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Cite This: Energy Fuels 2018, 32, 10266−10271
Torrefaction of Woody Waste for Use as Biofuel
C. M. Grottola,*,† P. Giudicianni,† J. B. Michel,‡ and R. Ragucci†
†
Istituto di Ricerche sulla Combustione (CNR), Piazzale Vincenzo Tecchio 80, 80125 Naples, Italy
Haute Ecole d’Ingénierie et de Gestion du Canton de Vaud (HEIG-VD), 1401 Yverdon-les-Bains, Switzerland
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‡
ABSTRACT: Biomass for energy production has been extensively studied in the recent years. To overcome some constraints
imposed by the chemical−physical properties of the biomass, several pretreatments have been proposed. Torrefaction is one of
the most interesting pretreatments because torrefied biomass holds a wide range of advantages over raw biomass. The
devolatilization of water and some oxygenated compounds influences the increase in the calorific value on both a mass and
volumetric basis. The increase in the density reduces the transportation costs. Moreover, the decreased moisture content
increases the resistance of biomass to biological degradation, thus facilitating its storage for long periods. Under torrefaction
conditions, approximately 10−40 wt % of the initial biomass is converted into volatile matter, including liquid and noncondensable combustible gases. The energy efficiency of the process could greatly benefit the exploitation of the energy content
of these products. Recent studies and technological solutions have demonstrated the possibility to realize polygeneration systems
that integrate torrefaction/pyrolysis to a combustion process with the aim of obtaining torrefied material/biochar and/or energy
from biomass. Some examples include Pyreg, Pyreg-Aactor GT, TorPlant, and Top Process. The identification of the main
volatiles produced under the torrefaction regime is useful for the optimization of the operating conditions of the integrated
system. The integrated process raises some concerns when biomass from phytoremediation and wood from demolition and
construction activities are used as feedstock because they could contain potential toxic elements (PTEs). During the torrefaction
treatment, the fate of PTEs should be controlled to avoid their release in the gas phase and to evaluate the extent of their
concentration in the torrefied biomass. The present work aims at studying torrefaction as an eco-sustainable process for the
combined production of a solid biofuel with improved characteristics with respect to the starting material and a combustible
vapor phase, embedded in the gas carrier flow, to be directly burned for energy recovery. Herein, torrefaction tests on Populus
nigra L. branches from phytoremediation and demolition wood were conducted at three temperatures, 250, 270, and 300 °C, at a
holding time of 15 min. The energetic content of torrefied materials was determined. At the same time, the fate of the heavy
metals (Cd, Pb, and Zn) in the raw biomass at different torrefaction temperatures was studied, and their mobility in the torrefied
biomass was investigated and compared to the mobility in the raw biomass.
1. INTRODUCTION
Energy consumption is increasing progressively with the rapid
population growth and economic development. A great interest
is oriented to the research of new renewable energy sources and
technologies to not only cope with the growing demand for
energy but also to facilitate a reduction in greenhouse gas
(GHG) emissions. Biomass conversion processes are viewed as
a viable option, even though it could be advantageous to
consider a number of biomass pretreatments to fit various
chemical and physical characteristics of biomass to the existing
combustion technologies.
Torrefaction was proposed as a pretreatment process for
improving inherent biomass characteristics, such as increasing
energy density and facilitating storage and handling systems,1−4
through the improvement of the grindability, the reduction in
the moisture content, the decrease in microbial degradation,
and the sanitization of pest-affected plants.5 The partial
decomposition of biomass at a low torrefaction temperature
generates condensable and non-condensable products and a
solid residue rich in carbon, which is referred to as torrefied
material; this material can be used as high-quality fuel in
different applications, including co-firing in power plants,
entrained flow gasification, and small-scale combustion
facilities.6 Extensive literature is available on the effect of the
two main operating variables, i.e., the final torrefaction
© 2018 American Chemical Society
temperature and the solid residence time. It was observed
that the temperature, in the range of 250−300 °C, affects the
physicochemical characteristics and energy properties of the
solid product more than the residence time.1,7−9 A residence
time ranging from a few minutes to 1 h was typically used in
torrefaction tests, and a residence time longer than approximately 30 min had only negligible effects.1,7−9
However, the environmental sustainability of the torrefaction
of lignocellulosic waste, such as woody waste and plants grown
on contaminated soils, must be addressed as a result of their
high content of potentially toxic elements (PTEs)10,11 that may
affect the quality of the gas product and the solid residue
depending upon the process temperature.
