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One dimensional steady-state circulating fluidized-bed reactor model for biomass fast pyrolysis
... Modeling biomass fast pyrolysis (FP) reactor systems is challenging because a multitude of factors can impact the process results. 1 A slate of more than a thousand species can be produced in such systems, 2 significant differences in which can result from variations in feedstock composition, as well as changes in heat and mass transfer effects due to feedstock particle size and reactor conditions and configurations. 3 Predictive models with reaction kinetics are therefore rarely put to practical use in overall process simulations; instead, explicit specification of yield is the most common way pyrolysis reactors are represented in large process simulations used for techno-economic analysis. ...
... 1-D Reactor Model in ACM. In the flowsheet simulation corresponding to Figure 1, the pyrolysis reactor is a one-dimensional steady-state biomass fast pyrolysis model previously described in Trendewicz et al. 1 The model features (1) a flexible pyrolysis reaction mechanism based on the prediction of lumped species for different product categories, as described by Ranzi and co-workers, 8−10 (2) gas−solids momentum transfer for entrained flow, and (3) gas−solids heat transfer. The model presented in Trendewicz et al. 1 was programmed in gPROMS. ...
... In the flowsheet simulation corresponding to Figure 1, the pyrolysis reactor is a one-dimensional steady-state biomass fast pyrolysis model previously described in Trendewicz et al. 1 The model features (1) a flexible pyrolysis reaction mechanism based on the prediction of lumped species for different product categories, as described by Ranzi and co-workers, 8−10 (2) gas−solids momentum transfer for entrained flow, and (3) gas−solids heat transfer. The model presented in Trendewicz et al. 1 was programmed in gPROMS. 13 For the present article, the model was converted to Aspen Custom Modeler (ACM); 3 gPROMS and ACM are both equation-oriented simulation environments ideal for mathematical definition and solution of reactor problems. ...
A biomass fast pyrolysis reactor model with detailed reaction kinetics and one-dimensional fluid dynamics was implemented in an equation-oriented modeling environment (Aspen Custom Modeler). Portions of this work were detailed in previous publications; further modifications have been made here to improve stability and reduce execution time of the model to make it compatible for use in large process flowsheets. The detailed reactor model was integrated into a larger process simulation in Aspen Plus and was stable for different feedstocks over a range of reactor temperatures. Sample results are presented that indicate general agreement with experimental results, but with higher gas losses caused by stripping of the bio-oil by the fluidizing gas in the simulated absorber/condenser. This integrated modeling approach can be extended to other well defined, predictive reactor models for fast pyrolysis, catalytic fast pyrolysis, as well as other processes.
... Those simulations showed that the presence of clusters delayed the conversion process by up to 85% compared to a corresponding homogeneous flow. However, the simulations did not account for spatial variations in the vertical direction that are known to have a large effect on biomass fast pyrolysis 39 . More details about CFD simulations of biomass pyrolysis can be found in a recent review by Xiong et al. 40 . ...
... These models represent a simplified picture of the complex processes that happen in a multiphase reactor to reduce the computational expense. In literature, several papers 56,57,39,58 employ various engineering models to study biomass thermochemical conversion in fluidized bed reactors. In general, these models divide the fluidized bed reactor into several parts, such as bubble or emulsion phases, and use empirical models to represent each part. ...
A recurring challenge among the variety of existing biomass‐to‐biofuel conversion technologies is the need to ensure optimal and homogeneous contact between the various phases involved. The formulation of robust design rules from an empirical standpoint alone remains difficult due to the wide range of granular flow regimes coexisting within a given reactor. In this work, a volume‐filtered Eulerian‐Lagrangian framework is employed that solves chemically reacting flows in the presence of catalytic particles. The simulation strategy is used to quantify the role of the particle clustering on catalytic upgrading of biomass pyrolysis vapor in risers. It is shown that particle clustering can reduce the catalytic conversion rate of biomass pyrolysis vapors by up to about 50%. The simulation results are also compared with an engineering model based on continuously stirred tank reactor (CSTR). A one‐dimensional Reynolds‐averaged transport equation is derived, and the unclosed terms that account for the heterogeneity caused by clusters are evaluated.
... Because the potential output of bio-oil is directly dependent on the initial pyrolysis tar yield and composition, there is considerable interest in experimental [4][5][6][7][8] and computational [9][10][11][12][13][14][15][16][17][18][19][20][21][22] investigations of how tar yield is affected by the biomass type and also by the employed conditions for pyrolysis. This interest should include both the mean tar yield as well as its variability, since large fluctuations in the condensable hydrocarbon stream used for catalytic upgrading would significantly complicate the process control. ...
... Compared with time-consuming and costly experiments, multi-phase CFD is able to provide detailed information on the spatiotemporal variations in species concentrations, flows, and temperatures within the reactor with reduced effort and developing circle. This makes CFD a promising platform to account for physical relationships that are beyond the capability of direct experimental measurements [7][8][9][10][11][12][13][14][15]. To make sure that the simulated reactor conditions were relevant, we based the simulations in the present study on an experimental laboratory-scale bubbling fluidized-bed pyrolyzer located at Iowa State University [16]. ...
... -se para o modelo cinético e para o dimensionamento do CFB um modelo estático como emTrendewicz et al.(2014). Dada a velocidade de fluidização, a pirólise rápida requer que a reação ocorra dentro de 2 a 2,5 s. ...
In order to mitigate ambiental impacts of trash Generation and to build up alternatives for work and revenue, this paper has investigated the dimensioning of a syngas generation plant from municipal solid waste (MSW) for collectors cooperatives and came to its conclusions by research on the literature. It was verified the applicability, partnerships for organizacional innovation in residue management and the possible necessary technologies to accomplish the lowest price in the implementation of the system, which is promising in the resolution of economical and socioenvironmental issues of the constant rising in the volume of trash generated in the cities. RESUMO Para mitigar impactos ambientais da geração do lixo e criar alternativas de geração trabalho e renda, este estudo investigou o dimensionamento de usinas de geração de gás de síntese a partir de resíduos sólidos urbanos (RSU) para cooperativas de catadores e chegou aos resultados através da pesquisa na literatura. Verificou-se vias para aplicabilidade, parcerias para inovação organizacional na gestão de resíduos e as possíveis tecnologias necessárias para atingir o menor custo ao implementar o sistema, que é promissor na resolução de problemas econômicos e socioambientais do aumento constante do volume de lixo gerado nas cidades. Palavras-chave: Inovação organizacional, Resíduos para energia, Economia circular, Pirólise.
... -se para o modelo cinético e para o dimensionamento do CFB um modelo estático como emTrendewicz et al.(2014). Dada a velocidade de fluidização, a pirólise rápida requer que a reação ocorra dentro de 2 a 2,5 s. ...
In order to mitigate ambiental impacts of trash Generation and to build up alternatives for work and revenue, this paper has investigated the dimensioning of a syngas generation plant from municipal solid waste (MSW) for collectors cooperatives and came to its conclusions by research on the literature. It was verified the applicability, partnerships for organizacional innovation in residue management and the possible necessary technologies to accomplish the lowest price in the implementation of the system, which is promising in the resolution of economical and socioenvironmental issues of the constant rising in the volume of trash generated in the cities. RESUMO Para mitigar impactos ambientais da geração do lixo e criar alternativas de geração trabalho e renda, este estudo investigou o dimensionamento de usinas de geração de gás de síntese a partir de resíduos sólidos urbanos (RSU) para cooperativas de catadores e chegou aos resultados através da pesquisa na literatura. Verificou-se vias para aplicabilidade, parcerias para inovação organizacional na gestão de resíduos e as possíveis tecnologias necessárias para atingir o menor custo ao implementar o sistema, que é promissor na resolução de problemas econômicos e socioambientais do aumento constante do volume de lixo gerado nas cidades. Palavras-chave: Inovação organizacional, Resíduos para energia, Economia circular, Pirólise.
... In this work, the kinetic model (Table 4) developed by Ranzi et al. [48] was chosen because it provides a detailed description of biomass pyrolysis. The kinetic model only considers primary chemical reactions because, for fast pyrolysis operations, secondary chemical reactions' contribution was insignificant (Trendewicz et al. [61]). The lignin was classified into three types (LigC, LigH, and LigC) according to its composition terms: Carbon, Hydrogen, and Oxygen. ...
Biofuels may significantly influence the world's transition from hydrocarbons to renewable energies. Pyrolysis uses thermal energy in an anaerobic ambiance to crack biomass and create biofuels (bio-oil and synthesis gas). This work reports a detailed computational study of a novel system to develop fast biomass pyrolysis with concentrated solar energy. A fluidized bed reactor was coupled to a solar thermal receiver to heat the inert fluid (nitrogen) using a biomimetic mini heliostat field which provides the required thermal energy. A detailed kinetic model for the pyrolysis of lignocellulosic biomass was solved simultaneously with a set of differential equations based on mass, momentum, and energy conservation principles. An Eulerian-Eulerian approach was considered with three phases. The computational model was compared with data reported in the literature for the fluidized bed reactor and heat transfer in the solar thermal receiver with good agreement. Concentrated solar fluxes on the receiver, nitrogen outlet temperatures, temperature contours inside the reactor, concentration contours of relevant gases, and global product percentages (Tar, Char, and Gas) are reported. The products reach an almost constant composition of Gas, Tar, and Char after 6 s of reaction, indicating the annual operational stability of the solar pyrolysis plant in terms of biofuel production.
... Comparably, rice straw and cassava stalk are found to have a high yield of gas than oak and beechwood, which could be due to the higher ash content in the feedstock. The same conclusion has been drawn by Trendewicz et al. [78] Furthermore, the yield of char from the pyrolysis of oak, beechwood, rice straw, and cassava stalk pyrolysis has been shown in Figure 7A-D. As can be seen from the figure, the yield of char decreased with increasing pyrolysis temperature, which is associated with the increase in the reactivity of the reacting components favouring the production of liquid and gas products. ...
Biomass pyrolysis process from a drop tube reactor was modelled in a plug flow reactor using Aspen Plus process simulation software. A kinetic mechanism for pyrolysis was developed considering the recent improvements and updated kinetic schemes to account for different content of cellulose, hemicellulose, and lignin. In this regard, oak, beechwood, rice straw, and cassava stalk biomasses were analyzed. The main phenomena governing the pyrolysis process are identified in terms of the characteristic times. Pyrolysis process was found to be reaction rate controlled. Effects of pyrolysis temperature on bio-oil, gases, and char yields were evaluated. At optimum pyrolysis conditions (i.e., 500 C), a bio-oil yield of 67.3, 64, 43, and 52 wt.% were obtained from oak, beechwood, rice straw, and cassava stalk, respectively. Oak and beechwood were found to give high yields of bio-oil, while rice straw produced high gas and char yields compared to other biomasses. Although temperature is the main factor that plays a key role in the distribution of pyrolysis products, the composition of cellulose, hemicellulose, and lignin in the feedstock also determines the yield behaviour and composition of products. With the rise in pyrolysis temperature, further decomposition of intermediate components was initiated favouring the formation of lighter fractions. Comparably, species belonging to the aldehyde chemical family had the highest share of bio-oil components in all the investigated feedstocks. Overall, the present study shows a good agreement with the experimental study reported in the literature, confirming its validity as a predictive tool for the biomass pyrolysis process.
