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CHEMICAL ENGINEERING TRANSACTIONS
VOL. 57, 2017
A publication of
The Italian Association
of Chemical Engineering
Online at www.aidic.it/cet
Guest Editors: Sauro Pierucci, Jiří Jaromír Klemeš, Laura Piazza, Serafim Bakalis
Copyright © 2017, AIDIC Servizi S.r.l.
ISBN 978-88-95608- 48-8; ISSN 2283-9216
Influence of the Type of Mixture and Concentration of
Different Binders on the Mechanical Properties of “Green”
Charcoal Briquettes
Karine Zanella*, Vinicius O. Concentino, Osvaldir P. Taranto
School of Chemical Engineering – Univesity of Campinas, Albert Einstein Ave., 500 – Campinas, SP – Brazil, Zip Code:
13083-852
karinezll@gmail.com
The application of biomass to generate energy has been highly studied as an alternative to fossil fuels. In
Brazil, there is a large production of orange juice, and their solid waste (bagasse) has as its main destination
the production of food for ruminants. Therefore, there is an interest among the industries to transformed this
waste into a by-product with higher benefit. In this way, this work has as main objectives, the use of a new
type biomass to produce “green” charcoal and the application of three different types of binders (industrial
cornstarch, pectin with high degree of esterification and pectin with low degree of esterification) using three
different proportions (5, 10 and 15%) and two types of mixtures in way to verify which briquette has the lowest
friability index a better compression resistance. To determine the friability index, the tumbling method was
applied. The compressive strength of the briquettes was also determined. The binder that brought better
characteristics to the charcoal briquettes, and therefore would be chosen for a production line is the industrial
cornstarch. For this binder, the briquettes showed higher mechanical strength when applied the second mixing
method. In this case, the briquette with a composition of 10 % of industrial cornstarch, presented
characteristics as non-friable and withstand a pressure of 4.093 MPa in the compression tests. The choice of
this binder is also because it is cheaper among the three tested ones.
1. Introduction
The search for new alternatives for power generation has been intensified in the scientific community. In this
context, there is an increased interest in the use of biomass waste as an energy source. Biomass is any
organic material of vegetable origin that has energy available for burning, such as wood and forest wastes,
livestock and agricultural wastes. Among the agricultural wastes, the solid waste from processing of orange
juice (orange’s bagasse) can be highlighted (Yaman, 2004; Carvalho and Poppe, 2010; Alho, 2012). So, the
development of researches for the use of these wastes as by-products becomes interesting. Orange solid
wastes were collected in local restaurants. In this way, “green” charcoal particles, a wood charcoal substitute,
has been obtained by carbonization process of those wastes. The particles were then processed to become
fines and an agglomeration step was necessary to facilitate the combustion and transport of the briquettes.
The charcoal briquettes production demands a binder to mix with the charcoal fines, since the charcoal by
itself does not have a good cohesive property among particles. Many materials can be used as binders;
however it is necessary that it does not harm the energy characteristics of the briquette, either reducing the
calorific yield or increasing volatile and ash content. Thus, the choice of type and amount of binder is the most
critical point on the briquettes production, which is the most sensitive stage to process costs. The search for
new binders has been increasing, as long as it provides the necessary requirements of a high-quality
briquette, for example, presents high mechanical strength, such as a low friability index and a high resistance
to compression.
The compressive strength is a significant parameter in the evaluation of the briquette to its storage (De Melo,
2010). In order to evaluate the influence of the forces applied in the energetic densification stage, the
DOI: 10.3303/CET1757034
Please cite this article as: Zanella K., Concentino V., Taranto O.P., 2017, Influence of the type of mixture and concentration of different
binders on the mechanical properties of “green” charcoal briquettes, Chemical Engineering Transactions, 57, 199-204
DOI: 10.3303/CET1757034
199
resistance of the briquettes to the compression is going to be determined in order to predict their mechanical
behavior when subjected to a given load or effort, considering their storage position.
The friability of a material is the property that it has to be turned into powder. In the case of charcoal, friability
is understood as the property that it has to generate fines when handled or during its storage and transport.
The lower the capacity of generation of fine, more resistance has the briquette (Gomes and Oliveira, 1980;
Tumuluru et al., 2011).
In this way, in this study, three different types of binders were tested (industrial corn starch, pectin with high
esterification degree and pectin with low esterification degree) in three different proportions (5, 10 and 15 %
w/w) and two ways of mixing in order to verify the mechanical resistance (compression and friability) at the
produced charcoal briquettes.
