A liquefaction system includes a source tank containing a supply of liquid nitrogen with a head space there above filled with nitrogen vapor. A pump transfers the liquid nitrogen to a heat exchanger. The heat exchanger also receives natural gas that has been processed in a purifier. The natural gas is liquefied by free cold from the liquid nitrogen so that liquid natural gas (LNG) is produced. The LNG travels to an LNG destination tank for storage and/or transport. The liquid nitrogen is vaporized in the heat exchanger. The resulting nitrogen gas is directed to a process system that may include, for example, cylinders for welding or other applications. Between liquefaction cycles, the purifier is regenerated by a vacuum and nitrogen vapor from the head space of the source tank. Steel shot is mixed with absorbent in the purifier so that the absorbent is cooled for increased performance.