Particulate beds which are mobilized and expanded by the application of mechanical vibrations are called vibrated beds. These beds are generally defined as shallow, if the depth-to-width ratio is less than unity. The dynamics of shallow vibrated beds and the heat transfer from immersed tubes to such beds are investigated using a vibrational frequency of 25 Hz. The vibration equipment is designed to minimize distortions in the applied displacement waveform. Transducers used are of a sufficiently high frequency response to accurately follow the variation of bed properties over a vibrational cycle. An electronic circuit is designed to exactly phase-match data collected by a transducer with the vibrational displacement. The circuit may also be used to trigger a strobe lamp at any phase angle, thus permitting an accurate examination of the evolution of bed characteristics over a cycle. Measurements of floor pressures beneath the bed, indicate cyclic characteristics, caused by the bed motion. Horizontal floor-pressure gradients cause the bed to pile up or bunker within the vessel. In bunkered beds, particle motion is determined by horizontal gas flows, and a compaction wave which propagates diagonally through the bed during the bed-vessel collision. In non-bunkered beds, particle motion is driven largely by wall friction. The observed instant of bed-vessel separation lags the theoretical prediction by several degrees, most likely because of bed expansion associated with the bed lift-off. Different "states" of shallow vibrated beds are identified, each with a unique set of characteristics. One state which exists in ultra-shallow beds of depths between 6 and 15 particle diameters is characterized by a high porosity and good gas-solid interaction, making it potentially useful for studies of reaction kinetics. Surface-to-bed heat-transfer coefficients are measured for Master Beads and glass beads, and found to vary with particle size and vibrational intensity. Heat-transfer coefficients as high as 484 W/m²-K are obtained. Heat transfer depends on particle circulation and the formation of air gaps which periodically surround the heater surface. A simplified theoretical formulation for the heat-transfer coefficient appears to qualitatively predict observed trends in heat transfer. / Ph. D.

Foi realizado um estudo sobre o efeito das concentrações de SO2 na sua absorção por calcários em fornalhas de leito fluidizado. Para observar a influência do SO2 sobre os diferentes parâmetros físicos e químicos do processo, foram criadas atmosferas compostas por quatro concentrações diferentes de SO2, que foram de 500, 1.000, 2.000 e 4.000 ppm. Utilizou-se ainda dois tipos de calcários, o Dolomítico-DP e o Calcítico-CI. O leito fluidizado borbulhante utilizado, possuía 160 mm de diâmetro interno e foi fluidizado com ar à temperatura de 850ºC, contendo SO2 na concentração desejada. Como material do leito foi utilizada areia de quartzo (99,9%), com diâmetro de 385 &#956m e aproximadamente 3,0 Kg de massa. O calcário foi adicionado em bateladas de 50 g com o reator já pré-aquecido, enquanto as variações das concentrações dos gases SO2, CO2, CO e O2 e suas descargas foram monitoradas continuamente na saída do ciclone que era utilizado para retenção do particulado fino. Para adquirir esses dados foi desenvolvido um programa em LabView. O modelo matemático escolhido possibilitou a determinação da conversão, da taxa de conversão e do coeficiente global de taxa de reação para todas as condições testadas. / A study of the effect of the concentrations of SO2 in its absorption by limestones in fluidized bed furnaces was conducted. For the determination of the SO2 influence on the different physical and chemical parameters of process, such as calcinations and sulfatation four different atmospheres were used in the reator with concentrations of SO2 of 500, 1.000, 2.000 and 4.000 ppm. Two types of limestones were used : Dolomitico-DP and Calcitico-CI. The bench scale bubbling fluidized bed reactor had a 160 mm internal diameter and was fluidized with air at 850ºC containing the required concentration of SO2. Bed material was quartz sand (99,9%), with 385 &#956m diameter and approximately 3 Kg of mass. The limestone was introduced in samples of 50 g, in the reactor previously stabilized, and the concentration of the gases SO2, CO2, CO and O2 and their discharges in the reactor exit were continually monitored. For the recording of this parameters a data acquisition program in LabView was developed. A mathematical model was used to allow the determination of the conversion, the conversion rate and the global coefficient of reaction rate for all the tested conditions.

