Gottwald presents first hybrid drive for mobile harbour cranes

With its new hybrid drive, Gottwald Port Technology GmbH, a subsidiary of Demag Cranes AG, demonstrates that improved energy efficiency contributes to both the economical and environmentally compatible operation of Mobile Harbour Cranes. This technology uses state-of-the-art diesel generators in connection with dynamic brake resistors and short-term energy storage to achieve fuel savings in the double-digit percentage range.

This is shown by the results of comprehensive tests carried out with a diesel-electric Model 6 crane, completed by Gottwald, the only manufacturer of Mobile Harbour Cranes with electric drive technology. The result is that Gottwald is able to improve the efficiency of Mobile Harbour Cranes which cannot be hooked up to an external power supply due to the quay infrastructure, which empowers terminal operators to sustainably reduce fuel consumption, fuel costs and exhaust gas emissions. By the same token, Gottwald makes it possible for terminal operators to position themselves in a strong position when it comes to negotiating terminal concessions.

Diesel-electric mobile harbour cranes

It has been possible for some time now, if a machine uses electric drive technology, to return the energy recovered from the machine's deceleration motions to the crane's internal power system. If, however, no consumers in the system currently require that energy, this excess energy is dissipated in brake resistors, i.e. converted to heat. Where, in the past, these resistors could only be switched in in relatively large steps, today it is possible to make use of dynamic brake resistors to improve the machine's energy rating considerably.

In response to demands for further improvements in efficiency, Gottwald has developed a hybrid drive which includes short-term energy storage for the recovered energy which is then made available to the crane's power system for the next work cycle. The conventional brake resistors only come into play if the capacity of the energy storage system is exceeded.

Choice of a suitable short-term storage system

Mobile Harbour Cranes work with rapid load changes combined with discontinuous hoisting, lowering and slewing actions including the associated acceleration and deceleration actions. This is why storage systems that can store and return energy quickly and allow high cycle rates in rough day-to-day crane operation are necessary. In this context, Gottwald has performed tests on mechanical, electrochemical and electrostatic short-term storage systems. The key requirements are met by electrostatic wear and friction free double-layer capacitors (ultracaps) with typical charge and discharge times of max. 30 s in this kind of operation and with a service life of 1 million cycles. An outstanding advantage of this system is that the energy is stored as electricity and is not converted at all, which provides a high degree of efficiency.

Pilot project confirms sustainability approach
The G HMK 6407 Mobile Harbour Crane, a variant of Model 6, is used in a maritime terminal for handling empty and full containers and fruit pallets for approx. 4,000 hours per year. This handling machine has a maximum lifting capacity of 100 t, hoisting speeds of up to 90 m/min and an installed diesel engine power of 895 kW. During the test phase, which immediately followed the upgrade of the crane to dynamic brake resistors and the installation of the new ultracaps, it was demonstrated that fuel savings in the double-digit percentage range can be achieved. At the same time, the quieter running characteristics of the diesel engine resulted in reduced noise emissions.

Taking More Advantage of Potential Green Technologies

As well as fitting new cranes with the technology, Gottwald will be offering existing owners of their Mobile Harbour Cranes upgrades to environmentally friendly, cost cutting dynamic brake resistors and hybrid drives. The new drive technology is of particular interest to operators of Mobile Harbour Cranes with comparable workloads and cargo handling profiles as the prototype and for harbour crane applications such as intensive container handling and professional bulk handling, where they are configured as 4-rope grab machines, equipped with two hoists and frequently work 6,000 hours a year. In addition, Gottwald intends in the medium term to take advantage of the latest drive technology to downsize its on-board diesel engines to achieve even higher economical and ecological savings.

Green drive technology by Gottwald
Under its "Gottwald Green Range" label, the company is developing green technologies with a view to making the sustainable management of maritime and intermodal terminals a reality. In mid-2009, Gottwald launched the first battery-driven Automated Guided Vehicle (AGV) and has now completed successful testing. With its new hybrid drives, Gottwald has taken a further step towards improving the electric drive system used on Mobile Harbour Cranes – electricity being the most energy-efficient source and, as a result, the one most commonly found in terminals.

(Source: Transport Weekly)