The combustion systems that use the oxygen and recycled flue gas mixture as oxidant have many benefits from the point of view of environment. In such a system, the excess $CO_2$ can be easily collected from the combustor exit since the exhaust gas contains $CO_2$ with high concentration. In the dry recycle mode of the system, where the flue gases are recycled after water removal, the oxidant can be regarded as the mixture of $O_2$ and $CO_2$. Applying the catalytic combustion to the system can compensate the reduction of efficiency. For the application of catalytic combustion, it is required to investigate the feature of the catalytic reaction of combustion mixture with $CO_2$.
This work did the validation of kinetics model in experiment with ignition temperature and modified the reaction kinetics to describe the gas mixture. We discuss new kinetic model to predict the ignition temperature of $H_2/O_2$ mixture in the practical region of composition.
We measure the ignition temperatures of the gas mixtures flowing towards resistively heated platinum with various composition ratios and various diluent gases, i.e., $N_2$ and Ar as well as $CO_2$. The numerical simulation includes detailed reaction mechanism for the surface reaction as well as gas phase transport properties of the mixtures. Compared with $N_2$ or Ar, the $CO_2$ dilution shows higher ignition temperature by about 50K, even at the same composition ratio. The ignition temperature increases imply the reduction of catalytic reactivity on the platinum catalyst. By the way, the heterogeneous ignition of hydrocarbon fuels shows that $CO_2$ has no effect on the surface reaction of hydrocarbon on platinum.
Catalytic combustion of $CH_4/O_2/CO_2$ in a channel is simulated by plug flow model which include detailed chemistry and reaction model in surface phase as well as in gas phase. Because heat capacity of $CO_2$ is larger than by 30-50% compared to that of $N_2$, the temperature distribution in the channel is smooth and the maximum temperature is lower with the same inlet temperature. The light off temperature of $CO_2$ diluted mixture at equivalence ratio of 0.4 is 742K which is 12K higher than that of $N_2$ diluted mixture. The channel length to acquire the complete conversion is larger in the $CO_2$ dilution case. The $C_2$ emission of $CH_4/O_2/CO_2$ mixture is significant since $CO_2$ has a role as a third body in the gas reactions which are major paths to produce $C_2$ hydrocarbon.
