Dissertations / Theses on the topic 'Circulating fluidized bed boiler'
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1
Karppanen, E. (Erkki). "Advanced control of an industrial circulating fluidized bed boiler using fuzzy logic." Doctoral thesis, University of Oulu, 2000. http://urn.fi/urn:isbn:9514255194.
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Abstract
Circulating Fluidized Bed (CFB) boilers are widely used for multi-fuel
combustion of waste and bio-fuels. When several non-homogeneous fuels, having varying heat values, are
burned simultaneously, the boiler control system can be affected by various control
challenges, especially since it is not feasible to reliably measure the energy content of the
multi-fuel flow. In order to fulfill energy production needs and maintain the ability to burn low grade
fuels, co-firing with high heat value fuels such as gas, oil or coal is needed.
Fuzzy Logic Control (FLC) has been successfully used for solving control
challenges, where operators' process expertise can be transformed into automation. Real life
control objects are often non-linear because the dynamics change with the operating point, or there might
be other essential non-linearities in the combustion process.
The proposed fuzzy control applications were developed to solve control
challenges the operators meet in daily operation of a 150 MW(th) CFB at Varenso Oy's (Stora
Enso Oyj) K6 boiler in Varkaus Finland. Before implementing the applications in the fullscale
boiler, they were tested at a 2 MW(e) pilot plant boiler at Foster Wheeler Energia Oy's Research
Center in Karhula, Finland.
According to the industrial experiments, the four applications (steam pressure
control, compensation of fuel quality fluctuation, fuel-feed optimization and increased
bed inventory monitoring) discussed in this thesis, showed satisfactory performance and
various improvements to the boiler control were achieved. Fuzzy logic control was shown to be a notable
tool to improve the multi-fuel CFB boiler control.
2
Niva, L. (Laura). "Self-optimizing control of oxy-combustion in circulating fluidized bed boilers." Doctoral thesis, Oulun yliopisto, 2018. http://urn.fi/urn:isbn:9789526221304.
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Abstract Energy production in combustion power plants is a significant source of anthropogenic carbon dioxide emissions. The targets of international climate agreements call for utilizing all available technologies to achieve rapid and cost-effective emission reductions. Carbon capture and storage is one of the possible technical solutions applied in combustion power plants. Circulating fluidized bed boilers have gained increasing popularity due to advantages in availability, emission control, fuel flexibility and option for using challenging fuels, and the possibility of using high-efficiency steam cycles. In the novel process of oxy-combustion, combustion air is replaced by a mixture of oxygen and recycled flue gas to facilitate the capture of carbon dioxide from the flue gas flow. Additional degrees of freedom become available for combustion control as the gas flow and composition can be controlled separately for fluidization and combustion purposes. In the research for this thesis, self-optimizing control was applied for the control structure design of a circulating fluidized bed boiler. Self-optimizing control offers a systematic tool for the early phases of control design, in which decisions have traditionally been made based on intuition, heuristics and previous experience. The self-optimizing control approach searches for controlled variables without a need for constant setpoint optimization when the process is affected by disturbances and implementation errors. Results presented in the thesis show that self-optimizing control can be applied in the control structure design of circulating fluidized bed combustion. A range of control structure alternatives were evaluated using steady-state approximations of a validated process model. For the novel oxy-combustion process, promising control structures were identified and could be dynamically demonstratedTiivistelmä Energiantuotanto polttovoimalaitoksissa on merkittävä hiilidioksidipäästöjen lähde. Kansainväliset ilmastotavoitteet edellyttävät kaikkien käytettävissä olevien teknologioiden hyödyntämistä päästövähennysten aikaansaamiseksi nopeasti ja kustannustehokkaasti. Hiilidioksidin talteenotto on yksi mahdollisista teknisistä ratkaisuista polttovoimalaitoksissa. Kiertoleijukattilat ovat saavuttaneet kasvavaa suosiota etuinaan hyvä käytettävyys, tehokas päästöjen hallinta, soveltuvuus erilaisten haastavienkin polttoaineiden hyödyntämiseen ja mahdollisuus tehokkaiden höyrykiertojen käyttöön. Uudessa happipolttoprosessissa palamisilma korvataan hapen ja kierrätetyn savukaasun seoksella, mikä mahdollistaa hiilidioksidin talteenoton savukaasuista. Kiertoleijupolton säädön kannalta vapausasteet lisääntyvät, sillä leijutukseen ja polttamiseen käytettävän kaasun määrää ja koostumusta voidaan säätää erikseen. Väitöstutkimuksessa käytettiin itseoptimoivaa säätöä kiertoleijukattilan säätörakenteiden suunnitteluun. Itseoptimoiva säätö tarjoaa systemaattisen menetelmän säätösuunnittelun alkuvaiheeseen, jossa päätöksenteko on perinteisesti tehty esimerkiksi intuition, heuristiikan ja aiempien ratkaisujen perusteella. Menetelmän tavoitteena on löytää säädettävät muuttujat, joiden asetusarvot eivät vaadi jatkuvaa optimointia, vaikka prosessiin vaikuttavat erilaiset häiriöt ja mittausvirheet. Väitöstutkimuksen tulokset osoittavat, että itseoptimoiva säätö soveltuu kiertoleijupolton säätörakenteiden suunnitteluun. Erilaisten säätörakenteiden toimivuutta arvioitiin käyttäen validoidun prosessimallin tasapainotilan approksimaatioita. Uudelle happipolttoprosessille löydettiin lupaavia säätörakenteita, joiden toimintaa voitiin demonstroida myös dynaamisesti
3
Biruk, David D. "Neural Network Based Control of Integrated Recycle Heat Exchanger Superheaters in Circulating Fluidized Bed Boilers." UNF Digital Commons, 2013. http://digitalcommons.unf.edu/etd/470.
Full textAbstract:
The focus of this thesis is the development and implementation of a neural network model predictive controller to be used for controlling the integrated recycle heat exchanger (Intrex) in a 300MW circulating fluidized bed (CFB) boiler. Discussion of the development of the controller will include data collection and preprocessing, controller design and controller tuning. The controller will be programmed directly into the plant distributed control system (DCS) and does not require the continuous use of any third party software.
The intrexes serve as the loop seal in the CFB as well as intermediate and finishing superheaters. Heat is transferred to the steam in the intrex superheaters from the circulating ash which can vary in consistency, quantity and quality. Fuel composition can have a large impact on the ash quality and in turn, on intrex performance. Variations in MW load and airflow settings will also impact intrex performance due to their impact on the quantity of ash circulating in the CFB. Insufficient intrex heat transfer will result in low main steam temperature while excessive heat transfer will result in high superheat attemperator sprays and/or loss of unit efficiency.
This controller will automatically adjust to optimize intrex ash flow to compensate for changes in the other ash properties by controlling intrex air flows. The controller will allow the operator to enter a target intrex steam temperature increase which will cause all of the intrex air flows to adjust simultaneously to achieve the target temperature. The result will be stable main steam temperature and in turn stable and reliable operation of the CFB.
