Waste Management 30 (2010) 804–807

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Waste Management

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Briquetting of charcoal from sugar-cane bagasse fly ash (scbfa) as an alternative fuel

S.R. Teixeira a,*, A.F.V. Pena a, A.G. Miguel b

a Department of Physics, Chemistry and Biology, Universidade Estadual Paulista – UNESP, P.O. Box 467, 19060-080 Presidente Prudente, SP, Brazilb Usina Alto Alegre S.A., Fazenda Alta Floresta – Distrito de Ameliópolis, 19140-000 Presidente Prudente, SP, Brazil

a r t i c l e i n f o a b s t r a c t

Article history:Accepted 10 January 2010Available online 4 February 2010

0956-053X/$ - see front matter � 2010 Elsevier Ltd.doi:10.1016/j.wasman.2010.01.018

* Corresponding author. Tel.: +55 18 32295355; faxE-mail address: rainho@fct.unesp.br (S.R. Teixeira)

Brazil is the largest worldwide producer of alcohol and sugar from sugar-cane and has an extensive alter-native program for car fuel which is unique. The objective of this work is to offer one management optionof a solid residue produced by this industrial segment. The pressed sugar-cane bagasse is burned to pro-duce steam and electricity by cogeneration. The combustion yields both bottom and fly ashes which con-tain high amounts of silicon oxide as a major component. Fly ash which contains a high volume (>30% byweight) of charcoal was used in this work. The ash was sieved to separate the thick charcoal from inor-ganic materials which are concentrated in the thinner fraction. The briquettes were hand pressed usingcharcoal mixed with a binder (starch) obtained from cassava flour (a tropical root). The results (density,mechanical resistance) obtained with 8% by weight of starch binder are presented here. Thermogravimet-ric analysis (TGA) and differential scanning calorimetry (DSC) were used to characterize the ashes and thebriquettes. The results show that sugar-cane bagasse fly ash (SCBFA) can be used to produce briquetteswith an average density of 1.12 g cm�3 and an average calorific value of 25,551 kJ/kg.

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1. Introduction

In recent years, energy sources which cause less pollution (bio-diesel and ethyl alcohol) have emerged as alternatives to fossilfuels (Proálcool, 2001). Brazil is the world’s largest producer ofalcohol and sugar from sugar cane (Ethanol fuel in Brazil, 2009).The fast carbon cycling in sugar-cane production and use areresponsible for the CO2 emission reduction (Macedo, 1992). Brazilis the only country worldwide that has an extensive alternativeprogram for automobile fuel. Today more than one million flex fuel(alcohol and/or gasoline) cars are in use, and more than 75% of thenew cars produced in the country use this system. The BrazilianPROALCOOL program (Proálcool, 2001) was 33 years old in 2008,and today almost five million cars (�25% of the nation’s total)which run on alcohol or flex fuel are in use. The new technologyof flex-fuel vehicles which was developed in 1990 decade and ap-plied to new cars in 2003 by Volkswagen (Proálcool, 2001) revivedthe program.

The strong internal demand and great interest shown by indus-trialized countries for ethyl alcohol facilitated competition in Brazilfor the implementation of a substantial number of factories for theproduction of alcohol and sugar. The necessity for expansion of thissector drives the national industry to improve the technologies forsugar/alcohol and sugar-cane production (new plant varieties, irri-gation, new cutting and harvesting technologies). The estimated2007/2008 sugar cane harvest (CONAB, 2009) is 629 Mton to pro-

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duce sugar (44.6%) and alcohol (55.4%). The volume of fly and bot-tom ash that will be produced in this harvest is �3.2 Mton(1000 kg cane ? 250 kg bagasse ? 6 kg ash) (FIESP/CIESP, 2001).

In the functioning of these factories, sugar-cane is ground, andthe resulting product is used for sugar extraction or in a fermenta-tion process to produce alcohol. Currently, sugar-cane bagasse isburned in a boiler to produce steam utilized in factory processesand also to power turbines for the production of electrical energywhich supplies the energy needs of the factories with the excessbeing commercialized in the region. In 2008, sugar cane productsrepresented 16.4% of the total energy produced in Brazil, and pro-duction is subsequently increasing (BEN, 2009).

