Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/282830
EQUIPMENT MANAGEMENT 21 AGGREGATES MANAGER April 2014 cyclone, but it does have a number of disadvantages. First and foremost, it reduces the classiﬁ cation ability of a cyclone (Figure 3C). A roping discharge of the cyclone will still preferentially send coarse material to the underﬂ ow and ﬁ ne material to the over- ﬂ ow (through the vortex ﬁ nder), but the sharpness or eﬃ ciency is signiﬁ cantly diminished. Because of this, the roped discharge method of dewatering is best suited for tailings and primitive dam building. Another signiﬁ cant disadvantage with this method is feed ﬂ uctuations will directly aﬀ ect the performance. In a situation where the tons per hour of the solids decreases, the spigot/ apex may not be small enough to force the cyclone into a roping condition. e percent solids by volume of the underﬂ ow will decrease, and the underﬂ ow will become a spray discharge. e additional water in the underﬂ ow will reduce or eliminate the stackable nature of the material. e opposite situation is less of a concern. Since the spigot/ apex is already acting as a bo leneck for the solids, an increase in the tons per hour of the solids will force the excessive material into the overﬂ ow. High recovery of solids into the underﬂ ow should never be a major focus when employing this cyclone dewatering method. A third disadvantage of this method is a higher wear rate on the cyclone liners, especially the spigot/apex liner and the vortex ﬁ nder. Water siphon dewatering rough the addition of an extended overﬂ ow pipe, siphon break control, and a discharge regulator (aka ﬁ shtail, lipseal, or ﬂ apper), a hydrocyclone can be used to dewater solids and still perform a sharp classiﬁ cation. e extended overﬂ ow pipe is used to create a siphon through the vortex ﬁ nder. e siphon draws water and ﬁ ne material, and the length of the overﬂ ow pipe has an eﬀ ect on the amount of si- phon force created. When the overﬂ ow pipe is too short, a smaller amount of siphon force is created and decreases the ability to de- water the material. When the pipe length is too long, the siphon force will be too great. is will cause additional material to report to the overﬂ ow. Most overﬂ ow pipes are designed to extend 6 feet below the underﬂ ow discharge of the cyclone. To provide a level of control, the siphon break control panel can adjust the siphon force. With the siphon break completely closed oﬀ , the full siphon force is applied, resulting in the driest underﬂ ow and the highest amount of ﬁ nes sent to the overﬂ ow. If the siphon break is completely open, the least amount of the siphon force is applied. e additional water in the underﬂ ow will carry some of the ﬁ nes and may cause issues when stacking the material. e discharge regulator is designed to seal oﬀ the spigot of the cyclone to prevent an air core from being formed while allowing the material to discharge. Material will build up in the spigot until the weight of the material is enough to open the discharge regulator. Water alone should not be able to overcome the seal as long as the cyclone is operating between the range of 6.5-14.5 psi at the inlet. When operating outside of the pressure range of 6.5-14.5 psi at the inlet, the performance of the cyclone can become unstable. At low pressure, the slurry can alternate between heavy discharge Roped discharged dewatering takes place when the air core is unable to form due to an excessive amount of material in relationship to the spigot/ apex opening. By reducing the spigot/apex to create a discharge point that preferentially allows solids to continue, further dewatering can be achieved. A. Spray discharge B. Semi-roping discharge C. Roping discharge Figure 1 Figure 2 Image credit: Barry A. Willis, "Mineral Processing Technology," 5th Edition, 34.