Fluidized Bed Reactor

While there are many semi-empirical correlations for estimating the wall-to-bed heat transfer coefficient in a fluidized bed, most are only usable in a limited range of operating conditions. The correlation developed by Molerus and Wirth (1997) provides the most expansive and successful model; however, it does not consider the influence of the properties of an immersed tube bank or a horizontal movement of particles (cross-flow). This study expands Molerus and Wirth’s correlation to include these additional influencing factors by identifying and introducing new dimensionless factors using dimensional analysis. Collected secondary data and measurements from a test rig were used to evaluate the extended model. The model’s estimates largely align with the collected secondary data and previously published models describing the influence of tube diameter and tube packing density on the wall-to-bed heat transfer coefficient. The model also provides new insight into the conditions under which a particle cross-flow contributes significantly to the wall-to-bed heat transfer coefficient. Future research should use these findings to conduct targeted measurements and further improve the model’s predictions.

Sewage sludge holds great potential for producing carbon nanotubes (CNTs) due to their abundance, renewability, and low-cost carbon source. The objective of this study is to investigate the production of CNTs through two-stage processes i.e. pyrolysis and catalytic chemical vapor deposition (CCVD) of sewage sludge-derived vapor. The central composite design (CCD) model of response surface methodology (RSM) was conducted to predict and optimise the yield of CNTs from sewage sludge vapour. The statistical results indicate that the optimal conditions are a catalyst loading of 0.5 and a temperature of 800 C. The catalyst loading has the greatest impact on CNTs yield, as evidenced by the F-value in the ANOVA. The actual CNTs yield under these optimal conditions was 30.53%, which is in close agreement with the predicted value of 33.60%. A quadratic model was employed to investigate the relationship between temperature and catalyst load on the deposition yield of CNTs. The CNTs were then characterised using Raman Spectroscopy, X-ray Diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM) and Transmission Electron Microscopy (TEM). The optimised CNTs had an outer diameter of 25.2 nm, and inner diameters of 3.2 nm. This research contributes to the advancement of the CNTs production from sewage sludge.

This article describes the bed expansion characteristics of a down-flow anaerobic fluidized bed reactor treating a synthetic wastewater. Experiments were carried out in a 0.08 m diameter and 1 m length PVC column. The carrier used was ground perlite (an expanded volcanic rock). Particles characteristics were 0.968 mm in diameter, specific density of 213 kg ⅐ m -3 and U mf (minimal fluidization velocity): 2.3 m ⅐ h -1 . Experimental data of terminal velocities and bed expansion parameters at several biofilm thicknesses were compared to different models predicting the bed expansion of up-flow and downflow fluidized beds. Measured bed porosities at different liquid superficial velocities for the different biofilm thicknesses were in agreement with the Richardson-Zaki model, when U t (particle terminal velocity) and n (expansion coefficient) were calculated by linear regression of the experimental data. Terminal velocities of particles at different biofilm thicknesses calculated from experimental bed expansion data, were found to be much smaller than those obtained when C d (drag coefficient) is determined from the standard drag curve or with others' correlations (Karamanev and Nikolov, 1992a,b). This difference could be explained by the fact that free-rising particles do not obey Newton's law for free-settling, as proposed by Karamanev and Nikolov (1992a,b) and . In the present study, the same freerising behavior was observed for all particles (densities between 213 and 490 kg ⅐ m -3 ).

A method of preparing a steam reforming catalyst characterized by improved resistance to attrition loss when used for cracking, reforming, water gas shift and gasification reactions on feedstock in a fluidized bed reactor, comprising: fabricating the ceramic support particle, coating a ceramic support by adding an aqueous solution of a precursor salt of a metal selected from the group consisting of Ni, Pt, Pd, Ru, Rh, Cr, Co, Mn, Mg, K, La and Fe and mixtures thereof to the ceramic support and calcining the coated ceramic in air to convert the metal salts to metal oxides.

The communication describes the idea to apply a magnetically stabilized bed as liquid control element in an airlift with an external loop. The experiments reported demonstrate the effect of the particle bed parameters and the field intensity on the liquid flowrate. The suitable fluidization mode and field orientations are discussed.

Abstract−In traditional chemical reaction engineering, it is possible to incorporate only the simplified aspects of fluid flow, mixing, and mass/heat transfer into the analysis of chemical reaction rates and reactor design. As a con-sequence of the advent of high-speed, high-capacity computing capacity, complex processes involving chemical reactions have become amenable to analysis and modeling. This has also resulted in the merging of various disciplines of chemical engineering in formulating detailed descriptions of complex processes. Developments that exemplify this trend over the years are discussed in this review. Several examples from the author’s previous work are used to illustrate the application of chemical reaction engineering principles to the modeling and analysis of complex systems involving the chemical processing of metals and other inorganic materials.

