Pusher centrifuge is a continuous filtering type centrifuge used for solid-liquid separation in the chemical and mineral industries. Pushers have been used for more than 60 years for dewatering relatively large, free-draining crystals. The pusher centrifuge has a unique design that minimizes moisture, impurity and crystal breakage in discharged cake. In this paper, the operation of the pusher centrifuge will be discussed. Scale-up variables and design will be briefly addressed and applications and advantages of the pusher centrifuge will be described.
Centrifugal devices, often used to achieve quick and efficient solid-liquid separation, work on two basic principles: sedimentation and filtration. Sedimentation or settling involves allowing the heavy phase to fall through the light phase and collect on an imperforate surface and typically involves fine solids with long settling times. Examples are decanters, disk nozzle centrifuge, etc. On the other hand, filtration depends on the particle size being large enough to build a cake on a filter cloth or a screen. The cake must also be porous enough to allow mother liquor to flow through it. Examples are pusher, peeler, vibrating screen centrifuge, etc.
Various types of centrifuges are manufactured, and each type of centrifuge has certain advantages over a specific range of process variables. Figure 1 shows the range of variables where the pusher centrifuge is generally used. The pusher centrifuge feed has 25-65 wt.% solids concentration of large free draining crystals (typically 80% retained on 150 microns). For most applications, these particles are crystalline in nature, but non-crystalline materials have been successfully dewatered on the pusher centrifuge. These particles must be distinct, free draining and the liquid must not be chemically attached to the solids, i.e., waters of hydration.
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