Control Valves for Pressure Swing Adsorption Plants

PSA plants (PSA = Pressure Swing Adsorption) are used to separate and clean gases such as hydrogen, helium, nitrogen. In the

case of hydrogen, it is possible to achieve cleanliness levels of 99.9999% by means of the PSA method. The method is very energy efficient since it takes place at ambient temperature.

At the heart of this method are 4 to 12 pressure tanks that are filled with an adsorbent. This adsorbent has the property of adsorbing certain gases at a particular pressure and of releasing them again at a lower temperature. By means of a systematic transfer of the gas between the individual adsorbers, the gas is cleaned in a staged manner. The typical cycle time of a PSA plant lies between 20 seconds and several minutes and thus places high requirements on all plant components – particularly on the control valves. These must work reliably for more than one million operating cycles per year and moreover must guarantee a bubble-tight shut-off. Control valves optimized for alternating pressure plants:

• are made of superior quality cast steel with a reduced carbon content to minimize the risk of hydrogen embrittlement

• have a reliable soft seal function and

• at nominal valve size of 80 (3") and higher provide a reliable pressure balancing system, since the travel times required are possible only with relatively small pneumatic actuators.

The trend to ever larger actuator forces within ever shorter switching times leads to the preferred use of double-acting piston actuators. In recent years, this type of actuator has proved itself in a large number of installations.