Capitulo 4F (1)

Esta é uma pré-visualização de arquivo. Entre para ver o arquivo original

4. Basic processes for wood energy conversion 
 
 The available energy in wood energy resources is always presented in the form 
of chemical energy imposing reactions for its release and, consequently, the 
performance of some actions of interest such as cooking or steam generation. Besides, 
there are a lot of situations where biomass conversion is required. Biomass, which is 
basically a solid fuel, must be converted into another more homogeneous or more 
suitable fuel for its end use form of energy such as, for example, a gaseous or liquid fuel 
for the generation of mechanical energy in internal combustion engines. In general, it 
can be said that biomass energy use is the inverse photosynthesis, for it tries to recovery 
the solar energy stored by the vegetable by consuming atmospheric oxygen and 
restoring carbon dioxide into the air. 
 
 This way, the employment of several technologies based on some conversion 
processes is justified. The processes of biomass energy conversion can be classified in 
three groups: physical, thermo-chemical and biological processes. Figure 4.1 shows a 
scheme of these processes indicating the main reagents and products that may be 
intermediate fuels or energy for end use. Densification, size reduction and the 
attainment of vegetable oils through pressing, typically when the original chemical 
composition of the raw material is not affected, are considered as physical processes. 
The thermo-chemical processes are characterized by high temperatures and include 
direct combustion, gasification, pyrolysis, and liquefaction, which are considered to be 
the most common for wood energy systems, above all, because of the wood low content 
of moisture. Among biological conversion processes, alcoholic fermentation and 
anaerobic digestion are the most used ones and they usually take place whenever there 
is high-moistured biomass, such as animal manure, and temperatures close to the 
ambient ones. They are not of much interest for the conversion of wood energy 
resources. 
 
 Considering the thermo-chemical processes to be the most interesting ones for 
wood energy, comprehending from the most simple combustion to the most 
sophisticated pyrolysis processes for the eventual production of liquid fuel, they will be 
presented in this chapter. The technological aspects and their present or developing 
applications are the objectives of the next chapters. 
 
 
 
 
 
 
 
 46
 
 
Figure 4.1 – Biomass energy conversion processes. 
 
 4.1. Biomass combustion 
 
 The direct burning, or combustion, is the oldest and the most commercially 
widespread conversion technology. It is basically applied for wood and for the most 
diverse agro-industrial residues such as sugar cane bagasse and rice husks. Biomass is a 
fuel rich in volatiles, which constitute almost 3/4 of its weight, as it can be observed in 
its immediate analysis previously shown in Table 3.12. This causes the combustion 
process to take place in 6 well-defined consecutive stages: 
 
1. Drying; 
2. Volatile emission; 
3. Volatile ignition; 
4. Volatile flame burning; 
5. Volatile flame extinction; 
6. Coke combustion 
 
 47
 Figure 4.2 shows the fraction of consumed mass and the corresponding 
temperature of each of those stages for burning wood as an example (HELLWIG, 
1982). During the biomass combustion process, it is mandatory to know that this 
process first takes place in an homogenous stage (volatile burning) and then in a 
heterogeneous stage (coke combustion). According to the conditions of air supplying 
and its mixture with the fuel, the velocity of the initial stages is generally higher than 
the velocity of the last stage when the fuel is burning in a solid state. 
 
 
 
Figure 4.2 – Wood combustion stages 
 
 When biomass is burnt in fixed bed on a grate, the volatiles are released and are 
burnt on the bed. This way, one can understand the reason why it is convenient to divide 
the combustion air flow into two parts: the primary air which is used for the coke 
combustion and the secondary air used for the volatile combustion. This procedure is 
carried out in industrial systems as shown in Figure 4.3. There are systems where the 
carbon of the fuel (C) is burned in the bed only until it becomes CO concluding its 
combustion as CO2 with the volatiles. In this case, according to Table 4.1, the 
secondary air is typically constituted of 83% of the total air. In the case of the carbon 
complete combustion on the bed or grate, the secondary air represents about 67% of the 
total air (HELLWIG, 1982). 
 