2. Material and Methods
The orange’s bagasse was kindly provided by local restaurants. It was chopped into 1 cm² pieces, dehydrated
in an oven at 105 °C for 24 hours approximately, to remove free moisture. After this first drying, the orange's
bagasse (dried) went through the carbonization process. This step was carried out at a temperature of 450 °C
(for 1 hour), with a rate of 10 °C/min. After carbonization, the obtained charcoal was grinded (TE 633, Tecnal)
and the charcoal particles (ca. 2.0 mm to 4.0 mm) were sent to the energetic densification step.
The process of energy densification is necessary to have a concentration of the energy supplied by the coal in
the briquette. In this step, it is need the addition of a binder, since the charcoal particles by itself do not shown
molecules cohesion. The binders used were industrial cornstarch, pectin with high esterification degree (Pec-
1) and pectin with low esterification degree (Pec-2). As a novelty the two different pectin were used as
binders. Therefore, cornstarch was applied for comparison, since its use as a binder has already been
elucidated in literature.
Three different proportions between the charcoal particles and binders were applied (5, 10 and 15 %
wbinders/wcharcoal) and two types of manual mixtures were prepared.
• In the first one, the binder and charcoal were mixed, and to this mixture was added water. Only for
the industrial cornstarch that this mixture still underwent a heating, so the activation of the starch
could occur.
• In the second mixture, the binders were first mixed with water (heated in the case of cornstarch), and
then the charcoal particles were added into this mixture.
The amount of water used for the Pec-1 and Pec-2 binders was 50 % water/coal. However, for the industrial
cornstarch was used the ratio of 100 % water/coal. These amounts were defined in previous assays.
In order to the charcoal briquettes be produced, a cylindrical mold and a uniaxial manual hydraulic press were
used (Figure 1). The briquetting time was 1 min with a 5-tf application (2.0 cm² area each piece).
After obtaining the charcoal briquettes, they were dehydrated in an oven at a temperature of 80 °C for about
12 hours, so that the briquettes moisture was around 10 %. After this drying, the mechanical strength tests
were performed.
Figure 1: A: Manual uniaxial press; B: Cylindrical mold.
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2.1 Friability Index
The friability test was performed using the tumbling method. For this, a friabilometer was used (300, Ethik®) in
which the charcoal briquette was subjected to 500 rotations. The ratio between the final and the initial mass
provides the friability index. According to the amount of mass lost during the test, the charcoal briquette can
be classified (Oliveira and Almeida, 1982), as shown in Table 1.
Table 1: Charcoal classification
Loss Mass (%) Classification
≥ 30 Extremely friable (EF)
25 - 29 Fairly friable (FF)
15 – 24 Medium Friability (MF)
10 – 14 Slightly Friable (SF)
< 10 Non-Friable (NF)
2.2 Compression Test
The hardness was measured by the compression test in a universal test machine (MTS). The parameters
used were pre-test velocity, velocity test and post-test velocity (all of 0.3 cm / min) and contact load (10 kN). In
the test, the briquette was subjected to continuous pressure until its rupture, as shown in Figure 2. The values
of the velocities test were based on the work of Quirino (1991).
Figure 2: Charcoal briquette before (A) and after (B) the compression test
3. Results and Discussions
3.1 Friability Index
The run results of the friability test for the charcoal briquettes obtained with the three binders and the two ways
of mixing are shown in Table 2, as well as the briquettes classification according to their loss mass. The
friability index graphical representation is shown in Figure 3.
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Table 2: Friability index results and charcoal classification
Amount of binder Mixture 1 Mixture 2
Classification
Mixture 1
Classification
Mixture 2
Cornstarch 5 % 31.461 ± 3.312 14.090 ± 2.064 EF SF
Cornstarch 10 % 4.320 ± 0.310 3.403 ± 0.806 NF NF
Cornstarch 15 % 3.811 ± 0.852 2.705 ± 0.054 NF NF
Pectin-1 5 % 42.442 ± 1.294 59.058 ± 1.677 EF EF
Pectin-1 10 % 13.822 ± 0.900 16.207 ± 2.921 SF MF
Pectin-1 15 % 10.177 ± 1.082 10.248 ± 1.995 SF SF
Pectin-2 5 % 27.488 ± 2.211 26.388 ± 4.569 FF FF
Pectin-2 10 % 16.911 ± 0.792 7.797 ± 0.476 MF NF
Pectin-2 15 % 14.032 ± 1.358 6.958 ± 0.730 SF NF
Figure 3: Friability index results. Illustration ‘A’ brings the results for mixture 1, while “B” brings the results for
mixture 2
Analyzing the data of the friability index presented previously, we can observe that as a greater the amount of
binder is added, the less friable the charcoal briquette becomes. This fact is expected due to the fact that with
the addition of the binder there is a greater adhesion between the coal particles. Despite there is a large
difference between the proportions of 5 and 10 % of binder on the results, there is no such notable difference
when there is an increase from 10 to 15 % in the ratio between the charcoal and the binder.