4
Fusey, Isabelle. "A novel circulating fluidized bed." Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/25094.
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A novel type of circulating fluidized bed has been investigated and tested. While a conventional circulating fluidized bed unit consists of two vessels standing side by side - a fast bed operating at high gas velocity, and a slow bed which acts as a recycle vessel and operates at a much lower velocity - the novel design incorporates the two beds into a unique concentric arrangement. The inner column acts as the fast bed and the annular region acts as the slow bed.
A baffle to separate the gas-solid mixture at the top of the inner column has been designed and tested. The baffle works reasonably well but design optimization is needed. Two types of air inlets for aeration of the insert have been tried: vertical and tangential. The vertical air inlet has been found to produce the highest solids circulation rates. Two types of solids have been investigated: polyvinyl chloride resin and cracking catalyst. The use of the heavier and smaller cracking catalyst particles resulted in higher circulation rates and greater solids hold-up in the inner column.
The hydrodynamic behavior of the system has been studied using pressure and circulation flux measurements. The solids circulation flux, the axial pressure profile, and the absolute pressure inside the system are generally all strong functions of air velocity in both the inner and outer sections, solids inventory, type of particle, and type of air inlet.Applied Science, Faculty of
Chemical and Biological Engineering, Department of
Graduate
5
Huang, Yue. "Dynamic model of circulating fluidized bed." Morgantown, W. Va. : [West Virginia University Libraries], 2006. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4823.
Full textAbstract:
Thesis (Ph. D.)--West Virginia University, 2006.Title from document title page. Document formatted into pages; contains ix, 133 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 103-114).
6
Gogebakan, Yusuf. "Simulation Of Circulating Fluidized Bed Combustors." Phd thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/2/12607775/index.pdf.
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A dynamic mathematical model for simulation of atmospheric circulating fluidized bed combustors has been developed on the basis of first principles and empirical correlations. The model accounts for dense and dilute zone hydrodynamics, volatiles release and combustion, char particles combustion and their size distribution, and heat transfer from/to gas, particles, waterwalls and refractory.
Inputs to the model include configuration and dimensions of the combustor and its internals, air and coal flows, coal analysis, all solid and gas properties, inlet temperatures of air, cooling water, and feed solids, size distribution of feed solidswhereas outputs include transient values of combustor temperatures, gas concentrations, char and inert hold-ups and their size distributions. The solution procedure employs method of lines approach for the governing non-linear partial differential equations and combined bisection and secant rule for non-linear algebraic equations. The initial conditions required for the model are provided from the simultaneous solution of governing equations of dynamic model with all temporal derivatives set to zero. By setting all temporal derivatives to zero, model can also be utilized for steady state performance prediction. In order to assess the validity and predictive accuracy of the model, it was applied to the prediction of the steady state behavior of Technical University of Nova Scotia 0.3 MWt CFBC Test Rig and predictions were compared with measurements taken on the same rig. Comparison of model predictions at steady state conditions revealed that the predictions of the model are physically correct and agree well with the measurements and the model is successful in qualitatively and quantitatively simulating the processes taking place in a circulating fluidized bed combustor.
7
Courbariaux, Yann. "Heat transfer in a circulating fluidized bed." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0006/MQ46243.pdf.
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8
Redemann, Kai. "Ash management in circulating fluidized bed combustors." Aachen Shaker, 2008. http://d-nb.info/991096231/04.
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9
Wu, Richard Lap. "Heat transfer in circulating fluidized beds." Thesis, University of British Columbia, 1989. http://hdl.handle.net/2429/31037.
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Heat transfer in circulating fluidized beds was studied in both a 7.3 m high, 152 x 152 mm square, pilot-scale combustor and a 9.3 m high, 152 mm ID transparent cold model unit. Results were obtained for particles of mean size 171-299 µm at superficial gas velocities from 4 to 9.5 m/s and for solids circulation rates up to 70 kg/m².s. For the combustor, results obtained by using membrane walls and a vertical tube as heat transfer surfaces show a strong influence of the cross-sectional area-averaged suspension density on time-averaged, length-averaged suspension-to-surface heat transfer coefficient. The influence of superficial gas velocity is found to be small. Radiation becomes significant at suspension temperatures higher than 400 C and at low suspension densities. Heat transfer coefficients were also found to vary with the lateral position of the tube. The vertical length of heat transfer surface is shown to be an important parameter, allowing seemingly discrepant published results to be reconciled.
For the cold model unit, sudden and dramatic peaks in instantaneous heat transfer coefficients were measured using an instantaneous heat transfer probe. Simultaneous heat transfer and capacitance measurements suggest that these peaks are caused by the arrivals of particle strands at the heat transfer surface. Two-probe heat transfer measurements suggest the existence of a characteristic residence length for the strands at the wall in this column.
A proposed heat transfer model, based on an overall core-annulus flow structure in the riser, and periodic formation, movement along the wall, and disintegration of strands in the annulus, gives reasonable agreement with a wide range of published data. It accounts successfully for the effects of heat transfer surface length and particle sizes. However, the effect of the heat transfer surface configuration on the flow pattern of particles must also be taken into account to give improved agreement with experimental data.Applied Science, Faculty of
Chemical and Biological Engineering, Department of
Graduate
10
Herbert, Peter M. "Hydrodynamic study of a downflow circulating fluidized bed." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0005/NQ32310.pdf.
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11
Moran, James C. (James Christopher). "Gas phase hydrodynamics inside a circulating fluidized bed." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/89304.
Full textAbstract:
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2001.Includes bibliographical references (p. 165-171).
Circulating Fluidized Beds (CFB's) offer many advantages over traditional pulverized coal burners in the power generation industry. They operate at lower temperatures, have better environmental emissions and better fuel flexibility. The motion of solids inside a CFB has been studied extensively over the previous twenty years. However the motion of gas is less well understood. There has previously only been indirect measurements of gas velocities and fluctuations. The gas phase is important as the motion of the particles is controlled by the gas. Accurate simulations of CFB's are not possible without accurate information on the gas phase. Instrumentation was developed for use in measuring gas phase fluctuations inside a scale model CFB. Results were unexpected in that gas fluctuations were substantially larger than expected. The fluctuation level without particle flow was around 0.15m/s. This was expected to stay constant or decrease with the introduction of particles. However with particle introduction the fluctuation level increased to 0.7m/s, an increase of over 400%. This is more than likely due to the clustering of particles which produces large scale structures with the resulting vortex shedding. A smaller riser was built which allowed the introduction of single individual clusters into the unit. The effect of single clusters on the surrounding gas flow was studied and modeled. These results indicate a mechanism by which, previously unknown, large scale fluctuations are generated inside a CFB.
by James C. Moran.
Ph.D.
12
Wischnewski, Reiner. "Simulation of large-scale circulating fluidized bed combustors." Aachen Shaker, 2008. http://d-nb.info/993341691/04.
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Ozkan, Mert. "Simulation Of Circulating Fluidized Bed Combustors Firing Indigenous Lignite." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612686/index.pdf.
