1,720,985 research outputs found
Molecular characterization of the thermally labile fraction of biochar by hydropyrolysis and pyrolysis-GC/MS
Full text linkAgroenvironmental benefits and limitations of biochar in soil applications require a full understanding of the stability and fate of the various carbon fractions. Analytical hydropyrolysis (HyPy) enables the determination of the stable black carbon (BCHyPy) and thermally labile (semi-labile; non-BCHyPy) fractions in biochar and soil samples. The non-BCHyPy fraction can be analysed at a molecular level by gas chromatography-mass spectrometry (GC-MS). In the present study, HyPy was applied to the characterisation of biochars produced from pine wood, beech wood and corn digestate with the same pyrolysis unit at low (340–400 °C) and high (600 °C) temperatures. Results were compared with those from Py-GC-MS. HyPy provided consistent information concerning the thermal stability of biochar samples, with BCHyPy levels related with the relative abundance of the charred fraction estimated by Py-GC-MS and the hydrogen/carbon (H/C) ratios. The non-BCHyPy fractions were featured by the presence of polycyclic aromatic hydrocarbons (PAHs) from two to seven rings, including alkylated derivatives up to C4. Partially hydrogenated PAHs were also detected. The yields of non-BCHyPy were higher for those biochars produced at lower temperatures and always more abundant than the levels of solvent-extractable PAHs. The methylated/parent PAH ratios from HyPy and Py-GC-MS exhibited lower values for the most charred biochar. The observed differences in the abundance of the stable fraction and the molecular chemistry of the semi-labile fraction can be usefully utilised to drive the process conditions to the desired properties of the resulting biochars and to predict the impact of biochar amendment to soil organic pools. The concentrations of priority PAHs in the semi-labile fraction was evaluated in the mg g−1 level suggesting that it could be an important fraction of the polyaromatic carbon pool in soil
Automatization of a technical-scale fixed-bed gasification plant
No full textExperimental studies of technical-scale-fixed-bed plant are needed to understand the
complex process of wood gasification and to be able to develop models. However these
experiments must be measure and controlled, so Labview software was implemented in
this work.
Because of all the flexibility it offers regarding hardware platforms, Labview has been
used to develop a one file program that will give the control and measurement of some
parameters in the gasification process. This main program was composed by five small
subprograms: the feeding control, the temperature measurement along the reactor, the
determination of the percentage of gases generated by the gasification processes in a
GC / TCD (Gas Chromatography /Thermal Conductivity Detector), the determination
of the total fluorescence intensity generate by the LIF( Laser Induced Fluorescence)
system and finally the pressure measurement. Together with Labview software mainly
the VI’s Express and DAQ Assistant tools have been used.
The result of this work is a one file program that contains information of the process
which take place in the updraft fixed bed reactor. Some of these information is on line
measurement, such as the temperatures all along in the bed reactor and the pressure
inside the reactor. While others correspond to analysis of information generated by the
the GC/TCD and the LIF, that give the user more knowledge about the parameters
that participated in the gasification process.
Labview is a powerful graphical programing software, a tool for engineers and scientists,
to create, dispose measurement and control systems through hardware integration.
And in this case it will make possible a continually innovation in the study of biomass
gasification
Automatization of a technical-scale fixed-bed gasification plant
No full textExperimental studies of technical-scale-fixed-bed plant are needed to understand the
complex process of wood gasification and to be able to develop models. However these
experiments must be measure and controlled, so Labview software was implemented in
this work.
Because of all the flexibility it offers regarding hardware platforms, Labview has been
used to develop a one file program that will give the control and measurement of some
parameters in the gasification process. This main program was composed by five small
subprograms: the feeding control, the temperature measurement along the reactor, the
determination of the percentage of gases generated by the gasification processes in a
GC / TCD (Gas Chromatography /Thermal Conductivity Detector), the determination
of the total fluorescence intensity generate by the LIF( Laser Induced Fluorescence)
system and finally the pressure measurement. Together with Labview software mainly
the VI’s Express and DAQ Assistant tools have been used.
