Intelligent Compressed Air: Refrigerant Dryers and How They Work

We’ve seen in recent blogs that Compressed Air Dryers are an important part of a compressed air system, to remove water and moisture to prevent condensation further downstream in the system.  Moisture laden compressed air can cause issues such as increased wear of moving parts due to lubrication removal, formation of rust in piping and equipment, quality defects in painting processes, and frozen pipes in colder climates.  The three main types of dryers are – Refrigerant, Desiccant, and Membrane. For this blog, we will review the basics of the Refrigerant type of dryer.

All atmospheric air that a compressed air system takes in contains water vapor, which is naturally present in the air.  At 75°F and 75% relative humidity, 20 gallons of water will enter a typical 25 hp compressor in a 24 hour period of operation.  When the the air is compressed, the water becomes concentrated and because the air is heated due to the compression, the water remains in vapor form.  Warmer air is able to hold more water vapor, and generally an increase in temperature of 20°F results in a doubling of amount of moisture the air can hold. The problem is that further downstream in the system, the air cools, and the vapor begins to condense into water droplets. To avoid this issue, a dryer is used.

Refrigerated Dryer

Fundamental Schematic of Refrigerant-Type Dryer

Refrigerant Type dryers cool the air to remove the condensed moisture and then the air is reheated and discharged.  When the air leaves the compressor aftercooler and moisture separator (which removes the initial condensed moisture) the air is typically saturated, meaning it cannot hold anymore water vapor.  Any further cooling of the air will cause the moisture to condense and drop out.  The Refrigerant drying process is to cool the air to 35-40°F and then remove the condensed moisture.  The air is then reheated via an air to air heat exchanger (which utilizes the heat of the incoming compressed air) and then discharged.  The dewpoint of the air is 35-40°F which is sufficient for most general industrial plant air applications.  As long as the compressed air stays above the 35-40°F temperature, no further condensation will occur.

The typical advantages of Refrigerated Dryers are-

  1.  – Low initial capital cost
  2.  – Relatively low operating cost
  3.  – Low maintenance costs

If you have questions about getting the most from your compressed air system, or would like to talk about any EXAIR Intelligent Compressed Air® Product, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

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Types Of Compressed Air System Dryers

Many times, when discussing product selection with a customer, we commonly reference supplying as clean and dry air as possible to promote peak performance. In iron piping systems for example, when moisture is present, rust can develop which can reduce the performance of end use compressed air operated devices like air tools or cause issues on the exhaust side as you could exhaust unwanted mist onto a surface, like in a painting operation.

Example of a desiccant dryer

Typically, an efficient and properly installed industrial compressed air system will include some type of dryer to remove any moisture that may be present in the supply.

Let’s take a look at the various types of dryers available.

Refrigerant and desiccant dryers are two of the more commonly used types of dryers.

Refrigerant based systems have several stages. The compressed air first passes through an air to air heat exchanger  which initially cools the air. The air is then delivered to an air to refrigerant exchanger where an external source of liquid refrigerant further cools the air and sends it to a separator, where the water vapors condensate and are removed through a drain trap. Now that the air is dry, it is then cycled back to the air to air exchanger where it is heated back to ambient temperature and exits the system.

Desiccant dryers typically incorporate 2 tanks containing a porous desiccant which causes the moisture to sort of “cling” to the surface. In these systems, compressed air flows through one tank, while, using it’s own regeneration cycle, heated or unheated air is blown through the desiccant in the other tank to remove the moisture and dry the air.

Membrane Dryers are typically used at the end use product. These types of systems utilize membranes to dissipate water vapor as it passes through the material, while allowing a small amount of the dry air to travel the length of the membrane to sort of “wipe” the condensate and remove it from the system.

Deliquescent Dryers use a drying agent which absorbs any moisture in the air. As the vapors react with the desiccant, like salt, the desiccant liquefies and is able to be drained at the bottom of a tank. These are the least expensive dryers to purchase and maintain because they have no moving parts and require no power to run.

When a dryer is being considered for a particular setup, there are 3 common reference points used when determining the dryers rating – an inlet air temperature of 100°F, supply pressure of 100 PSIG and an ambient air temperature of 100°F. Changes in supply pressure or temperature could change the performance of a particular dryer. You want to follow the manufacturer’s recommendations when dealing with variances as they will typically provide some type of conversion.

For help with this or any other topics relating to the efficient use of compressed air, please give us a call, we’d be happy to help.

Justin Nicholl
Application Engineer
justinnicholl@exair.com
@EXAIR_JN

 

Heated Desiccant Dryers image courtesy of Compressor1 via creative commons license

Atomization Nozzles For Better Grain Processing

I have been working with a customer from the grain milling industry.  They take a grain like corn, and mill it to sizes that range from coarse product like grits to fine product like flour. The customer had a special application where steam was injected into a mixing screw process to add moisture to the grain.  Steam can be expensive and dangerous to work with, due to the energy required to make, store, transport and use, along with the high temperatures and pressures involved.

