Fast devolatilization characteristics of ‘low cost’ biomass fuels, wood and reed. Potential feedstock for gasification

Fuel Processing Technology 142 (2016) 157–166

Contents lists available at ScienceDirect

Fuel Processing Technology journal homepage: www.elsevier.com/locate/fuproc

Research article

Fast devolatilization characteristics of ‘low cost’ biomass fuels, wood and reed. Potential feedstock for gasification K. Anastasakis ⁎, I. Kitsiou, W. de Jong Faculty of Mechanical, Maritime and Materials Engineering, Process and Energy Department, Delft University of Technology, Leeghwaterstraat 39, Delft, 2628 CB, The Netherlands

a r t i c l e

i n f o

Article history: Received 8 June 2015 Received in revised form 6 October 2015 Accepted 8 October 2015 Available online 22 October 2015 Keywords: Fast devolatilization Kinetics Tar Heated foil reactor Wood Reed

a b s t r a c t Fast devolatilization of woody (mixture of softwoods) and herbaceous (reed) biomasses has been studied in a heated foil reactor coupled to an FTIR spectrophotometer. Biomass fuels were chosen based on their potential for contributing to power generation on an industrial scale through gasification in The Netherlands. Heating rate (600 °C/s) and holding time (10 s) at peak pyrolysis temperature were chosen to correspond to conditions encountered in industrial processes. The effect of peak pyrolysis temperature on pyrolysis products was investigated. Particular emphasis was given to tar collection, and subsequent gravimetric quantification. The results indicated a strong total weight loss increase with temperature, to reach an asymptote char yield of 16.7 wt.% at 800 °C and of 32.4 wt.% at 700 °C for wood and reed, respectively. Reed primary devolatilization reactions ceased at lower temperatures compared to wood. The latter was confirmed by the lower activation energy of reed (32.1 kJ/mol) compared with that of wood (38.4 kJ/mol) during extrapolation of kinetic data from the fast devolatilization experiments. CO2 dominated the gaseous products released at lower temperatures (b700 °C) while CO became predominant at higher pyrolysis temperatures (N 700 °C) reaching a maximum of 19.1 wt.% and 18 wt.% for wood and reed, respectively, at 1000 °C. Maximum tar yields of 38.8 wt.% (d.b.) of dry wood and 23.3 wt.% (d.b.)of dry reed were able to be recovered at 600 °C. An overall mass balance of approximately 90 wt.% (d.b.) for both biomass fuels was obtained at high (900–1000 °C) pyrolysis peak temperatures. © 2015 Elsevier B.V. All rights reserved.

1. Introduction Gasification of biomass is an attractive option as a renewable energy conversion process. During gasification, biomass is converted into a gaseous fuel, the syngas, composed mainly of CO, CH4, CO2 and H2. Syngas, after cleaning, can be directly used in gas engines/turbines for combined heat and power generation, as a feedstock for the production of synthetic liquid fuels via the Fischer–Tropsch process or for the production of methanol, synthetic natural gas and hydrogen. While being one of the promising thermochemical conversion technologies for biomass, commercialization of this technology poses some challenges. These challenges include the supply of biomass feedstock, the type of gasifier and its operating variables as well as the gas cleaning from tars and other contaminants [1]. One of the key aspects in both selection of suitable biomass feedstock and design of gasifiers is the investigation of the primary devolatilization (pyrolysis) process. During devolatilization, biomass is decomposed into gases (CO2, CO, CH4, H2, H2O, CxHy), condensable volatiles (tar) and a solid residue (char) which then undergo the gasification reactions. Reproducing industrial scale conditions is fundamental to generate reliable data for implementing into models for the design of a suitable ⁎ Corresponding author. E-mail addresses: [email protected], [email protected] (K. Anastasakis).

http://dx.doi.org/10.1016/j.fuproc.2015.10.018 0378-3820/© 2015 Elsevier B.V. All rights reserved.

reactor. In this context, but as a separate thermochemical process as well, pyrolysis has received extensive investigation over the last 40 years. Knowledge of the yields and composition of the main devolatilization products as a function of process conditions is crucial for the development and optimization of industrial thermal conversion applications. Hence, substantial focus has been directed towards studying the involved phenomena both in large and small scale setups. Up to now, biomass devolatilization carried out on a small scale has been studied in a variety of different setups including thermogravimetric analyzers (TGA), curiepoint reactors, drop tube furnaces and heated grid reactors [2]. Among the different equipments, the heated foil (also named wire mesh, screen heater or heated grid reactor) setups are distinguished by their unique characteristics. The main advantage of this reactor type is that it is possible to reproduce similar conditions to industrial processes by employing very high heating rates (103–105 °C/s) and temperatures. Moreover, secondary reactions are minimized, since volatiles are immediately swept by some inert gas (i.e. helium or nitrogen) and condensed. The heated foil reactor setups were initially used for studying coal pyrolysis [3]. However, research has also been carried out on various types of biomass in a number of works. An overview of the previous studies on fast devolatilization of biomass and biomass components in heated foil reactor setups is presented in Table 1. As it can be seen from the table, operating temperatures vary from 250 to 1300 °C and heating rates used are up to 15,000 °C/s. Holding times applied are

158

K. Anastasakis et al. / Fuel Processing Technology 142 (2016) 157–166

Table 1 Overview of heated foil reactor setups used for fast pyrolysis experiments of biomass. Year

Feedstock

T (°C)

Heating rate (°C/s)

Holding time (s)

Reference

1979 1982 1985 1991 1993 1994 1994 1996 2008 2008

Kraft lignin Cellulose Sweet gum hardwood Sugarcane bagasse, silver birch Cellulose Pine wood Sugarcane bagasse Sugarcane bagasse, silver birch Olive kernel Rapeseed residues

[4] [5] [6] [7] [8] [9] [10] [11] [12] [13]

Corn cob and corn stalk

–

[14]

2009 2009 2009 2010 2011 2011 2012

Olive kernel Pine wood Chicken litter, MBM DDGS, PKC Pine wood MDF, bark pine, Avicel cellulose Pine wood and model compounds

250 100–15,000 1000 1–1000 1000 1–1000 200–10,000 0.1–1000 200 48 52 45 200 300–600 600–1000 600 300–600 300–500 50–7000

5–120 0–30 0 0–100 0–5 10 0–30 0–100 1.5 –

2009

400–700 300–1100 327–1127 300–900 400–1100 400–600 300–1100 300–900 300–600 480–790 360–730 380–680 300–600 500–700 500–1300 500–1200 500–700 435–1100 250–700

1.5 7–20 1–10 10 7–20 0–50 1

[15] [16] [2] [17] [18] [19] [20]

BGS: brewer spent grains, MBM: meat &bone meal, DDGS: dry distiller grains with solubles, PKC: palm kernel shells, MDF: medium density fibreboard.

