CFD Studies on Biomass Thermochemical Conversion

Thermochemical conversion of biomass offers an efficient and economically process to provide gaseous, liquid and solid fuels and prepare chemicals derived from biomass. Computational fluid dynamic (CFD) modeling applications on biomass thermochemical processes help to optimize the design and operation of thermochemical reactors. Recent progression in numerical techniques and computing efficacy has advanced CFD as a widely used approach to provide efficient design solutions in industry. This paper introduces the fundamentals involved in developing a CFD solution. Mathematical equations governing the fluid flow, heat and mass transfer and chemical reactions in thermochemical systems are described and sub-models for individual processes are presented. It provides a review of various applications of CFD in the biomass thermochemical process field

Modelamiento y simulación de un horno túnel industrial

La energía requerida en los procesos de cocción de ladrillo se obtiene generalmente por combustión directa de carbón, fuel oil o gas, mediante la cual se obtiene gases calientes que transfieren la energía al producto. Mediante este proceso se genera la energía suficiente para las diferentes etapas involucradas en el proceso, garantizando una curva de quema adecuada y exigida de acuerdo con los estándares de calidad, siempre y cuando se den las condiciones óptimas de contacto de gases calientes y producto. El desarrollo del presente trabajo permitió simular los fenómenos de la transferencia de energía entre gases y producto durante la cocción de ladrillo en un horno túnel utilizando como combustible carbón y gas de síntesis, sustituyendo el carbón por gas de síntesis hasta en un 60% de la energía requerida por el horno. Para la solución del modelo y su respectiva simulación se utilizó como herramienta computacional el CFD (Fluido Dinámica Computacional), utilizado para resolver procesos gobernados por la transferencia de masa, momento, energía. El modelo fue satisfactoriamente validado con las curvas de cocción con carbón y fueron realmente medidas en el horno túnel de la Empresa Ladrillera San Cristóbal S.A., permitiendo predecir el comportamiento térmico del horno. / Abstract. The energy required in the brick firing processes is usually obtained by direct combustion of coal, fuel oil or gas, which is obtained by hot gases that transfer energy to the product. Through this process generates enough energy for the different stages involved in the process, ensuring proper curve and required burning according to standards of quality, provided that conditions are optimal contact of hot gases and products. The development of this work allowed us to simulate the phenomena of energy transfer between gas and product during the firing of brick in a tunnel kiln using coal as fuel and synthetic gas, replacing coal with synthesis gas by up to 60% of the energy required by the furnace. To solve the model and its corresponding simulation computational tool was used as the CFD (Computational Fluid Dynamics) used to solve processes governed by mass transfer, momentum, energy. The model was successfully validated with the curves of cooking with charcoal and were actually measured in the tunnel kiln Brickworks Company San Cristobal SA, allowing to predict the thermal performance of the oven.Maestrí

A model of a rotary kiln incinerator including processes occurring within the solid and the gaseous phases

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Heat transfer mechanisms in an indirectly heated rotary kiln with lifters and its role in scaling

