THE UNIVERSITY OF DODOMA COLLEGE OF NATURAL AND MATHEMATICS SCIENCES SCHOOL OF PHYSICAL SCIENCES DEPARTMENT OF CHEMISTRY THE PRACTICAL TRAINING AT MTIBWA SUGAR ESTATE (MSE) LTD BASED ON SUGAR PRODUCTION WRITTEN BY: JATOSH SAMWEL WITH REGISTRATION NO: T/UDOM/2010/00492 A report submitted under partial fulfillment of the requirements of practical training course CH 212 for Bachelor of Science in chemistry, the University of Dodoma. NAME OF SUPERVISOR: POLYCARP W. MASHELE DATE OF SUBMISSION: 14/10/2012 THE PRACTICAL TRAINING AT MTIBWA SUGAR ESTATE (MSE) LTD BASED ON SUGAR PRODUCTION WRITTEN BY: JATOSH SAMWEL
WITH REGISTRATION NO: T/UDOM/2010/00492 A report submitted under partial fulfillment of the requirements of practical training course CH 212 for Bachelor of Science in chemistry, the University of Dodoma. INSTITUTION NAME: THE UNIVERSITY OF DODOMA THE PRACTICAL TRAINING WAS CONDUCTED AT MTIBWA SUGAR ESTATE IN MOROGORO REGION TANZANIA CODE NO: CH 212 DEGREE PROGRAMME: BACHELOR OF SCIENCE IN CHEMISTRY DEPARTMENT OF CHEMISTRY NAME OF SUPPERVISOR: POLYCARP W. MASHELE DATE OF SUBMISSION: 14/10/2012 TABLE OF CONTENTS DECLARATION
This is certify that I have supervised the student mentioned above at the company during the practical training and the presented report is hi work according to how he was …………………… ………………….. …………………….. Supervisor’s Name Signature Date ACKNOWLEDGEMENTS To my beloved God, I would like to thank you for strengthening me all the time during preparation of my practical training report at Mtibwa Sugar Estate. I would like to thank the administration of Mtibwa Sugar Estate for giving me the chance of learning all process of making sugar production.
To my lecturers, I would like to appreciate your efforts of teaching us practical subject and enlighten us on how to conduct practical training report. I would like to thanks Mr. Kihula, the Human Resource Manager and Mr. Polycarp W Mashele, the production manager, for their daily assistances during the whole training period. Thanks should also go to Mr. Issa Mdemu, Mr. Mohamed and Mr. Ng’wanabuzuka, the process shift Chemists; Mr. Masumba Stephen, (the laboratory supervisor)Fred Mrosso and Hassan Matua, (the laboratory shift analysts) for their useful assistance during the whole time of analysis processes in the laboratory.
I would like to thanks my fellow students for sharing different ideas during our studying of practical training at Mtibwa Sugar Estate. Lastly but not least I would like to appreciate my beloved Miss Josephina P Said for encouragement and social support during my practical training report. ABSTRACT This practical training was conducted at Mtibwa Sugar Estates in Morogoro region. It is based on the sugar production from sugar cane. Most of the sugar produced in Mtibwa is for home consumption and only a small proportion is exported to service foreign debts.
The production processes was done by methods of physical separations such as extraction of juice from sugarcane, clarification, mud filtration, evaporation, crystallization and centrifugation whereas the sample analyses were done by polarimetry, pH metry, TDS metry and titrimetry, depending on the type of sample being analyzed. As a result, a typical cane was found to contain 12% to 14% fibre with a 70% moisture contents to give about 25 to 30 tons of bagasse per 100 tons of cane or 10 tons of sugar, likewise a typical mixed juice from extraction contains about 13% sugar and the bagasse contains 1% to 2% sugar, having a brix of 12. , pol 13. 12, purity 88. 2% and about 50% moisture. Thus, the activity enhances clear understanding of chemistry related courses as it brings learners to the reality of what is actually happening rather than just reading from the books. MTIBWA SUGAR ESTATE ORGANIZATION CHART COMMON DEFINITIONS Extraction; the percentage ratio of sucrose in mixed juice to sucrose in cane. Imbibitions; the process in which water or juice is added to the bagasse to mix with and dilute the juice present in the later. The water so used is called Imbibitions water.
Dry substance; the material remaining after drying the product (bagasse) to constant weight. Ash; the residue after burning off all organic matter. Bagasse; the residue obtained from the cane after having passed through the mills and diffuser. Bagacillo; very small particles of bagasse separated from the mass of final bagasse for filtration. Brix; is the percentage by weight of dissolved solids in a sugar solution. It is given in grams per 100g of solution. Pol; Is the percentage of dissolved sucrose. A solution of 100g of water containing 48g of dissolved sucrose has a pol% of 48.
Purity; is an apparent percentage ratio (or pol) to the total soluble solids (or brix) in a sugar product. Fibre; these are water insoluble matter of cane and bagasse from which all water has been removed by drying. First expressed juice; the juice expressed by the first two rollers of the tandem. Last expressed juice; the juice expressed by the last two rollers of the tandem. Mixed juice; the mixture of juices from the extraction plant pumped into the juice scale. Clear juice; the juice obtained as a result of clarification.
Liming; is the process of adding calcium oxide (CaO) to the slightly heated mixed juice in order to raise its pH from around 5 to around 7. This prevents both sugar inversion and alkaline degradation. Syrup; the concentrated clarified juice having a brix between 60% to 70% and water below 25%. Jelly; this is a boiling of mixed grades of mother liquor, which has been concentrated without graining. Magma; is a mixture of crystals and water or juice produced by mechanical mixing. Massecuite; the mixture of crystals and mother liquor discharged from a vacuum pan. Molasses; the mother liquor separated from the crystals.
Mud; the material which has settled out in the clarifier. It contains most of the suspended solid. 1. 0 INTRODUCTION AND BACKGROUND Mtibwa Sugar Estate limited (MSE) is located at 380 E 60 S in Turiani Division 102km north of Morogoro town and 290 km from Dar es salaam. It is situated at an altitude of 350m above sea level at the Eastern foothills of the Uruguru mountain range. Sugarcane growing and the production of sugar and related products are the main activities of Mtibwa Sugar Estate limited. Cane is supplied from the company’s own fields and some small portion from small out growers surrounding villages.
Mtibwa Sugar Estate limited (MSE) was established under the companies’ ordinance (cape 212) in the year 1939, and was officially incorporated on 22nd day of December 1961. Among the company’s prime objectives being planters and producers of sugarcane for producing sugar. Since its inception the estate has passed through many hands of ownership. The company was a parastatal organization under the government till 1999 when it was privatized and purchased by Tanzania sugar industries Ltd. (TSIL), a local company incorporated in Tanzania. 1. 1 The vision of Mtibwa Sugar Estate Limited MSE is to plant and grow sugarcane and take up a leading position in Tanzania in production of white sugar and associated products. 1. 2 Mission of Mtibwa Sugar Estate Limited •To increase its production capacities and become as quickly as possible at low cost in order to improve its competitiveness in the emerging economic environment; i. e. to become profitable enterprise. •To contribute to the social development and welfare of the local community, in particular the employees and the people living in the surrounding villages. •To ensure that its activities are environmentally sound. 2. RAW MATERIALS FOR SUGAR PRODUCTION Sugar is a broad term applied to a large number of carbohydrates present in many plants and characterized by a more or less sweet taste. The primary sugar, glucose, is a product of photosynthesis and occurs in all green plants. In most plants, the sugars occur as a mixture that cannot readily be separated into the components. In the sap of some plants, the sugar mixtures are condensed into syrup. Juices of sugarcane (Saccharum officinarum) and sugar beet (Beta vulgaris) are rich in pure sucrose, although beet sugar is generally much less sweet than cane sugar.
These two sugar crops are the main sources of commercial sucrose. 2. 1 Sugarcane The sugarcane stalk is the main raw material used in production of sugar and other related products. Sugarcane is a thick, tall, perennial grass which belongs to the specie known as Saccharum officinarum that flourishes in tropical or subtropical regions. Sugar synthesized in the leaves is used as a source of energy for growth or is sent to the stalks for storage. It is the sweet sap in the stalks that is the source of sugar as we know it. The sugarcane, in which the sugar is stored, is divided by nodes into the several sections called internodes.
The length of these internodes may differ considerably and is dependent on the cane variety, soil type, growth conditions etc. The same goes to the thickness of the stalks. Each node carries a bud, which is capable of producing a plant, from which shoot develop forming a stool. Sugarcane contains large amount of sucrose as compared to other sugar containing plants, such as wheat stalk, maize stalk, sorghum stalk and fruits such as mangos, banana, pineapple etc. Sucrose in the juice and cellulose in the fiber are the two main constituents of sugarcane, and both are made of simple sugars.
The simple sugars glucose (dextrose) and fructose (levulose) occurs free in the sugarcane juice, usually in the lesser amounts than sucrose. The production of the sugar from the sugarcane is based on the ability of the sucrose to crystallize from thick syrup while glucose and fructose remain dissolved. Other sugars occur in cane but not in the Free State, these are constituents of the gums or cell walls. Sugars are classed as carbohydrates and as the name suggests, are composed of the Carbon, Hydrogen and Oxygen; Hydrogen and Oxygen are usually present in the same ratio occurring in water.
