Clean and green cargo systems

29 Apr 2011
MacRack reduces maintenance work for the shipowner, and the shipyard’s installation work is also simpler because fewer components need to be installed on the coaming

MacRack reduces maintenance work for the shipowner, and the shipyard’s installation work is also simpler because fewer components need to be installed on the coaming

The drive for more clean and green cargo ships is now penetrating down into the way the cargo is handled, writes Mark Langdon

There is huge pressure on the marine industry to reduce emissions which can be seen resulting in designs such as the Triality VLCC concept, recently showcased by DNV. However, so far most of the emphasis has been on improving the hull design and engine efficiency to reduce emissions.  

Another way to improve efficiency and reduce emissions is through efficient cargo handling systems; which is where the electric drive comes in. Electrically-driven cargo access and handling equipment reduces the amount of hydraulic oil carried onboard and minimises the environmental impact. In the car-carrying market in particular, there is a demand for clean and green vessels and car manufacturers are putting pressure on ship owners to reduce the risk of cargo damage by hydraulic oil.

There are also benefits when it comes to reduced power consumption. The efficiency of electric drives is only likely to improve in the future with the huge amount of research being carried out in the electric car market to improve the efficiency of electric motors. An example of this is the work being carried out at the Lund University Faculty of Engineering in Sweden. A key element of the electric motor is the magnetically conductive material, usually made up of bundled laminated thin plates with coils wound around them. Researchers at the university have found out that a composite plastic containing iron powder functions well in motor applications, among others, attaining good energy efficiency. By moulding melted plastic and iron particles, which make the part weakly magnetic, in various forms, full freedom of form can be achieved.

One of the leading players in the move towards electrically powered cargo handling equipment is Cargotec’s MacGregor division, with MacRack, a second-generation system that offers shipowners an economical, competitive and environmentally-friendly electric-drive system. MacRack represents a significant advance in electric drive technology, employing only one electric motor per hatch cover panel and a further-enhanced control system. “Development work is a continuous process and, as with all first-generation technology, improvements were needed,” says Torbjörn Dahl, senior naval architect for bulk ships at Cargotec. “These focused on safety, technical issues and the cost of electric drives.”

Traditionally, large bulk carrier side-rolling hatch covers use two types of drive for opening/closing operations: chain or rack-and-pinion drive. For both options there are two ways of lifting the panels up into the position at which they can be opened or closed: pot lifts (which can also be described as hydraulic jacks, or wheel lifters), or ‘roll-up-roll’ lifters, which enable automatic cleating to be adopted.

MacRack unites these lift and drive operations and so makes separate hatch cover lifters obsolete. This reduces maintenance work for the shipowner, and the shipyard’s installation work is also simpler because fewer components need to be installed on the coaming.

Another significant feature is that the actuators are installed on the hatch sides only, which ensures that the drive unit is well protected from cargo spills during loading and discharging. Detailed technical checks as well as prototype tests have been carried out, and a patent is pending.

The panels are kept in the closed position by an automatic lock (with a manual release). For intermediate stops the panels are held by the built-in brake on the motors. During the opening/closing procedure, auto-cleats are activated in the same way as for the roll-up-roll system.

“Reliability of these systems has been a key focus,” notes Dahl. “Some redundancy has been enabled in the control system design. For instance, if one of the deck PLCs is broken, the panel can be driven directly from the variable frequency drive (VFD) operating panel. It is also possible to manually cross-connect motors between VFDs. Also, if a problem in position control arises, the system goes into ‘safety mode’, which allows a panel to be driven, but only at low speed. If electrical power cannot be used, panels can be operated with the same emergency equipment usually used in all MacGregor hatch cover systems.

“Electric drives are also ideal for remote diagnostics technology, and by using the latest diagnostics tools it is now possible to offer real-time equipment condition analysis and reporting via telephone or satellite communication media.”

In addition, the company has confirmed new orders worth more than €20 million to deliver fully electrically-driven MacGregor cargo handling cranes and design and key components for hatch covers. The equipment is for eight general cargo vessels to be built at Zhejiang Ouhua Shipbuilding in China for the China Navigation Company. The ships will be delivered in 2013. The order includes an option for equipment for a further eight ships.

Each of the 31,000 dwt general cargo vessels will be equipped with four fully electrically driven cargo handling cranes with a SWL of 60 tonnes for hook operation and a SWL of 37 tonnes for grab operation. The hatch cover system is based on special customer requirements and comprises a combination of hatch covers maximising the ship’s cargo space.

Cargotec has signed a further contract to deliver six shipsets of environmentally-friendly variable frequency drive (VDF) MacGregor cargo cranes to Grieg Shipping’s new 48,700 dwt open-hatch general cargo ship series. The ships will be built at Hyundai Mipo Dockyard in South Korea for the Norwegian shipping group. In total, the order comprises 24 VFD electrically-driven cranes: each vessel will have four 75-tonne SWL units installed. The cranes are planned for delivery from 2012 until 2013.