between 0 and 120 s to approach complete conversion. Even though research using those setups focused on several aspects of biomass devolatilization, and product yields as well as compositions were determined by various techniques, only a few of the works have dealt with determination of the produced tar. A common practice to determine tar content is by the difference of the other quantified phases (gases and char) from the initial mass. Hence, limited information on the effect of operating conditions on tar formation is available. Furthermore, the aim of most of the studies was to maximize liquid (tar) yields as the scope was to examine pyrolysis as a standalone process for the production of liquid fuels (pyrolysis oil). Therefore in many studies very high heating rates, short residence times and rapid quenching of the reactor have been employed. The aim of this work is to investigate the devolatilization behaviour of some selected biomass fuels under conditions simulating industrial processes such as gasification and combustion. More specifically, the present study investigates the pyrolytic conversion behaviour of woody (mixture of softwoods) and herbaceous (reed) biomass fuels. The selected biomass fuels were chosen according to their availability and price in The Netherlands (for large scale utilisation). An attempt to quantify all product streams (including tar) and to close the mass balance is made. The effect of pyrolysis temperature on product yields (char, gas and tar) is under examination. Experimental data obtained by the present study are used to obtain kinetic parameters for total conversion and rates of gaseous species evolution under fast heating rate conditions. While there is a substantial amount of literature on fast pyrolysis of different types of wood biomass, literature data on fast pyrolysis of reed are scarce. The main objective of this study is to provide both experimental and kinetic data under fast heating rate conditions in order to advance the understanding of fast pyrolysis of the specific feedstocks and provide with data to be implemented in models for predicting thermochemical reaction behaviour. 2. Materials & methods 2.1. Proximate ultimate and biochemical analysis of the fuels The biomass fuels under investigation were supplied by the Dutch company Synvalor, currently employing research on the development and deployment of a novel gasification reactor. More specifically, a mixture of waste softwoods from a furniture company and whole reed (leaves and stems) harvested from Dutch wetlands, used as feedstock for the gasifier, were under investigation. Harvesting reed from Dutch wetlands is a common practice occurring every 1–2 years in order to

avoid formation of forests, by removing nutrients from the ground. Prior to the experiments the biomass specimens were ground and sieved to powder with a particle size between 250 and 425 μm. In this way the soil particles present in reed samples could be removed. Subsequently the 250 and 425 μm particle size fraction was further ground and sieved to powder with particle size b 90 μm. Proximate analysis of the fuels was performed by thermogravimetry. Thermogravimetric (TGA) and differential thermal (DTG) analysis were performed in nitrogen atmosphere using a TA-Instruments SDTQ600. A typical sample mass of 12–15 mg was heated to 900 °C at a ramp rate of 10 °C/min in a total flow rate of 100 ml/min. When the desired temperature (900 °C) was reached the atmosphere was switched from inert to oxidative in order for the burnout of any remaining carbon in the residue and thus ash determination. The C, H, N, S contents of the fuels were provided by the TLR international laboratories. For the calculation of the HHVs of the fuels the correlation provided by Channiwala and Parikh [21] was used. The proximate and ultimate analysis of the fuels is presented in Table 2. Wood was found to have a significantly higher calorific value than reed (20.6 MJ/kg and 11.4 MJ/kg, d.b., respectively) reflecting its higher volatile matter and lower ash content. Biochemical composition of the selected biomass fuels was determined according to the standard procedure for determination of structural carbohydrates and lignin in biomass (NREL/TP-510-42618) [22]. Extractives present in reed fuel were determined according to the standard procedure for determination of extractives in biomass (NREL/TP-510-42619) [23]. The biochemical composition along with the neutral sugars content of the fuels is presented in Table 3. Wood was found richer in cellulose and lignin while reed was richer in hemicellulose and extractives. Table 2 Proximate and ultimate analysis of wood and reed fuels. Wood

a

Moisture (wt.%) Asha (wt.%) VMa (wt.%) FCa (wt.%) C (wt.%) H (wt.%) N (wt.%) S (wt.%) Ob (wt.%) HHV (MJ/kg) a b

Reed

a.r.

d.b.

daf

a.r.

d.b.

daf

7.9 0.7 72.1 19.3 45.6 3.8 0.5 0.04 41.6 16

– 0.8 78.3 21.0 49.5 4.1 0.5 0.04 45.1 17.7

– – 78.9 21.1 49.8 4.1 0.5 0.04 45.5 17.9

8.8 19.4 57.9 13.9 30.5 3.8 0.2 0.06 37.2 10.8

– 21.3 63.5 15.2 33.4 4.1 0.2 0.07 40.8 12.3

– – 80.6 19.4 42.5 5.3 0.3 0.08 51.9 16.1

Calculated by TGA. Calculated by difference.

K. Anastasakis et al. / Fuel Processing Technology 142 (2016) 157–166 Table 3 Neutral sugars and biochemical composition of wood and reed fuels (wt.%, d.b.).

Glucan Xylan Galactan Arabinan Mannan Ash Cellulose Hemicellulose Lignin Extractives Total

Wood

Reed

38.4 8.2 2.4 1.6 5.4 0.8 38.4 17.6 33.6 – 90.4

34.9 17.4 0.5 2.3 0.4 8.3 34.9 20.6 25.5 8.7 98

159

and char was retrieved from the stainless steel foil and its mass was determined gravimetrically. The glass wool filters were collected and the reactor walls and lid were washed with dichloromethane (DCM) to collect the condensed tar. Tar was operationally defined as the condensable products within the reactor chamber at room temperature plus the condensables on the glass wool filters at 110 °C. The tars adsorbed on the filters were removed mechanically by DCM, mixed with the rest of the solution acquired from the reactor chamber and filtered through a Whatman 41 ashless filter paper to remove any solids present. Finally, after filtration, DCM was allowed for evaporation at room temperature, under hood, and – once totally removed – tar was determined gravimetrically. All the experiments were performed at least in triplicate and the mean values are reported. All product yields were expressed on a dry biomass base (d.b.).

2.2. Apparatus and experimental procedure 2.3. Slow and fast heating rate kinetics The fast pyrolysis experiments were carried out in a heated foil reactor integrated in an FTIR (Thermo Nicolet NEXUS 6700) for simultaneous analysis of the product gases. A schematic diagram of the reactor system is shown in Fig. 1. More details about the specific design can be found in previous works [2,17]. A significant difference was the placement of glass wool at the outlet of the main chamber (just before the circulation pump) for tar trapping. Small amounts (10 ± 1 mg) of the biomass fuels, prior ground and sieved to 90 μm, were compressed into tablets of 2.5 mm diameter and 0.7 mm thickness (by using pellet press, force of 2 t) in order to ensure a more even heat distribution in the sample and thus similar heat transfer behaviour in each experiment. Biomass fuels were introduced in the reactor in the form of a thin tablet in order to prevent loss of the material and to improve the reproducibility of the experiments. The specific tablet dimensions were chosen in order to ensure the complete release of the volatiles from the biomass fuels and to reduce the deviations of the temperature measured by the thermocouple at the centre of the foil. The biomass tablet was placed on the stainless steel foil (point 1 in Fig. 1), the reactor was sealed and the system was flushed with nitrogen in order to flush the system of any residual gases. Once flushing was complete, the inlet and outlet valves were closed and the tablet sample was heated to the final peak temperature (500–1000 °C) for 10 s (HT) at a heating rate (HR) of 600 °C/s. As the gaseous products were released they were transferred, via the circulation pump to the FTIR gas cell for analysis (point 9 in Fig. 1). The FTIR was calibrated for the quantification of CO2, CO, CH4 and H2O, the resolution was set to 0.25 cm−1 and 3 scans were averaged every 9 s for a total time of 3 min. Once the gas analysis was completed, the reactor chamber and circulation line heaters were turned off, and a flow of nitrogen was allowed to pass through the reactor system until the whole system was cooled down to room temperature. Then the reactor lid was removed

