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1
Bend, Stephen Leonard. "Coal characterisation and combustion". Thesis, University of Newcastle Upon Tyne, 1989. http://hdl.handle.net/10443/361.
Testo completoAbstract (sommario):
There are three related studies within this thesis that examine the relationships between the properties of coals and the characteristics of the chars produced during rapid pyrolysis in a laboratory based Entrained Flow Reactor (EFR) which simulates the rapid rates of heating (104 to 105 °C s-1 ) typical of pulverised fuel boilers. The first study, using a suite of nine coals, investigates the influence of coal rank upon the generation of specific types of char, their respective physical and structural characteristics and their relative combustabilities. The second study, using a suite of twenty-two coals, examines various coal characterisation techniques and the correlations between those techniques and the associated char, and specifically investigates petrographic techniques as a means of characterising coal feedstock. The third study, using freshly mined coals, investigates the effects of oxidation (100°C, air) and weathering (ambient) upon standard analytical techniques and relates such changes to the physical, structural and combustion characteristics of the associated char. There is a common relationship between the elemental oxygen content of the parent coal and the generation of specific types of char for both vitrinite rich coals of differing coal rank and for the oxidised or weathered coals. There is also an inverse relationship (R 2 = 0.97) between the elemental oxygen content of a vitrinite rich coal and the proportion of cenospheres generated by pyrolysis at 1000°C using the EFR. Furthermore, the enhancement of char combustion at 1000°C (in an EFR) is related to the physical and structural characteristics of the char, i.e. the presence or absence of porosity (visible using SEM and TEM), the CO2 surface area and optical texture. A relationship exists (R2 = 0.83) between the morphology of a char (1000°C / N2) and the petrographic composition of the parent coal. The new term microlithotype, is an amalgamation of various vitrinite rich microlithotype classes that simplifies the nomenclature. A combination of calorific value, microlithotype, and coal rank (vitrinite reflectance) illustrates the influence of petrographic composition upon calorific value and also suggests a 'Province' dependency amongst the Cretaceous/Tertiary and Carboniferous coals studied. The coal properties calorific value, microlithotype, and coal rank can be related (R 2 = 0.91) to the proportion of porous chars for the Cretaceous/Tertiary suite of coals, illustrating the use of multivariate analyses when characterising coal feedstock. The effects of oxidation and weathering upon vitrinite fluorescence is also reported. The oxidation of coal at 100°C produces rims of quenched fluorescence which are not apparent within the weathered coals. Furthermore, the intensity of fluorescence at 650 nm (1650) decreases due to progressive oxidation or weathering, but decreases at a rate that is dependent upon the severity (temperature) of the conditions employed. The proposed oxidation quotient (0/Q = I65W%Romax) is a sensitive indicator of the oxidative conditions up to 100°C.
2
Harding, Andrew W. "Environmental aspects of coal combustion". Thesis, University of Newcastle Upon Tyne, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360331.
Testo completo
3
Pourkashanian, M. "The combustion of residual fuel oil, coal and coal slurries". Thesis, University of Leeds, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380819.
Testo completo
4
Cavallo, Marincola Fabrizio. "Large eddy simulation of coal combustion". Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/34316.
Testo completoAbstract (sommario):
In this work an in-house code for large-eddy simulations of coal combustion is developed and tested, with a special focus on the issue of modelling radiative heat transfer effects inside a furnace. An Eulerian-Lagrangian approach is used to describe the continuous gas phase and the discrete particle phase, with a two-way coupling between the two phases (implemented by another group member). The radiative transfer equation is solved using the discrete ordinates method, testing several different angular and spatial discretisation schemes. The spectral properties of the participating media are approximated with different grey gas models of varying complexity and accuracy. The accuracy of the radiative solver is initially assessed on simple idealised static cases in both two- and three-dimensions, and validated against benchmark data found in literature. The code is then integrated, parallelised and optimised with the LES flow and combustion solver, and used to simulate a large 2.4 MW coal combustion furnace. The results of the simulations are compared quantitatively against experimental data in terms of velocity, temperature, species distribution and solid particle analysis, showing a good agreement overall. A parametric study is then also performed on the variables and parameters of the radiation solver, showing great sensitivity on the outcome of the simulations in certain cases, further highlighting the importance of accurate radiation modelling for closed coal combustion furnaces.
5
Hosin, Alyass Azzat. "Fiber reinforced coal combustion products concrete /". Available to subscribers only, 2007. http://proquest.umi.com/pqdweb?did=1342743231&sid=11&Fmt=2&clientId=1509&RQT=309&VName=PQD.
Testo completo
6
Megalos, Nikolaos Pandelis. "Coal combustion in precessing jet flames /". Title page, table of contents and summary only, 1998. http://web4.library.adelaide.edu.au/theses/09PH/09phm496.pdf.
Testo completo
7
Le, Manquais Katherine. "Combustion enhancing additives for coal firing". Thesis, University of Nottingham, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.582090.
Testo completoAbstract (sommario):
Opportunities exist for effective coal combustion additives that can reduce the carbon content of pulverised fuel ash to below 6%, thereby improving the efficiency of low NOx burners and making the ash saleable for filler/building material applications. However, catalytic performance under pulverised fuel boiler conditions has received relatively little consideration. For the first time, the research set out in this thesis systematically compares the reactivity of catalysed and uncatalysed bituminous coal samples during combustion in a drop tube furnace (DTF) and a thermogravimetric analyser (TGA). All of the inorganic compounds investigated were accordingly found to increase the rate of TGA char oxidation, with certain transition metal halides proving to be extremely successful additives. But these trends did not always translate into analogous carbon burnout improvements on th~ medium-scale DTF. This was due to the inherent variability associated with this experimental setup, the use of physical mixtures for catalyst dispersion and the intrinsic volatility of some of the tested salts. Furthermore several very effective additives on the TGA, the copper halides, seemingly deactivated under the conditions experienced in the DTF, reducing the attained carbon burnouts to levels below those observed with the uncatalysed coal fractions. Complex interactions were subsequently discovered between copper (I) bromide and the coal's mineral matter, implying that a copper-iron association could have been behind this behaviour. In contrast, the thermally labile iron halides were found to be exceptional additives for enhancing DTF carbon burnout, even at temperatures above their predicted boiling points in what could have previously been assumed to be a completely mass transfer controlled reaction regime. The combustion improvements associated with the introduction of iron (Ill) bromide were thus rigorously established and then related to the retention of the additive's cation, as indicated by SEM/EDX and ICP-MS.
8
Munir, Shahid. "Co-combustion of biomass with coal". Thesis, University of Leeds, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.531610.
Testo completo
9
Hirji, Karim Ahmedali Abdulla. "Combustion measurements in pulverised coal flames". Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/38035.
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10
Messig, Danny. "Numerical simulation of pulverized coal combustion". Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2017. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-228707.
Testo completoAbstract (sommario):
Die Arbeit befasst sich mit der Flamelet Modellierung für die Verbrennung von Kohlenstaub. Dabei liegt der Fokus sowohl auf der detaillierten Betrachtung der Gasphasenchemie als auch auf der Interaktion der Kohle mit der Gasphase. Ziel der Arbeit ist die Entwicklung einer Methode für die Simulation großtechnischer Kohlestaubfeuerungen.
Die energetische Umsetzung von Kohle läuft in drei wesentlichen Schritten ab: Verdampfung der Feuchtigkeit, Ausgasung der Kohle (Pyrolyse) und schließlich der Koksabbrand. Da die Struktur der Kohle als fossiler Brennstoff hoch komplex ist, existieren viele prädiktive, rechenaufwändige Modelle zur Beschreibung dieser Prozesse [1–4]. Diese Modelle können nicht direkt in numerischen Strömungssimulationen genutzt werden, dienen aber zur Kalibrierung einfacherer kinetischer Modelle. Diese in der Arbeit angewendete Prozedur wird in [5] beschrieben.
