<p>U doktorskoj disertaciji vr&scaron;eno je ispitivanje procesa pirolize i gasifikacije<br />oklaska kukuruza. Istraživanje procesa pirolize obuhvatalo je definisanje<br />uticaja procesnih parametara (temperature pirolize, reakcionog vremena,<br />brzine zagrevanja i veliĉine ĉestica) na prinos ĉvrstog ostatka i pirolitiĉkog<br />gasa. Osim toga, vr&scaron;eno je ispitivanje sastava gasa u zavisnosti od<br />temperature. UtvrĊeno je da ispitivani procesni parametri imaju uticaj na<br />prinos ĉvrstog ostatka i bio-ulja, kao i na prinos i sastav pirolitiĉkog gasa.<br />Tokom ispitivanja procesa gasifikacije razvijen je funkcionalni matematiĉki<br />model gasifikacije oklaska kukuruza u struji vazduha koji bi trebalo da<br />omogući optimizaciju procesa gasifikacije goriva u cilju dobijanja gasovitog<br />proizvoda.</p> / <p>Doctoral dissertation investigates pyrolysis and gasification of corncob.<br />Investigation of pyrolysis process included defining the influence of process<br />parameters (pyrolysis temperature, reaction time, heating rate and particle<br />size) on pyrolysis gas and char yield. Also, temperature dependence of<br />pyrolysis gas composition was investigated. It was confirmed that process<br />parameters influence char and bio-oil yield and pyrolysis gas yield and<br />composition. A functional mathematical model of air-stream gasification of<br />corncob was developed in order to enable optimization of gasification<br />process with the objective of obtaining gaseous product.</p>

Ce travail porte sur l'étude des potentiels du procédé de gazéification thermique (conversion en gaz combustible de la matière organique et du carbone fixe) pour associer traitement et valorisation (matière et énergie) durable des boues de station d'épuration. De ce procédé, il émane des rejets polluants (conséquences de la composition des boues, notamment des teneurs en métaux et azote). Dans un premier temps, la distribution des métaux entre les phases (solide et gaz) est examinée, en fonction des conditions opératoires du procédé. La localisation (phases porteuses), la spéciation et la mobilité des métaux retenus dans le solide obtenu sont aussi étudiées, afin de déterminer les risques environnementaux qu'il entraîne. Le suivi de la production de composés azotés et soufrés montre ensuite que température et atmosphère sont les paramètres opératoires clé. Grâce à cela, un procédé bi-étagé en température, avec un premier étage de dépollution et un deuxième étage de production de gaz combustibles est proposé. Enfin, la base d'un modèle théorique portant sur l'hydrodynamique et la cinétique dans un réacteur de gazéification à lit fluidisé est proposée. / This work focuses on the potential of thermal gasification process (organic matter and fixed carbon conversion to combustible gases) to combine sustainable sewage sludge treatment and valorization (matter and energy). Some pollutants are produced by this process (as a consequence of the sewage sludge composition, mainly metal and nitrogen's content). Firstly, the influence of operating conditions on metal's distribution among the phases (solid and gas) is investigated. The localization (bearing phases), speciation and mobility of metals retained in the produced solid are also analyzed, aiming to determine the environmental risks which they involve. Next, produced nitrogen and sulfur compounds are followed, showing that temperature and treatment atmosphere are the main parameters. Those findings allowed us to propose à two-thermal-stage process, the first stage aiming to get rid of pollutants in the solid and the second one aiming to produce combustible gases. Finally, a theoretical model basis concerning hydrodynamics and kinetics in a fluidized bed is proposed.

Integrated Gasification Combined Cycle (IGCC) power plants have been considered as one of the best options for energy production in an environmental friendly manner. IGCC power plants are demonstrating better results, both in terms of plant performance and economics, when compared to a Pulverised Coal (PC) power plant with CO2 capture. The additional components required for an IGCC power plant when it is desired to operate in CO2 capture mode, give research potential with respect to an improved IGCC power plant performance. The IGCC power plant design framework studied and developed was based in DOE/NETL report and is presented. The conventional and CO2 capture IGCC power plants have been benchmarked in rigorous process flow diagrams developed using the commercial software Honeywell UniSim Design R400. As an essential part of the Innovative Gas Separations for Carbon Capture project (IGSCC EPSRC – EP/G062129/1) predictive simulation tools were produced to investigate the IGCC performance. The case studies considered include different gasification options for non-capture and carbon capture IGCCs, with a two stage Selexol process for the CO2 capture cases. Particular effort has been made to produce an accurate simulation component to describe the behaviour of the syngas in the Selexol solvent. The two stage Selexol configuration was investigated in detail and novel schemes are presented. No similar approaches have been reported in the literature, in terms of the proposed configuration and the capture efficiency. Moreover, innovative CO2 capture schemes incorporating combined units of physical absorption and membranes have been examined with respect to the power plant’s performance. In this thesis, contrary to other studies, all simulations cases have been conducted in unified flow diagrams. The results presented include overall investigations and can be a helpful tool for engineers and stakeholders in the decision making process.