... Similarly, in 257 the solid phase are several species, of which it is required to determine molecular weight and 258 In this work, the kinetic model of Ranzi et al. (2008) was selected since it offers a more rigorous and detailed description than global and simple generalized models (Table 4). Only primary chemical reactions are considered in this study, as it has been shown by Trendewicz et al. (2014) that for fast pyrolysis operations, the contribution of secondary chemical reactions is not significant in the description of kinetics. This model makes some relevant considerations. ...
Biofuels are considered a promising source of renewable energy. Pyrolysis uses heat in an inert atmosphere to break down biomass
and produce biofuels like bio-oil (tar) and synthesis gas. This paper presents a computational study of fast biomass pyrolysis in a
laboratory fluidized reactor. A laminar flow regime and an Eulerian-Eulerian approach were considered. A comprehensive kinetic
model consisting of sixteen irreversible, first-order reactions was coupled with conservation equations of mass, momentum,
and energy. The computational model was validated with data reported in the literature. The e�ect of biomass type and reactor temperature on the thermal decomposition of biomass were analyzed, finding a direct relationship between the content of cellulose and production of tar and similarly between the content of lignin and production of char. Also, the absence of lignin in the biomass dramatically changes the tar and gas compositions. Energy requirements, temperature contours, the composition of the exit gases,
and final product yields (tar, char, and gas) are reported.
... However, our total volatile product yield, organics plus water, is still in an agreeable range for fast pyrolysis of switchgrass, 35-63 wt%, for our investigated temperature range [43]. The non-condensable yields are similar to findings reported for other simulated pyrolysis systems (15-25 wt%) [26,28,44]. These simulations show that when using this kinetic scheme, the fluidization velocity does not affect the overall bio-oil yield at a given temperature. ...
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.
... With growing research interests, biomass fast pyrolysis has emerged as a potentially attractive method for liquid fuels production from solid biomass. Pyrolysis of biomass generally results in variety of compounds depending upon fraction of primary building blocks of biomass i.e. cellulose, hemicellulose and lignin [6]. The process of pyrolysis in packed and fluidized beds has been frequently employed in recent years [7][8][9][10][11]. ...
Presence of meso-scale structures such as particle clusters and gas bubbles is ubiquitous in fluidized beds frequently used in pyrolysis of coal and biomass. In recent years, bubbling and circulating fluidized beds have become popular for highly efficient conversion of carbonaceous feedstock into pyrolysis products. The characterization and study of hydrodynamics inside these reactors can provide an insight into the mechanisms controlling the performance of these reactors. Among others, cluster size distribution and mean cluster size are the key parameters defining the hydrodynamics of these reactors. In the current work, Digital Image Analysis (DIA) was applied to computationally obtained instantaneous snapshots during the CFD simulations of gas-solid flows. Transient two fluid modeling (TFM) was applied to three different gas-solid systems in periodic domains with different particulate systems keeping same grid size. The dimensionless axial cluster size was defined in line with literature. The cluster sizes and their distributions are obtained and compared with the available empirical correlations present in the literature based on experimental observations having similar range of operating conditions as well as system characteristics. It is found that the results of current approach agree well with the available data. The methodology followed in current work presents an alternative to expensive experimentation for development of a universal cluster size correlation.
... A simple residence time model with no distinct fluid dynamics for different biomasses shows again that the influence of residence time and temperature can be calculated [91]. A 1-D steady-state CFB reactor model with kinetics for cellulose, hemicellulose, and lignin with mass and heat balancing equations shows that the fluid dynamics and yields for biomass with varying composition can be predicted and this model is applicable for use in flowsheeting [239]. In summary, models calculating the main fluid dynamics and product yields for either bubbling/stationary fluidized beds or circulating fluidized beds have been developed. ...
In search of an alternative for chemicals and energy from fossil fuels, lignin pyrolysis is experimentally investigated in a circulating fluidized bed. Deviation in pyrolysis behavior of a softwood Kraft lignin and a wheat straw hydrolysis lignin is analyzed by means of char morphology as well as overall yield and composition determination for gas, oil, and char. The influence of catalytically active mineral matter in lignin on the product distribution is investigated. Progressively, the fluidized bed pyrolysis process is modeled semi-empirically considering fluid dynamics, feedstock composition, micro-particle pyrolysis reactions and mass balances. The lignin secondary reaction kinetics from oil–to–gas are obtained from the Kraft lignin experimental data and a pyrolysis plant with integrated char and permanent gas combustion is modeled with a flowsheeting tool.
... Trendewicz et al. [519] integrated a one-dimensional steadystate biomass fast pyrolysis reactor CFD model with a biomass pyrolysis plant model. Their model considered products speciation, and particle velocity was computed from a solid-gas momentum balance instead of empirical correlations. ...
Biomass fast pyrolysis is potentially one of the cheapest routes toward renewable liquid fuels. Its commercialization, however, poses a multi-scale challenge, which starts with the characterization of feedstock, products and reaction intermediates at molecular scales, and continues with understanding the complex reaction network taking place in different reactor configurations, and in the case of catalytic pyrolysis and upgrading on different catalysts. In addition, crude pyrolysis oil is not immediately usable in the current energy infrastructure, due to undesirable properties such as low energy content and corrosiveness as a result of its high oxygenate content. It, therefore, needs to be upgraded and fractionated to desired specifications. While various types of pyrolysis reactors and upgrading technologies are under development, knowledge transfer and closing the gap between theory and application requires model development. In-depth understanding of the reaction mechanisms and kinetics should be combined with the knowledge of multi-scale transport phenomena to enable design, optimization, and control of complex pyrolysis reactors. Finally, underpinning economic and environmental impacts of biofuel production requires expanding the system boundaries to include the overall process and supply chain. The present contribution aims at providing a comprehensive multi-scale review that discusses the state of the art of each of these aspects, as well as their multi-scale interactions. The study is mainly focused on fast pyrolysis, although reference to other types of pyrolysis technologies is made for the sake of comparison and knowledge transfer.
... In addition, the highest organics yield of 65.5 wt% was obtained from pine, followed by 61.2 wt% from waste, 59.6 wt% from straw and 58.0 wt% from olive husks. They also concluded that the reactor model provided an acceptable approximation of fluid dynamics, heat transfer and pyrolysis product yields [256]. Dai et al. studied the pyrolysis of wood in a CFB reactor. ...
Lignocellulosic biomass can be convert to a condensable liquid named bio-oil, a solid product named as char and a mixture of gaseous products comprising CO 2 , CO, H 2 , CH 4 , etc. In recent years, much effort has been made on the investigation of conversion of biomass through pyrolysis. However, commercialisation of the biomass pyrolysis technology is still challenging due to various issues such as the deleterious properties of bio-oil including the low heating value and the high instability at elevated temperatures. To overcome such issues, many processes, reactors and catalysts have been developed for pyrolysis and catalytic pyrolysis of biomass. A state to the art of pyrolysis or catalytic pyrolysis of biomass need to be summarised to have an overall evaluation of the technologies, in order to provide a useful reference for the further development of pyrolysis technology. This study reviews the various pyrolysis process, especially focus on the effects of essential parameters, the process design, the reactors and the catalysts on the pyrolysis process. In addition, progress in commercialisation of pyrolysis technology was also reviewed and the remaining issues in the process of commercialisation were discussed. © 2019 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences
... To explore these trends, a counterflow fluidized bed model was developed based upon 1-D (vertically discretized) conservation equations for the gas-phase and solids mass, momentum, and thermal energy and for gas and solids species with reactive particles. The equations were adapted from computational fluidized bed models in the literature for the two-phase flow [95] including 1-D fluidized bed models with reacting particles [96][97][98]. This model builds upon the discretized thermodynamic models previously reported [55] and is described in detail elsewhere [85]. ...
Oxide particles have potential as robust heat transfer and thermal energy storage (TES) media for concentrating solar power (CSP). Particles of low-cost, inert oxides such as alumina and/or silica offer an effective, non-corrosive means of storing sensible energy at temperatures above 1000 deg. C. However, for TES subsystems coupled to high-efficiency, supercritical-CO2 cycles with low temperature differences for heat addition, the limited specific TES (in kJ/kg) of inert oxides requires large mass flow rates for capture and total mass for storage. Alternatively, reactive oxides may provide higher specific energy storage (approaching 2 or more times the inert oxides) through adding endothermic reduction. Chemical energy storage through reduction can benefit from low oxygen partial pressures (PO2) sweep-gas flows that add complexity, cost, and balance of plant loads to the TES subsystem. This paper compares reactive oxides, with a focus on Sr-doped CaMnO3 perovskites, to low-cost alumina-silica particles for energy capture and storage media in CSP applications. For solar energy capture, an indirect particle receiver based on a narrow-channel, counterflow fluidized bed provides a framework for comparing the inert and reactive particles as a heat transfer media. Low-PO2 sweep gas flows for promoting reduction impact the techno-economic viability of TES subsystems based on reactive perovskites relative to those using inert oxide particles. This paper provides insights as to when reactive perovskites may be advantageous for TES subsystems in next-generation CSP plants.
... Widespread applications of fluidized bed reactors (FBR) have prompted the use of CFD simulations as a tool in design [27][28][29][30][31][32][33][34][37][38][39][40][41], to investigate impacts such as nitrogen and sidewall temperature, sand particle size, biomass feed rate and particle size, feedstock material, Greek symbols α The initial mass composition of cellulose in the feedstock, dimensionless β ...
... An obvious trend in recent years with respect to the process modeling of biomass pyrolysis is to incorporate CFD results into the overall process modeling of the integrated system. Trendewicz et al. [42] incorporated the one-dimensional CFD results into their steady-state process modeling of biomass pyrolysis. The lumped process modeling of the integrated system except the biomass pyrolysis reactor was combined with a two-dimensional CFD by Lee et al. [43], as shown in Fig. 2. One merit of such coupling is that for sub-systems with homogeneous intra-reactor structure, process modeling can be still employed without Fig. 3. ...
Process intensification is critical to increase product yields and reduce external power consumption in biomass pyrolysis. Computational fluid dynamics offers great possibilities for fast and economical process intensification of biomass pyrolysis. This succinct but in-depth current-perspective feature article discusses the major trends and roadblocks with respect to CFD-aided process intensification of biomass pyrolysis. Major trends such as multiscale coupling, fast parametric analysis and design, and coupling between CFD and process modeling, are reviewed. Major roadblocks such as lack of accurate chemical kinetics, and difficulty in accurate description of microstructural change, are pointed out. It is believed that the clarification of these directions and problems will lead to a more objective but efficient application of CFD to process intensification of biomass pyrolysis.
