Investigation of Laminar Flame Speed of CH_4/N_2/O_2 and CH_4/CO_2/O_2, Mixtures Using Reduced Chemical Kinetic Mechanisms

摘要

The emission prevention of carbon dioxide has become an important problem recent years. In order to facilitate the sequestration of CO_2 from flue gases, the combustion can be carried out in the oxidizer, which contains a mixture of CO_2 and O_2 without the presence of nitrogen. The Computational Fluid Dynamics is widely used in order to design new devices and to improve existing ones. Computational costs, when detailed chemistry is employed in calculations of the flame, are too large for real applications, therefore, simplified mechanisms have to be used to solve those problems. Because the laminar flame speed is an important parameter for a burners design and has major influence on a combustion process control, therefore, a good prediction of this quantity, using reduced mechanisms, is crucial. The aim of the present work was to figure out the influence of oxidizer composition on the laminar flame speed and to examine simplified mechanisms in order to achieve similar laminar flame speed levels to those obtained for the detailed mechanism computations, during combustion of methane in the CO_2/O_2 atmosphere. All calculations were done using the Freely Propagating 1D Laminar Premixed Flames (FP1DLPF) package coupled with the COSILAB software. For the combustion of CH_4 in the CO_2/O_2 atmosphere, new reduced mechanisms were created for the oxidizer composition for which the laminar flame speed, for stoichiometric conditions, was similar to this obtained for the methane combustion in air. Similar laminar flame speed values for the conventional combustion and the oxy-combustion was obtained for the oxidizer composition of (X~(oxid))_(O_2)=0,385 (X~(oxid))_(O_2)=0,615. Modified reduced mechanisms of methane combustion in comparison with schemes that are used for the conventional combustion, improved the accuracy of the laminar flame speed prediction with the detailed mechanism considerably, for the oxy-combustion environment.