One of the greatest challenges of human today is to provide the continuous and sustainable energy supply to the worldwide society. This shall be done while minimizing all the negative consequences of the operation(s) to the environment and its living habitants including human beings, taking from the whole life cycle perspective. In this thesis work new solutions for treatment biomass and waste are analyzed.   Based on the fundamental research on the conversion of various materials (biomass: straw pellets, wood pellets; and waste: plastic waste, ASR residues after pyrolysis), converted by means of different systems (pyrolysis in a fluidized bed reactor, gasification in a fixed-bed reactor using highly preheated agents) it is recommended to classify materials against their charring properties under pyrolysis, in order to find the best destination for a given type of fuel.    Based on phenomenological research it was found that one of the important effects, affecting performance of downdraft gasifiers, is the pressure drop through the bed and grate. It affects, directly, the velocity profile, temperature distribution and of the height of the bed, especially for the grate with restricted passage surface, although it was not investigated in literature. The lower grate porosity, the higher conversion of fuel and heating value of gas is produced. However, the stability of the process is disturbed; therefore reducing the grate porosity below 20% is not recommended, unless the system is designed to overtake the consequences of the rising pressure inside the reactor. This work proposed the method for prediction of a total pressure drop through the fixed-bed downdraft gasifier equipped with a grate of certain porosity with an uncertainty of prediction ±7.10.     Three systems have been proposed; one for the treatment of automotive shredder residue (ASR), one for the treatment of plastic waste (polyolefins) and one for biomass (wood/straw pellets). Pyrolysis is an attractive mean of conversion of non-charring materials (like plastic waste) into valuable hydrocarbons feedstock. It gives directly 15-30% gaseous olefins while the residue consisting of naphtha-like feedstock has to be reformed/upgraded to olefins or other chemicals (e.g. gasoline generation) using available petrochemical technologies. Pyrolysis of complex waste mixture such as ASR is an attractive waste pretreatment method before applying any further treatments, whereby useful products are generated (gaseous and liquid fuel) and char, rich in precious metals. The solid residues are meant for further treatment for energy and metals recovery. Gasification is a complementary method for handling pyrolysis residues. However, metals can be removed before gasification. Pyrolysis of charring materials, like biomass, is a very important step in thermo-chemical conversion. However, the char being approximately 25%wt. contains still very high caloric value of about 30MJ/kg. This in connection with the High Temperature Steam Gasification process is a very promising technology for biomass treatment, especially, above 900oC. This enhances the heat transfer towards the sample and accelerates kinetics of the gasification. This, in turn, improves the conversion of carbon to gas, increases the yield of the producer gas and reduces tar content. At higher steam to fuel ratio the process increases the yield of hydrogen, making it suitable for second-generation biofuels synthesis, whereas at lower steam to fuel ratio (S/F&lt;2) the generated gas is of high calorific value making it suitable for power generation in a combined cycle. / <p>QC 20110607</p>

Numerical simulations of coal gasification process inside a generic 2-stage entrainedflow gasifier are carried out using the commercial CFD solver ANSYS/FLUENT. The 3-D Navier-Stokes equations and eight species transport equations are solved with three heterogeneous global reactions, three homogeneous reactions, and one thermal cracking equation of volatiles. Finite rates are used for the heterogeneous solid-gas reactions. Both finite rate and eddy-breakup combustion models are calculated for each homogeneous gas-gas reaction, and the smaller of the two rates is used. Lagrangian-Eulerian method is employed. The Eulerian method calculates the continuous phase while the Lagrangian method tracks each coal particle. Fundamental study is carried out to investigate effects of five turbulence models (standard k-ε, k-ω, RSM, k-ω SST, and k-ε RNG) and four devolatilization models (Kobayashi, single rate, constant rate, and CPD) on gasification simulation. A study is also conducted to investigate the effects of different operation parameters on gasification process including coal mixture (dry vs. slurry), oxidant (oxygen-blown vs. air-blown), and different coal distributions between two stages. Finite-rate model and instantaneous gasification model are compared. It is revealed that the instantaneous gasification approach can provide an overall evaluation of relative changes of gasifier performance in terms of temperature, heating value, and gasification efficiency corresponding to parametric variations, but not adequately capture the local gasification process predicted by the finite rate model in most part of the gasifier. Simulations are performed to help with design modifications of a small industrial demonstration entrained-flow gasifier. It is discovered that the benefit of opening the slag tap on the quench-type gasifier wider by allowing slag to move successfully without clogging is compromised by increased heat losses, reduced gasification performance, downgraded syngas heating value, and increased unburned volatiles. The investigation of heat transfer on fuel injectors shows that blunt tip fuel injector is less likely to fail compared to conical tip fuel injector because the maximum high temperature on the injector is scattered. Two concentric fuel/oxidant injections provide better fuel-oxidant mixing and higher syngas heating value than four separate fuel and oxidant injections.

