Disc-Stack Separator

Overview

A disc-stack separator is a high-speed centrifuge that clarifies a liquid or splits it into two liquid phases using a stack of closely spaced cones. It spins faster than any other food centrifuge, up to 10,000 rpm, reaching ten thousand times gravity or more. That force, combined with the very short settling distance between the discs, lets it separate particles down to half a micron and split phases that differ in density by only a few percent. Dairies use it to skim milk and standardize cream, breweries and wineries to clarify, and oil refiners to separate oil from water.

The defining component is the Disc Stack, a nest of conical discs that divides the bowl into many thin channels. A droplet or particle in any channel only has to travel a fraction of a millimeter to reach a disc surface, instead of crossing the whole bowl, so separation that would take hours by gravity happens in a fraction of a second.

How it works

Feed enters down the stationary Stationary Feed Pipe into the spinning Feed Distributor, which accelerates it to bowl speed and routes it to the bottom of the Disc Stack. The liquid then flows up through the aligned Rising-Channel Hole Set that form vertical channels through the stack, spreading sideways into the thin gaps between each Conical Separation Disc.

Inside those gaps the centrifugal field does the work. The heavy phase, whether solids or the denser liquid, is thrown outward and slides down the underside of each disc to the bowl periphery. The light phase moves inward and up. Because the discs split one big settling space into dozens of thin ones, the effective settling area is enormous. The clarified light phase rises to the Light Phase Outlet, and in a two-liquid separation the heavy phase exits separately at the Heavy Phase Outlet. A Paring Disc (Centripetal Pump), a stationary impeller dipping into the spinning liquid, converts the rotation into discharge pressure so the phases leave under pressure without foaming.

Self-cleaning bowl

Solids collected at the bowl periphery have to be removed. In a self-cleaning Bowl Assembly this happens without stopping. The Operating-Water System system sends a timed pulse of water beneath the Sliding Piston, driving it down so the Sediment Ejection Port around the bowl periphery open for a fraction of a second. Centrifugal force blasts the accumulated solids out, then the piston rises and the bowl reseals. The whole ejection takes well under a second, and the Control System schedules it on a timer or on a turbidity reading so production barely pauses.

Disc stack detail

Each Conical Separation Disc is a thin stainless cone, typically 0.4 to 0.6 mm thick. The gap between discs is set by Disc Caulk (Spacer Strip) caulks, narrow strips welded radially to each disc that hold the next disc the correct distance away. A wider gap suits viscous or solids-heavy feed, a narrower gap gives finer clarification. The Top Disc caps the stack and helps define the boundary, the dividing line where the two liquid phases meet, which the operator tunes with a ring gravity disc to set the split.

Spindle and high-speed bearings

Spinning a heavy bowl at 10,000 rpm demands careful bearing design. The bowl rides on the vertical Bowl Spindle, supported by a Flexible Neck Bearing at the top mounted on Coil Spring springs and damped so the bowl can find its own rotational center as it accelerates through critical speed. The Bottom Bearing locates the lower end. The springs let the assembly tolerate the small inevitable imbalance without transmitting damaging vibration into the Frame Casting.

Drive system

The Drive System must bring a heavy bowl up to full speed gently to avoid stalling the motor or shock-loading the gears. A Centrifugal Friction Clutch of the centrifugal type does this: at startup the Clutch Shoe shoes slip, so the Drive Motor accelerates first and then progressively engages the Clutch Drum, easing the bowl up to speed. A Worm Gear Set speed-increasing set or a flat belt then drives the spindle to its final rpm.

Control and instrumentation

The Control System sequences feed, separation, and ejection. A Bowl Speed Sensor confirms the bowl is at full speed before feed is admitted, a Vibration Sensor trips the machine if imbalance grows, and Pressure Sensor units on the Operating-Water System line verify each ejection pulse fired correctly. The operator sets ejection interval and feed rate from the Operator HMI Panel.

Variants and use

A clarifier has one liquid outlet and removes only solids, used for polishing beer, wine, or juice. A purifier or concentrator has two liquid outlets and splits phases, used to skim milk or separate oil from water. Solid-wall bowls are used where solids are very low and an operator can stop to clean by hand, while self-cleaning bowls handle higher solids continuously. The disc-stack principle, many thin settling channels under very high g, is common to all of them.