Energy characterization of wood and charcoal from Savannah forest species

Abstract

The objective of this study was to evaluate the energy potential of Astronium fraxinifolium and Enterolobium gummiferum wood species that grow in the Savannah of Minas Gerais, Brazil, focusing on the production of charcoal. Two discs were removed at 1.30 m from the ground of three trees of each species, and these were later sampled into wedges that were applied in the analysis of wood characteristics and charcoal production in a muffle furnace. The extractives content and basic density of the wood species were determined, and apparent density of charcoal, ash content, heating value, and energy density of both materials were also determined. The woods under study have potential for application in energy production. Emphasis was placed on A. fraxinifolium, which presented wood and charcoal that was denser, had higher energy density, and achieved greater gravimetric yield.

Full Article

Energy Characterization of Wood and Charcoal from Savannah Forest Species

Vaniele Bento dos Santos,^a,* Edy Eime Pereira Baraúna,^b Fernando Colen,^b Talita Baldin,^b Thiago Campos Monteiro,^c and Marina Donária Chaves Arantes ^d

The objective of this study was to evaluate the energy potential of Astronium fraxinifolium and Enterolobium gummiferum wood species that grow in the Savannah of Minas Gerais, Brazil, focusing on the production of charcoal. Two discs were removed at 1.30 m from the ground of three trees of each species, and these were later sampled into wedges that were applied in the analysis of wood characteristics and charcoal production in a muffle furnace. The extractives content and basic density of the wood species were determined, and apparent density of charcoal, ash content, heating value, and energy density of both materials were also determined. The woods under study have potential for application in energy production. Emphasis was placed on A. fraxinifolium, which presented wood and charcoal that was denser, had higher energy density, and achieved greater gravimetric yield.

DOI: 10.15376/biores.18.1.1780-1787

Keywords: Energy density; Heating value; Gravimetric yield; Renewable energy

Contact information: a: Federal University of Espírito Santo (UFES), Department of Forestry and Wood Sciences, Jerônimo Monteiro, ES, Brazil; b: Federal University of Minas Gerais (UFMG), Institute of Agricultural Sciences, Montes Claros, MG, Brazil; c: Federal University of Paraná (UFPR), Curitiba, PR, Brazil; d: Federal University of São João del-Rei (UFSJ), Sete Lagoas, MG, Brazil;

* Corresponding author: vanielebento@hotmail.com

INTRODUCTION

Brazil is the largest producer and consumer of charcoal in the world. Part of the material comes from planted trees, such as the Eucalyptus genus, and the other comes from native wood species from different Brazilian regions (IBÁ 2022). Charcoal is primarily employed in the steel industry and cast iron, in which its function is to provide heat for combustion, to indirectly supply carbon, which is the main alloying element of pig iron, in addition to providing carbon itself for the reduction of iron oxides (Jacomino et al. 2002). It also contributes as an alternative energy source to fossil fuels in other national sectors: industrial, commercial, agricultural, and residential areas (BEN 2021).

Charcoal is produced from wood via carbonization. Its quality is directly related to the parameters used for the carbonization process, such as the heating rate, final carbonization temperature, and oven pressure (Rousset et al. 2011; Vieira et al. 2013). The charcoal quality also depends on the characteristics of the wood, which influence the quality and yield of charcoal (Assis et al. 2016). Given that the properties of hardwoods impact the yield of charcoal and its physical, chemical, and mechanical properties (Dufourny et al. 2019; Couto et al. 2022), research on the quality of native wood for energy purposes is necessary. Brazilian Savannah is the second-largest biome in Brazil and is noted for its high number of tree species and biomass production. Thus, studies with wood species from this biome can help in its sustainable management plan and the introduction of little-known trees with high energy potential in the market. Astronium fraxinifolium Schott and Enterolobium gummiferum (Mart.) J.F. Macbr., for example, are native and endemic species of the Savannah, with a high potential for reforestation and management of degraded areas (Pilon and Durigan 2013; Calgaro et al. 2015). In addition, their wood already has commercial value for civil construction and structural purposes. It represents a viable option for planted forests and sustainable management, and may have potential for energy purposes and thus add value to the biome and region.

In this context, considering the wide availability of these species’ trees and that charcoal quality is directly correlated with properties of the raw material, the present study aimed to evaluate the energy potentials of A. fraxinifolium and E. Gummiferum from the energy characterization of wood and charcoal.