Zur detaillierten Beschreibung des Abbaus der entstehenden höheren Kohlenwasserstoffe werden in der Simulation große Reaktionsmechanismen benötigt. Die Benutzung solcher Mechanismen ist mit großen Rechenzeiten verbunden und daher bleibt deren Anwendbarkeit auf einfache Anwendungsfälle beschränkt. Der Vorteil der Flamelet Modellierung besteht darin, dass unter bestimmten Voraussetzungen der komplette thermo-chemische Zustand, bestehend aus Temperatur, Druck und Zusammensetzung, mit nur wenigen charakterisierenden Kontrollvariablen abgebildet werden kann. Durch Vorgabe und Variation der Kontrollvariablen können diese Zustände mittels kanonischer Flammenkonfigurationen vorberechnet und in sogenannten Flamelettabellen abgespeichert werden. Für das klassische Flamelet / Fortschrittsvariablen Modell [6] wird der thermo-chemische Zustand über Mischungsbruch und Fortschrittsvariablen parametriert, dabei bestimmt der Mischungsbruch den Anteil an Brenn- stoff im Gemisch und die Fortschrittsvariable den Fortschritt der chemischen Reaktion. Die Kontrollvariablen werden in der numerischen Simulation transportiert, an Stelle der Energie- und Speziesgleichungen. Dies stellt für große Mechanismen eine dramatische Reduktion der zu lösenden Gleichungen dar. Der thermo-chemische Zustand ergibt sich per Look-up aus den Flamelettabellen.
Im Zuge der Verbrennung trockener Kohle werden zwei Brennstoffe durch Pyrolyse und Koksabbrand freigesetzt. Für die Flamelet Modellierung bedeutet dies entsprechend je einen Mischungsbruch für Pyrolysegas und Produkte aus dem Koksabbrand. Neben der Fortschrittsvariablen wird ebenfalls die Enthalpie der Gasphase als Kontrollvariable benötigt aufgrund des intensiven Wärmeaustauschs zwischen Kohle und Gasphase. In der Arbeit erfolgt die Vorstellung der benötigten Transportgleichungen sowie die Beschreibung verschiedener Methoden zur Integration nicht-adiabater Zustände in Flamelettabellen. Dabei unterscheiden sich die vorgestellten Tabellierungstrategien hauptsächlich in der betrachteten Verbrennungsart.
IV Erfolgt die Mischung von Brennstoff und Oxidationsmittel erst in der untersuchten Flammenkonfiguration, spricht man von Diffusionsflammenstrukturen; sind beide schon gemischt, so entstehen Vormischflammenstrukturen. Die Detektion solcher Strukturen erfolgt in der Arbeit anhand einer Flammenstrukturanalyse mittels Flammenmarker. Die prinzipielle Übertragbarkeit des Flamelet / Fortschrittsvariablen Modells auf turbulente Kohlestaubfeuerung wurde von Watanabe [7] gezeigt, jedoch ist die Bewertung der eingesetzten Flamelet Modellierung in Grobstruktursimulationen nicht ohne weiteres möglich. Deshalb werden zur Verifizierung der entwickelten Tabellierungstrategie in der Arbeit einfache Flammenkonfigurationen betrachtet, die es erlauben, direkte Chemielösungen mit den Lösungen der tabellierten Chemie zu vergleichen. Für den entsprechenden Vergleich erfolgt die Vorstellung zweier Analysen. Bei der a priori Analyse wird der thermo-chemische Zustand der detaillierten Lösung mit dem tabellierten Zustand verglichen. Für den Look-up werden dabei die Kontrollvariablen der direkten Chemiesimulation benutzt. Die a posteriori Analyse ist der Vergleich einer voll gekoppelten Rechnung unter Benutzung der Tabellierungstrategie mit der zugehörigen detaillierten Rechnung.
Die erste untersuchte Konfiguration stellt eine Gegenstromanordnung mit vorgewärmter Luft und Kohlebeladung dar. Die Hauptergebnisse dieser rein numerischen Studie wurden bereits veröffentlicht [8] und es konnte die erfolgreiche Applikation der vorgestellten Tabellierungstrategie in dieser Anordnung für Tabellen basierend auf Diffusionflammenstrukturen gezeigt werden.
Für die Validierung der detaillierten Rechnungen erfolgt die Nutzung experimenteller Daten [9, 10] für magere Methan-Sauerstoff-Stickstoff Mischungen in Staupunktströmungen. Es zeigt sich, dass diese Konfigurationen stark von den vorgemischten Gasflammen dominiert werden und somit Tabellen basierend auf Vormischflammenstrukturen einzusetzen sind. Die entwickelte Tabellierungsmethode ist in der Lage, auch diese Flammenstrukturen abzubilden.
Abschließend wird numerisch eine Parametervariation hinsichtlich Einlassgeschwindigkeit und Kohlebeladung vorgestellt, um die Robustheit und breite Anwendbarkeit der entwickelten Tabellierungstrategie aufzuzeigen.
Zusammenfassend konnte mittels Flammenstrukturanalyse für jede vorgestellte Konfiguration der zu verwendende Typ der Tabelle bestimmt werden. In den untersuchten Konfigurationen führte deren Anwendung zu einer guten Übereinstimmung mit den detaillierten Rechnungen. Damit legt diese Arbeit den Grundstein für weiterführende Betrachtung zur Simulation großtechnischer Kohlestaubfeuerungen.
11
Cai, Haiyong. "Fast pyrolysis of coals and char characterisation in relation to pulverised coal combustion". Thesis, Imperial College London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337707.
Testo completo
12
Lapwood, Kevin John. "The combustion mechanisms of coal slurry fuels". Thesis, University of Surrey, 1986. http://epubs.surrey.ac.uk/842769/.
Testo completoAbstract (sommario):
The formation and subsequent burnout behaviour of coal slurry fuel chars has been studied using a suspended single droplet technique and solid sampling techniques in large turbulent diffusion flames. Both these techniques yielded comparable results on the structure of carbonaceous residues from a range of coal slurry fuels containing coals of different rank, size and concentration. The structure and burnout behaviour of all the fuels tested was dependant on coal rank, particle size, and concentration, although these variables did not always produce the same differences in behaviour in coal-oil and coal-water chars. Mid-rank coals, produced swollen well-fused chars which were substantially hollow and incorporated large surface blowholes. Such residues showed little tendency to fragment during combustion. Low and high rank coals produced less swollen chars which were comprised of loosely agglomerated coal particles causing more extensive internal structure and smaller surface blowholes. The furnace results of this and other studies indicate that the latter type of char structure is more conducive to rapid to rapid burnout. Small concentrations of emulsified water in coal-oil slurries were observed to increase the intensity of ebullition during devolatilisation although no evidence was obtained from any of the experimental techniques to suggest that this caused droplet shattering. However, water addition did increase the rate of combustion of coal-oil fuels. A theoretical model of the behaviour of coal slurry fuel chars during combustion has been presented which explains the experimental results in terms of the internal surface area of the char and the availability of this area to the gaseous reactants. It has been concluded that the rate of combustion of coal slurry chars of the size encountered in flames is largely controlled by the rate of internal diffusion of gaseous reactants and reaction within the porous char structure. The different reactivities of coal slurry fuels of different coal ranks has therefore been explained in terms of the various char structures which were observed The beneficial effects of water on the combustion of coal-oil fuels has also been explained within this theory since the addition of water could increase the porosity of the chars. However this has not been confirmed experimentally.
13
Beck, N. C. "The early stages of pulverised coal combustion". Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372642.
Testo completo
14
Prassas, Ilias. "Combustion of pulverised coal in swirl burners". Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286343.
Testo completo
15
Burchfield, Nicole Ashley. "Narrow Angle Radiometer for Oxy-Coal Combustion". BYU ScholarsArchive, 2020. https://scholarsarchive.byu.edu/etd/8423.
