氨是理想能源,为更好利用纯氨燃料,开发适用纯氨燃料的燃烧器,通过数值模拟对某10kWth天然气旋流燃烧器进行三维建模,并对其纯氨燃烧和氮氧化物排放性能进行计算及仿真分析,探讨空气射流特性对火焰形态、温度分布、NO生成及排放的影响规律,以优化燃烧器纯氨燃烧能力。燃烧早期,旋流对燃料和空气混合影响大,而燃烧后期湍流强度对该过程影响大。发现通过增大空气射流孔面积(由12.8mm2增至19.2mm2)、增加空气射流角度(由15°增至30°)均可增强旋流强度,促进燃料和空气混合,促进氨燃料快速着火和稳定燃烧,缩短着火距离。但过大的射流角度可能导致空气和燃料出现短暂分离,推迟混合过程,延长着火距离。此外,减小射流孔面积、增大射流角度还将增强燃烧器喷嘴附近湍流强度,促进氨燃料和空气混合燃耗,产生局部高温区,导致NO生成浓度升高。经对比优化,空气射流孔面积19.2mm2、射流角度15°、射流速度19.83m/s时纯氨燃烧器实现稳定低NO燃烧,着火距离0.024m、火焰长度0.446m,NO生成峰值浓度和排放浓度分别降至443×10-6和37.7×10-6。

Ammonia is an ideal energy source, in order to make better use of pure ammonia fuel and develop a burner suitable for pure ammonia fuel, this study conducted 3D modelling of a 10 kWth natural gas swirl burner by numerical simulation, and simulated the combustion and NO emission performance of pure ammonia in it. The influence of air jet characteristics on the flame morphology, temperature distribution, NO generation and emission was explored, in order to optimize the pure ammonia combustion capability of the burner. In theearly stage of combustion, the influence of swirl on the mixing of fuel and air is more significant, while in the late stage of combustion theturbulence intensity has a greater influence on the process. It was found that the swirl intensity could be enhanced by increasing the air jethole area (from 12.8 mm2 to 19.2 mm2) and the air jet angle (from 15° to 30°), which could promote the mixing of fuel and air, andthus promote the rapid and stable combustion of ammonia fuel and shorten the ignition distance. However, too large jet angle may lead to ashort separation of air and fuel, delaying the mixing process and prolonging the ignition distance. In addition, it was also found that decreasing the jet hole area and increasing the jet angle would also enhance the intensity of nearby turbulence near the combustor nozzle,which would promote the mixing and combustion of ammonia fuel and air, thus generating a localized high-temperature zone and leading toan increase in the concentration of NO generation. Through comparative optimization, the pure ammonia burner achieved stable low-NO combustion with air jet orifice area 19. 2 mm2, jet angle 15°, jet velocity 19. 83 m/ s, ignition distance 0. 024 m, flame length0.446 m, and the peak NO generation concentration and emission concentration were reduced to 443×10-6 and 37.7×10-6, respectively.

0 引言

1 研究方法

   1.1 燃烧器空气射流结构

   1.2 CFD数值模型及求解方法

   1.3 方法检验

2 结果和讨论

   2.1 火焰形态

   2.2 火焰温度及燃烧器壁面温度

   2.3 NO排放特性

   2.4 空气射流对火焰特征影响机制

3 结论