The sanscrit word sarkara is the origin of the word sugar in all the indo-European languages: sukkar in Arabic, saccharum in Latin, zucchero in Italian, seker in Turkish, zucker in German, sugar in English.

Sugar arrived in Europe in the 12th century. Important regions of production emerged in the following centuries, especially in the Far East. Interest in the spice grew from the 15th century, when new drinks such as coffee, tea and chocolate were sweetened with sugar. In 1493 Christopher Columbus began sugar cultivation in the Antilles. From that time onwards, the history of sugar in the world took on new dimensions.

“This plant sprouts from honey; we uproot it with honey; sweetness is born. I garland you with sugar cane so that you do not ignore me, so that you love me, so that you are not unfaithful to me”
Atharva-Veda, 4th. Book of Vedas, a sacred Hindu book.

In Brazil, sugar is produced from cane, while in Europe it almost entirely manufactured from sugar beet. Today sugar cane is also used to produce alcohol.

The cane stored in the yard is normally unloaded to the feed tables by tractors with rakes, while cane stored in the shed is unloaded onto the tables by hoists with hydraulic claws. In anticipation of occasional faults in the transport system, and its interruption at night, it is always sought to maintain a certain amount of cane in stock in covered sheds or open yards.

Stored cane should be replaced quickly to reduce sugar loss due to biological decomposition. Chopped cane, which should not be stored, is unloaded directly onto the conveyors. Unloading can be done with hoists equipped with hydraulic claws, hillo-type cranes, and in the case of chopped cane, with a hydraulic tilter for side tipper trucks.

Juice extraction, cane feed and washing
The first equipment – the feed table – receives the cane loads from stock, or directly from the trucks, transferring them to one or more metal conveyors that carry the cane to the mills, via a preparation system. This has a rolling section made from axles, belts and flights, which, according to its angle can be classified as:

• Conventional: angled between 5º and 17º
• Steep angle: 45º

Although the conventional tables have a large feed capacity, they make it irregular, since the cane layer is very high, creating feed difficulties and decreasing cane-washing efficiency.

The 45º tables work faster, with a very low layer that provides a much more regular and easily controllable feed and considerably increases cane-washing efficiency.

Washing – carried out on the feed tables – aims to remove foreign matter such as earth, sand, etc., to obtain better juice quality and extend the working life of the machinery by reducing wear. This washing is never performed on the chopped cane, as it would cause a very great separation of sucrose in the water.

Cane preparation
The feed table controls the amount of cane on a metal conveyor transferring it to the preparation sector. The basic purpose of cane preparation is to increase its density, and consequently its milling capacity, and also achieve maximum splitting of cells to release the juice within them, thus achieving greater extraction.

The preparation system comprises one or two knife sets – of which the first is only a leveler – that prepare the cane for sending to the shredder.

The knife set is a piece of equipment with fixed rotating knives running at a peripheral speed of 60m/s, which is used to increase cane density, cutting it into smaller pieces, preparing it for the shredding process.
The grinder comprises a feed drum that compacts the cane on entry, preceded by a rotor assembly of oscillating hammers that turns in the opposite direction to the conveyor, forcing the cane through a small opening (1cm) along a shredder plate.

The peripheral speed of the grinders, 60 to 90 m/s, manages to provide preparation figures of 80% to 92%. This figure is a relationship between the cells split by the shredder and the sugar from the cane.

Feed to the mill
After the preparation system, the height of the cane bed is made uniform by a piece of equipment called a spreader, where the cane is unloaded from the metal conveyor onto a rubber conveyor belt. This belt runs at high speed (90m/min) to reduce the thickness of the cane layer and facilitate the work of the electromagnet that removes ferrous material, protecting the extraction equipment and especially the milling rollers.

The next stage is feeding the mill with a device called a chute, or a more modern system known as the Donelly chute, or forced feed channel. The most common and efficient system has been the Donelly chute. In this channel the prepared cane forms a denser column assisting the feed and capacity of the mill. The level of cane in the channel is used to control the speed of the rubber conveyor, and consequently the feed to the mill.

Milling
The cane basically consists of juice and fiber. The sugar, which is the product we are really interested in, is dissolved in the juice; therefore our aim is to extract as much of this juice as possible.

At the industrial level there are two extraction processes, milling and diffusion.