TGA is widely used for calculating initial decomposition kinetics for a variety of fuels including e.g. biomass, coal. Various methods for extracting these kinetic parameters from the TGA data have been demonstrated [24,25]. In the present study the temperature integral approximation by Senum and Yang [26] was used for extracting the initial kinetic parameters from slow pyrolysis experiments. In this single first-order reaction model a nonlinear least-squares regression is used to calculate activation energy (Ea) and pre-exponential factor (A) from the integrated form of Arrhenius equation at a pre-determined heating rate B = dT/dt: − ln ð1−aÞ ¼

AEa pðxÞ RT

ð1Þ

where a ¼ 1− mm0, m and m0 corresponds to the current and initial sample mass respectively, p(x) is the polynomial approximation of Senum and Yang: pðxÞ≅

expð−xÞ x4 þ 18x3 þ 86x2 þ 96x : x2 x4 þ 20x3 þ 120x2 þ 240x þ 120

ð2Þ

where x = Ea/RT. More details about the method can be found elsewhere [27]. However, derivation of kinetic parameters by TGA, at slow heating rates, is questionable since the data are not directly applicable to many industrial processes where much higher heating rates are applied [24]. In accordance with the TGA models, a single first-order reaction model was used to fit the total conversion (100%-char yield) and individual gaseous components evolution under fast heating rates. The model has successfully been used in the past for extracting kinetic parameters under fast heating rate conditions for a variety of biomass feedstock and model compounds [5,6,10,11]. According to this model, the rate of formation of a product, i, in mass yield, Wi, over time is a function of its ultimate attainable yield (W⁎) and a constant, k, that follows the Arrhenius equation: dW i ¼ kðW  −W i Þ dt

ð3Þ

Ea

k ¼ Ae−RT

ð4Þ

By combining the above two equations and by integrating for a constant heating (B = dT/dt) and cooling rate (CR) over a holding time, HT, the following expression is derived: ( Wi ¼ W Fig. 1. Top view of the heated foil reactor integrated to FTIR.



"

RT 2 1− exp −A þ HT MEa

!

 #) Ea exp − RT

ð5Þ

160

K. Anastasakis et al. / Fuel Processing Technology 142 (2016) 157–166

BðCRÞ where, M ¼ BþðCRÞ . The experimental data of product yields were fitted to

this model by using the experimental values and by applying a nonlinear least-squares regression on Eq. (5). 3. Results and discussion 3.1. Thermogravimetric analysis Thermogravimetric analysis was introduced in order to study the devolatilization behaviour of wood and reed samples under slow heating rate conditions (10 °C/min). The resulting TGA and DTG curves of the two biomass samples are depicted in Fig. 2. Both feedstocks were found to exhibit a weight loss region due to moisture evaporation until a temperature of 120 °C, followed by a steady weight period until a temperature of about 200 °C where the devolatilization reactions begin. These reactions ended at about 600 °C with the majority of volatile matter being evolved between 200 °C and 400 °C. Above 600 °C to the final set temperature a slight weight loss due to the solid residue degradation was observed. The maximum rate of weight loss was found to occur at 360 °C and 350 °C for wood and reed, respectively. Differential thermogravimetry (DTG) has revealed a shoulder on the left of the main devolatilization DTG peak of reed which was absent for the case of wood. This can be attributed to the higher and different nature hemicellulose contents of reed. Hemicellulose present in reed was found to contain large quantities of xylan (Table 3) whose thermal decomposition produces the specific characteristic DTG shoulder [28]. Hemicellulose decomposition is known to begin at lower temperatures than the other biomass bio-polymers (cellulose and lignin) [29]. This, along with the higher inorganic content of reed, can also explain the slight shift to lower temperatures for reed devolatilization when compared to wood. The latter was verified by determining the initial kinetic parameters of primary devolatilization. Activation energies (Ea) were calculated as 62.6 kJ/mol and 50.5 kJ/mol for wood and reed, respectively. The lower Ea of reed indicates that pyrolysis reactions are easier to begin for the case of reed suggesting that devolatilization occurs at lower thermal (temperature) input. The corresponding pre-exponential factors in logarithmic form (lnA) were calculated as 5.8 and 3.3 for wood and reed, respectively. 3.2. Fast pyrolysis yields The heated foil reactor was used in order to investigate the influence of temperature on the product yields resulting from fast pyrolysis

(600 °C/s) of wood and reed. Under high heating rates similar conditions to industrial processes (e.g. pyrolysis, gasification and combustion plants) could be reproduced in the laboratory. The pyrolysis products, gaseous (including non-moisture water), condensable volatiles (tar) and solid (char) were all determined individually and the results are presented in Fig. 3 on a dry basis (d.b.). The mass balance of the collectable pyrolysis products for both wood and reed was between 80 and 90 wt.% (d.b.) of the feed. The majority of undetectable species is believed to be composed of the undetectable gases such as H2 and C2+ hydrocarbons and from tar as it will be explained in the following sections. In both cases the mass balance closure was improved with increased peak temperature. At high temperatures (900–1000 °C), about 90 wt.% of the total products was recovered, in accordance with previous reported results by Nunn et al. and Stubington and Aiman during pyrolysis of sweet gum hardwood and bagasse, respectively, in a similar reactor design [6,10]. Devolatilization product yields for both feedstock were found to follow the same trend, with char yields reducing (until reaching an asymptote), followed by an increase in gas yields over temperature. On the other hand tar yields go through a maximum between 600 °C and 700 °C and then decrease with increasing temperature. Despite their similar trend, significant differences were found between the product yields on d.b. basis for the two fuels. At lower temperature (500 °C), reed char yields were found lower than wood char yields (43.8 wt.% d.b. and 54.7 wt.% d.b. respectively), indicating the devolatilization of reed at lower temperatures. As was previously shown during slow pyrolysis experiments (TGA) and the extrapolation of the initial pyrolysis kinetic parameters, reed was expected to devolatilize at lower temperatures due to its higher inorganic content. Inorganic species catalyse the decomposition of hollocellulose during pyrolysis, favouring the formation of lighter compounds at lower temperatures [28]. At the same temperature the gaseous product release was higher for reed (17 wt.% d.b.) than that of wood (9.8 wt.% d.b.) as was expected due to the higher conversion of reed at low temperatures. However tar yields were found similar for both fuels at this temperature (18 wt.% d.b. and 19.8 wt.% d.b. for reed and wood, respectively). With increasing temperature the conversion of both fuels increased until a temperature of 700 °C for the case of reed and 800 °C for wood. At these temperatures the char yields reach an approximately constant value (16.7 wt.% d.b. for wood and 32.4 wt.% d.b. for reed) indicating the end of primary devolatilization. The plateau reached at 800 °C for the case of wood agrees with previous studies of woody biomass in similar reactors [6,20]. However, lower char yields were obtained during fast pyrolysis of sweet gum hardwood (7 wt.%, d.b.) and pine wood (5 wt.%, d.b.) ([6,20], respectively). This can be explained by the

Fig. 2. TGA (solid lines) and DTG (dotted lines) curves of wood (black lines) and reed (grey lines) at 10 °C/min in N2.

