Steam enters from the bottom of the tower. The evaporated gas phase comes into countercurrent contact with the descending liquid. During the contact between the two phases, the volatile (low boiling point) components in the descending liquid continuously transfer to the gas phase, while the non-volatile (* boiling point) components in the gas phase continuously transfer to the descending liquid. The closer the gas phase is to the top of the tower, the higher the concentration of the volatile components, and the closer the descending liquid is to the bottom of the tower, the more enriched the non-volatile components, thus achieving the purpose of component separation. The gas phase rising from the top of the tower enters the condenser, and a portion of the condensed liquid returns to the top of the tower as reflux and enters the distillation tower, while the remaining portion is taken out as distillate. Part of the liquid flowing out from the bottom of the tower is sent to the reboiler, heated and evaporated into a gas phase, and returned to the tower. The other part of the liquid is taken out as residual liquid from the kettle.