Article

A Kinetic Model for the Production of Liquids from the Flash Pyrolysis of Biomass

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Abstract

A kinetically based prediction model for the production of organic liquids from the flash pyrolysis of biomass is proposed. Wood or other biomass is assumed to be decomposed according to two parallel reactions yielding liquid tar and ( gas + char) The tar is then assumed to further react by secondary homogeneous reactions to form mainly gas as a productThe model provides a very good agreement with the experimental results obtained using a pilot plant fluidized bed pyrolysis reactorThe proposed model is shown to be able to predict the organic liquid yield as a function of the operating parameters of the process, within the optimal conditions for maximizing the tar yields, and the reaction rate constants compare reasonably well with those reported in the literature

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... In Figure 10, the yields obtained for Setup 2 through simulation are presented, considering different values of kinetic parameters for secondary TAR-GAS degradation [51,[63][64][65][66][67][68]. Each kinetic model was implemented and tested in both codes (OpenFOAM and ANSYS Fluent), and the results did not significantly change, so the same conclusions can be drawn for both software programs. ...
... It can be observed that the original kinetic model given by the coefficients of Liden et al. [51], as listed in Table 1, generally underestimates the formation of TAR, the predominant product in the studied case of fast pyrolysis. Consequently, the predicted CHAR and GAS yields are generally higher than the experimental values (as shown in Table 6). ...
... Reactions and kinetic parameters[51]. ...
Article
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This study investigated the fast pyrolysis of biomass in fluidized-bed reactors using computational fluid dynamics (CFD) with an Eulerian multifluid approach. A detailed analysis was conducted on the influence of various modeling parameters, including hydrodynamic models, heat transfer correlations, and chemical kinetics, on the product yield. The simulation framework integrated 2D and 3D geometrical setups, with numerical experiments performed using OpenFOAM v11 and ANSYS Fluent v18.1 for cross-validation. While yield predictions exhibited limited sensitivity to drag and thermal models (with differences of less than 3% across configurations and computational codes), the results underline the paramount role of chemical kinetics in determining the distribution of bio-oil (TAR), biochar (CHAR), and syngas (GAS). Simplified kinetic schemes consistently underestimated TAR yields by up to 20% and overestimated CHAR and GAS yields compared to experimental data (which is shown for different biomass compositions and different operating conditions) and can be significantly improved by redefining the reaction scheme. Refined kinetic parameters improved TAR yield predictions to within 5% of experimental values while reducing discrepancies in GAS and CHAR outputs. These findings underscore the necessity of precise kinetic modeling to enhance the predictive accuracy of pyrolysis simulations.
... Chen et al. [10] present a combustion model for a biomass particle where pyrolysis is modeled by a single global reaction. Values for the kinetics parameters under the different schemes, presented in the form of Arrhenius correlations, can be found in the the different works [6,7,11,12,17,[19][20][21][22][23][24][25][26]. ...
... Within these studies, diverse forms of biomass, varying particle sizes, and a range of operating parameters (including temperature, pressure, heating rate, atmosphere type, and volatiles' residence time) are investigated, yielding a broad spectrum of information [22]. Regarding experimental studies, different thermogravimetric analyses stand out [7,11,12,18,22,[27][28][29], including tube pyrolyzers with various configurations [7,11,12,[21][22][23][24]30,31], fluidized beds [22,24,32] and numerical models contrasted with experimental tests [20]. Depending on the type of pyrolysis and the configuration of the reactor, the phenomena referring to the primary and secondary reactions can be isolated. ...
... Within these studies, diverse forms of biomass, varying particle sizes, and a range of operating parameters (including temperature, pressure, heating rate, atmosphere type, and volatiles' residence time) are investigated, yielding a broad spectrum of information [22]. Regarding experimental studies, different thermogravimetric analyses stand out [7,11,12,18,22,[27][28][29], including tube pyrolyzers with various configurations [7,11,12,[21][22][23][24]30,31], fluidized beds [22,24,32] and numerical models contrasted with experimental tests [20]. Depending on the type of pyrolysis and the configuration of the reactor, the phenomena referring to the primary and secondary reactions can be isolated. ...
Article
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This work presents a comprehensive model for lignocellulosic biomass pyrolysis, addressing kinetics, energy balances, and gas product composition with the aim of its application in wood combustion. The model consists of a two-stage global mechanism in which biomass initially reacts into tar, char, and light gases (non-condensable gases), which is followed by tar reacting into light gases and char. Experimental data from the literature are employed for determining Arrhenius kinetic parameters and key energy parameters, like tar and char heating values and the specific enthalpy of primary and secondary reactions. A methodology is introduced to derive correlations, allowing the model’s application to diverse biomass types. This work introduces several novel approaches. Firstly, a pyrolysis model that determines the composition of light gases by solving mass, species, and energy balances is developed, limiting the use of correlations from the literature only for tar and char elemental composition. The mass rate of light gases, tar, and char being produced is also determined. Secondly, kinetic parameters for primary and secondary reactions are determined following a Shafizadeh and Chin scheme but with a modified Arrhenius form dependent on Tn, significantly enhancing the accuracy of product composition prediction. Additionally, correlations for the enthalpies of reactions, both primary and secondary, are determined as a function of pyrolysis temperature. Primary reactions exhibit an overall endothermic behavior, while secondary reactions exhibit an overall exothermic behavior. Finally, the model is validated using cases reported in the literature, and results for light gases composition are presented.
... Kinetic parameter sets as listed in Table 4 from Fagbemi et al. [38], Liden et al. [39], and Serio et al. [40] are investigated regarding their ability to predict the light gas and tar relations in the FBR. ...
... The following analysis shows how the light gas fraction is influenced by tar cracking reactions during the transport from the reaction zone to the FTIR analyzer. In Fig. 6 (top), the experimentally determined light gas mass fractions from cellulose pyrolysis are compared to the numerical predictions using three different parameters sets for tar cracking from the literature [38][39][40]. All sets of parameters significantly underestimate the tar cracking behavior in the considered temperature range. ...
... All sets of parameters significantly underestimate the tar cracking behavior in the considered temperature range. Even the reaction mechanism with the highest reaction rate crack from Liden et al. [39] predicts a significant decomposition only at temperatures FB > 773 K, while the experimental data show a light gas fraction of more than 60 % already at FB = 623 K. In order to be able to correctly represent the experimental behavior of the light gas formation with the model, significantly higher reaction rates are required. ...
... Kinetic parameter sets from Fagbemi et al. [13], Liden et al. [14], and Serio et al. [15] are investigated regarding their ability to predict the light gas and tar relations in the FBR. ...
... The following analysis shows how the light gas fraction is influenced by tar cracking reactions during the transport from the reaction zone to the FTIR analyzer. In Figure 4, the experimentally determined light gas mass fractions from cellulose pyrolysis are compared to the numerical predictions using three different parameters sets for tar cracking from the literature [13][14][15]. All sets of parameters significantly underestimate the tar cracking behavior in the considered temperature range. ...
... All sets of parameters significantly underestimate the tar cracking behavior in the considered temperature range. Even the reaction mechanism with the highest reaction rate r crack from Liden et al. [14] predicts a significant decomposition only at temperatures T FB > 773 K, while the experimental data show a light gas fraction of more than 60 % already at T FB = 623 K. In order to be able to correctly represent the experimental behavior of the light gas formation with the model, significantly higher reaction rates are required. ...
Conference Paper
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Within the Bio-CPD model, biomass is interpreted as a mixture of cellulose, hemicellulose, and lignin, where the components react independently and are linearly superimposed afterward. To simplify the reaction chemistry via minimizing interactions and to best approximate the model assumptions, experiments from extracted lignocellulosic biomass components in a small-scale fluidized bed reactor are used as reference data. The evaluation of available literature data sets revealed a suitable set for cellulose and hemicellulose, respectively, which could correctly predict the time-dependent release rate of volatile pyrolysis products. For lignin, the Genetti correlation to estimate structural parameters based on the ultimate and proximate analysis led to better results than all other sets. Further on, the analysis of light gas and tar fractions showed a high relevance to model secondary tar cracking reactions in the fluidized bed reactor system.
