Distillation device

A distillation apparatus comprising:

• a distillation column group in which a plurality of distillation columns, which are respectively equipped with a reboiler, are connected in the form of a distillation cascade;
• feed-gas condensers which liquefy feed gases from bottoms of respective former distillation columns and feed said liquefied feed gases to tops of respective latter distillation columns;
• gas-feeding lines which connect the bottoms of the respective former distillation columns and the respective feed-gas condensers;
• liquid-feeding lines which connect the respective feed-gas condensers and the tops of the respective latter distillation columns;
• top-gas condensers provided on the tops of the respective distillation columns;
• top-gas lines which introduce gases from the tops of the respective distillation columns to the respective top-gas condensers;
• liquid lines which withdraw condensate liquids from the respective top-gas condensers;
• liquid-reflux lines which introduce the condensate liquids from the respective liquid lines to the tops of the respective distillation columns;
• and
• liquid-return lines which return parts of the condensate liquids from the respective liquid lines to the bottoms of the respective former distillation columns.