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In firing systems of cement production plants and coal-fired power plants, regular fossil fuels are increasingly substituted by alternative fuels. Rising energy prices and ambitious CO2-reduction goals promote the use of alternative fuels as a significant contribution to efficient energy recovery. One possibility to protect energy resources are refuse-derived fuels (RDF), which are produced during the treatment of municipal solid, commercial and industrial waste. The waste fractions suitable for RDF have a high calorific value and are often not suitable for material recycling. With current treatment processes, RDF still contains components which impede the utilization in firing systems or limit the degree of substitution. The content of these undesired components may amount to 4 wt%. These, in most cases incombustible particles which consist of mineral, ceramic and metallic materials can cause damages in the conveying systems (e. g. rotary feeder) or result in contaminations of the products (e. g. cement, chalk). Up-to-date separation processes (sieve machine, magnet separator or air classifier) have individual weaknesses that could hamper a secure separation of these particles. This article describes a new technology for the separation of impurities from refuse derived fuels based on a rotating fluidized bed. In this concept a rotating motion of the particle bed is obtained by the tangential injection of the fluidization gas in a static geometry. The RDF-particles experience a centrifugal force which fluidized the bed radially. The technical principle allows tearing up of particle clusters to single particles. Radially inwards the vertical velocity is much lower thus particles of every description can fall down there. For the subsequent separation of the particles by form and density an additionally cone shaped plate was installed in the centre. Impurities have a higher density and a compact form compared to combustible particles and can be separated with a high efficiency. The new technology was experimentally investigated and proven using model-RDF, actual-RDF and impurities of different densities. In addition, numerical simulations were also done. The fluidization chamber was operated in batch mode. The article describes experiences and difficulties in using rotating fluidized bed systems.

The fast pyrolysis of spruce (Picea abies), short rotation willow coppice (Salix alba), Miscanthus (Miscanthus x giganteus), and wheat straw (Triticum aestivum) was compared on a laboratory scale bubbling fluidized bed reactor at 460–475 °C. The presence of ash, ranging from 0.26 wt.% for spruce to 3.76 wt.% for wheat straw (moisture free basis) favoured decomposition of cell-wall constituents to char (spruce [11.4 wt.%] < Salix [16.2 wt.%] < Miscanthus [21.8 wt.%] < wheat straw [21.5 wt.%]) with a reduction of liquid organic product (spruce [53.8 wt.%] > Salix [45.4 wt.%] > Miscanthus [37.3 wt.%] > wheat straw [37.2 wt.%]). Bio-oils from Miscanthus and wheat straw were inhomogeneous. Differences between absolute masses of compounds determined by GC/MS-FID of the bio-oils compared with Py-GC/MS-FID suggested a greater role of secondary reactions at the fluidised bed scale, with reduced concentrations of certain lignin-derived, furan and pyran compounds. Science Foundation Ireland Charles Parsons Energy Research Program

As general restrictions for the design of Oxyfuel pulverised coal-fired (PC) steam generators are commonly known, the purpose of this work is to show general restrictions for the design of an Oxyfuel coal-fired steam generator using a circulating fluidised bed combustor (CFBC) with external heat exchangers (EHEs). For the CFBC restrictions result on the one hand out of the used fuels composition. On the other hand certain restrictions out of state-of-the-art and steam generator geometries have to be considered within the design. © 2013 The Author.

In this work a novel measurement technique for pseudo-2D fluidised beds is developed. The objective is to give an estimation of the overall frictional force between the solids and the front and rear walls of the bed. For doing this, the measured pressure signal in the bed is processed in combination with the solids distribution (i.e. centre of mass position, velocity and acceleration) obtained from digital image analysis of the optically accessible front view of the bed. This is performed by acquiring the pressure signal in the bed simultaneously to the digital images. Both the pressure and the digital images are connected through a simple force balance in the bed, and a particle-wall interaction coefficient is obtained assuming that the overall frictional force is proportional to the centre of mass velocity. The particle-wall interaction coefficient found using this technique is of the order of 40-120 kg/m(2) s in the bed tested, and the standard deviation of the frictional forces reaches more than 70% of the weight of the bed. Therefore, the results indicate that the contribution of the particle-to-wall friction on the fluctuation of the pressure drop in a pseudo-2D bed is not negligible. This work has been partially funded by the Spanish Government (Project DPI2009-10518) and the Autonomous Community of Madrid (Project S2009/ENE-1660). Publicado

In the present study, particulate emissions from the co-combustion of forest biomass residues with sewage sludge in a pilot-scale bubbling fluidised bed combustor were characterised. The combustion flue gas was exhausted to the atmosphere after passing through a cyclone separator. Physical-chemical characteristics of the particles were studied: i) morphology and aerosol size, surface and volume distributions before the cyclone and ii) chemical composition (carbonates, water soluble-inorganic ions, organic and elemental carbon) before and after the cyclone. Chemical composition data were used to calculate aerosol density and refractive index. Aerosols showed a unimodal size distribution with a geometric mean diameter of 2.25 ± 0.02 μm and a geometric standard deviation of 1.27 ± 0.01. The surface and volume mean diameters were 2.64 ± 0.02 μm and 2.91 ± 0.05 μm, respectively. Water-soluble inorganic ions were predominant in the fine particle fraction (PM2.5). The filters were loaded of crystallised mineral particles. The analysis revealed a dominance of calcium carbonate/oxide and halide (NaCl or KCl), sulphate and aluminosilicate nanocrystals forming larger mixed aggregates. This work was supported by Portuguese Science Foundation (FCT) through the projects PTDC/AAC-AMB/098112/2008 Bias-to-soil — Biomass ashes: Characteristics in relation to its origin, treatment and application on soil and PTDC/AMB/65706/2006 (BIOEMI). The electron microscopy analyses were conducted at CNME-UCM through the AEROCLIMA project (Fundación Ramón Areces). Ana I. Calvo acknowledges the pos-doc grant SFRH/BPD/64810/2009 from the FCT. We would also like to thank Diana Patoilo (University of Aveiro, Portugal) for supporting the chromatographic analyses, and Véronique Pont (University of Toulouse, France) and Darrel Baumgardner (Droplet Measurement Technologies, Boulder) for their valuable comments. published