Olivine ((Mg,Fe) 2 SiO 4 ) has been extensively explored as an active bed material for catalytic cracking of tars during gasification of biomass in dual fluidized bed reactors. It is known that both the elemental composition, addition of Fe and high temperature calcinations influence the catalytic properties of this mineral. However, it is not clear how olivine responds to the fairly hostile environments present during gasification or what chemical state Fe takes during operation. We have investigated the stability of Austrian olivine under model conditions, resembling those in a gasifier. Powder samples were heated to 750 • C in a quartz-tube flow-reactor and sequentially exposed to oxidizing (O 2 , H 2 O, CO 2 ) or reducing gases (CO, H 2 ) or mixtures thereof, for various durations of time. Significant changes in phase composition of the material, depending on the gas composition and the duration of the treatments, were found using X-ray photo-electron spectroscopy (XPS), X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS) and scanning electron microscopy (SEM). A large fraction of the Fe in the investigated material is present as free Fe-phases, which are sensitive to changes in the gas environment. After exposure to oxidizing gases, the free Fe phases are: Fe 2 O 3 and Fe 3 O 4 or MgFe 2 O 4 . Upon exposure to reducing gases, the iron oxides are converted into Fe 0 and Fe 3 C and formation of graphitic carbon is observed. In addition, the elemental composition of the surface changes dramatically depending on the gas composition. After exposure to oxidizing environments, the amount of Fe at the surface is twice as high as after reduction. Both the change in chemical state of the Fe-phases, the amount of surface Fe and the build-up of surface carbon are fast processes under the applied conditions and significant changes are observed on the time scale of one minute. These observations have important implications for olivine as a tar cracking catalyst, especially when used in dual fluidized bed gasifiers. The fast reduction of the iron oxides upon switching from oxidizing to reducing conditions shows that olivine transports oxygen from the combustor into the gasifier. Furthermore, the catalytic properties of Fe depend strongly on its chemical state. Therefore, the catalytic function of olivine depends strongly on the gas environment and on the catalysts residence time in the gasifier. Finally, both the decreasing amount of surface-Fe and the carbon deposition observed after exposing olivine to reducing conditions can result in significant catalyst deactivation.

This work focuses on chloroform (CF) cometabolism by a butane-grown aerobic pure culture (Rhodococcus aetherovorans BCP1) in continuous-flow biofilm reactors. The goals were to obtain preliminary information on the feasibility of CF biodegradation by BCP1 in biofilm reactors and to evaluate the applicability of the pulsed injection of growth substrate and oxygen to biofilm reactors. The attached-cell tests were initially conducted in a 0.165-L bioreactor and, then, scaled-up to a 1.772-L bioreactor. Glass cylinders were utilized as biofilm carriers. The continuous supply of growth substrate (butane), which led to the attainment of the highest CF degradation rate (8.4 mg CF day -1 m biofilm surface -2 ), was compared with four schedules of butane and oxygen pulsed feeding. The pulsed injection technique allowed the attainment of a ratio of CF mass degraded per unit mass of butane supplied equal to 0.16 mg CF mg butane -1 , a value 4.4 times higher than that obtained with the continuous substrate supply. A procedure based on the utilization of integral mass balances and of average concentrations along the bioreactors resulted in a satisfactory match between the predicted and the experimental CF degradation performances, and can therefore be utilized to provide a guideline for optimizing the substrate pulsed injection schedule.

An experimental study on the combustion of liquid fuels in a bubbling fluidized bed is presented. Gas oil (diesel fuel) for automotive application, bio-diesel and N-dodecane have been burned during experiments carried out at low temperature. The focus is on the emissions of unburned species from the bed. Qualitative considerations on the phenomenology of the combustion are derived from the observation of the bed surface, which reveals the presence of micro-explosion events. It is confirmed that the temperature has a prominent and nonmonotone effect on the emissions. In addition, the dispersion air velocity was observed to affect the emissions in an unexpected way.

The present study develops a comprehensive kinetic model for ethylene polymerization in a gas-phase fluidized bed reactor (GPFBR) operating under industrial conditions. By integrating a mechanistic understanding of catalyst behavior, reaction kinetics, and fluid dynamics, the model captures essential features such as monomer conversion, polymer molecular weight distribution (MWD), and reactor temperature profiles. The model was validated experimentally using data collected from pilot-scale GPFBRs under varying feed compositions and temperature conditions. Results demonstrate strong agreement between predicted and observed polymer yield and molecular weight distributions. This work enhances the predictive capability of reactor-scale simulations, aiding process optimization in polyethylene production.

Accelerated aging was examined over a broad temperature range (40-290 °C) to determine the stability and different aging mechanisms for pyrolysis oil produced using fluid catalytic cracking (FCC) of solid particulate biomass material. Oil properties, including water content, high-molecular-mass (HMM) lignin content, viscosity, molecular weight, and chemical composition, were measured both before and after the accelerated aging study. Notably, at all aging times and temperatures explored, all samples remained as a single phase. Chemical composition of the pyrolysis oils was monitored using infrared and mass spectroscopies. Oils aged at temperatures above 60 °C showed marked increases in HMM lignin content and molecular weight with increasing aging time. Calorimetry results indicated that, at and above 200 °C, there were alternate aging mechanisms that occur, including sugar decomposition. A rapid increase in the water content and shift in the HMM fraction molecular weight corroborated the decomposition of sugars, which led to the formation of water and reactive monomers. Fourier transform infrared (FTIR) results showed that similar aging reactions occurred for oils aged between 40 and 80 °C and between 150 and 290 °C. Gas chromatography-mass spectrometry (GC-MS) results suggested the reactions among furfural, 2-cyclopenten-1-one, 2-hydroxy-3-methyl-2-cyclopenten-1-one, hydroxybenzenes with available ortho/para sites, and the active sites on HMM lignin contributed to property changes as a result of heat treatment.

