TERMINAL TECHNOLOGY 1

The flouting terminal is still a viable option oques H W Carisen

he idea of a floating terminal is t o allow for quick construction, with- out any major investments on the T dock (quay), quick and efficient

dismantling when the market i n a pam'cu- lar area diminishes, and easy reconstruc- tion i n another county where the market i s healthy, for the handling of cement or other product.

Generally, floating terminals can be divided into the following groups:

import terminals export terminals transfei terminals.

Most tCrminals that have been built so far, operate i n ports and thus i n sheltered water conditions. It i s also possible to design them for offshore operations.

The floating base The main idea i s that operations can begin within a minimum amount of time. Most floating terminals are based on second hand bulkers, that can be purchased quickly and cheaply, depending on the market situation. However, for certain rea- sons it can be more suitable t o choose a

Unlwdng cement from o flootmng temfnol

terminals Jan Pettersson, HW Carlsen A8

Orders f o r f l oa t i ng terminals used f o r cement handling, reached a peak between 1980 and 1985. This corresponded w i t h a boom in cement

i m p o r t s t o t h e Middle East and Africa. Whewcement impor t s in these coun- t r i es declined, t h e f l oa t i ng te rm ina l concept proved i t s f l e x i b i l i t y and many were moved t o o the r countries. Some terminals were even rebu i l t t o handle o the r commodit ies, l i k e grain. However, equ ipmen t suppliers have recently experienced a dramatic dec l ine in orders. Jan Pettersson o f HW Carlsen AB, Sweden h igh l i gh ts t h e advantages o f us ing f l oa t i ng terminals.

purpose built base, especially if the termi- nal is only going to be used for direct transfer.

When deciding upon the most suitable bulk ship, there are various factors that have to be considered:

Whether storage capacity i s needed, if so, how much

the classification of the terminal whether the ship i s suitable for instal-

lation of the equipment design of hatches and hatchcovers whether the ship is gearless or

equipped with cranes

Storage capacity The first question that needs to be asked is whether storage capacity i s needed. I n most cases, the answer wi l l be yes. However, for an export terminal there are cases when the need for storage capacity has to be questioned.

The need for storage capacity has to be accurately calculated. The size of the vessels that have to be unloaded and the daily output from the terminal has to be calculated. Spare storage capacity is normally a minor investment and a bigger ship can, depending on the market for secondhand ships, mean an even lower cost.

I f the ships delivering cement are of the 30,000dwt size, it i s recommended that the terminal has at least 35-40,OOOt of storage capacity. For the overall econ- omy it i s important t o unload incoming ships as quickly as possible and not t o keep them waiting due to a lack of storage i n the floating terminal.

A gearless vessel, where there is no interference from cranes seems to be the best alternative when taking into account that the cranes can be dismounted and sold. However, keeping cranes for service and maintenance of the unloading and reclaiming equipment on board and t o handle empty bags is a good idea.

Furthermore, when using the floating

INTERNATIONAL CEMENT REVIEW / JANUARY 2001

TERMINAL TECHNOLOGY

base jus t for direct transfer of cement from one ship t o another, it can be a good idea t o have some spare storage capacity, i n case the ship t o be loaded is delayed. With spare storage capacity, the unloading of feeder ships/barges can continue uninterrupted.

Where no storage capacity i s consid- ered t o be needed, a purpose bui l t cata- maran type of floating base is a very use- fu l alternative. I f cement i s t o be transferred on from barges t o bigger ocean-going ships, the barges are docked in between the legs of the catermaran and the cement is directly loaded onto the ocean-going vessels.

One important factor t o consider when using a secondhand ship i s how the ship unloader is t o be mounted. I s there enough space on the side of the ship or does the unloader have t o be bui l t wi th a beam that spans over the hatches? A ship unloader tha t travels on one side of the ship i s normally the best solution as the travelling can be done without interfering with open hatch covers. To be able t o travel on one side means that a certain minimum rail span i s needed for the ship unloader. However, even big unloaders with a capacity of 800tph. used t o unload ships of 40.000dwt. wi th a rail span of only six metres, are possible t o build.

