Article

Measuring and Modelling Residence Time Distribution of Low Density Solids in a Fluidized Bed Reactor of Sand Particles

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Abstract

An experimental study was carried out to estimate the residence time distribution of low density particles injected into a fluidized bed reactor containing sand particles. Tracer experiments were performed at room temperature, using a pilot plant pyrolysis reactor. A novel technique was used to detect and measure the flow of solid tracer particles having different physical characteristics entering and leaving the fluid bed. The experimental results demonstrated that the degree of particle entrainment was a function of the fluidizing gas velocity, the particle size and the particle density. Solid mixing, segregation and entrainment were also studied as functions of physical and operating parameters. Various models were tested to characterize the non-ideal solids flow patterns within the fluid bed. A circulation model appeared to give a good description of the physical mechanism involved and to provide the best agreement with the experimental results.

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... Compared with gas mixing, the particle residence time distribution and particle mixing are more important for the CFB because they a ect chemical reaction rate and product distribution. Although there are quite a number of studies on particle mixing in the CFB (Bellgardt & Werther, 1986;Berruti, Liden, & Scott, 1988;Cen, Fan, Luo, Yan, & Ni, 1988;Ambler, Milne, Berruti, & Scott, 1990;Talukdar & Mathur, 1996;Fujima, Deguchi, & Endo, 1999;Kojima, Ishihara, Guilin, & Furusawa, 1989;Lin, Winell, Hansen, & Dam-Johansen, 1999;Mirgain, Briens, Pozo, Loutaty, & Bergougnou, 1998;Neathery, Schaefer, & Stencel, 1995;Niven, Khalili, & Hibbert, 2000a, b;Peters, Fan, & Sweeney, 1982;Sivashanmugam & Sundaram, 2000;Stellema, Kolar, Goeij, Schouten, & Bleek, 1997;Yang, 1988), only a few models of particle mixing are published (Berruti et al., 1988;Cen et al., 1988;Ambler et al., 1990). Due to the coreannulus structure, it is not suitable to use a one-dimensional dispersion equation to describe mixing in the CFB. ...
... Compared with gas mixing, the particle residence time distribution and particle mixing are more important for the CFB because they a ect chemical reaction rate and product distribution. Although there are quite a number of studies on particle mixing in the CFB (Bellgardt & Werther, 1986;Berruti, Liden, & Scott, 1988;Cen, Fan, Luo, Yan, & Ni, 1988;Ambler, Milne, Berruti, & Scott, 1990;Talukdar & Mathur, 1996;Fujima, Deguchi, & Endo, 1999;Kojima, Ishihara, Guilin, & Furusawa, 1989;Lin, Winell, Hansen, & Dam-Johansen, 1999;Mirgain, Briens, Pozo, Loutaty, & Bergougnou, 1998;Neathery, Schaefer, & Stencel, 1995;Niven, Khalili, & Hibbert, 2000a, b;Peters, Fan, & Sweeney, 1982;Sivashanmugam & Sundaram, 2000;Stellema, Kolar, Goeij, Schouten, & Bleek, 1997;Yang, 1988), only a few models of particle mixing are published (Berruti et al., 1988;Cen et al., 1988;Ambler et al., 1990). Due to the coreannulus structure, it is not suitable to use a one-dimensional dispersion equation to describe mixing in the CFB. ...
... On the basis of the core-annulus structure, the cell-mixing model is developed in the present work. In contrast with other published models (Berruti et al., 1988;Cen, et al., 1988; Ambler et al., 1990), particle mixing in the present work is simulated directly without the utilization of any parameters (e.g., dispersion parameters) determined from regressing experimental data. The dynamics of a chemical reaction for sulfur capture models can generally be divided into two groups (Mattisson & Lyngfelt, 1998a;Lyngfelt & Leckner, 1999): lime models and reactor models. ...
Article
A mixing model has been developed to simulate the particle residence time distribution (RTD) in a circulating fluidized bed absorber (CFBA). Also, a gas/solid reaction model for sulfur dioxide (SO2) removal by lime has been developed. For the reaction model that considers RTD distribution inside the core and annulus regions of a CFBA, a macrochemical reaction can be simulated based on microchemical reaction dynamics. The presented model can predict SO2 and lime concentration distributions inside the CFBA, and give the amount of lime needed to remove a given percentage of SO2. It is found that SO2 concentration decreases with the increase of CFBA distance from the bottom in the core region. However, lime concentration exhibits a very slight variation in the core region. This means that lime is efficiently utilized to remove SO2. The model also predicts that SO2 partial pressure at the exit of the CFBA decreases with the increase in the percentage of fresh lime injected in the CFBA.
