WOOD ENERGY:
PRINCIPLES AND APPLICATIONS
Luiz Augusto Horta Nogueira
Electo Eduardo Silva Lora
2002
2
Translation from Portuguese to English by
Adriana Costa Candal Lopes
3
“Light of sun swallowed by the leaf,
translating it into a new green, into
grace, into power, into light.”
Índia, Caetano Veloso
“and everything will be born more beautiful
so green makes with blue and yellow
the link to color a grayed love”
Nem um dia, Djavan
4
Presentation
For ages, energy, an essential asset for human activities, was mainly attained from plants,
which through photosynthesis, patiently accumulate solar energy making it available to be used
in any form or whenever it is desired. So, from the pre-historic caves that were warmed up and
illuminated by fires until the 18th Century, firewood was practically the solely source of fuel for
mankind. It was only after industrial societies had flourished, it was replaced, partially, with
coal, petroleum, and natural gas, but today, it is still being widely used all over the developing
world, which maintains its traditional energy practices. Owing to its historical primacy and the
apparent modernity of the energy fossil sources, biomass energy is sometimes seen as oldfashioned, waiting for more modern alternatives. Surely, this judgment is wrong. Bio-energy
technologies have been evolving constantly and they are able to gather important economic and
environmental advantages. The use of energetic biomass is an increasing factor of the
improvement of energy system sustainability.
The goal of this study is to present the techniques of biomass production and energy
conversion, particularly considering lignocellulosic materials such as firewood, husks and straw,
and the adoption of thermal processes for their suitability to end uses such combustion and
gasification. Some years ago, Miguel A. Trossero, United Nations Food and Agricultural
Organization (FAO), created the term Dendroenergy, that means “energy from trees” to renew
the concepts and call more attention to these energy systems. Wood energy embraces the
traditional use of firewood in household stoves, which have undergone great developed, as well
as modern applications, either as firewood or residues, for electricity generation passing through
a wide scope of technologies and capacities.
The public targeted by this publication are undergraduate or graduate students of Forest
Engineering, Mechanical Engineering, and Energy Engineering, as well Agronomy students, and
also professionals of the energy and forestial areas who are interested in improving their skills in
the field of wood energy, which is presented in its principal aspects and its most relevant
applications already in use or still being developed to be used. In order to reinforce the correct
consideration of these energy technologies in a feasible way, the fundamental economic and
environmental conditions were included and commented, in addition to the technological
aspects.
The basic definitions, the present scenario and the perspectives of biomass utilization
emphasizing the importance of this energy sector are presented in the first chapter. The second
chapter presents a view of wood energy systems formed by an articulated system of productive
components where solar energy flows either being wood or other matters for an end use, with a
wide potential of integration and synergies. The following chapter is dedicated to biomass
attempting to include and characterize all of the biomass energy potential sources, from forest to
urban agro-industrial residues. The fourth chapter is dedicated to the elements and some
applications of the biomass transformation processes until its final energy for the user. This can
either be as heat or electricity for different kinds of consumers and employing technologies such
as gasification and pyrolysis. In the final chapters it is intended to analyze the wood energy
environmental, social and economical aspects, which are essential factors for the correct notion
of its need.
According to this study, the bio-energy, although treated in a wood energy oriented way,
represents a remarkably challenging issue because of the extent of its relation to the environment
and society, as well as its enormous diversity of cases and possibilities. Therefore, the authors
did not have the pretension to write an encyclopedia about this subject, instead they tried to write
5
a study that could motivate the proposition and development of future projects and studies and,
perhaps, new advances (discoveries).
