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Moderate-Temperature Pyrolysis of Pine Wood (Siberian
Cedar)
Maitree Polsongkram* and Geniy Varamirrovic Kuznetsov
Faculty of Heat and Power Engineering, Tomsk Polytechnic University, 30 Lenin
ave., Tomsk, 634050, Russia. Tel +7-8906-958-8497; E-mail:
Polsongkrammm@gmail.com
* Corresponding author
Abstract
This study deals with the slow pyrolysis of woody biomasses namely; pine wood
(Siberian cedar). The experiments were performed in a fixed-bed pyrolysis reactor
over the range of temperature between 250 to 600oC. The test results showed that the
temperature is crucial for the overall woody biomass pyrolysis process. The higher
char production varied from 30 to 62% mass throughout the temperatures between
300 to 550oC (at the heating rate of 10oC/min) while, the lower char production varied
from 27 to 50% mass throughout the same range of temperatures at the heating rate of
50oC/min. The pyrolysis gas product was analyzed in a gas chromatograph. The
amounts of CO gas was high at the lowest temperature (300oC). The maximum of
CH4 gas fraction in the pyrolysis gas product was 23.47 %v/v at 600oC, whereas has
also produced the lowest of CO2 fraction. The HHVg of pyrolyzed gas product from
pine wood ranged between 13.58-15.42 MJ/Nm3. Therefore, the pyrolysis gas and
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char from pine wood could be recommended as a promising feedstock for bio-fuels
production and they are suitable for energy and possibly activated carbon production.
Keywords: Pyrolysis, Woody biomass, Thermal decomposition, Depolymerization
Nomenclatures
HHVg
Higher heating value of pyrolysis gas
C
carbon dioxide gas
H
Hydrogen gas
O
Oxygen gas
N
Nitrogen gas
S
Sulphur
Introduction
The awareness of a possible climate change due to the increasing green house gases
(mainly CO2 content) in the atmosphere caused by burning of fossil fuels and the
world’s dependence on fossil fuel has increased because of rapid industrialization,
economic development and population increase. Fossil fuel reserves will be depleted
and renewable energy resource development should keep energy in a sustainable
form. Biomass is considered as a renewable and cleaned energy source that can be
utilized to mitigate the impact of energy production and use on the global
environment. Because of it appears to have formidably positive environmental
properties resulting in no net releases of CO2 and very low sulfur content, also it
appears to have significant economic potential provided that fossil fuel prices increase
in the future (Gheorghe et al., 2009). Biomass can be directly used combustion system
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or gasification to produce producer gas, hydrogen rich gas for substitution for natural
gas. However, pyrolysis seem to be a promising method to increase more valuable
and usable fuel and to convert it into easily transportable fuel. The investigations have
shown that the direct combustion of biomass is not such economical. So the upgrading
of biomass fuel by pyrolysis method becomes more attractive.
Pyrolysis describes the process of anaerobic decomposition of solid fuel at
elevated temperatures to produce solid residue (char), liquid and gaseous productions.
Pyrolysis of woody biomass has been studied with the final objective of recovering a
bio-fuel with medium calorific power (Maschio et al., 1992; Bridgewater et al.,
1999). The main pyrolysis reaction is
Biomass → gases + liquid + char
Depending on the operating conditions, the pyrolysis can be divided into three
subclasses; slow, fast and flash pyrolysis. Slow pyrolysis is defined as the pyrolysis
that occurs under a low heating rate. It produces more char. The char obtained can be
useful as fuel either directly a briquettes, activated carbon or soil amendment.
Pyrolysis liquid (bio-oil) contains many reactive species, which contribute to unusual
attributes. Chemically, bio-oil obtained from biomass is a complex mixture of water,
usually 20-30 %wt depending on feedstock. Pyrolysis liquid consists of carboxyl acid,
carbohydrates and others various components (Yanik et al., 2007). Since bio-oil
contains difference amounts of organic acids which result in low pH(2-3) and it is
corrosive to some common construction materials like carbon steel and aluminium (
Lindfors, 2009 ). However, various chemicals are presents in bio-oil that can be
covered and used for chemical and/or food industries. The gases obtained has a high
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content of hydrocarbons and a sufficiently high calorific value to be used for fire
process in industrial or used as fuel for run gas turbines or internal combustion
engines. Pine wood (Siberian cedar) is important pine species growing in Russia.
Spread over the Siberia territory. It not gives useful structural wood and furniture but
pine wood gives pine nut oil which amino acid rich that useful as medicines for native
people. The present work focused on studying the pyrolysis of pine wood, one of most
abundant species in Russia. The specific objective of this study was to assess the
potential of pyrolysis technology to transform pine wood saw dust from sawmill
waste to useful products as pyrolysis gases.
