Electricity and Control October 2020

MEASUREMENT + INSTRUMENTATION

Radar level measurement in extreme environments

Jürgen Skowaisa, Product Manager Radar at VEGA Grieshaber KG

The production of cement is without doubt one of the most energy-intensive industrial processes. The use of alternative fuels and raw materials, primarily waste products, has long become part of the process to make it more economical as well as to conserve primary raw materials and fuel resources and reduce landfill volumes. At Cementos Molins, S.A. in Barcelona, Spain, heavy knives plough through a mass of shredded waste to be used as fuel in the production plant. One tonne per hour is handled in a large storage silo.TheVEGAPULS 69 monitors the fill levels reliably.

T he alternative fuels and raw materials (AFR) used include whole and shredded tyres, waste timber or mixtures of plastics, paper, compound materials or textiles with a calorific value similar to that of lignite. The value of old tyres is even comparable with coal. However, the use of these alternative fuels also has its pitfalls. They must be processed prior to use so that they do not influence the later production process and, above all, the quality of the end product. And level measurement in the AFR silo is not unaffected either. Just one example: if the alternative fuel is made from recycled Tetrapaks, the metal particles contained in the packaging can create interference signals due to flying metal foils. An unusual agitator Cementos Molins has been working with VEGA for twelve years and a number of VEGA sensors are already in use at the site, including pressure transmitters, capacitive measuring instruments and vibration limit switches. The company needed a special solution for the storage silo that contains the alternative fuels. The silo has a height of more than 20 m and a diameter of 9 m. About 35% of the fuel used in the plant for the production of cement comes from alternative fuels. There is an unusual agitator on the inside floor of the silo with very sharp, vibrating knives which grind the waste continuously. Trucks arrive around the clock to fill the silo, unloading about one tonne of AFR material into it every hour. The challenge here is that the trucks loaded with waste must be completely emptied – and the capacity in the silo must therefore be sufficient to hold a complete truck load. The level measurement must provide protection against a risk of overfilling, and the empty warning is at least equally important. Complete emptying would cause damage to the agitator. A reliable measuring process is therefore necessary to

ensure continuous level measurement, 365 days a year, without interruption.

Challenges from the grinder Conditions in the building materials industry are generally a little harsher than in many other sectors and in this cement factory, the owners faced particular challenges. First, the AFR materials differ and stick very easily. And further, when the silo is filled from the trucks, a gigantic cloud of dust is created which makes level measurement extremely difficult and often leads to heavy deposits on the sensor. During

At Cementos Molins, trucks deliver alternative fuels to the factory around the clock.

Electricity + Control OCTOBER 2020

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