To our knowledge, few studies have addressed this issue. The
torrefaction of demolition wood was studied by Edo et al.12
The elemental trace metal analysis suggested that most of the
trace metals detected in the raw material remained in the chars
at the torrefaction temperature (220 °C) used in the work. Bert
et al.13 found that, up to 290 °C, heavy metals contained in the
Special Issue: SMARTCATs COST Action
Received: April 1, 2018
Revised: May 31, 2018
Published: June 4, 2018
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biomass were retained in the solid matrix. Nevertheless, other
authors14,15 showed that, when some heavy metals are present
in the form of chlorides, the devolatilization temperature was
greatly reduced, mainly under anoxic conditions. No investigation has been conducted on the mobility of heavy metals
retained in the torrefied biomass.
In this work, a comprehensive approach is proposed for
simultaneously studying the improvement of the energetic
characteristics of two kinds of contaminated woody wastes and
the environmental aspects related to the presence of
contaminants. Contaminations from different sources were
considered: Populus nigra L. branches (PN-B) containing heavy
metals translocated from the soil to the plant organs during
phytoremediation and demolition wood (DW) rich in heavy
metals derived from operational activities during the construction and the disposal of woody shipping crates. The aim of
the present work was 2-fold: studying the effect of the
torrefaction temperature on the energetic properties of the
torrefied biomass and evaluating the environmental impact of
the process by monitoring the release of heavy metals in the
vapor phase as well as their mobility in the torrefied materials.
Torrefaction tests were conducted under oxygen-limited
conditions at a constant heating rate (10 °C/min) and at three
final temperatures ranging from light to severe torrefaction
regime,16 namely, 250, 270, and 300 °C, with a residence time
of 15 min. The product yields were determined, and the
organic and inorganic fractions of the solid products were
characterized. The mobility of PTEs in the torrefied materials
was also investigated. Finally, condensable volatiles from
torrefaction tests were collected separately and analyzed by
gas chromatography (GC) to understand their potential
utilization.
Figure 1. Cross section of the “SOLO furnace”.
this increase was reproducible in all of the tests and did not affect the
average heating rate that remained equal to 5.6 °C/min. In all of the
tests, a maximum overshoot of 2 °C was observed.
The volatiles produced in the reaction unit entered the
condensation device, which consists of two Pyrex condensers in
series, where condensable volatiles cooled and condensed. At the
outlet of the condenser, a Pyrex flask was allocated for the collection of
the liquid products. The non-condensing phase was fed to the
analytical system for online characterization (Horiba Mexa 7170D).
After the process, the aluminum container was quenched by
immersing it rapidly in a glass beaker with 5 L of water at a
temperature of 10 °C. The water cooled the container, and any contact
between the torrefied material and water was avoided.
At the end of the test, the sample was immersed in a metal vessel
containing 10 °C water. The quenched sample was heated in the
furnace for 24 h at 105 °C before the final weight measurement to
remove the water. Solid yields were determined gravimetrically with
respect to the fed sample.
