FE11 JUICE EXTRACTION SYSTEMS: Mills and Diffusers

FE11
JUICE EXTRACTION SYSTEMS: Mills and Diffusers - The Brazilian Experience
By
J.L. OLIVERIO, A.C.R. D AVILA, A.N. FABER, P.A. SOARES
DEDINI S/A Indústrias de Base
Rod. Rio Claro-Piracicaba, km 26,3, CEP 13412-900, Piracicaba - São Paulo – Brazil
Email: jose.oliverio@dedini.com.br
KEYWORDS: juice extraction; diffuser; modular diffuser; chainless diffuser, crusher;
milling unit/tandem
Abstract
For cane juice extraction, two systems are used worldwide: milling
tandem or diffuser. In Brazil, the preference has been for the mills
solution. Data from the 2004/2005 milling season shows that, out of a
total of 347 mills in operation, 341 use mills and 6 the diffuser,
corresponding to 1.7% of the extraction systems. Since 2003, the
sucro-energy industry in Brazil has grown considerably, from 320
million tonnes of processed cane to 620 million in 2010/11, and new
Greenfield projects were implemented. In 2011, 455 mills had already
decided on the extraction system, with 32 mills using diffusers built or
contracted, representing 7%. Therefore, there has been a significant
increase of diffusers and a growth even more expressive if we
consider only the Greenfield projects defined since 2004: 108
decisions have been made, and 25 diffusers have been built or
contracted, accounting for 23.1% of the choices. Given the typical
characteristics of the sugarcane industry in Brazil, with plants
designed for expansion and high milling capacities, one of the factors
that contributed to the increased choice for the diffuser solution was a
new product, the chainless modular diffuser, which is expandible and
more easily applicable to process large amounts of sugarcane. This
paper presents a technical comparative review of both extraction
systems, milling and diffusion, their basic characteristics, operational
data, recommended use for one or other system, and ratio of
investments and costs between milling tandem and diffusers.. Taking
into account that the sector will continue to grow in Brazil– forecasted
to reach up to 1.2 billion tonnes of cane in the 2020 season and nearly
100 new Greenfield projects to be implemented – this work seems to
be opportune and may serve as a guide for future decision-making on
extraction systems, mills or diffuser, either for the new mills or
expansion of the existing ones.
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SISTEMAS DE EXTRAÇÃO DE CALDO: Moendas e Difusores – A Experiência
Brasileira
Por
J.L. OLIVERIO, A.C.R. D AVILA, A. N. FABER, P.A. SOARES
DEDINI S/A Indústrias de Base
Rod. Rio Claro-Piracicaba, km 26,3, CEP 13412-900, Piracicaba - São Paulo – Brazil
Email: jose.oliverio@dedini.com.br
PALAVRA-CHAVE: extração do caldo; difusor; difusor modular; difusor sem corrente,
moenda; unidade de moagem/tandem
Resumo
Para a extração do caldo de cana, dois sistemas são hoje utilizados no
mundo todo: moendas e difusores. No Brasil, a preferência tem sido
pela solução com moendas. Um levantamento feito sobre a safra
2004/2005 mostrou que de um total de 347 usinas em operação, 341
optaram por moendas, e 6 por difusores, o que corresponde a 1.7%
dos sistemas de extração. A partir de 2003, a indústria sucroalcooleira
brasileira cresceu significativamente, de 320 milhões de toneladas de
cana processada para 620 milhões em 2010/11, e novos projetos
“greenfield” foram implantados. Em 2011, 455 usinas há haviam
decidido sobre o sistema de extração empregado, com 32 usinas já
com difusores implantados ou contratados, representando 7%.
Portanto, houve um aumento significativo de difusores e um
crescimento ainda mais expressivo se considerarmos apenas os
projetos “greenfield” definidos desde 2004: 108 decisões já foram
tomadas, e 25 difusores foram implantados ou contratados,
respondendo por 23.1% das escolhas. Dadas as características da
indústria canavieira no Brasil, com plantas previstas para expansão e
elevadas capacidades de moagem, um dos fatores que contribuíram
para o aumento das opções por difusores foi o difusor modular sem
corrente, que é expansível e mais facilmente aplicável para processar
grandes quantidades de cana-de-açúcar. Este trabalho apresenta uma
análise técnica comparativa de ambos os sistemas de extração,
moagem e difusão, suas características básicas, dados operacionais,
uso recomendado para este ou aquele sistema, e a relação entre
investimentos e custos de um tandem de moendas e difusor.
