GB1417344A - Recovery of sucrose - Google Patents

Abstract

1417344 Recovery of sucrose TATE & LYLE Ltd 1 May 1974 [11 May 1973] 22594/73 Heading C6B A continuous process for recovering sugar from the clarifier scum produced by phosphatation flotation in sugar refining comprising subjecting the scum to at least two, preferably 2 or 3, consecutive stages of countercurrent aqueous extraction, wherein each extraction stage comprises the successive steps of (a) dispersing the scum in desweetening water, to give a homogeneous mixture, and aerating the mixture, (b) distributing an anionic organic polymeric flocculant uniformly throughout the aerated mixture, to flocculate the scum therein, (c) passing the mixture, without further agitation, to a clarifier, (d) allowing the flocculated scum to segregate from the mixture by flotation in the clarifier, and (e) separately removing a clarified dilute sugar solution and flocculated scum from the clarifier; passing the flocculated scum from step (e) of each except the last extraction stage to step (a) of the next extraction stage; passing the dilute sugar solution from step (e) of each except the first extraction stage to step (a) of the immediately preceding extraction stage, for use as desweetening water therein; discharging the flocculated scum from step (e) of the last extraction stage, as desweetened scum; and recovering the dilute sugar solution from step (e) of the first extraction stage. In step (a) of at least one of the said stages of countercurrent extraction, the homogeneous dispersion of the scum and aeration of the mixture may be simultaneously performed in a mixing tank provided with an external recirculation loop which includes a power-driven aerator, with injection of compressed air. Preferably the mean residence time of the mixture in the mixing tank is from 2 to 10 minutes and from 1% to 5% by volume of air is introduced into the mixture, on the basis of the mixture volume, and the recirculation rate in the loop is from 1 to 10 times the throughput in the mixing tank. In step (b) of each of the said stages of countercurrent extraction, there may be used from 0.1 to 5.0 parts by weight of flocculant per million parts by weight of melt sugar solids throughput in the refinery and the flocculant may be added to the aerated mixture in the form of an aqueous solution having a concentration of from 0.25 to 5.0 grams per litre. The flocculant is preferably an anionic polyacrylamide flocculating agent having a molecular weight of at least one million e.g. containing up to 20 mole per cent of acrylic acid or sodium acrylate units.