Coal production in Wilhelmshaven, Germany
Patented cleaning system: higher scraping performance reduces the dust emissions in the port
Every day in a slaking process, around 24,000 tonnes of coal is transported along a 3.6 kilometre long conveyors to the power plant in the North Sea city of Wilhelmshaven. Rhenus Midgard GmbH & Co. KG will be supplying coal to further power plants which is why this volume is currently being increased to 8 million tonnes a year. As a result, a decision needed to be made about the use of new belt scrapers because the various scraper systems used in the past did not achieve the desired cleaning results causing subsequent follow-on costs for extra cleaning, maintenance and repairs. Due to the fact that poor cleaning also means higher dust emissions, it would not have been possible to meet the new PM-10 standards. These guidelines define limit values for inhaled dust. For this reason, a decision was made in favour of a new scraper system from the company Schulte Strathaus GmbH & Co. KG which achieved the best scraping performance in a complex test procedure.
The project in Wilhelmshaven faced some challenges: due to the diffuse emissions caused by adhesion to the conveyor belts, the scraping equipment is now given a higher priority by the approval authorities than was the case in the approval procedure for the old system because as of 2002 the PM-10 emissions also need to be observed in addition to the previous regulations. Furthermore, the selection of the new scrapers also needs to take extreme requirements into account for example discharging frozen coal from Siberia. When material freezes to the belt the conveyors shall not be interrupted. In this case, the scraper must be able to remove the adhered material without causing any damage. This is why Kurt Kühn, plant engineer at Rhenus, spent more than a year carrying out complex tests on the various scraper systems in the old plant. The tests analysed the wear behaviour during an output of more than 1.6 million tonnes of coal.
The outcome: the best results were achieved by the Starclean system from Schulte Strathaus. Compared to the previously used scraping system, the residues that adhered to the belt were significantly reduced. This scraper was not only selected for this plant but also for the new plant, in particular due to the simplicity of the technical system, and the easy configuration, maintenance and servicing.
Optimised cleaning due to the overlapping scraper segment and patented twist-swing feature
The segmented scraper developed by Schulte Strathaus was used both as the primary and also secondary scraper. The secondary scraper segments comprise polyurethane feet with special rotatable mounted scrapers made of stainless steel with a carbide insert which are fitted into the segment shaft. The individual segments are overlapping so that none of the transported material can slip through. This ensures that the belt is cleaned to the optimum.
The special shape and geometry of the polyurethane feet allow a high level of flexibility. This is a prerequisite for the patented twist-swing function. "In contrast to complex parts with mechanical pivot joints, the individual segments adapt excellently to the conveyor belt under the freely configurable contact pressure", explains Andre Hanke, sales manager for conveyor equipment at Schulte Strathaus. The individual segments swing with the movements of the belt. This not only achieves excellent cleaning results, it also reduces the wear on the segments and the belt. “Strip scrapers or inflexible segment scrapers are that are usually used cannot cope with the unevenness of the belt and therefore always allow a certain amount of the transported material to fall through", Hanke continues.
Fast change of direction and higher flexibility
The reversible belts in the new systems of the Wilhelmshaven project have additional reverse belt scrapers that automatically disengage when the direction of the belt changes. Auxiliary blades designed for the opposite direction take over their function. This allows fast changes of direction without breaking the contact between the conveyor belt and the scraper. The system engages and disengages automatically as a result of the friction between the belt and the scraper segments, that means without any pneumatic, hydraulic or electrical support.
The secondary scrapers can be positioned anywhere, from directly below the drum right up to any point along the entire conveyor belt. Further benefits that ensure uninterrupted operation are the simple maintenance and the fact that the segments can be exchanged without tools. All the segments in these scrapers are fitted to the belt by setting the spindles to predetermined dimensions.
Simple maintenance ensures low follow-on costs
"If necessary, we can change the wear parts of the scraper ourselves. This not only saves time, it also means that this task can be scheduled at short notice to intervals when the systems is temporarily at a standstill before a ship arrives," says Rhenus project manager Udo Düser.
"We can also significantly save on maintenance costs thanks to the modular structure of the individual parts."
At the same time, the service life of the segments is very long as a result of design which specifically reduces material wear: According to Düser, the modules have not needed to be changed even after two years in operation.
Environmental protection due to less dust emission and conservation of resources
Thanks to the segment design and the twist-swing principle, ultrafine cleaning can be achieved during the transportation process. This reduces the dust emission, which is extremely important for protecting the water, especially in the port where the sea is often just a few meters away. Furthermore, the continuously high scraping performance conserves valuable resources.
"Naturally, the coal scraped from the belt remains in the transportation process", says Hanke.