Fluidization Behavior in a Gas- Solid Fluidized Bed with Thermally Induced Inter-Particle Forces

In this work, a new approach for increasing and controlling inter-particle forces (IPFs) was applied. This method used a spherical inert particle coated with a polymer material having a low glass transition temperature. Since IPFs depend on the temperature of the coated particles, they can be easily controlled by the temperature of the inlet air. For this reason, the temperature of the system was varied uniformly near the glass transition temperature of the polymer, between 20 – 40oC, to investigate the effect of IPFs on fluidization behavior at low and high gas velocitie

Characterization of Fluidization and Mixing of Binary Mixtures Containing Biomass at Low Velocities Through Analyzing Local Pressure Fluctuations

To judge qualitatively the effect of biomass properties on its fluidizability and mixing tendency with sand particles at low fluidization velocities, local pressure gradients in the top and bottom of the bed were compared for all investigated systems. It was found that changing the mass fraction and the size of biomass impacted the onset of bubbling and the size of bubbles across the bed, which, in turn, affected the mixing/segregation of the bed content

Investigation of DNA changes in wheat (Triticum aestivum L.) induced by cadmium using random amplified polymorphic DNA (RAPD) analysis

In recent years, many plants have been used as bioindicators or living indices and several experiments have been conducted to evaluate the genotoxic effects of environmental pollution on plant species. Plants such as Arabidopsis and barley have been used as biological indicators by several researchers and have been able to identify DNA changes using molecular markers. This study was conducted on wheat as an important cereal that provides human daily food and has an important role in human health. The purpose of study was to evaluate the effect of different concentrations of cadmium on amounts of the soluble proteins, investigation of growth and possible changes to the structure of DNA using random amplified polymorphic DNA (RAPD) marker. In the present study, wheat seedlings were used for detection of genotoxic effects of cadmium contamination in the range of 0 to 120 mg-1. The limiting effects of cadmium on length of root and plant height and total soluble proteins in root were quite evident by increase of cadmium concentration. Change in DNA was observed using RAPD marker as there was change in number of bands, present or absent of bands at the range of above 5 mg-1 cadmium concentration. In the previous studies conducted by several researchers, variation in DNA bands was reported at levels above 30 mg-1, whereas in the present study, band variation was observed at the concentration of 5 mg-1. This study also showed that DNA stability is highly affected by cadmium pollution at >5 mg-1 which was identified by RAPD markers.Keywords: Bioindicator, cadmium, genotoxic, random amplified polymorphic DNA (RAPD) marker, Triticum aestivum LAfrican Journal of Biotechnology Vol. 12(16), pp. 1921-192

Characterization of Hydrodynamics and Solids Mixing in Fluidized Beds Involving Biomass

