旋流对高温空气燃烧影响的模拟研究

Numerical Simulation of the Influence of a Swirling Flow on High Temperature Air Combustion

以工业炉的高温空气燃烧技术应用为背景,对一个同心式轴向旋流高温空气燃烧器单烧嘴燃烧室内的高温空气燃烧特性进行了模拟研究。湍流输运方程采用RSM模型,气相燃烧模型采用函数的PDF燃烧模型,辐射换热过程采用离散坐标法模拟,NOx模型为热力型。以天然气为燃料,在预热空气温度为1 273 K,空气含氧量为8%。燃烧总过量空气系数为1.1的条件下,进行了数值模拟计算,讨论了旋流角度和燃烧器的螺旋伸展长度等参数对NOx排放、局部温度、氧浓度和CO浓度分布等的影响。结果表明,旋流燃烧器能进一步降低NO排放,使燃烧更加完全。当螺旋肋片伸展因子R=2,燃料/空气速度比a=1.09,旋流角度θ=180°时,NO排放浓度最小,出口NO的摩尔分数为12.9×10-6,出口CO的摩尔分数为29×10-6。而当旋流角度θ=0°时(直射流),出口NO的摩尔分数为31.7×10-6,出口CO的摩尔分数为372×10-6。

Against the backdrop of the application of high temperature air combustion technology in industrial boilers,a simulation study was performed of the high temperature air combustion characteristics of the single-nozzle combustor of a concentric type axial swirling flow high temperature air burner.The Reynolds stress model(RSM) was used in the turbulent flow transmission equation and the PDF(probability density function)-based combustion model featuring the β function was employed by the gas phase combustion model.The radiation heat exchange process was simulated by using a discrete coordinate method.The NOx model is of the thermal type.With natural gas serving as the fuel,when the preheated air temperature is 1 273 K,the oxygen content of the air reaches 8%.Under the condition of the total excess air factor for combustion being 1.1,a numerical simulation calculation was conducted.The influence of such parameters as the swirling flow angle and the spiral extension length of the burner etc.on NOx emissions,local temperature,oxygen concentration and CO concentration distribution etc.was investigated.The research results show that the swirling flow burner can further reduce the NO emissions and make the combustion more complete.When the spiral rib extension factor R=2,fuel/air speed ratio a=1.09 and the swirling flow angle θ=180°,the NO emissions concentration attains the minimum,the outlet NO molar fraction hits 12.9×10-6 and the outlet CO molar fraction reaches 29×10-6.When the swirling flow angle θ=0(direct jet flow),the above-mentioned fractions are 31.7×10-6 and 372×10-6 respectively.