Thesis (MScFor (Forest and Wood Science))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Wood waste, when used for gasification is commonly pressed into briquettes, especially if no uniform particle size is available. This densification reduces problems of handling, storage and transportation and improves the combustion performance because of a more uniform fuel size. Briquettes have to be mechanically strong enough to be handled. Cohesive strength is provided by residual moisture and lignin present in the wood. The lignin acts as a natural binder. However, the briquetting process becomes more complicated if one wants to add other agricultural waste products that do not necessarily contain lignin as binders,, In this study we have investigated various briquetting process parameters, such as mixing ratios of briquettes containing wood chips, grape skins and chicken litter, moisture content and press time. The aim was to determine the optimum process parameters that allow the production of briquettes, containing a blend of biomaterials that are mechanically stable to allow further handling but yield high energy content at the same time. / AFRIKAANSE OPSOMMING: Wanneer houtafval vir vergassing gebruik word en die partikelgrootte daarvan varieer, word die materiaal normaalweg in ’n brikket gedruk. Brikketvorming vergemaklik opberging, hantering en vervoer. Weens die meer uniforme grootte en vorm van die brikkette is verbranding daarvan heelwat meer doeltreffend. Brikkette moet egter meganies sterk genoeg wees om hanteer te kan word. Die kohesiewe sterkte word deur residuele vog en lignien, wat as natuurlike bindmiddel in hout aanwesig is, verskaf. Indien ander materiale soos landbouafval, wat noodwendig geen lignien bevat nie egter gebruik word, word die brikketvormingsproses meer kompleks. In hierdie ondersoek is verskeie brikketvormingsparameters evalueer. Mengverhoudings van brikkette wat houtspaanders, druiwedoppe en hoendermis bevat, asook invloed van materiaalvoggehalte en druktyd is bestudeer. Die doel was om die optimale materiaal- en prosesparameters vas te stel wanneer ’n mengsel van biomateriale gebruik word om brikkette te lewer wat meganies sterk genoeg is maar steeds die hoogste energieopbrengs lewer. / Centre for Renewable and Sustainable Energy Studies

Parmi les procédés de conversion de la biomasse, la gazéification à l’air présente l’avantage d’un rendement de conversion électrique attractif, en particulier pour les petites puissances. Cependant, l’élimination des goudrons générés reste un verrou à lever pour permettre l’émergence industrielle du procédé de gazéification. Le traitement par absorption est considérée comme technologiquement mature mais le choix du solvant de lavage, sa gestion et l’optimisation du laveur représentent un élément crucial. Afin de mettre en avant les solvants envisageables, une méthodologie rapide et robuste de choix de solvant basée sur une analyse multicritère a été développée. La comparaison de plus d’une centaine de solvants conventionnels a permis de mettre en avant deux solvants. Afin d’étudier des performances de ces solvants, un pilote de lavage de type Venturi (laveur compact présentant une aire interfaciale importante et peu de risque d’encrassement) a été dimensionné et caractérisé. L’étude expérimentale sur gaz réel a permis d’une part d’étudier l’évolution de la charge en goudron dans le solvant et d’autre part de mesurer les efficacités de traitement des solvants sur le benzène, le naphtalène, l’anthracène et le pyrène. Ces données expérimentales ont ensuite été utilisées afin de valider la modélisation du laveur Venturi effectuée dans l’optique d’une optimisation et d’une extrapolation à l’échelle industrielle de l’unité de lavage. Afin d’estimer le coût de traitement en €/MWh, le dimensionnement des équipements à l’échelle industrielle a été effectué pour les deux solvants dans différents cas de figure afin d’effectuer leur évaluation technico-économique. / Among biomass conversion processes, air gasification has the advantage of an attractive electrical conversion yield, especially for small powers. However, the elimination of the generated tar remains a lock to lift to allow the industrial emergence of the gasification process. The treatment by absorption is considered to be technologically mature but the choice of cleaning solvent, its management and the optimization of the scrubber represent a crucial element. In order to highlight possible solvents, a fast and robust solvents screening methodology based on a multi-criteria analysis was developed. Comparison of more than 100 of conventional solvents allowed to forward two solvents. To investigate performance of these solvents, a pilot scale Venturi scrubber (compact scrubber with a large Interfacial area and low risk fouling risk) has been designed and characterized. The experimental study on real raw gas allowed to study the evolution of the tar loading factor in the solvent and to measure treatment efficiencies of solvents on benzene, naphthalene, anthracene and pyrene. These experimental data were then used to validate the modelling of the Venturi scrubber in the context of optimization and extrapolation on the industrial scale of the washing unit. In order to estimate the cost of treatment in €/ MWh, the sizing of the equipment on an industrial scale has been made for two solvents in different cases in order to process to a technico-economical evaluation.