The customer was aware of our products from previous work we had done involving Super Air Knives.  He approached me about the Atomizing Nozzles and whether they could be used to replace the steam injection system.  We reviewed the process details such as target flow rate, the spray pattern desired, and the available distance from the target we had to work with.   We determined that (3) of the EF1030SS – External Mix Flat Fan, each capable of delivering 14 Gallons Per Hour, were the solution.  The nozzles would be placed equidistant along the mixing screw, to provide an even delivery of water.

ef1030ss

EF1030SS

 

To operate the nozzles, all that is needed is a supply of water, and 3.5-15.1 SCFM of compressed air at 10-95 PSIG.  Varying the liquid and air pressure will change the flow rate and pattern size of the spray.  Charts are published to help with the set-up and tuning of the nozzles to match the process needs.

CaptureCapture

The use of the Atomizing Nozzle allows for precise application of very fine droplets.  For the External Mix type, droplets sizes of 39 to 57 micron are possible.  Smallest droplet size is achieved by operating at higher air pressures and lower liquid pressures.

EXAIR also manufactures Internal Mix type nozzles and even a Siphon type, that can operate under siphon or gravity fed conditions  (no liquid pump/pressure is required.)  Nozzles are available with flow rates from 0.1 to 303 Gallons per Hour, in flow patterns such as Narrow Angle Round, Wide Angle Round, Flat Fan, and 360° Hollow Circular.

To discuss your application and how the EXAIR Atomizing Spray Nozzle can be a benefit at your facility, feel free to contact EXAIR and myself or one of our other Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

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EXAIR Product Of The Year Candidate: Electronic Temperature Control for Dual Cabinet Cooler Systems

We have just found out that four of our new problem solving products have been nominated for Plant Engineering’s Product of the Year (Please Vote for us HERE).  The first candidate I would like to showcase is in the Automation & Controls category.  The Electronic Temperature Control for Dual Cabinet Cooler Systems effectively turn the compressed air supply to the Cabinet Coolers on and off as needed to maintain a constant temperature inside of a hot enclosure. Using the air intermittently to maintain a specific temperature is the most efficient way to operate.

Please Vote!

Please Vote!

The ETC Dual Cabinet Cooler Systems work in conjunction with EXAIR’s UL listed Cabinet Cooler Systems which provide cooling for your electrical enclosures without the use of refrigerant based coolants or fans.   The Cabinet Cooler Systems utilize a compressed air driven Vortex Tube which uses compressed air. This cold compressed air is exhausted into the enclosure which results in a cool working environment for your electronics. Warm air from inside the enclosure is vented safely back out of the cabinet through built in exhausts and the compressed air is only utilized when the internal air temperature reaches the digitally set temperature on the ETC.

How the EXAIR Cabinet Cooler System Works

How the EXAIR Cabinet Cooler System Works

Another added benefit of the ETC on the Cabinet Cooler system is the real time readout of the internal air temperature of your enclosures.  This is on top of the push button set point which will give you a +/-2°F ambient temperature inside of your enclosure.

EXAIR ETC Dual Cabinet Cooler System

EXAIR ETC Dual Cabinet Cooler System

The ETC Dual Cabinet Cooler Systems are designed for larger heat loads ranging from 3,400 BTU/hr. to 5,600 BTU/hr.   The units are available in NEMA 12, NEMA 4, and NEMA 4X ratings.   This means whether you are in a fairly clean environment or a dirty, hot, muggy environment, EXAIR has you covered.

If you would like to discuss either the ETC or the Cabinet Cooler Systems, please contact an Application Engineer.   If you would like to vote for our products, please check out the Plant Engineering Product of the Year page here.

Brian Farno
Application Engineer Manager
BrianFarno@EXAIR.com
@EXAIR_BF

Why 5 PSIG Matters

Last week I pointed out the important locations for measuring your compressed air system pressure throughout your compressed air system.   One of the critical points to measure system pressure was before and after each filter.  This leads into another question that I receive every once in a while, “How do I tell when the filter needs to be changed?”  The answer to this is easy, when you see more than a 5 PSIG pressure drop across the filter.  This means that the element within the filter has become clogged with sediment or debris and is restricting the volume available to your downstream products.

Filter

EXAIR 5 micron Auto Drain Filter Separator

 

This can lead to decreased performance, downtime, and even the possibility of passing contaminants through the filter to downstream point of use components.  In order to maintain an optimal performance when using EXAIR filter separators and oil removal filters, monitoring the compressed air pressure before and after the unit is ideal.

Replacement filter elements are readily available from stock, as well as complete rebuild kits for the filter units. Changing the filters out can be done fairly easily and we even offer a video of how to do it.

The life expectancy of a filter element on the compressed air is directly related to the quality of air and the frequency of use, meaning it can vary greatly.  If you tie a new filter onto the end of a compressed air drop that has not been used in years, you may get a surprise by the filter clogging rather quickly.   However, if you maintain your compressor and your piping system properly then the filters should last a long time. Generally we recommend checking your filters every 6 months.

