feed stream for said second heat exchanger;
(e) dividing the gaseous nitrogen exiting from said second heat exchanger into a recycle portion for introduction into said third heat exchanger and a heat exchange portion for introduction into indirect countercurrent heat exchange with said natural gas feed stream into said first heat exchanger;
and
(f) removing a liquid fraction containing C.sub.2 and higher hydrocarbons from the bottom of said separator and introducing said liquid fraction into indirect countercurrent heat exchange with said natural gas feed stream in said first heat exchanger.

4 more elements

Dependencies are inferred from the claim text.

Facts

Application: 08/143,924Filed 27 Oct 1993
Granted: 21 Feb 1995
Term ends: Not estimatedThe source records don’t support an estimate.

Classification9 codes

F25J 1/0045
Using the feed stream itself or separated fractions from it, i.e. "internal refrigeration": by vaporising a liquid return stream
F25J 1/0022
Characterised by the fluid to be liquefied: hydrocarbons, e.g. natural gas
F25J 1/0221
Requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units…:…
F25J 1/0255
Controlling particular process parameter, e.g. pressure, temperature: controlling the composition of the feed or liquefied gas, e.g. to achieve a…