Operating Guidelines
These general guidelines are to be used if the manufacturer’s guidelines are not available. If the manufacturer’s guidelines are available, the ACD shall be set-up, used and operated in accordance with the manufacturer’s recommendations. If a manufacturer’s operating instructions do not address a topic covered by these guidelines or if the guidelines are more stringent than the manufacturer’s instructions then these guidelines should be followed in those areas.
These guidelines provide installation and operating instructions for an Air Curtain Destructor. It is intended for those persons responsible for site and pit preparation and the loading of an ACD. Burning hours are within the period two hours after sunrise to two hours before sunset.
The only material that may be burned is wood waste consisting of trees, logs, limbs, large brush, and woody vegetation. Wood that has been treated, coated, or impregnated with any chemicals cannot be burned.
The ACD is recommended as a reasonable, practical, alternative to open burning throughout the country and has proved effective in reducing smoke and fly ash pollutants. The ACD creates and maintains a uniform curtain of air across the top of the burning pit to contain smoke and other particulate matter. The greatly increased air flow swirls into the pit increasing combustion efficiency and the burning rate. All this causes the resultant smoke (unburned particulates) to be confined under the air curtain and consumed by the intense 1600 – 2000° F temperatures, and it provides 3 to 5 times faster burning than with open pile burning.
Other than fuel for the ACD blower itself, no auxiliary fuel is needed once the fire is started and the air curtain is operating. A person is required only to keep the fire fed, which is accomplished by simply dumping additional burnable refuse into the pit. No ends of wood should be sticking up to break the air curtain’s “seal” since this would permit smoke and ash to escape. Most ACD’s work best when operated so that no flame is visible above the actual air curtain.
Site Preparation
The burning pit may be dug with a front-end loader or backhoe to an 8-feet width, 12-feet to 15-feet depth, and 10-feet to 40-feet length (the length depending upon the size of the ACD used). In no case should the 8-feet width be exceeded. Line one side of the proposed pit with a mound of earth 1.5-feet high running the length of the pit. In areas where rock or water occurs, the sides of the pit can be built up above ground level to obtain proper pit depth.
The ACD is positioned with the header resting on the prepared mound of earth with one end of the header even with the closed end of the pit. The nozzles should be tilted down at an angle no more than 30 degrees from the horizontal. NOTE: This angle is critical to the proper operation of the ACD. The air curtain is directed diagonally downward across the pit and this provides the high turbulence for combustion.
Start-up and Loading Guidelines
Load the pit half full with a mixture of trees, logs, limbs, and large brush. Douse the wood and/or strategically placed straw bales with fuel oil, putting the majority of the oil on the wood at the front center side of the pit. Waste oil or flammable materials like gasoline may not be used. Ignite the wood at the same point. Allow sufficient time for the fire to take hold before introducing any air from the ACD; (fifteen minutes is usually ample time for proper ignition). As the fire grows in intensity, gradually bring the blower up to optimum speed (generally between 1,100 and 1,400 RPM, depending upon size, type and make of blower). Once the fire reaches full intensity, successive intermittent charging may begin. Check with the manufacturer or rental company for guidelines specific to the ACD you are using.
The intervals between charging may be determined by observing the burning rate. Generally, if the fire is kept at its maximum intensity it will keep one man, operating a front-end loader or clamshell bucket, busy constantly. The charging should be alternated between light and heavy materials. Also, the material should be charged towards the back of the pit.
The pit must not be overloaded, that is, the material must not be piled so high that it will extend through or above the air curtain. No materials should extend outside the boundaries of the pit and air curtain where sufficient air is not available from the nozzle or header.
In general, a hot fire in an under-loaded pit will burn more wood than in an over-loaded pit. This can save both man-hours or operation and days of land-clearing.
Maintenance and Safety Requirements
Ash removal is required in order to maintain efficient and proper combustion. The pit MUST be cleaned of ashes each morning before burning begins. This should be done EARLY before the wind picks up and CAREFULLY so as to minimize ash dispersal to nearby inhabited properties.
To protect against the possible accident of a loader falling into the pit while charging, it is required that the pit be dug in stable soil and/or where necessary use earth anchors, buck-stays, and wire mesh for additional support. A “STOP GUIDE” or restraining board should be provided at the loading edge of the pit in order to keep the loader from getting too close to the pit during charging operations.
It is strongly suggested that the fire (after burning down from the day’s last load) be quenched with dirt by covering the pit. This is to prevent a “smoldering” pit’s wispy smoke from causing nuisance complaints. These conditions will occur mostly during the “calms” experienced at sunset and sunrise. The more unburned material remaining in the pit at day’s end, the more the need for covering.