Novel air gap membrane absorption structure for ammonium salt crystallization.

Area of Science:

• Chemical Engineering
• Environmental Science
• Materials Science

Background:

• Conventional membrane distillation for ammonia recovery is energy-intensive and yields low-value products.
• Developing efficient ammonia recovery technologies is crucial for renewable fertilizer production.

Purpose of the Study:

• To propose and evaluate a novel air gap membrane absorption (AGMA) structure for superefficient ammonia nitrogen recovery and crystallization.
• To address the limitations of existing ammonia recovery methods.

Main Methods:

• Designed an adiabatic air gap module (3 mm thickness) to minimize heat loss and water transfer.
• Investigated the heat flux, water flux, and ammonia mass transfer coefficient of the AGMA system.
• Conducted a 60-hour cyclic experiment using liquid digestate as feed solution.

Main Results:

• The AGMA process demonstrated a significantly lower heat flux (1019 W/m²) compared to systems without an air gap.
• Achieved a high water flux of 1.27 kg/(m² h) and an ammonia mass transfer coefficient of 2.38×10^-6 m/s.
• Obtained an ultrahigh ammonia separation factor (>200) and pure ammonium salt crystals from liquid digestate.

Conclusions:

• The AGMA structure enables efficient ammonia nitrogen recovery and crystallization, surpassing conventional membrane technologies.
• The system offers low energy consumption (64.35 kJ/mol-NH₃) and treatment costs ($2.01/m³), highlighting its economic viability.
• The AGMA system shows great potential for high-efficiency, low-cost ammonia recovery and renewable fertilizer production.