There two ways of organising the contaminant recovery systems, namely in series or in parallel. In a serial arrangement, the scouring liquor is taken from the hopper bottoms and passed through the dirt recovery devices before progressing to the wax recovery system. In a parallel arrangement the dirt and wax recovery systems operate independently. The latter has a number of advantages compared with the former. First, the performances of the individual recovery devices can be optimised. First, the take-off points can be optimised. Obviously the best take-off point for dirt recovery is from the hopper bottoms because the levels of dirt are higher. The best take-off point for wax recovery is a quiescent zone towards the top of a bowl because the recoverable component of the scouring emulsion is more likely to be found in this region and there are fewer erosive dirt particles present.

Serial Arrangement of Recovery Devices                  Parallel Arrangement of Recovery Devices

In modern scouring lines all discharges from the hopper bottoms of the bowls and side bowls are controlled by computer in order to optimise dirt removal and to prevent blockages. It is common practice to have dirt recovery loops, using hydrocyclones of different sizes, on individual bowls.

Some scours have wax recovery systems connected to just one bowl (first scouring bowl) whereas others have one to three bowls connected either to the one system or to several systems.