... The experimental methods that have provided the most direct measurement of particle RTDs have relied on measurements of the exit times of distinctive particles (e.g., particles with some distinctive physical characteristic such as color, size, or chemical composition that can be readily detected) after they have been injected as pulses into experimental bubbling or circulating fluidized beds. Typically, the particles that were measured have been classified either as Geldart A or B type, which characterizes the flow patterns they tend to exhibit [Geldart (1973), Kunii and Levenspiel (1991)]. 1 Some of the most relevant articles on these experiments include: Yagi and Kunii (1961a), Helmrich et al (1986), Berruti et al (1988), Ambler et al (1990), Smolders and Baeyens (2000), Harris et al (2003a&b), Bhusarapu et al (2004), andAndreux et al (2008). All of these studies have reported some common features in the observed RTDs: ...
... Many of the general modeling approaches developed for chemical reactors have been adapted for modeling particle RTDs in bubbling and circulating beds. Some relevant articles in the literature that discuss RTD modeling in this context include the following: Yagi and Kunii (1961a), Verloop et al (1968), Berruti et al (1988), Ambler et al (1990), Smolders and Baeyens (2000), Harris et al (2002), Bhusarapu et al (2004), and Andreux et al (2008). As with the modeling approaches used for the more general problem in chemical reactors, particle RTD models for bubbling and fluidized beds have adopted one of three basic approaches, listed below in increasing order of complexity: ...
... • The 1D continuum dispersion model [see for example Berruti et al ((1988), Levenspiel (1999), and Smolders and Baeyens (2000]; ...
... The experimental setup allowed for both the identification and quantification of the major products. Although this experimental set-up may not fully represent "real-world" conditions experienced by the catalyst during CFP of biomass at the industrial scale, the micro-pyrolysis unit has been used a convenient tool by many research groups to evaluate prospective catalysts with high accuracy [28,29]. ...
Article
The catalytic fast pyrolysis (CFP) of biomass represents an efficient integrated process to produce deoxygenated stable liquid fuels and valuable chemical products from lignocellulosic biomass. The zeolite ZSM-5 is a widely studied catalyst for the CFP process. However, its microporous structure may limit the diffusion of high molecular weight pyrolysis intermediates to its active sites. Mesoporous aluminosilicates such as Al-SBA-15 are promising materials with larger pore sizes that can overcome these diffusional limitations. Previous comparisons between mesoporous aluminosilicates and ZSM-5 for the CFP process have neglected the disproportionately high acidity of ZSM-5. In this study, an Al-SBA-15 catalyst has been synthesised with high acidity, comparable to that of a ZSM-5 catalyst with a Si:Al ratio of 15:1. The synthesised Al-SBA-15 catalyst was characterised by N2 physisorption, XRD and propylamine-TPD, and was compared to a ZSM-5 catalyst and a typical industrial equilibrium fluid catalytic cracking catalyst (e-FCC). All three catalysts were used at three different catalyst to biomass (C/B) ratios, to investigate the effect of varying concentrations of acid sites on the product distribution from the catalytic fast pyrolysis of beech wood. Interestingly, despite their dissimilar structural architectures, all three solid acid catalysts displayed similar reaction pathways towards the cracking of high molecular weight products such as levoglucosan and formation of intermediates including phenolics and furans. However, the selectivity towards the final catalytic products was dictated mainly by the structure of the catalysts. Despite their very similar surface area and acidity, the ZSM-5 exhibited high selectivity for the formation of desirable aromatic hydrocarbon products due to its shape-selective micropore structure, while Al-SBA-15 instead shifted the selectivity towards the formation of undesirable coke. The results highlighted the importance of catalyst shape-selectivity in the catalytic fast pyrolysis of biomass for the conversion of pyrolysis vapours into desirable products and the suppression of undesirable solid byproduct formation.
... The use of correlation analysis is possible when simulating the process of mixing in vibration and centrifugal mixers [4,6]. We use a similar approach for a continuous drum mixer. ...
