F1 car or vacuum cleaner?

Comparisons are often made between the relative productivity of pneumatic and mechanical ship-unloaders.
 
In essence, the issue boils down to ‘horses for courses’. There are differences between unloading rates and power consumption between the two systems. But, ultimately, the decision rests on what each individual terminal wants to achieve, and it is difficult to argue that one system is inherently superior to the other.
However, an often overlooked factor is the skill of the operator, which can make all the difference in the efficiency of machinery. 
 
Netherlands-based Lion Bulk Handling argued in a recent blog that, besides regular maintenance, there is a direct link between the skills of the operator and shipunloader capacity. In other words, when the operator is not sufficiently skilled, this will influence the unloader’s performance. 
 
With fully automated unloaders, this is less of a challenge. But, more often than not, this applies only to dockmounted unloaders working dedicated dry bulk vessels – say, a cement carrier, with its own fluidised floor, piping and valves. In such a combination, continuous high capacity is obtainable, irrespective of the operator’s skill level, says the dry bulk logistics firm. 
 
But the picture changes with semi-automated unloaders, as these are usually deployed on non-specialist dry bulk vessels, without the supporting infrastructure, on and off shore. 
 
The big vacuum
Lion Bulk likens the process to a big industrial vacuum cleaner looking to reach into each corner of the hold. As there is an interaction between the vacuum system (the manipulator arm) and the cargo, the skills of the operator  become all-important. 
 
To reach a high unloading capacity, it is necessary to maintain a ‘deep’ vacuum in the system and cargo, perhaps -650 millibars. The difficulty here is that the manipulator arm needs to be moved, rotated and angled into differentdirections during the whole process until the dry material is fully collected, and the hold bottom is reached. Just as with a domestic vacuum cleaner, when empty air is collected, it will reduce the vacuum’s operational efficiency and negatively impact overall capacity.
So what does this mean for individual circumstances in a particular port or terminal? With fully automatic unloaders, Lion Bulk says it can accurately calculate capacity based on pipe route, pipe diameters, material specifications, bends, and internal resistances, etc. 
However, there is no clear answer with semi-automatic unloaders. This is because while all the material and equipment variables can be determined, the limitation lies with the ambient conditions, cleaning-up procedures and operator skills on moving the manipulator arm in the correct direction so as to keep the nozzle submerged in the dry material, maintaining a solid ‘seal’ and corresponding vacuum. 
 
Operator skills cannot be quantified as a number or percentage. The fact is that, when the vacuum drops, less cargo will be collected. For example, when the operator moves the manipulator arm slightly out of cargo reach, empty air will be sucked in and lower the vacuum. 
Once the hold bottom is reached, maintaining full vacuum is difficult. At this stage cleaning-up is needed, which can be done by various means. 
 
To come back to the question of how fast the unloader will perform on average in local circumstances, Lion Bulk says a further analogy can be drawn from Formula One (F1) racing. The performance of the engine is calculated bythe engineers, the quality of the tyres is set, the length of the track is known, as are the weather conditions, but the driver’s skills have a huge influence on performance. 
 
It is relatively easy to forecast and calculate an F1 car’s maximum speed on the straight, but not, in advance, what the average speed and time would be around the track. After a couple of rounds, different tracks, multiple drivers, varying weather conditions, and tyre changes, experience builds up, and so predicting average speed in advance gets closer to reality. 
 
At the end of the day, unloading an open-top barge or vessel can be likened – using a further analogy – to playing chess, the firm says. You can move several chess pieces, and each piece has its own characteristics and its own type of move. With each move you are thinking of winning the game and to use all the pieces as efficiently as possible. You want to move the correct piece at the correct moment, within the minimum required time. But one wrong move  and you will end-up ‘losing time’ or, worse, losing the game. 
 
Down in Djibouti 
 
Pneumatic ship-unloader suppliers continue to pick up some interesting orders. Africa is witnessing substantial investment in port infrastructure and machinery. One of the most active areas is the small country of Djibouti. Port De Djibouti SA (PDSA) is building a new US$590M multipurpose port at Doraleh to relieve pressure on the existing Djibouti port. 
Belgium-based Vigan has been awarded a further turnkey project for a new grain and fertiliser terminal at Doraleh, on the back of its successful operation at the existing SDTV terminal in Port of Djibouti. The system was built entirely by Vigan and commissioned in 2009, and is now unloading more than 2 Mtpa of grain and fertiliser.
A Chinese consortium, China State Construction Engineering CorporationChina Civil Engineering Construction Corporation (CSCEC-CCECC), is the main contractor for the quay and terminal infrastructure at Doraleh, while the designand manufacturing of the new multipurpose unloading equipment and warehouses have been subcontracted to Vigan. 
 
The new terminal will discharge, handle, store and bag about 2 Mtpa of grain and fertiliser, handling vessels from 30,000 to 100,000 dwt. 
 
For the unloading, Vigan plans to manufacture and commission one railmounted pneumatic shipunloader model NIV600 with unloading capacity of 600 tph/500kW, a set of belt and chain conveyor systems, one hopper on wheels with three bagging lines of 60 tph and truck loading, and 14 lines of 60 tph bagging systems. Vigan will also install two flat warehouses with a total capacity of 85,000t for the grain terminal, and two more flat warehouses with total capacity of 145,000t for fertiliser, as well as two bulk truck loading stations and two bulk receiving hoppers.
The project is expected to be completed by the end of this year.