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A comprehensive model, previously developed for a rectangular parallelepiped shaped 0.3 MWt circulating fluidized bed combustor (CFBC) fired with high calorific value coal burning in sand and validated against experimental data is adapted to cylindrical configuration and is extended to incorporate NOx formation and reduction reactions and pressure drops around cyclone, downcomer and loop seal. Its predictive accuracy is tested by applying it to the simulation of Middle East Technical University (METU) 150 kWt CFBC burning low calorific value indigenous lignite with high Volatile Matter/Fixed Carbon (VM/FC) ratio in its own ash and comparing its predictions with measurements. Favorable comparisons are obtained between the predicted and measured temperatures, pressure profiles and emissions of gaseous species. Results reveal that predictive accuracy in pressure profile strongly depends on the correlation utilized for entrainment in dilute zone and that accuracy in NO emission requires data on
partitioning of coal nitrogen into char-N and volatile-N and is affected significantly by dilute zone oxygen content.
14
Stewart, Michael C. "Sulfation Phenomena Under Oxy-Fuel Circulating Fluidized Bed Conditions." Thèse, Université d'Ottawa / University of Ottawa, 2011. http://hdl.handle.net/10393/20024.
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Oxy-fuel fired circulating fluidized bed combustion (CFBC) provides a means to generate electrical power while reducing anthropogenic CO2 while at the same time reducing the acid-rain precursor, SO2 by utilizing in-situ limestone addition. Although the technology has been around for 30 years, it has only recently been gaining considerable attention, with a handful of pilot-scale units worldwide. Oxy-fuel is largely similar to standard air-fired combustion but differs in a few key respects, one of which is in the elevated concentrations of CO2 and H2O (up to 90% and 30%, respectively). The effects and mechanism of action of these gasses on limestone sulfation have long been a matter of debate in the literature. Using a thermogravimetric analyzer (TGA) and tube furnace (TF), the effects of elevated gas concentrations on the sulfation of limestone are studied using synthetic air-fired and oxy-fired flue gases (SO2: 3800 ppm, CO2: 12.5 – 82.5%, O2: 2.5%, H2O: 0 – 30%) at 850 °C. An explanation is provided for the contradictory findings in the literature in terms of the TGA/TF results. Microstructural analysis of sulphated samples using scanning electron microscopy (SEM), nitrogen adsorption analysis, and helium pycnommetery is used to support a mechanism based on solid-state diffusion. Further TF experiments are used to elucidate the effects and mechanism of action of H2O and CO2 on agglomeration of limestone particles during sulfation under oxy-fuel conditions. Finally, using a pilot-scale oxy-fuel fired CFBC, the observations from the bench-scale experiments are tested in a realistic combustion environment. The effects of elevated CO2 and H2O associated with oxy-fuel combustion of petroleum coke on the catalytic NOX formation over limestone are discussed and related back to the proposed mechanism of action H2O and CO2 on sulphation.La combustion avec de l’oxygène pur (i.e., oxy-combustible) en lit fluidisé circulant (LFC) permet de produire de l'électricité tout en réduisant les émissions anthropiques de CO2 ainsi que le précurseur des pluies acides, du SO2, en utilisant du calcaire de façon in-situ. Bien que la technologie existe depuis 30 ans, il a récemment pris de l'attention avec l’opération de quelques unités à l'échelle pilote dans le monde. La combustion avec de l’oxygène pur est en grande partie semblable à la combustion standard avec de l’air, mais diffère sur quelques points clés, dont l'un est les concentrations élevées de CO2 et H2O (jusqu'à 90% et 30%, respectivement). Les effets et le mécanisme d'action de ces gaz sur la sulfatation du calcaire ont longtemps été un sujet de débat dans la littérature. A l’aide d'un analyseur thermogravimétrique (ATG) et un four tubulaire (FT), les effets de concentrations élevées de gaz sur la sulfatation du calcaire sont étudiées en utilisant des gaz d’échappement typiques de la combustion à l’air et à l’oxygène pur (SO2: 3800 ppm, CO2: de 12,5 à 82,5% , O2: 2,5%, H2O: 0 à 30%) à 850 ° C. Une explication est fournie pour les résultats contradictoires dans la littérature en termes de résultats obtenues avec les ATG/FT. Une analyse microstructurale des échantillons sulfatés utilisant la microscopie électronique à balayage (MEB), l'analyse d'adsorption d'azote et la pycnométrie d'hélium est utilisée pour soutenir un mécanisme basé sur la diffusion à l'état solide. D'autres expériences dans le FT sont utilisées pour élucider les effets et le mécanisme d'action de H2O et CO2 sur l'agglomération des particules de calcaire au cours de la sulfatation dans des conditions d'oxy-combustible. Enfin, en utilisant un LFC à l’échelle pilote, les observations des expériences en laboratoire ont été testés dans un environnement réaliste de combustion. Les effets de concentrations élevées de CO2 et H2O associés à la combustion oxycombustible du coke de pétrole sur la formation catalytique de NOx sur du calcaire sont discutés et reliés au mécanisme proposé de H2O et CO2 sur la sulfatation.
15
Burkell, James J. "Solids circulation rate measurement in a circulating fluidized bed." Thesis, University of British Columbia, 1986. http://hdl.handle.net/2429/26217.
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This thesis documents the investigation of three methods of determining solids fluxes in a circulating fluidized bed (CFB). An impact flowmeter used the force of the recirculating particles striking a pan which spanned the diameter of the return column to measure solids circulation rates. A modified orifice, with a conical entrance section, used the additional pressure differential resulting from solids flowing counter-currently to gas to determine solids fluxes. The third method used the velocities of particles travelling through the vertical section of an L-valve to determine solids circulation rates.
The results obtained in this work show that the impact flowmeter and the method utilizing L-valve particle velocities are viable methods of measuring solids fluxes in a CFB. However, further research is required before these methods can be confidently used. The modified orifice, as studied, was not sensitive enough to sense solids circulation. However, the meter may offer potential if studied with co-current gas solids flow.Applied Science, Faculty of
Chemical and Biological Engineering, Department of
Graduate
16
Zheng, Ying. "Flow structure in a liquid-solids circulating fluidized bed." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0013/NQ42560.pdf.
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Sajjakulnukit, Boonrod. "Hydrodynamics and heat transfer in a circulating fluidized bed." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0018/NQ46298.pdf.
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Redemann, Kai [Verfasser]. "Ash Management in Circulating Fluidized Bed Combustors / Kai Redemann." Aachen : Shaker, 2008. http://d-nb.info/1161313621/34.
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Almond, Robert R. "Small particle separation in a circulating fluidized bed riser system." Morgantown, W. Va. : [West Virginia University Libraries], 2005. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4342.
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Thesis (M.S.)--West Virginia University, 2005.Title from document title page. Document formatted into pages; contains xiii, 104 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 86-87).
20
Gupta, Suneel Krishan. "Modeling the hydrodynamics of large-scale circulating fluidized bed risers." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0025/MQ31388.pdf.
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Puchyr, David Michael John. "A predictive model for a circulating fluidized bed riser reactor." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0030/NQ38498.pdf.