Considerando-se que o setor deverá continuar a crescer no Brasil – as
projeções indicam 1.2 bilhões de toneladas de cana na safra de 2020, e
cerca de 100 novos projetos “greenfield” a serem implantados – este
trabalho parece ser oportuno e poderá servir como um guia para
futuras decisões a serem tomadas quanto ao sistema de extração,
moendas ou difusor, tanto para novas usinas como para a expansão
das existentes.
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Introduction
Extraction of sugarcane juice began in the first half of the 16th century in the Brazilian
territory with the purpose of supplying sugar to the European countries and the incipient
domestic market. The expedition of Martin Afonso de Souza, in 1532, started cane cultivation
and implemented the first sugar mill in the state of São Paulo, the Engenho Eramos (a small
mill producing sugar and rum), in São Vicente. After that pioneer unit and to reduce transport
costs, sugar was produced in states nearer to Europe, in the current states of Pernambuco,
Bahia and Rio Janeiro. In this initial stage, the mills installed in São Paulo and Rio de Janeiro
states already showed the ability to make the sugar industry a profitable activity.
The first mills had a similar design, based on family farming activities. For centuries
sugar mills have evolved: initially, juice extraction was achieved by low efficiency and low
capacity mills driven by animal traction and/or water wheels; later by steam machines; and
finally they were mostly driven by steam turbines. (UNICA, 2012). This structure remained
until 1975, when the Brazilian government launched the ProAlcohol Program.
The National Alcohol Program – ProAlcohol was implemented to reduce the country’s
vulnerability to the oil crises. The goal of this program was to use ethanol to replace gasoline
from petroleum as a fuel for Otto-cycle engines in light vehicles. This program was supported
by the World Bank and led to the expansion of sugarcane crops and juice extraction units,
which began to meet the juice demand for sugar production in addition to the volumes
required to produce anhydrous ethanol to be blended with gasoline, and hydrous ethanol to be
used exclusively in 100% ethanol-powered vehicles (E100). Soon after the second world oil
crisis in 1984, national production of light vehicles reached its peak with 95.4% of the
engines running on hydrous ethanol. With the softening of the oil crisis and domestic
problems in the Brazilian economy, the production of ethanol-powered vehicles began to
decline in 1989, and production fell to the minimum level of 1.02% of new vehicles running
on hydrous ethanol in 2001. (UNICADATA, 2012)
In the early ProAlcohol period, focus was on capacity increase, without major
technological advancements but, in the second half of the 1980s, capacity increases came
from the combination of increased capacity of juice extraction and processing equipment with
technological improvements, which ensured higher extraction yields and better extraction of
the sugars contained in sugarcane, associated with major technological advancements in cane
cultivation with the introduction of new and more resistant cane varieties.
With the advent of the flexible-fuel technology (Flex) for light vehicles in 2003, which
can run on both hydrous ethanol (E100) or gasoline “C” (E18 to E25), a new phase of high
demand for sugarcane took place in order to produce fuel ethanol. Ethanol was used as a fuel
and additive to gasoline, replacing more polluting substances, such as MBTE and lead. This
phase is marked by the ethanol production in a free market: the final consumer dictates
demand and decision on consumption, based on the economic advantage offered by each fuel.
The free market requires that high-performance and high-capacity extraction systems are
implemented, so that economies of scale and the optimum use of the feedstock can be
attained. The consolidation of the Flex technology occurred simultaneously with the Brazilian
regulation of electricity exports to the domestic grid and the global acceptance of
sustainability principles for energy generation and utilisation.
From 2006, the sustainability concepts, in their broad aspect, especially with the
introduction of mechanical harvesting of green cane, became a key impact factor on the mills
and juice extraction systems: the mills should process a new raw material, chopped cane with
high contents of vegetable and mineral impurities. This is the current situation, in which some
paradigms regarding burned and clean sugarcane have already been broken, and a new
learning process has began, of how to handle the new raw material, coupled with
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requirements for a high economic performance, consistent with the free market but yet
compliant with the principles of the green economy.
Figure 1 shows the evolution of sugarcane milling in Brazil in the past decades, and
the projections made by the Brazilian Ministry of Mines and Energy – MME/EPE for 2021
(MME/EPE, 2012).