In the bagasse burning process, black fumes are expelledthrough the chimney (fly ash recovered in the gas washer), and aclearer ash falls to the bottom of the boiler (bottom ash). Tens ofthousands of tons of this fly ash (principally carbon and silica)are released into the atmosphere (airborne fly ash) every yearand can be a health hazard. All these solid residues of bottomand fly ash collected at the smoke washer, are again dumped intothe environment, increasing the concentration of sand in the soiland making it impermeable due to the fine charcoal powder. Inthe present work (see Section 3), it was determined that the blackfumes that pass through the gas washer contain gases and solidparticles (organic and inorganic). The inorganic particles are com-posed mainly of charcoal and a small volumetric portion of inor-ganic materials (silicon, iron oxides and other minerals). Todaynot all mills have filters or gas washers, but Brazilian environmen-tal legislation has mandated a time limit for improvement of thispollution control.

Fig. 1. Screw which press the fly ash through a stainless steel tube to lessen itsmoisture.

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The briquetting process converts the charcoal powder into highdensity energy-concentrated fuel pellets or other different geomet-ric forms (for example, cylindrical rods). Agricultural wastes bri-quettes are produced and utilized in different parts of the world(Charcoal Briquette, 2002; Kibwage et al., 2006; Brito and Nucci,1984; Faria and Brito, 1981; FAO, 1987; Smith, 2004; Erikssonand Prior, 1990). Because charcoal briquettes are not used in Brazil,there is only one vegetal charcoal briquette factory that export al-most all of the material produced. In general, the process beginswith burning wood for charcoal from which briquettes areproduced.

In the search for new alternative sources of ecologicallyfriendly energy, the utilization of charcoal powder from fly ashfor the production of briquettes has become a good alternative.In the production of charcoal, this residue is not dumped on thesoil but is used to produce energy, and trees are saved. Conven-tional charcoal production in Brazil is a destructive element ofnatural forests. The conversion of this residue into charcoal bri-quettes could provide a new market for factories. With thegrowth of this industrial sector, charcoal can be substituted aspart of the wood charcoal in some industrial processes to produceenergy and lessen deforestation. In published works about char-coal briquette production from sugar-cane bagasse (Kibwageet al., 2006; Smith, 2004; Zandersons et al., 1999; Karstad,2003), the authors propose to carbonize bagasse to produce char-coal briquettes. In Brazil, the sugar-cane/alcohol industries reduceall bagasse is burned to produce steam and electrical energy gen-erating the bottom and fly ash; today almost all industries aresmall thermal-electrical power plants (co-generating electric en-ergy). The steam and part of the electrical energy produced isused by the industry, and the energy surplus is sold to companiesresponsible for energy distribution.

The interest in this work is motivated by the environmental as-pect of protecting the atmosphere, the soil and the health of thepeople who live and work near the mills, the volume of this kindof fly ash produced and an increase in the activities of the sugar–alcohol sector in Brazil. Therefore, the objective of this study is todemonstrate the feasibility of recovering fine charcoal from flyash to produce charcoal briquettes. The use of charcoal collectedin the gas washer from the industry chimney to produce fuel mate-rial (briquettes) as is proposed in this work has not been studied asis shown by the small number of references cited. To attain thisobjective, the inorganic concentration in the SCBFA will be de-creased by sieving, then mixing with gum (binder) and pressingto produce briquettes. After drying, the product will undergo sev-eral tests such as residual humidity, density, mechanical resis-tance, residual ash and caloric value.

Fig. 2. Picture of the briquettes in different views.

2. Material and methods

Fly ash samples were collected at the solid/water exit of the gaswasher (Fig. 1) at the Alto Alegre mill in the nearby Presidente Pru-dente city in São Paulo State, Brazil. The SCBFA was passed througha 0.125 mm (120 Mesh) sieve, and the gross fraction (>0.125 mm)was used to prepare the briquettes. The moisture and organic andinorganic (ash) fractions were obtained using a laboratory ovenand balance. The values presented are the average of five samples(5 g each) dried (at 110 �C for 24 h) and then fired at 800 �C.

Thermogravimetric analysis (TGA) and differential scanning cal-orimetry (DSC) (TA Instruments model SDT – Q600) were used tocharacterize the ashes and briquettes (humidity, organic and inor-ganic concentrations and the homogeneity of the charcoal/binderblend). The calorific value (average value of three samples) wasdetermined using a bomb calorimeter system (Perkin Elmer modelKL-5) according to the guidelines of the Brazilian normalization

(ABNT, 1984). The chemical composition of the ash was deter-mined by X-ray fluorescence (Shimadzu, model XRF – 1800).