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Wischnewski, Reiner [Verfasser]. "Simulation of Large-Scale Circulating Fluidized Bed Combustors / Reiner Wischnewski." Aachen : Shaker, 2009. http://d-nb.info/1126378720/34.
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Bischi, Aldo. "Chemical Looping Reactor System Design : Double Loop Circulating Fluidized Bed (DLCFB)." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-16972.
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Chemical looping combustion (CLC) is continuously gaining more importance among the carbon capture and storage (CCS) technologies. It is an unmixed combustion process which takes place in two steps. An effective way to realize CLC is to use two interconnected fluidized beds and a metallic powder circulating among them, acting as oxygen carrier. The metallic powder oxidizes at high temperature in one of the two reactors, the air reactor (AR). It reacts in a highly exothermic reaction with the oxygen of the injected fluidizing air. Afterwards the particles are sent to the other reactor where the fuel is injected, the fuel reactor (FR). There, they transport heat and oxygen necessary for the reaction with the injected fuel to take place. At high temperatures, the particle’s oxygen reacts with the fuel producing CO2 and steam, and the particles are ready to start the loop again. The overall reaction, the sum of the enthalpy changes of the oxygen carrier oxidation and reduction reactions, is the same as for the conventional combustion. Two are the key features, which make CLC promising both for costs and capture efficiency. First, the high inherent irreversibility of the conventional combustion is avoided because the energy is utilized stepwise. Second, the CO2 is intrinsically separated within the process; so there is in principle no need either of extra carbon capture devices or of expensive air separation units to produce oxygen for oxy-combustion. A lot of effort is taking place worldwide on the development of new chemical looping oxygen carrier particles, reactor systems and processes. The current work is focused on the reactor system: a new design is presented, for the construction of an atmospheric 150kWth prototype working with gaseous fuel and possibly with inexpensive oxygen carriers derived from industrial by-products or natural minerals. It consists of two circulating fluidized beds capable to operate in fast fluidization regime; this will increase the particles concentration in the upper section of the reactors, thus the gas solids contact. They are interconnected by means of two pneumatically controlled divided loop-seals and a bottom extraction/lift. The system is designed to be as compact as possible, to help up-scaling and enclosure into a pressurized vessel, aiming pressurization in a second phase. In addition several industrial solutions have been utilized, from highly loaded cyclones to several levels of secondary air injections. The divided loop-seals are capable to internally re-circulate part of the entrained solids, uncoupling the solids entrainment from the solids exchange. This will provide a better control on the process increasing its flexibility and helping to fulfil downstream requirements. No mechanical valves are utilized, but gas injections. The bottom extraction compensates the lower entrainment of the FR which has less fluidizing gas availability and smaller cross section than the AR. The lift allows adjusting the reactors bottom inventories, thus the pressures in the bottom sections of the reactors. In this way the divided loop-seals are not exposed to large pressure unbalances and the whole system is hydrodynamically more robust. The proposed design was finally validated by means of a full scale cold flow model (CFM), without chemical reactions. A thorough evaluation of the scaling state-of-the-art in fluidization engineering has been done; two are the approaches. One consists of building a small scale model which resembles the hydrodynamics of the bigger hot setup, by keeping constant a set of dimensionless numbers. The other is based on the construction of a full scale model, being careful to be in the same fluidization regime and to utilize particles with the same fluidization properties as the hot setup. In this way the surface to volume ratio is kept the same as that one of the hot rig. The idea presented in this work combines those two strategies, building a full scale CFM. In this way, it can be used for the hot rig design debugging and it is at the same time the hydrodynamic small scale model of a ten times larger industrial application. The adopted scaling strategy and design brought to the construction of one of the world biggest and more complex fluidized bed cold flow model reactor systems. The air and fuel reactor have a height of 5 m and a diameter of respectively 0.230 and 0.144 m. The selected particles are fine and heavy being classifiable as high density Geldart A; there is almost no published literature regarding those particles utilization in circulating fluidized beds. Extensive test campaigns have been performed to hydrodynamically validate the proposed designs. It was possible to understand and evaluate the operational window, the sensitivity to the input parameters and the key design details performance. Control strategies were qualitatively developed. The presented double loop architecture design showed good stability and flexibility at the same time, so that can also suit the requirements of other chemical processes based on two complementary reactions taking place simultaneously and continuously.
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Boyd, David Anthony. "Internally circulating fluidized bed membrane reactor for high-purity hydrogen production." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/30745.
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A novel reactor configuration, the internally circulating fluidized bed membrane reactor (ICFBMR),
was studied in an experimental program for the steam reforming (SMR) of natural gas to produce
hydrogen. This work builds on previous fluidized bed membrane reactor (FBMR) research, in which
H[sub 2]-selective membranes were located within a fluidized bed of catalyst to produce a H[sub 2] streamdirectly
from the reactor, thereby shifting the chemical equilibrium of the reforming reaction forward.
The ICFBMR advances this concept by modifying the reactor geometry in order to induce circulation
of catalyst solids up a central core draft assembly, which house vertical planar H[sub 2] membranes, and
down an outer annular region. The catalyst solids circulation has a number of benefits, especially
when the reactor is applied to autothermal reforming (ATR), where the endothermic reforming heat is
supplied by direct addition of air to the reactor. In this case, the circulating solids transfer heat from
the upper oxidation zone to the core reforming zone, with very little circulation of the nitrogen
entering with the oxidation air.
The hydrodynamics of the ICFBMR geometry were studied using a Plexiglas cold model.
Dimensionless variables were used in an attempt to match key scaling parameters between the cold
model, which used air and fluidized catalytic cracking (FCC) solids, and the hot reformer. Solids
circulation was studied as a function of the main and annular gas feed rates for three different
membrane panel geometries. It was found that solid membrane panels, which prevented
communication between the core flow slots, led to maldistribution of solids and gas. Helium tracer
studies confirmed that only a small portion (~10%) of the N[sub 2] in the oxidation air fed to the upper
reactor transferred to the reactor core with the returning solids. Solids circulation was found to
increase linearly with the main feed rate up to a core superficial gas velocity of ~0.3 m/s, and tended
to level off after a superficial gas velocity of ~0.5 m/s. The experimental data were used to find predictive
equations for solids circulation that could be used for the hot reformer design.
Double-sided planar H[sub 2] membranes (each 83 x 280 x 6 mm) were prepared using 50-μm thick
palladium alloy foil using techniques of Membrane Reactor Technologies Ltd. Six membranes were
installed in a pilot reactor (diameter 0.135 m, height 2.3 m) and a number of pilot reforming
experiments were performed. The reformer was successfully operated up to 650°C and 1,500 kPa
with a feed of natural gas and steam, under both SMR (external heat) and ATR (direct air addition).
