NOVELTY - The method involves routing the natural gas stream from main liquefaction process including refrigeration cycles external to a nitrogen rejection unit. A distillation column is optional when the gas stream has about 50 mole% of nitrogen. A gas stream is condensed through a partial or full condenser (28) such as shell and tube exchanger by utilizing a refrigerant to transfer heat in cycles to form condensed stream. A portion of condensed stream is routed to other distillation column to separate a portion of gas stream into top and bottom fractions.    USE - Method for removing nitrogen from natural gas stream e.g. methane gas stream, used in LNG facility (all claimed). Can also be used in using methane gas stream as energy source or industrial feedstock used in manufacture of plastics.    ADVANTAGE - The nitrogen separation efficiency is increased during an LNG process and emissions of potentially environmentally-hazardous materials are reduced. The process efficiency over many existing nitrogen rejection unit technologies is improved and providing stable operation for both nitrogen rejection unit and main process. The stability of operation is improved. The nitrogen, helium, and/or argon separation efficiency is increased. The overall greenhouse emission and hydrocarbon emission are reduced. The LNG process stability is increased. The integrated nitrogen rejection unit integrates external heat and refrigerant sources contained within an LNG or gas plant to enhance thermal and separation efficiency as well as overall operating flexibility and stability.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) a nitrogen rejection unit;    (2) an liquefied natural gas (LNG) facility;    (3) a method for liquefying a methane gas stream; and    (4) a nitrogen removal unit.    DESCRIPTION OF DRAWING(S) - The drawing shows a flow diagram illustrating cascade refrigeration process for LNG production employing an integrated nitrogen rejection unit.    Partially or full condenser (28)    Ethylene economizer (34)    Ethylene compressor (48)    Heavies removal column (60)    Heat exchanger (62)