... In our work, the pre-exponential factor and the activation temperature for both pyrolysis and cracking are taken from Glaister [51], as cited in Grønli [36] (see Table 4.5 in Grønli [36]). Di Blasi [17] derived the pyrolysis rate from Roberts and Clough [50] and the cracking rate from Liden et al. [52]. Mandl et al. [24] derived them from Grønli [36] and Liden et al. [52], respectively (see the footnote to Table 4). ...
... Di Blasi [17] derived the pyrolysis rate from Roberts and Clough [50] and the cracking rate from Liden et al. [52]. Mandl et al. [24] derived them from Grønli [36] and Liden et al. [52], respectively (see the footnote to Table 4). Figure 3 shows that the rates are similar. ...
... The correction factor ξ, appearing in Equation (52), was already introduced into the modelling in the 1980s and 1990s [18], so it is around forty years old. As shown in Equation (52), the factor governs the energy transfer between the gas-and solid-phases; for ξ = 1, the rate is maximum, while for ξ = 0, there is no energy transfer between the phases. Thus, with ξ approaching 1, the differences between gas-phase and solid-phase temperatures are minimized. ...
Article
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The subject of this work is the mathematical modelling of a counter-current moving-bed gasifier fuelled by wood-pellets. Two versions of the model have been developed: the one-dimensional (1D) version-solving a set of Ordinary Differential Equations along the gasifier height-and the three-dimensional (3D) version where the balanced equations are solved using Computational Fluid Dynamics. Unique procedures have been developed to provide unconditionally stable solutions and remove difficulties occurring by using conventional numerical methods for modelling counter-current reactors.The procedures reduce the uncertainties introduced by other mathematical approaches, and they open up the possibility of straightforward application to more complex software, including commercial CFD packages. Previous models of Hobbs et al., Di Blasi and Mandl et al. used a correction factor to tune calculated temperatures to measured values. In this work, the factor is not required. Using the 1D model, the Mandl et al. 16.6 kW gasifier was scaled to 9.5 MW input; the 89% cold-gas efficiency, observed at 16.6 kW input, decreases only slightly to 84% at the 9.5 MW scale.
... An increase in the length can lead to a longer residence time of pyrolysis volatiles within the structure. It is suspected that above 500 • C such longer residence times can lead to enhanced deposition of secondary char due to cracking of evolved volatiles [47], and in consequence causes a distortion in the PSD of the pyrochar. The mineral matter and its composition is also an adjustable feedstock property, and it affects the development of the pore structures of the pyrochars as well. ...
... The pyrolysis temperatures were selected to contain three scenarios without secondary cracking of volatiles and three scenarios where secondary cracking will most likely occur. A temperature of 500 • C was selected as a threshold above which the secondary cracking of volatiles becomes significant [47]. Additionally, the lowest three temperatures were selected to indirectly investigate the influence of selective degradation of biomass constituents (hemicellulose, cellulose and lignin) [58]. ...
... When prepared at temperatures < 300 • C, the increase in SSA was negligible, and above that temperature, significant microporosity was noticed for the pyrochars. The difference in the microporous SSA between pyrochars prepared from wood cylinders of different length became noticeable for pyrolysis temperatures of 500-900 • C. The differences were consistent with that secondary char formation (char from thermal cracking of high molecular compounds), relevant at temperatures above 500 • C [47] was enhanced by an increased length of the wood cylinder. Vapours that evolved during the wood pyrolysis, due to a pressure difference move through the outer, highly-heated char layer. ...
Article
Char obtained from biomass pyrolysis is an eco-friendly porous carbon, which has potential use as a material for electrodes in supercapacitors. For that application, a high microporous specific surface area (SSA) is desired, as it relates to the accessible surface for an applied electrolyte. Currently, the incomplete understanding of the relation between porosity development and production parameters hinders the production of tailor-made, bio-based pyrochars for use as electrodes. Additionally, there is a problem with the low reliability in assessing textual properties for bio-based pyrochars by gas adsorption. To address the aforementioned problems, beech wood cylinders of two different lengths, with and without pre-treatment with citric acid were pyrolysed at temperatures of 300–900 °C and analysed by gas adsorption. The pyrolyzed chars were characterised with adsorption with N2 and CO2 to assess the influence of production parameters on the textual properties. The new approach in processing the gas adsorption data used in this study demonstrated the required consistency in assessing the micro- and mesoporosity. The SSA of the chars rose monotonically in the investigated range of pyrolysis temperatures. The pre-treatment with citric acid led to an enhanced SSA, and the length of the cylinders correlated with a reduced SSA. With pyrolysis at 900 °C, the micro-SSAs of samples with 10 mm increased by on average 717 ± 32 m²/g. The trends among the investigated parameters and the textual properties were rationalized and provide a sound basis for further studies of tailor-made bio-based pyrochars as electrode materials in supercapacitors.
... In our work, the pre-exponential factor and the activation temperature for both pyrolysis and cracking are taken from Glaister [51], as cited in Grønli [36] (see Table 4.5 in Grønli [36]). Di Blasi [17] derived the pyrolysis rate from Roberts and Clough [50] and the cracking rate from Liden et al. [52]. Mandl et al. [24] derived them from Grønli [36] and Liden et al. [52], respectively (see the footnote to Table 4). ...
... Di Blasi [17] derived the pyrolysis rate from Roberts and Clough [50] and the cracking rate from Liden et al. [52]. Mandl et al. [24] derived them from Grønli [36] and Liden et al. [52], respectively (see the footnote to Table 4). Figure 3 shows that the rates are similar. ...
... The correction factor ξ, appearing in Equation (52), was already introduced into the modelling in the 1980s and 1990s [18], so it is around forty years old. As shown in Equation (52), the factor governs the energy transfer between the gas-and solid-phases; for ξ = 1, the rate is maximum, while for ξ = 0, there is no energy transfer between the phases. Thus, with ξ approaching 1, the differences between gas-phase and solid-phase temperatures are minimized. ...
Chapter
Vorwort Der Flammentag ist das etablierte Forum für den Austausch von Wissenschaft und Praxis über die neuesten Betriebs- und Forschungsergebnisse auf dem Gebiet der Verbrennung und der Feuerungen. Teilnehmer aus Industrie und Hochschule treffen sich im zweijährigen Turnus auf dieser Veranstaltung, um bei Fachvorträgen, Posterpräsentationen und Fachgesprächen den Wissenstransfer voranzutreiben. Der 28. Deutsche Flammentag ist zu Gast an der Technischen Universität Darmstadt und lädt Sie ein, aktuelle Ergebnisse der Industrie- und Hochschulforschung mit Praktikern und Forscher aus den Gebieten der Flammenforschung, des Feuerungsbaus, aus Energieversorgungs-, Anlagenbau- und Zulieferunternehmen sowie aus Hochschulen und Forschungseinrichtungen zu diskutieren. Mit insgesamt 60 Vorträgen wird das gesamte Spektrum der Verbrennung und Vergasung von der Großfeuerung im zentralen Bereich bis zu den Fragestellungen der Prozessfeuerungen, thermische Behandlung und Biomassenutzung abged...
... Liden et al. (1988) estudaram o modelo cinético para produção de líquidos da pirólise e consideraram que a biomassa se decompõe de acordo com duas reações, produzindo alcatrão líquido (óleo) e gás + carvão. O óleo é então, através de reações homogêneas, convertido em gás como principal produto. ...
... O óleo é então, através de reações homogêneas, convertido em gás como principal produto. O modelo proposto se baseia emBradbury et al. (1979) e outros autores, e mostrou-se capaz de prever o rendimento do líquido orgânico produzido dentro das condições ideais para maximizar os rendimentos de alcatrão.Di Blasi (1994) estudou um modelo matemático para a pirólise da celulose, analisando o efeito do tamanho de partícula sobre a taxa de reação, adotando o modelo desenvolvido porBradbury et al. (1979) eLiden et al. (1988). O modelo proposto Brazilian Journal of Development, Curitiba, v.7, n.8, p. 78706-78719 aug. ...
... Modeling studies were also conducted to study the homogeneous decomposition of tar from biomass pyrolysis. 95,96 According to the kinetic model of Linden et al., 95 the wood undergoes flash pyrolysis and decomposes according to two parallel reaction mechanisms to give primary pyrolysis products (gas, char, and tar). These primary products undergo further secondary homogeneous decomposition reactions as shown in Figure 6. ...
