You designed your compressed air system to handle the volume you need for your plant, but your continued growth has started to tax that system with some high intermittent demand.
Managing high intermittent demand in the compressed air system requires evaluation of several elements of your system:
- Air compressor controls.
- System master controls.
- Piping and air velocity.
- Storage: wet, dry, and at points of use.
- Identifying and examining large air users.
- Designing with flexibility and the future in mind.
Today I’m going to cover #4, more specifically installing a secondary storage tank!
Utilizing a secondary receiver tank to mitigate the impact of larger volume-consuming events is a common and useful strategy that many compressed air professionals will pursue. In this kind of scenario, the receiver tank acts much like a capacitor in a camera flash. A camera battery charges a capacitor which then dumps its charge into the flash bulb when you take a photo for a notably bright flash, which is what one generally wants from your camera flash.
In this same way, a receiver tank acts like a capacitor to “dump” the air volume needed to make a compressed air device work at its design pressure and flow for some prescribed period of time. In situations like this, the high demand does need to be an intermittent one so that the tank can then re-charge from the compressor system and be ready for the next air use event. This means that certain calculations need to be made to ensure that the receiver tank is sized properly to provide the desired effect.
How do you size a receiver tank? Here’s the calculation to determine the proper size:
Let’s consider an example of an Air Amplifier solution. A customer wants to blow on hot metal parts coming out of an oven to cool them down as an “air quench”. We evaluate the application and determine that (2) 2″ Super Air Amplifiers will provide the right amount of flow. Those units are going to operate at 60 PSIG to provide the desired effect. (2) 2″ Super Air Amplifiers will consume 24.5 SCFM @ 60 PSIG. Each batch of parts comes out of the oven at a rate of one batch every 5 minutes. They want to provide the necessary cooling for a total of 30 seconds to have the air quench effect. So, every 5 minutes, the Air Amplifiers will be blowing for 1/2 minute. Each “on” event consumes 12.25 Standard Cubic Feet of air. We then have 4 minutes, 30 seconds left to replenish the tank.
The last piece of information we need to know is the system pressure for the compressed air header feeding the tank. The system pressure is 120 PSIG. And so, our calculation looks like this:
V = 0.5 min. x 24.5 rate of flow x (60 PSIG + 14.5 PSIA)
120 PSIG – 60PSIG
V = 913
60 PSIG
V = 15.2 ft.3
There are 7.48 gallons to a cubic foot, so our receiver tank in this example would be
15.2 ft.3 x 7.48 = 114 gallons.
Given the fact that receiver tanks are made in certain, standard sizes, a 120 gallon tank or two, 60 gallon tanks piped in upstream of the compressed air load would be appropriate for this application.
As a further note, for example, the refill rate for the tank(s) would need to be a minimum of 2.72 SCFM to get the volume replenished in time for the next event. This is less than 1 HP of industrial air compressor to maintain such a flow rate to refill the tank.
With some reasonably simple math to determine tank size, and a willingness to pursue this kind of air delivery solution, you can implement that compressed air solution at a fraction of the cost compared to a new compressor.
With some reasonably simple math to determine tank size, and a willingness to pursue this kind of air delivery solution, you can implement that compressed air solution at a fraction of the cost compared to a new compressor.
If you have any questions please reach out! We have a full team of Applications Engineers in the office M-F!
Jordan Shouse
Application Engineer
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