THE UNIVERSITY of QUEENSLAND
SCHOOL OF CHEMICAL ENGINEERING
CHEE3020 Group Project 1
Sugar Cane Milling Process Report
EX_PBL01 Group 6
Name
Student Number
Jingchen Zhang
45245428
Syed Muntaha Mazoor
45740969
Thalia Mursalina
46567109
Yunshenghao Qiu
45261035
Zandro Stephen Lagman
46375452
Summary
Sugar is a staple ingredient in households that undergo an intensive and complex production
in order to get to markets. The 3 main phases of this production are in the order of cultivation,
milling and refining. Each phase has its own technological requirements, inputs and products
which is further varied by the type of sugar crop utilised. Current sugar industry in Australia
is dominated by sugar mills producing raw sugar from sugarcane. As a result, sugar milling
has a key role in supplementing the Australian economy as well as earning Australia’s
reputation as a major raw sugar exporter. This context forms the basis of the investigation
which focuses on exploring the significance of sugar milling, analysing the production
process from cane to raw sugar and evaluating potential and challenges to the industry.
Sugar milling process has 8 main steps:
1.
2.
3.
4.
5.
6.
7.
8.
Cleaning – removal of outer dirt, debris and contaminants
Cutting – reducing size of cane feed for ease of proceeding steps
Extraction – crushing of cane obtain juice with dissolved sugars and non-sugars
Juice Treatment – purification of juice to remove non-sugars to miniscule amounts
Evaporation – concentration of juice to syrup
Crystallisation – initiation and growth of sugar crystals from concentrated syrup
Centrifugation – separation of sugar crystals from the liquid mixture
Drying – drying of sugar crystals to raw sugar set for storage and/or further processing
Analysis of the sugar milling process reveals that the crystallisation unit is critical to the success
of the mill, specially concerning raw sugar yield. In addition, this unit interacts closely with the
evaporation and centrifugation processes such that evaporator vacuum pans, crystallisers and
centrifuges design deserve particular attention.
Mass balance on the sugar mill, with a basis of 100 t/h of cane result in a raw sugar production
rate of 14 t/h. Economic analysis with this basis evaluates raw sugar with a potential to generate
profits of 3713.2 AUD per hour of the mill’s operation. Sustainable analysis reveals that despite
the industrial scale, raw sugar milling is environmentally, economically and socially
sustainable. Raw sugar prices are not likely to experience a sudden decrease in prices allowing
the industry to maintain social contributions in terms of employment, developments and
investments in addressing topical issues such as sustainability. In addition, sugar mills perform
highly in terms energy considerations as mills can co-generate energy such as from bagasse.
The potential for increased energy generation is likely as ethanol can also be produced from
by-products. These analyses, however, assume ideal (or nearly ideal) processes so ‘real’ results
will be more nuanced.
2
Table of Contents
Summary ................................................................................................................................................. 2
1.
Introduction..................................................................................................................................... 5
1.1.
Background.............................................................................................................................. 5
1.1.1.
Sugar Production Overview ............................................................................................. 5
1.1.2.
Aims ................................................................................................................................. 5
1.1.3.
Scope ............................................................................................................................... 5
1.2.
Technology .............................................................................................................................. 5
1.2.1.
Available Technologies .................................................................................................... 5
1.2.2.
Chosen Technology ......................................................................................................... 7
1.2.3.
Justification...................................................................................................................... 7
1.3.
Raw Materials .......................................................................................................................... 7
1.3.1.
1.4.
Products................................................................................................................................... 7
1.4.1.
Main Product: Raw Sugar ................................................................................................ 7
1.4.2.
By-products ..................................................................................................................... 8
1.4.2.1.
Molasses ...................................................................................................................... 8
1.4.2.2.
Bagasse ........................................................................................................................ 8
1.4.2.3.
Filter Cake .................................................................................................................... 8
1.4.3.
2.
Sugar Cane ....................................................................................................................... 7
Input-output Diagram ..................................................................................................... 8
1.5.
Importance .............................................................................................................................. 8
1.6.
Hazards .................................................................................................................................. 10
Process Analysis............................................................................................................................. 11
2.1.
Process Description ............................................................................................................... 11
2.2.
Flowsheet .............................................................................................................................. 14
2.3.
Assumptions .......................................................................................................................... 14
2.4.
Mass Balance ......................................................................................................................... 15
2.5.
Goals ...................................................................................................................................... 17
2.6.
Sustainability ......................................................................................................................... 17
2.6.1.
Environmental ............................................................................................................... 17
2.6.2.
Economic ....................................................................................................................... 18
2.6.3.
Social.............................................................................................................................. 18
2.7.
Process Stream and Unit Interactions ................................................................................... 18
2.8.
Storage .................................................................................................................................. 19
2.9.
Control ................................................................................................................................... 19
2.10.
Economic Potential............................................................................................................ 20
3
3.
Unit Operations—Crystallisation................................................................................................... 21
3.1.
Introduction........................................................................................................................... 21
3.2.
Process Chemistry & Physics ................................................................................................. 21
3.3.
Equipment ............................................................................................................................. 22
3.3.1.
Vacuum Pans ................................................................................................................. 22
3.3.2.
Crystallisers.................................................................................................................... 22
3.3.3.
Centrifuges .................................................................................................................... 22
3.4.
Design ................................................................................................................................ 23
3.4.1.
Vacuum Pan Design ....................................................................................................... 23
3.4.2.
Crystalliser Design ......................................................................................................... 24
3.4.3.
Centrifuge Design .......................................................................................................... 24
4.
Professional Engineers in Process Systems ................................................................................... 24
5.
Conclusion ..................................................................................................................................... 25
References ............................................................................................................................................. 26
Appendix A ............................................................................................................................................ 30
Appendix B ............................................................................................................................................ 30
4
1. Introduction
1.1. Background
1.1.1. Sugar Production Overview
Sucrose, commonly known as table sugar, is produced in many ways but mainly from sugarcane
and sugar beets. It is a staple in households, essential in large scale food and beverage
production and even for energy supply through bioethanol. The highest sugar producers by
volume are Brazil, India and China while Australia, the 2nd highest exporter of raw sugar
globally, also has significant stakes in the sugar market (Australian Sugar Milling
Council(ASMC) 2017). The 21st century pose a unique context in exploring sugar processing
partly due to increasingly unpredictable extreme weather, greater political awareness of
environmental issues and international politics. As a significant contributor to the Australian
economy, sugar production necessitates an investigation to explore the capabilities,
vulnerabilities and viability in the future.
1.1.2. Aims
The investigation aims to do the following:
• Understand the process of producing sugar with particular interest in the local
Queensland and Australian context
• Explore critical key technologies within sugar processing and their respective
requirements for successful operation
• Evaluate economic potential of sugar production whilst considering its potential hazards
• Identify current and future challenges to the sugar production industry
1.1.3. Scope
Sugar production and the required technology is dependent on the plant feedstock utilised and
by the desired qualities of produced sugar product. The investigation, therefore, chooses a sugar
crop feedstock and sugar product to determine which technology and unit operations are
explored. Table 1 scopes the focus of study for the chosen technology in Section 1.2.
Table 1: Scope of considerations and analyses conducted on chosen sugar production process
•
•
•
•
•
•
•
•
In Scope
Quantitative
economic
potential
evaluation on input/output basis
Process sustainability analysis
Raw material and product specific
requirements and conditions
Waste generation and by-products utility
Process mass balance for technology
chosen in upcoming Section 1.2
Significance of unit interactions in
process
Critical unit operations theory and design
Ideal processes
•
•
•
•
•
•
•
•
Out of Scope
Economic potential evaluation factors
from international market prices
Fuel and energy consumption and
maintenance including transport.
