The chemical percolation devolatilization model applied to the devolatilization of coal in high intensity acoustic fields

Neste trabalho, um modelo de percolação química (CPD), desenvolvido para o cálculo da evolução dos produtos de pirólise de partículas de carvão, foi estendido de forma a ser empregado em regimes de degradação térmica sobre a influência de campos acústicos de alta intensidade, típicos de combustores do tipo tubo de Rijke. As oscilações acústicas incrementam os processos de transferência de calor e massa no leito de combustível, bem como na região livre acima do mesmo. Os resultados obtidos em simulações com um combustor do tipo Rijke mostraram um aumento nas taxas de evaporação de água e de degradação térmica das partículas. O modelo de percolação química empregado, no regime pulsante, permitiu o cálculo da evolução dinâmica de CO, CO2, CH4, H2O, outros gases leves e alcatrão, importantes no processo de ignição e estabilização de chamas. O modelo também forneceu a quantidade e forma dos compostos nitrogenados liberados no processo de pirólise que são indispensáveis nas estratégias para abatimento da emissão de poluentes (NOx) em regimes de queima excitados por oscilações acústicas. O bioma Pantanal é caracterizado pela inundação sazonal que determina processos ecossistêmicos específicos, com a ocorrência de plantas e animais adaptados à mudança anual de encolhimento e expansão de hábitats em virtude do regime hidrológico sazonal. A biodiversidade do Pantanal é um componente fundamental dos serviços ecossistêmicos prestados à sociedade humana, que inclui reciclagem de nutrientes, produção pesqueira, ecoturismo, resgate de carbono, controle de enchentes, entre outros, que são importantes consequências ambientais em nível regional e global. O bioma tem sido afetado pelo impacto da conversão de sua vegetação natural em campos agrícolas e pasto para a pecuária, com alteração e perda de hábitats e biodiversidade. O impacto maior tem ocorrido nas terras altas do planalto do entorno da planície, com desmatamento do Cerrado nas áreas onde nascem os rios que alimentam o Pantanal. Este artigo discute as necessidades e prioridades futuras de pesquisa ecológica para melhor entender o ecossistema e, assim, atingir sua conservação e uso sustentável. _______________________________________________________________________________ ABSTRACTThe chemical percolation devolatilization model (CPD) was extended for the prediction of drying and devolatilization of coal particles in high intensity acoustic fields found in Rijke tube reactors. The acoustic oscillations enhance the heat and mass transfer processes in the fuel bed as well as in the freeboard, above the grate. The results from simulations in a Rijke tube combustor have shown an increase in the rate of water evaporation and thermal degradation of the particles. The devolatilization model, based on chemical percolation, applied in pulsating regime allowed the dynamic prediction on the yields of CO, CO2, CH4, H2O, other light gases as well as tar which are important on ignition and stabilization of flames. The model predicted the quantity and form of nitrogen containing species generated during devolatilization, for which knowledge is strategically indispensable for reducing pollutant emissions (NOx) in flames under acoustic excitation

Aproveitamento de resíduos: um estudo da estimativa da energia de ativação do caroço de pequi para análise de viabilidade como fonte de energia limpa / Utilization of waste: a study of the estimated activation energy of pequi seeds for feasibility analysis as a source of clean energy

A pirólise constitui uma tecnologia de conversão termoquímica utilizada para produção de carvão, bio-óleo e gás. A biomassa lignocelulósica é um importante insumo na conversão termoquímica via pirólise, comprovado pelo grande número de trabalhos de pesquisa publicados de diversos tipos de biomassa. O objetivo deste trabalho é estimar a energia de ativação do caroço de pequi para se modelar o processo de pirólise que permita, em termos práticos, aumentar a produção de alguns subprodutos de interesse. A árvore do pequi tem a sua frutificação de outubro a fevereiro tendo sido extraídas 17150 toneladas da fruta no Brasil, em 2017 (IBGE), tornando-o uma importante fonte de energia renovável para o país. Os resultados da análise termogravimétrica foram utilizados para se estimar a energia de ativação da pirólise do caroço de pequi com taxas de aquecimento de 5, 10 e 20°C/min. As energias de ativação calculadas para os picos referentes a holocelulose pelos métodos de Osawa, k-A-S e Starink, foram, respectivamente, 89032,12, 84984,48 e 85249,73 kJ/mol

