9. PSA unit reliability and degraded operating modes

The large number of valves used in a pressure swing adsorption unit, combined with a high cycle frequency, entails risks of fatigue or premature failure that must be taken into account when designing a PSA unit. As a result, it is common practice to implement emergency PSA operating modes, necessarily degraded, to ensure continued production of purified gas, even in the event of a major valve or adsorber failure. These back-up modes are called "exceptional operation" and may correspond to continued production thanks to :

• the use of fewer adsorbers per insulation and the removal of at least one adsorber (the most common) from the cycle;

• elimination of a transverse line of valves by reducing the number of balancing operations required by the