2.2. Material Characterization. 2.2.1. Solid Materials. PN-B
were collected during phytoremediation tests conducted in Litorale
Domitio, Agro Aversano NIPS (Campania region, South Italy) in the
framework of the European LIFE Project ECOREMED (LIFE11/
ENV/IT/275, ECOREMED), whereas DW was obtained from the
disposal of shipping crates. The material was ground, and the sieved
fraction, in the 400−600 μm size range, was recovered for the
torrefaction tests. The samples were oven-dried at 105 °C for 24 h and
kept in the desiccator before the characterization analyses and
torrefaction tests. The moisture content of feedstock and torrefied
biomass was measured with a thermobalance (Sartorius moisture
analyzer, model MA35) according to the ISO 18134-3 procedure. The
CHONS content was measured using the elemental analyzer
Analyseur Flash 2000 (Thermo Scientific) according to the ISO
16948:2015 procedure. The Carbolite AFF 1100 furnace was used for
the determination of ash and volatile contents according to the ISO
1171/18123:2015 and ISO 18123:2015 procedures, respectively. Fixed
2. MATERIALS AND METHODS
2.1. Torrefaction System. The experimental tests were performed
in a small-scale reactor “SOLO furnace”, available at HEIG-VD,
Switzerland. The cross section of the furnace is shown in Figure 1. The
reactor is divided into two connected and concentric cylindrical zones
separated by a perforated plate: the internal cylinder is the torrefaction
chamber (diameter of 20 cm and height of 40 cm), whereas the
external cylinder is for gas recirculation (diameter of 50 cm and height
of 80 cm).
A cylindrical steel container (diameter of 15 cm and height of 20
cm) with a perforated plate at the bottom is positioned in the internal
section of the reactor and is used to accommodate the feedstock (100
g for each test run) packed in an aluminum paper (15 × 5 cm) and
closed with a metal ring. The lid is provided with a hole that allows the
passage of the gas outlet line and the thermocouple. In the external
section, the recirculation of the exhausted gases produced during the
torrefaction test occurs. The recirculation is provided through a fan
located at the bottom of the external section under a perforated grid
(frequency = 30 Hz). No nitrogen flux was used during the
experiments. The fan located at the bottom of the reactor and the
extractor placed on the top section are both regulated with the aim to
reduce the oxygen content in the reaction environment.
The temperature of the sample and the reaction environment was
monitored constantly through six K-type thermocouples sketched in
Figure 1, connected to a Keysight (Agilent/HP) 34970A data
acquisition/data logger switch unit variable drive. The heat flux of
the heating coil was used as an adjustable variable in a proportional−
integral−derivative (PID) controller to produce a nominal heating rate
equal to 10 °C/min during the tests. The temperature of the sample
(TC2) was used as the set point temperature. As a result of the thermal
inertia of the system, the actual heating rate was 5.6 °C/min, up to 220
°C. At higher temperatures, the heating rate increased, probably as a
result of the exothermic decomposition of hemicellulose.17 In any case,
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Table 1. Feedstock Characterization: Elemental Analysis and HHVa
C (wt %, daf)
H (wt %, daf)
N (wt %, daf)
O (wt %, daf)
HHV (MJ/kg)
47.7 (0.3)
47.1 (0.2)
6.1 (0.2)
5.9 (0)
2.1 (0.4)
0.7 (0.1)
42.6 (0.1)
41.5 (0.1)
19.2 (0.3)
19.0 (0.3)
DW
PN-B
a
The relative error of three replicates is reported in parentheses.
Table 2. Feedstock Characterization: Proximate Analysis and Heavy Metal Contenta
moisture (wt %, as received)
volatiles (wt %, db)
fixed carbon (wt %, db)
ash (wt %, db)
Cd
(mg/kg)
Cu
(mg/kg)
Pb (mg/kg)
Zn (mg/kg)
1.1 (0.1)
7.0 (0.4)
80.2 (0.8)
77.0 (0.4)
18.3 (0.7)
18.2 (0.4)
1.5 (0)
4.8 (0)
0.1 (6)
2.2 (4)
6.4 (6)
8.2 (1.7)
30.6 (5.5)
60.3 (4.8)
142.4 (6.2)
50 (8.9)
DW
PN-B
a
The relative error of three replicates is reported in parentheses.
