Tag: receiver calculation

The Case – And The Math – For Intermediate Storage

Published on by Russ BowmanLeave a comment

If you use compressed air, you may have encountered this issue:

  • An operator hooks up a new compressed air operated device.
  • When they start using it, your compressed air header pressure drops.
  • This affects the operation of one, several, or ALL air-operated devices in the facility.
  • You might have gotten lucky, and it ONLY affected the operation of only one device in that particular area.

The simple solution – and one adopted by many users – is to increase header pressure. Let’s say the header pressure was 100psig, and the sudden startup of the new device caused it to drop to 85psig, when one (or several, or ALL) of the other loads needed at least 90psig. Sometimes algebra is required for calculations involving compressed air operations, but this isn’t one of them. If a 15psi drop caused the problem, adding 15psi to your header pressure will solve it. That’s just basic arithmetic.

Since most industrial air compressors are capable of generating pressures well above the 100psig you’re currently running at, all you need to do is turn up the pressure, right? Depending on the control scheme of your compressed air system, there are a number of ways to do that. So that solves your problem, and everything will be just fine…until someone checks the electricity bill. Thing is, increasing the discharge pressure makes the compressor work harder, meaning it’ll cost more to operate. There are formulas for that – all you need is your electricity bill and some compressor performance data – but there’s a fairly accurate thumb-rule which states that, for every 2psi change in compressor discharge pressure, there’s a change in power consumption of approximately 1%. Let’s say you increased discharge pressure to 120psig, just to be safe. That’s a 20psi increase, so you just increased the power consumption (and hence the operating cost) of your compressor by about 10%. To add insult to injury, you also just increased the flow out of those leaks in your system…you may have even started some new ones…and THAT’S costly as well.

Another solution is intermediate storage. Placing a properly sized Receiver Tank in the vicinity of critical loads on your compressed air system will prevent the adverse effects of those pressure drops upon energizing, by making sure they don’t happen in that particular part of the compressed air system. And, you don’t have to raise your header pressure (and compressed air costs) to do it. So, there’s the case for intermediate storage – now let’s do the math, and figure out how much we need, using this equation:

Let’s calculate the receiver size needed to protect a critical load that uses 5 SCFM @90psig, minimum. Because it’s critical, we want to ensure the Receiver Tank alone can keep system pressure above 90psig for at least one minute:

An EXAIR 60 Gallon Receiver Tank (Model 9500-60) would provide this level of protection. It’s 20″ in diameter and just over 50″ tall, so it doesn’t take up a lot of floor space. It comes with a drain valve and connections for compressed air flow in & out, a pressure gauge, a relief valve, etc.

Step Five of our Six Steps To Optimizing Your Compressed Air System: Use intermediate storage near the point of use.

Compressed air isn’t free. It isn’t even cheap. There are some very interesting methods for improving performance without adding cost to produce compressed air as described above. If you’d like to find out how EXAIR can help you get the most out of your compressed air system, give me a call.

Russ Bowman, CCASS

Application Engineer
Visit us on the Web
Follow me on Twitter
Like us on Facebook

Installing a Secondary Receiver Tank

Published on by exaircorp2 Comments
Picture by Clker-Free-Vector licensed by Pixabay

We often run into situations where a customer does not have enough compressed air volume to implement a solution. This leaves three possible options. 1) Abandon the project all together and continue to feel the pain the problem creates. 2) Install a larger compressor, with associated expense. 3) Install a secondary, or “point of use” receiver tank to store the compressed air volume local to the application, to be available immediately without having to rely on the distribution system for storage capability. This 3rd option is a cost-effective solution customers often use to mitigate the impact of installing a new compressed air consuming product onto the system.

Large demand events on a compressed air system can leave the system short on air. This can result in a system pressure drop which is undesirable. 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 recommend and 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 their camera flash.

In this same way, a receiver tank acts like the 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 re-plenish 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)
120-60

V = 913
60

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 to the example, the refill rate to 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.

EXAIR LLC
Visit us on the Web

Cover Photo by dkeissling and licensed by Pixabay

Secondary Receiver Tanks: Why Use Them and How to Size Them

Published on by John BallLeave a comment

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 events, it is beneficial to have additional storage.

As a 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 that 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.  In 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 for 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)

For this customer above, I am still getting more details about their system.  But 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”.  If you find that your compressed air system needs a boost for your pneumatic process, we may be able to recommend a secondary receiver 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: johnball@exair.com
Twitter: @EXAIR_jb

6 STEPS To Optimizing Compressed Air: Step 5 – Install Secondary Receiver Tanks

Published on by John BallLeave a comment

Since air compressors require electricity to make compressed air, it is important to optimize your compressed air system. EXAIR has six simple steps, and following these steps will help you cut electrical costs, reduce overhead, and improve your bottom line.  In this blog, I will cover the fifth step –intermediate storage of compressed air near the point-of-use. 

I had a customer that was looking at a model 1122108, 108” (2,743mm) Super Ion Air Knife Kit.  The application was removing static and debris from insulated panels which they used for large refrigerated trailers.  They were worried about how much compressed air that it would use; and they were considering a blower-type system.  I went through the negative aspects like noise, cost, maintenance, and ineffectiveness with turbulent air flows.  But, when you are limited in the amount of compressed air, I had to look at another way.  Since the process was intermittent, I used the fifth step to optimize their system to use a much better solution for their application.  The cycle rate was 2 minutes on and 10 minutes off.  I was able to calculate the size of a secondary tank to help their compressed air system.   

Model 9500-60

I would like to expand a bit more about secondary receiver tanks.  They 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.  They give additional capacity at the end of distribution lines.  Essentially, it is easier and more efficient for compressed air to travel out from a nearby source and into an application rather than traveling through long lengths of pipes from the distribution system.

For calculating the volume size for 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 for air drops will typically come from a header pipe and are generally smaller in diameter.  So, we have to look at the air restriction that can feed into the tank.  For example, a 1” NPT Schedule 40 Pipe at 100 PSIG can supply a maximum of 150 SCFM of air flow.  This value is used for Cap below in Equation 1.  C is the largest air demand for the machine or targeted area 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 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, 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 (cubic meter)

T – Time interval (minutes)

C – Air demand for system (cubic meter per minute)

Cap – Supply value of inlet pipe (cubic meter per minute)

Pa – Absolute atmospheric pressure (Bar)

P1 – Header Pressure (Bar)

P2 – Regulated Pressure (Bar)

For this customer above, I am still working on this purchase.  But we went from a “we don’t have enough compressed air” to a “we can possibly use the better solution with the Super Ion Air Knife”.  If you find that you might be having issues with your equipment running optimally, you may be able to install a secondary receiver to your system.  EXAIR offers 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, primary or secondary, you can contact an Application Engineer at EXAIR.

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