Every application and every process is different. In order to define the correct technology and the right instrument it is essential to analyse all different process parameters such as material properties, process temperatures, process pressure, process connections as well as the material of the silo or vessel, just to mention a few. The efficiency of an industrial plant is not only influenced by its mechanical and electrical installations, the appropriate planning, selection and engineering of the required overall infrastructure also play a critical role. Viewed as an integrated entity, the plant’s infrastructure also includes items like optimised measurement technology. The selection of the right technologies, their correct configuration and smart positioning will save substantial costs and add up to a significant improvement in the plants’ economic efficiency over its lifecycle.

Added value with innovative measurement technology

Cement based products have to meet specific project requirements. UWT offers a comprehensive package of solutions, products and services for the complete primary production chain for the cement industry. For example a level limit sensor has to cope with low bulk density, bridging, caking, abrasiveness, corrosion, leverage forces, high and low process temperatures, electrostatic charging and so on. Thus rotating level limit switches of UWT have been designed to meet the challenges, which are known to arise in the different plant processes and can cope with continually changing conditions and extreme applications. The rotating paddle switch can be used as full, demand or empty detectors in silos or containers. The trusted, multifunctional and maintenance free unit for level monitoring of bulk goods is versatile and has a modular design. The electromechanical measuring principle of the rotary paddle switch is simple: A motor driven shaft causes the vane to rotate; once the material level reaches the vane any further rotation is prevented and the torque converts the switching mechanism into an electric signal. When the vane is once again free of material the output signal is reset and the motor driven shaft rotates again.

A major cement producing company round the southern regions of Asia that manufactures and sells cement and clinker to the domestic and export markets was looking for measurement solutions for the different processes and materials during cement production. For their high strength cement the finest quality of limestone is used and state-of-the-art technology is deployed. The cement production process begins at the quarry where the raw materials (limestone and clay) are checked and evaluated to ensure that they are suitable for use. The mining process is made up of the follow steps: drilling, blasting, loading and transport of the raw materials to the crusher. The crushing process reduces the size of the extracted rock down to a size that is suitable for conveying and feeding to the grinding process. The crushed raw material is transported from the quarry on a conveyor belt; before being stored in the pre-homogenisation beds the material is checked using special online analysis equipment.

Raw materials are stored in two horizontal piles and extracted by cutting vertical slices. The entire process is aimed to ensure uniformity of the material. The extracted pre-homogenized material is transported to a silo, which feeds the raw meal mill. Then additives such as iron minerals, limestone or sand are added to the mix. The raw material, which has a maximum size of about 10 cm, is then fed to the raw grinding mill. This is generally a vertical mill with 3-4 rollers and a rotating table. Material is dragged under the rollers and is simultaneously dried and pulverized. The pulverized material is transported by the hot gases coming from the kiln system to the filters, where it is separated from the hot gas and conveyed to the homogenization silo. There, it is further homogenized to reach the ideal chemical composition that will be used for clinker production. Inside this silo the customer required robust sensors as measuring principle, which could cope with the heavy and abrasive aggregate material inside.

UWT suggested their tried and tested rotary paddle switch Rotonivo® of the RN 3000 series. This extremely reliable level switch is perfectly suited for the demanding cement applications for full and empty detection. The paddle limit switch provides very precise level limit detection as the sensor is unaffected by dust, humidity or build-up of adhesion. The Rotonivo 3000 high temperature models can handle process temperatures of up to +1100°C and – depending on the given conditions – the units are equipped with the necessary sealing (Viton, Teflon, ceramics). Further the Rotonivo 3000 is equipped with an integrated rotation control, which recognises a fault of the unit and immediately initiates an alarm. The ease of use of this maintenance free measuring device makes for a fast and easy installation, which can be carried out by the plant operator. There is no need for further maintenance and is easy to handle for the plant operator. The PNP electronics of the Rotonivo RN 3000 series uses 3-wire electronics technology with a non-contact output, open collector and PNP. These electronics can be connected to any standard PLC with 24 V DC power supply and PNP input card.

Supporting solutions for several cement processes

An electrostatic precipitator (ESP) or electrostatic air cleaner is a particle collection device that removes particles from a flowing gas (such as air) using the force of an induced electrostatic charge. The hot gas from the clinker process is lead back to the raw mill and is cleaned in the ESP. Once the cleaning process is completed it is discharged. The rotary paddle switch Rotonivo RN 3004 was used to solve the demanding limit detection in the filter dust hoppers and homogenize silos due to the robust design of the extension, which can withstand extremely high loads. The sensor features a sturdy shaft with a ball bearing and a robust aluminium die-cast housing. After the clinker burn process is completed the clinker is transported from the clinker cooler to the storage silos or halls from where it is later fed to the clinker grinding mills. The paddle switch Rotonivo was also the perfect solution for the limit detection in the clinker storage silos, as the sensor is not affected by material deposits or electrostatic charge. Even for the level limit detection in mixing hoppers where aggregates are dosed and compound, the Rotonivo 3000 models could be mounted without problems because they are insensitive against vibrations due to the separate electronic housing.

The final process is the dispatch of the finished product. When the customer purchases cement in bags, the packing operation is performed with packing machines that automatically fill the bags (normally 25, 40 or 50 kg capacity) and drop them to the transport conveyor, for direct delivery to customer vehicle or to a palletizer, which allows the product to be packaged, stored and loaded on demand. When the customer purchases bulk products, the cement is fed from the silos directly into the tank of the appropriate means of transportation used for shipping such as a truck, train or ship. The Rotonivo RN 3005 functions in this case as full-limit detector and is used as overfill protection. The device immediately stops the fill process when the appropriate container signals full. Especially for loading bellows the paddle switch has the advantage of an extremely fast reaction time during filling. The complete Rotonivo range boasts numerous international certifications such as ATEX, FM, INMETRO, TR-Cu-Ex, NEPSI to name just a few which testifies that the sensor conforms to regulations for use in hazardous areas all around the world.

Contact: Rahul Rathore, UWT Level Control India Pvt Ltd, Gurgaon. Tel: 0124-4121684. Mobile: 097172-03939. Fax: 91-124-4121611. Email: Rahul.rathore@uwt-india.com