... Modeling studies were also conducted to study the homogeneous decomposition of tar from biomass pyrolysis. 95,96 According to the kinetic model of Linden et al., 95 the wood undergoes flash pyrolysis and decomposes according to two parallel reaction mechanisms to give primary pyrolysis products (gas, char, and tar). These primary products undergo further secondary homogeneous decomposition reactions as shown in Figure 6. ...
Article
Biomass pyrolysis is a thermochemical conversion process that undergoes a complex set of concurrent and competitive reactions in oxygen-depleted conditions. A considerable amount of the literature uses lumped kinetic approaches to predict pyrolysis products. Despite the prolonged studies, the science of pyrolysis chemistry and models' capability to simulate the exact conversion phenomenon has unraveled yet. In this review, an initiative was made by compiling existing mathematical models for biomass pyrolysis viz., lumped and distributed kinetic models, particle, and reactor models. An absolute analysis of computational fluid dynamics (CFD), artificial neural network (ANN), and ASPEN Plus models was also conducted. It was observed that the coupling of distributed kinetic models with CFD provides a better understanding of the hydrodynamic reaction of particles under reactive flow with the influence on reactor performance and predicts exact product yield. Furthermore, the pros and cons of each modeling technique are also highlighted individually. Finally, considering the future perspective of biomass pyrolysis with respect to the modeling approach, suggestions have been incorporated.
... While the activation energies in the two sets are almost identical, the pre-exponential factor is more than two orders of magnitude higher. The faster reaction may be provoked by the contact between the gases and hot solid particles in the bed [64,71]. ...
Article
Biomass pyrolysis is typically modeled based on the three reference components cellulose, hemicellulose, and lignin. Most models rely on an individual decomposition of the materials and a linear superposition of the individual component products weighted by the present mass fractions. Models of varying complexity exist for the mathematical description of the pyrolysis process, ranging from the simplest single first-order (SFOR) model and the multi-step CRECK model to the chemical percolation devolatilization (CPD) model representing the molecular network of the solid. The models differ not only in their complexity but also in the used data for initial parameter calibration — thermogravimetric analysis (TGA) data for the CRECK model and mainly entrained flow, fluidized bed, or wire mesh reactor data for the Bio-CPD model. Within the present study, the predictive performance of these three models is compared with regard to the time-dependent total volatile release and the final volatile yield when applying two different thermal boundary conditions: low heating rate in a TGA and flash pyrolysis conditions realized with a small-scale fluidized bed reactor (FBR). The models are compared with one other and with experimental data on extracted, separately pyrolyzed biomass components to examine under which conditions reliable predictions can be made and when the trustability is limited. For the TGA data, the CRECK model has the closest proximity to the experimental measurements, also resolving most of the individual reactions, while the SFOR model can resolve only one globally dominating reaction, and the Bio-CPD model strongly overpredicts the reactivity of the biomass components during the slow heat-up. Under flash pyrolysis conditions in the FBR, by contrast, the Bio-CPD model predictions are closest to the experimental results when it comes to predicting the total volatile release rate. However, examining the integrally released yields, the CRECK model is closer to the experiments. Regarding the tar and light gas distribution, all models strongly overpredict tar from primary pyrolysis compared to the experimental results, indicating the presence of secondary gas-phase reactions in the FBR. Although different secondary gas-phase reaction models are used, the tar yield is significantly overestimated by the models compared to the experimental data.
... Slow pyrolysis produces high biochar yields at the expense of lower liquid yields, while fast pyrolysis is used to maximize the production of bio-oils. Commonly used biomass types for pyrolysis technology include wood and wood residues [26], agricultural crops, such as corn straw and rice husks [27], sunflower as an oilseed crop [28], as well as animal and agricultural residues [29]. Grapes are one of the world's largest fruit crops with vine rods generated as wastes, which have potential for use in bioenergy production [30]. ...
Article
Full-text available
The paper investigates the potential of biomass pyrolysis as a sustainable and renewable energy solution. The study focuses on three biomass types: corn cob, vine rod, and sunflower, which are abundant agricultural residues with potential for biofuel production. The pyrolytic gas, oil, and char produced during pyrolysis at a heating rate of 10 °C/min were analyzed. At the pyrolysis temperature of 500 °C, the corn cob showed the smallest final residual mass of 24%, while the vine rod exhibited the largest mass loss of 40%. Gas analysis revealed the concentrations of CO2, CO, H2, and CH4 in the pyrolytic gas, indicating its energy potential. Sunflower presented the largest calorific value of the produced biogas, while corn cob was the lowest. The chemical composition of the bio-oils was determined, with aliphatic acids identified as the dominant compounds, suggesting their potential for biodiesel production. Fourier Transform–Infrared Spectroscopy (FT-IR) analysis of raw biomass and char products demonstrated varying extents of decomposition among the biomass samples. A multicriteria assessment approach was employed to evaluate the differences between the selected three biomass feedstock and determined that sunflower biomass ranked the highest among the three, although the overall difference was small, confirming the suitability of all three biomass samples for pyrolysis conversion to higher-value-added fuels.
... Slow pyrolysis produces high biochar yields at the expense of lower liquid yields, while fast pyrolysis is used to maximize the production of bio-oils. Commonly used biomass types for pyrolysis technology include wood and wood residues [26], agricultural crops, such as corn straw and rice husks [27], sunflower as an oilseed crop [28], as well as animal and agricultural residues [29]. Grapes are one of the world's largest fruit crops with vine rods generated as wastes, which have potential for use in bioenergy production [30]. ...
... The stoichiometry of the tar cracking reaction is derived from the tar cracking scheme outlined in Ref. [47], and the kinetics are taken from Ref. [65]. These kinetics are utilized instead of those from Ref. [47] as they have demonstrated better suitability for this specific application, as observed in the simulation of a stove [32]. ...
... The kinetics of primary reactions is modeled according to Di Blasi and Branca. 59 The kinetics of secondary homogeneous reactions 4 and 5 are modeled according to Liden et al. 60 and Di Blasi, 61 respectively. ...
... The second class of models involve simultaneous reactions in which wood particles breaks down into various constituents of pyrolysis products [12,13]. Semi-global models assume a further reaction in which products deriving from primary decomposition of biomass, decompose into the secondary pyrolysis products [14,15]. Rath et al. have utilized a two-step pyrolysis reaction scheme in order to examine the heat of pyrolysis [16]. ...
Article
Under unprecedented environmental crisis associated with greenhouse gas emission, biomass has attracted a great deal of attention due to renewable and carbon neutral nature. In this study, the premixed combustion of various types of wood and its derived syngases are examined for steady and oscillating sates. For this purpose, the poplar, birch, beech and pin sawdust woods and syngases composing of H2, CH4 and CO are considered. To model dust cloud combustion, a novel and comprehensive flame structure consisting of drying, two-step pyrolysis and homogeneous and heterogeneous reactions is proposed. Afterward, the governing equations and their appropriate boundary conditions are derived and solved analytically-numerically. The oscillating combustion is also modeled by exerting an external perturbation on the velocity field. The results indicate that due to the occurrence of heterogeneous reactions in wood combustion, the flame propagation velocity of wood is higher than that of syngases which contributes to high oscillations amplitude of syngases. When the mixture initial temperature changes between 300 and 550 K, the flame velocities of woods and syngases vary in the ranges of 0.4–0.7 m/s and 0.1–0.27 m/s, respectively. The maximum amplitude of temperature oscillation of syngases is approximately 8 times more than that of woods.
... Furthermore, besides the structural components, the scheme considers the lignocellulosic biomass moisture, extractives, and ash. Unlike global, lumped pyrolysis reaction schemes (e. g., Broido-Shafizadeh [20], Liden [21], and Di Blasi [22]) for lignocellulosic biomass fast pyrolysis, it is detailed enough to enable tracking of specific evolved gas species in the vapors [23]. The Ranzi scheme is one of the most comprehensive pyrolysis reaction schemes available to date [9]. ...
