A technical assessment of a new continuous ion exchange decolourisation plant at the Tongaat-Hulett Rossburg refinery

Abstract

The Tongaat Hulett sugar refinery in Durban has recently commissioned a continuous ion-exchange (CIX) plant which has become a third ion-exchange stage in its sugar refining process following the existing two fixed bed (FB) batch ion-exchange stages. The plant will initially be evaluated and optimised as a third polishing stage using styrenic resin but the design is such that the plant can be operated as any stage with either acrylic or styrenic resin. The installed CIX plant consists of 30 resin vessels containing 1.3 m3 of resin each and has been designed to process up to 180 m3/h of refinery liquor. At the heart of the CIX plant is the Tongaat Hulett / IONEX Separations RDA technology, which has several advantages over the conventional carousel-based continuous ion exchange systems. The plant was commissioned in November 2018 and has operated with time efficiency to date above 98%. The CIX plant has 61% less resin inventory than the Fixed Bed plant. The colour removal efficiency is comparable for both systems. The CIX plant is using 71% less water per day than the FB plant and consumes 65% less chemicals. The CIX plant is producing on average 67% less effluent and 85% less sweetwater than the FB plant per day. Part of this remarkable performance is linked to water recovery design that was incorporated into the CIX plant. Modelling of the CIX plant operating as a first ion exchange stage, showed that there would be 31% reduction in water usage compared to the current first stage and about 11% reduction in effluent generation.