There are various types of air dryers with 4A molecular sieve such as the regenerative desiccant type, refrigerated type, deliquescent type, membrane type and point-of-use type dryer with 4A molecular sieve. Each type of dryer has its own limit on the air outlet dew point. Regenerative desiccant air dryers with 4A molecular sieve are commonly used in the process industry and are the most expensive.
The dryers work by adsorbing moisture on desiccant material such as alumina, silica gel molecular sieves. The desiccant material is contained in two packed towers which are alternately in service or being regenerated. The regeneration can be achieved by different methods, such as, using a purge of dry air from the operating tower or by using internal heaters or by an external heat source. Use of purge of dry air is a simple process with the discharge air purged to the atmosphere. However, use of purge air consumes about 15 to 20 percent of the compressed air capacity and is best utilized when there is sufficient excess air capacity.
The capacity of air dryers with 4A molecular sieve as provided by the vendor is generally in terms of “inlet scfm” at a service pressure of 100 psig and service temperature of 100F. At different service conditions, the inlet flow to the dryer needs to be corrected by multiplying by the pressure correction factor and the temperature correction factor.
If service pressure is higher than 100 psig (say 120 psig) the flow capacity of the dryer with 4A molecular sieve increases by the pressure ratio (120+14.7)/(100+14.7)=1.17. On the other hand, if service temperature is higher than 100F (say 115F), the flow capacity of the dryer decreases by the ratio of moisture saturation vapor pressure ratio at 100F and 115F (that is, 0.9492 psia/1.4711 psia=0.64).
"Note：This is normal specification, in case of a particular application, specification or requirement, please contact us by email at email@example.com for technical information."
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