sugar process and technology lecture 2020.pdf

SUGAR PROCESS, TECHNOLOGY and RELATED PRODUCTS 1 http://www.youtube.com/watch?v=MIgavNuBRRA http://www.youtube.com/watch?v=iT6IQx26eHk 2 3 4 PRODUCTION FROM SUGAR BEET Harvesting the beet The harvesting of the sugar bee...

SUGAR PROCESS, TECHNOLOGY and RELATED PRODUCTS 1 http://www.youtube.com/watch?v=MIgavNuBRRA http://www.youtube.com/watch?v=iT6IQx26eHk 2 3 4 PRODUCTION FROM SUGAR BEET Harvesting the beet The harvesting of the sugar beet, or the "campaign" as it is known, starts around the end of September and continues until mid-January. Production of sugar from the beet is a continuous process. Once the campaign starts it continues 24 hours a day, seven days a week, until all the beet is processed. Harvesting is also done by mechanical methods. It not alone takes the root out of the ground, it also cleans it and cuts off the top of the plants. The leaves are a valuable source of animal feed equal in value per acre to one acre of turnips. The beet is taken by lorry from the harvested field to one of Ireland's two sugar processing factories. For the duration of the "campaign" a steady stream of lorries/tractors can be seen on the roads to the sugar factories. 5 1. WEIGHING AND SAMPLING Once inside the factory grounds the lorries drive over a weighbridge where their gross weight is automatically measured. At the same time a sample of the particular load is taken to determine the sugar percentage and the amount of tare in the overall load. Tare may consist of clay, stones, beet tops, etc. It is deducted from the gross weight of the load in order to determine the net weight of clean beet delivered. The farmer is paid a predetermined price per ton of clean beet delivered based on a sliding scale related to sugar content. 6 Reception Each load is weighed and sampled before it gets tipped onto the reception area, typically a "flat pad" of concrete, where it is moved into large heaps. The beet sample is checked for soil tare - the amount of nonbeet delivered crown tare - the amount of low-sugar beet delivered sugar content ("pol") - amount of sucrose in the crop nitrogen content - for recommending future fertilizer use to the farmer From these elements, the actual sugar content of the load is calculated and the grower's payment determined.. The beet is moved from the heaps into a central channel or gulley, where it is washed towards the processing plant. 7 2. UNLOADING There are two systems of unloading - dry unloading and wet unloading. When dry unloading, the beet is conveyed from the lorry by a series of conveyer belts to open air silos where it is stored. In wet unloading the beet is washed from the lorry by means of a powerful jet of water. Beet is transferred from the silos to the factory by means of water. En route to the production process, stones and grass are removed in a series of stone and grass catchers. The beet is thoroughly washed before processing to remove all traces of clay and sand 8 3. DIFFUSION The actual sugar is inside the beet and has to be extracted. In order to extract the sugar the beet is first cut up into elongated slices. Sugar is then extracted from the beet by diffusing (see Diffusion) it out with hot water. This is done in a large vessel specially designed for this purpose. Beet slices are fed in continuously at one end and hot water at the other end. A solution of sugar emerges from one end and the exhausted beet slices emerge from the other. The exhausted beet slices, or pulp, are mixed with molasses then dried and sold as an animal feed. The solution now left to continue for the rest of the process is referred to as the raw juice. This contains about 14% sugar and is black in colour. 9  The sugar is extracted from the cossettes by means of hot water (around 70 °C) in a diffuser, with the cossettes moving in the opposite direction to the water flow (counter-flow-principle), in a process known as extraction. The raw juice or liquor obtained contains around 98% of the sugar in the sugar beet as well as organic and inorganic constituents (so-called non-sugars) from the beet. 10 11 Extraction Tower 12 Diffusion After reception at the processing plant, the beet roots are washed, mechanically sliced into thin strips called cossettes, and passed to a machine called a diffuser to extract the sugar content into a water solution. Diffusers are long vessels of many meters in which the beet slices go in one direction while hot water goes in the opposite direction. The movement may either be caused by a rotating screw or the whole rotating unit, and the water and cossettes move through internal chambers flow rates of cossettes and water are in the ratio one to two. Typically, cossettes take about 90 minutes to pass through the diffuser, the water only 45 minutes. These countercurrent exchange methods extract more sugar from the cossettes using less water than if they merely sat in a hot water tank. The liquid exiting the diffuser is called raw juice. The colour of raw juice varies from black to a dark red depending on the amount of oxidation, which is itself dependent on diffuser design. The used cossettes, or pulp, exit the diffuser at about 95% moisture, but low sucrose content. Using screw presses, the wet pulp is then pressed down to 75% moisture. 