Article
Fast pyrolysis is an intricate process due to the variability and anisotropy of lignocellulosic biomass and the complicated chemistry and physics during conversion in a bubbling fluidized bed reactor (BFBR). The complexity of biomass fast pyrolysis lends itself well to computational fluid dynamics (CFD) and discrete element (DEM) analysis, which promises to reduce experimental time and its associated cost. This study investigated switchgrass fast pyrolysis simulated by computational fluid dynamics coupled with a discrete element method to track individual reacting biomass particles throughout a bench-scale BFBR reactor. We accounted for the fast pyrolysis chemistry through a comprehensive reaction scheme with secondary cracking reactions. We performed a three-step reduction for secondary cracking reactions to convert the full cracking scheme into a reduced scheme easily incorporated into our model. We assessed the impact of operational conditions on the steady-state yields of liquid bio-oil, non-condensable gases (NCG), at 550 °C over a range of fluidization numbers (2 – 6 Umf), reported as a ratio to the minimum fluidization velocity (Umf). At steady-state, the volatile bio-oil yield had a range of 49.3–50.4 wt. %. Levoglucosan was the primary volatile component present with 21 wt. % of the bio-oil while water was the second largest with 20 wt. %. The reduction of the secondary reaction schemes did not appreciably affect the overall yields of switchgrass pyrolysis compared to the full secondary scheme.
... In their subsequent work, they derived the yield of gas, tar and solid residue [4]. A similar contribution can be recognized in the study of Liden et al. [5] focusing on the kinetic prediction model for the liquid fraction from fast pyrolysis. On the same issue, but focussing on slow pyrolysis, Hu et al. [6] compared different kinetic models on the ground of data derived from thermogravimetric analyses (TGA). ...
Article
Full-text available
In this study, the biomass degradation and the evolution of chemical species during pyrolysis are analysed with the main aim of evaluating the energy performance of a micro-cogeneration unit fed by biogas. The decomposition of the feedstock material is modelled as a two-stage process: Firstly, in the reactor, the biomass is decomposed in a residual solid fraction (char) and a gaseous mixture; then, the condensable gases are divided from permanent gases generating the pyro-oil. The mathematical model proposed in this work has been developed considering the dependence of the pyrolysis process from the temperature and within the interval 500-900°C. The kinetic of the reactions involved during the pyrolysis was also taken into account. Simulations run in AspenPlus exploiting the R-yield reactor supported by a calculator block. Afterwards, the energy recovery line for the valorisation of the pyroproducts has been analysed. The gas fraction obtained at the end of the cycle was firstly characterized and then used to feed a micro-CHP system. Results are very promising, with great potential in terms of thermal recovery; more than 60% of the initially fed biogas and about 30% power output can be derived.
... D'autres mécanismes font intervenir plusieurs étapes comme par exemple le modèle développé par Shafizadeh et Chin [64] (Figure 1.5). Ces réactions primaires qui conduisent à la formation des gaz, des goudrons ou du résidu charbonneux ont été étudiées à de multiples reprises dans la littérature pour différents types de bois [65][66][67][68][69]. En général, des réactions secondaires, c'est-à-dire des réactions qui se font à partir des goudrons ou du résidu charbonneux sont ensuite introduites pour décrire le craquage des goudrons en gaz et leur polymérisation en résidu charbonneux [70][71][72][73][74]. Les réactions secondaires se produisant à partir du résidu charbonneux correspondent à leur oxydation en cendres. ...
Thesis
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Ces travaux de thèse s’inscrivent dans l’amélioration de la compréhension des mécanismes de dégradation des combustibles pour l’incendie. Ils ont pour objectif d’étudier à travers une approche multi-échelle la dégradation thermique de plaques de bois.La dégradation thermique de deux types de bois : le chêne blanc (Quercus alba) et l’eucalyptus commun (Eucalyptus globulus), a tout d’abord été étudiée à l’échelle matière, où des échantillons de faibles masses ont été chauffés dans un analyseur thermogravimétrique. Les résultats ont montré que la dégradation thermique de ces deux bois pouvait se représenter en quatre étapes. A partir de ces résultats expérimentaux, quatre mécanismes réactionnels ont été développés : le mécanisme par constituants, le mécanisme global, le mécanisme actif et le mécanisme simplifié avec seulement deux étapes. Les paramètres cinétiques associés ont été déterminés par optimisation avec un algorithme du gradient descendant. La simulation a révélé que l’ensemble des mécanismes représente de manière efficace la perte de masse des deux bois aux différentes vitesses de chauffe étudiées. La meilleure performance est obtenue par le mécanisme global et la moins bonne par le mécanisme simplifié.La dégradation thermique des deux bois a également été étudiée à l’échelle matériau à l’aide d’un cône calorimètre. Différentes densités de flux variant entre 18 et 28,5 kW/m² ont été appliquées afin d’éviter l’auto-inflammation du bois. Deux conditions limites ont été imposées à la face inférieure des plaques de bois. La température des plaques de bois a été mesurée par thermocouples et par caméra infra-rouge. Les résultats expérimentaux ont révélé que plus la densité de flux augmente, plus la perte de masse est rapide et la température augmente rapidement. L’oxydation du résidu charbonneux prend dans ce cas l’allure d’un front bidimensionnel qui se propage au cours du temps.L’étude numérique menée sur les expériences réalisées à l’échelle matériau a permis de valider les mécanismes réactionnels développés à l’échelle matière, en utilisant le champ de température expérimental des plaques de bois fines. A cette échelle, la performance des mécanismes réactionnels est très proche. Une étude unidimensionnelle a été réalisée avec le code GPYRO afin de prédire la température et la perte de masse des plaques thermiquement fines. Les résultats obtenus sont très satisfaisants, grâce à une optimisation des propriétés thermiques du bois et une convolution pour représenter les phénomènes bidimensionnels. Pour les plaques thermiquement épaisses, les mécanismes à quatre étapes permettent de représenter la perte de masse durant la phase de gazéification mais ne permettent pas cependant de prédire la totalité de la phase d’oxydation du résidu charbonneux.
... These results show that it is not needed to described tar cracking in bed for this technology. Furthermore, for the case M8, with the highest temperatures at the pyrolysis front, a simulation was conducted including the tar cracking kinetics from Liden et al. [38] (A = 4.26 × 10 6 s − 1 , E = 108 kJ⋅mol − 1 ), which are the fastest among the most commonly employed tar cracking kinetics in literature [31]. The results showed that less than 0.2% of the tar was cracked for this case, confirming that tar cracking in the bed is minimal at these conditions. ...
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Fixed-bed biomass conversion with a low primary air ratio and a counter-current configuration has a high feedstock flexibility, as it resembles updraft gasification, and the potential to reduce emissions when integrated in biomass combustion systems. A 1D bed model was validated with experimental results from a biomass combustion boiler with such a bed conversion system, predicting with a good accuracy the temperatures in the reactor and producer gas composition. The model was applied for different cases to investigate the fuel flexibility of this combustion system, including the influence of moisture content and the maximum temperatures achieved in the bed. It was shown that with variations in fuel moisture content from 8 to 30% mass w.b. the producer gas composition, char reduction to CO or maximum temperatures at the grate were not affected due to the separation of the char conversion and pyrolysis/drying zones. Flue gas recirculation was the only possible measure with the tested configuration to reduce the maximum temperatures close to the grate, which is beneficial e.g. to avoid slagging with complicated fuels. A higher tar content was obtained than in conventional updraft gasifiers, which is attributed to the absence of tar condensation in the bed due to the limited height of the reactor and the integration in the combustion chamber. The presented model can support the development of such combustion technologies and is a relevant basis for detailed CFD simulations of the bed or gas phase conversion.
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A comprehensive model for wood pyrolysis has been developed. This model integrates detailed chemical reactions and interactions between chemistry, heat, and mass transfers within the porous medium. The Ranzi’s reaction scheme [1] is well-known for its detailed and comprehensive modelling of wood components (cellulose, hemicellulose, and lignin). This work extends Ranzi’s scheme to include secondary reactions for tars, which cannot be neglected when wood samples behave as thermally thick materials, as is often the case during fire scenarios involving woody materials. A novel aspect of this model is its detailed consideration of gas-solid interactions within wood pores, incorporating mass and heat transfer mechanisms. The model is based on the PATO code (Porous Analysis Toolbox based on OpenFOAM), which treats the porous medium as a continuum by using a homogenization process to establish conservation equations for averaged quantities defined on a Representative Elementary Volume (REV). This model is applied to simulate cone calorimeter experiments of wood thermal decomposition in a nitrogen-rich environment, providing detailed insights into the complex interplay of chemical and physical processes during pyrolysis. The results highlight the model’s potential as a powerful tool to predict wood thermal decomposition in cases of thermally thick sample behavior, where secondary tars reactions play a key role in describing the entire dynamics of the pyrolysis process at high temperatures.