Helium tracer studies were performed on the hot reformer, and internal solids circulation was
measured to be 0.21 kg/s at a typical operating condition, closely matching the value predicted from
cold model experimentation. Pure H[sub 2] (>99.999%, excluding N[sub 2] ) was produced for the first ~180 hours of testing, after which the H[sub 2] purity from two of the six membranes dropped to ~99.7% for the
remaining ~150 hours of hot operation. The highest hydrogen production from the pilot reactor was
1.06 Nm³/h. The highest measured ratio of permeate H[sub 2] to feed natural gas was 1.17 Nm³/Nm³, well
below the value required for economic operation (~2.5), highlighting how the reactor performance
was limited by the installed membrane area. ATR operation showed that permeate H[sub 2] production is
only marginally affected by the rate of air addition. Two types of catalyst powders, a SMR (NiO)
catalyst and a novel ATR catalyst, were used in the pilot reformer. Low catalyst activity affected a
number of the experimental runs.
The ICFBMR reactor was simulated using a commercial process simulator (HYSYS) to study the
influence of a number of variables on a reactor producing 30 Nm³/h of H[sub 2]. The simulation ignored
reaction kinetics, a reasonable assumption for this reactor configuration as reactor performance is
overwhelmingly controlled by membrane performance and reactor geometry, with reactor gases near
equilibrium. Simulations indicate that the predicted solids circulation rate is sufficient to maintain the
core temperature drop to below 30°C, and that there would be limited reduction in membrane area if
the circulation rate were to be increased. The reactor model was incorporated within a simulation for
the complete system, leading to a predicted overall energy efficiency of 69%, based on utility
consumption and the higher heating value of reactants. An economic evaluation of the ICFBMR
system was performed and compared with published data from a conventional small-scale SMR
system. Results indicate that the ICFBMR can achieve higher process efficiencies, but that membrane
cost and longevity are critical to making the process economically viable.Applied Science, Faculty of
Chemical and Biological Engineering, Department of
Graduate
25
Cruz, Torres Elizabet Ananay. "Modelling of a circulating fluidized bed using computational fluid dynamics software." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0007/MQ46244.pdf.
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Panday, Rupendranath. "Modeling, identification and control of a cold flow circulating fluidized bed." Morgantown, W. Va. : [West Virginia University Libraries], 2008. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=5833.
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Thesis (M.S.)--West Virginia University, 2008.Title from document title page. Document formatted into pages; contains xiii, 99 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 94-99).
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Hensler, Timo [Verfasser]. "Fluid Dynamic Characterization of Circulating Fluidized Bed Riser Reactors / Timo Hensler." München : Verlag Dr. Hut, 2020. http://d-nb.info/1219474754/34.
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Goldblatt, William M. "Electromagnetic induction sensing of individual tracer particles in a circulating fluidized bed." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/30918.
Full textAbstract:
Understanding the trajectories of particulate solids inside a flow-through reactor, such as the riser of a recirculating fluidized bed, is a basic requisite to accurately modelling the reactor. However, these trajectories, which are complicated by gross internal recirculation,
are not readily measurable. Conventional means of measuring the residence time distribution can be applied to closed boundaries, such as the exit of the riser. Doing so, however, does not directly provide the details of the trajectories within the riser. In order to determine these trajectories, meaningful measurements must be made at the open boundaries between the adjacent axial regions which, in total, make up the riser. Transient tracer concentration measurements at open boundaries are ambiguous because, as tracer material recirculates past the sensor, its concentration is repeatedly recorded, with no distinction as to which region (above or below the boundary) it has just resided in.
A method designed to eliminate this ambiguity at open boundaries is reported in this thesis. By repeatedly introducing single tracer particles into the riser, and measuring the time of passage through each axial region, the residence time distributions for each region can be obtained from the frequency density of these times. The crux of this approach is being able to sense individual tracer particles. The major thrust of this investigation has been to find a practical means to this end. The final sensor considered in this investigation is based on electromagnetic induction: a magnetic primary field induces an eddy current in a conductive tracer particle, and the resulting secondary field is sensed, indicating the presence of the tracer particle in the sensing volume. Noise, resulting from direct coupling between transmitter and receiver coils, electrostatics, and vibrations, determines the sensitivity of the device. The final prototype sensor is limited in sensitivity to relatively large tracer particles, and it is incapable of measuring tracer velocity. Nevertheless, the trajectory of large particles is of practical significance for circulating fluidized beds. Limited tests were conducted in a 0.15 m ID x 9.14 m tall acrylic riser where the tracer particles were injected opposite the solids re-entry point, and were sensed by a single sensor located at an open boundary 7.5 m downstream. At each of the two superficial gas velocities considered, and above a threshold solids flux, the time-of-flight frequency density between the injector and the sensor for these large tracer particles does not change with increasing flux of the fine solids. This result is incongruous with obvious changes in the macro-flow structure occurring in the riser.
Recommended changes in the sensor would allow measurement of the direction and speed of the tracer, as it passes by the sensor, as well as potentially reducing noise. With these improvements, it would be useful to install multiple sensors along the full length of
the riser. The information obtainable from such a configuration would greatly enhance understanding of the detailed trajectories within the riser.Applied Science, Faculty of
Chemical and Biological Engineering, Department of
Graduate
29
Ma, Ying L. "Heat transfer studies in a gas-solids downflow circulating fluidized bed, downer." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0003/MQ30689.pdf.
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Hassan, Mohamed. "Modelling and simulation of biomass gasification in a circulating fluidized bed reactor." Thesis, Aston University, 2013. http://publications.aston.ac.uk/20858/.
Full textAbstract:
Computational Fluid Dynamics (CFD) has found great acceptance among the engineering community as a tool for research and design of processes that are practically difficult or expensive to study experimentally. One of these processes is the biomass gasification in a Circulating Fluidized Bed (CFB). Biomass gasification is the thermo-chemical conversion of biomass at a high temperature and a controlled oxygen amount into fuel gas, also sometime referred to as syngas. Circulating fluidized bed is a type of reactor in which it is possible to maintain a stable and continuous circulation of solids in a gas-solid system. The main objectives of this thesis are four folds: (i) Develop a three-dimensional predictive model of biomass gasification in a CFB riser using advanced Computational Fluid Dynamic (CFD) (ii) Experimentally validate the developed hydrodynamic model using conventional and advanced measuring techniques (iii) Study the complex hydrodynamics, heat transfer and reaction kinetics through modelling and simulation (iv) Study the CFB gasifier performance through parametric analysis and identify the optimum operating condition to maximize the product gas quality. Two different and complimentary experimental techniques were used to validate the hydrodynamic model, namely pressure measurement and particle tracking. The pressure measurement is a very common and widely used technique in fluidized bed studies, while, particle tracking using PEPT, which was originally developed for medical imaging, is a relatively new technique in the engineering field. It is relatively expensive and only available at few research centres around the world. This study started with a simple poly-dispersed single solid phase then moved to binary solid phases. The single solid phase was used for primary validations and eliminating unnecessary options and steps in building the hydrodynamic model. Then the outcomes from the primary validations were applied to the secondary validations of the binary mixture to avoid time consuming computations. Studies on binary solid mixture hydrodynamics is rarely reported in the literature. In this study the binary solid mixture was modelled and validated using experimental data from the both techniques mentioned above. Good agreement was achieved with the both techniques. According to the general gasification steps the developed model has been separated into three main gasification stages; drying, devolatilization and tar cracking, and partial combustion and gasification. The drying was modelled as a mass transfer from the solid phase to the gas phase. The devolatilization and tar cracking model consist of two steps; the devolatilization of the biomass which is used as a single reaction to generate the biomass gases from the volatile materials and tar cracking. The latter is also modelled as one reaction to generate gases with fixed mass fractions. The first reaction was classified as a heterogeneous reaction while the second reaction was classified as homogenous reaction. The partial combustion and gasification model consisted of carbon combustion reactions and carbon and gas phase reactions. The partial combustion considered was for C, CO, H2 and CH4. The carbon gasification reactions used in this study is the Boudouard reaction with CO2, the reaction with H2O and Methanation (Methane forming reaction) reaction to generate methane. The other gas phase reactions considered in this study are the water gas shift reaction, which is modelled as a reversible reaction and the methane steam reforming reaction. The developed gasification model was validated using different experimental data from the literature and for a wide range of operating conditions. Good agreement was observed, thus confirming the capability of the model in predicting biomass gasification in a CFB to a great accuracy. The developed model has been successfully used to carry out sensitivity and parametric analysis. The sensitivity analysis included: study of the effect of inclusion of various combustion reaction; and the effect of radiation in the gasification reaction. The developed model was also used to carry out parametric analysis by changing the following gasifier operating conditions: fuel/air ratio; biomass flow rates; sand (heat carrier) temperatures; sand flow rates; sand and biomass particle sizes; gasifying agent (pure air or pure steam); pyrolysis models used; steam/biomass ratio. Finally, based on these parametric and sensitivity analysis a final model was recommended for the simulation of biomass gasification in a CFB riser.