Staffing and administration requirements
and expenses
Design of piping and intra-process
transport between units
Raw material qualitative analysis
Technology not chosen in Section 1.2
Detailed analysis of each unit operation
design requirements
Efficiency, cost and optimal reacting
conditions of chemical reactions
1.2. Technology
1.2.1. Available Technologies
Sugar production occurs in 3 phases:
1. Cultivation – the farming of sugar crops like sugarcane and sugar beet
5
2. Milling – extraction of raw sugar from the feedstock. Sugary liquid is crushed from the
feed and purified of contaminants (non-sugars) then filtered. The purified juice is
concentrated to precipitate and grow sugar crystals. Centrifuges are used to separate the
raw sugar from molasses. Feed remnants, like cane bagasse and filter mud, are byproducts of sugar milling(Australian Sugar Milling Council, 2013).
3. Refining – raw sugar undergoes further processing to obtain refined white sugar and
other sugar products. Common by-products include molasses and waste from chemicals
used to decolorise raw sugar.
Difference in composition, chemical and thermal properties of sugarcane and sugar beet impart
respective sugars produced with different qualities and require different processing. A
comparison between the two feeds is detailed in Table 2 and the difference in processes is
shown in Figure 1.
Figure 1: Cane vs Beet raw sugar milling process (Singh 2015)
Table 2: Comparison between sugar crops with respect to processing phases
Sugarcane
Sugar Beet
Cultivation Prefers hotter and more tropical Prefers colder climates such as
climates and more water intensive
European countries
Milling
Refining
Other
differences
More
suitable
to
Australian
climate(Griggs 2011)
Raw sugar has more non-sugars but
they are the more desirable kind
Has higher sugar content than cane
(Griggs 2011)
Beet juice less prone to caramelising
so can produce a lighter raw sugar
with less non-sugars (Griggs 2011,
Raw sugar is more consistent (Campos ASMC 2017)
2021, Griggs 2011)
More intensive refining to obtain white Shorter refining as it less non-sugars
sugar which increase environmental need removing from beet raw
footprint and expenses (ASMC 2013) sugar(ASMC 2013)
More widely used currently
Sugars may have an earthy aroma
considering beets are a root
crop(Campos 2021)
6
1.2.2. Chosen Technology
In consideration of the local Queensland and Australian setting, a sugarcane based sugar mill
was chosen to be explored in this investigation. The respective steps in the sugar milling will
use the equipment listed below with more detail provided in Section 2.1.
9. Cleaning – Rotary drum washer
10. Cutting – Rotary cutter - shredder
11. Extraction – Roller train
12. Juice Treatment – Clarifier vats
13. Evaporation – Vacuum pans
14. Crystallisation – Crystallisers
15. Centrifugation – Centrifuges
16. Drying – Rotating drum dryer and granulator
1.2.3. Justification
A sugar mill producing raw sugar from sugarcane is a configuration is the most reflective of
the Australian setting. Queensland and Australia’s climate is ideal for sugar cane cultivation
allowing large scale cultivation production. Australia’s high volume of raw sugar exports
supports this so it is only natural that the 24 sugar mills operating in Australia will be optimised
to use this sugar crop. Furthermore, only 5% of sugar is refined within Australia, with raw sugar
exports contributing significantly to the economy (ASMC 2017). Choosing sugarcane based
milling, therefore, is not only more relevant to the Australian context but allows more effective
process analyses like that concerning sustainability and economic potential.
The choice of sugar crop also considered their chemical properties and the effect on the
processing technology. Focusing on sugar mills, the main product is raw sugar which has a
higher percentage of non-sugars than refined white sugar. Sugarcane raw sugar, therefore, is
the more desirable feed than beets as the sugarcane non-sugars imparts its sugar products with
more marketable qualities. Raw sugar from cane has a higher non-sugar content but this may
be an advantage. Refineries using cane sugar to produce white sugar, light brown sugar and
coffee crystals can more easily and consistently control their product qualities (Campos 2021).
Cane raw sugar more, therefore, is more attractive to consumers and corporations alike which
complement the exporting stance of Australia on raw sugar.
1.3. Raw Materials
1.3.1. Sugar Cane
Sugar cane is the raw material used to make sugar. It is composed primarily of water (75 – 82%)
and soluble solids (10 - 25%), sugar (15.5 - 24 %) and other compounds such as organic acids
and phenolic compounds (Felipe 2014). Sugar cane leaves and roots are trimmed from the stem
which will then become sugar mill feed. Since cane deteriorates easily, it is critical to harvest
it in its entirety to prevent microbial contamination. Once the cane is trimmed, it starts to
deteriorate rapidly. Acids that destabilise sucrose content can be produced, making it unviable
to stockpile sugarcane for later milling. As sucrose is a desirable substrate, cane is prone to pest
and disease issues. Damages and cuts to the stem increase the risk of disease and rot, lowering
the sugar content (Colonna et al. 2006). The vulnerabilities of sugar cane require mills to
maximise raw sugar yield by stabilising sugar content by rapid processing of feed and
increasing sugar extraction from the cane.
1.4. Products
1.4.1. Main Product: Raw Sugar
The main product of milling is raw sugar, which is purified and crystallised sucrose. It is a
fructose/glucose mixture with a polarization (Pol) of 96–99° (Omprakash, 2018). Raw sugar is
7
primarily used in the production of refined sugar but can also be sold in supermarkets unrefined.
Milling produces large amounts of raw sugar which is stored bulk bins.
1.4.2. By-products
1.4.2.1. Molasses
Molasses is a significant by-product of the sugarcane industry. A tonne of sugarcane yields
around 2.5–4% molasses. It contains 47-48 % fermentable sugars, with sucrose being the most
abundant (Saric et al. 2016). It is primarily used to make alcohol like ethyl alcohol abundantly
used in chemical industries. The ethanol produced may become vehicle fuel as bioethanol.
Molasses is also used as livestock feed due to its high nutritional value. In food industry, it is
used as a sweetener, syrup or a colourant.
1.4.2.2. Bagasse
Bagasse is the smashed cane leaving the mills. Water makes up nearly half of the bagasse. Its
bulk consists of fibres, with a small amount of dissolved sugar. Bagasse may be used as a
combustion fuel to generate steam. It is also a raw material in manufacture of pulp and paper.
1.4.2.3. Filter Cake
The clarification process splits the insoluble particulate matter known as filter cake from the
cane juice. It is composed of 75–80% moisture, 2–5% sugar, and 5–10% fibre (Omprakash
2018). It is mostly utilised as a fertiliser. Moreover, the sterols and fatty acids formed can be
used to preserve fruits.
1.4.3. Input-output Diagram
Figure 2: Input-output diagram for sugar milling
1.5. Importance
Australia's first sugar refinery was founded in 1842 in Sydney to refine imported sugar while
sugarcane was successfully operated with the first sugar mill in the country back in 1862. Since
Australia started exporting raw sugar back in 1922, approximately 80% of production volume
is now exported as raw sugar (ACFA 2006). Currently, sugar production fulfills local demands
while significantly boosting the export revenue economy at large. Australia remains the world's
next-major exporter of 'raw' sugar behind Brazil, thus, an important player in the global sugar
market (QEAS 2019). Sugar production greatly contributes to Australian local and national
economies and global trade too.
