No more stick-slip with innovation for GEA decanters

New GEA Active Torque Control boosts efficiency, reliability and the bottom line


With its automatic Active Torque Control (ATC) for CF decanter centrifuges, GEA introduces a market innovation that makes production processes not only more reliable but also as profitable as possible under stick-slip conditions. GEA’s ATC solution features on-the-fly, automated correction of the differential speed by means of active torque control to ensure an optimal working point while avoiding stick-slip. This ensures maximum solid yield, minimum energy costs for thermal drying and significantly lower risk of system damage due to stick-slip.

“Even with products susceptible to stick-slip conditions, ATC’s automated differential speed correction feature means the decanter can be operated at the optimum working point under stick-slip conditions,” says Robert Zeldenrust, Product Manager Renewables, GEA Separation and Flow Technologies Division. “ATC reliably detects the occurrence of the stick-slip effect and makes the necessary adjustment, while still ensuring that the best possible process result is achieved in terms of dry substance yield and overall costs.”

Revolutionizing decanter technology

A perennial problem for decanter operators is finding the optimal working point to maximize dry substance yield while still avoiding stick-slip. Adding to the challenge is the fact that – like for products such as starch or casein – the optimal working point often approaches conditions where stick-slip can occur. GEA’s ATC solution now adds “intelligence” to the decanter system so it can make the necessary adjustments on the fly for an optimal working point with optimal safety and efficiency. “ATC essentially maximizes dry yield and minimizes the time and energy required for drying, while continually monitoring and adjusting to keep the system out of the stick-slip ‘red zone’,” says GEA’s Christian Becker, Product Manager Dairy, GEA Separation and Flow Technologies Division.

ATC represents a breakthrough in decanter technology by allowing calibration and adjustment during operation. “Without the benefit of ATC, decanter operators are essentially ‘flying blind’, having to approximate the optimal working point,” explains Robert Zeldenrust. “If the system is damaged, they may realize that stick-slip is happening and may find the root cause. Then they can adjust the working point, but they don’t know by how much. If they don’t correct enough, they risk further damage to the system, so the tendency is to overcorrect – to increase the differential speed to be on the safe side. But this means the solids are too wet, which significantly increases the time and energy spent on drying.”

“ATC dramatically reduces the risk of stick-slip and those dreaded shutdowns – and given the tremendous cost of downtime and repairs in these situations, the investment in ATC pays off even if it prevents just one production stop,” says Christian Becker. “But beyond that, ATC also enhances system capacity, ensures a more uniform structure of the casein flakes and generally optimizes total solids content for sustained, long-term savings on drying costs.”

In the case of starch production with a GEA CF 6000 decanter, for example, a dry substance value that is just 1% higher can achieve annual savings of approximately EUR 20,000 in drying costs. For the casein process, a 1-2% increase in dry substance can mean annual savings of roughly EUR 15,000. Moreover, these economic savings are accompanied by ecological benefits: less drying effort means savings in energy resources, which sustainably reduces the CO2 footprint of the production facilities.


ATC origins – GEA’s “smart” decanter breakthrough

GEA’s innovative ATC solution for decanters was the result of a deep-dive into the causes and effects of stick-slip. After conducting detailed analyses of damage patterns caused by the stick-slip effect, GEA research & development decided to monitor the decanter drivetrain – specifically the coupling between scroll motor and gearbox – using a high-speed camera and stroboscope. This revealed a visible oscillation of the coupling components generated by a dynamic torque when operating at a working point within the stick-slip boundary region. In response, GEA engineers developed a new sensor-based monitoring and control method – ATC – to detect the onset of torsional vibrations on the coupling and, depending on their intensity, to avoid them by automatically changing the working point.

GEA offers its revolutionary ATC automated monitoring and control system in new CF decanter series machines, as well as the option of retrofitting existing CF decanters with ATC.

Infobox: What is the stick-slip effect?

The stick-slip phenomenon is a detrimental effect that can occur in industrial machines like decanter centrifuges – irrespective of manufacturer and design – when the static friction between the solid bodies moving against each other is greater than the dynamic friction. If the slipping speed of the solid body becomes too slow, it gets stuck and needs additional energy to start slipping again. The stick-slip effect cannot be detected from the outside and leads to increased fatigue and wear to machine components such as the bowl, scroll, gearbox, shafts and coupling. Stick-slip increases the risk of unplanned, expensive downtimes with costly repairs.


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