Figure 4.3 – Industrial grate scheme 
 
 48
Table 4.1. Relation between primary and secondary air during wood combustion in an 
industrial furnace (HELLWIG, 1982). 
Air distribution Stoichiometric air for the 
combustion, (m3/kg) 
 C CO⇒ 2 C⇒ CO 
Secondary air 2.62 (67 %) 3.27 (83 %) 
Primary air 1.31 (33 %) 0.66 (17 %) 
Total 3.93 (100 %) 3.93 (100 %) 
 
 
 In summary, the combustion reaction of a fuel using air can be represented 
according to the following scheme: 
 
Biomass + Air = CO2 + SO2 + H2O + N2 + O2 + CO + H2 + CH4 + soot + ashes 
 
 1 2 3 4 
 
For biomass combustion, each one of the groups numerated from 1 to 4 correspond to: 
 
1. Complete oxidation products: CO2 , SO2 and H2O. Once the biomass sulfur 
content is usually low, the percentage of SO2 is almost insignificant. 
2. Excess air (N2 + O2) and, eventually, fuel and air moisture. 
3. Gaseous products (CO, H2 and CH4) and incomplete combustion solid 
products (soot). 
4. Biomass non-combustible mineral fraction (ashes). 
 
 In physical-chemical terms and in a little more detailed way, wood combustion 
and, generically, biomass combustion can be presented as a three-process sequence: 
drying, volatilization and oxidation as shown in Figure 4.4, where a chemical formula 
for dry wood is also presented, CH1.7O0.7 (NUSSBAUMER, 1991). It is interesting to 
analyze these reactions, especially to determinate the eventual air excess in the 
combustion, which is a fundamental factor regarding the efficiency of the equipment 
that uses biomass. 
 
 49
 
 
Figure 4.4 – Wood combustion process scheme (NUSSBAUMER, 1991). 
 
 
 It must be observed in the previous figure whether or not there are fuel gases 
such as carbon monoxide and hydrocarbons in the combustion products, if so the 
combustion is said to be incomplete. In order to continue the presentation of the 
biomass burning phenomenon, searching for, above all, the adequate comprehension of 
its energy aspects, it is convenient to show some important concepts which are 
associated with the mass relation between air and fuel: 
 
 
Stoichiometric or theoretical combustion 
(in this case the property is identified with an exponent “o”) 
 
 
 + m ma
o
g
o→1 kg of biomass 
 
 
 
Real combustion. 
 
 + m ma g→1 kg de biomass 
 
 
Where: 
 
 50
m a
o - theoretical or stoichiometric air mass: it is the amount of air which is theoretically 
necessary for the complete combustion of 1 kg of fuel. It is calculated from the 
combustion reactions of the elements that compound the fuel, as it will be shown 
afterwards; 
m a - real air mass: it is the amount of air which is necessary in real systems for the 
combustion of 1 kg of fuel. Evidently, in order to produce a complete combustion 
ma must always be greater than m0a, for the mixture of air and fuel is not perfect 
and it needs an air supply higher than the theoretical one so that the biomass can 
be completely consumed; 
m g
o - gas mass generated during the combustion of 1 kg of fuel with theoretical or 
stoichiometric air; 
m g - gas mass generated during the combustion of 1 kg
of fuel in real conditions. 
 
 These amounts can also be evaluated as gas volumes corresponding to V , V , 
 and within standard conditions of temperature and pressure, respectively, 
where is greater than . Table 4.2 displays the values of for some types of 
dry biomass taking into account the ultimate composition that has already been 
presented on Table 3.12. As one can see, the variation among the distinct types of 
vegetable origin fuel is small. The greatest influence is caused by the moisture of the 
matter, once: 
a
o
a
Vg
o Vg
Va Va
o m a
o
 
 (wet)m a
o ⎟⎟⎠
⎞
⎜⎜⎝
⎛ −=
100
Moisture
1)dry(m basiswetoa (4.1) 
 
 
Table 4.2 – Air theoretical mass to burn 1 kg of dry biofuel 
Type of biomass ma
o (dry), kg air / kg dry biomass 
Standard biomass (CH1.4O0.7) 5.58 
Pine tree 5.79 
Eucalyptus 5.73 
Rice husks 4.62 
Sugar cane bagasse 5.26 
Coconut shells 5.89 
Corncob 5.39 
Cotton branches 5.46 
 
 A very important parameter to indicate the condition of the combustion is the 
“air excess coefficient”. Relating the theoretical and the real amount of air for a 
determined combustion process there is: 
 
 α = =V
V
m
m
a
a
o
a
a
o (4.2) 
 
 It is interesting to observe that there is an optimum value for this coefficient, 
which is associated with the combustion system maximum efficiency (αopt). If the air 
 51
excess is greater, that is, if α > αopt the heat losses associated with the gases exhausted 
through the stack will increase, and also because the existence of fans will cause an 
excessive consumption of electricity to move the excess of air and gases. On the other 
hand, if there is a lack of air, that is, if α < αopt, products originated by an incomplete 
combustion will appear in the gases, which represents an energy waste. The desirable 
value for the air excess coefficient depends on the fuel and on the combustion system. 
However in a very generic way, in elation to biomass the following is recommended: 
αopt ≅ 1.2 for suspension burning and αopt ≅ 1.3 for grate burning, that is, 20% and 
30% of air excess respectively. 
 
