Shaking new ground

The advantages and disadvantages of mechanical versus pneumatic unloading systems for bulk products such as agri-bulks and other free-flowing cargoes have been debated on many occasions.

Both benefit from being continuous, closed-cycle processes, unlike unloading with a grab, but pneumatic unloaders have a reputation for using more energy to unload a given volume of cargo than mechanical systems, and mechanical unloaders thus have an advantage when it comes to high throughput ‘ship-to-silo’ type applications.

However, pneumatic unloaders tend to be better suited to mobile installations, and have an obvious advantage compared with mechanical systems when it comes to issues such as cross-contamination, which can be particularly important when handling agribulks such as genetically-modified (GM) and non-GM products. Moreover, as manufacturers highlight, newgeneration electronic controls have succeeded in reducing the energy consumption of the latest generation of pneumatic machines, thus enhancing the cost-effectiveness.

Pneumatic unloaders also have no internal ‘dead zones’ in which unwanted quantities of the product being handled can accumulate, thus making cleaning and maintenance easier. Furthermore, being able to access all areas of a ship’s hold, they have better ‘through ship’ efficiency, and can thus reduce unloading times and enhance turn-around time; can effectively remove dust which would otherwise be left inside the vessel, and can be fitted with filters which effectively remove dust which could otherwise cause contamination beyond the ship and the unloader.

For non-agri-bulk products, such as alumina, for instance, the continuous, fully enclosed nature of the pneumatic unloader and superior hold cleaning capacity make pneumatic unloaders the preferred choice, and the mobility and flexibility of pneumatic systems also makes them the preferred option where port infrastructure may not support high volume shipto- silo operations and ship to truck operation is required.

Neuero in Germany cites the example of the port of Qingdao in China, which recently installed two M300AL alumina unloaders from the company that are capable of handling 300 tonnes per hour.Highlighting the advantages of pneumatic systems in this particular role, Neuero notes that the M300AL has blowers designed to be insensitive to dust; the machinery is housed in such a way that it also acts as a counterweight, thus saving the extra weight involved in fitting a dedicated counterweight; and the flexible movement of the machine and its travelling, slewing, telescoping and luffing capability enable it to reach all parts of the holds.

Another recent delivery from Neuero saw the company deliver a Flexiport pneumatic unloader to the Garant Feed Mills group on the Danube river in Austria. Compared with the older unloader that the Flexiport system replaced, the new system has much greater capacity, is quieter, and eliminates a lot of the dust associated with older machines.

Apart from features such as a new type of drive control that makes use of FI frequency inverters, Neuero points out that the Flexiport has a number of other advantages including a rotating feeder which is capable of reaching cargo under the hatch wings on the vessel being unloaded. Using FI frequency inverters to control the blower drives has a number of advantages, Neuero believes, including reduced energy consumption, flow can be controlled at all stages during unloading – even at partial load – and system capacity can be set according to meet the specific requirements of individual cargo types,such as wheat, or sunflower seeds.

Switzerland’s Buhler AG is one of only a handful of companies that supply both mechanical and pneumatic ship unloaders. The company’s latest pneumatic ship unloader, the Portanova (see box),was specifically designed for unloading of cereals and other similar cargoes, allowing an economical continuous unloading of vessels with capacities of nominal 60,000 dwt-75,000 dwt.

Among recent examples of pneumatic ship unloading installations from Buhler are two Portanova machines for a new grain terminal in Sri Lanka. These Portanova 3000/60Rs are soon to be installed at a new flour mill at a grain terminal in Sri Lanka and are designed to unload ships of up to 75,000 dwt with a nominal rate of 310 tonnes/hour grain each.

Buhler is supplying all of the electro-mechanical equipment for the new flour mill, and the new silo installation in addition to the two pneumatic unloaders, which will operate on rails. Commercial operation with the new machines is due to commence in late 2007. Buhler is also heavily involved in the upgrade of an existing grain terminal in Germany. This interesting project at a long-established grain terminal is being carried out on behalf of Silo P Kruse in Hamburg.

Extension and refurbishment work carried out by Buhler and its partners in the project over a two-year period has seen a new stationary pneumatic unloading system installed with a capacity of 250 tonnes/hour; a loading system with a capacity of 250 tonnes/hour of grain; and the refurbishment of the existing dual-line pneumatic ship unloader with a loading line capable of 600tonnes/hour; thus converting the facility into a combined pneumatic ship unloader/mechanical loader. A connecting chain-type conveyor system has also been installed, linking the silo to the loading line of the converted ‘Combi’- unit.