Page 62 - Pneumatic ebook (2)_draft 13 sept 2021

Air dryer – adsorption

b. Adsorption (desiccant) Drying

1. Desiccant air dryer has different working principle where moisture from the air stream and onto
a desiccant material is adsorbed in a reversible process. Dew points produced is low which
means this is air dryer is a good choice when process require extremely dry air.

2. Silica gel or activated alumina in granular form is used as a chemical in this drying process.
This chemical contained in a vertical chamber to absorb moisture from the compressed air
passing through it. The drying agent is regenerated by drying or heating in a regenerating
column when it becomes saturated as shown in the Figure.

3. Wet compressed air enters to the column 1 through a directional control valve and comes out
as dried air to the outlet port.

4. 10 – 20% of the dry air will pass through the orifice O2 and go to the column 2 to reabsorb
moisture from the desiccant to regenerate it. The regenerating air flow then goes to exhaust.

5. To provide continuous dry air, a timer is used to switch periodically the directional control valve
so that the supply air is allowed alternately to one column.

Figure: Principle of the 6. The degree of saturation of the desiccant may be monitored by incorporating a colour
heatless adsorption air dryer indicator.

INTRODUCTION TO PNEUMATIC SYSTEM 26