 Once the air dilutes the products, the most simple way to determine the excess of 
air during the combustion is by analyzing the composition of the combustion products. 
The more O2 or the less CO2 presented in the combustion gases, the more elevated the 
excess of air will be. Considering the burning of (CH1.4O0.7) type firewood, Figure 4.5 
presents the concentration curves for these gases in the combustion products, which 
were evaluated in dry basis, that is, without considering the presence of water steam. 
The instruments that are usually employed to perform the analysis of the gases generally 
present the results in dry basis as water is usually condensed in sampling tubes tubes. In 
practical terms, the relations based on the CO2 or O2 concentrations that are present in 
the products can also be used to evaluate the excess of air as it is shown in Table 4.3. 
 
 
 
Figure 4.5 – Relation between the concentration of gases (measured in dry basis) in the 
complete combustion gases and the air excess coefficient. 
 
 It is observed that even in conditions where there is an excess of air, signs of 
incomplete combustion may be noticed, such as the presence of CO, which depend on 
the aerodynamic of the furnace and the air-fuel mixture residence time. In summary, the 
air excess, which is determined based on the measurements of CO2 or O2 concentrations 
present in the combustion products, must be maintained at the lowest possible level 
until the presence of soot or CO indicates the occurrence of an incomplete combustion. 
 Figure 4.6 shows the dependence between the combustion temperature and the 
CO and CO2 concentration regarding the cases of a theoretical process and a real 
process (HAREL and BAQUANT, 1992). Sugar cane bagasse was the fuel considered 
for these cases. 
 
 Table 4.4 displays the equations for the calculation of air volumes and 
combustion products. Such expressions are basic for designing systems for the removal 
 52
of gases resulting from the biomass burning, for example stacks and eventually induced 
and forced draft fans. In these equations and in those that will be presented later, the 
variables with the superscript t refer to the content of the different elements present in 
the fuel (wet basis) expressed in %. 
 
Table 4.3 – Equations to determine the air excess coefficient α based on the gas 
analysis results. 
Method 
denomination, 
application 
condition. 
Equations 
 
 
 
Carbon formulae 
 
 
2CO
21=α 
 
where: 
 
=2CO content of carbon dioxide in the gases, % 
 
Oxygen formulae 
 
a) Complete 
combustion 
 
 
b) Incomplete 
combustion 
 
 
 
 
2O48.01
1
−=α 
 
 ( )α = − − − −2121 0 5 0 5 22 2O CO H CH, , 4 
 
where 
 
=2O oxygen content in the gases, % 
 
 
 
 
Figure 4.6 – Variation of the combustion temperature and of the CO2 and CO 
concentrations with the air excess coefficient (HAREL and BAQUANT, 1992). 
 53
 4.2. Biomass gasification 
 
As it was shown in the last topic, during combustion the chemical reactions 
between biomass and air take place until the complete or almost complete fuel oxidation 
producing heat, which is the desirable useful effect. This topic presents the gasification 
process, where the production of heat is not the main goal, but the conversion of 
biomass into fuel gas through its partial oxidation at high temperatures. This gas, which 
is known as producer gas, is an intermediate energy carrier and further it will be able to 
be used in another conversion process in order to generate heat or mechanical power. It 
can be suited to systems where solid biomass cannot be used. Basically, the average 
content of combustible compounds in the gas resulting from biomass is between 9% and 
21% of CO, 6% and 19% for H2, and 3% and 7% for CH4 . 
 
