[关键词]
[摘要]
某电厂4号墙式布置机组燃用无烟煤和贫煤混煤,炉膛出口NOx排放质量浓度高达1 272 mg/m3 (6%O2),采取中心给粉旋流燃烧器(CFR)和两层燃尽风对其燃烧系统进行低NOx技术改造。采用数值仿真和改造后工业试验相结合的方法,研究了改造方案可行性。结果显示:不同燃尽风(OFA)风率条件下,低挥发分煤均能实现稳定燃烧;随OFA风率增加,主燃区化学当量比减小,O2质量分数降低,燃烧反应速度降低,高温区域范围呈缩小趋势,温度沿炉高分布更为均衡,主燃区相对低温贫氧氛围有效抑制了低挥发分煤燃烧条件下的NOx生成;27.50%的OFA风率条件时,炉内温度分布均衡,NOx排放质量浓度845.1 mg/m3,最终选定的OFA风率为27.50%。改造后工业试验显示,NOx排放质量浓度降为833.4 mg/m3,降幅达34.5%。数值仿真结果和改造后工业试验数据相吻合,证明机组低NOx技术改造方案可行。
[Key word]
[Abstract]
Lowvolatile coal of anthracite and lean coal was the design coal of No.4 wall fired boiler in the power plant, NOx emission of furnace outlet was 1 272 mg/m3(6%O2). Centrally fuel rich (CFR) swirl burner and twolayer overfire air (OFA) system were adopted for the combustion system during the low NOx technical transformation.The numerical simulation method combining with industrial test data was adopted to study the feasibility of reconstruction scheme.The results show that steady combustion of the lowvolatile coal can be achieved at different OFA rates. The chemical equivalence ratio,O2 mass fraction and combustion reaction speed of primary combustion zone decrease with the increase of OFA rate. In this way, the area of hightemperature zone declines, temperature profile is more uniform along furnace height direction. Under the relatively oxygendepleted and lowtemperature atmosphere, NOx emission from the lowvolatile coal is restrained in the primary combustion zone effectively.The temperature field of furnace is evenly distributed, and NOx emission is 845.1 mg/m3 at 27.50% OFA rate, so the finally selected OFA rate is 27.50%. After reconstruction, the industrial test shows that NOx emission is 833.4 mg/m3, reduced by 34.5%. Numerical simulation result is consistent with industrial test data, which proves that the low NOx technical reconstruction scheme of the unit is feasible.
[中图分类号]
TK16
[基金项目]