Wet Receivers and Condensate Drains

Receiver Tank

For properly designed compressed air systems, air compressors will use primary storage tanks, or receivers.  They are necessary to accommodate for fluctuations in airflow demand and to help prevent rapid cycling of the air compressor.  (Reference: Advanced Management of Compressed Air – Storage and Capacitance)  There are two types of primary receivers, a wet receiver tank and a dry receiver tank.  The wet receiver is located between the air compressor and the compressed air dryer where humid air and water will be stored.  The dry receiver is located after the compressed air dryer.  In this blog, I will be reviewing the wet receivers and their requirements as a storage tank.

Air compressors discharge hot humid air created by the internal compression.  A byproduct of this compression is water.  By placing a wet receiver on the discharge side of the air compressor, this will create a low velocity area to allow the excess water to fall out.  It will also give the hot air time to cool, allowing the compressed air dryers to be more effective.  With wet receivers, it will reduce cycle rates of your air compressors for less wear and store compressed air to accommodate for flow fluctuations in your pneumatic system.

But, there are some disadvantages with a wet receiver.  For compressed air dryers, it is possible to exceed the specified flow ratings.   If the demand side draws a large volume of air from the supply side, the efficiency of the compressed air dryers will be sacrificed, allowing moisture to go downstream.  Another issue with the wet receiver is the amount of water that the air compressor is pumping into it. As an example, a 60 HP air compressor can produce as much as 17 gallons of water per day.  As you can see, it would not take long to fill a wet receiver.  So, a condensate drain is required to get rid of the excess water.

Condensate drains come in different types and styles.  They are connected to a port at the bottom of the wet receiver where the water will collect.  I will cover the most common condensate drains and explain the pros and cons of each one.

  • Manual Drain – A ball valve or twist drain are the least efficient and the least expensive of all the condensate drains. The idea of having personnel draining the receiver tanks periodically is not the most reliable.  In some cases, people will “crack” the valve open to continuously drain the tank.  This is very inefficient and costly as compressed air is being wasted.
  • Timer Drain Valves – These valves have an electric timer on a solenoid to open and close a two-way valve or a ball valve. The issue comes in trying to set the correct time for the open and close intervals.  During seasonal changes, the amount of water going into the wet receiver will change.  If the timer is not set frequent enough, water can build up inside the receiver.  If too frequent, then compressed air is wasted.  Compared to the manual valve, they are more reliable and efficient; but there is still potential for compressed air waste.

    Timer Relay
  • No-waste Drains – Just like the name, these drains are the most efficient. They are designed with a float inside to open and close a drain vent.  What is unique about the float mechanism is that the drain vent is always under water.  So, when the no-waste drain is operating, no compressed air is being lost or wasted; only water is being drained.  The most common problem comes with rust, sludge, and debris that can plug the drain vent.

All wet receivers require a condensate drain to remove liquid water.  But, the importance for removing water without wasting compressed air is significant for saving money and compressed air.  EXAIR also has a line of Intelligent Compressed Air® products that can reduce your compressed air waste and save you money.  You can contact an Application Engineer for more details.

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb

 

Photo: Timer Relay by connectors distribution box.  Attribution – CC BY-SA 2.0

Removing Condensation Is Key To Maintaining Performance

When air is compressed, it is heated to a point that causes the water or moisture  to turn to vapor. As the air begins to cool, the vapors turn to condensation, which can cause performance issues in a compressed air system. Many times this condensation forms in the basic components in the system like a receiver tank, dryer or filter.

Condensation is formed from water vapor in the air

It’s important to remove this condensation from the system before it causes any issues. There are four basic types of condensate drains that can be used to limit or prevent loss of air in the system.

The first method would be to have an operator manually drain the condensation through a drain port or valve. This is the least reliable method though as now it’s the operator’s responsibility to make sure they close the valve so the system doesn’t allow any air to escape which can lead to pressure drops and poor end-use device performance.

Example of a float drain

Secondly, a float or inverted bucket trap system can be used in plants with regular monitoring and maintenance programs in place to ensure proper performance.. These types of drain traps typically require a higher level of maintenance and have the potential to lose air if not operating properly.

An electrically actuated drain valve can be used to automatically drain the condensate at a preset time or interval. Typically these incorporate a solenoid valve  or motorized ball valve with some type of timing control.  These types of systems can be unreliable though as the valve may open without any moisture being present in the line, which can result in air loss or it may not be actuated open long enough for acceptable drain off. With these types of drains, it’s best to use some type of strainer to remove any particulate that could cause adverse performance.

Lastly,  zero air-loss traps utilize a reservoir and a float or level sensor to drain the condensate and maintain a satisfactory level. This type of setup is very reliable but does require the reservoir be drained frequently to keep the system clean and free of debris or contaminants.

If you have any questions or would like to discuss a particular process, contact an application engineer for assistance.

Justin Nicholl
Application Engineer
justinnicholl@exair.com
@EXAIR_JN

 

Condensation image courtesy of Anders Sandberg via creative commons license

Float drain image courtesy of the Compressed Air Challenge

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