Compressed Air Knives vs. Blower Air Knives, an Application Comparison

A company was needing to dry vegetables after a washing system.  They currently had three blower air knives (as shown in the photo above) to remove the water before packaging.  The issues that they presented to me were in two parts.  They were not able to generate enough force to remove enough water from larger products like cauliflower and broccoli.  And, the heat from the blower system was affecting the appearance of the thinner vegetables like snow peas.  They purchased the blower-style air knives under the belief that they would save money by not using compressed air.  They found out quickly that it was not a true statement especially when it comes to the total cost of ownership.

Super Air Knife drying fruits and vegetables

When comparing the EXAIR Super Air Knife to a blower-type air knife, there are many features that should be reviewed.  For the customer above, they used an 18” (457mm) wide conveying system to wash more than twenty different fruits and vegetables.  So, they needed versatility to dry the different types of products.  With the Super Air Knife, we have a simple way to adjust the force by changing the inlet air pressure.  So, we can blow air at a light breeze for the snow peas to a very strong force to dry the cauliflower and broccoli.  With the engineered design of the Super Air Knife, we can achieve a 40:1 amplification ratio.  That means for every 1 part of compressed air, we are able to entrain 40 parts of ambient air.  This unique feature allows for the Super Air Knife to be very efficient with your compressed air as well as keeping the blowing air at ambient temperatures.  The design of a blower system allows the air to become hot, turbulent, and limited in force.  As noted in the photo above, they had to use three blower knives to try to remove the liquid water.  With the Super Air Knife, I recommended just one air knife to do the job.  They decided to try an EXAIR model 110218SS 18″ Stainless Steel Super Air Knife Kit to see if their concept of “saving money” with the blower-type air knife was valid.

To better explain the concept, I divided the comparisons into different categories.  You can decide if the Super Air Knife would be a better product than the blower-type air knife.  It sure was for the customer above.

  1. Initial Cost:
    1. Blower System – They are an expensive product when you have to include a blower, ducting, and a knife. To have any flexibility, a control panel with a VFD will be needed.  A capital expenditure is typical for a complete system.
    2. Super Air Knife – It is a fraction of the cost. With their system above, we were roughly 1/10 the cost.  A capital expense would not be required for ordering a Super Air Knife to remove the water.
  2. Maintenance:
    1. Blower System – The intake filter has to be changed periodically as well as the motor and belt has to be checked as a preventive maintenance. Being that the blower motor is a mechanical device, the bearings and belts will wear and have to be replaced.  Without proper maintenance, things can break prematurely.  Loss of production will cost you much money.
    2. Super Air Knife – They do not have any moving parts to wear out. Only compressed air is needed to operate.  The maintenance requirement is to change the compressed air filter once a year.
  3. Compressed air usage:
    1. Blower System – This device does not need any compressed air to work, but it does use an electric motor. For this customer, they had a 7.5KW blower motor.  With the inherent design of blower-type air knives, they have a reduced blowing force and turbulent air flow.  This combination required the maximum power output on the 7.5KW blower motor.
    2. Super Air Knife –With their unique design, it has one of the highest efficiencies in the market place. It can entrain 40 parts of ambient “free” air with every 1 part of compressed air.  With laminar flow and the power of compressed air, the Super Air Knives can be used at a much lower air pressure.  To compare with the electric blower motor above, the Super Air Knives would use 10KW of compressor power to operate at the highest force rating.  So, at lower air pressures, the blower motor and compressor requirement will be very similar.
  4. Noise:
    1. Blower System – With the turbulent air flow, the blower units are very loud. If operators are working near the system, they would need PPE for hearing protection, or elect to purchase (for even more money) a sound enclosure which some of the blower manufacturers offer.
    2. Super Air Knife – These units are very quiet. Even at a higher pressure, the sound level is only 72 dBA at 100 PSIG (6.9 Bar).  This level is well below the maximum noise exposure for hearing safety as marked in OSHA 29CFR 1910.95(a).
  5. Installation:
    1. Blower System –Just to begin, the installers will have to run electrical wires, controls, and ducting. The foot print is large and will need space to install.  They will have to drill holes in the floor to hold the blower in place, and perhaps build an attenuation chamber.  This can take days with no production to start operating.  And time is money.
    2. Super Air Knife –They are compact and do not take up much space. They mount easily into a system.  You can run a plastic tube or rubber hose to the Super Air Knife from a compressed air source.  If you use the Universal Mounting Kit, they will only need a 1/2″ hole for attaching.  Even if a fabricator has to make a bracket to fit into their system, the timing is in hours not days.
  6. Heat:
    1. Blower System – Besides being quite loud, blower systems get very hot as a function of the operation. While this may be sold as a benefit for some applications, it is considered a significant drawback for drying fruits and vegetables. The air can reach a target temperature of 180°F (82°C).
    2. Super Air Knife – The advantage for the Super Air Knife is the amplification ratio. The total volume of air that comes from it is 40 parts ambient and 1 part compressed air. So, the temperature of the airflow is going to be the same as the ambient environment surrounding the Super Air Knife.

The total cost of ownership is quite clear when you look at loss of output, loss of product, and breakdown of equipment.  After reviewing the information above, it was easy for them to try the model 110218SS Stainless Steel Super Air Knife Kit.  When they replaced the blower-type air knives, the customer did share some information with me.

First, they were amazed at the ease of installation and the compact design.  The customer also mentioned the amount of force that could be created by the Super Air Knife.  They were able to increase and decrease the required force to remove the liquid water from all the different fruits and vegetables.  This gave them the flexibility that they were looking for in their process.  And of course, the maintenance time and cost were eliminated.

Compressed air can be expensive, but if you use EXAIR products, you can use the compressed air very efficiently.  You do not have to sacrifice other areas within the total cost of ownership.  If you have a similar application, you can contact an Application Engineer at EXAIR.  We will be happy to discuss the benefits of using the EXAIR Super Air Knives over a blower-type air knife.

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

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