Each phase of sugar production offers jobs and generates revenue that includes the regional,
nationwide and comprehensive economies. Roughly 95% of sugar in Australia is grown in the
2,100km coastline in middle Mossman, North Queensland whilst the remaining 5% from
northern New South Wales (Department of Agriculture, Water and the Environment 2020). In
Queensland alone, sugar manufacturing industries contributed approximately $2.2 billion to the
economy. Nine sugar milling companies, including Bundaberg Sugar Ltd, handle the 24 sugar
mills in Queensland. Table 3 details the regions directly impacted by their operation in the
financial year 2017/2018 (Lawrence Consulting 2019).
8
Table 3: Revenue data of Queensland's sugar mills (Lawrence Consulting 2019)
The largest exporter of raw sugar is
Brazil. Australia follows behind brazil
in term of raw sugar exports.
Comparatively, USA share similar
production capacity as Australia but is
a significant exporter of raw sugar.
This is due to the difference between
national consumption and production
of the countries with some examples
in Figure 3. Moreover, the
competitiveness of a country in the
sugar market is also dictated by many
factor shown in Figure 4 such as
location factors, taxes and regulations.
As such, the collective of minor
importer countries that have low
production capacities ascertain
demand. Conversely, only 80% of raw
sugar exports are satisfied by only 10
major exporters including Australia
(Zimmermann & Zeddies 2002). This
information suggests that whilst
production and exports of raw sugar is
dominated by few countries, trends in
other countries, specifically
concerning global consumption,
require consideration in analysing
importance of raw sugar.
Figure 4: Production and consumption of sugar in
1998[million tons raw value] (Zimmermann & Zeddies 2002)
Figure 3: Factors influencing international competitiveness of
countries in sugar trade (Zimmerman & Zeddies 2002)
9
Raw sugar production influences the market and revenue of the individual country and the
world economy. World sugar market averages about 64 million tonnes/year. Between 2001 and
2018, global sugar consumption increased from 123.454 million tonnes to 172.441 million
tonnes, equivalent to typical annual growth of 2.01%. The latter half of the 2010-2020 indicated
extensive deceleration in global sugar consumption with the 2016-2018 growth of under 0.84%
per annum (ISO 2020). This is attributed to consumer pattern change from industrialisation. For
developing countries, rising population and salaries influence dietary change that increase
demand for more processed foods and drinks with sugar. In developed countries, meanwhile,
demand stagnates due to slowing population growth, health concerns regarding sugar
consumption and government regulations to address these issues (Voora, Bermúdez, Larrea, &
Baliño, 2019). Besides food and drinks, a significant portion of cane and sugar consumption is
by the energy industry for bioethanol. Rising oil prices directly impact the price of bioethanol,
thus, sugar prices in addition to indirect
impacts from the increased cost of
transport. The resulting global trend is
the decreasing growth in raw sugar
consumption rate.
Globally, sugar production increases
prospects and jobs available for all
involved in meeting supply and demand
networks.
For
instance,
many
multinational corporations such as
Coca-Cola, Nestle, Unilever, produce
many consumer supplies that require
sugar, thus, driving up demand (Voora,
Bermúdez, Larrea, & Baliño, 2019).
Furthermore, to sustain or increase their
production, transnational corporations
will invest in sugar production which Figure 5: Sustainable cane consumption of companies(Voora,
may result in increased employment, Bermúdez, Larrea & Baliño 2019)
increased profits and advancing
research concerning environmental sustainability. Figure 5 illustrates this dedication compared
with current consumption of cane sugar. Global fluctuations in the sugar market, therefore, can
critically impact national and local sugar production industries, not limited to sugar mills.
1.6. Hazards
Table 4 below shows potential hazards throughout the process and operation of sugarcane
production and how they are addressed:
Table 4: Sugar milling hazards and corresponding measures
Hazards and Causes
Measures
Respiratory hazards: caused by burning •
of sugarcane trash and bagasse for
energy, also fly ash and bagasse dust
•
from other processes (Le Blond, Woskie,
Horwell & Williamson 2017).
install some filtration equipment to make the
exhaust under health respiration standard;
instead of burning sugarcane trash and
bagasse, use other energy sources.
10
Physical hazards related to the working •
environment: exposure to noise and heat
in factories for a long time. (Taffere,
•
Bonsa & Assefa 2019)
Have proper personal protective equipment
(PPE) for all workers;
Physical hazards related to surrounding •
objects: hit by moving object (The State
•
of Queensland 2011)
Have proper PPE for all workers;
Physical hazard related to sugar dust: •
explosion at high concentration in air
(The State of Queensland 2011).
Have sensor to detect the concentration of
sugar in air and alarm it if the concentration
is too high;
Have a reasonable job rotation timetable to
prevent long time exposure to heat and noise
(Taffere, Bonsa & Assefa 2019).
Set warning signs/devices at place/equipment
that are possible to have accidents (The State
of Queensland 2011).
•
Have sign to exclude ignition source;
•
Separate equipment with open flame from
equipment that may have sugar dust around
it (The State of Queensland 2011).
Have ventilation or flame proof equipment;
Chemical hazard related to methane gas: •
explosion (The State of Queensland
•
2011).
Have sign to exclude ignition source (The
State of Queensland 2011).
The major hazard from all potential hazards is hitting by moving objects in sugarcane-based
sugar factories in Queensland (The State of Queensland 2011). Unlike other types of factories,
sugarcane-based sugar factories have less components in the process which require extremely
high temperature, high pressure or dangerous chemicals, so it is less probable for safety hazards
appearing within the production process. To ensure factory and workers’ safety, measures in
Table 4 should be taken.
2. Process Analysis
2.1. Process Description
Transportation of raw sugarcane is primarily completed through the railway system. Mills in
Australia regularly operate around 4,000km of the railway system, and roughly 95% of raw
sugar cane is transported to sugar mills using these platforms (ASMC 2013). After transport,
the process structure for the production of raw sugar from sugarcane occurs in eight major steps
as listed in Section 1.2. These are as follows:
1. Cleaning
The sugar cane arriving at the processing plant is first thoroughly washed. Belts that are
splashed with water in pipes that are brimming with water and rotating drums are regularly
utilized as washing stations. Water is showered into the drum, and the item turns inside the
drum, scouring against itself to eliminate soil. After washing, the cleaned sugar canes are passed
on into the processing plant utilizing screws or belts.
2. Cutting
11
Clean sugar canes are placed onto the transporter belts and shipped to a shredder. The shredder
shreds the cane into cassettes and bursts the juice cells (ASMC 2013). Here the sugar canes are
squashed utilizing swing-hammer shredders or intensely furrowed smasher rollers. Sugar canes
are cut utilizing slicing machines, which raptures them into small strips smaller than French
fries, called cassettes. The cassettes are absorbed into hot water tanks, while the squashed sugar
stick is showered with boiling water. Both processes are simultaneously conducted in this part
of the process to swell the plant cells in preparation for extraction (McHugh 2020).
Figure 7: Cutting Unit (ASMC 2013)
Figure 6: Extraction Unit (ASMC 2013)
3. Extraction
Sets of rollers feed the sugar cassettes through a progression of mills. Each mill comprises three
huge rollers in a three-sided arrangement, typically combined with pressure feeders (McHugh
2020). The sugar cassettes are siphoned into the lower part of 10-to 20-meter-tall tanks. A series
of five mills compresses the sugar cane strands to extract the juice from the bagasse. Bagasse
is recycled as fuel for the mill evaporator boiler furnaces. The extracted juice is dull green in
colour, acidic in nature, and murky. The juice is collected in massive tanks, and the sugar
fixation is estimated (McHugh 2020).