... It was shown that the presence of clusters delayed the conversion process by up to 85% compared to a corresponding homogeneous flow. However, the simulations did not account for spatial variations in the vertical direction that are known to have a significant effect on the overall process [12]. ...
Risers are used in a variety of industries, where rapid mixing between gas and solid particles is essential. More recently, risers are gaining importance in some of the novel combustion technologies, such as Chemical-looping combustion and thermochemical conversion of biomass. These reactor configurations provide challenging modeling issues, as the particulate flow is characterized by a highly fluctuating solid volume fraction due to the formation of dense clusters. This may severely reduce the mixing between gas and solid particles and affect the residence time of the particles in the reactor, and thus, the extent of heterogeneous reactions between gas and solid particles. In this work, we investigate how clustering impacts heterogeneous reactions in risers using a detailed Euler-Lagrange computational framework. For this purpose, three-dimensional laboratory-scale riser simulations are performed. A simplified reaction system is used, where the solid-fluid reaction is represented by a single isothermal reaction step. To asses the effect of multiphase dynamics of the bed on the heterogeneous chemistry, the three-dimensional simulation results are compared with reduced-order models.
... Several studies 4−7 have proposed process models for pyrolysis reactors. Trendewicz et al. 4 used finite difference to solve the transport equation for a 0.023 kg/h circulating fluidized-bed (CFB) reactor and the kinetic model by Ranzi et al. 8 This model assumes only primary reactions and did not include particle mass transfer. The results predicted the data extracted from literature well. ...
In this study, a process model for an auger style biomass pyrolysis reactor is developed to use as a tool in process optimization and scale up. The plug flow model for both solid and gas phases are assumed. A comparison between the kinetic models widely used in the literature with the experimental data was performed to determine the “best” kinetic model for our system. The transport equations for each phase are combined with the kinetic model to predict bio oil, char, and non condensable gas yields. The applied model was validated with experimental data from a 2-4 kg/h pilot scale auger reactor. This reactor uses steel shot as a heat carrier and without carrier gas. The results show good agreement between experimental data and model prediction. The model was used to predict yield of bio-oil as a function of temperature, feed flow rate and reactor pressure. These simulations indicate the model is a useful tool in design and scale up of auger type pyrolysis reactors using a heat carrier.
... Most reactor configurations use char produced from the process to heat the recycled sand through combustion. Thus CFB systems have a secondary combustion chamber to burn char produced (Trendewicz, Braun, Dutta, & Ziegler, 2014). The unburnt fraction or ash has to be removed. ...
Heat transfer analysis was performed on a novel auger reactor for biomass fast pyrolysis. As part of this analysis, correlations for specific heat capacity and heat transfer coefficients for biomass (sawdust) and sand (used as heat transfer medium) were developed. For sand, the heat transfer coefficient followed a power law distribution with reactor fill level and temperature. For raw biomass, the heat transfer coefficient also showed similar dependence on fill level, but was independent of temperature up to 300°C. These correlations were used in a one dimensional heat transfer model developed to calculate the heating time and heating rate of biomass in the presence of a heat transfer medium (HTM). A heating time of 3 seconds was obtained to raise the temperature of biomass from 298 K to 753 K. Instantaneous heating rates up to 530 K/s were obtained, thus ensuring fast pyrolysis. Further, to study the effect of heating rates on liquid product yields, a previously validated torrefaction-pyrolysis model was used to calculate the liquid yields for torrefied pine forest residues at various heating rates. A threshold heating rate value of 12 K/s was obtained from the model, above which the final product distribution was not affected. The model predicted liquid yield was 54%, in comparison to the experimental yield of 53%, for torrefied pine forest residues without HTM. The steady state experimental heating rate of 36 K/s was observed, which was above the 12 K/s threshold value thus ensuring fast pyrolysis. The results obtained in this paper will be used as a basis for scaling up the reactor configuration to carry out fast pyrolysis without HTM.
... In these studies, experimental validation and detailed description of the flow field and heat transfer characteristics were presented, as shown in Figure 4. A model reduction work was done by Trendewicz et al. 9 and Humbird et al. 76 in their 1D steady-state modeling of biomass pyrolysis in a circulating fluidized bed using Scheme E. It was attractive to find that the developed 1D model shows close predictability to 2D MFM. The effects of bed column size on lignocellulosic biomass pyrolysis were recently studied by Lee et al. 77 81 and Eri et al. 82 to simulate fluidized-bed biomass pyrolysis. ...
Computational fluid dynamics (CFD) has been widely used in both scientific studies and industrial applications of reactor-scale biomass pyrolysis. In this Perspective, the state-of-the-art progress in CFD modeling of reactor-scale biomass pyrolysis was summarized and discussed. First, because of the importance of biomass pyrolysis reaction kinetics to the predictability of CFD, the commonly used pyrolysis reaction kinetics in CFD modeling of reactor-scale biomass pyrolysis were reviewed. The characteristics of each reaction kinetics were described. Then, the theoretical basis and practical applications of three main CFD modeling approaches, i.e., porous media model, multifluid model, and discrete particle model for simulating reactor-scale biomass pyrolysis were presented. The activities and progresses with respect to each CFD modeling approach for reactor-scale biomass pyrolysis were reviewed. Aspects such as experimental validation, modeling speed, and capability were discussed. Finally, the paper was concluded with comments on future directions in CFD modeling of reactor-scale biomass pyrolysis.
... With measured pyrolysis kinetics data for their biomass samples, the product yields at a biomass particle residence time of 1.5-3.5 s were found to be in good agreement with experimental data, as shown in Figure 11.6. Using a CFD model (MFIX software), Trendewicz et al. [79] showed that at a riser temperature of 510°C, biomass particles were heated up to pyrolysis temperature within 0.15 m from the entrance, and pyrolysis reactions proceeded quickly to 99% conversion after 0.9 s. Those reactor models can serve as useful tools in assisting scale-up, design, and operation of commercial FB biomass fast pyrolysis reactors. ...
This chapter focuses on multiphase reactors' applications and challenges encountered in their applications to biomass processing and conversions to heat, power, biofuels, and chemicals. A number of multiphase reactors have been used for biomass combustion, including fixed bed, fluidized bed (FB), and entrained bed (pulverized fuel) combustors. Bed agglomeration, slagging, fouling, and corrosion are the major issues related to biomass combustion due to the relatively high salts (AAEMs), nitrogen, and chlorine contents of biomass feedstocks. The major problems for biomass feeding are blockage and plug seal failure to the reactor. Densified biomass (e.g., wood pellets and briquettes) is much more appropriate for transportation, handling, storage, and feeding. The high costs of pelletization can be justified by better operability of the fuel leading to improved boiler and combustion performance. The desirable moisture content of biomass feedstock must be lower than 15% (wb) for storage and various thermochemical applications.
... Gas-solid fluidized-bed reactors are widely used in the chemical industry, including biomass conversion [1][2][3][4], petroleum refining [5], and pharmaceutical [6,7] and commodity chemicals production [8]. For this reason, there is widespread interest in establishing a comprehensive understanding of the gas-solid hydrodynamics to optimize processes in which fluidized-bed reactors are key components. ...
We report results from a computational study of the transition from bubbling to slugging in a laboratory-scale fluidized-bed reactor with Geldart Group B glass particles. For simulating the three-dimensional fluidized-bed hydrodynamics, we employ MFiX, a widely studied multi-phase flow simulation tool, that uses a two-fluid Eulerian-Eulerian approximation of the particle and gas dynamics over a range of gas flows. We also utilize a previously published algorithm to generate bubble statistics that can be correlated with pressure fluctuations to reveal previously unreported details about the stages through which the hydrodynamics progress during the bubbling-to-slugging transition. We expect this new information will lead to improved approaches for on-line reactor diagnostics, as well as new approaches for validating the results of computational fluidized-bed simulations with experimental measurements.
... Circulating fluidized bed reactor schematic. Reproduced from:Trendewicz, Braun, Dutta, & Ziegler, 2014 ...
Significant volumes of biomass waste are generated each year as a result of agricultural practices in India. Despite the negative environmental impacts, in-situ incineration of crop residues is common practice for disposal of this waste. Transportation of raw biomass accounts for a significant portion of the cost of biomass conversion processes due to its low energy density and high bulk volume. The use of raw biomass also reduces the overall efficiency of thermochemical conversion processes due to high moisture content, over-oxidation of the fuel resulting from high oxygen content, and the relatively high oxygen to carbon ratio. There has been much recent interest in improving the properties of biomass prior to gasification and pyrolysis through densification, drying, and mild thermochemical treatments. One approach is a process known as torrefaction, which is a mild pyrolysis process that is shown to produce an energy-dense fuel with improved transport, storage, and feedstock characteristics. Particularly in the Indian context, there is a need for the development of a small-scale system which can densify and upgrade the properties of agricultural residues after harvest. This thesis presents the design and preliminary testing of a lab-scale moving-bed torrefaction reactor. Key learnings from the assembly and testing of this machine are identified and recommendations for improvement are made. A rudimentary model evaluating the heat transfer in packed bed of biomass is developed to provide a framework for analyzing future reactor designs. The functional requirements of a labscale screw conveyor torrefaction reactor are developed based on this analysis and a preliminary reactor architecture is proposed. Multiple studies are recommended to improve the reliability of the heat transfer model. Recommendations are made for future design iterations of the lab-scale screw conveyor torrefaction reactor.
... Our overall objective is to identify low-order reactor approximations based on this information that can be used to guide, interpret, and correlate lab and pilot-scale experiments on pyrolysis-based bio-oil generation now being carried out at national laboratories in support of the Department of Energy's (DOE's) Bioenergy Technology Office (BETO). We also seek to provide tools for consolidating information from more detailed computational reactor simulations [e.g., see the recent studies by Trendewicz et al (2014Trendewicz et al ( , 2015] and improving highlevel process simulations of bio-oil production needed for techno-economic analyses. ...
... The reaction details are shown in Table 1. In this work, the primary reactions only were considered because the secondary reactions were not found to be significant for fast pyrolysis as reported in the literature (Trendewicz et al., 2014). It has been reported in the literature that this scheme has the capability for the prediction of fast pyrolysis process (Mellin et al., 2014). ...
The present work concerns with CFD modelling of biomass fast pyrolysis in a fluidised bed reactor. Initially, a study was conducted to understand the hydrodynamics of the fluidised bed reactor by investigating the particle density and size, and gas velocity effect. With the basic understanding of hydrodynamics, the study was further extended to investigate the different kinetic schemes for biomass fast pyrolysis process. The Eulerian–Eulerian approach was used to model the complex multiphase flows in the reactor. The yield of the products from the simulation were compared with the experimental data. A good comparison was obtained between the literature results and CFD simulation. It is also found that CFD prediction with the advanced kinetic scheme is better when compared to other schemes. With the confidence obtained from the CFD models, a parametric study was carried out to study the effect of biomass particle type and size and temperature on the yield of the products.
