A Parametric Study of the Oxygen Elimination Process in a Packed Bed

Abstract

This study is concerned with an industrial application involved in the manufacture of the polymer Nylon12, which is polymerised from solid monomer particles. There exists interstitial air among those particles. Oxygen in the air is a strong inhibitor of the polymerization reaction and has to be eliminated from the packed bed of monomer particles before they are introduced into the polymerization reactor. This is done by injecting nitrogen into the packed bed from the bottom of the bed. The nitrogen spreads into the packed bed displacing the air inside. This process is already being employed in the polymer processing industries. The present research focuses on how to make this oxygen elimination process more effective.The information from a parametric study can be used to improve the design and operation of the packed bed to have a more effective oxygen elimination process. Conducting the parametric study numerically saves a lot of time and cost. The numerical model used to simulate the fluid flow in packed beds was successfully validated against experimental and analytical results in previous work. This model is used to carry out a numerical parametric study. It is found that having a single jet at the centre of the packed bed is better than having 4 jets closer to the wall. Having an inclined jet instead of a jet parallel to the wall also improves the oxygen elimination process. Simulations are also done with helium as the carrier gas; though economically, it is better to use nitrogen, the purpose of using helium is to investigate the effect of the properties of the carrier gas on the oxygen elimination process.