Pneumatic Ship Unloaders for Powder Cargoes
Vacuum, pressure and screw type unloaders for fine bulk cargoes: how each works, realised against nameplate rates, particle attrition, and matching the system to the ship.
A pneumatic ship unloader draws a powder cargo out of the hold through a suction pipe and delivers it directly into shore storage, which suits cargoes that are dusty, flowable and destined for an enclosed process feed system. The main types are vacuum systems, pressure and combined vacuum-pressure systems, and mechanical screw type unloaders that convey rather than entrain the material.
The full article will cover the working principle and duty of each type, the shipboard variants fitted to dedicated tonnage with aerated sloping hold bottoms and re-loader tanks, and the residue problem that leaves hold corners to be worked by hand or bulldozer whatever the system.
It will give particular attention to two things a fixture depends on. Realised through-ship rates run well below the nameplate capacity quoted for a machine, so planning on the latter overstates the discharge. And pneumatic conveying breaks particles, raising the fines fraction of the delivered cargo, which makes the choice of discharge system a cargo quality decision and not only a rate decision.