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Sugar Technology for Developing Countries: Short Term Training Programme at Guangxi International Business Vocational College -Peoples Republic of China 2018.

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The course covered basic information of China and Guangxi, current situation of sugar manufacturing industry in Guangxi, sugar manufacturing technology including; milling, juice clarification, juice evaporation, sugar crystallisation and all other factory operations. The etiquette, cultural heritage and the tea-art of China were also introduced. The expected outcomes of this course were to exchange knowledge of Chinese sugar manufacturing technology among developing countries and to enhance the economic and technical cooperation between China and other countries. Accordingly, the training programme was scheduled to cover theoretical and practical aspects of sugar manufacturing technology and it was designed with lectures, factory and field visits, discussions and meetings with sugar industry personals. The training cost was borne by the Ministry of Commerce of the People's Republic of China, including travelling, accommodation and meals. SRI provided incidental expenses for the trainees. The training was a great opportunity to expose ourselves to new technologies and machinery in the sugar manufacturing process. Building up of research relations at the international level was an added outcome of this visit by giving an opportunity to build links with mechanical engineers, process engineers and chemists. Experiences and information gathered during this training program would be useful to improve the local sugar manufacturing process by introducing international sugar quality standards and by identifying defects in the current sugar manufacturing process through collaborative programs with the sugar industries and SRI. iii Acknowledgement We wish to express our sincere appreciation and gratitude to the following individuals, personnel and institutions for their assistance and cooperation to make this training a success.
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i
Report on Attending the Short Term Training Programme at Guangxi International Business
Vocational College Peoples Republic of China
Course Title: 2018 Training Course on Sugar Technology for Developing Countries
15th October to 13th November 2018
G A A Chathuranga
Research Officer (Crop and Resource Management)
B R Kulasekara
Research Officer (Crop Nutrition)
M.G.G.N. Sewwandi
Research Officer (Processing Technology)
Sugarcane Research Institute
UdaWalawe
Sri Lank.
ii
Preface
The People’s Republic of China had invited Sri Lankan government officials to attend the training course
on Sugar Technology organised by Guangxi International Business Vocational College (GIBVC), Nanning
in October 2018 through the External Resource Department, Sri Lanka. Accordingly, the Sugarcane
Research Institute (SRI) was requested three nominations for this training programme and Messrs B R
Kulasekara (Research Officer, Crop Nutrition Division) and G A A Chathuranga (Research Officer, Crop
and Resource Management Division) and Miss M G G N Sewwandi (Research Officer, Processing
Technology Division) participated for this training program.
The course covered basic information of China and Guangxi, current situation of sugar manufacturing
industry in Guangxi, sugar manufacturing technology including; milling, juice clarification, juice
evaporation, sugar crystallisation and all other factory operations. The etiquette, cultural heritage and the
tea-art of China were also introduced.
The expected outcomes of this course were to exchange knowledge of Chinese sugar manufacturing
technology among developing countries and to enhance the economic and technical cooperation between
China and other countries. Accordingly, the training programme was scheduled to cover theoretical and
practical aspects of sugar manufacturing technology and it was designed with lectures, factory and field
visits, discussions and meetings with sugar industry personals.
The training cost was borne by the Ministry of Commerce of the People’s Republic of China, including
travelling, accommodation and meals. SRI provided incidental expenses for the trainees.
The training was a great opportunity to expose ourselves to new technologies and machinery in the sugar
manufacturing process. Building up of research relations at the international level was an added outcome
of this visit by giving an opportunity to build links with mechanical engineers, process engineers and
chemists. Experiences and information gathered during this training program would be useful to improve
the local sugar manufacturing process by introducing international sugar quality standards and by
identifying defects in the current sugar manufacturing process through collaborative programs with the
sugar industries and SRI.
iii
Acknowledgement
We wish to express our sincere appreciation and gratitude to the following individuals, personnel and
institutions for their assistance and cooperation to make this training a success.
Ministry of Commerce of the People’s Republic of China.
Guangxi International Business Vocational College, Nanning, People’s Republic of China
External Resource Department of Sri Lanka.
Chinese Embassy of Sri Lanka.
Secretary, Ministry of Plantation Industries.
