Theory Of Operation
In HOC type dryer, hot air at 120 degree celsius to 140 degree celsius from Compressor discharge is directly used for the desiccant regeneration. Running cost of this dryer is virtually NIL. It has two drying towers filled with the Activated alumina or molecular sieve desiccant and they alternate in process every 4-hour automatically.
Compressed air directly from air compressor discharge is taken to air dryer inlet through pipelines at 130 degree celsius (Min) temperature. This hot air is passed one drying vessel where saturated desiccant is regenerated by this high temperature air. After picking up moisture from bed, this air is cooled in an intermediate cooler. Here moisture is condensed and removed by an auto drain trap. At 40 degree celsius temperature this air passes through second drying vessel where moisture gets adsorbed and dry air comes out. Cycle time is 4-hours regeneration and 4-hours drying. After 4-hours changeover of vessels takes place. In the regeneration cycle heating of the bed is only for 2-hours and thereafter the bed is cooled by dry air. Dry air is cooled to 40 degree celsius temperature before going out of the air dryer.
Due to NIL operating cost, this design is becoming more popular. To utilize full heat energy of compressor discharge, HOC type dryer should be located very close to compressor discharge. These dryers are recommended only for Dew-Point (-) 40 degree celsius and the capacities above 300 Nm3 /hr. In smaller capacity the hot air discharge does not reach 140 degree celsius and hence this design can't be used.
Salient Features
1. No loss of compressed air in purge. It is a no purge loss design.
2. Maintenance is easy and simple as there are no heaters and no other moving parts except 4- way valves.
3. Fully automatic, continuous operation without any attention of operator.
4. Negligible operating cost. It neither requires electric power for regeneration nor there do any purge loss of     compressed air.

Theory Of Operation
In HOC type dryer, hot air at 120 degree celsius to 140 degree celsius from Compressor discharge is directly used for the desiccant regeneration. Running cost of this dryer is virtually NIL. It has two drying towers filled with the Activated alumina or molecular sieve desiccant and they alternate in process every 4-hour automatically.
Compressed air directly from air compressor discharge is taken to air dryer inlet through pipelines at 130 degree celsius (Min) temperature. This hot air is passed one drying vessel where saturated desiccant is regenerated by this high temperature air. After picking up moisture from bed, this air is cooled in an intermediate cooler. Here moisture is condensed and removed by an auto drain trap. At 40 degree celsius temperature this air passes through second drying vessel where moisture gets adsorbed and dry air comes out. Cycle time is 4-hours regeneration and 4-hours drying. After 4-hours changeover of vessels takes place. In the regeneration cycle heating of the bed is only for 2-hours and thereafter the bed is cooled by dry air. Dry air is cooled to 40 degree celsius temperature before going out of the air dryer.
Due to NIL operating cost, this design is becoming more popular. To utilize full heat energy of compressor discharge, HOC type dryer should be located very close to compressor discharge. These dryers are recommended only for Dew-Point (-) 40 degree celsius and the capacities above 300 Nm3 /hr. In smaller capacity the hot air discharge does not reach 140 degree celsius and hence this design can't be used.
Salient Features
1. No loss of compressed air in purge. It is a no purge loss design.
2. Maintenance is easy and simple as there are no heaters and no other moving parts except 4- way valves.
3. Fully automatic, continuous operation without any attention of operator.
4. Negligible operating cost. It neither requires electric power for regeneration nor there do any purge loss of     compressed air.