A mild gasification method has been developed to provide an innovative clean coal technology. The objectives of this study are to (a) incorporate a fixed rate devolatilization model into the existing 2D multiphase reaction model, (b) expand the 2D model to 3D and (c) utilize the improved model to investigate the mild-gasification process and guide modification of the mild-gasifier design. The Eulerain-Eulerian method is employed to calculate both the primary phase (air) and secondary phase (coal particles). The improved 3D simulation model, incorporated with a devolatilization model, has been successfully developed and employed to determine the appropriate draft tube dimensions, entrained flow residence time, The simulations also help determine the appropriate operating fluidization velocity range to sustain the fluidized bed depth without depleting the chars or blowing the char away. The results are informative, but require future experimental data for verification.

In recent years, Integrated Gasification Combined Cycle Technology (IGCC) has become more common in clean coal power operations with carbon capture and sequestration (CCS). Great efforts have been spent on investigating ways to improve the efficiency, reduce costs, and further reduce greenhouse gas emissions. This study focuses on investigating two approaches to achieve these goals. First, replace the subcritical Rankine steam cycle with a supercritical steam cycle. Second, add different amounts of biomass as feedstock to reduce emissions. Finally, implement several types of CCS, including sweet- and sour-shift pre-combustion and post-combustion. Using the software, Thermoflow®, this study shows that utilizing biomass with coal up to 50% (wt.) can improve the efficiency, and reduce emissions: even making the plant carbon-negative when CCS is used. CCS is best administered pre-combustion using sour-shift, and supercritical steam cycles are thermally and economically better than subcritical cycles. Both capital and electricity costs have been presented.

Orientador: Celso Eduardo Tuna / CoOrientador: José Luz Silveira / Banca: Eliana Vieira Canettieri / Banca: João Andrade de Carvalho Júnior / Banca: Christian Jeremi Coronado Rodriguez / Banca: Carlos Manuel Romero Luna / Resumo: O bagaço e a palha são resíduos do processamento industrial da cana-de-açúcar que constituem uma importante fonte de recurso para cogeração de energia no setor sucroalcooleiro. Os sistemas de cogeração neste setor geram potência mecânica ou elétrica e vapor, que são utilizados no próprio processo e o excedente é vendido as concessionárias de energia. Porém, estes sistemas encontram-se bem abaixo do potencial real. Uma alternativa tecnológica que poderá contribuir com a oferta de excedentes de energia elétrica é a introdução da tecnologia BIG-GT (gaseificadores de biomassa associados a turbina a gás e caldeira de recuperação). O presente trabalho, tem como objetivo o estudo termoeconômico da incorporação desta tecnologia em usinas sucroalcooleiras como alternativa para o aumento de geração de eletricidade. As análises energéticas e exergéticas foram realizadas para quatro possíveis configurações de uma usina sucroalcooleira com a integração da tecnologia BIG-GT com o objetivo de avaliar a eficiência de geração de eletricidade e vapor de processo, bem como o aproveitamento global de energia de cada uma delas. Na análise termoeconômica, é determinado o custo de produção de gás de gaseificação, eletricidade e vapor do processo no sistema proposto, assim como, tempo de recuperação do investimento. Na parte final do trabalho foi realizada a otimização multiobjetiva do sistema considerando três funções objetivo: tecnológica, econômica e ambiental, para identificar a configuração com... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Bagasse and straw are residues from the industrial processing of sugarcane that constitute an important source for cogeneration of energy in the sugar-alcohol sector. The cogeneration systems in this sector generate mechanical or electrical power and steam, which are used in the process itself and the surplus is sold to energy distribution companies. However, these systems are well below real potential. One of the technological alternatives that may improve the supply of surplus electricity is the introduction of BIG-GT technology (biomass gasifier associated with gas turbine and Heat recovery steam generator). In this work, it is proposed to conduct thermoeconomic studies of the incorporation of this technology in the sugarcane ethanol plants as an alternative to increasing the supply of electricity generation. The energetic and exergetic analyses were performed for four possible configurations of a sugarcane ethanol plant with the integration of BIG-GT technology with the objective of evaluating the efficiency of electricity generation and process steam as well as the global energy utilization of each one of them. In the thermoeconomic analysis, it is determined the cost of production of producer gas, electricity and steam of the process in the proposed system, as well as the investment payback period. In the final part of the work, it is developed the multiobjective optimization of the system considering three objective functions: technological, thermoeconomic and environmental, for identifying the configuration with better behavior. According to the results obtained in the study, it is concluded that case III and case IV are presented as the best of the proposed options / Doutor