 
Tabela 4.4 – Equations for the calculations of V , and , in ma
o Vg
o Vg
3/kg of fuel 
Parameter Equation 
 Va
o Air theoretical volume 
 V C S H Oa
o t t t= + + −0 0889 0 375 0 265 0 0333, ( , ) , , t
 
 
 
 
Vg
o 
 Gas theoretical volume (α = 1.0) 
 V V V Vg
o
R O N
o
H O
o= + +
2 2 2
S )
N
V
 Volume of triatomic gases: RO2 = CO2 + SO2
 V CR O
t t
2
0 01866 0 375= +, ( ,
 Nitrogen theoretical volume 
 V VN
o
a
o t
2
0 79 0 008= +, ,
 Water steam theoretical volume 
 V H WH O
o t t
a
o
2
0 111 0 0124 0 0161= + +, , ,
Vg Volume real de gases 
 V V Vg g
o
a
o= + −1 0161 1, ( )α
 
 Although the produced gas has a relatively low calorific value, about 5 MJ/m3, 
and there are also energy losses during the conversion process, the gasification presents 
some advantages when compared to direct combustion in several situations: 
 
− The combustion of the gas is possible to take place in kilns, steam boiler furnaces 
and internal combustion engines that were originally designed for liquid and 
gaseous fuels derived from petroleum without any great modification in its 
equipment and/or reduction in efficiency. This is very important when conventional 
systems that use fossil fuels are intended to be converted into biomass systems. 
 
− The small-scale electricity generation can be accomplished without the need of a 
steam cycle by using biomass gas directly in an internal combustion engine or 
respectively a gas micro turbine or fuel cell. These primary drivers are interesting 
because of their simplicity in operation and maintenance. They are also suitable for 
 54
isolated systems, exactly in places where the energetic biomass
can be eventually 
supplied at competitive prices. 
 
− The use of biomass in combined cycles with gasifiers and gas turbines, commonly 
known as BIG/GT Systems (Biomass Integrated Gasifier/Gas Turbine), which are 
still being developed showing good prospects within the next few years though, 
allows electricity generation with an efficiency which is equal or higher than the 
electricity generation using fossil fuels. In addition, the kWh cost is competitive, 
even when the capacity is only a few MWs. By using this technology, sectors that 
have a wide availability of biomass at a low cost, such as sugar and wood industries, 
will also be able to become great electricity producers. 
 
 The biomass gasification process is a result of complex reactions, which are not 
still completely known in a whole. However, in an introductory way and in theoretical 
terms, it can be divided in several stages: 
 
1. Pyrolysis or thermal decomposition stage volatilization – it takes place at 
temperatures close to 600oC; 
2. Oxidation of a part of the fuel fixed carbon – the thermal energy source for the 
volatilization and gasification processes; 
3. Gasification – it includes heterogeneous reaction between the gases and the 
coke, as well as heterogeneous reactions between the products that have already 
been formed; 
4. Tar cracking – a thermal destruction process of the molecules of the tar forming 
counponds obtaining CO, CO2, CH4 and other gases as products; 
5. Partial oxidation of the pyrolysis products. 
 
Depending on the gasification process organization (relative movement of the 
biomass and the gasification gas), these stages take place in different regions of 
the gasifier or inside the gasifier as a whole in a simultaneously way. The most 
important chemical reactions of each stage are presented next: 
 
 
I- Pyrolysis. 
 
 Biomass + heat → core + gases + tar + condensable products (4.3) 
 
 
II- Carbon oxidation 
 
 C + ½ O2 ↔ CO (4.4) 
 
 C + O2 ↔ CO2 (4.5) 
 
III- Gasification. 
 
- Heterogeneous reactions. 
 
 C + CO2 ↔ 2 CO (Bouduard reaction) (4.6) 
 55
 
 C + H2O ↔ CO + H2 (Water gas reaction or steam carbon reaction) (4.7) 
 
 C + 2 H2 ↔ CH4 (Methane forming reaction) (4.8) 
 
- Homogenous reactions. 
 
 CO + H2O ↔ CO2 + H2 (Water-shift reaction) (4.9) 
 
 CH4 + H2O ↔ CO + 3H2 (4.10) 
 
 
IV- Tar cracking. 
 
 Tar + steam + heat ↔ CO + CO2 + CH4 (4.11) 
 
V- Pyrolysis products partial oxidation. 
 
 (CO + H2 + CH4) + O2 ↔ CO2 + H2 (4.12) 
 
 As it has been already mentioned, the 10 equations that were presented are far 
from reflecting the complexity of the processes that take place during biomass 
gasification. However, it is possible to reach important conclusions based on them: 
 
− The addition of water steam to the gasification air, up to 30% in the current practice, 
increases the content of hydrogen and carbon monoxide in the obtained gas as it is 
shown by equations 4.7, 4.9 and 4.10. 
 
− According to equation 6, the rise in pressure favors methane formation because of a 
reduction in the number of moles when going from reagents to products. 
 