Mr. K. Francis Karunasena, Chairman and the members of Board of Governors of Sugarcane
Research Institute.
Dr. A.P. Keerthipala, Former Director/CEO, Sugarcane Research Institute.
Dr. Aruna Wijesuriya, Acting Director, Sugarcane Research Institute, Sri Lanka.
Dr. W.R.G Witharama, Former Deputy Director (Research & Technology transfer).
Dr. M.S. Perera, Principle Research Officer and Head of the division of Technology Transfer and
Development.
Officers at SRISL who attended our duties while we were out of the country and all other
supportive staff.
iv
Contents
Preface............................................................................................................................................. ii
Acknowledgements ........................................................................................................................ iii
01. Introduction ............................................................................................................................... 1
02. Objective ................................................................................................................................... 1
03. Sugarcane industry in PR-China ............................................................................................... 1
3.1 Sugarcane industry in Guangxi Province .............................................................................. 2
4.0 Cane sugar manufacturing process ........................................................................................... 2
4.1 Cane milling/crushing ........................................................................................................... 2
4.1.1. Cane preparation ........................................................................................................... 3
4.1.2. Measures to improve milling efficiency ....................................................................... 4
4.2 Juice clarification .................................................................................................................. 5
4.2.1 Majoor steps in clarification .......................................................................................... 5
4.2.2. Defecation ..................................................................................................................... 5
4.2.3. Clarification with Phosphoric acid................................................................................ 6
4.2.4. Sulphitation ................................................................................................................... 6
4.2.5.Carbonatation ................................................................................................................. 7
4.3 Process of evaporation .......................................................................................................... 7
4.3.1. Heat transfer in evaporators .......................................................................................... 8
4.3.2. Types of evaporatorsused ............................................................................................. 9
4.3.3. Chemical changes and tube fouling during evaporation ............................................... 9
4.3.4. Control of fouling ....................................................................................................... 10
4.3.5. Cleaning of fouling tubes ............................................................................................ 10
4.4 Sugar boiling and crystallization ........................................................................................ 10
v
4.4.1. Crystallisation of Sugar............................................................................................... 10
4.4.2. Solubility of pure sucrose ........................................................................................... 11
4.4.3. Centrifugal operation .................................................................................................. 13
05. Chinese technologies that could be adopted to improve the sugar manufacturing process in, Sri
Lanka............................................................................................................................................. 14
06. Conclusion .............................................................................................................................. 15
1
01. Introduction
The training course on Sugar Technology has been organized by the Ministry of Commerce of the People’s
Republic of China collaboratively with the Guangxi International Business Vocational College (GIBVC).
GIBVC is a state-owned college for higher education located in the “green city” in Nanning in the People’s
Republic of China (PR-China). GIBVC is featured by training foreign-oriented highly-qualified
professionals for the economic prosperity of the region and the nation. It is the “Model Vocational College”
in Guangxi, under the authority of the Commerce Department of Guangxi Zhuang Autonomous Region.
The college has successfully completed several training courses on different subjects since 2012. During
2018, many training programs were conducted at GIBVC with the participation of scientists from Jamaica,
Laos, Myanmar, Cambodia, the Philippines, Indonesia, Vietnam, Thailand and Sri Lanka.
The contents of this training course were; introduction to basic information of China and Guangxi, the
current situation of sugar manufacturing industry in Guangxi, the automation of sugar manufacturing in
China, milling technology, juice clarification and evaporation technology, sugar boiling technology, the
operation of sugar refineries, energy balancing in modern sugar refineries, the etiquette and the traditional
culture of China, the art of Chinese tea, etc. The expected outcome of this course was to transfer modern
sugar manufacturing technologies to the other countries.
Officials and professionals from Sugar Manufacturing Association of Guangxi, Guangxi University, Saier
Sugar Manufacturing Technology Limited, Nanning, Guangxi and Funan East- Asia Sugar Refinery of
Guangxi conducted lectures and lead the discussions. There were also extracurricular activities including
field trips and cultural experiencing activities for the participant’s, visits to the sugar refinery in Fujian,
Nanning and Xiaopingyang. The participants witnessed the progress that China has made in the sugar
manufacturing industry and learned advanced technologies. This training course enhanced the cooperation
between China and developing countries in the fields of both economy and technology.
