冬季烟塔合一烟气排放特性及其改善措施研究

针对烟塔合一冷却塔(Natural Draft Dry Cooling Tower,NDDCT)在冬季关闭冷却塔百叶窗时存在烟气排放困难的现象,以及导致冷却塔内污染物浓度大幅升高、进而增加冷却塔内壁腐蚀风险的问题,提出了增加烟囱高度的改善措施,并开展了风洞试验。基于计算流体力学(Computational Fluid Dynamics,CFD)方法建立了烟塔合一数值模型以获得冷却塔内部流场和污染物浓度场的分布特性,模拟对比了春季工况和冬季工况条件下烟塔合一冷却塔内部及出口位置的流场和烟气扩散特性。结果表明,由于百叶窗关闭导致冷却塔的通气量和换热量大幅度下降,冷却塔内部的流场变得杂乱无章,污染物质量分数大大增加。与春季相比,冬季冷却塔内壁污染物最大质量分数增加了1.5倍。随烟囱高度增加,烟气可以凭借其初始动能抵御冷却塔内的湍流冲出塔外,冷却塔内部的烟气扩散情况逐渐改善。定性风洞试验结果较好地验证了数值模拟结果,验证了该方法的可行性。虽然增加烟囱高度会增加施工初期的投资,但该方案能有效降低冷却塔的腐蚀风险,不但节省了后期防腐的投资,而且降低了安全风险。从长远来看,该措施利大于弊。

Study on flue gas emission characteristics and improvement measures for natural draft dry cooling tower with flue gas injection in winter

Based on the computational fluid dynamics(CFD),we have established a numerical model for the natural draft drycooling tower(NDDCT)with the flue gas injection to predict the flow field and pollutant diffusion.This is because the flue gas diffusion is characteristic of great concern of the pollutant control and the tower anticorrosion,which cannot be discharged smoothly from the NDDCT with the flue gas injection when the louvers are closed in winter,and the concentration of the pollutants inside the cooling tower may increase a lot and consequently aggravate the corrosion of the inner wall of the cooling tower.In terms of the said issue,the paper has proposed an improvement measure to increase the stack height and conduct the wind tunnel experiment.What is more,we have also simulated the flow field and the flue gas emission features for NDDCT with the flue gas injection in spring and winter.The results of our simulation show that the air mass flowing rate and the heat rejection rate of the cooling tower can be reduced greatly due to the shutting-up of the louvers in winter.Besides,the pollutant concentration rate on the inner shell of the cooling tower may increase by 1.5 times in the winter days as compared with those in spring.With the increase of the stack height,the flue gas can be discharged out of the cooling tower with its initial kinetic energy to resist the disturbance of the turbulence,and the diffusion feature of the flue gas in the cooling tower can be gradually improved.Thus,the results of the above said qualitative wind tunnel experiment well can faithfully verify the numerical simulation results and demonstrate the feasibility of the above said scheme.And,in turn,though the stack height increase can increase the investment in the early stage of construction,the scheme can effectively reduce the corrosion risk of the cooling tower,hence,not only saving the investment in the later stage of the corrosion protection,but also reducing the safety risk.And,so,the advantages of the said measure shall be able to outweigh the disadvantages in the long run.