Dirt - its implications for the clarifier and filter stations

This paper examines the effects on the clarifier and filters of the high dirt loadings that are occurring, particularly in the northern mills. Results obtained from investigations of options available to mills to maintain satisfactory clarification performance during periods of high mud solids loadings are presented. Of those options, the addition of extra flocculant will assist in maintaining an acceptable settling rate and the addition of extra phosphorus to the juice will reduce the turbidity of the juice. High pH levels will not provide any benefit in clarification performance. Another option proposed is recirculation of clarified juice to the clarifier feed. Options that can assist in maintaining the mud solids output at the filters include increasing the drum speed and adding flocculant to the filter feed. However, the success of these options relies on the fibre ratio being maintained. It is demonstrated that poor retention at the filters can compound the difficulties occurring in the clarifier from high mud solids loadings.