carbon was calculated as the amount required to complete the mass
balance. The calorific value was determined using a bomb calorimeter
(Oxygen Combustion Vessel 1108, Parr Instrument Company)
according to EN 14918. Ash composition was determined by
dissolving the biomass samples via microwave-assisted acid digestion
based on United States Environmental Protection Agency (U.S. EPA)
methods 3051 and 3052. The digested samples were then analyzed by
inductively coupled plasma mass spectrometry (ICP/MS) using an
Agilent 7500CE instrument. The results were reported in terms of the
content of the inorganic species and ion recovery in the torrefied
biomass. The first is defined as the mass of ion per mass of char and is
used to calculate the ion recovery by multiplying it by the torrefied
yield and then dividing by the mass of ions in the raw biomass.
The energy yields of the torrefied materials were calculated on a dry
basis by eq 1, where “t” stands for torrefied material and “f” stands for
feedstock.
energy yield =
HHV(t) × mass yield(t)
× 100
HHV(f)
3. RESULTS AND DISCUSSION
The results of the chemical characterization of PN-B and DW
samples are reported in Tables 1 and 2. It should be noted that,
Figure 2. Torrefied biomass yields at T = 250, 270, and 300 °C.
(1)
even though the origin of the waste was different, the results of
the elemental analysis were comparable, except for those of the
nitrogen content. The biomass from phytoremediation was
richer in ash than DW. The higher nitrogen content of DW
compared to that of PN-B could be attributed to adhesives used
in the production of timber goods (such as particle boards) that
ended up in the DW wood waste stream.19 The proximate
analysis highlighted a comparatively higher content of volatiles
in DW and a higher ash content in PN-B, whereas the fixed
carbon content was comparable. The heavy metals present in
both samples were Cd, Cu, Pb, and Zn, with the last two being
the most abundant, as shown in Table 2.
The torrefied biomass yields are shown in Figure 2. As
expected, for both the PN-B and DW, the mass yield decreased
with the torrefaction temperature. Despite the similar results
obtained from the elemental analysis and the higher volatile
content of DW, at each temperature, the mass loss was higher
for PN-B than for DW. The mass yield of the torrefied biomass
varied between 74.6 and 64.0 wt % for PN-B and between 87.4
and 80.5 wt % for DW. Basu et al.20 reported a yield of 78 wt %
for poplar wood torrefied at 250 °C, whereas Kim et al.21
obtained solid yields between 92 and 60 wt % for yellow poplar
torrefied in the temperature range of 240−280 °C. The results
on DW mixed with refuse-derived fuel (RDF) are available in
the temperature range of 220−270 °C12,22 and show yields
varying in the range between 94 and 84 wt %. According to the
previous findings, in the torrefaction regime, hemicellulose is
the main component undergoing devolatilization.23 The higher
solid yield observed for DW in this study could be explained by
the lower content of hemicellulose in the raw sample.
Metal mobility was determined through a leaching test on biomass and
corresponding torrefied materials using water and an ethylenediaminetetraacetic acid (EDTA)−NH4 solution, as reported by Gonsalvesh
et al.18 The amount of heavy metals in the leachate was estimated on
the basis of the PTEs recovered in the torrefied biomass. The ion
release was the ratio between the amount of PTEs released in the
leachate and the amount of PTEs in the torrefied material.
2.2.2. Liquid Product. For the identification and quantification of
the main condensable species, liquids obtained from torrefaction tests
at 250, 270, and 300 °C were filtered with 0.20 μm microfilters
(Millex-FG). Chemical analysis was performed by a gas chromatograph coupled with a flame ionization detector (GC/FID, Agilent
Technologies 7820A GC system) and a DB-1701 capillary column (60
m × 0.25 mm inner diameter, 0.25 mm film thickness). Helium
(99.9999%) was used as carrier gas with a constant flow of 1.0 mL/
min. The oven temperature was programmed from 318 K (4 min) to
508 K at a heating rate of 3 K/min and held at 508 K for 30 min. The
injector and the FID were kept at 523 and 573 K, respectively. A
sample volume of 1 μL (4.5 wt % pyrolysis liquid in acetone) was
injected.
