Analysis of a mechanical vapor recompression wastewater distillation system

• A design model of MVR system for wastewater treating was developed.
• The unit with a capacity of 20 kg/h is installed in the laboratory.
• The operational features of the unit were investigated.
• The effect of parameters on power consumption and heat transfer area was analyzed.
• The specific power consumption increases linearly with temperature difference.

This paper presents a comprehensive design model of single-effect mechanical vapor recompression (MVR) system. The analysis focuses on the prediction of the specific power consumption of the compressor and the heat transfer areas of the evaporator. The MVR unit, with a capacity of 20 kg/h and horizontal tube falling film evaporation, is designed and installed in the laboratory. The performance of the system was investigated using high salinity wastewater containing Na2SO4. Except for the compressor consumption, experimental data shows good agreement for the predictions. The specific power consumption for the vapor compressor is 55.6 kWh/m3. The experimental and theoretical results indicated that the evaporation rate increases by increasing the evaporate temperature from 70 °C to 85 °C. The evaporation rate, compressor consumption and heat transfer area of evaporator depend strongly on the temperature difference of heat transfer. The evaporation rate and specific power consumption increase linearly with temperature difference. On the other hand, the heat transfer area of evaporator goes down with the increase of temperature difference. This inferred that there is an optimum value of temperature difference that will lead to the optimum system with lower power consumption and smaller heat transfer area.