Cryogenic liquefier by integration with power plant

A method for producing liquid nitrogen, the method comprising the steps of:

• providing a residual gas stream, wherein the residual gas stream is sourced from a retentate stream of a cold membrane, wherein the residual gas stream comprises nitrogen, argon, oxygen, and carbon dioxide;
• purifying the residual gas stream in a front-end purification unit to remove carbon dioxide, thereby forming a purified residual gas stream;
• compressing the purified residual gas stream in a first compressor to form a pressurized residual gas stream;
• introducing the pressurized residual gas stream to a cold box, wherein a first portion of the pressurized residual gas stream is cooled in a main heat exchanger, expanded within the cold box, and then fed to a distillation column system for separation therein, thereby forming a nitrogen stream and a waste stream;
• withdrawing the waste stream from the distillation column system and warming said waste stream;
• and
• withdrawing the nitrogen stream from the distillation column system and compressing the nitrogen stream in a second compressor before liquefying the nitrogen stream within the cold box to produce a liquid nitrogen stream,
• wherein at least a portion of the liquid nitrogen stream is stored in a liquid nitrogen tank;
• wherein a second portion of the pressurized residual gas stream is partially cooled in the main heat exchanger and then expanded in a plurality of cold turbines;
• wherein the second compressor is a cold compressor operating with an inlet temperature less than −100 C.