L'intérêt croissant pour l'utilisation de la biomasse comme source renouvelable d'énergie propre a entraîné l'application vaste d'unités de traitement thermique de la biomasse à travers le monde. Ces unités, qui sont principalement basées sur la fluidisation gaz-solide, souffrent de certains obstacles hydrodynamiques tels que la ségrégation du lit. En outre, les aspects d'écoulement multiphasiques complexes de ces unités ont toujours demeuré largement inconnus. Par conséquent, la réalisation d'une recherche approfondie sur ce domaine est cruciale pour le design et l’optimisation du fonctionnement des unités de biomasse à lit fluidisé. Cette thèse se concentre donc sur la caractérisation de l'hydrodynamique et les phénomènes de mélange dans les lits fluidisés contenant des mélanges de sable et de particules irrégulières de biomasse. Le premier objectif de cette étude est de comprendre l'effet des grosses particules de biomasse sur les caractéristiques des bulles et le type de distribution de gaz dans les lits fluidisés de sable. Cela est essentiel pour atteindre le deuxième objectif qui est la caractérisation de mélange/ségrégation de la biomasse et des particules de sable dans les conditions de fluidisation. Explorer les paramètres régissant le mélange/ségrégation est utile pour ajuster les conditions d'exploitation afin d'améliorer ce phénomène bénéfique pour le système. En conséquence, la ségrégation est exploitée dans le dernier chapitre de cette thèse afin de séparer les composants combustibles des déchets solides municipaux par un processus par étapes. Une variété de techniques expérimentales est utilisée pour étudier le comportement des deux phases constituant un lit fluidisé, soit phase diluée (bulle) et dense (émulsion). L'exploration des vitesses de fluidisation pour les mélanges de sable et de biomasse dévoile que l'apparition des bulles dans ce système se produit à une vitesse de gaz plus élevée par rapport à la vitesse de fluidisation initiale de fluidisation (Uif). La vitesse initiale de bullage (Uib), la vitesse de fluidisation finale (Uff), et la vitesse du gaz de transition du régime de bullage au régime turbulent (Uc) augmentent avec l'augmentation de la fraction de la biomasse dans le mélange. Les fluctuations locales des signaux de pression et de porosité sont mesurées dans des positions différentes du lit à l'aide de capteurs de pression absolue et différentielle et des sondes à fibre optique. L'analyse statistique du signal de pression au dessus du lit révèle que l'augmentation de la charge de la biomasse empêche l’évolution des bulles à faible vitesse de gaz (U<0,6 m/s), tandis qu’à des vitesses élevées, la tendance de propagation de lits contenant différentes fractions de la biomasse est comparable. L’ajout de particules de biomasse à un lit de sable conduit à augmenter la porosité moyenne du lit, mais le degré de vide de chaque phase reste inchangé. On observe que les grandes particules de biomasse déclenchent l’éclatement de bulles, ce qui mène à l’augmentation de la fréquence de bullage. La fraction de bulles au centre du lit augmente avec la charge de biomasse. Cependant, en ajoutant 2% en masse de la biomasse au sable pur, cette fraction diminue à la paroi puis augmente à l’addition de biomasse supplémentaire. La technique de suivi des particules radioactives (RPT) est mise en œuvre dans la deuxième partie de ce travail pour étudier le mouvement et la distribution des particules de biomasse à U=0,36 m/s et U=0,64 m/s. À cet égard, une particule active de biomasse est suivie pour une longue période de temps et sa position instantanée est enregistrée. Les données acquises sont ensuite traitées pour obtenir le profil de concentration moyenne temporelle des particules de biomasse. Ce profil représente la ségrégation des particules de biomasse qui ont tendance à s'accumuler dans les niveaux supérieurs du lit. Les variations de la fraction de la biomasse avec la vitesse de la fluidisation sont déduites des changements locaux des valeurs de perte de charge moyenne temporelle au dessus du lit. Pour déterminer les paramètres affectant le mouvement et la ségrégation des particules de biomasse, le mouvement circulatoire de la biomasse est également examiné en utilisant les données RPT. A U=0,36 m/s, La circulation de la biomasse est empêchée lorsque la charge de biomasse monte, ce qui entraîne une ségrégation plus prononcée du sable et de la biomasse. Une tendance inverse est observée à U=0,64 m/s, lorsque la charge de la biomasse augmente de 2% à 16% en masse. C’est à dire, plus de particules de biomasse peuvent compléter leur circulation tout en coulant dans les parties les plus profondes du lit. Cela provoque une répartition plus uniforme de particules le long du lit et amène un plus haut degré de mélangeage. Ces phénomènes pourraient être directement liés à l'activité de bullage du lit qui est influencée par la vitesse du gaz et de la composition du lit, comme indiqué dans la première partie de cette étude. Sur la base des résultats RPT, la vitesse d'augmentation moyenne de la biomasse est de 0,2 fois la vitesse de bulle, indépendamment de la charge de biomasse ou de la vitesse de fluidisation. Un modèle unidimensionnel est proposé afin de prévoir la fraction volumique de la biomasse le long du lit. Certains des termes de ce modèle sont liés au comportement de fluidisation des particules de biomasse, déduits par RPT. Les résultats de ce modèle pourraient