Cane Processed - millions ton/crop
1.200
1.000
800
600
400
200
0
1981
1986
1991
1996
2001
2006
2011
2016
2021
Year
Fig. 1 – Brazilian sugarcane production and perspectives (UNICA, 2012 and MME/EPE,
2012)
Sugarcane Extraction Systems
Sugarcane juice extraction is the mill operation that takes place after cane receival,
cleaning, and preparation, in which the water and sugars contained in the cane are removed.
Basically there are two ways to perform this operation commercially: by cane preparation and
mechanical squeezing, which is the case of the mills, or by washing the prepared cane in
many stages when the sugars are extracted by diffusion in the unbroken cells (around 10% of
the cells) and by leaching in open cells (around 90% of cells) (Figure 13), the diffusers. In this
paper, we are considering as part of the extraction process the following steps: extraction
itself and final removal of the bagasse moisture, so that bagasse can be sent to the boilers to
be burnt with near 50% of moisture. The goal of extraction is to remove the maximum mass
amount of the sugar present in the prepared cane and, at the same time, produce bagasse with
suitable moisture content to be burnt in biomass or bagasse boilers. Figure 2 illustrates
extraction schematically (Wever and Olivério, 2006).
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Fig. 2 –Objective of the extraction system
Figure 3 shows how the mill units perform extraction in successive and gradual
compression stages. The combined arrangement of a series of mills forms what we call
“milling tandem” or “milling train”, where imbibition water is added in counter-current to the
bagasse as shown in Figure 4. The combination of imbibition with mechanical crushing
allows attaining extraction rates similar to those of diffusers. (Wever and Oliverio, 2006)
Fig. 3 – Juice extraction by mill
Fig. 4 – Arrangement of 6 mills forming a milling tandem
Figure 5 shows the operating principle of a diffuser, in which the liquid percolates
through a bed consisting of the cane fibrous material, the prepared sugarcane, employing
gravity as driving force. Since the goal is to extract sugars, the extraction liquid is the
imbibition water.. In order that the equipment operates continuously, it is necessary that the
cane bed moves continuously, and in counter-current to the imbibition water, enriched with
the sugar extracted (which is indicated by brix as the amount of dissolved solids in the
solution). Sugars are the predominant dissolved solids in the water solution.
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Fig. 5 – Juice extraction by lixiviation and diffusion (Oliverio, 2011)
Figure 6 illustrates different types of diffusers. In Brazil, the most popular diffuser
type until 2006 was the linear one with fixed screen deck. The chains in this equipment are
necessary to drag the bed forward (Oliverio, 2011).
Fig. 6 – Commercial types of diffusers
Another way to move the bed has been developed recently and is based on the
principle that when the frictional force between a support plate and the bed is not exceeded, it
can be displaced but, if the movement of the support plate exceeds the frictional force, the
support plate will move without carrying the bed. The cane bed is dragged in a continuous
forth-and-back motion of the parallel support plates or tracks that comprise the screen deck.
Forward and reverse hydraulic cylinders drive each track. Figure 7 illustrates the operating
principle of this equipment, and shows the interior of the chainless diffuser. The screen deck
is made of parallel tracks; they can be expanded by the addition of an even number of tracks.
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Fig. 7 – Modular Chainless Dedini-Bosch diffusers (Oliverio, 2011)
Up to 70 to 80% of the sugars contained in the prepared cane can be extracted by the
first stage of the tandem mil, called absolute juice. The solubility of undesirable substances is
lower than the sugar solubility in the water present in cane, and this is why it contains low
levels of other undesirable substances for edible sugar production, which is constituted of
sucrose. By adding one mill stage between cane preparation and the diffuser bed inlet, you
can extract absolute juice separately from the diffusion bed juice, called draft or mixed juice.
The absolute juice extracted by these first mill stages has characteristics that are more
appropriate for sugar production, and the mixed juice, which is more contaminated with other
substances existing in the cane cell wall, such as pentoses, polysaccharides, phenols,
colorants, etc, can be used for ethanol production, since part of such contaminant substances
can be converted into ethanol and the others do not affect the final ethanol quality and very
little the fermentation efficiency (Rein, 1995).
