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How does a manufacturer design a pump to meet particular client requirements? Axel Lüdecke, water transport GM at KSB Aktiengesellschaft, gives us the lowdown.
What does a manufacturer look at when designing a pump? What are the objectives? What are the associated benefits for the customers buying the pumps? “We are looking at the highest long-term efficiency and the maximum operational availability, which is very important in terms of service quality and especially ease of maintenance, because the equipment is likely to be used for 20 to 30 years,” explains Lüdecke.
All these objectives are focused towards providing customers with benefits in terms of the lowest operating cost, the best operational reliability and the most economic maintenance cost. What this equates to ultimately is “a commitment to a cost-effective solution that provides the lowest lifecycle cost,” says Lüdecke.
Take for example a district cooling application, where the flow/head range starts from 650 cubic metres or 2 800 gallons/min up to 4 000 cubic metres or 17 200 gallons/min respectively. In terms of head requirements, this starts from 16 m/52 feet up to 30 m for the highest flow requirements, corresponding to approximately 100 feet, up to a max of 160 m or 520 feet respectively. Lüdecke points out that these are rounded figures, and that the conversion rates may vary slightly.
Specific requirements
“We meet the specific requirements for district cooling with two different pump series, namely the Omega and the RDLO. The design principles of both pumps are very similar. The materials used are cast iron with bronze and chrome steel for the shaft and shaft sleeves. The Omega type, occasionally when the pressure rating requires it, utilises a nodular iron casing, with the same material combination for the rest of the components,” explains Lüdecke.
The RDLO series is supplied with a cast iron casing and bronze and chrome steel for the remainder of the components. “I gather that there is an increasing demand for district cooling plants to use seawater. Both pump series are available in a duplex steel material combination, and have been supplied successfully to various desalination applications. This gives our customers the assurance that they will be suitable for a district cooling application using seawater,” says Lüdecke.
At the end of the day, one of the most important benefits for customers is reduced operating cost.
“We perform computer-optimised flow design in order to maximise the overall efficiency. We provide replaceable wear rings on both the impeller and in the casing, which is the key element to re-establishing efficiency after a long period of operation. There may be wear due to suspended solids in the liquids. Having wear rings that can be replaced easily means it is equally easy to return a pump to its original efficiency,” says Lüdecke.
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Pump efficiency
While pump efficiency is a critical factor, there is an associated cost factor that customers sometimes balk at, ignoring the long-term cost-savings and reduced payback period. The simple fact of the matter is that high-efficiency pumps will incur a higher initial capital cost, just as high-efficiency motors and chillers do as well. “Superior equipment providing superior performance in terms of operating expenditure is usually not the lowest cost.”
In order to illustrate how important pump efficiency is to system efficiency, Lüdecke uses an example of a typical largescale district cooling installation with a hydraulic power demand of 2 000 kW, 3 000 operating hours a year, a power cost of AED0.2 kW/h and a total lifespan of 20 years. “Now suppose you have a pump with 85% efficiency and a pump with 87% efficiency. The better efficiency gives a lifecycle cost-saving of AED650 000.”
However, it is important to note that a 2% difference in efficiency is usually covered by the acceptance criteria standard. “You may be supplied with a pump with an 88% efficiency as listed in the data sheet. At the end of the day, you may get a pump with only an 85% efficiency, because that is covered in the efficiency tolerance class. Now we can tighten the acceptance class to no negative tolerance on efficiency, but this would have an adverse effect on the pump price, because the manufacturer may need another one or two trim runs as part of acceptance testing.
Supplier performance
“Alternatively, contractors out to buy pumps may want to observe and monitor in the long term how different suppliers perform, what they guarantee, and what they actually deliver. There may be suppliers always making full use of the tolerance band within the acceptance class, and there may be pump suppliers giving some efficiencies, but not using the full tolerance as per the applicable acceptance standard,” notes Lüdecke.
In terms of reliability and availability benefits, there are various technical solutions available to enhance these. One example is having shaft nuts and fixing the shaft sleeves on both sides, with an additional shaft nut at the very end. “The horizontal split-casing pump provided by ourselves has got full-length shaft sleeves all the way into the bearing housing. There is no shaft screw in-between, as this would mean having a thread exposed to ambient conditions such as dust and condensation water. In addition, any thread usually concludes in stress concentration, affecting availability and reliability in the long run.”
The single nut allows self-alignment of all the components alongside the shaft, including the mechanical seals and bearings. “As far as maintenance benefits are concerned, these usually tie in with the mechanical design and engineering. Overall we believe that our design objectives have met customer requirements with regard to associated maintenance benefits,” concludes Lüdecke.
Projects supplied by KSB
Burj Dubai Development Area
Supply of up to 10,000 m³/h cooling water
DCP-01: 36 pump sets in total
Burj Dubai: 31 pump sets in total
Yas Island, Abu Dhabi
Cooling water supply to F1 stadium and other related buildings
DCP-08 and DCP-09: 43 pump sets in total, 9 off RDLO at 3,450 m³/h (15,200 gpm) to 45 m (145 ft) each pump
Al Raha Beach, Abu Dhabi
RB-02 and RB-04: 54 pump sets in total, 18 off RDLO at 3,475 m³/h (15,300 gpm) to 34 m (110 ft) each pump
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