Sugar refinery

The origins of the art of refining sugar seem to stem from Khorasan in Persia. Next, the Venetians produced a primitive form of refined sugar, resembling sugar candy. Approaching the end of the 16th century, the art of refining sugar had spread to Germany, Fifty years later, the Dutch started their refinieries, which soon dominated the European market.[2] The risks involved in large refineries stimulated developments in the insurance industry.

Nyhavn 11 in Copenhagen was a traditional sugar refinery

In the early modern era (AD 1500 to 1800) the sugar refinery process consisted of some standard steps. First the raw sugar was put in a copper boiler and mixed with bullock's blood and lime-water. The mixture was then left to stand for a night in order to dissolve. In the morning, a fire was lit under the pan or boiler. The albumen of the blood then coagulated and entangled the mechanical impurities of the sugar, forming a scum that was constantly removed. The simmering was then continued till a sample of the mixture appeared transparent. It was then rapidly boiled down till such consistency that it could form threads between one's finger and thumb. At which point the fire was damped. The second step was granulation. For this, the syrup was transferred to a vessel called a cooler, where it was agitated with wooden oars till it granulated. The third step was to put the granulated sugar in moulds.[3]

These first sugar refineries were located in coastal cities throughout western Europe. They did not necessarily have to be in a port city, because at the time goods were generally transloaded from a ship onto a barge before reaching their destination. These refineries did not require special buildings. Ideally, they were located on a broad street along a broad canal with a good quay, so resources could be brought in at low cost by barge and by road. The refinery had to stand somewhat free from other buildings. It required wind to dry the produce and to keep it from sweating, especially in Summer. The chimneys also had to significantly stick out above the surrounding buildings.[4]

Sugar refineries are often located in heavy sugar-consuming regions such as North America, Europe, and Japan. Since the 1990s, many state-of-the art sugar refineries have been built in the Middle East and North Africa region, e.g. in Dubai, Saudi Arabia and Algeria. The world´s largest sugar refinery company is American Sugar Refining with facilities in North America and Europe.

Description of an ideal sugar refinery in 1793

For a long time the Dutch Republic dominated the trade in and refining of sugar. It led to some descriptions of sugar refineries and the refining process. In Holland, the ideal refinery was at least 150 Rijnland feet (0.3140 m) long and 30 feet wide. The warehouse of the refinery would be on the street/canal side. It had to be at least 30 feet wide, 40 feet long and 20 feet high, with enough natural light and two 10 feet doors to let pass 2000-3000 pound barrels. The warehouse needed a windlass for vertical transport and a scale to weigh at least 1,800 pounds.[5] Ideally, the warehouse and the refinery were separate buildings, but with the high real estate prices in Holland, this was rare.[6]

The refinery was often directly behind the warehouse in the same building. Closest to the warehouse was the storage for raw materials. Here, there were 4 rooms/boxes to store different kinds of raw sugar, which was fed into the boxes from the first floor.[7] These were each 6 feet long and 12-14 feet wide, making that the raw sugar storage part of the refinery was about 30 feet long, and as wide as the total building, i.e. at least 30 feet. In the 16-18 feet of width that was left there were all kinds of tools, and things like baskets to move the scum. Near the first box, there was a hole in the ceiling and all the floors above, in order to transport goods vertically by rope. On the first floor, there was a storage for lime, which was the same size as the pans, so enough lime could be stored to operate the refinery for 3-4 months.[7]

Behind the storage for raw materials was the drying house, were the sugar was dried in drying rooms. One or two were for drying the sugar loaves, two more were for making candy. These drying rooms were 10 feet long, 12 feet wide and 30 feet high. Each contained an iron stove burning on coal. It was set in brick, and fed from outside the room.

The part of the refinery where the actual refining took place was behind the drying house. Here were the pans ziedpannen were the sugar was boiled. Most of the Dutch refineries had four pans, many had three, and only a few had two. If there were four, these pans occupied a length of at least 25 feet. Each pan rested on a brick vault under which was its own stove. The location of these pans was in the rear of the refinery in order to have as much light as possible, and as little draft as possible. The light came from the rear façade of the building, which ended on an open space of about 25 feet long. Here earth and coal were stored.[8] Below the refinery was a lead tube that allowed to pump fresh water that, in Amsterdam, was brought by barge schuitwater to the rear of the building.[9] The same part of the building that contained the pans also contained the two lime boxes. These had to be founded at least 30 feet deep and stood 4 feet above ground level. They were 9 by 6 feet and stood opposite the pans.[10] Behind the lime boxes were the scum boxes of 8-9 feet high. Opposite the first pans (counted from the street) was the clearing tank klaarselketel. It was about 4 feet above ground and could contain about 8-9000 pounds of cleaned sugar.

