Experimental and kinetic modeling study on NH_3/syngas/air and NH_3/bio-syngas/air premixed laminar flames at elevated temperature

摘要

Ammonia (NH_3) can help achieve large-scale storage and long-distance transportation of renewable energy.The co-firing of NH_3 with syngas and bio-syngas and increasing the initial temperature of reactantsare economical and effective methods to enhance the reactivity of NH_3 flames in boilers and gasturbines. An accurate kinetic model is essential for developing corresponding burners. The current kineticmodels are not accurate enough in temperature dependence. Laminar burning velocities ( S_L ) ofNH_3 /syngas/air and NH_3 /bio-syngas/air mixtures were measured at various H_2 contents in syngas andNH_3 contents in the mixtures, equivalence ratios of 0.7～1.4, atmospheric pressure, and elevated temperatureup to 423 K in a high-pressure constant-volume combustion vessel. A detailed kinetic modelwas developed for NH_3 /syngas combustion and validated based on the literature data. The experimentalresults show that slightly rich flame, high mole fractions of syngas/bio-syngas, and elevated initial temperaturecontribute to increasing the S L . Kinetic modeling analysis was performed for interpreting theeffect of fuel composition, equivalence ratio and initial temperature on the laminar flame propagationcharacteristics. The elevated H_2 content in syngas provides a stronger chemical effect and the enhancedlaminar flame propagation of NH_3 /syngas/air and NH_3 /bio-syngas/air mixtures is dominated by chemicaleffect. Due to the presence of diluent (CO_2 and N_2 ), thermal effect has a negative influence on the enhancementof NH_3 /bio-syngas/air flame propagation. Although diluent hardly changes the NH_3 consumptionpathways, it will significantly reduce the NH_3 consumption. Different NH_3 consumption pathwaysare preferred by lean and rich flame. Sensitivity analysis shows that NH_2 chemistry is favored by richflames. Since NH_2 + NH = N_2 H_2 + H promotes the production of H radical in rich flames, it has thegreatest influence on the S L of rich flames. H_2 is more capable of improving the temperature dependenceof NH_3 /syngas/air flame than CO. The increased importance of NH_3 chemistry accounts for the strongtemperature dependence of NH_3 /bio-syngas/air flame.