Air Receiver Tanks: The Basics
For those not well versed in the compressor industry, an air receiver tank may seem unnecessary. But they are more than mere accessories for rotary screw compressors. Air receiver tanks actually play an incredibly important role in the overall compressed air system. Continue reading for more background on air receiver tanks and their effects on air systems.
Types of Air Receiver Tanks
Two main types of air receivers exist: “wet tanks” and “dry tanks.” The major difference between them is their placement.
Wet tanks are installed before the dryer and should be used in systems that have particularly high humidity levels. The wet tank arrangement allows much of the condensate to drop out of the air before entering the dryer, lightening the dryer’s overall load. A wet tank in combination with condensate drains (More About Condensate Handing) can have many benefits for a system.
Dry tanks are placed downstream of the dryer. This arrangement is especially useful when a system lacks a steady air stream. Dry tanks create protection from surges that can overburden dryers, affecting system pressure, and carrying water down-line. If fast compressor cycles are a concern in a system, then a dry tank arrangement may be a good fix.
Depending on the specifications of a system, a wet tank, a dry tank, or both may be used.
Functions
Air tanks, most obviously, serve the function of storing compressed air. This function is more useful in certain applications. For instance, sandblasting requires more system demand than other processes. Having reserved energy in the tank allows for these high demand activities to continue without draining the entire system’s power. The extra air creates a cushion of power accessible for uses that may exceed the general compressor horsepower.
However, air tanks have an unexpected second use. They can act as an additional heat exchanger. As the air moves through the tank, the general temperature cools approximately 10 degrees. Allowing the air more time to release excess heat lowers the temperature downstream. This decrease not only benefits the longevity of the system equipment, but it also decreases the energy consumption of the rest of the system.
Impact on Energy Consumption
Perhaps the most convincing reasons to install an air receiver tank are the energy benefits. As mentioned above, air tanks can act as heat exchangers with energy saving properties. As the air moves slowly through the tank, the moisture condenses and drains out of the bottom. When the air then moves to the dryer, there is less work to do. Much of the moisture has already been removed. The system dryer can, therefore, use energy more efficiently.
Air receivers also act as a safeguard against waste. By the nature of a rotary screw compressor setup, after every unload, the oil tank vents. The system loses air during this venting, which over time adds up. However, having a properly sized storage tank can lessen waste levels and lower the overall creation levels.
Stored energy in tanks can also reduce peak operation pressure. According to the U.S. Department of Energy, every reduction of 2 PSI results in a 1% decrease in compressor energy consumption. By preventing system pressure peaks, tanks can save a good deal of energy.
Sizing
As with any component of a compressed air system, air receiver tanks need to be sized and fitted to the particular system. Both the variation in consumption demand and the compressor size and modulation strategy will factor into the sizing process.
Though there’s no universal way of sizing an air tank, a common formula is:
t = V (p1-p2) / Cpa
where,
V = volume of the receiver tank (cu ft)
t = time for the receiver to go from upper to lower pressure limits (min)
C = free air needed (scfm)
pa= atmosphere pressure (14.7 psia)
p1 = maximum tank pressure (psia)
p2 = minimum tank pressure (psia)
There are also numerous online tools to help calculate the best size, like this one from Kaeser Compressors. Commonly required information for sizing include flow rate, buffer time, initial receiver pressure, and final receiver pressure.
Of course, talking to one of our system engineers is always the best way to ensure your receiver tank is perfectly sized. They can help with demand and configuration questions, too.
Still unconvinced that an air receiver tank could benefit your system? Check out the following resources to see how a seemingly small adjustment can have large returns for your company.
- The Importance of Using an Air Receiver Tank in a Compressed Air System – Parker
- Air Receivers Specifications – Kaeser Compressors
- Compressed Air Receivers – Engineering ToolBox
Interested in learning more about Compressed Air System components? Check out our Compressed Air 101 Pages.
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