Overview of the SUJ Sugar Refining Process



Raw sugar stored in the silo is loaded by a shovel machine (loader) into a bucket elevator which later on, discharges into a raw sugar holding bin as temporary storage before its introduction to the production process. All sugar entering the production process is carefully weighed to ensure correct measurement of the overall conversion yield to the final product of refined sugar.


The affination process comprises a U-mixer, hot magma mingler, centrifugal and sugar melter. In the U-mixer raw sugar is stirred with a measured amount of water before transfer to the mingler for heating and slurrying. This process loosens or detaches colour impurities sticking to the outside of the raw sugar crystals and makes them easy to remove when spun rapidly in the centrifuge. The liquid spun off (molasses) is removed from the process and sold as a by product whilst the sugar crystals are conveyed to the melter where they are dissolved in water to achieve a density (Brix) of 60-65 degrees.


Dissolved sugar from the melter is reacted under carefully controlled conditions of pH and temperature, with milk of lime (CaO) and Carbon Dioxide (CO2) to form a calcium carbonate (CaCO3) precipitate. In this reaction impurities in the raw sugar are trapped by the Calcium Carbonate making them easy to remove in the filtration stage of the process.


Carbonated liquor (solution) is pumped through a series of leaf filters which retain the calcium precipitate in the filter and discharge a clear but coloured sugar solution. Solids retained by the filter are known as filter cake which is sold as a by product to farmers who use it for enhancement of soil quality


The clear but tan-coloured sugar solution is pumped through a series of columns containing an ion exchange resin which absorbs the remaining colour to produce a clear and colourless solution known as fine liquor. After a time the ion exchange resin loses its ability to remove colour and must be regenerated with brine (salt) solution to restore its efficiency.


Water is evaporated from the fine liquor in specially designed equipment to concentrate the sugar solution into a stream known as thick liquor.


Thick liquor is transferred to boiling vessels known as pans, in which under controlled vacuum the liquor is boiled at low temperature to further concentrate the solution. As water evaporates and the liquor concentrates, sugar crystals begin to form; their growth is always being close supervision by careful adjustment of the boiling conditions. The resultant slurry of sugar crystals and solution is known as massecuite. When the crystal size reaches the desired size, the massecuite is transferred to gently stirred and cooled vessels (crystallizers) to complete the growth cycle.


Massecuite from the crystallizers is processed through centrifugals where the spinning action separates the sugar crystals from the remaining liquid solution (molasses).


The wet crystals are discharged through a rotating drum into which hot air is continuously blown to remove moisture and dry the crystals. At the exit of the dryer, the crystals are cooled and passed through a sieve to grade the crystal’s size. Any dust formed during this process is removed by vacuum and the sugar is then conveyed to the packing area for final packaging into fifty-kilogram bags.

Taken from: Internal SUJ