K. Anastasakis et al. / Fuel Processing Technology 142 (2016) 157–166

161

Fig. 3. Product yields (d.b.), with standard deviations, evolution over temperature during fast pyrolysis of wood and reed (600 °C/s, 10 s holding time).

different varieties of wood used as well as by the higher heating rates employed (1000 °C/s and 7000 °C/s, respectively). Similar data for reed are absent in literature. At the temperature of char stabilization gas yields of 37.3 wt.% (d.b.) and 29.8 wt.% (d.b.) and tar yields of 33.7 wt.% (d.b.) and 22.7 wt.% (d.b.) were obtained for wood and reed, respectively. The higher gaseous and tar yields of wood compared with reed, reflect the higher conversion, and thus the more volatile matter evolved, during pyrolysis of wood. However, collectable tar yields were found to have reached their maximum prior the char stabilization temperature. For both fuels the temperature of maximum tar evolution was found between 600 °C and 700 °C (38.8 wt.% d.b. and 22.7 wt.% d.b. for wood and reed, respectively). A similar temperature region for tar maximum yields was found by Nunn et al. (850–950 K) and by Fraga et al. (500–700 °C) during pyrolysis of sweet gum hardwood and silver birch, respectively, in a similar reactor setup [6,7]. However, higher maximum tar yields were reported by both studies (55 wt.% d.b. and 57.5 wt.% daf, respectively). The higher tar yields reported in literature will be further discussed in the tar analysis section. As temperature increases (higher than the char asymptote temperature) there is a continuous increase in gas yields while at the same time tar yields decline. The increase in gas yields, however, is much slower and less sharp than its increase before the char stabilization temperature. This high temperature gas yield increase originates from tar decomposition/cracking reactions as the char yields remain stable. At the final studied temperature (1000 °C) gas yields of 40.3 wt.% (d.b.) and 35.9 wt.% (d.b.) were obtained for wood and reed, respectively. These yields were higher than gas yields obtained by Nunn during pyrolysis of sweet gum hardwood (30.5 wt.% d.b., 900–1000 °C) and Peacocke et al. during pyrolysis of pine wood (32.2 wt.% d.b. at 600 °C) [6,9]. They were closer in range with the yields obtained by Drummond and Drummond, Stubington and Aiman and Fraga et al. during pyrolysis of silver birch, bagasse and silver birch, respectively (40 wt.% d.b., 500–600 °C, 40 wt.% d.b. at 1000 °C and 42.4 wt.% d.b. at 900 °C, respectively) [7,10,11]. These differences can be attributed to the different compositions of the feedstock used as well as to differences in reactor design and experimental procedure. The collectable tar yields at the final temperature of 1000 °C were 35 wt.% (d.b.) and 20.7 wt.% (d.b.) for wood and reed, respectively. While gas yields of the two fuels were close in range, a big difference was observed in their tar yields (35 wt.% (d.b.) and 20.7 wt.% (d.b.) at 1000 °C for wood and reed, respectively) indicating that the majority

of the higher volatile content of wood is evolved as tars rather than gases. 3.3. Gas composition FTIR analysis was employed for the analysis and quantification of the main gaseous species evolved during fast pyrolysis and the yields of the individual components (CO, CO2, CH4 and non-moisture H2O) on a dry basis (d.b.) determined as a function of peak temperature are shown in Fig. 4. Non-moisture H2O was estimated by subtracting the moisture content of each biomass feedstock (Table 2) from the total H2O quantified by FTIR. As illustrated by the figures, a raise in temperature induced an increase in the yield of all species, indicating their formation by thermally favoured reactions. These reactions are either primary decomposition reactions, where chemical bond scission occurs in cellulose, hemicelluloses and lignin, or secondary cracking reactions, where the products of primary depolymerization form volatiles. Fig. 4a depicts the effect of peak temperature on the yield of the main gaseous species evolved during fast pyrolysis of wood. At low temperatures (500 °C) CO2 is the major gaseous product formed (5.2 wt.% d.b.) followed by non-moisture H2O (3.2 wt.% d.b.). The yield of CO was considerably lower (1.3 wt.% d.b.) while only traces of CH4 were observed (0.05 wt.% d.b.). The increased CO2 yield at low temperatures can be attributed to the decomposition of the hemicellulose content of the wood. Hemicellulose is the first biomass bio-polymer to decompose during thermochemical conversion, producing an increased amount of CO2 rather than CO through decarboxylation reactions [30]. CO becomes the major product for temperatures exceeding 700 °C where a much sharper increase in its yield, compared to CO2 increase, is observed. With increasing temperature all gaseous products exhibit a sharp increase till the temperature of char stabilization, 800 °C. At this temperature CO is the major product followed by CO2, non-moisture H2O and CH4 (17.3 wt.% d.b., 10.5 wt.% d.b., 7.2 wt.% d.b. and 2.3 wt.% d.b., respectively). At higher temperatures to the final peak temperature there is a continuous but less sharp increase in CO, reaching a yield of 19.1 wt.% (d.b.) at 1000 °C. This increase at high temperatures (N800 °C) is believed to originate from tar cracking and secondary reactions as the char has yielded a constant weight at these temperatures. It is clear that although the present reactor setup utilises fast heating rates, low residence times and immediate sweep of the evolved volatiles, secondary and/or tar cracking reactions cannot be completely eliminated. The yields of the rest of the gaseous species, if we account the errors in

162

K. Anastasakis et al. / Fuel Processing Technology 142 (2016) 157–166

Fig. 4. Permanent gas evolution (d.b.) over temperature during fast pyrolysis (600 °C/s, 10 s holding time) of (a) wood and (b) reed.

this can also explain the higher CO2 and CO yields of reed at low temperatures, since herbaceous biomass generally contains a higher amount of hemicelluloses and cellulose than wood. At typical gasification temperatures (700–1000 °C) the main devolatilization reactions of the two fuels will have been completed. The average gaseous products evolved during pyrolysis at this temperature range are shown in Table 4. The energy recovered (on a HHV basis) in the gas produced by the two fuels expressed per unit mass of the fed biomass has also been calculated by taking into account the product mass yields on dry feedstock base of CO and CH4 and their respective lower heating value at 25 °C. The higher average yield of CO and CH4 for wood resulted in the higher energy recovery in wood pyrolysis gas. Of course, there are other combustible gaseous products such as H2 and C2+ hydrocarbons that contribute towards a higher energy recovery in the pyrolysis gas, but these individual components were not analysed during the present study. However, their yields during pyrolysis are much lower than the rest of the non-condensable gases. As an indication Nunn et al. found yields of approximately 1.1 wt.%, 0.17 wt.% and 0.42 wt.% on a dry basis for ethylene, ethane and propylene respectively during pyrolysis at high temperature (approximately 1000 °C) of sweet gum hardwood on a similar reactor setup [6]. Hydrogen yields are scarcer in literature. Hajaligol et al. reported yields of approximately 1 wt.% (d.b.) during pyrolysis of cellulose at 1000 °C in a similar reactor setup [5], while di Blasi et al. reported hydrogen yield of 0.4 wt.% (d.b.) during pyrolysis of wood at a temperature range between 700 and 800 °C by using a bed reactor in radiant furnace [34]. In any case the undetected gases should account for 2–5 wt.% (d.b.) at the high temperature region (700–1000 °C) and represent a significant loss from the mass balance closure as shown previously. Furthermore, despite their low yields, due to their high caloric value, they would contribute to a significant increase in energy recovered in the gas phase. 3.4. Kinetics