The identification of the main compounds (acetic acid, hydroxyacetone, furfural, 5-methylfurfural, and 5-hydroxymethylfurfural) is
based on the match with the retention times of the corresponding
standards (Sigma-Aldrich 319910) analyzed by GC/FID under the
same conditions. The identified compounds were quantified by the
internal standard method, using fluoranthene as an internal standard. A
calibration curve was prepared by the injection of four standard
solutions. The concentration range was determined by successive
approximations until it became relatively narrow and encompassed the
quantified value. Injections of the liquid samples were made in
duplicate, and the maximum relative error observed was ±5% of the
average values.
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Figure 3. (a) Gas species and (b) liquid compound concentration obtained from PN-B torrefied at T = 300 °C.
Table 3. Elemental Analysis and Energy Properties of Torrefied DW and PB-N Obtained at 250, 270, and 300 °Ca
C (wt %, daf)
DW 250
DW 270
DW 300
PN-B 250
PN-B 270
PN-B 300
a
H (wt %, daf)
50 (1.0)
53 (0.5)
54.4 (0.8)
51.4 (0.9)
51.8 (0.6)
54.2 (0.5)
5.8
5.8
5.8
5.4
5.2
5.1
N (wt %, daf)
(0.2)
(0.1)
(0.2)
(0.1)
(0.1)
(0.1)
2.4
3.0
3.4
1.0
0.8
0.9
O (wt %, daf)
(0.3)
(0.6)
(0.2)
(0.1)
(0.1)
(0.1)
39.0
36.0
34.5
38.0
37.3
34.0
HHV (MJ/kg)
(1.3)
(0.5)
(0.7)
(0.6)
(0.9)
(0.6)
19.3
21.5
22.5
20.8
21.5
23.3
energy yield (%)
(0.7)
(0.2)
(0.1)
(0.9)
(0.7)
(0.3)
88.1
95.6
94.3
78.1
75.8
75.0
The relative error of three replicates is reported in parentheses.
Table 4. Proximate Analysis and Heavy Metal Content of Torrefied DW and PB-N Obtained at 250, 270, and 300 °Ca
moisture
(wt %, as received)
DW 250
DW 270
DW 300
PN-B 250
PN-B 270
PN-B 300
a
1.3
1.5
1.3
1.2
1.5
1.6
(0.5)
(0.1)
(0.1)
(0.7)
(0.5)
(0.2)
volatiles
(wt %, db)
71.8
71.9
70.3
69.1
67.9
62.5
(6)
(0.8)
(0.6)
(0.1)
(2.8)
(0.1)
fixed carbon
(wt %, db)
25.4
25.9
27.9
25.7
27.2
31.7
ash
(wt %, db)
(5.0)
(1.2)
(0.6)
(0.5)
(3.2)
(0.2)
2.7
2.1
1.8
5.1
4.9
5.8
(1)
(0.5)
(0)
(0.1)
(2.8)
(0.1)
Cd
(mg/kg)
Cu
(mg/kg)
Pb (mg/kg)
Zn (mg/kg)
0.1
0.2
0.2
2.5
2.6
3.2
8.3
8.5
8.9
9.6
9.7
11.4
51.7 (10)
52.9 (17)
54.1 (71)
70.4 (10)
72.3 (3.2)
89 (4.6)
185 (7)
188 (15)
195.4 (7)
61 (0.6)
65.4 (4)
73.2 (0.1)
(19)
(4)
(2)
(3.4)
(1.8)
(3.5)
(5)
(26)
(7)
(0.3)
(4.3)
(5)
The relative error of three replicates is reported in parentheses.
