2021 sees the end of one of the most spectacular projects for the ecological transformation of a completely destroyed river system. The Emschergenossenschaft is transforming the course of the Emscher River from an open sewer into a living body of water. Some speak of a “blue miracle”, a miracle having something divine and inexplicable. However, there are no supernatural forces behind the unique Emscher conversion project, but rather worldly engineering skills and the firm will to reunite man and nature

The superlatives in connection with the revitalization of the Emscher are overflowing: 80 kilometers of redesign from the source to the estuary, 30 years of operation, 100 years of minimum service life, 73 kilometers of new underground Emscher sewer, up to 40 meters deep, wastewater from 2.2 million people, four large sewage treatment plants, three large pumping stations, around 5 billion euros of investment – it is one of the largest infrastructure projects in Europe. There has never been a comparable project in the world on this scale to ecologically transform an entire river system that was previously biologically dead. At the beginning, in the early 1990s, only a few local residents could have imagined that such a thing was even possible.

Green technology for blue wonder

The visionaries of the Emschergenossenschaft knew what they owed their river, the people and nature and made a promise: “You’ll get your river back!” It was the beginning of a generational project, which is now being completed after 30 years and which has a tremendous lighthouse function. Other major projects may be more prestigious and attract greater media attention, but here there is more at stake. It’s about proving that interdisciplinary engineering can reclaim habitat that was thought lost. Known internationally as “green engineering,” the buzzword stands for sustainable innovations that serve to protect the environment and nature as the basis for human life. It is also impressive that companies from Germany in particular have been able to set a milestone here. A future metier on which the well-being of many millions of people depends and a model project that would not be feasible without pumps with protective couplings.

Problem case Emscher

But who is the Emschergenossenschaft and how did the catastrophic pollution of the river come about? Around 1850, before industrialization, the Emscher meandered 109 km across the core zone of the Ruhr region from Holzwickede near Dortmund to Dinslaken, where it flows into the Rhine. The area was sparsely populated and characterized by floodplains, weirs and agriculture. With the beginning of coal mining came more and more coal and steel industry and numerous people settled in the Ruhr area. Because of mining, the ground was continually subsiding, which is why wastewater from industry and households could not be discharged underground. They collected in the depressions, which led to hygienically critical flooding of houses during floods.

That is why the Emschergenossenschaft was founded in 1899. As the first public-law water management association of cities, industry and mining, it eliminated the drainage emergency by means of the Emscher as an open sewer. For this purpose, the Emscher river was lowered from Dortmund to the Rhine, diked, straightened and shortened to 80 km. At the same time, a number of wastewater treatment plants were built, whose wastewater was fed via the open sewer system.

Start signal 1992

With the increasing end of coal mining, the subsidence of the mines has greatly diminished, and the Ruhr region has now been transformed from a heavily polluted region into a green urban living space. This change in the region is also reflected in the Emschergenossenschaft’s mission today. The aim is now to convert the Emscher system to a near-natural state and to make water management as sustainable as possible. The starting signal for this was given in 1992.

Emscher underground sewer

In order to free the Emscher River from wastewater, a gigantic underground main artery was built, the Emscher Wastewater Canal (AKE). It runs for 51 kilometers from Dortmund to Dinslaken and passes under highways, roads, the Rhine-Herne Canal and its locks as well as railroad tracks and industrial areas at a depth of up to 40 meters. The canal requires a gradient of 1.5 per mille and starts in Dortmund at the first shaft at a depth of 8 meters. The pipe diameter of the LFS is gradually increasing from 1.6 to 2.8 meters. It consists of reinforced concrete pipes that were precompressed and laid using pipe jacking machines. In its western section from Bottrop to Oberhausen, it was laid with interlocking concrete elements, so-called tubbings, and driven with state-of-the-art tunneling machines. If the gradient were simply continued at 1.50 meters per kilometer, the canal would arrive at its destination in Dinslaken in 80 meters, which would cause considerable construction problems and costs. Therefore, three large pumping stations in Gelsenkirchen, Bottrop and Oberhausen are interposed to lift the wastewater again selectively and feed it to the treatment plants. The main canal can thus maintain the gradient and is still deep enough to allow the approximately 400 km long tributary side canal system to flow in at a free gradient.

Heart of the pumping station: This is where the Emscher comes to life

The pumps are located in underground pumping station rooms and have a maximum flow rate of up to 16,500 l/second. At the largest wastewater pumping station in Oberhausen, 10 pumps can each pump wastewater upwards over 40 m at a rate of up to 2,060 l/second. The Oberhausen pumping station is the last of the three pumping stations before the Emscher sewer flows into the Emscher-Mündung (KLEM) wastewater treatment plant in Dinslaken after another 3.2 km of elevated sewer. About 7 km west of KLEM, the Emscher flows into the Rhine. At the time of construction, it was considered “currently the deepest construction site in the Ruhr region”. With a depth of 44 m and a diameter of 50 m, it is the largest of the three pumping stations and acts as the heart of the “wastewater main artery” AKE.