Five Chinese fuels (one AlSi rich coal with low S content (LSC), one sulphur rich coal with low AlSi content (HSC), two straws and one sawdust) were thoroughly analysed and burned alone and blended in a bench-scale fluidised bed reactor. Flue gases and mass flows of the elements in the fine fly ash (< 10 μm, including condensed vapours) were analysed. In addition, chemical equilibrium calculations were carried out. When burnt alone, both straws produced significant concentrations of alkali chlorides, which cause corrosive deposits on superheaters. Both coals were capable of destroying alkali chlorides during co-firing. The destruction was based mostly on sulphation with HSC, and alkali aluminium silicate formation dominated with LSC. Bed agglomeration occurred in most of the experiments, but it will be discussed elsewhere.

Calcium-looping technology is a promising CO2-capture technology. The economics and environmental impact of the process are affected by the rapid decay in reactivity of the limestone sorbent, which necessitates a high purge rate from the system to maintain sorbent reactivity. This work investigates techniques to improve long-term reactivity in such a system by doping the limestone with a variety of different dopants. It also demonstrates that the main reason for improvement is that the doping increases the volume of pores around 100 nm in diameter in the calcined material after a significant number of cycles, in comparison to the calcine from an undoped sorbent. Improved reactivity means a lower required purge-rate and potential disposal issues, and less fresh limestone to be used. Doped samples were subject to repeated cycles of carbonation and calcination in a Fluidised Bed Reactor (FBR). The work includes the use of inorganic salts MgCl2, CaCl2, Mg(NO3)2 and the Grignard reagent-isopropylmagnesium chloride. Three types of doping procedures were explored; wet impregnation, solid mixing and quantitative wet impregnation. Experimental results showed that MgCl2, CaCl2 and Grignard reagents as dopants improved the carrying capacity of Havelock limestone. X-ray fluorescence (XRF) analysis of the doped samples after 13 cycles revealed that the number of dopant ions does not increase further with an increase in the doping concentrations above a critical value. Gas adsorption analyses showed that sorbents have a very small surface area-below 4 m²/g, post-cycling. The pore size distribution appears to change significantly upon doping, and it is likely that optimising the pore size distribution upon cycling is one reason for the enhanced reactivity observed.

International audience; The simultaneous combined heat and power (CHP) production via biomass gasification is considered as one of the main alternatives to fossil energy. Yet, a major obstacle in the development of this advanced technology lies in the presence of tars in syngas that are responsible for clogging downstream process equipment. Mathematical modelling and simulation studies are powerful tools to predict the performance of new processes. Baratieri et al. (2009), Pérez-Fortes et al. (2011) or Damartzis et al. (2012) develop comprehensive models of integrated biomass gasification plant, but based on thermochemical equilibrium approach that do not take into account the formation of tars. Recently, extensive models of Dual Fluidised Bed (DFB) gasifier demonstrate the possibility of accurately predict the formation of tars in syngas (Abdelouahed et al., 2012). The work presented in this paper consists in integrating a rigorous model of a DFB gasifier capable of predicting tar and contaminants in a global biomass CHP process. Our model includes the steps of wood drying, wood gasification, syngas cleaning, and power production in gas engine. Heat integration is considered all over the process for intern consumption and extern district heating. The model is set in Aspen Plus® and external Fortran user-subroutines are used to precisely describe complex phenomena in gasification reactor and gas engine. The energey efficiency of the CHP plant is evaluated. Simulation results highlight the strong impact of the syngas cleaning step in the overall performance of the CHP plant.

Fluidized bed technology is used for thermal conversion of solid fuels (combustion and gasification) and is especially suitable for conversion of low-rank fuels such as biomass and waste. The performance of fluidized bed units depends on the fuel mixing and fuel-gas contact. Thus, it is important to understand these two phenomena in order to develop models for reliable design and scale up of fluidized bed units. This work investigates, under conditions representative for industrial fluidized bed units, the lateral fuel mixing (in a unit with a cross section of 1.44 m2 both at hot and cold conditions) and the bubble flow distribution (in a 1.2 m-wide 2-dimensional unit). The work confirms previous findings on the formation of preferred bubble paths and shows that these bubble paths are enhanced by lowering the fluidization velocity, increasing the dense bed height and reducing the pressure drop across the gas distributor. From the fuel mixing experiments, an estimation of the lateral effective dispersion coefficient to values in the order of 10-3 m2/s is obtained under both hot and cold conditions. The experiments under cold conditions give additional qualitative information on the fuel mixing patterns such as flotsam/jetsam tendencies. The camera probe developed for fuel tracking under hot conditions enables to study the fuel dispersion under real operation at relevant industrial scales. Based on the characteristics of the bubble path flow, a model for the horizontal fuel dispersion on a macroscopic scale is formulated and shown to be able to give a good description of the experimental data. As opposed to the commonly applied diffusion-type modeling of the lateral solids dispersion, the proposed model facilitates integration with models of the bubble flow. Thus, the present modeling work is a first step to provide a modeling of the fuel dispersion, which uses as inputs only the main operational parameters of the fluidized bed.

