What is it?
Typical adsorbents include (EIPPCB; 2016):
- granular activated carbon (GAC), the most common adsorbent with a wide efficiency range and not restricted to polar or non-polar compounds; GAC can be impregnated, e.g. with oxidants such as potassium permanganate;
- zeolites, properties depending on their manufacturing, working either as mere molecular sieves, selective ion exchangers or hydrophobic VOC adsorbers;
- macroporous polymer particles, which are used as granules or beads, without being highly selective with respect to VOCs;
- silica gel;
- sodium-aluminium silicates.
- fixed-bed adsorption;
- fluidised-bed adsorption;
- continuous moving-bed adsorption;
- pressure swing adsorption (PSA).
Design, maintenance and efficiency
Temperature monitoring of the gas outlet of the GAC adsorber is required to prevent fire risk. Another important measurement is the pressure drop across the adsorbent bed. Across the bed, the pressure should remain roughly constant. There should be an alarm for high pressure.
Table 1. Application limits and restrictions associated with adsorption.
|Gas flow (Nm3/h)||100-100000||<100000|
|Temperature (°C)||15-80 (ideally about 20)||<250|
|Pressure drop (mbar)||10 to 50||NI|
|Odour concentration (ouE/m3)||5000-100000||NI|
|Dust content (mg/Nm3)||Low concentration to prevent obstruction||Low concentration to prevent obstruction|
|Relative humidity of the waste gas||max 70%||NI|