Numerical Model Development for Supercritical CO2 Oxy-Combustion

Direct-fired supercritical CO2 (sCO2) power cycles with oxy-fuel combustion have been demonstrated to achieve clean energy goals with carbon capture. Supercritical-CO2 combustion at very high pressures (300 bar) create favorable conditions for CO2 capture as well as increased energy efficiency. However, most fuel feed stocks of natural gas and syngas contain nitrogen and sulfur impurities (e.g., NH3, H2S, etc.). These impurities have potential to generate acid gases such as NOx and SOx, which adversely affect the structural integrity and contaminate the carbon capture process. Therefore, it is important to understand the high- pressure oxy-fuel combustion process to mitigate these emissions. There are significant gaps in the understanding of oxy-fuel combustion under supercritical-CO2 conditions. In the ongoing Phase II work, the focus has been to understand the chemical kinetic effect of CO2 diluent and its impact on thermal radiation, and the effect of impurities on ignition properties of CH4 and syngas fuels through experiments and modeling. During Phase II, unique experimental platforms have been developed for the extreme combustion conditions encountered in sCO2 combustion. Significant progress was made in characterizing the combustion and heat transfer issues for sCO2, but several important factors remain to be investigated. The Phase IIA work will focus on acquiring NOx and SOx emission data using realistic natural and syngas gas compositions with nitrogen (e.g., NH3) and sulfur (i.e., H2S) impurities as well as ammonia using the experimental facilities developed in Phase II. The data will be used to validate the models developed in Phase II. Also, the experimental data will help to understand the effect of pressure on the pollutant emissions from oxy-fuel combustion, and to develop design mitigation strategies. The overall goal of Phase IIA is to deliver well-validated, physics-based computational models that are validated for a variety of fuel feed stocks to assist design engineers to: (a) generate uniform temperature profiles in the combustor exhaust, (b) design optimal CO2 flow splits to minimize heat transfer to the combustor wall while minimizing exhaust gas emissions, and (c) minimize (and mitigate) the formation of NOx and SOx emissions. The final products will be available to be incorporated into computational software suites as: (a) detailed and reduced chemical kinetic models validated for high-pressure sCO2 combustion conditions with impurities such as NH3 and H2S; (b) improved correlation-based models for fluid properties as well as thermal radiation at conditions relevant to sCO2 power cycles that are affordable, accurate, and robust in CFD.