The first version of chapters 1, 2, 3 and 7 was elaborated by Professor Horta Nogueira
during his internship as a Visiting Scientist in FAO, while the first version of chapters 4, 5 and 6
was prepared by Professor Silva Lora. The close interaction between the authors during the
revision of each chapter of the original manuscript made it seem that all of the chapters were
written by “four hands”, embodying complimentary points of view and experiences. As direct
predecessors of this work, we can mention the handouts of the Latin American Energy Planning
Course that Professor Horta Nogueira taught for several years at Institute for Energy Economics,
(Fundación Bariloche, Argentina), the books "Tecnologias de conversão energética da
biomassa", "Pruebas de balance térmico en calderas para bagazo" and the chapter "Perspectivas
da utilização da biomassa com fins energéticos" of the book “Tecnologia e Aplicação Racional
de Energia Elétrica e de Fontes Renováveis na Agricultura”. These last books had Professor Lora
as a co-author.
We thank our colleagues Miguel Angel Trossero and Torsten Frisk for the suggestions
and advices that greatly enriched the first edition of this work, particularly the second chapter.
We also thank UNIFEI’s PhD students, Vladimir Melián Cobas, Flávio Neves Teixeira and
Marcelo José Pirani, for without their help, it would have been impossible to issue the second
edition of this book. We want to thank the drawer Messias Tadeu Salgado, who works at
UNIFEI, for the splendid illustrations. We also thank the following institutions for the
encouragement and support in the elaboration of the first version of this book (written in
Spanish) and the publication of its first edition in Portuguese: FAO - United Nations Food and
Agricultural Organization, ANEEL - National Agency for Electrical Energy, MCT – Ministry of
Science and Technology, PNUD – United Nations Development Program. We also have to
mention the support given by the Human Resources Program of ANP – National Agency of
Petroleum (PRH-16 ANP/EFEI Petroleum and Energy Engineering) from which Professor Lora
received a scholarship as a Visiting Researcher for a few years.
Finally, we put ourselves at your disposal. You can contact us through our e-mail
addresses for eventual reviews, opinions and suggestions: [email protected], [email protected].
The Authors
6
Preface
In spite of the success of “modern biomass” programs, among which the Alcohol National
Program, which has been going on in Brazil since 1975 converting sugar cane biomass into high
quality ethanol, the use of “traditional biomass” based on the deforestation of native forests is
still significantly widespread all over the world.
In 1988, despite the existence of a reduction trend, “traditional biomass” still corresponded to 9.5
% of the world’s energy matrix, regardless of all the widely known negative environmental and
social impacts.
“Modern biomass”, in turn, includes the use of agricultural, forest, urban and rural residues for
heat and electricity generation, and in the transport sector as well.
This “modern biomass” is included in the category of the “new renewable energies”, together
with wind, solar and geothermal energy, and the energy coming from small hydropower plants
and from the tides, whose participation in the world’s energy matrix is highly desirable and must
be encouraged because of all their well-known strategic, environmental and social advantages.
Within this scenario, the contribution of the present text, which was written by two well-known
experts in the area, Electo Eduardo Silva Lora and Luiz Augusto Horta Nogueira, is irrefutable.
This publication analyzes the most diverse aspects of production, conversion and the use of
“energy from forests” – or “wood energy” – spreading the idea that this energy can certainly be
used aiming at contributing towards a sustainable development for the world.