Milling is a strictly volumetric process and consists of separating the juice contained in the cane. This separation is achieved by passing the cane through two rollers at a specific pressure and rotation, with the volume produced being less than the volume of the cane. The volumetric excess, rejecting the volume of juice reabsorbed by the bagasse, has to be separated, corresponding, therefore, to the volume of juice extracted.

A secondary, yet extremely important, aim of milling is to produce a final bagasse in suitable condition for fast burning in the boilers.

The greater part of overall extraction happens in the first milling unit, simply with juice extraction. The cane holds about seven parts of juice for each part of fiber; in the first bagasse this proportion drops to two to two and a half and it is easy to notice that, if we do not use some kind of device, the later mills will soon not be able to extract any juice even if pressure on the bagasse layer is increased. The device used is imbibition, which will be explained later.

Each mill roller assembly, mounted on a structure caller the “castle” constitutes a mill trio. The number of trios used in the milling process varies from four to seven and each consists of three rollers: the entry roller, the upper roller and the exit roller. Mills normally have a fourth roller, called the pressure roller, which improves feed efficiency. The load on the bagasse layer is transmitted by a hydraulic system operating on the upper roller.

Imbibition
The cane’s juice is removed or extracted as it passes through a series of mill trios. The device of adding water to the bagasse is called imbibition, and its purpose is to dilute the remaining juice in the bagasse, increasing sucrose extraction.

Imbibition can be:

• Simple
• Compound
• With recirculation

Efficiency increases from the first to the last, however the most used is compound, as the third can cause serious problems in the mill feed.

The most common process is compound imbibition, which consists of adding water between the two final trios and returning the juice extracted from the last one to the previous one, successively, back to the second trio.

The juices from the two first trios are normally mixed and comprise what is known as the mixed juice. With this system, extraction of 92% to 96% can be achieved, with final bagasse humidity of approximately 50%.
During the passage of the cane through the mills, fragments of the cane or bagasse are formed, called ‘bagacilho’. The amount of bagacilho has to be periodically controlled, since excessive breaking indicates incorrect mill adjustment.

Bagacilho that comes out of the mills with the mixed juice has to be strained and returned to the milling system, while the mixed juice, now free from bagacilho, is sent to the manufacturing sector.

Diffusion
The other process of extracting sucrose from the cane is diffusion, which is a process still little used in Brazil, whose technology benefits from part of the stages of the milling process:
Diffusion: cane preparation -> diffusion -> water removal

The basic difference between the two processes is in the way of separating the juice from the fiber. In this separation, the diffuser performs two operations:

• Diffusion: separation by osmosis, in relation only to the un-split cane cells, approximately 3%;
• Leaching: successive extraction with water of sucrose and impurities in the open cells.

Removal of water or draining of the bagasse after the diffusion stage is carried out with rollers, as in the milling process.

Energy generation
After extraction of the juice, the material called bagasse is obtained, consisting of fiber (46%), water (50%), and dissolved solids (4%). The amount of bagasse obtained ranges from 240kg to 280kg of bagasse per tonne of cane, and the sugar inside it represents one of the losses of the process.

Cane bagasse is fed to pressure boilers, where it is burned, and the available energy converts water in vapor. The steam generated in this equipments with an average pressure of 18 – 21 kgf/cm2 ( Modern boilers operates with pressure between 40 and 100 kgf/cm2), is utilized to move steam turbines where thermal energy is converted in mechanical energy.

These turbines are responsible for powering the choppers, shredders, mills etc, and also for generating electricity needed for the various sectors of the industry.

The steam released by these turbines is low pressure (1.3 – 1.7 kgf/cm2), called escape steam, which is reused as the basic energy needed in the sugar and alcohol manufacturing process.

Primary juice treatment
The juice obtained in the extraction process presents a varying amount of impurities, which could be soluble or insoluble. Primary treatment aims for maximum elimination of insoluble impurities (sand, mud, bagacilho, etc.), which are at levels of 0.1% to 1%. Elimination of this material improves the process and increases the efficiency and working life of the equipment, which also contributes to obtaining better quality end products. The basic equipment used for this treatment consists of:

Cush-cush
The cush-cush consists of fixed strainers with 0.5mm to 2mm holes, located very close to the mill, and whose purpose is to remove the thickest material in suspension (bagacilho). The retained material, principally consisting of juice and bagacilho, returns as scrapings between the first and second mill trio, or even before the first trio.

