What is an Air-Gravity Conveyor?
What it is
An air-gravity conveyor is a device for moving a variety of light-weight, fluidizable dry bulk powders. The conveyor consists of a rectangular chamber separated by an air-permeable, porous media. The media is placed along a horizontal plane to separate two chambers within the conveyor: An upper chamber to handle the material being conveyed, and a lower chamber to handle compressed air.
Air-gravity conveyors are typically manufactured in 10 ft | 3 m sections. Shorter sections are used to make up the exact required length of the total conveyor.
When installed, an air-gravity conveyor is sloped slightly downward – normally at 6 – 8° from horizontal. A benefit to air-gravity conveying is that the length of an air-gravity conveyor is limited only by available headroom versus headroom needed to accommodate the unit’s slope. Hypothetically, an air-gravity conveyor can be infinitely long – if the required headroom is available. In fact, air-gravity conveyors with lengths of 200 – 300 ft | 61 – 91 m are not uncommon.
How they Work
A positive fan or blower injects low pressure, dry air (typically 1 psig | 0.7 bar) into the lower chamber. The air permeates upward through the porous media. When the air is counterbalanced by gravity, a conveyor uses physics similar to an air hockey table to fluidize/aerate materials as they flow downstream through the conveyor’s upper chamber.
Air-gravity conveyors are used to handle a variety of dry, light-weight, easily fluidized powders, such as activated carbon, alumina, bentonite, calcium carbonate, cement, clays, detergent powders, fly ash, gypsum, lime, pulverized ores, silica sand, soda ash and talc, among others. To evaluate whether a powder is well-suited for air-gravity conveyance, a general rule of thumb is that the particle size is normally smaller than 50 mesh.
Industry Comparison: Air-Gravity Conveying Equipment
Several equipment manufacturers supply air-gravity conveyors; however, deficiencies may exist across product designs. Taking the time to pre-qualify the design quality of an air-gravity conveyor will pay significant dividends.