Carbon capture and storage technologies are necessary to start lowering greenhouse gas emissions while continuing to utilize existing thermal power generation infrastructure. Calcium looping is a promising technology based on cyclic calcination/carbonation reactions which utilizes limestone as a sorbent. Steam is present in combustion flue gas and in the calciner used for sorbent regeneration. The effect of steam during calcination on sorbent performance has not been extensively studied in the literature. Here, experiments were conducted using a thermogravimetric analyzer (TGA) and subsequently a dual-fluidized bed pilot plant to determine the effect of steam injection during calcination on sorbent reactivity during carbonation. In a TGA, various levels of steam (0-40% vol.) were injected during sorbent regeneration throughout 15 calcination/carbonation cycles. All concentrations of steam were found to increase sorbent reactivity during carbonation. A level of 15% steam during calcination had the largest impact. Steam changes the morphology of the sorbent during calcination, likely by shifting the pore volume to larger pores, resulting in a structure which has an increased carrying capacity. This effect was then examined at the pilot scale to determine if the phase contacting patterns and solids heat-up rates in a fluidized bed were factors. Three levels of steam (0%, 15%, 65%) were injected during sorbent regeneration throughout 5 hours of steady state operation. Again, all levels of steam were found to increase sorbent reactivity and reduce the required sorbent make-up rate with the best performance seen at 65% steam.

Foi realizado um estudo sobre o efeito das concentrações de SO2 na sua absorção por calcários em fornalhas de leito fluidizado. Para observar a influência do SO2 sobre os diferentes parâmetros físicos e químicos do processo, foram criadas atmosferas compostas por quatro concentrações diferentes de SO2, que foram de 500, 1.000, 2.000 e 4.000 ppm. Utilizou-se ainda dois tipos de calcários, o Dolomítico-DP e o Calcítico-CI. O leito fluidizado borbulhante utilizado, possuía 160 mm de diâmetro interno e foi fluidizado com ar à temperatura de 850ºC, contendo SO2 na concentração desejada. Como material do leito foi utilizada areia de quartzo (99,9%), com diâmetro de 385 &#956m e aproximadamente 3,0 Kg de massa. O calcário foi adicionado em bateladas de 50 g com o reator já pré-aquecido, enquanto as variações das concentrações dos gases SO2, CO2, CO e O2 e suas descargas foram monitoradas continuamente na saída do ciclone que era utilizado para retenção do particulado fino. Para adquirir esses dados foi desenvolvido um programa em LabView. O modelo matemático escolhido possibilitou a determinação da conversão, da taxa de conversão e do coeficiente global de taxa de reação para todas as condições testadas. / A study of the effect of the concentrations of SO2 in its absorption by limestones in fluidized bed furnaces was conducted. For the determination of the SO2 influence on the different physical and chemical parameters of process, such as calcinations and sulfatation four different atmospheres were used in the reator with concentrations of SO2 of 500, 1.000, 2.000 and 4.000 ppm. Two types of limestones were used : Dolomitico-DP and Calcitico-CI. The bench scale bubbling fluidized bed reactor had a 160 mm internal diameter and was fluidized with air at 850ºC containing the required concentration of SO2. Bed material was quartz sand (99,9%), with 385 &#956m diameter and approximately 3 Kg of mass. The limestone was introduced in samples of 50 g, in the reactor previously stabilized, and the concentration of the gases SO2, CO2, CO and O2 and their discharges in the reactor exit were continually monitored. For the recording of this parameters a data acquisition program in LabView was developed. A mathematical model was used to allow the determination of the conversion, the conversion rate and the global coefficient of reaction rate for all the tested conditions.