Suani T. Coelho
Professor in the Graduate Interunit Program
Executive Secretary of CENBIO - National Biomass Reference Center
7
WOOD ENERGY: PRINCIPLES AND APPLICATIONS
Index
Preface
1. Introduction
1.1. Definitions and concepts
1.2. The meaning of Wood Energy
1.3. Evolution and perspectives
References
6
8
8
11
15
17
2. Wood energy systems
2.1. Wood energy system structure
2.2. Optimized wood energy system implementation
References
18
18
20
23
3. Wood energy resources and fuels
3.1. Photosynthesis
3.2. Wood energy resources
A. Natural forest
B. Energy forest
B.1. Forestry
B.2. Annual crops
B.3. Transitional crops
C. Aquatic phytomass
D. Residues and biomass by-products
D.1. Agricultural residues
D.2. Forestial residues
D.3. Agro-industrial residues
D.4. Urban residues
3.3. Restrictions on biomass resource availability
3.4. Wood energy resources characterization
References
24
24
30
30
31
31
32
35
35
35
36
37
37
39
40
40
44
4. Basic processes for wood energy conversion
4.1. Biomass combustion
4.2. Biomass gasification
4.3. Biomass pyrolysis
References
45
46
53
55
59
5. Wood energy technologies
5.1. Pre-processing of wood energy resources
A. Size reduction
B. Drying
C. Densification
5.2. Biomass direct combustion
A. Residential systems
B. Industrial Systems (Process heat generation)
B.1. Grates and Combustion systems
61
61
61
62
65
67
67
70
71
8
B.2. Boilers
B.3. Boiler efficiency
5.3. Applied gasification
A. Gasifier comparison
B. Gasifier efficiency
C. The gas quality issue
5.4. Charcoal production
5.5. Fast pyrolysis and bio-oil attainment
References
73
76
80
83
84
89
91
93
94
6. Wood energy applications
6.1. The use of by-products for heat generation in ovens and boilers
A. Coffee husk ovens
B. Rice husk gasification systems for air heating in rice drying
C. Brick kilns that use sugar cane bagasse
6.2. Wood energy and electricity generation
A. Small and medium capacity systems
B. Biomass gasification for large scale electricity generation
6.3. Advanced Technologies: gas microturbines, Stirling engines, fuel cells
and hybrid systems
6.4. Wood energy and the iron and steel production
References
117
137
139
7. Wood energy and social and environmental issues
7.1. Energy x Food
7.2. Wood energy and job offer
7.3. Wood energy and the environment
A. Environmental effects during the agricultural phase
B. Environmental effects during the conversion phase
B.1. Direct combustion systems
B.2. Other wood energy processes
7.4. Wood energy and climate changes
A. Basic parameters
B. Sequestration and replacement of the carbon emissions
References
141
141
143
143
144
144
145
149
151
153
155
158
Appendix: Some links about bioenergy at internet
98
98
98
99
100
102
104
109
9
1. Introduction
The definitions regarding biomass energy use are presented briefly in this chapter,
and it was given a particular emphasis on wood fuels. In addition, a concise illustration of
its present importance in different regions of the world concerning forest and energetic
scopes was also demonstrated, showing its historical evolution and the perspectives for its
utilization.
1.1. Definitions and concepts
The term biomass comprises the vegetal matter generated through photosynthesis
and its derivatives such as forest and agricultural residues, animal waste and the organic
matter that is contained in industrial and urban waste. This matter contains chemical energy
that comes from the solar radiation energetic transformation and can be directly released by
means of combustion or converted into other more adequate energy sources - alcohol or
charcoal, for example - through any other process. Using nearly 1% of the total incident
solar radiation on Earth, it can be estimated that nearly 220 x 109 tons of biomass (dry
basis) are annually produced through the photosynthesis process, which is equal to 2 x 1015
MJ, that is, 10 times more than the global energy consumed in our planet every year
(SMIL, 1985). The total existing energy on the earth’s vegetal cover, including tropical and
temperate woods, is estimated to be about 100 times the present energy consumption on
earth throughout the year. Naturally, only one part of this enormous amount of energy can
be used to satisfy human needs, however these numbers can give us a notion of how
important the biomass energy potential is.
The biomass energy resources can be classified in several different ways,
nevertheless, one must recognize that biofuels are associated with biomass energy flows,
and they can be presented in three major groups according to the origin of the matter they
are constituted of. This way, there are biofuels coming from wood (wood fuels), fuels from
non-forest plantations (agricultural fuels) and urban waste. Table 1.1 shows the biofuels
classification, which will further be described in detail. It is a simple description presenting
the resources in such a way as to compare the typical treatments used in energy and forest
studies and comparing data from different sources.