prédire avec succès les valeurs expérimentales correspondantes. La fluidisation du sable et des particules de biomasse cylindriques est aussi simulé à l'aide du logiciel BARRACUDA CPFD, qui est basé sur la méthode Lagrange-Eulérienne. Les résultats des simulations et des expériences sont comparés dans le but d'évaluer la capacité de l'approche numérique pour prédire les caractéristiques de propagation du mélange sable-biomasse pour les systèmes différents en termes de composition et de vitesse de fluidisation. L'approche numérique choisie pourrait prédire avec succès la mesure de l'expansion du lit pour chaque espèce (sable ou biomasse). En outre, les propriétés statistiques de la distribution de la taille et la vitesse des bulles –telles que la moyenne, l’écart-type et l'asymétrie –obtenues à partir de la simulation sont comparables avec les valeurs expérimentales correspondantes. La dernière partie de cette thèse est consacrée à la séparation des principaux composants des déchets encombrants déchiquetés. Le motif derrière cela est la nécessité du contrôle de la composition des combustibles dérivés de déchets solides pour promouvoir l'efficacité de la combustion et de réduire le niveau des émissions qui en résultent. À cet effet, les écoulements presque purs des éléments combustibles dérivés des déchets solides sont exigés de fabriquer un combustible souhaitable. À cet égard, un processus par étapes est développé sur la base des phénomènes d’élutriation et de ségrégation. Après élimination des espèces légères et entrelacées de déchets déchiquetés par élutriation, les matériaux non élutriés sont en outre séparés dans deux colonnes successives de fluidisation. Polypropylène et perles de verre sont introduits comme les médias de fluidification dans ces colonnes afin de rendre la ségrégation des composants cible et non-cibles possibles. Par conséquent, les matériaux combustibles indésirables et les particules de plastique dur sont séparés comme le trop-plein de la première et la deuxième étape de fluidification. Une deuxième colonne d'élutriation est également conçue pour séparer la fibre et le plastique mou. Les pourcentages de recouvrement et la pureté des étapes constituant le processus global sont respectivement de 95% et 47% dans les conditions de fonctionnement optimales. Pour déterminer ces conditions, plusieurs paramètres d'influence tels que la vitesse d'élutriation, la durée de l'élutriation, la taille et la densité des médias de fluidisation et de la configuration initiale du déchet et les matières du lit sont explorés. La cinétique de ségrégation est également dérivée pour les deux étapes de fluidification. ---------- Growing interest in the use of biomass materials as a clean and renewable source of energy has resulted in the widespread application of thermal biomass processing units across the world. These units, which are mainly based on gas-solid fluidization, suffer from some hydrodynamic hurdles, such as the segregation of bed inventory. In addition, the complex multiphase flow aspects of these units have still remained largely unknown. Hence, conducting comprehensive research in this field is crucial for the optimal design and operation of fluidized bed biomass units. This thesis, therefore, focuses on the characterization of hydrodynamics and mixing phenomena in fluidized beds containing mixtures of sand and irregular biomass particles. In the first two chapters of this thesis the principal aspects of the hydrodynamic phenomena in fluidized beds involving biomass are briefly discussed and the most significant relevant findings are reviewed. The first objective of this study is understanding the effect of the large biomass particles on the bubbling characteristics and gas distribution pattern of sand fluidized beds. In this regard, the third chapter of this thesis is devoted to studying the local and global pattern of gas distribution between the dilute (bubble) and dense (emulsion) phases of a fluidized bed composed of sand and different weight fractions of biomass (2–16%). This is essential for achieving the second objective, which is the characterization of mixing/segregation of biomass and sand particles under fluidization conditions. It is the subject of the forth chapter of the present thesis in which the axial distribution of large biomass particles in a sand-biomass fluidized bed is discussed. In view of the growing importance of the numerical simulations in optimal design and operation of biomass fluidized bed units, the fifth chapter of this thesis focuses on the experimental validation of a Lagrangian-Eulerian numerical approach simulating fluidization of both sand and biomass particles. Exploring the parameters governing mixing/segregation is helpful to adjust the operating conditions to enhance either phenomenon that is beneficial. Accordingly, segregation is exploited in the sixth chapter of this thesis to separate the main combustible components of the shredded bulky waste through a step-wise process. A variety of experimental techniques are employed to study the behavior of two constituting phases of a fluidized bed, i.e., dilute (bubble) and dense (emulsion) phases. Exploring the characteristic fluidization velocities of sand-biomass mixtures unveils that the onset of bubbling in these systems occurs at a higher gas velocity compared to that of the initial fluidization velocity (Uif). The initial bubbling velocity (Uib), the final fluidization