Operating one of Switzerland’s largest grain mills is a complex task – every processing step is recorded and calculated meticulously. What makes it possible are VEGA level sensors.
The granary on the Limmat River, near the Swiss city of Zurich, is the site of one of the biggest grain stores in the world. Measuring 118 metres, it is the second tallest building in the city, and where a thousand tonnes of grain is processed every day.
Operated by Swissmill, the city’s rail network delivers the grain directly to the premises. Material comes from all around the world, with corn from Italy, durum from France or Canada, and oats from Norther Germany and Sweden. The majority of the resulting processed flours, farina or flakes are then trucked to be processed in industrial bakeries, pasta processing or in starch factories.
Karl Dahlke, Manager of the flour silos and batch logistics at Swissmill, explains why the location of the granary in the immediate vicinity of the city presents a challenge for production.
“On the one hand, we have to pay particular attention to the noise emissions, on the other hand, space is restricted. Expansion of the plant is not easily possible,” Dahlke says. However, he adds that there are some positives to the combined space, as it “stirs the imagination” to find new ways to get the most out of the plants.
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Processes at the facility have changed over time to reduce the number of steps required compared to other grain mills, as part of Swissmill’s goals to ensure its operations are trouble free and reduce energy usage. This has been assisted by the company’s close cooperation with its customers and the monitoring of product streams.
In the beginning, was the bran
From a level measurement point of view, flour is difficult to measure. When filling a silo, a lot of dust is created, which settles slowly. The dielectric constant differs significantly across the estimated 120 different types of flour, becoming even more difficult to measure when the grain gets drier in summer, causing a further drop in the dielectric constant.
Dahlke says the most difficult substance to measure is bran. In summer, it has an epsilon value of 1.4 and is stored in a slim, 10-metre-high, steel-reinforced concrete silo, making it hard to get an accurate level measurement.
Mario Keller, Head of Electrical Maintenance at Swissmill, says one product managed to solve this problem for good.
“I will never forget how, 25 years ago, a VEGA technician visited us, analysed the measuring situation with the bran and explained to us that we must approach the problem from a totally different angle,” Keller says.
“A few months later, a new device, at that time still a VEGAFLEX with adapted software, was installed and really did provide reliable measured values.”
Since then, Swissmill has recognised VEGA as a problem solver, working with the company to set the standard for level measurement at the factory. Over the years, new sensors from VEGA have been tested at the site to help solve some of the issues it was facing. At the granary, this included twisting of the cable in the guided microwave, trapping grain and sending a false measuring signal.
Replacing this was a VEGAPULS 69 radar level measuring instrument, which operates with an 80-gigahertz frequency. The device measured without needing to make contact with the grain and could provide reliable readings through heavy clouds of dust, eliminating false signals.
“However, we must say that, since we have been working with VEGA, measuring uncertainties have never really been a problem because VEGA always feels responsible and takes us seriously,” Keller says.
The VEGA devices not only measure product levels but are also used for process control, specifically in the production of fodder. When pelletising fodder, the preliminary depot must always be full to ensure the pellets have the right density later. A reliable measuring signal is crucial in the outflow cell in the pelletiser as a result. When the cell overflows, the feeders close and the mills may be shut down. As such, the process planners need a 100 per cent signal to avoid the whole production plan from getting out of control.
Saves time and money
Dahlke is convinced that work at the factory without level measuring technology would be quite different.
“When a holiday is coming up and the bakeries need more flour, we can start production a week earlier thanks to our reliable stocktaking. Previously, we had to work special shifts to compensate for bottlenecks,” he says.
In addition, bakeries previously would not know whether their silos were half-full or nearly empty, leading to situations where the Swissmill drivers would need to drive back with a full truck. These loads then had to be rebooked and handled separately, incurring unnecessary costs.
Dahlke also recalls another situation a few years ago when floods led to failure of compressors in a cellar, interrupting production for three days.
“However, we knew exactly how much every single silo contained and were able to juggle supplies to satisfy every customer. They never noticed the incident. This would never have been possible without the exact level display,” he says.
Another aspect the level measurement technology assist with is the grinding of organic products, which must be done separately for legal reasons. At the beginning of the process, there is a mixture of conventional grain, which is then fed back to the conventional section, but if not done properly this can lead to a quality downgrade.
“The more accurately I can feed this quantity, the less loss I have per milling cycle,” Dahlke says.
Level measuring technology has a special task in stocktaking. Swissmill does not only measure the level in its own 200 grain silo cells, but also within 150 of its customers’ silos as well.
Dahlke says that thanks to VEGA technology, the company can look directly into the customers’ silos and make an order as required.
“The companies therefore hand over the responsibility for their raw material management to us,” he says.