EXPERIMENTAL

Material Collection and Sample Preparation

Two discs with 5 cm of thickness were cut from three of Astronium fraxinifolium trees at 1.30 m above ground level in the Montes Claros, Minas Gerais, Brazil. And two discs were cut from three of Enterolobium gummiferum trees and were collected in the Carbonita, Minas Gerais, Brazil. Both species came from an area of remaining vegetation characterized as the seasonal semideciduous forest of the Savannah biome.

The disks from each tree were divided perpendicularly into four wedges. Two opposing wedges were used to determine wood basic density. The other wedges were sampled for wood chemical and energy analysis, charcoal production, and its characterization. Three replicates for each analyzed parameter were carried out.

Wood Carbonization

Carbonizations were performed using an electric muffle furnace. Approximately 300 g of wood previously dried at 105 ± 3 °C was used. The average heating rate to perform the pyrolysis was 1.67 °C/min, according to the methodology of Trugilho et al. (2005), which consisted of the initial temperature equal to 100 °C until the final temperature reached 450 °C, and was allowed to stabilize for a period of 30 min. Thus, the carbonization process was carried out in a period of 4 h.

Wood and Charcoal Characterization

For the chemical and energy analysis of the wood, the wood sawdust of mesh size between 40 and 60 was used and determined the absolutely dry content according to TAPPI 264 om-88 (TAPPI, 1997). The total extractive content of wood was determined as specified by TAPPI T204 cm-97 (1997). The extraction was performed with dichloromethane, 1:2 ethyl alcohol-toluene mixture, and ethyl alcohol using a Soxhlet apparatus. The ash content was determined according to TAPPI 211 om-12 (2012), which consisted of quantifying the ash via incineration in a muffle furnace at a temperature of 525 ± 25 °C for 3 h.

The basic density of the woods was determined according to NBR 11941 (2003), which consisted of the ratio between the dry mass of the wood and its saturated volume. For charcoal, the apparent density was determined by adapting the methodology of Vital (1984) with replacement of water by mercury. The high heating value of both materials was determined in an adiabatic bomb calorimeter according to NBR 8633 (1984), and the low heating value was calculated according to Costa et al. (2017). The energy density was obtained by the product of the basic density and the superior calorific value. The gravimetric yield in charcoal and carbonization energy yield were calculated according to Protásio et al. (2015).

Statistical Analysis

The data were submitted to the Shapiro-Wilk and Levene tests at 5% level of significance to test the normality of the residues and the homogeneity between the variances. Then, analysis of variance was applied using the F test at 5% significance. The analyses were performed with the software R Core Team (2019).

RESULTS AND DISCUSSION

Both wood species showed significant differences for all wood parameters evaluated in this study (Table 1). For the total extractives content, the wood of E. gummiferum presented values 1.3 times higher than that of A. fraxinifolium. The results were similar to those of Eucalyptus (1% to 5%), which is the main genus employed in the forest energy sector (Zanuncio et al. 2019; Vieira et al. 2021) in Brazil.

Table 1. Wood and Charcoal Characterizations of Astronium fraxinifolium and Enterolobium gummiferum

The nature and diverse composition of extractives and their amounts in the wood determine the biofuel heating value for energy purposes (Dadile et al. 2020). In this sense, woods with a high extractive content, such as those in the present study – especially E. gummiferum, are indicated to be better for charcoal production. The results for extractives of wood were similar to those presented in the literature for Savannah species, from 4% to 10% (Vale et al. 2010; Paes et al. 2013).

The wood species studied presented satisfactory ash content for energy purposes. The wood of E. gummiferum offered wood ash values 2.5 times lower than A. fraxinifolium, and, consequently, lower ash content was observed in the charcoal produced. Thus, it is a favorable species for charcoal production in the steel sector, given that a high percentage of mineral in charcoal can cause segregation during the process (Pimenta and Barcellos 2000). These wood ash values were closer to those described in the literature from Savannah species viz., 0.27% to 2.73% (Vale et al. 2002; Siqueira et al. 2020).

Astronium fraxinifolium wood presented higher energy potential than E. gummiferum. However, for charcoal the highest energy potential was observed for E. gummiferum charcoal. This may be associated with the chemical composition of the wood species, considering that the heating value is directly associated with the fixed carbon content of the material, and, consequently, with its potential and energy concentration. Thus, given that the calorific value portrays the effective amount of energy provided by the mass of the fuel (Costa et al. 2017), the charcoal of E. gummiferum was 1.05 times more energetic than that of A. fraxinifolium. All values for high heating value were consistent with the literature values for charcoal from Savannah species, from 30 to 33.36 MJ/kg (Figueiredo et al. 2018; Siqueira et al. 2020), and from the Eucalyptus genus, from 29.29 to 31.77 MJ/kg (Zanuncio et al. 2019; Protásio et al. 2021).