The scratch performance of powder-coated substrates depends on many factors, including the coating material and thickness, the deposition techniques, and the characteristics of the baking processes. In the present investigation, two thermoplastic (PPA571, an alloy of acid-modified polyolefins) and thermoset (TGIC-free, transparent, bronze-pigmented polyester) organic powders were deposited onto flat aluminium substrates by the 'hot dipping' fluidised bed and electrostatic spray coating technologies. In the former technology, the metal substrates were pre-heated to 300 °C before being dipped in the fluidised bed and powder coated. In the latter technology, after electrostatic painting, the coated substrates were submitted to a curing process for 20. min at 170 °C to allow the formation of continuous films.The resulting coatings differed in morphology, thickness and adhesion strength. The scratch responses of the coatings were evaluated by progressive-mode scratch tests. Different contact conditions between the scratching geometry and the coating surface were analysed using three conical (Rockwell C) diamond indenters with tip radii of 100, 200 and 800 μm.Electrostatically sprayed thermoset coatings showed a better overall scratch resistance with minor deformation events and damage of a lesser extent compared to the thermoplastic coatings. On the contrary, the thermoplastic coatings displayed very singular scratch properties regardless of the deposition process, having the largest deformation events and most massive interfacial rupture. © 2011 Elsevier B.V.

In this work we discuss the modeling and simulation of a fluidized bed coal gasifier which uses a mixture of coal and petcoke as its feed. A two phase model consisting of the bubble phase and the emulsion phase is used to describe the coal gasification process. We consider a non-isothermal model taking into account the effect of four heterogeneous reactions and four homogeneous reactions. We analyse the effect of various operating parameters such as composition of feed, location of feed point and ash content on the performance of the gasifier. The results of predictions of the simulations have been found to be in good agreement with the experimental results in the literature. It has been found that increase in petcoke content in the feed mixture tends to lower the efficiency and carbon conversion but increases the amount of syngas produced. Also, from the simulations, it has been found that increase in ash content of coal decreases the carbon conversion. We have concluded that the feed point of the solids should be above the point where O2 that is present in the bed gets exhausted, in order to obtain the maximum carbon conversion and efficiency. � 2010 Elsevier Ltd. All rights reserved.

The present study reports preliminary characterization about the fluidised bed drying of powdered materials. Tests were carried out in a Lexan® lab-scale fluidised bed with solids selected to effectively surrogate powders of interest in the manufacture of pharmaceuticals. The process was monitored to correlate the temperature and the flow rate of the fluidising gas, the temperature and the moisture level in the bed, the qualitative fluidisation patterns. Bed material was characterized to assess the modifications of the population of agglomerates as a function of the operating conditions.

The local void fraction profile around a surface immersed in a fluidised bed has a great importance for the estimation of transport phenomena and chemical reaction rates in these units but it is rarely reported in literature. The scope of this work is to demonstrate that heat transfer measurements can be reliably used to derive the void fraction profile once a proper correlation model is available. To this aim, measurements of local heat transfer coefficient around a horizontal cylinder were performed and the angular void fraction profile was reconstructed with a new heat transfer model. The modeled void fraction profile resulted coherent with experimental and numerical evidences available in literature.

The need to substitute fossil fuel feedstocks with endogeneous biomass to produce energy with lower environmental impact makes necessary to develop innovative and technologically more advanced processes for energy production. Gasification of Cynara cardunculus L. (cardoon) alone and mixed with Eucalyptus was carried out in a bench scale fluidized bed gasifier to study the influence of operating parameters that could lead to a gas rich in hydrogen. The gasification tests were carried out using a mixture of oxygen and steam, as gasifying agent, to avoid the dilution effect of nitrogen that exists in air. The effect of catalysts addition to the bed on gas composition was analyzed as well as the influence in the level of contaminants like H2S, HCl, NH3 and tars in the gas produced. Steam and temperature had a positive effect by promoting the hydrogen production. The higher heating value of the gas produced was determined to be in the range 12 – 15 kJ/nm3 in a dry-nitrogen-free basis. Cardoon contains N, S and Cl which may give rise to problems during the gasification process and to the eventual use of the syngas produced. The results obtained showed that the presence of contaminants could be decreased through retention in the solid phase and by employing a condensation system to separate out pollutants in the liquid phase. This paper will fully present and discuss the results obtained with the gasification of cynara cardunculus and eucalyptus in a fluidized bed gasifier.

The paper reports on a current research on fluidised bed gasification of biomass and coals. The focus is on the bed material agglomeration and fragmentation phenomena that are well known to affect the reliability and the efficiency of fluidized bed combustion processes. Preliminary results of dedicated tests at high temperature are reported and discussed in the paper. On the whole, agglomeration phenomena appear to be less relevant under gasification conditions than during combustion. Extensive fragmentation has been experienced for a bed of fresh or calcined dolomite, whereas other materials having catalytic properties (sintered dolomite, ?-alumina) are more suitable under this aspect. Attrition tests also confirm the lower mechanical resistance of the calcined dolomite.

Tars and CH4 generated from biomass gasification processes contribute significantly to the energy content of the producer gas: catalytic tar and CH4 steam reforming allows to clean the gaseous fuel and improve the H2 yield; in addition, the use of a CO2 sorbent minimises carbon oxides. As a result of the whole process, a H2 rich fuel gas may be obtained. This experimental work is addressed to study the practical feasibility of such concepts, choosing CH4, toluene and 1-methyl naphthalene (1-MN) as biomass gasification key primary products. Ni is used as a catalyst for steam reforming, and dolomite as a sorbent for CO2 capture. Two kinds of catalytic systems are tested as bed material: a mixture of dolomite and commercial nickel catalyst, and a new Ni/dolomite combined catalyst and sorbent. The experimental investigations have been carried out in a fixed bed microreactor and a bench scale fluidised bed reactor rig. Both combinations of catalyst and sorbent are found to be very effective in tar removing, with conversion values near to 100% for the compounds tested; simultaneous CO2 sorption reveals itself as the key process step, improving significantly the performance of the catalytic system that may then decrease considerably after sorbent saturation.

