The Study Of Vacuum-Air Gap And Multi- Stage Membrane Distillation For Saline Water Evaporation

In this work, the process of air gap membrane distillation (AGMD) supplemented by a vacuum pump was developed to eliminate the disadvantage of the air gap and to improve the process performance. The vacuum-air gap membrane distillation (V-AGMD) was evaluated by comparing with the AGMD while varying operating conditions such as the feed inlet temperature, feed flow rate, cooling water temperature and feed salt concentration. The optimal operating conditions were obtained by orthogonal experiments of the AGMD and V-AGMD processes. It was found the following results:-1. The vacuum pump could promote the permeate flux (Pf), thermal efficiency (η), gained output ratio (GOR) and performance ratio (PR).2. Under the optimal conditions, a feed flow rate of 4 1/min and feed inlet temperature of 50 ℃, the PF and GOR could be increased by 24.96% and 14.29%, respectively, from AGMD to V-AGMD. While, the feed inlet temperature at 80 ℃, cooling water temperature at 20 ℃ and feed salt concentration at 0.0253%, the PR and η achieved increases of about 15.25% and 11.99% at constant feed flow rates of 21/min and 41/min, respectively.3. Under the optimal orthogonal experiment conditions of feed inlet temperature of 80 ℃, feed flow rate of 4 1/min and feed salt concentration 0.0253%, the best PF and η were achieved, while at feed inlet temperature of 70 ℃, feed flow rate of 21/min and feed salt concentration of 1.6335%, higher PR and GOR were obtained in the case of AGMD. For V-AGMD process, under optimal conditions of 80 ℃,4 1/min and 0.0253%, PF, η and PR were improved, but better GOR was at 80 ℃,21/min and 4.4825%.4. The results of this work proved that improving the performance of AGMD is possible by using a supplementary vacuum pump.Also, minimization of high specific energy consumption (EC) and improvement the permeate flux of one-stage V-MEMD could be successfully achieved by following an efficient energy recovery process. The performance of one-stage V-MEMD was assessed by comparing with three-stage V-MEMD accompanied with an efficient energy recovery process at different operational conditions. It was discovered the following outstanding results:-1. The PF, RR and GOR were enhanced and specific energy consumption (EC)/m3 of permeate flux was decreased notably.2. Under the optimal conditions, feed flow rate of 400 L/hr, vacuum pressure of 0.085 MPa, feed inlet temperature of 80 ℃ and feed salt concentration of 5.71%, the PF and GOR of three-stage V-MEMD were progressed by 119.23% and 110.71%, respectively, compared to one-stage V-MEMD.3. At different feed salt concentrations varying from 5.71% to 19.60%, respectively, three-stage V-MEMD achieved a remarkably recovering ranged from 34.92% to 17.32% of condensation latent heat in case of specific EC Heat and recovering varied from 91.50% to 86.85% for specific EC Electric.4. The outcomes of this study confirmed that enhancing the performance of one-stage V-MEMD is potential by using an efficient energy recovery process (three-stage membrane module connected in series).