 In some special situations a solid fuel can be gasified by using pure oxygen or 
air enriched with this gas, this way reducing the calorific value reduction associated 
with the presence of inert gases, such as the nitrogen, that constitutes 79% in volume of 
the atmospheric air. The gas produced in this case presents a much more elevated 
calorific value, however, the high production cost of the oxygen is an important 
economical limitation against this alternative. 
 
 
 4.3. Biomass Pyrolysis 
 
 While the gasification deals with solid biomass being transformed into gas fuel 
through its partial combustion with air, the basic proposal of the pyrolysis is the thermal 
degradation of biomass in total or almost total absence of an oxidant reagent at 
relatively low temperatures (500 – 1.000oC). This way the biomass is transformed into 
other fuels: solid, liquid or gaseous fuel fractions. The required heat can be supplied by 
the biomass combustion, however the product does not come from this combustion, but 
from the thermal action. 
 The thermal analysis, a set of techniques based on the measurements of the 
variation of parameters that characterize a physic property of a substance with the 
 56
temperature, is a considerably useful tool to study the pyrolysis processes of 
lignocellulosic matter. As an example, figure 4.7 shows the results of a thermal analysis 
of 30 mg of sugar cane bagasse sample with particle size ranging between 
, in a nitrogen atmosphere and with a heating velocity of mm20.016.0 − s/K16.0 .
 
 
Figure 4.7 – Curve of the thermal analysis of the sugar cane bagasse pyrolysis in a 
nitrogen atmosphere. 
 
The following curves can be identified in this graphic: 
 
1 – Temperature inside the furnace T, in K; 
2 – Thermal Gravimetry (TG): it indicates the variation of the mass of the sample 
during the heating; 
3 – Differential Thermal Gravimetry (DTG): it indicates the value of the derivative of 
the curve TG in relation to time, that is dm/dτ; 
4 – Differential Thermal Analysis (DTA): it registers the temperature difference 
between the analyzed sample and another inert substance used as a reference. It 
indicates the energy effects on the reactions, that is, exothermic and endothermic 
effects. 
 57
 
 This way, it is possible to attain information on the thermal destruction 
mechanism of the main compounds of these materials (hemicellulose, cellulose and 
lignin), about the temperatures and the energy effects of the chemical reactions, and also 
about the kinetics and reaction mechanisms. 
 
 Based on figure 4.7, similarly to the wood pyrolysis process, the following 
conclusions can be reached: 
• According to the DTG curve, the sugar cane bagasse pyrolysis process can be 
divided into the following characteristic stages indicated in figure 4.7 (The 
temperatures refer to the values corresponding to curve T). 
I – (297-373 K) moisture evaporation; 
II – (373-663 K) emission of the first group of volatile substances; 
III – (663-973 K) emission of the second group of volatile substances and formation 
of the coke residue structure. 
 
• The hemicellulose and cellulose thermal destruction takes place in the second 
step/stage/phase of the bagasse pyrolysis process when the lignin is partially 
destroyed. The intermediary peak observed in the DTG curve at 598 K corresponds 
to the hemicellulose thermal destruction maximum velocity, and the main peak, at 
623 K, corresponds to cellulose destruction maximum velocity. 
 
• Steps/stages/phases I and II of the pyrolysis process have an endothermic character, 
whereas step/stage/phase III is exothermic. 
 
TG curve allows the attainment of the necessary parameters for a quantitative 
description of the pyrolysis (kinetic) reactions according to the equation: 
 
 n)1(K α−=τ∂
α∂ (4.13) 
 
where: α – mass fraction of the substance that has already reacted ; oo m/)mm( −
 n – reaction order; 
 K – reaction constant – it depends on the temperature according to Arrhenius 
Law. 
 
 (4.14) RT/Eo eKK
−=
 
where: Ko – Pre-exponential coefficient or frequency factor, 1/s 
 E – Driving/activation energy, mol/kJ
 R – Gas universal constant, Kkmol/kJ
 T – Temperature, K 
 
 Table 4.5 shows the values of the kinetic parameters (Ko, E and n) for different 
ligno-cellulosic materials attained by using the thermal analysis technique. The order of 
the reaction was assumed to be 1n = , which according to LEVIN (1980) and PIALKIN 
AND SLAVIANSKY (1968) does not lead to considerable mistakes in the results. 
 
