Centrifuges and Cyclones Reading Materials: Perry’s Handbook, Chapter 18 M. Rhodes, An Introduction to Particle Technology, Chapter 7

What are they?

Basic designs of industrial centrifuges, showing the flow of material within the bowls. Motor drives, cooling jackets. (a) Tubular bowl centrifuge. This is generally operated vertically, the tubular rotor providing a long flow path enabling clarification. The sludge collects and must be removed.

(b) Continuous scroll centrifuge (Decanter). This is operated horizontally. The helical screw scrolls the solids along the bowl surface and out of the liquid; the sludge being dewatered before discharge. The clarified liquor overflows over an adjustable weir at the other end of the bowl. The screw conveyer rotates at a slightly different speed to the bowl.

Continuous scroll centrifuge (Decanter).

(c) Continuous multi-chamber disc-stack centrifuge (c) Continuous multi-chamber disc-stack centrifuge. The bowl contains a number of parallel discs providing a large clarifying surface with a small sedimentation distance. The sludge is removed through a valve.

Continuous multi-chamber disc-stack centrifuge: .

Angular Speed and tangential velocity The acceleration of a centrifuge is measured in "g forces", one g force being equal to the normal acceleration of gravity on earth, 9.8 m/s2. The angular speed can be found by using the following formula: ω2 = ac/r, or a = rω2 ω being the angular speed in radians per second, ac being the centripetal acceleration, and r being the length of the arm of the centrifuge. u = r denotes the corresponding tangential velocities. ω2 = a/r, or a = rω2  a = rω2 =r (u/r)2 = u2/r

(between r1 to r2)

Centrifuge ω = 5000 rpm r = 0.2 m

= Qout (solids)/Q(in)=v*A(2πrx)/Q

Recovery is also can be given in this form

Unit (meter square!!?)

Under laminar flow

Particle Tracing

Volumetric Separated particle diameter Particle diameter

Design Correlation

= 18µm