MILD条件下氢-天然气混合燃烧特性及排放物分析

针对目前天然气掺氢后燃烧效率及氮氧化物排放研究较少的问题,应用组分输运模型、涡耗散概念燃烧模型和Do辐射模型,结合GRI-22化学反应机理,建立柔和燃烧模拟模型,通过与实验结果对比验证了模型的可靠性,进一步应用该模型分析不同掺氢比例对燃烧特性的影响。结果表明,随着掺氢比例增加,燃料与氧化剂的混合程度逐渐提高,混合气体的径向分量不断减小;由于反应速率和放热速率提高,燃烧器内部的温度升高,热力型氮氧化物含量增高,主要集中于燃烧器后端;燃料进口速度增大会导致燃烧器内燃烧不完全、出口处温度降低,氧气浓度升高,氮氧化物含量降低。研究发现,天然气中掺入氢气更有利于达到柔和燃烧条件。

ANALYSIS OF MIXED COMBUSTION CHARACTERISTICS AND EMISSIONS OF HYDROGEN AND NATURAL GAS UNDER MILD CONDITIONS

To address the using problem that the combustion efficiency and Nitrogen Oxides （NO_x） emission of Natural Gas （NG） after hydrogen doping （H₂） are less studied, using the component transport model, Eddy Dissipation Concept （EDC） combustion model and Do radiation model, at same time combining with the GRI-22 chemical reaction mechanism, to establish a soft （MILD, moderate or intense low oxygen dilution） combustion simulation model is established. The reliability of the model is verified by comparing it with the experimental results, and the model is further applied to analyze the effects of different hydrogen doping ratios on the combustion characteristics. The results show that with the increase of hydrogen doping ratio, the mixing degree of fuel and oxidant gradually increases, and the radial component of mixed gas decreases; due to the increase of reaction rate and exothermic rate, the temperature inside the burner increases, and the thermal NO_x content increases, mainly concentrated in the back end of the burner; the increase of fuel inlet speed leads to incomplete combustion inside the burner, the temperature at the outlet decreases, the oxygen concentration increases and the NO_x content decreases. It is found that hydrogen blending in natural gas is more favorable to achieve MILD combustion conditions.