Multiple/Simple Effect Stills
A multiple effect still consists of a series of pressure columns divided into two parts: a double tube sheet (DTS) heat exchanger that acts as an evaporator, and an upper column used to separate pyrogens; preventing drops carrying impurities from reaching the end of the column. The separation column’s diameter has been designed to obtain a sufficiently slow upward speed for the drops carrying impurities, to fall to the bottom of the column under the effect of gravity. The multiple effect still design increases the energy contribution from the mains steam by providing steam circulation successively around the various columns in the still.
A simple effect still is basically the same as the first distillation column of a multiple effect still and supplies pure steam to a condensing unit. The energy and steam consumption of a multiple effect still is much lower, since it reuses the steam calories to generate more steam and at the end of the series of columns the steam reaches the condensing unit at a lower temperature. Nevertheless, contrary to general belief, the number of effects does not affect the quality of the end product.