A binding material must be used (Charcoal Briquette, 2002;Smith, 2004; Fontes et al., 1991) to strengthen briquettes. In gen-eral, corn starch is used to produce the binder material; however,in this work cassava (or manioka) starch was utilized because itis widely produced in Brazil. The binder was prepared in the usualmanner; i.e., the starch was added to boiling water until polymermolecules (gum or porridge) were formed (FAO, 1987; Smith,2004). The briquettes were prepared in two different ways: (1)mixing the charcoal powder with the gum (8% by weight) until ahomogeneous paste was formed; and (2) mixing charcoal powder,starch (8% by weight) and water and heating to boiling until a pasteformed.

The cylindrical briquettes (/ = 30 mm) were pressed (Fig. 2)using a manual uniaxial hydraulic press and a steel cylindricalmold. An applied compression force of 5 tons was maintained for1 min on each sample.

3. Results and discussion

According to industry data, the SCBFA in the gas washer exit has�40% humidity. The average concentrations of organic and inor-ganic materials obtained in the laboratory using an oven and bal-ance to dry samples were 33% and 67%, respectively. Theseresults are close to those shown by TGA measurements (Fig. 3).

Considering the national sugar-cane production in 2008/2009(BEN, 2009) and that each ton produces 6 kg of ash (FIESP/CIESP,2001) containing �33% charcoal, the estimated volume of charcoalthat will be produced is greater than one million tons in the 2009harvest. Because this research about charcoal in SCBA is new, noreference for this value is available.

Fig. 3. Themogravimetric (TG) data of the SCBFA.

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The fly ash collected in the factory has a high moisture content(30–70%) depending on the process (filter press, belt press, extru-sion or in natura) used to reduce moisture after a pass throughthe gas washer. The fly ash is classified in two fraction: fine char-coal powder (<1 mm) and gross charcoal (from 1 to 5 mm). Thisparticle size distribution was determined by passing the ashthrough different sieves. Thermogravimetric analysis data showsthat the inorganic material is concentrated mainly in the fine frac-tion (<1 mm) separated using an 18 mesh (1 mm) screen. The bri-quettes were prepared by using the gross fraction (>1 mm).

Although the inorganic compounds are concentrated in the finefraction, they are present in the gross fraction that will produce ashafter briquette burning. Therefore, it is important to know the ashcomposition and component concentrations for further processing.The chemical composition of the fly ash is shown in Table 1. A com-parison of the chemical compositions of the sugar-cane bagasseash (SCBA) used in this work with other SCBA data in the literature(Eriksson and Prior, 1990; Teixeira et al., 2008) show differencesdue to variations in the soil where the sugar cane was grown. Mostof the ash comes from syngenetic minerals (minerals within theplant tissue before it burns), reflecting the mineralogical composi-tion of the soil in which the plant material grew (Tixeira et al.,2002). These chemical ash compositions are unchanged by thecombustion process, and the major phase in SCBA is crystalline sil-ica (Teixeira et al., 2008).

Although the volume of charcoal is larger than the mineral vol-ume, its weight represents �35% of the total fly ash mass. There-fore, it is important to reduce the inorganic material to obtain abetter relationship between heat production and the charcoal masswith a minor residual ash volume; e.g., to use this charcoal in steelproduction, a maximum limit value (<12%) of ash in the charcoal(or briquette) is required.

Preliminary compression tests in the axial cylinder directionshowed that the briquettes acquired greater density and mechan-ical resistance when the charcoal powder was ground to a very finegrain size before the preparation of the paste. The mechanicalresistance to compression (MRC) is very good (>7 MPa), facilitatingthe handling of the briquettes and the ability to store them in largepiles. A good mechanical resistance is important for the handling,

Table 1Chemical composition (%) of the inorganic fraction in the ash by X-ray fluorescence –XRF (Teixeira et al., 2008).

SiO2 Al2O3 Fe2O3 K2O CaO MgO MnO TiO2 P2O5

Ash 85.58 5.25 1.31 3.46 2.08 1.09 0.08 0.32 0.54

piling and transporting of the briquettes. This MRC value is nearthe values obtained for briquettes produced using different kindsof wood (Brito and Nucci, 1984). New studies are in progress toexamine different concentrations of binder and compression pres-sures for the best conditions during the production of thebriquettes.