Table 5. Ion Recovery of Torrefied DW and PB-N Obtained
at 250, 270, and 300 °Ca
ion recovery
DW 250
DW 270
DW 300
PN-B 250
PN-B 270
PN-B 300
a
Cd (g/g)
Cu (g/g)
0.99
1.00
1.15
0.99
1.01
1.02
0.98 (4.9)
1.15 (5)
1.1 (6)
0.97 (4.9)
1.07 (5)
1.04 (6)
(1.5)
(1.5)
(6)
(3)
(1.5)
(7)
Pb (g/g)
1.12
0.95
1.12
1.05
1.02
1.03
(9.7)
(1.75)
(5)
(2.8)
(1.75)
(5)
Zn (g/g)
1.06
0.97
1.00
0.99
1.00
1.06
(6.8)
(3)
(4)
(3)
(3)
(7)
The relative error of three replicates is reported in parentheses.
compounds. Among the detected liquid compounds, acetic
acid is the most abundant, followed by acetol and furan
derivatives. However, the torrefaction liquids are typically
greatly diluted in water.24
3.1. Torrefied Biomass Characterization. The results of
characterization of torrefied DW and PN-B obtained at
different temperatures are reported in Tables 3 and 4.
With an increasing torrefaction temperature, for both the
feedstocks, an increase in the amount of elemental carbon and a
decrease in the elemental oxygen and hydrogen amounts were
observed, in agreement with the literature.1 This result is due to
the breaking of the weak C−O and C−H bonds in the
hemicellulose matrix responsible for the release of volatile
species and permanent gases (mainly CO and CO2)25 that are
Figure 4. Van Krevelen diagram for untreated and torrefied PN-B and
DW.
Nevertheless, the results of DW suffer heavily from the
inhomogeneity of this type of woody refuse, and as a
consequence, this makes it impossible to draw firm conclusions
for these materials.
The evolution of the gas composition during the torrefaction
of PN-B at 300 °C (Figure 3a) and the main liquid compounds
identified at 300 °C (Figure 3b) confirm that the hemicellulosic
fraction of the PN-B sample is decomposed, producing mainly
CO2 from the decomposition of side chains (acetyl and
carboxylic groups), CO from the carbonyl end groups left after
dehydration of the side chain groups, and condensable
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Figure 5. Ion release of heavy metals in (a) water and (b) EDTA−NH4 leaching solution.
decrease in the O/C ratio in the char is smaller for PN-B than
that for DW. This result implies that DW released a lower
amount of vapors (condensable and permanent gases) with a
greater oxygen content. It is likely that mainly H2O was
produced and released and that most of the energy-containing
volatiles were still in the torrefied material.28 As a consequence,
with an increasing temperature, the increase in the char calorific
value is greater than the mass loss, thus determining the
increase in the energy yield.
The concentration and ion recovery of the detected heavy
metals, namely, Cd, Pb, Cu, and Zn, for the torrefied materials
are reported in Tables 4 and 5, respectively. The concentration
increased with the torrefaction temperature for both feedstocks.
The ion recovery for all torrefied materials is very close to 1,
and thus, it can be inferred that the condensable and gas phases
evolved from the torrefaction tests were essentially free of
heavy metals.
