During the production of cement, lime and gypsum hard conditions exist in the proper sense of the word. Industrial fans are especially exposed to extreme requirements during these applications (Fig. 1). The dust-containing gases are transported under extremely hard ambient conditions. The flowing-through mixture of gas and dust contains highly abrasive particles leading possibly to early material fatigue and – in the worst case – to the complete failure of the installation. Sedimentation on one side and component wear on the other side represent a real challenge for all mechanical parts, above all for the moving ones. Not to speak of the operating temperatures being able to reach up to 405 °C.
Rotamill Anlagen- und Ventilatorenbau GmbH manufactures fans ranging from small sealing air blowers with low driving power to cooling air fans belonging to the middle performance range down to process gas fans having a driving power of up to 6,5 MW and with an impeller diameter of 4200 mm.
The high working temperatures in the cement industry and the heterogeneous composition of the dust-gas mixture represent extreme requirements for each fan and thus a real challenge to the fan construction. Thus Rotamill equips the fans with a special material contributing essentially to minimize the wear and tear. Moreoever, the shaping, the geometry and the angle position of the impeller blades oppose the risk of wear and tear and failure. Here particular attention has to be paid to the repose angle of the transported solid matter. Therefore the blade angle should always be bigger than the repose angle to guarantee an optimal production process.
“That’s why it is important for the process gas fans to carry out an optimal aerodynamic design of the fan in order to guarantee a free-from-defect operating efficiency”, comments Mr. Christian Pohl, Business Development Manager at Rotamill. Furthermore, wear and tear protective systems such as hard-wearing sheet metals, powder coatings and composite armour plates with different carbide compositions as secondary protective measure are imperative alongside the aerodynamic construction. The Rotamill engineers do use a layer thickness of up to 5 mm and a surface hardness of up to 65 HRC.
In order to keep the wear and tear of the impeller and the housing during operation as low as possible, an optimal suction speed has also to be obtained. In general, low suction speeds guarantee a low wear and tear of the impeller and the housing. Speeds of up to 25 m/s would be optimal but cannot be put into practice. To obtain a maximal speed with a minimal wear and tear but a constantly high efficiency degree, the Rotamill team of engineers has developed special wear and tear solutions making a best possible suction speed of up to 50 m/s possible
Here the relative loading of the media as well as the composition of the grain size play a vital part and are of major importance. In order to avoid sedimentation and congestion of solid matter particles in the pipes, the Rotamill engineers attach great importance to reduce the number of bends to a minimum in the pipe system.
Rotamill industrial fans are equipped with a variable speed drive whenever possible. In case of variable speed drives with frequency converter the speed is adapted to the current requirement and thus no energy is wasted. The fan is always running in the optimal performance range. “By means of intelligently driven fans, we can achieve savings up to 60 %, in extreme cases, e. g. energy-intense applications up to 70 %”, Mr. Pohl comments. “Other regulation procedures are inappropriate for the area of solid matter transportation because especially with inlet vane controlling not defined zones of cakings and/or wear and tear do appear. Another advantage of this regulation procedure consists in the fact that the fan does automatically lower its sound emission when it is run in part load.
Another emphasis is put on the realization of an under construction with minimum torsion (Fig. 2). Only a system synchronizing in an optimal way impeller, bearing and foundations leads to low vibrations of the components and stands for operational safety for the operator (Fig. 3). Depending on the application, all kinds of fat or oil lubricated rolling bearings are used.
Beside the development, the construction and the commissioning of the industrial fans on site, the Rotamill service team maintains the installations worldwide. On demand the Rotamill specialists take performance measurements to draw from these results conclusions in order to get optimisation potential for existing fans. With regular maintenance wear and tear can be detected in good time and defective parts can be exchanged.
Rotamill Anlagen- und Ventilatorenbau GmbH
Tel.: +49 / (0)271 / 66123-0
Fax: +49 / (0)271 / 61866