The first diffuser installed in Brazil, in 1967, was the bagasse type, i.e., after cane
preparation, a milling stage was installed, from which absolute juice was extracted. Such
absolute juice was then blended to the draft or mixed juice from the diffuser and sent to sugar
production, because the mills at the time were almost entirely designed to produce only sugar,
and there was no suitable technology for cane preparation. The bagasse diffuser was not
accepted by the Brazilian market and was replaced by the so-called cane diffusers, in which
the goal of cane preparation was to “open” the cane structure, and the diffuser was fed with
the totality of cane, not producing absolute juice, but mixed juice in its totality. The primacy
of cane diffusers in Brazil is due to the fact that they were introduced preceded by highly
efficient cane preparation systems, with 90% open cells. Figure 8 illustrates the cane diffuser
system with the final dewatering stages.
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Fig. 8 – Complete juice extraction system by diffusion – cane diffuser
We understand that, in the near future, the bagasse diffuser solution may be
reintroduced to the Brazilian market, as these systems can deliver up to 70% of absolute juice
of good quality for sugar production and the mixed juice that can be sent for ethanol
production by means of an optimised juice treatment system designed for each final product.
This may result in a new technical and economic optimisation of the future mills.
Cane juice mill: historical evolution
Today we can distinguish two types of cane-processing plants in Brazil: those
producing sugar, ethanol and bioelectricity and those designed for energy production, ethanol
and electricity, referred to in Brazil as distillery or ethanol mill. According to the block
diagram below (Figures 9 and 10), we can see that, in both cases, there is the juice extraction
stage present. However, the optimised design of both types of plants requires different
considerations for all processing steps, because the optimum characteristics of the extracted
juice that is aimed at sugar production are not necessarily the same of those required for
ethanol production. Optimisation of the extracted juice will influence the definition and
characteristics of the mills unitary operations, requiring a customised project for each specific
case (Olivério, 2011).
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Fig. 9 – Typical mill diagram for sugar / ethanol / electricity production
Fig. 10 - Typical mill diagram for ethanol / electricity production
In Brazil, until 1968, all juice extraction systems consisted of mills, and the first
bagasse diffuser was introduced to the Brazilian market by Dedini Company in 1967, with a
capacity for 100 tonnes of cane/hour (TCH) in São Francisco Mill, Charqueada, SP. In 1983,
the same company installed a second and a third diffuser, both for cane, in Galo Bravo Mill,
Ribeirão Preto, SP, with a capacity for 150 TCH, and in Coamo Distillery, PR, currently
installed at DECOIL Mill.
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In Brazil, implementation of the new mills follows, almost in its totality, a phased
construction schedule in which investments in the industrial sector are compatible with the
agricultural sector i.e., according to the amount of cane that can be supplied, requiring that the
installed capacity be implemented in phases and expansible in the medium term. In this
context, juice extraction by mills allows more flexibility, because it just requires additional
mill units and/or the replacement of the first and last mills to achieve a significant capacity
increase. In our view, this was the main reason for the market’s almost rejection of extraction
performed by diffusers until 2005.
In the 2004/2005 crop, a total of 347 mills were in operation, 340 of them using mills,
and the other 7 using diffusers, besides two other diffusers being built. In 2005/06, a total of
347 mills were in operation, and 46 new mills were designed, built or started operations in the
period.
Data collected shows that from 1967 to the end of 2005, 10 diffusers were acquired, of
which 1 is inactive, 7 in operation, and 2 being built, totalling 9 diffusers. In 2007, 13
additional units were acquired. Therefore, it was during the 2005/06 crop that the decision on
the type of extraction was made, mill or diffuser. In this period, extraction by diffusion had a
unit increase of 144%, and of 305% if expressed in nominal processing capacity, making the
2005/06 crop a milestone marking the end of the almost total rejection of diffusers in Brazil.
The same data shows that 371 mills using mill tandems were operating in the said milling
season, representing 94% of the operating extraction systems, i.e., an absolute supremacy of
extraction performed by mill tandems. Figure 11 below summarises the data collected
(Olivério, 2011).
Fig. 11 – Number of diffusers in the 2004/05 milling season
In the period of 2005 to 2012, decisions on a total of 108 extraction systems were
made, of which 71 mills acquired new juice extraction systems, among them 25 diffusers,
representing 35.2% of the choices made. In the 2010/11 crop, a total of 455 mills were
operating in the Brazilian market. Figure 12 shows the percentage of diffusion extraction
systems over these years.
