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NO x emission control of lean methane-air combustion with addition of methane reforming products

Maintaining acceptable burning intensity and stability under lean premixed combustion is a challenge in gas turbine operation. Enhancing flame stability under such conditions is accomplished by preheating the fuel or by regulating its composition. Preheating increases the flame speed and resistance to extinction, but also increases the NO x emissions, since the combustion temperatures are higher. Regulating the composition is typically accomplished through H 2 addition, which even at small amounts can noticeably increase combustion stability and reduce NO x emissions. H 2 is expensive to produce, and CH 4 steam reforming with the use of waste heat has been proposed as a viable solution. Furthermore, it is far more economical to add the reformate mixture to the fuel, which in addition to H 2 also contains CO, CO 2 , unreacted steam, and CH 4 , rather than H 2 . Prior studies by our group have focused on the dynamics and structure of flames of lean mixtures of air with CH 4 /H 2 /CO/CO 2 /H 2 O, the five-gas fuel mix resulting when combining the reformer product with fresh CH 4 . In this article, the focus is on quantifying the NO x emissions characteristics. Experiments and simulations were carried out in a single jet-wall configuration. The experimental data compare favorably with the numerical predictions and indicate that adding the reformate mixture to CH 4 results in lower NO x emissions under the same burning intensity.