L’épuisement des ressources fossiles et la nécessité de réduire les émissions de gaz à effet de serre incitent à rechercher de nouvelles sources d’énergie à la fois renouvelables et moins polluantes. La biomasse, par son abondance, apparaît comme une filière intéressante de remplacement des énergies fossiles et notamment du pétrole. L’objectif de ce travail est d’effectuer une analyse 4E (Energétique, Exergétique, Environnementale et Economique) d’un système de production de l’électricité via la gazéification des déchets de palmiers. Ces derniers constituent l’une des richesses végétales les plus abondantes en Tunisie et qui de nos jours, restent très peu exploitées. Un gazéifieur à lit fixe couplé à un moteur à combustion interne est considéré pour produire 330kW d’électricité. Le rendement de gazéification « Cold Gaz Efficiency » du procédé est de 58,58%. Les résultats montrent que les rendements énergétique et exergétique du système étudié sont de 22,6% et 19,22%, respectivement. Les performances environnementales du système sont évaluées à l’aide d’une Analyse de Cycle de Vie (ACV). L’évaluation économique est réalisée dans le but d’évaluer le coût de production de l’électricité par l’installation de gazéification. Les résultats donnent un coût de 3,88ct€ pour 1kWh. / The fossil fuels depletion and the need to reduce greenhouse gas emissions encourage the search for new energy sources that are renewable and less polluting. Thanks to its abundance, biomass appears as an interesting sector of replacement of fossil fuels. The objective of this work is to perform a 4E analysis (Energy, Exergy, Environmental and Economic) of an electricity production system via the gasification of palm waste. Palm watse constitutes one of the most abundant vegetable wealth in Tunisia and which today, remain very little exploited. A fixed bed gasifier coupled to an internal combustion engine is considered to produce330 kW of electricity. The Cold Gas Efficiency of the process is 58.58%. The results show that the energy and exergy yields of the system are 22.6% and 19.22%, respectively. The environmental performance of the system is evaluated using a Life Cycle Assessment (LCA). The economic evaluation is carried out in order to evaluate the cost of electricity production by the gasification plant. The results give a cost of 3.88 ct€ for 1kWh.

This thesis "The influence of composition on biomass energy conversion efficiency in the gas combustion engine" deals with the matter of obtaining energy from biomass to propel engines. It describes the historical development and use of the wood gas treatment process for its production of biomass from the beginning of this discovery up to the use and large scale implementation around the world. The last section presents several experiments with different types of biomass and an experiment to determine the energy obtained in a simple gas combustion engine. Construction of a prototype is part of this thesis.

