REFINING OF RAW SUGAR

Cane-sugar refineries are always located in great seaport towns for the reason that, as practically all cane sugar is grown in the tropics, it must be transported by water to the world’s markets.

The refining operation is by no means as simple as may at first appear. It is essential that the finished product be almost chemically pure (99.8 per cent), and the greatest care must be exercised to obtain a perfectly white color, as well as a hard, lustrous grain.

The question naturally arises, why do not the planters of Hawaii, Cuba, Java and other raw-sugar-producing countries carry their process a few steps further and make a pure white sugar as the refiners do? This has been attempted many times, but has almost always been found impracticable, notwithstanding the fact that there is no mechanical or chemical reason why.

Among the arguments in favor of a mainland seaport site, the following may be mentioned:

1. The producing centers are generally far distant from consuming markets. Refineries located in the tropics would be under unusual expense for transporting and selling the refined article.

2. A refinery in the tropics would be out of direct and prompt touch with the individual requirements of the buyers.

3. Refined sugar should be moved and sold as soon as possible after its manufacture, so there follows the necessity for adequate dock and rail facilities as means of quick communication with the market.

4. An abundant supply of pure, soft water for refining purposes,and salt or fresh water for condensing, as well as fuel for the generating of steam, must be readily available. Another most important requisite is skilled labor, which is more easily obtained in populous seaport cities than in the small, isolated towns of the tropics.

5. There are many commodities used in the refining of sugar and in packing it for shipment that can be purchased more advantageously, both as regards price and promptness of delivery, in the great commercial ports than in the sugar-growing districts. Among these are bone-char, lime, acids, cotton filter-bags, burlap, cotton cloth, boxes, barrels, cartons, iron, steel and machinery of all kinds.

6. A sugar refinery is operated the entire twelve months of the year, while a raw-sugar mill must of necessity take care of the crop of cane in about eight months. To refine sugar where it is grown would require refining machinery capable of handling the entire output in the eight-month period, and during the remaining four months the plant would remain idle. This would mean a larger investment proportionately than that made in a refinery in a consuming center, running steadily the year round.

7. Refined sugar very rapidly absorbs moisture, and while in transit from the tropic to the temperate zone it is very apt to become lumpy or caked, which would involve reprocessing at great expense at the point of consumption. The unavoidable damage to the packages in loading and discharging results in heavy expense, as all packages must be delivered to the buyer in first-class condition. To avoid hardening, refined sugar should never be piled very high, and it is an unsolved problem whether refined sugar will stand long ocean transportation in cargo lots without caking and damage by breaking of the inside cotton sacks. If shipped in barrels, the freight rate is proportionately higher.

8. Larger capital would also be required, as refined sugar must be carried on hand and must await the consumer’s demand, while raw sugar generally has a prompt and ready market and can be quickly converted into cash.

With these difficulties presenting themselves to a prospective sugar refiner in a raw-sugar-producing country, the shipping of raw sugar to refineries at great distances does not seem at all unreasonable.

Raw sugars show considerable variance in their component parts, and so it follows that some are less easily refined than others. Such differences are generally due to diverse methods of culture, amount of fertilizer used, the processes of manufacture and the efficiency of extraction. If the extraction be high, a large percentage of the salts in the cane is taken up, and these salts prevent or retard the complete crystallization of the pure sugar in refining. One part of ash prevents several times its own weight of sugar from crystallizing, hence it is readily seen that raw sugars with a low ash content are preferred by refiners.

A MODERN REFINERY—SHOWING WATER AND RAIL TRANSPORTATION FACILITIES

PLAN ELEVATION OF A MODERN REFINERY

Sugar refining is the production of pure white sugar in granular form, after the removal of the impurities from the raw product. Nine operations are necessary to bring about this result:

A refinery consists of a group of buildings, each of which has been constructed for a special purpose and for convenience and economy in operation. They are as follows:

In addition there are offices, shops, laboratories, and last, but by no means least, very extensive warehouses.

