Thermoeconomics of some options of large mechanical vapor-compression units

The performance and the cost of three vapor-compression (VC) seawater distillation systems of unit capacities 2 to 10 mgd are analyzed within the current distillation technology and its scale control. The results of the analysis are summarized in a costefficiency diagram. Increased unit size is achieved at the expense of a tolerable decrease in efficiency. The design features of the desired compressors and the models used for cost-performance analysis are described elsewhere. The trend of the results points to the importance of developing a reliable chemical treatment that controls the scale for boiling seawater at atmospheric pressure. Excluding the cost contribution of the treatment to production cost of distillate, the development can reduce the current cost of seawater distillation by as much as 30% while increasing efficiency by about 50%.