... Reaction mechanism Heat transfer mechanism Assumptions Solution method Results One dimensional steady-state, Eulerian fluid dynamics and heat transfer [49] Circulating fluidizedbed (0.023 kg/ s) ...
The thermal decomposition of woody biomass in the absence of oxygen, or pyrolysis, is a series of complex reactions involving hundreds of compounds. The species of residue, form of residue (bark, sawdust, and other residues), age, storage conditions, among other factors, will impact the composition of the residue which in turn impacts the pyrolytic reactions. The reaction rates must be understood to optimize the pyrolysis reactor. However, the determination of intrinsic kinetics in this system is complex (both due to feedstock composition and the nature of reactions at pyrolysis temperatures) and as such the approach has been to use an overall reaction rate or series of simplified reactions. In this study, a review of large scale pyrolysis process units, reactor mathematical models, mechanisms for conversion of woody biomass and overview of heat of pyrolysis is presented. In addition, the presented kinetic models have been compared to experimental data obtained from pyrolysis of different liginocellulosic biomass (i.e. sawdust, bark, and wood chips) in a lab-scale tube furnace reactor, to determine the “best” kinetic model for the fast pyrolysis of sawmill residues. The results show that the chemical percolation devolatilization model (Lewis et al. Energy Fuels 2013; 27:942–953. doi:10.1021/ef3018783) predicts the pyrolysis products most accurately. Furthermore, the competitive model (Chan et al. Fuel 1985; 64:1505–1513. doi:10.1016/0016-2361(85)90364-3) shows very good agreement for bio-oil experimental data. Although the pyrolysis of biomass has been widely investigated in recent decades, the models have some limitations which could limit their application to a broad spectrum of feedstock and pyrolysis operating conditions.
... The heat and mass transfers occur slowly in the biomass and the distillation products started to appear at just below 600°C. According to Trendewicz et al. (2014) the conversion time is dependent on the particle size. When large biomass particles are heated, temperature gradients form inside the particle due to the relatively slow conductive heat transfer. ...
The aim of this study was to evaluate the potential of Hancornia speciosa GOMES (mangaba) seeds as a novel matrix for the production of bio-oil. The study was divided into three steps: (i) characterization of the biomass (through elemental analysis (CHN), infrared spectroscopy (FTIR-ATR), thermogravimetry (TG), and determination of biomass composition; (ii) pyrolysis of mangaba seed to obtain the bio-oil; and (iii) characterization of the bio-oil (thermogravimetry and gas chromatography/mass spectrometry-GC/qMS). The TG of the sample showed a mass loss of around 90% in 450°C. In the pyrolysis experiments the variables included temperature (450 and 600°C), sample mass (5 and 11g) and prior heating (with or without), with the best conditions of 600°C, 11g of seeds and prior heating of the furnace. The GC/qMS analysis identified carboxylic acids and hydrocarbons as the major components, besides the presence of other compounds such as furanes, phenols, nitriles, aldehydes, ketones, and amides.
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... For biomass fast pyrolysis simulation, CFD has been applied mainly to the fluidized-bed reactor because of the simple geometry and widespread applications of this reactor [26][27][28][29][30][31][32][33][34][35][36]. Fluidized beds can provide excellent gas-solid mixing and heat transfer. ...
... There are a number of technologies available in lab-scale and pilot-scale to investigate various factors that influencing the process. Table 2 shows the technologies used, operating conditions and their products [28,[44][45][46][47][48][49][50]. ...
The worldwide demand for energy is ever escalating commensurate with increasing populations and development. While fossil fuels as the current major energy resource are shrinking drastically, combustion of fossil fuel releases greenhouse gases, which are the main culprit for global warming and climate changes. Development of renewable energy appears to be a prominent solution to address these energy and environmental issues. Pyrolysis process converting biomass into energy offers a promising alternative for renewable energy supply. This paper reviews recent and state-of-art development of biomass pyrolysis research in producing biochar, bio-oil and biogas. Factors affecting pyrolysis processes and intrinsic properties of the pyrolysis products produced from different operating conditions are discussed. Advancement in pyrolysis technology as well as the challenges and prospects of pyrolysis for energy production are also outlined.
Meeting the needs of a growing population calls for a change from linear production systems that exacerbate the depletion of finite natural resources and the emission of environmental pollutants. These linear production systems have resulted in the human-driven perturbation of the Earth’s natural biogeochemical cycles and the transgression of environmentally safe operating limits. One solution that can help alleviate the environmental issues associated both with resource stress and harmful emissions is resource recovery from waste. In this review, we address the recovery of resources from food and beverage processing wastewater (FPWW), which offers a synergistic solution to some of the environmental issues with traditional food production. Research on resource recovery from FPWW typically focuses on technologies to recover specific resources without considering integrative process systems to recover multiple resources while simultaneously satisfying regulations on final effluent quality. Process Systems Engineering (PSE) offers methodologies able to address this holistic process design problem, including modelling the trade-offs between competing objectives. Optimisation of FPWW treatment and resource recovery has significant scope to reduce the environmental impacts of food production systems. There is significant potential to recover carbon, nitrogen, and phosphorus resources while respecting effluent quality limits, even when the significant uncertainties inherent to wastewater systems are considered. This review article gives an overview of the environmental challenges we face, discussed within the framework of the planetary boundary, and highlights the impacts caused by the agri-food sector. This paper also presents a comprehensive review of the characteristics of FPWW and available technologies to recover carbon and nutrient resources from wastewater streams with a particular focus on bioprocesses. PSE research and modelling advances are discussed in this review. Based on this discussion, we conclude the article with future research directions.
Cocoa beans and coffee husks, abundant and calorific biomass resources, hold significant promise. Fast pyrolysis offers a pathway to extract high-value products from these sources. Leveraging biomass aligns with UN Sustainable Development Goals, promoting health, sanitation, and clean water by curbing landfill waste, while also facilitating affordable clean energy from pyrolysis by-products. This approach contributes to a circular economy, fostering industry innovation and infrastructure development in developing nations, ultimately reducing poverty. This study employs Aspen Plus software to simulate steady-state circulating fluidized bed pyrolysis of cocoa bean and coffee husks, comparing bio-oil yield and composition across four scenarios. Examining cellulose, lignin, ash, and moisture content for each biomass feedstock, the research reveals the significance of the cellulose-to-lignin ratio in bio-oil yield. Coffee husks emerge as more promising than cocoa bean husks due to enhanced levoglucosan formation. Furthermore, environmental impact assessments using OPEN LCA software, aligned with ISO 14040 and 14044 standards, demonstrate that higher yields result in lower CO2eq emissions. This multifaceted approach underscores the potential of these biomass resources in advancing sustainable development and mitigating environmental impact.
Experimental investigation of biomass pyrolysis kinetics is challenging due to simultaneous complex chemical reactions, interphase heat and mass transfer. A CFD model and simulation overcome the challenges faced in experimental work and provides a detailed characterization of pyrolysis kinetics. In this work, a granular multiphase flow model with 17 heterogeneous reactions, 53 interphase mass transfer, and 35 pyrolysis species and Nitrogen (36 species) transport models was implemented to investigate the pyrolysis kinetics using a continuous flow drop tube reactor (DTR). The model predicted that 45 wt% biofuel, 25 wt. % permanent gases, 10 wt% water and 20 wt% biochar is produced from a biomass feedstock at a reactor wall temperature of 773 K. The majority of biofuel (35 wt%) is produced from cellulose. While hemicellulose and lignin mainly produce permanent gases (16 wt%) and biochar (8 wt%), respectively. Product characterization and visualization of the pyrolysis process in a virtual environment mimicking the actual reactor in real-time sheds light on the pyrolysis reaction processes lacking in the literature.
Investigating suitable waste management processes is essential nowadays. Anaerobic digestion and pyrolysis are among waste treatment processes that have demonstrated promising potentials. The objective of this study is to evaluate the integration of pyrolysis and anaerobic digestion comprehensively in terms of energy/exergy analysis and comparing the integrated energy system with bare systems. To that end, novel pyrolysis and anaerobic digestion plants are designed and proposed. MATLAB was used for developing a code that simulated the plants and meanwhile, Aspen Plus provided thermodynamic properties. Results showed that the exergy efficiency of the integrated plant is 45.71%, while this parameter is 27.60% and 88.71% for the simple pyrolysis and anaerobic digestion plants, respectively. Furthermore, to make pyrolysis plant energy-independent and maximize bio-oil production, the optimum chemical composition of biomass feedstock is obtained. Seven samples were scrutinized, of which the sample with 46.00 wt% cellulose, 29.33 wt% hemicellulose, and 24.67 wt% lignin showed the optimal conditions. This composition could raise the exergy efficiency of the pyrolysis plant to 40.03%, while more interestingly exergy efficiency of the integrated system would reach 51.15%. Taken together, the findings suggested that the integration of pyrolysis and anaerobic digestion improves both exergy efficiency and methane production.
Considering the depletion of natural resources, growing environmental problems, massive demand for petroleum, the investigation of pyrolysis of lignocellulosic biomass for liquid biofuel (bio-oil) production rich in monocyclic aromatics is getting popular. However, the crude bio-oil has many shortcomings which can be mainly attributed to its high content of oxygen in primary products. Catalytic co-pyrolysis is considered an economical method for producing considerable biofuels to replace conventional energy. The addition of co-feedings and catalysts and suitable reactors could significantly enhance the yield of bio-oil and promote the generation of monocyclic aromatics. This paper is aimed to introduce the structure of the main components of lignocellulosic biomass and reveals the pyrolysis chemistry through the behaviors that occurred during the catalytic co-pyrolysis. The recent progress and development in the field of biomass catalytic co-pyrolysis were comprehensively reviewed in terms of selection of biomass, pretreatment of raw materials, kinds of catalysts, application of co-feedings, and set of reactors, for promoting monocyclic aromatic hydrocarbon production in bio-oil and improving its quality.
Thermochemical processes, which include pyrolysis, torrefaction, gasification, combustion, and hydrothermal conversions, are perceived to be more efficient in converting waste biomass to energy and value-added products than biochemical processes. From the chemical point of view, thermochemical processes are highly complex and sensitive to numerous physicochemical properties, thus making reactor and process modeling more challenging. Nevertheless, the successful commercialization of these processes is contingent upon optimized reactor and process designs, which can be effectively achieved via modeling and simulation. Models of various scales with numerous simplifying assumptions have been developed for specific applications of thermochemical conversion of waste biomass. However, there is a research gap that needs to be explored to elaborate the scale of applicability, limitations, accuracy, validity, and special features of each model. This review study investigates all above mentioned important aspects and features of the existing models for all established industrial thermochemical conversion processes with emphasis on waste biomass, thus addressing the research gap mentioned above and presenting commercial-scale applicability in terms of reactor designing, process control and optimization, and potential ways to upgrade existing models for higher accuracy.
