| 摘要 |
<PICT:1119859/C4-C5/1> A distillation column for the removal of iso pentane from a mixture of hydrocarbons where the purity of the isopentane should be at least 97% and where the bottom product should not contain more than 2% isopentane is automatically controlled such that when a control action, e.g. change in reflux flow is effected to keep the desired quality of the isopentane the ratio between the vapour flow and the liquid flow in the lower part of the column is maintained unchanged so ensuring a constant desired quality of the bottom product. The ratio in the lower part is kept constant by adjusting the bottom product flow or the heat flow to a reboiler or the feed of the hydrocarbon mixture to the column by means of a signal derived from the liquid level at the bottom of the column, and by keeping the ratio between the bottom product flow and the heat flow to the reboiler at a desired level.
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