Strainers
Juice straining is currently performed by different types of strainer (DSM, rotational, vibrational), which use meshes of various types and openings (0.2 mm to 0.7mm) with an efficiency of 60% to 80%. The retained material is also returned to the mill.

Hydrocyclones
The equipment functions on the principal of the different densities of solids/liquids: during use, centrifugal force separates the sand and mud from the juice. In some cases separation efficiency of more than 90% of particles up to 40µ can be achieved.

Weighing of the juice
After initial treatment, the juice mass is sent for processing, and quantified using outflow measurers or juice scales, enabling better chemical control of the process.

Chemical treatment of the juice.
Despite the preliminary treatment mentioned, the juice still contains smaller impurities that may be soluble, colloidal or insoluble.

Therefore chemical treatment is principally directed at the coagulation, flocculation and precipitation of these impurities, which are removed by sedimentation. It is also necessary to correct the pH to prevent inversion and decomposition of the sucrose.

The treated juice can be sent for manufacture of sugar or alcohol. In the second case, the sulfurizing process described below is not essential.

Juice sulfurizing
This consists of absorption of the SO2 (sulfur dioxide) by the juice, lowering its original pH to 4.0– 4.5. Sulfurizing is usually carried out in an absorption column with perforated dishes inside it. The juice is pumped to the upper part of the tower and descends through the dishes by gravity against the SO2 gas, sucked by an extractor or ejector installed at the top of the column. Due to the great solubility of SO2 in water, up to 99.5% absorption can be obtained with this equipment.

Sulfur dioxide is produced in the sugar factory by direct burning of sulfur plus air, in special sulfur burners, according to the reaction:
S + O2 -> SO2

The main objectives of sulfurizing are:

• Inhibiting reactions causing color formation;
• Coagulation of soluble colloids;
• Formation of CaSO3 (calcium sulfate) precipitation;
• Decreasing the viscosity of the juice and consequently of the syrup, cooked pastes and molasses, facilitating evaporation and cooking operations.

Average consumption of sulfur can be estimated as between 250 and 500g/TC.

Liming
This is a process of adding milk of lime (Ca [OH]2) to the juice, raising its pH to a range of 6.8 to 7.2. Liming is carried out in tanks, in a continuous or discontinuous process, aiming at control of the final pH.

Milk of lime is also produced directly in the sugar mill through out the hydration of lime (CaO) in special tanks (swimming pool) or in special designed lime hydrators, according to the reaction:

CaO + H2O -> Ca (OH)2 + calor

The Ca(OH)2 produced has a 3º - 6º "Beaume" concentration before being added to the juice.

The aim of this neutralization is to remove colorants from the juice, neutralize organic acids and the formation of calcium phosphate and sulfate, which are products that, on sedimentation, carry with them impurities present in the liquid.
Lime consumption (CaO) ranges from 500 to 1,000g/TC, according to the treatment strength required.

Heating
Heating the juice is carried out in equipment called heat exchangers, consisting of a collection of tubes, through which the juice passes, inside a cylinder of saturated steam.

The juice is heated to approximately 105ºC to accelerate and facilitate the coagulation and flocculation of colloids and non-sugar proteins, emulsify fats and waxes, or in other words accelerate the chemical process, increasing decanting efficiency, and also enabling removal of gas from the juice.

Sedimentation
This is the stage of juice purification by removing the flocculated impurities from the previous treatments. This process is carried out continuously in equipment called a clarifier or decanter that has several compartments (trays) to increase the decantation surface.

The decanted juice is removed from the upper part of each compartment and sent to the evaporation sector to be concentrated. The sedimented impurities, with a solids concentration of approximately 10º Bé, comprise the sludge that is normally removed from the decanter by the base, and sent to the filtration sector for recovery of the sugar it contains.

The time the juice remains in the decanter ranges from 15 minutes to 4 hours, depending on the type of equipment used, and the amount of sludge removed represents 15% to 20% of the weight of the juice on entering the decanter.

Filtration
Before being sent to the rotary filters, the sludge removed from the decanter has about 3 – 5 kg of bagacilho/TC added to it, which will work as a filtration aid.

The purpose of this filtration is to recover the sugar contained in the sludge, returning it to the process as filtered juice. The material removed from the filter is called cake, and sent to the plantation to be used as fertilizer. It is extremely important to control sugar loss in the cake, as its level should be no more than 1%.

Evaporation
The clarified juice obtained in the decanters undergoes a concentration process by removing the water contained in it.