Capitulo 3F

Prévia do material em texto

3. Wood energy: Resources and wood energy fuels 
 
This chapter will first show the photosynthesis phenomenon that allows the plants to 
accumulate solar energy. This way, the different kinds of biomass resources that can be used, 
from the sustainable handling of native formations and the forestry for energy purposes to the 
energy crops and several types of residues will be introduced in the discussion, thus showing 
their main characteristics and availability indicators. 
 
3.1. Photosynthesis 
 
The photosynthesis constitutes one of the most fascinating phenomena regarding 
biological evolution on Earth. Life contradicts the normal tendency of system degradation 
implying a reduction in the local entropy, that is, simple compounds are grouped and ordered 
in complex molecules that form the cells of living organisms. However, this process requires 
external energy supply, and since the only available and abundant source of energy for the 
Earth is the sun, the primary living organisms have developed complex systems that allow the 
conversion of radiant energy into chemical energy, concentrating and improving the quality 
of the received energy. 
 
In general, the photosynthesis can be schematized by the following equation: 
 
 (3.1) 26126
lightsun
plants
22 O6OHCOH6CO6 +⎯⎯⎯ →⎯+
 
This simple transformation of carbon dioxide and water into sugar and oxygen takes 
place, in fact, by means of sophisticated ways and several intermediary stages enabling life, 
just the way we know it here on Earth. Actually, plants and animals, including humankind, 
live within a “symbiosis” consuming and exchanging resources in complex chains where 
food and energy flow, and the starting point is always the solar energy chemically 
synthesized by the plants. 
 
The main factors that affect the photosynthesis are the solar radiation, the temperature 
and water availability. As it is shown in Figure 3.1, the solar radiation of a clear day varies 
slightly throughout the year, according to the latitude and the seasons. Considering the 
radiation absorption and dispersion effects on the atmosphere, which can be well-defined in 
tropical areas, the total amount of solar energy decreases a lot. Thus, in general terms, it can 
be stated that the solar energy annual availability for tropical areas ranges between 5.0 and 
9.2 GJ/m2year, in average and between 1.5 and 6.0 GJ/m2year for tempered areas. Therefore, 
its influence on the level of photosynthetic activity is evident. The solar energy availability 
associated with the thermal impacts make biomass production potential productivity varies 
 25
considerably with the latitude, as it is shown in Figure 3.2. As it was expected, the biomass 
productivity is higher in inter-tropical regions. 
 
It is interesting to observe that not all the solar radiation that falls upon the plants can 
be used for the photosynthesis. Because of the luminous absorption properties of the 
chlorophyl, which is the principal pigment responsible for the photosynthesis, the only 
radiation that can be essentially used is the one with wave length ranging between 400 and 
700 mm. This range is called Photosynthetically Active Radiation, and it corresponds to 
nearly 50% of the available solar energy. Once it is situated on the region that corresponds to 
the red color, one can understand the reason why the vegetables are green, for they reflect the 
other light spectrum colors such as blue and yellow. 
 
 
 
Figure 3.1 – Solar radiation of a clear day in a horizontal surface. 
 
 
 
Figure 3.2 – Biomass gross productivity related to the Earth’s latitudes. 
 
 Trying to quantify the effects caused by temperature and water availability, LIETH’s 
studies (apud SMIL,1985) found typical relations between such variables and the gross 
vegetable productivity shown in Figures 3.3 and 3.4. 
 
 26
 B
Tm
= + − −
30
1 1 315 0 119exp( , , )
 (3.2) 
 
 (3.3) B m= − −30 1 0 000664( exp ( , h )
 
where B corresponds to the gross plant productivity evaluated in (t/ha.year), Tm corresponds 
to the annual average temperature expressed in (°C) and h m to the annual average 
precipitation in (mm/year). No doubt water is an important factor, and its relation with the 
photosynthesis is awfully complex. The hydric state of the plant determines the opening 
degree of the leaf stomata that allow the absorption of CO2. In addition, water is the 
transporting agent of the photosynthesized products, so there is a great loss of water steam in 
the vegetable production, ranging from 500 to 1.000 moles of H2O per mole of fixed CO2. 
For example, a corn stalk, which contains about 1 liter of water, needs nearly 200 liters of 
water for its formation. 
 
 
 
Figure 3.3 – Biomass gross productivity related to annual average temperature 
(Data calculated based on LIETH, apud SMIL, 1985). 
 
 
 
Figure 3.4 – Biomass gross productivity related to the annual average precipitation 
(Data calculated based on LIETH, apud SMIL, 1985). 
 27
Regarding the metabolic processes of CO2 fixation in the vegetables, it is necessary to 
characterize two groups: the C-3 plants and the C-4 plants. For the plants of the C-3 group, 
which constitute the great majority of species and all the trees and that convert solar energy 
by following a sequence of reactions known as Calvin Cycle, the first product formed during 
the photosynthesis is a molecule with three carbon atoms. In the same way, for the C-4 
plants, which follow the Hatch-Slack Cycle, the first product formed during the 
photosynthesis presents four carbon atoms. Only some species belong to the C-4 group such 
as the tropical-originated gramineous (sugar cane, corn and sorgo, typically plants of elevated 
yield). This classification is important because the needs and the efficiencies of converting 
solar radiation into biomass are different for each group as it is shown in Table 3.1. In 
relation to the metabolic process, there is also a group for the CAM plants, which typically 
concerns the species that are adapted to desert conditions, but still of interest as energetic 
biomass. 
 
Table 3.1 – Comparison of the photosynthesis metabolic processes 
Parameter Plants C-3 Plants C-4 
Photosynthesis optimum temperature (°C) 15-25 30-47 
Solar radiation saturation level (W/m2) 50-150 500 
Carbon dioxide net assimilation 
(mgCO2/dm2.h) 
20-30 50-70 
Gross productivity (GJ/ha.day) 5.8-6.7 8.6-9.3 
 
Another important parameter for vegetable production is the CO2 availability. The C-4 
plants are very superior to the others in this aspect, because CO2 penetration and fixation 
mechanisms are quite simple as it is shown in Figure 3.5. For example, based on the same 
CO2 assimilation, the plant’s water need, evaluated as transpired water during the 
photosynthesis, is nearly half for the C-4 plants in relation to the C-3 plants. Another 
parameter of interest is the availability of mineral salts (mainly nitrogen, phosphor and 
potassium) and organic matter in the soil. The leaf area and architecture also affect the 
vegetable productivity. In certain cases it has been possible to improve the plant productivity 
by handling the genetic selection of these leaf indexes correctly. All of these aspects are 
important and their considerations are interesting for biomass production with energy 
purposes. 
 
