基于CFD方法的燃煤电厂烟气排放数值模拟

为研究燃煤电厂的烟气扩散，采用计算流体力学（computational fluid dynamics，CFD）方法对燃煤电厂烟气排放中污染物（包含气态污染物和固态颗粒物）的扩散形态进行模拟.燃煤电厂的排烟方式主要有烟塔合一和烟囱两种，根据几何参数建立烟塔合一及烟囱的数值模型，采用纳维-斯托克斯方程（Navier-Stokes equations，N-S equations）求解流场及气态污染物浓度场，采用离散相模型（Discrete Phase Model，DPM）计算固态颗粒污染物运动轨迹.结果表明:对于气态污染物，由于冷却塔下游漩涡的卷吸作用，采用烟塔合一排放的烟气最大浓度和超标范围随环境风速的增加逐渐增大，不利于烟气扩散.但随着环境风速的增加，空气的对流作用逐渐增强，从而加速了烟气的扩散.在漩涡和环境风的综合作用下，烟气的最大浓度和超标范围在环境风速为6 m/s时达到最大值，随后随着环境风速增加而减小.采用烟囱排放的烟气由于漩涡作用很小，因此其最大浓度及超标范围随风速的增加呈递减趋势.得益于烟气在冷却塔内的预扩散，采用烟塔合一排放的烟气最大浓度比采用烟囱排放的烟气最大浓度低将近1个数量级，但这种优势会随着环境风速的增加而减小.对于固态污染物，冷却塔后方的漩涡会加速颗粒物的扩散，因此采用烟塔合一排放的颗粒物的扩散状态远优于采用烟囱排放的颗粒物的扩散状态. 

Numerical Simulation of Flue Gas Emissions from Coal-fired Power Plants Using Computational Fluid Dynamics Method

In order to understand the diffusion of flue gas in coal-fired power plants, the computational fluid dynamics (CFD) method was applied to simulate the distribution of pollutants such as gaseous pollutants and particulate matter from flue gas emissions in a coal-fired power plant. The emissions were studied in a natural draft cooling tower (NDCT) with flue gas injection and a chimney. The numerical models of NDCT with flue gas injection and chimney were established with the geometrical parameters. The flow field and concentration field of gaseous pollutants were calculated using Navier-Stokes (N-S) equations. In addition, the trajectory of particulate matter was computed by Discrete Phase Model (DPM). The results indicated that the maximum concentrations of gaseous pollutants in flue gas discharged from the NDCT with flue gas injection increased with the increasing wind speed due to the entrainment of vortex at the downstream side of the cooling tower. It was not conducive to the diffusion of the flue gas. However, the convection of air heightened with the increase of wind speed, which was beneficial for the diffusion. Under the combined action of vortex and convection, the maximum concentration of gaseous pollutants was obtained at wind speed of 6 m/s. However, the maximum concentration of gaseous pollutants in flue gas from the chimney decreased with the increase of wind speed, because the vortex effect in this case was very small. Due to the pre-diffusion of flue gas in the cooling tower, the maximum concentration of flue gas from NDCT with flue gas injection was almost one order of magnitude lower than that from the chimney, but this advantage gradually weakened with increasing wind speed. Meanwhile, it was noted that the diffusion of particulate matter from NDCT with flue gas injection was much better than that from the chimney for the vortex at the downstream side of the cooling tower. In general, NDCT with flue gas injection is more appropriate than chimneys for flue gas emission.