Efficiency or Reliability – Their Influences on Pump Selection and System Operation
By Bryan Orchard
This article looks at the challenges faced by Emschergenossenschaft, the organization responsible for the Emscher River Basin, and in particular the aspects of the project that influenced selection and specification of pumps needed for such a highly ambitious undertaking.
Restoring the highly polluted Emscher River between Dortmund and Dinslaken in Germany is Europe’s largest wastewater clean-up project costing an estimated Euros 4.5 billion. More of an open sewer than a river, the 80-km of waterway passes through abandoned coal-mines, industrial wastelands and urban areas. Due for completion in 2020, the regeneration project has faced many major challenges, ranging from collapsed coal mining tunnels, unexploded bombs, archaeological sites and the logistics of getting the slurry 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 toxic slurry.
The Emscher Conversion Project
In order to fully appreciate the project’s pumping requirements, it is necessary to have a full picture of just how large and complicated has been the Emscher Conversion project. Far from being a river clean-up, the project has had to address the crumbling infrastructure through which the highly toxic water flows and to construct a high-tech sewage system to treat the effluent. In addition, this has been the problem of flooding which poses a major threat to communities along the river. The ultimate goal has been to return the Emscher and its tributaries to a pristine state, thereby enhancing the environment for the benefit of the 2.6 million inhabitants and wildlife of the region.
Industrialization of the Ruhr Area, through which the Emscher flows, commenced in the 19th century and by the end of the century the commercial and household wastewater fed directly into the river had resulted in widespread contamination and appalling hygienic conditions. With the formation of Emschergenossenschaft in 1899 steps were taken to alleviate the problem. However, due to subsidence preventing the construction of a closed pipeline to carry the wastewater, the river was transformed into an open drain enclosed by concrete embankments. For the next 90 years, 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 move 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. In order to keep the wastewater flowing along the entire 51km, the tunnel has to 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. To KSB’s satisfaction no less than 21 of its Sewatec pumps were ordered.
Manfred Greisch, KSB project manager sums it up very simply: “The Sewatec pump is designed to meet the challenging requirements of the nature of the water in the Emscher system. It is resistant to chemical attack and abrasives. But most significantly KSB pumps have particularly efficient hydraulics compared to their competitors. And it almost goes without saying that KSB has the infrastructure and resources to support these pumps throughout their working lives.”
Planning for 100 Years
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 the brief given to all contractors on the project. 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.
Any equipment failures could result in damage to the entire system, including effluent treatment plants, and of course, flooding would be catastrophic. The pressures, therefore, were on the equipment manufacturers to have complete faith in their technologies and prove this to the customer. 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 so far ahead. Reviewing the long-term performance of similar pumps in similar applications does provide a good guide to their suitability.
The Winning Proposal
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 valley 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 meters of wastewater per hour.
To win the much-prized contract, KSB was successful in convincing Emschergenossenschaft of the significant benefits of using its Sewatec pumps. These highly versatile pumps were selected because they are in use in many parts of the world, delivering the type of performance and efficiency levels that the Emscher Conversion project required. These dry-installed pumps are fitted with variable-speed drives, IE4 motors and come with a variety impeller options. The optimized hydraulic system yields high efficiency, thereby helping to reduce energy consumption and minimize operating costs.
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This combination of excellent hydraulics and energy efficiency could not be matched by any of the other pump companies tendering for the contract.
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 optimized 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 this major 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 CFD (computational fluid dynamics) simulation. Each pump was tested individually prior to despatch and showed that the commitments made for efficiencies could be exceeded by 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.
For a project of this magnitude, it was important for Emschergenossenschaft to have a good idea of the Life-Cycle Costs 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 should not be seen as competing objectives. 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 at all times achieve efficiency and reliability. This saves on energy costs, wear on components and delivers smooth running, all of which contribute to lower levels of maintenance, this always being an expensive and time-consuming undertaking.
Having taken extensive briefings from Schachtbau Nordhausen GmbH, constructors of the pumping stations, KSB’s project team were able to deliver a proposal that would deliver outstanding efficiency at an excellent price/performance ratio. What’s more, they could demonstrate this in exacting witness-testing trials.
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, has the ability to monitor continuously its performance and react accordingly when events occur. To this end, it has the total cost of ownership for the entire designed working life.
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 benchmark for the wastewater handling industry. The bigger the project, the bigger the efficiencies pay-off for the end-user over the long term.
By showing flexibility in design, flexibility in thinking and the 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 pump-sets are not the end of the road for KSB. It will retain a close working relationship with its customer for many years through the provision of technical support services, ensuring that its pumps meet the ever-changing demands of Europe’s largest wastewater project.
About the Author
Bryan Orchard is an international freelance journalist who specializes in water and environmental engineering.
All Photos Courtesy of KSB SE & Co. KGaA.
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