 
Figure 3.5 – Biomass gross productivity in relation to the availability of CO2 in the 
atmosphere (DEMEYER et al., 1985). 
 28
 
 The studies about alterations in the production of organic matter caused by the 
variation of climate energetic components during relatively long periods of time, as well as 
the estimate of the plant solar energy conversion efficiency are traditionally carried out by 
using quantitative methods of analysis regarding the plant growth.Considering that an 
expressive part of the solar energy fixed by the photosynthesis is accumulated in the plant, 
the parameters that define its growth can be expressed in energy units. This way, the 
efficiency of bio-conversion accomplished by the plants is defined by the relation between 
the biomass energy content of a plant species and the amount of the solar energy flux falling 
upon the area occupied by the plant itself during the organic matter production period. The 
amount of energy fixed in the photosynthetic formed products is calculated by taking into 
account the chemical composition and the energetic value of the compounds resulting from 
the photosynthesis. Thus, once the accumulation of 1 kg of lipids represents an energetic rise 
of 37.7 MJ, while 1 kg of starch increases 17.6 MJ and 1 kg of added protein 12.6 MJ, one 
can obtain different rates of energy accumulation resulting from the photosynthetic process 
with the same CO2 fixation rate according to the plant that is being analyzed. Table 3.2 shows 
the energetic content value for some species of commercial interest. 
 
Table 3.2 – Organic matter energetic content of different plant species 
Vegetable Dry matter energy (kJ/kg) 
 Pasture 16.8 – 18.0 
 Potato 14.2 – 15.9 
 Sunflower 18.0 – 19.3 
 Beans 15.9 – 16.8 
 Corn 17.8 – 18.0 
 Coniferous 20.1 – 20.5 
 
Based on thermodynamic and balance studies, it is possible to expect a maximum 
theoretical bio-conversion efficiency from 8 to 11% (SMIL, 1983). This efficiency is an 
instantaneous value that can neither be extrapolated to all of the hours with solar radiation, 
nor to all the leaves, once these leaves present different efficiencies according to their age, 
physiological state and their position on the plant in relation to the incident radiation. 
 
Taking these factors into account, the energy bio-conversion maximum efficiency 
during the day period falls to values close to 7% or even less, depending on the plant 
physiological activity and climate conditions. This value could be taken as an approximation 
of the maximum daily bio-conversion efficiency, if a high availability of radiant energy and a 
high photosynthetic activity in all the leaves that form the aerial part of the plant were taken 
into account. 
 
Considering different plant covers and radiation availability, Table 3.3 could be 
elaborated. The values that are shown in this table reflect the primary productivity 
efficiencies derived from plant gross productivity measures. They are expressed in terms of 
accumulated energy in a year per m2 of land area and the amount of incident radiation 
photosynthetically active during the same period per ground surface unit. It can be observed 
that, in average, plant covers operate with an efficiency of radiant energy utilization under 
2%. Exceptionally they reach values close to 4% (in areas of intense agriculture such as sugar 
cane fields) or about 6% (in rice fields). In general, adverse climate conditions with 
 29
limitations regarding water and nutrient availability, extreme temperatures and unsuitable 
handling of the crop are responsible for low efficiencies. 
 
Table 3.3 – Energetic efficiency for different vegetable covers 
Sort of plant cover 
 
Energy fixation for 
gross productivity 
 (MJ/m2.year) 
Photosynthetically 
active radiation 
 (MJ/m2.year) 
Gross 
photosynthetic 
efficiency 
(%) 
Pluvial tropical forests 105 2,340 4.5 
Temperate climate 
forests 
30 1,840 1.6 
Tropical region bushes 25 2,510 1.0 
Tropical prairies 22 1,840 0.7 
Semi-arid regions 1,460 3,010 0.5 
 
It is interesting to notice that photosynthetic productivity losses can be associated with 
the vegetable’s own consumption (autotrophic losses) or with the losses caused by the action 
of animals, weeds and other ecological effects (heterotrophic losses). In Figure 3.6, such 
losses are presented for different kinds of plant communities. It can be observed that when 
only the autotrophic losses are considered the net photosynthetic productivity is obtained, but 
when the heterotrophic losses are included the net ecological productivity can be reached, the 
one that fundamentally matters for biomass utilization. 
 
 
 
Figure 3.6 – Plant communities productivity and losses (SMIL, 1985). 
 
The molecules that are synthesized by the green cell are distributed to different parts 
of the plant where they will be used to satisfy the growth and vegetative life energetic needs 
whereas the surplus is accumulated as reserve material. This accumulation is carried out by 
plant storage organs that assume distinct shapes in the plants. In a lot of vegetables, the stems 
are used to store such reserves, for example, trees and sugar cane. Regarding potato and 
manioc this function is fulfilled by underground stems. The roots and leaves can be used as 
plant storage organs as in carrots and onions, for example. Finally, grains and fruits can 
contain significant energetic reserves such as corn and olive. In general, one plant species 
accumulate its surpluses in more than one storage organ. 
 
 30
Structured (wall) products and reserve products are the typical vegetable substances 
that compound the storage organs. Among the wall products, there is cellulose (a sugar 
polymer) and lignin (a phenolic polymer). Cellulose, in general, represents nearly 20% of 
vegetable dry matter, and it associates itself to the lignin in older plants. Lignin grants 
mechanical and chemical resistance to the plant tissues where it is present, and that can cause 
difficulties in chemical processes of biomass energy utilization. The most important reserve 
products are the glucids such as starch and sucrose (both having great industrial value), the 
lipids such as most of oily substances of vegetal sources, and the protids, which are 
represented by the proteins and other nitrogenized molecules. The way in which the solar 
energy is stored in the vegetable is very important to determine the technological process that 
should be used to obtain and transform the biomass energy. 
 
 
3.2. Wood energy resources 
 
 The direct and indirect products that come from forests can be considered as wood 
energy resources, whether they were produced for energy purposes or not, in the latest they 
are recovered from the wood destined for other uses such as the manufacturing of pulp or 
wrappings. Such resources are particular cases of bio-energetic resources that include all of 
the case of biofuels, among those firewood is, for sure, one of the most important. A brief 
overview of the wood energy main resources will be presented next. 
 
 A. Natural Forest 
 
 The tempered and tropical woods, which in Latin America cover almost 943 million 
hectares (FAO, 1997), have functioned as energy reserves for centuries. However their 
intense exploitation and deforestation for agricultural and cattle activities, in many cases, 
have lead to the almost complete destruction of dense forests. Trees need time to grow and 
they cannot be considered as an inexhaustible source of energy. That is the reason why these 
are resources that need to be suitably handled so that they will continue to be available. A 
purely extractive attitude, besides the lack of firewood, has other serious consequences such 
as the impoverishment of the soil and the rise in erosion. These problems have been 
generalized in many countries. They harm the environment and the population, and the low-
income groups are the one who suffer their effects. Nevertheless, some forestry studies, 
including the ones that were developed in complex ecosystems such as the Amazon Jungle, 
have shown that a rational use of these resources regarding energy supply is possible once the 
agricultural and ecological sustainability is considered to be objectives, even resulting in 
higher short-termcosts. 
 
