Sugar factory transformation processes (part 1)

Sugar (sucrose) is produced from sugar beet or sugar cane. For example, world production, which totalled 130.5 million tonnes in 2000-2001, is divided between sugar cane (72%) and sugar beet (28%). In both cases, from the beginning of the chain to the production of the final sugar, the aim of sugar factories is to start with the purest possible raw material and produce quality sugar at optimum yields. The sugar factory is therefore primarily a separation and purification industry. A large number of unitary separation operations are carried out in beet sugar factories, for example:

• The washing department removes impurities from the raw material;

• Diffusion extraction limits the transfer of impurities into the juice;

• calco-carbonic purification precipitates some of the dissolved impurities;

• concentration by multiple-effect evaporation removes some of the water from the juice;

• and finally, crystallization is used to separate sucrose in the form of a pure crystal from a syrup still containing impurities.

The main aim of this article on transformation processes in the sugar industry is to illustrate the integration of a large number of unit operations within a specific sector.

Sugar production processes for sugar beet and sugar cane differ in several respects. For the sake of clarity, we have chosen to focus this presentation on sugar production from beet (France was the world's leading producer in 2001), with particular reference to the settings used in French factories. The first part of the article gives a brief overview of beet production and composition, as well as the criteria used to judge juice quality throughout the process. The following paragraphs are each dedicated to one of the major stages in the process.

Finally, the last paragraph will explain the main differences between sugar beet and sugar cane factories.