| 摘要 |
In a distillation column used in the separation of air, a liquid stream of composition intermediate those occuring at the top and bottom is taken from the column and is at least partial reboiled in an external heat exchanger by heat exchange with a heat exchange fluid. The resultant vapor is returned to the column. Its composition matches that of the vapor in the vapor space to which it is returned more closely than that of the vapor in the vapor space above the tray from which the liquid is taken for reboil. The heat exchange fluid is other than one which is taken from a liquid vapor contact column, is passed directly to the heat exchanger, and is then returned directly to the column from which it was taken. The distillation column is preferably the lower pressure column of a double column system, and the heat exchange fluid is preferably air which preferably condenses in the heat exchanger and is introduced into the column at a level above that from which the liquid stream of intermediate composition is taken. |