 In average, it is evaluated that dense forests have an amount of wood estimated in 
500 t/ha and open forests 200 t/ha, however, this resource will only be available when the 
preservation of this forest resource is not expected, as it happens in cases when reservoirs are 
built in a forest area. 
 
 Considering sustainable production, that is, a situation in which the biomass offer is 
the same as the increase in the vegetable formation, the following table shows the estimated 
productivity for some native forest covers in Brazil. The sustainable production is also 
defined as the annual potential capacity for sustainable extraction. For the energetic 
productivity values firewood was considered to present a density of 400 kg/m3st (volumetric 
or apparent cubic meter) and a calorific value lower than 13.8 MJ/kg. 
 31
 
Table 3.4 – Biomass sustainable productivity of some natural forests 
Forest Description Productivity 
Covers (m3 st/ha.year) (toe/ha.year) 
Dense tropical 
woods 
big trees that cover more 
than 60% of the soil 
13.7 1.78 
Open woods 
 
big trees that cover from 
10% to 60% of the soil 
7.1 0.92 
Bushes, Savannahs medium-size trees that 
cover up to 10% of the soil. 
1.6 0.21 
 
 In general, methodologies used for energetic evaluations of the amount of forest 
resources in non-homogenous formations are based on statistical analyses trying to relate the 
firewood available amount to the diameter of the tree, which was measured at a determined 
height of its trunk. It is usually measured at 1.3 meters above the ground and it is known as 
DAP. Thus, once the tree density per hectare and its distribution according to diameter class 
are known, one can estimate how many cubic meters of firewood is available per hectare. 
More specific studies are necessary in order to determine the sustainable productivity, so that 
it is possible to know whether the formation is regenerating in an appropriate way. Now-a-
days, methods to determinate the biomass production potential based on images generated by 
artificial satellites are already available. 
 
 B. Energy forest 
 
 Trying to increase the biomass productivity, either by increasing autotrophic 
productivity or reducing heterotrophic losses, plants can be cultivated with the specific 
purpose of producing energy. This way, this kind of bio-energy source is considered to be 
sub-divided among forestry, annual crops and seasonal crops. 
 
 B.1. Forestry 
 
 After people became aware of native woods exhaustibility facing intense 
exploitation, techniques for growing and handling forest species were developed in order to 
elevate productivity. After its birth, forestry attended industrial wood needs, specifically for 
the production of cellulose and paper. However, since the 80s began, new standards and 
concepts have sprung up regarding the formation of homogenous forests aiming at biomass 
energy production. 
 
 The neologism “energy forest” is being used to define the forest agglomeration 
whose goal is to obtain the greatest energy amount per hectare within the shortest period of 
time. The basic differences between energy forests and traditional forests lie in a shorter 
cycle for three harvests, between 2 and 4 years, and in a greater density, the space between 
the trees is usually inferior to 2 x 2 m representing 2,500 trees per hectare. Typically the most 
suitable species are Eucalyptus and “Pine”, however because of the weather and soil 
characteristics other species can be used such as Acacias, Silk trees, Leucaenas trees, which 
come from the family Leguminosae, and others, but it is always recommended to use plants 
that present fast growth features. For example, Poplars and Platanus can be used in temperate 
climates. 
 32
 Table 3.5 shown some values for the productivity of the most outspread tree species 
for energy forests. Observe that the eucalyptus is typically adopted in tropical climates. 
 
Table 3.5 – Typical productivities for planted forests in Brazil (Muller, 2002, based on data 
from Glufke et al., 1997, Gomes et al., 1997, Schneider et al., 2000, Schneider et al., 2001, 
Schneider et al., 1998, Scolforo et al., 2001, Moreira-Wachtel, 2001) 
Species Cutting production 
(SCM/ha) 
Cutting cycle 
(years) 
Average 
productivity 
(SCM/ha.year) 
Maximum 
productivity 
(SCM/ha.year) 
Eucalyptus* 280.0 7 40.0 60.00 − 80.0 
Pine** 325.5 15 23.5 40.0 
Acacial*** 232.0 6 38.7 − 
*Spacing: 3.0x2.0m 
**Spacing 2.5x2.8m 
***Spacing 1.7x3.0m 
 A productivity average value for planted forests is about 25 m3st/ha.year 
corresponding to approximately 3.25 toe/ha per year mainly in regions where the soil and the 
climate are good. The planting density, which is determined by the number of trees per 
hectare, is a factor that directly affects the productivity and depends on the species and 
climate conditions. The space between the trees may vary from 2x2 m for leucaena trees in 
dry climates to 1.5x1 for eucalyptus in wet regions. It is also observed that the firewood 
productivity, as any other agriculture activity, depends on cultural cares and treatments. An 
adequate crop formation and the protection against fire and ants are very important for the 
forests. 
 
 B.2. Annual crops 
 
 In addition to the possibility of tree lignocellulosic biomass energetic use, other 
crops, which are typically of annual cycles, can also be considered. They are usually 
classified according to their principal energy storage substance. Thus, we can name the 
saccharides, the amylases and the oleaginous that will be presented next with their main 
species already commercially cultivated, but usually with nourishing purpose. Nevertheless, 
other vegetables, which are not quite known, are been studied and they may present important 
advantages such as resistance to dry periods, reasonable productivity in poor soil and culture 
facility. 
 
Sugar cane (Saccarum officinarum): The sugar cane cultivation in one of the most important 
and traditional agriculture activity in several tropical countries reflecting greatly in their 
economy. Sugar cane is a perennial plant that needs deep and fertile soil, a well-distributed 
minimal pluviometric precipitation ranging from 1,200 to 1,300 mm/year and temperatures 
between 20 and 24°C, and it doesn’t tolerate frosts. It is convenient to harvest sugar cane only 
during some periods of the year because of its maximum sugar content. In general, right after 
the first harvest, sugar cane will grow again producing other 4 or 5 annual harvests with 
decreasing productivity. In average, throughout a production cycle the productivity ranges 
from 50 to 100 t/ha.year according to the agricultural practices that were adopted. Typically, 
12% of its weight is fiber that after being milled is called bagasse, and 16% is sugar. The 
juice can be converted into alcohol producing from 70 to 90 liters per ton of sugar cane. 
These percentages may vary according to the place where sugar cane is cultivated and its 
species. 
 
 33
Sweet Sorghum (Sorghum bicolor): like sugar cane, it belongs to the gramineae or grass 
family, so it also needs good soil. It has a very short life cycle from 100 to 130 days and a 
productivity of about 35 t/ha. After being milled it presents a juice, which is very similar to 
the sugar cane juice. 
 
