Gas-liquid two-phase contact through countercurrent for interphase heat and mass transfer. The volatile components in the liquid phase enter the gas phase, and the nonvolatile components in the gas phase enter the liquid phase, so almost pure volatile components can be obtained at the top of the tower and almost pure nonvolatile components can be obtained at the bottom of the tower. The feed liquid is added from the middle of the tower, and the tower section above the feed inlet further enriches the volatile components in the rising steam, which is called the distillation section; The tower section below the feed inlet extracts volatile components from the descending liquid, which is called the stripping section. After the steam from the tower top is condensed, part of the condensate returns to the distillation tower from the tower top as reflux, and the rest distillate is the tower top product.
