Sugar Milling in Natal and Some Observations on the Variables

OF PAPERS TWENTY-SECOND ANNUAL SUMMARY OF CHEMICAL LABORATORY REPORTS South African Sugar Factories, Season 1946-47~ By H. H. DODDS and J. L. DU Torr. For the third successive year rainfall, 32.02 inches, and humidity have been very low, though the rainfall was not quite so unfavourably distributed as in the two preceding years. The mean annual temperature, 69.4°F., was considerably above the average, and the total hours of sunshine, 2,446.3 or 56.3 per cent. of the total hours of daylight, were the highest on record at the Experiment Station. During the 1946-47 season 3,990,017 tons of cane were milled to make 474,769 tons of sugar, 98.70 pol., which represents 2.27 per cent. of the cane sugar and 1.51 per cent. of the estimated total world production of sugar. Largely as a' result of the drought conditions, the average sucrose and fibre contents were high, 14.21 and 16.21 per cent. respectively, but the purity of mixed juice low, 85.86 per cent. The peak of purity of mixed juice and the lowest reducing sugar ratio occurred abnormally early in the season, during June. The proportions of Uba and Co.290 continue to diminish, only 1.91 and 2.65 per cent. respectively being crushed, while the CO.,301 has increased to 28.16 per cent., and Co.281 still constitutes the bulk of the crop, 63.25 per cent. Extraction, 93.07 per cent., and boiling-house recovery, 89.12 per cent., are both somewhat lower than the previous season,; but the red~ced overall recovery, 83.82 per cent., continues to rise and is a record for Natal. The ratio of cane to sugar, 8.36, is one of the best ever recorded. Moisture in bagasse remains high at 50.32 per cent. Losses in filter cake fell to the new low level of 0.28 per cent. of sucrose in cane. The average loss of sucrose in molasses cannot yet be calculated, but the molasses purity, 41.75 per cent., is the lowest yet attained in. Natal for a season. Of the 19 factories reporting, two crushed at a rate in excess of 133 tons per hour (about 21 tons fibre per hour) to make 55,562 and 53,810 tons of sugar for the season, and two had a crushing rate of less than 25 tons of cane per hour. Agricultural Census Returns for ,the year 1945-46 show that European planters harvested Ifld.d7(acres out of a total area under cane of 343,149 acres, or 47.64 per cent. of the total area under cane, and produced 4,201,699 tons of cane. The average yield, 25.70 tons of cane per acre, is considerably lower than the two preceding seasons. This decrease in yield is due to the cumulative effects of the drought cycle extending from November, 1944, and the continued fertilizer shortage. Native and Indian planters were responsible for the production of 405,356 tons of cane or 8.8 per cent. of the total crop. SUGAR MILLING IN NATAL AND SOME OBSERVATIONS ON THE VARIABLES CONNECTED WITH MILLING., By J. H. G. ROYSTON. The paper is based mainly upon data compiled from a comprehensive questionnaire filled in by sugar mills in Natal. It goes further than analysing the data collected, however, by introducing certain conclusions and theories relative to milling practice, which offer scope for further research. In defining milling as a "process of extracting sucrose from cane by means of repeated pressure expressions of a rotary nature," the author qualifies this by detailed, analyses of the variables which govern the extent of extraction. These are listed as : (a) Capacity rating, (b) Preparation for the milling process, (c) Roll pressures, (d) Maceration, (e) Peripheral speeds, (1) Mill settings. . The main points under' these headings are as follows ;Cap~city rating.e-Tonnage crushed in Natal increased between the years 1937 and 1945 by 11.7 per cent., with increased recovery of sugar as well. This increase in capacity was due largely to the development' of new cane varieties and to added technique in operation. The author develops his formula for assessing the capacity rating of a plant under Natal conditions as D 2 x L x N Tons cane crushed per hour ' 6.17