Chemical: Ammonia Absorption into Water in a Packed Tower, VOF

Absorption of Ammonia into Water in a Packed Tower, VOF, ANSYS Fluent CFD Simulation Tutorial

Description

This project simulates the absorption of ammonia from air inside an absorption tower using ANSYS Fluent.

Absorption is a method of separating the components of a gas mixture by bringing it into contact with a liquid solvent. The process relies on the difference in solubility between the gas-phase components: where the gas meets the liquid solvent, one or more components transfer into the liquid phase and separate from the gas stream. In refineries, one common use of absorption towers is to strip ammonia out of a gas stream.

In this model, an airflow carrying one percent ammonia enters at 0.43 m/s through a nozzle at the bottom of the tower chamber. At the same time, liquid water enters at 0.0332 kg/s through a nozzle at the top. As the ammonia-laden gas rises and contacts the descending water, the ammonia is absorbed into the water.

The geometry was built in three dimensions in Design Modeler as a vertical absorption tower: the ammonia-air stream enters through the bottom nozzle and exits from the upper section, while the water enters through the top nozzle and exits from the lower section. The domain was meshed in ANSYS Meshing using an unstructured grid of 478,882 elements.

Simulation Methodology

The simulation uses the VOF multiphase model, with the air stream carrying one percent ammonia and liquid water acting as the solvent.

Results & Conclusion

After solving, we obtained two- and three-dimensional contours of pressure, velocity, turbulent (eddy) viscosity, density, and the volume fractions of water, air, and ammonia. The results show the ammonia transferring from the gas into the water stream, confirming that the water absorbs the ammonia and separates it from the gas.