Sludge incineration in fluidised bed is a very complex process, producing gaseous pollutants (carbon monoxide (CO) and nitrogen oxides (NOx)). The legislative norms need to be respected despite of variations of sludge in composition and in quantity. An oxygen regulation guarantees CO norm but not NOx norm. The NOx formation, due to lots of chemical reactions from the sludge nitrogen, is partly unknown. A model predicting the NOx emissions has been proposed. Literature study leads to neglect the solid reactants, simplifying greatly the hydrodynamics and the number of chemical reactions. The model has been validated with industrial data. The simulation results validate the simplification hypotheses, but need the reconstruction of sludge composition. A control strategy implemented further next guarantees the legislative norm of NOx.; L'incinération des boues en lit fluidisé est un processus très complexe, produisant des polluants gazeux (monoxyde de carbone (CO) et oxydes d'azote (NOx)). Les normes de rejet doivent être respectées malgré les variations en quantité et en composition des boues à traiter. Une régulation de l'oxygène du four assure la maîtrise du CO mais pas des NOx. Leur formation, due à de nombreuses réactions chimiques à partir de l'azote des boues, est mal connue. Un modèle prédisant les émissions de NOx a été établi. L'étude bibliographique a conduit à négliger les réactifs solides dans le four, et donc à simplifier fortement l'hydrodynamique et le nombre de réactions chimiques. Le modèle a été validé avec des mesures industrielles. Les résultats de simulation valident les hypothèses de simplification, mais nécessitent un recalage de la composition des boues. La stratégie de commande établie ensuite garantit le respect des normes des émissions de NOx.

Sludge incineration in fluidised bed is a very complex process, producing gaseous pollutants (carbon monoxide (CO) and nitrogen oxides (NOx)). The legislative norms need to be respected despite of variations of sludge in composition and in quantity. An oxygen regulation guarantees CO norm but not NOx norm. The NOx formation, due to lots of chemical reactions from the sludge nitrogen, is partly unknown. A model predicting the NOx emissions has been proposed. Literature study leads to neglect the solid reactants, simplifying greatly the hydrodynamics and the number of chemical reactions. The model has been validated with industrial data. The simulation results validate the simplification hypotheses, but need the reconstruction of sludge composition. A control strategy implemented further next guarantees the legislative norm of NOx., L'incinération des boues en lit fluidisé est un processus très complexe, produisant des polluants gazeux (monoxyde de carbone (CO) et oxydes d'azote (NOx)). Les normes de rejet doivent être respectées malgré les variations en quantité et en composition des boues à traiter. Une régulation de l'oxygène du four assure la maîtrise du CO mais pas des NOx. Leur formation, due à de nombreuses réactions chimiques à partir de l'azote des boues, est mal connue. Un modèle prédisant les émissions de NOx a été établi. L'étude bibliographique a conduit à négliger les réactifs solides dans le four, et donc à simplifier fortement l'hydrodynamique et le nombre de réactions chimiques. Le modèle a été validé avec des mesures industrielles. Les résultats de simulation valident les hypothèses de simplification, mais nécessitent un recalage de la composition des boues. La stratégie de commande établie ensuite garantit le respect des normes des émissions de NOx.

Costs of biofuel production from energy crops can be reduced by applying the crop residues in heat and power production. Perennial herbaceous crops like Cynara cardunculus L. are challenging fuels because they tend to have high ash and chlorine contents. Coals, however, are often rich in aluminium silicates and sulphur, and co-firing of these biofuels with coal could be expected to reduce operational problems. In addition, CO2 emissions are lower than during coal firing alone. Blends of Cynara and two coals, South African bituminous and Spanish sub-bituminous coal, were combusted in a 20 kW bubbling bed pilot reactor to ascertain the ability of the coals to reduce operational problems by alkali capture. The Cynara fuel sample contained almost 2 wt% chlorine. The South African coal was rich in kaolinite capable of capturing alkalies from chlorides to produce alkali aluminium silicate and HCl. The Spanish coal was rich in sulphur (mostly present as FeS2), and produced high concentrations of SO2 that partially oxidised to SO3. The SO3 can capture alkalies from chlorides by sulphation. Up to 30% Cynara, on energy basis, could be co-fired with Spanish coal without operational problems, whereas the same percentage of Cynara with South African coal led to strong Cl deposition. Co-firing of Cynara with both coals resulted in high HCl emissions (up to 1500 mg/Nm3 in 6% O2). In addition, co-firing of the Spanish coal led to very high SO2 emissions (up to about 16,000 mg/N m3 in 6% O2). Thus, a power plant capable of firing such blends must be equipped with flue gas cleaning equipment for effective SO2 and HCl capture in the flue gas channel after the superheaters, or else the quality of the Cynara must be markedly improved by changing the harvesting technology and fertilisers, which could be major sources of high ash and chlorine content in the fuel.