Accelerated aging was examined over a broad temperature range (40-290 °C) to determine the stability and different aging mechanisms for pyrolysis oil produced using fluid catalytic cracking (FCC) of solid particulate biomass material. Oil properties, including water content, high-molecular-mass (HMM) lignin content, viscosity, molecular weight, and chemical composition, were measured both before and after the accelerated aging study. Notably, at all aging times and temperatures explored, all samples remained as a single phase. Chemical composition of the pyrolysis oils was monitored using infrared and mass spectroscopies. Oils aged at temperatures above 60 °C showed marked increases in HMM lignin content and molecular weight with increasing aging time. Calorimetry results indicated that, at and above 200 °C, there were alternate aging mechanisms that occur, including sugar decomposition. A rapid increase in the water content and shift in the HMM fraction molecular weight corroborated the decomposition of sugars, which led to the formation of water and reactive monomers. Fourier transform infrared (FTIR) results showed that similar aging reactions occurred for oils aged between 40 and 80 °C and between 150 and 290 °C. Gas chromatography-mass spectrometry (GC-MS) results suggested the reactions among furfural, 2-cyclopenten-1-one, 2-hydroxy-3-methyl-2-cyclopenten-1-one, hydroxybenzenes with available ortho/para sites, and the active sites on HMM lignin contributed to property changes as a result of heat treatment.

This paper presents the experimental results and process analysis of residual food waste air gasification. The experiments were conducted on a batch tubular reactor at laboratory scale, using air at atmospheric pressure as oxidizer. Temperature and equivalent ratio (ER) were varied to assess the optimum process parameters for this particular type of biomass. The temperature was varied between 650°C and 850°C, and the ER between 0.25 and 0.35. The process performance was evaluated in terms of syngas specific energy content, carbon conversion efficiency and cold/hot-gas efficiency.

Energy demands keep increasing in this modern world as the world population increases, which leads to a reduction in fossil fuels. To resolve these challenges, Pennisetum purpureum, an invasive grass in Brunei Darussalam, was examined as the feedstock for renewable energy through a catalytic pyrolysis process. The activated carbon was applied as the catalyst for a simple and economical solution. The catalytic pyrolysis was executed at 500 °C (the temperature for the highest biofuel yield) for both reactors to produce the highest amount of upgraded biofuels. The biochar produced from the non-catalytic and catalytic pyrolysis processes showed a consistent yield due to stable operating conditions, from which the activated carbon was generated and used as the catalyst in this work. A significant amount of improvement was found in the production of biofuels, especially bio-oil. It was found that for catalysts, the number of phenolic, alcohol, furans, and ketones was increased by reducing...

In a recent publication (Aly et al., Intl. Comm. Heat and Mass Transfer, 37(6) pp 618-623), the authors have developed a new mathematical model for predicting spray and atomization characteristics in an Eulerian-Eulerian framework. The model takes into account both the drag and turbulence induced fragmentation stresses. In the present paper, the authors investigate the relative contribution of the two different stresses in the break-up process using the new model for a case of a co-axial air-blast atomizer. The results show that turbulent stresses play the dominant role in the fragmentation of liquid droplets.

This paper investigated the effect of inorganic chlorine on the formation of PCDDyFs from heating polyethylene (PE) in the presence of air. There was an increase in the formation of PCDDyFs with an increasing amount of metal chlorides except NaCl, which was not observed to have any effects on the formation of PCDDyFs without the presence of catalysts. Although the levels of PCDDyFs formation in this study have no relevance to full scale municipal solid waste incineration, the results of the present experiments can aid understanding of the mechanisms of the formation of PCDDyFs from heating PE in the presence of metal chlorides.

Using the scanning electronic microscopy, it was observed that natural zeolite possesses excellent physical characteristics as a support medium in anaerobic fluidized bed reactors (AFBR). Samples for biomass analysis were taken from two identical laboratory-scale AFBR (R-1 and R-2), which were operated with 25% of fluidization. These reactors treated distillery wastewaters (vinasses) at mesophilic temperature (30 AE 2 8C). The experiments were carried out with 0.25-0.50 and 0.50-0.80 mm zeolite particle diameter in reactors R-1 and R-2, respectively. The biomass concentration attached to zeolite in both reactors was found to be in the range of 40-45 g volatile solids/l. COD removal efficiencies as high as 90% were achieved at organic loading rate (OLRs) of up to 20 g COD/l day. The volatile fatty acid (VFA) levels were always lower that the suggested limits for digester failure. The yield coefficient of methane production was 0.29 l CH 4 (at STP)/g COD consumed and was virtually independent of the OLR applied. A hybridization technique (fluorescence in situ hybridization, FISH) helped determine the predominant anaerobic microorganisms that colonized the natural zeolite, which were found to be Methanosaeta and Methanosarcinaceae, observing a reduced number of sulphate reducing bacteria. The results obtained for reactors R-1 and R-2 were very similar, showing that the particle size did not significantly influence the microbial community immobilized on zeolite.

