Carbonatation

Carbonatation is the process used in the production of sugar from sugar beet, whereby raw beet juice is mingled with milk of lime and carbon dioxide enriched gas in carbonation tanks.

Carbonatation involves the following effects:

• The increase in alkalinity coagulates proteins in the juice.
• Calcium carbonate absorbs colourants
• Alkalinity destroys some monosaccharide sugars, mostly glucose and fructose

The target is a large particle that naturally settles rapidly to leave a clear juice. The juice at the end is approximately 15 Brix and 90% sucrose. The pH of the thin juice produced is a balance between removing as much calcium from solution and the expected pH drop across later processing. If the juice goes acidic in the crystallisation stages then sucrose rapidly breaks down to glucose and fructose; not only do glucose and fructose affect crystalisation but they are melassagenic taking equivalent amounts of sucrose on to the molasses stage.

The carbon dioxide bubbled through the mixture forms calcium carbonate. The non-sugar solids are incorporated into the calcium carbonate particles and removed by natural (or assisted) sedimentation in tanks.

There are several systems of carbonatation, named from the companies that first developed them. They differ in how the lime is introduced, the temperature and durations of each stage, and the separation of the solids from the liquid.

• Dorr (also Dorr-Oliver) - a continous process using two tanks with recycling to build up particle size for natural flocculation. The paticles are separated under gravity in a thickening stage in a vessel called a clarifier. The clear juice is then gassed further in another tank ("2nd Carbonatation") and filtered.

The concentrated mud is filtered and/or pressed to recover more liquid.

• DDS - multistage process involving pre-liming where the pH of the juice is gradually increased to start precipitation of proteins, followed by addition of further lime and gas.

The particles are removed at each stage by filtration.

• RT - another multistage process with a pre-liming stage. Particles also removed by filtration.

External Links

• Sugar Process at the Crystal Sugar website
• How Beet Sugar is Made