Search

• Investigating the NOx emissions of natural gas combustion during oxy-fuel operation. • Accurate NOx emission prediction for different oxy-fuel burner and nozzle designs. • Simulations provided information of the flame shape and the NO formation region. • Accurate NOx emission prediction for oxidizers containing up to 10% v N 2 in O 2. The aim of this work is to investigate and improve the understanding of the complex processes involved in NOx formation during oxy-fuel combustion of natural gas. In this study, two industrial non-premixed jet burner designs were experimentally and numerically analyzed for their sensitivity on NOx formation during the combustion of natural gas with pure oxygen and mixtures containing up to 10 % v nitrogen in oxygen. The two burners differed by their design: (1) a high-momentum co-axial burner with changeable nozzle designs, and (2) a low-momentum fish-tail burner. The study revealed that the high-momentum burner design outperformed the fish-tail burner during operation in similar operating points since at 1320 ° C the NOx emissions could be reduced by 60% using 10 % v N 2 in oxygen as oxidizer and decreased by 75% during pure oxy-fuel combustion. At 1320 ° C , the NOx emissions could thus be reduced from 858 to 339 mg kWh - 1 (3 % v O 2 reference on a dry basis) using 10 % v N 2 in oxygen as oxidizer and could be lowered from 215 to 51 mg kWh - 1 during oxy-fuel combustion. In addition to the experiments, a fast-solving computational fluid dynamics (CFD) model, representing the experimental setups, was developed to analyze NOx formation. Steady-state simulations including a multi-step skeletal mechanism applicable for oxy-fuel combustion were conducted and the NOx emissions were calculated in a post-processing step. A mixture fraction-based model (PPSFM) was used to reduce the computational expense of the model and it was able to predict the NOx formation rates over the entire investigated experimental matrix with good accuracy. [ABSTRACT FROM AUTHOR]

• Alternative fast-solving CFD model for oxy-fuel burners with shear rates near unity. • Accurate NOx emission prediction for oxidizers containing up to 10% v N2 in O2. • Classical species transport models should be used for the purpose of comparison. • Partially-premixed steady flamelet model predicts NOx and flame shape best. Accurate prediction of NOx emission is essential in designing combustion devices and troubleshooting of existing ones. The aim of this work is to investigate the sensitivity of NOx formation during the combustion of natural gas with oxygen using a numerically inexpensive computational fluid dynamics model. To this end, an industrial jet burner was experimentally and numerically analysed for NOx formation at 600 kW controlled at 1320 and 1450 ° C during the combustion of natural gas with pure oxygen and oxidizer mixtures containing up to 10 % v nitrogen. Two mixture-fraction based and two classical species transport models were investigated for their ability to: (1) predict the flame shape and temperature, (2) calculate the OH and CH emissions driving the NOx formation, and (3) fast and accurately predict the NOx emissions during oxy-fuel combustion and during the presence of low nitrogen amounts in the oxidizer. The study shows that the widely-used steady-flamelet model fails to correctly predict the flame shape and temperature, due to a too low velocity difference between the oxidizer and the fuel. It is highlighted that only the partially-premixed steady flamelet model predicted the flame shape and the NOx formation rates adequately, fitting the experimental and numerical data closely. Moreover, the shear rate in the annular gap was identified as a crucial parameter for the applicability of mixture fraction-based models. Species transport models should be used for validity checks but they disqualify as fast-solving alternatives due to their high computational demand (EDC) or lack of detailed chemistry interaction (EDM). [ABSTRACT FROM AUTHOR]