A study of the anaerobic treatment of wastewaters derived from red (RWWW) and tropical fruit wine (TFWWW) production was carried out in four laboratory-scale fluidized bed reactors with natural zeolite as bacterial support. These reactors operated at mesophilic temperature (35 • C). Reactors R1 and R2 contained Chilean natural zeolite, while reactors R3 and R4 used Cuban natural zeolite as microorganism support. In addition, reactors R1 and R3 processed RWWW, while reactors R2 and R4 used TFWWW as substrate. The biomass concentration attached to zeolites in the four reactors studied was found to be in the range of 44-46 g volatile solids (VS)/L after 90 days of operation time. Both types of zeolites can be used indistinctly in the fluidized bed reactors achieving more than 80%-86% chemical oxygen demand (COD) removals for organic loading rates (OLR) of up to at least 20 g COD/L d. pH values remained within the optimal range for anaerobic microorganisms for OLR values of up to 20 and 22 g COD/L d for RWWW and TFWWW, respectively. Toxicity and inhibition levels were observed at an OLR of 20 g COD/L d in reactors R1 and R3 while processing RWWW, whereas the aforementioned inhibitory phenomena were not observed at an OLR of 24 g COD/L d in R2 and R4, treating TFWWW as a consequence of the lower phenolic compound content present in this substrate. The volatile fatty acid (VFA) levels were always lower in reactors processing TFWWW (R2 and R4) and these values (<400 mg/L, as acetic acid) were lower than the suggested limits for digester failure. The specific methanogenic activity (SMA) was twice as high in reactors R2 and R4 than in R1 and R3 after 120 days of operation when all reactors operated at an OLR of 20 g COD/L d.

Numerical Simulations of a Biomass Fluidizing Bed with Side Port Air Injection FRANCINE BATTAGLIA, MIRKA DEZA, Virginia Tech, THEODORE J. HEINDEL, Iowa State University -Fluidized beds can be used to gasify biomass in the production of producer gas, a flammable gas that can replace natural gas in process heating. As part of the reactor design, side air ports strategically placed along the reactor column can help promote and improve mixing. Modeling these reactors using computational fluid dynamics is advantageous when performing parametric studies for design and scale-up. From a computational point of view, two-dimensional simulations are easier to perform than three-dimensional simulations, but they may not capture the proper physics. Comparisons of two-and three-dimensional simulations in a 10.2 cm diameter cold-flow fluidized bed with side air injection are used to determine when two-dimensional simulations are adequate to capture the bed hydrodynamics. The medium used to represent biomass is ground walnut shell, which has been shown to have desirable fluidization characteristics. The simulations will be quantitatively compared with X-ray computed tomography experiments for pressure drop through the bed, particle distribution and bed expansion height.

Simulations of fluidized beds are performed to study and determine the effect on the use of coordinate systems and geometrical configurations to model fluidized bed reactors. Computational fluid dynamics is employed for an Eulerian-Eulerian model, which represents each phase as an interspersed continuum. The transport equation for granular temperature is solved and a hyperbolic tangent function is used to provide a smooth transition between the plastic and viscous regimes for the solid phase. The aim of the present work is to show the range of validity for employing simulations based on a 2D Cartesian coordinate system to approximate both cylindrical and rectangular fluidized beds. Three different fluidization regimes, bubbling, slugging and turbulent regimes, are investigated and the results of 2D and 3D simulations are presented for both cylindrical and rectangular domains. The results demonstrate that a 2D Cartesian system can be used to successfully simulate and predict a bubbling regime. However, caution must be exercised when using 2D Cartesian coordinates for other fluidized regimes. A budget analysis that explains all the differences in detail is presented in Part II [N.

Sedimentation is still the most common method of biomass separation at majority of medium and large biological nutrient removal municipal wastewater treatment plants (BNR WWTP). In recent years some plants have been replacing this process with membrane separation and transforming their typical biological reactors into membrane units (MBR). This is often linked to the required increase in plant’s capacity and/or improvement in effluent quality. However, such modifications significantly affect plant functioning especially in regard to operation of biological processes, energy management and solids treatment. The article presents the results of computer simulation research on effects of the introduction of membrane filtration at a municipal BNR plant. The simulations allow to compare the most important operational parameters and effluent quality for the traditional layout with secondary clarifiers and the layout with membrane biological rectors. Wastewater treatment plants’ operators a...