Testo completoAbstract (sommario):
A new method of power production, called pressurized oxy-fuel combustion, burns coal with CO2 and oxygen, rather than air, bringing us closer to the end goal of developing zero emission coal-fired utility boilers. However, high-pressure, high-temperature systems such as these are under-studied, and their behavior is difficult to measure. An accurate model for previously untested conditions requires data for validation. The heat release profile of flames and their radiative intensity is one of the key data sets required for model validation of an oxy-coal combustion system. A radiometer can be used to obtain the necessary radiative heat flux data. However, several studies show significant measurement errors of past radiometer designs. This work focuses on developing a narrow angle radiometer that can be used to describe radiative heat transfer from a pressurized oxy-coal flame. The sensitivity of the instrument to outside environmental influences is thoroughly examined, making it possible to obtain the axial radiative heat flux profile of the flame in a 100kW pressurized facility by accurately converting the measured quantities into radiative heat flux. Design aspects of the radiometer are chosen to improve the accuracy of radiative heat flux measurements as well as conform to the physical constraints of the 100kW pressurized facility. The radiometer is built with a 0.079-inch aperture, an 8.63-inch probe internally coated with high emissivity coating, four baffles spaced evenly down the length of the probe, no optic lens, a thermopile as the sensor, argon purge gas, and a water-cooled jacket. The radiometer has a viewing angle of 1.33 degrees. The instrument is calibrated with a black body radiator, and these calibration data are used in combination with radiation models to convert the radiometer signal in mV to radiative heat flux in kW/m2. Environmental factors affecting accuracy are studied. The results of the calibration data show that the radiometer measurements will produce a calculated heat flux that is accurate to within 5.98E-04 kW/m2.
16
Kwong, Chi Wai. "Effect of co-combustion of coal and biomass on combustion performance and pollutant emissions /". View abstract or full-text, 2005. http://library.ust.hk/cgi/db/thesis.pl?MECH%202005%20KWONG.
Testo completoAbstract (sommario):
Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2005."Sponsored by: CLP Research Institute." "HKUST project no.: CLPRI02/03.EG01." Includes bibliographical references (leaves 76-83). Also available in electronic version.
17
Wan, Ab Karim Ghani Azlina. "Co-combustion of biomass fuels with coal in a fluidised bed combustor". Thesis, University of Sheffield, 2006. http://etheses.whiterose.ac.uk/14891/.
Testo completoAbstract (sommario):
Co-combustion of biomass with coal has been investigated in a 0.15 m diameter and 2.3 m high fluidised bed combustor under various fluidisation and operating conditions. Biomass materials investigated were chicken waste, rice husk, palm kernel shells and fibres, refuse derived fuel and wood wastes. These were selected because they are produced in large quantities particularly in the Far East. The carbon combustion efficiency was profoundly influenced by the operating and fluidising parameters in the decreased following order: fuel properties (particle size and density), coal mass fraction, fluidising velocity, excess air and bed temperature. The smaller particle size and lower particle density of the fuels (i.e. coal/chicken waste, coal/rice husk and coal/wood powder), the higher carbon combustion efficiency obtained in the range of 86-90%, 83-88%, 87-92%, respectively. The carbon combustion efficiency increases in the range of 3% to 20% as the coal fraction increased from 0% to 70%, under various fluidisation and operating conditions. Also, the carbon combustion efficiency increases with increasing excess air from 30- 50% in the range of 5 - 12 % at 50% coal mass fraction in the biomass mixture. However, further increased of excess air to 70% will reduced the carbon combustion efficiency. Relatively, increasing fluidising velocity contributed to a greater particle elutriation rate than the carbon to CO conversion rate and hence increased the unburned carbon. Furthermore, the bed temperature had insignificant influence of carbon combustion efficiency among the biomass fuels. Depending upon excess air ranges, fluctuations of CO emissions between 200 - 1500 ppm were observed when coal added to almost all biomass mixtures. In ash analyses, the percentages of unburned carbon were found to have increased in the range 3 to 30% of the ash content with the increases of coal fraction in the coal! biomass mixture. Furthermore, no fouling, ash deposition and bed agglomeration was observed during the combustion runs for all tests due to lower operating bed temperature applied. Lastly, a simple model was developed to predict the amount of combustion in the freeboard. This study demonstrated the capability of co-firing biomass with coal and also demonstrated the capability to be burnt efficiently in existing coal-fired boilers with minimum modification.
18
Garba, Mohammed Umar. "Prediction of ash deposition for biomass combustion and coal/biomass co-combustion". Thesis, University of Leeds, 2012. http://etheses.whiterose.ac.uk/4373/.
Testo completoAbstract (sommario):
In this thesis, a model that couples a reduced alkali kinetic mechanism for alkali sulphate formation during biomass combustion with an ash deposition model using computational fluid dynamics (CFD) techniques has been presented. Starting with a detailed gas-phase kinetic mechanism for the alkali chemistry, a systematic reduction procedure has been performed using a sensitivity analysis to reduce the reaction mechanism to a level that can be implemented into a CFD calculation. An ash deposition model that takes into consideration the ash-sticking probability and the condensation of potassium salts has been developed. The reduced mechanism and the deposition model developed are implemented into a CFD model to predict ash depositions in a 10 MWth biomass grate furnace. Also, a CFD model to predict the deposition rates for the co-combustion of coal with biomass has been developed. This deposition model is based on the combined sticking probabilities of the ash particle viscosity and the melting behaviour of the ash particles. A Numerical Slagging Index (NSI) is also employed to estimate the degree of the sintering of the deposits. Experimental data from the Entrained Flow Reactor (EFR) at Imperial College, London, have been used to validate the models. The predicted results from both the ash deposition models agreed with the experimental measurements, and the NSI has successfully ranked the investigated coal-biomass mixtures according to their degree of sintering.
19
Ejesieme, Obialo Vitus. "Evaluating the effect of microalgae biomass on the combustion of coal". Thesis, Nelson Mandela Metropolitan University, 2013. http://hdl.handle.net/10948/d1020641.
Testo completoAbstract (sommario):
In this work the combustion characteristics of coal, charcoal, microalgae biomass and blends between these three components were evaluated by means of non-isothermal thermogravimetry. Blends between coal, charcoal and microalgae biomass were made according to the specifications of a D-optimal mixture design so as to be able to model interactions between the three components with maximum precision despite multiple constraints built into the design. These constraints specified that coal can have a minimum value of 70 mass percent in any blend, while microalgae can have a maximum value of 20 mass percent. While coal and charcoal were blended by mixing the two respective dry components, microalgae biomass was incorporated into the blends by first absorbing microalgae onto fine coal from concentrated slurry of the microalgae in water. The microalgae in these blends were therefore intimately associated with the coal. This approach differed substantially from the normal practice of preparing coal – biomass blends (which are usually dry-mixed as for coal – charcoal blends). Proximate analyses of the starting materials showed that the microalgae biomass has a significantly higher volatile matter: fixed carbon content than both coal and charcoal, which should improve the combustion of these materials by providing a more stable combustion flame. Analyses of the thermogravimetric data obtained showed that coal and charcoal have much simpler combustion profiles than microalgae biomass for which five different thermal events could be observed in the DTG combustion profile. Qualitative kinetic analyses showed that the combustion of coal and charcoal follows first-order kinetics, but for microalgae biomass combustion, the first two combustion stages appear to follow first-order kinetics. The TG and DTG profiles for coal, charcoal, microalgae and blends of these three components were used to derive values for the so-called comprehensive combustion property index (S-value), which provides a combined measure of the ease of ignition, rate of combustion, and burn-out temperature. The S-values so obtained were used as response variable for the construction of a response surface model in the experimental domain investigated. Following statistical validation of the response surface model, the model was used to predict an optimum S-value or a blend that would display optimum combustion behaviour. Two optimum blends were obtained from the optimisation process, one in which only charcoal is added to coal, and one in which only microalgae is added to coal. Adding both charcoal and microalgae produced an antagonistic effect compared to when only one of these are used. Qualitative kinetic analyses of the combustion data of blends indicate that blends of coal and charcoal combust in a manner similar to the individual components (hence following first-order kinetics), but blends of coal and microalgae follow more complex kinetics despite the fact that the combustion profile is visibly more simple compared to the combustion profile for microalgae alone.
20
Gallagher, Neal Benjamin. "Alkali metal partitioning in a pulverized coal combustion environment". Diss., The University of Arizona, 1992. http://hdl.handle.net/10150/185896.