13 This recovers additional sucrose in the liquid pressed out of the pulp, and reduces the energy needed to dry the pulp. The pressed pulp is dried and sold as animal feed, while the liquid pressed out of the pulp is combined with the raw juice, or more often introduced into the diffuser at the appropriate point in the countercurrent process. The final byproduct, vinasse, is used as fertilizer or growth substrate for yeast cultures. During diffusion, a portion of the sucrose breaks down into invert sugars. These can undergo further breakdown into acids. These breakdown products are not only losses of sucrose, but also have knock-on effects reducing the final output of processed sugar from the factory. To limit (thermophilic) bacterial action, the feed water may be dosed with formaldehyde and control of the feed water pH is also practiced. Attempts at operating diffusion under alkaline conditions have been made, but the process has proven problematic. The improved sucrose extraction in the diffuser is offset by processing problems in the next stages. 14 4- SATURATION At the diffusion stage other substances are extracted from the beet as well as the sugar. But before sugar can be produced in a white crystalline form it is necessary to remove as many of these non-sugars as possible. This part of the process is referred to as juice purification. The main raw materials used in the purification are lime and carbon dioxide gas which are got by burning limestone in a kiln. These substances are added to the juice causing non- sugars to be precipitated out of the solution. The solid material is then filtered off. After juice purification the juice has a light yellow colour. 15 Carbonatation Carbonatation is a procedure which removes impurities from raw juice before it undergoes crystallization. First, 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. 16 Carbonatation Left untreated, these sugars and amines would eventually frustrate crystallization of the sucrose. Next, 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. Before entering the next stage, the thin juice may receive soda ash to modify the pH and sulphitation with a sulfur-based compound to reduce colour formation due to decomposition of monosaccharides under heat. 17 5- EVAPORATION The purified juice is a sugar solution containing approximately 14% sugar and 1% non- sugars. It is now necessary to concentrate this solution. This is done by boiling off water from the solution in large vessels known as evaporators. On entering the evaporators, the solution contains approximately 14% sugar. On leaving the evaporators it contains approximately 60% 18 Evaporation The thin juice is concentrated via multiple-effect evaporation to make a thick juice, roughly 60% sucrose by weight and similar in appearance to pancake syrup. Thick juice can be stored in tanks for later processing, reducing the load on the crystallization plant. Crystallization Thick juice is fed to the crystallizers. Recycled sugar is dissolved into it, 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 passed to a centrifuge, where the liquid is removed from the sugar crystals. The remaining syrup is rinsed off with water and the crystals are dried in a granulator using warm air. 19 The remaining syrup is fed to another crystallizer from which a second batch of sugar is produced. This sugar ("raw") is of lower quality with intense color and impurities, and is the main source of the sugar dissolved again into the mother liquor. The syrup from the raw is also sent to a crystalliser. 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. Actual procedures may vary from the above description, with different recycling and crystallisation processes. 20  White sugar centrifugals are for recovering sugar crystals from "boiled" syrup and moss. 21 22 23 24 6. VACUUM PANS In order to turn the sugar into a crystalline form it is now necessary to evaporate still more water. This is done at a reduced temperature and pressure in large vessels known as vacuum pans. Syrup is fed to the pans and as the water is evaporated off, the crystals of sugar begin to grow. When the pan is full it contains about 50 tonnes of a mixture of sugar crystals in syrup. The contents are then discharged into large holding vessels known as crystallizers. 25 7. CENTRIFUGALS The next step in the operation is to separate the sugar from the syrup. This is done in automatically controlled machines known as centrifugals. In them the syrup is spun off and the sugar crystals remain. The wet sugar is then dried, screened, cooled and sent to large bulk storage silos each of which can contain up to 50,000 tonnes. The syrup from the centrifugals still contains a lot of dissolved sugar. This syrup is put back through two more boiling stages in order to extract still more sugar. The final syrup from which it is no longer practical or economical to extract more sugar is known as molasses. It contains some sugar together with non-sugars which were not removed at the juice purification stage. It is mainly used for animal feed. The total time from beet washing to white sugar is about twelve hours. Depending upon sugar content of the beet, 100 tonnes of beet will give approximately 12-14 tonnes of sugar and 3-4 tonnes of molasses. 