Waldkraiburg, Germany, 05/02/2019
Until early 2013, a conventional rotary lobe pump was used to pump centrate into the aeration tank of a wastewater treatment plant. However, significant signs of wear appeared quickly, particularly on the elastomer lobes, due to the high content of magnesium ammonium phosphate (MAP) in the water. The unit required frequent maintenance. For this reason, the decision makers decided to replace the pump with a more robust and reliable model. They chose TORNADO® T2 T.Envi® rotary lobe pump by NETZSCH Pumpen & Systeme GmbH from Waldkraiburg. It is specially tailored to the requirements on site, and thus guarantees maximum operational safety. Wear could be minimized due to the reversal of material, typical of each particular model series, where metal lobes rotate in elastomer housing. This sets the T2 apart from rotary lobe pumps made by other manufacturers.
“Water discharged from the centrifuge – that is, the centrate, which is then pumped into the aeration tank – is contaminated with ammonium, nitrogen and MAP,” explains the plant supervisor. “The latter is a salt of ammonium, magnesium cations and phosphate anions, which crystallizes during the pumping process. It caused premature wear of the conventional rotary lobe pump, which was used until January 2013. “It affected mainly elastomer lobes. Their tips showed wear on a regular basis, because most of these forces act on these components. As a result, it was necessary to service the unit annually, even though the output was only 19,000 m³ a year on average.
In order to avoid this problem in the future, the plant managers decided to replace the previous model with TORNADO® T2 rotary lobe pump of the T.Envi® series. Maximally robust and long-lasting design was at the heart of the development of this type of pump. Its characteristic feature is a reversal of material: NETZSCH rotary lobe pumps of the new generation are made of hardened steel. Pads vulcanised onto the edges of the lobes create continuous hard-soft contact at any time during rotation. This prevents high-wear friction of rubber against rubber, which is typical for many other models. The specially attuned shapes of the rotary lobes and housing not only improve the pumping capacity, but also reduce friction and energy consumption. The rotary lobes run in a rubberised and flow-optimised housing.
T.Envi® has been in service at a German sewage treatment plant since February 2013, with an increased conveying volume of approximately 22,000 m3. Its special design dramatically reduced pump wear virtually to zero. The metal lobes are insensitive to the difficult medium and do not wear out. In addition, the new pump is larger than the previous one, and its speed could thus be reduced. This weakens shearing forces exerted by the lobes on the medium. “Presumably, this has had a negative effect on the crystallization of the salt,” says the plant supervisor. “We assume that lower shearing forces reduce the formation of crystals, which could wear out the rotating elements of the pump. However, the behaviour of MAP under these conditions has not been fully researched yet, so that we can only assume there is a positive correlation.”
Extremely high-quality materials and components were also used for the other parts of the rotary lobe pump. Torsion- and bend-resistant shafts, for example, guarantee reliable operation even at high pressure. Robust angular contact ball bearings guarantee the axial and radial stability of shafts and rotary lobes. The belt drive ensures that the pump unit operates extremely smoothly. This results in a reduced load and fewer vibrations, which affect the components. The service life is thus significantly longer overall.
The maintenance is also much simpler, compared to the previous rotary lobe pumps. Since the system is not lubricated, time-consuming lubricant changes and the risk of leakages are a thing of the past. If T.Envi® requires service or repair nonetheless, direct access to the pump chamber means work can be performed quickly and, above all, easily. After removing the drive cover, the entire synchronised belt drive can be accessed. Workload is kept to a minimum and downtimes are shorter. “However, such measures have not been necessary yet,” sums up the plant supervisor. The wastewater treatment plant was satisfied with T.Envi®, so much so that it decided to purchase another NETZSCH pump.
[5.138 Zeichen inkl. Leerzeichen]
For over 60 years, NETZSCH Pumps and Systems has served markets worldwide with NEMO® progressing cavity pumps, TORNADO® rotary lobe pumps, NOTOS® multi screw pumps, grinding machines, barrel emptying systems, dosing technology and accessories, providing customised, sophisticated solutions for applications in every type of industry. With a workforce of over 2,000 and a turnover of more than 275 million euros (2018 financial year), NETZSCH Pumps & Systems is the largest business unit with the highest turnover in the NETZSCH Group, alongside NETZSCH Analysing & Testing and NETZSCH Grinding & Dispersing.
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Author: Pitt Mair, Area Sales Manager