The thermal exploitation of wastewood with Greek lignite was investigated by performing tests in a laboratory-scale fluidized bed reactor, a 1-MW th semi-industrial circulating fluidized bed combustor, and an industrial boiler. Blends of natural wood, demolition wood, railroad sleepers, medium-density fiberboard residues, and power poles with lignite were used, and the co-combustion efficiency and the effect of wastewood addition on the emitted pollutants were investigated. Carbon monoxide, sulfur dioxide, and oxides of nitrogen emissions were continuously monitored, and, during the industrial-scale tests, the toxic emissions (polychlorinated dibenzodioxins and dibenzofurans and heavy metals) were determined. Ash samples were analyzed for heavy metals in an inductively coupled plasma-atomic emission spectroscopy spectrophotometer. Problems were observed during the preparation of wastewood, because species embedded with different compounds, such as railway sleepers and demolition wood, were not easily treated. All wastewood blends were proven good fuels; co-combustion proceeded smoothly and homogeneous temperature and pressure profiles were obtained. Although some fluctuations were observed, low emissions of gaseous pollutants were obtained for all fuel blends. The metal element emissions (in the flue gases and the solid residues) were lower than the legislative limits. Therefore, wastewood co-combustion with lignite can be realized, provided that the fuel handling and preparation can be practically performed in large-scale installations.

Vorgelegt von Prof. Dr. F. CSAKI Die AufgabensteIlung Gesetzt, es werden n/ Arte n der Produkte auf n g Maschinen hergestellt. Die Anwendungsreihenfolge ist gleichgültig. Die Arbeitszeiten der einzelnen Maschinen für die Erzeugung der einzelnen Produkte werden durch die Matrix M = [mi,j] mit (ngX n;) Elementen dargestellt. Die Zahl der berücksichtigten Zeitintervalle während des Produktionsprogramms (Schicht, Tag, Dekade, usw.) sei nn' Die Matrix K = [ki,j] mit (nix nn) Elementen enthält die Fertigungs-

Production of xylene isomers and other alkylbenzene products in normal, near and supercritical toluene using unmodified beta zeolite catalyst and methanol were investigated. The effect of different parameters such as toluene/methanol ratio, temperature, pressure, and flow rate of the reacting materials were investigated. The production optimum conditions for alkylbenzenes are temperature of 623 K, pressure of 55 bar and flow rate of 0.2 mL min -1 using 1 g beta zeolite as catalyst with Si/Al = 38. The selectivity of 47% was achieved for p-xylene production, conversion of methanol and toluene were 100 and 65%, and the production yield and liquid selectivity of xylenes were 72 and 97%, respectively. The catalyst's activity was investigated in a 20 h period and the catalyst were characterized by XRD, TGA, and FT-IR methods.

ABSTRACT: Fluidized-bed reactors are widely used in the production of polyethylene. In this work, the quadrature method of moments (QMOM), a chemical reaction engineering (CRE) model, and computational fluid dynamics (CFD) are combined to investigate the role of intrinsic kinetics and the catalyst particle size distribution (PSD) in a gas phase fluidized bed reactor. The catalyst PSD is represented by a few nodes using the QMOM and an intrinsic rate model based on the age of particles is used to solve the evolution of particle ...

In this article, turbulent-gas two-phase in a fluidized bed is investigated and solved. In order to study the above effect, a reactor with different shapes and geometries has been considered and the effect of reactor shapes on the expansion volume of the solid bed has been investigated. The fluidized bed reactor is a types of reactors that can be used to perform multiphase chemical reactions, as well as in the field of producing gasoline and other fuels, many polymers such as rubber, vinyl chloride, polyethylene and styrene, nuclear energy units, burning coal, water purification units, The catalytic cracking process is also used as a dryer. In the inclined fluidized bed, the fluid velocity increases, which increases the product recovery and removes the dried product from the bed. The velocity of phases and particles inside the bed also increases and shows changes in the velocity profile of the solid. Increasing the column diameter decreases the axial solids velocity and smaller particle sizes have more discharge. Increasing the height of the bed reduces the static pressure and increases the frictional pressure. For this purpose, computational fluid dynamics is considered as a useful tool and the most likely method for correct prediction and optimization. In the present research, due to the expensiveness of the experimental method and the lack of equipment, numerical solutions were used.

Glucoamylase (EC 3.2.1.3. from Aspergillus niger) was immobilized onto the magnetic polystyrene particles including active groups. These particles were used in a magnetically stabilized fluidized bed reactor, and performance of this reactor was investigated. Magnetically stabilized fluidized bed reactor was made of a jacketed glass column and a coaxial selenoid covering the whole column as the magnetic field source. An axial and homogeneous magnetic field was introduced to the column by using direct current. The effects of flow rate and magnetic field intensity on the particle behaviour in the column were investigated. The optimum operational conditions for magnetically stabilized fluidized bed reactor were determined and the activity performance of the immobilized glucoamylase in the reactor was researched. Higher activities were obtained at low magnetic field intensities because of no additional diffusion problems coming from particle agglomeration occured in the column when the magnetic field intensity was high. It was found that the fluid flow rate in the column must be as low as possible because higher flow rates require higher magnetic field intensities to keep the particles in the column.

