Dissertations / Theses on the topic 'Fluidized-bed combustion'
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1
Hossain, Abu Norman. "Combustion of solid fuel in a fluidized bed combustor." Ohio : Ohio University, 1998. http://www.ohiolink.edu/etd/view.cgi?ohiou1176492911.
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Hossain, Abu Noman. "Combustion of solid fuel in a fluidized bed combustor." Ohio University / OhioLINK, 1998. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1176492911.
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Rao, Arjun Shankar. "Carbonation of fluidized bed combustion solids." Thesis, University of Ottawa (Canada), 2006. http://hdl.handle.net/10393/27412.
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Fluidized bed combustion (FBC) ash from the combustion of high-sulphur fuels with limestone addition can contain from 15 to 25% quick lime content. This excess calcium oxide gives the ash numerous undesirable properties such as strong exothermicity on wetting and high-pH leachate that must be treated before discharge. It also leads to the formation of ettringite with significant deleterious expansion in the landfill. In consequence, carbonation of FBC ash is desirable in order to reduce its alkalinity and improve its disposal characteristics.
The current technique to reduce the exothermic character of the ash involves hydrating the ash in two stages, leading to the consumption of large quantities of water. Sonication along with simultaneous carbonation of the ash yields a product suitable for direct disposal in landfills with the minimum of water addition (to achieve the optimum proctor levels for maximum compaction of the ash in the landfill site). This work explores the use of sonochemical-enhanced carbonation of FBC ash. Tests have been conducted using four ashes, two of which differ in age only and are from the Nova Scotia Power 183 MWe CFBC (circulating fluidized bed combustor) boiler. The other two ashes are from the CFBC boilers at A/C power and Piney Creek, U.S.A. Tests with additives such as sodium chloride (at levels comparable with that in seawater) and seawater from Nova Scotia have also been carried out. Tests were carried out at low (20°, 40°C) and high (60°, 80°C) temperatures. Sonicated samples were also analyzed using TGA (Thermogravimetric analysis), TGA-FTIR (Thermogravimetric and Fourier transform infra red spectroscopy analysis) and XRD (X-ray diffraction) techniques to determine the influence of other calcium compounds (OCC). The size reduction brought about by sonication was quantified using wet sieving.
The ash reactivity displays a strong temperature dependency with almost complete carbonation of the ashes being achieved in minutes at higher temperatures. Additives were found to increase the level of hydration of the ashes in line with previous work; however, carbonation levels were unaffected. TGA, TGA-FTIR and XRD analysis of the samples indicated that other calcium compounds (OCC) were also formed during hydration.
4
Lin, Jeng-Liang Keener Harold M. "Corncob combustion in a fluidized bed /." Connect to resource, 1991. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1145451174.
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Lin, Jeng-Liang. "Corncob combustion in a fluidized bed." The Ohio State University, 1991. http://rave.ohiolink.edu/etdc/view?acc_num=osu1145451174.
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Xu, Jiangang Chemical Sciences & Engineering Faculty of Engineering UNSW. "Coal related bed material agglomeration in pressurized fluidized bed combustion." Awarded by:University of New South Wales. School of Chemical Sciences and Engineering, 2006. http://handle.unsw.edu.au/1959.4/25131.
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The thermodynamic behaviours in a PFBC combustor were simulated for the ash from all of the six coals with sand and limestone as bed material. Ash components determined the ash thermodynamic behaviour at high temperature, and each component had different effects. For assessment of the potential for bed material agglomeration, the temperature at which 15% of the ash would become liquid (T15) was calculated with the coal ash, the cyclone ash and the cyclone ash mixed with varying amounts of limestone. Both the bed ash and fly ash, collected from an industrial PFBC plant, consisted of limestone/lime particles with different extent of sulphation, and coal ash particles. The calcium aluminosilicate material formed on the coal ash particles but not on the limestone particles. The aluminosilicate materials appeared to be formed from fine ash and lime particles at some local hot zones in the boiler. The melted materials may glue ash and bed material particle into large particles leading to bed agglomeration and defluidization. Four mechanisms were proposed for the formation of bed material agglomeration in PFBC, which may occur under different conditions. One mechanism explains the bed material agglomeration with the high localized high temperature zone due to the improper design or operation, while the bed agglomeration through the other three mechanisms results from the unsuitable coals burnt in the PFBC combustor. The maximum char temperature and the minimum T15 were used simultaneously to predict the tendency towards bed material agglomeration in PFBC burning different coals. Both char properties and ash properties should be considered during coal selection process for PFBC, to ameliorate the potential problem of bed agglomeration.
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Wildegger-Gaissmaier, Anna Elisabeth. "Fluidized bed utilization of South Australian coals." Title page, contents and abstract only, 1988. http://web4.library.adelaide.edu.au/theses/09PH/09phw672.pdf.
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Gogolek, Peter Edmund Gordon. "Mathematical modelling of fluctuations in fluidized bed combustion." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0006/NQ31928.pdf.
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Vaart, D. R. van der. "The combustion of gas in a fluidized bed." Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355686.
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Yliniemi, J. (Juho). "Alkali activation-granulation of fluidized bed combustion fly ashes." Doctoral thesis, Oulun yliopisto, 2017. http://urn.fi/urn:isbn:9789526215624.