Materials and Methods
Raw materials
The woody biomass species used in this study is pine wood. It was collected
from local sawmill in Tomsk region, Russia. Contaminants were eliminated then sundried to reduce the moisture content. The size of particle was less than 1 mm. Prior to
the experiments, the samples were oven-dried for 3 hrs at 110oC. The proximate
analysis was carried out to determine a mineral’s thermal stability and it fraction of
volatile components by monitoring the weight change at different desired
temperatures. All experiments composed of three main different steps: drying,
devolatilization in inert atmosphere and combustion in oxygen. Determination of ash,
moisture and volatile matter was performed according to American Society for
Testing and Materials (ASTM) test methods (ASTM Standards (E872), 1986; ASTM
Standards (E871), 1986; ASTM Standards (D1102), 1986 ). The properties of raw
material, proximate and ultimate analysis results are given in Table 1.
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Experimental set up
The experimental set up fabricated for fixed-bed pyrolysis unit is shown in
Figure 1. This reactor is designed for atmospheric pyrolysis. The set up consists of a
reactor, condenser and liquid collector, helium source. The size of reactor was 40 mm
in diameter and 145 mm in length constructed of stainless steel with the heating
circuit consisting of various temperature controllers and time switches. It was heated
externally by electric heater. The helium gas was supplied in order to replace the air
in the reactor for keeping the inert atmosphere inside the reactor. The maximum
loading capacity of reactor vessel was 20g of sample woody biomass. The condenser
was fabricated in form of helical coiled tube, water at 10oC is used as coolant. The
experiments were performed at different pyrolysis temperatures (end-operating
temperatures) ranging from 250 to 600oC. The temperature within the reactor was
monitored by K-type thermocouple. The retention time was fixed for 3 hours in order
to allow the sample to go to through a complete pyrolysis process or no further
release of gas was observed then cools the reactor down to ambient temperature.
A weighed sample of 20g of the fresh feed was taken in the sample boat and
then placed in the reactor. Before the experiment, the system was driven off air by
allowing helium gas to flow through the system for 5 min at the flow rate of 2 l/min
and then helium gas supply was stopped. The feed was then heated up to desired
temperature by the temperature controller system. During heating, the system was
maintained at slightly above the atmospheric pressure. The produced gas has being
collected in the water container. The volume of water displaced determined the gas
volume. The liquid product was collected at the liquid collector point. The yields of
the different products obtained were determined by weighing the solid residue (char)
and liquid collected and gas evolution by difference. Yields are expressed as a percent
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by weight of the raw materials as a function of the pyrolysis temperature. In order to
test the reproducibility of the experiments, we tripled the experiment at desired
temperature.
The pyrolysis gas products were carried with a gas bag and analyzed on a gas
chromatograph (SHIMADZU-GC-14B). The carrier gas was helium gas and the
produced gas composed mostly by CO, CH4, CO2, and Air. The volume
concentrations were calculated by an external standard method, based on a linear
relationship between the concentration and area of the standard mixture measured by
program and presented on the results and discussion. Prior to identify gas species, the
gas chromatograph was set upon in a condition as follows;
- Column type
: Active carbon
- Column temperature
: 60๐C
- Injector temperature
: 80๐C
- Detector temperature
: 100๐C : 100๐C
- Carrier gas
: Helium Gas
- Carrier Gas Flow Rate : 50 l/min
- Calculate by
: Area
- Method
: External Standard
- Curve Fit type
: Linear
Conversion of Biomass
The conversion processes of biomass usually involve a reduction of the water content
of the material, resulting in the simultaneous increase in its thermal value and
preservation potential and in improving the handling characteristics of the biomass,
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for example turning it into a fluid, which may be either gas or liquid. Oxygen removal
from the biomass in the form of carbon dioxide (and carbon monoxide) will result in
products with high hydrogen to carbon (H/C) ratio.
Pyrolytic conversion of wood involves thermal separation of volatile matter
from the solid residue. The pyrolytic process is affected by the type of raw material
and process parameters, wherein the temperature plays an important role.
Below 260๐ C only charring takes place, while depolymerization of chemical
components generally predominates between 270๐ C and 400๐ C, hemi-cellulose is
readily converted into methanol and acetic acid between 200 to 280๐ C, from 200 to
500๐ C cellulose which has already undergone some thermal degradation decomposes
at an increasing rate which reaches a maximum at around 320๐ C while lignin
decomposes only at the temperatures above 280๐ C, forming mainly tar and char
(Saravana and Babu, 2005; Peters and Bruch, 2003; Rajvanshi, 1986).
