Tag: air reservoir

Wet Receiver Tanks: Why Use Them, and How to Size Them

Published on by John BallLeave a comment
9500-60 Receiver Tank

Compressed air is used to operate pneumatic systems within a facility, and it can be separated into three categories; the supply side, the demand side, and the distribution system.  The supply side will include the air compressor, after-cooler, dryer, and receiver tank.  It produces and treats the compressed air before it travels into the distribution system.  They are generally located in a compressor room somewhere in the corner of the plant.  In this blog, I would like to cover the wet receiver tank that is used as part of the supply side.

What is a receiver tank?  I like to compare pneumatic systems to electrical systems.  The receiver tanks store the pneumatic energy produced by an air compressor like a capacitor stores electrical energy.  The reason for this is to have a ready source of energy to increase efficiency and speed through the ebbs and flows of demand. 

A wet receiver, like the name imparts, is positioned downstream of the air compressor but before the air dryer.  A dry receiver would be located after the air dryer.  Some systems will utilize both types.  With the wet receiver, you remove some of the load of water that reaches the air dryer, which helps to make the air dryers more efficient and extends the life cycle.  When ambient air is compressed, the humidity will condense, making water.  Also, as air cools in the wet receiver, water vapor turns into liquid condensate—often mixed with traces of oil and dirt from the air compressor. To get rid of the contaminants, a condensate drain will be required to get rid of this unwanted liquid.

For sizing the wet receiver, it is roughly 1 to 3 gallons per cfm for a compressor.  So, for a 100 SCFM air compressor, you should have a tank that is roughly 100 to 300 gallons.  If you have large fluctuations on the demand side, you can also use Equation 1 below to calculate the minimum tank volume.  If you are using wet and dry receiver tanks in your system, you can divide the total volume.  The wet receiver tank should be one-third of the volume, and the dry receiver tank should be two-thirds of the volume. 

Equation 1:

V = T * C * (Pa) / (P1-P2)

Where:

V – Volume of receiver tank (cubic feet)

T – Time interval between pressure limits (minutes)

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

Pa – Absolute atmospheric pressure (PSIA)

P1 – Upper Pressure limit (PSIG)

P2 – Lower Pressure limit (PSIG)

Compressed air systems are the backbone of countless industries and operations.  But behind the scenes, components like the wet receiver and condensate drain play pivotal roles in ensuring these systems deliver clean, reliable air.  If you wish to discuss more ways to optimize your compressed air system, EXAIR has Application Engineers that would like to help you. 

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

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

Receiver Tank Calculations

Published on by John BallLeave a comment

Receiver Tank

My colleague, Lee Evans, wrote a blog about calculating the size of receiver tanks within a compressor air system.  (You can read it here: Receiver Tank Principle and Calculations).  But, what if you want to use them in remote areas or in emergency cases?  During these situations, the air compressor is not putting any additional compressed air into the tank.  But, we still have potential energy stored inside the tanks similar to a capacitor that has stored voltage in an electrical system.  In this blog, I will show how you can calculate the size of receiver tanks for applications that are remote or for emergency systems.

From Lee Evans’ blog, Equation 1 can be adjusted to remove the input capacity from an air compressor.  This value is Cap below.  During air compressor shutdowns or after being filled and removed, this value becomes zero.

Receiver tank capacity formula (Equation 1)

V = T * (C – Cap) * (Pa) / (P1-P2)

V – Volume of receiver tank (cubic feet)

T – Time interval (minutes)

C – Air requirement of demand (cubic feet per minute)

Cap – Compressor capacity (cubic feet per minute)

Pa – Absolute atmospheric pressure (PSIA)

P1 – Tank pressure (PSIG)

P2 = minimum tank pressure (PSIG)

 

Making Cap = 0, the new equation for this type of receiver tank now becomes Equation 2.

Receiver tank capacity formula (Equation 2)

V = T * C * (Pa) / (P1-P2)

With Equation 2, we can calculate the required volume of a receiver tank after it has been pre-charged.  For example, EXAIR created a special Air Amplifier to remove toxic fumes from an oven.  The Air Amplifier was positioned in the exhaust stack and would only operate during power failures.  In this situation, product was being baked in an oven.  The material had toxic chemicals that had to cross-link to harden.  If the power would go out, then the product in the oven would be discarded, but the toxic fumes had to be removed.  What also doesn’t work during power outages is the air compressor.  So, they needed to have a receiver tank with enough volume to store compressed air.  From the volume of the oven, we calculated that they need the special Air Amplifier to operate for 6 minutes.  The compressed air system was operating at 110 PSIG, and the Air Amplifier required an average air flow of 10 cubic feet per minute from the range of 110 PSIG to 0 PSIG.  We are able to calculate the required receiver volume to ensure that the toxic fumes are evacuated from the oven in Equation 2.

Receiver tank capacity formula (Equation 2)

V = T * C * Pa / (P1 – P2)

V = 6 minutes * 10 cubic feet per minute * 14.7 PSIA / (110 PSIG – 0 PSIG)

V = 8 cubic feet.

