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Improving second generation bioethanol production in sugarcane biorefineriesthrough energy integration
C.M. Oliveira , A.J.G. Cruz , C.B.B. Costa
PII: S1359-4311(14)01014-X
DOI: 10.1016/j.applthermaleng.2014.11.016
Reference: ATE 6125
To appear in: Applied Thermal Engineering
Received Date: 8 July 2014
Revised Date: 6 November 2014
Accepted Date: 9 November 2014
Please cite this article as: C.M. Oliveira, A.J.G. Cruz, C.B.B Costa, Improving second generationbioethanol production in sugarcane biorefineries through energy integration, Applied ThermalEngineering (2014), doi: 10.1016/j.applthermaleng.2014.11.016.
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Improving Second Generation Bioethanol Production in Sugarcane Biorefineries
through Energy Integration
C.M. Oliveiraa, A.J.G. Cruza,b and C.B.B Costaa,b*
aPPGEQ/UFSCar – Chemical Engineering Graduate Program, Federal University of
São Carlos
bDepartment of Chemical Engineering, Federal University of São Carlos
Rodovia Washington Luiz Km 235, 13565-905, São Carlos, São Paulo, Brazil
Phone: +55 16 3351-8947, Fax: +55 16 3351-8266
*corresponding author: [email protected]
Abstract
New technologies for producing ethanol from sugarcane bagasse and other raw
materials have been developed as an answer for the world claim for renewable energy.
Second generation ethanol is an alternative to increase the production of the renewable
fuel ethanol in Brazil. In this context, in this work energy integration of sugarcane
biorefineries was performed, using Pinch analysis. Biorefineries consist in processes for
first and second generation (1G/2G) ethanol and bioelectricity production, using
hydrothermal, dilute acid and steam explosion pretreatments of sugarcane bagasse. For
each process with a different pre-treatment, two different options were considered, to
know, to include or not pentoses fermentation step. For the six evaluated scenarios the
application of energy integration demonstrated a reduction in energy consumption of
more than 50% when compared to the corresponding cases without any energy
integration and of more than 30% when compared to processes with project integration,
as commonly found in Brazilian industrial plants. Besides the economical advantage,
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due to the decrease in costs of hot and cold utilities, energy integrated processes allow
increase the amount of bagasse that can be diverted for production of second generation
ethanol.
Keywords
Pinch analysis – Sugarcane Biorefinery - Bagasse hydrolysis - Ethanol
1 Introduction
In recent decades studies have demonstrated the use of sugarcane bagasse to
produce second generation ethanol (2G) [1-14]. Brazil is the second largest producer
and consumer of ethanol in the world behind the United States of America, producing
405,000 bbl/d of ethanol in 2012 [15] and the consolidation of second generation
ethanol technology will contribute to make Brazilian ethanol even more sustainable
[16].
Process integration techniques provide important advantages for the
industrial processes in terms of process improvement, increased productivity, energy
resources management and conservation, pollution prevention, and reductions in the
capital and operating costs of chemical plants [17]. Energy integration in a sugarcane
biorefinery can provide economical advantage, environmental benefits and increased
ethanol production. The last factor is related to lower steam consumption in the plant
due to energy integration and, consequently, less bagasse need to be burnt in the
cogeneration system and its surplus can be made available for the production of second
generation ethanol.
Pinch Analysis is one of the most important methods for energy integration.
It consists of a set of techniques for the systematic application of thermodynamic
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concepts and allows that process engineers obtain intuition needed in thermal
interactions among chemical processes and utility systems [18]. In recent years several
studies have shown the application of Pinch Analysis in processes to produce biodiesel
[19], biomethane [20], first generation ethanol [21] and ethanol from lignocellulosic
biomass [22-23], demonstrating the importance of the technique in processes of biofuels
production. Other techniques more robust for energy integration may be cited as
methods of mathematical programming for solving mixed-integer nonlinear
programming (MINLP) problems [24-30]. However, Pinch Analysis is a method simple,
easy to apply and achieves successful results, which justifies the use of this technique.