“We work closely together with our customers which enables us to introduce innovations that improve the safety, efficiency and sustainability of their operations”, says Per-Erik Nilsson, Cargotec sales and marketing director. “The MacGregor electric crane series inherits the best characteristics of proven designs, but also combines improved operability with a low environmental impact.”

GLE electric variable frequency drive (VFD) cranes are self-contained units with all machinery enclosed in the crane housing. This protects them from weather, corrosion and damage.

The standard GLE range covers lifting capacities from 25 to 100 tonnes, with outreaches of up to 41m. The crane can also be delivered in a stepless load/outreach combination, which makes maximum use of the crane due to its mechanical design. “This crane is by us seen as the next generation of cargo deck cranes,” says Per-Erik Nilsson. He told The Motorship: “It is environmentally superior compared to conventional electro hydraulic deck cranes. It is faster and better in positioning of the load. It is cheaper in maintenance costs. We have up to today signed contracts for 177 pieces of this model which is an overwhelming success in just one year on the market.”

Ro-ro takeup

This type of equipment has not been limited only to bulk carriers. The increase in uptake of electric drives on board ro-ro ships has been due to numerous factors, including environmental issues, but another technical reason for this development is the availability of improved electric drives, in the form of screwjack drives, to replace the hydraulic cylinders used for operating smaller items or in cleating and locking devices. As well as ‘green’ demands, car manufacturers are putting pressure on ship operators to reduce the level of damage to cargo; Japanese companies, like Toyota, are leading this improvement. “They are also easy to monitor, and installation is easier and more cost efficient,” says Magnus Sjöberg, sales director for ro-ro ships at Cargotec. “The PD Gram vessels were the first car carriers with complete electric-drive operation of the MacGregor ro-ro cargo access internal equipment. They were a breakthrough, and the result of Cargotec’s intensive R&D work, responding to customers wanting to move away from the use of hydraulic oil completely.” The PD Gram & Co vessels were built at Kyokuyo Shipyard in Japan in 2009.

Electric pumps

Electrically-driven systems are also having an impact on the offshore market, and fluids handling specialist Hamworthy is benefiting when it comes to the electrically-driven cargo pumps it supplies to the specialised floating production storage and offloading vessel (FPSO) sector.

The breakthrough in supplying electrically-driven FPSO deepwell pumps to feature electric drives came in 2004 when Hamworthy was chosen to supply the cargo handling system for the 900,000-barrel storage capacity FPSO Nganhurra, built by Samsung for the Australian oil company Woodside, which is now operating at the Enfield oilfield in Australia.

Among its growing FPSO reference list have been a number of Chinese-built vessels, including the circular type FPSO and Drilling unit from Sevan Marine and several conversions from COSCO. Hamworthy also supplied pumps for BW Offshore FPSO operation in the Gulf of Mexico as well as a shipset of 12 deepwell pumps for the 750,000 barrel Modec vessel Stybarrow Venture MV16, built at Samsung.

Efficiency studied

Hamworthy’s progress in the offshore sector has been built on a study by well-known technology consultancy Deltamarin, which compared the relative cost and performance benefits of electric versus hydraulic cargo pump arrangements on board an FPSO with a nominal offloading rate of 1 million barrels/day.

Deltamarin’s study concluded that, installed on tankers, electric pump systems used energy more efficiently than their hydraulic counterparts, with fuel savings of around 23%.

The study also concluded that control problems once associated with electrical systems were a thing of the past. “One additional benefit of having frequency converters to control the motor is that they can be programmed to be soft starters,” Deltamarin said. “This means that electric motor and pump can be started from zero speed and gradually increased. This reduces wear and tear of all system component as well as reducing generators ratings onboard diesel-mechanical ships.”

According to Lars Fischer, Hamworthy Svanehøj Offshore sales director, when comparing electric and hydraulic solutions: “Onboard maintenance is also lower when it comes to the electric system because of the shaft lubrication system used, the fact that the pump house is easily dismantled and cards on converters are easily interchanged.”

It was also the case that there are no limits onboard a diesel-electric ship to the number of pumps being operated concurrently, whereas the size of power packs limits the number of hydraulic pumps that can be operated at the same time.

Fischer added that concern for the marine environment was also driving the market towards electric drives. “In the operational phase, electric equipment is more environmentally friendly, because C02 emissions are minimal due to higher efficiency and lower power utilisation and there is no hydraulic oil spillage risk. There are also fewer parts to wear out and the components that do suffer wear and tear are cheaper to replace.”

In January, the company announced that its electrically-driven deepwell cargo pump technology had been accepted in a significant new shipbuilding market, following a breakthrough contract in Brazil.

Its cargo pump systems have been specified for eight FPSOs by Brazilian shipyard Engevix Construcões Oceânicas. The equipment will be delivered between 2012 and 2014.

Fischer said, “Ship owners have recognised the benefits of electrically-driven deepwell systems for many years but now FPSO operators are becoming increasingly convinced.”

