Evaluation of mechanical vapor recompression crystallization process for treatment of high salinity wastewater

Single/multiple-effect evaporation (SEE/MEE) along with single/multi-stage mechanical vapor recompression (SVR-MVR) systems were simulated for high salinity wastewater treatment. They were optimized for feed salinity of 70 g/kg and zero liquid discharge (i.e., salt saturation concentration of 285 g/kg). The compressor specific power consumption (e.g., 0.193-0.064 kWh/kg for SEE-SVR) and the required heat transfer surface areas of the evaporator (e.g., 2719.78-498.01 m(2) for SEE-SVR) decreased by increasing the evaporating temperature (from 50 to 90 degrees C), depending on the temperature difference between the condensing vapor and the boiling brine (Delta T). An optimum value was obtained for Delta T (almost 3 degrees C for SEE-SVR) to target either lower power consumption and heat transfer surface area. Operational expenditures (OPEX) showed a minimum at the feed salinity of 70 g/kg. The feed containing CaCl2 needed more treatment energy, compared to NaCl and MgCl2. Among the simulated systems, MEE-SVR showed the best performance, in terms of energy consumption and OPEX. So, the optimized MEE-SVR system was combined with a crystallization unit for better water recovery and solid salt removal from high salinity wastewater. Increment of the feed salinity caused decreased mean crystal size by raising nucleation rate and reducing growth rate.