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Fig. 12 – Percentage of diffusers on the total new Brazilian extraction system
Figure 12 shows that, until 2005, only 2.3% of the mills had diffusers, and in 2011 the
percentage of the mills with diffusers increased 286%. From 2006 to 2011, 71 new extraction
systems were effectively negotiated, among them 23 diffusers, 9 of them are the Modular
DEDINI-BOSCH, i.e., 39.1% of the new diffusers acquired were of the new Brazilian
chainless and modular type.
Technical comparison: milling and diffusers
In Brazil, the average percentage of extraction performed by mills and diffusers has a
similar order of magnitude: due to the introduction of mechanical harvesting and cane
processing without water washing, the expected advantage in extraction yield is of up to 1.0
percentage point for diffusers cannot be confirmed generically, but rather determined by the
levels of vegetable and mineral impurities found in each mill. The advantages of diffusers
should then be determined by the frequency and quality of maintenance performed in the mill
tandems, because they are subject to severe wear during the milling season, affecting the
average extraction rates, which is not frequent with diffusers. On the other hand, diffuser
extraction rates are more sensitive to vegetal and mineral impurities in the cane feedstock.
Figures 13 and 14 illustrate the extraction rates achieved by diffusers and mill tandems in
appropriate operating conditions, and are very similar if they are designed according to good
engineering practices.
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Note: Typically, sugar extraction is reached 90% in leaching and 10% in diffusion
Fig. 13 – Typical diffuser extraction parameters
Fig. 14 – Typical mill extraction parameters
Table 1 below summarises the main process differences between diffusion and milling
extractions, which we present without the intention of exhausting the subject, but rather
presenting a guide for the first and specific selection of a real case.
Process Parameter
Table 1 - Technical comparison between mills and diffusers
Characteristic
CANE DIFFUSER
Chain and Modular Diffuser
Mill
Attain good
extraction rates with
Cane preparation
85% preparation.
(Voigt, 2009)
Accepts greater
amounts of fines or
small particles.
Requires higher preparation, over 90%. Long
fibres are desirable, but fines hinder adequate
bed percolation.
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Causes mill wear but
Causes low impact on the apparatus
do not affect
maintenance. The effect of impurities on
momentary extraction extraction cannot be generally quantified both
rates
for diffusers and mills.
Impact of soil
Low impact on
Clay soils / sludge / gels tend to prevent
type / bed
extraction / Higher
adequate percolation, causing choking and
colmatation
wear of rollers in clay
extraction losses (Rama et al., 2006)
(clogging)
soils
Loss of 2.3
Impact of
percentage points of
Loss of 3.1 percentage points of capacity for
vegetable
capacity for every
every 1.0% of vegetal impurities. Short fibre
impurities (Dias
1.0% of vegetable
and fines tend to prevent adequate percolation
Paes, 2011)
impurity
Lower concentrations of suspended solids.
Quality of
Higher levels of
Extracts higher amounts of non-sugars
extracted juice
suspended solids.
substances (ex: phenols, colorants,
(Rein, 1995)
Requires filtration.
polysaccharides, etc.) (Manechini, 2011)
Allows up to 80%
separation of cane
Does not allow separation of absolute juice.
Juice dilution
absolute juice.
Mixed juice usually with higher brix if in
Remaining mixed
tandem mill, absolute juice is extracted.
juice is more diluted.
Typical: 200% Allows adjustments to achieve improved
250% of fibre /
Usual imbibition
process balance: juice brix / bagasse moisture /
limited by the mills
rate
extraction / energy consumption in juice
operation. May use
evaporation. Typical: 200% - 300% of fibre.
higher imbibition
(Voigt, 2010)
with low capacity.
Impact of
mineral
impurities
Required juice
evaporation
Typically lower
imbibition requires
lower thermal energy,
as steam consumption
and/or waste heat
recovery from
process stream.
The learning curve of operational experience
will determine the optimum point, particularly
in mills producing ethanol and bioelectricity,
but preliminary indicators show that imbibition
may be optimised from the experience learned
from the use of the not burned and
mechanically harvested cane. (Voigt, 2010)
Hardly exceeds 98%,
98.5% may be achieved with two dewatering
and tends to decline
Sugars
stages, and is barely impacted by wear during
extraction rates during the milling
the milling season. (Delfini, 2012)
in juice
season.