The simple sugars glucose and fructose are also classified as monosaccharide because they cane not be reduced to smaller carbohydrate molecule when attacked by acids or enzymes. The monosaccharide can be composed of two or more carbons atoms, with one carbon linked to an aldehydic (aldoses) or ketonic (ketoses) group, and other carbon atoms linked to hydroxyl group. Monosaccharide usually contains five (pentose) or six (hexose) carbon atoms. The arabinose in the cane gum is a pentose and glucose and fructose are hexodes.
This is the reason why sugarcane is the mostly used for production of sugar all over the world. A mature sugarcane stalk comprises of the following contents as tabulated bellow; Water65-75% Sucrose11-19% Non-sucrose0. 5-1. 5% Fibres11-19% Table1. Composition of sugarcane Furthermore there are small quantities of starch, gums, waxes, and pigments, organic and inorganic substances. 2. 2 Sugarcane cultivation Sugarcane is an important commercial crop in Tanzania; it is the main source of sugar produced for export and domestic consumption.
Currently, most sugar cane is grown in estates, owned by the sugar processing factories as well as contract growers. Sugarcane is cultivated in the tropics and subtropics in areas with plentiful supply of water, for continuous period of more than six to seven month each year, either from natural rainfall or through irrigation; this kind of cultivation is also applicable here at Mtibwa sugar estate Ltd. The crop does not tolerate severe frosts; therefore, most of the world’s sugarcane is grown between the altitude of 220N and 220S and some up to 330N and 330S Figure1. Young sugarcane plant
Sugarcane can be grown on many soils ranging from highly fertile well drained mollisols, through heavy cracking vertisols, infertile acid oxiols, peaty histosols to rock andisols. Both plentiful sunshine and water supply increases cane productions. Although sugarcane produces seeds, modern stem cutting has become the most common production method. Each cutting must contain at least one bud; this provides a certain security that a plant will develop from the cutting even if one bud is damaged. The seedlings are planted in rows in pre-prepared furrows (furrows depth Ca. 40cm).
On conversional sugarcane cultivations, the average distance between the rows is 150cm (120cm-180cm). On organic sugarcane cultivations, the best results have been achieved with double rows (40-50cm gap between two single rows and 110-180cm distance to the next double rows). In general the distance between the rows should take into account the special requirements of the organic sugarcane cultivations, the irrigation infrastructure which may be present and the degree of mechanization. The sugar is formed in the green leaves which contain green coloring matter called chlorophyll.
In the presence of light the leaf absorbs carbon dioxide gas from the air through holes (stomata) and the chlorophyll has the ability to combine this gas with water taken up by the roots to produce sugar. Certain cells of the plant transport the sugar to the stalk where it is stored. All energy required for the process is delivered from the sunlight. This process is called photosynthesis. Carbon dioxide + water monosaccharide + oxygen 6CO2 + H2O + C6H12O6 + O2 The sugar is unevenly distributed hrough the length of the cane stalk, the top part having the lowest sugar content. The tops are therefore cut off in the field. 2. 3 Sucrose Sugar in the ordinary sense is sucrose. It is the sugar of household and industry and is the most common sugar in the plant kingdom. Sucrose occurs in all part of the sugarcane plant and is the abundant in the stalk, where found in watery vacuoles of the storage cells (parenchyma). The sucrose content is in the actively growing regions, especially the soft portions of the stem tip and the leaf roll.
The monosaccharide sugars, glucose and fructose, condenses to form sucrose and water. C6H12O6+ C6H12O6 C12H22O11 + H2O Is a disaccharide sugar with chemical formula C12H22O11 and molecular weight of 242. 3; Sucrose crystals are monoclinic prisms having density of 1. 588; a 26% solution has a density 1. 108175 at 200C. Sucrose is optically active with the specific rotation [? ]20D+ 66. 53 when a normal weight is used, its melting point is 1880C (370F) and it decomposes on melting.
The refractive index is 1. 3740 for 26% solution. Sucrose is soluble in water and ethanol, saturated solution at 200C(67F) containing 67. 09 and 0. 9% by weight respectively. When the cane is cut, this building up process stops and under unfavorable condition such as high temperature and high humidity because of the rain, a decomposition process starts, and the monosaccharide are formed again; therefore it is important to process the cane as soon as possible after it has been cut.
When hydrolyzed, sucrose yields equimolar amounts of glucose and fructose, and the mixture is called invert. The decomposition process is known as inversion of sugar. However these sugars do not always occurs in equal amounts in raw juice, although sucrose is dextrorotatory and this feature is used to measure amounts of sucrose in solution. The specific rotation of invert is [? ]20D -39. 7 because the levorotatory activity of fructose is greater than the dextrorotatory activity of glucose. 2. 4 Pests and Diseases affecting Sugarcane Example of pests which affects sugarcane are cane beetle (also known as cane grub), these substantially reduce crop yield by eating roots. It cane be controlled with imidacloprid (confidor) or chlorpyrifos. Other important pests are larvae of some butterfly moth species, borer (Diatraea saccharalis), the Mexican rice borer (Eoreumaloftini); leaf cutting ants, termites, spittle burgs, and the beetle (Migdolus fyranus). The plant hopper insects (Eumetopina flavipes) acts as virus vector which causes the sugarcane disease called ramu stunt. •Example of pathogens and diseases which affects sugarcane.
Numerous pathogens and diseases infect sugarcane such as sugarcane grassy shoot disease caused by phytoplasma; whiptail disease or sugarcane smut caused by Fusarium moniliforme, gumming disease caused by bacteria and red root disease caused byColletotrichum falcatum. Viral diseases affecting sugarcane includes sugarcane mosaic virus, maize streak virus and sugarcane yellow leaf virus. 2. 5 Sugarcane harvesting Sugarcane takes about 11-12 months to mature, sugarcane harvesting starts when the leaves turns yellow (or when the optimum sugar content of 15% has been reached, that can be tested in the field by refractometer).
When it is ready for harvesting it stands two to four metres tall. Sugarcane is harvested by hand and mechanically. Hand harvesting accounts for more than half of the production and is dominant in the developing countries. 3. 0 SUGAR PRODUCTION PROCESSESS 3. 1 Weighing Except when stocktaking, weighing is the standard method of determining the quality of a product, measuring or calculating from analytical data are not permissible. Automatic scales provided with recording devices should be used and weighs expressed in conformity with the International System of Units (SI-units). . 2 Calibration of Scales The factory Chemistry should ensure that weighing devices are properly maintained and weighbridges should be checked frequently at regular intervals using official standard weighs. 3. 3 Weighing methods 3. 3. 1 Cane The weight of cane to be used for the purpose of chemical control should be that recorded at the factory weighbridge. Whenever possible, cane should be weighed immediately before being crushed. The accuracy of the daily chemical control figures will depend to a great extent on the chemist’s estimate of he amount of cane in stock every morning and, when the factory is working normally, every effort should be made to keep this stock to a minimum. Weighbridges must be fitted with digital display and connected to a computerized weighing system approved by the cane planters and millers. Arbitration and control Board they should be checked several times a day for zero setting. The net weight of cane is determined deducting the tare weight of the vehicle (to be after each unloading) from the gross weight. For purpose of factory control, no correction whatever is to be applied to the weight for the cane actually found. 3. 3. 2 Mixed Juice
Mixed juice should be weighed prior to the addition of any chemicals and preferably cold. For weighing of hot mixed juice, automatic tank scales of adequate capacity must be used. Manufacturer’s instructions should be strictly adhered too. To ensure accurate chemical control, frequent and regular checks of the scales should be carried out, preferably when in operation. When built in check weights are not available, check scales should be installed. 3. 3. 3 Imbibitions Water Automatic tank scales should be used. It is essential that every precaution be taken to prevent cooling water for mill bearings from finding its way into the juice. . 3. 4 Filter Cake It is recommended that all the cake produced be weighed as it leaves the filters. Care must be taken that no washing are included with the cake. 3. 3. 5 Final molasses Automatic scales of adequate capacity that totalize the actual differences in weight between the weight hoppers when full and empty are recommended. 3. 3. 6 Sugars The official net mass of sugar produced is the weight of raw recorded at the receiving station of the bulk sugar, terminal plus the weight of special sugar for local consumption recorded at the reception of official warehouses approved by the Mauritius Sugar Syndicate.
For daily factory control, sugar output should be weighed at the factory weighbridges. 3. 4 Cane Preparation The cane stalks are loaded on cane carts in the fields and sent to the factory by means of roads transport. All harvested cane, growers as well as the companies cane, is weighed on a regularly checked weighbridge, before entering the factory. Gross and Nelt weight, together with the name of the grower are mentioned on the weighbridge ticket. From each consignment of cane, a representative sample is taken after the shredder, by cane Testing Services, who analyses it on sucrose content in their separate laboratory.
The cane is transported to unloading cane yard where the crane unloads the trucks. The cane is fed on the cane table where they transported to the cane carriers by means of the kicker. The carrier the cane up to the carding drums where it is aligned properly in such a way that it can be sent to the cane knives, shredder and mills. To promote uniform distribution of cane and make pressure more effective, the cane is prepared by cutting it to shreds and small of pieces. This is done by a leveler, which is a set rotating knifes above the carrier turning a few centimeter above the horizontal part of the carrier.
For the final preparation, a shredder is used; it consists of a set of rapidly revolving hammers, which pass over anvil bars on which the cane is beaten and disintegrated into a small mass. The thickness of the cane blanket is maintained constant to ensure efficient crushing by exerting the pressure on all parts of cane as evenly as possible. Mills extract as much juice from the cane as possible and a good preparation of the cane juice contaminating cells of the cane. No juice is extracted by shredder.
