Seed is often stored in concrete silos, steel silos, or flat storage areas. Steel silos are usually galvanised which helps protect against corrosion. Flat storage areas are roofed in order to protect against the elements. The galvanised steel silo is sometimes referred to as a galvanised steel bin.
Steel silos are cheaper to construct than comparative capacity concrete silos or flat storage areas. Typical storage capacities for steel silos range up to 60,000 metric tonnes, although the size chosen depends upon the requirement.
Seed is delivered to the centre top of the silo via a series of conveyors. The seed then falls through the centre top entry with heavier materials tending to land in the centre, and lighter materials landing further towards the periphery. The centre storage area is often referred to as the ‘core’ and thus the phrase ‘core storage temperature’ is used to indicate the maximum temperature within the silo. If any significant temperature rise is noted during storage, it is likely to come from the centre core where the heavier material has accumulated.
Temperature and moisture content are the most important factors concerning correct seed storage. Seed deteriorates naturally over time and increased temperature accelerates this deterioration. Seed stored at temperatures in excess of 70°C will deteriorate within hours, whilst high moisture content will cause growth of moulds or fungi. It is possible to store soybeans for a year if the correct temperature and moisture level is maintained. If storing soybeans for a prolonged period of time, the operator should keep the moisture level below 12% at all times.
The screw sweep, or silo sweep, is used to remove the last remnants of the seed from the silo; this is typically when only 5% or less of the total storage capacity remains. The screw sweep discharges to grates where the seed then falls onto the conveyor. The sweep itself will often be driven by an electric or hydraulic motor. If a hydraulic motor is used, bio-degradable food grade oil should be employed to eliminate the risk of seed contamination following an oil leak.
A ladder provides access to the top of the silo. Access ladders should only be used by personnel with the correct training and certification. If possible, the base of the ladder should be located in a controlled area to prevent un-authorised use. Breathers prevent pressure accumulation within the silo, and the shape of the breather casing reduces the likelihood of rain water entering the silo. Seed is discharged through grates, also known as ‘nets’. If stored correctly, seed should not cause flow problems such as bridging, but this is heavily dependent upon the seed type and the storage conditions.
A single door or entry point is used for accessing the interior of the silo. The door should be kept closed during filling or discharging of the silo, and appropriate safety signs should be posted on the entrance side of the door. Ideally, the door should be locked to reduce the likelihood of un-authorised entry.
An electrical three phase motor is used to rotate a centrifugal fan. Centrifugal fans deliver ambient air into the silo for aerating and cooling the seed. Ambient air is blown into aeration channels, then through the seed, before being discharged through the breathers or centre top. Aerating the seed allows it to be cooled, but it also promotes a homogenous temperature throughout the stored seed. It is important to remember that the ambient air temperature and moisture level must be appropriate for the application; because inducing moisture into the silo via the aeration fans, should be avoided. Stored seeds with a relative humidity in excess of 70% should never be aerated.
The area under the silo houses the conveyor. The conveyor used for discharging the seed depends upon the seed stored; flatbed belt type conveyors are commonly employed for silo discharge applications.
3D Model Details
This 3D model shows all major components associated with a typical steel grain silo, these include:
- Silo Inlet
- Access Ladder
- Sealed Entrance
- Perforations for Ventilation
- Discharge Port
- Concrete Base
- Conveying Area
- Ventilation Channels