Production of fuel briquettes from olive refuse and paper mill waste

Abstract

Some processes have been widely applied to biomass in order to take advantage of its energy potential. In particular, these processes are based on pyrolysis or gasification. In this study, briquetting was applied to olive refuse and paper mill waste to form fuel briquettes. For this purpose, the particle sizes of both biomass samples were decreased to −250 μm and then they were briquetted in a steel die under pressure between 150 and 250 MPa at ambient temperature. Effects of the moisture content of the biomass samples and briquetting pressure on the shatter index, compressive strength, and water resistance of the briquettes obtained were investigated. This study showed that the mechanical strength of the briquettes produced only from the olive refuse was not high enough. On the other hand, strong briquettes were produced using paper mill waste. When olive refuse was blended with fibrous paper mill waste, briquettes with sufficiently high mechanical strength could be produced. Burning profiles of the samples were derived applying derivative thermogravimetry technique under dynamic dry air atmosphere up to 1273 K with a heating rate of 40 K·min−1 and then combustion characteristics of the briquettes were compared.

Full text

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Fuel Processing Technology 68 2000 23–31
www.elsevier.comrlocaterfuproc
Production of fuel briquettes from olive refuse and
paper mill waste
S. Yaman),M.S¸ahan, H. Haykiri-ac¸ma, K. S¸es¸en, S. Kuc¸ukbayrak
¨¨
Chemical and Metallurgical Engineering Faculty, Istanbul Technical UniÕersity 80626, Maslak,
Istanbul, Turkey
Received 3 January 2000; received in revised form 25 May 2000; accepted 1 June 2000
Abstract
Some processes have been widely applied to biomass in order to take advantage of its energy
potential. In particular, these processes are based on pyrolysis or gasification. In this study,
briquetting was applied to olive refuse and paper mill waste to form fuel briquettes. For this
purpose, the particle sizes of both biomass samples were decreased to y250 mm and then they
were briquetted in a steel die under pressure between 150 and 250 MPa at ambient temperature.
Effects of the moisture content of the biomass samples and briquetting pressure on the shatter
index, compressive strength, and water resistance of the briquettes obtained were investigated.
This study showed that the mechanical strength of the briquettes produced only from the olive
refuse was not high enough. On the other hand, strong briquettes were produced using paper mill
waste. When olive refuse was blended with fibrous paper mill waste, briquettes with sufficiently
high mechanical strength could be produced. Burning profiles of the samples were derived
applying derivative thermogravimetry technique under dynamic dry air atmosphere up to 1273 K
with a heating rate of 40 KPmin
y
1and then combustion characteristics of the briquettes were
compared. q2000 Elsevier Science B.V. All rights reserved.
Keywords: Biomass; Olive refuse; Briquetting; Paper mill waste; Thermogravimetry
1. Introduction
In order to meet rapidly increasing energy demand, alternative energy sources must
be utilised effectively. Of the alternative energy sources, biomass has a great potential
today and in the future, since it is renewable, in contrast to the nature of the fossil fuels.
)Corresponding Author. Tel.: q90-212-285-68-73; fax: q90-212-285-29-25.
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E-mail address: yamans@itu.edu.tr S. Yaman .
0378-3820r00r$ - see front matter q2000 Elsevier Science B.V. All rights reserved.
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PII: S03 7 8-3 8 2 0 00 00 1 1 1-9