Feeder table Magnetic separator Carding drums Feed drum Shredder Cane carrier 1 Cane carrier 2 Cane carrier 3 Mill Figure2. The diagram showing cane preparation and juice extraction 3. 5 The Milling process Harvested sugar cane is transported to a raw sugar mill. Because sugar cane must be milled as soon as possible, mill owners have railway networks and rolling stock.
At the mill, sugar cane is weighed and processed before being transported to a shredder. The shredder breaks apart the cane and raptures the juice cells. Rollers are used to separate sugar juice from the fibreness material, called bagasse. Here at Mtibwa Sugar Estate Limited. The milling process is conducted into four stages. The sugar cane fibrous from shredder are directed to the first milling machine whereby the sugar cane juice is extracted and the sugar cane residues are directed to the second milling machine, the sugar cane residue from the first milling plant/machine.
Are known magasse, magasses from the first milling machine contains sugar materials, the further extraction of sugar cane juice is done in second milling machine up to the fourth one. Under this process water is added to facilitate extraction of sugar cane juice from magasse. The residue obtained from the first fourth milling plant is known as Bagasse, the bagasse is recycled as fuel for the mill boiler furnace. 3. 6 Juice extraction and screening The prepared cane is fed to the mills by vertical Donelli chutes and a feeder drum, and enters the opening between the front and the top rollers, where the juice is extracted.
To prevent the cane from falling down between the feed roller and delivery roller, the curved disk is mounted between these two, which support the cane. As this, opening is less wide than the feed opening another quantity of juice is extracted. The extraction plant consists of four roller mills called milling train or tandem. In order to prevent a mill from breaking, when too much cane is feed, the top roller is made in such a way that it can upwards; pressure is exerted on this top roller by means of a hydraulic system.
Messchaert juice grooves are deep drainage grooves use on feed rolls and delivery rolls, as a lot of juice has to be drained. This groove improves sucrose extraction and increase mill capacity, since they provide a free exit for the juice and practically eliminate slipping. Extracted juice, flowing down the feed and delivery rollers, is collected in a juice tray. Juice from the first mill is mixed with juice from the other three mills and is called mixed juice. This juice is screened by means of Rotary screen filter to remove fine bagasse particles and sent to the weighing device. The bagasse is mixed with mbibitions water before the last mill, and the juice squeezed out in the last mill is diluted and this in turn can be used again for imbibitions one step forward in the milling train. The whole system of spraying water and dilute juices is called imbibitions. When the residue leaves the last mill, it is called bagasse, which is transported to the boiler by means of the bagasse carrier. The fine particles, called bagacillo, are removed by a screen to serve as filter aid in the rotary vacuum filter, with all these pressing and spraying operation about 97% of sugar in cane is extracted, the other 3% remains in the bagasse. . 7 Uses of Bagasse •Used as fuel for the boiler •Used for production of paper, paper board products and reconstituted pane board •Used as a raw material for production of Chemicals •Used in agricultural mulch. But the primary use of Bagasse and bagasse residual is a fuel source for the boiler in the generation of process steam in sugar plant. Table2. Composition of mixed juice In solution Colloidal In suspension SucroseRectinsBagasse Reducing sugarsGumsSands Inorganic saltsProteinsClay Organic saltsChlorophyll Organic acidsWax Color bodiesStarch Tannins Air Iron compounds . 8 Heating of Mixed Juice The mixed juice is heated in two stages; First stage: primary heating to 700c. This is normally done with vapor from the first effect or second effect evaporator Second stage: Secondary heating to appropriate 1050c. This normally done with exhausted steam. A juice heater consists in principle of a steam chest with tubes, through which the juice flows and around which steam is present. The tubes are felted in tubes plates. The cylindrical shell is extended beyond the tube plate at each end, thus forming compartment, which are enclosed by heavy cast doors.
To clarifier By pass line Mixed juice Relief valve I ncondensable gas Condensate Condensate Condensate Condensate Drains drains drains drains Figure3.
A diagram of Juice Heaters system The mixed juice is recommended to be heated between 1020c-1050c before being limed, because if this temperature is exceeding, the following may be happen; •Cane wax can be emulsified hence difficult to removed at clarification(cause carry over) •The sucrose can be inverted as the reaction is speeded up, when the temperature is higher •Caramelisation of sugars forming color •Fouling of heaters •Waste of heat •High vaporization could exceed flash tank vent hydraulic design causing poor flashing 3. 9 Importance of heating mixed juice before liming
Heating the mixed juice has the following importance/effect on sugar production; •Increases the reaction rate between the lime and juice acids •Coagulates some organic constituents like proteins •Coagulates some fats, waxes and gums •Allows for flashing of juice to remove air •Destroys micro-organisms and enzymes to prevent microbial losses. 3. 10 Juice clarification The mixed juice is a cloudy, grayish or greenish foaming liquid with water content of 80%-84%. In suspension, sand particles fine bagasse particles, can wax and air bubbles may be found in mixed juice.
To produce raw sugar, the mixed juice has to be clarified to remove as much of the impurities as possible and the commonly clarification process which used is liming process/defefecation process. Heated & limed juice Flocculants Overflow box Clarifier level testline Clear juice MUD MUD PUMP By pass valve Bagacillo To clear juice heaters To mud filter Figure4. The diagram showing Juice clarification process 3. 11 Liming process Mixed juice is always acidic; its pH is about 5. 2-5. 5.
The milk of lime is added to neutralize the acids and bring the juice at a pH of 7 to 7. 2. Also the milk of cause a calcium phosphate precipitates as the sugar cane juice contains soluble inorganic phosphate which after the addition of lime increases the pH to prevent sucrose inversion. 3. 11. 1 Preparation of milk of lime Limed is produced from limestone (CaCO3), which is heated and decomposed to CaO and CO2 CaCO3 CaO and CO2 Milk of lime is prepared by slaking burnt lime or quicklime in a slacker consisting of stirrer with cold water.
CaO + H2O Ca (HO) 2 In a milk if lime(slaked lime), by which for the largest part of the lime is present in suspension and only a small the lime particles from setting in the pipe lime, the milk of lime is pumped around continuously. 3. 11. 2 The quality of lime •A good quality lime should test 85% -95% available CaO. This must be checked in the laboratory. •A good quality lime should not contain more than 2% MgO or oxides of iron (Fe2O3), of silica of aluminum oxides and carbonates.
These impurities would cause deposits in the multiple effects. Magnesium oxide(MgO) would hamper proper and fast defecation 3. 11. 3 pH control The milk of lime is continuously added to the hot juice in the Perry tank, pH being controlled automatically. Effect pH control is vital and it is needed to be controlled to plus or minus 0. 05 units where by the targeted pH in clear juice is 7. 0. Acidic clear juice causes inversion of sucrose and alkaline clear juice causes destruction of reducing sugars.
C12H22O11 + H2O H+ C6H12O6 + C6H12O6 This reaction shows the sucrose inversion. If the pH controller fails to control to , it must be switched to manual and the lime dosing controlled manually with the aid of indicator, paper ,which dipped into a sample of the juice turn a shade green for the correct pH . If the color turns yellowish, more lime must be reduced. Also phenol red and bromthymol blue can be used for manual pH control. These indicators changes color at approximately pH 7.
Color change is from yellow (acid) to red (alkaline) for phenol red and yellow (acid) to blue (alkaline) for bromthymol blue. Mixed juice from Mill CaO Water line Correction water line Juice Heaters Heated juice Transfer pump limed juice to clarifier Milk of Lime tank Lime (Ca(OH) 2)
Figure5. Milk of lime Preparation and dosage system 3. 12 Evaporation system The clear juice from the clarifier’s is concentrated by boiling it under vacuum in a series of connected vessels called evaporators. There are two types of evaporators which are; •Kestner evaporator which is larger and powerful evaporator works under 1-1. 7 bar pressure. •Robert evaporator which is smaller and works under low pressure. At Mtibwa Sugar Estate there are six series of Robert evaporator which are 2A, 2B, 3A, 3B, 4A, and 4B.
Evaporators consist of heat exchanger for boiling the solution and a means to separate the vapor from the boiling liquid different types of evaporators are categorized by the length and alignment of evaporator’s tubes. The evaporator’s tubes may be located inside or outside of the main vessel where the vapor is driven off The clarified juice is concentrated to syrup consistency before it is sent to the vacuum pans to be crystallized into raw sugar The concentrates is made in several evaporators connected in series called multiple effect.
The juice is travel from one vessel to another because of gradual increase in vacuum. The vapors obtained in each body of the multiple effects serve to heat the calanderia tubes and to evaporate additional water in the following vessels. And after being evaporated in a multiple effect to be a syrup consistency clarified juice must be evaporated further for the sugar to crystallize. Steam Syrup Syrup Syrup To storage tank Fig6. Schematic diagram of evaporators . 13 Crystallization system Crystallization of sugar starts in the vacuum pans whose function is to produce sugar crystals from the syrup. Vacuum boiling occurs under low temperature (600-700) and therefore this helps to prevent destruction of sugar. In the pans boiling, the syrup is evaporated until it reaches the super saturation stage at which the crystallization is initiated by adding slurry. This is a mixture of grinded sucrose and alcohol and its role is to act as seeding to initiate crystals formation.