Computational fluid dynamic (CFD) models must be thoroughly validated before they can be used with confidence for designing fluidized bed reactors. In this study, validation data were collected from a fluidized bed of (Geldart's group B) alumina particles operated at different gas velocities involving two fluidization hydrodynamic regimes (bubbling and slugging). The bed expansion, height of bed fluctuations and frequency of fluctuations were measured from videos of the fluidized bed. The Eulerian-Eulerian two fluid model MFIX was used to simulate the experiments. Two different models for the particle stresses-Schaeffer [Syamlal, M., Rogers, W., O'Brien, T.J., 1993. MFIX documentation: theory guide. Technical Report DOE/METC-94/1004 (DE9400087), Morgantown Energy Technology Centre, Morgantown, West Virginia (can be downloaded from Multiphase Flow with Interphase eXchanges (MFIX) website ); Schaeffer, D.G., 1987. Instability in the evolution equations describing incompressible granular flow. Journal of Differential Equations 66, 61-74.] and Princeton [Srivastava, A., Sundaresan, S., 2003. Analysis of a frictional-kinetic model for gas-particle flow. Powder Technology 129(1-3), 72-85.] models-and different values of the restitution coefficient and internal angle of friction were evaluated. 3-D simulations are required for getting quantitative and qualitative agreement with experimental data. The results from the Princeton model are in better agreement with data than that from the Schaeffer model. Both free slip and Johnson-Jackson boundary conditions give nearly identical results. An increase in coefficient of restitution (e) from 0.8 to 1 leads to larger bed expansions and lower heights of fluctuations in the bubbling regime, whereas it leads to unchanged bed expansion and to a massive reduction in the height of fluctuations in the slugging regime. The angle of internal friction () in the range 10-40 • does not affect the bed expansion, but its reduction significantly reduces the height of fluctuations.

Reaction of silica (SiO2) with triethanolamine (TEA, N(CH2CH2OH)3) and ethylene glycol (EG) under conditions (∼200°C) where byproduct water is removed resulted in the formation of the neutral silatrane glycolate complex, N(CH2CH2O)3SiOCH2CH2OH (or TEASiOCH2CH2OH) in essentially quantitative yield. Solutions of this neutral precursor in EG, when rapidly pyrolyzed and then oxidized at 500°C, formed porous ceramic powders with high specific surface areas (&gt;500 m2/g). These powders were nitrided via ammonolysis in a fluidized‐bed reactor at temperatures of 700°‐1000°C. The resulting nitrided powders were characterized by thermal and chemical analyses, diffuse reflectance infrared spectroscopy, gas sorption, and X‐ray photoelectron spectroscopy. The apparent activation energy for the nitridation process was determined to be 54 kJ/mol. Following nitridation, the powders were amorphous and had nitrogen contents as high as 21 wt% with retained surface areas &gt;300 m2/g at 1000°C. Under ...

In traditional chemical reaction engineering, it is possible to incorporate only the simplified aspects of fluid flow, mixing, and mass/heat transfer into the analysis of chemical reaction rates and reactor design. As a consequence of the advent of high-speed, high-capacity computing capacity, complex processes involving chemical reactions have become amenable to analysis and modeling. This has also resulted in the merging of various disciplines of chemical engineering in formulating detailed descriptions of complex processes. Developments that exemplify this trend over the years are discussed in this review. Several examples from the author's previous work are used to illustrate the application of chemical reaction engineering principles to the modeling and analysis of complex systems involving the chemical processing of metals and other inorganic materials.

In this study, microscopic and molecular microbial analyses were integrated to characterize rapidly developing white filamentous tufts in a fluidized bed reactor used for nitrate removal from a marine recirculating fish culture system. Formation and rapid elongation of the tufts (often exceeding 50 mm day À1 ) was strongly correlated to transient elevated sulfide concentrations ( 4 50 mM) in the reactor. The dominant bacterial constituents of these tufts were filamentous gram-negative bacteria with densely packed intracellular sulfur granules. Using 16S rRNA gene analysis and fluorescence in situ hybridization it was found that these filamentous bacteria represented a novel Thiothrix phylotype closely related (97% sequence identity) to a previously identified Thiothrix strain endogenous to the marine crustacean Urothoe poseidonis. In addition to filamentous morphotypes, rosetteshaped morphotypes of Thiothrix were also detectable within the tufts.

In recent years, inulin enzymatic hydrolysis has become a very promising alternative for producing fructose on a large scale. Genetically modified chicory was used to extract inulin of industrial quality. By using an adequate kinetic model from the literature, this study aimed to determine the optimal operating alternatives of a batch (BR) or fed-batch (FBR) reactor used for the hydrolysis of inulin to fructose. The operation of the FBR with a constant or variable/dynamic feeding was compared to that of the BR to determine which best maximizes reactor production while minimizing enzyme consumption. Multi-objective optimal solutions were also investigated by using the Pareto-optimal front technique. Our in-silico analysis reveals that, for this enzymatic process, the best alternative is the FBR operated with a constant control variable but using the set-point given by the (breakpoint) of the Pareto optimal front under the imposed technological constraints. This set point reported the best performances, regarding all the considered opposite economic objectives. Also, the FBR with a constant, but NLP optimal feeding, reported fairly good performances.

