Development of an efficient compact multistage membrane distillation module for water desalination

To improve productivity and reduce the energy consumption and production cost of the membrane distillation (MD) process, a new compact design of a multistage MD module is experimentally evaluated for water desalination. The compact multistage MD module uses two membranes in each feed channel and two cooling plates in each coolant channel. The module is utilized to compare the performances of the air gap and water gap MD configurations as a step forward to scaling up for possible commercialization. The performance metrics include the system productivity, gained output ratio (GOR), and production cost, which are calculated and compared at different operating parameters. Results revealed that the water gap produces more freshwater than the air gap under the same conditions with a lower cost of production. However, the air gap is better in terms of energy consumption with higher GOR. The multistage air gap system produced up to 0.98 L/h of freshwater with the best GOR of 0.6 and production cost of 12 $/m3. At the same operating conditions, the multistage water gap system produced up to 1.95 L/h of freshwater with the best GOR of 0.49 and production cost of 6 $/m3.