Sugar processing from sugarcane & sugar beets
The processing of sugar cane and sugar beets for sugar has a global footprint, with 124 countries responsible for sugar processing and production. In 2020/2021, Brazil was responsible for a quarter of the world's raw sugar production, with India, China, Thailand, and the European Union following behind.
Sugarcane production contributes to 80% of the sugar industry, with cultivation in tropical and semitropical regions. In contrast, the cultivation of sugar beets to produce sugar happens in areas of temperate climates. In the United States, sugar beets cultivation and production are common in the western and northwestern states like Minnesota, Idaho, and North Dakota.
The rapid degradation of the crops after harvest discourages storage over extended periods and requires immediate processing, making the entire process seasonal. Sucrose makes up about 20% of the weight of the sugarcane and sugar beets and degrades through bacterial action. The first step of sucrose degradation produces fructose and glucose, which converts to lactic acid and dextran under prevailing conditions of sugar beet manufacture and sugarcane mills.
Processing of sugarcane & sugar beets
Sugar processing begins with the shredding of the cane crop before crushing it in a milling train to express the cane juice. The cane juice is heated and clarified to remove impurities of soluble and insoluble nature, such as plant debris and scale-forming ion species. Lime is added in the juice clarification process to help prevent sucrose degradation before concentrating the clarified juice in evaporators downstream.
For sugar beets, the first step involves washing the beets to remove dirt and slicing the washed beets into cossettes. After boiling the cossettes, hot water extracts the sugars in the diffusers to produce raw juice. This raw juice is then further processed through carbonatation in the clarifier. The addition of lime in carbonatation forces the precipitation of soluble impurities and organic compounds for removal. Thin juice is the final product drawn from the clarifier and is treated with sulfur dioxide to reduce color formation.
The clarified juice and thin juice from both processes concentrate in the evaporators, crystallize, and separate into raw sugar for drying.
Factors influencing fouling & scale formation
a) Type of juice used for sugar production
The thin juice from sugar beets processing has a lower level of impurities when compared to the clarified juice from sugarcane processing. The prewashing of the sugar beets and gentler method of sugar extraction effectively lowers the impurities level, indicating a lower extent of fouling observed in sugar beets factories.
b) Climate and weather changes
Undesirable weather conditions can push harvesting to the sequential sugar processing season, resulting in poorer quality juice and clarification. Stormy weather conditions can also increase the amount of soil and dirt collected during sugarcane harvesting, increasing the stress on milling trains and clarifiers. The reduced performance capacity of the clarifiers increases the concentration of suspended solids during processing and the tendency for scale formation.
c) Harvesting techniques and types of harvest
Sugarcane harvesting is carried out either through manual labor or mechanical efforts, with each process differing in the types of sugarcane collected. The harvest method harvesting a higher percentage of green sugarcane to burnt sugarcane observes poorer quality juices and clarification, due to increased impurities in the top of the cane plant. The lower level of juice purity increases the rate of scale formation occurring in the sugar processing mill.
Addressing scale formation in sugarcane mills
Scale formation occurs in the evaporator during concentration, with high operating temperatures and exceeding solubility limits driving the process.
Calcium carbonate scales are commonly encountered in sugar processing factories and processes using carbonatation during clarification. Carbonatation increases the concentration of calcium ion and carbonate ion species in solution and this species of scale forms in the prior stages of the evaporator sets.
Calcium oxalate scale formation also occurs in the concentration stage and is relatively more complex to manage due to the difficulty of removal using conventional cleaning methods. The solubility of calcium oxalate increases with the increase in temperature. In proportion, there are higher tendencies of calcium oxalate formation in the latter stages of the evaporator sets where the operating temperatures are lower.
Gypsum or calcium sulfate scale species is another type of formation that hinders operational output. Sugar processing factories that require sulfur-based compounds for color control or have increased content of sulfur compounds gathered from soil and plant matter face this problem of gypsum scale formation.
CrestoPro™ S520 is the preferred formulated solution designed to address scale formations occurring in the evaporator sets of sugarcane factories and has targeted inhibitive properties on a variety of calcium salt-forming species.