... To confirm the impact of inertia on particle entrapment, two successive numerical simulations with two particles of same diameter (40 μm), but made from different materials, steel (ρsteel=7800 kg/m 3 ) and sand (ρsand=2470 kg/m 3 [129]), are performed. The simulations show that the heavier the particle is, the more likely it will be entrapped. ...
Data
Full-text available
Contact lubrication is essential in a wide range of mechanical systems like rolling element bearings (REBs). A minimum quantity of clean lubricant all along the bearing life is necessary but difficult to ensure. In fact, lubricants contain inevitably wear debris or external particles, like dust. Carried by the lubricant in the vicinity of elastohydrodynamic (EHD) contacts, particles can be entrapped with disastrous consequences for contacting surfaces. Entrapment of micrometric particles in submicrometric contacting gaps means irreversible damages for the surfaces. Damages weaken the surfaces and reduce significantly the REBs lifetime. The goal of this work is to analyze the critical particle entrainments in the contact inlet. Entrapment of steel spherical particles was investigated from the numerical and experimental point of view. Firstly, the phenomenology of entrapment was explored with a new experimental method based on Particle Image Velocimetry (PIV) technique installed on a tribometer. It enabled the evaluation of velocity profiles in the contact inlet and the tracking of particles within EHD contacts. Secondly, a numerical modelling of the inlet flow for EHD contacts, including the particle tracking, was developed. Finally, tests on a twin-disc machine with a controlled level of well-defined contamination were conducted to validate previous conclusions. A first set of results showed that particle entrapment is highly dependent on the lubricant velocity profile. Depending on contact geometry, from point to wide elliptical contacts, different entrapment probability were revealed. Surprisingly, increasing contact width with wide elliptical contacts leads to a drop of entrapped particles. It was demonstrated that this phenomenon is due to backflows occurring upstream from these contacts. Introducing a hybrid pair of contacting materials (silicon nitride–steel), dents on the surfaces due to entrapped particles were explored. It has been confirmed that silicon nitride surface offers a real ability to resist to indentation. It was also noticed that the entrapment probability for silicon nitride–steel contacts is equivalent to a steel–steel one.
... Although it may be useful to determine individual RTD of solid and liquid phases, it is fair to note that the existing analytical techniques to measure concentrations within solids are prone to severe measurement error and may not be truly relied upon to construct RTD response curve for the solid phase. A literature review indeed shows that most of the studies on G-S or L-S systems pertain to injection and measurement of tracer in the gas or liquid phase only [8][9][10]. Therefore, the results presented in the following section on the RTD data for the liquid (water) phase may be considered reasonably accurate enough to qualitatively corroborate the mechanistic steps proposed in Section 2.3 with regard to the types of solid flow patterns existing on the stage in two columns (new and conventional). ...
Article
The design and development of a counter current multi-stage fluidized bed column for the removal of recalcitrant solutes such as fluorides, nitrates, arsenics and phosphates ions from wastewater are envisaged in this study. In treating wastewater using solid resins, the higher removal efficiency in multi-stage fluidized bed than that obtained in a single stage fixed and fluidized beds are experimentally demonstrated. In the proposed work, the many aspects of issues involved in the counter current multi-stage fluidized bed are studied. These include hydrodynamics, mass-transfer and scale-up. The design of the column includes column diameter, height of each stage, downspout size and water distributor. The hydrodynamics study predominantly focuses on determining loading/flooding criterion and the operating range of liquid-solid flows for proper fluidization on a single or multi-stage. The experimental results for determining the minimum fluidization conditions (flow rate, pressure drop and bed porosity) will be presented. The mass-transfer study will be carried out to determine the separation efficiency over a wide range of operating conditions under steady state such as different types of anions and cations such as fluorides, nitrates, arsenics and phosphates ions in waste water using stage-wise operation in fluidized beds. The effects of resin particle size and density on the hydrodynamics and mass-transfer will also be studied. The RTD analysis of the fluidized bed will be done to determine the channeling and mixing state of the particles in the bed. Key words: Waste water, Ion-exchange, Fluidized bed, Multi-stage column, Counter-current flow
... Although it may be useful to determine individual RTD of solid and liquid phases, it is fair to note that the existing analytical techniques to measure concentrations within solids are prone to severe measurement error and may not be truly relied upon to construct RTD response curve for the solid phase. A literature review indeed shows that most of the studies on G-S or L-S systems pertain to injection and measurement of tracer in the gas or liquid phase only [8][9][10]. Therefore, the results presented in the following section on the RTD data for the liquid (water) phase may be considered reasonably accurate enough to qualitatively corroborate the mechanistic steps proposed in Section 2.3 with regard to the types of solid flow patterns existing on the stage in two columns (new and conventional). ...
