ABB drive removes steeping production bottleneck.
Installing an ABB drive on a mechanical agitator at a production bottleneck has reduced stoppages, cut maintenance and saved energy. Bairds Malt has five malt houses across England and Scotland, supplying 250,000 tonnes of malt a year to brewers and distillers. The ABB ACS880 industrial drive controls four gear motors located on the corners of a 15-tonne turner. The turner – also called a trolley – plays a crucial role in the malting process.
After steeping, barley feeds into a 45-meter-long open-topped box for germination to take place. The trolley agitates the barley to stop its roots from knitting together as it moves along the box at exactly 0.42 rpm driven by the gear motors. As the trolley progresses, 12 motor-powered screws also turn the barley to break it apart.
In the original previous installation, a fixed speed motor powered the turner. This resulted in a production bottleneck as it was unable to slow down to negotiate any blockages, such as hard lumps of barley. The machine would attempt to break up any obstruction by trying to drive through it. This would cause a spike in current, leading to machine breakdowns.
“Each time the process broke down we had a window of around nine hours to fix it, otherwise the malt would ruin”. Says Dave Last, engineering manager at Bairds Malt. “Usually we were able to fix the problem within that timeframe. But, as malt is a live product, the roots continue to grow and knit together, setting almost like cement. It sometimes got to the point of having to break up the roots with forks.”
The blockages also had more serious implications by putting workers at risk of serious injury. When the machine attempts to drive through the restrictions it could cause the 15-tonne turner to ‘jump’ backwards. As a result, Bairds decided to upgrade its 40-year old turner and box systems with a new control package.
Removing the production bottleneck
With the new system, the ABB VSD takes signals from a programmable logic controller (PLC). The PLC monitors the load drawn by the gear motors and detects current spikes 20 percent or more, indicating a blockage. Should this occur, the drive reduces the speed of the motors to 50 percent, giving the turner time to work through the obstruction. If the blockage is not cleared after three attempts, the PLC triggers an alarm to notify the operator.
Since installing the new system, stoppages at the Witham site fell from an average of once a fortnight to almost zero. “With the drive installed, the lower inrush currents and torque control limit stresses on mechanical components. This results in fewer breakdowns from snapped screws and belt chains. The reduced maintenance costs are expected to deliver further savings.
By removing the production bottleneck, the new system increased productivity and enhanced safety for staff because the turner no longer jumps out of place. A smoother turning process also means lower energy consumption at the Witham site due to reduced work done bythe equipment
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