In the last 5 years, many changes were instituted in the residuecollection process in the sugar-cane/alcohol industry, resulting inresidues with a lower humidity content and a higher volume ofwater re-used by the process. TGA data show (Teixeira et al.,2007) that the dried SCBFA in natura had only 20% organic materialand 77% residual mass (ash). Today with the use of filter and beltpresses, the charcoal concentration is in the order of 34% and62% residual mass (ash) as is shown in Fig. 3.

Part of one briquette was submitted for TG analysis (Fig. 4). TGAdata show that the organic concentration in the briquette in-creased to 53% and the ash decreased to 35%. These changes in val-ues are associated with the sieve process and the addition of thebinder (organic material). TGA data (shown in two peaks) are dis-cussed after the next figure.

Fig. 5 displays thermal analysis results using DSC obtained for:(a) a briquette prepared by boiling the mixture of charcoal, starchand water (before pressing); and (b) a briquette obtained by press-ing charcoal powder mixed with a binder (starch and water heatedat 100 �C). Sample (a) demonstrates a doublet between 450 and500 �C; the first peak is associated with the charcoal burning,and the second peak is associated with the polymer burning. In(b) there is only one large peak, indicating a blend formation withonly one peak burning, i.e., a more homogeneous charcoal–poly-mer mixture. After these results, all the samples were preparedby the second method.

Curve (b) in Fig. 5 shows two nearby peaks at 300 and 500 �Cthat are in agreement with the loss of mass observed in the TG re-cord (Fig. 4). These peaks indicate the presence of organic matternot decomposed (cellulose and lignin) in the bulk of the charcoal.The high volume of bagasse fired and the high rate of firing prob-ably did not carbonize the bulk of the larger particles of bagassefarther from burning points.

The density of the briquettes measured with a balance and cal-iper varied from 0.91 to 1.33 g/cm3. These values are smaller thanthe values obtained from eucalyptus charcoal (1.41 g/cm3) usingtar as a binder (Brito and Nucci, 1984) but are in good agreementwith the values (1.08 g/cm3) obtained using others kinds of bindersand wood (Fontes et al., 1991).

The calorific value (the mean of three samples) was 25,551 kJ/kg, as determined by using a calorimeter according to the guide-

Fig. 4. Themogravimetric (TG) data of the briquette.

Fig. 5. Thermograms (DSC) of the briquettes and binder: (a) charcoal + starch and(b) charcoal + starch polymer.

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lines of Brazilian normalization; the amount of residual ash was13.2% (briquettes prepared with sieved charcoal, >1 mm).

Brazil possesses one of the largest charcoal-based industries inthe world, and charcoal represents the main wood fuel in demandin the country. Brazilian steel and ferroalloy production demandhigh volumes of charcoal. Consequently, this sector has divertedan enormous amount of wood fuel resources into charcoal produc-tion. Households occupy second place in terms of wood fuel con-sumption in Brazil for domestic use (Brito, 1997). Therefore,these kinds of briquettes can reduce the consumption of charcoaltaken from existing forests.

4. Conclusion

Results show that charcoal from sugar-cane bagasse fly ash canbe used to produce briquettes. This kind of briquette is a new op-tion of renewable fuel, and its utilization can reduce deforestationfor charcoal production or for use as wood fuel.

Results also show that the procedure adopted for the produc-tion of briquettes based on charcoal powder from the ash of su-gar-cane bagasse and cassava starch as the binder is efficient,yielding briquettes with properties that meet market technicalrequirements.

Moreover, the most representative parameters are compatiblewith or better than those parameters obtained utilizing othersources of charcoal. The average briquette properties obtainedare: a calorific value of 25,551 kJ/kg, a density of 1.12 g/cm3, amechanical resistance to compression of >7 MPa and a residualash of 13.2% after burning.

Acknowledgments

The authors wish to thank FUNDUNESP for the partial fundingand FAPESP for the laboratory financial support (2008/04368-4).

We are grateful to Usina Alto Alegre for the samples and collabora-tion; Dr. A.A. Paccola and J.E. Gonçalves (FCA/UNESP) for collabo-rating on the calorific value determination. We also thankundergraduate students for assistance in preparing the samples.

References

ABNT – Associação Brasileira de Normas Técnicas, NBR 8633 Carvão Vegetal –Determinação do Poder Calorífico, Outubro 1984. <http://www.abnt.org.br/catalogo>.

BEN – Balanço Energético Nacional, Ministério de Minas e Energia, 2009. Rio deJaneiro, Brasil. <http://www.mme.gov.br/mme/menu/todas_publicacoes.html>.

