Using Liquid Nitrogen-Powered Air Compression for Duct Cleaning

Posted on 06/24/2022

In most instances, when a duct cleaning technician arrives onsite at a job, the routine remains the same: unload a gasoline-powered air compressor from a vehicle, connect the necessary hoses and tools, and bring them into the space. Then, the technician will run a compressor to generate the proper level of air pressure and begin work.

However, occasionally circumstances arise that may alter the process — such as jobs that require hundreds of feet of air hose, challenging access to ductwork, or demand exits and doors to remain closed. 

When presented with these circumstances, liquid nitrogen as a compressed air source can be a valuable solution vs. gasoline-powered compressed air that might not be adequate.

Making Liquid Nitrogen

Almost 80% of the Earth’s atmosphere is made up of nitrogen, about four times the amount of oxygen we breathe every second. In other words, nitrogen is in abundant supply.

To create liquid nitrogen, the most effective phase used for duct cleaning, our everyday air undergoes the process of fractional distillation, during which it is compressed into a high-pressure tank and passed through a nitrogen membrane that separates the nitrogen from the other elements such as carbon dioxide and hydrogen. From there, any remaining moisture is dried out, leaving behind pure liquid nitrogen.

A benefit of liquid nitrogen is that it’s inert, meaning it doesn’t carry the same potential risks of igniting or burning.

The Advantages of Nitrogen

From the time after the tools are hooked up, the end-game for duct cleaning is the same whether you use nitrogen- or gasoline-powered air compressors. Both agitate dust and debris, enabling removal with a vacuum.

However, nitrogen can show its value even before the tools are hooked up, with one being its flexibility with locations. “What if you’re working on a 15-story high-rise?” said David Monson, ASCS, and Operations Manager at Armstrong Duct, Vent Hearth and Home. “Or a building with inoperable windows or security concerns where you can’t leave doors open to run an air hose?”

With more than 30 years as a technician, Monson has run into many such places: government facilities, prisons, and even a leftover underground bunker used during the Cold War and re-purposed by FEMA. “Since the nitrogen tanks are self-contained and on casters, you can wheel them anywhere you need,” he said.

Liquid nitrogen is also a valuable air compression source because of its consistency, both in preparation and use. Gasoline-powered air compressors require creating a setup to produce high pressure; the pressure is spent during the cleaning, causing the pressure to drop; and the compressor must kick on to generate more pressure while the technician waits. “Let’s say you’re using a whip head and you’re in a large duct,” Monson said. “As you’re bleeding air, the whips become less active. Then you have to stop and let the pressure build up again.”

In nitrogen tanks, the pressure remains the same regardless of the amount left, meaning the cubic feet per minute will never drop below the set amount. Using liquid nitrogen also allows technicians to worry less about air compressor maintenance, repair costs, or fuel.

But perhaps arguably the strongest proof of nitrogen’s benefit of use is its stability despite constant innovation. As technology grows and creates better and more efficient equipment, the use of nitrogen remains steady.

“We’re basically using nitrogen the same way I started using it back in 1991,” Monson said. “All the technology developed is at the lab.” That lack of change can mean a lessened learning curve for technicians who, once they gain the proper technique, may use that same technique no matter where they receive their nitrogen tanks.

The Disadvantages

Still, there is a reason gasoline-powered air compressors remain standard, as they have their own advantages, including convenience and usefulness for most jobs.

One argument against nitrogen is the size of the tank. “A cylinder of liquid nitrogen weighs 900 pounds,” Monson said. “Not only do you have to have vehicles that are able to transport, but you have to get the tank in and out of the vehicle.”

That tank has to get to an access point somehow, sometimes requiring other equipment to transport it. If the job is on a high-level floor of a high-rise, the tank must also be transported to the location of the job, not the hoses alone. “And if you’re getting the tanks delivered to the job site, you’re subject to possible delivery delays,” said Monson.

Best Practices for Using Nitrogen

Liquid nitrogen has its own set of best practices for handling, both in use and safety. Monson’s first bit of advice: talk to the supplier when deciding whether to use liquid nitrogen. “Speak with the people at the counter,” he said. “Not over the phone or online, so you can explain exactly what it is you want to do.”

Another best practice is finding a regulator — the attachment on the tank that allows you to control the pressure flow out of the tank — that will ensure the job is done properly. Monson specifically recommends a high-flow regulator that can deliver 25 cubic feet per minute — a measurement describing the volume at which gas expands at an atmospheric level — at 150 psi. Once found, the regulator should always be hooked up to the gas-phase outlet.

Another such practice: never draw liquid nitrogen from the tank. “The boiling point for liquid nitrogen is -320 degrees Fahrenheit. If it gets on you, it’s instantly freeze-drying.” Monson recommends the first step when handling a liquid nitrogen tank be locking the liquid valve. Also, technicians should never handle the tank with exposed skin, as any liquid will freeze flesh instantly. Generally, chemical-splash goggles and face shields should always be worn during the transfer and handling process of liquid nitrogen to guard against splashes and spills. Loose-fitting, insulated cryogenic gloves should also be worn.

Monson also recommends avoiding gaseous nitrogen to maintain efficiency and maximize effectiveness. “Gaseous nitrogen tanks have a smaller volume,” Monson said. “When I started using nitrogen, I was using those cylinders. It would take 12 for a moderately sized air duct cleaning in a house, and last only about a day. In a single liquid nitrogen tank, there is enough volume to keep a two-man crew operating for five-plus days.”

Regardless, while liquid nitrogen may not be a must-have for every job, knowing the proper protocols and best practices can ensure a technician can perform every job.

SAFE HANDLING OF LIQUID NITROGEN

  • Get a high-flow regulator that can deliver 25 cubic feet per minute at 150 psi.
  • Lock the liquid valve and never draw liquid nitrogen from the tank.
  • Never handle the tank with exposed skin.

This article originally appeared in the May/June 2022 edition of DucTales.

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