Túlio A S Vieira1,2*, Sónia A C Carabineiro2 and Paulo F Trugilho1*
1Science and Technology of Wood, Forest Sciences Department, UFLA - Federal University of Lavras, Brazil
2Laboratory of Catalysis and Materials (LCM), Associate Laboratory LSRE/LCM, Faculty of Engineering, University of Porto, Portugal
Submission: April 26, 2019; Published: May 21, 2019
*Corresponding author: Túlio A S Vieira, Science and Technology of Wood, Forest Sciences Department, UFLA - Federal University of Lavras, Av. Doutor Sylvio Menicucci, 1001 - Kennedy, Lavras - MG, 37200-000 - Brazil & Laboratory of Catalysis and Materials (LCM), Associate Laboratory LSRE/LCM, Faculty of Engineering, University of Porto, Rua Dr Roberto Frias s/n 4200-465 Porto, Portugal
How to cite this article: Túlio A S V, Sónia A C C, Paulo F T. Forestry Biomass as Energy Source in Brazil. Int J Environ Sci Nat Res. 2019; 19(2): 556013. DOI:10.19080/IJESNR.2019.19.556013
The demand for renewable energy is growing around the world. The participation of biomass, for the direct combustion of wood, charcoal, agricultural residues, among others, becomes more expressive. This opinion paper reports on the use of biomass as an energy source in Brazil, particularly the Eucalyptus genus.
Keywords: Renewable energy; Combustion; Chemical and energetic characterization
Planet Earth has a large potential for energy that can be obtained from renewable sources, including wind, solar, hydro and biomass sources . These sources play an increasing role in the mitigation of greenhouse gas emissions and provide an increasing fraction of primary energy in the world. Renewable sources are expected to significantly increase their share of global primary energy by 2050 .
An energy source is considered as renewable when the natural conditions allow its replacement in the short term  and are derived directly or indirectly from solar energy . Non-renewable energy sources are not restored by nature in a period compatible with its consumption . In general, they are widespread technol
ogy, but have a high environmental impact. It is noteworthy that
many industrial activities are dependent on fossil fuels, and those are exhausting and highly polluting sources of energy. Therefore, investments in renewable energy sources are indispensable. Renewable sources account for about 14% of the world’s generated energy. Brazil’s energy matrix differs from the world average, although energy consumption from non-renewable sources is larger than renewable energy. Firewood and charcoal, hydraulic, sugarcane and other renewable derivatives, totalize 42.9%, close to half of the Brazilian energy consumption matrix (Figure 1) .
Biomass is an important source of energy in Brazil, as it is very abundant. It is an alternative source of energy that offers significant economic and environmental gains, as it contributes to reducing dependence on petroleum derived fuels . According to the principles of sustainable development, the use of biomass for energy is recognized as a mitigation measure of global warming,
as it replaces fossil fuels and decreases the emission of greenhouse gases .
Biomass is distinguished using several raw materials, with different technologies for processing and transformation, playing a fundamental role in the environmental, energy and socioeconomic context [8,9].
In the world context, concerning the raw materials used as biomass supply sources, firewood predominates as a source of energy, followed by wood derivatives, such as charcoal and forest residues . However, in Brazil, the use of sugarcane by-products (40%), such as anhydrous and hydrated alcohol, as
well as sugarcane bagasse, followed using firewood and charcoal
(19%) is predominant .
Biomass energy can be obtained from biochemical, thermochemical
and physicochemical processes. Currently, there are numerous
technologies for this conversion, resulting in a diversity of
products that can be solid, liquid and gaseous. According to Patel
et al. , among the thermochemical processes, the three main
technologies used are pyrolysis, gasification and direct combustion.
The Eucalyptus genus, belonging to the Myrtaceae family,
which occurs naturally in Australia, has around 700 species
adapted to the most diverse climatic and soil conditions .
Due to its relevant amplitude of edaphoclimatic adaptation and
to its large number of species, the eucalyptus culture implanted
in Brazil has emerged as a promising alternative for multiple use
of commercial forest plantations . Figure 2 shows an image of
The Brazilian forest sector has grown in recent years, from the
application of new technologies, such as the genetic improvement
of forest species, in addition to environmental factors favorable
to forestry. This improvement made Brazil stand out in the forest
productivity of planted species .
