Tag: dryer

What Makes A Compressed Air System “Complete”?

Published on by Lee EvansLeave a comment

It’s a good question.  When do you know that your compressed air system is complete?  And, really, when do you know, with confidence, that it is ready for use?

A typical compressed air system. Image courtesy of Compressed Air Challenge.

Any compressed air system has the basic components shown above.  A compressed air source, a receiver, dryer, filter, and end points of use.   But, what do all these terms mean?

A compressor or compressed air source, is just as it sounds.  It is the device which supplies air (or another gas) at an increased pressure.  This increase in pressure is accomplished through a reduction in volume, and this conversion is achieved through compressing the air.  So, the compressor, well, compresses (the air).

A control receiver (wet receiver) is the storage vessel or tank placed immediately after the compressor.  This tank is referred to as a “wet” receiver because the air has not yet been dried, thus it is “wet”.  This tank helps to cool the compressed air by having a large surface area, and reduces pulsations in the compressed air flow which occur naturally.

The dryer, like the compressor, is just as the name implies.  This device dries the compressed air, removing liquid from the compressed air system.  Prior to this device the air is full of moisture which can damage downstream components and devices.  After drying, the air is almost ready for use.

To be truly ready for use, the compressed air must also be clean.  Dirt and particulates must be removed from the compressed air so that they do not cause damage to the system and the devices which connect to the system.  This task is accomplished through the filter, after which the system is almost ready for use.

To really be ready for use, the system must have a continuous system pressure and flow.  End-use devices are specified to perform with a required compressed air supply, and when this supply is compromised, performance is as well.  This is where the dry receiver comes into play.  The dry receiver is provides pneumatic capacitance for the system, alleviating pressure changes with varying demand loads.  The dry receiver helps to maintain constant pressure and flow.

In addition to this, the diagram above shows an optional device – a pressure/flow control valve.  A flow control valve will regulate the volume (flow) of compressed air in a system in response to changes in flow (or pressure).  These devices further stabilize the compressed air system, providing increased reliability in the supply of compressed air for end user devices.

Now, at long last, the system is ready for use.  But, what will it do?  What are the points of use?

Points of use in a compressed air system are referred to by their end use.  These are the components around which the entire system is built.  This can be a pneumatic drill, an impact wrench, a blow off nozzle, a pneumatic pump, or any other device which requires compressed air to operate.

If your end use devices are for coating, cleaning, cooling, conveying or static elimination, EXAIR Application Engineers can help with engineered solutions to maximize the efficiency and use of your compressed air.  After placing so much effort into creating a proper system, having engineered solutions is a must.

Lee Evans
Application Engineer
LeeEvans@EXAIR.com
@EXAIR_LE

Intelligent Compressed Air: Membrane Dryers – What are they and How Do they Work?

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Recently we have blogged about Compressed Air Dryers and the different types of systems.  We have reviewed the Desiccant and Refrigerant types of dryers, and today I will discuss the basics of  the Membrane type of dryers.

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.

Membrane Dryers are the newest type of compressed air dryer. Membranes are commonly used to separate gases, such as removing nitrogen from air. The membrane consists of a group of hollow fiber tubes.  The tubes are designed so that water vapor will permeate and pass through the membrane walls faster than the air.  The dry air continues on through the tubes and discharges into the downstream air system. A small amount of ‘sweep’ air is taken from the dry air to purge and remove the water vapor from inside the dryer that has passed through the membrane tubes.

Membrane Dryer
Typical Membrane Dryer Arrangement

Resultant dew points of 40°F are typical, and dew points down to -40°F are possible but require the use of more purge air, resulting in less final dry compressed air discharging to the system.

The typical advantages of Membrane Dryers are-

  1.  Low installation and operating costs
  2.  Can be installed outdoors
  3.  Can be used in hazardous locations
  4.  No moving parts

There are a few disadvantages to consider-

  1. Limited to low capacity systems
  2. High purge air losses (as high as 15-20% to achieve lowest pressure dew points
  3. Membrane can be fouled by lubricants and other contaminants, a coalescing type filter is required before the membrane dryer.

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

Send me an email
Find us on the Web 
Like us on Facebook
Twitter: @EXAIR_BB

 

Membrane Dryer Schematic – From Compressed Air Challenge, Best Practices for Compressed Air Systems, Second Edition

 

 

 

Intelligent Compressed Air: Refrigerant Dryers and How They Work

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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

Send me an email
Find us on the Web 
Like us on Facebook
Twitter: @EXAIR_BB

 

Intelligent Compressed Air: Desiccant Dryers – What are they and How Do they Work?

Published on by Tyler DanielLeave a comment
Desiccant dryer
Heat of Compression Desiccant Dryer

No matter where you are in the world, the atmospheric air will contain water vapor. As this air cools to the saturation point, also known as dew point, the vapor will condense into liquid water. The amount of this moisture will vary depending on both the ambient temperature and the relative humidity. According to the Compressed Air Challenge, a general rule of thumb is that the amount of moisture air can hold at a saturated condition will double for every 20°F increase in temperature. In regions or periods of warmer temperatures, this can create a significant problem. Some problems that can be associated with moisture-laden compressed air include:

  • Increased wear of moving parts due to removal of lubrication
  • Formation of rust in piping and equipment
  • Color variation, adherence, and finish of paint that is applied using moisture-laden compressed air
  • Create unstable conditions for processes that are dependent upon pneumatic controls. Malfunctions due to rust, scale, or clogged orifices can damage product or cause costly shutdowns
  • In colder temperatures, moisture in the compressed air flow can freeze in the control lines

To remove moisture from the lines, a dryer must be installed. One of the most commonly found dryers in a facility are referred to as desiccant dryers. There are three variations of desiccant dryers: Regenerative-Desiccant Dryers, Heat Reactivated Desiccant Dryers, and Heat of Compression Desiccant Dryers.

A Regenerative-Desiccant Dryer uses a porous desiccant that collects and adsorbs the moisture. This allows for large amounts of water to be retained with a minute amount of desiccant. Most regenerative-desiccant dryers consist of two towers. One where wet, moisture-laden compressed air flows through a desiccant bed. A second tower contains desiccant that is being regenerated. A controlled amount of dry air flows through the tower being regenerated, which causes the moisture to release from the desiccant and flow out with the purge flow. This saturated air exhausts to atmosphere. After a set time, the towers will switch and continue this cycle of drying/regenerating.

Another, and more efficient, regenerative-desiccant dryer uses heat to assist in removing water from the desiccant. As the tower is heated, the moisture is no longer adsorbed by the desiccant and is purged through the flow. This style is more efficient than the other styles of dryers because less compressed air is wasted removing the moisture in the tower.

The third type of desiccant dryer is the Heat of Compression dryer. This style utilizes the heat that is generated during compression to accomplish the regeneration of the desiccant. Typically, the heat that is generated from the air compressor is exhausted to atmosphere and wasted. With a heat of compression dryer, this heat is captured and used to regenerate the desiccant. The compressed air passes through the drying section of the desiccant bed, is dried, and exits through the discharge. A portion of the captured heat flows through the opposite side of the dryer to regenerate the desiccant. Afterwards, this hot air passes through a regeneration cooler and is combined with the main air stream. This results in ZERO loss of purge air, making this style of dryer the most efficient available.

If you have questions about how to optimize your compressed air system, contact EXAIR. An Application Engineer is standing by ready to assist you!

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@exair.com
Twitter: @EXAIR_TD

 

Heated Desiccant Dryer by Compressor1.  Creative Commons Attribution-NoDerivs 2.0 Generic.