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Abstract Biomass, such as wood, binds CO2 as it grows, and is thus considered an environmentally friendly alternative fuel to replace coal. In Finland, biomass is typically co-combusted with peat, and also municipal waste is becoming more common as a fuel for power plants. Wood, peat and waste-based fuels are typically burned in fluidized bed combustion (FBC) boilers. Ash is the inorganic, incombustible residue resulting from combustion. The annual production of biomass and peat ash in Finland is 600 000 tonnes, and this amount is likely to increase in the future, since the use of coal for energy production will be discontinued during the 2020s. Unfortunately, FBC ash is still largely unutilized at the moment and is mainly dumped in landfills. The general aim of this thesis was to generate information which could potentially improve the utilization of FBC ash by alkali activation. The specific objective was to produce geopolymer aggregates by means of a simultaneous alkali activation-granulation process. It was shown that geopolymer aggregates with physical properties comparable to commercial lightweight expanded clay aggregates (LECAs) can be produced from FBC fly ash containing heavy metals. Although the ashes were largely unreactive and no new crystalline phases were formed by alkali activation, a new amorphous phase was observed in the XRD patterns, possibly representing micron-sized calcium aluminate silicate hydrate-type gels. The heavy metal immobilization efficiency of alkali activation varied with the type of fly ash. Good stabilization was generally obtained for cationic metals such as Ba, Pb and Zn, but in common with the results obtained with alkali activation of coal fly ash, anionic metals became leachable after alkali activation. The efficiency of immobilization depended on the physical and chemical properties of the fly ash and was not related to the total content of the element. All the geopolymer aggregates met the criteria for a lightweight aggregate (LWA) as defined by EN standard 13055-1. Their strength depended on the reactivity and particle size distribution of the fly ash. Mortars and concretes prepared with such geopolymer aggregates had higher mechanical strength, higher dynamic modulus of elasticity and higher density than concrete produced with commercial LECA, while exhibiting similar rheology and workabilityTiivistelmä Biopolttoaineet, esimerkiksi puu, ovat ympäristöystävällinen vaihtoehto kivihiilelle, koska ne sitovat hiilidioksidia kasvaessaan. Suomessa biopolttoaineita poltetaan tyypillisesti turpeen kanssa, ja nykyään myös jätteen hyödyntäminen polttoaineena on yleistynyt. Puu, turve ja jätepolttoaineet poltetaan tyypillisesti leijupetipoltto-tekniikalla. Tuhka on polton epäorgaaninen, palamaton jäännös. Puun ja turpeen tuhkaa tuotetaan Suomessa 600 000 tonnia vuodessa ja määrän odotetaan kasvavan, sillä kivihiilen poltto lopetetaan 2020-luvulla. Leijupetipolton tuhkaa ei tällä hetkellä juurikaan hyödynnetä ja tuhka päätyykin pääasiassa kaatopaikoille. Tämän tutkielman päämääränä oli tuottaa tietoa, joka parantaisi leijupetipolton tuhkien hyödyntämistä alkali-aktivaatiolla. Erityisesti tavoitteena oli valmistaa geopolymeeriaggregaatteja yhtäaikaisella alkali-aktivaatiolla ja rakeistuksella. Tutkielmassa osoitettiin, että raskasmetalleja sisältävistä tuhkista valmistettujen geopolymeeriaggregaattien fysikaaliset ominaisuudet ovat vertailukelpoiset kaupallisten kevytsora-aggregaattien (LECA) kanssa. Vaikka tuhkien reaktiivisuus oli matala, ja uusia kidefaaseja ei muodostunut alkaliaktivaatiolla, uusi amorfinen faasi havaittiin XRD-mittauksissa. Uusi amorfinen faasi oli mahdollisesti mikrometrikokoluokan kalsium-aluminaatti-silikaatti-hydraatti-tyyppinen rakenne. Raskasmetallien stabiloinnin tehokkuus vaihteli tuhkien välillä. Kationiset metallit, kuten barium, lyijy ja sinkki, stabiloituivat pääasiassa hyvin, mutta anionisten metallin liukoisuus kasvoi alkali-aktivoinnin myötä. Stabiloinnin tehokkuus riippui tuhkien fysikaalisista ja kemiallisista ominaisuuksista, mutta raskasmetallin kokonaispitoisuudella ei ollu vaikutusta. Kaikki geopolymeeriaggregaatit olivat kevytsora-aggregaatteja standardin EN 13055-1 mukaisesti. Aggregaattien lujuus riippui tuhkan reaktiivisuudesta ja partikkelikokojakaumasta. Geopolymeeriaggregaateilla valmistettujen laastien ja betonien mekaaninen lujuus, Youngin moduuli ja tiheys olivat korkeampia kuin kaupallisella kevytsora-aggregaateilla valmistetut, vaikka niiden reologia ja työstettävyys olivat samanlaisia
11
Trivett, G. S. "Combustion of coal/water slurry in a fluidized bed." Thesis, University of Leeds, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371453.
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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.
13
Varol, Murat. "Combustion And Co-combustion Of Olive Cake And Coal In A Fluidized Bed." Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/12607182/index.pdf.
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In this study, combustion performances and emission characteristics of olive cake and olive cake+coal mixture are investigated in a bubbling fluidized bed of 102 mm inside diameter and 900 mm height. The average particle sizes of coal and olive cake used in the experiments were 1.57 mm and 1.52 mm, respectively. Flue gas concentrations of O2, CO, SO2, NOx, and total hydrocarbons (CmHn) were measured during combustion experiments. Operational parameters (excess air ratio, secondary air injection) were changed and variation of pollutant concentrations and combustion efficiency with these operational parameters were studied.
The temperature profiles measured along the combustor column was found higher in the freeboard for olive cake than coal due to combustion of hydrocarbons mostly in the freeboard. The location of the maximum temperature in the freeboard shifted to the upper part of the column, as the volatile matter content in the fuel mixture increased.
Combustion efficiencies in the range of 83.6-90.1% were obtained for olive cake with the excess air ratio of 1.12-2.30. The corresponding combustion efficiency for coal was 98.4-99.7% under the same conditions. As the CO and hydrocarbon concentration in the flue gas increased, the combustion efficiency decreased.
Also co-combustion experiments of olive cake and coal for various mixing ratios were carried out. As the amount of olive cake in the fuel mixture increased, SO2 emissions decreased because of the very low sulfur content of olive cake.
In order to increase the combustion efficiency, secondary air was injected into the freeboard which was a good solution to decrease the CO and hydrocarbon emissions, and to increase the combustion efficiency.
For the setup used in this study, the optimum operating conditions with respect to NOx and SO2 emissions were found as 1.35 for excess air ratio, and 30 L/min for secondary air flowrate for the combustion of 75 wt% olive cake and 25 wt% coal mixture. Highest combustion efficiency of 99.8% was obtained with an excess air ratio of 1.7, secondary air flow rate of 40 L/min for the combustion of 25 wt% olive cake and 75 wt% coal mixture.
14
Linjewile, Temi Makecha. "Temperature of burning carbonaceous particles in a fluidized-bed combustor /." Title page, contents and abstract only, 1993. http://web4.library.adelaide.edu.au/theses/09PH/09phl756.pdf.
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Sotudeh, Gharebaagh Rahmat. "Combustion of natural gas in a turbulent fluidized bed reactor." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0006/NQ42829.pdf.
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Agarwal, Gaurav. "Solid Fuel Blend Pyrolysis-Combustion Behavior and Fluidized Bed Hydrodynamics." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/51677.