31
Valmari, Tuomas. "Potassium behaviour during combustion of wood in circulating fluidised bed power plants /." Espoo [Finland] : Technical Research Centre of Finland, 2000. http://www.vtt.fi/inf/pdf/publications/2000/P414.pdf.
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Petersen, Inga [Verfasser]. "Sewage Sludge Gasification in the Circulating Fluidized Bed : Experiments and Modeling / Inga Petersen." Aachen : Shaker, 2004. http://d-nb.info/1172612110/34.
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Noymer, Peter Daniel. "Heat transfer by particle convection at the wall of a circulating fluidized-bed." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10435.
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Ratschow, Lars. "Three-dimensional simulation of temperature distributions in large scale circulating fluidized bed combustors." Aachen Shaker, 2009. http://d-nb.info/99450196X/04.
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Sarra, Angela M. "Particle-wall shear stress measurements within the standpipe of a circulating fluidized bed." Morgantown, W. Va. : [West Virginia University Libraries], 2001. http://etd.wvu.edu/templates/showETD.cfm?recnum=2078.
Full textAbstract:
Thesis (M.S.)--West Virginia University, 2001.Title from document title page. Document formatted into pages; contains xi, 137 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 136-137).
36
Johansson, William. "Experimental Study to Reduce CO Emissions in Skellefteå Kraft's 16 MW Bubbling Fluidized Bed Boiler." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-74398.
Full textAbstract:
Skellefteå Kraft has had high CO emissions problems in a bubbling fluidized bed (BFB) boiler in Malå.Statistical emissions data from 2013 to 2019 shows plant average emissions of 1230 ppm. Thisexceeds the recommended 440 ppm (6 % O2) that Naturvårdsverket proposes (Naturvårdsverket,2005). The aim of this project was to identify and map the cause of the BFB boilers high CO yield withthe help of a literature study as well as practical experiments to reduce CO, and; furthermore,suggest possible changes that can be implemented to resolve this problem.A literature study was conducted to gain a better understanding of possible causes of high CO influidized bed combustion of biomass. The results from the literature study showed that bedagglomeration, airflow symmetry, biomass moisture content, biomass particle size and biomass beddistribution all are common factors that can cause high CO emissions.Based on the literature study, statistical data from 2013 – 2019 and employee operator experience aseries of tests, calibrations and experiments were conducted on the boiler. The following methodswere used; Boiler statistical data analysis; Primary, secondary and tertiary airflow mapping;Pneumatic boiler feed system test (biomass bed distribution) and a bed material change test.From the statistical data analysis, it was found that sudden load variations had a minor contributionto the CO emissions. However, load variations were not the biggest contributing factor to high COemissions in the boiler in Malå. The primary, secondary and tertiary airflow were measured andmapped, uneven airflows between left and right were found. By calibration of even air distribution inthe primary systems CO levels were slightly reduced by 14 %. The primary air calibration improvedleft to right boiler air distribution from a 5 % difference to only a 0.7 % difference.A series of 11 tests was conducted on the pneumatic boiler feed system to obtain optimal fueldistribution. The test series that consisted of maximum parameters for transport air, spreading airand casting air obtained the lowest CO emissions levels of 350 ppm. An increase in airflow oftransport air in the pneumatic boiler feed system resulted in more even biomass bed distribution andincreased airflow in the lower secondary zone. This resulted in a dramatic CO emission decrease by63 %. A 45 °C temperature increase was also noticed in the secondary zone, a decrease intemperature before super heater 2 and a decrease in temperature before super heater 1. The changein transport air caused combustion of flue gasses to occur a lot lower in the furnace.This was clearly also documented through visual images taken inside the boiler with a special camerawhile the boiler was in operation. The images taken inside the boiler before and after theadjustments clearly showed that an increase of lower secondary air moves combustion closer to theboiler bed and reduces the CO emissions. The images also showed that uneven combustion wasoccurring in the boiler, as more violent and turbulent combustion was occurring on the right side ofthe boiler. This was an interesting finding as the measured airflow distribution was even in the boiler.This suggests that there is a major leakage in the air distribution pipes on the left side of the boiler.By reducing the airflow to the right section and increasing airflow to maximum on the left, an evenairflow distribution was obtained resulting in a more even combustion throughout the entire boiler.An increase in bed material change frequency from 1 time (3 % regeneration of total bed mass) to 3times (9 % regeneration of total bed mass) resulted in a CO emission decrease by 20 %. During thebed material change test bed agglomerates were observed which may explain the possible emissionsimprovement as the bed material was changed more frequently.All different tests were conducted independently of each other. The change that resulted in thehighest CO reduction was the increase of transport air to the secondary zone. Emissions werereduced by a total of 68 % as the transport air was set to maximum flow, the sand was changed threetimes and the primary airflow from left to right was even. The proposed adjustments will likely alsoincrease the boiler efficiency and reduce the maintenance of super heater 1, super heater 2 as wellas the economizer. The boiler produces around 400 ppm at 6 % O2 after the changes have beenimplemented. This is significantly lower compared to the original operation settings that during 2013to February 2019 have produced a CO emission of 1230 ppm (on average). The significant COdecrease in Skellefteå Kraft’s boiler has opened opportunity to operate the boiler with lower excessair which ultimately decreases exhaust heat losses. If Skellefteå Kraft were to succeed in operatingthe boiler at 3 % O2 excess, a sum of 255 kkr could be saved annually.The following recommendations are given in order to achieve low CO emissions:- Increase the bed material change frequency.- Clean pneumatic airflow system during summer stop annually.- Ensure airflow symmetry within the boiler is achieved annually.- Increase airflow to lower secondary zone.- Use recommended airflows for pneumatic boiler feed system.- Invest in a buffer tank to reduce load variation by Setra Sawmill.- Reduce secondary air nozzle size to increase combustion air in the middle of the boiler.- Increase the feed port ramp angle to increase biomass casting length in the boiler.- Investigate left side secondary air flow (possible leakage suggested)
37
De, Fonseca Pimentel Vittoria. "Technical comparison and economic evaluations of moving grate and circulating fluidized bed combustion technologies." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
Find full textAbstract:
The following work is the result of an internship carried out at STC POWER Company, in the proposal office, with the aim to make a technical comparison of two combustion technologies, Moving Grate (MG) and Circulating Fluidized Bed (CFB), in order to find out which is the optimal solution for a specific biomass power plant.
