Dust Control Handbook for Industrial Minerals Mining and Processing

Figure 1.13. Depiction of the horizontal and vertical velocityrelationship in a modified low-velocity system.The MLV system contains all the advantages of the low-velocity system relative to low abrasion,reduced maintenance, reduced power, and stability of the system balance. At the same time, itdoes not require the space-consuming sawtooth installation. Duct size (diameter) is acompromise between the high- and low-velocity systems, since velocities in all trunk lines willbe somewhere between the two. Another advantage of the MLV system is that it can readily beused in extensions to, or modifications of, existing high-velocity systems. Only under certainconditions can it be used in an extension of a low-velocity system. One would need to comparevelocities at the connecting points, recognizing that it is not feasible to move from a higher to alower velocity within a duct. A low-velocity extension can, however, be made to a MLV system.The basic design tips for low-velocity systems as detailed previously can be applied to MLVsystems, with a few exceptions:1. The reference to avoiding horizontal ducts does not apply.2. Orifice plates or blast gates should be installed at the top of the low-velocity vertical leg,not the bottom. Plates/gates should be as near to the higher-velocity leg as possible.3. Vertical leg velocity should be 1,000 to 1,200 fpm.4. Horizontal leg velocity should begin at a minimum of at least 2,000 fpm.Fundamentals of Dust Collection Systems 27