There were 24 participants for the training course (14 from Sri Lanka, 05 - Uganda, 04- Ethiopians and one
from South Africa). They represented Sugarcane Research Institutes and Sugar companies. The training
course was well organized and held from 15th October to 13th November 2018 including lectures and field
visits. Lectures were conducted in GIBVC classrooms equipped with modern teaching aids. This report
carries information on the training component and general background of the Chinese sugar industry.
02. Objectives
The main objectives of this training programme were to acquire theoretical and practical knowledge of
sugar manufacturing technologies adopted in PR-China and use that knowledge to improve the sugar
manufacturing process in Sri Lanka.
03. Sugarcane Industry in PR-China
The People’s Republic of China is a fast-industrializing country where new technologies are adopted in
every industry. China is the world’s third-largest sugar-producing country followed by Brazil and India. It
comprises 270 operating sugar mills of which 233 mills with sugarcane and 37 with sugar beet. Also, there
are 11 sugar refineries. The total sugar production comprises approximately 90% of cane sugar and 10% of
beet sugar. Moreover, the main product is the sugar and many co-products such as pulp, paper, alcohol,
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yeast, cane juice, bio-manure, animal feed and electricity are produced from sugarcane. The sugar industry
is the main contributor to the socio-economic development of the major cane-producing areas such as
Guangxi, Yunnan and Western Guangdong in China. However, mechanization of practices for sugarcane
is still low in China, and the hilly terrain in most of the areas makes difficult the adoption of mechanization.
Also, the cost of production continues to be very high. In fact, the price of labour for harvesting sugarcane
is one-third of the total cane purchase price. Therefore, among major sugar-producing countries, China has
the highest production costs.
3.1 Sugarcane Industry in Guangxi Province
The Guangxi region is located in south China, in subtropical humid monsoon climate zone. In the Guangxi
region, there are about 236,000 km2 suitable for sugarcane growing. In this region, the climate condition is
much better than other regions for sugarcane production. Guangxi is the dominant sugarcane and sugar
producer region in China, accounting 65% of sugar production in China. The sugar industry experienced
rapid development, and now the sugarcane production is one of the top industries in Guangxi. It has become
an important economic resource for a large number of farmers. Recently, one million hectares of sugarcane
has been grown annually, with a capacity of 7.00 million tons of cane sugar production.
4.0 Cane Sugar Manufacturing Process
4.1 Cane Milling/Crushing
Extraction of sugarcane juice is the process of squeezing the juice from the cane using high pressure with
heavy iron rollers. Generally, Chinese sugarcane factories use 5 mills for the process. The milling process
occurs in two steps: breaking the hard structure of the cane and grinding the cane. For breaking the cane
revolving knives, shredders, crushers or a combination of these processes are used. To improve the milling
and extraction performance, cane preparation equipment is normally used before the cane reaches the first
mill. Equipment used for cane preparation is the leveller, the cutter, the shredder, and the cutter-shredder.
The leveller is usually installed in front of the first cutter or behind the second cutter. The function of the
leveller is, levelling the disorderly sugarcane to avoid clogging when feeding the cutter.
Conveyors transport the crushed cane from one mill to the next. During the process of milling, imbibition
is done. Imbibition is the process in which water or juice is applied to the crushed cane to enhance the
extraction of the juice at the next mill. In imbibition, water or juice from other processing areas is introduced
into the last mill and transferred from the mill to mill towards the first two mills while the crushed cane
travels from the first to the last mill. The remaining of the crushed cane exiting the last mill is called bagasse.
The juice from the mills is strained to remove large particles and then transferred for clarification.
Following things can be done to enhance the imbibition efficiency.
Choose the suitable imbibition method to the sugar mill.
Improve the juice extraction rate and drainage efficiency of the mill.
Maintain the stable and even pumping of imbibition thin juice.
Decide the appropriate water temperature and amount.
Pay attention to the dewatering of the fine bagasse.
Increase the disintegration of cane.
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4.1.1. Cane Preparation
Before entering to the crusher, the sugarcanes are subjected to cane preparation. The leveller, cutter and
shredder are the equipment used for the cane preparation process.