To begin at the beginning it will be necessary to start with the steamer laden with raw sugar and made fast to the wharf in front of the warehouse that forms part of the refining plant.

The sugar is hoisted out of the ships in sling-loads by powerful winches, and landed on a platform on the dock alongside the ship. Each sling-load consists of from twelve to twenty sacks, or the equivalent weight in baskets or mats, as the case may be. As soon as the sacks are landed, they are sorted according to mark, put on trucks to be run over a scale set in the floor, and their gross weight recorded.

As the truck leaves the scale, the samplers take a sample fromeach sack. This is done with a tryer, a long, hollow steel tube, open on one side and sharp at one end, with a handle on the other for the sampler to grasp when forcing the tryer into the sack. The individual sample from each sack of each different mark is deposited in large closed cans until the cargo is completely discharged, when an average sample of all the individual samples of each mark is made up and used in the laboratory to determine the polarization or sucrose content of the various lots comprising the entire cargo. The value of the sugar is fixed by this polarization.

The weights of the various truck-loads of sugar passing over the scales are totaled and the weight of the sacks, baskets or mats deducted, giving the net weight of the sugar.

Hawaiian sacks weigh exactly one pound; Cuban, Javan and Peruvian sacks about three and one-half pounds. Javan baskets weigh from twelve to fifteen pounds, and Philippine mats about four pounds.

In order to facilitate the weighing and simplify the calculations, in cases where the exact weight of the sacks is known, every truck is made to weigh the same by ascertaining the weight of the heaviest and then putting small iron nuts or washers on the rods of the other trucks until each of them exactly counterbalances the heaviest. One truck is then placed on the scale and the scale is brought to a perfect balance, just as though there were no truck on it. In this way the weight of the truck is never recorded, which greatly simplifies the entire weighing operation.

One crew of men will discharge from 1300 to 1500 sacks of sugar per hour from each hatch of a steamer, or a minimum of 731 tons per day of nine hours. As three hatches are usually worked at the same time, it will be seen that from 2200 to 2500 short tons are taken out every day.

STEAMER DISCHARGING RAW SUGAR AT REFINERY DOCK

SUGAR STORED IN WAREHOUSE—TWENTY-FIVE THOUSAND TONS SHOWN IN THIS PICTURE

From the scales the sugar is deposited on a depressed conveyorin the floor and carried directly into the melt house of the refinery, except the sugar that must of necessity be stored in the warehouse for future use, in which case it is dumped from the trucks on piling machines that elevate it to any height desired, and it is arranged neatly and compactly by the piling crew.

The wharves and docks of a sugar refinery are, as a rule, scenes of unusual activity and interest. Besides the large number of men engaged in hoisting, trucking, weighing, sampling and piling the sugar, there are the sailors, whose calling always possesses a certain fascination for the landsman. A motley crew they are, bronzed by wind and sun, gathered from all countries and climes. There is the simple, kindly native of Hawaii, gentle-eyed, soft of speech and born with a love for the sea; he prides himself upon his skill in swimming and diving, and when the day’s work is done, entertains his shipmates by singing the plaintive melodies of his native land, accompanying himself on the ukulele, the stringed instrument of the South Seas. Should there be a number of his fellow islanders among the crew, the evening’s program is almost certain to be varied by the native hula hula dance, which generally brings marked applause from the onlookers. Presiding over the galley, or ship’s kitchen, is the almond-eyed Chinaman, now shorn of his queue; an excellent cook who loves to gamble after his pots and pans are washed and put away in place; a shrewd gamester, but scrupulously honest. Beside him stands a fierce-looking Malay, sullen, morose and taciturn, whose sharp, white teeth carry a sinister suggestion of the good old days of cannibalism. His neighbor is a Filipino, short in stature, keen-eyed and alert, while in the background are one or two individuals who from their appearance might be direct descendants of the buccaneers who ravaged the Spanish Main in Sir Henry Morgan’s time.

