High Speed Rotary Drying Machine For Drying Sugar

Product Specification

How to use Hengyang Rotary Dryer for Drying Sugar

Sugar is a common product found in kitchens worldwide. From its familiar appearance to its unmistakable taste, commercial sugar of today is easily recognizable. But even a staple as basic as sugar requires a great deal of processing in order to create a consistent final product. One fundamental step in sugar processing is the use of a sugar dryer. Drying is traditionally achieved using high-grade equipment, typically a rotary dryer, in order to produce a consistent, quality product free of lumps and discoloration.

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.

Drying mechanism of sugar

The moisture content of sugar must be reduced for two main reason.

Sugar discharged from centrifugal machine is having 0.1% – 0.4 % moisture and 60-80ºC temperature. This moisture sugar is not suitable for bagging because the sugar crystal forms linkage with each other and leads to lumps formation.

Secondly higher the moisture % sugar, higher the growth of microbial organisms leading to deterioration of sugar (loss of sugar or color formation).

For the above reasons sugar should be dried to a safe limit i.e. upto 0.04 % moisture due to improve handling properties of sugar and to avoid lumps during storage.

Sugar is discharged from the centrifugal it contains water in two forms

Inherent Moisture :

Water occluded within the crystal structure. It is uncertain whether this water is in the form of occluded liquor or chemically bound as sucrose hydrates or hydrated polysaccharides forming part of the sucrose complex.

This is water contained within the crystal structure. There is no evidence so far about the migration of this moisture to crystal surface.

Included water content is not able to be measured because it is not possible to extract it from the crystal structure so it may be considered to be inert.

Surface Moisture :

Water on the crystal surface, which exists as a saturated or even initially under-saturated syrup film of a purity less than or equal to that of the crystal.

Surface moisture is the water on crystal surface and also known as free moisture. Conventional drying help in removing free moisture + bound moisture.

Moisture available on the surface of the crystal which is readily evaporate known as free moisture, while moisture that is associated with sugar crystal or trapped under amorphous sugar is known as bound moisture.

The water be attached to the surfaces of the sugar crystal and removed by evaporative drying.

After drying process, the total water content of sugar should be less-than 0.1% with the Surface water content being 0.03%– 0.05% and leaving inclusion water content having 0.07% – 0.05% of .

Total water content: Measuring this value, using the Karl Fischer method with a solvent, such as formamide, as a solvent for the sugar, the inclusion sugar content can be determined by subtraction.

Three mechanisms thus take place in sugar drying:

1) Evaporation of moisture at a rate governed by the vapor pressure difference between the film and the surrounding air.

2) Diffusion of water molecules through the surface film, driven by the concentration gradient.

3) Crystallization of sucrose molecules in the film on to the crystal surface or as amorphous sugar diluting the film and making more moisture available for removal.

After drying of sugar should be cooled to ambient temperature (35ºC – 40ºC) due to draw backs as follows

Hot sugar is hygroscopic in nature. If this hot sugar is bagged directly, it absorbs moisture from atmosphere during cooling operation and form lumps.

Secondly due to high temperature the rate of melanoidin reaction increases to considerable extent and stored sugar changes it’s colour to pale yellow and then blackish tinge appears.