Regarding the type of mixture, it is noticed that there is a decrease in the friability of the charcoal briquette
when it was elaborated with the second mixing technique, except to Pec-1 as a binder. To this fact, it is
believed that when there is initial the mixing between the binder and the water, there is a better
homogenization of these two compounds, and when the charcoal is added, that mixture (binder and water)
reaches the pores of the charcoal particles. This effect do not happened when the first form of mixing is
applied. Similar results are reported in the literature for the use of the Pec-1 as binder. Concentino et al.
(2016) produced charcoal briquettes applying 3 minutes of compression during the briquetting step and,
verified the same influence as saw in this work on the proportions of binder in the final product.
Based on the results obtained, it was verified that the application of the binders Pec-1 and Pec-2 is not
feasible when compared to the use of cornstarch, due to the cost of these binders and the presented
resistance.
Based on this test, the application of 10 % (w/w) of the cornstarch binder to the production of charcoal
briquettes and the use of the second way of mixture for its production is indicated.
This is because the briquette presents as non-friable (loss of mass of 3.403%), according to the classification
presented in Table 1.
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3.2 Compression Test
The stress values required for the rupture of each briquette as well as the elongation (strain) that each
briquette showed are presented in Table 3. The uniaxial mechanical compression graphical results are shown
in Figure 3.
Table 3: Compression test results
Amount of binder
Stress (MPa)
Mixture 1
Strain (%)
Mixture 1
Stress (MPa)
Mixture 2
Strain (%)
Mixture 2
Cornstarch 10 % 3.243 ± 0.418 9.753 ± * 4.093 ± 0.232 11.563 ± *
Pectin-1 10 % 2.188 ± 0.256 10.266 ± * 1.414 ± 0.057 9.417 ± *
Pectin-2 10 % 1.776 ± 0.068 9.207 ± * 2.063 ± 0.159 11.636 ± *
*Value not computed by the equipment.
Figure 4: Compression tests results. Illustration ‘A’ brings the results for mixture 1, while “B” brings the results
for mixture 2
For these analyzes the briquettes whose composition had 10% binder were used. It is verified that the results
of the mechanical compression tests are in agreement with the results of the friability index, with respect to the
type of mixture. That is, the briquettes produced by the second type of mixture were more resistant to
compression, except for the briquette produced with Pec-1.
As there was a significant increase in the value of the compressive strength (26.21%) when the cornstarch
was used as binder and the second way of mixing was applied, again, this binder would be the suitable one
for the production of charcoal briquettes.
Similar results are found in the literature, however, for this, there was a need to use a larger amount of binder
than the one used in this study, as is the case of the papers presented by Rubio et al (1999) and Habib et al
(2013). Zanella et al. (2015), Worked with the production of charcoal briquettes using orange's bagasse and
commercial cornstarch, obtaining as best result for mechanical compression the value of 2.177 MPa, for a
proportion of 15 % of binder. In this way, the study of the type and amount of the binder becomes interesting
for future works.
It is also observed by the Stress x Strain curves and by the Strain values, presented in Table 3, that all
briquettes presented a similar elongation value until its rupture. This indicates that there is a uniformity in the
shape and size of the briquettes during the production process and therefore they behave in similar ways,
regardless of the type of mixture and the binder applied.
4. Conclusions
The data obtained in this work indicate that solid orange wastes can be used for thermal conversion in the
manufacture of charcoal. It also indicates that the use of 10 % (w/w) of industrial cornstarch as a binder in the
energetic densification step becomes interesting for the production of charcoal briquettes, with satisfactory
characteristics regarding their mechanical resistance. Given this, charcoal briquette made from the use of
orange's bagasse and cornstarch becomes an alternative to the use of fossil fuels.
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Acknowledgments
The authors would like to thank CNPq (National Counsel of Technological and Scientific Development) for the
financial support received.
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