Keep things on the simple side of the equation

What Does Your Compressed Air System Look Like??

 

Over the last 15 years Compressed Air has been dubbed the “4th Utility” next to electricity, natural gas & water.  However compressed air is the only one noted above where, you the customer, have the responsibility for generation and transmission of this valuable resource.  There are exceptions for larger companies who have the resources to participate in cogeneration, solar or wind farm projects to lower their average cost of power.  This article is looking to keep things on the simple side of the equation.  That being said many air systems evolve over time as manufacturing facilities rarely stay the same. Companies are either expanding or shrinking and with that comes opportunities and challenges. Compressed air systems evolve over time and it takes a trained eye to insure the costs to generate compressed air don’t get out of control.

When was the last time anyone took a close look at your equipment?  Please take a moment to review the graphic below which shows a typical system with some variables.

1- Air Compressor

Acts like a large vacuum cleaner ingesting all of the ambient air in the area into the compressor to create pressure that performs work.  A simple rule to follow would be to make it easy for the air compressor to draw the ambient air into the pump eliminating any negative pressure issues and also provide a means for the hot exiting air being exhausted (from the heat of compression) to be removed from the area without restriction and insuring this hot air doesn’t get re-ingested into the compressor intake.

Variables; Source and Quality of the ambient air (outside air or inside air that is potentially contaminated due to processes in the plant).   What pressure do you require on the plant floor (80, 90, 100 psi) or more.  Ambient temperature of the compressor room or area 90 degrees F or less is ideal (ductwork or exhaust fan should be considered to avoid overheating).  High ambient temperatures cause premature breakdowns.

 

2- Air Dryer

This is a device that helps to remove most of the water vapor that is in the compressed air stream.  This water if not removed can cause problems with your equipment, tools, and most importantly could be instrumental in your scrap and rework rate.  The two basic types of dryers are refrigerated or desiccant.  The difference is how much water you want to remove from the air stream.  A general rule of thumb if your compressed air piping is all indoors where the temperature doesn’t go below +40 degrees F a refrigerated dryer will suffice.  If you have specific processes that require ultra dry air then you would need to consider a desiccant dryer.  A desiccant dryer will remove all moisture from the air stream down to -40 degrees F.  This type of dryer is an excellent choice for compressed air piping that is outdoors and subject to the frigid winter temperatures or for processes that require ultra dry air.

Variables; Dewpoint of the air stream, quality of the air stream (general purpose, essentially oil free or definitely oil free), Refrigerated dryers don’t consume any of your compressed air but desiccant dryers do.  When selecting a desiccant dryer, the purge air (up to 15%) needs to be accounted for when sizing your air compressor.  Air filters for filtering out particulates, oil vapor, and tastes need to be included per the level of filtration required.  (ISO standards do exist to assist with this selection).

 

3- Wet Tanks

These are installed after the air compressor and before the pre-filter and dryer as shown in the illustration.  Wet tanks perform two functions; one is to provide a central sensing point for the compressor to read air pressure and adjust the compressor output accordingly, and also as a precooler allowing the air to start to cool down a bit before it leaves and enters the prefilter and dryer you have selected.  It is always good industrial practice to pipe the air from the compressor in the lower portion of the air tank and discharge near the top on the opposite side.  This allows for condensation in the air stream to drop to the bottom of the tank while your drier air leaves from the top of the wet tank on the way to the prefilter and selected dryer.

Variables: The size of the tank can vary but a good rule of thumb would depend on the part load controls installed on your compressor.  Part load controls like Variable Speed Drive, Modulation, Variable Capacity barring unique circumstances generally would work well with 1-2 gallons of storage per cfm of compressed air delivered.  Part Load controls like Load/No-Load would typically work well with 2-4 gallons of storage per cfm of compressed air delivered.  All tanks need to come equipped with a pressure gauge, safety relief valve and an auto drain for removing the moisture that condenses in the tank.

Did you know that Comairco performs walk through system assessments to include an inventory of your current air system, data logged supply side air audits with ROI solutions and works with local utility companies in acquiring rebates for new or upgraded energy efficient systems, Ultrasonic Leak audits and general design collaboration of compressed air and vacuum systems.  Check us out at www.comairco.com

Mark Pfeifer    U.S. Department of Energy Certified AIRMaster+ Specialist & CAGI Certified Compressed Air Systems Specialist