Preparation and Desalination Process of a Novel Spiral-Wound Air-Gap Membrane Distillation Module

Air gap membrane distillation has many advantages such as high thermal efficiency and strong technical adaptability, but the existence of air gap will also increase the mass transfer resistance, which leads to low permeate flux. Due to the negative pressure applied at the permeate side, vacuum membrane distillation has a higher permeate flux. A novel spiral-wound air-gap membrane distillation(SW-AGMD) module, combining the characteristics of flat PTFE membrane and modified PVDF heat-exchanger hollow fibers, was designed and loaded with the negative pressure at the permeate side. The influences of the module parameters and the operating conditions on the desalination performance were systematically studied with 3.5%(mass fraction) sodium chloride feed solution. The results show that the permeate flux(J D ) and gained output ratio(GOR) during the desalination process can improve effectively when increasing the membrane average pore size. When increasing the effective length of the module, J D decreases but GOR increases. The feed flow rate and temperature have dramatic influences on the J D and GOR values. Both J D and GOR values rise up when the permeable side vacuum(p V ) is improved (p V ≤0.04 MPa). However, when the vacuum pressure is over 0.04 MPa, J D value continues to increase while GOR value tends to fall. The conductivity of the permeate water was kept below 30 μs/cm during the whole experiment process. The maximum J D and GOR values achieved were 16.38 kg/(m 2 •h)and 3.22 respectively, which were much higher than other air gap membrane distillation modules with the same style as reported. © 2018, Editorial Board of Journal of Tianjin University(Science and Technology). All right reserved.