their determination, remain rather stable till the final peak temperature of 1000 °C (11.9 wt.% d.b., 6.8 wt.% d.b. and 2.4 wt.% d.b. for CO2, non-moisture H2O and CH4, respectively). Similar trends are reported in literature for a variety of different biomass feedstocks in similar reactor setups [5,6,17,19,31,32]. The yields of gaseous products evolved during fast pyrolysis of reed were found to follow a similar trend as those of wood, with some significant differences nevertheless as depicted in Fig. 4b. At low temperatures (500 °C) CO2 was again the major gaseous product but yields of both CO2 and CO were found to be significantly higher than the respective yields of wood at the same temperature (8.7 wt.% d.b. and 5.8 wt.% d.b. vs 5.2 wt.% d.b. and 1.3 wt.% d.b. for reed and wood, respectively), following the lower decomposition temperatures of reed as was shown previously. CO becomes the major gaseous product at lower temperature range (600–700 °C) than wood (700–800 °C) and follows a monotonous increase to yield 18 wt.% (d.b.) at the final peak temperature of 1000 °C. CO2 yields on the other hand appear to stabilize at the temperature of reed char stabilization (700 °C) indicating the cease of primary devolatilization. CO2 yield at the final peak temperature of 1000 °C was found to be 11.6 wt.% (d.b.). CH4, just as CO, follows a monotonous increase, less sharp above 700 °C, to yield 2.3 wt.% (d.b.) at the final peak temperature of 1000 °C. The results clearly reveal that CO2 and CO were in any case the main gaseous species acquired. Below 700 °C, CO2 was the primary gas released, while at elevated temperatures CO became predominant. This observed trend is comparable with findings of other researchers and is attributed to the fact that hemicelluloses which decompose first, at lower temperatures, produce an increased amount of CO2 rather than CO through decarboxylation reactions [33]. On the other hand, CO is mainly formed by degradation of cellulose and lignin occurring at a broader temperature range [33]. This can be an explanation of the enhanced production of CO2 at lower temperatures as well as the reason why CO becomes the main species as temperature increases. Moreover,

Knowledge of pyrolysis kinetics is of high importance since pyrolysis is the key step in every thermochemical conversion process such as gasification and combustion. During pyrolysis, biomass is thermally decomposed into volatiles, gases and char and the rate of these products release, quantities and composition, influences the quantity and quality of every thermochemical process product (e.g. pyrolysis oil, syngas). Extrapolating these kinetic parameters from experimental data obtained in conditions simulating industrial processes is therefore of primary importance. Hence, experimental data obtained from the heated foil reactor experiments were used to determine the rate of pyrolysis of the two biomass fuels (wood and reed) by assuming a single first order reaction. The calculated activation energies and pre-exponential factors for the total conversion and the main gaseous products evolved during fast pyrolysis of wood and reed are presented in Table 5. Since pyrolysis kinetic data obtained under fast heating rate conditions are scarce, Table 5 includes already published fast pyrolysis kinetic data for a variety of biomass feedstock as a comparison. Activation energies (E) for total conversion of both fuels were found relatively low (38.4 and 32.1 kJ/mol for wood and reed respectively) but still in the range of typical activation energies from fast pyrolysis of biomass fuels (25–200 kJ/mol) [25]. Nunn et al. found higher activation energy E Table 4 Average gaseous products yields and energy recovery on HHV basis of the total gas released at high fast pyrolysis peak temperature (wood: 800–1000 °C, reed 700–1000 °C).

CO (wt.% of feed, d.b.) CO2 (wt.% of feed, d.b.) CH4 (wt.% of feed, d.b.) H2O (wt.% of feed, d.b.) Total (wt.% of feed, d.b.) Energy recovery (MJ/kgfeed)

Wood

Reed

18.4 11.1 2.4 7 38.9 3.06

15.6 11.2 2 3.7 32.5 2.58

K. Anastasakis et al. / Fuel Processing Technology 142 (2016) 157–166

163

Table 5 Kinetic parameters for wood and reed pyrolysis at peak temperatures 500–1000 °C, HR 600 °C/s and HT of 10 s from the single first order reaction model and comparison with published kinetic parameters under fast pyrolysis conditions. Feedstock

HR (°C/s)

HT (s)

Product

E (kJ/mol)

Ln(A)

W⁎(wt.%)

Reference

Wood

600 −//− −//− −//− −//− −//− −//− −//− 1000 −//− −//− 1000 −//− −//− −//− 727 −//− −//− −//− 727 −//− −//− −//− n.a −//− −//− −//− −//− 104

10 −//− −//− −//− −//− −//− −//− −//− 1 −//− −//− 0 −//− −//− −//− 0 −//− −//− −//− 0 −//− −//− −//− n.a. −//− −//− −//− −//− 0.2 −//− −//− −//−

Conversion CO CO2 CH4 Conversion CO CO2 CH4 Conversion CO CO2 Conversion CO CO2 CH4 Conversion CO CO2 CH4 Conversion CO CO2 CH4 Conversion −//− −//− −//− −//− Conversion −//− −//− −//−

38.4 92.4 28.2 120.7 32.1 36.4 17.9 41.8 59.5 63.6 48.6 133 220.7 98 251.2 82 66.9 40.6 74.5 69 61 59.8 69 20.1 62 11 46.6 73.8 31.6 48.7 39.3 40.8

3.4 8.7 1.5 12.1 3.2 2.3 0.7 12.3 9.3 7.7 6.9 8.3 11.8 5.4 13 5.5 3.7 2.2 4.2 4.5 3.4 3.8 3.8 2.5 6.9 2.1 10.6 6.9 6.9 8.8 7.1 7.8

84.7 19.2 11.9 2.5 68.5 18 11.6 2.3 91.6 19.6 3.2 94.1 21.6 3.1 2.4 84.3 18.2 4 3.1 93 17 6 1.9 n.a. −//− −//− −//− −//− n.a. −//− −//− −//−

Present study −//− −//− −//− −//− −//− −//− −//− [10] −//− −//− [5] −//− −//− −//− [29] −//− −//− −//− [6] −//− −//− −//− [27] −//− −//− −//− −//− [32] −//− −//− −//−

Reed

Bagasse (dry)

Cellulose

Lignin

Sweet gum wood

Corn cob Corn stalk Olive prunings Olive kernels Sunflower residues Wheat straw Coconut shell Rice husk Cotton stalk