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Operates at 60
Thermal energy Celsius. Requires
in the system as lower thermal energy
steam demand in extraction
Required electric
power for drive
Bioelectricity
available for
exports
Biological
contamination
(Mackrory,
1984)
6000 kW installed for
3500 kW installed for a capacity of 13 000
a capacity of 13 000
TCD, except for preparation. The electric
TCD, except for
power consumption in preparation is similar to
preparation
the mills.
Lower electric power demand for drive / higher
Higher electric power thermal energy demand. Depending on the
demand for drive /
cogeneration design, similar exports can be
lower thermal energy obtained, especially in systems with low
demand.
percentage of condensation in the last
cogeneration turbine stage
Operates between 80 and 90 Celsius, reducing
Operates at lower
temperature,
microbial activity and losses of reducing
enhancing biological sugars.
activity.
Lower concentration
of mineral impurities;
higher homogeneity
Bagasse quality
of bagasse particle
sizes, higher moisture
stability.
Electricity
generation /
bagasse
moisture
Typically operates between 80 to 90 Celsius.
Requires more thermal energy in extraction
and, usually, in evaporation for higher
imbibition water rate.
Higher contents of mineral impurities; greater
amount of large “pieces”; moisture control
more difficult with only one mill or one
dewatering stage. Higher difficulties in burning
and wear of conventional boilers.
Bagasse moisture is
more stable and,
independent of the
level of impurities in It may require two complete dewatering mills
bagasse feed; it
to achieve the same stability obtained with mill
ensures more burning tandems.
stability in
conventional boilers
and in turbogenerator operation.
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Sugar
production
The mixed juice treatment is more difficult
Easy separation of
when the purpose is to achieve high quality
absolute juice for
final sugar, because of high level coloured
sugar production may contaminants and others.(Manechini, 2011 and
simplify juice
Delfini, 2012) Requires one mill after cane
treatment in sugar and
preparation to allow extraction of absolute
ethanol mills.
juice for sugar production for easier juice
treatment
Allows recycling of the juice treatment sludge
to diffuser. Some plants have already
eliminated the clarification stage. In this case,
fermentation will have higher concentration of
suspended solids, which may cause damage to
the centrifugals and accumulation of solids in
the system. This is still a controversial issue.
Ethanol
production
Produces juice with
higher concentration
of suspended solids
and does not allow
recycling of the
treatment sludge.
Variation in
cane feed
More stable when
cane feed fluctuates if
More sensitive to cane feed fluctuations. Longthere is control of
lasting stops and/ frequent start-ups should be
pressure / adjustment
avoided.
to the gap between
rollers.
Operational
flexibility
Allows mill bypass
for maintenance.
Demands more
operators and more
attention from
operators.
Failures of the bed drive system or traction
prevent operation. Easy automated control. In
the case of modular chainless diffusers,
operation will not be interrupted if one of the
tracks fails, and so there is no need to stop the
system.
Comparative maintenance: milling and diffusers
Cane milling systems are subjected to great efforts and mechanical loads caused by the
presence of impurities in sugarcane or cane feed fluctuations, resulting in mechanical wear of
the equipment and the need for constant welding repairs on rollers to ensure the optimum
performance of equipment. Diffusers operate under a low level of physical stress and minimal
dynamical loads, but are particularly affected by misalignments in the bed transporting
system. A failure or damage requiring one mill to stop impacts only this specific stage, which
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can be removed from service without stopping the whole set. In the case of chain diffusers,
such kind of damage requires stopping the whole system, though such occurrence is less
probable. Table 2 is a summary of the main maintenance differences or requirements for both
systems.
Table 2 – Comparative installation and maintenance requirements between mills and
diffusers
Characteristic
Cost, Installation and Maintenance Aspects
Installation
requirements
CANE DIFFUSER
Chain diffuser
Modular
Building and overhead Building/overhead crane not required. Requires
crane for maintenance less foundation work. Installation area is similar
are required
to the mill tandem area.
Mill
Requires a large and
Requires 40 to 50% smaller MCC size system
Electric power sophisticated electrical
due to the lower electrical power requirements.
feed
motor control centre I/Os in instrumentation panel is bigger.
MCC
Allows width
Expansible
Ideal for expansions
Requires a new
expansion in steps of
capacity
up to 3 capacity stages
diffusion assembly 1500 TCD capacity.
