随着污染物排放标准日益严格,SNCR已成为一种广泛应用于循环流化床(CFB)机组降低NOx排放的新技术,然而循环流化床机组变负荷时NOx排放浓度波动较大,加大SNCR控制难度。由于变负荷NOx动态排放模型研究较少,为实现变负荷过程循环流化床机组NOx的动态预测,对炉内NOx生成机理与SNCR反应机理进行分析,以给煤量、风量、喷氨量、床温等参数作为输入,结合数学建模方法,建立NOx动态排放模型。结合某300MW亚临界循环流化床机组实际运行数据进行不同负荷动态仿真,结果表明,该模型在动态过程中能较好拟合NOx排放趋势,300MW与150MW典型负荷工况及变负荷工况下模型计算值与真实值平均绝对误差分别为3.5、1.2、5.7mg/m3,精度较高,可实现CFB机组NOx排放实时预测,预测时间为4~5min。开展了不同工况给煤量、送风量、尿素流量及多变量的开环阶跃试验,结果表明,模型能较好反映NOx排放过程的动态特性。研究结果可为CFB机组超低排放控制优化提供参考。

With the increasingly strict pollutant emission standards, SNCR has become a new technology widely used in circulating fluid⁃ized bed (CFB) units to reduce NOx emissions. However, the difficulty of SNCR control will be increased due to the fluctuation of NOxemission concentration during variable load operation of circulating fluidized bed units. Due to the variable load dynamic NOx emis⁃sion model study is less, and in order to the realization of the dynamic prediction of NOx load change process of circulating fluidized bedunit, the article mechanism of NOx formation and SNCR reaction mechanism inside the furnace was analyzed, with coal and air volume,injection amount of ammonia, as input parameters, such as bed temperature, and mathematical modeling methods were used to establish aNOx dynamic emission model. Combined with the actual operation data of a 300 MW subcritical CFB unit, the dynamic simulation of dif⁃ferent loads was carried out. The results show that the model can better fit the NOx emission trend in the dynamic process. The average ab⁃solute errors between the calculated values of the model and the real values under 300 MW and 150 MW typical load conditions and varia⁃ble load conditions are 3.5, 1.2 and 5.7 mg/ m3, respectively, with high accuracy, which can realize the real-time prediction of NOxemission of CFB unit, with the predicted time of 4-5 min. Then, the open-loop step experiments of coal supply, air supply, urea flowand multi-variable under different working conditions were carried out. The experimental results show that the model can better reflect thedynamic characteristics of NOx emission process. The results can provide reference for the optimization of ultra-low emission control ofCFB units.

0 引言

1 NOx浓度排放模型

   1.2 燃烧模型

   1.3 NOx原始排放模型

   1.4 SNCR反应模型

2 模型仿真验证

   2.1 稳态验证

   2.2 动态验证

   2.3 开环阶跃试验

3 结论