Mechanical ship unloaders with screw conveyors can provide a highly-efficient solution to discharge cement from ships. The technology offers benefits such as low energy consumption and maintenance as well as a dust-free unloading operation. Materials handling specialist IBAU Hamburg shares its experience in designing road-mobile screw-type ship unloaders.
To carry out their unloading tasks efficiently, road-mobile screw-type ship unloaders have up to four separate screw conveyors (Figure 1), regardless of their size:
• Vertical screw 1 picks up the material assisted by a counter-rotating outer screw. Filling factors of up to 60 per cent can be achieved with IBAU Hamburg-designed vertical screws.
• Vertical screw 2 raises the material to the conveying height required for onward transport.
• Screw 3 provides the horizontal transport from the hold to the material transfer point. The efficiency of the screw conveyor is higher with a downward sloping screw. The required lifting height of only 4m above ground level ensures that the horizontal screw is actually in a horizontal position or inclined downwards for over 80 per cent of the unloading time. Therefore, less energy is needed for conveying and equipment is subject to less wear (Figure 2).
• A fourth screw (loading screw) either loads the material directly into trucks or transfers it to a downstream mechanical or pneumatic transport unit.