Optimal Control of Direct Contact Membrane Distillation Operated under Fluctuating Energy Source

Area of Science:

• Chemical Engineering
• Water Treatment Technologies
• Membrane Science

Background:

• Membrane distillation (MD) is a promising technology for water production.
• Renewable energy sources, like solar, cause fluctuating inlet temperatures in MD processes.
• Optimizing operational parameters is crucial for maximizing water output under variable conditions.

Purpose of the Study:

• To develop and test an optimal control strategy for a laboratory-scale membrane distillation (MD) process.
• To maximize time-averaged water production under fluctuating inlet hot temperatures.
• To investigate the impact of adapting membrane length in addition to cold stream flow rate.

Main Methods:

• Simulated an MD process with fluctuating hot stream inlet temperatures and a fixed hot stream flow rate.
• Implemented an optimal control strategy to regulate the cold stream flow rate.
• Modified the control strategy to adapt both cold stream flow rate and membrane length.

Main Results:

• Alternating the cold stream flow rate enhanced average water production by up to 4.2%.
• Performance enhancement was limited at very high or low cold to hot stream flow rate ratios due to mass flux degradation.
• Adapting membrane length along with cold stream flow rate yielded up to 40% enhancement in average water production.

Conclusions:

• Optimal control of cold stream flow rate can improve MD water production.
• Adapting membrane length offers a significant performance enhancement pathway for MD processes with variable conditions.
• The findings suggest a more robust and efficient MD operation strategy for renewable energy integration.