Patent ID: 9091478
Filing Date: 2015-07-28
Classification: F25J

Abstract:
1. A method for separating air by cryogenic distillation in an installation comprising a double or triple air-separation column, of which the column operating at the highest pressure operates at a medium pressure, and an exchange line where all the air intended for the distillation unit is cooled, the method comprising the steps of: a) pressurizing all the air to a high pressure at least 5 bar higher than the medium pressure and purifying the air at this high pressure to produce purified air; b) dividing the purified air into more than one fraction; c) sending a first fraction of the purified air at the high pressure to a hot booster, and then cooling in the exchange line to a first intermediate temperature; to form a first cooled fraction, d) dividing the first cooled fraction into a first portion and a second portion, and then expanding the first portion in a first turbine and expanding the second portion in a second turbine, to form a first expanded air stream and a second expanded air stream, respectively, wherein the first expanded air stream and the second expanded air stream are at a pressure that is approximately equal to the medium pressure; e) sending at least one of the first expanded air stream and the second expanded air stream to the column of the double or triple column operating at the medium pressure; f) cooling a second fraction of the purified air at the high pressure in a first series of passages in the exchange line to a second intermediate temperature and then boosting in a cold booster to produce a boosted second fraction, wherein the cold booster is mechanically connected to the second turbine and the hot booster is mechanically connected to the first turbine, wherein the boosted second fraction is at a temperature higher than the second intermediate temperature; g) reintroducing the boosted second fraction into a second series of passages in the exchange line, in which at least one portion of the boosted second fraction is condensed or undergoes pseudo-condensation; and h) vaporizing or pseudo-vaporizing at least one pressurized liquid coming from one of the columns of the double or triple column in the exchange line at a vaporization temperature, and i) wherein if the cold booster is not operating, air coming from the hot booster and the second fraction of the air purified at the high pressure, which has bypassed the hot booster, are both cooled in the exchange line to form the first cooled fraction, wherein the first cooled fraction is expanded in the first turbine coupled to the hot booster before being sent at least in part to the column operating at the medium pressure.