Annual Report 1961 - BEEP

- 80--Additional crystallizer and centrifugalcapacity required for the two-boiling system ascompared to the three-boiling system5216 - 44764476x 100 17%From the standpoint of equipment capacity,the above figures clearly show that the threeboilingprocess, as practised in Mauritius, ismore economical than the two-boiling processdiscussed above. This results from the factthat in the latter process the A massecuitepurity is only 73, as against a syrup purity of87. In other words. a considerable amount ofboiling back has to be resorted to.The question then arises whether it wouldbe practical and economical to adopt a twoboilingsystem when, as a result of unfavourableclimatic conditions for instance, the syruppurity is abnormally low, say, 82°. If the Amassecuite purity were to be kept at 73 as inthe two-boiling process discussed, the amount ofboiling back would no doubt be reduced. but itcan nevertheless be shown that, even then. theboiling scheme would require 20 /~ more pancapacity and 4 ~ ~ more crystallizer and centrifugalcapacity than the three-boiling system.On the other hand, it should be noted thatwith a syrup of low purity the two-boiling processmight prove beneficial if a first massecuite of80 instead of 73 purity were aimed at, beinggiven the appreciable reduction in boiling back.The main difficulty, however, would probablyreside in graining and building the final strikeon runnings of 56 purity assuming a purity dropof 24° between A massecuite and A molasses.Mention should here be made that such a schemehas already been studied by NOEL (1959) whohas shown that, apart from an increase in grainingtime of 15 to 20 ~,~, the use of molasses of56 - 57 purity as footing for the C massecuitewas not a serious drawback under the conditionsprevailing and with the equipment availableat St. Antoine factory in 1958.REFERE~CENOEL, R. (1959) The practical application of a straight two-boiling system. Pro r S. Agr. Sug: (Tech.)Ass. 33: 77 - 80.3. FILTERABILITY OF RAW SUGARE. C.VIGNESIntroductionThe filtcrability of a raw sugar is ofparticular interest to the refiner. Poor filteringsugars arc difficult and costly to refine. In thefirst place, they quickly bloek up filter pressesand, secondly, impair the rate of flow of liquorthrough char filters, resulting in loss of efficiency.All raw sugars contain a certain amount ofundesirable impurities. These occur as colloidmaterial or as particles too large to be trulycolloidal in nature. Some authorities believethat the filtration-impeding effect of theseparticles are primarily caused by their sizerather than their chemical nature. AI allevents, the percentage of insoluble solids has adirect bearing on the filtering characteristics ofraw sugar. The film of molasses surroundingsugar crystals does contain some of the unwantedconstituents but it is well known thatnon-sugars are fairly uniformly distributedthroughout the crystals as well. Althoughaffination removes the surface film, that part ofthe impurities which has found its way insidethe sugar crystal must be blamed for badfiltration.