Patent ID: 7922872

Claim:
A distillation apparatus comprising: a distillation column group in which a plurality of distillation columns comprising a condenser and a reboiler is connected in the form of a cascade; a gas-feeding line which feeds gas from a distillation column to a latter distillation column by using pressure difference between the distillation columns in the distillation column group; a gas line which introduces the gas from the distillation column to the condenser attached to the distillation column; a liquid line which withdraws a condensed liquid from the condenser; a liquid-reflux line which introduces a part of the condensed liquid from the liquid line to the distillation column; a liquid-return line which returns the remainder of the condensed liquid from the liquid line to a former distillation column; a valve provided on the liquid-return line; and a bypass line which connects the liquid-return line and the gas line so as to flow an evaporated gas generated in the liquid-return line to the gas line, wherein a position at which the bypass line and the gas line are connected is higher than a position at which the liquid-reflux line and the distillation column are connected, and a position at which the bypass line and the liquid-return line are connected is lower than a position at which the liquid line and the liquid-reflux line are connected.