Development of Fuel Briquettes from Biomass-Lignite … · Development of Fuel Briquettes from...
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Chiang Mai J. Sci. 2008; 35(1) 43
Chiang Mai J. Sci. 2008; 35(1) : 43-50
www.science.cmu.ac.th/journal-science/josci.html
Contributed Paper
Development of Fuel Briquettes from Biomass-LigniteBlendsSuparin Chaiklangmuang*, Suwit Supa, and Prattana KaewpetDepartment of Industrial Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand.
*Author for correspondence; e-mail: [email protected]
Received : 27 September 2007
Accepted : 24 October 2007.
ABSTRACT
The research was to study the briquetting of lignite combined with biomass binders.
The biomass binders were rice husk and sawdust treated with sodium hydroxide. The ratio of
biomass binders and lignite was 50:50 wt./wt. Rice husk was treated with 3% wt/v sodium
hydroxide at 80oC with a heating time of 1.5-4.5 hours, while sawdust was treated with a
series of sodium hydroxide solution with a concentration of 7-13 % wt/v at the same
temperature. The influence of time for sawdust digestion was investigated by increasing the
time from 1.5 to 2.0 and 2.5 hours. The briquettes were formed in the cylindrical mold and
the hydraulic press was used in the experiments. The mechanical, physical and combustion
tests were performed. The investigations indicated that mechanical and physical tests related to
NaOH concentration and digestion time depending on biomass used. The experiments showed
that the rice husk and sawdust treated with sodium hydroxide would yield the quality of
biomass-lignite briquetting.
Keywords: biomass binder, briquetting, biomass, sodium hydroxide.
1. INTRODUCTION
Thailand is a suitable base for the
production of a wide variety of crops. Rice
is dominant, but the production figures are
also high for cassava, sugar cane, maize and
soybeans. Agricultural wastes and fuelwood
can also be viewed as a potential raw material
supplier for fuel production. The wood
industry constitutes a largely untapped source
of material for fuel briquetting. Rice-husk and
sawdust are the materials known to be used
as raw materials for fuel briquettes of any
quantity. Meanwhile, Thailand has large
reserves of low-rank coal (e.g., lignite and
sub-bituminous), meaning that they posses a
relatively high amount of moisture and low
calorific value. In order to enhance the quality
of low-rank coal, briquetting may be
considered good utilization technology for
low grade lignite. It turned out that the fuel
briquettes from biomass-lignite blends are
excellent substitutes for alternative
conventional fuels. Many materials are used
as coal briquette binder; such as molasses, crop
residues, pulp wastes liquor, biomass and
inorganic materials. Some components in
biomass are heated or hydrolyzed so that the
44 Chiang Mai J. Sci. 2008; 35(1)
biomass can be used as binder, which is
commonly called biomass binder. Therefore,
this research was to study the briquetting of
lignite combined with biomass binders,
namely rice husk and sawdust treated with
sodium hydroxide. This research investigated
the effect of NaOH concentrations and
digestion times on briquette forming and the
physical properties of the fuel briquettes.
2. MATERIALS AND METHODS
2.1 Raw materials
The coal used was collected from lignite
mine located in the North of Thailand and
the biomass samples, rice husk and saw dust,
came from the same region. All samples were
grounded to 1.0 mm.
2.2 Preparation of biomass binder
Regarding to our previous work [1], rice
husk was treated with 3% wt/v sodium
hydroxide at 80oC with a heating time of 1.5,
3.0 and 4.5 hours, while sawdust was treated
with a series of sodium hydroxide solution
with a concentration of 7, 9, 11 and 13 %
wt/v at the same temperature of rice husk
experiments with a heating time of 1.5 hours.
The influence of time for sawdust digestion
was investigated by increasing the time from
1.5 to 2.0 and 2.5 hours. All biomass binders
were dried in the atmosphere.
Figure 1. Briquetting machine and mould.
Chiang Mai J. Sci. 2008; 35(1) 45
2.3 Briquetting process
According to our previous research
results, the optimal ratio of biomass binders
and lignite was 50:50 wt./wt. CaO was added
into the mixture to prevent the emission of
sulfur pollutants. The pressuring capacity of
hydraulic press used in the experiments was
at a constant pressure of 1,500 Ibf/in2 (psi).
The briquettes were formed in the cylindrical
mold with a hole at the center. The hole was
6.5 cm high and 2 and 8.5 cm inner and outer
diameters respectively as shown in Figure 1.
2.4 Physical properties of briquette testing
Compression strength, water resistance,
impact resistance and shatter index tests
were performed according to the methods
described in Refs 2-5.
The compressive strength of each
briquette was measured by using the Universal
Testing Machine, model 157835, Marui
Company. The flat surface of briquette sample
was placed on the horizontal metal plate of
machine. An increased load was applied at a
constant rate until the briquette failed by
cracking. Compressive strength was calculated
dividing the load at the fracture point by cross
sectional area of plane of fracture. The water
resistances of briquettes were tested by
immersing them in a container filled with cold
tap water and measuring the time required
for the onset of dispersion in water. Each
briquette sample was repeatedly dropped
from a stationary starting point at 2 m height
onto a concrete floor until it fractured. The
number of drops of each briquette broke
into pieces were recorded, the so-called
impact resistance was falling times. The shatter
index was determined by dropping each
briquette from a height of 1.8 m onto a steel
plate and measuring the percentage of sample
retained on the sieve having an opening of 20
mm. This was repeated until all parts of
briquettes passed through the sieve. The sum
of the percentages is called as the shatter index
of the briquette.
