600MW锅炉双尺度低氮改造后的燃烧特性及其机理分析

Mechanism Analysis on Combustion Characteristics of a 600 MW Boiler Retrofitted with Dual-scale Low Nitrogen Technology

结合大容量锅炉分区热力计算和全炉膛温度压力简化动态模型思想,以能量守恒定律和辐射换热理论为基础,针对某电厂600 MW锅炉建立改造前和双尺度低氮改造后炉膛三区机理模型,通过Simulink软件仿真炉膛纵向空间燃烧特性.采用Fluent软件模拟炉内横向空间温度和速度场变化,并对双尺度低氮改造技术进行了较全面的机理分析.结果表明:低氮改造后由于二次风射流方向偏斜,使得一次风与二次风旋流方向相反,旋流区横向增大、纵向缩短,从而部分区域燃烧效率提高,NO_x排放量显著减少,但却具有燃烧过程惯性增大、升负荷适应性下降的缺陷.

Combining the thermodynamic calculation in sections for large capacity boilers with simplified dynamic model of full-furnace pressure and temperature, and based on the law of energy conversation and the theory of radiation heat transfer, mechanism models of furnace temperature were set up for three zones of a 600 MW boiler before and after dual-scale low nitrogen retrofit, with which combustion characteristics in vertical space of the furnace was simulated using Simulink software. In addition, the temperature field and velocity field in horizontal space of the furnace were also simulated using Fluent software, while the mechanism of dual-scale low nitrogen combustion retrofit was analyzed comprehensively. Results show that the flow of primary air is in opposite direction to the secondary air due to the bias of primary air flow after retrofit, thus making the swirl region expanded in horizontal direction and shortened in vertical direction, resulting in increased combustion efficiency and lowered NO; emission in partial areas, but simulta- neously increased inertia of combustion process and reduced adaptability to uploading conditions.