SUGAR PLANT

Cane Carrier

This is used to transport cane to the milling tandem, and consists of chains and slats. Its width is normally equal to the mill size.

Mill

A cane-crushing unit having normally consisting of three rollers in a heavy steel housing. Cane first passes between the top and front rollers, then between the top and back rollers, to extract the juice.

Crushers

A cane crushing unit, preceding the first mill to crush the cane prior to extraction of juice, for the purpose of improving the quantity of juice extracted. Normally consists of two rollers.

Shredder

This has the same purpose as the crusher, but a different principle. Consists of a drum, with a concentric shaft, on which hammers are mounted on arms.

 

Mill Tandem

A complete mill is complex, consisting of crusher (or shredder) and all mills, together with drives and reducing gears.

 

Cane Knives

These are mounted on cane carriers prior to entrance to mills, for preventing entire cane stalks from entering the mills, straightening and precutting the cane, for the purpose of improving juice extraction and saving driving power at the same time.

 

Intermediate Carriers

These transport the milled cane (bagasse) from one mill to the next. BAGASSE CARRIER This carries the bagasse from the last mill to the boilers, and its excess to storage.

 

Power Plant

This produces electricity by means of non-condensing steam turbines, which drive generators.

 

Juice Heater

A heat exchanger in which juice is heated by using steam as a medium, normally a multi-pass system. Juice flows through tubes, while steam passes along the outside of the tubes, in the cylindrical body.

Clarifier

It is a large vertical cylindrical tank, where juice is given time for decantation, to separate the clear juice from the turbid, which still contains the mud. Juice flow is continuous.

Drum Filter

A device to separate the mud from the turbid juice; normally of the rotary vacuum type. , to let the juice pass and retain the mud on its surface.

Evaporator

A series of vessels, in which excess water from the juice is evaporated to form a more concentrated liquid, now called syrup. The vessels work in series under increasing vacuum conditions, to reduce the boiling temperature gradually as the concentration increases step-wise. This prevents overheating of juice and loss of sucrose. The vessels together form a triple-, quadruple- or quintuple-effect evaporator.

Vacuum Pan

Similar to an evaporator vessel, a continuation of the evaporating process, but carried so far that crystallization occurs. Also boils under vacuum for reduced boiling temperature. The syrup is now transformed into massecuite , which is a mixture of crystals and molasses.

Crystallizer

A strike receiver in which the charge from the vacuum pan is stored before going to the centrifugals. Its purpose is cooling, to increase grain size and reduce sucrose left in molasses.

Centrifugal

A machine with a fast spinning drum and a screen, inside, through which the molasses can pass while the crystals are retained. Separation is based on the difference in specific gravity, amplified by centrifugal force.

Dryer

A long drum-like rotating cylinder, where sugar is brought in contact with heated air, to reduce its moisture content.

Cooler

Same as a dryer, but air is dry and cooled to reduce temperature of sugar, heated by the dryer. This is to prevent caking during storage. The combination of dryer an

CRUSHING MILLS
After tipping the cane passes through a shredder, which reduces the billets of cane to a fibrous mass. The shredded cane then passes through a series of mill tandem to extract as much cane juice as possible. Most of the crushing mills are driven by electric motor. The juice from the first crushing mill is analysed in the laboratory for sugar content (CCS). Payment to growers is based on weight of cane and CCS value

STEAM GENERATING PLANT
The fibre remaining after the cane has passed through the milling train is called "bagasse". Bagasse is used as fuel for the boiler plant, which provides steam to power the entire factory including our electricity generating turbines. Bagasse is also stored for use in the lead up to the start of the crushing season and when wet weather disrupts harvesting operations. This makes our factory virtually independent of external energy needs during the crushing season

CLARIFICATION
The cane juice, as delivered from the milling tandems, contains some soil and other undesirable impurities. To remove these, the juice is heated and lime is added to settle the unwanted material. The impurities settle out in the clarifier and then go to the rotary vacuum filters, which filter out any remaining juice. The filter mud from the vacuum filters is rich in nutrients and is recycled back to cane fields. Clear amber coloured clarified juice containing about 15% sugar is decanted from the clarifiers to the evaporators

