Experiments and kinetic modeling of NO reburning by CH4 under high CO2 concentration in a jet-stirred reactor

Abstract

This paper presents new experimental results on NO reduction by CH4 under both N2 and CO2 atmospheres in a jet-stirred rector (JSR). The experiments are simulated using an updated reaction mechanism, and simulations are consistent with experiments. Both experiments and simulations suggest that there is a critical equivalence ratio (Φ) to achieve the maximum NO reduction at a fixed reaction temperature (T), and the critical Φ is increased with the increase of T. The maximum NO reduction in the CO2 atmosphere is achieved at T ≈ 1300 K, Φ ≈ 1.4, and CH4/NO ratio = 20 with a maximum reduction efficiency of 63%. When the CH4/NO ratio ≤5, relative to the N2 atmosphere, the NO reburning in the CO2 atmosphere is reduced by around 40%–60% at temperatures above 1100 K. Interestingly, at 1100 K the maximum NO reduction does not occur at fuel-rich environments but at Φ ≈ 0.7 due to the low reactivity to produce hydrocarbon radicals at low temperatures. Moreover, at 1300 K, as CO2 concentration increases from 30% to 60%, the critical Φ is reduced from 1.4 to 1.2 and the NO reduction efficiency is reduced by around 7% owing to the enhanced inhibition of CH4 oxidation. To improve reburning in oxy-fuel combustion, it is recommended to operate reburn zone at moderate temperatures (i.e., 1300–1400 K), the critical Φ (e.g., Φ ≈ 1.4 if T = 1300 K), long residence times (τ ≥ 2 s), and large reburning fuel/NO ratio (≥15).