Multiple-effect evaporation desalination systems. thermal analysis

Abstract

Seawater desalination by parallel feed multiple-effect evaporation has a simple layout in comparison with other multiple-effect or multistage desalination systems. Several operating configurations are analyzed, including the parallel flow (MEE-P), the parallel/cross flow (MEE-PC), and systems combined with thermal (TVC) or mechanical (MVC) vapor compression. All models take into account dependence of the stream physical properties on temperature and salinity, thermodynamic losses, temperature depression in the vapor stream caused by pressure losses and the presence of nondashcondensable gases, and presence of the flashing ☐es. Analysis was performed as a function of the number of effects, the heating steam temperature, the temperature of the brine blowdown, and the temperature difference of the compressed vapor condensate and the brine blowdown. Results are presented as a function of parameters controlling the unit product cost, which include the specific heat transfer area, the thermal performance ratio, the specific power consumption, the conversion ratio, and the specific flow rate of the cooling water. The thermal performance ratio of the TVC and specific power consumption of the MVC are found to decrease at higher heating steam temperatures. Also, an increase of the heating steam temperature drastically reduces the specific heat transfer area. Results indicate better performance for the MEE-PC system; however, the MEE-P has a similar thermal performance ratio and simpler design and operating characteristics. The conversion ratio is found to depend on the brine flow configuration and to be independent of the vapor compression mode.