| 摘要 |
A fractionation column 2 has a first vapour inlet 4 to a bottom mass exchange region of the column communicating with a source of the vapour mixture to be separated and a second vapour inlet 18 to an intermediate mass exchange region of the column. A valve 20 is operable to place the second inlet selectively in communication with the source of the vapour mixture to be separated in the event that the first inlet becomes blocked by a head of liquid in the column.
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