As volume of liquor and crystals (massecuite) reaches the pans capacity evaporation is allowed to proceed until the final massecuite is formed. At this point, the contents of vacuum pan (strikes) and discharged to the crystallizer to maximize the sugar crystals. The syrup (about 65%-70%) is concentrated by boiling in a vacuum pan and is seeded with small sugar crystals in a process called crystallization. The seed with small sugar crystals are called slurry (ethanol + sugar powdered). The sugar crystals are growth to the required size by adding more syrup while boiling continues.
When the crystals reach the required size, the mixture of syrup and crystals called “Massecuite” is discharged from the pan to the crystallizer. Massecuite is the mixture of sucrose, fructose, and other form of sugar. This is accomplished in a vacuum to form a heavy mixture of crystals and mother liquor called massecuite. The raw sugar massecuite is then crystallized by cooling. On this process residual syrup incapable of crystallizing called black syrup molasses is separated. Finally Batch and continues centrifugals are used to separate the liquid and had phase of raw sugar.
Syrup from Evaporators. Final molasses A SUGAR B SUGAR C SUGAR Hot water Figure7. Diagram showing Sugar boiling system 3. 14 Centrifugals system Syrup is separated from the raw sugar crystals in centrifugals which contains perforated baskets which spin at high speed in a casing. The dark syrup surrounding the crystals is known off and passes through the perforations. The spin off syrup is called molasses (mother liquor).
Molasses is produced in two forms; that is black strap which is not edible and syrup which is edible. Black strap molasses is used primarily as an animal feed, additive but also is used to produce ethanol. The spin- off syrup is boiled again and more raw sugar crystals are recovered. This procedure is repeated until like the amount of sugar obtained is too small to make further extractions economical. In these procedure three grades of sugar is obtained which are grade A resulted from syrup and grade B resulted from molasses A and grade C resulted from molasses B.
Molasses C is used in beer and feeding of animals but the interest here is sugar grade A which is used as commercial product. 3. 15 Sugar drying and bagging Sugar discharged from the ‘A’ centrifugals falling on a reciprocating conveyor, is moist and hot and has to be dried before being sent to storage or to the packing station. A basket elevator transports the sugar from the conveyor up to the sugar dryer There are different types of dryers, but at Mtibwa sugar estate the rotating drum type is used, through which the sugar passes in counter current with heated dry air.
The drum is slightly inclined to discharge and it is support by rollers. The inside of the drum is provided with longitudinal louvers which pick up the sugar and drop it as a curtain across the full diameter of the drum The hot air drawn through the drum provides enough heat to evaporate off the water (apart from the heat carried by the sugar itself when it leaves the centrifugals after steaming). When the sugar is lifted by the scoops, it falls down a little way further from the feed because of the angle of the drum. In this way it moves to the discharge end.
Air drowns in the counter current through the drum, will push it back a little toward the feed end but the next result of the forward movement (by the inclination) and the backward movement (by the air) is that the sugar will move forward. Out side air is heated by passing it through tubes of a heater exchanger with steam as a heating medium (radiator). This air is heated to about 650C and drowns by a fan through the drum passing a wet dust catcher (cyclone type) to remove dust particles. The main reasons of drying sugar before packaging are; •To reduce microbiological activities. To prevent caking by drying and cooling. The dry sugar from the dryer is carried by means of conveyor belt to the sugar bins which are equipped with an automatic weighing balance. Sugar is packed into 50Kg suck or bag and 25Kg suck after being weighed by these automated weighing balances. After packaging the sugar bags are carried by a conveyor belt to the warehouse for storage or ready for consumption. 4. 0 BOILER A boiler is a device used to create steam by applying heat energy to water. It can be said that older steam generators were commonly termed boilers and worked at low to medium pressure (1-300psi/0. 69-20. 684bar; 6,895-2068, 427kpa) but, at pressure above this, it is more usual to speak of a steam generator. A boiler or steam generator is used wherever a source of steam of is required. The form and size depend on the application mobile steam engines such as steam locomotives, portable engines and steam –powered roads vehicles typically use a smaller boiler that forms an integral part of vehicles, stationary steam engines, and industrial installations and power stations will usually have a larger separate steam generating facility connected to the point of –use by piping.
A notable exception is the steam powered (five less locomotive, where separated steam is transferred to a receiver (tank) on the locomotive. The steam generator or boiler is an integral component of a steam engine when considered of a prime mover. However it needs be treated separately, as to some extent a variety of generator types can be combine with variety of engine units. A boiler incorporates of firebox in order to burn the fuel and generate heat. The generated heat is transferred to water to make steam, the process of boiling. This produces saturated steam at a rate which can vary according to the pressure above the boiler water.
The higher the furnance temperature, the faster the steam production. The saturated steam thus produced can then either be used immediately to produce power via a turbine and alternator, or else may be further superheated to a higher temperature; this notably reduces suspended water content making a given volume of steam produce more work and creates a greater temperature gradient in order to counter tendency to condensation due to pressure and heat drop resulting from work plus contact with the cooler walls of the steam passages and cylinders and wiredrawing effect from strangulation at the regulator.
Any remaining heat in the combustion gases can then either be evacuated or made to pass through an economizer, the role of which is to warm the feed water before it reaches the boiler. 4. 1 Combustion The source of heat for a boiler is combustion of any of several fuels, such as wood, Coal, oil bagasse or natural gas. Nuclear fission is also used as a heat source for Generating steam. Heat recovery steam generators use the heat rejected from other Processes such as gas turbines. 4. 2 Solid fuel firing In order to create optimum burning characteristics of the fire, air needs to be supplied both through the grate and above the fire.
Most boilers now depend on mechanical draught equipment rather than natural draught. This is because natural draught is subjected to outside air conditions and temperature of the flue gases leaning the furnance, a well as chimney height. All these factors make effective draught hard to attain and therefore make mechanical draught equipment much more for economical. 4. 3 Fire-tube boiler The next stage in the process is to boil water and make steam. The goal is to make the heat flow as completely as possible from the heat source to the water. The water is confined in a restricted space heated by the fire.
The steam produced has lower density than water and therefore will accumulate at the highest level in the vessel; its temperature will remain at boiling point and will only increase as pressure increases. Steam in this state (in equilibrium with the liquid water which is being evaporated with the above) is named “saturated steam”. For example, saturated steam at atmospheric pressure boils at 1000 C. Saturated steam taken from the boiler may contain entrained water droplets; however a well designed boiler will supply virtually “dry” saturated steam, with very little entrained water.
Continued heating of the saturated steam will bring the steam to superheated states where the steam is heated to a temperature above the saturation temperature, and no liquid water can exist under this condition. 4. 4 Superheater A greater quantity of steam can be generated from a given quantity of water by superheating it. As the fire is burning at a much higher temperature then the saturated steam it produces, far more heat can be transferred to the once formed steam by superheating it and turning the water droplets suspended there into more steam and greatly reducing water consumption.
The equation given by L. D portal to determine the efficiency of a steam locomotive, applicable to steam engines of all kinds; Power (Kw) = steam production (kgh-1) Specific steam consumption kg/kwh The superheater works like oil on an air conditioning unit, however to a different end. The steam piping is directed through the flue gas path in the boiler furnance. This arc typically is between 1300-16000C, some super heaters are radiant type (absorb heat by thermal radiation), others are convection type (absorb heat via a fluid i. e. gas) and some are a combination of the two.
It is important to note that while the temperature of the steam is the superheater is rained, the pressure of the steam is not: The turbine or moving pistons after a continuously expanding space and the pressure remains the same as that of the boiler. The process of superheating is not importantly designed to remove all droplets entrained in the steam to prevent damage to the turbine balding aid/ or associated piping. Superheating the steam expands the volume of steam, which allows a given quantity (by weight) of steam to generate more power. When the totally of the droplets is eliminated, the steam is said to be in a superheated state. . 5 Water treatment for boiler Feed water for boilers needs to be as pure as possible with a minimum of suspended solids and dissolved impurities which cause corrosion, foaming and water carry over. Various chemical treatments have been employed over the years, the most successful being the use of resin which is hyroxidizeolite (Z (OH) 2). Resin is a synthetic or natural inorganic charged polymer produced by plants. It is insoluble in water and is used in softening of hard water by ionic interaction where by the higher charged particles cause water hardness such as Ca2+ and Mg2+.
If the efficiency of resin is lowered, table salt NaCl is used for regeneration. Regeneration is the removal or discharge of Ca2+ and Mg2+ from resin (Z (OH) 2 to increase its efficiency. 4. 6 Boiler safety When water is converted to steam it expands in volume over 1,000 times and travels a down a steam pipes at over 100km/hr. Because of this steam is great way of moving energy and heat ground a site from a central boiler house to where it is need, but without the night boiler feed water treatment, a system raising plant will suffer from scale formation and corrosion.
At best, this increases energy costs and can lead to poor quality steam, reduced efficiency, shorter plant life and a operation which is unreliable. At worst it can lead to catastrophic failure and loss of life. A failure mode includes; •Overpressurisation in the boiler •Insufficient water in the boiler causing overheating and vessel failure. •Pressure vessel failure of the boiler due to inadequate construction or maintenance. Condensate Return Superheated steam 2800C Make –up water Saturated steam Feed water 1050C 900C Super
Heater 10100C 2060C A 2240C 1890C ambient air 290C Fig8. Schematic diagram of boiler. 5. 0 WATER TREATMENT 5. 1 Hard water This is usually defined as water which contains a high concentration of Ca2+ and Mg2+ ions. Measurements of hardness are given in terms of the calcium carbonate equivalent, which is an expression of the concentration of hardness ions in H2O in terms of their equivalent value of CaCO3.