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Pyrolysis has been essential in the context of renewable energies, offering an innovative approach for biomass and solid waste valorization. Therefore, mathematical models that can represent its phenomena are of fundamental importance in understanding the reaction progression and optimizing the process. In this sense, we sought to analyze the capability of single-particle models in representing the yields of pyrolysis reactions in fluidized beds. To describe the behavior and interaction between the phases, we utilized an Eulerian–Lagrangian CFD modeling approach, solving the continuity, momentum, energy, species, and turbulence equations using OpenFOAM. We adopted the multicomponent and multi-stage model to describe the kinetics of pyrolysis in three different types of biomass. The numerical results obtained for the yields of pyrolysis reactions using the proposed modeling approach showed good agreement with the experimental data reported in the literature. We observed a maximum discrepancy of 3% in the study of pure cellulose reaction, 5.14% in red oak, and 0.56% in sugarcane bagasse. Therefore, we concluded that the single-particle model accurately represents the yields of pyrolysis reactions, making it suitable for estimating yields and conversion rates, providing valuable insights into pyrolysis behavior, and aiding in developing projects and optimization studies.
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The conversion of woody biomass is studied by means of a layer-based model for thermally-thick biomass particles (Thunman et al. 2002, Ström et al. 2013). The model implementation is successfully validated against experiments that study particle conversion in a drop tube reactor. After this validation step, this work focuses on the well-known problem of grid dependence of two-phase numerical simulations using the standard Euler–Lagrange (EL) framework. This issue is addressed and quantified by comparing EL data that models the particle boundary layers to corresponding simulations which fully resolve these boundary layers (fully-resolved, FR, simulations). A comparison methodology for the conceptually different FR and EL approaches by extracting the heat transfer coefficient from the detailed FR simulations is proposed and confirms that the EL results are strongly grid-dependent. This issue is overcome by applying a set of coarse-graining methods for the EL framework. Two coarse-graining methods are evaluated, a previously suggested diffusion-based method (DBM) and a new approach based on moving averages referred to as MAM. It is shown that both DBM and MAM can successfully recover the detailed FR data for pure particle heating for a case where the grid size is half the particle diameter, i.e. when the standard EL method fails. Both coarse-graining methods also give improved results for an EL simulation that considers the more complex combined physics of particle heating, drying and devolatilisation, given that the CG model parameters that scale the corresponding CG interaction volumes are sufficiently large. Based on the available FR data, recommended model parameter ranges for DBM and MAM are provided as a function of normalised boundary layer thickness. The novel MAM approach is shown to be significantly more efficient than the DBM and therefore suitable for future EL simulations with multiple particles.
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A non-stationary model of the biomass thermolysis process was built based on three primary independent parallel reactions of the biomass active part conversion into gas, liquid phase and char, taking into account the secondary reactions of tar decomposition into char and light gas. It is shown that the main role in the production of mixed pyrolysis gas (primary gas and light gas) is played by the light gas generation rate due to the secondary reaction of tar decomposition into light gas. This reaction rate significantly exceeds the primary gas production rate due to the fact that the activation energy of the primary gas formation reaction lignin → gas is higher than the activation energy of the lignin → tar reactions. It was found that the rate of generation of the primary reaction lignin → char significantly outweighs the rate of tar → char production, so the latter reaction can be neglected. It is shown that as the temperature of lignin pellets increases, CO and light hydrocarbon C1.16H4 increase and carbon dioxide CO2 and H2О decrease. The consumption of volatile components in the pyrolyzer depends on the temperature distribution of biomass pellets across the pyrolyzer cross-section, which decreases towards the center of the retort, following the consumption of gaseous components decreases as they approach the axis of the pyrolyzer. The amount of mixed pyrolysis gas released and char depends on the radial coordinate r. At r = 0.047 m and time τ = 380 s, the amount of mixed pyrolysis gas is 90 % and char is 10 %, at r = 0.016 m and τ = 380 s = 83 % and = 17 %. Bibl. 13, Fig. 7.
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A compartmental one‐dimensional model of a fluidized bed pyrolytic converter of biomass is presented. Reference conditions are those of non‐catalytic fast pyrolysis of biomass in a shallow fluidized bed with external regeneration of the bed material. The fate of biomass and of the resulting char has been modelled by considering elutriation of biomass and char particles, char attrition as well as bed drain/regeneration. The course of primary and secondary pyrolitic reactions is modelled according to a semi‐lumped reaction network using well established kinetic parameters taken from the literature. A specific focus of the present study is the role of the heterogeneous volatile‐char secondary reactions, whose rate has been modelled borrowing a kinetic expression from the neighbouring area of tar adsorption/decomposition over char. Results of computations highlight the relevance of heterogeneous volatile‐char secondary reactions and of the closely associated control of char loading in the bed. The sensitivity of the reactor performance on char elutriation and attrition, on proper management of bed drain/regeneration, on control of gas phase backmixing is demonstrated. Model results provide useful guidelines for optimal design and control of fluidized bed pyrolyzers and pinpoint future research priorities.
Thesis
As part of a European project, a new assembly using densified dowels to hold wooden slats is currently being validated at the structural level. This type of assembly has the advantage of not using glues and of making it possible to manufacture large-sized structures consisting only of wood. The principle consists of positioning the wooden planks as desired, then drilling and inserting densified dowels: under the effect of moisture absorption, the densified dowels swell and block the assembly, making the structure rigid.The use of this type of assembly requires a multitude of sizing and behavior checks under various stresses, including thermomechanical variations. Thus, within the framework of this thesis work, the objective will be to characterize the behavior of wood lamellar assemblies by densified dowels subjected to significant thermo-hydric stresses, in particular during the fire. To do this, we propose an approach coupled with experiments and numerical modeling. The experiments will first allow the acquisition of the basic data to develop the model. Numerical modeling will then make it possible to better understand the mechanisms involved in the fire of these types of structures in order to improve their performance. This will also reduce the number of expensive trials. The model will be validated by temperature measurements at different depths in the section of the lamellae, but also within the densified dowels. These results will then be compared to experimental tests for validation on a few fire tests under mechanical stress.This model can then be used to estimate the behavior of more complex structures subjected to fire and to provide basic data for the sizing of complete buildings. The results can also serve as a basis for amending regulatory texts such as Eurocode 5.
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The past decades have witnessed increasing interest in developing pyrolysis pathways to produce high-quality chemicals from biomass. However, the numerous defects of bio-oil produced by biomass pyrolysis severely restrict its further application. A promising upgrading technology is considered to be the application of catalytic methods in biomass pyrolysis. Among various catalysts, metal catalysts have been well developed due to their flexible tailorability and unique characteristics. This review is dedicated to revealing the reasons for the biomass conversion pathways catalyzed by different metal catalysts (single and multi-metal catalysts, including Na, Mg, Al, K, Ca, Ti, Fe, Co, Ni, Cu and their combinations) and the conversion mechanisms of metal catalysts in the catalytic process. The interaction between different metal catalysts and the reasons why the combination improves catalytic activity were also introduced. At last, the research trends and perspectives on future development of metal catalysis in the field of biomass pyrolysis were proposed.
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The study presents a parametric study of pyrolysis of poultry litters under isothermal heating conditions using a two-stage pyrolysis scheme and a downer separation technique. The study aims to increase the yield of biochar through pyrolysis using a two-stage kinetic process. The thermo-physical properties of mild steel and poultry litter were used to develop a simulation with a finite element method and COMSOL multiphysics to predict biochar yield at different temperatures and residence time. The numerical model was validated by comparing the predicted and the experimental results from the literature with a percentage difference of 1.3 to 11% and an R2 value of 0.9124. Further parametric studies showed that for the pyrolysis of 0.5 kg of poultry litters, a maximum yield of biochar of 42.9% was obtained at a lower temperature of 573.15oK with a residence time of 9000 s. Higher temperature favoured gas yield while biochar yield declined.