4. Juice Treatment
The extracted green sugar juice contains impurities that are removed by
liming, sulfitation, and heating the limed juice. The clarification process
typically takes several hours. Unclarified juice is introduced at the top of
the clarifier, and sulfur dioxide vapor is introduced from the bottom to
complete sulfitation (McHugh 2020). Liming neutralises the acidity and
precipitates impurities which settle out in clarifiers. Clarified sugar juice
is extracted from the top of clarifiers, while the muddy juice is extracted
from the bottom mixed with fine bagasse. Later on, filtered using a
cylindrical rotating vacuum to recover the sugar. The final filter mud
extracted is used as a fertilizer on the farm (ASMC 2013).
Figure 8: Evaporation
Unit -Vacuum Pan
5. Evaporation
(ASMC 2013)
The clarified juice is boiled in the evaporation chamber in a vacuum
evaporator cycle until it concentrates up to 50%–65% sugar. Each
successive evaporator in the process is set at a higher vacuum pressure
resulting in the sugar syrup boiling at progressively reduced temperatures
throughout the process. The residue is skimmed off the top of the
evaporators using paddle skimmers, producing a dense, nearly colourless
concentrated sugar syrup. The excess evaporated water is also removed
throughout the process (McHugh 2020).
6. Crystallisation
The pre-concentrated syrup is further concentrated up to 70% by boiling
in a vacuum pan and seeded with tiny sugar crystals. Whilst boiling, sugar
crystals are grown to the required size by adding more syrup. A single- Figure 9: Centifugation
stage vacuum pan is operated until it is saturated with sugar crystals Unit (ASMC 2013)
12
formed through seeding (McHugh 2020). The tiny grains of sugar present in the solution serve
as nuclei, aiding sugar in the syrup to form crystals. Regulatory boiling of the mixture in a
vacuum pan, water evaporates, and the sugar crystals continue to grow into a massecuite paste.
Massecuite is a dense mixture of syrup and sugar crystals (ASMC 2013).
7. Centrifugation
For the separation of sugar crystals and molasses, the massecuite is added
into a high-speed centrifuge. The raw sugar crystals in perforated baskets
spin at 1,000 to 2,800 revolutions per minute in centrifugal casting. The
dark syrup enveloping the crystals known as magma is tossed off and
passes through the crystalliser again. The magma is boiled again and used
to seed crystal growth so more raw sugar crystals are recovered.
Springwater is used to wash the formed raw sugar crystals as they are
centrifuged, and the leftover is molasses of the syrup from the final
centrifuging (McHugh 2020). This is stored for later sale. Both
crystalizing and centrifuging processes are repeated several times to Figure 10: Drying Chamber
(ASMC 2013)
maximize the yield of raw sugar.
8. Drying
The centrifuge’s raw wet sugar dries by tumbling through a stream of air in a rotating drum.
Once it achieves a moisture content of 0.02%, raw sugar is gradually tossed through the heated
air of a granulator. Dried raw sugar crystals are separated into different sizes through vibrating
screens and stored in bulk bins, and the extracted waters are removed (McHugh 2020).
13
2.2. Flowsheet
Figure 12 maps out the sugar mill processes describe in Section 2.1 as a process flow
diagram(PFD). This figure also incorporates the stream table which has the mass balance.
Figure 11 below is a simpler version of the PFD, which is a block flow diagram(BFD) which
depicts the same sugar milling process. The BFD references the same streams as that in the
PFD stream table.
Figure 11: Block Flow Diagram (BFD) for sugar milling
2.3. Assumptions
Assumptions in Table 5 are applied in analysing the process in Section 2.2. These assumptions
allow the quantification of stream flow rates, the summary of which is in Section 2.4.
Table 5: Assumptions taken in sugar milling mass balancing
Assumptions
No residue on all machines
Negligible volatilization
Steady state
No sugar loss
Basis of cut sugarcane at 100 t/h
Processing at room temperature
except treatment and crystallisation
Justification
Every part of sugarcane is collected completely
Ignore natural loss of water
The overall system acceleration = 0
No sugar loss in production
Input value to the shredders to simplify calculations
The temperature in the factory is 25 ℃ or 298 K
14
Sugar juice is treated at up to 105 ℃
Air pressure in factory is 101 kPa
Sugarcane contains 78.5% water
Raw sugar contains 0.975% water
105 ℃ typically used in clarifying (Dias et al. 2015)
Air pressure is equal to standard atmosphere pressure
Mean value of water content in Section 1.3
Sugar after drying contains 0.5% to 2% water (Dias et
al. 2015), the mean value is utilised in calculation
No chemical residue after treating All chemicals leave the treatment unit with impurities
the juice
All impurities are removed by Impurities are defined as the part of sugar cane
extraction and juice treatment
excluding water and sugar here
Impurities are mainly bagasse
Sugar concentration increases from Process evaporation results in significant increase of
15% to 80% after evaporating
15% - 65% in sugar concentration (Dias et al. 2015)
Efficiency of A centrifuges is 95% The flow will be separated by two parts, the flow rate
of larger part is 95% of the original flow (Castro et al.
2019)
Efficiency of B centrifuges is 90% The flow will be separated by two parts, the flow rate
of larger part is 90% of the original flow (Castro et al.
2019)
The magma contains 1% of water
The water flowrate is 1% of the magma inflow (Castro
et al. 2019)
The sugar yield is 14%
The quantity ratio of sugar to sugar cane is 14%
(Council 2019)
2.4. Mass Balance
The removal amount during cleaning is difficult to evaluate since different batches of sugarcane
may be covered by different amounts of impurities. Therefore, the mass balance part starts at
the cutting stage. The mass balance is tabulated in the PFD stream table of Figure 12 .
When the cleaning sugarcane input is 100t/h, the sugar yield of this production system is 14 t/h.
Stream 14 to 16 are about molasses which are side products of this system.
According to assumptions, stream 6 is much smaller than stream 4. Therefore, the flow rate of
stream 4 is tiny enough to ignore. For the convenience of calculation, supposing the flow rate
of stream 4 is 7.64 t/h. Bagasse is one of the most commonly used biofuel in Australia, and
each ton of that can provide 10 GJ heat (Technology 2001). In this system, stream 4 is
transferred to the evaporation process as fuel. Bagasse provides 76.4 GJ of heat each hour for
the boiler in the evaporator.
15
W-101
C-101
EX-101
R-101
E-101
CR-101
CT-101
D-101
CR-102
CT-102
Washer
Cropper
Extractor
Reactor
Evaporator
Crystalliser
Centrifuge
Dryer
Crystalliser
Centrifuge
Stream NO.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Name
Sugar cane
Cleaned sugarcane
Sugar cane cassettes
Bagasse
Sugar juice
Impurities
Clarified juice
Removed water
Syrup
A massecuite
Wet sugar
Raw sugar
Removed water
A molasses
B massecuite
Final molasses
Magma
Flow rate (t/h)
--100.0
100.0
7.64-F6
100-F4
7.64-F4
92.4
71.3
21.3
21.4
20.4
14.0
6.36
1.07
1.07
0.96
0.11
Figure 12: Process Flow Diagram(PFD) for sugar mill
Water mass fraction
--78.5
78.5
0
--0
85.0
100
35.0
34.8
31.9
0.975
100
90.1
90.1
100
1.00
Sugar mass fraction
--13.9
13.9
0
--0
15.0
0
65.0
65.2
69.1
99.0
0
9.90
9.90
0
99.0
Others mass fraction
--7.64
7.64
100
--100
0
0
0
0
0
0
0
0
0
0
0
Property state
solid
solid
solid
solid
liquid
solid
liquid
vapour
liquid
Solid - liquid
solid - liquid
solid
vapour
liquid
Solid - liquid
liquid
liquid
Temperature (℃)
25
25
25
25
25
105
105
100
100
25
25
100
100
25
25
25
25
Pressure (kPa)
101
101
101
101
101
101
101
101
101
101
101
101
101
101
101
101
101
2.5. Goals
Process goals for sugar milling are summarised in Table 6 which cover technical and
operational, economical, health and safety and environmental focus areas.