Water is considered to be hard if it has a hardness of 100mg/l or more as calcium carbonate. 5. 2 Softening It is usually defined as the removal of hardness from water. This is not a required part of the water treatment process since hard water does not have any health consequences. However, hard water is problematic for a variety of reasons, hard water makes soap precipitate at of H2O and foam a scum, such as the ring which forms around bath tubs. Hard water harms many industrial processes, so industries often require much softer water than is usually required by the general public.
Excessively hard water will nearly always have to be softened in order to protect the water treatment plant equipment and piping systems. At hardness greater than 300mg/l as CaCO3, scale will for on pipes as CaCO3 precipitates out of the water. The scaling damage equipment and should be avoided. 5. 3 Sources of hardness Hardness generally enters ground water as the water percolates through minerals containing calcium or magnesium. The most common sources of hardness are limestone (which introduce calcium into the water) and dolomite (which introducing magnesium).
Hardness is caused by calcium (Ca2+) and magnesium (Mg2+) ions dissolved in water. However, hardness can be caused by several other dissolved metals as well including strontium (Sr2+), iron (Fe2+) and manganese (Mn2+). All of the hardness causing ions is divalent cations, meaning that they have a charge of positive two. Metal such as sodium (Na+) and potassium (K+) with a charge of positive one do not cause hardness. 5. 4 Backwashing Backwashing the softener is very similar to backwashing a pressure filter and the purpose is the same.
Although the purpose of a softener is not to filter out particulate matter, come particles invert ably get caught in the softener. By sending water backwards through the softner, this particulate matter is removed. 5. 5 Regeneration After backwashing, the softener is ready to be regenerated. This is the part of the process in which Mg2+ and Ca2+ ions on the resins become replaced with sodium (Na) so that the softener can be used to treat more hard water. In order to regenerate the resin, a salt solution, known as brine, is allowed to flow through the softener for about an hour.
The salt used to regenerate the resin is ordinary table salt (sodium chloride), so it is easily to handle. When dissolved in water, the salt dissociates into its constituent ions, Na+ and Cl-. The Na+ ions on the resins in the following manner (where R preceding and ion means that the ion is bound to the resin. RCa + NaCl RNa + CaCl2. RMg + NaCl RNa + MgCl2. During regeneration calcium chloride, MgCl2 and excess NaCl plus to waste. 5. 6 Rinsed and Waste Disposal After the brine has been given a sufficient contact time, it must be rinsed out of the softener.
During the rinsed cycle, fresh water is passed through the units as it would be during treatment, but with the effluent going to waste. Rinsed usually takes about 20 to 40 minutes. Both the spent brine from generation and from the rinse must be disposed of carefully since the calcium, magnesium and sodium salts are corrosive and toxic to the environment, spent brine is sometimes discharged in sewers or into streams at very high dilutions. Alternatively, the brine can be disposed of in a land fill. 6. 0 LABORATORY ANALYSIS FOR FACTORY PRODUCTS 6. 1 Sampling
The main requirement for accurate chemical control of a sugar factory is proper sampling of the materials in-process. The most accurate analysis is of little or no value if the sample analyzed is not representatives of the bulk of the material. Samples should therefore be taken continuously and should be proportional to the quantities handled. Whenever possible, automatic sampling should be preferred to manual sampling. Appropriate sampling points and method must be chosen. An appropriate sampling point is one where there is easier access for the factory personnel and good mixing to the product to ensure product homogeneity.
An automatic sampling device should simple in design to minimize mechanical failures. It should be cleaned, sterilized and dried at frequent regular 9intervals and it should not bring about evaporation of the sample. At least two sets of automatic samplers should be provided. 6. 2 Receptacles Plastics, stainless or copper receptacles may be used. The should be cylindrical in shape to facilitate handling and cleaning of sufficient capacity to hold enough sample for the desire sampling period. Container of two up to three liters capacity will usually be satisfactory.
The containers should be cleaned , sterilized by means of steam jet, and dried before used, in complete drying of the container may lead to dilution of the sample. At least two sets of containers should be available. Receptacles lids should fit tightly to prevent evaporation of the samples. Containers for mills juices must have an appropriate sieve fitted to the container lid to remove any bagacillo present but, in order to avoid evaporation the sieve area must not be too large. Permanent label should be painted on the containers (not on the lids) for easier identification.
Preservation and composition of juices samples. To prevent juices deterioration during a sampling, which should take about 75munites, a juice preservative is placed in the container and the sample stirred Frequently, otherwise the preservatives tend to settle at the bottom of the container. A suitable preservative is mercury Iodide at rate of 0. 5mls per liter of a sample. This is prepared As follows: Prepared a saturated solution of potassium iodide (KI), GPR grade, in distilled water by dissolving 800g of KI in 500mls 0f warm water then cool.
To 500g of red mercury Iodide (HgI2) in a 1 liter volumetric flask, add some of the saturated Potassium Iodide solution until solution is complete, make up to 1 with saturated solution. The samples are brought to the laboratory where they should be thoroughly mixed, sieved through a 100-mesh screen, sub-sampled and composited. Composite samples should be kept in bottles of ample capacity about 2 liters provided with glass or plastics stoppers. These bottles should be thoroughly washed every day with dilute HCl, rinsed and allowed to dry.
They should be clearly labeled. Two bottles are required for juice compositing, one for determination of sucrose, pol and the other for determination of reducing sugars. With juices kept for pol and determination dried basic Horne’s lead acetate is added at the rate of 1% w/v or 2% w/v for each 50ml juice liquor added to the bottles, depending on whether the bottles are to be kept in a refrigerator at 40c or at room temperature respectively. Juices kept for reducing sugars determination must be preserved with 1% w/v neutral lead acetate and deep frozen.
Refrigeration at 40c is insufficient and will lead deterioration of samples after four hours storage. It is important that the amount of lead acetate used is proportional to the final volume of the composite. The total quantity lead acetate should therefore never be added before compositing begins, since an excess, especially when in the basic form, will precipitate some of the fructose out of solution and thus affected the subsequent polarimeter readings and cause errors. Samples should be composited over a period of 24 hours and analyzed the next day.
Refrigerated samples should first be brought to room temperature with the bottles still stopped to avoid condensation and dilution of the samples. Analyzing composite samples more than once a day is not recommended as a weighted average based on the mass of juice would then have to be calculated. 6. 3 Sampling of products 6. 3. 1 Whole cane Direct analysis of cane is a special analysis which is not required in the routine chemical control of a factory. Method 1 A sample of 30 canes is taken. Ten top, ten middle and ten bottom parts are etained from three separate sets of ten canes respectively. Since only half of each part passes into the chipper, five of the top, middle and bottom parts respectively are inverted; otherwise error would result from the sucrose concentration gradient that exists along the cane stack. The chips which are obtained represent 5 whole canes. Method 2 When a core sampler is used, the canes are sampled directly from the Lorries by taking four cores on each cane load according to a pattern which ensures that every part of the cane bulk has an equal chance of being sampled.
The usual pattern is that practiced by cane planters and Millers arbitration and control board. Facilities should be provided to enable the sample to be taken from either side of the lorry. The side from which the sample is taken is at discretion of the sampling personnel Figure9. Cane sampling at patterns 6. 3. 2 First expressed juice The composition of the first expressed juice is not uniform along whole length of the rollers and if a sample is taken manually, it must be taken at 5munites intervals from along the entire length of feed roller of the first mill.
In a two -rollers crusher, the juice may be sampled automatically by means of a spoon device or a juice wheel. The farmer has a spoon with a hollow stem and a support by the mill drive and each time dips into the juice, some of it is collected and flows down the hollow stem into a sample receptacle. The spoon has convex-shaped sieve soldered to it to prevent bagasse clogging the device. A wheel is a wheel formed by several paddles one of which is a spoon with a hollow stem as described above . movement of the juice in the juice gutter act on the paddles and revolves the wheel. 6. 3. First mill juice If this juice flows into an open gutter, it can be sampled automatically by means of a revolving spoon or a juice wheel. If automatic sampling is not possible, samples should be taken manually every 5min. 6. 3. 4 Mixed juice Mixed juice is manually composed of juice coming from the first and second mills. The sampling and analysis of mixed juice is of prime importance for accurate chemical control. Sampling is done prior to heating and any addition of chemicals. Samples can be taken automatically and continually by a device which consists of a sampler and holder and receiver. . 3. 5 Last expressed juice This is usually sampled by hand at 5-minites intervals along the full length of the bagasse roller of the last mill. To calculate the brix % bagasse, it is essential to sample the last expressed juice and not the last mill juice. 6. 3. 6 Bagasse Bagasse should be sampled as soon as it leaves the last mill and across the whole length of the roller and through the full depth of the bagasse blanket. The use of a board 15cm wide and as long as the roller is recommended. The collected bagasse should be placed be in a closed container.
Four or five successive samples should be taken and thoroughly mixed, making sure that fine particles are not separated out, to form a composite sample. Sub-samples are then taken and moisture determination carried out immediately. A composite sample should be taken at least every 75 minutes. 6. 3. 7 Clarified juice Clarified juice should be sampled continuously from the pipe leading the juice to the evaporators by means of a short by- pass leading to a petcock. Since the clarified juice is at the high temperature, great care must be taken to avoid evaporation.
