The catalytic interaction of potassium salts in the reaction of carbon with oxygen and carbon dioxide has been studied with the aim of elucidating the mechanism of the reaction. In order to achieve this the approach used has been to utilise a wide variety of physical techniques in order to identify the active species. These range from bulk in-situ techniques like X-ray diffraction and thermogravimetric analysis to surface sensitive techniques like photoelectron spectroscopy and scanning electron microscopy. Experimental apparatus was also developed that enabled thermogravimetric analysis of samples to be carried out with mass spectra analysis of gaseous products formed. These techniques enabled the behaviour of K<SUB>2</SUB>CO<SUB>3</SUB> with and without the presence of carbon to be characterised over a wide range of temperatures and under inert and reactive atmospheres. This showed that at room temperature K<SUB>2</SUB>CO<SUB>3</SUB> would readily react with the atmosphere to form hydrated carbonate as well as KHCO<SUB>3</SUB> however upon heating to above 100<SUP>o</SUP>C these phases would decompose to leave K<SUB>2</SUB>CO<SUB>3</SUB>. This phase remained upto 600<SUP>o</SUP>C where decomposition started. The decomposition products evaporated from the solids as CO<SUB>2</SUB> and K<SUB>2</SUB>O or K. The presence of K<SUB>2</SUB>CO<SUB>3</SUB> enhanced the reaction of graphite with O<SUB>2</SUB> and CO<SUB>2</SUB>. C<SUB>8</SUB>K and residually intercalated C<SUB>8</SUB>K were used as model compounds to aid the identification of the active potassium species present during gasification. This showed K intercalates and K metal to be unstable under gasification conditions and therefore played no role in the mechanism of catalytic gasification. Photoelectron spectroscopy identified C-O-K and carbon oxides to be the predominant surface species present during gasification, while scanning electron microscopy revealed that in general graphite gasification occurred along the prismatic plane, however gasification on the basal plane took place if a fine disperson of catalyst occurred in the graphite surface.

La production d'énergie à partir de biomasse ligno-cellulosique via la technologie de gazéification est une option intéressante dans le contexte énergétique actuel. La combinaison d‘une pyrolyse rapide décentralisée de la biomasse pour produire les bio-huiles, suivie par le transport et le vaporeformage dans des bio-raffineries, est apparue comme l'une des méthodes économiquement les plus viables pour la production de gaz de synthèse (H2+CO). L‘objectif de ce travail est de combler le manque de connaissances concernant les processus de transformation physicochimique de l‘huile de pyrolyse en gaz de synthèse utilisant la gazéification non catalytique dans des réacteurs à flux entrainé. Il s‘agit d‘un processus complexe, mettant en oeuvre la vaporisation, les réactions de craquage thermique avec formation de gaz, de tars et de deux résidus solides : le char et les suies, qui sont des produits indésirables. Ceci est suivi par le reformage des gaz et des tars, ainsi que la conversion du char et des suies. Pour mieux comprendre le processus, la première étape de la gazéification (la pyrolyse), et par la suite l'ensemble du processus (pyrolyse + gazéification) ont été étudiés. L‘étude de la pyrolyse est focalisée sur l‘influence de la vitesse de chauffe, de la température ainsi que de la teneur en cendres dans la bio-huile, sur les rendements en char, tars et gaz. A très grande vitesse de chauffe le rendement en char est inferieur à 1%. Les cendres semblent favoriser les réactions de polymérisation et provoquent la diminution du rendement en gaz. Concernant la gazéification, l'effet de la température sur le rendement et la composition du gaz de synthèse a été étudié. Une augmentation de la température de réaction implique une augmentation du rendement en hydrogène et une conversion très élevée du carbone solide. Un calcul d'équilibre thermodynamique a montré que l'équilibre a été atteint à 1400°C. Finalement les mécanismes de formation et d‘oxydation des suies ont été étudiés expérimentalement sous différentes atmosphères : inerte (pyrolyse), riche en vapeur d‘eau (gazéification) et en présence d‘oxygène (oxydation partielle). Un modèle semi empirique est proposé et validé. Il est fondé sur la chimie détaillée pour décrire les réactions en phase gaz, une seule réaction basée sur la concentration de C2H2 pour décrire la formation des suies et principalement une réaction hétérogène pour décrire l‘oxydation des suies. / Energy production from ligno-cellulosic biomass via gasification technology appears as an attractive option in the current energy context. The combination of decentralized fast pyrolysis of biomass to produce bio-oil, followed by transportation and gasification of bio-oil in bio-refinery has appeared as one of the most economically viable methods for syngas (H2+CO) production. The objective of this work is to bridge the lack of knowledge concerning the physicochemical transformation of bio-oil into syngas using non catalytic steam gasification in entrained flow reactors. This complex process involves vaporization, thermal cracking reactions with formation of gas, tars and two solid residues - char and soot - that are considered as undesirable products. This is followed by steam reforming of gas and tars, together with char and soot conversion. To better understand the process, the first step of gasification (pyrolysis) and thereafter the whole process (pyrolysis + gasification) were studied. The pyrolysis study focused on the influence of the heating rate, the final pyrolysis temperature and the ash content of bio-oil on char, tars and gas yields. At the higher heating rate char yield is smaller than 1%. In addition, ash seems to promote polymerization reactions and causes a decrease of gas yield. Concerning gasification, the effect of temperature on syngas yield and composition was studied. An increase in the reaction temperature implies higher hydrogen yield and higher solid carbon conversion. A thermodynamic equilibrium calculation showed that equilibrium was reached at 1400°C. Finally, the soot formation and oxidation mechanisms were investigated through experiments in three different atmospheres: inert (pyrolysis), rich in steam (gasification) and in the presence of oxygen (partial oxidation). A semi-empirical model was proposed and validated. It is based on detailed chemistry to describe gas phase reactions, a single reaction using C2H2 concentration to describe soot formation and one main heterogeneous reaction to describe soot oxidation.

