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Principle of Air Curtain Burning

In order to better understand how the air curtain burner works, why it is so cost efficient and environmentally friendly, we suggest that you review the principle of air curtain burning on this page. Please, also follow the links below to related reports that address combustion efficiency, greenhouse gas emissions, biogenic CO2, Black Carbon emissions and carbon neutrality.

Air Curtain Burners, also called FireBoxes, were designed principally as a pollution control device. The primary objective of an air curtain machine is to reduce the particulate matter (PM) or smoke, which results from burning clean wood waste. It is sometimes hard to visualize without seeing a machine in operation, but the machines do not burn anything, rather they control the results of something burning.firebox_sketch

You could look at it as a pollution control device for open burning. Clean wood waste is loaded into the FireBox, and an accelerant such as Diesel fuel is poured onto the wood and the pile is ignited. This is very similar to starting a campfire. The air curtain is not engaged until the fire has grown in strength or the air curtain may blow the fire out. Once the fire has reached suitable strength, usually in 15 to 20 minutes, the air curtain is engaged. The air curtain then runs at steady state throughout the burn operation and the waste wood is loaded at a rate consistent with the rate of burn. Our smallest machine will burn at a rate of 1 to 2 ton per hour, our largest machine can burn in excess of 10 tons per hour.

The purpose of the air curtain is to stall or slow down the smoke particles on their way out of the FireBox. In doing this the particles are subjected to the highest temperatures in the FireBox. Stalling the smoke particles in this region just under the air curtain causes them to re-burn, further reducing their size to an acceptable limit. The result is a very clean burn with opacities well under 10% per EPA Method 9 Testing (as compared to open burning which typically can run at 80% to 100% opacity).

BC_BurningThe picture to the right shows an Air Burners FireBox S-327 completely full and burning while in the background a pile of wood is open burned.

The wood pile that is open burning continued to burn for several days. That entire pile could have been eliminated with the FireBox in less than 2 hours.

For proper operation, the air curtain machine has to be designed to provide a curtain of air over the fire that has a mass flow and velocity that are in balance with the potential mass flow and velocity of the burning wood waste. If the air curtain velocity is too high, the FireBox can become over pressurized and over agitated. The higher pressure will lift the curtain and cause it to become ineffective. The over-agitation will cause embers and ash to be blown out of the FireBox or pit past the ineffective air curtain at a significantly higher rate than normal. If the mass flow of the curtain is too low then the unburned particles (smoke) will penetrate the curtain on the high velocity of the hot gases being generated from the burning wood.


old box_sketch

Air Curtain Burners do not
burn anything.

They are Pollution Control Devices for Open Burning.

They control the results of
something burning.


"The Wood Waste is the Fuel"

1 Air curtain machine manifold and nozzles directing high velocity air flow over and into refractory lined fire box or earthen trench.
2 Refractory lined wall as on the S-Series machines, or earthen wall as used with the T-Series trench burners.
3 Wood waste material to be burned.
4 Initial airflow forms a high velocity “air curtain” over fire.
5 Continued air flow over-oxygenates the fire keeping temperatures high. Higher temperatures provide near 100% combustion efficiency and that results in a cleaner and more complete burn.


The ash from typical wood waste is a useful soil additive and as such offers a commodity that can be marketed to plant nurseries, farms, etc. as a potting soil additive. Recycling our resources is not only socially and politically imperative, but it often reaps the additional benefit of tax incentives or tax credits.

Solid waste landfills are diminishing rapidly, and permits are difficult to secure for new sites. The Air Burners System provides an affordable and environmentally sound alternative to grinding and the indiscriminate depositing of woody debris into landfills.


Rev. 07.2013

To our Clients: Do you need permitting help?
As our machines are pollution control devices to make open burning of vegetative (wood) waste cleaner and as they are not incinerators, usually an "open- burn permit" from the local Fire Marshal or Forest Service Office will suffice. If you need help, contact us via our

To Air Quality Permitting Officers:
Please, go here for assistance or contact us should you wish to receive emissions data on our machines or any other regulatory compliance related information.

Thank you.

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1. Comparing Operating Cost and Emissions of Grinder to Firebox

2. FireBox Combustion Efficiency - Biogenic CO2
& Carbon Neutrality

3. Use of FireBox for Disposal of Trees Killed by Beetles and for Disposal of Invasive Species

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Last Updated March 15, 2017 by Air Burners, Inc.