LIME REDUCTION IN JUICE PURIFICATION

Although British Sugar has reduced its consumption of lime for purific ation 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 a nd transport of lime and for coke to burn the lime in conventional kil ns. Offset against these is the benefit of the valuable used carbonata tion lime now sold as a convenient high dry substance product. This pa per looks at some experimental work carried out by British Sugar to de velop practical means of further reducing lime consumption by factorie s. Working with the pilot purification system indicates that it may we ll be possible, in practise, to operate a defeco-carbonatation with UK beet at lower than 1% CaO on beet. The best option appears to be to e stablish a retention time in the Ist carbonatation and clarifier suffi cient to achieve the elimination of invert and glutamine equivalent to the current performance at 1.2% CaO on beet and to recycle clarifier underflow sufficient to achieve acceptable settling and filtration rat es. The addition of flocculants to facilitate settling might be necess ary and a significant increase in rotary vacuum filter area would be n eeded. The major uncertainties would be the scaling behaviour of the j uice with higher limesalts and the ability to produce current white su gar colors with the increased juice colors. Faced with these uncertain ties and the cost of decreasing juice purity it could well be argued t hat current lime usage is optimum at around 1.2% on beet.