After a preliminary description of the fuel considered (biomass) and an overview of the operating principle of a combined heat and power (CHP) plant, the attention has been paid to the main differences of the two boilers, focusing on: fuel characteristics, pollutant emissions, corrosion and fouling problems, performances and auxiliaries.
Then, the technical comparison has been applied to a biomass CHP plant that will be realized in France following a tendering process to which STC Power is participating. The overall power plant has been simulated with the software Thermoflex both with MG boiler and CFB boiler and, after several optimizations, the results in terms of performances and efficiencies have been compared. Particularly critical has been the corrosion problem, caused by the fuel composition, that has led to a limitation on the maximum temperature of the steam produced with MG boiler, thus limiting also the overall efficiency of the plant.
After the technical analysis, also the economic aspects have been evaluated, with a comparison of the main costs (CAPEX and OPEX) of MG and CFB boilers.
Finally, the reasons that have led to choose one specific boiler instead of the other have been explained.
38
Wang, Yi-Ning. "CFD investigation of gas-solid flow dynamics in monolithic micro-circulating fluidized bed reactors." Thesis, Université Laval, 2008. http://www.theses.ulaval.ca/2008/25760/25760.pdf.
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Salvaterra, Antonio de Barros R. L. A. "Hydrodynamics of gas-solid suspension in a circulating fluidized bed riser : a comparative study." Thesis, Heriot-Watt University, 2003. http://hdl.handle.net/10399/418.
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Tan, Richard Hing-Fung. "Experimental simulation of the hydrodynamics of dissimilar solids in a pressurized circulating fluidized bed." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10483.
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Mahmoudi, Shiva. "The circulating fluidized bed (CFB) combustion of biomass and the control of gaseous emissions." Thesis, University of Warwick, 2011. http://wrap.warwick.ac.uk/45425/.
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Wang, Yining. "CFD investigation of gas-solid flow dynamics in monolithic micro-circulating fluidized bed reactors." Master's thesis, Université Laval, 2008. http://hdl.handle.net/20.500.11794/20312.
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La biomasse est une des sources importantes d'énergie primaire et renouvelable. Le développement d'un procédé basé sur la conversion de celle-ci en énergie tout en demeurant respectueux de l'environnement, fait l'objet de recherches intenses aussi bien dans les mondes académique qu'industriel. La gazéification pour produire un gaz de biosynthèse est considérée comme une des options les plus prometteuses via la valorisation des sources de résidus de biomasse. La thermodynamique et la cinétique intrinsèque imposent que les réactions de gazéification de la biomasse doivent être effectuées à des températures élevées, exigeant la fourniture et la récupération de chaleur de manière efficace. Le concept de gazéification allotherme (par opposition à son pendant autotherme) offre une solution attrayante pour la mise en oeuvre à haute température du couplage de réactions fortement endothermique avec des réactions exothermiques. Toutefois, la mise en oeuvre pratique du concept sous haute température n'est pas aisée. Dans ce travail, un nouveau concept pour la gazéification de résidus de la biomasse est proposé impliquant l'hybridation de réactions à hautes températures de la gazéification et de la combustion dans un réacteur monolithique structuré. Clairement, le design et l'optimisation de ce nouveau procédé hybride requiert la compréhension précise, non seulement des phénomènes physico-chimiques de la conversion thermochimique de la biomasse, mais aussi du comportement hydrodynamique, complexe, des deux phases mises en oeuvre dans un microréacteur monolithique à lit fluidisé. À cet égard, la caractéristique hydrodynamique de la distribution des écoulements des phases gaz-solide au sein du réacteur revêt une importance cruciale pour la prédiction du comportement des processus de gazéification/combustion et pour l'examen de stratégies d'opération du procédé. En particulier, en raison de la nature complexe de l'interaction entre le gaz et les particules solides ainsi que la phase stationnaire représentée par le microréacteur monolithique, un des défis dans le design et l'opération de ces réacteurs est la prévention de la maldistribution des phases. Dans ce travail, la mécanique des fluides numériques (MFN) est mise à profit comme outil de simulation permettant d'explorer les distributions des écoulements gaz-solide dans un réacteur monolithique. L'ensemble des sections structurée 111 (le monolithe) et les parties terminales non-structurées (lits fixes aléatoires permettant l'alimentation et l'évacuation de la suspension gaz-solide) est globalement considéré dans la simulation afin de capturer les tendances lourdes des mécanismes contribuant à la dynamique gaz-solide. Les résultats des simulations ont démontré la capacité de la MFN à capturer la caractéristique de non-uniformité de l'écoulement dans ce type de géométrie
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McIntyre, Christopher. "CPFD Modeling of a Novel Internally Circulating Bubbling Fluidized Bed for Chemical Looping Combustion." Thesis, Université d'Ottawa / University of Ottawa, 2021. http://hdl.handle.net/10393/42054.
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Pressurized chemical looping combustion (PCLC) is a promising next generation carbon capture technology which operates on the fundamentals of oxyfuel combustion to concentrate carbon dioxide in the flue gas stream. Oxygen is supplied through cyclic oxidation and reduction of a solid metal oxide between an air reactor and fuel reactor to prevent the direct contact of fuel and air. CanmetENERGY-Ottawa, in collaboration with Hatch Ltd., is designing a pilot scale PCLC system which uses ilmenite as the oxygen carrier and a novel fluidized bed design called the Plug Flow Internally-recirculating Reactor (PFIR). The PFIR consists of an annular bubbling fluidized region in which particles are circulated by angle jets through two reactive zones separated by baffles. The overall objective of this thesis was to provide key design parameters and insight for the construction of the pilot facility.
