脱硝系统烟气流场的性能与优化

Performance and optimizing of smoke flow in denitration system

选择性催化还原(SCR)系统均匀喷氨后,空气预热器易出现堵塞,并且出口在线检测位置不具代表性。为此,根据国内典型SCR系统建立等尺寸的物理结构模型,利用计算流体力学(CFD)技术对烟道与装置内烟气分布、烟气与NH3的混合、压降分布及其原因进行分析,并对导流板的结构进行优化。同时,通过与现场实测入口速度、压降值的对比,论证了数值模型的准确性。结果表明,烟道缩放区域导流板促使烟气均匀分布的同时也使烟气产生倾斜的流动惯性,这使得喷氨格栅(AIG)区域的速度偏差过大,导致了烟气与NH3混和的不均匀,是氨逃逸率高与出口NOx不均匀的首要原因;优化的导流板结构消除了烟气倾斜的流动惯性,进一步促进了AIG区域与催化剂上层烟气的均匀分布以及烟气与NH3的均匀性混合。

An air preheaters was easy to block and the real-time monitoring point at the outlet was unrepresented after uniform spraying of ammonia in the selective catalytic reduction（ SCR） system. Therefore,a structural model of equal size was established based on the typical SCR system. A computational fluid dynamics（ CFD）method was used to analyze the distribution of flue gas,mixture of flue gas and NH3,and pressure drop distribution in the device. The guide plate structure was optimized in the research. Good agreements of inlet velocity and pressure drop between the simulation results and corresponding experimental data validated the accuracy of the mathematical model. The results show that the guide plates promoted uniform distribution of the flue gas. However,the guide plates also made the flue gas generate inclined flow inertia,which resulted in the overly large speed deviation in the ammonia injection grid（ AIG） area and the uneven mixture of the flue gas and NH3. In addition,this was the main reason for the high ammonia escape rate and uneven distribution of NOxin the outlet region. The inclined flow inertia of the flue gas was eliminated by the optimized guide plates,which promoted the uniform distribution of the flue gas in the AIG area and upper catalyst area and further facilitated the mixture of the flue gas and NH3.