Air Drying Systems
Compressed air is used in industry for instrument operation and also used for process purposes like intermingling with products, sulphonation, drying of polyester chips, etc. This air is normally through blower and is under low pressure.
However air is contaminated with moisture,dust, oil, grease, etc.These are acceptable according to national and international standards which vary from country to country. In India following limits are generally specified.
- Dew point required: -40 Deg. C to -80 Deg. C at atmospheric pressure.
- Dust: Between 1 microns to 5 microns Oil,
- Grease: Less than 1 ppm.
Moisture removal is done by knocking down the moisture in a separator (Knock out drum) and then passing the air through a chiller for smaller dew point. However, desiccants are used for dew point of below — 40 Deg. Most common desiccants are as follows:Silica gel, Activated Alumina, Molecular. Silica gel and Alumina are sufficient for a dew point up to -40 Deg C but for critical dew point molecular sieves are used.These are expensive and the temperature for regeneration is higher.
Elgin manufactures the following types of air dryers
This dryer works on the principle of pressure swing. The cycle time is 5 minutes and no heat is required for regeneration. However there will be loss of some Air.
A small air quantity is circulated through an embedded heater for regeneration.
NO LOSS PURGE TYPE
A small stream of Air is taken out through the distributor and heated for regenerating the desiccant. The Air stream is mixed with inlet air & hence there is no air loss.
HEAT OF COMPRESION TYPE
The air from Compressor outlet, which is around 140 deg C, is used directly for regenerating the desiccant thereby saving energy.
LOW PRESSURE DEHUMIDIFIER
Air is taken from the blower at small pressure and dried. Heater is required for regeneration.