Patent ID: 6962062

Claim:
A process for separating air by cryogenic distillation in a column system comprising a high pressure column and a low pressure column comprising the steps of: i. compressing all the feed air in a first compressor to a first outlet pressure, ii. sending a first part of the air at the first outlet pressure to a second compressor and compressing the air to a second outlet pressure, iii. cooling at least part of the air at the second outlet pressure in a heat exchanger to form cooled compressed air at the second outlet pressure, sending at least part of the cooled compressed air at the second outlet pressure to a third compressor and compressing the at least part of the cooled compressed air at the second outlet pressure to a third outlet pressure, iv. liquefying at least part of the air at the third outlet pressure and sending the liquefied air to at least one column of the column system wherein at least 50% of all liquefied air sent to the column system has been compressed in the third compressor, v. cooling a second part of the air at the first outlet pressure in the heat exchanger and expanding at least part of the second part of the air in an expander from the first outlet pressure to the pressure of a column of column system and sending the expanded air to that column, and vi. removing liquid from a column of the column system, pressurizing the liquid and vaporizing the liquid by heat exchange in the heat exchanger, and wherein: i. at least part of the first part of the air is cooled upstream of the second compressor, and ii. at least part of the first part of the air is cooled upstream of the second compressor in the heat exchanger.