Effects of wet CO oxidation on the operation of engines and power generators

A simplified method is used to determine the optimum water content in the flue gases of charcoal gasifiers to be utilized as alternative fuels in the operation of engines and gas turbines for power generation. Computational models of plug flow reactors and well stirred reactors are employed to simulate the reaction and post-flame zones, adopting different chemical mechanisms. In the simulations reactants enter the reactors at 1000 K, 1 atm and equivalence ratio 0.25. It was observed that mixtures about 3% to 4% in volume of water vapor allow to obtain optimal operation characteristics, including high blowout limit, low ignition delay, maximum reaction zone temperature, high CO2 prodution and low thermal NO formation. It was observed that increasing water contents reduce significantly ignition times up to 3% in volume, while blowout mass flow rates increase continuously up to 6 % in volume, the maximum value considered. Formation of NO decreases continuously with humidity after the flame zone, while there are peaks of NO formation within the flame zone below 1% in volume. Higher water vapor content decreases the final temperatures below 1700 K, leading to a lower thermal efficiency. The method can be used to estimate optimum operational conditions with other input parameters

A low-cost filament winding technology for university laboratories and startups

This paper systematically explains the methodology and results of empirical work on the development of a low-cost filament winding technology for manufacturing axisymmetric polymer composite structures with a high length-to-diameter ratio, such as tubes, motor casings, and pressure vessels. The principal objective was to examine the experiences and most optimal practices in the development of computer-controlled equipment and auxiliary tooling for the wet filament-winding process. To preclude expensive commercial software for the automated control of a winding machine, analytical equations were derived for the winding trajectory of a four-axis filament-winding machine. The feasibility of the proposed equations was successfully validated by laying the fiber along the geodesic path marked on the surface of a cylindrical mandrel with hemispherical ends. Moreover, the carbon/epoxy cylindrical casings with hemispherical ends and port openings of the same diameter were wound to determine the thickness distribution in the hemispherical dome. The fiber volume ratio in the wound composite parts was evaluated using an optical technique

An optimized hybrid rocket motor for the SARA platform reentry system

This paper has described a system design process, based on a multidisciplinary optimization technique, of a conceptual optimized hybrid propellant rocket motor. The proposed engine could be a technological option for the reentry maneuvering system of the Brazilian recoverable satellite (SARA), which was designed by the Brazilian Institute of Aeronautics and Space. The resulting optimized propulsion system must be viewed as a proof of concept allowing comparison to more conventional technologies, i.e., liquid and solid motors. Design effort was conducted for hybrid propellants engines based on a liquefying fuel (solid paraffin) and two different oxidizers, H2O2 (90% high-testperoxide) and self-pressurizing N2O. The multidisciplinary configuration optimization technique was supported on geometrical operating parameters of the motor, rather than on performance, in order to facilitate subsequent design and fabrication. Results from the code presented a hybrid motor, which was considered a competitive alternative for the deboost engine when compared to the traditional chemical systems, solid and liquid bipropellant, and monopropellant. The estimated mass of the reentry system, for the cases addressed in this study, varied from 22 to 29 kg, which is lower than either liquid bipropellant or solid engines formerly proposed

A STUDY OF THE ATOMIZATION PROCESS USING NUMERICAL SIMULATION

The liquid droplets atomization process plays an important role in several industrial processes and in many aspects of the combustion engines performance, gas turbines, diesel engines and rocket motors. The use of Computational Fluid Dynamics (CFD) to study the atomization process is relatively new and this work studies the atomization spray field using pressure swirl atomizers and the computation simulations was done by the using of the commercial software CFX 15. The parameter analyzed was the semi-angle of the spray. Particles were placed at the entrance and different settings for the primary and secondary breakup were studied. Two models for the primary breakup (BLOB and LISA models) were tested and two other for the secondary breakup (Reitz and Diwakar model and TAB model). The numerical results were compared with experimental data and showed acceptable compatibility.&nbsp

Theoretical and experimental study of combustion instability in hybrid rocket motors

This work describes a theoretical and experimental study of combustion instability in hybrid rocket motors. Results are highlighting that the parameter Δ /̅c (pressure drop between tank and chamber scaled by average chamber pressure) plays an important role in the oscillatory characteristics of the chamber pressure. By modifying the feed-system-coupled instability theory, a combustion time lag model has been developed; using this a new general analysis criterion is proposed. Results show good agreement with the experimental data and suggest that the combustion time delay of the liquid oxidizer is more important than the response time of solid fuel boundary layer

A STUDY OF THE ATOMIZATION PROCESS USING NUMERICAL SIMULATION

The liquid droplets atomization process plays an important role in several industrial processes and in many aspects of the combustion engines performance, gas turbines, diesel engines and rocket motors. The use of Computational Fluid Dynamics (CFD) to study the atomization process is relatively new and this work studies the atomization spray field using pressure swirl atomizers and the computation simulations was done by the using of the commercial software CFX 15. The parameter analyzed was the semi-angle of the spray. Particles were placed at the entrance and different settings for the primary and secondary breakup were studied. Two models for the primary breakup (BLOB and LISA models) were tested and two other for the secondary breakup (Reitz and Diwakar model and TAB model). The numerical results were compared with experimental data and showed acceptable compatibility