Heatless Type|
Heat of Compression Type (HOC) |
Internal Heater Type (IHD)
Blower Heat Regenerated Type (BRD)
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Split Flow-No Purge Loss Type (SFD)
Refrigerated Type | Custom Made
These dryers use heat which is available from the compressor itself. To successfully work, a desiccant bed must be heated to about 180 deg C to allow regeneration. Re-activation temperatures lower than this will not dry out saturated desiccant. With this type of dryer, the heat is taken from the compressed air immediately after compression and just before it passes through a water cooled intercooler or after cooler.
The air pipe-work must be plumbed in such a manner that it passes through the desiccant dryer. This means that the dryer must be near or attached to the compressor, or the interconnecting pipe-work must be well lagged to prevent heat loss. Unfortunately, very efficient air compressors have inter-stage temperatures much lower than 180 deg C, this means that heat of compression dryers would not work with them.
As a rule of thumb, single or two stage compressors will provide enough heat for this type of dryer to work. Three stages and more generally have 'air-off' temperatures lower than 150 deg C and therefore cannot reactivate desiccant. These dryers cut operating cost to near zero by using the heat of compression for the regeneration. Airox HOC minimizes potential for wear and mechanical failure. It also lowers the initial cost than other regenerative dryer’s designs.
Airox dryers averages less than $10 per year total electrical cost; there are no heaters or blowers to consume electricity and there is no purge air loss. The design delivers pressure dew-points in the specified range, depending on customers operating conditions. The design consumes none of the valuable dry air. The design can be equipped to provide -40°F dewpoints or lower, under every possible scenario, including operation of rental compressors.
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 ands 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.
Energy conservation by heat of Compression type compressed air dryer is a breakthrough in compressed air drying technology. The hot air from the compressor at 120 °C and higher temperature is used directly for regeneration of the desiccant. After regeneration, this air is cooled down to 40 °C and then it is dried in second tower. Thus the use of heaters is eliminated. For e.g. In the 6+6 Hrs. cycle the hot air is fed for regeneration for 4 hours and for balance 2 hrs. a changeover takes place where the air is first cooled in cooler, then dried and before going to the outlet, cools the regenerated desiccant bed, thus bringing it down to ambient temperature.
This cycle is reversed for next 4 hours where the adsorber drying the air in the previous cycle goes for regeneration and vice versa. The dryer is fully automatic with pneumatically actuated Ball/plug valves. A sequence timer controls operation of these valves. There is considerable power saving in this type of Air Dryers and the dew point is also better than the refrigerated type of dryers whereas, the power consumption is almost negligible.
• No loss of compressed air in purge. It is a no purge loss design.
• Maintenance is easy and simple as there are no heaters and no other moving parts except 4- way valves.
• Fully automatic, continuous operation without any attention of operator.
• Negligible operating cost. It neither requires electric power for regeneration nor there do any purge loss of compressed air.
• Minimizes potential for wear and mechanical failure.
• Lower initial cost than other regenerative dryer designs.
• The design consumes none of your valuable dry air.