In this context, this work performed energy integration in sugarcane biorefineries using
Pinch Analysis, in order to evaluate energy savings and contribute to enable integrated
processes for cellulosic biofuel production.
2 Process description
The biorefinery used in this work is the process for first and second
generation (1G/2G) ethanol and bioelectricity production by computer simulation
(virtual biorefinery) performed on free software EMSO (Environment for Modelling,
Simulation, and Optimization). EMSO is a tool for modelling, simulation and
optimisation of general process dynamic systems. It has an object-oriented modelling
language and a graphical user interface, in which the user can manipulate multiple
models along with results and graphical illustrations [31-32]. Six different scenarios
were considered in these biorefineries, since three different types of pretreatment for
bagasse (hydrothermal, dilute acid and steam explosion) and inclusion or not of
pentoses fermentation step were considered.
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The simulated process for 1G ethanol production uses the typical process
configuration of Brazilian plants. The processing of sugarcane begins with cleaning
stage, followed by milling, which produces sugarcane juice and bagasse. The juice is
chemically and physically treated to remove impurities and it is concentrated. After that,
the concentrated juice is fed to bioreactor for reduced sugars (glucose, fructose and
sucrose) fermentation by Saccharomyces cerevisiae, which produces ethanol, CO2, and
other compounds in lesser amounts. The wine produced in fermentation is driven to the
distillation unit, where hydrated ethanol fuel is produced.
In order to produce 2G ethanol, bagasse from the mills is divided into two
fractions, one is diverted to cogeneration system and the other is pretreated in order to
be hydrolyzed. The cogeneration system is responsible for steam and bioelectricity
production. The pretreatment alters the structure of biomass, making cellulose more
accessible to the enzymes that convert the carbohydrate into fermentable sugars [33].
Many studies with different types of pretreatment of lignocellulosic materials can be
found in the literature, such as steam explosion [34-36], organosolv [37-39], dilute acid
[40-42] or alkali [43-45] and hydrothermal [46-48]. In this work three different types of
pretreatment for bagasse were used: hydrothermal, dilute acid and steam explosion.
Hydrothermal pretreatment consists in contact of lignocellulosic biomass
with water in a liquid state at high temperatures (160–240°C) and pressure. It is an
attractive approach because it does not require the addition of chemicals such as acid or
alkali [47]. Hemicelluloses are depolymerized, in certain operating conditions, to
oligosaccharides and monomers, and high xylose recovery from biomass can be
obtained. The advantages of this pretreatment are due to the use of water, component
present in green biomass. Hydrothermal pretreatment is non-toxic, environmentally
benign and inexpensive medium [49].
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Dilute acid pretreatment is one of the most commonly used methods. It
solubilizes hemicellulose and exposes cellulose, making it more accessible for
enzymatic hydrolysis. It can be performed in two conditions: during a short residence
time at a high temperature (above 160°C) or a long residence time at a lower
temperature [40]. Often sulfuric acid [50] and phosphoric acid [51] are used. Dilute acid
pretreatment solubilizes not only the hemicellulose fraction, but also converts the
solubilized hemicellulose to fermentable sugars [52]. For a biorefinery this is an
important advantage because, commonly, hemicellulose sugars represent a third of
carbohydrate total in lignocellulosic biomass materials. However, depending on the
pretreatment severity, dilute acid pretreatment may produce inhibitory products for
fermentation, such as furfural and 5-hydroxymethylfurfural (HMF) [41].
Steam explosion pretreatment consists in contact of biomass with saturated
steam at high pressure, followed by a sudden decompression [53]. In steam explosion
pretreatment hemicellulose is partially hydrolyzed to monomers and oligomers soluble
in water. Crystallinity and degree of polymerization of cellulose is partially modified,
improving enzymatic hydrolysis [54]. Furthermore, steam explosion requires little or no
chemical in pretreatment, making it environmentally benign relative to other
technologies, such as acid hydrolysis [36].
