Development of Fuel Briquettes from Biomass-Lignite … · Development of Fuel Briquettes from Biomass-Lignite Blends ... as coal briquette binder; such as molasses, crop residues,

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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Engineering and Applied Chemistry, Bangkok,Thailand, 1-3 December 2004.

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[3] Husain Z., Zainac Z., and Abdullah Z.,Briquetting of palm fiber and shell fromthe processing of palm nuts to palm oil,Biomass and Bioenergy, 2002; 22: 505-509.

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[5] Rubio B., Izquierdo M.T. and Sequra E.,Effect of binder addition on the mecha-nical and physicochemical properties oflow rank coal char briquettes, Carbon,1999; 37: 1833-1844.

[6] Richards S. R., Physical testing of fuelbriquettes, Fuel Processing technology, 1990;25: 89-100.

[7] Gurbuz-Beker U., Kucukbayrak S. andOzer A., Briquetting of Afsin-Elbistanlignite, Fuel Processing technology, 1998; 55:117-127.