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S. Yaman et al.rFuel Processing Technology 68 2000 23–3124
Solar energy is indispensable for the plant life and by means of photosynthesis, plants
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deposit some of the solar energy as a mass in their body 1 . When biomass is burnt, this
energy is revealed. Biomass has either been burned directly or processed to take
advantage of its energy content. In the former case, since biomass usually contains a
high content of moisture, it is necessary to remove the moisture content before
combustion. Furthermore, the densities of almost all of the biomass samples are very
low and therefore some problems occur during their transportation. For these reasons,
direct combustion of biomass is not practical. In the latter case, some processes such as
pyrolysis or gasification have been widely applied to biomass to gain its energy content
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2,3 . However, these processes lead to new problems. The liquid products obtained by
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means of pyrolysis are rich in water that is detrimental for ignition 4 . Moreover, these
liquids contain oxygenated compounds, which cause unwanted thermal characteristics
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such as thermal instability, tendency to polymerise, corrosion and low heating value 5 .
On the other hand, some products obtained from pyrolysis or gasification are highly
carcinogenic and mutagenic and they have various compounds including even polyaro-
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matic hydrocarbons 6,7 . Besides, it is impossible to recover the calorific value
completely via these processes.
Some alternative studies have been conducted to use the biomass as a binder in the
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production of coal briquettes 8,9 . Moreover, some biomass samples such as cotton
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stalks 10 , tea waste 11 , waste paper and wheat straw 12 , pine cones and sawdust
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13 were used to obtain biobriquettes. However, the existing information about the
direct briquetting of the biomass samples is extremely limited and information about one
type of biomass sample cannot be applicable to another one.
The kind and amount of the biomass show important differences for different
geographical areas, depending on the characteristics of its climate, flora, and agriculture.
Olive is one of the most important agricultural products of the Mediterranean countries.
For example, the total amount of the olive production of Turkey in 1998 was approxi-
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mately 1,550,000 tonnes 14 . A great deal of the olive has been consumed in the form
of olive oil. For this purpose, a huge amount of olive is milled to produce olive oil and
meanwhile tonnes of its oily refuse remain. This refuse is one of the considerable
sources of biomass, and has locally been used as a domestic fuel. However, there are
some problems related to the direct combustion of this refuse. Some olive seeds, which
have not been properly broken during the milling, can burst in the combustion chamber.
This is an undesirable circumstance for a good fuel. In order to prevent such problems,
olive refuse should be grounded completely before combustion.
However, it is not practical to burn grounded olive refuse in the conventional
combustion chambers. In that connection, briquetting of the grounded olive refuse to
obtain firm briquettes is recommended. Thus, a compressed fuel can be obtained. Since
olive refuse is fibrous and contains some oily and sticky components, it maybe possible
that olive refuse does not need any binder material to form its briquettes.
Another valuable biomass type that cannot be evaluated properly is the paper mill
wastes of the paper industry. These wastes contain some organic materials and therefore
they have calorific value to some extent. Since, paper mill wastes are extremely fibrous,
it may be possible to produce its briquettes. In this study, production of the fuel
briquettes using olive refuse and paper mill waste were investigated.

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S. Yaman et al.rFuel Processing Technology 68 2000 23–31 25
2. Experimental
The olive refuse used in the experiments was the residue of the Turkish vegetable oil
industry using western Turkey olives. Likewise, paper mill waste was the remains of the
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Turkish paper industry SEKA . The both samples are abundant and have low economic
value. Analyses of these samples were conducted according to ASTM standards and
results are given in Table 1.
Briquetting experiments were performed using a hydraulic press. The maximum
pressurising capacity of the hydraulic press was 1110 MPa between two plates with a
speed of 50 mmrmin. The cylindrical briquetting die was made of hardened steel with
an inner diameter of 50 mm and a height of 100 mm. Before briquetting, olive refuse
and paper mill waste samples were ground to pass through a sieve having an opening of
250 mm. For each experiment, 40 g of these samples were filled into the die and
briquettes were produced under pressures of 150–250 MPa. Briquettes were stored
under ambient conditions for a week before testing. Three briquettes were prepared for
each set of the experimental conditions and the arithmetic averages of the measurements
were calculated.
Some standard tests were applied to determine the shatter index, compressive
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strength, and water resistance of the briquettes. The shatter indices ISO-R 616 were
determined by dropping each briquette from a height of 180 cm onto a steel plate and
measuring the percentage of the sample retained on the sieve having an opening of 20
mm. This was repeated until all the parts of the briquettes passed through the sieve. The
sum of the percentages is called as the Ashatter indexBof the briquette.
The compressive strength of the briquettes were determined using an Instron table
model 1195 testing machine. The flat surface of the briquette sample was placed on the
horizontal metal plate of the machine. A motorised screw slowly reduced the distance
between this metal plate and a second one parallel to it. An increased load was applied
at a constant rate until the briquette failed by cracking or breaking. Compressive strength
was calculated dividing the load at the fracture point by cross-sectional area of plane of
fracture.
The water resistance of the briquettes were tested by immersing them in a glass
container filled with distilled water at room temperature and measuring the time required
for dispersion in water.
Thermogravimetric analyses were performed using a Shimadzu TG41 thermal ana-
lyzer. Forty-milligram samples after grinding to pass 250 mm sieve were spread
Table 1
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Analysis results of the olive refuse and paper mill waste samples as received
Ž. Ž. Ž.
Sample Moisture Ash Volatile matter Gross calorific C % H % N %
Ž. Ž. Ž. Ž .
% % % value MJrkg
Olive refuse 7.5 5.0 67.5 21.4 39.0 4.8 1.5
Paper mill waste 9.0 15.5 65.5 13.0 35.2 4.9 0.2