The average sailor is fond of pets, and here there is no lack ofthem, parrots and monkeys for the most part, and the sayings of the former clearly indicate a total absence of Sunday-school training.

Sugar ships bring rare fruits and vegetables from the tropics, and the employés of the refinery have plenty of opportunities to enjoy such luxuries as fresh pineapples, bananas, guavas, papaias, alligator pears, breadfruit and mangoes.

A visit to the docks of a sugar refinery during the time vessels from foreign ports are lying there is well worth while, although in these days of steam, the picturesque features are not so pronounced as they were before the passing of the sailing vessel.

REMOVAL OF SUPERFICIAL IMPURITIES

As a starting point in the refining process the melt house will be first considered. It is so called because it is there that the raw sugar enters the refining process by being melted or dissolved in water.

The conveyor, upon which the bags were deposited in the warehouse, delivers them on a platform on the top floor of the building. As they come to this platform from the conveyor, workmen with keen-edged knives seize them and, with a deft, swift slash, cut the twine sewing at the top of the bag without injuring the burlap fabric. The bag is then pulled off the platform, mouth downward, so that the sugar falls out and passes through an iron grating into a large bin beneath. If the sugar should happen to be caked or lumpy, it is sent through crushers and broken up.

CUT-IN STATION—SHOWING SUGAR FIRST ENTERING THE REFINING PROCESS

CENTRIFUGAL MACHINE—MOTOR DRIVEN

As a certain amount of sugar adheres to the inside of the bags, they are washed in large revolving machines and in this operation the sugar dissolves in the water (called sweet water), from which it is extracted later. They are then partially dried in centrifugal machines and hung on hooks on a travelingchain conveyor that passes through the upper part of the boiler house, where the waste heat thoroughly dries them. In returning, the conveyor passes through the bag room and, by means of an automatic device, the bags are dropped alongside the printing presses. Here the name of the refinery, the kind of sugar and the net weight they are to contain are printed upon them. These burlap bags are then lined with a white cotton bag, after which they are made into bundles and sent to the packing room to be filled with sugar. It will be seen, therefore, that the bags from Hawaii in which the raw sugar is received are put to good use. This, however, does not apply to those that come from Cuba or Java; they are too large to serve as containers for the refined product, and after being washed and dried are sold for what they will bring.

The white cotton bags are made at the refinery, and a plant turning out one thousand tons of sugar each twenty-four hours will use twenty-five thousand yards of cotton sheeting per day if all the output is packed in one-hundred-pound bags.

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.

Finally he succeeded in gaining the ear of the manager of a large refinery, who, after listening attentively to his earnest argument, at length became convinced by it. As a result of the interview, it was arranged between them that the machines rejected by the beet-sugar factory should be installed in the refinery and operated for a period of thirty days, under the directsupervision of the inventor. The test was successful in every particular and conclusively proved the efficiency of the discharger.

The refiner was gratified because on account of the saving in time the capacity of the centrifugals was materially increased; the men operating the centrifugals were hugely pleased, as the arduous work of emptying by hand was entirely eliminated, and the inventor was happy, for he had vindicated himself.

An order for a large number of the machines was placed at once and every centrifugal in the refinery was equipped with one. Today they are installed in nearly every refinery and factory in the United States, and in many raw-sugar plantation mills as well.

CHANGING THE SOLID RAW SUGAR INTO LIQUID FORM

From the centrifugals the washed sugar drops to the melter pan on the floor below. This is a cylindrical tank in the center of which is a revolving vertical shaft, to which are attached horizontal paddles that serve to facilitate the dissolving of the sugar with the hot water that is now added. Only enough water is added to bring the resultant liquor to a density of 58.6 per cent of solid matter.

The raw sugar having been washed and, to use a technical term,melted, leaves the melt house at this point.

PRECIPITATION OF SUSPENDED AND INSOLUBLE IMPURITIES

From the “melt” the liquor is pumped to the top floor of the char house, which is usually a structure of from twelve to fourteen stories high. The reason for building to such a height is the advantage gained by utilizing the force of gravity and by this means handling the liquors and bone-char from floor to floor without mechanical aid.