Thesis
This investigation provides a comprehensive experimental dataset and kinetic model for biomass gasification, over a wide temperature range (1150-1350 °Ϲ) in CO2, H2O and the combination of these two reactant gases over the mole fraction ranges of 0 to 0.5 for H2O and 0 to 0.9 for CO2. The data come from a unique experimental facility that tracks continuous mass loss rates for poplar wood, corn stover and switchgrass over the size range of 6-12.5 mm. In addition, the data include char size, shape, surface and internal temperature and discrete measurements of porosity, total surface area, pore size distribution and composition. This investigation also includes several first-ever observations regarding char gasification that probably extend to char reactivity of all types and that are quantified in the model. These include: the effect of ash accumulation on the char surface slowing the apparent reaction rate, changes in particle size, porosity and density as functions of burnout, and reaction kinetics that account for all of these changes. Nonlinear least-squares regression produces optimized power-law model parameters that describe gasification with respect to both CO2 and H2O separately and in combination. A single set of parameters reasonably describes rates for all three chars. Model simulations agree with measured data at all stages of char conversion. This investigation details how ash affects biomass char reactivity, specifically the late-stage burnout. The ash contents ratios in the raw fuels in these experiments are as high as 40:1, providing a clear indication of the ash effect on the char reactivity. The experimental results definitively indicate a decrease in char reaction rate with increasing initial fuel ash content and with increasing char burnout – most pronounced at high burnout. This investigation postulates that an increase in the fraction of the surface covered by refractory material associated with either higher initial ash contents or increased burnout decreases the surface area available for reaction and thus the observed reaction rate. A quantitative model that includes this effect predicts the observed data at any one condition within the data uncertainty and over a broad range of fuel types, particle sizes, temperatures, and reactant concentrations slightly less accurately than the experimental uncertainty. Surface area, porosity, diameter, and density predictions from standard models do not adequately describe the experimental trends. Total surface area increases slightly with conversion, with most of the increase in the largest pores or channels/vascules not measurable by standard surface area techniques but most of the surface area is in the small pores. Porosity also increases with char conversion except for abrupt changes associated with char and ash collapse at the end of char conversion. Char particle diameters decrease during these kinetically controlled reactions, in part because the reaction is endothermic and therefore proceeds more rapidly at the comparatively warmer char surface. SEM images qualitatively confirm the quantitative measurements and imply that the biomass microstructure does not appreciably change during conversion except for the large pore diameters. Extant char porosity, diameter, surface area, and related models do not predict these trends. This investigation suggests alternative models based on these measurements.
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This study presents a three-dimensional finite element model to describe the thermomechanical behaviour of flax chipboards under fire conditions. The model is based on kinetic models considering the thermal degradation during the pyrolysis phase and the evolution of the physico-mechanical properties as functions of temperature. The numerical model is integrated into Abaqus via user subroutines (Umat and Umatht) and applied to the analysis of the fire behaviour of panels made of flax chipboards. Thermogravimetric tests are performed on flax particles to serve for the identification of the kinetic parameters of the pyrolysis models. Once these kinetic parameters are determined, they are integrated into a complete numerical model to simulate the behaviour under fire of flax chipboards on small and large scales. The obtained trends in the predicted values indicate good agreements when compared to the measured values. The simulations show that the numerical model is capable of accurately modelling the thermomechanical transfers taking place within the material during exposure to fire.
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Devolatilization kinetics were determined using a modified micropyrolyzer reactor for several biomass feedstocks: switchgrass, corn stover, red oak, and pine. The micropyrolyzer was directly coupled to a flame ionization detector (FID) to track the release of volatiles from the biomass. Time series data from these experiments was analyzed to determine apparent devolatilization rates. Care was taken to assure the experiments were isothermal and kinetically limited calculating a Biot number less than 0.1 and pyrolysis numbers greater than 10, which simplifies the derivation of devolatilization rates. A single, first order reaction was able to model devolatilization rates at temperatures up to 500 °C. No correlation was found between the inorganic content of the biomass and its rate of devolatilization. Apparent activation energies were in the range of 54.9–88.4 kJ mol⁻¹. The rate coefficient at 500 °C was calculated as 1.90–5.14 s⁻¹ for the four feedstocks.
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In the future, renewable energy technologies will have a significant role in catering to energy security concerns and a safe environment. Among the various renewable energy sources available, biomass has high accessibility and is considered a carbon-neutral source. Pyrolysis technology is a thermo-chemical route for converting biomass to many useful products (biochar, bio-oil, and combustible pyrolysis gases). The composition and relative product yield depend on the pyrolysis technology adopted. The present review paper evaluates various types of biomass pyrolysis. Fast pyrolysis, slow pyrolysis, and advanced pyrolysis techniques concerning different pyrolyzer reactors have been reviewed from the literature and are presented to broaden the scope of its selection and application for future studies and research. Slow pyrolysis can deliver superior ecological welfare because it provides additional bio-char yield using auger and rotary kiln reactors. Fast pyrolysis can produce bio-oil, primarily via bubbling and circulating fluidized bed reactors. Advanced pyrolysis processes have good potential to provide high prosperity for specific applications. The success of pyrolysis depends strongly on the selection of a specific reactor as a pyrolyzer based on the desired product and feedstock specifications.
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Around 2.7 billion people worldwide have no access to clean cooking equipment, which leads to major health problems due to high emissions of unburned products (VOC, CO and soot). A top-lit updraft gasifier cookstove with forced draft was identified as the technology with the highest potential for reducing harmful emissions from incomplete combustion in simple cookstoves. The basic variant of the stove was equipped with a fan for efficient mixing of product gas with air and fired with pellets to increase the energy density of low-grade residues. The development was conducted based on water boiling test experiments for wood and rice hull pellets and targeted CFD simulations of flow, heat transfer and gas phase combustion with a comprehensive description of the reaction kinetics, which were validated by the experiments. Emphasis was put on the reduction of CO emissions as an indicator for the burnout quality of the flue gas. The optimisation was carried out in several steps, the main improvements being the design of a sufficiently large post-combustion chamber and a supply of an appropriate amount of primary air for a more stable fuel gasification. The experiments showed CO emissions <0.2 g/MJdel for wood and rice hull pellets, which corresponds to a reduction by a factor of about 15 to 20 compared to the basic forced draft stove concept. Furthermore, these values are between 5 and 10 times lower than published water boiling test results of the best available cookstove technologies and are already close to the range of automatic pellet furnaces for domestic heating, which are considered to be the benchmark for the best possible reduction of CO emissions.
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A novel integrated biorefinery system consists of (1) pyrolysis of biomass into gas, bio-oil and char; (2) bio-oil hydrodeoxygenation and hydrocracking (hydroprocessing) producing renewable jet fuel and small chain alkanes; (3) alkane steam reforming and pressure swing adsorption (PSA) producing green hydrogen and carbon monoxide; (4) mixed ionic electronic conducting membrane (MIEC) splitting high pressure superheated steam (HPSS) into green hydrogen and oxygen; and (5) combined heat and power generation (CHP) using pyrolysis gas and carbon monoxide from PSA as fuel with oxygen from MIEC, to fulfil the demand for HPSS and electricity. Comprehensive mathematical models are shown for the design simulation of the integrated system: (1) kinetic model of biomass pyrolysis at temperature 300−500 °C, (2) stoichiometric chemical reaction model of hydroprocessing, (3) renewable aviation fuel property correlations from its chemical compositions for the ASTM D7566 standard, (4) mass and energy balance analyses of the integrated biorefinery system. Economic value and overall avoided environmental and social impacts have been analysed for sustainability. The ratios of mass and energy flows between biomass, bio-oil, renewable jet fuel, CHP-fuel, char and hydrogen are 1.33:1:0.45:0.3:0.16:0.05 and 1:0.82:0.7:0.41:0.14:0.22, respectively. For 10tph bio-oil processing, the capital cost of the plant is 13.7million,thereturnoninvestmentis1913.7 million, the return on investment is 19% and the cost of production of renewable jet fuel is 0.07/kg, which is lower than its market price, $0.27/kg. This production can curb 108 kt CO2 equivalent and 1.44 PJ fossil energy per annum. To enable the biorefinery simulation, user-friendly open-source TESARREC™ https://tesarrec.web.app/sustainability/bio-jet-fuel has been developed.