The container should therefore be provided with a tight cover and placed in a batch of cold running water. The flow of juice can be controlled by means of the cock. As clogging can occur, the pet cock should be inspected frequency. It is advisable to flash the sample pipe at full pet cock bore from time to time to get rid of any accumulation that might have occurred. If sampling has to be done manually, it should be at 5-minutes intervals. Cold water Figure10. A container for sampling clarified juice 6. 3. 8 Syrup Syrup should be sampled by pacing a pet cock on the pipe leading to the syrup tanks.
The cock should be cleaned frequently to avoid clogging, there is also the danger of crystallization occurring and modifying the sample composition. As syrup is at a relatively high temperature, it is advisable to place the sample in its container in a bath of cold running water. If automatic sampling is not possible, manual sampling should be carried out at 5 minutes intervals. Mercuric iodide solution must be added at 0. 5ml/l. 6. 3. 9 Massecuite The composition of massecuite varies from point within the pan, owing imperfect circulation; hence the sample should be taken continuously as the massecuite is being dropped.
It should be kept in a tightly closed container. Samples can also be taken from crystallizers about 15 minutes after the strike has been dropped and before the pan is steamed out. With a continuous crystallizer, massecuite should be sampled manually every 2 hours at the outlet of the crystallizer. 6. 3. 10 Magma Magma should be sampled from the mixer before it goes to the vacuum pans. 6. 3. 11 Molasses returned to the process Runnings are normally sampled by means of a pet cock 0n the pipe leading to the molasses tanks after dilution has been carried out.
If steam is used in the dilution tanks (a practice which is not recommended), samples of undiluted running should be taken to asses if there is any sucrose loss. 6. 3. 12 Final molasses Since final molasses is the product where the greatest sucrose loss occurs; It is advisable to sample with particular care to ensure accurate quantification of loss. Sampling can be done by means of an automatic sampling device placed on the pipeline after the molasses pump. An appropriate device consists of a 100mm diameter pipe cut longitudinally and placed in an inclined position.
The sample container is placed under three or four holes of different sizes drilled through the bottom of the pipe. Molasses is delivered to the device from the pipe taking molasses scale. A hole of the appropriate diameter is chosen and the other holes are plugged. All excess molasses is returned to the molasses gutter or waiting tank. Sampling is done before any dilution of molasses takes place. Separate samples of molasses can be taken from each C-massecuite strike or from each crystallizer to enable efficicient control over the boiling house performance. 6. 3. 13 Sucrose
Special attention must be paid to sampling of sugar because of its quality control and commercial significance. Sugar to be exported in bulk should be sampled at the time of dispatch from the factory when each vehicle is loaded. Automatic sampling by a mechanical device is recommended . The samples taken should be large and should be sub sampled mechanically. If the sugar is bagged, samples should be taken by a spoon or other small measure from each bag while it is being field. Once taken the sample must be kept in an air tight container so that no moisture is gained or lost.
A suitable container would be one 20cm square time 30cm high with hinged lid. The lid should have hole of 2cm diameter in the center into which fits funnel of 12cm cross section and 7cm high and having a high lid. About 5oog sugar is sub sampled in the laboratory and transferred to a wide mouth glass bottle with tight cover. 6. 3. 14 Condensates Condensates from the evaporators, vacuum pause and juice heater can be sampled manually at intervals or continuously at the discharge tube by a copper or stainless steel cooling coil, fitted with a pit.
Cods delivery being into a closed container with mercuric iodine solution added at the rate of 1ml per liter 0f condensate. A composite sample is prepared in laboratory and analyzed every 3hours. 6. 3. 15 Boiler water Boiler water coming from the steam drum is usually sampled through a long pipe down to a stainless or copper cooling coil to bring the temperature down to about 300c. The pipe bringing the thoroughly drained for at least 15minutes. Before collecting the sample in a stainless steel or plastic container. A sample should be collected every 3hours. 6. Methods of Analysis 6. 4. 1 Brix To control the sugar manufacturing process it is essential to know the amount of dissolved substances in every factory stream (i. e. juice, syrup, and molasses). “Brix” is the percentage by the weight of dissolved solids in a sugar solution. The percentage dissolved substance as read by saccharimeter is called degree brix in honor of Mr. Brix who worked early in this field. Brix is used by the factory staff to answer different important questions as; •Mixed juice brix indicates the imbibitions water being used and the cane quality. Syrup brix indicates steam pressure, mill crushing rate and the operation of the evaporator. •Massecuite brix indicates the quality of the pan boiling. •Molasses brix indicates the amount of water used in the centrifugals •Brix is used to indicate purity 6. 4. 1. 1 Determination of brix in first expressed, last expressed, mixed and clarified juices Apparatus used; •Erlenmeyer flasks, 250ml •Funnel •Filter paper, what man No. 91 •Saccharimeter •Watch glass Reagents used; •Kieselguhr filter aid, acid- washed dried at 1050C for 3 hours •Juices
Procedure (a)To 150ml juice in a 250ml, Erlenmeyer flasks, 2g of filter aid was added and mixed well. (b)The solution was filtered through a fluted Whatman No. 91 filter paper while covered the funnel with the watch glass. (c)The filtrate was transferred to saccharimeter for Brix reading. Results obtained are shown in the table below; Table3. Brix reading for first expressed, last expressed, mixed and clarified juices. Factory product parameters Brix standard (%)Brix reading (%) Purity (%) First expressed juice> 17. 0018. 6086. 1 Last expressed juice8. 0 to 10. 5010. 1591. 0 Mixed juice12. 00 to 12. 5012. 3088. 3 Clarified or clear juice12. 00 to 12. 5012. 4087. 3 6. 4. 1. 2 Determination of Brix in syrup, A and B molasses, and B and C Massecuite Apparatus used; •Erlenmeyer flasks, 250ml or Beakers, 150ml •Funnel •Watch glass •Filter paper, whatman No. 91 •Saccharimeter •Analytical balance Reagents used; •Kieselguhr filter aid, dried and washed at 1050C for 3 hours •Distilled water •Syrup, A and B molasses and B and C massecuite Procedure (a)100. 0g of each was weighed in a beaker and 400. g of distilled water was added to bring the mixture to 500. 0g and mixed well. (b)2g of Kieselguhr filter aid was added to each beaker. (c)The solution was filtered through a fluted whatman No. 91 filter paper while covered the funnel with a watch glass. (d)The filtrate was transferred to the saccharimeter for Brix reading. Results Brix of samples = saccharimeter reading x 5 (5 is dilution factor) Table4. Brix for Syrup, A and B – molasses and B and C- massecuite Factory products parametersBrix standard Saccharimeter reading Brix reading Syrup62. 0 to 65. 012. 964. A- Molasses82 to 8316 5582. 75 B- Molasses82 to 8316 5682. 8 B- Massecuite93 to 9418. 7293. 72 C- Massecuite95 to 9719. 3296. 6 6. 4. 2 Polarization Pol is the apparent sucrose content of any substance expressed as percentage by mass. It can be expressed as a percentage or as an actual mass. Although pol, is measured using a filtered sample, it is also adjusted to give pol% product based on the total mass of the product. 6. 4. 3 Principle of the method The pol of a sugar solution is the resultant optical rotation of the sucrose and other optically active substances, mostly glucose and fructose.
Pol is taken as an approximation of sucrose only in products like raw sugar, bagasse and filter cake. A sugar solution has to be clarified before its pol is determined. Horney dry basic lead acetate is a commonly used clarifying agent. The quantity of lead acetate used must be minimal, as any excess will precipitate some of the fructose out of the solution, resulting in a increase in dextrorotation or a higher pol will also affect the pol of the sucrose. However, sucrose is not the only substance present in factory products that rotates the plane of polarization.
Sucrose rotates to the right, glucose to the right and fructose +, the left. All three substances are present in any sugar solution since glucose and fructose are present in small quantities compared to sucrose; this effect on the rotation is correspondingly smaller than the effect of sucrose. Pol is used by process and engineering staff in daily work to note the following; •Pol in can and mixed juice indicates cane quality •Pol in bagasse indicates mill efficiency •Pol in clear juice indicates if the inversion has taken •Pol in massecuites and molasses indicates pan floor effect •Pol in sugar indicates centrifugals efficiency. . 4. 3. 1 Determination of pol in first expressed, last expressed, mixed and Clear juices Apparatus used; •Beakers, 600ml and 250ml •Funnel •Watch glass •Filter paper, Whatman No. 91 •Saccharimeter. Reagents used; •Kieselguhr filter aid, acid washed , dried at 1050C for 3 hours •Horney basic lead acetate dried at 1050C for 3 hours Procedure (a)To a 400ml sample in 600ml beakers, the minimum amount of Horney dry basic lead acetate was added for clarification followed by Kieselguhr filter aid. b)The mixture was mixed vigorously and set aside about 30 seconds to allowed flocculation to occur while covering the funnel with the watch glass. (c)The solution was filtered through fluted whatman No. 91 filter paper. (d)The filtrate was taken to saccharimeter for pol reading. Results obtained are shown in the table below; Table5. Pol reading for first expressed, last expressed, mixed and clear juices Factory product parametersPol reading in % First expressed juice18. 74 Last expressed juice11. 32 Mixed juice 13. 12 Clear juice13. 19 6. 4. 3. Determination of pol in syrup, A and B molasses and B and C Massecuite Apparatus used; •Beakers of 600ml and 250ml •Funnel •Watch glass •Filter paper, whatman No. 91 •Saccharimeter •Analytical balance Reagents used; •Kieselguhr filter aid, washed and dried at 1050C for 3 hours •Dry Horney basic lead acetate •Distilled water Procedure (a)100. 0g of each sample was weighed in a 600ml beaker and 400. 0g of distilled water was added to make 500. 0g of solution. (b)Minimum amount of Horney’s dry basic lead acetate was added for clarification followed by kieselguhr filter aid.
