A Mathematical Model for Study of Cyclic Purge in Vessels with Complex Geometry

Removal of impurities from stagnant regions in process vessels and flow components is a major bottleneck of purge operations and typically associated with large downtimes and UHP gas consumption.  A comprehensive mathematical model is developed for study of the purge process in chambers with complex geometry and stagnant regions inaccessible to gas flow.  The model takes into account the dynamics of removing impurities in the gas phase as well as those adsorbed on the chamber surfaces.  Using this model, the conventional Steady State Purge (SSP) is compared with a proposed unsteady Pressure Cyclic Purge (PCP) technique.  PCP is found to be advantageous over SSP in terms of gas usage and purge time required to reach a given target cleanliness.  The effects of a number of key design and operational parameters such as chamber geometry, pressure range, and cycling pattern are investigated.  The results show that the model is a powerful tool for finding the optimum operating conditions for purging a system.