Air Conveyance of grain
When should air conveyance be considered?
Air conveyance is the method of choice in many instances such as:
- Where no or poor infrastructure exist such as no electric power near the silo site.
- Where multiple silos are placed at different sites within a relatively short distance from each other but too far apart to be serviced by any one stationary conveyance system.
- Where one conveyance system is used for several silos for both load and unload.
- Where silos are filled and emptied once or twice per annum or at relatively low turnover.
- Where grain bags (sometimes referred to as silo bags) are used for storage.
- Where grain needs to be transferred from a grain car to a truck next to the fields.
- Where grain or spills of other free flowing material needs to be recovered such as accident sites for instance.
- Where storage dams and bunkers are used.
- Where flat storage in sheds are used.
- Where grain needs to be transferred over relatively long distances.
- Where grain are conveyed between silos.
- Where grain needs to be unloaded from a truck into a building or silo at a mill for instance where no dump pit can be placed or where the surrounding buildings are so crowded that a truck can’t move in close enough.
- Where silos and conveyors needs to cleaned out entirely for hygienic reasons.
- Ship unloaders are often using air conveyance which is usually much faster than clamshell grabs for instance.
Usually capacities can be as low as may be required and as high as 200 tons per hour in the case of ship unloaders for instance.
Farm or commercial type air conveyance offered by Walinga from Canada, an ABC Hansen supplier, ranges between 20 tons per hour and 80 tons per hour depending on the intake and unload distances.
Air conveyance equipment may be:
- Tractor PTO driven which in turn powers hydraulic motors. This is the least expensive option in terms of capital cost.
- Electric units
- Mobile units with self contained diesel engines.
The main disadvantage of air conveyance is the running cost in terms of kW needed to convey a ton of product which is more expensive than other conveyance options. The flexibility of air conveyance however often overshadows this cost aspect. Also considering that one unit may be used to serve several silos at different sites, it becomes substantially cheaper.
To convey 60 tons per hour of grain over a distance of 20 meters on the intake to around 10 meters on the unload at a height of some 5 meters, would require around 60-75kW. High when compared to other conveyance methods but inevitable when this is the only system that would work in a given circumstance.
Air conveyance is also benign on grain damage provided no sharp corners are placed in the air channel as the grain actually travels in the centre of the conveyance tubes and not actually touching the sides, except on sharp corners.
Flexible Stainless steel hoses are used by first class suppliers such as Walinga to prolong tubular life where rubber hoses are used at intake points for more flexibility and lighter manual handling.
What are the main aspects when considering an air conveyance system?
Select the right equipment in terms of capacity required. Make sure all distances are well measured. Capacity is not as much reduced on the intake end as it is on the unload end. Therefore try to position the conveyor close to the unload point. (it takes more air / energy to blow than to suck).
Some manufacturers supply equipment consisting of a suction system and an auger discharge system. This unload leg is therefore fixed and usually rather short. This limits flexibility and the equipment may seem to have a large output, but at a cost.
Blowers are all important. Regular centrifugal blowers are much lower in pressure and volume than positive displacement blowers. The longevity of blowers are also enhanced with chrome plating over mild steel.
Rotary valves are essential and equipment bearing the full load of every grain that passes through the system. Hard faced valves and chromed veins are important in prolonging the life of these air seals.
The gauge of steel used in cyclones and other discharge, hard wearing areas, as well as tubes and tube connections.
The type of petrol or diesel engine used in mobile units should be reputable.
An integrated cleaning system where grit and dust is trapped is very important in high production units to prolong the life of the rotary valve and to isolate such dust from the commodity.
A top of the range type conveying system like a Walinga, usually has a hydraulic boom system to place the unload cyclone at the correct position. This may work from the tractor hydraulics or from an integrated hydraulic system on the unit itself.
For more information on air conveyance, visit www.walinga.com.
Part of the ABC Africa Group of Companies