velocity (Uff), and the transition gas velocity from bubbling to turbulent regime (Uc) rise by increasing the fraction of biomass in the mixture. The local fluctuations of the pressure and voidage signals are measured in different positions of the bed using absolute and differential pressure transducers and optical fiber probes. Statistical analysis of the pressure signal at top of the bed reveals that increasing the biomass load hinders the evolution of bubbles at a low gas velocity (U<0.6 m/s), while at high velocities, the bubbling trend of beds containing different fractions of biomass is comparable. The addition of biomass particles to a bed of sand leads to an increase in the mean voidage of the bed; however, the voidage of each phase remains unaffected. It is observed that large biomass particles trigger a break-up of the bubbles, which results in boosting bubbling frequency. The fraction of bubbles at the center of the bed increases with the load of biomass. At the wall region, however, it starts to decrease by adding 2% wt. biomass to pure sand and then increases with the further addition of biomass. The Radioactive Particle Tracking (RPT) technique is implemented in the second section of this work to study the motion and distribution of biomass particles at U=0.36 m/s and U=0.64 m/s. In this regard, an active biomass particle is tracked for a long period of time and its instantaneous position is recorded. The acquired data is then processed to achieve the time-averaged concentration profile of biomass particles. This profile represents the segregation of biomass particles, which tend to accumulate in the upper levels of the bed. Changes in the fraction of biomass with increasing gas velocity are inferred from the local changes of the time-averaged pressure drop values at the top of the bed. To determine the parameters affecting the movement and segregation of biomass particles, their circulatory motion is also scrutinized using the RPT data. The circulation of biomass is impeded when the load of biomass rises at U=0.36 m/s, resulting in a more pronounced segregation of sand and biomass. The opposite trend is observed at U=0.64 m/s, i.e., when the biomass load increases from 2% to 16% wt., more biomass particles can successfully complete their circulation while sinking to the deeper parts of the bed. This prompts a more uniform distribution of particles along the bed and brings about a higher degree of mixing. These phenomena could be directly related to the bed bubbling activity which is influenced by the gas velocity and the composition of the bed inventory as noted in the first part of this study. Based on the RPT results, the average rise velocity of biomass is 0.2 times the bubble velocity, regardless of the biomass load or fluidization velocity. A one-dimensional model is proposed to predict the volume fraction of biomass along the bed. Some of the terms of this model are linked to the fluidizing behavior of biomass particles as deduced from the RPT findings. The model’s results could successfully predict the corresponding experimental values. The fluidization of sand and cylindrical biomass particles is also simulated using the BARRACUDA CPFD software, which is based on the Lagrangian-Eulerian approach. Simulation and experimental results are compared in order to evaluate the capability of the numerical approach to predict the bubbling characteristics of the sand-biomass mixture for systems differing in composition and fluidization velocity. The chosen numerical approach could successfully predict the extent of bed expansion for each species (sand or biomass particles). Moreover, the statistical properties of the distribution of both bubble size and velocity such as mean, standard deviation and skewness, obtained from the simulation are fairly comparable with the corresponding experimental values. The last part of this thesis is devoted to the separation of the main components of the shredded bulky waste. The motive behind this is the necessity of controlling the composition of the solid waste-based Engineered Fuel (EF) to promote combustion efficiency and lower the level of the resulting emissions. For this purpose, nearly pure streams of the combustible components derived from the municipal solid waste (MSW) are required to make a tailored EF. Therefore, a step-wise process has been developed based on the elutriation and density segregation techniques. After removal of the light and interwoven species of the shredded waste by elutriation, the non-elutriated materials are further separated into two successive fluidization columns. Polypropylene and glass beads are introduced as the fluidization media in these columns in order to make density segregation of the target and not-target components possible. Hence, undesirable combustible matters and hard plastic are separated as the overflow of the first and second fluidization steps. A second elutriation column is also devised to separate and recover fiber and soft plastic. The recovery and purity percentages of the steps of the overall process are respectively over 95% and 47% under optimal operating conditions. To determine these conditions, several influential parameters, such as the elutriation velocity and time, the size and density of the fluidization media, and the initial configuration of the feedstock and bed material, are explored. The kinetics of segregation is also derived for both fluidization steps

