Nimble giant

The planning and construction of the sludge processing plant took approximately 30 months and concluded at the end of 2010. Once finished it became operational for a period of no less than 15 years. "And these 15 years are set in stone", claims Joury van Gijseghem. As project manager, he is responsible for the planning and operation of the exterior plant. "All key components were designed for this minimum operational period. But the requirements profile goes a step further. The dewatering plant is in continual use nearly 365 days per year. Operational reliability is paramount. Unnecessary maintenance and downtime must be avoided.
 
A central component of the sludge processing plant is an imposing arched bridge with a span of nearly 180 m in the exterior grounds. Two mobile, independently operated high-performance pumps are mounted on the rotating bridge. These pumps travel a distance of nearly 140 m at a maximum speed of 15 m/min by means of an energy chain. The excavator pumps vacuum roughly 600 m³ of sediment or sludge every hour from the sediment basin below and convey the sludge through enormous hoses, with a diameter of 300 mm, for further processing. The basins are partitioned into four sections. Each has a capacity of roughly 120,000 m³. An extremely robust polymer chain from igus® GmbH, Cologne, is used to reliably guide the hoses across the entire distance. The maintenance-free E4.350 model can be opened from both sides and is from the E4.1 series, which has proven itself in countless applications. It has demonstrated its versatility in composting and water treatment plants, machine tools and construction equipment, crane technology and wood processing, among others.

The world's largest plastic energy chain to this point, the E4.350, with an inner height of 350 mm and inner widths of up to 1,000 mm, can be deployed on oil platforms as well as in steelworks and heavy machinery construction. Wear, corrosion, oil and sea water resistance are among its technical features. A number of tests were conducted at the in-house igus® laboratory under real-life conditions in the run-up to the decision in favor of using this chain model. These tests ultimately confirmed the suitability of the – at the time – newly designed energy supply system in this demanding environment. "In particular, we examined the behavior of the filled hoses under real-life conditions", explains Frank Schlögel, who manages the Projects/Energy Chain Engineering area at igus®. "The temperature and pressure changes cause the hose to expand in the chain by as much as 60 cm." “
 
The tests show that the energy chain has no difficulty guiding even voluminous and heavy loads. The weight of the hose filled with silt and sediment is around 100 kg/m. A special design using glide rollers was developed to perfectly guide the hose within the energy chain and to minimize the resulting mechanical abrasion. These rollers, made from the tribologically optimized bearing material iglidur® J, are integrated into the opening crossbars. Light, corrosion-free and insensitive to dirt, they ensure that the energy supply system can glide without problem around-the-clock. This significantly reduces the friction caused by the hose in the chain, thereby ensuring stability. "For this and comparable cases, where we wish to supply our customers with ideally adapted solutions, our expertise in developing special plastic materials continues to pay dividends, in that we have the required know-how under our own roof. The variety of special plastic materials from the energy chain and bearing field, in combination with our in-house test laboratory, gives us the ability to conduct on-the-spot tests under realistic conditions, resulting in the best solution for the customer", states a confident Frank Schlögel.
 
"We were also convinced by the fact that the entire energy chain system is very compact", reminisces Joury van Gijseghem. "This was genuinely important to us, for instance, because we had to deploy drive cables in addition to the hoses, and could not provide an unlimited amount of space. " Moreover, in comparison to a steel chain, the plastic chain is much lighter. This not only provides savings on the required drive rating on the traveling pump systems, but also in the weight of the overall rotating bridge system. %. "For example, we can use smaller motors. On the one hand, these are less expensive, and on the other, the weight load on the bridge is further reduced. This in turn improves economic feasibility."
 
A specially-designed guide trough made of hot-dipped galvanized steel and floating moving ends are deployed in addition to the energy supply. These are needed to compensate for potential lateral displacement tolerances. The energy chain, which is filled with hoses and cables, is now always reliably guided over the entire length under any weather conditions. Despite operational difficulties and environmental conditions, no failures have been recorded to the present day.

It was decided to integrate the PPDS (Push Pull Force Detection System) monitoring system in order to increase the operational reliability of the bridge design. The diagnostic tool, which in particular has proven to work over long distances, continuously measures the push/pull forces on the energy chain and compares these with a calculated target value. Should malfunctions occur, the plant is automatically stopped as a preventive measure to avoid damage.
 
"At any time, we can also consult the data stored on our data server retroactively ", the project manager confirms. "We are therefore always on the safe side, and, if needed, have enough advance notice to schedule maintenance and service work." “

The decision in favor of the relatively light-weight, plastic energy supply system was made quickly. From the very first day, both companies confidently cooperated on the engineering process. For one, this relates to the complex design process of the bridge structure. A host of design drawings for the respective project status were readily made available. The extensive laboratory tests, conducted in advance, also provided compelling evidence. According to Joury van Gijseghem, "the sustained support during this large-scale project ultimately led to success". "Our combined efforts from the first to the last day made this project possible." “
 
The plant construction company also relied on the available assembly expertise. The energy supply system specialist configured and installed the entire system on site and on time, while utilizing its own employees and assistance from the construction site. The system has been operating without a problem from day one. "At no time have we regretted the decision to use the plastic energy supply system", Joury van Gijseghem emphatically concludes. "We also benefitted greatly from bringing the system supplier into the project from the very beginning. From the very start all the way through system acceptance, our excellent collaboration contributed greatly to the smooth execution of the project". “