Efficiency Or Reliability? Selecting KSB Pumps For A Colossal Pumping Station
KSB Sewatec Pumps for Europe’s Largest Wastewater Project at Emscher Sewer Canal Pumping Stations Germany
Restoring the highly polluted Emscher River between Dortmund and Dinslaken in Germany is Europe’s largest wastewater clean-up project costing an estimated 4.5 billion Euros. The construction project involves converting the Emscher system from an open to a closed waste water discharge system as part of a mega re-naturalisation program.
More of an open water sewer than a river, the 80km of water passes through abandoned coalmines, industrial wastelands and urban areas. The regeneration project is due to complete in 2020, and has faced many major challenges, ranging from collapsed coal mining tunnels, unexploded bombs, archaeological sites, and the logistics of getting the waste water to flow down the newly constructed main sewage tunnel. This latter challenge could only be made possible by the construction of three colossal underground pumping stations to lift the waste water.
This article looks at the challenges faced by Emschergenossenschaft, the organisation responsible for the Emscher River Basin, and the aspects of the project that influenced the selection and specification of the pumps needed for such a highly ambitious undertaking.
The Emscher Conversion project
To fully appreciate the project’s pumping requirements, one needs a full picture of just how large and complicated the Emscher Conversion project has been. Far from being a simple river clean-up, the project has had to address the crumbling infrastructure through which the highly toxic water flows and floods posing a major threat to communities along the river. The ultimate goal has been to construct a high-tech sewage system to treat the effluent and return the Emscher and its tributaries to a pristine state, restoring the environment for the benefit of 2.6 million inhabitants and wildlife of the region.
Industrialisation of the Ruhr Area, through which the Emscher flows, began in the 19th century and within decades the commercial and household wastewater fed directly into the river had resulted in widespread contamination and appalling hygienic conditions. The formation of Emschergenossenschaft in 1899 initiated the steps needed to alleviate the problem. However, subsidence prevented the construction of a closed pipeline to carry the wastewater and the river was transformed into an open drain enclosed by concrete embankments. For nearly a century, nothing really changed until the ambitious plan created by Emschergenossenschaft and 19 local municipalities during the 1990’s was finally published as the Emscher Future master plan in 2006.
To sum up the Emscher Conversion project in simple terms; this is a massive 51km underground wastewater tunnel connected to a network of underground conduits and pumping stations that will remove all the wastewater currently flowing into and along the open drain. With the demolition of the open sewer systems the Emscher River and its tributaries will revert back to natural water courses.
Dealing with water flow
The main artery of the three meter diameter drainage tunnel starts at the Dortmund-Deusen sewage treatment plant and follows the course of the River Emscher due west to the Emschermündung sewage treatment plant near Dinslaken. At first sight this appears to be quite straightforward, but that is not the case. Along with all the other challenges faced by the project engineers, there was the matter of wastewater flow. To keep the wastewater flowing along the entire 51km, the tunnel must have a downward slope of 1.5m per 1km. This might not seem to be of great significance, but with such an incline the tunnel would be 75m below ground level when it reaches Dinslaken on the River Rhine.
After due consideration the solution to this problem was to build three large pumping stations at Gelsenkirchen, Bottrop and Oberhausen in order to raise the water from a depth of around 40m to 8m below ground level. This provides sufficient slope for the wastewater to flow off again down the tunnel. These pumping stations are essential to the successful operation of the entire system, which is why such exacting specifications were set out at the start.
As is to be expected for a project of this size and complexity, Emschergenossenschaft required a long term engineering solution that was robust, reliable, efficient, future-proof and capable of meeting all current demands and future expansion. Nothing short of a 100 year working life was necessary, and at no time during this period would there be any halt in the water flow, so all fluid handling equipment had to be fully functional at all times.
Moreover, equipment failure could have devastating effects to the entire system, as flooding would be catastrophic. The pressures, therefore, were on the equipment manufacturers to have complete faith in their technologies. However, even this is not enough. Emschergenossenschaft wanted pumps that would deliver reliability over the long term and economical operation that would deliver energy efficiency. Given that the complete system has a designed lifespan of 100 years, it is impossible to predict with total accuracy the many factors that will affect the performance of the pumping system. Although, reviewing the long-term performance of similar pumps in similar applications does provide a good guide to their suitability.