The Leveler
The leveller is usually installed in front of the first cutter or behind the second cutter. Leveler is used to
levelling the bulk of disorderly sugarcane to avoid clogging when feeding to the cutter. This means if the
layer of crushed sugarcane is not even in its thickness when entering to the feeding process, the leveller can
level the layer so that it is even. Leveler is mainly composed with the main shaft, the nave, the spoke arm,
the axis and the gearing. On the main shaft, there are several naves with 2 or 4 spoke arms. The shaft runs
across the cane belt. The spoke arms are curved without blades.
The Cutter
In this section, sugar canes are converted into the small fibrous matter by using a series of cutters. Cutters
mainly consist of the cutter head, blades, axis, bearing and gearing. There are some requirements for the
cutter process such as, low power consumption, wear resistance of blades that don’t break easily and
Smooth feeding.
Figure 0: Basic Structure of the Cutter
The Shredder
In this process, the cane is torn into shred by revolving hammers but no juice extraction.
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Figure 1: Basic Structure of the Shredder
4.1.2. Measures to Improve Milling Efficiency
Improve the preparation efficiency
Prepared cane with high preparation efficiency facilitates the good imbibition, thus facilitating the
extraction of juice. When the preparation index is high, the density of the cane material is high. Therefore
it facilitates the feeding more prepared cane into the mills, thus increasing the capacity of the mill. With
high preparation index, the sugar-containing cells are extensively disintegrated and exposed and the juice
is easier to extract when subjected to expression.
Improve the mill feeding
To improve the mill feeding, the gripping ability of rollers has to be improved by increasing the
friction between the roller surfaces and the cane materials. For this, Welding hard alloys to the top
roller, improving the surface roughness, hardness and wear resistance can be done. Also,
employing feeding devices is done. The feeding devices include high chute, top feeder roller,
below feeder roller, double feeder roller. Increasing the diameter of rollers can in increase the
contact surface of the rollers with the cane material, which increases the gripping ability of rollers,
thus the thickness of the cane layer can be increased, increasing the capacity of the mills.
Adequately increase the speed of the rollers
With the increase of the speed, the throughput is increased, but the duration for expression and drainage is
reduced, which affects the drainage of the juice and extraction. Therefore the speed cannot be infinitely
increased. The speed of rollers adopted in China is1718m/min, not exceeding 20m/min.
Using best mill settings
If feeding opening is large, the pressure on the feeding roller is reduced and the feeding is favourable. But
the expressed juice is reduced leading to a decrease of overall juice extraction. Meanwhile, the expressed
juice in the delivery roller is increased, causing an increase of reabsorption, reducing the milling efficiency.
Adequately apply the hydraulic pressure
5
The higher the pressure applied, expressed juice will be more and the extraction rate will be higher. The
hydraulic pressure adopted in China is 1.8~2.2MPa. At this range of pressure, both the extraction rate and
power consumption is favourable.
4.2 Juice Clarification
The clarification (or defecation) process is the removal of both soluble and insoluble impurities such as
sand, soil, and ground rock that have not been removed by preliminary screening. The juice from the mills,
a dark green colour, is acid and turbid. for the process of juice clarification, lime and heat are used as the
clarifying agents. Milk of lime (about 450 g per ton of cane) neutralizes the natural acidity of the juice,
forming insoluble lime salts. Heating the lime juice to boiling coagulates the albumin and some of the fats,
waxes, and gums, and the precipitate formed entraps suspended solids as well as the minute particles.
The muds separate from the clear juice through sedimentation and the non-sugar impurities are removed
by continuous filtration. The final clarified juice contains about 85 percent water and has the same
composition as the raw extracted juice except for the removed impurities.
4.2.1 Major steps in clarification
1. Defecation: Lime CaO (CaOH)
2. Sulphitation: SO2 (Sulphurous Acid)
3. Phoshpatation: H3PO4(Phosphoric Acid)
4. Carbonation: CO2(Carbonic Acid)
Traditionally, Defecation, Carbonation and Sulphitation processes were preferred in the industry for
clarification of juice. These processes are applied according to the target grade of the sugar.
