Aggregates Manager

April 2014

Aggregates Manager Digital Magazine

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AGGREGATES MANAGER April 2014 20 H ydrocyclones have traditionally been used for classifying, but they can also be used to produce a thick, dewatered underfl ow. is can be accomplished in two diff er- ent approaches. e fi rst approach uses a traditional hydrocyclone with key parameters altered to achieve the desired percent of solids in the underfl ow. is method can be used for dam building, with the coarse, underfl ow being used to help form the wall. Sometimes called a separator, the second approach modifi es the traditional cyclone. ese modifi cations still allow the cyclone to perform a predictable clas- sifi cation while producing a stackable material. Both approaches will be covered with a review of the advantages and disadvantages. Roped discharged dewatering is method consists of purposefully "roping" the hydrocyclone discharge. Roping occurs when the air core is unable to form due to an excessive amount of material in relationship to the spigot/apex opening. Under normal cyclone operation, the air core is essential to the classifi cation process (Figure 1) and a spray discharge (Figure 2A) is formed. e percent of solids in the underfl ow is normally in the range of 42 to 50 percent by volume. rough changing the spigot/apex opening, the actual underfl ow percent solids can be adjusted to a target range (which can be lower than 42 percent by volume). When a cyclone is operated with a spray discharge, the underfl ow is not suffi ciently dewatered to form a stack of material. Stepping away from the traditional method of operating the cyclone, further dewatering can be achieved by reducing the spigot/apex opening or roping (Figure 2C). is creates a choke point at the discharge that preferentially allows the solids to continue and forces the liquids toward the vortex fi nder. e percent of solids by volume range is increased to 52 to 56 percent, and this allows the underfl ow to be stacked into a pile. e main advantage of this approach is that it does not require any additional components to the hydro- By understanding the various methods of dewatering, an operator can select the best option for an operation. by Alan Bennetts Cyclones can be mounted to radial stackers or other structures to increase the capacity of the stockpile. Dewatering with Hydrocyclones

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