Production of ligninolytic enzymes by white-rot fungi is a phenomenon typically associated to the secondary metabolism, the main drawback of which is the limited yield of the enzyme obtained under growth-limiting conditions and the morphological behaviour of these filamentous microorganisms while growing. An efficient production system is needed for the promising applications of these enzymes in bioprocesses such as detoxification of effluents and biobleaching of kraft pulp. Several bioreactor configurations were considered which were operated in batch or semi-continuous modes. These operational conditions permitted high titres of enzymatic activity, however, the extent of production was limited. A different modus operandi is then to be proposed to overcome these limitations. The present work reviews the state of production of ligninolytic enzymes and proposes a new method to achieve continuous production of manganese peroxidase (MnP). The method comprises a feeding policy based on controlled feed rates of nutrients and the use of an adequate bioreactor configuration. They were both key factors to attain and sustain continuous production of MnP. The feeding of limited concentrations of nutrients kept secondary metabolism in steady-state conditions and limited the fungal growth. The configuration of two conventional bioreactors (fluidised bed and fixed bed bioreactors) was modified with the introduction of pulsation of gas. Pulsation proved to be a good alternative to enhance nutrients and oxygen transfer as well as to maintain fungal cultures as independent bioparticles both for pellets and foam blocks of mycelia. Other environmental factors such as a Mn 2 + concentration of 5 mM and high oxygen tension enhanced MnP production. The hydraulics of the bioreactor also had effect on MnP production, the optimum corresponded to a plug flow model with partial mixing and an operating HRT of 24 h. This policy facilitated long operation periods, obtaining higher productivity rates than the best reported to date.

In the case of A. niger. the pellet diameter corresponding to the pulsed system operated at 0.35 s-r was kept between 3.3 ? 0.1 mm after 22 days of operation: however, in the nonpulsed bioreactor which was operative for only 11 days, pellets with a diameter of 6.7 f 0.3 mm were produced. Similar results were obtained in the case of P. chtysosporium, since with a pulsing frequency of 0.0625 s-l, a pellet diameter of 2.1 f 0.4 mm after 34 days of operation was maintained. On the contrary, the system without pulsation presented great conglomerates of mycelia with an average diameter of 3 cm surrounded by free pellets with a diameter distribution of 2.75 * 0.5 mm. The nonpulsed bioreactor was only operative for 14 days. Both citric acid and manganese peroxidase production attained higher values and were maintained longer in the pulsed bioreactor.

This work investigated the removal of the reactive green (R.G) dye from wastewater using the photo-Fenton process. Batch experiments were carried out to research the role of the Impacts of operating parameters. The dosage of H2O2; dosage Fe+2; pH; temperature, and irradiation time were examined. Maximum decolorization efficiencies green dye were achieved at the [H2O2]=100 ppm; [Fe2+]=20 ppm; pH 3; temperature=56 °C and irradiation time=90 min. This research focuses on modeling, kinetics and thermodynamics of the removal of pollutant (reactive green dye) of water. The results showed that the decolorization kinetic of R.G followed pseudo-first-order reaction kinetic. Also the thermodynamic parameters ∆G˚, ∆H˚ and ∆S˚ were determined using the Van&#39;t Hoff equation for the oxidation processes. The changes in Gibbs free energy showed the oxidation process under normal conditions is non-spontaneous.

A new process utilizing pulsed fluidized limestone beds was tested for the remediation of acid mine drainage at the Friendship Hill National Historic Site, in southwestern Pennsylvania. A 230 liter-per-minute treatment system was constructed and operated over a fourteen-month period from June 2000 through September 2001. Over this period of time, 50 metric tons of limestone were used to treat 50 million liters of water. The influent water pH was 2.5 and acidity was 1000 mg/L as CaCO 3 . Despite the high potential for armoring at the site, effluent pH during normal plant operation ranged from 5.7 to 7.8 and averaged 6.8. As a result of the high influent acidity, sufficient CO 2 was generated and recycled to provide a net alkaline discharge with about 50 mg/L as CaCO 3 alkalinity. Additions of commercial CO 2 increased effluent alkalinity to as high as 300 mg/L, and could be a useful process management tool for transient high flows or acidities. Metal removal rates were 95% for aluminum (60 mg/L in influent), 50 to 90% for iron (Fe), depending on the ratio of ferrous to ferric iron, which varied seasonally (200 mg/L in influent), and <10% of manganese (Mn) (10 mg/L in influent). Ferrous iron and Mn removal was incomplete because of the high pH required for precipitation of these species. Iron removal could be improved by increased aeration following neutralization, and Mn removal could be effected by a post treatment passive settling/oxidation pond. Metal hydroxide sludges were settled in settling tanks, and then hauled from the site for aesthetic purposes. Over 450 metric tons of sludge were removed from the water over the life of the project. The dried sludge was tested by the Toxicity Characteristics Leaching Protocol (TCLP) and was found to be non-hazardous.

Experiments and simulations are performed to study flow behavior in biomass gasification reactor. Glass beads of particle size 350 µm and density 2500 kg/m 3 are used for experiments and simulations. A validated CFD model is established. Using the same CFD model, simulation is performed for quartz sand of particle size 500 µm fluidized with high temperature steam which is used as bed material in the gasification reactor.