Regarding the wood basic density, the wood of A. fraxinifolium had a specific mass 13.3% higher than that of E. gummiferum. For charcoal, A. fraxinifolium also showed higher apparent density, which is associated with the higher basic density of its wood, because there is a high correlation between the parameters (Vale et al. 2010). However, for both, the mean values ​​were similar to those described in the literature for charcoal from Savannah species, which range from 255 to 475 kg/m³ (Vale et al. 2010; Siqueira et al. 2020) and also when compared to Eucalyptus charcoal, 255 to 420 kg/m³ (Castro et al. 2013; Zanuncio et al. 2019). Thus, the species are within the average required by the energy sector (> 500 kg/m³), especially A. fraxinifolium, has the higher wood density, and a higher density means that the mechanical resistance of the charcoal produced is greater (Protásio et al. 2021; Couto et al. 2022).

Because the energy density is directly correlated to the density and calorific value of the material, both wood and charcoal from A. fraxinifolium presented a greater amount of heat in a given volume in relation to E. gummiferum, and also when compared to wood (7.83 to 16.16 GJ/m³) (Jesus et al. 2017; Silva et al. 2018), and charcoal of the Eucalyptus genus (8.37 to 12.61 GJ/m³) (Protásio et al. 2015; Protásio et al. 2021).

For the gravimetric yield in charcoal, as well as carbonization energy yield, A. fraxinifolium stood out, being approximately 1.10 times higher for both incomes, thus indicating that it is a species with greater energy potential for charcoal production. However, when analyzing the parameters of density and calorific value, both species studied have the average level required by the charcoal sector. Thus, they can be considered as species with potential for energy purposes, which in consonance with sustainable management can serve as an alternative to species traditionally used in the forest sector.

CONCLUSIONS

1. The species under study present wood with satisfactory properties for energy purposes.
2. Astronium fraxinifolium presented wood and charcoal that was denser, more energetic, and with greater gravimetric yield.
3. Thus, the results indicate the energy potential of the wood from two Savannah species, which, in the consonance with sustainable management, silvicultural treatments, and genetic improvement, can be a possibility of association with species traditionally used in the forest sector.

ACKNOWLEDGMENTS

The authors would like to thank the Institute of Agricultural Sciences of the Federal University of Minas Gerais (UFMG), the Research Development Foundation (FUNDEP), the Minas Gerais Research Funding Foundation (FAPEMIG), the Study Group on Wood Technology (GETEM), the Professor Cássia Carneiro, Lawrence Oliveira and members of Wood Panels and Energy Laboratory of Federal University of Viçosa (LAPEM) for research support.

REFERENCES CITED

ABNT NBR 8633 (1984). “Carvão vegetal: Determinação do poder calorífico [Charcoal: Determination of calorific value],” Associação Brasileira De Normas Técnicas, Rio de Janeiro, Brazil.

ABNT NBR 11941 (2003). “Madeira: Determinação da densidade básica da madeira [Wood: Determination of the basic density of wood],” Associação Brasileira De Normas Técnicas, Rio de Janeiro, Brazil.

Assis, M. R., Brancheriau, L., Napoli, A., and Trugilho, P. F. (2016). “Factors affecting the mechanics of carbonized wood: Literature review,” Wood Science and Technology 50, 519-536. DOI: 10.1007/s00226-016-0812-6

BEN (2021). Balanço Energético Nacional. Relatório Síntese: Ano 2020 [National Energy Balance. Synthesis Report: Year 2020], Empresa de Pesquisa Energética, Rio de Janeiro, Brazil.

Calgaro, H. F., Buzetti, S., Silva, L. R., Stefanini, L., Miranda, L. P. M., Moraes, M. A., and Moraes, M. L. T. (2015). “Distribuição natural de espécies arbóreas em áreas com diferentes níveis de antropização e relação com os atributos químicos do solo [Natural distribution of tree species in areas with different levels of anthropization and relationship with soil chemical attributes],” Revista Árvore 39(2), 233-243. DOI: 10.1590/0100-67622015000200003