No description available.

The last couple of decades have seen entrained-flow gasification of black liquor (BL) undergo an incremental process of technical development as an alternative to combustion in a recovery boiler. The ability of the technology to combine chemical recovery with the production of clean syngas renders it a promising candidate for the transformation of chemical pulp mills into integrated forest biorefineries. However, techno-economic assessments have shown that blending BL with the more easily transportable pyrolysis oil (PO) can not only increase the system efficiency for methanol production but remove a significant roadblock to development by partially decoupling production capacity from limitations on black liquor availability. The verification and study of catalytic co-gasification in an industrially-relative scale can yield both scientifically interesting and practically useful results, yet it is a costly and time-consuming enterprise. The expense and time involved can be significantly reduced by performing thermodynamic equilibrium calculations using a model that has been validated with relevant experimental data. The main objective of this thesis was to study, understand, quantify and compare the gasification behaviour and process performance of black liquor and pyrolysis oil blends in pilot-scale. A secondary objective of this work was to demonstrate and assess the usefulness and accuracy of unconstrained thermodynamic equilibrium modelling as a tool for studying and predicting the characteristics of alkali-impregnated biomass entrained-flow gasification. The co-gasification of BL/PO blends was studied at the 3 MWth LTU Green Fuels pilot plant in a series of experimental studies between June 2015 and April 2016. The results of the studies showed that the blending of black liquor with the more energy rich pyrolysis oil increased the energetic efficiency of the BLG process without adversely affecting carbon conversion. The effect of blend ratio and reactor temperature on the gasification performance of PO and BL blends with up to 20 wt% PO was studied in order to assess the impact of alkali-dilution in fuel on the conversion characteristics. In addition to unblended BL, three blends with PO/BL ratios of 10/90, 15/85 and 20/80 wt% were gasified at a constant load of 2.75 MWth. The decrease in fuel inorganic content with increasing PO fraction resulted in more dilute green liquor (GL) and a greater portion of the feedstock carbon ended up in syngas as CO. As a consequence, the cold gas efficiency increased by about 5%-units. Carbon conversion was in the range 98.8-99.5% and did not vary systematically with either fuel composition or temperature. The validation of thermodynamic equilibrium simulation of black liquor and pyrolysis co-gasifications with experimental data revealed the need to be mindful of errors and uncertainities in fuel composition that can influence predictions of equilibrium temperature. However, provided due care is to taken to ensure the use of accurate fuel composition data, unconstrained TEMs can serve as a robust and useful tool for simulating catalytic entrained-flow gasification of biomass-based feedstocks. / LTU Biosyngas (Catalytic Gasification)

<p>CO₂ concentration in the atmosphere poses a great threat to life on earth as we know it. The reduction of CO₂ concentration is key to avoid the critical turning point of 1.5^oC temperature increase highlighted by Intergovernmental Panel on Climate Change (IPCC). Gasification using CO₂ as reacting agent can potentially reduce the CO₂ concentration in the atmosphere. Naturally, biomass such as corn, uses great amounts of CO₂ for photosynthesis and produces O₂; hence, energy and fuel production using biomass can potentially be classified as carbon neutral. Moreover, if CO₂ is used as the gasifying agent, gasification can effectively be carbon-negative and collaborate to the reduction of CO2 in the atmosphere.</p> <p>The major setback of using CO₂ biomass gasification is the energy-intensive reaction between C + CO₂ -> 2CO. This reaction at atmospheric pressure and room temperature is heavily tilted towards producing char and CO2. The current investigation describes efforts to favor the right hand side of the reaction by using simple impregnation techniques and cost-effective catalysts to reduce the energy requirements of the reaction. Also, parameters such as pressure are explored to tilt the balance towards the production of CO. Corn stover is selected as the biomass for the present research due to its wide use and availability in the US.</p> <p>The results show that by using catalysts such as iron nitrate and sodium aluminate, the temperature required to achieve substantial char conversion is reduced. Also, increasing the pressure of the reactor, the temperature can be substantially decreased by 100 K and 150 K. The structure and chemical composition of the chars is studied to explain the differences in the reaction rate between chars. Further, chemical kinetics are calculated to compare the present work with previous work in the literature. Finally, data-driven analysis of the gasification data is explored. The appendices provide supplementary information on the application of deep learning to CO₂ recycling using turbulent flames and efforts to reduce the flame spread rate over a pool of Jet A by using Multi Walled Carbon Nanotubes (MWCNTS).</p>

No description available.