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Fast pyrolysis of biomass converts it mainly into bio-oil, which is incapable of being utilized directly as drop-in fuel because of high oxygen content, unstable nature, and lower heating value. The composition of bio-oil de-cides its quality, fitness for upgrading, and environmental influence. However, it is controlled by numerous essential pyrolysis reactions, which are difficult to characterize because of the multiphase thermal degradation of biomass happening in short time scales with inter-related reaction chemistry and transport effects. This review paper critically analyses the current progress on essential pyrolysis reactions, from reaction-controlled pyrolysis experiments and molecular simulations. In experiments, recently employed Frontier Micropyrolyzer, PHASR reactor, Wire mesh reactor, and Pyroprobe with the allied analytical system revealed essential pyrolysis reactions (i.e., glycosidic bond cleavage, dehydration, and successive fragmentation of C6 or C5 compounds, etc.). The effect of transport on individual pyrolysis products, especially forming bio-oil, is described using transport- controlled experiments. Besides, the role of catalysts in altering biomass pyrolysis reactions, and hence bio-oil composition, is highlighted through experimental and theoretical findings. The mechanistic insight of biomass compounds breaking (validated with experiments), with and without catalysts, is presented. Eventually, the particle level reaction-transport models capturing the inter-related effects of pyrolysis reactions (as reaction kinetics) and transport processes, under different pyrolysis conditions, are discussed. The collective information provided in this review would be beneficial for biomass pyrolysis investigators in designing operating conditions for the conversion of several biomass feedstocks into bio-oil, similar to drop-in fuel
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Numerical modeling of biomass pyrolysis is becoming a cost and timesaving alternative for experimental investigations, also to predict the yield of the by-products of the entire process. . In the present study, a two-step parallel kinetic model was used to predict char yield under isothermal condition. MATLAB ODE45 function codes were employed to solve a set of differential equations that predicts the %char at varying residence times and temperatures. The code shows how the various kinetic parameters and mass of pyrolysis products were determined. Nevertheless, the algorithm used for the prediction was validated with experimental data and results from past works. At 673.15K, the numerical simulation using ODE45 function gives a char yield of 27.84%. From 573.15K to 673.15K, char yield ranges from 31.7 – 33.72% to 27.84% while experimental yield decreases from 44% to 22%. Hence, the error between algorithm prediction and experimental data from literature is -0.26 and 0.22. Again, comparing the result of the present work with the analytical method from the literature showed a good agreement.
Article
In this study, a micro fluidized bed reactor analyzer (MFBRA) was adopted to test the isothermal reaction characteristics of tar catalytic reforming by char and thermal cracking by quartz sand from 1023 to 1223 K. The behaviors of tar conversion, the evolution of gaseous products generation, and the corresponding reaction kinetics were comprehensively analyzed. Compared to thermal cracking, the yield of catalytic cracking is higher. It can not only promote the tar conversion but also upgrade the fuel gas quality even at a low temperature of 1023 K, especially for CO, CH4, CO2, and C3H6. The tested activation energies (Ea) of tar conversion and gas generation (CH4, C2H6, C3H6, H2, CO2, and CO) in catalytic reforming were about 60.27, 45.48, 56.22, 71.34, 62.35, 51.51, and 60.75 kJ/mol, respectively, corresponding that of 78.16, 63.19, 71.16, 83.19, 84.33, 90.81 and 130.72 kJ/mol in thermal cracking. The lower Ea indicated the good catalytic activity of char on tar conversion and the change of gas generation paths by choosing char as a catalyst. Finally, the kinetics was compared with the results in the literature to verify the feasibility of MFBRA and the accuracy of testing results. This research deepened the understanding of tar catalytic reforming by char and was beneficial for developing a biomass gasification process with low tar generation.
Article
The pyrolysis of cellulose was studied by electrically heating in helium single strips (0.75 cm×2.5 cm) of low ash ( 9 s −1 . The correlation is slightly improved by use of a multiple-reaction model based on a set of independent parallel first-order reactions represented by a Gaussian distribution of activation energies with a mean of 37.0 kcal/mole and a standard deviation of 1.1 kcal/mole. Selected experiments at reduced pressures (0.0005 atm), elevated heating rates (10,000°C/s), or both resulted in rate constants smaller than those obtained at 400°C/s and 1 atm. The results indicate that the residence time of volatile products within the pyrolyzing cellulose matrix is extremely important in determining conversion. Suggested pathways for cellulose pyrolysis that are consistent with these findings and with much of the pertinent literature involve primary decomposition to an oxygen-rich intermediate (probably levoglucosan) which then participates in three processes to extents depending on experimental conditions: (a) direct escape from the decomposing material into the ambient gas; (b) polymerization, cross-linking and cracking to form char and (c) pyrolysis to smaller volatiles some of which inhibit the char formation in (b) or autocatalyze (c). Accordingly, char is not a primary product, and the yield of char is zero for extremely short residence times of the primary products within the matrix of the decomposing material or for conditions that permit complete inhibition of char formation by secondary pyrolysis products.
Article
The pyrolysis of cellulosic materials is studied by means of the thermal effect of the volatile products on a catalytic sensor which consists of a heated platinum wire. Tests with filter paper samples at different heating rates yield a single set of Arrhenius parameters. Tests with wood show contribution of its individual components. The technique is also used to estimate the effect of migration, condensation and regasification of the volatiles in a pyrolizing material on the apparent Arrhenius kinetics of pyrolysis. Migration of the volatiles into the cooler interior of a test specimen results in reduced gas sensor response but little change in the apparent kinetics. Deposition of the condensed volatiles on a pyrolyzing material tends to slightly reduce the rate of generation of the pyrolysis volatiles and to slightly shift the Arrhenius curve towards lower temperature. The finding does not lend positive support to the proposed explanation for the large variation in local kinetics in a thick pyrolyzing sample (observed with radiographic technique and reported in the literature) in terms of the migration and condensation of the volatiles.
Article
The temperature and surface-density histories of a radiantly heated thermally thin filter-paper sheet held freely in air were measured in order to study the dynamics of the ignition of paper. Analyses of these histories indicate that the chemically complex degradation reactions can be approximately represented for fire dynamics purposes by two competitive first-order reactions with Arrhenius kinetics as observed by Tang [3]. One of these reactions with a preexponential factor 5.9 × 106 sec−1 and an activation energy 26 kcal/gm-mole is dominant at less than about 655°K. At higher temperatures, the other reaction with a preexponential factor 1.9 × 1016 sec−1 and an activation cnergy 54 kcal/gm-mole is dominant. The heat-transfer rates to and from the test sheet were measured in order to estimate the energetics of the reactions. The data were insensitive to the small heat of the low-temperature reaction. Assuming this heat to be −88 cal/g (endothermic), based on DTA measurements of Tang and Neill [8], the heat of the high-temperature reaction is estimated to be about 444 cal/g (exothermic). An approximate formula is developed to predict the spontaneous ignition of a thermally thin sheet under known heating and cooling conditions, provided the Arrhenius kinetics and the heat of a first-order reaction in the sheet are known. Using the measured kinetics and heat of the high-temperature reaction in this formula, the results are compared with the measured data as well as with Martin's [9] ignition data.
Article
Beech sawdust, granular cellulose and sucrose-impregnated pumice have been separately decomposed in a fluidized bed of sand in an atmosphere of nitrogen at temperatures up to 400 °C. Reaction was followed by rapidly withdrawing samples of the bed and analysing for carbon content and ignition loss. The results were converted to weight loss by a correlation developed from subsidiary fixed-bed experiments and mass balances on the fluidized bed. In all cases, decomposition occurred in two stages, the primary stage giving about 85% of the total change at any temperature level in less than 10 min. The kinetics of weight loss in the first stage were approximately first-order with respect to residual weight of organic matter, while the second stage approximated to a second-order process with respect to the weight loss to be completed in reaching equilibrium. In both stages there was a marked change in the temperature dependence of the rate of decomposition of wood in the region 300–350 °C. Below this transition region the response is broadly similar to that found for sucrose in pumice and above it is similar to the behaviour of cellulose. The maximum weight loss at any temperature was a function of temperature, showing that reaction path was temperature-dependent.
