Modeling of Film Distillation with Membrane Condenser for Treatment of Reverse Osmosis Concentrate under Vietnam Tropical Conditions

This work is aimed at investigating a new process of film distillation with a membrane condenser (FDMC) for obtaining fresh water from a reverse osmosis concentrate. The behavior of a number of structural materials during their exposure for 4.5 months in the open air and in sea water has been investigated. In the Simulink/MATLAB program, a model of the FDMC unit with the possibility of using solar radiation as a renewable energy source has been built. The operation of the unit for one month was simulated and it was shown that the area of solar collectors has the greatest influence on the volume of water received during a month of operation. The area of the evaporator has little effect on the overall process performance, but it can reduce the initial costs while maintaining the same payback period. Modeling showed that the recovery of distilled water decreases by 2–3% (from ~71–72 to ~69%) with a decrease in the NaCl concentration of the output stream from 26 to 24 wt %. The mode with a lower concentration of the output solution was found to be optimal due to the absence of both the risk of pipeline clogging and the need for frequent flushing of the evaporating surface. The use of data on solar radiation for the most and least sunny months (April and November, respectively) shows a nonlinear drop (by 46–47%) in productivity for water, which is explained by both nonlinearity of the temperature dependence of water vapor pressure and a nonlinear relationship between the solar collector efficiency and radiation intensity and ambient temperature. Varying the temperature of the cold circuit shows that using a lower temperature increases the water productivity by 5–15%, while keeping the water recovery rate constant.