Understanding Deliquescent Dryers

Deliquescent Dryer

Deliquescent dryers can sometimes be confusing. Some compressed air dryer vendors use the terms deliquescent and desiccant synonomously as if they were interchangeable in describing their equipment. The deliquescent dryers are not a complex drying system and found most commonly in the petrochemical industry.

Unlike any other dryer, a deliquescent dryer is also used to reduce or remove moisture before it turns to liquid water. These dryers can be installed indoors, outdoors, offshore or any remote location. They do not require electric for operational purposes or have any moving parts, making them easy to maintain and economically more efficient. In a deliquescent dryer, moist air (gas) passes over a layer of deliquescent tablets which absorb moisture from the air. The pressure dew point lowers as the tablets slowly dissolve, the condensation falls into the drain area, and the drier air flows through the outlet into the piping system.

The best deliquescent materials are salts with a strong attraction for moisture. Deliquescent desiccants (drying tablets) are formulated from calcium chloride, magnesium chloride, potassium chloride and lithium chloride. Not all deliquescent desiccants are equal. The final formulation and properties of the desiccant can have significant impact on the design of a dryer tank. That is, the surface of the desiccant chemical, often beads or pellets, will liquefy, and the resulting liquid will flow to the bottom of the vessel. There is either a drain (manual or auto) at the base of the deliquescent dryer which is used to expel the collected fluid.

Some factors that will affect the consumption of the desiccant are the type of adsorbent, type of adsorbate, the size of the adsorbent bead or pellet, the concentration of the adsorbate in the compressed air stream, and the temperature of that air stream.

You will want to have a water trap, also known as a general purpose compressed air filter plumbed in line just upstream from the deliquescent dryer. Otherwise, any liquid water flowing with the compressed air into the air dryer will make short work of the desiccant chemical, requiring a more frequent – and expensive – recharge.

The compressing of air generates heat. That hot, moist compressed air will consume the desiccant chemical in the deliquescent dryer much more quickly. Best practice is to ensure the air flow to the dryer is as cool as possible with, if possible, a long air line and a dwell tank prior to the deliquescent dryer to allow the air to cool and have water saturate out naturally.

A deliquescent dryer can be expected to reduce the compressed air dew point by 20 – 30 deg. F, or so. The degree of drying depends how saturated the airflow is going in and on the type of deliquescent chemical used.

Unlike other forms of compressed air dryers, a deliquescent unit doesn’t guarantee the air will reach a certain dew point. The amount of water vapor in the air that exits the dryer is completely predicated on how much water vapor is in the air going into the dryer.

I hope this helps increase your understanding of deliquescent dryers. EXAIR has many Intelligent Compressed Air tools and accessories. We would love to help you learn more about our products. Please contact us as we are eager to help.

Eric Kuhnash
Application Engineer
E-mail: EricKuhnash@exair.com
Twitter: Twitter: @EXAIR_EK

Leave a Reply