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S. Yaman et al.rFuel Processing Technology 68 2000 23–3126
uniformly on the bottom of the crucible made of alumina. The samples were oxidised in
a dynamic dry air atmosphere of 40 ml miny1. Temperature was raised from ambient to
1273 K with a heating rate of 40 KPminy1.
3. Results and discussion
3.1. Combustion characteristics of the oliÕe refuse
The burning profile of the olive refuse is shown in Fig. 1. After releasing the
moisture content, the burning profile can be divided into two regions: the rapid burning
region and the slow burning region. First, as temperature increased, a sudden loss in the
mass of the sample occurred at 481 K, representing the release of some volatiles and
their ignition. In the rapid burning region, the rate of the mass loss proceeded so rapidly
that it reached its maximum value of 7.8 mgrmin at 529 K and it immediately slowed
down to 1 mgrmin at 641 K. Since the volatile matter content of the olive refuse was as
Fig. 1. Burning profile of the olive refuse.

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S. Yaman et al.rFuel Processing Technology 68 2000 23–31 27
high as 73% on the dry basis, the releasing and consequently, ignition of the volatiles
under oxidising atmosphere can be attributed to the rapid loss of mass. Likewise, the
oily components of the olive refuse may have accelerated the burning. Then, in the other
region, outer surfaces of the partly burned olive refuse particles were covered with the
forming ash and diffusion of oxygen through this layer into unburned combustible parts
became harder. Therefore, burning rate apparently decreased and consequently, some
small losses in the mass of the sample continuously went on as long as temperature was
increased up to 1273 K, indicating the slow burning of the partly carbonized residue. On
the dry-ash free basis, 62.8% of the combustible part burned in the first region, whereas
37.2% of the same burned in the second region. It is concluded that most of the calorific
value probably originated from the rapid burning region. These results showed that
ignition of the olive refuse was very easy but its burning does not proceed in a uniform
and regular regime. Under these circumstances, it is hard to maintain steady heating by
burning olive refuse directly. However, olive refuse can be burned after blending with
other fuels.
3.2. Briquetting of the oliÕe refuse
Some experiments were conducted to determine optimum briquetting pressure and
moisture content of the olive refuse sample. In order to determine the optimum
briquetting pressure, olive refuse having the moisture content of 7.5% was briquetted
under 150, 200, and 250 MPa pressures. Results of these experiments are shown in
Table 2.
Shatter index and compressive strength represent the level of the mechanical strength
of the briquettes against physical effects. Therefore, their values must be as high as
possible. With respect to these results, under 150 MPa pressure, compressive strength
was higher than those obtained under higher pressures. When pressure increased to 200
MPa, the highest shatter index was determined. However, compressive strength affected
negatively. The results of the experiments showed that increasing briquetting pressure
improved water resistance. However, the lowest mechanical strength results belonged to
the experiments carried out at 250 MPa. The effect of the briquetting pressure on the
mechanical strength of the briquettes is highly complex. Pressure provides the approach
of the biomass particles, decreasing the distance between them. Consequently, the
contact of the surfaces of the particles becomes augmented and gaps between them are
filled. However, in order to obtain firm briquettes, briquetting pressure should be
Table 2
Effect of the briquetting pressure on the strength of the olive refuse briquettes
Briquetting pressure Shatter index Compressive strength Water resistance time
2
Ž. Ž . Ž.
MPa kgrcm min
150 367 33 133
200 468 25 142
250 330 15 160