Testo completoAbstract (sommario):
Fouling, slagging, corrosion, and emission of submicron particulate from pulverized coal combustors have been linked to vapor alkali. Size segregated fly ash samples extracted from a 17 kW down-fired pulverized coal combustor showed strong evidence of alkali vaporization. The fraction of sodium in sizes smaller than 0.65 μm (f(8A)) showed a correlation with acid soluble sodium divided by total silicates in the parent coal. Addition of silicates to coal reduced f(8A) for sodium. Potassium existing primarily in the mineral matter, did not show a similar correlation, but f(8A) for potassium did correlate with f(8A) for sodium. Bench scale experiments indicated potassium does not vaporize in the presence of Na or Cl alone, but requires both, and was only released when sodium was captured. Additional of sodium acetate to coal increased f(8A) for potassium. Equilibrium calculations, experiment, and modelling of sodium capture by silicates during pulverized coal combustion identified several important mechanisms governing alkali behavior. The mode of occurrence of alkali in the parent coal dictates its ability to vaporize, its release kinetics, and its sate as it diffuses to the char surface. Other species such as chlorine, sulfur, moisture, and other metals influence alkali stability in the vapor, its reactivity, and its condensation characteristics. Char oxidation can influence alkali vaporization, and capture by affecting included silicate surface area. Sodium reaction with silicates captures from 70 to over 95% of total sodium for typical coals. Silicate additive appears to be a viable technique for reducing the fraction of alkali in the vapor during combustion.
21
West, Richard D. "NEW APPROACHES FOR MITIGATING ENVIRONMENTAL CONCERNS ASSOCIATED WITH COAL AND COAL COMBUSTION PRODUCTS". OpenSIUC, 2012. https://opensiuc.lib.siu.edu/dissertations/511.
Testo completoAbstract (sommario):
Currently, coal combustion plays an important role in meeting the energy needs of the United States. It is expected that the effective utilization of coal will be crucial for attaining energy independence for the nation in the next 25 to 30 years, if not longer. The United States burns about 20% of the world's annual coal production, second only to China. Strikingly, there are 200-300 more years of burn at our current rate of consumption, considering our massive coal reserves. Almost half of our electricity comes from coal power. Although coal is a fossil fuel that will become more and more depleted, it will be the principal fuel for utilities in the US for decades to come. Therefore, there is a need to design new strategies to clean coal. Mercury can be found in fly ash, bottom ash, and flue gas desulfurization (FGD) material. The Hg is transferred to these coal combustion products (CCPs) from its associated parent coal. These CCPs absorb a significant amount of the Hg released during the combustion process. With the EPA's recent emphasis on controlling the Hg emission by coal-burning electric utilities, the disposal and utilization of CCPs are under an environmental microscope. As EPA regulations become more stringent, Hg concentration in CCPs is expected to increase further; i.e., more Hg will be captured in the scrubber materials. The higher Hg concentrations will have serious consequences for the management of CCPs. Systematic measurements on Hg concentrations in the feed coal and the CCPs produced from two different power plants burning Illinois coal were carried out. Not only were there substantial variations in the total Hg concentration in the parent coal from week to week from a single mine, but there were also significant variations in the weekly Hg content of the CCPs. Surprisingly, there was no linear dependence between Hg content of coal and its CCPs. No correlation was observed between Hg content of fly ash and its loss-on-ignition (LOI) values. In order to control and further understand the fate of Hg in FGD scrubber material, the following was systematically examined: (a) whether there is a strong correlation between the parent coal and the Hg captured in FGD scrubber materials, (b) the thermal behavior of Hg in parent coal, FGD gypsum, and sulfite-rich FGD material, (c) whether there is a potential of Hg re-emission during gypsum-to-hemihydrate-to-gypsum transition, and (d) how Hg behaves in sulfite-rich scrubber material at higher temperatures and pressures. Ultimately, no direct correlation between the total Hg concentration of the parent coal and its associated FGD scrubber materials was found. Mercury desorbed from FGD gypsum at relatively low temperatures (90C < T < 250C), compared to the sulfite-rich scrubber materials which released Hg continuously at ambient pressures up to 600C. However, it was found that mildly-elevated pressures immobilized Hg, even at temperatures as high as 250C. Cleaning and dewatering coal has been a major challenge. Deeper pre-combustion cleaning of ashes and clays from coals can help utilize more of Illinois coal. Efforts have been underway for decades to reduce emissions from flue gas and toxic metal reduction. Now with carbon emissions under scrutiny, the effort to maximize coal's value is more important than ever before. In most coal preparation processes, significant amounts of fines and ultrafines are generated. Because these particles are difficult to dewater, they are often discarded in waste ponds. This translates into a major economic loss for the coal industry, not only because of the fuel value lost but also the substantial economic resources required to manage coal waste ponds in an environmentally-sound manner. A new approach developed using a high intensity sonication process in recovering, cleaning, and dewatering fine/ultrafine coal particles from the waste ponds, while concurrently reducing the Hg concentration in the fine and ultrafine particles was successful. Combining sonication with vegetable oil agglomeration significantly reduced the moisture, ash, and Hg content of the cleaned, recovered coal. Differential scanning calorimetry (DSC) measurements on the recovered coal were used to understand the interaction between the coal particles, water, and oil. The results suggested that vegetable oil was effective in displacing water from the coal-water interface, with the enthalpy of the water-vapor transition of oil-agglomerated coal particles decreasing on sonication of the particles. In fact, combining sonication treatment with oil agglomeration reduced the moisture content of run-of-mine (ROM) coal and waste coal, to 6 wt% and 12 wt% respectively, and increased their loss-on-ignition (LOI) content to 91 wt% and 76 wt%, respectively. Massive quantities of synthetic gypsum are produced when the flue gases from coal burning power plants are wet scrubbed with limestone. The sulfate-rich FGD scrubber material is largely construction-quality gypsum. Because of the large production of FGD gypsum every year, the economic and environmental impetus dictates that strategies be developed to effectively utilize FGD gypsum rather than just landfill it. Beneficial uses have been found in wallboard construction and agriculture. An important aspect of this research was to evaluate whether there was potential of Hg re-emission from scrubber materials during their utilization phase. Mercury emission occurs not only with elevated temperatures but with increased time. While external pressure retards these emissions, they are not the only concern associated with CCPs. The more global, urgent problems of greenhouse gases must be resolved. The dimension of the greenhouse gases problem is daunting; according to the Energy Information Agency, nearly 6 billion metric tons of CO2 were produced in the USA in 2007, with coal-burning power plants contributing about 2 billion metric tons. The success of large-size sequestration of CO2 in coal would hinge on a thorough understanding of coal-CO2 interactions and how these interactions control the mechanical behavior of coal. Moreover, these interactions could play a crucial role in evaluating any potential risks associated with sequestering CO2 in deep, unmineable coal seams. To evaluate the risk under non-equilibrium conditions, dynamic mechanical properties of pressurized Illinois coals were measured. The results suggest that Illinois bituminous coal in its unperturbed state, i.e., when not pressurized with CO2, showed large variations in its mechanical properties. The Young's modulus varied from 0.7 GPa to 3.4 GPa even though samples were extracted from a single chunk. No glass transition was observed for any Illinois bituminous coal under ambient conditions. Upon pressurizing the Illinois bituminous coals with CO2, the DMA results showed a transition at temperatures as low as ambient. This could be a potential risk for the structural integrity of a mine if any man-made or seismic activity were present.
22
Punjak, Wayne Andrew. "High temperature interactions of alkali vapors with solids during coal combustion and gasification". Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184599.
Testo completoAbstract (sommario):
The high temperature interactions of alkali metal compounds with solids present in coal conversion processes are investigated. A temperature and concentration programmed reaction method is used to investigate the mechanism by which organically bound alkali is released from carbonaceous substrates. Vaporization of the alkali is preceded by reduction of oxygen-bearing groups during which CO is generated. A residual amount of alkali remains after complete reduction. This residual level is greater for potassium, indicating that potassium has stronger interactions with graphitic substrates than sodium. Other mineral substrates were exposed to high temperature alkali chloride vapors under both nitrogen and simulated flue gas atmospheres to investigate their potential application as sorbents for the removal of alkali from coal conversion flue gases. The compounds containing alumina and silica are found to readily adsorb alkali vapors and the minerals kaolinite, bauxite and emathlite are identified as promising alkali sorbents. The fundamentals of alkali adsorption on kaolinite, bauxite and emathlite are compared and analyzed both experimentally and through theoretical modeling. The experiments were performed in a microgravimetric reactor system; the sorbents were characterized before and after alkali adsorption using scanning Auger microscopy, X-ray diffraction analysis, mercury porosimetry and atomic emission spectrophotometry. The results show that the process is not a simple physical condensation, but a complex combination of several diffusion steps and reactions. There are some common features among these sorbents in their interactions with alkali vapors: In all cases the process is diffusion influenced, the rate of adsorption decreases with time and there is a final saturation limit. However, there are differences in reaction mechanisms leading to potentially different applications for each sorbent. Bauxite and kaolinite react with NaCl and water vapor to form nephelite and carnegieite and release HCl to the gas phase. However, emathlite reacts to form albite and HCl vapor. Albite has a melting point significantly lower than nephelite and carnegieite; therefore, emathlite is more suitable for lower temperature sorption systems downstream of the combustors/gasifiers, while kaolinite and bauxite are suitable as in-situ additives.
