Patent ID: 6609393
Filing Date: 2003-08-26
Classification: C07C,F25J,Y10S

Abstract:
A method of rejecting nitrogen from a feed gas stream comprising methane and nitrogen so as to form a methane product, comprising:cooling the feed gas stream in a main heat exchanger; rectifying the cooled feed gas stream in a double rectification column comprising a higher pressure rectification column, a lower pressure rectification column, and a condenser-reboiler placing the higher pressure rectification column in heat exchange relationship with the lower pressure rectification column; recycling a flow of gas from the lower pressure rectification column to the higher pressure rectification column, a first part of the recycle gas flow being compressed, cooled, liquefied in the condenser-reboiler and introduced at least in part into the higher pressure rectification column; withdrawing a product methane stream in liquid state from the lower pressure rectification column; raising the pressure of the liquid product methane stream, and vaporising the liquid product methane stream at least partly in the main heat exchanger; wherein a second part of the recycle gas flow is compressed, is cooled, is liquefied in the main heat exchanger or by expansion, and is introduced into the double rectification column in liquid state, and at least part of the cooling of both parts of the recycle gas flow is performed in the main heat exchanger.