The pumping system
KSB’s principal areas of involvement were the provision of pumps for the Bottrop and Gelsenkirchen pumping stations. Both pumping stations lift the wastewater from the sewer sections at a lower level to the sewer sections at a higher level. The biggest pump sets each have a drive rating of 470 kW and handle up to 6,480 cubic metres of wastewater per hour.
Emschergenossenschaft was ensured that the KSB Sewatec pump systems were up to the task. Already in use in many parts of the world, the pumps are delivering the type of performance and efficiency levels that the Emscher Conversion project required. These highly-efficient, dry-installed pumps are fitted with variable-speed drives, IE3 motors and come with a variety impeller options. The optimised hydraulic system yields high efficiency, thereby helping to reduce energy consumption and minimise operating costs.
Several modifications were made to the pumps to meet the project’s special requirements. A special technical feature of the pumps is their casing design. Unlike Sewatec’s standard casing, the casings for this variant were designed with tangential discharge nozzles by KSB engineers to achieve even better efficiencies. The impellers were also optimised to ensure excellent efficiencies without compromising on the high level of operating reliability. In addition, the oil reservoir of the shaft seals and its monitoring device, plus the backstop on the pumps, was adapted to the customer’s requirements.
KSB’s factory in Halle/Saale produced all of the pump sets for the project, including two huge pumps in close-coupled design specially manufactured for the Gelsenkirchen pumping station. It was here that the efficiencies the pumps achieved on the test bed exceeded the values established through the computational fluid dynamics (CFD) simulation. Each pump was tested individually prior to despatch and showed that the efficiency commitments could be exceeded by up to three percent.
The requirement for the Bottrop pumping station was 10 pumps with discharge nozzles between 500mm and 700mm and impellers up to 900mm in diameter with universal-joint shafts. Nine pumps of the same design were commissioned for the Gelsenkirchen pumping station. In addition, two Sewatec pumps were supplied in the same size in close-coupled design.
Life-cycle costs
For a project of this magnitude, it was important for Emschergenossenschaft to have a good idea of the Life-Cycle Costs (LCC) for the pumping stations and thus, the Total Cost of Ownership. Knowing the LCC enables the customer to have a good idea when the total investment will be paid back. Of the many requirements for this project attaining high levels of pump efficiency and reliability came high on the wish list.
Pump efficiency and pump reliability can be achievable at the same time. In fact they complement each other. To achieve both objectives requires all parties involved in the design and operation of the pumping system to combine their resources and technical expertise to identify the factors that contribute to determining the Best Efficiency Point (BEP). Pumps running at their BEP always achieve efficiency and reliability. This saves on energy costs, components, and delivers a smooth-running system.
No compromise
The Emscher Conversion project is a highly innovative and complex project that has been many years in the planning. Now closing in on its full commissioning date, this closed wastewater discharge system is a state-of-the-art design that harnesses the highest levels of water transportation technologies that are available from world-leading equipment and materials manufacturers. Its owner and operator, Emschergenossenschaft, can now continuously monitor its performance, predict failures, and react to eventualities quickly and efficiently.
The Emscher Conversion project has provided KSB the opportunity to demonstrate its engineering resources and all-round capabilities in designing and delivering an energy efficient and reliable pumping solution that can be seen as a bench-mark for the wastewater handling industry. The bigger the project, the bigger the efficiencies pay-off for the end-user over the long term.
By being flexible in the design, thinking, and capabilities to tailor its products to the customer’s requirements KSB has made a major contribution to the Emscher Conversion project. Delivery, installation and commissioning of the 21 Sewatec pumpsets are just the beginning of Emschergenossenschaft’s relationship with KSB. A close working relationship will sustain the equipment for many decades through the provision of technical support services, ensuring that its pumps meet the ever-changing demands of Europe’s largest wastewater project.