Categories
Technical and
Operational
Economical
Table 6: Process goals and actions taken
Goals
Actions
Increase purity and quality Try to have high quality sugarcane as input to
of the product
improve production quality
A recycle stream is set from secondary
Maximise
production
centrifuge back to the first crystalliser to
yield
reduce raw sugar loss through molasses
Decrease the energy Sugarcane trash and bagasse from the mill are
recycled and burnt to provide energy for
consumption
extraction.
Comply with code of
practice and standards for Minimise the possibility of physical injury for
sugar mills in Australia
workers and respiratory hazards. Achieved by
following measures detailed in Table 3 of
Minimise the effect of
Section 1.6 for addressing hazards.
burning dust, fly ash and
bagasse dust to air quality
The recycle stream is set from secondary
centrifuge back to the first crystalliser can also
decrease the amount of waste.
Environmental
Minimise the amount of
discarded waste from the Energy generation from bagasse combustion
process
reduces fossil fuel consumption. CO2
emissions by this combustion is taken up by
cultivated sugarcanes, so a loop is established
Health and
Safety
2.6. Sustainability
Sustainability analysis of the sugarcane mill for this report considers a triple bottom line.
Following subsections discuss whether the process is environmental, economic and socially
sustainable.
2.6.1. Environmental
Environmental sustainability can be determined mainly by effect of process waste on the
environment. Impurities discarded from the juice treatment process consists of small solid
particles of sugarcane that are removed from juice treatment along the filter mud. The cane
particles are organic and will decompose while the mud is rich in organic matter and nutrients
that help fertilise soil. Water is also an output waste stream in the form of water vapour. Water
vapour is not considered harmful as unlike GHG emissions, it dissipates from the atmosphere
in a few days (Climate Change Connection 2016).
The waste that may cause environmental problems is the greenhouse gas emission from burning
sugarcane bagasse during the evaporation process. Due to high tonnage of bagasse burnt,
emissions of CO2 cannot be ignored, however, the emission rate is much lower than that of
fossil fuels. According to the Department of the Environment and Energy of Australia (2017)
approximately bagasse emits 1.2 kg CO2e per GJ of electricity generated while coal coke and
natural gas emit 107.24 kg CO2e/GJ and 51.53 kg CO2e/GJ respectively. As such, if bagasse is
not used to produce energy, electricity from fossil fuel will emit more GHG and may require
boiler exhaust gas treatment such as scrubbers to meet standards. Considering bagasse provides
76.4 GJ/h (from Section 2.4) to the mill, this translates to 3845.2 kg CO2e/h emission reduction
when bagasse is used instead of natural gas. Therefore, the use of bagasse as a fuel source
reduces the negative environmental impacts of the mill, so it is environmentally sustainable.
2.6.2. Economic
Economic sustainability depends on profit that the process made. The profit for the process
increases with the conversion rate from sugarcane to sugar (Chakraborty & Dutta 1983). The
process shown in previous sections has a recycle stream which decreases loss of sugar. In other
words, this process is more economically sustainable compared to the production process with
no recycling stream. As a basic material for cooking, the production amount of sugar increased
and stabilized around 1850 million tons per year during past years (Voora, Bermúdez & Larrea
2019). It can be predicted that sugar will not meet a sudden decrease in economic value, because
it is a daily necessity and the data prediction. Nearly 80% of sugar are produced by sugarcane
(The Sugar Market 2021), so this process should have a stable economic value. For the reasons
above, the sugarcane-based sugar production is economic sustainable
2.6.3. Social
Social sustainability is determined by the effect of the process on human life and society. For
industry, one of the effects to society is job generation. Australia is one of the largest sugar
exporters, which leads to a large amount of job generation in the sugar industry (Herreras
Martínez et al. 2013). Nearly 80% of sugar is produced by sugarcane (The Sugar Market 2021),
so it is expected that the sugarcane-based process generates lots of job positions for the society.
With a large amount of sugar export, people related to sugar business and sugarcane plantation
will also have benefits with their life. For those reasons, sugarcane-based sugar production is
socially sustainable.
2.7. Process Stream and Unit Interactions
In sugar milling, the unit processes are inter-reliant on each other to result in high-yielding
production within a possible economic scope of sugar production in the processing mill. The
key unit interactions in the process starts with extraction, which helps separate the juice of cane,
juice processing to get rid of impurities, crystallises to form sugar crystals, and centrifuge to
separate the sugar crystals. A recycling stream introduced at the final stage of centrifugation
drives the remaining magma back to the initial crystalliser unit to maximise produced raw sugar
yield. Magma at 0.22 t/h from produced raw sugar is rerun through the crystallising process to
precipitate more sugar crystals from the same mixture by providing the seed. The configuration
of these units and recycle loop reduces the loss of sugar through by-products such as molasses,
thus, increasing the raw sugar yield.
Recycling of biomass in the mill aids in increasing process efficiency and economic potential.
Biomass such as bagasse produced from the extraction unit is supplied to the evaporation
chamber's boiler furnace. Sugar mills may recycle bagasse like in Figure 13 to supplement
energy needed for more energy intensive processes such as evaporation, thus, reducing energy
Figure 13: Bagasse co-generation scheme (Birru 2016)
18
supply costs. Historical precedents further support the effectiveness of bagasse co-generation it
has been utilized as boiler fuel for Australia's sugar mills to generate electricity for over 50
years (Power Technology 2008). Energy content is critical in determining desirability of a
biomass as fuel. Studies suggest that higher heating value (HHV) of bagasse ranges from 5.63
to 23.46 MJ/kg, but, still a desirable fuel as its energy supply is mainly influenced by amount
of biomass produced per unit of the area rather than its quality (Coelho et al. 2019). As the mill
recycles almost 7.64 t/h bagasse, this unit interaction significantly reduces operation expenses
and energy usage from fossil fuels.
2.8. Storage
Raw sugar storage is designed to maintain quality of raw sugar while matching production
volume capacity and demands. After processing, raw sugar is stored temporarily in bulk bins
to then be distributed for exports or local market (ASMC 2013). Queensland has 6 bulk sugar
terminals in which raw sugar is kept all year round. The terminals can accommodate
approximately 2.4 million tonnes which allows market requirements to easily be satisfied
when the demand arises (ASMC 2017), Special care is taken in storage of raw sugar as it is
moisture sensitive and absorbs odour from other strongly scented products like tea and coffee.
An 80-85% relative humidity is critical for raw sugar, above which it may absorb moisture
rapidly causing stickiness. Conversely, too dry and sugar will lose its lustre, cake and cause
more dust which increases fire and explosion risks. Ideal relative humidity condition is 65%
which retains the free-flowing granular nature of the raw sugar which is convenient for
transport and presentable.