Text in English / There are limits on performance of processes and reactions set by material balances and by thermodynamics. The interaction of these theoretical limits and how they influence the behaviour of reactions and equipment is of interest to researchers and designers. This thesis looks at the conversion of biomass to gaseous products under various conditions, including a range of temperatures from ambient to 1500 ⁰C and in the presence or absence of oxygen. The limits of performance of the material balance can be represented as an Attainable Region (AR) in composition or extent space; we call this the MB-AR. The MB-AR represents all possible material balances that can be achieved for a given a set of feeds and set of possible products. The dimension of this space depends on the number of independent material balances. The extreme points of the MB-AR are of particular interest as these define the limiting compositions and the edges of the boundary of the MB-AR represent the limiting material balances. The MB-AR does not depend on temperature. The thermodynamic limits of performance of can be represented as an AR in the space of Gibbs Free Energy (G) and Enthalpy (H); this is called the G-H AR. The G-H AR is always two dimensional, no matter what the dimension of the MB-AR. Extreme points in the G-H AR are also extreme points in the MB-AR are; however not all extreme points in the MB-AR are extreme points in the G-H AR. The extreme points in the MB-AR are transformed by calculating G and H of the points at the condition of interest (reaction temperature and pressure). It is then necessary to find the convex hull in G-H space of this set of transformed points which gives us the boundary of the G-H AR. The extreme points in the G-H AR can be associated with material balances and the extreme point with the minimum G represents the global equilibrium or equivalently the most favoured material balance for the system. The edges of G-H AR are defined by the lines between neighbouring extreme points in the boundary of the G-H AR. These edges represent the limiting material balances in terms of defining the extremes of the G and H of the system. The G-H AR depends on the feed and products through the MB-AR, but also depends on temperature (and pressure). The set of points which are extreme points of both the MB-AR and the G-H AR changes with temperature. Geometrically, the transformed set of extreme points for the MB-AR moves in the GH space as temperature is changed and they move at different rates. Hence when finding the convex hull in the G-H space of the transformed extreme points of the MB-AR, G-H points become either boundary (extreme) points or move into the convex hull at different temperatures. Thus, the material balance which corresponds to the global minimum in G may change with temperature, as do the material balances which are associated with the edges of the G-H AR. Experiments are performed on biomass anaerobically at ambient temperature using microbes as the catalyst, and the products of this process are called biogas. The experiments were performed in a nitrogen plasma system on biomass at higher temperatures (400 ⁰C to 1000 ⁰C) also in the absence of oxygen, and this process would typically be referred to as pyrolysis. Oxygen was added to the plasma system and operated at temperatures between 700 ⁰C and 900 ⁰C, and this would typically be referred to as gasification. Thus, it was able to change the MB-AR by presence or absence of oxygen. By changing operating temperatures, the G-H AR is effectively changed with either the same or different MB-AR’s. The experiments show that in all cases, the product tends towards minimum G. Although this might not be surprising at the higher temperatures, minimizing G is not thought to be the driving force in microbial systems. An important insight from this is that if one were to try and make hydrogen only in a biological system, the system would need to have organisms that make hydrogen only. This is because the material balance that produces hydrogen has a lower change in G than the material balance that make methane. Thus, if there was a consortium of organisms and some of them could make methane, the methane producing organisms would dominate as they have the higher Gibbs Free Energy driving force. If the boundary of the G-H AR around the minimum G is fairly flat, or if many of the extreme points of the MB-AR lie close to the minimum G in the boundary of the G-H AR, then there are many material balances that will give the same G and H. Thus, there are a range of compositions with similar G and H and how one approaches the minimum G will determine the chemical composition of the product. This has important implications for the design, scale up and operation of equipment if a particular product is desired rather process efficiency. The low temperature anaerobic route to gasifying waste, using microbes as catalysts, has a very simple G-H AR, and the preferred products are CH4 and CO2, known as biogas. These units should be relatively stable to operate as none of the other products have G’s that are as negative as that of the biogas. Although not part of this thesis, small-scale anaerobic digesters were installed in communities and these do run easily and stably with fairly little intervention from the operator which seems to support our conclusion. We however could ask, why then have simple technologies, such an anaerobic digestion, not been widely adopted in Africa? To this end we worked with communities and spoke to people about their knowledge about the technology, their concerns and their possible interest in using new approaches to supply energy for cooking and lighting. We found that people were not aware of the technology but would be very interested in adopting a technology that supplied energy cheaply. To our surprise however, their major concern was around hygiene and safety, in that if the gas was made from “poo” how could the gas be clean and would cooking with it not contaminate the food and make people sick? This in hindsight is a very reasonable concern, although it had never occurred to us that this would be a perception. Engineers will have to work with social scientists and psychologist, amongst others, to address the concerns and needs of communities in order for sustainable technologies to be successfully adopted by communities. In summary, this thesis presents a tool for analysing biomass conversion to gaseous products in general, whether microbial or thermal. This tool gives insight into what is achievable, what the major factors are that affect the favoured product and how this can be manipulated to improve efficiency from an overall material and energy point of view. / Physics / D. Phil. (Physics)

