基于TRI锅炉燃烧模拟及煤粉颗粒湍流运动对辐射影响分析

Pulverized coal combustion simulation based on TRI and analysis of the effect of particle turbulence on radiation

以某电厂300 MW四角切圆煤粉锅炉为研究对象,采用数值模拟的方法,研究温度湍流和颗粒等对辐射换热以及污染物生成的影响。采用Realizable k-ε模型来模拟湍流流动;采用DO模型求解辐射换热,运用UDF(自定义标量法)将TRI(湍流辐射交互作用)和碳烟生成模型耦合到FLUENT中;使用Beta-PDF模型计算燃烧组分脉动变化影响;焦炭燃烧采用动力/扩散模型;挥发分析出模型采用化学渗透脱挥发份(CPD)模型。考虑湍流温度脉动和组分吸收系数引起的湍流辐射交互作用(TRI),并结合随机游走模型,分析颗粒散射对TRI的影响。结果表明:考虑TRI作用,模拟温度场与不考虑TRI温度更低,模拟结果更接近现场测量结果,误差在3%之内。碳烟体积与温度呈负相关,温度越高,碳烟越少,即考虑TRI后碳烟生成量增多。同时,TRI在煤粉燃烧传热模拟过程中不可忽略。其中对温度场、燃烧组分场的影响明显。考虑TRI后,炉膛的平均火焰温度峰值分别降低了73,47和58 K。温度场截面的平均温度差分别为57,51和54 K,O_(2)和CO含量相对增加但影响不大;整体温度下降后,NO_(x)产量减少。在140 MW的工况下发现由于其温度脉动引起的湍流辐射交互作用增加了炉膛火焰的辐射换热。同时燃烧颗粒的散射作用,炉膛内湍动能分布更扩散,湍动能数更大,颗粒数相对增加,各截面炉膛不透明度增大,增加炉膛背景辐射,因此TRI中颗粒湍流脉动不能忽略。

Taking a 300 MW four-corner tangentially rounded pulverized coal boiler in a power plant as the research object, some numerical simulation methods are used to study the effects of temperature turbulence and particle scattering on radiation heat transfer and pollutant generation.The study selects the realizable k-ε model to simulate turbulent flow and uses the DO model to solve radiative heat transfer.Also, the study uses the UDF(custom scalar method) to couple TRI(turbulent radiation interaction) and soot generation model with FLUENT.According to Beta-PDF,the model calculates the influence of the pulsation changes of combustion components.The power/diffusion model is used for coke combustion.The volatile matter precipitation model uses the chemical permeation devolatili-zation(CPD) model.Furthermore, the turbulent radiation interaction(TRI) caused by turbulent temperature fluctuations and component absorption coefficients is considered.Combined with the random walk model, the impact of particle scattering on TRI is analyzed.The results show that after considering the effect of TRI,the simulated temperature is closer to the on-site measurement result, and the error is within 3%.In addition, the increase in soot volume is negatively correlated with the furnace temperature.As the temperature increases, the less soot content, that is, more soot after TRI is considered.Moreover, TRI must not be ignored in the simulation process of pulverized coal combustion heat transfer.Among them, the influence on the temperature field and the combustion component field is obvious.After considering TRI,the peak average flame temperature of the furnace under different working conditions is reduced by 73,47 and 58 K,respectively.The difference of the average cross-section temperature is 57,51 and 54 K,respectively.The content of O_(2) and CO increases relatively but has little effect.After the overall temperature of the furnace decreases, the output of NO_(x) decreases.Under 140 MW operating conditions, it is found that the turbulent radiation interaction caused by its temperature fluctuation increases the radiation heat transfer of the furnace flame.At the same time, the scattering effect of burning particles makes the distribution of turbulent kinetic energy in the furnace more diffuse, the number of turbulent kinetic energy is larger, the number of particles increases relatively, the opacity of each section of the furnace increases, and the background radiation of the furnace increases.In summary, the turbulent pulsation of particles in TRI must not be ignored.