Study on vacuum membrane distillation coupled with mechanical vapor recompression system for the concentration of sulfuric acid solution

This paper presents a new vacuum membrane distillation (VMD) coupled with mechanical vapor recompression system for the concentration of sulfuric acid solution; the mathematical models based on the mass and energy balances in each part of the system are established. The influences of the corresponding operating parameters including feed concentration, feed temperature, feed velocity and permeate-side absolute pressure on membrane flux are investigated and discussed. The membrane flux increases with the increase in feed temperature and velocity, but it decreases with the increase in feed concentration and permeate-side absolute pressure. Furthermore, the energy consumption of the proposed system is explored through analyzing the influences from key factors, including boiling point elevation, temperature and concentration polarization and heat transfer temperature difference of heat exchanger on power consumption of compressor. Compared with the conventional VMD system and multi-effect MD system, the proposed system can save 77.6% and 20.4% energy due to a significant improvement in thermal efficiency by recovering the latent heat of vaporization. Eventually, an economic evaluation of the proposed system is performed comprehensively and the most optimized compression ratio of compressor can be obtained, which can guarantee the lowest energy consumption and total annual cost. Therefore, these results can provide significant references for the implementation and further optimization of the proposed system in the future.