Article
A hydrodynamic study was carried out on our patented radially cross-flow fluidized bed staged column, with the salt laden water and solid resins flowing counter-currently, to determine the loading/flooding criterion for a stable operation of the column, and also to ascertain the mal-distribution in flow. Residense time distribution measurements were taken to address the latter part of the study. The data collected from the hydrodynamic measurements show a wider range of liquid and solid flowrates that can be used for the stable operation of the column, in comparison to that obtained in the conventional multi-staged column. The extent of mal-distribution or channeling is also relatively smaller in the former. The observations are consistent with the mass-transfer results obtained in our recent study, where the separation of dissolved solids using the radially cross-flow ion exchange column was found to be 40% larger than that in the conventional column.
... Among the limited studies on the multiphase flow aspects of biomass fluidization, determination of characteristic fluidization velocities (Abdullah et al., 2003;Rao and Reddy, 2010;Rao and Bheemarasetti, 2001;Zhang et al., 2011), and the distribution and mixing pattern of biomass-inert materials (Berruti et al., 1988;Dos Santos and Goldstein, 2008;Shen et al., 2007;Yu et al., 2003) have been of particular interest to researchers. The impact of irregularly-shaped particles on the characteristics of the dilute and dense phases has received comparatively little attention, and it has generally been assumed that, due to the typically low ratio of biomass to sand in biomass processing units, the gas holdup in the bed is comparable to that of a bed of sand alone. ...
... It is fair to say that the existing analytical techniques to measure concentrations within solids are prone to measurement error and may not be truly relied upon to construct RTD response curve. A literature review indeed shows that most of the studies pertain to injection and measurement of tracer in the gas or liquid phase in G-S or L-S systems [19][20][21]. Only in recent years, thanks to the development of optical or other non-intrusive tomography techniques, including X-ray or IR, the visualization of solid voids and the measurement of solidvolume fractions in two-phase flow through packed columns have been made possible [22][23][24]. ...
Article
In our recent work we carried out mass transfer study on the multi-stage fluidized bed ion exchanger column with solids and liquid flowing in the counter current directions and demonstrated improved separation efficiency of dissolved anions from waste water in comparison to that achieved in a fixed bed operation. In this study, we report the results pertaining to hydrodynamic study with a view to ascertaining the type of fluidization prevailing on the column's stage and the operating range of liquid and solid flow rates for the steady and stable operation of the column without loading or flooding with excess solid or water flow rates. Residence time distribution (RTD) study was carried out to investigate the extent of mixing on the stages. In addition, the experimental measurements for pressure-drops were made over a wide range of operating conditions including number of stages, height of the downspout on every stage, and the liquid and solid flow rates. Based on the data, empirical correlations were developed using scale-up analysis for predicting pressure-drop, bed porosity and average bed height during cross-flow fluidization apparently prevalent on the stage. The results in this study assume significance from the perspective of design and stable operation of staged fluidized bed ion exchangers.
... Measurement and analysis of residence time distribution (RTD) provide necessary information pertaining to flow in industrial process systems (IAEA, 2008). Various authors have reviewed measurement of RTD of solid particles in laboratory-scale fluidized bed reactors (FBRs) (Berruti et al., 1988;Harris et al., 2002;Christophe et al., 2002). Different researchers have used different tracers such as chemical, magnetic, subliming, coloring and fluorescent tracers. ...
Article
Radiotracer investigations were carried out for measurement and analysis of residence time distribution (RTD) of coal particles in a pilot-scale gasifier fitted with a flat air/steam distributor. Measurements were made at different operating conditions using gold-198 ( ¹⁹⁸ Au) labeled coal particles as a radiotracer. The measured RTDs were treated and mean residence times (MRTs) were determined. Furthermore, the treated RTDs were simulated using a suitably conceptualized mathematical model and detailed information about hydrodynamics of coal particles within the gasifier was obtained. Results of model simulation indicated that the gasifier behaved as an ideal mixer of fine coal particles exiting from the top of the gasifier. A small fraction of the coarser particles was found to be bypassing at ambient temperature.