2.9. Control
Based on the stream data and hazard analysis, main parameters that need to be controlled are
shown in Table 7. The reason and method of control is also elaborated within the table.
Controlled area
Bagasse burning
section of the
evaporation
equipment
Evaporation
equipment
Vacuum pan
Table 7: Controlled Variables in the process
Controlled
variable
Concentration of
fly ash and
bagasse dust in
air
Temperature
Temperature
and pressure
Reason
Controlling method
To prevent respiration
Apply filter at the output
hazard caused by excess chimney
airborne fly ash and
bagasse dust
To ensure the temperature Include temperature sensors to
of the evaporation
monitor and control amount of
process stays at 105℃, so input energy
that the product sugar can
have higher quality
To make sure the
equipment operates
correctly. Prevent
explosion due to high
pressure and scald due to
high temperature.
Have sensors and alarm to
make sure that temperature
and pressure stays in safety
range.
19
Sugar
production
stream/sugar
storage
container
Molasses
production
stream/
molasses storage
container
2.10.
Concentration of To prevent explosion due Monitor airborne sugar dust
sugar dust in air to sugar dust
concentrations in air with
sensor
and
alarm
so
concentration does not exceed
safety range.
Concentration of To prevent explosion due Have sensor and alarm to
methane in air
to methane
make sure that concentration
and in the
of methane in air stays in
container
safety range
Economic Potential
Economic potential is analysed at the input/output structure. Table 8 displays prices for raw
materials, products and wastes discarded. The losses and gains from inputs and outputs
Table 8: Cost analysis based on input and output materials
Category
Material
Price (AUD/t)
Raw
material
Flow
rate(t/h)
Total Value
(AUD/h)
Sugarcane
100
300AUD/t (Cluff 2018)
-30000
Impurity
7.64
71
6.47
0 (assuming no treatment required)
0
Waste
0 (directly discard because it is safe
Water
0
material)
2300AUD/t (CSR Raw Sugar 2kg,
Main
Raw sugar
14.0
2021) (Woolworths Supermarket 32200
product
Buy Groceries Online 2021A)
780AUD/t (Woolworths
By-product Molasses
1.94
Supermarket - Buy Groceries
1513.2
Online 2021B)
Total
3713.2
The total economic potential of the whole process is 3713.2 AUD/h if the input rate of
sugarcane is 100t/h and only input/output structure is considered. In reality, the following
conditions apply which will alter the economic potential:
• Variable input rates make estimation higher or lower;
• Cost of workers and machinery, setup and maintenance, reduce the profit rate;
• The output water may also need to be treated before discarding to meet environmental
regulations;
• Over-estimation of product value because using the data from stores. Bulk sale of
product will reduce the profit potential;
• Slightly over-estimation of product value because Stream 6 is neglected;
• Energy consumption and generation from bagasse when considered will alter the
estimate;
20
3. Unit Operations—Crystallisation
3.1. Introduction
The syrup from the evaporators is directed to
vacuum pans to initiate crystallisation. The syrup
is boiled at low temperatures and evaporated until
it reaches the supersaturation phase during the
boiling process. “Seeding” is needed to activate
nuclei formation for sugar crystals to
grow. Throughout the process, the massecuite is
evaporated until the final molasses is produced. To
optimise sugar crystal removal from the
massecuite, the mixture is supplied to a
crystalliser. A-massecuite is then delivered to the
centrifuge where the first molasses (i.e. A
molasses) will be separated from the sugar Figure 14: Vacuum pan, crystalliser and centrifuge
crystals. Sugar is collected at this point.
arrangement (Braz 2019)
The A molasses from the A centrifuges is reboiled
in a vacuum pan (i.e. Pan B) to produce a secondary massecuite (i.e. B massecuite). A similar
process to A-massecuite follows. B-massecuite passes through a crystalliser and centrifuge to
separate the crystal sugar from the mother liquor (i.e. final molasses). A crystal suspension of
lower consistency, a lighter massecuite termed magma, is also recovered from this. Magma is
reboiled in the vacuum pan and acts as a “seeding” agent in the pan.
3.2. Process Chemistry & Physics
During crystallisation, chemical composition of the sugar remains unchanged. The
crystallisation process is considered to have crystal growth features identical to sucrose. Since
their physicochemical properties are similar, it tends to form clusters with it.
The saturation solubility must be surpassed for crystallisation to begin so supersaturation is the
main factor of crystallisation. Supersaturation decreases as the crystallising material is
withdrawn from the solution. The molecules begin to crystallise and the supersaturated solution
changes from liquid to liquid-crystal mixture. As temperature increases, solubility of sugar
decreases, so crystal sugar gradually separates out from syrup.
As seed magma is injected, the supersaturation coefficient ranges from 0.96 - 1.05 (Elgader
2014). Steam flow will be decreased, and more syrup is added to maintain the supersaturation
coefficient. Clusters form during nucleation, which is an arrangement of molecules that
integrates into a group of crystal structures. As the phase changes, it will emit latent heat. This
process is greatly influenced by the seed magma and operating conditions. Crystal growth
continues until the supersaturation is exhausted and the phase transition of the system
component remains constant over time.
As the concentration of hydrogen carbonate is changed, the pH of molasses increases to 9 to
10. There is no formation of non-sugar substances; only existing non-sugar substances react
with each other (Elgader 2014).
21
3.3. Equipment
3.3.1. Vacuum Pans
According to Stephens (2001), the most popular model in the Australian sugar
industry is the fixed calandria batch vacuum pan (p. 18). Vacuum pans are
used because they produce a consistent flow of steam with uniform grain size.
Moreover, the massecuite produced is uniform in grain size, consistency, and
purity. The heating surface is held in place and is made up of several vertical
tubes that are clamped by a flat tube plate at the top and bottom. Steam is
inserted into the cavity that surrounds the tubes and is enclosed by the tube
plates. Steam condenses on the tube's exterior at a steady temperature, latent
heat is released, which heats the liquid within the tube.
As water evaporates, the sucrose concentration rises, causing crystal
Figure 15
formation. More syrup would be added to maintain the concentration. The
Vacuum pan
boiling point varies as the pan's level increases. When no more magma or
illustration
syrup is added to the pan, the boiling process stops. After that, the crystals and (Stephens 2001)
massecuite mixture is removed from the pan and put in the crystallizer.
There is no need for an external source of circulation within the calandria pan. The buoyancy
force caused by temperature changes due to vapour production and adjacent massecuite is the
primary driving force for liquid movement. As well as a strong bond between heat transfer and
circulation. A flow of massecuite and vapor is expected to move upward through the calandria
tubes up to the surface. The vapor is drawn to the condenser, while the liquid travels radially
towards the centre and return to the bottom via the downtake and entering the calandria tubes
again. In a real-world process, variations in circulation can occur.
3.3.2. Crystallisers
The crystallisers serve as an insulated tank to assure that the
centrifuges have a steady flow. There will be no need for a cooling or
transfer system because massecuite is moved to the crystallizer
rapidly. Transfer equipment is not feasible to use due to its thickness
and difficulty in handling. Gravity would force the liquid to move.
Vacuum pans will be mounted above the crystallisers at a higher level.
Likewise, the crystallisers should be installed above the centrifugals.
Figure 16: Crystalliser
(Hugot 1986)
Since the massecuite is saturated, stirring is necessary to prevent
further crystallization of the present crystals, which could expand their
size. To keep the mixture flowing steadily and continuously, a Ushaped steel vessel with an agitator is used.