- wood biofuel (wood fuel): it basically includes firewood, which can be produced and
obtained through a sustainable way out of cultivated or native forests. It is necessary to
respect the limits that make the natural regeneration of such forests possible. Firewood
can also come from deforestation of native formation with the purpose of getting land
for agricultural or cattle activities. These fuels can also be obtained through activities
that process or use wood not exclusively for energy purposes, as for example saw-mills
and cellulose industries (Table/Fig. 1.1). The energy content of this biomass class is
basically associated with the cellulose and lignin contents of the biomass in question
presenting, in general, low moisture and preferably adopting thermochemical
transformation routes for its end use as the combustion or carbonization systems. Other
more complex examples of forest-origin fuels are: charcoal, black liquor (a by-product
from the cellulose industry) and methanol or methyl alcohol that is produced out of
wood.
10
Table 1.1 - Biofuel classification
1st level
Wood Biofuels
Direct wood fuels
Wood produced with energy
purposes which is direct or
indirectly used as fuel
(wood fuels)
Indirect wood fuels
It includes solid, liquid or gaseous
biofuels that are deforestation subproducts and the ones resulting
from forest wood “utilization” the
wood industrial processing with
non-energetic purposes.
Recycled wood
fuels
Wood that is direct or indirectly
used as fuel. It comes from socioeconomical activities that use
forest-origin products
Energy plantation
fuels
Typically solid and liquid fuels
which are produced in annual
crops such as the sugar cane
alcohol.
Agriculture byproducts
Mainly crop residues and other
sorts of cultivation residues such
as trash and leaves
Animal byproducts
Basically poultry, cattle and swine
manure
Agro-industrial byproducts
Basically by-products from agroindustries such as the sugar cane
bagasse and rice husks
Non-forest Biofuels
Fuel from energy
crops
(agricultural fuels)
Urban waste
2nd level
Definition
Solid and liquid residues produced
by cities or villages
- Non-forest biofuels (agrofuels): They are typically produced from annual crops.
They present more moisture than the forest biofuels. In general, its use demands a
conversion to another more suitable energetic product first. Within this class, for
example, there is the sugar cane of which calorific value is associated with the
content of cellulose, starch, sugars and lipids that determine the sort of energy
product that can be achieved. Several kinds of energetic by-products, which come
from activities related to the production and processing of agricultural products and
are sometimes in an incorrect and depreciative way named residues, can also be
denominated biofuels. As examples of these agricultural by-products there are: the
ones produced at agricultural properties that are directly associated with the
vegetable production; animal-origin by-products, basically several sorts of manure
11
and agro-industrial by-products resulting from the processing of agricultural
products, such as sugar cane bagasse, rice husks or coffee hulls, etc.
Figure 1.1 – Wood biofuel fluxes
- Urban waste: Although this category includes matters coming from diverse
origins, such as plastic and metal, most part of the garbage and practically all of the
organic matter from the sewage waters is represented by biomass. The use of these
residues with energy purposes may signify a considerable environmental benefit and
a gradual elimination of contaminant matter, which almost constantly causes
increasingly difficulties in cities and villages. The process of converting them into
other energy products is basically defined according to the moisture level, where the
anaerobic biodigestion and other direct combustion systems can be applied.
It is worth observing that, in general, the fuels can be considered to be primary
when they correspond to matters or products obtained directly from nature, as firewood and
sugar cane for example; or secondary which is the case of the fuels resulting from primary
energetic fuel conversion processes. The charcoal produced from wood and the alcohol
produced from fermentable substances are included in this class.
12
Some kinds of biomass are difficult to be classified, such as vegetable residues in
the initial phase of their transformation into mineral coal, or even the vegetable oils
produced from products derived from trees such as the oil palm tree, which could be
considered as a wood fuel or an “agro-fuel”. There are two other ways to classify biomass:
taking the technological routes to be adopted for the biomass use into account or
considering its development level. According to this last classification concept the
traditional biomass energy can be found (firewood, charcoal, rice trash and husks and
vegetable residues and animal waste, which are well known and widely used resources) and
the modern bioenergy (associated with wood industrial utilization residues, the sugar cane
bagasse, the energy plantations and the urban residues either in a more restrict diffusion or
in a development phase). However, besides looking for a perfect classification, it is
important to have in mind, whenever it is possible, the origin and the utilization of a certain
biofuel, so that it is possible to recognize its impacts and potential.
