An innovative process for producing plantation-white sugar of ultra-low SO2 content

摘要

The conventional double sulphitation process for producing plantation-white sugar suffers from three main draw backs: (i) formation of hard scale on the juice heater and evaporator tubes that is difficult to remove by chemical cleaning and, hence, requires frequent mechanical de-scaling during the crush; (ii) accelerated corrosion of downstream carbon steel pipelines and vessels due to the addition of sulphur dioxide gas during the process of juice clarification; and (iii) lower shelf life of white sugar due to presence of 30-50 ppm SO2. The bulk chemical requirement is also high, i.e. 0.7 kg sulphur and 2.0 kg lime per tonne of cane, which is expensive in countries like Sudan that have to import these chemicals. An innovative process named 'S-Pro Isgec Process' has been developed to produce better quality plantation-white sugar with a lower requirement of bulk chemicals, power and steam. Cane juice is clarified by hot liming and then concentrated to about 67 degrees Bx. The raw syrup is then heated to 85 degrees C, clarified by phospho-flotation and lightly sulphited to 5.6-5.8 pH. The conventional three massecuite boiling scheme is modified by incorporating an intermediate massecuite A1 which takes clarified syrup and A heavy molasses as feed. A1 and B massecuites are single cured and sent to melter. The quantity of A1 massecuite is adjusted to suit the final sugar colour requirement. C massecuite is double cured and then sent to the melter. The entire melt is clarified by phospho-flotation and used with clarified syrup for A massecuite boiling that is centrifuged to produce the desired sugar quality. This process, adopted in a 24,000 tonnes of cane per day sugar plant in Sudan, has successfully completed four harvest seasons and produced plantation-white sugar of about 100 ICUMSA and residual SO2 content less than 10 ppm. Sulphur, lime and power consumption were reduced by 70%, 50% and 5%, respectively, as compared with the double sulphitation process.