To investigate the effect of torrefaction on the mobility of the
heavy metals retained in the torrefied PN-B samples, two
leaching tests were performed, in water and in an EDTA−NH4
solution. A higher ion release in water was observed for Zn,
followed by Cu, Cd, and Pb, and their mobility decreased with
an increasing torrefaction temperature (Figure 5). This result
could be related to the increase in the hydrophobic character of
the torrefied biomass with the torrefaction temperature.1
Leaching with EDTA−NH4 was more severe, and all metals
were released from the raw materials. The temperature did not
have any effect on the PTE mobility up to 300 °C, where part
of the metals retained in the char are immobilized in the solid
matrix, even in more severe leaching conditions. It is likely that,
in acid conditions, the acid groups, associated with lignin,
hemicellulose, and extractives, were easily removed together
with the associated inorganic elements.29
rich in oxygen and hydrogen, thus causing the deoxygenation of
the torrefied biomass. The thermal behavior of elemental
nitrogen was different in the two feedstocks, revealing a
different chemical nature of the N compounds in PN-B and
DW. The nitrogen content always increased with the
torrefaction temperature for the DW sample, whereas for the
PN-B sample, the trend was not evident. The O/C and H/C
ratios, represented in the Van Krevelen diagram in Figure 4 for
both the PN-B and DW torrefied samples, are considered
important parameters to characterize solid biofuel composition
with respect to coal. Typical H/C and O/C values for torrefied
biomass are in the range of 1−1.5 and 0.4−0.65, respectively.26
An increase in the torrefaction temperature reduced both H/C
and O/C ratios to values that are within the typical ranges
observed for other torrefied biomasses, even though they were
still high in comparison to the characteristic values of coal. At
300 °C, it was observed that the O/C and H/C ratios were
greatly decreased to values close to the lignite coal range.27 The
lowest torrefaction temperature significantly affected the O/C
ratio for the PN-B sample, indicating that significant
devolatilization of oxygenated compounds occurred even at a
low temperature, in agreement with the observed weight loss
(Figure 2). At the highest torrefaction temperature, DW and
PN-B were characterized by comparable O/C ratios. At each
temperature, the H/C ratio, similar in both feedstocks, was
always lower for torrefied PN-B, denoting the devolatilization
of a greater amount of compounds containing saturated C−H
bonds as well as bound water.
Table 4 shows that, as expected, the volatile content of both
torrefied feedstocks decreased with the temperature, whereas
the fixed carbon content increased. According to the higher
mass loss observed for PN-B than for DW, the fixed carbon
content was higher and the volatile content was lower for the
corresponding material torrefied at 270 and 300 °C. The fixed
carbon content of torrefied DW and in particular the PN-B
sample increased greatly and was comparable to that of coal.1
The higher heating values (HHVs) of torrefied solids were
remarkably improved at higher torrefaction temperatures and
were always slightly higher for PN-B than those for DW across
the whole temperature range. However, it should be noted that
the energy yield was always lower for PN-B as a result of the
higher devolatilization. Moreover, in the case of DW, the
energy yield had a non-monotonous trend with the temperature, showing a maximum at 270 °C. In contrast, the energy
yield decreased with the temperature for PN-B. As the
temperature increased from 250 to 270 °C, the char yields
decreased for both PN and DW. Nevertheless, in the case of
PN-B, the mass loss is greater than that for DW. In contrast, the
4. CONCLUSION
The torrefaction of woody waste (demolition wood and
biomass from soil phytoremediation) was studied with the
aim of evaluating the energetic properties of the torrefied
material and the fate of heavy metals during the pretreatment.
It was found that, with an increasing torrefaction temperature,
the energy properties of both torrefied biomasses were
improved. In particular, the study revealed that DW has a
high potential in terms of its energy content as well as energy
yield. Some concerns arise for the high nitrogen content of DW
compared to that of PN-B in both the raw and torrefied
materials. For both feedstocks, PTEs were retained in the
torrefied biomass up to 300 °C, allowing for the production of a
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DOI: 10.1021/acs.energyfuels.8b01136
Energy Fuels 2018, 32, 10266−10271
Article
Energy & Fuels
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■
AUTHOR INFORMATION
Corresponding Author
*Telephone: +39-081-768-2245. E-mail: cm.grottola@irc.cnr.it.
ORCID
C. M. Grottola: 0000-0002-3994-9489
P. Giudicianni: 0000-0002-6700-8205
Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS
This paper is based on work from COST Action SMARTCATs
(CM1404), supported by the European Cooperation in Science
and Technology (COST, http://www.cost.eu). This work was
supported by the European Commission (Project LIFE11/
ENV/IT/275, ECOREMED) and the Accordo di Programma
CNR-MSE 2013-2014 under the contract “Bioenergia
Efficiente”.
■
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