The term wood energy is associated with the lignocellulosic energetic biomas in
general and its by-products, chiefly in a renewable basis. The technical, socio-economical
and environmental aspects related to forest production, the forest and similar resources preprocessing, and their eventual conversion into other forms of final energy and, at last, their
effective utilization are considered to be wood energy themes. Because of their affinity with
technologies of firewood utilization, other non-wood related products having similar
composition are also part of wood energy themes such as the bagasse and several residues
or agricultural and agro-industrial by-products. The present study is basically dedicated to
wood energy. It tries to analyze the information starting at its resources passing through the
technologies of conversion into other sources of final or secondary energy.
1.2. The meaning of Wood Energy
It is well known that the quality of the available information about biomass energy
use can be significantly improved. The frequent inexistence of commercialization regular
systems and institutional bases, which are responsible for attending and analyzing the
behavior of biomass markets, with a few exceptions, makes the data related to the total and
sectional wood fuel demands, in their various forms, to be a result from estimates or
disintegrated studies. Leaving these limitations aside, it is possible to carry out some
analyses of the present situation based on forest statistics and regional studies developed by
FAO considering different kinds of wood fuels and trying to evaluate their relative
influence.
Table 1.2 shows data regarding 1995. As it can be observed, the volumes of
consumed energetic fuel associated with wood are quite important, either in terms of its
participation in the energy offer or as a forest production percentage. Most part of this
consumption takes place in Asia, and about one quarter of the total consumption
corresponds to developed countries. The composition of this fuel resource, i. e., the product
composition of biomass consumption in different regions, is shown in Figure 1.3 using
absolute volumetric units (SCM, solid cubic meter) and Figure 1.4 displays the percentage
of each product, where it is possible to notice that in the developed countries most part of
the wood energy reaches the consumer as a wood-industry by-product.
13
In order to transform the distinct product flows into common units, charcoal, for
example, it was adopted a productivity of 165 kg charcoal for one solid cubic meter of
firewood (ONU, 1991), and for black liquor it was considered that each ton of cellulose
produced by means of chemical pulping generates an amount of liquor that corresponds, in
energetic terms, to 0.44 solid cubic meters of firewood. For the transformation of the wood
volumetric unit into energy, a density of 725 kg/SCM and a calorific value of 13.8 MJ/kg
were considered. (ONU, 1991). These values result in 1TJ (terajoules) for each 100 SCM,
that is, 10 GJ (gigajoules) for SCM.
Table 1.2 – Wood energy demand and importance (FAO, 1998)
Wood fuel total demand
Wood energy importance
Region
Developing countries - total
tropical total
non-tropical total
Africa
tropical
non-tropical
Asia
tropical
non-tropical
Oceania
Latin America and the
Caribbean
tropical
non-tropical
Developed countries – total
Europe and Israel
The former USSR
The USA and Canada
Oceania
World
1,000 SCM
PJ
1,763,262
1,368,439
394,822
486,248
464,077
22,171
1,002,846
654,221
348,625
5,804
268,364
17,633
13,684
3,952
4,862
4,641
222
10,028
6,542
3,486
58
2,684
244,338
24,027
536,754
194,653
42,585
272,438
27,079
2,300,016
2,443
240
5,368
1,947
426
2,724
271
23,000
Energy
Forest production,
production, %
% (2)
(1)
15
80
26
84
6
65
35
89
75
91
3
53
12
81
23
85
7
70
52
56
12
66
13
7
2
3
1
3
1
7
69
48
31
33
27
29
36
59
(1) In relation to the total primary energy, (2) In relation to the total forestial extraction
14
Figure 1.2 – Wood energy demand distribution, data from 1995 (FAO, 1998).