3.3.3. Centrifuges
The massecuite is stored in a cylindrical basket, which is then carried on a vertical shaft.. The
sugar is protected in the basket by metal gauze, which allows molasses to pass and exit through
the basket’s holes. Sugar passes from the basket’s bottom opening controlled by an adjoining
shaft. After the process is completed, the centrifugal is stopped by a brake with brake-shoes.
The magma is transported in a buffer tank. It will be positioned among the centrifuge B and the
vacuum pan A. The water would flow to move the magma at a rate of 1% of the magma flows.
There will also be a buffer tank before A molasses enters the B vacuum pans. It is used to
dissolve molasses in order to prevent formation of ice crystals in the feed.
22
3.4. Design
The primary design inputs for the crystallisation unit are the mass flows that enter and exit the
unit, as it will influence the machine capacity.
The crystallisation unit operation is based on the assumptions below:
• The massecuite is completely uniform in the whole volume of the vacuum pan.
• A and B vacuum pans have the same tube length, diameter, thickness, and pitch.
• For A and B massecuites, the boiling times are 4 hours while A and B crystallizers require
4 and 6 hours, respectively.
• The massecuite density is 1.45 tonnes/m3.
• One cycle takes 180 seconds to complete in centrifuges.
• Generally, e equals 0.12D. Moreover, the basket top plate angle is 5 degrees (Alluri n.d.).
• To determine the capacity of the centrifuge, expect one empty complete cycle in total cycles
per hour. Consider the purging potential, which is 10% higher because the massecuite is
always purged when it is loaded.
3.4.1. Vacuum Pan Design
The design procedure for vacuum pans is as follows:
Determine the capacity of the pan from inlet flows. A batch vacuum pan capacity is:
tonnes/day x 0.06. While, for B vacuum pans is: tonnes/day x 0.04 (Alluri n.d.).
• Determine number of vacuum pans required by measuring the amount of massecuite in each
strike. Then, divide it by the pan's capacity.
• Define the thickness, length, outer and inner diameters, and pitch of the tube.
• Calculate the heating surface using the heating surface-to-volume ratio and pan’s volume.
• Calculate the number of tubes required in the pans.
• Determine the volume of the downtake by calculating the diameter and sufficient area of
the downtake.
• Calculate pitch and true ligament of the tube. Pitch is the distance between the centers of
two parallel tubes. Moreover, ligament refers to the thickness of metal existing on the tube
plate among two neighboring tubes.
Appendix B describe the calculations in detail. Because the equipment in the B crystallisation
unit is the same, the design steps were followed. The main design variables and pan sizes in A
vacuum pan are in Table 9.
•
Table 9: Design variables for A Vacuum Pan
Design Variables
Steam Temperature
Steam Pressure
Pan total volume
Heating surface
No. of vacuum pans
Tube length
Tube Outer diameter
Tube Inner diameter
Tube thickness
No. of tubes
Downtake volume
Massecuite volume in tubes
Tube pitch
Ligament
Value
115
170
21.35
170.8
3
1.132
101.6
98.6
1.5
899
3.11
7.77
127
23.9
Units
C
kPa
m3
m2
m
mm
mm
mm
m3
m3
mm
mm
23
3.4.2. Crystalliser Design
The design procedure steps for crystallizer:
Calculate the crystallizer capacity. It would be equivalent to the vacuum pans, but raised by
15-20% (Hugot 1986). Consequently, for a 21.35m3 vacuum pan, the volume of A
crystallizer is 25.62m3.
• Determine the power and rotational speed based on the crystallizer volume. For crystallisers
with 20-50 m3, the speed is 0.5 rpm with a total power of 210 kW per 1,000 m3 (Hugot
1986).
• Define the amount of time required for each massecuite. In general, it is better to hold the
A and B massecuite in the crystalliser for a very short duration.
• Measure the number of crystallizers by dividing the massecuite's mass with the crystalliser's
capacity.
The main design variables and pan sizes in A crystallizer are Table 10.
•
Table 10: Design Variable for A Crystalliser
Design Variables
Crystalliser volume
No. of crystallizer
Rotational speed of agitator
Power
Time for crystallisation
Value
25.62
2
0.5
210
4
Units
m3
rpm
kW
hours
3.4.3. Centrifuge Design
Design procedure steps for the centrifuges:
Define the basket's height and diameter, and then measure the massecuite volume per period
(See equations 7 in Appendix B).
• Determine the volume of massecuite per hour (See equation 8 in Appendix B).
• To calculate the mass of massecuite needed, multiply the volume by the density.
• Add the height and diameter of the basket into the equation, use trial and error to determine
the correct mass flow of the massecuite. Follow these steps for both the A and B centrifuges.
The design variables of A and B centrifuges are described in Table 11.
•
Table 11: Design variables for A Centrifuges
Design Variables For A Centrifuges
Diameter of basket
Height of the basket
Rotational speed of the agitator
Value
1.4
1.085
1200
Units
m
m
rpm
4. Professional Engineers in Process Systems
Sugar milling involves complex processing to transform sugarcane to raw sugar and its byproducts which employ numerous engineers in various areas. The scale and complexity of the
production process require many employees for operation despite the automation incorporated
with Australian mills employing more than 4,500 people in total (ASMC 2021). Wilmar
Sugar, for example, employs 1600 people which consists of more than 130 apprentices and 21
graduates (Sugar Research Institute(SRI) 2015).
24
Engineers in this industry, apply project management skills and technical knowledge to grasp
the nuances of daily factory operations which may include managing and reviewing safety
standards, equipment maintenance oversight and resolution of issues during operation(SRI
2015). In addition, engineers may be employed in this industry for project management and in
efforts to modernising and increasing performance and efficiency of sugar mills. As such, the
sugar milling industry offers a variety of opportunities and areas in which engineers are able
to apply their skills and learn.
5. Conclusion
The report established an investigation on sugar milling with a focus on Queensland and
Australia in the 21st century. Raw sugar currently and will continue to be a significant
agricultural product contributing to the state and national economies of Queensland, Australia
as 80% of production volume is exported. The particular interactions between the
crystallisation, evaporation and centrifugation units in sugar milling are crucial in high
production rates while minimising waste. The recycling of bagasse in cane based mills reduce
its energy consumption but also it’s negative environmental impacts. Bagasse offers a
3845.2 kg CO2e/h emission reduction if used instead of natural gas as an energy source for
operation hours. In addition, raw sugar can generate income of 3713.2 AUD per hour of milling.