Orientador: Arai Augusta Bernardez Pecora / Tese (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

Carbon capture and storage technologies are necessary to start lowering greenhouse gas emissions while continuing to utilize existing thermal power generation infrastructure. Calcium looping is a promising technology based on cyclic calcination/carbonation reactions which utilizes limestone as a sorbent. Steam is present in combustion flue gas and in the calciner used for sorbent regeneration. The effect of steam during calcination on sorbent performance has not been extensively studied in the literature. Here, experiments were conducted using a thermogravimetric analyzer (TGA) and subsequently a dual-fluidized bed pilot plant to determine the effect of steam injection during calcination on sorbent reactivity during carbonation. In a TGA, various levels of steam (0-40% vol.) were injected during sorbent regeneration throughout 15 calcination/carbonation cycles. All concentrations of steam were found to increase sorbent reactivity during carbonation. A level of 15% steam during calcination had the largest impact. Steam changes the morphology of the sorbent during calcination, likely by shifting the pore volume to larger pores, resulting in a structure which has an increased carrying capacity. This effect was then examined at the pilot scale to determine if the phase contacting patterns and solids heat-up rates in a fluidized bed were factors. Three levels of steam (0%, 15%, 65%) were injected during sorbent regeneration throughout 5 hours of steady state operation. Again, all levels of steam were found to increase sorbent reactivity and reduce the required sorbent make-up rate with the best performance seen at 65% steam.

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 demonstrated. / Tiivistelmä 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.

La conversion thermochimique de la biomasse en lit fluidisé circulant permet la production d’un gaz à haute valeur ajoutée, utilisable dans de nombreuses applications. L’objectif de ces travaux est de mieux comprendre et modéliser les phénomènes couplés, hydrodynamiques et réactifs, se déroulant en lit fluidisé circulant. Dans un premier temps, un pilote de pyrogazéification de 20 kg/h de biomasse en lit fluidisé circulant a été conçu. L’étude hydrodynamique de ce pilote a ensuite été réalisée entre 20 et 950 °C. Les résultats ont permis d’établir des règles de design et de fonctionnement de réacteurs de gazéification en lit fluidisé circulant. Dans un second temps, une étude de la pyrogazéification de la biomasse a été réalisée en lit fluidisé dense ainsi qu’en lit fluidisé circulant, entre 750 et 850 °C. L’étude de l’influence de nombreux paramètres opératoires (températures, pression partielle de la vapeur d’eau, débit de biomasse, débit de circulation, inventaire et nature du média, forme de la biomasse) sur les performances de la gazéification a permis d’identifier les paramètres clés permettant de contrôler la composition ainsi que le volume de gaz de synthèse produit. Par ailleurs, à partir des résultats expérimentaux, un schéma réactionnel est proposé pour la pyrolyse de la biomasse étudiée. Enfin, un outil de modélisation du réacteur de gazéification de la biomasse en lit fluidisé dense et circulant, intégrant les réactions de pyrolyse, de gazéification, de water-gas shift et de reformage des goudrons a été développé et validé sur les résultats expérimentaux. / The biomass thermochemical conversion in fast internally circulating fluidized bed (FICFB) allows producing a high-added value syngas that can be used in many end-use applications. This work aims to better understand and model the coupled phenomena, hydrodynamic and reactive, occurring in FICFB processes. In a first time, a 20 kg/h FICFB biomass pyrogasification pilot was designed and erected. Then, the hydrodynamic study of this pilot was carried out between 20 and 950 °C. Results led to propose some design and operation rules for FICFB gasifiers. In a second time, biomass pyrogasification was studied in a dense fluidized bed (DFB) as in a FICFB, between 750 and 850 °C. From the survey of the effect of numerous operating parameters (temperatures, steam partial pressure, biomass feeding rate, circulation flow rate, bed material inventory and nature, biomass shape) on the gasification performances, the key parameters for the control of produced syngas volume and composition were identified. Finally, a modelling tool of DFB and FICFB biomass gasifiers, integrating pyrolysis, gasification, water-gas shift and tars reforming reactions was developed and validated on the experimental results.