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As a carbon neutral and renewable source of energy, biomass carries a high potential to help sustain the future energy demand. The co-firing of coal and biomass mixtures is an alternative fuel route for the existing coal based reactors. The main challenges associated with co-firing involves proper understanding of the co-firing behavior of blended coal-biomass fuels, and proper understanding of advanced gasification systems used for converting such blended fuels to energy.
The pyrolysis and combustion behavior of coal-biomass mixtures was quantified by devising laboratory experiments and mathematical models. The pyrolysis-combustion behavior of blended fuels was quantified on the basis of their physicochemical, kinetic, energetic and evolved gas behavior during pyrolysis/combustion. The energetic behavior of fuels was quantified by applying mathematical models onto the experimental data to obtain heat of pyrolysis and heat of combustion. Fuel performance models were developed to compare the pyrolysis and combustion performance of non-blended and blended fuels. The effect of blended fuel briquetting was also analyzed to find solutions related to coal and biomass co-firing by developing a bench scale fuel combustion setup. The collected data was analyzed to identify the effects of fuel blending and briquetting on fuel combustion performance, ignitability, flammability and evolved pollutant gases.
A further effort was made in this research to develop the understanding of fluidized bed hydrodynamics. A lab scale cold-flow fluidized bed setup was developed and novel non-intrusive techniques were applied to quantify the hydrodynamics behavior. Particle Image Velocimetry and Digital Image Analysis algorithms were used to investigate the evolution of multiple inlet gas jets located at its distributor base. Results were used to develop a comprehensive grid-zone phenomenological model and determine hydrodynamics parameters such as jet particle entrainment velocities and void fraction among others. The results were further used to study the effect of fluidization velocity, particle diameter, particle density, distributor orifice diameter and orifice pitch on the solid circulation in fluidized beds.Ph. D.
17
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
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He, Hanbing. "Layer Formation on Bed Particles during Fluidized Bed Combustion and Gasification of Woody Biomass." Doctoral thesis, Luleå tekniska universitet, Energivetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-63090.
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Although more than a hundred papers dealing with the agglomeration problem in combustion and gasification of biomass can be found in the literature, very few studies focusing on the bed particle layer formation process in fluidized bed combustion (FBC) and fluidized bed gasification (FBG) can be found. With increased knowledge of the bed particle layer formation process — i.e. the main route behind bed agglomeration and bed material deposition in wood combustion/gasification — suitable combinations of fuel/bed material and/or bed material management measures can be suggested. This would not only aim to reduce the risk of ash related operational problems but also to enhance the catalytic activity of the bed material (e.g. for tar removal in gasification). The present investigation was therefore undertaken to determine the layer formation process on and within typical bed materials (i.e. quartz and olivine) and for a potentially interesting new bed material, K-feldspar. Bed material samples were collected from four different combustion and two different gasification appliances: two bubbling fluidized beds (BFB) (5 kWth/30 MWth), two full-scale circulating fluidized beds (CFB) (90/122 MWth), and two dual fluidized bed gasifiers (DFB) (8/15 MWth). Scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS) and X-ray diffraction (XRD) were used to explore layer morphology and elemental composition and to gain information about crystalline phases of the layers. Phase diagrams and thermodynamic equilibrium calculations (TECs) were used to interpret the melting behavior of the layers and the melt fragments in deposits. In addition, a diffusion model was used to interpret the layer growth process. For quartz bed particles taken from BFB, the younger particles (< around 1 day) had only one thin layer, but for particles older than 3 days, the layer consisted of inner and outer layers. In addition to the inner and outer layers, a K-rich inner-inner layer was found for bed particles taken from CFB and DFB. No outer layers were found for quartz bed particles taken from DFB. The thin/absence of an outer layer could have resulted from the more significant attrition between particles in CFB and DFB. Reduced availability of Ca and a risk of layer breakage from the particle lead to the formation of the inner-inner layer. Similar elemental compositions of the layers upon the quartz bed particles taken from different fluidized bed techniques were found. The inner-inner layers are dominated by Si, K and Ca (excluding O), and the outer layers are rich in Ca, Si and Mg, which seem to resemble more closely the fuel ash composition. The inner layers, mainly consisted of Si and Ca, were found to have higher concentrations of Ca for older particles. The layer thickness increases with particle age, but the growth rate decreases. Melt was estimated to exist in the inner layer for younger particles (< around 1 day) and in the inner-inner layer. The existence of partially melted inner-inner layers, in particles from CFB and DFB, points towards higher risk of bed agglomeration in these techniques compared to BFB. Based on the experimental results, thermodynamic equilibrium calculations, and diffusion model analyses, a layer formation process on quartz bed particle was suggested: the layer formation is initiated by reaction of gaseous K compounds with quartz to form K-rich silicate melt, which prompts the diffusion of Ca2+. The gradual incorporation of Ca into the melt followed by the precipitation of Ca-silicates, e.g. Ca2SiO4, will result in the continuous inner layer growth. However, because of increasing concentration of Ca and release of K from the inner layer, the melt disappears in the inner layer and the layer formation process gradually becomes Ca diffusion controlled. The diffusion resistance increases with increasing thickness of a more Ca-rich layer, resulting in a decreasing layer growth rate. Crack layers with similar compositions dominated by Si, K and Ca were observed in relatively old quartz bed particles. A melt was predicted to exist in the crack layer according to thermodynamic equilibrium calculations. The crack layers found in quartz particles from BFB and CFB connect with the cracks in the inner layer, whereas for bed samples collected from DFB, the crack layers were found along existing cracks in the quartz particle. The different morphologies may indicate different routes of formation for crack layers in bed particles from different fluidized bed technologies. For quartz particles from BFB and CFB, crack formation through the inner layer down to the interface between the inner layer and the core of quartz bed particle initiates the cracks in the quartz bed particle. This allows for diffusion of gaseous alkali compounds to react with quartz in the bed particle core, thereby forming crack layers. The reaction is accelerated with bridge formation between crack layers. This may later lead to the breakdown of the bed particle into smaller alkali-silicate-rich fragments. For K-feldspar bed particles from BFB and CFB, only one layer was found for particles with an age of 1 day. For bed particles with ages older than 3 days, two layers including a homogenous inner layer containing cracks and a more particle-rich outer layer can be distinguished. Compared to bed particles from BFB with similar ages, the outer layer is thinner for bed particles from CFB. The inner layer is dominated by Ca, Si and Al (excluding O), whereas the outer layer is dominated by Ca, Si and Mg. The average concentration of Ca in the inner layer increases with bed particle age. Increasing layer thickness with decreasing growth rate was found, similar to that on quartz particles. For particles from DFB, the inner layer is also mainly consisted of Ca