Patent GB-994185-A (GB)
Title: Low temperature separation of gaseous mixtures
IPC: F25J3/04
Filed: 1961-08-23
Abstract: 994,185. Cold separation of gas mixtures. AIR PRODUCTS & CHEMICALS Inc. Aug. 23, 1961 [Aug. 25, 1960; March 21, 1961; Aug. 14, 1961], No. 30400/61. Heading F4P. In a process for separating a compressed gas mixture, e.g. air, in a high pressure column 16, Fig. 1, to provide a high boiling point liquid fraction, e.g. crude oxygen, and low boiling point gaseous fraction, e.g. crude nitrogen, followed by low pressure separation in a column 25 to provide liquid oxygen product withdrawn through a line 50 and gaseous nitrogen product withdrawn through a line 27, lixuid oxygen product is at least in part vaporized in an exchanger 44 traversed by high pressure gaseous material poorer in oxygen than is the crude liquid oxygen collecting in pool 21 at the base of the high pressure column 16 and which cooled gaseous material is thereafter passed to the high pressure column whilst the so-vaporized oxygen is in part returned through a line 52 to column 25 as reboil, and crude nitrogen gas withdrawn from the column 16 is liquefied in an exchanger 45 traversed by a liquid richer in oxygen than is the crude liquid 21 and withdrawn from an intermediate level in column 25 through a line 68; the so liquefied nitrogen being in part passed through a valved line 65, 66 to serve as reflux in column 25 and in part returned through a line 64 to column 16 as reflux therefor. In operation compressed air to be separated is admitted through a line 10 to a heat exchanger 11 where it is cooled to saturation temperature by oxygen product in a pass 38 and nitrogen effluent in a pass 34 from column 25 together with nitrogen effluent from column 16 after warming in an exchanger 13 and expansion in a turbine 41. Part of the so cooled air is fed through a line 15 to column 16 whilst the remainder is fed through a line 17 to the exchanger 44 and is then fed in part through a line 55 to column 16 and in part through a valved line 56 to column 25. In a modification the whole of the compressed air leaving the exchanger 11 (Fig. 2, not shown) is fed directly to column 16 and a gas mixture is withdrawn therefrom from a level just above the pool 21, and fed through the exchanger 44. In a further modification the whole of the compressed air leaving the exchanger 11 is passed direct to exchanger 44 and from thence to column 16. In a still further modification vaporization of product liquid oxygen withdrawn from the base of column 25 is effected in two exchangers 112, 115, Fig. 4 (not shown), in series and having a phase separating vessel 126 and a hydrocarbon absorber 130 therebetween. In a further modification said vaporization occurs in a dephlamator 150, Fig. 5 (not shown), in which occurs partial rectification of the incoming compressed air; each of the separated components being fed to the high pressure column 16. In a still further modification vaporization of product liquid oxygen is effected in a heat exchanger comprising a condenser 170, Fig. 6, and dephlamator 175 arranged in parallel in respect of the oxygen flow and in series in respect of the incoming compressed air flow. Thus product liquid oxygen is divided at a point 181 into a portion which is vaporized in dephlamator 175 and oxygen gas is discharged through a line 184 to a point 186 where it is joined by oxygen after vaporization in air condenser 170 and the combined oxygen stream is passed in part through pass 37 of exchanger 11 and in part back to column 25. Wet air from the base of condenser 170 is separated in a vessel 191 and is joined by oxygen-rich liquid withdrawn from dephlamator 175 before being fed through a line 22 and expansion valve 24 to the low pressure column 25. Uncondensed air from phase separator 190 is in part fed to the dephlamator 175 and in part through a line 200 to column 16 where it is joined by a portion of crude nitrogen effluent from the dephlamator; the remaining crude nitrogen being passed through a valved line 197, a line 103 in the cold end of exchanger 11 and the turbine 41 which discharges to the nitrogen pass 34 of exchanger 11.