Grain Sorghum (Sorghum vulgare): It is a variety of sorgo whose grains are rich in starch. Its 
productions range between 4 to 6 t/ha during cycles of 120 days. When it is used to produce 
alcohol its productivity is 340 l/t of dry grains. The grain sorgo is an important popular food 
in Asia and Africa where it is used as flour. 
 
Cassava or Manioc (Manihot utilissima): the starch that is stored in the tuberous roots of this 
plant is highly employed in human and animal nourishment and in industriesas well. It is a 
tropical culture, however it shows a good production within the most varied water conditions 
and in temperatures ranging from 16°C to 38°C. The greatest commercial plantations can be 
found between the 30° parallels. Its cultivation cycle varies between 10 to 18 months with a 
productivity of 12 to 20 t/ha.year. The high content of starch in manioc, from 27 to 37%, 
makes high yields of alcohol production possible, something about 170 liters per ton. 
 
Babassu Palm (Orbignya martiana): it is a medium-sized palm tree, which is rather 
widespread in Brazil. Its productivity ranges from 2.2 up to 15.6 tons of fruit (coconuts) per 
hectare/year with approximately 70% of starch in the mesocarp. The babassu palm tree 
productive cycle starts between the ages of 7 and 10 and it ends at the age of 35. Several 
systems have been developed for the commercial use of babassu, which must be carried out 
in an integral way to take out both the starch form the mesocarp and the coconut oil. 
 
Sweet potato (Ipomoea batatas): it is a herbaceous plant with a good efficiency in converting 
solar energy into starch. It has tuberous roots and it is used for human and animal 
nourishment. It does not need good soil nor climate, and it has a short vegetative cycle 
ranging from 90 to 120 days. It presents very good productivity in the Amazon: an area of 
about 25 t/ha. Its starch content varies from 22 to 24% and its content of total sugars from 5 
to 6%. 
 
Corn (Zea mays): it is a graminaea that can be cultivated in any climate, soil or altitude in the 
world. It is one of the basic cereals for human and animal nourishment. Its productivity varies 
a lot in relation to the soil fertility and the management of the crops. The average production 
for ordinary crops is 2.5 t/ha, however, by using improved technologies it is possible to 
obtain a much greater productivity. The corn energetic use has been being proved in the USA 
through alcohol production, mainly because of the huge production of the "corn belt" in that 
country. 
 
 Several other species have been proposed and studied for the production of biomass 
with energetic purposes, particularly because of their high productivity or adequacy to poor 
soils or dry climates. A culture that shows interesting outlooks is the graminaea Miscantus 
also known as elephant grass, a C-4 vegetable that presents a good production of 
lignocellulosic matter in successive annual cycles. In Europe the elephant grass productivity 
ranges between of 8-15 tons of day matter per hectare, per year (SCURLOCK, 1999). In 
Brazil, this parameter reaches 25-50 t/ha/year (ANDRADE, J. B. et al., 2002) 
 
 The term “oleaginous” involves a great number of plants that produces vegetable oil 
and fat with greatly varied chemical composition. Typically, oil is liquid at ambient 
 34
temperature, whereas fat is solid. Considering the possibility of their energy use, it is 
important to know the quality and the use adequacy of their oil, as well as the aspects of their 
production and extraction. Table 3.6 shows the main oleaginous plants and their most 
interesting characteristics. 
 
 
 The oil palm tree, which is an African palm tree and is recognized worldwide for its 
high potential in producing vegetable oils, occupies a highlighted position among these 
oleaginous species. The oil palm tree presents short or long-term possibilities of replacing 
petroleum derivatives, above all, because its cultivation is simple and permanent, in addition 
to a relatively simple industrial processing for oil extraction. Other potentially energetic 
oleaginous plants that can be taken into consideration because of their commercial use are the 
babassu palm, the sunflower and the rapeseed whose cultures are typical of tempered and 
sub-tropical climates. In spite of having a relatively low productivity, the castor seeds also 
offer prospects of commercial use replacing fossil hydrocarbons due to the excellent 
characteristics of their oil, which presents outstanding lubricant properties. In some Central 
European countries and in the USA, rapeseed is already being employed in the production of 
“bio-diesel” in semi-commercial exploration patterns. 
 
Table 3.6 -. Characteristics of some oleaginous vegetables with potential energetic use 
 
Species 
Oil 
Origin 
Oil 
Content 
(%) 
Maxi- 
mum 
efficien- 
cy cycle 
Harvest 
Months 
Yield in 
Oil 
(t/ha) 
Oil palm tree 
(Elacis guineensis) 
Nut 20 8 years 12 3.0-6.0 
West Indian avocado 
(Persia americana) 
Fruit 7-35 7 years 12 1.3-5.0 
Coconut 
(Cocus numifera) 
Fruit 55-60 7 years 12 1.3-1.9 
Babassu Palm 
(Orbingya martiana) 
Nut 66 7 years 12 0.1-0.3 
Sunflower 
(Helianthus annus) 
Grain 38-48 annual 3 0.5-1.9 
Rapeseed 
(Brassica campestris) 
Grain 40-48 annual 3 0.5-0.9 
Castor seeds 
(Ricinus comunis) 
Grain 43-45 annual 3 0.5-0.9 
Peanuts 
(Orachis hypogeae) 
Grain 40-43 annual 3 0.6-0.8 
Soybean 
(Glycine max) 
Grain 17 annual 3 0.2-0.4 
Cotton 
(Gossypium hirsut) 
Grain 15 annual 3 0.1-0.2 
 
 35
 In the 70s and early 80s, because of the high petroleum prices, a lot of studies about 
several vegetables sprung. These studies regarded the production of combustible oils out of 
species, which were not known or had restricted use. The “macaúba palm or grugru palm”, 
for example, has been investigated here in Brazil and in other countries. It is a palm tree from 
the "Acronomia" family and it can be found in extensions from Mexico as far as the north of 
Argentina. It is possible to obtain from 2.8 to 3.5 tons of oil per hectare. Macaúba palm 
average indexes are 140 kg of oil and 130 kg of charcoal out of 100 of coconut. Another plant 
that has drawn our attention is the physic nut or purging nut (Jatropha curcas), that comes 
from the family of the Euphorbiaceae, which originally comes from Africa and has good 
adaptation to warm regions in the American continent. The oil extracted from the purging nut 
is very like diesel oil. The Jojoba (Simmondsia chinensis), the “marmeleiro” (Croton 
sonderianus) and the “indaiá rasteiro” (Attalea olifera) could also be cited. They are all plants 
that present good adaptation to arid climate, and therefore have potential to be cultivated in 
low quality land. The development of researches is important in order to identify the most 
promising species within a determined socio-economical context, always considering the 
characteristics of soil and climate. 
 
