The Deliquescent type compressed air drying system is a portable compressed air drying package used mainly for media blasting and painting contractors who are doing metal surface preparation work.
This type of dryer has been used extensively in construction applications, outdoors, with engine driven portable air compressors where no external power source is available to run other types of air drying equipment.
The principals of operation for the moisture absorption are very simple, as outlined below, however, there are other components required for the system to function properly.
These would be:
- An inlet coalescing pre-filter to prevent oil carryover from the compressor entering the dryer and contaminating the drying material
- A particulate style after-filter to prevent air dryer media carryover from damaging downstream equipment
- A mechanical drain to remove water and liquefied dryer media from the dryer tank.
As with any type of air dyer, the cooler the inlet air into the dryer, the better it will perform. Therefore, some type of compressed air after-cooler is recommended as well.
There are a number of different types of media that can be used in this design of dryer, each offering different levels of drying capacity (dewpoint suppression).
It is important to note that the air temperature, at the point of use, must never fall below the suppressed dewpoint available or water will form in the outgoing air.
Incoming air enters the vessel near the base and passes through the mechanical separation section. Due to expansion, the free liquids and solids drop to the bottom of the vessel.
To some degree, this constitutes a pre-drying of the air.
The air then enters the desiccant bed of deliquescent materials such as water-soluble salts or shotted urea. The hygroscopic chemicals condense water vapor as they deliquesce or dissolve.
Absorption occurs until the tablets are completely consumed, at which time, they must be replaced.
Dew point suppression is subject to the following:
- Age and Composition of the deliquescent material.
- Compression of the tablets.
- The vessel configuration.
- The compressed air inlet temperature.
- The compressed air velocity. (Based on pressure)
- Lowest initial cost of all dryer types.
- No electrical hook-up.
- No moving parts.
- Simple operation.
- Dewpoint suppression is between 20º to 30º F (On average).
- Deliquescent material must be added to or replaced as it absorbs and melts.
- Ecological problem of disposing of the dissolved deliquescent material.
- Cost of replacement deliquescent and of disposal of dissolved deliquescent material.
- Carryover of corrosive deliquescent materials into the downstream piping network
and air using components.
- Parts of the deliquescent materials can solidify in the bed, causing channels for the air to
by-pass most of the drying material. This reduces the dryer’s performance.
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