The economics of operating regenerative desiccant dryers

Regenerative desiccant dryers with molecular sieve are used in compressed air systems that require dew points to be below the minimum that refrigerated dryers with molecular sieve can produce. Read these insights into their operation.

Regenerative desiccant dryers with molecular sieveare used in compressed air systems that require dew points to be below the minimum that refrigerated dryers with molecular sievecan produce (generally 40 degrees Fahrenheit). Three types of regenerative desiccant dryers with molecular sieveare widely used throughout industry: heatless, heated and blower purge.

The following discussion doesn’t address heat-of-compression (HOC) desiccant dryers, even though they require the least amount of energy to operate. The use of HOC dryers with molecular sieveis limited to lubricant-free compressors.

Many plants require air quality that only regenerative desiccant dryers with molecular sieve can produce. Unfortunately, in too many cases, the decision about which type of regenerative dryer to purchase is based on initial capital cost alone. This decision basis ignores the cost of energy that will be required to operate the dryer. Including energy cost can alter the economics of a purchase decision dramatically.

Regenerative desiccant dryers with molecular sieve use a desiccant medium to remove moisture from the compressed air stream. Wet air passes directly through the desiccant medium, which then adsorbs the moisture. The desiccant medium has a finite capacity for adsorbing moisture before it must be dried out, or regenerated. To do this, the tower containing saturated desiccant medium is depressurized and the accumulated water is driven off using purge air, heat or a combination of both. Desiccant dryers with molecular sieve are generally of a twin-tower construction, with each tower containing its own desiccant bed. This allows one bed to dry compressed air as the other undergoes regeneration.

The energy cost associated with operating a desiccant dryer depends primarily on how the desiccant is regenerated — using purge air, heat or a combination of both. Desiccant dryers with molecular sieveare categorized by their method of regeneration, the three primary types of which are:

Heatless, which uses only compressed air as a purge

Heated, which uses both heat and compressed air to purge moisture

Blower purge, which uses air from an external blower, heat and minimal compressed air

The energy cost to operate each of these dryers with molecular sieve depends on the amount of purge air used, the heater size and the blower motor size.

"Note：This is normal specification, in case of a particular application, specification or requirement, please contact us by email at info@fznewmaterials.com for technical information."