23
Puchakayala, Madhu Babu. "Mercury emission behavior during isolated coal particle combustion". [College Station, Tex. : Texas A&M University, 2006. http://hdl.handle.net/1969.1/ETD-TAMU-1153.
Testo completo
24
Zhao, Jiansheng. "Coal combustion in spouted and spout-fluid beds". Thesis, University of British Columbia, 1986. http://hdl.handle.net/2429/26347.
Testo completoAbstract (sommario):
This study of coal combustion was carried out in a half-column spout-fluid bed combustor, in which Forestberg coal, a sub-bituminous Alberta coal, was burned in inert beds of sand. The combustor consists of a half cylindrical stainless steel column of 0.152 m I. D. and 1.06 m long, a half cylindrical cone fitted with an inlet orifice of 15.9 mm and a perforated plate as distributor surrounded by a plenum chamber, and a flat stainless steel panel with quartz glass windows.
Aspects studied included hydrodynamic and combustion patterns, axial and radial temperature profiles, axial oxygen concentration profiles and burnout times of coal particles.
Depending on operating conditions and properties of bed materials, four different flow patterns were established: Stable spouting, pulsatory spouting, jet-in-fluidized-bed and slugging. It was found that the maximum stable spouting height decreased as the bed temperature increased.
Axial temperature profiles in the spout and annulus were found to be uniform for both spouted and spout-fluid beds except for a short distance above the inlet orifice. However, a temperature increase was found in the fountain above the spout when finer coal particles were employed. Above the annulus the temperatures increased substantially. More uniform axial temperature profiles could be achieved by introducing auxiliary air to create a spout-fluid bed. Radial temperature profiles were uniform both in the annulus and in the fountain region.
Axial oxygen concentration profiles were found to be closely related to the flow patterns and solids properties. When larger coal particles (1mm) were used the oxygen concentration profiles were uniform within and above the spout, but a decrease of concentration was observed when fine coal particles (0.6 mm) were used. In the annulus a sharp decline of concentration started near the bed surface, and a minimum was reached in the fountain region. Concentration profiles became more uniform when auxiliary air was introduced.
Compared with data reported in literature for fluidized bed combustion, the burnout times of coal particles in spouted and spout-fluid beds were found to be significantly shorter. A model for estimating the burnout times was proposed and tested against the experimental data. For the particle size and temperature range tested, the combustion was mainly controlled by chemical reaction.Applied Science, Faculty of
Chemical and Biological Engineering, Department of
Graduate
25
Allen, Deborah. "The removal of gaseous pollutants during coal combustion". Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335690.
Testo completo
26
Zebian, Hussam. "Multi-variable optimization of pressurized oxy-coal combustion". Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/67808.
Testo completoAbstract (sommario):
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 81-82).
Simultaneous multi-variable gradient-based optimization with multi-start is performed on a 300 MWe wet-recycling pressurized oxy-coal combustion process with carbon capture and sequestration. The model accounts for realistic component behavior such as heat losses, steam leaks, pressure drops, cycle irreversibilities, and other technological and economical considerations. The optimization study involves 16 variables, three of which are integer valued, and 10 constraints with the objective of maximizing thermal efficiency. The solution procedure follows active inequality constraints which are identified by thermodynamic-based analysis to facilitate convergence. Results of the multi-variable optimization are compared to a pressure sensitivity analysis similar to those performed in literature; the basecase of both assessments performed here is a favorable solution found in literature. Significant cycle performance improvements are obtained compared to this literature design at a much lower operating pressure and with moderate changes in the other operating variables. The effect of the variables on the cycle performance and on the constraints are analyzed and explained to obtain increased understanding of the actual behavior of the system. This study reflects the importance of simultaneous multi-variable optimization in revealing the system characteristics and uncovering the favorable solutions with higher efficiency than the atmospheric operation or those obtained by single variable sensitivity analysis.
by Hussam Zebian.
S.M.
27
Shaw, David William. "Determination of global kinetics of coal volatiles combustion". The Ohio State University, 1988. http://rave.ohiolink.edu/etdc/view?acc_num=osu1346770278.
Testo completo
28
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.
Testo completoAbstract (sommario):
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.
29
Dhungel, Bhupesh [Verfasser]. "Experimental Investigations on Combustion and Emission Behaviour During Oxy-Coal Combustion / Bhupesh Dhungel". Aachen : Shaker, 2010. http://d-nb.info/1084536072/34.
Testo completo
30
Wang, Muh-Rong. "Mechanisms and performance of coal burning Rijke type pulsating combustors". Diss., Georgia Institute of Technology, 1985. http://hdl.handle.net/1853/13032.
Testo completo
31
Vicente, Annalisa Sarga. "Assessing different coal combustion residue backfill scenarios in opencast coal mines, Mpumalanga, South Africa". University of Western Cape, 2020. http://hdl.handle.net/11394/7853.
Testo completoAbstract (sommario):
>Magister Scientiae - MScCoal-fired power stations produce large volumes of coal combustion residues (CCRs), which are disposed of in hold ponds or landfill sites. These ash storage facilities are limited in space and are approaching the end of their capacities, thus additional land is required for extensions. If new land is not sourced, power plants will be forced to cease operations, resulting in increased expenditure costs and environmental liability. A proposed disposal solution is to backfill opencast coal mines with CCR monoliths. However, there is limited knowledge on the hydraulic behaviour of CCRs in an opencast coal mine environment. This leads to an inability to assess this applications feasibility and determine whether this activity will have a positive, negligible or negative effect on groundwater quality. This study aims to address this gap in knowledge by assessing the flow and transport properties of CCRs under numerous theoretical backfilling conditions.
32
Makgato, Seshibe Stanford. "Microbial Desulphurization of Combustion Coal and Environmental Control in Carbonization Coal : Emissions Reduction Techniques". Thesis, University of Pretoria, 2020. http://hdl.handle.net/2263/78953.
Testo completoAbstract (sommario):
Coal use in electricity generation has attracted much attention recently mainly due to the sector been identified as the main source of sulphur dioxide (SO2) emissions globally. The combustion of coal releases sulphur dioxide emissions into the atmosphere that create air pollution and cause harmful effects on the ecosystem. In the current study, biodesulphurization of Waterberg steam coal was investigated using a bacterial consortium isolated from coal. Coal samples were obtained from the coal feed into the power plant mills, by auto sampling equipment. Coal samples with various particle size fraction of +4.60 mm, −4.60 + 2.30 mm, −2.30 + 1.00 mm and −0.85 mm were used in the biodesulphurization experiments. The characteristic properties of the coal samples were analysed by means of a number of techniques, including Leco S-628 Elemental analyser, UV Spectrophotometry, bomb calorimeter and X-Ray Fluorescence. The contribution of this study to the country's minimum emissions requirements and compliance could be outlined as follows: Coal was classified as medium sulphur coal when the sulphur content was detected in the range 1.15 – 1.49 wt.%. Four forms of sulphur - pyrite, mineral/sulphide sulphur, inorganic sulphates and organic sulphur were present in Waterberg coal with pyritic sulphur (≥ 0.51 wt.%) and organic sulphur (≥ 0.49 wt.%) accounting for the bulk of the total sulphur in coal.Thesis (PhD)--University of Pretoria, 2020.