After the pretreatment two fractions are obtained, one enriched with sugars
from hemicellulose (liquid fraction) and other enriched with cellulose and lignin (solid
fraction). Hydrolysis of solid fraction is performed by enzymes. The glucose liquor
produced in this step is concentrated with the sugarcane juice obtained in first
generation ethanol sector. Lignin and cellulose that was not hydrolyzed in hydrolysis
reactor are available for the cogeneration system. When considering pentose
fermentation in the biorefinery process, the hemicellulose fraction converted into
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fermentable sugars (mainly xylose) is sent to pentose fermentation process (catalyzed
by yeast Pichia stipitis). Wine produced by this fermentation process is then returned to
first generation ethanol sector to be mixed with wine produced by the fermentation with
Saccharomyces cerevisiae. Figure 1 shows a simplified diagram of processes for 1G/2G
ethanol and bioelectricity production. More details on process specifications can be
found on Furlan et al. [55].
Brazilian sugarcane biorefineries often present some degree of energy
integration, which depends on the design of each plant. The simulated biorefinery has
energy integration between streams of wine and vinasse and between the juice stream
coming out of sugarcane mills and the concentrated juice stream that comes out of
evaporator (see Figure 1). This degree of energy integration is commonly found in
Brazilian plants and is named in this work biorefinery "with project integration". When
no energy integration is present, every heating and cooling of streams is provided by hot
and cold utilities and the biorefinery process is then named in this work "without energy
integration".
3 Methodology
Initially, a study of the six different scenarios of biorefinery was conducted
to identify possible streams for energy integration, considering restrictions of process.
Pinch Analysis requires streams data such as initial and final temperature, mass flow
and definition of stream type (hot or cold). Information was obtained from simulations
in the free software EMSO. For each identified possible stream heat capacity and heat
duty were calculated. Heat capacity was assumed constant.
The choice of the minimum temperature difference between hot and cold
streams depends on the characteristic of a process [56]. In this work, a minimum
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temperature difference (∆Tmin) equal to 10°C was defined. The ∆Tmin value
influences consumption of utilities in the process. It could be optimized in order to
obtain more accurate values of energy savings, but, as it will be demonstrated on
Results and Discussion section, the adopted value already shows that great savings can
be attained. The aim of this work was to demonstrate that energy integration has a great
potential to, together with other studies, make second generation ethanol viable, due to
increased availability of bagasse. Therefore, optimization was out of the scope, and
different values of ∆Tmin were not analyzed.
To assist in the calculations the free software Hint [57] and the spreadsheet
available at Elsevier Ltd [58] were used. With the assistance of those tools heat
exchangers networks (HENs) were proposed that reduce the consumption of utilities. In
the final step comparisons were made among the biorefinery with energy integration,
without energy integration and with project integration.
4 Results and Discussion
The processing capacity is 12,000 t/day of sugarcane for all scenarios of
biorefinery presented in this paper. Table 1 presents processes information from
simulations. For Scenarios 2, 4 and 6 pentoses fermentation step shown in Figure 1 is
absent.
The amount of bagasse available for production of second generation
ethanol is larger in process using dilute acid pretreatment compared to other scenarios.
The partitioning of bagasse fraction between cogeneration system and 2G ethanol
production stems from the need for energy self-sufficiency of the process.
Consequently, ethanol production and consumption of utilities are higher in processes
that use the pretreatment with dilute acid.