Ces travaux concernent l'étude d'un procédé de vapogazéification de biomasse en lit fluidisé circulant. En résultent un ensemble d'outils théoriques (modèles de simulation et de dimensionnement) et expérimentaux (pilote de vapogazéification en lit fluidisé circulant) dans le but de permettre la construction d'un procédé à dimension industrielle. Le dimensionnement, la conception et la construction d'un pilote de vapogazéification de 20 kg/h de biomasse en lit fluidisé circulant ont été réalisés. L'hydrodynamique de ce pilote a été étudiée de manière à isoler les paramètres clés permettant d'en assurer le contrôle. Les résultats obtenus lors de l'opération de pilote ont en outre permis de mieux comprendre les mécanismes d'attrition de particules polydisperses (olivine et char) en lit fluidisé circulant. Pour compléter cette étude, les phénomènes de mélange et de ségrégation des particules ont été étudiés par voie expérimentale et numérique (CFD-3D MFIX). Enfin, un certain nombre de modèles numériques (0D, 1D bulle-émulsion, bilan de population) ont été proposés pour répondre aux besoins techniques d'aide à la conception des lits fluidisés circulants appliqués à la vapogazéification de biomasse. / The vapogasification of biomass in a Circulating Fluidized Bed has been studied in order to enable the design and the erection of an industrial process. Theoretical and experimental tools have been designed to allow an engineering approach. In order to understand the hydrodynamic behaviour of the reactor, a pilot plant has been designed and erected to feed 20 kg/h of biomass. An exhaustive study of process parameters has been carried out, to determine predominant parameters for the process global control. Operating the built system has also permit to understand attrition phenomenon of polydisperse particles (olivine and char) in the Circulating Fluidized Bed. In order to complete those results, a study of mixing and segregation of those polydisperse particles has been carried out in fluidized bed with both experimental and numerical (CFD-3D MFIX) approaches. A significant contribution has also been done to numerical models assisting biomass vapogasification in Circulating Fluidized Beds design: 0D, 1D, bubble-emulsion, population balance).

La conversion thermochimique à haute température (>700°C) de la biomasse en double lit fluidisé circulant est une voie alternative aux énergies fossiles (pétrole, charbon) pour la production d’un gaz de synthèse à haute valeur énergétique, utilisable dans de nombreuses applications. L’objectif de cette thèse est de développer des méthodologies et des outils théoriques et expérimentaux permettant d’accéder aux cinétiques des transformations élémentaires (pyrolyse de la biomasse, gazéification et combustion du char, craquage et reformage des goudrons) présentes dans le procédé de gazéification de la biomasse en double lit fluidisé circulant. Dans un premier temps, un mini-réacteur à lit fluidisé fonctionnant entre 300 et 1000°C avec une alimentation en gaz parfaitement contrôlée (N2, O2, H2, H2O et goudrons) a été conçu et mis au point au Laboratoire de Génie Chimique de Toulouse. Un système d’échantillonnage et d’analyse de la phase gaz permet de quantifier en continu les fractions molaires des gaz incondensables et des goudrons produits. Une étude hydrodynamique et thermique a permis de déterminer les points de fonctionnement du réacteur pour chaque transformation élémentaire étudiée. Dans un second temps, les études de gazéification et de combustion du char ont été réalisées dans le mini-réacteur à lit fluidisé. L’influence de nombreux paramètres opératoires (température, pression partielle des différents constituants) a permis de comprendre la formation des différents produits et de modéliser les cinétiques de transformation du solide. Dans le cas de la combustion du char, un mécanisme réactionnel a également été établi et la cinétique obtenue en lit fluidisé a été comparée à celle déterminée par analyse thermogravimétrique. Enfin, une étude sur le reformage d’un goudron modèle (toluène) en lit fluidisé a mis en évidence l’effet de l’atmosphère réactionnelle sur le mécanisme de dégradation du toluène sur l’olivine et le char. / The thermochemical conversion of biomass at high temperature (>700°C) in Fast Internally Circulating Fluidized Bed (FICFB) is a promising alternative route to fossil fuels (oil, coal) to produce syngas which can be used in several applications. The aim of the present work is to develop methodologies as well as theoretical and experimental tools for determining the intrinsic kinetic of biomass transformations (biomass pyrolysis, char gasification and combustion, cracking and reforming of tars). Firstly, a fluidized bed reactor has been designed and built at the Laboratory of Chemical Engineering (LGC). This reactor can operate for temperatures between 20 and 1000°C with a well-defined gas supply (N2, O2, H2, H2O and tars). A sampling and analysis gas system enables the continuous quantification of the non-condensable gases and tars molar fractions. A hydrodynamic and thermal study enabled the determination of the operating conditions for each experimental study. Secondly, the char gasification and combustion was performed in the fluidized bed reactor. The influence of the operating conditions (temperature and compounds partial pressure) led to the modelling of the different solid transformation kinetics. Besides, in the case of char combustion, a reaction scheme was proposed and the kinetic obtained in the fluidized bed was compared to that obtained in a thermogravimetric analyzer. Finally, a study on the tar reforming in a fluidized bed reactor highlighted the effect of the reactive atmosphere on the reaction scheme of toluene conversion over olivine and char.

