Emission analysis of the CH4/NH3/air co-firing fuels in a model combustor

Ammonia is regarded as one of the potential hydrogen carriers and a kind of carbon-free renewable energy source. However, there are still some challenges on ammonia application in combustion devices, i.e., the high NOX emission. In this study, the combustion performances and emission characteristics of co-firing CH4/NH3/air flame with NH3 mole fraction (eta NH3) from 0 to 1.0 are investigated in a swirl combustor. The emissions in the exhaust gas are analyzed by the Gasmet DX4000 Fourier Transform Infrared (FTIR) gas analyzer. The simulations of the chemical reactor networks (CRN) with a detailed mechanism are employed to extend the understanding of experimental data. Results show that the combustion efficiency is very low at fuel lean conditions for high eta NH3 flames, and NOX emission significantly increases when blending a small amount of ammonia. The co-firing flames produce large amount of NOx at lean conditions (phi less than 1.0). There exits an optimized condition (phi approximate to 1.1) where the NOx and NH3 emissions reach their lowest value simultaneously. The co-firing flame produces maximum NOx emission at eta NH3 = 0.5. Therefore, to control the NOX emission, the CH4/NH3/air co-firing flames should be operated far away from eta NH3 = 0.5 at rich conditions. NOX reaction pathway analysis shows the HNO pathway is dominant in fuel lean conditions. Thermal-NO pathway and NHi pathway are primary in stoichiometric ratio and fuel rich conditions, respectively.

Automated summary

This study investigates the combustion performances and emission characteristics of co-firing CH4/NH3/air flame in a swirl combustor, and finds that low combustion efficiency and significant increase in NOX emissions occur in high eta NH3 flames when blending a small amount of ammonia. The co-firing flames produce large amount of NOx at lean conditions.