... Furthermore, rice husk is difficult to burn in a fluidised bed combustor where the continuous upcoming air or fluidising media force the particles to elutriate out of the system. The findings of Berruti et al. (1988) demonstrated that a low density biomass particle entrains from the fluidised bed and this depends on the fluidising velocity, particle size and density. Similarly, the cold study of various biomass particles and coal by Abdullah et al. (2003) concluded that the Geldart type B particles such as sawdust, shells, coal and bottom ash exhibited good fluidisation behaviour compared to that of Geldart type D particles (rice husk) and Geldart type A particles (palm fibres) which gave poor fluidisation quality. ...
Article
Full-text available
The purpose of this study was to investigate the effect of bed height on the quality of rice husk ash in a 210-mm diameter pilot scale fluidised bed combustor. The degree of rice husk burning in the fluidised bed could be deduced from the temperature of the combustor and the particle size of the resulting ash. The turbulence in the bed would break down the char skeleton of the rice husk into finer size. From this study, the bed height of 0.5 Dc was found to give the lowest residual carbon content in the ash (1.9%) and the highest bed temperature (670°C). Moreover, the problem of contamination of amorphous rice husk ash with sand increased as the bed height was increased. Nevertheless, the results from the current study need to be validated in larger-scale fluidised beds to determine whether the bed height of 0.5 Dc is still applicable.
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Biomass is important in energy conversion processes due to their favourable status with respect to greenhouse gas emissions. However, biomass particles have unusual properties which make them difficult to fluidize and handle. This paper reviews recent research on the hydrodynamics and mixing of biomass particles in fluidized beds. Whereas there has been considerable effort to develop new biomass gasification, combustion, pyrolysis and bio-conversion processes, relatively few authors have characterized the relevant flow characteristics of biomass particles in fluidized beds or investigated measures that could assist in resolving flow issues. The limited work that has been reported on biomass fluidization primarily treats means of achieving fluidization, mixing and segregation. Most of the work has been in low-velocity fluidized beds, although circulating fluidized beds are also important. Further research is needed to provide general understanding of interactions among heterogeneous particles and guidance on conditions that can lead to viable and sustainable processes.
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A mathematical model, based on the core-annulus flow structure, is proposed to characterize the two-phase flow and the residence time distribution of solids within the riser of circulating fluidized beds. The model is tested against experimental data obtained in a laboratory unit utilizing a tracer technique. While the accuracy of the experimental technique is shown not to be sufficient to allow conclusive results, the model is capable of a good prediction of the observed trends of the characteristic bimodal residence time distributions with an excellent match of the times of arrival of the two peaks. Simulation runs have been performed to study the effects of key operating variables on the residence time distribution.
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Dense (or large) particles fall through liquid fluidized beds of light (or small) particles. In this work, a new contactor is described in which continuous, countercurrent transport of dense particles in a stationary, liquid fluidized bed of light particles is exploited to obtain selective and continuous transport of the dense phase. The system is refered to as the ‘trickle flow fluidized-bed reactor’. This sytem is evaluated in its application as a countercurrent adsorptive reactor. By selecting a suitable adsorbent as the dense phase, and a catalyst as the light phase, simultaneous reaction and countercurrent product removal may be achieved within one contactor. For a systematic design and optimization of such an adsorptive trickle flow fluidized-bed reactor, a predictive hydrodynamic model is required. In this work, the relation between the volume fractions and the fluxes of the three phases is investigated. A laboratory scale trickle flow fluidized-bed reactor has been constructed for experimental studies on hold-up and flux. A multi-component transport model to predict the volume fractions, fluxes and operating conditions is developed. The model is validated with the experimental hold-up and flux data from the trickle flow fluidized-bed reactor. To apply this concept as a countercurrent adsorptive reactor, a high countercurrent adsorbent flow, a high hold-up of the dense adsorbent and light catalyst are required, together with a stable operation. Hence, the reactor should operate at a minimum liquid fraction of approximately 50 vol% and a free area fraction of the supporting plate between 0.3 and 0.5. It is demonstrated that the system is very sensitive to the bulk density of the multi-component suspension. At a high hold-up of the dense particles, the bulk density of the bidisperse suspension may increase to a level which causes a complete wash-out of the light particles. Therefore, the difference in density between the light catalyst and dense adsorbent particles should be as small as possible.
