Water Solutions ...4

Water solutions... continued! On other pages I have talked about removing water from the compressed air via a number of different methods including after coolers and refrigerant dryers. Page one is here.

Now I would like to explore some additional compressed air water removal options, for you.

Desiccant Dryers

Some applications require the compressed air to be bone dry. The air will have a dew point down to the minus temperatures, in some cases down to -100 deg. F.

This means that as long as the temperature in the system is higher than that -100 deg. F, no more water can condense out of that compressed air anywhere in the plant.

There are costs associated with this type of system, and, as I always say, you only want to treat your air to the level of dryness that you need. Going further will add cost, with no real benefit for your compressed air using applications.

Desiccant dryers can be relatively small, in-line type, or twin tower units with regenerative capabilities for high compressed air-flow systems.

Simple, in-line desiccant dryers are not complex, relatively low cost, are easy to install, and work! They contain a desiccant chemical that is consumed as water is adsorbed.


You would install the in-line desiccant filter immediately just before the application for air. Just upstream from it I recommend that you install a general purpose compressed air filter. The G.P. filter will remove any free water before it can enter into, and perhaps overload, the in-line desiccant dryer.

Yes, the desiccant will remove free water but this will rapidly deplete the desiccant chemical. It is preferred that the desiccant dryer be applied to remove water vapor, and to dry the air to the point where its dew point will be well below the temperature of the application. If it does this, there should be no more condensation downstream from the desiccant dryer.


Some in-line desiccant dryers need to be drained regularly. Their use results in a pool of water and desiccant chemical in the bottom of the housing. If this filtrate is not drained regularly, it will ultimately destroy the desiccant dryers capacity for drying air.

Check the manufacturers specifications for the unit you wish to used to be sure you are familiar with its operation.

Refills Needed Regularly

The in-line desiccant dryers will require periodic charging with the desiccant material, and this means that you have to know when to do it, and of course someone has to do it.

This is an important maintenance issue. It is one of the down-sides of the in-line desiccant systems, particularly in companies that have more maintenance work to do in the plant than their down-sized maintenance staff can cope with.

Refill the in-line desiccant dryers regularly, or you will soon see water appearing in your tools and equipment.

Twin Tower Desiccant Dryer

If you need bone dry air, in your application, and you need quite a lot of that dry, vapor free, compressed air, there is another alternative. Compressed Air Dryer

The twin tower desiccant dryer has two desiccant dryer towers built into the one system.

Periodically, based on time, or perhaps a moisture sensor in the compressed air system, the air entering the dryer will change flow paths from one desiccant tower to the other.

Once air is flowing through the new path to be dried, dry air from that tower is then used to regenerate or dry the desiccant charge in the now unused tower.

After a certain time period, the valve shifts again, and the compressed air flows to the tower with the now-dry desiccant, and that new supply of dry air is used to regenerate the desiccant in the other tower.

These twin tower desiccant units are sized based on the expected flow demands of your compressed air system and the level of dryness required by the compressed air equipment in the shop.

Heated Or Heatless

One type of dryer is classified as heatless, meaning that no external heat is required or needs to be generated to help dry the desiccant.

Other similar-in-concept dryers do heat the air to speed the drying process.

The choice between them depends on your plant air demand, the level of dryness required, the speed with which the towers need to regenerate, and of course, the cost to buy and run.

In time, these twin-tower units will require maintenance, including recharging of the desiccant medium. Yet, they do provide well-dried compressed air for the whole plant, negating the need for installing multiple, in-line units throughout the whole facility, along with the need to maintain these multiple desiccant dryers.