With reference to present work, the general course of pyrolysis of
lignocellulosic materials is observed as follows: The thermal destruction of
lignocellulosic biomass starts at 100๐ C (the main process being hydrolysis), the rate
and amount of destruction are quite negligible up to 200๐ C. After the last traces of
water are removed, which requires the temperature of about 140๐ C, four classes of
products are produced by thermal decomposition of wood: 1) Non-condensable gases
(CO, CO2, H2, CH4) 2) Pyroligneous products (condensable, mainly water contain) 3)
Tar (moisture-free, condensable) 4) Char. Gas were evolved at the temperatures
between 200๐C and 400 to 450๐C , with a maximum at about 350 to 400๐C. The rate of
production of pyroligneous material passes through a maximum between 250๐ C and
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400๐C and virtually ceases at about 500๐C. Tar forms between about 300๐C and 400๐C
to 450๐C.
Results and Discussions
The proximate and ultimate analyses of the sample of pine wood are shown in Table1.
The results showed that pine wood are environment friendly energy source due to it
contains trace amount of N, S and mineral matters. If only the main elements (C, H,
O) are considered, the empirical molecular formula of the examined pine wood
sample based on one C atom can be written as CHxOy as listed in the Table 1.
Furthermore, the higher heating value of initial pine wood sample was calculated by
sheng’s formula as Equation(1) (Sheng and Azevedo, 2005), using the percentage by
weight on dry basis of C, H and O from ultimate analysis.
HHV (MJ/kg) = -1.3675+0.3137C+0.7009H+0.0318Ob
(1)
where C, H, O represents carbon, hydrogen, oxygen content of material.
From Table 1, biomass from pine wood promising for energy production
owing to it provides the higher heating value in medium level of solid fuel compared
to coal (26.8 MJ/kg) also has high fixed carbon content in char therefore it suitable for
char production that can be useful as raw material for activated carbon.
The effects of heating rate on distribution of pyrolysis product yields were
showed in the Figure 2. The pine wood sample was pyrolyzed at different heating
rates of 10oC/min and 50oC/min with the varying of pyrolysis temperature of 250 to
600oC. The study found that at the pyrolysis temperature of 500oC, the char yield was
decreased from 27 to 32% when heating rate was increased. This may be related to the
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rapid heating leads to a fast depolymerization of the solid material to primary
volatiles, whilst at the lower heating rate a dehydration is to be more stable and an
hydrocellulose is too slow and is limited to occur (Chen et al., 1997). The liquid yield
was low at the lower heating rate and increases with the increase of heating rate, the
liquid yield was increased from 44 to 46% at the pyrolysis temperature of 500oC. The
gas product yield also increases with the increase in heating rate. It was increased
about of 12% when the heating rate was changed from 10oC/min to 50oC/min. The
increasing of the liquid and the gas product yield with the increase of heating rate may
be due to the elimination of the mass and heat transfer barriers in the particles by
higher heating rates (Sensoz et al., 2006; Luo et al., 2004).
The distribution of gas composition from pyrolyzing pine wood sample mainly
depends on reaction temperature. Naturally, biomass material consists basically of
three types of polymers: cellulose, hemi-cellulose and lignin. Under inert or oxidative
pyrolysis, biomass materials firstly are decomposed thermally. Cellulose mainly
produces CO, CO2 and H2 etc. hemi-cellulose mainly produces CO2, H2O and some
hydrocarbons, while lignin mainly produces CO, CO2 and CH4 etc.(Chen et al., 2008).
In the present work, the experimental results are presented and elucidated as follows;
Figure 3 shows the concentrations of CO, CO2 CH4 and Air (N2+O2) from pine wood
gas product. On the range of temperature between 300 to 400oC the gas mixture
mainly composed of CO and together with CO2 and the some Air(N2+O2). The origin
of the CO and the CO2 are mainly dependent on degradation of hemi-cellulose and
cellulose. On the other hand, CO and CO2 evolution at higher temperature can be due
to the lignin degradation (Yang et al., 2007; Williams and Besler, 1996). Over the
range of temperature between 300 to 500oC, the CO2 content slightly decreased as the
temperature increased likewise, CO content obviously decreased as the temperature
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increased. After that, with the temperature increased further, CO2 decreased whilst
CO quite stable.
It is obviously that the increase of the temperature favours the methane (CH4)
production, whereas the Air (N2+O2) decreases. The formation of CH4 was occurred
due to the degradation of lignin, since their concentration increased as degradation
process at high temperatures. The formation of CH4 was due to the release of methoxy
groups, involving C-C rupture, and it was controlled by hydrogen transfer reaction
(Sukiran, 2008).
The higher heating value (HHVg, MJ/Nm3) (Nm3 = normal cubic meter) of the
dry pyrolysis gas product can be calculated from Equation(2).
HHVg =  Xi Hi
(2)
where; Xi is volume proportional of specie i and Hi is higher heating value of specie i
of pyrolysis gas (CO, CH4), where as CO = 13.1 MJ/Nm3 and CH4 = 41.2 MJ/Nm3 (
Higman and van der Burgt, 2008).
