David, Sargent; Emma, Philip; Maria Teresa Garcia, Cubero
Although British Sugar has reduced its consumption of lime for purification of beet raw juice by about 50% over the last 15 years, the costs of using lime are still significant. Costs are incurred in purchase and transport of lime and for coke to burn the lime in conventional kilns. Offset against these is the benefit of the valuable used carbonatation lime now sold as a convenient high dry substance product. This paper looks at some experimental work carried out by British Sugar to develop practical means of further reducing lime consumption by factories. Working with the pilot purification system indicates that it may well be pos-sible, in practise, to operate a defeco-carbonatation with UK beet at lower than 1% CaO on beet. The best option appears to be to establish a retention time in the 1st carbonatation and clarifier sufficient to achieve the elimination of invert and glutamine equi-valent to the current performance at 1.2% CaO on beet and to recycle clarifier underflow sufficient to achieve acceptable settling and filtration rates. The addition of flocculants to facilitate settling might be necessary and a significant increase in rotary vacuum filter area would be needed. The major uncertainties would be the scaling behaviour of the juice with higher limesalts and the ability to produce current white sugar colors with the increased juice colors. Faced with these uncertainties and the cost of de-creasing juice purity it could well be argued that current lime usage is optimum at around 1.2% on beet.
pdf download: 1998-442-448.pdf