In the important efforts to decrease the net CO2 emissions to the atmosphere, new, alternative fuels are being included in the fuel mixes used in utility boilers. However, these fuels have ash properties that are different from those of the traditionally used fuels and in some cases technical problems, such as ash fouling and corrosion occur due to this. Therefore, diagnostic and predictive methods are developed and used to avoid such problems. Determination of the chemical association forms of important elements, such as potassium and sodium, in the fuel by chemical fractionation is a method well defined for coal and biofuels, such as wood pellets, bark and forest residues. Chemical fractionation is a step by step leaching method extracting water soluble salts in the first step, ion exchangeable elements, such as organically associated sodium, calcium and magnesium in the second step and acid soluble compounds such as carbonates and sulfates in the third step. The solid residue fraction consists of silicates, oxides, sulfides and other minerals. The compound extracted in the two first steps is considered reactive in the combustion with a few exceptions. In this work, it has been applied to some waste fuels, i.e. sewage sludge, straw and refuse derived fuel (RDF), as well as to coal and wood. The present work also includes results from combustion tests in a fluidised bed boiler where three blends of the investigated fuels were used. The fractionation results for the fuel blends are weighted results of the fractionations of the pure fuels discussed above which are compared with fractionations of their corresponding fly ashes. The co-combustion strategy gave very good results in reducing ash problems. Possible chemical mechanisms involved are discussed in the article. © 2008 Elsevier Ltd. All rights reserved.

Bioartificial liver devices must allow patients to wait either for the organ to regenerate itself once toxins are eliminated or for a hepatic graft. These extracorporeal systems are based on the use of cells cultured in an adequate environment.The objective of the thesis is to characterize different geometries of bioartificial liver by comparing the metabolic activities of a same cell culture (C3A) for each of them:1) classical fluidized bed (reference case) with alginate beads of 1000 µm diameter2) new type of fluidization with lower bead diameter (600 µm)3) systems with hollow fiber membranes commonly used by other teams4) Air Lift reactor in which with air permits the fluid circulationIn each system, flow and mass transfers of nutrients and metabolites have been characterized in absence and in presence of cells both experimentally and using mathematical models.In cases 1 and 2, mass transfers were roughly identical for bead diameters of 600 and 1000 µm. Cell viability and metabolic activities have been studied for 48h cultures showing satisfactory results and proving the innocuousness of the system. In case 3, different types of hollow fibers have been characterized. It has been shown that the membrane with the intermediate porosity is the most promising for clinical application. In case 4, the Air Lift system has the advantage in absence of cells to have a mass transfer coefficient higher than in the case of fluidized bed., Les systèmes bioartificiels de suppléance hépatique doivent permettre au patient d'attendre, soit une greffe, soit la régénération de l'organe, une fois les agents toxiques éliminés. Ces dispositifs reposent sur l'utilisation de cellules fonctionnelles dans un environnement adapté et placées dans un circuit extracorporel.Dans ce travail, l'objectif a été de caractériser différentes géométries de foie bioartificiel en comparant les fonctionnalités de mêmes cellules (C3A):1) lit fluidisé classique (la référence) avec des billes d'alginate de 1000 µm de diamètre2) nouveau type de fluidisation avec des billes de diamètre plus faible (600 µm)3) dispositifs à fibres creuses utilisés classiquement par des équipes concurrentes4) système Air Lift doté d'un apport d'air permettant la circulation du fluideDans chaque système, les écoulements et les transferts de matière des nutriments et des métabolites ont été caractérisés en absence et en présence de cellules de façon expérimentale et à l'aide de modèles mathématiques.Dans les cas 1 et 2, il s'est avéré que les transferts de masse étaient quasiment identiques pour les diamètres de billes 600 et 1000 µm. La viabilité et les fonctionnalités des cellules ont été étudiées sur 48h de culture montrant des résultats très satisfaisants et prouvant ainsi l'innocuité du dispositif. Dans le cas 3, différents types de fibres creuses ont été caractérisées, permettant de déduire que la membrane de porosité intermédiaire est la plus prometteuse en vue de l'application clinique. Dans le cas 4, le système Air Lift a pour avantage d'avoir un coefficient de transfert de masse plus important que dans le cas du lit fluidisé, en absence de cellules

Dissertação para obtenção do Grau de Mestre em Ciência e Engenharia de Materiais do Instituto Superior Técnico No presente trabalho é apresentada a caracterização físico-química de Resíduos de Fragmentação Automóvel bem como das cinzas obtidas através da sua combustão num sistema piloto de leito fluidizado. A composição e a lixiviação do combustível foram comparadas com as cinzas utilizando as três metodologias de lixiviação mais usadas: o método europeu EN 12457-2, o método americano US TCLP 1311 e o método de disponibilidade holandês EA NEN 7371. Os resultados obtidos revelaram que, além da lixiviação de matéria orgânica, sob condições ácidas a libertação de metais pesados da FCRFA pode constituir um sério problema pelo que a sua deposição em aterro deverá ser abandonada. As cinzas resultantes do processo de combustão de FCRFA apresentaram alguns níveis de lixiviação de metais, como por exemplo Cr, todavia a destruição do conteúdo orgânico, associada à diminuição das quantidades de resíduo a depositar em aterro, fazem do tratamento térmico uma opcção a considerar na gestão deste tipo de resíduos.

