Scouring liquor is discharged from the bowl bottoms to the dirt recovery devices via a fibre strainer or wedgewire screen. These are needed to remove wool fibre in order to prevent blockages in both pumps and the recovery devices. A high flow of liquor from the bowl bottoms is needed to prevent the hoppers being blocked with dirt and anaerobic conditions from developing in the scouring bowls. Currently hydrocyclones are preferred to the settling tanks as the dirt recovery devices for a number of reasons that include negligible heat loss, lower capital costs, higher dirt separation efficiencies, shorter time to reach equilibrium conditions in the bowls, smaller installation footprint, and location next to the scouring bowls.

The dirt enriched underflows from the recovery devices, along with sludge discharges from the wax recovery plant, can be dewatered by a decanter centrifuge to produce a sludge containing 30-40% solids.

Dirt Recovery Loop         

Hydrocyclone Loop