Influence of H2 blending on NOx production in natural gas combustion: Mechanism comparison and reaction routes

Abstract

Hydrogen blending in natural gas is an effective way of carbon reduction. The effect of hydrogen blending on the reaction pathway of NOx emission from natural gas combustion in industrial furnaces is studied by chemical kinetic calculations. To ensure the reliability of kinetic calculation, the NOx prediction accuracy of the mechanisms GRI and PG2018 were compared by validation with corresponding experiments. It is found that the PG2018 mechanism is more accurate for NOx prediction than GRI 2.11 and GRI 3.0, especially for N2O-intermediate and NNH pathways. The effect of hydrogen blending on the chemical pathways of NOx production was obtained based on PSR reactor and burner stabilized laminar flame with a well-controlled temperature profile. The results show that in the PSR reactor, N2O-intermediate and thermal NOx are predominating pathways for NOx formation. NOx emissions of unit fuel heating value first rise with the increase of blending ratio and then reduces rapidly while the blending ratio is greater than 50%, which is mainly due to the suppression of thermal NOx and the increase of N2O-intermediate NOx. It can be found from calculation results of burner stabilized flame that the prompt NOx decreases dramatically in the laminar flame and the NOx production via NNH increases slightly as hydrogen blending ratio increases. With increasing hydrogen blending ratio, thermal NOx is suppressed, and the N2O-intermediate pathway is suppressed also at the flame sheet but enhanced in the flue gas due to the increment of the H2O content. NOx emission decreases with increasing hydrogen blending ratio in laminar flame at a given combustion temperature.