Currently, the main source of sugar extraction is through the extraction, preparation, and processing of sugarcane in large sugar mills, where the sugarcane undergoes multiple processes, transforming it from sugarcane to sugar with a glucose content of approximately 95%. This sugar is 100% consumable and commercial.

Behind the sugar mills, there is an extensive production line consisting of different interconnected processes until the final result is obtained, which is refined sugar. The following will explain in detail each of the processes currently carried out for the production of refined sugar.

Image.1 Processes of extraction, preparation and processing of sugar cane to obtain sugar [1].

Primarily, the harvesting of sugarcane is carried out in the cultivation fields, followed by weighing and sampling using mechanical probes to determine characteristics such as sucrose content and the amount of impurities it contains. It is then transported to the conveyor systems with slats that bring the sugarcane into contact with choppers and defibrillators.

In sugar mills, typically two choppers are used to facilitate the cane preparation process, providing a preparation percentage ranging from 65 to 79 on its own (this percentage represents the level of cane preparation for extracting more sucrose in the mills). These choppers convert the small canes into chips to achieve a uniform size and facilitate juice extraction in the mills. The choppers consist of a horizontal shaft mounted on the slat conveyors where the cane is transported. This shaft is supported by two bearings and is driven by an electric motor or a steam turbine directly coupled to the shaft. It comprises 48 tilting blades connected to an overlaid cast iron support on the shaft, rotating at an approximate speed of 650 RPM.

Following the choppers is a defibrillator, which defibrillates the outgoing chips from the choppers to improve the cane preparation percentage and facilitate juice extraction in the mills. The defibrillator consists of tilting hammers mounted along a rotor, and it is installed to leave a gap between the hammer tip and the defibrillating plate or anvil.

Image 2. Preparation and grinding process [2].

The milling process consists of approximately 5 to 6 tandem mills, each with 3 to 4 cylindrical rollers grooved between them, through which the previously chopped and defibrillated cane bed passes. This extracts the maximum amount of cane juice from mill to mill. In this process, water at a temperature of 90 degrees Celsius is added to the final mills to recirculate and increase the extraction of sucrose present in the fibrous material. The mills operate at a speed of 6 to 7 RPM each.

Residues from the last mill, commonly known as bagasse, are used primarily for energy generation. It serves as fuel in large boilers to generate steam or is also used in paper manufacturing.

The juice extracted by the mills is called diluted juice and has a pH between 5.4 and 5.5. This juice is sulfited with sulfur dioxide (SO2) in an absorption tower to eliminate color-forming substances. The resulting juice from this process is called sulfited juice with a pH between 4.5 and 4.8. Lime is added to the sulfited juice to neutralize acidity and initiate the flocculation process, allowing the separation of non-sugar solids that have entered the cane. This juice is called alkalized juice with a pH between 7.2 and 7.5.

The alkalized juice is then taken to heat exchangers (tubular or shell and tube) where it is heated to temperatures between 102 and 105 degrees Celsius. This step allows clarifiers to flocculate non-sugar solids through alkalization, heating, and polymer addition. The clarified juice is passed through fine screens to remove particles and impurities. After this, the resulting juice is sent to the evaporation process.

During clarification, residues called “cachaza” are generated and sent for composting to produce organic fertilizers. The filtered juice is returned to the juice heating process to be reprocessed in the clarification step.

Image 3. Preparation of the juice [3].

The clarified juice is taken to the evaporation process, where the water in the clarified juice is removed, bringing it to the boiling point of water (95 to 102 degrees Celsius). In this stage, approximately 90% of the water is eliminated, increasing the sucrose content from 21 brix to reach 60 to 70 brix. The technological process involves 3, 4, or 5 evaporators connected in series, where the first evaporator is fed by steam generated by a turbo-generator, and the remaining evaporators are heated with steam extracted from the evaporator before them, referred to as multiple-effect evaporation.

The evaporators commonly used by sugar mills for sugar production are of the Robert type. These evaporators have a vertical cylindrical body with tubes through which high-pressure and high-temperature steam passes, heating the liquid inside. These tubes are located between two horizontal tubular plates.

Image 4. Robert type multiple effect evaporators [3].

The resulting product from the evaporation process is a syrup with a sucrose content of 60% to 70%. This syrup is directed to vessels (single-effect vacuum evaporators) that can be continuous or batch. These vessels operate with steam from the first evaporator, maintaining controlled temperature and Brix levels to generate sugar crystals. Following this, sugar nuclei are introduced into the syrup in the first vessel. These nuclei absorb the sucrose in the syrup, growing to the desired size of the sugar to be produced.

Since not all the syrup crystallizes, the next step involves a centrifugation process where sugar crystals are separated from the uncristallized syrup. Hot water is added to wash the crystals and remove the remaining syrup, separating the crystals from the syrup in the first vessel. This process is repeated in the second and third vessels, each using the molasses from the previous vessel. The molasses resulting from the third vessel is sold as animal feed or used for alcohol production. The sugar crystals generated by the second and third vessels are added to the first vessel as sugar nuclei, aiding in the formation of crystals.

Image 5. Bins[4].

The sugar crystals generated in the first vessel are taken to a dryer because they contain 1% moisture. This is done to ensure that they are completely dry and ready to be packaged for commercialization.

PrismaQuímica SAS, a company with a 30-year history in the Colombian industry, providing services, technology, and innovation. We collaborate with our representatives Kadant Johnson, specializing in steam and condensate, and Quattro Separator, specializing in centrifuges.

Bibliographic references

  1. “Diagramas de flujo del proceso”. Sucden.
  • Rivas-Perez, Raul. (2011). Generadores de vapor de bagazo y su control. 10.13140/RG.2.1.4229.2648.

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