Beneficiation of fine coal (+500 μm –2000 μm) is a worldwide problem in the mining industry, especially dry beneficiation of fine coal. Coal beneficiation can be divided primarily into two methods, namely wet- and dry beneficiation. Wet beneficiation methods are utilized more in today‘s industry because of the sharp separation efficiency that can be achieved. These processes include wet jigging, dense medium cyclones, spiral beneficiation etc. Due to the lack of a sufficient water supply in some regions around the world including South Africa, dry beneficiation methods are becoming more popular. Recent mechanized mining methods caused the fraction of fines from coal mines to increase over the years. However, due to old inefficient technologies, coal fines contained in slurry ponds could not be beneficiated and had to be discarded. One new dry beneficiation technology that has been used and researched extensively is the fluidized dense medium bed (FDMB) technology. The purpose of this study is to determine whether fine coal can be successfully beneficiated with a FDMB. It also has to be determined whether adding magnetite and introducing a jigging (pulse) motion to the air feed will increase the separation efficiency of the fluidization process. Witbank seam 4 and a Waterberg coal was used in experiments during this study. A coarse (+1180 μm –2000 μm), fine (+500 μm –1180 μm) and a mix of the two samples were prepared and tested. It was found that adding magnetite to the feed of the fluidized bed did not increase the separation efficiency. However, previous studies indicated the opposite results with regards to magnetite addition. The difference in results obtained could be prescribed to the ultrafine nature of the magnetite and the small coal particles size range used. If the presence of fine particles in the bed increases, the stability of fluidization decreases. In turn, the separation efficiency of the process decreases. Subjecting the feed air flow to a pulsating motion did not have a significant effect on separation. Good results were still obtained with jigging experiments, although not better than with normal fluidization. Stratification of coal particles according to quality was evident by the results obtained during experiments. The quality of coal increases from the bottom to the top of the bed. Overall the fluidized bed, in the absence of magnetite, was found to be a sufficient de-ashing process and further research on this technology could be very beneficial to the coal industry. / MIng (Chemical Engineering), North-West University, Potchefstroom Campus, 2014

Beneficiation of fine coal (+500 μm –2000 μm) is a worldwide problem in the mining industry, especially dry beneficiation of fine coal. Coal beneficiation can be divided primarily into two methods, namely wet- and dry beneficiation. Wet beneficiation methods are utilized more in today‘s industry because of the sharp separation efficiency that can be achieved. These processes include wet jigging, dense medium cyclones, spiral beneficiation etc. Due to the lack of a sufficient water supply in some regions around the world including South Africa, dry beneficiation methods are becoming more popular. Recent mechanized mining methods caused the fraction of fines from coal mines to increase over the years. However, due to old inefficient technologies, coal fines contained in slurry ponds could not be beneficiated and had to be discarded. One new dry beneficiation technology that has been used and researched extensively is the fluidized dense medium bed (FDMB) technology. The purpose of this study is to determine whether fine coal can be successfully beneficiated with a FDMB. It also has to be determined whether adding magnetite and introducing a jigging (pulse) motion to the air feed will increase the separation efficiency of the fluidization process. Witbank seam 4 and a Waterberg coal was used in experiments during this study. A coarse (+1180 μm –2000 μm), fine (+500 μm –1180 μm) and a mix of the two samples were prepared and tested. It was found that adding magnetite to the feed of the fluidized bed did not increase the separation efficiency. However, previous studies indicated the opposite results with regards to magnetite addition. The difference in results obtained could be prescribed to the ultrafine nature of the magnetite and the small coal particles size range used. If the presence of fine particles in the bed increases, the stability of fluidization decreases. In turn, the separation efficiency of the process decreases. Subjecting the feed air flow to a pulsating motion did not have a significant effect on separation. Good results were still obtained with jigging experiments, although not better than with normal fluidization. Stratification of coal particles according to quality was evident by the results obtained during experiments. The quality of coal increases from the bottom to the top of the bed. Overall the fluidized bed, in the absence of magnetite, was found to be a sufficient de-ashing process and further research on this technology could be very beneficial to the coal industry. / MIng (Chemical Engineering), North-West University, Potchefstroom Campus, 2014