Feasibility study of multi-effect distillation dealing with high-salinity organic RO concentrates: Experiment and theoretical analysis

Abstract

Feasibility of the multi-effect distillation (MED) process was investigated experimentally and theoretically in present work to deal with the high-salinity organic reverse osmosis concentrates (ROCs) generated by the double membrane process for the treatment of wastewater from the refining and chemical enterprises. Two key problems involving the behaviors of organic and inorganic impurities in the ROCs during evaporation and process optimization of MED thermally and economically were highlighted. The experimental results indicated that about 6% and 8% of organic impurities volatilized during evaporation and entered into the produced water and the tail gas, respectively. The produced water and the tail gas which met the related China National standards could be reused or vented directly without further treatment. However, scaling of calcium sulfate was drastically occurred in the evaporator when about 30% water was recovered, indicating the necessity of removal of the hardness in ROCs before evaporation. A forward flow MED model established on Aspen Plus platform was employed to perform the thermal and economic analysis for the ROCs treatment. Performance analysis including the Gained Output Ratio (GOR), fresh steam flow and specific heat transfer area as functions of the effect number and the heating steam temperature were conducted. The results showed that the performance of the MED system was significantly influenced by effect number over the heating steam temperature. An increase in the effect number would improve the thermodynamic performance of MED system but increased the capital costs. The model established in this work could provide a theoretical guidance for the development of MED process dealing with ROCs.