The liquor is delivered into a number of cylindrical tanks equipped with a coil of pipe through which steam is passed for heating the liquor, each tank being capable of holding 25,000 pounds of liquor. Around the bottoms of the tanks are perforated pipes through which compressed air is forced to agitate and thoroughly mix the solution. On account of this air being blown in, these tanks are called blow-ups. By means of the steam coil the temperature of the liquor is kept at 190 degrees, which makes it less viscous than cold liquor, thus facilitating subsequent filtration and hastening the reaction of the lime and acid added at this point.

As the liquor comes into the blow-ups it varies in color from a straw yellow to a dark brown, and contains a considerable amount of suspended and insoluble impurities which must be removed. Some of these impurities are present in the raw sugar, and others, such as pieces of twine, lint from the bags, fine particles of leaves from the Java baskets and Philippine mats, are traceable to the opening of the containers in the melt house.

The process of removal is called defecation. In former years this was accomplished by adding bullocks’ blood to the raw-sugar liquor in the blow-ups and heating the mixture until the scum which rose to the surface cracked, when the solution below was found perfectly clear, or, in the language of the refinery man,bright. Today, however, chemicals are the defecating agents, those most commonly used being phosphoric acid and lime. Phosphoric acid, neutralized with lime, throws down a heavy, flocculent precipitate which, as it settles, sweeps the solution and drags down all the suspended matter, gums, etc., leaving the liquor above clear and transparent.

The precipitate must now be removed, and this is accomplished by running the liquor through the bag filters on the floor below. These filters are tight iron boxes, about sixteen feet long, six feet wide and seven feet high. The top of the box is depressedabout eight inches below the sides and ends, thus forming a tank. This top is perforated with five hundred holes, one and one-half inches in diameter. From the bottom of the iron box is an outlet pipe leading into tanks below.

In each of the holes on the inside top of the box is screwed a so-called “brass bottle,” conical in shape, to which is securely attached a closely-woven cotton filter bag, about twenty-four inches wide and seventy inches long. This filter bag is encased in a heavier and stronger cotton sheath, or sleeve, about eight inches wide, which adds strength and keeps the twenty-four-inch bag in folds so as to give an effect similar to that of a folded paper filter, frequently seen in drug stores. Each bag filter contains five hundred of these bags, suspended vertically from the top.

Before any liquor is run on the filters, the bags and the iron box are heated by means of steam to bring the apparatus to a temperature of about 190 degrees Fahrenheit. This prevents the chilling of the sugar liquor by cold bags, which would cause the bags to become “blocked,” as it is technically called. The liquor from the blow-ups, at 190 degrees temperature, is now turned into the depressed tank on the top of the filter and flows through the perforations into the bags attached on the inside, down through the bags, and finds an exit through the bottom of the filter into the tanks below.

As the first liquor comes through the bags, it is a little cloudy, but in a few minutes, as the pores of the bags fill with the insoluble substances, it becomes perfectly bright, all the suspended and insoluble impurities remaining in the bags, together with the precipitates drawn over from the blow-ups. The cloudy liquor is pumped to the top of the filter and clarified by being run through a second time. It is interesting to know that it is not really the bag that does the filtering, but the thin layer of sediment that is deposited from the liquor itself on the innersurface of the bag. The cotton bags are made in a particular manner, and from a fabric especially adapted to catch the sediment and to form, in conjunction with it, an excellent filtering medium.

BAG FILTERS—SHOWING BAGS IN PLACE

FILTER PRESSES

The liquor, as it runs into the tanks, must be carefully watched, for sometimes a bag inside the filter breaks, which causes cloudy liquor by allowing the precipitates to gain entrance into the clear liquor. As soon as this is noticed, samples are taken from the outlet of each filter and the defective one found and investigated.