The result of this work is a one file program that contains information of the process
which take place in the updraft fixed bed reactor. Some of these information is on line
measurement, such as the temperatures all along in the bed reactor and the pressure
inside the reactor. While others correspond to analysis of information generated by the
the GC/TCD and the LIF, that give the user more knowledge about the parameters
that participated in the gasification process.
Labview is a powerful graphical programing software, a tool for engineers and scientists,
to create, dispose measurement and control systems through hardware integration.
And in this case it will make possible a continually innovation in the study of biomass
gasification
Experimental investigation on biomass shrinking and swelling behaviour: Particles pyrolysis and wood logs combustion
No full textBiomass is a suitable energy source to reduce the carbon footprint and increase the use of renewable energy. However, the biomass exploitation is still slowed by many technical issues. In most practical applications, such as gasification or combustion devices, it is important to predict the fuel physical behavior in order to determine the emissions and heat release profile as well as for modeling and design purposes. Within this paper, the study of the dimensional evolution of a biomass fuel (beech wood) in pyrolysis and combustion processes were carried out with the use of the image analysis tool. Sizes from 15 mm to 300 mm characteristic length range were employed in the experiments and the collected data were related to the mass loss and temperature evolution of the biomass particle. It was found that for all the fuel sizes employed a similar volume reduction (60%–66%) was obtained at the end of pyrolysis. However, for the small particles with minor intra-particle gradients shrinkage took place mainly at the end of conversion, while for bigger particles the size variation patter was more linear. Furthermore, swelling was detected in the pyrolysis experiments, and it was higher for a bigger particle size, while cracking and fragmentation phenomena was observed for large wood logs combustion in the stove
Die Festbettpyrolyse von Biomasse: Mechanismen und Biokohleerzeugung
No full textThe objective of this thesis is to gain a deeper understanding on the slow pyrolytic conversion of biomass in conditions similar to the ones present at industrial scale. The purpose of this is to contribute to two topics of significant relevance in the biomass thermochemical conversion community nowadays. Firstly, the need for further development of more detailed pyrolysis mechanisms, which account not only for chemical reactions pathways, but also for the influence of transport phenomena on these chemical reactions, enhanced in conditions typical of industrial scale, due to bigger particle and bed sizes. Secondly, the use of slow pyrolysis for production of biochar, in particular, the understanding of how pyrolysis conditions may affect biochar properties and consequently its behavior in soil.
To this end, a technical-scale fixed bed reactor has been built, together with a novel combination of on-line characterization techniques, to perform an exhaustive on-line evaluation of the pyrolysis process. These techniques include temperature measurements inside the bed, characterization of permanent gas composition with gas chromatography - thermal conductivity detection (GC-TCD) and detection of fluorescence emitting compounds with laser-induced fluorescence spectroscopy (LIF). Differentiation between primary pyrolysis and secondary reactions of primary volatiles has been achieved, thanks to the selective detection of targeted species, products of these secondary reactions. Investigation on the source and production enhancement mechanisms of these species has been also carried out.
