New developments in offshore dry bulk handling

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Sanjeev Mathur, Country Manager, Bedeschi & BLL, Dubai

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Offshore transshipment facilities are becoming increasingly important in overcoming the bottleneck caused as vessel size outstrips port expansion

Since the beginning of the last century Bedeschi has been involved in handling various kinds of dry bulk material for a variety of industries such as cement, brick, clinker, coal, bauxite, iron ore, among others.

Based on the company’s 100-year know-how in the handling of several different and difficult bulk materials, several years ago Bedeschi realized the vast potential of the growing offshore transshipment market and started developing cargo handling systems for offshore applications too. Bedeschi is now among the market leaders in this sector too.
 

Offshore transshipment: an overview

Offshore transshipment essentially means transfer of dry bulk cargo, such as coal or iron ore, from large vessels into smaller vessels or vice-versa. The growth in vessels’ size has rapidly increased since the Second World War, but port development has not been able to keep pace with it. Vessels’ sizes have increased because of economy of scale, i.e. the larger the vessel size, the lower the per-ton transportation cost. Port development, unfortunately, has lagged behind, mainly because of a high gestation period and high development cost. The only way to overcome this bottleneck is offshore transshipment. Many kinds of transshipment devices have been devised and deployed in various parts of the world, mainly for coal and iron ore handling.

A classical transshipper essentially comprises of two main components: the cranes, and the cargo handling and delivery systems. Their application varies from the usage of the system, i.e. if the system is intended to carry out offshore loading of cargo from barges into ocean-going vessels (OGVs), or discharging the cargo from OGVs into barges.

For a loading system, the cranes need not have a very big outreach because they have to pick up cargo from barges, which are relatively smaller in size and berthed alongside. The cargo handling system instead should be equipped with a shiploader, with sufficient air draft and outreach to deliver cargo into the holds of large OGVs. The reverse is applicable for discharging systems where the cranes, which are supposed to pickup cargo from large OGVs, have large air draft and outreach; and the cargo handling system has a smaller barge loader sufficient to deliver cargo into barges, instead of a shiploader. Bedeschi has implemented various systems that are now in successful operation in different parts of the world. Let us now examine a few systems as case study to emphasize the application.
 

Princesse Chloe

Princesse Chloe is equipped with two heavy duty offshore fourrope Liebherr cranes, of 30 tons capacity each. They have been fitted with Peiner Smag grabs of 20.5m3 capacity. The cranes are strategically placed adjacent to the hoppers so as to minimize the slewing movement, thereby increasing the cycle time and efficiency.

The cargo handling system supplied by Bedeschi consists of two duly designed hoppers and an array of conveyor systems, leading to a telescopic/shuttle shiploader. The hoppers are of 50m3 volume, with a top opening sufficient to accommodate the large grabs in use. The trunk-pyramidal shaped hoppers have asymmetrical walls to ensure smooth flow of coal through the hoppers into the transfer chute. The hoppers are fitted with vibrators to ensure free flow of sticky coal, in order to maintain the required flow rate. The top of the hoppers are fitted with mesh grill to eliminate any oversize or undesirable material, which may potentially damage or block the conveyor system. The water sprinkler system is installed on top of the hoppers to suppress the coal dust during grab delivery.

Coal from each of the hoppers is extracted by means of individual variable speed belt feeders. These frequency controlled feeders extract coal from the hoppers and transfer it to the longitudinal conveyor. The belt width of the feeders is kept high and the speed is low to ensure uniform extraction of coal from the hoppers. Another conveyor then transports the coal longitudinally through the length of the Floating Terminal through to the transfer point – a transverse conveyor, which will help in crossing over the entire beam of the terminal, and will lead to the final conveyor leading to the shiploader. The inclinations of all the conveyors have been designed in accordance to the grade of coal to be handled, in order to achieve smooth flow of cargo and avoid back-flow. Special care has been taken in the design of the transfer points to ensure no blockage occurs and the material flows smoothly. All the conveyors are enclosed to avoid airborne pollution.

The shiploader is of shuttle/telescopic boom type. The shiploader has 19m air draft, which makes the Princesse Chloe capable of loading large vessels up to cape size. The ship-loader is capable of swiveling by means of geared slewing rings, and luffing by means of hydraulic mechanisms. The cargo handling equipment constructed and supplied by Bedeschi is manufactured with the highest classification for heavy duty work for open-sea conditions. The equipment has been designed for a heel and trim of 5° and 3° respectively.

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