UP Postgraduate Bursary
Chemical Engineering
PhD (Chemical Engineering)
Unrestricted
33
Cheng, Chin-Min. "Leaching of coal combustion products field and laboratory studies /". Columbus, Ohio : Ohio State University, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1133195856.
Testo completo
34
Bibrzycki, Jakub [Verfasser]. "Investigations of coal particle combustion and gasification / Jakub Bibrzycki". Clausthal-Zellerfeld : Universitätsbibliothek Clausthal, 2015. http://d-nb.info/1070571792/34.
Testo completo
35
Malik, Abdullah A. "A study of coal combustion using a rotating retort". Thesis, University of Newcastle Upon Tyne, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315571.
Testo completo
36
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.
Testo completo
37
Zeng, Taofang 1963. "Transformation of iron and trace elements during coal combustion". Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/9971.
Testo completo
38
Franchetti, Mario Alberto Benjamin. "Large eddy simulation of air and oxy-coal combustion". Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/32148.
Testo completoAbstract (sommario):
The main aim of the present work is to investigate the applicability of Large Eddy Simulations to pulverised coal combustion. The Navier-Stokes equations that describe an incompressible tur- bulent reactive flow are presented, with a source term which ac- counts for the effect of the coal particles on the gas phase. Both a Eulerian and Lagrangian approach are presented to describe the coal particles motion and their heat exchange with the gas phase. The main processes that characterise pulverised coal combustion: devolatilisation, volatile combustion and char combustion are described and the main models to represent them are presented. The performance of the numerical approximation is tested on two main experimental cases: 1) a pulverised coal jet flame surrounded by a methane pilot and 2) a 100 kWth swirling burner operating in an O2/CO2 environment. The results of the simulations are com- pared to qualitative and quantitative experimental measurements for both test cases. Finally a parametric study is performed on both test cases to understand firstly, which combustion processes are dominant and secondly to understand which models perform best for each experimental set-up. The results showed the Lagrangian approach to be more representative of the pulverised coal combustion process. The analysis for the pulverised coal jet flame, showed that the radiation and char combustion processes have almost negligible effect. Instead, the simulation results were highly sensitive to variations in the devolatilisation and volatile combustion models and model parameters. For the second test case, char combustion was dominant throughout most of the domain as the coal particles had a longer time to burn. The devolatilisation and volatile combustion processes were dominant at the initial stages of the combustion process and characterised the initial flame bhevaiour.
39
Makhadmeh, Leema al. "Coal pyrolysis and char combustion under oxy-fuel conditions". Aachen Shaker, 2009. http://d-nb.info/996033009/04.
Testo completo
40
Bulusu, Sowmya. "Remediation of abandoned mines using coal combustion by-products". College Park, Md. : University of Maryland, 2005. http://hdl.handle.net/1903/2992.
Testo completoAbstract (sommario):
Thesis (M.S.) -- University of Maryland, College Park, 2005.Thesis research directed by: Dept. of Civil and Environmental Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
41
Seames, Wayne Stewart. "The partitioning of trace elements during pulverized coal combustion". Diss., The University of Arizona, 2000. http://hdl.handle.net/10150/284196.
Testo completoAbstract (sommario):
The environmental impact resulting from the release of trace elements during coal combustion is an important issue for the coal-fired electric utility industry. Trace elements exit the combustor by partitioning between the flue gas and the fly ash particles. A comprehensive study has been conducted to investigate the mechanisms governing the partitioning of trace elements during pulverized coal combustion. The behavior of seven trace elements (arsenic, selenium, antimony, cobalt, cesium, thorium, and cerium) in six pulverized coals were studied under commercially relevant conditions in a well-described laboratory combustion environment. The partitioning of trace elements is governed by the extent of volatilization during combustion, the form of occurrence in the flue gas, and the mechanisms controlling vapor-to-solid phase transformation to fly ash particle surfaces. The most common vapor-to-solid phase partitioning mechanism for semi-volatile trace elements is reaction with active fly ash surfaces. Trace elements that form oxy-anions upon volatilization (e.g. arsenic, selenium, antimony) will react with active calcium and iron cation fly ash surface sites. Trace elements that form simple oxides upon volatilization (e.g. cobalt, cesium) will react with active aluminum oxy-anion fly ash surface sites. The maximum combustion temperature affects the availability of active calcium and iron surface sites but not aluminum sites. Sulfur inhibits the reactivity of oxy-anions with iron surface sites. For coals with high sulfur contents (>1 wt % as SO₂), volatilized trace elements that form oxy-anions will partition by reaction with calcium surface sites if sufficient sites are available. For coals with low sulfur contents, volatilized trace elements that form oxy-anions, will partition by reaction with iron surface sites. Volatilized trace elements that form oxy-anions will not partition by reaction if the coal sulfur content is high and the calcium content is low (<3 wt% as CaO). Transition metals (e.g. cobalt) may form simple oxides, oxy-anions or both upon volatilization. An appreciable fraction of trace elements with limited volatility (e.g. cobalt, thorium, cerium, cesium) will volatilize. These will partition back to the solid phase by homogeneous nucleation or surface reaction depending upon the post-combustion conditions present.
42
Ogden, Gregory E. "Pulverized coal combustion: Flame attachment and nitrogen oxide emissions". Diss., The University of Arizona, 2002. http://hdl.handle.net/10150/289822.
Testo completoAbstract (sommario):
To fully utilize coal as a long-term energy source, pollution prevention technologies must be developed to mitigate the negative environmental and health impacts of coal combustion. NOₓ emissions are of particular concern due to their role in forming ground-level ozone, photochemical smog, fine particulates and acid rain. A systematic evaluation of near-flame aerodynamics was conducted to determine how burner operating parameters and oxygen partial pressure influence flame attachment and coal ignition, two properties essential for proper low NOₓ burner operation. A laboratory scale (17kW) 2m tall, 0.5m diameter electrically heated furnace and axial burner with adjustable secondary combustion air annuli and primary fuel jets were used in the study. Transport air oxygen partial pressure (PO₂), coal particle size distribution, primary and secondary jet velocity, and wall temperature were varied independently to determine the effect of each variable on flame attachment and NOₓ. NOₓ emissions from the furnace were similar to those from full-scale tangentially-fired boilers. The tendency for flame attachment increased with velocity ratio (Θ), wall temperature, PO₂, and coal fines. Θ's greater than 1 were required for stable combustion. Increasing Θ reduced flame standoff distances and NOₓ for always-detached flames. NOₓ increased with Θ for always-attached flames. Increasing PO₂ reduced NOₓ by up to 50% by promoting flame attachment. However both oxygen enrichment and increasing fines had little impact on NOₓ for always-attached and always-detached flames. Wall temperature and excess air in leakage were the dominant variables affecting NOₓ. Furnace exhaust oxygen levels increased when operating under a slight vacuum with corresponding increases in NOₓ. Emissions for detached flames increased with wall temperature 3 times faster than attached flames. Emissions data obtained from the furnace under slight positive furnace pressure increased linearly with wall temperature. A novel dual flame was produced at high Θ and reduced PO₂ consisting of one flame attached to the burner and one stabilized 18" below the burner. This configuration is similar to staged combustion but without separate over-fire air. Emissions from the dual flame were significantly below those observed from conventional Type-O attached and detached flames.
43
Zailini, Ramlan. "Pulverised coal combustion in high CO₂ oxygen-rich environments". Thesis, University of Leeds, 2007. http://etheses.whiterose.ac.uk/4418/.
