A HIGH-FIDELITY MODELING TOOL TO SUPPORT THE DESIGN OF OXY-COMBUSTORS FOR DIRECT-FIRED SCO_2 CYCLES

摘要

The challenge in the design of oxy-combustors for direct-fired supercritical CO_2 (sCO_2) cvcles is in addressing disparate performance metrics and objectives. Key design parameters to consider include among others: injector design for mixing and flame stability, split of recycled CO_2 diluent between injectors and cooling films, target flame temperatures to control non-condensable products, and strategies to inject the diluent CO_2 for film cooling and thermal control. In order to support novel oxy-combustor designs, a high-fidelity yet numerically efficient modeling framework based on the CRUNCH CFD® flow solver is presented, featuring key physics-based sub-models relevant in this regime. For computational efficiency in modeling large kinetic sets, a flamelet/progress variable (FPV) based tabulated-chemistiy approach is utilized featuring a three-stream extension to allow for the simulation of the CO_2 film cooling stream in addition to the fuel and oxidizer streams. Finite-rate chemistry effects are modeled in terms of multiple progress variables for the primary flame as well as for slower-evolving chemical species such as NO_x and SO_x contaminants. Real fluid effects are modeled using advanced equations of states. The predictive capabilities of this computationally-tractable design support tool are demonstrated on a conceptual injector design for an oxy-combustor operating near 30 MPa. Simulations results provide quantitative feedback on the effectiveness of the film cooling as well as the level of contaminants (CO, NO, and N) in the exhaust due to impurities entering from the injectors. These results indicate that this framework would be a useful tool for refining and optimizing the oxv-combustor designs as well as risk mitigation analyses.