- Unequalled flexibility
- Lower residual cake moisture
Excellent wash results
The suspension is introduced into the rotating centrifuge basket via the feed distributor. Typically, this would include several intermittent feed pulses to prevent the suspension from spilling over the basket rim. The fill level is monitored and regulated by a feed controller. Normally, the basket is filled with solids up to 75-80% of the basket rim height. The feed step is complete when the filter cake has reached the desired level.
Primary filtration of the mother liquor through the filter medium installed in the basket begins with the feed step and ends when the liquor has submerged into the filter cake. The solids retained on the filter medium after completion of a cycle and discharge of product serve as a filter medium for subsequent cycles.
A cake wash step will often follow the primary filtration step. Wash liquid is introduced through the feed distributor or, for lower wash rates, through a separate spray bar. The wash liquid level is again monitored by the feed controller and the wash step is concluded once the pre-determined amount of wash liquid has been used an the liquid submerges into the filter cake.
Immediately following the feed and wash step, which may be carried out at a lower speed, the basket is accelerated to maximum allowable speed for the cake dry spinning step which ends when the desired residual cake moisture is reached, or after a predetermined spin time.
At the end of each centrifuge cycle, the filter cake is removed from the basket by a pivoting peeling device equipped with a broad peeler knife. Depending on the product characteristics, the peeling motion is conducted at full or reduced basket speed with adjustable swivel advance velocity. The scraped layers of product are diverted into a trough and discharged from the centrifuge trough an inclined chute or a horizontal screw conveyor. To protect the filter medium, a thin layer of filter cake is retained in the basket. This layer, called the residual heel, becomes the filter aid for subsequent cycles.
With the rotary siphon basket it is possible to feed backwash liquid from an overhead mounted prime tank through the siphon chamber to permeate the residual heel from underneath. This process re-suspends the residual heel and restores its permeability. It also primes the rotary siphon for the next filtration cycle. The liquid pool on top of the heel created through backwashing wil assist in evenly distributing the subsequent cycle's incoming suspension, which will virtually eliminate the potential for imbalances during the feed step.
After frequent cycles, the residual heel may have compacted with enough fine solids to make it impermeable, resulting in poor filtration performance. When this occurs, the heel may be regenerated (by backwashing in siphon peeler centrifuges) or removed pneumatically or hydraulically (in peeler centrifuges with filtration baskets).
In both procedures, the heel is removed at low basket speeds to prevent tearing of the filter medium. The hydraulic heel removal step has the added advantage of simultaneously cleaning the centrifuge interior. The most suitable procedure wil depend on the specific application.