Optimization of operational conditions for continuous membrane distillation crystallization process with zero discharge

• Main Author: Lim, Deric Weikang.
• Other Authors: Wang Rong
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Environmental engineering::Water treatment
• Online Access: http://hdl.handle.net/10356/52871
• Institution: Nanyang Technological University

Membrane Distillation Crystallization (MDC) is an innovative approach which involves the integration of the Membrane Distillation (MD) process together with a crystallizer unit. By tapping onto the potentials of MD, it becomes possible to operate under a supersaturated state of the solution, thereby achieving the objective of zero discharge to the environment while recovering valuable salts. However, in the current literature, only a few studies provided limited coverage about the optimization of a continuous MDC process performance with regard to supersaturated solutions. Selecting proper operational conditions for process control is necessary, as there is a need to prevent membrane wetting and crystal crystallization within the membrane module due to concentration and temperature polarization effects. As such, the concept of fractional experimental design was introduced to determine the optimum operational parameters. Results from the analysis were verified experimentally, and it was deduced that a feed flow rate and temperature of 0.64 L/min and 338 K respectively, together with a permeate flow rate of 0.35 L/min and permeate temperature of 303 K, gave the highest production rates of pure water and sodium chloride crystals. In addition, a runtime experiment lasting 21 hours was performed to determine its viability to be implemented on an industrial scale. Results showed the deterioration of the process performance and the quality of the permeate fluid worsening over time. Further analysis revealed that it was due to surface modifications on the membranes as a result of prolonged contact with high temperatures and a highly concentrated solution. Therefore, this implies the need for fabrication of membranes specially designed for continuous MDC processes operating in supersaturated solutions.