From Equation (2), it is obviously that methane’s coefficient has the maximum
effect in the HHVg. Figure 4 shows the higher heating value of pyrolysis gas of pine
wood sample. The higher heating value increases rapidly with increasing of the
temperature. Pine wood produces higher yields of gas rich in pyrolysis gas (CO +
CH4) and gave a gas product with higher energy content (~15.42 MJ/Nm3 at the
temperature of 600oC). A gas product with energy content between 12 - 15 MJ/Nm3
belongs to a medium level gas fuel, which can be used directly in internal combustion
engines, gas turbines and steam boilers for power production (Yang et al., 2006).
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Conclusions
It shows that for the above time-temperature history, decomposition of the wood is
first observed at about 180oC and becomes rapid from 250oC onwards. Weight loss
increases with temperature. Most of the devolatilisation takes place between 250 and
450oC. Beyond 450oC, the rate of decomposition becomes gradually stable.
The results show that the batch fixed-bed pyrolyser described can be used with
success on the pilot scale to pyrolyse biomass residues. Therefore, this preliminary
study shows that the development of a continuous pyrolysis process is possible. The
study of effect of heating rate on pyrolysis product distribution had shown that at the
lower heating rate (10oC/min) is better condition than higher heating rate (50oC/min)
for pyrolysis operation for char yield production. On contrary, at the higher heating
rate was suitable pyrolysis operation condition to produce liquid and gas yield
products. Because of at higher heating rate, heat and mass transfer limitation in
particles was eliminated and results an increasing of liquid and gas products.
The pyrolysis gas can in turn be further purified to syngas, which mainly
composed of carbon monoxide, methane, and used directly to fire processes such as
kilns, as fuel in steam boilers, and increasingly as a gaseous fuel in internal
combustion engines and gas turbines. It is noticeable that the temperature is crucial
for the overall biomass pyrolysis process.
Acknowledegements
The authors would like to thank RMUTI Thailand for providing the financial support
for the research study and Heat and Power Engineering Faculty laboratory of TPU
Russia for providing necessary facilities for experiment.
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References
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of biomass, J. Org. Geochem., 30:1479-1493.
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www.biocoup.com/fileadmin/user/pdf/18.../48_BIOCOUP_VTT_Aug09.pdf
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Using Pyrolysis: A State-of- the-Art Review, Session: Energy Engineering,
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New Delhi, India. Available from: http://discovery.bitspilani.ac.in/~bvbabu/PyrSB_CC_2005.pdf
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Goswami, D.Y., (eds). p. 83-102. Available from:
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fluidized fixed bed reactor, [MSc. thesis]. Faculty of science, University of
Malaya, Kualalumpur, Malasia, 122p.
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Higman, C. and van der Burgt, M. (2008). Gasification. 2nd ed. Elsevier, Oxford OX2
8DP, UK, 391p.
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palm oil wastes for enhanced production of hydrogen rich gases, J. Proc.
Tech., 87:935-942.
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Figure 1. Experimental set up
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Effect of heating rate on pyrolysis product yields
from Pine wood (Siberian cedar)
85
80
75
Liquid at 10 oC/min
Char at 10oC/min
Gas at 10 oC/min
Liquid at 50 oC/min
Char at 50 oC/min
Gas at 50 oC/min
Product yield (mass %)
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
200
250
300
350
400
450
500
550
600
650
o
Temperature, C
Figure 2. Effect of temperature on pyrolysis product at different heating rate
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Effect of temperature on gas composition
from Pine wood (Siberian cedar)
80
Air (N2+O2)
70
CO
Gas composition ( Vol. % )
CH4
60
CO2
50
40
30
20
10
0
-10
250
300
350
400
450
500
550
600
650
o
Temperature ( C )
Figure 3. Effect of temperature on pyrolysis gas composition at heating rate of 50
oC/min
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Effect of temperature on higher heating value
of pyrolysis gas from Pine wood
16
Higher heating value, MJ/Nm3
15
14
13
12
11
10
9
8
250
300
350
400
450
500
Temperature, oC
550
600
650
Figure.4. Effect of temperature on higher heating value of pyrolysis gas
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Table 1. Main characteristics of the pine wood, wt% dry basis
Characteristics
Proximate analysisa
Moisture content
Volatile matter
Fixed carbon
Ash
Ultimate analysis
C
H
Ob
N
S
Empirical formula
H/C molar ratio
O/C molar ratio
Calorific value (MJ/kg)
Pine wood
13.76
79.41
19.11
1.47
47.30
5.38
45.92
1.40
N.D.
CH1.36O0.73
1.36
0.73
18.70
a
As received
By difference
N.D. (Not Detected)
b
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