Pneumatic self-unloading vessels are built specifically to handle powder cargoes such as cement. Using lean-phase or dense-phase pneumatic conveying systems, they operate using compressed air to move the cargo through piping to load and unload.
Both the loading and unloading processes are completely enclosed, and this type of vessel is expected to operate completely dust-free.
From an environmental standpoint, this is one of the most effective methods of transporting cement by sea.
Handling and Transporting Cement
The cargo holds of the pneumatic self-unloader have sloping bottom surfaces fitted with air slides. Cement powder is fluidized when compressed air is injected into the air slides below the cargo, and the sloping surfaces of the cargo hold move the cement toward the center tunnel for discharging.
Rotary valves and cement screws in the tunnel inject the cement into the discharge piping where high volumes of transport air move the cement and carry it in suspension through the discharge pipelines to a storage silo ashore. The same pipelines are used to load the vessel through a single point. Distribution pipes on the vessel direct the cement powder into the hold to be loaded, and large dust collectors are used to evacuate the transport air from the holds and filter out the dust.
The pneumatic conveying technology on the ship is matched with the system on shore to account for pipeline restrictions and high volumes of air. This ensures optimum loading and discharging rates — typically 1,000 t/hr.