EVAPORATION
The clarified juice is concentrated to thick syrup by boiling off water in the evaporators. The juice passes continuously from vessel to vessel until it is concentrated to syrup containing approximately 70% sugar. The evaporators are operated under vacuum and in "multiple effects" configuration whereby the vapour space of one vessel is connected to the heating surface of the next throughout the set. This gives maximum efficiency in evaporation and steam usage. Boiling under a vacuum is very energy efficient because the boiling point of the liquid is much lower than at normal atmospheric pressure

PAN STAGE
At the pan stage the syrup from the evaporators is converted to crystal sugar. A charge of syrup is taken into a vacuum pan and again boiled under a vacuum. A quantity of very fine “seed” crystal is introduced. As water is evaporated fresh syrup is added and sugar is deposited on the seed crystal. This process continues until the crystals have reached the desired size (approx. 1 mm square). The resulting semi liquid mass of sugar crystals and molasses is called ‘massecuite'.

CENTRIFUGATION
Sugar crystals are separated from the syrup in the centrifugals. The centrifugals are perforated metal baskets spun at high speed by an electric motor. While the sugar is spinning in the baskets it is given a short burst of hot water to help wash the sticky molasses off the sugar crystals.

SUGAR DRYERS

Sugar has to be dried and cooled to precise levels to enhance its storage life. This is done in the sugar driers. Evaporation of excess water from the surface of the crystals results in the desired cooling of the sugar. In the generally wet conditions we use large air-conditioning units to provide the cool dry air to the sugar driers. The dried and cool sugar is now ready for shipment.

The sugar from open boiling process usually called the local term Khandsari is obtained from sugarcane juice by using open pans for concentration and clarified using sulphur.
 
Juice Extraction:The extraction of juice can be done by using horizontal three roller mills using hydraulic pressure on mills. The milling tandem should contain two or three mills, each of three rollers. This reduces the moisture content in the bagasse and loss of the sugar in bagasse. The extraction of juice in the Khandsari sugar industry ranges from 55-65%.The cold raw juice is received alternatively in two underground tanks in the mill house. This juice, which is acidic (pH 5.2-5.4), milk of lime is addedand the pH of the juice is raised to 10. With addition of milk of lime in the given proportions, pH of the juice rises as the natural free organic acids are neutralized and juice becomes alkaline. 
Juice Purification:The purification of juice was carried out sulphitation tank. In this process sulphur is burnt in a special furnace with the help of an air compressor using atmospheric air and the SO2 gas is produced. The gas is made to bubble through the juice in the sulphitation tank through a perforated coil located in the bottom of the tank at a high pressure until the pH of the juice is reduced to 6.8-7.0. After neutralization, the juice is heated to 100°C in the round bottom pan of the bel and then pumped into the settling tanks. Here the impurities are allowed to settle down to the bottom leaving a supernatant layer of clear juice. The time required for settling is approximately 45 minutes. The clear juice is drawn off in the tank by means of suitable cocks placed at different levels and is allowed to flow into standard bel for being concentrated to rab (massecuite). The muddy juice remaining at the bottom of the settling tank is pumped to filter presses for filtration for the recovery of any sucrose. The filtrate from these bag filter press and the washings are directed into the standard bel for being mixed with the rest of the clear juice. Juice Concentration:by Open Pan BoilingThere are several different configurations of boiling pans for concentration of sugarcane juice by open pan (in round bottom vessel called “bel” in local language) boiling. These bels are heated by firing bagasse in the furnace. The juice is heated to 96-98°C and then concentrated at temperatures between 105-106°C in various pans.
Solidification of concentrated Juice:The solidification and crystallization of the concentrated juice is done in crystallizers. The rab (106°C) is then transferred to crystallizer and allowed to remain there for about 36 hours for the growth of crystals. The crystallizers are fitted with special stirrers rotating slowly continuously for the formation and growth of crystals. When the rab has cooled down to room temperature after about 36 hours and is fully mature, is taken to centrifuge machine. Crystals are slightly washed with water in the centrifuge. The separated crystals are dried and bagged as first quality sugar.
 
