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Overview


Air Curtain Burners, also called Air Curtain Incinerators, FireBoxes, Trench Burners, etc., were designed principally as a pollution control device for open burning. The primary objective of an air curtain machine is to reduce the particulate matter (PM), or smoke, which results from burning clean wood waste. Using a technology  called "air curtain," the smoke particles are trapped and reburned, reducing them to an acceptable limit per U.S. EPA guidelines.

Clean wood waste is loaded into the FireBox, and an accelerant such as diesel fuel is used to ignite the wood waste, just as you would start a campfire or open burn pile. 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 a 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 tons per hour; our largest machine can burn in excess of 10 tons per hour.

Principle


The primary purpose of the air curtain is to create a "secondary burn chamber." The air curtain is like a lid covering the opening in a FireBox. The particles of smoke rising on the hot gasses of the fire are trapped under the air curtain. These smoke particles are then reburned and their size is significantly reduced. With this reduced size, they can now escape through the air curtain and appear more like waves of heat than smoke. 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).

Operation


The picture to the right shows two Air Burners FireBox S-327 series machines completely full and burning, while in the background, a pile of wood is open burned. The same amount of wood, 20 tons, was used at each of the two sites. The FireBoxes eliminated the 20 tons of waste wood in one hour. The open pile burned for more than 48 hours to handle the same amount of waste wood.

The picture to the right is an aerial view of this site. It shows the environmental impact of open burning versus air curtain burning. To eliminate 20 tons of wood waste, the FireBoxes took one hour, while the open burn took in excess of 48 hours. The open pile burn filled the valley with black carbon smoke, while the Air Burners were almost undetectable.

Burning onsite eliminates the need for grinders and trucks. Plus, it is much faster, saving money and protecting the environment.

It’s What You Can't See That Is Important

The most concerning black carbon smoke particles are the ones you can’t see. They are called PM2.5, and consist of particulate matter that is under 2.5 microns in size. These are the particulates that can hurt you, as they are small enough to get past your body's defenses. No other machine used for wood waste elimination, including grinders and chippers, can control PM2.5 as well as an Air Burners machine. Our air curtain works.

For proper operation, the air curtain machine has to be designed to provide a curtain of air over a fire that has a mass flow and velocity 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 past the ineffective air curtain at a significantly higher rate than normal. If the mass flow of the curtain is too low. the unburned particles (smoke) will penetrate the curtain on the high velocity of the hot gases being generated from the burning wood. Air Burners machines have been thoroughly tested by some of the finest environmental agencies in the world, including the U.S. EPA, EA UK, EPA Australia, and more to prove our ability to control particulate release and to control PM2.5 release.

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