(514d) Novel Cylindrical Cross-Flow Hollow Fiber Membrane Module for Direct Contact Membrane Distillation-Based Desalination

Direct contact membrane distillation (DCMD) process for desalination is attractive especially for high salt concentrations if low-cost steam/waste heat is available and waste brine disposal cost for inland desalination is factored in. We recently developed successfully a hollow fiber membrane potted in a rectangular module with hot brine in cross-flow over the fibers and obtained high and stable water vapor flux under demanding scaling conditions. However, the current rectangular membrane module design having a low membrane surface area/unit device volume appears to be inadequate for larger-scale plants. Here we have described a novel cylindrical cross-flow module containing high-flux composite hydrophobic hollow fiber membranes for membrane surface areas: 0.15 and 0.6 m². These two modules used respectively 316 or 1266 porous fluorosiloxane-coated porous hollow fibers of PP (ID/OD: 330, 630 µm). The pipe-like module design is simple, easily scalable and packs about four times larger membrane surface area per unit equipment volume compared to the earlier rectangular cross-flow module design. The distilled water production rates from 1 wt% salt-containing feed brine has been studied over a hot brine temperature of 60-91⁰C. A model has been developed to describe the observed water production rates of such devices in the dead-end brine feed introduction configuration. The model appears to describe the observed water vapor production rates well for different feed brine temperatures at various brine flow rates. The model flux predictions have been explored over a range of hollow fiber lengths to compare the present results with those obtained earlier from rectangular modules which had significantly shorter hollow fibers.