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Investigation of Laminar Flame Speed of CH4/N2/O2 and CH4/CO2/O2 Mixtures Using Reduced Chemical Kinetic Mechanisms

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Bibrzycki J. , Poinsot T.

2010

tom Vol. 30 nr 4

287-296

The emission prevention of carbon dioxide has become an important problem recent years. In order to facilitate the sequestration of CO2 from flue gases, the combustion can be carried out in the oxidizer, which contains a mixture of CO2 and O2 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 CO2/O2 atmosphere. All calculations were done using the Freely Propagating 1D Laminar Premixed Flames (FP1DLPF) package coupled with the COSILAB software. For the combustion of CH4 in the CO2/O2 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 XoxidO2=0,385 XoxidCO2=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.

Examination of simplified mechanisms of CH4 combustion in N2/O2 and CO2/O2 atmosphere using mathematical modeling

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Bibrzycki J. , Poinsot T.

2011

tom Vol. 31 nr 4

255-262

The oxy- fuel combustion is one of the most promising facilitation techniques of CO2 sequestration. This technology is founded on absence of nitrogen in the oxidizer, which is replaced by carbon dioxide. Thus, the combustion speed and temperature are limited in comparison with pure CH4-O2 combustion. The usage of the oxidation mechanism of methane combustion depends on the oxidizer composition. For conventional, CH4-air combustion, two found reduced mechanisms in the literature were used in the simulations. Whereas, modified versions of those schemes were employed in the calculation in the nitrogen-free atmosphere. The validation of those mechanisms was performed using detailed methane combustion mechanism (GRI Mech 3.0 [1]) and entire results were collected from COSILAB 1D Stretched Laminar Premixed Flames package. The simulation of one-dimensional stretched premixed laminar flames was performed in order to examine reduced schemes in the conditions, which may occur in real applications. Calculations of the flame for various fresh mixture compositions were performed for equivalence ratio equal to one, initial mixture temperature 300 K and pressure one bar. For two-step mechanism, the minimum velocity, which is an important quantity for premixed stretched laminar flames, for methane-air combustion, was in better agreement with detailed computations compared to the four-step scheme. The comparable outcomes using GRI Mech and reduced mechanisms, for combustion of methane in CO2/O2 atmosphere, were obtained, for two different examined oxidizer compositions.