The mixture of heavy and light molasses obtained after the separation of the crystals from the first rab is called ‘first molasses’. This is again boiled to give second rab. The second rab is allowed to cool and mature in crystallizers, which are also fitted with stirrers but these crystallizers are smaller in size. The second rab takes about 60-70 hours to mature and cool down to room temperature. The sugar separated from the second rab by centrifuging is sun dried and bagged as ‘second sugar, which is slightly inferior to the first sugar. The mixture of heavy and light molasses resulting from the purging of the second rab is known as ‘second molasses"

Sugarcane

The typical composition of Sugarcane is as follows:

15% dissolved matter (13% sucrose; 2% are other sugars-mainly glucose and fructose)

• 15% fibre (insoluble), and
• 70% water.

 

Though the basic raw material is sugar cane, for processing sugar cane into sugar, other chemicals are required, such as lime, sulphur, caustic soda, washing soda, other consumable like oils and greases, lubricants, gunny bags, fire wood etc.

Man - Power Requirement

The manpower requirement will be of two categories

• Permanent staff – Managerial, clerical staff, watch & ward etc.
• Seasonal Staff, workers – to be appointed during the crushing period only.

Land Requirement

Depending upon the capacity of the plant suitable land area is required for the Plant & Machinery, Godowns, Molasses tanks, Storage, Office Building, and Cane Yard etc. The land should have good approach road for transport of cane, Sugar, Molasses etc., & should have water facility.

 

Building, Plant & Machinery

All the stations of Plant, Milling, Boilers, Power House, Boiling House, Centrifugal System, Sugar House etc., shall have the building.

Juice Extraction

A basic cane mill consists of three grooved rollers. Prepared cane is squeezed between the rollers, thus forcing the juice out of the fibre. The bagasse left in the last set of roller will be used for fuel to power the boilers to produce steam and generate electricity for use in subsequent sugar production process.

 

Juice Clarification

Juice from a milling tandem contains a large amount of cane fibre, dirt and unwarranted particles that falls out with the juice between the rollers of the mills. To make it lucid and clear juice the juice is poured over a wire-mesh screen. And then the juice is heated and lime is added to neutralise the natural acidity. It is then placed in a Clarifier which produces a clear juice that is light in colour and free of suspended matter.

Evaporation

The clarified juice is then put through multiple evaporators to extract up to 60–65% of water from it, leaving the juice becoming concentrated or syrup with 60–65 brix. Multiple effect evaporation is the system where juice is boiled in series in several vessels, with steam fed to vessel 1 only. Vapour from vessel 1 boils the juice in vessel 2, vapour from 2 boils the juice in 3, and so on until vapour from the final vessel goes to waste.

Sugar boiling

Sugar boiling is conducted under “vacuum pan” process in order to lower operating temperatures, but some small scale manufacturer of sugar “open pan” processes. The syrup produced by the evaporators is concentrated further in pans. As the concentration rises the dissolved sugar crystallises and the work of the pans is to grow sugar crystals in several steps to maximise the amount of sucrose recovered in raw sugar.

Crystallization

When the massecuite is discharged from the pans it is retained in crystallisers, where the sugar crystals continue to grow through cooling rather than boiling. The crystallisers are U-shaped vessels where massecuite is slowly rotated and allowed to cool. This technique is often referred to as “crystallisation in motion”. Rotation promotes even cooling of the massecuit, which helps to achieve uniform crystal growth. Uniform crystal growth can also be encouraged by placing granulated massecuit from a previous batch into the crystalliser with the fresh massecuit. This process is known as “seeding”.

Centrifugation

A centrifugal is a machine that separates crystals from molasses. Centrifugation involves spinning massecuite in a perforated basket; centrifugal force acts on the molasses, forcing it through the perforations while the sugar remains on the basket wall. Water and steam may then be sprayed onto the crystals to wash off the remaining molasses.

Sugar drying

In a drier, the moisture is driven off from the surface of the liquor layer covering the crystal by passing heated air around the sugar crystals. The product from the process described so far is a raw sugar (Brown sugar) that can be used as is, or sent to a refinery to be converted to a white (refined) sugar.

By products

Bagasse is the final residual of the cane after it has underwent crushing/milling process. Nowadays, bagasse is used as fuel in generating electricity and steam the sugar production process. Furthermore, bagasse can be used as raw material for producing paper, insulating board, and hardboard, as well as furfural, a chemical intermediate for the synthesis of furan and tetrahydrofuran. The end product derived from sugar refining is blackstrap molasses.