3. RESULTS AND DISCUSSION
Table 1 shows the analysis results of raw
materials according ASTM standards. Con-
sidering the compressive strength, previous
and present research results show that 3% and
7% wt/v NaOH solution used to prepare
rice husk and sawdust binders, respectively,
were suitable NaOH concentrations that gave
the highest compressive strength values.
Figure 2 illustrates biomass-lignite
briquettes of rice husk-coal briquettes (a) and
saw dust-coal briquettes (b) at several digestion
times. It was found that at the heating time of
1.5 hours and sodium hydroxide concentrates
of 3% wt/v for rice husk and 7% wt/v for
saw dust, the briquettes attained more durable
shapes than the others by observation.
Table 1. Analysis results of raw materials.
coal saw dust rice husk
Proximate analysis (%)
moisture 12.2 8.7 6.0
volatile matter 38.3 61.3 54.3
ash 21.9 11.8 12.6
fixed carbon 27.6 18.2 27.1
Gross heating value, (cal/g) 3828 4074 4082
46 Chiang Mai J. Sci. 2008; 35(1)
Figure 2. Lignite-biomass briquettes (a) rice husk-coal briquettes and (b) saw dust-coal
briquettes at 3% wt/v and 7% wt/v NaOH, respectively.
(a)
(b)
Chiang Mai J. Sci. 2008; 35(1) 47
Figure 3. Relations between digestion times and compressive strength values of rice husk-
coal briquettes (a) and saw dust-coal briquettes (b) at 3% wt/v and 7% wt/v NaOH,
respectively.
Figure 3 indicates the relations between
digestion times and compressive strength
values of rice husk-coal briquettes at 3% wt/
v NaOH and saw dust-coal briquettes at 7%
wt/v NaOH. The results indicated that both
biomass binders treated with suitable
concentration of sodium hydroxide gave the
highest compressive strength values at
digestion time of 1.5 hours.
Consistent with impact resistance, the
impact resistances of rice husk and sawdust-
lignite briquettes were maximized at the
digestion time of 1.5 hours as shown in Figure
4. According to our previous investigation [1],
briquetting could not performed at the
digestion time lesser than 1.5 hours.
(a)
(b)
48 Chiang Mai J. Sci. 2008; 35(1)
Figure 4. Experimental results of impact resistance of (a) rice husk-lignite briquettes
(b) sawdust-lignite briquettes.
(a)
(b)
For water resistance experiments, it was
found that the highest water resistance values
were obtained at the heating times of 4.5 hours
and 2.0 hours for rice husk and sawdust
briquettes, respectively. Fuel briquettes were
bonded using water-sensitive binder and
porous filter materials were included in order
to make the products water-proof. The higher
water resistance values may be more stability
of briquettes in terms of weathering resistance
[6].
Some testes were applied to determine
the shatter index. Relating to shatter index
experimental method, when all biomass-coal
briquettes were dropped more than 100 times,
they still had retained sample that could not
Chiang Mai J. Sci. 2008; 35(1) 49
passed through the 20 mm sieve. As a result,
the sum of the percentage could not be
calculated, this might imply the shatter index
values were infinity. It could be noted that
the biomass-lignite briquettes obtained were
high interaction with the digested-biomass
binders. However, some literatures reported
that the shatter index increased as the sawdust
content was increased for the blends of coals
and sawdust without the digested-biomass
binder [2, 7].
By observing ash shape after combus-
tion, it was evident that rice husk and sawdust
ashes attained durable shapes (see Figure 5).
(a)
(b)
Figure 5. Observation of ash shape after combustion, (a) rice husk-coal briquette ashes and
(b)sawdust-coal briquette ashes.
50 Chiang Mai J. Sci. 2008; 35(1)
Rice husk and saw dust binders were
prepared at 80oC with NaOH solution, when
temperature rise to 80oC, the decomposition
of compounds was occurred and lignin,
semi-cellulose and cellulose in biomass would
be removed [3-4]. This part of compounds
acted as reinforcement in the briquette. In
addition to the carbohydrate, pectin and tannin
materials could also act as binders. From the
previous and present works, it is clear that the
briquette strength increased with an increase
in NaOH concentration. However, when
the NaOH concentration was higher than
7 %wt/v, those binder components were
decomposed largely, thus reducing the ability
of biomass binders.
4. CONCLUSION
In rice husks study, it was found that at a
heating time of 1.5 hours and a sodium
hydroxide concentration of 3% wt/v, the
briquettes attained more durable shapes than
the others. The research results indicated that
sawdust treated with sodium hydroxide at a
concentration of 7% wt/v and a heating time
of 1.5 hours yielded the best sawdust-lignite
briquettes in the aspects of shape, compressive
strength value and impact resistance. The
highest water resistance values were obtained
at heating times of 4.5 hours and 2.0 hours
for rice husk and sawdust briquettes
respectively. By observing ash shape after
combustion, rice husk and sawdust ashes
attained durable shapes. Shatter index of both
coal briquettes can not illustrate results. The
experiments showed that the rice husk and
sawdust treated with sodium hydroxide
yielded the biomass-lignite briquettes with
considerable quality. Hence, design, develop-
ment and dissemination of improved
briquette production should further be carried
out because Thailand has high amount of local
raw materials that can be used as alternative
fuels.
ACKNOWLEDGEMENTS
The authors would like to acknowledge
the Faculty of Science, Chiang Mai University,
Thailand, for financial support of this work.
REFERENCES
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