THE MANUFACTURE OF SUGAR FROM THE BEET The diffusion process extracts sucrose in preference to other con stituents of the juice. The roots are reduced to thin shreds (slices or cossettes) and the slices immersed in warm water in vertical cylindrical vessels (diffusers). These have a capacity of from 50o to 2,500 gals. each, according to the size of the factory, from io to 14 diffusers forming one battery. Fig. 6 represents a plan of a circular battery of 12 diffusers, and fig. 7 shows a vertical section of two of the diffusers, with connecting pipes. Each has a small door at top for charging with fresh slices, and a large discharge-door at bottom for removing the spent slices.
Liquids pass from the bottom of any one diffuser to the top of the next (see arrows in fig. 7), the slices remaining stationary in each. As all the water used for diffusion must afterwards be evaporated before the contained sucrose can crystallize, this water is passed through many diffusers, extracting sucrose from the slices in each, until it attains a sufficiently high density and sucrose-content to be drawn off, being then called diffusion juice.
In fig. 6 diffuser No. I has been longest in action, so that the extraction is nearly complete. It is less complete in No. 2, still less in No. 3, and so on up to No. io where extraction is just beginning, this diffuser having just been filled with fresh slices and also with liquid entering it from No. 9. Water is entering No. i (see arrow in fig. 6) in order to complete the extraction, and this water displaces an equal volume of liquid (already in No. I) into No. 2, that already in No. 2 into No. 3, and so on up to No. io, where it displaces an equal volume of diffusion juice (see arrows and dotted line in fig. 6). A part of this displaced juice flows through a pipe lead ing to a measuring tank, and the remainder passes forward into No. i r (just filled with slices), causing diffusion to begin in No. i 1. The extraction in No. z is now complete, and the spent slices are discharged. Water is now forced into No. 2; causing displacements of liquids from No. 2 into No. 3, from No. 3 into No. 4, and so on up to No. z 1, where it displaces an equal volume of diffusion juice. Part of this juice passes to the measuring tank and the remainder goes forward into NO. 12 (just filled with slices), causing diffusion to begin here. The extraction in No. 2 is now complete, and the spent slices are discharged. Water is now forced into No. 3 (continuing as before). The same series of operations is repeated round and round the battery. Fresh water is added to each diffuser in turn at one part of the battery; diffusion juice is drawn off from each diffuser in turn at another part; spent slices are discharged from each diffuser in turn ; and fresh slices enter each diffuser in turn. A diffusion battery may sometimes be arranged in two parallel lines Instead of in a circle. The tops of the diffusers project just above the floor, and the battery is operated from this position. The motions of the liquids are controlled by three valves attached to the top of each diffuser.
The efficiency of extraction is proportional to the number of diffusers in action at one time and to the volume of water added to the battery per ioo kilo. of fresh slices. An extraction of 99%
of the sucrose in the roots is easily obtained. Several forms of apparatus for continuous diffusion have been patented, the most successful being the Raabe System. It is a long, cylindrical vessel, divided transversely into numerous compartments, through which the slices and diffusion liquids move in opposite directions.
Chemical Treatment of the Juice.—The method used is called Double Carbonation, and its essential feature is the forma tion of an abundant precipitate of calcium carbonate in the juice, after the addition of quicklime (Ca0) and carbon di oxide gas These chemical agents are produced simultane ously in a lime-kiln attached to the factory. A mixture of lime stone and coke is added at the top of the kiln and gravitates very slowly to the bottom. The combustion of the coke produces a temperature of i,000° to 1,300° C and the limestone decomposes, as shown in the equation = Ca0+ CO2. The gases rising to the top of the kiln are drawn off by a pump and forced through a gas-washer and thence through pipes to the tanks containing the juice. The quicklime is removed from the bottom of the kiln in small quantities at suitable intervals.
The raw diffusion juice is pumped through heaters into liming tanks where from 2 to 3% of lime is added, either in the of quicklime (Ca0) or as lime-cream After thorough stirring, the mixture gravitates to tall, rectangular, closed tanks (carbonation tanks), fitted with a gas-distributor at bottom for injecting the carbon dioxide gas, juice inlet and outlet cocks, a steam-coil for regulating the temperature of the juice, and a chim ney at top for carrying off any unabsorbed gas. As the gas bubbles through the strongly alkaline juice, a gelatinous precipitate is first formed, this gradually decomposing with the formation of a granu lar precipitate of calcium carbonate, the final result being repre sented by the equation This treatment (first carbonation) is continued until the alkalinity of the juice is reduced to about o.i% of lime, when the opaque juice is pumped through filter-presses (see FILTRATION). The clear, filtered juice is still alkaline and passes to another set of carbonation tanks for a second treatment with the gas (second carbonation). This is continued until the alkalinity is reduced to 0.03 or o.o6% lime, causing a further precipitation of calcium carbonate, which is removed by a second filtration, yielding a transparent, light-col oured juice which, in some factories, is treated with sulphur dioxide gas (SO2), followed by filtration, in order to bleach it.
The subsequent operations—evaporation of water, crystalliza tion of the syrup, and separation of crystals from the mother liquor—have been described above under "cane sugar." By-products.—These include: (a) beet-pulp, used as fodder, either in the moist state or after drying; (b) filter-press cakes, which are sometimes used as fertilizer but more usually discarded; (c) molasses, which is used in the production of alcohol and cattle fodder; (d) waster waters of no commercial value.