In a second stage, several characterization methodologies have been developed and applied to get a deep characterization of the solid product (biochar), from two perspectives: structural properties and potential behavior in soil. The objective is to establish clear relations to "engineer" biochar, according to soil application demands and certification requirements. Besides, development of characterization techniques which may lead to a more complete evaluation and therefore better certification of this biochar has been considered, in particular for porosity characterization.Die Zielstellung dieser Dissertation ist es, ein tieferes Verständnis über die langsame pyrolytische Biomassenkonversion unter Bedingungen zu gewinnen, wie man sie im industriellen Maÿstab vor ndet. Hierdurch soll bezweckt werden, auf zwei Feldern von signi kanter Relevanz für die heutige Forschergemeinschaft der thermochemischen Biomassenkonversion einen Beitrag zu leisten. Denn zum einen besteht noch Entwicklungsbedarf für genauere Pyrolysemechanismen, welche nicht nur die chemischen Reaktionsabl äufe berücksichtigen, sondern auch den Ein uss durch Transportphänomene auf diese chemischen Reaktionsabläufe miteinbeziehen und angepasst an Bedingungen sind, wie man sie aufgrund von gröÿerer Partikel- und Bettgröÿe typischerweise im Industriemaÿstab vor ndet. Das zweite Feld beinhaltet die Produktion von Biochar durch eine langsame Pyrolyse und soll insbesondere klären, inwieweit die Pyrolysebedingungen die Eigenschaften des Biochars und konsequenterweise deren Reaktionen im Boden beein ussen. Um dieses Ziel zu erreichen wurde ein Festbettreaktor in Technikumsgröÿe errichtet und mit einer neuartigen Kombination von on-line Charakterisierungstechniken ausgestattet, welche es ermöglichen, den Pyrolysevorgang umfassend in-situ und on-line zu untersuchen. Diese Techniken umfassen die Temperaturerfassung im Reaktorbett, die Bestimmung der Permanentgaszusammensetzung durch Gaschromatographie-Wärmeleitfähigkeits detektor (GC-WLD) und der Nachweis von uoreszierenden Verbindungen durch laserinduzierte Fluoreszenzspektroskopie (LIF). Eine Unterscheidung zwischen der primären Pyrolyse und den Sekundärreaktionen der primär üchtigen Bestandteile war durchführbar, dank der selektiven Bestimmung von Schlüsselverbindungen, welche als Produkte der Sekundärreaktionen entstehen. Fernerhin wurde untersucht, welchen Ursprung diese Spezies haben und welche Mechanismen deren vermehrtes Auftreten fördern. In der zweiten Phase wurden mehrere Charakterisierungsmethoden entwickelt und angewendet, um das feste Produkt (Biochar) ausführlich in zweierlei Hinsicht zu charakterisieren. Zum einen Hinblick auf die strukturellen Eigenschaften, zum anderen auf das mögliche Verhalten im Boden. Zielstellung war es hier, klare Zusammenhänge herauszuarbeiten, um einen Biochar zu "konstruieren", welcher den Anforderungen bei Verwendung im Boden und Zerti zierungsvorgaben erfüllt. Auÿerdem wurde die Entwicklung weiterer Charakterisierungsmethoden geprüft, welche möglicherweise zu einer vollständigeren und daher auch besseren Zerti zierung von diesem Biochar führen, insbesondere in Hinsicht auf die Charakterisierung der Poren
Untersuchung des Pyrolyse-Mechanismus auf Partikelebene: Einblicke in heterogene Sekundärreaktionen mit Hilfe laserbasierter In-situ-Spektroskopie
No full textThe printed version includes ISBN 978-3-948268-56-5.Thermochemical conversion processes represent the main pathway for the conversion of lignocellulosic biomass into more useful energy sources. Among them, pyrolysis plays a key role. Its process conditions will have a major influence on the conversion efficiency and products distribution, not only of the process itself, but also of each of the other thermochemical conversion processes, such as gasification or combustion. Despite gaining great scientific relevance during the last decades, the exact pyrolysis mechanism is still unknown. Therefore, the aim of this thesis is to contribute to the better understanding of the pyrolysis process.
To this end, a particle-level reactor cell has been developed, together with the implementation of advanced laser-based spectroscopic techniques to characterize, on-line and in-situ, targeted volatiles in the pyrolysis gas stream. Infrared laser absorption spectroscopy (IRLAS) has been employed to quantitatively determine permanent gases and water vapor. Laser-induced fluorescence (LIF) spectroscopy has been applied to identify mainly aromatic compounds. Moreover, these optical methods have been combined with simultaneous on-line measurements of both mass and temperature, as well as with further characterization of pyrolysis products by means of gas chromatography, ex-situ (GC-TCD) and off-line (GC-MS).