In this study, a three-dimensional numerical analysis has been presented to simulate pyrolysis process involving transfer phenomena within a tubular reactor equipped with a rotating screw. A specific computational fluid dynamics code based on the finite volume method is developed in order to solve the general governing equations of momentum, energy and species concentration coupled with the thermochemical reaction of pyrolysis. The developed model aims to simulate the interaction between the kinetics of pyrolysis and transfer phenomena. Besides, the influence of various dimensionless numbers which are axial Reynolds number (Rea), mass Damköhler number (Dam), thermal Damköhler number (Dath), dimensionless activation energy (E*) and preheat parameter (τ) on the temperature and species concentration fields has been studied. It was found that the decrease in the axial Reynolds number, the thermal Damköhler number and the activation energy enhances the rate of conversion of the cellulose. However, the results of the numerical simulation have shown that the increase in the mass Damköhler number and the inlet temperature improves the cellulose conversion rate.
Modeling is regarded as a suitable tool to improve biomass pyrolysis in terms of efficiency, product yield, and controllability. However, it is crucial to develop advanced models to estimate products' yield and composition as functions of biomass type/characteristics and process conditions. Despite many developed models, most of them suffer from insufficient validation due to the complexity in determining the chemical compounds and their quantity. To this end, the present paper reviewed the modeling and verification of products derived from biomass pyrolysis. Besides, the possible solutions towards more accurate modeling of biomass pyrolysis were discussed. First of all, the paper commenced reviewing current models and validating methods of biomass pyrolysis. Afterward, the influences of biomass characteristics, particle size, and heat transfer on biomass pyrolysis, particle motion, reaction kinetics, product prediction, experimental validation, current gas sensors, and potential applications were reviewed and discussed comprehensively. There are some difficulties with using current pyrolysis gas chromatography and mass spectrometry (Py-GC/MS) for modeling and validation purposes due to its bulkiness, fragility, slow detection, and high cost. On account of this, the applications of Py-GC/MS in industries are limited, particularly for online product yield and composition measurements. In the final stage, a recommendation was provided to utilize high-temperature sensors with high potentials to precisely validate the models for product yield and composition (especially CO, CO2, and H2) during biomass pyrolysis. ➢Biomass pyrolysis methods and modeling are reviewed. ➢Pyrolysis mechanisms considering the effects of different biomass components are presented. ➢Models used for predicting product yields along with validation methods are reviewed and discussed. ➢Recommendations on using high-temp gas sensors to determine gas yield and composition are provided.
This work presents a dynamic model of the reactive side of large-scale fluidized bed (FB) boilers that describes the in-furnace transient operation of both bubbling and circulating FB boilers (BFB and CFB, respectively). The model solves the dynamic mass and energy balances accounting for the bulk solids,several gas species, and the fuel phase. The model uses semi-empirical expressions to describe the fluid dynamics, fuel conversion, and heat transfer to the furnace walls, as derived from units other than the studied ones. The model is validated against operational data from two different industrial units: an 80MW CFB and a 130 MW BFB, both at steady-state and transient conditions. The validated model is used to analyze: (i) the performance of the reactive side of two FB boilers under off-design, steady-state conditions of operation; and (ii) the open-loop transient response when varying load or fuel moisture. The results underline the key role of heat capacity on the stabilization time. Within a given unit, the differences in heat capacity between the top and bottom of the furnace affect also the stabilization times, with the furnace top (lower heat capacity) being 1−3 times faster in the CFB unit and up to 10 times faster in the BFB unit. Due to the differences in gas velocity, the investigated boilers are found to stabilize more rapidly to input changes when running at full load than at partial load. Lastly, a variable ramping rate analysis shows that the inherent transient responses of the reactive side disappear when disturbances are introduced at (slower) rates, typical of industrial operation. Thus, the reactive side could be modeled as pseudo-static.
The process intensification possibilities of a gas-solid vortex reactor have been studied for biomass fast pyrolysis using a combination of experiments (Particle Image Velocimetry) and non-reactive and reactive 3D CFD simulations. High centrifugal forces (greater than 30 g's) are obtainable, which allows for much higher slip velocities (> 5 m s⁻¹) and more intense heat and mass transfer between phases, which could result in higher selectivities of for example bio-oil production. Additionally, the dense yet fluid nature of the bed allows for a relatively small pressure drop across the bed (∼104 Pa). For the reactive simulations bio-oil yields of up to 70 wt. % are achieved which is higher than reported in conventional fluidized beds across the literature. Convective heat transfer coefficients between gas-solid in the range of 600 - 700 W m⁻² K⁻¹ are observed, significantly higher than those obtained in competitive reactor technologies. This is partly explained by reducing undesirable gas-char contact times due to preferred segregation of unwanted char particles towards the exhaust. Experimentally, systematic char entrainment under simultaneous biomass-char operation suggested possible process intensification and a so-called "self-cleaning" tendency of vortex reactors.
A numerical approach is presented for predicting the yields of char and volatile components obtained from fast pyrolysis of three types of lignin (enzymatic hydrolysis lignin, EHL; organic extracted lignin, OEL; and Klason lignin, KL) in a two-stage tubular reactor (TS-TR) at 773–1223 K. The heating rate of lignin particle in the TS-TR was estimated at 10²–10⁴ K/s by solving the heat transfer equation. The pyrolytic behavior of lignin and the formation of products in the temperature rising process were predicted using a semi-detailed kinetic model consisting of 93 species and 406 reactions, and the predicted yields of 8 primary products (i.e., char, tar, CO, CO2, H2O, CH3OH, C2H6, and C3H6) were compared with experimental data for the critical evaluation. For EHL, the predicted yields of char and H2O were in good agreement with the experimental results at all temperatures. However, the numerical simulation overestimated tar yield and underestimated CO yield at high temperature probably due to a lack of the kinetic model of the tar cracking reaction. The predicted yields of CH3OH, C2H6, and C3H6 were close to the experimental values at high temperature by adding the detailed chemical kinetic model of the secondary vapor-phase reaction. Moreover, the model reproduced the experimental observation that among the three types of lignin the char yield increased in the order of EHL < OEL < KL, whereas the tar yield decreased.
Using the validated simulation model developed in part one of this study for biomass catalytic fast pyrolysis (CFP), we assess the functional utility of using this validated model to assist in the development of CFP processes in fluidized catalytic cracking (FCC) reactors to a commercially viable state. Specifically, we examine the effects of mass flow rates, boundary conditions (BCs), pyrolysis vapor molecular weight variation, and the impact of the chemical cracking kinetics on the catalyst residence times. The factors that had the largest impact on the catalyst residence time included the feed stock molecular weight and the degree of chemical cracking as controlled by the catalyst activity. Because FCC reactors have primarily been developed and utilized for petroleum cracking, we perform a comparison analysis of CFP with petroleum and show that the operating regimes are fundamentally different.
Pyrolysis is a technology for producing fuels, chemicals, and engineered carbons from renewable feedstocks like lignocellulosic biomass. This work aims to address some of the scientific and technical hurdles that need to be overcome to control the products of pyrolysis. The first section aims to address knowledge gaps regarding primary pyrolysis reactions; in this study, pine wood was acid washed and small amounts of acid were impregnated into the biomass prior to pyrolysis. Results showed that the acid mitigated fragmentation reactions caused by residual metals and had further effect on production of sugars and oligomeric lignin products. The next section aims to address knowledge gaps regarding what reactions occur in the liquid intermediate phase in biomass pyrolysis; in these studies, a novel reactor system was built which could perform thin film fast pyrolysis studies at different pressures from 4 mbar to 1 atm with cellulose, milled wood lignin, and hybrid poplar wood. The reactor was carefully characterized to achieve comparable data between the different pressures. The use of vacuum allowed for control of the residence time of cellobiosan (one of cellulose oligomeric products) in the liquid intermediate. In the vacuum cellulose pyrolysis studies, a high resolution FT-ICR-MS was used for the first time to explore reaction chemistry for this system. The Van-Krevelen diagram of the resulting oligomeric products proved to be a powerful tool to study secondary reactions in the liquid intermediate. Our results show that the secondary reactions in the liquid intermediate are dominated by dehydration, fragmentation, and cross-linking reactions. The final section aims to address single particle external heat transfer problems; in this study, 500 µm long particles of pine and aspen poplar with realistic pore and surface morphologies were modeled in COMSOL to determine how microstructure effects the external heat transfer coefficients in the laminar flow regime. Results showed that microstructure did indeed affect heat transfer and that heat transfer correlations based on basic geometric shapes (sphere, cylinder, slab) were not accurate enough to estimate heat transfer coefficient for the conditions studied.
Direct numerical simulation of convective heat transfer from hot gas to isolated biomass particle models with realistic morphology and explicit microstructure was performed over a range of conditions with laminar flow of hot gas (500 °C). Steady-state results demonstrated that convective interfacial heat transfer is dependent on the wood species. The computed heat transfer coefficients were shown to vary between the pine and aspen models by nearly 20%. These differences are attributed to the species-specific variations in the exterior surface morphology of the biomass particles. We also quantify variations in heat transfer experienced by the particle when positioned in different orientations with respect to the direction of fluid flow. These results are compared to previously reported heat transfer coefficient correlations in the range of 0.1 < Pr < 1.5 and 10 < Re < 500. Comparison of these simulation results to correlations commonly used in the literature (Gunn, Ranz-Marshall, and Bird-Stewart-Lightfoot) shows that the Ranz-Marshall (sphere) correlation gave the closest h values to our steady-state simulations for both wood species, though no existing correlation was within 20% of both species at all conditions studied. In general, this work exemplifies the fact that all biomass feedstocks are not created equal, and that their species-specific characteristics must be appreciated in order to facilitate accurate simulations of conversion processes.
In this work about pyrolysis of lignocellulosic biomass, the individual reaction mechanisms of cellulose, hemicellulose and lignin are initially described. The recent advances in the understanding of the fundamental reaction pathways are described, including quantum-mechanical calculations, and the description of pyrolysis as a two-step process, i.e., primary pyrolysis and secondary charring, the effect of the presence of an intermediate liquid compound, and the influence of inorganic species are discussed.
The need to describe biomass pyrolysis as the sum of the contributions of its individual components is then emphasised. The process of determining biomass mass loss kinetics is analysed, and the product composition and heat of reaction that are experimentally obtained during pyrolysis are presented, along
with detailed schemes that can be used to predict them.