Dissertação para obtenção do Grau de Mestre em Bioenergia Com o presente estudo procurou-se avaliar a ocorrência de sinergias entre combustíveis, durante a co-combustão de carvão e combustíveis derivados de biomassa (CDB) em leito fluidizado, com potenciais impactes nas emissões atmosféricas de NOx, SO2, CO, Dioxinas e Furanos (PCDD/F) e Material Particulado (MP) (granulometria e quantidade total emitida). Utilizaram-se cinco lotes de carvão provenientes da Polónia e Colômbia, fornecidos por centrais termoeléctricas europeias, e cinco CDB (Pellets de Palha; Farinhas de Carne e Osso; Lamas Residuais Urbanas; Bagaço de Azeitona; Pellets de Madeira), em cinco campanhas de ensaios efectuadas num reactor de leito fluidizado borbulhante à escala piloto. Os ensaios realizados incluíram, para além da combustão destes materiais, a sua co-combustão em misturas com percentagens mássicas de biomassa de 5%, 15% e 25%. Foram identificadas algumas situações em que as emissões dos poluentes em estudo diminuíram durante a co-combustão, comparativamente à queima isolada dos combustíveis em causa (NOx e MP) ou caso se assumisse uma variação linear nas mesmas com a incorporação de maiores quantidades de biomassa na mistura combustível (CO, SO2, PCDD/F). Os seguintes mecanismos aparentaram relacionar-se com as tendências observadas: o aumento da eficiência na conversão de carbono e a consequente diminuição da presença deste elemento nas cinzas acumuladas nos ciclones (CO); a conjugação de mecanismos redução associados aos dois combustíveis em causa (NOx); a presença de elementos alcalinos, cloro e a sua disponibilidade nos combustíveis (SO2); a produção de menores quantidades de material inqueimado e o aumento dos diâmetros médios das cinzas volantes (MP); a relação entre o Cl presente nos combustíveis e a presença de S sob a forma de SO2 no reactor, a quantidade e granulometria do MP emitido e a natureza dos combustíveis utilizados (PCDD/F).Os resultados obtidos demonstraram que, embora a ocorrência de sinergias neste domínio seja fortemente dependente da natureza dos combustíveis utilizados (da especificidade das suas características físico-químicas) e da adequação dos parâmetros operacionais à mistura em causa, a co-combustão de determinados tipos de biomassa e carvão em leito fluidizado pode constituir, por si só, um mecanismo válido na diminuição dos índices de emissão dos poluentes em estudo.

This work reports experimental results on the local heat transfer coefficient on the surface of a horizontal cylinder immersed in a 500 µm glass beads bubbling fluidised bed . Experimental runs have been carried out at ambient pressure and temperature, with superficial velocity up to 0.45 m/s. The local value of the heat transfer coefficient has been determined with an angular shift of 10 deg. in order to derive a detailed profile of heat transfer rate around the cylindrical surface. Experimental results point out the occurrence of different heat transfer zones which directly reflect the existence of different hydrodynamic conditions around the cylindrical surface, previously observed by experimental (Buyevich et al. 1986) and numerical (Rong et al., 1999) studies. The highest value of the heat transfer coefficient is observed at the boundary of the lateral mixing and the upper sliding zone, as the result of a compromise between surface renewal frequency and particle concentration. Surface to bed voidage profile has been calculated from heat transfer coefficient measures by applying the Di Natale et al. (2008) model showing a good agreement with former studies and confirming the applicability of heat transfer data for the interpretation of fluid dynamic structure around surface immersed in fluidised beds.

This work is focused on the dry method synthesis of alkaline metal ferrates (A2FeVIO4, A = K, Na) by using chlorine as oxidant. The ferrates (VI) are compounds which contain iron under its oxidation state +6. They gain growing importance in the industrial effluent and water treatment because of multipurpose nature of FeVI. Although the existence of alkaline ferrates has been mentioned for one century, the alkaline ferrates were not the subject of a considerable number of studies. This is mainly due to their instability and difficulties concerning the methods of preparation. The alkaline ferrate synthesis in the rotary reactor was carried out at room temperature and the whole reaction of synthesis was exothermic. For the realized tests of synthesis, solid quantities of (iron salt + AOH) of a few tens of grams up to 400 grams were used. The effects of various parameters on the synthesis process were studied. In the perspective of improving the process of synthesis and applying the industrial extrapolation, the synthesis of ferrate was realised in a fluidized bed reactor. The proceeding occurs by two successive steps: the first consisting in mixing beforehand the sodium hydroxide with ferrous sulphate and the second to fluidize the mixture obtained in the presence of diluted chlorine. The application of this process makes possible to attain a yield in FeVI of about 56 % and the results obtained show a clean and innovative process of low cost for the synthesis of alkaline metal ferrates on a large scale, Ce travail est focalisé sur la synthèse par voie sèche des ferrates de métaux alcalins (A2FeVIO4, A = K, Na) en utilisant le chlore comme oxydant. Les ferrates (VI) sont des composés qui contiennent du fer sous son état d'oxydation +6. Leur importance s'avère grandissante dans le traitement des eaux et des effluents industriels du fait de la nature multifonctionnelle du FeVI. Bien que l'existence de ferrates alcalins soit citée depuis un siècle, ceux-ci n'ont pas fait l'objet d'un nombre considérable d'études. Ceci est principalement du à leur instabilité et aux difficultés concernant les méthodes de préparation. La synthèse de ferrates alcalins dans le réacteur rotatif a été réalisée à température ambiante et la réaction totale de synthèse fut exothermique. Pour les expériences effectuées, des quantités de réactants solides (sel de fer + AOH) allant de quelques dizaines de grammes jusqu'à 400 grammes ont été utilisées. Les effets de différents paramètres sur le déroulement de la synthèse ont été étudiés. Afin d'améliorer le processus de synthèse et appliquer l?extrapolation industrielle, la synthèse de ferrates a été réalisée au sein d'un réacteur à lit fluidisé. Le procédé consiste premièrement, à mélanger préalablement l?hydroxyde de sodium (NaOH) avec le sulfate ferreux (FeSO4 H2O) et deuxièmement, à fluidiser le mélange obtenu en présence du chlore dilué. L'application de ce procédé permet d'atteindre un rendement en FeVI d'environ 56 %. Les résultats obtenus témoignent d'un processus propre et innovant et d'un faible coût pour la synthèse des ferrates de métaux alcalins à plus grande échelle

A semi-empirical model is used to calculate the averaged surface void fraction in fluidized beds, εw, starting from experimental data on surface-to-bed heat transfer coefficient. The model is able to describe the effect of the main process parameters and shows that εw increases with minimum fluidization void fraction and particle Archimedes number.