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Fermentation of pentoses has little influence on ethanol production in
processes with hydrothermal (Scenarios 1 and 2) and steam explosion pretreatment
(Scenarios 5 and 6) because the fraction of bagasse diverted to production of second
generation ethanol is low in these process. For this reason, ethanol production is almost
the same when the comparison is made between Scenarios 1 and 2 and between
Scenarios 5 and 6. The fractions of lignin and not hydrolyzed cellulose in hydrolysis
reactor are made available for the cogeneration system, increasing the capacity of
producing energy. Lignin and not hydrolyzed cellulose come from the fraction of
bagasse sent to 2G sector of the plant (Pretreatment + Hydrolysis + Pentoses
Fermentation stages in Figure 1), thus the availability of these additional boiler fuels is
greater in processes that have greater availability of bagasse for production of second
generation ethanol production. Since the amount of bagasse diverted to second
generation ethanol production is far superior in scenarios that use dilute acid
pretreatment (Scenarios 3 and 4) when compared to the other evaluated scenarios, the
fractions of lignin and not hydrolyzed cellulose are also greater in these scenarios.
The production of electricity ranges from 45.1 to 73.6 MW in evaluated
process, with higher production in scenarios that use hydrothermal and steam explosion
pretreatment due to the increased amount of bagasse available for cogeneration system.
The turbine extraction steam (called total consumption of turbine extraction
steam in Table 1) is used both to concentrate pentoses and hexoses liquors and in the
steps of pretreatment. The mills are driven by bioelectricity produced by the process
itself, and the consumption of each mill is 16 kWh/t of fiber. Each scenario has six
mills. It is intuitive that the turbine extraction steam consumption is higher in cases with
hydrothermal and steam explosion pretreatment, because they use a large amount of
turbine extraction steam in pretreatment. However, the values of the total consumption
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of turbine extraction steam (see Table 1) show otherwise. Process with hydrothermal
and steam explosion pretreatment use turbine extraction steam at high pressure (around
20.0 bar) in pretreatment step and pretreatment with dilute acid use turbine extraction
steam at low pressure (2.5 bar). Thus, the steam mass flow rate required for heating the
fluid in pretreatment with dilute acid is superior to other pretreatments, resulting in
higher total consumption of turbine extraction steam compared to the other scenarios.
Ten streams participate in the energy integration network, which are
identified in Figure 1 by numbers. Due to conciseness and similarities reasons,
information such as data, composite curve diagram and heat exchangers networks
proposals are explicitly shown only for Scenario 1. Table 2 shows the energy demand of
its process streams. For Scenario 1 it is necessary to supply 117.3 MW of heating and
106.8 MW of cooling to operate the process.
Composite curve diagram consists in plotting temperature versus enthalpy
(heat duty) for hot and cold streams, which are separated by minimum temperature
difference. The vertical region between the two curves is the possibility of energy
recovery at a given minimum difference of temperature (∆Tmin). For Scenario 1,
∆Tmin = 10°C, the maximum heat recovery is 68.3 MW (see Figure 2). In the region
where the cold composite curve extends beyond the beginning of the hot composite
curve, the heat recovery is not possible, and then external hot utility must be supplied to
meet the energy balance. In the region where the hot composite curve extends beyond
the beginning of the cold composite curve, heat recovery is also not possible, and
external cold utility is required to meet the energy balance. The amount of energy
required to meet the balance represents the minimum demand of hot and cold utilities,
which in Scenario 1 corresponds to 49.0 MW of heating and 38.5 MW of cooling. Also,
by composite curve diagram, the point at which the minimum temperature difference
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(equal to ∆Tmin = 10°C) between the curves occurs is called the Pinch point. For this
scenario hot and cold Pinch temperatures are 111.9°C and 101.9°C, respectively. Table
3 shows the consumption of utilities of all scenarios without any energy integration, hot
and cold utility targets, and hot and cold Pinch temperatures.
The representation of heat exchangers networks (HENs) is made by a grid
diagram. The streams are horizontal lines, the heat exchangers are represented by two
circles connected by a vertical line, and the heaters and coolers are indicated by a circle
with letter H and C, respectively [59]. Application of feasibility criteria to the stream
data at the Pinch is necessary to identify essential matches at the Pinch, available design
options and the need to split streams [60]. In order to achieve the minimum energy
consumption, hot utilities must not be used below the Pinch point and cold utilities must
not be used above the Pinch point. Figure 3 presents heat exchangers network that meets
the minimum energy demand for Scenario 1. Energy units in the HEN are given in MW.