Through this comprehensive experimental approach, the influence of transport resistances (leading to the presence of heterogeneous secondary reactions), the influence of inorganic species, as well as their synergistic influence on the pyrolysis mechanism has been investigated. Moreover, a pyrolysis particle model has been adapted to the employed experimental conditions to reveal the capabilities and limitations of both numerical and experimental results. An extensive characteriazation of pyrolysis products by means of LIF has also been performed considering different LIF-relevant parameters. Its implementation in advance computational methods is going to be crucial to explore potential improvements in both sensitivity and selectivity of this spectroscopic technique when applied to pyrolysis.Thermochemische Konversionsverfahren repräsentieren einen zentralen Weg für die Umwandlung von holziger Biomasse in wertvollere Energiequellen. Unter diesen Verfahren spielt die Pyrolyse eine Schlüsselrolle. Die Prozessbedingungen haben hierbei einen großen Einfluss auf die Umwandlungseffizienz und die Produktverteilung, nicht nur des Prozesses selbst, sondern auch der anderen thermochemischen Umwandlungsprozesse, wie Vergasung oder Verbrennung. Obwohl die Pyrolyse in den letzten Jahrzehnten große wissenschaftliche Bedeutung erlangt hat, ist der genaue Mechanismus noch immer unbekannt. Ziel dieser Arbeit ist es daher, einen Beitrag zum besseren Verständnis des Pyrolyseprozesses zu leisten.
Zu diesem Zweck wurde eine Reaktorzelle auf Partikelebene entwickelt. Zudem wurden laserbasierte Spektroskopietechniken eingesetzt, um flüchtige Bestandteile im Pyrolysegasstrom on-line und in-situ zu charakterisieren. Die Laserabsorptionsspektroskopie im nahen Infrarot (IRLAS) wurde zur quantitativen Bestimmung von Permanentgasen und Wasserdampf eingesetzt. Daneben wurde laserinduzierte Fluoreszenzspektroskopie (LIF) zur Identifizierung hauptsächlich aromatischer Verbindungen eingesetzt. Darüber hinaus wurden diese optischen Methoden mit simultanen Online-Messungen von Masse und Temperatur, sowie mit einer weiteren Charakterisierung der Pyrolyseprodukte mittels Gaschromatographie, ex-situ (GC-TCD) und off-line (GC-MS) kombiniert.
Durch diesen umfassenden experimentellen Ansatz wurde der Einfluss von Stofftransportlimitierungen (die zu heterogenen Sekundärreaktionen führen), der Einfluss anorganischer Spezies, sowie deren synergistischer Einfluss auf den Pyrolysemechanismus untersucht. Darüber hinaus wurde ein Pyrolysepartikelmodell an die verwendeten experimentellen Bedingungen angepasst, um die Möglichkeiten und Grenzen sowohl der numerischen als auch der experimentellen Ergebnisse aufzuzeigen. Eine umfassende Charakterisierung der Pyrolyseprodukte mittels LIF wurde ebenfalls durchgeführt, wobei verschiedene LIF-relevante Parameter berücksichtigt wurden. Die Implementierung dieser in fortschrittliche Berechnungsmethoden, wird entscheidend sein, um potenzielle Verbesserungen sowohl der Sensitivität als auch der Selektivität dieser spektroskopischen Methode bei der Anwendung auf die Pyrolyse zu untersuchen
Investigation of the pore formation in biogenic carbonaceous residues for PAH adsorption in the product gas of gasification processes
No full textThe printed version includes ISBN 978-3-948268-68-8.Die Biomassevergasung wird als eine vielseitige Methode zur Nutzung der Bioenergie betrachtet, aber trotz technologischer Fortschritte konnte sie die kritischen Hürden für einen konventionellen Einsatz nicht überwinden. Eine wesentliche technische Herausforderung bei der wirtschaftlichen Umsetzung der Biomassevergasung ist nach wie vor die Bildung von kondensierbaren organischen Bestandteilen (ein- und mehrkernigen Aromaten) – der sogenannte „Teer“. Diese Arbeit verfolgt den Ansatz der Gasreinigung durch Adsorption von Teerkomponenten aus der Gasphase. Ziel ist, aus Materialien, die am Standort einer Biomassevergasungsanlage reichlich vorhanden sind bzw. relativ einfach erzeugt werden können, mit wenig Aufwand, Adsorptionsmittel herzustellen und diese zur Adsorption von Teerkomponenten aus dem heißen Produktgas einzusetzen.
