Ship loading/unloading trends
October 17, 2006
by Editorial Staff
There’s plenty to consider when choosing between pneumatic and mechanical systems
by Richard Miller
When it comes to discharging grain and grain derivatives from ships and barges, there are two basic choices: pneumatic or mechanical systems.
The former tends to consume more energy and cause more damage to brittle grains such as rice (although in recent years there have been major improvements in both of these areas), but advantages include minimal dust pollution, zero spillage and easier clean-up resulting in faster through-the-ship discharge rates.
The latter, which includes continuous and discontinuous (grab) systems, are normally more energy-efficient, though not as versatile in the case of continuous mechanical unloaders, and more prone to spillage in the case of grab discharge.
Until recently, power consumption was just one of many considerations in the overall equation, to be compared against environmental acceptability, capital cost, ease of maintenance, deadweight and versatility. However, the energy factor has now moved up the scale to become one of the prime considerations when selecting a ship unloader.
Nevertheless, pneumatic unloaders in many instances continue to be the preferred choice, as the following examples of recent machine installations testify.
PNEUMATICS REMAIN POPULAR Melle, Germany-based Neuero earlier this year supplied a 200-tph Flexiport stationary pneumatic unloader to Garant Feed Mills of Austria for handling non-free-flowing grain derivatives and feed products. Special features include a rotating feeder and a blower controlled by frequency inverters to help reduce power consumption.
In Greece, Neuero is currently erecting a 400-tph stationary unloader that will discharge soybean meal at a site close to Athens. A vibrating nozzle is being fitted to facilitate constant flow during the unloading cycle. This machine has been painted in colors to minimize visual impact without camouflaging it to the extent that it poses a safety hazard.
Another project completed earlier this year comprises a 600-tph combined ship unloader/loader delivered to Edible Oil Company of Dubai. It feeds a new oil extraction plant in Jebel Ali.
In Brazil, Maquinas Condor, Neuero’s regional partner in South America, recently commissioned a 300-tph pneumatic unloader at the Port of Santos. The rail-mounted unit is operated by Fertimport, a Bunge subsidiary, and discharges wheat for a nearby flour mill.
The machine replaces grab cranes that could not provide sufficient discharge capacity and also caused unacceptable levels of dust pollution. It has been equipped with a six-tonne capacity auxiliary winch capable of hoisting payloaders into the vessel’s hold to speed clean-up of residual cargo.
Buhler AG, Uzwil, Switzerland, reports that it recently delivered a new stationary 250-tph pneumatic unloading system as part of the upgrading of the Silo P. Kruse grain terminal in the Port of Hamburg, Germany.
This new system has been installed adjacent to the old building, which dates back to the 1940s. At the same time, Buhler refurbished the existing dual-line 600-tph pneumatic unloader, converting it to a combined unloader/loader.
MECHANICAL OPTIONS Among the most recent grain unloaders supplied by Buhler is a Portalink 600/70K mechanical unit that has just been delivered to Sayga Flour Mills, a major Sudanese flour milling company. The machine, which has a rated discharge capacity of 600 tph, can accommodate vessels up to 70,000 dwt and has been installed at Sayga’s marine terminal at Port Sudan. It works alongside two existing 300-tph Buhler ship unloaders, a pneumatic Portanova and a mechanical Portalino.
With the arrival of the new machine, total ship unloading capacity has been increased to 1,200 tph. Discharged grain is transferred to a 75,000-tonne-capacity dockside silo complex, from where it is transported to the mill in Khartoum either by rail or road.
A new Buhler Portalink mechanical ship unloader has also just been delivered for grain unloading at SABT, Durban, South Africa.
Vigan Engineering of Nivelles, Belgium earlier this year supplied two NIV 300 pneumatic unloaders that have been installed at a new marine terminal for transhipment of grain and fertilizer in Djibouti. The order for this equipment had been received in late 2005 from Compagnie Djiboutienne de Gestion du Terminal Vraquier (SDTV). Initially, it is expected that the terminal, which is not scheduled to be fully operational until mid-2007, will handle during its first year of operation about 1 million tonnes of bulk cargo, comprising mainly wheat, maize and diammonium phosphate. Some of this tonnage will be transhipped to nearby Somalia and Eritrea.
The two self-propelled NIV 300 machines, with a combined capacity of 600 tph, will work exclusively on grain handling while fertilizer materials will be discharged by grab crane.
The Vigan unloaders are powered by a diesel generator and will discharge ships in the 30,000-to-40,000-dwt range. Special abrasion-resistant alloys have been specified to minimize wear at vulnerable sections in the pneumatic pipeline and fully automatic controls help minimize energy consumption.
Just more than a year ago, Vigan successfully commissioned three railmounted pneumatic unloaders, each with a discharge capacity of 400 tph, at the Chinese port of Zhanjiang. They replaced three locally manufactured pneumatic ship unloaders that were no longer able to cope with growing volume of imported oilseeds. Tonnage is soon expected to increase to 2.5 million tonnes per year, compared with the present annual figure of about 1 million tonnes.