In the year 2015, the total area of trees planted in Brazil was
7.8 million hectares. Of these, 5.6 million hectares were occupied
by Eucalyptus plantations. The largest planted areas are in the
states of Minas Gerais (24%), São Paulo (17%) and Mato Grosso
do Sul (15%) .
The main species cultivated in Brazil are Eucalyptus grandis,
Eucalyptus urophylla and Eucalyptus camaldulensis . The
most widespread hybrids in Brazil are from the cross Eucalyptus
urophylla x Eucalyptus grandis. According to Gonçalez et al. ,
the objective of the crossbreeding between these two species is to
obtain plants with high resistance to water deficit (characteristic
of E. urophylla) and high potential of rooting and growth in the
field (characteristics of E. grandis). Combining the inherent
characteristics of the two species, we obtain a hybrid with good
characteristics adaptive to the most different conditions.
When selecting the genetic material to use, besides the final
use of the wood, the soil and climatic requirements must be
considered, which depend on the technological characteristics
Combustion is defined as a rapid chemical combination of
oxygen with a combustible material, being an oxidation reaction.
For energy purposes, direct combustion occurs mainly in stoves
(cooking of food), ovens (metallurgy, for example) and boilers
(like steam generation). Although very practical and sometimes
convenient, the process of direct combustion is usually very
inefficient. Other problems are the high humidity of the fuel
material (20% or more in the case of firewood) and the low
energy density of the fuel (firewood, straw, residues etc.) which
makes it difficult to store and transport .
The combustion of wood is a complex process consisting of
a sequence of homogeneous and heterogeneous reactions. The
procedure takes place in six consecutive well defined stages:
drying, volatile emission, ignition of volatiles, burning of volatiles
in flame, extinction of the flame of volatiles and combustion of
carbon residue .
The reaction for combustion of wood with air can be presented
1 – are products of complete oxidation: CO2, SO2, H2O. The
sulfur content of the wood is always low, its value being
2 – Excess air (N2 + O2) and likely the moisture of the fuel and
3 – Gas products (CO + H2 + CH4) and solids (soot) of incomplete
4 – Non-combustible mineral fraction of biomass (ashes).
According to Brutti et al. , among the main chemical
reactions of wood combustion, are the combustion of carbon and
hydrogen, according to equations:
In addition to the use of biomass as a solid fuel for the energy
conversion through direct burning, pyrolysis and gasification also
appear as differentials for better handling and burning of fuel
. The gas resulting from the gasification process can be used in
the generation of electric energy by means of internal combustion
engines, boilers and steam generators for steam turbines .
The quality of wood depends on the combination of physical,
chemical, anatomical and mechanical characteristics of a tree or its
parts that allow to define its best use. According to Vital et al. ,
wood characteristics, such as moisture, basic density, biomass
dry mass and lignin mass, structural and elemental chemical
composition, calorific value, volatile matter content, ash and fixed
carbon are properties generally used in the determination of their
The energetic evaluation is carried out with the purpose
of promoting the classification of superior genotypes, since
they are relevant for decision making in the implementation of
reforestation projects aiming at the use of biomass as an energy
source. The attributes of wood serve to promote differentiation
between genetic materials [24,25].
In addition to the genotype, several factors can affect
wood properties. The conditions of the site, age, plant spacing,
fertilization, silvicultural practices are known. It is necessary
to know the interrelationships of these factors so that this raw
material can be improved, since these factors cause considerable
physiological changes in the tree and, consequently, alter its
energetic properties .
Thus, the main properties of the wood aimed at energetic use
are high basic density, high calorific value; high lignin content; low
ash content and low humidity .
The basic density is considered as one of the most important
parameters among the physical properties of wood, since it affects
most of the other properties. Its effects, however, are interactive
and difficult to assess alone . The advantage of using wood
with high basic density is to store higher energy content in a
smaller volume, which also contributes to the increase of its
energetic density [25,29].
The calorific value is an excellent parameter for evaluating the
energy potential of biomass fuels . Woods with high calorific
value have the largest amount of energy available in the form of
heat. However, it is necessary that the wood is previously dry,
since much of the energy produced during the thermochemical
process is directed to evaporate the free water present, reducing
the energy potential .