This present research aims to obtain a fundamental understanding on solid transport, solid mixing and the complex heat transfer mechanisms related to the important installed segmented lifter in an indirectly heated rotary kiln. To accomplish these objectives in a systematic manner, the experimental and modelling studies on solid transport and mixing were first carried out in pilot-scale cold kilns at Curtin University of Technology, Perth, Western Australia then followed by heat transfer study in a pilot-scale hot kiln system available at ANSAC Pty Ltd, Bunbury, Western Australia.For design and scaling purposes, dimensional analysis was carried out. A series of experiments in cold kilns were also carried out, considering lifter design, lifter configurations, helix, a wide-range of solid and various kiln designs under different kiln operating conditions. The results showed that a flat bed depth profile can be achieved using purposely-designed segmented lifters at favourable practical low ReѠ values (less energy input to drive the kilns and more throughputs), with a low total kiln filling fraction and a high degree of axial mixing (Pe < 50 or Dz = 10-5 - 10-3 m2/s). This is essential to good heat transfer performance. The effects of helix, L/D, Fr and d/D have relatively insignificant differences on solid transport and mixing under the current experimental conditions. These findings demonstrate the unique advantages of the purposely-designed segmented lifters compared to other conventional lifters (e.g. single throughout lifters), providing important information for scaling criteria and modelling work.A preliminary DEM simulation, as an emerging simulation tool at a particle level, confirmed that axial displacement is mainly due to the function of the folded lifter sections of the segmented lifters. The folded lifter sections push the solids towards the kiln discharge end along the bed arc length and such effect increases as Reincreases. This finding leads to the development of a transport model, limited to underloading regimes, to predict the average bed depth in this type of kilns. The model predictions are in good agreement with experimental data. A set of global power-law dimensionless empirical correlations on solid transport and mixing, applicable to all three (over-, design-, underloading) regimes, were also developed based on the data obtained from our systematic experiments. The validity was tested with data presented in selected previous studies. It is found that the developed correlations are largely specific to the present lifter design and configurations.A steady-state axial heat transfer model has also been developed for a kiln with segmented lifters. The model predicts the temperature profiles at inner heat tube, in the freeboard gas, in the bed, on the tube wall and the outer heat tube in the flue gas. The model incorporates developed solid transport and mixing correlations, as well as suitable heat transfer modes and reaction model. It takes the form of ordinary differential equations which were solved numerically. The input data necessary for the model were obtained by our own experiments and/or extracted from the literature. The model was validated by the temperature profiles obtained from the hot kiln. Among the heat transfer modes considered, it is found that the limiting step of heat transfer in the kiln is the heat transfer from covered inner kiln wall to covered bed, which is highly influenced by solid transport and mixing. Under the current experimental conditions, the typical overall heat transfer coefficient was found to be 31 - 35 W/m2.K.The present research advances the fundamental understanding on solid transport, solid mixing and the complex heat transfer mechanisms in an indirectly heated rotary kiln with segmented lifters. The obtained data and knowledge are important to improve the kiln energy efficiency, reduce kiln manufacture and operation costs and widen the kiln applications at different scales

Modelagem e simulação térmica de um forno rotativo para a produção de agregado de argila calcinada

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Mecânica, Florianópolis, 2007.O principal objetivo deste trabalho é o desenvolvimento de um programa de simulação térmica de fornos rotativos, que seja bastante versátil e que permita avaliar o comportamento térmico deste tipo de forno com diferentes concepções e sob diferentes condições operacionais, para servir como uma ferramenta auxiliar no seu projeto e na avaliação de sua viabilidade técnica e econômica. O foco da utilização do programa de simulação desenvolvido neste trabalho é o projeto de um forno rotativo para a produção de agregado de argila calcinada, como forma de solucionar o problema da disponibilidade de materiais de qualidade para a construção civil e pavimentação em regiões distantes dos centros produtores. Assim, uma revisão da utilização de agregados de argila calcinada em obras de construção civil é apresentada e uma rota de produção deste agregado em um forno rotativo é proposta. O modelo matemático e o funcionamento geral do programa de simulação computacional de fornos rotativos desenvolvido neste trabalho são descritos, e resultados de diversas simulações realizadas são apresentados como estudos do comportamento térmico do forno rotativo da planta produtiva proposta. Finalmente, com base nos dados levantados no decorrer deste trabalho e nos resultados das simulações computacionais são sugeridas diversas recomendações de projeto para o forno rotativo para produção de agregado de argila calcinada, com vistas a um aumento da qualidade do processo de calcinação e a redução do consumo de combustível

Développement d’outils pour l’optimisation des procédés de valorisation thermique de la biomasse : de la conception d’expériences optimales en analyse thermique à la modélisation des fours tournants

Ce manuscrit présente deux contributions méthodologiques à l’étude des procédés et processus thermochimiques qui s’inscrivent dans le cadre du traitement ou de la valorisation thermique de la biomasse. Dans une première partie, sont présentées les différentes étapes de la modélisation d’un procédé continu de traitement thermique que constitue le four tournant. Bien que les aspects théoriques soient principalement détaillés dans ce manuscrit, le procédé pilote installé au centre RAPSODEE est également présenté puisqu’il a été utilisé pour le développement et la validation du modèle. Des exemples d’application concluent cette partie. Dans une seconde partie, on s’intéresse à la détermination de lois cinétiques pour la dégradation thermique de biomasse. La problématique du choix du modèle est discutée, le principe de la conception optimale basée sur un modèle est présenté, enfin des résultats en analyse thermique illustrent le propos