Water Removal

Most all industrial compressed air systems require some type of dryer. The reason is simple, to remove water from the compressed air prior to use downstream.

I saw a recent advertisement with the caption:

I’m not sure how one can determine the “best ways” to dry compressed air without a complete evaluation of the air usage

First things first:

Let’s look at where the water comes from?

Water comes from the atmospheric air that the compressor ingest through the intake. Keep in mind that most plants will look to have compressed air pressure at 100 PSIG. To achieve this pressure the compressor runs a compression ratio of 8 to 1 depending on your physical location. Meaning it must ingest 8 cubic feet of atmospheric air and compress this into 1 cubic foot to achieve the desire pressure.

When you compress 8 cubic feet of air your compressor also compresses all of the contaminants that were in that 8 cubic feet into one cubic foot, including the water that naturally exists in the atmosphere. Its important to know that the air’s ability to hold moisture in a vapor state is directly related to it’s temperature and pressure. In the atmosphere where the pressure is nominally 14.5 PSIA, water will stay in a vapor state until the air reaches it’s saturation point. ie. all the water it can hold at a given temperature (our pressure is already set at 14.5 PSIA). Once this level is exceeded – it rains. Or the water that was previously in a vapor state now converts to liquid form.

The same circumstance is happening inside the pipes of your compressed air system. Once you compress all of the contaminant (in this case water) into a single cubic foot, even with the increase in temperature and pressure, there is still more water than the air can hold in a vapor state so it rain inside your pipes. Additionally as the temperature drops the air’s moisture holding capacity will be lowered and water will continue to condense out as a liquid.

Water is extremely detrimental to compressed air uses downstream. To determine what type of dryer your system will require mandates a look at the possible end uses downstream. For example, if the air use downstream is solely to blow metal chips from a machining operation from a blow gun then chances are the water condensing out will not cause a problem. If however, you happen to have robotic paint spraying systems downstream then any water will be devastating not only to the robotics but will likely also ruin the paint finish when water mixes with the coating during the spraying process.

An additional consideration should also be reviewed, the ambient conditions! In your area are freezing temperatures observed at any time during the year? If the answer is yes then are any compressed air lines exposed to outdoor temperatures. For example, if the above mentioned application of blowing metal chips from a machining operation is the compressed air use (which wouldn’t require a dryer), but the compressors are located in a remote building and the pipe travels outside to the machining building then it would be likely that the air line between buildings could freeze in the winter thus shutting down your machining operation.

Once an assessment has been performed to review the uses of compressed air within the plant along with any ambient temperature issue’s, only then can a determination be made as to the type of dryer required, if any.

Obviously there are thousands of potential uses for compressed air and each one comes with it’s own particular concerns. Great news for end users is where air is being used for equipment, the equipment manufacturer will normally provide direction on the quality of air required for their particular machines.

One other consideration to keep in mind while looking to determine the air dryer requirements is the contaminants in the compressed air stream are not limited to water only. Thinking back to our requirement of 8 cubic feet of atmospheric air being ingested into the compressor is that all contaminants in the atmosphere are magnified 8 times during the compression cycle. This mean any particulate, hydrocarbons or other gas fumes that are in proximity of the compressor intake will also be ingested into the compressor. While our series of posts related to air dryers will not cross over to other contaminants it is worth noting that filtration selection usually goes hand in hand with selecting the air dryer.

In the world of compressed air dryers there are 4 basic classifications of dryers that are normally associated with industrial compressed air systems.

Refrigerated Type Dryers

Refrigerated dryers: The principle of operation is similar to a domestic refrigerator or home air conditioning system. The compressed air is cooled in an air-to-refrigerant heat exchanger to about 35°F, at which point the condensed moisture is separated and drained off.

Regenerative Type Desiccant Dryers (adsorbing)

These dryers use a desiccant, which adsorbs the water vapor in the air stream.

Deliquescent Type Air Dryers (absorbing)

The deliquescent desiccant type dryer uses a hygroscopic desiccant material having a high affinity for water. The desiccant absorbs the water vapor and is dissolved in the liquid formed.

Membrane Type Air Dryers

Specially designed membranes allow water vapor (a gas) to pass through the membrane pores faster than the other gases (air) reducing the amount of water vapor in the air stream at the outlet of the membrane dryer, suppressing the dew point.

Within each classification of air dryer there are different types, each with it’s own operating characteristics. While each type will provide the same end result, their operational modes are different as to be matched to each plants needs and energy requirements as well as initial investment costs.

With the goal of our blog posts to offer small bite size pieces of information that our users can easily digest, we will be writing separate posts for each classification of dryer over the next few weeks. This will allow our readers to learn about each classification and type of dryer as their needs require or the ability to review all of the posts for a comparative overview.

As always, if there are questions, feel free to contact us for additional assistance.

Industry is beginning to understand the true cost of compressed air and it is not cheap. We work with a host of companies every day to reduce their compressed air cost and improve on the reliability of the compressed air system.

If your company only takes one step on it’s own to create a more efficient system for yourself then consider installing the correct condensate drain valves.

Using compressed air for an intended purpose is an obvious goal but we often find that the compressed air ends up being used in unnecessary and wasteful ways. Like blowing debris from parts or workers which is an obvious waste of a utility. Even more concerning is waste that occurs from improperly selected equipment and drain valves fall firmly on that line.

Everyone knows that compressed air systems create huge volumes of water that must be eliminated from the system at any location in the system where the air temperature drops, thus creating liquid water. These area’s typically include intercoolers, aftercoolers, refrigerated dryers and receivers . At these points, equipment (drain valves) must be installed to remove the liquid water from the system collection points.

A simple solution utilized in many systems is a timed based solenoid drain.

There are a couple of potential problems with a solenoid type drain valve. First, most of these drains utilize a very small orifice (port) where the water is discharged from the system making it susceptible to blockage by dirt, sludge or rust particles. Second, the drain discharges compressed air with the water which is a waste of the utility and Third, the timed function of the drain never takes the amount of water into consideration. Maybe the drain is open too long or perhaps the timed event is too short and the water is not completely discharged from the system.

A much better approach is to utilize a zero air loss type automatic drain like the Dehydra 52 shown below.

How It Works

Condensate enter the drain through one of he two inlet connections. A non-metallic float is tethered to a float arm. As condensate is collected and the translucent reservoir fills, the float rises. When the condensate reaches a designed level, the float lifts the trigger assembly and a drain cycle is initiated. The trigger assemble opens and directs control air to the valve actuator, which in turn opens the full-port drain valve.

The compressed air line from the water collection point is closed and condensate will then exit the unit. As the condensate level drops, the trigger assembly closes and the valve actuator closes the drain valve. The drain is returned to a standby condition.

Thus the collection point is fully drained and the during the draining process, no compressed air is lost from the system.

The drain valve is an area your company can easily make an impact to improve your compressed air system.

Compressed Air Dryer – 101

Proper Drains Create A More Efficient Compressed Air System