Article
Kinetics of cellulose pyrolysis in nitrogen and steam at five different heating rates are presented. A single rate equation for each pyrolysis medium is discussed which provides a good engineering fit to the weight loss curves. The presence of steam in the pyrolysis medium was found to have no measurable affect on cellulose pyrolysis kinetics. The activation energy, pre-exponential factor and reaction order for nitrogen and 1 steam pyrolysis of cellulose are: 36.6 kcal/mol, 6.06 × 10sec, 0.46 and 34.2 kcal/mol, 1.67 / 109 sec, 0.51 respectively. Apparent differences in the data derived using steam rather than nitrogen as a pyrolysis medium are shown to be artifacts of heat transfer phenomenon within the TGA instrumentation used to measure rate of weight loss. Heat transfer effects observed here may explain the large discrepancies in previously reported studies of cellulose pyrolysis kinetics. Kinetic data given for steam pyrolysis are believed to be more accurate due to the more accurate measurement of sample temperature in the reactor system used for the steam experiments.
Article
A bench-scale continuous flash pyrolysis unit using a fluidized bed at atmospheric pressure has been employed to investigate conditions for maximum organic liquid yields from various biomass materials. Liquid yields for poplar-aspen were reported previously, and this work describes results for the flash pyrolysis of maple, poplar bark, bagasse, peat, wheat straw, corn stover, and a crude commercial cellulose. Organic liquid yields of 60-70% mf can be obtained from hardwoods and bagasse, and 40-50% from agricultural residues. Peat and bark with lower cellulose content give lower yields. The effects of the addition of lime and of a nickel catalyst to the fluid bed are reported also. A rough correlation exists between has content and maximum organic liquid yield, but the liquid yield correlates better with the alpha-cellulose content of the biomass. General relationships valid over all reaction conditions appear to exist among the ratios of final decomposition products also, and this correlation is demonstrated for the yields of methane and carbon monoxide.
Article
Systematic studies of the independent effects of temperature (300-1100°C), solids residence time (0-30 s), and heating rate (less than equivalent to 100-15000°C/s) on the yields, compositions, and rates of formation of products from the rapid pyrolysis of 0.0101 cm thick sheets of cellulose under 5 psig pressure of helium have been performed. The experiments mainly probe the primary decomposition of the cellulose, with contributions from post-pyrolysis reactions being confined to those occuring within and closely proximate to the sample. Temperature and sample residence time are the most important reaction conditions in determining the pyrolysis behavior, while heating rate effects are explicable in terms of their influence on these two parameters. A heavy liquid product of complex molecular composition accounted for 40 to 83 wt % of the volatiles above 400°C. Secondary cracking of this material increased with increasing residence time or temperature and was a significant pathway for producing several light gases. 9 refs.
Article
The kinetics of wood pyrolysis into gas, tar, and char was investigated in the range of 300 to 400/degree/C at atmospheric pressure. An experimental system which facilitates the monitoring of the actual sample temperature, collection of gas and tar, and measurement of the sample weight loss as a function of time was developed. It has been found that, in the range investigated, wood decomposition into gas, tar, and char can be described by three parallel first-order reactions as suggested by F. Shafizadeh and P.P.S. Chin. The activation energies for these reactions are 88.6, 112.7 and 106.5 kJ/mol, respectively and their frequency factors defined on a mass basis are 8.61*10/sup 5/, 2.47*10/sup 8/, and 4.43*10/sup 7/ min/sup -1/. 12 refs.
Article
The thermal decomposition of fibrous cellulose powder from 275° to 340°C has been studied by thermogravimetry, scanning electron microscopy, krypton adsorption, and gas-chromatographic analysis of the gaseous products arising from pyrolysis in various oxidizing and inert atmospheres. The reaction kinetics fit a phase boundary model where the rate is controlled by the movement of an interface through a cylindrical particle and the principal kinetic parameters fit a compensation curve described previously for the decomposition of wood products. An explanation of the physical mechanism of pyrolysis is proposed which is consistent with the observed rate data and the structural changes observed by scanning electron microscopy.
Article
A continuous fluidized bed bench scale flash pyrolysis unit operating at atmospheric pressure and feed rates of about 15 g/h has been successfully designed and operated. A unique solids feeder capable of delivering constant low rates of biomass has also been developed. Extensive pyrolysis tests with hybrid aspen-popular sawdust (105–250 μm) have been carried out to investigate the effects of temperature, particle size, pyrolysis atmosphere and wood pretreatment on yields of tar, organic liquids, gases and char. At optimum pyrolysis conditions high tar yields of up to 65% of the dry wood weight fed are possible at residence times of less than one second. On a conçu et employé avec succès, à l'échelle du laboratoire, une unité de pyrolyse-éclair à lit fluidisé continu; le dispositif fonctionnait à la pression atmosphérique et à des débits d'alimentation d'environ 15 g/h. On a aussi mis au point un dispositif unique d'alimentation en matières solides, capable d'assurer de faibles débits constants de biomasse. On a fait des expériences poussées de pyrolyse sur des sciures d'hybrides de peuplier-faux tremble (105—250 μm), dans le but d'étudier les effets de la température, de la granulométrie des particules, de l'atmosphère de la pyrolyse et d'un traitement préalable du bois sur les rendements en goudron, liquides organiques, gaz et matières carbonisées. Il est possible, dans les conditions optimales de pyrolyse, d'obtenir des rendements élevés en goudron, qui peuvent atteindre 65% du bois sec d'alimentation en poids pour des temps de séjour de moins d'une seconde.
Article
A continuous atmospheric pressure flash pyrolysis process for the production of organic liquids from cellulosic biomass has been demonstrated at a scale of 1–3 kg/hr of dry feed. Organic liquid yields as high as 65–70% of the dry feed can be obtained from hardwood waste material, and 45–50% from wheat straw. The fluidized sand bed pyrolysis reactor operates on a unique principle so that char does not accumulate in the bed and treatment of the sand is not necessary. The product gas, about 15% of the yield, has a medium heating value. The liquid product is an acidic fluid, which pours easily and appears to be stable. A preliminary economic analysis suggests that if the pyrolysis oil can be used directly as a fuel, its production cost from wood waste is probably competitive with conventional fuel oil at the present time. On a fait la démonstration d'un procédé continu de pyrolyse éclair à l'échelle de l à 3 kg/h d'alimentation sèche, à la pression atmosphérique, pour la production de liquides organiques à partir d'une biomasse cellulosique. On peut obtenir des rendements en liquide atteignant 65 à 70% de l'alimentation sèche à partir de déchets de bois dur et de 45 à 50% à partir de paille de blé. Le réacteur de pyrolyse, à lit de sable fluidisé, fonctionne sur un principe unique, de sorte que le charbon ne s'accumule pas dans le lit et qu'il n'est pas nécessaire de traiter le sable. Le produit gazeux, qui correspond à environ 15% de rendement, a une valeur calorifique moyenne. Le produit liquide est un fluide acide qui se déverse facilement et semble assez stable. Une analyse économique préliminaire indique que, si l'on peut employer directement l'huile de pyrolyse comme combustible, son coǔt de production à partir de déchets de bois est probablement compétitif actuellement avec celui de l'huile combustible classique.
Article
Thermal analysis and kinetic studies have shown that oxidative reactions are responsible for acceleration in the rates of weight loss and depolymerization of cellulose on pyrolysis in air at temperatures below 300°C. The oxidative reactions include production of hydroperoxide, carbonyl, and carboxyl groups, which have been investigated at lower temperatures along with the rates of depolymerization and production of carbon monoxide and carbon dioxide. The experimental results are consistent with an autoxidation mechanism involving initiation, propagation, and decomposition reactions. At temperatures above 300°, the rate of pyrolysis is essentially the same in both air and nitrogen, indicating that thermal degradation is independent of the oxidative reactions.
Article
It has been shown that the pyrolysis of cellulose at low pressure (1.5 Torr) can be described by a three reaction model. In this model, it is assumed that an “initiation reaction” leads to formation of an “active cellulose” which subsequently decomposes by two competitive first-order reactions, one yielding volatiles and the other char and a gaseous fraction. Over the temperature range of 259–341°C, the rate constants of these reactions, ki (for cellulose → “active cellulose”), kv (for “active cellulose” → “volatiles”), and kc (for “active cellulose” → char + the gaseous fraction) are given by ki = 1.7 × 1021e− (58,000/RT) min −1, kv = 1.9 × 1016e− (47,300/RT) min−1, and kc = 7.9 × 1011e− (36,600/RT) min−1, respectively.