Exergy analysis of a vacuum membrane distillation system integrated with mechanical vapor recompression for sulfuric acid waste treatment

A vacuum membrane distillation (VMD) system integrated with mechanical vapor recompression (MVR) concentrating sulfuric acid solution was proposed. Mathematical models were established based on the first and second laws of thermodynamics. The effects of operating parameters on exergy efficiency of the system were investigated by Matlab simulation. Besides, further experiment using pure water as feed was implemented to validate the feasibility of the integration of VMD in MVR process, and then the energy and exergy analysis were performed comprehensively. The obtained results showed that the total input power increased but exergy efficiency decreased at higher feed concentration and heat transfer temperature difference of heat exchanger, lower feed temperature and velocity. The energy efficiency was improved through recovering the latent heat of vaporization in the VMD process. But the current coupled system was still inefficient and far from perfect with lower exergy efficiency of 3.72% and higher exergy destruction of 3.563 kW, the compressor was identified as the most exergy destruction of 36.99% followed by VMD module, heat exchanger and circulating pump with 18.16%, 11.98% and 11.34%, respectively. Therefore, the incorporation of enhancing heat-insulating property and using more efficient compressor, heat exchanger and VMD module is expected to improve the exergy performance.