Liquid nitrogen generator and process

A process for production of liquid nitrogen from a system of columns comprised of a higher-pressure column, a lower-pressure column, a first condenser disposed in a bottom portion of the lower-pressure column, and a second condenser, the process comprising the steps of:

• purifying a feed air in a purification unit at a pressure greater than 15 bar(a) to yield a compressed dry air feed;
• cooling the compressed dry air feed in a heat exchanger;
• expanding a first portion of the compressed dry air feed in a cold turbine to form an expanded fluid;
• sending at least a portion of the expanded fluid to the higher-pressure column for separation therein;
• liquefying a second portion of the compressed dry air feed within the heat exchanger before sending at least a portion of the second portion of the compressed dry air feed to the higher-pressure column;
• sending an oxygen-rich liquid from a bottom portion of the higher-pressure column to an intermediate portion of the lower-pressure column;
• and
• sending a second oxygen-rich liquid from a bottom portion of the lower-pressure column to the second condenser, wherein at least a portion of the second oxygen-rich liquid is vaporized at less than 2 bar(a) to form a top gas, and wherein at least a portion of the top gas is warmed in the heat exchanger against the compressed dry air feed,
• mixing a first liquid nitrogen stream that was condensed by the first condenser with a second liquid nitrogen that was condensed by the second condenser to yield a liquid nitrogen product,
• wherein a lost air stream is warmed and expanded to less than 2 bar(a) in a warm turbine, wherein the lost air stream is selected from the group consisting of a portion of the expanded fluid from the cold turbine, a stream withdrawn from the higher-pressure column, and combinations thereof.