Experimental and kinetic modeling study on NH3/syngas/air and NH3/bio-syngas/air premixed laminar flames at elevated temperature

Abstract

Ammonia (NH3) can help achieve large-scale storage and long-distance transportation of renewable energy. The co-firing of NH3 with syngas and bio-syngas and increasing the initial temperature of reactants are economical and effective methods to enhance the reactivity of NH3 flames in boilers and gas turbines. An accurate kinetic model is essential for developing corresponding burners. The current kinetic models are not accurate enough in temperature dependence. Laminar burning velocities (SL) of NH3/syngas/air and NH3/bio-syngas/air mixtures were measured at various H2 contents in syngas and NH3 contents in the mixtures, equivalence ratios of 0.7~1.4, atmospheric pressure, and elevated temperature up to 423 K in a high-pressure constant-volume combustion vessel. A detailed kinetic model was developed for NH3/syngas combustion and validated based on the literature data. The experimental results show that slightly rich flame, high mole fractions of syngas/bio-syngas, and elevated initial temperature contribute to increasing the SL. Kinetic modeling analysis was performed for interpreting the effect of fuel composition, equivalence ratio and initial temperature on the laminar flame propagation characteristics. The elevated H2 content in syngas provides a stronger chemical effect and the enhanced laminar flame propagation of NH3/syngas/air and NH3/bio-syngas/air mixtures is dominated by chemical effect. Due to the presence of diluent (CO2 and N2), thermal effect has a negative influence on the enhancement of NH3/bio-syngas/air flame propagation. Although diluent hardly changes the NH3 consumption pathways, it will significantly reduce the NH3 consumption. Different NH3 consumption pathways are preferred by lean and rich flame. Sensitivity analysis shows that NH2 chemistry is favored by rich flames. Since NH2 + NH = N2H2 + H promotes the production of H radical in rich flames, it has the greatest influence on the SL of rich flames. H2 is more capable of improving the temperature dependence of NH3/syngas/air flame than CO. The increased importance of NH3 chemistry accounts for the strong temperature dependence of NH3/bio-syngas/air flame.