Performance improvement of membrane distillation of high-concentration saline solution with pulse feeding

Abstract

In this study, digital time delay and solenoid valve were incorporated into sweeping gas membrane distillation to generate pulsatile feed. It can be found that shorter pulse length (0.5 s) at a smaller pulse frequency of 1 min⁻¹ can most efficiently increase transmembrane flux, up to 16% improvement that of with steady flow. Moreover, L16(4⁵) orthogonal fractional factorial experiment results demonstrate that feed inlet temperature is the critical factor and the best combination of parameter values are feed flow rate of 50 L h⁻¹, feed inlet temperature of 333 K, coolant temperature of 283 K, gas-sweeping flow rate of 0.84 m³ h⁻¹, and filling factor of 12.8%, separately. Lastly, pulsatile feed flow with saturated NaCl aqueous solution (333 K) not only delayed the occurrence of sharp flux decline due to membrane pore blocking caused by crystal deposition as compared to continuous flow, but enhanced the thermal efficiency by more than 56.7%. Observations of fouling status on the membrane surface show good agreement with the experimental results.

Keywords:

• Membrane distillation
• Pulsatile feed
• Crystal deposition
• Fouling

Acknowledgment

Financial supports from the Department of Science & Technology of Hainan Province, P.R. China for program fund (XH201421) and of Hainan provincial College Students’ Innovation and Entrepreneurship Training Program (20140058) are greatly acknowledged.