Patent ID: 8776546

Claim:
A process for separating air using a cryogenic distillation system, the cryogenic distillation system comprising an air compressor, an air purifier, a heat exchanger, a distillation column, a LIN tank, a lower-liquid level controller, a LIN valve, a rich liquid expansion valve, the process comprising the steps of: a) compressing an air feed in the air compressor to form a compressed air feed; b) removing impurities from the compressed air feed in the air purifier; c) cooling the compressed air feed in the heat exchanger to form a cooled air stream; d) introducing the cooled air stream to the distillation column, the distillation column configured to separate nitrogen and oxygen; e) introducing a first amount of liquid nitrogen from the LIN tank to the distillation column; f) extracting nitrogen from the distillation column at a nominal flow rate; and g) measuring a liquid level of rich liquid near a bottom of the distillation column, wherein the cryogenic distillation system is configured to produce a second flow rate of nitrogen that is greater than the nominal flow rate by allowing an increased flow of liquid nitrogen from the LIN tank to the distillation column when the liquid level of the rich liquid near the bottom of the distillation column is at or below a maximum set point, wherein the increased flow of liquid nitrogen is in an amount greater than the amount needed to compensate for the second flow rate of nitrogen, thereby causing the liquid level of the rich liquid at the bottom of the distillation column to increase, h) extracting rich liquid from the distillation column; i) expanding the rich liquid across the rich liquid expansion valve; and j)introducing the expanded rich liquid to a condenser in thermal communication with the distillation column to provide additional refrigeration to the distillation column.