Atmospheric bubbling fluidised bed coal combustion (ABFBCC) of a bituminous coal and an anthracite with particle diameters in the range 500–4000 μm was investigated in a pilot-plant facility, with and without limestone addition. The experiments were conducted at steady-state conditions using three excess air levels (10, 25 and 50%) and bed temperatures in the range 750–900 °C. Combustion air was staged, with primary air accounting for 100, 80 and 60% of total combustion air. During limestone addition, in general, the NO emission decreases with the decrease in excess air and the increase in air staging, for both coals (as also observed without limestone). The bed temperature does not influence the NO emission significantly (as also observed without limestone); however, it was observed that during bituminous coal combustion there is a slight trend for a decrease on the NO emission with temperature increase in the range 825–900 °C, whereas for anthracite coal the trend is the opposite. On the other hand, the N 2 O emission increases with: the decrease in excess air, the increase in air staging (as opposed to what was observed without limestone), and the decrease in bed temperature (as also observed without limestone). Taking the coal combustion without limestone as reference, it was observed that the effect of limestone addition on the NO and N 2 O emission depends on the first stage stoichiometry: (1) under first stage fuel lean conditions the NO emission increases, while that of N 2 O decreases, (2) under first stage fuel rich conditions (for example, high air staging) the opposite trend is observed.

This work analyses the correlation between external heat transfer and fluid dynamic field near a surface immersed in a bubbling fluidised bed through a simplified model and detailed DEM-CFD simulations. The study is based on experimental results on surface-to-bed heat transfer between a fluidised bed at bubbling and slugging regime and two heat transfer probes with spherical and cylindrical shape. The model estimations and the DEM-CFD simulations have been compared in terms of estimated values of averaged surface void fraction εw. The two approaches give similar results for the case of the sphere while the value of εw for the cylinder deduced by numerical simulations appears to be underestimated.

The catalytic combustion of methane has been investigated in a 0.10 m bubbling fluidized bed reactor with nonpremixed feedings of reactants. Copper dispersed on porous ç-Al2O3 spheres (1 mm diameter) characterized by high mechanical strength has been used as catalyst. The effect of design variables such as methane inlet concentration, bed temperature, and superficial gas velocity on methane conversion has been quantified in the ranges 4-10 vol %, 650-750 °C, and 0.40-1.30 m s-1, respectively. The propensity to attrition of the catalyst has been separately investigated under the experimental conditions tested. Results have been interpreted in the light of a simple reactor model which assumes a plug-flow pattern for the gas through the bed and mth-order catalytic kinetics with respect to fuel concentration.

This work deals with the experimental analysis of heat transfer coefficient between a fluidised bed of fine particles and submerged surfaces of different shapes. Experiments have been carried out using different bed materials (polymers, ballotini, corundum, carborundum and quartz sand) characterized by a mean particle diameters ranging between 30 and 90 µm and an Archimedes number between 2 and 50. Dry air at 25°C and 100 kPa has been used as fluidising gas. Three different objects are used as heat transfer probes: a sphere and two cylinders with different base diameter and same height. Experimental results show that the heat transfer coefficient increases with particle Archimedes number and is almost independent from particle thermal conductivity for a Kp between 0.9 and 16 W/(m•K). Finally, the comparison of heat transfer coefficient for the different probes shows that the effect of the surface geometry may account for a 30% variation in the heat transfer coefficient, with higher differences occurring for coarser particles.

The heat-transfer coefficients around a workpiece immersed in an electrically heated heat treatment fluidised bed were studied. A suspension probe designed to simulate a workpiece of complex geometry was developed to measure local total and radiative heat-transfer coefficients at a high bed temperature. The probe consisted of an energy-storage region separated by insulation from the fluidised bed, except for the measuring surface, and a multi-thermocouple measurement system. Experiments in the fluidised bed were performed for a fluidising medium of 120-mesh alumina, a wide temperature range of 110–1050 °C and a fluidising number range of 1.18–4.24. It was found that the workpiece surface temperature has a more significant effect on heat transfer than the bed temperature. The total heat-transfer coefficient at the upper surface of the workpiece sharply decreased at the start of heating, and then steadily increased as heating progressed, while a sharp decrease became a rapid increase and then a slow increase for the radiative heat-transfer coefficient. A great difference in the heat-transfer coefficients around the workpiece was observed.

Gas mixing and hydrodynamics in the splash zone of gas-fluidized beds are largely determined by the interaction between bursting bubbles, the mainstream gas and the ejected bed solids. The present paper investigates the flow structures associated with the eruption of single bubbles at the surface of incipiently fluidized beds by a combination of non-intrusive optical diagnostic techniques, namely Planar Laser Light Scattering (PLLS) and Planar Laser Induced Fluorescence (PLIF). The influence of the depth of the bubble injection point below the bed surface on the phenomenology of bubble bursting is investigated.

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Atmospheric Bubbling Fluidised Bed Combustion (ABFBC) of a bituminous coal and anthracite with particle size in the range 500–4000 μm was investigated in a pilot-plant facility, with and without limestone addition (particle size in range 710–1000 μm). The experiments were conducted at steady-state conditions using three excess air levels (10%, 25% and 50%) and bed temperatures in the 750–900 °C range. Combustion air was staged, with primary air accounting for 100%, 80% and 60% of total combustion air. Limestone addition is suitable for in-situ SO2 removal during ABFBC, with removal efficiencies in the range 25–85%. In general, the efficiency of SO2 removal by limestone decreases with an increase in air staging and a decrease in excess air. The increase in the bed temperature range 825–900 °C decreases the efficiency of SO2 removal by limestone, and in some situations a maximum can occur around 825 °C bed temperature. The reducing conditions at the first stage level, the secondary combustion, and the reductive decomposition of CaSO4 could be responsible for the low efficiency of SO2 removal by limestone during both high air staging and high bed temperatures.