(69 kJ/mol) during fast pyrolysis of sweet gum hardwood in a similar reactor setup [6]. This can be attributed both to the different fuel qualities and to the zero holding time at peak temperatures during their experiments. Lower holding time at peak temperatures is expected to reduce the amount of secondary reactions, primary cracking reactions will become dominant and thus high E values are expected to predict the conversion better [24]. Activation energy for total conversion of reed (32.1 kJ/mol) was found to be lower than that of wood as was expected due to its lower temperature decomposition as shown before. It was found close in range with E of other herbaceous biomass feedstock such as wheat straw (31.6 kJ/mol) [35]. However, activation energies for both fuels under fast pyrolysis conditions were found significantly lower than their respective activation energies determined during slow pyrolysis (TGA) (62.6 and 50.5 kJ/mol for wood and reed during slow pyrolysis, respectively) as shown previously. Similar behaviour was observed by Zabaniotou et al. during fast and slow pyrolysis of corn cob, corn stalk, olive prunings and olive kernels [30]. Of course the kinetic parameters during fast pyrolysis were determined throughout the whole temperature range (500–1000 °C) while the kinetic parameters during slow pyrolysis were determined for the temperature range of the main devolatilization (200–400 °C). In addition, during high heating rates and short holding times at peak temperature conditions, thermal equilibrium between the foil and the pyrolysing sample might not be reached [11]. A certain thermal lag is usually established between the sample and the controlling thermocouple for heating rates above 40 K/min leading to reduced calculated values of the kinetic parameters [36]. In the specific reactor design this phenomenon was expected as the thermal conductivity of the biomass tablet is many orders of magnitude lower than the one of the stainless steel foil where the thermocouple is connected. As a result the heat penetration inside the biomass tablet is anticipated to be much slower than in the stainless steel foil. As a consequence the mass loss and the product yields are shifted to higher temperatures. This effect is subject to further investigation through computational modelling of the heat transfer in the

heated foil reactor and in the pyrolysing sample. In any case, significant difference exists in activation energies determined using fast and slow heating rate data, questioning the applicability of parameters determined by the latter during modelling of industrial processes. As shown previously, CO2 was the main gas released at low pyrolysis temperatures with CO concentration surpassing it between 700 and 800 °C. At higher temperatures, significant quantities of CH4 were also identified. Accordingly the kinetic parameters of the gases released were found to follow the inverse order, as expected, with E for CO2 b CO b CH4 for both fuels under investigation (Table 5). Activation energies for all gases released during reed pyrolysis were found lower than the respective gases released during wood pyrolysis, in accordance with the higher conversion of reed at lower pyrolysis temperatures. Higher activation energies for both gases released and total fuel conversion, were always accompanied with higher pre-exponential factors. This is consistent with literature as mathematical solutions are used to resolve the models [24]. Figs. A.1 and A.2 in Appendix A depict how the experimental data fit to the single first order reaction model. The effect of peak temperatures on total fuel conversion and main gas species evolution could be fitted reasonably well by the single first order reaction parameters, E and A. These kinetic parameters, for the total fuel conversion and main gaseous species released, could be used for modelling the devolatilization stage of the two biomass fuels in industrial thermochemical processes (e.g. pyrolysis, gasification, combustion). 3.5. Tar products yields During the fast pyrolysis experiments performed, an attempt to recover and subsequently determine the majority of the condensed volatiles (tars) in the reactor system was made. In this way, all product streams could be experimentally measured and not theoretically calculated by difference from the rest product streams, as is the common practice for tar determination in other studies. Tars were operationally defined as

164

K. Anastasakis et al. / Fuel Processing Technology 142 (2016) 157–166

the condensable products within the reactor chamber at room temperature plus the condensables on the glass wool filters at 110 °C. Fig. 5 depicts the comparison between gravimetrically determined and theoretically tar yield, calculated by difference of the other product streams quantified (char and gas) from the initial sample mass, for the two fuels. Both curves were found to follow a similar trend for both fuels. However, a significant difference between gravimetrically and theoretically determined tar yields exists. This difference was between 9 and 15.7 wt.% for dry wood and between 12 and 21 wt.% for dry reed. As discussed before a small fraction of this difference is attributed to the undetected gases (H2 and CxHx) but the sum of the undetected gases is expected to be in the range of 2–5 wt.% (d.b.) at high temperatures. Interestingly, the difference between gravimetric and theoretical tar yields was found to decrease with increasing peak pyrolysis temperatures. Thus, it can be deduced that more tar losses appear at lower pyrolysis peak temperatures according to the procedure followed. At lower pyrolysis temperatures, lighter (lower MW) volatiles are expected to be formed. At low pyrolysis temperatures (400–700 °C) mostly primary tars (e.g. acetic acid, levoglucosan) are formed [37]. A fraction of these primary tars could have been partly vaporized along with the solvent (dichloromethane) during the procedure followed for gravimetric tar determination. According to literature, in methods including evaporation of solvent at room temperature, compounds like acetic acid and methanol [3] or hydrocarbons lighter than phenanthrene [38] are likely to be lost during the vaporization step. Therefore, the amount of tar determined is related to the vapour pressures of the various compounds present in the tar samples. Moreover, some tars were found to have irreversibly been condensed on the glass wool filters used, and could not be recovered. Albeit, gravimetrically determined tar yields were closer to the theoretical tar yields for the case of wood pyrolysis rather than reed pyrolysis. During reed pyrolysis more primary tar is expected to be formed due to its higher hemicellulose and cellulose content compared to wood. Hemicellulose is known to decompose primarily to acetic acid while cellulose

decomposes primarily to levoglucosan during pyrolysis [29]. On the other hand, due to the higher lignin content of wood, and its aromatic structure, more secondary (phenolics) and tertiary (e.g. benzene and higher MW) tars would be expected to be formed during pyrolysis of wood. These tar compounds are less prone to vaporization during the extraction procedure. Nevertheless, in both cases tar appears to reach a maximum yield between 600 and 700 °C followed by a constant decrease with increasing temperature for the two fuels. Maximum tar yields are usually evaluated at the range of 550–650 °C in other small scale pyrolysis studies, where they are followed either by a drop and then stabilization or slight drop at higher temperatures [6,14,20,32] or they remain constant at the maximum value [9,11]. This decline in tar yield share is usually related to the secondary reactions of tar to light volatiles and gases. As was shown previously, in gas composition analysis (Section 3.3), there is a sharp increase in gas yields at temperature above 600 °C. Maximum tar yield of 38.8 wt.% (d.b.) (51.4 wt.% d.b. theoretical) at 600 °C was obtained from wood, followed by a decrease and stabilization to approximately 35 wt.% (d.b.) (44–45 wt.% d.b. theoretical) at higher temperatures. Similarly for reed, maximum tar yield of 23.3 wt.% (d.b.) (42.4 wt.% d.b. theoretical) was obtained at 600 °C followed by a decrease and stabilization to approximately 21.5 (d.b.) wt.% (33–35 wt.% d.b. theoretical) at higher temperatures. This decline in tar share is related to the secondary reactions of tar to form additional gases and/or char. Tar yields obtained in this study are quite low compared with yields reported in literature. Maximum tar yields between 45 and 84 wt.% have been reported during fast pyrolysis of sweet gum hardwood, sheets of cellulose, pine wood, sugar cane bagasse and silver birch in similar setups [5,6,9,11,20]. However, this difference can be attributed to different feedstocks used (i.e. lower ash content of feedstock) and different experimental conditions (i.e. very short residence times and rapid cooling to increase liquid yields) so a direct comparison is not applicable. Overall, it is clear that pyrolysis temperature plays a significant role in the amount of tars produced. Therefore, a good knowledge of the relation between process conditions and tar yields is quite important for the development of thermal conversion processes like gasification. Currently, the formation of tar has been the most important technical challenge in the development of gasification technologies. A good understanding of the tar formation mechanisms is, thus, appropriate for the design and optimization of these technologies. 4. Conclusions

Fig. 5. Effect of peak pyrolysis temperature on yields of gravimetrically determined (black lines) and theoretically calculated (grey lines) tars during fast pyrolysis (600 °C/s, 10 s holding time) of (a) wood and (b) reed, including standard deviations.