Figure 1.3 – Wood energy offer composition, absolute values, 1995.
Another way of showing the importance of the wood energy is through demand
specific indicators in relation to the population and to the economic product (Table 1.3).
Figure 1.5 shows the relation between bioenergy consumption (as the percentage of total
energy consumption) and the development level of different countries, expressed by the
Human Development Index – HDI. This indicator considers, in an integral way, the
percapita income, life expectancy, percentage of adult alphabetization and the percentage of
the population participating in educational programs.
As we can see in figure 1.5, it is possible to distinguish four country groups:
I. Countries with an intensive biomass utilization for domestic subsistence use. (mainly
low development countries);
15
II. Countries with a predominant use of fossil fuel energy (highly and medium developed
countries);
III. Medium and high development countries with an intensive biomass use, usually agroindustrial residues for energy applications (modern biomass). These are countries such
as Brazil, Costa Rica, Chile, Colombia, Cuba, Thayland and others;
IV. Highly developed countries, with a considerable percentage of bioenergy use, as a
consequence of incentives and taxes. In this group we can find Sweden and Norway.
In global terms, the wood fuel specific annual demand is equal to 4 GJ/per
capita.year, that is, 0.4 SCM/per capita.year, with a wide variation among distinct regions.
Figure 1.4 – Wood energy offer composition in percentage, 1995.
Table 1.3 – Wood energy per capita consumption indicators.
Region
Africa
Asia
Oceania (developing)
Latin America and the
Caribbean
Europe and Israel
Former USSR
The USA and Canada
Australia, New Zealand
and Japan
Energy
from wood
from other
sources
GJ/ person.year
6.7
12.3
3.1
22.0
8.8
8.0
5.6
40.0
3.4
1.5
9.3
1.8
121.7
106.4
334.7
159.8
Forest production
for energy for other
uses
SCM/person.year
0.716
0.092
0.282
0.068
0.876
0.702
0.578
0.293
0.249
0.146
0.842
0.224
0.508
0.397
2.020
0.406
16
Figure 1.5 – Bioenergy consumption and development level (UNDP, 2002).
1.3. Evolution and perspectives
The biomass, essentially as firewood, was undoubtedly the first energetic source
used by mankind. This was based on the fact that the control of fire production techniques
was initiated at the beginning of the Paleolithic period, i.e. nearly 1.4 million years ago. At
that time, in Africa and Asia, the first bonfires appeared in caves where our ancestors used
to live. Another important technology for biomass use is the alcoholic fermentation. It
probably appeared in Egypt at the end of this period, about 28,000 years ago. With the
improvement of firewood combustion systems and the progressive use of charcoal,
firewood became the energetic basis of the ancient civilization allowing the development of
important activities such as pottery and glass manufacturing and metal casting.
It was with the Industrial Revolution in Europe and later in the United States,
especially during the 19th Century, that the huge expansion of fuel demand could no longer
be satisfied by the solar energy accumulated in the plants, so the utilization of carbon and
petroleum oil is justifiable. In fact, the transition to these fuels was the only way out left for
a lot of countries after they had intensely and irrationally exploited their woods for
centuries, causing great forest extensions, mainly in Europe, to vanish. However, even
though the fossil energy sources has continually penetrated into the industrialized society,
at present the main source of energy in several countries is still the biomass, firewood
above all, which inclusively can result as a by-product from non-energetic wood activities.
17
Nearly half of the Earth’s population depends on biomass for cooking, heating and lighting.
This shows that the use of wood energy has, recently, also started to be considered as a
modern and clean form of energy supply and it has increasingly been adopted by some
industrialized countries.
The revival of the interest in bioenergies and the valorization of the biomass as a
modern energy source sprang up in the seventies and it shows two quite distinct phases.
