Popular Science Monthly/Volume 35/June 1889/The Production of Beet-Sugar
|THE PRODUCTION OF BEET-SUGAR.|
By A. H. ALMY.
IN the May number of this magazine a sketch was presented of the rise and progress of the beet-sugar industry. In this article it is proposed to outline the method of growing the plant, and the processes employed in extracting the sugar. The sugar-beet, like other plants, contains a definite number of chemical elements which are indispensable to its growth, and which must be present in suitable proportions in order to insure its highest development. Yet it is not long since the proportions of these constituents were looked upon as merely incidental, and without any direct bearing on the processes of growth. Plants are nourished by air, water, and the substances contained in the soil; but they differ in the kinds and quantities of nourishment required. Some need to have their roots constantly in water, others are best suited to dry soils, and others again prosper only on the best and most richly manured land. There are some elements common to all plants, and some peculiar to each kind. Like animals, plants are endowed with taste or choice regarding their food—they do not absorb indiscriminately nor in the same proportions all the substances presented to them. From this it follows that the fertilization of the soil should be adapted to the character of the plant that is to be cultivated. Wheat, rye, barley, and other cereals push up long stalks having few and slender leaves, which absorb little nourishment from the air. These plants consequently take most of their food through the roots, and are, therefore, great exhausters of the soil. Plants, on the contrary, having large, fleshy, green leaves, like the beet, take greater quantities of carbonic acid and water from the air, and hence withdraw less material from the ground. In the process of growth plants exhaust that portion of the soil which comes in contact with their roots; hence, after the surface layers have been drawn upon by short, creeping roots like those of the cereals, a long tap-root, like that of the beet, may be able to extract an abundance of nourishment from the deeper
The mechanical condition of the soil is another important factor in the cultivation of the sugar-beet. From the closeness of its texture, a stiff clay retains water, and does not readily admit heat or air among its particles; it also opposes much resistance to the fibrous roots making their way through it. By preventing the free growth of the roots downward, clay is especially unfavorable to the sugar-beet crop; for the beet, instead of producing the long, slim root which is necessary for the proper secretion of saccharine material in the sugar-cells, grows round, turnip-like roots, which are of no value for sugar-making. Sand is the opposite of clay, and, from the looseness of its texture, admits heat too freely, and is not capable of retaining a sufficient amount of moisture for the needs of vegetation. In sand, also, the particles of plant food are washed down by the rains below the reach of the roots, or are vaporized by heat and escape into the air. Plants grow best in loam, which is a mixture of these soils of opposite character, in such proportion that the faults of both are corrected. The depth of the soil and the nature of the underlying stratum are also important; for if the richest soil is only seven or eight inches deep, and lies on a cold, wet clay or on rock, it will not be as fruitful as a leaner soil that lies on gravel, for instance, which is perhaps the best subsoil. The best soil for the cultivation of the sugar-beet root is a mellow, sandy loam, with a free and permeable subsoil, such as would be called by the German agriculturist a first-class barley soil. It should be ten to sixteen inches deep—the deeper the better—rich in well decomposed organic matter and minerals.
Ordinary land can not be planted with the same crop year after year without a gradual diminution of product. This is owing to the fact that the specific food of the particular plant is exhausted from the soil by the constant drafts upon it. But if the land is planted one or more years with a vegetable which takes a different kind of nourishment from the soil, time is allowed for the chemical changes constantly going on in the ground to produce a supply of the food required by the first kind of crop. In the cultivation of the beet-root for sugar-producing, it must follow the cereals, such as wheat, rye, and barley, but, to be profitable, not oftener than every third year.
The advantages of correct fertilization in the cultivation of the beet-root are shown by the experiments of Lawes and Gilbert. On one acre of ground, cultivated without manure, 302 bushels of beets were grown. On another acre adjoining and possessing the same characteristics of soil, enriched with 550 pounds of nitrate of soda or Chilian saltpeter, 886 bushels of roots were obtained. The beets grown without manure contained 2,1151 pounds of sugar per acre; the beets grown with the mineral nitrogen contained 5,145 pounds per acre. In other words, with the use of a fertilizer, an increase of 3,030 pounds of sugar was obtained.
The application of highly nitrogenous fertilizers, or the incorporation of partly decayed organic substances—like stable manure—in the soil in the autumn or in the spring, directly preceding the cultivation of the sugar-beet, is known to act injuriously on the composition of the roots. Such manuring increases the foreign substances in the juice, prevents a desirable development of the sugar, besides placing the latter under unfavorable circumstances for separation. Thus no fertilization must be used during the year of the beet crop.