Moisture is an important factor that must be considered in
any biomass aimed at combustion, and it is always preferable
to use wood with the lowest possible humidity . The main
effects of high humidity on wood aimed for energy are the
reduction of useful calorific value, reduction of the temperature
in the combustion chamber with consequent loss of equipment
efficiency and productivity, increase in biomass consumption and
atmospheric emissions .
Another factor relevant to energy use is energy density,
defined as the amount of useful energy released by a fuel per unit
volume when subjected to combustion. The knowledge of the
energy density of a given biomass allows to evaluate its potential
for energy generation, considering that loads with higher energy
densities contribute positively to the optimization of transport
and reduction of costs.
The chemical composition of the material is also very
relevant for energy use, because when thermally degraded, wood
undergoes a transformation process, in which all its primary
components (cellulose, hemicellulose and lignin) are drastically
altered, which affects the energetic properties .
For the energy production, it is desirable that the wood
presents high levels of carbon and hydrogen and low levels
of oxygen due to the correlations between these elementary
components and the calorific value. High concentrations of oxygen
in the biomass favor a decrease in the calorific value , while
high levels of carbon and hydrogen contribute to an increase in
the calorific value of biomass fuels .
According to Bufalino et al. , the extractives can be
determinant in the choice of the wood use, because, besides
influencing the organoleptic properties, they can affect several
other properties, such as density, permeability, retractability and
The wood extractives contain several chemical compounds,
but they do not constitute the essential wood structure, for
example, polyphenols, oils, fats, resins, starch and waxes. As its
name says, it refers to what can be extracted by some process.
The phenolic origin of some extractives may act to increase the
calorific value of wood, due to the presence of high carbon content
The immediate chemical analysis of an energy source provides
the contents of volatile materials, fixed carbon and ash (residual
material), which influence the burning properties of the fuel, since
the volatile constituents burn rapidly and the fixed carbon burns
more slowly .
The higher the ratio volatile materials/fixed carbon the greater
the intensity of combustion. Volatile materials dissipate rapidly
during combustion: the higher the volatile material content, the
lower the ignition temperature of the biomass. Although biomass
ignites faster, it will have reduced burning time, which contributes
to the reduction of energy efficiency .
The content of volatile materials and fixed carbon is directly
related to the calorific value, increasing the time of burning of the
energy source. The volatile materials and the fixed carbon content
of the wood are dependent on each other, since the percentage of
ashes in their constitution is generally low [28,40].
Ashes or minerals are inorganic constituents that do not
participate in the combustion process of the biomass, representing
about 1% of the dry mass of wood. A high percentage of ash is
harmful to the energetic purpose. Minerals are undesirable,
therefore, a residue is formed, since they not degraded in the
thermochemical process; consequently, they contribute to the
reduction of the calorific value.
One of the important characteristics to select biomass that
presents/displays energetic potential is its thermal stability.
Techniques such as thermogravimetric analysis (TGA) make it
possible to understand the decomposition of biomass as a function
of heating in thermochemical conversion processes . The
thermogravimetric analysis consists of analyzing the variation of
the mass of samples in a system under the control of temperature
and atmosphere, which can vary both with temperature and time,
allowing to obtain information on composition, thermal stability,
as well on the ranges of temperatures at which decomposition is
more pronounced .
The evaluation of the energetic properties and efficiency
of the material allows to obtain more competitive materials
compared to other sources of energy. The energy density is an
important parameter to be determined, since it influences the
transport of the material, the amount of biomass consumed in
the burning process and the size of the biomass storage silo of a
machine, when the amount of energy required is associated with
the characteristics of the material [43-45].
Waste Wood biomass, particularly the Eucalyptus genus, have
are a good energy source in Brazil. The wood must have certain
properties in order to show efficiency in the direct burning (combustion)
To Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
(CAPES), Conselho Nacional de Desenvolvimento Científico
e Tecnológico (CNPq), Fundação de Amparo à Pesquisa do Estado
de Minas Gerais (FAPEMIG) and LCM (Laboratory of Catalysis and
Materials), FEUP (Faculty of Engineering - University of Porto)
for supporting this study. We acknowledge FCT (Fundação para
a Ciência e Tecnologia) for financial support (IF/01381/2013/
CP1160/CT0007, Investigador FCT program), with financing from
the European Social Fund and the Human Potential Operational
Program. This work was financially supported by Associate Laboratory
LSRE-LCM - UID/EQU/50020/2019 - funded by national
funds through FCT/MCTES (PIDDAC).