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It started when we supplied the first beet pulp rotary drum dryers. Not much later we installed the first crystal sugar dryer, the rotary dryer drums. Over the years we gained decades of experience with sugar cane and sugar beet where our clients and we still benefit from.
Table sugar can have two origins: either from sugar beet or from sugar cane. It is based on sucrose (saccharose). Regardless of the raw material, both processes are in principle almost the same.
After cleaning and sorting the raw material, the sucrose is extracted by cooking the sugar beet or by pressing the sugar cane. This creates two distinctive flows: the sugar juice and the cane fibres or beet pulp flow, depending on the source.
The sugar juice, rich in sucrose, is further refined and purified. It is then followed by the crystallisation and the centrifuging steps. The dewatered crystals from the centrifuge require drying and cooling. After cooling follows packing, storage, and transport.
Both drying and cooling stages are key process steps that determine the required appearance, functionality, and flow-ability of the final sugar crystal. It is the reason why these process steps receive so much attention.
Of paramount importance during drying and cooling is preventing water occlusion in the crystal. Furthermore, the creation of the crystal brilliance and its shiny look.
Lastly, crystals must be treated carefully in order not to damage the edges by mechanical impact.
A counter-current rotary drum is used for drying of the sugar crystals.
Most commonly used for the drying step is the rotary drum. The counter current drying process works best for controlled evaporation speed and so to avoid water occlusions. The rotary drum creates the ideal conditions for this process step: it allows the sugar crystals to slowly dry while the syrup adhering to the crystal surface undergo crystallisation. That is a process step which takes time. Actually, the last step of the crystallisation phase occurs in the cooler, not in the dryer.
Read more about our Rotary Drum Dryer as a drying technology.
Benefits Rotary Drum Dryer
A rotary drum as sugar dryer has several advantages both mechanically as well as process wise:
≡ A robust and an uncomplicated process
≡ Non sticky behaviour
≡ Efficient use of energy
≡ Available in stainless steel
≡ Ideal for bulk flows with variance in feed stock
Change of technology
For a long time it has been common practice to use a rotary drum cooler after the rotary drum dryer. The cooler also operates in counter current mode for the same reasons as for the dryer: it provides the best controllable process conditions for the sugar crystals.
While there is no doubt the rotary drum dryer is still the preferred technology for the drying step, concerns were raised about the rotary drum cooler.
With time, the requirements for the final crystal became stricter. Drying and cooling in rotary drums became the less favourable technology because the conclusion became that:
“In the rotary drum cooler, crystals
damage too much”.
Crystals in the fluidised bed cooler erode less, resulting in a more shiny, brilliant crystal while separating the fines from the process at the same time.
A different technology had to be found that would address this problem.
In close cooperation with sugar manufacturers, Ingetecsa has been able to demonstrate that the optimum process equipment arrangement is a combination of a rotary drum and a static fluidised bed technology. This resulted in a sugar crystal that met the latest strictest requirements in terms of:
≡ crystal brilliance
≡ shiny crystal appearance
≡ minimum particle damage
The combination of the rotary drum dryer with the fluidised bed cooler, offers the best of both worlds: energy efficient, reliable equipment, flexible in feed stock variance and gentle crystal polishing.
Sugar beet pulp, where it all started with...
More than a century ago, Ingetecsa supplied its first sugar beet pulp dryers. To date, sugar beet pulp is still a product we dry. Even though the concept of beet pulp drying hasn’t changed much, our drying technology has improved considerably.
Beet pulp is produced in high volumes: 1 tonne of sugar beets yields approximately 160-170 kg of sugar and 500 kg of wet beet pulp (or 210 kg pressed beet pulp, or 50 kg dehydrated beet pulp).
During sugar production, the beets are first cleaned, screened, washed, and milled, from which the juice is extracted thanks to hot water. The juice is then processed similar to that of sugar cane.
Wet beet pulp
The wet sugar beet pulp contains 10-15% dry matter. Mechanically dewatering the wet pulp to remove the excess water increases the dry matter content to 24-27%. The high water content and the high temperature of the water used for sugar extraction compromise the preservation of wet beet pulp. It spoils quickly, even faster in presence of oxygen. For longer storage, pressed beet pulp is ensiled which needs to be done under careful scheduling and conditions.
The typical high throughput in combination with relatively low value, make transport of wet beet pulp costly. Processing of the pressed pulp on site or in the vicinity of the sugar mill is the common way of practice (partly extracted from Legrand, 2015).
Drying wet beet pulp
Even though ensiling may look like a slightly more economical alternative, ensiling requires good timing, clean work conditions and large storage areas with more handling.
It makes drying still the preferred option since it offers:
≡ Long product shelf life
≡ Immediate processing possible
≡ No large intermediate storage areas required
≡ No risk of spoiling
≡ Large volume reduction between wet and dry product
The pressed pulp still contains much water and 1-3% of sugar. Drying of the wet beet pulp or beet fibres, requires for that reason vast amounts of energy. Up to an equivalent of 33% of the energy consumption of the sugar factory goes to beet pulp drying.
Hot air blows in co-current with the product stream through the dryer. Once the wet fibres are fed in the dryer, specially designed lifting plates lift the product. While the drum revolves, the lifting plates continuously drop the product as a curtain down in the hot gas flow. The product then flows in a section with cruciforms. These specially shaped internal plates act like heat exchangers. They create a very uniform end product and increase substantially the heat exchange area. The product is dried after the cruciform section and discharged from the dryer. The exhaust gases are partially recirculated to substantially reduce the energy requirement.
Drying of the fibre produces a free flowing end product. The dried product is suitable for storage, provided it is correctly packed or stored.
As the fibres of the sugar beet pulp are long, the rotary drum is the ideal technology to dry this. Many other drying technologies are less suitable for the long fibres.
After drying, the beet pulp can be pelletised to make animal feed pellets.
Wet bagasse (sugar cane fibres)
Contrary to sugar beet, the bagasse is not used as animal feed. Also, bagasse is not dried in a dedicated dryer. It is stable even when wet. It makes storage much easier.
For every 10 tonnes of sugar cane crushed, almost three tonnes of wet bagasse is produced. It’s challenging to use this byproduct directly as a fuel because of the high moisture content, typically 40–50%. The shredded cane residue is preferably mechanically dewatered first. After this pressing step it is sent to the power stations as a fuel source. The generated heat is enough to fully power a typical sugar mill, with some energy to spare.
Some tropical countries use the the bagasse for composting or for the production of pulp, paper and board. The bagasse is stored wet so as to facilitate the subsequent removal of any remaining sugar as well as the short pith fibres. These fibres would impede the paper making process.
Revamping and re-using your equipment
At Ingetecsa, we believe that it is often possible to reuse existing equipment. We have a solid track record in revamping machines for either a longer operation or a different process operation.
We may be able to convert your existing sugar dryer and add a static fluidised bed cooler. The static fluidised bed cooler ensures that the post-drying and cooling stages occur under minimum mechanical impact.
Based on pilot work, references, and know-how, Ingetecsa helps you to manufacture a top end quality product in a cost-effective way and against higher availability. Fully covered by extensive guarantees.
If you are interested how we can help you, please contact us. Our experienced process team looks forward to discussing your questions.