No presente trabalho são empregadas ferramentas de fluidodinâmica computacional (CFD) como base à criação de uma rede de reatores equivalente para o estudo de um reator de leito fluidizado borbulhante em escala piloto pertencente à CIENTEC-RS, empregado para a gaseificação de carvão das minas de Candiota-RS. Inicialmente, foram conduzidas simulações fluidodinâmicas em meio reacional gasoso (utilizando metano e ar) para análise do comportamento do escoamento no gaseificador. A partir de medições do equipamento real e dados de projeto do mesmo foi implementada no software CFX 13.0 a geometria do reator e foram realizados testes de convergência de malhas computacionais, de forma a escolher a mais apropriada para a realização das simulações em CFD. A avaliação de parâmetros como perfis de velocidade e concentrações ao longo do reator serviram para a escolha das malhas para a continuidade do estudo. Diferentes variações na geometria foram propostas, de modo a simplificá-la, reduzindo o custo computacional das simulações, porém mantendo a qualidade dos resultados. Foram, ainda, avaliados os padrões de escoamento típicos do reator, operando em fase gasosa e na presença de um leito fluidizado. De posse dos padrões de escoamentos obtidos foi proposta uma rede de reatores equivalentes – ERN (equivalent reactor network) a fim de modelar o reator da CIENTEC, empregando um modelo cinético detalhado para determinação das taxas de reação na fase gasosa. Para fins de avaliação da metodologia, conduziram-se simulações envolvendo a combustão de metano, analogamente ao estudo em CFD, e envolvendo o processo de gaseificação de carvão, com as características do obtido nas minas de Candiota. O objetivo do estudo foi avaliar os pontos cruciais no desenvolvimento de um modelo ERN e prever as características dos produtos obtidos para diferentes condições operacionais. Espera-se que este modelo seja aprimorado e usado para o melhoramento e otimização do processo, com o propósito de obter um gás de potencial energético e com características adequadas à utilização como insumo para processos carboquímicos. / In this dissertation, computational fluid dynamics (CFD) simulations were applied to develop equivalent reactor networks (ERN) for the study of a bubbling fluidized bed reactor from CIENTEC-RS, used for coal gasification. Initially, the computational geometry of the gasifier was created using the software CFX 13.0, based on field measurements and design data. Mesh convergence tests were carried out in order to choose the most appropriate for obtaining accurate solutions, using gas-phase reactions. Different variations in geometry were proposed in order to reduce the computational cost of the simulations, while maintaining the quality of the results. The simulations also evaluated the typical flow patterns of the reactor operating in the gaseous phase and in the presence of a fluidized bed. The flow patterns were used as a basis for proposing equivalent reactor networks for the CIENTEC reactor, using a detailed kinetic model to determine the reaction rates in the gas phase. For methodology evaluation purposes, simulations involving the combustion of methane were conducted, similar to the study in CFD, as well as the coal gasification process. The aim of the study was to evaluate the crucial points in the development of an ERN model and to predict the characteristics of the gaseous product streams obtained for different operating conditions. It is expected that this model can be used for the improvement and optimization of the gasification process, in order to obtain a gas with energetic potential and suitable for using it as a feedstock for carbochemical processes.