 B.3. Transitional crops 
 
 The end of extensive cattle activity in many properties and the generalized use of 
fertilizers make the land available in the period after the harvest and before the next culture. 
During this period, when the soil rests, the spread of green fertilizers, some winter fodder and 
the culture of short cycle energetic plants may present advantages, especially when the main 
cultures are precocious. In the southern hemisphere there are crops that allow transitional 
cultures from January to July. A good example of this kind of culture is the peanut, which is 
grown in sugar cane plantations. 
 
 C. Aquatic Phytomass 
 
 Among the aquatic plants, the “Pontedenaceae” or water hyacinth, water orchid and 
algae have been studied for energetic use purpose. The “Pontedenaceae" (Eichornia 
crassipes) is a herbaceous plant with an extraordinaire capacity of growth. Its excessive 
proliferation may even cause problems for dams, where the shed of water is necessary for its 
elimination. The “Pontedenaceae” productivity can be higher than 200 t/ha.year, however in 
average terms it is 15 t/ha.year. A proposed method, which is already in a pilot scale phase, 
for the conversion of the “Pontedenaceae” is the anaerobic bio-digestion with a production of 
13.9 m3 of biogas per ton of wet organic matter. This plant offersanother important 
advantage, which is the capacity of removing water contaminators. 
 
 Researches about algae utilization are promising, however they are still in their 
initial phase. The typical productivity is 100 t/ha.year and the most interesting species are the 
Spiruline and the Scenedesmus. The conversion technological routes that were considered are 
also by means of anaerobic treatment and bio-gas production. The main obstacle that needs to 
be overcome regarding the use of aquatic phytomass with energetic purposes is the difficulty 
is collecting these vegetables, for an adequate mechanization has not been developed yet. 
 
 D. Residues and biomass by-products 
 
 Several types of by-products from agricultural, rural, forestial, agro-industrial and 
urban activities such as shells and other lignocellulosic residues can be used as fuels. The 
 36
available potential of these residues are not always well known, but doubtlessly they 
correspond to significant volumes of energy. An essential aspect related to the energetic use 
of residues, above all the remains of farming and manure of animals extensively growth, is its 
dispersion, which brings about gathering and transportation difficulties. On the other hand, 
these residues often constitute an environmental problem and their final disposal has no easy 
solution. Therefore, the energetic use is a viable and opportune answer, once their volume 
and polluting potential is reduced. The Chinese wisdom says: "residue is ill-used raw matter”. 
 
 D.1. Agricultural residues 
 
 These residues comprise the agricultural and cattle residues. The agricultural 
residues are those resulting from harvests and crop processing, and their use must be 
accomplished in a rational way, for they may be useful to protect the soil against erosion and 
restore the nutrients that were extracted by the plant. These residues are basically constituted 
of straw (leaves and stems), and they have an average calorific value of 15,7 MJ/kg of dry 
matter. The energy stored in agricultural residues can be considerably high, representing in 
general twice as more than in the harvested product, and it contains nearly four times the energy 
that is necessary for the attainment of the principal cereals or oleaginous seeds. The following 
table shows the production coefficients of some crops. 
 
Table 3.7 – Vegetable residue availability 
Agricultural product Type of residue Residue production 
(t/ha) 
Dry matter 
(%) 
Rice Trash/straw 4.0 – 6.0 89.0 
Sugar cane Tip 7.0 – 13.0 23.4 
Beans Trash/straw 1.0 – 1.2 89.0 
Corn Trash/straw 5.0 – 8.0 90.5 
Cassava or Manioc Aerial part 6.0 – 10.0 90.4 
Soy beans Trash/straw 3.0 – 4.0 88.5 
Wheat Trash/straw 4.5 – 6.5 92.5 
 
 
Table 3.8 – Residue production coefficient average value for some crops 
Culture Main product Residue CR
Cereals 
 Wheat 
 Corn 
 Rice 
 
grain 
grain 
grain 
 
trash 
trash 
trash 
pod 
 
1.30 
1.00 
1.43-1.60 
0.18 
Tubercles and 
roots 
 Potato 
 Peanut 
 
tubercle 
seeds 
 
aerial part 
aerial part 
 
0.4 – 1.40 
1.0 – 1.48 
Cocoa fruit pod 0.20 
Sugar cane sugar tips and leaves 1.16 
Cotton fiber aerial part 2.45 
 
 37
 Another way that can be employed to determine the availability of an agricultural 
residue is the so-called residue production coefficient (CR). It relates the amount of residues 
in dry basis to the total mass of harvested product. It is presented in Table 3.8. 
 
 The cattle residue comprises the animal excretion such as manure from bovines, swines 
and fowls. Dry manure can be directly burned and it presents a typical calorific value of 14.6 
MJ/kg, however its most adequate form of energetic conversion is the anaerobic fermentation, 
which allows the production of fuel gas (bio-gas) and organic fertilizers showing good results in 
recovering and conserving the soil. Table 3.9 displays some of the basic indexes to evaluate the 
energetic potential of cattle residues. 
 
 Also, perennial cultures, such as fruit trees, generate agricultural residues. The 
annual pruning of one tree typically supplies nearly 2.5 kg/year of wood residue. In many 
countries, the pruning of coffee crops is used with energetic purposes. 
 
 
Table 3.9 – Bio-gas production out of the manure of some animals 
 
Animal 
Manure production 
(kg. animal. day) 
Bio-gas production 
(m3/animal.day) 
Energy 
production 
(toe/animal. 
year) 
 bovine 10.0 0.360 0.0657 
 equine 10.0 0.360 0.0657 
 buffalo 15.0 0.550 0.1038 
 swine (50 kg) 2.5 0.180 0.0329 
 fowl (2.5 kg) 0.18 0.011 0.0020 
 
 D.2. Forestial residues 
 
 These residues include by-products from silviculture activities such as tips and stems 
left on the field and according to the purpose of the produced wood – industrial or energetic 
purpose – present distinguishing specific productions. When the use of roots, in general 
problematic, is not considered, the forestial residues are approximately 33% when wood is 
cut with industrial purposes and 5% when wood is cut to be burnt. It is observed that the total 
generation of residues from forestial exploitation, including the sawing residues, may be 
greatly superior to the production of final commercial wood products. The wood calorific 
value must be adopted for these residues for each case, or in a preliminary way, the calorific 
value can be assumed to be 13.8 MJ/kg of produced residue. 
 
 D.3. Agro-industrial residues 
 
 Residues with energetic value are produced in most agro-industries. They can 
contribute towards the reduction of the dependence on the energy that is purchased for the 
generation of steam and electricity. Among the sectors of which residues are generated in 
great scale with use possibilities, some must be highlighted. 
 - sugar and alcohol industry; 
 - slaughterhouses and cold-storage houses; tanneries; fishing industries; 
 - sweet and canned food factories; 
 38
 - wood industry; 
 - paper and cellulose industry. 
 