Despite a decelerating growth in global sugar consumption, Australia’s sugarcane mills
25
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Appendix A
Mass Balance Calculations
F = flow rate (t/h), x = mass fraction, w = water, s = sugar, o = other substance
F2 = 100 t/h, xw = 78.5, Fw2 = 100 * 78.5%=78.5 t/h
F12 = 14% * F2 = 14 t/h, xs12 = 0.975, xs12 = 100 - 0.975 = 99.025 t/h
Fs12 = 14 * 99.025% = 13.8635 t/h, Fw12 = 14 * 0.975% = 0.1365 t/h
Fs2 = Fs3 = Fs5 = Fs7 = Fs9 = Fs12 = 13.8635 t/h
Fo2 = 100 - 13.8635 - 78.5 = 7.6365 t/h
F4 + F6 = Fo2 = 7.6365 t/h
F7 = 100 - 7.6365 = 92.3635 t/h, xs7 = 13.8635 / 92.3635 = 15, xw7 = 100 - 15 = 85
xs9 = 65, xw9 = 100 - 65 = 35, F9 = 13.8635 / 65% = 21.3285 t/h
F8 = 92.6365 - 21.3285 = 71.308 t/h
F9 + F17 = F10, F17 = (1 - 90%) * F15, F15 = F14 = F10 * 5%, solving: F17 = 0.1082 t/h
F10 = 21.3285 + 0.1082 = 21.4367 t/h, F14 = F15 = 1.0718 t/h
xs14 = xs15 = (13.8635 + 0.1082*99%) / 1.0718 = 90.1, xw14 = xs15 = 100 - 90.1 = 9.9
xs10 = (13.8635 + 0.1082 * 99%) / 21.4367 = 65.2, xw10 = 100 - 65.2 = 34.8
F11 = 21.4367 * 0.95 = 20.3649 t/h, F13 = 20.3649 – 14 = 6.3649 t/h
xs11 = (13.8635 + 0.1082 * 99%) / 20.3649 = 68.1, xw11 = 100 - 68.1 = 31.9
F16 = 1.0718 - 0.1082 = 0.9636 t/
Appendix B
A-VACUUM PAN
Calculate the capacity of batch vacuum pans and the number of vacuum pans needed
Pan capacity: 516
𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡
𝑑𝑑𝑑𝑑𝑑𝑑
× 0,06 = 30,96 𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡. The required volume:
30,96 𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡
1,45
𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡
𝑚𝑚3
= 21,35𝑚𝑚3
Calculating the amount of massecuite per strike and dividing it by the pan's capacity suggest 3
pans are needed.
Calculation for heating surface
For a batch calandria pan, ratio of heating surface to volume is 6, 7 or 8 m2/m3 respectively for
the tube lengths of 860, 1.000 and 1.140 mm (Hugot, 1986). Moreover, the average tube length
in Australia is 1.132 mm (Stephens, 2001). Therefore, heating surface to volume (S/V) ratio is
8 m2/m3. Thus, the heating surface is: 8 𝑚𝑚2 /𝑚𝑚3 × 21,35 𝑚𝑚3 = 170,8𝑚𝑚2 .
Calculation for number of tubes
(1)
Where S is heating surface of the vacuum pan (m ), 𝛱𝛱 is Pi (3.14), D is the mean diameter of
the tube (m), L is the tube’s effective length (m) and N is the number of tubes.
The tube diameter is 101.6 mm and the tube wall thickness is 1.5 mm (Hugot, 1986). Thus, D
𝑆𝑆 = 𝛱𝛱 × 𝐷𝐷 × 𝐿𝐿 × 𝑁𝑁
2
170,8𝑚𝑚2
is: 101.66mm – 1.5mm = 0.1001m. The number of tubes required:3,14×0,1𝑚𝑚×1,132𝑚𝑚= 481 tubes.
Calculation for volume of the downtake
For the area of downtake, divide the cross section area of the tube by the circulation ratio.
𝛱𝛱
The equation for calculating the total area of a tube: 𝐴𝐴 = 𝑁𝑁 × 4 × 𝐼𝐼𝐼𝐼2
The initial tube diameter: 𝑂𝑂𝑂𝑂 − (2 × 𝑇𝑇ℎ𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑠𝑠𝑠𝑠) = 98,6 𝑚𝑚𝑚𝑚 so area of the tube is 3.66 𝑚𝑚2
(2)
30
To achieve smooth flows, the circulation ratio should preferably be less than 2.5 (Alluri, n.d.).
Thus, the area of the down take is:
3,66𝑚𝑚2
2,5
4
= 1,47𝑚𝑚2 . The diameter of the downtake (DA) is:
� × 𝐴𝐴𝐷𝐷 = 1.37𝑚𝑚
𝛱𝛱
Calculate the amount of the downtake using the equation: 𝑉𝑉 =
Thus, the downtake’s volume is:
𝛱𝛱
4
𝛱𝛱
4
× 𝐷𝐷𝐷𝐷2 × 𝐿𝐿
(3)
× (1,37𝑚𝑚)2 × 1,132𝑚𝑚 = 1,67 𝑚𝑚3 .
Calculation for volume of massecuite in tubes
𝑉𝑉 =
𝛱𝛱
4
× 𝐼𝐼𝐼𝐼2 × 𝐿𝐿 × 𝑁𝑁
Thus, the volume of massecuite in tubes:
𝛱𝛱
4
(4)
× (0,0986 𝑚𝑚)2 × 1,132𝑚𝑚 × 481 = 4,16 𝑚𝑚3
Calculation for pitch and ligament of the tube
The tubes have 101.6 mm diameter and a ligament of 25.4 mm (Hugot, 1986). Thus, the pitch
is: 101.6 + 25.4 = 127 mm. Moreover, the true ligament is: pitch - OD- thickness = 127-101.61.5 = 23.9 mm.
Vacuum pan B followed the same steps, but with inlet flows of 51.6 tonnes/day. The steam
temperature and pressure are the same as A pan. As well as tube length, diameter, thickness,
pitch, and ligament.
Table X. Design Variables of B Vacuum Pan
Design Variables
Value
Units
Total volume of the pan
1.42
m3
No. of vacuum pans
4
Heating surface
96
m2
Number of tubes
Volume of the downtake
32
0.11
m3
Volume of the massecuite in tubes
0.28
m3
A CRYSTALLISER
Multiply the massecuite inlet flows by the crystallisation time to get the crystalliser's capacity,
which is 86 tonnes. Crystallizer capacity would be 20% greater than vacuum pan capacity.
86
Thus, it would be 37.152 tonnes. As a result, the number of A crystallizer needed is: 37.152 = 2
The B crystallizer is designed using the same steps. The capacity of vacuum pans clearly
influences the capacity. The following are the main design variables and sizes for B crystallizer.
Table X. Design Variables of B Crystalliser
Design Variables
Volume of the crystallizer
Value
1.704
No. of crystallizer
5
Rotational speed of the agitator
0.7
Units
m3
rpm
31
Power
Time for crystallisation
294
6
kW
hours
A CENTRIFUGES
Calculate the massecuite volume per period
𝑉𝑉 = 𝛱𝛱 × 𝑒𝑒 �𝐻𝐻 �𝐷𝐷 − 𝑒𝑒 + 𝑒𝑒 × 𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡�(3𝐷𝐷 − 4𝑒𝑒)/6��� (5)
Where V is the massecuite volume per cycle (m3/cycle). e is massecuite thickness (m). 𝜃𝜃is angle
of the basket top plate to the horizontal level (deg.). H is the basket height (m). D is the basket’s
diameter (m).
Anticipate one empty cycle. Include the purging potential. which is 10% higher. Thus. the
volume is:
(𝐶𝐶 − 1) × 𝑉𝑉 × 1.1
(6)
Where C is cycles per hour and V is the massecuite volume every cycle (m3/cycle).
Define the time needed for each cycle per hour. If time needed for each cycle is 180 seconds.
then C is:
3600
180
= 20 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐/ℎ𝑟𝑟. Consider one empty cycle. there will be 19 cycles/hr.
Multiply the volume by the density to get the mass of massecuite required. Use trial and error
to find the necessary mass flow of the massecuite by inserting the height and diameter of the
basket into the equation. The following are the main design variables and sizes for B
centrifuges.
Table X. Design Variables of B Centrifuges
Design Variables For B Centrifuges
Value
Units
Diameter of basket
0.5
m
Height of the basket
RPM of the basket
0.84
1200
m
rpm
32