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

Abstract

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, CO 2 , CH 4 , H 2 O, 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 (NO x ) em regimes de queima excitados por oscilações acústicas.The 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, CO 2 , CH 4 , H 2 O, 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 (NO x ) in flames under acoustic excitation . Keywords: chemical percolation devolatilization model, acoustic fields, Rijke tube IntroductionWith the decline of oil reserves expected for the first half of this century, coal raises as a potential candidate for energy production in large scales. Environmental concerns with the more stringent regulations on emissions is increasing the coal research for a more profound understanding on the possible harmful pollutants originated during its utilization. At present, coal is burned mostly in pulverized systems and in fluidized beds for gasification. Devolatilization of coal through heating is an important process in ignition, stabilization and emissions of the flames in combustion, and in the composition of the remaining char in gasification. The chemical structure of coal can be used to predict pyrolysis products from the thermal degradation, which includes, mostly, light gases, tar and char. Figure 1 depicts the schematic representation of a hypothetical coal molecule (Pi...