Design strategy for networking membrane module and heat exchanger for direct contact membrane distillation process in seawater desalination

An energy-efficient design strategy for networking membrane modules and heat exchangers in membrane distillation (MD) process was developed in this work. A numerical simulation model was used to describe heat and mass transfer in direct contact type MD membrane module. Mass transfer coefficients were evaluated under different feed flow rates and feed temperatures. Feed flow rate had the predominant effect on the mass transfer coefficient, while feed temperature had a minimal effect. Thus, an empirical equation for the mass transfer coefficient relative to feed flow rate was employed in the simulation to estimate flux and outlet temperatures of membrane module. This approach was verified by two-stage module test results, which showed a good correlation with simulation results. After comparison of different unit process designs, a desired one including partial brine recycle scheme was selected due to the highest efficiency of energy utilization. Replications of a selected unit process will be useful for design of a large scale MD process. © 2014 Elsevier B.V. All rights reserved.

MD is an emerging desalination process that has not been optimized yet. This process has a complex network of membrane modules and heat exchangers, which determine distillate production and thermal energy consumption. Design of such a process is a time-consuming work Fig. 6. Configurations of MD processes; (a) Type I: Partial brine recycle after heat recovery of distillate, (b) Type II: Partial brine recycle before heat recovery of distillate, and (c) Type III: MD modules connected in a series with heat recovery.