Today I want to discuss dryers and not the type that I have repaired many times due to having three kids in my house. Speaking of which, the amount of hair that gets trapped within a dryer is one of the things my nightmares are made from. You’d think we have a Yeti living in our home. While the picture below is of our first dryer and washer, that platform has been repurposed into a workbench and the metals have all been recycled back into something else now. That’s not what we are here to talk about. Instead, we are going to discuss deliquescent dryers.
Deliquescent dryers can sometimes be confusing. Some compressed air dryer vendors use the terms deliquescent and desiccant synonymously, as if they were interchangeable in describing their equipment. Deliquescent dryers are not complex drying systems and are most commonly found 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 in any remote location. They do not require electricity 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 that absorb moisture. 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 due to their strong attraction to 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 significantly impact 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.
Compressing air generates heat. That hot, moist compressed air will consume the desiccant chemical in the deliquescent dryer much more quickly. The best practice is to ensure the airflow to the dryer is as cool as possible, with a long airline and a dwell tank before 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.
Brian Farno, MBA – CCASS Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF
