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Written by Chuck Henderson, Vice President Henderson Engineering Co., Inc. DELIQUESCENT The deliquescent dryer is the simplest and easiest dryer to own and operate and will be the best choice for many compressed air applications. The deliquescent dryer is a pressure vessel, which is filled with a hygroscopic desiccant. This desiccant deliquesces, that is, it draws water vapor out of the air and in so doing slowly dissolves. The dissolved desiccant and liquid water collect in the bottom of the tank where they can be easily drained. See Illustration 1.
Illustration 1: Deliquescent Dryer Pressure Vessel The performance of the deliquescent air dryer varies directly with the inlet air temperature. For outdoor air lines, we can make best use of the deliquescent dryer's varying performance by installing the dryer and an air cooled aftercooler outdoors. By using the varied ambient temperatures, the deliquescent dryer can deliver dewpoints below 0°F and has been protecting outdoor air lines from freeze-ups for many years. For indoor general shop air, we can use a water-cooled aftercooler upstream of the deliquescent dryer for good year round protection. The only cost of operation for the deliquescent dryer is the replacement desiccant. Since the desiccant slowly dissolves while drying the air, you need to add more desiccant to the dryer every few months. The cost of the desiccant is inexpensive and because you only need add to the dryer as you use air, the overall cost of operation is the lowest of any type dryer. There is no electricity used and the dryer has no moving parts. There are, however, some drawbacks to the deliquescent dryer. If the temperature going into the dryer goes up due to a failure of the cooler, or whatever, the dryer will be overloaded and will be unable to perform. The desiccant used in the dryer is an inert compound, based mostly on sodium chloride, although one manufacturer uses potassium carbonate. The desiccant by itself is generally not corrosive; however, because of its affinity for moisture and the presence of oxygen in the air stream, it is very easy for rust or oxidation to occur. It is very important that the dryer be adequately protected on the inside so that the vessel will not rust, and even more importantly, the dryer must be supplied with an afterfilter. It is quite common for deliquescent desiccant to carry-over into the air lines where it can cause considerable damage. The only way of preventing this is by installing an afterfilter either inside of the dryer, as shown in Illustration 1, or mounted downstream of the dryer. We would not recommend the use of deliquescent dryer without using an afterfilter. | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
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