and Si, but cracks in the inner layer were not found. For all the particles, the Ca/Si molar ratio in the layer decreases towards the bed particle core and the change of concentration is more significant at the bed particle core/layer interface. The overall inner layer growth is resultant from the gradual incorporation of Ca into the layer. For olivine bed particles from DFB, the younger bed particles (< around 24 h) have only one layer, but after 24 h, an inner layer and an outer layer appear. Furthermore, for bed particles older than 180 h, the inner layer is separated into a distinguishable Ca-rich and Mg-rich zone. Two kinds of cracks in the inner layer either perpendicular or parallel to the particle surface were observed. Compared to the younger bed particles, the Ca concentration in the layer of older particles is much higher. A detailed mechanism for layer formation on olivine particles in fluidized bed gasification (most likely also applicable to combustion) based on the interaction between woody biomass ash and olivine has been proposed. The proposed mechanism is based on a solid-solid substitution reaction. However, a possible enabling step in the form of a Ca2+ transport via melts may occur. Ca2+ is incorporated into the crystal structure of olivine by replacing either Fe2+ or Mg2+. This substitution occurs via intermediate states where Ca-Mg silicates, such as CaMgSiO4, are formed. Mg2+ released from the crystal structure most likely forms MgO, which can be found in a distinguishable zone between the main particle layers. Due to a difference in the bond lengths between Mg/Fe and incorporated Ca2+ with their respective neighboring oxygen atoms, the crystal structure shifts, resulting in formation of cracks. The dominating elements in the inner layers are similar for each kind of bed material from BFB, CFB, and DFB, indicating limited effects of atmosphere on the inner layer formation. The initiation of layer formation differs depending on the bed material, but increasing Ca concentration in the inner layer with time for all bed materials indicates that the layer growth resulted from the incorporation of Ca into the layer. Compared to quartz, K-feldspar and olivine are more promising bed materials in wood combustion/gasification, especially in CFB and DFB techniques, from the perspective of mitigating bed agglomeration and bed material deposit build-up.
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Altindag, Hakan. "Mathematical Modeling Of Sulfur Retention In Fluidized Bed Combustors." Master's thesis, METU, 2003. http://etd.lib.metu.edu.tr/upload/1085661/index.pdf.
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A considerable number of modeling studies for the investigation of sulfur
retention in atmospheric bubbling fluidized bed combustors have been carried out
and well documented in the literature. Despite 30 years of intensive study of
sulfation process in fluidized bed combustors and numerous laboratory studies,
there are still many uncertainties and disagreements on the subject. In addition,
modeling sulfur retention performance of Turkish lignites with high sulfur, volatile
matter and ash contents has not drawn much attention to date. Recent trend in
utilization of indigenous lignites in fluidized bed boilers necessitated investigation of pollutant emissions and adaptation of fluidized bed combustion technology to
these lignites. In an attempt to achieve this objective, a system model, previously
developed and tested for the prediction of the combustion behavior of fluidized bed
combustors was extended to incorporate sulfur retention.
The predictive accuracy of the model was assessed by applying it to the
prediction of the behavior of METU 0.3 MWt ABFBC test rig burning indigenous
lignites in their own ashes, and comparing its predictions with measurements taken
on the same rig. Sulfur dioxide concentration predictions throughout the combustor
were found to be in good agreement with the experimental data except for the small
discrepancy between predictions and measurements in the bed section.
Measurements and model predictions revealed that recyling enhances calcium
utilization significantly by increasing the sorbent residence time leading to higher
sulfur retention efficiencies. The system model proposed in this study proves to be a
useful tool in qualitatively and quantitatively simulating the processes taking place
in an atmospheric fluidized bed combustor.
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Ngeleka, Tholakele Prisca. "Sulphur dioxide capture under fluidized bed combustion conditions / Tholakele Prisca Ngeleka." Thesis, North-West University, 2005. http://hdl.handle.net/10394/1416.
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An investigation was undertaken to determine the feasibility of increasing the hydrogen
production rate by coupling the water gas shift (WGS) process to the hybrid sulphur process
(HyS). This investigation also involved the technical and economical analysis of the water gas
shift and the H2 separation by means of Pressure swing adsorption (PSA) process. A technical
analysis of the water gas shift reaction was determined under the operating conditions selected
on the basis of some information available in the literature. The high temperature system (HTS)
and low temperature system (LTS) reactors were assumed to be operated at temperatures of
350ºC and 200ºC, respectively. The operating pressure for both reactors was assumed to be 30
atmospheres. The H2 production rate of the partial oxidation (POX) and the WGS processes was
242T/D, which is approximately two times the amount produced by the HyS process alone. The
PSA was used for the purification process leading to a hydrogen product with a purity of
99.99%. From the total H2 produced by the POX and the WGS processes only 90 percent of H2
is recovered in the PSA. The unrecovered H2 leaves the PSA as a purge gas together with CO2
and traces of CH4, CO, and saturated H2O. The estimated capital cost of the WGS plant with
PSA is about US$50 million. The production cost is highly dependent on the cost of all of the
required raw materials and utilities involved. The production cost obtained was US $1.41/kg H2
based on the input cost of synthesis gas as produced by the POX process. In this case the
production cost of synthesis gas based on US $6/GJ for natural gas and US $0/Ton for oxygen
was estimated to be US $0.154/kg. By increasing the oxygen and natural gas cost, the
corresponding increase in synthesis gas has resulted in an increase in H2 production cost of US $1.84/kg.Thesis (M.Sc. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2006.
21
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
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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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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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Suksankraisorn, Kriengkrai. "Co-combustion of municipal solid waste and thailignite in a fluidized bed." Mulhouse, 2002. http://www.theses.fr/2002MULH0713.
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On étudie les principales caractéristiques de la co-combustion des ordures ménagères (OM) et du lignite Thai͏̈landais. Les sorties aléatoires du système (yj) , liées à l'alimentation du solide (ui) et à la distribution d'air (uo) dans le réacteur en lit fluidisé sont filtrées et analysées autour d'états stationnaires. La co-combustion réduit les émissions de S02 et augmente légèrement celles des NOx en réduisant sensiblement l'efficacité de la combustion. Un rapport air secondaire sur air primaire (uo =0. 2) pour 40 à 60 % d'excès d'air (U2) et une composition massique de 20 % en OM permet de maximiser l'efficacité de la combustion et de minimiser les taux de rejet en CO et NOx. Les rejets de S02 peuvent être fortement réduits par addition de chaux- L'analyse statistique par des fonctions de corrélation, l'étude de la puissance spectrale des signaux filtrés (yj) de température et de concentration des gaz en sortie de réacteur montrent une compétition entre des réactions en phase gaz donnant lieu à un phénomène périodique. Des modèles linéaires obtenus montrent qu'il est possible de contrôler la combustion, mais de grandes erreurs résiduelles pour les sorties CO et S02 devraient être prises en compte par des modèles non-linéaires plus complexes.
