Patent ID: 7059152

Claim:
A method of rejecting nitrogen from a feed natural gas stream comprising methane and nitrogen so as to form a primary methane product, the moie fraction of nitrogen in the feed natural gas increasing over a period of time, the method comprising cooling said feed natural gas stream, rectifying said cooled natural feed gas stream, and withdrawing from the rectification a primary product methane stream and a secondary nitrogen-enriched product stream from the rectification, wherein said secondary nitrogen-enriched product stream has a mole fraction of methane at or above a chosen minimum value when the said mole fraction of nitrogen is at a minimum, and when the said mole fraction of nitrogen rises to a value at which the mole fraction of methane in the secondary nitrogen-enriched product stream falls below the chosen minimum, a part of the feed gas is introduced into the secondary nitrogen-enriched product stream so as to restore its mole fraction of methane to the chosen minimum value or a value thereabove.