To synthesize heat exchangers network it was necessary to split cold stream
number 10 (juice stream leaving the treatment, see Figure 1) into two parallel branches.
If the split was not performed, the proposed network would exceed the minimum energy
demand. For streams with high flow or temperature splitting can be advantageous if the
balance between energy costs and equipment costs is positive. However, splitting the
stream may not be compatible with the process and its restrictions, making the process
more complex and infeasible from a practical point of view. Therefore, a second
network without split streams was proposed (Figure 4). For the synthesis of the second
network the loop between heat exchangers 6 and 4 was broken with the removal of heat
exchanger 4, besides removing exchangers 3, 8, 10 and 12 and adding hot and cold
utilities to meet demand. This network relaxation aims to simplify the HEN, reducing
capital costs and improving project return [59]. The schematic representations of the
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biorefinery of Scenario 1 integrated with these HENs are shown in Figures 5 and 6.
In all other scenarios, two networks of heat exchangers were proposed,
except for Scenario 3, for which it was possible to propose a HEN that fulfills the
minimum energy demand without the need to split any process stream. During network
synthesis, some criteria to be satisfied by Pinch analysis imposed the need to split a cold
stream with high heat capacity into two parallel branches. In all networks that this
requirement was necessary stream 10 was chosen to be split, because it is the cold
stream that crosses Pinch point with higher heat capacity.
Table 4 shows the achieved economy with all heat exchangers networks
proposals in relation to process without energy integration and to the project integration,
as commonly found in Brazilian plants. The savings of utility in relation to processes
without energy integration approximate 60% for the 1st HEN and range between 40 %
and 50 % for the 2nd HEN. When compared to processes commonly found in Brazilian
plants (project integration), these values range between 30 % and 40 % for the 1st HEN
and between 10 % and 30 % for the 2nd HEN. Processes with the 2nd HEN have greater
amplitude in the range of economy due to attempts to propose networks that were
feasible from a practical point of view, resulting in an increase in energy demand to
greater or lesser degrees depending on the evaluated scenario.
Table 5 presents the number of heat exchange units for HENs proposed in
each evaluated scenario. The number of heat exchange units ranges between 14 and 17
for processes with the 1st HEN and 13 and 15 for processes with the 2nd HEN. In all
evaluated scenarios the number of heaters and coolers are equal for the 1st HEN.
However, for the 2nd HEN the values vary according to Pinch temperature. When the
hot and cold Pinch temperature is 111.9°C and 101.9°C, respectively, HENs have four
heaters and five coolers. When hot and cold Pinch temperature is equal to 78.2°C and
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68.2°C, respectively, HENs have three heaters and six coolers. The HENs proposals
with higher Pinch temperature have a heater below the Pinch in stream 10 and the HENs
proposals with lower Pinch temperature have a cooler above Pinch in stream 7. The
addition of heaters below the pinch and coolers above the pinch violates the criteria of
Pinch analysis and it was made to avoid the stream splitting, as well as to break the
loops and remove other heat exchangers with low energy demand.
Consumption of vegetal steam in processes without energy integration and
with energy integration is presented in Table 6. Consumption of vegetal steam in
processes without energy integration varies little among evaluated scenarios, from 3.1 to
3.4 kg steam/L hydrous ethanol. Vegetal steam is the term used to designate steam
produced in the evaporator due to concentrating sugarcane juice and it is also used in
the processes as hot utility (steam at 2.1 bar). The consumption of vegetal steam ranges
from 1.3 to 1.5 kg steam/L hydrous ethanol in processes with the 1st HEN. The saving is
lower with the 2nd HEN, with consumption varying from 1.5 to 1.9 kg steam/L hydrous
ethanol. The consumption of hot utility is greater in scenarios including pentose
fermentation due to the increased ethanol production. Energy integration reduces
operating costs in biorefinery and can increase the production of second generation
ethanol due to vegetal steam saving, which may help to make second generation ethanol
viable.