When a bag is torn, or develops a hole, the liquor runs through the opening on the top of the filter so fast that it forms a little whirlpool, which shows the bag that is broken. A wooden plug is immediately driven into the opening and that particular bag cut out. The men on the bag filters soon become so expert that they detect broken bags and plug them before the cloudy liquor gets to the inspection station. It is essential that the liquor be freed from all suspended impurities at this station before the next step is taken, hence great care and watchfulness must be exercised.

In time the coating of sediment, gums and precipitates on the inside of the bag becomes so thick that the liquor runs very slowly and finally stops. The refinery term for this condition is “stuck-up.” Depending on the impurities in the original liquor, the bag filters will continue to filter the liquor for from twelve to twenty hours and sometimes longer.

After the bags are “stuck-up,” the liquor remaining in them is sucked out by means of vacuum through a small pipe attached to a long rubber hose and inserted in the bags through the holes in the top of the filter. The liquor thus sucked out of the “stuck-up” bags is sent to the blow-ups and reprocessed with new liquor, thus beginning its journey anew.

As soon as the liquor is sucked out, hot water is run throughto reduce the sugar contents of the filter. This water is saved and the sugar it takes up is subsequently recovered. The filter is then opened by means of an electric hoist traveling on an overhead track immediately above the filters. Chains are attached to the top of the filter and the hoist elevates top, bags and all, to a point sufficiently high for the bags attached to the top to clear the adjoining filters. The top and bags are then moved along the track to the washing station. Meanwhile another hoist has delivered a duplicate top, with fresh bags attached, to the filter, where it is lowered into place. In this way the filter is again in operation within five minutes. At the washing station the bags just taken from the filter are detached from the top for washing, and the top is sent to a point where clean bags are again attached. It is then ready to go into another filter.

At the washing station the dirty bags are pulled out of the sheaths and turned inside out in tanks containing water, thus releasing a large quantity of the impurities. The bags and sheaths are then thrown into washing machines, where all the remaining impurities and sugar are washed out of them. From the washers the bags are put into centrifugal machines, or through powerful wringers, and dried sufficiently to permit being rehandled. They are then resheathed and made ready to be attached to another top.

The water from the washers contains a large amount of sugar and is conducted to a tank similar to one of the blow-ups, where it is treated with lime and diluted with water at 190 degrees Fahrenheit until it contains only from ten to twelve per cent of solid matter. This liquid is then pumped through filter presses and the impurities removed. The “sweet water,” as it is termed, which now contains practically all the sugar, is collected in tanks and the sugar is ultimately extracted by evaporation, filtration and boiling to grain.

MAKING NEW BAGS AND LINING THE WASHED BAGS

PRINTING THE EMPTY RAW-SUGAR BAGS

The impurities removed by the filter presses consist of sand, portions of bags and baskets, phosphates, hair, lime, salts and gums, in fact every kind of foreign matter that finds its way into raw sugar either in the process of manufacture or in transportation. A small amount of sugar accompanies this refuse, but as its recovery would cost more than it is worth, it is allowed to run to waste. The filter-press cake, as it is called, contains valuable fertilizing agents, and when conditions permit it is used for fertilizing purposes, otherwise it is run to waste.

REMOVAL OF COLOR

To resume the course of the bag-filtered liquor, from which the superficial, the suspended and insoluble impurities have been removed and which is now the color of clear amber, the next step is bone-char filtration.

Bone-char, bone-coal or bone-black, as it is variously called, is made from the bones of animals. After the fat and glue are removed, the bones are subjected to a dry distillation which carbonizes them. These charred bones are then broken into very small pieces, or until they will pass through a ten-mesh screen and remain on a thirty-mesh screen; in other words, the size of the grains used in a sugar refinery vary from one-tenth to one-thirtieth of an inch. If properly manufactured, the grains are hard, porous, and have a great affinity for moisture.

Bone-char has the peculiar property of removing from the sugar liquor, in some unknown mechanical way, not only the soluble salts but the coloring matter as well. The elimination of the salts and coloring matter facilitates the subsequent crystallization.