Defecation: For Raw sugar
Sulphitation: For Plantation White Sugar
Carbonation: Bolder Grain Plantation White Sugar
4.2.2. Defecation
During this process, lime milk will act on the cane juice and most organic acids will be eliminated. Protein
will be coagulated and part of colouring matters will be destroyed, colour reduced and finally Purity will
rises. This purification is predominantly physical and coagulated material will entrap suspended impurities
and removed. Good quality lime has to be used for this process (90-95%, CaO). Using high purity lime will
cause to better quality. The solubility of lime in cane juice will be increased with a lower temperature of
cane juice. In general lime, consumption is controlled at 0.6-1.0 kg of CaO per ton of cane for making raw
sugar. the target of the process is to use a minimum of lime, good clarification and good settling
performance. Also, the pH of clarified juice is controlled at 7.0-7.8. Using excessive lime will result in a
higher content of lime in clarified cane juice causing scale in evaporators.
Defecation Procedures
Cold liming
Cold liming is done when mixed juice pH at 5.5 and Limed juice pH at 7.2-8.3( normally at 7.8)
and heating to boiling point at 102-1040C.
6
Fractional liming with double heating
Mixed juice from mill pH at 5.5, Pre-Liming cold juice pH at 6.6-7.2, heating to 65-750C, re-
liming to pH at 7.6-8.2, heating again to boiling and leaving to settle.
4.2.3. Clarification with Phosphoric Acid
In this process, phosphoric acid is added before liming. Normally, H3PO4 is added in mixed juice tank with
a stirrer in the mill house. Also, it can be combined with sulphitation.
Role of H3PO4 in cane juice:
H3PO4 is reacted with lime and form a precipitate which constituting an important part of the floc produced
in the juice by the lime. Also, the part of colloids and colouring matter are removed. Greater concentration
of H3PO4 in juice results in easier clarification. Normally content is 350-500ppm as P2O5.
Advantages of H3PO4
1. Clarification of refractory juice will be improved.
2. Less expensive than sulphitation. (Do not require special equipment, corrosion and scale are
reduced.)
3. Phosphoric acid served as an addition to the main clarification process, not as a replacement.
4.2.4. Sulphation
Defecation is the universal process and sulphitation is secondary to defecation in China and India to produce
plantation white sugar. In here, sulphurous acid action cane juice and colouring matters are eliminated. It
reduces to colourless compounds of the ferric salts which formed by contact with mills, pipes and tanks. in
here good quality sulphur has to be used. the lime consumption is about 1.75kg of CaO/kg of sulphur and
sulphur consumption is 0.9-1.2kg sulphur/ ton cane for both juice and syrup sulphited.
Sulphitation Procedure
Hot sulphitation
First heating to 60-800C, then sulphitation, liming, heating to boiling and finally pumping to the
clarifier.
Fractional liming and sulphitation
Pre-liming to pH at 7.0-8.0, heating to 55-700C, sulphitation to pH at 5-5.3, second liming to pH
at 7.0-7.5, and finally reheating to boiling.
Sulphitation can be done before or after liming. Before liming is preferable for better coagulation of
impurities when treating bad or refractory cane. Sulphitation at high acidity (pH 3.8-4.0) and low
temperature (30-400C) and,at low acidity (pH 5.0-5.3) and high temperature (70-750C) are practiced. In
China, sulphitation and liming carried out simultaneously as nearly as possible in one vessel and results
are more superior. it is important that not to hold juice at high alkalinity and high temperature at the same
time, because reducing sugar will be destroyed.
Advantages of sulphitation
1. Juice settles more rapidly hence the capacity of the clarifier is improved
2. Less viscous massectuie and boil faster
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3. Better crystallization in consequence
4. Marked improvement of sugar colour
5. Time savings in clarification and boilings
6. Slight gain in the capacity of centrifugal
7. Better elimination of phosphates and waxed, leading to better refining quality and filterability.
Disadvantages of sulphitation:
1. Much heavier deposits in heaters, evaporators and pans. therefore more heating area is required.
2. High ash content in sugar produced.
3. High cost
4.2.5.Carbonatation
Carbonation was originated in a beet sugar factory in 1859. It is rarely practised in cane sugar mills due to
the caking problem and high cost. Carbonation extensively adopted in the refining of cane raw sugar.
Carbonation in cane mill is never carried out at a temperature above 550C due to the destruction of reducing
sugar. Normally it is done at 50-550C.
