Patent GB-704680-A (GB)
Title: An improved process for removing impurities from sugar juices
IPC: C13B20/06
Filed: 1951-03-13
Abstract: 704,680. Purifying saccharine liquids. AKTIESELSKABET DE DANSKE SUKKERFABRIKKER. March 13, 1951 [March 24, 1950]. No. 5984/51. Class 127 In a process for purifying sugar juice by liming and carbonation, whereby the juice, prior to the so-called first carbonation and the subsequent second carbonation is stabilized by adding CaO to produce alkalinity not exceeding 0.05 grams CaO per 100 millilitres, preferably between 0.02 and 0.03, and the lime medium employed having an alkalinity not exceeding 0.25 grams CaO per 100 millilitres, the so-called first carbonation is divided into two carbonation stages (1A and 1B), and the juice after stabilizing is partially limed and is then carbonated in stage 1A in the presence of calcium carbonate preferably as a slurry added to the juice prior to or during the carbonation, and decanted, whereafter the decanted juice either during or after further addition of CaO is subjected to a renewed carbonation in stage 1B until an alkalinity of the usual first carbonation is obtained. From the first carbonation and decanting stage 1A the slurry is filtered and mixed with the decanted juice prior to liming in connection with the second carbonating stage 1B so that all the juice is carried on. The juice obtained by the secondary carbonation stage 1B is then subjected to the socalled second carbonation, during which carbonation takes place down to an alkalinity of about 0.02 grammes CaO per 100 millilitres. This second carbonation may in known manner be carried out after the juice from the aforesaid secondary carbonation carbonation stage 1B is separated from the precipitate by decantation and/or filtration but may be carried out without decanting or filtration. The slurry from the second carbonation process 1B or from the second carbonation may be employed as CaCO3 addition so that some of the lime is returned to the process thus reducing consumption and also ensuring that CaCO3 is supplied free from colloidal matter. If the slurry from either of these two sources is insufficient slurry may be added from the primary carbonation stage 1A. In an example shown in Fig. 1 diffusion juice and a liming medium (0.15 grams CaO per 100 millilitres) are added to a tank 1 provided with an agitator 2 to produce a stabilizing alkalinity of 0.02 to 0.03 grams CaO per 100 millilitres. The stabilizing juice is then pumped through a preheater 5 to a continuously operating combined carbonating and decanting vessels 7 provided with a distributer 8 through which sufficient CO2 is added during the first carbonation 1A that the alkalinity is 0.09 grams CaO per 100 millilitres, and below this distributer with a decanting vessel 9 from which the decanted juice is removed by a pipe 10 to tank 11 the colloidal impurities being removed from the base of the vessel 7, and fed to a continuously operating filter 27, the filtrate being added to the decanted juice in pipe 10 passing to tank 11. Lime is added through a pipe 24 and slurry from the 1B and second carbonation via pipe 23. The decanted juice is again limed in tank 11 and then pumped for the second carbonation 1B to a carbonation receptacle 14 having a distributer 15 through which CO2 is passed until the juice carbonated down to an alkalinity of about 0.08 grams CaO per 100 millilitres and a decanting vessel 49 from which the decanted juice is conveyed through a similar combined carbonating and decanting receptacle having a CO2 distributer 18 and decanting vessel 19 where the second carbonation is carried out down to an alkalinity of about 0.02 grams CaO per 100 millilitres, purified juice with very low limed content emerging at 20. The 'slurry which has collected in the base cf the receptacles 14, 17, i.e. the second and third decantings, is removed and utilized as additional CaCO3 by returning to the receptacle 7 in a modification, Fig. 2 (not shown), the tank 1 is replaced by a continuously operating stabilizing and liming device and the lime which is normally added to tank 11 is added at the second carbonation 1B in receptacle 14, the tank 11 being dispensed with. The final receptacle 17 has no decanting vessel and slurry is returned to receptacle 7 and also to the stabilizing and liming device from the base of receptacle 14, addition from the base of receptacle 7 being made if necessary. In another modification, Fig. 3 (not shown), the tank 1 is replaced by a continuously operating stabilizing and liming device as in the modification above after which the limed juice passes into another tank where it may be further limed before passing on as described with reference to Fig. 1. After leaving the tank 11 the limed juice passes first through a preheater before entering the carbonation receptacle 14 which in this modification has no decanting vessel .-and then passes into the last carbonation receptacle 17. In this modification the slurry is removed from the base of the latter and returned to the receptacle 7, being made up if necessary by the slurry from the base of the receptacle 7.