 The technological procedures for the energetic use of agro-industrial residues are 
basically two: the burning in furnaces and boilers and the anaerobic bio-digestion. The first 
procedure is already traditional and the latest can be considered as an innovation. A decisive 
factor to select the energetic conversion method is the moisture content, once it is possible to 
burn residues with up to 50% - 60% of moisture. Thus, for example, sugar cane bagasse, 
sawing residues, cellulosic lixiviate and spent grounds from soluble coffee manufacturing are 
suitable for direct burning. On the other hand, distillery stillage resulting from alcohol 
production, effluents from slaughterhouses, dairy industry, etc, are appropriate for biogas 
production. Typically, the energetic potential of the liquid industrial residues is proportional 
to their polluting potential, due to its organic compounds content, and can be measured by the 
demand of oxygen for its biological stabilization expressed in BOD (biochemical oxygen 
demand) or COD (chemical oxygen demand). 
 The cogeneration technology is particularly interesting for the use of these by-
products once it envisages the simultaneous production of heat and energy with high 
efficiency. This issue will be approached on the next chapter. 
 
 Sugar cane bagasse is one of the most known and employed energetic residues in 
agro-industries. Each ton of milled sugar cane produces from 250 to 300 kg of bagasse with 
50% moisture and calorific value of 8.4 MJ/kg. In many cases, the improvement of the 
thermal balance in sugar and alcohol producing plants has provided bagasse surpluses 
ranging between 25 and 30% of the total bagasse produced, that is, the bagasse provides all 
the thermal and electric energy required for sugar and alcohol production and there is still 
some left matter, which iscommercialized as fuel or used for electricity surplus generation. It 
is convenient to reduce its moisture down to about 20-30% for its valorization. It can be done 
by using dryers or by natural drying. This by-product has an important alternative use in the 
manufacturing of cellulose and paper, as well as animal nourishment. Other important 
residues from the sugar cane industry are the distillery stillage and the filter cake however, 
their most important use is in sugar cane crops as fertilizer. 
 
 A cellulosic lixiviate called “black liquor” is produced during paper and cellulose 
manufacturing as a result of the wood lignin dissolution with soda. It generally presents 60% 
of solid concentration and a calorific value of 12.5 MJ/kg. Burning the black liquor in 
recovery boilers improves the energy balance, reduces the contamination and may generate 
up to 80% of the steam that is necessary in the industrial plant. Typically, 2.5 to 2.8 tons of 
black liquor are produced per ton of cellulose. 
 
 The production of soluble coffee generates a residue denominated spent coffee 
grounds. It can replace from 60 to 80% of the fuel that is needed in this sort of industry. For 1 
ton of coffee 4.5 tons of spent coffee grounds with 80% moisture is produced. This moisture 
must be reduced to 25% by means of drying, reaching a calorific value of approximately 14,6 
MJ/kg. 
 
 Vegetable husks and pods, from rice and peanuts for example, are also residues with 
energetic potential. Their use in burners is opportune, helping to solve the problem of their 
final disposal. Their specific productions are given in Table 3.10. More details about these 
residues are shown further on. Nevertheless, if there aren’t enough data, a calorific value of 
13.8 MJ/kg can be adopted for matters with less than 30% of moisture. 
 39
 
 D.4. Urban residues 
 
 These residues can be solid such as garbage and/or liquid such as sewage waters. 
Their energetic content is not high, however, in large cities the elevated volume of their 
production justifies their use, consequently environmental contamination is reduced. It is 
interesting to observe that the amount and the composition of the residues generated in a 
community does not depend on the number of inhabitants only, but it also depends on the 
level of income. The garbage from poor populations has a much greater organic content, so 
its potential to be converted in fertilizer is greater. Contrariwise, the residues coming from 
populations with a higher income present a large amount of industrialized and recyclable 
material. 
 
Table 3.10 – Especific productions of some vegetable residues in agro-industries 
Product Residue 
 manioc 0.80 t. residues/t of roots 
 coffee 0.21 t. pod/t of coffee in grains 
 coffee 0.20 t. pulp/t of coffee in grains 
 rice 0.22 t. husks/t rice with husks 
 cotton 0.18 t. pod /t seeds with pods 
 peanut 0.25 t. pod /t peanuts with pods 
 sunflower 0.20 t. pod /t seeds with pods 
 soy beans 0.01 t. pod /t of soy beans 
 coconut 0.34 t. pod /t of coconut 
 sesame 0.05 t. pod /t of sesame 
 
 The urban garbage consists of a heterogeneous mass of metal, plastic, glass, 
cellulosic remains and vegetables. Its treatment allows the recuperation of materials that can 
be recycled and the production of fertilizing compounds. The energetic conversion methods 
are: burning, gasification and bio-digestion in sanitary landfills. In average, in large Brazilian 
cities, the garbage has the characteristics mentioned in Table 3.11. 
 
 Urban sewage waters are highly diluted residues whose treatment is a sanitary 
imposition due to the presence of a high concentration of pathogenic germs. First they must be 
treated through the aerobic process with accumulation and production of sludge, which can be 
anaerobically treated generating bio-gas. This procedure has been adopted in some cities where 
biogas is used in car engines. Unfortunately, these treatment processes are expensive, therefore it 
is necessary to develop more simple systems that can be easily adapted to the reality of small 
populations. 
 
Table 3.11 – Average characteristics of the garbage from Rio de Janeiro and São Paulo 
(Brazil) 
 production per inhabitant 
 moisture 
 density (without being compacted) 
 calorific value 
 total of nitrogen 
between 0.6 and 0.8 kg/day 
between 40 and 55% 
between 250 and 300 kg/m3
between 11.5 and 13.4 MJ/kg 
between 0.7 and 1.4 % 
 40
 
 
3.3. Restrictions on biomass resource availability 
 
 When one tries to determine the energetic biomass availability in a country or region, it 
is important to take the economic, ecological and technological restrictions into account. This is 
the only way that all the potentially available biomass (resource) can assume the concept of 
reserve, from what the annual production potential can be determined. 
 
 The ecological restrictions are associated with environment and life quality 
preservation. Thus the protection of natural dense forests where there are river heads, in national 
parks and slopes subjected to erosion and etc is justified. However, the agricultural residues 
must be used cautiously for, in a long term, the environmental costs can be higher than the 
energetic benefits, because of an eventual reduction of organic matter and nutrients in the soil. 
For each condition of soil, climate and vegetation there is a biological threshold for biomass 
recovery, but once this threshold is surpassed, the ecosystem balance is compromised. 
Nevertheless, there are energetic conversion procedures that have almost no effect on the soil 
productive potential such as the anaerobic bio-digestion, which can recover energy from 
biomass without reducing its fertilizing capacity. There are still residues, specially agro-
industrial and urban residues, whose energetic use can be recommended in order to reduce its 
aggressiveness against the environment. 
 