Fast pyrolysis of woody (mixture of waste softwoods) and herbaceous (reed) biomasses has been studied in a heated foil reactor coupled to an FTIR spectrophotometer. An attempt to collect all product streams to close the mass balance was made. Mass balance closure ranged between 80 and 90 wt.% of dry feedstock, with increasing temperatures favouring the overall mass balance closure. Peak pyrolysis temperature was found to have a clear effect on biomass conversion, gases and tars released. Primary conversion for wood ceased at 800 °C while the main pyrolysis reactions ceased at the lower temperature of 700 °C for reed, indicating the lower temperature decomposition of reed. This lower temperature decomposition of reed was also depicted through the determination of its activation energy under fast heating rate conditions. Activation energy for reed (32.1 kJ/mol) was found lower than that of wood (38.4 kJ/mol). Kinetic parameters determined under fast heating rate conditions were found significantly lower than the respective parameters determined during slow heating rate conditions through thermogravimetry. CO2 was the dominant gaseous product released at lower temperatures (b700 °C) while CO became predominant at higher peak pyrolysis temperatures (N 700 °C). Maximum tar yields of 38.8 wt.% of dry wood and 23.3 wt.% of dry reed were able to be recovered at 600 °C. These results provide a crucial insight to the devolatilization behaviour of two ‘low cost’ fuels that could be used as feedstock for industrial thermal conversion processes like gasification, pyrolysis and combustion.

K. Anastasakis et al. / Fuel Processing Technology 142 (2016) 157–166

Acknowledgements The authors are grateful to the Groen Gas project of Rijksdienst voor Ondernemend Nederland (RvO) (reference no. TKIG01040)

165

and to the European Biofuels Research Infrastructure for Sharing Knowledge (BRISK) project (contract no. 284498) for funding. The authors would also like to thank Synvalor for supplying of the biomass samples.

Appendix A

Fig. A.1. Comparison of the single first order reaction model (line) fit with experimental data (single data points) for (a) total conversion, (b) CO, (c) CO2 and (d) CH4 production, on a dry wt.% of the feed from wood fast pyrolysis.

Fig. A.2. Comparison of the single first order reaction model (line) fit with experimental data (single data points) for (a) total conversion, (b) CO, (c) CO2 and (d) CH4 production, on a dry wt.% of the feed from reed pyrolysis.

166

K. Anastasakis et al. / Fuel Processing Technology 142 (2016) 157–166

References [1] M. Asadullah, Barriers of commercial power generation using biomass gasification gas: a review, Renew. Sust. Energ. Rev. 29 (2014) 201–215, http://dx.doi.org/10. 1016/j.rser.2013.08.074. [2] G. Di Nola, W. de Jong, H. Spliethoff, The fate of main gaseous and nitrogen species during fast heating rate devolatilization of coal and secondary fuels using a heated wire mesh reactor, Fuel Process. Technol. 90 (2009) 388–395, http://dx.doi.org/10. 1016/j.fuproc.2008.10.009. [3] E. Hoekstra, W.P.M. van Swaaij, S.R.A. Kersten, K.J.A. Hogendoorn, Fast pyrolysis in a novel wire-mesh reactor: design and initial results, Chem. Eng. J. 191 (2012) 45–58, http://dx.doi.org/10.1016/j.cej.2012.01.117. [4] B. Iatridis, G.R. Gavalas, Pyrolysis of a precipitated Kraft lignin, Ind. Eng. Chem. Prod. Res. Dev. 18 (1979) 127–130, http://dx.doi.org/10.1021/i360070a010. [5] M.R. Hajaligol, J.B. Howard, J.P. Longwell, W.A. Peters, Product compositions and kinetics for rapid pyrolysis of cellulose, Ind. Eng. Chem. Process. Des. Dev. 21 (1982) 457–465, http://dx.doi.org/10.1021/i200018a019. [6] T. Nunn, J. Howard, J.P. Longwell, W.A. Peters, Product compositions and kinetics in the rapid pyrolysis of sweet gum hardwood, Ind. Eng. Chem. Prod. Res. Dev. 24 (1985) 836–844, http://dx.doi.org/10.1021/i200030a053. [7] A.R. Fraga, A.F. Gaines, R. Kandiyoti, Characterization of biomass pyrolysis tars produced in the relative absence of extraparticle secondary reactions, Fuel 70 (1991) 803–809, http://dx.doi.org/10.1016/0016-2361(91)90186-E. [8] M. Hajaligol, J. Howard, W. Peters, An experimental and modeling study of pressure effects on tar release by rapid pyrolysis of cellulose sheets in a screen heater, Combust. Flame 95 (1993) 47–60, http://dx.doi.org/10.1016/0010-2180(93)90051-4. [9] G.V.C. Peacocke, E.S. Madrali, C.Z. Li, A.J. Güell, F. Wu, R. Kandiyoti, A.V. Bridgwater, Effect of reactor configuration on the yields and structures of pine-wood derived pyrolysis liquids: a comparison between ablative and wire-mesh pyrolysis, Biomass Bioenergy 7 (1995) 155–167. [10] J.F. Stubington, S. Aiman, Pyrolysis kinetics of bagasse at high heating rates, Energy Fuel 8 (1994) 194–203, http://dx.doi.org/10.1021/ef00043a031. [11] A.R.F. Drummond, I.W. Drummond, Pyrolysis of sugar cane bagasse in a wire-mesh reactor, Ind. Eng. Chem. Res. 35 (1996) 1263–1268, http://dx.doi.org/10.1021/ ie9503914. [12] T. Damartzis, G. Ioannidis, A. Zabaniotou, Simulating the behavior of a wire mesh reactor for olive kernel fast pyrolysis, Chem. Eng. J. 136 (2008) 320–330, http://dx. doi.org/10.1016/j.cej.2007.04.010. [13] A. Zabaniotou, O. Ioannidou, V. Skoulou, Rapeseed residues utilization for energy and 2nd generation biofuels, Fuel 87 (2008) 1492–1502, http://dx.doi.org/10.1016/j.fuel. 2007.09.003. [14] O. Ioannidou, A. Zabaniotou, E.V. Antonakou, K.M. Papazisi, A.A. Lappas, C. Athanassiou, Investigating the potential for energy, fuel, materials and chemicals production from corn residues (cobs and stalks) by non-catalytic and catalytic pyrolysis in two reactor configurations, Renew. Sust. Energ. Rev. 13 (2009) 750–762, http://dx. doi.org/10.1016/j.rser.2008.01.004. [15] T. Damartzis, M. Kostoglou, A. Zabaniotou, Simulation of the agro-biomass (olive kernel) fast pyrolysis in a wire mesh reactor considering intra-particle radial and temporal distribution of products, Int. J. Chem. React. Eng. 7 (2009)http://dx.doi. org/10.2202/1542–6580.1833. [16] M.J. Prins, J. Lindén, Z.S. Li, R.J.M. Bastiaans, J.A. Van Oijen, M. Aldén, et al., Visualization of biomass pyrolysis and temperature imaging in a heated-grid reactor, Energy Fuel 23 (2009) 993–1006, http://dx.doi.org/10.1021/ef800419w. [17] J. Giuntoli, J. Gout, A.H.M. Verkooijen, W. de Jong, Characterization of fast pyrolysis of dry distiller's grains (DDGS) and palm kernel cake using a heated foil reactor: nitrogen chemistry and basic reactor modeling, Ind. Eng. Chem. Res. 50 (2011) 4286–4300, http://dx.doi.org/10.1021/ie101618c. [18] M.J. Prins, Z.S. Li, R.J.M. Bastiaans, J.A. van Oijen, M. Aldén, L.P.H. de Goey, Biomass pyrolysis in a heated-grid reactor: visualization of carbon monoxide and formaldehyde using laser-induced fluorescence, J. Anal. Appl. Pyrolysis 92 (2011) 280–286, http://dx. doi.org/10.1016/j.jaap.2011.06.008.