25
Tureso, João Paulo. "Estudo de uma planta piloto para a combustão em leito fluidizado borbulhante de carvões minerais brasileiros com altos teores de cinzas e enxofre." Universidade de São Paulo, 2004. http://www.teses.usp.br/teses/disponiveis/18/18135/tde-10022017-162225/.
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O carvão mineral nacional representa uma alternativa atraente para a solução do problema energético do Brasil. Os maiores problemas técnicos associados à queima dos carvões minerais brasileiros referem-se à emissões de gases poluentes de enxofre e nitrogênio e a problemas causados por fusão de cinzas. Por outro lado, a queima eficiente e limpa de biomassa e resíduos industriais entre outros materiais combustíveis, pode trazer benefícios ambientais consideráveis. O processo de combustão em leito fluidizado é reconhecidamente flexível quanto ao uso de combustível, trabalha com baixas temperaturas que evitam a fusão de cinzas e diminuem a emissão de NOx e permite a remoção de SOx ainda dentro do leito, por meio da adição de calcário o que dispensa tratamento adicional para este gás. Considerando o exposto acima, uma planta piloto de combustão em leito fluidizado foi projetada e construída no NETeF da EESC/USP e utilizada inicialmente para testes de remoção de SO2 durante a queima de carvão. A concepção e construção do reator e de seus periféricos são discutidas e os resultados são apresentados. Na absorção de SO2 duas variáveis foram consideradas; a relação molar Ca/S e o excesso de ar de combustão. Os resultados mostram eficiência de remoção de SO2 de até 94% para relação Ca/S = 4 e excesso de ar de 21%. Para a relação Ca/S = 1, a mais baixa utilizada neste trabalho e que representa a condição estequiométrica, este valor cai para 55%. O excesso de ar mostrou um papel claro, porém mais modesto. A redução do excesso de ar de 21% para a condição estequiométrica levou a eficiência de 94 para 84%.The utilization of coal is an attractive way to reduce some of the energy problems in Brazil. Major problems associated with coal combustion are polutant emissions, mainly SOx and NOx and ash fusion. Additionally, the efficient combustion of biomass and industrial hazardous wastes, among other fuels, can bring a significant environmental benefit. Fluidized bed combustion is recognized to be flexible in the use of fuel, produce low temperature that avoid ash fusion and reduce NOx emissions, and allow SOx absorption by limestone inside the bed, what makes unnecessary additional gas treatment for this pollutant. Considering that, a fluidized bed combustion pilot plant was projected and built in NETeF at EESC/USP and initially used for investigations of the SO2 absorption by limestone during coal combustion. The concept and construction of the plant are presented and discussed and the results are shown. Regarding the absorption of SO2, two variables were investigated, namely the molar ratio Ca/S and the excess of combustion air. An absorption efficiency of up to 94% was achieved with Ca/S = 4 and excess air of 21%. When Ca/S = 1 was used - what represents the stoichiometric ratio and was the lowest used in this work, this efficiency dropped to 55%. Excess air showed a clear but more modest role. The decrease of excess air from 21% to the stoichiometric condition decreased the efficiency from 94 to 84%.
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Engman, Randy W. "Cyclone scale-up and radial gas concentration profiles." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/29937.
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A two part study was undertaken to explain the performance of cyclones operated in circulating fluidized bed combustion (CFBC) systems.
In the first part, collection efficiency tests were performed on a one-ninth scale polyacrylic cyclone model of the industrial scale cyclone at the 22 MWe CFBC facility at Chatham, New Brunswick. Emphasis was placed on scale-up considerations, loading effects, inlet geometry effects, and flow visualization trials. Experiments were performed at room temperature with inlet velocities between 3.7 and 5.5 m/s, solids loading between 0.05 and 7.5 mass solids/mass air with two different solids systems. There was disappointing agreement between the results from the Chatham unit, scaled according to Stokes Number scaling, and the findings obtained from the cold model unit. There was a minimum in the particle collection efficiency for particles of diameter 2.5 to 3.0 µm, apparently associated with agglomeration effects in the cyclone. Particle collection efficiency was found to increase with increased particle loading for the conditions studied. Changes in the inlet geometry gave inconclusive results. The experimental results were limited by problems associated with feeding and recycling the fines solids system used.
In the second part radial gas concentration profiles of a secondary cyclone serving the UBC pilot scale Circulating Fluidized Bed Combustor were performed at temperatures of about 870 ℃. Concentrations of O₂ , CO₂ , NO[formula omitted] , CH₄ , CO and SO₂ were measured. An increase in [CO], and to a lesser extent [CO₂], was measured near the cyclone wall. There appeared to be little radial variation in the concentration of other species.
Further work is required to allow the cold model to operate continuously, with particles which can be fed more freely, and to obtain radial gas concentration profiles within the primary cyclone of the UBC CFBC system.Applied Science, Faculty of
Chemical and Biological Engineering, Department of
Graduate
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Valentino, Karen Rose. "Durability testing of ceramic candle filters in pressurized-fluidized bed combustion environments." Thesis, Virginia Tech, 1993. http://hdl.handle.net/10919/42200.
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Ceramic candle filters were subjected to 500 hour high temperature/ high pressure (HTHP) exposure tests to examine their extended durability in simulated coal pressurized-fluidized bed combustion (PFBC) environments. The candle filter materials analyzed included two SiC filters, one with clay binder and one with a minimal amount of clay binder, a cordierite filter, a mullite candle filter and an aluminosilicate refractory concrete filter. Exposure testing conditions included a range of temperature from 700-850°C and a pressure ranging from 1.7-1.8 MPa. The HTHP tests included exposing the ceramic filter materials to steam and steam-alkali environments. The presence of alkali significantly accelerated the deterioration of the filters. The results of the analysis show that significant crushing strength losses were exhibited by the SiC filters after exposure to HTHP alkali-steam conditions at temperatures as low as 700°C. The expansive and destructive cristobalite phase developed in the SiC filters after most of the treatments. The cordierite candle filter showed a decrease in crushing strength associated with grain growth after each high temperature exposure but few other signs of deterioration were detected. The mullite candle filter and the refractory concrete candle filter showed the least amount of change in crushing strength and overall the most candle stability.Master of Science
28
Xu, Bao Hua. "Numerical simulation of the gas-solid flow in fluidized beds." Online version, 1997. http://bibpurl.oclc.org/web/22135.
