Patent GB-1288947-A (GB)
IPC: C01B3/52
Filed: 1969-12-17
Abstract: 1288947 Refrigeration; gas mixture rectification processes LINDE AG 17 Dec 1969 [18 Dec 1968] 61411/69 Headings F4H and F4P  Two gas streams having major constituents whose boiling points are different are cooled under pressures which are higher than the higher of the critical pressures of the major constituents to a temperature or temperatures below the critical temperatures of the major constituents. The streams are then mixed to produce a cooling effect which the Specification likens to the Joule-Thomson effect. As illustrated in Fig. 3 the invention is applied to a plant producing a mixture of hydrogen and nitrogen gases for the synthesis of ammonia. Crude hydrogen and nitrogen in lines 1 and 2 and at pressures of 73 and 80 atmospheres are cooled in heat exchangers 3-8, and, at start-up, additionally in a heat exchanger 9. Part of the nitrogen is expanded at 12 to liquefy and act as a washing liquid in a column 10 to remove carbon monoxide and methane from the crude hydrogen: Gas from the head of the column 10 mixes with further nitrogen from a mixing valve 13 to provide cooling which is utilized in the heat exchangers 3, 4 and 7. Nitrogen is added, if necessary, through a line 15 to the gas in the line 14 to provide the current hydrogen-nitrogen ratio for subsequent ammonia synthesis. Residual products from the bottom of the column 10 are expanded at 16 to provide cooling for the heat exchangers 5, 6 and 8. Nitrogen to be fed to the line 2 and oxygen for the production of hydrogen by the partial combustion of hydrocarbons are formed by separating the components of air in a double rectification column 55. Compressed air is passed through a line 50 to heat exchangers 51 and 60 of a reversing heat exchanger arrangement in which water and carbon dioxide are condensed from the air. The air stream is divided, is part expanded, and admitted to the rectification column through lines 57, 59 and 61 and through heat exchanger 54. Oxygen enriched liquid from the lower column is expanded at 64 and passed to the upper column. Reflux liquid collected at 65 is also passed to the upper column. Liquid oxygen from the upper column is passed by a pump 71 to the hydrocarbon combustion stage. Impure nitrogen from the top of the upper column is passed through a line 67 to the reversing heat exchanger arrangement from which it carries the condensed water and carbon dioxide. Nitrogen from the top of the lower column is passed through a line 82 and the reversing heat exchanger arrangement to a compressor 76 from which part of the stream is passed to the line 2 and part is returned to the lower rectification column. As illustrated in Fig. 3, a mixture of hydrogen, nitrogen, argon and methane from a line 20 at a pressure of between 50 and 80 atmospheres is fractionated to produce a mixture of nitrogen and hydrogen for the synthesis of ammonia. The mixture from the line 20 is cooled in heat exchangers 21 and 22 so that all the components but hydrogen condense and are separated at 23. The condensed constituents are expanded into a rectification column 24 from which liquid methane leaves through a line 25. The head product of gaseous nitrogen and argon is passed into a second column 26 from which liquid argon leaves through a line 27. Nitrogen from the head of the second column is in part, after heating the bottom of column 24, mixed with gaseous hydrogen from the separator 23 to produce the cooling effect of the invention. The cooled mixture of hydrogen and nitrogen cools the heat exchangers 21 and 22 prior to subsequent ammonia synthesis. The remainder of the nitrogen from the head of column 26 is expanded at 32, cooled by passage through the bottom of column 26, and then expanded to provide liquid nitrogen in a vessel 34. The liquid is used in part as a wash liquid in the column 26 and in part to cool the head of column 24 by evaporation in a coil 36.