In all Heat Reactivated designs described above, thermal energy is required from outside for regenerating the desiccant. In HOC type Dryer there is no requirement of external heat energy. Hot air at 120 to 1400C. from Compressor discharge is directly used for desiccant regeneration. Running cost of this dryer is virtually NIL. It has 2-Drying towers filled with Silica Gel desiccant and alternate every 6 hours automatically. Due to large size of vessels, big quantity of desiccant, initial cost of this type Air Dryer is also high.
This is the latest design in Air Dryers and is feasible only in capacities above 300 NM3 / hr. ( in smaller capacity Air Compressor, the hot air discharge temperature of 1400C. is not available and hence this design cannot be used ). Due to NIL operating cost, these dryers are becoming popular. To utilize full heat energy of compressor discharge, HOC
Type dryers should be located very close to Air Compressor discharge.
These Dryers are recommended only for Dew point upto (-) 400C and for capacities above 300 NM3 /hr. Operating pressures can be from 7 Kg/ cm2 to 20 Kg /hr cm2 .