Dual-shafted grinder from Sulzer eliminates breakdowns at pumping stations08 December 2021
Municipal utility company Servicebetrieb ASK, of Kamp-Lintfort in Nordrhein-Westfalen, Germany was experiencing frequent blockages and outages in one of its sewage pumping systems. The main cause was the proportion of solids in the wastewater, which is continuously increasing. Consequently, Sulzer recommended the upstream installation of a dual-shafted grinder, colloquially known as the Muffin Monster, and since its installation, the sewage pumps have been operating perfectly. Thanks to the savings in maintenance costs, the grinder has paid for itself in less than eighteen months.
For around ten years, wastewater plants in metropolitan regions such as the Ruhr area have faced constantly growing challenges, including the many things that are thoughtlessly discharged into the sewers. "Wipes especially are a big problem. They form long chains in the sewer and then block the pumps," explains Andreas Fockenberg from Sulzer. Weather extremes do the rest. "If a dry period is followed by a heavy downpour, with the flushing surge in the sewer, all the material arrives at the pumps at once. While these have become more robust, there are simply too many difficult-to-handle pieces of debris," continues Andreas.
The customer's pumps were clogging with increasing frequency because layers of scum were forming in the pump well and solidifying. "We were having to pump out these blockages once or twice per month with the suction tanker, which was very cost- and labour-intensive," states Norbert Leurs of Servicebetrieb ASK Kamp-Lintfort.
In the case of ASK, a 30K series inline grinder was specified with a flow rate of 140 m3/hour. Instead of the standard 2.2 kW motor, for ASK, a 4kW drive was specified, as this can cope with even the very largest and toughest solid materials that the customer frequently had to deal with. Since this application called for an inline grinder, the motor is designed with category IP68 protection, ensuring it can work in submerged conditions.
Within half a day of being delivered, the grinder was installed with its customised frame in the pumping plant intake. Since then, there have been no further pump outages.
Unlike macerators and pump crushers, the Muffin Monster grinder works with two shafts, fitted with sharp cutting wheels. These shafts run in opposite directions at different, very low speeds and correspondingly high torque. They grab, tear and cut up the material, allowing the pumps to effortlessly transfer it to the next pumping station.
The automatic load detection and reverse control of the dual-shafted grinder protects the system and optimises performance. If an object cannot be handled at the first attempt, it is put into reverse motion for a few seconds, before being grabbed again following repositioning. If this happens three times without success, for example with large metal parts, the unit shuts down for self-protection. While the reverse control is part of the regular operation and an important efficiency feature, there has yet to be a shutdown since the Muffin Monster was installed.
The grinder is automatically switched on and off by a radar level detection instrument, widely used in wastewater management in the region, and specifically requested by the customer. (As standard fitment, the grinder is usually equipped with an ultrasound level detection device.)
Apart from its three sizes and two design variants, Sulzer's Muffin Monster can be configured to meet the requirements of each customer. Apart from the customised installation frame in stainless steel, the motorization and the fill level measurement, there are various cutting wheel options to choose from, including with 'Wipes Ready' technology specifically aimed at one of the biggest challenges in the industry.
Demand is correspondingly high: "We have had 20 new installations in the past two years in this sales region," Fockenberg adds.
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