Maintenance
during the
milling period
Checks in the
milling season
Off-milling
season
maintenance
Maintenance
every 3 to 5
milling
seasons
Maintenance
every 10
milling
seasons
Weld repairs /
adjustments or
replacement of
scrapers / trash plate
Lubrication of
bearings and
gearboxes / large size
motors
Replacement of
scrapers / trash plates /
bearings sealing;
restoration of roller
ribs and welds
replacement
Replacement of rollers
/ pinions / bearing
bushings every 3-5
milling seasons
Same as for every 5
seasons
Checks on chains and
pins in bad access
area.
Checks on the
hydraulic system and
tracks in easier access
area.
Inspections on the
chains system / pins /
drive bushings; pumps
Inspection on tracks /
drive hydraulic
system; pumps
Weld repair on bed lifting screws/ inspection
on the cane transport system / pumps rotor and
sealing
Weld repair on bed
lifting screws/ tracks,
pins and chain
bushings /
Repairs on bed lifting
screws / repairs on
pistons and hydraulic
system.
Same as for every 5
Same as for every 5 seasons / coating of
seasons and complete moving tracks
replacement of costly channels (may be
chains(*)
expected)
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Mixed juice
treatment
Weld
electrodes
consumption
Lubricant oil
consumption
Cost of
investment in
extraction
Allows to obtain
mixed juice for ethanol
and absolute juice for
sugar
Considered as 100%
(typically 8 - 10 g/t
cane)
Considered as 100%
(typically 3g/t cane)
Considered as 100%
Produces only mixed juice. In plants not
producing sugar, it allows simplified juice
treatment and less investment. Still a
controversial issue. (Manechini, 2011)
20 to 35% of mill (both in diffuser and mill, it
depends on maintenance quality)
15 to 30% of mill (both in diffuser and mill, it
depends on maintenance quality)
Similar or lower than complete mill tandems
installations.
Considered as 100%
For the same processing capacity, maintaining
extraction and bagasse moisture levels: 60 to
80% of the mills cost
Maintenance
costs
Considered as 100%
For the same processing capacity, maintaining
extraction and bagasse moisture levels: 50 to
75% of the mills cost
Assembly
costs
Traditional level, as
commonly used in
mills
Requires more care in
chains alignment
Operational
costs
Requires more care in
tracks alignment /
pistons and clearances
control
(*)
If regularly submitted to appropriate preventive maintenance, the period for total replacement of chains can be
extended to 15 – 20 years.
Comparative expandability: milling and diffusers
The mills capacity can be expanded more easily, allowing increase of the number
and/or size of the mills, while chain diffusers do not allow gradual expansion – it requires a
new complete line. Modular diffusers allow capacity increases by expanding the bed width.
Figure 16 summarises the main expansion possibilities and respective extraction rates for a
milling tandem system.
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Fig. 16 – Possible expansion of mills and diffusers
Fig. 16 – Possible expansion of mills and diffusers (Schroder, 2007)
As indicated in Figures 16a and 16b, expansion of the mill tandems, as usually
implemented, results in lower extraction rates in the first stages of expansion, around 1
percentage point per stage, which does not occur in diffusers, which have constant extraction
rates. If there is a phased expansion plan, the cost of non-extracted sugars by the mills should
be considered in the feasibility studies and/or when deciding on the extraction equipment.
(Schorn, 2005)
The diffuser capacity can be increased or expanded when the cane diffuser will be
converted into a bagasse diffuser but, for such conversion, the equipment manufacturer should
be consulted.
Cost analysis should be made in a case-by-case basis and for all expected average
extraction rates in the first milling seasons. The best return on investment in the mill will be a
good parameter for a final decision.
Conclusion
The diffuser technology had a significant increase in South Africa in the 1960s and
1970s, and today it is widely accepted in this country, especially because of the existing
characteristics of lower capacity and for not requiring capacity expansion in the first years of
the mill implementation as done in Brazil. In other cane producing regions, mill tandems
predominate, as is the case of Brazil. The recent use of diffusers in Brazil has shown that the
correlations in the theory of the diffuser should be subject to further studies (Voigt, 2010),
such as the required volume of imbibition water, the influence of the type of soil, quality and
adequacy of the analytical methodologies, etc. However, diffusion is an alternative that has
proven to be feasible in Brazilian conditions, and the comparative selection criteria for
diffuser and mills show advantages and disadvantages that depend on specific technical and
operational aspects of each plant and, until now, it has not been possible to define a generic
choice for all cases.
References
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