The pumps have heart valves that provide life support – the clutches. Although they do not disconnect currents, they do disconnect the drive in the event of sudden overloads. This guard function is essential if turbines and drive shafts are to remain undamaged in the long term. In particular, such wastewater volumes may contain large foreign bodies such as pieces of wood. If they get into the impellers of the pumps, enormous forces have to be separated in milliseconds before total damage occurs. But even supposedly small items such as toilet paper, wet paper or hygiene articles can lead to a “pigtail formation” feared by wastewater specialists and can paralyze pumps.

Mechanics before electronics

Christopher Monka is the Senior Account Manager of R+W Antriebselemente GmbH from Wörth am Main. R+W torque limiters are a byword for quality in the industry. Each coupling is individually matched to the respective drive situation and is finely adjustable. He is in charge of the Oberhausen pumping station and Emscher sewer coupling project and emphasizes the need for mechanical protection: “The pumps may only be loaded up to a certain torque. If there is a sudden blockage, the coupling protects the pump, the motor and the entire input and output from a torque overload. This is done mechanically by disk springs that exert an axial force on balls. The ball sits on the output side in a corresponding mating seat. As soon as the tangential force acting on the ball becomes too great and the disk spring can no longer hold it in the ball seat, it slips into the safety segment. The clutch releases the connection and the flow of force is decoupled. This happens in the range of 10 to 15 milliseconds. Due to the inertia of the mass and the enormous kinetic energy, purely electronic monitoring of the motor current, with automatic switch-off in the event of an overload in an emergency, is unsuitable because it does not achieve this instantaneous separation of the drive forces. It takes 40 to 60 milliseconds just to detect the overload. Only then is the motor switched off, but without separating the forces from the drive train. Apart from this, electrical current and precise programming are required for the control system, which in turn entails risks that do not affect the mechanical torque limiters from R+W.”

Advantage adjustability

According to Christopher Monka, the precise adjustability of R+W clutches has clear advantages: “Other clutch manufacturers use shear bolts to trigger the immediate disconnection, which are destroyed when a defined force is applied. In contrast, the spring-loaded ball detent principle favored by R+W has the advantage that the disengagement torque of the coupling is very precisely defined over an adjustment range and the connection can be established immediately after release without spare parts. The torque limiters used for the Oberhausen pumping station are of the disengaging type, i.e. they are re-engaged manually within minutes. All you need is a rubber mallet. Thanks to their special design, the couplings are virtually maintenance-free and wear-free, yet can be flexibly adjusted. Particularly at the start of commissioning, it may be necessary to adapt the optimum setting value to practical conditions. However, this initial sensitivity and flexibility pays off for the operator in the long term. If too high values are simply defined at the beginning in order to avoid dropouts, this is at the expense of the service life of the pump, motor and drive train. If failures occur later, the consequences are more serious than simply re-engaging or adjusting a coupling.”

Reliable components

The high reliability and the safe mechanical principle speak in favor of the torque limiters from R+W as part of the Emscher sewer project. The aspect of simple and fast re-engagement was just as important to the planners of the pumping station as the fact that no spare parts have to be kept in stock. After all, the Emscher sewer has an operating horizon of 100 years.

One model, many areas

A total of ten R+W torque limiters from the STR/25 industrial series are used in the Oberhausen pumping station. The shaft journal measures 145 mm and has a key for connection to the cardan shaft, which runs vertically in the shaft and is almost 5 m long. Two of the clutches have a release torque of 11,700 Nm, and the clutches are adjustable from 9,000 to 18,000 Nm. The eight other clutches have a release torque of 16,000 Nm and an adjustment range of 15,000 to 25,000 Nm. All ten couplings have the same design, the adjustment range is defined by the number of segments. The STR/25 coupling model covers the considerable range from 9,000 to 25,000 Nm of torque. Although the dimensions of the Emscher sewer project are considerable, the couplings, each weighing approx. 80 kg, are not among the upper limits of feasibility at R+W. The largest clutch ever built there weighed over 20 tons and has a cut-off torque of 20 million Nm. It is needed at a test stand for wind turbines

Enormous experience

For Christopher Monka, individual project support is what counts at R+W: “We first clarify the basic parameters, such as the installation situation, torque, speeds, area of application and, of course, the geometric requirements such as the diameter of the shaft journal, the drive, the type of mounting flange and the nature of the output side. Ideally, we provide advice at the planning stage, because the wide range of options available to us as a coupling manufacturer with headquarters and production plant in Germany is very helpful for planners and designers of machines and plants. Internationally, we are represented in around 100 countries and are a safety coupling manufacturer where the accuracy in design and production is certified and monitored by TÜV. Our portfolio includes a wide variety of coupling types. It ranges from very small to very large couplings, some of which are used under the harshest outdoor conditions, e.g. extreme temperatures, dust, steam or gas. More than 30 years of experience in coupling design help us with such special requirements and we are happy to provide advice and support.”

Plan works

To everyone’s surprise, demanding fish such as bullheads have already reestablished themselves in the upper Emscher, which has already been ecologically redesigned. They are a sign of good water quality. As well as kingfishers, damselflies and trout. Species diversity has tripled since the early 1990s. Former sewage treatment plants have been converted into oases of tranquility, and a bike path runs along what is now a picturesque little river. Humans, animals and plants are reclaiming the destroyed habitat thanks to a unique engineering feat. The generation project gives hope and is at the same time an incentive for further environmental undertakings in which R+W participates with pleasure, expertise and technology.