Method and plant for the production of refined sugar from a sugared juice

1. Method for producing refined sugar from sugared juice, such as raw juice from sugar cane or from sugar beet, containing sugar and impurities, which comprises the operations of:

tangential filtration of the sugared juice in order to obtain a retentate and a filtrate,

softening of the filtrate in order to obtain a softened filtrate,

concentration of the softened filtrate in order to obtain a softened syrup,

chromatography of the softened syrup in order to obtain an extract enriched in sugars and a raffinate enriched in impurities, and

crystallisation of the extract in two or more crystallisation/separation steps in order to obtain refined sugar and a run-off,

characterised in that it comprises furthermore the operation of:

combination of the run-off with the softened syrup in order that they are both subjected to the chromatography operation.

2. Method according to claim 1 , characterised in that it comprises furthermore a clarification operation of the sugared juice before it is subjected to the tangential filtration operation.

3. Method according to claim 1 , characterised in that the tangential filtration operation is selected from a tangential ultrafiltration, a tangential microfiltration and a tangential nanofiltration.

4. Method according to claim 1 , characterised in that the softening operation comprises an ion exchange operation, having recourse to an ion exchange resin.

5. Method according to claim 4 , characterised in that it comprises furthermore a regeneration operation of the ion exchange resin used in the softening operation, by means of the raffinate produced during the chromatography operation.

6. Method according to claim 1 , characterised in that it comprises furthermore a concentration operation of the extract before it is subjected to the crystallisation operation, in order to obtain a concentrated extract.

7. Method according to claim 1 , characterised in that it comprises furthermore a decolouration operation of the extract before it is subjected to the crystallisation operation.

8. Method according to claim 7 , characterised in that the decolouration operation comprises the treatment of said extract by an absorbent resin.

9. Method according to claim 7 , characterised in that the decolouration operation is effected on the concentrated extract.

10. Plant for implementing the method of claim 1 , characterised in that it comprises:

a source of sugared juice,

means for tangential filtration of the juice derived from this source, these means including a filtrate outlet,

means for softening the filtrate, including a softened filtrate outlet,

means for the concentration of the softened filtrate, including a syrup outlet,

means for the chromatography of the syrup, including a raffinate outlet and an extract outlet,

means for the concentration of the extract, including a concentrated extract outlet,

means for the crystallisation, in two or more than two crystallisation/separation steps, of the concentrated extract, including means for recovering crystallised sugar and means for recovering the run-off from the last crystallisation/separation step of crystallisation, and

means for supplying this run-off at the head of the chromatography means.

11. Plant according to claim 10 , characterised in that it comprises furthermore means for the decolouration of the concentrated extract derived from the concentrated extract outlet of the concentration means.

12. Plant according to claim 10 , characterised in that the softening means comprise an ion exchange resin and in that it comprises furthermore means for supplying the raffinate at the head of the softening means with a view to the regeneration of said resin.