燃料稀释和喷嘴布置对甲烷非预混MILD氧燃烧的影响

Effects of Fuel Dilution and Nozzle Arrangement on Non-premixed MILD Oxy-combustion of Methane

中度与极度低氧稀释(moderate or intense low-oxygen dilution, MILD)氧燃烧能够同时实现低碳和低NOx排放,是一种很有前景的燃烧技术。通过实验研究CO2稀释甲烷的非预混MILD氧燃烧炉内CO2稀释量(30%~80%体积分数)和喷嘴布置(中心燃料喷嘴或中心氧化剂喷嘴)对燃烧和排放特性的影响。实验表明,随着燃料稀释程度的升高,炉内温度和NO排放均降低,但CO排放有所升高。另外,过高的稀释度(如80%)会导致炉内燃烧不稳定,易发生熄火。但预热燃料可以避免这一问题。70%燃料稀释度下,炉内温度分布均匀,NO排放较低(<20×10-6),且对当量比、燃料预热温度和氧化剂中氧气浓度的变化不敏感,更有利于MILD氧燃烧的实际应用。此外,实验发现,相比中心燃料喷嘴的布置,中心氧化剂喷嘴布置下,炉内温度分布更加均匀,NO排放极低(≈5×10-6),更有利于建立超低排放的MILD氧燃烧。因此,实际燃烧器设计时可以考虑这种布置。

Moderate or intense low-oxygen dilution(MILD) oxy-combustion is a promising combustion technology, which can both realize low carbon and low NOx emissions. This work experimentally investigated the effect of fuel dilution level(30% to 80% in volume) and nozzle arrangement(central fuel nozzle or central oxidant nozzle) on the combustion and emission characteristics in a non-premixed MILD oxy-combustion furnace firing CO2-diluted methane. The results show that as the fuel dilution level increases, the in-furnace temperature and NO emission decrease, but the CO emission increases. The combustion is unstable and prone to extinction at very high dilution level(e.g., 80%). However, this problem can be avoided by preheating the fuel stream. At 70% fuel dilution level, the in-furnace temperature distribution is uniform, and the NO emission is low(<20×10-6) and not sensitive to the increasing of equivalence ratio, fuel preheating temperature and oxygen concentration in the oxidant, thus benefiting for the practical application of MILD oxy-combustion. It is also found that comparing to the arrangement with central fuel nozzle, the temperature is more uniform, and the NO emission is extremely low(≈5×10-6) under the central oxidant nozzle mode. Thus, the latter can be considered for the design of MILD oxy-combustion burners.