High capacity unloading
Back to Ship unloading
Reaching the 3,000t/h milestone
Bruks Siwertell designs unloaders for ports with a variety of bulk material capacities. We are able to provide unloaders for exceedingly high capacity operations. The newest addition to our program is the 3,000t/h Siwertell unloader discharging nearly a tonne of coal a second the new unit offers massive initial and operational cost savings for large-scale operators.
All industries appreciate the economies of scale, and this is equally true when it comes to bulk cargoes. Bigger ships transport their bulk cargoes more cost effectively across the oceans, but they can lose time in port because discharge rates are not optimised for large vessels.
Recognising the need for higher discharge capacities at the intakes for power stations, Bruks Siwertell has for some time been engaged in a development programme for a 3,000t/h screw type unloader. The work was completed a few years ago, and customers can now take advantage of the cost savings that can be delivered by the 50 percent increase in unloading capacity.
Cost savings through the right combinations
Cost savings can be achieved both in terms of initial investment and through-life operational costs, depending on the overall unloading performance required. Specifying two 3,000t/h unloaders instead of three 2,000t/h machines – to achieve a 6,000t/h capacity – results in an investment saving of up to 25 percent in favour of the 3,000t/h ship unloaders.
If the maximum possible capacity is required from the outset, then three 3,000t/h unloaders will provide an unloading capacity of 9,000t/h, as opposed to 6,000t/h from three 2,000t/h units.
Considering a Capesize vessel of 200,000 dwt and a through-the-ship capacity of 65 percent the unloading time using three 2,000t/h unloaders would be 51 hours. This would be reduced to 34 hours using three of the 3,000t/h unloaders.
Choosing unloaders according to ship size
The 3,000t/h unloader has been designed for a maximum vessel size of 230,000 dwt or a maximum beam of 50m. In general it is aimed at ships between 100,000 and 200,000 dwt. It can be used to discharge smaller vessels, but the efficiency level will not be as high as experienced with larger vessels.
Developing the high capacity unloader was technically demanding; involving far more than simply scaling up the existing product. The whole conveyor chain is new. Re-use of existing design has been minor. While it was possible to scale up most of the parts in the conveyor chain, the existing steel supporting structure design could not be adapted and we have developed a completely new solution.
3,000t/h can also be expressed as 50 tonnes per minute. But it is even more impressive when you realise that this is nearly a tonne of coal each second.
The counter-rotating inlet feeder was invented by Siwertell to increase the efficiency of cargo pick-up and the filling factor of the vertical conveyor. It gathers material from below the cargo surface in the ship’s hold to minimize dust creation and then feeds it into the vertical screw conveyor. Different designs of feeder may be used to optimize the unloading performance depending on the material being handled.
The vertical conveyor is a screw-type device which elevates bulk material from below the cargo level in the ship’s hold up to the horizontal conveyor. The totally-enclosed vertical conveyor is built up from standard screw sections, outer tubes and intermediate bearings. It is mounted in a robust supporting steel structure.
Siwertell designed the unique Outer Diameter (OD) bearing to achieve a continuous screw flight for the vertical conveyor without any interruptions. A continuous screw reduces power consumption and minimizes the risk of material getting stuck in the tube.
Heavy items such as pay loaders and excavators are often used in the holds to assist the unloader during the final clean-up phase. A wire rope hoist, installed on the horizontal arm, is used for lifting equipment in and out of the hold.
The horizontal conveyor is normally a screw-type conveyor. Mounted on the horizontal boom steel structure, it receives bulk material from the vertical conveyor via an enclosed transfer chute. It then transports material to a vertical discharge chute in the center of the slewing turret. For some applications an enclosed belt conveyor is used instead of a screw conveyor.
The electrical system is installed in an insulated electrical housing equipped with a heating fan and an air-conditioning unit. It is made up of elements such as low voltage switchboards with a motor control center, contactors, a programmable logical control-system and the human machine interface.
The unloader can be operated either from the cabin or using a remote control unit directly from the side of the ship’s hold. Both arrangements offer excellent views of the unloading area. The cabin is mounted on an arm at the same level as the horizontal arm and it slews along with the horizontal arm. It is fully-insulated and equipped with a heating fan and an air-conditioning unit to provide the operator with a comfortable work place, even in extreme weather conditions.