The char house is, therefore, by far the most important station in a refinery, for failure in the char house means failure throughout.

Contrary to the general practice in Europe, beet-sugar factories in the United States do not use bone-char, and consequently do not take all the coloring matter and salts out of the liquor. They secure a white sugar by other methods, which will be explained later on. In a cane-sugar refinery, however, the coloring matter and impurities are entirely eliminated, and the product is invariably pure and white.

The char filters are cast-iron cylinders, usually ten feet in diameter and twenty feet high, with doors at the top for entrance of the char and openings at the bottom through which it is removed. There are also many pipe connections for the introduction and outlet of liquors, steam, hot water and compressed air. The filters are insulated on the outside with asbestos or some other non-conductor of heat to prevent the temperature of the liquor from being lowered as it passes through. Each filter has a capacity of from sixty thousand to eighty thousand pounds of bone-char.

At the bottom of the filter is a perforated iron plate. Over this is placed a coarsely woven cotton blanket, through which the liquor will pass, but which prevents the char from escaping from the filter with the liquor or wash water. After the blanket is set in place, the char is delivered by gravity through an overhead pipe into the filter, until it is entirely full. The char, as it goes in, has a temperature of from 170 to 180 degrees Fahrenheit, and the bag-filtered liquor which is then run on has a slightly higher temperature.

CHAR FILTERS

CHAR FILTERS—SHOWING OUTLET PIPES

When the liquor in the filter reaches the top and the char has settled in a compact mass, the cover is put on and fastened securely to prevent leakage. The liquor is again allowed to run into the filter by gravity, from the tanks about fifteen feet overhead. The valve on the bottom of the filter is then opened and the liquor, as it filters slowly through the char, is led through a copper pipe to the liquor gallery, to which station all the char-filteredliquor is delivered. This pipe, instead of leading downward from the filter, leads upward and nearly to the top, so that the flow of liquor through the char will be slow and uniform and the filter will always remain full of liquor. The diameter of the filter is ten feet, while that of the outlet pipe is two inches, so that the flow of liquor through the char is necessarily very slow. The reason for this is that the liquor must remain in contact with char a certain time to enable the char to absorb the coloring matter and soluble salts.

The first liquor from the filter appears cloudy and is sent back for refiltration, but it soon becomes bright, perfectly colorless and transparent as plate glass. This white liquor is pumped from the liquor gallery into the tanks on the top floor in the pan house, ready for the next process, which will be dealt with presently.

After a filter has been running for from twenty-four to thirty-six hours, depending on the character of the sugar in the liquor, the char becomes “tired” or spent. In other words, it has absorbed so much of the impurities and coloring matter from the liquor passing through it that its capacity to absorb more is gone and the liquor begins to show a slight straw or canary color. The inspector in the liquor gallery immediately notices this and orders the liquor stopped. Immediately afterwards a lower-grade liquor is turned into the filter, which forces the first liquor out before it. In due time the man at the liquor gallery notices the number two liquor coming from the filter and turns it into separate tanks. In time a still lower grade of liquor is turned on and the filter run until the bone-char is absolutely exhausted, when it is ordered “sweetened off.”

Hot water is then turned in at the top of the filter to wash out the remaining sugar liquor which gradually becomes more and more dilute. When its density has been lowered to about thirty-five per cent of solid matter, it is diverted to other tanks,and this is continued until only three-tenths of one per cent of sugar remains in the sweet water, as it is now called. The washing of the char in the filter in this manner, by hot water, is kept up for twelve hours, but as soon as the sugar content falls below three-tenths of one per cent the solution is allowed to run to waste, as the recovery of this small percentage of sugar would cost more than its value.

The sweet water is sent to the evaporators, concentrated to 58.6 per cent of solid matter, and it then begins its refining journey over again.

This long and continued washing of the filters is for the purpose of removing as much as possible of the organic and mineral impurities absorbed by the char.