Atmospheric Bubbling Fluidised Bed Combustion (ABFBC) of a bituminous coal and anthracite with particle diameters in the range 500–4000 μm was investigated in a pilot-plant facility (circular section with 0.25 m internal diameter and 3 m height). The experiments were conducted at steady-state conditions using three excess air levels (10, 25 and 50%) and bed temperatures in the 750–900 °C range. Combustion air was staged, with primary air accounting for 100, 80 and 60% of total combustion air. The effect of limestone addition was also tested. Large CO concentrations were observed inside the bed, up to 8 and 6% (v/v) in the cases of anthracite and bituminous coals, respectively. These concentrations decreased sharply as the gases emerged from the bed, and the CO flue gas concentration observed was in general less than 2000 and 4000 ppm, respectively. The CO flue gas concentration increased with air staging and with limestone addition, but decreased with either excess air or temperature increase. The observed results confirm the influence of sand particles (and probably of SO 2 ) in the ‘quenching’ of the oxygenated free radicals (HO and HO 2 ) reactions responsible for the CO oxidation inside the bed.

Fossil fuels still dominate the energy supply in modern societies. The resources, however, are depleting. Therefore, other energy sources are to be exploited further within this century. Biomass is one of the practically CO2 neutral, renewable contributors to the future energy production. Nowadays many modern, high efficiency (combined) power and heat producing systems using biomass are or become commercially available. One promising route to efficient power and heat supply is the Integrated Gasification Combined Cycle. This cycle is particularly of interest for medium to larger scale installations. Pressurised operation of the gasifier offers the advantage of smaller process equipment, including that for the necessary downstream gas cleaning. Also, the work needed to compress the gas for gasturbine use will be much smaller or not needed at all. High temperature gas filtration offers the benefit of increased overall efficiencies of the power and heat producing cycle. This integrated gasification technology, however, is still in a stage of development and demonstration. When instead of absorption gas cleaning, high temperature, dry gas filtration is applied, nitrogen compounds, like ammonia (NH3) and hydrogen cyanide (HCN), are not dissolved in the absorption liquid. As a result NOx emissions in gas turbine combustors are produced. NOx is known for its negative effects on the health of humans and animals and acidification of soil and water. Therefore, increasingly stringent emission restrictions are imposed on this component. Both coal and biomass contain nitrogen in their chemical structure and in gasification processes this so-called fuel bound nitrogen is converted to a large extent into NOx precursors. This PhD thesis assesses the experimental and theoretical work which was performed to study the behaviour of nitrogen compounds during air blown pressurised stationary fluidised bed gasification of biomass and brown coal, followed by high temperature ceramic gas filtration. Gasification experiments have been performed using a 1.5 MWthermal pilot plant situated in Delft and a smaller scale test rig at the university of Stuttgart. Under the pressurised fluidised bed gasification conditions studied, the main fuel bound nitrogen component produced is NH3, whereas HCN is formed to a minor extent (only a few percent of the fuel bound nitrogen). In cooperation with TU Eindhoven, small-scale fuel characterization experiments have been carried out to obtain model parameters for the gasification process. These form the input basis of a gasifier model that has been validated with measurements at the pilot facilities.

Fossil fuels still dominate the energy supply in modern societies. The resources, however, are depleting. Therefore, other energy sources are to be exploited further within this century. Biomass is one of the practically CO2 neutral, renewable contributors to the future energy production. Nowadays many modern, high efficiency (combined) power and heat producing systems using biomass are or become commercially available. One promising route to efficient power and heat supply is the Integrated Gasification Combined Cycle. This cycle is particularly of interest for medium to larger scale installations. Pressurised operation of the gasifier offers the advantage of smaller process equipment, including that for the necessary downstream gas cleaning. Also, the work needed to compress the gas for gasturbine use will be much smaller or not needed at all. High temperature gas filtration offers the benefit of increased overall efficiencies of the power and heat producing cycle. This integrated gasification technology, however, is still in a stage of development and demonstration. When instead of absorption gas cleaning, high temperature, dry gas filtration is applied, nitrogen compounds, like ammonia (NH3) and hydrogen cyanide (HCN), are not dissolved in the absorption liquid. As a result NOx emissions in gas turbine combustors are produced. NOx is known for its negative effects on the health of humans and animals and acidification of soil and water. Therefore, increasingly stringent emission restrictions are imposed on this component. Both coal and biomass contain nitrogen in their chemical structure and in gasification processes this so-called fuel bound nitrogen is converted to a large extent into NOx precursors. This PhD thesis assesses the experimental and theoretical work which was performed to study the behaviour of nitrogen compounds during air blown pressurised stationary fluidised bed gasification of biomass and brown coal, followed by high temperature ceramic gas filtration. Gasification experiments have been performed using a 1.5 MWthermal pilot plant situated in Delft and a smaller scale test rig at the university of Stuttgart. Under the pressurised fluidised bed gasification conditions studied, the main fuel bound nitrogen component produced is NH3, whereas HCN is formed to a minor extent (only a few percent of the fuel bound nitrogen). In cooperation with TU Eindhoven, small-scale fuel characterization experiments have been carried out to obtain model parameters for the gasification process. These form the input basis of a gasifier model that has been validated with measurements at the pilot facilities.

Direct combustion of biogenic wastes or substitute fuels is very difficult to control since various compositions and moisture contents result in too large variations in the calorific value. A technically elegant solution to those problems was proposed, which involves preliminary gasification of the solid fuel and subsequent burning of the combustible gas thus obtained. The new technology was successfully tested using a pilot plant.

2005