Receiver tanks are more commonly sized in gallons.  In converting 8 cubic feet to gallons, we get a 60-Gallon Receiver Tank.  EXAIR recommended the model 9500-60 to be used near the oven to operate the special Air Amplifier during power outage.

Another way to look at Equation 2 is to create a timing equation.  If the volume of the tank is known, we can calculate how long a system will last.  In this example for scuba diving, we can use this information to configure the amount of time that a tank will last.  The diver has a 0.39 cubic feet tank at a pressure of 3,000 PSIG.  I will use a standard Surface Consumption Rate, SCR, at 0.8 cubic feet per minute.  If we stop the test when the tank reaches a pressure of 1,000 PSIG, we can calculate the time by using Equation 3.

Receiver tank timing formula (Equation 3):

T = V * (P1 – P2) / (C * Pa)

T – Time interval (minutes)

V – Volume of receiver tank (cubic feet)

C – Air demand (cubic feet per minute)

Pa – Absolute atmospheric pressure (PSIA)

P1 – Initial tank pressure (PSIG)

P2 – Ending tank pressure (PSIG)

By placing the values in the Equation 3, we can calculate the time to go from 3,000 PSIG to 1,000 PSIG by breathing normal at the surface.

T = 0.39 cubic feet * (3,000 PSIG – 1,000 PSIG) / (0.8 cubic feet per minute * 14.7 PSIA)

T = 66 minutes.

What happens if the diver goes into deeper water?  The atmospheric pressure, Pa, changes.  If the diver goes to 100 feet below the surface, this is roughly 3 atmospheres or (3 * 14.7) = 44.1 PSIA.  If we use the same conditions above except at 100 feet below, the time will change by a third, or in looking at Equation 3:

T = 0.39 cubic feet * (3,000 PSIG – 1,000 PSIG) / (0.8 cubic feet per minute * 44.1 PSIA)

T = 22 minutes. 

If you have any questions about using a receiver tank in your application, you can contact an EXAIR Application Engineer.  We will be happy to solve for the proper volume or time needed for your application.

 

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

Receiver Tank Principle and Calculations

Published on by Lee Evans1 Comment

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A receiver tank is a form of dry compressed air storage in a compressed air system.  Normally installed after drying and filtration, and before end use devices, receiver tanks help to store compressed air.  The compressed air is created by the supply side, stored by the receiver tank, and released as needed to the demand side of the system.

But how does this work?

The principle behind this concept is rooted in pressure differentials.  Just as we increase pressure when reducing volume of a gas, we can increase volume when reducing pressure.  So, if we have a given volume of compressed air at a certain pressure (P1), we will have a different volume of compressed air when converting this same air to a different pressure (P2).

This is the idea behind a receiver tank.  We store the compressed air at a higher pressure than what is needed by the system, creating a favorable pressure differential to release compressed air when it is needed.  And, in order to properly use a receiver tank, we must be able to properly calculate the required size/volume of the tank.  To do so, we must familiarize ourselves with the receiver tank capacity formula.

An EXAIR 60 gallon receiver tank

Receiver tank capacity formula

V = ( T(C-Cap)(Pa)/(P1-P2) )

Where,

V = Volume of receiver tank in cubic feet

T = Time interval in minutes during which compressed air demand will occur

C = Air requirement of demand in cubic feet per minute

Cap = Compressor capacity in cubic feet per minute

Pa = Absolute atmospheric pressure, given in PSIA

P1 = Initial tank pressure (Compressor discharge pressure)

P2 = minimum tank pressure (Pressure required at output of tank to operate compressed air devices)

An example:

Let’s consider an application with an intermittent demand spike of 50 SCFM of compressed air at 80 PSIG.  The system is operating from a 10HP compressor which produces 40 SCFM at 110 PSIG, and the compressed air devices need to operate for (5) minutes at this volume.

We can use a receiver tank and the pressure differential between the output of the compressor and the demand of the system to create a reservoir of compressed air.  This stored air will release into the system to maintain pressure while demand is high and rebuild when the excess demand is gone.

In this application, the values are as follows:

V = ?

T = 5 minutes

C = 50 CFM

Cap = 40 SCFM

Pa = 14.5 PSI

P1 = 110 PSIG

P2 = 80 PSIG

Running these numbers out we end up with:

This means we will need a receiver tank with a volume of 24.2 ft.³ (24.2 cubic feet equates to approximately 180 gallons – most receiver tanks have capacities rated in gallons) to store the required volume of compressed air needed in this system.  Doing so will result in a constant supply of 80 PSIG, even at a demand volume which exceeds the ability of the compressor.  By installing a properly sized receiver tank with proper pressure differential, the reliability of the system can be improved.

This improvement in system reliability translates to a more repeatable result from the compressed air driven devices connected to the system.  If you have questions about improving the reliability of your compressed air system, exactly how it can be improved, or what an engineered solution could provide, contact an EXAIR Application Engineer.  We’re here to help.

Lee Evans
Application Engineer
LeeEvans@EXAIR.com
@EXAIR_LE

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