 The limits imposed by the economic aspects can be analyzed in two levels. First, it is 
necessary to evaluate whether biomass, which will be energetically used, has or has not got 
another more interesting use as industrial raw material or food, for these uses must be prioritized 
before the energetic issue. Second, it is necessary to demonstrate that the agricultural production 
costs, such as harvest, transportation, storage, industrial processing, environmental protection 
and equipment adaptation for final use, are compatible with the energetic benefits and 
comparable to the other fuel of current use. The energetic balance, relating the consumption and 
the energy production in the process, is an important tool when selecting biomass as potential 
energetic carriers. In a general manner, it is also necessary to evaluate the need of workmanship, 
the impact on local activities, money saving and etc. 
 
 Finally, the technological restrictions are related to the existence or not of reliable 
processes and operations to convert biomass into a fuel of a more general use. These restrictions 
are chiefly associated with the limits of economic feasibility of each process. Besides 
considering regional characteristics, according to which a certain sort of biomass may or may 
not be of energetic interest, the technological research has been continually improving biomass 
conversion systems trying to enhance the effective possibilities of its use. 
 
 3.4. Wood energy resources characterization 
 
The most important technical characteristics of biomass as a source of energy are: 
chemical composition (elementary and imediate), moisture and calorific value. The definition 
of these parameters is presented below. 
Elementary chemical composition: it corresponds to the mass percentage content of 
the main elements that constitute the biomass usually referring to the dry matter, that 
is, without considering the presenceof water. Generally, values for carbon (C), 
hydrogen (H), sulfur (S), oxygen (O), nitrogen (N) and ashes (A) are presented. This 
 41
last item aggregates all non combustible elements such as potassium, phosphorus and 
calcium. The elementary chemical composition constitutes the basis of the 
combustion calculations. 
The reference procedures to determinate this composition are presented in the 
American norms ASTM E 870-82 (approved in 1992) Standard test methods for 
analysis of wood fuel, ASTM E 778-87 (approved in 1992) Standard test method for 
nitrogen in the analysis sample of refuse derived fuel, and ASTM E 777-87 (approved 
in 1992) Standard test method for carbon and hydrogen in the analysis sample of 
refuse derived fuel. 
 
Immediate chemical composition: it refers to the percentage content of fixed carbon 
(F), volatile matter (V), ashes (A) and eventually moisture (W) based on the fuel 
mass. The volatile content expresses the facility in burning a material and it is 
determined as the fraction in fuel mass that volatilizes during the heating of a standard 
sample in inert atmosphere up to temperatures of nearly 850oC for 7 minutes. The 
fraction of carbon that remains in the sample right after the heating is called fixed 
carbon or coke. In order to evaluate this composition, the following norms can be 
used: ASTM D 1102-84 (approved in 1995) Standard test method for ash in wood and 
ASTM E 872-82 Standard test method for volatile matter in the analysis of 
particulate wood fuels. 
 
Moisture: it is the measure of free water in the biomass. It can be evaluated through 
the difference between the weights of a sample before and right after being submitted 
to drying. It is possible to present the moisture values in dry or wet basis according to 
the adopted reference condition as shown in the following expressions. 
 
dry basis moisture: 
 
 H
P P
Ps
t
s
= − s , evaluated as (kg water / kg dry matter) (3.4) 
 
wet basis moisture: 
 
 H
P P
Pu
t
t
= − s , evaluated as (kg water / kg matter in working conditions) (3.5) 
where Pt and Ps correspond, respectively, to the values of mass of a same fuel sample 
in burning conditions (wet basis) and dry, which is the state of the biomass dried in a 
stove at 105oC, until it presents constant weight. The ASTM E871-82 Method 
(approved in 1987), Standard method for moisture analysis of particulate wood fuel, 
details the conditions of this test. 
A situation that may take place during the biomass combustion system analysis is the 
necessity of converting from one reference basis to another, once the data of the fuel 
are usually presented in dry basis or for a moisture that is not always the condition of 
the burning. Figure 3.7 allows the conversion of the moisture values from one basis to 
the other. 
 
 42
 
 
 
 
Figure 3.7 – Wet basis and dry basis moisture 
 
Calorific Value: It is the amount of heat (thermal energy) that is released during the 
complete combustion of a fuel mass volume unit (kJ/kg or kJ/m3). An important 
distinction is summarized in Figure 3.8. Contrariwise to the high calorific value 
(HCV), the low calorific value (LCV) is defined when the moisture condensation 
latent heat, which is present in the combustion products, is not considered. 
In a simplified way, one can say that the LCV refers to the heat that is possible to be 
effectively used in fuels, whereas the HCV is about 10 to 20% more elevated. In order to 
evaluate the calorific value of the biomass solid fuels, the most usual condition is the 
utilization of a “calorimetric bomb”, which is compounded by a container where the biomass 
sample is placed, it is pressurized with oxygen, and then the burning is carried out. The 
released heat is measured by the water temperature variation in a chamber where the bomb 
was placed. The norm ASTM E 711-87, Standard test method for gross calorific value of 
refuse-derived- fuel by the bomb calorimeter is a reference for this kind of evaluation. 
 
 
 
Figure 3.8 – High and Low calorific value. 
 
 43
The calculations of the efficiency of the combustion systems can adopt both kinds of 
calorific value. It is worth to remember that the efficiency referred to the LCV is superior to 
the value determined according to the HCV. That is the reason why it is important to make it 
clear which calorific value was used when the calculation results of efficiency and heat losses 
in furnaces and boilers are presented. Once the condensation heat of the gas moisture is 
technically irrecoverable, the use of the LCV seems to be preferable. 
 
 Table 3.12 displays the values of the calorific value and of the elementary and 
immediate compositions for some biomass types of energetic interest using the symbology 
presented in this chapter. Table 3.13 shows some biomass reference value at typical 
conditions according to data from JENKINS (1990) and ONU (1987), the influence of the 
moisture was particularly considered. In table 3.12 the characteristics of the poultry litter, a 
residue from the intensive chicken production, was also included. This residue availability is 
1.04 Kg per chicken, and its moisture ranges between 17-44% with an average value of 
27.4%. 
Taking the data from these tables and from Figure 3.9 into account, it is possible to conclude 
that: 
• the biomass is basically composed by carbon and hydrogen. There is a slight 
variation from one type of firewood to the other; 
• most of types of biomass have a low content of ashes except rice husks and 
bagasse; 
• the influence of the moisture on the calorific value is awfully important; 
• the biomass carbon content is smaller than carbon content of the mineral coal or 
fuels derived from petroleum. 
 