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Sprung, Renato. "Studies in vibrofluidized beds and synthesis of silica catalysts." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/49901.
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The effect of the solid-circulation rate and pattern as well as the air-gap size on heat-transfer coefficients between a horizontal, cylindrical heater and vibrated beds of Master Beads (spherical alumina) and glass spheres was studied. Solid piles were observed to form at specific bed locations. Solid-circulation paths were directed from the shallowest toward the deepest region of the vibrated bed. For beds in which the solid pile formed above the heating surface, local solid-circulation loops were observed above and below the heater. Air gaps developed at the top and bottom of the cylindrical heater. Heat-transfer coefficients of 140-350 W/m²K in beds of glass spheres and 180-480 W/m²K in beds of Master Beads were determined for a temperature difference of 30°C between the heater and vibrated bed. The trends in the behavior of the heat-transfer coefficient could be explained in terms of a model that accounted for the air-gap size and particle renewal in the layer closest to the heater. Increased solid-circulation rates improved the heat-transfer performance until larger air-gap sizes eventually compromised any increase in solid circulation.
The expansion of the interlayer spacing of H-Magadiite (a layered silicic acid) by the introduction of pillars containing silicon atoms was investigated. A trisiloxane and two trichloroorganosilane compounds were used as the pillaring agents. The interlayer space of H-Magadiite was successfully expanded by pillaring with trichloroorganosilanes. The minimum dimensions of the pores that access the interlayer space of the pillared compounds were determined as being 6.2 Å and 9.5 Å (dimensions at perpendicular directions). Pillaring of H-Magadiite at low pH and temperatures close to 0 °C yielded the highest surface areas, e.g., increasing the surface area from 35 to 130-200 m²/g. The pillared compounds were found to be thermally stable up to temperatures of 650°C.Ph. D.
30
Huff, Jason. "Particle formation of smelt in a fluidized bed." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/7037.
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Hory, Rogerio Ishikawa. "Avaliação das emissões de S'O IND.2' em leito fluidizado circulante na combustão de carvão mineral brasileiro e dolomita." [s.n.], 2007. http://repositorio.unicamp.br/jspui/handle/REPOSIP/264647.
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Orientador: Arai Augusta Bernardez PecoraTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
Made available in DSpace on 2018-08-11T13:29:17Z (GMT). No. of bitstreams: 1 Hory_RogerioIshikawa_D.pdf: 3549862 bytes, checksum: 727c6ab5dce7454b6af9546842232b2e (MD5) Previous issue date: 2007
Resumo: Este trabalho apresenta o estudo experimental do processo de combustão de carvão mineral brasileiro em reator de Leito Fluidizado Circulante (LFC) com o objetivo de avaliar as taxas de emissões de di óxido de enxofre (S02) e eficiência de conversão de carbono no processo de combustão. Para diminuir a emissão do S02 nos gases de exaustão, foi adicionado, ao carvão, quantidades de calcário dolomítico (dolomita), de modo que a relação molar entre o cálcio (Ca) presente no calcário e o enxofre (S) presente no carvão variou entre 0,0 e 2,0. A variação na relação molar Ca/S, como é denominada na literatura, foi um dos dois fatores avaliados neste trabalho. O outro fator envolvido nos testes foi o excesso de ar utilizado para combustão do carvão. Trabalhou-se com excesso de ar na faixa de 20 a 30%. Foram realizados 11 ensaios seguindo um planejamento experimental estatístico do tipo CCD (Composite Central Design) e mais 02 ensaios complementares. A relação molar Ca/S de 0,6 apresentou emissão zero de S02 e propôs-se utilizar uma nova relação molar: (Ca+Mg)/S para retratar processos de sorção com dolomitas. Para emissão zero de S02, uma relação molar (Ca+Mg)/S de 1,8 já é suficiente. Foram obtidas eficiências de conversão do carbono entre 86,0 e 93,0% para combustão do carvão
Abstract: This work presents an experimental study with Brazilian mineral coal combustion in a Circulating Fluidized Bed (CFB) reactor with the objective to evaluate the sulphur dioxide emissions (S02) and the carbon conversion efficiency in the combustion processo Dolomite was added to the coal to minimize the S02 emissions during combustion. The quantity of dolomite added was calculated based on the molar relation of calcium (Ca) present in the dolomite and sulphur (S) present in the coal. Ca/S molar relation had a variation between 0,0 and 2,0. Two factors were evaluated in this work: Ca/S relation and excess of air during combustion which had a variation between 20 and 30%. Eleven (11) experimental tests were evaluated following a statistical experimental design called CCD (Composite Central Design) and 02 (two) more complementary tests. Emissions of S02 with zero value were obtained for a Ca/S of 0,6. It was also proposed in this work a new relation for sorption of S02 with dolomite: (Ca+Mg)/S relation. Tests showed that a relation of 1.8 for (Ca+Mg)/S is sufficient for zero emissions of S02. Carbon conversion efficiency between 86.0 and 93.0 was also obtained during coal combustion
Doutorado
Termica e Fluidos
Mestre em Engenharia Mecânica
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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.
33
Hosseinian, Aida. "Thermodynamic Equilibrium Prediction of Corrosion Tendency in Fluidized-Bed Combustion of Solid Waste." Thesis, Högskolan i Borås, Akademin för textil, teknik och ekonomi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:hb:diva-13619.