The first step, roughly equal to purification, was to fill the pans with fresh water and some lime water. The pan was then closed with half round metal sheet. Next raw sugar was put into the pan. The mixture would then be left to stand during the night to dissolve the sugar. On the morrow, the fire below the pan was lit, and the sugar brought to boil under continuous stirring. Just when the mixture was to boil, the fire was almost extinguished. The scum then solidified, and was removed with a big scum spatula.[11] As soon as this was done a solution of eggs in water was plunged into the sugar mixture, and more scum scraped off. This was repeated 5-6 times, till a white slimy layer appeared on the surface instead of more scum. The solution was then called klaarsel for being cleared.[12] For purifying very rough sugar, ground water was used, and more lime and more eggs.[13] The total use of eggs could be 400 or 500 a day, costing up four guilders for 100 in the winter. Adding fresh blood of oxen could help to further clarify sugar, but it was often used when not fresh, and as an alternative to expensive eggs. This led to rotten sugar, and an official, but ineffective ban of its use.[14]

The cleared mixture was brought to the clearing kettle by feeding it into a copper tube that ended above a filter that was placed over the kettle. This filter was a piece of cloth in a basket and caught things like egg scales, nails, pieces of wood etc.[15] The main purpose of the clearing kettle was to hold the cleared juice while the first two pans were cleaned.

The next step was equal to evaporation. Small portions of the clarified juice were fed to the first pan, which was brought to boil. When the sugar was 'done' and candy sugar was being made, it was put into a transport container, by which it was brought to the drying house, where it was put in pots. The operation to put the sugar in the transport containers and to fill the pots could take about two-three minutes. Ideally, the second pan was by then ready to fill the transport containers.[16] When finer qualities of sugar were being made, the sugar was transferred to the third or fourth pan, which were used as cooling pans (see granulation above).[17]

If candy sugar was made, the drying room could contain about 150 pots of candy made from the raw sugar of four pans after about 6 hours of work. The drying room was then cleaned, shut off, and the fire in its stove was lit.[18]

If sugar loaves were made, the sugar was put in transport containers that brought it to the filling room. Here molds were filled.[19] The day after, the molds were brought to one of the upper floors.[20] Here the stop of the forms was removed, and over a few days syrup leaked out and was gathered into collection pots. The forms were then put on top of a box, where sugar that stuck to the outside of the form was scraped off and collected. The loaves were carefully ticked out of the molds.[21]

ASR's Tate & Lyle Thames refinery in Silvertown, London

The British refining industry started in about 1544, when two sugar refineries were established in London. These were also known as 'sugar houses'. At first, their success was limited because of the strong competition from Antwerp. After the fall of Antwerp in 1585, the sugar refining industry in London expanded.[22] The first sugar refinery in Bristol was started in 1607, when Robert Aldworth founded a single pan refinery.[23] Sugar trade and refining would become the main source of prosperity for Bristol in the 18th century. At one time, there were some 20 refineries in Bristol.[24] In Liverpool, the first sugar refinery was established in 1667.[25]

The sugar refinery industry in Scotland started in 1667. By 1715 there were refineries on the Atlantic coast in Glasgow and on the North Sea coast in Leith. However, the real center of the Scottish refining industry would be established in Glasgow's outport Greenock. Here, the first sugar refinery was established in 1765. Up till 1826 five others followed. By 1869 there were 14 sugar refineries in Greenock, with the two largest processing 14,000 tons of sugar per week. Four more sugar refineries were also located on the River Clyde, and two were in Leith.[26] Glasgow was an important center for the production of the very heavy machinery required for cane sugar mills.[27] This probably contributed to the growth of Greenock as a center for sugar refining, which required lighter, but comparable machinery.

Tate & Lyle became Britain's dominant refining company in the 20th century, but sold its sugar refining business in 2010 to American Sugar Refining.[28]

Raw sugar storage in a sugar refinery

The raw sugar is stored in large warehouses and then transported into the sugar refinery by means of transport belts. In the traditional refining process, the raw sugar is first mixed with heavy syrup and centrifuged to wash away the outer coating of the raw sugar crystals, which is less pure than the crystal interior. Many sugar refineries today buy high pol sugar and can do without the affination process.

