R+W couplings in the largest pump station of the Emscher sewage canal

There is no end to the superlatives that can be used to describe the revival of the Emscher: 80 km reformation from the source to the estuary, 30 year term, 100 year minimum use duration, 73 km of new construction of the underground Emscher sewage canal, up to 40 m in depth, sewage from 2.2 million people, four major treatment plants, three major pump stations, investment of around five billion - it is one of the largest infrastructure projects in Europe. There has never been a comparable project on this scale worldwide for the ecological revival of an entire river system, which was previously considered biologically dead. Only a few residents could imagine in the beginning, in the early 1990s, that anything like this was even possible.

Green technology for a blue miracle

The visionaries of the Emscher Cooperative knew that they owed their river, the people and nature something, and promised: "You'll get your river back!" This was at the beginning of the generation project, which has been completed after 30 years, and is now a 'role model' for the world. Other projects may be more prestigious and arouse more media attention, but this involves something more. It is a matter of proving that interdisciplinary engineering skills can manage to recover what was believed to be a lost habitat. Internationally known as "green engineering", the keyword stands for sustainable innovations that serve to protect the environment and nature as the basis on which people live. What is also particularly impressive is that companies from Germany were able to establish a milestone here. A calling of the future on which the well-being of millions of people depends, and an exemplary project that would have been impossible without impressive pumps and protective couplings.

Problem case Emscher

What actually is the Emscher Cooperative and how did the catastrophic pollution of the river happen? Around 1850, before industrialisation, the Emscher wound its way across the core of the Ruhr area for 109 km, from Holzwickede near Dortmund to Dinslaken, its confluence with the Rhine. The area was sparsely populated and dominated by meadows, weirs and agriculture. Once coal mining began, the industry grew rapidly, and many people moved to the Ruhr area. The ground steadily subsided due to the mining, as a result of which, wastewater from industry and households could not be carried off underground. It collected in the hollows, which during high water resulted in a critical flooding of houses. This was why the Emscher Cooperative was founded in 1899. As the first public law water management cooperative of cities, businesses and mining operations, it eliminated the drainage emergency by using the Emscher as an open sewage canal. For this purpose, the Emscher was deepened from Dortmund to the Rhine, hemmed in by dikes, straightened and shortened to 80 km. Various sewage treatment plants were created in parallel, whose sewage supply occurred via the open canal system.

Kick-off 1992

With the gradual cessation of coal mining in the area, the subsidence greatly decreased, and the Ruhr area transformed itself from a heavily polluted area to a revegetated urban living area. This transformation is also reflected in the current task of the Emscher Cooperative. The goal is now to restore the natural state of the Emscher system with sustainable water management to the greatest extent possible. This kicked off in 1992.

Underwater sewage canal Emscher

To rid the Emscher of its sewage, a gigantic underground 'aorta' was established, the Emscher sewage canal ("Abwasserkanal Emscher" - AKE). It runs for 51 km from Dortmund to Dinslaken and, at depths of up to 41 m, passes below motorways, roads, the Rhine-Herne Canal, its locks, railway lines and industrial areas. The canal needs a gradient of 1.5 m per kilometre and starts in Dortmund at the first shaft at a depth of 8 m. The pipe diameter of the AKE expands successively from 1.6 to 2.8 m downstream. It consists of reinforced concrete pipes, which were pressed forward and laid by pipe jacking machines. In its main section from Bottrop to Oberhausen, laying occurred with concrete elements fitted into each other, so-called tubbing rings, which were pushed forward with the latest tunnel-building machinery. If the gradient had been continued at 1.5 m per kilometre, the canal would have arrived at Dinslaken at a depth of 80 m, causing considerable construction problems and expense. Consequently, three major pump stations were installed in Gelsenkirchen, Bottrop and Oberhausen, which raise the sewage at these points and supply it to the sewage treatment plants. As a result, the main canal can maintain its gradient and while remaining deep enough to allow the approximately 400 km of lateral supply canal system to flow in freely.

Centrepiece - Oberhausen pump station

The pumps are in underground pump station rooms and have a maximum pump capacity of up to 16,500 l/second. In the largest sewage pump station in Oberhausen, ten pumps can push sewage at up to 2,060 l/second over 40 m upwards. The Oberhausen pump station is the last of three pump stations before the Emscher sewage canal which, after a further 3.2 km higher-lying canal, flows into the Emscher estuary sewage treatment plant ("Klärwerk Emscher-Mündung" - KLEM). The Emscher flows into the Rhine about 7 km to the west of the KLEM. At the time of its construction, it was "the deepest building site in the Ruhr area." At a depth of 44 m and 50 m in diameter, it is the largest of the pump stations and functions as the centrepiece of the "sewage aorta" AKE. If one wishes to continue this metaphor, the pumps have cardiac valves that ensure the preservation of life - the so-called safety couplings. They do not separate any "streams", but instead the mechanical drives in the event of any suddenly occurring overloads. This "guard" function is indispensable if turbines and drive shafts are to remain undamaged in the long term. When it comes to such volumes of wastewater, large foreign bodies such as pieces of wood can occasionally enter the flow. If they get into the impellers of the pumps, tremendous forces result, and must be separated in milliseconds to prevent a total loss. Even supposedly innocuous items, such as toilet paper, wet wipes or other hygienic articles, can result in what sewage specialists refer to as the dreaded "braid formation", which can also cripple pumps.

