Seawater distillation from low-temperature streams: a case history

The paper describes the objectives and the operational results of an experimental project aimed for the exploitation of very low temperature differences (associated with many waste streams commonly available in industrial environments) for the distillation of seawater. The case described is relevant to the engineering, construction and operation of a seawater desalination plant, called LTF, able to utilize as prime energy source the cooling seawater discharged by a turbine condenser, at only 8°C above ambient seawater temperature. The project was developed in the early 1990s by the Italian company Sowit, with a grant from the European Community. The desalination plant is presently in operation at the Piombino power station (owned by ENEL, the Italian Electricity Board) for the production of high-purity distillate for boiler make-up. Plant operational results confirmed the feasibility and the technical-economical convenience of this process. From the design point of view, the most critical aspect is related to the vent system of non-condensible gases released in the evaporator, while plant operation showed various advantages, such as a good reliability, a very high purity of produced distillate, reduced environmental impact and a competitive operation cost.