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 2.2 Deliquescent (Absorption) Type. The deliquescent or absorption dryer is
lowest in initial cost but requires continual replenishment of the drying
medium (figure 4-10). Simple in design, this type of dryer is a pressure
vessel in which a bed of crystalline solids is placed on top of a screen which
is located close to the bottom of the vessel. Wet air from the aftercooler
and separator enters the bottom of the vessel and flows upward through the
bed. As it passes through the bed, the liquid water and vapor present in the
air, dissolve the drying medium in what is termed a deliquescent effect. The
resulting solution trickles to the bottom of the dryer where it is removed by
a trap. The frequency with which the crystalline absorbent material must be
replaced is a function of the design thickness of the bed and the amount of
water and vapor present in the air entering the dryer.
2.3 Refrigeration Type. Dryers that remove moisture from the air by
condensation incorporate a mechanical refrigeration unit (figure 4-11) or cold
water, if available. Inlet air passes through the precooler/reheater to the
air-to-refrigerant exchanger which contains the refrigeration coils. As the
air passes over the coils, further cooling takes place and moisture condenses
into droplets. The droplets of oil or water then pass through the
moisture/oil separator and are collected and drained through a condensate
trap. The cool, dry air is then directed back through the precooler/reheater,
warmed by the incoming air and discharged for reuse by the system.
FIGURE 4-10. Deliquescent (Absorption) Dryer
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