Mechanics rather than electronics

Christopher Monka is the Senior Account Manager at R+W Antriebselemente GmbH from Wörth am Main. R+W safety couplings are a byword for quality in the sector. Every coupling is individually tuned to the respective drive situation and can be finely adjusted as needed. He is in charge of the couplings project at the Oberhausen pump station, Emscher sewage canal, and emphasises the necessity of mechanical overload protection. "The pumps may only be subjected to loads up to a particular torque. If there is a sudden blockage, the coupling protects the pump, motor and entire in- and output rate against a torque overload. This occurs mechanically via disc springs, which exercise an axial force on the balls. The balls are seated on the output side in a corresponding fit bearing. As soon as the tangential force acting on the ball becomes too great and the disc springs can no longer hold it in the ball seat, it slips into the safety segment. The coupling separates the connection and the flow of force is decoupled. This occurs in a range of 10 to 15 milliseconds. Purely electronic monitoring of the motor current, with automatic shut-down in the event of an overload in an emergency, is unsuitable due to the inertia of the mass and enormous kinetic energy, because it does not achieve this instantaneous separation of the drive forces. It takes around 40 to 60 milliseconds just to detect the overload. Only then does the shut-down of the motor occur, but without separating the forces of the drive train. Apart from this, electric current and precise programming are needed for the controller, which in turn holds risks, which do not however affect the mechanical safety couplings of R+W."

Advantage - Adjustability

According to Christopher Monka, the precise adjustability of R+W couplings has clear advantages. "To achieve immediate separation, other coupling manufacturers use shear pins that self-destruct upon occurrence of a particular force. By contrast, the spring-preloaded ball-catch principle preferred by R+W has the advantage that the torque release of the coupling is very precisely defined and the connection establishment can occur immediately after triggering without spare parts. The safety couplings used for the Oberhausen pump station are of an unlocking design, i.e. they re-engage manually within minutes. All you need for this is a rubber hammer. Thanks to the special design, the couplings are virtually maintenance-free and can nevertheless be freely adjusted. Particularly upon initial start-up, adjusting the optimal setting in line with practical conditions may be necessary. However, this initial sensitivity and flexibility pay off for the operator in the long term. This is because if you simply choose a setting that is too high at the beginning, this will take its toll on the service life of the pump, motor and drive train. If breakdowns then occur there later, the consequences will be more severe that just re-engaging or adjusting a coupling."

Reliable components

The high reliability and robust mechanical principle make R+W safety couplings ideal as part of the Emscher sewage canal project. The notion of fast, easy re-engagement was just as important for the pump station planners as the fact that no spare parts needed to be maintained. After all, the Emscher sewage canal does have an operating horizon of 100 years.

One model, many applications

A total of ten R+W safety couplings of the STR/25 industrial series are used in the Oberhausen pump station. The shaft bore is 145 mm in diameter and the output has a connection to an almost 5 m long cardan shaft, which runs vertically in its own housing. Two of the couplings have a disengagement torque of 11,700 Nm and can be adjusted from 9,000 to 18,000 Nm. The eight other couplings have a disengagement torque of 16,000 NM and an adjustment range of 15,000 to 25,000 Nm. All ten couplings are identical in design aside from the adjustment range being defined by the number of disengaging modules. The design of the STR/25 covers a considerable bandwidth from 9,000 to 25,000 NM torque. Although the dimensions of the Emscher sewage canal are considerable, the couplings, each weighing about 80 kg, are not the upper limit of what is feasible from R+W. The largest safety coupling ever built there weighed over 20 tons and had a disengagement torque of 20 million Nm – used in a test stand for offshore wind turbines.

Enormous experience

For Christopher Monka, what counts at R+W is the individual project supervision. "First, we clarify the basic parameters, such as the installation situation, torque, speed, deployment area and of course the geometric requirements, such as diameter of the shaft journal, drive, type of mounting flange and the character of the output side. Ideally, we consult in advance of the planning, because the many different options we have as a coupling manufacturer with our headquarters and production plant in Germany are very helpful for planners and designers of machinery and equipment. We are represented in about 100 countries internationally and are a safety coupling manufacturer whose precision in design and production is certified and monitored by the TÜV. Our portfolio includes all kinds of couplings. It ranges from very small to very large couplings, which are in part deployed under the toughest external conditions, such as extreme temperatures, dust, steam or gas. Over 30 years in coupling construction help us in the case of such special requirements and we would be pleased to provide you with help and advice."

Plan succeeds

In the upper Emscher, which has already been ecologically revived, demanding fish types like sculpins have already recolonised the area, to the surprise of all. They are a sign of good water quality. Just like kingfishers, damselflies and trout. The variety of species has tripled since the beginning of the 1990s. Former sewage treatment plants have been converted to peaceful oases and a cycling path now runs along the picturesque river. People, animals and plants are reclaiming the destroyed habitat thanks to a unique feat of engineering. The generational project is a source of hope and simultaneously an impulse for additional environmental undertakings in which R+W participates with pleasure, expert knowledge and technology.

Please have a look at the safety couplings which used in the pump station.

Please whatch the video ot the amazing pump station in Oberhausen.