Table 3.12 – Technical characteristics of different types of biomass in dry basis. 
(Jenkins, 1990). 
Biomass 
type 
Elementary composition, % Immediate 
Composition, % 
LCV, 
MJ/kg 
 C H O N S A V A F 
Pine tree 49.29 5.99 44.36 0.06 0.03 0.30 82.54 0.29 17.70 20.0 
Eucalyptus 49.00 5.87 43.97 0.30 0.01 0.72 81.42 0.79 17.82 19.4 
Rice husks 40.96 4.30 35.86 0.40 0.02 18.34 65.47 17.89 16.67 16.1 
Sugar cane 
bagasse 44.80 5.35 39.55 0.38 0.01 9.79 73.78 11.27 14.95 17.3 
Coconut 
pod 48.23 5.23 33.19 2.98 0.12 10.25 67.95 8.25 23.8 19.0 
Corncobs 46.58 5.87 45.46 0.47 0.01 1.40 80.10 1.36 18.54 18.8 
Cotton 
stalks 47.05 5.35 40.97 0.65 0.21 5.89 73.29 5.51 21.20 
18.3 
Poultry litter* 37.49 5.12 31.82 3.70 0.45 21.62 62.73 23.40 13.87 14.9 
Miscanthus** 41.16 5.55 45.91 1.78 − 5.60 76.69 5.60 17.70 15.1 
*NRBP (1999), **OLIVARES (2002) 
 44
 
Table 3.13 - Technical characteristics of different types of biomass in dry or wet basis 
(ONU,1987). 
Biomass Moisture (%) Low Calorific Value 
 Dry Basis Wet Basis (MJ/kg) 
Green firewood 160 
100 
62 
50 
5.7 
8.2 
Air-dried firewood 60 
30 
38 
23 
10.8 
13.8 
Greenhouse/Stove-dried 
firewood 
20 
10 
0 
17 
9 
0 
15.2 
16.8 
18.7 
Charcoal 5 5 30.8 
Coal agricultural residues 5 5 25.7 
Manure 15 13 13.6 
Bagasse 100 50 8.4 
Coconut pods 8 8 16.7 
Coffee pods 30 23 13.4 
Palm husks and fibers 55 35 8.0 
Rice straw and husks 15 13 13.4 
 
 
 
Figure 3.9 – Firewood calorific value variation in regarding the moisture in wet basis. 
 
References 
ANDRADE, J. B. , FERRARI JUNIOR, E., COLOZZA, M. T., WERNER, J. C., 
DERENZZO, S., Extração da Umidade e Composição Química da Biomassa de 
Capim Elefante Cultivado para fins Energéticos, Anais do IX Congresso Brasileiro de 
Energia, Rio de Janeiro, 2002. 
CARIOCA, J. O. B., ARORA, H. L., Biomassa: Fundamentos e Aplicações Tecnológicas, 
Universidade Federal do Ceará, 1984. 
DEMEYER, A., JACOB, F., JAY, M., MENGUY, G., PERRIER, J., La Conversion 
bioenergetiquedu raynonnement solaire et les biotechnologies, Techniques & 
Documentation, Paris, 1985. 
 45
GLUFKE, C.; FINGER, C.A G.; SCHNEIDER, P.R., “Crescimento de Pinnus elliottii 
Enngelm, sob diferentes e intensidade de desbaste”, Ciência Florestal, v. 7, n. 1, p.11-
25, 1997. 
GOMES, F.S., MAESTRI, R.; SANQUETTA, C.R., “Avaliação da produção em volume 
total e sortimento em povoamentos de Pinnus taeda L. submetidos a diferentes condições 
de espaçamento inicial e sítio”, Ciência Florestal, v. 7, n.1, p. 101-126, 1997. 
JENKINS, B.M., “Fuel properties for Biomass Materials”, International Symposium on 
Application and Management of Energy in Agriculture: The Role of Biomass Fuels, 
New Delhi, 1990. 
MOREIRA – WACHTEL, S., Produção de madeira com melhor valor comercial agregado 
em plantações de Pinnus taeda no sul do Brasil, GTZ, Eschborn – Alemanha, 2001, 71p. 
MULLER, M. D., Comunicação Pessoal, Departamento de Engenharia Florestal, 
Universidade de Viçosa, 2002. 
NOGUEIRA, L. A. H., Biodigestão Anaeróbica: Uma Alternativa Energética, Editora 
Nobel, São Paulo, 1985. 
NRBP – Northeast Regional Biomass Program, Economic and Technical Feasibility of 
Energy Production from Poultry Litter and Ambient Filter Biomass on the Lower 
Delmarva Peninsula. 
OLIVARES, G. E., Estudo da Pirólise Rápida de Biomassa em Leito Fluidizado 
Borbulhante Através da Caracterização dos Finos de Carvão Elutriados como 
Etapa Inicial à Otimização do Processo, Tese de Doutorado, Universidade de 
Campinas, 2002. 
ONU, Department of International Economic and Social Affairs, Energy Statistics: 
Definitions, Units of Measure and Conversion Factors, Studies in Methods, Series F, 
No 44, United Nations, New York, 1987. 
SCHNEIDER, P.R.; FLEIG, C.A G.; KLLEIN, J.E.M., “Crescimento da Acácia – negra. 
Acacia mearnsii De Wild. em diferentes espaçamentos”, Ciência Florestal, v.10, n.2, p. 
101-112, 2000. 
SCHNEIDER, P.R.; FLEIG, C.A G; SPATHELF, P., “Produção de Madeira e casca verde 
por índice de sítio e espaçamento inicial de acácia-negra (Acácia mearnsii De Wild)”. 
Ciência Florestal, v. 11, n.1. p.151-165, 2001. 
SCHNEIDER, P.R.; FLEIG, C.A G.; HOPPE, J.M.; DRESCHER, R; SCHEEREN, 
L.W.;MMAINARDI, G.; FLEIG, F.D., “Produção de Eucalyptus grandis Hill ex Maiden. 
em diferentes intensidades de desbaste”, Ciência Florestal.. v.8. n.ª p. 129-140, 1998. 
SCOLFORO, J.R.; JUNIOR, F.W.A ; OLIVEIRA, A D.; MAESTRI, R., “Simulação e 
avaliação econômica de regimes de desbastes e desrama para obter madeira de Pinnus 
taeda livre de nós”, Ciência Florestal, v.11, n. 1. p. 121-139, 2001. 
SCURLOCK, J. M. O., Miscanthus: A Review of European Experience With a Novel 
Energy Crop, Environmental Science Division, Oak Ridge National Laboratory, 
Publication no 4845, 1999. 
SMIL,V., Biomass Energies: Resources, Links, Constraints, Plenum Press, New York, 1983. 
THIBAU, C. E. “Produção sustentada em florestas”, in Produção e utilização de carvão 
vegetal, CETEC, Belo Horizonte, 1982. 
	A. Natural Forest
	B. Energy forest
	B.1. Forestry
	B.3. Transitional crops
	C. Aquatic Phytomass
	D. Residues and biomass by-products
	D.3. Agro-industrial residues