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Sugar Refining

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Sugar Refining

  1. 1. Sugar Refining <ul><li>Affination </li></ul><ul><li>Melting </li></ul><ul><li>Carbonation </li></ul><ul><li>Filtration </li></ul><ul><li>Charring </li></ul><ul><li>Vacuum Pans </li></ul><ul><li>Centrifugal Machines </li></ul><ul><li>Drying </li></ul><ul><li>Packaging </li></ul>
  2. 2. AFFINATION: <ul><li>Mixed with Raw Syrup from a previous batch to soften the adhering molasses, the resulting Magma is spun in Centrifugal Machines to wash off as much molasses as possible. [the newly washed and collected raw syrup is partly used in further magma, the remaining sugar from the rest being 'recovered' by boiling in vacuum pans. The molasses is used in distilling, and as cattle feed.]   </li></ul>
  3. 3. AFFINATION: <ul><li>Affination is the key to good refining because one gets the best improvement in quality for the least capital and running cost. The mixture of syrup and raw sugar crystals is called the &quot;magma&quot;, and rightly so because it is an extremely viscous dark brown liquid mixture not unlike the magma flowing from some volcanoes. Careful control of its temperature and liquid content are critical: </li></ul><ul><li>too much liquid leads to excessive dissolution of the relatively pure sugar crystals; </li></ul><ul><li>too little liquid and the coating will not be washed off, nor will the liquid phase spin off the crystals; </li></ul><ul><li>too low a temperature and the coating will not soften and wash off, nor will the liquid phase spin off the crystals; </li></ul><ul><li>too high a temperature and extra colour will form as sugar degrades; </li></ul><ul><li>Typical operating conditions would be to have the magma at about 10% water content at 70 ºC. Once the crystals are recovered they are dissolved up to make a sugar liquor of about 50% solids content for passing forward to the next stage of refining.   </li></ul>
  4. 4. MELTING: <ul><li>The sugar from 'affination' and 'recovery' is stirred and dissolved in hot water to the correct concentration, whilst strainers and brushes remove 'foreign objects'. </li></ul>
  5. 5. CARBONATION: <ul><li>The solution is treated with Milk of Lime , and Carbon Dioxide is bubbled through it causing the chalk to precipitate removing further impurities.... </li></ul>
  6. 6. CARBONATION: <ul><li>Carbonatation is achieved by adding milk of lime [calcium hydroxide, Ca(OH) 2 ] to the liquor and bubbling carbon dioxide through the mixture. The gas, which is obtained by cleaning up the flue gas from the boiler, reacts with the lime to form fine crystalline particles of calcium carbonate which occlude the solids. To obtain a stable floc, the pH and temperature of the reaction are carefully controlled. </li></ul><ul><li>The filtration is usually undertaken with rotary leaf filters where the liquor is pumped from the outside of the leaf to the middle where the clear liquor is collected. As the layer of floc builds up on the leaf it increases the pressure drop across the system until the filter is effectively choked and taken off line for cleaning. The lime mud that is collected when cleaning the filters is still wet with sugar liquor so it is de-sweetened by slurrying with water - the resultant sweet water is used elsewhere in the process - and re-filtering it to a 50% moisture mud. The mud is then dumped or used as lime on fields. </li></ul><ul><li>Phosphatation is a slightly more complex process that is achieved by adding phosphoric acid to the liquor after it has been limed in the same way as above. In the presence of a small amount of lime sucrate a calcium phosphate precipitate is formed which is removed by a flotation process. The clean liquor is usually filtered to remove any remaining fine particles of precipitate. The flotation scum is desweetened by re-slurrying it and floating it again. </li></ul>
  7. 7. FILTERATION <ul><li>which are then filtered off, the resulting Brown Liquor being sparkling bright and pale yellowish brown in colour. </li></ul>
  8. 8. CHARRING( Decolourisation ): <ul><li>By running the brown liquor through filters of small granules of Bone Charcoal , it is decolourised and purified, leaving a water-white Fine Liquor . </li></ul>
  9. 9. CHARRING( Decolourisation ): <ul><li>Granular activated carbon is the modern equivalent of &quot;bone char&quot;, a carbon granule made from animal bones. Today's carbon is made by specially processing mineral carbon to give a granule which is highly active but also very robust: it can withstand the mechanical abrasion that results from transporting it around the plant. </li></ul><ul><li>The carbon is used in the process in very large columns, perhaps 10 or more metres high. The sugar liquor, at about 65% dry solids, is pumped through 2 columns in series. Because of limitations in distributing the liquor across the width of large columns it is quite normal to split the total liquor flow into three or more parallel streams, each of which passes through a pair of columns. The first column of the pair has been in use for some time while the second column is fresher. When the carbon in the first column reaches is practical limit of absorption, that column is switched out of line, the second column becomes the first column and a column with fresh carbon becomes the second column. In a typical refinery with say 3 streams of liquor, a column will come off line every three days so any one column has a life of 18 days of which 9 are hard working in the first column position. </li></ul><ul><li>Decolourisation with granular activated carbon typically achieves 90% effectiveness: a 1200 colour liquor entering the system will depart at about 120 colour. </li></ul>
  10. 10. VACUUM PANS: <ul><li>The fine liquor is now drawn into the Vacuum Pans for concentration and crystalisation. It is Evaporated under reduced pressure to form Sugar Crystals . [... which may sound easy, but requires all the skills of the highly experienced Pansmen to achieve the correct crystalisation.] </li></ul>
  11. 11. VACUUM PANS: <ul><li>Granular activated carbon is the modern equivalent of &quot;bone char&quot;, a carbon granule made from animal bones. Today's carbon is made by specially processing mineral carbon to give a granule which is highly active but also very robust: it can withstand the mechanical abrasion that results from transporting it around the plant. </li></ul><ul><li>The carbon is used in the process in very large columns, perhaps 10 or more metres high. The sugar liquor, at about 65% dry solids, is pumped through 2 columns in series. Because of limitations in distributing the liquor across the width of large columns it is quite normal to split the total liquor flow into three or more parallel streams, each of which passes through a pair of columns. The first column of the pair has been in use for some time while the second column is fresher. When the carbon in the first column reaches is practical limit of absorption, that column is switched out of line, the second column becomes the first column and a column with fresh carbon becomes the second column. In a typical refinery with say 3 streams of liquor, a column will come off line every three days so any one column has a life of 18 days of which 9 are hard working in the first column position. </li></ul><ul><li>Decolourisation with granular activated carbon typically achieves 90% effectiveness: a 1200 colour liquor entering the system will depart at about 120 colour. </li></ul>
  12. 12. CENTRIFUGAL MACHINES: <ul><li>The solution of mother syrup and crystals is then spun in Centrifugal Machines leaving the White Sugar Crystals which are then washed. [... and the mother syrup is further used to produce Golden Syrup and lower grade moist sugars.] </li></ul>
  13. 13. DRYING: <ul><li>The wet sugar is Dried in a current of hot air.   </li></ul>
  14. 14. PACKAGING: <ul><li>After grading, the Dry Granulated Sugar is packeted for the domestic market, and bagged for the commercial market. </li></ul>

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