Castro, A. F. N. M., Castro, R. V. O., Carneiro, A. C. O., Lima, J. E., Santos, R. C., Pereira, B. L. C., and Alves, I. C. N. A. (2013). “Análise multivariada para seleção de clones de eucalipto destinados à produção de carvão vegetal [Multivariate analysis for selection of eucalyptus clones intended for charcoal production],” Pesquisa Agropecuária Brasileira 48(6), 627-635. DOI: 10.1590/S0100-204X2013000600008

Costa, A. C. S., Oliveira, A. C., Freitas, A. J., Leal, C. S., and Pereira, B. L. C. (2017). “Qualidade do carvão vegetal para cocção de alimentos comercializado em Cuiabá – MT [Quality of charcoal for cooking food sold in Cuiabá – MT],” Nativa 5(6), 456-461. DOI: 10.31413/nativa.v5i6.4679

Couto, A. M., Monteiro, T. C., Trugilho, P. F., Lima, J. T., Silva, J. R. M., Napoli, A., and Almeida, D. P. (2022). “Influence of wood physical-anatomical variables on charcoal physical-mechanical properties,” Journal of Forestry Research (Online). DOI: 10.1007/s11676-022-01462-9

Dadile, A. M., Sotannd, O. A., Zira, B. D., Garba, M., and Yakubu, I. (2020). “Evaluation of elemental and chemical compositions of some fuelwood species for energy value,” International Journal of Forestry Research 2020, article ID 3457396. DOI: 10.1155/2020/3457396

Dufourny, A., Van De Steene, L., Humbert, G., Guibal, D., Martin, L., and Blin, J. (2019). “Influence of pyrolysis conditions and the nature of the wood on the quality of charcoal as a reducing agent,” Journal of Analytical and Applied Pyrolysis 137, 1-13. DOI: 10.1016/j.jaap.2018.10.013

Figueiredo, M. E. O., Júnior Longue, D., Pereira, A. K. S., Carneiro, A. C. O., and Silva, C. M. S. (2018). “Potencial da madeira de Pterogyne nitens tul. (madeira-nova) para produção de carvão vegetal [Potential of Pterogyne nitens tul wood. (new wood) for charcoal production],” Ciência Florestal 28(1), 420-431. DOI: 10.5902/1980509831620

IBÁ (2022). Indústria Brasileira de Árvores: Relatório 2021 [Brazilian Tree Industry: 2022 Report], IBÁ, São Paulo, Brazil.

Jacomino, V. M. F., Castro, L. F. A., Ribeiro, E. D. L., Leão, M. M. D., Souza, C. M., Gomes, A. M., Almeida, M. L. B., Furiatti, L. E. (2002). Controle Ambiental das indústrias de Ferro-gusa em altos fornos a carvão vegetal. [Environmental control of pig iron industries in charcoal blast furnaces]. Belo Horizonte: Projeto Minas Ambiente/SEGRAC, 302p.

Jesus, M. S., Costa, L. J., Ferreira, J. C., Freitas, F. P., Santos, L. C., and Rocha, M. F. V. (2017). “Caracterização energética de diferentes espécies de Eucalyptus [Energetic characterization of different species of Eucalyptus],” Floresta 47(1), 11-16. DOI: 10.5380/rf.v47i1.48418

Paes, J. B., Lima, C. R. L., Oliveira, E., and Neto, P. N. M. (2013). “Características físico-química, energética e dimensões das fibras de três espécies florestais do semiárido brasileiro [Physicochemical, energetic and fiber dimensions of three forest species from the Brazilian semiarid region],” Floresta e Ambiente 20(4), 550-555. DOI: 10.4322/floram.2013.022

Pilon, N. A. L., and Durigan, G. (2013). “Critérios para indicação de espécies prioritárias para a restauração da vegetação de cerrado [Criteria for indicating priority species for the restoration of cerrado vegetation],” Scientia Forestalis 41(99), 389-399.

Pimenta, A. S., and Barcellos, D. S. (2000). “Curso de atualização em carvão vegetal, [Charcoal refresher course],” Universidade Federal de Viçosa, Viçosa, Brazil.

Protásio, T. P., Couto, A. M., Trugilho, P. F., Guimarães Júnior, J. B., Lima Junior, P. H., and Silva, M. M. O. (2015). “Avaliação tecnológica do carvão vegetal da madeira de clones jovens de Eucalyptus grandis e Eucalyptus urophylla [Technological evaluation of charcoal from the wood of young clones of Eucalyptus grandis and Eucalyptus urophylla],” Scientia Forestalis 43(108), 801-816. DOI: 10.18671/scifor.v43n108.6

Protásio, T. P., Lima, M. D. R., Scatolino, M. V., Silva, A. B., Figueiredo, I. C. R., Hein, P. G. R., and Trugilho, P. F. (2021). “Charcoal productivity and quality parameters for reliable classification of Eucalyptus clones from Brazilian energy forests,” Renewable Energy 164, 34-45. DOI: 10.1016/j.renene.2020.09.057

R CORE TEAM (2019). “R: A language and environment for statistical computing,” R Foundation for Statistical Computing, Vienna, Austria.