The relationship between fluidized bed electrostatics and entrainment

Existing methods of predicting entrainment from gas-fluidized beds, based exclusively on hydrodynamic variables and mechanisms, show extremely wide discrepancies in their predictions and often deviate by many orders of magnitude from experimental values. Based on simultaneous measurement of electrostatic charges in the freeboard region and entrainment, this paper will show that inter-particle electrostatic forces on relatively fine particles can be at least of the same order of magnitude as the gravity forces that must be overcome for entrainment to take place. Moreover, incorporation of a term for inter-particle electrostatic force leads to substantial improvement in the ability to correlate our experimental entrainment data. These results show that it is essential to consider electrostatic forces when predicting entrainment from gas-fluidized beds

Sand-assisted fluidization of large cylindrical and spherical biomass particles: Experiments and simulation

In this study, bubbling fluidization of a sand fluidized bed with different biomass loadings are investigated by means of the experiments and numerical simulation. The radioactive particle tracking (RPT) technique is employed to explore the impact of the particle shape factor on the biomass distribution and velocity profiles when it is fluidized in a 152 mm diameter bed with a 228 mm static height. Using a pair of fiber optic sensors, the bubbling characteristics of these mixtures at the upper half of the dense bed are determined at superficial gas velocities ranging from U=0.2 m/s to U=1.0 m/s. The experimental results show that despite cycling with a similar frequency, spherical biomass particles rise faster and sink slower than the cylindrical biomass particles. Furthermore, bubbles are more prone to break in the presence of biomass particles with lower sphericity. In the separate series of experiments, the reliability of the “frozen bed” technique to quantify the axial distribution of biomass particles is assessed by the RPT results. Using NEPTUNE_CFD software, three-dimensional numerical simulations are carried out via an Eulerian n-fluid approach. Validation of the simulation results with the experiments demonstrates that, in general, simulation satisfactorily reproduces the key fluidization and mixing features of biomass particles such as the global and local time-average distribution and velocity profiles

Quantitative comparison of ammonia and 3-indoleacetic acid production in halophilic, alkalophilic and haloalkalophilic bacterial isolates in soil

In order to measure the concentration of ammonia production via corrected Nesslerization method and 3-indoleacetic acid as Salkowski method in halophilic, alkalophilic and haloalkalophilic bacterial isolates, soil samples were collected from six different areas of Khorasan Razavi and bacterial isolates isolated and purified using different growth medium accordingly. The alkalophiles isolates showed maximum ammonia production (0.055%) among the three groups of bacteria which this amount was 9.5 times of its average in haloalkalophiles isolates (0.0058%) and 13 times of ammonia production average in halophiles (0.004%). Mean comparison of the concentration3-indoleacetic acid production in three groups also showed that the most isolates of halophiles, alkalophiles and haloalkalophiles were IAA producer with 0.0003, 0.0001 and 0.0021percent respectively that the IAA amount in haloalkalophilic group was about 6 and 14.5 times of it in halophilic and alkalophilic isolates respectively. Equations to predict the concentration of ammonia and 3-indole acetic acid production was only significant in the haloalkalophilic isolates for ammonia production (P=0.046) and halophilic isolates for IAA production (P=0.015) under effect of electrical conductivity and pH in 0.05 probability level. Results represented that the multiple regression analysis for prediction of ammonia and IAA concentrations producing by isolates had not any significant performance in high and low concentrations under effect of electrical conductivity and pH. It seems that the uses of the two sensitive measuring methods (Nesslerization and Salkowski) after some modifications show promises and are recommend able in research due to their ease of implementation and relatively accurate results.Keywords: Alkalophiles; haloalkalophiles; halophiles; 3-indoleacetic acid; nesslerization method; salkowski method

Impact of Silicon Foliar Application on the Growth and Physiological Traits of Carthamus tinctorius L. Exposed to Salt Stress

Althought safflower is a tolerant crop against many environmental stresses, but its yield and performance reduce under stress. The aim of this experiment was to investigate the effect of silicon (Si) application on the possibility of increasing salinity resistance and related mechanisms in safflower. A greenhouse experiment was conducted to investigate the effects of Si spraying (0, 1.5 and 2.5 mM) on safflower plants grown under salt stress condition (non-saline and 10 dS m−1). Salinity reduced seedling emergence percent and rate, growth parameters and disrupted ion uptake but increased emergence time and specifc leaf weight. Spraying of Si increased plant height, fresh and dry weight, leaf area, relative water content (RWC), potassium, calcium and silicon content, while sodium absorption was decreased. As a result, the K+/Na+ and Ca2+/Na+ ratios were increased. Elevated ion contents and ratios indicate an enhanced selectivity of ion uptake following silicon application and may increase ion discrimination against Na+. Treatment with 2.5 mM Si showed the most positive effect on the measured growth traits. Decrement in leaf area ratio under salinity indicates a more severe effect of salinity on leaf area compared to biomass production. On the other hand, silicon reduced the specific leaf weight under stress and non-stress conditions, which revalues the positive effects of silicon on leaf area expansion. Improvement of RWC may a reason for the icrease in leaf area and biomass production. Data shows that spraying with Si especialy with 2.5 mM can reduce salinity stress damage to safflower and increase biomass production