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This study proposes an innovative approach for the study of particle entrapment in rolling element bearings (REBs). Two couples of contacting materials were considered, the classical steel–steel and silicon nitride–steel used in hybrid bearings. Numerical simulations, as well as experiments, combine theoretical trajectories for incoming contaminant particles and effective entrapment ratios observed within a twin-disc machine. Linking both approaches allows the highlighting of some key parameters leading to particle entrapment under pure rolling conditions in elastohydrodynamic point contacts.
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In this paper we study stochastic models for the transport of particles in a fluidized bed reactor, and compute the associated residence time distribution (RTD). Our main model is basically a diffusion process in [0; A] with reflecting/absorbing boundary conditions, modified by allowing jumps to the origin as a result of transport of particles in the wake of rising fluidization bubbles. We study discrete time birth-death Markov chains as approximations to our diffusion model. For these we can compute the particle distribution inside the reactor as well as the RTD by simple and fast matrix calculations. It turns out that discretization of the reactor into a moderate number of segments already gives excellent numerical approximations to the continuous model. From the forward equation for the particle distribution in the discrete model we obtain in the diffusion limit a partial differential equation for the particle density p(t; x) @ @t p(t; x) = 1 2 @ 2 @x 2 [D(x)p(t; x)] Gamma @ @...
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Regular circulation of the particulate phase can be induced in a shallow fluidized bed by means of an uneven distribution of fludizing fluid supplied to the base. Circulation is strongest with the particles traveling up at the walls and down at the middle of the bed, with a bed depth to bed width ratio around 0. 5. This ″Gulf Stream″ circulation provides a simple means of improving lateral mixing in shallow fluidized beds. Its application is discussed in relation to large fluidized bed reactors to which solid reactants are fed continuously.
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Elutriation characteristics of widely different solids (density from 920 to 5900 kg/m3) were measured in fluidized beds (up to 0.9 m in size) having high freeboard (7.5 m), using gas velocities up to 4 m/s.The experimental findings were compared with previously reported results and all the variables were well correlated with a simple empirical expression
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A critical survey is given of the different models proposed for solids transport in gas-fluidized beds. It is shown that many of the models can fit the residence time distribution curve—the Ft-t curve—fairly well despite the fact that the physical behaviour of the bed is not recognized in these models. The intensity curve is recommended as a good tool for comparison of the models with the experiments.
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A new mathematical model has been developed for the stirred tank reactor. The model assumes a circulating flow, created by the pumping action of the stirrer, and an isotropic homogeneous turbulence in the circulated fluid. For a continuously operating stirred reactor expressions are derived for the conversion of a first-order reaction, the spread in residence times and the distribution function. It is shown that at high circulation/feed rate ratios and/or at high turbulent diffusivities the model approaches the ideal mixer. Correlations are proposed for the circulation rate parameter and the turbulent diffusivity parameter. The mixing process in a stirred batch reactor is evaluated and described as a function of time and location. The expressions are useful for the correlation of some experimental results.
Article
A bench-scale continuous flash pyrolysis unit using a fluidized bed at atmospheric pressure has been employed to investigate conditions for maximum organic liquid yields from various biomass materials. Liquid yields for poplar-aspen were reported previously, and this work describes results for the flash pyrolysis of maple, poplar bark, bagasse, peat, wheat straw, corn stover, and a crude commercial cellulose. Organic liquid yields of 60-70% mf can be obtained from hardwoods and bagasse, and 40-50% from agricultural residues. Peat and bark with lower cellulose content give lower yields. The effects of the addition of lime and of a nickel catalyst to the fluid bed are reported also. A rough correlation exists between has content and maximum organic liquid yield, but the liquid yield correlates better with the alpha-cellulose content of the biomass. General relationships valid over all reaction conditions appear to exist among the ratios of final decomposition products also, and this correlation is demonstrated for the yields of methane and carbon monoxide.