After the plowing and harrowing of the soil, much the same as required for a potato crop, leaving the ground as smooth as a garden, the sowing of the seed commences early in the month of May, when the beet-planter, represented in Fig. 1, is brought into requisition.
Fig. 1.—The Germania Beet-Planter.
Like the mower, reaper, binder, and other agricultural wonders, it saves the labor of many workmen. It is drawn by two horses, and plants eight rows, eighteen inches apart, at each passage. The seed is placed in hoppers extending along the top of the machine; thence it descends through chutes or apertures, which can be enlarged or contracted at pleasure, into the body of the machine. A shaft, furnished with small spoons, runs through the body of the machine, and is made to revolve with greater or less rapidity by an arrangement of cog-wheels connecting the shaft with one of the driving-wheels. At each revolution each little spoon brings up a seed and deposits it in a small hopper, from which it descends through a series of funnel-shaped tubes, which telescope into each other, into the seed-box of the drill. Another series of cog-wheels is set in motion by the other driving-wheel, and these cause another shaft to revolve, faster or slower, according to the arrangement of the wheels. This shaft is furnished with eight wheels, with cams or projections on the circumference, which operate the valve-rods that open and shut the seed-boxes in the drills, and thus this gearing regulates the distance at which seeds are dropped, just as the other regulates the quantity of seed deposited in the seed-boxes. The seed-drills are furnished with little plows, which open furrows for the seed, deeper or shallower in proportion as they are laden with weights provided for the purpose, and, being hung on pivots, they readily adapt themselves to any inequalities on the surface of the land. In returning across the field, the inner wheel follows in the track made by the outer one in going, and thus the last row of a twenty-acre field is parallel to the first, and the spaces between the rows are uniform. With land thoroughly prepared, and with men and horses practiced in their work, the machine could plant twenty-five to thirty acres per day.
The beet-cultivator, Fig. 2, is also drawn by two horses, and cultivates five rows at each passage. It consists mainly of five
Fig. 2.—The Beet-Cultivator, with Attachment for protecting the Young Plants.
sets of scuffles or hoes, set in a framework, suspended between the hind-wheels of the machine. By means of a lever, terminating in a cog-wheel and playing on a cogged semicircle, this frame can be moved from side to side, or elevated to pass over obstructions, or for convenience in going to and returning from the field. Each set of hoes comprises three different forms of implements adapted to the cultivation of the crop at different stages of its growth. The first set consists of a broad, single scuffle, almost as wide as the distance between the rows; this is intended to be used about as soon as the rows can be traced, and it is provided with a contrivance which bestrides the rows, and protects the young plants from being covered with earth. The second set of implements consists of two narrow scuffles, which penetrate and stir the soil to a greater depth, and are used after the plants have been thinned out and have grown stronger, and there is no longer any danger of covering them with earth. The third set, connected with the beet-cultivator, is a kind of double mold-board plow, and is used for the last hoeing or hilling, Fig. 3. The shape and use of these implements will be seen by reference to the diagrams, which illustrate the cultivator rigged for use at different stages of the growth of the crop.
Every seed-vessel of the beet, containing from two to three germs, will produce as many plants, of which the strongest is left.
Fig. 3.—The Beet-Cultivator, with Attachment for covering the Roots at the last hoeing.
while the rest are pulled up or otherwise destroyed. The process of thinning out the plants, not unlike the same operation in the cultivation of corn, takes place after the first passage of the cultivator, as soon as the roots have reached the length of from four to five inches. The remaining plants are six to eight inches apart. The soil around the young plant is frequently loosened by the beet-cultivator, as shown in Fig. 2, every two or three weeks, until the leaves have acquired their proper development early in June. This treatment, by destroying the weeds and increasing the general absorbing properties of the soil, favors an undisturbed and early development of the leaves, which have a controlling influence in the formation of sugar.
The beet-digger, Fig. 4, is a powerful machine, also drawn by two horses. It consists of two long knives or coulters, fixed in a heavy framework, and so arranged that they may be set to run to a greater or less depth, as may be desired. These knives run under and lift two rows of beets at each passage. As the machine passes along, only a slight rippling or undulating motion is observed in the rows of beet-tops, but the roots are loosened and cleared of dirt more perfectly than could be done by hand, and, as no roots are broken or left in the ground, a considerable increase in the crop is obtained. Like the beet-cultivator, the digger is steered by a lever at the hind end of the machine, and can be lifted to pass over obstructions and for convenience of travel to and from the field. The beets being raised out of the soil, and the leaves cut off with sword-like knives about one half to an inch above the root, the harvesting is completed by the removal of the roots to the pits or factory.
