The model equations for four stages of PSA are identical, while different stages are distinguished from each other by their boundary conditions of pressure: Adsorption (Ads), Blowdown (Bd), Evacuation (Evac), and Feed pressurization (Press). In the following equations, @ (?(@A refers to the time duration for a PSA cycle. @ (?(@A is always (re-)initialized as 0 when starting a new PSA cycle.