Made available in DSpace on 2015-07-13T12:10:28Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-03-24. Added 1 bitstream(s) on 2015-07-13T12:24:14Z : No. of bitstreams: 1 000832562.pdf: 3624875 bytes, checksum: d21e3aeecb27b00f8db35e4b25d45d1f (MD5) / Os níveis significativamente elevados dos subprodutos disponíveis (bagaço e palha) no processamento da cana-de-açúcar oferecem um potencial atrativo para o uso de sistemas que utilizem um gaseificador de biomassa integrado a um ciclo combinado (BIG - GTCC). Neste trabalho propõe-se estudar a incorporação do processo de gaseificação de biomassa para uso em sistema de cogeração com ciclo combinado aplicado ao setor sucroalcooleiro. Foram realizados estudos energéticos, econômicos e ecológicos da incorporação do sistema BIG - GTCC como alternativa para o aumento da oferta de produção de eletricidade em uma típica indústria sucroalcooleira do Brasil. Propõe-se o suo de uma tecnologia de pré-tratamento do bagaço para superar os problemas técnicos existentes ao alimentar, de forma contínua, o reator de gaseificação de bagaço. Na análise econômica, determina-se, inicialmente, o custo de produção de gás de síntese, permitindo alocar os custos de produção de eletricidade, energia mecânica e calor de processo no sistema proposto, considerando três configurações. Na etapa final, são determinadas as emissões de poluentes, o dióxido de carbono equivalente, o indicador de poluição e a eficiência ecológica da planta utilizando o processo de gaseificação com ciclo combinado ao setor. Conclui-se que a aplicação do processo de gaseificação apenas do excedente de bagaço em fluxo de arraste com pré-tratamento de torrefação apresenta-se como a melhor das opções propostas, tanto do ponto de vista termodinâmico, como do econômico e do ecológico / The significantly elevated levels of byproducts (bagasse and trash) currently available in the sugar cane industries offer an attractive potential for the use of the BIG - GTCC in the sugar industry. This work aims to make an energetic, economic and ecological studies of the BIG -GTCC (Biomass Integrated Gasifier - Gas Turbine Combined Cycle) system incorporation in the sugar cane industry, as an alternative to increase the levels of electricity generation in this sector. A new technology for the bagasse pre-treatment is proposed in order to overcome the technical problems observed during the continuous feeding of gasifier with sugarcane bagasse as a setting for coupling the gasifier with the sugarcane mill. An energetic analysis of the proposed system was performed. The study also identified the production cost of the synthesis gas, as well as allocated the electricity, heat, and mechanical energy production cost in the proposed system, considering the three studied cases. In the final phase, the pollutant emissions, the carbon dioxide equivalent, the pollution indicator, and the ecological efficiency of the incorporation of the cogeneration process with combined cycle in the traditional Brazilian sugar industries were determined. The main result of the study was that the application of the configuration, where only the surplus bagasse of the conventional plant is gasified in an entrained flow reactor, after pretreatment of the bagasse through a torrefaction process, appears to be economically, ecologically, and technically the best of the proposed options

Made available in DSpace on 2014-12-02T11:16:53Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-07-30Bitstream added on 2014-12-02T11:21:15Z : No. of bitstreams: 1 000798880.pdf: 1604138 bytes, checksum: 0bac43d696a76f30babea284c17c75c9 (MD5) / A cogeração tem uma grande aceitação no setor sucroalcooleiro, pois o combustível empregado (bagaço ou palha de cana) é um subproduto de fabricação. Tais sistemas geram potência mecânica ou elétrica e vapor, que são utilizados no próprio processo industrial. Porém, este tipo de geração de energia no setor encontrase muito aquém de seu potencial. Uma das alternativas tecnológicas que poderá vir a melhorar a oferta de excedentes do setor sucroalcooleiro é o uso de gaseificadores de biomassa associados a ciclos combinados. Este trabalho se baseia em dados reais de uma Usina Sucroalcooleira que utiliza o processo de cogeração com turbina a vapor de condensação com duas extrações. A partir de modificações no processo da usina, foram estudados os benefícios da integração da tecnologia de gaseificação em leito fluidizado associada a ciclo combinado. Para efeito de análise da incorporação desta configuração, construiuse, inicialmente, um modelo energético dos equipamentos que compõem o sistema de cogeração, tendo como variável de decisão a quantidade de biomassa processada pela usina. Posteriormente, realizouse o estudo exergético do sistema. A partir de uma abordagem econômica dos equipamentos, foi possível realizar o estudo exergoeconômico que se baseia no Método da Análise Funcional Termoeconômica desenvolvido por Frangopoulos (1983). Foi possível avaliar a viabilidade desta tecnologia para o setor sucroalcooleiro brasileiro permitindo gerar inovações na cadeia produtiva do etanol e corroborando para o desenvolvimento do setor e para o aumento da oferta de eletricidade no país / The cogeneration has a wide acceptance in the sugarcane industry, because the fuel used (sugarcane bagasse or straw) is a byproduct of the manufacturing process. Such systems generate electrical or mechanical power and steam, which are used in the industrial process itself. However, this