These machines are constructed to work with mathematical exactness, and are used in Germany with great success, and accomplish a very important saving of labor. They have also been experimented with at the Massachusetts Agricultural College with the same results. It is obvious that the smoother and more level the land, the better for cultivation; but the beet machinery will do good work on rolling and uneven land. The beet-planter, or any part of it, may pass over stones or mounds without interfering with its operation, ample provision being made to enable each part to adapt itself to the inequalities of the land. Finally, the crop must be kept free from weeds until harvested, otherwise the root-lifter, which on clean land is a model of simplicity and effectiveness, will be clogged and will not work at all. In short, it requires and abundantly rewards careful preparation of the land, punctual performance of the various operations of tillage, and perseverance in destroying weeds. We may say, this machinery is well adapted to the culture of other crops, particularly corn.
The estimated cost of the cultivation of the sugar-beet per acre, without machinery, on the farm in New England, is about the same as for a crop of onions, corn, or potatoes, and, exclusive of fertilizers, may be estimated as follows:
|Marking and planting||1.00|
|First weeding and thinning||3.00|
|Cultivator with horse, three times||4.50|
It would be impossible, within the limits of this article, to describe in minute detail all the approved methods for the manufacture of beet-sugar; but an attempt will be made to give a general idea of the different processes, with a description of some of the ingenious mechanical contrivances introduced during the past decade, which have been important agencies in making it possible to manufacture beet-sugar at a profit. The method of extracting the sugar from the beet-root is entirely unlike the one usually-employed in manufacturing sugar from the cane-plant, but the principle of the former is equally applicable to the latter, and will probably be generally adopted when the cane-sugar manufacturer can afford to replace his old mechanical system with rotary diffusion batteries.
The beet-roots are dumped, by the farmers, into large bins about nine hundred feet long, capable of holding five thousand tons of beets, from which they are dropped by adjustable traps into a concrete ditch or canal, underneath the beet-house. This canal is provided with descents of brickwork or metal gutters, through which the roots are borne by the, rushing water into the wash-house, which constitutes the first stage of the factory. In the wash-house is a large screw or raising wheel arrangement, by which the beets are emptied into a hopper on the second floor.
Fig. 5.—The Beet-Cutter.
from which they pass into a large, drum-shaped iron cylinder, called the wash-barrel, where the roots are thoroughly cleaned. The washing of the beet is a. very important operation in the manufacture of the sugar, for the roots are thus freed from mold, small stones, and other kinds of dirt attaching to them, which not only saves the machinery employed in the actual preparation of the beets from injury, but keeps the sugar ultimately obtained free from impurity. With, the mere washing of the beets the sugar manufacturer is not content; they are therefore freed from those parts which are poor in saccharine, damaged or otherwise undesirable, by a machine called a carousal.
When cleaned, the beets are thrown from the wash-barrel into a hopper, from which they pass into an endless elevator which carries them to the top floor, where they are discharged-into a large hopper. They then pass into a cage which will hold one thousand pounds of beets, and, when this weight is indicated, the cage empties its load into the cutter or slicer. Fig. 5. The cage and the indicator enable the factory people to closely estimate the amount of raw material used each day. It is also a check on every department. It will show any error that may arise in the receiving or shipping departments. The slicer is a round iron shaft, rotating horizontally, and fitted with steel knives capable of slicing four hundred tons of beets in twenty-four hours. The rotating knives, which, descend upon the beets, cut them into thin slices, thus exposing the sugar-cells, which is an important factor in the diffusion system. The lower end of the cutter opens into a wooden trough about two feet square, on the bottom of which is an endless belt. As the sliced beets fall from the cutter, the belt carries them along to the diffusion tanks.