Full textAbstract:
Global warming and air pollution are two issues of greatest concerns to human life in recent years. Environmental concerns and econimal/political independency of fossil fuels have been the driving force of developing interest in renewable resources of energy for many countries. Different type of waste-derived fuels such as biomass, municipal solid waste and industrial waste are interesting energy resources for energy producing companies. There are mainly two main paths when it comes to waste-to-energy industry, which are thermal treatment of waste, as well as biochemical treatment. Thermal treatment of waste to produce energy could benefit both for hygienic consideration of waste management and avoiding waste landfill.Heat and power generation through combustion of waste or biomass has several environmental, and economical advantageous over utilization of fossil fuels. Thermal conversion of waste and biomass fuels, however, has some challenges mainly due to their chemical composition and high alkali metals (potassium and sodium) content. Combustion of these fuels usually can result in some operational challenges such as deposition, fouling, bed agglomeration and corrosion in different part of the boiler. The less reactive and non-combustible part of the fuel known as ash-forming matter has a major role in these operational challenges. Ash related problems in waste-to-energy boilers lead to lower efficiency, high maintenance costs and equipment failure. Therefore, investigating the chemical composition of fuel and ash-forming matter is essential prior to thermal conversion of waste-derived fuels. High-temperature corrosion due to formation of corrosive alkali chloride compounds during combustion is one of the main ash-related concerns in boilers.This study investigated high-temperature corrosion in circulating fluidized-bed (CFB) combustion of solid waste. Flue gas composition of solid waste combustion in the CFB boiler was analysed in two cases: combustion of the reference fuel, and combustion of the “same” fuel with a sulphur containing additive (ammonium sulphate), to decrease the corrosive alkali chlorides in the flue gas. Chemical fractionation was carried out for fuel samples to determine the reactive and less-reactive fraction of ash-forming matter. A thermodynamic equilibrium model was developed using Factsage thermochemical software, to predict the chemical composition of the flue-gas with a special focus on corrosive alkali chlorides. The modelling results were evaluated using In-situ Alkali Chloride Monitoring (IACM) results obtained during the full-scale combustion measurements.
34
Parmar, Manjeet Singh. "Fluidized bed combustion of carbons and reduction of NOâ†x and Nâ†2O." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243062.
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Campbell, Beverly. "A Study of Combustion Profiles of Co-Fired Coal/Biomass/Limestone Samples in a Fluidized Bed Combustor." TopSCHOLAR®, 1997. http://digitalcommons.wku.edu/theses/898.
Full textAbstract:
Concerns over declining landfill space and a renewed interest in waste-toenergy technologies have increased the possibilities of co-firing different types of fuels in atmospheric fluidized bed combustion systems. The laboratory sized atmospheric fluidized bed combustor (AFBC) at Western Kentucky University was designed to serve as a highly flexible research and development facility to gain operating experience, evaluate combustion performance, and estimate the effect of flue gas emissions on the atmosphere. The operating conditions for the AFBC system are similar to those used at the TVA 160-MW AFBC Pilot Plant located near Paducah, Kentucky. AFBC systems are ideal for co-firing because of their ease in heat conversion and ability to burn a wide range of fuels. GC/FTIR/IC techniques can be used to characterize the combustion of fuel blends by evolved gas analysis. This analysis can be used to determine the best combination of fuels.
36
Akpulat, Onur. "Co-combustion Of Coal And Olive Cake In A Fluidized Bed With Limestone Addition And Freeboard Extension." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/12611160/index.pdf.
Full textAbstract:
In this study, flue gas emissions and combustion efficiencies during combustion and co-combustion of olive cake and coal are investigated in a bubbling fluidized bed with an inside diameter of 102 mm and a height of 900 mm and 1900 mm.
Tunçbilek lignite coal and Edremit olive cake were used in the experiments as fuels. Temperature distributions along the combustion column were continuously measured. Flue gas concentrations of O2, CO, SO2 and NOx were measured during combustion experiments. Four sets of experiments were performed in order to examine the effect of fuel composition, excess air ratio, freeboard extension and limestone addition on flue gas emissions and combustion efficiency. The olive cake addition to coal were 25, 50, 75 % by wt. The bed temperature on the average was 850 oC. The results of the experiments showed that coal combustion occurs at lower parts of the combustion column whereas olive cake combustion takes place more in the freeboard region. As olive cake percentage in the fuel mixture increased, CO emissions increased, SO2 and NOx emissions decreased. The reason for the decrease of NOx emissions with increasing percentage of olive cake in the fuel mixture was due to a reducing atmosphere created in the combustion column. Mostly combustion losses resulted mainly from the unburnt carbon in the fly ash. With the freeboard extension, noticeable decrease in CO emissions and slight increase in combustion efficiencies were observed. Among the limestones tested, Ç
an limestone gave the best result with Ca/S = 3 at an optimum bed temperature of 850 oC. The SO2 reduction was 87% at this Ca/S ratio. For co-combustion experiments, it was observed that SO2 adsorption efficiency of limestone increased with the addition of olive cake to the fuel mixture.
37
Alagoz, Duriye Ece. "Mathematical Modeling Of Fluidized Bed Combustors With Radiation Model." Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/12607489/index.pdf.
Full textAbstract:
Simultaneous solution of the conservation equations for energy and chemical species in conjunction with radiative transfer equation was carried out by coupling a previously developed and tested system model of fluidized bed combustion (FBC) to an existing radiation model.
The predictive accuracy of the coupled code was assessed by applying it to 0.3 MWt METU Atmospheric Bubbling Fluidized Bed Combustor (ABFBC) Test Rig burning lignite in its own ash and comparing its predictions with the measured temperatures and concentrations of gaseous species along the combustor and radiative heat fluxes incident on the refractory-lined freeboard walls on two combustion tests, with and without recycle. The predictions of the coupled code were found to be in good agreement with the measurements.
For the investigation of the significance of coupling of the radiation model to the system model, temperature predictions of the coupled code were compared with those obtained by the original system model. It was found that the effect of incorporating a radiation model into the system model on the predictions was not significant because the high temperatures of refractory-lined freeboard walls and high surface to volume ratio of the test rig under consideration cause the incident radiative heat fluxes to be dominated by walls rather than the particle laden gas emissions. However, in industrial boilers, freeboard is surrounded by water-cooled membrane walls and boilers have much lower surface to volume ratio. In order to examine the effects of both on radiation in industrial boilers, an investigation was carried out on 16 MWt Stationary Fluidized Bed Boiler (SFBB) by applying radiation model, in isolation from the system model, to the freeboard of the boiler. It was found that in the boiler, incident radiative heat fluxes were dominated by particle laden gas emissions.
In brief, the coupled code proposed in this study proves to be a useful tool in qualitatively and quantitatively simulating the processes taking place in an atmospheric fluidized bed boilers.
38
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.
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Kramp, Marvin [Verfasser]. "Chemical Looping Combustion in Interconnected Fluidized Bed Reactors – Simulation and Experimental Validation / Marvin Kramp." München : Verlag Dr. Hut, 2014. http://d-nb.info/1060588080/34.
