Performance analysis of a single and multi-staged direct contact membrane distillation module integrated with heat recovery units

Abstract

In the present work, a single and multi-staged Direct Contact Membrane Distillation (DCMD) module is designed with optimal flow configuration to get the best DCMD system performance. An energy-efficient system was developed by integrating the DCMD module with heat exchangers (HXs). The heat exchangers were used to recover energy carried by the outgoing streams. The water productivity and energy requirement for the integrated DCMD-HX system was evaluated for both single and multistage DCMD configuration having the same membrane surface area. It was observed that the multistage DCMD configuration yielded a maximum water productivity of 16.34 LMH. An optimization problem was also developed with an objective to maximize the gain output ratio (GOR) of the integrated process. The multistage DCMD configuration could achieve the maximum GOR of 0.942. The minimum specific thermal energy consumption achieved for the integrated DCMD-HX system is 1100 kWh/m3 and 800 kWh/m3 for single and multistage DCMD, which is in accordance with the literature [1,2]. With optimization, the STEC value reduces to 711 kWh/m3 and 670 kWh/m3, respectively for single and multistage DCMD. The proposed flat sheet DCMD-HX configuration is found to be more energy-efficient than earlier literature reported DCMD-HX configuration without optimization. Further, optimization result concludes that a Mixed Integer Non Linear Programming (MINLP) problem can be formulated to achieve maximum GOR and product water by manipulating the number of DCMD stage and module for fixed membrane area.