Ammonia Absorption into the Water: Packed Tower, VOF Model

Ammonia Absorption into Water in a Packed Tower, VOF

Description

Absorption is a method of separating components from a gas mixture by bringing it into contact with a liquid solvent, relying on differences in solubility to draw one or more gas components into the liquid phase — a process refineries commonly use to strip ammonia out of a gas stream. This project simulates ammonia absorption from air within an absorption tower using ANSYS Fluent, tracking how the gas and liquid streams interact as they pass through the column.

The 3D vertical tower geometry was built in Design Modeler, with ammonia-laden airflow entering at 0.43 m/s through a bottom nozzle and exiting through the upper section, while liquid water enters at 0.0332 kg/s through a top nozzle and exits through the lower section — the two streams meeting and interacting as they move in opposite directions through the chamber. The domain was meshed in ANSYS Meshing using an unstructured grid totaling 478,882 elements.

Methodology

The VOF multiphase model was used to resolve the interaction between the one-percent-ammonia air stream and the water solvent as the two phases move counter-currently through the tower.

Conclusion

Post-processed results include 2D and 3D contours of pressure, velocity, turbulent viscosity, density, and the volume fractions of water, air, and ammonia, offering a complete picture of how each phase behaves throughout the tower. The volume fraction contours show ammonia concentration steadily declining in the gas phase as it rises through the chamber, while the corresponding water-phase contours show a matching increase in absorbed ammonia as the liquid descends and contacts the rising gas — direct confirmation that mass transfer occurs at the gas-liquid interface, rather than the two streams simply passing one another without interaction.

The velocity and pressure fields further illustrate how the counter-current nozzle arrangement establishes the internal flow pattern that sustains this prolonged gas-liquid contact, central to the tower's separation performance. Together, these results confirm that the water phase effectively absorbs ammonia and separates it from the gas stream, demonstrating the core mechanism that makes packed absorption towers effective for gas purification in industrial process design.