Miller Magazine Issue: 125 May 2020

56 COVER STORY MILLER / MAY 2020 • Developing action strategies if contamination is to occur. Grain Handling Grain handling and conveyor systems should be designed to minimize damage to grain. Pulses are more susceptible to impact damage than cereals and should not be moved in pneumatic grain conveyors, as the impact speed of grain is higher than the critical 12m/s. Augers smaller than 125mm in diameter should also be avoided with pulses. Augers should be run full, and preferably slow, to reduce grain damage. Grain Receival Hoppers A high capacity receival system is needed for efficient transfer of grain. Ideally, it should be possible to deposit a trailer load and pull away from the unloading area with- in minutes. An in ground receival hopper is typically fitted with a screw conveyor, or auger, to raise grain for condi- tioning or storage. Grain Conditioning and Metal Detection Foreign materials and dust must be removed to eliminate problems further down the grain storage and handling sys- tem. A grain conditioner, or scalper, removes foreign parti- cles. A dust extraction and collection system prevents dust entering the environment. All foreign metal objects must be detected and removed before they can cause damage. A permanent or electro-magnet must be located in the chute that feeds the grain conditioner, but needs to be checked and cleaned regularly. Belt and Bucket Elevators Bucket elevators are used mainly to lift grain vertically to silos. These usually deliver the grain directly into silos using diverters that direct grain into a gravity chute to the selected silo, or by using belted conveyors to transfer grain horizontally to the various silos. The capacity depends on the volume of the buckets, the spacing and the speed of the belt. Elevators up to 20m high and with a capacity of 50t per hour are available. Bucket elevators are self-cleaning by design and are typically fixed in position. Auger (Screw Conveyors) Auger elevators are one of the cheapest methods of ele- vating grain and can be fixed or portable. These are available in a wide range of lengths and capacities. They are compara- tively light in weight, depend- able in operation due to good portability. Long augers may be mounted on wheels for easy transport. The angle of opera- tion is adjustable, but the ca- pacity declines as the auger is raised. High moisture content in grain also reduces the ca- pacity of the auger. Old augers with worn flighting can dam- age split-prone grain. Belt Conveyors Belt conveyors are typically used to transfer grain hor- izontally. Inclines up to 15° are possible - and even up to 30° with ribs fitted to the belt. Belt conveyor capacity is high and grain can be loaded or unloaded anywhere along the belt. Belt conveyors do not damage the grain and raise little dust. Drag Chain Conveyor Drag chain conveyors, or paddle conveyors, use a series of paddles fixed to a loop of chain moving inside a fully en- closed conduit. The circular paddles are sized to fit snuggly in the conduit. This fully enclosed system prevents dust in a building. Drag chains can move grain at any angle, includ- ing horizontal, and are largely self-cleaning, although cor- ners of the chain loop will typically require attention. Drag chain conveyors are a permanent installation, but can be easily extended for facility expansion. Mobile Equipment Mobile augers, mobile belt conveyors, grain throwers and pneumatic conveyors may be used to load grain into stor- age facilities. Mobile augers or belt conveyors, with fixed and guarded cross sweeps, or a front-end loader can be used to empty the pad. Pneumatic conveyors also suit this job and allow easy final clean-up of grain. Operators using mobile elevating equipment must be made aware of any overhead power lines to prevent electrocution. Automation Controls, instrumentation and automation systems are key elements in the overall distribution system. The auto- mation system is governed by the overall facility design and operational requirements. Each individually controlled de- vice can be linked into a main PLC, enabling coordination of the controls between various equipment.