Use of a pre-coat filter for filtrate of rotary vacuum filter in double sulphitation plant

In the double sulphitation process, the filtrate from the rotary vacuum filter is added to mixed juice. This leads to recirculation of impurities resulting in increased consumption of clarificants, inversion of sugar, development of colour, reduction in capacity of equipment, and suppression in quality of sugar produced. Process managers have always desired to avoid this recirculation, but treatment of filtrate by flotation process or settling failed to give desired results. Filtration is unsuccessful as suspended impurities clog the filtering media within no time. The authors have successfully developed and tried a continuous filtration equipment employing the use of filter cloth and diatomaceous earth. The equipment continuously provides fresh filtration surface, overcoming the problem of clogging. The filtrate is clear enough to be forwarded to evaporators along with clear juice, and all disadvantages of impurities recirculation can be minimised.