Water solutions... continued! On previous 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 about compressed air water solutions 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 absolutely bone dry. The compressed air will have a dew point (link to information page on this site) down to the minus temperatures, in some cases down to -100 deg. F. That's dry air.
What that means for the compressed air with a dew point that low is that as long as the temperature in the system and ambient air 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 make dryer air yet add cost, and if the system does not require compressed air that dry, there will be no real benefit for your compressed air using applications to pay for greater dryness.
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.
Just upstream from the desicant dryer I recommend that you install a general purpose compressed air filter. This G.P. filter will remove any free water before it can enter into, and perhaps overload, the in-line desiccant dryer. It will also remove airborne contaminants that could, in time, coat the chemical in the dryer, rendering it ineffective.
Yes, the desiccant will remove free water too, but in so doing it will rapidly deplete the desiccant chemical. The in-line desiccant dryer should be installed to remove water vapor, and to dry the air to a dew point below the temperature of the application and ambient air. If it does this, there should be no more condensation downstream from the desiccant dryer.
Check the manufacturers specifications to determine how best, and how frequently, to drain a particular desiccant dryer.
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.
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.
Other similar-in-concept dryers heat the air to speed the drying of the desiccant.
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.