The mixture was sated aside for about 30 seconds to allowed flocculation. (c)The solution was filtered through fluted whatman No. 91 filter paper while covering with watch glass. (d)The filtrate was taken to saccharimeter for pol reading. The results obtained were shown in the table below; Table6. Pol reading for syrup, A and B molasses and B and C massecuite Factory product parametersPol reading (%) Syrup11. 89 A-Molasses11. 30 B-Molasses9. 67 B-Massecuite13. 84 C-Massecuite9. 65 6. 4. 3. 3 Determination of pol in final molasses Apparatus used; •Beakers 1500ml and 600ml Funnel •Watch glass •Filter paper, whatman No. 91 •Saccharimeter •Analytical balance Reagents used; •Kieselguhr filter aid, washed and dried at 1050C for 3 hours •Dried Horne’s basic lead acetate •Distilled water. Procedure (a)100. 0g of a sample was weighed in 1500ml beaker and brought to 1000g by adding 900g distilled water (b)The minimum quantity of Horne’s dry basic lead acetate was added followed by kieselguhr filter aid. (c)The solution was mixed well and at aside for at least 1 hour to obtain a cleared filtrate. (d)The solution was filtered through a fluted whatman No. 1 filter paper while covering with watch glass. (e)The filtrate was taken to saccharimeter for pol reading. Results Pol reading for final molasses = 12. 54% 6. 4. 3. 4 Determination of pol in final bagasse Apparatus used; •Jeffco wet disintegrator model 291 •Funnel •Erlenmeyer flasks, 500ml •Watch glass •Filter paper whatman No. 91 •Saccharimeter •Analytical balance Reagents used; •Horne’s basic lead acetate dried at 1050C for 3 hours Procedure (a)A 250 ¬¬ ¬plus or minus 1g bagasse was weighed out and transferred to the water jacketed bowl where 2500g water was added. b)The mixture was disintegrated for 20 minutes. (c)Minimum amount of Horne’s dry basic lead acetate was added for clarification. (d)The solution was filtered through a fluted whatman No. 91 filter paper while covering funnel with watch glass. (e)The cleared filtrate was taken to saccharimeter for pol reading. Result The pol reading for final bagasse = 3. 91% 6. 4. 3. 5 Determination of pol in filter cake Apparatus used; •Beaker, 1litre •Saccharimeter •Funnel •Filter paper, whatman No. 91 •Analytical balance Reagents used; •Horne’s basic lead acetate dried at 1050C for 3 hours •Distilled water
Procedure (a)25g of the filter cake from rotary vacuum filter was taken as the sample in a 1litre beaker. (b)75g of water was added to the sample to make 100g and mixed until a homogeneous mixture was obtained. (c)100g of the mixture was clarified with minimum amount of Horne’s dry basic lead acetate. (d)The mixture was filtered out through whatman No. 91 filter paper. (e)The filtrate was taken to saccharimeter for pol reading, where the saccharimeter gives directly the pol% filter cake. Results The pol reading for filter cake = 3. 12% 6. 4. 4 Sucrose Principle of the method
The difference in polarization of a sugar solution before and after inversion (carried out at 600 C by HCl) gives a measure of the sucrose concentration of the solution. It is assumed that only sucrose undergoes hydrolysis and those impurities such as leaven, raff nose and kestoses remain unchanged. A neutral salt, NaCl, is used in the direct polarization to offset the effect of the acid on the invert sugar in the invert polarization. Any excess basic lead acetate must be removed from the solution for two reasons; it is precipitates some of the fructose out of the solution, resulting in an increase in dextrorotation or higher polarization.
Although the effect of this reaction on fructose originally present does not affect the final results; its effect on the newly inverted fructose does. It affects the polarization of sucrose. Apparatus used; •Beaker, 1litre •Funnel •Watch glass •Erlenmeyer flasks, 500ml •Filter paper, whatman No. 91 •Volumetric flask, 100ml •Water-bath, thermostatically controlled at 600C plus or minus 10C •Saccharimeter Reagents used; •Horne’s basic lead acetate dried at 1050C for 3 hours •Kieselguhr filter aid, washed and dried at 1050C for 3 hours •Potassium oxalate •Sodium Chloride solution Standard acid used for inversion, 6. 34M HCl 6. 4. 4. 1 Determination of sucrose in first expressed, last expressed, Mixed and clear juices Procedure (a) Clarification To a 400ml sample in a 1litre beaker, the minimum amount of Horne’s basic lead acetate was added for clarification. The mixture was mixed vigorously and allowed to stand for about 30 seconds for flocculation to occur. The solution was filtered through a fluted whatman No. 91 filter paper with the aid of kieselguhr while covering the funnel with watch glass. 300ml of filtrate was collected in a 500ml Erlenmeyer flask. b) Deleading 1. 0g dried potassium oxalate was added to 300ml of the above filtrate, swirled to precipitate any excess lead present. The solution was filtered through a fluted whatman No. 91, filter paper, covering the funnel with watch glass The first 25ml of filtrate was discarded. The presence of excess lead ion was tested with a few crystals of potassium oxalate until the filtrate was cleared. About 250ml of clear filtrate was collected. (c) Polarization 50. 0ml portion of the clear filtrate was pipette into two 100ml volumetric flasks and 20ml distilled water was added to each flask.
To the first flask, 10. oml sodium chloride solution was added from pipette and mixed well. Inversion, to the seconds flask, 10. 0ml standard acid (HCl) used for inversion was added using a pipette; swirled gently to avoided local concentration of acid. The flask was placed in a hot water-bath thermostatically controlled at 600C plus or minus 10C. The flask was agitated for the first three minutes, and then allowed to stand for a further 7 minutes; it was then removed from the bath. The contents of the flasks are cooled rapidly to as close to 200C as possible by inversion in old running water and made up to mark with distilled water. It was ensured that the temperature of the two solutions do not differ by more than 0. 50C. The polarimeter readings are noted. The temperature of the invert solution in the polarimeter tube was measured. Results and calculation If p = direct pol P’ = invert pol m = gram solids in 100ml 0f invert solution t = the temperature of the invert solution Sucrose% juice = 2(p – p’) 100 x pol factor 143. 16+0. 0794(m-13) – o. 53t Brix = 12. 54 p = +21. 35 p’ = -7. 00 at 21. 80C (i)Clerget divisor = 143. 16+0. 0794 (m-13)
From table 10, where m = Brix = 12. 5 Clerget divisor = 142. 65 (ii)Temperature correction for clerget divisor = 11. 55 (iii)When Brix = 12. 54 From table 9, pol factor = 0. 24817 Sucrose% juice = 2(21. 35-(-7)) 100 x 0. 24817 =10. 73 142. 65-11. 55 Therefore sucrose% juice = 10. 73% 6. 4. 5 Boiler water analysis 6. 4. 5. 1 Determination of sulphite (0xygen scavenger) Apparatus used; •Beaker, 100ml •Conical flask •Burette, 20ml •Brass scoop Reagents used; •Starch indicator powder •Potassium Iodate, 0. 02NKI03 Procedure a)About 50ml of boiler water was taken in a 100ml beaker. (b)2 brass scoop of starch indicator powder were added to the sample and stirred. (c)The mixture was titrated against 0. 02N KI03 drop wise until a permanent faint blue as appeared. (d)The volume of 0. 02N KIO3 was reached. Results obtained were shown in the table below; Table7. Volume of 0. 02N KIO3 used No. of experiment12 Final volume in ml3. 206. 10 Initial volume in ml0. 003. 20 Volume used in ml3. 202. 90 Volume of 0. 02NKIO3 used = 3. 20+2. 90/2 = 3. 05ml Calculation Sulphite (ppm as SO3-2) = volume of 0. 2NKIO3 x 16 = 3. 05ml x 16 = 48. 8ppm Therefore sulphite = 48. 8ppm as SO3-2. 6. 4. 5. 2 Determination of caustic alkalinity in boiler water Apparatus used; •Pipette of 1oml •Conical flask •Dropper •Burette of 20ml Reagents used; •10% BaCl2 •Phenolphthalein indicator •0. 02N HCl Procedure (a)A 10ml of sample was pipetted into conical flask. (b)1ml of 10% BaCl2 was added followed by 2 to 3 drops of phenolphthalein indicator. (c)Pink color developed if caustic alkalinity was present and no pink if was zero caustic alkalinity. (d)For presence of caustic alkalinity, 0. 2N HCl was titrated against a pink solution until colorless. (e)The volume of 0. 02N HCl was recorded. Results obtained were shown in the table below; Table8. Volume of 0. 02N HCl used No. of experiment12 Final volume in ml2. 405. 00 Initial volume in ml0. 002. 40 Volume used in ml2. 402. 60 Volume of 0. 02N HCl used = 2. 40+2. 60/2 = 2. 50ml Calculation Caustic alkalinity (ppm as CaCO3) = volume of 0. 02N HCl x 100 = 2. 5ml x 100 Therefore caustic alkalinity = 250ppm as CaCO3 Note: The specific range was 150 – 300ppm as CaCO3. . 4. 5. 3 Determination of Total Hardness in the boiler water Apparatus used; •10ml pipette •Conical flask •Dropper •Burette Reagents used; •0. 02N EDTA •Total Hardness indicator Procedure (a)A 10ml of sample water to be tasted was pipetted into flask. (b)2-3 drops of Total Hardness indicator were added and stirred well. (c)For presence of Hardness, the solution (water sample) turns reddish and blue for zero hardness. (d)For presence of hardness, 0. 02N EDTA was titrated against the reddish solution until the red disappears and a pure blue color was obtained (e)The volume of 0. 2N EDTA used was recorded. Results obtained were shown in table below; Table9. Volume of 0. 02N EDTA used no. of experiment12 Final volume in ml0. 100. 25 Initial volume in ml0. 000. 10 Volume used in ml0. 100. 15 Volume of EDTA used = 0. 10 + 0. 15/2 = 0. 125ml Calculation Total Hardness, TH (ppm as CaCO3) = volume of EDTA x 100 = 0. 125ml x 100 = 12. 5ppm as CaCO3 Therefore Total hardness, TH (ppm as CaCO3) = 12. 5ppm as CaCO3 6. 4. 6 Analysis of lime (CaO) A good quality lime should test 85 – 95% available CaO