The three new unloaders are each fitted with electrical and control cable reels, and each machine is capable of accommodating almost any size of grain vessel thanks to a 28-meter suction boom comprising a three-part telescoping horizontal section.
These machines have been equipped with speed variators to optimize control of energy consumption as well as antiwear protection at points susceptible to premature abrasion damage, such as the elbow between horizontal and verti- cal suction pipes. Other recent Vigan contracts involving grain ship unloading include delivery earlier this year of four large NIV pneumatic unloaders, with capacities ranging from 250 to 300 tph, to Algeria. Also in recent months, the company has supplied mobile dockside pneumatic conveyors with capacities ranging from 140 to 250 tph to Cuba, Cameroon, Syria, Algeria and Nigeria. Most of these machines are employed for ship unloading of grain or feed products.
In November 2005, Gunnarstorp, Sweden-based BMH Marine, which earlier this year became part of Cargotec’s MacGREGOR business area, won an order to supply a PortMaster pneumatic unloader to Gigante NV, Curacao, Netherlands Antilles. Installed in the summer of 2006, the machine is capable of discharging grain at 250 tph from vessels up to 45,000 dwt. It will also handle soybeans.
In March 2005, BMH Marine won a contract to deliver two Siwertell screwtype continuous unloaders to Rizhao Port (Group) Co., in China. The two machines, which will be fully operational later this year, will discharge ships up to 70,000 dwt in Rizhao Port at a rated unloading capacity of 400 tph. Cassava is the main cargo handled but other materials will include grain and fertilizers.
Commissioning trials are about to be completed on a new Siwertell that was just installed at the Seaforth Grain Terminal, Liverpool, U.K. The unloader is operated by The Mersey Docks & Harbour Company and will discharge grain and maize from vessels up to 75,000 dwt at a rated capacity of up to 1,800 tph. In addition, soybeans will be handled at up to 1,700 tph.
COMBINATION OF THE TWO Another leading ship unloader manufacturer that offers both mechanical and pneumatic options is Hartmann, Offenbach, Germany. In the past, the company’s pneumatic unloaders have rarely been employed for grain.
However, according to marketing director Bernd Lampen, Hartmann is planning to become more active in the grain sector with its mechanical ship unloaders, which until now have normally been employed for handling heavier commodities such as coal.
Because mechanical unloaders traditionally require less power, the company anticipates that they will increasingly be preferred to pneumatic systems as energy costs continue to increase internationally. Hartmann is working on prototype designs which combine the advantages of pneumatic and mechanical conveying.
In the past, Hartmann has built mechanical unloaders with capacities of up to 1,200 tph, and last year it upgraded an existing machine that it had installed as long ago as 1975 in the Port of Bremen. It was converted from a ship elevator with a telescopic reclaimer feeder to a bucket-elevator-type continuous unloader.
Hartmann believes that this type of continuous mechanical unloader, which in recent months has undergone further technical refinement, ranks first among all available types of ship unloading systems in terms of energy efficiency (no more than about .20 kilowatt hours per tonne), wear resistance and serviceability.
Where there is a requirement to discharge small or infrequent volumes of imported grain, or where other categories of bulk cargo also need to be handled, grab cranes are usually the preferred option. With this mode of handling, spillage and dust pollution can be a problem, but it does feature high-discharge capacity and the crane’s inherent versatility. It can be rigged with a different type of grab for handling other bulk cargoes or with a hook or spreader for unloading or loading piece goods.
Self-propelled floating grab cranes of- fering discharge capacities from 400 to 1,000 tph are widely employed in the Dutch ports of Amsterdam and Rotterdam for unloading grain as well as other bulk cargoes. Two of these units frequently service a large bulk carrier simultaneously.
21ST CENTURY GRAB HANDLING Gottwald Port Technology of Germany, which invented the concept of the mobile harbor crane, earlier this year unveiled its new Generation 5 series, which offers enhanced performance and adaptability. The first four-rope grab version for ship unloading duties was ordered this spring by Ership in the Port of Huelva, Spain.
Where rope grab cranes are required to operate at maximum capacity, there is always the problem of grab swing, which in turn can give rise to unacceptable levels of spillage. This drawback is significantly reduced with the new generation of hydraulic cranes, in which the grab is attached directly to the end of the articulating boom. This allows for fast cycle times, and because there is a fixed grab pat, the likelihood of spillage is greatly reduced.
Mantsinen of Finland has also recently developed this type of crane, which is now available with an electric motor. Because of its quiet operation, the crane is suitable for use close to residential areas. Typical discharge capacities are 450 to 600 tph, significantly better than for a rope grab crane of comparable size and capacity. Two Mantsinen 60 MCT models were delivered earlier this year to Turkey for unloading grain and other bulk cargoes.
Richard Miller is a U.K.-based freelance writer. He can be reached at firstname.lastname@example.org.