Aggregates Manager

April 2014

Aggregates Manager Digital Magazine

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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.

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