Krauss-Maffei pusher centrifuges run in continuous operation. The product is fed through a feed pipe (or feed screw in the case of products that do not flow freely) into the feed distributor, which rotates with the basket. This accelerates the slurry and feeds it with uniform distribution to the feed zone, where the greater part of the liquid (approx. 80%) is filtered. In the feed zone, the solids form a stable filter cake ring. The filter cake is conveyed in the direction of the solids discharge stroke by stroke due to the relative axial movement between pusher bottom and screen basket. During this process, an intact filter cake forms over the entire length of the screen. As the filter cake progresses from the feed zone to the solids discharge, it can be washed, as required. For this purpose wash liquor is applied to the cake surface, displacing the suspension liquid and any impurities. Multi-stage washing is also possible, with several successive washing zones. Multi-stage centrifuges with several baskets loosen the filter cake and reshape it by moving it from the inner basket to the next larger basket. As a result of this re-shaping process, moisture that collects between the particles is exposed and filtered. The solids are discharged at the end of the basket after each pusher movement.
In order to optimize the machine size and achieve maximum operating reliability, it is important to provide uniform and concentrated slurry feed. As the upstream equipment, such as crystallizers or reactors, frequently do not meet these requirements satisfactorily, a pre-thickener system is usually applied. This system evens out fluctuations in the feed conditions and minimizes the hydraulic load of the centrifuge. As a result a smaller machine size is often selected. Stationary or dynamic units have become established as pre-thickeners, depending on the type of application. Examples of stationary equipment are sedimentation tanks and thickener filters, while possible dynamic equipment includes curved screens, hydrocyclones, vibration screens, and EC screen thickeners. In stationary thickeners, a metering unit is required to control the feed to the centrifuge, and in dynamic thickeners, the feed to the thickener must be monitored.
Alternatively, an integrated pre-thickening stage can be offered, which makes the machine less sensitive to changes in feed conditions and opens up a wider field of applications.
The feed system has the most significant impact on operation of the centrifuge. Uniform distribution of the slurry is the basic requirement for trouble-free operation of the centrifuge.