For stability reasons, this span can be considered a minimum for such a big unloader. It is of course possible and sometimes necessary t o build an unloader with a wider span that travels over the hatches. However, the height of the open hatch covers may be a drawback, as they may interfere wi th and hinder the unload- ing operation. This problem might arise during reclaiming of the material from the terminal's own hatches t o the packing machines and the bulk load as the unloader wi l l be used for the reclaiming operation. The hatch covers w i l l not inter- fere during the unloading of an incoming ship as the design means that the hatches of the terminal ship can be closed.

Classification of the floating base This i s a very important issue. The classifi- cation can be time consuming. The equip- ment t o be installed on deck has t o be designed for sea voyage. This means investment costs become higher. The advantage of having a classified ship i s tha t it gives more flexibility, as it i s easier t o move the terminal t o a different

Transferring bulk cement by a rail-mounted trovelling unit con improve turn-round times

location. However, i f you plan t o operate the terminal for several years a t the same point, it w i l l not be a drawback t o use the no classification alternative.

Another important factor i s t o consider the investment costs involved when the ship is t o be used as a floating terminal. A ship becomes cheaper i f it is not classified. It is even possible t o choose a ship with- out a functioning main engine and, in case of changing location, tow the ship t o the new site. However, the equipment for the unloading, reclaiming and Loading opera- t ion consumes energy so functioning gen- erators are important. I n the case of both the classified and non-classified, alterna- tive special measures have t o be taken when designing the sea stowage arrange- ments. The counterweight of the unloader has t o be dismantled and stored on deck, the bogies of the unloader w i l l be bolted t o special supports and the horizontal and vertical arms w i l l be attached t o supports.

During storm conditions i n sheltered water the stowage is much less compli- cated. It is recommended tha t a careful study is made as t o whether classification is needed.

Equipment to be installed The ship unlooder For cement, several options are a t hand. Grabs or pneumatic and mechanical ship unloaders are possible alternatives.

Grabs The clamshell grab i s s t i l l the dominating technology in ship unloading. It is the most versatile when it comes t o the differ- ent bulk materials it can handle. The draw- back is the spillage and dust, and this

means tha t for cement handling other types of unloaders are taking more and more of the market.

Pneumatic unloaders For capacities of up t o 600tph this tech- nology has taken a big part,of the market. It is a proven system with enclosed han- dling and thus environmentally accepted. I t s only drawback is the high-energy con- sumption, which i s a very important factor on shipbased equipment. . Mechanicol unloaders I n most floating terminals delivered, the mechanical screw type has been chosen. There are several reasons for this. Compared t o other systems the screw type unloader is relatively low i n power con- sumption, it is lightweight and it is very flexible when handling different types of materials. Furthermore, it i s an enclosed handling system creating a minimum of dust i f properly operated.

On a floating terminal the power has t o be generated t o the ship. The power consumption is an important factor. O f the enclosed systems, the screw i s therefore suitably compared t o the pneumatic tech- nology. The weight of the equipment i s also important. For high capacity unload- ers, the screw can be considered as the best solution. Whatever unloading system is chosen, a travelling unloader is strongly recommended. A travelling unit i s by far the most efficient solution and w i l l give the highest 'through-the-ship' capacity. Therefore, it i s important t o investigate whether or not a rail can be installed on the ship. To benefit from a travelling unloader the most, the design of the

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f TERMINAL TECHNOLOGY 1

following conveying equipment should be adopted.

The deck conveying system The deck conveyors are used for conveying the commodity from the ship unloader t o the different holds. Several possibilities exist today.

To benefit entirely from a travelling unloader, a system should be chosen where the unloader can freely travel while leading the deck conveyor. This means that loading the deck conveyor on every part of i t s length has t o be possible. Fixed inlet connections mean that the unloading operation has t o be stopped while con- neding and disconnecting. This loses time and efficiency.

