Simplified kinetic schemes for oxy-fuel combustion

This work presents simplified kinetic schemes to be adopted in the CFD modeling of oxy-fuel combustion. Oxy-fuel combustion is an important technology to control CO 2 emissions. The reduction of nitrogen content during combustion makes easier the CO 2 capture for its successive storage. Flue gas recirculation can be adopted for the eventual temperature control. Moreover, oxygen rich combustion finds several applications where high temperatures are required, like iron and steel industry, or when the plants undergo frequent startups and shutdowns, to minimize the transient times. Computational Fluid Dynamics (CFD) is also increasing its importance as a tool for industrial design and optimization. In many cases (for example oxy-fuel combustion), very simplified approaches, like ‘mixed is burned’ , which do not need any kinetic information, are completely meaningless, because the high temperatures promote dissociation reactions. For such systems it is necessary to use more detailed and complex approaches, which usually require the adoption of a finite rate chemistry. As an example, the Eddy Dissipation Concept Model (EDC), proposed by Magnussen (1, 2), is largely used for the numerical simulation of combustion devices for industrial applications. However, one of the main problems when using CFD in the full scale geometry and with a finite rate chemistry is represented by the dimension of the computational grid and then the large memory and CPU required. For this reason the level of description of combustion chemistry has to be drastically reduced down to a few species and a few reactions. The adoption of detailed chemistry for the CFD simulation of combustion devices is possible only for very simple geometries and fuels (like hydrogen and syngas) whose chemistry involves a small number of species. In general, simplified kinetic mechanisms are required to manage complex geometries and complex fuels. In the typical air combustion cases, when CO profiles are of interest or when temperature estimations have to be improved, a large number of simplified mechanisms is available, especially for methane. Typical and well known examples are the schemes of Westbrook and Dryer (3) and Jones and Lindstedt (4). Unfortunately, the temperature peaks of oxy-fuel combustion limit the validity of such mechanisms in these conditions. At temperatures higher than 2500 K, not only CO-CO 2 equilibrium is in favor of CO and H 2-H2O equilibrium foresees a significant amount of H 2, but also the radical pool has a significant impact in limiting the heat release. The simplified mechanisms do not always account for the dissociation reactions (3) and none of them include radicals. Therefore, it is necessary to revise simplified mechanisms already available in the literature or to formulate new mechanisms, specifically conceived for their direct