Finally, it is demonstrated that a multi-scale consideration of pyrolysis on multiple levels – specifically, on molecular, particle and reaction levels – is required to accurately describe biomass pyrolysis. Intra-particle phenomena and particle models are discussed and the reactor level is analysed with a focus placed on fixed bed and fluidised bed pyrolysis. In summary, a list of 10 research focal points that will be important in the future is presented.
We report results from computational simulations of an experimental, lab-scale bubbling bed biomass pyrolysis reactor that include a distributed activation energy model (DAEM) for the kinetics. In this study, we utilized multiphase computational fluid dynamics (CFD) to account for the turbulent hydrodynamics, and this was combined with the DAEM kinetics in a multi-component, multi-step reaction network. Our results indicate that it is possible to numerically integrate the coupled CFD-DAEM system without significantly increasing computational overhead. It is also clear, however, that reactor operating conditions, reaction kinetics, and multiphase flow dynamics all have major impacts on the pyrolysis products exiting the reactor. We find that, with the same pre-exponential factors and mean activation energies, inclusion of distributed activation energies in the kinetics can shift the predicted average value of the exit vapor-phase tar flux and its statistical distribution, compared to single-valued activation-energy kinetics. Perhaps the most interesting observed trend is that increasing the diversity of the DAEM activation energies appears to increase the mean tar yield, all else being equal. These findings imply that accurate resolution of the reaction activation energy distributions will be important for optimizing biomass pyrolysis processes.
Mo–Cu/HZSM-5 catalysts for pine sawdust thermal conversion were prepared using an impregnation method. The Mo–Cu/HZSM-5 catalysts and HZSM-5 were characterized by Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD) and transmission electron microscopy (TEM). All characterization results indicated that the introduction of CuO is beneficial to the dispersion of MoO3 in the HZSM-5. Combined with the two-stage catalytic pyrolysis system, the Mo–Cu/HZSM-5 catalysts were used for pine sawdust thermal conversion. The products included gas, bio-oil and bio-char. The gas was analyzed by Gas chromatography (GC). Gas chromatography–mass spectrometry (GC–MS) was used to identify the compounds in bio-oils. The water content, higher heating value (HHV) and viscosity of bio-oils were measured. The HHV and elements of bio-char were determined. The results indicated that Mo(3%)–Cu(3%)/HZSM-5 treatment yielded the highest amount of C6–C12 hydrocarbons, showed a robust ability to convert methane in the gas to bio-oil, and displayed no significant difference in the properties of bio-char when compared to different treatments in the same pyrolysis conditions.
This publication is an updated version of a study on testing and modifying standard fuel oil analyses (Oasmaa et al. 1997, Oasmaa & Peacocke 2001). Additional data have been included to address the wide spectrum of properties that may be required in different applications and to assist in the design of process equipment and power generation systems. In addition, information on specifications and registration is provided. Physical property data on a range of pyrolysis liquids from published sources have been added to provide a more comprehensive guide for users.
The pyrolysis of general biomass materials is modeled via a superposition of cellulose, hemicellulose and lignin kinetics. All three of the primary biomass components are modeled with multi-step kinetics involving both competetive primary pyrolysis and secondary tar decomposition reactions. Only "typical" (untreated) feedstocks are considered at atmospheric pyrolysis pressures. The kinetics scheme is then coupled to the porous particle model of Miller and Bellan (1996) along with appropriate properties and heats of reaction to provide a complete model for the pyrolysis of arbitrary biomass feedstocks and sample sizes. Comparisons with past isothermal and thermogravimetry experiments for a variety of biomass materials under both kinetically controlled and diffusion limited conditions show favorable agreement with the model predictions. In addition, discussions are provided which support the use of competetive char production kinetics over single and successive reaction schems which cannot currently be reconciled with observed pyrolysis behavior.
This work presents a novel Aspen Plus® model of pyrolysis processes for lignocellulosic feedstocks.
Based on kinetic reaction mechanisms, the simulation calculates product yields and composition depending on reactor conditions (temperature, residence time, flue gas flow rate) and feedstock composition (cellulose, hemicellulose and lignin fraction, atomic composition, ash and alkali metal content). The produced bio-oil is modelled with a high level of detail (33 compounds including organic acids, aldehydes, alcohols, ketenes, phenols, sugar derivatives and degraded lignin), and the char product shows realistic atomic compositions. N, S and Cl trace element release is taken into account and the corresponding emissions caused by the process can be determined.
Numerous simulation runs are made in order to cross-check the simulation results with experimental data based on published literature. The results show a high correlation of the results for the most common pyrolysis processes (e.g., fast pyrolysis in bubbling or circulating fluidised beds), which is somewhat decreasing for slow pyrolysis processes. The simulation model is found to be suitable for predicting pyrolysis yields and products within the typical range of operation for pyrolysis processes.
The National Energy Technology Laboratory (NETL) worked with Particulate Solids Research Inc. (PSRI) to conduct the third CFD Challenge Problem in granular fluid flow to evaluate the progress and state of the art in simulating gas solids flow in a circulating fluidized bed. Both Group A and B particles were tested at several gas velocities and solids circulation rates. For both particle groups pressures and particle velocities were measured within the riser. For the Group B cases local radial solids fluxes and high speed pressure fluctuations were measured. Model predictions were compared against these experimental results and vetted in the workshop at the Circulating Fluid Bed X. The modelers were given detailed descriptions of the experimental facilities as well as physical property and small scale fluidization data on the different bed materials tested. Two general types of modeling simulations were submitted: Eulerian-Eulerian and Eulerian-Lagrangian. Both types of model had successes and failures indicating that good results are strongly influenced by resources such as available time, computational facilities, and experience level of the modeler. By comparing the predicted behavior the strengths and weaknesses associated with the different modeling approaches were identified and shortcomings could be targeted for future development and improvements. Published by Elsevier B.V.
Simulations of cold flow fluidized gas-solid systems have been conducted for both riser and bubbling bed reactors, alone and combined in a circulating fluidized bed reactor. An Eulerian continuum two-fluid model with the Constant Particle Viscosity closure for the stresses term was employed for the granular phase whereas an algebraic turbulence model was used for the gas phase. An in-house code was developed, based upon the Finite Volume Method applied to the governing equations with a staggered grid arrangement. The velocities for both gas and solid phases are obtained solving the 1D Reynolds averaged Navier-Stokes equations using the Partial Elimination Algorithm (PEA) algorithm and a coupled solver, while a pressure correction equation allows to solve for pressure based on gas continuity.The void fraction profile is computed from the solid continuity. Cold flow simulations of fluidized systems form the basis for the modeling of chemical processes such as Sorption-Enhanced Steam Methane Reforming (SE-SMR).
This report describes the MFIX (Multiphase Flow with Interphase exchanges) computer model. MFIX is a general-purpose hydrodynamic model that describes chemical reactions and heat transfer in dense or dilute fluid-solids flows, flows typically occurring in energy conversion and chemical processing reactors. MFIX calculations give detailed information on pressure, temperature, composition, and velocity distributions in the reactors. With such information, the engineer can visualize the conditions in the reactor, conduct parametric studies and what-if experiments, and, thereby, assist in the design process. The MFIX model, developed at the Morgantown Energy Technology Center (METC), has the following capabilities: mass and momentum balance equations for gas and multiple solids phases; a gas phase and two solids phase energy equations; an arbitrary number of species balance equations for each of the phases; granular stress equations based on kinetic theory and frictional flow theory; a user-defined chemistry subroutine; three-dimensional Cartesian or cylindrical coordinate systems; nonuniform mesh size; impermeable and semi-permeable internal surfaces; user-friendly input data file; multiple, single-precision, binary, direct-access, output files that minimize disk storage and accelerate data retrieval; and extensive error reporting. This report, which is Volume 1 of the code documentation, describes the hydrodynamic theory used in the model: the conservation equations, constitutive relations, and the initial and boundary conditions. The literature on the hydrodynamic theory is briefly surveyed, and the bases for the different parts of the model are highlighted.
The pyrolysis of general biomass materials is modeled via a superposition of cellulose, hemi-cellulose and lignin kinetics. All three of the primary biomass components are modeled with multi-step kinetics involving both competetive primary pyrolysis and secondary tar decomposition reactions. Only “typical” (untreated) feedstocks are considered at atmospheric pyrolysis pressures. The kinetics scheme is then coupled to the porous particle model of Miller and Bellan (1996) along with appropriate properties and heats of reaction to provide a complete model for the pyrolysis of arbitrary biomass feedstocks and sample sizes. Comparisons with past isothermal and thermogravimetry experiments for a variety of biomass materials under both kinetically controlled and diffusion limited conditions show favorable agreement with the model predictions. In addition, discussions are provided which support the use of competetive char production kinetics over single and successive reaction schems which cannot currently be reconciled with observed pyrolysis behavior.
The purpose of this study was to evaluate the amounts of various pyrolysis products (gases, water, tar and charcoal) from three biomasses (wood, coconut shell and straw) and to suggest a kinetic equation for the thermal cracking of tar at temperatures varying from 400 to 900°C. From the results, a comparative analysis is done for the biomasses, and a kinetic model of thermal cracking of tar is proposed for a residence time ranging from zero to 4s . This can be applied to the purification of gasification gases used as a feed gas to a combustion engine, and so contributes to the design of gasifiers.
This paper analyzes the main kinetic features of biomass pyrolysis, devolatilization, and the gas phase reactions of the released species. Three complex steps are faced in sequence: the characterization of biomasses, the description of the release of the species, and finally, their chemical evolution in the gas phase. Biomass is characterized as a mixture of reference constituents: cellulose, hemicellulose, and lignin. This assumption is verified versus experimental data, mainly relating to thermal degradation of different biomasses. Devolatilization of biomasses is a complex process in which several chemical reactions take place in both the gas and the condensed phase alongside the mass and thermal resistances involved in the pyrolysis process. A novel characterization of the released species is applied in the proposed devolatilization models. The successive gas phase reactions of released species are included into an existing detailed kinetic scheme of pyrolysis and oxidation of hydrocarbon fuels. Comparisons with experimental measurements in a drop tube reactor confirm the high potentials of the proposed modeling approach.
Meso-scale structures that take the form of clusters and streamers are commonly
observed in dilute gas–particle flows, such as those encountered in risers. Continuum
equations for gas–particle flows, coupled with constitutive equations for particle-phase
stress deduced from kinetic theory of granular materials, can capture the formation of
such meso-scale structures. These structures arise as a result of an inertial instability
associated with the relative motion between the gas and particle phases, and an
instability due to damping of the fluctuating motion of particles by the interstitial
fluid and inelastic collisions between particles. It is demonstrated that the meso-scale
structures are too small, and hence too expensive, to be resolved completely in
simulation of gas–particle flows in large process vessels. At the same time, failure
to resolve completely the meso-scale structures in a simulation leads to grossly
inaccurate estimates of inter-phase drag, production/dissipation of pseudo-thermal
energy associated with particle fluctuations, the effective particle-phase pressure and
the effective viscosities. It is established that coarse-grid simulation of gas–particle
flows must include sub-grid models, to account for the effects of the unresolved meso-scale
structures. An approach to developing a plausible sub-grid model is proposed.
