Secondary receiver tanks can be strategically placed throughout the plant to improve the “ebbs and flows” of pneumatic demands. The primary receiver tanks help to protect the supply side when demands are high, and the secondary receiver tanks help pneumatic systems on the demand side. The purpose of secondary air storage is for dedicated end-use systems or for additional capacity at the end of distribution lines. Essentially, it is easier and more efficient for compressed air to travel from a nearby source rather than traveling through long lengths of pipe. With any high-demand use equipment, it is beneficial to have additional storage installed nearby within the compressed air system.
For comparison, I would like to relate a pneumatic system to an electrical system. The receiver tanks would be like capacitors. They store pressurized air like a capacitor stores energy from an electrical source. If you have ever seen an electrical circuit board, you will notice many capacitors of different sizes throughout the circuit board. The reason for this is to have a ready source of energy to increase efficiency and speeds with the ebbs and flows of electrical signals. The same can be said for a pneumatic system with secondary receiver tanks.
To cover a current application, I had a customer that was looking at a model 1122108; 108” (2,743mm) Gen4 Super Ion Air Knife Kit. The application was to remove static and debris from insulated panels for large refrigerated trailers. They were worried about how much compressed air it would use, and they were considering a blower-type system. I went through the negative aspects of blower-type systems, like loud noise levels, capital expense, high maintenance cost, large footprint, and ineffectiveness with turbulent air flows. But, when you are limited to the amount of compressed air, it may seem difficult to get the best product for your application. Looking at it another way, I asked him if the process was intermittent; and it was. The cycle rate was 2 minutes on and 10 minutes off. I was able to recommend a secondary tank to help ease the high demand for their compressed air system.
To calculate the volume size of your secondary receiver tank, we can use Equation 1 below. It is the same for sizing a primary receiver tank, but the scalars are slightly different. The supply line to this tank will typically come from a header pipe that supplies the entire facility. Generally, it is smaller in diameter, so we have to look at the air supply that it can feed into the tank. For example, a 1” NPT Schedule 40 pipe at 100 PSIG (7 bar) can supply a maximum of 150 SCFM (255 M3/hr) of air flow. This value is used for Cap below. The C value is the largest air demand for the machine or equipment that will be using the tank. If the C value is less than the Cap value, then a secondary tank is not needed. If the Cap is below the C value, then we can calculate the smallest tank volume that would be needed. The other value in the equation is the minimum tank pressure. In most cases, a regulator is used to set the air pressure for the machine or area. If the specification is 80 PSIG (5.5 bar), then you would use this value as P2. P1 is the header pressure that will be coming into the secondary tank. With this collection of information, you can use Equation 1 to calculate the minimum tank volume.
Equation 1:
V = T * (C – Cap) * (Pa) / (P1-P2)
Where:
V – Volume of receiver tank – Imperial (ft3) or SI (M3)
T – Time interval (minutes)
C – Air demand for system – Imperial (SCFM) or SI (M3/min)
Cap – Supply value of inlet pipe – Imperial (SCFM) or SI (M3/min)
Pa – Absolute atmospheric pressure – Imperial (PSIA) or SI (Bar)
P1 – Header Pressure – Imperial (PSIG) or SI (Bar)
P2 – Regulated Pressure – Imperial (PSIG) or SI (Bar)
In many cases, you can also lengthen the time to refill the secondary receiver by restricting the refill rate with a valve, so that it is more of a constant, but much lower draw on the compressor system. This technique also helps to diminish the impact of the large-use items attached to a customer’s system.
For the customer above, I am still getting more details about their system before we finalize on a solution. But the important point in utilizing this concept is that we went from a “we don’t have enough compressed air” to a “we can use a better solution with the Super Ion Air Knife” and here’s how.
If you find that your compressed air system needs a boost for your pneumatic process, we may be able to recommend a secondary receiver tank for your system. EXAIR does offer 60-gallon tanks, model 9500-60, to add to those specific areas. If you have any questions about using a receiver tank in your application, you can contact an Application Engineer at EXAIR. We will be happy to help.
John Ball
Application Engineer
Email: [email protected]
Twitter: @EXAIR_jb