Initially, with the strong rise in petroleum oil prices in 1973 and 1979, biomass was
considered to be an economically interesting alternative to satisfy thermal energy demands
for industries and small and medium capacity power plants, and in some cases as a source
of fuel for vehicle alternative engines. During this period, the major justification was
bioenergies smaller prices when compared to conventional energy. However, in 1985, the
prices of petroleum oil went back to its initial levels, so that the interest in these new or rediscovered sources of energy supply (bioenergies) was significantly reduced.
The second phase of this expansion and interest in the energetic biomass appears in
the nineties with the development of advanced transformation technologies and with the
definitive incorporation of the environmental issues into the discussions about energy.
Within this new scenario biomass starts to be considered as an opportune way of satisfying
the energy demand due to a wide set of reasons such as a minor environmental impact and
its renewability, the possibility of generating jobs and the possibility of making regional
economies more dynamic, in addition to the strictly economic factors.
The inevitable nexus between biomass energy and agricultural activities, at the same
time that it imposes a greater complexity on these energetic systems, may also be translated
into new synergies and important positive externalities. Such aspects are been paid much
more attention and they constitute the new favorable arguments allowing the biomass to
show, at present, a collection of very interesting realizations in different countries what is
an indication of new opportunities. According to HALL (1995), some of the successful
programs that can be pointed out are: the utilization of charcoal within the steel and iron
industry and the automotive alcohol program in Brazil, the massive diffusion of the biogas
in China, the implementation of energy forests and the bioelectricity production in the
USA, the utilization of wood with energetic purposes in Austria and Sweden, the use of
agricultural residues in Great Britain and the Netherlands, the eucalyptus plantations in
Ethiopia and the use of sugar cane bagasse in the Mauritius Islands among many others.
What is certain is that some of these programs have been facing difficulties, but,
undoubtedly, they show results and an important feasibility in many senses.
Biomass is not a panacea, nor can it be adopted as the only single solution for the
wide diversity of energy systems situations, but unquestionably it is an important
alternative to be considered. By evaluating the new prospects of bio-energy expansion
within the renewable sources boundaries, JOHANSSON et al. (1992) estimate that the
biomass produced in a sustainable way and with modern transformation technologies could
provide nearly 17% of the electricity and 38% of the direct fuel consumption in the world
in 2050.
Fisher and Schrattenholzer (2001) evaluate the world bioenergy “economic”
potential in 1990 as 225 EJ (5.4. 105 toe), from which only 46 EJ were used, corresponding
to 20.4 %. For the year 2050 this potential is estimated as 370-450 EJ (8.8 – 10.8.105 toe), a
value equivalent to the present total world energy consumption in a year.
18
Bioenergy potential is expressed by toe units (tons of oil equivalent). This is a
hypothetical fuel, realeasing as burned a quantity of energy of 41,868.00 MJ per kilogram.
An interesting example is the new scenario of biomass demand. In Brazil this
energetic source in its different forms represents about 20% of the total energy
consumption at present. Firewood consumption in the Brazilian household sector has been
decreasing along the last decades, specially because of the intense urbanization process
inasmuch as the former consumers from the rural areas have moved to the cities,
consequently demanding petroleum derivatives. However, this firewood use reduction is
being compensated by the expansion of biomass modern uses. This transition is observed in
other countries as well, but Brazil represents one of the cases in which the modern use of
biomass shows some of the best results, in a short cycle for sugar cane or a long cycle for
forest resources, showing updated industrial systems that are based on these resources as
fuels, as well as reducers in iron and steel industries. It is this type of context that
ROSILLO-CALLE (1987) denominate as “biomass society”, and it can, with the necessary
adaptations, be considered as an alternative for the sustainable development.
References
HALL, D.O.; HOUSE, J., 1995, “Biomass: an environmentally acceptable fuel for the
future”, Proceedings of the Institution of Mechanical Engineers (Part A: Journal of
Power and Energy) Vol. 209(A3), London, pp.203-213, 1995.
JOHANSSON, T.B., KELLY, H., REDDY, A.K.N., WILLIAMS, R.H., 1993, “Renewable
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