Patent GB-856683-A (GB)
Title: Improvements in or relating to the rectification of low boiling point gas mixtures
IPC: F25J3/04
Filed: 1957-10-09
Abstract: 856,683. Cold separation of gas mixtures. GESELLSCHAFT FUR LINDES EISMASCHINEN A.G. Oct. 9, 1957 [Oct. 18, 1956], No. 31615/57. Class 8(2). In a process for separating a low boiling point component A from a slightly higher boiling point component B comprising feeding the mixture of A and B to an intermediate point e.g., through an expansion valve 2, Fig. 1, of the first of at least three rectification columns 1, 2 and 3 operating at successively lower pressures, feeding a component separated in the first column 1 to an intermediate point in the succeeding column 2 corresponding to its composition e.g., B contaminated with A and expanded through a valve 24, feeding a component separated in column 2 to an intermediate point in the next column 3 corresponding to its composition e.g., B contaminated with a small amount of A and expanded through a valve 25; and so on until the last column is reached, at least part of the gaseous component separated in the first and any intermediate column is condensed at the top thereof in condensers 11, 12 and the heat of condensation is transferred to the bottom of the succeeding column and effects evaporation of liquid therein. The so condensed component rich in component A is expanded at valves 22, 23 and fed to the top of the last column to serve as reflux and from which gaseous product A is discharged from the head and gaseous product B is discharged from a point just above the condenser 12. Extra refrigeration is supplied by leading pure product A from a point 60 through an expansion valve 26, a compressor 8 and aftercooler 7, a boiling coil 20 at the base of column 1 and in which the compressed gas is liquefied and an expansion valve 27 after which the resulting cold liquid component A is fed to the head of column 3 as reflux. The apapratus of Fig. 1 is suitable for separating deterium hydride from a hydrogenrich mixture thereof. In a modification the mixture is fed to the first column in the gaseous phase. In a further modification product B is withdrawn in the liquid phase from the base of the last column, evaporated in a coil 10, Fig. 2, (not shown), in the head of said last column and a portion of the product gas B is used to supply refrigeration by compression, after cooling, condensation in coil 20 of column 1, expansion in valve 27 and evaporation in the coil 10 thus forming a closed cycle. Instead of being superposed the columns may be arranged side by side as shown in Fig. 6. to the first column 4 of which a mixture rich in component B is fed after traversing a liquefying coil 19 and an expansion valve 21. Contaminated component A from the top of column 4 is expanded through a valve 45 and fed to an intermediate point in the next column 5 and slightly contaminated component A is similarly fed to column 6 and pure product A is discharged from the top thereof. Part of component A at the heads of column 4, 5 are condensed outside coils 16, 17 and the heat of condensation is transferred by impure component B from the bases of columns 4, 5 traversing coils 16, 17 and being fed to the bottoms of columns 5, 6, product B being discharged from the base of the last column 6 through a vaporizing coil 18 and part of this gaseous product B is taken from a point 65 expanded at a valve 44, compressed and cooled at 8, 7 and fed to the column 4 as extra refrigerant.