Earmarked as a strong area for growth by the company, the latest order sees Hamworthy quickly following up on a string of contracts for FPSO delivery into Brazilian waters from overseas shipyards.

Earlier this year, Gusto BV specified seawater lift pumps and electric fire pumps from Hamworthy for installation on board the Cidade de Paraty FPSO, initially converted from a VLCC at the Keppel yard, Singapore, and due for delivery in 2013 after completion in Brazil. The run of contracts also saw Hamworthy selected to supply cargo pump room systems equipment for the Papa Terra FPSO, for BW Offshore, converted at COSCO Dalian.

The latest eight FPSOs, each having the storage capacity of 1,600,000 barrels of oil, are in principle assigned to various field developments in the pre-salt area of Santos Basin. Hamworthy said that, for each FPSO, it would deliver 12 cargo pumps, two slop pumps, two ballast pumps and two emergency pumps, including switchboards and electric motors.  

Fischer said, “We have built up a reasonable reference list. Now, an increasing number of operators are coming to see the benefits of electrically-driven pumps.”

Continuous development

Electrically-driven pumps are also showing themselves to be amenable to further development to meet the requirements of the offshore operators of today and tomorrow. Hamworthy Svanehøj recently launched the first of what will become an entirely new range of combined sea water lift and fire pumps that meet the requirements of the offshore market.

The new deepwell seawater lifting pumps and fire pumps, known as DWS, will eventually be available ranging in capacity from 700 m3/hr to 1700 m3/hr and with a differential pressure up to 180 mlc. In the first instance, Hamworthy has developed two new DWS pumps with a capacity of 950 and 1425 m3/hr.

“Combined with our existing pump technology we can now deliver sea water lift pumps up to a capacity of 2600 m3/h and meeting API610 requirements,” said Fischer.

These pumps are driven by a dry mounted electric motor in explosion-proof execution, through a pipe stack with transmission shaft and cargo lubricated bearings. These pumps are in addition to in-line Hamworthy pumps already available for seawater lift and firewater applications.

Fischer said that the pump head had been designed for optimum efficiency using the company´s design experience, computational fluid dynamics and full scale tests. Impellers have been trimmed to provide 15% higher head per flow unit, while the semi-radial design provide a more stable performance curve at higher capacities.

After finite element analysis, moulded intermediate chambers had been selected to maximise stiffness, with the result that weight across the new range had been reduced by 30% compared to similarly constructed units featuring welded chambers.

Considerable attention has also been given to bearing performance. The use of conical thrust bearings in the upper drive shaft arrangement minimises vibrations. Furthermore the thrust bearing arrangement has been designed with oil circulation for American Petroleum Institute (API) compliance and increased lifespan. The distance between the transmission shaft bearings is in accordance with API610 in order to assure stable operation under all service conditions.

The pump can be delivered with either a labyrinth seal or mechanical seal. The mechanical seal is of the cartridge type, and as an option it can be delivered in compliance with API682.

For sea water lift pumps and fire pumps installed in caissons, Hamworthy Svanehøj can supply its patented inflatable intermediate support system. The support system is developed in order to secure proper installation and support of the pump in the caisson.

Fischer said that the new DWS pumps will be available in a wide range of materials, such as AISI 316L, Duplex and Super Duplex. Optionally the pumps can be delivered with strainer, galvanic protection and anti fouling system.

The company is in the process of rolling out a new range of offshore process and cargo pumps (OPCs), which are also API 610 compliant. Featuring an explosion-proof electric motor on deck, oil-lubricated transmission shaft/bearings with oil circulation and filtration, a double mechanical seal with liquid-filled cofferdam, the new range has been specifically designed to be suitable for liquids containing solids, abrasive liquids or aggressive chemicals.

Other significant design features picked out by Fischer included the fact that Hamworthy’s new range of OPCs are capable of at least a 5% head increase at rated conditions by replacement of the impeller with one of larger diameter. Furthermore, “The wear ring clearance is according to API 610 and designed in such a way that there is no contact between impeller and stator,” said Fischer. “Wear rings are available in different materials in order to prevent galling, secure a hardness difference of minimum 50 Brinell and low abrasive wear. The thrust bearing is also designed according to API610, oil-lubricated, with a minimum life expectancy of 25,000 hours.”

He added, “With our strong focus on the offshore industry, we are fulfilling the overall objective to develop a series of sea water lift and fire pumps and OPCs that meet the requirements of API610 and NFPA-20, secure long mean time between repair, and reliable and efficient operation.”

Boxout

One technical reason is the availability of improved electric drives in form of electric actuators, to replace the direct-acting hydraulic cylinders used for operating smaller items or in cleating and locking devices.

Electric versus hydraulic drive

  • Electric motors and gears replace the hydraulic motors
  • Electric actuators replace the cleat cylinders
  • Electric winches or actuators replace the operating cylinders, for car decks and ramps for example
  • Electric actuators replace the operating cylinders, for ramp way doors and ramp covers
  • Electric winches with power feedback system replace the hydraulic winches for the side and stern ramp

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