type of power generation is far below its potential. One of the technological alternatives which may improve the supply of surplus to the sugarcane sector is the use of biomass gasifiers associated with combined cycles. This work is based on real data from a sugar and alcohol plant that uses the process of cogeneration with condensing steam turbine with two extractions. From the plant process modifications, the benefits of integration of fluidized bed gasification technology associated with combined cycle were studied. For purposes of analysis of the incorporation of this technology, initially built up an energy model of equipment that compose the cogeneration system, having the amount of biomass processed by the plant as a decision variable. Subsequently, we carried out the study of the exergetic system. From an economic approach of the equipment, it was possible to perform the exergeticeconomic study that is based on the Thermoeconomic Functional Analysis Method developed by Frangopoulos (1983). It was possible to assess the viability of this technology for the Brazilian sugarcane sector allowing to generate innovations in the ethanol production chain and supporting the development of the sector and to increase the supply of electricity in the country

Although nonlinear model predictive control (NMPC) might be the best choice for a nonlinear plant, it is still not widely used. This is mainly due to the computational burden associated with solving online a set of nonlinear differential equations and a nonlinear dynamic optimization problem in real time. This thesis is concerned with strategies aimed at reducing the computational burden involved in different stages of the NMPC such as optimization problem, state estimation, and nonlinear model identification. A major part of the computational burden comes from function and derivative evaluations required in different parts of the NMPC algorithm. In this work, the problem is tackled using a recently introduced efficient tool, the automatic differentiation (AD). Using the AD tool, a function is evaluated together with all its partial derivative from the code defining the function with machine accuracy. A new NMPC algorithm based on nonlinear least square optimization is proposed. In a first–order method, the sensitivity equations are integrated using a linear formula while the AD tool is applied to get their values accurately. For higher order approximations, more terms of the Taylor expansion are used in the integration for which the AD is effectively used. As a result, the gradient of the cost function against control moves is accurately obtained so that the online nonlinear optimization can be efficiently solved. In many real control cases, the states are not measured and have to be estimated for each instance when a solution of the model equations is needed. A nonlinear extended version of the Kalman filter (EKF) is added to the NMPC algorithm for this purpose. The AD tool is used to calculate the required derivatives in the local linearization step of the filter automatically and accurately. Offset is another problem faced in NMPC. A new nonlinear integration is devised for this case to eliminate the offset from the output response. In this method, an integrated disturbance model is added to the process model input or output to correct the plant/model mismatch. The time response of the controller is also improved as a by–product. The proposed NMPC algorithm has been applied to an evaporation process and a two continuous stirred tank reactor (two–CSTR) process with satisfactory results to cope with large setpoint changes, unmeasured severe disturbances, and process/model mismatches. When the process equations are not known (black–box) or when these are too complicated to be used in the controller, modelling is needed to create an internal model for the controller. In this thesis, a continuous time recurrent neural network (CTRNN) in a state–space form is developed to be used in NMPC context. An efficient training algorithm for the proposed network is developed using AD tool. By automatically generating Taylor coefficients, the algorithm not only solves the differentiation equations of the network but also produces the sensitivity for the training problem. The same approach is also used to solve online the optimization problem of the NMPC. The proposed CTRNN and the predictive controller were tested on an evaporator and two–CSTR case studies. A comparison with other approaches shows that the new algorithm can considerably reduce network training time and improve solution accuracy. For a third case study, the ALSTOM gasifier, a NMPC via linearization algorithm is implemented to control the system. In this work a nonlinear state–space class Wiener model is used to identify the black–box model of the gasifier. A linear model of the plant at zero–load is adopted as a base model for prediction. Then, a feedforward neural network is created as the static gain for a particular output channel, fuel gas pressure, to compensate its strong nonlinear behavior observed in open–loop simulations. By linearizing the neural network at each sampling time, the static nonlinear gain provides certain adaptation to the linear base model. The AD tool is used here to linearize the neural network efficiently. Noticeable performance improvement is observed when compared with pure linear MPC. The controller was able to pass all tests specified in the benchmark problem at all load conditions.