 58
Table 4.5 – Thermal decomposition kinetic parameters of different ligno-cellulosic
materials. 
Type of 
Material 
Temperature 
Interval 
K 
Heating Velocity 
K/min 
E 
 Ko n 
Fin1
pine1
298−1273 10 
10 
85.68 
84.26 
2.950.107
0.400.107
1 
birch2
pine2
298−753 14 
14 
86.48 
84.38 
5.800.104
6.200.104
1 
Sugar cane 
bagasse3
25−500 10 78.84 1.026.106 1 
Wood4 − 49.8 83.8 2.500.104 1 
1 – DERVAN and ZAPASHNIK (1981) 
2 – POLE and ZAROR (1983) 
3 – SILVA and BEATON (1988) 
4 – CHANG and KRIEGER (1982) 
 
 The biomass pyrolysis can be accomplished in different conditions of 
temperature and residence time, variables that affect directly the sort of resulting 
product and the proportion of solid, liquid and gaseous fractions as it is indicated in 
Figure 4.8. The effect of the reactor operating pressure shows a small influence, but it is 
also important. 
 
 
 
Figure 4.8 – Biomass pyrolysis technologies 
 
 A case that causes particular interest is the carbonization, a slow form of 
pyrolyses employed centuries ago in order to convert firewood into a more homogenous 
fuel with greater energy density. Other pyrolysis technologies which are faster and 
employ low temperature levels and small-sized biomass particles distributions are, in 
general, oriented for the production of liquid fractions (tar, pyroligneous acid, bio-oils, 
etc.) or fuel gases. However, they are still being developed. In all these cases, the 
physical-chemical reactions of biomass decomposition and formation of new 
 59
compounds are complex and they are still subjected to studies. A summary of the 
characteristics and parameters of the most important up-to-date pyrolysis technology in 
presented in Table 4.6. 
 
Table 4.6 – Characteristics of the technologies for biomass pyrolysis 
(BRIDGEWATER, 1991). 
Technology Residence 
time 
Heating rate Maximum 
temperature, oC 
Main product 
Carbonization hours – days very low 400 carbon 
Conventional 5 – 30 min. low 600 gas and liquid 
Fast 0.5 - 5 s intermediate 650 gas and liquid 
Flash < 1 s high < 650 gas and liquid 
Ultrafast < 0.5 s very high 1,000 gas and liquid 
Vacuum 2 - 30 s intermediate 400 gas and liquid 
 
 
References: 
 
BRIDGEWATER, A.V., Review of Thermochemical Biomass Conversion, ESTU 
B1202, Crown, 1991. 
 
CHANG, W.C.R., KRIEGER, B.B., Analysis of Chemical and Physical Process 
During Devolatilization of a Single Large Particle of Wood, Chemical Reaction 
Engineering, ACS Symposium Series 1982, no 196, pp. 459-471, 1982. 
 
DERVAN, T.I., ZAPASHNIK, L.M., Experimental Research on the Thermal 
Destruction of Different Types of Wood, Izvestia Akademik Nauk BSSR, Seria 
Fiziko-Energeticheskij Nauk, no 4, pp. 110-112, 1981. (in Russian). 
 
HAREL, P., BAQUANT, J., Bagasse Combustion, International Sugar Journal, Vol. 
94, No 1117, pp. 11-18, 1992. 
 
HELLWIG, M., Basic of the Combustion of Wood and Straw, Energy from Biomass 
Conference, EEC/Elsevier, pp. 793-798, 1982. 
 
LEVIN, E.D., Theoretical Principles of Charcoal Production, Moscou, 1980. (in 
Russian). 
 
NUSSBAUMER, T., Low emission Wood Combustion: Fundamentals and 
Technologies, Woodworking International, No 4, 1991. 
 
PIALKIN, V.N, SLAVIANSKY, A.K., Research on the Wood Pyrolysis Process 
Using the Thermal Gravimetry Analysis Method, Izvestia Vuzov, Lesnoi 
Zhurnal, no 1, pp. 127-133, 1968 (In Russian). 
 
 60
POLE, D.L., ZAROR, C.A., The Effect of Alkali Salts on Law Temperature 
Pyrolysis, Energy from biomass, Proceeding Int. Conf. of Biomass, Berlin (west), 
26-28 Sept, 1982, New York, 1983 pp. 16-21, 1982. 
 
SILVA, E.L., BEATON, P.S., Determinación de los Parámetros Cinéticos que 
Rigem el Processo de Descomposición Térmica y Combustión del Bagazo, 
Ingenieria Energética, Vol IX, no 2, 1988, p. 164-168, 1988. 
 
	Air distribution
	Carbon formulae