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Lawrence, Andrew David. "The emission of nitrogen oxides from the combustion of coal in a fluidized bed." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308279.
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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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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.
Full textAbstract:
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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Pandey, Preetanshu. "Application evaluation of a prototype backscatter imaging LDV system (BILS)." Morgantown, W. Va. : [West Virginia University Libraries], 2002. http://etd.wvu.edu/templates/showETD.cfm?recnum=2660.
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Thesis (M.S.)--West Virginia University, 2002.Title from document title page. Document formatted into pages; contains xi, 100 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 83-86).
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Afacan, Onur M. "Mathematical Modeling Of Nox Emissions In Bubbling Fluidized Bed Combustors." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606463/index.pdf.
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A comprehensive model, previously developed and tested for prediction of behavior of continuous fluidized bed combustors is extended to incorporate NOx formation and reduction reactions and applied to the simulation of METU 0.3 MWt Atmospheric Bubbling Fluidized Bed Combustor (ABFBC) burning lignites with high volatile matter in their own ashes.
The predictive accuracy of the model was assessed by comparing its predictions with measurements taken previously on the same rig. Favorable comparisons are obtained between the predicted and measured temperatures and concentrations of gaseous species along the combustor. Results show that determination of partitioning of coal nitrogen into char nitrogen and volatile nitrogen, and release of volatile nitrogen along the combustor are found to be the most important parameters that affect NOx formation and reduction in bubbling fluidized bed combustors. The system model proposed in this study proves to be a useful tool in qualitatively and quantitatively simulating the processes taking place in an atmospheric fluidized bed combustor.
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LIN, CHUN-HONG, and 林春宏. "Coal combustion in a vortexing fluidized bed combustor." Thesis, 1992. http://ndltd.ncl.edu.tw/handle/82078293047378729797.
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Lin, Shih-Min, and 林士閔. "Combustion of corncob in a vortexing fluidized bed combustor." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/05814733518107872711.
Full textAbstract:
碩士中原大學
化學工程研究所
99
In this study, combustion of corncob was investigated in a vortexing fluidized bed combustor. The combustor has a 4.6m height, an area of 0.8m × 0.4m of combustion chamber and a 0.75 inner diameter of freeboard. The second air was inducted into the freeboard tangentially at 2.05m height above the air distributor. Corncob was shattered into particles of 5mm under. Use different operating modes (only with 1st air, stage combustion and flue gas recirculation (FGR)) and different operating conditions (bed temperature, air ratio, stoichiometric oxygen percentage in the bed) to discuss the axial temperature distribution, CO and NOx emissions, combustion efficiency, combustion proportion and heat removed from the bed. These were carried out 13 experiments. Besides, there was an additional experiment that corncob was cut into cylinders with about 30mm both in length and diameter to discuss the fuel particle size effect. The results show that the optimum operating mode in this study is FGR. Use FGR to operate at 700℃, with 46% excess air and 100% stoichiometric oxygen percentage in the bed is optimum condition and with combustion efficiency of 85%~90%. Additionally, large particle size is better than small particle size. Use large particle size as fuel can improve combustion efficiency, decrease NOx emission and only increase CO emission slightly. If taking energy recovery into consideration, operating mode of only with 1st air can be the first choice. It gets higher combustion efficiency and more combustion proportion in bed zone, so heat removed by heat transfer tube from the bed was much higher. Heat energy in the bed can recover one-quarter of the heat generated from fuel combustion when operating condition is at 700℃ and with 83% excess air and using small fuel particle size. The pollutant emissions are all conformed to EPA regulations. Furthermore, combustion efficiency and combustion proportion in bed zone can be higher and NOx emission can be lower, if large particle size of corncob was taken as fuel.
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Yang, Chih-Yun, and 楊智雲. "Study of In-bed Combustion fraction in a Vortexing Fluidized Bed Combustor." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/96542818942882960645.
Full textAbstract:
碩士中原大學
化學工程研究所
103
An arrangement of heat exchanger is a key point in the design of fluidized boiler. This arrangement is depend on the amount of heat released in each section of the combustor, including bubbling zone and freeboard zones. In addition, heat release rate is defined as the amount of heat released in each section of the combustor. Heat release rate can be calculated from the oxygen consumption of each section per total oxygen consumption. The purpose of this study is to investigate the relationship between in-bed heat release rate and fuel properties, such as particle size, volatile/fixed carbon ratio. The effects of in-bed stoichiometric oxygen ratio on in-bed heat release rate are also investigated. Combustor can be divided into two regions from bottom to top, namely, bed zone and freeboard zone. The two types of fuels, coal and thorny bamboo are used as feeding material. The particle size of the coal ranges from 854 to 3644 μm. The operated in-bed stoichiometric oxygen ratios are between 80% and 100%. Total primary air is 3 Nm3/min and the secondary air is 2 Nm3/min. The excess oxygen ratio was kept at 40%. The silica sand is used as the bed material. The experimental result shows that the in-bed heat release rate is increased with the decreasing volatile/fixed carbon ratio in all fuels. As the mean particle size is increased, the in-bed heat release rate is also increased. Here we regress the data to build the empirical equation, . It can be summarized that the effect of fuel properties on the in-bed heat release rate is insignificant.
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Sheng-Hau, Cheng, and 程盛豪. "Combustion of Rice Husks in a Vortexing Fluidized Bed Combustor." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/35764152547994574227.
Full textAbstract:
碩士中原大學
化學工程研究所
86
In order to understand the combustion phenomena within a vortexing fluidized bed combustor(VFBC), an investigation is carried out in a 0.45m I.D. and 5m height pilot scale VFBC. Rice husk is used as the feeding material. Silica sand serves as the bed material. The effects of various parameters on the combustion efficiency and CO emissions are investigated. Defluidization phenomena caused by burning rice husk is also studied. Experimental results show that the concentration of CO emission increases with primary air and excess air,but decreases with the air ratio and the bed temperature The combustion efficiency decreases with the the air ratio and the excess air increasing , but it is not affected by the that primary air and bed temperature. Adding iron can prevent the defluid- ization behavior and adding aluminum can increase the combustion temperature.
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Chin, Yu Chen, and 秦玉城. "Combustion of Rice Husks in a Vortexing Fluidized Bed Combustor." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/99729522899478095676.
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Lee, Chung Yu, and 李崇裕. "Combustion of Waste Tires in a Vortexing Fluidized Bed Combustor." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/40581479610619369004.
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