Cement Americas

WIN 2016

Cement Americas provides comprehensive coverage of the North and South American cement markets from raw material extraction to delivery and tranportation to end user.

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6 CEMENT AMERICAS • Winter 2016 • www.cementamericas.com FEATURE In order to help the cement industry meet the special requirements for handling abrasive materials, Coperion has developed the DuroProtect group of rotary and di- verter valves. Components with the DuroProtect option enable Coperion to reliably convey all powder bulk ma- terials in a cement plant, including raw meal, by-pass dust, clinker, cement, fy ash, petcoke, lignite and plas- tic fuff. The blow-through rotary valve ZXQ, for exam- ple, is designed to achieve conveying capacities of over 220 tph for bulk materials like cement. WEAR TYPES AND MECHANISMS Extensive testing has shown that erosive wear is the main type of wear in rotary and diverter valves. Materi- al properties such as particle shape, size and hardness are key factors that lead to erosive wear. Based on de- tailed research, Coperion engineered three wear-pro- tection designs proven to have signifcant impact on the lifespan of rotary and diverter valves when han- dling abrasive materials. FEEDING TECHNOLOGIES IN PNEUMATIC CONVEYING SYSTEMS Screw pumps and pressure vessels are the traditional feeding technologies used in pneumatic conveying sys- tems in the cement industry. Rotary valves are also a well-known technology for feeding bulk materials into a pneumatic conveying line. In mineral applications, such as the cement industry, the use of rotary valves is limit- ed because they are subject to high wear. ROTARY VALVES IN GENERAL A rotary valve is a continuous rotating feeding device, which creates a barrier between the non-pressure feed- ing side and the pressurized conveying line. Rotary valves have a very tight clearance between the housing and the rotor, resulting in very low air leakage. There are two different types of rotary valves available on the market, which are applicable for pneumatic conveying systems. A drop-through rotary valve (Figure 1) can be used for system pressures up to approximately 14.5 psi for grain and powders. For conveying pressures above 14.5 psi and high conveying capacities, it is recommend- ed to use a blow through rotary valve (Figure 2) which has a higher pressure rating, especially for powders, and features better emptying of the rotor pockets. WEAR LOCATIONS IN A ROTARY VALVE A drop-through rotary valve has various potential locations for wear, which can negative- ly impact the performance of the rotary valve. These wear locations can be seen in Fig- ure 3. The inlet (Location 1) is subject to high wear from the upstream leakage air from the conveying system. Particles destroy the surfaces of the housing and the rotor which leads to an increase of the gap between them (Location 2). In the area between the sealing system and the shaft (Location 3), it is possible for wear to destroy the shaft and/or the sealing system. In addition to the abovemen- tioned wear locations (Lo- cations 1 to 3) in the drop- through rotary valve, the blow-through rotary valve has an additional wear point which is the blow through channel itself (Location 4). This channel can be worn down by the material being conveyed due to the high conveying velocities at the pick-up point. Pneumatic Conveying Using Wear-Resistant Rotary And Diverter Valves To Help The Cement Industry Meet Requirements For Handling Abrasive Materials. By Keith Kressley, Gary Werth and Frank Speck Figure 1: Drop-through rotary valve. Figure 2: Blow-through rotary valve. 1 2 3 Figure 3: Wear locations on drop-through rotary valve. 1 2 3 Figure 4: Blow-through rotary valve wear points.

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