In the purification step, the juice is mixed with hot milk of lime (a suspension of calcium hydroxide in water). This treatment precipitates a number of impurities, including multivalent anions such as sulfate, phosphate, citrate and oxalate, which precipitate as their calcium salts and large organic molecules such as proteins, saponins and pectins, which aggregate in the presence of multivalent cations. In addition, the alkaline conditions convert the simple sugars, glucose and fructose, along with the amino acid glutamine, to chemically stable carboxylic acids. Left untreated, these sugars and amines would eventually frustrate crystallization of the sucrose. [29]

In the carbonation step carbon dioxide is bubbled through the alkaline sugar solution, precipitating the lime as calcium carbonate (chalk). The chalk particles entrap some impurities and absorb others. A recycling process builds up the size of chalk particles and a natural flocculation occurs where the heavy particles settle out in tanks (clarifiers). A final addition of more carbon dioxide precipitates more calcium from solution; this is filtered off, leaving a cleaner, golden light-brown sugar solution called "thin juice".[30]

In 1935, the inputs required to process 1 short ton (2,000.00 lb; 907.18 kg) of beets to sugar was outlined as follows:[31]

• 80 pounds (36 kg) limestone
• 250 pounds (110 kg) coke (to convert limestone to quicklime)
• 2,500 US gallons (9,500 l; 2,100 imp gal) water

Phosphatation is achieved by adding phosphoric acid after adding calcium hydroxide to form calcium phosphate.[30]

The remaining sugar is then dissolved to make a sugar liquor (about 70 percent by weight solids), which is clarified by the addition of phosphoric acid and calcium hydroxide that combine to precipitate calcium phosphate. The calcium phosphate particles entrap some impurities and absorb others, and then float to the top of the tank, where they are skimmed off.

After any remaining solids are filtered out, the clarified sugar liquor is decolorized by filtration through the use of bone char, which is made from the bones of cattle,[32] a bed of activated carbon or, in more modern plants, ion-exchange resin.

The thin juice is concentrated by multiple-effect evaporation to make a "thick juice", roughly 60% sucrose by weight and similar in appearance to maple syrup. It is also sterilised with UV light. Thick juice can be stored in tanks for later processing, reducing the load on the crystallization plant.

Vacuum pans

Continuous sugar centrifugal for recovery products

Feeding the thick juice to the crystallizers is the first step of this subprocess. Recycled sugar is dissolved into the juice and the resulting syrup is called mother liquor. The liquor is concentrated further by boiling under a vacuum in large vessels (the so-called vacuum pans) and seeded with fine sugar crystals. These crystals grow as sugar from the mother liquor forms around them. The resulting sugar crystal and syrup mix is called a massecuite, from "cooked mass" in French.

The massecuite is then passed to a centrifuge, where the High Green syrup is removed from the massecuite by centrifugal force. After a predetermined time, water is then sprayed into the centrifuge through a spray bar to wash the sugar crystals which produces Low Green syrup. The centrifuge then spins at very high speed to partially dry the crystals. The machine then slows down and a plough-shaped arm is deployed which ploughs out the white refined sugar from the sides of the centrifuge from the top to the bottom onto a conveying plant underneath where it is transported into a rotating granulator where it is dried using warm air.

The high green syrup is fed to a raw sugar vacuum pan from which a second batch of sugar is produced. This sugar ("raw") is of lower quality with more color and impurities, and is the main source of the sugar dissolved again into the mother liquor. The syrup from the raw (Low green syrup) is boiled for a long time in AP Pans and sent to slowly flow around a series of about eight crystallizers. From this, a very low-quality sugar crystal is produced (known in some systems as "AP sugar") that is also redissolved. The syrup separated is molasses, which still contains sugar, but contains too much impurity to undergo further processing economically. The molasses is stored on site and is added to dried beet pulp to make animal feed, sold in bulk tankers, fermented to alcohol, or further processed.[33]

Since molasses still contain sugar, it is advantageous to recover it. The Steffen Process was used to recover some, so advanced factories had a "Steffen house" next to the plant. During World War I, when imported potash from European sources was unavailable in the United States, "Steffen's wastewater" provided a good source, leading to a profitable income stream for a factory. The need disappeared immediately after the war. In the 1950s, industrial fermentation advanced to produce monosodium glutamate (MSG), previously produced in Japan by the expensive racemization process. Beet sugar molasses, with a Corynebacterium (especially Corynebacterium glutamicum) and combined with penicillin or a surfactant to block biotin, produced MSG as a result, which effectively produced large profits from what was formerly waste.[33][34]