Carbonation Procedure
i. Heating to 550C
ii. Heavy liming is done to pH at 9.8-10.5 and first carbonation is done batch-wise leaving very high
alkalinity. ( adding lime and CO2 simultaneously)
iii. Filtration
iv. Second continuous carbonatation at lower alkalinity (pH=8.2-8.5)
v. Heating to 85 0C
vi. Second filtration
vii. First sulphitation to pH at 7.0-7.3
viii. Concentration to 60-65RDS (Refractometric dry solids)
ix. Second sulphitation of raw syrup to pH at 6.0-6.8
x. Third filtration
4.3 Process of Evaporation
Evaporation is the process of removing water from the clarified sugarcane juices to concentrate the
sugarcane juice. In general, about two-thirds of the water is removed through vacuum evaporation (Figure:
3). Generally, four vacuum-boiling cells are arranged in series so that each succeeding body has a higher
vacuum that supports boiling at a lower temperature. The vapours from one body can boil the juice in the
next one. The vapour from the last cell goes to a condenser. The syrup leaves the last body continuously
with about 65 percent solids and 35 percent water. The point at which cane juice begins to crystallize is in
8
the range of 78 - 80 Bx. Theoretically, the evaporation could be carried out up to 72 or 75 Bx. In practice,
the sugar boilers require a syrup capable of dissolving further crystals, so that they may dissolve false grain
which may form at the beginning of a charge; this condition is indispensable for obtaining good results at
the pan stage. For this reason, a brix figure of 72°is never exceeded.
Figure 3: Diagram of the evaporation process
4.3.1. Heat Transfer in Evaporators
A sugar evaporator consists essentially of a tubular calandria serving as a heat exchanger. The heating steam
surrounds the outside of the tubes and the juice to be evaporated circulates inside the tubes (Figure: 4).
Figure 4: Simple diagram of an evaporator
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The heat transfer is important to evaporate water from the juice and it is identified as the following formula.
S- Heating surface, k- heat transfer efficiency, Δt- temperature difference
According to the equation, in order to increase the evaporation of water, increasing the heating surface (S),
improving the heat transfer efficiency (k) and increasing the temperature difference (Δt) have to be done.
The heating surface of an evaporator is the total surface of all the heating tubes.
dlnS
n = number of tubes, d = diameter of the tube, l = length of the tube
4.3.2. Types of Evaporator Used
Basically, there are 4 types of evaporators used in the sugar industry.
Roberts Type
Kestner's
Falling Film Tubular Evaporator
Plate Evaporator
4.3.3. Chemical changes and tube fouling during evaporation
During the evaporation process, there are some chemical changes. They are,
Conversion of sucrose
C12H22O11 + H2O → C6H12O6 + C6H12O6 (Increase with time, temperature and acidity.)
Rise in Colour
pH change
Precipitations
Purity change
Fouling of heating tube
Substances such as CaCO3 and CaSO4 are crystallized due to the concentration of the solution and these
crystalized material are deposited inside the tubes. This causes to corrosion of metal.
Growing of scales
The growing of scales in heating tubes is a comprehensive result of deposits and breakages. At the start, the
deposits prevail and the scaling develops faster than the breakage rate increases. The developing of scale
slows down at a certain time after the deposit and the breakage become balance. If the concentration of
fouling ingredients (calcium) in the juice is higher, the scaling will be strong and if the juice flow is faster,
the scaling will be thin.
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4.3.4. Control of fouling
Improvement of juice quality will help to control the fouling. For this, improving the purification of juice,
reducing the content of calcium is very important. Also, strengthening the slaking of lime, strengthening
the sulphitation and neutralization reaction or the carbonation reaction, improving the clarifier operation or
prolong the retention time of settling is done. Scale prevention with ultrasound is also practised.
4.3.5. Cleaning of fouling tubes
i. Chemical cleaning
In here, alkaline and acidic solutions are used to boil the tubes before physical cleaning is performed. There
are several techniques for chemical cleaning.
(a) Boiling with alkaline solution
This is the most commonly used method and the chemical is the caustic soda or a mixture of caustic soda
and soda ash. Sometimes, salt is added and it is believed to increase the solubility of Si02 in alkaline solution
and make to scale become looser. Boiling in alkaline medium shows effective calcium sulfate and silicate
scaling. The concentration of the alkaline solution is 4-6and the concentration of the salt solution is 30%
on alkaline agents. The solution is boiled at 110-120 for5-6h.
