Something about sugar

by George M. Rolph

The bin into which the raw sugar is dumped holds enough sugar to keep the refinery supplied during the twenty-four hours run, but the entire quantity is “cut in” during the day. The advantages of this arrangement are that it avoids any delay in operation due to mechanical troubles with conveyors and because more efficient work is accomplished during the daylight hours. The employés prefer to work on the day shift and, wherever possible, night work is avoided.

From the bottom of the bin the sugar falls into a mixing machine, called the mingler. This is an oblong tank with a semi-cylindrical bottom, near which is a revolving horizontal shaft, with arms or paddles attached which thoroughly stir and mix the sugar with syrup that is added at this point. The reason for using syrup instead of water is that the former, being a saturated sugar solution, does not melt the sugar as water would.

The resultant mixture, called magma, looks a good deal like a soft, brown mortar. It is, in fact, raw-sugar crystals swimming in syrup. This consistency is needed to allow the magma to work freely in the centrifugals, the next operation. Most of the impurities contained in raw sugar are superficial, that is, adhering to the outside of the grain. They may be more or less readily removed by washing the surfaces of the crystals with water.

From the mingler the magma drops to the floor below into centrifugal machines running at the rate of 1100 revolutions per minute. A “charge” consists of about nine hundred pounds of magma. As the machine fills, the centrifugal force causes the magma to rise in a vertical wall around the inside circumference of the basket, at the same time throwing off the syrup that was added on the floor above, and leaving in the machine about five hundred pounds of the raw sugar as it came from the plantation. Water is then sprayed into the machine under high pressure, through a nozzle which divides it into very fine particles and throws it against the wall of sugar in the machine. The water, passing through the sugar by the centrifugal force, washes each face of each crystal and carries off the impurities, together with a certain amount of sugar. The quantity of water used per machine in each filling is from one to two and a half gallons, depending upon the quality of the sugar.

This water, now a syrup, with the impurities and sugar it contains, is drawn from the machine, part of it being pumped to the floor above to mix with new raw sugar coming in. The remainder is treated, filtered, boiled and made into raw sugar, which, in turn, goes direct to the melt or through the washing process again. The result of this washing is that the purity of Hawaiian raw sugar is raised from about 97.2 to 99.2 per cent, and there now remains but 0.8 per cent of impurities to be removed.

The washed sugar is dropped from the centrifugal basket through a large opening in the bottom of the machine with the aid of a mechanical device called a discharger, which greatly reduces the manual labor.

Until very recently the sugar was discharged from the centrifugals by hand, the men digging it out with wooden paddles in a difficult, laborious way. One day, a few years ago, a clear-brained, observant American lad working in a beet-sugar factory, conceived the idea that a centrifugal could be emptied by mechanical means. He worked long and assiduously upon the problem, and after much experimenting and many trials and disappointments was granted a patent by the United States government. Full of hope and confidence, he had several machines constructed and took them to a sugar refiner, sure of being favorably received. He met with rebuff and ridicule. The refinery engineer was too busy with other matters to examine or give any attention to the appliance. The next man to whom he presented it was even more indifferent than the first; he coldly informed the patentee that he had been in the sugar business for thirty years, that no such machine would work, and that the only way to take sugar out of a centrifugal was by hand.

After months of effort and repeated failures, he induced the superintendent of a beet-sugar factory to allow him to install and test the device at his own expense. It was thrown out after a few days’ trial, and the inventor became well-nigh desperate, although still positive as to the merits of his discharger.