MEASURING IN A
CLOUD OF DUST
A large agitator with sharp knives ploughs its way through the mass in the storage silo for alternative fuels
C
ement manufacturing is highly energy intensive because of the extreme heat required to produce it. However, by using alternative fuels and raw materials (AFR), the production process becomes more economical, primar y raw materials and fuel resources are conser ved, and landfill volumes are reduced.
AFRs AFRs consist of whole and shredded tyres, waste timber or mixtures of plastics, paper, compound materials or textiles whereby their calorific value hardly differs from that of lignite (brown coal). The value of old tyres is even comparable with coal. But the use of these alternative fuels has pitfalls. They must be processed prior to use in such a way that they do not influence the later production process and the quality of the cement.
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A radar level measuring instrument that performs in challenging conditions. transmitters, capacitive measuring instruments and vibration limit switches) for over a decade. Cementos Molins needed a solution for the storage silo that contained AFR. With a height of more than 20 m and a diameter of 9 m, the storage silo has an unusual agitator on the inside floor of the silo, which consists of very sharp, vibrating knives to grind the waste continuously. About 35% of the fuel in the plant that is required for the later production of cement comes from alternative fuels. About one tonne of AFR material is unloaded into the silo per hour. The trucks loaded with waste must be completely emptied so the capacity in the silo must therefore be sufficiently great to hold a complete truck load. Level measurement provides protection against the threat of over filling and being empty.
Cementos Molins
Challenges with measurement when filling the silo
The Barcelona subsidiary of construction materials company Cementos Molins has used a range of Vega sensors (pressure
AFR materials stick very easily. Furthermore, when filling the silo from the trucks, a cloud of dust forms – creating heavy deposits on the
IMIESA May 2022
sensor and making measurement extremely difficult. During simultaneous stirring and chopping, a 2 m high wave of material is pushed along in front of the agitator blades. The stirring itself also generates a cloud of dust in the container that never settles due to the vibrations. This dust influences the technology and measurements. The previously installed 26 GHz radar sensor with horn antenna from another manufacturer created many issues. The dust stuck to the horn antenna and caused false measured values. The constant vibrations caused by the cloud of dust made reliable signals possible. Furthermore, the metal particles from the Tetrapaks in the silo also caused false signals in the sensor. Metal particles from Tetrapaks can create interference signals due to flying metal foils.
VegaPuls 69 Vega’s 80 Ghz radar level measuring instrument promises a much more reliable operation because of the higher focusing of the medium. At that time, a few test measurements had already been made in comparably difficult measuring situations. It