[pt] O Revestimento Gasto de Cuba, comumente conhecido pelas suas siglas em inglês como SPL (spent potliner), é um resíduo gerado na indústria de alumínio, indicado como o maior problema ambiental ligado a esta indústria. O SPL é formado por duas frações: carbonácea e refratária. Segundo a Norma Brasileira NBR 10004, o SPL é classificado como resíduo perigoso (K088) devido ao fato de possuir elevadas concentrações de cianetos (complexos). O presente trabalho busca desenvolver métodos para melhorar o gerenciamento do SPL, principalmente fazer uma caracterização química de acordo com as leis Brasileiras. E também desenvolver um método para tratar a fração carbonácea do SPL. Segundo as análises químicas, apenas a fração carbonácea do SPL foi classificada como Resíduo Classe I (resíduo perigoso), enquanto os materiais refratários foram classificados como Resíduo Classe II-A (resíduo não perigoso). A classificação e segregação do SPL permitiram à Valesul a recuperação e reutilização deste resíduo, manifestando-se em ganhos econômicos estimados em R00000/ano e na redução de 4% na geração de SPL. A fração carbonácea do SPL foi caracterizada mediante o uso de microscopia ótica, MEV/EDS, DRX e TG. A fração carbonácea foi tratada em um Sistema de Gaseificação e Combustão Combinadas (GCC) em escala piloto. Neste processo a destruição dos compostos de cianetos foi maior que 86%. A temperatura no reator de combustão, inicialmente foi de 1000oC (operando com lenha), elevando-se para temperaturas maiores que 1250oC depois de alimentado o SPL, mostrando que é possível recuperar quantidades apreciáveis de energia. Neste processo atingiu-se a gaseificação de aproximadamente 21% do SPL. Os resultados mostraram que o tratamento do SPL por gaseificação é um processo alternativo, com potencial para seguir sendo desenvolvido. Mediante testes em forno tubular (escala de bancada) foi determinado que a volatilização de fluoretos do SPL ocorre em temperaturas maiores a 850oC. / [en] Spent Potliner (SPL) is a residue from the primary aluminium production. It is indicated as the major environmental problem in the aluminum industry. SPL is formed by two fractions: Carbonaceous and refractory. According to Brazilian Standards NBR 10004, the SPL is listed as hazardous waste (K088) because it contains high levels of cyanides (complex). The present work has as objective to develop methods to improve SPL management, mainly carrying out a chemical characterization according Brazilian regulations and to develop a method to treat the SPL carbonaceous fraction. According to the chemical analysis only a carbonaceous fraction was listed as Resíduo Classe I (hazardous waste), while the refractory materials were listed as Resíduo Classe II-A (no hazardous waste). The SPL classification and segregation allow Valesul to recovery and reuse this waste, it reveals in an earning calculated in R00000/year and 4% reduction of SPL generation. SPL carbonaceous fraction was characterized by optical microscopy, SEM/EDS, XRD and TGA. SPL carbonaceous fraction was treated in a Gasification and Combustion Combined System (GCC). In this process, cyanide destruction was higher than 86%. In the GCC process was registered an increase in the combustion reactor temperature, initially it was 1000oC (operating with wood) and after the SPL feeding it increased above 1250oC. In this process was obtained approximately 21% of SPL gasification. The results showed that the gasification is a potential alternative process to treat SPL and it should be improved. Tubular furnace tests (laboratory scale) for SPL combustion showed that the fluorides volatilization occurs at temperatures higher than 850oC.