Brazilian plants commonly perform energy integration (project integration)
between the streams of juice at the outlet of the mills (stream number 1, see Figure 1)
and concentrated one (stream 2) and between the streams of wine before entering
distillation column (stream 3) and vinasse (stream 4). 1st and 2nd HENs proposed for
Scenarios 1, 3 and 4 have energy integration between the same streams of process
commonly found in Brazilian plants (project integration), besides energy integration
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between other process streams. For Scenarios 2, 5 and 6, the networks that meet the
minimum energy demand (1st HEN) do not integrate energy between the streams of
wine (stream 3) and vinasse (stream 4). If it was supposed to maintain the exchange
between them, the HEN would exceed the energy target. However, there is energy
integration between the streams of juice that leaves the mills and the concentrated one.
In all evaluated scenarios with the 2nd HEN energy integration between the same
streams of process commonly found in Brazilian plants is performed. The match of
stream 1 with stream 2 and of stream 3 with 6 in heat exchangers have big exchanges
due to high energy demand of these streams. In all eleven proposed HENs there is
match between streams 1 and 2, and in eight of them there is match between streams 3
and 6.
There are advantages and disadvantages among the proposed heat
exchangers networks. The first ones have higher utilities saving, but have more heat
transfer units and split streams, which can make the process more complex and
infeasible from a practical point of view. The second networks provide fewer saving in
utilities, but have less heat exchange units and have no split streams. However,
choosing the best network depends on economic criteria such as investment costs,
savings by the reduction in consumption of utilities and the increase in ethanol
production.
In the studied process the bagasse fraction diverted to cogeneration system
is burned, providing steam at 65.0 bar. Then, this steam drives the turbine, generating
turbine extraction steam at low pressure (2.5 bar) and turbine extraction steam at high
pressure (around 20.0 bar), whereas the last one is only generated in process with
hydrothermal and steam explosion pretreatment. Turbine extraction steam at high
pressure is used in the pretreatment steps (hydrothermal and steam explosion) and the
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turbine extraction steam at low pressure is used both in the evaporators for
concentrating sugarcane juice and pentoses liquor and in pretreatment with dilute acid.
Vegetal steam at 2.1 bar generated in the evaporator is used as hot utility. Consumption
of steam in distillation columns is included in consumption of vegetal steam. Energy
integration reduces consumption of vegetal steam and it can reduce the consumption of
bagasse in cogeneration system. Thus, the surplus can be made available for production
of second generation ethanol. However, for effective implementation of this, some
modifications must be made in simulated process. The single evaporator used in
synthesizing this process must be replaced by a multiple-effect one. With this process
modification, juice can be concentrated on the same specifications using less turbine
extraction steam and generating less vegetal steam, but enough to meet the thermal
energy demand of the plant. Consequently, less bagasse is driven to the cogeneration
system and the surplus is diverted to 2G ethanol sector, increasing ethanol production.
Concerning the consumption of turbine extraction steam by the different
pieces of equipment, Scenario 1 diverts 88.0% in mass (which corresponds to 77.4% in
terms of thermal energy consumption) of extraction steam to evaporators (sugarcane
juice and pentoses liquor), and, so, pretreatment stage consumes only 12% (in mass) of
it. In order to illustrate the differences among scenarios, the consumption of turbine
extraction steam by evaporators in Scenario 3 corresponds to 86.9% (both in mass and
in thermal energy terms, because in this scenario only low pressure extraction steam is
used) while in Scenario 6 it achieves 98% in mass (99.9% in terms of thermal energy
consumption). The replacement of single evaporator by a multiple-effect one would
reduce this consumption. Energy integration reduces consumption of vegetal steam and
thus assists in reducing the consumption of turbine extraction steam in evaporators.
