Dry Desiccant Systems
In a typical dry desiccant system, the desiccant is mounted on a rotating wheel.
As the wheel turns, the desiccant passes alternately through the incoming process
air where the moisture is adsorbed and through a “regenerating” zone where the
desiccant is dried and the moisture expelled. The wheel continues to rotate and the
adsorbent process is repeated.
Typically, about three-fourths of the desiccant
wheel is exposed to the incoming air throughout the process. During regeneration,
the desiccant is heated by a direct-fired gas burner or indirect-fired water or steam
coil.
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Process Inlet—Air to be
dried. May be outside air, inside air or, more
commonly, a mixture of air with high humidity content. Process Outlet—Air is dried by
desiccant wheel. May be cooled, filtered or
otherwise handled. Relative humidity is
substantially lower and temperature slightly raised. |
Reactivation Inlet—Air
flow, usually outside air, that drives moisture off wheel.
Reactivation air is heated by direct-fired gas burner or indirect-fired
water or steam coils.
Reactivation Outlet—Hot,
wet air from wheel is exhausted outside or passed through an air-to-air heat exchanger. Using a heat exchanger to preheat incoming process
air offers substantial savings in northern climates.
Liquid
Desiccant Systems
Like
a dry desiccant system, a liquid desiccant system relies on the ability of certain
materials to absorb moisture from air. In a liquid system, the moist incoming air
passes over a high-surface area medium containing the liquid desiccant solution, usually
lithium chloride. As the moisture absorbs into the desiccant liquid, the diluted
lithium chloride solution flows to a heat exchanger where the heat from a gas-fired burner
removes the moisture, reconcentrating the solution. The regenerated desiccant
solution then flows back to the medium for re-use.
Schematic courtesy of Kathabar, a division of Ross Air
Systems |
