Patent GB-285468-A (GB)
Title: Improvements in or relating to the rectifying of mixed gases
IPC: F25J3/04
Filed: 1927-10-11
Abstract: 285,468. Allen, S. G., (Assignee of Baufre, W. L. de). Feb. 18, 1027, [Convention date]. Separating gaseous mixtures. - In the rectification of air &c. containing water vapour, the gases being cooled by the returning fluids, additional cool. ing is simultaneously effected at the temperature of condensation and freezing of the water vapour. Air compressed say to 6 atmospheres absolute in a turbo-compressor 7 is purified from carbon dioxide in towers a, b, c. The tower a contains water; the towers b. c contain alkali and may be used in series, either being cut out to renew its contents by stirring with lime in tubs b<1>, c<1>, The air then passes in series through reversible interchanger sections 8 and a further section 9. Water is condensed in sections 8 the order of which is periodically reversed to melt ice formed in the second of them. The loss of cold by this reversal is compensated by an auxiliary turbine B in which nitrogen is expanded to drive an electric generator C, the nitrogen joining the returning stream of rectified nitrogen. The air from the interchangers 8, 9 is further cooled and partly liquefied in an exchanger 10 wherein it vaporizes oxygen from the bottom 15 of the rectifier. The air is introduced around the bottom of the tubes in section 11 whence the part to be rectified is throttled into the tray section 12; the excess, mainly nitrogen, passes around the tubes of section 13 and is partly liquefied and throttled into the space around the upper tubes 16, the vapour is drawn off cooled in the vaporizer 23 and liquefied by liquid nitrogen in the external cycles and returned to the bottom of section 13. The nitrogen from the rectifier is. admitted to the suction side of the turbo-compressor 17 of the external cycle, excess of nitrogen being discharged by an automatic valve 24. The rectification pressure is controlled by this valve or by a controller varying the speed of the compressor to maintain its inlet pressure. When the nitrogen from the rectifier is insufficient, a part of the nitrogen from the refrigeration cycle is compressed by an auxiliary turbine 17<1> and returned to the compressor 17. This auxiliary compressor may be governed to give a constant pressure at its outlet or other point, or may work at constant speed, the valve 24 alone regulating the pressure. The interchanger tubes of both the main and refrigerator cycles are about 1400 times as long as their diameters. The refrigeration cycle comprises reversible interchanger sections 20 and a section 21 permanently in circuit, from which a part of the nitrogen passes to the liquefier 22 and a part to the expansion turbine B<1>. From the turbine it unites with nitrogen vaporized in the vaporizer 23, and cools the nitrogen passing down the liquefier 22. The turbines B, B<1> are connected to synchronous electric machines C, C<1>, the machine C<1> having a direct current exciter by which the turbine B<1> is started', the refrigerating compressor being also started. The turbine comprises several nozzles which may be closed one at a time as the pressure drops. An expansion engine run a,t constant speed with variable, cut-off may replace the turbine. At starting, air is used in the refrigerating cycle, being drawn in through an alkali tower 18; water is removed in the sections 20, the inflow of air through the valve 29 ceases when the separator system supplies nitrogen. Rare gases accumulate in the excess air of the separation system and are reproved from the vaporizer through valve 31. Liquid refrigerant may be supplied around the top tube section 16 from the external cycle through a connection 32.