Driven by efficiency

30 Jan 2008

Sinamics drives family with regenerative feedback

Ports can make significant fuel savings by selecting the right drive for their container handling operations, writes Patrik Wheater

It is predicted that by 2015 Europe's electrical energy requirement will be a whopping 1,320 terawatt hours (TWh)/year, with about 707TWh delivered through electric motors of one sort another. However, to counter the associated increase in CO2 emissions, industry is vehemently looking at installing advanced drive technologies and switching to more efficient electric motors in a bid to reduce energy consumption. Finland's Vacon, a specialist in AC drives and controls, believes that by using high efficiency motors instead of standard ones and by using drives the energy saving potential in Europe alone could be some 90TWh a year, with a corresponding reduction of about 36m tonnes of CO2 emissions.

Vacon points to the voluntary agreement between the European Union and the European Committee of Manufacturers of Electrical Machines and Power Electronics (CEMEP) as the driving force behind the development of high-efficiency systems. The accord has also paved the way for a reduction in the sale of EEF3-type motors, which has declined from 68% to 9% in the period from 1998 to 2004.

In its in-house magazine Driven, Vacon writes: "The energy saving potential from using drives is significantly higher than what can be achieved by using high efficiency motors. This is basically because when an AC drive is used only the energy that the process needs is taken from the mains, no extra energy input is needed to drive the process against some sort of control mechanism."

Finland's ABB, whose family of ACS800 regenerative drives are being marketed for use in container handling equipment, suggests a number of ways operators can reduce their cranes' environmental footprint: providing additional protection inside the drives by coating the electronic boards; by installing air or water cooling systems, although cooling fans can increase noise pollution; ensuring the cabinet is mounted via dampers to reduce vibration stress; considering dedicated crane control programs for AC drives; considering interfacing and use the same user interface for all input/output boards, drives and control panels; and to ascertain the global service level of the drives company and the availability of spare parts before investing.

Liebherr, however, favours a diesel-hydraulic drive configuration over diesel-electrical systems. Its hydrostatic (diesel-hydraulic) crane drive consists of a splitter gear - which can actually be driven by a diesel motor or alternatively by electric motors - feeds variable displacement axial piston pumps for the hoisting, slewing and luffing operations.

Liebherr says that a closed hydraulic circuit provides for a "highly responsive, smooth and sensitive operation by fast and controlled acceleration and deceleration, maximising the operating safety even in continuous operation or high ambient temperatures (-40°C to +45°C)".

A further advantage compared with diesel-electric drive systems, claims Liebherr, is the repeated use of the reverse power generated by lowering movements or braking. This "returning" energy can be re-used for other crane movements as well as to cover certain basic loads as cooling, main- and auxiliary supply, heating, lighting and air conditioning. Energy is wasted within the resistant banks of diesel-electric drive systems, which also require more energy (fuel). The close loop system of its 300 kW+ hydrostatic drives require up to 75% less hydraulic oil as open loop systems.

This is largely due to the inclusion of a unique fuel saving device designated ECO-Control, which economises diesel consumption without any impact on turnover output. The control system automatically calculates the minimal revolutions per minute required and can save operators up to 20% in fuel in grab operations and up to 25% in container operations.

The company's mobile harbour cranes have also been adapted to run on alternative fuels and biodegradable hydraulic oil and in collaboration with Avia, Liebherr has developed a bio-degradable oil especially for its own product line. In combination with spectrographic oils analysis techniques, oil life time is extended, which in turn helps to reduce the wear and tear of individual components, such as pumps and motors.

Aside from the extended lifetime that operators can expect, there is also a noticeable reduction in noise pollution. As the unit's hydraulic oil cooler is equipped with a cooling fan, turbulence is minimised, resulting in a decrease in noise emissions, while elastic suspension of the winches is said to reduce vibrations and noise even further.

While reduced noise and vibration can be a benefit afforded by the use of Siemens' ECO-rubber tyred gantry (RTG) drive system, energy savings have been the primary driving force behind the development. And such is the perceived potential of the advances made by Siemens in drive technology that APM Terminals in Algeciras, Spain, offered to refurbish one of its RTGs with the system, to allow the company to benchmark the unit in container operations.

Thirty sequences were simulated in an operating time of one hour and 45 minutes. The crane moved as in normal operation, handling different sizes of containers but whereas a conventional RTG crane consumed 16.1 litres of fuel as hour, the prototype ECO-RTG crane's fuel consumption was reduced by 50%.

The tests were a success on which APM based its decision to order 20 RTG cranes fitted with the ECO-RTG drive system from the Zhenua Port Machinery Company (ZPMC) in Shanghai, China. 

The first ten cranes came into operation at the end of 2006, but APM realised by early 2007 that a quick return on the investment was attainable as average fuel consumption was 9.2 litres per hour. The reduced fuel consumption also meant that, together, the CO2 output of all 20 cranes would be about 4,100t of CO2 less per year.

Other benefits gleaned by APM were lower maintenance requirements and fewer refuelling stops. However, following recent noise measurement tests at one of Siemens' project locations, reduced noise and vibration levels are also deemed significant.

Speaking to Port Strategy, Siemens Cranes business development manager Rob Kuilboer says that although the data has to be evaluated, "RTG's equipped with our ECO-RTG drive package are much less noisy than conventional drive systems".

Siemens says: "The ECO-RTG hybrid drive system has been specially designed for fast growing, flexible and innovative container terminal operators, which are confronted with rising fuel prices. The amortisation period for the additional costs of an ECO-RTG crane compared with a conventional RTG crane is less than four years."

Since the advancements made to its ECO-RTG range, Siemens has recently introduced a new product to its range of low voltage drives systems. Designated the Sinamic range, it is the S120 that is being marketed for crane use.

The cabinet module system harmonises several individual modules with standardised interfaces for the power and communication connections. This means that individual cabinet modules can be combined as required to optimise configuration dependent on the application. Its compact design together with the possibility of pre-configuring the drive system in the plant is claimed to save considerable space and minimise the time and costs associated with installation and commissioning on-site.

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