The HTGN utilizes a cryogenic distillation process with a waste gas expansion cycle to produce from 400 to 1200 Nm3/hr. Custom plant sizes are available on request. The plant can be operated in either self-refrigerated (liquefier ON) or liquid add (liquefier OFF) mode. In self-refrigerated mode, the liquefier provides sufficient process refrigeration for production of product nitrogen gas and an additional stream of liquid nitrogen which can be utilized for back-up and peak shaving. In liquid add mode, a small stream of liquid nitrogen, approximately 3% of total nitrogen product, is withdrawn from the liquid nitrogen storage tank to provide the required process refrigeration. The liquid add nitrogen is later recovered to the product nitrogen stream.