By Larry Blitz
Aeromechanical conveyors are completely dust tight, versatile, and efficient conveyors that can handle virtually any powder, granule, flake, or mixture. Nevertheless, there are many misconceptions about them.
A Floveyor discharges into a hopper
The basic concept is the following: the disk is traveling at a constant speed, which in turn creates draft pockets behind each disk. The material is transferred within these draft pockets until exiting at the top end with centrifugal force. This is much like an airplane attaining take off: until a high speed is reached, there is insufficient lift to get the airplane into the air.
An aeromechanical conveyor is a constant-speed machine, and that speed is necessitated to attain a proper draft pocket. It is the feed of material to the aeromechanical conveyor that controls the material’s throughput rate. In order for the material to get into such a draft pocket, it must be regulated into the hopper (actually a funnel) in order for the material not to exceed the capacity of the draft pockets being created. It is this material that drafts the disk.
In essence, there are pyramids of material particles that follow the disks up the tube. Given the speed of the rope assembly, the material is within the tube for a short amount of time (usually between 1 and 4 seconds, depending upon the length of the machine). This results in a total amount of material within the conveyor being significantly less as compared with any other mechanical type of conveyor. With the material traveling so fast, the hourly throughput rate is significantly higher than for any other conveyor machine on the worldwide market for its size, horse-power usage, reliability, cleanliness, physical size of the machine, throughput rate, and the small amount of product left over.
There are many misunderstood mechanical parameters about an aeromechanical conveyor. Some false assumptions are presumed. These scenarios are discussed below.
Stopping and Starting
As an aeromechanical conveyor rope assembly moves at a high rate of speed, and with low material loading, there is no reason to stop the machine in mid stream. If such a stop is necessary, the process is not set up correctly. However, if there is a power failure, the conveyor will obviously stop with a small amount of material in it. If this happens, rest assured that the machine will restart. Remember, there is little material within the tube at any instant. It is crucial to understand that for a 12,000 lb/hr flow rate, there are only 6½ lb of material distributed within a 25-ft length, while there are around 170 lb of material within the same length of a typical drag conveyor. Yet both types of conveyors have the same throughput rate. As a matter of typical operation, it is best to stop an aeromechanical conveyor a suitable amount of time after stopping the feed of material to it. Running an aeromechanical conveyor for an extra few seconds to ensure minimal residue and that all material was conveyed into the destination equipment is, at most, a minor concern. These machines are constructed to operate in the empty condition.
Rope Assembly Life
The rope assembly lasts for a long period of operational time, much like tires on a car. If you drive your car 100,000 miles, you would expect to buy new tires within about four months. If you drive the car into curbs and the wheels become out of alignment quickly, you would expect high wear on the tires and need to replace them within a shorter amount of time. It is the same with a rope assembly. If you don’t keep atmospheric conditions at both ends, if you flood-feed the bulk solid material, if you block the outlet, plus various other unsuitable process conditions, you can expect to replace the rope assembly within a shorter amount of time.
The process conditions dictate how long the rope assembly is going to last. Therefore, an understanding of how an aeromechanical conveyor is actually transferring the material is imperative. Obviously normal wear and tear will eventually catch up, but that is after at least 10,000 hours of operation. By understanding all of the process conditions within a given application, the aeromechanical conveyor rope
assembly runs for long periods of time.
The aeromechanical conveyor is extremely efficient. The amount of hp (amperage) used is the lowest for the same throughput rate compared with any other conveyor machine (tubular and standard drag conveyors, inclined flexible and rigid screws, bucket elevators, pneumatic conveyors). An aeromechanical conveyor has the lowest amount of material within it, yet equates or surpasses the throughput of any other conveyor. It is the actual amperage usage that dictates the power consumption (electrical cost).
This is strictly a function of the material characteristic itself.Aeromechanical conveyors are designed to handle those cohesive, dusty, fine, floodable, flake, fluffy, fragile, granular, heavy, hygroscopic, lumpy, pellet, powder, prill, sticky types of bulk solid materials. Aeromechanical conveyors also handle beans, corn kernels, oats, peas, tea leaves, and many other similar coarse materials without breakage.
While an aeromechanical conveyor’s rope assembly is traveling above 750 ft/min, there is no blower assembly associated with the machine that would cause a high velocity airflow within it. Therefore, by definition, there is no material fluidization. The conveyor’s disks mounted on the high-speed traveling rope assembly redirect the air that they are traveling through to create draft pockets, within which the
material is suspended. The only air movement within the conveyor is the displacement of air from the destination bin to the feed chute by virtue of the material exiting and entering the aeromechanical conveyor.
Some product materials are dustier than others. It is this dustiness factor that has a major effect on the size of a destination bin. Drag conveyors typically don’t do well with dusty, sticky powders because their inherent mode of dragging the material just adds to the effect of the material sticking to the inside conveyor walls. An aeromechanical conveyor’s design inherently offers friendly operating conditions to handle the dusty, sticky, floodable, cohesive, etc. powder-handling applications, as well as for conveying easier-flowing materials such as flour, grains, pellets and granules, sugar, etc.
Aeromechanical conveyors are virtually self-cleaning. They do not need a special disk to wipe the inside tube walls. With its rope assembly’s speed of travel, the tubes are virtually clean, much like a pneumatic conveying system’s tubes. There is only a small amount of material left over within the feed and discharge housings that can be held within the palms of your hands. No other mechanical conveyor that is transferring powders (and similar material) can claim this. The feed and discharge housings are typically designed for quick access to vacuum out (or blow out) the small amount of residual material, should it be necessary. As an alternative, an aeromechanical conveyor does pump water, and thereby circulates the water through the machine; such an option is available when it is an acceptable means of cleaning.
Regulated Material Feed
Material is not flooded into the hopper of an aeromechanical conveyor. The hopper is a funnel, so a regulated feed of material into the hopper is necessary. Furthermore, a feeder is a control valve for bulk solid material flow. Feeders have the ability to condition bulk solid materials in their hoppers and produce a consistent output flow of the material. Some feeders are more accurate than others, but the aeromechanical conveyor only needs a flowing stream of material into its feed housing where the material particles begin their conveyance. There are several different hopper styles to ensure the continuous material flow through the hopper and into the feed housing.
The speed of the aeromechanical conveyor’s rope assembly is constant. The material throughput rate is a function of the regulated material feed to the machine. Different speeds can be offered based upon certain types of materials, but this only relates to a quasi-aeromechanical function. There is an optimum speed that creates the necessary draft pocket for the aeromechanical conveying function. However, every material has its own ability to fill those created draft pockets. Therefore, every material has its own maximum capacity.
Understanding the above-mentioned mechanical parameters in context with the operation of the aeromechanical conveyor is important. However, other aspects relevant to overall process parameters that should also be considered include: just in time or reliable gravity flow for material to arrive at the use point; material flow rate; feed source; and destination equipment effects.
Aeromechanical conveyors are unparalleled in their efficiency for quickly loading a bulk solid material into an elevated surge container. They allow a production facility’s manufacturing process to maintain its own reliability factor.
Larry Blitz is president of FloAero Inc. (Encino, CA), a manufacturer of dry bulk material conveying systems. For more information, visit www.floaero.com.