One of the most efficient deck convey- ors is a screw installed along the deck. On top of the open trough of the screw, a special cover belt is installed. On the out- let chute of the unloader a 'belt l i f te f l i fts the belt during the travelling motion and can thus fill the deck conveyor on every part of i t s length. From the deck, a number of transversal conveyors connect t o the different hooks. The transversal conveyors can be also of different design. Normally, screws or air slides are used for the pur- pose of cement handling.

With the above-described system, any hold can be fed with material from any position of the unloader. There are, of course, other, cheaper and not so flexible alternatives to feed the holds. The ship unloader can feed the holds directly and not via a deck conveyor. The simplest and cheapest way is via a gantry conveyor with an outlet bellow connected directly or via air slides t o an inlet chute on the hatch

cover. However, this means that the unloader has t o be i n a satisfactory position. To obtain limited possibility t o travel, the gantry conveyor can be built as a scissor arm. A l l the systems described last, although cheaper i n price, are less efficient and give a lower 'through-the- ship' capacity.

Reclaiming equipment in the holds The most flexible i s t o install fluidised bot- toms and vertical screw conveyors or suc- tion i n a l l holds. This means that the ia ter ia l can be reclaimed and delivered to packing machines and/or bulk load out, with closed hatches and without using the ship unloader for this operation. The alter- native is the most flexible one but expen- sive and therefore only used for environ- mental reasons.

The normal way of operating i s t o use the ship unloader from the hold and via the earlier described deck conveyor, trans- fer the material t o one hold with fluidised bottom and via a mechanical or pneumatic system feed that paiking machine(s) and/or bulk load out. The drawback with this system is that the ship unloader has t o be tied up for reclaiming when the flu- idised hold has to be fed and that you have t o work with open hatches during the reclaim operation.

The simplest solution is t o feed the packing machines and/or bulk load out by reclaiming and feeding with the ship unloader only.

Bulk load out The bulk out conveyor can be of various designs. The bulk load out arm conveyor is

Bulk load out ensures quick speed but dust emissions must be kept to u minimum

I

normally a screw or an air slide. These technologies are very suitable as their designs are enclosed to control dust.

The advantage of using the air slide conveyor, is that power consumption is low and it is also light. The advantage with the screw conveyor is that it is easy t o equip with a number of outlets, should they be needed. The screw can also handle a wider range of commodities.

The ships or trucks wil l be fed via a bellow and a dust collector wi l l minimise dust emissions. To adopt high variations in distance between the deck of the ship and the ship or truck to be loaded and to min- imise the length of the bellow, the arm can be additionally equipped with a luffing motion. A slewing of travelling motion of the arm wi l l increase i t s working range and enables stowage during non-operation or long sea voyages.

Investment costs The investment cost greatly depends on the alternative chosen, tbe price of the floating base and the conversion cost. Below are some examples:

floating import terminal with unloading capacity 800tph, packing capacity 360tph and based on a bulk carrier of 35,000- 40,000dwt for USS3.5m-USS4m. Total investment cost including the conversion i s USS15-20m. Remark: the ship is classifiedfor sea voyage

floating export terminal with unloading capacity of 800tph and based on a ship of 50,000-60,000dwt (20 years old) for USS2 t o USS3m. Total investment cost including conversion is USSIO-12m. Remark: the ship is not class@ed.

Time schedule The total time for carrier of 35,000- 40,000dwt i s estimated at 12-14 months. The total time for carrier of 50,000- 60,000dwt is estimated at 8-10 months.

Summary By using a floating terminal, it means that the customer wil l be i n possession of a very sophisticated terminal on-stream i n less than one year.

I f choosing the right unloading and conveying equipment, the terminal can be used for a wide range of materials with minor modifications. Taking al l this into account, the floating terminal may be considered a very attractive alternative for the future.

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