Testo completoAbstract (sommario):
Experiments on pulverised coal combustion in air and 02/C02 mixtures of various molar ratios, were conducted in a 20 kW-rated, down-fired furnace equipped with a single pulverised fuel (pt) burner, which was designed for the laboratory-scale experimental studies on coal combustion in air. In coal-02/C02 combustion tests, all the oxidants and fuel were delivered into the furnace with the same configurations as those in the coal-air combustion firing tests. In each test, the coal firing rate was fixed, and the furnace stoichiometric ratio was fixed at SR=1.20. Seven bituminous coals with fuel ratio ranging from 1.50 to 2.33 were used in the study. The effectiveness of air/oxidant staging on reducing NOx emissions was investigated for combustion in air and 02/C02 mixtures. The fate of recycle NO in combustion with different oxidants and combustion conditions was also investigated. Continuous furnace operations with stable flames and a comparable operating temperature to that in air were established for 02/C02 combustion, without major operational problems related to burner ignition, flame stability, coal firing and the effect of oxidants switching, both in unstaged and staged conditions. The results show that temperature and emission profiles are highly influenced by the oxidant compositions. A continuous flame could not be sustained by the direct replacement of combustion air with 02/C02 mixture with the same O2 concentration as air (21 :79-02/C02). In 02/C02 atmospheres, NOx Conversion Ratio (CRNO'..) decreased with the increasing concentration of the CO2 in the oxidant and combustion with 21 :79-02/C02 produced NOx of about one-fourth to that in air. With a same firing rate and combustion stoichiometry. coal combustion in 30:70-02/C02 produced a similar flame temperature profile to that in air combustion.while producing a significantly lower furnace NO, emISSIOn and a higher char burnout. The NO" Conversion ratio (CRNox) ranged from 27.7 - 39.70/0 in air and 18.4 - 35.5% in 30:70-02:C02. The Burnout Efficiency (1180) in air and in 30:70- 02/C02 ranged from 92.5-98.50/0 and 95.0-99.3 % respectively. Compared to that in air combustion, NOx conversion was more sensitive to coal prope11ies in 30:70- 02/C02. The CO concentration in the combustion zone of the 30:70-02/C02 mixture was more than 50% higher than that of air but the Je\'eJ decreased to an insignificant level at the exhaust. With the presence of air in the oxidant from atmospheric leakages, a high CO2 concentration of more than 80% of the flue gas was attained in 30:70-02:C02 combustion, compared to around 15% in air firing. The CO2 concentration in the flue gas could be increased further to more than 90 % by reducing air infiltration into the combustor. The staged combustion tests result show that oxidant staging is a very effective method in reducing NOx emissions for coal combustion in 30:70-02IC02. and can be more effective than in staged air combustion. For coal combustion in air, staging with SR1=0.80 reduced NOx emission by 54 - 650/0, while combustion in 30:70-02/C02. reduced NO" by 44 - 73 %. Compared to normal air combustion, staged combustion in 30:70-02:C02 reduced the overall furnace NOx by 67-77 0/0. The recycled NO tests results show that the NO Reduction Efficiency (l1No) depends on the combustion media. combustion conditions and NO recycling injection locations, and is influenced by the coal properties but not by the recycled NO concentrations. Compared to that in air, NO Reduction Efficiency in 30:70- 02:C02 is more sensiti\'e to coal properties, particularly coal Fuel Ratio (FR).
44
Kubacki, Michal Lukasz. "Co-pyrolysis and co-combustion of coal and biomass". Thesis, University of Leeds, 2007. http://etheses.whiterose.ac.uk/274/.
Testo completoAbstract (sommario):
Sustainability, security of supply, and diversity, as well as economic competitiveness are key components of energy policy. There is increasingly stringent legislation on the environmental impact of energy production, and there is growing pressure to reduce not just NOx and SOx emissions, but also C02 emissions. For both heating and electricity production it is likely that the plants will need to be fuel-flexible and could use one or more of several different feedstocks, for example coal and biomass. When coal is co-utilized with biomass there is added attractiveness because the biomass is C02 neutral, and there is interest in using wood waste, short rotation woody crops (e. g. willow coppice), or herbaceous crops (e. g. Miscanthus), refuse and waste derived fuels, or wastes such as sewage sludge or chicken litter. The co-utilisation of coal and biomass for heat and/or energy production results in pollutant reduction. Most notable is the impact on the emission of NOx, SOx, volatile organic compounds and polyaromatic hydrocarbons. These latter compounds largely arise from their formation and release during incomplete combustion/gasification. There is evidence that co-firing or co-gasifying coal and biomass results in a significant decrease in the emission of these compared to coal alone. The synergistic activity observed for toxic organic emissions is not well understood and is thought to involve chemical interaction between the volatiles from each fuel coupled with possible catalytic activity from the inorganic constituents of the fuels. Laboratory scale data on synergies in co-pyrolysis is conflicting. Characterisation of co-pyrolysis products from coal and biomass pyrolysis has received limited attention and the data is conflicting. Therefore this thesis seeks to understand possible interactions occurring during co-combustion and co-pyrolysis of fuels and looks at a number of variables, including coal rank, biomass type (with different amounts of catalytic components), heating rate, residence time and the physical form of the fuels. A better understanding of the factors influencing non-additive interactions may lead to optimization of the blending process and minimisation of toxic organic emissions. This work is of particular relevance to fixed bed and fluidised bed processes where the bed temperature is ca. 1000 'C (or there is a temperature profile through the bed). In these cases particle heating and pyrolysis occurs relatively slowly and interactions between the volatiles can take place. While studying the co-pyrolysis, thermogravimetry, batch pyrolysis and pyroprobe-GC/(MS or FID) were used. In addition, apart from the traditionaltechniques, this study aimed to develop a new technique - heated wire mesh pyrolysis coupled to a GUMS via a probe, which can sample at varying heights from the pyrolysing fuel, and these findings were complemented by the pyrolysis-GC/MS studies of the fuels. These studies suggest that biomass type can lead to a small change of the rate of the coal pyrolysis. Thus, slight synergistic effects were seen for the TGA study, where co-pyrolysed coals in blends often had lower peak temperatures compared to the coal alone, and higher volatile matter yields were produced. Analysis of the gases evolved were consistent with higher gas yields. This effect was present for certain biomass (e. g. oat straw) even after minerals were removed, and so this is not purely the result of catalytic ash components. For combustion studies two techniques were applied. Low heating rate was obtained in a TGA analyser. The high heating rate experiments were performed on pellets exposed to the flame of Meker-type burner. This combustion process was recorded with a high speed frame video recording system. These studies showed that strong synergy can be observed. The TGA combustion revealed the importance of the catalytic elements, particularly potassium, and showed that, ignition of biomass char in the blend aids the ignition of the coal char. As a result, mixtures reach maximum temperatures faster, than seen for the separate fuels. In many cases though, the char burn-out of the blends lasted a similar time to the coals alone. The combustion tests of stationary pellets revealed no pattern for the ignition delay, but exposed strong synergy in volatile combustion, indicating that for pellets of untreated fuel blends the combustion events are dominated by the coal behaviour i. e. the addition of demineralised biomass to the pellet, made it burn in a very similar way to coal alone. The synergy observed in the organic emissions during the combustion of coal and biomass in small appliances is not simply due to interactions of hot volatiles from coal and biomass above the combustion bed. Co-pyrolysis studies suggest that biomass type can lead to a small effect on the rate of the coal pyrolysis, and on the total volatile matter released, but that there are no major changes in the nature of the volatiles. Combustion studies indicate that synergy stronger than seen for pyrolysis tests can be observed, and the coal ignites and burns at lower temperature as a result of the earlier ignition and combustion of the biomass. The overall combustion time is still dominated by the coal char burn-out. Thus, synergy in emission reduction in the co-utilisation of coal and biomass is not simply due to interactions of volatiles in the vapour phase, rather, the processes of pyrolysis and combustion are linked and as such need to be studied together.
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No, Soo Young. "Processes involved in coal combustion in non-slagging cyclone combustors". Thesis, Cardiff University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316386.
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Ribeiro, Natália da Silva [UNESP]. "Estudo termogravimétrico da combustão e oxicombustão de misturas carvão mineral-biomassa". Universidade Estadual Paulista (UNESP), 2017. http://hdl.handle.net/11449/149903.