These combined procedures reduce the consumption of bagasse in cogeneration system
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and enable a greater surplus of bagasse to be available for production of second
generation ethanol.
Pinch analysis, the methodology used for improving energy efficiency in
this work, is a simple technique, of easy application and understanding. Although it
does not involve the optimization of total annualized cost as some modern methods, it is
possible to obtain very good results that promote real savings in operating costs of
processes, besides better energy management and reduction in the emission of gaseous
and aqueous effluents.
5 Conclusion
The development of technology for second generation ethanol will ensure
increased ethanol production and competitive advantages in the market. Presented
results indicate that energy integration provides considerable reduction in energy
consumption and consequently in operating costs of the plant for all evaluated
scenarios. Vegetal steam consumption reduces from 3.4 to 1.3 kg steam/L hydrous
ethanol, depending on the evaluated scenario. However, the choice of the best network
of heat exchangers to be implemented into process is not straightforward, since the
proposed HENs exhibit pros and cons when number of units, achieved economy and
splitting of streams are considered. Besides the economical aspect, due to the decrease
in utility costs (hot and cold ones), there are environmental benefits and the possibility
of increasing bagasse availability for production of second generation ethanol. Energy
integration provides significant advantages to a biorefinery and can help, along with
other works, to make viable the production of second generation ethanol.
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Acknowledgements
The authors acknowledge the support from CTBE (The Brazilian Bioethanol Science
and Technology Laboratory), DEQ/UFSCar (Chemical Engineering Department, São
Carlos Federal University), FAPESP (São Paulo State Research Funding Agency),
CNPq (National Council for Scientific and Technological Development) and CAPES
(Coordination of Higher Educational Personnel Improvement).
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Figure Captions
Figure 1. Schematic representation of the general sugarcane biorefinery process
Figure 2. Composite curve diagram for Scenario 1
Figure 3. First heat exchangers network for Scenario 1
Figure 4. Second heat exchangers network for Scenario 1
Figure 5. Schematic representation of the process with first heat exchangers network for
Scenario 1
Figure 6. Schematic representation of the process with second heat exchangers network
for Scenario 1
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Table 1. Data of biorefinery process for the six considered scenarios
Scenario Pretreatment
Pentoses
Fermentation
Bag.
Cog.a
(t/day)
Bag.
2Gb
(t/day)
L+ C
Cog.c
(t/day)
Total cons.
turb. ex.
Steamd (kg/t)
Ethanol
production
(m3/day)
Bioelectricity
production
(MW)
1 Hydrothermal Yes 2,655 350 110 531.3 1,144 68.5
2 Hydrothermal No 2,655 350 110 441.7 1,123 73.6
3 Dilute acid Yes 733 2,272 1,120 585.1 1,382 45.5
4 Dilute acid No 650 2,355 1,161 579.2 1,253 45.1
5 Steam
explosion
Yes 2,866 151 49 430.4 1,123 71.8
6 Steam
explosion
No 2,866 151 49 399.5 1,115 73.5
a Bag. Cog. - bagasse availability for cogeneration system;
b Bag. 2G - bagasse availability for production of second generation ethanol;
c L + C Cog. - lignin and not hydrolyzed cellulose availability for cogeneration system.
d Total cons. turb. ex. steam - total consumption of turbine extraction steam at 20.0 bar
and 2.5 bar.