A new capability is developed that enables the modeling of hydrocarbon fuel reforming for certain reactor geometries. The system described in this paper considers a shell-and-tube configuration for which the catalytic reforming chem. is confined within the tubes. The models are designed to accommodate detailed gasphase and catalytic reaction kinetics, possibly including hundreds of species and thousands of reactions. The shell flow can be geometrically complex, but does not involve any complex chem. An iterative coupling algorithm is developed with which the geometrically complex flow is modeled with FLUENT and the chem. complex reforming is confined to straight tubes. The paper illustrates the model using propane partial oxidn. and reforming as an example. [on SciFinder(R)]
Biomass fast pyrolysis is of rapidly growing interest in Europe as it is perceived to offer significant logistical and hence economic advantages over other thermal conversion processes. This is because the liquid product can be stored until required or readily transported to where it can be most effectively utilised. The objective of this paper is to review the design considerations faced by the developers of fast pyrolysis, upgrading and utilisation processes in order to successfully implement the technologies. Aspects of design of a fast pyrolysis system include feed drying; particle size; pretreatment; reactor configuration; heat supply; heat transfer; heating rates; reaction temperature; vapour residence time; secondary cracking; char separation; ash separation; liquids collection. Each of these aspects is reviewed and discussed. A case study shows the application of the technology to waste wood and how this approach gives very good control of contaminants. Finally the problem of spillage is addressed through respirometric tests on bio-oils concluding with a summary of the potential contribution that fast pyrolysis can make to global warming.
When designing industrial furnaces for combustion of biomass particles, it is of technical importance to know the time of pyrolysis at high heating conditions. We numerically investigated pyrolysis of a single biomass particle using a one-dimensional model which assumes that the conversion process of a pyrolyzing particle takes place through three parallel reactions yielding light gases, tar and char. A novel idea that has been established in this paper is that the heat of pyrolysis in the energy conservation equation is calculated by accounting for the exothermicity of char formation and the endothermicity of volatiles generation in accordance with the correlations proposed in the literature. As the idea is to investigate biomass particle pyrolysis at high heating conditions, three different sets of experimental data conducted at high surrounding temperatures are selected for validation of the improved model. It is found that employing the correlations of Milosavljevic et al. and Mok and Antal to compute the heat of pyrolysis together with kinetic constants of Di Blasi and Branca in the model provides a good prediction of the final char yield and conversion time. In the next stage of the study, the pyrolysis model is utilized to investigate the effects of particle shape, size and initial density on conversion time and final char density of a biomass particle at high heating environments. Typical results are presented which are expected to enable a designer to estimate the pyrolysis time and final char density of a biomass particle undergoing thermochemical conversion at the conditions of industrial combustors. Finally, the homogeneity of the pyrolysis process inside small particles exposed to high reactor temperatures is investigated. It is found that adaption of such an assumption in a particle conversion model may result in undesired reduction of the accuracy of the model predictions.
Fast pyrolysis of biomass is an attractive route to transform solid biomass into a liquid bio-oil, which has been envisioned as a renewable substitute for crude oil. However, lack of fundamental understanding of the pyrolysis process poses a significant challenge in developing cost-effective pyrolysis based technologies for producing transportation fuels. The fundamental knowledge of pyrolysis pathways, product distribution and underlying mechanisms will have a direct and significant impact on the reactor design, strategic operation and kinetic modeling of the pyrolysis process. However, this knowledge has remained obscure due to the complexity of the pyrolysis process and lack of well established analytical methodologies.
The present work provides a systematic approach to study pyrolysis, where many factors that affect the pyrolysis process are decoupled and their effect is systematically studied. The study employs a combination of analytical techniques such as Gas Chromatography - Mass Spectrometry, Gas analysis, Liquid Chromatography - Mass Spectrometry, Capillary Electrophoresis, Ion Chromatography and Gel Permeation Chromatography to identify and quantify the pyrolysis products and establish the mass balance.
Pyrolysis involves a complex scheme of reactions consisting of several primary and subsequent secondary reactions. Disassociating primary and secondary reactions is often challenging because of the typical residence time of pyrolysis vapors in the traditional pyrolysis reactors. However, mechanistic understanding of the pyrolysis pathways needs information of the primary pyrolysis products, prior to complex series of secondary reactions. This was achieved by employing a system consisting of a micro-pyrolyzer which had vapor residence time of only a few milliseconds, directly coupled with the analytical equipment. The problem was further simplified by considering the pyrolysis of each individual component of biomass (hemicellulose, cellulose and lignin) one at a time. Influence of minerals and reaction temperature on the primary pyrolysis products was also studied. Secondary reactions, which become important in industrial-scale pyrolysis systems were studied by comparing the cellulose pyrolysis product distribution from micro-pyrolyzer and a bench scale fluidized bed reactor system.
The study provides fundamental insights on the pyrolysis pathways of hemicellulose, cellulose and lignin. It shows that the organic components of biomass are fragmented completely into monomeric compounds during pyrolysis. These monomeric compounds re-oligomerize to produce heavy oligomeric compounds and aerosols. It also provides the understanding of the effect of parameters such as presence of minerals and temperature on the resulting product distribution. This knowledge can help tailor the pyrolysis process in order to obtain bio-oil with desired composition. The pyrolysis product distribution data reported in this dissertation can also be used as a basis to build descriptive pyrolysis models that can predict yield of specific chemical compounds present in bio-oil. Further, it also serves as a basis for distinguishing secondary reactions from the primary ones, which are important consideration in the industrial-scale systems.
A novel, highly integrated tubular SOFC system intended for small-scale power is characterized through a series of sensitivity analyses and parametric studies using a previously developed high-fidelity simulation tool. The high-fidelity tubular SOFC system modeling tool is utilized to simulate system-wide performance and capture the thermofluidic coupling between system components. Stack performance prediction is based on 66 anode-supported tubular cells individually evaluated with a 1-D electrochemical cell model coupled to a 3-D computational fluid dynamics model of the cell surroundings. Radiation is the dominate stack cooling mechanism accounting for 66–92% of total heat loss at the outer surface of all cells at baseline conditions. An average temperature difference of nearly 125°C provides a large driving force for radiation heat transfer from the stack to the cylindrical enclosure surrounding the tube bundle. Consequently, cell power and voltage disparities within the stack are largely a function of the radiation view factor from an individual tube to the surrounding stack can wall. The cells which are connected in electrical series, vary in power from 7.6 to 10.8W (with a standard deviation, σ=1.2W) and cell voltage varies from 0.52 to 0.73V (with σ=81mV) at the simulation baseline conditions. It is observed that high cell voltage and power outputs directly correspond to tubular cells with the smallest radiation view factor to the enclosure wall, and vice versa for tubes exhibiting low performance. Results also reveal effective control variables and operating strategies along with an improved understanding of the effect that design modifications have on system performance. By decreasing the air flowrate into the system by 10%, the stack can wall temperature increases by about 6% which increases the minimum cell voltage to 0.62V and reduces deviations in cell power and voltage by 31%. A low baseline fuel utilization is increased by decreasing the fuel flowrate and by increasing the stack current demand. Simulation results reveal fuel flow as a poor control variable because excessive tail-gas combustor temperatures limit fuel flow to below 110% of the baseline flowrate. Additionally, system efficiency becomes inversely proportional to fuel utilization over the practical fuel flow range. Stack current is found to be an effective control variable in this type of system because system efficiency becomes directly proportional to fuel utilization. Further, the integrated system acts to dampen temperature spikes when fuel utilization is altered by varying current demand. Radiation remains the dominate heat transfer mechanism within the stack even if stack surfaces are polished lowering emissivities to 0.2. Furthermore, the sensitivity studies point to an optimal system insulation thickness that balances the overall system volume and total conductive heat loss.
Particle characterization and dynamics, Wen-Ching Yang Flow through fixed beds, Wen-Ching Yang Bubbling fluidized beds, Wen-Ching Yang Elutriation and entrainment, Joachim Werther and Ernst-Ulrich Hartge Effect of temperature and pressure, J.G. Yates Gas distributor and plenum design in fluidized beds, S.B. Reddy Karri and Joachim Werther Effect of internal tubes and baffles, Yong Jin, Fei Wei, and Yao Wang Attrition, Joachim Werther and Jens Reppenhagen Modelling, Thomas C. Ho Heat transfer, John C. Chen Mass transfer, Thomas C. Ho General approaches to reactor design, Peijun Jiang, Fei Wei, and Liang-Shih Fan Fluidized bed scaleup, Leon R. Glicksman Applications for fluid catalytic cracking, Ye-Mon Chen Applications for gasifiers and combustors, Richard A. Newby Applications for chemical production and processing, Behzad Jazayeri Applications for coating and granulation, Gabriel I. Tardos and Paul Mort Applications for fluidized bed drying, Arun Mujumdar and Sakamon Devahastin Circulating fluidized beds, John R. Grace, Hsiaotao Bi, and Mohammad Golriz Other nonconventional fluidized beds, Wen-Ching Yang Standpipes and nonmechanical valves, T.M. Knowlton Cyclone separators, T.M. Knowlton Dilute phase pneumatic conveying, George E. Klinzing Electrostatics in pneumatic conveying, George E. Klinzing Instrumentation and measurements, Rafal Kobylecki, Mayumi Tsukada, and Masayuki Horio Liquid-solids fluidization, Norman Epstein Gas-liquid-solid three-phase fluidization, Liang-Shih Fan and Guoqiang Yang Liquid-solids separation, Shiao-Hung Chiang, Daxin He, and Yuru Feng
A reaction scheme of a set of three parallel reactions followed by a set of two parallel reactions has been used to describe the primary and secondary reactions of biomass pyrolysis in a fluidized bed reactor. A simple first-order kinetic approach has been applied to predict the product yields. The pyrolysis model detailed in this paper is actually a sub-model. The effects of operating parameters on biomass pyrolysis product yield were simulated. Results show that reaction temperature plays an important role in the yield of bio-oil. The model is robust and can predict good results in a gasification environment as well. Good agreement between predicted and published results was obtained.
Flash pyrolysis of wood in a circulating fluidized bed is studied. The results of a comprehensive gas-solid reaction model are used successfully in analysing the system. The changes in the structure, the transient nature of heat and mass transfer and the reaction scheme are accounted for. All the structural parameters and thermophysical properties are used as continuously changing variables.
