Reaction Characteristics of NOx and N2O in Selective Non-Catalytic Reduction Using Various Reducing Agents and Additives

Artificial nitrogen oxide (NOx) emissions due to the combustion of fossil fuels constitute more than 75% of the total NOx emissions. Given the continuous reinforcement of NOx emission standards worldwide, the development of environmentally and economically friendly NOx reduction techniques has attracted much attention. This study investigates the selective non-catalytic reduction (SNCR) of NOx by methane, ammonia, and urea in the presence of sodium carbonate and methanol and the concomitant generation of N2O. In addition, the SNCR mechanism is explored using a chemical modeling software (CHEMKIN III). Under optimal conditions, NOx reduction efficiencies of 80–85%, 66–68%, and 32–34% are achieved for ammonia, urea, and methane, respectively. The N2O levels generated using methane (18–21 ppm) were significantly lower than those generated using urea and ammonia. Addition of sodium carbonate and methanol increased the NOx reduction efficiency by methane to ≥40% and 60%, respectively. For the former, the N2O level and reaction temperature further decreased to 2–3 ppm and 850–900 °C, respectively. The experimental results were well consistent with simulations, and the minor discrepancies were attributed to microscopic variables. Thus, our work provides essential guidelines for selecting the best available NOx control technology.

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.

Emission Characteristics for Swirl Methane–Air Premixed Flames with Ammonia Addition

This paper details the experimental and numerical analysis of a combustion process for atmospheric swirl burners using methane with added ammonia as fuel. The research was carried out for lean methane–air mixtures, which were doped with ammonia up to 5% and preheated up to 473 K. A flow with internal recirculation was induced by burners with different outflow angles from swirling blades, 30° and 50°, where tested equivalence ratio was 0.71. The NO and CO distribution profiles on specified axial positions of the combustor and the overall emission levels at the combustor outlet were measured and compared to a modelled outcome. The highest values of the NO emissions were collected for 5% NH3 and 50° (1950 ppmv), while a reduction to 1585 ppmv was observed at 30°. The doubling of the firing rates from 15 kW up to 30 kW did not have any great influence on the overall emissions. The emission trend lines were not proportional to the raising share of the ammonia in the fuel. 3D numerical tests and a kinetic study with a reactor network showed that the NO outlet concentration for swirl flame depended on the recirculation ratio, residence time, wall temperature, and the mechanism used. Those parameters need to be carefully defined in order to get highly accurate NO predictions—both for 3D simulations and simplified reactor-based models.

Robust, site-specifically immobilized phenylalanine ammonia-lyases for the enantioselective ammonia addition to cinnamic acids

Phenylalanine ammonia-lyases (PALs) catalyse the non-oxidative deamination of L-phenylalanine to trans-cinnamic acid, while in the presence of high ammonia concentration the synthetically attractive reverse reaction occurs. Although intensively studied, the...

Computational modelling of ammonia addition on partially reduced graphene oxide flakes

Density Functional Theory is employed to model the chemisorption of ammonia on epoxy-containing polycyclic aromatic hydrocarbons (PAHs) and understand the reaction mechanism of ammonia addition on partially reduced graphene oxide...