Heat recovery system

A heat recovery system for an installation producing heavy water by the method of bithermal isotopic exchange between two fluids, one of the fluids serving as a source of heavy hydrogen and the other fluid serving as an isotope exchange medium, comprises a cold tower, a hot tower, a closed circuit means for circulating gaseous fluid between the two towers, a first liquid circuit for cooling hot gaseous fluid at the output of the hot tower in an indirect heat exchanger and for transferring this heat to cold gaseous fluid before the fluid enters the hot tower, in a direct contact exchanger arranged before the input of the hot tower, a second liquid circuit for removing the remaining heat energy from the gaseous fluid in a direct contact exchanger before the fluid enters the cold tower and for transferring this remaining heat energy by means of an indirect liquid to liquid exchanger to a third liquid circuit which also serves the said exchanger having direct contact arranged before the input of the hot tower.