(b) Boiling with acidic solution
Boiling in the acidic solution is mainly done to dissolve carbonate, phosphate and sulphate scales. The
concentration of the hydrochloric solution is 0.5-1%, which is boiled for 1-6hours. As the acid is corrosive,
molasses or furfural is usually added as anti-corrosions. The concentration of hydrochloric solution could
increase to 3% when 2-2.5% of furfural is added thus the boiling time could be much reduced.
(c) Boiling with both alkaline and acidic solutions
For the hard scales, boiling with both alkaline and acidic solutions are practised. First, boiling in alkaline
solution is done to loosen the scales and then in an acidic solution to further dissolve the scales.
ii. High-pressure water injection cleaning
Here, pressurized water is injected and the water pressure could be 75MPaand the highest up to100MPa.
iii. Mechanical cleaning
Mechanically removal of scales in tubes are also practised.
4.4 Sugar Boiling and Crystallization
After sulphitation process, the syrup is going to further process of crystallization. This syrup boiling process
is done in vacuum pans. The pan boiling process essentially consists of further removal of water by
evaporation in single effect and crystallizing out sugar by increasing the concentration.
4.4.1. Crystallisation of Sugar
Boiling system
Mainly there are two types of boiling systems used in the sugar industry. These boiling systems are varied
according to final product quality. Following flow charts are represented the two types of boiling systems.
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4.4.2. The solubility of pure sucrose
The solubility is the quantity of sucrose which can be dissolved in water to produce a saturated solution at
a given temperature. Normally it is expressed in g sucrose /100g of water.
Figure 5: Sugar Saturation with temperature
Figure 6: Three boiling system for White sugar
A massecuite B massecuite C massecuite
Syrup B Seed C Seed
Syrup
A green
Syrup
A wash
Syrup
White
Sugar B green
Syrup
B Sugar C Sugar Final
molasses
P-7P-8
Delivery Delivery
12
Figure 7: Three boiling system for raw sugar
Degree of supersaturation (DSat)
Degree of Supersaturation is expressed by the supersaturation coefficient (DSat) and it can be calculated
by dividing the sucrose /water ratio of the supersaturation solution by the sucrose /water ratio of a saturated
solution under the same conditions of temperature and purity. If DSat1, under saturated, DSat1,
saturated, DSat1, supersaturated.
Supersaturated solutions
Solution with Supersaturation Coefficient is greater than 1, is called as a supersaturated solution. This kind
of solutions cannot be made by dissolving sugar in water and only they can be made by:
Evaporating water to increase concentration
Cooling the solution to decrease the solubility
Example Calculation
Cooling a saturated pure sugar solution from 50 to 40
At 50 the saturated solution will hold 258.6g of sugar in 100g of water
At 40a saturated solution would hold only 234.5g sugar in 100g of water
Therefore at 40°C,
The solution has 258.6−234.5
234.5 = 10% of more sugar than a saturated solution at this temperature
A massecuite
P=85 B massecuite
P=72
C massecuite
P=60
A Centrifuge B Centrifuge C Centrifuge
P-22
P-23 P-24
A
molasses
P= 65
A Sugar B Sugar
P=97.5
B
molasses
P=50
C Sugar Final
molasses
P-26
P-27 P-28
P-29
P-30
Syrup
P-31P-32 P-33P-34 P-35P-36
P-37
Delivery
P=98.5 To Distillery
P-38
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Therefore Supersaturation is a driving force for the crystallisation. Once the solution or melt has become
supersaturated, there is a thermodynamic driving force for crystallization. That is, the molecules tend
toward crystalline state to lower the energy level of the system. During nucleation, the molecules in the
liquid state rearrange and eventually form into a stable cluster that organizes into a crystalline lattice.
Supersaturation stage further can be divided into Metastable Zone and Labile Zone.
If the solution is reached to the labile zone, spontaneous crystallization will be formed and it will be caused
to the formation of uneven sugar crystals. Therefore solution should be maintained within the metastable
zone to avoid that uneven crystal formation. Then the solution should be stayed in the Metastable Zone to
avoid ‘spontaneous crystallization’ but as close as possible to the Labile Zone to maximise driving force
for crystal growth.