26 27  combination of a small amount of road and aSUAGR large amount CANE of rail transport. SUGAR AfterPRODUCTION PROCESS: harvesting, cane is transported to the mill where it is weighed and processed at automated cane receiving stations. At this time the producer of In Australia the sugar miller is mostly responsible for transport of the caneThis sugarcane. and the weight is mainly achievedisthrough recorded. a substantial cane railway network ible for and rolling transport of stock. Australian mills operate over 4,000km of narrow-gauge railway and almost 95% of the cane crop is transported esubstantial tipped cane onto to sugar a railway mills cane carrier There using railways. and transported are however some mills that use erate over 4,000km shredder reducesof and shreds the only road cane into transport and most mills use a cane crop is transported nd ruptures the juice cells.combination of a small amount of road and ver some mills that use a large amount of rail transport. and most mills use a dallthe cane of amount through road and a series ofharvesting, After mills. Each cane mill is transported to the mill where it is weighed and ilrge rollers arranged in a processed transport. triangular at automated cane receiving stations. At this time the producer of the cane and the weight is recorded. ly coupled with pressure feeders. This the ne is sugar juice transported The cane from to are billets the millfibrous thetipped where onto a itmaterial, is weighed cane carrier andand transported ated e sugarcane receiving to ajuice stations. is pumped shredder. The Atreduces away shredder this fortime the producer processing and shreds theinto of caneraw into sugar and the bagasse is ightthe or isfibrous material and ruptures the juice cells. recorded. mill boiler furnaces. Pairs of rollers feed the cane through a series of mills. Each mill and transported consists of three large rollers arranged inJuice extracted from the crushing mills contains a triangular eds theformation, cane into normally coupled with pressure feeders. This impurities which are removed by adding lime and process separates the sugar juice from the fibrous material, called bagasse. The sugar juice is pumped heating away forthe limedinto processing juice. The and raw sugar limetheneutralises bagasse is recycled of mills. Eachasmill acids and precipitates impurities which "settle a fuel for the mill boiler furnaces. angular out" in large specially designed vessels called Juice extracted from the crushing mills contains eders. This clarifiers. The clearwhich impurities sugar arejuice is run removed off from by adding the lime and 28 rous material, top of eachheating clarifier. the limed juice. The lime neutralises called bagasse. formation, The coupled normally sugar juicewithis pressure pumped feeders. away for This processing into raw sugar and the bagasse is recycledseparates process as a fuel for thethe milljuice sugar boiler fromfurnaces. the fibrous material, called bagasse. The sugar juice is pumped away for processing into raw sugar and the bagasse is recycled as a fuel for the mill boiler furnaces. Juice extracted from the crushing mills contains impurities which are removed by adding lime and Juice extracted heating fromjuice. the limed the crushing The limemills contains neutralises impurities acids andwhich are removed precipitates by adding impurities which lime and "settle heating out" inthe limed large juice.designed specially The limevessels neutralises called acids and precipitates clarifiers. impurities The clear sugar which juice is "settle run off from the out" in large specially top of each clarifier. designed vessels called clarifiers. The clear sugar juice is run off from the Muddy juice extracted from the bottom of the clarifiers topisof each with mixed clarifier. fine bagasse and then filtered using cylindrical rotating vacuum filters to recover the sugar. The mud and bagasse Muddy juice mix (filter extracted mud) frombythe extracted thebottom ofused filters is the clarifiers as a soil istreatment mixed with onfine canebagasse farms. and Thisthen filtered using cylindrical recycles much ofrotating vacuum filters the phosphorous takento up recover from the the sugar. soil by The mud and the cane bagasse plant. mix (filter mud) extracted by the filters is used as a soil treatment on cane farms. This recycles The clearmuch juiceof the the from phosphorous clarifiers istaken up from the concentrated soil by the by boiling cane vacuum it under plant. in a series of connected vessels called effets or evaporators. The concentrated juice is The clear called juice from the clarifiers is concentrated by boiling it under vacuum in a syrup. series of connected vessels called effets or evaporators. The concentrated juice is called syrup. The syrup (about 65-70 percent sugar) is concentrated by boiling in a vacuum pan and is seeded with small sugar crystals in a process called crystallisation. The syrup (about 65-70 percent sugar) is concentrated by boiling in a vacuum pan and is seeded with small sugar crystals in a process called crystallisation. 29 The sugar crystals are grown to the required size by adding more syrup while boiling continues. When the crystals reach the required size (approximately 1.0mm), the mixture of syrup and crystals called massecuite is discharged from the pan. Syrup is separated from the raw sugar crystals in centrifugals which contain perforated baskets which spin at high speed in a casing (similar to a household washing machine). The dark syrup surrounding the crystals is "thrown off" and passes through the perforations. The spun-off syrup is boiled again and more raw sugar crystals are recovered. This procedure is repeated until the amount of sugar obtained is too small to make further extractions economical. Molasses is the syrup left over from the final centrifuging. This is stored for later sale. The raw sugar from the centrifugals is dried by tumbling through a stream of air in a rotating drum. The raw sugar is then transferred for short-term storage in bulk bins at the mills. 30