Emission and performance of a micro gas turbine combustor fueled with ammonia-natural gas

Ammonia as a carbon-free fuel has great potentiality to be utilized in power generation sectors such as micro gas turbines (MGT) to mitigate carbon dioxide emission from combustion systems. It is also easy to store and transport at room temperature compared to hydrogen, and in liquid form has equal volumetric energy density to liquid hydrogen. However, some challenges regarding its NOx pollution and flame stabilization inhibit its usage in these areas which requires further studies. In the present study, thermal performance and NOx emission of an MGT combustor fueled with ammonia-natural gas blends has been analyzed numerically through chemical reactant networks (CRN). The combustor's inlet conditions are at atmospheric conditions and diffusion flame is stabilized using air swirler. In the first part of the paper, the CRN model has been developed based on empirical and semi-empirical equations. Series of experiments have been carried out to find the required parameters for the CRN model. Also, the results of NOx emission and temperature distribution have been validated with the experimental results. In the second part, effects of ammonia addition to the natural gas fuel are studied for various ammonia percentages using the CRN. The results show that by increasing ammonia molar percentage in the fuel, NO emission rises dramatically and reaches up to 330 PPM, but after a certain threshold (about 12.5 molar percent of ammonia) further ammonia addition reduces NO emission. Moreover, the overall temperature of the combustor decreases with ammonia addition due to lower LHV (lower heating value) of ammonia relative to natural gas. However, the overall efficiency of the combustor does not change significantly. The results also reveal that most of the NO is produced in the primary and secondary zones of the combustor. NO2 is mostly created in the secondary zone of the combustor and comprises about 10% of total NOx emission.

Automated summary

The study demonstrates that by increasing the molar percentage of ammonia in the fuel, NO emissions rise dramatically, but further increasing ammonia beyond a certain threshold (about 12.5 molar percent) reduces NO emissions. Additionally, with the addition of ammonia, the overall temperature of the combustor decreases due to the lower heating value of ammonia compared to natural gas, while the overall efficiency of the combustor does not change significantly.