Method for natural gas and nitrogen liquefaction

A process for producing liquefied natural gas and a liquid nitrogen stream comprising at least the following steps: - Step a): production of nitrogen gas by an air separation unit (ASU); - Step b): liquefying a natural gas stream in a natural gas liquefaction unit comprising a main heat exchanger and a refrigeration generating system; - Step c): Liquefaction of the nitrogen stream from step a) in said main exchanger of the natural gas liquefaction unit in parallel to the liquefied natural gas in step b); characterized in that all the cold required for liquefaction of the nitrogen stream and to the liquefaction of natural gas is supplied by said system (8) for producing refrigeration of natural gas liquefaction unit.