THE THROUGHPUT capacity of a clarifier is based on its ability to perform the
two-fold functions of clarifying the juice, and thickening and removing the
settled mud at a rate to match the factory throughput. The high throughput rates
and low residence times that are achievable with the new generation clarifier,
have focussed attention on the need to improve the settling and thickening
characteristics of the mud, and its handling and transport properties in the mud
thickening zone. As juice rates increase, the residence time of the mud must
reduce to maintain satisfactory mud levels in the mud zone. This places more
emphasis on the ability of the mud scraper designs to thicken the mud to an
acceptable consistency and to transport the mud towards the centre mud cone in
a significantly reduced time. The investigations into the factors affecting mud
thickening have been conducted using pilot tests and two factory clarifiers of
similar size. One of the clarifiers was a standard design and the other was a
modified design incorporating the new generation technology. There appears to
be a maximum mud density that can be achieved in the clarifier and this is
achieved within 30 minutes. The final density is not dependent on either the
depth of mud or the addition rate of flocculant. The results obtained with a
settling tube were similar to those obtained directly from the clarifiers. Tests
with the settling tube indicated that final mud densities will be lower if the rakes
extend the full depth of the mud layer and into the juice. The largest increase in
mud density was achieved when a maximum number of rakes was used provided
all rakes remained below the level of the mud-juice interface. The speed of the
rakes did not affect the final mud density.