Sugar Production

Sugar beet is harvested in the autumn. Harvesting usually starts at the end of September and ends in late November. The average sugar beet root weighs 0.75 kilograms and contains 16% of sucrose. After harvesting, sugar beet is left at the edges of fields and transported in stages to the sugar mill. One hectare usually yields 50-60 tons of beet.

Beet acceptance, washing and cutting, diffusion

Photo-gallery: Beet acceptance, washing and cutting, diffusion

Following the transport to the sugar mill by large-volume trucks, sugar beet is sampled to establish the sugar and loam content and then stored in the yard. The data on the sugar and loam content are necessary for setting the final price paid to the farmers.

Sugar beet then floats by water from the pile to the sugar mill itself, while loam, sand, stones, leaves and grass is removed.

At the start of the production process, the beet surface is cleaned in a beet washing machine, which is a water channel with rotating blades. Washing water, containing removed loam, flows to settling ponds where the loam settles and water returns to floating and washing. After the campaign, the loam is excavated and returns to the cultivators' fields. Accumulated floating and washing water is gradually led to a waste-water treatment plant.

Once washing water is separated, sugar beet is cut into chippings, which look like thin French fries. Sugar is extracted from the chippings by desugarisation using hot water. After entering the diffusion chamber, which is a large cylindrical, slightly slanting vessel, the chippings are pushed against the flowing hot water. Under these conditions, majority of sugar is extracted in this hot water, creating so-called diffusion juice of ca. 16% sugar content.

The chippings, devoid of sugar, leave the diffusion chamber in the form of slurry and continue to so-called pulp presses where their water content is reduced to 80%, enough for their utilisation as fodder for livestock, either directly or after ensilage.

Juice Purification

Photo-gallery: Juice purification

Apart from sugar, the diffusion juice contains various other substances like salts and complex organic compounds, some of which are very coloured. These organic compounds are called non-sugars. All such compounds complicate the extraction of sugar in its solid, clean, crystalline form. The main cleaning process in the sugar mill is the evaporating crystallisation, a process where the juice is heated and evaporated until sugar crystallises spontaneously. During this process, the presence of non-sugars is very undesirable, as they prevent the crystallisation and reduce the process yield, but they also add colour to sugar by entering its crystal lattice. It is therefore necessary to remove as much inorganic salts and organic compounds as possible before crystallisation. The main cleaning method is the addition of lime in the form of lime milk with the consequent removal of lime in the form of calcium carbonate once non-sugars are tied.

Each sugar mill has its own lime plant for the production of lime milk. Burnt lime is made from limestone and coke, and then it is converted into lime milk after mixing with water. Such lime milk is then mixed with the diffusion juice. This leads to the condensation of a majority of non-sugars, forming a precipitate, which is, however, poorly filterable. Therefore, carbon dioxide, a by-product of lime burning, is blown into the juice with added lime milk, thus creating extra fine calcium carbonate precipitate that ties precipitated non-sugars. This precipitate is easy to filter and is separated from the juice in a decanter, sludge presses and thickening filters. So-called thin juice is created, having roughly the same sugar content as the initial diffusion juice. Therefore, this juice must undergo evaporation in the evaporator.

Evaporator, Steam and Electricity Production

Photo-gallery: Evaporation pan

The sugar mill evaporator is a set of large standing cylindrical vessels, where thin juice evaporates in five successive stages. This extraordinary, smart and very ancient method ensures that using one ton of steam, as much as five tons of water evaporates from the juice. So-called thick juice leaves the evaporator, from which sugar is made, while evaporated water leaves the separate evaporator vessels in the form of several kinds of steam of various pressures and temperatures. These steams, so-called plumes, are then utilised for the heating of juices in the cleaning process and during sugar boiling in graining pans. This multiple utilisation of steam is very efficient.

Steam that enters the evaporator is generated in the sugar mill boiler room with three boilers. From boilers, steam flows to a steam turbine, which propels the power generator. Only after leaving the turbine, the steam flows to the evaporator. All energy produced this way is utilised at the sugar mill.

White Sugar Boiling

Photo-gallery: White sugar boiling

Leaving the evaporator, the thick juice contains approximately 63% sugar, which is not enough for sugar crystallisation. To increase the sugar content, the thick juice is enriched with other kinds of sugar acquired in the subsequent production stages, the formation of which will be explained later. So-called unified draw-in, a highly concentrated sugar solution which is not capable of spontaneous crystallisation, is created. Therefore, this unified draw-in is heated by plumes, i.e. steam leaving the evaporator, and then evaporates in so-called graining pans, large vessels with a ca. 45,000-litre volume. Evaporation proceeds in a partial vacuum in order to reduce the boiling point, otherwise sugar browning would occur. Following the increase of the sugar content by water evaporation, sugar starts to crystallise, while the graining pan content is still being heated and unified draw-in is being added, until the graining pan is full of the mixture of juice and sugar crystals. This mixture is called the massecuite, which is a mixture of sugar and syrup. The syrup is the residual juice, in which sugar is dispersed. Then the massecuite heating process is interrupted and massecuite is released to large vessels called the crystallising pans. From these crystallising pans, the massecuite flows to filtering centrifuges where syrup is separated from sugar; the sugar is the rinsed by hot water and slightly pre-dried by steam. Sugar is then removed from the centrifuges, dried in the sugar curing house and stored in a silo as finished white sugar. A silo is a standing cylindrical building filled with free-falling sugar. Sugar is removed from the silo bottom through unloading hatches and filled in packages ranging from 5 grams to 1 ton.

Middlings and Low-Grade Massecuite

Photo-gallery: Middlings and low-grade massecuite

As syrup that leaves the white sugar centrifuges contains a large quantity of sugar, it is boiled once more in the subsequent stage using further graining pans, where crystallisation occurs again. Centrifuging produces so-called middling sugar, which is not as white as sugar obtained in the first stage, and therefore it returns to production. It is dissolved in the thick juice and becomes part of the unified draw-in, described in the previous part of the white sugar production.

After middling sugar centrifuging, further syrups leave the centrifuges. The syrups still include a large quantity of sugar, which may be obtained by crystallisation and centrifuging. This is done in the third boiling stage in further graining pans and centrifuges, thus obtaining so-called low-grade sugar, which is then washed and further centrifuged and dissolved in the thick juice together with the middling sugar, and it is therefore contained in the unified draw-in. This way, the sugar yield from the initial thick juice is maximised. Syrup leaving the third set of centrifuges is called molasses. Molasses still has high sugar content, around fifty per cent, but it also includes all salts and non-sugars which passed through the production process and were separated from the sucrose by crystallisation and centrifuging. These non-sugars and salt prevent further crystallisation, and sugar can be extracted from the molasses only by special methods. The molasses from our sugar mill are sold as a raw product to distilleries; they are also used in livestock fodder.