Patent ID: 6449984
Filing Date: 2002-09-17
Classification: F25J,Y02C,Y10S

Abstract:
A process for liquefaction of and nitrogen extraction from natural gas under pressure containing methane, C2, and higher hydrocarbons and nitrogen in order to obtain liquefied natural gas essentially free of nitrogen, and gaseous nitrogen essentially free of hydrocarbons, the process includinga first step in which natural gas is cooled, has its pressure reduced, and is liquefied in order to provide pressure-reduced liquefied natural gas flow and the pressure-reduced liquefied natural gas is separated, in a first fractionation column containing a number of stages, into a first top fraction that is more volatile and that is nitrogen enriched, relative to a bottom fraction, and collected in a last stage of the first fractionation column; and a second step in which the first top fraction is cooled and liquefied in order to provide a first cooled and liquefied fraction, that is separated into a second top fraction that is more volatile and nitrogen enriched relative to a second bottom fraction, the second bottom fraction is introduced into a last stage of the first fractionation column, the second top fraction is heated in order to produce gaseous nitrogen, and, the first bottom fraction is cooled in order to produce liquefied natural gas essentially free of nitrogen.