A 6500-litre tank containing air at 1 atm and 300k is to be inserted to 0.8 mol% oxygen concentration by using pure nitrogen. you are required to assess the following inerting techniques:

Pressure purging with nitrogen at 350 kpa, followed by venting to an atmosphere.

Vacuum purging to 10 kpa absolute and the vacuum releases the nitrogen until the pressure returns to atmospheric condition.

Combined vacuum and pressure purge with the vacuum pressure of 10 kpa absolute and pressure purge of 350 kpa.