Von dem eingesetzten (biogenen) Brennstoff bei der Biomassevergasung wird ein Teil in einem separaten Prozess pyrolysiert. Hieraus werden in einem nachfolgenden thermischen Aktivierungsverfahren unter Variation der Reaktionsbedingungen eine Reihe von Aktivkohlen hergestellt. Ferner werden kohlenstoffhaltige Materialien, die durch unvollständige Vergasungsreaktionen in Biomassevergasungsanlagen anfallen, als Alternative zum Vorprodukt bzw. zur Aktivkohle herangezogen.
Die Porenstruktur der genannten Materialien wird umfangreich charakterisiert und der Einfluss von Reaktionsbedingungen auf die Porenbildung untersucht. Anschließend werden die erzeugten Aktivkohlen zur Adsorption von Teer-Modellkomponenten (Toluol, Naphthalin) aus der Gasphase bei erhöhter Temperatur eingesetzt und die Adsorptionskapazitäten ermittelt.
Diese Arbeit zeigt den Einfluss des Vergasungsmittels und des Abbrands auf die Entwicklung der Porenstruktur und der Porengrößenverteilung in den untersuchten kohlenstoffhaltigen Materialien und bietet so die Grundlage für gezielte Aktivierungsverfahren. Ferner wird die Bedeutung der verschiedenen Porenklassen hinsichtlich der Adsorptionskapazität erörtert.Biomass gasification is considered a versatile approach for bioenergy utilization, with plenty of options for product gas use. But the formation of organic condensable species (mono aromatics, PAH) – referred to as “tar” – remains a major technical implementation and economic challenge in emerging these technologies. Instead of costly gas scrubbing or catalytic degradation of tar species, the possible application of the “onboard” available char, generated in the gasification process, is in the focus of this work. The aim is to produce adsorbents from this „onboard“ available material with little effort and to use them to adsorb tar components from the hot product gas.
Char pyrolyzed in an intermediate biomass pyrolysis process is activated in a subsequent thermal activation process. A number of activated carbons are produced, varying the reaction conditions. Besides, chars produced by incomplete gasification reaction in biomass gasifiers (process char) are used as an alternative.
The pore structure of the mentioned material is extensively characterized and the effect of reaction conditions on pore development is investigated. Finally, the produced activated carbons and the collected process chars are used for adsorption of tar model components (toluene, naphthalene) from a hot gas stream and the adsorption capacities are determined.
This work reveals the effect of the gasification agent and the carbon burn-off on the development of pore structure and pore size distribution in the studied carbonaceous material and thus provides the basis for targeted development of porous systems in biogenic process chars. Furthermore, the impact of the different pore classes with respect to the adsorption capacity of the investigated chars is discussed
Investigation on the impact of potassium and mild transport limitations on the pyrolysis behavior of beech wood and its macrocomponents
No full text80 páginas.- 21 figuras.- 3 tablas.- 93 referenciasThe existing pyrolysis mechanisms for biomass rarely take into consideration certain feedstock-specific features, such as the interaction between macrocomponents or the influence of inorganic species. This research delves deeper into the impact of potassium (K) and mild transport limitations on the pyrolytic behavior of beech wood and its biopolymers (modeled in the present work by cellulose, xylan, and alkali lignin). Special attention was given to the interactions between macrocomponents in the beech wood in comparison to their individual behavior. A combination of experimental techniques has been applied, which enabled investigation on (I) the devolatilization behavior and heats of reaction through thermogravimetric analysis/differential scanning calorimetry (TGA/DSC), (II) the in-situ evolution of functional groups in the solid thanks to diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and the pyroylsis products composition by means of pyrolysis gas chromatography/mass spectrometry (Py-GC/MS). The interactions between the components was addressed via a five parallel-reaction kinetic model and its comparison with the commercial model compounds. Detailed information about the pyrolysis mechanistic pathways was extracted from the in-situ DRIFTS by means of a two dimensional perturbation correlation infrared spectroscopy (2D-PCIS) analysis. This technique revealed strong impact of K on cellulose, xylan, and beech wood behavior during the pyrolysis process, enhancing ring opening and dehydration reactions and hindering the formation of anhydrosugars. However, pyroylsis products of beech wood were dominated by those of lignin. It is shown that a detailed understanding on the mechanistic behavior of wood pyrolysis requires not only the understanding of the behavior of its macrocomponents but also of their interaction at a multiple level.N
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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