Disc Stack Machine

If the solids are retained in the roachine the sludge capacity becomes important, and this varies with machine size ffom 0.8 to 23 1 for bowl diameters between 0.24 

The liquor to be clarified flows between closely spaced conical discs from the outside to the axis. A parabolic velocity distribution exists between the discs and the.particles settle to the underside of the discs by virtue of the radial centniugal force, settling from the high-velocity zone to 4lere the velocity is zero. Thus the settled solids slide down the underside of the discs and into the chamber outside the disc. If a is the distance between the stacks and n is the number of stacks  

These two expressions for residence time, after integration, can be equated in a critical particle trajectory analysis similar to that described in Section 8.2.2. When considering only 50% capture of particles the volumes processed now have to be related to the area of a ftustum (a truncated cone), the start radius being that value that has equal volumes of the section between each disc above and below it. The resulting expression for sigma (machine parameter) is  

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Decanter centrifuges are well suited to high solids concentrations at feed rates between 1 and 100 m3/hr. They cannot achieve such high standards of separation as a disc stack machine, and are more difficult to engineer as truly hygienic or contained units. They are suitable for continuous operation and can discharge solids continuously. 

The disc stack centrifuge is a versatile device, which may be used for separating sohd/hquid mixtures in continuous, semi-continuous and batch configurations (see Figures 1.12 and 1.13). All except some batch-operated machines are able to handle toxic, flammable and volatile feeds at throughputs up to 200 m h k... 

The original type of disc-stack centrifugal separator is the solids-retaining machine, used on liquid-liquid or Uquid-solids separation when the solids content in the feed... 

The disc-stack centrifuge with continuous solids discharge is called a nozzle discharge machine. The special nozzles mounted in the periphery of the bowl allow for continuous operation with a liquid-Uqnid-soUd feed, separating this mixture into two relatively clean liquid streams and a thick solids suspension. The concentration of this solids discharge can be controlled to meet process requirements. 

The disadvantage of the disc machine lies in the clogging problem. Trash in the sludge and unexpected power failures can cause clogged internals, and cleaning die machine is a tedious process. The stack must be disassembled one disc at a time. 

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