If you have questions about where and why to filter your compressed air contact us.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

 

Video Blog: Effectiveness of Filtering Your Compressed Air

The video below will give a brief demonstration on the importance of point of use filtration in order to remove unwanted material such as water, scale, particulate and oil from your compressed air stream. Point of use or end-use filtration will keep your air clean and your compressed air products running smooth.  If you have any comments or questions, please feel free to contact us.

 

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

Compressed Air and Dew Point

Today’s discussion is on dew point of air as it has a significant impact on a compressed air system. The dew point is the temperature at which the water vapor in the air  can no longer stay in a vapor form, and condenses from a vapor into a liquid. The amount of water vapor contained in air is directly proportional to its temperature. The warmer the air the more space there is between molecules thus it is able to hold more water vapor.Capture

It is when air temperature drops below the dew point that issues develop in a compressed air system. Let’s take the example of a warm summer day at 90 F and 50% relative humidity. From the chart we see the dew point temperature to be 70 F. So at night, when all the equipment is shut down and the temperatures drop into the 60’s, water will condensate throughout the entire system. In the morning when the equipment is turned on, water blows through sensitive valving.

Compressing air will increase the dew point. Hot compressed air exiting the compressor and cooling while it makes its way through distribution systems is one reason for condensate in compressed air lines. Drying the compressed air is recommended to reduce or eliminate water condensate problems in a compressed air system.

There are several methods to dry out your compressed air. Each have their advantages and disadvantages. The following short review of the various options will help you decide which is best for your application.

After-coolers

The compressor’s after-cooler  which looks similar to a car’s radiator or the condenser in an air conditioner, is the first step to dryer air. It is placed at the compressor’s air outlet and uses either ambient air or water to cool the compressed air and condense some of the water vapor into a liquid that can be removed with a water separator.

The simplicity of design is a positive. The negative is that it can never cool below ambient but something above ambient depending on its capacity. After-cooler performance is rated by approach temperature, which is how closely the compressed air leaving the after-cooler will approach the temperature of the cooling medium used.

For example, if an air-cooled after-cooler is rated for a 10°F approach temperature, and the temperature of the ambient air is 90°F, the temperature of the air leaving the after-cooler will be 100°F. Assuming 50% relative humidity day the dew point will be 80 F.

Mechanical Water Separators

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Wet compressed air enters the separator and passes through a set of vanes that spins it in a vortex. Centrifugal force causes liquid to fly out of the compressed air stream and run down the inside of the filter bowl, where it can be drained off. These are installed at the point of use as a final defense before entering sensitive compressed air equipment. They are an inexpensive assurance of quality air. The ones EXAIR has also include a sintered bronze filter element to remove dirt and scale as well as water.

Deliquescent Dryer

A deliquescent dryer is basically a tank full of salt tablets. As the compressed air passes through the salt, the salt attracts water and dissolves into a brine that can be drained off. These are the least expensive dryers to purchase and maintain because they have no moving parts and require no power to run. The operating cost consists of the cost of more salt tablets.

Desiccant Air Dryers

These are similar to the deliquescent driers except they use a desiccant that attracts water but holds it. When they have reached their saturation limit they are either replaced or regenerated in one of three methods.

Operating cost of these dryers varies with the method used to remove water from or regenerate the desiccant.

Heatless regenerative dryers take a portion (about 15%) of the dry compressed air leaving the dryer and passes it through the desiccant to absorb the moisture out of it. Purchase cost economical but operational costs are high because if all the compressed air used to dry out the desiccant.

Heated purge regenerative dryers take advantage of the fact that hot air can hold more water than cold air. These dryers take about 5% of the dry compressed air leaving the dryer and pass it through an electric heater and then sends it through the wet desiccant bed. This dryer cost more than the heat less dryer but is offset by using half the compressed of that used by the heat less dryer.

Blower Purge Dryers

These are similar in concept to the had dryers found in restrooms but on a larger scale. Heated air is sent trough the desiccant with a blower. These are not quite as efficient because they are heating up ambient air which would not be as dry as compressed air.

Membrane Air Dryers

These dryers use pass the compressed air through a membrane with pores large enough to allow air molecules through but not large enough to allow water molecules through. The lower a dew point is needed, the more purge air is required. These

Refrigerated Air Dryers

Is an A/C system that refrigerate  the compressed air as close to freezing as possible in order to condense out as much water as possible then use a mechanical water separators to remove the condensed water. They require electricity to operate along with the associated cost of operation and maintenance.

Hopefully this gives you a better understanding on how to qualify your compressed air.

Feel free to contact me at any time with questions or concerns, or if I can be of any further assistance. I genuinely appreciate the opportunity! 1-800-903-9247 or click on the live chat icon in the upper left hand corner.

Joe Panfalone

Application Engineer
Phone (513) 671-3322
Fax (513) 671-3363
Web: http://www.exair.com
Twitter: http://www.twitter.com/exair_jp
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