Patent GB-1031107-A (GB)
Title: Improvements in or relating to the production of low temperatures
IPC: F27B1/18
Filed: 1964-09-10
Abstract: 1,031,107. Refrigerating. L'AIR LIQUIDE S.A. POUR L'ETUDE ET L'EXPLOITATION DES PROCEDES GEORGES CLAUDE. Sept. 10, 1964 [Sept. 23, 1963], No. 37160/64. Heading F4H. In a process for the production of cold by the vaporization of liquid nitrogen, the nitrogen vapour is heat exchanged with a gas which has a high nitrogen content and from which the liquid nitrogen is to be produced by liquefaction and rectification, said gas having a high nitrogen content being formed by the admixture of air, gaseous nitrogen separated from the gas having a high nitrogen content and gaseous nitrogen obtained from the vaporization of liquid nitrogen to produce cold. As shown, atmospheric air introduced through line 1 has moisture and carbon dioxide removed therefrom at 2 and gaseous nitrogen added thereto from line 3, the mixture being compressed at 4 and passed through heat exchangers 6, 12 which are cooled by the gaseous nitrogen in line 3. Part of the mixture is tapped off from between heat exchangers 6 and 12, expanded in an expansion machine 8 and passed into the bottom of a high pressure rectification column 10, the remainder of the mixture from heat exchanger 12 being passed through a coil 14 in the sump of column 10, through a heat exchanger 16 and then expanded through valves 18, 19 into column 10. Liquid oxygen from the bottom of the latter is withdrawn through line 22 and heat exchanger 23 and expanded through valve 25 into a lowpressure column 21 which communicates with column 10 through a condenser-vaporizer 20. Liquid nitrogen is withdrawn from the top of column 10 through line 26 and heat exchanger 27 and part is refluxed through line 29 and valve 30 to column 21, the remainder being supplied via line 31 and expansion valve 32 to a storage reservoir 33 communicating with a coil 36 in a chamber to be cooled. Vapour from coil 36 and from the vapour space of reservoir 33 is returned via lines 37, 38, 39 to line 3 for recycling to the compressor 4. Gaseous nitrogen from column 21 is supplied via lines 41-44 and heat exchangers 27, 23, 16 to line 39 and thence to compressor 4. Gaseous oxygen from column 21 passes to waste via lines 45-47 and heat exchangers 6, 12. In operation, at zero cold consumption the air only has added thereto gaseous nitrogen from column 21 and reservoir 33, but as the cold consumption increases vapour from coil 36 is supplied to the compressor and the air intake is reduced by the same amount. The quantity of gas expanded at 8 is progressively reduced as is the quantity of liquid nitrogen refluxed to column 21 through line 29, so that the quantity of liquid nitrogen supplied through line 31 to reservoir 33 is increased. Eventually valve 30 in line 29 is closed completely, no air is drawn in through line 1, no gas is expanded at 8 and valve 18 is opened and valve 19 closed so that the rectifier columns are by-passed and the apparatus functions merely as a nitrogen liquefier. In the modification of Fig. 2 (not shown), the reflux stream to column 21 is taken from the middle of column 10 instead of from line 26 while in a further modification (Fig. 3, not shown) the low pressure column 21 is omitted.