Rousset, P., Figueiredo, C., Souza, M., and Quirino, W. (2011). “Pressure effect on the quality of eucalyptus wood charcoal for the steel industry: A statistical analysis approach,” Fuel Processing Technology 92(10), 1890-1897. DOI: 10.1016/j.fuproc.2011.05.005

Silva, M. F., Fortes, M. M., and Junior, C. R. S. (2018). “Characteristics of wood and charcoal from Eucalyptus clones,” Floresta e Ambient 25(3), article ID e20160350. DOI: 10.1590/2179-8087.035016

Siqueira, H. F., Patrício, E. P. S., Lima, M. D. R., Guimarães Júnior, J. B., Carneiro, A. C. O., Trugilho, P. F., and Protásio, T. P. (2020). “Avaliação de três madeiras nativas do cerrado goiano visando à utilização energética [Evaluation of three native woods from the cerrado of Goiás for energy use],” Nativa 8(5), 615-624. DOI: 10.31413/nativa.v8i5.10338

TAPPI T204 cm-97 (1997). “Solvent extractives of wood and pulp: Standards regulations and style guidelines,” TAPPI Press, Atlanta, GA, USA.

TAPPI T264 om-88 (1997). “Preparation of wood for chemical analysis,” TAPPI Press, Atlanta, GA, USA.

TAPPI T211 211 om-12 (2012). “Ash in wood, pulp, paper and paperboard: Combustion at 525 °C,” TAPPI Press, Atlanta, GA, USA.

Trugilho, P. F., Silva, J. R. M., Mori, F. A., Lima, J. T., Mendes, L. M., and Mendes, L. F. B. (2005). “Rendimentos e características do carvão vegetal em função da posição radial de amostragem em clones de Eucalyptus [Charcoal yields and characteristics as a function of the radial sampling position in Eucalyptus clones],” Cerne 11(2), 178-186.

Vale, A. T., Brasil, M. A. M., and Leão, A. L. (2002). “Quantificação e caracterização energética da madeira e casca de espécies do cerrado [Quantification and energetic characterization of wood and bark of cerrado species],” Ciência Florestal 12(1), 71-80. DOI: 10.5902/198050981702

Vale, A. T., Dias, I. S., and Santana, M. A. E. (2010). “Relações entre propriedades químicas, físicas e energéticas da madeira de cinco espécies de cerrado [Relationships between chemical, physical and energetic properties of wood from five cerrado species],” Ciência Florestal 20(1), 137-145. DOI: 10.5902/198050981767

Vieira, R. S., Lima, J. T., Monteiro, T. C., Selvatti, T. S., Baraúna, E. E. P., and Napoli, A. (2013). “Influência da temperatura no rendimento dos produtos da carbonização de Eucalyptus microcorys [Influence of temperature on the yield of carbonization products of Eucalyptus microcorys],” Cerne 19(1), 59-64. DOI: 10.1590/S0104-77602013000100008

Vieira, T. A. S., Arriel, T. G., Zanuncio, A. J. V., Carvalho, A. G., Branco-Vieira, M., Carabineiro, S. A. C., and Trugilho, P. F. (2021). “Determination of the chemical composition of Eucalyptus spp. for cellulosic pulp production,” Forests 12(12), Article ID e1649. DOI: 10.3390/f12121649

Vital, B. R. (1984). “Métodos de determinação da densidade da madeira [Wood density determination methods],” Sociedade de Investigações Florestais, Viçosa, Brazil.

Zanuncio, A. J. V., Carvalho, A. G., Carneiro, A. C. O., Colodette, J. L., and Rocha, M. F. V. (2019). “Chemical and energetic characterization of Eucalyptus grandis × Eucalyptus urophylla clones subject to wind damage,” Revista Árvore 43(4), Article ID e430401 DOI: 10.1590/1806-90882019000400001

Article submitted: October 4, 2022; Peer review completed: December 21, 2022; Revised version received and accepted: January 9, 2023; Published: January 18, 2023.

DOI: 10.15376/biores.18.1.1780-1787