The effective thermal conductivity is one of the most important parameters for modelling of thermo-chemical conversion of wood. It changes both with temperature and with conversion of the wood. There have been suggestions on modelling of this problem, together with measurements, in earlier works, especially for wet and dry wood, but for char the knowledge is poor. Here, two principle models of effective thermal conductivity on the basis of the pore structure in wood are validated by a comparison with direct numerical simulation of the fibre structure. The validation leads to a more general model, both for conductivity in the perpendicular and parallel directions relative to the fibres in the wood. In addition, the model expresses the effective thermal conductivity of char, since the wood material maintains its fibre structure during conversion. The effective thermal conductivity is estimated from given values of temperature, density and moisture content of the wood. It can also be applied to pellets and chipboards.
The book covers fluidization engineering. Topics covered include: Industrial applications of fluidized beds; The dense bed: distributors, gas jets, and pumping power; Bubbling fluidized beds. High-velocity fluidization; Particle-to-gas mass and heat transfer; Conversion of gas in catalytic reactions; Heat transfer between fluidized beds and surfaces; Circulation systems. Design of catalytic reactors. Reviews principles and applications of fluidization engineering; coverage of historical and current research influencing the development of this engineering field; bed-wall heat transfer; drying of solids, fast fluidization, heat exchangers, K-L model for catalytic reactions, mass transfer, and particle movement in beds.
The aim of this work is to analyze the optimal operating conditions for fast biomass pyrolysis. The operating conditions required to maximize the yield of liquid products are investigated and discussed on the basis of a comprehensive mathematical model of wood/biomass devolatilization. Crucial issues are the fast and complete heating of biomass particles to reduce char formation and the rapid cooling of released products to reduce the role of secondary gas-phase pyrolysis reactions. Chemical kinetics as well as heat- and mass-transfer phenomena play an important role in this process; thus, a comprehensive kinetic model is applied. The proposed model, when compared to the majority of other devolatilization models, attempts to characterize pyrolysis reactions with a lumped stoichiometry using a limited number of equivalent components to describe not only gaseous products but also tar species. Model predictions are compared to experimental measurements not only with further validation in mind but also principally to verify the reliability of this comprehensive kinetic model of biomass devolatilization and combustion.
The dependence of the fully-developed flow profiles on the inlet flow conditions for gas–solids two-phase flows, i.e. the flow multiplicity phenomenon, in circulating fluidized bed (CFB) risers was proposed and discussed in this article. The flow multiplicity phenomenon for gas–solids two-phase flows was first proved mathematically based on the conservation equations of mass and momentum. Then the CFD model using Eulerian–Eulerian approach with k–ε turbulence model for each phase was further adopted to analyze the details of this flow multiplicity phenomenon. It is theoretically and numerically revealed that for gas–solids two-phase flows, the flow profiles in the fully-developed region are always dominated by the flow profiles at the inlet. The solids concentration profile is closely coupled with the velocity profile, and the inlet solids concentration and velocity profiles can largely influence the fully-developed concentration and velocity profiles.Highlights► For gas-solids two-phase flows, the solids concentration and velocity profiles in the fully-developed region are always dominated by the solids concentration and velocity profiles at the inlet of the riser. ► The solids concentration profile is closely coupled with the velocity profile. ► The velocity difference between the two phases at the inlet of the riser is one of the main factors dominating the solids accelerating-diluting process in a CFB riser.
Fluidized bed-fast pyrolysis of biomass is considered as having a high commercial potential for the thermal treatment of biomass.This paper mainly presents a model developed further to improvements in the understanding of the science, and capable of predicting pyrolysis yields that are in satisfactory agreement with literature data.The kinetics and endothermicity of biomass pyrolysis are reviewed from extensive TGA and differential scanning calorimetry experiments. For most biomass species, the reaction rate constant is >0.5 s−1, corresponding to a fast reaction, so the requirement of a short reaction time for a high conversion can be met. Lab-scale batch experiments and pilot-scale CFB experiments show that an oil yield between 60 and 70 wt% can be achieved at an operating temperature of 510±10 °C, in line with literature data. Pyrolysis fundamentals are the basis of the developed model, applied to predict the yields of the different products as functions of process operation variables. The predictions are in fair agreement with our own conversion experiments and literature data. Finally, all findings are used and are illustrated in the design strategy of a CFB for the pyrolysis of biomass.
A detailed computational model of pyrolysis of a moist, shrinking biomass particle is presented. This model is used to examine the effect of varying the moisture content for a single shrinking biomass particle subjected to a constant external temperature. Particle half-thicknesses ranging from 5 μm to 2 cm, temperatures from 800 to 2000 K, moisture contents from 0 to 30% (dry basis), and shrinkage factors from 1.0 to 0.4 are examined. The impact of moisture content and shrinkage was found to be a function of pyrolysis regime. In general, coupling between moisture content and shrinkage was found to result in longer pyrolysis times than if they were considered separately. Additionally, coupling between moisture content and shrinkage increased tar yield and decreased light hydrocarbon yield compared to considering moisture and shrinkage separately.
Reactors for flash pyrolysis of biomass are designed to maximize the yield of bio-oil, at the expense of the by-products gas and char. To understand which chemical and physical factors influence the yield to bio-oil, the flash pyrolysis of a cylindrical wood particle with a maximum diameter of 1000 μm has been simulated by solving the governing equations for mass, enthalpy and momentum conservation for the reactant and products (one dimensional). The flow of vapours is described using the Dusty Gas model [A. Bliek, W.N. Poelje, W.P.M. van Swaaij, F.P.H. van Beckum, AIChE J. 31 (1985) 1666], and the structure of wood is incorporated in the model by applying the random pore model of [N. Wakao, J.M. Smith, Chem. Eng. Sci. 17 (1962) 825]. Typical conversion times for a cylindrical particle increase from 1 to 10 s when the diameter increases from 200 to 1000 μm at a surface temperature of 823 K. The bio-oil yield (approximately 77%) is hardly affected by the particle size (200–1000 μm diameter). Obviously tar cracking inside the particle does not occur for the simulated conditions. The heating of a particle is notably delayed by the outflow of vapours. While assuming that they leave the particle in a direction perpendicular instead of parallel to the heat flux, the simulated conversion times appear to decrease with sometimes more than 50%. Finally, the sign and size of the pyrolysis reaction heat is shown to have a distinct effect on the calculated particle conversion time. As an overall conclusion, the results of this work show that an extensive description of internal mass transport phenomena in flash-pyrolysis modelling is not necessary, while accurate knowledge of the reaction kinetics and heat transfer parameters is crucial.
This techno-economic study examines fast pyrolysis of corn stover to bio-oil with subsequent upgrading of the bio-oil to naphtha and diesel range fuels. Two 2000 dry tonne per day scenarios are developed: the first scenario separates a fraction of the bio-oil to generate hydrogen on-site for fuel upgrading, while the second scenario relies on merchant hydrogen.The modeling effort resulted in liquid fuel production rates of 134 and 220 million liters per year for the hydrogen production and purchase scenarios, respectively. Capital costs for these plants are 200 million. Fuel product value estimates are 2.11 per gallon of gasoline equivalent (0.56 per liter). While calculated costs of this biofuel are competitive with other kinds of alternative fuels, further research is required to better determine the effect of feedstock properties and process conditions on the ultimate yield of liquid fuel from bio-oil. Pioneer plant analysis estimates capital costs to be 585 million for construction of a first-of-a-kind fast pyrolysis and upgrading biorefinery with product values of 3.41 per gge (0.90 per liter).
This review reports the state of the art in modeling chemical and physical processes of wood and biomass pyrolysis. Chemical kinetics are critically discussed in relation to primary reactions, described by one- and multi-component (or one- and multi-stage) mechanisms, and secondary reactions of tar cracking and polymerization. A mention is also made of distributed activation energy models and detailed mechanisms which try to take into account the formation of single gaseous or liquid (tar) species. Different approaches used in the transport models are presented at both the level of single particle and reactor, together with the main achievements of numerical simulations. Finally, critical issues which require further investigation are indicated.
The purpose of this study was to evaluate the amounts of various pyrolysis products (gases, water, tar and charcoal) from three biomasses (wood, coconut shell and straw) and to suggest a kinetic equation for the thermal cracking of tar at temperatures varying from 400 to 900°C. From the results, a comparative analysis is done for the biomasses, and a kinetic model of thermal cracking of tar is proposed for a residence time ranging from zero to 4s . This can be applied to the purification of gasification gases used as a feed gas to a combustion engine, and so contributes to the design of gasifiers.
This two-part paper covers the development and validation of a multiscale homogenization model for macroscopic transport properties of wood. The starting point is the intrinsic structural hierarchy of wood, which is accounted for by several homogenization steps. Starting on a length scale of a few nanometers the model ends up with macroscopic properties by including the morphology of the intermediate hierarchical levels. In this first part this is done for thermal conductivity, based on a six-level homogenization scheme. The used homogenization technique is continuum micromechanics in terms of self-consistent and Mori-Tanaka schemes. Model validation rests on statistically and physically independent experiments: the macroscopic thermal conductivity values predicted by the multiscale homogenization model on the basis of tissue-independent (universal) phase conductivity properties of hemicellulose, cellulose, lignin, and water (input data set I) for tissue-specific data (input data set II) are compared to corresponding experimentally determined tissue-specific conductivity values (experimental data set).
The literature on biomass pyrolysis regarding kinetics, models (single particle and reactor), and experimental results is reviewed from an engineering point of view. Predictions of existing single particle models derived from a detailed description of the transport phenomena and literature data on measured intrinsic chemical kinetics are presented. The main conclusions from the literature and modeling studies can be summarized as follows: (1) the available knowledge on kinetics and transport phenomena has not been integrated properly for reactor design, (2) complex two-dimensional single particle models do not provide more accurate, or otherwise better, information for engineering calculations than do the simple one-dimensional models, and (3) single particle models predict (for all available kinetics) that the influence of the particle size on the liquid yield is limited. This effect can be explained with the effective pyrolysis temperature, a parameter that represents the particle's average temperature at which the conversion is essentially taking place.
A detailed single-particle model, including a description of transport phenomena and a global reaction mechanism, is coupled with a plug-flow assumption for extraparticle processes of tar cracking, in order to predict the fast pyrolysis of wood in fluid-bed reactors for liquid-fuel production. Good agreement is obtained between predictions and measurements of product yields (liquids, char, and gases) as functions of temperature. Particle dynamics are very affected by the convective transport of volatile products. The average heating rates are on the order of 450-455 K/s, whereas reaction temperatures vary between 770 and 640 K (particle sizes of 0.1-6 mm and a reactor temperature of 800 K). The effects of several factors, such as size, shape, and shrinkage of wood particles, and external heat-transfer conditions are also examined.
A broad perspective of pyrolysis technology as it relates to converting biomass substrates to a liquid bio-oil product and a detailed technical and economic assessment of a fast pyrolysis plant.
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Corrigendum
Corrigendum to ''One dimensional steady-state circulating fluidized-bed
reactor model for biomass fast pyrolysis'' [Fuel 133 (2014) 253-262]