The washing completed, compressed air is applied to the filter to force out the remaining water. The bottom doors of the filter are then opened and the char, containing about twenty per cent of water, drops to the floor below. Here it passes through mechanical driers and is delivered comparatively free from moisture to the kilns. There it is revivified, that is, the organic matter in the char which could not be removed by washing is converted into carbon by being heated to a cherry red in the absence of air. This is accomplished by allowing the char to pass by gravity through the red-hot retorts of the kilns.

As the wet char leaves the filter, it drops on a moving belt which carries it to large cast-iron hoppers leading to the driers immediately beneath, where the greater part of the moisture is expelled from the char prior to its being treated in the revivifying kilns. The driers are made up of a number of thin, hollow, cast-iron, triangular pipes, enclosed in a large, rectangular, outside casing. The wet bone-char passes over these hollow pipes as it falls slowly through the drier. The hot gases from the furnaces of the kilns below pass through these cast-iron pipes, giving off heat as they ascend, thus driving off the moisture inthe char as it falls down over the outer surface of the pipes. At the same time, hot air obtained from cooling the char in the cooling pipes below the retorts is drawn through the drier, coming in direct contact with the char. The moisture given off by the char is absorbed by this hot air and carried out of the drier and building by fans or smokestacks. By this means the water in the char is reduced to ten per cent, and in this comparatively dry, hot state it runs freely by gravity from the bottom of the drier into a second set of hoppers, through which it drops into the retorts of the kiln. The hot gases, after drying the char, pass out at the top of the drier through a flue leading to a stack outside the building.

TOP OF CHAR FILTERS—SHOWING PIPE CONNECTIONS

EXTERIOR VIEW OF CHAR DRIER

The kilns are large square boxes of brick, built around a strong supporting iron structure. On each side of these boxes are a number of large flat pipes of cast iron, nine feet long and twelve inches by three inches in section, the iron being three-quarters of an inch thick. These pipes are called retorts and are arranged vertically in the kilns, forty on each side. The space in the center between the retorts is known as the furnace and extends the entire length of the kiln, a distance of about sixteen feet. Intense fires are maintained in this central space and the flames playing around the retorts keep them red-hot. The upper ends of the retorts lead into the hoppers above and the lower ends to the cooling pipes below. As the char passes gradually through the red-hot retorts, it becomes heated to 900 degrees Fahrenheit and the organic matter it absorbed from the sugar liquor is changed into carbon. In this way the char becomes almost as good as new, or, as the term goes, revivified. Each kiln has a capacity of revivifying sixty thousand pounds of bone-char per day.

If the char in this red-hot state were suddenly exposed to the air, the contact with oxygen would bring about combustion and the char would be quickly reduced to ashes, so a coolingprocess is necessary. It is, therefore, drawn from the cast-iron retorts into cooling pipes located directly beneath. These pipes are of thin sheet-iron and are about three by four and a half inches in section. There are three under each retort, and a mechanical device at the bottom allows only a small amount of char to escape at a time. This amount can be regulated at will by the operator, and in this way the char is held in the retorts the exact time necessary for its revivification.

A current of cold air circulates continually around the cooling pipes, taking up the heat from the char and delivering it through pipes to the drier overhead, so that when the char leaves the bottom of the pipes its temperature is about 180 degrees Fahrenheit. From the cooling pipes, it drops on a belt conveyor from which it is carried by endless belt or chain bucket elevators to the top of the char filters to be used again.

The manipulation of the char filters varies in different refineries, some running the liquor over the char for a longer period than others, but a fair average of the time required for filling, settling running liquors and syrups, sweetening off, washing, applying air and emptying, is eighty-six hours, the shortest time being seventy-two hours. Taking eighty-six hours as a basis, it will be seen that the char is handled and revivified eighty-one times each year after making due allowance for Sundays, holidays and annual clean-up periods.

Each time the char is handled, a certain amount of it is broken into dust, and this is taken out by passing it over fine screens, and also by exhaust fans. Obviously, the amount of dust taken out each day must be replaced by its equivalent in new char. It is estimated that the original char put into the filters will last from five to six years before it finally becomes disintegrated and is taken out as dust.