Brito, J.A., Nucci, O., 1984. Estudo Tecnológico da Madeira de Pinus spp para aprodução de carvão vegetal e briquetagem. Instituto de Pesquisas e EstudosFlorestais – IPEF, Circular Técnica no 26, Brasil. <http://www.ipef.br/publicacoes/ctecnica/nr138.pdf>.

Brito, J.O., 1997. Fuelwood utilization in Brazil. Biomass Bioenergy 12 (1), 69–74.Charcoal Briquette: How Products are Made. In: Stacey L. Blachford (Ed.), Gale

Cengage, 2002. <http://www.enotes.com/how-products-encyclopedia/charcoal-briquette>.

CONAB – Companhia Nacional de Abastecimento, 2009. Acompanhamento da SafraBrasileira Cana-de-Açucar, Brasília, Brasil. <http://www.conab.gov.br/conabweb/download/safra/2cana_de_acucar.pdf>.

Eriksson, S., Prior, M., 1990. The briquetting of agricultural wastes for fuel. FAOEnvironment and Energy Papers, Food and Agriculture Organization (FAO),Publication Division, Rome, Italy. <http://www.fao.org/docrep/T0275E/T0275E00.htm>.

Ethanol fuel in Brazil, 2009. <http://en.wikipedia.org/wiki/Ethanol_fuel_in_Brazil>.FAO, Food and Agriculture Organization of the United Nations, 1987. Forestry Paper

41, Briquetting of charcoal. In: Simple Technologies for Charcoal Making(Chapter 11). <http://www.fao.org/docrep/X5328E/x5328e0c.htm>.

Faria, L.M., Brito, J.O., 1981. Carvão vegetal pulverizado como opção energética,Instituto de Pesquisas e Estudos Florestais – IPEF, Circular Técnica no 138,Piracicaba – SP, Brasil. <http://www.ipef.br/publicacoes/ctecnica/nr138.pdf>.

FIESP/CIESP – Federação/Confederação das Indústrias do Estado de São Paulo, 2001.Ampliação da Oferta de Energia Através de Biomassa. <http://www.fiesp.com.br/publicacoes/pdf/ambiente/relatorio_dma.pdf>.

Fontes, P.J.P., Quirino, W.F., Brito, J.O., 1991. Aglutinantes para briquetagem decarvão vegetal, Instituto de Pesquisas e Estudos Florestais – IPEF, Brasil. <http://www.funtecg.org.br/arquivos/aglutinantes.pdf>.

Karstad, E., 2003. Canecoal: charcoal from sugar cane bagasse, Renewable EnergyPolicy Project (REPP), Washington, DC, USA. <www.repp.org/discussiongroups/resources/stoves/Karstad/canecoal/canecoal.html>.

Kibwage, J.K., Munywe, S.N., Mutonyi, J., Savala, C.N., Wanyonyi, E., 2006. OrganicResource Management in Kenya: Perspectives and guidelines. In: RecyclingWaste into Fuel Briquettes, Kenya (Chapter 15). <http://www.formatkenya.org/ormbook/Chapters/chapter15.htm>.

Macedo, I.C., 1992. The sugar cane agro-industry: its contribution to reducing CO2

emissions in Brazil. Biomass Bioenergy 3 (2), 77–80.Proálcool – Programa Brasileiro de Álcool, 2001. Biodieselbr Online Ltda. <http://

www.biodieselbr.com/ proalcool/pro-alcool.htm>.Smith, A., 2004. Fuel from the fields: a guide to converting agricultural waste into

charcoal briquettes. Massachusetts Institute of Technology – MIT,Massachusetts, USA.

Tixeira, S.R., Dixon, J.B., White, G.N., Newsom, L.A., 2002. Charcoal in soils: apreliminary view. In: Soil Mineralogy with Environmental Applications, SSSABook Series: 7, Soil Science Society of America, Madison, WI, USA. pp. 819–830(Chapter 28).

Teixeira et al., 2007. UNINDU.Teixeira, S.R., Souza, A.E., Santos, G.T.A., Pena, A.F.V., Miguel, A.G., 2008. Sugar cane

bagasse ash (SCBA) as a potential quartz replacement in red ceramic. J. Am.Ceram. Soc. 91, 1883–1887.

Zandersons, J., Gravitis, J., Kokorevics, A., Zhurinsh, A., Bikovens, O., Tardenaka, A.,Spince, B., 1999. Studies of the Brazilian sugarcane bagasse carbonizationprocess and products properties. Biomass Bioenergy 17, 209–219.