Experimental work was first conducted investigating the minimum fluidization velocity (Umf), gas bubble size, and tube-to-bed heat transfer coefficients of different ilmenite particle size distributions (PSDs) at varying pressures up to 2000 kPa. The data was compared to a variety of literature correlations. The Saxena & Vogel (1977) constants for the Wen-Yu type correlations (Remf=√C12+C2Ar-C1) resulted in the best fit for predicting the Umf of the PSDs with Sauter mean diameters (SMD) less than 109 μm, while the Chitester et al. (1984) constants resulted in better predictions for the larger particle size distributions (SMD greater than 236 μm). Gas bubble size was found to be marginally impacted by pressure, with the Mori & Wen (1975) correlation best fitting the data. The heat transfer coefficient was found to also be marginally increased by pressure with the the Molerus et al. (1995) correlation matching the atmospheric data. A computational particle fluid dynamic (CPFD) model of the experimental unit was then created and validated using the obtained data for minimum fluidization velocity and bubble size. The accuracy of the model was found to be dependent on the particle close packing factor input variable, with a value of 0.58 resulting in the best results for each of the ilmenite PSDs modeled. Finally, a CPFD model was created for a cold flow design of the PFIR to investigate the impacts of different operating parameters on the solids circulation rate and gas infiltration rate between the two reactor zones. This model used the validated parameters of the previous CPFD model to add confidence to the results. The impacts of increasing superficial gas velocity, fluidizing gas jet velocity, bed height, and pressure were all found to increase the solids circulation rate through their respective impacts on the momentum rate of the fluidizing gas. A polynomial function was fit between these two variables resulting in a method to predict the solids circulation rate. Similarly, the rate of gas infiltration between sections was found to be dependent on the solids circulation rate, allowing for a function to be made to predict the gas infiltration at different operating conditions.
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Pugalia, Neeraj. "Numerical modeling of cold flow and hot gas desulfurization in a circulating fluidized bed." Morgantown, W. Va. : [West Virginia University Libraries], 2001. http://etd.wvu.edu/templates/showETD.cfm?recnum=2056.
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Thesis (M.S.)--West Virginia University, 2001.Title from document title page. Document formatted into pages; contains xvi, 119 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 103-106).
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Seachman, Steven M. "Application of a reflective optical probe to measure solids fractions in a circulating fluidized bed." Morgantown, W. Va. : [West Virginia University Libraries], 2007. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4988.
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Thesis (M.S.)--West Virginia University, 2007.Title from document title page. Document formatted into pages; contains xiii, 97 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 72-74).
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Batu, Aykan. "Investigation Of Combustion Characteristics Of Indigenous Lignite In A 150 Kwt Circulating Fluidized Bed Combustor." Phd thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609432/index.pdf.
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Coal is today the fossil fuel which offers the greatest proven reserves. Due to increasingly stringent environmental legislation, coal fired combustion systems should be based on clean coal combustion technologies. For clean and efficient
energy generation from coal reserves, the most suitable technology known to date is the &lsquoFluidized Bed Combustion&rsquo
technology. Applications of circulating fluidized bed combustion (CFB) technology have been steadily increasing in both capacity and number over the past decade for the utilization of this resource. Designs of these units have been based on the combustion tests carried out in pilot scale facilities to determine the combustion and desulfurization characteristics of the coals and limestones in CFB conditions. However, utilization of Turkish lignites with high ash, volatile matter and sulfur contents in CFB boilers necessitates adaptation of CFB combustion technology to these resources. Therefore, it has been the objective of this study to investigate combustion characteristics of an indigenous lignite in a circulating fluidized bed combustor. In this study, a 150 kWt Circulating Fluidized Bed (CFB) Combustor Test Unit was designed and constructed in Chemical Engineering Department of Middle East Technical University, based on the extensive experience acquired at the existing 0.3 MWt Bubbling Atmospheric Fluidized Bed Combustor (AFBC) Test Rig. Following the commissioning tests, combustion tests were carried out for investigation of combustion characteristics of Ç
an lignite in CFB conditions and for comparison of the design of the test unit with experimental findings. The steady state results of the combustion tests reveal that Ç
an lignite is fired with high combustion efficiency. Temperature profile along the riser is achieved to be almost uniform by good control of cooling system. Pressure drop through the dilute zone is found to be negligible because of low solid hold up in this zone. CO and NO concentrations within the flue gas are fairly lower, whereas N2O concentration is higher compared to the ones obtained in the bubbling AFBC test rig firing the same lignite. The deviation of particle size distributions of bottom ash and circulating ash among the tests are in line with the deviation of superficial velocity. In order to assess the validity and predictive accuracy of the pressure balance model, it was reapplied to the test unit utilyzing the revised input data based on the results of the combustion tests. Comparison of the model predictions with experimental results revealed that the predictions have acceptable agreement with the measurements. In conclusion, the performance of 150 kW CFBC Test Unit was found to be satisfactory to be utilized for the long term research studies on combustion and desulfurization characteristics of indigenous lignite reserves in circulating fluidized bed combustors.
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Chevrier, Solène. "Development of subgrid models for a periodic circulating fluidized bed of binary mixture of particles." Phd thesis, Toulouse, INPT, 2017. http://oatao.univ-toulouse.fr/19905/1/CHEVRIER_Solene.pdf.
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Detailed sensitivity numerical studies have shown that the mesh cell-size may have a drastic effect on the modelling of circulating fluidized bed with small particles. Typically, the cell-size must be of the order of few particle diameters to predict accurately the dynamical behaviour of a fluidized bed. Hence, the Euler-Euler numerical simulations of industrial processes are generally performed with grids too coarse to allow the prediction of the local segregation effects. Appropriate modelling, which takes into account the influence of unresolved structures, have been already proposed for monodisperse simulations. In this work, the influence of unresolved structures on a binary mixture of particles is investigated and models are proposed to account for those effect on bidisperse simulations of bidisperse gas-solid fluidized bed. To achieve this goal, Euler-Euler reference simulations are performed with grid refinement up to reach a mesh independent solution. Such kind of numerical simulation is very expensive and is restricted to very simple configurations. In this work, the configuration consists of a 3D periodical circulating fluidized bed, that could represent the established zone of an industrial circulating fluidized bed. In parallel, a filtered approach is developed where the unknown terms, called sub-grid contributions, appear. They correspond to the difference between filtered terms, which are calculated with the reference results then filtered, and resolved contributions, calculated with the filtered fields. Then spatial filters can be applied to reference simulation results to measure each sub-grid contribution appearing in the theoretical filtered approach. A budget analysis is carried out to understand and model the sub-grid term. The analysis of the filtered momentum equation shows that the resolved fluid-particle drag and inter-particle collision are overestimating the momentum transfer effects. The analysis of the budget of the filtered random kinetic energy shows that the resolved production by the mean shear and by the mean particle relative motion are underestimating the filtered ones. Functional models are proposed for the subgrid contributions of the drag and the inter-particle collision.
48
Ratschow, Lars [Verfasser]. "Three-Dimensional Simulation of Temperature Distributions in Large-Scale Circulating Fluidized Bed Combustors / Lars Ratschow." Aachen : Shaker, 2009. http://d-nb.info/1156518016/34.
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Ebert, Todd Alan. "An experimental investigation of particle and gas convection heat transfer in a circulating fluidized bed." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/13833.
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Lan, Qingdao. "Development of a continuous ion exchange system for protein recovery using liquid-solid circulating fluidized bed." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ58401.pdf.
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