CFD ANALYSIS OF NOx FORMATION IN WASTE-TO-ENERGY SYSTEMS USING DETAILED CHEMICAL KINETIC MODELING

This study was undertaken to better understand the governing processes and reaction conditions under which NOx is produced in Waste to Energy (WtE) boilers. A three dimensional CFD model was created and calculated using the GRI 3.0, 50 species, 309 step detailed chemical kinetic model (DCKM) for methane/ethane combustion. Model results for primary NOx emissions and other pollutants agree well with collected data, proving the fidelity of the model. NO was the primary pollutant accounting for approximately 99% of the total NOx emissions. Fuel bound nitrogen was found to be the main source of NO produced in the boiler with thermal and prompt mechanisms having lesser impacts. Three principal intermediates were identified in the formation of NO; NH, HNO, and NCO. The assumption of fuel nitrogen conversion to either NH3 or HCN is an unknown parameter that was shown to have a small impact on NO emissions, indicating that this is an area that should not be explored further in this continuing study. Furthermore, varying the boiler pressure had a small impact on final NO emissions, indicating that this is not a condition that should be considered for plant operation. The next phase of this research will include the development of a reduced DCKM in order to expedite the running of new scenarios for future studies as well as optimization of boiler geometry and combustion mixing to achieve the lowest possible NOx emissions.