Abstract: A method and apparatus are disclosed relating to the recovery and reuse of heat during fractionation of liquids in a tray-type fractionating tower. According to this method, a portion of the feed to the tower is directed through heat exchange tubing positioned on the trays in such a way that the tubing is in contact with liquid there present so as to bring about an indirect exchange of heat between the said liquid on the trays and the liquid in the tubing, at the same time that there is occurring the normal transfer of heat by direct contact between the vapor and the liquid on the trays and the normal interchange of material components by direct contact between vapor and liquid on the trays, the said heat exchange tubing being serially connected so as to carry liquid from tray to tray.

Abstract: Hydrogen sulphide is stripped from hot effluent, in a heavy water separation plant of the dual temperature isotope separation type, by taking liquid effluent from the hot tower before passage through the humidifier, passing the liquid through one or more throttle devices to flash-off the H.sub.2 S gas content, and feeding the gas into an absorption tower containing incoming feed water, for recycling of the gas through the process.