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Nesta dissertação, investiga-se através da análise termogravimétrica o comportamento da combustão de amostras de carvão mineral, bagaço de cana-de-açúcar, bagaço de sorgo biomassa e das misturas de carvão-biomassa. A biomassa e o carvão possuem propriedades físico-químicas diferentes que proporcionam comportamento térmico diferente durante o processo de co-combustão, desta forma o objetivo desta pesquisa é caracterizar o comportamento térmico de misturas de carvão mineral com bagaço de cana-de-açúcar e bagaço de sorgo em atmosferas simuladas de combustão (O2/N2) e oxicombustão (O2/CO2). Os experimentos foram realizados em duplicata em um analisador termogravimétrico utilizando uma razão de aquecimento de 10 °C/min. Foi considerada uma granulometria uniforme para todos os materiais (63 µm) com a finalidade de garantir uma mistura homogênea. Foram estudadas quatro proporções de biomassa na mistura (10, 25, 50 e 75%). A partir das técnicas de termogravimetria (TG) e termogravimetria derivada (DTG) foram determinados parâmetros tais como Índice de combustão, sinergismo e energia de ativação, bem como avaliada a influência da atmosfera de combustão sobre esses parâmetros. Os resultados indicam que o bagaço de cana-de-açúcar apresenta valor de energia de ativação inferior ao registrado para o bagaço de sorgo e desempenho de combustão superior ao do bagaço de sorgo. Para as misturas, os melhores resultados foram registrados até a proporção de 25% de biomassa na mistura. Avaliando individualmente cada material, quando se substitui o N2 por CO2 pode-se observar um aumento na reatividade da reação, uma maior oxidação dos materiais e uma melhora nos parâmetros avaliados. Para ambas as misturas não foram observadas mudanças significativas no perfil de combustão quando o N2 é substituído por CO2. No entanto, a presença da biomassa na co-combustão com o carvão, além dos benefícios econômicos e ambientais, aumentou o desempenho da combustão do carvão mineral em ambas as atmosferas.
This dissertation investigates by thermogravimetric analysis the behavior of the combustion of coal, sugarcane bagasse, sorghum biomass bagasse and coal-biomass blends. The biomass and coal have different physicochemical properties that provide different thermal behavior during the process of co-combustion, thus the aim of this research is to characterize the thermal behavior of coal mixed with sugarcane bagasse and sorghum bagasse in simulated atmospheres of combustion (O2/N2) and oxycombustion (O2/CO2). The experiments were performed in duplicate in a thermogravimetric analyzer using a heating rate of 10 ° C/min. A uniform particle size for all materials (63 μm) in order to ensure a homogeneous mixture was considered. Four biomass ratios were studied in the blend (10, 25, 50 and 75%). From the techniques of Thermogravimetry (TG) and Derivative Thermogravimetry (DTG) curves were determined parameters such as: Combustion index, synergism and activation energy and evaluated the influence of combustion atmosphere on these parameters. The results indicate that the sugarcane bagasse presents a lower activation energy value than sorghum bagasse and combustion performance higher than sorghum bagasse. For mixtures, best results were recorded up to 25% proportion of biomass in the blend. Individually evaluating each material, when replacing N2 by CO2 can be seen an increase in the reactivity of the reaction, the increased oxidation of the materials and an improvement in the evaluated parameters. For both blends, no significant changes in combustion profile when N2 substituted by CO2. However, the presence of biomass in co-combustion with coal in addition to economic and environmental benefits increased the combustion performance of coal in both atmospheres.
CNPq: 134366/2015-8
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Scotto, Mark Vincent 1960. "A mechanism for the oxidation and fragmentation of a char particle". Thesis, The University of Arizona, 1988. http://hdl.handle.net/10150/276699.
Testo completoAbstract (sommario):
A mechanism for the oxidation and fragmentation of a char particle was developed. Qualitative agreement between the model simulations and experimental data observed in the literature, is found for the higher gas temperatures (1700K). However fundamental differences are found in the particle temperature histories and burnout times at low temperature (1250K). The role that fragmentation plays on the char particle history is incorporated into the model and the possible production of fine particulate through fragmentation is examined. A relatively large fraction of the mass of char available for fragmentation is produced early in the combustion history of the particle. Therefore, if this mechanism is important in the generation of fine particulate matter during char combustion, the simulations indicate that it would occur early in the combustion process. Due to the limited experimental data in the literature on the time resolved particle size distribution in the early stages of combustion, corroboration between model and experiment was not possible.
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Bose, Arun Chand. "Pulverized coal combustion: Fuel nitrogen mechanisms in the rich post-flame". Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184635.
Testo completoAbstract (sommario):
Chemical kinetic mechanisms governing the fate of coal nitrogen in the fuel-rich stage of a pulverized-coal staged combustion process were investigated. Emphasis was on determination of the effects of coal rank, temperature and stoichiometric ratios on the speciation and rates of destruction of nitrogenous species and correlation of coal data by a unif1ed mechanism. The relative importance of homogeneous and heterogeneous mechanisms during post-flame interconversion reactions of the fuel nitrogen pool was quantified. Experiments with doped propane gas and a high- and low-grade coals, burned under a variety of conditions in a 2 Kg/h downflow combustor, yielded timeresolved profiles of temperature, major (H₂, CO, CO₂, O₂ and N₂), nitrogenous (NO, HeN and NH₃) and hydrocarbon (CH₄ and C₂H₂) species. These profiles allowed global mechanisms describing the speciation and destruction of fuel nitrogen species to be explored, using predictive models of increasing levels of sophistication. Fuel nitrogen speciation varied significantly from coal to coal and depended on stoichiometric ratio and temperature, which were varied independently. A general correlation describing the destruction rate of NO was derived from data. This rate, which was first-order in both NO and NH₃, was generally valid for all coals and all conditions examined. Fuel nitrogen interconversion reactions, especially destruction of NO and HeN, was predominantly homogeneous, but no single elementary reaction was controlling. Temperature quench down the combustor is the origin of OH equilibrium overshoot. Expressions for estimating the OH equilibrium overshoot as a function of the axial temperature decay along the combustor were derived both empirically and kinetically from fundamental considerations using data from doped propane gas runs. These expressions, together with available literature values of gas phase rate coefficients, could adequately describe the post-flame NO and HeN profiles of coal and gas runs. HeN profiles in the far postflame zone of the coal flames are strongly influenced by the slow release of nitrogen from the coal residue. This devolatilization plays a critical role in supplying the HeN that drives the multistep process converting fuel N into molecular nitrogen.
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Mill, Christopher John School of Chemical Engineering & Industrial Chemistry UNSW. "Pyrolysis of Fine Coal Particles at High Heating Rate and Pressure". Awarded by:University of New South Wales. School of Chemical Engineering and Industrial Chemistry, 2000. http://handle.unsw.edu.au/1959.4/33358.
Testo completoAbstract (sommario):
High-intensity pyrolysis, rapid heating in an inert gas atmosphere at up to 20 atm pressure, of 6 Australian coals was examined to gain further insight into high-intensity processes such as Integrated Gasification Combined Cycles (IGCC). Experiments focussed on pyrolysis in a specially developed Wire Mesh Reactor (WMR). The particle temperature lagged that of the mesh by 0.2 seconds at a heating rate of 100??~C s -1 and was predicted by modelling. This is part of the reason the volatile yield (VY) results for 10 s hold-time at ???b1.7 wt% daf of coal, is much more reproducible than 1 s hold-time experiments at ???b4.2 wt% daf of coal. Four coals of the same rank did not behave identically when heated. Three of the coals had a pyrolysis VY the same as the proximate VM when heated to 100??~C at 1 atm but the fourth, higher inertinite coal had a 1 atm pyrolysis VY 90% of its proximate VM. All four coals of similar rank had a significant decrease in VY, between 10 and 20 wt% daf of coal, with pressure increasing from 1 to 20 atm. The two lower rank coals showed less decrease in VY with increasing pressure than the higher rank and higher inertinite coals. The lower decrease in VY with increased pressure was mostly attributed to the lower inertinite levels for both the coals of similar rank and VM, and the coals of lower rank. Char characteristics examined focussed on pore Surface Area (SA). For high intensity WMR and Drop Tube Furnace (DTF) pyrolysis experiments CO2 SA for char from a particular coal was similar but the BET SA different. This was due to the char in the WMR experiments having longer to form larger pores determined by BET N2 SA. Both the N2 and CO2 SA was more than an order of magnitude greater than for low intensity pyrolysis char. This highlights that the WMR can be used to attain char with similar CO2 SA characteristics as other high intensity pyrolysis experiments and to provide a more meaningful insight into char reactivity than low intensity chars do.
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Harris, Benjamin James. "The hydrodynamics of circulating fluidized beds". Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385331.
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