[19] A.V. Sepman, L.P.H. de Goey, Plate reactor as an analysis tool for rapid pyrolysis of biomass, Biomass Bioenergy 35 (2011) 2903–2909, http://dx.doi.org/10.1016/j. biombioe.2011.03.030. [20] E. Hoekstra, W.P.M. Van Swaaij, S.R.A. Kersten, K.J.A. Hogendoorn, Fast pyrolysis in a novel wire-mesh reactor: decomposition of pine wood and model compounds, Chem. Eng. J. 187 (2012) 172–184, http://dx.doi.org/10.1016/j.cej.2012.01.118. [21] S.A. Channiwala, P.P. Parikh, A unified correlation for estimating HHV of solid, liquid and gaseous fuels, 81 (2002). [22] A. Sluiter, B. Hames, R.O. Ruiz, C. Scarlata, J. Sluiter, D. Templeton, et al., Determination of structural carbohydrates and lignin in biomass, Biomass Anal. Technol. Team Lab. Anal. Proced. 2011 (2004) 1–14. [23] A. Sluiter, R.O. Ruiz, C. Scarlata, J. Sluiter, D. Templeton, D. of energy, determination of extractives in biomass, Biomass Anal. Technol. Team Lab. Anal. Proced. (2004) 1–8. [24] A. Saddawi, J.M. Jones, A. Williams, M.A. Wójtowicz, Kinetics of the thermal decomposition of biomass, Energy Fuel 24 (2010) 1274–1282, http://dx.doi.org/10.1021/ ef900933k. [25] R. Weber, Extracting mathematically exact kinetic parameters from experimental data on combustion and pyrolysis of solid fuels, J. Energy Inst. 81 (2008) 226–233, http://dx.doi.org/10.1179/014426008X370997. [26] G.I. Senum, R.T. Yang, Rational approximations of the integral of the Arrhenius function, J. Therm. Anal. 11 (1977) 445–447, http://dx.doi.org/10.1007/BF01903696. [27] K. Anastasakis, A.B. Ross, J.M. Jones, Pyrolysis behaviour of the main carbohydrates of brown macro-algae, Fuel 90 (2011) 598–607, http://dx.doi.org/10.1016/j.fuel. 2010.09.023. [28] P. Giudicianni, G. Cardone, G. Sorrentino, R. Ragucci, Hemicellulose, cellulose and lignin interactions on Arundo donax steam assisted pyrolysis, J. Anal. Appl. Pyrolysis 110 (2014) 138–146, http://dx.doi.org/10.1016/j.jaap.2014.08.014. [29] W.C. Park, A. Atreya, H.R. Baum, Experimental and theoretical investigation of heat and mass transfer processes during wood pyrolysis, Combust. Flame 157 (2010) 481–494, http://dx.doi.org/10.1016/j.combustflame.2009.10.006. [30] A. Zabaniotou, O. Ioannidou, E. Antonakou, A. Lappas, Experimental study of pyrolysis for potential energy, hydrogen and carbon material production from lignocellulosic biomass, Int. J. Hydrog. Energy 33 (2008) 2433–2444, http://dx.doi.org/10.1016/j. ijhydene.2008.02.080. [31] A.V. Bridgwater, Review of fast pyrolysis of biomass and product upgrading, Biomass Bioenergy 38 (2012) 68–94, http://dx.doi.org/10.1016/j.biombioe.2011.01.048. [32] T.R. Nunn, J.B. Howard, J.P. Longwell, W.A. Peters, Product Compositions and Kinetics in the Rapid Pyrolysis of MiHed Wood Lignin, 1985 844–852, http://dx.doi.org/10. 1021/i200030a054. [33] B. Drzezdzon, A.V. Larcher, Characterisation of biomass pyrolysis by stepwise product collection and analysis: mallee wood, J. Anal. Appl. Pyrolysis 104 (2013) 308–315, http://dx.doi.org/10.1016/j.jaap.2013.07.002. [34] C. Di Blasi, G. Signorelli, C. Di Russo, G. Rea, Product distribution from pyrolysis of wood and agricultural residues, Ind. Eng. Chem. Res. 38 (1999) 2216–2224, http:// dx.doi.org/10.1021/ie980711u. [35] X. Shuangning, L. Zhihe, L. Baoming, Y. Weiming, B. Xueyuan, Devolatilization characteristics of biomass at flash heating rate, Fuel 85 (2006) 664–670, http://dx.doi. org/10.1016/j.fuel.2005.08.044. [36] C. Di Blasi, Modeling chemical and physical processes of wood and biomass pyrolysis, Prog. Energy Combust. Sci. 34 (2008) 47–90, http://dx.doi.org/10.1016/j.pecs. 2006.12.001. [37] P. Morf, P. Hasler, T. Nussbaumer, Mechanisms and kinetics of homogeneous secondary reactions of tar from continuous pyrolysis of wood chips, Fuel 81 (2002) 843–853, http://dx.doi.org/10.1016/S0016-2361(01)00216-2. [38] P. Simell, P. Ståhlberg, E. Kurkela, J. Albrecht, S. Deutsch, K. Sjöström, Provisional protocol for the sampling and anlaysis of tar and particulates in the gas from large-scale biomass gasifiers, Biomass Bioenergy 18 (2000) (Version 1998) 19–38, http://dx.doi.org/10.1016/S0961-9534(99)00064-1.