Apparatus used; •Analytical balance •Hot plate •Volumetric flask of 250ml •Filter paper, whatman No. 91 •Pipette of 25ml •Burette of 50ml Reagents used; •Graduated sugar •P. O. P indicator •Powder lime •0. 357N H2SO4 Procedure (a)5. 0g of the finely powdered sample was weighed and transferred to a 250ml volumetric flask with 75 – 90ml of freshly boiled and cooled distilled water. (b)The mixture was boiled gently on the hot plate for 3 minutes while shaken with a rotary motion to break up any lumps. (c)The flask and contents are cooled to room temperature. d)40g of graduated sugar was dissolved in 40ml of freshly boiled water. This solution was added to the flask with the lime. (e)The mixture (lime + dissolved sugar) was shaken for 30 minutes with rotary motion of the flask, keeping the lime in suspension. (f)The volume was completed with freshly boiled distilled water and shaken well. (g)The mixture was filtered out with filter paper, whatman No. 91. (h)25ml of the filtrate was pipetted in a 250ml Erlenmeyer flask followed by 5 drops of P. O. P indicator solution where the solution turns pink. (i)0. 57N H2SO4 was titrated against a pink solution until colorless which was the end point and the volume of 0. 357N H2SO4 was titrated. The results obtained were recorded in table below; Table10. Volume of 0. 357N H2SO4 used no. of experiment12 Final volume in ml44. 0044. 30 Initial volume in ml0. 000. 00 Volume used in ml44. 0044. 30 Volume of 0. 357N H2SO4 used = 44. 00 + 44. 30/2 = 44. 15ml Therefore the volume of 0. 357N H2SO4 = 44. 15ml Calculation Available CaO% = volume of 0. 357N H2SO4 x 2 44. 15ml x 2 = 88. 3% Available CaO3 = 88. 3% 7. DISCUSSION
During sugar production, the harvested sugarcanes are weighed and subjected to a feeder table where by the kicker abstract them to cane carrier. The carding drums align the canes and direct them to shredder. The shredder cuts the canes in a small piece and beat them in hammering like process. The crushed materials are subjected to the milling machine. The milling machine recrushes the pieces of canes and imbibitions water is added to enhance the extraction of juice. Four milling systems are used for juice extraction and juices from all systems are mixed together in a tank to get unscreened mixed juice.
The by- product of milling process is bagasse. The mixed unscreened juice is filtered by the help of the rotary screen where by the fine bagasse particles are removed and the screened juice is sent to the weighing device. The mixed juice is heated by the exhausted steam from turbines and mills. It is recommended to heat the mixed juice at temperature between 1030C – 1050C before being limed in order to prevent the disintegration (inversion) of sucrose into glucose and fructose as the inversion reaction is speeded up hen the temperature is higher. Other importance of heating juice before liming is to enable destruction of micro-organisms and enzymes to prevent microbial losses and to increase reaction rate between the lime and juice acids. The mixed juice is always acidic with pH about 5. 5. After being heated, the milk of lime is added to a mixed juice to neutralize the acids and bring the juice at a pH 7. 00 to 7. 2, as acidic clear juice causes inversion of sucrose and alkaline clear juice cause destruction of reducing sugars.
Also liming of mixed juice cause a Calcium Phosphate precipitate as the sugarcane juice contains soluble inorganic phosphate which after the addition of lime increases the pH to prevent sucrose inversion. The flocculants, polyacrylamide is added to the limed juice to improve settling of juice in the clarifier and also to assist filtration. The clear juice from clarifier is heated to a temperature between 1100C – 1150C and subjected to evaporator where by considerable quantities of water are removed by evaporation until the solution is at least saturated with sugar.
Steam is used for evaporation where vapor is produced. This vapor is used to heat the juice again in order to get more evaporation and hence save on the amount of exhaust steam. The boiling point of sugar solution varies with the pressure. The lower the pressure or the higher the vacuum, the lower the boiling point. Lowering the pressure on the juice side of the next body results in a lower boiling point and the vapor produced can be used for boiling the juice in the next body. This is called multiple effect evaporation. The concentrated juice from evaporators is called syrup.
The muddy juice from the clarifier is filtered by the rotary vacuum filter and the filter cake is obtained. Syrup from the evaporators is sent to the mult-storage tank and from there to the feed tanks at the pan floor. In the vacuum pans the sugar in solution is forced to crystallize by evaporating water and this way increasing the sugar concentration until the saturation point is reached. When a strike is ready, the discharge valve of the pan is opened, after breaking the vacuum on the pan and strike is dropped into a vertical crystallizer.
When the mass is cooled, the super saturation of the sugar in the mother liquor around the crystals will rise and more sucrose molecules will be deposited on the surface of the crystals. The raw sugar crystals are separated from the mother by centrifugal force in the machine called centrifugal which contains perforated baskets which spin at high speed in a casing. The strike made from syrup is called “A” strike, which is separated into “A” molasses and A- sugar. The strike boiled from A- molasses is called B- strike which is separated into B- molasses and B- sugar.
In the same way finally a C- strike is made from B- molasses, from which the final molasses is produced. A “C” – strike is very viscous, so it is very difficult for the sugar molecules to migrate to the crystal present, hence very fine seed grain is used, consisting slurry of powdered sugar in ethanol. Boiling B- molasses, this is rich in color and impurities, no high quality sugar can be made. Therefore the sugar from the C- strike is remitted and boiled in an A- strike again. The same applies for boiling A-molasses in a B- strike, but because the sugar is of high quality than the C-sugar, the part of the sugar is used as seed in A- strikes.
Sugar discharged from the centrifugals is moist and hot and has to be dried before being bagged. A rotating drum is used for sugar drying through which the sugar passes in counter current with heated air. The importances of drying sugar are to reduce microbiological activity and to prevent caking by drying and cooling. Laboratory analysis is done to the first expressed juice, last expressed juice, mixed juice, clear juice, filtrate syrup, molasses, massecuite and raw sugar for testing parameters like Brix, polarization (Pol) and purity to maintain the quality of the final product and for economic purposes.
Brix is used to indicate the purity; the higher the brix, the lower is the purity and vice versa. Since brix expresses the amount of dissolved substances in sugar solution; higher the brix indicates many dissolved substances which in turn lower the purity of the sample. Pol is an apparent sucrose content of any substance expressed as a percentage by mostly. For a sugar, the pol is the resultant optical rotation of the sucrose and other optically active substances, mostly glucose and fructose. Pol is taken as an approximation of sucrose only in products like raw sugar, bagasse and filter cake.
There should be high pol of about 98. 5% in raw sugar to ensure the minimum losses. Differently to bagasse and filter cake their pol should be about 2. 5% and 2. 0% respectively to avoid high losses of sucrose. For other products like juices, syrup, molasses and massecuite, the pol is determined focusing on the pol of the raw sugar, bagasse and filter cake. If there is high pol in bagasse, this implies that efficiency of mill has dropped hence the operator may solve the problem by increasing the
THE UNIVERSITY OF DODOMA COLLEGE OF NATURAL AND MATHEMATICS SCIENCES SCHOOL OF PHYSICAL SCIENCES DEPARTMENT OF CHEMISTRY THE PRACTICAL TRAINING AT MTIBWA SUGAR ESTATE (MSE) LTD BASED ON SUGAR PRODUCTION WRITTEN BY: JATOSH SAMWEL WITH REGISTRATION NO: T/UDOM/2010/00492 A report submitted under partial fulfillment of the requirements of practical training course CH 212 for Bachelor of Science in chemistry, the University of Dodoma. NAME OF SUPERVISOR: POLYCARP W. MASHELE DATE OF SUBMISSION: 14/10/2012 THE PRACTICAL TRAINING AT MTIBWA SUGAR ESTATE (MSE) LTD BASED ON SUGAR PRODUCTION WRITTEN BY: JATOSH SAMWEL