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S. Yaman et al.rFuel Processing Technology 68 2000 23–3128
selected at the optimum value. As the briquetting pressure increases, first, mechanical
strength of the briquettes increases as a result of the plastic deformation. On the other
hand, related to the reversible nature of the plastic deformation above an optimum
briquetting pressure, a sudden dilatation takes place and consequently, some fractures
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and splits appear in the briquette 6 . Results in Table 2 confirmed this fact for 250 MPa.
Minimum shatter index and compressive strength values were measured under 250 MPa.
The highest results of shatter index and compressive strength were determined for 200
and 150 MPa, respectively. It is apparent that the selection of the optimum briquetting
pressure should be done between 200 and 150 MPa. Since, the water resistance time for
200 MPa was longer than that for 150 MPa, 200 MPa was selected as the optimum
briquetting pressure. Then, briquetting pressure was fixed at 200 MPa, and moisture
content of the olive refuse was changed between 5% and 15%. Results of these
experiments are given in Table 3.
These results designated that decreasing moisture content to 5% led to a serious
reduce in the shatter index, compared with that for 7.5% of moisture content. Likewise,
compressive strength and water resistance also decreased. When moisture content
increased to 15%, some increase took place in the compressive strength. Although
shatter index for 15% moisture content was higher than that for 5% moisture content, it
was considerably lower than the result of the experiment in which moisture content was
7.5%. On the other hand, the lowest water resistance time was observed when the
moisture content increased to 15%. On the basis of the results of these experiments, 200
MPa briquetting pressure and 7.5% of moisture content were allowed as the optimum
values of these parameters.
3.3. Briquetting of oliÕe refuse with paper mill waste
In order to obtain more firm briquettes from the olive refuse, mechanical strengths of
the briquettes must be increased. For this purpose, into olive refuse, addition of a more
fibrous biomass sample having similar combustion behaviour, moisture, and volatile
matter contents should be investigated. In fact, moisture and volatile matter contents of
the paper mill waste and the olive refuse are very close to each other. However, since
the ash content of the paper mill waste was higher, its calorific value was lower.
Burning profile of the paper mill waste is illustrated in Fig. 2.
It can be seen from Fig. 2 that there is a good similarity in the burning characteristics
of both biomass samples. After release of the moisture content, a sudden loss in the
Table 3
Effect of the moisture content on the strength of the olive refuse briquettes
Moisture content Shatter index Compressive strength Water resistance time
2
Ž. Ž . Ž .
%kgrcm min
5 164 22 62
7.5 468 25 142
15 235 29 26

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S. Yaman et al.rFuel Processing Technology 68 2000 23–31 29
Fig. 2. Burning profile of the paper mill waste.
mass occurred and following this, some small losses appeared. The main peak began at
510 K and finished at 689 K. Maximum rate of loss was 11 mgrmin at 577 K. On the
dry-ash free basis, 70.6% of the combustible part burned during rapid burning region
and only 29.4% burned in the slow burning region.
The own briquetting capacity of the paper mill waste was investigated under different
conditions. The results of these experiments are tabulated in Table 4.
Table 4
Analyses results of the briquettes obtained from paper mill waste
Moisture content Briquetting pressure Shatter index Compressive strength Water resistance
2
Ž. Ž . Ž . Ž .
% MPa kgrcm time min
5 250 36227 815 19
9 250 155802 1299 31
15 250 168875 1057 15
9 150 43604 1249 25
9 200 84249 1096 29

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S. Yaman et al.rFuel Processing Technology 68 2000 23–3130
Paper mill waste having 9% of moisture content was briquetted under 150, 200, and
250 MPa pressures. These results showed that at fixed moisture content, increasing
briquetting pressure so improved mechanical strength that very strong briquette having a
shatter index of 155802 can be produced under 250 MPa. Likewise, the compressive
strength of these briquettes was very high. However, when the moisture content of the
paper mill waste was changed to 15%, some increase in the shatter index and some
reduction in the compressive strength were determined, whereas when the moisture
content decreased to 5%, both of the parameters were affected negatively. On the other
hand, water resistance times were shorter than those of the olive refuse. Nevertheless, it
can be concluded from these results that addition of the paper mill waste into the olive
refuse can give rise to the mechanical strengths of the briquettes to be produced.
Olive refuse and paper mill waste samples having their own original moisture
contents were blended in equal ratios and then this blend was briquetted under 200 MPa
pressure. Shatter index of this briquette was calculated as 4813, and compressive
strength was measured as 319 kgrcm2. Water resistance time was determined as 27 min.
Differential thermogravimetry technique was also applied to the mixture and the shape
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of the curve was seen as the average of the two parent biomass samples Fig. 3 .
Fig. 3. Burning profile of the mixture.

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S. Yaman et al.rFuel Processing Technology 68 2000 23–31 31
4. Conclusion
Of the biomass samples, olive refuse and paper mill waste can be used in the
production of durable fuel briquettes. The mechanical strength of the briquettes obtained
from only olive refuse was quite low. However, strong briquettes can be produced using
fibrous paper mill waste by itself or adding it to the olive refuse. When olive refuse and
paper mill waste were blended and then this blend was briquetted, both strong and good
quality briquettes can be produced. Therefore, these abundant and cheap biomass
samples can be used as an alternative energy source.
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