Particle receivers are gaining much interest mainly for their potential of high temperature operation and as thermal energy storage Dense gas-solid suspensions thanks to their excellent thermal properties  RECEIVER: Collection of highly concentrated (100-1000 suns) incident solar radiation  EXCHANGE: heat transfer to the working fluid of the thermodynamic cycle  STORAGE: thermal energy for equalizing the inherent timevariability of the incident solar radiation System optimized to accomplish three complementary tasks: Challenge: compartmented fluidization without physical confinements just by partitioning of the fluidizing gas to a compartmented distributor to preserve the fluidized bed thermal properties Conclusions

The stability, in long-term operation, of fluidized bed reactors utilised to pyrolyse plastics waste can be seriously compromised by particle agglomeration phenomena. These phenomena can cause poor fluidization and eventually lead to defluidization. In order to investigate this phenomenon, a polypropylene waste from a food-packaging industry was utilised in a laboratory-scale bubbling fluidized Ž . bed reactor. The effect of the main operating variables bed hold-up, size of inert material, fluidizing velocity, feed rate of plastic pellets was investigated by means of experiments carried out under an inert atmosphere. The time at which defluidization occurred was correlated with some process variables by means of linear relationships. A new modelling approach was also proposed in order to predict the risk of defluidization under different operating conditions.

Fluidized bed pyrolysis is a special class of feedstock recycling processes for plastics recycling which provides for a rather uniform spectrum of products, reduces the maintenance time and cost and gives the possibility to apply the process even on a relatively small scale. The present study describes investigations carried out by injecting recycled polyethylene in a laboratory scale fluidized bed reactor, batchwise or continuously operated. The batchwise experiments allowed to investigate the polymer-to-particles interactions inside the fluidized bed reactor, which strongly affect the phenomenology and the rate of polymer degradation. The continuous experiments indicated how the yield and the composition of products are affected by two key operating variables of the process: the bed temperature and the residence time in the reactor.

Seven mixtures of coals, plastics and wood have been pelletized and fed into a pre-pilot scale fluidized bed gasifier in order to investigate the main aspects of the co-gasification of these materials. The main components of the obtained syngas (CO, H 2 , CO 2 , N 2 , CH 4 , C n H m ) were measured by means of on-line analyzers and a gas cromatograph. The performance of the gasifier was evaluated on the basis of syngas composition, carbon conversion efficiency, energy content of syngas, cold gas efficiency and yield of undesired by-products (tar and soot-like particulate). The results of a first series of experimental tests showed the effect of gas fluidizing velocity and that of equivalence ratio on the main performance parameters for a specific coal-plastics mixture. A second series of tests has been carried out by changing the mixture composition keeping fixed the gas velocity and equivalence ratio. The presence of wood and coal in the mixture with plastics contributed to reduce the tar production even though it is accompanied by a lower syngas specific energy.

The paper studies in depth a new technique for mass production of MWCNTs that is based on thermal cracking of polymers in a solid-gas fluidized bed reactor, operated under specific thermal and hydrodynamic conditions. The paper provides information about the phenomenology of interactions between the bed material and the polymer particles injected into the fluidized bed reactor, which in turn affect the mechanism of formation of MWCNTs. Results obtained with different reactor temperature and bed materials are reported in terms of yield and quality of obtained MWCNTs, all characterized by TG-DTA, SEM and TEM microscopy and Raman spectroscopy. It is noteworthy that high-quality MWCNTs were obtained from virgin or recycled polyolefins as well as from recycled polyethylene terephtalate. * These values have not been used for y CNT calculation due to excessive contamination related to waxes stuck on the wall. ** In the case of the test with PET the sample obtained by the reactor wall and by the external line is quite the same due to the less amount of waxes and oil produced with PET pyrolysis. As a consequence the y p value utilized to calculate the MWCNT yield is the mean value instead of

A new technique for a continuous, mass production of high-quality multi-wall carbon nanotubes (MWCNTs), based on fluidized bed pyrolysis of polymers (virgin or recycled polyolefins and recycled polyethylene terephtalate), is described in detail. The study investigates the role of interactions between the bed material and the polymer particles injected into the reactor as well as that of the reactor temperature. Results are reported in terms of yield and quality of obtained MWCNTs, all characterized by thermogravimetrical analysis and SEM microscopy. The production of MWCNTs, in a relatively large quantity and at a low cost, is demonstrated as technically feasible.

Gasification is a thermochemical process that aims to convert solid fuels into a synthetic gas that can be addressed to an end-use apparatus to produce electric energy and heat or can be further refined to be transformed in chemical valuable products. Many solid fuels, included waste (wood, biomass, plastics, municipal solid waste, etc.), can be gasified under different operating conditions (pressure, temperature, reactants) in different kind of reactors. This paper aims to correlate the descriptive model for the gasification of a mixture of commodity plastic waste to the basic design of a bubbling fluidized bed gasifier on the basis of experimental data and mathematical calculations.