Controlling the supersaturation stage
Controlling the supersaturation stage within the metastable zone is very important in the crystallization
process. Therefore following things can be done to control the supersaturation in crystallization.
Figure 8: controlling methods of required Desaturation
4.4.3. Centrifugal Operation
After crystallization, the sugar crystals are separated from the massecuite by centrifuging. Separation of
sugar crystals from the mother liquor by means of centrifugal force is done as a result of high-speed rotation
of the centrifugal machine. The centrifugal force depends on the speed of rotation and the diameter of the
basket.It is usually expressed by Gravity factor (G). Gravity factor of separation is the ratio of centrifugal
acceleration to acceleration of the earth’s gravity. It can be represented by the following formula.
G = d.n2/1790 d - Basket diameter, n - Speed of rotation
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Major types of centrifugal
There are two types of Centrifugal machines are available in sugar industries.
1. Batch Centrifugal
In the batch centrifugal machine, a sugar cake is formed from which the mother liquor drains under the high
centrifugal force. There still remains a layer of mother liquor around the crystals, particularly at the
interstices between crystals. Therefore a washing stage is always included, where water and /or steam are
applied in the centrifugal basket to wash mother liquor off the crystal. Most of the time batch centrifugal
machines are used to separate high-grade sugar (White sugar and A Sugar).
2. Continuous Centrifugal
In the continuous centrifugal machine, the crystal moves continuously up the sloping screen by the
centrifugal force. The crystal layer is thin. With the movement of crystals, it is easier for the mother liquor
to drain. Water and steam are added for improving fluidity as the massecuite enters the machine. Most of
the time-continuous centrifugal machines are used to separate low-grade sugar (B sugar and C sugar). Both
advantages and disadvantages are included in this type of centrifugal machine. Advantages: cheaper, easier
to operate and low maintenance cost. Disadvantage: Achievable sugar quality is not as good as in a batch
centrifuge. Leading to breakage of sugar crystals when discharged from the machine.
05. Chinese technologies that could be adopted to improve the sugar manufacturing process
in, Sri Lanka
Sri Lankan sugar mills are operating at a low level of efficiency at present and the sugar recovery is low
compared to the Chinees sugar factories. These issues should be addressed to improve the sugar industry
in Sri Lanka. Therefore this training course helps to improve the knowledge through different subjects and
based on that, new research activities could be started and implemented to find solutions to these issues.
Throughout the lectures, we could identify the main factors affected to the low level of factory efficiency
and the low rate of sugar recovery. Basically, sugar recovery can be depected by the following equation.
Overall Recovery = Pol % cane - (Pol % in bagasse + Po l% in Filter cake + Pol % molasses + unknown losses)
According to the above equation, Pol % cane should be increased or total losses should be reduced to
increase the overall recovery. Enhancing the Pol % cane would be a one of the research areas to increase
the total recovery and profit.
The optimum machine performances can be maintained by monitoring factors related to mill sanitation,
cane preparation and juice extraction. As well as, mill extraction is one of the important parameters which
can be used to select the best mill tandem among different mill tandem with different features.Also,
calculation of steam consumption for evaporator configurations is very important to select the best
evaporator scheme among different schemes with less steam consumption. Investigation of these factors
under Sri Lankan scenario would be beneficial to improve the efficiency in the sugar manufacturing
process.
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Also, the technical knowledge gain through lectures and field visits is important to plan new
research in large mill testing of new sugarcane varieties. Furthermore, information gathered on
world sugar quality standards will be useful to analyse locally produced and imported sugar for
their quality parameters.
06. Conclusion
This short-term training program provided us with a great opportunity to exchange scientific knowledge
and experiences in sugar manufacturing process, between China and Sri Lanka. We were able to build links
with mechanical engineers, factory specialist, chemists and instrument specialists who are actively engaged
in advanced scientific research and sugar factory operations in China. It made a platform to share
knowledge and experiences with other scientists engaged in sugarcane industry in Ethiopia, Uganda and
South Africa. The technologies that we learnt in China are applicable to improve the sugar manufacturing
process in Sri Lanka.
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