05.03.2018

Skeleton Technologies GmbH

Making a Deal With Gravity - Muuga Crane Case Study

In the container port of Muuga, in Estonia, there is an interesting experiment taking place.

The role of a crane is simple, it needs to move a container, a piece of cargo, or anything that can be hooked to it from point A to point B.  The main movement is up and down, and also the crane can move on the ground thanks to its rubber tire wheels.

During the up and down movement, a diesel crane needs to be powered at all times, energy is consumed during lift and also during the laying down of freight.

How can this energy be harvested to be used again?

Ultracapacitors allow energy storage, at a very quick rate.  So, if a crane is fitted with ultracapacitors it should be able to capture the energy whilst braking the drop down of a container and reuse it for the next lift phase.

The initial tests at Muuga showed that energy was saved thanks to the ultracapacitor module.  The test highlighted the need for liquid cooling as during the 10 minutes of testing,  the temperature inside the module had raised by about 5°C.

During the braking phase, the voltage increases inside the ultracapacitors, the energy gets stored, and when the voltage decreases as the module releases energy during the next lift phase.  This system works very similarly to a KERS system on a car or a truck.  The idea is to capture the braking energy in order to redistribute it later for acceleration phases, it the case of a crane, this is for lifting.

A complete system including ultracapacitor modules with their cell balancing ability together with the DC-DC converter and the control panels has been fitted to the crane to capture and monitor the on-board parameters.

The DC-DC converter is used to reduce the voltage during charging and discharging. The rated voltage of the crane's system is 620 VDC, and the rated voltage of both capacitor modules is 320 VDC (160VDC each), hence the requirement for the DC-DC converter.  The ultracapacitor modules can now store the energy released by the brakes of the engines instead of it being dissipated by the crane's resistors. 

The control unit controls the energy transfer between the capacitor modules and the direct current line. In the event of an error or a fault, the control unit switches off the system to prevent any damage to the equipment.

Results :

The purpose of crane hybridization is to reduce fuel consumption and thereby save money.

Measurements of the fuel consumption were done before and after the addition of supercapacitors. 

Prior to adding the capacitors, a total of 274.4 crane use hours were logged, and 4498 liters of fuel were consumed. The average fuel consumption was 16.67 l/h.

After the addition of capacitors, 200 hours have been recorded and 2205 liters of fuel have been consumed. The average fuel consumption during this period is 11.0 l/h.

Fuel consumption decreased by 34%. 

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