Thermovapor compression desalters: energy and availability - Analysis of single- and multi-effect systems

Sidem (France) has made some recent advancements in thermal vapor compression (TVC) systems [1,2] by installing four units, each having four effects, 1 migd in capacity with a gain ratio of 8, and another four units of 12 effects each, with 2 migd capacity per unit and a gain ratio close to 17. This increased the interest in the system particularly for plants of low and medium capacity. The new system is characterized by the following: (1) the compression of most of the generated vapor and its usage as a heating medium drastically reduce the primary heat source (boiler) and heat sink (i.e., cooling water and condenser), as compared to conventional single-effect desalting systems; (2) low energy consumption; (3) simple water pretreatment as compared with reverse osmosis (RO) systems, which are the main competitors of mechanical and thermal vapor compression systems in small and medium capacities; (4) low capital and operating costs; and (5) recently developed reliable thermocompressors. Since very little is known about the principles and design of the system, a parametric analysis, using the first and second laws of thermodynamics, was conducted for the TVC system components, e.g., steam ejector, evaporator, condenser, as well as the system as a whole. The analysis pinpoints the deficiencies in the system and the methods of overcoming these deficiencies.