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Table 2. Data of process streams for Scenario 1
Stream Type Flow (t/h) T in (°C) T out (°C) Heat duty (MW)
1 Cold 547.66 32.13 58.32 15.23
2 Hot 338.17 121.90 31.00 -31.48
3 Cold 423.35 31.00 82.00 24.19
4 Cold 353.84 111.69 111.89 42.74
5 Cold 32.14 108.28 108.38 5.02
6 Hot 37.38 78.17 77.43 -34.46
7 Hot 353.84 111.89 25.00 -35.89
8 Hot 32.14 108.38 25.00 -2.93
9 Hot 37.38 77.43 25.00 -2.10
10 Cold 548.87 58.25 110.00 30.17
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Table 3. Consumption and targets of utilities, hot and cold pinch temperatures for the
six considered scenarios
Scenario
Hot
utilitye
(MW)
Cold
utility f
(MW)
Hot utility
targetg
(MW)
Cold utility
targeth
(MW)
Hot Pinch
temperature
(°C)
Cold Pinch
temperature
(°C)
1 117.3 106.8 49.0 38.5 111.9 101.9
2 113.0 102.1 46.7 35.8 78.2 68.2
3 148.2 143.9 66.9 62.6 111.9 101.9
4 122.1 116.5 51.4 45.8 111.9 101.9
5 114.3 103.2 47.4 36.3 78.2 68.2
6 112.5 101.3 46.6 35.4 78.2 68.2
e Hot utility - demand of hot utility in process without energy integration;
f Cold utility - demand of cold utility in process without energy integration;
g Hot utility target - minimal demand of hot utility in process with energy integration;
h Cold utility target - minimal demand of cold utility in process with energy integration.
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Table 4. Savings of utilities for heat exchange networks (HENs) proposed for all
evaluated scenarios when compared to process without integration and to project
integration
Scenario
Hot/cold utility saving (MW)
(without integration, %)i
Hot/cold utility saving (MW)
(project integration, %)j
1st HEN 2nd HEN 1st HEN 2nd HEN
1 58.2/63.9 41.5/45.5 37.1/43.0 11.9/14.0
2 58.7/65.0 51.8/57.5 38.0/44.4 27.8/32.5
3 54.8/56.5 - 30.6/32.0 -
4 57.9/60.6 41.8/43.8 36.5/39.2 12.2/13.1
5 58.6/64.8 51.6/57.1 37.4/44.3 27.4/32.0
6 58.6/65.0 51.7/57.4 38.0/44.7 27.8/32.6
i Hot/cold utility saving (without integration, %) - saving of hot/cold utility of processes
with the proposed networks in relation to process without energy integration, in %;
j Hot/cold utility saving (project integration, %) - saving of hot/cold utility of processes
with the proposed networks in relation to process with project integration, in %.
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Table 5. Number of heat exchange units for the proposed HENs for all evaluated
scenarios
Scenario 1st HEN 2nd HEN
NEHUk Heaters Coolers NEHUk Heaters Coolers
1 17 3 5 13 4 5
2 17 3 5 15 3 6
3 14 3 5 - - -
4 15 3 5 13 4 5
5 17 3 5 15 3 6
6 17 3 5 15 3 6
k NHEU - number of heat exchange units.
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Table 6. Consumption of vegetal steam for process without integration and with
integration for all evaluated scenarios
Scenario
Steam consumption (without
energy int., kg steam/L
hydrous ethanol)l
Steam consumption (with energy int.,
kg steam/L hydrous ethanol)m
1st HEN 2nd HEN
1 3.3 1.4 1.9
2 3.2 1.3 1.5
3 3.4 1.5 -
4 3.1 1.3 1.8
5 3.2 1.3 1.6
6 3.2 1.3 1.6
l Steam consumption (without energy int., kg steam/L hydrous ethanol) - vegetal steam
consumption (2.1 bar) of process without energy integration;
m Steam consumption (with energy int., kg steam/L hydrous ethanol) - vegetal steam
consumption (2.1 bar) of process with networks proposals.
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• Energy integration of sugarcane biorefinery was performed using Pinch analysis. • Biorefinery produces bioelectricity, first and second generation ethanol. • Six different scenarios were evaluated. • A reduction in energy consumption of more than 50% was observed. • Energy integrated processes allow second generation ethanol production
increase.
