Treatment of high-concentration wastewater using double-effect mechanical vapor recompression

A double-effect mechanical vapor re-compression (MVR) evaporation system for the treatment of highly concentrated inorganic salt wastewater was investigated, and its characteristics were analyzed taking ammonium sulfate wastewater as the treated solution. Mathematical models were established based on the energy and mass balance equations as well as correlations of the thermophysical properties and the heat-transfer coefficients. A parametric study was performed to observe the effects of the temperature rise in the heater, the emission concentration of the first effect, the evaporation temperature and the temperature difference between the condensing steam and the boiling solution on the power consumption and on the heat-transfer area. The results showed that the temperature rise should be in the range of 2.5 to 4 °C. The power consumption increased as the evaporation temperature decreased and reached a minimum when the first effect emission concentration was approximately 32%. The heat-transfer area decreased as the emission concentration of first effect, the evaporation temperature or the temperature difference between the condensing steam and the boiling solution increased. The model results were found to be consistent with published industrial data. Compared to the single-effect MVR system, the power consumption of double-effect MVR system was lower. Therefore, the system can be used to treat highly concentrated inorganic salt wastewater and can save energy.

► A double-effect MVR system for treating high concentrated wastewater is proposed.
► Mathematical models are established including thermophysical property correlations.
► It analyzes the effect of variables on power consumption and heat transfer area.
► Power consumption is minimum at the first section emission concentration about 32%.
► The model results are consistent with industrial data and the system can save energy.