Pressure Purging with Impure Nitrogen

Vacuum and Pressure Purging with Impure Nitrogen 

The equations developed for vacuum and pressure purging apply to the case of pure nitrogen only. Many of the nitrogen separation processes available today do not provide pure nitrogen they typically provide nitrogen in the 98%+ range. 

Assume that the nitrogen contains oxygen with a constant mole fraction of yoxy. For a pressure purging procedure the total moles of oxygen present at the end of the first pressurization is given by the moles initially present plus the moles included with the nitrogen. This amount is 

The total moles in the vessel at the end of the first pressurization are given in Equation 7-1. Thus the mole fraction of oxygen at the end of this cycle is 

This result is generalized into the following recursive equation (Equation 7-11) and a generalized equation (Equation 7-12) for the oxygen concentration at the end of the /th pressure cycle  

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