INTERIOR ARRANGEMENT OF CHAR DRIER

EXTERIOR VIEW OF CHAR KILNS—SHOWING OIL-BURNING APPARATUS

As approximately one pound of char is required for every pound of sugar melted, it will be seen that as the liquor isin contact with the char for only twenty-four hours out of seventy-two, a refinery turning out two million pounds of sugar per day should have filter capacity for six million pounds of char. The amount of the latter that is handled each year is, therefore, very great and requires a large and costly plant to take care of it properly.

PRODUCTION OF CRYSTALS BY CONCENTRATION

The refining process has been described up to and including the purification and decolorizing of the sugar liquor, the last step being the delivery of the pure white liquor into the receiving tanks in the pan house.

After the white liquor leaves the char filters, the greatest care must be exercised to keep all the machinery, piping and apparatus scrupulously clean, for if any foreign matter becomes mixed with the liquor or sugar it can only be removed by refiltering or remelting.

By means of vacuum, the liquor is drawn from the tanks into the vacuum pans, this being the last operation in which the sugar is handled in a liquid state. From this point on it drops by gravity from floor to floor in a solid or semi-solid form, until it reaches the packing room as a finished product. In a first-class refinery, the vacuum pans, as well as all the piping through which the liquor passes, are made of copper instead of iron and steel, which eliminates the possibility of rust or scale getting into the sugar.

Refinery vacuum pans are usually from fourteen to sixteen feet in diameter and from sixteen to seventeen feet high, while in shape they appear almost spherical. The boiling takes from one hour and twenty-five minutes to one hour and forty-five minutes, and about forty-five tons of granulated sugar can be made at each boiling in a fourteen-foot pan. Before the liquoris drawn in, the pan is thoroughly cleansed with hot water and steam. All openings are then closed and the vacuum pump started. The air is quickly exhausted, a valve in the pipe line leading from the receiving tank is opened and the pan is given a charge of liquor. Steam is turned into the coils of the pan and the boiling process begins. Soon sufficient moisture is driven off to cause the sugar to “grain.” Shortly after the grain forms, another charge of liquor is drawn into the pan and the operation is repeated until the pan is full of a thick, white, mushy substance called massecuite, that looks very much like half-formed ice. The vapor driven off in the boiling passes out through a large pipe at the top of the pan and is condensed by being sprayed with cold water. On account of the high vacuum, the liquor boils violently at temperatures ranging from 140 degrees to 195 degrees Fahrenheit; thus the risk of scorching, discoloration or caramelization of the sugar is minimized.

On the front of the pan is a vertical row of windows made of heavy plate-glass, and through these the liquor is watched during the boiling. The massecuite in the pan is sampled at intervals by the sugar boiler, by means of a “proof stick,” a brass rod about three feet long and one and one-quarter inches in diameter, in the pan end of which there is a hollow space. This stick is pushed through an opening in the side of the pan into which it fits tightly, and then partly withdrawn. A small quantity of the contents of the pan remains in the hollow space, and this the sugar boiler removes and places on a piece of clear glass. On holding it up to the light, he sees exactly how the crystallization of the sugar is progressing, and by observing and feeling the crystals, he is enabled to control the boiling perfectly. When he concludes that the evaporation is complete and the massecuite of the proper consistency, the pump is stopped and the vacuum broken by opening a valve near the top of the pan, admitting the outside air. The foot valve is then openedand the massecuite drops from the pan into a mixer directly underneath. There it is kept constantly in motion by a revolving shaft with paddles, to prevent the crystals from sinking to the bottom. From the mixer it is drawn into the centrifugals and purged of the mother liquor, the pure crystals being left in the machine. The liquor thus drawn off contains whatever impurities may have remained in the original liquor. It is now pumped back and run through the char filters again, after which it is boiled in the vacuum pan and the granulated sugar taken out in the centrifugals. This completes the process of producing crystallized sugar by concentration.

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