In alluding to the operation of the diffusion battery in the article on Growth of the Beet-Sugar Industry," it was said that "though simple in its conception, it nevertheless illustrates well known laws of chemical science in the transfusion of liquids, and successfully opens the membranous walls of the sugar-cells of the plant, giving a higher grade of juice, with less gummy, nitrogenous, and fibrous impurities, at less cost than by the old methods of mechanical pressure." By membranous diffusion is understood the process of exchange between two fluids of unequal density, contained in two vessels separated only by a membrane. Supposing the sugar-cells to be brought in contact with pure water, then, theoretically, if the cells contain twelve per cent of sugar, transfusion will go on till an equal weight of water contains six per cent of sugar, while by the passage of water into the cells the juice there is reduced to the same degree. Taking the six-per-cent watery solution and treating with it fresh roots containing twelve per cent of sugar, a nine-per-cent solution will be obtained, which, on being brought a third time in contact with fresh roots, would be raised to a density of 10·5 per cent. Thus, seven eighths of the whole sugar would be obtained at the third operation, and it is on this theory that the diffusion process is based.A diffusion battery, Fig. 6, consists of a range of twelve large, close, upright cylinders called diffusers, provided with man-holes above and perforated false bottoms, with a like number of heaters.
Fig. 6.—Vertical and Horizontal Sections of Robert's Diffusion Battery (Stammer),
arranged in alternation with the diffusers, revolving on a center. As the pure water from an elevated tank percolates through the mass of the two or three tons of sliced beets, under a pressure of eighty pounds, the fluid contents of any one cylinder can be forced into another through the communicating pipes, and thus—under
Fig. 7.—Furnace for supply of Lime and Carbonic-Acid Gas to Factory ("Journal des Fabricants de Sucre").
the combined influence of heat and pressure—the whole solution becomes richly charged with sugar. From cylinder No. 1, which contains the slices almost exhausted of their soluble contents, the fluid passes into No. 2, where it acts on slices somewhat richer in juice. So it goes on through the series, meeting in each cylinder slices increasingly rich in juice, and acquiring density in its progress. Before entering the last cylinder the solution is heated, and the richly charged fluid is sent forward to the carbonation tanks. This process of saturation consists in the treatment of the diffusion juices with lime and carbonic acid, whereby the non-saccharine substances are precipitated and partly decomposed,
Fig. 8.—Vacuum Strike-Pan, Vertical Section (Maumené).
the sugar remaining unaltered in solution. These foreign or non-saccharine substances, which are present in the juice in consider-able proportions, would interfere with the crystallization of the sugar.
The carbonic-acid gas is generated in a lime-kiln. Fig. 7, which consists of a hollow circular chamber of incombustible material provided with furnaces and delivery apertures, and is generally placed in the open air in the factory yard. The lime and carbonic-acid gas are obtained by the decomposition of marble chips by a fire of coke and a bath of sulphuric acid. The process of saturation being complete, the juice is drawn through sand-catchers by means of a lye-pump, which conveys it under pressure into the filter-presses of the first saturation, where the precipitated substances are received. The presses consist of a number of four-cornered plates or frames, over which cloths are stretched. The
Fig. 9.—Centrifugal Filter (Maumené).
residuum is deposited between the plates or in the frames, as the case may be, while the fluid passes through the cloths before leaving the press, and is thus filtered.
From the presses the liquid mass passes to the evaporator. This consists of one or more cylindrical vessels, either in a vertical or a horizontal position, according as its effect is single. double, triple, or quadruple, and provided with a system of heating pipes. The steam which proceeds from the boiling juice of the first vessel serves to heat the second vessel, and so on through the entire series. The evacuation of the heating system on the evaporator is effected by means of small tubes leading from one vessel to the other and connected with a condenser.
When the sirup has attained to a certain degree of concentration, it is drawn off by means of pneumatic suction direct into the vacuum boiler. The vacuum boiler. Fig. 8, consists of a vertical, cylindrical, or ball-shaped vessel, with a conical base, containing heating worm tubes. The mass obtained from the vacuum boiler is first of all placed in a refrigerator, which consists of a trough provided with a stirrer and a refrigerator jacket. The mass of sugar crystals must now be separated from the sirup, so that raw sugar may be obtained, and hence it is sent forward from the refrigerator to the centrifugal machines.
A centrifugal machine. Fig. 9, consists of a cylindrical drum, over which is a finely perforated sieve, and which rotates with great rapidity on its own axis. The mass placed in the drum is pressed against the sieve by the action of centrifugal force, and the fluid escapes through the small apertures. The sirup having been disposed of, the yellow sugar obtained is called the first product, and this, having been emptied from the drum, is transferred to another sieve, where it is freed from the lumps which it may contain, and the raw sugar is finally emptied into sacks on the lower floor, when it is ready for the refinery. The process of refining raw sugar into the block sugar of commerce is an independent industry.