D-1200Decanter Centrifuge

How it works

1. The idea — Gravity gives a particle 1 g and a settling tank gives it hours. Spin the tank instead and the same particle feels two to three thousand g — it reaches the wall in seconds. Everything else about a decanter is housekeeping around that one fact.
2. Sigma and the cut point — The bowl is rated by sigma, the area of a gravity settler that would do the same job — tens of thousands of square metres from a machine the size of a car. What sigma actually tells you is the cut point: the particle size below which solids leave with the centrate. Watch it move as the speed changes.
3. Polymer is the process — Settling velocity goes as the square of diameter. Raw sludge floc is a few microns and would be lost entirely. Polymer builds it to 50–200 µm, which is four orders of magnitude of settling velocity. Drag the floc size down and watch capture collapse — that is an under-dosed machine, and no amount of G-force rescues it.
4. The beach — Past the pool the bowl narrows into a cone. The scroll pushes cake up this beach, clear of the liquid, where it drains before it is discharged. Deepen the pool and the centrate gets cleaner, the beach gets shorter, and the cake comes out wetter. Every setting on a decanter sits somewhere on that trade.
5. Residence time — Below about 20 seconds in the pool, solids never reach the wall however hard you spin. This is the check that catches an over-fed machine, and the one most often skipped because G-force is the number everyone quotes. Push the flow up and watch the flag.
6. Counter-current — Feed enters part way along the cylinder and the centrate travels back over the settling zone to leave at the far end. Simple, and every published performance curve assumes it — but at high loading the returning liquid scours solids it has already deposited.

Design parameters

The panel opposite runs the same correlations as the D-1200 design sheet, so the animation and the calculator cannot disagree. Every parameter below is live — drag one and the picture responds.

Open the full D-1200 design sheet for the other one inputs, all thirty-two results with their envelopes, the six equations printed beside the numbers they produce, and a calculation record you can export and put in a design file.