Article
A continuous fluidized bed bench scale flash pyrolysis unit operating at atmospheric pressure and feed rates of about 15 g/h has been successfully designed and operated. A unique solids feeder capable of delivering constant low rates of biomass has also been developed. Extensive pyrolysis tests with hybrid aspen-popular sawdust (105–250 μm) have been carried out to investigate the effects of temperature, particle size, pyrolysis atmosphere and wood pretreatment on yields of tar, organic liquids, gases and char. At optimum pyrolysis conditions high tar yields of up to 65% of the dry wood weight fed are possible at residence times of less than one second. On a conçu et employé avec succès, à l'échelle du laboratoire, une unité de pyrolyse-éclair à lit fluidisé continu; le dispositif fonctionnait à la pression atmosphérique et à des débits d'alimentation d'environ 15 g/h. On a aussi mis au point un dispositif unique d'alimentation en matières solides, capable d'assurer de faibles débits constants de biomasse. On a fait des expériences poussées de pyrolyse sur des sciures d'hybrides de peuplier-faux tremble (105—250 μm), dans le but d'étudier les effets de la température, de la granulométrie des particules, de l'atmosphère de la pyrolyse et d'un traitement préalable du bois sur les rendements en goudron, liquides organiques, gaz et matières carbonisées. Il est possible, dans les conditions optimales de pyrolyse, d'obtenir des rendements élevés en goudron, qui peuvent atteindre 65% du bois sec d'alimentation en poids pour des temps de séjour de moins d'une seconde.
Article
A 0.27 m diameter fluidized bed reactor has been designed to allow experimental measurement of the axial and radial mixing behaviour of the solids.A unique method has been developed which permits the continuous determination of solid tracer concentration with time at different radial and axial positions within the fluidized bed.Solids mixing has been described by a model in which vertical mixing is instantaneous and lateral mixing occurs by dispersion.The lateral solids dispersion coefficients have been evaluated at various operating conditions from the experimental results of tracer concentration versus time. Based on the results, a modification of an existing correlation is proposed.On a conçu un réacteur à lit fluidisé de 0.27 m de diamètre, qui permet de mesurer expérimentalement le comportement des mélanges axiaux et radiaux des solides.On a mis au point une méthode unique qui permet la détermination continue de la concentration d'un traceur solide en fonction du temps, à différentes positions radiales et axiales à l'intérieur du lit fluidisé.On décrit le mélange des solides au moyen d'un modèle, dans lequel le mélange vertical est instantané et le mélange latéral se fait par dispersion.Les coefficients de dispersion latérale des solides ont été évalués dans différentes conditions opératoires, à partir des rèsultats expérimentaux de la concentration du traceur en fonction du temps. On propose, à partir des résultats obtenus, une modification d'une corrélation existante.
Article
A continuous atmospheric pressure flash pyrolysis process for the production of organic liquids from cellulosic biomass has been demonstrated at a scale of 1–3 kg/hr of dry feed. Organic liquid yields as high as 65–70% of the dry feed can be obtained from hardwood waste material, and 45–50% from wheat straw. The fluidized sand bed pyrolysis reactor operates on a unique principle so that char does not accumulate in the bed and treatment of the sand is not necessary. The product gas, about 15% of the yield, has a medium heating value. The liquid product is an acidic fluid, which pours easily and appears to be stable. A preliminary economic analysis suggests that if the pyrolysis oil can be used directly as a fuel, its production cost from wood waste is probably competitive with conventional fuel oil at the present time. On a fait la démonstration d'un procédé continu de pyrolyse éclair à l'échelle de l à 3 kg/h d'alimentation sèche, à la pression atmosphérique, pour la production de liquides organiques à partir d'une biomasse cellulosique. On peut obtenir des rendements en liquide atteignant 65 à 70% de l'alimentation sèche à partir de déchets de bois dur et de 45 à 50% à partir de paille de blé. Le réacteur de pyrolyse, à lit de sable fluidisé, fonctionne sur un principe unique, de sorte que le charbon ne s'accumule pas dans le lit et qu'il n'est pas nécessaire de traiter le sable. Le produit gazeux, qui correspond à environ 15% de rendement, a une valeur calorifique moyenne. Le produit liquide est un fluide acide qui se déverse facilement et semble assez stable. Une analyse économique préliminaire indique que, si l'on peut employer directement l'huile de pyrolyse comme combustible, son coǔt de production à partir de déchets de bois est probablement compétitif actuellement avec celui de l'huile combustible classique.
Transverse mixing of particles in a fluidized bed with small ratio of the height of the bed to the linear transverse dimension
  • Gel'perin
Residence time and dispersion of fine particles in a 2-D fluidized bed of large particles
  • Valenzuela
Transport and residence time of particles in a shallow fluidized bed
  • Heertjes