Computational Fluid Dynamics Modeling of NOx Reduction Mechanism in Oxy-Fuel Combustion

Oxy-fuel combustion is a promising carbon capture technology in which both the conversion of fuel-N to NO and the reduction of recycled NO contribute to lowering of final NO exhausted from the coal combustion system. Combustion characteristics for both air and oxy-fuel conditions were numerically investigated in a pilot scale test facility for an Australian sub-bituminous coal. On the basis of De Soete's mechanism, the additional reactions for formation of fuel-NO and reduction of recycled NO were added into computational fluid dynamics (CFD) codes, using user-defined Functions (UDFs). The NOx predictions in air and oxy-fuel combustion were compared to experimental data. The NO emission in oxy-fuel condition is predicted to be significantly lower than that in air combustion, even without recycled NO. The effect of the nitrogen partitioning ratio between volatile and char on the NOx emission was also investigated.